Performance Analysis of Orthogonal Beamforming with User Selection in MIMO Broadcast Channels

This work considers the problem of multiuser transmission in a downlink transmission system where a transmitter with multiantenna elements sends information to a set of scheduled users with each having a single antenna. We investigate the sum rate performance of an orthogonal beamforming (OBF) scheme called adaptive OBF, which is a suboptimal low-complexity alternative to the capacity-achieving dirty paper coding approach. We develop a simple order statistics framework to evaluate the probability density functions (pdfs) of the scheduled users´ signal-to-interference plus noise ratio (SINR) values based on the knowledge of channel statistics and selection procedure. In particular, the pdf expressions for first and second scheduled users´ SINR values are obtained in closed-form. The analysis is verified by numerical results.