Experimental analysis of CCA threshold self-adjusting method for EWM dissemination

Emergency warning message (EWM) transmission insurance is one of the most interesting topics for Vehicular Ad-Hoc Network (VANET) 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, 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 done to evaluate the impact of proposed method on EWM dissemination. The experimental results show that an appropriate CCA threshold is benefit to improving global dissemination successful rate and shortening packet delivery delay.