CN102724151B - Communication system, communication method, multichannel adaptive equalizer and OFDM (orthogonal frequency division multiplexing) signal demultiplexing method - Google Patents

Abstract

The invention discloses a communication system, a communication method, a multichannel adaptive equalizer and an OFDM (orthogonal frequency division multiplexing) signal demultiplexing method. The OFDM signal demultiplexing method includes the steps: receiving OFDM optical signals multiplexed by N-channel optical subcarrier waves, demodulating the OFDM optical signals by respectively using series intrinsic light different in angular frequency so as to obtain corresponding OFDM electrical signals; and after adjacent frequency band signals except for baseband signals are subjected to attenuation of a low-pass filter, sampling the OFDM electrical signals in each channel so as to obtain corresponding OFDM electrical signal sampling values, and then reducing data carried by the corresponding optical subcarrier waves in each channel by using a multichannel balance matrix to multiply by the N-channel OFDM electrical signal sampling values. The OFDM signal demultiplexing method has the advantages that a receiving end does not require strict match of sampling time of signal demodulation in each channel, sampling rate is determined by modulating signal rate carried by single optical carrier wave, ADC (analog-to-digital converter) bottleneck restriction can be bypassed, and the method is applicable to the high-speed optical communication system.

Description

The method of communication system, communication means and multi-channel adaptive equalizer and ofdm signal demultiplexing

Technical field

The present invention relates to communication system, be specifically related to the method for communication system, communication means and multi-channel adaptive equalizer and ofdm signal demultiplexing.

Background technology

Optical communication mainly contains time division multiplexing (TDM) and wavelength division multiplexing (WDM) two kinds of technology paths to high speed development.Time division multiplexing is interweaved within the different time periods by different signals, along same transmission, again the signal extraction in each time period is out reduced into primary signal at receiving terminal, at present, adopt coherent optical communication technology and palarization multiplexing QPSK (quarternary phase-shift keying (QPSK)) modulation, the transmission rate of Single wavelength 100G can be realized, but, this protocols call is the analog to digital converter of tens G in receiving terminal employing sample rate, because this is close to the limit of electronic device, therefore, the method of direct raising transmission rate cannot be used for the TDM optical communication system of higher rate.The way of wavelength division multiplexing is, at transmitting terminal, signal is divided into multichannel, and the light carrier being modulated to different frequency respectively transmits, and carry out demultiplexing recovery again at receiving terminal, therefore, the processing speed of receiving terminal electronic device requires to be determined by each road signal rate, relatively low.So WDM is the Main way of high speed optical communication development.

But traditional wavelength-division multiplex system requires there is the protection interval much larger than spectrum modulation signal between different light carrier, so that optical filter is separated, thus causes huge frequency spectrum waste.Propose OFDM (Orthogonal Frequency Division Multiplexing for this reason, OFDM) technology, WDM signal (hereinafter referred to as ofdm signal) after adopting OFDM multiplexing is made up of the mutually orthogonal multiple optical carriers be close to, because light carrier each in ofdm signal is closely adjacent, be accustomed in the industry each light carrier to be called subcarrier, the general principle of OFDM is as follows:

If the transmission cycle of ofdm signal is T, then the interval delta f between different sub carrier is Δ f=1/T, so Received signal strength r (t) can be expressed as wherein:

C _kthe transmission data of a kth subcarrier, f _kt () represents a kth subcarrier.

Received signal strength r (t) and intrinsic light are done cross-correlation in a code-element period, then has

${\∫}_0^{T}r\left(t\right)f_m\left(t\right)\mathrm{dt}={\mathrm{\δ}}_{\mathrm{km}}{C}_k---\left(1\right)$

The δ as k=m _km=1, the δ as k ≠ m _km=0.

As can be seen from formula (1), even if different sub carrier spectrum overlapping, still different interchannel crosstalk can be eliminated completely.Receive the signal of certain subcarrier, only the light signal received need be done cross-correlation with corresponding intrinsic light carrier in a code-element period, sent out data-signal can be proposed, and the crosstalk of other light carriers of cancellation.

Owing to producing serial intrinsic light and receiving optical signals, to do cross-correlation with high costs, so the coherent light OFDM receive mode that reality generally adopts is, first use an intrinsic optical modulator ofdm signal, use high-speed AD (analog to digital converter) to sample to restituted signal again, then do discrete Fourier transform (DFT).Such as, suppose that the ofdm signal received has 128 subcarriers, then need to carry out 128 time domain samples in a code-element period, then do the discrete Fourier transform (DFT) of 128, obtain the data-signal entrained by each subcarrier.

Although OFDM adopts the parallel transmitting-receiving of N number of subcarrier, also require each symbol sample N time (N is carrier number).So use discrete fourier transform method process ofdm signal at present, its receiving velocity is the same with single carrier, is still subject to the restriction of ADC sampling rate.

Summary of the invention

For the defect existed in prior art, the object of the present invention is to provide a kind of method of the optical carrier demultiplexing for adopting OFDM multiplexing, comprising the following steps:

Receive by N road photon carrier multiplexing become OFDM light signal, multiplexing method for: the data entrained by the photon carrier wave of kth road are by modulation signal I _k+ jQ _kbeing modulated at angular frequency is Ω _c+ k Ω ₀kth road photon carrier wave on, Ω _cbe the angular frequency of the 0th road photon carrier wave, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, k=0 .., N-1;

Use the serial intrinsic light of different angular frequency to described OFDM optical signal demodulation respectively, obtain the corresponding OFDM signal of telecommunication; Demodulation method is: use angular frequency is Ω _c+ m Ω ₀intrinsic light the m road OFDM signal of telecommunication is obtained to OFDM optical signal demodulation, each road OFDM signal of telecommunication is made up of, with intrinsic light Ω a baseband signal and N-1 the band signal adjacent with this baseband signal _c+ m Ω ₀the photon carrier down-conversion that frequency is identical is baseband signal, with intrinsic light Ω _c+ m Ω ₀the photon carrier down-conversion that frequency is different is the nearby frequency bands signal adjacent with this baseband signal, m=0 .., N-1;

Each road OFDM signal of telecommunication, sample after the nearby frequency bands signal that low pass filter is decayed beyond its baseband signal respectively, obtain corresponding OFDM signal of telecommunication sampled value, wherein, m road OFDM signal of telecommunication sampled value is in formula, I _m+ jQ _mand I _k+ jQ _kbe respectively the modulation signal of m road photon carrier wave and the modulation signal of kth road (k ≠ m) photon carrier wave, and; h _mmbe superposition coefficient corresponding with m road photon carrier wave in the OFDM signal of telecommunication of m road, h _mkbe superposition coefficient corresponding with other subcarriers in the OFDM signal of telecommunication of m road, h _mmand h _mkform N × N multichannel superposition matrix, described multichannel superposition inverse of a matrix matrix is the balanced matrix of multichannel of multichannel equilizer, and the matrix element of the balanced matrix of described multichannel is called equalizing coefficient, and described equalizing coefficient adopts gradient algorithm to calculate;

Be multiplied by described N road OFDM signal of telecommunication sampled value with the balanced matrix of described multichannel and restore data entrained by the photon carrier wave of corresponding each road.

