CN114337805A

CN114337805A - Signal processing method, device and system

Info

Publication number: CN114337805A
Application number: CN202011057697.8A
Authority: CN
Inventors: 陆佳宁; 周概; 董振华
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2022-04-12
Also published as: WO2022068702A1

Abstract

The application discloses a signal processing method, a signal processing device and a signal processing system, and belongs to the field of optical communication. The method comprises the following steps: acquiring a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relation parameter in an optical transmission link, wherein the relation parameter is used for reflecting the relation between the correlation of an upper sideband and a lower sideband of a signal in the optical transmission link and frequency offset; acquiring a second relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a signal-to-noise ratio in the optical transmission link; acquiring a target relation parameter of a target signal received through an optical transmission link; acquiring a target signal-to-noise ratio of a target signal; and determining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relation parameter, the target signal-to-noise ratio, the first relation and the second relation. The method and the device can effectively distinguish the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to the signal. The method is used for detecting the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio.

Description

Signal processing method, device and system

Technical Field

The present application relates to the field of optical communications, and in particular, to a method, an apparatus, and a system for processing a signal.

Background

In an optical Transmission system, an operator may detect an optical signal-to-noise ratio (OSNR) in an optical Transmission link according to an OSNR monitoring device to evaluate a Transmission Quality of the optical Transmission link (Quality of Transmission, QoT). However, the optical signal-to-noise ratio actually includes a linear signal-to-noise ratio caused by an optical amplifier or the like and a nonlinear signal-to-noise ratio caused by the optical transmission link itself or the like. At present, a signal processing method is needed to effectively distinguish a linear snr and a nonlinear snr corresponding to a signal.

Disclosure of Invention

The embodiment of the application provides a signal processing method, a signal processing device and a signal processing system. The technical scheme is as follows:

in a first aspect, a signal processing method is provided, the method including:

acquiring a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relation parameter in an optical transmission link, wherein the relation parameter is used for reflecting the relation between the correlation of an upper sideband and a lower sideband of a signal in the optical transmission link and frequency offset; acquiring a second relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a signal-to-noise ratio in the optical transmission link; acquiring a target relation parameter of a target signal received through the optical transmission link; acquiring a target signal-to-noise ratio of the target signal; and determining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relation parameter, the target signal-to-noise ratio, the first relation and the second relation.

The method and the device determine the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio of the target signal by establishing a first relation among the linear signal-to-noise ratio, the nonlinear signal-to-noise ratio and the reduction rate in the optical transmission link and a second relation among the linear signal-to-noise ratio, the nonlinear signal-to-noise ratio and the signal-to-noise ratio in the optical transmission link and adopting the actually obtained target relation parameter and the target signal-to-noise ratio based on the two relations, thereby realizing the effective distinguishing of the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio of the signal.

In an optional implementation manner, the first relationship is characterized by independent variables of the linear snr and the nonlinear snr, the dependent variables of the relationship parameter are first relations, the second relationship is characterized by independent variables of the linear snr and the nonlinear snr, and the dependent variables of the signal-to-noise ratio are second relations, and the process of determining the linear snr corresponding to the target signal and the nonlinear snr corresponding to the target signal based on the target relationship parameter, the target snr, the first relation and the second relation includes: substituting the target relation parameter into the first relation, substituting the target signal-to-noise ratio into the second relation, and obtaining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal by solving a linear equation system.

In the embodiment of the application, the linear signal-to-noise ratio corresponding to the target signal and the nonlinear signal-to-noise ratio corresponding to the target signal are obtained in an equation solving mode, the obtaining mode is simple and fast, and the operation efficiency is high.

In an optical transmission link, chromatic dispersion causes a certain time delay to signals with different frequencies, and upper and lower sidebands of a target signal correspond to different frequencies, so that the upper and lower sidebands generate time domain offset in the transmission process, which affects the accuracy of the correlation of the upper and lower sidebands of the determined target signal, thereby affecting the detection accuracy of target relationship parameters. Therefore, after receiving the digital signal, the signal processing apparatus performs chromatic dispersion compensation on the received digital signal to obtain a chromatic dispersion compensated digital signal. And then, the signal processing device detects the relation parameter of the digital signal after chromatic dispersion compensation to obtain a target relation parameter. Therefore, the digital signal is calibrated in time, and the accuracy of the acquired target relation parameter can be improved. The chromatic dispersion compensation can be implemented by using a time domain digital filter or a frequency domain digital equalizer to modify the phase of the received signal.

In an alternative implementation, the process of obtaining a first relationship between a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relationship parameter in an optical transmission link includes: determining a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different; obtaining a relation parameter of each signal in the at least three signals; and fitting to obtain the first relation based on the at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the obtained relation parameters. Illustratively, the at least three signals differ by at least one parameter selected from: transmit power, amplification of the corresponding optical amplifier, type of the corresponding optical amplifier, or actively loaded noise.

The correlation of the upper sideband and the lower sideband of the signal spectrum is damaged due to linear noise and nonlinear noise. However, linear noise is flat in frequency spectrum, and non-linear noise is not flat in frequency spectrum, so when frequency offset exists, the influence of the linear noise and the non-linear noise on the correlation of the upper and lower sidebands of the frequency spectrum has different trends, and therefore a bivariate linear equation can be established to reflect the first relation between the correlation of the linear signal-to-noise ratio and the non-linear signal-to-noise ratio and the frequency. For example, the first relationship may be represented by the following first relationship:

wherein A represents a relation parameter, SNR_linearRepresenting linear signal-to-noise ratio, SNR_nonlinearRepresenting the nonlinear signal-to-noise ratio, B₁Represents the degree of contribution of linear noise to the relation parameter A, B₂Represents the degree of contribution of nonlinear noise to the relation parameter A, B₃Indicating the bias introduced by other intrinsic factors. Illustratively, the inherent factors include transmitter-induced noise, receiver-induced noise, and/or resolution of the receiving end (e.g., a coherent receiver).

In a first alternative, the process of obtaining the relation parameter of each of the at least three signals may include: and loading at least two different frequency offsets on the first signal in a digital domain respectively to obtain at least two sub-signals, wherein the first signal is any one of the at least three signals, and the relation parameter of the first signal is used for reflecting the relation between the correlation of the upper sideband and the lower sideband of the first signal and the frequency offsets. Determining a correlation of an upper sideband and a lower sideband of each of at least two sub-signals; and fitting to obtain a relation parameter of the first signal based on the at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each of the at least two seed signals.

In a second alternative, the process of obtaining the relation parameter of each of the at least three signals may include: at least two sub-signals are received, where the at least two sub-signals are signals obtained by loading at least two different frequency offsets on the first signal, for example, signals obtained by loading at least two different frequency offsets on the first signal by a coherent receiver. The first signal is any one of the at least three signals, and the relation parameter of the first signal is used for reflecting the relation between the correlation of the upper sideband and the lower sideband of the first signal and the frequency offset. Determining a correlation of an upper sideband and a lower sideband of each of at least two sub-signals; and fitting to obtain a relation parameter of the first signal based on the at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each of the at least two seed signals.

In the embodiment of the present application, the upper sideband component (i.e., a portion of the upper sideband) and the lower sideband component (i.e., a portion of the lower sideband) of each seed signal may be obtained by filtering, and then the correlation between the upper sideband component and the lower sideband component is determined. In this way, the overall correlation of the upper and lower sidebands can be reflected by the correlation of the portions of the upper and lower sidebands, reducing the computational complexity of the correlation.

For example, the process of determining the correlation of the upper and lower sidebands of each of the at least two sub-signals comprises:

for each sub-signal in the at least two sub-signals, acquiring an upper sideband component obtained by filtering an upper sideband component of the sub-signal, acquiring a lower sideband component obtained by filtering a lower sideband component of the sub-signal, and taking the correlation between the upper sideband component and the lower sideband component as the correlation between the upper sideband and the lower sideband of the sub-signal; wherein, the filtering positions of the upper sideband component filtering of the at least two seed signals are the same, and the filtering bandwidths are the same; the filtering positions of the lower sideband components of the at least two sub-signals are the same, and the filtering bandwidths are the same; the filtering bandwidth of the upper sideband component filtering of the same sub-signal is the same as that of the lower sideband component filtering, so that the correlation of the upper sideband component and the lower sideband component can be ensured to be determined under the same filtering bandwidth, the upper sideband component and the lower sideband component do not need to be aligned on the bandwidth, and the calculation complexity of the correlation is reduced.

In an optional implementation, the process of obtaining a second relationship between a linear snr, a nonlinear snr, and a snr in an optical transmission link includes:

determining a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different; acquiring the signal-to-noise ratio of each of the at least three signals; and fitting to obtain the second relation based on the at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the acquired signal-to-noise ratios. Illustratively, the at least three signals differ by at least one parameter selected from: transmit power, amplification of the corresponding optical amplifier, type of the corresponding optical amplifier, or actively loaded noise.

Since both linear noise and nonlinear noise have an effect on the overall signal-to-noise ratio (e.g., the signal-to-noise ratio is determined by the SNR monitoring method based on the correlation between the upper and lower sidebands of the frequency spectrum of the signal) in the absence of frequency offset, but the nonlinear noise in the upper and lower sidebands does not have a correlation as gaussian noise, nor has a very strong correlation as the signal itself, the nonlinear noise does not contribute to the overall signal-to-noise ratio, but does not contribute as much as the linear noise. A first equation of two-fold can be established to reflect the second relationship between the linear snr and the nonlinear snr. For example, the second relationship may be represented by the following second relationship:

wherein the SNR_measRepresenting signal-to-noise ratio, SNR_linearRepresenting linear signal-to-noise ratio, SNR_nonlinearRepresenting the nonlinear signal-to-noise ratio, C₁Representing linearityNoise to signal-to-noise ratio SNR_measDegree of contribution of C₂Representing nonlinear noise versus nonlinear signal-to-noise ratio SNR_nonlinearDegree of contribution of C₃Indicating the bias introduced by other intrinsic factors.

Before fitting, at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios are carried out, and the obtained signal-to-noise ratios are known numbers; c₁、C₂And C₃Is an unknown number. By substituting at least three pairs of linear and nonlinear SNR's, and the obtained SNR's into the second relation, C can be obtained by fitting₁、C₂And C₃. Fitting to obtain C₁、C₂And C₃Substituting the second relational expression into the first relational expression to obtain the first relational expression with known coefficient.

In an alternative implementation, the relationship parameter is a rate of decrease, which is a rate of decrease of the correlation of the upper and lower sidebands of the signal in the optical transmission link with increasing frequency offset.

The relationship between the correlation and the frequency offset can be expressed as a cubic function. The cubic function can more accurately reflect the relation between the correlation and the frequency offset, and the accuracy of the final fitting result can be effectively improved by describing the relation between the correlation and the frequency offset through the cubic function. Illustratively, the cubic function is a first formula, which is: y is Ax³+ Z, where a denotes the rate of decrease, y denotes the correlation, x denotes the frequency offset, and Z denotes the bias introduced by other intrinsic factors, which is not zero.

In a second aspect, there is provided a signal processing apparatus, the apparatus comprising: comprising at least one module operable to implement the signal processing method as provided by the first aspect above or various possible implementations of the first aspect.

In a third aspect, a signal processing system is provided, the signal processing system comprising: a coherent receiver and a signal processing apparatus as claimed in any one of the preceding second aspects; the coherent receiver is used for receiving an optical signal from an optical transmission link, converting the received optical signal into a digital signal, and sending the converted digital signal to the signal processing device.

In an alternative implementation, the coherent receiver includes:

the local oscillator laser is used for generating coherent light; the polarization optical splitter is used for splitting an optical signal transmitted by the optical transmission link into first polarized light and second polarized light which are vertical to each other, and splitting the coherent light into third polarized light and fourth polarized light which are vertical to each other;

two 90 ° mixers, one 90 ° mixer for mixing the first polarized light and the third polarized light, and the other 90 ° mixer for mixing the second polarized light and the fourth polarized light; the optical detector is used for converting optical signals output by the two 90-degree frequency mixers into analog current; the filter is used for filtering the analog current to obtain an electric signal corresponding to the target signal; and the analog-to-digital converter is used for converting the electric signal corresponding to the target signal into a digital signal. The optical detector can be a balanced optical detector, and the balanced optical detector can be used for realizing the cancellation of noise and reducing the noise in the output analog current.

