CN105812309B - A kind of modulator approach reducing OFDM-VLC system peak-to-average power ratio - Google Patents
A kind of modulator approach reducing OFDM-VLC system peak-to-average power ratio Download PDFInfo
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- 239000013598 vector Substances 0.000 claims abstract description 63
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2614—Peak power aspects
- H04L27/2623—Reduction thereof by clipping
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
- H04B10/116—Visible light communication
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Abstract
Modulator approach provided by the invention is by carrying out specific peak clipping to visible light vector signal and mapping is handled so that the peak-to-average power ratio of the visible light communication system based on orthogonal frequency division multiplexing is effectively reduced, while can also lifting system bit error rate performance.
Description
Technical field
The present invention proposes one kind towards the field visible light communication (Visible Light Communication, VLC)
Based on can effectively being promoted for light orthogonal frequency division multiplexing (Optical Frequency Division Multiplexing, OOFDM)
Bit error rate (Bit Error Rate, BER) performance and reduction system peak-to-average power ratio (Peak-to-Average Power
Ratio, PAPR) new type of modulation scheme.
Background technique
With light emitting diode in the development and daily life of modern science and technology (Light-emitting Diode,
LED) commonly used, technology is gradually for the visible light communication (Visible Light Communication, VLC) based on LED light
It is paid close attention to by each side and expands research to it.VLC mainly passes through intensity modulated (Intensity Modulation, IM) and straight
Detection (Direct Detection, DD) technology is connect, realizes information using the insignificant fast-changing light intensity of power of human eye
Transmission, that is, accomplish " Bian Zhaoming, Bian Tongxin ".At the same time, the widely applied orthogonal frequency division multiplexing in traditional wireless communication
(Orthogonal Frequency Division Multiplexing, OFDM) technology also relies on it in anti-interference, confrontation frequency
The advantage of rate Selective intensity etc. obtains more application in the field VLC.It can efficiently use indoor VLC channel
Feature realizes high speed data transfer, improves the transmission performance of VLC system.Therefore, in conjunction with the VLC system of OFDM technology also gradually at
For one of the hot spot of current research high speed VLC communication.
In actual typical indoor environment, a VLC system generally includes LED light, the Photoelectric Detection of transmitting optical information
Device (Photodetector, PD), physical layer, MAC layer etc., and realize that signal transmits by IM/DD technology.Basic interior
It can be seen that in light model, it is seen that optical channel link includes sighting distance (Line-of-Sight, LOS) and non line of sight (Non-LOS, NLOS)
Two kinds.Link and higher transmission loss due to dispersion, performance of the VLC system in high transfer rate is by intersymbol interference
The influence of (Inter-Symbol Interference, ISI).And ISI can be effectively inhibited using OFDM technology, promote VLC
System performance.However, traditional OFDM symbol is plural form, IM/DD modulation /demodulation can not be passed through.In this regard, many researchers
A variety of modified form OFDM suitable for visible light are proposed, such as non-homogeneous clipping light orthogonal frequency division multiplexing (Asymmetrically
Clipped Orthogonal Frequency Division Multiplexing, ACO-OFDM), direct current biasing orthogonal frequency
It is multiplexed (Orthogonal Frequency Division Multiplexing, DCO-OFDM, unipolarity light orthogonal frequency division multiplexing
(Unipolar Orthogonal Frequency Division Multiplexing, U-OFDM) etc., and to these new departures
Performance evaluation is carried out.These schemes are in bit error rate (Bit Error Rate, BER), peak-to-average power ratio (Peak to
Average Power Ratio, PAPR), the performances of the various aspects such as spectrum efficiency (Spectral Efficiency, SE) refers to
Mark respectively has superiority and inferiority.Therefore, it for the optimization of these performance indicators, is of great significance for the development and maturation of VLC technology.
Summary of the invention
The present invention on the basis of OFDM-VLC technology, has lacking compared with high papr values for it in existing conventional chamber
Point designs a kind of novel smooth OFDM modulation scheme with more excellent PAPR and BER performance.
