Faculty Profiles - YAMAZATO Takaya

Papers - YAMAZATO Takaya

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A study on the mitigation of the influence of ADC nonlinearity in an OFDM receiver

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

DENSO TECHNICAL REVIEW Vol. 11 ( 1 ) page： 115-120 2006.5

Language：Japanese

An orthogonal frequency division multiplexing (OFDM) scheme, with highly spectrum efficiency and robustness against frequency selective fading, is applied to IEEE802.11a/g for high-speed wireless local area network (LAN) systems and digital terrestrial television broadcasting (DTTB) systems. The OFDM signal has large fluctuation in its amplitude, large dynamic range and high linearity are required for its transmitter and receiver. In the receiver, the Bit Error Rate (BER) performance is degraded by analog-to-digital converter (ADC) nonlinearity. We propose a new scheme to mitigate the influence of ADC nonlinearity in an OFDM receiver. In the proposed receiver, the weight for the soft Viterbi decoder is controlled based on the ADC output amplitude. We evaluate the BER performance for the proposed receiver when the control errors occur in the AGC amplifier. As a result, the effect of the proposed receiver on the BER performance is shown.

Multi-route Coding in Wireless Multi-hop Networks Reviewed

H. Okada, N. Nakagawa, T. Wada, T. Yamazato, M. Katayama

IEICE Transactions on Communications Vol. E89-B ( 5 ) page： 1620-1626 2006.5

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

Wireless multi-hop networks have drawn much attention for the future generation mobile communication systems. These networks can establish multiple routes from a source node to a destination node because of flexible construction of network topology. The transmission by multiple routes has enough capability to achieve reliable communication because we can expect to obtain diversity gain by multiple routes. In this paper, we propose the multi-route coding scheme. At first, we discuss a channel model in multi-hop networks employing regenerative relay, which we named the virtual channel model. By using the virtual channel model, a packet is encoded on multiple routes as follows; a bit sequence of a packet is encoded and divided into subpackets, and each subpacket is transmitted on each route. We evaluate its packet error rate performance, and clarify effectiveness of the proposed scheme. In general, we should face degradation of a route condition such as the case when a subpacket does not reach a destination node. Hence, we have to consider the influence of subpacket loss. We also investigate it, and show tolerance of the proposed scheme over that.

A study on position estimation method based on MAP estimation for multiple targets in car radar networks

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

Technical Report of IEICE Vol. ITS2006-3 page： 39402 2006.5

Language：Japanese

In this paper, we consider radar networks for cars. The radar networks are the networks built with multiple radars. Using measured ranges provided by radars, target positions are estimated. The measured ranges include measurement errors. The estimation method of the target positions using a MAP stimation is an optimum method. However, when the number of targets increases, the MAP estimation method becomes complex. So we introduce the simpler methods based on the MAP estimation method. The performance is evaluated by computer simulations.

Cooperative transmission scheme using coded FSK

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

Technical Report of IEICE Vol. SN2006-28 page： 67-72 2006.5

Language：Japanese

In sensor networks, many sensor nodes are distributed. The observation data are collected at a fusion center. They are transmitted to a fusion center by direct or multihop transmission. In this paper, we consider the situation that the transmission by those ways is not possible (e.g. a helicopter collects the data). We realize the transmission by a cooperative transmission among the nodes. An approach proposed for cooperative transmission is assumed coherent propagation or multi-channel, or applied to only a few nodes. In this paper, we propose a scheme to achieve the cooperative co-channel transmission only coding by multiplying a random phase per symbol.

