CN115296729B - Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer - Google Patents
Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer Download PDFInfo
- Publication number
- CN115296729B CN115296729B CN202210818207.4A CN202210818207A CN115296729B CN 115296729 B CN115296729 B CN 115296729B CN 202210818207 A CN202210818207 A CN 202210818207A CN 115296729 B CN115296729 B CN 115296729B
- Authority
- CN
- China
- Prior art keywords
- matrix
- ofdm
- simplex
- signal
- decoding
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
- 230000003287 optical effect Effects 0.000 title claims abstract description 52
- 238000000034 method Methods 0.000 title claims abstract description 36
- 239000011159 matrix material Substances 0.000 claims abstract description 211
- 238000000253 optical time-domain reflectometry Methods 0.000 claims abstract description 49
- 238000001514 detection method Methods 0.000 claims abstract description 40
- 239000013307 optical fiber Substances 0.000 claims abstract description 26
- 238000006243 chemical reaction Methods 0.000 claims abstract description 21
- 230000009466 transformation Effects 0.000 claims abstract description 16
- 238000012545 processing Methods 0.000 claims description 22
- 239000013598 vector Substances 0.000 claims description 19
- 108091026890 Coding region Proteins 0.000 claims description 13
- 239000000835 fiber Substances 0.000 claims description 9
- 238000012935 Averaging Methods 0.000 claims description 4
- 238000009825 accumulation Methods 0.000 claims description 4
- 230000003321 amplification Effects 0.000 claims description 4
- 238000003199 nucleic acid amplification method Methods 0.000 claims description 4
- 230000001131 transforming effect Effects 0.000 claims description 4
- 230000001934 delay Effects 0.000 claims description 3
- 238000001208 nuclear magnetic resonance pulse sequence Methods 0.000 claims description 3
- 239000000523 sample Substances 0.000 description 10
- 238000005070 sampling Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 5
- 230000006870 function Effects 0.000 description 4
- 238000005259 measurement Methods 0.000 description 3
- 230000006872 improvement Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000006467 substitution reaction Methods 0.000 description 2
- 230000002238 attenuated effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- GQYHUHYESMUTHG-UHFFFAOYSA-N lithium niobate Chemical compound [Li+].[O-][Nb](=O)=O GQYHUHYESMUTHG-UHFFFAOYSA-N 0.000 description 1
- 230000008569 process Effects 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2626—Arrangements specific to the transmitter only
- H04L27/2627—Modulators
- H04L27/2634—Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Electromagnetism (AREA)
- Discrete Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Mathematical Physics (AREA)
- Optical Communication System (AREA)
Abstract
The invention provides a coding and decoding method and system of an OFDM-Simplex code and an optical time domain reflectometer, wherein the method comprises the following steps: generating an L-order Simplex coding matrix according to the Hadamard matrix, and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted; expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix; performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal; performing serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix; performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix; and performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve. Compared with the traditional single pulse OTDR, the signal to noise ratio of the OTDR curve after coding is higher, and only one coded detection light is required to be transmitted into the optical fiber and then received, so that the time efficiency of the system is greatly improved.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to an encoding and decoding method and system of an OFDM-Simplex code and an optical time domain reflectometer.
Background
Currently, optical Time Domain Reflectometry (OTDR) technology is a distributed fiber sensing technology. The basic principle is that a detection laser pulse (the pulse width is generally 10-500 ns) is emitted at one end of the optical fiber. When the detection pulse propagates along the optical fiber, rayleigh scattering (Rayleigh scattering) is generated around the optical fiber due to elastic collision of photons with molecules in the optical fiber, and a part of laser light is scattered back in the propagation direction. The rayleigh scattered light from the fiber locations varies in time to reach the fiber emission end according to distance. In addition, fresnel reflection (Fresnel reflection) is generated due to abrupt refractive index changes at the optical fiber breakage, splice, etc., and a light signal with higher intensity is returned to the incident end. Therefore, the distribution of the collected Rayleigh scattered light signals and the Fresnel reflected light signals in time corresponds to the distribution of scattered light in space, and a group of OTDR curves are formed, and the curves can reflect the perfect condition and the fault state of the optical fiber link.
The signal-to-noise ratio (SNR) is the ratio of the power of the back-scattered signal of the OTDR to the power of the noise, which is one of the key indicators of the OTDR system, and OTDR with a high signal-to-noise ratio can usually better distinguish each event point, and the measurable maximum length is also longer. The rayleigh scattering signal is weak, so that a wider probe pulse is often required to improve the signal-to-noise ratio of the received signal. But wider pulses also occupy a larger range in space, thus sacrificing spatial resolution. In order to not sacrifice the spatial resolution and improve the signal to noise ratio, an accumulated average method can be adopted, and because noise in a received signal is generated by dark current of a receiver, the noise has uncorrelation, and the duty ratio of the noise in the signal can be reduced and the duty ratio of effective signals in the signal can be improved by overlapping and averaging signals at a receiving end for a plurality of times. However, with the increase of the average frequency, the time cost of the system is gradually increased, and the time required for measuring an OTDR curve by the system is increased. And the accumulation average method has very limited improvement on the OTDR signal-to-noise ratio, the average frequency and the signal-to-noise ratio are in an exponential relationship, the amplitude of the signal-to-noise ratio improvement can be gradually reduced and tends to be stable, and the limitation exists in practical engineering application.
