CN105072065A - Precoding and drive current joint optimization method for four-color visible light communication system - Google Patents

Abstract

The invention discloses a precoding and drive current joint optimization method for a four-color visible light communication system, which aims at minimizing sum mean square error (MSE) of signal estimation in a corresponding light channel while lighting quality requirements are met. Compared with the existing three-color visible light communication precoding matrix optimization problem, the four-color visible light communication system adds a light communication wavelength division multiplexing channel, and an ability of adjusting indoor lighting quality is also provided. In view of the optimization problem, nonlinear color rendering index constraints are firstly converted into linear light mixing ratio constraints via linear light mixing equations, and optimization solution is carried out on the MSE minimal value through introducing semidefinite relaxation algorithm.

Description

The precoding of four look visible light communication systems and drive current combined optimization method

Technical field

The invention belongs to the technical field of wireless light communication, particularly relate to a kind of precoding and drive current combined optimization method of four look visible light communication systems.

Background technology

Due to the low cost of LED, long-life and high effect, in nowadays illumination market, LED occupies rapidly main status, substituted for traditional lighting apparatus.The fast switching capability of LED also makes to transmit broadband signal by light simultaneously becomes a kind of possibility, and finally achieves indoor visible light communication (VLC).Although use the high speed VLC system of phosphorus excited white light LED to realize, the limited modulation bandwidth of LED is still the bottleneck that VLC continues development.Therefore, the key factor be applied to continue to promote VLC performance future of the multiple-input and multiple-output (OMIMO) of light.

Multiple-input and multiple-output (OMIMO) system realizing light mainly contains two kinds of approach, space multiple-input and multiple-output (SMIMO) and colour gamut multiple-input and multiple-output (CMIMO).SMIMO channel is mainly realized by LED array imaging on receiving terminal PD array; CMIMO channel is produced by the wavelength division multiplexing of different colours light.Owing to specifying the illumination white light of colour temperature can be synthesized according to a certain percentage by different primary colours, the wavelength division multiplexed channel be parallel to each other in color gamut space is just existed.

Compared to RGB (RGB) three-color LED, a kind of multi-colored led equipment newly engenders in VLC communication system.Four look LED, usually be made up of red, green, blue and yellow (RGBA) four kinds of colors, not only many than RGB three-color LED wavelength division multiplexed channels, and under the colour temperature of specifying synthesize white light, RGBA tetra-look LED has the ability of fine adjustment mixed light color rendering index (CRI).Based on this, while VLC communications system transmission speed is improved, also can well both in-door illumination demand.

Different from traditional radio frequency, the drive current due to LED must be unipolar signal, and this just causes the range constraint of LED very complicated.Under VLC communication scenes, existing a few thing considers the combined optimization design of pre-coding matrix and drive current.Especially, by being quadratic constraints by LED dynamic range constrained approximation, researcher is had to propose to be solved by the method for semi definite programming (SDP) the combined optimization problem of pre-coding matrix and bias current.

When coloured light number is more than 3, consider color rendering index (CRI) constraint, it is a very large challenge that very complicated nonlinear CRI constraint is incorporated in the combined optimization problem of pre-coding matrix and bias current.Existing work only discuss the optimization under RGB three-color LED communication system, and then after colour temperature CT is designated, color rendering index just can not regulate, and is not well positioned to meet the demand of room lighting.

In addition, when existing work only considers that number of data streams is equal with actual physics channel number mostly, pre-coding matrix and bias current are optimized.When number of data streams is less than actual physics channel number, the mean square error (MSE) for the estimated signal of target VLC system will obtain better performance.

Summary of the invention

Technical problem: the invention provides one can at indoor lighting conditions (CT, CRI) under constraint, try to achieve optimum pre-coding matrix and bias current, the mean square error of the estimated signal of four look visible light communication systems is minimized, is applicable to precoding and the drive current combined optimization method of four look visible light communication systems of situation when data fluxion is less than the actual physics number of channel simultaneously.

