Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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Direct wireless link to out-of-range node with assistance of surrounding nodes Reviewed Open Access

Hiroya Tanaka, Shintaro Hiraoka, Shintaro Arai, Takaya Yamazato, Yukihiro Tadokoro

IEEE Transactions on Vehicular Technology Vol. 68 ( 11 ) page： 10703 - 10712 2019.11

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

We propose a method that establishes a direct wireless link from a transmission source to an out-of-range destination with the assistance of the surrounding communication nodes. In this method, a weak (subthreshold) signal is amplified by utilizing the interference signals transmitted from the surrounding communication nodes. To evaluate the amplification gain, we study the mutual information in a multipath fading channel. As a result, we reveal that the mutual information is enhanced owing to the interference signals, and the proposed method enlarges the radio coverage area of the source node. To understand the enhancement mechanism, we introduce a toy model of the propagation channel and discuss the role of the interference signals. We find that the interference signals allow the subthreshold signals into the detectable region in the signal space. Moreover, the mutual information is maximized at the optimal power of the interference signals. In addition, a detailed discussion of the channel capacity shows that there exists an optimal a priori probability of symbol transmission.

DOI： 10.1109/TVT.2019.2934502

Proposal for Identification Scheme of Driver and Impostor based on Acceleration Data Reviewed

Yuki Mori, Ryota Ono, Takuya Mitani, Katsuhiro Naito, Takaya Yamazato

IEEE International Conference on Connected Vehicles and Expo:ICCVE 2019 2019.11

Proposal for identification scheme of driver and impostor based on acceleration data Reviewed

Mori Y.

2019 8th IEEE International Conference on Connected Vehicles and Expo, ICCVE 2019 - Proceedings 2019.11

Noise-aided demodulation of direct spread-code division multiple access signals with a 1bit analog-to-digital converter Reviewed

Yasuo NAKASHIMA, Takaya YAMAZATO, Shintaro ARAI, Hiroya TANAKA, Yukihiro TADOKORO

IEICE TRANSACTIONS on Communications Vol. J102-B ( 8 ) 2019.8

High performance demodulation method with less complexity for image-sensor communication Reviewed Open Access

Ohira Yuki, Yendo Tomohiro, Arai Shintaro, Yamazato Takaya

OPTICS EXPRESS Vol. 27 ( 15 ) page： 21565 - 21578 2019.7

MD2.3-visible light communication and ranging system using high-speed stereo cameras (Invited) Reviewed

Masayuki Kinoshita, Koji Kamakura, Takaya Yamazato

IEEE Photonics Society Summer Topical Meeting Series 2019, SUM 2019 2019.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Electrical and Electronics Engineers Inc.

We will introduce an integrated system of visible light communications (VLC) and ranging using high-speed stereo imaging. The system simultaneously decodes VLC signal while its source tracking portion outputs range information.

DOI： 10.1109/PHOSST.2019.8794881

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{For the applications of Stochastic resonance in the telecommunications Reviewed

IEICE TRANSACTIONS on Communications Vol. J102-B ( 6 ) page： 445 - 458 2019.6

Maximum Likelihood Decoding Based on Pseudo-Captured Image Templates for Image Sensor Communication Reviewed Open Access

Shintaro ARAI, Haruna MATSUSHITA, Yuki OHIRA, Tomohiro YENDO, Di HE, Takaya YAMAZATO

Nonlinear Theory and Its Applications, IEICE Vol. 10 ( 2 ) page： 173 - 189 2019.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

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.

DOI： 10.1587/nolta.10.173

Parallel Transmission Using M-Point DFT for Image-Sensor-Based Visible Light Communication Reviewed

Syuto Kibe, Koji Kamakura, Takaya Yamazato

2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings 2019.2

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Electrical and Electronics Engineers Inc.

This paper proposes a parallel transmission (PT) system using M-point discrete Fourier transform (DFT) for image-sensor-based (IS-based) visible light communications (VLC). We make use of M-point inverse DFT (IDFT) to generate pulse width modulation (PWM) signals transmitted by M spatially aligned LEDs. The M PWM signals are pre-calculated to give N phase shifted carriers after M-point DFT, where N=\\lfloor(M-1)/2\\rfloor and \\lfloor z\\rfloor stands for the maximum integer not exceeding z. Therefore, the IS receiver of a high-speed camera captures the LEDs to obtain the M inputs to the DFT from the luminance values of the captured LEDs. During a symbol interval equal to the exposure time of the high-speed camera, N\\ \\log-{2}P bits in total are simultaneously transmitted between the LEDs and IS-based receiver, when P-ary PSK is used for all the carriers. We experimentally demonstrate our PT system at the distance of nine meters between M PWM-modulated LEDs and a 2000-fps high-speed camera. Our experimental results validate that PSK symbols are demodulated without errors for smaller values of M and P, with controlling the aperture of the lens of the camera receiver.

