Hybrid Beamforming Design for mmWave Joint Unicast and Multicast Transmission

Abstract

In this letter, we investigate the beamforming design for millimeter-wave (mmWave) joint unicast and multicast (JUM) systems, in which the common and private signals are transmitted simultaneously. Due to the hardware limitation, the conventional fully digital beamforming methods are infeasible. We propose a suboptimal low-complexity hybrid zero-forcing (ZF) beamforming scheme for the mmWave JUM systems. The analog precoder and combiner are first optimized to maximize the effective channel gains. The ZF algorithm is then used to decide the unicast beamforming directions for cancelling the inter-user interference so that the optimization problem is reduced. With the unicast beamforming directions, the unicast power allocation and multicast beamformer are finally optimized by employing successive convex approximation (SCA) iteratively. The simulation results demonstrate that the sum-rate of the proposed algorithm is slightly inferior to the fully digital beamforming algorithm, but outperforms the orthogonal multiple access scheme.