Abstract :
Based on Alamouti code, Lee et al. proposed two-branch transmit diversity OFDM systems, namely, space-time block coded OFDM (STBC-OFDM) and space-frequency block coded OFDM (SFBC-OFDM). However, they employed the simple maximum-likelihood (SML) detector, which was designed under the assumption that the channel is static over the duration of a space-time/frequency codeword. Therefore, STB-COFDM/SFBC-OFDM suffers from the high time/frequency-selectivity of the wireless mobile fading channel. In our work, in addition to the original SML detector, three novel detectors, proposed by Vielmon et al., are applied to improve the two-branch TDBC-OFDM systems. Additionally, assuming sufficient cyclic prefix (CP), the performances of all systems in spatially uncorrelated time-varying multipath Rayleigh fading channels are evaluated by theoretical derivation and computer simulation, as well. Numerical results have revealed that significant performance improvement can be achieved even when the systems are operated in highly selective channels.
