CN104717171A - Leader design and channel estimation method for multicolor visible light DCO-OFDM communication system - Google Patents

Abstract

The invention discloses a leader design and channel estimation method for a multicolor visible light DCO-OFDM communication system. Any of the following methods is adopted for designing a leader sequence to finish channel estimation of various colored light links and interference estimation between different light links; firstly, leader OFDM symbols and various colored light are grouped, two beams of colored light are selected in each group, and a ZC sequence is placed on all effective sub-carriers of the two leader OFDM symbols based on an Alamouti coding method; secondly, the effective sub-carriers are divided into odd groups and even groups at equal intervals, after the various colored light is grouped, two beams of colored light is selected in each group, and a ZC sequence is placed on the odd sub-carriers or the even sub-carriers through an Alamouti method; thirdly, one beam of colored light is selected for sending signals on all the sub-carriers, the sub-carriers are grouped at equal intervals, the light links of in other colors each occupy one group of sub-carriers, and the ZC sequence is placed on the two leader OFDM symbols through the Alamouti method. The leader design and channel estimation method supports frame synchrony and channel and interference estimation functions, supports a superframe structure and can be adjusted according to practical system requirements.

Description

The leading design of multicolor visible light DCO-OFDM communication system and channel estimation methods

Technical field

The present invention relates to visible light communication field, in particular to the leading design in indoor multicolor visible light DC BiasedOptical Orthogonal Frequency Division Multiplexing (DCO-OFDM) communication system and channel estimation methods.

Background technology

Visible light communication technology becomes the focus of communications field research in recent years gradually.It has the wide-band spectrum resources independent of radio spectrum, and without electromagnetic interference and radiation, green safety, is easy to cut off signal, the advantages such as good confidentiality.Use the multicolor visible light communication system of RGB or RGBA LED that the visible ray of different-waveband can be utilized to provide multilink, coordinate OFDM to realize MIMO-OFDM communication system.

Consider in polychromatic light communication system, integrate at the circuit of the assorted optical channel of transmitter and receiver, the crosstalk of the interchannel signal of telecommunication may be there is.The filter that receiving terminal uses also may the wave band of accurate corresponding each coloured light, causes there is crosstalk in the light signal received.For improving the transmission performance of polychromatic light ofdm system, need channel and interference estimation method accurately and effectively.

Summary of the invention

The object of the invention is to provide indoor multicolor visible light DCO-OFDM, and (the present invention relates generally to DCO-OFDM, following all referred to as OFDM for the purpose of brief) leading design in communication system and channel estimation methods, for the solution using the polychromatic light communication system of OFDM to provide channel and Interference Estimation under noisy condition, can need for different polychromatic light channel situation and systematic function, leading design is adjusted, weigh between the leading amount of overhead that takies and the accuracy of channel estimating, strengthen system availability.

For reaching above-mentioned purpose, the present invention proposes leading design in indoor multicolor visible light ofdm communication system and channel estimation methods.The scene that the method is suitable for is: the transmitting terminal of multicolor visible light ofdm system sends light signal by multiplex signal modulates to multi-color LED light source, receiving terminal uses the filter of different-waveband to obtain the Received signal strength of different colours light path, by the Combined Treatment settling signal receiving function to multi-pass signal.In multicolor visible light ofdm communication system, system frame structure is: a frame comprises N _findividual OFDM symbol, N wherein _pindividual OFDM symbol is leading symbol, for realizing synchronous and channel estimation function.Total number of sub-carriers is K.If use M coloured light signal (M >=2) in this system, the M on k sub carriers ties up transmission signal vector and is

$X_k={\left[\begin{array}{cccc}{X}_k^{\left(0\right)}& X_k^{\left(1\right)}& ...& X_k^{(M-1)}\end{array}\right]}^T.$

The channel coefficients that k sub carriers is transmitted into j road light-receiving from i road light is made to be m on k sub carriers ties up received signal vector

$Y_k={\left[\begin{array}{cccc}{Y}_k^{\left(0\right)}& Y_k^{\left(1\right)}& ...& Y_k^{(M-1)}\end{array}\right]}^T.$

Then have

Y _k＝H _kX _k，

Wherein

For M × M ties up channel matrix.And in indoor visible light communication system, channel condition is commonly considered as quasi-static channel opens, in a frame time, channel coefficients remains unchanged substantially.Under noisy condition, H _kbe not diagonal matrix, in order to improve efficiency of transmission, make full use of polychromatic light channel condition, receiving terminal needs H _kin each coefficient estimate, to carry out the demodulation work such as Interference Cancellation.

