Sum-Rate Analysis of Multiuser MIMO System with Zero-Forcing Transmit Beamforming

In this paper, we present the exact sum-rate analysis of the multiuser multiple-input multiple-output (MIMO) broadcast channel with zero-forcing transmit beamforming. We develop the analytical expressions of the ergodic sum-rate for two low-complexity user selection strategies for the important dual- transmit-antenna scenario. Based on the analytical results, we examine the parameter optimization problem to properly trade off between channel power gain and directional gain in term of maximizing the ergodic sum rate offered by multiuser diversity.