KR100873106B1 - Apparatus and method for amplifying using adaptive predistortion based on the direct learning architecture - Google Patents

Abstract

The present invention is a predistortion technique having a direct learning architecture for linearization of nonlinear power amplifiers. The transmitter employing the scheme of the present invention includes a digital predistorter at the baseband stage to compensate for the nonlinearity of the power amplifier, and the predistorter is represented based on a polynomial. In this case, the polynomial coefficients of the predistorter for compensating for the nonlinearity of the power amplifier are adaptively obtained by using the relationship between the original signal and the feedback signal to be transmitted in the adaptive block by feeding back the amplifier output. The present invention is a direct learning structure having a simpler structure than the indirect learning architecture of most existing polynomial based predistortion schemes. The indirect learning approach requires additional blocks such as postdistorters or training blocks in the feedback loop, but the present invention does not require such additional blocks in the feedback loop. Therefore, the present invention has the advantage that it is simpler than the predistortion method based on the existing indirect learning. The present invention also includes a conditional adaptive coefficient update scheme for improving the convergence characteristics near the saturation region of the amplifier.

Predistortion, Direct Learning Structure, RLS Algorithm

Description

Apparatus and method for amplifying using adaptive predistortion based on the direct learning architecture}

1 is a structural diagram of a transmitter to which a polynomial based predistortion scheme of a direct learning structure according to the present invention is applied.

2 is a partial linear model of a power amplifier with no memory effect applied to algorithm derivation.

3 is a table summarizing the RLS predistortion algorithm 1 derived from the direct learning structure proposed in the present invention.

4 is a table summarizing the RLS predistortion algorithm 2 that simplifies the RLS algorithm 1 of the direct learning structure of the present invention.

5 is a learning curve of the present invention method and the existing indirect learning structure method.

6 is a spectral comparison diagram between the present invention method and the existing indirect learning structure method (fixed to PBO = 1.5dB, changed to P = 1 to 5, and simulated results).

7 is a signal quality comparison diagram according to the present invention method and the existing indirect learning structure method. Fix P = 4, change PBO value to -3 ~ 3dB, and green EVM graph.

Figure 8 is a comparison of the effect of the predistorter initial coefficient value of the present invention method and the existing indirect learning structure method. After fixing P = 4 and PBO = 1.5dB, the figure shows the initial tap value of the first tap of the predistorter, changing from 0 to 5.

9 is a table summarizing the conditional adaptive algorithm of the present invention.

10 is a diagram comparing the quality performance of the signal by applying the conditional adaptive algorithm of the present invention.

<Description of Major Symbols in Drawing>

5, 6, 7, 8, and 10

Proposed 1: Performance graph of RLS predistortion algorithm 1 of direct learning structure

Proposed 2: Performance Graph of RLS Predistortion Algorithm 2 for Direct Learning Structure

Indirect: Performance Graph of Predistortion Algorithm of Existing Indirect Learning Structure

The present invention relates to a predistortion technique for compensating for nonlinearities in broadband power amplifiers. More specifically, a transmitter having a structure that compensates for the nonlinearity of the power amplifier includes a digital predistorter at the baseband stage to compensate for the nonlinearity of the power amplifier, and the predistorter is represented based on a polynomial. In this case, the polynomial coefficients of the predistorter for compensating for the nonlinearity of the power amplifier are adaptively obtained by using the relationship between the original signal and the feedback signal to be transmitted in the adaptive block by feeding back the amplifier output.

In mobile communication systems, the transmit amplifier operates close to the nonlinear operating point to achieve high efficiency. Nonlinearity of these power amplifiers causes spectral regrowth due to intermodulation distortion (IMD), resulting in inter channel interference and in-band signal distortion. Decrease the performance of your system. In order to prevent performance degradation caused by the nonlinear characteristics of the amplifier, various various linearization schemes have been developed. Linearization includes feed-forward, feed-back, envelope elimination and restoration (ERE), linear amplifier with nonlinear components (LINC), combined analogue locked loop universal modulator (CALLUM), and predistortion ( Various methods such as predistortion have been introduced, and the predistortion method can be divided into analog and digital methods. The most popular of these methods is a cost-effective baseband digital predistortion technique.

