A multi-hop broadcast protocol design for emergency warning notification in highway VANETs

Multi-hop broadcast transmission is used in vehicular ad hoc networks (VANETs) to alert all vehicles within a geographical area of an emergency situation. However, the successful dissemination of multi-hop warning messages beyond the transmission range of a vehicle faces three major issues: (i) the broadcast storm, (ii) the severe interference with the existing periodic single-hop safety messages, and (iii) the hidden nodes. In this paper, we propose an efficient time-slotted multi-hop broadcast protocol that significantly reduces the number of required transmissions, while ensuring a timely and successful delivery of the warning messages. To alleviate the broadcast storm problem, we select only a subset of vehicles on the road to serve as the potential relay nodes. Each of these ‘segment leaders’ is responsible for forwarding the warning messages arrived in its own road segment. To avoid interfering with the safety messages transmitted periodically, we propose to allocate separate time slots for the warning messages. We also devise a signaling mechanism that ensures the reliable delivery of these multi-hop messages. Simulation results confirm that the developed protocol substantially outperforms existing schemes in terms of the number of required multi-hop transmissions and the dissemination delay. At the same time, the proposed solution maintains a high reception rate and low end-to-end delay for the single-hop safety messages.