Open-Loop Receiver Processing and Filtering of GNSS Signals Traversing Troposphere Structures

Jiawei Xu, Y. Jade Morton

Peer Reviewed

Abstract:	Radio waves traversing moist troposphere or ionospheric plasma structures can experience signal fading and carrier phase fluctuations. For GNSS receivers implemented using closed-loop (CL) tracking, these complex propagation media may result in substantial errors and loss of lock. Open-loop (OL) tracking has proven effective in tracking these challenging signals. However, due to the absence of feedback loops, OL tracking outputs are highly noisy and require additional filtering. In our previous study, an unscented Kalman filter (UKF)-based OL filtering algorithm, referred to as the complex waveform filter (CWF), has demonstrated superior performance in robust carrier cycle slip correction and pseudorange bias reduction. In this study, the CWF is adapted and applied to GNSS data collected using a side-facing horn antenna installed atop Mount Haleakala (3060 m) ¯ on the island of Maui, HI. These data are particularly difficult due to not only moist lower troposphere, but also pronounced multipath effects, as signals reflected from the ocean surface and the mountain itself interfere with the direct signal. To address this, the CWF is extended to track multiple signal paths - both direct and multipath reflections - resulting in the multi-target CWF (mt-CWF). Triple-frequency GNSS data (GPS L1, L2, and L5) is recorded at intermediate frequency (IF) and tracked in both OL and CL modes. The OL tracking results are filtered using the SCANF (simultaneous cycle slip and noise filtering), CWF, and mt-CWF methods, while CL tracking is based on the conventional single-frequency tracking (SFT). The filtered OL and CL tracking outputs are then analyzed and compared in terms of code delay, carrier phase, and detrended signal intensity (SI). The technique presented in this paper can be adapted for signals transmitted from LEO satellites and for receivers onboard aircraft or spacecraft.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	3172 - 3183
Cite this article:	Xu, Jiawei, Morton, Y. Jade, "Open-Loop Receiver Processing and Filtering of GNSS Signals Traversing Troposphere Structures," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 3172-3183. https://doi.org/10.33012/2025.20299
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