Low Complexity Hybrid Beamforming Based on Orthogonal Constraint and Phase Extraction

Hybrid beamforming (HBF) has been widely accepted to offer a compromise between cost and system performance in millimeter wave (mmWave) systems, while its performance is highly dependent on the corresponding computation complexity. Using an assumption of orthogonal constraint and phase extraction, an effective HBF algorithm is presented in this paper, which consists of a digital beamformer (DBF) stage and an analog beamformer (ABF) stage. Firstly, the optimal DBF with orthogonal constraint is derived for a given RF beamformer. Secondly, when the orthogonal property of the digital beamformer is enabled, the analog beamformer can be developed by extracting the phases of the unconstraint solution of the optimization in RF domain. Specifically, we consider the case of that the number of RF chains is equal to the number of data streams, which can further improve the energy efficiency of mmWave systems. Simulation results show that our proposed algorithm can effectively approach the full digital beamformer performance limit.