Adaptive Equalization Method, Apparatus, and Readable Storage Medium of Probability Shaping System

Abstract

The present application discloses an adaptive equalization method, apparatus, and readable storage medium for a probability shaping system, the method including: determining a tap length of a filter and setting an initial coefficient of an equalizer (S110); butterfly filtering an input signal of two polarization states based on the coefficient of the equalizer to obtain an output signal of two polarization states (S120); calculating an error signal from the output signals of the two polarization states, the error signal being the sum of a first error, which is the minimum value of the difference between a target convergence radius and the squared modulus value of the output signal, and a second error, which is the difference between an average value of the squared modulus values ​​of a plurality of the output signals and a target average power (S130); and adjusting the coefficient of the equalizer based on the error signal (S140).

Description

Technical Field

[0001] This application is filed based on the Chinese patent application with application number 202111191070.6 and filing date October 13, 2021, and claims the priority of the Chinese patent application. All the contents of the Chinese patent application are incorporated herein by reference in this application.

[0002] This application relates to the field of communications, and in particular to an adaptive equalization method, apparatus, and readable storage medium for a probability shaping system.

Background Art

[0003] As the demands such as the development of big data, 4K video, virtual reality, and 5G bearers become increasingly urgent day by day, optical transmission systems require higher transmission capacities. In 1948, Shannon, the founder of information theory, proved in the paper "A Mathematical Theory of Communication" that when the source distribution matches the channel distribution, the channel has the maximum transmission capacity. In recent years, the probability shaping (PS: Probabilistic Shaping) optical communication system, which has been intensively studied, improves the system transmission performance by changing the probability distribution of the source to be closer to the Gaussian distribution.

[0004] The damage to devices and channels in an optical communication system is usually compensated by digital signal processing (DSP: Digital Signal Processing) technologies on the receiving side, including dispersion compensation, adaptive equalization compensation, clock recovery, carrier phase recovery, etc. The introduction of probability shaping causes some conventional DSP algorithms to fail. For example, when the degree of probability shaping is very large, the conventional constant modulus algorithm (CMA: Constant Module Algorithm) fails, and the polarization crosstalk and polarization mode dispersion in the channel cannot be compensated correctly, and as a result, the system finally stops operating.

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present application is to solve at least one of the technical problems existing in the prior art and to provide an adaptive equalization method, apparatus, and readable storage medium for a probability shaping system.

Means for Solving the Problems

[0006] In a first aspect, an embodiment of the present application includes: determining a tap length of a filter and setting an initial coefficient of an equalizer; butterfly-filtering input signals in two polarization states based on the coefficients of the equalizer to obtain output signals in two polarization states; calculating an error signal that is a sum of a first error that is a minimum value of a difference between a target convergence radius and a square of a modulus value of the output signal and a second error that is a difference between an average value of squares of modulus values of a plurality of the output signals and a target average power from the output signals in the two polarization states; adjusting the coefficients of the equalizer based on the error signal, and providing an adaptive equalization method for a probability shaping system.

[0007] In a second aspect, an embodiment of the present application includes: a setting module configured to determine a tap length of a filter and set an initial coefficient of an equalizer; a filtering module configured to butterfly-filter input signals in two polarization states based on the coefficients of the equalizer to obtain output signals in two polarization states; an error calculation module configured to calculate an error signal that is a sum of a first error that is a minimum value of a difference between a target convergence radius and a square of a modulus value of the output signal and a second error that is a difference between an average value of squares of modulus values of a plurality of the output signals and a target average power from the output signals in the two polarization states; an adjustment module configured to adjust the coefficients of the equalizer based on the error signal, and providing an adaptive equalization apparatus for a probability shaping system.

[0008] In a third aspect, an embodiment of the present application provides a digital signal processing chip including an adaptive equalization device described in the embodiment of the second aspect of the present application.

[0009] In a fourth aspect, an embodiment of the present application provides a computer-readable storage medium storing computer-executable instructions for causing a computer to execute the adaptive equalization method described in the embodiment of the first aspect of the present application.

[0010] Other features and advantages of the present application will be described in the following specification, will be partially apparent from the specification, or will be understood by implementing the present application. The objectives and other advantages of the present application can be achieved by the structures particularly pointed out in the specification, the claims, and the drawings.

[0011] The drawings are used to provide a further understanding of the technical solution of the present application, constitute a part of the specification, and are used to explain the technical solution of the present application together with the embodiments of the present application, and do not limit the technical solution of the present application.

[0012] Hereinafter, the present application will be further described with reference to the drawings and embodiments.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0014] In this section, specific embodiments of the present application will be described in detail, and preferred embodiments of the present application are shown in the drawings. The role of the drawings is to supplement the description of the text part of the specification with graphics, so that each technical feature and the overall technical solution of the present application can be intuitively and vividly understood, but it should not be understood as limiting the protection scope of the present application.

[0015] In the specification of the present application, "first", "second" are described for the purpose of simply distinguishing technical features, and should not be understood as implicitly indicating the number of the indicated technical features or the sequence relationship of the indicated technical features, nor indicating or implying relative importance.

