CN106357317A - Method for restraining atmosphere turbulence interference in free-space optical communication - Google Patents

Abstract

The invention relates to a method for restraining atmosphere turbulence interference in free-space optical communication, comprising the following steps: loading a user signal on OAM (Operation Administration and Maintenance) light for transmission, transmitting OAM light of multipath loading information in a combined manner through different atmosphere turbulence channels, demultiplexing and demodulating the distorted OAM light of output multipath of each atmosphere turbulence channel at a receiving terminal, as multipath OAM light of a transmitting terminal in a multipath signal transmission model passes through the different atmosphere turbulence channels, and fading characteristics of the respective channels are similar to a multi-antenna fading channel model, a space diversity technology is adopted to restrain the atmosphere turbulence interference, the receiving terminal restores useful signals of respective users to the maximum extent through the demultiplexed and demodulated user information and a space diversity and combination technology, influence of the atmosphere turbulence interference on system-received signals is reduced, and system reliability is improved. Therefore, the invention provides a reference for the practicability of free-space orbit angular momentum multiplexing optical communication.

Description

The suppressing method of atmospheric turbulance interference in a kind of FSO

Technical field

The present invention relates to the suppressing method that in a kind of FSO, atmospheric turbulance disturbs, more specifically to one Plant the atmospheric turbulance disturbance restraining method that orbit angular momentum state is multiplexed FSO, research contents belongs at signal of communication Technical field of photo communication in reason.

Background technology

Free sky is had become as based on orbital angular momentum (orbital angular momentum, oam) state multiplex system Between one of the study hotspot that communicates of light (free-space optical, fso).Oam state is one kind of photon angular momentum, with ripple letter The spatial distribution of number is relevant.Different with spin of photon angular momentum (spin angular momentum, sam), for single light Son, in theory oam can obtain infinite many-valued significant condition, and mutually orthogonal between different oam state.Oam state multiplex system energy pole The earth lifting band efficiency.

However, free-space optical communication system is inevitably affected by spatial environmentss, particularly atmospheric turbulance pair The impact that signal transmission produces.Because oam state essence is spatially distributed functions, the multiplex communication system based on oam state can not Avoid being affected by atmospheric turbulance.Atmospheric turbulance not only affects single channel oam state, and leads to generation between oam state of not going the same way Crosstalk.Ren in 2014 et al. proposes to suppress the interference to oam light for the atmospheric turbulance using shark-hadman wave front correction method (ren y,xie g,huang h,et al.adaptive optics compensation of multiple orbital angular momentum beams propagating through emulated atmospheric turbulence [j] .optics letters, 2014,39 (10): 2845-2848.), xie in 2015 et al. proposes with a kind of Wave-front phase school Correction method, improves under atmospheric turbulence channels, performance (xie g, ren y, huang h, the et of oam state multiplex communication system al.phase correction for a distorted orbital angular momentum beam using a zernike polynomials-based stochastic-parallel-gradient-descent algorithm[j] .optics letters, 2015,40 (7): 1197-1200.), inventor Zou Li in 2016 proposes one kind and utilizes Multiuser Detection Method suppress atmospheric turbulance interference (zou l, wang l, zhao s m, et al.turbulence mitigation scheme based on multiple-user detection in orbital–angular-momentum multiplexed system[j].chinese physics b,2016.25(11):114215.).But these methods are simple Ground to be treated atmospheric turbulance as a kind of noise jamming of the phase parameter amount of only impact oam light, strongly wants to remove this Noise jamming.However, atmospheric turbulance interference is far from the noise that the simple phase parameter amount causing oam light changes, it can be same The change of the light intensity of Shi Yinqi oam light, and atmospheric turbulance can cause channel fading characteristic, and the above paper of these factors does not all have Consider.The present invention regards the interference through atmospheric turbulance fading channel for the oam Multiplex optical transmission as atmospheric turbulance interference, using sky Between deversity scheme suppression atmospheric turbulance interference, thus lift system communication quality, thus there is important theory significance and application It is worth.

