CN109617841A - Solid state power amplifier ofdm signal digital pre-distortion block and implementation method in airborne data link - Google Patents
Solid state power amplifier ofdm signal digital pre-distortion block and implementation method in airborne data link Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/38—Synchronous or start-stop systems, e.g. for Baudot code
- H04L25/40—Transmitting circuits; Receiving circuits
- H04L25/49—Transmitting circuits; Receiving circuits using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels ; Baseband coding techniques specific to data transmission systems
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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
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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
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Abstract
The invention discloses solid state power amplifier ofdm signal digital pre-distortion block in a kind of airborne data link, including iteration limit filtration unit, raised cosine filter unit and over-sampling pre-distortion unit, iteration limit filtration unit for reducing input signal peak-to-average force ratio；Raised cosine filter unit reduces signal spectrum out-of-band interference；Over-sampling pre-distortion unit carries out Nonlinear Processing to the oversampled signals amplitude received in signal, obtains the ofdm signal of pre-distortion and output.The present invention further discloses the implementation methods of the predistortion module can reduce the peak-to-average force ratio of signal using the module and implementation method, realize in signal band and with outer complex optimum, and will not aggravate the complexity of transmitter design and realize cost.
Description
Technical field
The present invention relates to digital wireless communication transmission technique fields, in particular to solid state power amplifier OFDM believes in airborne data link
Number digital pre-distortion block and implementation method.
Background technique
In Unmanned Aerial Vehicle Data catenary system, type onboard data link terminal needs to transmit high speed image data to ground station terminal,
The power amplifier that Airborne Terminal is exported frequently with several watts, the general class A amplifier A is solid-state power amplifier, is generally had
The preferable linearity.But poor nonlinear characteristic is still had near the saturation point of solid state power amplifier.Orthogonal frequency division multiplexing
OFDM technology under low elevation angle environment can be achieved high speed reliable data transmission, but its higher peak-to-average force ratio characteristic also to weight,
Power consumption etc. limits more airborne power amplifier and proposes more stern challenge.For high peak-to-average power ratio signal, it is often necessary to logical
Cross power amplifier rollback, peak-to-average force ratio inhibits to carry out pre-distortion to signal with technologies such as nonlinear transformations.
In document " WANG Y, Ge J H, WANG L, et al.Nonlinear Companding Transform for
Reduction of Peak-to-Average Power Ratio in OFDM Systems.IEEE Transactions on
Broadcasting, 2013,59 (2): 369-375. " and document " WANG L Q, TELLAMBURA C.A Simplified
Clipping and Filtering Technique for PAR Reduction in OFDM Systems.IEEE
Signal Processing Letters, 2005,12 (6): devised in 453-456. " ofdm signal be based on compressed transform with
The peak-to-average force ratio suppression technology of limit filtration.Such technology is more suited to engineering field, but technology is more wide in range, does not account for
Characteristic of the airborne power amplifier of Unmanned Aerial Vehicle Data Link frequently with solid state power amplifier.In document " Song Zuxun；Luo Chaobang；Zhang Ping Jun；The party and the masses without
OFDM peak-to-average ratio rejection studies electronic design engineering, 2012,20 (23): in 117-119. " in man-machine HRT high-rate telemetry channel
There is also such design problems.In document, " peak-to-average force ratio inhibits to grind with predistortion United Technologies in Lin Qian, Guo Liting .OFDM system
Study carefully DTV, 2011,35 (2): for TWTA travelling-wave tube amplifier in 17-19. ", ofdm signal being reduced using margining amplitude technique
Then peak-to-average force ratio expands the range of linearity of power amplifier by pre-distortion technology, but without being directed to solid state power amplifier and out-of-band interference etc.
Problem is studied.
In document, " Huang Zhenpeng, Luo Zhinian wireless communication RF non-linearity of power amplifier aberration optimizing design computer
Emulation, 2017. ", " Xu Gaoming non-linearity of power amplifier characteristic and correcting technology research University Of Ningbo, 2015. ", " Hu Li
Memory pre-distortion technology software is analyzed and had to jasmine, Ai Bo power amplifier memory effect, and 2011. ", " in Wu Jing .OFDM system
Pre-distortion technology study Xian Electronics Science and Technology University, 2008. ", " Ai B, Yang Z-x, Pan C-y, et
al.Analysis on LUT based predistortion method for HPA with memory.IEEE
Transactions on Broadcasting 2007,53 (1): devised in 127-131. " various feedback-types based on memory
Or non-memory pre-distortion algorithms and realize structure.But such algorithm realization needs to increase a hardware corridor, extreme influence
The unstability and realization cost of system.
