Study on optimal transmission and reception schemes for mobile communications

点击翻译按钮获取中文摘要

This study aims to realize the optimum signal transmission in mobile radio OFDM systems, and focuses upon (i) minimum bit error rate (BER) precoding, (ii) the optimal receiver under co-channel interference conditions, and (iii) multiuser detection for the random access protocol. The details are described below.(1)When a receiver performs the maximum likelihood detection (MLD), a MIMO-OFDM precoder that can minimize BER of MLD is proposed. The proposed precoder controls linear processing of transmitted signals so that the upper bound of BER based on the pairwise error can be minimized. Thus it can improve BER of MLD more drastically than the conventional MMSE precoder.Furthermore, a precoder for a base station is also derived. It utilizes feedback information on a covariance matrix of interference plus noise from mobile stations, besides channel impulse responses of desired signals which are estimated by the base station. It is superior in BER performance to the conventional one that us … More es information on only the estimated channel impulse responses.(2)A receiver based on the maximum likelihood criterion is proposed to cope with co-channel interference in MIMO-OFDM systems. The proposed receiver suppresses co-channel interference by prewhitening signals received by multiple antennas, and performs signal detection by using an error between a whitening filter output and its replica. Both coefficients of the whitening filters and channel impulse responses for the replica are estimated by the eigenvalue decomposition. Computer simulations show that the proposed receiver can drastically compensate for degradation caused by the interference.(3)To improve packet throughput, a combination of the multiuser detection that can separate collided packets and the auto repeat request (ARQ) that performs metric combining is proposed. The proposed scheme identifies users whose packets collide by detecting user IDs, and then separates collided packets by nonlinear multiuser detection. When packet errors occur, it can reduce the number of retransmissions of ARQ by the metric combining. It is demonstrated that the proposed scheme can achieve about twice as much throughput as that of a conventional one. Less