Laser Communication Terminal Acquisition Using Beacon Segmentation
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Solution Overview
Problem
Free-space laser communication systems face challenges in acquiring and tracking laser communication terminals on moving platforms due to reduced signal power, limited beamwidth, and susceptibility to glint and solar radiation, especially in airborne environments where rapid and unpredictable movements occur.
Innovation Solution
The system employs acquisition and tracking beacon laser beams with varying divergences and wavelengths, using a gimbal system with a beacon aperture assembly and a steering mirror for precise pointing, and modulates beacon laser beams to differentiate terminals and reduce interference from solar radiation and glint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a portion of the received data laser beam is used for position detection, then the angular direction of the far-end terminal can be determined, but the signal power at the receiver is reduced and the maximum operating range is reduced
Solution Approach 1:
The system divides the laser communication function into separate acquisition beacon beams and data laser beams. The acquisition beacon beams carry position information for terminal detection, while the data laser beams carry communication data. This segmentation allows position detection without sacrificing data signal power, as each beam type is optimized for its specific function.
Solution Approach 2:
The patent introduces acquisition beacon beams as an intermediary mechanism for position detection. These beacon beams serve as a separate channel that mediates the position detection function, allowing the main data laser beam to remain intact for communication without being diverted for position sensing.
2Reliability
If the beamwidth of the data laser beam is minimized to maximize signal strength and operating range, then initial acquisition of a remote terminal becomes difficult
Solution Approach 1:
The system segments the beam function into wide acquisition beacon beams for initial terminal detection and narrow data laser beams for high-rate communication. The wide beamwidth of acquisition beacons enables easy initial acquisition, while the narrow data beams maximize signal strength and operating range during communication.
Solution Approach 2:
The acquisition beacon beams are transmitted before the data laser beam to perform preliminary terminal detection and positioning. This preliminary action establishes the communication link geometry before high-rate data transmission begins, making the system easier to acquire and initialize.
3Reliability
If narrow data laser beams are used for communication, then signal strength is maximized, but terminals can quickly move out of the beam when relative angular direction changes rapidly
Solution Approach 1:
The system uses separate tracking beacon beams with wider beamwidth than data laser beams. These tracking beacons enable continuous position monitoring of moving terminals, allowing the narrow data laser beams to maintain optimal signal strength while the wider tracking beacons ensure continuous terminal acquisition during rapid motion.
Solution Approach 2:
The tracking beacon beams continuously monitor terminal position throughout the communication session, providing ongoing feedback for beam steering. This continuous tracking action ensures that even with narrow data beams, the system can adapt to rapid terminal motion and maintain the communication link.
4Measurement precision
If AC coupled position sensing detectors are used for angle of arrival detection, then the system can determine terminal position, but the detectors cannot sense gigahertz modulation frequencies used for data modulation
Solution Approach 1:
The system separates position detection and data detection into different channels. Position sensing detectors use AC coupling optimized for low-frequency angle of arrival detection of beacon beams, while data detection uses direct detection or demodulation circuits optimized for gigahertz data rates. This segmentation allows each detector to be optimized for its specific frequency range.
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 enables effective acquisition and tracking of laser communication terminals over long distances with improved signal strength and range, maintaining accuracy even in rapidly changing environments and adverse conditions.
Implementation Method 1
acquiring the laser communication terminals by exchanging acquisition beacon laser beams between the laser communication terminals; and tracking the terminals by exchanging tracking beacon laser beams between the laser communication terminals
Implementation Method 2
a steering mirror for controlling an angle at which laser beams are transmitted and received by the data aperture
Data Source
AI summary
A technique for acquiring and tracking terminals in a free-space laser communication system involves exchanging beacon laser beams between the terminals to acquire and then track the terminals such that data laser beams exchanged by the terminals for communication are steered based on feedback from detection of the beacon laser beams. The beacon laser beams used for acquisition have a greater beam divergence than those used for tracking. Gimbals provide coarse steering of the data laser beams, and steering mirrors provide fine steering. GPS position data exchanged via an RF link can be used for initial pointing of the beacon laser beams for acquisition. The beacon laser beams can be chopped such that all terminals can use the same beacon wavelength and are distinguished by using different chopping frequencies. By detecting a chopped signal, the position sensor detector can be AC coupled to reduce sensitivity to solar radiation and glint.