CN107222261B - The optimization method of multiple light courcess multi-carrier visible light communication system under non-flat forms channel - Google Patents
The optimization method of multiple light courcess multi-carrier visible light communication system under non-flat forms channel Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
- H04B10/116—Visible light communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
- H04B10/505—Laser transmitters using external modulation
- H04B10/5057—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output
- H04B10/50575—Laser transmitters using external modulation using a feedback signal generated by analysing the optical output to control the modulator DC bias
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- H—ELECTRICITY
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- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/50—Transmitters
- H04B10/501—Structural aspects
- H04B10/503—Laser transmitters
- H04B10/505—Laser transmitters using external modulation
- H04B10/5059—Laser transmitters using external modulation using a feed-forward signal generated by analysing the optical or electrical input
- H04B10/50595—Laser transmitters using external modulation using a feed-forward signal generated by analysing the optical or electrical input to control the modulator DC bias
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
- H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
- H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
- H04B7/0613—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
- H04B7/0615—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
- H04B7/0617—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal for beam forming
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- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
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Abstract
The invention discloses a kind of optimization methods of multiple light courcess multi-carrier visible light communication system under non-flat forms channel, include the following steps: the parameter of (1) setting multiple light courcess multi-carrier visible light communication system, including channel parameter, noise size and maximum luminous power, to maximize data rate R as objective optimization；(2) direct current biasing b is optimized, the direct current biasing b after being optimized*；(3) normalization beam shapes vector { ukOptimize, k=1 ..., K-1, wherein K is the total number of subcarrier, and the normalization beam after being optimized shapes vector(4) vector is shaped according to the normalization beam after optimizationObtain the beamforming vectors ω of near-optimization*.Optimization method of the invention does not need additionally to change the external conditions such as system hardware, only by simply calculating, can greatly promote system performance；When the maximum luminous power of system is by limited time, the system light intensity after optimization is able to maintain constant, can take into account illumination；Optimization method fast convergence rate of the present invention, it is easy to accomplish, robustness is high.
Description
Technical field
The present invention relates to visible light communication field, multiple light courcess multicarrier visible light communication under especially a kind of non-flat forms channel
The optimization method of system.
Background technique
Visible light communication (VLC) is a kind of emerging access technology, has taken into account illumination and communication, has been able to satisfy high-speed data industry
Business, possess including low in cost, green safe, good confidentiality, be easily achieved, Electro Magnetic Compatibility fortunately in numerous advantages.
A large amount of broadband visible light communication systems use multi-transceiver technology, and multi-transceiver technology is easily achieved, can obtain higher
Spectrum efficiency and power efficiency.Multi-transceiver technology and visible light communication technology are combined, it is made to have had both visible light communication
It is a kind of technology with higher research significance and practical value with the advantage of multi-transceiver technology.
Unlike conventional radio frequency wireless communication, it is seen that optic communication use intensity modulation directly detection (IM/DD) is sent out
End light strong representation signal amplitude is penetrated, light intensity is detected to eat in receiving end.Electric signal is changed into light by LED by transmitting terminal
Signal converts optical signals to electric signal by photodiode in receiving end after dissemination channel, at demodulator circuit
Reason.It is light intensity due to sending signal vehicle, thus requires to send signal be nonnegative real number.
It is necessary for nonnegative real number due to sending signal, the multi-transceiver technology in conventional radio frequency needs improvement that can just be applied to can
The light-exposed communications field.Direct current biasing OFDM multi-carrier technology (Direct-Current-Biased Optical
OFDM, abbreviation DCO-OFDM) one of as many evolutionary approach, there is high excellent of spectrum efficiency compared to other schemes
Gesture.DCO-OFDM has been superimposed DC component on sending signal, the part after superposition still less than zero is pruned, so that bipolar
Property signal becomes unipolar signal, to meet the condition of signal nonnegativity in visible light communication.
