Angle-of-arrival based beamforming for FDD massive MIMO

A key challenge in FDD massive MIMO is the large overhead in CSI acquisition for closed-loop MIMO transmission. In this paper, we propose two novel types of angle-of-arrival (AoA) based beamforming schemes that harness the reciprocity of dominant AoA. Both schemes require CSI acquisition overhead that only scales with the number of served mobiles, not the number of base-station antennas. We analyze the performance of the proposed schemes both analytically and numerically. We show that both our proposed schemes lead to sum throughput that scales with the number of base-station antennas, and hybrid beamforming performs close to ideal zero-forcing beamforming.