CN108631832A - In conjunction with the multiuser MIMO-OOFDM visible light communication methods of index modulation - Google Patents

In conjunction with the multiuser MIMO-OOFDM visible light communication methods of index modulation Download PDF

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CN108631832A
CN108631832A CN201810455353.9A CN201810455353A CN108631832A CN 108631832 A CN108631832 A CN 108631832A CN 201810455353 A CN201810455353 A CN 201810455353A CN 108631832 A CN108631832 A CN 108631832A
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subcarrier
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CN108631832B (en
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江明
蔡鲲翼
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Wuhu Fangchang Information Technology Co ltd
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Sun Yat Sen University
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0452Multi-user MIMO systems
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B10/00Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/11Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
    • H04B10/114Indoor or close-range type systems
    • H04B10/116Visible light communication
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0456Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L1/00Arrangements for detecting or preventing errors in the information received
    • H04L1/004Arrangements for detecting or preventing errors in the information received by using forward error control
    • H04L1/0056Systems characterized by the type of code used
    • H04L1/0071Use of interleaving
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2602Signal structure
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2626Arrangements specific to the transmitter only
    • H04L27/2627Modulators
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2697Multicarrier modulation systems in combination with other modulation techniques

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Radio Transmission System (AREA)
  • Detection And Prevention Of Errors In Transmission (AREA)

Abstract

The present invention considers the stronger high-speed transfer VLC scenes of indoor reflection, excavate potential technology binding site and innovative point, by introducing IM concepts, it is combined with OOFDM technologies and multi-User Indoor scene, devises the multiuser MIMO OOFDM visible light communication systems based on IM.By IM technologies, each user can be carried out data transmission using symbolic information on carrier wave and carrier index information simultaneously, and multi-user system is made to obtain more steady transmission link in typical indoor environment, effectively improve the whole bit error rate of system(Bit Error Ratio, BER)Performance.

Description

In conjunction with the multiuser MIMO-OOFDM visible light communication methods of index modulation
Technical field
The present invention is towards the field visible light communication (Visible Light Communication, VLC), it is proposed that a kind of Based on index modulation (Index Modulation, IM) new indoor multi-user pre-coding (Multi-User Precoding, MUP) multiple-input and multiple-output (Multiple-Input Multiple-Output, MIMO) light orthogonal frequency division multiplexing (Optical Orthogonal Frequency Division Multiplexing, OOFDM) VLC communication means.
Background technology
With in era development and daily life, the extensive of light emitting diode (Light-Emitting Diode, LED) answers With the VLC technologies based on LED light are gradually favored by various countries researcher, and expand numerous studies to it.VLC technology masters It to be based on intensity modulated and directly detect, it is transmitted using the insignificant fast-changing light intensity of power of human eye into row information. The MIMO technology being widely used in traditional wireless communication is also obtained in the advantage of System Expansion etc. in VLC technologies by it Extensive use is obtained, it effectively can realize that house data transmits using multiple LED light simultaneously, the transmission rate of raising VLC systems.Cause This, MIMO technology is combined with VLC technologies and is increasingly becoming the research hotspots of current VLC communication systems.
Extension and application of multi-user's (Multi-User, MU) MIMO technology as MIMO technology, are also studied recently The extensive concern of person.It is belonged to a user with all photodetectors (Photodetector, PD) in common MIMO-VLC systems The case where terminal, is different, and multiuser MIMO-VLC systems support that multiple user terminals, each terminal include one or more PD.Multi-user MIMO system eliminates inter-user interference (Multi-User by certain interference cancellation algorithm Interference, MUI), so that multiple user terminals is led to without interfering with each other using identical LED light array simultaneously Letter.
Orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) technology is more A kind of multi-subcarrier multiplexing technology that carrier modulation (Multi-Carrier Modulation, MCM) develops, can be effective Inhibit intersymbol interference (Intersymbol Interference, ISI) caused by fading channel, therefore is developed by OFDM technology And the OOFDM technologies come also are increasingly being used for high speed VLC systems, overcome indoor light in high-speed transfer to signal Negative effect caused by scattering, to support the indoor VLC signal transmissions of higher rate.Currently, in conjunction with OOFDM to indoor anti- The research for penetrating the high speed multiuser MIMO visible light communication system under stronger environment is also fewer.It introduces New Wireless Technologies and excavates Binding site is potentially applied, is a kind of common thinking for designing novel indoor high-speed multi-user's VLC systems.Orthogonal frequency division multiplexing Index modulation (Orthogonal Frequency Division Multiplexing with Index Modulation, OFDM-IM) technology is a kind of Novel OFDM concept of rising in recent years, it utilizes this new dimension of index information into row information Transmission, the transmission performance of system is improved with this.Specifically, IM concepts are on the basis for transmitting information using subcarrier modulation symbols On, also further realize that information is transmitted using the index information dimension of sub-carrier activation combination simultaneously.With conventional OFDM technique phase Than OFDM-IM is in such as binary phase shift keying (Binary Phase Shift Keying, BPSK) and orthogonal amplitude keying In low-order-modulateds such as (Quadrature Phase Shift Keying, QPSK) can utilize IM concepts in index information it is potential Transmission reliability obtains certain performance gain, has potential binding site and innovative space with various technologies.
Invention content
The present invention considers the stronger high-speed transfer VLC scenes of indoor reflection, excavates potential technology binding site and innovative point, By introducing IM concepts, it is combined with OOFDM technologies and multi-User Indoor scene, devises the multiuser MIMO-based on IM OOFDM visible light communication methods.By IM technologies, each user can use symbolic information and carrier index on carrier wave to believe simultaneously Breath carries out data transmission, and multi-user system is made to obtain more steady transmission link in typical indoor environment, effectively improves and is Whole bit error rate (Bit Error Ratio, BER) performance of system.
