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Dive into the research topics where Takashi Dateki is active.

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Featured researches published by Takashi Dateki.


vehicular technology conference | 2006

New OFDM Channel Estimation Method by Adding a Virtual Channel Frequency Response

Takashi Dateki; Daisuke Ogawa; Hideto Furukawa

A discrete Fourier transform (DFT)-based channel estimation method which exploits outside of the active frequency band is proposed for orthogonal frequency division multiplexing (OFDM) systems. Usually the DFT-based channel estimation method is degraded due to leakage from non-sample locations of the multi-path timing. In the proposed method, an additional virtual channel frequency response is added outside of the active frequency band so that the total channel frequency response is smooth and periodically continuous in the DFT size. This method decreases the leakage effect in the time domain, and therefore has better performance than conventional time domain methods. Simulation results show that the mean square error and block error rate performance of the proposed method is greatly improved, especially in high signal-to-noise ratio regions, for example, MIMO 4times4,16QAM, R=8/9.


personal, indoor and mobile radio communications | 2015

Efficient selection of user sets for downlink non-orthogonal multiple access

Takashi Seyama; Takashi Dateki; Hiroyuki Seki

Non-orthogonal multiple access (NOMA), which uses superposition coding at the transmitter side and successive interference cancellation at the receiver side, is a promising new downlink multiple access scheme. The product of user average throughputs among all users within a cell can be maximized by optimal proportional fair (PF) scheduling, but this is computationally complex because it requires an exhaustive search for all possible user sets and optimal power allocation among users. In this work, we propose a novel method of selecting user sets for PF scheduling in downlink NOMA. Unlike conventional suboptimal methods, the proposed method is based on the mathematical characteristics of the PF metric. The proposed method can reduce the complexity when the maximum number of multiplexed users is three and four as well as two by judging whether a user set is worth multiplexing or not on the basis of a simple condition between the weakest two users within the set. Computer simulation showed that the proposed method can significantly reduce the average number of searched user sets while achieving almost the same total and cell-edge throughput as the optimal method.


vehicular technology conference | 2013

A Low Complexity PMI/RI Selection Scheme in LTE-A Systems

Daisuke Ogawa; Chimato Koike; Takashi Seyama; Takashi Dateki

Recent wireless radio technologies have utilized precoding matrix and rank adaptation as a technique to increase frequency efficiency. In 3rd generation partnership project (3GPP) long term evolution (LTE) and LTE-advanced (LTE-A) systems, codebook based precoding is utilized. In the codebook based system, a mobile station (MS) needs to estimate optimum channel state information (CSI) which includes a channel quality indicator (CQI), a precoding matrix indicator (PMI) and rank indicator (RI) and to feed back the CSI to the base station (BS) in order to get higher frequency efficiency. Generally, the MS estimates the optimum precoding matrix from all possible precoding matrices which are predefined as the codebook. When such an exhaustive search algorithm is utilized in LTE-A MS, the MS needs huge computation power because the number of rank and precoding matrix patterns is large in a LTE-A system. In this paper, we propose a novel PMI/RI selection algorithm which is less complex than the exhaustive search algorithm in a LTE-A system. After evaluating the throughput performances by simulation and analyzing the computations, it is described that the proposed algorithm has the same throughput performances as the conventional algorithm and 13% of the computations compared with the conventional algorithm.


vehicular technology conference | 2012

MLD-Based MU-MIMO Detection Scheme for LTE Downlink

Chimato Koike; Daisuke Ogawa; Takashi Seyama; Takashi Dateki

Currently Multi-User MIMO (MU-MIMO) attracts attention to improve frequency usage efficiency. When using Maximum Likelihood Detection (MLD) for MU-MIMO detection, we need to know the modulation type of the transmitted signals. However in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system, the user to whom MU-MIMO is applied cannot be informed about the modulation type of the signals for a multiplexed interference user. Therefore, linear filters such as Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) are typically applied. In this paper, we propose an MLD-based MU-MIMO detection method with modulation-type estimation. In this method, we perform MLD by assuming possible modulation types to calculate metrics, and by comparing them, we determine the modulation type of the signals for an interference user. From the computer simulation results, we find that the proposed method can obtain better performance than MMSE with a slight increase in complexity from SU-MIMO detection.


vehicular technology conference | 2006

Evaluation of New NLMS and RLS Chip Equalizers using Tentative Decision Data for HSDPA Systems

Daisuke Ogawa; Takashi Dateki; Hideto Furukawa

Equalizers are currently being studied to improve the performance of wideband code division multiple access (WCDMA) downlinks. Especially for high data rate wireless systems (e.g. high-speed downlink packet access (HSDPA)), reduction of multiple access interference (MAI) and inter symbol interference (ISI) are key issues. We propose a new chip equalizer using tentative decision data and show that it has a high throughput performance for HSDPA systems. The normalized least mean square (NLMS) algorithm or the recursive least square (RLS) algorithm is used as the adaptive algorithm for the equalizer because these equalizers are well known to have lower complexity than the maximum mean square error (MMSE) equalizer. In the proposed method, high-speed physical downlink shared channel (HS-PDSCH) data is tentatively determined and used as a training signal to add to the common pilot channel (CPICH). In this paper, we show that the proposed equalizer has a good throughput performance compared with the conventional equalizer, and that the proposed RLS equalizer has a throughput performance that is approximately 73% of the ideal MMSE


Journal of the Acoustical Society of America | 2012

WIRELESS COMMUNICATION SYSTEM

Takashi Dateki; Tetsuya Yano


Archive | 2004

OFDM receiving method and OFDM receiving apparatus

Tsuyoshi Hasegawa; Takashi Dateki


Archive | 2012

Mobile wireless communication system and wireless communication apparatus

Takashi Dateki


Archive | 2011

Radio channel control method and receiving apparatus

Hideto Furukawa; Takashi Dateki


Archive | 2012

RADIO COMMUNICATIONS METHOD, TRANSMITTER, AND RECEIVER

Takashi Dateki; Takashi Seyama

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