IEEE Global Communications Conference (GLOBECOM) 2024, Capetown, South Africa
2024年12月
This paper proposes a transmitter that rearranges the 16-QAM constellation for a 1-bit ADC receiver. A 1-bit ADC receiver is more eco-friendly and lower-cost than receivers with a high-resolution ADC. However, in conventional 1-bit ADC receivers, severe degradation of SER (Symbol Error Rate) in high Es/N0 poses a critical problem. This degradation is due to the lack of noise power in high Es/N0, which prevents the receiver from sufficiently benefiting from stochastic resonance. To solve this issue, we propose a novel transmitter that rearranges a 16-QAM constellation based on the probability density function of noise. The rearrangement of constellations mitigates the nonlinearity of a 1-bit ADC, enabling reliable demodulation of multilevel signals in high Es/N0. Numerical examples demonstrate that the proposed transmitter achieves good SER performance across a wide range of Es/N0, even when a 1-bit ADC receiver is employed, compared to conventional transmitters.
小鹿文也，山里敬也，齋藤将人，表英毅，佐藤彰弘，木村翔，田中翔馬，林合祐
電子情報通信学会論文誌, Vol.J107-B,No.11,pp.-
24年11月
移動無線通信システムにおいて，伝搬路特性を把握することは極めて重要である．特に，移動無線通信システムのチャネル推定において，雑音電力を相対的に低減させ，低信号対雑音電力比 (SNR) の信号の利用は重要である．仮にこのような低信号対雑音電力比の信号を利用できるようになれば，本来通信ができなかった環境でも通信を可能にすることができ，基地局の通信範囲の拡大が可能となる．そこで筆者らは，短区間電力遅延プロファイルを用いて雑音電力を低減させる手法を提案した．本論文では，アッテネータを使用することであえて微弱信号を再現した電波伝搬測定を行うことで提案手法の有効性を確認した．提案手法ではパスが同じ方向から発生するという仮定をおいているが，これをシミュレーションによって検証した．提案手法によって短区間電力遅延プロファイルで SNR が 10dB の信号を 30 dB まで改善することができた．
In this study, authors evaluate 1-bit ADC receivers proposed in previous studies in Rician and Rayleigh fading channels where the ampli- tude and phase of the signal fluctuate dynamically in terms of SNR (Signal- to-Noise Ratio) vs. BER (Bit Error Rate). We confirm that the 1-bit ADC receiver is effective even in such environments. However, the degree of degradation of SNR vs. BER due to variations in signal amplitude and phase depends on the demodulation method.
A rolling shutter based visible light communication (VLC) system is possible to achieve high data rate by utilizing characteristics of rolling shutter image sensors, but some signal loss occur. In this study, we propose a synchronization method to decode a loss correct code in a rolling shutter based VLC system. To synchronize the received signal with the transmitted signal, we employ a combination of pulse width modulation (PWM) and Barker codes. The PWM technique helps in aligning the timing of the received signal with the transmitted signal, while the Barker codes provide a correlation property that aids in identifying the synchronization points. The experimental results show that this synchronization method enables us to use loss correct codes. Additionally, the bit error rate depends on a parameter of image processing on received images and the way to set a posteriori probabilities in the decoding.
Z. Tang, T. Yamazato, S. Arai
International Conference on Emerging Technologies for Communications (ICETC), O1-1, Sapporo, Japan
This paper proposes an image sensor communication (ISC) system based on light trails using rotary LEDs. The light trail refers to an optical phenomenon where light appears elongated and forms a trajectory due to the movement of luminous objects. In this study, we developed a propeller LED transmitter (P-Tx) that rotates LEDs with a propeller to generate and transmit light trail signals. According to the LED's rotation radius, the proposed system segments light trails to achieve high-capacity data transmission at short distances and high-trust transmission at long distances. In addition, we perform the rotation coordinates system conversion for the captured light trails to accurately and simply detect the signal LEDs' coordinates. We experimentally evaluate the proposed system's communication performance and data rate. The experimental results demonstrate that our system is capable of meeting communication requirements at various distances and exhibits significant potential in enhancing the data transmission rate of ISC.
A. Isozaki, T. Yamazato, M. Saito
International Conference on Emerging Technologies for Communications (ICETC)
2023年12月
In this study, we propose the 1-bit ADC receiver that performs frequency conversion in the digital domain to simplify the circuitry in the receiver and reduce power consumption. Then, we evaluate the SNR vs. BER of the 1-bit ADC receiver we propose. In the proposed receiver, the average of the 1-bit ADC outputs in parallel is taken, the received signal is restored, and the baseband signal is demodulated by multiplying the restored received signal by the carrier wave.
R. Huang, T. Yamazato, M. Kinoshita, H. Okada, S. Arai, K. Kamakura, T. Yendo, T. Fujii
An essential issue in image sensor communication (ISC) is reliable and high-speed data transmission. In order to increase the data rate, this study uses pulse-width modulation (PWM). However, the symbol decision for PWM will become challenging with increasing numbers of luminance levels because of pixel saturation. In this study, we mitigate the pixel saturation problem by achieving high dynamic range (HDR) using two high-speed image sensors with varied exposure settings. Furthermore, we proposed HDR combining for signal demodulation. The field trial experiment results show that a throughput of higher than 87.5 kbps within the communication distance of 50 m can be achieved.
This paper proposes an image sensor communication (ISC) system based on light trails using rotary LEDs. The light trail refers to an optical phenomenon where light appears elongated and forms a trajectory due to the movement of luminous objects. In this study, we developed a propeller LED transmitter (P-Tx) that rotates LEDs with a propeller to generate and transmit light trail signals. According to the LED's rotation radius, the proposed system segments light trails to achieve high-capacity data transmission at short distances and high-trust transmission at long distances. In addition, we perform the rotation coordinates system conversion for the captured light trails to accurately and simply detect the signal LEDs' coordinates. We experimentally evaluate the proposed system's communication performance and data rate. The experimental results demonstrate that our system is capable of meeting communication requirements at various distances and exhibits significant potential in enhancing the data transmission rate of ISC.
This paper focuses on image sensor communication (ISC) using cameras to receive wireless signals transmitted by visible lights. We summarize the technical principles of ISC from the perspective of transmitting devices. An introduction to the development and applications of ISC was provided, starting with the history of image sensors and visible light communication (VLC). Moreover, the communication mechanism of ISC using complementary metal–oxide–semiconductor (CMOS) sensors is explained in this paper. Specifically, we investigate studies using an optical communication image sensor and the rolling shutter technique for high-speed ISC. Further, we highlight three distinctive transmitting devices in ISC: a LED array, rotating LEDs, and displays, and explain them in terms of structure and signal transmission methods. In particular, we present the parallel transmission of LED arrays and their application in traffic systems and introduce an optical flow-based signal transmission method using rotating LEDs. In addition, two visual transmission techniques in displays-based-ISC using brightness-difference and high-frequency flashing are introduced, respectively. This paper intuitively explains these ISC techniques and reveals ISC's high versatility.
S. Kamiya, Z. Tang, T. Yamazato, M. Kinoshita, K. Kamakura, S. Arai, T. Yendo, T. Fujii
This paper presents the successful reception of visible light communication (VLC) signals, transmitted from an LED array, by an image sensor that utilizes a rolling shutter while driving at 40 km/h. The rolling shutter image sensors used in commercial cameras, such as those found in smartphones and dashcams, capture images line by line at a fast rate, allowing for VLC signal reception in vehicular environments. By analyzing the relationship between the signal reception rate for each line and the frame rate, we demonstrate that parallel VLC signals transmitted from the LED array can be received even while in motion. Notably, to our knowledge, this is the first time that an automobile moving at 40 km/h has successfully received a VLC signal.
M. Hattori, A. Tsujii, T. Kasashima, H. Hatano, T. Yamazato
This paper proposes MAP estimation using two temporally consecutive data using signals from eight ultrasonic sensors forming a linear array. First, we estimate the distance to the obstacle from the time difference between the eight received signals. Then, assuming that the ranging error follows a Gaussian distribution and that each of the eight ranging values is independent, we can get the existence probability of the obstacle’s position by a pair of two obtained distances. Finally, we estimate the position of the obstacle by multiplying 28 (8C2) existence probabilities obtained. The conventional method estimates the position of an obstacle by the above procedure. However, the estimation accuracy in the angular direction was poor, resulting in the spread of the existence probability in the horizontal direction. In the proposed MAP estimation using two temporally consecutive data, we obtain the existence probability of an obstacle by the procedure shown above, and then use it as a prior probability of the obstacle’s estimated position. Furthermore, we recursively perform the same process to obtain the existence probability of the obstacle. In this way, we improve the accuracy of the estimation of the position of the obstacle by the existence probability. We present the experiment results to show the effectiveness of the proposed method.
J. Zheng, T. Yamazato, K. Naito
IEEE Symposium on Computers and Communications (ISCC) Workshop on Optical Wireless Communications
This paper reports an extension of the private 5G service area to the outside of the licensed area by integrating visible light communication (VLC). As VLC is license-free, integrating the VLC function into the private 5G networks gives a more flexible system design. For example, it will be possible to provide services to mobile vehicles and robots working outside the service area of a private 5G network. Alternatively, private 5G networks in different locations can be connected. A challenge is integrating the VLC function into a 5G core network. We successfully designed a testbed and an experiment using open-source 5G projects to evaluate and compare methods to integrate VLC and private 5G, including the simulation of poor network environments. Experimental results demonstrate the availability of integrating private 5G with VLC, which are compared with image-based methods and show better latency performance.
T. Yamazato
IEEE Symposium on Computers and Communications (ISCC) Workshop on Optical Wireless Communications
2023年7月
Visible light communications (VLC) is a promising technology for automotive applications because it offers several advantages over traditional wireless communication technologies using radio waves. For example, VLC is more secure, as it is difficult to intercept VLC signals, and VLC is more reliable, as VLC signals are less susceptible to interference from other signals. As a result of these advantages, VLC is being considered for various automotive applications, such as in-car infotainment and navigation systems, advanced driver assistance systems (ADAS), and autonomous driving. In this talk, he will explain VLC for cars using image sensor communication, one of the VLCs that use a camera as a receiver.
R. Huang, M. Kinoshita, T. Yamazato, H. Okada, K. Kamakura, S. Arai, T. Yendo, T. Fujii
IEICE Transactions on Fundamentals, vol.E106-A, no.7, pp.990-997
Visible light communication (VLC) and visible light ranging are applicable techniques for intelligent transportation systems (ITS). They use every unique light-emitting diode (LED) on roads for data transmission and range estimation. The simultaneous VLC and ranging can be applied to improve the performance of both. It is necessary to achieve rapid data rate and high-accuracy ranging when transmitting VLC data and estimating the range simultaneously. We use the signal modulation method of pulse-width modulation (PWM) to increase the data rate. However, when using PWM for VLC data transmission, images of the LED transmitters are captured at different luminance levels and are easily saturated, and LED saturation leads to inaccurate range estimation. In this paper, we establish a novel simultaneous visible light communication and ranging system for ITS using PWM. Here, we analyze the LED saturation problems and apply bicubic interpolation to solve the LED saturation problem and thus, improve the communication and ranging performance. Simultaneous communication and ranging are enabled using a stereo camera. Communication is realized using maximal-ratio combining (MRC) while ranging is achieved using phase-only correlation (POC) and sinc function approximation. Furthermore, we measured the performance of our proposed system using a field trial experiment. The results show that error-free performance can be achieved up to a communication distance of 55 m and the range estimation errors are below 0.5 m within 60 m.
This paper proposes a new estimation method of short-term power delay profile to reduce the noise power included in the short-term power delay profile. By reducing the noise, the multipath signal components buried in the noise can be utilized, thereby reducing the transmitted signal power and extending the cell range of a mobile communications. The proposed method iteratively creates the short-term power delay profile while lowering the threshold which distinguishes between signal and noise. The purpose of the threshold is to suppress the noise in each profile and to extract the effective multipath components. Furthermore, the method aligns and averages the phase of each instantaneous delay profile. In this way, only the noise component can be reduced while maintaining a high multipath power. As a result, we successfully reduced the noise power by 15 dB by analyzing the raw data of 200 instantaneous delay profiles measured in the 50 MHz bands at 3.35 GHz. Furthermore, the delay spread increased from 0.66 μs to 1.47 μs.
H. Omote, A. Sato, S. Kimura, S. Tanaka, H. Y. Lin, T. Yamazato
IEEE Vehicular Technology Conference (VTC), pp. 1-4
High-Altitude Platform Station (HAPS) has recently been attracting much attention as a new mobile communication platform for ultra-wide coverage areas and disaster-resilient networks since it can provide communication services from an altitude of approximately 20 km via a balloon, an Unmanned Aerial Vehicle (UAV) or other aircraft. In order to design efficient cell configurations for HAPS-based services, we need radio wave propagation models that consider various factors of vegetation, terrain, urban-suburban areas, and building entry loss. This paper focuses on propagation loss at high-elevation angles in urban and suburban areas. Recommendation ITU-R (International Telecommunication Union Radio communication sector) P.2108-1 describes the clutter loss model, which is the propagation loss caused by features such as buildings. The applicable frequency for ITU-R P.2108-1 is above 10 GHz; however, this model has no parameters for urban structure. Therefore, it needs to consider a correction for an urban structure to precisely evaluate clutter loss. We propose a new model that corrects Recommendation ITU-R P.2108 using shielding building heights as the urban structure. Since this new model was created based on measurements from 0.7 GHz to 5.7 GHz, the applicable frequencies are from 0.7 GHz to 5.7 GHz. Therefore, it is necessary to confirm whether the model applies to frequencies above 5.7 GHz. This paper compares the results of new propagation measurements at 29.3 GHz using a helicopter with the predicted results of the proposed model. The results show that the proposed model is applicable above 5.7 GHz.
Image sensor communication (ISC), also known as optical camera communication, is a form of visible light communication that utilizes image sensors rather than a single photodiode, for data reception. ISC offers spatial separation properties and robustness to ambient noise, making it suitable for outdoor applications such as intelligent transportation systems (ITSs). This review analyzes the research trends in ISC, specifically concerning its application in ITSs. Our focus is on various ISC receivers, including rolling shutter cameras, global shutter high-speed cameras, optical communication image sensors, and event cameras. We analyze how each of these receivers is being utilized in ISC vehicular applications. In addition, we highlight the use of ISC in range estimation techniques and the ability to achieve simultaneous communication and range estimation. By examining these topics, we aim to provide a comprehensive overview of the role of ISC technology in ITSs and its potential for future development.
Using a rolling shutter camera as a receiver, visible light communication (VLC) can achieve a significantly higher sampling rate than the frame rate because of its sequential exposure mechanism. This study focuses on optical orthogonal frequency division multiplexing (OFDM) in a rolling shutter based VLC for further high-speed data rates. Because an image sensor is employed, conventional optical OFDM, such as DC-biased optical OFDM (DCO-OFDM), must fit in the grayscale range of 0–255 levels. Therefore, DCO-OFDM suffers from poor error performance owing to its high PAPR. To address this problem, we propose a polarity-separated transmission, in which the bipolar OFDM signal is separated into positive and negative parts and then transmitted by two LEDs simultaneously. Polarity-separated transmission is expected to double the grayscale range, i.e. 0–511, and improve error performance because it reconstructs the original bipolar signal by combining the received signals from two LEDs. We experimentally demonstrate and compare the symbol error rate (SER) performance of DCO-OFDM and polarity-separated transmissions. Consequently, polarity-separated transmission improved the SER performance by 10– 2 in the fundamental frequency range of 300–700 Hz when 16-PSK was adopted for subcarrier modulation.
1-bit analog-to-digital converters (ADCs) have low power consumption and can easily speed up the analog-to-digital conversion and sampling. However, due to their resolution of only 1 bit, the nonlinearity between the input with multiple amplitude levels and output is large. With the method of utilizing noise proposed in previous studies, 1-bit ADCs can be linearized to demodulate signals with multi-level amplitude modulation like pulse amplitude modulation (PAM) and quadrature amplitude modulation (QAM). In this letter, we construct a receiver circuit using a 1-bit ADC, evaluate its performance, and show its availability through demodulation experiments on 4-PAM signals.
M. Hattori, A. Tsujii, T. Kasashima, H. Hatano, T. Yamazato
International Conference on Emerging Technologies for Communications (ICETC), O5-5, Waseda University
2022年12月
We are working on the measurement of obstacle positions by an ultrasonic sensor array. This paper proposes a recursive position estimation method using signals from eight ultrasonic sensors forming a linear array. First, we estimate the distance to the obstacle from the time difference between the eight received signals. Then, assuming that the ranging error follows a Gaussian distribution and that each of the eight ranging values is independent, we can get the existence probability of the obstacle's position by a pair of two obtained distances. Finally, we estimate the position of the obstacle by multiplying 28 (8C2) existence probabilities obtained. The conventional method estimates the position of an obstacle by the above procedure. However, the estimation accuracy in the angular direction was poor, resulting in the spread of the existence probability in the horizontal direction. In the proposed recursive position estimation, we obtain the existence probability of an obstacle by the procedure shown above, and then use it as the prior probability of the obstacle's estimated position. Furthermore, we recursively perform the same process to obtain the existence probability of the obstacle. In this way, we improve the accuracy of the estimation of the position of the obstacle by the existence probability. We present the experiment results to show the effectiveness of the proposed method.
D. Ehara, Z. Tang, M. Kinoshita, T. Yamazato, H. Okada, K. Kamakura, S. Arai, T. Yendo, T. Fujii
International Conference on Emerging Technologies for Communications (ICETC), S9-5, Tokyo
2022年12月
山里敬也
電子情報通信学会技術研究報告, WBS2022-43, pp. 48-53, 立命館大学 BKC エポック立命21 3階
Most of the previous research on the acquisition of the LED Array transmitter assumes that the onboard receiver approaches the LED transmitter from the car’s front. In this study, we considered a case where the vehicle’s receiver crosses the LED transmitter. This letter modifies the algorithm using spatial-temporal gradient values to detect LED arrays. As a result, we achieved error-free acquisition and successfully communicated up to 9728 [bits] at a vehicle speed of 25 [km/h].
S. Kamiya, Z. Tang, T. Yamazato,
IEEE ICC Workshop on Optical Wireless Communications (OWC), Seoul, South Korea
2022年5月
In this study, we investigate the application of visible light communication (VLC) to intelligent transport systems (ITS) using rolling shutter image sensors as receivers. The use of a global shutter high-speed image sensor as a receiver has been widely examined in ITS-VLC so far. However, this image sensor is impractical for general-purpose applications due to the high cost. This study aims to perform ITS-VLC using the rolling shutter image sensor. The rolling shutter image sensor is widely used in the smartphone camera. By using it as a receiver, ITS-VLC can be used in more opportunities. In this study, we propose a ITSVLC system using rolling shutter image sensor. The proposed system demodulates data from images captured in a moving environment. We evaluate the communication performance by measuring the bit error rate for the ITS-VLC experiments.
Z. Tang,T. Yamazato, S. Arai
IEEE ICC Workshop on Optical Wireless Communications (OWC), Seoul, South Korea
2022年5月
This study investigates a new communication scheme for the event camera-based visible light communication (VLC) using a propeller-type rotary LED transmitter. Conventional camera-based VLC suffers from low data rates and high latency due to the limited camera frame rates. To solve this problem, the event camera has been used as the receiver in VLC. Event cameras detect changes in brightness and asynchronously output these changes as events in microsecond order. The high temporal resolution gives the event camera-based VLC good potential in terms of high speed and low latency. However, when an event camera is used as the VLC receiver, the light of the transmitter needs to be changed constantly. If the transmitter LED is continuously in the same blinking state, the event camera may not output any events and the data could not be recovered until the blinking state changes. To transmit the optical signal for event cameras, we use a propeller-type rotary LED transmitter for the event camera-based VLC. The transmitter rotates the blinking LED in circles and uses the afterimage of LED light to transmit signals. The event camera detects the afterimages and constantly outputs them as a stream of events. We filter the noise events and recover data using signal events. This study verifies the operation for the proposed system through an implementation experiment. As a result, we achieved the communication in the proposed system and provided a basic evaluation in terms of communication speed and quality.
This study proposes a simplified Alamouti-type space-time coding (STC), improving the performance of image sensor communication (ISC) using a rotary LED transmitter. The rotary LED transmitter was developed to increase the data rate of ISC using afterimages of LED lights. The transmitter simultaneously causes the LEDs to blink and rotates them around a vertical axis. Owing to the movement of the blinking LEDs that occurs within the exposure time of the camera, multiple blinking states are captured as afterimages, thus increasing the amount of information that can be received per image. However, with increasing communication distance, the size of the LED light captured on the image sensor decreases. In this case, it is difficult to distinguish each LED blinking state, leading to a degradation of the demodulation performance. To overcome this problem, the proposed STC encodes adjacent angular afterimages as symbol pairs and transmits these symbol pairs using two symbol times. In addition, we simplified the data decoding process by using normalized LED luminance values. We evaluate the demodulation performance of the proposed method through experiments. Compared with conventional coding methods, the proposed STC requires no channel estimation and significantly improves the demodulation performance.
M. Kinoshita, T. Toguma, S. Yamaguchi, S. Ibaraki, K. Kamakura, T. Yamazato
IEEE Consumer Communications and Networking Conference (CCNC), pp.843-847, online
Intelligent Transport Systems Visible Light Communication (ITS-VLC) is attracting significant attention as a solution to solve various problems that vehicles have, or for the installation of new systems in the vehicles. In ITS-VLC, the acquisition of the VLC transmitter via light-emitting diodes (LEDs) in the onboard camera’s captured image is the first and essential step when receiving the VLC signal. Most of the previous research on the acquisition of the LEDs assumes that the vehicles approach the LEDs source from the front of the vehicle. However, there are many situations in which vehicles cross the LEDs. In this study, we considered a case in which the vehicle’s receiver crosses the LED transmitter. We modified the acquisition algorithm based on the spatial-temporal gradient utilized in our model in which the transmitter and the receiver cross each other. We found that we can acquire the transmitter by correcting the difference of the transmitter’s position in the captured image. When validating the specific signal, we achieved 100% acquisition success rate.
T. Yamazato
Wireless World Research Forum Meeting 46, Paris, France
2021年12月
Optical wireless communication has been around since the 1980s. Why has its time come now in 5G/6G? What is the change?
T. Ohtaguro, M. Saito, T. Yamazato
International Conference on Materials and Systems for Sustainability (ICMaSS), online
This study describes intelligent transport image sensor communication (ITS-ISC) systems that use LED arrays as transmitters that imitate traffic lights. Three signal-transmission schemes -luminance modulation, spatial modulation, and combined luminance and spatial modulation- use LED array. However, their suitability for ITS-ISC has not been explored yet. Therefore, we compare the communication performance of these three systems under strong saturation and present the results.
R. Huang, T. Yamazato, M. Kinoshita, H. Okada, K. Kamakura, S. Arai, T. Yendo, T. Fujii
IEEE Intelligent Vehicles Symposium, Nagoya, Japan
Visible light communication based intelligent transportation systems (ITS-VLC) show great potential for future urban mobility. This study presents a performance evaluation of range estimation between vehicles and infrastructures in an ITS-VLC system. In the proposed ITS-VLC system, it is easy to simultaneously conduct communication and ranging using stereo cameras. However, the stereo camera calibration becomes a problem during simultaneous communication and ranging due to vehicle vibration. Using the data from LED transmitters and stereo cameras, it can obtain multiple measurements of distance. The monocular-stereo fusion algorithm is applied to visible light ranging in the proposed scheme using particle swarm optimization. We employed real data from the field trial experiment and achieved a ranging accuracy of 60±1.0 m.
M. Hattori, A. Tsujii, T. Kasashima, H. Hatano, T.Yamazato
In this study, we propose a method for reducing angle error in position estimation of a moving target. The distance between the transmitting array and target is approximated by two receiving sensors close to the transmitting array. This enables more accurate distance measurement between the receiving sensor and the target.
This study focuses on visible light communication (VLC) using a photodiode as a receiver. Accurate data transmission by this type of VLC is a challenge because the photodiode cannot detect weak light of subthreshold intensity owing to its insufficient light sensitivity. To overcome this problem, we employ a stochastic resonance, which is a nonlinear phenomenon in which the response characteristics of a system improve as its noise intensity increases, for the receiver of this VLC system. We also employ additive light-emitting diode light, which interferes in the photodiode as intentional noise. As an experimental result, the stochastic resonance was achieved by setting the parameters of the noise source appropriately, and we recovered the weak transmitting signal at the receiver.
We discuss herein whether an optical wireless communication (OWC) system can be a candidate for post 5G or 6G cellular communication. Almost once per decade, cellular mobile communication is transformed by a significant evolution, with each generation developing a distinctive concept or technology. Interestingly, similar trends have occurred in OWC systems based on visible light and light fidelity (Li-Fi). Unfortunately, OWC is currently relegated to a limited role in any 5G scenario, but the debate whether this is unavoidable has yet to be settled. Whether OWC is adopted post 5G or 6G is not the vital issue; rather, the aim should be that OWC coexists with 5G and 6G communication technologies. In working toward this goal, research and development in OWC will continue to extend its benefits and standardize its systems so that it can be widely deployed in the market. For example, given that a standard already exists for a visible-light beacon identifier and Li-Fi, a service using this standard should be developed to satisfy user demand. Toward this end, we propose herein a method for visible-light beacon identification that involves using a rolling shutter to receive visible-light communications with a smartphone camera. In addition, we introduce a rotary LED transmitter for image-sensor communication.
2020
R. Okema, D. Goto, T. Yamazato, F. Yamashita, H. Shibayama
IEEE Global Communications Conference (GLOBECOM), Taipei, Taiwan
Multiple-input multiple-output (MIMO) communication systems using multiple low-Earth orbital (LEO) satellites achieve higher capacity than conventional LEO systems. However, in previous research, control signals are allocated to a different frequency band for each satellite signal in order to estimate its Doppler frequency. The increase in the number of satellites reduces unoccupied MIMO signal bandwidth and hence the overall capacity. This study aimed to prevent such capacity reduction by introducing the superimposition of control signals. Such control signals occupy a frequency bandwidth of the equivalent of only one control signal; therefore, they can prevent the reduction of the overall capacity. The main challenge is estimating the satellites' Doppler frequencies from the waveforms of Doppler-affected superimposed control signals. To overcome this challenge, we propose the adoption of a deep learning technique.
R. Huang, M. Kinoshita, T. Yamazato, H. Okada, K. Kamakura, S. Arai, T. Yendo, T. Fujii
IEEE GLOBECOM Workshop on Optical Wireless Communications (OWC), Taipei, Taiwan
Stereo cameras, serving as the “eyes” of automotive vehicles, can determine the distance between objects and the vehicles. In this paper, stereo cameras are introduced into image-sensor-based visible light communication (IS-VLC) systems, in which the combination of VLC and stereo ranging shows promising prospects for intelligent transport systems. However, one of the problems of IS-VLC stereo ranging is that the luminance level of LEDs in the captured images would greatly affect disparity estimation, which would result in inaccurate range estimation. This paper gives the performance evaluation of this problem using phase-only correlation algorithm with luminance election. The proposed scheme using stereo cameras exhibited a ranging accuracy of 60±0.15 m in static conditions.
T. Yamamoto, T. Yamazato, H, Okada, M. Kinoshita, K. Kamakura, S. Arai, T. Yendo, T. Fujii
International Conference on Emerging Technologies for Communications (ICETC), B4-1, online
Image sensor communication uses an LED light as a transmitter and an image sensor as a receiver. LED light sources are widely used in traffic lights and car tail lights. In addition, since image sensors are used for driving assistance and drive recorder applications, image sensor communication can be used in parallel with other intelligent transport systems(ITS) applications. This study describes an ITS image sensor communication (ITS-ISC) system, which uses an LED array as a transmitter to imitate traffic lights. There are three schemes of signal transmission using an LED array: luminance modulation, spatial modulation, and both luminance and spatial modulation. However, which of these schemes is the most suitable for ITS-ISC is not yet considered. In this study, we compare the communication performance of these three modulation schemes, present-ing the configuration of an LED array capture simulator and performance comparison results.
M.Hattori, A. Tsujii, T. Kasashima, H. Hatano, T. Yamazato
International Conference on Emerging Technologies for Communications (ICETC), I2-4, Online
In this study, a method for reducing the angle error in the position estimation of a target is proposed. In this method, the distance between the transmitting array and the target approximates two receiving sensors close to the transmitting array. This enables the attainment of a more accurate distance between the receiving sensor and the target.
S. Horiuchi, H. Hatano, K. Sanada, K. Mori, T. Yamazato, A. Shintaro, M. Saito, Y. Tadokoro, H. Tanaka
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.101-104, online
2020年11月
M. Saito, T. Ohtaguro, Y. Nakashima, T. Yamazato, S. Arai, H. Hatano, H. Tanaka, Y. Tadokoro
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.105-108, online
2020年11月
S. Arai, T. Yamazato, H. Hatano, M. Saito, H. Tanaka, Y. Tadokoro
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.97-100, online
本研究では，画像の高速・高輝度投映が可能なDMD (Digital Micromirror Device)プロジェクタをITS (Intelligent Transport Systems)イメージセンサ可視光通信の送信機として応用することを検討する．実機を用いて構築したシステムにより，屋外移動環境において行った通信性能評価について報告する．
T. Yamazato
International Conference on Optoelectronic and Microelectronic Technology and Application 2020, Nanjing, China
2020年10月
Almost once per decade, cellular mobile communication is transformed by a significant evolution, with each generation developing a distinctive concept or technology. Interestingly, similar trends have occurred in visible light communication systems and vehicle automation. In this talk, the presenter looks back to the brief history of vehicle automation and related communication technologies. He then introduces visible light communication and its application for automotive intelligence. Some of his research results on VLC for automotive applications will also be provided.
Signal Processing in Photonic Communications (SPPCom), The 2020 OSA Advanced Photonics Congress, 2020., Online
2020年7月
Since the LED (light-emitting diode) is a semiconductor device, high-speed modulation is possible. The communication for transmitting information by blinking (modulating) the LED at such a high speed that the human eye cannot recognize is called visible light communication (VLC) [1]. The visible light beacon is an exciting application of VLC that transmits the short ID. In this article, the trend of the visible light beacon, a part of VLC is described.
Y.H.J Lai, A. Tsujii, T. Kasashima, T. Yamazato, H. Hatano
IEICE General Conference, A-4-2, p.35, Hiroshima, Japan
2020年3月
Ultrasonic sensors are an attractive option for target detection purposes due to their low cost, functionality in all light and weather conditions and easy implementation. Multiple ultrasonic sensors arranged in an array were shown to strengthen ultrasonic waves and increase detection range at static conditions in an indoor environment. In this article, we report a conducted experiment on a moving target in an outdoor environment to analyze its performance and will aim to use the obtained data for localization in future works.
R. Huang, M. Kinoshita, T. Yamazato, H. Okada, K. Kamakura, S. Arai, T. Yendo, T. Fujii
IEICE General Conference, A-9-21, p.100, Hiroshima, Japan
2020年3月
T. Yamazato
The Optical Networking and Communication Conference & Exhibition (OFC2020), San Diego, USA
This paper presents an image sensor communication (ISC) using a digital micromirror device (DMD) projector as a transmitter. In particular, we focus on ISC for intelligent transport systems (ITSs) because DMD projectors are expected to be used in road traffic, such as vehicle headlights, street lights, and traffic signs. The DMD projector controls light patterns by switching tilt of micromirrors at high speed. Compared to the conventional LED array transmitter, DMD projector can design and alter the shape of the light pattern and data rate of transmission more easily. In the proposed system, the data rate can be easily increased by increasing the number of multiplexes. However, as the number of multiplexes is increased, the number of received pixels on the image sensor is decreased, and thus the performance of symbol detection deteriorates. Therefore, the purpose of this paper is to examine the relation between the num- ber of received pixels per cell and communication performance for transmission pattern design. Hence, we experimentally clarify this relation using our prototype system via a DMD projector and a high-speed camera.
2019
T. Arisue, T. Yamazato, H, Okada, M. Kinoshita, S. Arai, T. Yendo, K. Kamakura, T. Fujii
Workshop on Optical Wireless Communication for Smart City (OWC2), pp.1-4, Toyota, Japan
2019年12月
This paper presents an image sensor communication (ISC) using a digital micromirror device (DMD) projector as a transmitter. In particular, we focus on ISC for intelligent transport systems (ITSs). DMD projectors are expected to use in road traffic, such as vehicle headlights, street lights, and projectors of traffic signs. Our proposed system projects data patterns on a road or signage for transmission in addition to primary lighting/display function. In this paper, we report a basic experiment of the proposed system using the DMD projector as a vehicle headlight in driving conditions.
K. Yamamura, K. Kamakura, M. Kinoshita, T. Yamazato
Workshop on Optical Wireless Communication for Smart City (OWC2), pp.33-36, Toyota, Japan
2019年12月
R. Huang, T. Yamazato, H. Okada, M. Kinoshita, K. Kamakura, S. Arai, T. Yendo, T. Fujii
Workshop on Optical Wireless Communication for Smart City (OWC2), pp.49-52, Toyota, Japan
2019年12月
The recognition of traffic light is important in self-driving cars nowadays. In this paper, we proposed a ranging method for traffic light on the road based on stereo ranging. By introducing the idea of visible light communication, it is simple to extract the traffic light from a complicated background. Experimental result shows that it can work well for the real traffic light.