Various digital predistortion techniques have been introduced so far, and can be classified into lookup table (LUT) methods [2]-[5] and polynomial-based methods [6]-[10]. The lookup table method is a method of implementing nonlinear predistortion characteristics by a set of discontinuous linear functions. The biggest problems with the lookup table approach are long convergence time proportional to the lookup table size and performance reduction due to quantization. On the other hand, the polynomial-based approach represents a predistorter as a polynomial of several orders. This method shows faster convergence and better performance than the lookup table. Moreover, it is easy to expand to broadband power amplifier with memory effect [9]-[10]. Most polynomial predistorter coefficients are obtained by an indirect learning architecture [7]-[10]. In this case, coefficient acquisition is performed in a postdistroter or training block of the feedback loop, and the obtained coefficient value is copied to the actual predistorter of the transmitter. However, the problems of the predistortion technique of the indirect learning structure are complicated as shown in the future, and are likely to diverge because they are sensitive to the initial tap coefficient value of the predistorter and the operation in the saturation range of the power amplifier. Is to have.

[ references ]

[1] R. Raich and GT Zhou, "On the modeling of memory nonlinear effects of power amplifiers for communication applications," Digital Signal Processing Workshop , pp. 7-10, Oct. 2002.

[2] JK Cavers, "Amplifier linearization using a digital predistorter with fast adaptation and low memory requirements," IEEE Trans . Veh . Technol . vol. 39, no. 4, pp. 374-382, Nov. 1990.

[3] AS Wright and WG Durtler, "Experimental performance of an adaptive digital linearized power amplifer," IEEE Trans . Veh . Technol . vol. 41, no. 4, pp. 395-400, Nov. 1992.

[4] KJ Muhonen, M. Kavehrad, and R. Krishnamoorthy, "Look-up table techniques for adaptive digital predistortion: a development and comparison," IEEE trans . Veh . Technol . Vol. 49, no. 5, pp 1995-2002, Sep. 2000.

[5] AN D'Andrea, V. Lottici, and R. Reggiannini, "Efficient digital predistortion in radio realy links with nonlinear power amplifiers," IEE Proc . Commun . , vol. 147, no. 3, pp. 175-179, June. 2000.

[6] M. Ghaderi, S. Kumar, and DE Dodds, "Fast adaptive polynomial I and Q predistorter with global optimization," IEE Proc . Commun , vol. 143, no. 2, pp. 78-86, Apr. 16.

[7] Y. Qian and T. Yao, "Structure for adaptive predistortion suitable for efficient adaptive alogorithm apllication ," Electron lett . , vol. 143, no. 2, pp. 1282-1283, Oct. 2002.

[8] R. Marsalek, P. Jardin, and G. Baudin, "From post-distortion to predistortion for power amplifiers linearization." IEEE Commun . Letters , vol. 7, no. 7, pp308-310, July. 2003.

[9] J. Kim and K. Konstantinou, "Digital predistortion of wideband signals based on power amplifier model with memory," Electron . Lett ., Vol. 37, no. 23, pp. 1417-1418, Nov. 2001.

[10] L. Ding, GT Zhou, DR Morgan, Z. Ma, S. Kenney, J. Kim, and CR Giardina, "A robust digital baseband predistorter constructed using memory polynomials," IEEE Trans . Commun ., Vol. 52, no. 1, pp. 159-165, Jan. 2004.

[11] L. Ding, Digital Predistortion of Power Amplifiers for Wireless Applications , Ph. D dissertation, Georgia Institute of Tech. Mar. 2004

[12] AAM Saleh, "Frequency-independent and frequency-dependent nonlinear models of TWT amplifiers , " IEEE Trans . Commun ., Vol. COM-29, no. 11, pp. 1715-1720, Nov. 1981.

[13] S. Haykin, Adaptive filter theory , Prentice Hall, 1996

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to develop a predistortion technique based on a direct learning structure that does not have additional blocks such as a post-distorter required in an indirect learning structure, and a conventional predistortion transmitter. The present invention provides an amplifying apparatus and method having a predistortion structure which exhibits a fast convergence characteristic with a simpler predistortion transmitter structure and exhibits robust characteristics such as an initial condition of the predistorter, operation in a saturation region of a power amplifier, and the like.

