Multi-User Gain and Maximum Eigenmode Beamforming for MIMO Systems with Rate Constraints

We consider the sum-power minimization problem for multi-user multiple-input multiple-output (MIMO) systems with rate constraints. We show that significant performance improvements, qualified by multiuser gain (MUG), can be achieved by allowing multiple users to transmit simultaneously on their individual maximum eigenmodes. We also show that a major part of MUG can be achieved even with quite a small number of users and increasing the number of antennas at the base station is an efficient method for maximizing MUG.