T. Yamamoto, T. Yamazato, H, Okada, M. Kinoshita, K. Kamakura, S. Arai, T. Yendo, T. Fujii
Workshop on Optical Wireless Communication for Smart City (OWC2), pp.53-56, Toyota, Japan
2019年12月
In this research, we describe visible light communication (VLC) using an LED array as a transmitter and a high-speed image sensor as a receiver. Such VLC is called an image sensor communication (ISC), and it assigns a symbol to the multilevel brightness of the LED. An issue is a nonlinearity caused by both LED and image sensors. In order to increase the data rate, it is necessary to handle this nonlinearity. In this paper, we first show the nonlinearity by experimental results. We then show that we can ease such nonlinearity by an introduction of an inverse pattern used to track the LED array. We show by the experimental result that the inverse pattern can mitigate the nonlinearity and thus improve the data rate.
K. Takahashi, K. Kamakura, M. Kinoshita, T. Yamazato
Workshop on Optical Wireless Communication for Smart City (OWC2), pp.9-12, Toyota, Japan
R. Huang, M. Kinoshita, T. Yamazato, H. Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
International Conference on Materials and Systems for Sustainability (ICMaSS), Nagoya, Japan
2019年11月
Camera calibration is an essential part of stereo camera system. By using stereo cameras, it enables simultaneous range estimation and visible light communication (VLC) data transmission, and we can use them for VLC-based intelligent transport system (ITS-VLC).
The ranging accuracy greatly relies on the accurate camera calibration. As the range increases, the estimation error of calibration parameters will make the ranging result worse. In this paper, we introduce stereo cameras into ITS-VLC system, and discuss the calibration method for range estimation. Considering the effect of camera calibration, the proposed scheme using stereo cameras confirms a great ranging accuracy in a static condition, and the estimation errors of calibration parameters are given within 0.05%.
T. Mitani, T. Yamazato, K. Naito, Y. Mori
The 8th IEEE International Conference on Conected Vehicles and Expo (ICCVE), Gratz, Austlia
Emergency services around the world face the problem of increasing patient transportation times. The operation of emergency vehicles is fundamentally different from that of general vehicles ; hence, algorithms recommending optimal routes in a conventional way are not always applicable to emergency vehicles. In this study, we analyzed data of inter-vehicle and road-vehicle communication collected at 700 MHz band intelligent transport systems and demonstrated that the overall travel time of emergency vehicles can be reduced by decreasing their travel time at intersections.
We will introduce an integrated system of visible light communication (VLC) and ranging using high-speed stereo imaging. The system simultaneously decodes a VLC signal while its source tracking portion outputs ranging information. These image sensors are mainly used to provide visual information to the driver.
This study presents a novel method for signal demodulation for use with visible light communication systems composed of an image sensor as a receiver and light-emitting diode (LED) transmitters. Demodulation is a central challenge in the design of such a system, as the image captured at the image-sensor receiver is deteriorated by distance and noise. We propose a demodulation method that offers performance approaching that of the maximum-likelihood decoding (MLD) method and with significantly less complexity. The proposed method first applies the minimum mean square error (MMSE) method to each LED into reliable LEDs and unreliable LEDs according to the MMSE results and it demodulates the LEDs judged as reliable directly. Then, the MLD method is applied only to the unreliable LEDs to demodulate their signals. The results of numerical simulations and lab experiments are presented to evaluate the performance of this modified demodulation method.
This paper focuses on an image sensor communication system that uses an LED as the transmitter and a high-speed image sensor (camera) as the receiver. Communication in this scheme depends on the quality of images transmitted from the LED to the sensor. If the image becomes unfocused on the way to the receiver, the LED luminance that make up the signal cannot be detected, so the receiver cannot demodulate the signal data. To overcome this problem, this study proposes a novel demodulation scheme to recover data from a degraded image, based on a maximum likelihood decoding (MLD) algorithm. The proposed method creates template images that imitate all possible blinking patterns produced by the LED transmitter, and then calculates the Euclidean distances between pixels in the captured image and the pseudo images for all possible blinking patterns. Finally, the algorithm chooses the image template with the smallest Euclidian distance from the received signal as the recovered data. Though an exhaustive set of image templates must be prepared for the proposed MLD, the number of templates depends on the number of LEDs on the transmitter. Thus, the computational complexity of this method increases as the number of transmitter LEDs increases. To reduce the computational complexity of the proposed MLD algorithm, the binary differential evolution (BDE) algorithm is used, which is a swarm intelligence technique. Computer simulations are used to evaluate the BDE algorithm's usefulness for reducing computational complexity and improving the BER of the communication system.
M. Hori, M. Kinoshita, T. Yamazato, H. Okada, T. Fujii, K. Kamakura, T. Yendo, S. Arai
3rd International Conference and Exhibition on Visible Light Communications (ICELVC), Seoul, Korea
2019年3月
Image sensor communication (ISC) is a type of visible light communications (VLC) that has high affinity with the field of intelligent transport systems (ITSs). In an ISC, accurate detection of the transmitter from a captured image is critical, because the receiver uses pixels that sense VLC signal for data reception. The purpose of this study is to reduce the false-positive and the false-negative probabilities of the transmitter. To achieve this goal, we propose a novel LED transmitter detection method composed of two stages: the candidate extraction stage by a linear support vector machine (SVM) and the classification stage by a convolutional neural network (CNN). Then, we show that the proposed method is robust to vehicle vibration and other noises such as non-transmitter LED compared to the conventional method.
Stochastic resonance (SR) is a noise-enhancement phenomenon that enables the detection of sub-threshold signals by adding noise and using nonlinear systems. This paper explores the applicability of SR in a BPSK receiver with sub-threshold signals. Although received signals are amplified as a result of the nonlinear behavior of the receiver, they are somewhat distorted. This results in the lower performance of SR receivers in comparison with linear receivers. Employing a parallel network of SR systems is expected to solve this problem. The present theoretical analysis demonstrates that in a certain noise intensity range, the output of the network can fully describe an input sub-threshold signal, and hence, the performance close to that of the linear receivers can be obtained. The effectiveness of the SR receiver was also demonstrated through a numerical example of the bit error rate (BER). However, achieving good BER performance requires an infinite number of arrayed SR systems, which is not realistic in practical systems. A design framework for an SR network with a finite number of elements and an appropriate noise intensity that can realize BER performance close to that in linear systems is also provided.
This paper proposes a new demodulation method using a one-bit analog-to-digital converter (ADC). With one bit resolution, a signal having a multilevel signal, such as a quadrature amplitude modulated (QAM) signal, is largely degraded by nonlinearity. To demodulate the signals, a high-resolution ADC is used to receive the signals with high linearity. This study sets out to demodulate the QAM signals using a one-bit ADC, whose resolution is the lowest (one-bit) and possesses outputs of binary (nonlinear) values. We propose to solve the issue by focusing on the statistical characteristics of the output signals of the one-bit ADC combined with noise. The proposed demodulation method is based on maximum a posteriori (MAP) criterion. The theoretical analysis presented illustrates that reliable demodulation is possible even with the one-bit ADC, provided the output probability of the ADC corresponds to each transmitted symbol is known.
S. Kamegawa, M. Kinoshita, T. Yamazato, H. Okada, T. Fujii, K. Kamakura, T. Yendo, S. Arai
IEEE GLOBECOM Workshop on Optical Wireless Communications, Abu Dhabi, UAE
Light-emitting diodes (LEDs) can add visible light communication (VLC) by high-speed blinking to their original lighting function. VLC using image sensors as receivers is referred to as image sensor communication (ISC). ISC eliminates noise and interference and enables multiple and simultaneous communication; hence it is suitable for outdoor mobile environments such as intelligent transport systems (ITSs). On the other hand, since the communication rate depends on the frame rate, it is difficult to increase. Therefore, the purpose of this study is to increase the communication rate by multilevel pulse width modulation (PWM). When the modulation level is increased, demodulation becomes difficult due to the bit per pixel (bpp) limitation of the image sensor. First, in order to perform efficient luminance extraction in limited bpp, we compare the maximum luminance extraction and the average luminance extraction. Then, we propose improving the nonlinearity between the transmitter and receiver, which is a problem in average luminance extraction suitable for a mobile environment, by applying precoded PWM. Finally, we evaluate effectiveness of precoded PWM experimentally.
This paper proposes a demodulation method using a one-bit comparator for signals processed by multilevel pulse amplitude modulation (PAM). The proposed method is simple and provides an alternative to using an analog-to-digital converter to describe multilevel input signals. Because of the noise present in the transmitted multilevel PAM signal, the two-level output of the one-bit comparator shows different statistical behavior for each level of the signal. Thus, it is possible to detect the signal level, or perform symbol decision, based on the maximum likelihood (ML) criterion. The present theoretical analysis reveals that reliable demodulation is possible even with a one-bit comparator if the probability mass function of the two-level outputs of each received symbol plus intentionally added noise is known.
The present letter discusses a detectability enhancement induced by co-channel interference signals in the polarization diversity reception. The challenge is the detection of weak (subthreshold) signals, the level of which is less than the detection limit of radio receivers. To understand the theory underlying the mechanism in the presented diversity scheme, we introduce an analytic model of a dual polarized antenna array in the fading channel. In addition, the channel capacity in a binary data transmission is derived. As a result, we reveal that the interference-aided diversity reception enables us to detect signals even below the detection limit of the receiver. Moreover, the appropriate source code is needed to achieve the channel capacity because the transmission channel is asymmetric in the present reception scheme.
S. Hiraoka, Y. Nakashima, T. Yamazato, S. Arai, Y. Tadokoro, H. Tanaka
International Symposium on Nonlinear Theory and its Application (NOLTA), pp. 705-708, Tarragona, Spain
2018年9月
We present a numerical study of an interference-aided detection of a weak (subthreshold) signal in a polarization diversity. We show that the nonlinear signal processing dramatically improves the detectability of the weak signal, supported by an interference signal generated by an appropriate beam control of the antenna arrays. The method takes advantage of subthreshold signal detection by the Stochastic resonance. To postulate a performance of the interference-aided detection, we numerically evaluate the channel capacity provided by the proposed diversity reception on a fading model. Through the numerical analysis, we find that the channel capacity depends on the threshold level of the detector and also the beam pattern determined by the diversity weights in the antenna arrays.
Progress In Electromagnetics Research Symposium (PIERS), Toyama International Conference Center, Toyama, Japan
2018年8月
This article introduces image sensor communications (ISC), a subset of visible light communication (VLC), that use high-speed image sensor and its application to automotive. Li-Fi (light fidelity) and OCC (optical camera communication) or also know as CamCom are also VLC family. Li-Fi is a high-speed wireless system and is currently in the process of being standardized in IEEE 802.11. The OCC uses an ordinary camera, e.g. a smartphone camera, as a receiver while ISC uses a high-speed image sensor as a reception device. The principal component of a camera, an image sensor, is used for both ISC and OCC. The main difference is that ISC focuses on a high-speed image sensor while OCC concentrates on low-cost consumer applications using smartphones and similar contemporary devices. For automotive usage, a high-speed image sensor is the best choice for the VLC receiver because the image sensor has a spatial separation of noise and target source. The VLC family uses LED as the transmitter and LED light sources are everywhere on streets: in signs, traffic lights, street lights, and other stationary objects. So if we can send IDs or exact location data (latitude and longitude) by way of VLC from those LEDs, then they can be used as anchor nodes placed on roads, sidewalks, or landmarks. Those anchor nodes help autonomous cars and connected vehicle for robust navigation with centimeter accuracy. The image sensor is the suitable detection device as it can be used for both positioning and VLC data detection. The author has been working on ISC for automotive applications. In this article, some of the author research, as well as his findings, are introduced.
This article overviews image sensor communication (ISC), a subset of visible light communication (VLC) system that uses a high-speed image sensor as a reception device. Owing to a massive number of pixels and spatial separation of multiple light souces, ISC can be used in an outdoor mobile environment, suitable for automotive applications. The paper also introduces some results from the authors’ work on ISC and its application to vehicle-to-everything (V2X) communication.
T. Yamazato
Visible Light Communications Workshop, Pacific Rim Conference on Lasers and Electro-Optics (CLEO-PR), Hong Kong Convention and Exhibition Centre, Hong Kong
2018年7月
Back in 1998, Prof. Masao Nakagawa invented the concept of visible light communications (VLC) that adopts light emitting diodes (LEDs) as a transmitter. Twenty years of research progress make VLC attractive not only to researchers but also to practitioners. We are about to see blooms of VLC products. Image-sensor communication (ISC) is a form of VLC that uses image-sensor as a reception device. A particular advantage of ISC is an ability to spatially separate light sources. We can use ISC in the outdoor mobile environment. In this presentation, I will review ISC, its application, and future perspective. Some results from the author vis-a-vis ISC and its application to the automobile are also introduced.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
International Conference and Exhibition on Visible Light Communications (ICEVLC), Yokohama, Japan
2018年3月
In this paper, we propose using a high-speed stereo camera as the image sensor communication (ISC) receiver of an intelligent transport system (ITS). The stereo camera is used for front recognition of the vehicle, making it possible to estimate distances and enabling an integrative system that comprises vehicle front recognition and communication. Furthermore, several stereo images from slightly different views can be obtained at the same time, which provides diversity. Thus the proposed method enhances communication performance owing to the stereo diversity. We also provide experimental results obtained using the high-speed stereo camera and compare them with that of a conventional single high-speed camera. The proposed method improves the bit error rate (BER) performance with respect to the conventional method.
Takaya Yamazato
International Conference on Optical Wireless Communications, Beijing, China
2018年3月
木下雅之，山里敬也，岡田啓，藤井俊彰，荒井伸太郎，圓道知博，鎌倉浩嗣
電子情報通信学会 総合大会, A-9-8, p.95, 東京
2018年3月
本稿では LED 光源を送信機,高速イメージセンサを受信機に想定した ITS( 高度道路交通システム ) イメージセンサ可視光通信を扱う.従来のイメージセンサ可視光通信では受信機に単眼カメラを用いていたが, 本稿では高速二眼カメラを用いる受信機構成を提案し, 左右の撮影画像から得られるダイバーシティを利用した通信性能の改善手法について検討する.
This tutorial article presents an outline of image sensor communication (ISC) technologies realized by light sources and cameras. It discusses the revision of the IEEE 802.15.7-2011 standard, namely, the IEEE 802.15.7m Optical Wireless Communications Task Group, which has significantly influenced the development of the ISC technology. It also reviews the ISC technical proposals of the task group and compares them with related works. The essential technical considerations of the ISC specifications are presented, and the future directions of research and development are discussed.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, vol.E101-A, no.1, pp.176-184
Image sensor communication (ISC), derived from visible light communication (VLC) is an attractive solution for outdoor mobile environments, particularly for intelligent transport systems (ITS). In ITS-ISC, tracking a transmitter in the image plane is critical issue since vehicle vibrations make it difficult to select the correct pixels for data reception. Our goal in this study is to develop a precise tracking method. To accomplish this, vehicle vibration modeling and its parameters estimation, i.e., representative frequencies and their amplitudes for inherent vehicle vibration, and the variance of the Gaussian random process representing road surface irregularity, are required. In this paper, we measured actual vehicle vibration in a driving situation and determined parameters based on the frequency characteristics. Then, we demonstrate that vehicle vibration that induces transmitter displacement in an image plane can be modeled by only Gaussian random processes that represent road surface irregularity when a high frame rate (e.g., 1000 fps) image sensor is used as an ISC receiver. The simplified vehicle vibration model and its parameters are evaluated by numerical analysis and experimental measurement and obtained result shows that the proposed model can reproduce the characteristics of the transmitter displacement sufficiently.
The concept of visible light communications (VLC) originates from an Asian professor and adopts light emitting diodes (LEDs) as a transmitter. Three Asian born Nobel Prize winners developed blue LEDs, key devices that produce white lighting. Consequently, VLC and its other forms can be considered as an Asian born wireless technology. This paper overviews VLC with emphasis on image sensor communication (ISC) that uses an image sensor as a reception device for VLC signals. Some results from the author vis-a-vis ISC and its application to automobile are also introduced.
S. Kibe, K. Kamakura, T. Yamazato
IEEE Global Communications Conference (GLOBECOM), pp. 1-6, Singapore, Singapore
This paper proposes an N-stream superimposed system for image-sensor-based visible light communications (ISbased VLC). Based on the principle of m-point discrete Fourier transform (DFT), a phase shift keying (PSK) signal is transmitted over m consecutive time slots mT, where T is a slot duration. In practice, the symbol rate of this paper is R/(m + 1) because a guard slot is inserted every m slots. In the superimposed system, N data streams where the symbol rate of the nth data stream, n = {1, 2, . . . , N}, is 1/(m + 1)n-1 times the symbol rate of the first data stream are combined to form a pulse-width modulated (PWM) wave with a period time T. An IS receiver with a camera operating at a frame rate of R/(m + 1)n-1 fps demodulates data streams whose symbol rate is R/m + 1)n symbol/s or lower. Our experimental results validate that from a superimposed PWM wave of 500-symbol/s and 125-symbol/s data streams, a 2000-fps camera receiver demodulates both of the two data streams and the 500-fps camera receiver does the 125-symbol/s data stream successfully, without shortening individual error-free transmission ranges, compared with non-superimposed systems in which 500-symbol/s and 125-symbol/s data streams are independently transmitted by different light emitting diode (LED) transmitters and received by 2000-fps and 500-fps camera receivers, respectively.
Y. Nakashima, T. Yamazato, Y. Tadokoro, S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.291-294, Cancun, Mexico
2017年12月
Stochastic Resonance (SR) is considered as a noise enhanced phenomenon, that a response of a nonlinear system is improved by noise. In previous studies, an application of SR for wireless communication has been discussed and an SR receiver, the receiver that demodulate a received signal by SR, was proposed. However, these studies have used a basic modulation signal and have not focused on a signal that transmit information by multi-level amplitude. In this paper, we consider an SR receiver for 4-pulse amplitude modulation (4-PAM) signals. By applying SR, it can demodulate 4-PAM signals by a 1-bit resolution device. We show the system model of the receiver, evaluate its performance by simulation, and show its availability.
Takaya Yamazato
Journal of Communications and Information Networks, vol.2, no.4, pp.65-74
This paper introduces infrastructure-to-vehicle and vehicle-to-vehicle communications using VLC. A VLC coupled with a high-speed image sensor is introduced (i.e., image sensor communication). The high-speed image sensors provide eyes for autonomous and connected vehicles. VLC imparts data reception capability to image sensors with necessary functions, which can then be provided to autonomous and connected vehicles. In this paper, some of our research on coupling VLC to high-speed image sensors is introduced, including our key findings: the basics of ISC, a vehicle motion model, and range estimation.
堀将大，木下雅之，山里敬也，岡田啓，藤井俊彰，鎌倉浩嗣，圓道知博，荒井伸太郎
電子情報通信学会技術研究報告, ITS2017-56, pp.251-256, 沖縄
2017年12月
本稿では高度道路交通システム（ITS）のためのイメージセンサ可視光通信に着目する．この通信では送信機として LED アレイを，受信機として高速度カメラを用いる．可視光通信を行うために、高速度カメラで撮影した画像中のLEDアレイ送信機の位置を特定する必要がある．先行研究では LED アレイは高い時間勾配と低い空間勾配を持つことを示し，これらの特徴量を用いたLEDアレイ検出手法を提案した．しかし，その手法では情報源であるLEDアレイ送信機と情報を持たない人工光源を区別することが困難である．また，LEDアレイに比べ非LEDアレイの画素が非常に多いため，データの不均衡性の問題も生じた．そこで，本稿ではより正確なLEDアレイの検出を行うため，k平均法に基づくアンダーサンプリングを行い，それらのデータからSVMで学習したモデルを用いるLEDアレイ検出手法を提案する．
木部修斗，鎌倉浩嗣，山里敬也
電子情報通信学会技術研究報告, CS2017-58, pp.21-2, 阿蘇
2017年11月
T. Yamazato, N. Kawagita, H. Okada, T. Fujii, T. Yendo, S. Arai, K. Kamakura
This paper presents a feasibility study of the uplink visible light communication (VLC) beacon system for the universal traffic management system (UTMS). The UTMS is a traffic management system beneath the National Police Agency of Japan. Currently, 55 000 UTMS infrared beacon systems have been installed, and they provide expressway and ordinary road information to cars. However, the data rate is 1 Mbps, and a faster data rate is necessary to support automotive and smart mobility devices. In this paper, we propose an uplink V2I system for the UTMS. The system is designed to match the current beacon system as closely as possible, so that the system can easily be replaced and still provide sufficient bandwidth for future automotive and smart mobility devices. We adopt a photo diode (PD) as the VLC receiver and a commercially available off-the-shelf LED headlight as a transmitter. Unfortunately, the bandwidth of such an LED is usually small, so we consider applying a bit-loading algorithm to direct-current-biased optical orthogonal frequency division multiplexing. To reduce strong background noise, such as from the sun, we narrow down the field-of-view by applying a lens to the PD, which forms a tiny communication area, smaller than the current infrared beacon system. We then consider multiple PDs with the lens to create a similar communication area as the infrared beacon system. As a result, we achieve 3.1-Mbps throughput.
K. Kamakura, T. Yamazato
IEEE Photonics Conference (IPC), pp.235-236, Orlando, FL, USA
Most practical visible light communication (VLC) systems being currently deployed with image sensor receivers use intensity modulation and direct detection scheme for outdoor and indoor applications. A number of modulation and coding techniques that are used for image sensor-based VLC systems are presented.
木下雅之，山里敬也，岡田啓，藤井俊彰，荒井伸太郎，圓道知博，鎌倉浩嗣
電子情報通信学会ソサイエティ大会, A-9-7, p.92, 東京
2017年9月
本稿では LED 光源を送信機,高速イメージセンサを受信機に想定した ITS( 高度道路交通システム ) イメージセンサ通信を扱う.従来のイメージセンサ通信では受信機に単眼カメラを用いていたが,本稿では高速二眼カメラを用いる受信機構成を提案する.高速二眼カメラでは左右のカメラで見え方が異なり,この違いを利用することで通信性能の改善を図る.
Signal filtering is necessary for wireless communication. However it causes the signal amplitude to fluctuate and affects the performance of stochastic resonance (SR) receivers. In this study, we evaluate the bit error rate (BER) performance of filtered binary phase-shift keying (BPSK) on an SR receiver. The results show that filtering improves the BER performance of the SR receiver because the amplitude fluctuation contributes to improving the SR effect. We also evaluate the effect of the roll-off factor, which determines the bandwidth of the filter and the amplitude fluctuation. The results demonstrate the applicability of the SR receiver to bandlimited BPSK signals.
ITS(Intelligent Transport Systems:高度道路交通システム)可視光通信にイメージセンサを用いる場合,イメージセンサの特性から高速化が課題となる.従来の伝送方式は,送信信号の変調にPWM(Pulse Width Modulation:パルス幅変調)を用いる方式であり,受信側で振幅変調として捉えて通信を行う.これに対して,高速伝送を実現できる伝送方式の候補として,仮想正弦波を用いる方式がある.仮想正弦波方式は,送信信号のパルスの振幅,位置の変調を,受信側で振幅,位相の変調として捉えて通信を行う.しかし,この 2 つの伝送方式の優位性が明らかでないため,本研究では比較実験を行い, ITS イメージセンサ可視光通信の高速化のための伝送方式について検討する.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
IEEE International Conference on Communications Workshop on Optical Wireless Communications, pp.144-149, Paris, France
Image sensor communication (ISC), which is derived from visible light communication (VLC), is a novel form of wireless communication that uses an image sensor as a receiver. ISC is an attractive solution for outdoor mobile environments and is particularly wellsuited to intelligent transport systems (ITS). The purpose of this paper is to derive the dominant components of vehicle vibrations and road surface irregularities that induce transmitter displacement in ITS-ICS in paved road scenarios. Such displacements make it difficult for a ISC receiver to select the correct pixels. We measured vehicle vibrations during an actual driving scenario using a sixaxis acceleration sensor installed in a smartphone. Using the results obtained, we performed a frequency analysis of the vehicle vibrations and determined the parameters of vehicle vibrations based on the frequency characteristics. This paper explains that the vehicle vibrations that affect the communication performance can be modeled by solely using Gaussian random processes when a high frame rate (e.g. 1000 fps) image sensor is used as the ISC receiver.
T. Yamazato
Presentation at Professor Jean Armstrong's Laboratory, Monash University, Monash University, Australia.
2017年3月
N. Kawagita, T. Yamazato, H. Okada, T. Fujii, S. Arai, T. Yendo, K.Kamakura
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp.129-132, Guam
2017年3月
In this paper, we focus on the vehicle to infrastructure visible light communication (V2I-VLC) for intelligent transportation systems (ITS). We propose a V2I-VLC system using LED headlights as transmitters and photodiodes (PDs) with an optical lens as receivers. We adopt DC biased optical orthogonal frequency division multiplexing (DCO-OFDM) as a modulation scheme in order to realize high speed communication. As a results of the data transmission experiments in the driving situation, we achieve data rate of 2.7 Mbps using 32QAM.
W. Kihara, T. Yendo, S. Arai, T. Yamazato, H. Okada, K. Kamakura
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp.133-136, Guan, USA
2017年3月
R. Ohno, T. Yamazato
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp.81-84, Guam, USA
2017年3月
In this paper, we propose a traffic flow management at an intersection using the 760 MHz band V2X (Vehicle-to-X) system based on ARIB STD-T109. Using the V2X system, a road side unit (RSU) can obtain the vehicular information such as the vehicle position, speed and route. Based on the vehicular information, a ``support phase'' can be inserted to a cycle of traffic signal that controls traffic flow at an intersection. We define the “support phase” as the phase of changing the stop/go sign of the traffic signal on an intersection as necessary. In this way, it is expected to shorten the travel time of the vehicles. We evaluate the algorithm by a traffic simulator in terms of mean speed of all vehicles while passing through the intersection with considering V2X penetration rate.
本稿では LED 光源を送信機,高速イメージセンサを受信機に想定した ITS( 高度道路交通システム ) イメージセンサ通信を扱う. ITS イメージセンサ通信では車輌の移動や振動により,画像上での送信機の位置がフレームごとで変動する.こうしたフレーム間での送信機の移動は通信路変動として扱われ,情報を持つ正しいピクセルの選択を困難にし,誤りの原因となる.本稿では,通信路変動の要因となる車輌振動のモデル化とそのパラメータ推定を舗装路及び未舗装路における振動測定の結果を基に行う.
新井雄大，山里敬也，岡田啓，藤井俊彰，荒井伸太郎，圓道知博，鎌倉浩嗣
電子情報通信学会 総合大会, A-9-15, p.124, 名古屋
2017年3月
本研究では車輌のヘッドランプや信号機,照明,標示などへの普及が増えつつある LED を用いてイメージセンサ通信を行うことにより,次世代 ITS の技術として期待されている車車間・路車間通信を含んだ運転支援システムの実現を目指す.ITS イメージセンサ通信の環境を想定すると,多数の送信機からの信号を同時に受信する必要がある.これらの信号は互いに同期がとれていないので,それぞれの信号の復調のタイミングは異なり,一度に復調する手法は提案されていない.本稿では,この互いに非同期な複数信号の同時受信・復調を行うための実験系を構築した
増田圭亮，鎌倉浩嗣，山里敬也
電子情報通信学会 総合大会, B-10-57, p.310, 名古屋
2017年3月
山里敬也
電子情報通信学会 総合大会, BI-10-2, pp.SS-81 - SS-82, 名古屋
2017年3月
無線通信方式は移動体を相手とする通信手段としてはほとんど唯一のものであり，とりわけ自動車については，携帯電話，無線LANの普及に歩調を合わせるようにして発展してきている．図1に1980年以降の車車間・路車間通信と携帯電話，GPSの略史を示す．こうして並べてみると，自動車での無線利用は携帯電話の10年遅れて推移しているように思えてくる．もっとも，車車間・路車間通信は携帯電話のように人を対象にしたものでは無く，モノ（自動車）を対象にしたものであり，その意味ではIoT(Internet of Things)を先取りしているとも言える．本稿では路車・車車間通信システムについて解説する．とりわけ，現行の路車・車車間通信システムである700 MHz 帯高度道路交通システム（ARIB STD-T109）を取り上げ，その概要を紹介する．
新井雄大
電子情報通信学会東海支部卒業研究発表会
2017年3月
山里敬也
名古屋大学附属図書館研究開発室報告会, 名古屋大学
2017年3月
Stefano Bregni, Takaya Yamazato, Vasile Bota, Liangping Ma
This is the fourth article in the series of eight, started in November 2016 and published monthly in the IEEE ComSoc Global Communi- cations Newsletter, which covers all areas of IEEE ComSoc Member and Global Activities. In this series of articles, I am introducing the six MGA Directors (Sister and Related Societies; Membership Services; AP, NA, LA, EMEA Regions) and the two Chairs of the Women in Communications Engineering (WICE) and Young Professionals (YP) Standing Committees. In each article, one by one they present their sector activities and plans. In this issue, I interview Takaya Yamazato, Director of the Asia/ Paci c Region (AP). Takaya is a professor at the Institute of Liberal Arts and Sciences, Nagoya University, Japan. He received the Ph.D. degree from Keio University, Yokohama, Japan, in 1993. From 1993 to 1998 he was an assistant professor in the Department of Information Electronics, Nagoya University, Japan. From 1997 to 1998 he was a visiting researcher in the Research Group for RF Communications, Department of Electrical Engineering and Information Technology, University of Kaiserslautern, Germany. In 2006 he received the IEEE Communication Society Best Tutorial Paper Award. He served as symposium co-chair of ICC 2009 and ICC 2011. From 2008 to 2010 he was the chair of the IEEE ComSoc Satellite and Space Communications Technical Committee and the editor-in-chief of the Japanese Section of IEICE Transactions on Communications. His research interests include visible light communication, intelligent transport systems, stochastic resonance, and open educational resources. It is a pleasure for me to interview Takaya for this issue and o er him this opportunity to outline his current activities and plans as Director of the AP Region.
山里敬也
第３９回 東海地区 国公立大学情報システム研究会（東海ＩＳ研）, 名古屋大学
2017年2月
2016
T. Asai, T. Yendo, S. Arai, T. Yamazato, H. Okada, T. Fujii, K. Kamakura
Asia-Pacific Signal and Information Processing Association Annual Summit and Conference (APSIPA), pp.1 - 5
We focus on the road-to-vehicle visible light communication (VLC) that system is composed of a LED matrix as a transmitter and a high-speed camera as a receiver. In this VLC system, intensity of each LED cannot be determined from received image directly in case that the receiver is distant from the transmitter. In previous research, a method to estimate intensity of the LED from received image is proposed. In this method, intensity of LED is estimated by using Moore-Penrose pseudo-inverse matrix of coefficient matrix, which expresses relation between intensity of LEDs and pixel values. However, the coefficient matrix changes every moment because it is determined by positional relation between the receiver and the LED traffic light in VLC system. In this paper, we propose a method to estimate position of the LED matrix using simulated images. We measure sensitivity distribution of image sensor to generate simulated images. We evaluated degree of similarity between simulated images and real images.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
Cambodia-Japan Joint Workshop on Ambient Intelligence and Sensor Networks, シュムリアップ
2016年12月
Image sensor communication (ISC) enables multiple and simultaneous signal reception because of its ability spatially separate multiple sources. Therefore, ISC is an attractive solution for an outdoor mobile environment, in particular, in the field of intelligent transport systems (ITS). In ISC, since a transmitter position moves in an image plane according to vehicle movement, detection and tracking of transmitter is critical issue for robust data reception. Such movement referred to as optical ow causes ISC channel to fluctuate and must be considered to receive the signal accurately. In this paper, we conducted vehicle vibration measurement in well paved road and analyzed the frequency characteristic. According to the measured result, we proposed a vehicle vibration model and determined its parameters.
