Speed adaptive probabilistic flooding for vehicular ad hoc networks

A significant issue in vehicular ad hoc networks (VANETs) is the design of an effective broadcast scheme that can facilitate the fast and reliable dissemination of emergency warning messages in the vicinity of an unexpected event, such as a traffic accident. In this paper, we propose a novel solution to this problem, which we refer to as speed adaptive probabilistic flooding. The scheme employs probabilistic flooding to mitigate the effects of the broadcast storm problem, which is typical when using blind flooding, and its unique feature is that the rebroadcast probability is adaptively regulated based on the vehicle speed to account for varying traffic densities within the transportation network. The motivation behind this choice is the identification of the existence of phase transition phenomena in probabilistic flooding in VANETs, which dictate a critical probability being affected by the varying vehicle traffic density and are shown to be linearly related to the vehicle speed (a locally measurable quantity). The scheme is evaluated using simulations on different sections of the freeway system in the City of Los Angeles, CA, USA. Simulation results indicate that the proposed scheme fulfills its design objectives, as it achieves high reachability and low latency of message delivery with low overhead in a number of representative scenarios. The scheme is also shown to outperform existing solutions, including Global-Positioning-System-based, and exhibits robustness with respect to different road topologies and parameters such as the transmission range of vehicles and the number of hops.