Energy Efficient Hybrid Beamforming in Massive MU-MIMO Systems via Eigenmode Selection

Hybrid beamforming in massive multiple-input multiple-output (MIMO) systems is one of the most promising techniques to meet rapidly increasing data rate demand of the fifth generation cellular system with reduced implementation costs. In this paper, we focus on a downlink communication scenario where a hybrid beamforming base station (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 radio frequency (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.