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IEICE Transactions on Communications 2008 E91-B(3):829-836; doi:10.1093/ietcom/e91-b.3.829
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Copyright © 2008 The Institute of Electronics, Information and Communication Engineers

Regular Section -- Papers -- Wireless Communication Technologies

MIMO Systems in the Presence of Feedback Delay

Kenichi KOBAYASHI1, Tomoaki OHTSUKI2 and Toshinobu KANEKO3

1 The author is with the Graduate School of Electrical Engineering, Tokyo University of Science, Noda-shi, 278-8510 Japan. E-mail: j7305620{at}ed.noda.tus.ac.jp, 2 The author is with the Department of Information and Computer Science, Keio University, Yokohama-shi, 223-8522 Japan., 3 The author is with the Department of Electrical Engineering, Tokyo University of Science, Noda-shi, 278-8510 Japan.


  Abstract

Multiple-Input Multiple-Output (MIMO) systems can achieve high data-rate and high capacity transmission. In MIMO systems, eigen-beam space division multiplexing (E-SDM) that achieves much higher capacity by weighting at the transmitter based on feedback channel state information (CSI) has been studied. Early studies for E-SDM have assumed perfect CSI at the transmitter. However, in practice, the CSI fed back to the transmitter from the receiver becomes outdated due to the time-varying nature of the channels and feedback delay. Therefore, an outdated E-SDM cannot achieve the full performance possible. In this paper, we evaluate the performance of E-SDM with methods for reducing performance degradation due to feedback delay. We use three methods: 1) method that predicts CSI at future times when it will be used and feeds the predicted CSI back to the transmitter (denoted hereafter as channel prediction); 2), 3) method that uses the receive weight based on zero-forcing (ZF) or minimum mean square error (MMSE) criterion instead of those based on singular value decomposition (SVD) criterion (denoted hereafter as ZF or MMSE-based receive weight). We also propose methods that combine channel prediction with ZF or MMSE-based receive weight. Simulation results show that bit error rate (BER) degradation of E-SDM in the presence of feedback delay is reduced by using methods for reducing performance degradation due to feedback delay. We also show that methods that combine channel prediction with ZF or MMSE-based receive weight can achieve good BER even when the large feedback delay exists.

Key Words: MIMO, CSI, E-SDM, SVD, ZF, MMSE

Manuscript received October 31, 2006. Manuscript revised August 3, 2007.


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