[0016] In the description of the present application, unless otherwise clearly defined, terms such as "installation", "attachment", "connection", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meaning of the above terms in the present application in combination with the specific content of the technical solution.

[0017] As the demands such as the development of big data, 4K video, virtual reality and 5G bearer become increasingly urgent day by day, optical transmission systems are in need of higher transmission capacity. In 1948, Shannon, the founder of information theory, proved in the paper "A Mathematical Theory of Communication" that when the source distribution coincides with the channel distribution, the channel has the maximum transmission capacity. In recent years, the probability shaping (PS: Probabilistic Shaping) optical communication system, which has been intensively studied, improves the system transmission performance by changing the probability distribution of the source to be closer to the Gaussian distribution.

[0018] Damage to devices and channels in an optical communication system is usually compensated by digital signal processing (DSP) techniques on the receiving side, including dispersion compensation, adaptive equalization compensation, clock recovery, carrier phase recovery, and the like. The introduction of probabilistic shaping causes some conventional DSP algorithms to fail. For example, when the degree of probabilistic shaping is very large, the conventional constant modulus algorithm (CMA) fails, and polarization crosstalk and polarization mode dispersion in the channel cannot be correctly compensated, and as a result, the system finally stops operating.

[0019] Embodiments of the present application provide an adaptive equalization method, apparatus, and readable storage medium for a probabilistic shaping system that can effectively compensate for channel damage and reduce the bit error rate.

[0020] Hereinafter, embodiments of the present application will be further described with reference to the drawings.

[0021] As shown in FIG. 1 or FIG. 2, an embodiment of the first aspect of the present application provides an adaptive equalization method for a probabilistic shaping system including steps S110 to S140.

[0022] Step S110: Determine the tap length of the filter and set the initial coefficient of the equalizer.

[0023] Step S120: Based on the coefficients of the equalizer, filter the input signals in two polarization states through a butterfly filter to obtain output signals in two polarization states.

[0024] Step S130: Calculate an error signal that is the sum of a first error that is the minimum value of the difference between the target convergence radius and the square of the modulus value of the output signal, and a second error that is the difference between the average value of the squares of the modulus values of the plurality of output signals and the target average power, from the output signals in the two polarization states.

[0025] Step S140: Adjust the coefficients of the equalizer based on the error signal.

[0026] TIFF0007714128000001.tif40170

[0027] TIFF0007714128000002.tif72170

[0028] TIFF0007714128000003.tif50170

[0029] Note that after the coefficients of the equalizer are adjusted, it is necessary to return to step S120 again and filter the input signal.

[0030] In the above adaptive equalization method, the modulation format of the probability shaping system adopts a PS-16QAM format, a PS-64QAM format, or a PS-QAM format higher than 64-order.

[0031] In the adaptive equalization method of the probability shaping system according to the embodiments of the present application, when calculating the error signal, a second error is introduced, that is, the difference between the average value of the squares of the modulus values of a plurality of output signals and the target average power is introduced, which is involved in the adjustment of the coefficients of the equalizer. It is mainly distinguished from the conventional constant modulus algorithm by the improvement of the error calculation unit. Compared with the conventional constant modulus adaptive equalization algorithm, it can accurately compensate for damages such as polarization state crosstalk and polarization mode dispersion in the probability shaping system, thereby effectively compensating for channel damage and reducing the bit error rate.

[0032] Hereinafter, with reference to specific embodiments, the adaptive equalization method according to the present application will be further introduced and described.

[0033] TIFF0007714128000004.tif40170

[0034] TIFF0007714128000005.tif40170

[0035] TIFF0007714128000006.tif44170

[0036] Adjust the equalizer coefficients in step S140 and set the step size μ to 0.0001.

[0037] FIG. 2 is a schematic diagram of the simulation comparison results between the adaptive equalization method of the probability shaping system according to the embodiment of the present application and the conventional CMA adaptive equalization method. It has been found that although the bit error rate of the conventional CMA adaptive equalization method is always high, the adaptive equalization method proposed in the present application can effectively compensate for channel damage and reduce the bit error rate.

[0038] As shown in FIG. 3, the embodiment of the second aspect of the present application includes a setting module 310 configured to determine the tap length of the filter and set the initial coefficients of the equalizer; a filtering module 320 configured to perform butterfly filtering on the input signals in two polarization states based on the coefficients of the equalizer to obtain output signals in two polarization states; an error calculation module 330 configured to calculate an error signal that is the sum of a first error that is the minimum value of the difference between the target convergence radius and the square of the modulus value of the output signal, and a second error that is the difference between the average value of the squares of the modulus values of the plurality of output signals and the target average power, from the output signals in the two polarization states; and an adjustment module 340 configured to adjust the coefficients of the equalizer based on the error signal, and provides an adaptive equalization device for a probability shaping system.

[0039] TIFF0007714128000007.tif40170

[0040] TIFF0007714128000008.tif66170

[0041] TIFF0007714128000009.tif53170

[0042] In the above-described adaptive equalization device, the modulation format of the probability shaping system adopts a PS-16QAM format, a PS-64QAM format, or a PS-QAM format higher than the 64th order.

