Transmit precoding for MIMO relay systems with partial CSI under correlated fading

In this paper, we study the transmit precoding problem for multiple-input multiple-output (MIMO) two-hop amplify-and-forward (AF) relay systems, where the source terminal (ST), relay terminal (RT), and destination terminal (DT) are equipped with multiple correlated antennas and there exists a direct link between ST and DT. It is assumed that DT has perfect channel state information (CSI) while ST and RT only have the channel covariance information (CCI). We derive the asymptotic mutual information (MI) expressions for the MIMO-AF relay channel for any given signaling input distributions in the large-system limit. Using the asymptotic results, we design the optimal source covariance matrix and the relay precoding matrix that maximizes the asymptotic MI of the system if CCI is exploited.