CN117251676A - Phase signal noise reduction method and system for optical cable vibration signal - Google Patents
Phase signal noise reduction method and system for optical cable vibration signal Download PDFInfo
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Abstract
The invention discloses a phase signal noise reduction method and a system of an optical cable vibration signal, wherein the phase signal noise reduction method comprises the following steps: collecting vibration signals of the optical cable to obtain phase signals of disturbance points; decomposing the phase signal to obtain a high-frequency component and a low-frequency component; performing decomposition and quantization treatment on the high-frequency component to obtain a noise-reduced high-frequency component; reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal. The invention can more accurately restore the vibration invasion signal on the sensing link.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a phase signal noise reduction method and system for an optical cable vibration signal.
Background
The phase sensitive optical time domain reflectometry (Φ -OTDR) is an advanced novel distributed optical fiber sensing technology, and the Φ -OTDR can calculate the waveform of distributed vibration by identifying the differential phase in the sensing system. Due to the outstanding technology, a plurality of physical parameters can be measured accurately at the same time, so that vibration detection of long-distance optical fibers is realized, and meanwhile, high spatial resolution is maintained along the sensing optical fibers. In recent years, the method is widely applied to remote monitoring of vibration signals, and is commonly used in the fields of petroleum pipeline leakage detection, speed monitoring, perimeter protection and the like in practice.
However, due to the high sensitivity of the backscattered light, it is easily affected by the surrounding environment in practical applications. In addition, random noise such as electric noise and phase noise of laser can degrade the phi-OTDR signal, and increase the difficulty of vibration detection. Therefore, in order to locate interference and improve the signal-to-noise ratio (SNR) of Φ -OTDR, some noise reduction methods need to be introduced to improve the overall performance of the system. For example, the literature AReal-Time Distributed Deep Learning Approach for Intelligent Event Recognition in Long-Distance Pipeline Monitoring with DOFS, jiping Chen, huijuan Wu, xiangrong Liu, yao Xiao, yunjiang Rao, proposes a real-time distributed deep learning model that learns identifiable features of different disturbances using an efficient one-dimensional convolutional neural network (1-D CNN) and automatically identifies by training raw event data (signals). They have proposed a further Wavelet Packet Decomposition (WPD) denoising method before building and training a 1-D CNN network. However, pure wavelet packet decomposition does not handle nonlinear and non-stationary signals well. Document Disturbance pattern recognition based on an ALSTM in a long-distance phi-OTDR sensing system, X Chen, C Xu, uses an adaptive denoising method based on spectral subtraction to enhance signal characteristics. Whereas spectral subtraction requires an estimation of the noise spectrum, over-subtraction may occur, which affects the final noise reduction. For another example, CN109726642a discloses a method for noise reduction of distributed optical fiber vibration signals based on decomposition of variation modes, which comprises: the distributed optical fiber vibration signals are obtained, the distributed optical fiber vibration signals are subjected to variable-mode decomposition, the original signals can be divided into components with different modes, high-frequency noise in the vibration signals can be filtered in the decomposition process, the high-frequency noise of the vibration signals is filtered, and the distributed optical fiber vibration signals have good signal-noise separation performance; the wavelet threshold denoising is carried out on each modal component, so that the noise of the types such as shot noise, low-frequency noise and the like in the environmental noise can be further filtered; reconstructing the processed signal to obtain noise-reduced optical fiber vibration data, wherein although the signal-to-noise ratio of the optical fiber vibration data and the accuracy of optical fiber vibration signal processing can be improved, the link vibration signal is processed, and the disturbance signal on the sensing link is more accurately restored by reducing the influence of noise on the disturbance point phase signal according to the phase signal of the disturbance point; secondly, in the process of modal decomposition, the local extremum of certain signals can jump for a plurality of times within a short time interval to possibly cause the occurrence of modal aliasing, thereby influencing the final noise reduction effect; in addition, the application does not describe the denoising of the wavelet threshold in detail, and the used threshold quantization method may cause constant deviation between the estimated wavelet coefficient and the real wavelet coefficient or discontinuous phenomenon at the threshold, and finally cause deviation of the reconstructed signal.
Therefore, how to solve the influence of the surrounding environment on the Φ -OTDR signal is a problem that is urgent to be solved in the field at present.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a phase signal noise reduction method and system for an optical cable vibration signal. The influence of noise on the phase signal can be reduced, and the disturbance signal on the sensing link can be restored more accurately.
In a first aspect, the present invention provides a method for noise reduction of a phase signal of an optical cable vibration signal, including:
collecting vibration signals of an optical cable link to obtain phase signals of disturbance points;
decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
performing decomposition and quantization treatment on the high-frequency component to obtain a noise-reduced high-frequency component;
reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
Further, optical pulse signals are injected into the optical cable link through the phi-OTDR system, and vibration signals in the optical cable link are collected.
