Optimal transmit strategy of a two-hop decode-and-forward MIMO relay system with mean and covariance feedback

This letter proposes an optimal transmit strategy to maximize the cut-set bound on the ergodic capacity for the two-hop decode-and-forward (DF) MIMO relay system with the mean and covariance feedback. Upon the analysis of the ergodic capacity, we show that the optimal transmit beamforming directions in the first hop are along the eigenvectors of the difference between the source-relay channel and the source-destination channel. In the second hop, the relay should transmit along the eigenvectors of the relay-destination channel. Using the optimization theory, we then investigate the optimal power allocation for the source and the relay with the constraint of the total transmit power. Simulation results are then presented for illustration.