CN106411403A - Ultra-wide brightness adjustment visible light transmission method based on clipping movement - Google Patents

Ultra-wide brightness adjustment visible light transmission method based on clipping movement Download PDF

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Publication number
CN106411403A
CN106411403A CN201610542520.4A CN201610542520A CN106411403A CN 106411403 A CN106411403 A CN 106411403A CN 201610542520 A CN201610542520 A CN 201610542520A CN 106411403 A CN106411403 A CN 106411403A
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ofdm
length
rsqb
lsqb
lambda
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CN201610542520.4A
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CN106411403B (en
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孔令恺
曹聪聪
李孟超
张思源
吴亮
张在琛
党建
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东南大学
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114Indoor or close-range type systems
    • H04B10/116Visible light communication
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/501Structural aspects
    • H04B10/502LED transmitters
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/516Details of coding or modulation
    • H04B10/5165Carrier suppressed; Single sideband; Double sideband or vestigial
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/50Transmitters
    • H04B10/564Power control
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2626Arrangements specific to the transmitter only

Abstract

The invention discloses an ultra-wide brightness adjustment visible light transmission method based on clipping movement. The method is characterized in that an original DCO-OFDM (DC-biased Optical Orthogonal Frequency Division Multiplexing) time domain symbol without direct-current bias is multiplied by a control factor, and an OFDM sub-frame of which the length is N is added to carry a negative value of a part of information exceeding an LED (Light-Emitting Diode) linear range after the part of information is added with the direct current bias, so that a system reaches a stable state which is irrelevant to a direct-current bias value; light intensity is adjusted by adjustment of the direct-current bias value and the control factor; and a reachable brightness adjustment range is determined by the control factor. The system performance can reach the stable state in which the performance is not influenced by the magnitude of the direct-current bias value, so that the light intensity can be adjusted easily by adjustment of the direct-current bias value and the control factor; an ultra-wide light adjustment range is achieved; and meanwhile, a relatively high transmission rate can still be kept.

