Various Road User Charging (RUC) mechanisms are used to control the traffic and its resulting pollution, as well as revenue sources for reinvestment in the road infrastructure. Among them, Electronic Toll Collection (ETC) systems based on user positions estimated with Global Navigation Satellite Systems (GNSS) are particularly attractive due to their flexibility and reduced roadside infrastructure in comparison to other systems like tollbooths. Because GNSS positioning may be perturbed by different errors and failures, ETC systems, as liability critical applications, should monitor the integrity of GNSS signals in order to limit the use of faulty positions and the consequent charging errors. The integrity monitoring systems have been originally designed for civil aviation, so they need to be adapted to the ETC requirements. This paper studies the use of Receiver Autonomous Integrity Monitoring (RAIM), which are algorithms run within the GNSS receiver, and therefore easier to tune to ETC needs than other systems based on external information. The Weighted Least Squares Residuals (WLSR) RAIM used in civil aviation is analyzed, and an algorithm modification for ETC is proposed. Simulations demonstrate that the proposed RAIM algorithm has a superior level of availability over civil aviation based RAIM procedures, particularly in urban environments.

Certain GNSS applications conceived for road users in urban scenarios must meet some particular integrity requirements to assure the system safety, reliability or credibility. For instance, GNSS-based Road User Charging is one of these applications that recently has attracted special interest. A correct design of such applications needs the knowledge of the GNSS error distribution. Furthermore, the GNSS error model should have been built with overbounding techniques. The user is a vehicle equipped with a GNSS receiver that may track different signals of various systems (GPS, Galileo, SBAS), in a single-or dual-frequency configuration. The different error sources contributing to the total pseudorange error are identified, analyzed and modeled, using overbounding techniques when necessary. Finally the pseudorange measurement error model is obtained and analyzed for different receiver configurations.

GNSS-based Road User Charging (RUC) systems are particularly interesting because of their flexibility and reduced roadside infrastructure. At present, truck toll collection systems based on GPS receivers installed on the vehicles are already deployed in German and Slovak motorways. Reliability of road tolling systems is fundamental in order to limit the loss of revenue because of undercharging and the user claims because of overcharging. Consequently, GNSS integrity monitoring plays a key role in such systems, providing trustful positioning data that keep position errors and their associated legal or economical consequences within given limits. Nevertheless, the design of GNSS integrity algorithms like RAIM requires a deep knowledge of the characteristics of the application and GNSS errors. This paper analyzes the required parameters to develop RAIM algorithms for road tolling applications in urban and rural environments.

BiographiesGuillaume NOVELLA graduated as a space and aeronautical telecommunications engineer from ENAC (Ecole Nationale de l'Aviation Civile) in 2019. He is now a Ph.D student at the TELECOM lab of the ENAC. His Ph.D topic deals with drone C2Link and GNSS operating margins.