CN106453183B - A kind of blind ICI phase noise compensation method suitable for big line width CO-OFDM system - Google Patents
A kind of blind ICI phase noise compensation method suitable for big line width CO-OFDM system Download PDFInfo
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- CN106453183B CN106453183B CN201610576238.8A CN201610576238A CN106453183B CN 106453183 B CN106453183 B CN 106453183B CN 201610576238 A CN201610576238 A CN 201610576238A CN 106453183 B CN106453183 B CN 106453183B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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- H—ELECTRICITY
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- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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- H04L27/2601—Multicarrier modulation systems
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Abstract
A kind of blind ICI phase noise compensation method suitable for big line width CO-OFDM system, this method will first receive end data and carry out CPE phase noise compensation；Then, the time domain data after CPE phase noise compensation is subjected to rough blind ICI phase noise compensation；Next, frequency domain data after rough blind ICI phase noise compensation is made decisions, it is fast fourier transformed to the frequency domain data after judgement to arrive time domain data, it is several sub- symbols by each OFDM data symbol segmentation in the time domain data before the time domain data and CPE phase noise compensation, finds out the phase noise approximation of the Asia symbol；Finally, carrying out fine ICI phase noise compensation.A kind of computation complexity lower blind ICI phase noise compensation method suitable for big line width high speed CO-OFDM system while the present invention provides effect with good compensation.
Description
Technical field
The invention belongs to optical communication network technology field, in particular to a kind of blind ICI phase of big line width CO-OFDM system
Noise compensation method.
Background technique
Coherent light ofdm system is due to its outstanding resisting chromatic dispersion and polarization mode dispersion ability, not only to following high
Fast long distance optical communication systems, and become one of the alternate transmission technology most possibly used in the following optical access network.
CO-OFDM system structure is as shown in Figure 1, can be divided into 5 modules: CO-OFDM system transmitting terminal mould by its function
Block 101, optical modulator module 102, optical fiber transmission module 103, Photoelectric Detection module 104 and CO-OFDM system receiving terminal module
Up-conversion of the electrical domain signal that 105, CO-OFDM transmitting end modules generate Jing Guo Electro-optical Modulation becomes the CO-OFDM signal of area of light,
CO-OFDM signal transmits through optical fiber, after balanced detector through photoelectric conversion at the signal of electrical domain, CO-OFDM is docked receiving end again
The electric signal received carries out signal processing to restore original transmission segment data.In conjunction with Fig. 1, to the course of work of whole system
It is stated in detail.The data 106 of CO-OFDM system serial input pass through serioparallel exchange module 107, become parallel N number
According to；The signal after serioparallel exchange is subjected to digital modulation 108 according to different modulation formats；Inverse fast Fourier transform IFFT mould
Block 109 realizes conversion of the signal from frequency domain to time domain；Cyclic prefix CP 110 is added；Obtained electrical domain signal is carried out and is gone here and there to turn
Change 111.The in-phase component and orthogonal component signal of above-mentioned signal pass through digital analog converter 112,113 respectively and are transformed to analog signal
And pass through low-pass filter 114,115；The in-phase component 116 of signal and quadrature component 117 are amplified and injected using amplifier
Realize in-phase component I and quadrature component Q to the orthogonal modulation of optical signal into I/Q modulator；I/Q modulator is by 3 both arms
Mach increases Dare MZM modulator 120,121 and 122 and forms, and two of them modulator realizes the modulation to signal, third modulation
Device 122 controls the phase difference of the in-phase component I and quadrature component Q of light modulation；The direct current of two modulators 120,121 is adjusted respectively
Biasing guarantees to realize that the modulator of signal modulation works in minimum power point, and the modulator work of third control phase difference exists
There are 90 ° of phase differences to guarantee two paths of signals for orthogonal points；118 indicate the emitting laser of CO-OFDM system, pass through splitter
119 are divided into the same laser of two beams, for driving two optical modulators 120 and 121.The signal of two optical modulators output passes through
Bundling device 123 becomes the optical signal of single channel, is then inputted into fiber channel and is transmitted.The CO-OFDM signal of generation is in optical fiber
In 124 after the transmission of long-distance, by direct light -125 compensated optical fiber of image intensifer-erbium-doped fiber amplifier (EDFA)
It is transmitted again after loss, indicates the optical fiber of long range, 126 indicate optical band pass filter.After the transmission of the optical fiber of long-distance,
Area of light signal is transformed into the signal of electrical domain by Photoelectric Detection module.127 indicate the local laser of CO-OFDM system receiving terminal,
It is divided into the same laser of two beams by splitter, 128 indicate one 90 ° of phase-shifter；129 and 130 indicate two couplers, drive
Move 4 photodiodes (PD) 131,132,133 and 134.135 and 136 indicate two subtracters, respectively correspond output and receive letter
Number in-phase component I and quadrature component Q.Obtained in-phase component I and quadrature component Q passes through low-pass filter 137,138 and mould
Number converter 139,140 enters the receiving end CO-OFDM after converting.The receiving end CO-OFDM carries out Digital Signal Processing 141, carries out
The inverse process of CO-OFDM transmitting terminal carries out serioparallel exchange 142, removes cyclic prefix CP 143, then carries out FFT transform 144, right
CO-OFDM signal carries out digital demodulation 145, and it is defeated finally to obtain original transmitting terminal serial data by the recovery of parallel-serial conversion 146
Out 147.
