MMSE precoder design for a non-regenerative MIMO relay with covariance feedback

In this paper, we propose a precoder using a minimum mean-square error (MMSE) criterion for a non-regenerative relay system. It is assumed that the relay knows the channel covariance information (CCI) of the relay-destination link and the full channel state information (CSI) of the source-relay link. We start by assuming the precoder has a specified structure. We derive an upper-bound of the mean-square error (MSE) and obtain a closed form solution to minimize the upper-bound of the MSE. Although the proposed scheme is suboptimal, simulation results show that the proposed scheme has better performance in terms of the MSE and the bit error rate (BER) than the conventional schemes.