Robustness of transmit diversity schemes with multiple receive antennas at imperfect channel state information

Transmit diversity is essential for efficient operation of many wireless systems. The well known simple transmit diversity (STD) system of Alamouti achieves diversity without any bandwidth expansion and without channel feedback [S. M. Alamouti, Oct. 1998]. Alamouti's system is susceptible to imperfect channel state information. In this paper we introduce a new transmit selection diversity technique, by modifying an existing technique and we compare the performance of three selection diversity systems utilizing 2 transmit antennas. The first system (hybrid SD-STD) compares the strengths of the signals coming to the receive antennas and if the channels associated with one transmit antenna have the highest amplitudes at all receiver antennas, then that transmit antenna is selected [A. E. Pusane and U. Aygolu, June 12-14, 2002]. For other outcomes the system uses simple transmit diversity of Alamouti [S. M. Alamouti, Oct. 1998]. The second system compares the total amplitude of the channels from the transmit antennas and makes the selection (STSD) [S. Thoen et al., 2001]. The third system, which is introduced here, simplifies the operation by choosing the transmit antenna to which the best channel belongs (SBSD). We have observed that for 2 receive antenna case; STSD has the best performance among the systems. Hybrid STD-SD has better performance at 3 receive antenna case if there are no channel estimation errors. In the presence of imperfect channel state information, other selection schemes could outperform Hybrid STD-SD and STD.