Downlink transmit diversity: feedback efficiency and robustness

A recently introduced method for closed-loop transmit diversity (see Nagaraj, S. and Huang, Y.F., Asilomar Conference on Signals, Systems and Computers, 2000) is further analyzed in this paper. Specifically, the amount of power saving possible due to the inherent feature of selective feedback is quantified via a capacity analysis. An optimal adaptive algorithm for channel estimation, in the sense of maximum likelihood, is derived to provide robustness against feedback errors, which arise due to incorrect detection at the mobile.