Group-oriented beamforming for multi-stream multicasting based on quality-of-service requirements

We address the problem of multi-stream multicasting, where independent data streams are transmitted from a multi-antenna transmitter to several groups of independent single-antenna receivers. Multi-antenna multicasting allows forming spatial beams. By properly shaping the beam patterns, intergroup interference can be avoided and the SINR at all receivers can be jointly controlled. In addition, we assume that dirty paper preceding (DPC) is employed at the transmitter to further reduce the interference. We first consider the problem of minimizing the total power subject to individual SINR constraints. We propose a near-optimal algorithm based on semidefinite relaxation, combined with optimal power allocation. We also derive a low-complexity algorithm, which shows good performance in the low-SNR regime. Then, we consider the problem of maximizing the worst-case SINR subject to a total power constraint. We propose a near-optimal solution based on a bisection strategy