As unmanned aerial vehicle onboard data-link high-speed digital transmission bit rate rises in the order of magnitude, ofdm signal is under low elevation angle environment
High speed reliable data transmission advantage is shown, but the equal ratio characteristic of its higher peak proposes great challenge to airborne solid state power amplifier.
On the one hand method in above-mentioned document only considers to reduce the peak-to-average force ratio of signal, can not achieve in signal band and with outer complex optimum；
On the one hand the feedback pre-distortion method of design has aggravated transmitter design complexities and has realized cost.
Summary of the invention
It is an object of the invention to overcome the deficiencies of the prior art and provide solid state power amplifier ofdm signal numbers in airborne data link
Word predistortion module and implementation method reduce the peak-to-average force ratio of signal, realize in signal band and with outer complex optimum, Bu Huijia
The complexity and realization cost of machine of re-emissioning design.
Above-mentioned purpose of the invention is achieved by following technical solution:
Solid state power amplifier ofdm signal digital pre-distortion block in airborne data link, including more than iteration limit filtration unit, liter
String filter unit and over-sampling pre-distortion unit, iteration limit filtration unit and export for reducing the peak-to-average force ratio of input signal
Give raised cosine filter unit；Raised cosine filter unit reduces signal spectrum out-of-band interference, and exports and give over-sampling pre-distortion unit；
Over-sampling pre-distortion unit carries out Nonlinear Processing to the oversampled signals amplitude received in signal, obtains pre-distortion
Ofdm signal simultaneously exports.
Predistortion implementation method based on digital pre-distortion block, includes the following steps:
Step (1) configures digital pre-distortion mould according to the parameter characteristic of type onboard data link terminal solid-state power amplifier
Block, the target clipping amplitude A including iteration limit filtration unitM, raised cosine filter unit Out-of-band rejection γC, over-sampling number
The power amplifier of predistortion is saturated amplitude DS；
Step (2), iteration limit filtration unit carry out preliminary pre-distortion to the ofdm signal of Airborne Terminal, obtain
Ofdm signal after peak-to-average force ratio reduction；
Step (3), raised cosine filter unit are to i-th of OFDM symbol x after peak-to-average force ratio reductioni(n) time domain is carried out to add
Window obtains Out-of-band rejection γ after adding windowCOfdm signal xi,w(n), to the ofdm signal x after adding windowi,w(n) sinc interpolation is used
Function joint Kaiser window filter carries out time domain up-sampling and obtains OFDM oversampled signals y (n) with filtering；
Step (4), over-sampling pre-distortion unit carry out amplitude mistake according to nonlinear function to OFDM oversampled signals y (n)
True processing, obtains the ofdm signal s (n) of pre-distortion.
In the step (1), the parameter characteristic of type onboard data link terminal solid-state power amplifier is input signal s's (t)
The amplitude relation characteristic of amplitude and output signal z (t), phase relation characteristic remain unchanged, if the general amplitude of solid state power amplifier
Relation property F (AI(t),AO(t)) are as follows:
Wherein, AI(t) amplitude leyel for being solid state power amplifier input signal s (t), indicates are as follows: AI(t)=| s (t) |, AO(t)
For the amplitude leyel of solid state power amplifier output signal z (t), AO(t)=| z (t) |, ASFor the saturation level of solid-state power amplifier.
The implementation method of the step (2) is as follows:
(2.1), iteration limit filtration unit generates Airborne Terminal time-domain equivalent digital base band OFDM signal x (n):
(2.2), time domain clipping is carried out to time domain digital equivalent base band OFDM signal x (n), method particularly includes:
According to target clipping amplitude AM, according to criterion | x (n) | > AMOr | x (n) |≤AMAmplitude is made decisions, wherein |
| expression asks signal amplitude to operate, and is handled as follows after judgement:
Wherein, x'(n) be time domain clipping after signal；θ (n) is the phase of signal x (n), and c (n) is the component that is limited；
(2.3), FFT transform is carried out to frequency domain data C (k) to the component c (n) that is limited, frequency domain data C (k) is filtered
Wave, the OFDM data x updatedi+1(n)；
(2.4), the update OFDM data x that step (2.3) is obtainedi+1(n), it is iterated update by step (2.2), such as
Fruit the number of iterations reaches the maximum number of iterations M of design0, then iteration and output signal are terminated, otherwise iteration executes step (2.2)
~(2.4), until reaching the maximum number of iterations M of design0。
The implementation method of the step (2.1) is as follows:
It is N by length on frequency domain to information source data X (k)sInverse Fourier transform IFFT obtain time-domain equivalent number
Base band OFDM signal x (n), expression formula are
Wherein: n is positive integer, and 0≤n≤Ns-1；K is positive integer, and 0≤k≤Ns-1；Length is NsData X (k)
Include NuA data subcarrier and Ns-NuA zero void subcarrier；EsTo send signal power.