Correspondingly, the signal processing device comprises: a first digital band-pass filter for filtering an upper band component of the received signal; a second digital bandpass filter for filtering a lower sideband component of the received signal.

In another alternative implementation, the system further includes: the number of the coherent receivers is 2, the optical splitter is configured to receive an optical signal from an optical transmission link, divide the received optical signal into 2 optical signals, and input the optical signals to 2 coherent receivers, respectively, where one coherent receiver of the 2 coherent receivers is configured to perform upper sideband component filtering, and the other coherent receiver is configured to perform lower sideband component filtering.

Optionally, each of the aforementioned coherent receivers comprises:

two 90 ° mixers, one 90 ° mixer for mixing the first polarized light and the third polarized light, and the other 90 ° mixer for mixing the second polarized light and the fourth polarized light; the optical detector is used for converting optical signals output by the two 90-degree frequency mixers into analog current; the low-pass filter is used for filtering the analog current to obtain an electric signal corresponding to the sideband component; and the analog-to-digital converter is used for converting the electric signal of the corresponding sideband component into a digital signal.

In an alternative example, the aforementioned coherent receiver is further configured to load a frequency offset for the received optical signal. In an example, at least two different frequency offsets are applied to the received signal to obtain at least two sub-signals.

Optionally, when the signal processing system comprises 2 coherent receivers, the 2 coherent receivers are used to load the frequency offset for the received optical signal. For example, if the center frequency of the optical signal is T, the baud rate of the optical signal is E, and the frequency offset to be loaded is L, the center frequency of the local oscillator laser of one coherent receiver corresponding to the upper sideband of the signal is adjusted to be T + L + E/2, so that the position of the signal spectrum of the electrical signal corresponding to the upper sideband of the optical signal moves forward by L relative to the origin; and adjusting the center frequency of a local oscillator laser of the other coherent receiver corresponding to the lower sideband of the signal to be T + L-E/2, so that the position of the signal spectrum of the electric signal corresponding to the lower sideband of the optical signal can be moved forward by L relative to the origin. When the two coherent receivers are further used for respectively performing upper sideband component filtering and lower sideband component filtering, the positions of the signal spectrums of the electric signals corresponding to the upper sideband component and the lower sideband component obtained by final filtering are both shifted forward by L relative to the origin.

Illustratively, the system further comprises: a power measurement device for receiving an optical signal from the optical transmission link and measuring the power of a target signal in the optical signal.

The local oscillator laser has multiple adjustable center frequencies.

In a fourth aspect, the present application provides a computer device comprising a processor and a memory. The memory stores computer instructions; the processor executes the computer instructions stored by the memory to cause the computer device to perform the methods provided by the first aspect or the various possible implementations of the first aspect, to cause the computer device to deploy the signal processing apparatus provided by the second aspect or the various possible implementations of the second aspect.

In a fifth aspect, the present application provides a computer-readable storage medium having stored therein computer instructions that instruct a computer device to execute the method provided by the above first aspect or various possible implementations of the first aspect, or instruct the computer device to deploy the signal processing apparatus provided by the above second aspect or various possible implementations of the second aspect.

In a sixth aspect, the present application provides a computer program product comprising computer instructions stored in a computer readable storage medium. A processor of a computer device may read the computer instructions from a computer-readable storage medium, and the processor executes the computer instructions to cause the computer device to perform the method provided by the above first aspect or various possible implementations of the first aspect, to cause the computer device to deploy the signal processing apparatus provided by the above second aspect or various possible implementations of the second aspect.

In a seventh aspect, a chip is provided, which may comprise programmable logic circuits and/or program instructions, and which, when run, is adapted to implement the signal processing method according to any of the first aspect.

In an eighth aspect, an optical transmission system is provided, which includes the signal processing system of any one of the foregoing third aspects. Illustratively, the optical transmission system further comprises one or more optical devices, such as WSSs and/or optical amplifiers.

The technical scheme provided by the embodiment of the application has the following beneficial effects:

In addition, the embodiment of the application can simultaneously acquire the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to the signal, the acquisition efficiency of the signal-to-noise ratio is high, and the staff can conveniently and effectively analyze the transmission quality of the optical transmission link.

Further, the signal processing method provided in the embodiment of the present application does not limit the modulation format supported by the DSP, and can support monitoring of the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio of signals of different modulation formats, thereby improving monitoring flexibility.

Drawings

Fig. 1 is a schematic application environment diagram of an optical transmission system related to a signal processing method according to an embodiment of the present application;

fig. 2 is a schematic application environment diagram of an optical transmission system according to another signal processing method provided in the embodiment of the present application;

fig. 3 is a schematic flowchart of a signal processing method according to an embodiment of the present application;

FIG. 4 is a graph illustrating wavelength versus optical power of a signal according to an embodiment of the present disclosure;

fig. 5 is a schematic diagram illustrating a frequency offset loading principle of an optical transmission system according to an embodiment of the present application;

fig. 6 is a schematic diagram illustrating a frequency offset loading principle of an optical transmission system according to another signal processing method provided in the embodiment of the present application;

fig. 7 is a schematic diagram illustrating a filtering principle of an optical transmission system according to a signal processing method provided in an embodiment of the present application;

fig. 8 is schematic diagrams illustrating filtering principles of an optical transmission system according to another signal processing method provided in the embodiment of the present application;

fig. 9 is a schematic diagram of a filtering principle of an optical transmission system according to an embodiment of the present application, based on the signal processing method in fig. 8;

FIG. 10 is a graph illustrating a fitting result of a falling rate of a first signal according to an embodiment of the present disclosure;

FIG. 11 is a schematic diagram illustrating a method for calculating a signal-to-noise ratio of a signal by using out-of-band interpolation according to an embodiment of the present disclosure;

FIG. 12 is a schematic diagram of an embodiment of the present application for calculating a signal-to-noise ratio of a signal using an error vector magnitude meter algorithm;

fig. 13 is a schematic structural diagram of a signal processing apparatus according to an embodiment of the present application;

fig. 14 is a schematic structural diagram of a first relationship obtaining module according to an embodiment of the present application;

FIG. 15 is a possible basic hardware architecture of a computer device provided by an embodiment of the present application;

fig. 16 is a schematic structural diagram of a signal processing system according to an embodiment of the present application;

fig. 17 is a schematic structural diagram of another signal processing system provided in an embodiment of the present application;

fig. 18 is a schematic structural diagram of another signal processing system provided in an embodiment of the present application;

fig. 19 is a schematic structural diagram of another signal processing system according to an embodiment of the present application;

fig. 20 is a schematic structural diagram of a signal processing system according to another embodiment of the present application;

fig. 21 is a schematic structural diagram of another signal processing system according to another embodiment of the present application;

fig. 22 is a schematic structural diagram of another signal processing system according to another embodiment of the present application.

Detailed Description

In order to make the principle and technical solution of the present application clearer, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

Optical fiber (also called line fiber) communication is a communication mode in which optical signals are used as information carriers and optical fibers are used as transmission media. Fig. 1 and fig. 2 are schematic application environment diagrams of an optical transmission system (also referred to as an optical fiber communication system or an optical transmission network) related to a signal processing method provided in an embodiment of the present application. The optical transmission system is based on optical fiber communication, which includes one or more optical devices. Fig. 1 assumes that the optical transmission system includes 1 Wavelength Selective Switch (WSS) 101 and 1 optical amplifier 102; fig. 2 assumes that the optical transmission system includes 2 WSSs 101 and 2 optical amplifiers 102. Illustratively, the optical Amplifier 102 is an Erbium Doped Fiber Amplifier (EDFA) or a raman Amplifier.

The number and types of optical devices included in the optical transmission system are not limited in the embodiments of the present application. The optical transmission systems in fig. 1 and 2 may use Wavelength Division Multiplexing (WDM) technology to transmit service information through optical signals.

In the foregoing optical transmission system, the transmission quality of an optical signal can be evaluated by monitoring an optical signal-to-noise ratio (abbreviated as signal-to-noise ratio) of an optical transmission link (such as an optical fiber). Signal-to-noise ratio refers to the ratio of signal power to noise power. However, the current signal processing method can only monitor the overall signal-to-noise ratio of the optical transmission link, and cannot distinguish between a nonlinear signal-to-noise ratio and a linear signal-to-noise ratio, so that the transmission quality of the optical transmission link cannot be accurately evaluated. Further, when a problem occurs in the optical transmission system, the source of the problem cannot be accurately located based on the acquired signal-to-noise ratio.

The embodiment of the application provides a signal processing method, which can effectively distinguish a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio of an optical transmission link. The signal processing method can be applied to a signal processing device, and the signal processing device can be arranged on an optical transmission link of the optical transmission system. Fig. 3 is a schematic flow chart of a signal processing method provided in an embodiment of the present application, in practical application, there may be one or multiple signals to be processed by a signal processing device, for convenience of understanding of a reader, a signal processed by the signal processing device is taken as an example for description in a subsequent embodiment, and a processing process of other signals refers to a processing process of the signal. As shown in fig. 3, the method includes:

s201, the signal processing device obtains a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relation parameter in the optical transmission link, wherein the relation parameter is used for reflecting the relation between the correlation of an upper sideband and a lower sideband of a signal in the optical transmission link and frequency offset.

Illustratively, the relationship parameter is a rate of decrease, or other parameter that is a variation of the rate of decrease, of the correlation of the upper and lower sidebands of the signal in the optical transmission link with increasing frequency offset.

Assuming that the center frequency of a signal is FO, the upper edge frequency of the signal is the frequency higher than FO in the signal, and the lower edge frequency of the signal is the frequency lower than FO in the signal. Since the wavelength and frequency of the signal are inversely related. Accordingly, assuming that the center wavelength of a signal is λ, the upper sideband of the signal is wavelengths below λ in the signal and the lower sideband of the signal is wavelengths above λ in the signal. Fig. 4 is a schematic diagram of a relationship between a wavelength and an optical power of a signal according to an embodiment of the present disclosure. Taking the signal X in fig. 4 as an example, the wavelength range of the signal X is λ 1- α to λ 1+ α, the center wavelength is λ 1, the wavelength range of the upper sideband of the signal X is λ 1- α to λ 1, and the wavelength range of the lower sideband is λ 1 to λ 1+ α.

In the same optical transmission system, the correlation of the upper and lower sidebands of a signal transmitted in the optical transmission link varies with the frequency offset, e.g., the correlation of the upper and lower sidebands of the signal decreases with increasing frequency offset, and typically decreases at a fixed rate of decrease. The relationship between the aforementioned correlation and the frequency offset (also called the rate of change) is related to the linear snr and the nonlinear snr, and the relationship parameter can reflect the relationship. Therefore, the embodiment of the present application obtains the first relationship among the linear snr, the nonlinear snr and the relationship parameter in the optical transmission link, so as to determine the linear snr and the nonlinear snr of the signal (referred to as the target signal in the embodiment of the present application) to be measured in the optical transmission link in the subsequent process based on the first relationship.

In an alternative, the obtaining of the first relationship comprises the following steps:

a1, signal processing device determining lightAt least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios are obtained according to the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to each of at least three signals in a transmission link, and the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different. For example, the at least three signals include N signals, and the at least three pairs of linear and non-linear signal-to-noise ratios include N linear signal-to-noise ratios: SNR_linear1，SNR_linear2，…SNR_linearNAnd N nonlinear signal-to-noise ratios: SNR_nonlinear1，SNR_nonlinear2，…SNR_nonlinearN. Wherein the SNR_linear1And SNR_nonlinear1Is a pair of linear and non-linear signal-to-noise ratios, SNR_linear2And SNR_nonlinear2Is a pair of linear signal-to-noise ratio and nonlinear signal-to-noise ratio, and so on, and finally obtains N pairs of linear signal-to-noise ratio and nonlinear signal-to-noise ratio (SNR)_linear，SNR_nonlinear)。

The embodiment of the present application assumes that the at least three signals are all optical signals. The signal processing means may acquire at least three signals different from each other in the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio in various ways. The embodiments of the present application take several following alternative implementations as examples for illustration:

in a first alternative implementation, as can be seen from a noise accumulation formula and a non-linear theoretical equation of an optical amplifier (e.g., EDFA), the transmission power of the transmitter has an influence on both linear noise (also called gaussian noise) and non-linear noise of the transmitted signal, so that the at least three signals can be obtained by adjusting the transmission power of the transmitter on the optical transmission link. Accordingly, the transmission power of the at least three signals is different.

