Vertical Handoff Mechanism Based On The Application Of Heterogeneous Wireless Networks And Qos Guarantee

How to optimize the performance of vertical handoff to realize seamless handoff has become a very important challenge for heterogeneous wireless networks fusion. Aiming at the applications' quality of service guarantee, this thesis focuses on the selection of handoff target network and the execution flow of handoff signaling. They are two key problems of vertical handoff technology in heterogeneous wireless networks.The factors such as the diversification of interfaces, applications' quality of service, terminal's position, energy consumption, and speed are different and complex in heterogeneous wireless networks of dynamical environment. A context-aware-based vertical handoff decision scheme is proposed. The dynamic perception environmental information includes terminal's position, speed and link quality and so on. It is normalized by means of linear fuzzy membership function. Energy consumption is used to judge whether to continue to handoff. The speed screening is used to determine the optional handoff network. The comprehensive utility evaluation function is constructed to evaluate the comprehensive effect of the optional networks. The weights of decision factors are calculated by the hierarchical analytical theory. Based on it, in order to maximize the user's interests, the handoff target network is selected adaptively. The perception environmental information and the corresponding decisions are stored in the knowledge base to make the terminal select the handoff target network quickly.Due to the reduction of handoff delay and the applications'QoS guarantee, a vertical handoff protocol based on load balance and QoS is proposed to realize seamless vertical handoff. Firstly, for the applications' QoS guarantee, the transferring packets are mapped to form four kinds of queues by the priority levels. And it is designed queue admission control rules and bandwidth borrowing rules to reduce the network congestion of the access points/base stations. Secondly, in the multi-streaming multi-host performance of mobile stream control transmission protocol, it is introduced three kinds of service signaling in the media independent handoff. It could build the link with the handoff target access point in advance. It is used the signaling of dynamic address reconfiguration to carry on the new link on and the old link off quickly. Then it could reduce handoff delay.Finally, performance evaluations of the proposed decision scheme and handoff protocol are taken under OPNET simulation. The performance of hit probability of handoff, average times of ping-pong, handoff delay, packet loss rate, signaling overhead, etc. are analyzed. The results show the effectiveness of the proposed decision scheme and handoff protocol.