Study On CDMA Blind Multi-User Detector Based On Signal Subspace

Since the advantages of high capacity, soft capacity, soft handover, higher spectral efficiency, the ability to resist the effects of multi-path fading and so on, DS-CDMA communication system has been widely put into application. However, the Multi-Access Interference (MAI) and near-far problem in DS-CDMA steadily limit the further application of this technique.Nowadays for the third generation mobile communication system, multi-user detection (MUD) techniques has been regarded as an effective method to overcome MAI, most of the researches to MUD focus on the blind multi-user detector because of its special advantages.Based on the analysis and discuss of several typical MUD techniques, the main work of this thesis is focused on the study of the blind multi-user detection techniques based on the subspace approach and its performance simulation and evaluation. There are five chapters in this thesis:In chapter one based on the analysis of the merit and shortcoming of CDMA system, the necessity of MUD techniques is explained, the research history and status of MUD are introduced. In chapter two the DS-CDMA system model is deduced, the performance of the conventional single-user detector(CD),the optimal multi-user detector(OMUD),the decorrelating detector(DD) and the minimum mean . square error(MMSE) multi-user detectors are discussed. In chapter three for the synchronous CDMA system, the subspace signal model of blind MUD, the subspace expression of DD and MMSE MUD are provided. On this foundation, we probe into several blind multi-user detection algorithms based on subspace. After the simulation and performance evaluation, effective blind multi-user detection algorithms are demonstrated in this paper. For the asynchronous system, in chapter four a method to resist multi-path fading is introduced, Simulation shows that the improved blind MUD has the ability of restrict the effects of MAI and multi-path fading. Finally, the work of this thesis is concluded and the future research work is discussed.