In the present invention, in order to achieve the above object, in the polynomial-based amplification device for compensating for the nonlinearity of the nonlinear amplifier,

을 입력받아 계수 추출부로부터 전송받은 다항식 계수

을 이용하여 다항식 기반 방식으로 보상된 출력 신호를 출력하는 전치 왜곡기와;Input signal

Polynomial coefficient received from coefficient extraction unit

A predistorter for outputting a compensated output signal in a polynomial based manner using a;

을 입력받아 증폭 된 출력신호

을 출력하는 증폭기와;An input signal connected to an output side of the predistorter

Amplified output signal

An amplifier for outputting;

에 증폭기의 이득

만큼 나누어진 피드백(feedback) 신호 및 입력신호

을 입력받아 전치 왜곡기의 다항식 계수를 구하고, 구한 계수를 상기 전치 왜곡기에 전송하는 계수 추출부를 포함하고,Output signal of the amplifier

Benefits of the amplifier on

Feedback signal and input signal divided by

A coefficient extractor for receiving a polynomial coefficient of the predistorter and transmitting the obtained coefficient to the predistorter,

An amplification apparatus and method are provided in the feedback loop between the output side of the amplifier and the coefficient extractor without post-distorters or training blocks.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the embodiment of the present invention.

을 출력한다.

은 전치왜곡기에 의해

이 되고, 이 값은 이득

의 증폭기에 의해 증폭된다. 비선형 증폭기 출력,

을 보상하기 위하여

을 이득

로 나누고 적응 알고리즘 블록으로 궤환 (feedback) 시킨다. 이때, 도 1의 RF(radio frequency) up/down 변환은 이상적이라고 가정하였다. 적응 알고리즘 블록은 펄스 성형 필터의 출력과 궤환된 증폭기 출력 신호를 가능한 한 같도록 하는 전치왜곡기의 계수를 구한다. 만약 증폭기가 메모리 효과가 없다면, 그 특성은 AM-AM, AM-PM으로 나타난다. AM-AM, AM-PM은 각각 입력 신호의 진폭 크기에 해당하는 출력신호의 진폭 및 위상의 응답을 나타낸다. 이러한 증폭기의 특성을

로 정의하면, 결국 증폭기의 출력

은 다음과 같이 쓸 수 있다. 1 shows a structure of a transmitter of a direct learning method incorporating an adaptive coefficient update predistorter of the present invention. The symbol to be transmitted is band limited by a pulse shaping filter (PSF).

Outputs

By predistorter

Becomes the gain

Is amplified by an amplifier. Nonlinear amplifier output,

To compensate

Gain

Divide by and feed back to the adaptive algorithm block. In this case, it is assumed that the RF (radio frequency) up / down conversion of FIG. 1 is ideal. The adaptive algorithm block finds the coefficients of the predistorter such that the output of the pulse shaping filter and the feedback amplifier output signal are as equal as possible. If the amplifier has no memory effect, its characteristics are shown as AM-AM and AM-PM. AM-AM and AM-PM represent the response of the amplitude and the phase of the output signal corresponding to the amplitude of the input signal, respectively. Characteristics of these amplifiers

Defined as, the output of the amplifier eventually

Can be written as

라고 정의하면,

은 다음과 같이 표현된다.Similarly, the function of the predistorter

If you define,

Is expressed as:

In [Equation 1] and [Equation 2], the ideal predistorter satisfies the following equation.

를 얻는 빠른 수렴특성을 갖는 알고리즘을 개발하는 것이다. Therefore, the present invention is a function having a predistortion characteristic satisfying [Equation 3] in the transmission structure of the direct learning method as shown in FIG.

It is to develop an algorithm that has a fast convergence characteristic.

The present invention is characterized by including a predistortion transmitter structure of the direct learning structure and an algorithm for obtaining coefficients of the predistorter. Hereinafter, with reference to the accompanying drawings for the configuration and operation of the embodiment of the present invention will be described.

