Feedback decision functions for WCDMA serial interference cancellation receivers with pilot-aided channel estimation

Serial interference cancellation (SIC) is a very promising receiver structure for enhancing the uplink capacity of WCDMA cellular systems. It can be implemented easily in practice with low complexity compared to other multiuser detection techniques, and it offers an effective performance enhancement over conventional receiver structures. The system model we adopt resembles the WCDMA FDD mode of UMTS. We investigate different feedback decision functions for SIC receivers. The aim of the decision feedback function is to map the soft values of a given user at the output of the RAKE receiver to proper estimates of the interference to be canceled. We show that by using hard output decoding, the performance approaches that of a single user system where the complexity and memory requirements increase significantly. On the other hand, using soft detected feedback based on minimizing the mean square error, a significant performance enhancement with low implementation complexity can be achieved. Taking advantage of the structure of SIC receivers, we propose an enhanced pilot-aided channel estimation for SIC receivers without a significant increase in complexity. It is shown that the performance gains achieved by SIC are valid as well with real channel estimation. Performance simulation results are presented to compare and assess the different proposed implementation issues.