Research And Design Of QoS Based OLSR Ronting Protocol In Ad Hoc Network

Wireless ad-hoc network is composed of a group of mobile nodes which carry with wireless communications transmitters and receivers. It is a kind of multi-hop network without any temporary centers it means that all nodes have equality in status in the network, each node can be either terminal can also be a router, in addition that it need not rely on any fixed network infrastructure.Routing protocol which is a major research hotspot and difficulty plays a most crucial role in ad hoc networks. The characters of random movement of the nodes in the network and other issues such as limited bandwidth and time-varying links can cause link disruption or network routing congestion. Base on the current study, some improvements in the OLSR (Optimized Link State Routing Protocol) have been done in this paper to meet the QoS (Quality of Service). The core idea of improved OLSR routing protocol is adding evaluation model on the link quality change form the physical layer and the sent data size form the transport layer to the MPR (Multipoint Relays) selection and route selection algorithm which is called Dijkstra. Through the physical access to the signal-to-noise ratio of the effective signal, the frame error rate and the stability of the link as the measure of synthetical link quality can be calculated in the given channel model, and obtain the appropriate amount of sent data packets from the transport layer as a measure of the saturation of nodes.Link stability is needed to introduce to this paper due to the staleness of topology messages so that simply use of frame error rate as a measure of link quality standards isn’t accurate enough. In a very short time, since the environment of transmission will not change too much, and therefore the greatest impact on the transmission quality is relative motion between the nodes. Calculating the variance of the signal quality for a period of time in the receivers to evaluate the motility of nodes in the local scope, it can be the measure of the stability of the link.The shortest path based routing method may lead to network congestion or packet loss due to the oversaturation node in consequence of oversaturation node so that the assessment of the saturation of nodes is necessarily added to this paper, the node saturation probability is calculated over a period of time in a given model and it can be the measure of the saturation of a node.Based on the aforementioned work, the extensions of packet message of OLSR protocol have been done in the first. Secondly, corresponding improvements of multi-point relay MPR selection method and the routing algorithm have been done by considering the coverage and minimum hop while adding the synthetical consideration of link quality, link stability and node saturation to make the best choice overall quality of the link. Finally, make nodes under the condition of different rate of movement simulation to verify the improved OLSR routing protocol. Simulation results indicate that compared with OLSR, in the scene of fast moving nodes and the dynamically changing topology, QoS-OLSR routing protocol has no significant increase in the end to end delay and the number of hops, except the packet arrival rate is significantly improved.