To realize the above goal of the invention, the technical solution adopted is that:
In conjunction with the multiuser MIMO-OOFDM visible light communication methods of index modulation, include the following steps:
S1. for multiuser MIMO-OOFDM systems, each user can be first divided into per the B bits of data stream input G groups, this withThe G IM sub-block that a available subcarrier is divided into is corresponding, NFIt is Fast Fourier Transform (FFT) and anti-fast Fourier The points of transformation;Wherein, the number of sub carrier wave N that each IM sub-blocks includeSFor
S2. the N of each IM sub-blocksSThere was only L in a subcarrierSA subcarrier, which is indexed selector, to be chosen and is activated, remaining NS-LSA subcarrier, which is not activated, to be set to 0;Therefore sub-carrier activation combination can indicate in p bitsA ratio Spy, whereinIndicate the total number of combinations for taking b element to be combined number operation in the set for having a element at one,It indicates Downward floor operation;Therefore sharedThe different sub-carrier activation combination of kind, all C kinds in each IM sub-blocks is possible The set of sub-carrier activation combination is denoted as
ΩU={ U1,U2,...,UC} (2)
Wherein Indicate l in c-th of activation combinationsA son being activated Carrier index, and for all c=1,2 ..., C and ls=1,2 ..., LSHaveRemaining p2=Lf log2(M) a bit will pass through M rank planispheres ΩMIt is mapped as LfA M ranks constellation symbols, are denoted as
S=[s (1), s (2) ..., s (Lf)] (3)
Wherein for ls=1,2 ..., LfThere are s (ls)∈ΩM, they will be modulated at IM sub-blocks LfA son being activated On carrier wave;
S3. r is usedj(j=1,2 ..., J) indicates the data stream number of j-th of user, definitionTo pass through the above IM The user j r that method obtainsjG-th of (1 × N on data streamS) dimension IM sub-blocks, whereinIndicate user j rjN-th in g-th of IM sub-block on data streamsA IM Signal in sub-block on subcarrier;
S4. in each OOFDM symbol times, the overall transmission rate of the multi-user system is
Wherein NCPFor the length of the cyclic prefix of OFDM symbol;
S5. it definesFor user j rjAll G (1 × N on data streamS) Tie up IM sub-blocksCompositionIM total data blocks are tieed up, are indicated as follows
S6. the subcarrier element between same user's different data streams is interleaved operation, by all data of the user Stream is considered as a virtual long data flow, is then interleaved operation, defines Xj(j=1,2 ..., J) it is obtained by formula (5) All R of user jjThe corresponding R of data streamjA IM total datas blockCompositionDimension waits for that interleaving block is as follows:
It operates, can be obtained by interweavingThe interleaved data of dimensionIt is as follows:
S7. after interweaving in formula (7)Dimension data vectorIt is reclassified as RjIt is aDimension data Block, as user j per the data block of data stream actual transmissions;After repartitioning, the r of j-th of userjOn data streamDimensional data blockFor
S8. it is N to be based on total number of sub carrier waveFIt is assumed that enabling subcarrier number nfValue from 0 to NF-1;It defines on frequency domain N-thf(R × N on a subcarrierT) all user's frequency domain channel matrix of dimension are
H(nf)=[H1(nf)T,H2(nf)T,...,HJ(nf)T]T (9)
Wherein Hj(nf) indicate j-th of user n-thf(R on a subcarrierj×NT) dimension frequency domain channel matrix;In ACO- In OFDM,A available subcarrier corresponds to subcarrier numberIt only needs to these subcarrier numbers Corresponding frequency domain channel matrix carries out BD pre-encode operations;
S9. forUsing BD method for precoding to H (nf) operation is carried out, it finds out on the frequency domain point Each user pre-coding matrix;Define n-thfIn addition to j-th of ((R-R with open air on a subcarrierj)×NT) Wesy's family letter Mend matrix in road:
It is rightSVD decomposition steps be accordingly written as
Wherein ((R-Rj)×(R-Rj)) dimension matrixContain all left singular vectors, ((R-Rj)×NT) dimension square Battle arrayIndicate singular value matrix;Definition Tie up matrixBefore containing A right singular vector,Tie up matrixRemaining right singular vector is then contained,In it is each Vector is located atKernel in;It usually assume that channel full rank, haveTo obtain n-thfHeight The equivalent channel matrix of user j is on carrier waveTo equivalent channel matrixContinue The step of SVD is decomposed accordingly is written as:
Wherein Λj(nf) it is (Rj×Rj) dimension singular value diagonal matrix, Uj(nf) it is for last demodulated signal (Rj× Rj) dimension unitary matrice, (Rj×Rj) dimension matrixContain right singular vector;Finally obtain j-th of user n-thfHeight carries (N on waveT×Rj) dimension pre-coding matrix Pj(nf)
S10. F (n are definedf) it is n-th after precodingf(N on a subcarrierT× 1) dimension frequency domain data vector;ForThisThe available subcarrier of a ACO-OFDM, has
Wherein uj(nf) it is j-th of user n-thf(R on a subcarrierj× 1) dimension pre-code data vector, it is by formula (8) Middle transmission data blockInterior corresponding element is constituted
Also i.e. by data blockIn element according to the mapping ruler of ACO-OFDM available subcarriers, be mapped to corresponding position It postpones and carries out precoding again;
Due to the zero padding operations of ACO-OFDM, work as nfFor even number when, have (NT× 1) dimension data vector F (0)=F (2) =... ,=F (NF- 2)=0;Symmetry operation is conjugated by ell rice spy, and is hadMost (the N of J user is constituted eventuallyT×NF) dimension ACO-OFDM frequency domain matrix FsinputFor
S11. corresponding time domain real number signal is obtained after IFFT is handled, and remembers the time domain after IFFT on i-th of LED Real number signal is x0,i(t), which is a real number signal;Negative real-valued signal slicing is obtained according to the principle of ACO-OFDM It is to final transmission signal
In the VLC systems using intensity modulated and Direct Inspection Technology, definition LED electro-optic conversion coefficients are μ, then i-th The mathematic expectaion of a light emitted signals of LED is the average emitted luminous power P of the lampopt,i=E { μ xi(t)};In conjunction with ACO-OFDM Time-domain signal characteristic it is found that i-th of LED average emitted luminous power Popt,iThe frequency domain data after precoding with i-th of LED Electrical power is directly proportional;Usual each subcarrier in frequency domain is after pre-coding matrix is handled, the frequency domain data electric work on each LED Rate is different, therefore the transmitting luminous power of each LED is different;And LED is usually symmetrically arranged on indoor ceiling in practice On plate, in order to ensure indoor Uniform Illumination, the average light power P that needs each LED to send outopt,i(i=1,2 ..., NT) to the greatest extent may be used Can be identical, therefore in multiuser MIMO-OOFDM visible light communication systems, it should the LED smaller to average light power adds volume Outer direct current biasing remembers N to ensure Uniform IlluminationTGreatest hope luminous power in a LED is
The additional dc that should be added on i-th of LED biases sizeBy straight After stream biasing adjustment, while reaching VLC information transmission purpose, it can also meet the needs of indoor Uniform Illumination;By uniform After illumination adjustment, the transmitting signal on i-th of LEDFor
It is consistent that they meet the average light power that all LED are sent out, that is, has
S12. in subscriber terminal side, PD receives the optical information from free space;After VLC transmissions, r-th of PD On time-domain received signal can be expressed as
Wherein hr,i(t) the VLC time domain channel impulses response between i-th of LED and r-th of PD is indicated,It indicates the The time domain optical signal sent out on i LED, nr(t) the time domain zero-mean real number additive white Gaussian noise on r-th of PD, γ are indicated Indicate the photoelectric conversion coefficient of PD,Indicate the convolution operation of time-domain signal;