The noise accumulation formula of the optical amplifier is as follows:

is the power of ASE noise，NF_nIs the noise figure, G, of the nth optical amplifier (e.g. EDFA) in the optical transmission link_nIs the amplification gain of the nth optical amplifier (such as EDFA) in the optical transmission link, h is Planck constant, v is the channel center frequency, B_signalIs the signal bandwidth.

The aforementioned nonlinear theoretical equation satisfies: order to

The power of the nonlinear noise can be obtained by integrating the nonlinear power spectral density of the signal. And the nonlinear power spectral density of the signal is obtained by superposing and summing the nonlinear power spectral densities generated by each section of optical fiber in the optical transmission link. The nonlinear power spectral density generated by the nth section of optical fiber is as follows:

wherein the content of the first and second substances,

representing the nonlinear power spectral density produced by the nth section of fiber, G (f) is the power spectrum of the signal, f represents the frequency (also called frequency domain), L_n,α,β₂And γ are the length, loss coefficient, dispersion coefficient and nonlinear coefficient, respectively, of the nth segment of optical fiber, exp represents an exponential function with a natural constant e as the base.

An optical Transmission system may include a plurality of optical signal nodes, which may also be referred to as Transmission nodes (transport nodes), for example, Reconfigurable optical add-drop multiplexers (ROADMs). Each optical signal node includes one or more optical devices. For example, 1 WSS101 and 1 optical amplifier 102 of fig. 1 each belong to one optical signal node. The 2 WSSs 101 and the 2 optical amplifiers 102 in fig. 2 each belong to one optical signal node. The signal processing device may be provided in one optical signal node, or may be provided between two optical signal nodes. The transmitter refers to a transmitter upstream of the signal processing device, i.e. a signal emitted by the transmitter may pass through the signal processing device.

In an alternative example, the at least three signals are received by the signal processing device by manually adjusting the transmission power of the transmitter. In another alternative example, the signal processing apparatus may establish a communication connection with the transmitter, and control the transmitter to adjust the transmission power so that the signal processing apparatus receives the at least three signals respectively.

In a second alternative implementation, since the amplification factor of the optical amplifier has an influence on both linear noise and nonlinear noise of the signal on the optical transmission link, the at least three signals can be obtained by adjusting the amplification factor of the optical amplifier on the optical transmission link. Accordingly, the amplification factor of the optical amplifier corresponding to the at least three signals is different.

Since the amplification factor of the optical amplifier located after the signal processing means does not greatly affect the signal processed by the signal processing means, the aforementioned adjusted optical amplifier is an optical amplifier disposed upstream of the signal processing means. The optical amplifier has a plurality of different amplification factors, and the amplification factors of the optical amplifier can be adjusted. In an alternative example, the signal processing device receives the at least three signals respectively by manually adjusting the amplification factor of the optical amplifier. In another alternative example, the signal processing device may establish a communication connection with an optical amplifier, and control the optical amplifier to adjust the amplification factor so that the signal processing device receives the at least three signals respectively.

In a third alternative implementation, the at least three signals are obtained by adjusting the type of optical amplifier on the optical transmission link, since different types of optical amplifiers have an effect on both linear and nonlinear noise of the signals on the optical transmission link. Accordingly, the at least three signals correspond to different types of optical amplifiers.

Since the type of optical amplifier located after the signal processing means does not greatly affect the signal processed by the signal processing means, the aforementioned adjusted optical amplifier is an optical amplifier disposed upstream of the signal processing means. In an alternative example, the types of the optical amplifiers are adjusted in such a manner that different optical amplifiers are replaced by manual disassembly and assembly, so that the signal processing device receives the at least three signals respectively. In another alternative example, an optical amplifier switching device may be disposed on the optical transmission link before the signal processing device, and configured to switch different types of optical amplifiers to the optical transmission link, so that the signal processing device receives the at least three signals respectively. The optical amplifier switching device can be controlled manually or by a signal processing device.

In a fourth alternative implementation, the at least three signals are acquired by actively loading different noise on the optical transmission link. Accordingly, the actively loaded noise for the at least three signals is different.

As an example, a noise adding device may be disposed upstream of the signal processing device, and is used to actively load different noise into the optical transmission link, so that the signal processing device receives the at least three signals respectively. The noise adding device can be controlled manually or by a signal processing device.

In an alternative, the true value of the linear snr can be obtained by a conventional wave dropping method or a calculation formula of the linear snr. Taking the wave dropping method as an example, assuming that the first signal is any one of the at least three signals, the obtaining process of the linear signal-to-noise ratio of the first signal includes: the channel transmission of the first signal is turned on and the total power s1 of the signal and linear noise in the channel is read in the spectrometer at the receiving end. The channel transmission of the first signal is then turned off and the power of the linear noise in the channel is read by the spectrometer at the receiving end s 2. And calculating the two obtained powers to obtain a true value of the linear signal-to-noise ratio of the first signal. For example, the true value of the linear signal-to-noise ratio of the first signal is equal to s2/(s1-s 2).

In an alternative, the true value of the nonlinear snr can be calculated from a theoretical model, such as a gaussian noise model (GNmodel) or the aforementioned nonlinear theoretical equation. For another example, the theoretical model is a model that is modeled in the time domain and approximates additive gaussian noise.

Optionally, the non-linear signal-to-noise ratio can also be obtained by adding a pilot signal to the signal transmitted in the optical transmission link.

A2, the signal processing device acquires the relation parameter of each signal in at least three signals.

In the embodiments of the present application, it is assumed that the signal processing apparatus is a Digital Signal Processing (DSP) apparatus, which is in a Digital domain. Fig. 5 and fig. 6 are schematic diagrams illustrating a frequency offset loading principle of a signal processing system according to two signal processing methods according to embodiments of the present application. The signal processing system includes: a coherent receiver 301 and signal processing means 302. The coherent receiver 301 is configured to receive an optical signal from an optical transmission link, convert the received optical signal into a digital signal, and send the converted digital signal to the signal processing apparatus 302; the signal processing means 302 is arranged to process the received digital signal. The coherent receiver is adopted to acquire the optical signal, so that complete information of the optical signal can be reserved, and subsequent Chromatic Dispersion (CD) compensation and/or frequency offset loading can be realized conveniently. The complete information of the optical signal includes the intensity and phase of the signal. It should be noted that, in practical implementation, the coherent receiver may be replaced by another type of receiver as long as the complete information of the optical signal can be obtained through the other type of receiver.

As shown in fig. 5, it is assumed that the first signal is any one of at least three signals transmitted in the optical transmission link. In fig. 5, the relationship parameters of the first signal are obtained at the signal processing means by applying a frequency offset to the first signal in the digital domain, i.e. at the signal processing means. In fig. 6, the relationship parameters of the first signal are obtained at the signal processing apparatus by loading the first signal with frequency offset in the optical domain (i.e. at the coherent receiver).

As shown in fig. 5, the process of acquiring the relation parameter of the first signal includes:

a21, the signal processing device loads at least two different frequency offsets to the first signal in the digital domain, and at least two sub-signals are obtained.

Assuming that the first signal is an optical signal, the signal processing apparatus receives a digital signal converted from the first signal, and processes the digital signal to implement the processing of the first signal in the digital domain by the signal processing apparatus, where the processing includes: the first signal is loaded with at least two different frequency offsets in the digital domain, and the process of loading the frequency offsets can be realized by a specified algorithm. For example, the first sub-signal is assumed to be any one of at least two sub-signals obtained by adding at least two carrier frequency offsets to the first signal. The acquisition process of the first sub-signal comprises the following steps: determining an initial phase increment factor based on the baud rate of the first signal in the digital domain and a target frequency offset to be introduced, wherein the initial phase increment factor is the ratio of the target frequency offset to the baud rate of the first signal; and multiplying the code elements in the first signal in the digital domain by the corresponding phase increment factors respectively to obtain the first sub-signals. The phase increment factor corresponding to the qth code element is the product of the initial phase increment factor and q, q is more than or equal to 1 and less than or equal to m, and m is the number of the code elements in the first signal.

For example, assuming that the baud rate of the first signal in the digital domain is 28GHz, the target frequency offset to be introduced for the first sub-signal is 1GHz, and the phase increment factor is 1/28. Assume that the first signal is a signal sequence of length m: [ A ]₁,A₂,A₃,A₄…A_m]Wherein A is_qIs the q-th symbol in the first signal, q is greater than or equal to 1 and less than or equal to m. The process of frequency offset loading the first signal in the digital domain includes: multiplying the signal sequence by the corresponding phase increment factors in sequence to obtain the following signal sequence, wherein the signal sequence is the first subsignal:

[A₁×exp(1i×2π×(1/28)),A₂×exp(1i×2π×(2/28)),A₃×exp(1i×2π×(3/28)),A₄×exp(1i×2π×(4/28)),…A_m×exp(1i×2π×(m/28))]。

where i represents a complex field and exp represents an exponential function with a natural constant e as the base.

The process of acquiring other sub-signals except the first sub-signal in the at least two sub-signals may refer to the process of acquiring the first sub-signal, which is not described in detail in this embodiment of the present application.

A22, the signal processing device determines the correlation of the upper sideband and the lower sideband of each of at least two sub-signals.

In the embodiment of the present application, the upper sideband component (i.e., a portion of the upper sideband) and the lower sideband component (i.e., a portion of the lower sideband) of each seed signal may be obtained by filtering, and then the correlation between the upper sideband component and the lower sideband component is determined. In this way, the overall correlation of the upper and lower sidebands can be reflected by the correlation of the portions of the upper and lower sidebands, reducing the computational complexity of the correlation. Illustratively, the process includes: for each of at least two sub-signals, obtaining an upper sideband component obtained by filtering an upper sideband component of the sub-signal, obtaining a lower sideband component obtained by filtering a lower sideband component of the sub-signal, and taking the correlation between the upper sideband component and the lower sideband component as the correlation between the upper sideband and the lower sideband of the sub-signal. And the upper sideband component and the lower sideband component obtained by filtering are respectively a group of time domain signals in a digital domain. The correlation of the upper sideband component and the lower sideband component can be determined through a preset correlation algorithm.

Wherein, the filtering positions of the upper sideband component filtering of the at least two seed signals are the same, and the filtering bandwidths are the same; the filtering positions of the filtering of the lower sideband components of the at least two sub-signals are the same, and the filtering bandwidths are the same. I.e. the filtering position of the upper band component filtering is fixed. The filtering position of the lower sideband component filtering is fixed. The filtering bandwidth of the upper sideband component filtering of the same sub-signal is the same as that of the lower sideband component filtering, so that the correlation of the upper sideband component and the lower sideband component can be ensured to be determined under the same filtering bandwidth, the upper sideband component and the lower sideband component do not need to be aligned on the bandwidth, and the calculation complexity of the correlation is reduced.

The aforementioned process of acquiring the upper sideband component and the lower sideband component can be implemented in the digital domain, and can also be implemented in the optical domain. FIG. 7 and FIG. 8 are two signals provided by the embodiments of the present application, respectivelyThe processing method relates to a filtering principle schematic diagram of a signal processing system. The signal processing system includes: a coherent receiver 301 and signal processing means 302. The functions of the coherent receiver 301 and the signal processing means 302 refer to the aforementioned fig. 5 and 6. As shown in fig. 7, taking the first sub-signal as an example, the upper sideband component and the lower sideband component are obtained by performing upper sideband component filtering and lower sideband component filtering on the first sub-signal in the digital domain (i.e. at the signal processing apparatus) in fig. 7. In an alternative implementation, the signal processing means may perform the filtering of the upper and lower sidebands by a digital band-pass filter (band-pass filter). The digital band-pass filter is used for allowing signals of a specific frequency band to pass through in a digital domain, and shielding signals of other frequency bands. Wherein the digital band-pass filter for obtaining the upper sideband component is located at f + alpha of the first signal₀At/2, the digital band-pass filter for obtaining the lower sideband component is positioned at f- α of the first signal₀A position/2, where f is the center frequency, α₀Is the baud rate of the first signal. Illustratively, the center frequency of the first signal corresponds to 0GHz, and the baud rate is 28 GHz. The position of the first digital band-pass filter for upper band component filtering is +14 GHz; the position of the second digital bandpass filter for filtering the lower sideband component is-14 GHz.

