Beam-Sweeping Design for mmWave Massive Grant-Free Transmission

To address the escalating demand for spectrum resources in emerging massive machine-type communication applications, it is promising to integrate massive grant-free transmission into millimeter-wave (mmWave) systems. As beam-sweeping schemes under hybrid beamforming architectures are commonly used to enhance signal power and extend coverage, this paper investigates an efficient beam-sweeping scheme for mmWave massive grant-free transmission under hybrid beamforming architectures. In this scheme, we propose a beam-sweeping design algorithm to optimize beamforming matrices, aiming to maximize spectral efficiency while ensuring quality of service (QoS) based on statistical information on uplink angles of arrival (AoAs). To address the intricate interdependence of beamforming matrices across different beam-sweeping slots, our solution begins with a two-stage genetic algorithm that pre-assigns users' access slots based on their uplink AoAs, decomposing the beamforming design problem into independent subproblems for each slot. Subsequently, a dual-layer beamforming design algorithm is proposed to solve these subproblems, optimizing beamforming matrices that enhance spectral efficiency and meet the QoS constraint. Numerous simulation results verify the effectiveness of the proposed beam-sweeping design algorithm in improving spectral efficiency and the capability to satisfy the required QoS.