Research On The Key Technologies Of Vertical Handoff In Heterogeneous Networks

Mobility management is one of the most challenging technologies in the future ubiquitous and heterogeneous network environments. As one of the key control functions of the future mobility management technology, vertical handoff is used to provide session continuity across heterogeneous networks.The heterogeneity of different wireless access networks is the most challenging issue of the future mobility management technology. Such heterogeneity exists in the different network architectures, radio interfaces, control mechanisms such as AAA and QoS, as well as the different features in coverage, data rate and mobility supporting capability etc. With respect to the research on vertical handoff, it still faces the challenges in handoff performance, handoff decision and interoperability etc. In the existing researches, some limitations do exist: 1) Handoff performance optimization. In order to realize the access-independent handoff, vertical handoff is often implenmented at the network layer or above and incurres considerable performance problems. 2) Vertical handoff decision is a typical multi-criteria decision problem. But the existing schemes still have some disadvantages such as unfeasibility, ping-pong effects and inefficient utilization of wireless network resources. 3) The interoperability in vertical handoff must be considered to deal with the differences in the control mechanisms such as AAA and QoS.Based on the systematical summary and analysis of the latest researches on vertical handoff, this dissertation focuses on the issues of performance analysis of the typical handoff protocols, the handoff decision method, the connectivity management, the QoS mapping in vertical handoff and so on.The major contributions of this dissertation are as following: 1) Performance analysis of the typical vertical handoff supporting protocols. Considering the asymmetry feature of vertical handoff and the error-prone feature of wireless links, this paper analyzes the handoff performance of MIPv6 ,mSCTP and SIP based on unified analysis model. Qualitative and quantitative analysis and comparison of the handoff performance including handoff delay, handoff packet loss and signaling overhead are given accordingly. Besides, the main factors influencing vertical handoff performance are pointed out and possible performance improvement schemes are discussed.2) With regards to the vertical handoff decision, a QoS evaluation based and application-oriented vertical handoff decision method is proposed. mSCTP is adopted as the transport layer protocol in the terminal architecture. It supports cooperation among heterogeneous network interfaces. Different QoS requirements of various application types are considered in weight value determination. The handoff decision follows "per application" and "the most suitable" principles for efficient network resources utilization. Simulation results show that the proposed method can reduce the unnecessary handoff and realize well tradeoff between the performance optimization of single application and efficient utilization of network resources.3) From vertical handoff to connectivity management based on mSCTP. A connectivity management scheme based on mSCTP is proposed to realize the integration of bandwidth aggregation and mobility supporting at transport layer. The major path management functions are defined and the path handoff procedure is introduced. A transport path subset selection policy based on wide-sense path definition is proposed. The simulations on the effect of the throughput improvement, the path subset selection policy and the mobility supporting are complemented respectively. The simulation results show that the proposed scheme can realize efficient integration of bandwidth aggregation and mobility and the application-based path subset selection policy has apparent performance advantages.4) QoS mapping among heterogeneous wireless networks. Based on the research of the different QoS class definition and QoS guarantee mechanisms in UMTS network, 802.11e WLAN network and 802.16 WiMAX network, the problems and challenges of the QoS mapping in vertical handoff are analyzed. Based on the loose-coupling internetworking architecture of the heterogeneous access networks, the service traffic performance after the mobile users move from UMTS to 802.11e EDCA, 802.11e HCCA and 802.16 are simulated and analyzed.This work is jointly supported by: National High-technology (863) Program of China (No. 2006 AA01Z229, No. 2005AA121630, No. 2005AA121110) and the Chinese Ministry of Education for Returnee of Studying Abroad.