CN110336767A - A method of for reducing DCO-OFDM signal PAPR - Google Patents

A method of for reducing DCO-OFDM signal PAPR Download PDF

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CN110336767A
CN110336767A CN201910705950.7A CN201910705950A CN110336767A CN 110336767 A CN110336767 A CN 110336767A CN 201910705950 A CN201910705950 A CN 201910705950A CN 110336767 A CN110336767 A CN 110336767A
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papr
signal
dco
ofdm
value
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CN110336767B (en
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洪文昕
李蔚泽
李天屿
王炯乾
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Nanjing Post and Telecommunication University
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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
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
    • Y02D30/00—Reducing energy consumption in communication networks
    • Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Digital Transmission Methods That Use Modulated Carrier Waves (AREA)

Abstract

A method of for reducing DCO-OFDM signal PAPR, input signal first obtains the road N paralleled code element X through serioparallel exchangei, quadrature amplitude modulation M-QAM acquisition is carried out on N number of subcarrier corresponding to the road NIt is right againInverse fast fourier transform is carried out, 2N equivalent complex code sequences are generatedAnd it willAfter serial/parallel conversion, the sample value of discrete signal S (k) is obtained；Discrete signal S (k) is superimposed by SLM algorithm by different phase rotation coefficient Pm (i) later, output sequence Sm is obtained, then inverse fast fourier transform is carried out to Sm, obtains output SM‑OutSequence；In SM‑OutCyclic prefix T is inserted into sequenceCPWith protection bandwidth TG, obtain complete ofdm signal time span Tsym=Tued+Tcp+TG, according to TsymIt calculates time-domain signal x (t), and DC compensation d is provided0；Then PAPR (db) is obtained according to time-domain signal x (t), and judges whether PAPR (db) is more than threshold value PAPR0If PAPR > PAPR0, then d is reduced0Value, if PAPR≤PAPR0, then d is not reduced0Value；Finally export DCO-OFDM signal.This method combines traditional SLM thought and DC compensation dynamic equilibrium, can preferably reduce the PAPR of DCO-OFDM, improves system reliability.

