CN105812309A - Modulation method for reducing peak-to-average power ratio of orthogonal frequency division multiplexing-visible light communication (OFDM-VLC) system - Google Patents
Modulation method for reducing peak-to-average power ratio of orthogonal frequency division multiplexing-visible light communication (OFDM-VLC) system Download PDFInfo
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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
Abstract
The invention discloses a modulation method for reducing a peak-to-average power ratio of an orthogonal frequency division multiplexing-visible light communication (OFDM-VLC) system. According to the modulation method provided by the invention, through performing specific peak clipping and mapping treatments on visible light vector signals, the peak-to-average power ratio of the OFDM-VLC system can be effectively reduced, and meanwhile the bit error rate performance of the system can also be improved.
Description
Technical field
The present invention is towards visible light communication (Visible Light Communication, VLC) field, it is proposed that a kind of
Based on light OFDM (Optical Frequency Division Multiplexing, OOFDM) can effectively promote
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 technology
Along with light emitting diode in the development of modern science and technology and daily life (Light-emitting Diode,
LED) commonly used, technology is gradually for visible light communication based on LED (Visible Light Communication, VLC)
Paid close attention to by each side and it is expanded research.VLC is mainly by intensity modulated (Intensity Modulation, IM) and directly
Connect detection (Direct Detection, DD) technology, utilize the human eye fast-changing light intensity of insignificant power to realize information
Transmission, i.e. accomplish on " limit illumination, limit communication ".Meanwhile, wide variety of OFDM in traditional wireless communication
(Orthogonal Frequency Division Multiplexing, OFDM) technology also relies on it at anti-interference, antagonism frequency
The advantage of the aspects such as rate Selective intensity, obtains more application in VLC field.It can effectively utilize indoor VLC channel
Feature realizes high speed data transfer, improves the transmission performance of VLC system.Therefore, the VLC system in conjunction with OFDM technology the most gradually becomes
One of focus for the communication of current research high speed VLC[i]。
In actual typical indoor environment, a VLC system generally includes the transmitting LED of optical information, Photoelectric Detection
Device (Photodetector, PD), physical layer, MAC layer etc., and realize signal transmission by IM/DD technology[ii].Basic room
In interior visible ray model, it is seen that optical channel link include sighting distance (Line-of-Sight, LOS) and non line of sight (Non-LOS,
NLOS) two kinds[iii].Due to scattered link and higher loss, the VLC system performance when high transfer rate is accorded with
The impact of (Inter-Symbol Interference, ISI) is disturbed between number.And use OFDM technology effectively to suppress
ISI, promotes VLC systematic function.But, traditional OFDM symbol is plural form, it is impossible to by IM/DD modulation /demodulation.To this,
Many researcheres propose the multiple modified form OFDM being applicable to visible ray, such as non-homogeneous amplitude limit light OFDM
(Asymmetrically Clipped Orthogonal Frequency Division Multiplexing, ACO-OFDM),
Direct current biasing OFDM (Orthogonal Frequency Division Multiplexing, DCO-OFDM, one pole
Property light OFDM (Unipolar Orthogonal Frequency Division Multiplexing, U-OFDM)
Deng, and these new departures have been carried out performance evaluation.These schemes are equal at bit error rate (Bit Error Rate, BER), peak
Power ratio (Peak to Average Power Ratio, PAPR), spectrum efficiency (Spectral Efficiency, SE) etc. are each
The performance indications of individual aspect are respectively arranged with quality.Therefore, for the optimization of these performance indications, for development and the maturation of VLC technology
Significant.
Summary of the invention
The present invention on the basis of OFDM-VLC technology, has lacking of relatively 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.
