CN101800546A - Method and device for improving link distortion over-compensation of digital pre-distortion system - Google Patents
Method and device for improving link distortion over-compensation of digital pre-distortion system Download PDFInfo
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- CN101800546A CN101800546A CN 201010113726 CN201010113726A CN101800546A CN 101800546 A CN101800546 A CN 101800546A CN 201010113726 CN201010113726 CN 201010113726 CN 201010113726 A CN201010113726 A CN 201010113726A CN 101800546 A CN101800546 A CN 101800546A
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03878—Line equalisers; line build-out devices
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/10—Calibration or testing
- H03M1/1009—Calibration
- H03M1/1033—Calibration over the full range of the converter, e.g. for correcting differential non-linearity
- H03M1/1038—Calibration over the full range of the converter, e.g. for correcting differential non-linearity by storing corrected or correction values in one or more digital look-up tables
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/03—Shaping networks in transmitter or receiver, e.g. adaptive shaping networks
- H04L25/03006—Arrangements for removing intersymbol interference
- H04L25/03343—Arrangements at the transmitter end
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
- H03M1/00—Analogue/digital conversion; Digital/analogue conversion
- H03M1/66—Digital/analogue converters
Abstract
The invention discloses a method for improving link distortion over-compensation of a digital pre-distortion system. The method comprises the following steps: acquiring a distortion compensation characteristic parameter of an input signal in a forward link of the digital pre-distortion system to form a forward distortion compensation table, and compensating the input signal before the input signal enters a digit-analog converter (DAC); acquiring an ideal compensation characteristic parameter of the input signal in a small closed loop link without power amplification to form a feedback distortion compensation table for compensating in a feedback link; and acquiring an ideal compensation characteristic parameter of the input signal in a big closed loop link with power amplification to form a digital pre-distortion table dealing with power amplification non-linear distortion for compensating in the forward link. The invention also discloses a device for improving the link distortion over-compensation of the digital pre-distortion system. Through the method, the over-compensation characteristic of the feedback link can be further effectively counterbalanced based on compensation to forward link distortion so as to achieve the aim of improving the performance of the digital pre-distortion system.
Description
Technical field
The present invention relates to the adaptive digital pre-distortion technology, relate in particular to a kind of method and apparatus that improves link distortion over-compensation of digital pre-distortion system.
Background technology
The sky that makes at the frequency spectrum resource growing tension, Modern Communication System more trends towards adopting than constant envelope modulation mode has the more linear modulation mode of the non-constant envelope of spectral efficient, and this modulation system is had relatively high expectations to the linearity of high power amplifier, so adopt this modulation system need adopt linearization technique to improve the linearity of power amplifier.
On the other hand,, the performance of base station power amplification has been proposed more and more higher requirement, promptly required under the prerequisite satisfying higher linearity, made power amplifier that higher efficient be arranged along with the development of digital mobile communication technology.In order to reach this requirement, will allow not only linearity but also efficient of amplifier, the demand of linearization process promptly radio frequency amplifier or radio system has been proposed, development radio frequency amplifier linearization technique adopts various means to realize amplifier high efficiency and high linearity.This point has very great practical significance for the development and the realization of following wireless mobile telecommunication technology.
A most important step is exactly the appearance of pre-distortion technology in the linearization technique development, it is applied to the radio frequency part in the analog communication system at first, along with Digital Signal Processing (DSP, Digital Signal Processing) development of technology, also can in numeric field, realize, form digital pre-distortion technology.Digital pre-distortion technology both can be applied in the baseband portion of digital communication system, also can be applied in radio frequency part, and pre-distortion technology can also utilize adaptive principle to follow the tracks of the error that the compensation power amplifier causes owing to the change of environmental factors such as temperature, humidity.In a word, pre-distortion technology not only can promote the efficient of transmitter, reduces cost and reduced volume, and also the linearity that can effectively increase transmitter is a kind of linearization technique that adapts to the modern digital Communication Development with elevator system usefulness and communication quality.