To realize the above goal of the invention, the technical solution adopted is that:
A kind of modulator approach reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: the following steps are included:
(1) transmitting terminal
S1. serial/parallel conversion is carried out to bit stream information, bit stream information is mapped on planisphere, wherein the constellation
Figure is two dimensional constellation figure or three-dimensional constellation map；
S2. the constellation point on planisphere can be expressed as a space vector, then constellation point all in planisphere can be with
With a real number matrix SRIt indicates；
S3. real number matrix S S2 obtainedRIt is transformed to complex matrix SC；
S4. to complex matrix SCHermitian symmetry transformation is carried out, obtains meeting the symmetrical matrix S of Hermitianh；
S5. to matrix ShIFFT transformation is carried out, the real number matrix s in time domain is obtainedt；
S6. to real number matrix stAfter carrying out parallel-serial conversion, vector signal is obtained
S7. vector signal is calculatedAverage amplitude Vavg；
S8. reference amplitude V is calculated according to average amplituderef:
Vref=lVavg；
L indicates ratio of the reference amplitude relative to average amplitude；
S9. to vector signalOn each element skPeak clipping and mapping processing are carried out by formula (1), constructs vector
Wherein, m, n are the parameter of any value, and k meets 1≤k≤QN, and N is the quantity of symbol to be sent, and Q is planisphere
Dimension；
S10. vector is constructedCome record mapping processing Q-character, wherein
xck(1≤k≤QN) meets formula (2) or formula (3) or formula (4) or formula (5):
S11. in vectorElement between in be uniformly inserted into vectorElement, obtain length be 2QN vector
S12. by vectorLaunched by intensity modulation, and by modulated signal by LED light；
(2) receiving end
S13. the length that receiving end receives is set as the vector of 2QN
Then seek the reference level amplitude V of receiving endr′ef:
S14. implement " peak clipping mapping reduction " operation, obtain the vector that length is QN
Shown in specific as follows:
xckMeet formula (2)；
OrxckMeet formula (3)；OrxckMeet formula (4)；
OrxckMeet formula (5)；
The range of k meets 1≤k≤QN；
S15. to serial vectorSerioparallel exchange is carried out, the real number matrix of one (Q × N) can be obtained, to real number square
Battle array carries out FFT transform and obtains meeting symmetrical (Q × N) complex matrix of Hermitian, according to planisphere and maximum likelihood algorithm
Complex matrix is demodulated, bitstream data is obtained.
Preferably, the planisphere is three-dimensional constellation map；Then each constellation point can be expressed as a three-dimensional space to
AmountWherein xk,yk,zkFor three real number values, respectively representReference axis, so 2N three-dimensional star
The corresponding symbol of seat point can be expressed as one (3 × 2N) real number matrix SR:
Based on real number matrix SRThe complex matrix S of variationCIt indicates are as follows:
Wherein
Then meet the symmetrical matrix S of HermitianhIt indicates are as follows:
Wherein
ShCarry out IFFT transformation, obtained real number matrix stIt indicates are as follows:
Real number matrix stAfter carrying out parallel-serial conversion, the vector that length is 3N is obtained
It, will for the sake of intuitiveIt is write as:
For signal vector.
Preferably, after step S6 carries out parallel-serial conversion, to vector signalIn addition cyclic prefix, then executes step S7；
Step S14 seeks obtaining simultaneouslyAfterwards, rightCirculation prefix processing is gone in execution, then executes step S15.
Preferably, the calculating vector signalAverage amplitude VavgDetailed process is as follows:
Compared with prior art, the beneficial effects of the present invention are:
Modulator approach provided by the invention is by carrying out peak clipping and mapping processing to visible light vector signal, so that being based on
The peak-to-average power ratio of the visible light communication system of OFDM is effectively reduced, at the same can also lifting system bit error code it is forthright
Energy.
Detailed description of the invention
Fig. 1 is the schematic diagram using the OFDM-VLC system of " peak clipping mapping techniques ".
Fig. 2 is 16 planispheres of 3-D.
Fig. 3 is real number OFDM time domain signal vectorTiming diagram.
Fig. 4 is the positive number OFDM time domain signal vector by mapping processingTiming diagram.
Fig. 5 is peak clipping mapping treated signal vectorWith the vector comprising characteristic information of constructionTiming diagram.
Fig. 6 is the positive real number time domain OFDM signal vector transmitted in transmitting terminalTiming diagram.
Fig. 7 is the PAPR performance comparison schematic diagram of OFDM-VLC system.
Fig. 8 is the BER performance comparison schematic diagram of OFDM-VLC system.
