Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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Performance Improvement of Downlink MC-CDMA Cellular System using Different Arrival Time of the Adjacent Cell Signal

M. Fushiki, T. Yamazato, M. Katayama

Technical Report of IEICE Vol. RCS2007-68 page： 87-91 2007.8

Language：Japanese

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 adjacent cell signal power is large. Key wor

Measurement of the Narrowband Channel Characteristics \\in Single-Phase Three-Wire Indoor Power-Line Channels

Y. Sugiura , T. Yamazato, M. Katayama

Technical Report of IEICE page： - 2007.8

Language：Japanese

This manuscript reports the measurement results of narrow-band signal propagation of PLC channels between a pair of outlets. In Japan, in-house wiring is of 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 are also classified by these three types of paths. The results show that frequency responses of narrow-band PLC channels are relatively smooth, compared with that of wide-band PLC. It is also found that propagation loss in lower frequency range is larger than in higher frequency range. The time independence of narrow-band PLC channels are confirmed when no electric appliance is connected to the same live conductor.

Performance evaluation of cooperative transmission in distributed sensor networks using FPGA

K. Nakao, T. Yamazato, M. Katayama

Proceedings of 9th DSPS Educators Conference page： 91-92 2007.8

Throughput evaluation of CSMA and CDMA slotted ALOHA in Inter-Vehicle communication

A.Sakata, T.Yamazato, H.Okada, M.Katayama

Technical Report of IEICE Vol. RCS2007-55 page： 13-18 2007.8

Language：Japanese

This paper evaluate 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 results, 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 receive many packets simultaneously. This is much preferable feature for safety driving.

Ultrasonic Array Emitter for Short-range Automotive Targets Detection System

H. Hatano, T. Yamazato, M. Katayama

Technical Report of IEICE Vol. ITS2007-12 page： 15-20 2007.7

Language：Japanese

We consider application of ultrasonic sensor to automotive targets detection system for short-range. The ultrasonic sensors are low cost and widely used. However the detection range is short. In addition, wide detection area is needed. To apply for high functional parking aid system, we propose the array emitter which can emit signals to desired area within desired cycle time. As a result, we show the ability of the ultrasonic sensor for parking aid systems.

A Method for Reducing the Influence of the Interference Considering ADC Nonlinearity in an OFDM Receiver Reviewed Open Access

M. Sawada, T. Yamazato, M. Katayama

IEICE Transactions on Communications Vol. J90-B ( 6 ) page： 577-584 2007.6

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

In this paper we propose an OFDM receiver that mitigates the performance degradation caused by interference. The mitigation process is done all in digital after ADCs. The receiver estimates the reliability of each OFDM symbol based on its number of out-of-range samples. This reliability is then used as the external information in soft Viterbi decoding process. The results of numerical simulations for 16QAM/OFDM show that the proposed receiver is robust to strong interference.

Open Access

Cooperative Transmission Scheme in Distributed Sensor Network for Extension of Transmission Range Reviewed

K. Nakao, T. Yamazato, H. Okada, M. Katayama

Fourth International Conference on Networked Sensing Systems page： 89-92 2007.6

Language：English

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.

Throughput Comparison of CSMA and CDMA slotted ALOHA in Inter-Vehicle Communication Reviewed

A.Sakata, H.Okada, T.Yamazato, M.Katayama

The 7th International Conference on ITS Telecommunications page： 52-57 2007.6

Language：English

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.

Experiments on a Wireless Visible-Light Communication System using an LED Sign Panel

T. Ohtsuji, T. Yamazato, M. Katayama

Technical Report of IEICE Vol. OCS2007-14 page： 25-29 2007.6

Language：Japanese

This manuscript focuses on a wireless visible-light communication system with an LED-back-lighted sign board. Possibilities of the system are confirmed by experiment. In the experimental system, the transmitter uses frequency shift keying (FSK), which has constant envelope to avoid fluctuation of luminance and can be received without carrier phase synchronization. Since the noise and signal propagation in Electric/Optical/Electric channel are not flat in frequency, we introduce a weighting equalization before the decision circuit of the receiver. Experimental results show that this weighting improves bit error rate (BER) performance and extend distance between the transmitter and the receiver.

