KR101464753B1 - Method for extracting nonlinear model parameter of wideband signal using narrowband signal, apparatus and method for digital predistortering its using - Google Patents

Abstract

The present invention extracts parameters of a nonlinear model while changing a frequency after generating a narrow-band two-tone signal in a frequency band of a wideband signal, sets parameters extracted immediately before as a current initial value, A nonlinear model parameter extracting method of a wideband signal using a narrowband signal, and a predistortion apparatus using the same and a method thereof.

In order to achieve the above object, the present invention provides a nonlinear model parameter extraction method for a wideband signal, the method comprising the steps of: (a) outputting a predicted output value of a nonlinear model using a first initial value; Calculating an error of the error; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed the threshold value; And increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then setting the parameter of the stored nonlinear model as the second initial value to extract the parameters of the non- .

Wideband signal, narrowband signal, nonlinear model, two-tone signal, output predictive value, predistortion

Description

TECHNICAL FIELD The present invention relates to a method of extracting nonlinear model parameters of a wideband signal using a narrowband signal and a predistorter using the narrowband signal and a predistorter using the narrowband signal,

The present invention relates to a nonlinear model parameter extracting method of a wideband signal using a narrowband signal and a predistortion apparatus using the same and a method thereof. More particularly, the present invention relates to a method of extracting a narrowband two tone signal within a frequency band of a wideband signal A nonlinear model parameter extraction method of a wideband signal using a narrowband signal for extracting parameters of a nonlinear model while changing a frequency and setting a parameter extracted immediately before as a current initial value and extracting parameters of a nonlinear model To a predistortion apparatus and a method thereof.

In a typical mobile communication system using radio frequency signals, a RF amplifier is classified into a low-power low-noise receiving amplifier and a high power amplifier (HPA). Here, the high power transmission amplifier operates close to the nonlinear operating point to obtain high efficiency since efficiency is more important than noise.

In this case, the output of the amplifier produces an Intermodulation Distortion (IMD) component that affects not only the in-band but also spurious signals in other frequency bands. Therefore, the feed forward method is mainly used to remove the spurious components.

However, the feedforward method can almost completely eliminate the spurious component, but it has a disadvantage in that the amplification efficiency is lowered and the control is required at the RF stage, which increases the volume and cost of the system.

Digital predistortion (DPD) schemes have been studied in the field of mobile communication systems in consideration of high efficiency and low cost. The digital predistortion scheme takes the inverse of the nonlinearity of the nonlinear amplifier in the digital stage and precompensates the input signal to linearize the output signal of the nonlinear amplifier.

The nonlinear characteristics of the nonlinear amplifier are based on AM / AM (Amplitude Modulation to AM) characteristics, in which the magnitude of the output signal changes according to the magnitude of the input signal, and AM to Phase Modulation ) Characteristics.

To date, most precompensators have been studied extensively for single tone or narrowband frequency signals. Therefore, most of the schemes compensate only for the non-linear characteristics of the nonlinear amplifier (ie, the current input only affects the current output) without considering the memory effect.

However, the memory nonlinear characteristics of a nonlinear amplifier at a wide frequency range significantly change the AM / AM and AM / PM characteristics by affecting not only the current input signal but also past input signals to the output of the current nonlinear amplifier. This phenomenon is called memory effects, and the nonlinearity of the power amplifier depends on the frequency of the input signal.

In recent years, as the frequency band used in mobile communication systems has become wider, studies and developments have been actively conducted considering the memory effect of nonlinear amplifiers. Representative methods to compensate both the non-linearity of the nonlinear amplifier and the memory effect are the simplified Volterra model, the memory polynomial method and the Hammerstein predistortion method.

The Volterra series is a type of memory added to the Taylor series that is used to accurately model nonlinear systems. In other words, the Volterra model precompensator eliminates the nonlinearity of the nonlinear amplifier by taking the inverse of the Volterra series that accurately models the nonlinear amplifier.

The memory polynomial method is a simplified version of the Volterra method, which expresses the output as a polynomial for the current input and past inputs. The ability of the amplifier to remove nonlinearities depends on how many previous inputs are taken into account and how much the order of the polynomial is.

Hammerstein preamble compensation scheme refers to a structure in which a linear time invariant (LTI) system is connected in series to a memoryless nonlinear system. Hammerstein preamble compensation has used a matrix inversion method to obtain the exact coefficients of a memoryless nonlinear system and a linear time invariant system. Here, matrix inverse transformation refers to a method of arranging equations satisfying predetermined conditions in a matrix form and taking the inverse thereof to obtain solutions of coefficients.

1 is a configuration diagram of an example of a conventional digital predistorter.

As shown in FIG. 1, a conventional digital predistorter 100 includes a digital predistorter 110 and a digital signal processor 120 for predicting nonlinear distortion characteristics caused by power amplification.

The digital predistorter 110 is connected to the power amplifier 150 through a digital-to-analog converter (DAC) 130 and a frequency up converter 140.

The power amplifier 150 is connected to the digital signal processor 120 through a frequency down converter 160 and an analog-to-digital converter (ADC) 170.

