JP2014158230A - Digital pre-distorter and method of controlling the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a PAPR of a digital pre-distorter output.SOLUTION: A digital pre-distorter includes a linear transfer path, a third-order distortion generation path, a bandwidth determiner for determining a bandwidth of an input signal, a combiner for combining an output of the linear transfer path and an output of the third-order distortion generation path, and a peak-to-average power ratio (PAPR) observer for observing a PAPR from an output of the combiner. The third-order distortion generation path includes a third-order distortion generator, a third-order distortion vector adjuster and a third-order distortion frequency characteristic compensator. The third-order distortion generator raises the input signal to the third power to generate a third-order distortion component. The third-order distortion vector adjuster adjusts the amplitude and phase of the third-order distortion component. The third-order distortion frequency characteristic compensator divides an output signal of the third-order distortion vector adjuster into a plurality of bands in the frequency domain and adjusts the amplitude and phase in each divided band. The third-order distortion frequency characteristic compensator is controlled so as to reduce the PAPR with respect to the amplitude and phase within a band narrower than the bandwidth determined by the bandwidth determiner with the use of an observation result of the PAPR observer.

Description

  The present invention relates to a digital predistorter and a control method thereof, and more particularly to a power series type digital predistorter and a control method thereof.

  In mobile communications, a transmission power amplifier (hereinafter referred to as a power amplifier) is an important radio circuit having a role of amplifying a transmission signal output from a transmission antenna of a base station or a mobile station to a predetermined power. Since power amplifiers handle large amounts of power, high efficiency is desired.

  Generally, in order to operate a power amplifier with high efficiency, the operating point of the power amplifier is set near the saturated output, in other words, output back-off indicating a margin from the saturated output of the power amplifier is reduced. . At this time, a distortion component is generated due to the nonlinear characteristic of the power amplifier. In particular, the distortion component increases as the operating point of the power amplifier approaches the saturated output. Furthermore, the distortion component has frequency dependence.

  On the other hand, looking at the power amplifier input signal, in recent years, OFDM (Orthogonal Frequency Division Multiplexing) transmission has attracted attention from the viewpoint of frequency utilization efficiency. An OFDM signal has a high frequency utilization efficiency, but has a high average power-to-peak power ratio (PAPR). Since the power amplifier cannot amplify the power amplifier input signal beyond the saturation output, if the output backoff is lower than the PAPR of the power amplifier input signal, the waveform of the power amplifier output signal is clipped. Even in this case, a distortion component is generated in the power amplifier output signal.

  The distortion component becomes interference to a wireless communication system using an adjacent frequency band. For this reason, it is essential to reduce the distortion component to a level defined by the specifications of various wireless communication systems.

  There is a distortion compensation method typified by a predistortion method as a method for reducing (compensating for) distortion components generated by the nonlinear characteristics of the power amplifier. The predistortion method uses a predistorter to add a distortion compensation component that cancels a distortion component generated in the power amplifier to the power amplifier input signal. As a predistorter that compensates for a frequency-dependent distortion component, there is a series digital predistorter (hereinafter referred to as a digital predistorter) that should compensate for the frequency dependence of the distortion component. (For example, Non-Patent Document 1).

  On the other hand, the distortion component caused by the waveform clip cannot be compensated by the distortion compensation method. This is because the power amplifier cannot amplify the signal beyond the saturation output. As a method of reducing the distortion component, there is a PAPR reduction method represented by a method using clipping and filtering. In the method using clipping and filtering, the waveform is clipped so that the amplitude value of the power amplifier input signal is equal to or lower than a predetermined threshold before the digital predistorter, and then distortion components generated by the clipping are reduced by filtering. (For example, Non-Patent Document 2). In this method, when the PAPR of the input signal is larger than a predetermined threshold, clipping and filtering are repeated until the limiter and the filter are equal to or lower than the threshold, and then a distortion component compensation process is performed by the digital predistorter. However, the PAPR at the output of the digital predistorter may exceed the threshold value due to this distortion compensation processing. In such a case, it is necessary to repeatedly perform PAPR reduction by clipping and filtering and distortion compensation processing by a digital predistorter, which takes time.

  FIG. 1 shows the configuration of the digital predistorter disclosed in Non-Patent Document 1. This configuration shows a case where a digital signal (sample sequence) represented by a complex envelope is input to an input terminal as an input signal x (t).

  The digital predistorter 10 includes a linear transmission path 12, a third-order distortion generation path 13, a synthesizer 14, a digital-analog converter (hereinafter referred to as DAC) 15, an analog-digital converter (hereinafter referred to as ADC) 16, A strain observer 17 and a controller 18 are included. In Non-Patent Document 1, a fifth-order distortion generation path is also provided, but is omitted for the sake of simplicity. The linear transmission path 12 has a delay device 12A. The third-order distortion generation path 13 includes a third-order distortion generator 13A, a third-order distortion vector adjuster 13B, and a third-order distortion frequency characteristic compensator 13C.

The input signal x (t) is distributed to the linear transmission path 12 and the third-order distortion generation path 13. The third-order distortion generator 13A raises the distributed input signal to the third power and generates a third-order distortion component. The third-order distortion vector adjuster 13B multiplies the third-order distortion component generated by the third-order distortion generator 13A by the third-order distortion vector adjuster coefficient given from the controller 18 to thereby change the phase of the third-order distortion component. And adjust the amplitude. Third-order distortion frequency characteristic compensator 13C (also referred to as transmission band) input signal band, as shown in FIG. 2 FB _S from the upper third-order distortion component lower band (hereinafter sometimes referred to as a lower side band simplified For each divided band (band B ₁ to band B _M ) that is divided into M by combining FB _DL and the upper third-order distortion component upper band (hereinafter sometimes referred to simply as the upper band) FB _DU . The third-order distortion frequency characteristic compensator coefficients given from the controller 18 are respectively multiplied. Incidentally, the third-order distortion component of the input signal has a bandwidth FB _D containing lower band FB _DL, an input signal band FB _S, the upper band FB _DU.

  The combiner 14 combines the output of the linear transmission path 12 and the output of the third-order distortion generation path 13. The DAC 15 converts the output of the synthesizer 14 into an analog transmission signal. The analog transmission signal is converted into a high frequency signal having a carrier frequency by the up-converter 22, and the high frequency signal is power amplified by the power amplifier 23. The power-amplified high frequency signal is supplied from an output terminal to an antenna via a duplexer (not shown), for example. A part of the output signal of the power amplifier 23 is taken out as a feedback signal, down-converted by the down-converter 32, and given to the ADC 16.

  The ADC 16 converts the feedback signal from the output of the power amplifier 23 into a digital signal. The distortion observer 17 detects a distortion component from the output of the ADC 16. The controller 18 sets the third-order distortion vector adjuster coefficient (the amplitude value and the amplitude value) to be set in the third-order distortion vector adjuster 13B so that the distortion component detected by the distortion observer 17 becomes minimum (or less than a predetermined threshold). Phase value) and a plurality of third-order distortion frequency characteristic compensator coefficients (amplitude values and phase values) set in the third-order distortion frequency characteristic compensator 13C.

  In the digital predistorter shown in Non-Patent Document 1, a third-order distortion vector adjuster coefficient given to the third-order distortion vector adjuster 13B or a third-order distortion frequency characteristic compensator coefficient given to the third-order distortion frequency characteristic compensator 13C. Depending on the case, the PAPR of the output signal of the synthesizer 14 may increase. A digital predistorter capable of suppressing an increase in PAPR due to such distortion compensation processing and a control method thereof have been proposed in Patent Document 1 by the present applicant. The digital predistorter will be briefly described below.

FIG. 3 shows a digital predistorter 100 proposed in Patent Document 1, an amplifying device 20 as a peripheral device thereof, and a feedback signal generating device 30. In this example, I-phase and Q-phase digital signals are input from the input terminal T _IN . The predistorter 100 includes a distributor 11, a linear transmission path 12, a third-order distortion generation path 13, a combiner 14, a DAC 15, an ADC 16, a distortion observer 17, a PAPR observer 19, and a controller. 180.

Distributor 11, respectively distributes the input signal S _IN from the input terminal T _IN to the linear transmission path 12 and the third-order distortion generating path 13. The linear transmission path 12 includes a delay path 12A, and delays the input signal of the delay device 12A by a delay time generated in the distortion generation path 13. The third-order distortion generation path 13 includes a third-order distortion generator 13A, a third-order distortion vector adjuster 13B, and a third-order distortion frequency characteristic compensator 13C. The synthesizer 14 synthesizes the output signal of the delay unit 12A and the output signal of the third-order distortion frequency characteristic compensator 13C, and provides them to the DAC 15 and the PAPR observer 19 respectively. The DAC 15 converts the digital signal output from the synthesizer 14 into an analog signal. The PAPR observer 19 observes the PAPR in the output signal of the synthesizer 14.

  The amplifying apparatus 20 includes a quadrature modulator 21, an up converter 22, and a power amplifier 23. The quadrature modulator 21 performs quadrature modulation on the output signal from the DAC 15. The up-converter 22 up-converts the output signal from the quadrature modulator 21 to a predetermined frequency. The power amplifier 23 amplifies the output signal of the up converter 22 to a predetermined power.

  The feedback signal generation device 30 includes a directional coupler 31, a down converter 32, and a quadrature demodulator 33. The directional coupler 31 extracts a part of the output signal from the power amplifier 23. The down converter 32 down converts the signal extracted by the directional coupler 31 to a predetermined frequency. The quadrature demodulator 33 performs quadrature demodulation on the output signal from the down converter 32 and outputs an I-phase signal and a Q-phase signal.

  The ADC 16 converts the I-phase signal and the Q-phase signal, which are analog signals output from the draft signal generation device 30, into digital signals. The distortion observer 17 measures the distortion component power generated by the power amplifier 23 of the amplifying apparatus 20 for each predetermined band. The controller 180 controls the third-order distortion vector adjuster 13 </ b> B so as to compensate for the distortion component generated by the power amplifier 23 based on the result observed by the distortion observer 17. Further, the third-order distortion frequency characteristic compensator 13C is controlled so as to reduce the PAPR of the signal output from the digital predistorter 100 based on the observation result of the PAPR observer 19. In addition, the third-order distortion frequency characteristic compensator 13C is controlled so as to compensate the distortion component generated by the power amplifier 23.

