Optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology

Abstract

The invention discloses an optical transmission system based on an FEC extended perturbation optical fiber nonlinear compensation technology, and relates to the technical field of optical fiber communication. A receiving end comprises an adaptive perturbation equalization module, a soft decision demodulation module, a de-interleaving module, an FEC decoding module, an interleaving module and a symbol reconstruction module based on soft information which are connected in sequence. The self-adaptive perturbation nonlinear equalization module is of a double-input structure and is connected with the output end of the symbol reconstruction module based on soft information besides receiving signals. The output data of the interleaving module and the output data of the soft decision demodulation module are added and then input to the second input end of the soft decision demodulation module; and the output end and the sending end of the FEC decoding module adopt a decoding mode with the same code pattern, and a received bit result is output. According to the invention, the receiver sensitivity and the optical fiber nonlinear effect tolerance in the optical system can be improved.

Description

Technical Field

[0001] The present invention 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 Art

[0002] With the rapid growth of user demand for transmission distance and communication capacity, the growth rate and capacity expansion of modern fiber-optic communication systems are facing severe challenges. Based on the existing spectrum resources, high-order modulation is an inevitable way to improve the spectrum efficiency of fiber-optic communication systems. According to Shannon's 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 greater the input optical power or transmission power, the greater the channel capacity. However, as the input fiber power increases, the nonlinear effect of the optical fiber increases rapidly. On the other hand, as the number of high-order modulation increases, the Euclidean distance of the transmission signal constellation points becomes smaller, and the rotation and distortion effects of the constellation points caused by the nonlinearity of the optical fiber become more and more obvious.

[0003] The traditional digital signal processing methods for optical fiber nonlinear damage compensation mainly include: 1. Digital Backward Transfer (DBP); 2. Traditional equalizer method. The DBP method uses the Split-Step Fourier Method (SSFM) to perform time domain and frequency domain compensation within each small step, which has a high complexity. The traditional equalizer method either attempts to compensate for nonlinear inter-symbol interference with a linear method or requires the insertion of a certain number of training sequences, which increases system overhead and reduces communication efficiency.

[0004] Therefore, it is an urgent problem for technical personnel in this field to propose an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology to solve the problems of obvious distortion effect and low communication efficiency in the optical fiber communication system in the prior art. Summary of the invention

[0005] In view of this, the present invention provides an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, which can achieve the effect of improving the receiver sensitivity and fiber nonlinear effect tolerance in the optical system.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] An optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology comprises a transmitting end and a receiving end, wherein the receiving end comprises 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 dual-input structure, which is connected to the output end of a symbol reconstruction module based on soft information in addition to receiving a 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 a decoding method with the same code type as the transmitting end, and outputs a received bit result.

[0008] Adaptive perturbation nonlinear equalization module, used to equalize the received signal;

[0009] A soft decision demodulation module, used for outputting soft demodulation information;

[0010] A deinterleaving module, used for deinterleaving the received signal using an interleaving rule;

[0011] An FEC decoding module is used to encode and decode symbols using a soft-demodulated FEC encoding and decoding scheme;

[0012] An interleaving module, used for interleaving the received signal using an interleaving rule;

[0013] The soft information-based symbol reconstruction module is used to estimate the transmitted symbol using the decoded and interleaved soft information.

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

[0015] Optionally, the adaptive coefficient estimation unit includes estimating the X-polarization and Y-polarization perturbation equalization parameters of the i-th iteration respectively using the least square method

[0016]

[0017]

[0018] in, 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 the nonlinear transfer function based on perturbation, and f H (·) is its Hammett transpose, where f(·) is expressed as follows:

[0019]

[0020] Among them, m, n, k are time shifts, r x is the X-polarization received signal, r yIt is the Y polarization receiving signal.

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

[0022]

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

[0024] Optionally, the soft decision demodulation module outputs soft demodulation information and assumes that each symbol follows a Gaussian distribution with the same variance N(s i ,σ 2 ),

[0025]

[0026] Among them, LLR x [k,l] represents the soft information of the lth bit in the soft demodulated information of the kth multi-ary symbol received in the X-polarization channel, {s 0 =0} represents the symbol set whose lth position is 0 in the symbol-to-bit mapping relationship, {s 1 =1} represents the symbol set whose first bit is 1 in the symbol-to-bit mapping relationship, is the kth symbol information of the X-polarized symbol. When i=0, it is the directly received symbol. When i>0, it is the symbol information after nonlinear equalization.