In the step (2.2), c (n) is expressed as follows:
In the step (2.3), frequency domain data C (k) is filtered, the OFDM data x updatedi+1(n), method
It is as follows:
By Ns-NuA void subcarrier C (k) is set as zero, obtains frequency domain data C'(k)；IFFT is carried out to frequency domain data C'(k)
Transformation obtains time domain data c'(n), and carry out i-th update:
xi+1(n)=xi(n)+μci(n)
Wherein, xi(n) be i-th iteration when time-domain signal, xi+1(n) signal updated for i+1 time iteration, μ are more
New step parameter.
In the step (3), xi,w(n) it is expressed as
Wherein, NgFor the length of ofdm signal cyclic prefix, it is set as Ng=Ns/8；xi,w(n) after for i-th of time-domain windowed
OFDM symbol, cpIt is respectively cyclic prefix windowing coefficient and cyclic suffix windowing coefficient with cs, prefix windowing coefficient is cp=[0
0.0125 0.0495 0.1091 0.1883 0.2831 0.3887 0.5 0.6113 0.7169 0.8117 0.8909
0.9505 0.9875 1], suffix windowing coefficient and prefix windowing coefficient are symmetry equivalent.
The implementation of the step (4) is as follows:
According to the input signal power of selected solid state power amplifier and output signal power relationship, pass through mathematical regression method point
Analysis obtains the amplitude relation characteristic F (A of solid state power amplifierI(t),AO(t)) function of, then negating obtains nonlinear function F (DI(n),
DO(n)):
F(DI(n),DO(n))=F-1(AI(t),AO(t))
The Non-linear function expression of solid state power amplifier amplitude relation are as follows:
Wherein, DI(n) range value for being input signal y (n): | y (n) |=DI(n)；DO(n) width for being output signal s (n)
Angle value: | s (n) |=DO(n)；DSFor the saturation level A of corresponding solid-state power amplifierSPower amplifier be saturated amplitude.
The implementation of the step (4) is as follows:
Airborne power amplifier is according to aircraft altitude difference, and locating temperature environment is different, to influence the input of power amplifier
Signal power-output signal power characteristic, is set as F (AI(t),AO(t),Ta(t)), wherein TaIt (t) is the temperature of airborne solid state power amplifier
Degree, which can generally be acquired by airborne sensor and be obtained, and be transferred to type onboard data link terminal, be denoted as Ta(n)；To temperature
Ta(t) parameter can be used for assisting nonlinear function F (DI(n),DO(n)) digital pre-distortion, mathematical relationship indicate are as follows:
F(DI(n),DO(n), Ta(n))=F-1(AI(t),AO(t),Ta(t))；
The Non-linear function expression of solid state power amplifier amplitude relation are as follows:
Wherein, DI(n) range value for being input signal y (n): | y (n) |=DI(n)；DO(n) width for being output signal s (n)
Angle value: | s (n) |=DO(n)；DSFor the saturation level A of corresponding solid-state power amplifierSPower amplifier be saturated amplitude.
Compared with prior art, the present invention has the following advantages:
(1) solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention passes through integrated configuration number
Iteration limit filtration unit, raised cosine filter unit, over-sampling pre-distortion unit in predistortion module, to OFDM in Practical Project
Peak-to-average force ratio inhibits to inhibit index to carry out complex optimum with out-of-band interference in signal band；
(2) solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention first passes through the filter of iteration clipping
Wave unit reduces signal peak-to-average ratio, then reduces signal spectrum out-of-band interference by raised cosine filter, realizes airborne OFDM data chain
Signal is in a sampling rate pre-distortion；
(3) solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention, according to selected solid-state function
The input signal power and output signal power relationship of rate amplifier, analyze to obtain the width of solid state power amplifier by mathematical regression method
Relation property is spent, and then completes over-sampling rate signal amplitude predistortion, is not necessarily to hard wired feed back channel, transmitter design will not be aggravated
Complexity and realize cost.
