Analysis And Improvement On AODV Routing Protocol Based On Tree-topology Network

With the development of the society, in order to satisfy the requirements of free communication at any time, at any place and among any devices, a new network technology——Ad hoc network was born. Ad hoc network is a multi-hopped and self-organized network, and is composed by amount of nodes with wireless transceiver and mobility. According to its advantages of flexible organization, fast deployment, independence on the fixed infrastructure, independently working or connecting with Internet and wireless cellular network, it is used by a wide range of applications.The traditional protocols and technologies, which based on the distance vector and link state, used in wired network can not be used in Ad hoc network because of the specificities of Ad hoc network such as using wireless channel, multi-hop and dynamic changing of network topology. And the protocols and technologies for Ad hoc network should be redesigned. On the other side, compared to the wired and centralized network, Ad hoc network is more vulnerable to eavesdropping, active aggression, denial service attack and deception for using the shared wireless channel and distributed management technologies.This paper introduces AODV (Ad hoc On-demand Distance Vector) routing protocol, which is the typical reactive routing protocol used in Ad hoc network, and the detailed analysis on the mechanisms in route discovery phase and route maintenance phase in AODV routing protocol. Subsequently, the paper shows the analyses and the improvements on the shortcomings, such as transmission jitter generated by neighbor node selecting mechanism and optimum route mechanism, the signal frame flooding generated by local repair mechanism and security issue in the traditional AODV routing protocol used in the searching and rescue communication system that has a central node in the network and tree-topology.In this paper, to restrict the jitter of the transmission in the safe Ad hoc network, the following methods are adopted: adding received signal strength intensity threshold and dynamically selecting the optimum route to choose the stable node as the neighbor; to restrict the flooding of the signal frame, decrease the time of routing repair and enhance the reliability of the transmission by using the improved local repair mechanism which is based on the information of next one hop and next two hop nodes. And the simulation results of the original and improved AODV routing protocol, which are obtained in the case of different movement speed and pause time of the nodes, show that, the improved AODV routing protocol has a better performance than the original one in end-to-end transmission delay and successful packet delivery ratio. And in the unsafe Ad hoc network, a better successful packet delivery ratio is achieved while sacrificing some transmission delay and protocol overhead by using signal frame authentication and verification between the source node and destination node, which is aim to increase the security of the routing protocol.