S13. optical signal is received after the light-intensity test of PD and photoelectric conversion processing, optical signal is converted into electric signal, Electric signal progress ACO-OFDM demodulation is received to time domain, frequency domain data can be obtained;According to BD precoding record principles, forJ-th of user n-thfEquivalent frequency domain on a subcarrier receives signal Yj(nf) be
Wherein nj(nf) indicate j-th of user n-thfCorresponding frequency domain zero-mean AWGN vectors on a subcarrier;Use formula (12) matrix U generatedj(nf) conjugate transposition Y that formula (22) is obtainedj(nf) handled, obtain j-th of user n-thfIt is a (R treated on subcarrierj× 1) dimensional vectorAs follows
S14. for all j=1,2 ..., J and corresponding rj=1,2 ..., Rj, the ACO- that is obtained using formula (23) Received vector on OFDM available subcarriersRepresent user j r as followsjData stream OnThe reception data block of dimension
Wherein
It indicates from singular value diagonal matrix Λj(2lc- 1) (r is taken inj,rj) a element operation,Indicate demodulated frequency domain AWGN signals;Convolution (15), hasTherefore It isCorresponding reception data vector;Since the sub-carrier interleaving of formula (6) and formula (7) operates, each IM is in the block each Symbol is dispersed in the lower different sub-carrier of correlation and transmits, at this time can not be byDirectly recover user j rjItem IM sub-blocks to be demodulated each of in data flow, thus need first to will be dispersed in the IM sub-blocks internal symbol of user's j pieces of data streams with And corresponding equivalent channel singular value extracts, and is reconstructed into IM sub-blocks to be demodulated;
Specifically, first by all R of user j in formula (24)jIt is obtained on data streamTie up data block to be demodulatedCompositionThe data vector of dimension
S15. it in user's j receiving terminals, is pressed again by formula (25) by the sub-carrier interleaving rule defined in formula (6) and formula (7) Formula reconstructs rjG-th of (1 × N on data streamS) dimension IM sub-blocks to be demodulated
For all ns=1,2 ..., NS, have
Secondly as in IM sub-blocks to be demodulated each element be once dispersed to a plurality of data flow of user everywhere into Row transmission, therefore before the demodulation of completion pair, it is also necessary to the undergone actual channel of each element by Correspondence singular value by same rule extraction reconstruct;User j rjCorrespondence on the last available subcarrier of data stream is unusual Value, can arrange the singular value vector for dimension
WhereinExpression is derived from singular value matrix Λ in formula (23)j(2lc- 1) r injItem number According to the correspondence singular value of stream;By all R of user jjData stream is correspondingCompositionThe singular value vector λ of dimensionj(j =1,2 ..., J)
Similarly, by formula (28) it is restructural go out user j rjG-th of (1 × N received on data streamS) dimension IM to be demodulated Sub-blockCorresponding demodulation singular value vector
For all ns=1,2 ..., NS, have
S16. pass through the above operation, you can obtain and belong on the every data stream of each user after deinterleaving at user terminal IM sub-blocks to be demodulatedWith corresponding user's equivalent channel singular value
S17. according to IM concept principles, for each IM sub-blocks to be demodulatedDemodulation is based primarily upon two kinds of criterion, a kind of It is to be based on ML criterion, one is based on LLR criterion;
When selecting based on the demodulation of ML criterion, for each IM sub-blocks, need to search for all possible transmitting vector combination; Specifically, defining the collection that all possible transmitting vector combination is constituted is combined into ΩX, defined according to maximum likelihood, the IM of estimation Sub-blockIt can be generated by following formula
WhereinIt indicates with vectorGenerate the operation of corresponding diagonal matrix;By all possible IM sub-blocks Transmitting vector substitutes into (30) and combines the IM sub-blocks transmitting vector for solving estimationThe index of p bits can be recovered simultaneously Information and symbolic information;Obviously, ML demodulated complexs degree is with the exponent number M of the modulation symbol planisphere carried on subcarrier and each IM sub-blocks are activated sub-carrier number LSAnd the trend exponentially risen;
Demodulation based on LLR criterion is a kind of linear demodulation method, it avoids the demodulated complex degree of index rising;Have Performance identical with ML;Therefore it is a kind of better choice to this system demodulation using LLR criterion;In the method, first First calculate each IM sub-blocks to be demodulatedIn n-thsThe LLR value of a subcarrierWherein ns=1,2 ..., NS, as follows It is shown
Wherein sχIt is the χ modulation symbol of mapped on M rank planispheres,It is the correspondence for the calculating of LLR ratios Frequency domain AWGN power;Therefore, according toThe subcarrier in whole IM sub-blocks, i.e., total N can be calculatedSThe LLR value of a subcarrier; In next step, all c=1,2 ..., C are taken out in the definition of sub-carrier activation combination in convolution (2)Corresponding son carries Wave activation combinationThe sum of LLR
It is all according to what is be calculatedA LLR and, judgement it is as follows
Namely it chooses with maximum LLR and corresponding theA setAs IM sub-blocks Sub-carrier activation combination optimal solution, to obtain corresponding index information bit group p1;Then according toFor lsIt is a The subcarrier of activation solves the constellation symbols being activated on subcarrier
Finally obtain LfA sign information bits group p being activated on subcarrier2
Description of the drawings
Multi-User Indoor MIMO-OOFDM visible light communication system the general frames of the Fig. 1 based on IM
The example of operation schematic diagram of sub-carrier interleaving between Fig. 2 IM data block customer traffics
The generalized flow chart of multiuser MIMO-OOFDM visible light communication methods of the Fig. 3 based on IM
The BER performances of different system compare figure under two kinds of position examples when Fig. 4 M=2
The BER performances of different system compare figure under two kinds of position examples when Fig. 5 M=4
The BER performances of different system compare figure under two kinds of position examples when Fig. 6 M=8
Specific implementation mode
The attached figures are only used for illustrative purposes and cannot be understood as limitating the patent;
Below in conjunction with drawings and examples, the present invention is further elaborated.
Embodiment 1
It is the new indoor multiuser MIMO-OOFDM visible light communication system models based on IM as shown in Figure 1.Assuming that room It is uniformly distributed N on the ceiling of inner roomTA LED has J user terminal in room, and j-th of user terminal is equipped with RjA PD It works, needs the data fluxion Q supportedjIt can be set as Qj=Rj.The core of multi-user pre-coding algorithm is sending out signal Sending end is handled to eliminate MUI, and block diagonalization method (Block Diagonalization, BD) is a kind of simple linear Method for precoding, its decoding complex degree is low, can be conveniently used in small-sized receiving device to reduce energy consumption.BD precodings The basic principle of method is to design the interference that pre-coding matrix is used to eliminate between user to want under the limitation of BD method for precoding The number of data streams Q of j-th of user transmission when seeking transmission signalj≤RjAndFor convenience, might as well assumeTherefore haveBit information of each user per data stream passes through respective IM moulds Block processing, generates frequency domain IM modulation datas;The IM modulation datas of same user are handled by the sub-carrier interleaving of this user, finally Form each user frequency domain data to be transmitted.In order to also meet the transmission requirement of VLC channels, frequency domain while eliminating MUI Data generate nonnegative real number time-domain signal after corresponding pre-encode operation and OOFDM processing, are finally carried on NTOn a LED It sends.