Technical scheme: the precoding of four look visible light communication systems of the present invention and drive current combined optimization method, travels through all feasible zone [α that the power α of the yellow light LED meeting colour temperature constraint and color rendering index constraint is corresponding _i, α _j], obtain feasible zone [α that is all and α _i, α _j] corresponding local optimum pre-coding matrix, therefrom choose local optimum pre-coding matrix corresponding to least mean-square error as the optimum pre-coding matrix F of four look visible light communication systems _opt, choose local optimum drive current corresponding to least mean-square error as the optimum drive current b of four look visible light communication systems _opt;

Wherein each feasible zone of power α is processed, determine and feasible zone [α _i, α _j] concrete steps of corresponding local optimum pre-coding matrix are:

(1) the colour temperature constraint according to following formula, choose the initial driving current b (0) that can blend together white light:

KDb(0)＝α ₀c ₁+c ₂

Wherein, K is the transition matrix gathered together by homochromy LED, and D is the conversion coefficient of LED drive current vector and light intensity vector, α ₀for the power of initial yellow light LED, c ₁, c ₂the once item conversion coefficient of each monochromatic LED power and yellow light LED power and constant term conversion coefficient when being respectively four color contamination white lights;

(2) first according to channel matrix H and the initial driving current b (0) of four look visible light communication systems, the order constraints that the illumination constraints obtaining being made up of the target function of precoding and drive current combined optimization, Condition of Non-Negative Constrains, colour temperature and color rendering index, data fluxion cause

Then according to described target function and constraints, set up the model of precoding and drive current combined optimization, ignore this order constraints of Rank (Q)=K, utilize the method for solving of semi definite programming problem, obtain the optimum precoding covariance matrix Q of local and optimum drive current b;

(3) judge that whether initial driving current b (0) is equal with optimum drive current b, if equal, record local optimum precoding covariance matrix Q and optimum drive current b, enter step (4), otherwise, make b (0)=b, and return step (2);

(4) according to optimum precoding covariance matrix, list and a series ofly meet Condition of Non-Negative Constrains and covariance matrix is the gaussian random matrix of local optimum precoding covariance matrix Q

(5) the gaussian random matrix listed by calculating corresponding mean square error, therefrom chooses random matrix corresponding to least mean-square error as local optimum pre-coding matrix F.

Further, described illumination constraints is determined by following formula:

$\left\{\begin{array}{c}KDb={\mathrm{\αc}}_1+c_2\\ \mathrm{\α}\∈\[{\mathrm{\α}}_1,{\mathrm{\α}}_2\]\∪\[{\mathrm{\α}}_3,{\mathrm{\α}}_4\]\∪...\end{array}\right.,$

Wherein, b is drive current.

Described order constraints is determined by Rank (Q)=K, and wherein Q is precoding covariance matrix, and K is data fluxion.

Further, the gaussian random matrix in described step (4) choose according to the following step:

1) the random Gaussian vectors in 4NK × 1 is produced

2) new pre-coding matrix is calculated according to following formula

$\hat{F}={(Q/K)}^{\frac{1}{2}}\·reshape(f,4N,K)$

3) from described new pre-coding matrix every a line choose gaussian random matrix as follows:

${\stackrel{\‾}{F}}_l=diag\left(\frac{b_1}{\mathrm{\δ}\left|\right|e_1^T\hat{F}\left|\right|},...,\frac{b_{4N}}{\mathrm{\δ}\left|\right|e_{4N}^T\hat{F}\left|\right|}\right)\hat{F}$

Wherein, δ is the amplitude transmitted, b _ifor i-th element of drive current b, for the i-th row of unit matrix.

The inventive method for four look visible light communication system transmitting terminals be made up of N group red, green, blue, Huang (RGBA) four look LED, signal blendes together white light by light mixing lens and launches, be mapped to the receiving terminal be made up of N group photodiode array corresponding with it through imaging len and carry out Received signal strength s employing M system PAM modulation, arbitrary element s _kscope be [-δ, δ], s _iwith s _jbetween covariance matrix be

$E(s_i,s_j)=\{\begin{array}{cc}g,& i=j\\ 0,& i\≠j\end{array},\begin{array}{cc}where& g=\frac{{\mathrm{\δ}}^2}{3}\frac{M+1}{M-1}\end{array}$

(1) described four look visible light communication systems obtain the channel information formation channel matrix of transmitting terminal and receiving terminal

(2) a continuous print feasible zone [α of the power α of the yellow light LED meeting colour temperature constraint and color rendering index constraint is chosen _i, α _j].

