Multiuser Detection Algorithm Research For Direct Sequence Spread Spectrum-code Division Multiple Access System

With the development of date forms, information amount, user requirements, real-timesignal processing and other factors in modern wireless mobile communication field, theinformation processing capability of traditional Multi-user Detection (MUD) algorithms havebeen unable to meet the further requirement of mobile communication system anti-jammingperformance. This paper focuses on the convergence, tracking performance, processingprecision and stability, proposes a series of new concept MUD algorithms to improve theintegrated interference suppression performance of multiple access communication system,which represented by the Direct Sequence Spread Spectrum-Code Division Multiple Access(DS-CDMA) system, to satisfy the requirement of complex mobile communication.The main research results of this dissertation are as follows:(1) For excess detection error problem in the multi-user approximate process andtime-varying noise statistical process of single MMSE algorithm and Kalman algorithm,which easily decreases the algorithm stability of DS-CDMA system, an improvedMMSE-MUD algorithm and an improved blind adaptive Kalman filtering MUD algorithm areproposed. The proposed algorithms can improve the convergence and stability of singlealgorithm by reducing decision error generation or optimizing the iterative process, therebyenable the algorithm to handle the dynamic communication problems effectively.(2) For the various limiting factors of single adaptive MUD algorithms in complextime-varying communication environment, an adaptive steepest descent RLS-MUD algorithm,an adaptive blind Newton iterative Kalman filtering MUD algorithm and a blind adaptiveSOR/JGS iterative Kalman MUD algorithm are proposed, which according to the steepestdescent, Newton iterative, Jacobi and Gauss-Seidel iterative theory respectively. The proposedalgorithms can effectively improve the iterative process stability, real-time mutationprocessing capability and relaxation/damping/matrix norm parameters selection decisions ofsingle algorithm by matching the corresponding algorithm iteration methods according to themulti-user detection environmental differences. Simulation results show that the improvedalgorithms have better time-varying noise statistics estimation capability, convergence anddynamic tracking capability, therefor extending the application of algorithm effectively.(3) For the low detection precision problem cause by excessive repeated user sorting indetection process of traditional Successive Interference Cancellation (SIC) algorithm, aMMSE-SIC MUD algorithm, an asynchronous continuous Schwarz-SIC MUD algorithm and a blind adaptive Kalman-SIC MUD algorithm are proposed, which according to the MMSE,Schwarz and Kalman theory criterion. Simulation results of the synchronization BER accurateanalysis, asynchronous BER approximate analysis and algorithm performance comparison ofDS-CDMA communication system show that the improved algorithms can effectively ensurethe single detection level MUD precision and improve the overall detection of traditional SICalgorithm through reducing the user sorting in different actual application environment, whenthe independent judgment unit of single SIC algorithm has been rebuilt by the introduction ofreasonable MMSE, Schwarz or Kalman algorithm criteria units.(4) For the excess unnecessary calculation accumulation problem, which easily lead thealgorithm can not quickly converge to the expected user, caused by the Parallel InterferenceCancellation (PIC) algorithm that uses the same method multiple iterative computing in stagesto deal with all users, an asynchronous continuous parallel Schwarz-PIC algorithm and a blindadaptive Kalman-PIC algorithm are proposed. Based on the Schwarz and Kalman criteria, theimproved algorithms firstly divide the solving problem region into some sub-regionsaccording to actual systematic differences, then alternately solve the various sub-regionalissues, eventually merge the sub-results to achieve the solution of whole problem. Simulationresults show that the improved algorithms can accurately correct the MUD boundary valueproblems and track all users in real-time, furthermore simplify the operation process andimprove convergence speed and detection precision of PIC algorithm.(5) For the high complexity and slow convergence problem, which uses several phasesiteration for all users to avoid the detection error diffusion, caused by the traditional cascadestructure IC algorithm, an adaptive Kalman asynchronous IC multi-user detector for fadingchannel is proposed. The proposed MUD algorithm takes full advantage of the parallelcomputing features in the serial pattern, firstly selects the specific range, delay and phase ofthe corresponding spread spectrum sequence to secondary modulate detect data code, thenremoves the secondary modulated signal and cancels MAI, finally recovers the effective userdata from the received signal. Because the improved algorithm can adaptively determine thetermination of detection process according to the latest information data rather than the inputdata method, so it can effectively avoid the high complexity and low convergence caused byexcessive multiple several phases iterations. Simulation results show that the improvedalgorithm is of high detection precision, stable onvergence and low complexity.