Orthogonal space time block coding in fast flat fading channels

Transmit diversity techniques increase transmission reliability over wireless fading channels. Complex orthogonal codes can be used to generate redundant transmit signals from multiple antennas. We consider the decoding of a high order orthogonal space time block coding under fast fading channel environments. In an effort to mitigate the severe performance degradation of the conventional simple decoding, least squares decoding and a quadratic optimization decoding (QOD) are applied to the problem. Simulation experiment results suggest that QOD obtains a significant SNR gain at SER of 10^-3 and is rather robust to a degree of time variation of the channels. We also show that least squares decoding achieves a significant performance improvement relative to conventional decoding when the time variation degree is significant (f_DT_s=0.01, where f_D is the Doppler frequency and T_s is the symbol period), however, it does not obtain a significant SNR gain when channel variation is not significant (f_DT_s=0.005). Therefore. we can conclude that QOD is a good decoding technique for fast fading channels.