Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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A Study on Effects of Variations of Transmitter LED's Luminance for Hierarchical Coding in Parallel Optical Wireless Communication Systems

K. Masuda, T. Yamazato, H. Okada, and M. Katayama

Communications Society Conference of IEICE Vol. B-8-17 page： 209 2005.9

On the Second-order Statistics of the Channel Parameters for BFDM/OQAM Systems Reviewed

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

2nd International Symposium on Wireless Communication Systems page： 534-538 2005.9

Language：English

Recently, there has been increased interest in using multicarrier systems in rapidly time-varying multipath environment. Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) is an attractive modulation method since it allows time-frequency well-localized pulses even at critical sampling (i.e. maximum spectral ef ciency). BFDM/OQAM system is naturally strong against intersymbol and intercarrier interference (ISI/ICI). However, for further improvement of the system a study on the channel statistics is needed. In this paper we analytically examine the channel parameters for BFDM/OQAM and derive their second-order statistics.

A New Coded QAM Modulation Scheme for Broadband Satellite Communication Reviewed

T. Yamazato, T. Yamaoka, H. Okada, M. Katayama, A. Ogawa

23rd AIAA International Communications Satellite Systems Conference (ICSSC-2005) Vol. MOD-3-3 page： - 2005.9

Language：English

In this paper, we propose a new multi-rate coded QAM for broadband satellite communication system. The overall coding rate is (m?2)/2 and Turbo code is adopted. The mapping is similar to bit-interleaved coded modulation (BICM) systems; unlike BICM mapping, we only assign four of Turbo coded bits. This brings a set-partitioning. We also consider the effect of quantization bits. Actually we try to realize high-order QAM by using the available quantization bits, which reduces the signal accuracy so the performance may degrade. As results, our proposed scheme achieve good performance even when the available quantization bits are less.

Influence of the Nonlinearity of the ADC in an OFDM Receiver Reviewed

M. Sawada, H. Okada, T. Yamazato, and M. Katayama

The 10th International OFDM-Workshop 2005 page： 220-224 2005.8

Language：English

This paper discusses the influence of the nonlinearity of an analog-to-digital converter (ADC) in an orthogonal frequency division multiplexing (OFDM) receiver. We evaluate a signal constellation and a bit error rate (BER) performance with the consideration of quantization errors and clippings. As a result, the trade off between the quantization error and the clipping and the optimum range for an ADC input amplitude are shown. In addition, it is shown that the peak to average power ratio (PAPR) of the signal is not a good measure of the BER performance, since the peaks occur only with very low probabilities.

Target position detection using MMSE in radar networks

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

Technical Report of IEICE Vol. ITS2005-15 page： 45-49 2005.7

[Technical Exhibition] Software Defined Receiver with SFQ Digital Devices

A. Sekiya, Y. Nishido, H. Akaike, H. Okada, M. Inoue, T. Yamazato, A. Fujimaki, M. Katayama

Technical Report of IEICE Vol. SR2005-34 page： 91-96 2005.7

Single-user MAP Based Soft-in/Soft-output Parallel Interference Canceler Utilizing Retransmission Diversity Reviewed

Y. Tadokoro, H. Okada, T. Yamazato, and M. Katayama

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. J88-A ( 6 ) page： 739-750 2005.6

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

In packet communication systems, unsuccessful packets should be retransmitted. By exploiting the information on the unsuccessful packets such as log-likelihood ratio(LLR), the retransmitted packets may be correctly demodulated. Some authors have proposed the interference cancellation schemes using such a retransmission diversity technique. However, these schemes uses the traditional approach of interference cancellation. In addition, the received signals are just combined at the output of the canceler. This paper develops the novel interference cancellation scheme which maximize a posteriori probability utilizing the LLR on unsuccessful packets. Performance evaluation shows that not only retransmitted packets but also new-generated packets can be successfully transmitted in the proposed scheme.

