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The mobile WiMAX standard (802.16e) uses multiple-input multiple-output (MIMO) limited feedback linear precoding to exploit the channel state information at the transmitter. Although the performance of limited feedback linear precoding in relation to traditional open-loop MIMO-OFDM has been extensively studied in the literature, these studies commonly assume perfect channel estimation at the receiver. In a practical OFDM-based system, the estimated channel matrix often differs from the actual channel matrix due to errors incurred in the channel estimation process. This results in degraded performance relative to the case with perfect channel estimation. To date, few researchers have studied the impact of channel estimation error on the performance of an OFDM limited feedback linear precoding system. This paper investigates the channel estimation error using 1) an MMSE channel estimator that takes into account the subcarrier correlation when estimating the channel, 2) a Low Rank (LR) channel estimator that relaxes the requirement for a perfect channel covariance matrix in the MMSE receiver, and 3) a ZF estimator where this correlation information is ignored. Simulation results show that with the MMSE estimator the system suffers very little array gain loss with a performance degradation of 0.2dB SNR. Compared to the MMSE estimator, the LR estimator incurs a small performance loss of around 0.5dB. Finally, when the ZF estimator is implemented, a significant performance degradation is observed with approximately 4-5dB loss in array gain loss.
Date of Conference: 26-30 Sept. 2010