Above-mentioned is the general structure of multicarrier coherent optical communication system, compared to the coherent light communication technology of single carrier
(PDM-QPSK that such as current 100G/s industrial standard uses), CO-OFDM can be realized higher spectrum efficiency (i.e. bandwidth usage
Rate), more flexible frequency spectrum uses, more effective channel equalization and higher frequency compose scalability, be widely regarded as by scholar next
For 400G/s and the important solutions of 1Tb/s (1T=1000G) optical fiber telecommunications system.
Compared with traditional single carrier optical communication system, the CO-OFDM multicarrier system OFDM symbol period is longer, and is connecing
Receiving end increase laser generate local carrier to coherent reception, therefore the multicarrier system be more vulnerable to transmitting terminal laser and
The influence of phase noise caused by frequency departure and line width between local laser.The phase noise of laser is to CO-OFDM system
System generates two kinds of adverse effects, one is making all subcarriers of each OFDM symbol rotate a common angle, referred to as
Common phase error (CPE), it will be so that serious rotation occurs for receiving end planisphere.Another is that additivity random phase is made an uproar
Sound, it will interfere with each other (ICI) so that generating between subcarrier, and make receiving end planisphere that serious diverging occur.In view of such reason,
Most of relevant optical OFDM systems use expensive outside cavity gas laser as light source, because its line width is maintained at less than 100kHz,
To which receiving end phase noise variance is maintained at lesser value.It distributed feedback (DFB) laser so inexpensively and hangs down
Straight Cavity surface transmitting (VCSEL) laser cannot use in this coherent system.What is more, in order to improve transmission rate, needs
Using high order modulation, outside cavity gas laser must be selected in this case.Therefore, it is to reduce system cost and improve
It is imperative to carry out effective compensation to phase noise for system transmission rate.CO-OFDM system phase noise compensation be divided into CPE and
Two stages of phase noise compensation of ICI.The comparative maturity that wherein phase compensating method of CPE has been studied.But it is passed through in system
It crosses to after CPE phase noise compensation, being become by the remaining time-varying phase noise that inter-carrier interference generates influences system performance
Key factor.The blind phase noise compensation method of several couples of ICI has been proposed in researcher.In order to improve the spectrum utilization of system
Rate, have researcher with dummy pilot signal substitute frequency pilot sign carry out phase noise compensation (document 1, C.Zhao, C.Yang,
F.Yang,F.Zhang,and Z.Chen,A CO-OFDM system with almost blind phase noise
Suppression ", IEEE Photon.Technol.Lett, 2013,25 (17): 1723-1726, i.e. document 1, C.Zhao,
C.Yang, F.Yang, F.Zhang, and Z.Chen are bordering on the CO-OFDM system of blind phase noise reduction, IEEE photon technology
Journal, 2013,25 (17): 1723-1726.).There are also researchers directly to carry out ICI phase noise using symbol hard decision result
Compensate (document 2, S.CAO, P.KAM, and C.YU, Decision-aided, pilot-aided, decision-feedback
phase estimation for coherent optical OFDM[J],IEEE Photon.Technol.Lett,2012,
24 (22): 2067-2069, document 2, S.CAO, P.KAM, and C.YU, decision-aided and the pilot tone in optical OFDM system of being concerned with are auxiliary
The decision-feedback phase estimation helped, IEEE photon technology journal, 2012,24 (22): 2067-2069).However in both methods
In, symbol judgement mistake will generate Error propagation problems, severe exacerbation phase noise compensation effect.M.E.Mousa-Pasandi
(document 3, Mohammad E.Mousa-Pasandi, and David V.Plant, Noniterative interpolation-
based partial phase noise ICI mitigation for CO-OFDM transport systems,IEEE
Photon.Technol.Lett., 2011,23 (21): 1594-1596, i.e. Mohammad E.Mousa-Pasandi, and
It is compensated without iteration based on the fractional phase noise ICI of interpolation in David V.Plant, CO-OFDM Transmission system, IEEE photon skill
Art journal, 2011,23 (21): 1594-1596.) etc. propose it is a kind of based on linear interpolation without iteration ICI phase noise compensation
Method, however linear interpolation carries out between OFDM symbol in this approach, needs to receive next OFDM (Orthogonal
Frequency Division Multiplexing, OFDM) symbol could compensate the ICI phase noise of current sign, therefore