FIG. 2 schematically shows the spectrum of the output signal of the third-order distortion vector adjuster 13B. In the figure, the transmission band FB _S indicates the band of the signal input from the input terminal T _IN, third-order distortion components lower band FB _DL on its lower side, upper side third-order distortion components upper band FB _DU is located .

An example of the configuration of the third-order distortion frequency characteristic compensator 13C is shown in FIG. The third-order distortion frequency characteristic compensator 13C includes a serial / parallel conversion unit 13C1, a J-point FFT (Fast Fourier Transform) unit 13C2, and J (J ≧ M) complex multipliers 13C3 _j (j = 1,..., J ) Having a complex multiplication unit 13C3, a J-point IFFT (Inverse Fast Fourier Transform) unit 13C4, and a parallel-serial conversion unit 13C5. The serial / parallel converter 13C1 performs serial / parallel conversion on the input signal from the third-order distortion vector adjuster 13B. The J-point FFT unit 13C2 converts the input signal from the serial / parallel conversion unit 13C1 from the time domain to the frequency domain every J samples.

The output of the J-point FFT part 13C2 is M divided combined third-order distortion component upper band FB _DU and third-order distortion component lower band FB _DL as shown in FIG. 2, the complex multiplier 13C3 was sub-bands (Band B ₁ to Band B _M ) is multiplied by a third-order out-of-band distortion compensation coefficient corresponding to each divided band given from the controller 180, and given to the J-point IFFT unit 13C4. That is, the output signal corresponding to the divided band B ₁ is input to the complex multiplier 13C3 corresponding to the band B ₁ and multiplied by the third-order distortion frequency characteristic compensator coefficient given from the controller 180. The amplitude and phase are adjusted so that the distortion observed by the distortion observer 17 is reduced. The same applies to the divided bands B _{2 to} B _M. Also, the output corresponding to the input signal band FB _S is PAPR observed by PAPR observer 19 by multiplying the cubic-band distortion coefficient provided from the controller 180 by the corresponding complex multiplier 13C3 is reduced The amplitude and phase are adjusted as follows. The output corresponding to the band lower than the divided band B ₁ and the output corresponding to the band higher than the divided band B _M are input to the J-point IFFT unit 13C4 without being multiplied by a coefficient in the complex multiplier.

  The J-point IFFT unit 13C4 converts the input signal from the previous stage from the frequency domain to the time domain every J samples. The parallel-serial conversion unit 13C5 performs parallel-serial conversion on the input signal from the J-point IFFT unit 13C4 for every J samples.

  A control procedure for the third-order distortion vector adjuster 13B and the third-order distortion frequency characteristic compensator 13C by the controller 180 will be described with reference to the processing flow of FIG.

A third-order vector adjuster for the third-order distortion component output from the third-order distortion generator 13A so that the distortion component of the third-order distortion component lower band FB _DL or upper band FB _DU observed by the distortion observer 17 is minimized. The phase and amplitude of the signal are set by adjusting the coefficient to be multiplied by 13B (third-order distortion vector adjuster coefficient adjustment process S11). The coefficient is adjusted by a perturbation method, for example. Then, the third-order distortion by the frequency characteristic compensator @ 13 C, the third-order distortion vector adjusting the coefficients to be multiplied by the components within the transmission band FB _S output distortion component of the regulator 13B, the combiner was observed by PAPR observer 19 The phase and amplitude are set so that the PAPR in the 14 output signals is equal to or less than the threshold (third-order in-band distortion coefficient adjustment processing S12). Next, the third-order distortion frequency characteristic compensator 13C multiplies the components of the divided bands B _{1 to} B _M of the lower band FB _DL and the upper band FB _DU of the output distortion component of the third-order distortion vector adjuster 13B. And the phase and amplitude are set so that the distortion components in the bands corresponding to the respective divided bands observed by the distortion observer 17 are minimized (third-order out-of-band distortion coefficient adjustment processing S13).

  The phase and amplitude for reducing the PAPR in the process S12 may be obtained by the perturbation method, or may be obtained by calculation as follows. As preparation for calculation, the principle of a power series digital predistorter will be described with reference to FIG.

  FIG. 6 shows a simple model of a power series digital predistorter. This model is composed of a linear transfer path 12 and a third-order distortion generation path 13, and the third-order distortion generation path 13 has a third-order distortion generator 13A and a third-order distortion vector adjuster 13B.

The input complex envelope signal x _in (t) of the digital predistorter is expressed as x _in (t) = s (t) e ^{jθ (t),} and the phase value and amplitude value of the third-order distortion vector adjuster 23B are expressed as X _P (−π ≦ X _P ≦ π) and X _A (0 <X _A ). At this time, the output signal x _out (t) of the digital predistorter can be expressed by the following equation.

The second term on the right side of Equation (1) represents the output signal of the third-order distortion generation path 13. That is, the third-order distortion vector adjuster 13B multiplies the output of the third-order distortion generator 13A by the complex coefficient X _A e ^jXp . In the foregoing and in the following description, to set the amplitude value X _A and the phase value X _P is meant to multiplying the complex coefficient ^X _A e jXp, 3-order distortion frequency characteristic shown this in FIG. 4 The setting of the phase value and the amplitude value by the complex multiplier in the compensator 13C is the same. If the time at which the peak power Pout occurs at x _out (t) at time t (0 ≤ t ≤ T) is t ₁ , Pout is
Pout = | x _out (t ₁ ) | ² = | s (t ₁ ) | ² (1 + 2 | s (t ₁ ) | ² X _A cos (X _P ) + | s (t ₁ ) | ⁴ X _A ² ) (2)
It can be expressed. At this time, the instantaneous power Pin of the input signal x _in (t ₁ ) is
Pin = | s (t ₁ ) | ² (3)
The instantaneous power P3rd of the output signal in the third-order distortion generation path 13 is
P3rd = | s (t ₁ ) | ⁶ X _A ² (4)
It can be expressed. Here, lambda = the 10 log ₁₀ and (P3rd / Pin), ΔP expressed in logarithmic peak power ratio of the instantaneous power and x _out of _{x in (t 1) (t} 1) is
ΔP = 10log ₁₀ | (Pin / Pout) |
= 10log ₁₀ (1 / (1 + 2 | s (t ₁ ) | ² X _A cos (X _P ) + | s (t ₁ ) | ⁴ X _A ² ))
= 10log ₁₀ (1 / (1 + 2 × 10 ^{(λ / 20)} cos (X _P ) +10 ^{(λ / 10)} )) (5)
It becomes. The equation (5), when the amplitude value X _A constant, when the phase value X _P was - [pi] (or [pi), it can be seen that the ΔP minimized. At this time, ΔP is larger than 0 dB if X _A is equal to or smaller than a certain value. Therefore, the phase of the output signal in the third-order distortion generation path 13 is reversed with respect to the digital predistorter input signal. PAPR in the output signal of the predistorter can be reduced.

と一意に求められる。 For amplitude, if you want to reduce Pout from Pin by ΔP _red (dB), X _A is

And is uniquely required.

Even thereby reducing the this way the distortion occurring in the power amplifier 23 to set the phase value X _P and the amplitude value X _A obtained irrespective of the third-order distortion vector adjuster 13B PAPR, third-order distortion generator Since the output signal of the path 13 does not become a component that cancels the distortion component generated in the power amplifier 23, the third-order distortion component cannot always be compensated. Therefore, in the digital predistorter of Patent Document 1 shown in FIG. 3, the PAPR is reduced by adjusting the phase value and the amplitude value of the input signal band in the frequency domain using the third-order distortion frequency characteristic compensator 13C. Proposed. This makes it possible to reduce PAPR while compensating for the third-order distortion component. Specifically, when the phase of the distortion component observed at the lower or upper band is set to the third-order distortion vector adjuster 13B as possible to minimize the X _P, with respect to the output signal of the third-order distortion vector regulator 13B , to the output signal of the linear transmission path 12 by setting the (π-X _P) as the phase of the transmit band FB _S at the third-order distortion frequency characteristic compensator 13C, the phase of the output signal of the third-order distortion generating path 13 Can be out of phase.

Regarding the amplitude, specifically, a difference ΔPAPR (= PAPR _IN −PAPR _TH ) between PAPR (represented as PAPR _IN ) in the input signal of the digital predistorter 100 measured by the PAPR observer 19 and a predetermined threshold PAPR _TH. ) (dB). Then, set to calculate the amplitude values Y _A to give the complex multiplier 13C3 of the third-order distortion frequency characteristic compensator 13C corresponding to the input signal band F _S following the equation (6) by the following equation (7).

Here, | s (t ₁ ) | ⁴ is the square of the instantaneous power value of the input signal at time t ₁ when the peak power of the combiner output occurs, and is observed and calculated by the PAPR observer 19. However, in this case, it is necessary to give the input signal distributed from the distributor 11 to the PAPR observer 19 as indicated by a broken line in FIG.

  The phase may be determined by calculation as described above, and the amplitude may be determined by the perturbation method instead of the calculation by Equation (7).

WO2012-111153

S. Mizuta, Y. Suzuki, S. Narahashi and Y. Yamao, "A New Adjustment Method for the Frequency-Dependent IMD Compensator of the Digital Predistortion Linearizer", IEEE Xiaodong Li and Cimini, L.J., Jr., "Effects of clipping and filtering on the performance of OFDM," 47th IEEE Vehicular Technology Conference 1997, pp. 1634-1638, May, 1997.

When the digital predistorter according to Patent Document 1 described above is used, the third-order distortion component full band (transmission band FB _S , third-order distortion component upper side) is adjusted by the phase and amplitude adjustment by the third-order distortion vector adjuster 13A. The third order distortion component generated by the power amplifier 23 in the band FB _DU and the third order distortion component lower band FB _DL ) can be compensated to some extent. However, third-order distortion to the signal phase and amplitude is adjusted so that the vector adjuster 13A is third-order distortion component decreases, adjusted by further transmission band FB _S amplitude and third-order distortion frequency characteristic compensator 13C the phase To reduce PAPR. Therefore, the distortion components generated in the transmission band FB _S in the power amplifier 23 may not be compensated for by the digital predistorter. If the distortion component in the transmission band FB _S is not compensated, the EVM (Error Vector Magnitude) that degrades problem in the output signal of the power amplifier 23 for the distortion component in the transmission band FB _S remains or increases. In a digital predistorter according to Patent Document 1, since the process the entire transmission band FB _S to reduce the PAPR, the case of using a communication scheme such as OFDM, EVM of subcarriers included in the transmission band FB _S Deteriorates due to distortion components.

