Improving Accuracy and Algorithm Integrity for Train Localization in Harsh Urban Environments Using GNSS Time-Difference Carrier-Phase Displacement and GNSS Map-Modulation with Inertial Navigation Over Hundreds of Hours of Real-Life Data

Pierre d’Harcourt, Laurent Poletti, Jean-Baptiste Lacambre, Sophie Glevarec, Tim Barford

Abstract:	Most existing train localization systems use odometers to measure the distance travelled between physical beacons on the tracks. Railway odometry usually relies on wheel sensors with a drift up to 5% of the travelled distance and is subject to slip when breaking and accelerating, adding additional error. Since this drift is significant, numerous beacons are required on the railway to ensure a given level of position precision. Today, the objective of the European railway traffic management System (ERTMS) is to find a solution that ensures a positioning precision up to ten meters, including in very challenging environments. ERTMS’s framework promotes train-embedded localization systems instead of high footprint railway infrastructure. As in many other challenging position applications, inertial navigation systems (INS) are a good answer to ERTMS’s continuous localization needs. Global navigation satellite system (GNSS) provides long-term stability while inertial measurement unit (IMU) maintains navigation continuity through harsh GNSS environments. The problem with this approach is that the GNSS errors are very difficult to model in a railway environment. In those conditions, not only the performance can be degraded, but, even worse, the confidence in the solution can be overly optimistic, which creates an issue for the positioning algorithm integrity. This paper proposes a complementary way to use the GNSS/INS, when the integrity of the GNSS position cannot be ensured by the satellite-based augmentation systems (SBAS) or others alternative augmented GNSS solutions, using Time-Difference Carrier-Phase measurement (TDCP). GNSS Map-Modulation is an additional way to use the GNSS/INS when the integrity of the GNSS position cannot be ensured by the SBAS. A GNSS quality map is built by comparing the SBAS with references. This map is than used to increase SBAS standard deviation in areas where its errors are not correctly modeled.
Published in:	Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023) September 11 - 15, 2023 Hyatt Regency Denver Denver, Colorado
Pages:	2270 - 2281
Cite this article:	d’Harcourt, Pierre, Poletti, Laurent, Lacambre, Jean-Baptiste, Glevarec, Sophie, Barford, Tim, "Improving Accuracy and Algorithm Integrity for Train Localization in Harsh Urban Environments Using GNSS Time-Difference Carrier-Phase Displacement and GNSS Map-Modulation with Inertial Navigation Over Hundreds of Hours of Real-Life Data," Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023), Denver, Colorado, September 2023, pp. 2270-2281. https://doi.org/10.33012/2023.19459
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In