In the method for above-mentioned demultiplexing,

be m road frequency be Ω _c+ m Ω ₀the initial phase of intrinsic light;

θ _kfor the initial phase of kth road photon carrier wave;

T _mbe the sampling instant of the m road OFDM signal of telecommunication in code element 0.

In the method for above-mentioned demultiplexing, the balanced matrix of described multichannel is following superposition inverse of a matrix matrix:

$\left[\begin{array}{ccccc}{h}_{00}& ..& h_{0k}& ..& h_{0(N-1)}\\ ..& ..& ..& ..& ..\\ h_{m0}& ..& h_{\mathrm{mk}}& ..& h_{m(N-1)}\\ ..& ..& ..& ..& ..\\ h_{(N-1)0}& ..& h_{(N-1)k}& ..& h_{(N-1)(N-1)}\end{array}\right].$

In the method for above-mentioned demultiplexing, every subcarriers signal of transmitting terminal adopts two polarization states to carry out multiplexing respectively, and the balanced matrix of described multichannel is F=(HP) ^-1, wherein:

H is multicarrier superposition matrix,

$H=\left[\begin{array}{cccccccc}{h}_{00}^x& 0& ..& h_{0k}^x& 0& ..& h_{0(N-1)}^x& 0\\ 0& h_{00}^y& ..& 0& h_{0k}^y& ..& 0& h_{0(N-1)}^y\\ ..& ..& ..& ..& ..& ..& ..& ..\\ h_{m0}^x& 0& ..& h_{\mathrm{mk}}^x& 0& ..& h_{m(N-1)}^x& 0\\ 0& h_{m0}^x& ..& 0& h_{\mathrm{mk}}^y& ..& 0& h_{m(N-1)}^y\\ ..& ..& ..& ..& ..& ..& ..& ..\\ h_{(N-1)0}^x& 0& ..& h_{(N-1)k}^x& 0& ..& h_{(N-1)(N-1)}^x& 0\\ 0& h_{(N-1)0}^y& ..& 0& h_{(N-1)k}^y& ..& 0& h_{(N-1)(N-1)}^y\end{array}\right];$

P is Jones matrix, $P=\left[\begin{array}{cccccccc}{A}_0& B_0& ..& 0& 0& ..& 0& 0\\ C_0& D_0& ..& 0& 0& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& A_m& B_m& ..& 0& 0\\ 0& 0& ..& C_m& D_m& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& 0& 0& ..& A_{N-1}& B_{N-1}\\ 0& 0& ..& 0& 0& ..& C_{N-1}& D_{N-1}\end{array}\right];$

X and y represents two polarization states, and A, B, C, D in Jones matrix represent the change of signal state of polarization.

In the method for above-mentioned demultiplexing, the mode combined with time-domain equalizer is adopted to reduce the unit impulse response of the OFDM signal of telecommunication, the length of described time-domain equalizer is 2L-1 tap, after being multiplied by time domain equalization coefficient by 2L-1 sample value, linear, additive is sued for peace, L value is by signal impulse response length decision in the time domain, and the balanced expression formula in conjunction with the multichannel equilizer of time-domain equalizer is:

${\mathrm{Eout}}_g^x\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

${\mathrm{Eout}}_g^y\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

Wherein, n represents the n-th code-element period, and g represents that the data sequence number that multichannel equilizer exports, l are the tap sequence number of time-domain equalizer, and m represents the channel sequence number that multichannel equilizer inputs, the sampled value of corresponding m road ofdm signal, equalizing coefficient with the mode adopting gradient method automatically to upgrade converges on satisfied filter factor of offsetting ICI and ISI automatically.

In the method for above-mentioned demultiplexing, equalizing coefficient with the step of automatic renewal is as follows:

(1) initialization:

work as m=k, work as m=k, its residual value is all 0;

(2) use gradient algorithm to upgrade, and be defined as automatically converging to ε ²minimum value time value, more new formula is as follows:

$F_{\mathrm{gm}}^{\mathrm{xx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_x}^2}{\∂F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{xy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_x}^2}{\∂F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{yx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_y}^2}{\∂F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{yy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_y}^2}{\∂F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)};$

In formula: ε represents error, ε ²corresponding ICI and the ISI minimum value of minimum value, n represents the coefficient value before renewal, and n+1 represents the coefficient value more, and μ represents a fractional increments.

In the method for above-mentioned demultiplexing, error ε adopts training sequence method to obtain,

${\mathrm{\ϵ}}_g^x=d_g^x\left(n\right)-{\mathrm{Eout}}_g^x\left(n\right);$

${\mathrm{\ϵ}}_g^y=d_g^y\left(n\right)-{\mathrm{Eout}}_g^y\left(n\right).$

In the method for above-mentioned demultiplexing, error ε adopts blind estimating method to obtain,

${\mathrm{\ϵ}}_g^x=1-{\mathrm{Eout}}_g^x\left(n\right){\left[{\mathrm{Eout}}_g^x\left(n\right)\right]}^{*};$

${\mathrm{\ϵ}}_g^y=1-{\mathrm{Eout}}_g^y\left(n\right){\left[{\mathrm{Eout}}_g^y\left(n\right)\right]}^{*}.$

Present invention also offers a kind of ofdm signal Deplexing apparatus, comprise down-conversion device, low pass filter, acquisition module and digital signal processing module that intrinsic light source, multicarrier generation module, 90 degree of frequency mixers and balanced reciver are formed, described intrinsic light source produces intrinsic light Ω _c, Ω _cfor the angular frequency of intrinsic light source; Described multicarrier generation module is according to described intrinsic light Ω _cproducing angular frequency after shift frequency is respectively Ω _c+ m Ω ₀serial intrinsic light, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, and m represents m road intrinsic light, m=0 .., N-1; The down-conversion device that described 90 degree of frequency mixers and balanced reciver are formed with the OFDM optical signal demodulation that N road photon carrier multiplexing becomes by described serial intrinsic light, obtains the corresponding N road OFDM signal of telecommunication respectively; Described low pass filter to be decayed the signal beyond its baseband signal to each road OFDM signal of telecommunication respectively; Described acquisition module gathers each road OFDM signal of telecommunication respectively, obtains corresponding OFDM signal of telecommunication sampled value; Described digital signal processing module restores the data entrained by corresponding each road photon carrier wave to described multichannel equilibrium matrix multiple respectively to N road OFDM signal of telecommunication sampled value.

