Faculty Profiles - YAMAZATO Takaya

Image sensor communication and its transmitting devices Reviewed

Zhengqiang Tang, Takaya Yamazato

Optics Communications 2023.8

Achieving Successful VLC Signal Reception Using A Rolling Shutter Image Sensor While Driving at 40 km/h Reviewed

Shunki Kamiya, Zhengqiang Tang, Takaya Yamazato, Masayuki Kinoshita, Koji Kamakura, Shintaro Arai, Tomohiro Yendo, Toshiaki Fujii

IEEE Photonics Journal Vol. 15 ( 4 ) 2023.8

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

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.

DOI： 10.1109/JPHOT.2023.3287211

Simultaneous Visible Light Communication and Ranging Using High-Speed Stereo Cameras Based on Bicubic Interpolation Considering Multi-Level Pulse-Width Modulation Reviewed

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

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E106A ( 7 ) page： 990 - 997 2023.7

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

Visible light communication (VLC) and visible light rang-ing are applicable techniques for intelligent transportation systems (ITS). They use every unique light-emitting diode (LED) on roads for data trans-mission 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 esti-mating 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 ap-ply bicubic interpolation to solve the LED saturation problem and thus, im-prove the communication and ranging performance. Simultaneous commu-nication 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. Fur-thermore, 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.

DOI： 10.1587/transfun.2022EAP1078

Exposure Synchronization in Optical Camera Communications for Time Division Multiplexing Reviewed

Hiroaki Matsunaga, Tomohiro Yendo, Shintaro Arai, Takaya Yamazato

IEEE Photonics Journal Vol. 15 ( 2 ) 2023.4

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

Optical camera communication (OCC) is a type of visible light communication that employs a camera as the receiver. Various flicker-free OCC methods using a general-purpose low-frame rate camera have been proposed. In particular, the undersampling method uses a short exposure camera and a light-emitting diode that blinks faster than the camera's frame rate. Despite the short exposure time, the transmitter has to send a symbol for a frame period or longer because the relationship between the symbol timing of the transmitter and exposure timing of the receiver is indeterminate. We propose resolving this indeterminacy by synchronizing the exposure timing to the transmitter. In the proposed method, the transmitter sends multiple data channels in a frame period by time division multiplexing, and the receiver selects a channel. Then, a single symbol of multilevel phase shift keying is extracted from a single pixel value in a frame. Experiments confirmed that the exposure timing could be synchronized even with a degraded signal-noise ratio and that the receiver could select the desired channel. The proposed method achieved a bit error rate of 10(-6)at a signal-noise ratio of 46.2 dB under various modulation schemes.

DOI： 10.1109/JPHOT.2023.3247908

$M$-Point Combinatory for Parallel Transmission Image Sensor-Based Visible Light Communications Reviewed

Takumi Sato, Koji Kamakura, Masayuki Kinoshita, Takaya Yamazato

Journal of Lightwave Technology 2023.1

High-Speed Image Sensor Com-munication Using High Dy-namic Range Combining Reviewed

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

IEICE COMMUNICATIONS EXPRESS Vol. 12 ( 9 ) page： 493 - 498 2023

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

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.

DOI： 10.1587/comex.2023XBL0075

Experimental Demonstration of Optical OFDM With Polarity-Separated Transmission in Rolling Shutter Based Visible Light Communication Reviewed

Hiroshi Shimizu, Kota Kanata, Masayuki Kinoshita, Koji Kamakura, Shintaro Arai, Takaya Yamazato

2023 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS, ISCAS 2023

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

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 300-700Hz when 16-PSK was adopted for subcarrier modulation.

DOI： 10.1109/ISCAS46773.2023.10181518

An Experimental Study on A Noise-aided 1-bit ADC Receiver for 4-PAM Reviewed

Zheng Jinxing, Yamazato Takaya, Saito Masato

IEICE Communications Express Vol. advpub ( 0 ) 2022.8

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

<p>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.</p>

DOI： 10.1587/comex.2022COL0032

CiNii Research

Noise-assisted nonlinear estimation of a one-bit ADC output and its application to a multi-antenna receiver Reviewed

Masato Saito, Yasuo Nakashima, Takaya Yamazato, Shintaro Arai, Hiroyuki Hatano, Hiroya Tanaka, Yukihiro Tadokoro

2022.4

Simplified Alamouti-Type Space-Time Coding for Image Sensor Communication Using Rotary LED Transmitter Reviewed

Zhengqiang Tang, Shintaro Arai, Takaya Yamazato

IEEE Photonics Journal Vol. 14 ( 1 ) 2022.2

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

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.