SNR can also be improved by using pulse coding techniques, where groups of sequences with good autocorrelation properties are used to code the sounding pulses. The total energy of the coded detection pulses is increased, so that the signal-to-noise ratio of the system can be improved, and the spatial resolution of the system is not changed after the received signals are decoded. Simplex coding is a pulse coding technique with higher coding gain, and the coding needs to use an l×l S matrix as coding basis. The matrix is converted from a (L+1) -order Hadamard matrix, the first row and the first column of the Hadamard matrix are removed, and the element '1' in the matrix is changed to be '1', and the element '0' is changed to be '1', so that an S matrix can be obtained. Each row in the S matrix is a set of Simplex codes. Modulating each group of Simplex codes into detection light pulses, injecting the detection light pulses into optical fibers in a multi-time mode, receiving the detection light pulses in a multi-time mode, and finally carrying out decoding operations such as inverse Hadamard transformation, time shift addition and the like on the received group results respectively to obtain a decoded OTDR curve.
Based on the OTDR of Simplex coding, the longer the coding length is, the higher the signal-to-noise ratio of the system is. But as the code length increases, the time cost of the system increases. Assuming that the code length is increased to 255 bits, 255 groups of probe light pulses need to be transmitted into the optical fiber respectively, 255 times of probe light pulses are received respectively, and the time required for system measurement is more.
Disclosure of Invention
The purpose of the invention is that: providing a coding and decoding method, a coding and decoding system and an optical time domain reflectometer of an OFDM-Simplex code, and coding detection pulse light by using a Simplex coding technology on the basis of the OTDR of a traditional accumulated average method so as to further improve the signal to noise ratio of the system; on the basis of Simplex coding, an OFDM-Simplex coding sequence is formed by using an orthogonal frequency division multiplexing technology, and only single transmission and single measurement are needed, so that the signal-to-noise ratio of the system can be improved on the premise of not sacrificing the spatial resolution of an OTDR system, and the time efficiency of the system can be greatly improved.
In order to achieve the above object, a first aspect of the present invention provides a method for encoding and decoding an OFDM-Simplex code, the method comprising: generating an L-order Simplex coding matrix according to the Hadamard matrix, and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted; expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix; performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal; performing serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix; performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix; and performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve.
Preferably, the generating an L-order Simplex coding matrix according to the Hadamard matrix, and transforming the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted, includes the following steps: transforming the Hadamard matrix through the following formula (2) to obtain an L+1-order Hadamard matrix;
wherein the formula (1) is a Hadamard matrix H L Is a basic constitution of (1);
removing the first row and the first column of the L+1-order Hadamard matrix, changing the element '1' into '0', and changing the '1' into '1', so as to obtain the L-order Simplex coding matrix; the L-order Simplex coding matrix has the following form:
the L-order Simplex coding matrix S L Constructing a pulse sequence to obtain the L-order pulse matrix to be transmitted:
wherein eta 1 (t)、η 2 (t)…η L (t) consists of pulses P (t) of width τ.
Preferably, the extending the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetric transformation and IFFT operation to obtain an OFDM modulation matrix, includes the following steps: expanding the column length of the L-order pulse matrix to be transmitted into the number of points of the IFFT operation; performing the Hermitian symmetric transformation on the expanded L-order pulse matrix to be transmitted to obtain a matrix with a Hermitian symmetric structureThe matrix->Has the following form:
wherein eta * A conjugate vector representing η;
the matrix is processedThe following calculation is performed to obtain the coordinate position and the rest positions are complemented with 0 to obtain the matrix +.>The calculation formula is as follows:
C co ＝L IFFT -C ca +2 (7)
wherein C is ca And C co Respectively representing an original signal coordinate set and a conjugated signal coordinate set; c (C) cL The expression interval is [1, L]Coordinate vectors with an interval of 1; l (L) ca Representing the number of subcarriers, numerically equal to the coding length L; l (L) IFFT Representing the number of IFFT points;representing a down-rounding function for element x;
the matrixThe form of (2) is as follows:
wherein z (t) represents a zero vector; eta (t) is defined by C ca Composition; η (t) * From C co Composition;
for the matrixAnd performing IFFT operation on each column of the OFDM modulation matrix.
Preferably, the performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix includes the following steps: performing FFT operation on each column of the parallel signal matrix to obtain a matrix R (t), wherein R (t) has the following form:
wherein ca represents the original signal start coordinate, co represents the conjugate signal start coordinate,is the original signal vector, ++>Is a conjugate signal vector;
selecting an original signal vector for the matrix R (t) to obtain a matrix R c (t)：
For the matrix R c Performing modular operation on the elements in (t) to obtain the OFDM decoding matrix r (t):
where e represents noise carried each time a signal is received, and ψ (t) represents an OTDR curve function obtained after different delays are injected into the optical fiber.
