Passive Geolocation Using Asynchronous Clock Drift Estimation
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Solution Overview
Problem
Existing geolocation methods fail to accurately determine the position of a receiver in restrictive environments where GPS signals are unavailable or disrupted, and the receiver must operate discreetly without emitting detectable radio signals, due to synchronization issues with beacons' clocks and the difficulty in measuring one-way distance or TDOA in such conditions.
Innovation Solution
A method using multiple beacons (M ≥ 3) that transmit radio signals with navigation information, allowing the receiver to estimate clock drift and distance by collecting time-of-arrival measurements, and applying a maximum likelihood estimator to determine the receiver's location without requiring synchronized clocks or signal emission from the receiver.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the receiver uses onboard clocks to measure time of arrival of radio signals from beacons, then geolocation can be performed without external synchronization, but the position determination accuracy deteriorates due to clock drift between the receiver and beacons
Solution Approach 1:
The patent changes the mathematical model parameters by introducing nuisance parameters (αj, δj) that represent clock drift characteristics. Instead of assuming synchronized clocks, the estimation algorithm explicitly models and estimates these drift parameters alongside the position coordinates, transforming the problem from a synchronized-clock model to an asynchronous-clock model that can handle onboard clock variations.
Solution Approach 2:
The patent introduces nuisance parameters as intermediary variables that mediate between the observed time of arrival measurements and the true position. These parameters act as intermediaries that absorb the clock drift effects, allowing the position estimation to proceed even when direct synchronization is unavailable. The maximum likelihood estimator simultaneously solves for both position and clock drift parameters.
2Object-affected harmful factors
If the receiver must not emit radio signals to remain undetected in restrictive environments, then operational security is improved, but distance measurement capability deteriorates since traditional TDOA and round-trip methods require signal transmission
Solution Approach 1:
The patent inverts the traditional active ranging approach by making the receiver completely passive. Instead of the receiver transmitting signals to beacons or actively measuring two-way time of flight, the system uses the receiver's onboard clock to measure the one-way time of arrival of signals from beacons. The inversion lies in using the receiver's own unsynchronized clock as the measurement reference rather than requiring it to be synchronized with beacon clocks or to transmit signals.
Solution Approach 2:
The patent extracts the essential measurement capability from the signal transmission function. By removing the need for receiver signal transmission entirely, the invention isolates the position determination problem to purely passive reception and processing of beacon signals, combined with onboard clock measurements. This extraction of the transmission requirement enables undetected operation while maintaining geolocation capability.
3Measurement precision
If traditional radiolocation methods using TDOA or distance measurements are used, then position can be determined with synchronized clocks, but the method becomes unsuitable for environments where the receiver cannot emit signals or where clocks cannot be synchronized
Solution Approach 1:
The patent creates a universal geolocation method that functions in both synchronized and asynchronous clock environments. The maximum likelihood estimation framework is designed to handle general cases with unsynchronized onboard clocks, while still reducing to accurate position determination when clocks are synchronized. This multi-functionality allows the same algorithm to operate in diverse environments including wartime conditions, GPS-denied areas, and normal operational settings.
Solution Approach 2:
The patent introduces dynamic modeling of clock behavior through nuisance parameters that capture time-varying drift characteristics. Rather than assuming static synchronized clocks, the model dynamically adapts to varying clock offsets and drift rates between the receiver and beacons. This dynamic approach allows the system to maintain accuracy despite changing temporal relationships between unsynchronized clocks during movement and operation.
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
Enables precise geolocation of the receiver in restrictive environments without emitting signals, using asynchronous clock estimates and noise correction, allowing discreet operation and accurate positioning even in environments where traditional methods fail.
Implementation Method 1
collection of M measurements, each measurement corresponding to the time of arrival of the radio signals carrying the navigation information from one of the beacons
Implementation Method 2
the first and second estimates are determined by a maximum likelihood estimator
Data Source
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AI summary
The present invention relates to a method for geolocating (200) a receiver moving in an environment containing M beacons. The method (200) comprises the steps of collecting (210) M measurements, each measurement corresponding to the time of arrival of the radio signals carrying the navigation information from one of the beacons, determining (220) a first estimate corresponding to the estimation of at least one interference parameter relating to the drift of the receiver's clock with respect to the clock of the corresponding beacon, determining (230) a second estimate corresponding to the estimation of the distance between the corresponding beacon and the receiver, and determining (240) the location of the receiver from the locations of the beacons and the distances between these beacons and the receiver in this position.