On the Sum-Rate of Opportunistic Beamforming Schemes with Multiple Antennas at the Receiver

The capacity region of gaussian multi-input- multiple-output (MIMO) broadcast channels has been shown to be achieved by dirty paper coding (DPC). However, due to the high complexity of DPC and the infeasibility of the channel state information (CSI) at the transmitter, in this paper we focus on random beamforming with multiple beams (RB- MUX). The main advantages of RB-MUX are multiuser diversity and spatial multiplexing gain at limited feedback load. In this paper we analytically assess the ergodic sum-rate of RB-MUX scheme with multiple antennas at the receiver by considering three combining techniques: maximum ratio combiner (MRC), optimum combiner (OC) and antenna selection (AS). The analysis relies on the assumption of large average SNR, so that the additive noise can be assumed negligible as compared to the beams mutual interference. Simulation results corroborate our analysis.