Sum-rate Analysis of Multiuser MIMO Systems with Codebook-based Incremental Beamforming

In this paper, we present the sum-rate analysis of multiuser multiple-input multiple-output (MIMO) downlink systems with incremental beamforming (IB). We develop the analytical expressions of the ergodic sum-rate for the dual-transmit-antenna scenario. Based on the analytical results, we compare the performance of the proposed IB scheme with popular random beamforming techniques, such as random unitary beamforming (RUB) and conventional random beamforming (CRB), and analyze their respective superiority and shortcomings. We show through selected numerical examples that our approach achieves similar performance as RUB but with much lower feedback load and system complexity. Ultimately, we introduce a modified version of our scheme that adaptively selects a second user for sum-rate benefit.