A priority-based CCA threshold adjusting method for EWM dissemination in vehicular ad-hoc networks.

Emergency warning message (EWM) transmission insurance is one of the most interesting topics for vehicular ad-hoc network application. Clear channel assessment (CCA) threshold is deemed to be a key factor influencing EWM dissemination performance. Considering vehicle abnormal event hazard level and EWM's important level, a new parameter, EWM priority rank, is defined. Based on EWM priority rank, a new CCA threshold self-adjusting method is proposed in this paper. Moreover, according to the proposed CCA threshold selection method, an EWM dissemination algorithm is designed. A series of experiments on the sensor network testbed are conducted to evaluate the impact of proposed method on EWM dissemination. The experimental results show that an appropriate CCA threshold is beneficial to increase global dissemination success rate and to shorten packet delivery delay. [ABSTRACT FROM AUTHOR]