The frequency range corresponding to the bandwidth range of the first digital bandpass filter and the second digital bandpass filter may be tens of MHz (megahertz) to hundreds of MHz, as long as effective acquisition of the corresponding sideband components is ensured. The first sub-signal is swept, so that the upper sideband component is filtered by the first digital band-pass filter, and the lower sideband component is filtered by the second digital band-pass filter.

As shown in fig. 8, taking the first sub-signal as an example, in fig. 8, the upper sideband component and the lower sideband component are obtained by performing upper sideband component filtering and lower sideband component filtering on the first sub-signal in the electrical domain of the coherent receiver. Accordingly, the signal processing device 302 receives the upper and lower sideband components.

Fig. 9 is a schematic diagram of a filtering principle of a signal processing system according to a signal processing method based on fig. 8 according to an embodiment of the present application. The coherent receiver may perform filtering of the upper and lower sidebands by filters. The filter for obtaining the upper sideband component and the filter for obtaining the lower sideband component are Low-pass filters (Low-pass filters) with center frequencies located at zero frequency. The low-pass filter has a filtering rule that low-frequency signals can normally pass through, and high-frequency signals exceeding a set critical value are blocked or weakened. In fig. 9, it is assumed that the signal processing system includes a first coherent receiver 301a and a second coherent receiver 301b, and the first coherent receiver 301a includes a first Local Oscillator (Local Oscillator) laser, a first optical detector, and a first filter; the second coherent receiver 301b includes a second local oscillator laser, a second optical detector, and a second filter. The bandwidth range of the first filter and the bandwidth range of the second filter can be from tens of MHz (megahertz) to hundreds of MHz, as long as effective acquisition of corresponding sideband components is guaranteed, and the first local oscillator laser and the second local oscillator laser have various adjustable center frequencies. In the coherent detection process of the first coherent receiver 301a, the first local oscillator laser sweeps the optical signal to position the upper sideband component, and then the first low-pass filter filters the upper sideband component after the first optical detector performs photoelectric conversion; in the coherent detection process of the second coherent receiver 301b, the optical signal is swept by the second local oscillator laser to position the lower sideband component, and then the lower sideband component is filtered out by the second low-pass filter after the second optical detector performs photoelectric conversion.

The signal processing system of fig. 9 is implemented by adjusting the difference between the center frequencies of the local oscillator laser and the optical signal to filter the upper and lower sideband components. In the first coherent receiver 301a, when the center frequency of the first local oscillator laser is different from the center frequency of the optical signal, the frequency spectrum of the electrical signal converted by the first optical detector based on the optical signal is shifted from the zero-frequency origin, and the frequency near the origin can be filtered out if the first filter is always located at the zero frequency. For example, assuming that the baud rate of the optical signal is 28GHz, when the center frequency of the first local oscillator laser is 14GHz higher than the center frequency of the optical signal, the frequency spectrum of the obtained electrical signal has a 14GHz offset from the 0-th origin, and the first filter filters out the upper sideband component. Similarly, when the center frequency of the second local oscillator laser is lower than the center frequency of the optical signal by 14GHz, the component of the lower sideband is filtered out by the second filter.

It is worth mentioning that other elements may be present in the coherent receiver, and the elements of fig. 9 are only schematically illustrated.

A23, the signal processing device obtains the relation parameter of the first signal by fitting based on at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each sub-signal in at least two sub-signals.

The relationship parameter of the first signal is used to reflect the relationship of the correlation of the upper sideband and the lower sideband of the first signal with the frequency offset. Based on the obtained at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each of the at least two seed signals, a relationship parameter of the first signal can be obtained through fitting.

It is worth noting that the more the types of the frequency offsets loaded in the foregoing steps a21 to a23, the higher the accuracy of the relation parameters obtained by fitting. Illustratively, the aforementioned at least two frequency offsets may include 10 to 30 frequency offsets, and the correspondingly obtained correlations may include 10 to 30 correlations.

For example, the relation parameter is a decreasing rate, and fig. 10 is a schematic diagram of a fitting result of the decreasing rate of the first signal provided in the embodiment of the present application. In fig. 10, the horizontal axis represents frequency offset in GHz, and the vertical axis represents correlation. The descending rate can be obtained by introducing different frequency offsets, calculating a series of corresponding correlation values, and fitting the correlation values and the frequency offset values. The relationship between the correlation and the frequency offset can be expressed as a cubic function. It is demonstrated that if the relationship between the correlation and the frequency offset is represented by other functions such as quadratic function or quartic function, the accuracy is far less than that of the cubic function. Therefore, the relation between the correlation and the frequency offset can be reflected more accurately by the cubic function, and the accuracy of the final fitting result can be effectively improved by describing the relation between the correlation and the frequency offset by the cubic function.

Illustratively, the cubic function is a first formula, which is: y is Ax³+ Z, where a denotes the rate of decrease, y denotes the correlation, x denotes the frequency offset, and Z denotes the bias introduced by other intrinsic factors, which is not zero. Illustratively, the inherent factors include transmitter-induced noise, receiver-induced noise, and/or resolution of the receiving end (e.g., a coherent receiver). The obtained values of at least two frequency offsets and the corresponding correlation value adopt a first formula y ═ Ax³And fitting by + Z to obtain a relation curve corresponding to the first formula, wherein the relation curve is used for reflecting the descending trend of the correlation along with the increase of the frequency offset, and A is obtained based on the relation curve. Fig. 10 shows a relationship curve obtained by fitting a plurality of data points, each data point representing a value of frequency offset and a corresponding value of correlation. Wherein, a value of frequency offset corresponds to a value of correlation, which means that the two belong to the same sub-signal. For example, when the frequency offset is 1GHz, the correlation is 0.8; when the frequency offset is 2GHz, the correlation is 0.7, and the correlation gradually decreases as the frequency offset increases.

As shown in fig. 6, the process of acquiring the relation parameter of the first signal includes:

a24, the signal processing device receives at least two sub-signals, wherein the at least two sub-signals are signals obtained by loading at least two different frequency offsets on the first signal.

Illustratively, the at least two sub-signals are signals obtained by loading the first signal with at least two different frequency offsets by the coherent receiver 301. In an optional implementation manner, the coherent receiver 301 includes a local oscillator laser, where the local oscillator laser has multiple adjustable center frequencies, and different frequency offsets may be loaded on the first optical signal received by the coherent receiver 301 by changing the center frequency of the local oscillator laser, so as to obtain at least two sub signals. Accordingly, the signal processing means receives the at least two sub-signals. For example, in the coherent detection process of the coherent receiver 301, the local oscillator laser sweeps the frequency of the optical signal, so as to implement frequency offset loading of the optical signal.

In an alternative example, referring to fig. 9, in the structure of the signal processing system, in the coherent detection process of the first coherent receiver 301a, the first local oscillator laser sweeps the optical signal to implement frequency offset loading on the upper sideband component; in the coherent detection process of the second coherent receiver 301b, the second local oscillator laser sweeps the frequency of the optical signal, so as to implement frequency offset loading on the lower sideband component. Assuming that the central frequency of the optical signal is T, the baud rate of the optical signal is E, and the frequency offset to be loaded is L, adjusting the central frequency of the first local oscillator laser to be T + L + E/2, so that the position of the signal spectrum of the electrical signal corresponding to the upper sideband of the optical signal moves forward by L relative to the origin; and adjusting the center frequency of the second local oscillator laser to be T + L-E/2, so that the position of the signal spectrum of the electric signal corresponding to the lower sideband of the optical signal can be moved forward by L relative to the origin.

Taking the implementation of frequency offset loading by the coherent receiver shown in fig. 9 as an example, assuming that the center frequency of the optical signal is T, the baud rate of the optical signal is 28GHz, and a frequency offset of 1GHz needs to be loaded, the center frequencies of the first local oscillator laser and the second local oscillator laser are adjusted to be "15 GHz higher than the center frequency of the optical signal" (i.e., T +15GHz) and "13 GHz lower than the center frequency of the optical signal" (i.e., the center frequency is T-13GHz), respectively. The interval between the center frequencies of the first local oscillator laser and the second local oscillator laser is 28GHz, that is, the baud rate of the optical signal.

For another example, assume that the center frequency of the first signal is T and the baud rate is 28 GHz. When the center frequency of the optical signal of the first local oscillator laser is T +14GHz and the center frequency of the optical signal of the second local oscillator laser is T-14GHz, the signal filtered by the upper sideband component and the lower sideband component filtered by the first filter and the second filter is an electrical signal corresponding to the first signal (namely, no frequency offset is loaded, which is also called loaded frequency offset 0); when the central frequency of the optical signal of the first local oscillator laser is T +15GHz and the central frequency of the optical signal of the second local oscillator laser is T-13GHz, the signal filtered by the upper sideband component and the lower sideband component filtered by the first filter and the second filter is an electric signal corresponding to the 1GHz frequency offset loaded on the first signal; and when the central frequency of the optical signal of the first local oscillator laser is T +16GHz and the central frequency of the optical signal of the second local oscillator laser is T-12GHz, the signal filtered by the upper sideband component and the lower sideband component filtered by the first filter and the second filter is the electric signal corresponding to the 2GHz frequency offset loaded on the first signal.

It should be noted that, the foregoing embodiments only take the case where the signal processing system includes two coherent receivers, and the frequency offset loading in the optical domain is taken as an example for description. In practical implementation, the signal processing system may also use one coherent receiver or three or four coherent receivers to implement the loading of the frequency offset. For coherent receivers with different numbers, the method for performing frequency offset loading by adjusting the center frequency of the local oscillator laser in the coherent receiver is all covered in the protection scope of the embodiment of the present application.

A25, the signal processing device determines the correlation of the upper sideband of each of at least two sub-signals.

Step a25 may refer to the aforementioned step a22, which is not described in detail in this embodiment of the present application.

A26, the signal processing device obtains the relation parameter of the first signal by fitting based on at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each sub-signal in at least two sub-signals.

Step a26 may refer to the aforementioned step a23, which is not described in detail in this embodiment of the present application.

It should be noted that, referring to fig. 5 to fig. 9, the target signal transmitted in the optical transmission link is an optical signal, and the signal processing device receives a digital signal converted from the optical signal. In an optical transmission link, chromatic dispersion may cause a certain time delay (delay) to signals of different frequencies, and upper and lower sidebands of the same signal correspond to different frequencies, so that the upper and lower sidebands may generate a time-domain offset during transmission, which may affect the accuracy of the correlation of the upper and lower sidebands of the same signal determined subsequently, thereby affecting the detection accuracy of the relation parameter. Therefore, after receiving the digital signal, the signal processing apparatus performs chromatic dispersion compensation on the received digital signal to obtain a digital signal after chromatic dispersion compensation. Wherein, the chromatic dispersion compensation refers to compensating the phase of the digital signal. Then, the signal processing device obtains the relation parameter of the digital signal after chromatic dispersion compensation. That is, before the aforementioned a21 or a24, the signal processing apparatus needs to perform chromatic dispersion compensation on the received digital signal, so as to achieve temporal calibration of the digital signal, thereby improving the accuracy of the acquired relationship parameter. The chromatic dispersion compensation can be implemented by using a time domain digital filter or a frequency domain digital equalizer to modify the phase of the received signal.

A3, the signal processing device fits to obtain a first relation based on at least three pairs of linear signal-to-noise ratio and nonlinear signal-to-noise ratio, and the obtained relation parameters.

