Hybrid sum rate maximization beamforming for multi-user massive MIMO millimeter wave system

Precoding for millimeter wave (mmWave) system is different from conventional sub-6GHz system due to the architecture and hardware constraints. In this work, we propose a new two-stage hybrid sum rate maximization precoding algorithm for a downlink mmWave multi-user multiple data streams system with large number of antennas at both the transmitter (TX) and the receiver (RX) side. The proposed algorithm will first select the radio frequency (RF) domain precoder and combiners based on the channel state information (CSI) locally available at each user. Conventional sum rate maximization base band precoding is then performed at TX with CSI feedback of the smaller dimension equivalent user channel. Simulation shows that the proposed algorithm offers higher sum rates compared with the state of the art two-stage hybrid precoding algorithm in the literature. It also approaches the sum rate performance of the conventional full digital sum rate maximization design.