Description

A kind of transmission of visible light method is lightened based on the ultra-wide that slicing is moved
Technical field
The invention belongs to technical field of visible light communication, particularly to a kind of wireless optical transmission method.
Background technology
Visible light communication as one of future mobile communications key technology has the spies such as green, safety, wide available frequency band Point, is one for frequency spectrum resource Radio-Frequency Wireless Communication in short supply and supplements well.OFDM technology can not only be effectively Strengthen message transmission rate, increase system transmission capacity, and can effectively suppress multipath fading and interference, this technology is wide General it is applied in Modern wireless communication.
In intensity modulated direct detection optical communication system, the information of required transmission is represented by the intensity of optical signal, this Can be non-negative unipolar real signal, photoreceiver utilizes square-law detector Direct-detection Optical signal strength.Existing several suitable OFDM mode for intensity modulated, direct detection optic communication is suggested, including:OFDM (DC-biased based on direct current biasing Optical OFDM, DCO-OFDM), OFDM (Asymmetric clipping optical OFDM, the ACO- of asymmetric pruning OFDM).
Dimming control technique allows people to adjust room lighting feelings according to oneself requirement to lighting intensity Condition, realizes effective energy-conservation.In traditional DCO-OFDM system, dimming control technique can be divided into analog-modulated and numeral to adjust Two ways processed, that is, at present the wide continuous current of application adjust (Continuous Current Reduction, CCR) and Pulse width modulation (Pulse Width Modulation, PWM).First method is simple, stable, but due to LED light wire Property scope restriction so that when light modulation depth is relatively low or higher truncation noise excessive, dimming scope very little in this way. Generally use PWM at present, this method can sufficiently utilize the range of linearity of LED.
Due to the restriction of the LED range of linearity, when the dc-bias of DCO-OFDM is excessive or too small, the blocking of system Noise is very big, leads to the method adjusting light intensity in system traditional in actual applications by dc-bias can reach Scope too small.
Content of the invention
It is an object of the invention to provide a kind of lighten transmission of visible light method based on the ultra-wide that slicing is moved, existing to solve Adjust too small the asking of scope that the method for light intensity can reach by dc-bias in traditional system present in technology Topic.
For achieving the above object, the technical solution used in the present invention is:
A kind of transmission of visible light method lightened based on the ultra-wide that slicing is moved, by by script not plus direct current biasing Then plus length is the OFDM subframe of N DCO-OFDM time-domain symbol is first multiplied by controlling elements, carries that to add direct current inclined Postpone the negative value of the part information that can exceed LED linear scope;System is made to reach the stable shape unrelated with dc-bias State, thus adjusting light intensity by regulation direct-current bias value and controlling elements, the scope that lightens that can reach is determined by controlling elements Fixed.
The present invention comprises the following steps that:
Step one, obtains not adding the time-domain signal x [n] of the DCO-OFDM of direct current biasing according to conventional method first, more right Time-domain signal now is multiplied by controlling elements α, i.e. xd[n]=α x [n];Then, the OFDM subframe that a length is N is added to use To carry the negative value of this partial information that can exceed LED linear scope plus direct current biasing;X after then slicing is movedud[n] and x'ud[n] forms a data pair, wherein n=1,2,3 ..., N-1;
Step 2, more respectively to xud[n] and x'ud[n] this two subframes add Cyclic Prefix it is assumed that the length of Cyclic Prefix Spend for △, then △ chronomere of time delay N+ to be carried out frame multiplexing and finally plus required compared to the first subframe by the second subframe The dc-bias wanted;So final OFDM symbol x sending "ud[n] length is 2 (N+ △);
Step 3, after optical channel, through over-sampling and remove Cyclic Prefix, receiving terminal obtains the time domain symbol that length is 2N Number;Again removing DC bias DC is gone to rear N number of sequence, before definition, N length is y1[n], rear N length is y'2[n];Then the former is subtracted Go the latter;I.e. y [n]=y1[n]-y'2[n].;
Y [n] is subsequently carried out serioparallel exchange and removes removing DC bias DC by step 4, then carries out the FFT of N point and go forward side by side Row equilibrium just can obtain demodulated signal.
The formula that slicing moves employing is:
Wherein, [λminmax] representing LED linear scope, DC is direct current biasing.
Beneficial effect:Compared with traditional DCO-OFDM system, the performance of the method for the present invention is up to one and is not subject to directly The stable state of stream biasing size impact, such that it is able to adjust light by simple regulation direct-current bias value and controlling elements By force.The scope that lightens of system is greatly improved.And compared with commonly used PWM method, realizing of the present invention is simpler, Stable.Be embodied in following some:
1st, it is only necessary to be adjusted by adjusting controlling elements and direct current biasing under conditions of limited by the LED range of linearity Light intensity, the control very simple to the light intensity and performance of system is not affected by direct current biasing size, reach one and stablize shape State, the scope that lightens such that it is able to make system is greatly improved and keeps higher transfer rate simultaneously.
2nd, be directed to energy saving and meet green illumination theory it is achieved that not losing information transfer reliability under the premise of Low power illumination regulatory function.Therefore the program has good application prospect in the low place of some illuminances.
3rd, the complexity of the whole system that the method for the present invention is used is relatively low, and transmitter and receiver is all very easily real Existing.
Brief description
Fig. 1 is the system transmitting terminal block diagram that the method for the present invention is used;
Fig. 2 is the system receiving terminal block diagram that the method for the present invention is used;
Fig. 3 is LED nonlinear model figure;
Fig. 4 is that slicing moves schematic diagram, and wherein, LED linear scope is [0,1], DC=0.3;
Fig. 5 is the final time domain beamformer sending, and wherein, LED linear scope is [0,1], DC=0.3;
Fig. 6 is the final frame assumption diagram sending;