Detailed description of the invention
Fig. 1 is solid state power amplifier ofdm signal digital pre-distortion method module composition block diagram in airborne data link of the present invention；
Fig. 2 is the solid state power amplifier of solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention
Input-output characteristic curve of the RFPA2026 in 2.14GHz；
Fig. 3 be airborne data link of the present invention in solid state power amplifier ofdm signal digital pre-distortion method solid state power amplifier characteristic and
Nonlinear function characteristic；
Fig. 4 is the predistortion ofdm signal of solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention
Power spectrum performance.
Specific embodiment
The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments:
As shown in Figure 1, the module of three joint pre-distortions of configuration: iteration limit filtration unit, raised cosine filter list
Member, over-sampling pre-distortion unit pass through predistortion index of distributing according to need.Iteration limit filtration unit is for reducing input signal
Peak-to-average force ratio, raised cosine filter unit reduce signal spectrum out-of-band interference, and over-sampling pre-distortion unit adopts the mistake received in signal
Sample signal amplitude carries out Nonlinear Processing.Based on the nonlinear function digital pre-distortion of solid state power amplifier characteristic inverse function, machine is realized
Carry the digital pre-distortion of solid state power amplifier ofdm signal in data-link.
Solid state power amplifier ofdm signal digital pre-distortion method, mainly includes the following steps: in airborne data link
Step (1) configures digital pre-distortion mould according to the parameter characteristic of type onboard data link terminal solid-state power amplifier
Block, the target clipping amplitude A including iteration limit filtration unitM, raised cosine filter unit Out-of-band rejection γC, over-sampling number
The power amplifier of predistortion is saturated amplitude DS。
Wherein, the parameter characteristic of type onboard data link terminal solid-state power amplifier be mainly input signal s (t) amplitude with
The amplitude relation characteristic of output signal z (t), phase relation characteristic remain unchanged, if the general amplitude relation of solid state power amplifier is special
Property F (AI(t),AO(t)) are as follows:
Wherein, AI(t) amplitude leyel for being solid state power amplifier input signal s (t), indicates are as follows: AI(t)=| s (t) |, AO(t)
For the amplitude leyel of solid state power amplifier output signal z (t), AO(t)=| z (t) |, ASFor the saturation level of solid-state power amplifier.
Step (2), iteration limit filtration unit carry out preliminary pre-distortion to the ofdm signal of Airborne Terminal, obtain
Ofdm signal after peak-to-average force ratio reduction.
(1), Airborne Terminal digital equivalent base band OFDM signal: the information source data X on frequency domain Jing Guo linear modulation is generated
It (k), is N by lengthsInverse Fourier transform IFFT obtain time domain OFDM signal x (n), expression formula is
Wherein: n is positive integer, and 0≤n≤Ns-1；K is positive integer, and 0≤k≤Ns-1；Length is NsData X (k)
Include NuA data subcarrier and Ns-NuA zero void subcarrier；EsTo send signal power.
(2), time domain clipping is carried out to time domain OFDM signal x (n), method particularly includes:
According to target clipping amplitude AM, criterion is carried out to amplitude | x (n) | > AM, or | x (n) |≤AM, wherein | | expression is asked
Signal amplitude operation, is handled as follows after judgement:
Wherein, x'(n) be clipping after signal；θ (n) is the phase of signal x (n).The component c (n) that is limited is expressed as follows:
(3), FFT transform is carried out to frequency domain data C (k) to the signal c (n) being limited, frequency domain data C (k) is filtered
Wave: by Ns-NuA void subcarrier C (k) is set as zero, obtains frequency domain data C'(k)；When converting to obtain to frequency domain data C'(k) IFFT
Numeric field data c'(n), and carry out i-th update:
xi+1(n)=xi(n)+μci(n)
Wherein, xi(n) be i-th iteration when time-domain signal, xi+1(n) signal updated for i+1 time iteration, μ are more
New step parameter.
