CN101895499A - Method for demultiplexing polarization by using constant rotation sign training sequence - Google Patents

Abstract

The invention belongs to the field of optical communication, and is applied to the polarization demultiplexing of a polarization diversity multiplexing coherent optical communication system. According to the invention, for the problem of the polarization demultiplexing in the polarization diversity multiplexing coherent optical communication system, a special training sequence and related algorithms are designed. Through the method, a coherent receiver can fast, automatically and accurately perform the polarization demultiplexing. As the track of the training sequence, viewed from a planisphere, rotates along a unit circle after sign power is normalized, the training sequence provided by the invention is called a constant rotation sign training sequence. The invention discloses two processing algorithms for the constant rotation sign training sequence, which are a frequency-domain algorithm and a time-domain algorithm respectively, wherein the frequency-domain algorithm can be combined with frequency-domain dispersion compensation without adding a frequency spectrum calculation module. Through the method, the receiver does not need synchronizing with an initial position of the training sequence.

Description

With the multiplexing method of constant rotation sign training sequence depolarization

Technical field

The invention belongs to optical communication field, be applied to the multiplexing coherent optical communication system of polarization diversity, carry out polarization demultiplexing.

Background technology

Coherent optical communication not only can use high order modulation technology, polarization diversity multiplex technique to improve spectrum efficiency, can also use the self-adaptive digital signal treatment technology to come the damage of dynamic compensation signal.It is a kind of important technology that broad prospect of application is arranged.In the multiplexing coherent optical communication system of polarization diversity, transmitting terminal is input to the orthogonal two ways of optical signals in polarization direction in the optical fiber and transmits.Fig. 1 represents the input signal of polarization diversity multiplex system.Light signal transmission in optical fiber can be subjected to the influence of optic fiber polarization mould dispersion.The polarization mode dispersion meeting is rotated the polarization state of light signal.As shown in Figure 2.And optic fiber polarization mould dispersion is at random, causes the polarization state of the light signal of process Optical Fiber Transmission to be rotated at random.The light signal polarization state of receiving terminal as shown in Figure 3.

The multiplexing coherent optical communication system receiving terminal of polarization diversity as shown in Figure 4, polarization beam apparatus 402 resolves into two mutually perpendicular light signals of polarization state with received signal 401, enters X polarization branch 403 and Y polarization branch 404 respectively.Identical with the optical signal carrier frequency or the very approaching laser of local laser (LO) 405 emissions is divided into two-way, and the signal with X polarization branch 403, Y polarization branch 404 enters two 90 ° of frequency mixers 406,407 respectively.The output of two 90 ° of frequency mixers is received by photodiode 408 and changes into the signal of telecommunication, and the signal of telecommunication is by after analog-to-digital conversion device (ADC) 409 samplings, and what obtain is the baseband digital signal 410 of receiving optical signals 401.Baseband digital signal enters DSP module 411 and carries out operations such as dispersion compensation, clock synchronization, polarization demultiplexing, polarization mode dispersion (PMD) compensation, demodulation, recovers initial data 412.

Polarization beam apparatus 402 placing directions of receiving terminal are fixed, i.e. received signal on fixing orthogonal two polarization directions.Generally, these two polarization directions can not be aimed at two polarization directions of the light signal that arrives receiving terminal respectively.This makes the light signal each some on two polarization directions enter the X polarization branch 403 and the Y polarization branch 404 of receiving terminal.Received signal on X polarization branch 403 and the Y polarization branch 404 is the stack of two transmission signals on the polarization direction.Usually the butterfly filter 506 in coherent receiver (Fig. 4) utilization Digital Signal Processing (DSP) module (Fig. 5) carries out polarization demultiplexing, and giving butterfly filter configuration rational numerical is the multiplexing key of depolarization.

The present invention is intended to solve the polarization demultiplexing problem of the multiplexing coherent optical communication system of polarization diversity.

