Performance analysis of Alamouti scheme in Rayleigh channel

The next-generation wireless systems are required to have high voice quality as compared to current cellular Mobile radio standards and provide high bit rate data services. The fundamental phenomenon which makes reliable wireless transmission difficult is time-varying multipath fading. In most scattering environments; antenna diversity is a practical, effective and, a widely applied technique for reducing the effect of multipath fading. Diversity techniques are mostly used in base stations to improve their reception quality. Hence transmit diversity schemes are very attractive. In this scheme, copies of the same symbol are transmitted through multiple antennas at different times, hence creating an artificial multipath distortion. A maximum likelihood sequence estimator (MLSE) or a minimum mean squared error (MMSE) equalizer is then used to resolve multipath distortion and obtain diversity gain. This paper presents performance analysis of the Alamouti (two-branch transmit diversity) scheme which provides the same diversity order as maximal-ratio receiver combining (MRC) with one transmit antenna, and two receive antennas. It is shown that the scheme may easily be generalized to two transmit antennas and M receive antennas to provide a diversity order of 2M. The digital modulation techniques employed in this work are BPSK and different orders of QAM.