CN118944750A

CN118944750A - Estimation Method of Optical Signal-to-Noise Ratio

Info

Publication number: CN118944750A
Application number: CN202410937468.7A
Authority: CN
Inventors: 王奕杰; 王浩南
Original assignee: Jiyiwei Semiconductor Shanghai Co ltd
Current assignee: Jiyiwei Semiconductor Shanghai Co ltd
Priority date: 2024-07-12
Filing date: 2024-07-12
Publication date: 2024-11-12
Anticipated expiration: 2044-07-12
Also published as: CN118944750B

Abstract

The application relates to the technical field of optical communication and discloses an optical signal to noise ratio estimation method. The method comprises the following steps: inserting a predetermined number of zero sequences into subframes of a frame structure of the optical signal sequence according to a predetermined period, and transmitting the optical signal sequence to a receiving end; the receiving end receives the optical signal sequence and judges whether the current subframe of the optical signal sequence comprises a zero sequence or not; if so, acquiring a signal of the position of the zero sequence in the subframe, and removing partial signals adjacent to other parts of the subframe in the signal to obtain a noise sequence; performing noise whitening treatment on the noise sequence by adopting a Berger algorithm, and calculating the power of the noise sequence after the noise whitening treatment; if not, selecting a load signal at a partial position in the subframe as a payload signal and calculating power of the payload signal; the osnr is calculated from the power of the noise sequence and the power of the payload signal. The application reduces the colored distortion of noise in the transmission process and obviously improves the estimation precision of the link OSNR.

Description

Optical signal to noise ratio estimation method

Technical Field

The application relates to the technical field of optical communication, in particular to an optical signal to noise ratio estimation method.

Background

Optical signal to noise ratio (Optical Signal Noise Ratio, OSNR) measurement reporting is an important means of digital diagnostic monitoring (Digital Diagnostic Monitoring, DDM) of optical communication links. OSNR is defined as:

Where P _sig is the power of the in-band effective signal and P _noise is the in-band noise power over a fixed 0.1nm range bandwidth.

Early point-to-point networks were typically reported by measuring out-of-band OSNR. This method measures out-of-band noise in the non-valid signal region to obtain an OSNR value as shown in fig. 1. The assumption of the out-of-band OSNR measurement method is that the noise is a wideband signal, with out-of-band and in-band noise being substantially the same. When the network evolution is more complex as in ROADM networks, the assumption of this approach is generally difficult to hold, and thus the measurement error is large.

Thus requiring in-band noise measurements. But the signal and noise of the in-band part are mixed together, how to separate the signal and noise without interrupting the actually occurring traffic is a problem. One common practice at present is to fix a signal sequence sent as 0 at some positions in the frame structure design, acquire signals at these positions as noise signals of the optical fiber link at the receiving end, calculate the noise power, and thus calculate the OSNR value. The method can improve OSNR accuracy over out-of-band noise methods. This method is referred to herein as the zero insertion method, as shown in FIG. 2.

In optical fiber long-distance transmission, a problem faced by the zero insertion method is colored distortion of noise due to various optical fiber link damages and multi-stage filtering effects in complex networking. For example, because equalization processing is required to be performed on the receiving end digital signal after long-distance transmission, white noise of a link can be changed into colored noise, so that error deviation of base noise estimation is caused, and the accuracy of an OSNR estimated value is reduced. In addition, inter-symbol interference ISI can also lead to the formation of colored noise.

This section is intended to provide a background or context to the embodiments of the application that are recited in the claims. The description herein is not admitted to be prior art by inclusion in this section.

Disclosure of Invention

The application aims to provide an optical signal to noise ratio estimation method, which reduces the colored distortion suffered by noise in the transmission process and remarkably improves the link OSNR estimation precision.

