Synthetic Aperture PNT Using LEO Signals of Opportunity
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Solution Overview
Problem
Traditional satellite navigation systems face challenges in determining position and timing information when fewer than four satellites are visible due to environmental factors or satellite signal interference, particularly in regions with high RF interference or signal loss, and they require precise ephemeris data and stable clocks, which can be costly and complex to implement.
Innovation Solution
The method leverages Signals of Opportunity (SoOPs) from fast-moving Low Earth Orbit (LEO) communication satellites to estimate position and timing information using a synthetic aperture approach, time-warped ambiguity function, and extended time-weighted fitting techniques, allowing PNT calculation with as few as two emitters and without decoding broadcast data, primarily relying on time of arrival measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional GPS/GNSS systems use four satellites to determine position and timing, then position accuracy is improved, but the system fails when fewer than four satellites are visible due to environmental factors or signal interference
Solution Approach 1:
The patent changes the fundamental parameters of the navigation system by using fast-moving LEO satellites instead of traditional GPS satellites, and by using time-of-arrival measurements from Signal of Opportunity sources instead of traditional navigation signals. This allows position determination with fewer satellites because the synthetic aperture technique accumulates measurements over time as satellites move, effectively increasing the information content from each satellite pass
Solution Approach 2:
The patent exploits the dynamic motion of fast-moving LEO satellites to create a synthetic aperture. By collecting and processing signals from satellites as they move rapidly across the sky, the system dynamically builds up positional information over time, allowing accurate position determination even when only two satellites are visible, compared to the static four-satellite requirement of traditional GPS
2Quantity of substance
If GPS receivers use synchronized clocks to reduce satellite requirements to three, then position calculation becomes possible with fewer satellites, but the cost and complexity of the receiver increases significantly
Solution Approach 1:
The patent uses inexpensive, unsynchronized clocks in the receiver by relying on time-of-arrival measurements from satellites with known transmission times. Instead of requiring expensive synchronized atomic clocks, the system uses the known ephemeris data and signal transmission times from satellites to calculate position, effectively replacing the need for expensive clock synchronization hardware with computational methods
Solution Approach 2:
The patent introduces ephemeris data and signal transmission time information as intermediaries between the satellites and the receiver clock. By using these intermediary references, the system can determine position without requiring the receiver clock to be synchronized with satellite clocks, thereby reducing receiver complexity while still enabling position calculation with fewer satellites
3Measurement precision
If receivers decode navigation signals and access ephemeris data to know satellite positions, then position determination is possible, but the requirement for signal decoding capability and ephemeris access increases system complexity
Solution Approach 1:
The patent extracts only the essential timing information (time of transmission and time of arrival) from the satellite signals, ignoring the need to decode full navigation messages or ephemeris data. By extracting just the critical time-stamp information and using independently obtained satellite position data, the system simplifies the receiver requirements while maintaining position determination accuracy
Solution Approach 2:
The patent replaces the traditional signal decoding mechanism with a time-of-arrival measurement approach. Instead of using complex signal processing and decoding hardware to extract satellite position information, the system measures the time when signals arrive and uses pre-known satellite ephemeris data, substituting computational methods for hardware-based signal decoding
4Quantity of substance
If the system uses fast-moving LEO satellites with high motion rates, then the number of required satellites is reduced to two, but the high motion rate introduces challenges in maintaining accurate position and timing measurements
Solution Approach 1:
The patent performs preliminary calculations of satellite positions and signal propagation times based on predicted satellite trajectories. By pre-computing where satellites will be and what their signals should look like, the system can accurately process the actual received signals even though the satellites are moving rapidly, thereby handling the high motion rates without sacrificing measurement accuracy
Solution Approach 2:
The patent continuously accumulates and integrates signal measurements throughout the satellite pass, rather than relying on a single measurement point. By continuously collecting time-of-arrival data as the fast-moving satellites traverse the sky and integrating this information over the entire observation period, the system maintains accurate position and timing measurements despite the high relative motion between receiver and satellites
Data Source
AI summary
A system and method for estimating the position of a receiver and/or timing information for a receiver based on emissions from radio signal sources meant for applications other than position/navigation/time (PNT) estimation.