Performance Enhancement of Random Unitary Beamforming Based Multiuser MIMO Systems With Optimum Combining

Random Unitary Beamforming (RUB) is an attractive low-complexity transmission scheme for multiuser MIMO broadcast channel. When there are a moderate number of users in the system, the sum rate performance of this signaling scheme becomes mainly interference-limited over high Signal-to-Noise Ratio (SNR) region. In this paper, the authors study the performance of RUB-based multiuser MIMO systems when optimum combining is employed at multiple-antenna mobile receivers to suppress multiuser interference. They adopt a geometric approach to derive the statistics of the output Signal-to-Interference Ratio (SIR) of the optimum combiner, based on which a sum rate upper bound is obtained over high SNR region.