In receiver side, after the PD of each user terminal receives optical signal, frequency is recovered by corresponding OOFDM demodulation Numeric field data, operates further according to multi-user's demodulation method and with corresponding inverse IM, and each user is modulated per the IM on data stream Data extract, and finally use maximum likelihood (Maximum Likelihood, ML) or log-likelihood ratio (Log- Likelihood Ratio, LLR) demodulate the Information recovering for completing each user.
The focus of system is its new structural structure and design, namely emits from signal, signal transmission to signal The whole process for receiving processing, sequentially will be specifically introduced and illustrate according to this below.Simultaneously for ease of description, this hair It is bright with asymmetric slicing light OFDM (Asymmetrically Clipped Optical Orthogonal Frequency Division Multiplexing, ACO-OFDM) for system is illustrated, but, the present invention points out, the program is same Suitable for other OOFDM systems, such as direct current biasing light OFDM (DC Biased Optical OFDM, DCO-OFDM), monopole Property OFDM (Unipolar OFDM, U-OFDM) etc..
Assuming that NFIt is Fast Fourier Transform (FFT) (Fast Fourier Transform, FFT) and an inverse fast fourier The points of (Inverse Fast Fourier Transform, IFFT) namely the total number of sub-carriers of an OOFDM symbol.For The non-negative real value time-domain signal for meeting VLC transmission conditions is generated, OOFDM needs to carry out zero padding and ell rice spy's conjugate pair Claim operation, therefore in the N of ACO-OFDMFIn a subcarrier, onlyA available subcarrier.If used in this system Other OOFDM modulation techniques then can accordingly be pre-processed by its feature, be wanted with meeting identical nonnegative real number signal It asks.
For traditional multiuser MIMO-OOFDM systems, it is assumed that each user is defeated per data stream in per OOFDM symbols Enter B bits, this B bit will all be mapped as corresponding quadrature amplitude modulation (Quadrature Amplitude Modulation, QAM) constellation symbols and it is modulated at all of ACO-OFDMOn a available subcarrier.But in IM concepts In, only some bit information can indicate that another part bit information is then by specific using constellation symbols in B bits Activation sub-carrier indices information indicate.Therefore, in the present system, each user can be first per the B bits of data stream input First be divided into G groups, this withThe G IM sub-block that a available subcarrier is divided into is corresponding.Wherein, the son that each IM sub-blocks include Carrier number NSFor
Therefore, each IM sub-blocks correspond toA bit.
It is different with all available subcarriers are all activated in traditional OOFDM modes mode, according to setting for IM concepts Count principle, the N of each IM sub-blocksSThere was only L in a subcarrierSA subcarrier, which is indexed selector, to be chosen and is activated, remaining NS- LSA subcarrier, which is not activated, to be set to 0.Therefore sub-carrier activation combination can indicate in p bitsA ratio Spy, whereinIndicate the total number of combinations for taking b element to be combined number operation in the set for having a element at one,It indicates Downward floor operation.In other words, it sharesKind different sub-carrier activation combinations, specific sub-carrier activation combination can be by Lookup table mode is determined.The set of the possible sub-carrier activation combination of all C kinds in each IM sub-blocks is denoted as
ΩU={ U1,U2,...,UC} (2)
Wherein Indicate l in c-th of activation combinationsA son being activated Carrier index, and for all c=1,2 ..., C and ls=1,2 ..., LSHaveRemaining p2=LS log2(M) a bit will pass through M rank planispheres ΩMIt is mapped as LSA M ranks constellation symbols, are denoted as
S=[s (1), s (2) ..., s (LS)] (3)
Wherein for ls=1,2 ..., LSThere are s (ls)∈ΩM, they will be modulated at IM sub-blocks LSA son being activated On carrier wave.
For the convenience of description, present invention rj(j=1,2 ..., J) indicates the data stream number of j-th of user.DefinitionTo pass through the above IM The user j r that method obtainsjG-th of (1 × N on data streamS) dimension IM sub-blocks, whereinIndicate user j rjN-th in g-th of IM sub-block on data streamsA IM Signal in sub-block on subcarrier, it had both been likely to be some symbol in planisphere, it is also possible in zero son not being activated The nil symbol being arranged on carrier wave.
With NS=4, LSFor=3, table 1 gives tabling look-up for IM sub-blocks and realizes example.In this embodiment, every per user Each IM sub-blocks index information partial bit number of data flow is p1=2.
Table 1NS=4, LS=3, p1=2 IM sub-block examples
Index bit combines (p1=2) Activate the index of subcarrier combination IM sub-blocks
[0 0] {1 2 3} [s(1)s(2)s(3)0]
[0 1] {1 2 4} [s(1)s(2)0 s(3)]
[1 0] {1 3 4} [s(1)0 s(2)s(3)]
[1 1] {2 3 4} [0 s(1)s(2)s(3)]
Therefore, in each OOFDM symbol times, the overall transmission rate of the multi-user system is
Wherein NCPFor the length of the cyclic prefix of OFDM symbol.
DefinitionFor user j rjAll G (1 × N on data streamS) dimension IM Sub-blockCompositionIM total data blocks are tieed up, are indicated as follows
To give full play to the potentiality of IM technologies, this system use sub-carrier interleaving mode come to multi-user VLC systems into Row design, i.e., the subcarrier element between same user's different data streams is interleaved operation.Specifically, by the institute of the user There is data flow to be considered as a virtual long data flow, is then interleaved operation.Specifically, defining Xj(j=1,2 ..., J) For all R of user j obtained by formula (5)jThe corresponding R of data streamjA IM total datas blockCompositionDimension waits for Interleaving block is as follows
It operates, can be obtained by interweavingThe interleaved data of dimensionIt is as follows
For purposes of illustration only, Fig. 2 gives user's schematic diagram of j data flow sub-carrier interleavings.The figure assumes that user j shares Rj =2 data streams, NF=32,NS=4, there is G=2 IM sub-block per data stream.
As shown in Figure 2, it after intertexture, originally belongs to no longer be placed adjacent with a symbol for IM sub-blocks, but it is discrete To entire frequency domain.Therefore, belong to and can be uploaded in the alap sub-carrier channels of correlation with the symbol in IM sub-blocks It is defeated, the channel selectivity that signal transmission is undergone is increased, to can get frequency selectivity diversity gain, this will improve each Same group of p corresponding to IM sub-blocks1The BER performances of a IM bits, so as to improve overall performance.
It particularly points out herein, Fig. 2 is only a kind of interleaving scheme of Exhibition Design thinking, and not unique scheme.It is practical In system, the interleaving scheme to match can be reasonably selected according to the fading profiles of channel.
