An optical transmission system based on FEC spread perturbation fiber nonlinear compensation technology

Abstract

This invention discloses an optical transmission system based on FEC (Fiber Optic Expansion Coefficient) extended perturbation fiber nonlinearity compensation technology, belonging to the field of optical fiber communication technology. Its receiver includes, in sequence, an adaptive perturbation equalization module, a soft-decision demodulation module, a deinterleaving module, an FEC decoding module, an interleaving module, and a soft-information-based symbol reconstruction module. The adaptive perturbation nonlinear equalization module has a dual-input structure, connected to the output of the soft-information-based symbol reconstruction module in addition to the received signal. The output data of the interleaving module is added to the output data of the soft-decision demodulation module and then input to the second input of the soft-decision demodulation module. The output of the FEC decoding module uses the same decoding method as the transmitter to output the received bit result. This invention can improve the receiver sensitivity and fiber nonlinearity tolerance in optical systems.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical fiber communication technology, and in particular to an optical transmission system based on FEC extended perturbation optical fiber nonlinear compensation technology. BACKGROUND

[0002] With the rapid growth of user demand for transmission distance and communication capacity, the modern optical fiber communication system is facing severe challenges in increasing rate and expanding capacity. On the basis of existing spectrum resources, high-order modulation is an inevitable way to improve the spectral efficiency of optical fiber communication systems. According to Shannon theory, the channel capacity of a communication system is logarithmically related to the signal-to-noise ratio, that is, when the noise level is constant, the larger the input fiber optical power or transmission power, the larger the channel capacity. However, with the increase of input fiber power, the optical fiber nonlinear effect increases rapidly, on the other hand, with the increase of high-order modulation order, the Euclidean distance of the transmission signal constellation point becomes smaller, and the constellation point rotation and distortion effect caused by optical fiber nonlinear effect becomes more and more obvious.

[0003] The traditional digital signal processing method for compensating optical fiber nonlinear damage mainly includes: 1. Digital back propagation (DBP); 2. Traditional equalizer method. The DBP method uses the step Fourier method (SSFM) to compensate in time domain and frequency domain for each small step, which has high complexity. The traditional equalizer method either tries to compensate for nonlinear inter-symbol interference with a linear method or needs to insert a certain number of training sequences, which increases the system overhead and reduces the communication efficiency.

[0004] Therefore, the present application provides an optical transmission system based on FEC extended perturbation optical fiber nonlinear compensation technology to solve the problems of obvious distortion effect and low communication efficiency of the existing optical fiber communication system, which is a problem that needs to be solved by those skilled in the art. SUMMARY

[0005] Therefore, the present application provides an optical transmission system based on FEC extended perturbation optical fiber nonlinear compensation technology to solve the problems of obvious distortion effect and low communication efficiency of the existing optical fiber communication system, which is a problem that needs to be solved by those skilled in the art.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] An optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, comprising a transmitting end and a receiving end, the receiving end comprising an adaptive perturbation equalization module, a soft decision demodulation module, a deinterleaving module, an FEC decoding module, an interleaving module and a symbol reconstruction module based on soft information connected in sequence; the adaptive perturbation nonlinear equalization module is a double-input structure, and is connected with the output end of the symbol reconstruction module based on soft information in addition to the received signal; the output data of the interleaving module is added to the output data of the soft decision demodulation module and then input into the second input end of the soft decision demodulation module; the output end of the FEC decoding module adopts the same decoding mode as that of the transmitting end, and outputs the received bit result.

[0008] The adaptive perturbation nonlinear equalization module is used for equalizing the received signal.

[0009] The soft decision demodulation module is used for outputting soft demodulation information.

[0010] The deinterleaving module is used for deinterleaving the received signal by using an interleaving rule.

[0011] The FEC decoding module is used for encoding and decoding the symbol by using an FEC encoding and decoding scheme of soft demodulation.

[0012] The interleaving module is used for interleaving the received signal by using an interleaving rule.

[0013] The symbol reconstruction module based on soft information is used for estimating the transmitted symbol by using the soft information after decoding and interleaving.

[0014] Optionally, the adaptive perturbation nonlinear equalization module comprises an adaptive coefficient estimation unit and a nonlinear equalization unit.

[0015] Optionally, the adaptive coefficient estimation unit comprises an adaptive coefficient estimation unit for estimating the X-polarization and Y-polarization perturbation equalization parameters of the i-th iteration by using a least square method.

[0016]

[0017]

[0018] wherein, are the X-polarization and Y-polarization transmitted symbols estimated by the symbol reconstruction module based on soft information at the i-th iteration, f(·) is a nonlinear transfer function based on perturbation, and f H (·) is the Hammett transpose thereof, wherein the expression of f(·) is as follows:

[0019]

[0020] wherein m, n and k are time shift amounts, and r x is the X-polarization received signal, and r yThe Y polarization received signal is polarized.

