CN106888054B - A kind of method of the FIR time domain dispersion equilibrium of weighted optimization - Google Patents
A kind of method of the FIR time domain dispersion equilibrium of weighted optimization Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/25—Arrangements specific to fibre transmission
- H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
- H04B10/2513—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion
- H04B10/25133—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion due to chromatic dispersion including a lumped electrical or optical dispersion compensator
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/60—Receivers
- H04B10/61—Coherent receivers
- H04B10/616—Details of the electronic signal processing in coherent optical receivers
- H04B10/6161—Compensation of chromatic dispersion
Abstract
The present invention relates to a kind of methods of the FIR time domain dispersion equilibrium of weighted optimization, belong to technical field of photo communication.It include: Step 1: obtaining sampled signal electric field, then calculated complex electric field to the light pulse signal progress coherent demodulation and analog-to-digital conversion after optical fiber transmission；Step 2: calculating the tap number of FIR time domain dispersion equilibrium method；Step 3: calculating the tap coefficient of FIR time domain dispersion equilibrium method；Step 4: the tap coefficient that step 3 exports is multiplied with majorized function, then the optimization of optimized functional parameter, the tap coefficient after being optimized；Step 5: carrying out balanced dispersion with the tap coefficient after step 4 optimizes.This method can be used for the optical communication link of different transmission speeds and variety classes modulation format, carry out the dispersion equilibrium of optical fiber link.
Description
Technical field
The present invention relates to a kind of method of the finite impulse response (FIR) time domain dispersion equilibrium of optimization more particularly to a kind of weighting are excellent
The method of the FIR time domain dispersion equilibrium of change, belongs to technical field of photo communication.
Background technique
Optical signal can have effect of dispersion after optical fiber transmits.In optical fiber digital communication syst, effect of dispersion causes
Pulse broadening, the system of limiting can transmit the flank speed of signal.At present for dispersion balanced way there are two types of, one is when
Domain dispersion equilibrium, another kind are frequency domain dispersion equilibriums.
Time domain dispersion equilibrium can be divided into two kinds of FIR time domain dispersion equilibrium and time domain dispersion equilibrium (TDE).FIR time domain dispersion
Balanced principle is: according to the frequency response of dispersion in optical fiberDesign a frequency response
ForFilter carry out dispersion equilibrium.The corresponding impulse response of the filter isAccording to nyquist sampling law and frequency aliasing is avoided, time domain equalization filter
The window time domain scale of wave device isTs is the sampling period.In view of the feasibility of practical operation,
Two samplings are generally used, the impulse response of endless is usually truncated in digital signal processing with rectangular window, that is,
H on frequency domaineqConvolution sampling function Sa (ω), then time domain is transformed to, just obtain the tap coefficient of FIR time domain equalization dispersion.FIR
The tap number N and tap coefficient a of time domain equalization dispersionkFor
Wherein,
The principle of another method TDE of time domain dispersion equilibrium is: to the frequency response function H of filter on frequency domaineq
Adding window truncation, length of window are signal duration corresponding frequency range.By the H after truncationeqTurned by inverse Fourier transform
Change to time domain.The result of conversion is the tap coefficient of TDE.The tap number N of TDE also presses above-mentioned formula calculating.
Mainly using balanced (OFDE) method of overlapping frequency domain dispersion, principle is: input is believed for equilibrium of the dispersion on frequency domain
Number being divided into length is LfftMultiple windows, length of window, that is, Fast Fourier Transform (FFT) length.There are overlay regions between two windows
Loverlap, each window by being fourier transformed into frequency domain, and it is balanced with tap coefficient multiplication progress.The tap coefficient of OFDE
ForWherein,Finally, equilibrium result inverse Fourier transform is returned to time domain, and lose
Fall the data of overlay region.
Above method all plays the effect of balanced dispersion.Wherein, the application of FIR time domain dispersion equilibrium method is more universal.
The shortcomings that the method is that tap coefficient modulus value is constant, and it is bad that this will lead to equilibrium result.Therefore, how equal in FIR time domain dispersion
On the basis of weighing apparatus, tap coefficient is advanced optimized, is current problem to be solved to reach optimal equalization effect.
