CN106101044B - A kind of frequency deviation estimating method based on multistep interpolation for coherent optical communication system - Google Patents
A kind of frequency deviation estimating method based on multistep interpolation for coherent optical communication system Download PDFInfo
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- CN106101044B CN106101044B CN201610380284.0A CN201610380284A CN106101044B CN 106101044 B CN106101044 B CN 106101044B CN 201610380284 A CN201610380284 A CN 201610380284A CN 106101044 B CN106101044 B CN 106101044B
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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
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
- H04L27/2659—Coarse or integer frequency offset determination and synchronisation
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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
- H04B10/612—Coherent receivers for optical signals modulated with a format different from binary or higher-order PSK [X-PSK], e.g. QAM, DPSK, FSK, MSK, ASK
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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
- H04B10/6164—Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator
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Abstract
The present invention relates to a kind of frequency deviation estimating methods based on multistep interpolation, comprising the steps of: carries out 4 power MQAM modulation formats or M power MPSK modulation format operation to the sampled value L of certain length, then therefrom chooses a small amount of one piece of data N0Make FFT, the corresponding frequency of maximum spectrum value is acquired, as coarse frequency offset value；At coarse frequency offset value ± 0.5, N is used0A sampled point carries out DFT respectively, obtains two spectrum values, calculates offset estimation error using the two values, corrects to coarse frequency offset value, the offset estimation value after obtaining a step interpolation；At offset estimation value ± 0.5 after a step interpolation, 2N is used0A sampled point carries out DFT respectively, obtains two spectrum values, calculates evaluated error using the two values, corrects to coarse frequency offset value, the frequency deviation value after obtaining two step interpolation；And so on, offset estimation value to the end is obtained until carrying out DFT interpolation with L sampled point.The algorithm complexity is low, is suitable for all coherent optical communication systems.
Description
Technical field
The present invention relates to the communications fields, more specifically to the frequency based on multistep interpolation in coherent optical communication system
Rate bias estimation scheme.
Background technique
In order to improve the availability of frequency spectrum and message capacity, higher order modulation formats modulated signal is used in optical communications, together
When the amplitude and phase information of light carrier is utilized.This signal using higher order modulation formats is needed using coherent demodulation ability
Signal is restored.So needing to be equipped with coherent receiver in receiving end.Local laser is provided in coherent receiver, for pair
It receives signal and carries out coherent demodulation.
For homodyne coherent detection mode, it is desirable that the local laser of receiving end will be with transmitting terminal laser co-wavelength.So
And the unstability of the manufacture craft and laser itself due to laser, it is difficult to produce the laser of two complete co-wavelengths
Device obtains the light source of the wavelength as transmitting terminal, or produce to this frequency departure so needing to carry out carrier auxiliary in receiving end
Raw influence compensates.
Wavelength correction is carried out according to optical device, locking phase can be carried out to received optical signal using Optical phase-locked loop, made
Obtain local light and transmitting terminal light source wavelength having the same.However, this mode uses Optical phase-locked loop, somewhat expensive.It is another
Kind mode is that the signal after coherent reception is first become electric signal, is then carried out analog-to-digital conversion using digital coherent receiver,
Become digital signal, with Digital Signal Processing (DSP) technology, signal is compensated.This mode can not only compensate frequency
Offset, can also compensate for dispersion, phase noise etc., and cheap, and institute has been widely adopted in this way.
Frequency deviation, i.e. frequency shift (FS) or frequency departure refer to the difference of transmitting terminal optical source wavelength and receiving end optical source wavelength, number
Frequency deviation compensation in receiver is generally divided into two steps, i.e., first makees offset estimation, estimate frequency deviation value, then carry out frequency deviation benefit
It repays, by frequency deviation value compensation into signal.
Frequency is estimated using FFT operation and interpolated DFT algorithm, is widely used in wireless communication field.It
Have many advantages, such as that anti-noise ability is strong, estimated accuracy is high.The present invention is improved this algorithm, is proposed to be stepped up and be adopted
Sampling point carries out the thought of multistep interpolation, and this algorithm can achieve estimated accuracy identical with original conventional DFT interpolation algorithm,
But complexity is significantly reduced.