Specific embodiment
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
Novel " peak clipping mapping techniques " proposed by the present invention, core are the electric signal by complex field with certain mapping rule
Preferable PAPR inhibitory effect and BER can be reached by the optical signal of the positive real number form of light intensity modulation by being then converted into
Energy.After optical signal is launched by LED light, complex field electric signal is reduced to same rule in receiving end.
Method provided by the invention the following steps are included:
One, receiving end
Step 1: as shown in Figure 1, bit information is mapped to constellation firstly the need of serial/parallel conversion is carried out by bit stream information
On figure.Planisphere involved in the present embodiment is three-dimensional constellation map.
Step 2: as shown in Fig. 2, each constellation point on 3-D planisphere is represented by a three-dimensional space vectorWherein xk,yk,zkFor three real number values, respectively representReference axis.Therefore, 2N three-dimensional star
The corresponding symbol of seat point can be expressed as the real number matrix of one (3 × 2N):
Step 3: needing to carry out quick inversefouriertransform to matrix since method provided by the invention is subsequent, so square
Battle array SRThe complex matrix of one (3 × N) can be further transformed to:
By the conversion process of complex matrix, behind Fourier transformation (Fast to be treated
FourierTransform, FFT) symbol lengths only have original half.
Step 4: in time domain obtaining real number matrix, needs the matrix carrying out Hermitian symmetry transformation, be expired
Symmetrical (3 × N) the matrix S of sufficient Hermitianh:
Wherein
Step 5: to matrix ShIFFT transformation is carried out, the real number matrix s in time domain is obtainedt；
The formula of IFFT transformation is as follows:
Wherein n1、n2Meet 0≤n respectively1≤ 2,0≤n2≤ N-1, k1And k2Then respectively indicate signal matrix SCRow subscript
With column subscript.
Step 6: to real number matrix stAfter carrying out parallel-serial conversion, vector signal is obtained
VectorIt is real vector.
Step 7: calculating vector signalAverage amplitude Vavg；
Wherein Q indicates planisphere dimension, is herein 3-D planisphere, therefore Q=3
Step 8: calculating reference amplitude V according to average amplituderef:
Vref=lVavg
L indicates that ratio of its reference amplitude relative to average amplitude, l are the customized parameter of user in formula.
Step 9: to vectorOn each element by it is following rule carry out peak clipping and mapping processing, construct vector
It is wherein the customized parameter of user.User can choose m, n and l value appropriate according to the design requirement of system.
Step 10: construction vectorCome record mapping processing Q-character, restore original signal for receiving end:
Wherein xck(1≤k≤QN) meets formula (2) or formula (3) or formula (4) or formula (5):
Step 11: in vectorElement between in be uniformly inserted into vectorElement, obtain length be 2QN vectorIt can be used to light intensity modulation:
Step 12: by vectorLaunched by intensity modulation, and by modulated signal by LED light.
Receiving end:
Step 13: receiving end receives the vector that length is 2QN by optical detectorAccording to central-limit theorem, when N is sufficiently large, OFDM symbol skIt falls
It is identical in the probability of positive and negative number interval.Therefore, the vector x constructedckIt also can be with (1/2) VrefSymmetrically, therefore in receiving end
The estimated value of reference level amplitude can acquire according to the following formula:
Step 14: implementing " peak clipping mapping reduction " operation according to algorithmic rule below, the vector that length is QN is obtained
xckMeet formula (2)；
OrxckMeet formula (3)；
OrxckMeet formula (4)；
OrMeet formula (5)；
The range of k meets 1≤k≤QN；
Step 15: to serial vectorSerioparallel exchange is carried out, the real number matrix of one (Q × N) can be obtained, to reality
Matrix number carries out FFT transform and obtains meeting symmetrical (Q × N) complex matrix of Hermitian, according to planisphere and maximum likelihood
Algorithm demodulates complex matrix, obtains bitstream data.
The embodiment of one " peak clipping mapping techniques " is provided below by way of Fig. 3-Fig. 6:
The embodiment that Fig. 3 is shown is after IFFT, parallel-serial conversion, meets N=3, the discrete OFDM time domain that length is 9 is believed
NumberIt can be seen that the characteristic of OFDM, maximum amplitude is higher, therefore PAPR is also higher, and signal amplitude have just have it is negative.
