Abstract: 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%.

Key words: WLAN, 3G, Average forecasting, Gradient prediction