VCAST: An Infrastructure-Less Vehicular Traffic Information Service with Distance-Sensitive Precision

In this paper, we describe VCAST, an algorithm for obtaining individual vehicle location as well as aggregate traffic information over an infrastructure-less multi-hop wireless vehicular network. 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. To ensure scalability in forwarding information over multiple hops, we exploit a notion of distance sensitivity in information propagation, by which traffic information is propagated 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_h²) where d_h is the communication hop distance from the source of the information. At the same time, the required communication rate per unit time at each node only depends on the radius of the region in terms of communication hops, and not on the vehicular density or the number of vehicles in the region. 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.