Abstract—Emergency warning message (EWM) transmission insurance is one of the most interesting topics for Vehicular Cyber-physical System (V-CPS) application. A relatively low transmission requirement should improve EWM’s real-time delivery, and however, decrease reliability of packet delivery by its corresponding burst converge-cast, especially under multi-hop condition. In this paper, based on a series experiments, a clear channel assessment (CCA) threshold ladder selection method is proposed to ensure both real-time and reliability for EWM transmission. The experimental results show that the threshold adjusting method has a positive effect on the delivery rate. With an appropriately diminishing clear channel assessment threshold related to the packet hops, the global dissemination successful rate can be up to 73.5%, and more than 90% of the 1-hop nodes can receive the correct packet. The experiment results provide a practicable method to improve EWM dissemination performance.

Index Terms—Inter-vehicle communication, emergency warning message, clear channel assessment, delivery ratio, ladder CCA threshold selection mechanism

Cite: Qingwen Han, Zhe Zhang, Lingqiu Zeng, Lei Ye, and Yingxiang Zhu, "A Ladder CCA Threshold Selection Mechanism for Multi-Hop Vehicle EWM Transmission," Journal of Communications, vol. 10, no. 1, pp. 33-42, 2015. Doi: 10.12720/jcm.10.1.33-42