For this scene, the frequency domain symbol of m road light on the k sub carriers of the n-th leading OFDM symbol is made to be wherein n=0,1 ..., N _p-1, k=0,1 ..., K-1, m=0,1 ..., M-1.The leading design that the present invention proposes and channel estimation methods place ZC sequence on the frequency domain of leading OFDM symbol, and its Cycle Length is set to identical with the effective sub-carrier number in an OFDM symbol.Utilize the frequency-domain and time-domain autocorrelation performance that ZC sequence is good, can achieve frame synchronizing function.In addition, the ZC sequence s utilizing this known _kas targeting sequencing, channel estimating can be completed.

The leading design of a kind of multicolor visible light DCO-OFDM communication system provided by the invention and channel estimation methods, comprise the steps:

(1) transmitting terminal is selected to adopt following (A) ~ (C) either method to produce leading symbol according to actual channel conditions and system performance requirements;

(A) leading OFDM symbol and polychromatic light are divided into groups respectively, often organize and comprise two leading OFDM symbol and two color light respectively, often organize two color light and on all effective subcarrier of one group of two leading OFDM symbol, place ZC sequence with Alamouti coding method;

(B) each coloured light places ZC sequence on all effective subcarrier of first leading symbol, effective subcarrier of all the other leading symbols is equally spaced divided into odd number group and even number set, and polychromatic light is divided into groups, often organize two color light and in odd subcarriers or even subcarriers, place ZC sequence with Alamouti coding method;

(C) get a shade and place ZC sequence on all effective subcarrier of all leading symbols, and effective subcarrier of each leading symbol is divided into groups at equal intervals, all the other coloured light take one group of subcarrier separately, coordinate selected coloured light in the subcarrier group of the correspondence of two leading OFDM symbol, to place ZC sequence with Alamouti coding method respectively;

(2) after receiving terminal receives multi-pass signal, the Received signal strength each subcarrier adopting the two color light of Alamouti method in two leading OFDM symbol is merged, calculate the channel between each link and interference coefficient estimated value.

More preferably, in described method (A), polychromatic light is four coloured light, leading OFDM symbol number N _p=4,4 leading OFDM symbol are divided into two groups, and four coloured light are divided into two groups, often organize two color light and on all effective subcarrier of one group of leading symbol, place ZC sequence by Alamouti coding method respectively, specifically arrange satisfied:

$X_k^{\left(m_0\right)}\left(n_0\right)=s_k,X_k^{\left(m_0\right)}\left(n_1\right)=-s_k^{*},$

$X_k^{\left(m_1\right)}\left(n_0\right)=s_k,X_k^{\left(m_1\right)}\left(n_1\right)=s_k^{*},$

Wherein 0≤k≤K-1, s _kfor the ZC sequential value on k sub carriers, m ₀and m ₁represent same group of two color light sequence number, n ₀and n ₁represent same group of two leading symbol sequence numbers.

Light signal in different groups is isolated by this leading design in time domain, with group signal by Alamouti method orthogonalization, therefore direct estimation can go out H _kin all coefficients.And in some leading OFDM symbol, have sent complete original ZC sequence due to each optical link ensure that, make can complete frame synchronization on the optical link of random colour.

More preferably, in described method (B), polychromatic light is four coloured light, odd number group and even number set is divided into by equally spaced for effective subcarrier of all the other the leading OFDM symbol except first leading OFDM symbol, four coloured light are also divided into two groups, often organize two color light and in odd subcarriers or even subcarriers, place ZC sequence with Alamouti method respectively, for group two color light of on even number or odd subcarriers, specifically arrange satisfied:

$X_k^{\left(m_0\right)}\left(n_1\right)=s_k,X_k^{\left(m_0\right)}\left(n_2\right)=-s_k^{*},$

$X_k^{\left(m_1\right)}\left(n_1\right)=s_k,X_k^{\left(m_1\right)}\left(n_2\right)=s_k^{*},$

Wherein, s _kfor the ZC sequential value on k sub carriers, m ₀and m ₁represent the same group of two color light sequence number taking odd number or even subcarriers, n ₁and n ₂represent two leading OFDM symbol sequence numbers.

Subcarrier is divided into nonoverlapping odd and even number group by this leading design, and two groups of light signals are isolated on frequency domain.All signals on two leading symbols with Alamouti mode orthogonalization.The program can estimate H _kin the half coefficient of every a line or each row, second half coefficient is by producing the coefficient interpolation on adjacent sub-carrier.

