Performance Loss of Hybrid Beamforming with Imperfect Phase Shifters in Millimeter Wave Systems

Hybrid beamforming(HBF) is widely adopted for power saving and cost reduction in millimetre wave(mmWave) massive MIMO systems. It includes analog beamforming in phase shifted array and digital beamforming in baseband. Phase shifted array is usually made up with a large amount of phase shifters. Due to production process in mmWave, phase shifters are unavoidable to have phase-shifting error and gain error. In the paper we study the influence of imperfect phase shifter upon the performance of the mmWave massive MIMO systems. We derived the closed-form expression of the loss of spectral efficiency in multi-stream point-to-point scenario. Both the theoretical results and simulation results show that there is a spectral efficiency ceiling due to phase-shifting error and gain error. The analytic procedure can be applied for both the sparse channel and the rich-scattering channel.