Pseudolite Receiver Clock Drift Correction via GPS Intermediary
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Solution Overview
Problem
Mobile communication devices face accuracy issues in determining position indoors due to weak GNSS signals and clock drift in pseudolite receivers, which affect the accuracy of Multilateration Location and Monitoring Service (M-LMS) pseudolite systems.
Innovation Solution
A method that corrects for clock drift by using GPS signals to estimate the frequency offset and apply it to pseudolite receivers, updating polynomial coefficients to improve accuracy over time, and leveraging outdoor corrections for indoor navigation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pseudolite receivers are used for indoor positioning, then positioning capability is provided in areas where GNSS signals are unavailable, but clock drift and frequency offset reduce positioning accuracy
Solution Approach 1:
The patent uses GPS signals as an intermediary to estimate and correct the clock drift in pseudolite receivers. By receiving both GPS and pseudolite signals and comparing their timing, the system calculates the frequency offset of the local oscillator and applies corrections to pseudolite position calculations, thereby maintaining accuracy without requiring direct GPS visibility indoors.
Solution Approach 2:
The system performs preliminary clock drift correction by acquiring GPS signals when available (outdoor or transitional areas) to estimate the frequency offset before entering areas where GPS is unavailable. This preliminary characterization of oscillator drift is stored and applied during indoor pseudolite-only operation to maintain positioning accuracy.
2Adaptability or versatility
If the device operates independently using only pseudolite signals, then indoor positioning is achieved without external assistance, but clock aging and frequency drift cause accumulating position errors
Solution Approach 1:
The patent implements feedback by continuously monitoring the difference between GPS-derived position and pseudolite-derived position when GPS is available. This error signal is used to update the clock drift model and adjust future pseudolite position calculations, creating a closed-loop system that compensates for oscillator instability over time.
Solution Approach 2:
The system dynamically adjusts the polynomial coefficients that model clock drift based on observed GPS-pseudolite position differences. By changing these parameters in real-time or near-real-time, the system adapts to varying oscillator conditions and maintains positioning accuracy despite aging and environmental effects.
3Measurement precision
If GPS signals are continuously used to correct pseudolite receivers, then positioning accuracy is improved, but system complexity and computational load increase
Solution Approach 1:
The patent applies partial correction by using GPS signals only when available to update the clock drift model, rather than requiring continuous GPS processing. The system performs corrections at opportune moments (when GPS visibility exists) and applies these corrections during pseudolite-only operation, reducing computational burden while maintaining accuracy.
Solution Approach 2:
The positioning system is segmented into two operational modes: GPS-assisted mode for clock calibration and pseudolite-only mode for indoor positioning. This segmentation allows the system to use computationally intensive GPS processing only when necessary for calibration, while relying on lighter pseudolite processing during indoor operation, thereby managing computational resources efficiently.
Data Source
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AI summary
A method, apparatus and computer-readable medium for determining a frequency drift of clock of a mobile communication device is disclosed. A first positioning signal, such as M-LMS signals, is received at a first positioning engine of the mobile communication device controlled by the clock. A second positioning signal, such as GNSS signals, is received at a second positioning engine of the mobile communication device controlled by the clock. A first position is determined from the first positioning signal, and a second position is determined from the second positioning signal. A difference between the first position and the second position is determined, and the frequency drift of the clock is determined from the difference between the first position and the second position. The frequency drift determined may be subsequently applied to the clock, and thus enhance the accuracy of M-LMS positioning when GNSS signals are unreliable.