CN114696897A - Optical signal-to-noise ratio monitoring method and device - Google Patents
Optical signal-to-noise ratio monitoring method and device Download PDFInfo
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Abstract
The application discloses an optical signal to noise ratio monitoring method and device, the method can determine noise power under any frequency according to a pre-acquired noise baseline function under the condition that any channel is not closed, and then real-time OSNR of any channel is calculated by combining with real-time analysis of a channel spectrum. Because the method does not need to close the tested channel, the OSNR of the system can be monitored in real time under the condition of not influencing the operation of the system. In addition, the method can also monitor the OSNR of all channels in the optical fiber link at the same time, has high test efficiency, is not influenced by the signal types of the channels, and can be suitable for various modulated signals and non-modulated false optical signals.
Description
Technical Field
The present application relates to the field of optical communication technologies, and in particular, to a method and an apparatus for monitoring an optical signal-to-noise ratio.
Background
The OSNR is a ratio of optical signal power to noise power in an optical transmission link, and is the most important index for measuring a DWDM (Dense Wavelength Division Multiplexing) system. In the operation process of the DWDM system, monitoring the OSNR of the system is an important technical means for knowing the working performance of the system and estimating the signal transmission quality.
Based on the wave dropping method defined by OSNR, the noise in the channel can be directly measured by closing the signal of the channel to be measured. The method comprises the steps of firstly, acquiring a first spectrum of a tested channel under the condition of starting a tested channel signal, and calculating the total power P1 in the tested channel according to the first spectrum; then under the condition of closing the signal of the channel to be detected, acquiring a second spectrum of the channel to be detected, and calculating noise power P2 in the channel to be detected and total power P3 in the central frequency of 12.5GHz according to the second spectrum; and finally, calculating the OSNR of the measured channel according to the OSNR of 10 XLog ((P1-P2)/P3).
Then, when the above-mentioned drop method measures the OSNR, the signal source needs to be turned off, i.e. the service must be interrupted, so that the method cannot monitor the OSNR of the system in operation.
Disclosure of Invention
The application provides an optical signal to noise ratio monitoring method and device, which aim to solve the problem that the prior art cannot monitor the OSNR of a system in operation.
In a first aspect, the present application provides a method for monitoring an osnr, which includes: acquiring the central frequency and the optical signal power of a channel to be detected at a signal receiving end; calculating the noise power of the measured channel according to the center frequency and a pre-acquired noise baseline function; and determining the optical signal-to-noise ratio of the channel to be detected according to the optical signal power and the noise power.
The method for acquiring the center frequency and the optical signal power of the channel to be detected at the signal receiving end comprises the following steps: collecting channel spectrum at a signal receiving end; and determining the center frequency and the optical signal power of the tested channel according to the channel spectrum. Determining the optical signal-to-noise ratio of the channel to be tested according to the optical signal power and the noise power, wherein the method comprises the following steps:
calculating the optical signal-to-noise ratio of the measured channel according to the following formula,
wherein v represents the center frequency of the tested channel, P (v) represents the optical signal power of the tested channel, fn (v) represents the noise power of the tested channel within 12.5GHz of the reference bandwidth, and Bs represents the channel bandwidth.
Therefore, under the condition of not closing any channel, the noise power under any frequency can be determined according to the pre-acquired noise baseline function, and the real-time OSNR of any channel can be calculated by combining the real-time analysis of the channel spectrum. Because the method does not need to close the tested channel, the OSNR of the system can be monitored in real time under the condition of not influencing the operation of the system. In addition, the method can also monitor the OSNR of all channels in the optical fiber link at the same time, has high test efficiency, is not influenced by the signal type in the channel, and can be suitable for various modulated signals and non-modulated false optical signals.
In one implementation, the step of obtaining a noise baseline function includes: determining a frequency sequence to be tested, wherein the frequency sequence to be tested comprises channel frequencies corresponding to partial or all channels in a link; acquiring a baseline noise sequence according to the frequency sequence to be detected, wherein the baseline noise sequence comprises baseline noise of a part of or all channels in a reference bandwidth before the operation of the optical fiber communication system; and fitting a noise baseline function according to the baseline noise contained in the baseline noise sequence.
Therefore, the noise power under any frequency can be determined by using the noise baseline function, the tested channel does not need to be closed, the noise power of all channels can be obtained simultaneously, and the testing efficiency is improved.
In one implementation, the frequency sequence to be tested includes channel frequencies corresponding to all channels of a full bandwidth in a link; obtaining a baseline noise sequence according to the frequency sequence to be measured, comprising: optical fiber communication systemBefore the system operation, the target test frequency v is sequentially transmitted and removed at a signal transmitting endiTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]N is the total number of channels; sequentially collecting channel spectrums corresponding to each group of test signals at a signal receiving end; according to the channel spectrum acquired each time, determining the frequency v of each target testiBaseline noise of the corresponding channel within the reference bandwidth.
By the implementation mode, the baseline noise of each channel in the optical fiber link can be acquired one by one, and the baseline noise distribution condition of the system in the whole frequency band can be accurately described according to the noise baseline function fitted by the baseline noise of each channel, so that the noise power of the channel to be measured can be accurately calculated by using the noise baseline function under the condition of giving the channel to be measured.
In one implementation mode, the frequency sequence to be tested comprises channel frequencies corresponding to part of specified channels in a link, and the specified channels are distributed at equal intervals; obtaining a baseline noise sequence according to the frequency sequence to be measured, comprising: before the operation of the optical fiber communication system, a signal sending end transmits test signals corresponding to all channel frequencies except the channel frequency in the frequency sequence to be tested; and at a signal receiving end, acquiring a channel spectrum, and determining the baseline noise of each appointed channel in a reference bandwidth according to the channel spectrum.
Compared with the implementation mode, the implementation mode can test the baseline noise of part of the designated channels in the optical fiber link at one time, and the part of the channels are uniformly distributed in the link, so that the implementation mode has higher test efficiency while ensuring the accuracy of the test result.
