Geolocation via Non-Simultaneous Satellite TDOA and FDOA
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Solution Overview
Problem
Current methods for determining the geolocation of an emitter using satellite signals face challenges when TDOA and FDOA measurements are not acquired simultaneously or from the same satellite pair, due to technical limitations and satellite velocity errors.
Innovation Solution
The system employs a virtual primary satellite location and a Taylor-series technique to derive closed-form solutions for TDOA-TDOA, TDOA-FDOA, and FDOA-FDOA measurements, allowing for accurate geolocation estimation even when measurements are not simultaneous or from the same satellite pair, using a cost function minimized with weighting values based on intersection angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TDOA and FDOA measurements are acquired simultaneously from the same satellite pair, then measurement accuracy is improved, but system complexity and operational constraints increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating virtual satellite positions and velocities at intermediate times between actual measurement times. This allows the system to process non-simultaneous measurements as if they were simultaneous, eliminating the need for strict simultaneous acquisition while maintaining geolocation accuracy. The virtual satellite states are computed in advance to bridge the time gap between actual measurements.
Solution Approach 2:
The patent introduces virtual satellite positions and velocities as intermediary elements that mediate between actual non-simultaneous measurements. These virtual intermediaries allow the system to combine measurements taken at different times from different satellite pairs by translating them into a common reference frame, effectively decoupling the measurement acquisition constraints from the processing requirements.
2Measurement precision
If satellite positions and velocities are precisely known, then geolocation accuracy is improved, but system complexity increases
Solution Approach 1:
The patent creates copies of satellite positions and velocities at virtual time points between actual measurements. Instead of requiring continuous precise tracking, the system generates virtual copies of satellite states at intermediate times using propagation algorithms. This copying approach maintains accuracy without requiring the complex infrastructure of continuous precise satellite tracking.
Solution Approach 2:
The system performs preliminary calculation of virtual satellite positions and velocities at intermediate times using simplified propagation models. This preliminary action allows the system to work with approximate intermediate states rather than requiring precise real-time knowledge of satellite positions, reducing the complexity of the tracking system while maintaining sufficient accuracy for geolocation.
3Adaptability or versatility
If multiple satellite pairs are used for measurements, then measurement flexibility is improved, but error accumulation from different measurement times increases
Solution Approach 1:
The patent creates an equipotential reference frame by translating all measurements to a common virtual time point. Measurements from different satellite pairs at different times are all transformed to reference the same virtual satellite positions and velocities. This equipotential approach ensures that all measurements operate from the same reference state, eliminating errors that would otherwise accumulate from using different satellite states.
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 accurate geolocation of emitters by combining multiple measurement solutions, effectively mitigating satellite velocity and measurement noise errors, and improving location estimation accuracy.
Implementation Method 1
Because the satellites s1, s2, and s3 have non-zero velocities with respect to the earth, the received signals 114 at the ground station 120 relayed through the satellites s1, s2, and s3 will be subject to Doppler frequency shift. This causes a frequency difference of arrival (FDOA) of the signals 112 relayed through satellite pair s1 and s2
Implementation Method 2
The ground station 120 computes the time-difference of arrival (TDOA), denoted as d21, between the signal 112 from the emitter 110 through the primary satellite s1 to the ground station 120 and the signal 112 from the emitter 110 through another satellite s1 to the ground station 120
Data Source
AI summary
Embodiments provide systems and methods for determining the geolocation of an emitter on earth. A solution is obtained from two TDOA measurements that need not be acquired at the same time. A solution is obtained from a TDOA measurement and an FDOA measurement that need not be acquired at the same time and need not be coming from the same satellite pair. A location of an emitter can be determined from minimizing a cost function of the weighted combination of the six solutions derived from the two TDOA measurements and the two FDOA measurements, where the weight of each solution in the combination is determined based on the intersection angle of the two curves that define the possible locations of the emitter based on the TDOA and/or FDOA measurements.