The Research Of Multiuser Detection Technology Based On Genetic Algorithm In DS-CDMA Systems

Direct Sequence-Code Division Multiple Access(DS-CDMA) communication system is an interference-limited system.A DS-CDMA system employing conventional detection techniques will be degraded in performance and limited in capacity because of multiple access interference(MAI) and near-far effects.Multi-user detection(MUD) is one of the key techniques for these problems in CDMA system. Due to the fact that computational complexity of the optimum detector grows exponentially with the number of users in system, the optimum detector cannot be put into practice.How to obtain a fast and high-efficient multiuser detector with good performances will have significant theoretic and practical meaning for both present and future communication systems.The nonlinear MUD based on Genetic Algorithms(GA) is studied in this dissertation.The main work is summarized as follows:l)According to the model of DS-CDMA system,the performance of Simple Genetic Algorithms Multi-User Detector(SGA-MUD) is analyzed.Considering the premature convergence of adaptive genetic algorithms(AGA), a kind of multiuser detector based on Improved Adaptive Genetic Algorithms (IAGA-MUD) is designed. Simulation results show that IAGA-MUD performs well in resisting MAI and near-far effects and successfully overcomes the defects of AGA.2)With respect to the larger population scale , slow convergence rate and premature convergence of single group's genetic operation, a kind of Decorrelating Multiuser Detector based on Distributed Genetic Algorithms with migration strategy (DGAD-MUD) is designed combining the resisted MAI performance of decorrelating algorithms with the global fast optimum performance of distributed geneticalgorithms. Simulation results show that DGAD-MUD is better than SGA-MUD and converges more quickly on the optimums because of migration strategy.3)By comparing IAGA-MUD with DGAD-MUD under the same experimental simulation environment, simulation results prove that DGAD-MUD performs better than IAGA-MUD in resisting the near-far effects and the capacity of DS-CDMA system.