Research On Congestion Optimization Of Safety Messages In VANET

With the development of modern industry,the number of traffic accidents is rapidly increasing along with the sharp growth of car ownership.In order to achieve a greater driving safety,Vehicle Ad-hoc Network is created.It acts as the core of an intelligent traffic system,providing abundant real-time traffic information and efficiently managing the traffic resources.However in a heavy traffic scenario,the reliability of the system will be vitally compromised if the communication channel is congested by excessive number of broadcasting messages.To lower the probability of this congestion,we proposed optimization of two types of broadcasting messages,periodic message and alert message.For the periodic messages,(1)we use channel-busy-ratio in carrier sense mechanism to estimate the current network status,(2)when the systems workload is heavy,which indicates a traffic congestion,algorithm forces all node in congestion area dynamically compete for the highest transmitting power.The winner node will transmit message to all surrounding nodes,avoiding aggravating the whole system's workload.(3)By receiving winner node's message and extract network status information,the rest competing nodes will adjust their own transmitting power on a preset power curve.(4)So a quick self-tuning of transmit power is completed based on the number of surrounding nodes and their transmitting power.For the alert messages,we do a Slotted 1-persistence algorithm based optimization.(1)A individual node estimates its surrounding vehicle density based on neighbor node list.(2)According to the estimation,it does a dynamic segmentation of forwarding path which will lower average message forwarding time.(3)We also set a message forwarding probability in inverse of channel-busy-ratio,so when channel is busy,the forwarding probability and thus the number of forwarding nodes is lower,so does the channel burden.Therefore the successful delivery of alert messages is ensured.Finally we created a Vehicle Ad-hoc Network simulation with SUMO traffic environment simulator and OMNET++ communication network.Result shows that(1)For periodic security messages,the proposed dynamic power algorithmis superior to fixed power algorithm in terms of packet delivery rate and distribution delay.(2)The optimization we adopted on Slotted 1-persistence algorithm shows a higher delivery rate and a lower broadcasting redundancy to traditional Slotted 1-persistence algorithm.To conclude,simulation result prove our method has prominent improvement on the reliability of Vehicle Ad-hoc Network.