KR100487209B1 - Predistortion apparatus and method for compensating non-linearility of the power amplifier using look-up table - Google Patents

Abstract

The present invention relates to predistortion for linearizing the amplification characteristics of a complex modulated baseband signal. The adaptive controller determines the polynomial coefficients by modeling the inverse nonlinear distortion characteristics of the power amplifier with the signal samples input by the operator or in the periodic learning mode, and using the determined polynomial coefficients to determine the range of possible input signals. Compute the predistortion gains and update the lookup table, which stores the complex predistortion gains addressed with the magnitudes of the input signal, with the calculated predistortion gains. When a complex modulated baseband input signal is input to the predistorter, the predistorter accesses a complex predistortion gain corresponding to the magnitude of the input signal from the lookup table, and multiplies the complex predistortion gain by the input signal. Output to the power amplifier. The present invention can obtain a small calculation amount and a fast convergence speed in compensating the nonlinear distortion characteristic of the power amplifier having the memory effect.

Description

Predistortion Apparatus and Method for Compensating Nonlinear Distortion Characteristics of Power Amplifiers Using Lookup Tables {PREDISTORTION APPARATUS AND METHOD FOR COMPENSATING NON-LINEARILITY OF THE POWER AMPLIFIER USING LOOK-UP TABLE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to wideband power amplification, and more particularly, to a predistorter and a predistortion method for linearizing nonlinear distortion characteristics of a complex modulated baseband signal by a power amplifier.

In a typical mobile communication system using radio frequency (RF) signals, RF amplifiers are classified into low power, low noise receive amplifiers, and high power transmit amplifiers. In high power transmit amplifiers, efficiency is more important than noise. As a result, high power amplifiers (HPAs), which are widely used in mobile communication systems, operate near nonlinear operating points for high efficiency.

In this case, the amplifier's output produces an inter modulation distortion (IMD) component that affects spurious signals in other bands as well as in-band. In order to remove the spurless component, a feed forward method is mainly used. The feedforward method can almost completely remove the spurious component, but it has a disadvantage that the amplification efficiency is lowered and the volume is high because the control in the RF stage is required.

In the field of mobile communication systems, digital predistortion (DPD) is being studied in consideration of high efficiency and low cost. The digital predistortion method linearizes the output signal of the power amplifier by precompensating the input signal by taking an inverse of the nonlinearity of the power amplifier in the digital stage. Nonlinear characteristics are classified into AM / AM (Amplitude Modulation to AM) characteristics, in which the output signal scales according to the magnitude of the input signal, and AM / PM (AM to Phase Modulation) characteristics, in which the phase of the output signal changes in accordance with the magnitude of the input signal. Can be.

A typical method of compensating for the nonlinear characteristics of a power amplifier is to use a complex polynomial. Since the complex polynomial predistorter uses a polynomial that accurately models the inverse nonlinear distortion characteristics of the power amplifier, the time taken to remove the nonlinearity of the power amplifier is short. In other words, the convergence speed is fast. If the memory effect is not taken into account, the transposition polynomial of the P-order is represented by Equation 1 below.

Here, d (n) is a predistortion signal, and the portion of {} multiplied by the input signal x (n) can be regarded as a predistortion gain of x (n).

To date, most predistorters have been heavily studied for signals of single-tone or narrowband frequencies, so they only compensate for the memoryless nonlinear nature of the power amplifier (i.e., only the current input affects the current output). Most of the way was. However, the memory nonlinearity of the nonlinear amplifier at wideband frequencies significantly changes the AM / AM and AM / PM characteristics by affecting the output of the current nonlinear amplifier as well as the current input signal. This phenomenon is called memory effects, and the nonlinearity of the power amplifier depends on the frequency bandwidth of the input signal. Recently, as the frequency band of mobile communication system is gradually widened, research and development considering the memory effect of nonlinear amplifiers are being actively conducted. The discrete Volterra series approach uses a polynomial that takes into account past input samples to compensate for the memory effect.

The nonlinear rejection capability of a polynomial predistorter depends on how many past input samples are considered and how many orders of the polynomial are. Since the computational amount increases exponentially with each increase of the past input sample to be considered, the polynomial predistorter has a fast convergence rate, but the formula is very complicated and computational, which is not easy to implement, but also a large number of high-speeds. Multipliers are needed, which increases the size of the logic.

