Abstract: The development of urban city greatly promotes the application of vehicular ad-hoc network, among which the safety-related emergency message broadcast is one of the key research points. The emergency message broadcast needs to meet the requirements for the quality of service such as low latency, high reliability, high scalability and so on. Most existing emergency message broadcasting methods, when selecting the next hop forwarding node, assume that there is an approximately equal probability of being selected as the relay area for each location, and the nodes of all positions are treated equally, which lacks the study of the distribution of the optimal node position so that it cannot adapt well to the distribution of the optimal forwarding node. However, the key to reducing the delay in emergency messaging is to quickly determine the appropriate relay forwarding node. Therefore, in order to further improve the timeliness of emergency message broadcasting and reduce the propagation delay, in this paper, we propose a Huffman coding-based emergency message broadcasting method. Generally, we first analyze the probability distribution of the optimal forwarding nodes in urban roads. And based on it, we then use the principle of Huffman coding to design a fast partition method, which can achieve the goals of quickly selecting optimal relay node, reducing the delay of emergency message broadcast, and improving the speed of emergency message transmission by minimizing the optimal node selection time. Our simulation results show that the proposed method can reduce the delay of emergency message broadcasts in different scenarios by 5.3%~18.0%, and improve the speed of emergency message transmission by 8.9%~24.5%.

Key words: vehicular ad hoc network, multi-hop broadcast protocols, emergency message dissemination, black-burst, Huffman coding