Performance Modeling of Safety Messages Broadcast in Vehicular Ad Hoc Networks

In vehicular ad hoc networks (VANETs), because all vehicles in range are shown as destination nodes and less time is spent for the medium access process, broadcast communication is considered a highly appropriate technique for the dissemination of safety messages in such networks. However, the lack of request-to-send/clear-to-send handshaking and packet acknowledgment makes the communication more vulnerable to interferences, thus resulting in lower communication reliability. In this paper, we present an analytical model for the performance evaluation of safety message dissemination in vehicular ad hoc networks with two priority classes. In particular, considering the IEEE 802.11 broadcast protocol and using 2-D Markov modeling, we derive the joint distribution of the numbers of low-priority periodic messages, which are in transmission mode and in a backoff process in a highway. Then, the result is used to derive the average dissemination delay of high-priority event-driven messages in the presence of the low-priority traffic in the network. The results are helpful in determining a good tradeoff between network parameters such as vehicles' transmission range, safety traffic generation rate, and medium access control (MAC) parameters to satisfy the required delay bounds for the critical high-priority traffic.