A pre-compensation technique that can solve this problem is a technique using a look-up table (LUT). Since the lookup table stores the predistortion gains over the range of possible amplitude levels of the input signal, they typically require very little computation. However, in order to accurately remove the nonlinearity of a power amplifier having a memory effect, it is necessary to apply an adaptive algorithm to each of the elements of the lookup table, that is, the precompensation gains, so that it takes a long time to linearize the power amplifier. In other words, the convergence speed is slow.

Accordingly, the present invention, which was devised to solve the problems of the prior art operating as described above, provides a predistorter and a predistortion method for compensating for nonlinear distortion characteristics of a power amplifier having a memory effect using a lookup table.

The present invention provides a predistorter and a predistortion method for calculating components of a lookup table using predistortion parameters extracted through a predistortion polynomial.

Apparatus according to a preferred embodiment of the present invention is a polynomial predistorter that compensates for nonlinear distortion characteristics of a power amplifier,

Upon receiving a complex modulated baseband input signal, the complex predistortion gain is accessed from a lookup table that stores the complex predistortion gains addressed with the magnitudes of the input signal, thereby accessing the complex predistortion gain corresponding to the magnitude of the input signal. A predistorter multiplying the gain by the input signal and outputting the gain to a power amplifier;

Modeling the inverse nonlinear distortion characteristic of the power amplifier to determine polynomial coefficients, and using the determined polynomial coefficients to calculate predistortion gains over a range of possible input signals, and using the calculated predistortion gains It characterized in that it comprises an adaptive controller for updating the.

A method according to a preferred embodiment of the present invention is a polynomial predistortion method for compensating for nonlinear distortion characteristics of a power amplifier,

Modeling the inverse nonlinear distortion characteristics of the power amplifier to determine polynomial coefficients,

Calculating predistortion gains for all possible magnitudes of the input signal using the determined polynomial coefficients;

Updating, with the calculated predistortion gains, a lookup table storing complex predistortion gains addressed with the magnitudes of the input signal to compensate for nonlinear distortion characteristics by the power amplifier;

When a complex modulated baseband input signal is received, accessing a complex predistortion gain corresponding to the magnitude of the input signal from the lookup table;

And precompensating the input signal with the complex predistortion gain and outputting the predistorted signal to a power amplifier.

In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

A feature of the present invention described below is to calculate the predistortion parameters for linearization of power amplification by a predistortion polynomial, and convert the calculated predistortion parameters into a look-up table (LUT) form. Predistortion parameters here in particular mean complex polynomial coefficients.

1 is a block diagram illustrating a transmitter for outputting a linearized amplified signal using a predistorter having a lookup table according to an embodiment of the present invention. The transmitter of this structure is used in, for example, a mobile communication system that performs radio communication using radio frequency (RF).

Referring to FIG. 1, a forward path of the transmitter 100 includes a digital pre-distorter (DPD) 102, a digital modulator (MOD) 104, and a digital / analog converter ( Digital to Analog Converter (DAC) 106, Intermediate Frequency (IF) Band Pass Filter (BPF) 108, Frequency Up Converter 110 and Radio Frequency: RF band pass filter (BPF) 112, a power amplifier (PA) 114 and the transmit antenna 132. A feedback path of the transmitter 100 includes a directional coupler (DC) 116 and a frequency down converter 122 between the power amplifier 114 and the transmission antenna 132. FB BPF (124), Analog to Digital Converter (ADC) 126, De-Modulator (DEM) 128, and Adaptation Controller (ADAP) 130).

A baseband digital input signal consisting of an in-phase (I) signal component and a quadrature (Q) signal component is input to the predistorter 102. The predistorter 102 converts the in-phase and quadrature input signals to compensate for the distortion occurring in the power amplifier 114. According to the present invention, the predistorter 102 obtains predistortion gains using polynomial coefficients modeling the inverse nonlinear distortion characteristics of the power amplifier 114, and stores the obtained predistortion gains in a lookup table. A more detailed description of this predistortion scheme will be given later.

The output of the predistorter 102 is applied to the digital modulator 104, which converts the in-phase and quadrature input signals into a single digital signal by quadrature modulation. The digital signal from the digital modulator 104 is converted into an analog signal of intermediate frequency IF by the digital-to-analog converter 106. The intermediate frequency bandpass filter 108 removes out-of-band components from the intermediate frequency signal from the digital-to-analog converter 106.

