Measuring location privacy in V2X communication systems with accumulated information

Vehicle-to-vehicle/vehicle-to-infrastructure (V2X) communication systems are envisioned to greatly improve road safety, traffic efficiency, and driver convenience. However, many V2X applications rely on continuous and detailed location information, which raises location privacy concerns. A multitude of privacy-protection mechanisms have been proposed in recent years. However, few efforts have been made to develop privacy metrics, which can provide a rigorous way to assess the privacy risk, evaluate the effectiveness of a given mechanism, and exploit the full possibilities of protection methods in V2X systems. Therefore, in this paper we present a trip-based location privacy metric for measuring user location privacy in V2X systems. The most distinguishable aspect of the metric is to take into account the accumulated information, which is the privacy-related information acquired by an adversary for an extended period of time, e.g., days or weeks. We develop methods to model and process the accumulated information, and reflect the impact on the privacy level in the metric. We further prove the viability and correctness of the metric by various case studies. Our simulations find out that under certain conditions, accumulated information can significantly decrease the level of user location privacy. The metric and our findings in this paper give some valuable insights into location privacy, which can contribute to the development of effective privacy-protection mechanisms for the users of V2X systems.