A method and system for equalization compensation based on nonlinear constraints

Abstract

The application discloses a kind of equalization compensation method and system based on nonlinear constraint, comprising: extracting signal amplitude, radial clustering is carried out to signal based on signal amplitude;Each radial center signal is tangential clustering based on signal phase after clustering;Based on the adjustment of center mapping relationship of optical fiber nonlinear effect test inner and outer ring phase rotation relationship.This application faces the signal compensation method and system of coherent optical communication system, by radial, tangential clustering to signal, then according to different amplitude nonlinear phase rotation constraint mapping relationship, so as to realize the nonlinear damage compensation of signal, eliminate frequency deviation offset and phase noise influence, can provide reliable and stable communication system, has great potential and application prospect in the field of optical fiber communication.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to a method and system for equalization compensation based on nonlinear constraints of radial tangential clustering. Background Technology

[0002] To meet the rapidly growing network demands, the development of high-speed, high-capacity optical fiber communication technology is an inevitable trend in information and communication research. However, the performance of high-speed and long-distance optical fiber communication systems is significantly affected by the nonlinear effects of equipment and transmission links. Therefore, nonlinear impairment compensation is crucial for improving the capacity and performance of optical communication systems.

[0003] In recent years, due to advancements in optical communication technology, computer processing speed, digital signal processing (DSP), and high-speed analog-to-digital converter (ADC) chips, optical signal digital equalization technology has developed rapidly. These equalization techniques can effectively compensate for signal impairments by estimating the characteristics of the transmission system, thereby accurately recovering signals affected by noise in complex environments.

[0004] Efficient and low-complexity nonlinear compensation methods are crucial for long-distance transmission in extended optical communication systems. Currently, many traditional DSP algorithms are well-known in related fields, such as Digital Backpropagation (DBP) and Volterra Series Transfer Function (VSTF).

[0005] DBP is a nonlinear damage compensation algorithm based on stepwise computation, which has been widely used in the field of fiber nonlinear compensation; VSTF is one of the earliest methods for characterizing nonlinear systems and can effectively compensate for linear and nonlinear effects; Blind Phase Search (BPS) is a commonly used carrier recovery algorithm in coherent optical communication. Using BPS in conjunction with a series of clustering algorithms, typically kmeans, to compensate for nonlinearity has been proven to be an effective means.

[0006] However, some of these traditional algorithms require prior knowledge of the transmission link parameters, while others have high computational complexity. Currently, a method with low complexity that can effectively compensate for nonlinear impairments is still lacking. Summary of the Invention

[0007] The purpose of this invention is to propose a low-complexity and efficient equalization compensation method and system based on nonlinear constraints for coherent optical communication systems. By performing radial and tangential clustering of the signal, and then mapping the nonlinear phase rotation constraint relationship according to different amplitudes, the nonlinear impairment of the signal is compensated, which can provide a reliable and stable communication system and has great potential and application prospects in the field of optical fiber communication.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides an equilibrium compensation method based on nonlinear constraints, comprising the following steps:

[0010] S1. Extract the signal amplitude and perform radial clustering on the signal based on the signal amplitude;

[0011] S2. Perform tangential clustering on the radial center signals of the already clustered signals based on the signal phase;

[0012] S3. Adjust the center mapping relationship based on the phase rotation relationship between the inner and outer rings tested by the nonlinear effect of optical fiber.

[0013] Furthermore, in step S1, the specific steps for radial clustering of the signal based on the signal amplitude include:

[0014] S11. Amplify the signal to match the amplitude of the transmitted signal.

[0015] S12. Calculate the amplitude information for each signal;

[0016] S13, with the transmitter signal amplitude A j Using the initial center, and utilizing the Manhattan distance d m =|a i -A j Perform k-means clustering on the signal amplitude.

[0017] Furthermore, in step S11, the specific steps for amplitude scaling of the signal are as follows:

[0018] First, calculate the average signal power:

[0019]

[0020] Where N represents the total number of signal data points, S i This represents the i-th signal data;

[0021] Then, the received signal is normalized:

[0022]

[0023] Next, calculate the average signal power at the standard constellation points:

[0024]

[0025] Where M represents the modulation order, C k This represents the k-th standard constellation point;

[0026] Finally, the normalized signal at the receiving end is scaled:

[0027]

[0028] Furthermore, in step S12, the formula for calculating the amplitude information of each signal is as follows:

[0029]

[0030] Where S' is the normalized signal of the received signal, and S” is the scaling signal of the normalized signal of the received signal.