It completes to interweave after operation, after the present invention will interweave in formula (7)Dimension data vectorIt is reclassified as RjIt is aDimensional data block, as user j per the data block of data stream actual transmissions.After repartitioning, j-th of user RjOn data streamDimensional data blockFor
It is N based on total number of sub carrier waveFIt is assumed that enabling subcarrier number nfValue from 0 to NF-1.It defines the on frequency domain nf(R × N on a subcarrierT) all user's frequency domain channel matrix of dimension are
H(nf)=[H1(nf)T,H2(nf)T,...,HJ(nf)T]T (9)
Wherein Hj(nf) indicate j-th of user n-thf(R on a subcarrierj×NT) dimension frequency domain channel matrix.In ACO- In OFDM,A available subcarrier corresponds to subcarrier numberIt only needs to these subcarrier numbers Corresponding frequency domain channel matrix carries out BD pre-encode operations.
Therefore, forUsing BD method for precoding to H (nf) operation is carried out, find out the frequency domain point On each user pre-coding matrix.Pay attention to it being to be used the frequency domain channel matrix corresponding to subcarrier to carry out to each here Operation.Define n-thfIn addition to j-th of ((R-R with open air on a subcarrierj)×NT) dimension subscriber channel mend matrix be
It is rightSVD decomposition steps be accordingly written as
Wherein ((R-Rj)×(R-Rj)) dimension matrixContain all left singular vectors, ((R-Rj)×NT) dimension square Battle arrayIndicate singular value matrix.Definition Tie up matrixBefore containing A right singular vector,Tie up matrixRemaining right singular vector is then contained,In it is each Vector is located atKernel in.It usually assume that channel full rank, haveTo obtain n-thfHeight The equivalent channel matrix of user j is on carrier waveTo equivalent channel matrixContinue The step of SVD is decomposed accordingly is written as
Wherein Λj(nf) it is (Rj×Rj) dimension singular value diagonal matrix, Uj(nf) it is for last demodulated signal (Rj× Rj) dimension unitary matrice, (Rj×Rj) dimension matrixContain right singular vector.Finally obtain j-th of user n-thfHeight carries (N on waveT×Rj) dimension pre-coding matrix Pj(nf)
In addition, defining F (nf) it is n-th after precodingf(N on a subcarrierT× 1) dimension frequency domain data vector.ForThisThe available subcarrier of a ACO-OFDM, has
Wherein uj(nf) it is j-th of user n-thf(R on a subcarrierj× 1) dimension pre-code data vector, it is by formula (8) Middle transmission data blockInterior corresponding element is constituted
Also i.e. by data blockIn element according to the mapping ruler of ACO-OFDM available subcarriers, be mapped to corresponding position It postpones and carries out precoding again.
Secondly as the zero padding operations of ACO-OFDM, work as nfFor even number when, have (NT× 1) dimension data vector F (0)=F (2)=... ,=F (NF- 2)=0.Symmetry operation is conjugated by ell rice spy, and is had Finally constitute (the N of J userT×NF) dimension ACO-OFDM frequency domain matrix FsinputFor
Corresponding time domain real number signal is obtained after IFFT is handled, and remembers the time domain real number after IFFT on i-th of LED Signal is x0,i(t), which is a real number signal.Negative real-valued signal slicing is obtained most according to the principle of ACO-OFDM Sending signal eventually is
In the VLC systems using intensity modulated and Direct Inspection Technology, definition LED electro-optic conversion coefficients are μ, then i-th The mathematic expectaion of a light emitted signals of LED is the average emitted luminous power P of the lampopt,i=E { μ xi(t)}.In conjunction with ACO-OFDM Time-domain signal characteristic it is found that i-th of LED average emitted luminous power Popt,iThe frequency domain data after precoding with i-th of LED Electrical power is directly proportional.Usual each subcarrier in frequency domain is after pre-coding matrix is handled, the frequency domain data electric work on each LED Rate is different, therefore the transmitting luminous power of each LED is different.And LED is usually symmetrically arranged on indoor ceiling in practice On plate, in order to ensure indoor Uniform Illumination, the average light power P that needs each LED to send outopt,i(i=1,2 ..., NT) to the greatest extent may be used Can be identical, therefore in multiuser MIMO-OOFDM visible light communication systems, it should the LED smaller to average light power adds volume Outer direct current biasing remembers N to ensure Uniform IlluminationTGreatest hope luminous power in a LED is
The additional dc that should be added on i-th of LED biases sizeBy straight After stream biasing adjustment, while reaching VLC information transmission purpose, it can also meet the needs of indoor Uniform Illumination.By uniform After illumination adjustment, the transmitting signal on i-th of LEDFor
It is consistent that they meet the average light power that all LED are sent out, that is, has
In addition, central subcarrier does not carry any data, therefore OOFDM systems in the present invention in OOFDM systems In to realize the time domain DC component added of Uniform Illumination, DC subcarriers are only appeared in after FFT is handled in receiving terminal On, do not interfere with the demodulation of any data-signal.
In subscriber terminal side, PD receives the optical information from free space.After VLC transmissions, on r-th of PD Time-domain received signal can be expressed as
Wherein hr,i(t) indicate that the VLC time domain channel impulses between i-th of LED and r-th of PD respond, x~i(t) it indicates The time domain optical signal sent out on i-th of LED, nr(t) the time domain zero-mean real number additive white Gaussian noise on r-th of PD is indicated (Additive White Gaussian Noise, AWGN), γ indicate the photoelectric conversion coefficient of PD,Indicate time-domain signal Convolution operation.
Optical signal is received after the light-intensity test of PD and photoelectric conversion processing, optical signal is converted into electric signal, clock synchronization Domain receives electric signal progress ACO-OFDM demodulation and frequency domain data can be obtained.According to BD precoding record principles, forJ-th of user n-thfEquivalent frequency domain on a subcarrier receives signal Yj(nf) be
Wherein nj(nf) indicate j-th of user n-thfCorresponding frequency domain zero-mean AWGN vectors on a subcarrier.Use formula (12) matrix U generatedj(nf) conjugate transposition Y that formula (22) is obtainedj(nf) handled, obtain j-th of user n-thfIt is a (R treated on subcarrierj× 1) dimensional vectorAs follows
For all j=1,2 ..., J and corresponding rj=1,2 ..., Rj, the ACO-OFDM obtained using formula (23) can With the received vector on subcarrierRepresent user j r as followsjOn data streamThe reception data block of dimension
Wherein
It indicates from singular value diagonal matrix Λj(2lc- 1) (r is taken inj,rj) a element operation,Indicate demodulated frequency domain AWGN signals.Convolution (15), hasTherefore It isCorresponding reception data vector.Since the sub-carrier interleaving of formula (6) and formula (7) operates, each IM is in the block each Symbol is dispersed in the lower different sub-carrier of correlation and transmits, at this time can not be byDirectly recover user j rjItem IM sub-blocks to be demodulated each of in data flow, thus need first to will be dispersed in the IM sub-blocks internal symbol of user's j pieces of data streams with And corresponding equivalent channel singular value extracts, and is reconstructed into IM sub-blocks to be demodulated.