Receiving end needs the memory buffer of an additionally reserved symbol.In document (document 4, W.Chung, A matched
filtering approach for phase noise suppression in CO-OFDM system,IEEE
Photon.Technol.Lett., 2011,22, (24): 1802-1804, i.e. W.Chung inhibit phase to make an uproar in CO-OFDM system
A kind of matched filter of sound, IEEE photon technology journal, 2011,22, (24): 1802-1804.) in, with a pilot aided
Adaptively there is limit for length's unit impulse response (Finite Impulse Response, FIR) filter to filter out ICI phase noise.
But this method is only applied to low-order-modulated format (Quadrature Phase Shift Keyin, QPSK), and is needed
By that could restrain compared with successive ignition, method complexity is higher.Since the laser phase noise of ICI and time-varying directly generates, because
This increase time domain phase noise estimated accuracy can effectively improve ICI phase noise compensation effect (document 5, M.LEE,
S.LIM,and K.YANG,Blind compensation for phase noise in OFDM systems over
Constant modulus modulation, IEEE Trans.Commun., 2012,60 (3): 620-625., that is, M.LEE,
S.LIM, and K.YANG, based on permanent mould modulation the blind phase noise compensation of ofdm system, IEEE Trans.Commun.,
2012,60(3):620-625.).Therefore have researcher by each CO-OFDM symbol from temporal segmentation be several sub- symbols
(Avg-BL-ICI phase noise method) then estimates the phase noise of each sub- symbol respectively, improves phase and make an uproar
The estimated accuracy of sound obtains good phase noise compensation effect (document 6, S.Cao, P.Kam, and C.Yu, Time-
domain blind ICI mitigation for non-constant modulus format in CO-OFDM,IEEE
Photon.Technol.Lett, 2013,25 (24): 2490-2493, i.e. S.Cao, P.Kam, and C.Yu, CO-OFDM system
In non-permanent mould the blind ICI phase noise compensation of time domain, IEEE photon technology journal, 2013,25 (24): 2490-2493.).It is based on
Blind ICI phase is unfolded in the Asia symbol temporal segmentation method, the orthogonal basis that Peking University Yang Chuanchuan et al. proposes pilot beacon auxiliary
Noise compensation method (document 7, LIU Yue, YANG Chuan-chuan, LI Hong-bin.Cost-effective and
spectrum-efficient coherent TDM-OFDM-PON aided by blind ICI suppression.IEEE
Photonics Technology Letters, 2015,27 (8): 887-890., that is, LIU Yue, YANG Chuan-chuan, LI
The low cost and the relevant TDM-OFDM-PON of spectral efficient of the blind phase noise reduction auxiliary of Hong-bin, ICI, IEEE photon skill
Art journal, 2015,27 (8): 887-890.), it is applied to (Time in relevant time division multiplexing orthogonal frequency division multiplexing passive optical network
Division Multiplexing Orthogonal Frequency DivisionMultiplexing Passive
Optical Network, TDM-OFDM-PON) inhibit ICI phase noise, in high order modulation and laser linewidth greatly to 700kHz
Still achieve preferable phase noise compensation effect.South China Normal University Hong Xuezhis etc. are based on this time domain Asia symbol segmentation method
A kind of blind ICI phase noise estimation method (document 8, HONG Xue-zhi, HONG are proposed with sub- intersymbol linear interpolation method
Xiao-jian and HE Sai-ling,Linearly interpolated sub-symbol optical phase
Noise suppression in CO-OFDM system, Opt.Express, 2015,23 (4): 4691-4702. are that flood is learned
Intelligence, Hong Xiaojian, He Sailing, the sub- symbol light phase noise suppressed linearly interleave in CO-OFDM system, Opt.Express,
2015,23 (4): 4691-4702.), in the case where an OFDM symbol divides small number Asia symbol, achieve preferable
Phase noise compensation effect and method complexity is lower.However the CPE estimation that this blind ICI method needs in advance is based on pilot tone
Progress, be not proper total blindness's phase noise method, reduce the availability of frequency spectrum of system.It is previous at us
Research in, be the method for sub- symbol based on this segmentation OFDM symbol, by combine time domain ICI phase noise approximation on the average and
Frequency domain symbol decision-aided estimation method proposes a kind of ICI phase noise inhibition method, obtains in the system of high optical signal to noise ratio
Obtain good compensation effect (patent 1, a kind of more sub-block phase noise estimation compensation process suitable for CO-OFDM system, application
Number: 201510611121.4), however when this method need obtain better effects, required Asia symbol segmentation number is excessive, this causes
Method computation complexity is excessive.
