模糊理论在CDMA软切换中的应用

Application of Fuzzy Theory to CDMA Soft Hand-off

传统软切换一般采用常数阈值,若设置过小,则将占用过多的业务信道;设置过大,则软切换减少,掉话率增加。基于此,本文研究了模糊理论在码分多址移动通信系统软切换阈值中的应用及仿真技术。采用模糊软切换,通过剩余业务信道数量(CHrm)及与移动台连接的基站数量(noBS)输入获得软切换阈值,提出了输入T_DROP、CHrm,输出noBS采用三角形隶属函数及利用加权平均公式的解模糊方案。仿真结果表明,模糊软切换比传统软切换更灵活,它依靠系统环境动态地给出软切换阈值,降低了系统的呼叫阻塞率,提高了资源效率。

Conventional soft hand-off generally uses constant thresholds. If the constant threshold is set too small, then it will occupy more traffic channels; if it is too large, then it will reduce soft hand-off and increase interruption rates of conversation. The application and simulation of the fuzzy theory in soft hand-off thresholds of direct-sequence code-division multiple-access mobile communication systems are studied. The soft hand-off thresholds are considered to depend on two inputs, the number of the remaining traffic channels（CHnn）and the number of base stations connected to each mobile station（noBS）. The defuzzification scheme uses the weighted average formula and triangular membership functions of T_DROP, CHn and noBS. Simulation shows that fuzzy soft hand off is more flexible than conventional soft hand-off, because it depends on the system circumstances and gives thresholds dynamically and it yields lower call blocking probability and higher trunk-resource efficiency.