[0031] Furthermore, in step S13, the amplitude A of the transmitting signal is... j The calculation formula is:

[0032]

[0033] Among them, C j This represents any constellation point in the j-th circle from the inside out under the standard constellation points.

[0034] Furthermore, in step S2, the specific steps for performing tangential clustering of the already clustered radial center signals based on signal phase include:

[0035] S21. Normalize each signal to obtain S i ';

[0036] S22. Based on the distribution of constellation points of different amplitudes in the standard constellation diagram under the transmission modulation format, set initial cluster centers for each radial cluster.

[0037] S23, According to Euclidean distance The signals under each radial cluster are further clustered, where C jn This represents the nth standard constellation point in the j-th orbit;

[0038] S24. Recalculate the centroid to obtain the new cluster center C. m :

[0039] S25. Repeat steps S22 to S25 until the change in cluster centers is less than the set threshold.

[0040] Furthermore, in step S3, the specific steps for center mapping based on testing the phase rotation relationship between the inner and outer rings using fiber nonlinear effects include:

[0041] S31. Calculate the phase shift of each cluster obtained by radial clustering relative to the standard constellation points. Where C m This represents the clusters obtained from radial clustering;

[0042] S32. Calculate the nonlinear rotation error when the relative phase shift of a larger cluster is assumed to be n times less than pi / 2 compared to the actual phase shift, according to the following formula:

[0043]

[0044] The n with the smallest error is the actual n of the cluster; where △ represents the error, and △ with the smallest error is the actual △ of the cluster; Indicates a cluster with a larger class center; Indicates a cluster with a smaller cluster center; C Lmax C represents the center value of the cluster with the larger cluster center; Lmin This represents the center value of clusters with smaller cluster centers.

[0045] On the other hand, the present invention also provides an equalization compensation system based on nonlinear constraints, including a DSP module, the DSP module comprising:

[0046] IQ quadrature module: The IQ quadrature module is connected to the analog-to-digital converter of the received signal. It is used to address the quadrature imbalance caused by the receiving device, ensure the orthogonality of the I and Q channels, and guarantee system performance.

[0047] Clock recovery module: The clock recovery module is connected to the IQ quadrature module and is used to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced during optical fiber transmission on clock information;

[0048] Dispersion compensation module: The dispersion compensation module is connected to the clock recovery module and is used to perform dispersion compensation on the I and Q signals of the X and Y polarization states that are subject to dispersion interference in the channel.

[0049] Channel equalization module: The channel equalization module is connected to the dispersion compensation module and is used to eliminate the influence of polarization mode dispersion on the signal during optical fiber transmission;

[0050] Carrier phase recovery module: The carrier phase recovery module is connected to the channel equalization module and is used to remove frequency offset interference and laser phase noise;

[0051] Nonlinear compensation module: The nonlinear compensation module is connected to the carrier phase recovery module and is used to implement the nonlinear constraint-based equalization compensation method described in any of the above items.

[0052] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0053] The equalization compensation method and system based on nonlinear constraints proposed in this invention first performs radial clustering on the signal amplitude, which can effectively obtain a hierarchical distribution. Then, it performs tangential clustering on the center of the clustered signal and combines nonlinear rotation constraint relationship and nonlinear mapping constraint relationship to achieve nonlinear compensation of the signal, eliminate the influence of frequency offset and phase noise, and provide a reliable and stable communication system. It has great potential and application prospects in the field of optical fiber communication. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0055] Figure 1 A flowchart of the equilibrium compensation method based on nonlinear constraints provided by the present invention;

[0056] Figure 2 A block diagram of a digital signal processing system for the nonlinear damage compensation method based on radial tangential clustering provided by this invention.

[0057] Figure 3 The image shows the effect of processing the 16QAM signal using a nonlinear damage compensation algorithm based on tangential radial clustering in the embodiment provided by the present invention.

[0058] Figure 4 The bit error rate curves of 16QAM signals under different optical emission powers provided in the embodiments of the present invention after being processed by a nonlinear damage compensation algorithm based on tangential radial clustering and a nonlinear damage compensation algorithm based on k-means clustering. Detailed Implementation

[0059] To better understand this technical solution, the technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described examples are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of the present invention.

[0060] Example 1

[0061] This embodiment uses a 16QAM signal as an example to illustrate the specific implementation of the present invention.

[0062] Coherent optical communication systems can simultaneously achieve high spectral efficiency and long-distance transmission. However, the performance of high-speed, long-distance coherent optical communication systems is significantly degraded due to nonlinearities caused by equipment and transmission links. Therefore, system nonlinearity suppression is considered a key technology for improving the capacity and performance of optical communication systems.