In DCO-OFDM system, direct current biasing is adjustable, but does not transmit signal.The effective information of signal is by passing
The waveform of defeated effective power driving carries, and effective power is determined by beamforming vectors.Excessive direct current biasing can waste energy,
And too small it will lead to signal Severe distortion；Excessive effective power can reinforce signal but can aggravate slicing.Direct current biasing and have
Imitate power simultaneously by optical power limit, it is desirable to provide a desired illumination level, thus need to design one it is most suitable
The compromise proposal of direct current biasing and effective power.
Visible light communication channel is usually direct-view diameter in nature, for illuminating and communicating under complicated indoor environment
For all exist and different degrees of block influence.Under normal circumstances, lighting system is to be made of multichannel light source, therefore visible light is logical
It can use multiple light courcess in letter system and increase system robustness, eliminate complicated indoor environment to the unfavorable shadow of illumination and communication
It rings.Multiple light courcess can provide higher transmission rate and better communication quality, to need to reach with eye required illumination safely
Strength control provides flexibility ratio.
Summary of the invention
Technical problem to be solved by the present invention lies in it is logical to provide multiple light courcess multicarrier visible light under a kind of non-flat forms channel
The optimization method of letter system can provide the direct current biasing and beamforming vectors for maximizing system velocity.
In order to solve the above technical problems, the present invention provides multiple light courcess multicarrier visible light communication system under a kind of non-flat forms channel
The optimization method of system, includes the following steps:
(1) parameter of multiple light courcess multi-carrier visible light communication system, including channel parameter, noise size and maximum light are set
Power, to maximize data rate R as objective optimization；
(2) direct current biasing b is optimized, the direct current biasing b after being optimized*；
(3) normalization beam shapes vector { ukOptimize, k=1 ..., K-1, wherein K is the total number of subcarrier,
Normalization beam after being optimized shapes vector
(4) vector is shaped according to the normalization beam after optimizationObtain the beamforming vectors ω of near-optimization*。
Preferably, direct current biasing b is optimized in step (2), is specifically comprised the following steps:
(21) it introduces intermediate variable and simplifies problem, normalize to obtain direct current biasing by effective power, take its negative conduct
Intermediate variableWhereinIt is transmission effective power；
(22) consider the situation under flat channel, solve optimal intermediate variable x*=x*1, wherein x*=argxf(x；
γt)=0,γ in formulaiIt is the signal-to-noise ratio of the i-th road light source,
It is total signal-to-noise ratio of whole system, wherein φ (x) is the probability density function of standardized normal distribution, and Q (x) is Normal Integral letter
Number；(23) approximate solution under non-flat forms channel in the case of high s/n ratio is similar to the optimal solution x in the case of flat channelA=xA·
1, wherein xA=argxf(x；γA)=0,In formulakm
It is the number of effective subcarrier,It is total signal-to-noise ratio on k-th of subcarrier, γi,kIt is the i-th road light source
The signal-to-noise ratio of k subcarrier；
(24) result approximate solution x is utilizedACalculate the direct current biasing of near-optimizationWhereinIt is average light power,It is the average light power of the i-th road light source.
Preferably, Equation f (x is solved in step (23)；γAThe root x of)=0AMethod: dichotomy.
Preferably, optimal normalization beam is solved in step (3) shape vector uk, specifically comprise the following steps；
(31) normalization beam forming matrix is defined
(32) optimal solution is soughtWherein ()+=max, 0 },λ meetsgkIt is the equivalent channel of k-th of subcarrier
Gain.