In one implementation, before calculating the noise power of the measured channel, the method further includes: acquiring a first noise power and a second noise power corresponding to a reference point frequency, wherein the first noise power is determined according to a channel spectrum of a signal receiving end, the second noise power is calculated according to a noise baseline function, and the reference point is positioned at each sub-band interval of the optical fiber communication system; judging whether the difference value of the first noise power and the second noise power is larger than a preset value or not; and if the difference corresponding to the frequency of at least one reference point is larger than the preset value, correcting the noise baseline function according to the difference.
In one implementation, modifying the noise baseline function according to the difference comprises: fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference point frequency on the two sides of each sub-band; determining a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be measured, wherein the new baseline noise sequence comprises the latest baseline noise of a part or all of channels in a reference wide band after the operation of the optical fiber communication system, and the latest baseline noise is calculated according to the channel frequency and the difference correction function corresponding to the sub-band to which the channel frequency belongs; and fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
In the implementation mode, a reference point is set at a sub-band interval of the system, whether a noise baseline function needs to be corrected is judged by monitoring the difference between the first noise power and the second noise power at the reference point, and when the noise baseline function needs to be corrected, the noise baseline function is automatically corrected according to the difference between the first noise power and the second noise power at the reference point, so that the accuracy of an OSNR monitoring result is ensured.
Correspondingly, in one implementation, calculating the noise power of the measured channel according to the center frequency and a pre-acquired noise baseline function includes: when the difference value corresponding to the frequency of at least one reference point is larger than a preset value, calculating the noise power of the measured channel according to the frequency of the measured channel and the corrected noise baseline function; and when the difference values corresponding to all the reference point frequencies are not greater than the preset value, directly calculating the noise power of the measured channel according to the frequency of the measured channel and the current noise baseline function. Thereby ensuring the accuracy of the monitoring result.
In a second aspect, the present application further provides an osnr monitoring apparatus, including: the data acquisition module is used for acquiring the central frequency and the optical signal power of the channel to be detected at the signal receiving end; the first processing module is used for calculating the noise power of the channel to be measured according to the central frequency and a pre-acquired noise baseline function; and the second processing module is used for determining the optical signal-to-noise ratio of the measured channel according to the optical signal power and the noise power.
The data acquisition module may specifically include: the spectrum acquisition unit is used for acquiring a channel spectrum at the signal receiving end; and the spectrum analysis unit is used for determining the center frequency and the optical signal power of the measured channel according to the channel spectrum. The second processing module may calculate the osnr of the measured channel according to the following formula,
wherein v represents the center frequency of the tested channel, P (v) represents the optical signal power of the tested channel, fn (v) represents the noise power of the tested channel within 12.5GHz of the reference bandwidth, and Bs represents the channel bandwidth.
Therefore, under the condition of not closing any channel, the noise power under any frequency can be determined according to the pre-acquired noise baseline function, and the real-time OSNR of any channel can be calculated by combining the real-time analysis of the channel spectrum. Because the method does not need to close the tested channel, the OSNR of the system can be monitored in real time under the condition of not influencing the operation of the system. In addition, the method can also monitor the OSNR of all channels in the optical fiber link at the same time, has high test efficiency, is not influenced by the signal type in the channel, and can be suitable for various modulated signals and non-modulated false optical signals.
In one implementation, the apparatus further comprises: the baseline acquisition module may specifically include: the frequency sequence to be tested comprises channel frequencies corresponding to part or all of channels in a link; the base line noise test unit is used for acquiring a base line noise sequence according to the frequency sequence to be tested, wherein the base line noise sequence comprises base line noise of a part of or all channels in a reference bandwidth before the operation of the optical fiber communication system; and the baseline function fitting unit is used for fitting a noise baseline function according to the baseline noise contained in the baseline noise sequence.
Therefore, the noise power under any frequency can be determined by using the noise baseline function, the tested channel does not need to be closed, the noise power of all channels can be obtained simultaneously, and the testing efficiency is improved.
In one implementation, the frequency sequence to be tested includes channel frequencies corresponding to all channels of the full bandwidth in the link; a test cell comprising: a signal transmitting subunit for sequentially transmitting the target-divided test frequency v at the signal transmitting endiTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]N is the total number of channels; the spectrum acquisition subunit is used for acquiring channel spectra corresponding to each group of test signals at the signal receiving end; a spectrum analysis subunit for determining target test frequency v according to the acquired channel spectrumiBaseline noise of the corresponding channel within the reference bandwidth.
By the implementation mode, the baseline noise of each channel in the optical fiber link can be acquired one by one, and the baseline noise distribution condition of the system in the whole frequency band can be accurately described according to the noise baseline function fitted by the baseline noise of each channel, so that the noise power of the channel to be measured can be accurately calculated by using the noise baseline function under the condition of giving the channel to be measured.
In one implementation, the frequency sequence to be tested includes channel frequencies corresponding to some designated channels in the link, and the designated channels are distributed at equal intervals; a test cell comprising: the signal transmitting subunit is used for transmitting test signals corresponding to all the channel frequencies except the channel frequency in the frequency sequence to be tested at the signal transmitting end; the spectrum acquisition subunit is used for acquiring a channel spectrum at the signal receiving end; and the spectrum analysis subunit is used for determining the baseline noise of each specified channel within the reference bandwidth according to the channel spectrum.
Compared with the implementation mode, the implementation mode can test the baseline noise of the partial channels distributed at equal intervals in the optical fiber link at one time, and the partial channels are distributed uniformly in the link, so that the implementation mode has higher test efficiency while ensuring the accuracy of the test result.
In one implementation, the apparatus further comprises: a baseline modification module, the baseline modification module comprising: a reference point noise obtaining unit, configured to obtain a first noise power and a second noise power corresponding to a reference point frequency, where the first noise power is determined according to a channel spectrum of a signal receiving end, the second noise power is calculated according to the noise baseline function, and the reference point is located at each sub-band interval of the optical fiber communication system; the difference judging unit is used for judging whether the difference value of the first noise power and the second noise power is larger than a preset value or not; and the baseline correction unit is used for correcting the noise baseline function according to the difference value if the difference value corresponding to the frequency of the at least one reference point is larger than the preset value.
