Research On Vertical Handover Algorithm In Heterogeneous Wireless Network

With the rapid development of mobile communication and broadband wireless access technology, it has been gradually realized that the mobile communications in the future is no longer a certain kind of technology to provide services for mobile users. In those collaborative networks with multiple wireless access technologies, a variety of services are provided to guarantee the seamless access in different networks and the demand of personal wireless communications. Due to the differences in characteristics of the various radio access networks, there are some new challenges about the network’s stability, reliability and efficiency in heterogeneous wireless communication system. While designing and implementation the heterogeneous wireless communication system, a lot of technical problems appeared. Vertical handover technology is one of the key issues which should be investigated in heterogeneous wireless networks.The vertical handover in heterogeneous wireless networks can be divided into two important processes:handover trigger and target network selection. Taking UMTS and WLAN integrated network for example, the existing vertical handover algorithms are investigated in the paper including its shortcomings and deficiency. Meanwhile, a new vertical handover algorithm with the consideration of terminal speed is proposed. The vertical handover trigger best time is analyzed in the handover trigger process. Subsequently, a vertical handover trigger mechanism based on adaptive increment is proposed. This mechanism estimates the moving direction of the terminal through the measurements of received signal strength value, and applies the moving direction to the vertical handover trigger process. Simulation results show that the proposed vertical handover trigger mechanism can effectively reduce the probability of mobile terminal handover and the packet loss of the terminal. Afterwards, the related factors influencing network selection are analyzed in the target network selection process. Due to the dwell time varies when the mobile terminal moves between the multiple access networks with different coverage area, the joint network selection algorithm is addressed by introducing a velocity threshold. Simulation results show that the improved joint vertical handover network selection algorithm can choose the optimal target network to access according to the mobile terminal speed.