ABSTRACT:In this paper, an analysis for the bit error rate (BER) performance of space-time block codes (STBC) from generalized orthogonal designs for QAM modulation has been presented. Space-time block codes (STBC) offer high diversity gain and among which orthogonal STBCs are very attractive due to its relatively simpler design and low decoding complexity. Performance of Alamouti STBC and Orthogonal STBC with rate ½ for different transmitting and receiving antennas under Rayleigh fading situation has been analyzed. The decoding techniques used for this analysis are ZF, MMSE and ML. In all the cases, the bit error rate has been treated as the figure of merit and its change with SNR are observed due to different parameter variations of the channel distribution as well as different antenna configurations.