The Research And Application Of Blind Multi-User Detection Algorithm In DS-CDMA System

In the third generation (3G) mobile communication Code Division Multiple Access (CDMA) system, the main interference are multiple access interference (MAI), multi-path fading,"near-far"effect, the noise in the system and some narrow-band interference. Because CDMA system is a kind of system whose performance will be limited by the interference being. The capability and performance of the system will be improved with the elimination of the interfe- rence. Multi-user detection (MUD) is a kind of effective measure against interfe- rence based on relation detection in recent ten years. It can effectively eliminate MAI and suppress the"near-far"effect. Combining MUD technology and Rake receiver can have good suppression effect of multi-path fading and MAI. In this paper, from this point of eliminating interfence and improve the performance of system, we put the emphases on the research of blind MUD algorithm without training sequences and saving spending of channel and its application in CDMA system.In this paper, based on the analysis and research of the detectors from ori- ginal detector to blind adaptive detector, three blind adaptive multi-user detec- tion algorithm are analyzed and compared, including decision-feedback variable step-size minimum output energy (MOE) blind adaptive algorithm, blind adap- tive Least Mean Square (LMS) algorithm and variable step-size blind adaptive LMS algorithm. Furthermore, places emphasis on optimizing systemically the important convergence parameter used to control maladjustment of variable step-size blind adaptive LMS algorithm, which is combined with decision- feedback variable step-size MOE blind adaptive algorithm, and bring forth a blind adaptive MUD algorithm for dynamic environment. The result from simulation indicates that this algorithm has good suppression effect on dynamic strong MAI and"near-far"effect. Finally, the improved algorithm brought forthin this paper is combined with Rake receiver and is applied to frequency- selective slowly fading channel, the bit error rate (BER) of conventional Rake receiver is compared and analyzed systemically with that of Kalman blind algo- rithm for slowly time-varying fading channel and algorithm brought forth in this paper. The result from simulation indicates that when the algorithm brought forth in this paper is combined with Rake receiver, it can reach lower bit error rate and its complexity is lower than that of the Kalman algorithm. It is fore- seeable that the combination and optimization of MUD technology and other technologies will promote effectively the development and application of mobile communication technologies.