Reliable Broadcast Mechanism For Emergency Message In Urban VANETs

The safety service of Vehicular Ad Hoc Networks(VANETs)is particularly important in urban roads because of the frequent traffic accidents.However,the transmission of emergency messages in urban VANETs is facing some serious challenges,such as great changes in network topology and vulnerable wireless transmission signals produced by high buildings in the city.In order to minimize redundancy and delay of network as well as ensuring high reception rate of vehicles in target area when spreading the emergency message,this thesis proposed a reliable broadcast mechanism based on local topological information and vehicle’s position.Different from existing mechanism in urban VANETs,in the straight,the proposed mechanism regards effective communication distance based on prediction rather than fix distance as one of the parameter of waiting time calculation,the other two parameters are traffic density and relative velocity.Considering the obstacles such as buildings around intersection in the actual urban scenario,this thesis proposed to set up a pre-selected area for intersections(IPA)and the intersection area(IA).The vehicle in the IA of the target area will have an additional broadcast if certain conditions are not met.If there are no vehicles in the IA,the vehicle in the IPA has chance to broadcast when it enters IA and certain conditions are not met,which avoids the possible failure of emergency message transmission in some segment because of the obstacle around the intersection and ensures the coverage and reliability of emergency message.When vehicles receive the message,the back off procedure of the proposed mechanism is that different receivers will calculate appropriate waiting times according to different effect factors and set waiting timer.The message receiver that first ends the waiting is the best forwarding vehicle.This thesis combined SUMO and NS3 to simulate the proposed method and compared it with the other two existing methods.The experimental results show that the proposed broadcast mechanism is accurate and effective,and the proposed method is more reliable than the compared schemes.