DOI： 10.1109/GLOCOMW.2018.8644501

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Performance Evaluation of Precoded Pulse Width Modulation for Image Sensor Communication Reviewed

Satoshi Kamegawa, Masayuki Kinoshita, Takaya Yamazato, Hiraku Okada, Toshiaki Fujii, Koji Kamakura, Tomohiro Yendo, Shintaro Arai

2018 IEEE Globecom Workshops, GC Wkshps 2018 - Proceedings 2019.2

Publishing type：Research paper (international conference proceedings)

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.

DOI： 10.1109/GLOCOMW.2018.8644347

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Enhancing a BPSK receiver with Stochastic resonance by employing practical parallel arrayed network Reviewed Open Access

Yukihiro Tadokoro, Hiroya Tanaka, Yasuo Nakashima, Takaya Yamazato, Shintaro Arai

Nonlinear Theory and Its Applications, IEICE Vol. 10 ( 1 ) page： 106 - 114 2019.1

Language：English Publishing type：Research paper (scientific journal) Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

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.

DOI： 10.1587/nolta.10.106

Analysis of Data Collected by the 700 MHz Band Intelligent Transport Systems for Reducing Ambulance Transportation Time Reviewed

Mitani Takuya, Yamazato Takaya, Naito Katsuhiro, Mori Yuki

2019 8TH IEEE INTERNATIONAL CONFERENCE ON CONNECTED VEHICLES AND EXPO (IIEEE CCVE) 2019

Proposal for Identification Scheme of Driver and Impostor based on Acceleration Data Reviewed

Mori Yuki, Ono Ryota, Mitani Takuya, Naito Katsuhiro, Yamazato Takaya

2019 8TH IEEE INTERNATIONAL CONFERENCE ON CONNECTED VEHICLES AND EXPO (IIEEE CCVE) 2019

Noise-aided demodulation with one-bit comparator for multilevel pulse-amplitude-modulated signals Reviewed Open Access

Yasuo Nakashima, Takaya Yamazato, Shintaro Arai, Hiroya Tanaka, Yukihiro Tadokoro

IEEE Wireless Communication Letters Vol. 7 ( 5 ) page： 848 - 851 2018.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

This letter 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 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.

DOI： 10.1109/LWC.2018.2831683

Technical Issues on IEEE 802.15.7m Image Sensor Communication Standardization Reviewed

Trang Nguyen, Amirul Islam, Takaya Yamazato, Yeong Min Jang

IEEE Communications Magazine Vol. 56 ( 2 ) page： 213 - 218 2018.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical and Electronics Engineers Inc.

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.

DOI： 10.1109/MCOM.2018.1700134

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N-Stream Superimposed System with m-Point DFT for Image-Sensor-Based Visible Light Communication Reviewed

Syuto Kibe, Koji Kamakura, Takaya Yamazato

2017 IEEE Global Communications Conference, GLOBECOM 2017 - Proceedings Vol. 2018- page： 1 - 6 2018.1

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Institute of Electrical and Electronics Engineers Inc.

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.

DOI： 10.1109/GLOCOM.2017.8254784

Research data storage URL： http://ieeexplore.ieee.org/document/8254784/

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可視光通信実用化技術 Invited

Takaya Yamazato

電子情報通信学会誌 Vol.101 No.1 Vol. 101 ( 1 ) page： 59-65 2018.1

Simplified Vehicle Vibration Modeling for Image Sensor Communication Reviewed Open Access

KINOSHITA Masayuki, YAMAZATO Takaya, OKADA Hiraku, FUJII Toshiaki, ARAI Shintaro, YENDO Tomohiro, KAMAKURA Koji

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. 101 ( 1 ) page： 176-184 2018

Interference-Aided Detection of Subthreshold Signal Using Beam Control in Polarization Diversity Reception. Reviewed Open Access

Shintaro Hiraoka, Yasuo Nakashima, Takaya Yamazato, Shintaro Arai, Yukihiro Tadokoro, Hiroya Tanaka

IEEE Communications Letters Vol. 22 ( 9 ) page： 1926 - 1929 2018

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

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.

DOI： 10.1109/LCOMM.2018.2851583

A Comparison of Reception Methods for Visible Light Communication Using High-speed Stereo Cameras Reviewed

Kinoshita Masayuki, Yamazato Takaya, Okada Hiraku, Fujii Toshiaki, Arai Shintaro, Yendo Tomohiro, Kamakura Koji

2018 IEEE GLOBAL COMMUNICATIONS CONFERENCE (GLOBECOM) page： . 2018

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Papers - YAMAZATO Takaya