Improving performance of a space-time turbo code in a Rayleigh fading channel

Starting with an ordinary parallel concatenated turbo encoder in a block fading Rayleigh channel, we introduce bit-interleaving of the outputs, not for time diversity, but to increase the coding gain. We develop a guideline metric for designing QPSK space-time codes which reveals both the coding and diversity advantage of the systems as well as showing that it is unnecessary to guarantee full space diversity to achieve good performance in Rayleigh fading. Using channel a priori information in the MAP iterations for decoding, we achieve frame error rates within 1 dB of the outage probability with only modest increases in decoding complexity.