Channel measurement of a visible light communication system with an LED sign panel

D. Ishida , T. Yamazato, M. Katayama

Technical Report of IEICE Vol. OCS2007-15 page： 31-35 2007.6

Language：Japanese

As one of visible light communications systems, this paper focuses on a system using LED sign panel as a transmitter. The characteristic between the panel (E/O) input and the APD(O/E) output is measured. Linearity, frequency response, and the levels of harmonics of the channel is measured. The effects of the distance between the panel and the APD on the signal level is clarified. After the measurement of noise spectrum caused by an inverter-driven fluorescent lamp, the SNR in frequency is calculated.

A Study on Joint Decoding for Wireless Sensor Networks

K. Kobayashi, T. Yamazato, H. Okada, M. Katayama

Proc. of Academia Program, Wireless Technology Park 2007 page： 26-27 2007.4

Language：Japanese

Development of tiny sensor equipped with wireless communication function is remarkable with the advancement of small, light, and high-performance wireless devices. In the near future, we will see tens or hundreds of these nodes deployed in town and inside buildings. In such an environment, since many sensor nodes observe a same target or field, the information observed by each sensor node are correlated. Such correlated information are collected at a fusion center. Our purpose is to reduce channel error by using the correlation properties of observed data at the fusion center. Related works on the distributed encoding and joint decoding are the case of two correlated sources. By using the weighted correlation feedback, we extend the iterative joint decoding scheme for the general case where more than two sensor nodes are employed. We show that when the number of sensor nodes is increased, decoding performance improvement cannot be achieved by simple weighting. For more appropriate weighting, we find the weight that minimizes the bit error rate from the analytical formula of MAP decision and apply it to the case of Turbo code.

A Simple Estimator of Multiple Target Positions for Automotive Short Range Radar Networks Reviewed

H. Hatano, T. Yamazato, H. Okada, M. Katayama

IEEE Vehicular Technology Conference (VTC) page： 2511-2515 2007.4

Language：English

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.

Visible Light Communication using LED TrafficLight and car equipped with camera

T. Yamazato, M. Katayama

Proc. of Academia Program, Wireless Technology Park 2007 page： 38-39 2007.4

MIMO Equalizer for Pulse-ShapingOFDM Systems in Dispersive Time-Varying Channels

B. Mongol , T. Yamazato, H. Okada, M. Katayama

Proc. of Academia Program, Wireless Technology Park 2007 page： 50-51 2007.4

Language：Japanese

Pulse-shaping OFDM is well-known that it performs well in a mobile environment, i.e. time-varying channel, compared with conventional OFDM. However, as the time-variance becomes higher, the 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, we have proposed 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 have proposed maximum-likelihood channel estimator and its low-complexity version. The proposed system can significantly improve the performance of the pulse-shaping systems in the dispersive time-varying channels.

A-21-25 Noncoherent Detection for Cooperative Transmission in Distributed Sensor Network Reviewed

Nakao Kouji, Yamazato Takaya, Okada Hiraku, Katayama Masaaki

Proceedings of the IEICE General Conference Vol. 2007 page： 416 2007.3

*Nagoya University OpenCourseWare Invited Open Access

T. Yamazato

Annals of Nagoya UniversityAnnals of Nagoya University Vol. 第５号 page： 51-55 2007.3

Language：Japanese Publishing type：Research paper (bulletin of university, research institution)

The Nagoya University OpenCourseWare Committee is currently working to make some of the university's teaching materials openly available for instructors, students and self-directed learners around the world via the Internet. In this report, OpenCourseWare activity in Nagoya University is introduced.

DOI： 10.18999/annul.5.51

Open Access

Inter-Network Communication Method for Multihop Token Line Protocol

M. Masamura, H. Okada, T. Yamazato, M. Katayama

IEICE General Conference page： - 2007.3

Power-line communication system using correlations of instantaneous noise powers at a transmitter and a receiver

A. Kawaguchi, H. Okada, T. Yamazato, M. Katayama

IEICE General Conference Vol. A-5-22 page： - 2007.3

Performance Improvement of MC-CDMA System using Different Arrival Time of the Other Cell Signal

M. Fushiki, T. Yamazato, H. Okada, M. Katayama

IEICE General Conference page： - 2007.3

Radio Resource Allocation using Priority Based on User Position for Multiuser OFDM

K. Kimura T. Yamazato, M. Katayama

IEICE General Conference Vol. B-5-122 page： 536 2007.3

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Papers - YAMAZATO Takaya