Preferably, equivalent channel gain g in step (32)kDefinition content:Wherein hkIt is
Channel coefficient vector,It is ambient noise, A is the damping matrix of clipping procedure, A=Diag (a),
C is defined as:
Preferably, vector is shaped according to the normalization beam after optimization in step (4)Obtain the wave beam of near-optimization at
Shape vector ω*, specifically comprise the following steps:
(41) according to power constraints, available effective powerWherein qo(xi)=φ
(xi)-xiQ(xi)；
(42) the approximate solution x of the intermediate variable found out according to step (23)A, find out corresponding effective powerFurther find out the approximate solution of normalization beam forming vector
(43) approximate solution of vector is shaped according to normalization beamFind out near-optimization beamforming vectors
The invention has the benefit that (1) this optimization method is logical for multiple light courcess multicarrier visible light under non-flat forms channel
The case where believing system optimization method, including direct current biasing and beamforming vectors combined optimization, and considering optical power limit, this
Invention has very strong practical value；(2) optimization method of the invention passes through the DCO-OFDM visible light communication to multiple light courcess
Nonlinear process modeling in system takes out the mathematical form of the problem, which is a complicated nonlinearity
Non-convex optimization problem, it is understood that there may be multiple local maximums, the present invention is based on the equivalence transformations to the problem to give specific calculation
Method can obtain accurate optimal solution；(3) this optimization method does not need additionally to change the external conditions such as system hardware, only passes through
It is simple to calculate, system performance can be greatly promoted.The direct current biasing b and beamforming vectors w obtained using this optimization method
The data rate of system can be maximized；(4) when the maximum luminous power of system is by limited time, the system light intensity after optimization is able to maintain
It is constant, illumination can be taken into account；(5) optimization method fast convergence rate of the present invention, it is easy to accomplish, as a result precision is high, and robustness is high.
Detailed description of the invention
Fig. 1 is the emitter structures schematic diagram of multiple light courcess multi-carrier visible light communication system of the invention.
Fig. 2 is method flow schematic diagram of the invention.
Fig. 3 is under non-flat forms channel of the present invention in two-way light-source system, relative to the number of signal-to-noise ratio under Different Optimization strategy
According to rate comparison schematic diagram.
Fig. 4 is the system data rates comparison under non-flat forms channel of the present invention under different signal-to-noise ratio, under Different Optimization strategy
Schematic diagram.
Fig. 5 is the system data rates under different channels status information under non-flat forms channel of the present invention under different signal-to-noise ratio
Contrast schematic diagram.
Specific embodiment
As shown in Fig. 2, under a kind of non-flat forms channel multiple light courcess multi-carrier visible light communication system optimization method, including such as
Lower step:
(1) parameter of multiple light courcess multi-carrier visible light communication system, including channel parameter, noise size and maximum light are set
Power, to maximize data rate R as objective optimization；
(2) direct current biasing b is optimized, the direct current biasing b after being optimized*；
(3) normalization beam shapes vector { ukOptimize, k=1 ..., K-1, the normalization beam after being optimized
Shape vector
(4) vector is shaped according to the normalization beam after optimizationObtain the beamforming vectors ω of near-optimization*。
Direct current biasing b is optimized in step (2), is specifically comprised the following steps:
(21) it introduces intermediate variable and simplifies problem, normalize to obtain direct current biasing by effective power, take its negative conduct
Intermediate variableWhereinIt is transmission effective power, effective transmission on every paths of LEDs
Power
(22) consider the situation under flat channel, solve optimal intermediate variable x*=x*1, wherein x*=argxf(x；
γt)=0,In formulaIt is total signal-to-noise ratio of whole system, γi
It is the signal-to-noise ratio of the i-th road light source, wherein φ (x) is the probability density function of standardized normal distribution, and Q (x) is Normal Integral function；
(23) approximate solution under non-flat forms channel in the case of high s/n ratio is similar to the optimal solution x in the case of flat channelA
=xA1, wherein xA=argxf(x；γA)=0,In formulakmIt is the number of effective subcarrier,It is total signal-to-noise ratio on k-th of subcarrier,
γi,kIt is signal-to-noise ratio of the i-th road light source in k-th of subcarrier；Solve Equation f (x；γAThe root x of)=0AMethod: dichotomy；
(24) result approximate solution x is utilizedACalculate the direct current biasing of near-optimizationWhereinIt is average light power,It is the average light power of the i-th road light source.
Optimal normalization beam is solved in step (3) shapes vector uk, specifically comprise the following steps；
(31) normalization beam forming matrix is defined
(32) optimal solution is asked to beWherein ()+=max, 0 },λ meetsgkIt is the equivalent channel of k-th of subcarrier
Gain.
