Hybrid Beamforming with Variable RF Attenuator for Multi-User mmWave Systems

In this paper, we propose a novel hybrid beamforming design algorithm in multi-user massive multiple-input-multiple-output millimeter-wave channels. In the proposed structure, we employ variable radio frequency attenuators at each phase shifter which flexibly controls the transmit signal amplitude to achieve the performance of fully digital (FD) precoders. We formulate a power loss minimization problem which can be easily solved via the alternating optimization process. Simulation results demonstrate that the proposed architecture achieves the same performance as the FD scheme with the reduced number of radio frequency chains and the proposed scheme exhibits a 37.4% power gain over conventional methods.