More preferably, in described method (C), get a shade and place ZC sequence on all effective subcarrier of all leading symbols, arrange satisfied:

$X_k^{\left(m_i\right)}\left(n_0\right)=s_k,X_k^{\left(m_i\right)}\left(n_1\right)=-s_k^{*},$

Wherein, 0≤k≤K-1, m _irepresent coloured light sequence number of getting, n ₀and n ₁represent two leading OFDM symbol sequence numbers;

The quantity of subcarrier according to all the other coloured light divided into groups at equal intervals, all the other every coloured light take one group of subcarrier separately again.The ZC sequence of every coloured light in the subcarrier group of correspondence arranges satisfied:

$X_{k_j}^{\left(m_j\right)}\left(n_0\right)=s_{k_j},X_{k_j}^{\left(m_j\right)}\left(n_1\right)=s_{k_j}^{*},$

Wherein m _jrepresent all the other coloured light sequence numbers, k _jrepresent m _jthe sequence number of the grouping subcarrier that road coloured light is corresponding, 0≤k _j≤ K-1, for k _jzC sequential value on sub carriers.

This leading design only needs less leading OFDM symbol, the channel coefficients of the number of delivering letters that wherein riches all the way can be estimated at all subcarriers, the channel coefficients of all the other optical path signals only can direct estimation on the subcarrier placing ZC sequence, and the coefficient on its remaining sub-carriers can be produced by interpolation.

More preferably, the channel in described step (2) between each link of calculating and the concrete grammar of interference coefficient estimated value comprise:

Alamouti method is pressed n-th for the i-th, j two-way light ₁and n ₂the k sub carriers of individual leading OFDM symbol there is transmission signal $X_k^{\left(i\right)}\left(n_1\right)=s_k,X_k^{\left(i\right)}\left(n_2\right)=-s_k^{*},X_k^{\left(j\right)}\left(n_1\right)=s_k,X_k^{\left(j\right)}\left(n_2\right)=s_k^{*}$ Time, then by any l road light receiving signal with channel or interference coefficient is obtained according to following formula with estimated value

${\tilde{h}}_k^{\left(\mathrm{il}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}-Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

${\tilde{h}}_k^{\left(\mathrm{jl}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}+Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

Obtain the channel between any two optical links or interference coefficient (being channel coefficients when i, l are equal, is interference coefficient when not waiting) thus;

For the channel value do not placed on the subcarrier of ZC sequence, utilize and have the channel coefficients estimated value on the subcarrier of ZC sequence to carry out interpolation to obtain.

Further, present invention also offers a kind of leading design and channel estimation methods of multicolor visible light DCO-OFDM communication system, be applied to the DCO-OFDM communication system adopting superframe structure, if the length of superframe is N _sindividual OFDM symbol, wherein comprises multiple short frame, comprises the targeting sequencing supporting frame synchronization in each superframe, and in all the other each short frames, only comprise the targeting sequencing supporting channel and Interference Estimation.Short frame frame length is N _findividual OFDM symbol, N wherein _pindividual OFDM symbol is leading symbol, and method comprises the steps:

(1) transmitting terminal generates the leading symbol of first short frame of superframe according to method described in claim 1 (A) ~ (C) either method;

(2) transmitting terminal generates the leading symbol of all the other each short frames according to the method for all the other leading symbols generated except first leading symbol in method described in claim 1 (A) ~ (C) either method or described method (B);

(3) after receiving terminal receives multi-pass signal, the Received signal strength each subcarrier adopting the two color light of Alamouti method in two leading OFDM symbol is merged, calculate the channel between each link and interference coefficient estimated value.

Beneficial effect

From the above technical solution of the present invention shows that, leading design in indoor multicolor visible light DCO-OFDM communication system of the present invention and channel estimation methods complete the leading design work in indoor multicolor visible light ofdm communication, achieve channel and Interference Estimation function, its beneficial effect is:

(1) the leading OFDM symbol designed by can support frame synchronization, channel and Interference Estimation function, can obtain the estimated value of channel in polychromatic light link on all effective subcarriers and interference coefficient.

(2) for the different requirements of systematic function, selection adjustment can be carried out between kinds of schemes, to weigh between amount of overhead and channel estimation accuracy.

(3) can adjust flexibly scheme for the channel between different polychromatic light links and disturbed condition, improve the channel estimation accuracy on some coloured light road on demand, find out the channel estimation methods of applicable actual conditions.

