Hybrid Beamforming Structure Using Grouping with Reduced Number of Phase Shifters in Multi-User MISO

This paper proposes a novel hybrid beamforming (HBF) structure that groups transmit antennas and users in multiuser multiple-input single-output (MUMISO) systems. In the conventional HBF structure, all transmit antennas are utilized to make radio waves directional in the direction of each user. In this case, radio frequency (RF) signals after digital-to-analog conversion are joined with the antenna with the smallest channel gain due to the variation in channel gain of each antenna based on the base station (BS) location and users, and the transmit antenna used is not optimized. Small channel gain antennas transmit signals that can be affected by interference and noise, degrading communication performance. Therefore, we propose a HBF structure that optimizes the transmit antennas used to make radio waves directional in the direction of each user by grouping users and antennas with a focus on the channel gain of each transmit antenna obtained from channel estimation. Phase shifters can be reduced in the analog precoder by the proposed method in comparison with the conventional method while still keeping performance of sum rate, as shown through simulations.