The filtered output from the intermediate frequency bandpass filter 108 is converted into a high frequency signal having a frequency within the frequency band of the mobile communication system by the frequency raising converter 110. More specifically, the frequency rising converter 110 has a reference clock (Ref. CLK) from a phase locked loop (PLL) 118 and is transmitted by the oscillator 120. Mixer to generate a desired frequency by mixing a local oscillation signal (Transmit Local Oscillation Signal (LO _TX )) to the filtered intermediate frequency output. The reference clock is also used for the modulation operation in the digital modulator 104.

The high frequency bandpass filter 112 removes an out-of-band component from the high frequency signal converted by the frequency rising converter 110. The power amplifier 114 amplifies and transmits the filtered high frequency output from the high frequency bandpass filter 112 to the transmit antenna 132.

The path environment for precompensation operation of the predistorter 102 monitors the amplified signal from the power amplifier 114. To this end, the directional coupler 116 transfers a portion of the signal output from the power amplifier 114 to the transmit antenna 132 to the frequency down converter 122. The frequency down converter 122 operates in an opposite manner to the frequency up converter 112. In particular, the frequency down converter 122 lowers the frequency of the signal amplified by the power amplifier 114 to an intermediate frequency. To this end, the frequency down converter 122 is configured as a mixer which generates a desired frequency by mixing a received local oscillation signal (LO _RX ) generated by the oscillator 120 to the amplified high frequency output. . The feedback bandpass filter 124 removes the out-of-band signal from the intermediate frequency output from the frequency down converter 122.

The analog intermediate frequency output filtered by the feedback bandpass filter 124 is converted into a digital signal by the analog / digital converter 126. The digital demodulator 128 demodulates the digital signal in a manner opposite to the digital modulator 104 in synchronization with the reference clock to output an in-phase signal component and a quadrature signal component signal to the adaptive controller 130. do.

The adaptive controller 130 also periodically monitors the output signal from the predistorter 102. As a result, the adaptive controller 130 receives the output signal (the signal to be transmitted) from the predistorter 102 and the output signal (the signal actually transmitted) from the digital demodulator 128, and uses the inputs. The coefficients for calculating the predistortion polynomial are determined and the predistortion gains for all possible magnitudes of the input signal are calculated using the determined polynomial coefficients. The calculated predistortion gains are stored in a lookup table in the predistorter 102.

A detailed configuration of the predistorter 102 including the lookup table is illustrated in FIG. 2. Referring to FIG. 2, the predistorter 102 includes a magnitude calculator 202 that calculates an instantaneous magnitude of an input signal. The calculated magnitude is used to access the complex predistortion gain corresponding to the calculated magnitude in a lookup table (LUT) 204. The complex predistortion gains are to compensate for the transmission characteristics of the power amplifier 114. The lookup table 204 is periodically updated by the adaptive controller 130 to allow the complex predistortion gains to reflect the change in transmission characteristics of the power amplifier 114.

The complex predistortion gain from the lookup table 204 is provided to a multiplier 206, which multiplies the input signal by the complex predistortion gain to precompensate the input signal. When the predistorted signal is amplified by the power amplifier 114, the nonlinear distortion caused by the power amplifier 114 is removed.

Hereinafter, an operation of converting a predistortion characteristic given in a polynomial form into a lookup-table form will be described with reference to FIG. 3, which shows a detailed configuration of the adaptive controller 130. Referring to FIG. 3, the adaptive controller 130 includes a memory 130a and a digital signal processor (DSP) 130b, and the digital signal processor 130b is functionally a coefficient calculator. (Coefficient Calculator: Coeff Cal.) 130c and Gain Calculator: Gain Cal. 130d.

In the following, the precompensation polynomial coefficients are determined in consideration of the input signal and the past precompensated signal, and a polynomial method of precompensating the input signal using complex vector multiplication will be described as an example. It is to be understood that the precompensation gains obtained by storing in the lookup table are not limited by the precompensation scheme used here.

According to this polynomial method, the predistortion of the input signal is expressed as Equation 2 below.

Where A and B represent in-phase signal components and quadrature signal components of the input signal, respectively, and p, q, r, and s represent in-phase and quadrature predistortion gains extracted using an adaptive algorithm, respectively. As mentioned above, p and r are in-phase and quadrature pre-compensation gains for precompensating the in-phase signal component A of the input signal, and q and s are for compensating the quadrature signal component B of the input signal. Phase and quadrature predistortion gain.

