Communication protocols for vehicular ad hoc networks

Abstract

SummaryVehicular networks are envisioned for large scale deployment, and standardization bodies, car manufacturers and academic researchers are solving a variety of related challenges. After a brief description of intelligent transportation system architectures and the main already-established low-level standards, this tutorial elaborates on four particular aspects of vehicular networks, which are i) the potential for a large set of innovative applications, ii) a review of the main modeling approaches used for both roads and traffic, and finally two important communication primitives, that are iii) data dissemination via broadcasting/geocasting, and iv) routing in both highway and urban environments. A particular emphasis is on recent protocols that realistically consider the inherently complex nature of vehicular mobility, such as intermittent connectivity, speed variability, and the impact of intersections.

Information propagation speed in bidirectional vehicular delay tolerant networks

“…With applications such as safety, ad hoc vehicular networks are receiving increasing attention (see recent survey [4]). Delay tolerant architectures have thus been considered in this context, and various analytical models have been proposed.…”

“…In this context, our contributions are as follows: (1) we develop a new vehicule-to-vehicule model for information propagation in bidirectional vehicular DTNs in Section II; (2) we show the existence of a threshold (with respect to vehicle density), above which information speed increases dramatically over vehicle speed, and below which information propagation speed is on average equal to vehicle speed, and (3) we give the exact expression of this threshold, in Section III; (4) in Section V, we prove that, under the threshold, even though the average propagation speed equals the vehicle speed, DTN routing using cars moving on both directions provides a gain in the propagation distance, and this gain follows a simple power law with respect to vehicle density below this threshold, is bounded by a sub-linear power law with respect to the elapsed time, in the referential of the moving cars; (5) we characterize information propagation speed as increasing quasi-exponentially with the vehicle density when the latter becomes large above the threshold, in Section IV; (6) we cover both infinite radio propagation speed cases, then finite radio propagation speed cases in Section VI; (7) we validate the provided analysis with simulations in several environments, Information propagation threshold with respect to (λe, λw) for infinite radio speed in red. In blue for radio speed vr = 10v, in green vr = 2v, in yellow vr = 1.25v.…”

Mitigating flash crowd effect using connected vehicle technology

“…In the literature this is referred to as the Flash Crowd Effect (FCE) [4], similar advice problem [5], or overreaction [6]. In this case real-time information about prevailing conditions can be misleading, as it does not include the delayed effect of vehicles entering the route in its associated travel time.…”

“…Research literature gives very little attention to how to cope with the FCE problem in practice. While it is noticed in [4,5,6]-only general indications, such that a mixed route guidance strategy should be used instead of the pure shortest-time route guidance [7]-are given.…”

“…While there is a consensus that route guidance based on the shortest-time principle leads to the FCE [4,5,6,7], very little attention has been devoted to how to practically solve the problem. The exception-work reported by Davies [3]-focuses on the FCE in a two-route scenario.…”