基于3G与WLAN网络改进的切换策略研究

Research on Improved Handoff Scheme between 3G and WLAN Networks

传统垂直切换技术缺乏切换对称性的考虑,从而导致了切换过程计算复杂度较高。通过对3G和WLAN之间切换过程的分析,提出了基于背景扫描机制的滑动平均值预测法和坡度预测法的改进切换策略。其中滑动平均值预测策略首先实时地计算接收的信号强度平均值,然后统计新接收的信号强度小于该平均值的个数,最后做出切换决策;而坡度预测策略通过计算所接收信号强度的一阶导数来决定是否发起切换。这两种策略的结合使用提高了移动终端发起切换的效率,缩短了切换过程中处于无连接状态的延时。设计了移动终端穿过3G网络、WLAN及其重叠区域的实验,其结果显示切换延迟平均减少了40%,切换过程丢包率平均减少了35%。

The lack of consideration of handoff symmetry in traditional vertical handoff technology leads to the high computation complexity of handoff procedure. Thus, the Background Scanning based Moving Average Forecasting Scheme （MAFS） and Gradient Prediction Scheme （GPS） were proposed. MAFS firstly calculates the average value of the received signal strength, and counts the number of signal strengths which are small than average value. MAFS finally triggers the handoff procedure. GPS starts the procedure of handoff through computing the first derivative of the received signal strength. The combination of MAFS and GPS improves the efficiency of vertical handoff and abbreviates the disconnecting time. An experiment in which Mobile Terminal passes through 3G network, WLAN and the overlap area was designed and implemented. The experimental results show that the average handoff delay is cut off 40% and the average handoff packet loss is also reduced 35%.