Precoding for Multiple Antenna Broadcast Channels with Channel Mismatch

We consider the downlink of a multiuser broadcast channel with multiple transmit antennas at the base station and users each with single receive antenna. We consider the case when the transmitter has partial knowledge of the channel state information (CSI) due to channel estimation errors or the existence of a limited-rate feedback link. With partial CSI at the transmitter we derive a precoding technique based on a minimum mean square error (MMSE) criterion, and using rate-distortion theory we specialize our results to the case of limited feedback when the generalized Lloyd algorithm is employed. Compared to other precoding techniques such as channel inversion or regularized channel inversion, it is shown by simulation results that the bit error rate (BER) of the proposed precoding technique significantly outperforms the BER of the previous precoding techniques. In addition, we consider the performance of the proposed precoding technique in the high signal-to-noise ratio (SNR) regime and show that similar to [2], [7], the BER of the system is asymptotically limited.