Accompanying drawing explanation

Fig. 1 is the emulation of preferred embodiment of the present invention four coloured light system signal interference ratio situation maps used.

Fig. 2 is the simulation result figure of the normalized mean squared error that preferred embodiment lower channel of the present invention is estimated.

Fig. 3 is direct independent demodulation and carry out the simulation result figure of the frame error rate that counteracting serial interference obtains to received signal under preferred embodiment of the present invention.

Embodiment

In order to more understand technology contents of the present invention, institute's accompanying drawings is coordinated to be described as follows especially exemplified by specific embodiment.

The leading design of a kind of multicolor visible light DCO-OFDM communication system that the embodiment of the present invention provides and channel estimation methods, comprise the steps:

(1) transmitting terminal is selected to adopt following (A) ~ (C) either method to produce leading symbol according to actual channel conditions and system performance requirements;

(A) to use the four coloured light systems of RGBA LED, make red, green, blue, gold-tinted is respectively the 0th, 1,2,3 road light.Get N _p=4, and leading OFDM symbol is divided into two groups.Four coloured light links are also divided into 2 groups simultaneously, often group 2 optical links take one group is 2 leading symbols, and on all effective subcarriers, places ZC sequence by Alamouti (hereinafter referred to as Alamouti) method of encoding in these two leading OFDM symbol.

Such as, by { N=0,1,2,3} tetra-leading OFDM symbol is divided into { N=0,2} and { N=1,3} two groups.Ruddiness and green glow take N=0,2} two leading symbols, and make similar, blue light and gold-tinted take N=1,3} two leading symbols, and make $X_k^{\left(2\right)}\left(1\right)=s_k,X_k^{\left(2\right)}\left(3\right)=-s_k^{*},X_k^{\left(3\right)}\left(1\right)=s_k,X_k^{\left(3\right)}\left(3\right)=s_k^{*}.$ This leading design is as shown in table 1.

The leading method for designing of table 1 (A) exemplary scenario

Light signal in different groups is isolated by this leading design in time domain, with group signal by Alamouti method orthogonalization, therefore direct estimation can go out H _kin all coefficients.And in some leading OFDM symbol, have sent complete original ZC sequence due to each optical link ensure that, make can complete frame synchronization on the optical link of random colour.

(B) to use the four coloured light systems of RGBA LED, make red, green, blue, gold-tinted is respectively the 0th, 1,2,3 road light.Get N _p=3, when N=0, each coloured light all sends complete original ZC sequence, makes each optical link to complete frame synchronization.For N=1,2, be divided into odd subcarriers and even subcarriers two groups at frequency domain by equally spaced for subcarrier, often organize the corresponding two color light road of subcarrier.All optical link signals all on selected subcarrier with Alamouti method at N=1,2 two leading OFDM symbol place ZC sequence.

Such as, select ruddiness and green glow to take even number subcarrier, blue light and gold-tinted take odd number subcarrier, then have $X_{2k}^{\left(0\right)}\left(1\right)=s_{2k},X_{2k}^{\left(0\right)}\left(2\right)=-s_{2k}^{*},X_{2k}^{\left(1\right)}\left(1\right)=s_{2k},X_{2k}^{\left(1\right)}\left(2\right)=s_{2k}^{*},$ $X_{2k+1}^{\left(2\right)}\left(1\right)=s_{2k+1},X_{2k+1}^{\left(2\right)}\left(2\right)=-s_{2k+1}^{*},X_{2k+1}^{\left(3\right)}\left(1\right)=s_{2k+1},X_{2k+1}^{\left(3\right)}\left(2\right)=s_{2k+1}^{*}.$ This leading design is as shown in table 2,2k and 2k+1 represents even number subcarrier and odd number subcarrier sequence number respectively herein, 0≤2k, 2k+1≤K-1.

The leading method for designing of table 2 (B) exemplary scenario

Subcarrier is divided into nonoverlapping odd and even number group by the program, and two groups of light signals are isolated on frequency domain.All signals at N=1, with Alamouti mode orthogonalization on 2 two symbols.The program can estimate H _kin the half coefficient of every a line or each row, second half coefficient is by producing the coefficient interpolation on adjacent sub-carrier.Compared to scheme (A), scheme (B) decreases leading symbol quantity, makes system transfers efficiency higher.But some channels obtained by interpolation and interference coefficient may have larger channel estimation errors.In addition, the leading OFDM symbol in N=0 moment is only for frame synchronization, when single receiving terminal receives all optical links simultaneously, following improvement can be done: only select a road light signal to send ZC sequence at whole effectively subcarrier at N=0, rely on this road signal to complete frame synchronization, LS estimation or LMMSE method of estimation can be utilized simultaneously to obtain H _kthe column vector channel coefficients of this road signal of middle correspondence.N=1, the leading symbol of 2 still can press such scheme design, and the channel estimation results obtained thus can be averaged with the result that obtains on the symbol of N=0 further, thus makes some coefficients estimate more accurate.