Summary of the invention
In order to overcome the phase noise compensation mode of existing CO-OFDM system to cannot be considered in terms of compensation effect and calculate complicated
The deficiency of degree, it is lower suitable for big line width CO- that the present invention provides a kind of computation complexity while having good compensation effect
The blind ICI phase noise compensation method of ofdm system.
The present invention is realized by the following technical solution:
A kind of blind ICI phase noise compensation method suitable for big line width CO-OFDM system,
This method will first receive end data and carry out CPE phase noise compensation；
Then, the time domain data after CPE phase noise compensation is subjected to rough blind ICI phase noise compensation；
Next, being made decisions to the frequency domain data after rough blind ICI phase noise compensation, to the frequency domain after judgement
Data are fast fourier transformed to arrive time domain data, will be every in the time domain data before the time domain data and CPE phase noise compensation
One OFDM data symbol segmentation is several sub- symbols, finds out the phase noise approximation of the Asia symbol；
Finally, carrying out fine ICI phase noise compensation.
Further, the blind ICI phase noise compensation method includes the following steps:
(1) receiving end carries out coherent detection reception to the CO-OFDM signal received, then carries out analog-to-digital conversion, obtains
The signal of electrical domain；
(2) electrical domain optical fiber dispersion compensation.Specifically the analytical form of fiber channel frequency domain transfer function is become through Fourier
Time domain is changed to, designs the long unit impulse response of time-domain finite (FIR) filter to realize, the order of the filter is accumulated with dispersion
And increase.
(3) serioparallel exchange.
(4) cyclic prefix CP is removed.
(5) Frequency offset estimation and compensation.
(6) signal is become from time domain by frequency domain using Fast Fourier Transform (FFT) (FFT), while saves the time-domain signal.
(7) the blind phase noise compensation of CPE is carried out to frequency domain data.
(8) rough blind ICI phase noise compensation.It is assumed that an OFDM frame includes N number of OFDM symbol in time domain, each
OFDM symbol includes K subcarrier (K point Discrete Fourier Transform, DFT) in frequency domain.If each OFDM at this time
Signal is divided into NB1A Asia symbol, then the data sampling number in each sub- symbol is S1=K/NB1, N hereB1It is smaller.It is then every
Phase noise average value indicates in a Asia symbol are as follows:
It can thus be concluded that neglecting additive noise in the biggish situation of signal-to-noise ratio, can obtain in nth symbol, k-th of son carries
Meet following formula when wave,
Here|En,k|2It is signaling point in the modulation of permanent mould
Energy is the average energy for taking each signaling point in non-permanent mould modulation.By above formula it is estimated that the phase of each Asia symbol
Position noise average.Then the frequency domain data after carrying out rough ICI phase noise compensation is expressed as,
(9) it adjudicates.To the frequency domain data after rough ICI phase noise compensationIt makes decisions.As transmitting terminal is originally
16QAM modulation, then this process first carries out 16QAM demodulation, is then modulated again.
