VCAST: Scalable Dissemination of Vehicular Information with Distance-Sensitive Precision

Real-time information about the state (location, speed, direction) of other vehicles in the system is critical for both safety and navigation applications in future intelligent transportation systems. However, reliably obtaining this information over multiple hops in a wireless network while avoiding network congestion in the shared channel poses a significant challenge. In this paper, we describe an algorithm VCAST that addresses this challenge by exploiting a notion of distance sensitivity in information propagation, in which information is forwarded at a rate that decreases linearly with distance from the source. By doing so, traffic information can be obtained with a staleness, which is a measure of error in the traffic information, that is bounded by O(d) where d is the distance from the source of the information. At the same time, the required communication overhead per node can be significantly reduced to O( √ N), thereby reducing channel contention, allowing higher information supply rates and scaling to larger network sizes. VCAST can be used to improve safety against collisions, inform about approaching emergency vehicles and lane merging vehicles (that may even be beyond a single hop communication range) and to enable dynamic routing and navigation techniques by providing aggregate traffic information in an extended neighborhood. VCAST does not require any special hardware or modification to vehicular transmission standards; instead it can simply piggyback on basic Here I am communication for vehicular networks. The performance of VCAST is validated using extensive ns-3 simulations under different network sizes and densities with an IEEE 802.11b transmission model and the advantages of VCAST in comparison to non distance-sensitive approaches are