Alternative Navigation Techniques for RealTime LEO Precise Navigation During QZSS Invisible Zone with QZSS MADOCA-PPP for Visibility

Hideki Yamada, Toshitaka Sasaki, Saya Matsushita, Keito Yoshida, Tatsuya Nagano, Satoshi Kogure, Tomoya Osawa, Aki Sakamoto, and Aki Taniyama

Peer Reviewed

Abstract:	Quasi-Zenith Satellite System (QZSS) MADOCA-PPP, broadcast via the L6E signal, enables precise point positioning (PPP). This study refines a real-time LEO precise orbit determination (POD) algorithm based on RTKLIB, incorporating satellite dynamic models and enhanced ambiguity resolution. Using 31 days of Sentinel-6A GNSS data (May 2024), we evaluated positioning performance. A key contribution is the application of fine-tuned weighting parameters to the PPP filter's observation error model, which significantly reduced average convergence time from 720 to 623 seconds. PPP-AR demonstrated stable performance across multiple test cases. To ensure continuity during QZSS L6E signal outages, we proposed and compared five alternative navigation techniques, including orbit propagation and ephemeris-assisted PPP. The combination of QZSS MADOCA-PPP and ultra-rapid ephemerides achieved the highest accuracy, with decimeter-level 3D-RMS over one month. While fine-tuning generally improved positioning accuracy for most methods, a critical finding was its initial degradation of 3D-RMS error for orbit propagation. Fine-tuning's inappropriate criteria led to misidentified anomalies due to un-converged state. We mitigated this by optimizing the PPP convergence judgment threshold to 1/10 of its original value, restoring orbit propagation’s 3D-RMS error to pre-tuning levels. This indicates fine-tuning primarily benefits the PPP convergence process, with limited direct effect on subsequent non-GNSS orbit propagation. This work highlights a practical, robust approach for real-time LEO navigation using QZSS MADOCA-PPP, emphasizing optimizing tuning parameters considering their phase-specific trade-offs. Future work will focus on enhancing LEO navigation's autonomy and accuracy, especially during extended outages. This includes designing and validating onboard orbit propagation methods that utilize highly accurate GNSS satellite orbits derived from L6E-corrected PPP solutions as initial inputs. Furthermore, to continuously optimize positioning performance, we aim to develop adaptive tuning strategies for the PPP filter itself. These efforts collectively ensure greater resilience and precision for real-time LEO navigation.
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:	3266 - 3280
Cite this article:	Yamada, Hideki, Sasaki, Toshitaka, Matsushita, Saya, Yoshida, Keito, Nagano, Tatsuya, Kogure, Satoshi, Osawa, Tomoya, Sakamoto, Aki, Taniyama, Aki, "Alternative Navigation Techniques for RealTime LEO Precise Navigation During QZSS Invisible Zone with QZSS MADOCA-PPP for Visibility," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 3266-3280. https://doi.org/10.33012/2025.20348
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