In said apparatus, also comprise the time-domain equalizer of the unit impulse response for reducing the OFDM signal of telecommunication, the length of described time-domain equalizer is 2L-1 tap, after being multiplied by time domain equalization coefficient by 2L-1 sample value, linear, additive is sued for peace, L value is by signal impulse response length decision in the time domain, and the balanced expression formula in conjunction with the multichannel equilizer device of time domain equalization is:

${\mathrm{Eout}}_g^x\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

${\mathrm{Eout}}_g^y\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

Wherein, n represents the n-th code-element period, g represents the data sequence number that multichannel equilizer exports, corresponding to the modulating data of the g light carrier calculated, l is the tap sequence number of time-domain equalizer, m represents the channel sequence number that multichannel equilizer inputs, the sampled value of corresponding m road ofdm signal, equalizing coefficient with the mode adopting gradient method automatically to upgrade converges on satisfied filter factor of offsetting ICI and ISI automatically.

Present invention also offers a kind of communication system, comprise transmitting terminal and receiving terminal, described receiving terminal is provided with above-mentioned Deplexing apparatus.

Present invention also offers a kind of communication means, at the transmitting terminal of communication system, modulate data in N number of orthogonal sub-carriers, and then each orthogonal sub-carriers is closed ripple is sent to communication system receiving terminal through optical fiber, at receiving terminal, adopt above-mentioned for adopting the method for the multiplexing optical carrier demultiplexing of OFDM to carry out demultiplexing.

The present invention, common fourier transform method is not adopted to carry out demultiplexing to OFDM light signal, but utilize the special characteristic of each subcarrier in light ofdm signal mutually orthogonal (namely inter-carrier frequency interval equals chip rate), the sampled value deriving the OFDM signal of telecommunication is the linear superposition of each sub-carrier modulation data and the feature of superposition coefficient constant, adopt the method for multi-channel adaptive equilibrium to carry out inverse operation to synergistic effect, demultiplexing OFDM light signal also eliminates ICI (interchannel interference).The present invention also can reduce the unit impulse response of sub-carrier signal simultaneously in conjunction with Time Domain Equalization techniques, namely eliminate ICI (interchannel interference) and ISI (symbol interference) simultaneously.

The multi-channel adaptive equilibrium acceptance method of ofdm signal of the present invention, be easy to practical, its advantage is:

(1) to receiving light with after different intrinsic optical modulator, with ADC to each road restituted signal parallel sampling, sample rate is with modulation signal speed to determine by single light carrier, can walk around the bottleneck restriction of ADC.

(2) transmitting terminal does not need to be IFFT.

(3) impact of receiving terminal and transmitting terminal light source frequency difference is not subject to.

(4) do not require the strict coupling in the sampling time of each road restituted signal at receiving terminal, the sampling ADC quantification gain of not also being strict with each road restituted signal is equal.

Accompanying drawing explanation

Fig. 1 communication system principle schematic diagram provided by the invention;

The demodulation part schematic diagram (for a passage) of ofdm signal Deplexing apparatus in Fig. 2 the present invention;

The signal processing schematic diagram of ofdm signal Deplexing apparatus in Fig. 3 the present invention.

Embodiment

OFDM light signal described in the present invention refers to the multi-path light subcarrier of a series of mutually orthogonal (up-conversion), and each road photon carrier wave carries corresponding high-speed data respectively, and the described OFDM signal of telecommunication refers to that by angular frequency be Ω _c+ m Ω ₀the intrinsic light signal of telecommunication that OFDM optical signal demodulation (down-conversion) is obtained, each road OFDM signal of telecommunication is made up of, with intrinsic light Ω a baseband signal and N-1 the band signal adjacent with this baseband signal _c+ m Ω ₀the photon carrier down-conversion that frequency is identical is baseband signal, with intrinsic light Ω _c+ m Ω ₀the photon carrier down-conversion that frequency is different is the nearby frequency bands signal adjacent with this baseband signal, m=0 .., N-1.

Innovative point of the present invention is: do not adopt conventional Fourier transform to carry out demultiplexing to OFDM light signal, but utilize the special characteristic of each photon carrier wave in OFDM light signal mutually orthogonal (namely inter-carrier frequency interval equals chip rate), derive linear superposition and the feature of superposition coefficient constant that the OFDM signal of telecommunication sampled value after sampling is each photon carrier modulation data, the method of multi-channel adaptive equilibrium is adopted to carry out inverse operation to synergistic effect, thus the data restored entrained by the photon carrier wave of each road, and the unit impulse response of the OFDM signal of telecommunication is reduced in conjunction with Time Domain Equalization techniques, eliminate ICI (interchannel interference) and ISI (symbol interference) simultaneously.For this reason, the invention provides a kind of method of communication system, communication means and multi-channel adaptive equalizer and ofdm signal demultiplexing, below in conjunction with accompanying drawing, the present invention is described in further detail.

As shown in Figure 1, communication means provided by the invention, adopts known IQ modulation technique in the industry to modulate data on N number of orthogonal photon carrier wave (this process is also referred to as up-conversion process) and close ripple through Optical Fiber Transmission at transmitting terminal; At receiving terminal, the OFDM light signal using a series of mutually orthogonal intrinsic optical modulator to receive obtains the N road OFDM signal of telecommunication, each road OFDM signal of telecommunication is sampled respectively more respectively after the nearby frequency bands signal beyond baseband signal during this road OFDM signal of telecommunication decayed by low pass filter, then to the data that sampled result utilizes multi-channel adaptive equalizer to reduce entrained by each photon carrier wave, and compensate the channel impairments that CD (chromatic dispersion), PMD (polarization mode dispersion) etc. cause simultaneously.Digital processing is undertaken by DSP module, and DSP module can be FPGA, can be also custom-designed dsp chip, but above two kinds of elements below being not limited to.

Specifically:

A. at the transmitting terminal of communication system, the mode of data acquisition by known IQ modulation technique up-conversion is in the industry modulated data on N number of orthogonal photon carrier wave, and then will each photon carrier wave close ripple after to be sent to the receiving terminal of communication system by optical fiber.Modulator approach for: the data entrained by the photon carrier wave of kth road are by modulation signal I _k+ jQ _kbeing modulated at angular frequency is Ω _c+ k Ω ₀kth road photon carrier wave on, Ω _cbe the angular frequency of the 0th road photon carrier wave, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, k=0 .., N-1.