는 다음과 같이 표현된다. 이는 상기한 참고문헌 [8]에 근거한다.Assuming that the predistorter is composed of a complex polynomial of 2P + 1 order with odd order in FIG.

Is expressed as This is based on the reference [8] above.

here,

및

은 다음과 같이 표현되는 전치왜곡기 다항식 계수 및 입력 벡터이며,

And

Are the predistorter polynomial coefficients and the input vector,

() ^* Is a conjugate, () ^H is a Hermitian transpose of () ^* , and () ^T is a transposition operator.

The output of the power amplifier through the predistorter is

이 되고, 그에 해당하는 전력 증폭기의 입력은

이다. 결국

은

입력에 대한 이상적인 전치왜곡기의 출력이다. 본 발명의 전치왜곡 알고리즘을 유도하기 위하여 오차 신호

을 이상적인 전치왜곡기의 출력

과 실제출력

의 차이로 정의한다.Assuming that the predistorter works ideally, the output of the power amplifier

And the corresponding power amplifier input is

to be. finally

silver

It is the output of the ideal predistorter for the input. Error signal to derive the predistortion algorithm of the present invention

Ideal predistorter output

And actual output

It is defined as the difference of.

The proposed algorithm is based on least squares (LS). Therefore, the cost function to be minimized is defined as the sum of squares of errors as follows. This is based on reference [13] above.

는 망각인자 (forgetting factor)이고, 0과 1사이의 값을 갖는 다.

은

에 대해서 2차 함수 (quadratic function)이므로, [수학식 7]을

에 대해 미분함으로써 최소값을 구할 수 있다. 미분한 값을 0으로 놓음으로써 얻어지는 정규식 (normal equation)은 다음과 같다. 이는 상기 참고문헌 [13]에 근거한다.here

Is a forgetting factor and has a value between 0 and 1.

silver

Since it is a quadratic function for

By differentiating against, we can find the minimum value. The normal equation obtained by setting the derivative to zero is This is based on reference [13] above.

here,

은 [수학식 7]을 최소화하는 전치왜곡기의 다항식의 최적 계수를 의미한다. 더 나아가

를 계산하기 위해 직접 역행렬을 계산하지 않고, RLS (recursive least squares) 알고리즘을 적용하고, 알고리즘이 수렴하면

이 되어 RLS 전치왜곡 알고리즘은 다음과 같이 유도된다. 이는 상기 참고문헌 [13]에 근거한다. In [Equation 8]

Is the optimal coefficient of the polynomial of the predistorter that minimizes [Equation 7]. Furthermore

RLS (recursive least squares) algorithm is applied without calculating the inverse matrix directly to calculate

Thus, the RLS predistortion algorithm is derived as follows. This is based on reference [13] above.

,

,

,

,

,

,

은 전치왜곡기 입력 벡터,

은 이득 벡터(gain vector),

은 역 상관 행렬(inverse correlation matrix),

는 사전오차 (a priori error),

은 전치왜곡기 다항식 계수이다.here,

Predistorter input vector,

Is a gain vector,

Is the inverse correlation matrix,

Is a priori error,

Is the predistorter polynomial coefficient.

를 계산함에 있어 전력 증폭기의 역함수 특성을 필요로 한다. 하지만 전력 증폭기의 역함수 특성은 일반적으로 알려져 있지 않으므로 위 RLS 전치왜곡 알고리즘은 실용적이지 않다. 알고리즘을 구현 가능하도록 만들기 위해 다음과 같이 증폭기 함수

에 대한 가정을 세운다.The RLS predistortion algorithm of Equation 9 is a priori error.

In computing the power function, we need the inverse function of the power amplifier. However, the inverse function of the power amplifier is not generally known, so the RLS predistortion algorithm is not practical. To make the algorithm implementable, the amplifier function is

Make a home for

은 도 2와 같이 M개 영역을 갖는 부분 선형 함수 (piecewise linear function)로 근사할 수 있다. 입력 신호

이

번째 영역에 있을 때,

은 다음과 같이 표현된다. Assumption 1 : power amplifier

2 may be approximated as a piecewise linear function having M regions as shown in FIG. 2. Input signal

this

In the first zone,

Is expressed as:

Its inverse function is also

,

그리고

은 각각

번째 영역의 기울기, 입력과 출력의 절편 값이다.here,

,

And

Are each

The slope of the first region, the intercept value of the input and output.

