Adaptive Space-Division Multiplexing for Multiuser MIMO Antenna Systems in Downlink

In a multiple-input multiple-output (MIMO) antenna system using space-division multiplexing (SDM) in downlink channels, co-channel users can be differentiated from their spatial signatures using linear signal processing at the transmitter and receivers. Much works have been done on the optimization of the multiuser MIMO antenna weights for maximizing channel utilization. In contrast to the previous works, our main objective is to address the optimization of the number of users’ activated spatial modes in minimizing the sum-power of the base station whilst performing MIMO antenna optimization and bit-power allocation of the spatial modes given the data-rate and error-rate constraints of the users. Based on the understanding that the number of activated spatial modes for a user should highly depend on the data-rate and error-rate required by the user, we devise an adaptive SDM algorithm that leads to near-optimal performance as a brute-force approach at much reduced-complexity. Simulation results demonstrate that there is a significant gap between performance with and without adaptive SDM.