At receiving terminal, the OFDM optical signal demodulation adopting the mode of down-conversion to receive, obtains the corresponding OFDM signal of telecommunication; Demodulation method is: use angular frequency is Ω _c+ m Ω ₀intrinsic light the m road OFDM signal of telecommunication is obtained to OFDM optical signal demodulation, each road OFDM signal of telecommunication is made up of, with intrinsic light Ω a baseband signal and N-1 the band signal adjacent with this baseband signal _c+ m Ω ₀the photon carrier down-conversion that frequency is identical is baseband signal, with intrinsic light Ω _c+ m Ω ₀the photon carrier down-conversion that frequency is different is the band signal adjacent with baseband signal, m=0 .., N-1, and the frequency of the down-conversion of the receive path corresponding with the m road OFDM signal of telecommunication is f _c+ m Δ f, then frequency is f _cthe photon carrier signal of+m Δ f is down converted to the base band in the OFDM signal of telecommunication of m road, and the both sides that the signal of other frequencies is down converted to the base band in the OFDM signal of telecommunication of m road form nearby frequency bands signal, like this, through down-conversion, obtain the N road OFDM signal of telecommunication.

In Fig. 1, the modulation of transmitting terminal represents with a mathematic(al) representation by signal times, and what reality was corresponding is IQ modulation, general by the realization of both arms MZ interferometer.The solution of receiving terminal is called signal times and is represented with a mathematic(al) representation, and corresponding is IQ demodulation, and realized by ofdm signal Deplexing apparatus, the concrete structure of ofdm signal Deplexing apparatus will be described in further detail afterwards.

B. by each road OFDM signal of telecommunication respectively by low pass filter, decling phase answers the adjacent signals beyond baseband signal.

C. sampled to each road OFDM signal of telecommunication by ADC acquisition module, once or secondary, the N road OFDM signal of telecommunication sampled value obtained, each road OFDM signal of telecommunication sampled value is the linear superposition of N road photon carrier wave institute adjusting data to each data periodic sampling.

D. at digital signal processing module, utilize the balanced matrix of multichannel to be multiplied by each road OFDM signal of telecommunication sampled value and restore data in OFDM light signal entrained by each photon carrier wave, concrete grammar will be described in further detail afterwards.

Fig. 2 shows the demodulation part schematic diagram of ofdm signal Deplexing apparatus, this schematic diagram only illustrates with a passage, as shown in Figure 2, ofdm signal Deplexing apparatus provided by the invention comprises: intrinsic light source, multi-carrier generation device, optical filter, polarization beam apparatus, the demodulating equipment, low pass filter, acquisition module and the digital signal processing module that are made up of 90 degree of frequency mixers and balanced reciver.Intrinsic light source is laser, sends the intrinsic light that frequency is fC, and produces carrier frequency through multi-carrier generation device (frequency is the modulation signal shift frequency of Δ f) and be respectively f _c, f _c+ Δ f, f _c+ 2 Δ f ..., f _cthe serial intrinsic light of+(N-1) Δ f, then be f through the optical filter frequency leached needed for m passage down-conversion _cthe intrinsic light of+m Δ f, the demodulating equipment be made up of 90 degree of frequency mixers and balanced reciver, to OFDM optical signal demodulation, obtains the corresponding N road OFDM signal of telecommunication.Acquisition module is sampled to each road OFDM signal of telecommunication, the N road OFDM signal of telecommunication sampled value obtained, and digital signal processing module utilizes the balanced matrix of multichannel to be multiplied by each road OFDM signal of telecommunication sampled value and restores data in OFDM light signal entrained by each photon carrier wave.Multi-carrier generation device adopts known frequency shift technique to realize, and the dispersion compensation in Fig. 2 adopts known technology in the industry, does not repeat them here.

Below in conjunction with operation principle and the reasoning process method to the optical carrier demultiplexing for adopting OFDM multiplexing provided by the invention, be described in detail.

At the transmitting terminal of communication system, N road photon carrier multiplexing becomes OFDM light signal, and modulator approach as previously mentioned, does not now repeat at this.

The carrier frequency of N road photon carrier wave is respectively f _c, f _c+ Δ f, f _c+ 2 Δ f ..., f _c+ (N-1) Δ f, so the expression formula of OFDM light signal is:

(I ₀+jQ ₀)exp[jΩ _Ct+θ ₀]+..+( _IK+jQ _K)exp[jΩ _Ct+j(K)Ω ₀t+θ _k]+..+

(2)

(I _N-1+jQ _N-1)exp[jΩ _Ct+j(N-1)Ω ₀t+θ _N-1]

I _k+ jQ _kfor the modulation signal of kth road photon carrier wave, θ _kfor the initial phase of kth road photon carrier wave, Ω _cbe the angular frequency of the 0th road photon carrier wave, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, k=0 .., N-1.

At receiving terminal, use the serial intrinsic light of different angular frequency respectively, to described OFDM optical signal demodulation in a code-element period, obtain the corresponding OFDM signal of telecommunication, the concrete practice is: use angular frequency is Ω _c+ m Ω ₀intrinsic light to the m road OFDM signal of telecommunication obtained after OFDM optical signal demodulation, the m road OFDM signal of telecommunication is expressed as:

formula (3)

Wherein: be the initial phase of m road intrinsic light, m=0 .., N-1.

Each road OFDM signal of telecommunication is still made up of N number of sub-carrier signal, comprise the nearby frequency bands signal that a baseband signal is adjacent with this baseband signal with N-1, but which photon carrier wave is determined to the frequency of corresponding base band by demodulation intrinsic light by shift frequency, such as: the baseband signal in the OFDM signal of telecommunication of m road and nearby frequency bands signal are obtained, with Ω by such as under type _c+ m Ω ₀the baseband signal that the photon carrier signal (i.e. k=m) that intrinsic light frequency is identical will down-convert in the OFDM signal of telecommunication of m road, with Ω _c+ m Ω ₀the photon carrier signal (i.e. k ≠ m) that intrinsic light frequency is different will down-convert to and the band signal adjacent with baseband signal in the OFDM signal of telecommunication of m road.

