Enhancing safety messages dissemination over 802.11p/DSRC

Direct radio-based vehicle-to-vehicle (V2V) communication can be used to prevent accidents and to provide accurate information on road state or surrounding vehicles intention. Both kinds of information can be used to enable drivers to react in time and avoid hazardous situations. While the IEEE 802.11p standard has specifically been adopted for vehicular communications, its Distributed Coordination Function (DCF) operation can cause poor delivery rates when the communication channel is congested or when messages need to be transmitted over distances higher than 300 meters. In this paper, we propose MORS, a technique for transmission power adjustment to avoid channel congestion, combined with an efficient multi-hop data dissemination scheme. The purpose is to ensure low delays and high delivery rates for V2V communications at distances higher than it would normally be possible with the same effectiveness with 802.11p alone. The power adjustment technique is fully distributed and asymmetrical, and the multi-hop data dissemination scheme is based on a newly designed multi-metric which characterizes the available links capacity. MORS determines, at each hop, the best available link choice to ensure both reliable transmissions and a minimum delivery delay while reducing congestion and network load though adaptive power adjustment. Simulation results confirm the effectiveness of the proposed transmit-power adaptation and multi-hop relaying schemes under various realistic traffic constraints.