The digital predistorter 110 includes an address determiner 111, a lookup table (LUT) 112, and a multiplier 113.

The address determiner 111 calculates the size of the received digital input signal Xn and determines an address of a lookup table 112 for reading a distortion control value corresponding to the digital input signal.

The lookup table 112 receives a feedback signal from the digital signal processing unit 120 and outputs a distortion control value corresponding to the determined address. The nonlinear characteristic of the power amplifier 150 may be used for all sizes And stores the distortion control values as digital data. Here, the initial lookup table 112 stores a predetermined initial value, for example, 1 or default values determined by the manufacturer, and is composed of a plurality of lookup tables.

The multiplier 113 applies the distortion control value provided from the lookup table 112 to the digital input signal Xn and outputs the digital control signal to the DAC 130.

The digital signal processor 120 includes a loop delay tracker 121, a predistortion (PD) adaptor 122, a lookup table converter 123, and a subtractor 124. The loop delay tracker 121 is connected to the PD adaptor 122 to compensate the delay time of the feedback signal from the ADC 170.

The PD adapter 122 includes an equalizer 125 that performs an equalizer function for one tap therein. Here, the equalizer 125 may be set to be performed only once at the beginning in the embodiment of the present invention, but may be arbitrarily set to be performed several times, or may be configured outside the PD adapter 122 shall.

The lookup table converter 123 is connected to the PD adapter 122, converts the result determined according to the adaptive algorithm into a digital data form stored in the lookup table, and provides it to the lookup table 112 to update the lookup table.

The subtractor 124 subtracts the feedback signal FB from the transmission signal Tx output from the predistorter 110 and provides the result to the PD adapter 122. [ Here, the subtraction result value is a value for applying to the error value in the adaptive algorithm used in the PD adaptor 122. [

Also, the digital signal processor 120 uses an LMS (Least Mean Square) method. In the LMS method, a coefficient for minimizing an error is obtained, and a digital data form to be stored in the LUT 112 by the LUT converter 123, that is, a lookup table is created using the converged values, It is applied to a digital input signal.

Hereinafter, the operation of the transmitter will be described.

When the digital input signal Xn is inputted, the address determiner 111 calculates the size of the digital input signal and determines the address of the lookup table 112 for reading the distortion control value corresponding to the input. Here, the magnitude of the digital input signal is obtained by squaring the In-phase (I) side signal and the imaginary (Quadrature phase: Q) side signal and summing them (I2 + Q2).

Then, the lookup table 112 outputs a distortion control value corresponding to the determined address. Accordingly, the multiplier 113 multiplies the digital input signal Xn by the distortion control value received from the look-up table 112, and outputs the distorted transmission signal to the digital-to-analog converter 130.

The digital-to-analog converter 130 receiving the transmission signal from the multiplier 113 converts the input transmission signal into an analog signal and outputs the analog signal to the up-converter 140. The up converter 140 analogizes up-converts the frequency of the transmission signal to a desired carrier frequency band, and outputs the converted analog transmission signal to the power amplifier 150. Accordingly, the power amplifier 150 amplifies the received up-converted analog transmission signal.

The down converter 160 receives the amplified transmission signal output from the power amplifier 150 and down converts the amplified transmission signal into an intermediate frequency band and the ADC 170 converts the down- And outputs the converted digital feedback signal to the digital signal processing unit 120. [

The loop delay tracker 121 of the digital signal processor 120 calculates the delay between the transmission (Tx) signal and the feedback (FB) signal output from the multiplier 113.

The equalizer 125 of the PD adaptor 122 adjusts the optimum coefficient so that the difference between the Tx and FB signals inputted before the start of the distortion becomes 0 when the initialization is performed and the adaptation step size and the iteration block ) Is determined by adjusting the number. Here, the equalizer 125 is initially set to obtain an optimum coefficient by being driven only once, but it may be set to be able to obtain an optimum coefficient arbitrarily by driving even if it is not initial according to an implementation.

The PD adapter 122 then updates the polynomial coefficients used with the lookup table 112 using an adaptation algorithm and outputs the obtained coefficients to an input The signal is distorted.

At this time, the adaptive algorithm is a method of finding the optimum coefficient so that the difference between the signal output value and the target value becomes 0 with the LMS, and can be expressed as Equation (1) below.

는 수렴(convergence) 계수로서 1보다 작은 값이며, *는 쌍(conjugate)을 나타낸다. 그리고 원 탭 이퀄라이져는 w(k)가 하나의 계수를 갖는 경우, 즉 원텝인 경우로서 계수를 구하는 과정은 동일하다.Equation (1) is a polynomial coefficient obtained from the PD adaptor, which is an inverse function of the nonlinear power amplifier. (K) is a polynomial coefficient, u (k) is a signal input to the PD adaptor 122, and e (k) 122), that is, an error value.

Is a convergence factor less than 1, and * denotes a conjugate. And the one-tap equalizer is the same when w (k) has one coefficient, that is, when it is one-step, and the process of obtaining the coefficient is the same.

