Research On Vertical Handoff Decision Scheme In Heterogrnrous Network

The future of the communication network is a heterogeneous network with different access technologies. It can provide different access methods, transmission rates, capacity sizes and the ability to support different quality of service. As one of the key function of the future mobility management technology, vertical handoff which is used to provide session continuity across heterogeneous networks has been one of the most challenging technologies in heterogeneous network environments.The dissertation is a part of results of two projects, which are "Joint Resource Allocation and Scheduling Algorithm Research In Multi-cell OFDM/OFDMA System" and "Resource Allocation and Interference Coordination Mechanism Research In Multi-hop OFDMA Cellular System" sponsored by Science and Technology Foundation of Huawei. In this paper, the development of vertical handoff is tracked, a heterogeneous network's coexistence system level simulator is designed and developed and vertical handoff decision methods are in-depth studied. Main contents include:First, the principle of vertical handoff technology is studied, comparing the difference between vertical handoff and horizontal handoff, describing the three stages of vertical handoff and researching current decision-making algorithms which are based on cost function.Then, a wireless heterogeneous network system level simulation platform is designed and developed. The whole structure of platform, the function of each module and the simulation parameters are described. This platform is the basis of verifying proposed vertical handoff decision scheme.At last, considering the inadequacies of current decision making algorithms, a vertical handoff decision scheme based on QoS evaluation is proposed. This scheme includes two parts: network selection algorithm and adaptive stability period algorithm. The network selection algorithm fully considers the difference of application's quality of service and network performance. Each selection follows 'per application'. Adaptive stability period algorithm delays the waiting time before executing vertical handoff to avoid 'ping pong' effect which is caused by network performance's instability. Simulation results show that the proposed scheme can select most suitable network for applications to meet their QoS requirements and adjust stability period adaptively to avoid the unnecessary handoff.