Evaluating Multi-Hop Beaconing Forwarding Strategies for IEEE 802.11p Vehicular Networks

Multi-hop propagation of situational information is a promising technique for improving beaconing performance and increasing the degree of situational awareness onboard vehicles. However, limitation on beacon size prescribed by standardization bodies implies that only information about 3-4 surrounding vehicles can be piggybacked in a beacon packet. In most traffic situations, the number of vehicles within transmission range is much larger than 3-4, implying that multi-hop forwarding strategies must be devised to select which neighboring vehicle's information to include in a transmitted beacon. In this paper, we investigate the effectiveness of different multi-hop forwarding strategies in delivering fresh situational information to surrounding vehicles. Effectiveness is estimated in terms of both average information age and probability of experiencing a situational-awareness blackout of at least 1 sec. Both metrics are estimated as a function of the hop distance from the transmitting vehicle. The investigation is based on extensive simulations whose multi-hop communication performance is corroborated by real-world measurements. The results show that network-coding based strategies substantially improve forwarding performance as compared to a randomized strategy, reducing the average information age of up to 60%, the blackout probability of two orders of magnitude, and providing a performance similar to that of an idealized strategy in which complete situational information is included in the beacon.