田中裕也，中島康雄，山里敬也，田所幸浩，荒井伸太郎
情報理論とその応用シンポジウム, pp.147-151, 岐阜
2016年12月
川北直明，山里敬也，岡田啓，藤井俊彰，荒井伸太郎，圓道知博，鎌倉浩嗣
情報理論とその応用シンポジウム, pp.555-560, 高山
2016年12月
山里敬也
電磁環境工学情報 月刊EMC, vol.29, no.8, pp.98-109
2016年12月
自動運転の研究開発は，1960年代から始まっており，その度に話題に上ってきた．Google による自動運転プロジェクトに触発されたことが原因と思うが，現在，自動運転に関する話題がマスコミを賑わしている．我が国の自動運転研究開発の第一人者である津川定之氏によると，現在のブームは第4期であり，ここに来てようやく実用化を目指した技術の検証が始まっている状況であり，加えて，各国政府も自動運転車を睨んだ政策・規制の立案に着手しつつある(1)．また，自動車メーカも2025年以降の自動運転車のリリースを発表するなど，自動運転はまさにホットトピックと言っても過言で無い． 現在，検討されている自動運転車の多くは自律走行車である．具体的には，車輌に搭載されたレーダ，LIDAR (Light Detection and Ranging)，車載カメラ，超音波センサなどを用いて車輌周辺の詳細な3次元地図を作成し，この地図情報と予め車輌に持ち合わせている情報およびGPS等で得られる外部情報からコンピュータが総合的に解析し、ハンドル、アクセル、ブレーキなどの運転に必要となる動作を行う仕組みである(2)．自律走行車は，特段のインフラ設備も必要としない，つまり，自動車メーカの努力で実現できる可能性がある．また，ディープラーニングなどの高度な画像認識技術，人工知能（AI）など自動運転に必須の演算・処理も，コンピュータの計算能力が飛躍的に増加した現在では，実用レベルで利用できる状況にある．このことも自律走行車の実用化に向けた研究開発を促進させている理由と考えられる．一方で，今後の自動運転車の動向に目を向けると，自律走行車を基礎にしつつも，路車・車車間通信を活用することで道路インフラおよび周辺車輌と常時情報交換を行いながら走行する，いわゆる「つながる車（コネクテッドカー）」が注目される(3)．とりわけ，その基盤となる路車・車車間通信については，実用に耐えるシステム運用が始まったばかりであり，自動運転車を見据えた今後の動向に注目が集まっている(4)．道路インフラから車輌に対し情報伝送を行う路車間通信システムは，道路側の漏洩同軸ケーブルを用いてカーラジオ（AM波）で伝送する路側放送に始まり，VICS（Vehicle Information and Communication Systems），そして 5.8 GHz帯DSRCによるITSスポットとして進展している．また，有料道路における料金自動収受システム（ETC: Electronic Toll Collection）も路車間通信システムである．さらに，警察庁のITSプロジェクトによって設置された光ビーコンによるUMTS（Universal Traffic Management System）も路車間通信による交通情報を提供している(5)．車車間通信システムとしては，700 MHz 帯高度道路交通システム（ARIB STD-T109）がある．このシステムで利用する周波数帯は，もともとアナログTV放送で使用していた周波数帯である．それまでも，5.8 GHz帯狭域通信(DSRC)システムを用いて車車間通信を行うことができたが，5.8 GHz 帯は、電波の直進性が強く、ビル影、大型車の後方等の見通し外には、電波が回り込みにくい．このため，ビルや壁に囲まれた交差点等の見通し外での利用に適さないとの指摘があった．そこで，700 MHz帯をITSに利用する案が検討され，2011年12月には総務省から認可された(4)． 本稿では，我が国における路車・車車間通信について解説する．とりわけ，現行の路車・車車間通信システムである700 MHz 帯高度道路交通システム（ARIB STD-T109）を取り上げ，その概要を紹介する．700 MHz 帯高度道路交通システム（ARIB STD-T109）は，当初（2007年）は車車間通信システムとして検討が始まったが，その後，2009年には車車間・路車間共用方式として検討され，2012年の完全デジタルTVの移行の年にARIB STD-T109として標準化されている．この方式の特徴としては，単一周波数帯の共用による車車・路車共用通信方式がある．本稿では，この概説を中心に述べていく．本稿は次のように構成される．まず第2章ではITSと関連する無線通信技術の略史について述べる．容易に想像できることであるが，無線通信技術の進展に歩調を合わせるように自動車向け無線通信技術も進展している．とりわけ，携帯電話の普及に伴う技術の進展，各種デバイスの小型・省電力化は大きいと考える．また，自動運転技術もまた無線通信技術の進展に呼応する形で発展しており，興味深い．第3章では現行の路車・車車間通信システムである700 MHz 帯高度道路交通システム（ARIB STD-T109）について概説する．第4章では，未来のITSとそれを支える無線通信技術，とりわけ未来の自動運転車である「つながる車」について筆者の愚考を述べる．最後に第5章でまとめる．
Y. Nakashima, H. Tanaka, T. Yamazato, Y. Tadokoro and S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.407-410, Yugawara,Japan
2016年11月
Signal filtering is necessary for wireless communication however it fluctuates the signal amplitude and affects the performance of a stochastic resonance (SR) receiver. In this paper, we evaluate the bit error rate (BER) performance of filtered binary phase shift keying (BPSK) on an SR receiver. The result shows that filtering improves the BER performance of the SR receiver because the amplitude fluctuation contributes to improving the SR effect, indicating the applicability of the SR receiver to bandlimited BPSK signals.
佐藤翔, 岡田啓, 山里敬也, 和田忠浩, 小林健太郎, 片山正昭
可視光通信ワークショップVLCWS2016, 東京
2016年11月
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
23rd World Congress on Intelligent Transport Systems , Melbourne, Australia
2016年10月
In this paper, we focus on the visible light communication (VLC) for ITS application using LED light source as a transmitter and high-speed image sensor as a receiver (image sensor communication: ISC). In ISC, the data reception is performed by extracting luminance corresponding to the transmitter from captured images. However, since either transmitter, receiver, or both moves with vehicles, the transmitter position is moved between frames and it confuses receiver to select the correct pixels. Hence, we treat such movement referred to as optical flow as channel fluctuation. In our previous work, we proposed a model that expressed motion of transmitter in captured images by using a single pinhole camera. In this paper, we derive channel fluctuation characteristic by numerical analysis based on the proposed model and evaluate its validity by comparing with channel fluctuation characteristic obtained by actual measurement.
S. Sato, H. Okada, K. Kobayashi, T. Yamazato, M. Katayama
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), pp.1242-1247, Valencia, Spain
Digital signage, which is advertising media using a liquid crystal display (LCD), is increasing in popularity. One possible application is wireless communications between digital signage and viewers. We focus on image-sensor-based visible light communication (VLC). Image-sensor-based VLC requires only an image sensor (IS), which is common equipment in smart phones. In the proposed method, an nformation signal is displayed on LCD. However, embedding the information signal into an advertisement may decrease the quality. We propose blue color difference modulation to make such signals imperceptible. We implemented a VLC system between digital signage and IS to demonstrate, the effectiveness of the proposed modulation in a real environment.
K. Masuda, K. Kamakura, T. Yamazato
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), pp.1254-1259, Valencia, Spain
This paper discusses the stochastic resonance (SR) effect in a binary communication system for subthreshold signal reception. We focus on the problem of no communication when received signal strength is below receiver sensitivity. Subthreshold signal reception requires a device that exhibits SR, such as a Schmitt trigger or a comparator. Previously, we proposed an alternative three-level device and demonstrated its high performance for subthreshold signal reception in an SR receiver. In the present study, we show that our proposed three-level device outperforms the three devices and discuss reasons for this superior performance. Contributions of our present paper are twofold: first, we analytically derive bit error rate (BER) performances of SR receivers installed with a Schmitt trigger and a comparator; second, we compare performances of the Schmitt trigger, comparator, and three-level device.
As a new technology for next-generation vehicle-to-everything (V2X) communication, visible-light communication (VLC) using light-emitting diode (LED) transmitters and camera receivers has been energetically studied. Toward the future in which vehicles are connected anytime and anywhere by optical signals, the cutting-edge camera receiver employing a special CMOS image sensor, i.e., the optical communication image sensor (OCI), has been prototyped, and an optical V2V communication system applying this OCI-based camera receiver has already demonstrated 10-Mb/s optical signal transmission between real vehicles during outside driving. In this paper, to reach a transmission performance of 54 Mb/s, which is standardized as the maximum data rate in IEEE 802.11p for V2X communication, a more advanced OCI-based automotive VLC system is described. By introducing optical orthogonal frequency-division multiplexing (opticalOFDM), the new system achieves a more than fivefold higher data rate. Additionally, the frequency response characteristics and circuit noise of the OCI are closely analyzed and taken into account in the signal design. Furthermore, the forward-current limitation of an actual LED is also considered for long operational reliability, i.e., the LED is not operated in overdrive. Bit-error-rate experiments verify a system performance of 45 Mb/s without bit errors and 55 Mb/s with BER < 10-5.
High-speed image sensors, designed for machine vision and control, provide the eyes for autonomous and connected vehicle. A noteworthy feature of high-speed image sensors is their ability to be used as a reception device for visible light communication (VLC) signals. Due to the massive number of pixels available and the ability to spatially separate sources, a signal-receiving pixel in the image sensor plane represents the actual position of the transmitter. The VLC signal can be represented not only by a VLC time domain signal but also by the position of the transmitter. In this paper, we propose a robust range estimation scheme that integrates with a VLC function for infrastructure-to-vehicle visible light communication (I2V-VLC). The scheme is composed of an LED array transmitter and a high-speed image sensor receiver. It measures a range by taking phase-only correlation (POC) and avoids vehicle vibration from road irregularity. Field trials confirm an accuracy range of 0.3 m, even on rough road conditions, with the measurement time of 2 ms, which is much faster than that of light detection and ranging (LIDAR).
Complex interleaved orthogonal design (CIOD) can offers diversity gain to the part of the source in spatial modulation which has single radio frequency (RF) front-end at the transmitter despite multiple-inputmultiple-output, but emits the undesired component out-of-band. For the reducing out-of-band emission, we give up indicating the information source by the antenna switching and increase both the interleaver size and the antenna switching interval. The increase reduces the discontinuities in the waveform and out-of-band emission. We propose such a scheme as transmit diversity with single RF front-end using CIOD. The diversity gain of the proposed scheme is equivalent to the case for CIOD. Moreover, we evaluate the increase of out-of-band emission and confirm that of the proposed scheme compared to the ideal case is only 3dB.
This paper proposes a novel data detection scheme based on the occurrence of blurred output images in image-sensor-based visible light communication systems. This system's receiver suffers from an inability to detect correct LED luminance values and demodulation of data because the captured image blurs owing to defocusing. The proposed method assumes that the light emitted by all LEDs that is diffused by the blur can be approximated by applying a Gaussian filter and expressesall LED luminance values as convolution equations based on this diffusion of the LED light. We estimate each LED light's condition by simultaneously solving these convolution equations and recover data according to the estimated result. To confirm the accuracy of the proposed method, we conduct computer simulations and an implementation experiment to evaluate the bit error rate performance of the proposed method.
H. Tanaka, T. Yamazato, Y. Tadokoro, S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), Hong Kong, China
2015年12月
Stochastic resonance (SR) is an interesting phenomenon in that noise enhances system responses. Despite an attractive phenomenon of SR that noise enhances a weak signal below a receiver sensitivity, few researchers have addressed the SR effect in communication systems. Previously, we proposed an analysis method for the SR receiver with a device exhibiting SR and evaluated its bit error rate (BER) performance. However, the device was limited to a non-dynamical device, and there is room for improving the performance of the SR receiver by changing the device. In this paper, we use two typical devices exhibiting SR, i.e., a comparator as a non-dynamical device and a Schmitt trigger as a dynamical device. We evaluate the BER performances of these devices with analysis methods and numerical simulations. A performance comparison of these devices is also shown.
C. Fuwa, H. Okada, K. Kobayashi, M. Katayama
International Symposium on EcoTopia Science (ISETS), no.P-6-2, Nagoya, Japan
2015年11月
IEEE 802.11ac, which is the latest standard of IEEE 802.11, supports forward-link (downlink) MU (Multi-User)-MIMO (Multiple-Input Multiple-Output), and it can improve the transmission efficiency. IEEE 802.11ax, which is under standardization, is considered to apply reverse-link (uplink) MU-MIMO, and a further improvement of the efficiency is expected. In this paper, we propose to introduce reverse-link MU-MIMO in addition to forward-link MU-MIMO for wireless mesh networks, and evaluate the performance in terms of area transmission efficiency, which indicates a number of packets in a unit area. Then, we clarify that the proposed system achieves the higher area transmission efficiency than forward-link MU-MIMO.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
International Workshop on Vision, Communications and Circuits (IWVCC) , Yokohama, Japan
2015年11月
Image-sensor-based visible light communications (IS-VLC), or also known as image sensor communication (ISC) and camera communications (CamCom), is one of emerging segment in the field of visible light communications (VLC). As the name indicates, IS-VLC uses light-emitting diodes (LEDs) or an LED array for the transmitter by modulating LED’s intensity at high speeds that are undetectable to the human eye. For the reception device, IS-VLC adopts image-sensor. In our previous work, we have proposed vehicle motion model that expresses the motion of VLC transmitter in image plane by single pinhole camera model. In this paper, we performed a simulation based on vehicle motion model for infrastructure-to-vehicle VLC (I2V-VLC) with actual vehicle vibration measured by 6- axis acceleration sensor of smartphone and evaluated its channel characterized by optical flow.
H. Tanaka, T. Yamazato, S. Arai
International Workshop on Vision, Communications and Circuits (IWVCC) , Yokohama, Japan
2015年11月
This paper evaluates the performance of the stochastic resonance (SR) receiver for subthreshold signal reception. We focus on the problem of no communication when received signal strength is below receiver sensitivity. Previously, we proposed a SR receiver installed with a typical device exhibiting SR in BPSK modulation and presented the performance improvement for subthreshold signals. However, the performances of other nonlinear devices exhibiting SR are not clear, and we require the performance evaluation for various nonlinear devices. And also, the performance evaluation in multi-level modulation is not presented. In this paper, we evaluate bit error rate (BER) performances of SR receivers installed with a three-level device, a Schmitt trigger and a comparator in QPSK modulation.
S. Sato, H. Okada, K. Kobayashi, T. Yamazato, M. Katayama
International Conference and Exhibition on Visible Light Communications (ICEVLC), Yokohama, Japan
2015年10月
Y. Kawai, T. Yamazato, H. Okada, T. Fujii, T. Yendo, S. Arai, K. Kamakura
International Conference and Exhibition on Visible Light Communications (ICEVLC), Yokohama, Japan
2015年10月
This paper focuses on image sensor based vehicle-to-infrastructure visible light communication (V2IVLC) for Intelligent Transport Systems (ITSs). Because the image sensor can spatially separate multiple or noise sources, its receiver can simultaneously demodulate multiple sources. Thus, we consider multiple source reception from multiple vehicles. In image sensor based VLC, the transmitted data are received by extracting the luminance corresponding to the VLC transmitter from the captured image. Transmitter detection and tracking are an important requirement of these systems but are degraded by occlusion, which causes non-line of sight (NLOS). We focus on tracking of transmitters that may be occluded by moving vehicles in V2I-VLC. Our proposed method detects multiple LED headlights by combining a background difference method with an LED detection method based on time and space gradients. We also propose a tracking method based on optical flow-based tracking, which handles occlusion by linear or second-curve interpolation. The proposed methods were evaluated by a high-speed camera placed by the roadside. The false-positive and falsenegative tracking rates were 6.25% and 3.32%, respectively, at κ = 60 (where κ defines the permissible error in the optical flow).
K. Chiga, H. Tanaka, T. Yamazato, Y. Tadokoro, S. Arai
Nonlinear Theory and Its Applications, IEICE, vol. 6, no. 4, pp. 520-533
Stochastic resonance (SR) is a nonlinear phenomenon that, under certain conditions, can enhance system response by adding noise to the signals of some nonlinear system. A particular advantage of SR over conventional linear systems is that it is able to detect subthreshold signals that linear systems hardly sense. Unfortunately, most research of SR in wireless communication systems has focused on fundamental analysis, leaving work to be done in experimental SR research despite the attractiveness of its application. Few attempts have so far addressed the development of SR receivers to show the feasibility of subthreshold signal detection. Those receivers that have been developed are simple ones specially made to confirm the usefulness of SR without needing to support state-of-the-art wireless radio technology. The purpose of this study is to examine the feasibility of using an SR receiver to receive subthreshold radio frequency (RF) signals. A new add-on SR device is developed and confirmation that the SR phenomenon exists within RF is obtained when using software defined radio (SDR) as the post-processing receiver. Furthermore, bit error rate (BER) performance is mainly governed by the add-on SR device's output signal quality.
Channel modeling is critical for the design and performance evaluation of visible light communication (VLC). Although a considerable amount of research has focused on indoor VLC systems using singleelement photodiodes, there remains a need for channel modeling of VLC systems for outdoor mobile environments. In this paper, we describe and provide results for modeling image sensor based VLC for automotive applications. In particular, we examine the channel model for mobile movements in the image plane as well as channel decay according to the distance between the transmitter and the receiver. Optical flow measurements were conducted for three VLC situations for automotive use: infrastructure to vehicle VLC (I2V-VLC); vehicle to infrastructure VLC (V2I- VLC); and vehicle to vehicle VLC (V2V-VLC). We describe vehicle motion by optical flow with subpixel accuracy using phase-only correlation (POC) analysis and show that a single-pinhole camera model successfully describes these three VLC cases. In addition, the luminance of the central pixel from the projected LED area versus the distance between the LED and the camera was measured. Our key findings are twofold. First, a single-pinhole camera model can be applied to vehicle motion modeling of a I2V-VLC, V2I-VLC, and V2V-VLC. Second, the DC gain at a pixel remains constant as long as the projected image of the transmitter LED occupies several pixels. In other words, if we choose a pixel with highest luminance among the projected image of transmitter LED, the value remains constant, and the signal-to-noise ratio does not change according to the distance.
This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (ISbased) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity-modulated signals from two different light emitting diodes (LEDs) are detected by one pixel of an IS, STC allows us to decouple them; thus, succeeding to receive them with no errors. Consequently, STC offers extended transmission distance to pixel-resolution-limited IS-based VLC links. In the layered STC presented in this paper, additional bit streams are laid on the 2n × 2n LED array for increasing the transmission rate per symbol duration for the case where the pixel resolution is improved. A prototype of a threelayered STC is built with an 8 × 8 LED array, where each of the LEDs is modulated at 1 kb/s and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that the two additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155 and 55 m, respectively, from the LED array, without decreasing 210 m of the transmission distance of layer-1 bit stream.
This paper demonstrates the feasibility of layered space-time coding (STC) in an outdoor image-sensor-based (IS-based) visible light communication (VLC) system. We examined that for low-resolution IS-based VLC channel where intensity modulated signals from two different light emitting diodes (LEDs) are detected at one pixel on the image plane, STC allows to decouple them, thus receiving data with no errors. Consequently, STC offers extending the transmission distance. In the layered STC presented here, additional bit streams are aligned in the 2n×2n LED array for increasing the transmission rate per symbol duration for the case where the spatial resolution is improved. A prototype of three layered STC is built with an 8×8LED array, where each of the LEDs is modulated at 1 kbps and a high-speed camera with IS operating at 1000 fps. Our experimental results validate that additional bit streams (layer-2 and -3), aligned in the layer-1 STC matrix pair, are extracted with no errors when the receiver comes within 155m and 55 m, respectively, from the LED array, without decreasing 210m of the transmission distance of layer-1 bit stream.
Abstract: This invited paper focuses on a high-speed image sensor as a visible light communication (VLC) reception device to develop the intelligent transport systems (ITS) application using VLC technique. We refer to the VLC using a high-speed image sensor as image-sensor-based VLC. A major advantage of the image sensor is the ability to spatially separate multiple sources. Based on this ability, we proposed several methods for the image-sensor-based VLC in our previous researches. Especially, we focused on unique characteristics of the image sensor and proposed the hierarchical coding and the overlay coding to improve the data reception performance. However, to perform the image-sensor-based VLC in an actual environment, the receiver has to acquire the VLC transmitter from captured images before recovering data. Namely, the VLC transmitter acquisition and tracking are critical problem. the image-sensor-based VLC technique. This invited paper introduces two proposed methods to acquire the VLC transmitter from images captured by the image sensor.
Stochastic resonance (SR) is an interesting phenomenon in that noise enhances system response. Despite attractive phenomenon of SR that noise enhances system response, enhancement of the weak signal below device sensitivity, and few researchers have addressed the SR effect in communication systems. This paper discusses the SR effect in communication systems. We focus on the problem in which communication cannot be established when the received signal strength is below receiver sensitivity. The purpose of this study is to evaluate the bit error rate (BER) performance of the SR receiver and reveal the SR effect in communication systems. We propose an analysis method for the SR receiver using a non-dynamical device that exhibits SR effect. The numerical results show that the SR effect can improve the BER compared to a system without SR. The contribution of the paper is two folds: The first contribution of our present study is that the BER of the SR receiver using a non-dynamical device can analytically be derived. The second contribution of our study is that the number of samples per symbol, the received signal amplitude, and the receiver sensitivity are three important parameters. We further derive the maximum performance gain by the SR system. Although our focus is on primary communication systems; however, our findings can be applied to other systems.
山里敬也
電子情報通信学会技術研究報告, vol. 115, no. 2, RCS2015-6, pp. 31-31, , 湯布院・湯布郷館
本論文では,発光ダイオード(LED)およびイメージセンサを用いた可視光通信(VLC)において Alamouti 時空間符号(STC)の適用を提案する.送信機及び受信機が独立に動作するシステムでは,送受信機間で 完全なシンボル同期がとれないことから,一つのシンボルを二シンボル時間にわたって繰り返し送信する反復送 信方式が用いられてきた.STC 送信方式では,LED アレイ内の隣接する LED を組付けし,組付けしたペアの単 位で,二シンボル時間で一方の LED から送信されるシンボルのみが強度反転するよう事前処理をして送信する. STC 送信方式によれば,非シンボル同期状況下にあっても,完全シンボル同期状況下と同程度の受信品質が得られ ることを実験により明らかにする.さらに,伝送距離が長いうちは受信画素平面内で LED アレイを捉えるピクセ ル数が少ないために隣接 LED を分離できないが,このような遠距離の場合においても,誤りなしの伝送が可能で あることを確認した.実験の結果,誤りなし伝送距離が,反復送信方式では 26 m であったのに対して,STC 送信 方式では 48 m にまで拡大できたことを示す.
Shlomi Arnon, Jae Kyun Kwon, Sang Hyun Lee, Wen-De Zhong, Zixiong Wang, Mohsen Kavehrad, Weizhi Zhang, Zhengyuan Xu, Chen Gong, Bo Bai, Kang Tae-Gyu, Klaus-Dieter Langer, Shinichiro Haruyama, Takaya Yamazato
Cambridge University Press
2015年2月
Y. Ohira, E. Souke, S. Arai, T. Yamazato, T. Yendo, H. Okada, T. Fujii and K. Kamakura
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp.274-277, Kuala Lumpur, Malaysia
2015年2月
The present paper considers receiving characteristics of an image-sensor-based visible light communication (VLC) using an LED and a high-speed-image sensor. In general, a size of LED on an image decreases with increasing a communication distance. In this case, the receiver is difficult to recover data because the intensity of brightness of LED (i.e., luminance) cannot be enough recognized from the image. However, the previous studies about the image-sensor-based VLC have not enough discussed the communication distance and the recognition of LED on the image, i.e., the receiving characteristics. We focus on the communication distance and investigates the relationship between the distance and the receiving characteristics in the image-sensor-based VLC.
山里敬也
可視光通信協会, 慶應義塾大学
2015年2月
C. Premachandra, T. Yendo, M. P. Tehrani, T. Yamazato, H. Okada, T. Fujii, M. Tanimoto
International Journal of Intelligent Transportation Systems Research, vol.13, no.1, pp.28-36
We propose a road-to-vehicle Visible Light Communication (VLC) system for ITS. Here, the communication between road and a vehicle is approached using an LED array as a transmitter and an on-vehicle high-speed camera as a receiver. Modulation is conducted at the transmitter by blinking LEDs in high frequency and demodulation is conducted at the receiver by capturing the blinking patterns of the transmitter, by processing the high-speed camera images captured in high frame rate. This paper proposes an effective image processing method for capturing those blinking patterns. Out door communication experiments of the proposed VLC system are also present.
2014
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
IEEE GLOBECOM Workshop on Optical Wireless Communications, pp.535-540, Austin, USA
Visible light communication (VLC) using light-emitting diodes (LEDs) is drawing much attention. There are two types of VLC reception devices, a photodiode and an image sensor. VLC using image sensor is called image sensor based VLC. As the receiver only uses the image sensor pixels that sense LED transmission sources and discards other pixels, including those sensing noise sources, image sensor based VLC is an attractive solution for outdoor mobile applications. However, little evidence is available for channel modeling of image sensor based VLC in mobile outdoor environments, especially for motion modeling of VLC transmitter. In this paper, we propose a motion model of VLC transmitter. In particular, we consider three cases; infrastructure-to-vehicle VLC (I2V-VLC), vehicle-to-infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). As a result, we show that the motion model of the VLC transmitter on the captured image for the three aforementioned situations (i.e., I2V-VLC, V2I-VLC, and V2V-VLC) can be expressed in the identical pinhole camera model.
E. Souke, Y. Ohira, S. Arai, T. Yamazato, T. Yendo, H. Okada, T. Fujii and K. Kamakura
Proceedings of 2014 IEEE Workshop on Nonlinear Circuit Networks (NCN'14), pp. 93-94, Tokushima, Japan
2014年12月
The present paper considers an optical spatial channel in visible light communication (VLC) using LED and a high-speed camera. In general, the optical spatial channel affects the communication performance. However, the previous studies have not enough discussed the channel for VLC. This study focuses on the communication distance, which is one of channel parameters, and investigates the relationship between the distance and a receiving characteristic in the VLC.
Light-emitting diode (LED) transmitters based optical wireless communication (OWC) systems offer the potential for new generation communication systems. Particularly, an image sensor based OWC systems consist of the LED transmitters and camera receivers are expected to contribute to intelligent transport system (ITS) for driving supports. For high achievable data rates, orthogonal frequency division multiplexing (OFDM) based OWC systems have attracted a great deal of attention. Despite attractive features of optical OFDM, only few attempts have so far been made to adopt it as a modulation scheme of an image sensor based OWC system. There remains a need for an evaluation of adopting an optical OFDM to the image sensor based OWC systems. Another important issue needs to be addressed is the performance degradation due to a frequency response of an actual image sensor device, especially a signal attenuation loss in higher frequency. In addition to such loss, a narrow band noise generated by its circuits also degrades the performance. The purpose of this paper is to investigate BER performances of the optical-OFDM using an actual image sensor device, the optical communication image sensor (OCI). From simulation results, it is found that the frequency response and the narrowband noise at 12MHz of the OCI lead to the significant reduction of BER performances. Additionally, the results shows that ACO-OFDM shows a little better performance compared to DCO-OFDM with the same bandwidth efficiency.
M. Kinoshita, T. Yamazato, H, Okada, T. Fujii, S. Arai, T. Yendo, K. Kamakura
IEEE Asia Pacific Conferece on Circuits and Systems (APCCAS), pp.332-335, Okinawa, Japan
In image sensor based VLC, transmitter acquisition and tracking are critical issue. However, the fluctuation of the VLC transmitter in the image plane caused by vehicle movement, complicates correct data reception. Therefore, in this paper, we present results of channel fluctuation measurements for infrastructure-to-vehicle VLC (I2V-VLC), vehicle-to-infrastructure VLC (V2I-VLC), and vehicle-to-vehicle VLC (V2V-VLC). We analyze channel fluctuation in terms of optical flow from measured data.
This study introduces an image sensor based visible light communication (VLC) and its application to pose, position, and range estimations. There are two types of visible-light receiver: a photodiode and an image sensor. A photodiode is usually used as a reception device of VLC, and an image sensor consisting of a large number of pixels can also be used as a VLC reception device. A photodiode detects the signal intensity of incoming light, while an image sensor not only detects the incoming signal intensity but also an accurate angle of arrival of light emitted from a visible light transmitter such as a white LED light. After angles of arrival of light are detected by an image sensor, positioning and data reception can be performed. The ability of an image sensor to detect an accurate angle of arrival will provide attractive applications of VLC such as pose, position calculation, and range estimation. Furthermore, because the image sensor has the ability to spatially separate sources, outdoor positioning even with strong sunlight is possible by discarding the associated pixels of noise sources.
K. Chiga, H. Tanaka, T. Yamazato, Y. Tadokoro, S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), Luzern, Switzerland
2014年9月
Stochastic Resonance (SR) is well known as a phenomenon in which the weak signal in a nonlinear system can be detected by added noise. We consider the application of SR phenomenon to a wireless communication system. The receiver using SR phenomenon can detect the subthreshold signal which is not detectable by the conventional receiver. The effect of SR receiver has been verified, but it has never been verified in radio frequency which is used by a wireless system. In this paper, we consider the implementation of SR System for Radio Frequency and evaluate its performance of Signal to Noise Ratio (SNR).
H. Tanaka, K. Chiga, T. Yamazato, Y. Tadokoro, and S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.193-196, Luzern, Switzerland
2014年9月
Stochastic resonance (SR) enhances system responses by increasing noise. By applying SR to a receiver, a subthreshold signal not receivable by a conventional linear receiver could be received. Previously, we proposed an analysis method of the SR receiver using a comparator, and evaluated its bit error rate performance. The comparator is known as a simple non-dynamical system exhibiting SR. However, a dynamical system can have better performance since it has a memory effect. In this sense, we propose an analysis method of the SR receiver using a Schmitt trigger known as a simple dynamical system, and evaluate its bit error rate performance. A performance comparison of the comparator and the Schmitt trigger is also shown.
The present article introduces VLC for automotive applications using an image sensor. In particular, V2I-VLC and V2V-VLC are presented. While previous studies have documented the effectiveness of V2I and V2V communication using radio technology in terms of improving automotive safety, in the present article, we identify characteristics unique to image-sensor-based VLC as compared to radio wave technology. The two primary advantages of a VLC system are its line-of-sight feature and an image sensor that not only provides VLC functions, but also the potential vehicle safety applications made possible by image and video processing. Herein, we present two ongoing image-sensor-based V2I-VLC and V2VVLC projects. In the first, a transmitter using an LED array (which is assumed to be an LED traffic light) and a receiver using a high-framerate CMOS image sensor camera is introduced as a potential V2I-VLC system. For this system, real-time transmission of the audio signal has been confirmed through a field trial. In the second project, we introduce a newly developed CMOS image sensor capable of receiving highspeed optical signals and demonstrate its effectiveness through a V2V communication field trial. In experiments, due to the high-speed signal reception capability of the camera receiver using the developed image sensor, a data transmission rate of 10 Mb/s has been achieved, and image (320 × 240, color) reception has been confirmed together with simultaneous reception of various internal vehicle data, such as vehicle ID and speed.
The present paper proposes a novel M-ary modulation scheme based on separation and reconstruction of deterministic chaotic dynamics for noncoherent chaos-based communications. The M-ary modulation scheme can transmit b-bit data at a time by using M=2b distinct sequences. In order to generate M distinct sequences and recover b-bit data, the proposed system separates the chaotic dynamics having the chaotic sequence by using M interleavers, and reconstructs the original sequence based on the chaotic dynamics from the separated one by using M deinterleavers. In advance, each data symbol among M symbols is allocated to each interleaver-deinterleaver pair. The transmitter selects an interleaver corresponding to a data symbol and separates the order of samples of the chaotic sequence using the selected interleaver. The receiver feeds the received sequence into all M deinterleavers and outputs M reconstructed sequences. The proposed system can reconstruct the original chaotic sequence only when the correct deinterleaver, which becomes paired with the interleaver, is selected. Therefore, the receiver can recover b-bit data by analyzing the chaotic dynamics of each reconstructed sequence. We carry out computer simulations and evaluate performances of the proposed M-ary modulation scheme.
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp. 61-64., Hawaii, USA
2014年2月
The present paper focuses on an application of Stochastic Resonance (SR) for an LED visible light communication (LED-VLC) receiver. SR is well-known as a phenomenon, which enhances the response by additive noise. We consider that a weak optical signal, which is distorted due to an influence of ambient light noise, can be detected by using SR system. This study makes a simple SR circuit for LED VLC and performs its circuit experiment for exploring the possibility and availability of the LED-VLC receiver using SR system.
The present paper proposes a novel multiple-LED-arrays acquisition for an infrastructure-to-vehicle visible light communication (I2V-VLC) using LED arrays (transmitter) and an in-vehicle high-speed image sensor (receiver). In order to achieve a robust detection of LED arrays, we employ the block matching algorithm, which is a way of finding a corresponding position between two successive frames. The proposed method divides a captured image into a number of small domains (blocks) and determines if the LED array is present or absent using the block matching. We perform I2V-VLC experiments with multiple-LED arrays and evaluate the acquisition capability of the proposed method.
S. Usui, T. Yamazato, S. Arai, T. Yendo, T. Fujii, H. Okada
20th World Congress on Intelligent Transport Systems , Tokyo, Japan
2013年10月
In this paper, we focus attention on visible light communication systems using an LED array as a transmitter and a high-speed camera as a receiver for road-to-vehicle communications (R2V-VLC) in intelligent transport systems. To implement R2V-VLC, it is necessary for the receiver to search the target LED array from the captured images (LED array acquisition) before data demodulation. We propose a new approach for LED array acquisition. We focus on spatio-temporal image and spatio-temporal cross-section image and show LED array in the spatio-temporal image has high time-gradient value and low space-gradient value. Using such characteristic gradient values, we propose new LED array acquisition method. As the results of the experiment in driving situation, we can achieve acquisition miss rate = 0%.
A. Ohmura, T. Yamazato, H. Okada, T. Fujii, T. Yendo, S. Arai
20th World Congress on Intelligent Transport Systems, Tokyo, Japan
2013年10月
In this paper, we focus on a distance estimation scheme using camera. Our distance estimation scheme is based on triangulation. The accuracy of camera based scheme is governed by resolution of a camera, or equivalently the size of pixel. Therefore we introduce phase only correlation (POC) to estimate with subpixel accuracy. As a result of experiment, we will show that our scheme achieves less than 0.3m estimation error at the distance of 60m. By using POC, the resolution of estimation reaches nearly 0.02 pixel, much less than one pixel.