Summary of the invention

The present invention is applicable in the multiplexing coherent optical communication system of polarization diversity that the modulation system of system can be MPSK (M 〉=4) or MQAM (M 〉=4).The present invention is directed to the problem of polarization demultiplexing in the multiplexing coherent optical communication system of polarization diversity, designed a kind of special training sequence and related algorithm.Use this method coherent receiver can carry out polarization demultiplexing fast and automatically, exactly.The training sequence that the present invention proposes after the symbol power normalization, is seeing on the planisphere that its track rotates on unit circle, so the called after constant rotation sign training sequence.Send the inequality and constant symbol sebolic addressing of velocity of rotation of certain-length on two polarization directions of transmitting terminal respectively, wherein velocity of rotation implication inequality comprises that slewing rate is inequality or rotation direction is different (for example, turn clockwise on the polarization direction, be rotated counterclockwise on another polarization direction).The velocity of rotation of the training sequence that the known transmitting terminal of coherent receiver sends on two polarization directions.The present invention proposes two kinds of Processing Algorithm at constant rotation sign training sequence.These two kinds of algorithms are used for receiving terminal, give proper weight can for butterfly filter 506, carry out polarization demultiplexing.

In these two kinds of algorithms, a kind of algorithm need calculate the frequency spectrum of received signal, estimates the channel transfer functions matrix from the frequency domain of received signal, thereby gives butterfly filter 506 initializes.Therefore, this algorithm called after frequency domain algorithm.The key step of algorithm comprises:

(1) ask discrete Fourier transform (DFT) to calculate frequency spectrum to the training sequence that receives;

(2) from frequency spectrum, find peak value;

(3) estimate channel transfer functions from peak value;

(4) with the contrary weights that come initialization butterfly filter of transfer function.

Can also estimate local oscillator the coherent receiver (LO) 405 and the frequency difference that sends optical signal carrier easily from the position that spectrum peak occurs.

Another kind of algorithm belongs to least mean-square error (LMS) algorithm, handles on the time domain of received signal, optimizes the weights of butterfly filter 506.Therefore, this algorithm called after Time-Domain algorithm.The key step of algorithm comprises:

(1) angle of last moment butterfly filter two branch output signals (this signal is a plural number) of calculating;

(2) from last one constantly the training sequence symbols velocity of rotation of the angle of output signal and this polarization branch extrapolate the desired value of current time output signal;

(3) difference of the actual value of the desired value of current time output signal and current time output signal is as the error signal of LMS algorithm.

Description of drawings

Fig. 1: the schematic diagram that transmits of polarization diversity multiplex system;

Fig. 2: the schematic diagram that optic fiber polarization mould dispersion rotates the light signal polarization state of transmission at random;

Fig. 3: receiving terminal is receiving optical signals polarization state schematic diagram just;

Fig. 4: the receiver of the multiplexing coherent optical communication system of polarization diversity;

Fig. 5: the DSP module in the receiver of the multiplexing coherent optical communication system of polarization diversity;

Fig. 6: the planisphere of the multiplexing QPSK of polarization diversity system, the rotation schematic diagram of constant rotation sign training sequence on planisphere;

Fig. 7: the frequency domain algorithm structure chart that carries out polarization demultiplexing with constant rotation sign training sequence;

Fig. 8: frequency domain algorithm detail flowchart;

Fig. 9: the Time-Domain algorithm structure chart that carries out polarization demultiplexing with constant rotation sign training sequence;

Figure 10: Time-Domain algorithm detail flowchart.

