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Session G2b: Resilient and Secure PNT Against Interference and Emerging Threats 1

Bridging Reference Frames and Maps Using PPP-RTK Correction
Rui Hirokawa, Natsuko Hayase, Mitsubishi Electric Corporation
Location: Palm
Date/Time: Wednesday, Sep. 16, 4:46 p.m.

High-precision satellite positioning services that broadcast correction data, including precise point positioning (PPP) and PPP with real-time kinematic enhancements (PPP-RTK), are becoming core infrastructure for automated driving and other safety-critical applications. A persistent problem for such applications
is reference-frame consistency: the receiver solution is naturally obtained in a global, time-dependent terrestrial reference frame, whereas road maps and national geodetic products are often maintained in a static or piecewise-static frame tied to a specific epoch. In Japan, this mismatch is severe because steady crustal
deformation causes coordinate changes of several centimeters per year, and major earthquakes can introduce sudden offsets on the order of meters. Consequently, even when PPP or PPP-RTK achieves high accuracy in the global frame, the position used in map coordinates can be biased, time-varying, and potentially unsafe if the user cannot continuously retrieve updated transformation information via the Internet.
This paper aims to bridge the dynamic Earth and the static map by disseminating crustal deformation correction parameters through the same low-rate satellite broadcast channel that already carries PPP
or PPP-RTK state-space representation corrections. We propose a compact modeling and messaging approach that represents the conversion from the dynamic reference frame to the target map frame as a spatially varying transformation composed of two parts. First, a smooth regional component captures the dominant deformation trend and is encoded using a low-order polynomial in horizontal position so that users can reconstruct it with minimal transmitted data. Second, a residual component captures local departures from the smooth trend and is represented on a sparse grid over the service region with quantization and packaging designed to fit strict broadcast constraints. To support operational use and receiver autonomy, the transmitted information includes version identifiers and quality indicators that allow a receiver
to select the appropriate parameter set and to judge whether the expected conversion accuracy is adequate for its application. We evaluate the approach using nationwide reference station data in Japan and demonstrate its applicability to an open satellite broadcast PPP-RTK service. The combined polynomial and gridded residual modeling reproduces semi-dynamic crustal corrections with only a few centimeters of root-mean-square error across the network while maintaining a data footprint compatible with low-rate broadcast delivery. The design supports routine periodic updates consistent with geodetic maintenance and also enables rapid parameter updates after large earthquakes by deriving a new parameter set from post-event station coordinates. For areas near an epicenter where deformation gradients are exceptionally large, the quality indicator mechanism can explicitly flag regions where conversion accuracy is not guaranteed, enabling safer receiver-side decision making. These results show that broadcast dissemination of
crustal correction parameters is feasible and can substantially reduce map-coordinate errors caused by reference-frame mismatches, especially for users who cannot rely on continuous network connectivity. The proposed integration of geodetic frame maintenance into the broadcast correction infrastructure improves
long-term map consistency and post-earthquake robustness for automated driving and other applications requiring stable coordinates.

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