V-GRADIENT: A Density-Aware Geocast Routing Protocol for Vehicular Delay-Tolerant Networks

Vehicular Delay-Tolerant Networks (VDTNs) are networks of vehicles that communicate wirelessly, where there are no permanent end-to-end connections. VDTNs have a highly variable topology, with frequent partitions, and possibly low node density. Thus, delay-tolerant routing adopts a store-carry-and-forward message transfer paradigm, where messages have a useful Time To Live (TTL) and are stored until a good contact opportunity arises. Multiple message replicas can be generated to improve delivery probability at the cost of increasing network congestion. In this paper, we propose the V-GRADIENT geocast routing protocol that monitors node density and buffer occupancy, to adapt dynamically the forwarding techniques used to disseminate messages within the geographic region of interest. Simulation results show that V-GRADIENT is capable of controlling network congestion and efficiently deliver messages resulting in better delivery ratios (13-99%) and lower latencies when compared with existing protocols.