  The present invention has been made in view of these points, and an object of the present invention is to provide a digital predistorter that can reduce PRPR with little degradation of EVM and a control method thereof.

According to a first aspect of the present invention, a digital predistorter that adds a distortion compensation component for canceling a distortion component generated by a power amplifier to an input signal and outputs the linear signal is provided with a linear transmission path for delay transmission of the input signal. N-th order distortion generation path for generating a distortion compensation component from the input signal, N-order distortion generation path for determining the bandwidth of the input signal, and linear transmission path for the input signal and N-order distortion generation A divider that distributes the path and bandwidth determiner, a synthesizer that combines the output of the linear transfer path and the output of the Nth order distortion generation path, and a PAPR that observes the peak-to-average power ratio (PAPR) from the output of the synthesizer Including an observer and a controller,
The Nth order distortion generation path includes an Nth order distortion generator that generates an Nth order distortion component by raising the input signal to the Nth power, an Nth order distortion vector adjuster that adjusts the amplitude and phase of the Nth order distortion component, and a frequency domain. An N-order distortion frequency characteristic compensator that divides the output signal of the N-order vector adjuster into a plurality of bands and adjusts the amplitude and phase for each of the divided bands, and the controller uses the observation results of the PAPR observer Thus, the N-order frequency characteristic compensator is configured to control the PAPR with respect to the amplitude and phase in the band that is smaller than the bandwidth determined by the bandwidth determiner.
According to a second aspect of the present invention, the digital predistorter control method includes a process for determining whether the PAPR observed by the PAPR observer is higher than a predetermined threshold, and when the PAPR is higher than the threshold, A process for determining the signal bandwidth, a process for adaptively setting a PAPR reduction band narrower than the bandwidth according to the determined bandwidth, and an Nth-order distortion so as to reduce the PAPR observed by the PAPR observer And adjusting the amplitude and phase in the PAPR reduction band by the frequency characteristic compensator.
According to a third aspect of the present invention, a digital predistorter that adds a distortion compensation component for canceling a distortion component generated by a power amplifier to an input signal and outputs the signal is a linear transmission path for delay transmission of the input signal. N-th order distortion generation path for generating a distortion compensation component from the input signal, N-order distortion generation path for determining the bandwidth of the input signal, and linear transmission path for the input signal and N-order distortion generation A divider that distributes the path and bandwidth determiner, a synthesizer that combines the output of the linear transfer path and the output of the Nth order distortion generation path, and a PAPR that observes the peak-to-average power ratio (PAPR) from the output of the synthesizer Including an observer and a controller,
The Nth order distortion generation path includes an Nth order distortion generator that generates an Nth order distortion component by raising the input signal to the Nth power, an Nth order distortion vector adjuster that adjusts the amplitude and phase of the Nth order distortion component, and a frequency domain. An N-order distortion frequency characteristic compensator that divides the output signal of the N-order vector adjuster into a plurality of bands and adjusts the amplitude and phase for each of the divided bands, and the controller uses the observation results of the PAPR observer The PAPR reduction band that is equal to or less than the bandwidth determined by the bandwidth determiner is determined, and the PAPR is reduced for the amplitude and phase of each of the divided bands determined by dividing the PAPR reduction band into a plurality of bands. The N-order frequency characteristic compensator is configured to be controlled.
According to a fourth aspect of the present invention, a digital predistorter for adding a distortion compensation component for canceling a distortion component generated by a power amplifier to a plurality of input signals having different frequency bands is provided with a plurality of input signals. A plurality of linear transmission paths for delay transmission, a distortion generation path for generating distortion compensation components based on a plurality of input signals, a distributor for distributing each input signal to the corresponding linear transmission path and distortion generation path, and linear transmission A combiner that combines the output of the path and the output of the distortion generation path, a PAPR observer that observes a peak-to-average power ratio (PAPR) from the output of the combiner, and a controller,
The distortion generation path includes an Nth order distortion generator that generates each N (N is an odd number of 3 or more) order distortion component of each input signal, and the amplitude of the Nth order distortion component generated by each Nth order distortion generator. N-order distortion vector adjuster for adjusting phase, N-order intermodulation distortion calculator for generating intermodulation distortion components between a plurality of input signals, and sub-Nth order distortion for adjusting the amplitude and phase of each intermodulation distortion component A vector adjuster, and outputs the output of the Nth-order distortion vector adjuster and the output of the sub-Nth-order distortion vector adjuster as distortion compensation components,
The intermodulation distortion component is the intermodulation distortion component in the band of the Nth order distortion component of each input signal, hereinafter referred to as the inband intermodulation distortion component, and the intermodulation outside the band of the Nth order distortion component of each input signal. The controller is configured to control the corresponding vector adjuster to reduce the PAPR for the amplitude and phase of the out-of-band intermodulation distortion component. It is characterized by.

According to the first to third aspects of the present invention, it is possible to reduce the influence of the PAPR reduction processing by setting a PAPR reduction band that is equal to or less than the transmission band, thereby reducing EVM degradation.
According to the fourth aspect of the present invention, PAPR reduction processing is not performed by adjusting the phase and amplitude in the transmission band, and the PAPR is reduced by adjusting the phase and amplitude of the out-of-band intermodulation distortion component. Can be prevented.

The block diagram which shows the structure of the conventional digital predistorter shown by the nonpatent literature 1. FIG. The figure which shows the example of a band division | segmentation in a tertiary distortion frequency characteristic compensator. The block diagram which shows the structure of the digital predistorter proposed by patent document 1, and a peripheral device. The figure which shows the structural example of a 3rd distortion frequency characteristic compensator. The figure which shows the example of the control flow in the digital predistorter of FIG. The figure for demonstrating the principle of a digital predistorter. 1 is a block diagram showing the configuration of a digital predistorter and peripheral devices according to Embodiment 1 of the present invention. The figure which shows the example of the control flow in the digital predistorter of FIG. FIG. 3 is a diagram illustrating a setting example of a PAPR reduction band in the first embodiment. The block diagram which shows the structure of the digital predistorter and peripheral device by Example 2 of this invention. FIG. 10 is a diagram illustrating a setting example of a PAPR reduction band in the second embodiment. The block diagram which shows the structure of the digital predistorter and peripheral device by Example 3 of this invention. FIG. 10 is a diagram illustrating a setting example of a PAPR reduction band in the third embodiment. FIG. 10 is a diagram illustrating another setting example of the PAPR reduction band according to the third embodiment. The block diagram which shows the structure of the digital predistorter and peripheral device by Example 4 of this invention. The spectrum figure which shows typically the relationship between an input signal zone | band and each 3rd-order distortion component. The block diagram which shows the structural example of the tertiary distortion generation path | route in FIG. The figure which shows the example of the control flow in the digital predistorter of FIG. The block diagram which shows the structure of the modification of the tertiary distortion generation path | route of FIG. FIG. 9 is a block diagram showing the configuration of a digital predistorter and peripheral devices according to Embodiment 5 of the present invention. The figure which shows the example of the control flow in the digital predistorter of FIG. It is a figure which shows the example of the computer simulation result in Example 1, A is a PAPR value with respect to PAPR reduction zone | band reduction ratio (gamma), B shows the EVM value with respect to (gamma).

  Hereinafter, embodiments of the present invention will be described in detail. In addition, the same number is attached | subjected to the structure part which has the same function, and duplication description is abbreviate | omitted.

Prior to the description of the embodiments, the principle of the present invention will be briefly described. In the present invention provided a narrower PAPR reduction band FB _CTL than in the input signal band FB _S, is adaptively be changed in accordance with the input signal bandwidth and the bandwidth. For example, as shown in FIG. 9, by reducing from the transmission band FB _S a PAPR reduction band FB _CTL, provided the band not included in the PAPR reduction zone FB _CTL in the input signal band FB _S, the component of the band EVM is reduced by not performing PAPR reduction processing. Alternatively, the phase and amplitude may be adjusted so as to positively improve the EVM for the band components. Also, for example, as shown in FIG. 11, the PAPR reduction band FB _CTL is divided into a plurality of bands (B _CTL1 and B _{CTL2 in} FIG. 11), and among the divided bands, the band that can allow the degradation of EVM is divided. Adjust the amplitude and phase so that the amount of PAPR reduction is greater than the bandwidth. As a result, EVM may be greatly degraded in some bands, but degradation of EVM can be reduced in other bands. When a signal such as OFDM is input, it is possible to reduce EVM degradation of subcarriers due to PAPR reduction processing by setting a plurality of bands not including subcarriers as PAPR reduction band FB _CTL . Further, the same bandwidth FB _s and FB _CTL, if the PAPR is lower than the target value when given an initial value of the phase and amplitude FB _CTL, reduced FB _CTL so PAPR becomes the target value Adjust to

FIG. 7 is a block diagram showing the overall configuration of the digital predistorter 101 and peripheral devices according to this embodiment. In FIG. 7, the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be simplified as much as possible. As peripheral devices of this embodiment, an amplifying device 20 and a feedback signal generating device 30 are provided. Particularly below unless otherwise specified, the signal S _IN applied to the input terminal T _IN is the complex baseband signal. In the example shown below, a configuration example for compensating the third-order distortion component is shown. However, when the fifth-order and higher-order distortion components are compensated, a higher-order distortion generation path is added in parallel to the third-order distortion generation path. do it. PAPR reduction using a higher-order distortion generation path can be handled by the following concept using a third-order distortion generation path.

