The impact of channel correlation on space-time block codes for different modulation schemes

Space-time (ST) block codes have been used to achieve transmit diversity in wireless communication systems. In this paper, the performance of the ST block code proposed by Alamouti is investigated for correlated channels in combination with higher order modulation. Despite a cross-correlation coefficient of 0.9, for example, the diversity gain for all QAM (quadrature amplitude modulation) schemes investigated is about the same and approximately 6.5 dB for an uncoded bit-error ratio (BER) of 10^-3. In contrast using the same crosscorrelation coefficient, the diversity gain varies (by maximal 1 dB for a BER of 10^-3) for different PSK modulation schemes, but is still in the range between 5.5 dB - 6.5 dB for a BER of 10^-3. For forward error correction (FEC) coded transmission the same relative diversity gain is obtained as in the uncoded case.