CN106789793B - The LMS method without frequency difference difference feedback updated for adaptive equalizer coefficients - Google Patents
The LMS method without frequency difference difference feedback updated for adaptive equalizer coefficients Download PDFInfo
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- CN106789793B CN106789793B CN201611233246.9A CN201611233246A CN106789793B CN 106789793 B CN106789793 B CN 106789793B CN 201611233246 A CN201611233246 A CN 201611233246A CN 106789793 B CN106789793 B CN 106789793B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/01—Equalisers
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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
- H04B10/50—Transmitters
- H04B10/516—Details of coding or modulation
- H04B10/548—Phase or frequency modulation
- H04B10/556—Digital modulation, e.g. differential phase shift keying [DPSK] or frequency shift keying [FSK]
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Abstract
The invention discloses a kind of LMS methods without frequency difference difference feedback updated for adaptive equalizer coefficients, are related to coherent light communication technical field.The LMS method is the following steps are included: X polarized reception signal and Y polarized reception signal to adaptive equalizer carry out time domain equalization；Define the error formula of above-mentioned time domain equalization；It is defined according to above-mentioned error, updates adaptive equalizer coefficients using gradient algorithm, to guarantee that adaptive equalizer persistently tracks the variation of polarization state, and without frequency difference and the feedback that differs.The feedback that the present invention can make the update of adaptive equalizer coefficients eliminate the reliance on frequency difference and differ, even if encountering extreme polarization state variation, coherent optical communication system also can be tracked correctly, ensure that the robustness of system.
Description
Technical field
The present invention relates to coherent light communication technical fields, are specifically a kind of to update for adaptive equalizer coefficients
LMS (Least mean square, lowest mean square) method without frequency difference difference feedback.
Background technique
The theory of coherent light communication and experiment start from the eighties.Coherent optical communication system be acknowledged as with high sensitivity,
The feature that frequency selectivity is good, spectrum efficiency is high, these features are conducive to the raising of message capacity.In addition, in coherent light communication
In, dispersion and polarization mode dispersion are all linear damage to the damage of signal, and communication channel can be modeled as linearly invariant system at this time
System, therefore can be compensated by complicated DSP (Digital Signal Processing, the Digital Signal Processing) technology of appropriateness
Linear damage, so that the chromatic dispersion problem of puzzlement industry becomes relatively easily to solve.And in 40G, 100G optic communication epoch, phase
Dry optic communication is combined with Digital Signal Processing, and obtains huge business success.Comprehensively consider spectrum efficiency and optical signal to noise ratio
The requirement of tolerance, 100G commercial system is using the PM-QPSK (Polarization based on coherent light communication
Multiplexed Quadri Phase Shift Keying, palarization multiplexing quadriphase PSK) technology.
Due to the progress of electronic technology, so that the cost of DSP is greatly lowered, coherent optical communication system of new generation generally draws
Enter DSP technology.After using intrinsic light carrier demodulated signal light, ADC (Analog-Digital Converter, mould are reused
Number converter) electronic signal after demodulation is sampled, finally carry out Digital Signal Processing.Shown in Figure 1, coherent light communication receives
The process of the Digital Signal Processing of machine is general are as follows: and dispersion compensation → clock recovery → adaptive equalization → carrier auxiliary (estimate by frequency difference
Count and compensation) → carrier auxiliary (differing estimation and compensation) → bit decision.
Adaptive equalizer is the chief component of Digital Signal Processing, plays polarization demultiplexing and residual chromatic dispersion compensation
Effect, is usually made of linear equalizer and adaptive equalization coefficient update algorithm.Coherent light communication uses to enter 2 × 2 more
Have more adaptive equalizer, two polarization signals after output is balanced.
Currently, the more popular adaptive equalization coefficient update algorithm that can be used for PM-QPSK is CMA (Constant
Modulus Algorithms, constant modulus algorithm).Because CMA does not need training sequence, and does not need to compensate frequency difference in advance, relatively
Simply and there is certain robustness, is widely used by mainstream commercial system.The error defined formula of constant modulus algorithm are as follows:
Wherein,It is exported for the port X of adaptive equalizer,It is exported for the Y-port of adaptive equalizer, |
| it is calculated for modulus, 1 is the permanent mould size of setting, and n is data sequence number.The coefficient update formula of adaptive equalizer is according to public affairs
Error formula given by formula (1), (2) is obtained by gradient algorithm.
