Research On Turbo Multiuser Detection Technology For CDMA System

CDMA has become one of the key techniques of 3G mobile communication system. However, multiple access interference (MAI) affects not only the system performance, but also the increasing of its capacity. Multi-user detection (MUD) is the way to cancel MAI from receiver. It is also good for eliminating near-far effect and multipath interference.In this paper, some techniques of MUD and Turbo code/decode are studied, and some simulations were done. Turbo MUD theory and some methods based on the idea of Turbo decoding were emphasized. To solve the problem of system delay which caused by the iterative in turbo MUD, a new algorithm named SW-Threshold-Log-MAP, combining the sliding window method with Threshold-Log-MAP, was proposed. Follow the rule of this algorithm, the received signal sequences was divided into two blocks for reducing the system delay, the threshold was set for simplifying the complexity of exponent operation in decoding. At the same time, considering that one threshold may produce more errors, another SW-Threshold-Log-MAP with two thresholds was presented. In this algorithm, the value domain of correlation function was divided into three regions.Simulation results show that the bit error rate of SW-Threshold-Log-MAP with one threshold is higher than standard Log-MAP algorithm, but the system delay is reduced to half of the standard Log-MAP algorithm. The performance of SW-Threshold-Log-MAP with two thresholds is better than the one with one threshold, and its performance is more approached to standard Log-MAP algorithm.