Performance of closed loop transmit diversity with feedback delay

Closed loop multi-antenna diversity transmission methods are being considered for 3(rd) generation wireless standards. In these techniques, information about the downlink channel is fed back to the base station and utilized to provide diversity as well as antenna gain at low mobile velocities under flat fading conditions. The performance, however, drops at higher velocities, mainly due to the delay involved in the feedback of antenna weights. We analyze this behavior, with the aim of quantifying the degradation in average received signal power as a function of velocity. The two cases of complex weight feedback and pure phase feedback are considered. The analysis will help to determine a useful velocity range in which closed loop diversity is feasible.