(C) to use the four coloured light systems of RGBA LED, N is got _p=2, get a certain Lu Guangru ruddiness and send signal on all subcarriers, and for other three road light, subcarrier is divided into three groups at equal intervals, every road light takies wherein one group of subcarrier, two leading OFDM symbol coordinates first via light place ZC sequence (making each subcarrier can place sequence by Alamouti method in two color light and two time-domain symbol) with Alamouti method.Such as, make $X_{k_2}^{\left(2\right)}\left(0\right)=s_{k_2},X_{k_2}^{\left(2\right)}\left(1\right)=s_{k_2}^{*},X_{k_3}^{\left(3\right)}\left(0\right)=s_{k_3},X_{k_3}^{\left(3\right)}\left(1\right)=s_{k_3}^{*},$ Wherein k ₁, k ₂, k ₃for the subcarrier sequence number of dividing into groups at equal intervals, 0≤k ₁, k ₂, k ₃≤ K-1.This leading design is as shown in table 3.

The leading method for designing of table 3 (C) exemplary scenario

The program is compared with scheme (A), (B), required leading OFDM symbol is less, but except the channel coefficients of riches all the way the number of delivering letters is except all subcarriers can be estimated, the channel coefficients of all the other optical path signals only can direct estimation on the subcarrier of 1/3rd, and the coefficient on its remaining sub-carriers is produced by interpolation.

(2) after receiving terminal receives multi-pass signal, the Received signal strength each subcarrier adopting the two color light of Alamouti method in two leading OFDM symbol is merged, calculate the channel between each link and interference coefficient estimated value.

The present invention, when carrying out leading design, make use of Alamouti coding method, is one group sends orthogonal signalling with two color light signal on appointment subcarrier and two leading OFDM symbol.When receiving terminal carries out channel coefficients and interference coefficient estimates, the Received signal strength in these two leading OFDM symbol is merged, with the diversity gain utilizing Alamouti method to bring.Specifically, if the i of configuration, j two ways of optical signals meets at n=n ₁, n ₂two leading OFDM symbol have $X_k^{\left(i\right)}\left(n_1\right)=s_k,X_k^{\left(i\right)}\left(n_2\right)=-s_k^{*},X_k^{\left(j\right)}\left(n_1\right)=s_k,$ then for arbitrary l road light receiving signal with have

$Y_k^{\left(l\right)}\left(n_1\right)=h_k^{\left(\mathrm{il}\right)}{X}_k^{\left(i\right)}\left(n_1\right)+h_k^{\left(\mathrm{jl}\right)}{X}_k^{\left(j\right)}\left(n_1\right)=h_k^{\left(\mathrm{il}\right)}{s}_k+h_k^{\left(\mathrm{jl}\right)}{s}_k$

$Y_k^{\left(l\right)}\left(n_2\right)=h_k^{\left(\mathrm{il}\right)}{X}_k^{\left(i\right)}\left(n_2\right)+h_k^{\left(\mathrm{jl}\right)}{X}_k^{\left(j\right)}\left(n_2\right)=h_k^{\left(\mathrm{il}\right)(-s_k^{*})}+h_k^{\left(\mathrm{jl}\right)}{s}_k^{*}$

Channel coefficients can be obtained thus with estimated value with for

${\tilde{h}}_k^{\left(\mathrm{il}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}-Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

${\tilde{h}}_k^{\left(\mathrm{jl}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}+Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

Because the light signal that each group uses by Alamouti method in above-mentioned each scheme is isolation in subcarrier in frequency domain, then can estimate sent optical link signal to the channel of any light path or interference coefficient on corresponding subcarrier.There is the subcarrier do not placed and send signal in some light paths in scheme (B) and (C), and the estimated result interpolation of adjacent sub-carrier can obtain by the channel on these subcarriers or interference coefficient.

