Space-time coded systems for high data rate wireless communications

The wideband high data rate wireless communications has recently received increasing attention because of its ability to provide high speed, high quality multimedia data services anywhere at anytime as well as its attractive compatibility with various wireless systems.; Though the information capacity of wireless communications systems increases dramatically by employing multiple transmit and receive antennas, increasing the signal quality or reducing the effective error rate is still a challenging issue because of the random nature of propagation channels. Accordingly, space-time block coding (STBC) relying on multiple antenna transmission is introduced in a narrowband system as an effective blind transmit coding scheme without requiring channel state information (CSI) and bandwidth expansion. It has the advantage of linear processing at the receive side, and thus has potential practical use, especially in high data rate systems.; However, wideband high data rate transmission may lead to severe frequency-selective channel fading that causes intersymbol interference (ISI) and corrupts the received signal. Furthermore, in an environment with several cochannel users, there exist cochannel interfering (CCI) signals. Therefore, rejection of interference from various sources is required to improve the signal reception in a space-time transmit diversity (STTD) system with STBC.; The dissertation is concerned with the problem of interference mitigation and performance enhancement in an STTD system. Different solutions are proposed depending on the type of system under study and the amount of knowledge available about the signal and the propagation environment.; By exploiting the spatial and temporal structure of STBC, a novel scheme is presented first to suppress ISI, coherently demodulate the information symbols with estimated CSI.; Considering an environment with several cochannel users, a method for solving this in a joint fashion is suggested based on maximum likelihood (ML) estimating. It is shown that how a combined transmit diversity, equalization and CCI suppression strategy can improve the system performance noticeably.; Adaptive space-time transmit diversity (ASTTD) is proposed as a closed-loop approach for further performance enhancement, which combines the ordinary STTD scheme with simpler feedback information. This scheme is easy to be included in the current 3GPP standard without any change of the air interface.; The performances of the proposed methods are evaluated by theoretical analysis and numerical simulations, and compared favorably with other alternative methods. It is demonstrated that an STTD system, both open-loop and closed-loop, is extremely effective for a high data rate communications.