Study On Improved AODV Routing Protocols In AD-HOC Networks

Ad-hoc is a kind of multi-hop, self-organizing wireless network with its topology changing dynamically; which consists of a set of mobile terminal nodes equipped with wireless transceivers. Ad-hoc network can be deployed rapidly without any fixed infrastructures. Therefore, it is often applied in battlefield, disaster relief, personal communication and wireless sensor networks etc. Due to the frequently changing topology of Ad-hoc network, traditional Internet route protocols are not able to meet requirements for network routing performance. So, it is necessary to develop special route protocols with well routing performance for Ad-hoc network, which is now a key point of research on Ad-hoc network.The paper conduct a deep research on AODV routing protocol and discuss two drawbacks in its route discover process: high frequency of route discovery, which brings in high routing overhead, and simple route metric. For these two faults, the paper presents two corresponding improvement solutions:(1)During the route discovery process of AODV, only source node is involved in route learning. In order to get more route information, extra route discovery processes are needed, which of course induce high routing overhead and transmission delay. The paper presents an improvement project of AODV, which is called AODV-FA routing protocol. AODV-FA makes use of source route strategy of DSR protocol, accumulating the address information of first hop in routing messages. The routes created or updated to the first hop by intermediate node upon receiving route messages are disjoint according to a key attribute of flooding. The disjoint routes break independently, which confirm stability connection. Also these disjoint routes can achieve route balancing when the load of network is high.(2)AODV routing protocol adopts hop count as routing metric, merely considering the number of forwarding nodes when choosing routes. However, AODV routing protocol with this simple route metric can not make satisfactory routing performance in some special Ad-hoc networks, in which nodes have different WLAN data rate. To solve this problem, the paper presents another improvement project of AODV, which is called AODV-HM routing protocol. AODV-HM adopts both hop count and cost as routing metric, considering the number of forwarding nodes and their different data rate when choosing routes.Using ns2, the paper creates wireless scenarios to simulate the routing performance of the two improved AODV protocols, verifying their routing performance gain.