In one implementation, the baseline modification unit includes: the difference correction function determining subunit is used for fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference point frequency on the two sides of each sub-band; the baseline noise calculation subunit is used for determining a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be measured, wherein the new baseline noise sequence comprises the latest baseline noise of a part or all of channels in a reference wide band after the operation of the optical fiber communication system, and the latest baseline noise is calculated according to the channel frequency and the difference correction function corresponding to the channel frequency attribution sub-band; and the function fitting subunit is used for fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
In the implementation mode, a reference point is set at a sub-band interval of the system, whether a noise baseline function needs to be corrected is judged by monitoring the difference between the first noise power and the second noise power at the reference point, and when the noise baseline function needs to be corrected, the noise baseline function is automatically corrected according to the difference between the first noise power and the second noise power at the reference point, so that the accuracy of an OSNR monitoring result is ensured.
Correspondingly, in an implementation manner, when the difference value corresponding to at least one reference point frequency is greater than a preset value, the first processing module calculates the noise power of the measured channel according to the frequency of the measured channel and the corrected noise baseline function; when the difference values corresponding to all the reference point frequencies are not larger than the preset value, the first processing module directly calculates the noise power of the measured channel according to the frequency of the measured channel and the current noise baseline function. Thereby ensuring the accuracy of the monitoring result.
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In order to more clearly describe the technical solution of the present application, the drawings required to be used in the embodiments will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.
FIG. 1 is a schematic diagram of a dense optical wave multiplexing system shown in some embodiments of the present application;
FIG. 2 is another compact optical wave multiplexing system shown in some embodiments of the present application;
FIG. 3 is a flow diagram of an OSNR monitoring method shown in some embodiments of the present application;
FIG. 4 is a flow diagram illustrating a method of obtaining a noise baseline function in some embodiments of the present application;
FIG. 5 is a flowchart of an implementation manner of S120 in the embodiment shown in FIG. 4 of the present application;
FIG. 6 is a flowchart of another implementation manner of S120 in the embodiment shown in FIG. 4 of the present application;
FIG. 7 is a flow chart of another OSNR monitoring method illustrated in some embodiments herein;
FIG. 8 is a partial schematic view of a channel spectrum shown in some embodiments of the present application;
FIG. 9 is a flowchart of one implementation of S750 in the embodiment of FIG. 7 of the present application;
fig. 10 is a block diagram of an osnr monitoring apparatus according to some embodiments of the present disclosure.
Detailed Description
In order to make those skilled in the art better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.
The osnr monitoring method provided in the present application can be applied to a dense optical wavelength multiplexing system (hereinafter referred to as DWDM system) shown in fig. 1. As shown in fig. 1, the system includes: a plurality of optical transmitters 101, a wave-combining device 102, an optical supervisory channel transmitter 103, an optical fiber link 104, an optical supervisory channel receiver 105, a wave-splitting device 106, and a plurality of optical receivers 107. When the system works, the plurality of optical transmitters 101 are respectively configured to generate signal lights with different wavelengths, the combining device 102 is configured to combine the signal lights with different wavelengths into one beam, the optical supervisory channel transmitter 103 is configured to feed the beam of light combined by the combining device 102 into the optical fiber link 104, the optical supervisory channel receiver 105 is configured to receive light transmitted in the optical fiber link 104, the wavelength splitting device 106 is configured to separate signal lights with different wavelengths from the received light, and the plurality of optical receivers 107 are respectively configured to receive signal lights with different wavelengths.
It should be noted that the DWDM system may further include various amplifiers not shown in fig. 1, such as an optical power amplifier BA, an optical line amplifier LA, and a preamplifier PA. It should be understood that the signal light power mentioned in this application refers to the power of the signal light after being transmitted through the optical communication system, i.e. the power after being amplified or lost, and the noise power refers to the accumulated noise power introduced by various amplifiers in the transmission link.
Typically, fiber optic communication systems divide the entire frequency band into several working sub-bands, e.g. fiber optic communication systems comprising ROADMs (reconfigurable optical add-drop multiplexers).
Fig. 2 shows another possible DWDM system according to an embodiment of the present application, which, as shown in fig. 2, includes: a plurality of sub-band input interfaces 201, a pseudo-light generating device 202, a wave combining device 203, a submarine cable transmission system 204, a wave splitting device 205 and a plurality of sub-band output interfaces 206. When the system works, each sub-band input interface 201 is used for transmitting one or more beams of service optical signals with different wavelengths to the wave combining device 203, the false light generating device 202 is used for generating false optical signals with one or more wavelengths and transmitting the false optical signals to the wave combining device 203, and the wave combining device 203 is used for combining the signal light with different wavelengths into one beam and feeding the beam into the submarine cable transmission system 204 through the interface of the submarine cable transmission system; the submarine cable transmission system 204 includes an optical fiber link and an amplifier, the signal light is transmitted to the wavelength division device 205 through the submarine cable transmission system, and the wavelength division device 205 separates the received signal light with different wavelengths and outputs the signal light through the sub-band output interfaces 206.
It can be seen that, unlike the DWDM system of fig. 1, a portion of the DWDM system of fig. 2 is deployed subsea, i.e., a submarine cable transmission system. Limited by the operating environment, the submarine cable transmission system includes amplifiers that need to operate in a saturated mode of operation at all times without being able to modify the configuration of the amplifiers at any time. In addition, when the wave number of the service optical signal is insufficient, it is necessary to maintain the basic stability of the power of each channel by emitting a dummy optical signal, i.e., a non-service optical signal, which may be a comb-filtered light source of ASE (amplified spontaneous emission) or a continuous wave light source (continuous wave light source).
As known from the wave dropping method described in the background art, the method cannot monitor the OSNR of the system in operation because the signal source needs to be turned off when the OSNR is used, i.e. the service must be interrupted.
In addition, because the method can test one channel at a time, for a large-capacity optical fiber communication system, if the test of each channel is to be completed, the test process is very complicated, and the test efficiency is low.
An OSNR test method based on the spectrum correlation is characterized in that under the premise that a channel signal is a PDM modulation signal, according to the characteristic that the spectrum components in the signal are correlated and the spectrum components in noise are uncorrelated, the OSNR is calculated by measuring the correlation between two time-varying wavelength components which are separated by a preset interval in the channel spectrum. Wherein for measuring the correlation properties of the spectral components two independently tunable optical receivers are required and an ultra high resolution in the range <50Hz is required of the optical receivers, such as coherent detectors.