Summary of the invention
It is an object of the invention to overcome traditional FIR time domain dispersion equilibrium to lead to balanced effect there are tap coefficient modulus value is constant
The undesirable technological deficiency of fruit, dispersion equilibrium effect propose a kind of FIR time domain color of weighted optimization it is necessary to further increase
Dissipate balanced method.
The purpose of invention is achieved through the following technical solutions.
A kind of method of the FIR time domain dispersion equilibrium of weighted optimization, central idea are constant with modulus value with majorized function
The mode that is multiplied of FIR time domain dispersion equilibrium tap coefficient, optimize the weight of tap coefficient, then equal with the tap coefficient after optimizing
Dispersion of weighing achievees the purpose that improve dispersion equilibrium effect to change the constant situation of tap coefficient modulus value.
Specifically comprise the following steps:
Step 1: carrying out coherent demodulation and analog-to-digital conversion to the light pulse signal after optical fiber transmission, sampled signal electricity is obtained
, then calculated complex electric field；
The real part for sampling electric field, is denoted as EI(n)；Imaginary part is denoted as EQ(n), then calculated complex electric field, pass through following formula (1)
It calculates:
E (n)=EI(n)+jEQ(n) (1)；
Wherein, E (n) represents plural electric field, and j represents imaginary unit；
Step 2: calculating the tap number of FIR time domain dispersion equilibrium method；
It is calculated especially by following formula (2):
Wherein, N is the tap number of FIR time domain dispersion equilibrium method, and D is dispersion parameter, and λ is laser center wavelength, and L is
Fiber lengths, c are the light velocity, and Ts is the sampling period,It indicates to be rounded downwards；
Step 3: calculating the tap coefficient of FIR time domain dispersion equilibrium method；
It is calculated especially by following formula (3):
Wherein, akFor tap coefficient,π is pi；
Step 4: the tap coefficient that step 3 exports is multiplied with majorized function, then to the optimized parameter of majorized function, obtain
To the tap coefficient of weighting；
Specific steps are as follows:
Step 4.1 is by akIt is multiplied with majorized function, to reach optimization akThe effect of weight；
Functional parameter of the step 4.2 based on optimization, to ensure the tap coefficient C after optimizingkOptimal equalization effect can be reached；
Wherein, majorized function is chosen as raised cosine, also known as Raised Cosine function, referred to as RC function, i.e.,
RC-FIR time domain dispersion equilibrium；Also then Gaussian function, referred to as Gaussian function, i.e. G-FIR time domain dispersion equilibrium be can choose；
Or the other majorized functions of selection.
For RC function, functional parameter is halfwidthWith rolloff-factor α,
Wherein, TwindowFor the length of window of FIR time domain dispersion equilibrium method.For different X1With α value, according to C-FIR time domain color
The portfolio effect of optic communication signal after dissipating the balanced transmission to different length optical fiber, obtains parameter X under different condition1Most with α
Good value is constant, thereby determines that X1With the value of α；
For Gaussian function, functional parameter to be optimized is halfwidth TG_FWHM=X2·Twindow,
Compare X2When taking different numerical value, according to G-FIR time domain dispersion equilibrium to the optic communication after the transmission of different length optical fiber
The portfolio effect of signal can obtain parameter X under different condition2Best value it is constant, thereby determine that X2Best value；
To other majorized functions, the optimization of parameter is also according to the optic communication signal after the transmission of different length optical fiber
Portfolio effect carries out.
Step 5: carrying out balanced dispersion with the tap coefficient after step 4 optimizes；
Dispersion equilibrium is carried out especially by following formula (4):
Wherein, E (n-k) is sampling electric field, EeqIt (n) is output electric field,It represents ckWith E's (n-k)
The N item of product and, the variation range of k be from 0 to N-1 sum；
So far, from step 1 to step 5, the method that completes a kind of FIR time domain dispersion equilibrium of weighted optimization.
