JP2014003527A - Transmitter, and distortion compensation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of unwanted waves, including harmonic waves and intermodulation distortion, generated at a simultaneous amplification of a plurality of radio band signals.SOLUTION: A transmitter includes: an amplifier for simultaneously amplifying a plurality of transmission signals; an output frequency response characteristic compensation part for compensating an output frequency response characteristic for a plurality of input signals based on an amplifier model separately modeled in an input frequency response characteristic, a non-linear characteristic, and an output frequency response characteristic, of the amplifier; a non-linear characteristic compensation part for calculating a compensation signal for a signal obtained by compensation at the output frequency response characteristic compensation part, by solving a non-linear simultaneous equation corresponding to outputs of the amplifier at a plurality of frequency bands based on the non-linear characteristic of the amplifier model; and an input frequency response compensation part for compensating the input frequency response characteristic of the amplifier model according to a compensation signal calculated by the non-linear characteristic compensation part, and for outputting a signal obtained by the compensation to the amplifier.

Description

  The present invention relates to a distortion compensation method for compensating for distortion generated when a signal including components in a plurality of frequency bands is amplified, and a transmitter using the distortion compensation method.

  As the use of wireless communication is advanced and diversified, there is a demand for a transmitter that can simultaneously transmit signals in a plurality of frequency bands in order to accommodate various wireless systems in an integrated manner. In order to realize such a transmitter, it is necessary to make the radio band multiband or broadband.

  As the radio band supported by the transmitter becomes wider, unwanted waves such as harmonics of signals in a certain radio band, intermodulation distortion and intermodulation distortion between signals in multiple radio bands, and spurious generated in the transmission mixer are generated. Therefore, there arises a problem that it becomes an interference component for signals in other radio bands. For removing unnecessary waves, bandpass filters having good characteristics in a radio band such as SAW filters, dielectric filters, and waveguide filters are widely used.

  However, for example, when signals in the 300 MHz band and the 900 MHz band are transmitted at the same time, if a third harmonic (unnecessary wave) with respect to the signal in the 300 MHz band generated by the nonlinearity of the transmission amplifier is suppressed by a bandpass filter, transmission is performed. The 900 MHz band signal to be suppressed is also suppressed. In such a case, it is not appropriate to suppress unnecessary waves using a bandpass filter.

  Further, when signals in the 300 MHz band and 900 MHz band are transmitted simultaneously, unnecessary waves in the 600 MHz band and 1200 MHz band are generated by the second order intermodulation distortion, and unnecessary waves in the 1500 MHz band are generated by the third order intermodulation distortion. However, when there is a signal to be transmitted also in the 600 MHz band, 1200 MHz band, or 1500 MHz band, it is not appropriate to suppress unnecessary waves using a bandpass filter.

  Further, when signals in the 300 MHz band and 900 MHz band are transmitted simultaneously, even if third-order or fifth-order intermodulation distortion occurs in the 300 MHz band and 900 MHz band, which are the fundamental wave components, due to the nonlinearity of the transmission amplifier. Similarly, it is not appropriate to suppress unwanted waves using a bandpass filter.

  As described above, when signals in a plurality of frequency bands are transmitted simultaneously, if the generated unwanted waves are suppressed by the bandpass filter, the signal to be transmitted may be suppressed. Therefore, it is necessary to suppress the generation of harmonics, intermodulation distortion, and intermodulation distortion.

  One method of suppressing nonlinear distortion that occurs in an amplifier is to output only a signal with sufficiently low power relative to the output saturation power of the amplifier (operation in the linear region), but the power efficiency of the amplifier is low. End up. In addition, other methods for suppressing nonlinear distortion generated in an amplifier include distortion such as a digital pre-compensation type distortion compensation method, an analog pre-compensation type distortion compensation method, a feedback type distortion compensation method, and a feed-forward type distortion compensation method. There is a compensation technique (Non-Patent Document 1 to Non-Patent Document 4).

