Frequency Error Correction in FDOA Geolocation Systems
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Solution Overview
Problem
Frequency difference of arrival geolocation systems face challenges in accurately measuring frequencies of target signals due to errors in relative frequency measurements between distant radio receiving systems, which can be exacerbated by the limitations of GPS signals and the need for high-quality oscillators.
Innovation Solution
A method that determines the frequency of a target signal at each collector using a reference timebase source, calculates the relative timebase error between collectors, and applies a proportional scaling factor to correct the frequency difference, allowing for geolocation without relying on separate cooperative reference transmitters or high-accuracy atomic clocks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cooperative reference transmitters are deployed to correct frequency errors, then measurement precision improves, but device complexity and deployment cost increase
Solution Approach 1:
The patent extracts the frequency reference function from separate cooperative transmitter devices and integrates it into the signal collectors themselves. Each collector uses its own local oscillator as a reference, eliminating the need for deployed reference transmitters while maintaining frequency measurement capability through the two-way signal exchange method.
Solution Approach 2:
The system enables each signal collector to serve its own frequency reference needs by using its local oscillator in conjunction with the remote collector's oscillator. The two-way signal exchange allows each collector to measure the other's frequency stability, making the system self-calibrating without external reference devices.
2Measurement precision
If high-accuracy atomic clocks are used as reference timebase sources, then measurement precision improves, but weight, volume, and power consumption increase
Solution Approach 1:
The patent merges the signal transmission function and frequency reference function into a single integrated system. The local oscillators serving as timebase sources are combined with the signal transmission/reception capabilities, allowing frequency measurements to be performed using existing operational components rather than separate high-precision atomic clock devices.
Solution Approach 2:
The local oscillators in the signal collectors serve multiple functions: they generate the transmission signals and simultaneously serve as frequency references for measurement. This multi-functionality eliminates the need for dedicated high-precision atomic clocks, reducing power consumption while maintaining measurement capability through mutual calibration between collectors.
3Measurement precision
If integration time is extended to compensate for GPS inaccuracies, then measurement precision improves, but loss of time increases
Solution Approach 1:
The system performs preliminary frequency calibration through two-way signal exchange between collectors before conducting the actual frequency difference of arrival measurement. This preliminary mutual calibration establishes accurate relative frequency relationships, enabling precise measurements without requiring extended integration times to compensate for GPS inaccuracies.
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 frequency measurement and geolocation of target signals with reduced reliance on expensive, large, and power-intensive reference timebase sources, and can be implemented in real-time or post-processing, improving the accuracy and efficiency of frequency error correction.
Implementation Method 1
the first state vector and the second state vector. Calculating the relative timebase error may include compensating for the frequency shift based upon, at least in part, the relative movement between the first collector and the second collector
Data Source
AI summary
A frequency correction for frequency difference of arrival geolocation of transmitted target signals may be provided. A frequency of a target signal may be determined at a first collector based upon a first reference timebase source. A frequency of the target signal may be determined at a second collector based upon a second reference timebase source. An observed frequency of a reference carrier signal based upon the first reference timebase source may be determined at the second collector based upon the second reference timebase source. A relative timebase error between the first collector and the second collector may be calculated based upon a difference between the intended frequency of the reference carrier signal and the observed frequency of the reference carrier signal. A corrected frequency difference for the target signal may be calculated based upon the relative timebase error and a proportional scaling factor.