Variable rate space-time block codes in MPSK systems

We consider a multiple antenna system when combined array processing with spacetime coding is used. We present variable rate space-time block codes for two, three, and four transmit antennas and optimize the transmit power so that the average BER is minimized. Numerical results show that this optimum power allocation scheme provides significant gain over the equal power allocation scheme. We then classify all the variable rate space-time block codes having the same code rates and identify the unique code that achieves the lowest BER. We explicitly compute the performance of the variable rate codes over a Rayleigh fading channel. The proposed variable rate space-time block codes are useful for unequal error protection in multiple transmit antenna systems.