[0021] Optionally, the nonlinear equalization unit is a perturbation-based nonlinear equalization, and the expression is as follows:

[0022]

[0023] Wherein, r x,i+1 , r y,i+1 are the output symbols of the X polarization and the Y polarization after the i+1th equalization respectively.

[0024] Optionally, the soft decision demodulation module outputs soft demodulation information, and assumes that each symbol is subject to a Gaussian distribution N(s i ,σ 2 ).

[0025]

[0026] Wherein, LLR x [k,l] represents the soft information of the lth bit in the soft demodulation information of the kth multi-valued symbol received by the X polarization channel, {s0=0} represents a symbol set in which the lth position in the symbol-to-bit mapping relationship is 0, {s1=1} represents a symbol set in which the lth bit in the symbol-to-bit mapping relationship is 1, is the kth symbol information of the X polarization symbol, i=0 is a directly accepted symbol, and i>0 is symbol information after nonlinear equalization.

[0027] Optionally, the symbol reconstruction module based on the soft information comprises: the interleaved soft information is obtained through symbol estimation and The expression is as follows:

[0028]

[0029] Pr{b k,l =0} =1-Pr{b k,l =1},

[0030] Wherein, i is the i th iteration, j is the j th constellation point in the constellation diagram, q is the bit sequence length represented by each symbol, is the lth bit in the bit sequence represented by the input symbol s j , Pr{·} is an event probability, and similarly, the Y polarization channel obtains

[0031] Via the technical solution, compared with the prior art, the application provides an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, realizes efficient and low complexity fiber nonlinear damage compensation through a forward error correction LDPC encoding auxiliary equalization method based on the extended perturbation theory, and thus improves the receiver sensitivity and fiber nonlinear effect tolerance in the optical system. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only a part of the embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of the provided drawings.

[0033] Figure 1 A block diagram of an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology is disclosed for the present application.

[0034] Figure 2 A principle diagram of an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology is disclosed for the embodiment of the present application.

[0035] Figure 3 A received signal constellation diagram is disclosed for the embodiment of the present application.

[0036] Figure 4 A bit error rate diagram under different signal-to-noise ratios is disclosed for the embodiment of the present application.

[0037] Figure 5 A processed signal constellation diagram is disclosed for the embodiment of the present application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort belong to the scope of protection of the present application.

[0039] In this application, the terms such as first and second are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between such entities or operations, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, so that a process, method, article, or apparatus that comprises a list of elements does not include only those elements recited, but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0040] Referring to Figure 1 The application discloses an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, comprising a transmitting end and a receiving end, the receiving end comprising an adaptive perturbation equalization module, a soft decision demodulation module, a deinterleaving module, an FEC decoding module, an interleaving module and a symbol reconstruction module based on soft information, which are connected in sequence, the adaptive perturbation nonlinear equalization module is a double-input structure, and is connected with the output end of the symbol reconstruction module based on soft information in addition to the received signal, the FEC decoding module adopts the same decoding mode as the transmitting end, and outputs a received bit result.

[0041] The adaptive perturbation nonlinear equalization module is used for equalizing the received signal.

[0042] The deinterleaving module is used for deinterleaving the received signal according to an interleaving rule.

[0043] The FEC decoding module is used for encoding and decoding the symbol according to an FEC encoding and decoding scheme of soft demodulation.

[0044] The interleaving module is used for interleaving the received signal according to an interleaving rule.

[0045] The soft decision demodulation module is used for outputting soft demodulation information.

[0046] The symbol reconstruction module based on soft information is used for estimating the transmitting symbol according to the soft information after decoding and interleaving.

[0047] Further, the adaptive perturbation nonlinear equalization module comprises a symbol estimation unit, an adaptive coefficient estimation unit and a nonlinear equalization unit.

[0048] Further, the symbol estimation unit comprises that the interleaved soft information is obtained through symbol estimation And The expression is as follows:

[0049]

[0050] Pr{b k,l = 1 - Pr{b k,l = 1},

[0051] where i is the i-th iteration, j is the j-th constellation point in the constellation, q is the length of the bit sequence represented by each symbol, is the input symbol s j , the l-th bit is 1 or 0, Pr{·} is the probability of the event, and similarly, for the Y polarization channel, we have

[0052] Further, the adaptive coefficient estimation unit includes estimating the equalization parameters by the least square method

[0053]

[0054] where, are the X polarization and Y polarization transmit symbols estimated by the soft information based symbol reconstruction module at the i-th iteration, f(·) is the perturbation based nonlinear transfer function, and f H (·) is the Hadamard transpose thereof.