The lookup table converter 123 receives the distorted signal and converts it into the LUT form using the converged polynomial coefficients at the PD adapter 122, and outputs the result to the lookup table 112 for updating. Then, the lookup table 112 outputs updated distortion control values corresponding to the addresses determined by the address determiner 111.

Such a conventional digital predistortion method requires a long time for extracting a nonlinear model parameter of a wideband signal and requires a high sampling rate which is a stumbling block in acquiring characteristics of a wideband nonlinear signal.

It is an object of the present invention to solve such a problem.

Therefore, in the present invention, the narrow-band two-tone signal is generated within the frequency band of the wideband signal, and the parameters of the nonlinear model are extracted while changing the frequency. The parameter extracted immediately before is set as the initial value, A method of extracting a nonlinear model parameter of a wideband signal using a narrowband signal.

It is another object of the present invention to provide a predistortion apparatus using a nonlinear model parameter of a wideband signal and a method thereof for predistorting an input signal using the nonlinear model parameter of the extracted wideband signal.

The objects of the present invention are not limited to the above-mentioned objects, and other objects and advantages of the present invention which are not mentioned can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily apparent that the objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

According to another aspect of the present invention, there is provided a method of extracting a nonlinear model parameter of a wideband signal, the method comprising: generating a narrow-band two-tone signal within a frequency band of a wideband signal; And extracting a parameter of the nonlinear model while changing the frequency of the generated two-tone signal, and extracting a parameter of the nonlinear model by setting a parameter extracted immediately before as a current initial value, Extracting an error between an output predicted value of the nonlinear model calculated using the first initial value and an output measured value of the nonlinear model measured using the two-tone signal; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed the threshold value; And increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then setting the parameter of the stored nonlinear model as the second initial value to extract the parameters of the non- .

According to another aspect of the present invention, there is provided a method of extracting a nonlinear model parameter of a wideband signal, the method comprising: outputting a predicted output value of a nonlinear model using a first initial value; Calculating an error between the output measurements of the model; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed the threshold value; And increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then setting the parameter of the stored nonlinear model as the second initial value to extract the parameters of the non- .

According to another aspect of the present invention, there is provided a predistortion apparatus using a nonlinear model parameter of a wideband signal. The predistortion apparatus generates a narrowband two-tone signal whose frequency is constantly increased within a frequency range of a broadband signal A signal generating means for generating a signal; A digital signal processing means for extracting a parameter of a nonlinear model using the narrowband two-tone signal generated by the signal generation means, and setting a parameter extracted immediately before as a current initial value to extract a parameter of the nonlinear model; And predistortion means for predicting the inverse of the nonlinear model parameters extracted by the digital signal processing means and predistorting the input signal, wherein the digital signal processing means calculates the output predicted value of the nonlinear model calculated using the first initial value An error calculating means for calculating an error between the measured output values of the nonlinear model measured using the two-tone signal; Parameter storing means for storing the corresponding parameter of the nonlinear model as the error calculated by the error calculating means does not exceed the threshold value; And increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wide-band signal, and then setting the parameter of the stored non-linear model as the second initial value to extract the parameters of the non- And a parameter extracting unit.

According to another aspect of the present invention, there is provided a predistortion method using a nonlinear model parameter of a wideband signal, the method comprising the steps of: generating a narrowband two-tone signal in which a frequency is constantly increased within a frequency range of a wideband signal step; Extracting a parameter of the nonlinear model using the generated narrowband two-tone signal, setting a parameter extracted immediately before as a current initial value, and extracting a parameter of the nonlinear model; And predistorting the input signal by obtaining an inverse function of the extracted nonlinear model parameters, wherein the step of extracting the parameters of the nonlinear model includes the steps of: using the output predictive value and the two-tone signal of the nonlinear model calculated using the first initial value; Calculating an error between the measured output values of the nonlinear model; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed a threshold value; And increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wide-band signal, and then setting the parameter of the stored non-linear model as a second initial value, .

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In addition, the present invention relates to a technique for efficiently extracting characteristics of a wideband signal and a design of a pre-linearizer using the nonlinear model parameter extraction of the RF power amplifier and the design of a digital predistorter based thereon, Signal processing, wireless communication, WiBro, RF power amplifier, transmitter, ADC, predistorter and the like.

In addition, the present invention uses a narrowband signal to extract characteristics of a wideband signal occupying a wide frequency band, and provides a predistortion method of a wideband signal based on the narrowband signal.

In addition, the present invention solves the problem of increasing the price of implementation by requiring an ADC that requires a high sampling frequency for modeling a wideband signal, Lt; / RTI >

In addition, the present invention extracts a model using a two-tone signal that is mathematically easy to analyze, thereby reducing the calculation time used for extracting the nonlinear model.

In addition, the present invention uses a narrowband signal for modeling a wideband signal, extracts a model by sequentially changing the frequency of a two-tone signal, and uses a Wiener-Hammerestein to consider characteristics of input / output frequencies in a broadband system. Model to apply the Wiener-Hammerstein model to a given tone signal from a sequential change of a given tone signal, and to provide a predistortion scheme that can implement a low sampling frequency for an output signal by applying this signal extraction scheme.