The predistortion gains are obtained by calculating the predistortion polynomial using complex polynomial coefficients. Using the input signal x (n), the predistortion signal d (n) is given by Equation 3 below.

Where n is a time index in units of samples, and c _i and c _q are in-phase signal components and quadrature signal components of a complex polynomial coefficient for the input signal x (n).

The input signal x (n) and past predistorted signals d (n-1) to d (nm) are stored in the memory 130a, and the coefficient calculator 130c receives the signals stored in the memory 130a. And use a known adaptive algorithm such as Recursive Least Square (RLS) / Least Mean Square (LMS) to calculate complex polynomial coefficients that minimize distortion by the power amplifier 114. When using a polynomial of order P and considering past samples up to M sample times, the input signal x (n) and the complex polynomial coefficients are given in the form of a matrix as shown in Equation 4 below.

Where c _i is an in-phase polynomial coefficient consisting of c _ii affecting the in-phase signal component of the input signal and c _iq affecting the quadrature signal component, and c _q is an in-phase signal component affecting the in-phase signal component of the input signal. A quadrature polynomial coefficient consisting of c _ii and c _iq that affects quadrature signal components, where [] ^T represents the transpose matrix. Then, among the precompensation gains calculated by the gain calculator 130d with the polynomial coefficients, the gains corresponding to the current input signal sample are expressed by Equation 5 below.

Where p and q are in-phase pre-compensation gains multiplied by the in-phase and quadrature signal components of the input signal, respectively, and q and s are quadrature transposed to be multiplied by the quadrature and quadrature signal components of the input signal, respectively. Compensation gains. Equation 5 shows the input signal x (n), but the precompensation gains for the m-th pre-compensated signal d (nm) are also c _{ii, m, (0 ~ P-1)} , It can be expressed similarly using c _{iq, m, (0 ~ P-1)} , c _{qi, m, (0 ~ P-1)} , c _{qq, m, (0 ~ P-1)} .

The in-phase gain parts to be multiplied by each input signal sample can be divided into Equation 6 below.

Then, the precompensation gain for x _i (n) is expressed by Equation 7 below.

or

These are the entries of the lookup table 204 addressed by the size | x (n) | of x (n).

The gain calculator 130d determines the resolution of the input signal by dividing the maximum size of the input signal by the number N _LUT of entries that can be stored in the lookup table 204, and all possible sizes of the input signal according to the resolution. Compute the predistortion gains corresponding to. Therefore, the predistortion gain for x _i (n) is calculated by Equation 8 below.

Where k is 0,1,2, ... N _LUT -1, When addressing by dividing the size of the input signal evenly It is decided. If you do not divide the size of the input signal evenly, Has a predetermined step size that is determined to be non-uniform.

Equations 6 to 8 are different signal samples x _i (n), d _i (n-1), d _q (n-1), ..., d _i (nM), d _q The same applies to (nM). For example, the predistortion gains of the lookup table 204 for x _i (n) are shown in FIG. 4. The x-axis represents the number of entries in the lookup table and the y-axis represents the predistortion gain.

5 shows an example of the configuration of the predistorter 102 for outputting the predistortion signal d (n) with respect to the input signal x (n). Here, the configuration using the past two predistorted signal samples is shown.

Referring to FIG. 5, the first complex multiplier 310 calculates pre-compensation gains corresponding to in-phase signal components and quadrature signal components of the current input signal x (n) (denoted as x _n ). The output of the first complex multiplier 310 is combined with the outputs of the second and third complex multipliers 320 and 330 to form a predistortion signal d (n) (denoted as d _n ). The second complex multiplier 320 corresponds to a signal d (n-1) (denoted as d _n-1 ) in which the predistortion signal d (n) is delayed by the delayer 354 by one sample time. Multiply and output the predistortion gain, and the third complex multiplier 330 delays the first predistortion signal d (n) by two samples by the delayers 354 and 356. Multiply the precompensation gains by (d _n-2 ) and output them.

In more detail, the first complex multiplier 310 detects an in-phase signal component Re {x (n)} by the real detector 312a with the input signal x (n) and an imaginary detector 312b. The quadrature signal component Im {x (n)} is detected by using. The detected signal components are provided to four multipliers 314a, 314b, 314c, and 314d.

In addition, the first complex multiplier 310 has an input signal x (n) and detects the magnitude | x (n) | of the input signal x (n) by the absolute value calculator 318a to the lookup table 318. Provided as an address. The lookup table 318 outputs in-phase predistortion gains p, q and quadrature predistortion gains r, s corresponding to the magnitude | x (n) | of the input signal.

