Design And Simulation On Topology Reconstruction Scheme In Ad Hoc Networks

Ad Hoc networks is a multi-hop temporary autonomous system of mobile nodes with wireless transmitters and receivers without relying on preexisting network infrastructure. Because of its important applications such as military field, emergency rescue and disaster relief, it has attracted a wide attention. The features of Ad Hoc networks such as distributed networking, node mobility and wireless communications, make it easily encounter faults which lead to the decreasing of the network performance. It has great significance to research on the topology reconstruction for assuring reliability, invulnerability and robustness in Ad Hoc networks.Research on the problem of topology reconstruction in Ad Hoc networks, and it divides into two stages, which are the trigger stage and the implementation stage. In the first stage, a fault diagnosis algorithm based on directed graph is proposed for topology level. The faults are divided into single unreachable node, connected subnet of unreachable nodes, and unconnected subnet of unreachable nodes. Three kinds of fault models is designed and transformed. The faults can be located by the comparison of the node fault probability and the link fault probability. In the second stage, the maintenance mechanism in routing protocol is used to implement routing reconstruction. Relatively, a topology reconstruction scheme based on k-hop neighborhoods dispersion is proposed for the situations that routing reconstruction cannot work effectively. Moreover, a topology optimization scheme based on topology high effectiveness is proposed.The network simulation software NS2 was adopted to evaluate network performance after using the topology reconstruction scheme.Simulation results show that the network faults can be located with higher correct ratio by fault diagnosis algorithm based on directed graph as the increment of network scale and the frequency of network topology changing. And the connectivity of network can be effectively recovered after using the topology reconstruction scheme, and the network performances are improved such as the parameters of the packet delivery ratio, transmission delay, and control overhead and so on.