Beneficial effect
A kind of method of the FIR time domain dispersion equilibrium of weighted optimization of the present invention has compared with existing balanced dispersion method
Following beneficial outcomes:
1. this method can apply to the optical communication link system of variety classes modulation format, the dispersion for carrying out optical fiber link is equal
Weighing apparatus；
2. this method can effectively improve the effect of time domain equalization dispersion, suitable for different optic communication modulation format and a variety of
Character rate, wherein the effect of optimization ratio G-FIR time domain dispersion equilibrium of RC-FIR time domain dispersion equilibrium is more significant；
3. pair QPSK signal transmitted by length for the optical fiber within 1000km, RC-FIR time domain dispersion equilibrium EVM value
Smaller by 4% to 6% than FIR time domain dispersion equilibrium, 3%, G-FIR time domain dispersion equilibrium EVM value ratio FIR time domain dispersion smaller than TDE is equal
Weigh small 2% to 5%, it is smaller than TDE by about 1%；
4. pair QPSK signal transmitted by the optical fiber that length is 1000km-2000km, RC-FIR time domain dispersion equilibrium EVM
It is worth about 3%, G-FIR time domain dispersion equilibrium EVM value ratio FIR time domain dispersion equilibrium lower than FIR time domain dispersion equilibrium and TDE and TDE
Low about 2%.
Detailed description of the invention
Simulation dispersion of the Fig. 1 for a kind of method of FIR time domain dispersion equilibrium of weighted optimization of the present invention and in embodiment 1 is equal
System block diagram used by weighing；
Fig. 2 is the DSP basic flow in a kind of embodiment of the method 1 and 2 of the FIR time domain dispersion equilibrium of weighted optimization of the present invention
Cheng Tu；
Fig. 3 is a kind of method schematic of the FIR time domain dispersion equilibrium of weighted optimization of the present invention；
Fig. 4 is RC-FIR time domain dispersion in a kind of embodiment of the method 1 of the FIR time domain dispersion equilibrium of weighted optimization of the present invention
The calculation flow chart of equalization methods；
Fig. 5 is in the embodiment 1 of specific implementation method, and the QPSK signal of 40Gb/s passes through 500km, X1With α value range
With the relationship of equilibrium result EVM；
Fig. 6 is in the embodiment 1 of specific implementation method, and the QPSK signal of 40Gb/s passes through 1000km, X1With α value range
With the relationship of equilibrium result EVM；
Fig. 7 is in the embodiment 1 of specific implementation method, and the QPSK signal of 40Gb/s passes through 1500km, X1With α value range
With the relationship of equilibrium result EVM；
Fig. 8 is RC-FIR time domain dispersion equilibrium, FIR time domain dispersion equilibrium and TDE in the embodiment 1 of specific implementation method
The tap coefficient comparison diagram of three kinds of methods；
Fig. 9 is in the embodiment 1 in specific embodiment, and the QPSK signal of 40Gb/s is through the standard single mode light of different length
After fibre transmission, the EVM Comparative result that time domain dispersion equilibrium obtains is carried out with three kinds of methods.Scheming X-axis in (a) is fiber lengths, Y-axis
For the EVM after balanced dispersion, three curves in figure indicate equal using FIR time domain dispersion equilibrium, TDE and RC-FIR time domain dispersion
Weigh three kinds of resulting EVM values of method equilibrium dispersion, when figure (b), figure (c), figure (d) are respectively optical fiber long 500km, through FIR time domain
Signal constellation (in digital modulation) figure after dispersion equilibrium, TDE and RC-FIR time domain dispersion equilibrium；
Figure 10 is in the embodiment 1 in specific embodiment, and 16QAM signal is transmitted through the standard single-mode fiber of different length
The EVM Comparative result that time domain dispersion equilibrium obtains is carried out with three kinds of methods afterwards, wherein the symbol rate and QPSK of 16QAM signal are believed
It is number identical；
Figure 11 is in the embodiment 1 in specific embodiment, and 32QAM signal is transmitted through the standard single-mode fiber of different length
The EVM Comparative result that time domain dispersion equilibrium obtains is carried out with three kinds of methods afterwards, wherein the symbol rate and QPSK of 32QAM signal are believed
It is number identical；
Figure 12 is the parameter X of G-FIR time domain dispersion equilibrium in the embodiment 2 of specific implementation method2Optimization process；
Figure 13 is RC-FIR time domain dispersion equilibrium, FIR time domain dispersion equilibrium, TDE in the embodiment 2 of specific embodiment
It is compared with the tap coefficient of four kinds of methods of G-FIR time domain dispersion equilibrium；
Figure 14 (a) is in the embodiment 2 of specific embodiment, and QPSK signal uses RC- after standard single-mode fiber transmits
Four kinds of FIR time domain dispersion equilibrium, FIR time domain dispersion equilibrium, TDE and G-FIR time domain dispersion equilibrium methods progress time domain dispersions are equal
The comparison diagram of EVM after weighing apparatus；When Figure 14 (b), 14 (c), 14 (d), 14 (e) are respectively fiber lengths 500km, FIR time domain dispersion is equal
Signal constellation (in digital modulation) figure obtained by weighing apparatus, TDE, RC-FIR time domain dispersion equilibrium and FIR time domain dispersion equilibrium；
Figure 15 is in the embodiment 2 of specific embodiment, and 16QAM signal is transmitted through standard single-mode fiber, when with RC-FIR
After four kinds of domain dispersion equilibrium, FIR time domain dispersion equilibrium, TDE and G-FIR time domain dispersion equilibrium methods carry out time domain dispersion equilibrium
EVM comparison；
Figure 16 is in the embodiment 2 of specific embodiment, and 32QAM signal is transmitted through standard single-mode fiber, when with RC-FIR
After four kinds of domain dispersion equilibrium, FIR time domain dispersion equilibrium, TDE and G-FIR time domain dispersion equilibrium methods carry out time domain dispersion equilibrium
EVM comparison.