Peformance analysis of UWB Impulse Radar Receiver using Parallel IPCP Reviewed Open Access

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

IEICE Transaction on Fundamentals Vol. J89-A ( 6 ) page： 544-556 2006.5

Multi-route coding in wireless multi-hop networks Reviewed

Hiraku Okada, Nobuyuki Nakagawa, Tadahiro Wada, Takaya Yamazato, Masaaki Katayama

IEICE TRANSACTIONS ON COMMUNICATIONS Vol. E89B ( 5 ) page： 1620 - 1626 2006.5

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

Wireless multi-hop networks have drawn much attention for the future generation mobile communication systems. These networks can establish multiple routes from a source node to a destination node because of flexible construction of network topology. Transmissions by multiple routes have enough capability to achieve reliable communication because we can expect to obtain diversity gain by multiple routes. In this paper, we propose the multi-route coding scheme. At first, we discuss a channel model in multi-hop networks employing regenerative relay, which we named the virtual channel model. By using the virtual channel model, a packet is encoded on multiple routes as follows; a bit sequence of a packet is encoded and divided into subpackets, and each subpacket is transmitted on each route. We evaluate its packet error rate performance, and clarify effectiveness of the proposed scheme. In general, we should face degradation of a route condition such as the case when a subpacket does not reach a destination node. Hence, we have to consider the influence of subpacket loss. We also investigate it, and show tolerance of the proposed scheme over that.

DOI： 10.1093/ietcom/e89-b.5.1620

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Reliable Robust Radio for Wireless Control of Industrial Machines

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

Proc. of Academia Program, Wireless Technology Park 2006 page： - 2006.4

Language：Japanese

Wireless control of industrial machines in factories has a lots of advantages over wired control. To achieve wireless control safely, high reliability of the wireless transmission system is required. In this manuscript, wireless transmission system with high reliability 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 transmission system is confirmed.

Automotive radar network technique for short range

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

Proc. of Academia Program, Wireless Technology Park 2006 page： 34-35 2006.4

Language：Japanese

We consider a radar system for vehicles in order to detect obstacles in a short range (up to 10m). In comparison with a long range radar, a short range radar needs wide angular range. Therefore a radar network which is set at front of a vehicle with multiple radars is being considered. The short range radar system also needs estimating obstacle positions with high accuracy. Therefore, by this research, we consider improving accuracy of the position estimation with the radar network. We use MMSE (Minimum Mean Square Error) and estimate parameters to get accurate positions from ranges measured by multiple radars. For MMSE, we consider three methods which differ in terms of objective functions to minimize or parameters to estimate. For these methods, we evaluate position estimation characteristics using computer simulations. We show that each method has characteristic performance at environment of use of cars.

A-21-19 Joint Decoding of Convolutional Codes using the Correlation of Transmitted Information Sequences in Sensor Networks Reviewed

KOBAYASHI Kentaro, YAMAZATO Takaya, OKADA Hiraku, KATAYAMA Masaaki

Proceedings of the IEICE General Conference Vol. 2006 page： 367 2006.3

Robust BFDM/OQAM Receiver for Time-Frequency Dispersive Channels

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

Technical Report of IEICE Vol. WBS2005-112 page： 19-24 2006.3

Language：English

Biorthogonal Frequency Division Multiplexing based on Offset QAM (BFDM/OQAM) system is one of the pulse-shaping versions of Orthogonal Frequency Division Multiplexing (OFDM) systems. It allows optimal Gaussian transmitting pulse at critical sampling i.e., maximum spectral efficiency. In this paper we propose a robust receiver for BFDM/OQAM systems in highly mobile environment. The idea behind our approach is to employ Multi-Input Multi-Output zero-forcing (MIMO-ZF) transversal filter to equalize the channel. The equalizer requires knowledge of the channel status. The channel is estimated by using Maximum-Likelihood method. We evaluate the error rate performance of the proposed system in the time-frequency dispersive channels.