The application discloses a method for estimating an optical signal to noise ratio, which comprises the following steps:

Inserting a predetermined number of zero sequences into subframes of a frame structure of an optical signal sequence according to a predetermined period, and transmitting the optical signal sequence to a receiving end;

the receiving end receives the optical signal sequence and judges whether the current subframe of the optical signal sequence comprises a zero sequence or not;

if so, acquiring a signal of the position of the zero sequence in the subframe, and removing partial signals adjacent to other parts of the subframe in the signal to obtain a noise sequence;

performing noise whitening treatment on the noise sequence by adopting a Berger algorithm, and calculating the power of the noise sequence after the noise whitening treatment;

if not, selecting a load signal at a partial position in the subframe as a payload signal and calculating the power of the payload signal; and

And calculating the optical signal to noise ratio according to the power of the noise sequence and the power of the effective load signal.

In a preferred embodiment, the noise whitening process further comprises:

P-order primary lattice estimation is carried out on a noise sequence R, the length of the noise sequence is N1, the whitening coefficient is a _m, m 1,2, & gt, p is that an initialization forward sequence is efp ₀ =R, an initialization backward sequence is ebp ₀ =R, and an mth-order coefficient is

Wherein efp _m＝efp_m-1(2:end+k_mebp_m-1 (1:end-1);

ebp_m＝ebp_m-1(1:end-1)+k_mefp_m-1(2:end；

a_m＝[a_m-1;0]+k_m[0;conj(flipud(a_m-1)；

The noise sequence after the noise whitening processing is R' =conv (R, a _m);

Wherein efp _m and ebp _m are forward and backward sequences at the mth order iteration, m 1, 2. N is a sequence index of efp _m and ebp _m, and when the m-th order iterates, the value range of the index N is (0, N1-m); conj () is a conjugate function, flipud is a data flip function; conv () is a convolution function.

In a preferred embodiment, the p-th order of the primary lattice estimation has a value of 1 st order or 2 nd order.

In a preferred embodiment, after calculating the power of the noise sequence after the noise whitening process, the method further comprises: an average of the power of the noise sequence over the window length is calculated as the power of the noise sequence.

In a preferred embodiment, selecting the load signal at a partial position in the subframe as the payload signal and calculating the power of the payload signal further comprises: an average of the power of the payload signal over the window length is calculated as the power of the payload signal.

In a preferred embodiment, the frame structure of the optical signal sequence comprises a plurality of frames, each frame comprising a plurality of subframes, the zero sequence being inserted in the same position of the same subframe of each frame.

In a preferred embodiment, the optical signal-to-noise ratio is calculated from the power of the noise sequence and the power of the payload signal, further comprising: calculating a signal to noise ratio according to the power of the noise sequence and the power of the effective load signal, and calculating an optical signal to noise ratio according to the signal to noise ratio, wherein the calculation formula of the optical signal to noise ratio and the signal to noise ratio is as follows:

Wherein OSNR is optical signal-to-noise ratio, SNR is signal-to-noise ratio, B _s is signal bandwidth, and B _ref is reference bandwidth.

The application also discloses an optical signal to noise ratio estimation system, which comprises:

A transmitting end, configured to insert a predetermined number of zero sequences into a subframe of an optical signal sequence according to a predetermined period, and transmit the optical signal sequence;

The receiving end is used for receiving the optical signal sequence and judging whether the current subframe of the optical signal sequence comprises a zero sequence or not; if so, acquiring a signal of the position of the zero sequence in the subframe, removing partial signals adjacent to other parts of the subframe in the signal to obtain a noise sequence, performing noise whitening on the noise sequence by adopting a Berger algorithm, and calculating the power of the noise sequence after the noise whitening; if not, selecting a load signal at a partial position in the subframe as a payload signal and calculating the power of the payload signal; and calculating the osnr based on the power of the noise sequence and the power of the payload signal.

The application also discloses a computer readable storage medium having stored therein computer executable instructions which when executed by a processor implement the steps in the method described above.

Compared with the prior art, the embodiment of the application has the main differences and effects that:

1) The method can reduce the colored distortion of noise in the transmission process, and is more similar to the white noise of the substrate in an actual link.

2) The estimation precision of the link OSNR is remarkably improved, and the error is controlled within 0.5 dB.

