A Novel Two-Stage Beam Selection Algorithm in mmWave Hybrid Beamforming System

Abstract

A hybrid beamforming structure, which consists of digital precoding and analog beamforming, is a low-cost solution to millimeter wave (mmWave) large-scale antenna systems. In this letter, we study the sum rate maximization problem where an analog beamformer is selected from a discrete codebook. A two-stage scheme is proposed in order to avoid an exhaustive search. First, the lower bound of the sum rate is derived, and the trace inverse of the equivalent channel is determined as a novel metric for beam selection. Based on this metric, we formulate a convex problem to derive an initial beam set. Finally, an iterative algorithm is designed to update beams for further performance improvement. Simulation results demonstrate that the proposed scheme achieves a near-optimal sum rate performance and outperforms existing schemes.