Low-Complexity Hybrid Analog/Digital Beamforming For Multicast Transmission In Mmwave Systems

This paper studies multi-group multicast beamforming with a hybrid large-scale antenna array in millimeter wave (mmWave) communication systems. A low-complexity hybrid structure is adopted, where each RF chain is only connected to part of the antenna elements. We formulate a hybrid analog and digital beamforming design problem for multi-group multicast transmission with the objective of minimizing the total transmit power at the base station, subject to an individual signal-to-interference-plus-noise ratio constraint for each multicast group. The problem is very challenging and its global optimal solution is difficult to obtain. We first adopt alternating minimization method to design the analog and digital beamformer alternatively. Then we solve each of the analog and digital subproblems through solving a sequence of convex problems via concave-convex procedure (CCP). Each convex CCP subproblem is reformulated as a novel alternating direction method of multipliers (ADMM) form. Our ADMM reformulation enables that each updating step can be decomposed into multiple subproblems with much smaller size, which can be solved optimally in parallel with closed-form expressions. Simulation results show that our algorithm can achieve favorable performance with very low complexity compared with the state-of-art methods.