Downlink MMSE transceiver optimization for multiuser MIMO systems: MMSE balancing

We study the problem of mean square error (MSE) transceiver design for point-to-multipoint transmission in multiuser multiple-input-multiple-output (MIMO) systems. We focus on four optimization problems: minimizing the maximum weighted layer-wise or user-wise MSE under a total power constraint; minimizing the total transmit power subject to a set of layer-wise or user-wise MSE requirements. The non-convexity of these problems makes the derivation of globally optimal algorithms very difficult for transceiver design. New optimal power allocation strategies are derived for the problems considered here. Based on the power allocation, we study how this can be used for iterative transceiver optimization. We propose iterative algorithms and prove the monotonic convergence of the algorithms. The major advantages of the proposed algorithms are their low complexity and fast convergence behavior during the first few iterations. The proposed algorithms are suitable not only for downlink transmission, but also for uplink transmission with a total power constraint.