Nojima, Okamoto, Oyama, "Predistortion nonlinear distortion compensation circuit for microwave SSB-AM system", IEICE Transactions, Vol. J67-B No. 1, pp.78-85, 1984. J.C. Pedro, J. Perez, “An MMIC linearized amplifier using active feedBack,” IEEE Microwave and Millimeter-Wave Monolithic Circuits Symp. Dig., Pp. 113-116, 1993. S. Andreoli, H.G. McClure, P. Banelli, S. Cacopardi, “Digital linearizer for RF amplifiers,” IEEE Trans. On Broadcasting, vol.43, 1, pp.12-19, 1997. H. Seidel, “A feedforward experiment applied to an L-4 Carrier System Amplifier”, IEEE Trans. On Communication Technology, Vol.COM-19, No.3, pp.320-325, June 1971.

  However, the techniques described in Non-Patent Document 1 to Non-Patent Document 4 are intended to reduce intermodulation distortion generated in a frequency band used for transmission, and harmonics and intermodulation distortion generated in other frequency bands are reduced. It is not intended to reduce. In addition, since these techniques do not assume that distortion compensation is performed simultaneously on signals in a plurality of frequency bands, it is difficult to cope with non-linear characteristics that differ for each frequency band, or Even if it can be coped with, there is a problem that the calculation becomes very complicated in performing the distortion compensation processing.

  In other words, the above distortion compensation technique is intended to reduce intermodulation distortion that occurs in a certain frequency band used for transmission, and does not reduce harmonics and intermodulation distortion that occur in other frequency bands. . In addition, it is difficult to handle different non-linear characteristics for each frequency band at the same time, and the compensation process is complicated, so a method suitable for multiband or widening of the radio band is required.

  The present invention has been made in view of such circumstances, a transmitter capable of suppressing the generation of unnecessary waves such as harmonics and intermodulation distortion generated when signals of a plurality of radio bands are simultaneously amplified, and distortion. An object is to provide a compensation method.

  In order to solve the above problems, the present invention provides a transmitter that simultaneously amplifies and transmits transmission signals in a plurality of frequency bands, and amplifies the plurality of transmission signals simultaneously, and the amplifier has an input frequency characteristic. An output frequency characteristic compensator that compensates the output frequency characteristic for a plurality of input signals based on an amplifier model that is separated and modeled into a nonlinear characteristic and an output frequency characteristic; and based on the nonlinear characteristic of the amplifier model. A nonlinear characteristic compensator that calculates a compensation signal for a signal obtained by compensation by the output frequency characteristic compensator by solving a nonlinear simultaneous equation corresponding to the output of the amplifier in the plurality of frequency bands; and the amplifier The input frequency characteristic of the model is compensated with respect to the compensation signal calculated by the nonlinear characteristic compensator, and the signal obtained by the compensation is compensated for in advance. A transmitter, characterized in that it comprises an input frequency characteristic compensation unit for outputting to the amplifier.

  Further, the present invention is the invention described in the above, wherein the nonlinear characteristic compensator calculates a compensation signal for suppressing an unnecessary wave generated in a frequency band of the transmission signal when solving the nonlinear simultaneous equations. Features.

  Further, the present invention is characterized in that, in the above-described invention, the nonlinear characteristic compensator calculates a compensation signal in a frequency band different from the frequency band of the signal obtained by the compensation by the output frequency characteristic compensator. To do.

  Further, the present invention is characterized in that, in the above-described invention, the nonlinear characteristic compensator does not output a compensation signal whose power level is lower than a predetermined first threshold among the calculated compensation signals. To do.

  In the invention described above, the output frequency characteristic compensation unit may not perform compensation for an input signal whose power level is lower than a predetermined second threshold among the input signals, or When the nonlinear characteristic compensator solves the nonlinear simultaneous equations, a signal having a power level lower than the second threshold among signals obtained by compensation by the output frequency characteristic compensator is equal to or higher than a predetermined order. This term is characterized in that the term of 0 is regarded as 0.

  Further, the present invention is the above-described invention, wherein one or both of the output frequency characteristic compensator and the input frequency characteristic compensator are a maximum value and a minimum value of gain in the frequency band of the input signal. When the difference is equal to or smaller than a predetermined third threshold value, no compensation is performed.