According to the present invention as described above, a narrow-band two-tone signal is generated within a frequency band of a wideband signal, and a parameter of the nonlinear model is extracted while the frequency is changed. The parameter extracted immediately before is set as a current initial value, By extracting the parameters of the model, it is possible to quickly extract the parameters of the nonlinear model at a low sampling rate.

In addition, when the predistorter of the power amplifier is implemented, it is possible to implement a predistorter capable of lowering the sampling rate which is the most stumbling block in order to obtain characteristics of a wideband nonlinear signal, It is possible to achieve a design and linearization performance improvement of a predistorter of a wider wideband signal in the future.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, Can be easily performed. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail. Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a diagram for explaining a non-linear model parameter extraction method of a wideband signal using a narrowband signal according to an embodiment of the present invention.

First, assume that the bandwidth of the input signal is B and that the nonlinear characteristic of the output signal includes the odd-number difference of the (2n-1) th order.

Then, the bandwidth of the output signal is (2n-1) * B, and a sampling rate of 2 * (2n-1) * B or more is required to extract the output signal from the ADC.

의 대역폭을 가지는 투 톤(Two-tone) 신호 등과 같은 협대역 신호를 사용하여, ADC에서 요구하는 샘플링의 속도를

만큼 감소시킨다. 이때, 협대역 신호를 낮은 주파수 대역에서부터 높은 주파수 대역까지 옮겨가며(sweep), 광대역 신호의 특성을 모델링한다.Therefore, in the present invention,

Bandwidth signal such as a two-tone signal with a bandwidth of 1 MHz, the sampling rate required by the ADC is

. At this time, the narrowband signal is swept from the low frequency band to the high frequency band, and the characteristic of the wideband signal is modeled.

In the present invention, the nonlinear model is preferably a Wiener-Hammerstein model as shown in FIG. 3, taking into consideration the input frequency characteristic and the output frequency characteristic for a wideband signal.

,

는 각각 비선형 모델에서 입력 주파수 특성과 출력 주파수 특성을 나타내며, g(ㆍ)는 비선형 특성을 나타내는 함수이다. 이러한 'Wiener-Hammerstein' 모델의 파라미터(변수값)를 추출하기 위해, 도 2에 도시된 바와 같은 투 톤 신호의 주파수를 순차적으로 변경한다.3,

,

Represent the input frequency characteristic and the output frequency characteristic in the nonlinear model, respectively, and g (.) Is a function representing the nonlinear characteristic. In order to extract the parameters (variable values) of this 'Wiener-Hammerstein' model, the frequency of the two-tone signal as shown in FIG. 2 is sequentially changed.

는 두 주파수의 차를 나타낸다.Hereinafter, a method of extracting a nonlinear model parameter of a wideband signal using a narrowband signal will be described. First, in a frequency band of a signal to be extracted, that is, a signal in consideration of spectral regrowth due to nonlinear characteristics of an RF power amplifier, And generates a narrow-band two-tone signal. At this time, f ₁ and f ₂ represent frequencies of respective _two -tone signals,

Represents the difference between two frequencies.

Then, parameters of the nonlinear model are extracted using the generated two-tone signal.

만큼 증가시킨 후 비선형 모델의 파라미터를 추출한다.Then, each frequency value of the two-tone signal is divided by 2

And the parameters of the nonlinear model are extracted.

In this manner, the frequency band of the two-tone signal is continuously increased (sweeping), and the parameters of the nonlinear model are extracted to the highest frequency region of the wideband signal.

In order to extract the Wiener-Hammerstein model parameters, a two-tone signal having two frequency components is defined as Equation (2) below.

Here, A _-1 represents a phasor value indicating the magnitude and phase of a signal having a frequency f ₁ , and A ₊₁ indicates a phasor value indicating a magnitude and phase of a signal having a frequency f ₂ . That is, A _-1 and A ₊₁ are complex numbers that simultaneously represent magnitude and phase. Also, A composed of these values is a 2x1 vector.

When the two-tone input signal that can be represented by A is input to a system having nonlinearity of (2n-1) th order, the output signal has 2n frequency components, 3].

값은 출력으로 발생하는 2n개의 주파수 성분 신호의 크기 및 위상을 나타내는 페이저 값을 나타낸다.here,

Value represents a phasor value indicating the magnitude and phase of 2n frequency component signals generated as an output.

이며, 두 주파수 간의 차이의 1/2인 변조주파수는

이고, 각주파수(angular frequency)는

,

이 된다. 이때, 출력 파형은 각주파수를 기준으로 하기의 [수학식 4]에서 출력 신호가 발생한다.On the other hand, f ₁ < f ₂ , the center frequency is

, And the modulation frequency, which is 1/2 of the difference between the two frequencies,

, And the angular frequency is

,

. At this time, an output signal is generated from the following equation (4) with respect to each frequency as an output waveform.

에서 발생하는 신호의 크기와 위상을 나타내는 페이저 값을

로 표현한다. 이때, 페이저의 집합을 Y₂로 나타내며, Y₂는 2n×1의 벡터가 된다.In other words,

A phase value indicating the magnitude and phase of a signal generated in

. At this time, the set of phasers is represented by Y ₂ , and Y ₂ is a vector of 2n × 1.