(10) Fast Fourier Transform.It is time-domain signal that signal after judgement, which is passed through FFT transform,
(11) symbol temporal segmentation is multiple sub- symbols.Time-domain signalTime domain OFDM signal before being compensated with original by CPE
yn,t(0≤t≤K-1) is divided into NB2A Asia symbol, the phase noise valuation of data sampling in the sub- symbol of q-th of the nth symbolIt can be acquired by following formula,
Here ' and No. * respectively indicate transposition and conjugate operation.In view of NB2For arbitrary integer, thenAnd yn,qTable respectively
It is shown as,
HereWherein [A] indicates the maximum integer for being not more than A.
(12) fine ICI phase noise compensation.Frequency domain ofdm signal after fine ICI phase noise compensationIt can be close
Like expression are as follows:
(13) frequency domain data after fine ICI phase noise compensation is subjected to conclusive judgement.
Technical concept of the invention are as follows: be directed to big line width coherent light orthogonal frequency division multiplexing (CO-OFDM) system, propose one kind
Blind ICI phase noise compensation method (A-CPEC).The blind ICI phase noise compensation method is realizing blind CPE phase noise compensation
On the basis of, it is carried out first using a kind of blind ICI method (Avg-BL method) for effectively avoiding symbol judgement error propagation rough
ICI phase noise compensation, when being transformed to again through fast Flourier (FFT) after then making decisions compensated frequency-region signal
Domain, the original time domain signal for compensating preceding receiving end to the time-domain signal and CPE carry out temporal segmentation, to obtain each sub- symbol
Phase noise approximate average, finally realize fine ICI phase noise compensation.By selecting suitable OFDM symbol segmentation
Number, can be realized the compromise between method performance and method complexity.The blind phase noise method of the ICI and other phase noise sides
Method is compared, and has preferable compensation effect and the availability of frequency spectrum to big line width CO-OFDM system.This method effectively reduces CO-
Requirement of the ofdm system to laser light source line width has application of the CO-OFDM system in long range access net or Metropolitan Area Network (MAN)
Significance.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the CO-OFDM system of pair high-order digit modulation and big line width laser, blind ICI phase noise estimation of the invention
Method obtains preferable phase noise portfolio effect.But blind ICI phase noise estimation method of the invention does not use one to lead
Perhaps training symbol greatly improves the frequency spectrum benefit of system to frequency compared with the method (document 8) based on pilot tone or training symbol
With rate.
2. blind ICI phase noise compensation method proposed by the present invention effectively overcomes symbol judgement mistake in document 8 and causes
The problem of.Rough ICI phase noise compensation method before fine ICI phase noise compensation overcomes symbol judgement mistake completely
Accidentally bring influences, so that method compensation effect significantly improves in the CO-OFDM system of big line width laser, passes through
The sub- number of symbols for suitably selecting each OFDM symbol segmentation in fine ICI phase noise compensation, can be in method performance and method
Reach compromise between complexity.
Detailed description of the invention
Fig. 1 is the schematic diagram of CO-OFDM system in the prior art.
Fig. 2 is the method schematic of the embodiment of the present invention 1.
Fig. 3 is in the embodiment of the present invention 1 in NB1=NB2=4, several phase noise compensation methods (A-CPEC, Avg-BL,
CPEC relation curve when bit error rate performance) changes with laser linewidth.
Fig. 4 is N in the embodiment of the present invention 1B1=4, A-CPEC method under various lasers line width (0.3MHz, 0.5MHz,
And 0.7MHz) bit error rate performance with NB2Relation curve when variation.
Fig. 5 is to receive the unused any phase noise of end data in the embodiment of the present invention 1 when laser linewidth is 500kHz
The planisphere of method compensation.
Fig. 6 is to receive end data when laser linewidth is 500kHz in the embodiment of the present invention 1 only to use blind CPE phase noise
The planisphere of method compensation.
Fig. 7 is that when laser linewidth is 500kHz, reception end data is blind with blind CPE and Avg-BL in the embodiment of the present invention 1
The planisphere of ICI phase noise method compensation.
Fig. 8 be in the embodiment of the present invention 1 laser linewidth be 500kHz and NB2When=4 receive end data with blind CPE with
The planisphere of ICI phase noise method (A-CPEC) compensation proposed by the present invention.
Specific embodiment
The present invention is described in further detail below with reference to examples and drawings, but embodiments of the present invention are unlimited
In this.
Embodiment 1
The method of the present invention relates generally to the signal processing problems of coherent light orthogonal frequency division multiplexing CO-OFDM system receiving terminal,
With reference in background technique to the detailed description of CO-OFDM system structure.
