Capacity and Optimization of Alamouti Coded OFDM System

In time-varying multipath Rayleigh fading channels, Alamouti coded orthogonal frequency division multiplexing (OFDM) systems suffer from time selectivity of the channels. Recently, the uncoded bit error rate performance of Alamouti coded OFDM systems with several detection schemes have been investigated. In this paper, another important system performance criterion, i.e., the achievable capacity, is addressed for Alamouti coded OFDM systems. Based on the effective signal-to-noise ratio, the bound of ergodic and outage capacities are derived analytically. Numerical results show that these bounds are tight enough and can be used to predict the system performance. Furthermore, based on these bounds, we observed that there exists an optimal value of the number of OFDM subcarriers from the point of view of maximal capacity, which can be obtained through simple numerical computation.