Fig. 7 is in target BER=2*10-3The lower present invention and traditional accessible spectrum efficiency of DCO-OFDM and light modulation depth Curve map.
Specific embodiment
Below in conjunction with the accompanying drawings the present invention is further described.
The transmitting terminal of system used in the present invention and receiving terminal flow chart are respectively as depicted in figs. 1 and 2.Traditional DCO- OFDM is affected by truncation noise, and directly adjustment direct current biasing lightens scope very come what the method to adjust light intensity can reach Limited.And the present invention passes through for the time-domain OFDM symbol obtaining to be multiplied by controlling elements α, then with one and former OFDM symbol xud [n] length identical subframe x 'ud[n] is being loaded beyond the negative value of this partial information of the LED range of linearity.Make whole system Reach the stable state unrelated with direct current biasing amount, such that it is able to pass through simple adjustment direct current in the range of a non-constant width Bias to carry out the regulation and control of light intensity with controlling elements.
Below in conjunction with the accompanying drawings the method for the present invention is illustrated more in detail.
(1) in transmitting terminal, the sub-carrier number of ofdm system is N, in all subcarriers onlyIndividual sub- carrier-wave transmission is effective Data.The binary source sequence that transmitting terminal produces modulates (M-QAM) through M-ary Quadrature Amplitude, forms frequency domain to be sent Data, then map that on each subcarrier, and make it meet conjugate symmetry and the 0th andIndividual subcarrier data is 0. The final frequency domain data obtaining is X=[X (0), X (1) ..., X (N-1)], and it meets following property:
AndWherein ()*Represent and take complex conjugate.
(2) time-domain signal that frequency-region signal is transformed to real number through N point IFFT is as follows:
Wherein n represents the position of OFDM time-domain symbol, and j represents imaginary symbols.
(3) pass through pre-distortion technology, the nonlinear characteristic of LED is reduced to the bilateral simplification Mathematical Modeling blocked, such as Shown in Fig. 3.Concrete formula is as follows:
Wherein G (s) represents the LED nonlinear model simplifying, [λmin, λmax] represent LED linear scope.
First controlling elements α are multiplied by time-domain signal now, i.e. xd[n]=α x [n].Traditional DCO-OFDM added After direct current biasing the signal exceeding the LED range of linearity directly can be carried out slicing, this can make when direct current biasing DC less or When higher, the truncation noise of whole system is very big.And here, the present invention adds the OFDM subframe that a length is N in order to hold The negative value of this partial information that load can be shaved.X after then slicing is movedud[n] and x'ud[n] forms a data pair, wherein n =1,2,3 ..., N-1.Concrete slicing move employing formula as follows:
Wherein, [λminmax] representing LED linear scope, DC is direct current biasing.
As shown in figure 4, wherein, LED linear scope is [0,1] to the process that slicing is moved, DC=0.3.Again respectively to xud[n] And x'ud[n] this two subframes add Cyclic Prefix.The length of hypothesis Cyclic Prefix is △, then the second subframe x'ud[n] compared to First subframe xud△ chronomere of time delay N+ is sent by [n].The OFDM symbol time domain waveform finally giving and structure are respectively As shown in Figure 5 and Figure 6.It can be seen that the OFDM symbol length after slicing is moved expands to original twice.
(4) after optical channel, through over-sampling and remove Cyclic Prefix, receiving terminal receives the time-domain symbol that length is 2N. Again removing DC bias DC is gone to rear N number of sequence.Here, before definition, N length is y1[n], rear N length is y'2[n].Then use y1 [n] deducts y'2[n], obtains y [n], that is,:Y [n]=y1[n]-y'2[n].
Subsequently y [n] is carried out serioparallel exchange and remove removing DC bias DC, then carry out after the FFT of N point through equilibrium Device, just can obtain demodulated signal.
(5) average of the final OFDM symbol sending is ID, and this value only also has controlling elements α with direct current biasing DC Relevant.Definition light modulation depth η=(IDmin)/(λmaxmin).Also have the value of controlling elements α by adjusting direct current biasing, permissible Reach the purpose adjusting light intensity.But the performance of system will not be affected by direct current biasing DC size completely, and dimming scope obtains Greatly improve.Achieve the low power illumination regulatory function do not lost under the premise of information transfer reliability.The therefore program is one A little low places of illuminance have good application prospect.
Although the present invention has been multiplied by controlling elements α in transmitting terminal to signal, receiving terminal simultaneously requires no knowledge about this value, this It is because that this coefficient may be considered a part for equivalent channel status information, so the channel estimator of receiving terminal can be estimated Count out this equivalent channel status information so that the equilibrium of rear end.
Fig. 7 illustrates the present invention accessible spectrum efficiency and light modulation depth in the case of limited by the LED range of linearity Curve.Simulated environment is set to:NLOS channel, sub-carrier number N=128, E [x2[n]]=1, noise power is -10dbm, LED linear scope is [0,1].Target bit is 2 10-3.In figure compares DCO-OFDM and the accessible frequency of the present invention Spectrum efficiency and the curve map lightening depth.During emulation, the system being proposed has carried out likelihood filtering in receiving terminal, even (y1[n]+y'2[n])∈[λminmax], then y'2[n] is judged as 0.For the justice comparing, DCO-OFDM is multiplied by time domain One adaptation coefficient is reducing non-linear distortion.As can be seen from the figure the dimming scope of traditional DCO-OFDM is less, Just cannot work on when lightening depth and being higher or lower.And the performance of system used in the present invention is sufficiently stable, permissible Reach and very big lighten scope, and when lightening depth η > 80%, or η<When 20%, system used in the present invention is permissible The spectrum efficiency reaching can exceed DCO-OFDM.When even in extreme circumstances, as η=2%, system still can reach The spectrum efficiency of 0.75bit/s/Hz.
The above be only the preferred embodiment of the present invention it should be pointed out that:Ordinary skill people for the art For member, under the premise without departing from the principles of the invention, some improvements and modifications can also be made, these improvements and modifications also should It is considered as protection scope of the present invention.

