Free Space Optical Tracking with Electronic Boresight Compensation
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Solution Overview
Problem
Conventional Pointing, Acquisition, and Tracking (PAT) control systems for Free Space Optical (FSO) communication systems face challenges in maintaining high-bandwidth performance over long distances due to time delays and overhead from handshaking processes, which degrade alignment and communication performance.
Innovation Solution
A PAT control system that uses local beam steering elements and alignment error measurement to calibrate and direct transmit beams, incorporating co-boresighted optics and electronic boresight compensation to align received and transmitted beams through a common aperture, reducing alignment time and eliminating the need for additional beam steering elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the traditional power-peaking approach is used for PAT control, then the transmit beam can be scanned and aligned with the receive aperture, but time delay and handshaking overhead degrade alignment performance and communication performance for long distance links
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the relationship between receive beam position and corresponding transmit beam direction in a lookup table during system calibration. During operation, the PAT controller directly queries this pre-computed table to determine the required transmit beam direction based on the measured receive beam position, eliminating the need for real-time handshaking and iterative scanning. This pre-computation approach resolves the contradiction by providing rapid alignment (reducing time loss) while maintaining high alignment accuracy through the pre-calibrated relationship.
2Measurement precision
If handshaking process is implemented for beam alignment, then the transmit and receive systems can coordinate their alignment, but the overhead and communication complexity increase
Solution Approach 1:
The patent extracts and removes the handshaking communication layer from the PAT control system. Instead of requiring bidirectional communication between transmit and receive systems to coordinate alignment, the invention uses unidirectional local control where each terminal independently determines its beam direction based on local measurements and pre-stored calibration data. This extraction of the handshaking mechanism reduces control system complexity while maintaining alignment accuracy through the pre-computed lookup table approach.
Solution Approach 2:
The patent implements self-service by enabling each FSO terminal to independently perform alignment without relying on the other terminal's active participation in the alignment process. The local PAT controller uses the measured receive beam position and queries the pre-stored lookup table to autonomously determine the required transmit beam direction. This self-service capability eliminates the need for complex coordinated handshaking protocols, reducing system complexity while achieving accurate alignment.
3Device complexity
If co-boresighted optics are used with electronic boresight compensation, then additional beam steering elements are eliminated, but precise calibration of the lookup table is required
Solution Approach 1:
The patent applies preliminary action by performing detailed optical alignment calibration during system manufacturing or initial setup, storing the results in a lookup table. The co-boresighted optics are pre-calibrated to establish the precise relationship between receive beam position and transmit beam direction. This pre-calibration work, done when the system is stationary and easily accessible, captures the precise optical alignment characteristics. During field operation, this pre-established calibration data is used directly, eliminating the need for additional beam steering elements while maintaining high alignment precision through the accuracy of the initial calibration.
Data Source
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AI summary
Exemplary embodiments described herein include a bi-directional Free Space Optical (FSO) communication unit that may be used in a multi-node FSO communication system. The bi-directional FSO unit may include a co-boresighted optical unit such that received and transmitted beams are coincident through a common aperture. Embodiments described herein may be used to correct or accommodate the alignment errors of the received and transmitted beams.