Capacity of Alamouti Coded OFDM Systems in Time-Varying Multipath Rayleigh Fading Channels

The orthogonal frequency division multiplexing (OFDM) systems that exploit Alamouti transmit diversity technique can be divided into two categories, i.e. Alamouti space-time block-coded OFDM (STBC-OFDM) and space-frequency block-coded OFDM (SFBC-OFDM). In time-varying multipath Rayleigh fading channels, these systems suffer from both time and frequency selectivity of channels. Recently, several detection schemes have been proposed to improve the bit error rate (BER) performance of these systems. In this paper, the achievable average capacities of different detectors are investigated. Based on the probability density function (pdf) of the effective instantaneous signal-to-noise ratio (SNR) obtained by each detector, the analytical expressions of achievable average capacities for those systems with different detectors are derived. Numerical results are also presented to give some insights