Research And Improvement Of On-Demand Routing Protocols In Ad Hoc Networks

With the development of science and technology, portable computer and palmtop computer are increasingly prevalent, and the wireless communication technology develops promptly. In some cases, for instance, the rapid expansion of the army in a war, the rescue after earthquake or flood, it needs one communication technology that needn't depend on any network facility erected beforehand. Then Ad Hoc network emerge as the times require. Ad Hoc network is one special kind of mobile networks that don't need fixed basestation. It's a self-creation, self-organization and self-supervisory network that formed by the cooperation of a boodle of autonomic wireless nodes or terminals with wireless R-T units.In Ad Hoc network, every host must be a router at the same time. And nodes in the network could move discretionarily, which make the topology change frequently and the routing protocol be expected to reconstructing and maintaining routing path in time. Because of the highly dynamic variation of topology in Ad Hoc network, the conventional distance vector routing protocols and link status routing protocols are not suitable. Since 1970 year, DARPA subsidized one extraordinary research—Ad Hoc network, a lot of protocols of Ad Hoc are under exploitating and developing. The route mechanism of Ad Hoc network should conform to three basic features: the population density of mobile node, the topology of nodes, and the operating mode of network.There are two kind of routing protocols for Ad Hoc network: table-driven and on-demand routing protocol. Considering the mobility, dynamic of topology, bandwidth limitation and power restriction, on-demand routing protocols are more suitable for Ad Hoc network.The thesis firstly described the significance and its' target, it also describes the current status of the schedule. And then through analyzing and comparing many routing protocols of Ad Hoc Network, an optimized protocol: OAODV is presented which is preformed by AODV routing protocol. Rout table in OAODV is extended by adding two fields to save the previous two hop and the next two hop. And then, according the discovery packets, marked down the previous two hop of the router and the reverse router. When break occurred and need to local repair, the downstream node of the break point send the repair packets to its previous two hop. Thus can not only increase the probability of success, also repair the router immediately which decreased the end-to-end delay and increased the data delivery ratio.Simulation with different scenes is completed based on NS2, the popular simulated formwork, and performance of OAODV is analyzed according the data obtained by simulation to show that it is superior to the AODV.This thesis is supported by National Natural Science Foundation of China (Projects No: 90304018, 60672137) and Specialized Research Fund for the Doctoral Program Foundation of Ministry of Education of China Under Gram (No. 20060497015 ).