Specific embodiment
Objects and advantages in order to better illustrate the present invention, are with reference to the accompanying drawing described further summary of the invention.
The time domain dispersion equilibrium system block diagram of the method for the present invention is as shown in Figure 1.Wherein, I/Q modulator generates signal, and mixes
Doped fiber amplifier (EDFA) is connected, and EDFA is used to control output power, transmits using standard single-mode fiber, every transmission
100km places an EDFA and is used to compensate decaying, after coherent reception and analog-to-digital conversion, into Digital Signal Processing process.
Fig. 2 is day number signal processing flow figure, wherein by the data of analog-to-digital conversion, passes through clock and data recovery respectively, dispersion is equal
Weighing apparatus, polarization is balanced and carrier phase recovery, finally, making decisions and error rate calculation.Time domain dispersion equilibrium method schematic is such as
Shown in Fig. 3, wherein signal is multiplied after delay with tap coefficient, and addition is equalized result.
Embodiment 1
The present embodiment is using raised cosine as a kind of FIR time domain color of weighted optimization of majorized function this realization present invention
Dissipate balanced method.
The calculation process of this method is as shown in Figure 4.First pass around analog-to-digital conversion and obtain E (n), then according to formula (2) and
The tap number N and tap coefficient a of formula (3) calculating FIR time domain dispersion equilibriumk.Again by tap coefficient akIt is multiplied, obtains with RC function
To the tap coefficient C of RC-FIR time domain dispersion equilibrium methodk, then according to the balanced dispersion of formula (4), finally, calculating output letter
Number EVM.
Sampled signal after analog to digital conversion is expressed as
E (n)=EI(n)+jEQ(n)
The tap number and tap coefficient for calculating FIR time domain dispersion equilibrium first, can obtain according to formula
Wherein, akFor tap coefficient,N is tap number.
In order to tap coefficient akOptimization, needing will be with akRaised cosine is multiplied.The halfwidth of raised cosineOptimum value should be reached with rolloff-factor α, the tap coefficient after optimization can be made
Reach optimal equalization chromatic dispersion effects.In order to X1It is optimized with α, X1It takes range 0.5-1.5, α to take range 0-1, simulates to QPSK
Signal carries out at RC-FIR time domain dispersion equilibrium after the standard single-mode fiber transmission of tri- length of 500km, 1000km, 1500km
Reason.As a result such as Fig. 5, Fig. 6 and Fig. 7.Fig. 5 conveying length is 500km, Fig. 6 1000km, Fig. 7 1500km.Wherein, Fig. 5, figure
The X-axis of 6 and Fig. 7 is halfwidth parameter X1, Y-axis is rolloff-factor α, and Z axis is the EVM value after equilibrium.In figure, color is brighter, then
EVM value is bigger, and portfolio effect is poorer；Color is deeper, and EVM value is smaller, and portfolio effect is better.As can be seen that different long at three
Under degree, the maximum value of EVM is consistent with minimum value appearance position.Minimum value (black region) appears in X1The position of=0.7, α=0.3
It sets；Maximum value (red area) concentrates on X1The position of=0.5, α=0.6.It is therefrom it was determined that equal in RC-FIR time domain dispersion
Parameter X in weighing apparatus method1Value with α is respectively 0.7 and 0.3.
