Robust Rank-Two Beamforming For Multicell Multigroup Multicast

In practical cellular communication systems, perfect channel state information is not available at the base stations. Assuming that the channel uncertainty is bounded within a known spherical region, the authors consider in this study robust rank-two multicast beamforming for multiple groups of users in multicell systems. Worst-case robust beamforming is designed to guarantee that the predefined signal-to-interference-plus-noise ratio targets of all users are met for any channel instance in the bounded region. The Alamouti code is employed to double the degrees of freedom in the beamformer design. The authors apply the semi-definite relaxation (SDR) technique to address the formulated non-convex robust rank-two beamforming problem. Analytical results show that the SDR is tight when the number of users in each multicast group is no more than two and the channel uncertainty is sufficiently small. Finally, extensive simulations are carried out to validate the proposed beamforming design and the analytical studies.