Reliable and Efficient Broadcasting in Vehicular Ad Hoc Networks

Most of the envisioned services over vehicular networks need to deliver information to all vehicles inside a certain region. Several such broadcasting protocols have been reported so far, but surprisingly only one of them addresses the issue of intermittent connectivity. In this paper, we present a broadcast protocol which is suitable for a wide range of vehicular scenarios and traffic conditions. The protocol employs local position information acquired via periodic beacon messages. Beacons are used by cars to decide whether or not they belong to a connected dominating set (CDS). Vehicles in the CDS use shorter waiting period before possible retransmissions. Identifiers of circulated broadcast messages are added to beacons as piggybacked acknowledgements. When waiting timeout expires, vehicle retransmits if it has at least one neighbor which did not acknowledge circulated message with the last beacon, and sets a new waiting period. Our algorithm does not depend on any parameter or threshold which varies its operation. Despite its simplicity, the protocol is shown to provide high reliability and efficiency by means of a simulation-based performance evaluation. It also greatly outperforms the only competing algorithm we found in the literature which explicitly considers different mobility scenarios.