Massive MIMO (M-MIMO), which consists of a large number of antennas at the base station (BS), is a promising technology to meet the high data rate and quality of service requirements of 5G wireless systems, while the hybrid beamforming architecture reduces the implementation costs with a low dimensional baseband processing unit combined with a massive phase array. In this project, we investigated how to reduce the BS power via QoS-aware eigenmode selection hybrid beamforming. We focus on a downlink communication scenario where a hybrid beamforming (BS) transmits data to multiple single-antenna users.
Given the knowledge of channel state information of all users, the hybrid beamformers at the BS are designed to minimize the BS power consumption while the data rate needed to meet quality of service (QoS) requirement of each user is satisfied. Herein, the zero-forcing (ZF) beamforming is directly applied on the effective baseband channel, and the RF beamformer is generated by matching the beamforming matrix columns, selected from a preset discrete Fourier transform (DFT) basis codebook, with the eigenvectors of the aggregated propagation channel, which is termed as eigenmode selection. We also present a phase array batch-switching structure to realize the eigenmode selection beamforming economically. Simulations demonstrate that substantial transmission power can be saved with the proposed eigenmode selection beamforming compared to existing propagation path matching schemes, especially in rich-scattering channels, while satisfying given QoS (data rate) requirements.