Although the OSNR testing method based on the inter-spectrum correlation can monitor the OSNR of the operating system in real time, for the DWDM system deployed on the sea floor as shown in fig. 2, the OSNR testing cannot be performed on the dummy optical signal because the dummy optical signal is not a PDM modulated signal. Moreover, based on fourier transform (used in the inter-spectral correlation analysis based on the frequency domain spectrum) and a correlation statistical algorithm, the test speed is very slow, and the efficiency is low. In addition, the need for coherent detectors in this approach increases test costs.
The present application provides a method for monitoring osnr, as shown in fig. 3, the method may include:
and S200, acquiring the central frequency and the optical signal power of the channel to be detected at a signal receiving end.
In order to keep the power of each channel stable, the optical fiber link has uniform signal light distribution of different wavelengths when the system is operated. When the wave number of the traffic signal is insufficient, a false light signal with a certain wave number is emitted, so that the signal distribution in the link is uniform. As an example, each fiber link may include up to 40 channels, 30 of which may be used to transmit traffic signals and the other 10 of which may be used to transmit dummy optical signals. Or, 18 channels with the same interval are used for transmitting the traffic signals, and the other 2 channels with the same interval are used for transmitting the false optical signals.
The channel under test may be any one or more channels in the fiber link. In specific implementation, a spectrum monitoring device can be arranged at a signal receiving end or an OSNR monitoring point of the optical fiber communication system. In the system operation process, a spectrum monitoring device is used for collecting the channel spectrum of the optical fiber link in real time, and the central frequency of the channel to be measured is determined by analyzing the collected channel spectrum.
In addition, the optical signal power of the measured channel may specifically be the total power of the measured channel within a channel bandwidth Bs, and the channel bandwidth Bs may be a 3dB bandwidth of the spectral analysis channel, which may be determined according to the configured bandwidth of the multiplexing device in the optical communication system. The total power of the measured channel in the channel bandwidth can be calculated according to the spectrogram of the measured channel.
It should be appreciated that in S200, the center frequency and optical signal power of each channel in the optical fiber link may be acquired simultaneously.
And S300, calculating the noise power of the measured channel according to the central frequency of the measured channel and the pre-acquired noise baseline function.
The noise baseline function is a function describing the baseline noise distribution of the system in the whole frequency band, and under the condition of known noise baseline function, the noise power of any channel can be determined by an interpolation method. For ease of illustration, the noise baseline function can be denoted as fn, and the noise power of the channel can be calculated as fn (v) by substituting the channel frequency v into the noise baseline function fn.
In some embodiments, the noise baseline function of the fiber optic communication system is obtained by actual measurement prior to operation of the system.
Referring to fig. 4, the step of obtaining the noise baseline function may specifically include:
s110, determining a frequency sequence to be tested, wherein the frequency sequence to be tested comprises channel frequencies corresponding to part or all of channels in the optical fiber link.
In one example, the frequency sequence to be measured can be expressed as [ v ]1,ν2，……，ν39,ν40]. In this example, the total number of channels in a fiber link is 40, and the channel frequencies of channel 1, channel 2, … …, channel 39, and channel 40 are v1、ν2、……，ν39、ν40. The frequency sequence to be tested comprises channel frequencies corresponding to all full-bandwidth channels in the optical fiber link.
In another example, the frequency sequence to be measured may be expressed as [ v ]2，ν4，……，ν38,ν40]In this example, the total number of channels in a fiber link is 40, and the channel frequencies of channel 1, channel 4, … …, channel 39, and channel 40 are v1、ν2、……，ν39、ν40. The frequency sequence to be measured comprises channel frequencies corresponding to half of channels distributed at equal intervals in the optical fiber link. S120, according to the frequency sequence to be measuredThe column obtains a baseline noise sequence that includes a baseline noise of a portion or all of the channels in the fiber link within a reference bandwidth before the fiber optic communication system is operated.
In one implementation, the frequency sequence to be measured includes channel frequencies corresponding to all channels of the full bandwidth. Referring to fig. 5, in this implementation, S120 may further include S1211-S1213, which may be performed before the operation of the optical fiber communication system.
S1211, at the signal sending end, sequentially transmitting the object test frequency viTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]And n is the total number of channels. Wherein the test signals of all frequencies may be false light signals generated by the false light generating device.
And S1212, sequentially collecting channel spectrums corresponding to each group of test signals at the signal receiving end.
S1213, according to the channel spectrum collected each time, determining each target testing frequency viBaseline noise of the corresponding channel within the reference bandwidth. Wherein, the reference bandwidth is 12.5GHz according to the definition requirement of the ITUT standard on the OSNR.
For example, v in the frequency sequence to be measured is first treated1Testing, i is 1, the target testing frequency is v1. Specifically, at the signal transmitting end, a first group of false optical signals are transmitted, and the first group of false optical signals comprise v2～νnA corresponding false optical signal; collecting a first channel spectrum corresponding to the first group of false light signals at a signal receiving end through a spectrum monitoring device; and determining the baseline noise of the channel 1 in the reference bandwidth according to the first channel spectrum.
Then v in the frequency sequence to be measured2Testing is carried out, i is equal to i +1, and the target testing frequency is v2. Specifically, at the signal transmitting end, a second group of false optical signals are transmitted, and the second group of false optical signals comprise v1、ν3～νnA corresponding false optical signal; collecting a second channel spectrum corresponding to a second group of false light signals at a signal receiving end through a spectrum monitoring device; then, according to the second channel spectrum, determining that the channel 2 is in the reference bandBaseline noise within the width.
Repeating the steps, sequentially changing i to i +1 to respectively treat v in the frequency sequence to be measured3～νnAnd testing to respectively obtain the baseline noise of the channels 3-n in the reference bandwidth.
In one example, the baseline noise sequence may be represented as [ P ]ν1,Pν2，……，Pν39,Pν40]. In this example, the baseline noise sequence is based on the frequency sequence [ v ] to be measured1,ν2，……，ν39,ν40]Obtained, P in sequenceν1,Pν2，……，Pν39,Pν40Baseline noise within the reference bandwidth for channel 1, channel 2, … …, channel 39, and channel 40, respectively.
