Research Of The Vertical Handover Algorithm Based On 802.21 Standard Of Heterogeneous Network

Mobile terminals have to accomplish vertical handovers among heterogeneous networks for the purpose of realizing seamless roaming, guaranteeing Quality of Service (QoS) and making full use of various kinds of wireless access networks. Media Independent Handover (MIH) mechanism defined by IEEE 802.21 standard is a possible approach to this problem.In this paper, we propose a novel user-adaptive vertical handover scheme based on MIH in UMTS, WLAN and WiMAX networks. At the same time, improvements have been made to realize dynamic flow scheduling among networks in order to realizing the load balance of heterogeneous networks and ensure efficient integrated utilization of the whole network resources.The thesis first describes the key techniques and network characteristics of UMTS, WLAN and WiMAX networks, analyses the new features of vertical handovers, introduces the protocol modules and realizing scheme of multi-mode terminals in heterogeneous networks. Then it introduces the vertical handover supporting characteristics of different levels according to different layering structure, which involves 802.21 protocol above data link layer, mobile IPv6 protocol at network layer and SCTP protocol at transport layer, in addition this thesis designs complete vertical handover process using these protocols and addresses a more flexible choosing scheme compared with classical MADM to select the proper one according to subscribers'need. The simulation results show that the proposed scheme provides smaller handover times and better QoS than the basic vertical handover scheme and the proposed load balance algorism deduces the user outlet ratio in heterogeneous networks and increases network resource utilization ratio.