Iterative Multiuser Detection for Turbo Coded Synchronous CDMA inGaussian and Non - Gaussian Impulsive

| In this paper, we develop an iterative multiuser receiver for decoding Turbo coded synchronous CDMA signals in both Gaussian and non-Gaussian noise. A soft-input soft-output non-linear multiuser detector is combined with a set of single user channel decoders in an iterative detec-tion/decoding structure. The non-linear multiuser detector utilizes the prior probabilities of each user's bits to form soft estimates used for multiple access interference cancellation. The channel decoders perform Turbo code decoding and produce posterior probabilities which are fed back to the multiuser detector for use as prior probabilities. Simulation results show that the proposed multiuser receiver performs well in both Gaussian and non-Gaussian noise. In particular, single user Turbo code performance can be approached within a few iterations with medium to low cross-correlation (0:5). I. Introduction Recently, there has been growing interest in the communications community in studying the combination of forward error correction (FEC) techniques and multiuser detection 1]]2]. Similarly, Turbo codes have received a great deal of attention since their introduction. By exchanging the \extrinsic information" between two \constituent decoders", the typical decoder employed for Turbo codes iteratively reduces the decoding error 3]. This iterative decoding structure (\Turbo principle") can also be utilized in other applications 4] and has stimulated research on iterative decoding of convolution-ally coded CDMA signals 5]-8]. Although the \Turbo prin-ciple" has been a focus of a number of researchers, there has been only limited research on using Turbo codes in CDMA systems 9]. Most of the past research assumes that the channel noise is Gaussian. Multiuser detection in non-Gaussian noise still remains a largely unexplored area. In this paper, we develop a low-complexity parallel interference cancellation (PIC) algorithm for multiuser detection of Turbo coded synchronous CDMA signals in correlated Gaus-sian and non-Gaussian noise. Our work is most related to 8] and 13], although Turbo codes were not considered in either of these papers. Our iterative detection/decoding structure is similar to that of 8]. However our approach has much lower complexity than 8], yet our approach provides similar