Research On Safety Messages Dissemination Control In VANET

VANET is a technology that uses a vehicle on the road as a mobile node and uses a dedicated short-range communication standard to form a wireless mobile network.The interaction of safety messages between vehicles or between vehicle and infrastructure are both suported by VANET so as to ensure the safety of the vehicles.Therefore,how to design a reasonable dissemination control strategy is very important for the transmission of safety related messages to vehicles in specific areas.Safety messages in VANET usually deliver by broadcast.Different type of safety messages have different broadcast methods.This thesis will both research the single-hop broadcast control strategy of periodic basic safety messages and multi-hop broadcast control strategy of emergency safety messages in VANET.Firstly,for periodic basic safety messages,when the distribution of vehicles is very sparse,the network segmentation problem will hanppen,resulting in failure of safety messages transmission.On the contrary,when the distribution of vehicles is very dense,a lot of vehicles contention for the wireless channel in the same conflict area,which will cause channel congestion,and lead to a significant reduction in the deliver ratio of safety message.Therefore,This thesis proposes a power control algorithm based on channel load prediction for periodic safety messages,which including channel load evaluation,channel load prediction and adaptive power control.The algorithm mainly obtains the current channel load value through channel load evaluation methods,predicts the next moment's load value according to the current channel load value and historical value,and finally adaptively adjusts the periodic safety message transmission power through the predicted value.Secondly,for emergency safety messages,when the vehicle density is high,the vehicle nodes will forward a large number of duplicate packets,leading to a sharp increase network load and causing the "broadcast storm" problem.Therefore,this thesis proposes a Multi-hop Broadcast Routing Algorithm based on Distance and Probability.Firstly,different road sections are set up according to the single-hop forwarding distance and traffic flow density of source node,and select the node in the furthest road segment as a relay node;Then,different message forwarding probability set according to the location and load of the relay node;Then,different message forwarding probabilities are set according to the positions and load conditions of the candidate relay nodes,which can reduce redundant forwarding delays while avoiding redundant transmission of messages.Finally,a timeout retransmission mechanism is used to ensure the reliability of secure message propagation.Finally,the algorithm was verified by simulation results and analysis.The adaptive power transmission algorithm proposed for periodic safety messages outperforms the fixed power algorithm in the performance of transmission delay and message packet delivery rate.Compared with the traditional flood broadcast,the multi-hop broadcast algorithm proposed by emergency safety messages effectively reduces the amount of redundant data in the network and has better performance in both real-time and reliability.