Content of the invention

In order to overcome the above-mentioned deficiencies of the prior art, the present invention proposes atmospheric turbulance in a kind of FSO and does The suppressing method disturbed, step is as follows:

1st step, oam light as modulation carrier wave, by subscriber signal s_kT () is loaded into and is transmitted on oam light, k ∈ [1, N], t represents the moment, and each road oam light is mutually orthogonal；

2nd step, the oam light to n road subscriber signal synthesize, and obtain oam state multiplexed optical；

3rd step, described oam state multiplexed optical pass through m atmospheric turbulence channels respectively, are disturbed by atmospheric turbulance；

4th step, each road oam state multiplexed optical is demultiplexed and oam state conversion, obtaining user can receipt signal y_mk (t), wherein, k ∈ [1, n], m ∈ [1, m]；

5th step, utilization space diversity combining method remove crosstalk between each subscriber signal, obtain the user that receiving terminal recovers Signal

The present invention also with the further feature that

1st, in step 1, it is used index different lg light in azimuth to carry out oam state conversion as oam light, the oam light obtaining ForWherein,

${\lg }_{l_k}(r,\mathrm{\θ})=\sqrt{\frac{2p!}{\mathrm{\π}(p+|l_k\left|\right)!}}\frac{1}{w_0}{\[\frac{\sqrt{2}r}{w_0}\]}^{\left|l_k\right|}\×l_p^{l_k}\[\frac{2r^2}{w_0^2}\]\exp \[\frac{-r^2}{w_0^2}\]\exp (-{\mathrm{il}}_k\mathrm{\θ})$

Wherein l_kFor the azimuth index of the corresponding lg light of kth road subscriber signal, p is radiation index, w₀It is the bundle of Gaussian beam Waist radius, r is the radiation radius of light wave propagation, and θ is the radiation angle of light wave propagation,It is laguerre multinomial.

2nd, in the 2nd step, the light intensity of oam state multiplexed optical is the aperture Coaxial Superimposed of oam light, the multiplexing oam state signal obtaining It is expressed as u_mux(r, θ, t),

$u_{mux}(r,\mathrm{\θ},t)=\underset{k=1}{\overset{n}{\mathrm{\σ}}}{s}_k\left(t\right){\lg }_{l_k}(r,\mathrm{\θ}).$

3rd, in the 3rd step, it is output as by the oam multiplexing optical signal after atmospheric turbulance interference

WhereinFor the corresponding atmospheric turbulance phase screen of m-th channel, n_mT () is the corresponding Gauss of m-th channel White noise signal, m ∈ [1, m].

4th, in the 4th step, by oam multiplexed opticalWith lg lightSeek inner product, obtain n road and contain phase The signal y of closing property_mk(t), It is Conjugate complex number.

Additionally, a kind of the invention allows for space diversity suppression oam multiplexing atmospheric turbulance interference realizing said method Model is it is characterised in that composition includes:

N oam state transducer, for n road subscriber signal is loaded onto oam light, each road oam light is mutually orthogonal；

1 oam state multiplexer, for being synthesized n road oam light, obtains oam state multiplexed optical；

M atmospheric turbulence channels, for carrying out atmospheric turbulance interference space diversity to oam state multiplexed optical respectively；

M oam state demultiplexer, for demultiplexing to the oam state multiplexed optical disturbed through atmospheric turbulance, respectively To n road oam light；

M oam state transducer, demodulates the oam light of corresponding n path channels respectively, and obtaining user can receipt signal y_mk(t), Wherein, k ∈ [1, n], m ∈ [1, m]；

1 oam state space diversity merging receiver, utilization space diversity combining method removes goes here and there between each subscriber signal Disturb, obtain the subscriber signal that receiving terminal recovers

Wherein, atmospheric turbulence channels adopt kolmogorov atmospheric turbulance model.Atmospheric turbulance is equivalent to multiple random The phase screen producing, between two neighboring phase screen at equal intervals.