DOI： 10.1109/JPHOT.2021.3137601

A Preliminary Investigation For Event Camera-Based Visible Light Communication Using The Propeller-type Rotary LED Transmitter Reviewed

Zhengqiang Tang, Takaya Yamazato, Shintaro Arai

2022 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS WORKSHOPS (ICC WORKSHOPS) page： 646 - 650 2022

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

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, which is under development, 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 of communication quality.

DOI： 10.1109/ICCWORKSHOPS53468.2022.9814467

Roadside LED array acquisition for road-to-vehicle visible light communication using spatial-temporal gradient values Reviewed

Kento Nakamura, Ruiyi Huang, Takaya Yamazato, Masayuki Kinoshita, Koji Kamakura, Shintaro Arai, Tomohiro Yendo, Toshiaki Fujii

IEICE COMMUNICATIONS EXPRESS Vol. 11 ( 8 ) page： 462 - 467 2022

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

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].

DOI： 10.1587/comex.2022TCL0008

Luminance Inversion for Parallel Transmission Visible Light Communication Between LCD and Image Sensor Camera Reviewed

Kotomi Takahashi, Koji Kamakura, Masayuki Kinoshita, Takaya Yamazato

Journal of Lightwave Technology 2021.11

Vehicle distance measurement based on visible light communication using stereo cameras Reviewed

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

IEEE Intelligent Vehicles Symposium, Proceedings Vol. 2021-July page： 853 - 858 2021.7

Publishing type：Research paper (international conference proceedings)

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.

DOI： 10.1109/IV48863.2021.9575534

Luminance Inversion for Parallel Transmission VLC between LCD and Image Sensor Camera Reviewed

Kotomi Takahashi, Koji Kamakura, Masayuki Kinoshita, Takaya Yamazato

IEEE International Conference on Communications 2021.6

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

Luminance inversion (LI) is proposed to compensate for nonlinear characteristics between a liquid crystal display (LCD) and an image sensor (IS) camera of the parallel transmission (PT) visible light communication (VLC). In the PT system reported in [1], which incorporates N spatial frequencies with phase shift keying (PSK) through M-point inverse discrete Fourier transform (IDFT), data are transmitted from M different regions of pixels on an LCD spatially in parallel. Since the transfer characteristics between the LCD and IS camera is nonlinear, the received signal at IS camera receiver is distorted. The effect is severe because signals of the PT system are, in essence, the OFDM signal, thus suffering from high peak-to-average ratio (PAPR). To linearize it between the LCD and IS camera, our approach is to calculate a complement of the digital data fed to the driver of the pixel and then to feed the pair of the digital data and its complement to the driver during two successive frames. In the receiver, the difference of the signals during the two frames is calculated for each of the M detected regions on the IS plane, and then they input to the following M-point DFT in the PT system. By introducing this LI process, wider linear characteristics in the PT system is obtained than without LI. Experimental results show that the number of bits per frame that the PT system with LI can accommodate without any error is 315bits/frame and 100bits/frame for 8- and 16-PSK, which are much larger than 12bits/frame and 0bits/frame for the 8- and 16-PSK PT system without LI, respectively.

DOI： 10.1109/ICC42927.2021.9500287

Special section on intelligent transport systems Reviewed

Saho K.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E104A ( 2 ) 2021.2

Optical Wireless Communication: A Candidate 6G Technology? Reviewed

Shintaro Arai, Masayuki Kinoshita, Takaya Yamazato

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E104A ( 1 ) page： 227 - 234 2021.1

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

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.

DOI： 10.1587/transfun.2020WBI0001

Circuit Experiment of Photodiode-type Visible Light Communication Using the Stochastic Resonance Generated by Interfering Light Noise Reviewed

Shintaro Arai, Wataru Tamura, Takaya Yamazato, Hiroyuki Hatano, Masato Saito, Hiroya Tanaka, Yukihiro Tadokoro

2021 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS) Vol. 2021-May 2021

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

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.

DOI： 10.1109/ISCAS51556.2021.9401452