荒井伸太郎, 西尾芳文, 山里敬也
電子情報通信学会技術研究報告, NLP2013-108, pp. 205-209, 高松（香川）
2013年10月
カオス系列によって変調された信号のみを用いて復調を行うノンコヒーレントカオス通信システムは, カオスの特徴を活かした独特の通信システムとして知られている．しかしながら，一般的な通信システムと比較すると，通信特性は劣るため，ノンコヒーレント通信の特性向上のためには，カオスの特徴を利用したさらなる工夫が必要である．私達はこれまでの研究で，カオスダイナミクスの分離・再構成を利用した誤り訂正手法を提案した．シミュレーションを行った結果，従来手法(誤り訂正無し) と比較して，BER 特性において2～2.5 dB の利得が得られた事を確認した．本稿では，カオスダイナミクスの分離・再構成による効果をより詳細に解析するために，本誤り訂正手法の性能評価を行う．具体的には，一度に送信される信号ブロック数とその信号の組み合わせに注目し，誤り訂正能力の解析を行う．
K. Chiga, H. Tanaka, T. Yamazato, Y. Tadokoro, S. Arai
International Symposium on Nonlinear Theory and its Application (NOLTA), pp.269-271, Santa Fe, USA
2013年9月
We consider an application of Stochastic Resonance to wireless communication system. Stochastic Resonance (SR) is well known as a phenomenon in which weak signal in nonlinear system can be detected by added noise. A receiver using Stochastic Resonance (SR Receiver) can detect a weak signal which is not detectable in the conventional receiver. In this paper, we consider the implementation of bi-polar pulse SR Receiver using Schmitt Trigger and evaluate the performance in Signal-to-Noise Ratio (SNR) and Bit Error Rate (BER).
本稿では、可視光通信の交通信号への適用として、著者らが進めている路車間可視光通信について 紹介する。この研究では、LED 信号機に見立てた LED アレイを高速に変調させることで、移動す る車輌へ情報伝送を行う。LED 信号機から情報伝送を行うことで、ドライバーが目で見て確認する信 号情報に加えて、データ伝送も行うことができるため、交差点での安全運転支援などに有効である。
T. Yamazato
IEICE Global Plaza, No.55, Aug., 2013
2013年8月
IEICE launched the new metadata search system called “I-Scover” on April 3, 2013[1]. For the time being, I-Scover provides the metadata search service of all papers published in IEICE transactions covering from the first edition published in 1968 up to the present edition, Technical Reports (from 2006) and international conference papers of ISPA and EMC. The total number of searchable contents reaches 150,000 as listed in Table.1. This article briefly introduces I-Scover. Before going to the details, let me start with a quiz. What phrase do you guess if you say “I-Scover” for three times?
H. Tanaka, K. chiga, T. Yamazato, Y, Tadokoro, S. Arai
NANOENERGY2013, pp.58-59, Perugia, Italy
2013年7月
Stochastic Resonance (SR), known as a noise-enhanced phenomenon, can improve the performance of communication systems. By applying SR in the receiver, it is possible to detect a weak signal that is not detectable in the traditional linear receiver. In the SR systems, the input of multi-carrier has not ever been discussed. So this paper proposes the SR receiver for multi-carrier detection and evaluates its Bit-Error-Rate (BER) performance．
This paper focuses on a road-to-vehicle visible light communication (VLC) system using LED traffic lights and high-speed cameras on cars. So as to improve the transmission reliability, an error correcting code like a low-density parity-check (LDPC) is applied to the road-to-vehicle VLC system. The decoder of the LDPC code needs channel information in order to maximize decoding performance. Usually, it is calculated from a signal-to-noise ratio (SNR) or bit error rate (BER) of a channel, where noise is a dominant factor of the channel characteristic. In the road-to-vehicle VLC system, not noise but interference among LEDs decides the channel characteristic. In this paper, we propose a channel information estimation method for the road-to-vehicle VLC system. The proposed method estimates a signal-to-interference ratio (SIR) from the receiving image, and calculates the channel information using the SIR. The proposed method is evaluated by experiment. As a result, the proposed method can achieve almost the same performance with the optimum case, and then maximize the decoding performance.
T. Kasashima, T. Yamazato, H. OKada, T. Fujii, T. Yendo, S. Arai
IEEE International Symposium on Wireless Vehicular Communications (WiVeC), Dresden, Germany
This paper aims to improve the transmission distance for the road-to-vehicle visible light communication system (R2V-VLC) using LED array and high-speed camera by reducing interference caused at the receiver. As we can transmit multiple data using LED array and high-speed camera, parallel data transmission can be possible. However, due to the diffusion of LED and the finiteness of the pixel size of image sensor, the focused LED will affect not only the actual corresponding pixel but also its surrounding pixels. We call this phenomenon as “interpixel interference (IPI)” and it causes degradation in error rate performance. To mitigate the IPI, we propose IPI cancellation scheme for the R2V-VLC system. As the results of the experiment, we can extend the error-free distance from 40m to 60m by the IPI cancellation.
T. Yamazato
IEICE Communications Society – GLOBAL NEWSLETTER Vol. 37, No. 2, Jun., 2013.
2013年6月
The IEICE launched new metadata search system called I-Scover (http://i-scover.ieice.org) from April 3rd, 2013. I-Scover provides metadata search of the IEICE transactions papers (from its first edition published in 1968), Technical Reports (from 2006) and international conference papers of ISPA and EMC. The total of the contents that can be searched is more than 150,000. This article briefly introduces I-Scover. Before going to detail, let me start with a quiz. What phrase do you guess if you say I-Scover for three times?
T. Yamazato, I. Takai, H. Okada, T. Fujii, T. Yendo, S. Arai, M. Andoh, K. Yasutomi, K. Kagawa, S. Kawahito
International Symposium on Optical Wireless Communications, Beijing Jade Palace Hotel, China
2013年6月
This talk introduces visible light communication (VLC) for automotive applications using an image sensor. In particular, vehicle-to-infrastructure visible light communication (V2I-VLC) and vehicle-to-vehicle visible light communication (V2V-VLC) are presented. Previous studies have documented the effectiveness of V2I and V2V communication using radio technology for improving automotive safety. In this talk, I identify characteristics unique to the introduced image sensor based VLC as compared to radio wave technology. The advantages of VCL are twofold: the line-of-sight feature of visible light links and an image sensor that provides not only the VLC function but also vehicle safety applications using image and video processing. We present two on-going image sensors based V2I-VLC and V2V-VLC projects.
T. Ito, T. Yendo, S. Arai, T. Yamazato, H. Okada, T. Fujii
Proc. SPIE 8663, Video Surveillance and Transportation Imaging Applications, 86630V, Burlingame, California, USA
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp. 225-228, Hawaii, USA
2013年3月
This paper analyzes the performance of the error-correcting method, which was proposed in the previous research, using the separation and the reconstruction of chaos for noncoherent chaos communications. Especially, we focus on a number of transmitting data and a combination of symbols (i.e., data pattern). We consider that the capability of the error correction depends on the number of data and the data pattern because the proposed method performs the error correction using successive data symbols. This study performs simulations for the number of data and the data pattern, and evaluates BER performance of the proposed method.
T. Fukumoto, S. Arai, T. Yendo, T. Yamazato, H. Okada and T. Fujii
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp. 33-36, Hawaii, USA
2013年3月
This paper develops a simple simulator for the visible light communication (VLC) system using a LED traffic light and a camera for intelligent transport systems (ITS). We use image processing techniques for simulating effects of optical spatial channel which is a unique channel in VLC. We describe a system model of the VLC simulator and perform the simulation with various parameters of the image processing.
This paper aims to the improve the data rate for the visible light communication system using LED array and high-speed camera. Previously, we have proposed the decoding algorithm using inverted signals for driving situation. However, using this method the data rate become a half, because we transmit original signals and inverted signals alternately for LED array tracking. In this paper, we propose the data rate improving method for overlay coding which is coding method that overlay two data which are called as the long range data and the short range data. In the proposed method, for the long range data, we transmit original signals and inverted signals alternately. On the other hand, for the short range data, we transmit only original signals while we transmit inverted signals of long range data. We confirm that we can improve data rate as compared with the previous method.
T. Fukumoto, S. Arai, T. Yendo, T. Yamazato, H. Okada and T. Fujii
Proceedings of IEEE Workshop on Nonlinear Circuit Networks (NCN'12), pp. 124-127, Tokushima, Japan
2012年12月
This paper develops a simple simulation program for visible light communication (VLC) systems using LED (Transmitter) and a camera (Receiver). In the simulation, we generate an image of LED array transmitter which consists of LEDs arranged in a square matrix. In addition, effects of optical spatial channel, which is a unique channel in VLC, are constructed by using image processing techniques. We describe a system model of the VLC simulator and carry out the simulation with various parameters of the image processing.
International Symposium on Nonlinear Theory and its Applications (NOLTA), pp.801-804, Palma, Majorca, Spain
2012年10月
This paper focuses on characteristics of the chaotic dynamics and improves our previous errorcorrecting method using them for noncoherent chaos communications. Our previous method is performed by using a chaotic sequence generated according to the chaotic dynamics. In this case, it is very difficult to recover data without a successive sequence based on the chaotic dynamics. We focus on this feature and consider that an improved method separates and reconstructs the chaotic dynamics of the sequence according to a specific rule. Namely, the separation and reconstruction of the chaotic dynamics can be applied for our improved method as additional information. As results of simulations, we have confirmed that the advantage gained in BER performance of our improved method is about 2–2.5 dB compared to a conventional method (without coding).
As for cluster-based wireless sensor networks (WSNs), cluster lifetime is one of the most important subjects in recent researches. Besides reducing the energy consumptions of the clusters, it is necessary to make the clusters achieve equal lifetimes so that the whole network can survive longer. In this paper, we focus on the cluster lifetimes in multi-hop WSNs with cooperative multi-input single-output scheme. With a simplified model of multi-hop WSNs, we change the transmission schemes, the sizes and transmission distances of clusters to investigate their effects on the cluster lifetimes. Furthermore, linear and uniform data aggregations are considered in our model. As a result, we analyze the cluster lifetimes in different situations and discuss the requirements on the sizes and transmission distances of clusters for equal lifetimes.
This paper addresses the cluster partitioning problem in wireless sensor networks deployed in a continuous area. We present the model of the network and describe its operational details firstly. Both single-hop and multi-hop transmissions with cooperative Multi-Input Single-Output (MISO) scheme are considered for the inter-cluster communications. Besides, uniform and linear data fusions are discussed. Then the calculations of energy consumptions are derived. Different from other researches, the energy consumptions of intra-cluster communication in each cluster are included and modeled as functions of the cluster size. Finally, we simulate all possible cluster partitions by changing the numbers of clusters and cooperative transmitting nodes, and find the maximal network lifetimes. As a result, the relationships between cluster partitions and network lifetimes are clarified in different situations.
H. Tanaka, T. Yamazato, S. Arai
RISP International Workshop on Nonlinear Circuits, Commuations and Signal Processing (NCSP), pp.64-67, Honolulu, Hawaii, USA
2012年3月
Stochastic Resonance (SR), known as a noise-enhanced phenomenon, can improve the performance of commutation systems. In this paper, we present a preliminary study on SR and its application to BPSK receiver. We discuss a basic question arises from a receiver using SR that shall we perform SR process in a radio-frequency (RF) band or in a baseband (BB)? As results, we found that SR process in RF band shows better Bit Error Rate (BER) performance. This comes from the fact that a down conversion process that reduces the signal amplitude causes weak noise suppression by SR. While a double frequency term obtained also by the down conversion process do not affect much to the noise reduction performance.
S. Arai, S. Ozaki, T. Yamazato, Y. Nishio
RISP International Workshop on Nonlinear Circuits, Communications and Signal Processing (NCSP), pp.60-63, Honolulu, Hawaii, USA
2012年3月
This paper analyzes a stochastic resonance (SR) in a quadruple-well potential, which extended the SR in a doublewell potential, to control of SR. For achieving the control of SR, it is important to analyze the state of the SR by injecting the noise. In this study, we calculate existence probabilities of the SR’s state to analyze how the state changes by a noise intensity.
T. Yamaoka, Y. Hara, N. Fukui, H. Kubo, T. Yamazato
IEICE Transactions on Communications, vol .E95-B, no. 2, pp.643-646
2012年2月
Cooperative diversity using space-time codes offers effective space diversity with low complexity, but the scheme needs the space-time coding process in the relay nodes. We propose a simple cooperative relay scheme that uses space-time coding. In the scheme, the source node transmits the Alamouti coded signal sequences and the sink node receives the signal sequence via the two coordinated relay nodes. At the relay nodes, the operation procedure is just permutation and forwarding of the signal sequence. In the proposed scheme, none of the relay nodes need quadrature detection and space-time coding and the simple relay process offers effective space diversity. Moreover, simulations show the effectiveness of the proposed relay process by some simulations.
International Symposium on EcoTopia Science (ISETS), p.106, Nagoya, Japan
2011年12月
Solar-powered wireless sensor networks are attracting attention for outdoor long time operation such as environmental monitoring. Even if sensor nodes are charged by solar energy, nodes far from the BS (Base-Station) are stopped due to the lack of energy during nighttime. To prevent this problem, we consider the use of cooperative transmission. In cooperative transmission, energy consumption is balanced among the nodes because of the use of another node as a relay for data transmission of distant nodes. The conventional scheme to select a relay node is based on available battery energy and the expectation of energy consumption of each node. In this paper, we propose a relay selection scheme which is based on the prediction of harvested energy in addition to the available battery energy and the expected value of energy consumption. We evaluate the proposed scheme through packet delivery ratio and show its effectiveness.
T. Yamazato
Asia Regional OpenCourseWare Conference (AROCC) 2011, Meiji University, Tokyo, Japan
2011年11月
五藤大介、山里敬也、モンゴルバヤルプレブ
電子情報通信学会技術研究報告, RCS2011-11, pp.91-95 , 名古屋
2011年11月
本研究は,高速移動環境下での時間-周波数分散通信路おいて生じるシンボル間干渉(ISI)とキャリア間干(ICI)の低減に対して有効とされている陪直交周波数分割多重(BFDM)と,Wavelet Based OFDMとの特性比較を行う.ISI,ICIは信号のパルス形状に大きく依存する.BFDM はパルス設計の自由性が高いことから,時間-周波数制限性の高いガウスパルスを用いることで干渉低減を行うことができる.また,Wavelet Based OFDMはウェーブレットを基底関数とした伝送方式であり,干渉低減に有効とされている.本研究では,BFDMのガウスパルスの最適化を送受信機パルスの不確定性関数の比を最大化することで行い,Wavelet Based OFDMとの特性比較を行う.
Y. Shiraki, T. Nagura, T. Yamazato, S. Arai, T. Yendo, T. Fujii, H. Okada
18th World Congress on Intelligent Transport Systems , Orlando, Florida, USA
2011年10月
In this paper, we focus attention on the visible light communication systems using an LED array as a transmitter and a high-speed camera as a receiver for road-to-vehicle communications in intelligent transport systems. Previously, we have proposed the hierarchical coding scheme which enables reception of high-priority data even if the receiver is far from the transmitter and have confirmed the effectiveness of the hierarchical coding scheme from results of primitive implementation experiments. However, there are many important works to develop the real-time communication system for an actual driving situation. In this paper, we discuss a robust receiver design in an actual driving situation. We introduce a series of image processing operations and demonstrate their effectiveness by field trials. As the results of the field trials, we have achieved 16kbps transmission and error-free communication up to communication distance of 70m using 16x16 LED array (transmitter) and high-speed camera (receiver) with the frame rate of 1000.
山里敬也
ICT イノベーションフォーラム 2011, 幕張メッセ 国際会議場 1F 会議室(CEATEC JAPAN 2011 と同時開催)
2011年10月
本研究開発課題では、運転者が視覚的に認識する信号機情報に加えて、LED信号機から安全運転支援情報 を可視光通信により伝送することで、交差点事故の削減を目指す。具体的には、車輌が遠方より信号機 のある交差点へ進入するケースを想定し、データ伝送装置として LED 信号機(LED アレイ)、その受信 装置として車輌に搭載する高速度カメラを用いた路車間通信システムの研究開発を行う。さらに、運転 者への安全運転支援を効果的に行うことを目的に、LED 信号機と車輌までの距離に応じて異なる情報が伝 送できる階層的符号化方式の試作装置の研究開発を行う。
Z. Huang, K. Kobayashi, M. Katayama, T. Yamazato
IEICE Transactions on Communications, vol.E94-B, no.10, pp.2881-2885
This letter investigates the cluster lifetime of single-hop wireless sensor networks with cooperative Multi-Input Single-Output (MISO) scheme. The energy consumptions of both intra-cluster and out-cluster communications are considered. Moreover, uniform and linear data aggregations are discussed. It is found the optimal transmission scheme varies with the distance from the cluster to the base station. More interestingly and novelly, the effect of cluster size on the cluster lifetime has been clarified.
S. Nishimoto, T. Nagura, T. Yamazato, T. Yendo, T. Fujii, H. Okada, S. Arai
International IEEE Conference on Intelligent Transportation Systems (ITSC), pp.1704-1709, Washington D.C., USA
This paper aims to improve the visible light communication system using LED array and high-speed camera by proposing what we call “overlay coding”. “Overlay coding” is a new coding method to realize a hierarchical coding, through which a high-priority data can be received even if the receiver is far from a transmitter. Conventionally, the hierarchical coding has been realized through the wavelet transform that has a limitation of number and disposition of LEDs, and as a result it does not always match with the design of the transmitters (e.g. traffic lights, etc.) used in real life. To solve the limitation problem, we propose a more flexible way of designing the application of LEDs depending on the transmitters. In particular, overlay coding is realized through the procedures of coding and decoding. In coding, we replace one LED with a flexible number of LEDs, and the number depends on whether the data is high-priority or low-priority, then high-priority data and low-priority data are overlaid. In decoding, we first obtain the high-priority data, and then the low-priority data using retrieved high-priority data. The experimental result shows that the distance for receiving error-free data is extended from 30m to 70m in the overlay coding.
Our goal is the improvement of the node activity rate in solar-powered wireless sensor networks. We consider the application of a cooperative transmission scheme that uses a relay node when a node sends data to reduce the consumption of energy of the entire network. However, if we do not consider the variations in energy harvesting, the node activity rate declines during nighttime. In this paper, we smooth out the day-and-night node activity rate variations by introducing the new inactive node reactivation condition and achieve the required high node activity rate.
Dr. Takaya Yamazato is a professor at Japan's Nagoya University, where he also heads the OpenCourseWare (OCW) team. The Education Insider caught up with him after the 2011 OCW Consortium conference to learn more about Nagoya's unique approach to putting course materials on the Web.
T. Yamazato, S. Haruyama
IEEE International Conference on Communications (ICC), Kyoto, Japan
2011年6月
Visible light communications (VLC) is the latest optical wireless communications technologies that uses low-power light emitting diodes, or LEDs, not only to provide light but also to broadcast data. LEDs are extremely energy-efficient and predicted to become widespread in general lighting application. It is expected that LED market will reach $29 billion in 2017 that is comparable to today's NAND and DRAM markets [1]. Because LED is a solid-state lighting device, it can be modulated at high-speed compared with other lighting sources. VLC uses LEDs, which send data by flashing light at speeds undetectable to the human eye. The pioneer of VLC using LEDs is Professor Masao Nakagawa of Keio University. His first paper on this subject appeared in the early 2000, together with his successor Prof. Shinichiro Haruyama, the instructor of this tutorial. Later in 2003, he formed Visible Light Communication Consortium (VLCC). Now VLCC is lead by Prof. Haruyama. Please see the following video, an interview of Prof. Haruyama about VLC, which has been broadcast by NHK World in June 4, 2009. http://www.naka-lab.jp/movie/nhk_world.wmv So far various experimental VLC systems and prototypes are demonstrated. Such includes 4.8kbps visible light ID as an infrastructure to mobile-terminal application, independent sound transmission through RGB visible lights and 100Mbps VLC wireless LAN system. Using LED array, the data rate of 1 Gbps achieved by Keio University (Prof. Haruyama) that is the fastest at the moment [1]. In terms of longer range, there has been a demonstration by VLCC that achieved 1kbps transmission of the distance 2km, that is the world's longest distance for VLC. Samsung and ETRI are also active in developing VLC applications. They have demonstrated 120Mbps full duplex mobile-to-mobile transmission and 100Mbps signboard transmission. Please see the following video of Nakagawa lab. http://www.youtube.com/watch?v=QEh5f49LsB4 Widespread use of LEDs in traffic applications and growing interest in Intelligent Transport System (ITS) presents an opportunity for VLC. Data transmission using LED traffic lights, LED road illumination, and LED brake lights are typical application. Dr. Yamazato, the instructor of this tutorial, is a leader in VLC application to ITS and he recently achieved 16kbps data transmission and distance up to 70m in a driving situation with a vehicle moving with 30km/h. Today VLC using LED is a hot topic and VLC projects have been initiated in Europe and US. In 2006 Siemens launched VLC project. Later in 2008, European Commission established OMEGA project with a consortium of 20 European partners from industry and the scientific community [3]. Meanwhile, in 2008, the US National Science Foundation has approved a grant of $18.5 million to help establish and the Engineering Research Center focuses on VLC. The members of the Center include the Rensselaer Polytechnic Institute in New York, Boston University and the University of New Mexico. The University of California also have launched five-year research project called the Ubiquitous Communication by Light (UC-Light) that is founded with $3.5 million from the University. The project is anticipated to begin in 2009 and run for five years. VLC is in the process of standardization by the IEEE 802.15 TG7 and VLCC as well as other standard organizations. The first VLC specification standard was released from JEITA in conjunction with VLCC in 2007. Later in 2008, VLCC released their first specification standard adopting and expanding the IrDA physical layer. IrDA transceiver transmission wavelength (IrDA physical layer) is expanded to accommodate the visible light wavelength. By adapting this specification, the existing IrDA optical modules can be used for VLCC data transmission with slight modification. In January 2009, IEEE 802.15 (Wireless Personal Area Networks) Task Group 7 (Visible Light Communication) has been launched. At the 6th meeting held in November 2009 they adopted the baseline draft text for the development of the 802.15.7 standard. The goal of this tutorial is to introduce current VLC technology and its trends. Starting with an overview of VLC, participants will learn basics of VLC, on-going standardization activities and VLC. We will provide some experimental results and furthermore detail to enhance VLC application.
T. Yamazato
International Symposium on Emerging Short Range Communications, Room 1-312, FIT Building, Tsinghua University, China
IEICE Transactions on Fundamentals, Vol.E94-A No.3 pp.964-971
2011年3月
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal 3D Time Difference of Arrival (TDOA) positioning, at least four receivers with an unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel method for TDOA positioning using only three receivers is presented. TDOA positioning with three receivers is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls. The proposed method was verified using data from a measurement campaign.
H. C. N. Premachandra, T. Yendo, M. P. Tehrani, T. Yamazato, H. Okada, T. Fujii, M. Tanimoto
The Journal of the Institute of Television Engineers of Japan, vol.65, no.3, pp.354-360
2011年2月
We propose a visible light road-to-vehicle communication system at intersection as an ITS (Intelligent Transport System) technique. In this system, the communication between a vehicle and an LED traffic light is conducted using an LED traffic light as a transmitter and an on-vehicle high-speed camera as a receiver. The LEDs in the transmitter emit light at high frequency, and those emitted light is captured by the high-speed camera for communications. Here, the luminance value of the LEDs in the transmitter should be found, and then it should be tracked in consecutive frames while the vehicle is moving by processing the images from the high-speed camera. In this paper, we propose new algorithms for finding and tracking the transmitter, which result in increased communication speed and data rate compared to the previous methods. Experiments using appropriate images showed the effectiveness of the proposals.
小澤俊之，名倉徹，山里敬也，圓道知博，藤井俊彰，岡田啓
電子情報通信学会 総合大会, A-17-6, p.252, 要旨集
2011年2月
LED アレイと高速度カメラを用いた路車間可視光通信による安全運転支援情報の提供を目的とした研究を行っている．このシステムの実現のためには送受信機間距離の増加に伴う受信画像の劣化が問題となる．これは隣接するLED が互いに干渉し受信されることが原因として考えられる．そこで本稿では干渉の影響を考慮した通信路モデルを作成し，LED の点光源を用いて通信路特性を実験的に測定しその伝達関数を求めた。
In this paper, we focus on a road-to-vehicle visible light communication (VLC) system using LED traffic lights. In this system, an LED traffic light consists of a 2-dimensional LED array (2D LED array), and cars are equipped with high-speed 2-dimensional cameras (2D image sensors). An important issue of this system is frame loss. Sometimes, 2D image sensor in a car fails to get a frame. So as to mitigate the influence of frame loss, we propose to apply erasure coding to the road-to-vehicle VLC system. In the proposed system, a data sequence is encoded by LDPC code whose length is much longer than the size of 2D LED array. In addition, code synchronization is required for the proposed system. We also propose a code synchronization scheme, which makes use of error detection capability of LDPC code. We evaluate the performance of our proposed system, and show that it can recover frame loss for high SNR when less than 8 frames among total 18 frames are lost. In addition, we show that our proposed code synchronization scheme can ignore its errors.
K. Maeno, T. Yendo, M. P. Tehrani, T. Fujii, H. Okada, T. Yamazato, M. Tanimoto
International Workshop on Advanced Image Technology (IWAIT), Jakarta, Indonesia
2011年1月
Previous studies on visible light communication uses visually lighting LEDs. However, LEDs are not always lighting. In this paper, we propose visible light communication method using visually non-lighting LEDs. This method enables us to communicate in different situations, e.g. using visually non-lighting tail lamps of cars or visually non-lighting traffic lights. We realize visually non-lighting LEDs by reducing luminescence energy of LEDs according to the brightness in the environment. To reduce luminescence energy of LEDs, we reduce the number of emitting LEDs, increase the interval of emitting, and decrease the luminance of emitting LEDs. In our research we consider the case that the transmitter is tail lamps of cars and the receiver is high-speed camera. We conduct two types of experiments to demonstrate the performance of the proposed system. One is to confirm that LEDs are visually non-lighting. The other is measurement of Bit Error Rate of communication using visually non-lighting LEDs. Experimental results demonstrate that it is possible to make communication using visually non-lighting LEDs. In our future work, we plan to use different sensor devices such as photo diode or CCD in order to decrease the error rate in communication.
T. Masuda, T. Yendo, T. Yamazato, H. Okada, M. P. Tehrani, T. Fujii, M. Tanimoto
International Workshop on Advanced Image Technology (IWAIT), Jakarta, Indonesia
2011年1月
In this paper, we propose the new visible light road-to-vehicle communication system. We use the LED traffic light as the transmitter and the high-speed camera on the vehicle as the receiver. In this system, the data is encoded hierarchically and assign with the each frequency components of the image. We use the DFT for hierarchical encoding considering channel characteristic and quantization of the luminance. The communication experiments were conducted to confirm the effectiveness of the proposed method.
H. C. N. Premachandra, T. Yendo, M. P. Tehrani, T. Yamasato, H. Okada, T. Fujii, M. Tanimoto
International Workshop on Advanced Image Technology (IWAIT), Jakarta, Indonesia
2011年1月
Visible Light Communication(VLC) has been introduced as a new wireless communication method. In this paper, we propose a VLC system for Intelligent Transport System (ITS) to communicate between infrastructure and the vehicle. In this system, we use a LED array as a transmitter and on-vehicle high speed camera as a receiver. Here, LEDs in the transmitter emit light in 500Hz and the emission patterns are used to achieve communication, by capturing them using the high speed camera in high frame rate. The images captured by high speed camera are processed to find the transmitter, track the found transmitter, and capture the emission pattern of transmitter in consecutive frames. In our previous work, we proposed algorithms to finding and tracking. In this paper, we introduce method to capture the emission pattern of the transmitter. Then out door communication experiments were conducted to confirm the effectiveness of the proposed VLC system.
IEEE Global Communications Conference (GLOBECOM), FLORIDA, U.S.A
2010年12月
In this paper, we propose two dynamic bandwidth allocation (DBA) schemes, a game theory based DBA and a successive DBA, for satellite/terrestrial integrated mobile communication system (STICS). The game theory based DBA allocate the bandwidth according to a utility function based on a weighted demand bandwidth of both satellite and terrestrial system. The successive DBA recursively allocates an unit of bandwidth according to a weighted number of bandwidth unfilled cells of both satellite and terrestrial systems, until the total bandwidth is fulfilled. As results, both DBA outperform the conventional fixed bandwidth allocation scheme. Between two proposed DBA, the successive DBA shows better spectral improvement ratio than the game theory based DBA.
K. Kobayashi, T. Yamazato, M. Katayama
IEICE Transactions on Communications, vol.E93-B, no.12, pp.3509-3513
We develop a mathematical framework for the extrinsic information transfer (EXIT) analysis to assess the convergence behavior of maximum a posteriori (MAP)-based joint iterative decoding of correlated sources, which are separately encoded and transmitted over noisy channels. Unlike the previous work, side information about the correlation is not perfectly given at the joint decoder but is extracted from decoder output and updated in an iterative manner. The presented framework provides a convenient way to compare between schemes. We show that it allows us to easily and accurately predict joint decoding gain and turbo cliff position.
J. Kietlinski-Zaleski, T. Yamazato, M. Katayama
IEICE Transactions on Communications, vol.E93-B, no.12, pp.3624-3631
2010年12月
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival (ToA) positioning, at least three receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel algorithm for ToA positioning using only two receivers is presented. This is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls. The proposed algorithm was tested using data from a measurement campaign.
H. C. N. Premachandra, T. Yendo, M. P. Tehrani, T. Yamazato, H. Okada, T. Fujii, M. Tanimoto
Workshop on Picture Coding and Image Processing, PCSJ2010/IMPS2010, Nagoya, Japan
2010年12月
Intelligent transport system has been introduced to reduce traffic problems such traffic accidents and traffic congestions. In this paper, we introduce a receiver for a road to vehicle Visible Light Communication (VLC) system which is proposed as an Intelligent Transport System (ITS) technique. In this system, an on-vehicle high-speed camera is used as a receiver and an LED array is used as a transmitter. VLC is a wireless communication using luminance. Here, transmitter send information by emitting light and receiver receive them by capturing the luminance of emitting LEDs in the array(Luminance: whether each LED is on or off). For capturing the Luminance, it is necessary to find the transmitter and track it in consecutive frames. In our previous works we introduced methods for finding and tracking. In this paper, we shortly explain the proposed transmitter finding and tracking methods and then a new method is proposed for capturing the luminance of LEDs to achieve communication.
T. Masuda, T. Yendo, T. Yamazato, H. Okada, M. P. Tehrani, T. Fujii, M. Tanimoto
Workshop on Picture Coding and Image Processing, PCSJ2010/IMPS2010, Nagoya, Japan
2010年12月
This paper discusses the visible light road-to-vehicle communication system at intersection as one of ITS (Intelligent Transport System) technique. The communication between a vehicle and an LED traffic light is approached using an LED traffic light as a transmitter, and on-vehicle high-speed camera as a receiver. In this system, it is able to send data by blinking the LEDs of the traffic light in two dimensional patterns, and able to receive them by high-speed camera with image processing. Here, we aim to conduct long-distance high-speed visible light communication. When the distance between transmitter and receiver is far, the image of the LED traffic light captured by on-vehicle high-speed camera is very small. So, if the data are put on two dimension patterns without modification, data would be mistaken, because the two dimension patterns can’t be realized correctly. To solve this problem, data are encoded hierarchically before they are lighted by the LED traffic light. This is called as hierarchical encoding that the data are assigned with each spatial frequency.
K. Maeno, T. Yendo, M. P. Tehrani, T. Fujii, T. Yamazato, H. Okada, M. Tanimoto
Workshop on Picture Coding and Image Processing, PCSJ2010/IMPS2010, Nagoya, Japan
2010年12月
The proposed visible light communication method uses visually non-lighting LEDs, which enables us to communicate in different situations, e.g. using visually non- lighting tail lamps of cars or visually non-lighting traffic lights. We realize visually non-lighting LEDs by reducing luminescence energy of LEDs according to the brightness in the environment. Experimental results demonstrate that it is possible to make communication using visually non-lighting LEDs.
IEICE Transactions on Communications, vol.E93-B, no.11, pp.2959-2962
2010年11月
We consider a distributed transmission of data packet to a sink where the distance of a sensor node to a sink is much longer than the maximum communication range of each sensor node. We give a simple modification to the transmitter, i.e., multiplication of random phase before the transmission. Thanks to Turbo Code, it is possible to extend the trans- mission range as the received amplitude varies symbol by symbol for our scheme while whole data packet may be lost for the conventional scheme. In this letter, we report the experimental results of our scheme equivalently developed using visible light communication.
S. Mitsuya, K. Kobayashi, T. Yamazato, M. Katayama
International Symposium on Communications and Information Technologies (ISCIT), no. FA1-1-3, pp.968-973, Tokyo, Japan
In a cooperative spectrum sensing system, many nodes perform spectrum sensing and report their decisions to one fusion center via control channels. This paper considers efficient use of the frequency band for the control channels. For this purpose, sequential-test is introduced for the local decision at each node. With this scheme, the transmission timing of the reports from the nodes becomes at random and necessary maximum bandwidth for the control channels decreases. Numerical results show that this sequential-test-base-scheme not only decreases the number of simultaneous reports but also improves sensing reliability. For further improvement, this paper also introduces a decision scheme at the fusion center based on probabilistic features of the reports from the nodes.