For the ease of realizing, in the prior art, the predistortion structure adopts is to table look-up that (as shown in Figure 1, the pre-distortion system structure comprises two passages for LUT, method Look-UpTable): the loop passage and the predistortion passage of data training.Data training passage is a loop structure, and its core is the pre-distortion algorithms module, and this module is handled output of the feedback behind power amplifier and original input signal, obtains the distorted characteristic of power amplifier, obtains the LUT parameter of power amplification distortion anti-espionage then.When the power amplifier characteristic changes along with time or external environment change, can upgrade predistortion anti-espionage LUT parameter by adaptive pre-distortion algorithms.Fig. 2 has provided a kind of basic extraction predistortion table lattice structure, and wherein, X is an input signal, and Y is output (feedback) signal.Determine power output at first according to demand, when moving for the first time, system is straight-through, LUT parameter complete " 1 ", X '=X, signal obtains first group of dateout by after the power amplifier, and feedback is carried out pre-distortion, obtain the LUT parameter by finding the solution min|Y '-X|, constantly revise the LUT parameter then in iterative process, extraction LUT parameter this moment is used for system as the predistortion LUT under this power output.
In the digital pre-distortion system of reality, but the nonlinear energy of many systems is arranged, comprise non-linear element such as transistor and inductance, electric capacity.When analog signal conversion becomes digital signal, more can introduce nonlinear characteristic continually, add the additional nonlinear source of analog to digital converter (ADC) itself, comprise the time constant of sampling capacitor, the inaccuracy in the comparator level and the gain error in the amplifier etc., make based on feedback link introduce very big nonlinear distortion.For general digital pre-distortion system, the nonlinear distortion that based on feedback link is introduced not only can't be compensated by pre-distortion algorithms, can when extracting the LUT parameter of power amplification distortion anti-espionage, obtain unwanted based on feedback link overcompensation characteristic on the contrary, reduce the predistortion effect.
Figure 3 shows that the principle of the distortion compensation of forward link, based on feedback link and power amplifier.With temporal properties is example, and desirable LUT compensation characteristic is Fb ()
-1* H ()
-1* Tx ()
-1, wherein, Fb ()
-1Be the contrary characteristic of based on feedback link distortion, H ()
-1Be the contrary characteristic of power amplification distortion, Tx ()
-1Be the contrary characteristic of forward link distortion, and the power amplifier output characteristic of this moment is:
Y＝X*Fb(·)
-1*H(·)
-1*Tx(·)
-1*Tx(·)*H(·)＝X*Fb(·)
-1，
Wherein, H () is a power amplification distortion, Tx (being) forward link distortion, and obvious, LUT comprises unnecessary overcompensation characteristic Fb ()
-1, this can reduce the predistortion effect significantly.
Patent documentation about this field is a lot, mainly concentrate on Optichron Inc., as CN1985442A, CN1998140A, US2004228488 or the like, its main thought is to introduce linear circuit at the based on feedback link distortion separately to carry out the distortion estimation, and then compensation output, but all there is deficiencies such as realizing complexity, increase hardware circuit expense in this method.
Summary of the invention
In view of this, main purpose of the present invention is to provide a kind of method and apparatus that improves link distortion over-compensation of digital pre-distortion system, can solve the problem of link distortion over-compensation of digital pre-distortion system simply, reliably.
For achieving the above object, technical scheme of the present invention is achieved in that
A kind of method of improving link distortion over-compensation of digital pre-distortion system provided by the invention, this method comprises:
Obtain the distortion compensation characterisitic parameter of input signal, form forward direction distortion compensation table (LUT_e), enter preceding the compensating of digital to analog converter (DAC) at input signal at the digital pre-distortion system forward link;
Obtain the ideal compensation characteristic parameter of input signal, form feedback distortion compensation meter (Pre_LUT) and compensate at based on feedback link without the little closed loop link of power amplifier;
Obtain the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier, the digital pre-distortion table (PA_LUT) that forms reply power amplifier nonlinear distortion compensates at forward link.