This Y ₂ can be obtained through the Fourier transform of the 'Inphase' and 'Quadrature Phase' signals obtained through 'Attenuator', 'Down-converter' and 'ADC' in the feedback loop of the output of the PA .

In addition, a system having a nonlinear model characteristic as shown in FIG. 3 is expressed using a matrix and a vector as shown in the following equation (5). At this time, since the region to be linearized at the time of model extraction is the center frequency adjacent channel, it is interpreted as a baseband equivalent circuit. In order to extract the model of FIG. 3, a signal in the time domain is converted into a signal in the frequency domain through Fourier transform and processed.

Here, H ₁ represents a (2 × 2) diagonal matrix, H ₂ represents a (2n × 2n) diagonal matrix, and a represents an (n × 1) vector.

는 주파수

에 대한 입력 필터(Input Filter)의 전달함수를 나타내고, H₂ 행렬에서

는 주파수

에 대한 출력 필터(Out Filter)의 전달함수를 나타낸다.Also, in the H ₁ matrix

Frequency

Represents the transfer function of the input filter to the H ₂ matrix,

Frequency

Represents the transfer function of the output filter (OutFilter).

In addition, 'a' denotes 'Memoryless Nonlinear Function g (.)' In the 'Wiener-Hammerstein' model shown in FIG. 3 and is a form of 'Taylor Series' for input and output signals as shown in Equation (6) Lt; / RTI &gt;

Where x represents the complex envelope signal, which is the baseband equivalent signal to the input signal.

The proposed algorithm effectively extracts H ₁ , H ₂ , and a, which are the parameters of the system defined above. For this, a matrix T as shown in Equation (7) below is defined and used. At this time, the following matrix T has a size of ((2n-1) x n).

Here, the elements of the matrix are defined by the following equation (8).

를 나타내고,

를 나타내며,

를 나타낸다.here,

Lt; / RTI &gt;

Lt; / RTI &gt;

.

As a result, the following equation (9) holds.

Here, the (2n × 2) matrix Γ is defined by the following equation (10).

,

,

를 순환적으로 추출한다.In Equation (9), Y ₂ and A vector are known values as input and output values of the power amplifier. Therefore, it is possible to use the system parameter

,

,

Is extracted cyclically.

4 is a flowchart illustrating a nonlinear model parameter extraction method of a wideband signal using a narrowband signal according to an embodiment of the present invention.

First, an initial value of a nonlinear model parameter is set (401). At this time, the frequency-based output measurement value of the narrow-band signal (for example, two-tone signal) for the system is measured and stored.

Thereafter, an output predicted value of the nonlinear model is calculated using the set initial value (402).

Then, it is determined whether the error between the calculated output predicted value and an output measurement value corresponding to the frequency exceeds a threshold value (403).

If the result of the check is 403, if the threshold value is exceeded, the parameter of the nonlinear model is updated, and the process proceeds to the step 402 (step 404).

)이 바로 이전의 메모리리스 비선형 함수값(

)과 동일한지 판단한다(405). 이때, 초기 단계에서는 이전에 산출한 메모리리스 비선형 함수값이 존재하지 않으므로 하기의 "407" 과정으로 진행한다.If the result of the check (403) is not exceeded, the memoryless nonlinear function value (

) Is the previous memoryless nonlinear function value (

(405). At this time, since the memoryless nonlinear function value previously calculated does not exist in the initial stage, the process proceeds to the step 407 described below.

If the determination result is not the same as the determination result (405), the memoryless nonlinear function value extracted immediately before is replaced with the currently extracted memoryless nonlinear function value to calculate remaining parameters of the nonlinear model, and then the process proceeds to step 402 (step 406) . That is, the parameters of the nonlinear model are extracted again in the previous frequency band.

If the determination result is the same as the determination result (404), the corresponding parameter of the nonlinear model is stored (407).

Then, it is checked whether the frequency of the two-tone signal exceeds the frequency range of the wideband signal (408).

If the result of the check is not more than 408, the frequency of the two-tone signal is increased, and the parameter of the stored nonlinear model is set to an initial value.

If the check result (408) is exceeded, the process is terminated. At this time, the parameters of the nonlinear model for each frequency are additionally interpolated (410). That is, a discrete signal is connected together with an analog signal to extract a parameter of a nonlinear model for a frequency that is not selected.

In addition, the parameters of the extracted nonlinear model are ignored when the frequency of the two-tone signal exceeds the frequency range of the wideband signal.

Let's look at this in more detail.

씩 증가하는 상태를 나타낸다. v=1인 경우가 가장 낮은 주파수 대역을 나타내고, v를 1씩 증가시키면서 입력된 투 톤 신호의 주파수를 변경한다. 이때, 주파수의 변경은 RF 전력증폭기의 비선형 특성에 의한 스펙트럼 'Regrowth'를 고려한 광대역 신호의 주파수 범위 내에서 이루어진다.V is a value representing the frequency change of the two-tone signal,

Respectively. The case of v = 1 represents the lowest frequency band, and the frequency of the input two-tone signal is changed while increasing v by one. At this time, the frequency change is made within the frequency range of the wideband signal considering the spectrum 'Regrowth' due to the nonlinear characteristic of the RF power amplifier.

s represents the number of iterations for extracting the system (non-linear model) parameter value. The previous value is upgraded through an iterative process to extract the correct parameter value.