Each road OFDM signal of telecommunication, samples respectively, obtains corresponding OFDM signal of telecommunication sampled value, if the sampling instant of the m road OFDM signal of telecommunication is t after the nearby frequency bands signal that low pass filter is decayed beyond its baseband signal _m, then the sampled value of the m road OFDM signal of telecommunication is:

${\mathrm{Ein}}_m=(I_m+{\mathrm{jQ}}_m)h_{\mathrm{mm}}+\underset{k\≠m}{\overset{N-1}{\mathrm{\Σ}}}(I_k+j{Q}_k)h_{\mathrm{mk}}---\left(4\right)$

Section 1 in formula (4) represents the data be modulated on the photon carrier wave of m road, Section 2 from crosstalk, h _mmfor constant, represent the superposition coefficient of corresponding m road photon carrier wave in the OFDM signal of telecommunication of m road, h _mkbe the superposition coefficient of other road photon carrier waves corresponding in the OFDM signal of telecommunication of m road, visible, sampled value E _inmthe crosstalk closing on photon carrier wave must be subject to.

Superposition coefficient h _mmand h _mkin, first m corresponding m road OFDM signal of telecommunication in subscript, the corresponding kth road of the k in subscript photon carrier wave, as k=m, h _mkdirectly can be written as h _mm, I _m+ jQ _mand I _k+ jQ _kbe respectively the modulation signal of m road photon carrier wave and the modulation signal of kth road photon carrier wave.

Superposition coefficient h _mmand h _mkform N × N matrix, be called multichannel superposition matrix, multichannel superposition inverse of a matrix matrix is called the balanced matrix of multichannel, be multiplied by N road sampled value with the balanced matrix of multichannel and then can recover the data be modulated on the photon carrier wave of N road, the matrix element of the balanced matrix of multichannel is called the equalizing coefficient of multichannel equilizer, the equalizing coefficient of multichannel equilizer can not first record superposition coefficient, and direct gradient algorithm calculates.

Supposing the sampling instant in code element 0, is t to the OFDM signal of telecommunication sampling instant of m road _m, then in the sampling instant of code element n, be t to the sampling instant of the m road OFDM signal of telecommunication _m+ nT, so in the sampling instant of code element n:

formula (7)

In formula (7), represent the superposition coefficient of code element n, represent the superposition coefficient of code element 0, visible, h _mkalso be constant.Then each element of multichannel superposition matrix keeps constant in different code element, so correspondence can try to achieve the balanced matrix of multichannel to the crosstalk of sampled data enforcement linear equalization elimination interchannel.

Like this, N number of OFDM signal of telecommunication sampled value that sampling obtains is all the linear superposition of the modulating data entrained by the photon carrier wave of N road, can be expressed as:

$\left[\begin{array}{c}{\mathrm{Ein}}_0\\ ..\\ {\mathrm{Ein}}_m\\ ..\\ {\mathrm{Ein}}_{N-1}\end{array}\right]=\left[\begin{array}{ccccc}{h}_{00}& ..& h_{0k}& ..& h_{0(N-1)}\\ ..& ..& ..& ..& ..\\ h_{m0}& ..& h_{\mathrm{mk}}& ..& h_{m(N-1)}\\ ..& ..& ..& ..& ..\\ h_{(N-1)0}& ..& h_{(N-1)k}& ..& h_{(N-1)(N-1)}\end{array}\right]\·\left[\begin{array}{c}{I}_0+j{Q}_0\\ ..\\ I_k+j{Q}_k\\ ..\\ I_{n-1}+{\mathrm{jQ}}_{N-1}\end{array}\right]---\left(8\right)$

Visible according to formula 8, can solve data entrained by the photon carrier signal of N road by N number of sampled value, be exactly briefly the inverse matrix that formula (8) is each side multiplied by H.Because the OFDM signal of telecommunication is made up of baseband signal, the nearby frequency bands signal adjacent with base band, the OFDM signal of telecommunication is after low pass filter, nearby frequency bands signal will be attenuated, therefore, in superposition matrix, corresponding to the absolute value of the superposition coefficient of nearby frequency bands much smaller than the superposition coefficient of baseband signal, above-mentioned relation mathematical expression is, ABS (h _mm) > > ABS (h _mk), the difference of m ≠ k, k and m is larger, its coefficient h _mkless, such matrix determinant can not be 0, therefore can there is inverse matrix all the time.

Owing to generally adopting polarization multiplexing in optical communications, every road photon carrier wave is made up of the light carrier of two independent polarization states, like this, need modulating data respectively at transmitting terminal and produce the OFDM light signal of palarization multiplexing, to there is the change of polarization state in the polarization signal light of both direction, it changes available original polarization state and is multiplied by Jones matrix after Optical Fiber Transmission $\left[\begin{array}{cc}{A}_m& B_m\\ C_m& D_m\end{array}\right]$ Represent, so after considering palarization multiplexing, the 2N road OFDM signal of telecommunication obtained after sampling can be expressed as with matrix multiple:

$\left[\begin{array}{c}{\mathrm{Ein}}_0^x\\ {\mathrm{Ein}}_0^y\\ ..\\ {\mathrm{Ein}}_m^x\\ {\mathrm{Ein}}_m^y\\ ..\\ {\mathrm{Ein}}_{N-1}^x\\ {\mathrm{Ein}}_{N-1}^y\\ \end{array}\right]=\left[\begin{array}{ccccccccc}{h}_{00}^x& 0& ..& h_{0k}^x& 0& ..& h_{0(N-1)}^x& 0& \\ 0& h_{00}^y& ..& 0& h_{0k}^y& ..& 0& h_{0(N-1)}^y& \\ ..& ..& ..& ..& ..& ..& ..& ..& \\ h_{m0}^x& 0& ..& h_{\mathrm{mk}}^x& 0& ..& h_{m(N-1)}^x& 0& \\ 0& h_{m0}^x& ..& 0& h_{\mathrm{mk}}^y& ..& 0& h_{m(N-1)}^y& \\ ..& ..& ..& ..& ..& ..& ..& ..& \\ h_{(N-1)0}^x& 0& ..& h_{(N-1)k}^x& 0& ..& h_{(N-1)(N-1)}^x& 0& \\ 0& h_{(N-1)0}^y& ..& 0& h_{(N-1)k}^y& ..& 0& h_{(N-1)(N-1)}^y& \\ & & & & & & & & \end{array}\right]\·$

$\left[\begin{array}{cccccccc}{A}_0& B_0& ..& 0& 0& ..& 0& 0\\ C_0& D_0& ..& 0& 0& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& A_m& B_m& ..& 0& 0\\ 0& 0& ..& C_m& D_m& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& 0& 0& ..& A_{N-1}& B_{N-1}\\ 0& 0& ..& 0& 0& ..& C_{N-1}& D_{N-1}\end{array}\right]\·\left[\begin{array}{c}{I}_0^x+j{Q}_0^x\\ I_0^y+j{Q}_0^y\\ ..\\ I_k^x+j{Q}_k^x\\ I_k^y+j{Q}_k^x\\ ..\\ I_{N-1}^x+j{Q}_{N-1}^x\\ I_{N-1}^y+j{Q}_{N-1}^y\end{array}\right]$ Formula (9)

In definition (9), first matrix is H, corresponding to receiving terminal signal filtering with sampling after superpose coefficient; Defining second matrix is P, and corresponding to the change of polarization state in Signal transmissions, therefore only demand goes out its inverse matrix F=(HP) ^-1, and be multiplied by the OFDM signal of telecommunication sampled value that obtains of sampling and namely can restore data entrained by OFDM light signal.

