Research On Transmit Multicast Beamforming Algorithms

Smart antenna technology, which improves the signal quality and controls interferes, has an increasing application in multicast scenarios nowadays, such as wireless digital television systems and trunking communication systems. In some multicast systems, the transmitters cannot obtain the downlink channel state information effectively. However, the angles between the users and the reference plane of the smart antenna can still be used in transmit multicast beamforming.The basic principles and signal models of smart antenna are introduced in this paper, as well as the principles and simulation methods of space-time models. Then transmit multicast beamforming algorithms under single-group scenarios are discussed. Two angle based algorithms are given:Maximize Average Beamforming Gain Algorithm and Maximize Minimum Beamforming Gain Algorithm. The simulation results show that the angle based algorithms can improve the signal quality effectively. Compared to the algorithms which are based on perfect CSI (channel state information), the angle based algorithms have some performance loss. However, all transmit multicast beamforming algorithms are not suitable when the users distribute randomly. Under this condition, an omnidirectional antenna is preferred. Transmit multicast algorithms under single group can be applied when the signals of different groups don't have mutual interferes.Transmit multicast beamforming algorithms under multiple-group scenarios are discussed at the last part of the paper. A perfect CSI based algorithm named Maximize Minimum SINR Algorithm is introduced, as well as two angle based algorithms named Maximize Minimum SIR Algorithm and Least Square Algorithm respectively. The simulation results show that the Maximize Minimum SINR algorithm performs best; the Maximize Minimum SIR algorithm can restrain the interferes effectively, but it also restrains some signals; the Least Square algorithm improves the signal while restrains the interferes. Furthermore, the simulation results also show that the algorithms in this part are not suitable when the users distribute randomly. Transmit multicast algorithms under multiple groups can be applied when the signals of different groups interferes mutually.