The impact of finite rate feedback on adaptive double space-time transmit diversity in Rayleigh fading channels

We investigate the impact of feedback signaling on the performance of adaptive double space-time transmit diversity (STTD) systems in wireless fading channels. We consider four transmit antennas with two space-time block encoders, where at least two receive antennas are required for detection. In adaptive double STTD systems, transmit power weights are adaptively adjusted relative to channel fading based on the feedback information. In our work, the optimum power weights are determined by a numerical search, which are functions of the number of feedback bits and the modulation size employed. We apply symmetric and asymmetric modulation methods in each space-time block encoder in cooperation with adaptive antenna weights. It is shown that the performance of adaptive double STTD with asymmetric modulations depends on the number of available feedback bits, while the same system with symmetric modulations has a relatively robust performance to variable feedback bits. Our results also show that in adaptive double STTD with asymmetric modulations, the number of feedback bits can be reduced with little performance degradations.