3) The realization is simple.

The numerous technical features described in the description of the present application are distributed among the various technical solutions, which can make the description too lengthy if all possible combinations of technical features of the present application (i.e., technical solutions) are to be listed. In order to avoid this problem, the technical features disclosed in the above summary of the application, the technical features disclosed in the following embodiments and examples, and the technical features disclosed in the drawings may be freely combined with each other to constitute various new technical solutions (which should be regarded as having been described in the present specification) unless such a combination of technical features is technically impossible. For example, in one example, feature a+b+c is disclosed, in another example, feature a+b+d+e is disclosed, and features C and D are equivalent technical means that perform the same function, technically only by alternative use, and may not be adopted simultaneously, feature E may be technically combined with feature C, and then the solution of a+b+c+d should not be considered as already described because of technical impossibility, and the solution of a+b+c+e should be considered as already described.

Drawings

Fig. 1 is a schematic diagram of measuring out-of-band osnr.

Fig. 2 is a schematic diagram of the in-band osnr measured by the zero insertion method.

Fig. 3 is a flow chart of a method for estimating osnr according to an embodiment of the present application.

Fig. 4 is a schematic diagram of inserting a zero sequence in an optical signal sequence according to one embodiment of the application.

Fig. 5 is a more detailed flowchart of a osnr estimation method according to one embodiment of the present application.

Fig. 6 is a graph of the results of osnr measurements in one embodiment according to the application.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be understood by those skilled in the art that the claimed application may be practiced without these specific details and with various changes and modifications from the embodiments that follow.

Description of the partial concepts:

Optical signal to noise ratio (Optical Signal Noise Ratio, OSNR): the osnr is specifically the power ratio of the optical signal to noise on the optical link, usually expressed in dB. The main difference between the osnr and the SNR (Signal Noise Ratio, SNR) is that the noise power calculation defined by the osnr is limited to the in-band noise range of 0.1nm (about 12.5 GHz), and thus has a reduced relationship with the SNR.

The berg Algorithm (Burg algorism): a classical recursive algorithm for calculating power spectrum estimates directly from a known time signal sequence is proposed by J.P-berg, the so-called berg algorithm.

For the purpose of making the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

One embodiment of the present application relates to a method for estimating an osnr, the flow of which is shown in fig. 1, and the method comprises the following steps:

step 101, inserting a predetermined number of zero sequences in a subframe of a frame structure of the optical signal sequence according to a predetermined period, and transmitting the optical signal sequence to a receiving end. In one embodiment, the frame structure of the optical signal sequence comprises a plurality of frames, e.g. comprising a plurality of multiframes, each multiframe comprising a plurality of subframes, e.g. each frame comprising N subframes, e.g. subframe 1, subframe 2, … …, subframe N, a zero sequence being inserted in the same position of the same subframe of each multiframe. The term "zero sequence" means a continuous piece of data with a value of zero. For example, a zero sequence is inserted at the same position of subframe 1 of each multiframe. And, the optical signal sequence is transmitted to the receiving end in units of time slots.

Step 102, the receiving end receives the optical signal sequence and determines whether the current subframe of the optical signal sequence includes a zero sequence. For example, the receiving end receives a time slot of the optical signal sequence and determines whether the current time slot is a time slot where the zero sequence is located.

Step 103, if the receiving end judges that the current subframe comprises a zero sequence, obtaining a signal of the position of the zero sequence in the subframe, and removing partial signals adjacent to other parts of the subframe in the signal to obtain a noise sequence. Specifically, if the receiving end judges that the current time slot is the time slot where the zero sequence is located, the current subframe is determined to comprise the zero sequence. It should be understood that the data signals in the zero sequence adjacent to other parts of the subframe may be affected, so that the guard interval is added at both ends of the zero sequence in the present application, i.e. a part of the data signals (guard interval) in the zero sequence adjacent to other parts of the subframe is removed.

And 104, performing noise whitening processing on the noise sequence by adopting a Berger algorithm, and calculating the power of the noise sequence after the noise whitening processing.