The channel information that four look visible light communication systems obtain transmitting terminal and receiving terminal forms channel matrix by colour gamut mimo channel matrix H _cwith space mimo channel matrix H _skronecker product determine:

$\stackrel{\‾}{H}=H_c\⊗H_s$

Wherein, element [H _c] _ijrepresent the gain being transmitted into the i-th look receiver from jth look LED, element [H _s] _ijrepresent the gain from jth group four look LED to i-th group of photodiode array;

Colour temperature and development index constraint is determined by following formula:

$\left\{\begin{array}{c}KDb={\mathrm{\αc}}_1+c_2\\ \mathrm{\α}\∈\[{\mathrm{\α}}_1,{\mathrm{\α}}_2\]\∪\[{\mathrm{\α}}_3,{\mathrm{\α}}_4\]\∪...\end{array}\right.,$

Wherein, [α _i, α _j] for meeting a continuous print feasible zone of the power α of the yellow light LED of colour temperature and development index constraint, c ₁, c ₂the conversion coefficient of each monochromatic LED power and yellow light LED power when being four color contamination white lights, D is the conversion coefficient of LED drive current vector and light intensity vector, and K is the transition matrix gathered together by homochromy LED;

According to colour temperature constraint, choose the initial driving current b (0) that can blend together white light, wherein each element definition is the drive current initial value be carried on i-th LED, and b (0) is chosen by following formula:

KDb(0)＝α ₀c ₁+c ₂

Wherein, α ₀for the power of initial yellow light LED;

According to channel matrix with initial driving current b (0), obtain the target function of precoding and drive current combined optimization, Condition of Non-Negative Constrains and the illumination such as colour temperature, color rendering index constraints, set up precoding and drive current combined optimization model, obtain the optimum precoding covariance matrix Q of local and optimum drive current b, described combined optimization model is:

$\begin{array}{cc}\underset{Q,T,b,\mathrm{\α}}{\min }& Tr\left(T\right)\end{array}$

$Q_{ii}\≤\frac{1}{{\mathrm{\δ}}^{2}K}\[b{\left(0\right)}_i^2+2b{\left(0\right)}_i(b_i-b{\left(0\right)}_i)\]$

Rank(Q)＝K

KDb＝αc ₁+c ₂

α∈[α ₁，α ₂]∪[α ₃，α ₄]∪…

Wherein, $T={\[g^{-1}I+R_n^{-\frac{1}{2}}{\mathrm{HQH}}^T{R}_n^{-\frac{1}{2}}\]}^{-1},H=\stackrel{\‾}{H}D,$ R _nfor noise covariance matrix, K is data fluxion;

According to described optimum precoding covariance matrix, list and a series ofly meet Condition of Non-Negative Constrains and covariance matrix is the gaussian random matrix of Q choose according to the following step:

1) the random Gaussian vectors in 4NK × 1 is produced

2) new pre-coding matrix is calculated based on this

$\hat{F}={(Q/K)}^{\frac{1}{2}}\·reshape(f,4N,K)$

3) right each line operate of advancing, choose described random matrix as follows:

${\stackrel{\‾}{F}}_l=diag(\frac{b_1}{\mathrm{\δ}\left|\right|e_1^T\hat{F}\left|\right|},...,\frac{b_{4N}}{\mathrm{\δ}\left|\right|e_{4N}^T\hat{F}\left|\right|})\hat{F}$

A series ofly Condition of Non-Negative Constrains is met and covariance matrix is the gaussian random matrix of Q according to listed calculate corresponding mean square error, therefrom choose random matrix corresponding to least mean-square error as local optimum pre-coding matrix F; To the feasible zone of each different α, according to described local optimum pre-coding matrix F, therefrom choose the minimum F of mean square error as final pre-coding matrix F _opt.

Beneficial effect: the present invention compared with prior art, has the following advantages:

1, in the present invention, the combined optimization of precoding and drive current makes the synthesize white light quality of launching can meet certain lighting requirement.Four look LED are made up of red, green, blue and yellow (RGBA) four kinds of colors usually, when mixed white light is for throwing light on, and corresponding tristimulus values matrix A _tvbe 3 × 4 matrixes, there is one degree of freedom, can be used for the size regulating color rendering index.And three look RGBLED are when mixed white light, corresponding A _tvbe 3 × 3 matrixes, without the degree of freedom, corresponding to a fixing color rendering index, cannot regulate lighting quality.Therefore compared with three coloured light communication systems, four colour system systems are not only many a wavelength division multiplexed channel (gold-tinted channel), and under the colour temperature of specifying synthesize white light, four colour system blanket insurances have the ability of fine adjustment mixed light color rendering index (CRI).Based on this, while VLC communications system transmission speed is improved, also can well both in-door illumination demand.