But what CMA algorithm utilized is QPSK (Quadri Phase Shift Keying, quadriphase PSK) signal
Permanent model's point, can not distinguish tracked polarization state, so algorithm wrong may restrain, keep two of adaptive equalizer defeated
A polarization state is all exported out.When polarization state occur and quickly changing, when acutely shaking under typhoon such as aerial optical cable, CMA can
Tracked polarization state can be lost, and mistake converges to two outputs all one polarization states of output of balanced device, brings system
Collapse.
And as improved LMS (Least mean square, lowest mean square) algorithm based on training sequence, due to making
First order statistic can track faster polarization variations than CMA.Also, due to the guide function of training sequence, adaptively
Balanced device can export polarization state corresponding to training sequence used.But in coherent optical communication system, due to for demodulation
Local laser with originator laser there are frequency difference with differ, so use LMS algorithm when, it is necessary to from frequency difference and phase thereafter
Poor compensating module introduce frequency difference with differ the calculating fed back for error signal, specific error calculation formula are as follows:
Wherein, DxWith DyFor expected data, for the training sequence numerical value being known in advance, Δ f is frequency difference, and T is code-element period,
ΦxWith ΦyThe respectively difference of X, Y polarization signal, n are data sequence number.
But the problem of existing LMS method, is: in actual signal processing, frequency difference estimation with differ estimation
All rely on the correct output of adaptive equalizer.In the system of actual deployment, although polarization state variation is slow in most cases
Slowly, the polarization variations being exceedingly fast but instantaneously are likely to occur, at this time it cannot be guaranteed that the correct output of adaptive equalizer, no correct
Frequency difference with differ feedback, existing LMS method cannot correctly work, so not ensured that using existing LMS method and being
Existence of the system under the polarization variations being exceedingly fast.
Summary of the invention
The purpose of the invention is to overcome the shortcomings of above-mentioned background technique, provide a kind of for adaptive equalizer coefficients
Update without frequency difference difference feedback LMS method, can make the update of adaptive equalizer coefficients eliminate the reliance on frequency difference with differ
Feedback, even if encountering extreme polarization state variation, system also can be tracked correctly, ensure that the robustness of system.
To achieve the above objectives, the technical solution adopted by the present invention is that: provide it is a kind of for adaptive equalizer coefficients more
The new LMS method without frequency difference difference feedback, the LMS method the following steps are included:
S1: to the X polarized reception signal [Ein of adaptive equalizerx] and Y polarized reception signal [Einy] carry out time domain it is equal
Weighing apparatus, the formula of time domain equalization are as follows:
Wherein,WithThe respectively output of adaptive equalizer X polarization signal and Y polarization signal,
Fxx、Fxy、Fyx、FyyFor four adaptive equalizer coefficients, n is sequence number, and L is adaptive equalizer series, and l is adaptive equal
Weighing apparatus series serial number；
S2: the error formula of above-mentioned time domain equalization is defined are as follows:
Error (n)=| Error_xy1 (n) |2+|Error_xy2(n)|2, in which:
In formula, Dx、DyIt is previously known training sequence numerical value for expected data；For the end X of adaptive equalizer
Mouth output,It is exported for the Y-port of adaptive equalizer；| | it is calculated for modulus, []*To take conjugation；
S3: defining according to above-mentioned error, adaptive equalizer coefficients is updated using gradient algorithm, to guarantee adaptive equalization
Device persistently tracks the variation of polarization state, and without frequency difference and the feedback that differs.
Based on the above technical solution, the formula of adaptive equalizer coefficients is updated described in step S3 are as follows:
In above-mentioned formula, * is conjugate of symbol, and g indicates the g times update, μ1、μ2It is small coefficient used as needed.
Based on the above technical solution, the μ in step S3, in the formula for updating adaptive equalizer coefficients1
And μ2It may be the same or different.
Based on the above technical solution, the μ in step S3, in the formula for updating adaptive equalizer coefficients1
And μ2Value range be 1~10-9。
Based on the above technical solution, in step S3, when adaptive equalizer updates adaptive equalizer coefficients, meeting
Lock the difference Φ of X polarization signalxWith the difference Φ of Y polarization signaly, so that Φx=Φy；Also, work as sef-adapting filter just
Really when output, the output of adaptive equalizer X polarization signalWith the output of Y polarization signalIt is respectively as follows:
Wherein, j is plural number, and Δ f is frequency difference, and T is code-element period；And the frequency difference Δ f in above-mentioned output formula will be in error
It is eliminated in formula.