번째 영역에 있을 때 사전 오차는 다음과 같이 쓸 수 있다. Using hypothesis 1, the input signal of the power amplifier

In the first region, the dictionary error can be written as

번째 영역의 기울기

임을 알 수 있다. 하지만 여전히 전력 증폭기의 특성은 알지 못하므로,

을 추정해야 하는 문제가 남아 있다. 이 문제를 해결하기 위해, 임의의 시간

에서의 전력 증폭기의 기울기

을 전력 증폭기의 현재 입력과 과거 입력의 표본 (sample)값을 사용하여 추정한다. 현재와 이전의 입출력을 이용하면 기울기는 다음과 같이 증폭기 입력과 출력의 비로 간단하게 표현할 수 있다.Equation 10 is used in Equation 10. In Equation 10, the information needed for the predistortion RLS algorithm is not the inverse of the amplifier characteristic function.

Slope of the first area

It can be seen that. But still we do not know the characteristics of the power amplifier,

There remains a problem that needs to be estimated. To solve this problem, random time

Slope of the power amplifier at

Is estimated using a sample of the current and past inputs of the power amplifier. With the current and previous inputs and outputs, the slope can be simply expressed as the ratio of the amplifier input to the output:

를 사용한다. 결과적으로 기울 기

은 다음과 같이 얻어진다.However, when the current input value and the previous input value are the same, Equation 11, which estimates the slope, causes a problem because the estimated slope becomes infinity, and when the current output and the previous output value are the same, the slope becomes 0 and the problem occurs. Occurs. Therefore, to solve this problem, if the current input value and the previous input value are the same or the current output value and the previous output value are the same, the previous slope estimate is

Use As a result the slope

Is obtained as follows.

Applying [Equation 12], the prior error equation [Equation 10] is replaced by the following equation.

Finally, the proposed method is completed by replacing Equation 13 in Equation 10. This method is called predistortion algorithm 1 in the future.

가 되므로 [수학식 14]와 같이 단순화된 사전 오차식으로 정리된다.In the extreme case of a partial linear model for amplifier characteristics, a simpler pre-error equation can be obtained assuming that the amplifier has one linear interval. in this case

Since it is summarized as a simplified dictionary error equation as shown in [Equation 14].

The algorithm to which Equation 14 is applied is referred to as a predistortion algorithm 2. Algorithm 2 has the advantage of reducing the amount of computation in the prior error calculation because there is no process of calculating the instantaneous slope. The simulation results show that the convergence speed of Algorithm 2 is slower than Algorithm 1, but after convergence, it has a performance comparable to that of Proposed Method 1.

The effects of the present invention were verified through computer simulations. The simulation environment is as follows. The transmit symbol was modulated with 16-QAM (quadrature amplitude modulation), and the pulse shaping filter uses a square root raised cosine filter with a 10-fold over sampling roll-off of 0.22. Used. The Saleh power amplifier model [12] given by Equation 15 was used as the amplifier model.

)로 가정하였다. 전력 증폭기가 포화 전력 대비 얼마나 멀리서 동작하는지 나타내는 지표로 PBO (peak back-off) 값이 많이 쓰이는데, 이는 [수학식 16]과 같이 출력 포화 전력과 신호의 순간최대 전력의 비로 정의된다.The gain of the power amplifier is 1 (

) Is assumed. PBO (peak back-off) value is used as an indicator of how far the power amplifier operates compared to saturation power, which is defined as the ratio of output saturation power and signal instantaneous maximum power as shown in [Equation 16].

는 증폭기의 포화 출력,

는 신호의 순간 최대 출력이다.here,

Is the saturation output of the amplifier,

Is the instantaneous maximum output of the signal.

