IEEE 802.11p VANets: Experimental evaluation of packet inter-reception time

Periodic exchange of situational information (beacons) is at the basis of most active safety applications in vehicular environments, which explains recent interest in measurement-based characterization of beaconing performance. However, existing studies are focused on measuring a specific link-level performance parameter, namely, the packet delivery rate (PDR). While PDR is an important performance metric, application requirements of many active safety applications are expressed in terms of the packet inter-reception (PIR) time, whose real-world performance has not been studied so far. In this paper, we fill this gap by presenting an extensive study of the PIR times observed in real-world highway scenarios. We start by showing that the PIR metric cannot be reliably estimated from PDR, since the two metrics are only weakly correlated. Motivated by this finding, we present a thorough characterization of the PIR time distribution, which is shown to be a power law in a variety of configurations. The shape of the PIR time distribution indicates that potentially dangerous “situational awareness” blackouts are relatively frequent. Most importantly, blackout events are found to be directly correlated in time. We also study the effect of vehicle configuration on the PIR time, quantifying the adverse effect of NLOS conditions on the probability of experiencing blackouts. To lessen this effect, we implemented and evaluated, by means of both experiments and simulations, a simple lightweight technique for multi-hop propagation of beaconing information, showing that even relatively simple multi-hop beaconing techniques substantially improve PIR statistics and, hence, safety. A final contribution of this paper is promoting the Gilbert-Elliot model, previously proposed to model bit-error bursts in packet switched networks, as a very accurate model of beacon reception behavior observed in real-world scenarios. A preliminary version of this paper appeared in the Proceedings of IEEE Infocom, 2012 [19]. Corresponding author: M. Elena Renda (email: [email protected]).