Preferably, the performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve includes the following steps: calculating the L-order Simplex coding matrix S L Is the inverse of the matrix of (a)
Inverting the matrixMultiplying the OFDM decoding matrix r (t), performing inverse Hadamard transformation, performing time shift and accumulation by taking pulse width tau as a unit, and finally averaging to obtain the OTDR curve:
the second aspect of the invention provides a coding and decoding system of an OFDM-Simplex code, which comprises a first matrix module, a first operation module, a coding module, a second matrix module, a second operation module and a decoding module; wherein,
the first matrix module is used for generating an L-order Simplex coding matrix according to the Hadamard matrix and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted;
the first operation module is used for expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix;
the coding module is used for carrying out parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal;
the second matrix module is used for carrying out serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix;
the second operation module is used for performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix;
and the decoding module is used for performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve.
A third aspect of the invention provides an optical time domain reflectometer comprising: the laser is used for inputting continuous laser to the modulation module; the sequence generation module is used for acquiring an OFDM-Simplex coding sequence according to the encoding and decoding method of the OFDM-Simplex code; the modulation module is used for carrying out orthogonal frequency division multiplexing on the continuous laser according to the OFDM-Simplex coding sequence and modulating the continuous laser into detection light carrying OFDM-Simplex coding information; the light processing module is used for performing backward Rayleigh scattering on the detection light; the photoelectric detector is used for converting the optical signal after the backward Rayleigh scattering into an electric signal; the electric signal processing module is used for carrying out analog-to-digital conversion and average processing on the electric signal to obtain a signal to be decoded; and the decoding module is used for decoding the signal to be decoded according to the encoding and decoding method of the OFDM-Simplex code to obtain an OTDR curve.
Preferably, the modulation module comprises an arbitrary waveform generator and an electro-optic modulator; the random waveform generator is used for generating a modulation signal according to the OFDM-Simplex coding sequence; the electro-optical modulator is used for carrying out orthogonal frequency division multiplexing on the input continuous light through the modulation signal and modulating the continuous light into detection light carrying OFDM-Simplex coding information.
Preferably, the optical processing module comprises an optical amplifier, an optical circulator and a single-mode optical fiber; the optical amplifier is used for performing power amplification processing on the detection light received from the modulation module; the optical circulator is used for receiving the amplified detection light from the optical amplifier and outputting the detection light to the single-mode optical fiber to generate backward Rayleigh scattered detection light.
Preferably, the light processing module further comprises an attenuator; the attenuator is used for receiving the detection light scattered by backward Rayleigh from the optical circulator, carrying out power attenuation treatment and outputting the detection light to the photoelectric detector.
Compared with the prior art, the encoding and decoding method and system for the OFDM-Simplex code and the optical time domain reflectometer provided by the invention have the following advantages:
(1) The signal to noise ratio is improved. Compared with the traditional single-pulse OTDR, the signal to noise ratio of the encoded OTDR curve under the same pulse width and the same average times is higher than that of the traditional single-pulse OTDR.
(2) The time efficiency is improved. Compared with the traditional coding technology OTDR, the coding OTDR based on the orthogonal frequency division multiplexing technology does not need to transmit coding detection light to the optical fiber for multiple times and receive scattering signals for multiple times. Only one coded detection light is transmitted into the optical fiber, and the coded detection light is received again, so that the time efficiency of the system is greatly improved.
Drawings
In order to more clearly illustrate the technical solutions of the present invention, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a flowchart of a coding and decoding method of an OFDM-Simplex code according to an embodiment of the present invention;
fig. 2 is a system block diagram of a coding and decoding system of an OFDM-Simplex code according to another embodiment of the present invention;
FIG. 3 is a block diagram of an optical time domain reflectometer according to yet another embodiment of the present invention;
FIG. 4 is a block diagram illustrating a modulation module in an optical time domain reflectometer according to another embodiment of the present invention;
FIG. 5 is a block diagram illustrating an optical processing module in an optical time domain reflectometer according to another embodiment of the present invention;
fig. 6 is a diagram of an encoded OTDR curve and a single pulse OTDR curve with different code lengths according to still another embodiment of the present invention: (a) code length 31; (b) code length 15; (c) code length 7; (d) monopulse.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. 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.
It should be understood that the step numbers used herein are for convenience of description only and are not limiting as to the order in which the steps are performed.