In one embodiment, the noise whitening process further comprises the steps of:

Performing p-order primary lattice estimation on a noise sequence R, setting the length of the noise sequence as N1, the whitening coefficient as a _m, m1, 2, &..p, initializing a forward sequence as efp R, initializing a backward sequence as ebp R, and setting the m-th order coefficient as

Wherein efp _m＝efp_m-1(2:end+k_mebp_m-1 (1:end-1);

ebp_m＝ebp_m-1(1:end-1)+k_mefp_m-1(2:end；

a_m＝[a_m-1;0]+k_m[0;conj(flipud(a_m-1)；

The noise sequence after the noise whitening processing is R' =conv (R, a _m);

Wherein efp _m and ebp _m are forward and backward sequences at the mth order iteration, m1, 2. N is a sequence index of efp _m and ebp _m, and when the m-th order iterates, the value range of the index N is (0, N1-m); conj () is a conjugate function, flipud is a data flip function; conv () is a convolution function, input R is the original noise sequence of length N1, input a _m is the whitening coefficient of length p, and output R' is the whitened noise sequence of length N1.

In one embodiment, the p-th order of the primary lattice estimate is either 1-th order or 2-th order.

In one embodiment, after calculating the power of the noise sequence after the noise whitening process, further comprising: the average of the power of the noise sequence over the window length is calculated as the power of the noise sequence.

Step 105, if the receiving end judges that the current subframe does not include the zero sequence, selecting a load signal at a part of the subframe as a payload signal and calculating the power of the payload signal.

In one embodiment, selecting the load signal at a partial position in the subframe as the payload signal and calculating the power of the payload signal further comprises: the average of the power of the payload signal over the window length is calculated as the power of the payload signal.

And 106, calculating the optical signal to noise ratio according to the power of the noise sequence and the power of the effective load signal.

In one embodiment, the formula for calculating the osnr and the snr is:

In order to better understand the technical solution of the present application, the following description is given with reference to a specific example, in which details are listed mainly for the purpose of understanding, and are not intended to limit the scope of protection of the present application.

As shown in fig. 4, in the payload signal, a zero sequence with a length of N is inserted at a fixed position according to a multiframe period, that is, no signal is sent in the time window, in an ideal state, the noise signal received by the receiving end in the time window is link base noise, and the noise signal of the receiving end is distorted in a link damage state. The purpose of this is to make the distorted noise signal at the receiving end reflect the link noise state more accurately as much as possible.

Factors that need to be considered by the zero insertion method include:

1. The zero insertion period is reasonably selected. Too short a period can result in excessive overhead and also impact random convergence. For example, if a zero sequence is inserted in a plurality of subframes of each multiframe, overhead must be increased as compared to inserting a zero sequence in one subframe of each multiframe (e.g., subframe 1).

2. The number of zero insertion is reasonable. The amount of zero-inserted data is too short and inter-symbol interference can lead to severe inaccuracy in the noise estimation. For example, if the length of the zero insertion sequence is smaller than the inter-symbol interference length caused by the required dispersion, the zero insertion sequence tends to be severely contaminated, and thus an appropriate number of zero insertion is selected according to the inter-symbol interference length.

Aiming at the noise estimation difficulty brought by colored noise, the method adds a protection interval and improves noise signals to the maximum extent through a noise whitening technology. The process flow diagram is shown in fig. 5.

First, it is determined whether it is a slot in which a zero sequence is located. If so, finding the zero sequence position with the length of N, and removing the protection intervals at the two ends to obtain the noise signal with the length of N1. Next, a noise whitening process is performed, noise power is calculated and an accumulated average value Pnoise is recorded, and window length counting is performed. The window length count counts in terms of the number of multiframes that the effective noise calculates.

The invention calculates the noise whitening coefficient by the Berger algorithm. The berger algorithm is a recursive algorithm that computes power spectrum estimates directly from a known time signal sequence, and can solve for reflection coefficients directly from observed data. The algorithm is effective for power spectrum estimation of shorter data sequences and is therefore suitable for estimation of short sequence noise signals.