(4), the update OFDM time domain data x that step (3) is obtainedi+1(n), it is iterated update by step (2), if
The number of iterations reaches the maximum number of iterations M of design0, then terminate iteration and output signal, otherwise iteration execute step (2)~
(4), until reaching the maximum number of iterations M of design0。
The Airborne Terminal iteration limit filtration ofdm signal that step (3), raised cosine filter unit obtain step (2),
Using raised cosine window filter to i-th of OFDM symbol xi(n) time-domain windowed is carried out, Out-of-band rejection γ after adding window is obtainedCOFDM
Signal xi,w(n), it is expressed as
Wherein, NgFor the length of ofdm signal cyclic prefix, it is set as Ng=Ns/8；xi,w(n) after for i-th of time-domain windowed
OFDM symbol.cpAnd csRespectively cyclic prefix windowing coefficient and cyclic suffix windowing coefficient, prefix windowing coefficient are cp=[0
0.0125 0.0495 0.1091 0.1883 0.2831 0.3887 0.5 0.6113 0.7169 0.8117 0.8909
0.9505 0.9875 1], suffix windowing coefficient and prefix windowing coefficient are symmetry equivalent.
To the ofdm signal x after raised cosine adding windowi,w(n), it is carried out using sinc interpolating function joint Kaiser window filter
Time domain up-sampling obtains OFDM oversampled signals y (n) with filtering.
The Windowed filtering ofdm signal y (n) that step (4), over-sampling pre-distortion unit obtain step (3) is to according to non-
Linear function carries out amplitude distortion and obtains s (n), can be believed according to the input signal power and output of selected solid-state power amplifier
Number power relation, analyzes to obtain the amplitude relation characteristic F (A of solid state power amplifier by mathematical regression methodI(t),AO(t)) it, then asks
Inverse function obtains the nonlinear function
F(DI(n),DO(n))=F-1(AI(t),AO(t))
In general, the Non-linear function expression of solid-state power amplifier amplitude relation are as follows:
Wherein, DI(n) range value for being input signal y (n): | y (n) |=DI(n)；DO(n) width for being output signal s (n)
Angle value: | s (n) |=DO(n)；DSFor the saturation level A of corresponding solid-state power amplifierSPower amplifier be saturated amplitude.
Particularly, airborne power amplifier is according to aircraft altitude difference, and locating temperature environment is different, thus shadow
Input signal power-output signal power the characteristic for ringing power amplifier, is set as F (AI(t),AO(t),Ta(t)), wherein Ta(t)
For the temperature of airborne solid-state power amplifier, which can generally be acquired by airborne sensor and be obtained, and be transferred to on-board data
Chain terminal, is denoted as Ta(n)；To temperature Ta(t) parameter can be used for assisting nonlinear function F (DI(n),DO(n)) number is pre- to be lost
Very, mathematical relationship indicates are as follows:
F(DI(n),DO(n), Ta(n))=F-1(AI(t),AO(t),Ta(t))
After the above pre-distortion, by simulation ofdm signal of the output OFDM signal s (n) after DA digital-to-analogue conversion
S (t) send to solid-state power amplifier and sends signal amplification.
Embodiment 1
The Performance Simulation Results of solid state power amplifier ofdm signal digital pre-distortion method in airborne data link of the present invention are carried out
Analysis.
Analogue system is constructed according to Fig. 1, ofdm system parameter is Ns=1024, Nu=720, Ng=128, the filter of iteration clipping
Wave unit inhibits 3dB according to peak-to-average force ratio, configures target clipping amplitude A.The prefix windowing coefficient of raised cosine filter unit is cp=
[0 0.0125 0.0495 0.1091 0.1883 0.2831 0.3887 0.5 0.6113 0.7169 0.8117 0.8909
0.9505 0.9875 1], suffix windowing coefficient and prefix windowing coefficient are symmetry equivalent.Solid-state power amplifier is public with reference to rfmd
3 states of department, 2W export power amplifier RFPA2026, frequency range 700MHz-2700MHz.
Power amplifier module RFPA2026 as shown in Figure 2 in 2.17GHz, temperature be 40 DEG C when input signal power is-
When 20dBm, -10dB, -6dBm, -4dBm, -2dBm, 0dBm corresponding output signal power be 18dBm, 28dBm, 32dBm,
33dBm, 34dBm, 34.5dB, when temperature is increased to 85 DEG C, output signal power integrally reduces 1dBm~0.5dBm, to the number
Regression fit, which is carried out, according to characteristic goes out nonlinear function.Solid state power amplifier characteristic and nonlinear function are special in airborne data link shown in Fig. 3
Property.
