QoS-Aware Hybrid Beamforming With Minimal Power in mmWave Massive MIMO Systems

Hybrid beamforming is used to leverage the benefits of both massive multiple input and multiple output (MIMO) systems and millimeter waves for significantly increasing the capacity of wireless networks. Existing schemes for hybrid beamforming in multiple radio frequency (RF) chains optimize a global measure of performance and ignore quality of service (QoS)
per data stream
. In this paper, we propose a novel scheme for hybrid beamforming to minimize the transmit power while satisfying QoS defined as the mean square error (MSE)
per data stream
. We propose a two-stage cascade structure for the baseband precoder and combiner, and obtain their respective matrices in both single- and multi-user systems. We also propose a simplified scheme for designing hybrid beamformers with no nested loops in the alternating optimization method. Simulations show less than 2 dBW optimality gap for the multi-user scenario, with significantly less transmit power as compared to other existing schemes. Our simplified scheme consumes a negligible amount of 0.1 dBW more transmit power than our scheme with nested loops.