J. Naganawa, K. Kobayashi, M. Katayama, T. Yamazato
International Symposium on Communications and Information Technologies (ISCIT), no. FA1-1-4, pp.974-979, Tokyo, Japan
This manuscript considers a secondary system sharing the spectrum with the primary system at the same time and on the same frequency. We propose a cognitive overlay system in which the secondary system relays the primary signal and piggybacks its own data on it. Furthermore, the secondary system uses the channel coding based on the dirty paper coding (DPC). The result of the analysis shows that the proposed scheme allows the secondary system to communicate at the same speed as the primary system without any harm to it.
B. Mongol, T. Yamazato, M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), Taichung, Taiwan
2010年10月
Pulse-shaping OFDM, or more generally BFDM and BFDM/OQAM, systems are originally proposed to combat inter- carrier interference (ICI) caused by time-variance of the channel. The main property that makes these signals robust against ICI is that they allow to employ time-frequency well localized pulses, particularly Gaussian pulse which has the best time-frequency localization. However, this property also suppresses the outband or inband spectral leakage of the BFDM and BFDM/OQAM signal, making them attractive physical layer modulation scheme for cognitive radio. In this paper we analyze the power density spectra of the BFDM and BFDM/OQAM signals and numerically evaluate the inband and outband spectra for truncated Gaussian pulses.
S. Arai, Y. Nishio and T. Yamazato
NOLTA, IEICE, vol. 1, no. 1, pp. 196-206, Oct. 2010.
2010年10月
This paper proposes a novel error-correcting scheme using chaotic dynamics for noncoherent chaos communications. In our proposed system, two successive chaotic sequences are generated from the same chaotic map; the second sequence is generated with an initial value which is the last value of the first sequence. In this case, successive chaotic sequences having the same chaotic dynamics are created. This feature gives the receiver additional information to correctly recover the information data and thus improves the bit error performance of the receiver. As results of the computer simulation, we confirm that the advantage gained in BER performance of the proposed error-correcting method is about 1-1.5 dB compared to conventional method. In addition, we achieve that the proposed error-correcting scheme is performed without the new additional redundancy code by using the chaotic dynamics.
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal 3D Time Difference of Arrival (TDoA) positioning, at least four receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel method for TDoA positioning using only three receivers is presented and tested using real-world measurements. Positioning with three receivers is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, reflectors, for example ceiling and walls.
T. Nagura, T. Yamazato, M. Katayama, T. Yendo, T. Fujii, H. Okada
IEEE International Symposium on Wireless Communication Systems (ISWCS), pp.765-769, York, United Kingdom
In this paper, we discuss on a decoding algorithm for visible light communication systems in the driving situation using an LED array transmitter and a high-speed camera receiver. We propose an LED array detection method using M-sequence and an LED array tracking method using inverted signals. We confirm that we can distinguish LED array candidates correctly with M-sequence. We also confirm that we can suppress the flicker of the LED and improve the data rate as compared with the previous method.
K. Kobayashi, T. Yamazato, M. Katayama
IEEE International Workshop on Wireless Distributed Networks (WDN), pp.484-489, Istanbul, Turkey
In densely deployed wireless sensor networks, observations of the sensor nodes are spatially correlated. In this paper, we study a joint channel decoding scheme utilizing bit correlation of the sensor observations according to bit levels of analog-digital converter (ADC). If sensor ADC output is interpreted as natural binary numeral, carry propagation may occur between adjacent ADC output values. Such carry propagation leads to the degradation of joint decoding gain. We focus on the use of Gray code for avoiding the carry propagation. The performance of our approach is demonstrated by simulations using sensor data from experiments in a real indoor environment.
J. Kietlinski-Zaleski, T. Yamazato
International Conference on Indoor Positioning and Indoor Navigation (IPIN), Zurich, Switzerland
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival (TOA) positioning, at least three receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In our previous work \\\\cite{Kietlinski-Zaleski2010PLANS} we presented a novel 3D TOA UWB indoor positioning method that uses only two receivers. This is possible by exploiting the knowledge of some of the indoor features, namely ceiling and walls. In this work, we verify the usability of the method using measurement results in three environments: a lecture room, a cluttered laboratory and a corridor. By comparing the results of the method for three environments, we draw conclusions about its strengths and weaknesses.
歩行者認識システムとして,まず思い浮かぶのがボルボ社の歩行者検知機能付きフルオートブレーキシステムである. 同様のシステムはダイムラー社も既に実現している. これらのシステムでは車載カメラで取得した映像から歩行者を何らかのパターン認識アルゴリズムで検知する. 当然ながら,精度良く歩行者を検知するためには対象とする歩行者についての十分な画像情報が必要となる. 具体的には取得された画像における歩行者の占めるピクセル数がある程度無ければならない. 十分な画像情報が得られたとしても,歩行者は様々なテクスチャーを持つため歩行者として認識するための特徴 抽出も難しい. また,歩行者を認識するためには,雑音となる背景と歩行者を効率良く分離できなければならない. 加えて,移動する車輌の場合,取得画像全体が動くため,動き補償を行うアルゴリズムが必要となる. 当然, 歩行者認識アルゴリズムは高速,すなわち数フレームで完了しなければ実用上問題となる. 我々は LED アレイを送信機,高速度カメラを受信機とする路車間可視光通信について検討している. 通信を行うに当たっては,高速度カメラで取得した画像から LED アレイを認識,さらに追従しなければならない. 既に LED アレイの高速認識・追従のためのアルゴリズムは完成しており, 現在,リアルタイム動作を行うための装置の試作を行っている. 本稿では,歩行者が LED アレイを身につけているものとし,歩行者の認識を LED アレイの認識に置き換えた状況を想定し, 高速度カメラによる LED アレイの高速認識を考える.
LED を用いた無線通信システムである可視光通信が提案されている.本稿では,視覚的に非点灯状態 の LED を用いた並列可視光通信の提案を行う.本研究の目的は,日中の自動車のテールランプ􏰀,視覚的に非点灯 状態の信号機の灯火などの,視覚的に非点灯状態の LED を用いた並列可視光通信を実現することである.その為に LED を視覚的に非点灯状態にする手法と,視覚的に非点灯状態の LED を用いたテールランプ型送信機との通信手 法の提案を行う.また,その有用性を確認する実験を行い,その結果と考察を示す.
As one of ITS technique, a new visible light road to- vehicle communication system at intersections is proposed. In this system, the communication between a vehicle and an LED traffic light is conducted using an LED traffic light as a transmitter, and an on-vehicle high-speed camera as a receiver. The LEDs in the transmitter emit light in high frequency and those emitting LEDs are captured by the high-speed camera for making communication. Here, the luminance value of LEDs in the transmitter should be captured in consecutive frames to achieve effective communication. For this purpose, first the transmitter should be found, then it should be tracked in consecutive frames by processing the images from the high-speed camera. In this paper, we propose new effective algorithms for finding and tracking the transmitter, which result in a increased communication speed, compared to the previous methods. Experiments using appropriate images showed the effectiveness of the proposals.
The paper discusses the optimal cluster partitioning for wireless sensor networks deployed in continuous areas. Both single-hop and multi-hop transmissions with cooperative Multi-Input Single-Output (MISO) scheme are considered for inter-cluster communications. The effects of cluster size in the energy consumption of intra-cluster communication and the amount of fused data are included in calculation. As a result, the dominant factors of the maximal network lifetimes are listed as: the cluster farthest from base station in single-hop transmission and the closest cluster in multi-hop transmission. In addition, the maximal network lifetimes of single-hop and multi-hop transmissions are compared and it is found that there exists a threshold of network size that determines which transmission is the better candidate.
S. Arai, Y. Nishio, T. Yamazato, S. Ozawa
IEEE International Symposium on Circuits and Systems (ISCAS), Paris, France
This paper considers a novel error-correcting scheme exploiting chaotic dynamics for noncoherent chaos communication. In our proposed system, two successive chaotic sequences are generated from the same chaotic map; the second sequence is generated with an initial value which is the last value of the first sequence. In this case, successive chaotic sequences having the same chaotic dynamics are created. This feature gives the receiver additional information to correctly recover the information data and thus improves the bit error performance of the receiver. Further, enhanced efficiency also comes from operating on successively modulated data; by involving less redundancy in the error correction system, it can be designed with high coding rate. In this paper, we analyze the scheme’s capability, by examining computational times and accuracy rates of error correction. bounds on its capability.
T. Nagura, T. Yamazato, M. Katayama, T. Yendo, T. Fujii, H. Okada
In this paper, we consider visible light communication systems using LED array as a transmitter and high-speed camera as a receiver for Intelligent Transport System (ITS). Previously, we have proposed the hierarchical coding scheme which allocates data to spatial frequency components of the image depending on the priority. This scheme is possible to receive information of the high-priority even if communication distance is long. However, we need to distinguish multi-valued data from the received image by using a hierarchical coding. In this paper, we propose two improved decoding methods, and demonstrate to distinguish multi-valued data more correctly in the experiment.
J. Kietlinski-Zaleski, T. Yamazato, M. Katayama
IEEE/ION Position Location and Navigation Symposium (PLANS), Palm Springs, California, USA
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival (ToA) positioning, at least three receivers with unblocked direct path to the transmitter are required. This requirement is not always met. In this work, a novel algorithm for ToA positioning using only two receivers is presented and validated using data from a measurement campaign. Positioning with two receivers is possible by exploiting the knowledge of some of the indoor features, namely positions of big flat reflective surfaces, for example ceiling and walls.
This paper proposes a media access control method for a multipoint cyclic data gathering system, in which each node transmits its data to the base-station periodically. In such condition, by broadcasting ACK/NACK signals from the base-station, the proposed method ensures assignment of a time slot for each node once the node succeeds to transfer its data. It is confirmed that the proposed scheme reduces packet collisions and outperforms conventional slotted-ALOHA scheme in throughput of data even with ACK/NACK errors. Furthermore the proposed scheme realizes adaptive slot assignment under cyclostationary channel environment.
周波数共用のために既存(一次)システムと二次システムが同じ周波数帯域で同時に通信を行う重畳通信の実現例として，著者らは二次システムが一次システム信号を中継する方式を提案している．しかしこの方式では，一次システムの信号が干渉となり，二次システムの特性に大きな影響を与えるという問題があった．そこで本稿では，二次システムの特性改善を図るために\\\Dirty Paper Coding\\\"(DPC)を提案方式に適用する．そして数値例により，一次システムの誤り率特性の劣化無しに二次システムの特性が改善されることを示す．
LED アレイと高速度カメラを用いた階層的符号化光空間通信方式におけるターボ符号を用いた逐次型干渉除去を提案する．提案する逐次型干渉除去では，まず，高優先度データの復調およびターボ復号を行う．この高優先度データを再変調し，受信信号から減算することで高優先度データによる中優先度データへの干渉成分を取り除く．こうすることにより，中優先度データの誤り率特性を改善する．また，この干渉除去法の特性は高優先度データの誤り率特性，つまりターボ符号の誤り率特性に依存する．そこで，これまで採用していたMaxLogMAP アルゴリズムによるターボ復号では無く，新たにLogMAP アルゴリズムを採用することで誤り率特性の改善を図る．
We propose a visible light road-to-vehicle communication system at intersection as one of ITS technique. In this system, the communication between vehicle and an LED array is approached using LED array as a transmitter, and on-vehicle high-speed camera as a receiver. The LEDs in the transmitter are emitted in 500Hz and those emitting LEDs are captured by a high-speed camera for making communication. Here, the luminance value of LEDs in the transmitter should be captured in consecutive frames to achieve effective communication. For this purpose, first the transmitter should be identified, then it should be tracked in consecutive frames while the vehicle is moving, by processing the images from the high-speed camera. In this paper, we mainly introduce an algorithm to track the transmitter using optical flow and edge information.
We propose an iterative channel decoding scheme for two or more multiple correlated sources. The correlated sources are separately turbo encoded without knowledge of the correlation and transmitted over noisy channels. The proposed decoder exploits the correlation of the multiple sources in an iterative soft decision decoding manner for joint detection of each of the transmitted data. Simulation results show that achieved performance for the more than two sources is also close to the Shannon and Slepian-Wolf limit and large additional SNR gain is obtained in comparison with the case of two sources. We also verify through simulation that no significant penalty results from the estimation of the source correlation in the decoding process and the code with a low error floor achieves good performance for a large number of the correlated sources.
S. Arai, Y. Nishio, T. Yamazato, S. Ozawa
International Symposium on Nonlinear Theory and its Applications (NOLTA), Chateraise Gateaux Kingdom Sapporo Hotel & Spa Resort, Sapporo, Japan,
2009年10月
This paper proposes a new M-ary modulation scheme for noncoherent chaos-based communications. A chaotic sequence is successive based on the chaotic dynamics. Without the successive sequence based on the chaotic dynamics, general noncoherent systems are very difficult to demodulate the data. However, we consider that the systematic separation and the reconstruction of the chaotic dynamics can be applied as additional information. Namely, M -ary data symbols can be expressed by separating the chaotic dynamics purposely. We carry out computer simulations of the proposed scheme and confirm that a saving of over 3–4 dB is realized in transmitter energy by increasing M.
Y. Sugiura, T. Yamazto, M. Katayama
Third Workshop on Power Line Communications , Udine, Italy
2009年10月
Phase transfer functions of power-line channels often show sharp and periodic variation synchronous to the (double of) mains frequency. This is a result of impedance change of nonlinear devices connected to the power-lines. This manuscript proposes a phase estimation strategy for phase compensation at a receiver under such environment. In the proposed method, phase estimates are calculated using cyclic observation (average) of the channel phase. The numerical examples under periodic phase variation of the channel and cyclostationary noise show that the receiver with the proposed phase estimation scheme outperforms that with the conventional phase estimation, which uses average over the whole observation period without considering the periodic feature of the channel.
This manuscript proposes a cognitive radio system that shares a frequency with an existing primary system. In the proposed method, a secondary transmitter relays the primary signal and piggybacks its own data on it. Symbol error probabilities of the system are derived analytically. The result shows that the proposed system can communicate at a relatively high speed on the same frequency of the primary system without harm to it.
J. Kietlinski-Zaleski, T. Yamazato, M. Katayama
International Conference on Ultra-Wideband (ICUWB), pp.376-380, Vancouver, Canada
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival(ToA) positioning, at least 3 receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel algorithm for ToA positioning using only 2 receivers is presented. This is possible by exploiting reflections from a set of known flat reflectors, for example ceiling and walls. The proposed algorithm was tested using self-developed UWB propagation simulator testbed.
T. Aman, T. Yamazato, M. Katayama
International Workshop on Satellite and Space Communications (IWSSC), Siena-Tuscany, Italy
The recent development of large aperture on-board multi-beam antennas enables a small-size, low-powered and cellular phone like hand-held terminal as a satellite earth terminal. A single mobile terminal can communicate to both mobile satellite systems and terrestrial systems depend upon his location, QoS and availability of resources among satellite and terrestrial communication systems. In this paper, we propose a new traffic prediction scheme for the integrated satellite/terrestrial frequency sharing mobile communication system. The system shares a common frequency bandwidth in order to enhance the total capacity by a dynamic bandwidth allocation. A key for this allocation depends on a traffic prediction scheme of a few hundreds of terrestrial cells under a footprint of a satellite with a large aperture onboard multi-beam antennas. We propose three traffic predictors based on neural networks for dynamic resource allocation. The performances of the proposed schemes are evaluated in terms of the Relative Traffic Prediction Error and Maximum Traffic Prediction Error by the computer simulation. For the evaluation, we adopt the actual traffic statistic published by Ministry of Internal Affairs and Communications of Japan with population density of terrestrial cells based on the actual population of Aichi, Japan. As results, average traffic prediction error of less than 0.25 is achieved for the prediction interval of one hour, enough for dynamic resource allocation.
We propose a visible light road-to-vehicle communication system at intersection for ITS. In this system, the communication between vehicle and a LED traffic light is approached using LED traffic light as the transmitter, and on-vehicle high-speed camera as the receiver. The LEDs in the transmitter are emitted with 500Hz and the images of those emitting LEDs are captured by a high-speed camera for conducting communication. In this communication, it is extremely necessary to find the transmitter and detect it for consecutive frames while vehicle is moving. In this paper, we introduce proposals for finding and detecting it for consecutive frames by image processing. Experimental results using appropriate images showed the effectiveness of the proposal.
山里敬也
電子情報通信学会論文誌，Vol. J92-B，No. 8，pp. 1211-1211，
2009年8月
山里敬也
平成21年度工学教育研究講演会講演論文集，10-219, 名古屋大学
2009年8月
H.C. N. Premachandra, T. Yendo, M. P. Tehrani, T. Yamazato, T. Fujii, M. Tanimoto, Y. Kimura
Journal of Broadcast Engineering published by KoSBE, the Korean Society for Broadcast Engineers, Vol. 14, No. 4, pp.475-487, July 2009
2009年7月
We propose a visible light road-to-vehicle communication system at intersection as one of ITS technique. In this system, the communication between vehicle and a LED traffic light is approached using LED traffic light as a transmitter, and on-vehicle high-speed camera as a receiver. The LEDs in the transmitter are emitted in 500Hz and those emitting LEDs are captured by a high-speed camera for making communication. Here, the luminance value of each LED in the transmitter should be found for consecutive frames to achieve effective communication. For this purpose, first the transmitter should be identified, then it should be tracked for consecutive frames while the vehicle is moving, by processing the images from the high-speed camera. In our previous work, the transmitter was identified by getting the subtraction of two consecutive frames. In this paper, we mainly introduce an algorithm to track the identified transmitter in consecutive frames. Experimental results using appropriate images showed the effectiveness of the proposal.
Robust channel estimation scheme is essential for pulse-shaping OFDM systems in the multipath mobile environment. This paper proposes three types of channel estimation schemes for the general class of pulse-shaping OFDM systems. The first two types are suboptimal low-complexity maximum likelihood estimators. The last type is adaptive Kalman filter channel estimator. We numerically evaluate the performance of each estimator using computer simulation.
This paper proposes the error-correcting scheme without redundancy sequences based on the chaotic dynamics for noncoherent chaos communications. We generate successive chaotic sequences from the identical chaotic map. And for the next sequence we set the initial value to the end value of the former sequence. By such way we can create the successive chaotic sequences having the same chaotic dynamics. This feature gives the receiver additional information to correctly recover the received noisy signal. Therefore, by analyzing the chaotic dynamics at the receiver, it is possible to improve the error performance without redundancy signal. As results of computer simulations, we confirm about 3 dB gain in BER performance as compared with the conventional suboptimal receiver when using the short chaotic sequence length per 1 bit.
This manuscript discusses the adaptive OFDM system for narrow-band power-line communications with nonwhite and cyclostationary noise environment. The bit and power allocation algorithm is proposed with the considerations on the cyclostationarity of power-line noise. Numerical evaluation shows that the proposed method can improve the average BER performance under PLC noise environment.
J. Kietlinski-Zaleski, T. Yamazato, M. Katayama
Technical Report of IEICE, vol.WBS2008-90, pp.211-216, Hakodate, Japan
2009年3月
Ultra-Wideband is an attractive technology for short range positioning, especially indoors. However, for normal Time of Arrival(ToA) positioning, at least 3 receivers with unblocked direct path to the transmitter are required. A requirement that is not always met. In this work, a novel algorithm for ToA positioning using only 2 receivers is presented. This is possible by exploiting reflections from one known flat reflector, for example ceiling or wall. The proposed algorithm was tested using self-developed UWB propagation simulator testbed.
H.C. N. Premachandra, T. Yendo, T. Yamazato, T. Fujii, M. Tanimoto, Y. Kimura
International Workshop on Advanced Image Technology (IWAIT), Korean Hall of Science and Technology, Seoul, Kore
2009年1月
In this paper, we propose a visible light road-to-vehicle communication system at intersection as one of ITS technique. In this system, the communication between vehicle and a LED traffic light is approached using LED traffic light as the transmitter, and on-vehicle high-speed camera as the receiver. The LEDs in the transmitter are emitted with 500Hz and those emitting LEDs are captured by a high-speed camera for making communication. The images from the high-speed camera are processed to get luminance value of each LED in the transmitter. For this purpose, first transmitter should be found, then it should be tracked for each frame, and the luminance value of each LED in the transmitter should be captured. In our previous work, transmitter was found by getting the subtraction of two consecutive frames. In this paper, we mainly introduce an algorithm to detect the found transmitter in consecutive frames. Experimental results using appropriate images showed the effectiveness of the proposal.
In this paper, the energy efficiency of cooperative Multiple-Input Single-Output (MISO) technique for a multi-hop wireless sensor network is investigated and compared with other transmission schemes. Firstly, we present different schemes for data transmission of the cluster farther from base station and calculate their energy consumptions. The results show that the optimal transmission scheme varies with the inter-cluster distance in different networks. Then we explore the lifetime of the network and find that it is not always the optimal to employ the multi-hop transmission and the single-hop transmission outperform the multi-hop under a certain distance threshold. In addition, the effects of the transmission bit rate and the required bit error ratio (BER) on the distance threshold are also clarified.
K. Kobayashi, T. Yamazato, H. Okada, M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), pp.930-934, Auckland, New Zealand
In densely deployed wireless sensor networks, sensor observations are spatially correlated. Furthermore, the nature of physical phenomena constitutes a temporal correlation between transmitted observations of an individual sensor node. In this paper, we propose a joint iterative channel decoding scheme using turbo codes. The proposed decoder exploits the spatial and temporal correlations of two binary data sequences to achieve additional coding gain. Simultaneously exploiting the spatial and temporal correlation, the proposed decoder achieves large performance gain.
International Workshop on Smart Info-Media Systems in Bangkok (SISB), PS-4, pp.69-74, Swissotel Le Concorde, Bangkok, Thailand
2008年12月
In this paper, we present hierarchical coding scheme using LED traffic lights and high-speed camera for Intelligent Transport Systems (ITS) application. If each of LEDs in traffic lights is individually modulated, parallel data transmissions are possible using a camera as a reception device. Such parallel LED-camera channel can be modeled as spatial low-pass filtered channel of which the cut-off frequency varies according to the distance. To overcome, we introduce hierarchical coding scheme based on 2D fast Haar wavelet transform.
S. Arai, Y. Nishio, T. Yamazato
Proceedings of IEEE Workshop on Nonlinear Circuit Networks (NCN'08), pp. 49-51, Tokushima, Japan
2008年12月
We investigate and evaluate a suboptimal receiver using chaotic sequences with biased values. In our previous research, we investigated a differential chaos shift keying (DCSK) using chaotic sequences with biased values purposely and confirmed its better performance. However, our previous study only performed the computer simulation of DCSK using these chaotic sequences. In this study, we focus on the suboptimal receiver and evaluate its performance with chaotic sequences with biased values.
S. Arai, S. Mase, T. Yamazato, T. Yendo, T. Fujii, M. Tanimoto, Y. Kimura
15th World Congress on ITS, New York, USA
2008年11月
In this study, we focus attention on the parallel optical wireless communication systems using LED array transmitter and a high-speed camera as the receiver for road-to-vehicle communications in ITS. Previously, we have proposed a hierarchical coding scheme which allocates data to spatial frequency components depending on the priority. This scheme is possible to receive the high priority data even if the receiver is far from the transmitter. However, since vehicles drive on a road in actual road-to-vehicle communications, there are many important works to develop the real-time communication system. For example, it is a difficult to synchronize the timing to release the shutter with the lighting cycle of LEDs, i.e., the sampling of the data. This paper details our road-to-vehicle communication system using the LED array and the high-speed camera and proposes their solutions. Moreover, based on proposed solutions, we perform a driving field trial using the LED array and a vehicle with the high speed camera. As the result, we observe the bit error rate and confirm the reception of the data during the driving.
K. Takeshima, T. Yamazato, M. Katayama
International Workshop on Vision, Communications and Circuits (IWVCC), pp.149-152, Xi'an, China
2008年11月
In this paper, we look at communication protocol designed for cluster-based cooperative transmission. As it can increase the spatial diversity of wireless channel, cluster-based cooperative transmission is effective not only for reliable transmission but also in reduction of the transmitted power. The overall energy dissipation is, however, governed by a cluster head selection criterion. We show that the conventional random cluster head selection, as in low-energy adaptive clustering hierarchy (LEACH), and the best link quality cluster head selection may not be optimal for cluster-based cooperative transmission. Based on our finding, we propose a new energy-aware protocol for cluster-based cooperative transmission that considers not only the link quality but also the residual energy of sensor nodes. As results, our protocol shows the best in the availability ratio of sensor nodes and outage probability for the number of cluster-to-cluster transmissions.
S. Arai, Y. Nishio, T. Yamazato
International Workshop on Vision, Communications and Circuits (IWVCC), pp.221-224, Xi'an, China
2008年11月
We investigate the chaotic sequence with biased values in chaos-based communication systems. In our previous research, we investigated the the performance of chaos communications using the sequence with biased values purposely. As results, we concluded that the chaotic dynamics affect the performance of chaos communications greatly. However, our previous study only performed the computer simulation the DCSK system using the chaotic sequence with biased values. In this study, we focus on the suboptimal receiver as one of chaos communication systems and observe its performance with the chaotic sequence with biased values.
S. Mase, S. Arai, T. Yamazato, T. Yendo, T. Fujii, M. Tanimoto, Y. Kimura
International IEEE Conference on Intelligent Transportation Systems (ITSC), pp.1113-1117, Beijing, China
In this paper, we propose an improved coding scheme for optical wireless communication systems using a LED array transmitter and a high-speed camera as the receiver on a vehicle. Previously, we have proposed a hierarchical coding scheme which allocated the data to spatial frequency components depending on the priority. In that scheme, the high-priority data can be received even if the receiver was far from the transmitter. We confirmed the advantage of the hierarchical coding scheme, but the bit error performance was not sufficient. In this paper, we divide the data into spatial frequency components, and use error correcting code for each spatial frequency components’ data. Experimental evaluation demonstrates the improvement in BER performance. This improvement implies that the system range increased compared to the previous method.
In this paper, we propose a new SC/MMSE Turbo equalizer for MC-CDMA to use in inter-vehicle communication (IVC). We modify the weight of the MMSE filter of SC/MMSE Turbo equalizer so that it can combat with frequency-selective fading in highly mobile IVC environment and also can mitigate the effect of multiple access interferences (MAI). As results, we show that better throughput is obtained by the proposed SC/MMSE equalization than the conventional one. The average reception range can be up to 70 [m] and the signals from 16 surrounding cars can be received. While for the conventional scheme, only three signals from the nearest cars are achieved.
S. Arai, Y. Nishio, T. Yamazato
International Symposium on Nonlinear Theory and its Applications (NOLTA), pp. 652-655, Budapest, Republic of Hungary
2008年9月
This paper proposes the error-correcting method based on the chaotic dynamics for noncoherent chaos communications. We generate successive chaotic sequences from the identical chaotic map. And for the next sequence we set the initial value to the end value of the former sequence. By such way we can create the successive chaotic sequences having the same chaotic dynamics. This feature gives the receiver additional information to correctly recover the received noisy signal. Therefore, by analyzing the chaotic dynamics at the receiver, it is possible to improve the error performance. In other words, error performance of the receiver can be improved by the utilization of the suboptimal receiver with the analysis of chaotic dynamics of the successive received sequence. As results of computer simulations, we confirm about 3 dB gain in BER performance compared to the conventional suboptimal receiver.
This paper compares the throughput performance of orthogonal frequency division multiple access (OFDM) and multicarrier CDMA (MC-CDMA) in inter-vehicle communications (IVC).In particular, we compare the throughputs in a situation where hidden terminals are no longer negligible. We encounter the situation in an intersection where two or more cars are crossing by. Due to the hidden terminal degradation, poor throughput performance is obtained with OFDM scheme. On the other hand, MC-CDMA has a resistance to the hidden terminals as it can support simultaneous packets. However, the transmission data rate is much slow because of the spreading. Thus the total throughput may not be as high as the OFDM. As results, we show that throughput of the OFDM is better than the MC-CDMA in a low traffic region. We found that the OFDM can communicate only with the nearest car. On the contrary, when the traffic is high, the MC-CDMA shows better throughput than the OFDM. In addition, we show that many packets can be received simultaneously in MC-CDMA. These results lead to the conclusion that when we want high-speed communication to a few cars, the OFDM is a good candidate. And when low speed but simultaneous communication with many surrounding cars is our desire, then the MC-CDMA is our choice. As MC-CDMA has a compatibility with an OFDM by setting a spreading factor to one, MC-CDMA system may be the preferable choice for IVC.
H. Okada, H. Imai, T. Yamazato, M. Katayama, K. Mase
Academy Publisher Journal of Netowkrs, vol.3, no.7, pp.34-40
2008年7月
Since the network topology in multihop cellular networks is flexible, multiple routes from a user station to a base station can be established. To reduce packet reception errors of wireless links, a multi-route coding scheme was proposed. An important issue of the multi-route coding is to develop an efficient route establishment scheme. In this paper, we propose a route establishment scheme for multi-route coding in multihop cellular networks. Our proposed scheme consists of a route selection method based on the bit error rate of each wireless link and a hybrid-type multiple-tree routing protocol. We evaluate the performance of our proposed scheme by a computer simulation and show the resulting improvement in the packet error.
羽多野裕之，山里敬也，片山正昭
自動車技術, vol.62, no.7, pp.29-34
2008年7月
We consider radar network systems using multiple ultrasonic radars for parking assistance. Our radar network has an ultrasonic array emitter and multiple sensors. The ultrasonic array emitter is composed of multiple ultrasonic emitters and can emit signals to the side area which is the desired monitoring area of parking aid. Target positions are estimated by the data processing form multiple ultrasonic sensors which are set at distributed points of the front bumper. In this paper we especially describe our proposed array emitter.
本研究では，LED アレイと高速度カメラを用いた路車間可視光通信に述べる．LED アレイと高速度カメラを用いることで，個々の LED を独立に変調させた場合でもカメラを用いることで，それぞれ個別に受信できる．これより，LED の数だけ並列にデータ伝送が可能になる．しかしながら，LED 送信機と受信カメラ間の距離が長い場合，受信画像におけるピクセル数の減少や焦点ずれなどによって LED の点灯パターンが劣化して受信される．著者等は，以上の問題に対処できる階層的符号化方式を提案しており，既に静止環境での有効性を確認している．本稿では，昨年度実施した，移動環境での受信特性について紹介する．
This manuscript reports the measurement results of narrowband signal propagation of PLC channels. In Japan, in-house wiring is single-phase three-wire, and each branch between an outlet of 100V and the panel board is connected to one of two live conductors and the neutral. Thus a pair of outlets can be classified into three types: connected to different live conductors, connected to the same live conductors by different branches from the panel board, and on the same branch to the same live conductor. It is confirmed that the results of the measurements can be classified by these three types of paths. The results show that frequency responses of narrowband PLC channels are relatively smooth, compared with that of wideband PLC. It is also found that propagation loss in lower frequency range is larger than in higher frequency range. The time independence of narrowband PLC channels are confirmed when no electric appliance is connected to the same live conductor.
R. Chandradasa, T. Yamazato, M. Katayama
IEICE General Conference, B-20-28, p.569, Kyushu, Japan
2008年3月
Traditional MAC protocols for Sensor Networks are mostly based on random access methods, which cause message collision and energy loss. Several TDMA based methods have been proposed to prevent signal collision with the help of a base station. We propose an algorithm which assigns time slots to sensor nodes without the help of a base station and realizes time-slot reuse.
Throughput performance of MC-CDMA systems depends on the success in managing interference arising from intercell transmission. In this paper, we propose a new intercell interference mitigation scheme for downlink MC-CDMA scheme. In the proposed scheme, a base station transmits downlink signals intermittently to mobile terminals at the edge of cell. The intercell interference can be seen as a partial interference depend upon the on and off period of the adjacent downlink signals. So it is possible for the channel equalizer to suppress this partial intercell interference by setting the weight changes in accordance with the intercell interference. As results, the frame error rate of the proposed scheme is always better than that of the conventional scheme and good throughput performance is achieved especially when the traffic is high.
2007
S. Arai, Y. Nishio, T. Yamazato
Proceedings of IEEE Workshop on Nonlinear Circuit Networks (NCN'07), pp. 54-56, Tokushima, Japan
2007年12月
This paper proposes the error-correcting for noncoherent chaos communications. To improve the error performance, we focus attention on the successive chaotic sequence based on the chaotic dynamics. Concretely, error performance of a noncoherent receiver improves by analyzing the chaotic dynamics of the successive received sequence. As results of computer simulations, we confirm about 3 dB gain in BER performance compared to the conventional suboptimal receiver.
Technical Report of IEICE, vol. 107, no. 299, SAT2007-29, pp. 59-64, Okinawa, Japan
2007年11月
OFDM or multicarrier systems have emerged as a key technology for current existing terrestrial wireless systems. Because of their advantages over a single carrier system, OFDM is undergoing rapid progress and inspiring numerous applications. However, many technical issues still exist for adopting OFDM to satellite communications, i.e., non-linear amplifier compensation. In this article, we present a detailed investigation of various non-linear compensation techniques and provide a better understanding of the research challenges.