It is to be understood that the terminology used in the description 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 specification 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 terms "comprises" and "comprising" indicate the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
The term "and/or" refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
In one embodiment, as shown in fig. 1, there is provided a coding and decoding method of an OFDM-Simplex code, including the steps of:
s10, generating an L-order Simplex coding matrix according to a Hadamard matrix, and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted;
the method comprises the steps of generating an L-order Simplex coding matrix according to a Hadamard matrix, and generating the L+1-order Hadamard matrix, wherein the Hadamard matrix basically comprises the following components:
the Hadamard matrix of order l+1 can be obtained by the following formula:
and then removing the first row and the first column of the matrix, changing the element '1' in the matrix into '0', and changing the '1' into '1', thereby obtaining the L-order Simplex matrix, wherein the form of the Simplex matrix is shown as the following formula:
matrix S L The pulse sequence is constructed, and then the following L-order pulse matrix to be transmitted exists:
wherein eta 1 (t)、η 2 (t)…η L (t) consists of pulses P (t) of width τ.
S20, expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix;
the pulse matrix to be transmitted in the L-order is subjected to Hermitian symmetry to eliminate complex numbers generated in the subsequent fast Fourier transform (IFFT) operation, and signals with the Hermitian symmetry structure do not contain complex numbers after being subjected to IFFT according to the property of discrete Fourier transform. The number of IFFT points is required to be a power of 2 during the operation, where the number of IFFT points is set to λ (λ > L), that is, the IFFT operation is performed on λ signals on the matrix column. Since each column element of the signal matrix after Hermitian symmetry is smaller than the number of IFFT points λ, it is necessary to extend the original matrix column length to λ and calculate coordinates of the Hermitian symmetry structure.
Therefore, to obtain the OFDM modulation matrix, the column length of the L-order pulse matrix to be transmitted needs to be extended to the number of points of the IFFT operation; and then carrying out the Hermitian symmetrical transformation on the expanded L-order pulse matrix to be transmitted to obtain a matrix with a Hermitian symmetrical structureThe matrix->Has the following form:
wherein eta * A conjugate vector representing η;
matrix againThe following calculation is performed to obtain the coordinate position and the rest positions are complemented with 0 to obtain the matrix +.>The calculation formula is as follows:
C co ＝L IFFT -C ca +2 (7)
wherein C is ca And C co Respectively representing an original signal coordinate set and a conjugated signal coordinate set; c (C) cL The expression interval is [1, L]Coordinate vectors with an interval of 1; l (L) ca Representing the number of sub-carriers, equal in value toA coding length L; l (L) IFFT Representing the number of IFFT points;representing a down-rounding function for element x;
matrix arrayThe form of (2) is as follows:
wherein z (t) represents a zero vector; eta (t) is defined by C ca Composition; η (t) * From C co Composition;
pair matrixAnd performing IFFT operation on each column of the array to obtain an OFDM modulation matrix.
S30, performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal;
wherein finally the matrix isAnd performing parallel/serial conversion to obtain the OFDM-Simplex coding sequence to be transmitted. Because the encoded signal contains negative numbers, a direct current bias needs to be added on the basis of the signal to enable the optical signal to be single polarized so as to be transmitted in the optical fiber.
S40, performing serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix;
after receiving OFDM-Simplex coded signals, the signals are subjected to serial/parallel conversion to form an N x lambda parallel signal matrix.
S50, performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix;
wherein, first, fast Fourier Transform (FFT) is performed on each column of the parallel signal matrix to obtain a matrix R (t), where R (t) has the following form:
wherein ca represents the original signal start coordinate, co represents the conjugate signal start coordinate, as can be seen from formulas (6) and (7),is the original signal vector, ++>For the conjugate signal vector, only the original signal vector is selected to obtain a matrix R c (t)：
And matrix elements obtained by FFT also contain complex numbers, and the OFDM decoding matrix r (t) can be obtained by taking the modulus of the elements in the matrix:
where e represents noise carried each time a signal is received, and ψ (t) represents an OTDR curve function obtained after different delays are injected into the optical fiber.
S60, performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve;
in order to perform Simplex decoding, a matrix S is first calculated L Is the inverse of the matrix of (a)
To restore the original OTDR curve, a matrix is usedMultiplying by a matrix r (t), and performing inverse Hadamard transformation:
and (3) performing time shift and accumulation on all the results of the formula (13) by taking pulse width as a unit, and finally averaging to obtain a final original OTDR curve:
the embodiment of the application designs a coding and decoding method of an OFDM-Simplex code based on the problems that the signal to noise ratio is limited and the time cost of a system can be increased along with the increase of the code length caused by the traditional single pulse OTDR, which realizes the generation of an L-order Simplex coding matrix according to a Hadamard matrix and transforms the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted; expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix; performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal; performing serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix; performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix; and performing Simplex decoding on the OFDM decoding matrix to obtain the technical scheme of the OTDR curve.
The OFDM-Simplex code adopts a mode of combining Simplex coding and OFDM technology, based on the principle that orthogonal subcarriers in the OFDM technology cannot interfere with each other, simplex coding sequences needing to be transmitted for many times are respectively modulated onto a plurality of subcarriers, and are simultaneously transmitted into an optical fiber after being overlapped.
Although the steps in the flowcharts described above are shown in order as indicated by arrows, these steps are not necessarily executed in order as indicated by the arrows. The steps are not strictly limited to the order of execution unless explicitly recited herein, and the steps may be executed in other orders.