Embodiment

The receiver of polarization diversity multipurpose photo-communication system as shown in Figure 4, coherent receiver comprises front-end processing part 413 and Digital Signal Processing (DSP) module 411.Front-end processing part 413 becomes baseband digital signal 410 to light signal.411 pairs of baseband digital signals 410 of DSP module are handled, and carry out clock synchronization, compensate various signal impairments, and operation recoveries such as demodulation go out data 412.The detailed structure of DSP module 411 as shown in Figure 5,412 in the output 510 corresponding coherent receivers of DSP module, the input 501,502 of DSP module connects the baseband digital signal 410 in the coherent receivers.Notice the input x of DSP circuit _In501, y _InThe 502nd, plural number with 410 relation is:

x _in＝x _Re+i×x _Im

y _in＝y _Re+i×y _Im

Input signal x _In501, y _In502 at first enter 503 carries out dispersion compensation and clock synchronization.The output x of dispersion compensation and clock synchronization module 503 _p504, y _pThe 505th, synchronous signal then enters butterfly filter 506 and carries out polarization demultiplexing, polarization mode dispersion (PMD) compensation and residual chromatic dispersion compensation.Butterfly filter 506 is made up of 511,512,513,514 and two adders 515,516 of 4 complex filters.The weights h of complex filter 511,512,513,514 _Xx, h _Xy, h _Yx, h _YyBeing plural number, can be the one or more dimensions vector.Being operating as of butterfly filter 506:

x _out＝x _p*h _xx+y _p*h _xy

y _out＝x _p*h _xy+y _p*h _yy

Wherein, the variable in the formula all is a plural number; * be convolution operation; x _Out507, y _OutThe 508th, filter output; Suitably set the weights h of filter _Xx, h _Xy, h _Yx, h _YyGet final product polarization demultiplexing.The output 507,508 of butterfly filter enters phase bit recovery reconciliation mode transfer piece 509 and obtains demodulating data 510.

The linear channel model of polarization diversity multipurpose photo-communication system

The transmission signal of polarization diversity multiplex system, time domain and frequency domain representation are respectively:

$\stackrel{\→}{s}\left(t\right)=\left[\begin{array}{c}{s}_x\left(t\right)\\ s_y\left(t\right)\end{array}\right],$ $\stackrel{\→}{S}\left(\mathrm{\ω}\right)=\left[\begin{array}{c}{S}_x\left(\mathrm{\ω}\right)\\ S_y\left(\mathrm{\ω}\right)\end{array}\right]$

X wherein, y is two orthogonal polarization directions.

The time domain and the frequency domain representation of received signal are respectively:

$\stackrel{\→}{r}\left(t\right)=\left[\begin{array}{c}{r}_x\left(t\right)\\ r_y\left(t\right)\end{array}\right],$ $\stackrel{\→}{R}\left(\mathrm{\ω}\right)=\left[\begin{array}{c}{R}_x\left(\mathrm{\ω}\right)\\ R_y\left(\mathrm{\ω}\right)\end{array}\right]$

The Channel Transmission matrix:

$\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left(\mathrm{\ω}\right)& H_{\mathrm{xy}}\left(\mathrm{\ω}\right)\\ H_{\mathrm{yx}}\left(\mathrm{\ω}\right)& H_{\mathrm{yy}}\left(\mathrm{\ω}\right)\end{array}\right]$

The Channel Transmission equation:

$\left[\begin{array}{c}{R}_x\left(\mathrm{\ω}\right)\\ R_y\left(\mathrm{\ω}\right)\end{array}\right]=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left(\mathrm{\ω}\right)& H_{\mathrm{xy}}\left(\mathrm{\ω}\right)\\ H_{\mathrm{yx}}\left(\mathrm{\ω}\right)& H_{\mathrm{yy}}\left(\mathrm{\ω}\right)\end{array}\right]\·\left[\begin{array}{c}{S}_x\left(\mathrm{\ω}\right)\\ S_y\left(\mathrm{\ω}\right)\end{array}\right]$

Constant rotation sign training sequence

The training sequence that the present invention proposes after the symbol power normalization, is seeing on the planisphere that its track rotates on unit circle, so the called after constant rotation sign training sequence.Send the inequality and constant symbol sebolic addressing of velocity of rotation of certain-length on two polarization directions of transmitting terminal respectively, wherein velocity of rotation implication inequality comprises that slewing rate is inequality or rotation direction is different (for example, turn clockwise on the polarization direction, be rotated counterclockwise on another polarization direction).