After peak clipping mapping variation, change as shown in Figure 4, vectorPeak-peak halves, and whole absolute values of real number meet IM/
DD modulation requires.Fig. 5 then illustrates the signal vector for needing to transmit simultaneouslyWith constructed to record its variation characteristic etc.
Long vectorEach element of two vectors shown in fig. 5 is intersected and is placed, just having obtained will be by IM/DD modulation and LED light
The vector of transmissionAs shown in Figure 6.
Embodiment 2
More fully to illustrate beneficial effect possessed by the present invention, below in conjunction with simulation analysis and as a result, further right
Effectiveness of the invention and advance are explained.Analogue system chooses typical indoor room model, and room-size is set as
Length and width are respectively 5 meters, 3 meters high.LED light is arranged as optical signal launch end in ceiling centre, and optical detection is arranged in floor centre
Device is not provided with other barriers as receiving end.Room light order of reflection is set as 3 times.To even things up, each OFDM scheme
Effective sub-carrier signal both be set to 32.In this example, l=4 is taken, m=2, n=2 are taken.
The peak power ratio that the OFDM symbol in OFDM-VLC system is shown in Fig. 7 is more than the probability for specifying threshold value Z,
Its abscissa is defined as:
X in formulatmaxIndicate symbol peaks, PtIndicate the mean power of OFDM symbol.As can be seen from Figure 7, compared to traditional
ACO-OFDM-VLC system, the OFDM-VLC system using " peak clipping mapping techniques " proposed by the present invention have in PAPR aspect of performance
Biggish advantage.In the identical situation of other simulated conditions, the time-domain signal PAR peak to average ratio of traditional 3-D ACO-OFDM system
Probability more than 14dB is up to 1.7 × 10-2, and the probability is reduced two orders of magnitude by the present invention, is limited in 10-4, have bright
Aobvious PAPR performance gain.
Fig. 8 gives the comparison of BER performance.Compared to traditional ACO-OFDM-VLC system, new departure tool proposed by the present invention
There is improved BER performance, it is shown that higher reliability.For example, when target BER is 10-5When, novel 3-D proposed by the present invention
OOFDM reduces about 0.5dB than signal-to-noise ratio needed for traditional 3-D ACO-OFDM, and when use 2-D 16QAM, the solution of the present invention
About 4dB is then greatly reduced than traditional 2-D ACO-OFDM system required signal-to-noise ratio.
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
Made any modifications, equivalent replacements, and improvements etc., should be included in the claims in the present invention within the spirit and principle of invention
Protection scope within.
Claims (4)
1. a kind of modulator approach for reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: the following steps are included:
(1) transmitting terminal
S1. serial/parallel conversion is carried out to bit stream information, bit stream information is mapped on planisphere, wherein the planisphere is
Two dimensional constellation figure or three-dimensional constellation map；
S2. the constellation point on planisphere can be expressed as a space vector, then constellation point all in planisphere can use one
A real number matrix SRIt indicates；
S3. real number matrix S S2 obtainedRIt is transformed to complex matrix SC；
S4. to complex matrix SCHermitian symmetry transformation is carried out, obtains meeting the symmetrical matrix S of Hermitianh；
S5. to matrix ShIFFT transformation is carried out, the real number matrix s in time domain is obtainedt；
S6. to real number matrix stAfter carrying out parallel-serial conversion, vector signal is obtained
S7. vector signal is calculatedAverage amplitude Vavg；
S8. reference amplitude V is calculated according to average amplituderef:
Vref=lVavg；
L indicates ratio of the reference amplitude relative to average amplitude；
S9. to vector signalOn each element skPeak clipping and mapping processing are carried out by formula (1), constructs vector
Wherein, m, n are the parameter of any value, and k meets 1≤k≤QN, and N is the quantity of symbol to be sent, and Q is planisphere dimension；
S10. vector is constructedCome record mapping processing Q-character, whereinxck(1
≤ k≤QN) meet formula (2) or formula (3) or formula (4) or formula (5):
S11. in vectorElement between in be uniformly inserted into vectorElement, obtain length be 2QN vector
S12. by vectorLaunched by intensity modulation, and by modulated signal by LED light；
(2) receiving end
S13. the length that receiving end receives is set as the vector of 2QNThen ask
Take the reference level amplitude V ' of receiving endref:
S14. implement " peak clipping mapping reduction " operation, obtain the vector that length is QN
Shown in specific as follows:
xckMeet formula (2)；
OrxckMeet formula (3)；
OrxckMeet formula (4)；
OrxckMeet formula (5)；
The range of k meets 1≤k≤QN；
S15. to serial vectorCarry out serioparallel exchange, the real number matrix of one (Q × N) can be obtained, to real number matrix into
Row FFT transform obtains meeting symmetrical (Q × N) complex matrix of Hermitian, according to planisphere and maximum likelihood algorithm to multiple
Matrix number is demodulated, and bitstream data is obtained.