In one embodiment, as shown in fig. 2, there is provided a coding and decoding system of an OFDM-Simplex code, the system comprising:
the first matrix module 1 is used for generating an L-order Simplex coding matrix according to the Hadamard matrix and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted;
the first operation module 2 is used for expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix;
the encoding module 3 is used for performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex encoded signal;
the second matrix module 4 is configured to perform serial/parallel conversion on the OFDM-Simplex encoded signal to obtain a parallel signal matrix;
the second operation module 5 is used for performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix;
and the decoding module 6 is used for performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve.
The above-described respective modules in the coding and decoding system of the OFDM-Simplex code may be implemented in whole or in part by software, hardware, and combinations thereof. The above modules may be embedded in hardware or may be independent of a processor in the computer device, or may be stored in software in a memory in the computer device, so that the processor may call and execute operations corresponding to the above modules.
In one embodiment, as shown in fig. 3, the present invention provides an optical time domain reflectometer, which is based on the encoding and decoding method of the OFDM-Simplex code, and includes:
a laser 11 for inputting continuous laser light to the modulation module;
wherein the laser used here emits laser light at a wavelength of 1550nm in order to make the frequency stability of the laser sufficient to avoid interference with the measurement results.
The sequence generating module 12 is used for acquiring an OFDM-Simplex coding sequence according to the encoding and decoding method of the OFDM-Simplex code;
the OFDM-Simplex coding sequences are formed by modulating each Simplex coding sequence to be transmitted respectively onto orthogonal parallel subcarriers by using an Orthogonal Frequency Division Multiplexing (OFDM) technology on the basis of Simplex coding, and finally merging the subcarriers; the encoding and decoding method can be used for the OFDM-Simplex code to acquire an OFDM-Simplex coding sequence.
The modulation module 13 is configured to perform orthogonal frequency division multiplexing on the continuous laser according to the OFDM-Simplex coding sequence, and modulate the continuous laser into probe light carrying OFDM-Simplex coding information;
as shown in fig. 4, the modulation module 13 includes an arbitrary waveform generator 131 and an electro-optical modulator 132.
Specifically, the arbitrary waveform generator 131 is configured to generate a modulation signal according to the OFDM-Simplex coding sequence. Meanwhile, the sampling rate of the arbitrary waveform generator is as high as possible, so that orthogonality of all subcarriers is not destroyed, and interference to decoding caused by subcarrier distortion due to too low sampling rate is avoided, and the sampling rate used by the arbitrary waveform generator is 2.5GHz.
And an electro-optical modulator 132 for performing orthogonal frequency division multiplexing on the input continuous light through the modulation signal, and modulating the continuous light into detection light carrying OFDM-Simplex coding information.
The electro-optic intensity modulator may be a conventional lithium niobate waveguide electro-optic Mach-Zehnder intensity modulator. The modulator needs to be dc biased at the lowest output power when operating, i.e. the modulator has the lowest output power when no modulation signal is applied. The modulator is driven with a bipolar signal (both positive and negative) so that the modulator converts the incoming continuous light into switching between two phases differing by pi in accordance with the incoming code sequence. In theory, the electro-optical intensity modulator could be replaced by another type of modulator, as long as it is possible to "transform the incoming continuous light into switching between two phases differing by pi according to the incoming code sequence". However, currently, the use of electro-optic intensity modulators as described herein is a widely used and better performing solution.
A light processing module 14 for performing backward rayleigh scattering on the probe light;
as shown in fig. 5, the optical processing module 14 includes an optical amplifier 141, an optical circulator 142, a single-mode optical fiber 143, and an attenuator 144.
An optical amplifier 141 for performing power amplification processing on the probe light received from the modulation module 13; the optical circulator 142 has three ports, wherein the port 1 is connected to the optical amplifier 141, and is configured to receive the probe optical signal subjected to power amplification by the optical amplifier 141; the No. 2 port is connected with the single-mode fiber 143, and the detection light is output to the single-mode fiber 143 connected to the No. 2 port of the optical circulator 142 to generate backward Rayleigh scattering detection light to be output backward along the fiber; the attenuator 144 is connected to the port No. 3, and is configured to receive the backward rayleigh scattering probe light generated on the single-mode fiber 143 from the port No. 3 of the optical circulator 142, perform power attenuation processing, and output the power attenuation processing to the photodetector.
A photodetector 15 for converting the optical signal after the backward rayleigh scattering into an electrical signal;
the sampling rate of the photodetector 15 needs to satisfy nyquist sampling law, that is, the sampling rate is twice that of the arbitrary waveform generator, when the photodetector converts the optical signal into the electrical signal, so that the subcarrier orthogonality is prevented from being destroyed, and the decoding cannot be performed. The photodetector sample rate used here is 9GHz.
An electric signal processing module 16, configured to perform analog-to-digital conversion and average processing on the electric signal to obtain a signal to be decoded;
the electrical signal processing module 16 is an analog-to-digital converter, and is configured to convert an electrical signal received from the photodetector 15 into a digital signal, and collect and average the digital signal multiple times to obtain a signal to be decoded. The signal processing after this module operates in the digital domain. In order to make each orthogonal subcarrier immune to noise, the average number of times needs to be as high as possible, where the average number of times is 2048 times.