Equivalent channel gain g in step (32)kDefinition content:Wherein hkIt is channel system
Number vector,It is ambient noise, A is the damping matrix of clipping procedure, A=Diag (a),C definition
Are as follows:
Vector is shaped according to the normalization beam after optimization in step (4)Obtain the beamforming vectors of near-optimization
ω*, specifically comprise the following steps:
(41) according to power constraints, available effective powerWherein qo(xi)=φ
(xi)-xiQ(xi)；
(42) the approximate solution x of the intermediate variable found out according to step (2.3)A, find out corresponding effective powerFurther find out the approximate solution of normalization beam forming vector
(43) approximate solution of vector is shaped according to normalization beamFind out near-optimization beamforming vectors
Fig. 1 is the transmitter block diagram of multiple light courcess multi-carrier visible light communication system.If DCO-OFDM system in the present embodiment
Sub-carriers sum is 2K, if provided method is modulated to obtain symbol z k-th of subcarrier through the inventionk, and into
Traveling wave beam shaping handles to obtain transmission signal sk=ωkzk.Since optic communication requires output time-domain signal for real number, thus frequency domain
Signal needs to meetAnd s0=sK=0.Due toBring symmetry, so in the present embodiment only
Consider sk, k=1 ..., K-1.Time-domain signal s (n) is obtained by fast discrete Fourier inverse transformation (IFFT).Then i-th
Time-domain signal s on the light source of roadi(n) it is b that size is superimposed oniDC component obtain sdc,i(n)=si(n)+bi, and by signal
It prunes to meet nonnegativity requirement, i.e. s part after superposition DC component still less than zerodc,i(n)=sdc,i(n)u(sdc,i
(n)), wherein u (sdc,iIt (n)) is unit-step function.Finally, digital signal sdc,i(n) pass through digital simulation converter (D/A)
Signal s is obtained with LEDdc,i(t)。sdc,i(t) optical power is limited, it is believed that the optical power size for exporting channel is
By taking optical power more typical in visible light communication system is limited as an example, target is turned to system velocity maximum, is calculated
Optimal direct current biasing b and beamforming vectors ω.
Specific implementation step is as follows:
(1) parameter setting: multiple light courcess multi-carrier visible light communication system is obtained in optical power by maximum luminous power in limited timeThe noise power of systemWith the signal-to-noise ratio γ of k-th of subcarrier on the i-th road light sourcei,k, the number k of effective subcarrierm；
Define standard normal distribution functionWith Normal Integral function
(2) x is calculatedA=xA1, wherein xA=argxf(x；γA)=0,In formulakmIt is the number of effective subcarrier,It is total signal-to-noise ratio on k-th of subcarrier；
(3) according to xAObtain near-optimization direct current biasingWith near-optimization effective powerWherein qo(xi)=φ (xi)-xiQ(xi)；
(4) according to b*And σ*Find out corresponding equivalent channel gain gk, calculate near-optimization normalization beam shape to
AmountWherein ()+=max, 0 },λ meets
(5) vector is shaped using the normalization beam of near-optimizationObtain near-optimization beamforming vectors are as follows:
Fig. 3 is the data under Different Optimization strategy relative to each road signal-to-noise ratio under non-flat forms channel in two-way light-source system
Rate comparison schematic diagram.It is inclined that direct current biasing beamforming vectors short cut technique combined optimization proposed by the present invention, direct current are compared respectively
Beamforming vectors are set to search thoroughly under the strategy of method combined optimization, fixed direct current biasing b=2 σ and b=4.4 σ relative to signal-to-noise ratio
Data rate, it is known that the system performance under the method proposed through the invention is carried out close to the system performance searched under method thoroughly
The data rate of system after combined optimization is apparently higher than the system under the strategy of fixed direct current biasing, the system performance after optimization
It is in close proximity to algorithm globally optimal.