  The digital predistorter 101 of this embodiment includes a distributor 11, a linear transmission path 12, a third-order distortion generation path 13, a combiner 14, a DAC 15, an ADC 16, a distortion observer 17, a PAPR observer 19, a controller 181, and a band. A width determiner 181D. The controller 181 includes a third-order distortion generation path control unit 181A, a PAPR determination control unit 181B, and a PAPR reduction band control unit 181C.

Distributor 11 distributes each input signal S _IN from the input terminal T _IN to the linear transmission path 12 third-order distortion generating path 13 and bandwidth determinator 181 D. The PAPR observer 19 observes the PAPR in the output signal of the synthesizer 14. The bandwidth determiner 181D determines the bandwidth of the input signal S _IN distributed from the distributor 11.

  The configuration of the third-order distortion frequency characteristic compensator 13C is the same as that shown in FIG. 4, and will be described with reference to FIG.

The serial / parallel converter 13C1 performs serial / parallel conversion on the output signal from the third-order distortion vector adjuster 13B. The J point FFT unit 13C2 performs a J point Fourier transform to convert the output signal of the serial / parallel conversion unit 13C1 from the time domain to the frequency domain. The complex multiplier 13C3 includes J complex multipliers 13C3 _{1 to} 13C31 _J , and adjusts the amplitude and phase of each output of the J-point FFT unit 13C2 based on control information from the third-order distortion generation path control unit 181A. . The J-point IFFT unit 13C4 performs a J-point inverse Fourier transform to convert the output signal from the complex multiplication unit 13C3 from the frequency domain to the time domain. The parallel-serial conversion unit 13C5 performs parallel-serial conversion on the output signal from the J-point IFFT unit 13C4 and outputs it to the synthesizer 14.

In the complex multiplier 13C3, the complex multiplier 13C3 _j to which a signal corresponding to the divided band is input adjusts the amplitude and phase based on the control information from the third-order distortion generation path control unit 181A.

  A control flow P1 of the controller 181 will be described with reference to FIG.

[Third-order distortion vector adjuster coefficient adjustment processing S11]
The third-order distortion vector adjuster coefficient adjustment process S11 is the same as the process S11 in FIG. 5, and the third-order distortion generation path control unit 181A is based on the observation result of the distortion observer 17, and the third-order distortion component lower band FB _DL. Alternatively, the amplitude V _{A, MIN} and the phase V _{P, MIN} given to the third-order distortion vector adjuster 13B are adjusted so as to reduce the distortion component in any band of the upper band FB _DU .

[Threshold determination S121]
The PAPR determination control unit 181B determines whether or not the PAPR in the output signal from the synthesizer 14 observed by the PAPR observer 19 is higher than the threshold PAPR _TH , and if so, performs a bandwidth determination process S122 described later. To the bandwidth determination unit 181D. When PAPR is equal to or less than the threshold PAPR _TH , the third-order distortion generation path control unit 181A is instructed to perform the same third-order out-of-band distortion compensation coefficient adjustment process S13 as the process S13 in FIG.

[Bandwidth determination processing S122]
When receiving an instruction to determine the transmission band FB _S from PAPR judgment control unit 181B, the bandwidth determination unit 181D determines transmission bandwidth FB _S of the input signal S _IN that is dispensed from the dispensing device 11. Determining an input signal from the distributor 11 to a Fourier transform, may be determined bandwidth FB _S from the result of the Fourier transform, or synchronizing signal contained in the input signal S _IN from the distributor 11, from a control signal the transmission bandwidth FB _S may be determined. The determined result is transmitted to the PAPR reduction band control unit 181C. PAPR reduction bandwidth control unit 181C is obtained predetermined ratio α (1>α> 0 predetermined value) FB _CTL = αFB _S a PAPR reduction zone obtained by multiplying the relative transmission bandwidth FB _S was To the third-order distortion generation path control unit 181A.

Here magnification α may be a constant value but is preferably set to a value corresponding to the modulation level of the transmission bandwidth FB _S and modulation scheme. It may be possible to reduce the amount of degradation EVM by selecting the magnification α in accordance with the bandwidth FB _S and modulation level. Therefore, the transmission bandwidth FB _S, modulation level, prepared an LUT (Look Up Table) that associates the magnification alpha, may be determined magnification alpha refers to the LUT. When the modulation multi-level number is high, the allowable value of EVM is low. When the modulation multi-level number is high, it is preferable to reduce the magnification α. This is because the PAPR reduction band FB _CTL is reduced to narrow the band where EVM deteriorates. Alternatively, the larger the transmission bandwidth FB _S, it may be determined magnification α to reduce the magnification α in stages.

[Third-order in-band distortion compensation coefficient adjustment processing S123]
Third-order distortion generating path control unit 181A reduces PAPR by adjusting the amplitude X _A and phase X _P of the complex multiplier corresponding to PAPR reduction zone PB _CTL of the complex multiplier 13C3 respectively. Here, as shown in FIG. 9, the complex multiplier corresponding to between the bands B ₂ and FB _CTL and between the bands FB _CTL and B ₃ outputs to the J-point IFFT section without adjusting the amplitude and phase. Thereby, it is possible to avoid degradation of EVM due to PAPR reduction between the bands B ₂ and FB _CTL and between the bands FB _CTL and B ₃ . Thus the bandwidth to reduce the PAPR reduced in accordance with the transmission band FB _S, that can reduce the degradation of EVM is different from the technique according to Patent Document 1.

In Figure 9, the PAPR reduction zone FB _CTL is placed in the center of the transmission band FB _S, depending constellation of FB _S may be placed FB _CTL above or below the center of the FB _S . In some cases, changing the placement point can reduce the degradation of EVM. Arrangement of FB _CTL, when using a multi-carrier signal such as OFDM as described below, may be performed adaptively according to the subcarrier arrangement and modulation scheme FB _S. The subcarrier arrangement in the FB _CTL may be observed by the bandwidth determiner 181D, and may be performed by the PAPR reduction band controller 181C according to the result.

In the adjustment of the phase in the PAPR reduction band FB _CTL , X _P = π−V _{P, MIN} using the phase V _{P, MIN} set in the third-order distortion vector adjuster 13B in the process S11 as in the process S12 of FIG. The phase _XP is set to all the complex multipliers in the band FB _CTL . When adjusting the amplitude, in the case of the perturbation method, the initial value X _A arbitrarily set at first and the PAPR at the values before and after that are observed, and the amplitude is changed by a predetermined offset value ΔX _A in the direction in which the PAPR decreases. Observe PAPR. By repeatedly changing the amplitude and observing the PAPR, the amplitude value X _{A, MIN} where the PAPR is equal to or less than a predetermined threshold PAPR _TH is obtained and set to all the complex multipliers in the band FB _CTL . When PAPR becomes equal to or less than PAPR _{TH, the} process proceeds to third-order distortion out-of-band distortion compensation coefficient adjustment processing S13. Since the phase V _{P, MIN} set in the third-order distortion vector adjuster 13B is necessary for the phase adjustment in the process S123, the third-order in-band distortion compensation coefficient adjustment process S123 is the same as the third-order distortion vector adjuster coefficient adjustment process S11. To do later.

[Third-order distortion out-of-band distortion compensation coefficient adjustment processing S13]
The third-order distortion out-of-band distortion compensation coefficient adjustment processing S13 by the third-order distortion generation path control unit 181A is the same as the processing S13 in FIG. 5, and each of the divided bands B _{1 to} B ₄ based on the observation result of the distortion observer 17. The amplitude and phase of the corresponding complex multiplier are adjusted so as to reduce the distortion component of the divided band. In this case, the distortion observer 17 is configured to observe the power for each divided band by FFT of the feedback signal or divide the feedback signal for each divided band by a filter.

After adjusting the amplitude and phase of the complex multiplier, when the power of the third-order distortion component lower band FB _DL and the third-order distortion component upper band FB _DU is larger than the threshold value P _TH , the third-order distortion is shown as shown by the broken line. You may make it return to vector adjuster coefficient adjustment processing S11. Here, the threshold value P _TH may be set for each divided band. By setting a threshold value P _TH for each divided band, the performance of the power amplifier 23 and the distortion compensation amount required for the digital predistorter 101 may be alleviated.

Thus, in the present embodiment, the point of reducing the PAPR reduction band FB _CTL adaptively depending on the bandwidth FB _S of the signal input to the input terminal T _IN is different from the digital predistorter in Patent Document 1.
In the above embodiment, although adjusting the amplitude and phase so as to reduce the PAPR after decided FB _CTL according to FB _S, after setting phase and the amplitude of reducing PAPR, and PAPR to target The FB _CTL may be reduced so that Details are described below.
In S122, α = 1 is temporarily set, that is, FB _S = FB _CTL . Next, in S123, the phase X _P is set for all the complex multipliers in the band FB _CTL so that X _P = π−V _{P, MIN} . Next, an initial value X _{A of} amplitude is set. At this time, when the observation result of the PAPR observer 19 is smaller than the threshold PAPR _TH , the adjustment of the phase and amplitude in the FB _CTL is finished. Next, the FB _CTL is reduced by the PAPR reduction band control unit 181C until the PAPR becomes PAPR _TH based on the observation result of the PAPR observer 19. Here, 1.0 amplitudes giving the band which does not overlap with the FB _CTL in FB _S, to a phase with 0, EVM by the unregulated in other words improves. FB _CTL is reduced to a predetermined magnification, and the magnification may be multiplied by FB _CTL until PAPR _TH is reached. FB _CTL list (FB _CTL1 > FB _CTL2 >...> FB _CTLI ) is created in advance. You may set in order from a wide thing. When a list is used, a memory is required, but there is an advantage that the amount of signal processing can be reduced because multiplication is unnecessary. In this case, it is assumed that the PAPR observer 19 and the PAPR reduction band control unit 181C are connected as indicated by a broken line. By reducing the FB _CTL without adjusting the phase and amplitude in the FB _CTL by a method such as a perturbation method, the PAPR may be changed to the PAPR _TH while suppressing the EVM degradation in a shorter adjustment time than the above method.
Shown FIGS. 22A and B to X _P and in the case of reduced X _A was a constant FB _CTL PAPR and EVM a computer simulation by the determined results, respectively. The computer simulation was used LTE signal modulation scheme QPSK, FB _{S =} 5MHz. Phase V _P applied to the third-order distortion vector _{regulator, MIN} amplitude V _{A, MIN,} phase and amplitude supplied from B ₁ to B ₄ are from experiments with 1W-class power amplifier of this LTE signal and AB class operation Value. In the experiment, the output back-off of the power amplifier is 10.1dB. The PAPR reduction zone reduction ratio γ of the horizontal axis is the ratio FB _S of FB _CTL (FB _CTL is set around the center frequency (f _c)). PAPR and EVM were obtained by increasing the phase X _P given to FB _CTL to π−V _{P, MIN} and increasing the amplitude X _A from 1.0 to 5.0.
Results from, the reduction in the constant X _P and X _A gamma of 100%, although PAPR reduction amount is reduced EVM is seen to improve. From the above, when PAPR when setting X _P and X _A is smaller than the threshold value PAPR _TH, can improve EVM by reducing the FB _CTL until PAPR is PAPR _TH.