And the decoding module 17 is configured to decode the signal to be decoded according to the encoding and decoding method of the OFDM-Simplex code, so as to obtain an OTDR curve.
The working process of the optical time domain reflectometer provided by the invention is as follows: a laser in the optical time domain reflectometer emits 1550nm continuous laser, the coded detection sequence is input into an arbitrary waveform generator, the laser passes through a modulation module formed by the arbitrary waveform generator and an electro-optical modulator, the continuous laser is modulated into detection light carrying OFDM-Simplex coding information, and the detection light is amplified to required power by an optical amplifier and then is injected into a No. 1 port of the optical circulator; the detection light is output to a single mode fiber connected to a No. 2 port of the optical circulator; the back scattered light generated by the detection light in the optical fiber is transmitted backwards along the optical fiber, enters an attenuator from a 3 port of the optical fiber circulator to be attenuated to required power, and then reaches a photoelectric detector to convert an optical signal into an electric signal; and finally, finishing the repeated collection and the average of the signals by the analog-to-digital converter, and outputting the result to a decoding module for decoding the signals to obtain a decoded OTDR curve.
In one embodiment, as shown in fig. 6, the results obtained by using 31, 15, and 7 bits of OFDM-Simplex codes and 50ns monopulses as OTDR probe light respectively, it is obvious from the graph that the signal-to-noise ratio of the coded OTDR curve is greatly improved compared with that of the monopulse OTDR curve, and the signal-to-noise ratio is further improved with the increase of the code length.
In summary, the invention discloses a coding and decoding method, a system and an optical time domain reflectometer of an OFDM-Simplex code, compared with the traditional single pulse OTDR, the signal to noise ratio of the coded OTDR curve under the same pulse width and the same average times is higher, and the coded OTDR based on the orthogonal frequency division multiplexing technology does not need to transmit coded detection light to an optical fiber for multiple times and receive scattered signals for multiple times; only one coded detection light is transmitted into the optical fiber, and the coded detection light is received again, so that the time efficiency of the system is greatly improved.
In this specification, each embodiment is described in a progressive manner, and all the embodiments are directly the same or similar parts referring to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments. It should be noted that, any combination of the technical features of the foregoing embodiments may be used, and for brevity, all of the possible combinations of the technical features of the foregoing embodiments are not described, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The foregoing examples represent only a few preferred embodiments of the present application, which are described in more detail and are not thereby to be construed as limiting the scope of the invention. It should be noted that modifications and substitutions can be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and substitutions should also be considered to be within the scope of the present application. Therefore, the protection scope of the patent application is subject to the protection scope of the claims.
Claims (10)
1. A method for encoding and decoding an OFDM-Simplex code, the method comprising:
generating an L-order Simplex coding matrix according to the Hadamard matrix, and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted;
expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix;
performing parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal;
performing serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix;
performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix;
and performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve.
2. The method for encoding and decoding an OFDM-Simplex code according to claim 1, wherein the generating an L-order Simplex coding matrix according to a Hadamard matrix and transforming the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted comprises the steps of:
transforming the Hadamard matrix through the following formula (2) to obtain an L+1-order Hadamard matrix;
wherein the formula (1) is a Hadamard matrix H L ；
Removing the first row and the first column of the L+1-order Hadamard matrix, changing the element '1' into '0', and changing the '1' into '1', so as to obtain the L-order Simplex coding matrix; the L-order Simplex coding matrix has the following form:
the L-order Simplex coding matrix S L Constructing a pulse sequence to obtain the L-order pulse matrix to be transmitted:
wherein eta 1 (t)、η 2 (t)…η L (t) consists of pulses P (t) of width τ.
3. The method for encoding and decoding an OFDM-Simplex code according to claim 2, wherein the expanding the column length of the L-order pulse matrix to be transmitted and performing Hermitian symmetric transform and IFFT operation to obtain an OFDM modulation matrix comprises the following steps:
expanding the column length of the L-order pulse matrix to be transmitted into the number of points of the IFFT operation;
performing the Hermitian symmetric transformation on the expanded L-order pulse matrix to be transmitted to obtain a matrix with a Hermitian symmetric structureThe matrix->Has the following form:
wherein eta * A conjugate vector representing η;
the matrix is processedThe following calculation is performed to obtain the coordinate position and the rest positions are complemented with 0 to obtain the matrix +.>The calculation formula is as follows:
C co ＝L IFFT -C ca +2 (7)
wherein C is ca And C co Respectively representing an original signal coordinate set and a conjugated signal coordinate set; c (C) cL The expression interval is [1, L]Coordinate vectors with an interval of 1; l (L) ca Representing the number of subcarriers, numerically equal to the coding length L; l (L) IFFT Representing the number of IFFT points;representing a down-rounding function for element x;
the matrixThe form of (2) is as follows:
wherein z (t) represents a zero vector; eta (t) is defined by C ca Composition; η (t) * From C co Composition;
for the matrixAnd performing IFFT operation on each column of the OFDM modulation matrix.