As described in the foregoing a2, for each of at least three signals, the relationship parameter thereof is acquired. For example, the falling rate of each signal is obtained, and still taking fig. 10 as an example, assuming that the aforementioned at least three signals are N signals in total, a first formula is adopted: y is Ax³N reduction rates obtained by fitting with + Z are respectively A₁，A₂,…A_N. And, for each of the aforementioned at least three signals, a linear signal-to-noise ratio and a non-linear signal-to-noise ratio thereof are obtained.

wherein A represents a relation parameter, SNR_linearRepresenting linear signal-to-noise ratio, SNR_nonlinearRepresenting the nonlinear signal-to-noise ratio, B₁Represents the degree of contribution of linear noise to the relation parameter A, B₂Representing non-linearityDegree of contribution of noise to relation parameter A, B₃Indicating the bias introduced by other intrinsic factors. Illustratively, the inherent factors include transmitter-induced noise, receiver-induced noise, and/or resolution of the receiving end (e.g., a coherent receiver).

Before fitting, at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios are obtained, and the obtained relation parameter A is a known number; b is₁、B₂And B₃Is an unknown number. At least three pairs of linear signal-to-noise ratio and nonlinear signal-to-noise ratio (such as the aforementioned N pairs of linear signal-to-noise ratio and nonlinear signal-to-noise ratio) and the acquired relation parameter (such as the aforementioned A₁，A₂,…A_N) Substituting the first relational expression to obtain B₁、B₂And B₃. Fitting to obtain B₁、B₂And B₃The first relational expression with known coefficient can be obtained by substituting the first relational expression.

S202, the signal processing device obtains a second relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a signal-to-noise ratio in the optical transmission link.

In the same optical transmission system, a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to a signal of an optical transmission link have an association relationship with the signal-to-noise ratio. In the embodiment of the present application, a second relationship among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio, and a signal-to-noise ratio in an optical transmission link is obtained, so that a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio of a signal (referred to as a target signal in the embodiment of the present application) to be measured in the optical transmission link are determined based on the second relationship in a subsequent process.

In an alternative, the obtaining of the second relationship comprises the following steps:

b1, the signal processing device determines the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different.

Step B1 may refer to step a1, which is not described in detail in this embodiment of the present application. The at least three signals in B1 may be the same as or different from the at least three signals in a 1. When at least three signals in B1 are the same as at least three signals in a1, the signal acquisition flow can be reduced, and the processing steps can be simplified.

B2, the signal processing device acquires the signal-to-noise ratio of each of at least three signals.

The signal-to-noise ratio is the overall signal-to-noise ratio. The signal-to-noise ratio of each signal is the signal-to-noise ratio when no frequency offset is loaded, that is, the signal-to-noise ratio of each signal is the signal-to-noise ratio of each signal when both the frequency offsets loaded in the optical domain and the digital domain are 0. In the embodiment of the present application, the signal-to-noise ratio of each of the at least three signals may be obtained by using a conventional method for obtaining the signal-to-noise ratio. For example, the SNR can be determined by out-of-band interpolation or error vector magnitude calculation or SNR monitoring based on the correlation of the upper and lower spectral sidebands of the signal or by theoretical model calculation or other algorithms based on channel parameters. For example, assuming that the aforementioned at least three signals include N signals, a series of signal-to-noise ratio measurements can be obtained as long as the signal-to-noise ratio is obtained by the aforementioned method when the frequency offset is set to 0 for each received signal: SNR_meas1，SNR_meas2,…SNR_measN。

Fig. 11 is a schematic diagram illustrating a principle of calculating a signal-to-noise ratio of a signal by using an out-of-band interpolation method according to an embodiment of the present application. The spectrum shown in fig. 11 can be monitored by a spectrometer. In-band refers to the region occupied by the signal spectrum, i.e., within the bandwidth of the signal. As shown in fig. 11, assuming that the target signal is a signal X, the in-band of the signal X refers to a region having a wavelength range of λ 1- α to λ 1+ α, and the out-of-band refers to outside the bandwidth of the signal. The out-of-band difference method refers to interpolating noise in a band by noise out-of-band on both sides of the signal X, and determining a signal-to-noise ratio from the interpolated (e.g., linear interpolation) in-band noise and the total power of the signal and noise at the center frequency of the signal X. Assuming that the out-of-band noise is Amplified Spontaneous Emission (ASE) noise, the out-of-band noise of the upper sideband of the signal X is ASE1, and the out-of-band noise of the lower sideband is ASE2, then the interpolated in-band noise ASE3 is (ASE1+ ASE 2)/2; assuming that the total power of the signal and noise at the center frequency of the signal X is M, the signal-to-noise ratio is (M-ASE3)/ASE 3.

Fig. 12 is a schematic diagram of a principle of calculating a signal-to-noise ratio of a signal by using an error vector magnitude meter algorithm according to an embodiment of the present application. The horizontal axis of fig. 12 represents the I-path, i.e., the real part, and the vertical axis represents the Q-path, i.e., the imaginary part, and the circles represent the constellation of the received signal. Assume that the received signal is represented by a series of signal sequences of length u: [ A1, A2, A3, A4 … Au ], that is, the signal sequence includes u symbols, each symbol corresponds to one signal in the received signal, and rk represents the magnitude of the position vector of the kth signal after the constellation diagram of the received signal is recovered. K is more than or equal to 1 and less than or equal to u. sk represents the amplitude of the position vector of the point where the kth signal is located on the constellation diagram after signal decision (for example, in four cases, 1+1i, 1-1i, -1+1i, -1-1i, where the vector amplitude is equivalent to root 2, for Quadrature Phase Shift Keying (QPSK) signals can be decided). nk represents the magnitude of the vector of noise experienced by the k-th signal and can be calculated by concatenating the sk end and the rk end. The average power of the signal is represented by averaging the square of sk for each of the u symbols. Averaging the square of nk for each of the u symbols may represent the average power of the noise. The signal-to-noise ratio of the signal is then obtained by dividing the average power of the signal by the average power of the noise.

The process of determining the signal-to-noise ratio based on the SNR monitoring method of the correlation of the upper and lower sidebands of the frequency spectrum of the signal may include: determining the signal-to-noise ratio based on a signal-to-noise ratio calculation formula, wherein the signal-to-noise ratio calculation formula is as follows:

wherein the SNR_measRepresenting the signal-to-noise ratio, i.e. the overall signal-to-noise ratio, f representing the frequency, P_SRepresenting the signal power, P_NRepresenting the noise power. B is_measIs the measurement bandwidth of the signal (i.e., the measurement bandwidth of the target signal), E [ 2 ]]Meaning that the average is taken in the time domain,

is represented by a center frequency at f_cThe maximum frequency and the minimum frequency are separated by alpha₀The upper and lower sidebands of the signal (e.g., the correlation calculated using the upper and lower sideband components). The foregoing SNR calculation formula is based on correlation

And SNR_measThe principle of the interrelationship of (a). Wherein the content of the first and second substances,

indicating the measurement bandwidth to be monitored (i.e. the aforementioned measurement bandwidth B)_meas) The total power of the signal and noise in (a), t represents time (also called time domain),

the expression assumes that f is equal to f on the premise that the noise spectrum is flat_c±α₀The noise power at/2 extends to the total power of the entire measurement bandwidth, followed by-1 due to the need to remove the noise present in the molecule to comply with the definition of signal-to-noise ratio.

For the traditional sparse wavelength division multiplexing and point-to-point optical transmission system, the signal-to-noise ratio determined by adopting an out-of-band interpolation method is more accurate. However, with the application of ROADM, the out-of-band ASE noise and the in-band ASE noise may be different, which easily affects the reliability of the signal-to-noise ratio; in addition, for the dense wavelength division multiplexing optical transmission system, the noise between adjacent channels cannot be effectively read, so that the signal-to-noise ratio cannot be effectively obtained. The SNR monitoring method based on the correlation of the upper and lower sidebands of the frequency spectrum of the signal determines the signal-to-noise ratio, is not influenced by an in-band or an out-of-band and is not influenced by a dense wavelength division multiplexing system, and the acquired signal-to-noise ratio is more reliable.

In the process of acquiring the signal-to-noise ratio by adopting the error vector magnitude calculation method, signals need to be completely solved, so that all DSP processes need to be carried out, the power consumption is high, and for the signals needing to be analyzed, the corresponding modulation formats of the DSP need to be configured for different modulation formats, and the universality for different modulation formats is low. For example, in an optical transmission system, 1 signal represents 4 bits of data under one modulation format; in another modulation format, 1 signal represents 8 bits of data. The modulation format of the DSP needs to be configured separately for these two modulation formats. In addition, this approach may introduce noise from the DSP. The SNR monitoring method based on the correlation of the upper and lower sidebands of the frequency spectrum of the signal determines the SNR, does not need to completely solve the signal, does not need to carry out all DSP flows, reduces the power consumption, does not limit the modulation format supported by the DSP, and has higher flexibility in acquiring the SNR.

B3, the signal processing device fits to obtain a second relation based on at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the obtained signal-to-noise ratios.

wherein the SNR_measRepresenting signal-to-noise ratio, SNR_linearRepresenting linear signal-to-noise ratio, SNR_nonlinearRepresenting the nonlinear signal-to-noise ratio, C₁Representing linear noise versus signal-to-noise ratio SNR_measDegree of contribution of C₂Representing nonlinear noise versus nonlinear signal-to-noise ratio SNR_nonlinearDegree of contribution of C₃Indicating the bias introduced by other intrinsic factors.

At least three pairs of linear signals before fittingThe signal-to-noise ratio and the nonlinear signal-to-noise ratio, and the acquired signal-to-noise ratio are known numbers; c₁、C₂And C₃Is an unknown number. By substituting at least three pairs of linear and nonlinear SNR's, and the obtained SNR's into the second relation, C can be obtained by fitting₁、C₂And C₃. Fitting to obtain C₁、C₂And C₃Substituting the second relational expression into the first relational expression to obtain the first relational expression with known coefficient.

S203, the signal processing device detects a target relation parameter of the target signal received through the optical transmission link.

The target relation parameter is a relation parameter of the target signal. Referring to fig. 5 to 9, the target signal transmitted in the optical transmission link is an optical signal, and the signal processing device receives a digital signal converted from the optical signal. In an optical transmission link, chromatic dispersion causes a certain time delay to signals with different frequencies, and upper and lower sidebands of a target signal correspond to different frequencies, so that the upper and lower sidebands generate time domain offset in the transmission process, which affects the accuracy of the correlation of the upper and lower sidebands of the determined target signal, thereby affecting the detection accuracy of target relationship parameters. Therefore, after receiving the digital signal, the signal processing apparatus performs chromatic dispersion compensation on the received digital signal to obtain a chromatic dispersion compensated digital signal. And then, the signal processing device detects the relation parameter of the digital signal after chromatic dispersion compensation to obtain a target relation parameter. Therefore, the digital signal is calibrated in time, and the accuracy of the acquired target relation parameter can be improved.

S204, the signal processing device acquires a target signal-to-noise ratio of the target signal.

In the embodiment of the present application, the signal processing apparatus may obtain the snr of the target signal by using a conventional snr obtaining method, so as to obtain the target snr. For example, the target SNR may be determined by out-of-band interpolation or error vector magnitude calculation or SNR monitoring based on the correlation of the upper and lower sidebands of the spectrum of the signal or by theoretical model calculation or other algorithms based on channel parameters. The process of acquiring the target signal-to-noise ratio may refer to the process of acquiring the signal-to-noise ratio of the signal in step B2.

It is worth to be noted that the signal-to-noise ratio of each of the at least three signals obtained by the signal processing device and the signal-to-noise ratio obtaining method used for obtaining the target signal-to-noise ratio may be the same, so that interference introduced by other inherent factors in the optical transmission link can be offset, and more accurate linear signal-to-noise ratio and nonlinear signal-to-noise ratio can be obtained in the subsequent process.

Optionally, the signal processing apparatus obtains the target signal-to-noise ratio by using an SNR monitoring method based on correlations between upper and lower sidebands of a frequency spectrum of the signal. The method has the advantages of high accuracy of obtaining the target signal-to-noise ratio and simple calculation.

S205, the signal processing device determines a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relation parameter, the target signal-to-noise ratio, the first relation and the second relation.