By the implementation mode, the baseline noise of each channel in the optical fiber link can be acquired one by one, and the baseline noise distribution condition of the system in the whole frequency band can be accurately described according to the noise baseline function fitted by the baseline noise of each channel, so that the noise power of the channel to be measured can be accurately calculated by using the noise baseline function under the condition of giving the channel to be measured.
In another implementation, the frequency sequence to be tested includes channel frequencies corresponding to some designated channels in the optical fiber link, and the some designated channels are distributed at equal intervals in the link. For example, when the total number of channels in the link is 2n, part of the designated channels may be equally spaced channels 2j, and the frequency sequence to be measured includes a channel frequency v corresponding to the channel 2j in the optical fiber link2jWherein j is a positive integer less than or equal to n, i.e., j belongs to [1, n ]]. Referring to fig. 6, in this implementation, S120 may further include S1221-S1223:
and S1221, at the signal sending end, sending test signals corresponding to all channel frequencies except the channel frequency in the frequency sequence to be tested.
For example, if the frequency sequence to be measured includes the channel frequency v corresponding to the channel 2j in the optical fiber link2jThen, the channel frequency other than the channel frequency in the frequency sequence to be measured is the channel frequency corresponding to the channel (2j +1)ν2j+1。
In one example, the frequency sequence to be measured is [ v ]2，ν4，……，ν38,ν40]Then, according to S1221, it is necessary to transmit v at the same time at the signal transmitting end1，ν3，……，ν39The false light signal of (2).
S1222, at the signal receiving end, acquiring a channel spectrum corresponding to the test signal.
And S1223, determining the baseline noise of each appointed channel in the reference bandwidth according to the channel spectrum.
Following the example in S1221, the baseline noise P for channel 2j within the reference bandwidth can be determined from the channel spectrumν2j。
For example, when the frequency sequence to be measured is [ v ]2，ν4，……，ν38,ν40]In the example shown, the baseline noise P for channel 2, channel 4, … …, signal 38, channel 40 within the reference bandwidth may be determined from the channel spectrumν2，Pν4，……，Pν38,Pν40The resulting baseline noise sequence may be denoted as [ P ]ν2，Pν4，……，Pν38,Pν40]。
Compared with the first implementation mode, the implementation mode can test the baseline noise of part of the designated channels in the optical fiber link at one time, and the part of the channels are uniformly distributed in the link, so that the implementation mode has higher test efficiency while ensuring the accuracy of the test result.
And S130, fitting a noise baseline function according to the baseline noise contained in the baseline noise sequence.
For example, a least squares fit is used to fit the baseline noise data in the baseline noise sequence to obtain a noise baseline function.
In other embodiments, the baseline noise of each channel in the link can be calculated according to the configuration parameters of the amplifier in the transmission link, so that the noise baseline function can be fitted according to the baseline noise of each channel. The specific implementation process herein can be implemented according to the prior art, and is not described herein in detail.
In S300, the noise power of the measured channel can be calculated by substituting the center frequency of the measured channel into the noise baseline function.
S400, determining the optical signal-to-noise ratio of the channel to be detected according to the optical signal power and the noise power.
Specifically, the osnr of the measured channel may be calculated according to the following formula:
wherein v represents the center frequency of the tested channel, P (v) represents the optical signal power of the tested channel, fn (v) represents the noise power of the tested channel within 12.5GHz of the reference bandwidth, and Bs represents the channel bandwidth.
From the above embodiments, the present application provides an OSNR monitoring method, which can determine a noise power at any frequency according to a pre-obtained noise baseline function without closing any channel, and then calculate a real-time OSNR of any channel by combining with a real-time analysis of a channel spectrum. Because the method does not need to close the tested channel, the OSNR of the system can be monitored in real time under the condition of not influencing the operation of the system. In addition, the method can also monitor the OSNR of all channels in the optical fiber link at the same time, has high test efficiency, is suitable for being not influenced by the signal types of the channels, and can be suitable for various modulated signals and non-modulated false optical signals.
Fig. 7 is a diagram illustrating another embodiment of the osnr monitoring method according to the present application. As shown in fig. 7, the method may include:
and S710, collecting the channel spectrum at a signal receiving end.
S720, determining the center frequency of the tested channel, the optical signal power and the first noise power corresponding to the reference frequency according to the collected channel spectrum.
In the application, a spectrum monitoring device is arranged at a signal receiving end or an OSNR monitoring point of an optical fiber communication system. And in the system operation process, a spectrum monitoring device is used for collecting the channel spectrum of the optical fiber link in real time. From the collected channel spectra, the center frequency of the signal in each channel can be determined, and the total power can also be determined using an integration method and channel bandwidth.
Typically, some optical fiber communication systems divide the entire frequency band into several working sub-bands, for example, optical fiber communication systems including ROADMs (reconfigurable optical add-drop multiplexers), with a predetermined spacing between each sub-band. For example, in the channel spectrogram shown in fig. 8, the interval between the working subband X and the working subband Y is (Xb, Ya). Since the transmission characteristics of the system determine that the change of the noise floor in the sub-band is monotonous along with the change of the system performance, the real noise floor of the system can be reflected at the sub-band interval.
Based on the reference point, the first noise power corresponding to the frequency of the reference point, namely the current baseline noise at the reference point can be determined according to the channel spectrum.
It should be noted that at least two reference points need to be predetermined. Therefore, according to the first noise power corresponding to each reference point frequency, the distribution rule of the current local baseline noise of the system can be determined.
And S730, calculating a second noise power corresponding to the reference point frequency according to the reference point frequency and the current noise baseline function.
Specifically, the reference point frequency is substituted into the current noise baseline function, and the second noise power corresponding to the reference point frequency is calculated.
S740, judging whether the difference value between the first noise power and the second noise power is larger than a preset value; if so, go to S750, otherwise, go to S770.
It should be understood that, if the difference between the first noise power and the second noise power is greater than the preset value, it indicates that the system noise floor distribution described by the current noise baseline function is greatly different from the system real noise floor distribution, and at this time, the current noise baseline function needs to be corrected according to the difference, so that the corrected noise baseline function can accurately reflect the real noise floor of the system.