  Further, according to the present invention, in the above-described invention, the nonlinear characteristic compensator calculates in order from a compensation signal having a lower center frequency based on a harmonic component of the transmission signal when solving the nonlinear simultaneous equations. It is characterized by.

  Further, the present invention is the invention described in the above, wherein the nonlinear characteristic compensator performs intermodulation distortion by an iterative method with initial values of compensation signals calculated in ascending order of center frequencies based on harmonic components of the transmission signal. Alternatively, a compensation signal reflecting intermodulation distortion is calculated.

  According to the present invention, in the above-described invention, the signal obtained by the compensation by the input frequency characteristic compensation unit is provided in the frequency band of the transmission signal, provided between the input frequency characteristic compensation unit and the amplifier. A frequency converter that converts the frequency and outputs the converted signal to the amplifier is further provided.

  In order to solve the above problem, the present invention provides a distortion compensation method for compensating for distortion generated when a single amplifier amplifies signals in a plurality of frequency bands, and the amplifier includes input frequency characteristics and nonlinear characteristics. An output frequency characteristic compensation step for compensating the output frequency characteristic for a plurality of input signals based on an amplifier model separated and modeled into an output frequency characteristic, and based on the nonlinear characteristic of the amplifier model, A nonlinear characteristic compensation step for calculating a compensation signal for a signal obtained by compensation in the output frequency characteristic compensation step by solving a nonlinear simultaneous equation corresponding to the output of the amplifier in a plurality of frequency bands, and the amplifier model An input frequency characteristic is compensated for the compensation signal calculated in the nonlinear characteristic compensation step. A distortion compensation method characterized by having a frequency compensation step.

  According to the present invention, the characteristics of the amplifier are modeled for each of the characteristics of the input frequency characteristic, the nonlinear characteristic, and the output frequency characteristic, and compensation for the input signal is performed based on the nonlinear characteristic that does not depend on the frequency of the input signal and the output signal. The signal was calculated. This makes it easy to handle different nonlinear characteristics for each frequency band at the same time, and suppresses the generation of unnecessary waves such as harmonics and intermodulation distortion that occur when signals in multiple radio bands are simultaneously amplified. can do.

It is a schematic block diagram which shows the structure of the transmitter 10 in 1st Embodiment. 3 is a schematic block diagram showing a model of an amplifier 500 in the same embodiment. FIG. It is a flowchart which shows the distortion compensation process which the distortion compensation part 200 in the embodiment performs. It is a figure which shows the process of step S102 in the embodiment. 6 is a diagram illustrating a configuration example in which a band limiting unit 700 is provided between an amplifier 500 and an antenna 600. FIG. It is a figure which shows the transmitter 11 which is a modification of the transmitter 10 in 1st Embodiment. It is a schematic block diagram which shows the structure of the transmitter 20 in 2nd Embodiment. It is a flowchart which shows the distortion compensation process which the distortion compensation part 210 in the embodiment performs. It is a schematic block diagram which shows the structure of the transmitter 30 in 3rd Embodiment.

  Hereinafter, a transmitter and a distortion compensation method according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic block diagram illustrating a configuration of the transmitter 10 according to the first embodiment. The transmitter 10 transmits signals of a plurality of frequency bands B _{1 to} B _M. As shown in the figure, the transmitter 10 includes a signal generator 100, a distortion compensator 200, digital-analog converters (DACs) 300-1 to 300-M, a combiner 400, an amplifier 500, And an antenna 600.

The signal generation unit 100 generates transmission signals S _{1 to} S _M to be transmitted by digital signal processing. Transmission signals _{S 1} is a digital signal of the frequency band _{B 1.} Similarly, the transmission signals S _{2 to} S _M are digital signals in the frequency bands B _{2 to} B _M.