2, present invention employs SDR algorithm, when making number of data streams be less than actual physics channel number, system still can normally work.When existing work only considers that data fluxion is equal with the actual physics number of channel mostly, adopt SDP optimization method, combined optimization is carried out to pre-coding matrix and bias current.Because SDP method can only process full rank problem, when data fluxion is less than the actual physics number of channel, optimum results can not meet this order constraints of Rank (Q)=K.Present invention employs SDR algorithm, a series of order of stochastic generation is K and covariance is Q meets constraints and meet the random pre-coding matrix of Gaussian Profile then minimum one of mean square error is therefrom selected as optimum pre-coding matrix.When this makes data fluxion to be passed be less than the actual physics number of channel, this system still can normally work, and the scope of application is wider.

3, the SDR algorithm of the present invention's employing, when making data fluxion equal the actual physics number of channel, gained MSER existing SDP algorithm gained is less.Dynamic constraints is loosened as relevant with Q by a series of abundant inessential condition by existing work mostly

$Q_{ii}\≤\frac{1}{{\mathrm{\δ}}^{2}K}\[b{\left(0\right)}_i^2+2b{\left(0\right)}_i(b_i-b{\left(0\right)}_i)\]$

Obviously, this estimation reduces the hunting zone of pre-coding matrix.In the randomisation process that we propose, selected pre-coding matrix F strictly meets Dynamic constraints, make use of original constraints better, has less mean square error.

Accompanying drawing explanation

Fig. 1 is the transceiver model of four look visible light communication systems;

Fig. 2 is the logic diagram of optimization method proposed by the invention;

Fig. 3 is the change curve of the color rendering index corresponding under fixing colour temperature of the RGBA tetra-look LED of LZ4-00MA00 model with α;

Fig. 4 is for the least mean-square error that obtains under Fig. 1 institute representation model is with the change curve of illuminance;

Fig. 5 compares with in harness for the optimization method of the present invention obtained under Fig. 1 institute representation model.

Embodiment

Below in conjunction with Figure of description and embodiment, technical solution of the present invention is described in further detail.

As shown in Figure 1, this four looks visible light communication system is made up of N group four look LED, often organizes the monochromatic LED that four look LED have again RGBA tetra-kinds of colors.Interference between each group of four look LED is only relevant with position, and the interference of single four look LED inside is only relevant with each monochromatic LED luminescent spectrum power distribution.In order to make the expression of channel matrix more short and sweet, it is by colour gamut mimo channel matrix H _cwith space mimo channel matrix H _skronecker product determine:

$\stackrel{\‾}{H}=H_c\⊗H_s$

Wherein, element [H _c] _ijrepresent the gain being transmitted into the i-th look receiver from jth look LED, element [H _s] _ijrepresent the gain from jth group four look LED to i-th group of photodiode array;

As shown in Figure 2, the precoding of four look visible light communication systems of the present invention and drive current combined optimization method, travel through all feasible zone [α that the power α of the yellow light LED meeting colour temperature constraint and color rendering index constraint is corresponding _i, α _j], obtain feasible zone [α that is all and α _i, α _j] corresponding local optimum pre-coding matrix, therefrom choose local optimum pre-coding matrix corresponding to least mean-square error as the optimum pre-coding matrix F of four look visible light communication systems _opt, choose local optimum drive current corresponding to least mean-square error as the optimum drive current b of four look visible light communication systems _opt;

Wherein, all feasible zone [α that α is corresponding _i, α _j] obtained by the method for numerical analysis, concrete steps are as follows:

A) for appointment colour temperature (CT) synthesize white light, need to solve following mixed light equation group, then CT constraint is as follows:

A _tvK(Db+c)＝a _CT

B) 4 × 1 vectorial z are defined,

z＝KDb

Then above-mentioned CT constraints can be converted into

A _tvz＝a _CT-A _tvKc

C) tristimulus values matrix A _tvbe 3 × 4 matrixes, in the solution of vectorial z, have one degree of freedom, then can do following segmentation:

