Research On On-demand Unicast Routing Protocol In Mobile Ad Hoc Networks

With the miniaturization and practicality of portable mobile computing devices, mobilewireless network is more and more important in human society and has wide applicationrequirements. Mobile Ad hoc Network (MANET) is an important development direction ofmobile wireless network. The routing protocol is one of the core issues in MANET, whichshould have the smaller control overhead and better adaptability because of the quicklychanging network topology and limited cyber sources in MANET. The on-demand routingprotocol finds routes only when needed, so it is suitable for MANET.Taking National High-Tech Research and Development Program (863Program) ofChina as research background, on-demand unicast routing protocols are studied in thisdissertation in point of the characteristics on the structure of MANET such as Vehicular Adhoc Network (VANET) and Wireless Mesh Networks (WMN). The performanceimprovement of routing protocol, the analysis of network traffic complexity and the securityimprovement of routing protocols are focused. The research in the dissertation has academicsignificance and promising application.The main research works and innovative achievements of this dissertation can besummarized as follows:1) Frequently restart the route discovery process due to link errors will increase thenetwork overhead controlling and decrease the performance of routing protocol. Thetraditional backup routing protocols use the backup routes for local route repair only whenthe link error occurs, which can not to adapt to the rapid changes in the network topology.The proposed backup routing protocol in this dissertation can fine tune the routes in time,which reduces the disconnect probability of whole route and the network control overhead.The proposed backup routing protocol in this dissertation can fine tune the routes in time,which reduce the disconnect probability of whole route and the network control overhead andimprove the adaptability of the routing protocol. Furthermore, the proposed routing protocollocally repairs the routes in small range, which improves the route local repair success rateand efficiency.By improving the classical backup routing protocol AODV-ABL, the proposed backuprouting protocol merges the primary routes with the alternate routes, and updates routes whenoverhearing data packets, thus the routes can be optimized as soon as possible. The proposedbackup routing protocol has two schemes: AODV-FABL and AODV-BFABL. AODV-FABL maintains the routing information in real time by overhearing the forwarded data packets.Aiming at the application scene of bidirectional asymmetric traffic, AODV-BFABL alsomaintains the routing information in positive and negative directions. Simulation results showthat the two proposed backup routing protocols improve the speed of response and havebetter adaptability to node movement speed and network load. The average end to end delayof proposed routing protocols is less than70%of that of AODV, which indicating the betterspeed of response.2) Unstable routes may cause frequent route discovery process, thereby increasingnetwork overhead and reducing the routing protocol performance. VANET is a practical for mof MANET, whose motion information can be used as a routing metric to improve thestability of routing protocol. When taking into account the stability and the delayperformance of route protocols, a comprehensive routing metric weight mechanism isproposed for VANET in this dissertation, which is composed of link expiration time, queuesaturation and hop-count. A routing protocol AODV-CM based on the weighted link stabilityis also proposed by using the comprehensive routing metric. By looking for the stable route,AODV-CM can reduce the route disconnect probability and balance the routing load,therefore can improve the performance of routing protocol. Simulation results show that theroute discovery frequency of AODV-CM is only about70%of that of AODV, whichindicating the better stability of route than AODV.3) Analysis of network traffic complexity caused by routing protocols can provide animportant basis for designing routing protocols. Network traffic in MANET shows thedifferent complexity in different time scales. The cause of network traffic complexity is verycomplex and is difficult to be accurately described. The research on relationship betweenrouting protocol and network traffic complexity is still at the starting stage. In thisdissertation, the multiscale entropy analysis method is used to analyze this relationship.The network traffic complexities of the classical routing protocol AODV and theproposed routing protocols AODV-FABL and AODV-CM at different time scales arequantitatively analyzed. Analysis results confirm that the network traffic complexity of thoserouting protocols are all higher and have large fluctuation in smaller time scales, and are alllower and shows the long-range dependence in larger time scales. The relationship betweenthe network traffic complexity of those routing protocols and the network topology changespeed is also pointed out and analyzed.4) Security is a key problem of research on routing protocol. The gray-hole attack is atypical internal routing attack, which is covert and destructive. The core idea of judging gray-hole nodes in traditional gray-hole attack detection method is to overhear their neighbornodes, which does not take into account the characteristics on the structure of WMN, so thismethod lacks the synthetically judgment. In addition, if multiple nodes judge one node is agray-hole node, they will broadcast the information to the whole network, which will inducebroadcast storm problem.WMN is an extension of MANET and, in which the mesh gateway (MG) nodes connectwireless network to wired network. Based on the WMN’s architecture, which is the mixtureof centralized control and distributed control, a gateway based gray-hole detection (GBGHD)method is proposed in this dissertation. GBGHD protocol makes the gateway analyze andsynthesize the monitoring information collected by the wireless nodes and decrease therouting overhead by piggybacking technology without bringing additional broadcast storm.Simulation results show that GBGHD protocol can detect gray-hole nodes quickly andexclude the gray-hole node from the network, which can greatly decrease the packetsdropping caused by the gray-hole node and thus improve the network performance. Thegray-hole node can be detected in10seconds when the default packet loss rate of gray-holenode is no less than0.3.