Optimal transmit strategies for MIMO systems with partial channel state information

We study the optimal transmission strategy of a single-user multiple-input multiple-output (MIMO) communication system with covariance feedback. We consider the situation with correlated receive and correlated transmit antennas in Rayleigh flat fading. Furthermore, we assume that the receiver has perfect channel state information (CSI) while the transmitter knows only the transmit correlation matrix and the receive correlation matrix. We show that transmitting in direction of the eigenvectors of the transmit correlation matrix is the optimal transmission strategy. In addition to this, the optimal power allocation is studied and a necessary and sufficient condition for optimality of beamforming is derived. The impact of the receive correlation on the achievable capacity and on the capacity-range of beamforming is analyzed. All theoretical results are illustrated by numerical simulations.