Performance analysis of volterra-based nonlinear blind multiuser detector for DS-CDMA systems

Multiuser detection is an effective method to suppress the multiple access interference (MAI) and improve the performance of direct sequence code division multiple access (DS-CDMA) communication systems. Since the optimum decision boundary is nonlinear in nature, a nonlinear structure in the optimum multiuser detector can improve the performance of the receiver. The authors of this paper have proposed two nonlinear blind adaptive interference cancellation algorithms (the exact Newton and the approximate Newton) in one of their earlier works III. In this paper, a complete performance analysis and characterization of the nonlinear schemes with respect to various parameters are investigated in both synchronous and asynchronous DS-CDMA systems. The numerical results show that the adaptive blind multiuser detectors yield significant bit-error-rate (BER) improvement over the conventional matched filter detector in the presence of strong MAI. Further, the two nonlinear adaptive algorithms outperform the linear algorithm due to the nonlinear nature of the transmitted signals. Most attractively, the approximate Newton algorithm offers lower computational complexity, higher numerical stability and similar BER performance in comparison to the exact Newton algorithm.