Comparison of different soft demodulation and decoding algorithms in coded M-ary orthogonal DS-CDMA systems

The system under study is a convolutionally coded and orthogonally modulated DS-CDMA system in time-varying frequency selective Rayleigh fading channels. In this paper, we investigate several iterative schemes based on soft demodulation and decoding algorithms. The performance of different strategies are evaluated numerically and proved to achieve substantial performance gain compared to the conventional hard decision based scheme, especially when the soft demodulator is assisted by decision directed channel estimation and interference cancellation techniques, and also when demodulation and decoding are performed jointly in an iterative manner.