Performance Evaluation of Route Coding Scheme in Wireless Multi-hop Networks Reviewed

H. Okada, T. Wada, K. Ohuchi, M. Saito, T. Yamazato, M. Katayama

IEEE Vehicular Technology Conference (VTC) page： 3092-3096 2005.6

Language：English

Wireless multi-hop networks have been much attention for the future generation mobile communication systems. Due to the possibility of flexible construction in the wireless multi-hop networks, multiple routes from a source node to a destination node can be established. In this paper, we propose the route coding scheme in the wireless multi-hop networks. In the proposed scheme, a packeted data sequence is encoded by the convolutional code at the source node. Each digit of the code word is assigned to sub-packets on multiple routes. At the intermediate nodes, the sub-packets are regenerated-relayed to the next node. The sub-packets transmitted via multiple routes are decoded by the Viterbi decoder with the modified metric computation at the destination node. We also evaluate the system performance, and clarify the improvement of the packet error rate by the proposed scheme. Furthermore, we investigate the influence of the route loss due to topological change or recognizing failure.

Target position estimation using MMSE for UWB IPCP receivers Reviewed

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

The 5th International Conference on ITS Telecommunications page： 131-134 2005.6

Language：English

In this work, we present target position estimation methods using minimum mean-square error (MMSE) algorithm for short-range radar systems. We consider UWB IPCP (inter-period correlation processor) receiver and improve target position accuracy by using a set of measured ranges. Depend on how we set the objective functions for MMSE, we propose three methods. And we evaluate the performance of position estimations using computer simulations.

Faculty Inventories for Student Involvement in Web-Enhanced Learning

H. Nakajima, H. Okada, T. Nakai, T. Yamazato

Webct User Conference page： 109-113 2005.6

Evaluation of the Channel Parameter Statistics for BFDM/OQAM System in Multipath Time-Varying Channels

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

Technical Report of IEICE Vol. RCS2005-33 page： 35-40 2005.6

Language：English

Recently, there has been increased interest in using Orthogonal Frequency Division Modulation (OFDM) systems in rapidly time-varying multipath environment. The performance of the systems in such time-frequency dispersive channels, depends critically on the time-frequency localization of the transmitter pulse. Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) is attractive modulation method since it allows time-frequency well-localized pulses at critical sampling (i.e. maximum spectral efficiency). In this paper we consider BFDM/OQAM system with Gaussian transmitter pulse and evaluate channel parameter statistics in multipath time-varying channels.

Improvement of the estimation quality using the correlation of the observation data - When sensor nodes are uniformly distributed -

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

Technical Report of IEICE Vol. SN2005-5 page： 15-20 2005.6

Performance Analysis of Multiple-route Packet Combining Scheme for Real-time Communications in Wireless Multihop Networks

Y. Hirayama, H. Okada, T. Yamazato, and M. Katayama

Proc. of Cooperation Industry Academia Government 2005 page： 92-93 2005.6

Application of Successive Interference Cancellation to a Packet-Recognition/Code-Acquisition Scheme in CDMA Unslotted ALOHA Systems Reviewed

Y. Tadokoro, H. Okada, T. Yamazato, M. Katayama

IEICE Transaction on Fundamentals of Electronics, Communications and Computer Sciences Vol. E88-A ( 6 ) page： 1605-1612 2005.6

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

Packet-recognition/code-acquisition (PR/CA) is one of the most important issues in packet communication systems. In a CDMA Unslotted ALOHA system, Multiple Access Interference (MAI) may bring about error in PR/CA. The MAI mainly stems from already recognized packets and newly arriving packets under the execution of PR/CA. This characteristic of asynchronous transmission in CDMA U-ALOHA systems implies that only one or a few packets arrive at the receiver within a short interval of a execution. Furthermore, newly arriving packets are recognized and code-acquired by using a short preamble part. Consequently, the MAI from the packets under the execution of the PR/CA will be small. Focusing on that point, this paper proposes applying the IC scheme in order to suppress the MAI from the already recognized and code-acquired packets. A performance evaluation demonstrates that such an application is valid due to the small amount of MAI from the packets under the execution of PR/CA. In addition, we demonstrates that the scheme reduces false recognition rather than mis-recognition. Such a scheme improves the performance of not only PR/CA, but also the throughput.