Distortion compensating unit 200 performs the transmission signal _S 1 to S _M to the signal generation unit 100 generates a processing for reducing unnecessary wave generated when the amplified transmission signal _S 1 to S _M in the amplifier 500. Here, the undesired wave generated upon amplifying the transmission signal _S 1 to S _M, for example, harmonics and resulting from the transmission signal _S 1 to S _M, intermodulation distortion and mixing occurring between the transmission signal _S 1 to S _M Modulation distortion and the like. The distortion compensation unit 200 is based on a model of the amplifier 500 using a generalized Wiener model.

  FIG. 2 is a schematic block diagram showing a model of the amplifier 500 in the present embodiment. The amplifier model obtained by modeling the amplifier 500 shown in the figure is modeled using the generalized Wiener model as described above. As shown in the figure, the amplifier 500 is modeled using a linear element 501, a linear element 503, and a nonlinear element 502. The linear element 501 is an element having the input frequency characteristics of the amplifier 500. The linear element 503 is an element having the output frequency characteristic of the amplifier 500. The nonlinear element 502 is an element having nonlinear characteristics of the amplifier 500. That is, the amplifier 500 is modeled separately into an input frequency characteristic, a nonlinear characteristic, and an output frequency characteristic.

  The model of the amplifier 500 is a model in which a linear element 501, a nonlinear element 502, and a linear element 503 are connected in cascade. In this model, an input signal is input to the linear element 501, an output of the linear element 501 is input to the nonlinear element 502, an output of the nonlinear element 502 is input to the linear element 503, and an output of the linear element 503 is output as an output signal. Is done.

Returning to FIG. 1, the description of the configuration of the transmitter 10 will be continued.
The distortion compensation unit 200 includes output frequency characteristic compensation units 203-1 to 203-M, a nonlinear characteristic compensation unit 202, and input frequency characteristic compensation units 201-1 to 201-M.

The output frequency characteristic compensation unit 203-i (i = 1, 2,..., M) is provided corresponding to the transmission signal S _i . The output frequency characteristic compensation unit 203-i has an inverse characteristic for compensating for the output frequency characteristic of the linear element 503 in the frequency band B _i of the transmission signal S _i . The output frequency characteristic compensator 203-i performs compensation based on the inverse characteristic on the input transmission signal S _i and outputs it to the nonlinear characteristic compensator 202.

The nonlinear characteristic compensator 202 amplifies unnecessary waves including harmonics, intermodulation distortion, and intermodulation distortion generated in the nonlinear element 502 with respect to the signals input from the output frequency characteristic compensators 203-2 to 203 -M. The signals of the respective frequency bands B _{1 to} B _M to be suppressed are calculated. The nonlinear characteristic compensation unit 202 outputs the calculated signals in the frequency bands B _{1 to} B _{M to} the input frequency characteristic compensation units 201-1 to 201-M as compensation signals.

The input frequency characteristic compensator 201-i (i = 1, 2,..., M) receives the input of the linear element 501 in the frequency band B _{i with} respect to the signal in the frequency band B _i input from the nonlinear characteristic compensator 202. It has an inverse characteristic for compensating the frequency characteristic. The input frequency characteristic compensator 201-i performs compensation based on the inverse characteristic on the input signal in the frequency band B _i and outputs the signal to the digital-analog converter 300-i.

  The digital-analog converter 300-i (i = 1, 2,..., M) converts the signal input from the distortion compensation unit 200 into an analog signal. The digital-analog converter 300-i outputs an analog signal obtained by the conversion to the synthesizer 400.

The combiner 400 combines the analog signals input from the digital-analog converters 300-1 to 300-M into one analog signal. The synthesizer 400 outputs the analog signal obtained by the synthesis to the amplifier 500.
Amplifier 500 amplifies the signal input from synthesizer 400 and transmits the amplified signal from antenna 600.

FIG. 3 is a flowchart illustrating a distortion compensation process performed by the distortion compensation unit 200 according to the present embodiment.
When distortion compensation processing is started in the distortion compensator 200, each output frequency characteristic compensator 203-i (i = 1, 2,..., M) has a frequency band of the transmission signal S _i input thereto. Accordingly, the output frequency characteristic of the linear element 503 is compensated for the transmission signal S _i (step S101).

