MmWave Multiuser MIMO Precoding With Fixed Subarrays and Quantized Phase Shifters

Millimeter-wave (mmWave) wireless communication promises high data-rates when combined with multiuser multiple-input multiple-output (MU-MIMO) technology. A practical deployment of these technologies, however, faces numerous challenges, including the design of energy-efficient analog hardware. To address these challenges, we consider a hybrid base station architecture that consists of a set of fixed subarrays with quantized phase shifters (FS-QPS). For this system, we investigate the multiuser beamforming gains with different phase-quantization levels and subarray geometries. We show that for zero forcing baseband precoding, analog precoder optimization becomes an eigenvalue maximization problem, which can be approximated efficiently by received power maximization. We develop an efficient, optimal analog precoder for well-established mmWave channel models, and provide performance bounds characterizing the required phase-shifting accuracy for a beam-steering codebook as a function of the geometric size of the subarray. To demonstrate the efficacy of the proposed FS-QPS architecture, we show simulation results using the latest 3GPP mmWave channel model for multiuser spectral efficiency, and compare our solution to existing architectures.