Robust beamforming optimization for multi-group multicast system

In next-generation wireless communication systems, multimedia multicast could improve spectrum efficiency markedly. In this paper, a angle-based limited feedback model is built for downlink multi-group multicast systems. Two parts of the channel state information (CSI), i.e., the quantized channel direction information (CDI) and the accurate channel quality information (CQI) are fed back to the base station (BS) simultaneously, where a proper codebook is shared by all users in the system and the BS. With the imperfect CSI available at the BS, the Quality of Service (QoS) problem for multi-group multicast systems is reformulated and the closed-form lower bound of the average signal to interference and noise ratio (SINR) of each user is derived. Conventional semi-definite relaxation (SDR) and Gaussian randomization are employed jointly to solve the original problem. Several simulation results are presented to demonstrate the satisfying performance of the proposed beamforming scheme.