Claims (3)

1. a kind of transmission of visible light method is lightened based on the ultra-wide that slicing is moved it is characterised in that:By script is not plus straight The DCO-OFDM time-domain symbol of stream biasing is first multiplied by controlling elements, then plus length is the OFDM subframe of N, carry plus The negative value of the part information of LED linear scope can be exceeded after crossing direct current biasing;System is reached unrelated with dc-bias Stable state, thus adjusting light intensity by regulation direct-current bias value and controlling elements, can reach lightens scope by controlling The factor processed determines.
2. according to claim 1 transmission of visible light method is lightened based on the ultra-wide that slicing is moved it is characterised in that:Specifically Step is as follows:
Step one, obtains not adding the time-domain signal x [n] of the DCO-OFDM of direct current biasing according to conventional method first, then to now Time-domain signal be multiplied by controlling elements α, i.e. xd[n]=α x [n];Then, add the OFDM subframe that a length is N in order to hold Carry the negative value of this partial information that can exceed LED linear scope plus direct current biasing;X after then slicing is movedud[n] and x'ud [n] forms a data pair, wherein n=1,2,3 ..., N-1;
Step 2, more respectively to xud[n] and x'ud[n] this two subframes add Cyclic Prefix it is assumed that the length of Cyclic Prefix is Δ, then the second subframe compared to the first subframe, time delay N+ ΔGe chronomere to be carried out frame multiplexing and finally plus required Dc-bias;So final OFDM symbol x sending "ud[n] length is 2 (N+ Δs);
Step 3, after optical channel, through over-sampling and remove Cyclic Prefix, receiving terminal obtains the time-domain symbol that length is 2N;Again Removing DC bias DC is gone to rear N number of sequence, before definition, N length is y1[n], rear N length is y'2[n];Then after the former being deducted Person;I.e. y [n]=y1[n]-y'2[n].;
Y [n] is subsequently carried out serioparallel exchange and removes removing DC bias DC by step 4, then carries out the FFT of N point and carry out all Weighing apparatus just can obtain demodulated signal.
3. according to claim 2 transmission of visible light method is lightened based on the ultra-wide that slicing is moved it is characterised in that:Step In one, the formula that slicing moves employing is:
( x u d &lsqb; n &rsqb; , x &prime; u d &lsqb; n &rsqb; ) = ( x d &lsqb; n &rsqb; - D C , - D C ) &lambda; min - D C &le; x d &lsqb; n &rsqb; &le; &lambda; max - D C ( &lambda; max - D C , &lambda; max - D C - x d &lsqb; n &rsqb; ) &lambda; max - D C < x d &lsqb; n &rsqb; ( &lambda; min - D C , &lambda; min - D C - x d &lsqb; n &rsqb; ) x d &lsqb; n &rsqb; < &lambda; min - D C
Wherein, [λminmax] representing LED linear scope, DC is direct current biasing.
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