FIG. 10 is a block diagram showing the overall configuration of the digital predistorter 102 and peripheral devices according to this embodiment.
The digital predistorter 102 includes a distributor 11, a linear transmission path 12, a third-order distortion generation path 13, a combiner 14, a DAC 15, an ADC 16, a distortion observer 17, a PAPR observer 19, a bandwidth determiner 181D, and a controller 182. including. The controller 182 includes a third-order distortion generation path control unit 182A, a PAPR determination control unit 181B, and a PAPR reduction band determination unit 182C.

  The third-order distortion generation path control unit 182A and the PAPR reduction band control unit 182C are different from the first embodiment, and the control process is different from the third-order in-band distortion compensation coefficient adjustment process S123 in FIG. Different points will be described below.

PAPR reduction band determining unit 182C instructs the bandwidth determiner 181D to determine the transmission band FB _S. Bandwidth determiner 181D provides the transmission bandwidth FB _S was determined by the aforementioned method in PAPR reduction band determining unit 182C. PAPR reduction band determining unit 182C may determine the PAPR reduction band FB _CTL based on the FB _S obtained as shown in FIG. 11 is divided into a plurality of bands predetermining _{FB CTL (B CTL1, B CTL2} ) ( However, in this embodiment, FB _CTL ≦ FB _S ). Although FIG. 11 shows an example in which the FB _CTL is divided into two equal bandwidths, the division number M _DIV may be arbitrarily set to 2 or more, and the divided bandwidth is also set independently for each band. Good. B _CTL1 and B _CTL2 may be discontinuous. Predetermined large division number M _DIV enough bandwidth FB _S is large, as described above, the bandwidth FB _S and the division number M _DIV, associate the bandwidth of each divided band _{B CTL1, B CTL2 LUT (Look} Up Table) May be prepared, and the division number M _DIV and the bandwidth of each of the divided bands B _CTL1 and B _CTL2 may be determined with reference to the LUT. There are cases where the EVM degradation amount can be further reduced by dividing the PAPR reduction band FB _CTL into a plurality of parts and changing the amplitude and phase for reducing the PAPR for each divided band as compared with the case of M _DIV = 1.

Third-order distortion generating path controller 182A includes, in the complex multipliers 13C3, to individually adjust the amplitude X _A and phase X _P of the complex multiplier corresponding to the divided band B _CTL1 and B _CTL2, respectively above the same procedure To reduce PAPR. That is, in the phase adjustment, the phase X _P of each divided band may be adjusted to be X _P = π−V _P , or may be adjusted by the perturbation method with X _p = π−V _P as an initial value. Also good. In the amplitude adjustment, the amplitude value X _{A, MIN} at which PAPR is equal to or less than a predetermined threshold PAPR _TH is obtained in each divided band using the perturbation method described above. The phase adjustment and the amplitude adjustment may be performed one by one in order, but the time required for the PAPR to be equal to or less than the threshold PAPR _TH may be shortened by performing in parallel.

In a wireless communication system such as LTE-Advanced, there is a technology called carrier aggregation (hereinafter also referred to as CA) that uses a plurality of frequency bands (hereinafter also referred to as component carriers (CC)) simultaneously. Although FIG. 13 shows an example in which five CCs (CC1 to CC5) are continuously arranged, they may be discontinuously arranged. In this example, the PAPR reduction band FB _CTL is divided into the same number in accordance with each CC bandwidth, and the amplitude and phase of the complex multiplier are adjusted for each divided band (B _{CTL1 to} B _{CTL5 in} FIG. 13). Shows the case. The division number M _DIV and the bandwidth of the FB _CTL are not limited to those shown in this example, and may be set arbitrarily.

At this time, in B _{CTL1 to} B _CTL5 , if there is a band where it is not desired to greatly degrade EVM, the phase and amplitude of the band may be adjusted so as not to degrade EVM. For example, the EVM tolerance for B _CTL1 and B _CTL4 is set to EVM _TH , the EVM in B _CTL1 and B _CTL4 is less than EVM _TH , and the EVM tolerance in B _CTL2 , B _CTL3 , B _CTL4 is higher than EVM _TH The case where it may be sufficient is demonstrated.

  FIG. 12 is a block diagram showing the overall configuration of the digital predistorter 103 and peripheral devices according to this embodiment.

  The digital predistorter 103 includes a distributor 11, a linear transmission path 12, a third-order distortion generation path 13, a combiner 14, a DAC 15, an ADC 16, an EVM / distortion observer 171, a PAPR observer 19, a bandwidth determiner 181D, and a control. A container 183. The controller 183 includes a third-order distortion generation path control unit 183A, a PAPR determination control unit 181B, and a PAPR reduction band determination unit 183C.

  The third-order distortion generation path control unit 183A, the PAPR reduction band control unit 183C, and the EVM / distortion observer 171 are different from the second embodiment, and the control process is different from the third-order in-band distortion compensation coefficient adjustment process S123 in FIG. Different points will be described below.

PAPR reduction band determining unit 183C instructs the bandwidth determiner 181D to determine the transmission band FB _S. Bandwidth determiner 181D provides the transmission bandwidth FB _S was determined by the aforementioned method in PAPR reduction band determining unit 182C. PAPR reduction band determining unit 183C may determine the PAPR reduction band FB _CTL based on the FB _S obtained as shown in FIG. 13, divides the FB _CTL into a plurality of bands (B _CTL1 ~B _CTL5) in accordance with the CC (However, the FB _CTL ≦ FB _S in this example). FIG. 12 shows an example in which the FB _CTL is divided into five equal bandwidths according to the number of CCs.

  In addition to the function of observing the distortion component of each band of the feedback signal (distortion observation means), the EVM / distortion observer 171 includes the input signal samples distributed from the distributor 11 and the feedback signal samples timed with them. Has a function to calculate EVM (EVM observation means).

Third-order distortion generating path controller 183A includes, in the complex multipliers 13C3, respectively the amplitude X _A and phase X _P of the complex multiplier corresponding to the divided band B _CTL1 .about.B _CTL5 based on observations PAPR and EVM individual Adjust to. The adjustment starts from the divided band with the highest EVM tolerance. When EVM reaches the EVM allowable value of the divided band for adjusting the amplitude and phase, the amplitude and phase of the next divided band are adjusted. Here, the EVM allowable value may be set for each band. By setting for each band, the range in which the amplitude and phase can be adjusted may be widened, and the time to reach PAPR _TH may be shortened. In the phase adjustment of the band do not want to degrade the the EVM, rather than a phase with the X _P = π-V _P, it is desirable to adjust the X _P to be close to zero. Bringing the X _P to 0, there are cases in other words capable of reducing the in distortion component and no adjustment the phase of the band, because that can avoid degradation of EVM. A margin ΔEVM may be added to the EVM allowable value of each divided band. In this case, when EVM becomes the EVM allowable value −ΔEVM, the process shifts to adjustment of the amplitude and phase of another divided band. By adding a margin, there may be a case where the EVM allowable value can be satisfied even when there is EVM degradation due to the effect of adjusting the amplitude and phase of other divided bands.

If PAPR for observing PAPR observer by adjusting the amplitude and phase of B _CTL1 .about.B _CTL5 is significantly below the PAPR _TH, the B _CTL1 .about.B _CTL5 so PAPR improves the EVM within a range below the PAPR _TH amplitude and phase May be adjusted. At this time, the amplitude and phase are adjusted from the band having the worst EVM among B _{CTL1 to} B _CTL5 . Thereby, it may be possible to avoid that the EVM is greatly deteriorated only in a specific band. In amplitude adjustment, the amplitude is changed by the offset value D, EVM is observed, the amplitude is changed by D in the direction in which EVM improves, and EVM and PAPR are observed. By repeating the amplitude change and EVM and PAPR observations, the amplitude that best improves EVM within the range not exceeding PAPR _TH is obtained. The same applies to the phase.
If PAPR for observing PAPR observer by adjusting the amplitude and phase of B _CTL1 .about.B _CTL5 is significantly below the PAPR _TH, by reducing the B _CTL1 .about.B _CTL5 without adjusting the amplitude and phase in a range that does not exceed the PAPR _TH Also good. Bandwidth reduction is performed in order from the worst EVM or closest to the EVM tolerance. This is because the EVM degradation amount may be improved as compared with the case where the amplitude and phase of B _{CTL1 to} B _CTL5 are adjusted.

[Modification 1 of Example 3]
In LTE-Advanced, one CC is composed of a plurality of resource blocks (hereinafter also referred to as RBs). The modulation scheme is adaptively assigned for each RB. Also, the allowable value of EVM is lower as the modulation multi-level number is higher. Therefore, the modulation scheme of each RB may be discriminated, and the PAPR reduction band FB _CTL may be divided in accordance with the RB to increase the amplitude of the RB having a low modulation multilevel number and increase the PAPR reduction amount. This is because the lower the modulation multi-value number, the larger the allowable value of EVM. When the phase is X _P = π−V _P , the PAPR reduction amount generally increases by increasing the amplitude.

The discrimination of the modulation method is performed by the bandwidth determiner 181D in FIG. 12, and the PAPR reduction band control unit 183C uses the result to divide and allocate the PAPR reduction band FB _CTL .