Leading symbol design during such scheme describes can change according to the channel situation of real system and performance requirement.Such as, in scheme (C), ZC sequence can be laid by the good a shade of prioritizing selection Signal to Interference plus Noise Ratio condition on whole effectively subcarrier, obtain its channel estimation value more accurately, thus more adequately eliminate this coloured light signal to the interference of other chrominance signal in the operation of follow-up Interference Cancellation.The corresponding relation on scheme (B) and (C) sub-carriers group and different color light road also can substitute in turn in every frame, and by the channel estimation results of consecutive frame is average, improves overall channel estimation accuracy.

Leading design provided by the invention also can be used in the ofdm communication system using superframe structure, and adjusts as required.If the length of a superframe is N _sindividual OFDM symbol, and containing multiple short frame in a superframe.For the indoor visible light communication system with quasi-static channel opens, synchronously can carry out in cycle longer each superframe, and only need carry out the estimation of channel and interference in each short frame.Therefore need in each superframe to comprise the targeting sequencing supporting frame synchronization, and only need to comprise the targeting sequencing supporting channel and Interference Estimation in remaining each short frame.Selection collocation can be carried out for this situation in above-mentioned 3 kinds of schemes, thus improve system effectiveness.Such as: Choice (B), the leading OFDM symbol number of getting first short frame in superframe is 3, and described in placement schemes (B) { n=0,1,2} tri-OFDM symbol are to complete synchronous and channel estimation function simultaneously.And the leading OFDM symbol number of follow-up short frame is taken as 2, in a delivery plan (B) { n=1,2} two symbols are to complete the estimation of channel and interference coefficient.Also can by used in combination for three kinds of leading schemes, such as, in superframe, the leading symbol of first short frame is by scheme (C) design, and the leading symbol of follow-up short frame get in scheme (B) { n=1,2} two symbols can make each short frame length be consistent like this.

The effect of the inventive method is described below in conjunction with concrete simulation example, considers the four coloured light ofdm communication systems using RGBA LED, use 128 subcarriers, wherein effectively subcarrier is 4 ~ No. 123 120 altogether.Signal bandwidth is 50MHz.

Shown in Fig. 1 is the signal interference ratio of each optical path signal that the channel condition used in emulation produces.

The transmission signal setting four coloured light in emulation adopts identical modulation system, and wherein 4 ~ 31 sub carriers adopt 256-QAM modulation, and 32 ~ 79 sub carriers adopt 64-QAM modulation, and 80 ~ 123 sub carriers adopt 16-QAM modulation, and its remaining sub-carriers does not send data.The data acquisition encoding low density parity check of 3/4 identical code check.Transmitting terminal produces 4 random road independent data streams, after a series of activities such as coding, QAM modulation, OFDM modulation, produces 4 tunnel time domains and sends signal, sent by RGBA LED with four coloured light signals.Light signal, after polychrome channel, adds white Gaussian noise, obtains the 4 road Received signal strength be disturbed of making an uproar at receiving terminal.

The performance of three kinds of leading designs of example that the present invention proposes is compared respectively in emulation.Being implemented as follows of three kinds of schemes:

(1) N is got _p=4.Four leading OFDM symbol are divided into { N=0,2} and { N=1,3} two groups.Ruddiness and green glow take { N=0,2} two leading OFDM symbol, { N=1,3} two leading OFDM symbol that blue light and gold-tinted take.The modes of emplacement of ZC sequence is see table 1.

(2) N is got _p=3.When N=0, each coloured light all sends complete original ZC sequence.For N=1,2, select ruddiness and green glow to take even number subcarrier, blue light and gold-tinted take odd number subcarrier.The modes of emplacement of ZC sequence is see table 2.Cubic algebraic curves method is used during interpolation.

(3) N is got _p=2.Ruddiness sends signal on all subcarriers of two leading OFDM symbol.Subcarrier is divided into three groups at equal intervals, green, blue, yellow every coloured light takies wherein one group of subcarrier simultaneously.The modes of emplacement of ZC sequence is see table 3.Cubic algebraic curves method is used during interpolation.

In emulation, under the signal interference ratio condition that Fig. 1 is given, the power of the additive white Gaussian noise in adjustment channel, obtains different Signal to Interference plus Noise Ratio conditions at receiving terminal, the receptivity under more different Signal to Interference plus Noise Ratio.

The channel parameter of channel estimation methods to each link that receiving terminal provides by the present invention is to received signal estimated, and compare with the channel theory value that sets in emulation, observe the normalized mean squared error (NMSE) of channel estimating, its computing formula is:

$\mathrm{NMSE}=\frac{1}{L}\underset{l=1}{\overset{L}{\mathrm{\Σ}}}\frac{{\left|\right|h-{\tilde{h}}_l\left|\right|}^2}{{\left|\right|h\left|\right|}^2}$

Wherein L is the totalframes of emulation, be the channel estimation value in l frame, h is channel theory value.

