The Study Of Linear Multi-User Detect Technology In DS-CDMA Communication Systems

Direct Sequence-Code Division Multiple Access(DS-CDMA) communication systems are interference-limited systems. A CDMA system employing conventional detect techniques will be degraded in performance and limited in capacity because of multiple access interference(MAI) and near-far effects. Multi-user detector (MUD) is one of the key techniques for these problems in CDMA systems, which deals with multiple access interference as useful information and eliminates it by utilizing correlation characteristics between signature waves. MUD techniques can dramatically relax "near-far" effects, significantly improve the system's performance and increase the capacity of CDMA systems. The computational complexity of the optimum detector grows exponentially with the number of users in system, so the optimum detector cannot be realized in practical. Linear MUD techniques in DS-CDMA systems are studied in this dissertation. The main works of the dissertation can be summarized as follows:1. By exploring the model of DS-CDMA systems, the performances of the decorrelating multi-user detector and minimum mean square error(MMSE) multi-user detector are studied. Further, the performances of blind adaptive MUD and adaptive MMSE MUD( LMS style ) with fixed step size and varied step size respectively are studied based on MMSE linear detect algorithms.2. With the principles of statistical signal processing theory and density function estimating theory, the minimum bit error rate(MBER) MUD and the least bit error rate(LBER) MUD using optimum designing methods under synchronous DS-CDMA downlink are studied. 3. The characteristics of chaotic sequences generated by using logistics-map modelare studied, then some generic principia are put forward for optimizing design of chaotic spreading spectrum sequences. Finally, the system's performances are studied when spreading spectrum with optimized chaotic spreading spectrum sequences and traditional spreading spectrum sequences respectively based on the minimum bit error rate MUD.This project is supported by scientific research project of Guangxi Educational Department(No.[2002] 316)...