For realizing above goal of the invention, the technical scheme is that
A kind of modulator approach reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: comprise the following steps:
(1) transmitting terminal
S1. bit stream information is carried out serial/parallel conversion, bit stream information is mapped on planisphere, wherein said 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 in planisphere, all of constellation point is permissible
By real number matrix SRRepresent；
S3. real number matrix S S2 obtainedRIt is transformed to complex matrix SC；
S4. to complex matrix SCCarry out Hermitian symmetry transformation, be met the symmetrical matrix S of Hermitianh；
S5. to matrix ShCarry out IFFT conversion, obtain real number matrix s in time domaint；
S6. to real number matrix stAfter carrying out parallel-serial conversion, obtain vector signal
S7. vector signal is calculatedAverage amplitude Vavg；
S8. reference amplitude V is calculated according to average amplituderef:
Vref=l Vavg；
L represents the reference amplitude ratio relative to average amplitude；
S9. to vector signalOn each element skCarry out peak clipping by formula (1) and mapping processes, structure 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 constructedRecord the Q-character that mapping processes, wherein
xck(1≤k≤QN) meets formula (2) or formula (3) or formula (4) or formula (5):
S11. at vectorElement between in uniformly insert vectorElement, obtain the vector of a length of 2QN
S12. by vectorBy intensity modulation, and the signal after modulation is launched by LED；
(2) receiving terminal
S13. the vector of a length of 2QN that receiving terminal receives is setThen ask for datum amplitude V of receiving terminal
′ref:
S14. implement " peak clipping maps reduction " operation, obtain the vector of a length of QNShown in specific as follows:
xckMeet formula (2)；
OrxckMeet formula (3)；
OrxckMeet formula (4)；
OrxckMeet formula (5)；
The scope of k meets 1≤k≤QN；
S15. to serial vectorCarry out serioparallel exchange, just can obtain the real number matrix of (Q × N), to real number square
Battle array carries out FFT and is met symmetrical (Q × N) complex matrix of Hermitian, according to planisphere and maximum likelihood algorithm
Complex matrix is demodulated, obtains bitstream data.
Preferably, described planisphere is three-dimensional constellation map；Then each constellation point can be expressed as a three-dimensional space to
AmountWherein xk,yk,zkIt is three real number values, represents respectivelyCoordinate axes, so 2N three-dimensional star
Symbol corresponding to seat point can be expressed as real number matrix S of (3 × 2N)R:
Based on real number matrix SRThe complex matrix S of changeCIt is expressed as:
Wherein
Then meet the symmetrical matrix S of HermitianhIt is expressed as:
Wherein
ShCarry out IFFT conversion, real number matrix s obtainedtIt is expressed as:
Real number matrix stAfter carrying out parallel-serial conversion, obtain the vector of a length of 3N
For the sake of directly perceived, willWrite as:
For signal vector.
Preferably, after step S6 carries out parallel-serial conversion, to vector signalPlus Cyclic Prefix, then perform step S7；
Step S14 is asked for obtaining simultaneouslyAfter, rightCirculation prefix processing is gone in execution, then performs step S15.
Preferably, described calculating vector signalAverage amplitude VavgDetailed process as follows:
Compared with prior art, the invention has the beneficial effects as follows:
The modulator approach that the present invention provides processes by visible ray vector signal carries out peak clipping and mapping so that based on
The peak-to-average power ratio of the visible light communication system of OFDM is effectively reduced, and the bit error code that the most also can promote system is forthright
Energy.
Accompanying drawing explanation
Fig. 1 is for using the schematic diagram of 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 vectorSequential chart.
Fig. 4 is the positive number OFDM time domain signal vector processed through mappingSequential chart.
Fig. 5 is the signal vector after peak clipping mapping processesThe vector comprising characteristic information with structureSequential chart.
Fig. 6 is the arithmetic number time domain OFDM signal vector in transmitting terminal transmissionSequential chart.
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.
Detailed description of the invention
Accompanying drawing being merely cited for property explanation, it is impossible to be interpreted as the restriction to this patent；
Below in conjunction with drawings and Examples, the present invention is further elaborated.
Embodiment 1
Novel " the peak clipping mapping techniques " that the present invention proposes, its core is with certain, signal of telecommunication of complex field is mapped rule
Then it is converted into and can reach preferable PAPR inhibition and BER by the optical signal of the arithmetic number form of light intensity modulation
Energy.After optical signal is launched by LED, it is reduced to the complex field signal of telecommunication at receiving terminal with same rule.