Further, the step of collecting the vibration signal of the optical cable to obtain the phase signal of the disturbance point includes:
and carrying out quadrature demodulation on the acquired vibration signals, and carrying out arctangent operation on the obtained in-phase component and the quadrature component to obtain phase signals of disturbance points.
Further, decomposing the phase signal to obtain a high frequency component and a low frequency component, including:
processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components;
performing approximate reconstruction and analysis treatment on the connotation modal components to obtain a continuous mean square error;
the content modal components are divided into a high frequency component and a low frequency component based on a continuous mean square error.
Further, processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components, including:
adding Gaussian white noise with different amplitude values for a preset number of times to the phase signals respectively;
performing empirical mode decomposition on the phase signal added with the Gaussian white noise each time to obtain a predetermined number of connotation mode components;
and obtaining the connotation modal components through aggregate average preset times and giving out the final preset number of connotation modal components.
The predetermined number of content modal components is determined by the phase signals, that is, different content modal components can be obtained after different phase signals are subjected to empirical mode decomposition.
Further, adding gaussian white noise having different magnitudes to the phase signal cumulatively a predetermined number of times includes:
x i (t)＝x(t)+n i (t)
where i=1, 2,3, M are the number of times gaussian white noise is added, n i (t) represents the i-th added Gaussian white noise sequence, x i (t) represents the phase signal obtained by adding gaussian white noise for the ith time, and x (t) represents the original phase signal to which gaussian white noise is not added;
performing empirical mode decomposition on the phase signal after adding the Gaussian white noise each time to obtain a predetermined number of connotation mode components, wherein the method comprises the following steps:
carrying out empirical mode decomposition for a predetermined number of times on the phase signal added with the Gaussian white noise each time to obtain residual components and content mode components with the number corresponding to the predetermined number of times; the following relationship is satisfied:
wherein, c i,j (t) is the j-th connotation modal component obtained by decomposing the ith added Gaussian white noise, r i,j (t) J is the J-th residual component obtained by decomposing the ith added Gaussian white noise, J is the number of content modal components, j=1, 2,3, … and J;
and giving a final preset number of connotation modal components by collecting and averaging connotation modal components obtained by decomposing each time, wherein the method comprises the following steps:
overlapping the connotation modal components obtained by the same decomposition times;
carrying out average treatment on the superimposed connotation modal components to obtain average connotation modal components after each decomposition;
integrating all the average connotation modal components to obtain a final preset number of connotation modal components;
the connotation mode component satisfies the following relationship:
wherein, c j (t) is the j-th connotation modal component obtained by ensemble averaging.
Further, performing approximate reconstruction and analysis processing on the connotation modal components to obtain a continuous mean square error, including:
all the residual components are overlapped and subjected to average treatment, so that a final residual component is obtained;
sorting the final preset number of content modal components according to the decomposition sequence;
and selecting any connotation modal component except the first one, and overlapping all connotation modal components and final residual components after the connotation modal component to obtain an approximate reconstruction signal, wherein the approximate reconstruction signal specifically meets the following relation:
in the method, in the process of the invention,an approximate reconstruction signal representing the kth content modal component, c i (t) represents the ith content modal component, r C (t) is the final residual component, and C is the number of the connotation mode components obtained by final decomposition;
each approximate reconstruction signal and one adjacent approximate reconstruction signal after the approximate reconstruction signal are analyzed and processed to obtain continuous mean square error, and the following relation is satisfied:
in the method, in the process of the invention,represents the continuous mean square error of the kth approximate reconstruction signal, N represents the sequence length of the approximate reconstruction signal, t i Represents the i-th point, c, of the approximate reconstructed signal k (t i ) Representing the value of the kth content modality component at the ith point.
Further, based on the continuous mean square error, dividing the connotation mode component into a high frequency component and a low frequency component includes:
comparing all the continuous mean square errors to give a minimum continuous mean square error;
obtaining an connotation modal component corresponding to the minimum continuous mean square error according to the superposition process of the connotation modal components and the analysis processing process of the approximate reconstruction signal;
taking an connotation modal component corresponding to the minimum continuous mean square error as a demarcation point;
and dividing the connotation mode components before the demarcation point into high-frequency components, and dividing the connotation mode components after the demarcation point into low-frequency components.
Further, the method for performing the decomposition and quantization processing on the high-frequency component to obtain the noise-reduced high-frequency component comprises the following steps:
performing wavelet decomposition on all high-frequency components based on a preset wavelet basis function to obtain respective wavelet coefficient sets, wherein the following relation is satisfied:
I W ＝{ω 1 ,ω 2 ,…,ω i ,…,ω L }
wherein I is w Is a wavelet coefficient set, omega i The i wavelet coefficient is the number of the wavelet coefficients L;
determining a threshold based on the connotation modality components; the following relationship is satisfied:
wherein T is a threshold value, sigma is the variance of noise, and N is the sequence length of the connotation mode component;
performing compromise threshold quantization processing on all wavelet coefficient sets based on the threshold value to obtain the wavelet coefficient sets subjected to the compromise threshold quantization processing; the following relationship is satisfied:
I WT ＝{ω 1T ,ω 2T ,…,ω iT ,…,ω LT }
wherein I is WT To the wavelet coefficient set after the compromise threshold quantization processing, omega iT For the ith threshold quantized wavelet coefficient, alpha is the added adjustment factor and alpha E [0,1 ]]；
And reconstructing the wavelet coefficient set after the threshold quantization processing to obtain each high-frequency component after noise reduction.