[0063] This invention mainly designs the modulation format identification module of a coherent optical communication receiver. It focuses on using the tangential radial clustering method, based on nonlinear rotation constraints, to obtain the rotation relationship between the inner and outer rings under nonlinear effect testing, and then perform center mapping to achieve nonlinear compensation of the signal and eliminate the influence of frequency offset and phase noise.

[0064] The equilibrium compensation method based on nonlinear constraints of this invention has the following process: Figure 1 As shown, the specific steps include:

[0065] 1. Perform standard scaling on the 16QAM signal that has undergone orthogonal balancing, dispersion compensation, clock recovery, channel equalization, and frequency offset estimation. in Calculate the amplitude information for each signal separately. With the amplitude A of the 16QAM signal at the transmitting end j Using the initial center, and utilizing the Manhattan distance d m =|a i -A j |K-means clustering of the signal amplitude yields inner, middle, and outer clusters. Where S i This represents the i-th signal data (0≤i≤N, where N represents the total number of signal data points). C j This represents any constellation point in the j-th (1≤j≤3) ring from the inside out under the standard constellation point.

[0066] 2. Power normalization is performed on the 16QAM signal that has undergone radial clustering to obtain S. i ', and extract complex signals to represent the angles of each signal. Using 16QAM standard constellation points as initial cluster centers, Euclidean distance was calculated. Tangential clustering is performed on the 16QAM signal, and new cluster centers are recalculated. This process is repeated until the change in cluster centers is less than a set threshold.

[0067] 3. For 16QAM signals that have achieved radial and tangential clustering, calculate the phase shift of all clusters obtained by radial clustering relative to the standard 16QAM constellation points. Test the phase rotation relationship between the inner and outer rings based on nonlinear effects, and calculate the nonlinear rotation error. Further compensation of phase rotation is achieved to realize nonlinear compensation of 16QAM signals.

[0068] The equilibrium compensation system based on nonlinear constraints proposed in this invention is as follows: Figure 2 As shown. The digital signal processing (DSP) module includes:

[0069] IQ quadrature module: The IQ quadrature module is connected to the analog-to-digital converter of the received signal. It is used to address the quadrature imbalance caused by the receiving device, ensure the orthogonality of the I and Q channels, and guarantee system performance.

[0070] Clock recovery module: The clock recovery module is connected to the IQ quadrature module and is used to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced during optical fiber transmission on clock information;

[0071] Dispersion compensation module: The dispersion compensation module is connected to the clock recovery module and is used to perform dispersion compensation on the I and Q signals of the X and Y polarization states that are subject to dispersion interference in the channel.

[0072] Channel equalization module: The channel equalization module is connected to the dispersion compensation module and is used to eliminate the influence of polarization mode dispersion on the signal during optical fiber transmission;

[0073] Carrier phase recovery module: The carrier phase recovery module is connected to the channel equalization module and is used to remove frequency offset interference and laser phase noise;

[0074] Nonlinear compensation module: The nonlinear compensation module is connected to the carrier phase recovery module and is used to implement the nonlinear constraint-based equalization compensation method of the present invention.

[0075] like Figure 2 As shown, after the DSP system signal is received by zero-difference coherent reception, the analog-to-digital converter outputs the signal to the IQ quadrature module for quadrature balancing, and then inputs it to the clock recovery module to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced during fiber transmission on the clock information. Next, a dispersion compensator compensates for the dispersion of the I and Q signals in the X and Y polarization states that are affected by dispersion interference in the channel. The dispersion-compensated signal is connected to the channel equalizer to eliminate the effects of differential group delay and fiber Kerr effect received during fiber transmission. The channel-equalized signal is output to the carrier phase recovery module to remove interference caused by frequency offset and phase noise. A nonlinear compensation module then eliminates interference caused by signal phase offset and laser phase noise, thus achieving signal compensation.

[0076] The effect of processing the 16QAM signal using a nonlinear damage compensation algorithm based on tangential radial clustering is as follows: Figure 3 As shown, symbols carrying nonlinear damage are accurately divided into 16 clusters. At the transmitting end, the same symbols are basically assigned to the same cluster center. The correspondence between the cluster center and the standard constellation point can achieve a decision with almost zero error.

[0077] The bit error rate curves of 16QAM signals under different optical emission powers after processing by a nonlinear impairment compensation algorithm based on tangential radial clustering and a nonlinear impairment compensation algorithm based on k-means clustering are shown below. Figure 4 As shown, compared with the nonlinear equilibrium compensation algorithm based on k-means clustering, the equilibrium compensation algorithm based on nonlinear constraints proposed in this invention has a better nonlinear compensation effect and a significant performance advantage.