In the such scheme, the described input signal that obtains further comprises before the ideal compensation characteristic parameter of the little closed loop link of power amplifier: digital pre-distortion system is carried out connection without power amplifier, obtain little closed loop link;
Described obtaining before the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier further comprises: open the connection without power amplifier, obtaining input signal can be through the big closed loop link of power amplifier.
In the such scheme, the described input signal that obtains is specially at the distortion compensation characterisitic parameter of digital pre-distortion system forward link: be listed as input signal with first sequencing, after process DAC, by ADC to sampling through the signal behind the DAC, set up the DAC error model again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, and the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
Perhaps, the signal behind application discrete Fourier transform (DFT) or fast Fourier transform (FFT) the method extraction process DAC and the difference of input signal are as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link.
In the such scheme, the described input signal that obtains is specially in the ideal compensation characteristic parameter without the little closed loop link of power amplifier: the ADC in the little closed loop link is set up error model, input signal and output signal according to little closed loop link obtain the error equation group, obtain the ideal compensation characteristic parameter of little closed loop link by the solving equation group.
In the such scheme, the described ideal compensation characteristic parameter of obtaining the big closed loop link of input signal process power amplifier is specially: input signal obtains output signal through the big closed loop link of power amplifier, set up the error model of power amplifier, the error model of using power amplifier according to output signal and input signal obtains the error equation group, finds the solution the output signal that satisfies equation group and the parameter of the minimum differential mode of input signal.
In the such scheme, described formation PA_LUT table compensates further at forward link and comprises: by the method for iteration, constantly revise the ideal compensation characteristic parameter of big closed loop link, upgrade the PA_LUT table.
In the such scheme, described first sequencing row are meant and are single-tone sequence, double-tone sequence or multitone sequence by the training sequence of knowing numerical value in advance;
When obtaining the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, the sample frequency of described ADC is the 1/K of DAC, and the value of K is 4 or 8; Obtaining input signal without the ideal compensation characteristic parameter of the little closed loop link of power amplifier the time, described K gets 1;
This method further comprises: be connected low pass filter between the DAC of forward link and ADC, be used to avoid occurring the phenomenon of frequency domain aliasing when ADC samples.
A kind of device that improves link distortion over-compensation of digital pre-distortion system provided by the invention, this device comprises: forward direction distortion compensation module, feedback distortion compensating module, distortion compensating power amplifier module; Wherein,
The forward direction distortion compensation module is used to obtain the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, forms the LUT_e table, compensates before input signal enters DAC;
The feedback distortion compensating module is used to obtain input signal in the ideal compensation characteristic parameter without the little closed loop link of power amplifier, forms the Pre_LUT table and compensates at based on feedback link;
The distortion compensating power amplifier module is used to obtain the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier, forms the PA_LUT table and compensates at forward link.
In the such scheme, described forward direction distortion compensation module is obtained input signal and is specially at the distortion compensation characterisitic parameter of digital pre-distortion system forward link: be listed as input signal with first sequencing, after process DAC, by ADC to sampling through the signal behind the DAC, set up the DAC error model again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, and the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
Perhaps, the signal behind application DFT or the FFT method extraction process DAC and the difference of input signal are as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link.
In the such scheme, described distortion compensating power amplifier module is further used for the method by iteration, constantly revises the ideal compensation characteristic parameter of big closed loop link, upgrades the PA_LUT table.
A kind of method and apparatus that improves link distortion over-compensation of digital pre-distortion system provided by the invention obtains the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, forms the LUT_e table, compensates before input signal is entered DAC; Obtain input signal in ideal compensation characteristic parameter, form the Pre_LUT table and compensate at based on feedback link without the little closed loop link of power amplifier; Obtain the ideal compensation characteristic parameter of input signal, form the PA_LUT table and compensate at forward link through the big closed loop link of power amplifier; So, can further effectively offset the overcompensation characteristic of based on feedback link on the basis of compensation forward link distortion, improve the overcompensation of digital pre-distortion system link distortion, method is simple, reliable.
