An Adaptive Emergency Broadcast Strategy for Vehicular Ad Hoc Networks

In recent years, since the adoption of the IEEE 802.11p and IEEE 1609 standards, Vehicular Ad hoc Networks (VANETs) have received a significant amount of attention in Ad hoc Network studies. Vehicular safety applications have thus played an important role in VANETs, and many emergency broadcast systems have been proposed. However, some of these broadcast mechanisms might result in the broadcast storm problem. The emergency broadcast strategy proposed in this paper is that when a car accident occurs, the vehicle's sensors detect impacts and immediately send emergency messages to inform other vehicles nearby. In addition, we propose a way to eliminate redundant broadcasts and to ensure that emergency messages can be transmitted properly. We propose a stability function to estimate the reliability of the transponder. The backoff procedure of this proposed method assigns appropriate waiting times to different forwarders. The proposed scheme is implemented with NS2 simulator based on WAVE/DSRC standards. Simulation results show that the proposed protocol exhibits outstanding performance in terms of forwarding counts, packet loss rate, and delay time in different environments. In addition, our protocol maintains stability in different vehicle density scenarios so that each vehicle receives emergency messages and holds a low latency to ensure that the driver has adequate safety response time to enhance traffic safety.