The p, r is multiplied by the in-phase signal component Re {x (n)} by the multipliers 114a and 114b, and the r and s are quadrature signals by the multipliers 114c and 114d. The component Im {x (n)} is multiplied. That is, the predistortion gains p, r are in-phase and quadrature predistortion gains for in-phase signal components of the input signal x (n), and the predistortion gains q, s are the input signal x (n Are the in-phase and quadrature predistortion gains for the quadrature signal component. Finally, the adder 316a sums the outputs of the multipliers 314a and 314c and outputs them as in-phase signal components, and the adder 316b sums the outputs of the multipliers 314b and 314d and outputs the quadrature signals. .

Similarly, the remaining second and third complex multipliers 320 to 330 respectively look up pre-compensation gains corresponding to the corresponding | d (n-1) | and | d (n-2) | of the corresponding input signal. It reads from the tables 328 and 338, and multiplies and outputs the in-phase signal components and quadrature signal components of the corresponding input signals d (n-1) and d (n-2), respectively.

A summer 320 adds in-phase and quadrature outputs of the first to third complex multipliers 310 to 330 by in-phase adders 342 and 346 and quadrature adders 344 and 348, respectively. The summed quadrature signal component is shifted by 90 degrees by the multiplier 352 and then combined with the summed in-phase signal component by the adder 350 to become the predistortion signal d (n).

5 also shows a digital signal processing processor 360 for updating the lookup tables 318-338. This is included in the adaptive controller 130 shown in FIG. 2, wherein the digital signal processing processor 360 determines polynomial coefficients with current and historical samples provided from memory 364 and the lookup tables 318-338. Calculate the precompensation gains to be stored in. To this end, the sample memory 364 receives and stores the current sample x (n) and the past samples d (n) through the multiplexer 362, and provides the same to the digital signal processor 360. Here, the sample memory 364 has a memory size capable of storing samples of a predetermined length.

In an embodiment of the present invention, in the training mode, the transmitter shown in FIG. 2 receives a predetermined number, for example, hundreds of complex modulated signal samples, and a predistortion gain accurately modeling an inverse nonlinear distortion characteristic of a power amplifier. Are calculated by an adaptive algorithm, and the calculated predistortion gains are stored in a lookup table in the predistorter. After that, the transmitter enters an operation mode and precompensates the complex modulated signal to be actually transmitted by the lookup table and then amplifies the signal by a power amplifier. The transmitter may operate in a learning mode periodically or when instructed by an operator.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

The present invention can take advantage of both the fast convergence obtained in the predistortion method using the polynomial in the predistorter used in the linearization of the power amplifier, and the small calculation amount obtained in the predistortion method using the lookup table. In addition, the configuration of the predistorter having the memory capability necessary to compensate for the nonlinear characteristics of the power amplifier exhibiting the memory effect becomes very simple.

1 is a block diagram showing a configuration of a transmitter for outputting a linearized amplified signal using a predistorter according to an embodiment of the present invention.

2 is a block diagram illustrating a detailed configuration of a predistorter including a lookup table.

3 is a block diagram illustrating a detailed configuration of an adaptive controller for updating a lookup table according to the present invention.

Figure 4 shows the predistortion gains stored in the lookup table for the magnitude of the input signal.

5 is a diagram illustrating an example of a configuration of a predistorter for outputting a predistortion signal d (n) with respect to an input signal x (n).

Claims (15)

