Real-Time Satellite Subset Geometry Screening for Ionosphere Gradient
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Solution Overview
Problem
Conventional methods for calculating the Vertical Ionosphere Gradient standard deviation (σ vig) in Ground Based Augmentation Systems face challenges when satellites are included or excluded from the calculation, leading to discontinuities and inefficiencies in real-time geometry screening.
Innovation Solution
A real-time subset geometry screening method that determines a list of satellites in view for a future time interval, calculates σ vig values for various subset geometries, and selects the larger values between current and previous intervals to ensure continuous and optimal satellite corrections, pre-calculating up to five σ vig values for each inflation interval to account for satellite rises and sets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional methods calculate σ vig for each time interval based on current satellites in view, then the calculation is simpler and faster, but discontinuities and inefficiencies occur when satellites are included or excluded from the calculation
Solution Approach 1:
The patent applies preliminary action by pre-calculating σ vig values for all possible satellite subset geometries before they are actually needed. The system determines σ vig for multiple potential satellite configurations in advance, including satellites that may rise or set during the interval. This pre-computation ensures that when satellites are included or excluded from the view, continuous and optimal σ vig values are already available, eliminating discontinuities and avoiding the need for recalculation during real-time operation.
2Productivity
If σ vig is calculated at 1 minute intervals to minimize satellite rises and sets, then fewer calculations are performed, but satellite geometry changes may still cause inaccuracies in the broadcast value
Solution Approach 1:
By pre-calculating σ vig for multiple satellite subset geometries in advance, the system ensures that the most accurate value is available without needing to increase calculation frequency. The preliminary computation covers all possible satellite configurations that may occur during the broadcast interval, so the selected value remains accurate even as satellite geometry changes.
Solution Approach 2:
The patent changes the parameter approach by calculating σ vig for multiple different satellite subset configurations simultaneously rather than performing sequential calculations as satellites enter or leave view. This allows the system to account for geometry changes within the same computational cycle, maintaining precision without increasing the broadcast update frequency.
3Reliability
If multiple σ vig values are pre-calculated for different satellite subsets, then the most appropriate value can be selected for broadcasting, but the computational complexity increases
Solution Approach 1:
The patent manages computational complexity by performing the multiple calculations in advance during a pre-computation phase. Rather than complexity being a real-time burden, the system prepares multiple σ vig values beforehand when computational resources are more readily available. This shifts the computational load to an offline or background process, keeping the real-time broadcast selection simple.
Solution Approach 2:
The system calculates σ vig for more satellite subsets than strictly necessary (excessive action), including all possible combinations of satellites that may be in view. While this appears to increase complexity, it actually simplifies the selection process by ensuring the correct value is already computed and available, eliminating the need for complex real-time determination logic.
4Reliability
If the maximum σ vig value between current and previous intervals is broadcast, then safety is ensured by protecting against worst-case scenarios, but the broadcast value may be overly conservative and reduce system availability
Solution Approach 1:
The patent changes from broadcasting a single conservative maximum value to broadcasting multiple σ vig values corresponding to different satellite subset geometries. This allows the receiver to select the appropriate value based on the actual satellite configuration, providing safety without unnecessary conservatism. The parameter approach shifts from a single worst-case value to multiple context-specific values.
Data Source
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AI summary
A method for real time subset geometry screening comprises the steps of determining a list of satellites in view of a ground based augmentation system in a navigation satellite system for a subsequent time interval in the future, defining at least one set of subset geometries from the list of available satellites, calculating a respective first à vig for each of the at least one set of subset geometries, setting a respective broadcast à vig for each set of subset geometries as the larger of the first à vig and a second à vig , wherein the second à vig was calculated for the previous time interval, saving the first à vig for a next iteration of the method, and selecting from the plurality of broadcast à vig to match an available broadcast constellation. à vig is a vertical ionosphere gradient standard deviation.