Research On Emergency Message Broadcasting Strategies Of VANETs For Urban Roads

As one of the core technology of the intelligent transportation system(ITS),vehicular ad hoc networks(VANETs)can effectively enhance the traffic perception ability,build a smart transportation system,and realize the intelligentization and networking of the transportation system.In VANETs,in order to meet the low-latency and high-reliability communication requirements of emergency messages(such as traffic accidents,road congestion,etc.),multi-hop broadcast protocols for emergency messages transmission have received extensive attention.However,in the face of complex and time-varying urban road scenarios,factors such as changes in road structure,high mobility of vehicles,high-frequency data interaction and complex wireless communication environments seriously affect the efficiency and reliability of emergency messages broadcasting,only using wireless multi-hop transmission will be difficult to meet the requirements of emergency messages broadcasting.For this reason,this paper focuses on the emergency messages broadcasting strategies for urban roads in VANETs,and designs an roadside units(RSUs)-assisted hybrid emergency messages broadcast protocol for urban roads;on this basis,considering the impact of RSU deployment on emergency messages broadcasting,an RSU deployment strategy based on emergency messages broadcasting in urban scenarios is proposed.The main work and innovations of this paper are summarized as follows:1)Aiming at how to improve the efficiency and reliability of emergency messages broadcasting,an RSU-assisted hybrid emergency messages broadcasting protocol(RA-HEMB)for urban roads is designed.The protocol first generates broadcasting target region based on twoway grid roads in urban scenes,and which region should be notified of emergency messages are determined according to instantaneous road trafic network status and specific emergency messages types.Then,considering the wireless multi-hop transmission mechanism,an efficient adaptive forwarding nodes selection scheme based on position is proposed to improve network performance.The scheme defines the existence ratio(ER)of forwarding nodes,and dynamically adjusts the forwarding area based on parameters such as vehicle densities and vehicle to vehicle(V2V)communication ranges to adapt to various traffic scenarios.For the entire target region of emergency messages broadcasting,based on the adaptive forwarding nodes selection scheme and the deployment of RSUs in urban roads,by properly utilizing wired links between RSUs and combining wireless V2V and vehicle to roadside unit(V2R)communication links to cooperatively broadcast emergency messages until the broadcast requirements in the target region are met or the life cycle of the emergency messages ends.The simulation results show that the proposed RA-HEMB protocol has higher message reception rate and lower delivery delay than the benchmark protocols.2)Aiming at how to balance the low-latency and high-reliability of emergency messages broadcasting and the system cost of RSU deployment,an RSU deployment strategy based on emergency messages broadcasting(EMB-RD)for urban roads is proposed.The paper first constructs a novel RSU deployment model applied to urban roads and the RA-HEMB protocol;and the RSU deployment problem is modeled as a multi-objective optimization problem based on message reception rate and delivery delay of the emergency messages broadcasting and the system cost of RSU deployment.Then an improved deployment strategy EMB-RD based on the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ)is proposed to solve this problem.In EMB-RD,a collaborative initialization strategy based on RSU coverage and emergency message location is proposed to improve the quality of initialization solution;then a local search reconstruction algorithm is designed to quickly generate high-quality solutions.Furthermore,for the Pareto optimal solution set obtained by EMB-RD,an synthetic utility function is proposed to evaluate the total revenue of the RSU deployment strategy to obtain the optimal solution.Finally,simulation results verify the effectiveness of the proposed EMB-RD deployment strategy in broadcasting emergency messages;and compared with deployment strategies based on other multi-objective optimization algorithms,the results indicate that the proposed strategy improves the performance by about 20%in solving this problem.