Fig. 2 gives leading design that the present invention provides and the normalized mean squared error that channel estimation methods is estimated at different signal to noise ratio condition lower channel.Because the gain for four coloured light of channel used in emulation is different, the received signal to noise ratio that each road signal obtains is not identical yet.In general, the error of channel estimating reduces along with increasing of received signal to noise ratio.Compare In the view of between three kinds of leading designs, the growth owing to using interpolation to bring channel estimation errors to a certain extent in scheme (2) and (3).

Receiving terminal, after carrying out channel estimating, needs to carry out the process such as solution mediation decoding to received signal, to obtain receiving data.The frame error rate performance of system under relatively following two kinds of demodulation schemes in simulations: scheme one directly carries out independently soft demodulation to four road light signals, sends into decoder for decoding after obtaining soft amount information; Scheme two is that Xian Dui tetra-road light signal carries out counteracting serial interference according to signal to noise ratio order from high to low, carries out independently demodulation coding process again after counteracting.Fig. 3 gives the leading design and channel estimation methods that utilize the present invention to provide, after the estimated value obtaining channel and interference coefficient, and the frame error rate simulation result obtained after receiving terminal uses above-mentioned two schemes to process respectively.Can find out, scheme (2) and (3) due to channel estimation errors comparatively large, the rising of error probability to a certain extent can be brought, but 3 kinds of schemes overall performance after having carried out counteracting serial interference process is closely.Therefore, enough and under higher scene is required to efficiency of transmission in signal to noise ratio condition, the scheme using expense less can be considered.

Although the present invention with preferred embodiment disclose as above, so itself and be not used to limit the present invention.Persond having ordinary knowledge in the technical field of the present invention, without departing from the spirit and scope of the present invention, when being used for a variety of modifications and variations.Therefore, protection scope of the present invention is when being as the criterion depending on those as defined in claim.

Claims (6)

1. the leading design of multicolor visible light DCO-OFDM communication system and channel estimation methods, if frame length is N in multicolor visible light DCO-OFDM communication system _findividual OFDM symbol, N wherein _pindividual OFDM symbol is leading symbol, it is characterized in that, described method comprises the steps:

(1) transmitting terminal is selected to adopt following (A) ~ (C) either method to produce leading symbol according to actual channel conditions and system performance requirements;

(A) leading OFDM symbol and polychromatic light are divided into groups respectively, often organize and comprise two leading OFDM symbol and two color light respectively, often organize two color light and on all effective subcarrier of one group of two leading OFDM symbol, place ZC sequence with Alamouti coding method;

(B) each coloured light places ZC sequence on all effective subcarrier of first leading symbol, effective subcarrier of all the other leading symbols is equally spaced divided into odd number group and even number set, and polychromatic light is divided into groups, often organize two color light and in odd subcarriers or even subcarriers, place ZC sequence with Alamouti coding method;

(C) choose a shade and place ZC sequence on all effective subcarrier of all leading symbols, and effective subcarrier of each leading symbol is divided into groups at equal intervals, all the other coloured light take one group of subcarrier separately, coordinate selected coloured light in the subcarrier group of the correspondence of two leading OFDM symbol, to place ZC sequence with Alamouti coding method respectively;

(2) after receiving terminal receives multi-pass signal, the Received signal strength each subcarrier adopting the two color light of Alamouti method in two leading OFDM symbol is merged, calculate the channel between each link and interference coefficient estimated value.

2. the leading design of multicolor visible light DCO-OFDM communication system according to claim 1 and channel estimation methods, it is characterized in that, in described method (A), polychromatic light is four coloured light, leading OFDM symbol number N _p=4,4 leading OFDM symbol are divided into two groups, and four coloured light are divided into two groups, often organize two color light and on all effective subcarrier of one group of leading symbol, place ZC sequence by Alamouti coding method respectively, specifically arrange satisfied:

$X_k^{\left(m_0\right)}\left(n_0\right)=s_k,X_k^{\left(m_0\right)}\left(n_1\right)=-s_k^{*},$

$X_k^{\left(m_1\right)}\left(n_0\right)=s_k,X_k^{\left(m_1\right)}\left(n_1\right)=s_k^{*},$

Wherein S _kfor the ZC sequential value on k sub carriers, m ₀and m ₁represent same group of two color light sequence number, n ₀and n ₁represent same group of two leading symbol sequence numbers.