As shown in Figure 1, CO-OFDM system includes CO-OFDM system transmitting end module 101, CO-OFDM optical modulator module
102, optical fiber transmission module 103, Photoelectric Detection module 104 and CO-OFDM system receiving terminal module 105, system transmitting terminal produce
The up-conversion that raw signal have passed through light modulation becomes the CO-OFDM signal of area of light, and CO-OFDM signal is transmitted through optical fiber, balanced
Through photoelectric conversion at the signal of electrical domain after detector, system receiving terminal again to the electrical domain signal received carry out signal processing to
Restore original transmission end data.Initial 50Gb/s pseudo noise code binary data stream with high-order QAM modulation (16QAM and
It 32QAM) is mapped on 512 subcarriers, the points of FFT or IFFT are 1024.Before circulation in each OFDM data symbol
Sewing CP length is 128 points.Every 50km single mode optical fiber is followed by an erbium-doped optical fiber amplifier EDFA, which is 13dB,
Noise coefficient is 4dB.Entire optical fiber link shares 2 sections of 50km single mode optical fibers and amplifier EDFA is added to constitute.The color of the single mode optical fiber
Dissipating coefficient is 16.75ps/nmkm, and chromatic dispersion gradient is 0.075ps/ (nm2Km), nonlinear factor 1.5W-1·km-1, PMD
Coefficient isLoss factor is 0.2dB/km.Transmitting terminal laser and coherent reception end laser are having the same
Line width and wavelength, wavelength 1550nm.
Below with reference to Fig. 2, to a kind of blind ICI phase noise compensation suitable for big line width CO-OFDM system of the invention
The step of method, is described in detail.
S201: receiving end carries out coherent detection reception to the CO-OFDM signal received, then carries out analog-to-digital conversion, obtains
To the signal of electrical domain.
S202: electrical domain optical fiber dispersion compensation.Specifically by the analytical form of fiber channel frequency domain transfer function through Fourier
Time domain is transformed to, designs the long unit impulse response of time-domain finite (FIR) filter to realize, the order of the filter is tired with dispersion
It accumulates and increases.
S203: serioparallel exchange.
S204: cyclic prefix CP is removed.
S205: Frequency offset estimation and compensation.
S206: signal is become from time domain by frequency domain using Fast Fourier Transform (FFT) (FFT), while saving the time-domain signal.
S207: the blind phase noise compensation of CPE is carried out to frequency domain data.
S208: rough blind ICI phase noise compensation.It is assumed that an OFDM frame includes N number of OFDM symbol in time domain, each
OFDM symbol includes K subcarrier (K point Discrete Fourier Transform, DFT) in frequency domain.If each ofdm signal
It is divided into NB1A Asia symbol, then the data sampling number in each sub- symbol is S1=K/NB1, N hereB1It is smaller.Then each Asia
Phase noise average value indicates in symbol are as follows:
It can thus be concluded that neglecting additive noise in the biggish situation of signal-to-noise ratio, can obtain in nth symbol, k-th of son carries
Meet following formula when wave,
Here|En,k|2It is signaling point in the modulation of permanent mould
Energy is the average energy for taking each signaling point in non-permanent mould modulation.By above formula it is estimated that the phase of each Asia symbol
Position noise average.Then the frequency domain data after carrying out rough ICI phase noise compensation is expressed as,
S209: judgement.To the frequency domain data after rough ICI phase noise compensationIt makes decisions.As transmitting terminal is originally
16QAM modulation, then this process first carries out 16QAM demodulation, is then modulated again.
S210: Fast Fourier Transform.It is time-domain signal that signal after judgement, which is passed through FFT transform,
S211: symbol temporal segmentation is multiple sub- symbols.Time-domain signalTime domain OFDM letter before being compensated with original by CPE
Number yn,t(0≤t≤K-1) is divided into NB2A Asia symbol, the phase noise of data sampling is estimated in the sub- symbol of q-th of the nth symbol
ValueIt can be acquired by following formula,
Here ' and No. * respectively indicate transposition and conjugate operation.In view of NB2For arbitrary integer, thenAnd yn,qTable respectively
It is shown as,
HereWherein [A] indicates the maximum integer for being not more than A.
S212: fine ICI phase noise compensation.Frequency domain ofdm signal after fine ICI phase noise compensationIt can be close
Like expression are as follows:
S213: the frequency domain data after fine ICI phase noise compensation is subjected to conclusive judgement.