Description of drawings
Fig. 1 is a pre-distortion system structural representation in the prior art;
Fig. 2 is a kind of structural representation of basic extraction predistortion form;
Fig. 3 is the principle schematic of the distortion compensation of forward link, based on feedback link and power amplifier in the prior art;
Fig. 4 realizes a kind of method flow schematic diagram that improves link distortion over-compensation of digital pre-distortion system for the present invention;
Fig. 5 is the internal structure schematic diagram of forward direction distortion compensation module of the present invention;
Fig. 6 realizes a kind of structural representation that improves the device of link distortion over-compensation of digital pre-distortion system for the present invention.
Embodiment
Basic thought of the present invention is: obtain the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, form the LUT_e table, compensate before input signal is entered DAC; Obtain input signal in ideal compensation characteristic parameter, form the Pre_LUT table and compensate at based on feedback link without the little closed loop link of power amplifier; Obtain the ideal compensation characteristic parameter of input signal, form the PA_LUT table and compensate at forward link through the big closed loop link of power amplifier.
The present invention is described in further detail below by drawings and the specific embodiments.
The present invention realizes a kind of method of improving link distortion over-compensation of digital pre-distortion system, and as shown in Figure 4, this method comprises following step:
Step 401: obtain the distortion compensation characterisitic parameter of input signal, form the LUT_e table, before input signal enters DAC, compensate at the digital pre-distortion system forward link;
Concrete, as shown in Figure 5, be listed as input signal with first sequencing, after process DAC, to sampling through the signal behind the DAC, set up the DAC error model by ADC again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link, forms the LUT_e table according to the distortion compensation characterisitic parameter; Method inquiry LUT_e table by LUT before input signal enters DAC compensates, and can think to be undistorted signal before input signal after the compensation is entering power amplifier;
Further, the method that this step is obtained the distortion compensation characterisitic parameter of forward link can also be: the signal behind the methods extraction process DAC such as application DFT, FFT and the difference of input signal are as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
In this step,, also need between DAC and ADC, be connected low pass filter for avoiding when ADC samples, occurring the phenomenon of frequency domain aliasing; Described first sequencing row are meant the training sequence of knowing numerical value in advance, can be single-tone sequence, double-tone sequence or multitone sequence; The sample frequency of described ADC is the 1/K of DAC, and the value of K can be 4,8 equivalences, can choose according to actual conditions.
The distortion compensation characterisitic parameter that this step is obtained forward link is that example is specifically described with the DAC error model of formula (1) below,
e(x
k)＝α+βx
k+λ
1(α+βx
k)
2+λ
2(α+βx
k)
3
+δ
1(α+β(x
k-x
k-1))
2+δ
2(α+β(x
k-x
k-1))
3+... (1)
+γ
1(α+β(x
k-x
k-M))
2+γ
2(α+β(x
k-x
k-M))
3
Wherein, e (x
k) error of input signal of current time; x
kInput signal for current time; x
K-mPreceding m input signal constantly, m=1,2 ..., M, M are positive integer; α, β, δ
1, δ
2, λ
1, λ
2, γ
1, γ
2Deng coefficient is the distortion compensation characterisitic parameter of forward link;
The sample rate of negate feedback ADC is 1/4 of a forward direction DAC sample rate, i.e. K=4, and establishing this moment input signal is X=(x
1x
2X
n), output signal is Y=(y
1y
2Y
n), then have according to formula (1):
e(x
k)＝α+βx
k+λ
1(α+βx
k)
2+δ
1(α+β(x
k-x
k-1))
2
+γ
1(α+β(x
k-x
k-2))
2
E (x wherein
k)=y
k-x
k, k=3,4,5 ... n, set up following error equation group according to following formula:
By finding the solution above-mentioned equation group, then can obtain distortion compensation characterisitic parameter α, β, the λ of forward link
1, δ
1, γ
1, form the LUT_e table.
