Navigation Receiver Trajectory Correction Using Ephemeris Difference
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Solution Overview
Problem
GPS receivers face challenges in accurately determining their trajectory using non-current ephemeris, leading to position estimation errors and increased Time-To-First-Fix (TTFF), especially when current ephemeris is not available due to prolonged power-offs or weak signal conditions, requiring methods to improve accuracy without additional aiding stations or high computational load.
Innovation Solution
The system computes the difference in position between current and non-current ephemeris at different times to apply a correction to subsequent trajectory calculations, allowing for accurate navigation in stand-alone mode, using saved positions, e-compass, motion sensors, and user input to initialize and correct the receiver's position.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-current ephemeris is used for trajectory determination, then the receiver can operate in stand-alone mode without external aiding, but position estimation accuracy deteriorates
Solution Approach 1:
The patent changes the parameter of ephemeris age from current to non-current, enabling stand-alone operation. To compensate for the accuracy loss, it applies trajectory correction by transforming the problem from 3D position correction to 1D trajectory offset correction, effectively mitigating the precision deterioration while maintaining adaptability.
2Measurement precision
If current ephemeris is used, then position estimation accuracy is improved, but the receiver requires external aiding stations or continuous signal availability
Solution Approach 1:
The receiver serves itself by using its own previously saved position information and e-compass data to correct its trajectory when operating with non-current ephemeris. This self-service mechanism eliminates the need for external aiding stations while maintaining acceptable accuracy, achieving both precision and independence.
3Measurement precision
If the receiver waits to download new ephemeris before computing position, then position accuracy is improved, but Time-To-First-Fix increases
Solution Approach 1:
The receiver performs preliminary trajectory computation using non-current ephemeris immediately upon signal acquisition, rather than waiting for new ephemeris download. The saved position from previous operations is used as a preliminary reference, enabling fast first-fix while maintaining the option to refine accuracy later when current ephemeris becomes available.
4Measurement precision
If trajectory correction is applied using saved positions and e-compass, then position accuracy with non-current ephemeris is improved, but device complexity increases
Solution Approach 1:
The patent introduces the e-compass and saved position information as intermediary elements to bridge the gap between non-current ephemeris and accurate positioning. These intermediaries provide additional constraints (heading information and previous position) that enable trajectory correction without requiring complex computational algorithms or additional expensive hardware sensors.
Data Source
AI summary
The present invention provides methods and systems that enable a mobile navigation receiver to accurately determine its trajectory with non-current ephemeris in stand-alone mode. In an embodiment, the receiver computes the position for the same location using non-current ephemeris and current ephemeris at different time instances. The receiver then determines a position correction by finding the difference between these two computed positions, and applies this correction to the trajectory generated with non-current ephemeris to obtain a more accurate trajectory. In another embodiment, the receiver computes an initial position of the receiver using non-current ephemeris and finds the difference between the computed initial position and an accurate approximation of the initial position. The receiver then shifts the subsequent receiver trajectory computed using non-current ephemeris by the difference to obtain a more accurate trajectory.