Kinematic Positioning Signal Synchronization via Doppler Compensation
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Solution Overview
Problem
Existing methods for synchronizing positioning signals in kinematic location networks fail when reference transmitters and positioning-unit devices are moving relative to each other, leading to inaccurate position solutions due to Doppler shifts and propagation delays.
Innovation Solution
A method that involves a positioning-unit device receiving and interpreting reference signals, generating a unique signal aligned with a steered transmitter clock, measuring frequency and time differences, estimating Doppler and propagation delays from trajectory data, and adjusting the signal to achieve frequency coherence and chronological synchronization with the reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Time Lock Loop (TLL) methodology is used to synchronize positioning-unit devices to a reference transmitter, then chronological synchronization and position determination accuracy are improved, but the system fails when the reference transmitter and positioning-unit devices move relative to each other due to Doppler shifts being indistinguishable from clock drift
Solution Approach 1:
The patent applies preliminary action by having the positioning-unit device estimate Doppler shift in advance based on known or predicted trajectory information before the Doppler effect corrupts the synchronization measurement. This allows the device to pre-compensate for the expected frequency shift, enabling accurate clock synchronization even in kinematic environments where relative motion occurs.
2Device complexity
If the positioning-unit device attempts to synchronize to the reference transmitter without Doppler compensation, then the synchronization process is simple, but the device erroneously slews its clock due to Doppler shifts, severely degrading position solution accuracy
Solution Approach 1:
The patent implements feedback by continuously measuring the frequency difference between the reference transmitter signal and the local oscillator, then using this measurement to adjust the local oscillator frequency. The feedback loop incorporates Doppler estimation based on trajectory data, allowing the system to distinguish between actual clock drift and Doppler-induced frequency shifts, thereby maintaining accurate position solutions.
3Adaptability or versatility
If ground-based transceivers use GNSS timebase for positioning signals, then position determination is enabled in poor satellite reception regions, but time accuracy is constrained to 50-100 ns due to error sources, translating to position accuracies only in the order of tens of metres
Solution Approach 1:
The patent uses intermediary devices (ground-based transceivers or pseudolites) that receive and process satellite signals, then retransmit localized positioning signals with improved time synchronization. These intermediaries act as mediators between the satellite constellation and ground receivers, providing enhanced time accuracy (better than 100 ns) through local clock synchronization and signal regeneration, thereby achieving meter-level or sub-meter-level position accuracy in areas with poor direct satellite reception.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables accurate position solutions for mobile apparatuses by correcting for Doppler shifts and propagation delays, maintaining frequency coherence and synchronization even in kinematic environments.
Implementation Method 1
measuring a frequency difference between the received reference positioning signal and the received unique positioning signal; estimating Doppler associated with the relative movement
Implementation Method 2
adjusting the frequency of said steered transmitter clock by an amount derived from the measured frequency difference and the estimated Doppler
Implementation Method 3
measuring a time difference between the received reference positioning signal and the received unique positioning signal; estimating a reference signal propagation delay between said reference transmitter and itself
Data Source
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AI summary
Methods and devices are presented for synchronizing positioning signals in a kinematic location network. In particular, methods and devices are presented for synchronizing a unique positioning signal generated by a positioning-unit device to a reference positioning signal generated by a reference transmitter, where the positioning-unit device and the reference transmitter are moving relative to each other. In certain embodiments the reference transmitter or the positioning-unit device, or both, self-monitor trajectory data comprising one or more of location, velocity or acceleration, e.g. using inertial navigation systems, and broadcast that data in their positioning signals. The trajectory data enables estimation of Doppler shifts and propagation delays associated with the positioning signals, allowing measurement and correction of clock drift for synchronization of the positioning signals.