Performance Analysis of Transmit Diversity Systems With Antenna Replacement

We propose a new closed-loop transmit diversity scheme for multiple-input-multiple-output (MIMO) diversity 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 transmit antenna resulting in the poorest path with an unused antenna 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 of the received SNR. We show through numerical examples that the proposed scheme offers a significant performance gain with a very minimal feedback load over existing open-loop MIMO diversity systems, and for a properly chosen threshold, its performance is commensurate with a more complicated generalized-selection-combining-based transmit diversity system while requiring a much smaller feedback load.