[0055] Specifically, the expression of f(·) is as follows:

[0056]

[0057] where m, n, k are time shift amounts, r x is the X polarization received signal, r y is the Y polarization received signal

[0058] Further, the nonlinear equalization unit is a perturbation based nonlinear equalization, and the expression is as follows:

[0059]

[0060] where r x,i+1 , r y,i+1 are the X polarization and Y polarization output symbols after the i-th equalization, f(·) is the perturbation based nonlinear transfer function, and is calculated as follows:

[0061]

[0062] r xxx = r x [k + m] r x [k + m + n] r x [k + n],

[0063] r yyx = ry [k+m]r y *[k+m+n]r x [k+n].

[0064] Furthermore, the soft-decision demodulation module outputs soft-demodulation information, assuming that each symbol follows a Gaussian distribution N(s) with the same variance. i ,σ 2 ),

[0065]

[0066] Among them, LLR x [k,l] represents the soft information of the l-th bit in the soft demodulation information of the k-th multi-ary symbol received from the X-polarization channel, {s0=0} represents the set of symbols whose l-th bit is 0 in the symbol-to-bit mapping relationship, and {s1=1} represents the set of symbols whose l-th bit is 1 in the symbol-to-bit mapping relationship. The symbol information of the kth symbol in X polarization, where i = 0 is the directly received symbol and i > 0 is the symbol information after nonlinear equalization.

[0067] In one specific embodiment, the receiver constellation diagram of the coherent optical transmission system refers to... Figure 3 As shown, the FEC method at this time uses the WiMAX standard 3 / 4 rate LDPC code (information bit length 1512, code length 2016), employs 64QAM signal transmission, uses standard single-mode fiber (SSMF), and the FEC decoder uses an LDPC decoder based on the sum-product algorithm. The number of iterations within the LDPC decoder is 10, referring to... Figure 2 As shown, the system flow is as follows:

[0068] S1. The transmitting end generates a bit sequence of a certain length;

[0069] S2. Encoded using a 3 / 4 rate LDPC code encoder according to the WiMAX standard;

[0070] S3. Perform interleaving using bit interleaving rules;

[0071] S4. After high-order symbol mapping, it is converted into a 64QAM signal;

[0072] S5. Passed through an IQ modulator and loaded into SSMF fiber using a polarization multiplexing method;

[0073] S6. The receiver receives symbol information r through a coherent detector via dispersion compensation, polarization demultiplexing, frequency offset estimation, and phase recovery. x,0 r y,0 ;

[0074] S7. Soft demodulation is performed by using the soft demodulator in the fiber nonlinear compensation scheme to obtain the demodulation soft information of the X polarization and Y polarization channels

[0075] S8. Deinterleaving is performed according to the bit interleaving rule to obtain

[0076] S9. Decoding is performed by using the LDPC decoder based on the sum-product algorithm to obtain

[0077] S10. Symbol estimation is performed by using the symbol estimation unit in the fiber nonlinear compensation scheme to obtain and

[0078] S11. Nonlinear equalization coefficient estimation is performed by using the adaptive coefficient estimation unit in the fiber nonlinear compensation scheme to obtain the coefficient of the i-th step iteration

[0079] S12. Nonlinear equalization is performed by using the nonlinear equalization unit in the fiber nonlinear compensation scheme.

[0080] S13. The above S7-S12 is repeated, and after reaching the i-th set number of times, the decoded bit stream is output from S8.

[0081] The above process is calculated under different signal-to-noise ratios, and the bit error rate is calculated when i = 0, 1, 2, 3, 4, and 5. The bit error rate image is shown in Figure 4 , and the processed signal constellation diagram is finally obtained, and the result is shown in Figure 5 .

[0082] Each of the embodiments in the specification is described in a progressive manner, and the same and similar parts between the embodiments can be referred to each other. Each embodiment focuses on the difference from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, it is described more simply, and the related parts can be referred to the part of the method embodiment. The above-described system and system embodiment are only illustrative, and the units described as separate components can be or can not be physically separated, and the components displayed as units can be or can not be physical units, that is, they can be located in one place or distributed on multiple network units. Part or all of the modules can be selected to achieve the purpose of the embodiment according to the actual needs. Those skilled in the art can understand and implement it without creative labor.

