Research On Rake Receiver For CDMA Systems Based On Interference Cancellation

Code division multiple access (CDMA) is an interference-limited system, and itscapacity is mainly affected by multiple-access interference and multipath interference. Toeliminate the interference, the Rake receiver is often used in the CDMA system. Whilethe Rake receiver technology only merges multipath signals in some kind of way, inorder to improve the signal to noise ratio. In the case of more users, multiple-accessinterference will lead to a sharp decline of the Rake receiver performance, because themultiple-access interference is in fact equivalent to a non-Gaussian colored noise, in thecombination of the multipath signal, multiple-access interference may not only be offset,but also may be strengthened, especially in the disturbance intensity stronger than theideal signal strength. Therefore, optimizing the Rake receiver technology is practicallysignificant and applicable in future.This paper explores the algorithm of interference-cancellation-based Rake receiverfor CDMA，and proposes the optimum algorithm of joint detection of Rake receiver/interference cancellation and decoding, by combining recently-proposed Turbo signalprocessing technology.The main work in this paper includes:(1) By analysis of the structure of Rake receiver for CDMA systems, the simulationmodel of Rake receiver for CDMA systems is built. The results show that the number ofthe diversities will affect the performance of the system. And, in the case of multi-users,the system is not only affected by multipath interference, multiple-access interference isalso a key factor to affect the system performance.(2) The algorithm of interference-cancellation-based Rake receiver is proposed, andwe focus on simulation research. The experimental results show that the techniques of Rake receiver based on interference cancellation can effectively suppress multipathinterference and multiple-access interference and improve system performance forCDMA system.(3) By applying Turbo signal processing, and combining Rake receiver/interference cancellation and viterbi decoding, we propose an optimization algorithm ofjoint detection, and set up corresponding simulation model. The computer simulationresults show that the joint algorithm can effectively reduce the implementationcomplexity with almost no system performance loss.