The noise whitening processing module in the method is concretely realized as follows.

1. The noise sequence is subjected to p-order primary lattice estimation, and a whitening coefficient a _m, =1, 2. Let the input noise sequence be R, the length be N1, the initialization forward sequence be efp R, the backward sequence be ebp R.

The m-th order coefficient is

The recursive formula is

efp_m＝efp_m-1(2:end+k_mebp_m-1(1:end-1)；

ebp_m＝ebp_m-1(1:end-1)+k_mefp_m-1(2:end；

a_m＝[a_m-1;0]+k_m[0;conj(flipud(a_m-1)

Wherein efp _m and ebp _m are forward and backward sequences at the mth order iteration, m1, 2. N is a sequence index of efp _m and ebp _m, and when the m-th order iterates, the value range of the index N is (0, N1-m); conj is a conjugate function, flipud is a data inversion function. In general, p 1 or 2 is taken.

2. Performing whitening filtering on the noise sequence to obtain a whitened corrected noise signal:

R′＝conv(n,a_m)

where conv () is a convolution function. The new noise signal R' can then be power calculated.

If the time slot is not the time slot where the zero sequence is located, selecting a part of load signals, obtaining effective signals of signal power to be calculated, calculating the signal power, recording the accumulated average value Psig, and counting the window length. When the average window length is reached, the SNR Psig/noise is calculated and the OSNR value is calculated.

Specifically, the signal-to-noise ratio SNR is defined as

Where N ₀ is the noise spectral density and B _s is the signal bandwidth.

OSNR is defined as

Where P _s is the signal power and B _ref is the reference bandwidth, the industry typically selects a wavelength width of 0.1nm, and the corresponding frequency bandwidth range at 1550nm is about 12.5G. The conversion relationship between OSNR and SNR is thus as follows:

In high-speed optical communication chips, both link impairments and DSP digital signal processing chips can cause whitened noise to become colored noise. Noise whitening is introduced into the OSNR report and the whitening coefficient is calculated. In the optical polarization multiplexing transmission, two paths of polarized signals can support respectively and independently calculating whitening coefficients and can also support average processing. Fig. 6 is a graph of OSNR measured by OSNR estimation methods of the present application, which is closer to a standard value, as can be seen from the result of OSNR measurement in one embodiment.

The application also discloses an optical signal to noise ratio estimation system, which comprises a transmitting end and a receiving end. The transmitting end is used for inserting a preset number of zero-sequence in the subframe of the optical signal sequence according to a preset period and transmitting the optical signal sequence. The receiving end is used for receiving the optical signal sequence and judging whether the current subframe of the optical signal sequence comprises a zero sequence. If so, acquiring a signal of the position of the zero sequence in the subframe, removing partial signals adjacent to other parts of the subframe in the signal to obtain a noise sequence, performing noise whitening processing on the noise sequence by adopting a Berger algorithm, and calculating the power of the noise sequence after the noise whitening processing. If not, selecting a load signal at a partial position in the subframe as a payload signal and calculating the power of the payload signal; and the receiving end calculates the optical signal to noise ratio according to the power of the noise sequence and the power of the effective load signal.

The first embodiment is a method embodiment corresponding to the present embodiment, and the technical details in the first embodiment can be applied to the present embodiment, and the technical details in the present embodiment can also be applied to the first embodiment.

Accordingly, embodiments of the present application also provide a computer-readable storage medium having stored therein computer-executable instructions which, when executed by a processor, implement embodiments of the methods of the present application. Computer-readable storage media, including both non-transitory and non-transitory, removable and non-removable media, may implement information storage by any method or technology. The information may be computer readable instructions, data structures, modules of a program, or other data. Examples of storage media for a computer include, but are not limited to, phase change memory (PRAM, static random access memory (SRAM, dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices, or any other non-transmission medium, which can be used to store information that can be accessed by a computing device.