The method that the present invention provides comprises the following steps:
One, receiving terminal
Bit information, as it is shown in figure 1, bit stream information is firstly the need of carrying out serial/parallel conversion, is mapped to constellation by step one
On figure.Planisphere involved by the present embodiment is three-dimensional constellation map.
Step 2 is as in figure 2 it is shown, each constellation point on 3-D planisphere is represented by a three-dimensional space vectorWherein xk,yk,zkIt is three real number values, represents respectivelyCoordinate axes.Therefore, 2N three-dimensional star
Symbol corresponding to seat point can be expressed as the real number matrix of (3 × 2N):
Step 3, the follow-up needs of method provided due to the present invention carry out quick inversefouriertransform to matrix, so square
Battle array SRCan be transformed to the complex matrix of (3 × N) further:
By the conversion process of complex matrix, after need Fourier transformation to be processed (Fast Fourier
Transform, FFT) symbol lengths only has original half.
Step 4, obtain real number matrix in time domain, need this matrix is carried out Hermitian symmetry transformation, expired
(3 × N) matrix S that foot Hermitian is symmetricalh:
Wherein
Step 5, to matrix ShCarry out IFFT conversion, obtain real number matrix s in time domaint；
The formula of IFFT conversion is as follows:
Wherein n1、n2Meet 0≤n respectively1≤ 2,0≤n2≤ N-1, k1And k2Represent signal matrix S the most respectivelyCRow subscript
With row subscript.
Step 6, to real number matrix stAfter carrying out parallel-serial conversion, obtain vector signal
VectorIt it is real number vector.
Step 7, calculating vector signalAverage amplitude Vavg；
Wherein Q represents planisphere dimension, is 3-D planisphere, therefore Q=3 herein
Step 8, calculate reference amplitude V according to average amplituderef:
Vref=l Vavg
In formula, l represents its reference amplitude ratio relative to average amplitude, and l is user-defined parameter.
Step 9, to vectorOn each element carry out peak clipping and mapping by following rule and process, structure vector
It it is wherein user-defined parameter.User can choose suitable m, n and l value according to the design requirement of system.
Step 10, structure vectorRecord the Q-character that mapping processes, restore original signal for receiving terminal:
Wherein xck(1≤k≤QN) meets formula (2) or formula (3) or formula (4) or formula (5):
Step 11, at vectorElement between in uniformly insert vectorElement, obtain the vector of a length of 2QNI.e. can be used for light intensity modulation:
Step 12, by vectorBy intensity modulation, and the signal after modulation is launched by LED.
Receiving terminal:
Step 13, receiving terminal receive the vector of a length of 2QN by photo-detector
According to central limit theorem, when N foot
Time the biggest, OFDM symbol skFall identical at the probability of positive and negative number interval.Therefore, the vector x constructedckAlso can be with (1/2) Vref
Symmetry, therefore the estimated value in the datum amplitude of receiving terminal can be tried to achieve according to following formula:
Step 14, implement " peak clipping maps reduction " operation according to following algorithmic rule, obtain the vector of a length of QN
xckMeet formula (2)；
OrxckMeet formula (3)；
OrxckMeet formula (4)；
OrMeet formula (5)；
The scope of k meets 1≤k≤QN；
Step 15, to serial vectorCarry out serioparallel exchange, just can obtain the real number matrix of (Q × N), to reality
Matrix number carries out FFT and is met symmetrical (Q × N) complex matrix of Hermitian, according to planisphere and maximum likelihood
Complex matrix is demodulated by algorithm, obtains bitstream data.
The embodiment of one " peak clipping mapping techniques " is given below by way of Fig. 3-Fig. 6:
The embodiment that Fig. 3 shows is after IFFT, parallel-serial conversion, meets N=3, the discrete OFDM time domain letter of a length of 9
NumberIt can be seen that the characteristic of OFDM, its maximum amplitude is higher, and therefore PAPR is the highest, and signal amplitude have just have negative.