As everyone knows, due to dispersion interaction in communication system, the unit impulse response of optical carrier may continue multiple baud, so when designing multichannel equilizer, in order to recovering signal better, also need in conjunction with time-domain equalizer technology, the accuracy of further raising data convert, by sampled result with input, as the equalizer described by balanced formula (10) (11), obtains corresponding data.

The length of getting time-domain equalizer is 2L-1 tap, and the sampled value corresponding to the code element of 2L-1 in time domain is multiplied by the linear superposition after time domain equalization coefficient.Consider and process 2L-1 code element, N number of light carrier, two polarizations simultaneously, export 2N result, therefore, equilibrium calculation is difficult to use matrix notation, therefore provides the balanced expression formula of ofdm signal Deplexing apparatus with cumulative fashion:

${\mathrm{Eout}}_g^x\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right]---\left(10\right)$

${\mathrm{Eout}}_g^y\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right]---\left(11\right)$

In formula (10), (11), n represents the n-th code-element period, and g represents the data sequence number that multichannel equilizer exports, l is the tap sequence number of time-domain equalizer, m represents the channel sequence number that multichannel equilizer inputs, the sampled value of corresponding m road ofdm signal with for equalizing coefficient.

Introduce below and how to determine that the value of above-mentioned each equalizing coefficient meets the requirement of offsetting ICI and ISI to make the equalizing coefficient of equalizer.

Due to the gradual character of channel, the sampling instant of adding filter parameter that receiving terminal each road OFDM signal of telecommunication passes through and ADC is difficult to coupling, each matrix element of superposition matrix is difficult to actual measurement, so be difficult to obtain above-mentioned equalizing coefficient by the method for inverting, but the mode adopting gradient method automatically to upgrade restrains automatically, make equalizing coefficient automatically converge on correct equalizing coefficient, specific practice is:

(1) initialization equalizing coefficient:

As m=k, its residual value is all 0.

(2) use gradient algorithm to upgrade, equalizing coefficient converges to ε automatically ²for value during minimum value, more new formula is as follows:

$F_{\mathrm{gm}}^{\mathrm{xx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_x}^2}{\∂F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)}---\left(12\right);$

$F_{\mathrm{gm}}^{\mathrm{xy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_x}^2}{\∂F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)}---\left(13\right);$

$F_{\mathrm{gm}}^{\mathrm{yx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_y}^2}{\∂F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)}---\left(14\right);$

$F_{\mathrm{gm}}^{\mathrm{yy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)-\mathrm{\μ}\frac{\∂{{\mathrm{\ϵ}}_y}^2}{\∂F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)}---\left(15\right);$

In formula: ε represents error, ε ²corresponding ICI and the ISI minimum value of minimum value, n represents the equalizing coefficient value before renewal, and n+1 represents the equalizing coefficient value more, and μ represents a fractional increments.

(3) training sequence or blind estimate two kinds of method error of calculation ε can be adopted.

CMA (constant modulo n arithmetic) is a kind of conventional blind estimate algorithm, if transmission is QPSK signal, then just in time meets constant mould condition.

Now error expression is:

${\mathrm{\ϵ}}_g^x=1-{\mathrm{Eout}}_g^x\left(n\right){\left[{\mathrm{Eout}}_g^x\left(n\right)\right]}^{*}$

${\mathrm{\ϵ}}_g^y=1-{\mathrm{Eout}}_g^y\left(n\right){\left[{\mathrm{Eout}}_g^y\left(n\right)\right]}^{*}---\left(16\right)$

In conjunction with (16) formula and (12) ~ (15) formula, can obtain

$F_{\mathrm{gm}}^{\mathrm{xx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)+4\mathrm{\μ}{\mathrm{\ϵ}}_g^x{\mathrm{Eout}}_g^x\left(n\right){\left[{\mathrm{Ein}}_g^x(n-l)\right]}^{*}---\left(17\right)$

$F_{\mathrm{gm}}^{\mathrm{xy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)+4\mathrm{\μ}{\mathrm{\ϵ}}_g^x{\mathrm{Eout}}_g^x\left(n\right){\left[{\mathrm{Ein}}_m^y(n-l)\right]}^{*}---\left(18\right)$

$F_{\mathrm{gm}}^{\mathrm{yx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)+4\mathrm{\μ}{\mathrm{\ϵ}}_g^y{\mathrm{Eout}}_g^y\left(n\right){\left[{\mathrm{Ein}}_m^x(n-l)\right]}^{*}---\left(19\right)$

$F_{\mathrm{gm}}^{\mathrm{yy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)+4\mathrm{\μ}{\mathrm{\ϵ}}_g^y{\mathrm{Eout}}_g^y\left(n\right){\left[{\mathrm{Ein}}_m^y(n-l)\right]}^{*}---\left(20\right)$

If employing training sequence, find corresponding training sequence bits postpone, if correct reception value is d _xwith d _y, then error expression is

${\mathrm{\ϵ}}_g^x=d_g^x\left(n\right)-{\mathrm{Eout}}_g^x\left(n\right)---\left(21\right)$

${\mathrm{\ϵ}}_g^y=d_g^y\left(n\right)-{\mathrm{Eout}}_g^y\left(n\right)---\left(22\right)$

Substitute into the equalizing coefficient newer that (12) ~ (15) also can obtain using training sequence method.

Adaptive equalization above merges balanced for multichannel with time domain equalization.Also can divide two stages for the treatment of by balanced for multichannel with time domain equalization in reality, release its equalizing coefficient more new formula.In this case, the coefficient of multichannel equilizer, once obtain, can be set to fixed value.

In addition, in the demodulating process of reality, there is frequency difference δ f with transmission light in the intrinsic light of receiving terminal, surface is seen (7), and formula will no longer be set up.But in the present invention, intrinsic light is that a laser shift frequency K Δ f produces, and its frequency is f _c+ δ f, f _c+ Δ f+ δ f, f _c+ 2 Δ f+ δ f ..., f _c+ (N-1) Δ f+ δ f.So to all channels, sending light with receiving optical frequency difference is all δ f, and its impact can regard all restituted signal I as _k+ jQ _kbe multiplied by a multiple parameter exp (-j2 π δ fnT), do not affect the elimination of inter-channel crosstalk, additional complex vector can be eliminated in subsequent treatment.

