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.

An Unattended Wireless Sensor Network (UWSN) can be used in many applications to collect valuable data. Nevertheless, due to the unattended nature, the sensors could be compromised and the sensor readings would be maliciously altered so that the sink accepts the falsified sensor readings. Unfortunately, few attentions have been given to this authentication problem. Moreover, existing methods suffer from different kinds of DoS attacks such as Path-Based DoS (PDoS) and False Endorsement-based DoS (FEDoS) attacks. In this paper, a scheme, called AAD, is proposed to Acquire Authentic Data in UWSNs. We exploit the collaboration among sensors to address the authentication problem. With the proper design of the collaboration mechanism, AAD has superior resilience against sensor compromises, PDoS attack, and FEDoS attack. In addition, compared with prior works, AAD also has relatively low energy consumption. In particular, according to our simulation, in a network with 1, 000 sensors, the energy consumed by AAD is lower than 30% of that consumed by the existing method, ExCo. The analysis and simulation are also conducted to demonstrate the superiority of the proposed AAD scheme over the existing methods.