Such as Fig. 4 is composed to solid state power amplifier output signal power is obtained after above-mentioned nonlinear function predistortion according to the method for the present invention
It is shown.As it can be seen that without raised cosine filter and when over-sampling predistortion, the outer normalized spatial spectrum of ofdm signal band about reduces 25dB for analysis；
When over-sampling predistortion and when without raised cosine Windowed filtering, the outer normalized spatial spectrum extension about 60% of ofdm signal band；When addition changes
After being total to three parts joint pre-distortion for limit filtration unit, raised cosine filter unit, over-sampling pre-distortion unit, band is returned outside
One change frequency spectrum is about reduced more than 50dB.Thus, it could be seen that the method for the present invention can effectively realize the OFDM of airborne data link solid state power amplifier
Signal predistortion.
The above, optimal specific embodiment only of the invention, but scope of protection of the present invention is not limited thereto,
In the technical scope disclosed by the present invention, any changes or substitutions that can be easily thought of by anyone skilled in the art,
It should be covered by the protection scope of the present invention.
The content that description in the present invention is not described in detail belongs to the well-known technique of professional and technical personnel in the field.
Claims (10)
1. solid state power amplifier ofdm signal digital pre-distortion block in airborne data link, it is characterised in that: including iteration limit filtration
Unit, raised cosine filter unit and over-sampling pre-distortion unit, iteration limit filtration unit are equal for reducing the peak of input signal
Than, and export and give raised cosine filter unit；Raised cosine filter unit reduces signal spectrum out-of-band interference, and exports pre- to over-sampling
Distortion unit；Over-sampling pre-distortion unit carries out Nonlinear Processing to the oversampled signals amplitude received in signal, obtains pre- mistake
The ofdm signal really handled and output.
2. the predistortion implementation method based on claim 1 digital pre-distortion block, it is characterised in that include the following steps:
Step (1) configures digital pre-distortion block, packet according to the parameter characteristic of type onboard data link terminal solid-state power amplifier
Include the target clipping amplitude A of iteration limit filtration unitM, raised cosine filter unit Out-of-band rejection γC, over-sampling number is pre- loses
Genuine power amplifier is saturated amplitude DS；
Step (2), iteration limit filtration unit carry out preliminary pre-distortion to the ofdm signal of Airborne Terminal, and it is equal to obtain peak
Than the ofdm signal after reducing；
Step (3), raised cosine filter unit are to i-th of OFDM symbol x after peak-to-average force ratio reductioni(n) time-domain windowed is carried out, is obtained
Out-of-band rejection γ after adding windowCOfdm signal xi,w(n), to the ofdm signal x after adding windowi,w(n) joined using sinc interpolating function
It closes Kaiser window filter progress time domain up-sampling and obtains OFDM oversampled signals y (n) with filtering；
Step (4), over-sampling pre-distortion unit carry out at amplitude distortion OFDM oversampled signals y (n) according to nonlinear function
Reason, obtains the ofdm signal s (n) of pre-distortion.
3. predistortion implementation method according to claim 2, it is characterised in that: in the step (1), airborne data link
The parameter characteristic of terminal solid-state power amplifier be input signal s (t) amplitude and output signal z (t) amplitude relation characteristic,
Its phase relation characteristic remains unchanged, if the general amplitude relation characteristic F (A of solid state power amplifierI(t),AO(t)) are as follows:
Wherein, AI(t) amplitude leyel for being solid state power amplifier input signal s (t), indicates are as follows: AI(t)=| s (t) |, AOIt (t) is solid
The amplitude leyel of state power amplifier output signal z (t), AO(t)=| z (t) |, ASFor the saturation level of solid-state power amplifier.
