Satellite Clock Bias Prediction Correction
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Solution Overview
Problem
GPS receivers face challenges in determining position when current broadcast ephemeris data is unavailable, leading to inaccuracies in satellite clock bias predictions over extended periods.
Innovation Solution
A method and device that use predicted satellite states spanning a period of time, with modifications to satellite clock bias predictions based on received broadcast ephemeris data, allowing for position determination even without current broadcast ephemeris.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If broadcast ephemeris data is used for position determination, then position accuracy is maintained, but the system fails when ephemeris data becomes unavailable after the four-hour validity period
Solution Approach 1:
The system performs preliminary action by collecting and storing broadcast ephemeris data before the validity period expires. The receiver accumulates historical ephemeris data from multiple satellites over time, preparing advance information that can be used when current ephemeris becomes unavailable. This preliminary data collection enables continuous position determination even after the four-hour validity period ends.
Solution Approach 2:
The system introduces an intermediary mechanism by using historical ephemeris data as a bridge between current satellite signals and position calculation. When current broadcast ephemeris is unavailable, the receiver retrieves and applies previously stored ephemeris data from the same or different satellites, allowing position determination to continue without interruption despite the expiration of the original ephemeris validity period.
2Duration of action of stationary object
If extended ephemeris techniques are used to predict satellite states beyond the validity period, then position determination can continue, but prediction accuracy deteriorates over time
Solution Approach 1:
The system implements feedback by continuously monitoring and comparing predicted satellite states against actual observed data when new broadcast ephemeris becomes available. The receiver uses received ephemeris data to verify and adjust its predictions, correcting accumulated errors in clock bias and satellite position. This feedback loop maintains prediction accuracy over extended periods by regularly recalibrating against ground truth data.
Solution Approach 2:
The system applies parameter changes by dynamically adjusting prediction models based on the age and quality of available ephemeris data. When historical ephemeris is used for extended predictions, the receiver modifies prediction parameters and uncertainty estimates to reflect the deteriorating accuracy over time. This allows the system to maintain operational functionality while being transparent about the decreasing precision of extended predictions.
3Measurement precision
If the receiver collects new broadcast ephemeris data frequently, then position accuracy is maintained, but the system becomes vulnerable when signal strength is insufficient for decoding
Solution Approach 1:
The system applies beforehand cushioning by maintaining a buffer of historical ephemeris data from multiple satellites in memory. When current signal strength becomes insufficient for decoding new ephemeris, the receiver has pre-stored ephemeris data available as a cushion to continue position determination. This buffer protects the system against temporary signal degradation or complete loss of ephemeris reception.
Solution Approach 2:
The system uses copying by retrieving and applying ephemeris data from other satellites that may have been received under better signal conditions. When one satellite's ephemeris is unavailable or too weak to decode, the receiver can use ephemeris data from alternative satellites to maintain position determination accuracy, effectively copying the functionality from one satellite to another.
Data Source
AI summary
Devices and methods are described for determining position information without broadcast ephemeris data for a spanned time period using predictions of future satellite states. These predictions include predictions of satellite clock bias. During the spanned time period, broadcast ephemeris is received such that a broadcast-ephemeris-derived satellite clock bias may be determined. The predictions of satellite clock bias subsequent to the receipt of the broadcast ephemeris may then be corrected based upon the broadcast-ephemeris-derived satellite clock bias.