As an implementation manner, when a difference between the first noise power and the second noise power corresponding to at least one reference point frequency is greater than a preset value, it is considered that the trigger condition for correcting the noise baseline function is satisfied. And if the difference value between the first noise power and the second noise power corresponding to all the reference point frequencies is not greater than the preset value, determining that the trigger condition for correcting the noise baseline function is not met.
S750, correcting the noise baseline function according to the difference value of the first noise power and the second noise power.
In a possible implementation manner, S750 may specifically include the steps shown in fig. 9:
and S751, fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference points on the two sides of each sub-band.
Following the example shown in FIG. 8, the reference points on both sides of sub-band X are A and B, and the reference points on both sides of sub-band Y are B and C, assuming that reference point A corresponds to a difference of δAThe difference corresponding to the reference point B is deltaBThe difference corresponding to the reference point C is deltaCThen, according to δAAnd deltaBThe difference correction function f corresponding to the sub-band X can be fittedmxAccording to δBAnd deltaCThe difference correction function f corresponding to the sub-band Y can be fittedmy。
And S752, determining a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be detected.
The new baseline noise sequence comprises the latest baseline noise of a part or all of channels in a reference broadband, and the latest baseline noise is calculated according to the channel frequency and the difference correction function corresponding to the channel frequency attributive sub-band.
It should be understood that each channel frequency has one home subband. And substituting each channel frequency in the frequency sequence to be detected into the difference correction function corresponding to the channel frequency attributive sub-band to obtain the difference value corresponding to each channel frequency. And adding the difference value corresponding to each channel frequency with the baseline noise determined in advance to obtain the latest baseline noise corresponding to each channel frequency.
In one example, the calculation process according to S751-S753 can be as shown in Table 1. At the position ofIn the example, reference point frequencies at reference point A, B and C in FIG. 8 are denoted as v, respectivelya、νb、νcV. willa、νb、νcThe corresponding first noise powers are respectively denoted as Pa、PbAnd PcV. willa、νb、νcThe corresponding second noise powers are respectively denoted as fn (v)a)、fn(νb)、fn(νc) V is thena、νb、νcCorresponding difference deltaA、δBAnd deltaCAre respectively deltaA＝Pa-fn(νa)、δB＝Pb-fn(νb)、δC＝Pc-fn(νc) Using least squares to δA、δBFitting to obtain a difference correction function fmx corresponding to subband X, for δBAnd deltaCFitting may result in a difference correction function fmy for subband Y. The frequency sequence to be tested comprises a channel frequency v of channels 1-n1-νnWherein v is1＜νa＜νi，νi＜νb＜νj，νj＜νc＜νn(ii) a V in frequency sequence to be measurediThe attribution sub-band is a sub-band X, vjThe attributive sub-band of (2) is a sub-band Y; v is toiV can be calculated by sequentially substituting into the difference correction function fmxiCorresponding difference fmx (v)i) V. willjThe v can be calculated by substituting the difference correction function fmyjCorresponding difference fmy (v)j). The original baseline noise sequence comprises original baseline noise Pv of channels 1-n1-PνnFmx (v)i) And P viAdd up to get the latest baseline noise corresponding to channel i, fmy (v)j) And P vjThe latest baseline noise for channel j can be obtained by addition.
TABLE 1
And S753, fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
Specifically, a least square method is adopted to fit baseline noise data in the latest baseline noise sequence to obtain a new noise baseline function.
And S760, calculating the noise power of the measured channel according to the central frequency of the measured channel and the corrected noise baseline function.
And S770, calculating the noise power of the measured channel according to the central frequency of the measured channel and the current noise baseline function.
And S780, determining the optical signal-to-noise ratio of the measured channel according to the optical signal power and the noise power of the measured channel.
According to the embodiments, the OSNR monitoring method provided by the present application sets the reference point at the sub-band interval of the system, determines whether the noise baseline function needs to be corrected by monitoring the difference between the first noise power and the second noise power at the reference point, and corrects the noise baseline function according to the difference between the first noise power and the second noise power when the noise baseline function needs to be corrected, so as to ensure the accuracy of the OSNR monitoring result.
An optical signal to noise ratio monitoring apparatus is further provided in an embodiment of the present application, as shown in fig. 10, the apparatus may include: the data acquisition module M101 is used for acquiring the central frequency and the optical signal power of the channel to be detected at a signal receiving end; the first processing module M102 is configured to calculate a noise power of the measured channel according to the center frequency and a noise baseline function obtained in advance; and the second processing module M103 is configured to determine an optical signal-to-noise ratio of the measured channel according to the optical signal power and the noise power.
In some embodiments, the apparatus further comprises: a baseline acquisition module, the baseline acquisition module comprising: the frequency sequence to be tested comprises channel frequencies corresponding to part or all of channels in a link; a baseline noise test unit, configured to obtain a baseline noise sequence according to the frequency sequence to be tested, where the baseline noise sequence includes baseline noise of the partial or all channels in a reference bandwidth before an optical fiber communication system operates; and the baseline function fitting unit is used for fitting the noise baseline function according to the baseline noise contained in the baseline noise sequence.
In some embodiments, the second processing module calculates the osnr of the measured channel according to the following formula,
wherein v represents the center frequency of the channel to be tested, P (v) represents the optical signal power of the channel to be tested, fn (v) represents the noise power of the channel to be tested within the reference bandwidth of 12.5GHz, and Bs represents the channel bandwidth.
In some embodiments, the data acquisition module comprises: the spectrum acquisition unit is used for acquiring a channel spectrum at the signal receiving end; and the spectrum analysis unit is used for determining the center frequency and the optical signal power of the measured channel according to the channel spectrum.
In some embodiments, the frequency sequence to be tested includes channel frequencies corresponding to all channels in a full bandwidth in a link; the test unit includes: a signal transmitting subunit for sequentially transmitting the target-divided test frequency v at the signal transmitting endiTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]N is the total number of channels; the spectrum acquisition subunit is used for sequentially acquiring channel spectra corresponding to each group of test signals at the signal receiving end; a spectrum analysis subunit for determining target test frequency v according to the acquired channel spectrumiBaseline noise of the corresponding channel within the reference bandwidth.