We propose a contention-free medium access control (MAC) protocol for inter-vehicle communication systems that share information for the improvement of safety drive on the highway. In the proposed system, contention-free medium access is achieved by periodical one-way token transmissions. The token contains the frame information about the transmission/reception phase. While the token is relaid by one-way, the vehicle which has the token can send a packet to both up- and down-link. The token transmission interval is set not to be interfered from other transmit vehicles at a receive vehicle. In addition, multiple channels are used and allocated dynamically for every token transmission to reduce the transmission waiting time. We also evaluate the maximum end-to-end transmission delay of the proposed protocol, and clarify that the proposed protocol can guarantee the transmission within allowable delay time.
H. Hatano, T. Yamazato, M. Katayama
IEEE International Symposium on Wireless Communication Systems (ISWCS), pp.355-359, Trondheim, Norway
We consider an application of a ultrasonic array emitter to automotive targets detection systems for short-range. Ultrasonic sensors are low cost and widely used. However detectable ranges do not meet the requirements for short-range applications, such as parking aid systems. In this paper, we propose a method which may achieve the emission to a desired area within limited time. We evaluate the expected accuracy of target position estimations by computer simulations. As a result, we show the ability of the ultrasonic sensors for parking aid systems.
H. Okada, H. Imai, T. Yamazato, M. Katayama, K. Mase
IEEE Vehicular Technology Conference (VTC-Fall), Baltimore, USA
In the multihop cellular networks, multiple routes from a user station to a base station can be established because of the flexibility of network topology. In order to reduce packet errors of wireless transmissions, we proposed the multi-route coding scheme, in which packets are encoded and divided into subpackets, and they are transmitted on several routes from the user station to the base station. In order to improve the performance of the multi-route coding, a route selection scheme is very important issue. In this paper, we propose the route selection scheme for the multi-route coding in multihop cellular networks. The proposed scheme is based on the bit error rate of wireless links. We also apply the proposed route selection scheme to a hybrid routing protocol and evaluate its performance.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), Athens, Greece
2007年9月
In this manuscript, a spatial diversity scheme with multiple transmit and receive antennas together with multiple relay terminals for packet radio is considered. Correctly received signals at some relay terminals are re-transmitted to the receiver with the spatial diversity by STBC cooperative relaying scheme. To achieve high diversity order with the conventional STBC cooperative relaying scheme, relay terminals which re-transmit the signals are required to exchange signaling information with each another. However, the exchanging of the information causes delay of the signal transmission. Thus, in this manuscript, a novel signaling scheme for the STBC cooperative relaying is proposed. The proposed scheme releases relay terminals exchanging the signaling information. The proposed scheme also saves communication resources to provide flexibility for installation of relay terminals.
S. Arai, S. Mase, T. Yamazato, T. Endo, T. Fujii, M. Tanimoto, K. Kidono, Y. Kimura, Y. Ninomiya
IEEE International Symposium on Wireless Vehicular Communications (WiVeC), Baltimore, USA
LEDs are expected as lighting sources for next generation, and data transmission system using LEDs attract attention. In this paper, we present hierarchical coding scheme using LED traffic lights and high-speed camera for Intelligent Transport Systems (ITS) application. Further, if each of LEDs in traffic lights is individually modulated, parallel data transmissions are possible using a camera as a reception device. Such parallel LED-camera channel can be modeled as spatial low-pass filtered channel of which the cut-off frequency varies according to the distance. To overcome, we propose hierarchical coding scheme based on 2D fast Haar wavelet transform. As results, the proposed hierarchical transmission schemes outperform the conventional on-off keying and the reception of high priority data is guaranteed even LED-camera distance is further.
S. Arai, Y. Nishio, T. Yamazato
International Symposium on Nonlinear Theory and its Applications (NOLTA), pp.144-147, Vancouver, Canada
2007年9月
In this paper, we analyze a chaotic dynamics generating a chaotic sequence with biased values and apply it to noncoherent chaos communications. We examine a behavior of the chaotic dynamics by increasing the slope of the chaotic map and investigate the invariant measure and the correlation function. A high quality performance of noncoherent chaos communications is obtained by controlling the distribution of the chaotic sequence with biased values. Finally we carry out the computer simulation using its sequence and discuss the obtained results and the future problem for chaos communication.
B.Mongol, T. Yamazato, M. Katayama
International Symposium on Nonlinear Theory and its Applications (NOLTA), pp.92-95, Vancouver, Canada
2007年9月
This paper proposes a low-complexity channel estimation sheme for the pulse-shaping OFDM systems in the highly mobile multipath environment. The estimation scheme is based on the tapped-delay-line model for the channel. The main idea behind our scheme is to approximate the fading process for each tap with finite terms of its Taylor series expansion. The proposed scheme also tracks the channel. We show that the channel can be estimated and tracked with reasonable mismatch error while using considerably short training period.
羽多野裕之, 山里敬也, 岡田啓, 片山正昭
自動車技術会論文集, vol.38, no.5, pp.191-196
2007年9月
We research automotive radar networks with multiple radars set in the front of car. Especially, we consider data processing using measured ranges provided by the radars in order to estimate multiple target positions with high accuracy. This paper is composed of three steps. Firstly, we derive a method based on MAP estimation. Secondly, we propose a method which reduces the calculation complexity compared with the above MAP method. Finally, we introduce a method which can detect targets without ghost-targets in case the lacks of measured ranges are happened because of miss-detection. We evaluate the methods with computer simulations.
This paper compare the throughput performance of a carrier-sense multiple access (CSMA) scheme that uses an orthogonal frequency division multiple access (OFDM) physical layer and a CDMA slotted ALOHA scheme based on multicarrier CDMA (MC-CDMA) in inter-vehicle communication (IVC). In particular, we compare the throughputs in a situation where a hidden terminal is no longer negligible. We encounter such a situation in an intersection where two or more cars are crossing by. In a hidden terminal situation, the CSMA scheme may degrade throughput. On the other hand, CDMA slotted ALOHA has a resistance to the hidden terminal situation as it can support simultaneous packets. However, the transmission data rate is much slow because of the spreading. Thus the total throughput may not be as high as the CSMA based OFDM even in a hidden terminal situation. As a result, we show that the CSMA based OFDM system shows better total throughput than CDMA slotted ALOHA in all region. But, only the signal from the nearest car can be received. On the contrary, CDMA slotted ALOHA can be received many packets simultaneously. This is much preferable feature for safety driving.
K. Nakao, T. Yamazato, H. Okada, M. Katayama
Fourth International Conference on Networked Sensing Systems, pp.89-92, Braunschweig, Germany
We consider a distributed transmission of data packet to a sink where the distance for a sensor node to the sink is much longer than a sensor node can transmit. We give a simple modification in the transmitter, i.e., multiplication of random phase before the transmission. Thanks to a strong error correcting code, it is possible to extend the transmission range as the received amplitude varies symbol by symbol for our scheme while whole data packet may be lost for the conventional scheme.
In sensor networks, because of densely deployment of sensor nodes, sensing area of each sensor node is overlapped with each other and its observed data sequence is correlated. The joint decoding scheme that uses the correlation between the observed data sequences can reduce bit errors in the wireless channel. In this paper, we extend the joint decoding to the case of more than two-hop transmission. For such extension, selection of fusion scheme is very important issue. If the global fusion scheme is employed and the observed data sequence of each sensor node is transmitted on an independent route, route diversity effect could be obtained by using the correlation between observed data sequences. We compare the bit error rate performance of local and global fusion schemes and clarify the route diversity effect.
For safety applications, automotive radar networks show an interesting potential. Apart from long range radars, networked short range radar systems are under development. Additional applications can be accomplished, such includes precrash detection, parking aid and blind spot surveillance. We research the automotive radar networks using short range radars. The network is built with multiple radars. In this paper, we consider data processing using measured ranges provided by the radars in order to estimate multiple target positions with high accuracy. Firstly, we derive a method based on MAP stimation. Secondly, we propose a method which reduces the calculation complexity compared to the above MAP method. Finally, we introduce a method which can detect targets with low ndetected targets. The case often happens when the measured ranges are lost because of miss-detections.We evaluate the performance th computer simulations.
小林健太郎，山里敬也，岡田啓，片山正昭
Wireless Technology Park 2007 アカデミアプログラム, pp.26-27, 横浜
IEICE Transactions on Communications, vol.E89-B, no.12, pp.3250-3256
2006年12月
This paper discusses the influence of the nonlinearity of analog-to-digital converters (ADCs) on the performance of orthogonal frequency division multiplexing (OFDM) receivers. We evaluate signal constellations and bit error rate performances while considering quantization errors and clippings. The optimum range for an ADC input amplitude is found as a result of the trade-off between quantization error and the effects of clipping. In addition, it is shown that the peak-to-average power ratio (PAPR) of the signal is not a good measure of the bit error rate (BER) performance, since the largest peaks occur only with very low probabilities. The relationship between the location of a subcarrier and its performance is studied. As a result, it is shown that the influence of the quantization error is identical for all subcarriers, while the effects of clipping depend on the subcarrier frequency. When clipping occurs, the BER performance of a subcarrier near the center frequency is worse than that near the edges.
Pulse-shaping OFDM is well-known that it performs well in a mobile environment comparing with conventional OFDM. However, in highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time-frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.
B. Mongol, T. Yamazato, H. Okada, M. Katayama
IEICE Transactions on Fundamentals, vol.E89-A, no.11, pp.3114-3122
2006年11月
Pulse-shaping OFDM is well-known that it performs well in a mobile environment compared with conventional OFDM. However, in a highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Proper channel equalization is needed for further improvement of the systems. In this paper, a more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We propose a multi-input multi-output (MIMO) transversal filter to equalize the time-frequency dispersive channel. Tap weights are calculated using the zero-forcing (ZF) algorithm. We also propose maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of BFDM/OQAM systems in the highly mobile environment.
R. Uchida, H. Okada, T. Yamazato, M. Katayama
MObile Radio Interdisciplinary Workshop (MORI Workshop), Daejeon, Korea
International Symposium on Information Theory and Its Applications (ISITA), pp.454-459, Seoul, Korea
2006年10月
In this manuscript, spatial diversity for in-factory environments is considered. The proposed scheme uses multiple antennas at a transmitter and a receiver, and also multiple relay terminals to provide diversity gain against fading and shadowing. If the separation of antennas at the transmitter or the receiver is not enough, then diversity gain is influenced by correlation at the transmitter or the receiver. This manuscript shows the analytical and numerical results of the effects of transmit and receive correlations on bit error performance of the proposed spatial diversity scheme.
K. Kobayashi, T. Yamazato, H. Okada, M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), pp.808-813, Seoul, Korea
2006年10月
In this study, we consider joint channel decoding of Turbo code for multiple correlated data that are observed by sensor nodes densely deployed in a sensor field. We focus on the correlation properties of observation data and try to reduce decoding error by an iterative procedure. An approach to use practical channel codes for more than two correlated data is still not presented. A problem in the extension to cases of more than two sensor nodes is how to use the information of correlation obtained from observation data. In this study, we propose an iterative channel decoding scheme that uses them with weighting. We show that when the number of sensor nodes is increased, decoding performance improvement cannot be achieved by simple weighting, and so a more appropriate weight is needed. We find the optimum weight that minimizes the bit error rate from the analytical formula for uncoded BPSK and apply it to the case of Turbo code.
IEEE International Symposium on Personal Indoor and Mobile Radio Communication (PIMRC), Helsinki, Finland
2006年9月
This paper examines multihop cellular networks. There are some issues in these networks, such as route loss due to topological change and packet errors due to wireless nodes relay. To overcome these issues, we use a multiple route coding scheme in which packets are transmitted on multiple routes from a user node to multiple base stations. This scheme can achieve a diversity gain by combining packets that are transmitted along multiple routes. Some challenges must be met to establish multiple routes for this scheme. In this paper, we propose a routing protocol for multiple route coding. The key idea of this proposed scheme is using a hybrid routing protocol. This can mitigate an increase in control packets and multiple disjoint routes can be constructed. We evaluate the performance of this proposed scheme.
B. Mongol, T. Yamazato, H. Okada, and M. Katayama
International Symposium on Wireless Communication Systems (ISWCS), pp.159-163, Valencia, Spain
Pulse-shaping OFDM is well-known that it performs well in a mobile environment comparing with conventional OFDM. However, in highly mobile environment intersymbol and intercarrier interferences (ISI/ICIs) increase and can no longer be neglected. These ISI/ICIs deteriorate the performance of the systems. Practically, proper channel equalization and estimation are needed for further improvement of the systems. In this paper, more general case, namely Biorthogonal Frequency Division System based on Offset QAM (BFDM/OQAM) is considered. We first derive analytical equations for the channel statistics. Further, we propose maximum-likelihood channel estimator and its low-complexity versions. The performance analysis shows that the estimators are robust against Doppler spread of the channels.
We research automotive radar networks with multiple radars set in the front of car. Especially, we consider data processing using measured ranges provided by the radars in order to estimate multiple target positions with high accuracy. This paper is composed of three steps. Firstly, we derive a method based on MAP estimation. Secondly, we propose a method which reduces the calculation complexity compared with the above MAP method. Finally, we introduce a method which can detect targets without ghost-targets in case the lacks of measured ranges are happened because of miss-detection. We evaluate the methods with computer simulations.
IEEE Journal on Selected Areas in Communications, vol.24, no.7, pp.1267-1275
2006年7月
This manuscript introduces a mathematically tractable and accurate model of narrowband power-line noise based on experimental measurements. In this paper, the noise is expressed as a Gaussian process whose instantaneous variance is a periodic time function. With this assumption and representation, the cyclostationary features of power-line noise can be described in close form. The periodic function that represents the variance is then approximated with a small number of parameters. The noise waveform generated with this model shows good agreement with that of actually measured noise. Noise waveforms generated by different models are also compared to that of the proposed mode.
For reduction in bit errors on wireless channels, we proposed the multi-route coding scheme on multiple routes for wireless multi-hop networks. In this paper, we introduce ARQ to the multi-route coding. In the multi-route coding, the destination node combines and decodes sub packets which are encoded and divided by the source node. The intermediate node relays a sub packet, that is, only a part of a packet. Therefore, the intermediate node cannot detect packet errors, and only the destination node can do after combining and decoding sub packets. We propose the ARQ scheme between the source node and the destination node. We analyze the proposed ARQ scheme and evaluate the throughput performance.
H. Okada, N. Nakagawa, T. Wada, T. Yamazato, M. Katayama
IEICE Transactions on Communications, vol.E89-B, no.5, pp.1620-1626
2006年5月
Wireless multi-hop networks have drawn much attention for the future generation mobile communication systems. These networks can establish multiple routes from a source node to a destination node because of flexible construction of network topology. The transmission by multiple routes has enough capability to achieve reliable communication because we can expect to obtain diversity gain by multiple routes. In this paper, we propose the multi-route coding scheme. At first, we discuss a channel model in multi-hop networks employing regenerative relay, which we named the virtual channel model. By using the virtual channel model, a packet is encoded on multiple routes as follows; a bit sequence of a packet is encoded and divided into subpackets, and each subpacket is transmitted on each route. We evaluate its packet error rate performance, and clarify effectiveness of the proposed scheme. In general, we should face degradation of a route condition such as the case when a subpacket does not reach a destination node. Hence, we have to consider the influence of subpacket loss. We also investigate it, and show tolerance of the proposed scheme over that.
IEEE International Symposium on Power Line Communications and Its Applications (ISPLC), pp.92-97, Orlando, Florida, USA
2006年3月
This manuscript discusses the relationships of noise waveforms measured at different outlets in a three-wire single-phase (one neutral and two live conductors) power-line network. As a result of experimental measurements, it is confirmed that instantaneous noise voltages at two different outlets have high correlations if the outlets are connected to the same live conductor in a distribution board, while the outlets for the different live conductors provide noise waveforms with low correlations. It is also shown that the instantaneous noise powers and cyclic averaged noise powers as time functions have large correlations even at a pair of outlets connected to the different live conductors. The correlation coefficients for instantaneous voltages and powers are also calculated as the frequency functions.
B. Mongol, T. Yamazato, H. Okada, and M. Katayama
Technical Report of IEICE, vol.WBS2005-112, pp.19-24, Nagoya, Japan
2006年3月
Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) system is one of the pulse-shaping versions of Orthogonal Frequency Division Multiplexing (OFDM) systems. It allows optimal Gaussian transmitting pulse at critical sampling i.e., maximum spectral efficiency. In this paper we propose a robust receiver for BFDM/OQAM systems in highly mobile environment. The idea behind our approach is to employ Multi-Input Multi-Output zero-forcing (MIMO-ZF) transversal filter to equalize the channel. The equalizer requires knowledge of the channel status. The channel is estimated by using Maximum-Likelihood method. We evaluate the error rate performance of the proposed system in the time-frequency dispersive channels.
Journal of Signal Processing, vol.9, no.6, pp.473-478
2005年12月
Chaos could generate nonperiodic sequences with infinite lengths theoretically. In this paper, we propose a UWB (ultra-wideband) chaotic radar, whose transmitted signal is generated by a chaotic map. Since it is important to remove various noises called clutter in a radar, we focus mainly on the removal of clutter by applying three clutter reduction methods. We derive the probability density function of power, the distances between the transmitted signals and the recovered signals, and the detection probability, using computer simulations, and the performance of the proposed radar is evaluated.
Asia-Pacific Conference on Communications (APCC), pp.788-792, Perth, Australia
2005年10月
A parallel optical wireless communication system using two-dimensional LED array (2D LED array) and two-dimensional image sensor (2D image sensor) was proposed for the visible light communication systems. In this system, each LED of the 2D LED array is individually modulated, and the 2D image sensor recognizes each LED modulated data. However, the received data pattern will be degraded due to reduction of pixel size and/or defocussing of the LED data pattern. This phenomenon corresponds to the degradation of high spatial frequency components of the received data pattern. To overcome, we employ a hierarchical transmission scheme at a transmitter and a successive interference cancellation at a receiver. By allocating high priority data to low frequency components and low priority data to high frequency components, the reception of high priority data can be guaranteed. We also attempt to apply interference cancellation to overcome the degradation of high spatial frequency components of the received data pattern. By evaluating the bit error rate, we clarify the effect of the proposed system.
R. Uchida, H. Okada, T. Yamazato, M. Katayama
IEICE Transactions on Fundamentals, vol.E88-A, no.10, pp.2945-2951
2005年10月
In this manuscript, a layered macro / micro diversity scheme is introduced at the receiver side of a MIMO STBC wireless control system under fading and shadowing environment. The combination of the outputs of micro diversity is based on soft-decision values, while the macro diversity branches are combined based on hard decision values. As a measure of the reliability of the system, the outage probability of frame-error rate is employed. The performance of the proposed system is analytically and numerically evaluated and the impact of the macro diversity in the outage probability is clarified.
T. Yamazato, A. Ogawa
Technical Report of IEICE, vol.SAT2005-21, pp.27-32, Nagoya, Japan
2005年10月
We have been working on a relay process of communication satellite. We omit the regenerative process at the satellite. Only routing and other necessary operation are performed at satellite. Simple configuration and signal processing may promise robust and long-lasting operations in space. We call it simple regenerating repeater. However, an issue is how to realize the reliable transmission even if we omit the error correcting and detecting process at the satellite. To overcome this issue, we propose to place the error detection code prior to QAM mapping. Using the status of error detector, it is possible to give accuracy to the received signal so we can improve the performance by soft decoding. The FPGA experimental boards of the system are also introduced
H. Kuwamura, A. Ogawa, T. Yamazato
Technical Report of IEICE, vol.SAT2005-22, pp.33-35
2005年10月
T. Yamazato, A. Ogawa
AIAA International Communications Satellite Systems Conference (ICSSC), MOD-1-1, Rome, Italy
2005年9月
In this paper, we focus on relay process of broadband communication satellite. We omit the demodulation, error decoding and re-encoding process at the satellite. Just store the received signal as it is and then forward it to the destination in which the information is extracted from the header. We discuss the issue of analog-to-digital converter for this relay process. For given quantization level, reduction of signal accuracy can improve the transmission rate as we can adopt higher order of QAM. However, the degradation occurred due to the reduction of available quantized bit for accuracy. To overcome this issue, we propose to place the error detection code prior to QAM mapping. Using the status of error detector, it is possible to give an accuracy to the received signal so we can improve the performance by soft decoding.
T. Yamazato, T. Yamaoka, H. Okada, M. Katayama, A. Ogawa
AIAA International Communications Satellite Systems Conference (ICSSC), MOD-3-3, Rome, Italy
2005年9月
In this paper, we propose a new multi-rate coded QAM for broadband satellite communication system. The overall coding rate is (m?2)/2 and Turbo code is adopted. The mapping is similar to bit-interleaved coded modulation (BICM) systems; unlike BICM mapping, we only assign four of Turbo coded bits. This brings a set-partitioning. We also consider the effect of quantization bits. Actually we try to realize high-order QAM by using the available quantization bits, which reduces the signal accuracy so the performance may degrade. As results, our proposed scheme achieve good performance even when the available quantization bits are less.
R. Uchida, H. Okada, T. Yamazato, M. Katayama
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), pp.1626-1630, Berlin, Germany
2005年9月
In this manuscript, wireless communication system for reliable wireless control of industrial machines in indoor environment is considered. In indoor environment, transmitted signal fluctuates due to fading and shadowing. To combat the fading and shadowing, macro / micro spatial diversity can be used as an effective countermeasure. In this manuscript, macro / micro diversity is achieved by multiple wireless relay terminals, which is convenient in setting and moving the macro diversity branches. In the proposed scheme, channel between the transmitter and the receiver through relay terminals is considered as a MIMO channel and separation of the signals re-transmitted from the relay terminals is not required. This feature makes it possible to have higher order diversity without the cost of bandwidth inefficiency. In numerical examples, the performance of the proposed scheme is evaluated by average frame-error rate and outage probability of frame-error rate. With two relay terminals, the diversity gain of the proposed scheme is about 5-6 dB, which is 1 dB higher than that of conventional macroscopic diversity.
B. Mongol, T. Yamazato, H. Okada, M. Katayama
International Symposium on Wireless Communication Systems (ISWCS), WS4-6, Siena, Italy
2005年9月
Recently, there has been increased interest in using multicarrier systems in rapidly time-varying multipath environment. Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) is an attractive modulation method since it allows time-frequency well-localized pulses even at critical sampling (i.e. maximum spectral ef ciency). BFDM/OQAM system is naturally strong against intersymbol and intercarrier interference (ISI/ICI). However, for further improvement of the system a study on the channel statistics is needed. In this paper we analytically examine the channel parameters for BFDM/OQAM and derive their second-order statistics.
10th International OFDM-Workshop 2005, pp.220-224, Hamburug, Germany
2005年8月
This paper discusses the influence of the nonlinearity of an analog-to-digital converter (ADC) in an orthogonal frequency division multiplexing (OFDM) receiver. We evaluate a signal constellation and a bit error rate (BER) performance with the consideration of quantization errors and clippings. As a result, the trade off between the quantization error and the clipping and the optimum range for an ADC input amplitude are shown. In addition, it is shown that the peak to average power ratio (PAPR) of the signal is not a good measure of the BER performance, since the peaks occur only with very low probabilities.
5th International Conference on ITS Telecommunications, pp.131-134, Brest, France
2005年6月
In this work, we present target position estimation methods using minimum mean-square error (MMSE) algorithm for short-range radar systems. We consider UWB IPCP (inter-period correlation processor) receiver and improve target position accuracy by using a set of measured ranges. Depend on how we set the objective functions for MMSE, we propose three methods. And we evaluate the performance of position estimations using computer simulations.
H. Okada, T. Wada, K. Ohuchi, M. Saito, T. Yamazato, M. Katayama
IEEE Vehicular Technology Conference (VTC-Spring), pp.3092-3096, Stockholm
2005年6月
Wireless multi-hop networks have been much attention for the future generation mobile communication systems. Due to the possibility of flexible construction in the wireless multi-hop networks, multiple routes from a source node to a destination node can be established. In this paper, we propose the route coding scheme in the wireless multi-hop networks. In the proposed scheme, a packeted data sequence is encoded by the convolutional code at the source node. Each digit of the code word is assigned to sub-packets on multiple routes. At the intermediate nodes, the sub-packets are regenerated-relayed to the next node. The sub-packets transmitted via multiple routes are decoded by the Viterbi decoder with the modified metric computation at the destination node. We also evaluate the system performance, and clarify the improvement of the packet error rate by the proposed scheme. Furthermore, we investigate the influence of the route loss due to topological change or recognizing failure.
Y. Tadokoro, H. Okada, T. Yamazato, M. Katayama
IEICE Transactions on Fundamentals, vol.E88-A,no.6, pp.1605-1612
2005年6月
Packet-recognition/code-acquisition (PR/CA) is one of the most important issues in packet communication systems. In a CDMA Unslotted ALOHA system, Multiple Access Interference (MAI) may bring about error in PR/CA. The MAI mainly stems from already recognized packets and newly arriving packets under the execution of PR/CA. This characteristic of asynchronous transmission in CDMA U-ALOHA systems implies that only one or a few packets arrive at the receiver within a short interval of a execution. Furthermore, newly arriving packets are recognized and code-acquired by using a short preamble part. Consequently, the MAI from the packets under the execution of the PR/CA will be small. Focusing on that point, this paper proposes applying the IC scheme in order to suppress the MAI from the already recognized and code-acquired packets. A performance evaluation demonstrates that such an application is valid due to the small amount of MAI from the packets under the execution of PR/CA. In addition, we demonstrates that the scheme reduces false recognition rather than mis-recognition. Such a scheme improves the performance of not only PR/CA, but also the throughput.
B. Mongol, H. Okada, T. Yamazato, M. Katayama
Technical Report of IEICE, vol.RCS2005-33, pp.35-40, Nagoya
2005年6月
Recently, there has been increased interest in using Orthogonal Frequency Division Modulation (OFDM) systems in rapidly time-varying multipath environment. The performance of the systems in such time-frequency dispersive channels, depends critically on the time-frequency localization of the transmitter pulse. Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) is attractive modulation method since it allows time-frequency well-localized pulses at critical sampling (i.e. maximum spectral efficiency). In this paper we consider BFDM/OQAM system with Gaussian transmitter pulse and evaluate channel parameter statistics in multipath time-varying channels.
This manuscript introduces a mathematically tractable and accurate model of narrowband power-line noise based on experimental measurements. In this model, the noise is expressed as the sum of cyclostationary Gaussian processes. The non-stationary features of power-line noise are represented with a small number of parameters, and the noise waveforms generated with the model achieve good agreement with those of actually measured noise.
Y. Hirayama, H. Okada, T. Yamazato, M. Katayama
IEICE Transactions on Fundamentals, vol.E88-A, no.3, pp.755-760
2005年3月
The noise on power-lines is non-stationary, while the instantaneous noise power in different frequency bands are dependent. Under such noise environments, the instantaneous noise power in a frequency band can be estimated by observing the noise in other frequency bands. In this paper, we propose a receiver structure which uses the estimated instantaneous noise power in the decoding process and show its superiority in BER performance to conventional systems.
N. Dake, Y. Uwate, Y. Nishio, T. Yamazato
RISP International Workshop on Nonlinear Circuits and Signal Processing (NCSP), pp. 367-370, Honolulu, Hawaii
WebCT(Web Course Tools)は、カナダのブリティッシュコロンビア大学で開発された Web を用いた授業（コースと呼ぶ）の設計、開発、管理を行う統合コース管理システム（Course Management System: CMS）である。WebCTでは、htmlの表示、掲示板、Eメール、オンラインクイズなどが簡単にでき、いわば授業のホームページを運用するためのツールである。WebCTの日本語化は、1999年に当時名古屋大学情報メディア教育センターの助手であった梶田将司氏によって行われた。以来、情報メディア教育センターではWebCTを利用した授業支援を行っている。私も 1999年からWebCTを講義に利用している。本稿では、私の授業実践として、1998年～2002年に開講した「計算機基礎数理」を紹介する。具体的には、WebCTをどう活用したのかについて、ダイナミックな授業、掲示板による学生同士のサポート、広範な授業内容について述べる。最後に本学で WebCTを活用するためにはどうすれば良いのか、私見を述べる。
A. Jamalipour, T. Yamazato, T. Wada
IEEE Communication Magazine, vol.43, no.2, pp.110-117
2005年2月
Beyond third-generation (B3G) wireless cellular systems are recognized as systems that can achieve high data-rate transmission beyond those currently provided by the second- and third-generation (2G/3G) wireless cellular systems and are capable of delivering multiple services to users at different locations under very diverse channel conditions. B3G systems should provide services comparable to those offered by wired networks for a variety of applications such as interactive multimedia, VoIP (voice over Internet protocol), network games, videoconferencing, etc. The current trend is that B3G will be based on IP technology, and therefore, all-IP [1] architecture design has been an important research topic in the past few years. Those systems will need to support multiple services ubiquitously in different types of environment including indoor, outdoor (with low and high velocity), and up to global broadband access (satellite). Thus, they would be deployed in a heterogeneous environment of various physical access networks of wireless and wired systems. The network heterogeneity means that the physical access network underlying the B3G system will support different levels of data rates and different mobility and traffic management techniques govern individual systems. In this context, the B3G mobile systems will face at least two predominant constraints: a) heterogeneity in physical access network, and b) change of application types from commonly low data rates into more bandwidth demanding real-time and multimedia ones. In such situation, providing quality of service to users would become even more difficult that what we are currently dealing. One of the main issues involved in the development of B3G systems is the choice of multiple access (MA) technology that could efficiently share the available bandwidth to large number of users. The choice of MA technique could significantly enhance or damage the service quality delivered to end users. It is known that the existing MA techniques used in 2G/3G systems, including those based on time division multiple access (TDMA) and direct sequence code division multiple access (DS-CDMA) [2], and other combinations of the two schemes are basically suitable for voice communications and not for the burst data traffic, which would be the dominant portion of traffic load in B3G systems. Therefore, the need for developing new MA techniques for B3G becomes imperative. In this article, we will review the main technical concepts of the MA schemes in wireless mobile systems and try to find the path for the development of an appropriate MA scheme for B3G through those fundamentals govern the existing MA schemes. In the following section, multiple access technologies will be reviewed from historical and technical points of view. This review will be followed by a section that provides simple formulization of MA schemes through mathematical expressions that could simplify the process of developing new MA schemes for B3G wireless cellular systems. We will then list the most important features of multiple access schemes in 3G mobile system. Finally we conclude this article by reviewing the most promising MA schemes for B3G mobile systems.
Y. Hirayama, H. Okada, T. Yamazato, M. Katayama
International Journal of Wireless Information Networks, vol.12, no.1, pp.35-45
2005年1月
In this paper, we apply the multiple-route packet combining scheme to wireless multihop networks in order to support delay-sensitive applications. The performance of the system is time-dependent and is greatly affected by network-level performance. Therefore, it is necessary to develop an analytical framework to evaluate the per- formance of the system with taking into account its time-dependency. We use queuing theory to analyze the performance of the system. From numerical results, it is shown that the performance degradation of the system is mainly caused by the increase of packet delay, which is due to the increase of the traffic intensity. To prevent the increase of traffic,we propose a packet discarding scheme. We analyze the average packet error probability of the proposed system with the equilibrium point analysis (EPA). Numerical results show that the packet discarding scheme can improve the average packet error probability under heavy traffic conditions.
IEICE Transactions on Fundamentals, vol.E87-A, no.10, pp.2599-2606
2004年10月
Sensor networks, in which a large number of sensor nodes are connected with each other through communication networks, are potential to provide extensive new applications with various research and technical challenges and attracting much attention all over the world. In this paper we describe information and signal processing for sensor networks with emphasis on the concepts of collaboration and fusion as one of the most important issues for the sensor networks. We also review some basic aspects of sensor networks in terms of their features and the network architecture.
R. Uchida, H. Okada, T. Yamazato, M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), pp.1353-1358, Parma, Italy
2004年10月
In this paper, we propose a 2-layer spatial diversity scheme to guarantee the reliability of indoor wireless communication/control systems. The performance in uplink is numerically evaluated with the outage probability of a required bit-error rate (BER). As a result, the superiority of the proposed system to conventional ones is clarified.
N. Nakagawa, H. Okada, T. Wada, T. Yamazato, M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), pp.1535-1539, Parma, Italy
2004年10月
In this paper, we consider the improvement of packet error rate on wireless multi-hop networks. One of the important and interesting techniques for wireless multi-hop networks is multi-path routing. By using multi-path routing, multiple routes can be established from a source node to a destination node. In this paper, we propose the error correcting scheme in which the coded different packets are transmitted using multiple routes on wireless multi-hop networks. Hence, we can achieve a coding gain for multiple routes and expect the improvement of performance. In wireless multi-hop networks, the route loss due to topological change or recognizing failure may be happened. From the above discussion, we evaluate the proposed scheme by packet error rate in consideration of the influence of the route loss.
T. Yamaoka, T. Yamazato, H. Okada, M. Katayama and A. Ogawa
Technical Report of IEICE, vol.SAT2004-148, Seoul Korea
2004年10月
In order to achieve high speed satellite communication, we propose a new R=m-2/m error correcting scheme for hard detected 2^m-QAM signal, where we consider m
1st International Symposium on Wireless Communication Systems, pp.115-119, Port Louis, Mauritius
2004年9月
UWB impulse radar has high accuracy of measurement because it uses a transmitted signal whose pulse length is below some nanosecond. In this paper, we propose two novel inter-period correlation processing (IPCP) receivers for UWB impulse radar. The conventional IPCP receiver uses the signal periodicity of signals, so it avoids estimation of unknown parameters determined by the targets and propagation. However, its accuracy of measurement is poor because the time resolution is restricted to a signal periodicity. We propose a parallel IPCP receiver to improve accuracy. When there are multiple targets, the conventional IPCP receiver needs multiple thresholds to detect. This results in complexity of the receiver. So, we propose a parallel differential IPCP receiver. We present the analysis of the outputs, and the performance of proposed receivers.
