The Design And Implementation Of Layer-? Fast Handoff Protocol For The Emergency Communication System

In recent years,disasters such as earthquake,typhoon,deluge and emergencies such as terrorist attack,fires often occur around the world,which has aroused wide attention of various countries to the Emergency Communication System.However,the traditional Emergency Communication System exists many problems;for example,immobility,limited bandwidth and poor support to real-time service are common shortcomings in traditional emergency communication system.Moreover,the data transmission speed is highly limited in high-speed services by the long handoff delay and fixed handoff trigger threshold when the mobile terminals moving between network nodes.In order to overcome these shortcomings,we design a new emergency communication system with multi-frequency hierarchical clustering structure.A new Layer-II fast handoff protocol is designed for such network structure to deal with handoff issue in real-time services.In this handoff protocol,the handoff trigger threshold is self-adaption based on the moving velocity of mobile terminals.The specific study and work are in follow:(1)Design the Emergency Communication System.Use the Multi-frequency multilayer clustering network structure's survivability,expandability,high mobility and high data rate,to make sure the demand to the Emergency Communication System in the battle and the disaster scene.(2)Proposed a handoff model to apply to the Emergency Communication System.By starting with the Layer-II handoff in WLAN,analyzing the different reference standards in handoff strategy and their own problems,stating the wireless communication channel model and pointed out the channel features,integrated received signal strength and the transmission rate with distance,this article put forward fast switching model.(3)Design a complete Layer-? fast handoff protocol,which suitable for the ECS,the protocol composed by channel assignment,a quick scan mode,and fast authentication & associated.Then put forward a scanning mechanism,which is,adjusted itself to the migration rate,compared with the rational distributed channel separation strategy,driven by the channel's scanning mode,then decrease the scanning delay largely.This protocol use 802.11 r based three key hierarchy to form the encryption key,then,use CCMP to encrypt the MAC data frame and the data of cluster nodes to synchronized update to realize the fast dependable authentication and association.Finally,put up an experiment platform and achieve above-mentioned handoff protocol,then compare the handoff delay,package loss between 802.11 protocol and its improvement protocol.The experimental result indicates that the protocol has a good ability of adaptive mobile rate,and reduce the handoff delay largely.Therefore,it support the real-time traffic data transmission in the ECS very well.