  The non-linear characteristic compensator 202 is based on the signal compensated for the output frequency characteristic by the output frequency characteristic compensators 203-1 to 203-M and the non-linear characteristic of the non-linear element 502. Is calculated in the amplifier 500, and the calculated compensation signal is output to the input frequency characteristic compensators 201-1 to 201-M (step S102).

The input frequency characteristic compensators 201-1 to 201-M compensate the input frequency characteristic of the linear element 501 with respect to the compensation signal according to the frequency band of the compensation signal calculated by the nonlinear characteristic compensator 202, and obtain it by compensation. The obtained signals are output to the digital-analog converters 300-1 to 300-M (step S103), and the distortion compensation process is terminated.
By inputting the compensation signal calculated in the distortion compensation process to the amplifier 500, an amplified signal in which unnecessary waves during transmission are suppressed can be obtained.

Here, the process in step S102 will be described in detail.
FIG. 4 is a diagram illustrating the processing in step S102 in the present embodiment. The figure shows distortion compensation in the case where M frequency band signals are input and signals are output from M or more L frequency bands. The process in step S102 is an ideal output Y (ω ₁ ), which is a compensation signal corresponding to the input signals X ₁ (ω ₁ ),..., X _M (ω _M ) in the frequency band, which is an ideal output signal. _{..., Y (ω M),} Y (ω M + 1), ..., Y compensating signal X (omega _L) in the frequency domain for outputting the non-linear element _{502 '1 (ω 1),} ..., X' M (ω Corresponds to calculating _M ).

  The nonlinear characteristic of the nonlinear element 502 can be expressed by Volterra series expansion. When the input signal of the nonlinear element 502 is x (t) and the output signal is y (t), the output signal y (t) is 1).

In Expression (1), h _n (τ ₁ ,..., Τ _n ) is an n-th order kernel function, and y _n (t) is an output signal component expressed by an n-th order kernel function.

Next, when a signal x _m (t) (m = 1, 2,..., M) having a center frequency ω _m , an amplitude A _m , and a phase φ _m is synthesized and input to the amplifier 500, the input signal x (t ) And the frequency components X (ω) and X _m (ω) obtained by Fourier transforming the signal x _m (t) are expressed by the following equations (2) to (4).

n nucleation _{H n} the n-th order Fourier transform of a function _{(Ω 1, ..., Ω n} ) When the signal y _(t), a frequency component Y which _y n (t) is the Fourier transform (Omega), _{Y n} (Omega ) Becomes the following formulas (5) to (7).

Here, assuming that Ω1,..., Ωnε {± ω ₁ ,..., ± ω _M } from the center frequency ω _m (m = 1,..., M) of the signal x _m (t), output of the frequency ω _l The signal Y (ω _l ) (l = 1,..., L; M ≦ L) is expressed by the following equation (8).

Here, the frequency ω _l is the following equation (9).

Each term of Expression (8) will be described below.
(A) When ω ₁ = ω _m , Ω ₁ ,..., Ω _n ∈ {± ω _m }, each term represents the n-th order fundamental wave component of the input signal X _m (ω) on the frequency ω _m .
(B) When Ω ₁ ,..., Ω _n ∈ {± ω _i } (i = 1,..., M; i ≠ m), each term is on the frequency ω _l generated from the input signal X _i (ω). The nth-order harmonic component of is shown.
_{(C) ω l = ω m} , Ω 1, ..., Ω n ∈ {± ω 1, ..., ± ω M} Ω 1 of, ..., at least one of Omega _n is ± omega _m, the In the cases other than (A) and (B), each term indicates an nth-order intermodulation distortion component on the frequency ω _m generated between a plurality of input signals including the input signal X _m (t).
(D) In the cases other than the above (A) to (C), each term indicates an n-order intermodulation distortion component on the frequency ω ₁ generated between a plurality of input signals.

The calculation in step S102 for compensating for Y (ω _l ), which is the frequency component of the output signal corresponding to the frequency ω _l , with the compensation signal X ′ (ω _m ) is performed using the non-linear characteristic represented by equation (8). To do.

