FGO-Based Integrity Monitoring for Urban Positioning with Dynamic Covariance Scaling

Oussama Tahri, Ni Zhu, and David Bétaille

Peer Reviewed

Abstract:	Urban navigation using low-cost Global Navigation Satellite System (GNSS) sensors has garnered significant attention in the navigation and transportation fields, particularly due to the increasing requirements for positioning accuracy. In open-sky conditions, GNSS solutions are typically reliable and offer a decimeter level accuracy for a wide range of applications. However, in more challenging environments, like urban canyons where the availability of clear satellite signals is compromised, positioning accuracy often degrades significantly due to multipath effects and non-line-of-sight (NLOS) signals. Despite considerable research efforts, there is a lack of a generalizable model to address these urban GNSS challenges, as they are highly dependent on the local environment. This paper aims to enhance both the accuracy and integrity of urban GNSS positioning through advanced filtering and smoothing models. Specifically, we adopt a Factor Graph Optimization (FGO) approach, and evaluate its potential for integrity monitoring, a critical aspect often overlooked in FGO-based methods. A key focus is on the integration of Dynamic Covariance Scaling (DCS) to optimize signal weighting and minimize the influence of erroneous measurements. Real-world urban tests compare various state estimation techniques, to assess the impact of this additional constraint. The findings demonstrate that FGO, with DCS can outperform traditional methods like the Extended Kalman Filter (EKF) and the regular FGO in providing robust and reliable navigation solutions for urban environments. Index Terms—low-cost GNSS, urban environments, factor graph optimization, integrity monitoring, covariance scaling
Published in:	2025 IEEE/ION Position, Location and Navigation Symposium (PLANS) April 28 - 1, 2025 Salt Lake Marriott Downtown at City Creek Salt Lake City, UT
Pages:	1403 - 1410
Cite this article:	Tahri, Oussama, Zhu, Ni, Bétaille, David, "FGO-Based Integrity Monitoring for Urban Positioning with Dynamic Covariance Scaling," 2025 IEEE/ION Position, Location and Navigation Symposium (PLANS), Salt Lake City, UT, April 2025, pp. 1403-1410.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In