On the X polarization signal on planisphere with angular frequency _xRotate:

s _x(t)＝exp(iφ _x)exp(iω _xt)

Wherein, φ _xBe the initial phase of training sequence, t=0,1,2...

On the Y polarization signal on planisphere with angular frequency _yRotate:

s _y(t)＝exp(iφ _y)exp(iω _yt)

Wherein, φ _yBe the initial phase of training sequence, t=0,1,2...

Note, X, the velocity of rotation on the Y polarization direction is inequality, i.e. ω _x≠ ω _y

For example, for QPSK signal, ω _x, ω _yBe taken as respectively

The rotation direction of training sequence on planisphere as shown in Figure 6.The planisphere that sends training sequence on the X polarization direction is shown in Figure 60 5, and the phase place of symbol sebolic addressing is followed successively by

Deng, by that analogy.The planisphere that sends training sequence on the Y polarization direction is shown in Figure 61 0, and the phase place of symbol sebolic addressing is followed successively by

Deng, by that analogy.

The transmission of X polarization direction is gone up signal frequency-domain and is represented:

$S_x\left(\mathrm{\ω}\right)=\left\{\begin{array}{cc}\exp \left({\mathrm{i\φ}}_x\right),& \mathrm{\ω}={\mathrm{\ω}}_x\\ 0,& \mathrm{\ω}\≠{\mathrm{\ω}}_x\end{array}\right.$

Sending signal frequency-domain on the Y polarization direction represents:

$S_y\left(\mathrm{\ω}\right)=\left\{\begin{array}{cc}\exp \left(i{\mathrm{\φ}}_y\right),& \mathrm{\ω}={\mathrm{\ω}}_y\\ 0,& \mathrm{\ω}\≠{\mathrm{\ω}}_y\end{array}\right.$

With S _x(ω), S _yExpression formula (ω) is brought the side signal transmission journey into:

$\left[\begin{array}{c}{R}_x\left(\mathrm{\ω}\right)\\ R_y\left(\mathrm{\ω}\right)\end{array}\right]=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left(\mathrm{\ω}\right)& H_{\mathrm{xy}}\left(\mathrm{\ω}\right)\\ H_{\mathrm{yx}}\left(\mathrm{\ω}\right)& H_{\mathrm{yy}}\left(\mathrm{\ω}\right)\end{array}\right]\·\left[\begin{array}{c}{S}_x\left(\mathrm{\ω}\right)\\ S_y\left(\mathrm{\ω}\right)\end{array}\right]$

Obtain:

R _x(ω)＝H _xx(ω _x)exp(iφ _x)+H _xy(ω _y)exp(iφ _y)

R _y(ω)＝H _yx(ω _x)exp(iφ _x)+H _yy(ω _y)exp(iφ _y)

Carry out the frequency domain algorithm of polarization demultiplexing with constant rotation sign training sequence:

Fig. 7 is the structure chart of frequency domain algorithm, and transmitting terminal sends constant rotation sign training sequence, and the input that arrives the butterfly filter is x _p701, y _p702.The butterfly filter is output as x _Out705, y _Out706.x _p701, y _p702 enter channel transfer functions estimator 704, and estimator 704 estimates channel transfer functions and gives the weights initialize of butterfly filter 703 according to transfer function.Butterfly filter 703 after the assignment can successfully carry out polarization demultiplexing.Fig. 8 is the flow chart of transfer function estimator 704.803,804 couples of input signal x of discrete Fourier transform (DFT) module _p801, y _p802 ask frequency spectrum, and frequency spectrum is R _x(ω) 805 and R _y(ω) 806.Frequency spectrum R _x(ω) 805 and R _y(ω) 806 be input to respectively and get peak value module 807,808.807,808 couples of R of peak value module _x(ω) and R _y(ω) at ω=ω _xAnd ω=ω _yNear the point of seeking the absolute value maximum is a peak value, should find 4 peak values altogether, is respectively:

1.R _x(ω) at ω=ω _xNear peak value size is h ₁=H _Xx(ω _x) exp (i φ _x), peak is ω=ω ₁

2.R _x(ω) at ω=ω _yNear peak value size is h ₂=H _Xy(ω _y) exp (i φ _y), peak is ω=ω ₂

3.R _y(ω) at ω=ω _xNear peak value size is h ₃=H _Yx(ω _x) exp (i φ _x), peak is ω=ω ₃

4.R _y(ω) at ω=ω _yNear peak value size is h ₄=H _Yy(ω _y) exp (i φ _y), peak is ω=ω ₄

Peak value size 812,813 is input to and is used for estimating channel transfer functions matrix 814, and peak 809,810 can estimate the frequency difference 811 of local oscillator (LO) 405 and flashlight carrier wave.814 modules are estimated the channel transfer functions matrix from spectrum peak.Concrete operations are: frequency spectrum R _x(ω) and R _yPeak value composition matrix H (ω) ':

$H^{\′}=\left[\begin{array}{cc}{h}_1& h_2\\ h_3& h_4\end{array}\right]=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left({\mathrm{\ω}}_x\right)\exp \left({\mathrm{i\φ}}_x\right)& H_{\mathrm{xy}}\left({\mathrm{\ω}}_y\right)\exp \left({\mathrm{i\φ}}_y\right)\\ H_{\mathrm{yx}}\left({\mathrm{\ω}}_x\right)\exp \left({\mathrm{i\φ}}_x\right)& H_{\mathrm{yy}}\left({\mathrm{\ω}}_y\right)\exp \left({\mathrm{i\φ}}_y\right)\end{array}\right]$

H ' can be written as:

$H^{\′}=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{xy}}\left({\mathrm{\ω}}_y\right)\\ H_{\mathrm{yx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{yy}}\left({\mathrm{\ω}}_y\right)\end{array}\right]\·\left[\begin{array}{cc}\exp \left(i{\mathrm{\φ}}_i\right)& 0\\ 0& \exp \left({\mathrm{i\φ}}_y\right)\end{array}\right]=H\·\mathrm{\Φ}$

Wherein, $H=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{xy}}\left({\mathrm{\ω}}_y\right)\\ H_{\mathrm{yx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{yy}}\left({\mathrm{\ω}}_y\right)\end{array}\right],$ $\mathrm{\Φ}=\left[\begin{array}{cc}\exp \left({\mathrm{i\φ}}_x\right)& 0\\ 0& \exp \left({\mathrm{i\φ}}_y\right)\end{array}\right].$

The length of supposing the unit impulse response of channel transfer functions is 1.Like this, its Fourier transform H _Xx(ω), H _Xy(ω), H _Yx(ω), H _Yy(ω) on all ω, equate.So can estimate channel transfer functions:

$\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left(\mathrm{\ω}\right)& H_{\mathrm{xy}}\left(\mathrm{\ω}\right)\\ H_{\mathrm{yx}}\left(\mathrm{\ω}\right)& H_{\mathrm{yy}}\left(\mathrm{\ω}\right)\end{array}\right]=\left[\begin{array}{cc}{H}_{\mathrm{xx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{xy}}\left({\mathrm{\ω}}_y\right)\\ H_{\mathrm{yx}}\left({\mathrm{\ω}}_x\right)& H_{\mathrm{yy}}\left({\mathrm{\ω}}_y\right)\end{array}\right]=H$

To the H ' H ' that inverts ^-1, and with H ' ^-1Compose weights for the butterfly filter.The total transfer function of channel and butterfly filter is:

