Robust Precoding Scheme in Downlink Multiuser MIMO-OFDM Systems with Imperfect CSI

This paper proposes a precoding scheme for downlink multiuser MIMO-OFDM systems. The proposed precoding employs the minimum bit error rate (BER) criterion and estimates precoding matrices to minimize total BER of mobile stations by the steepest descent algorithm. As the cost function of the proposed scheme, an upper bound of the total BER is derived from the pairwise error probability (PEP) and is averaged with respect to channel state information (CSI) errors. Thus, the proposed scheme can be robust to imperfect CSI. Computer simulations under a frequency-selective fading condition demonstrate that the proposed precoder is more robust to the CSI errors than the zero-forcing (ZF) precoder, and that it is superior in BER to the conventional scheme.