Gauss light is converted into oam light by spatial light modulator by the present invention first, as modulation carrier wave, by user profile It is loaded into and is transmitted on oam light, then the oam light merging of multichannel load information is transferred through different atmospheric turbulence channels, Atmospheric turbulance adopts a kind of kolmogorov atmospheric turbulance model, and atmospheric turbulance is equivalent to multiple phase screen randomly generating, Between two neighboring phase screen at equal intervals.Secondly, the output multi-channel of each atmospheric turbulence channels is distorted change in receiving terminal The oam light of shape is demultiplexed and is demodulated.Due in this multipath signal propagation model transmitting terminal multichannel oam light respectively through difference Atmospheric turbulence channels, each interchannel atmospheric turbulance fading characteristic similar to multiple antennas fading channel model, therefore adopts space Diversity technique suppression atmospheric turbulance interference, receiving terminal passes through space diversity combining technique skill again through the user profile of demultiplexing and demodulation Art recovers the useful signal of each user to greatest extent, and reducing system receipt signal and being disturbed by atmospheric turbulance is affected, and improves System reliability.Therefore, the present invention provides reference for the practical of free space orbit angular momentum state multiplexed optical communications.

To sum up, beneficial effects of the present invention are as follows:

1st, by oam multiplexed signals through different atmospheric turbulence channels transmission, air is regarded in optical signal interference in each road as to the present invention Turbulent flow influence of fading, free space diversity models treated.

2nd, utilization space diversity and combining techniques of the present invention, eliminate interfering between user in receiving terminal, reach raising The purpose of receipt signal correctness.

Brief description

Fig. 1 is a kind of space diversity suppression oam multiplexing atmospheric turbulance interference model proposed by the present invention.

Fig. 2 passes through and the qpsk planisphere without space diversity for the present invention.

Fig. 3 receives the bit error rate for the present invention and changes numerical simulation figure with atmospheric turbulance.

Specific embodiment

The present invention will be further described with specific embodiment below in conjunction with the accompanying drawings.

Fig. 1 is that a kind of space diversity proposed by the present invention suppresses oam atmospheric turbulance interference model, and this model is as shown in Figure 1 Include successively from left to right:

N oam state transducer, for n road subscriber signal is loaded onto oam light, each road oam light is mutually orthogonal；

1 oam state multiplexer, for being synthesized n road oam light, obtains oam state multiplexed optical；

M atmospheric turbulence channels, for carrying out atmospheric turbulance interference space diversity to oam state multiplexed optical respectively；

M oam state demultiplexer, for demultiplexing to the oam state multiplexed optical disturbed through atmospheric turbulance, respectively To n road oam light；

M oam state transducer, demodulates the oam light of corresponding n path channels respectively, and obtaining user can receipt signal y_mk(t), Wherein, k ∈ [1, n], m ∈ [1, m]；

1 oam state space diversity merging receiver, utilization space diversity combining method removes goes here and there between each subscriber signal Disturb, obtain the subscriber signal that receiving terminal recovers

The orbit angular momentum state based on space diversity technology for the embodiment of the present invention is multiplexed the air in FSO Turbulent flow disturbance restraining method, step is as follows:

1st step, oam light as modulation carrier wave, by subscriber signal s_kT () is loaded into and is transmitted on oam light, k ∈ [1, N], t represents the moment, and each road oam light is mutually orthogonal.In this step, the lg light being used azimuth index different is carried out as oam light Oam state is changed, and the oam light obtaining isWherein,

${\lg }_{l_k}(r,\mathrm{\θ})=\sqrt{\frac{2p!}{\mathrm{\π}(p+|l_k\left|\right)!}}\frac{1}{w_0}{\[\frac{\sqrt{2}r}{w_0}\]}^{\left|l_k\right|}\×l_p^{l_k}\[\frac{2r^2}{w_0^2}\]\exp \[\frac{-r^2}{w_0^2}\]\exp (-{\mathrm{il}}_k\mathrm{\θ})$

Wherein l_kFor the azimuth index of the corresponding lg light of kth road subscriber signal, p is radiation index, w₀It is the bundle of Gaussian beam Waist radius, r is the radiation radius of light wave propagation, and θ is the radiation angle of light wave propagation,It is laguerre multinomial.l_kFor oam light Topological charge, l_kBigger, corresponding oam light intensity iris radius are bigger.Gained oam light intensity is shown in that the oam state transducer output ring of light shows.