에 해당하는 학습 곡선 (learning curve)을 보여준다. 모의 실험에서 PBO는 1.5dB로 고정하였고, 전치왜곡기의 차수는 P=1~5까지 1씩 변화시켰으며, 500번의 독립적인 시도를 통해 실험에 의한 MSE 값을 얻었다. 제안 방식 1과 기존 간접학습 방식 [8]은 유사한 수렴시간과 MSE값을 가짐을 알 수 있다. 제안 방식 2는 수렴 속도에 있어 앞의 두 방식에 비해 100~200 샘플 정도 늦고, P=4,5에서 더 높은 MSE값을 가짐을 알 수 있다. 이는 증폭기 전체 구간을 선형으로 가정함으로써 발생하는 오차에 의한 수렴시간 지연과 오차이다. 도 6은 앞에서와 같은 조건으로 전력 스펙트럼을 비교한 그림이다. 전치왜곡기의 차수 P가 증가할수록 선형화 성능은 좋아지며, 특히 P=4~5에서 거의 완벽히 선형화되어 전송 하고자 하는 신호 (도 6의 reference)와 증폭기 출력신호의 스펙트럼이 거의 동일하다. 학습곡선과 스펙트럼 비교는 제안방식들이 기존 간접 학습 구조에 비해 간단한 구조에도 불구하고 견줄만한 성능을 가짐을 보여준다. 5 is a mean square error (MSE) of the present invention and the conventional method.

Show the learning curve corresponding to In the simulation, the PBO was fixed at 1.5dB, the order of the predistorter was changed by 1 from P = 1 ~ 5, and the MSE value was obtained through 500 independent trials. The proposed method 1 and the existing indirect learning method [8] have similar convergence time and MSE value. Proposed scheme 2 is about 100 ~ 200 samples later than the previous two schemes in convergence speed, and has higher MSE value at P = 4,5. This is the convergence time delay and error due to the error caused by assuming the entire amplifier section is linear. 6 is a diagram comparing the power spectrum under the same conditions as before. As the order P of the predistorter increases, the linearization performance is improved. In particular, the linearity of the predistorter is almost completely linearized at P = 4 to 5, and the spectrum of the signal to be transmitted (reference in FIG. 6) and the amplifier output signal are almost identical. The learning curve and spectral comparison show that the proposed schemes have comparable performance in spite of the simple structure.

The quality of the transmission signal at the amplifier output may be determined by an error vector magnitude (EVM) value. EVM is defined as in Equation 17.

은 증폭기 출력 신호를 복조 했을 때 얻어지는 복조 신호 이고

은

이 가져야 할 이상적인 값을 나타낸다. 따라서 EVM값이 0에 가까울수록 송신 신호의 품질이 우수함을 나타낸다. 도 7은 PBO값에 따른 EVM값을 보인다. PBO값은 -3~3dB까지 0.5dB 단위로 모의 실험하였다. PBO값이 -0.5보다 큰 경우 제안 방식과 기존 간접학습 방식은 0.1%이내의 EVM값을 가지며, 거의 동일한 성능을 보인다. 하지만 -0.5보다 작은 PBO값에서 간접학습 방식은 성능이 크게 열화 되며, 특히 -1dB이후에서는 알고리즘이 발산하여 정상적인 동작을 기대할 수 없었다. 반면 제안 방식은 더 강인하게 동작하여 PBO값이 -1.5dB까지 1% 이내의 EVM값을 보인다. here,

Is the demodulation signal obtained when demodulating the amplifier output signal.

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This represents the ideal value you should have. Therefore, the closer the EVM value is to 0, the higher the quality of the transmitted signal. 7 shows EVM values according to PBO values. PBO values were simulated in 0.5dB increments from -3 to 3dB. If the PBO value is greater than -0.5, the proposed method and the existing indirect learning method have an EVM value of less than 0.1% and show almost the same performance. However, the performance of the indirect learning method is significantly degraded at PBO values smaller than -0.5. Especially, the algorithm is divergent after -1dB. On the other hand, the proposed method works more robustly and shows an EVM value of less than 1% up to -1.5dB.

