The Research On Multi-user Detection Technology In The Code Division Multiple Access Communication System

CDMA has become the main technology of the third generation mobiletelecommunication. Many users in CDMA system are distinguished by differentspread sequences and have the same time chip and frequency unlike in theconventional TDMA system or FDMA system. But the practical spread sequences cannot reach the ideal condition, the correlation function equals zero, so that it will causethe multiple access interference (MAI) when lots of people are communicating.Multi-user detection (MUD) makes joint detection on the received signals by makingfull use of the information of all users', which relaxes MAI and increases the capacityof system.This article introduces the principle of MUD,the optimum MUD, some classicalsuboptimum MUD based on the research on spread spectrum communication theoryfoundation, spread spectrum modes, spread spectrum sequences and CDMAcommunications system. It tells in detail the detection based on Hopfield neuralnetwork (HNN), which translates the problem of minimizing the objective function ofthe optimal MUD into resolving the minimization of energy function for HNNand hasthe disadvantage of easily getting into the local minimization of energy function. Aimat this disadvantage, this paper gives a novel detection based on genetic algorithm andHNN (GAHNN) and the model of GAHNN, which makes use of the globalconvergence advantage of genetic algorithm to provides a better initial value to HNN,then HNN will not get into the local minimization of energy function and get theglobal optimal solution to improve detection performance.Computer simulation results show that the detection based on genetic algorithmand HNN has better performance than the detection based on HNN, closer to theoptimal detection. It can realize multi-user detection quite well and improve thereceiving performance to some extent.