Point Ahead Offset Angle for FSO Nodes
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Solution Overview
Problem
Free space optical communication nodes in motion experience significant misalignment between transmit and receive beams, leading to substantial coupling losses due to the need for precise pointing, which existing technologies struggle to optimize effectively.
Innovation Solution
The implementation of a point ahead offset angle in the direction of the transmit beam, based on both the estimated reception of the transmit and receive optical beams, to minimize the sum of transmit pointing losses and receive coupling losses without adding additional components, using a control system and beam steering unit to adjust the beam directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the Tx beam is directed along a point ahead angle to account for relative motion, then the transmit pointing accuracy is improved, but the receive coupling efficiency deteriorates due to large misalignment between Rx beam and FSO node
Solution Approach 1:
The patent modifies the point ahead angle by applying a point ahead offset to create a corrected transmit pointing direction. This parameter adjustment optimizes the balance between transmit pointing accuracy and receive coupling efficiency by shifting the Tx beam direction from the standard point ahead angle to a corrected angle that accounts for both transmit and receive beam alignment requirements
Solution Approach 2:
The system dynamically adjusts the transmit beam direction based on real-time calculation of point ahead offset, which varies with relative motion parameters between nodes. The control system continuously updates the Tx pointing direction to maintain optimal coupling efficiency while accounting for changing relative positions and velocities
2Reliability
If the Tx beam is directed along a point ahead angle to account for relative motion, then the future location targeting is improved, but the sum of Rx coupling losses and Tx pointing losses increases
Solution Approach 1:
The patent calculates an optimal point ahead offset that minimizes the total loss function combining both Rx coupling losses and Tx pointing losses. This involves adjusting the transmit angle parameter to find the optimal balance point where the sum of losses is minimized, rather than using the standard point ahead angle alone
Solution Approach 2:
The system uses feedback from measured or estimated relative motion parameters to dynamically calculate and adjust the point ahead offset. The control system continuously monitors the FSO link performance and adjusts the Tx pointing direction to maintain optimal efficiency while targeting the future location of the remote node
Data Source
AI summary
A free space optical (FSO) communication node communicates via an FSO link with a remote FSO communication node that moves relative to the FSO node. The FSO node may be highly directional, and transmit (Tx) and receive (Rx) beams of the FSO node may share optical paths (at least in part). Instead of directing a Tx beam along a point ahead angle relative to a Rx beam (which may result in undesirable Rx coupling losses), the Tx beam is directed based on the point ahead angle and a point ahead offset angle. The point ahead offset angle modifies the point ahead angle to reduce Rx coupling losses while keeping Tx pointing losses at least low enough to maintain the FSO link. In some cases, due to the point ahead offset angle, the Tx direction minimizes a sum of the Rx coupling losses and the Tx pointing losses.