H. Okada, N. Koie, N. Nakagawa, T. Yamazato, M. Katayama
1st International Symposium on Wireless Communication Systems, pp.183-187, Mauritius
2004年9月
Wireless multi-hop networks have been much attention for the possibility of flexible construction of the network topology. One of the important and interesting techniques for multi-hop networks is a multi-path routing. By using the multi-path routing, multiple routes from a source node to a destination node can be established. In this paper, we propose the error correcting and diversity combiner scheme on multiple routes in wireless multi-hop networks to reduce bit errors. The diversity combiner outputs the likelihood information from the packets transmitted via multiple routes. By feeding the likelihood information into the Viterbi decoder, the diversity gain can be obtained. We evaluate the packet error rate and the total traffic. As a result, the packet error rate can be improved. Furthermore, the total traffic can be reduced in the low Eb/N0 in spite of the traffic increase due to transmission via redundant routes.
T. Yamazato, H. Okada, M. Katayama, A. Ogawa
1st International Symposium on Wireless Communication Systems, pp.398-402, Mauritius
2004年9月
In this study, we focus on relay process of intermediate node of wireless sensor networks. In conventional wireless sensor networks, the intermediate node performs the regenerative repeating process such that error correction, detection and re-encoding are processed. This is reliable, but it requires a lot of processing effort and may take much energy. To reduce a burden of relay process, we propose to omit error decoding and/or re-encoding process at the intermediate nodes. Further, we propose a method that realizes soft-decision decoding for hard-detected signals. With this method, we can employ Turbo code to wireless sensor networks. As results, we show that though omitting the decoding and re-encoding process at the intermediate node may not affect much to the performance.
Y. Hirayama, N. Nakagawa, H. Okada, T. Yamazato, M. Katayama
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), vol.1, pp.140-144, Barcelona, Spain
2004年9月
In real-time packet communications, packet retransmission is generally not used because it may produce undesired delays. In this case, however, packet errors caused by a channel may lead to a loss of transmitted information directly. Then, it is necessary to employ a technique which can reduce the influence of packet errors. We propose to employ a multiple-route packet combining scheme in real-time communications on wireless multihop networks. The scheme can achieve a diversity gain by combining multiple copies of the same packet that are transmitted along different routes. We analyze two characteristics of the proposed system. One is the average packet error probability, which is obtained as a function of elapsed time after transmission requests for copied packets are generated. The other is the required time for achieving a required packet error probability. The results are evaluated from a quality of service (QoS) point of view. From numerical results, it is shown that for a given tolerable delay, there exists a number of multiple routes that minimizes the achievable average packet error probability. Moreover, if the number of multiple routes is selected appropriately, the required time for achieving a required packet error probability can be minimized.
Y. Tadokoro, H. Okada, T. Yamazato, M. Katayama
IEEE International Symposium on Spread Spectrum Techniques and Applications, pp.37-41, Sydney, Australia
2004年9月
In CDMA packet communication systems employing Successive Interference Cancellation(SIC) scheme, the suppression of MAI depends on the received signal-power distribution, in addition to the cross-correlation characteristic of spreading sequences and the number of transmitted packets. Some works have been done about discovering the received signal-power distribution which makes MAI be suppressed effectively. This distribution minimizes the averaged Bit Error Rate(BER). However, in packet communication systems, it is dominant to the performance if packets can be transmitted successfully or not. Even if the averaged BER is high, many packets can be correctly transmitted. It implies that the optimum distribution on averaged BER does not give the best performance of packet transmission.In this paper, the received signal-power distribution which gives the best performance of packet transmission is derived. Such a distribution will make clear the limit of performance improvement using SIC.
H. Yamamoto, T. Yamazato, H. Okada, and M. Katayama
IEEE International Symposium on Spread Spectrum Techniques and Applications, pp.67-71, Sydney, Australia
2004年9月
In this paper, we analyze the performance of multi-carrier CDMA (MC-CDMA) system with and without guard interval (GI) in two-path channel. As results, we show that the BER performance of two cases are almost the same. This implies the removal of GI for the MC-CDMA system.
N. Dake, Y. Nishio, T. Yamazato
Shikoku Shibu Rengo Taikai, no.17-11, p.319, Kagawa, Japan
2004年9月
In this study, we propose UWB random noise radar, whose noise signal is generated by a chaotic sequence [1]. Chaos is non-periodic and could generate sequences with infinite length theoretically. Although the sequences appear like noise, the values can be predicted exactly if the dynamics and the initial value are provided. Thus, it is suitable to use a chaotic sequence for generation of noise signal than a sequence generated by a Gaussian random noise formally used for the UWB radar [2]. In this study, we focus mainly on removal of clutters by employing three ML (Maximum-Likelihood) decodings [3]. The ML algorithms are based on the characteristics of chaos and good performances are expected.
本報告では，米国オーランドで開催された第６回WebCTユーザカンファレンスでの発表を中心に，大学間連携におけるWebCT Vistaの活用状況をまとめる．特に，ASP(Application Service Provider)型で展開されているConneticut Distanoe Learning Consortium, 複数キャンパス間での共有型で展開されているPurdue University, 複数大学間での共有型で展開されているUniversity System of Georgiaについて詳しく報告する．
4th International Workshop on ITS Telecommunications, pp.181-185, Singapore
2004年7月
In this paper, we propose AHS system using DGPS, RVC and IVC. And, we evaluate the system performance in simulation. From simulation results, we find that if the RVC bit error rate is about 10^-5, it is possible to accomplish the same tracking performance as the case that RVC bit error does not occur. Moreover, we confirm that when IVC packet error rate is less than 10^-3, it can be enough to achieve ideal platooning performance.
ガートナージャパンが2004年6月に発表した、ビジネスマンを対象としたeラーニングの利用者意識調査結果によると、「効果がある」と回答した利用経験者が8割に達しているとし[1]、また、北米の高等教育現場では、2005年には７割の学生がeラーニングを利用した講義を受講、5割以上の教員がeラーニングを活用した講義を行うものと予想している[2]。我が国においても、e-Japan重点計画にみられるように、eラーニングは注目を集めており、文科省公募研究「知的資産の電子的な保存・活用を支援するソフトウェア基盤技術の構築」が始まるなど、（高等）教育改革、大学改革を語るうえで重要な意味を持つようになってきた。WebCTは、カナダのブリティッシュコロンビア大学で開発された Web を用いた授業（コースと呼ぶ）の設計、開発、管理を行う統合コース管理システム（Course Management System: CMS）である。2004年4月現在、81ヶ国2,600（日本：45）を越える高等教育機関でも利用されており、約1/3の世界シェアを誇り、Blackboardと並び商用CMS では最も広く利用されている。WebCTは、1999年に当時名古屋大学情報メディア教育センターの助手であった梶田将司氏によって日本語化された。以来、本センターではWebCTを利用した授業支援を行っている。本稿では、まずWebCTの概要を述べ、名古屋大学でその利用を支える3センターの連携を紹介する。最後に北米の動向、日本WebCTユーザ会での議論の流れから、講義支援システムとしてのWebCTについて述べていく。
T. Yamazato
NETS: Finland-Japan Workshop on Future Networks 4th June 2004 in Oulu, Oulu, Finland
2004年6月
Under the 21st Century COE Program by the Ministry of Education, Culture, Sports, Science and Technology in Japan, Intelligent Media (Speech and Images) Integration for Social Information Infrastructure (IMI) seeks to form the Intelligent Media Integration (IMI) Research and Education Center to promote world-class research and educational activities. As members of IMI, (Prof. Kawaguchi and) I will talk about our COE project. Further, I will introduce the IEICE Technical Group on Sensor Networks (SN). The SN is a new technical group under Engineering Science Society (ESS), which officially will start from this June. On be half of start up members of SN, I will introduce our objective and goals of this technical committee.
Y. Hirayama, H. Okada, T. Yamazato and M. Katayama
8th International Symposium on Power-Line Communications and Its Applications, pp.116-121, Zaragoza, Spain
2004年3月
The noise on power-lines is non-stationary, while the instantaneous noise power in different frequency bands are dependent. Under such noise environments, the instantaneous noise power in a frequency band can be estimated by observing the noise in other frequency bands. In this paper, we propose a receiver structure which uses the estimated instantaneous noise power in the decoding process and show its superiority in BER performance to conventional systems.
H. Shibata, A. Ogawa, T. Yamazato
RISP International Workshop on Nonlinear Circuits and Signal Processing (NCSP), pp.25-28, Honolulu, USA
2004年3月
This paper is concerned with the performance evaluation for the diversity decoding scheme in which space diversity technique and iterative decoding for non systematic convolutional error-correcting code are effectively combined. The concept of the diversity decoding is applied to an OFDM system (e.g. the digital terrestrial TV broadcasting system). This paper shows the performance evaluation for the diversity decoding scheme under multipath environment with OFDM.
H. Takeuchi, T. Yamazato, H. Okada, M. Katayama
RISP International Workshop on Nonlinear Circuits and Signal Processing (NCSP), pp.57-60, Hawaii, USA
2004年3月
This paper evaluates the performance of adaptive MMSE receiver operating in the frequency-domain for(time-domain) DS-CDMA systems. As results, the frequency-domain MMSE receiver shows the robustness of multipath, noise, dynamic channe land the rate change, compared to the time-domain MMSE receiver
Technical Report of IEICE, vol.SAT2003-122, pp.95-100, Tokyo,Japan
2003年10月
To increase the channel efficiency, most of the Low Earth-Orbital satellites (LEOs) systems use the multibeam antenna and reuse the available channels. But in such systems, a beam handover occurs very frequently and a dropping probability becomes very high compared with the one beam systems. In this paper, we propose the nondropping handover and channel allocation scheme in the above LEOs systems. In the proposed scheme, we allocate an extra idle channel for a new call. Because of the predictable change of channel reuse distances, each user can always use the same channel as before. Furthermore, we propose some cost functions used by channel selection and channel reassignment. For comparison, we show the lower bound of blocking probability by maximal complete dependent set (MCDS). We confirm that the proposed channel selection scheme improves the system performance by computer simulation.
M. Harada, T. Yamazato, H. Okada, M. Katayama, A. Ogawa
IEICE Transactions on Fundamentals, vol.E86-A, no.6, pp.1541-1549
2003年6月
In an attempt to improve the performance under frequency selective fading environment, we develope in this paper an orthogonal frequency division multiplex (OFDM) system in which adaptive interleaving is applied. The adaptive interleaving is a method that assigns symbols adaptively to the subcarriers in order to cope with frequency selective fading based on a channel state information (CSI) sent back from the reception end. The concept of adaptive interleaving is to maximize a free Euclidean distance in the limited interleave size. In this paper, we extend the method by an introduction of bit interleaving and multiple trellis coded modulation (MTCM). MTCM assigns two or more symbols to one trellis branch and shows good performance in frequency selective fading. If we could assign those set of symbols with an aid of the adaptive interleaving, the performance improvement can be expected. Another improvement method considered in this paper is the use of bit interleaving. The bit interleaving techniques randomize the effect of channel more efficiently compared to the case of symbols interleaving. Thus the further performance improvement is expected. One draw back is that since the interleaving process is done in bit level, bit interleaving can not be applied to TCM nor MTCM. In this paper, we mainly focus on adaptive bit and symbol interleaving and discuss the performance from the point of interleaving effect, and the error correcting code (convolutional code and MTCM).
7th International Symposium on Power Line Communications and Its Applications,pp.185-190, Kyoto,Japan
2003年3月
This manuscript discusses on the signaling method for inhouse power-line communication(PLC) system with server-client model. The power-lines considered are three-wire type, and the transmitter of the server is on all of the three wires, while each client receiver of clients is on a pair of power-lines. Because of the mutual coupling between wires, the communication between the transmitter and a receiver is as on two mutually connected channels. Thus transmit diversity technique is introduced to the PLC broad cast system, and the performance of the system with three types of coding schemes for transmit diversity technique is compared by numerical examples.
Y. Hirayama, H. Okada, T. Yamazato and M. Katayama
7th International Symposium on Power-Line Communications and Its Applications, pp.142-147, Kyoto, Japan
2003年3月
This manuscript reports the results of the measurement of wide-band PLC noise with high speed (50MHz) sampling and long (10.4s) observation duration. The measured noise is divided in frequency, and stochastic properties of the noise waveforms in each frequency bands, such as autocorrelations, probability density functions, and correlation coefficients between noise waveforms of different frequency bands are discussed. Cyclostationary features of the noise in each band is confirmed. It is found that the amplitude distribution in each band is different, and that Gaussian noise model is not a good approximation in higher frequency bands.
C. Zheng, T. Yamazato, H. Okada, M. Katayama, A. Ogawa
IEICE Transactions on Communications, vol.E86-B, no.3, pp.1022-1030
2003年3月
We propose a method to realize soft-decision decoding for hard-detected signals. In this paper, a novel concept is introduced as error-detected reliability. The method is very useful for optical fiber communications (OFC) as hard detection is the only detection method for the OFC systems. We demonstrate our proposed method using the turbo code in which soft information is required for decoding. As a result, the simulation shows slight difference in the range of moderate to high signal-to-noise ratio between the proposed decoding scheme and the conventional turbo decoding scheme. Moreover, the bit error rate of 10-11 can be achieved by serial concatenation of a Reed-Solomon code and a turbo code for Q-factor lower than 8.0 dB with a bandwidth expansion ratio of 33.3%.
C. Zheng, T. Yamazato, H. Okada, M. Katayama, A. Ogawa
IEICE Transactions on Communications, vol.E86-B, no.3, pp.1132-1135
2003年3月
A soft-decision decoding scheme of low-density parity-check codes (LDPC) is proposed for hard-detected signals of optical fiber communication (OFC) systems. Based on the error detection, the proposed scheme converts the received hard-decision into soft reliability for the input of the LDPC decoder, and soft-decision decoding is performed. Simulation results under OFC channels are shown and superior performance is obtained by using the proposed decoding scheme of the LDPC codes.
N. Ichikawa, M. Katayama, H. Okada, T. Yamazato, A. Ogawa
IEICE Transactions on Communications, vol.E86-B, no.2, pp.785-791
2003年2月
This paper describes an analytical method to estimate the amount of interference in multibeam non-geostationary satellite systems. The performance of CDMA is compared with that of FDMA (or TDMA) by employing the maximum acceptable number of users per cell in uplink as a measure. Numerical examples shows that the maximum acceptable number of users in FDMA (or TDMA) systems varies according to the altitude of the satellites, while the performance is insensitive to the altitude in CDMA systems. Then, it is found that the superior multiple access scheme depends on the altitude of the satellite.
IEICE Transactions on Fundamentals, vol.E85-A, no.12 pp.2822-2829
2002年12月
In narrow band power-line communication (PLC) systems, which use frequency band below a few hundred kHz, the noise on power-line is non-white and non-stationary. Under such environment, the performance of Orthogonal Frequency Division Multiplex (OFDM) modulation system is analyzed, and time and frequency dependence of bit error rate (BER) is clarified. In addition, the possibility of performance improvement with the symbol level repetition coding employing cyclo-stationary feature of power-line noise is presented.
Y. Hirayama, H. Okada, T. Yamazato, and M. Katayama
IEICE Transactions on Fundamentals, vol.E85-A, no.12, pp.2868-2876
2002年12月
In this paper, we propose a medium access control (MAC) protocol for multimedia code division multiple access (CDMA) communications. In the proposed protocol, a base station (BS) estimates the instantaneous number of simultaneously transmitted packets in the future slots with exploiting a stochastic property of traffic. In order to carry out this estimation, we employ an adaptive algorithm. We evaluate the performance of the proposed protocol by comparing that with two different cases. One is no estimation case and the other is perfect estimation case. From these results, we clarify the advantage of the proposed MAC protocol.
International Symposium on Information Theory and Its Applications (ISITA), pp.183-186, Xian, China
2002年10月
This paper discusses a scheme in which space diversity technique and iterative decoding for non systematic convolutional error-correcting code are effectively combined. Simulation results of the bit-error-rate performance of this scheme with respect to the punctured convolutional codes under AWGN and Rayleigh fading environment are presented.
C. Zheng, T. Yamazato, H. Okada, M. Katayama, A. Ogawa
International Symposium on Information Theory and Its Applications (ISITA), pp.331-334, Xi'an, China
2002年10月
A soft-decision decoding scheme of low-density parity-check codes (LDPC) is proposed for hard-detected signals of optical fiber communication (OFC) systems. The scheme converts the received hard-decision into soft reliability for the input of the LDPC decoder, and soft-decision decoding is performed. Simulation results under OFC channels are shown and superior performance is obtained by using the proposed decoding scheme of the LDPC codes.
M. Harada, T. Yamazato, H. Okada, and M. Katayama
International Symposium on Information Theory and Its Applications (ISITA), pp.435-438, Xi'an
2002年10月
In this paper, we propose a spread sequence for asynchronous multicarrier code division multiple access (MC-CDMA). In MC-CDMA systems, performance degradation is mainly caused by nonlinear distortion due to high power amplifier (HPA) and multi-user interference. Since the peak envelope power (PEP) of multicarrier signals show large value, it is desirable to reduce the PEP as well as the multiuser interference components. The sequence, we propose, is based on the Hadamard and complementary sequence. Both of sequences are generated by similar procedures. To evaluate the performance of MC-CDMA system applying proposed sequence, we simulate the system under the effect of nonlinear amplifier.
T. Shibata, N. Itoh, M. Fujimoto, N. Suzuki, A. Ogawa, T. Yamazato
International Symposium on Information Theory and Its Applications (ISITA), pp.539-542, Xian, China
2002年10月
In this paper, a novel symbol synchronization scheme for OFDM signals is propsed. The scheme is based on the subtraction operation for the purpose of achieving reliable synchronization and frequence offset detection capabilities with a simple implementation.
N. J. Thomas, H. Okada, T. Yamazato, M. Katayama
Technical Report of IEICE, SST2002-34, pp.45-50, Akiho
2002年10月
A statistical technique to calculate the location of a signal source, e.g. a mobile phone, in a multipath, non--line of sight environment, is proposed. The technique relies on angular spread and relative time of arrival measurements of multipath signals received at a base station antenna array. The source location is estimated using an a priori known statistical model for the distribution of single bounce multipath scatterers around the signal source, and fitting the measured channel impulse response received at the base station to this model. Further improvement in location estimation accuracy is demonstrated using the Kalman filter, or time average filter on the time sequence of location estimates in a moving scenario.
In this paper, we propose a novel coding scheme to reduce a peak envelope power of convolutionally coded orthogonal frequency devision multiplexing (OFDM) signals. In this system, convolutionally coded bits are mapped onto symbol sequence. The symbol sequence have multiple symbols which are adjusted so as to show low peak envelope power. Also, applying a set partition to the symbol sequence enable to enlarge an Euclidean distance between each sequence. We evaluate the performance of proposed system under the effect of nonlinear amplifier.
T. Shibata, N. Itoh, M. Fujimoto, N. Suzuki, A. Ogawa, T. Yamazato, M. Harada
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), vol.2, pp.619-623, Lisboa, Portugal
2002年9月
In multimedia wireless communications, various types of traffic are handled. Generally, each of these traffic has a different stochastic property. An access control protocol for multimedia wireless communications, therefore, are required to adopt a stochastic property of multimedia traffic. Conventional access control protocols, however, do not consider such characteristics of multimedia traffic. In this paper, we propose an access control protocol for multimedia CDMA packet communications. The proposed protocol controls the data packet transmissions based on the estimation of the instantaneous number of simultaneously transmitted voice and video packets. This estimation exploits the stochastic property of multimedia traffic. To carry out such estimation, we employ an adaptive algorithm as an estimation method. We evaluate the performance of the proposed protocol by comparing it with the performance in the case where a stochastic property of traffic is not considered.
H. Okada, T. Yamazato, M. Katayama
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), vol.2, pp.941-945, Lisbon, Portugal
2002年9月
A CDMA unslotted ALOHA system is a connectionless-type of CDMA packet communication system. In this system, a user station can transmit a packet asynchronously and randomly, and so the packet birth/death event is one of the most important problems for multiuser detection. We have proposed the CDMA unslotted ALOHA system using an adaptive filter receiver based on minimum mean square error criterion in [8], and shown the improvement in the throughput performance even considering the effect of birth/death event. The ensemble-averaged squared error, however, increases at the point of packet birth. In this paper, we employ interleaving and forward error correction (FEC) coding techniques to mitigate the momentary increase in ensemble-averaged squared error. The use of FEC, however, causes the increase in MAI due to redundancy bits of FEC. Moreover, signal power is reduced under the condition that the energy of an information bit is the same. In such cases, whether an adaptive filter can operate effectively or not interests us. We evaluate the system performance and show that the improvement in throughput is achieved with interleaving and FEC techniques.
C. Zheng, T. Yamazato, H. Okada, M. Katayama, and A. Ogawa
We propose a method to realize the soft-decision decoding for the hard-detected signals. In this paper, a novel concept is introduced as error-detected reliability. The method is very useful for fiber optical communication systems as hard detection is the only detection method for the systems. We demonstrate our proposed method using the turbo code in which the soft information is required for the decoding. As a result, the simulation shows slight difference in the range of moderate to high signal-to-noise ratio between the proposed decoding scheme and the conventional turbo decoding. Moreover the bit error rate of 10^-11 can be achieved by serial concatenation of Reed-Solomon and turbo code for Q-factor lower than 8.0 dB with the bandwidth expansion ratio of 33.3%.
K. Naito, H. Okada, M. Saito, T. Yamazato, and M. Katayama
IEICE Transactions on Fundamentals, vol.E85-A, no.7, pp.1501-1510
2002年7月
We propose a new analytical model of Transmission Control Protocol (TCP) in wireless environments where transmission errors occur frequently. In our proposed model, we consider the exponential increase of a congestion window and the exponential increase of a timeout back-off. Finally, we have clarified the behavior of TCP mechanisms of different versions and TCP throughput characteristics analytically. From our result, the behavior of TCP mechanisms is different in each implementation version. These differences mean that the required characteristics of wireless links are different in each implementation version. Therefore, our proposed model is a base analysis of designing wireless link mechanisms.
T. Kume, T. Yamazato, K. Ban, H. Okada, and M. Katayama
IEEE Wireless Communications and Networking Conference (WCNC), vol.1, pp.379-383, Orlando, USA
2002年3月
In this paper, we propose a new packet recognition and signal acquisition scheme with an adaptive linear filter based on an Least Mean Square (LMS) algorithm for code-division multiple access (CDMA) packet systems. In CDMA systems, conventional receivers with matched filtering suffer from the near-far problem due to multiple access interference (MAI). In general, closed-loop power control is used in order to reduce the influence of the near-far problem. However, closed-loop power control is unsuitable for packet systems. Hence, in order to eliminate the influences of the near-far problem, we focus on an adaptive receiver based on an LMS algorithm for a packet recognition and signal acquisition in CDMA packet systems.
R. Chang, C. Zheng, T. Yamazato, M. Katayama, A. Ogawa
IEICE General Conference, B-5-221, p.672, Tokyo, Japan
Y. Tadokoro, H. Okada, T. Yamazato, M. Katayama, A. Ogawa
IEEE Global Communications Conference (GLOBECOM), vol.5, pp.3173-3177, San Antonio, U.S.A
2001年11月
A packet detection is one of the most important problems in packet communication systems. In a CDMA Unslotted ALOHA system, which is one of the wireless packet communication systems, Multiple Access Interference(MAI) makes the performance of the packet detection worse. To reduce the effect of MAI, we propose a new packet detection scheme in this paper. In this scheme, Successive Interference Cancellation(SIC) is applied. The packet\\\'s signal is detected after the cancellation of MAI using SIC. This proposed scheme gives good performance of the packet detection.
M. Honjo, S. Makido, T. Yamazato, H. Okada, M. Katayama, A. Ogawa
IEEE Global Communications Conference (GLOBECOM), vol.6, pp.3395-3399, San Antonio, USA
2001年11月
In this paper, we propose a hierarchical transmission of video signal using multi-code DS/SS modulation. Assigning an appropriate distribution of transmission energy to DCT coefficients, it is possible to control the picture quality depending on the channel quality. We consider a hierarchical structure based on the variance of DCT coefficient and transmit each coefficient using multi-code DS/SS modulation. The analysis is carried out to show the effectiveness of our scheme using 2-D Gauss-Markov random field, which represents image data. It is shown that by an appropriate energy assignment to each stratum (a branch of multi-code DS/SS), it is possible to maintain picture quality even in bad channel quality.
We consider an adaptive antenna selection scheme for transmit diversity in OFDM systems. In the proposed system, the mapping of the subcarriers to antennas is adaptively operated by transmitter according to the Channel State Information(CSI). The performance of the system is improved greatly with this scheme even in slow fading environment. In addition, major modification is necessary only at the transmitter. This is very advantageous for systems with small terminals.
Y.Tadokoro, H.Okada, T.Yamazato, M.Katayama and A.Ogawa
Technical Report of IEICE, vol.SST2001-41, pp.1-6, Tokyo, Japan
2001年10月
In wireless packet communication systems, it is well known that the system performance(throughput) depends on the errors of packet detection. Moreover, in a CDMA Unslotted ALOHA system, Multiple Access Interference(MAI) has much influence on the performance of packet detection, and the system performance. Our aim is to improve the system performance. To achieve it, we study the new packet detection scheme to reduce the effect of MAI on packet detection in this paper. In the proposed scheme, the effect is reduced by Successive Interference Cancellation(SIC) and the received signal with less MAI is left. The packet's signal is detected for the received signal with less MAI. This scheme gives good performance of the packet detection and throughput.
インターネットでの通信を考えた場合、多くのアプリケーションはTCP(Transmission COntrol Protocol)を利用し通信を行っている。しかし、TCPは有線通信環境下の特性を基に設計されてきたため、無線通信環境では特性が劣化することが知られている。本研究では、無線層としてCDMA(Code-Devision Multiple-Access)を利用した場合、ＴＣＰ層でのスループット特性からCDMA方式の特性がどのように変化するのかについて議論する。また、無線層において誤り訂正機構を導入した場合の特性変化についても議論する
A. Sandouk, M. Harada, H. Okada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transactions on Fundamentals, vol.E84-A, no.7, pp.1723-1731
2001年7月
In this letter, we present bit error analysis (BER) of orthogonal multi-carrier direct sequence code division multiple access (DS-CDMA) system with multi-rate (multimedia) traffic. Analysis is carried out with random signature codes for an AWGN channel. Interference in such a system is severe because all users of all media transmit over the same assigned sub-carriers. This makes the analysis difficult. In our analysis, we divide this interference into different types and carry out our analysis to obtain the BER taking into account all these types. We show that the performance of the system is improved as the number of assigned sub-carriers M increases until a limit where the improvement does not continue even when M increases more. This is because of, as we show, the interference due to other sub-carriers becomes constant even in the case of M->infinite and the interference in a multi-rate multi-carrier system is bigger than that in a single-carrier (M=1) by a factor of pai^2/3.
T. Yamazato (Session Organizer)
International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), Tokushima, Japan
2001年7月
C. Zheng, T. Yamazato, M. Katayama and A. Ogawa
International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC), Tokushima, Japan
2001年7月
In this work, a serially concatenated coding scheme of an outer Reed-Solomon code and an inner high rate Turbo code is proposed for the optical communication systems. The simulation results show the reduction of the error floor influence of the Turbo code. This reduction is due to the outer cascaded Reed-Solomon decoding process and the increase of the interleaver size of the inner Turbo code. The effect of quantization is also considered for inner Turbo decoder. As results, 4-bit quantization is satisfied.
N. Ichikawa, M. Katayama, H. Okada, T. Yamazato, and Akira Ogawa
IEEE International Conference on Communications (ICC), pp.3167-3171, Helsinki, Finland
2001年6月
We compare CDMA and FDMA (or TDMA) schemes in multi-beam non-geostationary satellite systems, taking the effects of antenna patterns on inter-cell interference into consideration. The maximum acceptable number of users per cell in uplink is employed as a measure of the system capacity. We have found that in FDMA (or TDMA) systems the maximum acceptable number of users varies according to the altitude of the satellites, while the performance is insensitive to the altitude in CDMA systems. For this reason, the altitude of the satellites is found to be an important factor for selecting multiple access schemes in non-geostationary satellite systems.
A. Sandouk, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transactions on Communications, vol. E84-B, no. 6, pp. 1588-1595
2001年6月
In this letter, performance evaluation of a system that combines between Code-Division Multiple Access (CDMA) and ALOHA protocol in multimedia networks is presented. In our analysis, we compare the performance between the two basic techniques of ALOHA protocol, i.e., Slotted-ALOHA (S-ALOHA) and Unslotted-ALOHA (U-ALOHA), when combined with CDMA scheme to support voice and data users operating in same CDMA channel. The quality of service (QoS) required for voice and data media is completely taken care of. We obtain the throughput of data media, and the outage probability for voice considering both voice and data offered loads. Throughput performance of S-ALOHA technique is almost twice of that of U-ALOHA. However, we show in this letter that when we combine CDMA with the two basic techniques of ALOHA to accomplish multimedia transmission, both techniques have almost same performance. And, thus, CDMA U-ALOHA can be a good candidate for multimedia networks.
S. Makido, T. Yamazato, H. Okada, M. Katayama, and A. Ogawa
IEEE International Symposium on Circuit and Systems, vol.IV, pp.136-139, Sydney, Australia
2001年5月
In this paper we will discuss the MAP receiver design for the reception of the image signal. It is impractical to use the MAP algorithm for the source detection because of its huge calculation costs. To solve this problem we propose a novel MAP receiver structure, where the receiver contains a predictor within it. With an aid of the predictor we can reduce the calculation. Furthermore we can approximate the a priori probability by the prediction error distribution.
K. Naito, H. Okada, T. Yamazato, M. Katayama, and A. Ogawa
IEEE Vehicular Technology Conference (VTC-Spring), vol.3, pp.2128-2132, Rhodes Island, Greece
2001年5月
In this paper, we propose a new analytical model for the TCP, and analyze the bulk throughput performance of different versions of TCP Transmission Control Protocol), viz., Tahoe, Reno and NewReno. We focus on the performance of a single wireless TCP connection which has random segment losses. In our analytical model, we model the TCP mechanisms as a Markov chain. In our result, we found that TCP Tahoe, Reno and NewReno have similar performance with random segment losses. This will lead us to design a lower layer mechanisms.
渡辺崇, 内山知実, 山里敬也, 梶田将司, 岡田啓, 外池俊幸, 結縁祥治, 阿草清滋, 濱口毅
昭晃堂
2001年5月
K. Sugimoto, M. Katayama, T. Yamazato, H. Okada
5th International Symposium on Power-line Communications and Its Applications, pp35-40, Scandic Triangeln, Malmo, Sweden
2001年4月
In this manuscript, we employ OFDM (Orthogonal Frequency Division Multiplexing) modulator with the cyclo-stationary Gaussian model for power-line noise. Under this environment, the relation of the bit error rate (BER) to time and frequency is analyzed. In addition, we introduce guaranteed BER as a measure of the performance and show performance improvement by changing the number of sub-carriers and omitting a part of data from transmission.
H. Shi, M. Katayama, T. Yamazato, H. Okada, A. Ogawa
IEICE General Conference, SB-139, pp.17-18, Siga, Japan
2001年3月
Adaptive Subcarrier Assignment(ASA) schemes for OFDM systems with multiple transmit antennas are proposed and compared to the Fixed Subcarrier Selection(FSS)[3] scheme. In the proposed schemes each subcarrier is assigned to one of the transmit antennas adaptively with the priori knowledge of Channel State Information(CSI).
M. Saito, H. Okada, T. Yamazato, M. Katayama, and A. Ogawa
IEICE Transactions on Communications, vol. E84-B, no.3, pp.576-580
2001年3月
In this letter, we present a method to generate sets of sequences suitable for multicode transmission in quasi-synchronous (QS) CDMA systems. We focus on Gold code but extension to orthogonal Gold code is straightforward. We show that by appropriate classification of sequences, it is possible to have sets whose cross correlation is small in QS situations.
Y. R. Senhaji, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transactions on Communications, vol.E84-B, no.3, pp.511-519
2001年3月
A modified version of the SAGE algorithm is presented for joint delay-azimuth-attenuation parameters' estimation in a multiuser DS-CDMA system. The introduced modification consists of using different time interval lengths when calculating the time correlations for optimizing the different channel parameters. This modification was proposed for the purpose of a further reduction in the algorithm's computational weight in case of receiving sufficiently resolvable waves. Specifically, we found that short interval windows are sufficient for estimating delays and azimuth angles, which is quite effective in reducing the computational burden in their optimization processes. As for the estimation of the attenuation parameters, a longer time window, equal to the preamble length, is considered for more accurate estimation. Also two other estimators are proposed. The first one combining the modified SAGE with a sequential estimation of the attenuation parameters, suitable for slowly varying channels. Another one, similar to the first, and primarily designed to alleviate the influence of present strong interferers. Through a numerical example, the performances of the three presented estimation schemes, in terms of their near-far resistance, are compared. And it is shown that the proposed second combined estimator outperforms the modified SAGE in environments with high MAI levels.
