Satellite Ephemeris Error Compensation via Iterative Calibration
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Solution Overview
Problem
Satellite ephemeris errors significantly impact the accuracy of geolocation measurements, particularly in identifying unauthorized ground-based transmitters causing interference in satellite telecommunications, as current methods rely on imprecise ephemeris data and are often dominated by ephemeris-related uncertainties.
Innovation Solution
A method and apparatus for compensating satellite ephemeris errors using multiple calibration transmitters to iteratively refine ephemeris estimates through time and frequency difference measurements, employing a least mean squares fit and singular value decomposition to minimize measurement errors, thereby improving the precision of ephemeris data for geolocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional geolocation techniques using standard satellite ephemeris data are used, then the system is simple and easy to operate, but the geolocation accuracy is poor due to dominant ephemeris errors
Solution Approach 1:
The patent applies preliminary action by pre-determining satellite ephemeris errors using a network of reference transmitters before performing geolocation measurements. The system calculates correction factors for satellite position and velocity in advance, which are then applied to improve subsequent geolocation accuracy without adding complexity to the actual measurement process
Solution Approach 2:
The patent introduces an intermediary correction mechanism by using reference transmitters at known locations to determine ephemeris errors. These reference transmitters act as mediators between the satellites and the geolocation target, providing calibration data that corrects satellite position and velocity errors without requiring direct modification of the satellite systems
2Measurement precision
If high precision ephemeris data are acquired to improve geolocation accuracy, then measurement precision improves, but acquisition difficulty increases and such data are not readily available
Solution Approach 1:
The patent applies self-service by enabling the ground-based reference transmitter network to autonomously determine and provide ephemeris correction data. The system uses locally available reference transmitters to self-calibrate satellite ephemeris errors without requiring external provision of high-precision ephemeris data from satellite operators or specialized agencies
3Measurement precision
If satellite ephemeris error is reduced through calibration, then geolocation accuracy improves, but the number of reference transmitters and calibration steps increase
Solution Approach 1:
The patent applies universality by designing reference transmitters that serve multiple functions: they act as calibration sources for determining ephemeris errors, provide known position references for geolocation validation, and enable correction of both satellite position and velocity errors. This multi-functionality reduces the total number of transmitters needed compared to dedicated single-purpose calibration systems
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
A method of compensating for or correcting satellite ephemeris error involves measuring time difference of arrival (TDOA) and frequency difference of arrival (FDOA) for signal replicas received via two satellites (34, 46) from calibration transmitters (42a to 42d) at different geographical locations. An initial satellite ephemeris consisting of position and velocity vectors is used to calculate ephemeris changes yielding estimated TDOA and FDOA values providing a best fit to measured TDOA and FDOA values. This provides estimated changes required to compensate for or to correct errors in the initial satellite ephemeris. The method may be iterated to deal with large ephemeris changes: i.e. the changes obtained in one iteration may be used to correct ephemeris for use as a new initial ephemeris in a following iteration. The method may be used to correct ephemeris errors in one or both satellites, if so a greater number of calibration transmitters EphemCal 1 to EphemCal 10 may be used.