Further, reconstructing the low frequency component and the noise-reduced high frequency component to obtain a noise-reduced phase signal, including:
integrating all the high-frequency components after noise reduction to obtain a total high-frequency component, wherein the following relation is satisfied:
wherein I is WT,i (t) represents the ith noise-reduced high frequency component, x H (t) represents the total high frequency component
The total high-frequency component and the low-frequency component are overlapped to obtain a phase signal after noise reduction, and the following relation is specifically satisfied:
x D (t)＝x H (t)+x L (t)
wherein x is D (t) represents the phase signal after noise reduction, x L (t) represents a low frequency component.
In a second aspect, the present invention further provides a phase signal noise reduction system for an optical cable vibration signal, and the phase signal noise reduction method for the optical cable vibration signal is adopted, where the identification system includes:
the acquisition processing module is used for acquiring vibration signals of the optical cable link to obtain phase signals of the disturbance points;
the signal decomposition module is used for decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
the high-frequency noise reduction module is used for carrying out decomposition and quantization processing on the high-frequency components to obtain noise-reduced high-frequency components;
and the signal reconstruction module is used for reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
Further, the signal decomposition module is further configured to:
processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components;
performing approximate reconstruction and analysis treatment on the connotation modal components to obtain a continuous mean square error;
the content modal components are divided into a high frequency component and a low frequency component based on a continuous mean square error.
Further, the signal decomposition module is further configured to:
adding Gaussian white noise with different amplitude values for the phase signal for a preset number of times;
performing empirical mode decomposition on the phase signal added with the Gaussian white noise each time to obtain a predetermined number of connotation mode components;
and obtaining the connotation modal components through aggregate average preset times and giving out the final preset number of connotation modal components.
Further, the high-frequency noise reduction module is further configured to:
performing wavelet decomposition on all high-frequency components based on a preset wavelet basis function to obtain respective wavelet coefficient sets;
determining a threshold based on the connotation modality components;
performing compromise threshold quantization processing on all wavelet coefficient sets based on the threshold value to obtain the wavelet coefficient sets subjected to the compromise threshold quantization processing;
and reconstructing the wavelet coefficient set after the threshold quantization processing to obtain each high-frequency component after noise reduction.
In a third aspect, the invention also provides a phase signal noise reduction device for an optical cable vibration signal, which comprises a transmitting unit, a modulating unit, a detecting unit and a processing unit, wherein the transmitting unit is connected with the modulating unit, and the transmitting unit, the detecting unit and the processing unit are sequentially connected;
the transmitting unit injects an optical pulse signal into the optical cable to be tested through the modulating unit;
the detection unit acquires a vibration signal in the optical cable to be detected;
the processing unit adopts the phase signal noise reduction method of the optical cable vibration signal to carry out noise reduction processing on the vibration signal acquired by the detection unit.
Further, the transmitting unit further comprises a narrow linewidth laser and a 1*2 optical fiber coupler, the split ratio of the 1*2 optical fiber coupler is 90:10, the 1 x 2 optical fiber coupler divides signals sent by the narrow linewidth laser into a first optical path A and a second optical path B, the first optical path A is used as a probe light input modulating unit, and the second optical path B is used as a local oscillation light input detecting unit.
Further, the modulation unit comprises an acousto-optic modulator and an erbium-doped fiber amplifier.
Further, the optical cable to be tested comprises an optical fiber circulator and a sensing optical fiber, and is connected with the erbium-doped optical fiber amplifier.
Furthermore, the sensing optical fiber is a single-mode optical fiber, the length of the sensing optical fiber is 14km, a piezoelectric ceramic tube is used as a disturbance source at the 10km position of the optical fiber to be detected, and a standard sinusoidal signal is applied.
Further, the detection unit comprises a 2 x 2 optical fiber coupler, a balanced photoelectric detector and a data acquisition card;
the split ratio of the 2 x 2 optical fiber coupler is 50:50, the split ratio is connected with the narrow linewidth laser and the optical fiber circulator, and Rayleigh scattered light in the optical cable to be tested is coupled with the second optical path B at the 2 x 2 optical fiber coupler;
the balanced photoelectric detector is connected with the 2 x 2 optical fiber coupler, and the coupled signals are transmitted into the balanced photoelectric detector in a split mode and converted into beat frequency electric signals;
the data acquisition card is connected with the balance photoelectric detector, and the beat frequency electric signal is acquired by the digital acquisition card to obtain a digital signal.
