Transmit diversity systems with antenna replacement and its application to space time block coding transmission

We propose a new closed-loop transmit diversity scheme for MIMO systems based on orthogonal space-time block coding (OSTBC). The receiver of the proposed scheme checks the output signal-to-noise ratio (SNR) of the space-time decoder against an output threshold and requests the transmitter to replace the antenna corresponding to the weakest path with an unused one if the output SNR is below the threshold. We provide some interesting statistical analysis and obtain closed-form expressions for the cumulative distribution function (CDF), the probability density function (PDF), and the moment generating function (MGF) of the received SNR. We show through numerical examples that the proposed scheme offers significant performance gain with very minimal feedback load over existing open-loop MIMO diversity systems and its performance is commensurate with more complicated systems such as transmit generalized selection combining (GSC).