$z=\left[\begin{array}{c}{z}_{1:3}\\ z_4\end{array}\right],$ A _tv＝[A _1:3a ₄]

Substitute into aforementioned CT constraints can obtain

Obtain the solution space of one dimension, CRI constraint can be converted into the function of constant α, just can obtain the feasible zone of α as shown in Figure 3 by the method for numerical analysis; Finally, the illumination constraints of colour temperature and development index composition is determined by following formula:

$\left\{\begin{array}{c}KDb={\mathrm{\αc}}_1+c_2\\ \mathrm{\α}\∈\[{\mathrm{\α}}_1,{\mathrm{\α}}_2\]\∪\[{\mathrm{\α}}_3,{\mathrm{\α}}_4\]\∪...\end{array}\right.,$

During fixing colour temperature color rendering index with α change curve as shown in Figure 3, limit color rendering index and be not less than 75, i.e. all feasible zones of available α.

Each feasible zone of α is processed, determines and feasible zone [α _i, α _j] concrete steps of corresponding local optimum pre-coding matrix are:

1) the colour temperature constraint according to following formula, choose the initial driving current b (0) that can blend together white light:

KDb(0)＝α ₀c ₁+c ₂

Wherein, K is the transition matrix gathered together by homochromy LED, and D is the conversion coefficient of LED drive current vector and light intensity vector, α ₀for the power of initial yellow light LED, c ₁, c ₂the once item conversion coefficient of each monochromatic LED power and yellow light LED power and constant term conversion coefficient when being respectively four color contamination white lights;

2) first according to channel matrix H and the initial driving current b (0) of four look visible light communication systems, obtain the target function by precoding and drive current combined optimization, Condition of Non-Negative Constrains, the illumination constraints that colour temperature and color rendering index form, the order constraints that data fluxion causes, then according to described target function and constraints, set up the model of precoding and drive current combined optimization, ignore this order constraints of Rank (Q)=K, utilize the method for solving of semi definite programming problem, obtain the optimum precoding covariance matrix Q of local and optimum drive current b,

Particularly, signal s adopts M system PAM modulation, arbitrary element s _kscope be [-δ, δ], s _iwith s _jbetween covariance matrix be

$E(s_i,s_j)=\{\begin{array}{cc}g,& i=j\\ 0,& i\≠j\end{array},\begin{array}{cc}where& g=\frac{{\mathrm{\δ}}^2}{3}\frac{M+1}{M-1}\end{array}$

Signal stream s is by a real matrix F _{4N × K}carry out precoding, then have

x＝Fs+b≥0

Wherein, b is that the positive reality in 4N × 1 is biased, and is unipolar signal with what ensure driving LED; Because signal stream s is depended in above-mentioned constraint, therefore can be further converted to

$\mathrm{\δ}\·\left|\right|e_i^{T}F|{|}_1\≤e_i^{T}b,(i=1,...,4N),$

Through electro-optic conversion, LED current vector x is converted into corresponding light intensity vector i, and conversion process can be approximately

i＝Dx+c

Wherein, diagonal matrix D=diag (d ₁..., d _4N) and parameter vector c obtain by device data handbook;

Through channel H, the reception vector obtained at receiving terminal polychrome PD is

Each element of noise vector n is the combination of Johnson noise and thermal noise, supposes to meet Gaussian Profile wherein R _nfor the covariance matrix of noise;

The linear equalizer W of a K × 4Q is used to estimated signal s,

$\begin{array}{c}\hat{s}=Wy\\ =WHFs+Wn\end{array}.$

Then evaluated error covariance matrix R is

According to MMSE criterion, optimum linearity equalizer W is the function of pre-coding matrix F

W＝F ^TH ^T(g ^-1R _n+HFF ^TH ^T) ^-1

Then error co-variance matrix R can be reduced to

$R={\left(g^{-1}I+F^T{H}^T{R}_n^{-1}HF\right)}^{-1}$

Target function can carry out following equivalence transformation

$Tr\left({(g^{-1}I+F^T{H}^T{R}_n^{-1}HF)}^{-1}\right)=Tr\left({\left(g^{-1}I+R_n^{-\frac{1}{2}}{\mathrm{HQH}}^T{R}_n^{-\frac{1}{2}}\right)}^{-1}\right)+K-4Q$