When there is not frequency difference or after frequency difference compensates, h in theory _mkfor constant.But, because actual samples clock exists jitter phenomenon, can t be expressed as at the sampling time of code element m to m optical carrier sampling instant _m+ nT+ δ t _m.So (7) formula becomes

Observation type (23) can be found out, as abs (K-m) > > 1, and h _mkconstant can not be approximately.So, can first with carrier wave institute band signal far away apart from intrinsic carrier wave in low pass filter Decay of Solutions tonal signal after demodulation, reduce its impact on result.Another benefit that low pass filter brings is, the F as abs (K-m) > > 1 _mknumerical value is less so that can ignore.The equalizer that historical facts or anecdotes border adopts can only offset the impact closing on carrier wave, greatly simplifies than formula (10), (11) formula.

The present invention, utilizes the sampled result of the OFDM signal of telecommunication for the linear superposition of all photon carrier wave institutes tonal signal, and the feature of superposition coefficient constant, by sampling respectively at N number of passage, obtain N number of sampled value, this N number of sampled value is all the linear superposition that N road sends data, but superposition coefficient is different.By the mode of similar solution linear equation calculate each photon carrier wave with data.

The present invention is not limited to above-mentioned preferred forms, and anyone should learn the structural change made under enlightenment of the present invention, and every have identical or close technical scheme with the present invention, all falls within protection scope of the present invention.

Claims (11)

1., for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, comprise the following steps:

Receive by N road photon carrier multiplexing become OFDM light signal, multiplexing method for: the data entrained by the photon carrier wave of kth road are by modulation signal I _k+ jQ _kbeing modulated at angular frequency is Ω _c+ k Ω ₀kth road photon carrier wave on, Ω _cbe the angular frequency of the 0th road photon carrier wave, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, k=0 .., N-1;

Use the serial intrinsic light of different angular frequency to described OFDM optical signal demodulation respectively, obtain the corresponding OFDM signal of telecommunication; Demodulation method is: use angular frequency is Ω _c+ m Ω ₀intrinsic light the m road OFDM signal of telecommunication is obtained to OFDM optical signal demodulation, each road OFDM signal of telecommunication is made up of, with intrinsic light Ω a baseband signal and N-1 the band signal adjacent with this baseband signal _c+ m Ω ₀the photon carrier down-conversion that frequency is identical is baseband signal, with intrinsic light Ω _c+ m Ω ₀the photon carrier down-conversion that frequency is different is the nearby frequency bands signal adjacent with this baseband signal, m=0 .., N-1;

Each road OFDM signal of telecommunication, sample after the nearby frequency bands signal that low pass filter is decayed beyond its baseband signal respectively, obtain corresponding OFDM signal of telecommunication sampled value, wherein, m road OFDM signal of telecommunication sampled value is ${\mathrm{Ein}}_m=(I_m+{\mathrm{jQ}}_m)h_{\mathrm{mm}}+\underset{k\≠m}{\overset{N-1}{\mathrm{\Σ}}}(I_k+{\mathrm{jQ}}_k)h_{\mathrm{mk}},$ In formula, I _m+ jQ _mand I _k+ jQ _kbe respectively modulation signal and the kth road of m road photon carrier wave, k ≠ m, the modulation signal of photon carrier wave, and; h _mmbe superposition coefficient corresponding with m road photon carrier wave in the OFDM signal of telecommunication of m road, h _mkbe superposition coefficient corresponding with other subcarriers in the OFDM signal of telecommunication of m road, h _mmand h _mkform N × N multichannel superposition matrix, described multichannel superposition inverse of a matrix matrix is the balanced matrix of multichannel of multichannel equilizer, and the matrix element of the balanced matrix of described multichannel is called equalizing coefficient, and described equalizing coefficient adopts gradient algorithm to calculate;

Be multiplied by described N road OFDM signal of telecommunication sampled value with the balanced matrix of described multichannel and restore data entrained by the photon carrier wave of corresponding each road;

be m road frequency be Ω _c+ m Ω ₀the initial phase of intrinsic light;

θ _kfor the initial phase of kth road photon carrier wave;

T _mbe the sampling instant of the m road OFDM signal of telecommunication in code element 0.

2. as claimed in claim 1 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, the balanced matrix of described multichannel is following superposition inverse of a matrix matrix:

$\left[\begin{array}{ccccc}{h}_{00}& ..& h_{0k}& ..& h_{0(N-1)}\\ ..& ..& ..& ..& ..\\ h_{m0}& ..& h_{\mathrm{mk}}& ..& h_{m(N-1)}\\ ..& ..& ..& ..& ..\\ h_{(N-1)0}& ..& h_{(N-1)k}& ..& h_{(N-1)(N-1)}\end{array}\right].$

3. as claimed in claim 1 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, every subcarriers signal of transmitting terminal adopts two polarization states to carry out multiplexing respectively, and the balanced matrix of described multichannel is F=(HP) ^-1, wherein:

H is multicarrier superposition matrix,

$H=\left[\begin{array}{cccccccc}{h}_{00}^x& 0& ..& h_{0k}^x& 0& ..& h_{0(N-1)}^x& 0\\ 0& h_{00}^y& ..& 0& h_{0k}^y& ..& 0& h_{0(N-1)}^y\\ ..& ..& ..& ..& ..& ..& ..& ..\\ h_{m0}^x& 0& ..& h_{\mathrm{mk}}^x& 0& ..& h_{m(N-1)}^x& 0\\ 0& h_{m0}^x& ..& 0& h_{\mathrm{mk}}^y& ..& 0& h_{m(N-1)}^y\\ ..& ..& ..& ..& ..& ..& ..& ..\\ h_{(N-1)0}^x& 0& ..& h_{(N-1)k}^x& 0& ..& h_{(N-1)(N-1)}^x& 0\\ 0& h_{(N-1)0}^y& ..& 0& h_{(N-1)k}^y& ..& 0& h_{(N-1)(N-1)}^y\end{array}\right];$

P is Jones matrix, $P=\left[\begin{array}{cccccccc}{A}_0& B_0& ..& 0& 0& ..& 0& 0\\ C_0& D_0& ..& 0& 0& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& A_m& B_m& ..& 0& 0\\ 0& 0& ..& C_m& D_m& ..& 0& 0\\ ..& ..& ..& ..& ..& ..& ..& ..\\ 0& 0& ..& 0& 0& ..& A_{N-1}& B_{N-1}\\ 0& 0& ..& 0& 0& ..& C_{N-1}& D_{N-1}\end{array}\right];$

X and y represents two polarization states, and A, B, C, D in Jones matrix represent the change of signal state of polarization.