$H_{\mathrm{total}}=H^{\′-1}H={\left(\mathrm{H\Φ}\right)}^{-1}\·H={\mathrm{\Φ}}^{-1}{\mathrm{HH}}^{-1}={\mathrm{\Φ}}^{-1}=\left[\begin{array}{cc}\mathrm{exo}(-{\mathrm{i\φ}}_x)& 0\\ 0& \exp \left({-\mathrm{i\φ}}_y\right)\end{array}\right]$

Notice that total transfer function successfully carried out polarization demultiplexing, just to x, the input signal on the y polarization direction has been taken advantage of a phase factor exp (i φ respectively _x), exp (i φ _y), this phase factor can be conciliate in the mode transfer piece 509 at follow-up phase bit recovery and be removed.

Matrix inversion module 816 usefulness H's ' is contrary, and to the weights initialize of butterfly filter.

The contrary of H ' is:

$H^{\′-1}={\left[\begin{array}{cc}{h}_1& h_2\\ h_3& h_4\end{array}\right]}^{-1}=\frac{1}{h_1{h}_4-h_2{h}_3}\left[\begin{array}{cc}{h}_4& -h_2\\ -h_3& h_1\end{array}\right]$

If the weight vector h of butterfly filter _Xx, h _Xy, h _Yx, h _YyLength is 1, then establishes initial value respectively to be:

$h_{\mathrm{xx}}=\frac{h_4}{h_1{h}_4-h_2{h}_3},$ $h_{\mathrm{xy}}=\frac{-h_2}{h_1{h}_4-h_2{h}_3}$

$h_{\mathrm{yx}}=\frac{-h_3}{h_1{h}_4-h_2{h}_3},$ $h_{\mathrm{yy}}=\frac{h_1}{h_1{h}_4-h_2{h}_3}$

If, the weight vector h of butterfly filter _Xx, h _Xy, h _Yx, h _YyLength then is made as top value with the final middle weights of weight vector greater than 1, and all the other locational weights are made as 0.The above is the frequency domain algorithm that carries out polarization demultiplexing with constant rotation sign training sequence.

Frequency spectrum R according to received signal _x(ω) 805 and R _yThe position 809,810 that peak value occurs (ω) can estimate the frequency difference 811 of local oscillator (LO) 405 and signal carrier easily, and its method is as follows:

If: r is that the received signal angular frequency is ω _rL is local laser output light signal, and its baseband representation is:

ω wherein _LBe the angular frequency of LO, ω _rBe the signal angular frequency,

The initial phase difference of LO and received signal and the phase noise of LO have been comprised.

R and L are input to 90 ° of frequency mixers, and the signal after receiving through PD is:

Wherein, Δ ω=ω _L-ω _rIt is the difference on the frequency of LO and signal.

As seen from the above analysis, when the carrier frequency of LO and signal has difference on the frequency, received signal can be on planisphere with the angular frequency rotation of-Δ ω.From frequency domain, frequency difference makes the frequency spectrum shift-Δ ω of Frequency spectrum ratio received signal r of PD received signal.If r is a constant rotation sign training sequence, pass through DFT so after, its peak value will not appear at ω _xOr ω _yOn, but skew-Δ ω T _s, T wherein _sIt is a symbol period.R _x(ω) at ω=ω _xNear peak is ω=ω ₁, should satisfy-Δ ω T _s=ω ₁-ω _x, available following formula is estimated frequency difference Δ f:

$\mathrm{\Δf}=-\frac{{\mathrm{\ω}}_1-{\mathrm{\ω}}_x}{2\mathrm{\π}{T}_s}$

T wherein _sThe is-symbol cycle.Can also unite utilization ω ₁, ω ₂, ω ₃, ω ₄Improve the accuracy of frequency difference estimation.