Summary of the invention
In order to solve the above-mentioned technical problems, the present invention provides a kind of for coherent optical communication system based on multistep interpolation
Frequency deviation estimating method, carried out multiple DFT interpolation calculation with different sampled points, gradually obtained accurate frequency deviation value, including
Step:
(1) 4 powers or M power operation are carried out to the sampled value that a segment length is L, obtains the data value of modulated signal；
(2) N before choosing0A data value for going modulated signal, makees FFT operation, obtains its spectrum value；
(3) to each spectrum value modulus, and its maximum value is searched, obtains its corresponding frequency, as coarse frequency offset value f0；
(4) at a distance of coarse frequency offset value f0± 0.5 at, i.e. f0At ± 0.5, to preceding N0A data for going modulated signal
Value calculates the size of two amplitudes with DFT, and calculates evaluated error δ with the two amplitudes；
(5) with evaluated error δ to coarse frequency offset value f0It is modified, the offset estimation value f after obtaining a step interpolation1；
(6) f is used1Instead of f0, use 2N0Instead of N0, repeat step (4), (5), the f arrived2；
(7), until L sampled value is all used, final offset estimation value is obtained.
In the above-mentioned technical solutions, MQAM signal adopts mpsk signal using 4 power operations in the step (1)
With M power operation；The integral number power that sampled value length L is 2.
In the above-mentioned technical solutions, N in the step (2)0For 2 integral number power.
In the above-mentioned technical solutions, the step (4), (5) have carried out multiple interpolation, and interpolation number can pass through following public affairs
Formula is calculated: m=log2(L/N0)+1。
The present invention achieves following technical effect:
Algorithm complexity is low, is suitable for all coherent optical communication systems.
Detailed description of the invention
Fig. 1 is the flow chart of the frequency deviation estimating method based on multistep interpolation for coherent optical communication system；
Fig. 2 is the relation curve of the normalized mean squared error and Signal to Noise Ratio (SNR) that are emulated to multistep interpolation algorithm
Figure；
Fig. 3 be multistep interpolation algorithm frequency offset estimation range figure (signal-to-noise ratio 10dB, total strong point number be 1024)；
Fig. 4 is multistep interpolation algorithm in different total data lengths, the relational graph of MSE and SNR；
Fig. 5 be multistep interpolation algorithm frequency offset estimation range figure (signal-to-noise ratio 12dB, total strong point number be 2048)；
Fig. 6 is the normalized mean squared error of multistep interpolation algorithm and the graph of relation of Signal to Noise Ratio (SNR)；
Fig. 7 is that the multistep interpolation algorithm that conventional DFT interpolation algorithm and this patent propose carries out offset estimation, required multiple
The comparison diagram of number multiplication number.
Specific embodiment
Understand for the ease of those of ordinary skill in the art and implement the present invention, with reference to the accompanying drawing and specific embodiment
The present invention is described in further detail.
The present invention provides a kind of frequency excursion algorithms, for the coherent light communication system with MQAM and MPSK modulation format
System, algorithm estimated accuracy with higher and lower computational complexity.Fig. 1 is frequency excursion algorithm provided by the invention
Flow chart comprising following steps:
1) the sampled point y for being L to the length receivedkMake the operation of power side, wherein for the signal of MPSK modulation format
M power operation is done, biquadratic operation is done for the signal of MQAM modulation format, obtains the data point of modulated signal:
2) preceding N is taken0A data point for going modulated signal, makees FFT transform, obtains its spectrum value.
3) to each spectrum value modulus value, the maximum value of its spectral magnitude is searched, obtains the corresponding frequency values f of maximum valuepeak,
Then coarse frequency offset value can be expressed asIt is all illustrated by taking MQAM as an example below, for
Mpsk signal, as long as replacing the coefficient 4 that appear below for M.
