Turbo Equalization for Alamouti Space-Time Block Coded Transmission

Recently, space-time block coding (STBC) has received a remarkable interest as an effective transmit diversity technique to combat channel fading, but STBC provides little or no coding gain. However, as channel coding is usually employed in wireless systems, the combination of channel coding and STBC can be used to achieve high throughput gains over wireless channels. On the other hand, turbo (iterative) equalization can be employed in channel coded broadband wireless systems to further enhance the performance. Hence, in this paper, we propose a minimum mean square error (MMSE)-based turbo equalization scheme for Alamouti space-time (ST) block coded multiple-input multiple-output (MIMO) systems. In the proposed iterative receiver, widely linear (WL) processing is used to exploit the rotational variance of the ST block coded transmit signal. Equalization and ST block decoding are jointly carried out at each iteration using the a priori information delivered by the convolutional channel decoder from the previous iteration. The extrinsic information generated by the combined soft equalization-ST block decoding stage is passed to the channel decoder as the a priori information. The simulation results demonstrate that high performance improvement can be obtained using the proposed iterative scheme in comparison with thenon-iterative equalization. Due to the low-complexity, the proposed iterative scheme may be highly attractive to be implemented in future Alamouti ST block coded wireless systems.