Fig. 4 is the system data rates contrast schematic diagram under Different Optimization strategy.It is inclined to direct current proposed by the present invention respectively
Set beamforming vectors short cut technique combined optimization, direct current biasing beamforming vectors search method combined optimization thoroughly, fixed direct current biasing b
Data rate under the different situations of=σ, b=2 σ and b=4.4 σ, the system performance under the method proposed through the invention are close
Search thoroughly and method and evenly distribute the system performance under beamforming vectors, the method proposed through the invention optimize after system
Data rate be apparently higher than the systematicness than the system under single optimization direct current biasing and fixed direct current biasing strategy, after optimization
Algorithm globally optimal can be in close proximity to.
Fig. 5 is the system data rates pair under different channels status information (CSI) under non-flat forms channel under different signal-to-noise ratio
Compare schematic diagram.The system data rates under different channels status information (CSI) are compared respectively, it is known that the connection proposed through the invention
It is insensitive for channel state information to close optimization method, robustness is high.
Although the present invention is illustrated and has been described with regard to preferred embodiment, it is understood by those skilled in the art that
Without departing from scope defined by the claims of the present invention, variations and modifications can be carried out to the present invention.
Claims (3)
1. the optimization method of multiple light courcess multi-carrier visible light communication system under a kind of non-flat forms channel, which is characterized in that including such as
Lower step:
(1) parameter of multiple light courcess multi-carrier visible light communication system, including channel parameter, noise size and maximum light function are set
Rate, to maximize data rate R as objective optimization；
(2) direct current biasing b is optimized, the direct current biasing b after being optimized*；Specifically comprise the following steps:
(21) it introduces intermediate variable and simplifies problem, normalize to obtain direct current biasing by effective power, take its negative as intermediate
VariableWhereinIt is transmission effective power, effective transimission power on every paths of LEDs
(22) consider the situation under flat channel, solve optimal intermediate variable x*=x*1, wherein x*=argxf(x；γt)=
0,WhereinIt is total signal-to-noise ratio of whole system, γiIt is
The signal-to-noise ratio of the road i light source, φ (x) are the probability density functions of standardized normal distribution, and Q (x) is Normal Integral function；
(23) approximate solution under non-flat forms channel in the case of high s/n ratio is similar to the optimal solution x in the case of flat channelA=xA·
1, wherein xA=argxf(x；γA)=0,In formulakm
It is the number of effective subcarrier,It is total signal-to-noise ratio on k-th of subcarrier, γi,kIt is the i-th road light source
The signal-to-noise ratio of k subcarrier；
(24) result approximate solution x is utilizedACalculate the direct current biasing of near-optimizationWherein
It is average light power,It is the average light power of the i-th road light source；
(3) normalization beam shapes vector { ukOptimize, k=1 ..., K-1, wherein K is the total number of subcarrier, is obtained
Normalization beam after optimization shapes vectorSpecifically comprise the following steps；
(31) normalization beam forming matrix is defined
(32) it solves optimalWherein ()+=max, 0 },λ meetsgkIt is the equivalent channel of k-th of subcarrier
Gain；
(4) vector is shaped according to the normalization beam after optimizationObtain the beamforming vectors ω of near-optimization*；Specific packet
Include following steps:
(41) according to power constraints, available effective powerWherein qo(xi)=φ (xi)-
xiQ(xi)；
(42) the approximate solution x of the intermediate variable found out according to step (23)A, find out corresponding effective powerFurther find out the approximate solution of normalization beam forming vector
(43) approximate solution of vector is shaped according to normalization beamFind out near-optimization beamforming vectors
2. the optimization method of multiple light courcess multi-carrier visible light communication system under non-flat forms channel as described in claim 1, special
Sign is, Equation f (x is solved in step (23)；γAThe root x of)=0AMethod: dichotomy.
3. the optimization method of multiple light courcess multi-carrier visible light communication system under non-flat forms channel as described in claim 1, special
Sign is, equivalent channel gain g in step (32)kDefinition content:Wherein hkIt is channel coefficients
Vector,It is ambient noise, A is the damping matrix of clipping procedure,C is defined as:
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