Based on the above technical solution, under QPSK application scenarios, previously known training sequence described in step S2
Columns value need to meet claimed below when being pre-designed: Dx(n)/Dy(n) 1, j is equably taken, -1, four numerical value of-j.
The beneficial effects of the present invention are:
(1) present invention two paths of signals frequency difference having the same and the spy that differs using what is demodulated in coherent optical communication system
Point proposes the error formula of new follow-on X, Y polarization signal.Using follow-on error formula, it can be achieved that without frequency
Difference with differ feed back LMS algorithm.Compare traditional LMS algorithm must rely on frequency difference with differ feedback for, this method due to
The coefficient update of adaptive equalizer eliminate the reliance on frequency difference with differ feedback, even if encountering extreme polarization state variation, system
It can correctly track, ensure that the robustness of system, meet actual use demand.
(2) present invention realizes simple, has very strong practicability；And use of the invention is not limited to coherent light communication neck
Domain, it is applied widely.
Detailed description of the invention
Fig. 1 is the Digital Signal Processing flow chart of coherent optical communication receiver in the prior art；
Fig. 2 is the side LMS without frequency difference difference feedback updated in the embodiment of the present invention for adaptive equalizer coefficients
The flow chart of method.
Specific embodiment
With reference to the accompanying drawing and specific embodiment the present invention is described in further detail.
It is shown in Figure 2, the embodiment of the present invention provide it is a kind of for adaptive equalizer coefficients update without frequency difference phase
The LMS method of difference feedback, comprising the following steps:
Step S1: to the X polarized reception signal [Ein of adaptive equalizerx] and Y polarized reception signal [Einy] carry out when
Domain is balanced, the formula of time domain equalization are as follows:
Wherein,WithThe respectively output of adaptive equalizer X polarization signal and Y polarization signal,
Fxx、Fxy、Fyx、FyyFor four adaptive equalizer coefficients, n is sequence number, and L is adaptive equalizer series, and l is adaptive equal
Weighing apparatus series serial number, is transferred to step S2.
Step S2: the error formula of above-mentioned time domain equalization is defined are as follows:
Error (n)=| Error_xy1 (n) |2+|Error_xy2(n)|2, (7)
In formula, Dx、DyIt is previously known training sequence numerical value for expected data；For the end X of adaptive equalizer
Mouth output,It is exported for the Y-port of adaptive equalizer；| | it is calculated for modulus, []*To take conjugation, it is transferred to step S3.
It is understood that when being pre-designed training sequence numerical value, Dx(n) and Dy(n) difference should uniformly take all
Value may be obtained.By taking QPSK as an example, that is, requires in project training sequential digit values, to meet Dx(n)/Dy(n) 1 is equably taken,
J, -1, four numerical value of-j, wherein j is plural number.
Step S3: according to above-mentioned error defined formula (7)~(9), updating adaptive equalizer coefficients using gradient algorithm,
To guarantee that adaptive equalizer persistently tracks the variation of polarization state, and without frequency difference and the feedback that differs.
Wherein, the coefficient update formula of adaptive equalizer are as follows:
In above-mentioned formula, * is conjugate of symbol, and g indicates the g times update, μ1、μ2It is small coefficient used as needed,
The two may be the same or different, and μ1And μ2Value range can be 1~10-9。
Further it will be understood that X polarization signal can be locked when adaptive equalizer updates adaptive equalizer coefficients
Difference ΦxWith the difference Φ of Y polarization signaly, so that Φx=Φy, so that the coefficient update of adaptive equalizer is no longer
Rely on the feedback of difference；Also, when sef-adapting filter correctly exports, the output of adaptive equalizer X polarization signalWith the output of Y polarization signalIt is respectively as follows:
Wherein, j is plural number, and Δ f is frequency difference, and T is code-element period；And the frequency difference Δ f in above-mentioned output formula will be in error
It is eliminated in formula, so that the coefficient update of adaptive equalizer eliminates the reliance on the feedback of frequency difference.
