Efficient and accurate DS-SSMA deterministic signature sequence performance evaluation over wireless fading channels

This paper presents a quick and accurate performance evaluation technique for direct-sequence spread-spectrum multiple-access (DS-SSMA) systems with deterministic signature sequences over Rician flat-fading and frequency-selective fading channels (with RAKE receivers), without resorting to any assumptions with respect to the distribution of the multiple-access interference (MAI). The method is based on a reduced-complexity formulation of the characteristic function method and its computational complexity is simply proportional to the spreading gain thus rendering it attractive for the study of future wideband CDMA systems. The paper also presents novel results with respect to the accuracy of a Gaussian approximation of MAI as a function of various channel and system parameters. It is notably observed that the type of signature sequence has a strong influence on the Gaussian approximation´s accuracy which can degrade severely under a variety of conditions (e.g. with Walsh sequences over frequency-selective fading channels) even for a moderate to large number of users