Fiber DAS I/Q Imbalance Correction for Accurate Quadrature Demodulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical fiber Distributed Acoustic Sensing (DAS) technologies face challenges in achieving high-accuracy phase demodulation due to inherent errors such as DC bias, amplitude imbalance, and phase imbalance, leading to phase noise that is difficult to remove in signal processing.
Innovation Solution
A method involving DC bias correction, followed by amplitude and phase imbalance correction using Hilbert transforms, to accurately correct I/Q signals in optical fiber DAS data, enhancing demodulation accuracy and noise suppression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional quadrature demodulation is used for distributed fiber acoustic sensing, then the system structure is simple, but I/Q channel imbalance causes demodulation accuracy to deteriorate
Solution Approach 1:
The patent applies preliminary action by performing I/Q channel balance calibration before actual acoustic signal demodulation. The system pre-determines balance correction coefficients through a calibration process using known test signals, then applies these coefficients to subsequent measurements. This preliminary calibration step eliminates the need for complex real-time balancing mechanisms while ensuring high demodulation accuracy.
Solution Approach 2:
The patent changes the parameter space by introducing balance correction coefficients that adjust the I and Q channel parameters. Instead of modifying the physical hardware structure, the system modifies the electrical parameters (amplitude and phase) of the I/Q channels through software-based coefficient adjustment. This parameter transformation resolves the contradiction by maintaining simple hardware while achieving precise demodulation through parameter optimization.
2Measurement precision
If I/Q channel balance calibration is performed, then demodulation accuracy is improved, but calibration time increases
Solution Approach 1:
The calibration process is performed once during system initialization or setup phase, before actual acoustic monitoring begins. The correction coefficients determined during this preliminary calibration are then reused for all subsequent demodulation operations. This approach concentrates the time investment in a single calibration event rather than requiring continuous calibration, thus improving demodulation accuracy without significantly increasing operational time loss.
Solution Approach 2:
The system employs periodic action by performing calibration only when necessary (e.g., during system setup or when environmental conditions change significantly), rather than continuously recalibrating. The correction coefficients remain valid over extended periods, allowing the system to alternate between calibration mode and normal demodulation mode, thereby minimizing time loss while maintaining accuracy.
3Speed
If conventional demodulation algorithms are used, then processing speed is fast, but vibration signal detection accuracy deteriorates under noisy conditions
Solution Approach 1:
The patent implements feedback by using the determined I/Q channel balance correction coefficients to continuously correct demodulation results. The system feeds back the correction information from the calibration phase into the actual signal processing phase, allowing conventional fast algorithms to operate on already-balanced I/Q signals. This feedback mechanism maintains processing speed while improving vibration signal detection accuracy under noisy conditions.
Solution Approach 2:
The patent replaces complex adaptive signal processing mechanisms with a simpler substitution approach: instead of using computationally intensive real-time balancing algorithms, the system substitutes pre-calculated correction coefficients into the conventional demodulation process. This substitution maintains the speed advantage of conventional algorithms while achieving the accuracy benefits of balanced I/Q channels.
Data Source
Figure 1~3
Figure 4~6
Figure 7~9
AI summary
A quadrature demodulation imbalance correction method and system for distributed fiber acoustic sensing data. The method comprises : acquiring I/Q signals I0 and Q0 of each observation point on an optical fiber; performing direct-current bias correction on the I/Q signals I0 and Q0 to obtain I/Q signals I1 and Q1 after direct-current bias correction; performing, by using Hilbert transform, amplitude imbalance correction on the I/Q signals I1 and Q1 after direct-current bias correction so as to obtain I/Q signals I2 and Q2 after amplitude imbalance correction; and performing, by using Hilbert transform, phase imbalance correction on the I/Q signals I2 and Q2 after amplitude imbalance correction so as to obtain I/Q signals I3 and Q3 after imbalance correction. By means of the method, I/Q signals can be accurately corrected, and fiber demodulation noise can be accurately and efficiently suppressed, thereby improving the acquisition quality of distributed fiber acoustic sensing data.