Specifically, first by all R of user j in formula (24)jIt is obtained on data streamTie up data block to be demodulatedCompositionThe data vector of dimension
Again by the sub-carrier interleaving rule defined in formula (6) and formula (7), in user's j receiving terminals, weighed as the following formula by formula (25) Structure goes out rjG-th of (1 × N on data streamS) dimension IM sub-blocks to be demodulated
For all ns=1,2 ..., NS, have
Secondly as in IM sub-blocks to be demodulated each element be once dispersed to a plurality of data flow of user everywhere into Row transmission, therefore before the demodulation of completion pair, it is also necessary to the undergone actual channel of each element by Correspondence singular value by same rule extraction reconstruct.User j rjCorrespondence on the last available subcarrier of data stream is unusual Value, can arrange the singular value vector for dimension
WhereinExpression is derived from singular value matrix Λ in formula (23)j(2lc- 1) r injItem number According to the correspondence singular value of stream.By all R of user jjData stream is correspondingCompositionThe singular value vector λ of dimensionj(j =1,2 ..., J)
Similarly, by formula (28) it is restructural go out user j rjG-th of (1 × N received on data streamS) dimension IM to be demodulated Sub-blockCorresponding demodulation singular value vector
For all ns=1,2 ..., NS, have
By operating above, you can obtain to belong to after deinterleaving on the every data stream of each user at user terminal and wait for Demodulate IM sub-blocksWith corresponding user's equivalent channel singular value
According to IM concept principles, for each IM sub-blocks to be demodulatedDemodulation is based primarily upon two kinds of criterion, and one is bases In ML criterion, one is based on LLR criterion.
When selecting based on the demodulation of ML criterion, for each IM sub-blocks, need to search for all possible transmitting vector combination. Specifically, defining the collection that all possible transmitting vector combination is constituted is combined into ΩX, defined according to maximum likelihood, the IM of estimation Sub-blockIt can be generated by following formula
WhereinIt indicates with vectorGenerate the operation of corresponding diagonal matrix.By all possible IM sub-blocks Transmitting vector substitutes into (30) and combines the IM sub-blocks transmitting vector for solving estimationThe index of p bits can be recovered simultaneously Information and symbolic information.Obviously, ML demodulated complexs degree is with the exponent number M of the modulation symbol planisphere carried on subcarrier and each IM sub-blocks are activated sub-carrier number LSAnd the trend exponentially risen.
Demodulation based on LLR criterion is a kind of linear demodulation method, it avoids the demodulated complex degree of index rising.Have Performance identical with ML.Therefore it is a kind of better choice to this system demodulation using LLR criterion.In the method, first First calculate each IM sub-blocks to be demodulatedIn n-thsThe LLR value of a subcarrierWherein ns=1,2 ..., NS, as follows It is shown
Wherein sχIt is the χ modulation symbol of mapped on M rank planispheres,It is the correspondence for the calculating of LLR ratios Frequency domain AWGN power.Therefore, according toThe subcarrier in whole IM sub-blocks, i.e., total N can be calculatedSThe LLR value of a subcarrier. In next step, all c=1,2 ..., C are taken out in the definition of sub-carrier activation combination in convolution (2)Corresponding son carries Wave activation combinationThe sum of LLR
It is all according to what is be calculatedA LLR and, judgement it is as follows
Namely it chooses with maximum LLR and corresponding theA setAs IM sub-blocks Sub-carrier activation combination optimal solution, to obtain corresponding index information bit group p1.Then according toFor lsIt is a The subcarrier of activation solves the constellation symbols being activated on subcarrier
Finally obtain LSA sign information bits group p being activated on subcarrier2
Finally, the present invention has been presented in Fig. 3 the generalized flow chart of present system.
Embodiment 2
It is further right below in conjunction with simulation result and analysis more fully to illustrate advantageous effect possessed by the present invention Effectiveness of the invention and advance are explained.
In the present embodiment, analogue system chooses typical indoor room model, and room dimension is 6m × 6m × 3m, room center Centre is coordinate origin, and N is symmetrical arranged on ceilingT=4 LED light, are located at the center of four quadrants.User terminal number J=2, each user terminal are equipped with 2 PD and support two data streams, i.e. Q1=Q2=R1=R2=2.It is small in order to meet equipment The demand of type is set as the 10cm in classical model with the distance between 2 PD of user terminal, and is set to reduce miniaturization The channel relevancy of standby middle PD, 2 PD with user terminal are used as one using different field angles (Filed-of View, FOV) Kind reduces the realization method example of channel relevancy, is set to 70 ° and 50 °, while assuming that user terminal is all located at from the ground In the use plane of 0.85m high.Interior VLC channels emulate the signal-to-noise ratio of use using classical ray tracing model in emulation (Signal-to-Noise Ratio, SNR) is consistent with document, is the SNR of LED transmitting terminals, is defined asWherein PTIt is total average intensity that shines of indoor all LED,It is time domain AWGN power.
BPSK, QPSK and 8QAM and 16QAM of the present invention selection M=2, M=4, M=8 are more as the tradition not using IM The modulation scheme of user's MIMO-OOFDM systems.In order to keep the system peak transmission rate consistent with comparison system scheme, adopt The specific embodiment of this system is provided as with such as the following table 2:
The parameter list of 2 this system specific embodiment of table
Assuming that user terminal 1 is located among room (0,0,0.85), user terminal 2 chooses two positions as the imitative of system Position 1 is set as (0.2,0.2,0.85) by true example, and position 2 is set as (2.7,2.7,0.85).Particularly, it is preferably to present Importance of the system features with embodiment sub-carrier interleaving in the present system, other than traditional multiuser MIMO-OOFDM systems, The present invention also without using sub-carrier interleaving but will use the system schema of IM and be compared together.Fig. 4 to fig. 6 gives each system System compares figure using the BER performances in the case of different M values.
As shown in Figures 4 to 6, in simulating scenes, user terminal 2 in two user distance proximity 1, due to Channel relevancy is extremely strong, and the systematic performance of institute is decreased obviously.From figure it can also be seen that, in two exemplary scenes, due to room The particularity of interior VLC channels, the last performance of multiuser MIMO visible light communication system are deep by user terminal specific location Influence, but the rule of difference is similar between the relative performance between different system.Therefore, below will under position 2 not It discusses for the performance of homologous ray.
It can be seen from fig. 4 to fig. 6 in M=2, with multi-user's IM visible light communication systems of sub-carrier interleaving in BER It is 10-5To 10-6When the about gain of 3dB compared with legacy system, when M=4 is visible using the multi-user IM of sub-carrier interleaving Optical communication system performance when SNR is 146dB starts to be better than tradition OOFDM systems, is 10 in BER-5To 10-6When have about The gain of 1.2dB.When M=8, declined using the novel system gain of sub-carrier interleaving, but still have about 0.6dB in high SNR Gain.
It can thus be seen that under interior VLC environment of the present invention, it can using the multi-user IM of sub-carrier interleaving Light-exposed communication system can obtain certain performance gain under different low-order-modulateds, to improve communication system as far as possible Transmission reliability.According to IM technological concepts, after rationally designing system using IM, have benefited from combining using sub-carrier indices The overall performance of the promotion of the information of transmission reliability at higher SNR, system can also make moderate progress.
