Satellite Navigation Ephemeris Data Compression via Scaling Factors
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Solution Overview
Problem
Conventional GPS receivers face delays in acquiring valid ephemerides, especially under 'warm' or 'cold' start conditions and weak signal conditions, and large ephemeris files consume significant time and memory resources for transfer and storage.
Innovation Solution
Representing ephemeris data using scaled values and scaling factors to compress the data, allowing for efficient transmission and storage, with a week's worth of data stored in less than 15 KB, reducing transfer time and memory usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ephemeris data is stored in a large file format, then the data can be complete and accurate, but the file transfer time and memory consumption increase significantly
Solution Approach 1:
The patent transforms the ephemeris data representation by changing parameters from storing complete coordinate values to storing differential corrections and orbital elements. This parameter transformation reduces the data size while maintaining accuracy, as the corrections required are much smaller than the full ephemeris data sets.
Solution Approach 2:
The patent extracts only the essential correction elements and orbital parameters needed for ephemeris calculation, separating them from the complete ephemeris data set. By extracting and storing only the differential corrections and key orbital elements, the file size is dramatically reduced while retaining the ability to generate accurate ephemeris data.
2Reliability
If ephemeris data is stored in a large file format, then the data can be complete and accurate, but the device memory consumption increases
Solution Approach 1:
The patent changes the data parameters from storing complete high-precision coordinate values to storing compact orbital elements and differential corrections. This parameter transformation reduces memory requirements by storing only the essential variables needed to reconstruct ephemeris data through mathematical calculations.
Solution Approach 2:
The patent uses a compact representation that can be mathematically expanded into full ephemeris data when needed. Instead of storing complete data sets, the system stores a compressed mathematical model that can generate the full ephemeris information on-demand, reducing memory usage while maintaining data availability.
3Reliability
If the receiver waits for broadcast ephemerides under warm or cold start conditions, then the ephemeris data will be valid and accurate, but the time to first fix extends to several minutes
Solution Approach 1:
The patent performs preliminary calculations by pre-computing orbital elements and correction parameters that can be quickly applied to generate ephemeris data without waiting for complete broadcast messages. This preliminary preparation allows the receiver to generate valid ephemeris information immediately upon receiving the compressed data, significantly reducing time to first fix.
Solution Approach 2:
The patent implements a dynamic ephemeris generation approach where the receiver can quickly compute satellite positions using the compact orbital elements and corrections, rather than statically waiting for complete broadcast ephemeris messages. This dynamic computation allows for faster position estimation while maintaining accuracy.
Data Source
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AI summary
A device can access scaled values and scaling factors, which are used to convert the scaled values into coefficients and residuals. The coefficients and residuals can in turn be used with time-dependent functions to reconstruct predicted ephemeris data, including clock correction data, for satellite navigation system satellites. Ephemeris data that is broadcast from any of the satellites can be used to update the calculated ephemeris data.