Multistage interference cancellation with multipath decorrelating for QPSK asynchronous DS/CDMA system over multipath fading

A combined multistage interference cancellation (MIC) and multipath decorrelating scheme (MIC-DECO) for asynchronous QPSK DS/CDMA over frequency-selective multipath Rayleigh fading channels is introduced. Unlike the conventional MIC, which attempts to cancel the multiple-access interference (MAI) and total self interference (SI) the introduced scheme aims to remove the MAI, and partial SI incurred by the self intersymbol interference (SII). After cancellation, decorrelating is used first to separate the multipath signals and then to re-combine the resulting fading replicas for symbol decision. If the noise correlation in the fading replicas is known, an optimum combining structure (MIC-OPTM) can be achieved. Furthermore, when the MAI and SII are successfully removed, the MIC-OPTM can be replaced by the MIC using RAKE combining (MIC-RAKE) with reduced complexity. The simulation results show that the MIC-DECO, MIC-OPTM, and MIC-RAKE in a multi-user environment provide a good performance close to the ideal performance in a single-user system, and outperform the conventional MIC even in the presence of channel estimation error