As can be seen from the above-described embodiment, the present invention realizes simple, has very strong practicability.Due to adaptive equalizer
Coefficient update eliminate the reliance on frequency difference with differ feedback, even if encountering extreme polarization state variation, system also can be tracked correctly, be protected
The robustness for having demonstrate,proved system meets actual use demand.
The present invention is not limited to the above-described embodiments, for those skilled in the art, is not departing from
Under the premise of the principle of the invention, several improvements and modifications can also be made, these improvements and modifications are also considered as protection of the invention
Within the scope of.The content being not described in detail in this specification belongs to the prior art well known to professional and technical personnel in the field.
Claims (4)
1. a kind of LMS method without frequency difference difference feedback updated for adaptive equalizer coefficients, which is characterized in that should
LMS method the following steps are included:
S1: to the X polarized reception signal [Ein of adaptive equalizerx] and Y polarized reception signal [Einy] time domain equalization is carried out, when
The formula of domain equilibrium are as follows:
Wherein,WithThe respectively output of adaptive equalizer X polarization signal and Y polarization signal, Fxx、
Fxy、Fyx、FyyFor four adaptive equalizer coefficients, n is sequence number, and L is adaptive equalizer series, and l is adaptive equalizer
Series serial number；
S2: the error formula of above-mentioned time domain equalization is defined are as follows:
Error (n)=| Error_xy1 (n) |2+|Error_xy2(n)|2, in which:
In formula, Dx、DyIt is previously known training sequence numerical value for expected data；It is defeated for the port X of adaptive equalizer
Out,It is exported for the Y-port of adaptive equalizer；| | it is calculated for modulus, []*To take conjugation；
S3: defining according to above-mentioned error, adaptive equalizer coefficients is updated using gradient algorithm, to guarantee that adaptive equalizer is held
The variation of continuous tracking polarization state, and without frequency difference and the feedback that differs；
Wherein, adaptive equalizer coefficients more new formula are as follows:
In above-mentioned formula, * is conjugate of symbol, and g indicates the g times update, μ1、μ2It is small coefficient used as needed；
Meanwhile when adaptive equalizer update adaptive equalizer coefficients, the difference Φ of X polarization signal can be lockedxIt polarizes and believes with Y
Number difference Φy, so that Φx=Φy；Also, when sef-adapting filter correctly exports, adaptive equalizer X polarization signal
OutputWith the output of Y polarization signalIt is respectively as follows:
Wherein, j is plural number, and Δ f is frequency difference, and T is code-element period；And the frequency difference Δ f in above-mentioned output formula will be in error formula
In be eliminated.
2. the LMS method without frequency difference difference feedback updated as described in claim 1 for adaptive equalizer coefficients,
It is characterized in that: the μ in step S3, in the formula for updating adaptive equalizer coefficients1And μ2It may be the same or different.
3. the LMS method without frequency difference difference feedback updated as described in claim 1 for adaptive equalizer coefficients,
It is characterized in that: the μ in step S3, in the formula for updating adaptive equalizer coefficients1And μ2Value range be 1~10-9。
4. the LMS method without frequency difference difference feedback updated as described in claim 1 for adaptive equalizer coefficients,
Be characterized in that: under QPSK application scenarios, previously known training sequence numerical value described in step S2 need to expire when being pre-designed
Foot is claimed below: Dx(n)/Dy(n) 1, j is equably taken, -1, four numerical value of-j.
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| CN108173794B (en) * | 2017-12-27 | 2020-05-12 | 武汉邮电科学研究院 | Novel LMS (least mean square) method and real number adaptive equalizer using same |
| CN109510668B (en) * | 2018-12-11 | 2020-06-30 | 武汉邮电科学研究院有限公司 | Adaptive equalizer based on quasi feedforward control in coherent optical communication and method |
| CN114650097A (en) * | 2020-12-21 | 2022-06-21 | 富士通株式会社 | Polarization state tracking recovery method, device and optical receiver |
| CN112929083B (en) * | 2021-02-04 | 2022-04-26 | 烽火通信科技股份有限公司 | Coherent optical module and monitoring method thereof |
| CN114362832B (en) * | 2022-01-13 | 2023-08-11 | 武汉邮电科学研究院有限公司 | Analog coherent optical communication receiving method and device for realizing differential detection in electric domain |
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