Navigation System Multipath Discrimination via Elevation Filtering
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Solution Overview
Problem
Navigation systems, such as GPS receivers, face challenges in managing and detecting multipath signals, which degrade positioning accuracy and integrity due to the inability to process indirect multipaths within conventional integrity verification mechanisms.
Innovation Solution
Implementing an elevation control method that discriminates between satellites based on their elevation angle relative to the carrier, using a minimum elevation filter to exclude pseudo-distances from satellites with low elevations prone to multipaths, and employing a hybrid inertial/GPS filter to maintain navigation solution integrity even with fewer satellites above the minimum elevation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If all raw GPS measurements from tracked satellites are used to develop the navigation solution, then the quantity of satellite data is maximized, but the integrity of the navigation solution is degraded due to undetected multipath errors
Solution Approach 1:
The patent applies preliminary action by performing RAIM integrity monitoring on all raw GPS measurements before selecting which measurements to use for navigation solution development. The system pre-identifies and excludes measurements with integrity issues (such as multipath errors) before the navigation calculation, ensuring that only validated measurements are used while maintaining maximum satellite utilization.
2Reliability
If elevation masks are used to exclude low elevation satellites, then the impact of indirect multipaths is reduced, but the number of tracked satellites decreases potentially below the minimum required for navigation solution
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the minimum elevation angle threshold based on the actual integrity status of each satellite's measurements. Instead of using a fixed elevation mask, the system modifies the selection criterion (elevation angle parameter) for each satellite individually based on RAIM analysis results, allowing flexible optimization between integrity and satellite quantity.
3Ease of manufacture
If a fixed minimum elevation angle is applied to all satellites, then the complexity of measurement selection is reduced, but the adaptability to different operational conditions and multipath scenarios is limited
Solution Approach 1:
The patent applies dynamics by making the minimum elevation angle threshold a dynamic parameter that adjusts based on operational conditions and individual satellite measurement quality. The system continuously evaluates measurement integrity and adapts the elevation criterion accordingly, transitioning from a static fixed-angle approach to a dynamic condition-based selection process.
Data Source
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AI summary
According to a first aspect, the invention relates to a method for controlling the navigation system of a carrier (P) receiving signals from a plurality of transmitters (T1-T3) and capable of measuring a pseudo-distance to each transmitter, wherein the elevation of each of the transmitters (T1-T3) is controlled relative to the horizontal (H) of the carrier (P), and a navigation solution is developed from the pseudo-distances (Pd-a) for which the elevation of the corresponding transmitter is higher than a minimum elevation (Em), characterised in that it comprises carrying out a discrimination of the multiple routes from the pseudo-distances (formula I) measured for the transmitters (T3) having an elevation lower than the minimum elevation (Em), and further retaining, during the development of the navigation solution, the pseudo-distances (Pd-ad) authorised after said discrimination. The invention also relates to a navigation system capable of implementing the method according to the first aspect of the invention.