[0078] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention, based on the ideas provided by the present invention, should be considered within the scope of protection of the present invention.

Claims

1. A method for equilibrium compensation based on nonlinear constraints, characterized in that: Includes the following steps: S1. Extract the signal amplitude and perform radial clustering on the signal based on the signal amplitude; S2. Perform tangential clustering on the radial center signals of the already clustered signals based on the signal phase; S3. Adjust the center mapping relationship based on the phase rotation relationship between the inner and outer rings tested by fiber nonlinear effect test; The specific steps for center mapping based on testing the phase rotation relationship between the inner and outer rings using fiber nonlinear effects include: S31. Calculate the phase shift of each cluster obtained by radial clustering relative to the standard constellation points. ,in This represents the clusters obtained from radial clustering; S32. Calculate the nonlinear rotation error when the relative phase shift of a larger cluster is assumed to be n times less than pi / 2 compared to the actual phase shift, according to the following formula: ， The n that minimizes the error is the actual n of the cluster; where, Indicates the error, with the smallest error being... This is the actual cluster. ; Indicates a cluster with a larger class center; Clusters with smaller cluster centers; The value representing the center of a cluster with a larger cluster center; This represents the center value of clusters with smaller cluster centers.

2. The equilibrium compensation method based on nonlinear constraints according to claim 1, characterized in that, In step S1, the specific steps for radial clustering of the signal based on the signal amplitude include: S11. Amplify the signal to match the amplitude of the transmitted signal. S12. Calculate the amplitude information for each signal; S13, based on the amplitude of the transmitting signal Using Manhattan distance as the initial center Perform k-means clustering on the signal amplitude.

3. The equilibrium compensation method based on nonlinear constraints according to claim 2, characterized in that, In step S11, the specific steps for amplitude scaling of the signal are as follows: First, calculate the average signal power: ； Where N represents the total number of signal data points, S i This represents the i-th signal data; Then, the received signal is normalized: ； Next, calculate the average signal power at the standard constellation points: ， Where M represents the modulation order, This represents the k-th standard constellation point; Finally, the normalized signal at the receiving end is scaled: 。 4. The equilibrium compensation method based on nonlinear constraints according to claim 3, characterized in that, In step S12, the formula for calculating the amplitude information of each signal is as follows: ， Where S' is the normalized signal of the received signal, and S'' is the scaling signal of the normalized signal of the received signal.

5. The equilibrium compensation method based on nonlinear constraints according to claim 3, characterized in that, In step S13, the amplitude of the transmitting signal... The calculation formula is: ， in, This represents any constellation point in the j-th circle from the inside out under the standard constellation points.

6. The equilibrium compensation method based on nonlinear constraints according to claim 1, characterized in that, In step S2, the specific steps for performing tangential clustering of the radial center signals of the already clustered data based on signal phase include: S21. Normalize each signal to obtain ; S22. Based on the distribution of constellation points of different amplitudes in the standard constellation diagram under the transmission modulation format, set initial cluster centers for each radial cluster. S23, According to Euclidean distance The signals under each radial cluster are further clustered, among which... This represents the nth standard constellation point in the j-th orbit; S24. Recalculate the centroid to obtain the new cluster centers. : S25. Repeat steps S22 to S25 until the change in cluster centers is less than the set threshold.

7. A nonlinear constraint-based equalization compensation system, comprising a DSP module, characterized in that, The DSP module includes: IQ quadrature module: The IQ quadrature module is connected to the analog-to-digital converter of the received signal. It is used to address the quadrature imbalance caused by the receiving device, ensure the orthogonality of the I and Q channels, and guarantee system performance. Clock recovery module: The clock recovery module is connected to the IQ quadrature module and is used to eliminate the influence of chromatic dispersion and polarization mode dispersion introduced during optical fiber transmission on clock information; Dispersion compensation module: The dispersion compensation module is connected to the clock recovery module and is used to perform dispersion compensation on the I and Q signals of the X and Y polarization states that are subject to dispersion interference in the channel. Channel equalization module: The channel equalization module is connected to the dispersion compensation module and is used to eliminate the influence of polarization mode dispersion on the signal during optical fiber transmission; Carrier phase recovery module: The carrier phase recovery module is connected to the channel equalization module and is used to remove frequency offset interference and laser phase noise; Nonlinear compensation module: The nonlinear compensation module is connected to the carrier phase recovery module and is used to implement the equalization compensation method based on nonlinear constraints as described in any one of claims 1-6.

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