Description

A method of for reducing DCO-OFDM signal PAPR
Technical field
The invention belongs to wireless light communication technical fields, and in particular to a kind of side for reducing DCO-OFDM signal PAPR Method.
Background technique
Visible light communication VLC (Visible Light Communication) has level security strong, anti-interference By force, the features such as message capacity is big, quick without frequency license and deployment, before having good application in terms of the military and civilian Scape.Orthogonal frequency division multiplex OFDM technology is introduced into radio optical communication system by prior art, to inhibit intersymbol interference to system Influence, improve the rate of information throughput of system.The spectrum efficiency for being commonly used in VLC-OFDM technology at present is as shown in table 1,
Modulation scheme Advantages/disadvantages Spectrum efficiency
DCO-OFDM Spectrum efficiency is high；Power efficiency is low 50%
ACO-OFDM Power efficiency is high；Spectrum efficiency is low 25%
Flip-OFDM Complexity is low；Spectrum efficiency is low 25%
U-OFDM Complexity is low；Spectrum efficiency is low 25%
μ-OFDM PAPR is lower；Complexity is high 50%
PM-OFDM Complexity is high 25%
1 difference OFDM modulation scheme performance comparison table of table
Wherein, DCO-OFDM is because its spectrum efficiency is high, it is simple to implement, it is only necessary to the advantage that DC compensation can be realized is provided, It is widely studied in VLC modulation technique.But lead to PAPR problem existing for ofdm signal itself because it provides DC compensation Also just more obvious, higher PAPR is always ofdm system one of the critical issue to be overcome.It is higher in VLC system PAPR VLC system can be made to be easier influence by non-linear distortion, substantially reduce the reliability of system.Therefore, for The research of PAPR suppression technology is particularly important.Higher PAPR producing cause: OFDM be by N number of modulation carrier wave be added after, It may will appear that wave crest is superimposed with wave crest, at this moment trough and the superimposed situation of trough just will appear relatively high peak value Power, when N number of carrier wave is with being added, peak power reaches N times of single carrier.N is bigger, and peak-to-average ratio is higher.Currently, inhibiting The PAPR of ofdm signal mainly has three classes method: signal distortion class, probability class and coding class, as shown in Figure 1；
In probability class method, selective mapping (SeLected Mapping, SLM) is with its good PAPR reduction property It can be concerned.SLM method uses different phase offsets, and multiplied by transmitting information sequence, therefrom selecting has minimum PAPR Transmitting sequence and transmitted.Therefore, it is a simple effective method that PAPR is reduced using SLM method, but SLM phase Position offset has randomness, still can there is the signal of a small amount of PAPR.
Summary of the invention
The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, and one kind is for reducing DCO-OFDM signal The method of PAPR combines traditional SLM thought and DC compensation dynamic equilibrium, can preferably reduce DCO-OFDM's PAPR。
The present invention provides a kind of method for reducing DCO-OFDM signal PAPR, includes the following steps:
Step S1, input signal obtains the road N paralleled code element X through serioparallel exchangei, carry out on N number of subcarrier corresponding to the road N Quadrature amplitude modulation M-QAM is obtained
Step S2, rightInverse fast fourier transform is carried out, 2N equivalent complex code sequences are generatedAnd it willIt is logical After crossing serial/parallel conversion, the sample value of discrete signal S (k) is obtained；
Step S3, discrete signal S (k) is superimposed by SLM algorithm by different phase rotation coefficient Pm (i), obtains output Sequence Sm, then inverse fast fourier transform is carried out to Sm, obtain output SM-OutSequence；
Step S4, in SM-OutCyclic prefix T is inserted into sequenceCPWith protection bandwidth TG, obtain the complete ofdm signal time Length Tsym=Tued+Tcp+TG, according to TsymIt calculates time-domain signal x (t), and DC compensation d is provided0；
Step S5, PAPR (db) is obtained according to time-domain signal x (t), and judges whether PAPR (db) is more than threshold value PAPR0If PAPR > PAPR0, then d is reduced0Value, if PAPR≤PAPR0, then d is not reduced0Value；
Step S6, DCO-OFDM signal is exported.
As further technical solution of the present invention, in step S1, input signal is serial binary bit stream, bit week Phase is Tsym, bit stream is divided into several frames, each frame includes L bit, this L bit is randomly divided into N group, then by every group biA bit is as a MiSystem symbol is converted by serial/parallel by N group serial data biBecome the road N paralleled code element Xi；Each road The paralleled code element duration is a frame time, i.e. Tf=LTs, when carrying out quadrature amplitude modulation M-QAM, a symbol XiIt can To be mapped to a bit in planisphere, and converts and pluralize
Further, multiple since DCO-OFDM modulation is using light intensity modulation/directly demodulation in step S2 Number signal has Hermite symmetrical, so that the item number of inverse fast fourier transform is equal to 2 times of number of subchannels purpose, thenBy inverse Fast Fourier Transform (FFT) generates 2N equivalent complex symbol sequencesWherein n=0,1,2 ... 2N-1；It will be parallelIt is logical After crossing parallel/serial conversion, the sample value of OFDM discrete signal S (k) is obtained, S (k) is
Further, in step S3, by frequency-region signalMultiplied by different phase rotatioies because Sub- Pm (i)=exp (j φ mi) obtains the vector sequence Pm=[Pm (0), Pm (1), Pm (3) ... Pm (K-1)] that m length is K； Wherein, m=1,2 ..., m；Then, the output sequence after phase rotation are as follows: Sm=S (k) ⊙ Pm=[S (0) Pm (0), S (1) Pm(1),,,,S(K-1)Pm(K-1)]；Inverse fast Fourier transform is carried out to Sm again to be exported according to PAPR minimum SM-OutSequence.