As 4N>K, notice that Q should consider the constraint of extra order:

Rank(Q)＝K

Consider and instead of pre-coding matrix F with Q, Dynamic constraint then needs to carry out with down conversion:

According to norm inequalities

$\left|\right|e_i^{T}F|{|}_1\≤\sqrt{K}|\left|e_i^{T}F\right|{|}_2$

Can obtain

$Q_{ii}\≤\frac{1}{{\mathrm{\δ}}^{2}K}{b}_i^2$

First two that utilize Tai Te to launch, can be by be approximately

$b_i^2\≈b{\left(0\right)}_i^2+2b{\left(0\right)}_i\left(b-b{\left(0\right)}_i\right)$

Like this, whole problem has just changed into the form of following SDP

$\begin{array}{cc}\underset{Q,T,b,\mathrm{\α}}{\min }& Tr\left(T\right)\end{array}$

$Q_{ii}\≤\frac{1}{{\mathrm{\δ}}^{2}K}\[b{\left(0\right)}_i^2+2b{\left(0\right)}_i(b_i-b{\left(0\right)}_i)\]$

Rank(Q)＝K

KDb＝αc ₁+c ₂

α∈[α ₁,α ₂]∪[α ₃,α ₄]∪…

Ignore this order constraints of Rank (Q)=K, utilize the method for solving of semi definite programming problem, obtain the optimum precoding covariance matrix Q of local and optimum drive current b;

3) judge that whether initial driving current b (0) is equal with optimum drive current b, if equal, record local optimum precoding covariance matrix Q and optimum drive current b, enters step 4), otherwise, make b (0)=b, and return step 2);

4) according to optimum precoding covariance matrix, list and a series ofly meet Condition of Non-Negative Constrains and covariance matrix is the gaussian random matrix of local optimum precoding covariance matrix Q choose according to the following step:

A, produce the random Gaussian vectors in 4NK × 1

B, calculate new pre-coding matrix according to following formula

$\hat{F}={(Q/K)}^{\frac{1}{2}}\·reshape(f,4N,K)$

C, from described new pre-coding matrix every a line choose gaussian random matrix as follows:

${\stackrel{\‾}{F}}_l=diag(\frac{b_1}{\mathrm{\δ}\left|\right|e_1^T\hat{F}\left|\right|},...,\frac{b_{4N}}{\mathrm{\δ}\left|\right|e_{4N}^T\hat{F}\left|\right|})\hat{F}$

Wherein, δ is the amplitude transmitted, b _ifor i-th element of drive current b, for the i-th row of unit matrix.

5) the gaussian random matrix listed by calculating corresponding mean square error, therefrom chooses random matrix corresponding to least mean-square error as local optimum pre-coding matrix F.

As shown in Figure 3, for the RGBA tetra-look LED of LZ4-00MA00 model, the color rendering index constraint under fixing colour temperature, the feasible zone of α only has one.Meanwhile, under different colour temperatures, the feasible zone of α is different.This is because a that different colour temperatures is corresponding _cTdifferent.In fact α reflects the power ratio of gold-tinted, and α=0 represents the sight of RGB three primary colors mixed light just.Obviously, if cancel gold-tinted, no matter be cold light or warm light, the color rendering index of white light that mixes out all very little, about 40.Therefore, the gold-tinted quoted herein can promote the color rendering index of white light LEDs very effectively, improves the optical characteristics of this LED light source.

As shown in Figure 4, for RGBA tetra-coloured light channel and RGB tri-coloured light channel, along with the increase of system illuminance, and MMSE constantly reduces, and systematic function is become better and better.For RGBA tetra-coloured light channel, under identical level conditions, reduce the data fluxion of transmission, to reduce with MMSE of system, this is because under identical illuminance, data fluxion reduces, luminous power assigned by each data flow can increase thereupon, thus reduce system and MMSE.That is, when the data fluxion of system transmission is less than optical channel number physically, the performance of system will obviously improve.In addition, when transmitting identical data flow, RGBA optical channel is better than rgb light channel performance.This is because RGBA optical channel is after the constraint meeting colour temperature CT, the mode still having multiple power to distribute is available, and RGBLED is after CT is fixing, and its power division also will uniquely be determined.