Carry out the Time-Domain algorithm of polarization demultiplexing with constant rotation sign training sequence:

This algorithm belongs to least mean-square error (LMS) algorithm.Algorithm structure figure as shown in Figure 9, LMS algoritic module 904 utilizes the input x of butterfly filter 903 _p901, y _p902 and output x _Out905, y _Out906 upgrade the weights of butterfly filter 903.Iteration repeatedly after, the weights h of butterfly filter 903 _Xx907, h _Xy908, h _Yx909, h _Yy910 will converge on the channel transfer functions inverse of a matrix, thereby successfully depolarization is multiplexing.The basic thought of Time-Domain algorithm is a character of utilizing constant rotation sign training sequence: in training sequence, the symbol phase that sends on the X polarization direction, back one always than previous increase ω _xThe symbol phase that sends on the Y polarization direction, back one than previous increase ω _yIn addition, symbol should be on the unit circle on the planisphere.Therefore, the error signal of LMS algorithm is:

Wherein, x _OutThe 905th, the output signal of current time butterfly filter x branch road, x _Out' be a last moment output signal,

Be the output x of last one constantly defeated x branch road _Out' angle, promptly

ε _xError for the x branch road; y _OutThe 906th, the output signal of current time butterfly filter y branch road, y _Out' be a last moment output signal,

Be the output y of last one constantly defeated y branch road _Out' angle, promptly

ε _yError for the y branch road.

Upgrade the weights h of butterfly filter 903 with following formula _Xx907, h _Xy908, h _Yx909, h _Yy910:

$h_{\mathrm{xx}}\→h_{\mathrm{xx}}-\frac{\mathrm{\μ}}{2}\frac{d{\left|{\mathrm{\ϵ}}_x\right|}^2}{d{h}_{\mathrm{xx}}}=h_{\mathrm{xx}}+\mathrm{\μ}{\mathrm{\ϵ}}_x{x_p}^{*}$

$h_{\mathrm{xy}}\→h_{\mathrm{xy}}-\frac{\mathrm{\μ}}{2}\frac{d{\left|{\mathrm{\ϵ}}_x\right|}^2}{d{h}_{\mathrm{xy}}}=h_{\mathrm{xy}}+\mathrm{\μ}{\mathrm{\ϵ}}_x{x_p}^{*}$

$h_{\mathrm{yx}}\→h_{\mathrm{yx}}-\frac{\mathrm{\μ}}{2}\frac{d{\left|{\mathrm{\ϵ}}_y\right|}^2}{d{h}_{\mathrm{yx}}}=h_{\mathrm{yx}}+\mathrm{\μ}{\mathrm{\ϵ}}_y{x_p}^{*}$

$h_{\mathrm{yy}}\→h_{\mathrm{yy}}-\frac{\mathrm{\μ}}{2}\frac{d{\left|{\mathrm{\ϵ}}_y\right|}^2}{d{h}_{\mathrm{yy}}}=h_{\mathrm{yy}}+\mathrm{\μ}{\mathrm{\ϵ}}_y{y_p}^{*}$

Wherein, μ is the step-length of LMS algorithm, and * gets complex conjugate operation.

Figure 10 upgrades h _Xx907 algorithm structure figure upgrades h _Xy908, h _Yx909, h _Yy910 algorithm similarly.The input x of butterfly filter _p1002 and output x _OutThe 1001st, the input of update algorithm, ω _x1007 and μ 1012 are parameters of update algorithm.x _Out1001 enter and get protractor 1003, and the gained angle is through delayer 1006, again by adder 1008 and ω _x1007 additions, addition result enter module 1009 and calculate

x _Out1001 enter opposite sign device 1005, pass through again adder 1010 with Addition obtains

x _p1002 enter conjugator 1004, enter multiplier 1011 and parameter μ 1012 and ε again _x1015 multiply each other obtains h _XxCorrection μ ε _xy _p ^*1016.Correction 1016 and h _Xx1014 additions 1013, addition result 1017 is as h _XxNew value.h _Xx New value output 1018 upgrade the butterfly filter weights.The above is the Time-Domain algorithm of carrying out polarization demultiplexing with constant rotation sign training sequence.