2nd step, the oam light to n road subscriber signal synthesize, and obtain oam state multiplexed optical.In walking in this step, oam state The light intensity of multiplexed optical is the aperture Coaxial Superimposed of oam light, sees ring of light stacking chart shown in the output of oam state multiplexer.The multiplexing obtaining Oam state signal is expressed as u_mux(r, θ, t),

$u_{mux}(r,\mathrm{\θ},t)=\underset{k=1}{\overset{n}{\mathrm{\σ}}}{s}_k\left(t\right){\lg }_{l_k}(r,\mathrm{\θ}).$

3rd step, described oam state multiplexed optical pass through m atmospheric turbulence channels respectively, are disturbed by atmospheric turbulance, obtain oam multiple Use space diversity transmission model.Assume there are m atmospheric turbulence channels, affected by atmospheric turbulance, also contain white Gaussian noise simultaneously Each channel oam multiplexing optical signal of impact is output as

Wherein,For the corresponding atmospheric turbulance phase screen of m-th channel, n_mT () is the corresponding height of m-th channel This white noise signal, m ∈ [1, m].

4th step, by the reception multiplexed signals through space diversity transmissionCarry out demultiplexing and oam state turns Change, obtaining user can receipt signal y_mk(t), wherein, k ∈ [1, n], m ∈ [1, m].In this step, multiplexed signals is demultiplexed With changing with oam state, its simulation process can be calculated with a step:

By oam multiplexed opticalWith lg lightSeek inner product, obtain the signal that dependency is contained on n road y_mk(t), It isConjugate complex Number.

5th step, utilization space diversity combining method remove crosstalk between each subscriber signal, obtain the user that receiving terminal recovers Signal

In order to verify a kind of orbit angular momentum state multiplexing free space based on space diversity technology proposed by the invention Atmospheric turbulance disturbance restraining method in optic communication, is now verified by numerical simulation.The light source ripple that this numerical simulation uses A length of λ=1550nm, waist radius w₀=0.035m, atmospheric turbulance is by the equidistant analogue transmission 1000 of 10 random phase screens Rice, yardstick l in turbulent flow₀=0.001m, external measurement l₀=50m, oam state multiplexed optical azimuth index selection l=+1 ,+2 ,+3 ,+4.

It is respectively shown in Fig. 2, Fig. 3 and uses space diversity technology and not using under space diversity technology, system qpsk is believed Number planisphere and system receive the bit error rate and change numerical simulation figure with atmospheric turbulance construction of indexes constant.Result of study shows, profit The constellation plot quality of qpsk signal can be obviously improved with space diversity method, simultaneously when signal to noise ratio is equal to 20db, moderate strength Under turbulent flow and weak turbulent flow, using space diversity technology, than not, using space diversity technology, the system reception bit error rate is low, performance Good；In atmospheric turbulance construction of indexes constantWhen, do not divided using space using space diversity technology ratio Collection technology, system receives bit error rate performance and lifts 3 orders of magnitude, even in medium turbulent flowWhen, it is System receives bit error rate performance and can also lift the 1-2 order of magnitude, and other methods all cannot accomplish this degree substantially.Therefore, use Space diversity technical method can be obviously improved oam multiplexing free-space optical communication system unfailing performance.

In addition to the implementation, the present invention can also have other embodiment.All employing equivalents or equivalent transformation shape The technical scheme becoming, all falls within the protection domain of application claims.

