General-rank Transmit Beamforming for Multi-group Multicasting Networks Using OSTBC

Abstract—This paper addresses adaptive beamforming in multi-group multicasting networks where groups of users sub-scribe to independent services that are simultaneously served by the base station. Beamformers are designed to maximize the minimum signal-to-interference-plus-noise ratio (SINR) of the users in all groups subject to a total transmit power constraint. By combining multi-group multicast beamforming with Alamouti space-time block coding, the degrees of freedom in the beamformer design is doubled resulting in drastically improved beamforming performance. In our paper we extend recent approaches in [1] and [2] for rank-two beamforming, originally devised for single-group multicasting networks that are free of multi-user interference, to multi-group multicasting networks, where multi-user interference represents a major challenge. Simulation results demonstrate that the proposed approach significantly outperforms the existing approaches. Index Terms—Adaptive beamforming, multicasting, orthogo-nal space-time block coding (OSTBC), semi-definite relaxation (SDR), inner approximation I