Adaptive Mode Selection for Multiuser MIMO Downlink Systems

This paper proposes a block diagonalization (BD) method, which nullifies the multiuser interference and, hence, increases the sum capacity in a multiuser multiple-input multiple-output (MU-MIMO) downlink system. The proposed BD scheme employs all users' receive processing as well as channel information. In addition, this paper proposes three adaptive mode selection schemes for the proposed BD: namely, an exhaustive mode search (EMS); an up-tree-based mode search (UTMS); and a down-tree-based mode search (DTMS). The EMS is a greedy search, whereas UTMS and DTMS are simplified searches that reduce the EMS computations significantly but have almost the same performance as the EMS. Simulation results show that the proposed BD method with the proposed adaptive mode selection schemes can increase the sum capacity significantly.