Further, in step S4, the calculation formula of time-domain signal x (t) isAnd provide DC compensation d0, d0Can with dynamic regulation, It is adjusted according to the PAPR value of signal.
Further, in step S5, PAPR (db) is obtained according to time-domain signal x (t), calculation formula isThreshold valueIf PAPR > PAPR0, then d is reduced0Value, d0 =d0-△d0,△d0=A/n.The present invention does not limit △ d0Occurrence, it is intended to indicate △ d0With the relationship of A, therefore the setting of n It is not limited to setting of the present invention.
The present invention can solve orthogonal frequency division multiplexing (the Direct Current Offset based on DC compensation Orthogonal Frequency Division Multiplexing, DCO-OFDM) there are higher peaks in transmission process The problem of causing transmission reliability to reduce than (Peak to Average Power Ratio, PAPR), thinks traditional SLM Want to combine with DC compensation dynamic equilibrium, can preferably reduce the PAPR of DCO-OFDM, improves system reliability.
Detailed description of the invention
Fig. 1 is the three types schematic diagram of PAPR in background technique of the invention；
Fig. 2 is signal-to-noise ratio and bit error rate performance schematic diagram under SLM algorithm of the invention；
Fig. 3 is signal-to-noise ratio and throughput concerns schematic diagram under SLM algorithm of the invention；
Fig. 4 is signal-to-noise ratio and PAPR performance schematic diagram under SLM algorithm of the invention；
Fig. 5 is PAPR and CDF performance schematic diagram under SLM algorithm of the invention.
Specific embodiment
Referring to Fig. 1, the present embodiment provides a kind of algorithms for reducing DCO-OFDM signal PAPR, for reducing PAPR value packet Containing secondary adjustment, with realize effectively, comprehensively reduce PAPR, improve system reliability.Specific steps include:
Step S1, input signal obtains N number of (road) paralleled code element X by serioparallel exchangei.Here N number of (road) correspondence is N number of Subcarrier.Quadrature amplitude modulation M-QAM is carried out on N number of subcarrier to obtainIt is prepared to enter into inverse Fast Fourier Transform IFFT。
Step S2, it is converted into IFFT, the item number of IFFT is made to be equal to 2 times of number of subchannels purpose, i.e., by being given birth to after IFFT At 2N equivalent complex symbol sequences(wherein n=0,1,2 ... 2N-1).These are parallelPass through parallel/serial conversion Afterwards, the sample value of discrete signal S (k) is obtained:
Step S3, using SLM algorithm, to by frequency-region signalIt is revolved multiplied by different phases Transposon Pm (i)=exp (j φmi)；Obtain m length be K vector sequence Pm=[Pm (0), Pm (1), Pm (3),, Pm (K-1)]；M=1,2,, m.Then, output sequence is obtained after phase rotation: Sm=S (k) ⊙ Pm=[S (0) Pm (0), S (1) Pm (1),, S (K-1) Pm (K-1)], IFFT conversion is carried out to Sm, selects PAPR minimum, obtains output SM-OutSequence.
Step S4, it is inserted into a cyclic prefix TCP(cyclic prefix) is inserted into protection bandwidth TG(guard Band), a complete ofdm signal time span T is obtainedsym=Tued+Tcp+TG, time-domain signal is calculated, and provide straight Stream compensation d0, setting of embodiment of the present invention d0Initial value, d0=A/2
Step S5, it calculates againJudge whether PAPR is more than thresholding threshold Value PAPR0,Wherein, A is the linear region optical power rated value of transmitting terminal LED.Because of this hair It is bright to provide a kind of way of thinking, the power of the device used, therefore the PAPR are not limited0、d0It is not that a fixation is unique Value, but a relative quantity.
If PAPR > PAPR0, reduce d0Value, d0=d0-△d0,△d0=A/n, the present invention do not limit △ d0Specifically Value, is herein the citing of specific embodiment, and n=6 is arranged.
Until detecting PAPR≤PAPR0, that is, no longer reduction d0。
Step S6, DCO-OFDM signal is exported.The signal has been the DCO-OFDM signal reduced after PAPR at this time.
Based on above step, following performance is calculated in MATLAB modeling and simulating:
It will be seen from figure 1 that with the increase of signal-to-noise ratio (Signal Noise Ratio, SNR), DCO-OFDM system The bit error rate (Bit Error Ratio, BER) is in be decreased obviously trend, in same equivalent code error rate, SLM algorithm of the invention Gain 2.5dB or so in terms of signal-to-noise ratio.Fig. 2 can be seen that the throughput of system under SLM algorithm of the invention can be substantially reduced, This is because the PAPR that SLM algorithm belongs to non-distortion class reduces algorithm, needs to transmit auxiliary phase information, cause throughput of system Decline.Measurement for PAPR has certain fluctuation from Fig. 3 discovery numerical value, biggish increase and decrease does not occur, and Also there is changing for overall reduction under the SNR range of 0~30dB in the SLM algorithm of the invention of reduction using to(for) PAPR Kind, SLM algorithm generally of the present invention has the gain of 0.3dB for reducing for PAPR.The system that Fig. 4 utilizes CDF to be distributed PAPR Meter characteristic is measured, it can be found that in the dynamic d combined using SLM method of the invention0Afterwards, in identical PAPR0Threshold value Under, PAPR is higher lower than the probability of threshold value, and especially when SNR is located at 12.5~13dB, likelihood ratio original method highest increases 40% or so, PAPR value is reduced significantly, improves system reliability.
The basic principles, main features and advantages of the invention have been shown and described above.Those skilled in the art should Understand, the present invention do not limited by above-mentioned specific embodiment, the description in above-mentioned specific embodiment and specification be intended merely into One step illustrates the principle of the present invention, and under the premise of not departing from spirit of that invention range, the present invention also has various change and changes Into these changes and improvements all fall within the protetion scope of the claimed invention.The scope of protection of present invention is by claim Book and its equivalent thereof.

