Research On Interference Rejection Algorithm Of Direct Sequence Spread Spectrum System

In recent years,spread spectrum communication has the wide application because of its own strong interference rejection and particular working. Now one of the mostly applications of spread spectrum technology is the popular CDMA mobile communication system. On the every different application environment , this system must adopt the effective , advanced and applied technology to reject signal fading caused by MAI, mutipath and near-far effects ,and also to solve the corresponding problem existented at the practice communication.In this paper the figures of sending end and receiving end of the direct sequence spread spectrum system are introduced. Also it describe the realization process of DS-SS system from the math theory. At the same time various adaptation algorithms used in CDMA system are discussed , such as SGD,LMS, NLMS, decision-direct algorithm, MOE and Griffthms' algorithm. This paper overviews some commonly used cost function of the adaptation algorithms that minimize them and analyse convergence simply. Secondly, the stationary points of the LCCM cost function are analyzed to demonstrate that the LCCMA attempts to suppress multipath of the desired user's signal rather than exploit it. Analysis is performed both with and without the assumption that the received signal is Gaussion to obtain the same conclusion. Lastly, aimed at this shortcoming of LCCMA, a new blind algorithm that is suitable formultipath channels is proposed--multi-channel LCCMA. Then we establish thesystem model and make the simulation experiments. It is shown that the performance of the algorithm is better than that of the conventional Rake receiver combining the same number of multipath components and approaches that of an adaptive receiver in the decision-directed following training.