The major technique advantage

The present invention is directed to the problem of polarization demultiplexing in the multiplexing coherent optical communication system of polarization diversity, designed a kind of special training sequence and be called and use constant rotation sign training sequence and related algorithm to comprise frequency domain algorithm and Time-Domain algorithm. Use this method coherent receiver can carry out fast and automatically, exactly polarization demultiplexing. The most important advantage of using constant rotation sign training sequence be receiving terminal do not need and the training sequence that sends synchronous, that is receiving terminal does not need to know the initial phase of transmission training sequence.

The present invention proposes two kinds for the Processing Algorithm of constant rotation sign training sequence, is respectively frequency domain algorithm and Time-Domain algorithm. The advantage of frequency domain algorithm is directly to estimate according to the frequency spectrum that receives signal the weights of butterfly wave filter. If coherent receiver must need to obtain receiving the frequency spectrum of signal so in the frequency domain compensation chromatic dispersion. Frequency domain algorithm can directly use this frequency spectrum, and does not need to increase the module of extra calculating frequency spectrum.

The advantage of Time-Domain algorithm is to use least mean-square error (LMS) algorithm to upgrade the butterfly filter weights, and this algorithm complex is low.

Claims (8)

1. with the method for constant rotation sign training sequence polarization demultiplexing in the multiplexing coherent optical communication system of polarization diversity, it is characterized in that, said method comprising the steps of:

(1) at the communication system initial phase, transmitting terminal sends the different constant rotation sign training sequence of velocity of rotation respectively on two polarization directions;

(2) coherent receiver received training sequence and it is handled, the weights of initialization butterfly filter, thus carry out polarization demultiplexing.

2. constant rotation sign training sequence according to claim 1, it is characterized in that, this training sequence rotates with constant speed along unit circle through see its track after the symbol power normalization on planisphere, and the implication that velocity of rotation is different comprises that slewing rate is inequality or rotation direction is different.

3. step according to claim 1 (2) coherent receiver received training sequence is also handled it, it is characterized in that the method for the weights of described coherent receiver initialization butterfly filter has frequency domain algorithm and Time-Domain algorithm.

4. frequency domain algorithm according to claim 3 is characterized in that, described frequency domain algorithm comprises following steps:

(1) ask discrete Fourier transform (DFT) to calculate frequency spectrum to the training sequence that receives;

(2) from frequency spectrum, find peak value;

(3) estimate channel transfer functions from peak value;

(4) with the contrary weights that come initialization butterfly filter of transfer function.

5. from frequency spectrum, find peak value according to the described step of claim 4 (2), it is characterized in that, accessory rights requires on the frequency spectrum of 4 described step (1) gained, equals to seek near the angle of rotation frequency that sends constant rotation sign training sequence on two polarization directions the point of absolute value maximum at angular frequency.

6. claim 4,5 described frequency domain algorithms is characterized in that, can go out the frequency difference of coherent receiver local oscillator (LO) and transmission signal(-) carrier frequency from the location estimation that spectrum peak occurs.

7. Time-Domain algorithm according to claim 3 is characterized in that, this algorithm belongs to least mean-square error (LMS) algorithm, is used for adjusting the weights of butterfly filter.

8. according to claim 3,7 described Time-Domain algorithm (belonging to the LMS algorithm), it is characterized in that the error signal calculation step of LMS algorithm is:

(1) angle of last moment butterfly filter two branch output signals (this signal is a plural number) of calculating;

(2) from last one constantly the training sequence symbols velocity of rotation of the angle of output signal and this polarization branch extrapolate the desired value of current time output signal;

(3) difference of the actual value of the desired value of current time output signal and current time output signal is as the error signal of LMS algorithm.

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