If a signal obtained by ideally linearly amplifying the input signal X (ω ₁ ) is Y ′ (ω ₁ ), the signal Y ′ (ω ₁ ) is expressed by the following equation (10).

If X ′ (Ω _k ) is substituted for X (Ω _k ) in equation (8) and the solution at that time is Y ′ (ω _l ), Y ′ (ω _l ) becomes the following equation (11).

Assuming that an equation is established for each frequency ω _l (l = 1,..., L), a non-linear system is applied to the compensation signal X ′ (ω _m ) that outputs the ideally linearly amplified signal Y ′ (ω _l ). Calculate by solving the equation. As a method for obtaining the compensation signal X ′ (ω _m ) satisfying this nonlinear simultaneous equation, a Newton method, an inverse system derived from nonlinear characteristics, or the like may be used.

Here, in order to compensate for the non-linearity, it is necessary to obtain in advance all the n-th order kernel functions H _n (Ω ₁ ,..., Ω _n ) that are complex coefficients of the equation (11). As shown in the 500 model configuration, the nonlinear characteristic does not depend on the input / output frequency characteristic. Therefore, when the frequency components input to the _n- th order kernel function H _n (Ω ₁ ,..., Ω _n ) are all a constant α times, the relationship of the following equation (12) is satisfied.

  Thereby, the number of estimated values of complex coefficients necessary for nonlinear distortion compensation can be reduced. In addition, a compensation signal can be calculated using complex coefficients estimated with signals of other frequencies even for signals having different frequencies.

In the equation (11), the frequency components of the output signal corresponding to the frequency ω ₁ are required by the number of frequencies obtained by the equation (9), and when considering the higher-order nonlinearity with a larger value of the order n, or When M is large as the number of input signals having different frequencies, the number L of frequency components to be compensated for increases, and the amount of calculation for solving equation (11) also increases. Therefore, by limiting the frequency component of the output signal to be compensated to the frequency band of the signal transmitted from the transmitter 10, the amount of calculation of Expression (11) can be reduced.

The limited frequency band is determined by the frequency gain of the transmitter 10 including the amplifier 500 to the antenna 600. For example, when a band limiter (bandpass filter) in the radio frequency band is connected between the amplifier 500 and the antenna 600, a frequency band in which the frequency gain from the amplifier 500 to the antenna 600 exceeds the threshold Th ₁ is transmitted. The frequency band shall be compensated. However, even if it does not correspond to the transmission frequency band, a band to be compensated for calculation may be added to the frequency band to be compensated.

  FIG. 5 is a diagram illustrating a configuration example in which a band limiting unit 700 is provided between the amplifier 500 and the antenna 600. FIG. 5A illustrates the configuration of the present embodiment illustrated in FIG. 1, and FIGS. 5B to 5E illustrate a configuration example in which the band limiting unit 700 is provided.

  The configuration example illustrated in FIG. 5B includes a band limiting unit 700 that allows a wideband signal or a plurality of bands to pass through, and transmits a signal output from the band limiting unit 700 from the antenna 600. The configuration example shown in FIG. 5C includes a band limiting unit 700 that allows a wideband or a plurality of bands of signals to pass therethrough. Transmit from 600-L.

  The configuration example shown in FIG. 5D includes band limiting units 700-1 to 700-L corresponding to the bands of signals to be transmitted, and an antenna 600 connected to each of the band limiting units 700-1 to 700-L. Signals are transmitted from −1 to 600-L. The configuration example shown in FIG. 5E includes band limiting units 700-1 to 700-L corresponding to the bands of signals to be transmitted, and signals output from the band limiting units 700-1 to 700-L are one. Transmit from antenna 600.

If the transmission frequency band as shown in FIG. 5 is determined by the band restriction unit 700, by the distortion compensation processing for the frequency band in which the frequency gain exceeds a threshold value Th _1, to reduce the amount of calculation in the distortion compensation processing be able to.

