A position-based reliable emergency message routing scheme for road safety in VANETs

Reliable emergency message (EM) transmission in vehicular adhoc networks (VANETs) necessitates an effective routing scheme. Position-based routing is considered more suitable for VANETs for not having to maintain any routing table or sharing connection states with neighbors. However, position-based routing is challenging in VANETs because vehicles change their positions instantly, and the next-hop can often go out of the communication range in greedy forwarding mode. This unstable behavior of the next-hop triggers route redundancy and leads to a high end-to-end delay (ED) and lower packet delivery ratio (PDR). Moreover, routing decisions based on a next-hop (relay) vehicle may be less optimal if we do not consider the stability and predict the position of a next-hop vehicle in such dynamic environments. To that end, we propose a position-based reliable emergency message routing (REMR) scheme based on our mobility metrics, which exploits the vehicle moving behaviors to enhance EM delivery. We describe how the choice of next-hop in greedy forwarding can be enhanced by leveraging neighbor's future location information. By taking into account the Euclidean distance and position information, REMR predicts the relative positions of neighbor vehicles to exclude unstable neighbors from the list of candidate next-hops. In addition, REMR employs the vehicles' movement information (e.g., position, speed variation, and moving angle) to minimize a possible link disruption and to choose an optimal next-hop for robust routing of EMs. REMR also offers a beaconing control strategy to enhance message reliability and to deal with the problem of beacons congestion. To minimize beacons congestion, REMR adjusts the beacon interval based on the neighborhood density. By consolidating mobility metrics and beacon control strategy, REMR can respond adequately to variation in the network traffic and frequent topology changes as validated by our simulation results.