Research on relation between error performance of coded QAM and qauntized bits --Proposal of multi-rate coded QAM--

T.Yamaoka,T.Yamazato,H.Okada,M.Katayama and A.Ogawa

Technical Report of IEICE Vol. SAT2005-9 page： 19-23 2005.6

A Macro and Micro Diversity Scheme with Relay Terminals for Reliable Wireless Control

R. Uchida, H. Okada, T. Yamazato, and M. Katayama

Technical Report of IEICE Vol. RCS2005-28 page： 39275 2005.6

Language：Japanese

In this manuscript, wireless communication system for reliable wireless control of industrial machines in indoor environment is considered. In indoor environment, transmitted signal fluctuates due to fading and shadowing. To combat the fading and shadowing, macro / micro spatial diversity can be used as an effective countermeasure. In this manuscript, macro / micro diversity is achieved by multiple wireless relay terminals, which is convenient in setting and moving the macro diversity branches. In the proposed scheme, channel between the transmitter and the receiver through relay terminals is considered as a MIMO channel and separation of the signals re-transmitted from the relay terminals is not required. This feature makes it possible to have higher order diversity without the cost of bandwidth inefficiency. By numerical calculations, performance of the proposed scheme is evaluated and the improvement of the reliability of the communication system is confirmed.

Application of successive interference cancellation to a packet-recognition/code-acquisition scheme in CDMA unslotted ALOHA systems Reviewed

Y Tadokoro, H Okada, T Yamazato, M Katayama

IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCES Vol. E88A ( 6 ) page： 1605 - 1612 2005.6

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

Packet-recognition/code-acquisition (PR/CA) is one of the most important issues in packet communication systems. In a CDMA Unslotted ALOHA system, Multiple Access Interference (MAI) may bring about errors in PR/CA. The MAI mainly stems from already recognized packets and newly arriving packets under the execution of PR/CA. This characteristic of asynchronous transmission in CDMA U-ALOHA systems implies that only one or a few packets arrive at the receiver within a short interval of a execution. Furthermore, newly arriving packets are recognized and code-acquired by using a short preamble part. Consequently, the MAI from the packets under the execution of the PR/CA will be small. Focusing on that point, this paper proposes applying the IC scheme in order to suppress the MAI from the already recognized and code-acquired packets. A performance evaluation demonstrates that such an application is valid due to the small amount of MAI from the packets under the execution of PR/CA. In addition, we demonstrates that the scheme reduces false recognition rather than mis-recognition. Such a scheme improves the performance of not only PR/CA, but also the throughput.

DOI： 10.1093/ietfec/e88-a.6.1605

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Special section on papers selected from 2004 International Technical Conference on Circuits/Systems, Computers and Communications (ITC-CSCC 2004) Reviewed

Kikuchi H.

IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences Vol. E88-A ( 6 ) 2005.6

再送ダイバーシチを用いて事後確率を最大にする軟入力/軟出力並列型干渉除去法 Reviewed Open Access

田所幸浩, 岡田啓, 山里敬也, 片山正昭

電子情報通信学会論文誌 A Vol. J88-A ( 6 ) page： 739 - 750 2005.6

Activity Report of Information Security Promotion Agency, Nagoya University Open Access

Y. Takeuchi, Y. Yamaguchi, N. Kawaguchi, T. Yamazato, A. Hasegawa, T. Sakabe

IPSJ SIG Technical Report Vol. 2005-CSEC-29(1) page： 39088 2005.5

Language：Japanese

The Informaton Security Promotion Agency (ISPA), Nagoya University was established in November, 2003. It is an expert group of information security and technology operation as promptly and actively as possible to respond information security incidents. There are two missions in ISPA. One is to engage in educational activities on information security for all members in Nagoya University. The other is to respond information security incidents as promptly and actively. In this report, we describe information security training, building of information security incident database, investigation of wireless LAN and information security audit. We also report security incidents which occur in our university.

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Papers - YAMAZATO Takaya