End-to-end acknowledgement of geocast in vehicular networks

Vehicular networks suffer from fundamental reliability problems, which preclude basing safety-critical decisions on the expected outcome of communication. To enable safe, distributed decision making, reliable feedback on the success of communication is of critical importance. In this paper, we address the problem of end-to-end acknowledgement of geocast, in order to allow an application to know to which vehicles its geocast messages were successfully transmitted. Acknowledgements are gathered in a wave of fixed velocity to obtain results with a predictable delay. Acknowledgements are aggregated into larger messages and aggregators are selected using consistent hashing to increase the probability of acknowledgements from different vehicles being forwarded to the same aggregator. The source is found using a combination of a sink tree towards its original position, which is overlaid on the road network, and position updates by the source. We show that the algorithm is effective under various traffic conditions on a simulated highway.