Faculty Profiles - YAMAZATO Takaya

Visible Light Communication Systems Using Blue Color Difference Modulation for Digital Signage Reviewed

Sho Sato, Hiraku Okada, Kentaro Kobayashi, Takaya Yamazato, Masaaki Katayama

2016 IEEE 27TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC) page： 1219 - 1224 2016

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

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 information 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.

DOI： 10.1109/PIMRC.2016.7794761

Position Estimation of LED Matrix in Image Sensor Communication Reviewed

Takazumi Asai, Tomohiro Yendo, Shintaro Arai, Takaya Yamazato, Hiraku Okada, Toshiaki Fujii, Koji Kamakura

2016 ASIA-PACIFIC SIGNAL AND INFORMATION PROCESSING ASSOCIATION ANNUAL SUMMIT AND CONFERENCE (APSIPA) page： 1 - 5 2016

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

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.

DOI： 10.1109/APSIPA.2016.7820809

Spatial Modulation in Layered Space-Time Coding for Image-Sensor-Based Visible Light Communication Reviewed

Keisuke Masuda, Koji Kamakura, Takaya Yamazato

2016 IEEE 27TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC) page： 1231 - 1236 2016

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Spatial modulation (SM) is introduced into layered space-time coding (L-STC) used in image sensor (IS)-based visible light communication (VLC) systems. STC was basically investigated for extending the communication range of the IS-based VLC link [1], although it is out of the range when IS receivers are at the long distance from the LED array of the transmitter where the number of pixels capturing the transmitter on the image plane is less than the number of LEDs of the array. Furthermore, L-STC was done in [2] for increasing the reception rate with improving the pixel resolution while the receiver was approaching the transmitter. In this paper, SM is combined into L-STC by mapping additional information bits on the location of the pair of STC bit matrices of each layer. Experimental results show that additional SM bits are extracted with no error, without deteriorating the reception quality of and shrinking the transmission range of the original L-STC.

DOI： 10.1109/PIMRC.2016.7794763

Position Estimation of LED Matrix in Image Sensor Communication Reviewed

Asai Takazumi, Yendo Tomohiro, Arai Shintaro, Yamazato Takaya, Okada Hiraku, Fujii Toshiaki, Kamakura Koji

2016 ASIA-PACIFIC SIGNAL AND INFORMATION PROCESSING ASSOCIATION ANNUAL SUMMIT AND CONFERENCE (APSIPA) 2016

Spatial Modulation in Layered Space-Time Coding for Image-Sensor-Based Visible Light Communication Reviewed

Masuda Keisuke, Kamakura Koji, Yamazato Takaya

2016 IEEE 27TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC) page： 1231 - 1236 2016

Transmit Diversity with Single RF Front-end using CIOD Reviewed

Yamaoka Tomoya, Hara Teruyuki, Okazaki Akihiro, Yamazato Takaya

IEICE ComEX Vol. 5 ( 2 ) page： 44 - 48 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：The Institute of Electronics, Information and Communication Engineers

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-input multiple-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.

DOI： 10.1587/comex.2015XBL0170

Visible Light Communication Systems Using Blue Color Difference Modulation for Digital Signage Reviewed

Sato Sho, Okada Hiraku, Kobayashi Kentaro, Yamazato Takaya, Katayama Masaaki

2016 IEEE 27TH ANNUAL INTERNATIONAL SYMPOSIUM ON PERSONAL, INDOOR, AND MOBILE RADIO COMMUNICATIONS (PIMRC) page： 1219 - 1224 2016

LED acquisition methods for image-sensor-based visible light communication Reviewed

Shintaro Arai; Takaya Yamazato; Hiraku Okada; Toshiaki Fujii; Tomohiro Yendo

2015 Opto-Electronics and Communications Conference (OECC) page： 1 - 3 2015.11

Language：English Publishing type：Research paper (scientific journal)

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.

DOI： 10.1109/OECC.2015.7340210

Layered Transmission of Space-Time Coded Signals for Image-Sensor-Based Visible Light Communications Reviewed

Katsunori Ebihara, Koji Kamakura, Takaya Yamazato

JOURNAL OF LIGHTWAVE TECHNOLOGY Vol. 33 ( 20 ) page： 4193 - 4206 2015.10

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

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 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 2(n) x 2(n) LED array for increasing the transmission rate per symbol duration for the case where the pixel resolution is improved. A prototype of a three-layered STC is built with an 8 x 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.

DOI： 10.1109/JLT.2015.2470091

IEICE technical committees' contribution to I-scover keyword metadata improvements and selecting effective article keywords Reviewed

Image sensor based visible light communication for V2X Reviewed

Takaya Yamazato

2015 IEEE Summer Topicals Meeting Series (SUM) page： 165 - 166 2015.9

Signal Demodulation Method from Degraded Image for Visible Light Communication Using LED and High-Speed Camera Reviewed

Y. Ohira, S. Arai, T. Yendo, T. Yamazato, H. Okada, T. Fujii, K. Kamakura

IEICE Transactions on Communications Vol. J98-B ( 7 ) page： 696-706 2015.7

Yamazato T.

Journal of the Institute of Electronics, Information and Communication Engineers Vol. 98 ( 6 ) page： 494 - 499 2015.6

Vehicle Motion and Pixel Illumination Modeling for Image Sensor Based Visible Light Communication Reviewed

Takaya Yamazato; Masayuki Kinoshita; Shintaro Arai; Eisho Souke; Tomohiro Yendo; Toshiaki Fujii; Koji Kamakura; Hiraku Okada

IEEE Journal on Selected Areas in Communications Vol. 33 ( 9 ) page： 1793 - 1805 2015.5

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

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 single-element 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.

DOI： 10.1109/JSAC.2015.2432511

Noise-Enhanced subthreshold signal reception by a stochastic resonance receiver using a non-dynamical device Reviewed

Hiroya Tanaka, Keita Chiga, Takaya Yamazato, Yukihiro Tadokoro, Shintaro Arai

Nonlinear Theory and Its Applications, IEICE Vol. 6 ( 2 ) page： 303 - 312 2015.4

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

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.

DOI： 10.1587/nolta.6.303