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研究了Rayleigh多径衰落信道下的直扩 /码分多址 (DS/CDMA)多用户系统的误码率.由于系统的复杂性 ,其误码率很难通过分析获得 ,Monte -Carlo仿真是一种可代替的性能分析工具.但是 ,Monte -Carlo仿真经常被过大的计算量所限制.重要抽样技术是一种方差减少技术 ,它能显著地减少运算时间.该文将描述重要抽样的基本原理 ,并分别利用Monte -Carlo和重要抽样技术仿真Rayleigh多径衰落信道下的DS/CDMA多用户系统的误码率.仿真结果表明 :重要抽样技术仿真与Monte -Carlo仿真结果吻合得很好 ,并且在低误码率的场合 ,与Monte -Carlo仿真相比 ,重要抽样技术能显著地降低运算量.“,”In this paper, the bit-error-rate(BER) performance of the asynchronous direct-sequence CDMA(DS/CDMA) multiuser system in a wireless radio communications environment characterized by Rayleigh multipath fading channels is investigated. Because of the system complexity, the BER performance of CDMA systems in such an environment is difficult to assess analytically. Monte-Carlo(MC) simulations can offer an alternative performance evaluation tools. But such an alternative is often limited by an excessive computational burden. Importance Sampling(IS) is a variance reduction technique which can significantly reduce the computational cost required by MC simulations. This paper will describe the basic principles of IS and the BER of DS/CDMA multiuser system in Rayleigh multipath fading channels is simulated using MC method and IS technique respectively. Simulation results indicate that IS results and MC results are in close agreement and that IS simulation can significantly reduce the computational cost required by MC simulation when the BER is very low.