Step 402: digital pre-distortion system is carried out connecting without the little closed loop link of power amplifier, obtain the ideal compensation characteristic parameter of input signal, form the Pre_LUT table and compensate at based on feedback link in little closed loop link;
Concrete, the forward link of digital pre-distortion system is carried out being connected without power amplifier with based on feedback link, obtain little closed loop link, ADC in the little closed loop link is set up error model, input signal and output signal according to little closed loop link obtain the error equation group, obtain the ideal compensation characteristic parameter of little closed loop link by the solving equation group, ideal compensation characteristic parameter is formed the Pre_LUT table, inquiring about the Pre_LUT table at the output of based on feedback link by the method for LUT compensates, if inquiry Pre_LUT table offset data is Fb (), at the forward link input signal is X, and the output signal of little closed loop link is Y, then:
Y＝X*Tx(·)
-1*Tx(·)*Fb(·)*Fb(·)
-1＝X
Offset the overcompensation characteristic Fb () of based on feedback link as can be seen
-1This step is obtained input signal when the ideal compensation characteristic parameter of little closed loop link, and the sample rate that ADC can be set is identical with DAC's, i.e. K=1.
Step 403: obtain the ideal compensation characteristic parameter of input signal, form the PA_LUT table and compensate at forward link through the big closed loop link of power amplifier;
Concrete, in the opening steps 402 without the connection of power amplifier, obtaining input signal can be through the big closed loop link of power amplifier, this input signal obtains output signal through after the big closed loop link of power amplifier, and therefore the forward link of this moment and based on feedback link distortion only exist the distortion of power amplifier all by step 401 and step 402 compensation; Set up the error model of power amplifier, error model according to output signal and input signal application power amplifier obtains the error equation group, find the solution the parameter of the minimum differential mode of the output signal that satisfies equation group and input signal, distorted characteristic parameter as power amplifier, it is the ideal compensation characteristic parameter of big closed loop link, ideal compensation characteristic parameter is formed the PA_LUT table, when input signal process forward link, method inquiry PA_LUT table by LUT compensates, method by iteration, constantly revise the ideal compensation characteristic parameter of big closed loop link, also upgrade the PA_LUT table simultaneously;
The ideal compensation characteristic parameter that this step is obtained big closed loop link is that example is specifically described with the error model of the power amplifier of formula (2) below,
Wherein, q is an exponent number, n=1,2,3 ..., x
nThe expression signal;
If input signal is X=(x
1x
2X
n), output signal is Y=(y
1y
2Y
n), then obtain according to formula (2):
X
DPD(n)＝f
1(P
n)*X(n)+f
2(P
n-1)*X(n-1)+f
3(P
n-2)*X(n-2)
Wherein, X
DPD(n) calculate P for the error model of input signal X by power amplifier
nBe the mould value of input signal, i.e. P
n=| x
n|, P
N-1=| x
N-1| f
m() (m=1,2,3) is the form of the fitting of a polynomial of formula (2);
Output signal Y calculates Y ' by the error model of power amplifier, asks for the parameter that satisfies min|Y '-X|.Promptly
ε(n)＝f
1(P
n)*Y(n)+f
2(P
n-1)*Y(n-1)+f
3(P
n-2)*Y(n-2)-X(n) (6)
The parameter of value minimum, wherein, ε (n)=| Y '-X|.Being write as matrix form has:
ε＝(P*Y)*W-X
Wherein W is by f
mThe multinomial coefficient ω of ()
m=[α
M0, α
M1..., α
Mq] form, its multinomial top step number is q; The matrix that P forms for the signal mode value; Matrix launches promptly to have:
Wherein,
W
1＝[α
10，α
11，...，α
1q]′，W
2＝[α
20，α
21，...，α
2q]′，W
3＝[α
30，α
31，...，α
3q]′，X＝[x
3x
4…x
N]′；
Then make the ε minimum coefficient vector W separate for:
W=(P*Y)
-1* X is the ideal compensation characteristic parameter of big closed loop link.