Referring to the foregoing step a3 and step B3, the first relationship is represented by a first relationship in which the independent variables are linear signal-to-noise ratio and nonlinear signal-to-noise ratio, the dependent variables are relationship parameters, the second relationship is represented by a second relationship in which the independent variables are linear signal-to-noise ratio and nonlinear signal-to-noise ratio, and the dependent variables are signal-to-noise ratio, the signal processing device substitutes the target relationship parameters into the first relationship, and substitutes the target signal-to-noise ratio into the second relationship, that is, the known numbers are the target relationship parameters and the target signal-to-noise ratio, and the unknown numbers are the linear signal-to-noise ratio corresponding to the target signal and the nonlinear signal-to-noise ratio corresponding to the target signal, and the linear signal-to-noise ratio corresponding to the target signal and the nonlinear signal-to-noise ratio corresponding to the target signal can be obtained by solving a binary linear equation set.

It is worth mentioning that the first relation is established by using the correlation and the relation between the linear signal-to-noise ratio and the non-linear signal-to-noise ratio; the second relation is established by utilizing the signal-to-noise ratio and the relation between the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio; therefore, the first relation can be modified based on the correlation and the relation between the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio to obtain other forms of relations; the second relation may be modified based on the signal-to-noise ratio and the relationship between the linear signal-to-noise ratio and the non-linear signal-to-noise ratio to obtain other forms of relations. The method is only required to establish a linear equation set taking a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio as variables based on the obtained relational expression, and realize the joint monitoring of the linear and nonlinear signal-to-noise ratios by utilizing the linear equation set.

In another implementation, since linear noise and linear signal-to-noise ratio have a negative correlation (e.g., an inverse relationship), and non-linear noise and non-linear signal-to-noise ratio have a negative correlation (e.g., an inverse relationship), the first relation may also be established by using the correlation and the relationship between linear noise and non-linear noise; the second relation is established using the signal-to-noise ratio and the relationship between linear noise and non-linear noise. And establishing a linear equation set with linear noise and nonlinear noise as variables based on the acquired relational expression, realizing the joint monitoring of the linear noise and the nonlinear noise by using the linear equation set to the received target signal, and acquiring a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio based on the acquired linear noise and the nonlinear noise.

The operation and reconstruction of signals on the optical transmission link depend on the quality of the optical transmission link, and the accurate optical signal-to-noise ratio can reflect the quality of the optical transmission link. The optical signal-to-noise ratio actually includes a linear signal-to-noise ratio caused by an optical amplifier or the like and a nonlinear signal-to-noise ratio caused by the optical transmission link itself (such as an optical fiber) or the like. According to the embodiment of the application, the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to the target signal are effectively distinguished, and the acquisition granularity of the signal-to-noise ratio is refined. In practical application, the monitoring and maintenance of the optical transmission system can be performed based on the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to the acquired target signal. For example, after the linear signal-to-noise ratio corresponding to the target signal is greater than the linear signal-to-noise ratio threshold, the signal processing apparatus determines that there is a risk of failure in the optical amplifier in the optical transmission link upstream of the signal processing apparatus, and the signal processing apparatus may send out a first warning message indicating that there is a risk of failure in the optical amplifier in the optical transmission link upstream of the signal processing apparatus, so as to facilitate maintenance or replacement of the optical amplifier by a worker. For another example, after the nonlinear signal-to-noise ratio corresponding to the target signal is greater than the nonlinear signal-to-noise ratio threshold, the signal processing apparatus determines that the optical transmission link (e.g., the optical fiber) upstream of the signal processing apparatus is at a risk of failure, and the signal processing apparatus may send a second warning message indicating that the optical transmission link upstream of the signal processing apparatus is at a risk of failure, so that a worker can repair or replace the optical transmission link.

It should be noted that, in the foregoing embodiment, the signal processing apparatus is respectively described to perform the filtering of the upper sideband component and the filtering of the lower sideband component (refer to the corresponding explanation in fig. 7), and the signal processing apparatus performs the frequency offset loading (refer to the corresponding explanation in fig. 5); the coherent receiver performs filtering of the upper sideband component and filtering of the lower sideband component (refer to the corresponding explanations in fig. 8 and 9), and the coherent receiver performs frequency offset loading (refer to the corresponding explanations in fig. 6 and 9), and so on. In practical implementation, the implementation of the signal processing method may include the following combination: the signal processing device carries out upper sideband component filtering and lower sideband component filtering, and carries out frequency offset loading; or, the coherent receiver performs upper sideband component filtering and lower sideband component filtering, and the coherent receiver performs frequency offset loading; or, the signal processing device carries out upper sideband component filtering and lower sideband component filtering, and the coherent receiver carries out frequency offset loading; or, the coherent receiver performs upper sideband component filtering and lower sideband component filtering, and the signal processing apparatus performs frequency offset loading. Any simple modifications of the above combinations are intended to be included within the scope of the present application.

In summary, according to different characteristics of the flat linear noise spectrum and the non-flat non-linear noise spectrum, the embodiment of the present application establishes a first relationship between a linear signal-to-noise ratio, a non-linear signal-to-noise ratio, and a relationship parameter in an optical transmission link, and a second relationship between the linear signal-to-noise ratio, the non-linear signal-to-noise ratio, and the signal-to-noise ratio in the optical transmission link, and determines a linear signal-to-noise ratio and a non-linear signal-to-noise ratio corresponding to a target signal by using an actually obtained target relationship parameter and a target signal-to-noise ratio based on the two relationships, thereby achieving effective differentiation between the linear signal-to-noise ratio and the non-linear signal-to-noise ratio corresponding to the signal.

As described in the aforementioned step a2, the non-linear signal-to-noise ratio can also be obtained by adding a pilot signal to the signal transmitted in the optical transmission link, but this sacrifices spectral efficiency and system flexibility. In the embodiment of the application, once the first relation and the second relation are obtained, the linear noise and the nonlinear noise can be obtained by solving a linear equation system, the signal-to-noise ratio is high in obtaining flexibility, and the influence on the spectrum efficiency and the system flexibility is reduced.

Referring to fig. 12, when the signal-to-noise ratio of a signal is calculated by using a conventional error vector magnitude calculation method, the signal needs to be completely recovered, and the complexity of obtaining the signal-to-noise ratio of the signal is high.

It should be noted that, the order of the steps of the signal processing method provided in the embodiments of the present application may be appropriately adjusted, and the steps may also be increased or decreased according to the circumstances, and any method that can be easily conceived by those skilled in the art within the technical scope of the present application shall be covered by the protection scope of the present application. For example, the foregoing S201 and S202 may be obtained when the optical transmission system is networked (or after the optical transmission system is initialized), and then in the process of signal transmission performed by the subsequent optical transmission link, execute S203 to S205; still alternatively, during the signal transmission in the optical transmission link, S201 to S205 are performed. Optionally, the signal processing device may further periodically execute the steps S201 and S202, so as to obtain the latest first relationship and the latest second relationship, ensure that the monitored linear snr and the monitored nonlinear snr are updated along with the change of the quality of the optical transmission link, and improve the accuracy of the determined linear snr and the determined nonlinear snr.

Fig. 13 is a schematic structural diagram of a signal processing apparatus 40 according to an embodiment of the present application, and as shown in fig. 13, the apparatus 40 includes:

a first relation obtaining module 401, configured to obtain a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio, and a relation parameter in an optical transmission link, where the relation parameter is used to reflect a relation between a correlation between an upper sideband and a lower sideband of a signal in the optical transmission link and a frequency offset; a second relation obtaining module 402, configured to obtain a second relation between a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio, and a signal-to-noise ratio in an optical transmission link; a parameter obtaining module 403, configured to obtain a target relationship parameter of a target signal received through an optical transmission link; a signal-to-noise ratio obtaining module 404, configured to obtain a target signal-to-noise ratio of a target signal; a determining module 405, configured to determine a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relationship parameter, the target signal-to-noise ratio, the first relationship, and the second relationship.

In summary, in the present application, a first relationship among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio, and a relationship parameter in an optical transmission link is established by a first relationship acquisition module, a second relationship among the linear signal-to-noise ratio, the nonlinear signal-to-noise ratio, and the signal-to-noise ratio in the optical transmission link is established by a second relationship acquisition module, and a determination module determines the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to a target signal by using an actually acquired target relationship parameter and a target signal-to-noise ratio based on the two relationships, thereby effectively distinguishing the linear signal-to-noise ratio and the nonlinear signal-to-noise ratio corresponding to the signal.

In an alternative example, the first relationship is characterized by the independent variables being linear snr and non-linear snr, the dependent variable being a first relation of the relationship parameters, the second relationship is characterized by the independent variables being linear snr and non-linear snr, the dependent variable being a second relation of snr, the determining module 405 is configured to: substituting the target relation parameters into the first relation, substituting the target signal-to-noise ratio into the second relation, and obtaining the linear signal-to-noise ratio corresponding to the target signal and the nonlinear signal-to-noise ratio corresponding to the target signal by solving a linear equation system.

In an alternative example, the target signal received by the optical transmission link is an optical signal, and the parameter obtaining module 403 is configured to: carrying out chromatic dispersion compensation on the digital signal, wherein the digital signal is obtained by converting an optical signal; and detecting the relation parameters of the digital signals after chromatic dispersion compensation to obtain target relation parameters.

Fig. 14 is a schematic structural diagram of a first relationship obtaining module 401 according to an embodiment of the present disclosure. As shown in fig. 14, the first relationship obtaining module 401 includes:

the determining submodule 4011 is configured to determine a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link, so as to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, where the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different; the obtaining sub-module 4012 is configured to obtain a relationship parameter of each of the at least three signals; the fitting submodule 4013 is configured to fit to obtain a first relationship based on at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, and the obtained relationship parameters.

Optionally, the obtaining sub-module 4012 is configured to: loading at least two different frequency offsets on the first signal in a digital domain respectively to obtain at least two sub-signals, or receiving at least two sub-signals, wherein the at least two sub-signals are signals obtained by loading at least two different frequency offsets on the first signal, and the first signal is any one of at least three signals; determining a correlation of an upper sideband and a lower sideband of each of at least two sub-signals; and fitting to obtain a relation parameter of the first signal based on the at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each of the at least two sub-signals.

Further, the obtaining sub-module 4012 is configured to: for each sub-signal in at least two sub-signals, acquiring an upper sideband component obtained by filtering an upper sideband component of the sub-signal, acquiring a lower sideband component obtained by filtering a lower sideband component of the sub-signal, and taking the correlation between the upper sideband component and the lower sideband component as the correlation between the upper sideband and the lower sideband of the sub-signal; the filtering positions of the upper sideband component filtering of the at least two seed signals are the same, and the filtering bandwidths are the same; the filtering positions of the lower sideband component filtering of at least two sub-signals are the same, and the filtering bandwidths are the same; the filtering bandwidth of the upper sideband component filtering of the same sub-signal is the same as the filtering bandwidth of the lower sideband component filtering.

In an alternative example, the second relationship obtaining module 402 is configured to: determining a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in an optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different; acquiring the signal-to-noise ratio of each of at least three signals; and fitting to obtain a second relation based on at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the obtained signal-to-noise ratios.

Optionally, the at least three signals differ by at least one parameter selected from: transmit power, amplification of the corresponding optical amplifier, type of the corresponding optical amplifier, or actively loaded noise.

It is worth noting that the relation parameter may be a rate of decrease, which is a rate of decrease of the correlation of the upper and lower sidebands of the signal in the optical transmission link with increasing frequency offset.

Fig. 15 is a possible basic hardware architecture of a computer device provided by an embodiment of the present application. The computer device may be the aforementioned signal processing apparatus. Referring to fig. 15, a computer device 500 includes a processor 501, a memory 502, a communication interface 503, and a bus 504.

In the computer device 500, the number of the processors 501 may be one or more, and fig. 15 illustrates only one of the processors 501. Alternatively, the processor 501 may be a Central Processing Unit (CPU). If the computer device 500 has multiple processors 501, the types of the multiple processors 501 may be different, or may be the same. Alternatively, the plurality of processors 501 of the computer device 500 may also be integrated as a multi-core processor.