[0043] The adaptive equalization device of the probability shaping system according to the embodiment of the present application is involved in adjusting the coefficients of the equalizer by introducing a second error when calculating the error signal, that is, introducing the difference between the average value of the squares of the modulus values of a plurality of output signals and the target average power. Compared with the conventional fixed-modulus adaptive equalization algorithm, it can accurately compensate for damages such as polarization state crosstalk and polarization mode dispersion in the probability shaping system, thereby effectively compensating for channel damages and reducing the bit error rate.

[0044] Further, the embodiment of the third aspect of the present application provides a digital signal processing chip including the adaptive equalization device described in the embodiment of the second aspect.

[0045] The digital signal processing chip according to the embodiment of the present application is involved in adjusting the coefficients of the equalizer by introducing a second error when calculating the error signal, that is, introducing the difference between the average value of the squares of the modulus values of a plurality of output signals and the target average power. Compared with the conventional fixed-modulus adaptive equalization algorithm, it can accurately compensate for damages such as polarization state crosstalk and polarization mode dispersion in the probability shaping system, thereby effectively compensating for channel damages and reducing the bit error rate.

[0046] Further, the embodiment of the fourth aspect of the present application provides a computer-readable storage medium storing computer-executable instructions for causing a computer to execute the adaptive equalization method described in the embodiment of the first aspect of the present application, for example, the method steps S110 to S140 in FIG. 1.

[0047] The computer-readable storage medium according to an embodiment of the present application is involved in adjusting the coefficients of an equalizer by introducing a second error when calculating an error signal, that is, by introducing a difference between the average value of the squares of the modulus values of a plurality of output signals and the target average power. Compared with the conventional constant modulus adaptive equalization algorithm, it can accurately compensate for impairments such as polarization state crosstalk and polarization mode dispersion in a probability shaping system, thereby effectively compensating for channel impairments and reducing the bit error rate.

[0048] All or part of the steps in the method disclosed above, the system may be implemented as software, firmware, hardware, and suitable combinations thereof. Some or all of the physical components may be implemented as software executed by a processor such as a central processor, a digital signal processor, a microprocessor, etc., or as hardware, or as an integrated circuit such as an application-specific integrated circuit. Such software may be distributed on a computer-readable medium that may include a computer storage medium or a non-transitory medium and a communication medium or a transitory medium. As is well known to those skilled in the art, the term computer storage medium refers to any method or technology for storing information, such as a computer-readable program, data structure, program module, or other data, including volatile and non-volatile, removable and non-removable media. Computer storage media include RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disk DVD or other optical disk storage devices, magnetic cartridges, magnetic tapes, magnetic disk storage devices or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer, but is not limited thereto. Further, it is well known to those skilled in the art that a communication medium typically includes a computer-readable program, data structure, program module, or other data in a modulated data signal such as a carrier wave or other transmission mechanism, and may include any information distribution medium.

[0049] As described above, the embodiments of the present application have been described in detail with reference to the drawings. However, the present application is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present application within the scope of the knowledge possessed by those skilled in the art.

Claims

1. An adaptive equalization method for a probability shaping system, comprising: determining a tap length of a filter and setting an initial coefficient of an equalizer; butterfly-filtering input signals in two polarization states based on the coefficients of the equalizer to obtain output signals in the two polarization states; calculating an error signal that is the sum of a first error, which is the minimum value of the difference between a target convergence radius and the square of the modulus value of the output signal, and a second error, which is the difference between the average value of the squares of the modulus values of the plurality of output signals and a target average power, from the output signals in the two polarization states; adjusting the coefficients of the equalizer based on the error signal.

2.

3.

4.

5. The adaptive equalization method according to claim 1, wherein the modulation format of the probability shaping system employs a PS-16QAM format, a PS-64QAM format, or a PS-QAM format higher than 64-order.

6. An adaptive equalization apparatus for a probability shaping system, comprising: a setting module configured to determine a tap length of a filter and set an initial coefficient of an equalizer; a filtering module configured to butterfly-filter input signals in two polarization states based on the coefficients of the equalizer to obtain output signals in the two polarization states; an error calculation module configured to calculate an error signal that is the sum of a first error, which is the minimum value of the difference between a target convergence radius and the square of the modulus value of the output signal, and a second error, which is the difference between the average value of the squares of the modulus values of the plurality of output signals and a target average power, from the output signals in the two polarization states; an adjustment module configured to adjust the coefficients of the equalizer based on the error signal.

7.

8.

9.

10. The adaptive equalization apparatus according to claim 6, wherein the modulation format of the probability shaping system employs a PS-16QAM format, a PS-64QAM format, or a PS-QAM format higher than 64-order.

11. A digital signal processing chip including the adaptive equalization apparatus according to any one of claims 6 to 10.

12. A computer-readable storage medium storing computer-executable instructions for causing a computer to execute the adaptive equalization method according to any one of claims 1 to 5.

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