A Spatial Multiplexing Beamforming Scheme for Multicasting to Cooperators

This paper addresses the transmissions of a multi-antenna Base Station (BS), when communicating simultaneously with groups of radios in a multi-hop network of single-antenna radios. Each group is supposed to receive a distinct data stream, such that all members of the group receive the same packet at the same time. The intention is that each group will perform cooperative transmission in the next time slot or slots. We focus on just the first hop, in which the BS chooses the group members and beamforms to them, so that their individual signal to interference and noise ratios all exceed a minimum threshold. The problem we address, therefore, is a combination of spatial multiplexing and multicasting. Our approach does zero forcing on selected nodes and then checks that an adequate number of nodes in each group have at least the minimum signal-to-noise-and-interference ratio (SINR). Using simulation, we compare our approach to others and we consider the effects of errors in transmit-side channel state information.