Memory 502 stores computer instructions and data; the memory 502 may store computer instructions and data needed to implement the signal processing methods provided herein, e.g., the memory 502 stores instructions for implementing steps of the signal processing methods. The memory 502 may be any one or any combination of the following storage media: nonvolatile memory (e.g., Read Only Memory (ROM), Solid State Disk (SSD), hard disk (HDD), optical disk), volatile memory.

The communication interface 503 may be any one or any combination of the following devices: a network interface (e.g., an ethernet interface), a wireless network card, etc. having a network access function.

The communication interface 503 is used for the computer device 500 to perform data communication with other computer devices or terminals.

The bus 504 may connect the processor 501 with the memory 502 and the communication interface 503. Thus, the processor 501 may access the memory 502 via the bus 504 and may also interact with other computer devices or terminals via the communication interface 503.

In the present application, the computer apparatus 500 executes computer instructions in the memory 502, so that the computer apparatus 500 implements the signal processing method provided herein, or so that the computer apparatus 500 deploys a database system.

In an exemplary embodiment, a non-transitory computer-readable storage medium comprising instructions, such as a memory comprising instructions, executable by a processor of a server to perform a signal processing method as shown in various embodiments of the present application is also provided. For example, the non-transitory computer readable storage medium may be a ROM, a Random Access Memory (RAM), a CD-ROM, a magnetic tape, a floppy disk, an optical data storage device, and the like.

Fig. 16 is a schematic structural diagram of a signal processing system 60 according to an embodiment of the present application, and as shown in fig. 16, the signal processing system 60 includes: a coherent receiver 601 and a signal processing apparatus 602 provided in the embodiments of the present application. The signal processing device 602 may be the signal processing device 40 or the computer apparatus 500. The structure of the signal processing system 60 may refer to the structure of the signal processing system described in any of fig. 5 to 9.

The coherent receiver 601 is configured to receive an optical signal from an optical transmission link, convert the received optical signal into a digital signal, and send the converted digital signal to a signal processing apparatus. The coherent receiver is adopted to obtain the optical signal, so that the complete information of the optical signal can be reserved, and the signal processing device can conveniently carry out chromatic dispersion compensation and/or frequency offset loading. In practical implementation, the coherent receiver may be replaced by another type of receiver as long as the complete information of the optical signal can be obtained through the other type of reception.

Further, the coherent receiver 601 is configured to download optical signals from the optical transmission link through coherent light, convert the downloaded optical signals into two optical signals with mutually perpendicular polarization directions, and then convert the optical signals into two digital signals, so as to send the two digital signals to the signal processing device, and correspondingly, the signal processing device 602 processes the two digital signals respectively to obtain a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each digital signal. In the foregoing S201 to S205, one of the two digital signals is taken as an example for explanation, and in actual implementation, the foregoing S201 to S205 are performed on both the two digital signals.

The structure of the coherent receiver 601 may be various, and the embodiments of the present application are described by taking the following two alternative implementations as examples.

Fig. 17 is a schematic structural diagram of a signal processing system 60 according to an embodiment of the present application, where a coherent receiver 601 includes:

the local oscillator laser 6011 is configured to generate coherent light, and input the coherent light to the polarization beam splitter 6012. The center frequency of the local oscillator laser 6011 is the same as the center frequency of the target signal to be detected, so that the target signal can be downloaded under the action of the local oscillator laser 6011. For example, as shown in fig. 4, if the target signal to be downloaded is a signal X, the center wavelength of the local oscillator laser 6011 is the same as the center wavelength of the signal X; if the target signal to be downloaded is signal Y, the center wavelength of local laser 6011 is the same as the center wavelength of signal Y.

The polarization beam splitter 6012 is configured to split a received optical signal (i.e., an optical signal transmitted by an optical transmission link) into a first polarized light and a second polarized light perpendicular to each other, and split coherent light into a third polarized light and a fourth polarized light perpendicular to each other.

Two 90 ° mixers 6013, one 90 ° mixer for mixing the first polarized light and the third polarized light, and the other 90 ° mixer for mixing the second polarized light and the fourth polarized light. The polarization directions of the first polarized light and the third polarized light are the same, and the polarization directions of the second polarized light and the fourth polarized light are the same; alternatively, the first polarized light and the third polarized light have different polarization directions, and the second polarized light and the fourth polarized light have different polarization directions. Illustratively, the first polarized light and the third polarized light are both x-polarized light, and the second polarized light and the fourth polarized light are both y-polarized light.

And the optical detector 6014 is configured to convert the optical signals output by the two 90 ° mixers into analog currents. The light detector 6014 may be a balanced light detector, and the balanced light detector 6014 may be used to cancel noise and reduce noise in the output analog current. The optical detector outputs 4 paths of real signals, namely an x-polarized I path (real part) signal, an x-polarized Q path (imaginary part) signal, a y-polarized I path signal and a y-polarized Q path signal.

And a filter 6015, configured to filter the analog current to obtain an electrical signal corresponding to the target signal. Referring to fig. 4, a plurality of signals with different center wavelengths may be transmitted on the optical transmission link, and the signal actually required to be monitored by the signal processing system may be only one target signal of the plurality of signals, so that the target signal needs to be processed specifically. Assuming that the target signal is X, the filter 6015 may filter out the electrical signal corresponding to the target signal X from the analog currents corresponding to the multiple signals. The filter 6015 outputs 4 paths of real signals, which are respectively a filtered x-polarization I path signal, a filtered x-polarization Q path signal, a filtered y-polarization I path signal, and a filtered y-polarization Q path signal.

The analog-to-digital converter 6016 is configured to convert the electrical signal corresponding to the target signal into a digital signal. For example, the analog-to-digital converter 6016 obtains a digital signal by sampling an electrical signal corresponding to the target signal. The analog-to-digital converter 6016 is further configured to input the converted digital signal to the signal processing apparatus 602. Analog-to-digital converter 6016 outputs 2 paths of complex signals, which are x-polarization signal and y-polarization signal, respectively. The x-polarization signal is obtained by sampling a complex signal composed of the filtered x-polarization I path signal and the filtered x-polarization Q path signal, and the y-polarization signal is obtained by sampling a complex signal composed of the filtered y-polarization I path signal and the filtered y-polarization Q path signal.

Accordingly, the signal processing device 602 receives two paths of complex signals, which are x-polarized signal and y-polarized signal respectively. The foregoing S201 to S205 are exemplified by one of the x-polarized signal and the y-polarized signal, and in practical implementation, the foregoing S201 to S205 are performed on both the x-polarized signal and the y-polarized signal.

It should be noted that the coherent receiver 601 may have other structures, and for example, the optical detector 6014 may be replaced with other optical detectors. The two 90 ° mixers described above may be replaced by other types of mixers, such as one mixer.

As mentioned above, the digital signal input to the signal processing apparatus 602 by the analog-to-digital converter 6016 is obtained by converting the entire target signal, and if the upper sideband component and the lower sideband component of the digital signal corresponding to the target signal need to be obtained, the upper sideband component filtering and the lower sideband component filtering need to be performed in the digital domain. Fig. 18 is a schematic structural diagram of another signal processing system 60 according to an embodiment of the present application. The signal processing apparatus 602 includes: a first digital band pass filter 6021 for upper band component filtering of the received signal. A second digital bandpass filter 6022 for filtering the lower sideband component of the received signal. The function of the first digital bandpass filter 6021 in the signal processing apparatus 602 may refer to the function of the first digital bandpass filter in fig. 7, and the function of the second digital bandpass filter 6022 in the signal processing apparatus 602 may refer to the function of the second digital bandpass filter in fig. 7. This is not described in detail in the embodiments of the present application.

Fig. 19 is a schematic structural diagram of another signal processing system 60 according to an embodiment of the present application. The system 60 further comprises: the number of the coherent receivers 601 is 2, the optical splitter 603 is configured to receive an optical signal from the optical transmission link, and split the received optical signal into 2 optical signals, which are respectively input to the 2 coherent receivers 601, where one coherent receiver 601 of the 2 coherent receivers 601 is configured to perform upper sideband component filtering, and the other coherent receiver 601 is configured to perform lower sideband component filtering. The function of the coherent receiver for filtering the upper sideband component in the 2 coherent receivers 601 may refer to the function of the first filter in fig. 9, and the function of the coherent receiver for filtering the lower sideband component may refer to the function of the second filter in fig. 9.

Fig. 20 is a schematic structural diagram of a signal processing system 60 according to an embodiment of the present application. Wherein each coherent receiver 601 comprises: the local oscillator laser 6011 is configured to generate coherent light, and input the coherent light to the polarization beam splitter 6012.

A polarization beam splitter 6012 configured to split the received optical signal (i.e., the optical signal transmitted by the beam splitter 603) into a first polarized light and a second polarized light perpendicular to each other, and split the coherent light into a third polarized light and a fourth polarized light perpendicular to each other.

Two 90 ° mixers 6013, one 90 ° mixer for mixing the first polarized light and the third polarized light, and the other 90 ° mixer for mixing the second polarized light and the fourth polarized light.

And the optical detector 6014 is configured to convert the optical signals output by the two 90 ° mixers into analog currents. The light detector 6014 may be a balanced light detector.

A low-pass filter 6017, configured to filter the analog current to obtain an electrical signal corresponding to the sideband component, for example, the low-pass filter 6017 in the coherent receiver for performing upper sideband component filtering is configured to filter the analog current to obtain an electrical signal of the upper sideband component; the low pass filter 6017 in the coherent receiver for lower sideband component filtering is used to filter the analog current to get the electrical signal of the lower sideband component. Optionally, the low pass filter 6017 is a narrow band filter.

An analog-to-digital converter 6018 is used to convert the electrical signal corresponding to the sideband component into a digital signal.

The filter 6015 needs to filter out a complete target signal from the received signal, and accordingly, the bandwidth of the target signal is relatively wide, and the analog-to-digital converter 6016 is a high-speed analog-to-digital converter to achieve effective conversion from an electrical signal corresponding to the target signal to a digital signal, that is, the analog-to-digital converter 6016 is a high-speed analog-to-digital converter that can process a relatively wide bandwidth. Since the low-pass filter 6017 only needs to filter out a part of the target signal, which is a narrow-band filter, the analog-to-digital converter 6018 is an analog-to-digital converter with a relatively low speed and can process a bandwidth, and the analog-to-digital converter 6018 is a relatively low speed analog-to-digital converter with respect to the aforementioned analog-to-digital converter 6016. The low-speed analog-to-digital converter can save the manufacturing cost.

Referring to step B2, if the SNR is determined by the SNR monitoring method based on the correlation between the upper and lower sidebands of the spectrum of the signal, the overall SNR is obtained_measIn the meantime, the total power of the signal and the noise in the measurement bandwidth needs to be monitored, and if the signal processing system adopts the structure shown in fig. 20, since the 2 coherent receivers 601 only acquire the sideband component of the target signal and do not acquire the complete target signal, the signal processing apparatus cannot determine the total power of the signal and the noise in the measurement bandwidth based on the digital signals output by the 2 coherent receivers 601. A power measuring device needs to be additionally provided to acquire the total power of the signal and noise in the measurement bandwidth.

Fig. 21 is a schematic structural diagram of another signal processing system 60 according to an embodiment of the present disclosure. The system further comprises: a power measurement device 604, the power measurement device 604 being configured to receive an optical signal from the optical transmission link and measure a power of a target signal in the optical signal.

Fig. 22 is a schematic structural diagram of another signal processing system 60 according to an embodiment of the present application. Wherein, the power measuring device 604 comprises:

the local oscillator laser 6011 is configured to generate coherent light, and input the coherent light to the polarization beam splitter 6012.

The polarization beam splitter 6012 is configured to split the received optical signal into a first polarized light and a second polarized light that are perpendicular to each other, and split the coherent light into a third polarized light and a fourth polarized light that are perpendicular to each other.

And the optical detector 6014 is configured to convert the optical signals output by the two 90 ° mixers into analog currents. Illustratively, the light detector 6014 may be a balanced light detector.

A filter 6015, configured to filter the analog current to obtain an electrical signal corresponding to the target signal, is referred to the function of the filter 6015 in fig. 17.

The analog-to-digital converter 6018 is configured to convert the electrical signal corresponding to the target signal into a digital signal.