Correlations of noise waveforms at different outlets in a power-line network Reviewed

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

IEEE International Symposium on Power Line Communications and Its Applications page： - 2006.3

Language：English

This manuscript discusses the relationships of noise waveforms measured at different outlets in a three-wire single-phase (one neutral and two live conductors) power-line network. As a result of experimental measurements, it is confirmed that instantaneous noise voltages at two different outlets have high correlations if the outlets are connected to the same live conductor in a distribution board, while the outlets for the different live conductors provide noise waveforms with low correlations. It is also shown that the instantaneous noise powers and cyclic averaged noise powers as time functions have large correlations even at a pair of outlets connected to the different live conductors. The correlation coefficients for instantaneous voltages and powers are also calculated as the frequency functions.

An Implementation of Multiple Route Coding Scheme in Wireless Multihop Networks

M.Umakoshi,H.Okada,K.Suzuki,T.Yamazato,M.Katayama

IEICE General Conference Vol. B-21-9 page： 569 2006.3

A method to mitigate the influence of ADC nonlinearity in an OFDM receiver

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

IEICE General Conference Vol. B-17-4 page： 583 2006.3

A Study on Signal Separation Scheme for Wideband Software-defined Radio Base Station

Toru KITAYABU, Hiraku OKADA, Takaya YAMAZATO, Masaaki KATAYAMA

IEICE General Conference Vol. B-17-6 page： 585 2006.3

A Study on Effects of Transmit/Receive Correlations on Performance of Diversity with Multiple Antennae/Relay Terminals

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

IEICE General Conference Vol. B-5-161 page： 514 2006.3

Joint Decoding of Convolutional Codes using the Correlation of Transmitted Information Sequences in Sensor Networks

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

IEICE General Conference Vol. A-21-19 page： 367 2006.3

Performance Evaluation of Packet Combining and ARQ Schemes of Multiple Route Coding in Wireless Multihop Networks

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

Technical Report of IEICE Vol. RCS2005-207 page： 175-180 2006.3

Language：Japanese

For reduction in bit errors on wireless channels, we proposed the multi-route coding scheme on multiple routes for wireless multi-hop networks. In this paper, we introduce packet combining and ARQ to the multi-route coding. In the multi-route coding, the destination node combines and decodes sub packets which are encoded and divided by the source node. The intermediate node relays a sub packet, that is, only a part of a packet. Therefore, the intermediate node cannot detect packet errors, and only the destination node can do after combining and decoding sub packets. We propose the ARQ scheme between the source node and the destination node, and evaluate the performance of the proposed scheme.

Experiment on Hierarchical Coding Scheme for Parallel Optical Wireless Communications

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

Technical Report of IEICE Vol. WBS2005-91 page： 75-79 2006.3

Language：Japanese

In this paper, we evaluate the performance of hierarchical transmission scheme using LED traffic lights and high-speed camera for ITS application. By using camera as a receiving device, parallel data transmissions are possible if each of LEDs in traffic lights is individually modulated. In such parallel LED-camera channel, if a receiver is far from a transmitter the received data pattern degrade and it is hard to distinguish adjacent LEDs. To overcome, we have proposed hierarchical coding schemes. Experimental results show that the proposed hierarchical coding schemes outperform the conventional on-off keying(OOK) if LED-camera distance is further.

Applying OFDM modulation to Simple Regenerative Repeating Process of Broadband Satellite

T. Yamazato, H. Kuwamura, A. Ogawa

Technical Report of IEICE Vol. SAT2005-53 page： 23-28 2006.2

Language：Japanese

The authors have been working on the simple regenerative repeater for satellite communication systems that omit the process of error-correction-decoding and re-encoding in the satellite side. We have implemented coded QAM system to FPGA board and confirmed the effectiveness till now. If a header part is common by this simple regenerative, transmission is theoretically possible with a signal of any kind of signal format. In this study, we introduce the FPGA implementation of OFDM signal and show the effectiveness of regenerative repeating process for OFDM transmission.

A Proposal of Iterative Nonlinear Distiortion Compensation Scheme for OFDM Trandmission in Satellite Channel

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

Technical Report of IEICE Vol. SAT2005-56 page： 37-42 2006.2

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Papers - YAMAZATO Takaya