,

,

로 표기한다.Therefore, the predicted values of the parameters H ₁ , H ₂ , a after the s-th iteration for the v-th input-

,

,

.

,

의 초기값으로 단위행렬을 설정한다. 그리고 A 와

값을 이용하여

행렬을 추출하고 최소좌승법을 이용하여

(v=1인 주파수의 입력에 대하여 a의 첫 번째 예상값)를 추출한다.First, when v = 1 and s = 0,

,

The unit matrix is set as the initial value of the unit matrix. And A and

Using the value

The matrix is extracted and the least squares method is used

(the first expected value of a for an input of frequency at v = 1).

,

,

를 이용하여

를 계산한다.And extracted

,

,

Using

.

는 추출된 파라미터

,

,

을 통해 예측되는 출력 신호의 주파수 영역에서의 페이저 값으로서 하기의 [수학식 11]과 같이 구할 수 있다.Generally,

Lt; / RTI &gt;

,

,

Can be obtained as the phasor value in the frequency domain of the output signal predicted through the following equation (11).

는 Γ 행렬에 대하여 H₁, a 대신 예측된 값

,

를 이용하여 구한 행렬이 된다.here,

For the Γ matrix, H ₁ , a instead of a predicted value

,

Is used as a matrix.

)를 하기의 [수학식 12]와 같이 정의한다. 이때,

는 2n×1 벡터이다.Then, the error vector between the phasor of the actually measured output value and the predicted phasor (

) Is defined as &quot; (12) &quot; At this time,

Is a 2n x 1 vector.

이 된다.Here, when v = 1 and s = 0

.

와 임계치를 비교한다.after,

And the threshold value.

,

,

를 업데이트한다.As a result of the comparison, if the value is greater than the threshold value, the value of s is increased to 1 in the state of v = 1,

,

,

Lt; / RTI &gt;

의 대각 행렬 성분을 하기의 [수학식 13]을 통해 업데이트한다.That is,

Is updated through the following equation (13). &Quot; (13) &quot;

() _{M, m} means an element in the m-th row and column in a given matrix, and () _m denotes an element in the m-th row in the vector. do.

의 관계식을 이용하여, 이를 만족시키는

,

를 찾아내고,

로부터

를 찾아낸다.And

, We use the relational expression

,

, &Lt; / RTI &gt;

from

.

,

를 찾아내고, 이를 이용하여 다시 출력의 페이저 값

및

를 계산한다.That is, when v = 1 and s = 1

,

And using this, the pager value of the output again

And

.

와 임계치의 크기를 비교한다.after,

And the size of the threshold value.

At this time, when the magnitude of the error value exceeds the threshold value, it is increased again to s = 2.

와 같이 표기한다.On the other hand, if the error value does not exceed the threshold value,

As shown in Fig.

씩 증가시킨 후 비선형 모델의 파라미터를 추출한다.Thereafter, the process proceeds from v = 1 to v = 2. That is, when the frequency value of the input to-tone signal is v = 1 as in Equation (14) below,

And then the parameters of the nonlinear model are extracted.

으로 이전의 수렴 값인

을 이용함으로써 수렴 속도를 향상시킬 수 있다. 즉, v=2인 경우에 대한 초기값으로

을 이용하여 에러의 크기가 주어진 임계치를 초과하지 않는

를 추출한다.At this time, the initial value for the (v + 1)

The previous convergence value

The convergence speed can be improved. That is, as an initial value for the case of v = 2

RTI ID = 0.0 &gt; error &lt; / RTI &gt; does not exceed a given threshold

.

를 만족하는지 확인한다.after,

Is satisfied.

If this is not the case, repeat the process of finding a new convergence value by lowering the value of v by one.

라고 하고, v=2인 경우 s번 반복하여 수렴했을 때의 파라미터가

라고 하자.For example, when v = 1, the parameter when the convergence (the error is below the threshold value) is repeated s times

, And when v = 2, the parameter when it converges repeatedly s times

Let's say.

=

인지 확인하여 동일하지 않은 경우, v=1로 되돌아가

를

로 대체한 후 나머지 파라미터를 다시 산출한 후 이후의 과정을 수행한다. 일반적으로, v=3까지만 동일하면 그 이후의 값은 대체로 동일하다.At this time, when v = 2

=

If it is not the same, v = 1 is returned

To

And the remaining parameters are calculated again, and the subsequent steps are performed. Generally, if v = 3 is the same, the values thereafter are generally the same.

This process is performed to extract the coefficient values of the g () function having the same characteristics in all frequency domains.

5 is a block diagram of a predistortion apparatus using nonlinear model parameters of a wideband signal according to an embodiment of the present invention.