Based on said method, the present invention also provides a kind of device that improves link distortion over-compensation of digital pre-distortion system, and as shown in Figure 6, this device comprises: forward direction distortion compensation module 61, feedback distortion compensating module 62, distortion compensating power amplifier module 63; Wherein,
Forward direction distortion compensation module 61 is used to obtain the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, forms the LUT_e table, compensates before input signal enters DAC;
Be specially, switch among Fig. 6 is all opened, forward direction distortion compensation module 61 as shown in Figure 5, utilize ADC to sampling through the signal behind the DAC, set up the DAC error model again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, and the solving equation group obtains the distortion compensation characterisitic parameter of forward link, forms the LUT_e table according to the distortion compensation characterisitic parameter; Method inquiry LUT_e table by LUT before input signal enters DAC compensates;
Further, described forward direction distortion compensation module 61 is obtained the method for input signal at the distortion compensation characterisitic parameter of digital pre-distortion system forward link, can also be: the signal behind the methods extraction process DAC such as application DFT, FFT and the difference of input signal be as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
For avoiding when ADC samples, occurring the phenomenon of frequency domain aliasing, also need between DAC and ADC, be connected low pass filter; The sample frequency of described ADC is the 1/K of DAC, and the value of K can be 4,8 equivalences.
Feedback distortion compensating module 62 is used to obtain input signal in the ideal compensation characteristic parameter without the little closed loop link of power amplifier, forms the Pre_LUT table and compensates at based on feedback link;
Concrete, with switch S 3, S4, S5 closure, S1, S2 open, obtain little closed loop link without power amplifier, feedback distortion compensating module 62 is set up the ADC error model, obtains the error equation group according to the input signal and the output signal of little closed loop link, obtains the ideal compensation characteristic parameter of little closed loop link by the solving equation group, ideal compensation characteristic parameter is formed the Pre_LUT table, inquire about the Pre_LUT table at the output of based on feedback link by the method for LUT and compensate; Wherein, the sample rate that ADC can be set is identical with DAC's, i.e. K=1.
Distortion compensating power amplifier module 63 is used to obtain the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier, forms the PA_LUT table and compensates at forward link;
Concrete, with switch S 3, S4, S5 opens, S1, the S2 closure, obtaining input signal can be through the big closed loop link of power amplifier, distortion compensating power amplifier module 63 obtains error by the minimum value of finding the solution output signal and input signal absolute difference, set up the error model of power amplifier, the error model of using power amplifier obtains the error equation group, the solving equation group obtains the distorted characteristic parameter of power amplifier, it is the ideal compensation characteristic of big closed loop link, ideal compensation characteristic is formed the PA_LUT table, when input signal process forward link, inquire about the PA_LUT table by the method for LUT and compensate;
Distortion compensating power amplifier module 63 is further used for the method by iteration, constantly revises the ideal compensation characteristic parameter of big closed loop link, upgrades the PA_LUT table.
The above is preferred embodiment of the present invention only, is not to be used to limit protection scope of the present invention, all any modifications of being done within the spirit and principles in the present invention, is equal to and replaces and improvement etc., all should be included within protection scope of the present invention.
Claims (10)
1. a method of improving link distortion over-compensation of digital pre-distortion system is characterized in that, this method comprises:
Obtain the distortion compensation characterisitic parameter of input signal, form forward direction distortion compensation table (LUT_e), enter preceding the compensating of digital to analog converter (DAC) at input signal at the digital pre-distortion system forward link;
Obtain the ideal compensation characteristic parameter of input signal, form feedback distortion compensation meter (Pre_LUT) and compensate at based on feedback link without the little closed loop link of power amplifier;
Obtain the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier, the digital pre-distortion table (PA_LUT) that forms reply power amplifier nonlinear distortion compensates at forward link.
2. method according to claim 1 is characterized in that,
The described input signal that obtains further comprises before the ideal compensation characteristic parameter of the little closed loop link of power amplifier: digital pre-distortion system is carried out connection without power amplifier, obtain little closed loop link;
Described obtaining before the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier further comprises: open the connection without power amplifier, obtaining input signal can be through the big closed loop link of power amplifier.
