Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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Decline in Probability of False Recognition of Non-Information Sources in Visible Light Communication for Intelligent Trasport System Reviewed Open Access

SHIRAKI Yasutake, YAMAZATO Takaya, ARAI Shintaro, YENDO Tomohiro, OKADA Hiraku, FUJII Toshiaki

IEICE technical report Vol. 111 ( 386 ) page： 13 - 18 2012.1

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

Visible light communication systems which enable data transmission by blinking LEDs at fast rate attract attention for their applications to Intelligent Transport Systems (ITS). In this paper, we assume that there are multiple information sources and we recognize them with on-vehicle high-speed camera in such systems. To lower probability of false recognition which represents how often non-information sources are recognized as information sources, we propose an improved multiple sources recognition method. We evaluate the proposed method by performing experiments.

Open Access

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High-Speed LED Traffic Light Tracking Method Using Image/High-Speed Communication Hybrid Sensor Reviewed

K. Maeno, M. Tehrani, T. Fujii, H. Okada, T. Yamazato, M. Tanimoto, T. Yendo

International Workshop on Advanced Image Technology (IWAIT2012) page： CD-ROM 2012.1

Language：English

Visible Light Communication (VLC) is a wireless communication method using LEDs. In this paper, we use a hybrid sensor designed for VLC which has advantages of photodiode and high-speed camera, that is, high transmission rate and easy detecting of the transmitter. The light receiving section of the sensor consists of communication pixels and video pixels. This sensor can communicate in static environment in previous research. However in dynamic environment, high- speed tracking of the transmitter is essential. We realize the high-speed tracking of the transmitter using the information of the communication pixels. Experimental results show the possibility of communication in dynamic environment.

High-speed Transmission of Overlay Coding for Road-to-Vehicle Visible Light Communication Using LED Array and High-Speed Camera Reviewed

Sayaka Nishimoto, Takaya Yamazato, Hiraku Okada, Toshiaki Fujii, Tomohiro Yendo, Shintaro Arai

2012 IEEE GLOBECOM WORKSHOPS (GC WKSHPS) ( pp.1234-1238 ) page： 1234 - 1238 2012

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

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.

DOI： 10.1109/GLOCOMW.2012.6477757

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8-331 Demand of Teaching Material Development and OCW Reviewed Open Access

YAMAZATO Takaya

Proceedings of Annual Conference of Japanese Society for Engineering Education Vol. 2012 ( 0 ) page： 718 - 719 2012

A Study on Cluster Partitioning with Cooperative MISO Scheme in Wireless Sensor Networks Reviewed Open Access

Zheng Huang, Hiraku Okada, Masaaki Katayama, Takaya Yamazato

INTERNATIONAL JOURNAL OF DISTRIBUTED SENSOR NETWORKS Vol. 8 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：HINDAWI PUBLISHING CORPORATION

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 multihop transmissions with cooperative Multi-Input Single-Output (MISO) scheme are considered for the intercluster 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 intracluster 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.

DOI： 10.1155/2012/490823

B-10-103 A Distance Estimation Scheme between the LED Array and On-Vihicle High-Speed Camera Using Visible Light Communication Reviewed

OHMURA Akihiro, YAMAZATO Takaya, OKADA Hiraku, FUJII Toshiaki, YENDO Tomohiro, ARAI Shintaro

Proceedings of the IEICE General Conference Vol. 2012 ( 2 ) page： 426 2012

Gaussian Pulse Shape Optimization of BFDM in Time-Frequency Dispersive Channels Reviewed

Goto Daisuke, Yamazato Takaya, Mongol Bayarpurev

2012 IEEE 75TH VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING) 2012

High-speed Transmission of Overlay Coding for Road-to-Vehicle Visible Light Communication Using LED Array and High-Speed Camera Reviewed

Nishimoto Sayaka, Yamazato Takaya, Okada Hiraku, Fujii Toshiaki, Yendo Tomohiro, Arai Shintaro

