Multi-Mode Multi-User MIMO System with Finite Rate Feedback

Multiple-input multiple-output (MIMO) transmission techniques improve spectral efficiency and/or reliability over wireless communications link. Spatial division multiple access (SDMA, or called multi-user MIMO) is a potential solution to achieve high system throughput among various MIMO approaches. However, rank deficiency of the varying wireless channel degrades the throughput performance of SDMA. Moreover, when the number of users with non-empty traffic buffers in a sector is small, multi-user MIMO suffers performance loss caused by receiver difference: linear receiver vs. successive interference cancellation (SIC) receiver. Multi-user MIMO solution is difficult to support SIC receivers due to the causal/sequential decoding, whereas single user MIMO could easily extended to SIC receiver case. In this paper, we propose a preceded multi-user MIMO transmission scheme with rank selection and single user/multi-user MIMO mode switch, which is called multi-mode per-user unitary rate control (multi-mode PU²RC). Feedback from each mobile station to base station is quantified and the limited feedback rate is always preferred at the expense of minimum performance degradation. Simulation results reveal that our proposed scheme outperforms multi-mode single-user schemes, single-mode multi-user MIMO schemes and single user MIMO schemes with SIC receivers altogether in terms of the achievable throughput bound.