Research On Data Dissemination In Vehicular Ad Hoc Network

With unique characteristics of large-scale, dynamic changing topology, a strongenvironment interference and a limited mobility, the application of Vanet are greatlychallenged. So a special research on Vanet is meaningful. The thesis focused on datadissemination in Vanet. Due to a large number of nodes requesting for informationservices in the range of infrastructure and a high-speed movement of the vehicle,there is a problem that a vehicle may leave off the infrastructure without a service or acomplete one. With the progress of current research, an algorithm on datadissemination based on network coding (DDNC) is proposed. On the low reliability ofbroadcasting caused by a complex road topology, a reliable broadcast algorithm (EBV)is also proposed.Firstly, a research is on the application of WAVE in Vanet. The serviceparameters of RSU (Roadside Unit) are analyzed from a mathematical point. Thesimulation results have proved that a poor service may happen in the range of RSU,caused by a large number of requests for service, a high-speed mobility, frequentchannel switching and other factors.Secondly, with the characteristic of vehicles moved in a cluster in Vanet, thethesis solved above problems by DDNC. In DDNC, a proxy node is elected in a groupof nodes, which carries the service requests of multiple nodes and requests for servicein the range of RSU, and other nodes suppress service requests. For an incompletedata transmission, a mechanism of data exchange in V2V (Vehicle to Vehicle) isproposed, in which nodes exchange information list and then exchange data ifpossible. With multiple requests of other nodes, the role node disseminates data tomany nodes in a multicast manner. The smallest finite field is obtained based on themaximum distance separable codes and the forwarding node set of nodes. A codingcoefficient matrix is obtained by the non-zero elements of the smallest finite fields.The simulations show that DDNC performs well on the delivery rate and the collisionrate.Lastly, aimed at the lower reliability of broadcasting in data disseminationcaused by a complex road topology, a reliable broadcasting algorithm is proposed.The nodes are classified into certain classes based on the node position and movementdirection. At an intersection, the nodes of each class are further divided into two types. A distance-based scheme is applied to select an appropriate relay node, by which amulti-hop broadcast is realized. Different schemes are adapted to different vehicledensities. As to the problem of communication hole, the algorithm solved it by carryand forward. The node needs detect a hole, then rebroadcast when one node enter itscommunication range. Simulation results show that the algorithm have a goodperformance in the packet delay, success percentage and average load generated byeach broadcast packet.