[0027] The above-mentioned optical fiber nonlinear compensation method and system, optionally, the symbol reconstruction module based on soft information includes: the interleaved soft information is obtained by symbol estimation and The expression is as follows:

[0028]

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

[0030] Where i is the i-th iteration, j is the j-th constellation point in the constellation diagram, and q is the length of the bit sequence represented by each symbol. For input symbol s j In the bit sequence represented by, the first bit is 1 or 0, Pr{·} is the event probability, and similarly, for the Y polarization channel,

[0031] It can be seen from the above technical solution that, compared with the prior art, the present invention provides an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, which realizes efficient and low-complexity fiber nonlinear damage compensation through a forward error correction LDPC coding assisted equalization method based on extended perturbation theory, thereby improving the receiver sensitivity and fiber nonlinear effect tolerance in the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0033] Figure 1 A block diagram of an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology disclosed in the present invention;

[0034] Figure 2 A schematic diagram of an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology disclosed in an embodiment of the present invention;

[0035] Figure 3 A constellation diagram of a received signal disclosed in an embodiment of the present invention;

[0036] Figure 4 A bit error rate diagram under different signal-to-noise ratios disclosed in an embodiment of the present invention;

[0037] Figure 5 This is a processed signal constellation diagram disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. The terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, the elements defined by the sentence "comprise one..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0040] Reference Figure 1 As shown, the present invention discloses an optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology, including a transmitting end and a receiving end, the receiving end includes 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 dual-input structure, in addition to receiving a signal, it is also connected to the output end of the symbol reconstruction module based on soft information, the output end of the FEC decoding module adopts the same code type decoding method as the transmitting end, and outputs the received bit result;

[0041] Adaptive perturbation nonlinear equalization module, used to equalize the received signal;

[0042] A deinterleaving module, used for deinterleaving the received signal using an interleaving rule;

[0043] An FEC decoding module is used to encode and decode symbols using a soft-demodulated FEC encoding and decoding scheme;

[0044] An interleaving module, used for interleaving the received signal using an interleaving rule;

[0045] A soft decision demodulation module, used for outputting soft demodulation information;

[0046] The soft information-based symbol reconstruction module is used to estimate the transmitted symbol using the decoded and interleaved soft information.

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

[0048] Further, the symbol estimation unit includes: the interleaved soft information is obtained by symbol estimation and The expression is as follows:

[0049]

[0050] Pr{b k,l =0}=1-Pr{b k,l =1},

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

[0052] Furthermore, the adaptive coefficient estimation unit includes estimating the equalization parameters using the least squares method.

[0053]

[0054] in, 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 the nonlinear transfer function based on perturbation, and f H (·) is its Hammett transpose.

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

[0056]

[0057] Among them, m, n, k are time shifts, r x is the X-polarization received signal, r y Receive signal for Y polarization

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

[0059]

[0060] Among them, r x,i+1 , r y,i+1 are the output symbols of X polarization and Y polarization after the i-th equalization, respectively. f(·) is the nonlinear transfer function based on perturbation, which 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 and assumes that each symbol follows a Gaussian distribution with the same variance N(s i ,σ 2 ),

[0065]

[0066] Among them, LLR x [k,l] represents the soft information of the lth bit in the soft demodulated information of the kth multi-ary symbol received in the X-polarization channel, {s 0 =0} represents the symbol set whose lth position is 0 in the symbol-to-bit mapping relationship, {s 1 =1} represents the symbol set whose first bit is 1 in the symbol-to-bit mapping relationship, is the kth symbol information of the X-polarized symbol. When i=0, it is the directly received symbol. When i>0, it is the symbol information after nonlinear equalization.