A polynomial predistorter for compensating for nonlinear distortion characteristics of a power amplifier, Receiving a complex modulated baseband input signal, accesses a complex predistortion gain corresponding to the magnitude of the input signal in a lookup table that stores the complex predistortion gains addressed with the magnitudes of the input signal, A predistorter for precompensating the input signal with a gain and outputting it to a power amplifier; Modeling the inverse nonlinear distortion characteristic of the power amplifier to determine polynomial coefficients, and using the determined polynomial coefficients to calculate precompensation gains over a range of possible input signals, and look up the calculated precompensation gains. And a adaptive controller for updating the table. The method of claim 1, wherein the adaptive controller, Pre-compensation device for updating the look-up table by calculating the pre-compensation gains instructed or in a periodic learning mode by an operator. The k th precompensation gain of the precompensation gains includes: a polynomial coefficient c ₀ , c ₁ , ... c _P-1 , an input signal x (n), and a magnitude resolution of the input signal. And according to polynomial order P And k is 0,1,2, ... N _LUT-1 and N _LUT-1 is the number of entries in the lookup table. 4. The method of claim 3, wherein the address is divided evenly by the magnitude of the input signal. Is Preposition compensation device, characterized in that. The method of claim 1, wherein the input signal, And a combination of past input signal samples previously processed by the predistorter and the current input signal samples. The method of claim 1, wherein the input signal, A predistorter comprising a combination of past predistorted signal samples previously processed by the predistorter and the current input signal samples. The method of claim 6, wherein the predistorter is, A first complex multiplier for multiplying the complex precompensation gains accessed in the lookup table by the in-phase signal component and the quadrature signal component corresponding to the magnitude of the current input signal, respectively; At least each of the complex pre-compensation gains accessed in the lookup table corresponding to the magnitude of the one past pre-compensated signal, respectively, and multiplied by the in-phase signal component and the quadrature signal component of the corresponding past pre-compensated signal, respectively. One second complex multiplier, And a summer for adding the outputs of the first and second complex multipliers to output the predistorted signal to the power amplifier. The predistorter of claim 7, wherein the predistorted signal is calculated as in the following equation. Where d (n) is a precompensated signal composed of in-phase signal component d _i (n) and quadrature signal component d _q (n), and x (n) is quadrature with in-phase signal component x _i (n) Is an input signal consisting of the signal component x _q (n), c _i is an in-phase polynomial coefficient consisting of c _ii affecting the in-phase signal component of the input signal and c _iq affecting the quadrature signal component, c _q Is a quadrature polynomial coefficient consisting of c _qi affecting the in-phase signal component of the input signal and c _qq affecting the quadrature signal component, P is the order of the polynomial, and M is the number of past signals to consider . A polynomial predistortion method for compensating for nonlinear distortion characteristics of a power amplifier, Modeling the inverse nonlinear distortion characteristics of the power amplifier to determine polynomial coefficients, Calculating predistortion gains for all possible magnitudes of the input signal using the determined polynomial coefficients; Updating, with the calculated predistortion gains, a lookup table storing complex predistortion gains addressed with the magnitudes of the input signal to compensate for nonlinear distortion characteristics by the power amplifier; When a complex modulated baseband input signal is received, accessing a complex predistortion gain corresponding to the magnitude of the input signal from the lookup table; And precompensating the input signal with the complex predistortion gain and outputting the predistorted signal to a power amplifier. 10. The method of claim 9, wherein the kth predistortion gain of the predistortion gains is determined by the polynomial coefficients c ₀ , c ₁ , ... c _P-1 and the input signal x (n) and the magnitude resolution of the input signal. And according to polynomial order P Wherein k is 0,1,2, ... N _LUT-1 and N _LUT-1 is the number of entries in the lookup table. 12. The method of claim 10, wherein when the size of the input signal is equally divided and addressed, Is Prepositional compensation method characterized in that. The method of claim 9, wherein the input signal, And a combination of past input signal samples previously processed by the predistorter and the current input signal samples. The method of claim 9, wherein the input signal, And a combination of the past predistorted signal samples previously processed by the predistorter and the current input signal samples. The process of claim 13, wherein the predistortion process comprises: Multiplying the complex predistortion gains accessed in the lookup table by the in-phase signal component and the quadrature signal component corresponding to the magnitude of the current input signal, respectively; Multiplying the complex precompensation gains accessed in the lookup table by the inverse signal component and the quadrature signal component of the corresponding past precompensated signal, respectively, in response to the magnitude of the corresponding one of the past precompensated signals, respectively; Wow, Summing the multiplication results to output a precompensated signal to the power amplifier. The predistortion method of claim 14, wherein the predistorted signal is calculated as in the following equation. Where d (n) is a precompensated signal composed of in-phase signal component d _i (n) and quadrature signal component d _q (n), and x (n) is quadrature with in-phase signal component x _i (n) Is an input signal consisting of the signal component x _q (n), c _i is an in-phase polynomial coefficient consisting of c _ii affecting the in-phase signal component of the input signal and c _iq affecting the quadrature signal component, c _q Is a quadrature polynomial coefficient consisting of c _qi affecting the in-phase signal component of the input signal and c _qq affecting the quadrature signal component, P is the order of the polynomial, and M is the number of past signals to consider .