Multi-user Detection In DS-CDMA

In CDMA system, Multi-access interference is one of the important factors that affect the systematic performance and capacity . Multi-user detection suppressing the interferences at the receiver. The problem that it should solve is: How demodulate the bit information reliably of some specific user or all of the users from digital bits sequence that interfere with each other. Multi-user's detection technique cancel the multi-access interferences effectively by joint detection or subtract the MAI from the receiving signal according to the knowledge of sequences of all users basing on traditional detection of filter bank. Thus it can improve the performance of the system and increases capacity of the system.This paper introduced the arisen background of CDMA, the problem to be solving in terms of the developing course of mobile communication. And presents the necessity of multi-user detection by analysis the advantage and disadvantage of the DS-CDMA system. Also, this paper gives a detailed description of the principle, main parameter in CDMA system and Gold sequence used in spreading spectrum communication system . Furthermore, this paper providing the mathematics model of DS-CDMA system, particularly the matrix formula of the receiving signals in synchronous and asynchronous channels, giving a theory analysis of the performance of error bit rate in traditional detection of filter bank.Basing on above analysis, the paper present the basic model of multi-user's detection, the principle, the character and the performance in the optimal multi-user algorithm and linear multi-user detection algorithm including the decorrelator and the MMSE. Also this paper present a introduction to SIC , PIC and improved PIC detection . At last ,this paper present a polynomial-expansion linear detector in theory and giving a simulation.