Research On Seamless Vertical Handoff Scheme In Heterogeneous Networks

Network technologies such as WLAN and 3G are developing fast recent years. Integrating those two wireless technologies will make complements of the difference between WLAN and 3G such as signal coverage area, maximum data rate and fees. The researches on vertical handoff scheme are one of the important contents of multinetwork integrationFirstly, this thesis introduces the technical theory and the integrated structures of 3G/UMTS and WLAN, and the existing vertical handoff schemes. Then, by the analysis of the theory about Mobile IPv4 and Mobile IPv6, their characteristics are compared. The likely questions are discussed arising from Mobile IP being used to vertical handoff, and the schemes of Fast Vertical Handoff, Smooth Vertical Handoff and Cost Function-based Vertical Handoff are analyzed in details. Aiming at the insufficiency of Cost Function-based Vertical Handoff Scheme (CFVHS), this thesis proposes the Adaptive Initiative Predictive Vertical Handoff Scheme (AIPVHS). AIPVHS takes a cost function which orients active application to evaluate and select available networks, automatically adjusts the stable period, and enables the mobile nodes to adaptively carry out vertical handoffs. Furthermore, by adopting the technology of initiative predictive multicast forwarding, AIPVHS reduces the handoff delay and packet loss, achieves a fast and smooth handoff.Finally, Network testing conditions is constructed on the NS simulation platform, and CFVHS and AIPVHS are compared and tested. The results of the experiment show that AIPVHS can reduce the handoff latency and the counts of handoff greatly, increase the handoff performance of the system, and maintain a better QoS compared with CFVHS.