After the parameter for determining raised cosine, by itself and akIt is multiplied, obtains the tap coefficient of RC-FIR time domain dispersion equilibrium
Ck.To the QPSK signal for transmitting 1000km in standard single-mode fiber, Fig. 8 compared RC-FIR time domain dispersion equilibrium, FIR respectively
The modulus value of tap coefficient needed for time domain dispersion equilibrium and TDE；Wherein, X-axis is tap number, and Y-axis is tap coefficient amplitude.From figure
In as can be seen that the tap coefficient modulus value of FIR time domain dispersion equilibrium method is constant, and RC-FIR time domain dispersion equilibrium method is to pumping
The weight of head coefficient has obvious optimization function.
Formula used in RC-FIR time domain dispersion equilibrium method equilibrium dispersion is
Wherein, EeqIt (n) is the signal after equilibrium.
The optical signal that Fig. 9, Figure 10 and Figure 11 compared different modulating format transmits certain length in standard single-mode fiber
Afterwards, using signal after tri- kinds of RC-FIR time domain dispersion equilibrium, FIR time domain dispersion equilibrium and TDE equalization methods progress dispersion equilibrium
EVM.Optical signal modulation format is QPSK, 16QAM and 32QAM respectively, and conveying length range is 200km to 2000km.Fig. 9
(a) in, X-axis is optical fiber conveying length, and Y-axis is EVM value after equilibrium.Fig. 9 (b), 9 (c), 9 (d) are passed through after transmitting 500km respectively
The QPSK signal constellation (in digital modulation) figure of FIR time domain dispersion equilibrium, TDE and RC-FIR time domain dispersion equilibrium.It can be obvious from three planispheres
Find out, the portfolio effect of RC-FIR time domain dispersion equilibrium is more preferably compared with other two method.The X-axis of Figure 10 and Figure 11 is fiber lengths, Y
Axis is EVM value after equilibrium.Complex chart 9-11 can be seen that the signal for being less than 500km to transmission range, and RC-FIR time domain dispersion is equal
Weighing apparatus gained EVM ratio FIR time domain dispersion equilibrium and the small 4%-6% of TDE；To the long distance transmission signal of 1000km-2000km, RC-
The EVM of FIR time domain dispersion equilibrium can be reduced by about 3%.
Embodiment 2
The present embodiment realizes that a kind of FIR time domain dispersion of weighted optimization of the present invention is equal as majorized function using Gaussian function
The method of weighing apparatus.
Figure 12 is the halfwidth parameter optimisation procedure of G-FIR time domain dispersion equilibrium, wherein X-axis X2, Y-axis is EVM value,
Three curves respectively represent optical fiber transmission 500km, 1000km and 1500km.Gaussian function halfwidth is according to TG_FWHM=X2·
TwindowIt determines.In order to X2Analysis is optimized, by X2Value range is set to 0.5-1.5, simulates QPSK signal point within the scope of this
After transmitting 500km, 1000km, 1500km not in standard single-mode fiber, using the result of G-FIR time domain dispersion equilibrium.It can be with
Find out, under three kinds of optical fiber conveying lengths, halfwidth parameter X2Best value be all 0.7, parameter X2Value thereby determine that.
QPSK signal transmits 1000km, the corresponding tap coefficient modulus value such as Figure 13 of four kinds of methods.It can be seen that G-FIR time domain color
Dissipating equalization methods also has effect of optimization to the weight of tap coefficient, but obvious not as good as RC-FIR time domain dispersion equilibrium.
Figure 14, Figure 15 and Figure 16 are after the optical signal of different modulating format transmits in standard single-mode fiber, using RC-
FIR time domain dispersion equilibrium, FIR time domain dispersion equilibrium, the four kinds of method equilibrium dispersions of TDE and G-FIR time domain dispersion equilibrium result
Comparison, format modulation signal is QPSK, 16QAM and 32QAM, conveying length 200km-2000km respectively.Figure 14 (a), Tu15He
The X-axis of Figure 16 is fiber lengths, and Y-axis is the EVM value after signal equalization.It is equal when Figure 14 (b) -14 (e) is optical fiber transmission 500km
Signal constellation (in digital modulation) figure after weighing apparatus, when equalization methods are respectively FIR time domain dispersion equilibrium, TDE, RC-FIR time domain dispersion equilibrium and G-FIR
Domain dispersion equilibrium.Complex chart 14-16, when optical fiber transmits 200km-1000km, when G-FIR time domain dispersion equilibrium EVM value ratio FIR
The small 4%-2% of domain dispersion equilibrium, when optical fiber transmits 1000km-2000km, G-FIR time domain dispersion equilibrium EVM can be reduced by about
1%.
