Abstract: Aiming at the soft handover key technology of the 3G and B3G CDMA mobile communication systems，in supposition that the far and near effect question is soloved by power control，and introduction the conception of logarithmic cross entropy，the soft handover model of overlaid cellular based on marcocell and microcell is analyzed.At the same time，the probability of soft handover user in microcell handovered to marcocell，as the important performance index in this model，is analyzed quantitatively，and the performance is simulated.Through the simulation result，it is shown that call blocking ratio of soft handover is decreased and communication quality is improved in CDMA systems.

Key words: logarithmic cross entropy, soft handover, overlaid cellular, communication quality

摘要： 针对3G及B3GCDMA移动通信系统软切换关键技术，在假设通过功率控制解决远近效应问题的基础上，引入对数交叉熵概念，对宏小区和微小区重迭小区的软切换性能进行了分析。同时对该系统的重要性能指标：微小区中软切换用户可切换到宏小区的概率进行了定量分析和性能仿真。通过分析可看出：该系统可合理地降低CDMA系统微小区软切换呼叫阻塞率，改善CDMA系统的通信质量。

关键词: 对数交叉熵, 软切换, 重迭小区, 通信质量