Claims (6)

1. a kind of method for reducing DCO-OFDM signal PAPR, which is characterized in that include the following steps,
Step S1, input signal obtains the road N paralleled code element X through serioparallel exchangei, carry out on N number of subcarrier corresponding to the road N orthogonal Amplitude is modulated M-QAM and is obtained
Step S2, rightInverse fast fourier transform is carried out, 2N equivalent complex code sequences are generatedAnd it willPass through After serial/parallel conversion, the sample value of discrete signal S (k) is obtained；
Step S3, discrete signal S (k) is superimposed by SLM algorithm by different phase rotation coefficient Pm (i), obtains output sequence Sm, then inverse fast fourier transform is carried out to Sm, obtain output SM-OutSequence；
Step S4, in SM-OutCyclic prefix T is inserted into sequenceCPWith protection bandwidth TG, obtain complete ofdm signal time span Tsym=Tued+Tcp+TG, according to TsymIt calculates time-domain signal x (t), and DC compensation d is provided0；
Step S5, PAPR (db) is obtained according to time-domain signal x (t), and judges whether PAPR (db) is more than threshold value PAPR0If PAPR > PAPR0, then d is reduced0Value, if PAPR≤PAPR0, then d is not reduced0Value；
Step S6, DCO-OFDM signal is exported.
2. a kind of method for reducing DCO-OFDM signal PAPR according to claim 1, which is characterized in that the step In rapid S1, the input signal is serial binary bit stream, bit period Tsym, bit stream is divided into several frames, each Frame includes L bit, this L bit is randomly divided into N group, then by every group of biA bit is as a MiSystem symbol, by string/ And it converts N group serial data biBecome the road N paralleled code element Xi；Each road paralleled code element duration is a frame time, i.e. Tf= L·Ts, when carrying out quadrature amplitude modulation M-QAM, a symbol XiIt can be mapped to a bit in planisphere, and convert and pluralize
3. a kind of method for reducing DCO-OFDM signal PAPR according to claim 1, which is characterized in that the step In rapid S2, since DCO-OFDM modulation is using light intensity modulation/directly demodulation, complex signal has Hermite pairs Claim, so that the item number of inverse fast fourier transform is equal to 2 times of number of subchannels purpose, thenIt is generated by inverse fast fourier transform 2N equivalent complex symbol sequencesWherein n=0,1,2 ... 2N-1；It will be parallelAfter parallel/serial conversion, obtain The sample value of OFDM discrete signal S (k), S (k) are
4. a kind of method for reducing DCO-OFDM signal PAPR according to claim 1, which is characterized in that the step In rapid S3, by frequency-region signalMultiplied by different phase rotation coefficient Pm (i)=exp (j φ Mi), the vector sequence Pm=[Pm (0), Pm (1), Pm (3) ... Pm (K-1)] that m length is K is obtained；Wherein, m=1,2 ..., m；Then, the output sequence after phase rotation are as follows: and Sm=S (k) ⊙ Pm=[S (0) Pm (0), S (1) Pm (1),, S (K-1) Pm(K-1)]；Inverse fast Fourier transform is carried out to Sm again, according to PAPR minimum, obtains output SM-OutSequence.
5. a kind of method for reducing DCO-OFDM signal PAPR according to claim 1, which is characterized in that the step In rapid S4, the calculation formula of time-domain signal x (t) isAnd DC compensation d is provided0, d0It can be adjusted with dynamic regulation according to the PAPR value of signal.
6. a kind of method for reducing DCO-OFDM signal PAPR according to claim 1, which is characterized in that the step In rapid S5, PAPR (db) is obtained according to time-domain signal x (t), calculation formula isThreshold valueIf PAPR > PAPR0, then d is reduced0Value, d0 =d0-△d0,△d0=A/n.
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