[Modification 2 of Example 3]
Adjusted for amplitude and phase in the transmission band FB _S at Patent Document 1 of the method shown in FIG. 3, there is a case where distortion components can not be compensated by the digital predistorter is generated in the power amplifier. This third-order distortion to adjust to reduce PAPR for the amplitude and phase of the distortion compensation component in the frequency characteristic compensator 13C in the band FB _S in, the distortion component in the FB _S the power amplifier to generate increases, there may be a case that affect the third-order distortion component lower band FB _DU, third-order distortion component upper band FB _DU in FIG. This distortion component cannot be compensated because it becomes an unexpected distortion component in the digital predistorter. Therefore, there is a concern that the distortion component power exceeds the threshold value P _TH of the third-order distortion component lower band FB _DL, third-order distortion component upper band FB _DU.

There are similar problems in the band configuration in Figure 13, To avoid this problem, the PAPR reduction bandwidth control unit 183C, established the PAPR reduction zone only the CC band in the center of the transmission band FB _S, other It may be preferable not to provide the CC band. For example, in the example of FIG. 13, only the band B _{CTL3 of} CC3 is used for PAPR reduction. As a result, the distortion component generated in the band B _CTL3 may affect the adjacent CC2 and CC4 bands, but may affect the third-order distortion component lower band FB _DL and the third-order distortion component upper band FB _DU. Can be reduced. This is because a distortion component that is three times as large as that generated in the band B _CTL3 is generated, and therefore, EVM degradation in CC2 and CC4 is assumed, whereas the third-order distortion component lower band FB _DL , third-order distortion component This is because the upper band FB _DU is at a frequency farther than the bandwidth (band of CC2 to CC4 in FIG. 13) three times the band B _CTL3 .

[Modification 3 of Example 3]
When CA is used, the bandwidth determination unit 181D may determine the number of CCs and the CC bandwidth, and based on the result, the PAPR reduction bandwidth control unit 183C may divide the FB _CTL as shown in FIG. Here, the predetermined level difference (for example 20dB higher) and a band only provided PAPR reduction divided band B _CTL1 .about.B _CTL4 respect to the peak level of or the input signal component is no input signal component of the transmission band FB _S. Third-order distortion generation path control unit 183A adjusts the amplitude and phase of the complex multiplier corresponding to bands B _{CTL1 to} B _CTL4 so as to reduce PAPR.

When the bandwidth of each CC is 20 MHz in LTE-Advanced, subcarriers are arranged within 18.015 MHz from the center of the band, but no subcarriers are arranged on the upper 0.9925 MHz and the lower 0.9925 MHz. By using a band (B _{CTL1 to} B _{CTL4 in} FIG. 14) in which no subcarrier is arranged (no input signal component) for PAPR reduction, PAPR may be reduced without degrading EVM.

In this example, the input signal component of the transmission band FB _S and B _CTL1 .about.B _CTL4 is that there is no band. It is easy to set the same value for the amplitude and phase _applied to B _{CTL1 to} B _CTL4 , but when the EVM deterioration becomes large due to the influence of the distortion component described above, it is adjusted individually. The reason why no band is allocated to the lower end side of CC1 and the upper end side of CC5 is that the distortion components of the third order distortion component lower band FB _DL and the third order distortion component upper band FB _DU may increase as described above. However, if it is known in advance that the influence is small, it may be used for PAPR reduction.

  The PAPR reduction band control unit 183C designates the bandwidth of CC1 to CC5, and transmits the bandwidth to the third-order distortion generation path control unit 183A. The third-order distortion generation path control unit 183A may adjust the amplitude and phase applied to the complex multipliers corresponding to the designated CC1 to CC5 so as to improve the EVM.

  When a method such as OFDM is used, the bandwidth determiner 181D may determine the subcarrier interval, and the amplitude and phase may be adjusted so as to reduce PAPR using a component between subcarriers. For example, in LTE, the subcarrier interval is 15 kHz. Therefore, when the bandwidth determination unit 181D determines that the input signal from the distributor 11 is LTE (or the subcarrier interval is 15 kHz) and the frequency interval when the input signal is FFT is narrower than 15 kHz, the third order distortion PAPR is reduced using a component between subcarriers in a compensation signal input to the frequency characteristic compensator 13C.

In each embodiment described above, by controlling the PAPR reduction band FB _CTL to set in the transmission band FB _S, was suppressed an increase in EVM to cause the PAPR reduction process, in Example 4, the band is separated For the two input signals, PAPR reduction processing is performed by providing a PAPR reduction band in the intermodulation distortion component band outside the transmission band, thereby reducing PAPR while avoiding an increase in EVM.

FIG. 15 is a block diagram showing the overall configuration of the digital predistorter 104 and peripheral devices according to this embodiment. The peripheral device includes an amplification device 20 and a feedback signal generation device 30. In this example, as shown in FIG. 16, a digital predistorter corresponding to a case where the bands FB _S1 and FB _{S2 of} two input signals are in separate bands is shown. Here, a signal corresponding to the signal band FB _S1 in FIG. 16 is inputted from the input terminal T _IN1 to a digital predistorter 104, a signal corresponding to the signal band FB _S2 is input from an input terminal T _IN2 to a digital predistorter 104 Shall be. Here is described for the allocated bandwidth FB _S1 and FB _S2 to the respective one CC, and when assigned to each of a plurality of CC in FB _S1 and FB _S2, a third band other than the FB _S1 and FB _S2 The same approach can be used when using.

ここで、||は絶対値、^＊は複素共役を示す。以下においては、式(8)中の|s₁|²s₁と|s₂|²s₂をそれぞれ信号ｓ₁の３次歪成分、信号ｓ₂の３次歪成分と呼び、2|s₁|²s₂、2|s₂|²s₁、s₁ ²s₂ ^*、s₂ ²s₁ ^*を信号ｓ₁とｓ₂の相互変調歪成分と呼ぶことにする。式(8)において、相互変調歪成分s₁ ²s₂ ^*とs₂ ²s₁ ^*はそれぞれ入力信号帯域FB_S1、FB_S2の外側の相互変調歪成分下側帯域FB_ML、相互変調歪成分上側帯域FB_MUに発生する歪成分である。信号帯域FB_S1とFB_S2の中心周波数f_C1とf_C2の間隔をΔＦとすると、s₁ ²s₂ ^*とs₂ ²s₁ ^*は中心周波数f_C1、f_C2からそれぞれΔＦだけ下側及び上側に離れた周波数に発生する。ΔＦが大きい場合、電力増幅器の出力側にFB_S1とFB_S2を通過させるフィルタを設置することでs₁ ²s₂ ^*とs₂ ²s₁ ^*は抑圧できる。そのため、s₁ ²s₂ ^*とs₂ ²s₁ ^*はディジタルプリディストータで補償しなくともよいことから本実施例ではこの２つの相互変調歪成分を補償する信号をPAPR低減に用いる。PAPR低減に用いる帯域をFB_S1とFB_S2とは異なる帯域にすることでEVMを劣化させることなくPAPRを低減できる点が他の実施例と異なる。 As shown in FIG. 16, when a signal in which CCs are assigned to two bands is amplified by one power amplifier 23, the third-order distortion component lower bands FB _DL1 and FB _DL2 and the third-order distortion component upper band FB shown in FIG. _DU1, FB _DU2, intermodulation distortion component lower band FB _ML, distortion component intermodulation distortion component upper band FB _MU is generated respectively. For example, assuming an equivalent low-frequency system, the complex baseband signal using FB _S1 is s ₁ , the complex baseband signal using FB _S2 is s _2, and the distortion generation model of the power amplifier is a third power series , the distortion component D ₃ that occurs in the power amplifier can be expressed by the following equation (8).

Where || is an absolute value and ^* is a complex conjugate. In the following, | s ₁ | ² s ₁ and | s ₂ | ² s ₂ in equation (8) are called the third-order distortion component of signal s _{1 and} the third-order distortion component of signal s ₂ , respectively. ₁ | ² s ₂ , 2 | s ₂ | ² s ₁ , s ₁ ² s ₂ ^* , and s ₂ ² s ₁ ^* are referred to as intermodulation distortion components of the signals s ₁ and s ₂ . In equation (8), the intermodulation distortion components s ₁ ² s ₂ ^* and s ₂ ² s ₁ ^* are the inter-modulation distortion component lower band FB _ML and inter-modulation distortion component outside the input signal bands FB _S1 and FB _S2 , respectively. This is a distortion component generated in the upper band FB _MU . When the interval between the center frequencies f _C1 and f _C2 of the signal bands FB _S1 and FB _S2 is ΔF, s ₁ ² s ₂ ^* and s ₂ ² s ₁ ^* are lower than the center frequencies f _C1 and f _C2 by ΔF, respectively. Occurs at a frequency distant from the upper side. When ΔF is large, s ₁ ² s ₂ ^* and s ₂ ² s ₁ ^* can be suppressed by installing a filter that passes FB _S1 and FB _S2 on the output side of the power amplifier. For this reason, since s ₁ ² s ₂ ^* and s ₂ ² s ₁ ^* do not need to be compensated by the digital predistorter, in this embodiment, signals for compensating these two intermodulation distortion components are used for PAPR reduction. It differs from the other embodiments in that PAPR can be reduced without degrading EVM by making the band used for PAPR reduction different from FB _S1 and FB _S2 .

Intermodulation distortion component 2 in the formula ^{_{(8) | s 1 | 2}} s 2 have the same band FB _D2 and the third-order distortion component of the input signal s _2, also intermodulation distortion component 2 | s ₂ | ² s ₁ has the same band FB _D1 and the third-order distortion component of the input signal s _1.

  Here, the case where the third-order distortion component is used has been described, but the case where a fifth-order or higher-order distortion component is used can be dealt with in the same way.

  The digital predistorter 104 includes distributors 111 and 112, a combiner 113, a linear transmission path 12, a third-order distortion generation path 130, a combiner 14, a DAC 15, an ADC 16, a distortion observer 17, a PAPR observer 19, and a controller 184. including. The controller 184 includes a third-order distortion generation path control unit 184A and a PAPR determination control unit 181B.