3. method according to claim 1, it is characterized in that, the described input signal that obtains is specially at the distortion compensation characterisitic parameter of digital pre-distortion system forward link: be listed as input signal with first sequencing, after process DAC, by analog to digital converter (ADC) to sampling through the signal behind the DAC, set up the DAC error model again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, and the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
Perhaps, the signal behind application discrete Fourier transform (DFT) or fast Fourier transform (FFT) the method extraction process DAC and the difference of input signal are as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link.
4. method according to claim 1, it is characterized in that, the described input signal that obtains is specially in the ideal compensation characteristic parameter without the little closed loop link of power amplifier: the ADC in the little closed loop link is set up error model, input signal and output signal according to little closed loop link obtain the error equation group, obtain the ideal compensation characteristic parameter of little closed loop link by the solving equation group.
5. method according to claim 1, it is characterized in that, the described ideal compensation characteristic parameter of obtaining the big closed loop link of input signal process power amplifier is specially: input signal obtains output signal through the big closed loop link of power amplifier, set up the error model of power amplifier, the error model of using power amplifier according to output signal and input signal obtains the error equation group, finds the solution the output signal that satisfies equation group and the parameter of the minimum differential mode of input signal.
6. method according to claim 1 is characterized in that, described formation PA_LUT table compensates further at forward link and comprises: by the method for iteration, constantly revise the ideal compensation characteristic parameter of big closed loop link, upgrade the PA_LUT table.
7. method according to claim 3 is characterized in that, described first sequencing row are meant and are single-tone sequence, double-tone sequence or multitone sequence by the training sequence of knowing numerical value in advance;
When obtaining the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, the sample frequency of described ADC is the 1/K of DAC, and the value of K is 4 or 8; Obtaining input signal without the ideal compensation characteristic parameter of the little closed loop link of power amplifier the time, described K gets 1;
This method further comprises: be connected low pass filter between the DAC of forward link and ADC, be used to avoid occurring the phenomenon of frequency domain aliasing when ADC samples.
8. a device that improves link distortion over-compensation of digital pre-distortion system is characterized in that, this device comprises: forward direction distortion compensation module, feedback distortion compensating module, distortion compensating power amplifier module; Wherein,
The forward direction distortion compensation module is used to obtain the distortion compensation characterisitic parameter of input signal at the digital pre-distortion system forward link, forms the LUT_e table, compensates before input signal enters DAC;
The feedback distortion compensating module is used to obtain input signal in the ideal compensation characteristic parameter without the little closed loop link of power amplifier, forms the Pre_LUT table and compensates at based on feedback link;
The distortion compensating power amplifier module is used to obtain the ideal compensation characteristic parameter of input signal through the big closed loop link of power amplifier, forms the PA_LUT table and compensates at forward link.
9. device according to claim 8, it is characterized in that, described forward direction distortion compensation module is obtained input signal and is specially at the distortion compensation characterisitic parameter of digital pre-distortion system forward link: be listed as input signal with first sequencing, after process DAC, by ADC to sampling through the signal behind the DAC, set up the DAC error model again, the signal and the input signal application DAC error model that obtain according to sampling obtain the error equation group, and the solving equation group obtains the distortion compensation characterisitic parameter of forward link;
Perhaps, the signal behind application DFT or the FFT method extraction process DAC and the difference of input signal are as error, this error is converted to the error waveform of time domain, set up the DAC error model again, use the DAC error model and obtain the error equation group, the solving equation group obtains the distortion compensation characterisitic parameter of forward link.
10. device according to claim 8 is characterized in that, described distortion compensating power amplifier module is further used for the method by iteration, constantly revises the ideal compensation characteristic parameter of big closed loop link, upgrades the PA_LUT table.
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| CN201010113726.8A CN101800546B (en) | 2010-02-09 | 2010-02-09 | Method and device for improving link distortion over-compensation of digital pre-distortion system |
| PCT/CN2010/072572 WO2011097844A1 (en) | 2010-02-09 | 2010-05-10 | Method and apparatus for reducing link distortion overcompensation of digital pre-distortion system |
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| CN101800546B (en) | 2014-07-02 |
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