Research On Data Dissemination Mechanisms In Vehicular Ad Hoc Networks

With the rapid development of intelligent transport systems, Vehicular Ad hoc Networks(VANET) has gradually become the focus of attention, and its main applications include safety application and entertainment application. VANET always uses multi-hop broadcast to complete data dissemination, but some problems like broadcast storm will be brought to VANET by the inherent characteristics of the broadcast. When transmitting data in highway scenarios, some of existing broadcast algorithms will result in serious broadcast storm. With the aim of improving the reliability and reducing the average delay in the process of transmitting data, this thesis proposes two broadcast algoritms to suppress broadcast storm.Firstly, this thesis introduces the background, the significance of the reseach. Then, the research status of VANET and broadcast model are recommended.Secondly, VANET in highway scenarios uses multi-hop broadcast to disseminate data, but the existence of relative speed will have an effect on the selection of relay node. In this thesis, an algorithm named two-hop neighbor information based Multiple candidates Relay Data Dissemination(MRDD) is proposed. When relay node is selected in MRDD, the speed, position, direction of vehicles will also be taken into consideration. MRDD constructs a two-hop neighbor information table by exchanging Hello Message with around vehicles constantly, thus MRDD can make the optimal relay nodes to rebroadcast the data packets and reduce the delay. Besides, MRDD also takes several vehicles as the candidate relay nodes, which will forward data when the optimal relay node fails to rebroadcast. Thus, the reliability of data retransmission will be improved.Thirdly, this thesis proposes a data dissemination mechanism based on OPPosite vehicles(OPP), which make use of the vehicles in the opposite direction to forward data and the vehicles in the same direction will not rebroadcast any more. OPP will segment the communication radius in the process of selecting optimal relay node, and the segment number is the criterion for optimal relay node. Relaying data packets via opposite direction vehicles, OPP can send data packets to target area rapidly and make the delay low.Finally, both MRDD and OPP are implemented on the platform NS2(Network Simulator Version 2). Experimental results show that, compared with other algorithms, MRDD and OPP can achieve better packets transmission delay and higher reliability.