The distributor 111 distributes the signal from the input terminal T _IN1 to the third-order distortion generation path 130 and the combiner 113. The distributor 112 distributes the signal from the input terminal T _IN2 to the third-order distortion generation path 130 and the combiner 113. When the signals input to the input terminals T _IN1 and T _IN2 are baseband signals centered on DC, the distributors 111 and 112 are connected to the input terminals so that the frequency difference between the center frequencies f _C1 and f _C2 is ΔF. The frequency of each signal is shifted. The frequency is shifted by, for example, converting the signal into the frequency domain by FFT, and shifting the signal to the desired frequency (for example, the signal from the input terminal T _IN1 is −ΔF / 2 and the signal from the input terminal T _IN2 is + ΔF / 2). Later, it is done by IFFT. The combiner 113 combines the signals from the distributor 111 and the distributor 112 and outputs the combined signal to the linear transmission path 12.

  FIG. 17 shows the configuration of the third-order distortion generation path 130. The third-order distortion generation path 130 includes signal distributors 13D1 and 13D2, signal generation units 1301 and 1302, a sub-signal generation unit 1303, and a signal synthesizer 13G. The signal distributor 13D1 distributes the distribution signal from the distributor 111 to the signal generation unit 1301 and the sub signal generation unit 1303. The signal distributor 13D2 distributes the distribution signal from the distributor 112 to the signal generation unit 1302 and the sub signal generation unit 1303.

The signal generation unit 1301 includes a third-order distortion generator 13A1 and a third-order distortion vector adjuster 13B1. The third-order distortion generator 13A1 generates the third-order distortion component (| s ₁ | ² s _{1 in} Expression (8)) by cubeing the signal from the signal distributor 13D1. The third-order distortion vector adjuster 13B1 is based on the control information from the controller 184 so that the distortion component of the third-order distortion component lower band FB _DL1 or the upper band FB _DU1 observed by the distortion observer 17 is minimized. s ₁ | ² Adjust the amplitude and phase of s ₁ . The signal generation unit 1302 includes a third-order distortion generator 13A2 and a third-order distortion vector adjuster 13B2. The third-order distortion generator 13A2 generates the third-order distortion component (| s ₂ | ² s _{2 in} Expression (8)) by cubeing the signal from the signal distributor 13D2. The third-order distortion vector adjuster 13B2 is based on the control information from the controller 184 so that the distortion component of the third-order distortion component lower band FB _DL2 or the upper band FB _DU2 observed by the distortion observer 17 is minimized. s ₂ | ² Adjust the amplitude and phase of s ₂ .

The sub-signal generation unit 1303 includes a third-order intermodulation distortion calculator 13E and sub-third-order distortion vector adjusters 13F1, 13F2, 13F3, and 13F4. The third-order intermodulation distortion calculator 13E receives third-order intermodulation distortion components (2 | s ₂ | ² s ₁ , 2 | s ₁ | ² s ₂ in Expression (8)) from the signals from the signal distributors 13D1 and 13D2. s ₁ ² s ₂ ^* , s ₂ ² s ₁ ^* ) are generated. Sub third-order distortion vector regulator 13F1 is the third-order distortion vector adjuster 13B1 adjusted by 2 distortion component bands based on the control information from the controller 184 to be the minimum using a | of ² s ₁ | s ₂ Adjust amplitude and phase. Sub third-order distortion vector regulator 13F2 is the third-order distortion vector adjuster distortion component bands used in the adjustment of 13B2 is based on the control information from the controller 184 so as to be minimum 2 | of ² s ₂ | s ₁ Adjust amplitude and phase. The sub third-order distortion vector adjuster 13F3 adjusts the amplitude and phase of s ₁ ² s ₂ ^* based on the control information from the controller 184 so that the PAPR of the band FB _S1 observed by the PAPR observer 19 is minimized. To do. The sub third-order distortion vector adjuster 13F4 adjusts the amplitude and phase of s ₂ ² s ₁ ^* based on the control information from the controller 184 so that the PAPR of the band FB _S2 observed by the PAPR observer 19 is reduced. .

The control flow P2 of the controller 184 will be described with reference to FIG. Here, it is assumed that the input signal bands FB _S1 and FB _S2 are set in the controller 184 in advance.

[Sub-third-order distortion vector adjuster coefficient adjustment processing S21]
The third-order distortion generation path control unit 184A adjusts the phase Z _P and the amplitude Z _A given to the sub-third-order distortion vector adjusters 13F3 and 13F4 so that the PAPR of the bands FB _S1 and FB _S2 is reduced.

In the phase adjustment, the phase Z _P = π is given to the sub third-order distortion vector adjusters 13F3 and 13F4 (based on the principle explained in FIG. 6). When adjusting the amplitude, observe the PAPR at the initial value Z _A set arbitrarily and the values before and after it, and change the amplitude by a preset offset value ΔZ _A in the direction of decreasing PAPR, and observe the PAPR. To do. By repeatedly changing the amplitude and observing the PAPR, the amplitude Z _{A, MIN} is obtained so that the PAPR is equal to or less than a predetermined threshold PAPR _TH . When PAPR becomes equal to or less than PAPR _{TH, the} process proceeds to the third-order distortion vector adjuster coefficient adjustment process S32. When observing the PAPR, the third-order distortion generation path control unit 184A instructs the PAPR determination control unit 181B to measure the PAPR and transmit the measurement result.

In the above example, the phase and amplitude set in the sub third-order distortion vector adjusters 13F3 and 13F4 have the same value, but may have different values. When the values are different, the adjustment of the sub third-order distortion vector adjuster 13F3 and the sub third-order distortion vector adjuster 13F4 is performed in order, not simultaneously. This is because the PAPR reduction effect may be canceled when adjustments are made simultaneously. At this time, in the phase adjustment, the phase change and the PAPR observation are repeated similarly to the amplitude adjustment, and the amplitudes Z _{P and MIN} that are equal to or less than the threshold PAPR _TH may be obtained.

[Third-order distortion vector adjuster coefficient adjustment processing S22]
The third-order distortion generator path control unit 184A uses third-order distortion vector adjusters 13B1 and 13B2 and a sub-third-order distortion vector adjuster so as to compensate for distortion components generated in the power amplifier 23 using the method described in FIG. The amplitude V _{A, MIN} and the phase V _{P, MIN} given to 13F1, 13F2 are adjusted. That is, the third-order distortion vector adjusters 13B1 and 13B2 are set so that the powers of the third-order distortion component lower bands FB _DL1 and FB _DL2 or the upper bands FB _DU1 and FB _DU2 observed by the distortion observer 17 are minimized. , 13F1, and 13F2 are adjusted in amplitude and phase. Here, the adjustments of the respective third-order distortion vector adjusters may be performed one by one, but when the adjustment time is desired to be shortened, the third-order distortion vector adjusters 13B1 and 13B2 may be adjusted simultaneously. This is because distortion components compensated by the third-order distortion vector adjusters 13B1 and 13B2 are generated in different bands. Similarly, the sub third-order distortion vector adjusters 13F1 and 13F2 may be adjusted simultaneously.

It is preferable to perform the third-order distortion vector adjuster coefficient adjustment process S22 after the sub-third-order distortion vector adjuster coefficient adjustment process S21. This is because the distortion component generated in the power amplifier 23 can be compensated after the PAPR is reduced. When PAPR exceeds PAPR _TH by S22, S21 and S22 may be repeated.

  When the distortion component generated in the power amplifier 23 does not have frequency dependency, the PAPR can be reduced without using a third-order distortion frequency characteristic compensator in the embodiment as described above. As a result, signal processing circuits such as DSP and FPGA can be simplified because signal processing such as FFT and IFFT can be reduced.

[Modification of Example 4]
When the distortion component has frequency dependence, as a modification of the third-order distortion generation path 130 in FIG. 17, a third-order distortion generation path 131 is shown in FIG. The third-order distortion frequency characteristic compensators 13C01 and 13C02 may be provided, and the sub-third-order distortion frequency characteristic compensators 13H1 and 13H2 may be installed at the subsequent stage of the sub-third-order distortion vector adjusters 13F1 and 13F2, respectively.

In the control flow in this case, a third-order out-of-band distortion coefficient adjustment process S23 is added after the process S22 as indicated by a broken line in FIG. In the process S23, each third-order distortion component lower band FB _DL1 , upper band FB _DU1 , third-order distortion component lower band FB _DL2 and lower band FB _DU2 are divided into a plurality of distortions in the same manner as in FIG. The phase of the corresponding divided band in the frequency domain in the third-order distortion frequency characteristic compensators 13C01 and 13C02 and the sub-third-order distortion frequency characteristic compensators 13H1 and 13H2 is reduced so that the distortion component of each divided band observed by the observer 17 is reduced. And adjust the amplitude.

In the modification of the fourth embodiment, when the sub-third-order distortion vector adjusters 13F3 and 13F4 cannot reduce the PAPR to PAPR _TH or less, the frequency is set so as to reduce the PAPR using the method shown in the other embodiments 1, 2, or 3. The characteristic compensator may be controlled.

  FIG. 20 is a block diagram showing the entire digital predistorter 105 and peripheral devices according to this embodiment.

  The digital predistorter 105 includes distributors 111 and 112, a combiner 113, a linear transmission path 12, a third-order distortion generation path 131, a combiner 14, a DAC 15, an ADC 16, a distortion observer 17, a PAPR observer 19, and a bandwidth determination. 181D and controller 185. The controller 185 includes a third-order distortion generation path control unit 185A, a PAPR determination control unit 181B, and a PAPR reduction band control unit 185C. 15 differs from the configuration of FIG. 15 in that a bandwidth determination unit 181D is added and signals from the distributors 111 and 112 are given, and a PAPR reduction band control unit 185C is added to the controller 185 to generate third-order distortion. The path control unit 185A has a function of adjusting the phase and amplitude with respect to the PAPR reduction band in the transmission band in addition to the function of the third-order distortion generation path control unit 184A in FIG. The configuration and operation of the tertiary distortion generation path 131 are the same as those shown in FIG.

  The control flow P3 of the controller 184 will be described with reference to FIG. The entire flow is obtained by inserting the processes S121, S122, and S123 of FIG. 8 between the processes S22 and S23 in FIG.

