H1 Protection Level for GPS Integrity Against Ephemeris Faults
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Solution Overview
Problem
Conventional GPS navigation systems face challenges in maintaining high integrity and accuracy, particularly during initial deployment or when ephemeris faults occur, as existing monitoring methods may not detect faulty measurements promptly, leading to potential errors in positioning.
Innovation Solution
The implementation of an H1 protection level system, which generates a protection level from an N−1 position by removing measurements from a single GPS satellite, allowing for quick startup and maintaining integrity by accounting for possible ephemeris errors, even when ephemeris history is not available, using an ephemeris H1 monitor to support rapid deployment and high-integrity operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional monitoring methods are used to detect faulty GPS measurements, then system complexity is reduced, but integrity and detection speed deteriorate during initial deployment and ephemeris faults
Solution Approach 1:
The system performs preliminary integrity assessment by generating an H1 protection level from N-1 positions before full ephemeris data is available. This allows the system to establish integrity monitoring capability during rapid startup phase without waiting for complete ephemeris history, thereby improving reliability during critical initial deployment period
Solution Approach 2:
The integrity monitoring function is segmented into distinct protection level calculations: H0 protection level from N satellite positions and H1 protection level from N-1 satellite positions. This segmentation allows independent calculation and comparison of integrity metrics, enabling faster detection of ephemeris faults while maintaining manageable system complexity
2Reliability
If extensive warm-up times are used to ensure ephemeris integrity, then measurement reliability improves, but system startup speed deteriorates
Solution Approach 1:
The system calculates H1 protection levels from N-1 satellite positions as a preliminary integrity check before full RTK processing is complete. This preliminary action enables the system to provide integrity-assured positioning during warm-up period without requiring extensive ephemeris history, reducing warm-up time while maintaining measurement reliability
Solution Approach 2:
The system performs integrity monitoring with partial satellite data (N-1 positions) rather than requiring complete N satellite convergence. This partial action approach provides sufficient integrity assurance for rapid startup applications, trading some conservatism for significantly reduced warm-up time
3Measurement precision
If N satellite measurements are used for positioning, then positioning accuracy improves, but vulnerability to single satellite ephemeris faults increases
Solution Approach 1:
The system preemptively counteracts ephemeris fault vulnerability by calculating H1 protection levels from N-1 satellite positions. This preliminary anti-action creates a defensive integrity check that can detect and mitigate single satellite faults before they compromise the full N satellite solution, maintaining positioning accuracy while reducing fault vulnerability
Solution Approach 2:
The system uses feedback from H1 protection level calculations to monitor the integrity of each satellite's ephemeris data. By comparing H1 (N-1 positions) and H0 (N positions) protection levels, the system can identify and exclude faulty satellite measurements, thereby maintaining high positioning accuracy while protecting against ephemeris faults
Data Source
AI summary
Technology for generating a H1 protection level from an N−1 position in a global positioning system (GPS) receiver is disclosed. One approach can include an H1 monitor configured to generate an H1 protection level from an N number of N−1 positions. The N−1 position can be derived by a differential global positioning system (GPS) satellite measurement removed from a plurality of N differential GPS satellites measurements.