4. A method for encoding and decoding an OFDM-Simplex code according to claim 3, wherein the performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix comprises the following steps:
performing FFT operation on each column of the parallel signal matrix to obtain a matrix R (t), wherein R (t) has the following form:
wherein ca represents the original signal start coordinate, co represents the conjugate signal start coordinate,is the vector of the original signal and is used for generating the vector of the original signal,is a conjugate signal vector;
selecting an original signal vector for the matrix R (t) to obtain a matrix R c (t)：
For the matrix R c Performing modular operation on the elements in (t) to obtain the OFDM decoding matrix r (t):
wherein e N (t) represents noise carried each time a signal is received, n=1, 2, L, ψ N (t) represents the OTDR curve function obtained after different delays are injected into the fiber.
5. The method for encoding and decoding an OFDM-Simplex code according to claim 4, wherein the performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve comprises the following steps:
calculating the L-order Simplex coding matrix S L Is the inverse of the matrix of (a)
Inverting the matrixMultiplying the OFDM decoding matrix r (t), performing inverse Hadamard transformation, performing time shift and accumulation by taking pulse width tau as a unit, and finally averaging to obtain the OTDR curve:
6. the encoding and decoding system of the OFDM-Simplex code is characterized by comprising a first matrix module, a first operation module, a coding module, a second matrix module, a second operation module and a decoding module; wherein,
the first matrix module is used for generating an L-order Simplex coding matrix according to the Hadamard matrix and converting the L-order Simplex coding matrix into an L-order pulse matrix to be transmitted;
the first operation module is used for expanding the column length of the L-order pulse matrix to be transmitted, and performing Hermitian symmetrical transformation and IFFT operation to obtain an OFDM modulation matrix;
the coding module is used for carrying out parallel/serial conversion on the OFDM modulation matrix to obtain an OFDM-Simplex coded signal;
the second matrix module is used for carrying out serial/parallel conversion on the OFDM-Simplex coded signal to obtain a parallel signal matrix;
the second operation module is used for performing FFT operation and modulo operation on the parallel signal matrix to obtain an OFDM decoding matrix;
and the decoding module is used for performing Simplex decoding on the OFDM decoding matrix to obtain an OTDR curve.
7. An optical time domain reflectometer, comprising:
the laser is used for inputting continuous laser to the modulation module;
a sequence generation module, configured to obtain an OFDM-Simplex coding sequence according to the coding and decoding method of any one of claims 1-5;
the modulation module is used for carrying out orthogonal frequency division multiplexing on the continuous laser according to the OFDM-Simplex coding sequence and modulating the continuous laser into detection light carrying OFDM-Simplex coding information;
the light processing module is used for performing backward Rayleigh scattering on the detection light;
the photoelectric detector is used for converting the optical signal after the backward Rayleigh scattering into an electric signal;
the electric signal processing module is used for carrying out analog-to-digital conversion and average processing on the electric signal to obtain a signal to be decoded;
a decoding module, configured to decode the signal to be decoded according to the coding and decoding method of any one of claims 1-5, so as to obtain an OTDR curve.
8. An optical time domain reflectometer as in claim 7, wherein: the modulation module comprises an arbitrary waveform generator and an electro-optic modulator; wherein,
the random waveform generator is used for generating a modulation signal according to the OFDM-Simplex coding sequence;
the electro-optical modulator is used for carrying out orthogonal frequency division multiplexing on the input continuous laser through the modulation signal and modulating the continuous laser into detection light carrying OFDM-Simplex coding information.
9. An optical time domain reflectometer as in claim 7, wherein: the optical processing module comprises an optical amplifier, an optical circulator and a single-mode optical fiber; wherein,
the optical amplifier is used for performing power amplification processing on the detection light received from the modulation module;
the optical circulator is used for receiving the amplified detection light from the optical amplifier and outputting the detection light to the single-mode optical fiber to generate backward Rayleigh scattered detection light.
