Geolocation of Transmitters via Wavelength-Scaled Phase Differences
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Solution Overview
Problem
Current geolocation technologies face challenges in precisely locating moving or non-cooperative transmitters due to ambiguity in carrier phase measurements and frequency drift, especially when observed by multiple collectors with unknown phase offsets and varying geometries.
Innovation Solution
The method involves obtaining wavelength-scaled phase difference measurements from independent pairs of collector devices to solve for the three-dimensional position of a moving transmitter, using differential phase measurements to eliminate ambiguities and reduce biases, and applying complex-conjugate product calculations to form an image of fixed transmitters and multipath components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If carrier phase measurements are used to improve location accuracy from meters to millimeters, then measurement precision is improved, but ambiguity in cycle counting increases the complexity of determining the true location
Solution Approach 1:
The patent employs dynamic motion of collectors to resolve static ambiguities. By moving collectors through different geometries relative to the transmitter, the system transforms a static ambiguity problem into a dynamic one where the true location can be distinguished from false locations based on consistent geometric relationships across multiple observations.
Solution Approach 2:
The system uses feedback from multiple phase measurements taken at different collector geometries to iteratively resolve ambiguities. Each measurement provides feedback that constrains the possible locations, and by combining multiple such measurements, the system converges on the true transmitter location while eliminating false candidates.
2Measurement precision
If multiple collectors are used to resolve ambiguities and improve accuracy, then location precision is improved, but the number of unknown phase offsets and measurement complexities increase
Solution Approach 1:
The patent segments the measurement process into independent pairwise comparisons between collectors. By forming phase difference measurements between pairs of collectors rather than treating all collectors simultaneously, the system breaks down the complex multi-collector problem into manageable segments that can be processed independently and then combined.
Solution Approach 2:
The system extracts and eliminates the unknown phase offsets by taking differences between collector measurements. By subtracting phase measurements from different collectors, the constant phase offsets are removed from the equations, leaving only the geometric relationships that depend on transmitter location.
3Measurement precision
If wavelength-scaled phase difference measurements are used to reduce ambiguity spacing, then location accuracy is improved, but the sensitivity to frequency drift and propagation effects increases
Solution Approach 1:
The patent employs periodic sampling of phase differences at multiple discrete times. By taking measurements at regularly spaced time intervals and combining these periodic observations, the system can distinguish between true geometric relationships and transient effects like frequency drift, as the true location will produce consistent periodic patterns across all measurements.
Solution Approach 2:
The system performs preliminary calibration and bias estimation before final location determination. By initially estimating phase offsets and propagation effects from the measurement data, the system can then correct for these effects in subsequent processing, reducing their impact on the final location accuracy.
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 precise geolocation of transmitters with improved accuracy, reducing ambiguity spacing and enhancing location determination even with unknown phase biases, allowing for accurate tracking of transmitter motion and multipath components.
Implementation Method 1
The fundamental approach is to use carrier phase observations of many GPS satellites to determine the location of a static or moving GPS receiver
Implementation Method 2
These possible locations form a lattice pattern with spacing typically on the order of a wavelength apart
Implementation Method 3
measuring range to GPS satellites using carrier phase
Data Source
AI summary
A method of geolocating a stationary transmitter observed by a fixed receiver device and at least two receiver devices, at least one of the receiver devices moving includes obtaining wavelength-scaled phase difference measurements between pairs of receiver devices, and obtaining a result lattice of possible locations of the transmitter, one location more probable than the remainder. A method of geolocating a moving transmitter observed by a plurality of fixed or nearly fixed receiver devices, and a moving receiver device, includes obtaining wavelength-scaled phase difference measurements from the plurality of fixed or nearly fixed receiver devices to obtain a shape of the transmitter trajectory, measuring the phase difference between the moving receiver device and at least one of the plurality of fixed or nearly fixed receiver devices to obtain a phase error residual, and moving an estimated starting point of the transmitter to obtain a best-fit residual.