Clock Error Estimation for DFMC SBAS Ground Monitoring Stations Based on Dual-Frequency Multipath Characteristics

Kun Fang, Zhuoran Xu, Wang Li, Xiaowei Lan, Xu Bo

Peer Reviewed

Abstract:	The precise calculation of satellite orbit and clock corrections in Dual-Frequency Multi-Constellation (DFMC) Satellite-Based Augmentation Systems (SBAS) relies heavily on the accurate estimate of ground monitoring station clock errors. However, the use of the ionosphere-free (Ifree) combination in DFMC SBAS exacerbates the impact of multipath effects and degrades the measurement quality. To address this challenge, this study proposes a robust clock error estimation algorithm that incorporates the statistical characteristics of dual-frequency multipath errors into the weighting matrix. First, the Code Noise and Multipath Correction (CNMC) method is employed to analyze and extract the multipath errors of single-frequency and dual-frequency Ifree combined signals. Subsequently, a pseudorange residual weighting method is adopted to estimate the master station clock error, where the weighting matrix is optimized using the estimated multipath variance. Finally, a Kalman filter is applied to the time series of all ground station clock errors to enhance stability and continuity. The method is validated using real data collected from monitoring stations in the China region, covering a hybrid orbital configuration of the BDS-2/3, GPS, and Galileo constellations. The results indicate that the Ifree combination significantly amplifies signal multipath errors. However, compared to the traditional elevation-dependent weighting strategy, the improved algorithm effectively mitigates the impact of jumps in the number of satellites caused by satellites entering and exiting the field of view, yielding more stable ground monitoring station clock estimates. The stability of GNSS receiver clock errors (measured by Standard Deviation) is improved by 3.53% (GPS), 1.85% (BDS), and 1.26% (Galileo), respectively. Consequently, this method provides higher-quality inputs for the subsequent calculation of DFMC SBAS satellite orbit and clock corrections.
Published in:	Proceedings of the ION 2026 Pacific PNT Meeting April 13 - 16, 2026 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	49 - 61
Cite this article:	Fang, Kun, Xu, Zhuoran, Li, Wang, Lan, Xiaowei, Bo, Xu, "Clock Error Estimation for DFMC SBAS Ground Monitoring Stations Based on Dual-Frequency Multipath Characteristics," Proceedings of the ION 2026 Pacific PNT Meeting, Honolulu, Hawaii, April 2026, pp. 49-61. https://doi.org/10.33012/2026.20570
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