[0083] ​The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the appended claims are intended to cover all such modifications that do not depart from the true spirit and scope of the application. Therefore, the application is not limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An optical transmission system based on FEC extended perturbation fiber nonlinear compensation technique, comprising a transmitting end and a receiving end, characterized in that, The receiving end comprises, in sequence, an adaptive perturbation equalization module, a soft decision demodulation module, a deinterleaving module, an FEC decoding module, an interleaving module and a symbol reconstruction module based on soft information. The adaptive perturbation nonlinear equalization module is a double-input structure, and is connected to the output end of the symbol reconstruction module based on soft information in addition to the received signal. The output data of the interleaving module is added to the output data of the soft decision demodulation module and then input to the second input end of the soft decision demodulation module. The output end of the FEC decoding module adopts the same decoding mode as the sending end, and outputs the received bit result. The adaptive perturbation nonlinear equalization module is used for equalizing the received signal. The deinterleaving module is used for deinterleaving the received signal by using an interleaving rule. The FEC decoding module is used for encoding and decoding the symbol by using a soft demodulation FEC encoding and decoding scheme. The interleaving module is used for interleaving the received signal by using an interleaving rule. The soft decision demodulation module is used for outputting soft demodulation information. The symbol reconstruction module based on soft information is used for estimating the sending symbol by using the decoded and interleaved soft information. In the optical transmission system, the FEC mode adopts a 3 / 4 code rate LDPC code of the WiMAX standard, 64QAM signal transmission is adopted, a standard single-mode optical fiber is used, and an LDPC decoder based on the sum-product algorithm is used as the FEC decoder, and the system flow is as follows: S1. The sending end generates a bit sequence of a certain length. S2. The bit sequence is encoded by a 3 / 4 code rate LDPC code encoder of the WiMAX standard. S3. The bit sequence is interleaved by using a bit interleaving rule. S4. The bit sequence is mapped to a 64QAM signal. S5. The 64QAM signal is input to a SSMF optical fiber by using an IQ modulator and a polarization multiplexing method. S6. The receiving end receives the symbol information through the coherent detector by dispersion compensation, polarization demultiplexing, frequency offset estimation, and phase recovery , ; S7. Soft demodulation is performed using the soft demodulator in the optical fiber nonlinear compensation scheme to obtain the demodulation soft information of the X polarization and Y polarization channels , ; S8. De-interleave according to the bit-interleaving rule, resulting in , ; S9. Decoding with an LDPC decoder based on the sum-product algorithm, yielding , , ;​ S10. performing symbol estimation using the symbol estimation unit in the optical fiber nonlinear compensation scheme to obtain and ; S11. Perform nonlinear equalization coefficient estimation with the adaptive coefficient estimation unit in the optical fiber nonlinear compensation scheme to obtain the coefficient of the i-th step iteration , ; S12. Nonlinear equalization is performed by using a nonlinear equalization unit in the optical fiber nonlinear compensation scheme. S13. The above S7-S12 is repeated, and after a set number of times, the decoded bit stream is output from S8.

2. The optical transmission system based on the FEC extended perturbation optical fiber nonlinear compensation technology according to claim 1, wherein The adaptive perturbation nonlinear equalization module comprises an adaptive coefficient estimation unit and a nonlinear equalization unit.

3. The optical transmission system based on the FEC extended perturbation optical fiber nonlinear compensation technology according to claim 2, wherein The adaptive coefficient estimation unit includes estimating the equalization parameters with a least square method , , ， ， in, , The first i In the next iteration, the X-polarized and Y-polarized transmitted symbols are estimated by the symbol reconstruction module based on soft information. For perturbation-based nonlinear transfer functions, Its Hammett transpose, in which, The expression is as follows: ， ， ， wherein m , n , is a time shift amount, is the X-polarized received signal ， is the Y-polarized received signal.

4. The optical transmission system based on the FEC extended perturbation optical fiber nonlinear compensation technology according to claim 2, wherein The nonlinear equalization unit is a perturbation-based nonlinear equalization, and the expression is as follows: ， ， wherein , are the first i equalized X-polarized and Y-polarized output symbols, respectively.

5. The optical transmission system based on the FEC extended perturbation optical fiber nonlinear compensation technology according to claim 1, wherein The soft decision demodulation module outputs soft demodulation information, and assumes that each symbol is subject to a Gaussian distribution with the same variance , ， in, Indicates receipt of the X-polarized channel number 1 k In the soft demodulation information of multi-ary symbols, the first l One bit of soft information, The first symbol to bit mapping relationship l The set of symbols at position 0. The first symbol to bit mapping relationship l The set of symbols with a bit set to 1 The symbol for X-polarization k Symbolic information, i =0 means the symbol is accepted directly. i When the value is greater than 0, it represents the symbol information after nonlinear equalization.

6. The optical transmission system based on the FEC extended perturbation optical fiber nonlinear compensation technology according to claim 2, wherein The soft information based symbol re-estimation module includes: the interleaved soft information is obtained through symbol estimation and , The expression is as follows: ， ， ， wherein i is the i th iteration, j is the j th constellation point in the constellation, q is the length of the bit sequence represented by each symbol, is the bit sequence represented by the input symbol , the th bit is 1 or 0, is the event probability, and similarly, for the Y polarized channel, we obtain .

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