2012 IEEE GLOBECOM WORKSHOPS (GC WKSHPS) page： 1234 - 1238 2012

Gaussian Pulse Shape Optimization of BFDM in Time-Frequency Dispersive Channels Reviewed

Daisuke Goto, Takaya Yamazato, Bayarpurev Mongol

2012 IEEE 75TH VEHICULAR TECHNOLOGY CONFERENCE (VTC SPRING) page： 1 - 5 2012

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

The objective of this research is to reduce inter-symbol interference (ISI) and intercarrier interference (ICI) in a highly mobile environment by optimizing the performance of Biorthogonal Frequency Division Multiplexing (BFDM). In time-frequency dispersive channels, reducing the signal interference depends on the shaping of the signal pulse. BFDM was invented to reduce the interference through a flexible design of the signal pulse shaping. However, the shape of the Gaussian pulses used in BFDM is not always optimized in every situation and as a result the interference is not always minimized. This research seeks to optimize the shape of the Gaussian pulse. In particular, we optimize the Gaussian pulse in BFDM by maximizing the ratio of the ambiguity function of the transmitter (Gaussian) and its receiver pulses. Numerical results obtained show that the proposed method is effective for the optimization of BFDM. Furthermore, we show that the optimized BFDM outperforms the conventional OFDM in time-frequency dispersive channels.

DOI： 10.1109/VETECS.2012.6240287

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Visible light communication in dynamic environment using image/high-speed communication hybrid sensor Reviewed

Keita Maeno, Mehrdad Panahpour Tehrani, Toshiaki Fujii, Hiraku Okada, Takaya Yamazato, Masayuki Tanimoto, Yendo Tomohiro

BROADBAND ACCESS COMMUNICATION TECHNOLOGIES VI Vol. 8282 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE-INT SOC OPTICAL ENGINEERING

Visible Light Communication (VLC) is a wireless communication method using LEDs. LEDs can respond in high-speed and VLC uses this characteristics. In VLC researches, there are two types of receivers mainly, one is photodiode receiver and the other is high-speed camera. A photodiode receiver can communicate in high-speed and has high transmission rate because of its high-speed response. A high-speed camera can detect and track the transmitter easily because it is not necessary to move the camera. In this paper, we use a hybrid sensor designed for VLC which has advantages of both photodiode and high-speed camera, that is, high transmission rate and easy detecting of the transmitter. The light receiving section of the hybrid sensor consists of communication pixels and video pixels, which realizes the advantages. This hybrid sensor can communicate in static environment in previous research. However in dynamic environment, highspeed tracking of the transmitter is essential for communication. So, we realize the high-speed tracking of the transmitter by using the information of the communication pixels. Experimental results show the possibility of communication in dynamic environment.

DOI： 10.1117/12.907697

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Relay Selection Scheme Using Prediction of Harvested Energy for Solar-Powered Wireless Sensor Networks Reviewed

K. Ota, K. Kobayashi, T. Yamazato, M. Katayama

International Symposium on EcoTopia Science 2011 page： 106 2011.12

Language：English

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.

Interference Comparison of BFDM with Optimum Gaussian Pulse and Wavelet Based OFDM in Highly Mobile Environments Open Access

D. Goto, T. Yayazato, B. Mongol

Technical Report of IEICE Vol. RCS2011-11 page： 91-95 2011.11

Language：Japanese

In this paper, we conduct a comparison between the Biorthogonal Frequency Division Multiplexing (BFDM) and the Wavelet Based Orthogonal Frequency Division Multiplexing (OFDM) in terms of intersymbol interference (ISI) and intercarrier interference (ICI) reduction in highly mobile environments with assumed time-frequency dispersive channels. ISI and ICI depend largely on the pulse shaping of the signal. BFDM can reduce the signal interference by applying a Gaussian pulse known as a properly localized time-frequency pulse with adaptable characteristics. On the other hand, Wavelet Based OFDM is known to lower interference due to its wavelet basis. In this paper, we propose an optimization method for the Gaussian pulse in BFDM to minimize ISI/ICI by maximizing the ratio of the ambiguity function. In addition, we compare its performance with BFDM and Wavelet Based OFDM.

