Virtual Mirror Clock Synchronization for Moving Platform Optical Links
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Solution Overview
Problem
Existing methods for synchronizing clocks between moving platforms, such as land vehicles, ships, and aircraft, face challenges due to unsynchronized clocks and insufficient accuracy of GPS signals, leading to errors in sharing data dependent on accurate timestamps and relative positions.
Innovation Solution
Utilizing optical signals from femtosecond or continuous wave lasers to synchronize clocks between moving platforms through a virtual mirror system, where one platform acts as a mirror to reflect pulses at the same time they are received, allowing for precise adjustment of pulse repetition frequency to determine time and frequency offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS signals are used for time transfer between moving platforms, then clock synchronization can be achieved, but the accuracy is insufficient leading to positioning errors
Solution Approach 1:
The patent replaces GPS-based radio frequency time transfer with a direct optical link using pulsed lasers. This substitution of the physical medium (from RF to optical) enables picosecond-level timing precision, resolving the contradiction between measurement precision and positioning reliability by eliminating GPS signal inaccuracies.
Solution Approach 2:
The patent employs periodic pulsed laser signals with precise repetition frequencies to establish time references between platforms. By using periodic optical pulses instead of continuous GPS signals, the system achieves superior timing accuracy for clock synchronization, directly improving both measurement precision and positioning reliability.
2Reliability
If two-way time transfer is used to synchronize clocks on moving platforms, then relative positioning can be determined, but clock offsets prevent accurate data sharing
Solution Approach 1:
The patent introduces an optical pulse train as an intermediary carrier for time transfer between moving platforms. This optical intermediary enables precise measurement of clock offsets by serving as a common reference that both platforms can measure against, achieving the sub-10-picosecond synchronization accuracy needed for reliable data sharing.
Solution Approach 2:
The patent uses one platform to generate optical pulses and another platform to replicate them by transmitting identical pulse trains. This copying approach creates a reference relationship between the two clocks, allowing precise offset measurement and synchronization that enables accurate data sharing between platforms.
3Measurement precision
If pulse repetition frequency is not adjusted for Doppler shift, then system complexity is reduced, but pulse overlap and synchronization accuracy deteriorate
Solution Approach 1:
The patent implements feedback control where the receiving platform measures the actual pulse repetition frequency affected by Doppler shift and sends correction information back to the transmitting platform. This feedback loop enables automatic adjustment of the pulse repetition frequency to maintain pulse overlap accuracy despite relative motion, achieving high precision without manual intervention.
Solution Approach 2:
The system uses the receiving platform to autonomously measure the Doppler-shifted pulse frequency and generate the necessary correction commands. This self-service approach allows the system to automatically compensate for frequency shifts, maintaining synchronization accuracy while distributing the complexity across both platforms rather than requiring complex pre-calibration.
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
Achieves synchronization of clocks with an accuracy of less than 10 picoseconds, enabling accurate sharing of sensor and location data between moving platforms.
Implementation Method 1
transmit a second optical signal that includes the second plurality of pulses to the different platform
Implementation Method 2
an optical receiver configured to receive a first optical signal transmitted by a different platform through free space
Data Source
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AI summary
Aspects herein describe techniques for synchronizing clocks between two moving platforms using optical signals generated from lasers to measure clock offsets and determine a separation distance between moving platforms. Once the clocks are synchronized (e.g., an offset between the clocks is determined), the moving platforms can share sensor data, location data, and other information which is dependent on accurate timestamps and relative positions. In one aspect, one of the platforms serves as a virtual mirror. That is, the platform transmits a pulse at the same instance a pulse is received, similar to a mirror that reflects incident light. For example, the first platform may transmit pulses which are received at the second platform. The second platform can use optical or electrical components to form the virtual mirror that transmits an optical pulse to the first platform each time a pulse is received at the second platform.