In some embodiments, the frequency sequence to be tested includes channel frequencies corresponding to some designated channels in the link, and the designated channels are distributed at equal intervals; the test unit includes: the signal transmitting subunit is used for transmitting test signals corresponding to all the channel frequencies except the channel frequency in the frequency sequence to be tested at the signal transmitting end; the spectrum acquisition subunit is used for acquiring a channel spectrum at the signal receiving end; and the spectrum analysis subunit is used for determining the baseline noise of each specified channel within the reference bandwidth according to the channel spectrum.
In some embodiments, further comprising: a baseline modification module, the baseline modification module comprising: a reference point noise obtaining unit, configured to obtain a first noise power and a second noise power corresponding to a reference point frequency, where the first noise power is determined according to a channel spectrum of a signal receiving end, the second noise power is calculated according to the noise baseline function, and the reference point is located at each sub-band interval of the optical fiber communication system; the difference judging unit is used for judging whether the difference value of the first noise power and the second noise power is larger than a preset value or not; and the baseline correction unit is used for correcting the noise baseline function according to the difference value if the difference value corresponding to the frequency of at least one reference point is larger than a preset value.
In some embodiments, the baseline modification unit comprises: the difference correction function determining subunit is used for fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference points on the two sides of each sub-band; a baseline noise calculation subunit, configured to determine a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be measured, where the new baseline noise sequence includes a latest baseline noise of a part or all of channels in a reference wide band after the optical fiber communication system operates, and the latest baseline noise is calculated according to a channel frequency and a difference correction function corresponding to a sub-band to which the channel frequency belongs; and the function fitting subunit is used for fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
In some embodiments, when the difference value corresponding to at least one reference point frequency is greater than a preset value, the first processing module calculates the noise power of the measured channel according to the frequency of the measured channel and the corrected noise baseline function; and when the difference values corresponding to all the reference point frequencies are not greater than the preset value, the first processing module directly calculates the noise power of the measured channel according to the frequency of the measured channel and the current noise baseline function.
From the above embodiments, the present application provides an OSNR monitoring apparatus, which can determine noise power at any frequency according to a pre-obtained noise baseline function without closing any channel, and then calculate real-time OSNR of any channel by combining with real-time analysis of a channel spectrum. Because the method does not need to close the tested channel, the OSNR of the system can be monitored in real time under the condition of not influencing the operation of the system. In addition, the method can also monitor the OSNR of all channels in the optical fiber link at the same time, has high test efficiency, is not influenced by the signal types of the channels, and can be suitable for various modulated signals and non-modulated false optical signals.
In specific implementation, the present invention further provides a computer storage medium, where the computer storage medium may store a program, and the program may include some or all of the steps in each embodiment of the osnr monitoring method provided by the present invention when executed. The storage medium may be a magnetic disk, an optical disk, a read-only memory (ROM) or a Random Access Memory (RAM).
Those skilled in the art will readily appreciate that the techniques of the embodiments of the present invention may be implemented using software plus any required general purpose hardware platform. Based on such understanding, the technical solutions in the embodiments of the present invention may be essentially or partially implemented in the form of a software product, which may be stored in a storage medium, such as ROM/RAM, magnetic disk, optical disk, etc., and includes several instructions for enabling a computer device (which may be a personal computer, a server, or a network device, etc.) to execute the method according to the embodiments or some parts of the embodiments.
The same and similar parts in the various embodiments in this specification may be referred to each other. In particular, as for the apparatus embodiment, since it is substantially similar to the method embodiment, the description is simple, and the relevant points can be referred to the description in the method embodiment.
The above-described embodiments of the present invention should not be construed as limiting the scope of the present invention.
Claims (18)
1. An osnr monitoring method, comprising:
acquiring the central frequency and the optical signal power of a channel to be detected at a signal receiving end;
calculating the noise power of the measured channel according to the central frequency and a pre-acquired noise baseline function;
and determining the optical signal-to-noise ratio of the channel to be detected according to the optical signal power and the noise power.
2. The method of claim 1, wherein the step of obtaining the noise baseline function comprises:
determining a frequency sequence to be tested, wherein the frequency sequence to be tested comprises channel frequencies corresponding to partial or all channels in a link;
acquiring a baseline noise sequence according to the frequency sequence to be detected, wherein the baseline noise sequence comprises baseline noise of the partial or all channels in a reference bandwidth before the operation of the optical fiber communication system;
and fitting the noise baseline function according to the baseline noise contained in the baseline noise sequence.
3. The method according to claim 2, wherein the frequency sequence to be tested includes channel frequencies corresponding to all channels in a full bandwidth within a link; obtaining a baseline noise sequence according to the frequency sequence to be detected, including:
before the operation of the optical fiber communication system,
at a signal sending end, sequentially transmitting a target test frequency viTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]N is the total number of channels;
sequentially collecting channel spectrums corresponding to each group of test signals at a signal receiving end;
according to the channel spectrum acquired each time, determining the frequency v of each target testiBaseline noise of the corresponding channel within the reference bandwidth.
4. The method according to claim 2, wherein the frequency sequence to be tested comprises channel frequencies corresponding to some designated channels in the link, and the designated channels are distributed at equal intervals; obtaining a baseline noise sequence according to the frequency sequence to be detected, including:
before the operation of the optical fiber communication system,
at a signal sending end, sending test signals corresponding to all channel frequencies except the channel frequency in the frequency sequence to be tested;
and at a signal receiving end, acquiring a channel spectrum, and determining the baseline noise of each appointed channel in a reference bandwidth according to the channel spectrum.
5. The method of claim 2, wherein before calculating the noise power of the measured channel, the method further comprises:
acquiring a first noise power and a second noise power corresponding to a reference point frequency, wherein the first noise power is determined according to a channel spectrum of a signal receiving end, the second noise power is calculated according to the noise baseline function, and the reference point is positioned at each sub-band interval of the optical fiber communication system;
judging whether the difference value of the first noise power and the second noise power is larger than a preset value;
and if the difference corresponding to the frequency of at least one reference point is larger than a preset value, correcting the noise baseline function according to the difference.