The sub third-order distortion vector adjuster coefficient adjustment process S21 is the same as the corresponding process S21 in FIG. 18, and the third-order distortion generation path control unit 185A determines the phase Z _P to be given to the sub-third order distortion vector adjusters 13F3 and 13F4. The amplitude Z _A is adjusted so that the PAPR of the bands FB _S1 and FB _S2 is reduced.

The third-order distortion vector adjuster coefficient adjustment process S22 is the same as the corresponding process S22 in FIG. 18, and the third-order distortion generator path control unit 185A uses the technique described in FIG. The amplitude V _{A, MIN} and the phase V _{P, MIN} given to the third order distortion vector adjusters 13B1, 13B2 and the sub third order distortion vector adjusters 13F1, 13F2 are adjusted so as to compensate the components. That is, the third-order distortion vector adjusters 13B1 and 13B2 are set so that the powers of the third-order distortion component lower bands FB _DL1 and FB _DL2 or the upper bands FB _DU1 and FB _DU2 observed by the distortion observer 17 are minimized. , 13F1, and 13F2 are adjusted in amplitude and phase.

The PAPR determination control unit 181B determines whether or not the PAPR in the output signal from the synthesizer 14 observed by the PAPR observer 19 is higher than the threshold PAPR _TH , and if so, performs a bandwidth determination process S122 described later. To the bandwidth determination unit 181D. When PAPR is equal to or less than the threshold PAPR _TH , the third-order distortion generation path control unit 181A is instructed to perform the same third-order out-of-band distortion compensation coefficient adjustment process S23 as the process S13 in FIG. 5 (S121).

When receiving an instruction to determine a transmission band FB _S from PAPR judgment control unit 181B, the bandwidth determination unit 181D, the transmission bandwidth FB _S1, FB divider 111 and 112 input signal distributed from S _IN1, S _{IN2 S2} is determined, and the result is transmitted to the PAPR reduction band control unit 185C. The PAPR reduction band controller 185C obtains FB _CTL1 = αFB _S1 obtained by multiplying the obtained transmission bandwidths FB _S1 and FB _S2 by a predetermined magnification α (a predetermined value of 1>α> 0), FB _CTL2 = αFB _S2 is transmitted as a PAPR reduction band to the third-order distortion generation path control unit 185A (S122).

Third-order distortion generating path control unit 185A includes third-order distortion frequency characteristic compensator, respectively adjust the amplitude X _A and phase X _P of the complex multiplier corresponding to PAPR reduction zone PB _CTL among the complex multiplier of 13C01,13C02 This reduces PAPR (S123).
The third-order distortion out-of-band distortion compensation coefficient adjustment processing S23 by the third-order distortion generation path control unit 185A is the same as the processing S13 in FIG. 8, and the third-order distortion component lower bands FB _DL1 and FB _DL2 and upper bands of each input signal The amplitude and phase of the corresponding complex multiplier are adjusted so as to reduce the distortion component of each divided band based on the observation result of the distortion observer 17 for each divided band of FB _DU1 and FB _DU2 . After adjusting the amplitude and phase of the complex multiplier, if the power of the third-order distortion component lower band FB _DL1 , FB _DL2 and the third-order distortion component upper band FB _DU1 , FB _DU2 is greater than the threshold value P _TH , As shown, the third-order distortion vector adjuster coefficient adjustment processing S22 may be returned to.

  Each embodiment and modification of the digital predistorter described above may be configured such that the operation is executed by a computer according to a program, or the constituent elements thereof are DSP (Digital Signal Processor) or FPGA (Field Programmable). Gate Array).

Claims (8)

A digital predistorter that outputs a distortion compensation component for canceling a distortion component generated by a power amplifier to an input signal,
A linear transmission path for delay transmission of the input signal;
N (N is an odd number greater than or equal to 3) order distortion generation path for generating a distortion compensation component from the input signal;
A bandwidth determiner for determining the bandwidth of the input signal;
A distributor for distributing the input signal to the linear transmission path, the Nth-order distortion generation path, and the bandwidth determination unit;
A synthesizer that synthesizes the output of the linear transfer path and the output of the Nth-order distortion generation path;
A PAPR observer that observes the peak-to-average power ratio (PAPR) from the output of the combiner;
A controller;
Including
The Nth order distortion generation path includes an Nth order distortion generator that generates an Nth order distortion component by raising the input signal to the Nth power, an Nth order distortion vector adjuster that adjusts the amplitude and phase of the Nth order distortion component, An N-order distortion frequency characteristic compensator that divides the output signal of the N-order vector adjuster into a plurality of bands in the frequency domain and adjusts the amplitude and phase for each of the divided bands;
The controller uses the observation result of the PAPR observer to determine a PAPR reduction band that is smaller than the bandwidth of the input signal determined by the bandwidth determiner, and the amplitude and phase within the PAPR reduction band A digital predistorter configured to control the Nth order frequency characteristic compensator so as to reduce the PAPR. A digital predistorter that outputs a distortion compensation component for canceling a distortion component generated by a power amplifier to an input signal,
A linear transmission path for delay transmission of the input signal;
N (N is an odd number greater than or equal to 3) order distortion generation path for generating a distortion compensation component from the input signal;
A bandwidth determiner for determining the bandwidth of the input signal;
A distributor for distributing the input signal to the linear transmission path, the Nth-order distortion generation path, and the bandwidth determination unit;
A synthesizer that synthesizes the output of the linear transfer path and the output of the Nth-order distortion generation path;
A PAPR observer that observes the peak-to-average power ratio (PAPR) from the output of the combiner;
A controller;
Including
The Nth order distortion generation path includes an Nth order distortion generator that generates an Nth order distortion component by raising the input signal to the Nth power, an Nth order distortion vector adjuster that adjusts the amplitude and phase of the Nth order distortion component, An N-order distortion frequency characteristic compensator that divides the output signal of the N-order vector adjuster into a plurality of bands in the frequency domain and adjusts the amplitude and phase for each of the divided bands;
The controller uses the observation result of the PAPR observer to determine a PAPR reduced band that is equal to or less than the bandwidth determined by the bandwidth determiner, and to divide the PAPR reduced band into a plurality of divided bands A digital predistorter configured to control the Nth-order frequency characteristic compensator so as to reduce PAPR with respect to amplitude and phase in each of the bands.   3. The digital predistorter according to claim 1, further comprising EVM observation means for observing EVM (Error Vector Magnitude) between a feedback signal from the output of the power amplifier and the input signal, and the controller Is configured to execute the process of reducing the PAPR for the third-order distortion frequency characteristic compensator within a range in which the EVM observed by the EVM observation means is equal to or less than a predetermined allowable value. Digital predistorter.   3. The digital predistorter according to claim 1, wherein when the observation result of the PAPR observer is lower than a target value, the controller uses the observation result of the PAPR observer and uses the PAPR reduction band. The digital predistorter is configured to control the Nth-order distortion frequency characteristic compensator so as to reduce the bandwidth of the Nth distortion until it reaches the target value.   3. The digital predistorter according to claim 1, wherein the controller reduces the PAPR with respect to the amplitude and phase of a band having no input signal component in the bandwidth determined by the bandwidth determiner. A digital predistorter configured to control an Nth-order distortion frequency characteristic compensator. A digital predistorter for adding a distortion compensation component for canceling a distortion component generated by a power amplifier to a plurality of input signals having different frequency bands,
A plurality of linear transmission paths for delay transmission of the plurality of input signals,
A distortion generation path for generating the distortion compensation component based on the plurality of input signals;
A distributor for distributing each of the input signals to the linear transmission path corresponding to the input signal and the distortion generation path;
A synthesizer that synthesizes the output of the linear transmission path and the output of the distortion generation path;
A PAPR observer that observes the peak-to-average power ratio (PAPR) from the output of the combiner;
A controller;
Including
The strain generation path is
An Nth order distortion generator for generating respective N (N is an odd number greater than or equal to 3) order distortion component of each of the input signals;
An Nth order distortion vector adjuster for adjusting the amplitude and phase of the Nth order distortion component generated by each Nth order distortion generator;
An Nth order intermodulation distortion calculator for generating an intermodulation distortion component between the plurality of input signals;
A sub Nth-order distortion vector adjuster for adjusting the amplitude and phase of each intermodulation distortion component;
And outputs the output of the Nth order distortion vector adjuster and the output of the sub Nth order distortion vector adjuster as the distortion compensation component,
The intermodulation distortion component is an intermodulation distortion component in the band of the Nth order distortion component of each input signal, hereinafter referred to as an inband intermodulation distortion component. Including distortion components, hereinafter referred to as out-of-band intermodulation distortion components,
The digital predistorter, wherein the controller is configured to control the vector adjuster corresponding to PAPR reduction for the amplitude and phase of the out-of-band intermodulation distortion component. 7. The digital predistorter according to claim 6, further comprising a distortion observer for observing a distortion component of a feedback signal from the output of the power amplifier, wherein the distortion generation path is connected to each of the Nth-order distortion vector adjusters. An Nth-order distortion frequency characteristic compensator for adjusting the output of the sub-Nth order distortion, and a sub-Nth order distortion frequency characteristic adjuster for adjusting the in-band intermodulation distortion component of the output of the sub-Nth order distortion vector adjuster in the frequency domain; Including
The controller controls the Nth-order distortion vector adjuster and the sub-Nth-order distortion vector adjuster so as to reduce the Nth order distortion component lower band or upper band component of each input signal observed by the distortion observer. In the Nth order distortion frequency characteristic compensator and the sub Nth order distortion frequency characteristic compensator, the amplitude and phase of the Nth order distortion component lower band and upper band of each input signal were observed by the distortion observer. A digital predistorter configured to adjust so as to reduce a distortion component of a corresponding band. A method of controlling a digital predistorter according to claim 1,
A process of determining whether the PAPR observed by the PAPR observer is higher than a predetermined threshold;
When the PAPR is higher than the threshold, a process for determining the bandwidth of the input signal;
A process of adaptively setting a PAPR reduction band narrower than the bandwidth according to the determined bandwidth;
A process of adjusting the amplitude and phase in the PAPR reduction band by the Nth-order distortion frequency characteristic compensator so that the PAPR observed by the PAPR observer is reduced;
The control method characterized by including.

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