10. An optical time domain reflectometer as in claim 9, wherein: the light processing module further comprises an attenuator; wherein,
the attenuator is used for receiving the detection light subjected to backward Rayleigh scattering from the optical circulator, carrying out power attenuation treatment and outputting the detection light to the photoelectric detector.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210818207.4A CN115296729B (en) | 2022-07-12 | 2022-07-12 | Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210818207.4A CN115296729B (en) | 2022-07-12 | 2022-07-12 | Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN115296729A CN115296729A (en) | 2022-11-04 |
| CN115296729B true CN115296729B (en) | 2024-01-19 |
Family
ID=83822225
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202210818207.4A Active CN115296729B (en) | 2022-07-12 | 2022-07-12 | Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN115296729B (en) |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010031131A1 (en) * | 2008-09-18 | 2010-03-25 | Commonwealth Scientific And Industrial Research Organisation | Vector quantization in wireless communication |
| CN102636251A (en) * | 2012-05-15 | 2012-08-15 | 电子科技大学 | Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof |
| CN103048070A (en) * | 2013-01-17 | 2013-04-17 | 广东电网公司电力调度控制中心 | Stress monitoring method of distributed optical fiber system |
| CN106953687A (en) * | 2017-01-19 | 2017-07-14 | 中铁第四勘察设计院集团有限公司 | Method is determined based on the Simplex POTDR systems encoded and its signal |
| CN110243493A (en) * | 2019-06-03 | 2019-09-17 | 太原理工大学 | Brillouin optical time-domain reflectometer device and method based on super continuous spectrums |
| CN112713929A (en) * | 2020-12-02 | 2021-04-27 | 广东工业大学 | Optical time domain reflectometer based on chirped pulses |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7167651B2 (en) * | 2000-09-26 | 2007-01-23 | Celight, Inc. | System and method for code division multiplexed optical communication |
-
2022
- 2022-07-12 CN CN202210818207.4A patent/CN115296729B/en active Active
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010031131A1 (en) * | 2008-09-18 | 2010-03-25 | Commonwealth Scientific And Industrial Research Organisation | Vector quantization in wireless communication |
| CN102636251A (en) * | 2012-05-15 | 2012-08-15 | 电子科技大学 | Phase sensitivity light time domain reflection system and method for improving SNR (signal to noise ratio) thereof |
| CN103048070A (en) * | 2013-01-17 | 2013-04-17 | 广东电网公司电力调度控制中心 | Stress monitoring method of distributed optical fiber system |
| CN106953687A (en) * | 2017-01-19 | 2017-07-14 | 中铁第四勘察设计院集团有限公司 | Method is determined based on the Simplex POTDR systems encoded and its signal |
| CN110243493A (en) * | 2019-06-03 | 2019-09-17 | 太原理工大学 | Brillouin optical time-domain reflectometer device and method based on super continuous spectrums |
| CN112713929A (en) * | 2020-12-02 | 2021-04-27 | 广东工业大学 | Optical time domain reflectometer based on chirped pulses |
Non-Patent Citations (2)
| Title |
|---|
| 分布式光纤传感器关键技术研究;孙茜子;《中国博士学位论文全文数据库信息科技辑》;第I140-10页 * |
| 基于信道估计的布里渊分布式光纤传感技术;赵灿;《中国博士学位论文全文数据库信息科技辑》;第I140-28页 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN115296729A (en) | 2022-11-04 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN109282839B (en) | Distributed optical fiber sensing system and method based on multi-pulse and multi-wavelength | |
| CN109489801B (en) | Multi-core optical fiber distributed acoustic wave sensing system based on space division multiplexing | |
| US5000568A (en) | Spread spectrum optical time domain reflectometer | |
| CN109297425B (en) | Brillouin optical time domain reflectometer modulated by physical random number | |
| CN106768277B (en) | A kind of demodulation method of distributed optical fiber vibration sensing device | |
| CN109891197B (en) | Brillouin scattering measurement method and Brillouin scattering measurement device | |
| JP7086200B2 (en) | High-speed frequency hopping DAS interrogation with AOM gate recirculation loop and frequency shift receiver LO | |
| WO2009097736A1 (en) | Chaotic optical time domain reflectometer and measuring method thereof | |
| EP3414542B1 (en) | Optical time domain reflectometry | |
| WO2012146078A1 (en) | Method and device for detecting optical time-domain detection signals | |
| Cui et al. | Interference-fading-suppressed pulse-coding Φ-OTDR using spectrum extraction and rotated-vector-sum method | |
| Shiloh et al. | Highly-sensitive distributed dynamic strain sensing via perfect periodic coherent codes | |
| CN108955733A (en) | A method of it is encoded based on assembled pulse and improves BOTDA system signal noise ratio | |
| CN115296729B (en) | Encoding and decoding method and system of OFDM-Simplex code and optical time domain reflectometer | |
| JP2023526842A (en) | Distributed Acoustic Sensing Using Multiband Time-Gated Digital Orthogonal Frequency-Domain Reflectometry | |
| Zhao et al. | SNR-enhanced fast BOTDA combining channel estimation technique with complementary pulse coding | |
| Feng et al. | The OTDR with high dynamic range based on LFM signal and FDM | |
| JP6824861B2 (en) | OTDR device | |
| CN114878141B (en) | Airborne optical cable connection fault positioning method and system | |
| CN115900787A (en) | Method and system for realizing spectral domain reflectometer | |
| EP0864081B1 (en) | Device for interrogating an optical fibre network | |
| JPS63145938A (en) | Time area reflectometer | |
| CN115112219A (en) | Long-distance optical fiber distributed vibration sensing device and working method | |
| WO2020177644A1 (en) | Multi-layer encoding of optical signals | |
| Muhammad et al. | Hybrid Coding Technique for Pulse Detection in an Optical Time Domain Reflectometer. |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PB01 | Publication | ||
| PB01 | Publication | ||
| SE01 | Entry into force of request for substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |