A two-stage partially adaptive linear receiver for CDMA MIMO systems with Alamouti's space–time block codes

Abstract

The code-division multiple-access (CDMA) multiple-input multiple-output (MIMO) systems with Alamouti's space-time block codes (STBC) have been widely investigated for the great demand of capacities and transmission rates in the future wireless communication systems. The semi-blind Capon multiuser receiver is designed to achieve the goal by the usage of linearly constrained minimum variance (LCMV) filters. However, the Capon receiver suffers finite samples and signature vector errors. In this paper, we propose a novel two-stage receiver containing partially adaptive linear filters in parallel followed by the channel estimator and symbol detector. Two transformation schemes based on subspace techniques are designed in the partially adaptive linear filters. The channel estimation is executed after the partially adaptive linear filter where the computational complexity is saved considerably. A performance enhancement method is introduced by using the forward-backward averaging technique. According to the weighting analysis, we also present a simplified two-stage receiver with lower complexity. Furthermore, the diagonal-loading (DL) technique based on the worse-case performance optimization is often used to alleviate the drawbacks of Capon receiver. In the end, we apply the proposed the forward-backward averaging technique and the weighting analysis onto the DL-based Capon receivers. Computer simulations are given to demonstrate the effectiveness of the two-stage partially adaptive linear receivers for the CDMA MIMO systems with Alamouti's STBC schemes and the performance improvement of the DL-based Capon receivers with the forward-backward averaging technique and the weighting analysis.