Open Access

Interference Comparison of BFDM with Optimum Gaussian Pulse and Wavelet Based OFDM in Highly Mobile Environments Reviewed Open Access

GOTO Daisuke, YAMAZATO Takaya, MONGOL Bayarpurev

Technical report of IEICE. RCS Vol. 111 ( 289 ) page： 91 - 95 2011.11

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

Open Access

CiNii Research

Overlay Coding for Road-to-Vehicle Visible Light Communication using LED Array and High-Speed Camera Reviewed

S. Nishimoto, T. Nagura, T. Yamazato, T. Yendo, T. Fujii, H. Okada, S. Arai

International IEEE Conference on Intelligent Transportation Systems page： 1704-1709 2011.10

Language：English

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.

A Study on Cluster Lifetime of Single-hop Wireless Sensor Networks with Cooperative MISO Scheme Reviewed

Z. Huang, K. Kobayashi, M. Katayama, T. Yamazato

IEICE Transactions on Communications Vol. E94-B ( 10 ) page： 2881-2885 2011.10

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

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.

A Study on Cluster Lifetime of Single-Hop Wireless Sensor Networks with Cooperative MISO Scheme Reviewed

Zheng Huang, Kentaro Kobayashi, Masaaki Katayama, Takaya Yamazato

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E94B ( 10 ) page： 2881 - 2885 2011.10

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

DOI： 10.1587/transcom.E94.B.2881

Estimation of Channel Information for Error Correcting Code in Visible Light Communication Using LED Array and High-Speed Camera

S. Misawa, H. Okada, T. Yamazato, T. Yendo, T. Fujii

Enginnering Sciences Society Conference of IEICE Vol. A-17-6 page： 210 2011.9

Cooperative Transmission Scheme with Inactive Node Reactivation Condition for Solar-Powered Wireless Sensor Networks Reviewed

K. Ota, K. Kobayashi, T. Yamazato, M. Katayama

IEEE International Workshop on Wireless Distributed Networks (WDN2011) page： 2394-2398 2011.9

Language：English

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.

Instructor's message that can be read from Nagoya Univeristy OCW teaching materials Open Access

T. Yamazato

Journal of Japanese Society for Engineering Education (JSEE) page： 9-217 2011.9

I-074 Road-to-vehicle Visible Light Communication Using High-speed Camera in Driving Situation Reviewed

Premachandra Halpage Chinthaka Nuwandika, Yendo Tomohiro, Tehrani Mehrdad Panahpour, Yamazato Takaya, Okada Hiraku, Fujii Toshiaki, Tanimoto Masayuki

情報科学技術フォーラム講演論文集 Vol. 10 ( 3 ) page： 459 - 464 2011.9

Publishing type：Research paper (scientific journal) Publisher：FIT(電子情報通信学会・情報処理学会)運営委員会

Intelligent Transport System(ITS) has been proposed to give solutions for traffic problems such as traffic accidents and traffic jams. On the other hand, high frame rate image techniques are getting popular in last several years. In this paper, we propose a Visible Light Communication(VLC) system using high frame rate techniques for Intelligent Transport System. Here, the communication between infrastructure and the vehicle is approached using an LED array as a transmitter and on-vehicle high speed camera as a receiver. The LEDs in the transmitter emit light in 500Hz and the emission patterns are used to achieve communication, capturing them in high frame rate(1000fps) utilizing a high-speed camera. The images captured by high-speed camera are processed to find the transmitter, track the found transmitter, and capture the LED lighting 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 lighting pattern of the transmitter. Then, out door communication experiments were conducted to confirm the effectiveness of the proposed V LC system.

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Papers - YAMAZATO Takaya