Aquatic Time Synchronization via Doppler Shift Compensation
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Solution Overview
Problem
In subsea communication networks, maintaining time synchronization among nodes is challenging due to random phase shifts and drift rates of oscillators, leading to loss of synchronization, especially in dynamic environments where vessel movement affects clock offset calculations.
Innovation Solution
An aquatic time synchronization system comprising a static first acoustic communications apparatus and a dynamic second acoustic communications apparatus, where the dynamic apparatus calculates and communicates Doppler shifts to determine a time offset, minimizing movement-related inaccuracies by using average Doppler shift calculations and acoustic signal propagation data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If vessels carrying USBL transceivers communicate with seabed transponders to determine time offsets, then clock synchronization can be achieved, but vessel movement introduces measurement errors requiring complex inertial compensation systems
Solution Approach 1:
Instead of having the moving vessel transmit signals and compensate for its own movement, the patent inverts the roles: the static seabed transponder transmits signals and the moving AUV compensates for its movement. This allows the calculation of Doppler shifts and time offsets while accounting for the receiver's motion, eliminating the need for complex inertial systems on the vessel side.
Solution Approach 2:
The AUV uses its own motion sensors (Doppler Velocity Log or inertial measurement unit) to self-compensate for its movement during signal transmission and reception. By calculating its own velocity and position changes, the AUV can correct for motion-induced errors in time offset measurements without requiring external compensation systems.
2Ease of operation
If local clocks at each node are used for time measurement, then autonomous operation is enabled, but random phase shifts and drift rates cause loss of synchronization
Solution Approach 1:
The patent implements a feedback mechanism where the AUV receives time offset information from the static transponder, compares it with its local clock, and adjusts its clock accordingly. This continuous feedback loop corrects for oscillator drift and phase shifts, maintaining synchronization reliability while preserving autonomous operation.
Solution Approach 2:
The system performs preliminary clock synchronization before data logging or navigation operations begin. By establishing accurate time offsets in advance and periodically updating them, the system ensures that subsequent operations can proceed autonomously with reliable time reference, preventing synchronization loss during critical operations.
3Measurement precision
If measurements are made over extended periods to improve accuracy, then more data can be collected, but movement of the dynamic apparatus increases measurement errors
Solution Approach 1:
The patent replaces mechanical timing methods with acoustic Doppler-based velocity measurement. By using the Doppler Velocity Log to measure the AUV's velocity through water and integrating it to obtain position, the system can accurately compensate for motion effects during very short measurement intervals, achieving high precision without requiring long measurement times.
Solution Approach 2:
The system changes the measurement parameters by using Doppler frequency shift as the primary measurement quantity rather than direct time of flight. By measuring the Doppler shift caused by the AUV's motion and using it to calculate velocity and position, the system can correct for motion effects in real-time during brief measurement windows, maintaining precision while minimizing measurement duration.
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 enhances precision in maintaining synchronization within aquatic communication systems by minimizing measurement time and accounting for movement, thereby improving the accuracy of clock offset calculations.
Implementation Method 1
the dynamic aquatic second acoustic communications apparatus is arranged to calculate a Doppler shift observed thereby in respect of propagation of the first acoustic signal along the first acoustic propagation path
Implementation Method 2
the aquatic first acoustic communications apparatus is arranged to calculate another Doppler shift observed thereby in respect of propagation of the second acoustic signal along the second acoustic propagation path
Implementation Method 3
the aquatic first acoustic communications apparatus is arranged to communicate a first acoustic signal having a first acoustic propagation path associated therewith to the dynamic aquatic second acoustic communications apparatus
Data Source
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AI summary
An aquatic time synchronisation system (100) comprises an aquatic first acoustic communications apparatus (116) capable of communicating acoustically with a dynamic aquatic second acoustic communications apparatus(114). The first acoustic communications apparatus (116) comprises a first time source (117) and the second acoustic communications apparatus (114) comprises a second time source(115). The first acoustic communications apparatus (116) is arranged to communicate a first acoustic signal to the second acoustic communications apparatus (114) and the second acoustic communications apparatus (114) is arranged to communicate a second acoustic signal to the first acoustic communications apparatus (116) in reply to the first acoustic signal. The first acoustic communications apparatus (116) is arranged to use data associated with the first and second acoustic signals in order to determine a time offset between the first and second time sources(117, 115).