3. the leading design of multicolor visible light DCO-OFDM communication system according to claim 1 and channel estimation methods, it is characterized in that, in described method (B), polychromatic light is four coloured light, odd number group and even number set is divided into by equally spaced for effective subcarrier of all the other the leading OFDM symbol except first leading OFDM symbol, four coloured light are also divided into two groups, often organize two color light and in odd subcarriers or even subcarriers, place ZC sequence with Alamouti method respectively, for group two color light of on even number or odd subcarriers, specifically arrange satisfied:

$X_k^{\left(m_0\right)}\left(n_1\right)=s_k,X_k^{\left(m_0\right)}\left(n_2\right)=-s_k^{*},$

$X_k^{\left(m_1\right)}\left(n_1\right)=s_k,X_k^{\left(m_1\right)}\left(n_2\right)=s_k^{*},$

Wherein, s _kfor the ZC sequential value on k sub carriers, m ₀and m ₁represent the same group of two color light sequence number taking odd number or even subcarriers, n ₁and n ₂represent two leading OFDM symbol sequence numbers.

4. the leading design of multicolor visible light DCO-OFDM communication system according to claim 1 and channel estimation methods, it is characterized in that, in described method (C), get a shade and place ZC sequence on all effective subcarrier of all leading symbols, arrange satisfied:

$X_k^{\left(m_i\right)}\left(n_0\right)=s_k{,X}_k^{\left(m_i\right)}\left(n_1\right)=-s_k^{*},$

Wherein, m ₁represent coloured light sequence number of getting, n ₀and n ₁represent two leading OFDM symbol sequence numbers;

The quantity of subcarrier according to all the other coloured light divided into groups at equal intervals, every coloured light takies one group of subcarrier, and often organizing, arranging of ZC sequence on subcarrier is satisfied:

$X_{k_j}^{\left(m_j\right)}\left(n_0\right)=s_{k_j},X_{k_j}^{\left(m_j\right)}\left(n_1\right)=s_{k_j}^{*},$

Wherein, m _jrepresent all the other coloured light sequence numbers, k _jrepresent m _jthe subcarrier sequence number of road coloured light correspondence grouping, for k _jzC sequential value on sub carriers.

5. the leading design of multicolor visible light DCO-OFDM communication system according to claim 1 and channel estimation methods, is characterized in that, the concrete grammar calculating channel between each link and interference coefficient estimated value in described step (2) comprises:

Alamouti method is pressed n-th for the i-th, j two-way light ₁and n ₂the k sub carriers of individual leading OFDM symbol there is transmission signal $X_k^{\left(i\right)}\left(n_1\right)=s_k,X_k^{\left(i\right)}\left(n_2\right)=-s_k^{*},$ $X_k^{\left(j\right)}\left(n_1\right)=s_k,X_k^{\left(j\right)}\left(n_2\right)=s_k^{*}$ Time, then by any l road light receiving signal with channel or interference coefficient is obtained according to following formula with estimated value

${\tilde{h}}_k^{\left(\mathrm{il}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}-Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

${\tilde{h}}_k^{\left(\mathrm{jl}\right)}=\frac{Y_k^{\left(l\right)}\left(n_1\right)s_k^{*}-Y_k^{\left(l\right)}\left(n_2\right)s_k}{2{\left|\right|s_k\left|\right|}^2}$

Obtain the channel between any two optical links or interference coefficient thus;

For the channel value do not placed on the subcarrier of ZC sequence, utilize and have the channel coefficients estimated value on the subcarrier of ZC sequence to carry out interpolation to obtain.

6. the leading design of multicolor visible light DCO-OFDM communication system and channel estimation methods, if adopt superframe structure in multicolor visible light DCO-OFDM communication system, the length of superframe is N _sindividual OFDM symbol, wherein comprise multiple short frame, it is characterized in that, described method comprises the steps:

(1) transmitting terminal generates the leading symbol of first short frame of superframe according to method described in claim 1 (A) ~ (C) either method;

(2) transmitting terminal generates the leading symbol of all the other each short frames according to the method for all the other leading symbols generated except first leading symbol in method described in claim 1 (A) ~ (C) either method or described method (B);

(3) after receiving terminal receives multi-pass signal, the Received signal strength each subcarrier adopting the two color light of Alamouti method in two leading OFDM symbol is merged, calculate the channel between each link and interference coefficient estimated value.