6. The method of claim 5, wherein modifying the noise baseline function based on the difference comprises:
fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference points on the two sides of each sub-band;
determining a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be measured, wherein the new baseline noise sequence comprises the latest baseline noise of a part or all of channels in a reference wide band after the operation of the optical fiber communication system, and the latest baseline noise is obtained by calculation according to the channel frequency and the difference correction function corresponding to the sub-band to which the channel frequency belongs;
and fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
7. The method of claim 5, wherein calculating the noise power of the measured channel based on the center frequency and a pre-obtained noise baseline function comprises:
when the difference value corresponding to at least one reference point frequency is larger than a preset value, calculating the noise power of the measured channel according to the frequency of the measured channel and the corrected noise baseline function;
and when the difference values corresponding to all the reference point frequencies are not greater than a preset value, directly calculating the noise power of the measured channel according to the frequency of the measured channel and the current noise baseline function.
8. The method of claim 1, wherein determining the osnr of the measured channel based on the optical signal power and the noise power comprises:
calculating the optical signal-to-noise ratio of the measured channel according to the following formula,
wherein v represents the center frequency of the tested channel, P (v) represents the optical signal power of the tested channel, fn (v) represents the noise power of the tested channel within 12.5GHz of the reference bandwidth, and Bs represents the channel bandwidth.
9. The method of claim 1, wherein the obtaining the center frequency and the optical signal power of the measured channel at the signal receiving end comprises:
collecting channel spectrum at a signal receiving end;
and determining the center frequency and the optical signal power of the measured channel according to the channel spectrum.
10. An osnr monitoring apparatus, comprising:
the data acquisition module is used for acquiring the central frequency and the optical signal power of the channel to be detected at the signal receiving end;
the first processing module is used for calculating the noise power of the channel to be measured according to the central frequency and a noise baseline function acquired in advance;
and the second processing module is used for determining the optical signal-to-noise ratio of the channel to be tested according to the optical signal power and the noise power.
11. The apparatus of claim 10, further comprising: a baseline acquisition module, the baseline acquisition module comprising:
the frequency giving unit to be tested is used for determining a frequency sequence to be tested, and the frequency sequence to be tested comprises channel frequencies corresponding to part or all of channels in a link;
a baseline noise test unit, configured to obtain a baseline noise sequence according to the frequency sequence to be tested, where the baseline noise sequence includes baseline noise of the partial or all channels in a reference bandwidth before an optical fiber communication system operates;
and the baseline function fitting unit is used for fitting the noise baseline function according to the baseline noise contained in the baseline noise sequence.
12. The apparatus of claim 11, wherein the frequency sequence to be tested includes channel frequencies corresponding to all channels in a full bandwidth within a link; the test unit includes:
a signal transmitting subunit for sequentially transmitting the target-divided test frequency v at the signal transmitting endiTest signals corresponding to all other channel frequencies, i ∈ [1, n ]]N is the total number of channels;
the spectrum acquisition subunit is used for sequentially acquiring channel spectra corresponding to each group of test signals at the signal receiving end;
a spectrum analysis subunit for determining target test frequency v according to the acquired channel spectrumiBaseline noise of the corresponding channel within the reference bandwidth.
13. The apparatus according to claim 11, wherein the frequency sequence to be tested includes channel frequencies corresponding to designated channels in a link, and the designated channels are distributed at equal intervals; the test unit includes:
the signal transmitting subunit is used for transmitting test signals corresponding to all the channel frequencies except the channel frequency in the frequency sequence to be tested at the signal transmitting end;
the spectrum acquisition subunit is used for acquiring a channel spectrum at the signal receiving end;
and the spectrum analysis subunit is used for determining the baseline noise of each specified channel within the reference bandwidth according to the channel spectrum.
14. The apparatus of claim 11, further comprising: a baseline modification module, the baseline modification module comprising:
a reference point noise obtaining unit, configured to obtain a first noise power and a second noise power corresponding to a reference point frequency, where the first noise power is determined according to a channel spectrum of a signal receiving end, the second noise power is calculated according to the noise baseline function, and the reference point is located at each sub-band interval of the optical fiber communication system;
the difference judging unit is used for judging whether the difference value of the first noise power and the second noise power is larger than a preset value or not;
and the baseline correction unit is used for correcting the noise baseline function according to the difference value if the difference value corresponding to the frequency of at least one reference point is larger than a preset value.
15. The apparatus of claim 14, wherein the baseline modification unit comprises:
the difference correction function determining subunit is used for fitting a difference correction function corresponding to each sub-band according to the difference value corresponding to the reference points on the two sides of each sub-band;
a baseline noise calculation subunit, configured to determine a new baseline noise sequence according to the difference correction function corresponding to each sub-band and the frequency sequence to be measured, where the new baseline noise sequence includes a latest baseline noise of a part or all of channels in a reference wide band after the optical fiber communication system operates, and the latest baseline noise is calculated according to a channel frequency and a difference correction function corresponding to a sub-band to which the channel frequency belongs;
and the function fitting subunit is used for fitting a new noise baseline function according to the latest baseline noise contained in the new baseline noise sequence.
16. The apparatus of claim 14, wherein:
when the difference value corresponding to at least one reference point frequency is larger than a preset value, the first processing module calculates the noise power of the measured channel according to the frequency of the measured channel and the corrected noise baseline function;
and when the difference values corresponding to all the reference point frequencies are not greater than the preset value, the first processing module directly calculates the noise power of the measured channel according to the frequency of the measured channel and the current noise baseline function.
17. The apparatus of claim 10, wherein the second processing module calculates the OSNR of the measured channel according to the following formula,
wherein v represents the center frequency of the tested channel, P (v) represents the optical signal power of the tested channel, fn (v) represents the noise power of the tested channel within 12.5GHz of the reference bandwidth, and Bs represents the channel bandwidth.
18. The apparatus of claim 10, wherein the data acquisition module comprises:
the spectrum acquisition unit is used for acquiring a channel spectrum at the signal receiving end;
and the spectrum analysis unit is used for determining the center frequency and the optical signal power of the measured channel according to the channel spectrum.
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