Emitter Geolocation via Weighted Least-Squares Estimation
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Solution Overview
Problem
Current methods for determining the geolocation of an emitter using satellite signals face challenges when signals from different satellites are acquired at different times, as they require simultaneous measurements, which is often not feasible due to technical limitations and satellite velocity-induced Doppler frequency shifts.
Innovation Solution
The use of weighted least-squares estimation based on four time-difference of arrival (TDOA) and frequency-difference of arrival (FDOA) measurements, where weights are determined and applied to minimize the errors in the measurements to accurately estimate the emitter's location, regardless of the timing of signal acquisition from different satellites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If simultaneous TDOA measurements from multiple satellites are used to determine emitter location, then measurement precision is improved, but ease of operation deteriorates due to technical limitations preventing simultaneous acquisition
Solution Approach 1:
The patent applies preliminary action by using a coarse location estimate (obtained from preliminary processing of TDOA and FDOA measurements) to predict satellite positions and velocities at future measurement times. This allows the system to prepare expected satellite parameters in advance, enabling accurate emitter location determination even when measurements are taken at different times rather than simultaneously.
Solution Approach 2:
The patent changes the parameter reference frame by expressing satellite positions and velocities relative to the predicted coarse location rather than assuming simultaneous measurement times. The method transforms the problem from requiring simultaneous measurements to handling sequential measurements by adjusting satellite ephemeris parameters to correspond to the actual (different) measurement times based on the coarse location estimate.
2Measurement precision
If weighted least-squares estimation is applied to minimize measurement errors, then emitter location precision is improved, but device complexity increases due to iterative optimization requirements
Solution Approach 1:
The patent implements feedback through an iterative weighted least-squares optimization process. The coarse location estimate is used to compute weights based on expected measurement errors, which then refine the location estimate. This refined estimate feeds back into the weight calculation, and the process repeats until convergence, progressively improving location precision while managing computational complexity through controlled iteration.
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 provides a more accurate geolocation of the emitter by iteratively minimizing the weighted errors function, accounting for measurement noise and satellite position/velocity errors, even when signals are received at different times, improving the precision of emitter location determination.
Implementation Method 1
the location of an unknown emitter can be found through measurements of the Doppler frequency shift in the received signals at the ground station
Data Source
AI summary
Embodiments provide systems and methods for determining the geolocation of an emitter on earth based on weighted least-squares estimation based on two TDOA and two FDOA measurements, none of which need to be acquired at the same time. The four TDOA and FDOA measurements and the errors in each of the measurements are determined. Weights for the errors in the TDOA and FDOA measurements are determined, and the weights are applied in a weighted errors function. The weights account for the errors in the measurements and the errors in the satellite positions and velocities, and are dependent on the localization geometry. The weighted errors function is minimized to determine the location estimate of the unknown emitter.