Research On Reliability And Effectiveness Of Multi-hop Broadcast

Vehicular ad hoc network has attracted the attention of many researchers both at home and abroad in recent years, it will play an important role in the construction of intelligent transportation system in the future. VANET can support a large number of applications, such as safety, traffic management, and entertainment, which safety applications are considered as the basic needs of VANET. Against to the distribution mechanism of warning message triggered by events is the emphasis of the security application, it is very important for warning message to cover the network reliable and effective through multi-hop broadcast protocol, so this paper mainly discussed how to improve the reliability and effectiveness of multi-hop broadcast protocol.Evaluations of multi-hop broadcast protocol in VANET are usually accomplished by simulation, and it is important to approach the realistic wireless channel and vehicle mobility model when setting the simulation. The current description of wireless channel and vehicle mobility model are relatively simple, hence this paper first modelled wireless channel and vehicle mobility comprehensively aim at the highway environment. In which we used TwoRayGround model to describe the wireless channel fading, took consider into both macroscopic and microscopic traffic flow model to describe the characteristics of the vehicle mobility. According to the analysis of communication link existing in the mentioned environment, we could get the link duration time, which could reflect the reliability of link, and this parameter is the basis of relay node selection.Then this paper proposed a new multi-hop broadcast protocol combined delamination technology and distributed time coordination mechanism, which was based on the reliable and effective transmission of the warning message. There are there main problems in multi-hop broadcast protocol for distributing the warning message: the broadcast storm; the hidden nodes; the interference of the periodic safety message. To alleviate the broadcast storm problem, we used delamination technology to partition highway, each segment only have one relay node can forward the warning message, also in order to improve the reliability of this protocol, we select the relay node according to the size of the average time of link duration. Distributed time coordination mechanism divides channel based on the time slot, it use time slot as unit node to occupy channel, and each time slot are independent from each other. We sent warning messages at a designed time slot, and the dissemination of safety message had been suspended at the same time, thus could alleviate the interference of periodic safety message. The NOTICE packet delivered at a special time slot could also solve the hidden nodes problem. Besides, a mechanism aim at the loss of ACK packet has also been researched, which could enhance the effectiveness of the proposed protocol.Finally, the performance metrics, obtained by controlling different simulation environments, such as successful reception rate of message、number of transmissions and transmission delay of the proposed protocol had been compared with that of the smart broadcast and blind flooding, it could verify the superiority of the proposed protocol. Simulation results showed that the proposed protocol could improve the reliability and effectiveness of warning message transmission, and it can provide references for future engineering practice.