After peak clipping maps change, change as shown in Figure 4, vectorPeak-peak halves, the absolute value of whole real numbers, meets IM/
DD modulates requirement.Fig. 5 illustrates the most simultaneously needs the signal vector of transmissionWith construct to record its variation characteristic etc.
Long vectorEach element vectorial for shown in Fig. 5 two is intersected and places, just obtained being modulated by IM/DD and LED
The vector of transmissionAs shown in Figure 6.
Embodiment 2
By illustrating that the present invention is had the advantage that more fully, below in conjunction with simulation analysis and result, the most right
Effectiveness of the invention and advance are explained.Analogue system chooses typical indoor room model, and room-size is set to
Length and width are respectively 5 meters, high 3 meters.Ceiling centre arranges LED and arranges optical detection as optical signal launch end, floor centre
Device, as receiving terminal, is not provided with other barriers.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, take l=4, take m=2, n=2.
Fig. 7 is shown that the peak power ratio of the OFDM symbol in OFDM-VLC system and exceedes the probability of appointed threshold value Z,
Its abscissa is defined as:
X in formulatmaxRepresent symbol peaks, PtRepresent the mean power of OFDM symbol.As can be seen from Figure 7, compare traditional
ACO-OFDM-VLC system, uses the OFDM-VLC system of " the peak clipping mapping techniques " of present invention proposition to have at PAPR aspect of performance
Bigger advantage.In the case of other simulated conditions are identical, the time-domain signal PAR peak to average ratio of tradition 3-D ACO-OFDM system
Probability more than 14dB is up to 1.7 × 10-2, and this 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.Compare tradition ACO-OFDM-VLC system, new departure tool that the present invention proposes
There is the BER performance of improvement, it is shown that higher reliability.Such as, it is 10 when target BER-5Time, the novel 3-D that the present invention proposes
OOFDM reduces about 0.5dB than the signal to noise ratio needed for traditional 3-D ACO-OFDM, and when using 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 is only for clearly demonstrating example of the present invention, and is not right
The restriction of embodiments of the present invention.For those of ordinary skill in the field, the most also may be used
To make other changes in different forms.Here without also cannot all of embodiment be given exhaustive.All at this
Any amendment, equivalent and the improvement etc. made within the spirit of invention and principle, should be included in the claims in the present invention
Protection domain within.
Claims (4)
1. the modulator approach reducing OFDM-VLC system peak-to-average power ratio, it is characterised in that: comprise the following steps:
(1) transmitting terminal
S1. bit stream information being carried out serial/parallel conversion, bit stream information be mapped on planisphere, wherein said 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 in planisphere, all of constellation point can be with one
Individual real number matrix SRRepresent；
S3. real number matrix S S2 obtainedRIt is transformed to complex matrix SC；
S4. to complex matrix SCCarry out Hermitian symmetry transformation, be met the symmetrical matrix S of Hermitianh；
S5. to matrix ShCarry out IFFT conversion, obtain real number matrix s in time domaint；
S6. to real number matrix stAfter carrying out parallel-serial conversion, obtain vector signal
S7. vector signal is calculatedAverage amplitude Vavg；
S8. reference amplitude V is calculated according to average amplituderef:
Vref=l Vavg；
L represents the reference amplitude ratio relative to average amplitude；
S9. to vector signalOn each element skCarry out peak clipping by formula (1) and mapping processes, structure 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 constructedRecord the Q-character that mapping processes, wherein
xck(1≤k≤QN) meets formula (2) or formula (3) or formula (4) or formula (5):
S11. at vectorElement between in uniformly insert vectorElement, obtain the vector of a length of 2QN
S12. by vectorBy intensity modulation, and the signal after modulation is launched by LED；
(2) receiving terminal
S13. the vector of a length of 2QN that receiving terminal receives is setThen ask for datum amplitude V of receiving terminal
′ref:
S14. implement " peak clipping maps reduction " operation, obtain the vector of a length of QNShown in specific as follows:
xckMeet formula (2)；
OrxckMeet formula (3)；
OrxckMeet formula (4)；
OrxckMeet formula (5)；
The scope of k meets 1≤k≤QN；
S15. to serial vectorCarry out serioparallel exchange, just can obtain the real number matrix of (Q × N), real number matrix is carried out
FFT is met (Q × N) complex matrix that Hermitian is symmetrical, and foundation planisphere and maximum likelihood algorithm are to plural number
Matrix is demodulated, and obtains bitstream data.
