HF Transmitter Geolocation via Ionospheric Backpropagation
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Solution Overview
Problem
Current geolocation methods for high-frequency (HF) transmitters in the HF domain suffer from low accuracy and limited geographic coverage due to the complexities of ionospheric propagation, especially when signals bounce off the ionosphere, making it difficult to precisely determine the transmitter's location, especially at longer distances.
Innovation Solution
A method that accounts for the instantaneous state of the ionosphere in a backpropagation algorithm to model signal propagation, using satellite-borne receivers to measure parameters like direction of arrival, time difference, and frequency difference, which allows for more accurate geolocation by generating a propagation model that associates modeled values with candidate transmitter positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If conventional DOA receivers with antenna arrays are used for geolocation, then long-distance detection is enabled, but geolocation accuracy deteriorates due to ionospheric propagation complexity and narrow channel bandwidth
Solution Approach 1:
The patent transitions from ground-based antenna arrays operating in two dimensions (azimuth and elevation) to satellite-based receivers operating in three dimensions (adding the vertical dimension of satellite orbit). This dimensional change enables geometric dilution of precision (GDOP) reduction, where the satellite's high-altitude position provides superior geometric geometry for triangulation, thereby improving geolocation accuracy while maintaining long-distance detection capability
Solution Approach 2:
The patent changes the operational parameters by moving receivers from ground level to satellite orbit (altitude parameter change). This parameter change fundamentally alters the propagation path geometry and reduces the impact of ionospheric irregularities on measurement accuracy. The satellite's position above the ionosphere provides a more stable reference frame for DOA measurements, improving geolocation precision without sacrificing detection range
2Ease of manufacture
If ground-based antenna arrays are used for DOA detection, then simple implementation is achieved, but geographic coverage is limited by the radio horizon
Solution Approach 1:
By deploying receivers on satellites rather than ground-based arrays, the system exploits the third dimension (altitude) to achieve beyond-horizon coverage. Satellites positioned in orbit can detect HF signals from transmitters anywhere within their coverage footprint, which extends far beyond the radio horizon limitations of ground-based systems. This dimensional transition enables global or regional coverage while maintaining relatively simple receiver implementation
3Device complexity
If conventional ionosphere models are used in backpropagation algorithms, then computational simplicity is maintained, but geolocation precision deteriorates due to inability to capture instantaneous ionospheric state
Solution Approach 1:
The patent implements feedback by using real-time or near-real-time ionospheric measurements (from ionosondes, GPS total electron content, or other monitoring systems) to update and refine the ionospheric model used in backpropagation algorithms. This feedback loop allows the system to adapt to changing ionospheric conditions, significantly improving geolocation precision without requiring excessively complex modeling approaches. The measured ionospheric parameters feed back into the propagation model to correct for actual atmospheric conditions
Solution Approach 2:
The patent applies preliminary action by pre-computing or pre-characterizing ionospheric propagation paths and characteristics for various candidate transmitter positions before actual geolocation occurs. These pre-computed propagation models, which incorporate expected ionospheric conditions, are stored and then matched against actual measurements during operation. This preliminary preparation reduces computational complexity during real-time geolocation while maintaining high precision through accurate propagation modeling
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 significantly improves the geolocation accuracy and coverage of HF transmitters by incorporating real-time ionospheric conditions, leveraging satellite measurements to refine the geolocation process, resulting in more precise determination of transmitter positions.
Implementation Method 1
bounces of radio signals off the ionosphere
Implementation Method 2
bounces of radio signals off the ionosphere
Data Source
Figure 1
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AI summary
The invention relates to a method (100) for geolocating a transmitter (30) of a radio signal in the high-frequency (HF) range. A value of at least one parameter pertaining to the radio signal transmitted by the transmitter (30) is determined from measurements taken from the signal by one or more receivers (40a, 40b, 40c), at least one of which is on-board a satellite orbiting the Earth, the value of the parameter being dependent on the geographical position of the transmitter (30) at the time when the signal is transmitted. A propagation model of a signal in the ionosphere is generated based on modelling of an instantaneous state of the ionosphere. The propagation model associates a modelled value of the selected parameter with each of a plurality of candidate positions within a geographic region of interest. Finally, the geographical position of the transmitter (30) at the time when the signal is transmitted is estimated from the propagation model generated in this manner.