4) make first step interpolation arithmetic: settingWherein TsFor symbol period, k indicates k-th of data point, first
In n0Left and right is at 0.5, with preceding N0(N0Integral number power for 2) a modulation data point is gone to calculate its spectrum value, it may be assumed thatThen the error amount of rough estimate frequency deviation is calculated:
5) coarse frequency offset value is modified with the evaluated error of rough estimate frequency deviation, obtains the offset estimation of a step interpolation
Value:
6) make second step interpolation arithmetic: settingIn n1Left and right is at 0.5, with preceding 2N0It is a to go modulation data
Point calculates its spectrum value, it may be assumed thatThen the offset estimation error amount of a step interpolation is calculated:Obtain the offset estimation value of two step interpolation:
7) and so on, m walks interpolation arithmetic, in nm-1Left and right is at 0.5, with preceding LmIt is a that modulation data point is gone to calculate
Its spectrum value, it may be assumed thatThen the offset estimation error of m-1 step interpolation arithmetic is calculated
Value:Obtain the offset estimation value of m step interpolation:Wherein, m
=1,2,3..., the order or step number of multistep interpolation are represented, it determines the estimated accuracy and required total data point of algorithm
Number Lm(Lm=N0·2m-1)。
Fig. 2 is the normalization that is emulated to multistep interpolation algorithm under 28-Gbaud QPSK coherent optical communication system
(MSE is defined as mean square error)) with the graph of relation of Signal to Noise Ratio (SNR).When emulation, laser linewidth
It is set as 100kHz, frequency deviation value is randomly selected out of [- 3.4GHz, 3.4GHz] range, and each SNR has carried out 2000 emulation,
Total strong point length is L=1024.It compared the performance of different step number interpolation in Fig. 2.N0=1024, N0=512, N0=256,
N0=128 correspond respectively to m=1, m=2, m=3, m=4.N0Selection be according to signal-noise ratio threshold value required in practice
Come what is determined, as shown in Figure 2, N0Value is chosen bigger, and signal-noise ratio threshold is lower, works as N0Signal-noise ratio threshold is minimum when=L, at this time
Due to only having done an interpolation calculation, so the regression of multistep interpolation algorithm is traditional DFT interpolation algorithm.And the L that always countsm
(or the selection of iterative steps m) is determined according to required estimated accuracy to be achieved in practice, as long as more specifically, meeting
Working range allowed by next step phase estimation algorithm.
Fig. 3 is illustrated under 28-Gbaud QPSK coherent optical communication system, the frequency offset estimation range of multistep interpolation algorithm.It is imitative
In very, signal-to-noise ratio 10dB, total data point number is L=1024, and each frequency deviation value has carried out 2000 emulation, N0It takes
256 (i.e. m=3).From the figure, it can be seen that the estimation range of the multistep interpolation algorithm can achieve [- 3.4GHz, 3.4GHz].
Fig. 4 is illustrated under 28-Gbaud QPSK coherent optical communication system, and as N0=256, multistep interpolation algorithm is in difference
In the case where total data length L=1024 and L=2048, the relationship of MSE and SNR.It can be seen from the figure that L is bigger, the algorithm
Estimated accuracy it is higher, but because the N0 value that uses in L=1024 and L=2048 all for 256, signal-noise ratio threshold
It is identical, it is all 7dB.
Fig. 5 is illustrated under 28-Gbaud 16QAM coherent optical communication system, the frequency offset estimation range of multistep interpolation algorithm.It is imitative
In very, signal-to-noise ratio 12dB, total data point number is L=2048, and each frequency deviation value has carried out 2000 emulation.From figure
It can be seen that for 28-Gbaud 16QAM coherent optical communication system, the estimation range of the multistep interpolation algorithm can achieve [-
3.4GHz,3.4GHz]。
Fig. 6 is illustrated under 28-Gbaud 16QAM coherent optical communication system, the normalized mean squared error of multistep interpolation algorithm
With the graph of relation of Signal to Noise Ratio (SNR).When emulation, frequency deviation value is randomly selected out of [- 3.4GHz, 3.4GHz] range, each SNR
2000 emulation is all carried out, total strong point length is L=2048.From the figure, it can be seen that the multistep interpolation algorithm is identical
Total strong point length L, difference N0Under, estimated accuracy having the same, N0Determine signal-noise ratio threshold, N0Value is chosen bigger, letter
It makes an uproar lower than thresholding, works as N0Signal-noise ratio threshold is minimum when=L, at this time due to only having done an interpolation calculation, so multistep interpolation
Algorithm regression is traditional DFT interpolation algorithm.