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

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

[0069] S2. Encoded by WiMAX standard 3 / 4 rate LDPC code encoder;

[0070] S3. Interleave using bit interleaving rules;

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

[0072] S5. After the IQ modulator and loaded into the SSMF optical fiber by polarization multiplexing method;

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

[0074] S7. Use the soft demodulator in the fiber nonlinear compensation scheme to perform soft demodulation to obtain the demodulation soft information of the X-polarization and Y-polarization channels.

[0075] S8. Deinterleave according to the bit interleaving rule to obtain

[0076] S9. Using the LDPC decoder based on the sum-product algorithm Decode and get

[0077] S10. Use the symbol estimation unit in the fiber nonlinear compensation scheme to perform symbol estimation, and obtain and

[0078] S11. Use the adaptive coefficient estimation unit in the optical fiber nonlinear compensation scheme to estimate the nonlinear equalization coefficient and obtain the coefficient of the i-th step iteration

[0079] S12. Perform nonlinear equalization using the nonlinear equalization unit in the optical fiber nonlinear compensation scheme;

[0080] S13. Repeat the above S7-S12, and after reaching the set number of times i, output the decoded bit stream 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, 5. The bit error rate graph is as follows: Figure 4 As shown, the final processed signal constellation diagram is obtained. Figure 5 shown.

[0082] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without creative work.

[0083] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to 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 technology, comprising a transmitting end and a receiving end, characterized in that: The receiving end includes 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 has a dual-input structure, which is connected to the output of the symbol reconstruction module based on soft information in addition to receiving the signal; The output data of the interleaving module and the output data of the soft decision demodulation module are added and then input into the second input end of the soft decision demodulation module; The output end of the FEC decoding module uses the same decoding method as the transmitting end to output the received bit result; Adaptive perturbation nonlinear equalization module, used to equalize the received signal; A deinterleaving module, used for deinterleaving the received signal using an interleaving rule; An FEC decoding module is used to encode and decode symbols using a soft-demodulated FEC encoding and decoding scheme; An interleaving module, used for interleaving the received signal using an interleaving rule; A soft decision demodulation module, used for outputting soft demodulation information; The soft information-based symbol reconstruction module is used to estimate the transmitted symbol using the decoded and interleaved soft information.

2. The optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology according to claim 1, characterized in that: The adaptive perturbation nonlinear equalization module includes an adaptive coefficient estimation unit and a nonlinear equalization unit.

3. The optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology according to claim 2, characterized in that: The adaptive coefficient estimation unit includes estimating the equalization parameters using the least squares method in, 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 the nonlinear transfer function based on perturbation, and f H (·) is its Hammett transpose, where f(·) is expressed as follows: Among them, m, n, k are time shifts, r x is the X-polarization received signal, r y It is the Y polarization receiving signal.

4. The optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology according to claim 2, characterized in that: The nonlinear equalization unit is a nonlinear equalization based on perturbation, and the expression is as follows: Among them, r x,i+1 , r y,i+1 are the output symbols of X polarization and Y polarization after the i-th equalization.

5. The optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology according to claim 1, characterized in that: The soft decision demodulation module outputs soft demodulation information and assumes that each symbol follows a Gaussian distribution with the same variance N(s i ,σ 2 ), Among them, LLR x [k,l] represents the soft information of the lth bit in the soft demodulated information of the kth multi-ary symbol received in the X-polarization channel, {s0=0} represents the symbol set whose lth position is 0 in the symbol-to-bit mapping relationship, and {s1=1} represents the symbol set whose lth position is 1 in the symbol-to-bit mapping relationship. is the kth symbol information of the X-polarized symbol. When i=0, it is the directly received symbol. When i>0, it is the symbol information after nonlinear equalization.

6. The optical transmission system based on FEC extended perturbation fiber nonlinear compensation technology according to claim 2, characterized in that: The symbol reconstruction module based on soft information includes: the interleaved soft information is obtained by symbol estimation and The expression is as follows: b k,l =0}=1-Pr{b k,l =1}, Where i is the i-th iteration, j is the j-th constellation point in the constellation diagram, and q is the length of the bit sequence represented by each symbol. For input symbol s j In the bit sequence represented by, the first bit is 1 or 0, Pr{·} is the event probability, and similarly, for the Y polarization channel,

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