The modulator approach of reduction OFDM-VLC system peak-to-average power ratio the most according to claim 1, 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,zkIt is three real number values, represents respectivelyCoordinate axes, so 2N three-dimensional symbol energy corresponding to constellation point
It is expressed as real number matrix S of (3 × 2N)R:
Based on real number matrix SRThe complex matrix S of changeCIt is expressed as:
Wherein
Then meet the symmetrical matrix S of HermitianhIt is expressed as:
Wherein
ShCarry out IFFT conversion, real number matrix s obtainedtIt is expressed as:
Real number matrix stAfter carrying out parallel-serial conversion, obtain the vector of a length of 3N
For the sake of directly perceived, willWrite as:
For signal vector.
The modulator approach of reduction OFDM-VLC system peak-to-average power ratio the most according to claim 2, it is characterised in that: step
After S6 carries out parallel-serial conversion, to vector signalPlus Cyclic Prefix, then perform step S7；Step S14 is asked for obtaining simultaneouslyAfter, rightCirculation prefix processing is gone in execution, then performs step S15.
The modulator approach of reduction OFDM-VLC system peak-to-average power ratio the most according to claim 3, it is characterised in that: described
Calculate vector signalAverage amplitude VavgDetailed process as follows:
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| CN106849963A (en) * | 2017-03-28 | 2017-06-13 | 中国地质大学（武汉） | Three-dimensional coherent light peak average power ratio of OFDM system reduction method and apparatus |
| CN107948113A (en) * | 2017-11-10 | 2018-04-20 | 中国地质大学（武汉） | Being inserted into based on three dimensional signal reduces the method and system of ofdm system peak-to-average power ratio |
| 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 |
| CN109547381A (en) * | 2019-01-17 | 2019-03-29 | 山东建筑大学 | A kind of DCO-OFDM system PAPR suppressing method and system based on self-encoding encoder |
| CN109600335A (en) * | 2019-01-17 | 2019-04-09 | 山东建筑大学 | The comprehensive PAPR suppressing method of ACO-OFDM system neural network based and system |
| CN112564798A (en) * | 2020-11-30 | 2021-03-26 | 哈尔滨工业大学（深圳） | Signal processing method, device, system and storage medium for visible light communication system |
| CN113141214A (en) * | 2021-04-06 | 2021-07-20 | 中山大学 | Deep learning-based underwater optical communication misalignment robust blind receiver design method |
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| CN106849963A (en) * | 2017-03-28 | 2017-06-13 | 中国地质大学（武汉） | Three-dimensional coherent light peak average power ratio of OFDM system reduction method and apparatus |
| 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 |
| CN107948113A (en) * | 2017-11-10 | 2018-04-20 | 中国地质大学（武汉） | Being inserted into based on three dimensional signal reduces the method and system of ofdm system peak-to-average power ratio |
| 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 |
| CN109547381A (en) * | 2019-01-17 | 2019-03-29 | 山东建筑大学 | A kind of DCO-OFDM system PAPR suppressing method and system based on self-encoding encoder |
| CN109600335A (en) * | 2019-01-17 | 2019-04-09 | 山东建筑大学 | The comprehensive PAPR suppressing method of ACO-OFDM system neural network based and system |
| 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 |
| CN112564798A (en) * | 2020-11-30 | 2021-03-26 | 哈尔滨工业大学（深圳） | Signal processing method, device, system and storage medium for visible light communication system |
| CN113141214A (en) * | 2021-04-06 | 2021-07-20 | 中山大学 | Deep learning-based underwater optical communication misalignment robust blind receiver design method |
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