After Fig. 7 illustrates modulated signal, using identical sum strong point L, calculated with conventional DFT interpolation
The multistep interpolation algorithm that method and this patent propose carries out offset estimation, the comparison diagram of required complex multiplication number.From figure
As can be seen that complex multiplication number needed for multistep interpolation algorithm is compared with conventional DFT interpolation algorithm with the increase of total strong point L
There is apparent reduction.
The present invention be not limited to it is above-mentioned for offset estimation mode, it is all that there is same or similar technical side with of the invention
Case is applied to other environment, falls within the scope of protection of the present invention.
Claims (3)
1. a kind of frequency deviation estimating method based on multistep interpolation for coherent optical communication system, is carried out with different sampled points
Multiple DFT interpolation calculation, gradually obtains accurate frequency deviation value, it is characterised in that comprising steps of
(1) operation of power side is made to the sampled value that a segment length is L, obtains the data value of modulated signal, in which: MQAM is believed
Number, using 4 power operations, the operation of M power is used for mpsk signal；The integral number power that sampled value length L is 2；
(2) N before choosing0A data value for going modulated signal, makees FFT operation, obtains its spectrum value；
(3) to each spectrum value modulus, and its maximum value is searched, obtains its corresponding frequency fpeak, as coarse frequency offset value
Then coarse frequency offset value can be expressed as
(4) it setsWherein TsFor symbol period, k indicates k-th of data point, first in n0Left and right is at 0.5, before
N0It is a that modulation data value is gone to calculate its spectrum value, then calculate the evaluated error δ of rough estimate frequency deviation；
(5) with evaluated error δ to coarse frequency offset valueIt is modified, the offset estimation value after obtaining a step interpolation
(6) it usesInstead ofUse 2N0Instead of N0, step (4), (5) are repeated, the offset estimation value of two step interpolation is obtained:
(7), until L sampled value is all used, final offset estimation value is obtained.
2. the frequency deviation estimating method according to claim 1 based on multistep interpolation, it is characterised in that: N in the step (2)0
For 2 integral number power.
3. the frequency deviation estimating method according to claim 1 based on multistep interpolation, it is characterised in that: the step (4),
(5) multiple interpolation has been carried out, interpolation number can be calculated by following formula: m=log2(L/N0)+1。
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| CN108881087A (en) * | 2018-09-13 | 2018-11-23 | 哈尔滨工业大学（深圳） | One kind being used for the received frequency deviation estimating method of K-K |
| CN110868368B (en) * | 2019-11-18 | 2022-03-15 | 紫光展锐(重庆)科技有限公司 | Channel estimation method, system, electronic device, and medium |
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| CN102355305A (en) * | 2011-10-10 | 2012-02-15 | 北京邮电大学 | Linear chirp z transform based frequency offset estimation algorithm in M-QAM (M-ary Quadrature Amplitude Modulation) coherent optical communication system |
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| CN102355305A (en) * | 2011-10-10 | 2012-02-15 | 北京邮电大学 | Linear chirp z transform based frequency offset estimation algorithm in M-QAM (M-ary Quadrature Amplitude Modulation) coherent optical communication system |
| CN102647381A (en) * | 2012-03-22 | 2012-08-22 | 中兴通讯股份有限公司 | Method and device for elevating frequency deviation in MPSK (Mary Phase Shift Keying) coherent light communication system |
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