Decoded Orbcomm and Iridium-NEXT Signals for Standalone LEO Doppler Positioning Using EKF and UKF

Fan-Chi Hsiao, Ya-Xun Yang, Shau-Shiun Jan

Peer Reviewed

Abstract:	This paper presents a unified receiver architecture for standalone navigation using decoded signals from Orbcomm and IridiumNEXT low Earth orbit (LEO) communication satellite constellations. The proposed framework jointly processes continuous Orbcomm downlink transmissions and burst-type Iridium-NEXT signals by aligning carrier synchronization and frequency tracking strategies with the respective signal structures of each constellation. Constellation-specific demodulation and decoding are performed according to each constellation’s modulation scheme, enabling the extraction of satellite identifiers and, when available, satellite state information. Frequency and Doppler measurements are obtained via dedicated signal processing pipelines tailored to the distinct temporal and spectral characteristics of Orbcomm and Iridium-NEXT signals, enabling reliable Frequency of Arrival (FOA) observations. Satellite identification from decoded messages allows direct measurement-to-satellite association, significantly reducing computational complexity and mitigating false associations. Receiver positioning is performed using Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) frameworks that fuse multi-satellite FOA measurements. Compared to EKF, UKF can improve positioning accuracy by approximately 50% for highly nonlinear LEO models. The estimated receiver states demonstrate stable convergence and improved accuracy in orbit and measurement uncertainties. The results show that integrating satellite signal decoding with FOA-based positioning provides additional observation sources for LEO SOP-based navigation, positioning, and timing (PNT).
Published in:	Proceedings of the ION 2026 Pacific PNT Meeting April 13 - 16, 2026 Hilton Waikiki Beach Honolulu, Hawaii
Pages:	700 - 713
Cite this article:	Hsiao, Fan-Chi, Yang, Ya-Xun, Jan, Shau-Shiun, "Decoded Orbcomm and Iridium-NEXT Signals for Standalone LEO Doppler Positioning Using EKF and UKF," Proceedings of the ION 2026 Pacific PNT Meeting, Honolulu, Hawaii, April 2026, pp. 700-713. https://doi.org/10.33012/2026.20575
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