Hybrid Beamforming for Ergodic Rate Maximization of mmWave Massive Grant-Free Systems.

To meet the escalating demand on spectral resource in massive machine-type communication (mMTC) applications, a critical solution is applying massive grant-free transmission to the millimeter-wave (mmWave) band. In this paper, to maximize the ergodic rate, we propose an efficient hybrid analog/digital beamforming (HBF) design algorithm for the massive grant-free transmission in uplink mmWave systems. Specifically, to make the HBF design problem tractable, we first leverage the deterministic equivalent method to derive an approximate expression of the ergodic rate for the mMTC in the mmWave system. Since the ergodic rate maximization-based HBF design problem is nonconvex, we leverage the alternating optimization strategy and propose a semidefinite relaxation-based HBF algorithm to improve the ergodic rate. Simulation results verify the superior performance of the proposed HBF design algorithm in improving the ergodic rate.