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 PDFInfo
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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
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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