2. the modulator approach according to claim 1 for reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: described
Planisphere is three-dimensional constellation map；Then each constellation point can be expressed as a three-dimensional space vectorWherein
xk,yk,zkFor three real number values, respectively representReference axis, so symbol energy corresponding to 2N three-dimensional constellation point
It is expressed as one (3 × 2N) real number matrix SR:
Based on real number matrix SRThe complex matrix S of variationCIt indicates are as follows:
Wherein
Then meet the symmetrical matrix S of HermitianhIt indicates are as follows:
Wherein
ShCarry out IFFT transformation, obtained real number matrix stIt indicates are as follows:
Real number matrix stAfter carrying out parallel-serial conversion, the vector that length is 3N is obtained
It, will for the sake of intuitiveIt is write as:
For signal vector.
3. the modulator approach according to claim 2 for reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: step
After S6 carries out parallel-serial conversion, to vector signalIn addition cyclic prefix, then executes step S7；Step S14 seeks obtaining simultaneouslyAfterwards, rightCirculation prefix processing is gone in execution, then executes step S15.
4. the modulator approach according to claim 3 for reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: described
Calculate vector signalAverage amplitude VavgDetailed process is as follows:
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| CN106849963B (en) * | 2017-03-28 | 2023-03-31 | 中国地质大学（武汉） | Method and device for reducing peak-to-average power ratio of three-dimensional coherent light orthogonal frequency division multiplexing system |
| CN107948113B (en) * | 2017-11-10 | 2019-12-03 | 中国地质大学（武汉） | The method and system for reducing ofdm system peak-to-average power ratio are inserted into based on three dimensional signal |
| CN108900462A (en) * | 2018-09-27 | 2018-11-27 | 西安理工大学 | A method of reducing indoor visible light DCO-OFDM system peak-to-average power ratio |
| CN109547381B (en) * | 2019-01-17 | 2021-06-01 | 山东建筑大学 | Self-encoder-based DCO-OFDM system PAPR suppression method and system |
| CN109600335B (en) * | 2019-01-17 | 2021-03-16 | 山东建筑大学 | ACO-OFDM system comprehensive PAPR suppression method and system based on neural network |
| CN112564798B (en) * | 2020-11-30 | 2022-06-17 | 哈尔滨工业大学（深圳） | Signal processing method, device, system and storage medium for visible light communication system |
| CN113141214B (en) * | 2021-04-06 | 2022-03-15 | 中山大学 | Deep learning-based underwater optical communication misalignment robust blind receiver design method |
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| CN101414994A (en) * | 2008-10-16 | 2009-04-22 | 京信通信系统（中国）有限公司 | Method and apparatus for reducing peak average power ratio of multi-carrier system |
| CN101478521A (en) * | 2009-01-20 | 2009-07-08 | 华南理工大学 | Peak cutting method for adaptive in-band processing |
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| JP2007259445A (en) * | 2006-03-20 | 2007-10-04 | Fujitsu Ltd | Transmitters and methods in ofdm communication systems |
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| CN101035105A (en) * | 2007-04-06 | 2007-09-12 | 西安电子科技大学 | Method and device for reserving the sub-carrier to reduce the peak average power ratio of the OFDM system based on IFFT/FFT |
| CN101414994A (en) * | 2008-10-16 | 2009-04-22 | 京信通信系统（中国）有限公司 | Method and apparatus for reducing peak average power ratio of multi-carrier system |
| CN101478521A (en) * | 2009-01-20 | 2009-07-08 | 华南理工大学 | Peak cutting method for adaptive in-band processing |
| CN101834822A (en) * | 2009-03-13 | 2010-09-15 | 大唐移动通信设备有限公司 | Peak value offset method and device based on peak value elimination |
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