New parallel interference cancellation for convolutionally coded CDMA systems

Based on BCJR algorithm proposed by Bahl et a/and linear soft decision feedback, a reduced-complexity parallel interference cancellation (simplified PIC) for convolutionally coded DS CDMA systems is proposed. By computer simulation, we compare the simplified PIC with the exact PIC. Itshows that the simplified PIC can achieve the performanceclose to the exact PIC if the mean values of coded symbols arelinearly computed in terms of the sum of initial a prior loglikelihood rate (LLR) and updated a prior LLR, while a significant performance loss will occur if the mean values of coded symbols are linearly computed in terms of the updated aprior LLR only. Meanwhile, we also compare the simplifiedPIC with MF receiver and conventional PICs. The simulationresults show that the simplified PIC dominantly outperformsthe MF receiver and conventional PICs, at signal-noise rate(SNR) of 7 dB, for example, the bit error rate is about 10 4for the simplified PIC, which is far below that of matchedfilter receiver and conventional PIC.