5, a predistortion apparatus using nonlinear model parameters of a wideband signal according to the present invention includes a signal generation unit for generating a narrowband two-tone signal whose frequency is constantly increased within a frequency range of a wideband signal, The parameters of the nonlinear model are extracted using the narrowband two-tone signal generated by the signal generation unit 51, and the parameter extracted immediately before is set as the current initial value to extract the parameters of the nonlinear model And a predistortion unit 53 for predicting the inverse function of the nonlinear model parameters extracted by the digital signal processing unit 52 and predistorting the input signal using the inverse function.

In addition, the apparatus further includes an interpolator for interpolating the parameters of the nonlinear model extracted by the digital signal processor 52.

Here, the digital signal processor 52 calculates the error between the output predicted value of the nonlinear model calculated using the initial value and the output measured value of the nonlinear model measured using the two-tone signal A parameter storage 522 for storing a corresponding parameter of the nonlinear model as the error calculated by the error calculator 521 does not exceed a threshold value, And a parameter extractor 523 for increasing the frequency of the two-tone signal as the frequency of the signal is not exceeded and then extracting the parameters of the nonlinear model by setting the parameters of the stored nonlinear model as initial values do.

의 역함수에 해당하며, 출력 주파수 응답특성은 추출된

의 역함수에 해당한다. 또한, 중간의 비선형함수는 g(ㆍ)의 비선형을 보상할 수 있는 구조(역함수)를 가지도록 설계된다.In addition, the predistorter 53 has a Wiener Hammerstein structure in which the input frequency response characteristic is extracted

And the output frequency response characteristic corresponds to the inverse function of the extracted

. &Lt; / RTI &gt; In addition, the intermediate nonlinear function is designed to have a structure (inverse function) that can compensate for the nonlinearity of g ().

6 is a flowchart illustrating a predistortion method using nonlinear model parameters of a wideband signal according to an embodiment of the present invention.

First, a narrow-band two-tone signal in which a frequency is constantly increased within a frequency range of a wideband signal is generated (601).

Next, parameters of the nonlinear model are extracted by using the generated narrowband two-tone signal, and parameters of the nonlinear model are extracted by setting the extracted parameters to the current initial values (602).

That is, an error between the output predicted value of the nonlinear model calculated using the first initial value and the output measured value of the nonlinear model measured using the two-tone signal is calculated, and if the calculated error does not exceed the threshold value And the frequency of the two-tone signal does not exceed the frequency range of the wide-band signal, the frequency of the two-tone signal is increased, and the parameters of the stored non-linear model are stored And sets the second initial value to extract the parameters of the nonlinear model.

Thereafter, an inverse function of the extracted nonlinear model parameters is obtained, and the input signal is predistorted using the inverse function (603).

Meanwhile, the method of the present invention as described above can be written in a computer program. And the code and code segments constituting the program can be easily deduced by a computer programmer in the field. In addition, the created program is stored in a computer-readable recording medium (information storage medium), and is read and executed by a computer to implement the method of the present invention. And the recording medium includes all types of recording media readable by a computer.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. The present invention is not limited to the drawings.

The present invention can be used for digital predistortion and the like.

1 is a configuration diagram of a conventional digital predistorter;

2 is a diagram for explaining an embodiment of a nonlinear model parameter extraction method of a wideband signal using a narrowband signal according to the present invention.

FIG. 3 is a structure diagram of an embodiment of a 'Wiener-Hammerstein' model used in the present invention,

FIG. 4 is a flowchart illustrating a nonlinear model parameter extraction method of a wideband signal using a narrowband signal according to an embodiment of the present invention.

5 is a block diagram of a predistorter using nonlinear model parameters of a wideband signal according to an embodiment of the present invention.

6 is a flowchart illustrating a predistortion method using nonlinear model parameters of a wideband signal according to an embodiment of the present invention.

DESCRIPTION OF THE REFERENCE NUMERALS

51: Signal generator 52: Digital signal processor

53: Predistortion section

Claims (21)

