Routing Control Overhead In Mobile Ad Hoc Network

Due to the high mobility of nodes in a mobile ad hoc network (MANET), the network topology changes unpredictably. Therefore, there exist frequent link breakages, which lead to frequent path failures and route reconstructions, so as to increase the overhead of routing control traffic. The routing overhead of route discovery in a route reconstruction can not be neglected. In a route discovery, broadcasting is a fundamental and effective data dissemination mechanism, where a mobile node blindly rebroadcasts received Route Request (RREQ) packets until they have reached the destinations, thus it causes the broadcast storm problem. So reducing routing overhead in route discovery and maintenance is an essential problem in routing design.In this dissertation, we propose two approaches to optimize the routing control overhead of route discovery, which are given as follows.Firstly, we propose a Neighbor Coverage based Probabilistic Rebroadcast (NCPR) algorithm for reducing redundant RREQ of route discovery in mobile ad hoc network. This algorithm is the optimization for broadcasting. The NCPR uses residual link lifetime to select the strong neighbors and eliminate the weak neighbors. And then NCPR uses the upstream coverage ratio of RREQs received from the previous node to calculate the rebroadcast delay, and uses the additional coverage ratio of RREQs forwarding to the next nodes and connectivity factor to calculate the rebroadcast probability. This approach combines the advantages of neighbor coverage knowledge, network connectivity, local node density and probabilistic mechanism, which can significantly decrease the retransmission and redundant RREQ so as to reduce the routing overhead, and could also improve the routing performance.Secondly, we propose an Estimated Distance based Routing Protocol (EDRP) to steer the route discovery in the general direction of the destination, and thus restrict the RREQ's propagation range so as to reduce the RREQ number. This protocol is the optimization for finding destination. The EDRP uses an Estimated Geometrical Distance (EGD) based on the change rule of Received Signal Strength (RSS) to estimate the geometrical distance of node pairs. The simulation experiments using Random WayPoint (RWP) model show that when EGD is less than the expected value of distance (which is called E-Radius) between any node pairs, it can effectively estimate the distance between two nodes. The zone which a node can effectively estimate the distances with other nodes is called E-Zone. We also propose an Estimated Topological Distance (ETD) which is the sum of distance in every hop of the previous route as an aid of EGD, which can eliminate the inaccurate EGD. The Estimated Distance (EstD) is a combination of EGD and ETD. Then we divide the entire networks area into 3 zones: src-Zone, dst-Zone and other-Zone, and in different zone use different forwarding strategy, which can significantly reduce the RREQ's propagation range and nodes that participated in route discovery, so as to reduce the routing overhead and improve the routing performance.