In addition, the embodiment of the application also provides an optical signal to noise ratio estimation system, which comprises a memory for storing computer executable instructions and a processor; the processor is configured to implement the steps of the method embodiments described above when executing computer-executable instructions in the memory. The Processor may be a central processing unit (Central Processing Unit, abbreviated as "CPU"), other general purpose Processor, digital signal Processor (DIGITAL SIGNAL Processor, abbreviated as "DSP"), application SPECIFIC INTEGRATED Circuit, application Specific Integrated Circuit (ASIC), etc. The aforementioned memory may be a read-only memory (ROM), a random access memory (random access memory RAM), a Flash memory (Flash), a hard disk, a solid state disk, or the like. The steps of the method disclosed in the embodiments of the present application may be directly embodied in a hardware processor for execution, or may be executed by a combination of hardware and software modules in the processor.

It should be noted that in the present patent application, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element. In the present patent application, if it is mentioned that an action is performed according to an element, it means that the action is performed at least according to the element, and two cases are included: the act is performed solely on the basis of the element and is performed on the basis of the element and other elements. Multiple, etc. expressions include 2,2 times, 2, and 2 or more, 2 or more times, 2 or more.

All references mentioned in this specification are to be considered as being included in the disclosure of the application in its entirety so as to be applicable as a basis for modification when necessary. Furthermore, it should be understood that the foregoing description is only of the preferred embodiments of the present application and is not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement, or the like, which is within the spirit and principles of one or more embodiments of the present disclosure, is intended to be included within the scope of one or more embodiments of the present disclosure.

In some cases, the actions or steps recited in the claims can be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. A method for estimating an optical signal-to-noise ratio, comprising:

2. The estimation method of claim 1, wherein the noise whitening process further comprises:

P-order primary lattice estimation is carried out on a noise sequence R, the length of the noise sequence is N1, the whitening coefficient is a _m, m=1, 2, & gt, p, the initialization forward sequence is efp ₀ =R, the initialization backward sequence is ebp ₀ =R, and the m-order coefficient is

Wherein efp _m＝efp_m-1(2:end)+k_mebp_m-1 (1:end-1);

ebp_m＝ebp_m-1(1:end-1)+k_mefp_m-1(2:end)；

a_m＝[a_m-1;0]+k_m[0;conj(flipud(a_m-1)；

The noise sequence after the noise whitening processing is R' =conv (R, a _m);

Wherein efp _m and ebp _m are forward and backward sequences at the mth order iteration, m=1, 2. N is a sequence index of efp _m and ebp _m, and when the m-th order iterates, the value range of the index N is (0, N1-m); conj () is a conjugate function, flipud () is a data flip function; conv () is a convolution function.

3. The estimation method according to claim 2, wherein the p-th order of the berger estimation has a value of 1 st order or 2 nd order.

4. The estimation method according to claim 1, further comprising, after calculating the power of the noise sequence after the noise whitening process: an average of the power of the noise sequence over the window length is calculated as the power of the noise sequence.

5. The estimation method according to claim 1, wherein selecting the load signal at a partial position in the subframe as a payload signal and calculating the power of the payload signal further comprises: an average of the power of the payload signal over the window length is calculated as the power of the payload signal.

6. The estimation method according to claim 1, wherein the frame structure of the optical signal sequence comprises a plurality of frames, each frame comprising a plurality of subframes, the zero sequence being inserted in the same position of the same subframe of each frame.

7. The estimation method of claim 1 wherein calculating the osnr based on the power of the noise sequence and the power of the payload signal further comprises: calculating a signal to noise ratio according to the power of the noise sequence and the power of the effective load signal, and calculating an optical signal to noise ratio according to the signal to noise ratio, wherein the calculation formula of the optical signal to noise ratio and the signal to noise ratio is as follows:

8. An optical signal to noise ratio estimation system, comprising:

A transmitting end, configured to insert a predetermined number of zero sequences into a subframe of a frame structure of an optical signal sequence according to a predetermined period, and transmit the optical signal sequence;