As shown in Figure 5, no matter be to RGBA optical channel or concerning rgb light channel, after introducing SDR algorithm, the pre-coding matrix of gained is all better than the result not doing random process.This is because the pre-coding matrix herein strictly meets Dynamic constraints, and existing research is when asking optimum pre-coding matrix, in order to problem being converted into the convex optimization problem easily solved, has all carried out loosening process to Dynamic constraints.

Above-described embodiment is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention; some improvement and equivalent replacement can also be made; these improve the claims in the present invention and are equal to the technical scheme after replacing, and all fall into protection scope of the present invention.

Claims (3)

1. the precoding of four look visible light communication systems and a drive current combined optimization method, is characterized in that, the method traversal meets all feasible zone [α corresponding to the power α of the yellow light LED that colour temperature constraint and color rendering index retrain _i, α _j], obtain feasible zone [α that is all and α _i, α _j] corresponding local optimum pre-coding matrix, therefrom choose local optimum pre-coding matrix corresponding to least mean-square error as the optimum pre-coding matrix F of four look visible light communication systems _opt, choose local optimum drive current corresponding to least mean-square error as the optimum drive current b of four look visible light communication systems _opt;

Wherein each feasible zone of power α is processed, determine and feasible zone [α _i, α _j] concrete steps of corresponding local optimum pre-coding matrix are:

(1) the colour temperature constraint according to following formula, choose the initial driving current b (0) that can blend together white light:

KDb(0)＝α ₀c ₁+c ₂

Wherein, K is the transition matrix gathered together by homochromy LED, and D is the conversion coefficient of LED drive current vector and light intensity vector, α ₀for the power of initial yellow light LED, c ₁, c ₂the once item conversion coefficient of each monochromatic LED power and yellow light LED power and constant term conversion coefficient when being respectively four color contamination white lights;

(2) first according to channel matrix H and the initial driving current b (0) of four look visible light communication systems, the order constraints that the illumination constraints obtaining being made up of the target function of precoding and drive current combined optimization, Condition of Non-Negative Constrains, colour temperature and color rendering index, data fluxion cause

Then according to described target function and constraints, set up the model of precoding and drive current combined optimization, ignore this order constraints of Rank (Q)=K, utilize the method for solving of semi definite programming problem, obtain the optimum precoding covariance matrix Q of local and optimum drive current b;

(3) judge that whether initial driving current b (0) is equal with optimum drive current b, if equal, record local optimum precoding covariance matrix Q and optimum drive current b, enters step (4), otherwise, make b (0)=b, and return step (2);

(4) according to optimum precoding covariance matrix, list and a series ofly meet Condition of Non-Negative Constrains and covariance matrix is the gaussian random matrix of local optimum precoding covariance matrix Q

(5) the gaussian random matrix listed by calculating corresponding mean square error, therefrom chooses random matrix corresponding to least mean-square error as local optimum pre-coding matrix F.

2. the precoding of four look visible light communication systems as claimed in claim 1 and drive current combined optimization method, is characterized in that: described illumination constraints is determined by following formula:

$\left\{\begin{array}{c}KDb={\mathrm{\αc}}_1+c_2\\ \mathrm{\α}\∈\[{\mathrm{\α}}_1,{\mathrm{\α}}_2\]\∪\[{\mathrm{\α}}_3,{\mathrm{\α}}_4\]\∪...\end{array}\right.,$

Wherein, b is drive current.

Described order constraints is determined by Rank (Q)=K, and wherein Q is precoding covariance matrix, and K is data fluxion.

3. the precoding of four look visible light communication systems as claimed in claim 1 and drive current combined optimization method, is characterized in that: the gaussian random matrix in described step (4) choose according to the following step:

1) the random Gaussian vectors in 4NK × 1 is produced

2) new pre-coding matrix is calculated according to following formula

$\hat{F}={(Q/K)}^{\frac{1}{2}}\·reshape(f,4N,K)$

3) from described new pre-coding matrix every a line choose gaussian random matrix as follows:

${\stackrel{\‾}{F}}_l=diag\left(\frac{b_1}{\mathrm{\δ}\left|\right|e_1^T\hat{F}\left|\right|},\mathrm{...},\frac{b_{4N}}{\mathrm{\δ}\left|\right|e_{4N}^T\hat{F}\left|\right|}\right)\hat{F}$

Wherein, δ is the amplitude transmitted, b _ifor i-th element of drive current b, for the i-th row of unit matrix.