4. predistortion implementation method according to claim 2, it is characterised in that: the implementation method of the step (2) is such as
Under:
(2.1), iteration limit filtration unit generates Airborne Terminal time-domain equivalent digital base band OFDM signal x (n):
(2.2), time domain clipping is carried out to time domain digital equivalent base band OFDM signal x (n), method particularly includes:
According to target clipping amplitude AM, according to criterion | x (n) | > AMOr | x (n) |≤AMAmplitude is made decisions, wherein | | table
Show and signal amplitude asked to operate, is handled as follows after judgement:
Wherein, x'(n) be time domain clipping after signal；θ (n) is the phase of signal x (n), and c (n) is the component that is limited；
(2.3), FFT transform is carried out to frequency domain data C (k) to the component c (n) that is limited, frequency domain data C (k) is filtered, is obtained
To the OFDM data x of updatei+1(n)；
(2.4), the update OFDM data x that step (2.3) is obtainedi+1(n), it is iterated update by step (2.2), if repeatedly
Generation number reaches the maximum number of iterations M of design0, then terminate iteration and output signal, otherwise iteration execute step (2.2)~
(2.4), until reaching the maximum number of iterations M of design0。
5. predistortion implementation method according to claim 4, it is characterised in that: the implementation method of the step (2.1) is such as
Under:
It is N by length on frequency domain to information source data X (k)sInverse Fourier transform IFFT obtain time-domain equivalent digital baseband
Ofdm signal x (n), expression formula are
Wherein: n is positive integer, and 0≤n≤Ns-1；K is positive integer, and 0≤k≤Ns-1；Length is NsData X (k) include Nu
A data subcarrier and Ns-NuA zero void subcarrier；EsTo send signal power.
6. predistortion implementation method according to claim 4, it is characterised in that: in the step (2.2), c (n) is indicated such as
Under:
7. predistortion implementation method according to claim 4, it is characterised in that: in the step (2.3), to frequency domain data
C (k) is filtered, the OFDM data x updatedi+1(n), the method is as follows:
By Ns-NuA void subcarrier C (k) is set as zero, obtains frequency domain data C'(k)；IFFT transformation is carried out to frequency domain data C'(k)
Obtain time domain data c'(n), and carry out i-th update:
xi+1(n)=xi(n)+μci(n)
Wherein, xi(n) be i-th iteration when time-domain signal, xi+1(n) signal updated for i+1 time iteration, μ are to update step
Long parameter.
8. predistortion implementation method according to claim 2, it is characterised in that: in the step (3), xi,w(n) it indicates
For
Wherein, NgFor the length of ofdm signal cyclic prefix, it is set as Ng=Ns/8；xi,wIt (n) is the OFDM after i-th of time-domain windowed
Symbol, cpAnd csRespectively cyclic prefix windowing coefficient and cyclic suffix windowing coefficient, prefix windowing coefficient are cp=[0
0.0125 0.0495 0.1091 0.1883 0.2831 0.3887 0.5 0.6113 0.7169 0.8117 0.8909
0.9505 0.9875 1], suffix windowing coefficient and prefix windowing coefficient are symmetry equivalent.
9. predistortion implementation method according to claim 2, it is characterised in that: the implementation of the step (4) is such as
Under:
According to the input signal power of selected solid state power amplifier and output signal power relationship, analyzed by mathematical regression method
To the amplitude relation characteristic F (A of solid state power amplifierI(t),AO(t)) function of, then negating obtains nonlinear function F (DI(n),DO
(n)):
F(DI(n),DO(n))=F-1(AI(t),AO(t))
The Non-linear function expression of solid state power amplifier amplitude relation are as follows:
Wherein, DI(n) range value for being input signal y (n): | y (n) |=DI(n)；DO(n) amplitude for being output signal s (n)
Value: | s (n) |=DO(n)；DSFor the saturation level A of corresponding solid-state power amplifierSPower amplifier be saturated amplitude.
10. predistortion implementation method according to claim 2, it is characterised in that: the implementation of the step (4) is such as
Under:
Airborne power amplifier is according to aircraft altitude difference, and locating temperature environment is different, to influence the input signal of power amplifier
Power-output signal power characteristic, is set as F (AI(t),AO(t),Ta(t)), wherein TaIt (t) is the temperature of airborne solid state power amplifier,
The parameter can generally be acquired by airborne sensor and be obtained, and be transferred to type onboard data link terminal, be denoted as Ta(n)；To temperature Ta
(t) parameter can be used for assisting nonlinear function F (DI(n),DO(n)) digital pre-distortion, mathematical relationship indicate are as follows:
F(DI(n),DO(n), Ta(n))=F-1(AI(t),AO(t),Ta(t))；
The Non-linear function expression of solid state power amplifier amplitude relation are as follows:
Wherein, DI(n) range value for being input signal y (n): | y (n) |=DI(n)；DO(n) amplitude for being output signal s (n)
Value: | s (n) |=DO(n)；DSFor the saturation level A of corresponding solid-state power amplifierSPower amplifier be saturated amplitude.
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