A multi-user multi-beam selection scheme based on orthonormal random beamforming for mimo downlink system

This paper investigates multi-user scheduling with limited feedback of partial channel state information for MIMO downlink system based on orthonormal random beamforming (ORBF). It already shows that ORBF could reduce feedback information remarkably at the same time the throughput is asymptotically optimal and scale as DPC. However ORBF yields severely degraded performance with low to moderate number of users. In this work, we present a multi-user multi-beam selection scheme based on ORBF. The core idea is to feedback more channel information for the group of users identified by ORBF so that much more sum-rate could be achieved even with low number of users. We analyze equal power allocation and adaptive power allocation among beams respectively. Simulation results show that substantial gain could be achieved at the expense of more feedback channel state information and more complexity at the transmitter.