Clustered Block Diagonal Digital Precoding for BDMA Downlink Transmissions

Beam Division Multiple Access (BDMA) has recently been proposed for massive multiple-input multiple-output (MIMO) systems by simultaneously transmitting multiple users’ data streams via different beams. Meanwhile, the block hybrid precoding has been proposed to reduce the computational complexity. However, previous works mostly rely on a crucial condition that the number of RF chains must be not less than the number of data streams. In this paper, we propose a BDMA based hybrid block precoding system to break the ceiling on minimal required RF chains where the data streams are processed cluster-by-cluster. Then two digital precoding approaches are investigated to suppress the intra-cluster interference by separately considering the signal-to-interference-and-noise ratio (SINR) and signal-to-leakage-and-noise ratio (SLNR). To overcome the performance degradation arisen from block hybrid precoding scheme, a greedy user clustering algorithm is proposed to minimize the intercluster interference. Simulation results confirm the effectiveness of proposed block clustering precoding scheme compared to conventional hybrid beamforming scheme.