Major technique advantage of the present invention:
The present invention " a kind of method of the FIR time domain dispersion equilibrium of weighted optimization " is described in detail above, but this
The specific implementation form of invention is not limited thereto.The explanation of the implementation is merely used to help understand method and its core of the invention
Thought is thought；At the same time, for those skilled in the art in specific embodiment and applies model according to the thought of the present invention
Place that there will be changes, in conclusion the contents of this specification are not to be construed as limiting the invention.Without departing substantially from this hair
To the various obvious changes of its progress all in the present invention in the case where the spirit and scope of the claims of bright the method
Protection scope within.
Claims (1)
1. a kind of method of the FIR time domain dispersion equilibrium of weighted optimization, it is characterised in that: constant with majorized function and modulus value
The mode that FIR time domain dispersion equilibrium tap coefficient is multiplied optimizes the weight of tap coefficient, then balanced with the tap coefficient after optimization
Dispersion achievees the purpose that improve dispersion equilibrium effect to change the constant situation of tap coefficient modulus value；Specifically include following step
It is rapid:
Step 1: carrying out coherent demodulation and analog-to-digital conversion to the light pulse signal after optical fiber transmission, sampled signal electric field is obtained, then
Calculated complex electric field；
Wherein, the real part for sampling electric field, is denoted as EI(n)；Imaginary part is denoted as EQ(n), then calculated complex electric field, pass through following formula
(1) it calculates:
E (n)=EI(n)+jEQ(n) (1)；
Wherein, E (n) represents plural electric field, and j represents imaginary unit；
Step 2: calculating the tap number of FIR time domain dispersion equilibrium method, calculated especially by following formula (2):
Wherein, N is the tap number of FIR time domain dispersion equilibrium method, and D is dispersion parameter, and λ is laser center wavelength, and L is optical fiber
Length, c are the light velocity, and Ts is the sampling period,It indicates to be rounded downwards；
Step 3: calculating the tap coefficient of FIR time domain dispersion equilibrium method, calculated especially by following formula (3):
Wherein, akFor tap coefficient,π is pi；
Step 4: the tap coefficient that step 3 exports is multiplied with majorized function, then optimized function optimization, after being optimized
Tap coefficient, specific steps are as follows:
Step 4.1 is by akIt is multiplied with majorized function, to reach optimization akThe effect of weight；
Step 4.2 is based on majorized function parameter, to ensure the tap coefficient C after optimizingkOptimal equalization effect can be reached；
Wherein, majorized function is chosen as raised cosine, also known as Raised Cosine function, referred to as RC function, i.e. RC-
FIR time domain dispersion equilibrium；Also then Gaussian function, referred to as Gaussian function, i.e. G-FIR time domain dispersion equilibrium be can choose；Or
Person selects other majorized functions；For RC function, functional parameter is halfwidth TFWHM=X1·Twindow,With
Rolloff-factor α, wherein TwindowFor the length of window of FIR time domain dispersion equilibrium method；For different X1With α value, according to
The portfolio effect of the optic communication signal after the transmission of different length optical fiber can be obtained under different condition in RC-FIR time domain dispersion equilibrium
Parameter X1It is constant with the best value of α, thereby determine that X1With the value of α；
For Gaussian function, functional parameter to be optimized is halfwidth TG_FWHM=X2·Twindow,
Compare X2When taking different numerical value, according to G-FIR time domain dispersion equilibrium to the optic communication signal after the transmission of different length optical fiber
Portfolio effect can obtain parameter X under different condition2Best value it is constant, thereby determine that X2Best value；
Step 5: carrying out balanced dispersion with the tap coefficient after step 4 optimizes, color is carried out especially by following formula (4)
Dissipate equilibrium:
Wherein, E (n-k) is sampling electric field, EeqIt (n) is output electric field,It represents ckWith the product of E (n-k)
N item and, the variation range of k be from 0 to N-1 sum.
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