Fuzzy-based adaptive partial parallel interference canceller for CDMA communication systems over fading channels

The authors propose a fuzzy inference system (FIS) for the multistage partial parallel interference cancellation (PIC) multiuser detectors in a direct-sequence code-division multiple-access (DS-CDMA) communication system. The multistage PIC scheme is an effective method for the multiuser detection in the DS-CDMA systems, but the performance still suffers degradations in the near-far situations. The partial PIC (PPIC), which tries to reduce the cancellation error due to the wrong interference estimations in the earlier stages, outperforms the conventional PIC (CPIC) when the system load is high. An adaptive fuzzy inference mechanism is proposed to generate the adequate cancellation weights for the multistage PPIC by using the measured SNR and signals´ amplitudes, which reveal the reliability of the received signals. Simulation results show that the proposed fuzzy-based PPIC (FB-PPIC) detector is more robust over the fading channels and is more near-far resistant than both the CPIC and constant weight PPIC (CW-PPIC) schemes.