Generalized adaptive STTD with L-stage feedback information decoding [3GPP applications]

The closed-loop adaptive space-time transmit diversity (ASTTD) scheme with real, non-binary transmit weighting functions has been proposed for the 3GPP standardization. Predictive feedback quantization is used for the encoding of feedback information (FBI) in the ASTTD receiver and its regeneration (decoding) in the ASTTD transmitter. The FBI decoder in the transmitter consists of an L-stage delay-line buffer for storing a number L of most recently received FBI bits, and a look-up table with amplitude weights that are selected by the state of the delay-line buffer. In this paper, the method for finding the optimum antenna weights for the ASTTD scheme with predictive feedback quantization, as a function of L most recently received FBI bits, is presented. It is based on the minimization of the Chernoff bound of the ASTTD bit error rate and gives a scheme robust to feedback errors. The Alamouti transmit scheme and switched transmit diversity follows as special cases of this more general theory.