Exploiting downstream mobility to achieve fast upstream message propagation in vehicular ad hoc networks

Vehicular ad-hoc networks (VANETs) promise to enable many novel applications in transportation systems including accident avoidance, congestion sensing, traffic metering, and general in-car information services. Yet implementing multi-hop vehicular communications is highly challenging due to the highly time-varying nature of vehicles. In addition to node mobility and the impediments of wireless communication, a network comprised of moving vehicles is a dynamic system that can be fragmented into many individual components of disparate connectivity. In this paper we describe and analyze a routing scheme that exploits this dynamic connectivity for the purpose of message propagation of attributed (or labelled) data in a fragmented VANET. Our analysis provides upper and lower bounds on message propagation rate as a function of the traffic density, vehicle speed, and radio range; and sheds light into the role played by each of these network parameters. An important insight from our analysis is that vehicle mobility in the opposite traffic direction can be used to achieve substantial gains in message propagation rates. Our analytical findings are supported by extensive simulations. The simulation results indicate that under certain traffic conditions an increase in vehicle mobility results in an order-of-magnitude increase in message propagation rate.