Transmit diversity techniques for multicasting over wireless networks
Transmit diversity (TD) is one of the key technologies to achieve high data rate communications in wireless fading environments. While transmit diversity techniques have been extensively studied for point-to-point communications, their applications in wireless multicast scenario have not been fully exploited. In this paper, we first design an adaptive transmit antenna array for multicasting, with the assumption of perfect channel information at the transmitter and the performance criteria as maximizing the worst signal-to-noise ratio (SNR) among all receivers. Compared with the existing beamforming scheme that aims to maximize the average SNR, a performance gain in decoding bit error rate is obtained. Then, the proposed close-loop scheme is compared with space-time block coding that does not require feedback of channel information. When the number of multicast receivers is below a certain threshold, the proposed close-loop scheme outperforms the space-time codes. When the multicast group size is large, the space-time codes have better performance. Finally, jointly considering close loop and open loop techniques based on group size and availability of channel information feedback is suggested.