可变速率CDMA系统的话务模型

A Traffic Model of Variable-Rate CDMA Systems

本文研究可变速率码分多址 (CDMA)系统中的话务模型 .由于可变速率CDMA系统中采用的正交扩频码是正交可变扩频因子 (OVSF)码 ,信道的传输速率和可用信道的数目随着选择的码字不同而不同 .针对用户的服务时间是时变的任意分布 ,我们运用M/G/K队列模型 ,用近似法获得用户平均延迟时间等话务模型的重要参数 .文中给出了采用可变速率正交扩频码的CDMA系统的话务模型 ,以及相应的话务流量 ,平均延迟时间 ,用户平均停留时间等系统参数的计算式 ;得出采用可变速率的数据传输后 。

A traffic model for the Code Division Multiple Access (CDMA) systems supporting variable rate services is developed.In the system where Orthogonal Variable Spreading Factor (OVSF) codes are used,the number of channels available and the transmission rates of the channels are determined by the selection of the spreading codes.In the view that the service time has a time varying arbitrary distribution,an M/G/K queue is adopted and the average user delay time is approximated.The traffic model of the CDMA systems using OVSF codes is then established,and traffic throughput,average delay time and average holding time are derived.It is also concluded that the variable rate data transmission can introduce twice average delay time compared to the fixed rate transmission.