A. Sandouk, M. Harada, H. OKada, T. Yamazato, M. Katayama, A. Ogawa
Technical Report of IEICE, vol.SST2000-87, pp.137-142, Yokosuka, Japan
2001年3月
In this work, orthogonal multi-carrier direct sequence code division multiple access (DS-CDMA) system with multi-rate traffic is presented. Interference in such a system is severe because all users of all media transmit over the same assigned sub-carriers. We divide this interference into different types and analyze the system to obtain the bit error rate (BER) with random signature codes for an AWGN channel taking into account all interference types.
IEICE Transactions on Fundamentals, vol.E84-A, no.2, pp.653-659
2001年2月
We propose the analytical calculation method of average packet success probability of CDMA slotted ALOHA systems, which derives accurate probability, and that is applicable to the system with any spreading codes and any amplitude distributions. In the method, we consider the bit-to-bit dependence of amplitude of signals, used spreading sequences, relative timing delays, and relative carrier phases. This bit-to-bit dependence is the case that the parameters above mentioned are constant for a slot time. By using the method to obtain the average packet success probability, we derive useful throughput performance of CDMA slotted ALOHA systems on fading channel, and show that the normalized throughput becomes worse in the case of larger spreading factor.
Y. R. Senhaji, T. Yamazato, M. Katayama, and A. Ogawa
IEEE Global Communications Conference, vol.3, no.3, pp.1483-87, San Francisco, California, U.S.A.
2000年11月
A modified version of the SAGE algorithm applied for joint estimation of delays, incidence azimuths and attenuation parameters characterizing the channel is presented. The modifications are based on using different observation intervals in optimizing the parameters and using time correlation in estimating delays, for the purpose of a further reduction in SAGE's computational weight, and improving its accuracy in delay estimation. We show analytically that short observation intervals are sufficient for optimizing the delays and the azimuths, and verify through simulation the reliability of using time correlation. Two other estimators are proposed combining the modified SAGE with a sequential estimation of the attenuation parameters suitable for slowly varying channels.
Y. Ikai, M. Katayama, T. Yamazato, A. Ogawa
IEICE Transaction on Fundamentals, vol.E83-A, no.11, pp. 2070-2077
2000年11月
In this paper, we study macro/micro diversity techniques for code acquisition of a direct-sequence spread-spectrum signal in an indoor packet communication system. In the system discussed, the base station has several radio ports each with a cluster of antennas, and the terminal also has multiple antennas. The performance in the uplink of this system is analyzed under Lognormal shadowing and flat Rayleigh fading. The numerical results show great performance improvements by proposed diversity techniques. In addition, it is clarified that the mean acquisition time, which is often used as the measure of performance, is not suitable for packet radio systems as it underestimates the necessary preamble length for initial code acquisition.
A. Sandouk, T. Yamazato, M. Katayama, and A. Ogawa
IEICE Transactions on Fundamentals, vol.E83-A, no.11, pp.2085-2092
2000年11月
In this paper, we discuss the access control in multimedia CDMA ALOHA protocol. We introduce a new algorithm for the access control based on Modified Channel Load Sensing Protocol (MCLSP) in an integrated voice and two different classes of data users, high bit rate and low bit rate, exist in a multi-code CDMA Slotted ALOHA system. With our new algorithm, we show that the throughput of high bit rate data users, as well as, the total throughput of the data medium can be optimized and take a maximum value even at high values of offered loads. We also investigate the performance when voice activity detection (VAD) is considered in voice transmission.
Y. Tadokoro, H. Okada, M. Saito, T. Yamazato, M. Katayama, A. Ogawa
International Symposium on Information Theory and Its Applications, pp. 728-731, Honolulu, Hawaii, USA
2000年11月
In CDMA ALOHA system, Multiple Access Interference(MAI) is in existence and it has large influence on the system performance. To suppress the influence, we proposed new system in which SIC is applied to CDMA Unslotted ALOHA. But because of random access and time-short packets, it is very difficult to detect packet existence perfectly. So, in this paper, we evaluate the influence of detection error of packet existence in proposed system by throughput performance.
T. Wada, and T. Yamazato
International Symposium on Information Theory and Its Applications, pp.576-579, Honolulu, USA
2000年11月
In this paper, we deal with the constant amplitude orthogonal multicode systems. The constant amplitude transmission has the advantage of the high power efficiency because the high power amplifier which has non-linear characteristic can be applied for the amplification of the signals. In this paper, we show the bent sequences can achieve the constant amplitude transmission and also show the effectiveness of the constant amplitude transmission in terms of symbol error rate.
W.Z. Wang, T. Yamazato, C. Zheng, H. Okada, M. Katayama, and A. Ogawa
International Symposium on Information Theory and Its Applications, pp.964-967, Honolulu, Hawaii, USA
2000年11月
In this paper, we propose a new diversity reception and decoding scheme for a convolutionally encoded signal. Aiming at obtaining an additional gain by combining diversity reception and decoding technique, we extend notion of space diversity technique to error correction coded signal and consider an iterative decoding. As a result, we have found $2.0$ dB coding gain in 2 path Rayleigh fading channels at BER $=10^{-5}$ after 6 iterations. This reception technique is particularly useful when used in mobile communications.
Y. R. Senhaji, T. Yamazato, M. Katayama, and A. Ogawa
IEICE General Conference, SB-11-4, pp. 525-526, Nagoya Institute of Technology, Japan
2000年10月
Many valuable sub-optimum schemes for multiuser demodulation of CDMA systems have been proposed. Among these schemes, there is the Multi-Stage receiver described by Varanasi for asynchronous systems, which proved to be computationally efficient compared with the optimum maximum-likelihood receiver. Other sub-optimum multiuser detectors were proposed by Nelson, based on the expectation-maximization (EM) approach. These EM-based multiuser receivers showed, similarly to the Multi-Stage receiver interesting performance improvements, as well as good resistance against near-far situations. However, the EM-based demodulation schemes were debated in the special case of synchronous CDMA systems only. In this work, we present the EM and its extended version, the space-alternating generalized EM (SAGE) algorithms for multiuser detection of the more general situation of asynchronous CDMA systems.
H. Shi, H. Oowa, M. Katayama, H. Okada, T. Yamazato, and A. Ogawa
IEICE General Conference, SB-11-5, pp. 527-528, Nagoya, Japan
2000年10月
Under slow fading environment, FEC which relies on time diversity is not effective. Thus in this paper we introduce a new type of trnsmit diversity scheme which shows its great performance improvement.
M. Harada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transactions on Fundamentals, vol.E83-a, no.10, pp.1992-1995
2000年10月
In this paper, we discuss on the realization of reduced peak power transmission for the multicarrier systems. Since the signals have large amplitude fluctuations in conventional multicarrier systems, signals amplified by a nonlinear amplifier are greatly distorted, resulting in severe performance degradation. In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the nonlinear distortion by using the set of the signal point series which show low peak to mean envelope power ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence detection.
K. Naito, H. Okada, M. Saito, T. Yamazato, M.Katayama, and A. Ogawa
Mobile Multimedia Communications(MoMuC2000), pp.4B-4-1 -- 4B-4-6, Tokyo, Japan
2000年10月
In the INTERNET, TCP (Transmission Control Protocol) is used for a reliable transport protocol. Originally, the TCP has been designed for wired networks, and not for wireless ones. It is reported that the performance of TCP is very poor in wireless environments. In this paper, we propose a new analytical model of the TCP, where the congestion window is modeled as a Markov chain. In the presence of random bit errors on a wireless link, we analyze the throughput of the TCP for the proposed model. Also, in a wireless link, we attempt to employ Reed Solomon code as FEC or Go-Back-N as ARQ, and discuss about throughput of TCP with FEC or ARQ.
M. Saito, T. Yamazato, H. Okada, M. Katayama, and A. Ogawa
Symposium on Information Theory and Its Applications (SITA), vol. 2, 32.1, pp. 555-558, Aso, Kumamoto, Japan
2000年10月
In this study, we introduce classification methods of Gold codes and Gold sequences aiming to generate a pair of Quasi-Synchronous Multi Code (QSMC) sets, suitable for multicode transmission. Each set of QSMC pair have small cross correlation to each other in quasi-synchronous (QS) situation. We mainly focus on Gold code but extension to orthogonal Gold code is straightforward.
H.shi H.Oowa M.katayama H.Okada and T.Yamazato
Symposium on Information Theory and Its Applications (SITA), vol.1, pp.93-96, Aso, Kumamoto
2000年10月
In this paper we introduce a new type of transmit diversity scheme that combines forward error correction code(FEC) with space diversity in OFDM systems. With this scheme, coding uses not only time dimension but also space and frequency diversities. In addition, we consider dynamic assignment of subcarriers to transmit antennas. As the results of simulations under indoor wireless environment with slow and frequency selective fading, we confirm the great performance improvement by the proposed transmit diversity scheme and additional gain with the dynamic assignment of subcarriers.
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, pp.1520-1524
2000年9月
M. Harada, T. Yamazato, M. Katayama, and A. Ogawa
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication, vol. 1, pp. 814-818, London, United Kingdom.
2000年9月
In an attempt to improve the performance under frequency selective fading environment, we propose in this paper an Orthogonal-Frequency-Division-Multiple-Access (OFDM) system in which MTCM (Multiple Trellis Coded Modulation) is applied to a set of multiple subcarriers. The code is designed to enlarge the summation of the Euclidean distance and the product distance. We also propose a scheme for assigning the symbols to subcarriers adaptively based on the channel state information (CSI) fed back from the reception receive end, and evaluate the performance applying these two codes and the proposed scheme under a multipath Rayleigh fading environment.
T. Yamazato, A. Fujiwara, M. Katayama and A. Ogawa
IEEE International Symposium on Spread Spectrum Techniques and Applications, Vol.F3B.5, pp.751-755, New Jersery, USA
2000年9月
In mobile communications, power is a very important factor and non-linear amplification of power amplifier cannot be avoided due to their high power efficiency. HPSK modulation scheme has been proposed as the spreading technique for W-CDMA and cdma2000. HPSK is a complex spreading scheme that is designed to minimize the zero-crossing signal transition. However, there is a possibility that signal transition of HPSK go through zero. In this paper, we propose a new modulation scheme for W-CDMA and cdma2000. The scheme is based on HPSK, but we modified the complex scrambling to avoid zero-crossing. We call it as modified HPSK (m-HPSK). It is shown that m-HPSK outperforms HPSK in the presence of non-linear amplification.
M. Harada, T. Yamazato, H. Okada, M. Katayama, and A. Ogawa
In this paper, we discuss on the realization of reduced peak power transmission for the OFDM systems. Since the signals have large amplitude fluctuations in conventional OFDM systems, signals amplified by a non-linear amplifier are greatly distorted, resulting in severe performance degradation. In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the non-linear distortion by using the set of the signal point series which show low Peak-to-Mean-Envelope-Power-Ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence (MLS) detection.
C. Zheng, T. Yamazato, M. Katayama, and A. Ogawa
IEICE General Conference, A-5-10, p.146, Nagoya, Japan
2000年9月
The chip-by-chip Turbo coding is a coding scheme for DS/SS systems. The input data is first spread by spreading sequence and then fed into the Turbo code which operates in chip timing. We would have long sequence length in Turbo code to improve the performance. The main problem to realize this coding scheme is how the received sequence is compensated, since the chip sequence has lower energy than that of bit. In this paper, a correlating operation for the chip-by-chip Turbo coding scheme is proposed. The coded sequence is transmitted repetitively. Thus the repetitive coding affects as a compensation due to the correlation of received chips. The correlating effects are discussed.
T. Hara, M. Katayama, H. Okada, T. Yamazato, A. Ogawa
Third European Workshop on Mobile/Personal Satcoms, pp.215-220, London, UK
2000年9月
In Low Earth-Orbital(LEO) satellite mobile communication systems, one of the most important technical issues is handover between cells formed by spot-beams of a satellite. In this study, we proposed a three-layered hierarchical channel structure to improve handover performance of a LEO satellite system. Uniform and non-uniform distributions of users are considered in analysis the system performance. As the result, it is shown that the hierarchical channel structure improves overall performance and mitigates performance degradation caused by non-uniformity of user distribution.
K. Mori, T. Kobayashi, T. Yamazato, A. Ogawa
Wireless Communications and Networking Conference, pp.321-326
IEICE Transactions on Communications, vol.E83-B, no.8, pp.1697-1704
2000年8月
We study the joint optimization problem of a transmitter with multiple transmit antennas and a receiver with multiple receive antennas in a narrow-band communication system. We discuss the problem of designing a pre-filter at the transmitter, a post-filter at the receiver, and a bit allocation pattern to multiple symbols in the sense of minimizing the average bit error rate. With the optimized filters and the bit allocation, we could realize high efficiency and high data rate in band-limited channels.
K. Mori, T. Kobayashi, T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E83-B, no.7, pp.1445-1453
2000年7月
Site diversity causes unfairness in packet reception that depends on the location of the mobile stations in the up-link of CDMA cellular packet communication systems. This paper proposes an adaptive transmit permission probability control scheme that reduces this unfairness in CDMA cellular slotted-ALOHA systems with site diversity. The proposed scheme adaptively controls the transmit permission probability according to the offered load and the location of the mobile stations. Successful packet reception rate, fairness coefficient and throughput performance are evaluated in fading environments with imperfect power control. Computer simulation shows that adaptive transmit permission probability control improves fairness of service for all mobile stations and throughput performance across all channel loads compared with the conventional scheme.
4th International Symposium on Power-Line Communications and its Applications, pp.123-127, , Limerick, Ireland
2000年4月
This manuscript introduces a mathematically tractable and accurate model of power-line noise, in which the nose is expressed as the sum of cyclostationary Gaussian processes. This model can represent non-stationary power-line noise with a small number of parameters and generate the waveforms which achieve good agreement with actually measured noise waveforms. In this manuscript, parameter determination method is explained and then necessary observation length, influence of the frequency of a reference signal, and fidelity of determined parameters are discussed.
K.Ono, M. Katayama, T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E83-B, no.4, pp.782-790
2000年4月
In this paper, we analytically study the effects of overlap and overlay structure on the quality of service (QoS) of Low Earth-Orbital Satellite (LEOS) communication systems. We consider two-layered overlay of cells and intentional overlap of neighboring small cells. In order to measure the QoS, the probabilities of rejection of a newly arrived call (blocking) and forced termination due to failure of a handover (call dropping) are derived. In addition to these measures, the largest traffic intensity which guarantees the required blocking and dropping probabilities is also used.
IEEE Global Communications Conference, pp.655-660, Rio de Janeiro, Brazil
1999年12月
A. Morimoto, M. Katayama,T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E82-A, no.12, pp.2687-2696
1999年12月
This paper discusses the employment of adaptive array antennas at the base station of a Multi Processing Gain (MPG) CDMA system. It is shown that the adaptive array antenna with the weight control scheme based on the signal before despreading procedure does not increase but even decreases the performance than that with an omni-directional antenna, and the cause of this serious performance degradation is revealed. Then it is shown that the performance with the weight control scheme based on the signal after despreading procedure is always better than that with an omni-directional antenna. Furthermore, the possibilities of performance improvement by the combination of adaptive array antenna and interference cancellation techniques are mentioned.
Y. Ikai, M. Katayama,T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E82-A, no.12, pp.2728-2734
1999年12月
In this paper, we propose the introduction of space diversity techniques to the code acquisition of a direct-sequence spread-spectrum signal. In this scheme, both a transmitter and a receiver have multiple antennas and the signals corresponding to all the combinations of the transmitter and receiver antennas are combined at the acquisition circuit of the receiver. The performance is evaluated for an indoor packet radio communication system from the viewpoints of the average time for acquisition, the probability of success of acquisition, and the necessary preamble length. As the result, we show great performance improvements by the proposed scheme under slow and flat Rayleigh fading environment.
K. Mori, T. Kobayashi, T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E82-B, no.12, pp.1964-1973
1999年12月
C. Zheng, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E82-A, no.12, pp.2751-2757
1999年12月
Most of error correcting codes applying to DS/SS systems are such that information data is first (bit-by-bit) encoded and then spread by pseudo noise (PN) sequence. Thus, coding gain achieved by such systems are mainly due to the error correcting codes and the redundancy produced by the spreading codes shows no effect on the coding gain. In this paper, a chip-by-chip Turbo coding for DS/SS systems is proposed. The input information data is first spread by PN sequence and then fed into the Turbo-encoder which operates in chip timing. As the Turbo-encoder operates in chip timing, a large interleaving size would be obtained, which improves the performance. As results, superior performances with coding gain of more than 3.0 dB and 5.0 dB for AWGN and Rayleigh-fading channel, respectively, were found with short frame size of information data.
H. Hiraiwa, M. Katayama,T. Yamazato, A. Ogawa
IEICE Transaction on Fundamentals, vol.E82-A, no.12, pp.2774-2777.
1999年12月
The design of a liner decorrelating detector for multi-processing gain code-division multiple-access (MPG-CDMA) systems is proposed, and its performance is discussed. As the result, the performance improvement by this detector is confirmed. Also, it is found that that the degrees of the noise enhancement depend on the processing gains of the signals.
王偉忠, 山里 敬也, 片山 正昭, 小川 明
情報理論とその応用シンポジウム, pp.165-168
1999年12月
原田政明, 山里敬也, 片山正昭, 小川明
情報理論とその応用シンポジウム, pp.563-566
1999年12月
松井宗大, 山里敬也, 片山正昭, 小川明
情報理論とその応用シンポジウム, vol.1, pp.13-16
1999年12月
K. Mori, T. Kobayashi, T. Yamazato, and A. Ogawa,
IEEE International Workshop on Mobile Multimedia Communications (MOMUC'99), pp.35-42, San Diego, California, USA
1999年11月
N. Ichikawa, M. Katayama T. Yamazato and A. Ogawa
International Symposium on Communications, pp.534-538 Kaohsiung, , Kaohsiung, Taiwan
1999年11月
山里敬也
Proc. of 2001 Microwave Workshops and Exhibition, MWE2001., パシフィコ横浜
1999年11月
移動体通信の急速な需要増加のため、現行のシステムではほぼ通信容量の限界にまで達してきている。また、音声やデータ、画像などの伝送ができるマルチメディア移動体通信への要求も高まっている\cite{trikepsu}-\cite{adachi-JSAC98}。以上を背景に、現在、次世代移動体通信システムの研究開発が活発に行われているが、その殆どが符号分割多元接続(Code Division Multiple Access : CDMA)方式をベースにしたシステムである。CDMA方式が脚光を浴び始めたのはアメリカのQualcom社が米国での新しい自動車・携帯電話システム（現在ではcdmaOneと呼ばれている）を提唱した1990年頃からである．当時、アメリカではアナログＦＭ方式を用いたAMPS(Advanced Mobile Phone System)を使ったセルラ方式が運用されていたが、セルラ無線用の周波数がニューヨーク、ロサンゼルス、シカゴなどの大都市で著しく不足しており、周波数利用効率の高いセルラシステムが渇望されていた．このため、AMPSの３倍の加入者数増の望めるFDMA/TDMA混在方式の検討がすすめられていた．ところが、Qualcom社はそのセールトークの中でAMPSに比べ収容加入者数が18倍にも達する、と述べたのである．18倍という数字はいささか大袈裟な感もあるが、それ以降、CDMA方式の研究が盛んに行われる様になったのは事実である。日欧を中心に開発がすすんでいる広帯域CDMA(W-CDMA)は、世界標準の無線伝送技術として2001年の実用化をめざし、急ピッチで開発が行われている\cite{adachi-JSAC98}。本稿では、CDMA方式の基礎について解説する。特にCDMAの特性を向上させる基礎技術について解説し、FDMA, TDMAとの比較を通してCDMAの特徴を明らかにする。
山里敬也, 梶田将司, 濱口毅, 結縁祥治
情報処理学会研究報告, vol.DMS99-16, pp.55-60
1999年11月
松原一雄，片山正昭，山里敬也，小川明
電子情報通信学会技研報告, vol.SR99-19, pp.67-72
1999年11月
A. Sandouk, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Communications, vol.E82-A, no.10, pp.2105-2114
1999年10月
柴田伝幸, 伊藤修朗, 藤元美俊, 伊藤秀昭, 鈴木徳祥, 山里 敬也, 小川 明
電子情報通信学会技研報告, vol.RCS99-135, pp.97-101
1999年10月
山里敬也，鄭辰、片山正昭、小川明
1999年電子情報通信学会ソサエティ大会, vol.A-5-14, p.97
1999年9月
Y. Ikai, M. Katayama, T. Yamazato and A. Ogawa
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), pp.1526-1530, Osaka, Japan
1999年9月
Youssef R. Senhaji, H. Okada, T. Yamazato, M. Katayama and A. Ogawa
IEEE International Symposium on Personal, Indoor and Mobile Radio Communication (PIMRC), vol.3, pp.982-986, Osaka, Japan
1999年9月
The concept of diversity in space using adaptive array antennas at the base stations of wireless communication systems have long been debated, and have demonstrated great ability in increasing system capacity, as well as suppressing interferences from undesired users. But, yet the increasing demand for mobile communication services with more improvements in performance is motivating the search for new techniques. This paper shows that implementing array antennas at both the base and mobile stations in a cellular CDMA system results in a substantial increase in capacity over the conventional system using the array antennas at the base station only.
Second International Symposium on Wireless Personal Multimedia Communications (WPMC'99), vol. 1, no. 9.5, pp. 354-359, Amsterdam, The Netherlands
1999年9月
M. Honjo, S. Makido, T. Yamazato, M. Katayama and A. Ogawa
Second International Symposium on Wireless Personal Multimedia Communications (WPMC), vol. 1, no. 4.2, pp. 214-218, Amsterdam, The Netherlands
1999年9月
In this paper, we propose a new video coding system which maintains picture quality and keeps frame rate. In the event of error, the system requests only high priority frame data for retransmission. Low priority frame data is positively discarded. This discarding frame data helps not to lower the frame rate, while it is important to maintain the picture quality to some extent. We realize such by the coding algorithm which processes on the premise of the discarded frame data. The simulation results shows that proposal system is more efficient in wireless communications.
原田政明, 山里敬也, 片山正昭, 小川 明
電子情報通信学会技研報告, vol.SST99-32, pp.13-18
1999年9月
田所幸浩, 岡田啓, 齋藤将人, 山里敬也, 片山正昭, 小川 明
電子情報通信学会技研報告, vol.SST99-34, pp.25-30
1999年9月
森香津夫, 小林岳彦, 山里敬也, 小川 明
電子情報通信学会技研報告, vol.RCS99-91, pp.29-36
1999年8月
原田政明, 山里敬也, 片山正昭, 小川 明
電子情報通信学会技研報告, vol.IT99-34, pp.7-12 (1999-07)
1999年7月
齋藤将人, 山里敬也, 片山正昭, 小川 明
電子情報通信学会技研報告, vol.SST99-21, pp.37-42 (1999-07)
1999年7月
A. Sandouk, H. Okada, T. Yamazato, M. Katayama, and A. Ogawa
IEEE International Conference on Communications (ICC), pp.1079-1083, Vancouver, Canada
Technical Report of IEICE, vol.SST99-8, 06.1999, pp.49-54, Nagoya, Japan
1999年6月
小川 明, 山里 敬也, 岡田 啓, 片山 正昭
電子情報通信学会衛星通信研究会, vol.SAT99-41, p.99 (1999-06)
1999年6月
市川 直樹, 片山 正昭, 山里 敬也, 小川 明
電子情報通信学会技研報告, vol.SAT99-39, pp.83-90 (1999.6)
1999年6月
Y. R. Senhaji, T. Yamazato, M. Katayama, and A. Ogawa
1999 IEICE General Conference, vol.B-5-37, p.388, Keiyou-Univ, Japna
1999年3月
In this work, we are concerned with inhancing transmission performance from a mobile towards a base station. Aware of its ability to concentrate radiation power at desired transmit directions by reducing power at undesired ones, we propose the use of an adaptive array antenna at a mobile station supported by an eigenstructure based algorithm for updating transmission beams. After introducing the beamforming algorithm, we show through comparison with the conventional omnidirectional system that our proposed one can insure heigher received power at the base station with similar dynamic range.
本庄勝, 牧戸知史, 山里敬也, 片山正昭, 小川明
1999年電子情報通信学会総合大会, vol. B-5-243, pp. 594, 慶応大学日吉キャンパス
In wireless video transmission, powerful forward error correction such as TURBO code may be used to avoid the effect of channel errors. But it may not be appropriate for successive video signal processing because of its complexity. In this paper, we propose a new decoding scheme for compressed video signal with TURBO code. Powerful error correction can be achieved as a result of recursive decoding structure of TURBO code. In proposed scheme, reference frame for interframe is decoded by alternative H.263 decoder and TURBO decoder. Thus, error correction may be achieved more as a result of longer decoding process time by TURBO decoder.
T. Shibata, N. Suzuki, M. Fujimoto, K. Nishikawa, T. Yamazato and A. Ogawa
Asia-Pacific Microwave Conference, vol.3, pp.853-856, Yokohama, Japan
1998年12月
A. Makido, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Communications, vol.E81-B, no.12, pp.2283-2289
1998年12月
A. Sandouk, T. Yamazato, M. Katayama, and A. Ogawa
A CDMA unslotted ALOHA system with finite size of queueing buffers is discussed. We introduce an analytical model in which the system is divided into two Markov chains; one is in user part, and the other is in channel part. We analyze the queueing system using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, rejection probability and average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.
H. Okada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E81-A, no.10, pp.2083-2091
1998年10月
CDMA unslotted ALOHA system with finite size of queueing buffers is discussed in this paper. We introduce an analytical model in which the system is divided into two Markov chains; one is in the user part, and the other is in the channel part. In the user part, we can model the queueing behavior of the user station as an M/G/1/B queue. In the channel part, we can consider the number of simultaneously transmitted packets as an M1+M2/D/infinity//K queue. We analyze the queueing system by using this analytical model, and evaluate the effect of buffer capacity in terms of the throughput, the rejection probability and the average delay. As a result, increase in the buffer size brings about an improvement in the grade of service in terms of higher throughput and lower rejection probability.
T. Wada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E81-A, no.10, pp.2166-2169
IEICE Transaction on Fundamentals, vol.E81-A, no.7, pp.1473-1478
1998年7月
In this paper, CDMA slotted ALOHA system with finite size of buffers is proposed. To analyze the system performance, we use the linear approximate solution based on restricted occupancy urn models. We evaluate the system performance in terms of throughput, average delay, and rejection probability and clarify the effect of buffer capacity.
In this paper, we analyze the CDMA slotted ALOHA systems with finite buffer and finite population assumptions by expanding the linear approximate solution based on restricted occupancy urn models. We evaluate the system performance in terms of throughput, average delay, and rejection probability. Moreover, we clarify the effect of buffer capacity by changing the buffer size.
International Symposium on Power-Line Communications and its Applications, pp.115-222, Tokyo, Japan
1998年3月
牧戸知史, 山里敬也, 片山 正昭, 小川 明
電子情報通信学会技研報告, vol.SST97-117, pp.19-24 (1998-03)
1998年3月
森本彰人, 片山正昭, 山里敬也, 小川明
電子情報通信学会技研報告, vol.A・P97-215, pp.101-108 (1998-02)
1998年2月
張立嵩, 片山正昭, 山里敬也, 小川明
電子情報通信学会技研報告, vol.CS97-165, pp.119-124 (1998-01)
1998年1月
牧戸知史, 山里敬也, 片山正昭, 小川明
電子情報通信学会技研報告, vol.CS97-173, pp.37-42 (1998-01)
1998年1月
1997
T. Wada, T. Yamazato, M. Katayama and A. Ogawa
Asia-Pacific Conference on Communications (APCC), vol.1, pp.362-366, Sydney
1997年12月
H. Hiraiwa, M. Katayama, T. Yamazato and A. Ogawa
Asia-Pacific Conference on Communications (APCC), vol.3, pp.1611-1615, Sydney
1997年12月
K. Ban, M. Katayama, T. yamazato and A. Ogawa
IEICE Transaction on Communications, vol.E80-B, no.12, pp.1790-1796
1997年12月
A. Ogawa, M. Katayama, T. Yamazato, A. Jamalipour
IEICE Transaction on Fundamental, vol.E80-A, no.12, pp.2347-2356
1997年12月
This paper is concerned with CDMA applied to personal and mobile communications on a global basis using multiple low earth orbital satellites (LEOS). We focus our attention on some unique aspects of LEOS systems and discuss their influences on the CDMA system performance as well as the techniques for coping with these aspects. We deal with three kinds of important items that are unique to LEOS systems; Doppler frequency shift due to satellite movement, propagation delay affecting packetized data transmission and geographical nonunifomity in traffic.
K. Ban, M. Katayama, W .E .Stark, T. Yamazato, A. Ogawa
IEICE Transaction on Fundamentals, vol.E80-A, no.12, pp.2437-2444
1997年12月
T. Wada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E80-A, no.12, pp.2477-2484
1997年12月
T. Sato, S. Abbas, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E80-A, no.12, pp.2500-2516
1997年12月
H. Niwa, O. Oono, M. katayama, T. Yamazato, A. Ogawa, N. Isaka
IEICE Transaction on Fundamentals, vol.E80-A, no.12, pp.2526-2533
1997年12月
M. M. Asadullah Galib, Takaya Yamazato, Masaaki Katayama, Akira Ogawa
The 20th Symposium on Information Theory and Its Applications, 5-4-7, pp.597-600 (1997-12)
IEEE Journal on Selected Areas in Communications, vol.14, no.9, pp.1748-1757
1996年12月
I. Wakaki, T. Ishiguro, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E79-A, no.12, pp.1957-1962
1996年12月
H. Okada, M. Saito, T. Sato, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E79-A, no.12, pp.2035-2042
1996年12月
The one of the problems in the satellite packet communication system is the existence of a long time delay, which may cause an improper packet access control resulting in a great deal of degradation of the system performance. In this paper, we clarify the effect of long time delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we show that a significant improvement in the throughput performance was obtained with MCLSP even in the presence of a long time delay.
The one of the problems that arise in the satellite packet communication system is the existence of a long access timing delay. In this paper, we clarify the effect of this access timing delay on the performance of CDMA ALOHA systems and then propose a new access control protocol, called Modified Channel Load Sensing Protocol (MCLSP), for the CDMA ALOHA systems. As a result, we found that by employing MCLSP, a significant improvement in the throughput performance was obtained even in the presence of a long access timing delay.
浅井 裕介, 西田 邦生, 山里 敬也, 片山 正昭, 小川 明
1996年電気関係学会東海支部連合大会, 511
1996年10月
K. Kashyap, T. Wada, M. Katayama, T. Yamazato and A. Ogawa
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), pp.492-496
IEICE Transaction on Communications, vol.E79-B, no.9, pp.1248-1255
1996年9月
M. Ichiba, M. Katayama, T. Yamazato, A. Ogawa
IEICE Transaction on Communications, vol.E79-B, no.9, pp.1333-1338
1996年9月
T. Sato, H. Okada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Communications, vol.E79-B, no.9, pp.1339-1345
1996年9月
T. Wada, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E79-A, no.9, pp.1415-1422
1996年9月
T. Wada, T. Yamazato, M. Katayama and A. Ogawa
International Symposium on Information Theory and Its Applications (ISITA), pp.770-773
1996年9月
A. Ogawa, T. Yamazato, K. Nishida, H. Okada, T. Sato and M. Katayama
Japan-Canada International Workshop on Multimedia Wireless Communications and Computing, pp.23-24
1996年9月
A. Jamalipour, M. Katayama, T. Yamazato and A. Ogawa
XXVth General Assembly of the International Union of Radio Science, C8.3, p157
1996年8月
H. Okada, T. Sato, T. Yamazato, M. Katayama and A. Ogawa
2nd International Workshop on Multi-Dimensional Mobile Communications, pp.391-395, Seoul, Korea
1996年7月
A novel access control method for CDMA unslotted ALOHA systems is presented. We analyze the throughput performance considering packet retransmission and the stability of the systems. Based on these results, we propose an optimal access control protocol (OACP). The OACP is the method controlling the packet transmission and the packet retransmission. As a result, we indicate that the throughput performance with OACP is better before.
H. Okada, T. Sato, T. Yamazato, M. Katayama, A. Ogawa
IEICE Transaction on Fundamentals, vol.E79-A, no.7, pp.1004-1010
1996年7月
In this paper, we analyze the throughput and delay performances of the CDMA unslotted ALOHA system considering packet retransmission. We also clarify the stability of the system. Based on these results, we propose the optimal retransmission control (ORC) to improve the performances. The ORC is the scheme to prevent the system from drifting to an undesirable operating point by controlling the birth rate of retransmitted packets. As a result, it is shown that the throughput and delay performances of the system with the ORC are better than without the ORC and the system does not drift to an undesirable operating point.
若木 勇, 山里 敬也, 片山 正昭, 小川 明
電子情報通信学会技研報告, vol.SST96-34, pp.37-42 (1996-07)
1996年7月
A. Jamalipour, M. Katayama, T. Yamazato and A. Ogawa
IEEE International Conference on Communications (ICC), pp.1740-1744