In contrast, the multiuser MIMO-OOFDM-IM visible light communication systems and tradition of sub-carrier interleaving are not used MIMO-OOFDM visible light communication systems are compared, and good performance gain can hardly be all embodied under all settings.Big In most cases, the BER performances of the system only approach in high SNR or are slightly better than legacy system, this is also further embodied Importance of the sub-carrier interleaving in terms of playing the multiuser MIMO-OOFDM visible light communication system potentiality based on IM.
Obviously, the above embodiment of the present invention be only to clearly illustrate example of the present invention, and not be pair The restriction of embodiments of the present invention.For those of ordinary skill in the art, may be used also on the basis of the above description To make other variations or changes in different ways.There is no necessity and possibility to exhaust all the enbodiments.It is all this All any modification, equivalent and improvement etc., should be included in the claims in the present invention made by within the spirit and principle of invention Protection domain within.

Claims (1)

1. combining the multiuser MIMO-OOFDM visible light communication methods of index modulation, it is characterised in that:Include the following steps:
S1. for multiuser MIMO-OOFDM systems, each user can be first divided into G groups per the B bits of data stream input, This withThe G IM sub-block that a available subcarrier is divided into is corresponding, NFIt is Fast Fourier Transform (FFT) and an inverse fast fourier Points;Wherein, the number of sub carrier wave N that each IM sub-blocks includeSFor
S2. the N of each IM sub-blocksSThere was only L in a subcarrierSA subcarrier, which is indexed selector, to be chosen and is activated, remaining NS-LS A subcarrier, which is not activated, to be set to 0;Therefore sub-carrier activation combination can indicate in p bitsA bit, WhereinIndicate the total number of combinations for taking b element to be combined number operation in the set for having a element at one,Indicate to Lower floor operation;Therefore sharedThe different sub-carrier activation combination of kind, by all possible sons of C kinds in each IM sub-blocks The set of carrier activation combination is denoted as
ΩU={ U1,U2,...,UC} (2)
Wherein Indicate l in c-th of activation combinationsA subcarrier being activated Index, and for all c=1,2 ..., C and ls=1,2 ..., LSHaveRemaining p2=Lflog2 (M) a bit will pass through M rank planispheres ΩMIt is mapped as LfA M ranks constellation symbols, are denoted as
S=[s (1), s (2) ..., s (Lf)] (3)
Wherein for ls=1,2 ..., LfThere are s (ls)∈ΩM, they will be modulated at IM sub-blocks LfA subcarrier being activated On;
S3. r is usedj(j=1,2 ..., J) indicates the data stream number of j-th of user, definitionTo pass through the above IM The user j r that method obtainsjG-th of (1 × N on data streamS) dimension IM sub-blocks, whereinIndicate user j rjN-th in g-th of IM sub-block on data streamsA IM Signal in sub-block on subcarrier;
S4. in each OOFDM symbol times, the overall transmission rate of the multi-user system is
Wherein NCPFor the length of the cyclic prefix of OFDM symbol;
S5. it definesFor user j rjAll G (1 × N on data streamS) dimension IM BlockCompositionIM total data blocks are tieed up, are indicated as follows
S6. the subcarrier element between same user's different data streams is interleaved operation, and all data flows of the user are regarded For a virtual long data flow, it is then interleaved operation, defines Xj(j=1,2 ..., J) it is the user obtained by formula (5) All R of jjThe corresponding R of data streamjA IM total datas blockCompositionDimension waits for that interleaving block is as follows:
It operates, can be obtained by interweavingThe interleaved data of dimensionIt is as follows:
S7. after interweaving in formula (7)Dimension data vectorIt is reclassified asDimensional data block is made It is the data block of the every data stream actual transmissions of user j;After repartitioning, the r of j-th of userjOn data streamDimensional data blockFor
S8. it is N to be based on total number of sub carrier waveFIt is assumed that enabling subcarrier number nfValue from 0 to NF-1;It defines n-th on frequency domainf (R × N on a subcarrierT) all user's frequency domain channel matrix of dimension are
H(nf)=[H1(nf)T,H2(nf)T,...,HJ(nf)T]T (9)
Wherein Hj(nf) indicate j-th of user n-thf(R on a subcarrierj×NT) dimension frequency domain channel matrix;In ACO-OFDM,A available subcarrier corresponds to subcarrier numberIt only needs to the corresponding frequency of these subcarrier numbers Domain channel matrix carries out BD pre-encode operations;
S9. forUsing BD method for precoding to H (nf) operation is carried out, it finds out every on the frequency domain point The pre-coding matrix of a user;Define n-thfIn addition to j-th of ((R-R with open air on a subcarrierj)×NT) dimension subscriber channel benefit Matrix is:
It is rightSVD decomposition steps be accordingly written as
Wherein ((R-Rj)×(R-Rj)) dimension matrixContain all left singular vectors, ((R-Rj)×NT) dimension matrixIndicate singular value matrix;Definition Tie up matrixBefore containingIt is a Right singular vector,Tie up matrixRemaining right singular vector is then contained,In respectively to Amount is located atKernel in;It usually assume that channel full rank, haveTo obtain n-thfHeight carries The equivalent channel matrix of user j is on waveTo equivalent channel matrixContinue The step of SVD is decomposed accordingly is written as:
Wherein Λj(nf) it is (Rj×Rj) dimension singular value diagonal matrix, Uj(nf) it is for last demodulated signal (Rj×Rj) dimension Unitary matrice, (Rj×Rj) dimension matrixContain right singular vector;Finally obtain j-th of user n-thfOn a subcarrier (NT×Rj) dimension pre-coding matrix Pj(nf)
S10. F (n are definedf) it is n-th after precodingf(N on a subcarrierT× 1) dimension frequency domain data vector;ForThisThe available subcarrier of a ACO-OFDM, has
Wherein uj(nf) it is j-th of user n-thf(R on a subcarrierj× 1) dimension pre-code data vector, it in formula (8) by passing Transmission of data blockInterior corresponding element is constituted
Also i.e. by data blockIn element according to the mapping rulers of ACO-OFDM available subcarriers, after being mapped to corresponding position Precoding is carried out again;
Due to the zero padding operations of ACO-OFDM, work as nfFor even number when, have (NT× 1) dimension data vector F (0)=F (2)=..., =F (NF- 2)=0;Symmetry operation is conjugated by ell rice spy, and is hadMost (the N of J user is constituted eventuallyT×NF) dimension ACO-OFDM frequency domain matrix FsinputFor
S11. corresponding time domain real number signal is obtained after IFFT is handled, and remembers the time domain real number after IFFT on i-th of LED Signal is x0,i(t), which is a real number signal;Negative real-valued signal slicing is obtained most according to the principle of ACO-OFDM Sending signal eventually is