Numerical Validation is carried out to blind ICI phase noise compensation (A-CPEC) method that the invention proposes.In Fig. 2 only not
It is known as CPEC method by the method that rough ICI phase noise method compensates, which is known as Avg-BL
Method.In order to the A-CPEC method proposed to Fig. 1 compares assessment, the also Numerical Validation performance of other two methods.Hair
End and receiving end laser wavelength having the same (1550nm) are penetrated, the best emitted energy of transmitting terminal laser is -2dBm.
Fig. 3 is shown in NB1=NB2When=4, the mistake of several phase noise compensation methods (A-CPEC, Avg-BL, CPEC)
Relation curve when code rate performance changes with laser linewidth.As laser linewidth increases, phase noise variance becomes larger, CPEC
The probability that symbol symbol error is adjudicated in method is increasing, and CPEC method bit error rate performance has larger decline at this time, such as
When line width 500kHz, CPEC method is adjudicated by serious symbol error to be influenced, and the bit error rate declines about compared with Avg-BL method
0.6dB.And A-CPEC method ratio Avg-BL method performance then improves 0.5dB, shows that this method preferably resolves the former side CPEC
Method symbol error adjudicates propagation problem.It is worth noting that, working as the process that laser linewidth changes from 300kHz to 1000kHz
In, bit error rate performance more corresponding than Avg-BL method improves 0.4dB to A-CPEC method always, shows that this method becomes in laser linewidth
When change, bit error rate performance improves the stability with height.At this time in 300kHz, A-CPEC method performance can achieve FEC
The error correction upper limit, show at this time should A-CPEC method, can be used completely in the CO-OFDM system line width for 300kHz swash
Light device.
Fig. 4 show A-CPEC method under various lasers line width (0.3MHz, 0.5MHz, and 0.7MHz) error code
Rate performance is with NB2Relation curve when variation.N is still selected at this timeB1=4, to keep lesser algorithm complexity.In NB2From 4 to
During 32 variations, A-CPEC method performance improves about 0.7dB under the conditions of three kinds of different line widths.Wherein NB2It is right when=8
Laser linewidth is 500kHz, and the bit error rate can reach the FEC error correction upper limit, and NB2When=16, it is to laser linewidth
700kHz, the bit error rate can reach the FEC error correction upper limit.NB2Increase effectively increases the precision of fine ICI phase noise compensation, this
Certainly using the increase of method complexity as cost, therefore in practical applications, it should select a suitable NB2Value, the side of making
There is a compromise between method performance and method complexity.
Fig. 5-8 shows the planisphere when laser optimum transmission power-2dBm and line width are 500kHz.Fig. 5 is
By the receiving end original signal constellation of any equalization methods compensation, serious rotation and diverging are had occurred, therefore
The balanced of receiving end carries out electrical domain dispersion compensation first.Followed by OFDM symbol is synchronous and carrier frequency synchronization.Next again into
Row phase recovery, i.e. phase noise compensation, including blind CPE phase noise compensation and blind ICI phase noise compensation.Fig. 6 is shown
The planisphere only obtained by blind CPE compensation method.It is blind by being realized on the basis of the CPE of Fig. 6 compensation from Fig. 7-8
ICI phase noise compensation.Fig. 7 shows the planisphere obtained with Avg-BL phase noise compensation method, it is clear that planisphere diverging
There is certain improvement compared with Fig. 6.Fig. 8 is shown on the basis of Fig. 7 with A-CPEC method in NB2It is obtained when respectively equal to 4,10 and 24
Planisphere.It can be seen that Fig. 8 obtains preferable planisphere, the bit error rate also has larger reduction.
The computation complexity of Avg-BL method, which is mainly reflected in, calculates Ck,q(document 6, equation (5)),(document 23, equation
(6)),rk(document 6, equation (7)) and Am,n(document 6, equation (8)).The complexity of its multiplication and addition is respectively O
(NB1Klog2(K)),O((NB1-1)2K)+O((NB1-1)3),With O ((NB1-1)2K).It is proposed in this paper
A-SCPEC method complexity is other than the above rough ICI phase noise compensation (Avg-BL) (i.e. CPEC method), major embodiment
In receiving end, frequency-region signal needs to adjudicate after rough ICI phase noise compensation, through FFT transform to time domain after judgement, and
Equation (10) and (12) in context of methods description, addition or multiplicative complexity are respectively O (K), O (Klog2(K)), O (K)
With O (NB2Klog2(K)).Therefore in each symbol segmentation Asia symbolic number NB1=NB2In identical situation, CPEC method ratio Avg-
BL method computation complexity is slightly lower.Therefore 2 times close to Avg-BL method of A-CPEC method complexity at this time.However NBValue pair
This method performance is affected, and N is chosen in Fig. 4B2=10 obtain preferable method compensation effect, and A-CPEC method is complicated at this time
Degree will be more than the 3 of Avg-BL method times.Therefore, N appropriate can chosenB2To be carried out between method complexity and method effect
Compromise.