4. as claimed in claim 3 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, the mode combined with time-domain equalizer is adopted to reduce the unit impulse response of the OFDM signal of telecommunication, the length of described time-domain equalizer is 2L-1 tap, after being multiplied by time domain equalization coefficient by 2L-1 sample value, linear, additive is sued for peace, L value is by signal impulse response length decision in the time domain, and the balanced expression formula in conjunction with the multichannel equilizer of time-domain equalizer is:

${\mathrm{Eout}}_g^x\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

${\mathrm{Eout}}_g^y\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

Wherein, n represents the n-th code-element period, and g represents that the data sequence number that multichannel equilizer exports, l are the tap sequence number of time-domain equalizer, and m represents the channel sequence number that multichannel equilizer inputs, the sampled value of corresponding m road ofdm signal, equalizing coefficient with the mode adopting gradient method automatically to upgrade converges on satisfied filter factor of offsetting interchannel interference ICI and symbol interference ISI automatically.

5., as claimed in claim 4 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, equalizing coefficient with the step of automatic renewal is as follows:

(1) initialization:

work as m=k, work as m=k, its residual value is all 0;

(2) use gradient algorithm to upgrade, and be defined as automatically converging to ε ²minimum value time value, more new formula is as follows:

$F_{\mathrm{gm}}^{\mathrm{xx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xx}}(l,n)-\mathrm{\μ}\frac{{{\∂\mathrm{\ϵ}}_x}^2}{{\∂F}_{\mathrm{gm}}^{\mathrm{xx}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{xy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{xy}}(l,n)-\mathrm{\μ}\frac{{{\∂\mathrm{\ϵ}}_x}^2}{{\∂F}_{\mathrm{gm}}^{\mathrm{xy}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{yx}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yx}}(l,n)-\mathrm{\μ}\frac{{{\∂\mathrm{\ϵ}}_y}^2}{{\∂F}_{\mathrm{gm}}^{\mathrm{yx}}(l,n)};$

$F_{\mathrm{gm}}^{\mathrm{yy}}(l,n+1)=F_{\mathrm{gm}}^{\mathrm{yy}}(l,n)-\mathrm{\μ}\frac{{{\∂\mathrm{\ϵ}}_y}^2}{{\∂F}_{\mathrm{gm}}^{\mathrm{yy}}(l,n)};$

In formula: ε represents error, ε ²corresponding ICI and the ISI minimum value of minimum value, n represents the coefficient value before renewal, and n+1 represents the coefficient value after renewal, and μ represents a fractional increments.

6. as claimed in claim 5 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, error ε adopts training sequence method to obtain,

${\mathrm{\ϵ}}_g^x=d_g^x\left(n\right)-{\mathrm{Eout}}_g^x\left(n\right);$

${\mathrm{\ϵ}}_g^y=d_g^y\left(n\right)-{\mathrm{Eout}}_g^y\left(n\right).$

7. as claimed in claim 5 for the method for the optical carrier demultiplexing adopting OFDM multiplexing, it is characterized in that, error ε adopts blind estimating method to obtain,

${\mathrm{\ϵ}}_g^x=1-{\mathrm{Eout}}_g^x\left(n\right){\left[{\mathrm{Eout}}_g^x\left(n\right)\right]}^{*};$

${\mathrm{\ϵ}}_g^y=1-{\mathrm{Eout}}_g^y\left(n\right){\left[{\mathrm{Eout}}_g^y\left(n\right)\right]}^{*}.$

8.OFDM signal Deplexing apparatus, is characterized in that, comprising:

Intrinsic light source, produces intrinsic light Ω _c, Ω _cfor the angular frequency of intrinsic light source;

Multicarrier generation module, according to described intrinsic light Ω _cproducing angular frequency after shift frequency is respectively Ω _c+ m Ω ₀serial intrinsic light, Ω ₀=2 π Δ f, Δ f=1/T, T are the transmission cycle of OFDM light signal, and m represents m road intrinsic light, m=0 .., N-1;

The down-conversion device that 90 degree of frequency mixers and balanced reciver are formed, respectively with the OFDM optical signal demodulation that N road photon carrier multiplexing becomes by described serial intrinsic light, obtains the corresponding N road OFDM signal of telecommunication;

Low pass filter, to decay the signal beyond its baseband signal to each road OFDM signal of telecommunication respectively;

Acquisition module, gathers each road OFDM signal of telecommunication respectively, obtains corresponding OFDM signal of telecommunication sampled value;

Digital signal processing module, restores the data entrained by corresponding each road photon carrier wave to multichannel equilibrium matrix multiple according to claim 1 respectively to N road OFDM signal of telecommunication sampled value.

9. device as claimed in claim 8, it is characterized in that, also comprise the time-domain equalizer of the unit impulse response for reducing the OFDM signal of telecommunication, the length of described time-domain equalizer is 2L-1 tap, after being multiplied by time domain equalization coefficient by 2L-1 sample value, linear, additive is sued for peace, L value is by signal impulse response length decision in the time domain, and the balanced expression formula in conjunction with the multichannel equilizer device of time domain equalization is:

${\mathrm{Eout}}_g^x\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{xy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

${\mathrm{Eout}}_g^y\left(n\right)=\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yx}}\left(l\right)\left[{\mathrm{Ein}}_m^x(n-l)\right]+\underset{l=-L+1}{\overset{L-1}{\mathrm{\Σ}}}\underset{m=0}{\overset{N-1}{\mathrm{\Σ}}}{F}_{\mathrm{gm}}^{\mathrm{yy}}\left(l\right)\left[{\mathrm{Ein}}_m^y(n-l)\right],$

Wherein, n represents the n-th code-element period, g represents the data sequence number that multichannel equilizer exports, corresponding to the modulating data of the g light carrier calculated, l is the tap sequence number of time-domain equalizer, m represents the channel sequence number that multichannel equilizer inputs, the sampled value of corresponding m road ofdm signal, equalizing coefficient with the mode adopting gradient method automatically to upgrade converges on satisfied filter factor of offsetting interchannel interference ICI and symbol interference ISI automatically.

10. communication system, comprises transmitting terminal and receiving terminal, it is characterized in that, described receiving terminal is provided with Deplexing apparatus as claimed in claim 8.

11. communication meanss, at the transmitting terminal of communication system, modulate data in N number of orthogonal sub-carriers, and then each orthogonal sub-carriers is closed ripple is sent to communication system receiving terminal through optical fiber, it is characterized in that, at receiving terminal, adopt the method for claim 1 to carry out demultiplexing.