Rank-Two Transmit Beamformed Alamouti Space-Time Coding for Physical-Layer Multicasting
In physical-layer multicasting over a multiuser MISO downlink channel, transmit beamforming using Semi-Definite Relaxation (SDR) has been a popular approach. In this paper, the authors propose a rank-2 transmit beamformed Alamouti space-time code scheme, which may be seen as a generalization of the previous SDR-based beamforming framework. The beamforming problem arising from the proposed scheme is a rank-2 constrained Semi-Definite Program (SDP). They deal with it using the SDR technique, but this time using rank-2 approximation rather than rank-1 approximation in the previous transmit beamforming.