Robust GNSS Dual-Frequency Code Tracking with Multipath Aware and Inter-Frequency Bias Estimation

Jing Zhou, Zuping Tang, Jiaolong Wei, Xiuxun Liu, Jie Sun

Peer Reviewed

Abstract:	Multi-frequency Global Navigation Satellite System (GNSS) signals provide frequency diversity gains and can improve tracking robustness under fading, interference, and partial blockage, especially in urban environments. However, multi-frequency joint code tracking faces three key challenges: (a) inter-frequency code bias (IFB) induced by hardware group delays and ionospheric dispersion, which prevents natural alignment of correlation peaks across bands; (b) the S-curve distortion generated by multipath at different bands is inconsistent, and long-delay multipath error from a low-chip-rate band may contaminate the high-chip-rate bands; and (c) at the correlation-function level, the IFB and multipath error difficult to distinguish, because both appear as code-delay biases in the discriminator output. To address these issues, this paper proposes a multipath-aware dual-frequency joint code tracking loop. A multi-interval consistency metric is first used to quantify and normalize multipath error on each band. The resulting metrics are mapped to equivalent multipath variances, and then combined with the thermal noise variances of the discriminator outputs to form effective per-band weights. Under this weighted framework, the discriminator outputs are fused to jointly estimate a common-delay while IFB is modeled as a differential-delay. Distinct loop filters are then designed for the common-delay and differential-delay channels to match their distinct dynamics. Simulation results show that, on L1, the proposed loop achieves higher code-tracking accuracy than a conventional standard tracking loop (STL), reducing the steady-state tracking error by about 68%, while maintaining L5 tracking accuracy comparable to the STL. Moreover, the proposed dual-frequency architecture mitigates the additional multipath bias that introduced by simple multi-frequency combination. Field-test results with real GPS L1/L5 data further indicate that the proposed loop improves L1 3D positioning accuracy by 36.17%, while preserving comparable positioning accuracy on L5, thereby validating the effectiveness of the proposed method.
Published in:	Proceedings of the 2026 International Technical Meeting of The Institute of Navigation January 26 - 29, 2026 Hyatt Regency Orange County Anaheim, California
Pages:	787 - 800
Cite this article:	Zhou, Jing, Tang, Zuping, Wei, Jiaolong, Liu, Xiuxun, Sun, Jie, "Robust GNSS Dual-Frequency Code Tracking with Multipath Aware and Inter-Frequency Bias Estimation," Proceedings of the 2026 International Technical Meeting of The Institute of Navigation, Anaheim, California, January 2026, pp. 787-800. https://doi.org/10.33012/2026.20552
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