In the VLC systems using intensity modulated and Direct Inspection Technology, definition LED electro-optic conversion coefficients are μ, then i-th of LED The mathematic expectaion of light emitted signal is the average emitted luminous power P of the lampopt,i=E { μ xi(t)};In conjunction with ACO-OFDM when Domain characteristics of signals it is found that i-th of LED average emitted luminous power Popt,iFrequency domain data electric work after precoding with i-th of LED Rate is directly proportional;For usual each subcarrier in frequency domain after pre-coding matrix is handled, the frequency domain data electrical power on each LED is each It differs, therefore the transmitting luminous power of each LED is different;And LED is usually symmetrically arranged in indoor ceiling in practice, In order to ensure indoor Uniform Illumination, the average light power P for needing each LED to send outopt,i(i=1,2 ..., NT) phase as far as possible Together, therefore in multiuser MIMO-OOFDM visible light communication systems, it should which the LED smaller to average light power adds additional Direct current biasing remembers N to ensure Uniform IlluminationTGreatest hope luminous power in a LED is
The additional dc that should be added on i-th of LED biases sizeIt is inclined by direct current After setting adjustment, while reaching VLC information transmission purpose, it can also meet the needs of indoor Uniform Illumination;By Uniform Illumination After adjustment, the transmitting signal on i-th of LEDFor
It is consistent that they meet the average light power that all LED are sent out, that is, has
S12. in subscriber terminal side, PD receives the optical information from free space;After VLC transmissions, on r-th of PD Time-domain received signal can be expressed as
Wherein hr,i(t) the VLC time domain channel impulses response between i-th of LED and r-th of PD is indicated,It indicates at i-th The time domain optical signal sent out on LED, nr(t) indicate that the time domain zero-mean real number additive white Gaussian noise on r-th of PD, γ indicate The photoelectric conversion coefficient of PD,Indicate the convolution operation of time-domain signal;
S13. optical signal is received after the light-intensity test of PD and photoelectric conversion processing, and optical signal is converted into electric signal, clock synchronization Domain receives electric signal progress ACO-OFDM demodulation and frequency domain data can be obtained;According to BD precoding record principles, forJ-th of user n-thfEquivalent frequency domain on a subcarrier receives signal Yj(nf) be
Wherein nj(nf) indicate j-th of user n-thfCorresponding frequency domain zero-mean AWGN vectors on a subcarrier;It is raw using formula (12) At matrix Uj(nf) conjugate transposition Y that formula (22) is obtainedj(nf) handled, obtain j-th of user n-thfA subcarrier Upper treated (Rj× 1) dimensional vectorAs follows
S14. for all j=1,2 ..., J and corresponding rj=1,2 ..., Rj, the ACO-OFDM obtained using formula (23) can With the received vector on subcarrierRepresent user j r as followsjOn data streamThe reception data block of dimension
Wherein
It indicates from singular value diagonal matrix Λj(2lc- 1) (r is taken inj,rj) a element operation,Indicate demodulated frequency domain AWGN signals;Convolution (15), hasTherefore It isCorresponding reception data vector;Since the sub-carrier interleaving of formula (6) and formula (7) operates, each IM is in the block each Symbol is dispersed in the lower different sub-carrier of correlation and transmits, at this time can not be byDirectly recover user j rjItem IM sub-blocks to be demodulated each of in data flow, thus need first to will be dispersed in the IM sub-blocks internal symbol of user's j pieces of data streams with And corresponding equivalent channel singular value extracts, and is reconstructed into IM sub-blocks to be demodulated;
Specifically, first by all R of user j in formula (24)jIt is obtained on data streamTie up data block to be demodulated CompositionThe data vector of dimension
S15. it in user's j receiving terminals, is weighed as the following formula by formula (25) by the sub-carrier interleaving rule defined in formula (6) and formula (7) again Structure goes out rjG-th of (1 × N on data streamS) dimension IM sub-blocks to be demodulated
For all ns=1,2 ..., NS, have
Secondly as IM sub-blocks to be demodulatedIn each element be once dispersed to and passed everywhere with a plurality of data flow of user It is defeated, therefore in completion pairDemodulation before, it is also necessary to willIn each elementPair of undergone actual channel It answers singular value to extract by same rule to reconstruct;User j rjOn data streamCorrespondence singular value on a available subcarrier, It can arrange and beThe singular value vector of dimension
WhereinExpression is derived from singular value matrix Λ in formula (23)j(2lc- 1) r injData stream Corresponding singular value;By all R of user jjData stream is correspondingCompositionThe singular value vector λ of dimensionj(j=1, 2,...,J)
Similarly, by formula (28) it is restructural go out user j rjG-th of (1 × N received on data streamS) dimension IM sub-blocks to be demodulatedCorresponding demodulation singular value vector
For all ns=1,2 ..., NS, have
S16. by the above operation, you can obtain to belong to after deinterleaving on the every data stream of each user at user terminal and wait for Demodulate IM sub-blocksWith corresponding user's equivalent channel singular value
S17. according to IM concept principles, for each IM sub-blocks to be demodulatedDemodulation is based primarily upon two kinds of criterion, and one is bases In ML criterion, one is based on LLR criterion;
When selecting based on the demodulation of ML criterion, for each IM sub-blocks, need to search for all possible transmitting vector combination;Specifically For, it defines the collection that all possible transmitting vector combination is constituted and is combined into ΩX, defined according to maximum likelihood, the IM sub-blocks of estimationIt can be generated by following formula
WhereinIt indicates with vectorGenerate the operation of corresponding diagonal matrix;All possible IM sub-blocks are emitted Vector substitutes into (30) and combines the IM sub-blocks transmitting vector for solving estimationThe index information of p bits can be recovered simultaneously And symbolic information;Obviously, ML demodulated complexs degree with the modulation symbol planisphere carried on subcarrier exponent number M and each IM Block is activated sub-carrier number LSAnd the trend exponentially risen;
Demodulation based on LLR criterion is a kind of linear demodulation method, it avoids the demodulated complex degree of index rising;Have and ML Identical performance;Therefore it is a kind of better choice to this system demodulation using LLR criterion;In the method, it counts first Calculate each IM sub-blocks to be demodulatedIn n-thsThe LLR value of a subcarrierWherein ns=1,2 ..., NS, as follows
Wherein sχIt is the χ modulation symbol of mapped on M rank planispheres,It is the correspondence frequency domain for the calculating of LLR ratios AWGN power;Therefore, according toThe subcarrier in whole IM sub-blocks, i.e., total N can be calculatedSThe LLR value of a subcarrier;It is next It walks, the definition of sub-carrier activation combination in convolution (2), to all c=1,2 ..., C, taking-upCorresponding subcarrier swashs Combination livingThe sum of LLR
It is all according to what is be calculatedA LLR and, judgement it is as follows
Namely it chooses with maximum LLR and corresponding theA setAs IM sub-blocksSon The optimal solution of carrier activation combination, to obtain corresponding index information bit group p1;Then according toFor lsA activation Subcarrier, solve the constellation symbols being activated on subcarrier
Finally obtain LfA sign information bits group p being activated on subcarrier2
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