Claims (6)

1. the suppressing method that in a kind of FSO, atmospheric turbulance disturbs, step is as follows:

1st step, oam light as modulation carrier wave, by subscriber signal s_kT () is loaded into and is transmitted on oam light, k ∈ [1, n], t generation In the table moment, each road oam light is mutually orthogonal；

2nd step, the oam light to n road subscriber signal synthesize, and obtain oam state multiplexed optical；

3rd step, described oam state multiplexed optical pass through m atmospheric turbulence channels respectively, are disturbed by atmospheric turbulance；

4th step, each road oam state multiplexed optical is demultiplexed and oam state conversion, obtaining user can receipt signal y_mk(t), its In, k ∈ [1, n], m ∈ [1, m]；

5th step, utilization space diversity combining method remove crosstalk between each subscriber signal, obtain the subscriber signal that receiving terminal recovers

2. in FSO according to claim 1 atmospheric turbulance interference suppressing method it is characterised in that: step In rapid 1, it is used index different lg light in azimuth to carry out oam state conversion as oam light, the oam light obtaining isWherein,

${\lg }_{l_k}(r,\mathrm{\θ})=\sqrt{\frac{2p!}{\mathrm{\π}(p+|l_k\left|\right)!}}\frac{1}{w_0}{\[\frac{\sqrt{2}r}{w_0}\]}^{\left|l_k\right|}\×l_p^{l_k}\[\frac{2r^2}{w_0^2}\]\exp \[\frac{-r^2}{w_0^2}\]\exp (-{\mathrm{il}}_k\mathrm{\θ})$

Wherein l_kFor the azimuth index of the corresponding lg light of kth road subscriber signal, p is radiation index, w₀It is with a tight waist the half of Gaussian beam Footpath, r is the radiation radius of light wave propagation, and θ is the radiation angle of light wave propagation,It is laguerre multinomial.

3. in FSO according to claim 1 atmospheric turbulance interference suppressing method it is characterised in that: the In 2 steps, the light intensity of oam state multiplexed optical is the aperture Coaxial Superimposed of oam light, and the multiplexing oam state signal obtaining is expressed as u_mux(r, θ, t),

$u_{mux}(r,\mathrm{\θ},t)=\underset{k=1}{\overset{n}{\σ}}{s}_k\left(t\right){\lg }_{l_k}(r,\mathrm{\θ}).$

4. in FSO according to claim 1 atmospheric turbulance interference suppressing method it is characterised in that: institute State in the 3rd step, be output as by the oam multiplexing optical signal after atmospheric turbulance interference

WhereinFor the corresponding atmospheric turbulance phase screen of m-th channel, n_mT () is the corresponding Gauss white noise of m-th channel Acoustical signal, m ∈ [1, m].

5. in FSO according to claim 1 atmospheric turbulance interference suppressing method it is characterised in that: institute State in the 4th step, by oam multiplexed opticalWith lg lightSeek inner product, obtain the letter that dependency is contained on n road Number y_mk(t), It isConjugate complex Number.

6. a kind of space diversity suppression realizing the suppressing method of atmospheric turbulance interference in FSO described in claim 1 Oam multiplexing atmospheric turbulance interference model processed is it is characterised in that composition includes:

N oam state transducer, for n road subscriber signal is loaded onto oam light, each road oam light is mutually orthogonal；

1 oam state multiplexer, for being synthesized n road oam light, obtains oam state multiplexed optical；

M atmospheric turbulence channels, for carrying out atmospheric turbulance interference space diversity to oam state multiplexed optical respectively；

M oam state demultiplexer, for demultiplexing to the oam state multiplexed optical disturbed through atmospheric turbulance, respectively obtains n Road oam light；

M oam state transducer, demodulates the oam light of corresponding n path channels respectively, and obtaining user can receipt signal y_mk(t), wherein, K ∈ [1, n], m ∈ [1, m]；

1 oam state space diversity merging receiver, utilization space diversity combining method removes crosstalk between each subscriber signal, obtains Obtain the subscriber signal that receiving terminal recovers