8 is a diagram comparing the effects of the predistorter initial coefficient value. The first coefficient of the polynomial coefficients of the predistorter was measured in 0.2 units from 0 to 5. The MSE value is the value obtained after the algorithm converges. The existing indirect learning method did not converge at the value of initial coefficient greater than 0 or 3, while the proposed methods 1 and 2 converged at 0 to 5 intervals. This result shows that the proposed scheme is very robust to the initial value compared with the existing indirect learning structure.

In addition, the following conditional adaptive algorithm is proposed to further improve the convergence characteristics in the saturation region. If the amplifier operates near the saturation region, the coefficients of the predistorter tend to diverge. Therefore, to solve this problem, updating the predistorter coefficients only when the output of the predistorter is smaller than an arbitrary threshold value (where the threshold value is smaller than the saturation input value) can prevent the problem of diverging. have. When the output of the predistorter is larger than the threshold value, the predistorter coefficient update is not performed, and since the previous predistortion coefficient is applied as it is, no abnormal coefficient update by the saturation signal occurs. Applying a conditional adaptive algorithm has the advantage of extending the amplifier's operating region to near the saturation region. 9 illustrates a conditional adaptive algorithm, and FIG. 10 shows that the adaptive algorithm operates robustly without being diverted by applying the conditional adaptive algorithm.

According to the present invention as described above as a predistortion technique of the direct learning structure that does not require additional blocks, such as the post-distorter has an indirect learning structure does not require a post-distorter or training block required by the existing indirect learning method. This has the advantage of being simple to implement. In addition, the predistortion technique of the present invention has more robust characteristics compared with the predistorter initial polynomial coefficient value of the conventional indirect learning method and the operation in the saturation region of the power amplifier.

Claims (8)

A polynomial based amplification apparatus for compensating for nonlinearity of a nonlinear amplifier, Input signal

Polynomial coefficients

A predistorter for outputting a compensated output signal in a polynomial-based manner by applying a; An input signal connected to an output side of the predistorter

Amplified output signal

An amplifier for outputting; Output signal of the amplifier

Benefits of the amplifier on

Feedback signal and input signal divided by

Polynomial Coefficients of Predistorter

And a coefficient extraction unit for transmitting the obtained coefficients to the predistorter. here,

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More time later. The method according to claim 1, The coefficient extractor calculates the following equations to determine the polynomial coefficients of the predistorter

Amplifying apparatus characterized in that to obtain. [Equation]

,

,

,

here,

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More time forward,

Predistorter input vector,

Is a gain vector,

Is the inverse correlation matrix,

Is a priori error,

Is the predistorter polynomial coefficient,

Denotes a forgetting factor having a value between 0 and 1, respectively. delete The method according to claim 2, The prior error

The amplification apparatus characterized in that the operation is simplified by the following equation (A) or (B). [Equation A]

,

[Equation B]

The method according to claim 1 or 2, An arbitrary threshold is set which is smaller than the saturation input of the amplifier, If the input signal to be input to the amplifier is greater than or equal to the threshold, the polynomial coefficient of the predistorter is

=

Amplification apparatus characterized in that. here,

Is

More time means one step back. In the method for obtaining the polynomial coefficients of the predistorter using a polynomial-based scheme to compensate for the nonlinearity of the nonlinear amplifier, Input signal

And an output signal of the amplifier with respect to the input signal.

Gain of the amplifier on

Receiving a feedback signal divided by one; Input signal by calculating the following equations

Polynomial coefficients of the predistorter to be applied to

And obtaining the polynomial coefficients of the predistorter. [Equation]

,

,

,

here,

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More time later,

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More time forward,

Predistorter input vector,

Is a gain vector,

Is the inverse correlation matrix,

Is a priori error,

Is the predistorter polynomial coefficient,

Denotes a forgetting factor having a value between 0 and 1, respectively. The method according to claim 6, The prior error

Is a method of obtaining a polynomial coefficient of a predistorter, which is simplified by Equation A or Equation B below. [Equation A]

,

here,

Means an input signal to be input to the amplifier. [Equation B]

The method according to claim 6, An arbitrary threshold is set which is smaller than the saturation input of the amplifier, If the input signal to be input to the amplifier is greater than or equal to the threshold, the polynomial coefficient of the predistorter is

=

A method for obtaining a polynomial coefficient of a predistorter.

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