Above to the blind ICI phase noise compensation in coherent light orthogonal frequency division multiplexing CO-OFDM system of the present invention
Method has carried out introduction in detail, and above example illustrates to be merely used to help understand method and its core concept of the invention
Rather than be limited, it is other it is any make to change without departing from the spirit and principles of the present invention, modify, substitute,
Combination simplifies, and should be equivalent substitute mode, is included within the scope of the present invention.
Claims (2)
1. a kind of blind ICI phase noise compensation method suitable for big line width CO-OFDM system, it is characterised in that: this method is first
End data will be received and carry out CPE phase noise compensation；Then, the time domain data after CPE phase noise compensation is carried out rough
Blind ICI phase noise compensation；Next, being made decisions to the frequency domain data after rough blind ICI phase noise compensation, to judgement
Frequency domain data later is fast fourier transformed to arrive time domain data, by before the time domain data and CPE phase noise compensation when
Each OFDM data symbol segmentation is several sub- symbols in numeric field data, finds out the phase noise approximation of the Asia symbol；Most
Afterwards, fine ICI phase noise compensation is carried out；The blind ICI phase noise compensation method includes the following steps:
(1) receiving end carries out coherent detection reception to the CO-OFDM signal received, then carries out analog-to-digital conversion, obtains electrical domain
Signal；
(2) electrical domain optical fiber dispersion compensation；
(3) serioparallel exchange；
(4) cyclic prefix CP is removed；
(5) Frequency offset estimation and compensation；
(6) signal is become from time domain by frequency domain using Fast Fourier Transform (FFT), while saves the time-domain signal
(7) the blind phase noise compensation of CPE is carried out to frequency domain data；
(8) rough blind ICI phase noise compensation, process are as follows:
It is assumed that an OFDM frame includes N number of OFDM symbol in time domain, each OFDM symbol includes K subcarrier in frequency domain, at this time
Each OFDM symbol is divided into NB1A Asia symbol, then the data sampling number in each sub- symbol is S1=K/NB1, then each Asia
Phase noise average value indicates in symbol are as follows:
Meet following formula in nth symbol, k-th of subcarrier,
Here|En,k|2In the energy that the modulation of permanent mould is signaling point, non-
Permanent mould is the average energy for taking each signaling point when modulating, and the phase noise average value of each sub- symbol is estimated by above formula,
Then the frequency domain data after carrying out rough ICI phase noise compensation is expressed as,
(9) it adjudicates: to the frequency domain data after rough ICI phase noise compensationIt makes decisions；
(10) signal after judgement is transformed to time-domain signal by IFFT by Fast Fourier Transform
(11) symbol temporal segmentation is multiple sub- symbols, time-domain signalTime domain OFDM signal y before being compensated with original by CPEn,t(0
≤ t≤K-1) it is divided into NB2A Asia symbol, the phase noise valuation of data sampling in the sub- symbol of q-th of the nth symbolBy
Following formula acquires,
Here ' and No. * respectively indicate transposition and conjugate operation, consider NB2For arbitrary integer, thenAnd yn,qIt is expressed as,
HereWherein [A] indicates the maximum integer for being not more than A；
(12) fine ICI phase noise compensation, the frequency domain ofdm signal after fine ICI phase noise compensationApproximate representation
Are as follows:
(13) frequency domain data after fine ICI phase noise compensation is subjected to conclusive judgement.
2. being suitable for the blind ICI phase noise compensation method of big line width CO-OFDM system, feature as described in claim 1
It is: in the step (2), by the analytical form of fiber channel frequency domain transfer function through Fourier transform to time domain, when design
Domain has limit for length's unit impulse response FIR filter to realize, the order of the filter is accumulated with dispersion and increased.
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| CN111865432B (en) * | 2020-06-12 | 2022-04-05 | 浙江工业大学 | Blind phase noise compensation method in CO-FBMC/OQAM system |
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