Further, after the 1*2 optical fiber coupler divides the signal emitted by the narrow linewidth laser into the first optical path a and the second optical path B, the method further includes:
the acousto-optic modulator modulates a first light path A serving as probe light into an optical pulse signal, shifts the frequency of the light to high frequency 200MHz, amplifies the light by an erbium-doped fiber amplifier, and transmits the light into a sensing fiber through a fiber circulator, and the Rayleigh scattered light generated by the action of the optical pulse signal is reversely transmitted back to the fiber circulator; the local oscillation light transmitted to the 2 x 2 optical fiber coupler through the optical fiber circulator interferes with the local oscillation light of the second optical path B, is acquired by the data acquisition card after being converted by the balanced photoelectric detector, and finally is transmitted to the processing unit to finish noise reduction processing.
The invention provides a phase signal noise reduction method and a system for an optical cable vibration signal, which at least comprise the following beneficial effects:
(1) According to the invention, the phase signals of the disturbance points are processed, and for the problem that modal aliasing is possibly caused by common empirical mode decomposition, the Gaussian white noise is added during decomposition calculation in the aggregated empirical mode decomposition, so that the statistical characteristics of uniform frequency distribution of the Gaussian white noise are utilized, the extreme point characteristics of the signals are changed by adding the Gaussian white noise with different amplitudes each time, and then the added Gaussian white noise is counteracted by carrying out ensemble average on corresponding connotation modal components obtained by multiple empirical mode decomposition, thereby effectively reducing the influence of modal aliasing and improving the noise reduction effect.
(2) For the phase signals affected by noise, the advantages of empirical mode decomposition and wavelet decomposition noise reduction are combined, wavelet decomposition is carried out on the high-frequency components, threshold quantization processing is carried out on the high-frequency components, and finally, the signals are reconstructed, so that the influence of the noise on the phase signals is further removed, and the vibration invasion signals on the sensing link can be restored more accurately.
(3) When the wavelet decomposition is carried out on the high-frequency component and the threshold quantization is carried out, the compromise threshold quantization is used, the adjustment factor is added, and the adjustment factor is properly adjusted during the processing, so that compared with the traditional threshold processing, the influence caused by the problems of constant deviation and discontinuity is reduced, and the performance of the wavelet reconstruction signal is improved.
Drawings
FIG. 1 is a flow chart of a method for reducing noise of phase signals of optical cable vibration signals;
FIG. 2 is a flow chart of obtaining content modal components according to an embodiment of the present invention;
FIG. 3 is a flowchart of a process for performing decomposition quantization on high frequency components according to an embodiment of the present invention;
FIG. 4 is a graph comparing phase signals before and after noise reduction according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of a phase signal noise reduction system for optical cable vibration signals according to the present invention;
fig. 6 is a schematic diagram of a phase signal noise reduction device for an optical cable vibration signal according to the present invention.
Reference numerals illustrate: the device comprises a 100-transmitting unit, a 101-narrow linewidth laser, a 102-1*2 optical fiber coupler, a 200-modulating unit, a 201-acousto-optic modulator, a 202-erbium-doped optical fiber amplifier, a 300-optical cable to be tested, a 301-optical fiber circulator, a 302-sensing optical fiber, a 400-detecting unit, a 401-2 x 2 optical fiber coupler, a 402-balance photoelectric detector, a 403-data acquisition card and a 500-processing unit.
Detailed Description
In order to better understand the above technical solutions, the following detailed description will be given with reference to the accompanying drawings and specific embodiments. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, the "plurality" generally includes at least two.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a product or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such product or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a commodity or device comprising such element.
As shown in fig. 1, the present invention provides a phase signal noise reduction method for an optical cable vibration signal, including:
collecting vibration signals of an optical cable link to obtain phase signals of disturbance points;
decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
performing decomposition and quantization treatment on the high-frequency component to obtain a noise-reduced high-frequency component;
reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
The invention injects optical pulse signals into the optical cable through the phi-OTDR system and collects vibration signals in the optical cable.
Wherein, gather the vibration signal of optical cable, obtain the phase signal of disturbing the moving point, can include:
and carrying out quadrature demodulation on the acquired vibration signals, and carrying out arctangent operation on the obtained in-phase component and the quadrature component to obtain phase signals of disturbance points.
In this embodiment, decomposing the phase signal to obtain a high-frequency component and a low-frequency component includes:
processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components;
performing approximate reconstruction and analysis treatment on the connotation modal components to obtain a continuous mean square error;
the content modal components are divided into a high frequency component and a low frequency component based on a continuous mean square error.
As shown in fig. 2, the processing of the phase signal based on empirical mode decomposition to obtain a plurality of connotation mode components may include:
adding Gaussian white noise with different amplitude values for a preset number of times to the phase signals respectively;
performing empirical mode decomposition on the phase signal added with the Gaussian white noise each time to obtain a predetermined number of connotation mode components;
and obtaining the connotation modal components through aggregate average preset times and giving out the final preset number of connotation modal components.