A method for extracting a nonlinear model parameter of a wideband signal, Generating a narrow-band two-tone signal within a frequency band of a wideband signal; And Extracting a parameter of the nonlinear model while changing the frequency of the generated two-tone signal, and extracting a parameter of the nonlinear model by setting a parameter extracted immediately before as a current initial value, The step of extracting the parameters of the non- Calculating an error between an output predicted value of the nonlinear model calculated using the first initial value and an output measured value of the nonlinear model measured using the two-tone signal; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed the threshold value; And A step of increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then setting the parameter of the stored nonlinear model as a second initial value to extract the parameters of the non- A method for extracting a nonlinear model parameter of a wideband signal using a narrowband signal. A method for extracting a nonlinear model parameter of a wideband signal, Calculating an error between an output predicted value of the nonlinear model calculated using the first initial value and an output measured value of the nonlinear model measured using the two-tone signal; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed the threshold value; And A step of increasing the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then setting the parameter of the stored nonlinear model as a second initial value to extract the parameters of the non- A method for extracting a nonlinear model parameter of a wideband signal using a narrowband signal. 3. The method of claim 2, Wherein the calculating the error comprises: Setting a first initial value of a nonlinear model parameter; Calculating an output predicted value of the nonlinear model using the set initial value; And Calculating an error between the calculated output predicted value and an output measured value corresponding to the frequency, A method for extracting a nonlinear model parameter of a wideband signal using a narrowband signal. 3. The method of claim 2, Wherein the step of storing the parameter comprises: Determining whether the calculated error exceeds a threshold value; A parameter updating step of updating the parameter of the nonlinear model and calculating the error when the threshold value is exceeded; Determining whether the nonlinear function value of the nonlinear model parameters is equal to the immediately preceding nonlinear function value if the threshold is not exceeded; Calculating a residual parameter of the nonlinear model by replacing the nonlinear function value extracted immediately before with the currently extracted nonlinear function value if the result of the determination is not the same; And As a result of the determination, if the same is true, the step of storing the calculated parameter of the nonlinear model A method for extracting a nonlinear model parameter of a wideband signal using a narrowband signal. 5. The method according to any one of claims 2 to 4, Interpolating the parameters of the extracted nonlinear model And extracting a nonlinear model parameter of the wideband signal using the narrowband signal. The method of claim 3, The first initial value is a value A nonlinear model parameter extraction method of a wideband signal using a narrowband signal, which is a unitary matrix. The method according to claim 3 or 6, The output predicted value is a value A method for extracting a nonlinear model parameter of a wideband signal using a narrowband signal, the phasor value in the frequency domain. A predistortion apparatus using nonlinear model parameters of a wideband signal, Signal generating means for generating a narrow-band, two-tone signal whose frequency is constantly increased within a frequency range of a wideband signal; A digital signal processing means for extracting a parameter of a nonlinear model using the narrowband two-tone signal generated by the signal generation means, and setting a parameter extracted immediately before as a current initial value to extract a parameter of the nonlinear model; And And predistortion means for predicting the inverse of nonlinear model parameters extracted by the digital signal processing means and predistorting the input signal, Wherein the digital signal processing means comprises: An error calculating means for calculating an error between the output predicted value of the nonlinear model calculated using the first initial value and the output measured value of the nonlinear model measured using the two-tone signal; Parameter storing means for storing the corresponding parameter of the nonlinear model as the error calculated by the error calculating means does not exceed the threshold value; And To increase the frequency of the two-tone signal as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and to set the parameter of the stored nonlinear model as the second initial value to extract the parameters of the non- Parameter extracting means And a nonlinear model parameter of the wideband signal. 9. The method of claim 8, An interpolation means for interpolating the parameters of the nonlinear model extracted by the digital signal processing means, And a nonlinear model parameter of the wideband signal. delete 9. The method of claim 8, The first initial value is a value A predistortion unit using a nonlinear model parameter of a wideband signal, which is a unitary matrix. 12. The method of claim 11, The output predicted value is a value A predistortion device using a nonlinear model parameter of a wideband signal that is a phasor value in the frequency domain. In a predistortion method using nonlinear model parameters of a wideband signal, Generating a narrowband tone signal in which the frequency is constantly increasing within a frequency range of a wideband signal; Extracting a parameter of the nonlinear model using the generated narrowband two-tone signal, setting a parameter extracted immediately before as a current initial value, and extracting a parameter of the nonlinear model; And And predistorting the input signal by obtaining an inverse function of the extracted nonlinear model parameters, The parameter extracting step of the non- Calculating an error between an output predicted value of the nonlinear model calculated using the first initial value and an output measured value of the nonlinear model measured using the two-tone signal; Storing the corresponding parameter of the nonlinear model as the calculated error does not exceed a threshold value; And The frequency of the two-tone signal is increased as the frequency of the two-tone signal does not exceed the frequency range of the wideband signal, and then the parameter of the stored nonlinear model is set as a second initial value, Step of extracting And a nonlinear model parameter of the wideband signal. delete 14. The method of claim 13, Wherein the calculating the error comprises: Setting a first initial value of a nonlinear model parameter; Calculating an output predicted value of the nonlinear model using the set initial value; And Calculating an error between the calculated output predicted value and an output measured value corresponding to the frequency, And a nonlinear model parameter of the wideband signal. 14. The method of claim 13, Wherein the step of storing the parameter comprises: Determining whether the calculated error exceeds a threshold value; A parameter updating step of updating the parameter of the nonlinear model and calculating the error when the threshold value is exceeded; Determining whether the nonlinear function value of the nonlinear model parameters is equal to the immediately preceding nonlinear function value if the threshold is not exceeded; Calculating a residual parameter of the nonlinear model by replacing the nonlinear function value extracted immediately before with the currently extracted nonlinear function value if the result of the determination is not the same; And As a result of the determination, if the same is true, the step of storing the calculated parameter of the nonlinear model And a nonlinear model parameter of the wideband signal. The method according to any one of claims 13, 15 and 16, Interpolating the parameters of the extracted nonlinear model And a nonlinear model parameter of the wideband signal. 16. The method according to claim 13 or 15, The first initial value is a value A predistortion method using a nonlinear model parameter of a wideband signal, which is a unitary matrix. 19. The method of claim 18, The output predicted value is a value A method of predistortion using a nonlinear model parameter of a broadband signal, the phasor value in the frequency domain. delete delete

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