And a power measurement module 6041 for measuring the power of the received digital signal.

The functions of the local oscillator laser 6011, the polarization beam splitter 6012, the 90 ° mixer 6013, the optical detector 6014, the filter 6015, and the analog-to-digital converter 6016 in fig. 18 to fig. 22 may refer to the functions of the corresponding blocks in fig. 17, which is not described again in this embodiment of the present application.

The local oscillator laser 6011 in fig. 17 to 22 may have multiple adjustable center frequencies. The center frequency of the target signal is adjustable, so that the target signal with different center frequencies can be detected (also called positioning the target signal). As shown in fig. 4, the local oscillator laser 6011 may download the signal X by adjusting the center wavelength to be the same as the center wavelength of the signal X; the local oscillator laser 6011 may download the signal Y by adjusting the center wavelength to be the same as the center wavelength of the signal Y. Therefore, one local oscillator laser 6011 can download signals with different central wavelengths, compatibility detection of the signals with different wavelengths is achieved, manufacturing cost of a signal processing system is reduced, and flexibility of the system is improved.

Further, referring to fig. 9, the center frequency of the local laser 6011 may be adjusted to implement the loading of the frequency offset in the optical domain and/or the filtering of the upper sideband component and the lower sideband component.

It should be noted that the optical signal detected in the foregoing embodiment is an optical signal extracted by an optical splitter installed in the optical transmission link, and the optical power of the extracted optical signal has a small ratio to the optical power of the optical signal transmitted by the optical transmission link, and does not affect the normal transmission of the optical signal in the optical transmission link. For example, the ratio of the optical power of the optical signal extracted by the optical splitter to the optical power of the optical signal transmitted by the optical transmission link is 1: 99.

The signal-to-noise ratio in the embodiment of the present application refers to an optical signal-to-noise ratio, the linear signal-to-noise ratio refers to a linear optical signal-to-noise ratio, the nonlinear signal-to-noise ratio refers to a nonlinear optical signal-to-noise ratio, and the center frequency of the local oscillator laser refers to the center frequency of coherent light output by the local oscillator laser. In the foregoing embodiments, the position of the filter is located at zero frequency as an example, but in actual implementation, the position of the filter may be set according to actual needs. In the signal processing apparatus provided in the foregoing embodiment, when executing the signal processing method, only the division of the functional modules is illustrated, and in practical applications, the functions may be distributed by different functional modules according to needs, that is, the internal structure of the apparatus may be divided into different functional modules to complete all or part of the functions described above. In addition, the signal processing apparatus and the signal processing method provided by the above embodiments belong to the same concept, and specific implementation processes thereof are described in the method embodiments and are not described herein again.

It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.

The above description is only exemplary of the present application and should not be taken as limiting, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method of signal processing, the method comprising:

acquiring a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relation parameter in an optical transmission link, wherein the relation parameter is used for reflecting the relation between the correlation of an upper sideband and a lower sideband of a signal in the optical transmission link and frequency offset;

acquiring a second relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a signal-to-noise ratio in the optical transmission link;

acquiring a target relation parameter of a target signal received through the optical transmission link;

acquiring a target signal-to-noise ratio of the target signal;

and determining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relation parameter, the target signal-to-noise ratio, the first relation and the second relation.

2. The method of claim 1, wherein the first relationship is characterized by independent variables being the linear signal-to-noise ratio and the non-linear signal-to-noise ratio, dependent variables being a first relation of the relationship parameters, the second relationship is characterized by independent variables being the linear signal-to-noise ratio and the non-linear signal-to-noise ratio, dependent variables being a second relation of the signal-to-noise ratio,

the determining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relationship parameter, the target signal-to-noise ratio, the first relationship, and the second relationship includes:

substituting the target relation parameter into the first relation, substituting the target signal-to-noise ratio into the second relation, and obtaining a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal by solving a linear equation system.

3. The method according to claim 1 or 2, wherein the target signal received via the optical transmission link is an optical signal, and the obtaining the target relation parameter of the target signal received via the optical transmission link comprises:

carrying out chromatic dispersion compensation on a digital signal, wherein the digital signal is obtained by converting the optical signal;

and detecting the relation parameters of the digital signals after chromatic dispersion compensation to obtain the target relation parameters.

4. A method according to any one of claims 1 to 3, wherein said obtaining a first relationship of linear signal-to-noise ratio, non-linear signal-to-noise ratio and relationship parameters in the optical transmission link comprises:

determining a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different;

acquiring a relation parameter of each signal in the at least three signals;

and fitting to obtain the first relation based on the at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the obtained relation parameters.

5. The method of claim 4, wherein the obtaining the relationship parameter of each of the at least three signals comprises:

loading at least two different frequency offsets on a first signal in a digital domain respectively to obtain at least two sub-signals, or receiving at least two sub-signals, wherein the at least two sub-signals are signals obtained by loading at least two different frequency offsets on the first signal, and the first signal is any one of the at least three signals;

determining a correlation of an upper sideband and a lower sideband of each of at least two sub-signals;

and fitting to obtain a relation parameter of the first signal based on the at least two frequency offsets and the correlation between the upper sideband and the lower sideband of each of the at least two sub-signals.

6. The method of claim 5, wherein determining the correlation of the upper and lower sidebands of each of the at least two sub-signals comprises:

for each sub-signal of the at least two sub-signals, acquiring an upper sideband component obtained by filtering an upper sideband component of the sub-signal, acquiring a lower sideband component obtained by filtering a lower sideband component of the sub-signal, and taking the correlation between the upper sideband component and the lower sideband component as the correlation between the upper sideband and the lower sideband of the sub-signal;

the filtering positions of the upper sideband component filtering of the at least two seed signals are the same, and the filtering bandwidths are the same; the filtering positions of the lower sideband component filtering of the at least two sub-signals are the same, and the filtering bandwidths are the same; the filtering bandwidth of the upper sideband component filtering of the same sub-signal is the same as the filtering bandwidth of the lower sideband component filtering.

7. The method according to any of claims 1 to 3, wherein said obtaining a second relationship of linear signal-to-noise ratio, non-linear signal-to-noise ratio and signal-to-noise ratio in the optical transmission link comprises:

acquiring a signal-to-noise ratio of each of the at least three signals;

and fitting to obtain the second relation based on the at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the acquired signal-to-noise ratios.

8. The method according to claim 4 or 7, wherein the at least three signals differ by at least one of the following parameters: transmit power, amplification of the corresponding optical amplifier, type of the corresponding optical amplifier, or actively loaded noise.

9. The method according to any of claims 1 to 8, wherein the relation parameter is a rate of decrease, the rate of decrease being a rate of decrease of the correlation of the upper and lower sidebands of the signal in the optical transmission link with increasing frequency offset.

10. A signal processing apparatus, characterized in that the apparatus comprises:

the first relation acquisition module is used for acquiring a first relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a relation parameter in an optical transmission link, wherein the relation parameter is used for reflecting the relation between the correlation of an upper sideband and a lower sideband of a signal in the optical transmission link and frequency offset;

the second relation acquisition module is used for acquiring a second relation among a linear signal-to-noise ratio, a nonlinear signal-to-noise ratio and a signal-to-noise ratio in the optical transmission link;

a parameter obtaining module, configured to obtain a target relationship parameter of a target signal received through the optical transmission link;

the signal-to-noise ratio acquisition module is used for acquiring a target signal-to-noise ratio of the target signal;

a determining module, configured to determine a linear signal-to-noise ratio corresponding to the target signal and a nonlinear signal-to-noise ratio corresponding to the target signal based on the target relationship parameter, the target signal-to-noise ratio, the first relationship, and the second relationship.

11. The apparatus of claim 10, wherein the first relationship is characterized by independent variables being the linear signal-to-noise ratio and the non-linear signal-to-noise ratio, dependent variables being a first relation of the relationship parameters, wherein the second relationship is characterized by independent variables being the linear signal-to-noise ratio and the non-linear signal-to-noise ratio, dependent variables being a second relation of the signal-to-noise ratio,

the determining module is configured to:

12. The apparatus according to claim 10 or 11, wherein the target signal received via the optical transmission link is an optical signal, and the parameter obtaining module is configured to:

13. The apparatus according to any one of claims 10 to 12, wherein the first relationship obtaining module comprises:

the determining submodule is used for determining a linear signal-to-noise ratio and a nonlinear signal-to-noise ratio corresponding to each of at least three signals in the optical transmission link to obtain at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios, wherein the linear signal-to-noise ratios and the nonlinear signal-to-noise ratios corresponding to the at least three signals are different;

the obtaining submodule is used for obtaining the relation parameter of each signal in the at least three signals;

and the fitting submodule is used for fitting to obtain the first relation based on the at least three pairs of linear signal-to-noise ratios and nonlinear signal-to-noise ratios and the obtained relation parameters.

14. The apparatus of claim 13, wherein the acquisition sub-module is configured to:

15. The apparatus of claim 14, wherein the acquisition sub-module is configured to:

16. The apparatus according to any one of claims 10 to 12, wherein the second relation obtaining module is configured to:

acquiring a signal-to-noise ratio of each of the at least three signals;

17. The apparatus according to claim 13 or 16, wherein the at least three signals differ by at least one of the following parameters: transmit power, amplification of the corresponding optical amplifier, type of the corresponding optical amplifier, or actively loaded noise.

18. The apparatus of any of claims 10 to 17, wherein the relationship parameter is a rate of decrease, the rate of decrease being a rate of decrease in the correlation of the upper and lower sidebands of the signal in the optical transmission link with increasing frequency offset.

19. A signal processing system, characterized in that the signal processing system comprises: a coherent receiver and a signal processing apparatus according to any one of claims 10 to 17;

the coherent receiver is used for receiving optical signals from the optical transmission link, converting the received optical signals into digital signals, and sending the converted digital signals to the signal processing device.

20. The system of claim 19, wherein the coherent receiver comprises:

the local oscillator laser is used for generating coherent light;

the polarization optical splitter is used for splitting an optical signal transmitted by the optical transmission link into first polarized light and second polarized light which are vertical to each other, and splitting the coherent light into third polarized light and fourth polarized light which are vertical to each other;

two 90 ° mixers, one 90 ° mixer for mixing the first polarized light and the third polarized light, and the other 90 ° mixer for mixing the second polarized light and the fourth polarized light;

the optical detector is used for converting the optical signals output by the two 90-degree frequency mixers into analog current;

the filter is used for filtering the analog current to obtain an electric signal corresponding to the target signal;

and the analog-to-digital converter is used for converting the electric signal corresponding to the target signal into a digital signal.

21. The system of claim 20, wherein the signal processing means comprises: a first digital band-pass filter for filtering an upper band component of the received signal;

a second digital bandpass filter for filtering a lower sideband component of the received signal.

22. The system of claim 19, further comprising: the number of the coherent receivers is 2, the optical splitter is configured to receive an optical signal from an optical transmission link, divide the received optical signal into 2 optical signals, and input the optical signals to the 2 coherent receivers respectively, where one coherent receiver of the 2 coherent receivers is configured to perform upper sideband component filtering, and the other coherent receiver is configured to perform lower sideband component filtering.

23. The system of claim 22, wherein each of the coherent receivers comprises:

the local oscillator laser is used for generating coherent light;

the low-pass filter is used for filtering the analog current to obtain an electric signal corresponding to a sideband component;

and the analog-to-digital converter is used for converting the electric signals of the corresponding sideband components into digital signals.

24. The system according to claim 22 or 23, characterized in that the system further comprises: a power measurement device to receive an optical signal from an optical transmission link and to measure a power of a target signal in the optical signal.

25. A system according to any one of claims 20 to 24, wherein the local oscillator laser has a plurality of centre frequencies which are adjustable.

26. A computer device, characterized in that the computer device comprises a processor and a memory,

the memory stores computer instructions; the processor executes the computer instructions stored by the memory to cause the computer device to perform the signal processing method of any of claims 1 to 9.

27. A computer-readable storage medium having stored thereon computer instructions for instructing a computer device to execute the signal processing method according to any one of claims 1 to 9.

28. A chip comprising programmable logic circuits and/or program instructions for implementing a signal processing method as claimed in any one of claims 1 to 9 when said chip is operated.