By carrying out ensemble averaging on corresponding connotation modal components obtained by multiple ensemble empirical mode decomposition, the added Gaussian white noise can be counteracted.
Wherein adding gaussian white noise of different magnitudes to the phase signal cumulatively a predetermined number of times includes:
x i (t)＝x(t)+n i (t)
where i=1, 2,3, M are the number of times gaussian white noise is added, n i (t) represents the i-th added Gaussian white noise sequence, x i (t) represents the phase signal obtained by adding gaussian white noise for the ith time, and x (t) represents the original phase signal to which gaussian white noise is not added;
performing empirical mode decomposition on the phase signal after adding the Gaussian white noise each time to obtain a predetermined number of connotation mode components, wherein the method comprises the following steps:
carrying out empirical mode decomposition for a predetermined number of times on the phase signal added with the Gaussian white noise each time to obtain residual components and content mode components with the number corresponding to the predetermined number of times; the following relationship is satisfied:
wherein, c i,j (t) is the j-th connotation modal component obtained by decomposing the ith added Gaussian white noise, r i,j (t) J is the J-th residual component obtained by decomposing the ith added Gaussian white noise, J is the number of content modal components, j=1, 2,3, … and J;
and giving a final preset number of connotation modal components by collecting and averaging connotation modal components obtained by decomposing each time, wherein the method comprises the following steps:
overlapping the connotation modal components obtained by the same decomposition times;
carrying out average treatment on the superimposed connotation modal components to obtain average connotation modal components after each decomposition;
integrating all the average connotation modal components to obtain final connotation modal components;
the connotation mode component satisfies the following relationship:
wherein, c j (t) is the j-th connotation modal component obtained by ensemble averaging.
In an actual application scenario, processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components, including:
through adding Gaussian white noise into a phase signal and carrying out multiple empirical mode decomposition, finally obtaining a plurality of connotation mode components through set average operation, the method specifically comprises the following steps:
setting a total average calculation number M, namely the number of times of adding Gaussian white noise in advance;
adding a Gaussian white noise with a standard normal distribution to the original phase signal to generate a plurality of new phase signals x i (t)＝x(t)+n i (t), wherein i=1, 2,3,; in n i (t) represents the ith additive white Gaussian noise sequence, x i (t) represents a signal obtained by adding white gaussian noise for the ith time;
for phase signal x of the obtained noise-containing signal i (t) respectivelyPerforming empirical mode decomposition to obtain respective sum forms;
adding Gaussian white noise signals with different amplitudes into each decomposition, and obtaining an connotation modal component set { c ] through M times of calculation 1,j (t),c 2,j (t),c 3,j (t),…,c M,j (t) }, where j=1, 2,3, …, J;
and carrying out aggregate average operation on the corresponding content modal components to obtain final content modal components after aggregate empirical mode decomposition.
After obtaining a plurality of connotation modal components, the method carries out approximate reconstruction and analysis processing on the connotation modal components to obtain continuous mean square error, and can comprise the following steps:
all the residual components are overlapped and subjected to average treatment, so that a final residual component is obtained;
sorting the final preset number of content modal components according to the decomposition sequence;
and selecting any connotation modal component except the first one, and overlapping all connotation modal components and final residual components after the connotation modal component to obtain an approximate reconstruction signal, wherein the approximate reconstruction signal specifically meets the following relation:
in the method, in the process of the invention,an approximate reconstruction signal representing the kth content modal component, c i (t) represents the ith content modal component, r C (t) is the final residual component, and C is the number of the connotation mode components obtained by final decomposition;
each approximate reconstruction signal and one adjacent approximate reconstruction signal after the approximate reconstruction signal are analyzed and processed to obtain continuous mean square error, and the following relation is satisfied:
in the method, in the process of the invention,represents the continuous mean square error of the kth approximate reconstruction signal, N represents the sequence length of the approximate reconstruction signal, t i Represents the i-th point, c, of the approximate reconstructed signal k (t i ) Representing the value of the kth content modality component at the ith point.
After the continuous mean square error of all the approximate reconstruction signals is obtained, the method divides the connotation modal components into a high-frequency component and a low-frequency component based on the continuous mean square error and can comprise the following steps:
comparing all the continuous mean square errors to give a minimum continuous mean square error;
obtaining an connotation modal component corresponding to the minimum continuous mean square error according to the superposition process of the connotation modal components and the analysis processing process of the approximate reconstruction signal;
taking the kth connotation modal component corresponding to the minimum continuous mean square error as a demarcation point; the concrete representation mode is as follows:
wherein k is a demarcation point;
and dividing the connotation mode components before the demarcation point into high-frequency components, and dividing the connotation mode components after the demarcation point into low-frequency components.
In this embodiment, as shown in fig. 3, performing a decomposition quantization process on the high-frequency component to obtain a noise-reduced high-frequency component may include:
performing wavelet decomposition on all high-frequency components based on a preset wavelet basis function to obtain respective wavelet coefficient sets, wherein the following relation is satisfied:
I W ＝{ω 1 ,ω 2 ,…,ω i ,…,ω L }
wherein I is W Is a wavelet coefficient set, omega i The i wavelet coefficient is the number of the wavelet coefficients L;
determining a threshold based on the connotation modality components; the following relationship is satisfied:
wherein T is a threshold value, sigma is the variance of noise, and N is the sequence length of the connotation mode component;
performing compromise threshold quantization processing on all wavelet coefficient sets based on the threshold value to obtain the wavelet coefficient sets subjected to the compromise threshold quantization processing; the following relationship is satisfied:
I WT ＝{ω 1T ,ω 2T ,…,ω iT ,…,ω LT }
wherein I is WT To the wavelet coefficient set after the compromise threshold quantization processing, omega iT For the ith threshold quantized wavelet coefficient, alpha is the added adjustment factor and alpha E [0,1 ]]According to practical conditions, it is [0,1]Adjusting the time;
and reconstructing the wavelet coefficient set after the threshold quantization processing to obtain each high-frequency component after noise reduction.
Obtaining a wavelet coefficient set I after threshold quantization processing WT And reconstructing to obtain each high-frequency component I after noise reduction WT,i (t) integrating all the high frequency components to obtain an overall high frequency component x H (t), namely:
wherein I is WT,i (t) represents the ith noise-reduced high frequency component, x H (t) represents the total high frequency component.
The invention can improve the noise reduction effect by selecting a proper wavelet base. Specifically, the selected wavelet base characteristic is consistent with the phase signal characteristic. In the wavelet threshold noise reduction process, a proper number of decomposition layers needs to be selected. In an actual application scene, when the noise reduction processing of the communication optical cable is realized based on the phi-OTDR, the noise reduction can be performed after 4 layers of decomposition by using a db8 wavelet basis function of dbN wavelet family aiming at the acquired vibration signal, and the noise reduction method has the optimal noise reduction effect in the current application scene.
In this embodiment, reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal includes: superposing the total high-frequency component and the low-frequency component to obtain a phase signal after noise reduction; the concrete representation mode is as follows:
x D (t)＝x H (t)+x L (t)
wherein x is D (t) represents the phase signal after noise reduction, x L (t) represents a low frequency component.
Referring to fig. 4, after the noise reduction processing is performed by the phase signal noise reduction method, the noise-reduced phase signal waveform is reduced by more burrs compared with the waveform before noise reduction, the waveform is smoother and more similar to the shape of the sine wave of the added disturbance, the reduction effect of the disturbance signal is improved, and the finally obtained phase signal effect is better.
In addition, the invention carries out noise reduction treatment on the phase signal of the disturbance point on the link, and can better restore the disturbance signal. According to the invention, the Gaussian white noise is added during decomposition and calculation, the statistical characteristic that the Gaussian white noise has uniform frequency distribution is utilized, the extreme point characteristic of the signal is changed by adding the Gaussian white noise with different amplitudes each time, and then the added Gaussian white noise is counteracted by carrying out overall average on corresponding connotation modal components obtained by multiple empirical mode decomposition, so that the generation of modal aliasing can be effectively inhibited. The noise of the phase signal processed by the method mainly exists in the high-frequency component, so that the wavelet threshold processing is carried out on the high-frequency component, and the reconstruction is finally carried out to achieve the noise reduction effect, so that unnecessary data operation processing can be reduced, and the noise reduction processing efficiency and instantaneity are greatly improved. In addition, an adjustment factor is introduced during threshold quantization processing, so that the influence caused by constant deviation and discontinuity problems is reduced, and the performance of the wavelet reconstruction signal is improved. The invention aims to better recover the disturbance signal so as to analyze the disturbance type later, and the disturbance type is mainly reflected on the change of the phase signal of the disturbance point, so that the invention is mainly aimed at the processing of the phase signal.
Referring to fig. 5, the present invention further provides a phase signal noise reduction system for an optical cable vibration signal, and the method for noise reduction of the phase signal of the optical cable vibration signal is adopted, where the identification system includes:
the acquisition processing module is used for acquiring vibration signals of the optical cable link to obtain phase signals of the disturbance points;
the signal decomposition module is used for decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
the high-frequency noise reduction module is used for carrying out decomposition and quantization processing on the high-frequency components to obtain noise-reduced high-frequency components;
and the signal reconstruction module is used for reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
The signal decomposition module is also used for:
processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components;
performing approximate reconstruction and analysis treatment on the connotation modal components to obtain a continuous mean square error;
the content modal components are divided into a high frequency component and a low frequency component based on a continuous mean square error.
The signal decomposition module is also used for:
adding Gaussian white noise with different amplitude values for the phase signal for a preset number of times;
performing empirical mode decomposition on the phase signal added with the Gaussian white noise each time to obtain a predetermined number of connotation mode components;
and obtaining the connotation modal components through aggregate average preset times and giving out the final preset number of connotation modal components.
The high frequency noise reduction module is also used for:
performing wavelet decomposition on all high-frequency components based on a preset wavelet basis function to obtain respective wavelet coefficient sets;
determining a threshold based on the connotation modality components;
performing compromise threshold quantization processing on all wavelet coefficient sets based on the threshold value to obtain the wavelet coefficient sets subjected to the compromise threshold quantization processing;
and reconstructing the wavelet coefficient set after the threshold quantization processing to obtain each high-frequency component after noise reduction.
Referring to fig. 6, the present invention further provides a phase signal noise reduction device for an optical cable vibration signal, which includes a transmitting unit 100, a modulating unit 200, a detecting unit 400 and a processing unit 500, wherein the transmitting unit 100 is connected with the modulating unit 2000, and the transmitting unit 100, the detecting unit 400 and the processing unit 500 are sequentially connected;
the transmitting unit 100 injects an optical pulse signal into the optical cable 300 to be measured through the modulating unit 200;
the detection unit 400 acquires a vibration signal in the optical cable 300 to be tested;
the processing unit 500 performs noise reduction processing on the vibration signal acquired by the detection unit 400 by using the phase signal noise reduction method of the optical cable vibration signal.
Specifically, the transmitting unit 100 further includes a 1*2 optical fiber coupler 102, where the splitting ratio of the 1×2 optical fiber coupler 102 is 90:10, and the signal sent by the narrow linewidth laser 101 is divided into a first optical path a and a second optical path B, where the first optical path a is used as probe light, and the second optical path B is used as local oscillation light. A modulation unit 200 including an acousto-optic modulator (AOM) 201 and an Erbium Doped Fiber Amplifier (EDFA) 202, the modulation unit 200 being connected to the transmission unit 100; the optical cable 300 under test, which includes an optical fiber circulator 301 and a sensing fiber 302, is connected to an Erbium Doped Fiber Amplifier (EDFA) 202.
Preferably, the sensing optical fiber 302 is a single-mode optical fiber, the length of the sensing optical fiber 302 is 14km, a piezoelectric ceramic tube (PZT) is used as a disturbance source at the position of 10km of the optical fiber to be measured, and a standard sinusoidal signal is applied.
In use, an acousto-optic modulator (AOM) 201 modulates a first optical path a as probe light into an optical pulse signal and frequency shifts the light to a high frequency of 200MHz, amplified by an Erbium Doped Fiber Amplifier (EDFA) 202, and transmitted back to the fiber circulator 301 through the fiber circulator 301 into the sensing fiber 302 where the rayleigh scattered light generated by the action of the optical pulse signal in the sensing fiber 302. Specifically, the sensing optical fiber 302 is an optical fiber to be measured, then the light pulse passing through the optical fiber circulator 301 is transmitted into the sensing optical fiber 302, the returned scattered light in the sensing optical fiber 302 returns to the optical fiber circulator 301, then is transmitted to the 2×2 optical fiber coupler 401 to interfere, is acquired by the data acquisition card 403 after being converted by the balanced photoelectric detector 402, and is transmitted to the processing unit 500 to be acquired and noise reduction is completed.
The device also comprises a detection unit 400, wherein the detection unit 400 comprises a 2 x 2 optical fiber coupler 401, a Balanced Photoelectric Detector (BPD) 402 and a data acquisition card (DAQ) 403; the 2 x 2 optical fiber coupler 401 has a splitting ratio of 50:50, and is connected with the narrow linewidth laser 101 and the optical fiber circulator 301, and the rayleigh scattered light in the optical cable to be tested is coupled with the second optical path B at the 2 x 2 optical fiber coupler 401; a Balanced Photodetector (BPD) 402 is connected to the 2 x 2 fiber coupler 401, and the coupled signal is split into two and transmitted into the Balanced Photodetector (BPD) 402 and converted into a beat signal; a data acquisition card (DAQ) 403 is connected to the Balanced Photodetector (BPD) 402, and the beat signal is acquired by the digital acquisition card (DAQ) 403 to obtain a digital signal.
The apparatus further comprises a processing unit 500, preferably a computer, connected to the data acquisition card (DAQ) 403.
In the use process, after the data acquisition card 403 acquires the disturbance intrusion signals of various types, the disturbance intrusion signals are transmitted into the processing unit 500, and the processing unit 500 is used for processing and identifying the signals acquired by the data acquisition card 403.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (10)
1. A phase signal noise reduction method for identifying a vibration signal of an optical cable, comprising:
collecting vibration signals of an optical cable link to obtain phase signals of disturbance points;
decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
performing decomposition and quantization treatment on the high-frequency component to obtain a noise-reduced high-frequency component;
reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
2. The phase signal noise reduction method according to claim 1, wherein collecting vibration signals of the optical cable to obtain phase signals of disturbance points comprises:
and carrying out quadrature demodulation on the acquired vibration signals, and carrying out arctangent operation on the obtained in-phase component and the quadrature component to obtain phase signals of disturbance points.
3. The phase signal noise reduction method according to claim 1, wherein decomposing the phase signal to obtain a high frequency component and a low frequency component comprises:
processing the phase signal based on the ensemble empirical mode decomposition to obtain a plurality of connotation mode components;
performing approximate reconstruction and analysis treatment on the connotation modal components to obtain a continuous mean square error;
the content modal components are divided into a high frequency component and a low frequency component based on a continuous mean square error.
4. A method of denoising a phase signal as claimed in claim 3, wherein processing the phase signal based on a collective empirical mode decomposition to obtain a plurality of content mode components comprises:
adding Gaussian white noise with different amplitude values for a preset number of times to the phase signals respectively;
performing empirical mode decomposition on the phase signal added with the Gaussian white noise each time to obtain a predetermined number of connotation mode components;
and obtaining the connotation modal components through aggregate average preset times and giving out the final preset number of connotation modal components.
5. The method of noise reduction of a phase signal according to claim 4, wherein performing empirical mode decomposition on the phase signal after each addition of white gaussian noise to obtain a predetermined number of content modal components, comprises:
carrying out empirical mode decomposition for a predetermined number of times on the phase signal added with the Gaussian white noise each time to obtain residual components and content mode components with the number corresponding to the predetermined number of times;
and giving a final preset number of connotation modal components by collecting and averaging connotation modal components obtained by decomposing each time, wherein the method comprises the following steps:
overlapping the connotation modal components obtained by the same decomposition times;
carrying out average treatment on the superimposed connotation modal components to obtain average connotation modal components after each decomposition;
and integrating all the average connotation modal components to obtain the final preset number of connotation modal components.
6. The method of noise reduction of a phase signal according to claim 5, wherein performing approximate reconstruction and analysis on the content modal components to obtain a continuous mean square error comprises:
all the residual components are overlapped and subjected to average treatment, so that a final residual component is obtained;
sorting the final preset number of content modal components according to the decomposition sequence;
selecting any connotation modal component except the first one, and overlapping all connotation modal components and final residual components after the connotation modal component to obtain an approximate reconstruction signal;
and analyzing each approximate reconstruction signal and one adjacent approximate reconstruction signal after the approximate reconstruction signal to obtain continuous mean square error.
7. The phase signal noise reduction method according to claim 6, wherein dividing the content modal component into a high frequency component and a low frequency component based on a continuous mean square error comprises:
comparing all the continuous mean square errors to give a minimum continuous mean square error;
obtaining an connotation modal component corresponding to the minimum continuous mean square error according to the superposition process of the connotation modal components and the analysis processing process of the approximate reconstruction signal;
taking an connotation modal component corresponding to the minimum continuous mean square error as a demarcation point;
and dividing the connotation mode components before the demarcation point into high-frequency components, and dividing the connotation mode components after the demarcation point into low-frequency components.
8. The phase signal noise reduction method according to claim 7, wherein the performing of the decomposition quantization processing on the high frequency component to obtain the noise-reduced high frequency component comprises:
performing wavelet decomposition on all high-frequency components based on a preset wavelet basis function to obtain respective wavelet coefficient sets;
determining a threshold based on the connotation modality components;
performing compromise threshold quantization processing on all wavelet coefficient sets based on the threshold value to obtain the wavelet coefficient sets subjected to the compromise threshold quantization processing; the following relationship is satisfied:
Iwr＝{ω1r,2r,…,ωr,…,①Lr}
wherein I is WT To the wavelet coefficient set after the compromise threshold quantization processing, omega i Is the ith wavelet coefficient，ω iT Is the wavelet coefficient after the ith threshold quantization, alpha is the adjustment factor and alpha is [0,1 ]]T is a threshold;
and reconstructing the wavelet coefficient set after the threshold quantization processing to obtain each high-frequency component after noise reduction.
9. The phase signal noise reduction method according to claim 8, wherein reconstructing the low frequency component and the noise-reduced high frequency component to obtain the noise-reduced phase signal comprises:
integrating all the high-frequency components after noise reduction to obtain an overall high-frequency component;
and superposing the total high-frequency component and the low-frequency component to obtain the phase signal after noise reduction.
10. A phase signal noise reduction system for optical cable vibration signals, employing the phase signal noise reduction method for optical cable vibration signals according to any one of claims 1 to 9, characterized in that the identification system comprises:
the acquisition processing module is used for acquiring vibration signals of the optical cable link to obtain phase signals of the disturbance points;
the signal decomposition module is used for decomposing the phase signal to obtain a high-frequency component and a low-frequency component;
the high-frequency noise reduction module is used for carrying out decomposition and quantization processing on the high-frequency components to obtain noise-reduced high-frequency components;
and the signal reconstruction module is used for reconstructing the low-frequency component and the noise-reduced high-frequency component to obtain a noise-reduced phase signal.
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