Further, when there is a transmission signal with a lower power level than other transmission signals among the transmission signals generated in the signal generation unit 100, the transmission signal with the lower power level is raised to a higher order in Equation (8). It is conceivable that this term has little influence on the value of the output signal including terms composed of other transmission signals. Therefore, a term in which a transmission signal having a power level smaller than a predetermined threshold Th ₂ is raised to the power of the order β is regarded as a minute value or “0 (zero)”, and the minute value obtained from the equation (8) is obtained. It is also possible to delete the value term from Equation (11) and reduce the amount of calculation when calculating Equation (11).

Next, omission of step S101 and step S103 in the distortion compensation process (FIG. 3) will be described.
The output frequency characteristic compensation units 203-1 to 203-M have a difference ΔG _O between the maximum value and the minimum value of the gain in each frequency band corresponding to the transmission signals S _{1 to} S _M input from the signal generation unit 100 in advance. If it is equal to or less than the predetermined threshold Th ₃ , the output frequency characteristics in the amplifier 500 are considered to be constant, and the input transmission signals S _{1 to} S _M can be output as they are without the compensation process in step S101. .

In addition, the input frequency characteristic compensators 201-1 to 201-M have a predetermined difference ΔG _i between the maximum value and the minimum value of the gain in each frequency band corresponding to the compensation signal input from the nonlinear characteristic compensator 202. If it is within the threshold Th _4, it assumed to be constant input frequency characteristic in the amplifier 500, a compensation signal which is input to omit the compensation process in step S103 may be output as it is.
Further, the distortion compensation unit 200 may be configured by removing both or one of the output frequency characteristic compensation units 203-1 to 203-M and the input frequency characteristic compensation units 201-1 to 201-M.

  In the present embodiment, the configuration in which the signals output from the input frequency characteristic compensators 201-1 to 201-M are analogized by the digital-analog converters 300-1 to 300-M and then combined is described. However, the present invention is not limited to this, and the signals output from the input frequency characteristic compensators 201-1 to 201-M may be combined before being analogized. FIG. 6 is a diagram illustrating a transmitter 11 that is a modification of the transmitter 10 according to the first embodiment. As shown in the figure, after the signals output from the input frequency characteristic compensation units 201-1 to 201-M are combined into one signal, the digital-analog converter 300 may convert the signal into an analog signal.

(Second Embodiment)
FIG. 7 is a schematic block diagram illustrating the configuration of the transmitter 20 according to the second embodiment. As shown in the figure, the transmitter 20 includes a signal generation unit 100, a distortion compensation unit 210, digital-analog converters 300-1 to 300-P, a combiner 400, an amplifier 500, and an antenna 600. It has. In the transmitter 20, the same components as those of the transmitter 10 (FIG. 1) in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The distortion compensation unit 210 includes output frequency characteristic compensation units 203-1 to 203-M, a nonlinear characteristic compensation unit 212, and input frequency characteristic compensation units 201-1 to 201-P.
The nonlinear characteristic compensator 212 in this embodiment corresponds to a frequency other than the frequency of the input signal, whereas the nonlinear characteristic compensator 202 in the first embodiment outputs a compensation signal corresponding to the frequency of the input signal. The difference is that a compensation signal is output or a compensation signal corresponding to a part of the frequencies of the input signal is output. The nonlinear characteristic compensation unit 212 outputs P (P ≠ M) compensation signals for M input signals.

Since the number of compensation signals output from the nonlinear characteristic compensation unit 212 is P, the number of input frequency characteristic compensation units 201 provided corresponding to the compensation signals and the number of digital-analog converters 300 are also the first. Unlike the embodiment, there are P pieces.
As described above, in the transmitter 20 according to the present embodiment, the configuration of the nonlinear characteristic compensator 212 provided in the distortion compensator 210 is different from that of the first embodiment (FIG. 1).

FIG. 8 is a flowchart showing a distortion compensation process performed by the distortion compensator 210 in the present embodiment.
When distortion compensation processing is started in the distortion compensator 210, each output frequency characteristic compensator 203-i (i = 1, 2,..., M) has a frequency band of the transmission signal S _i input thereto. In response, the output frequency characteristic of the linear element 503 is compensated for the transmission signal S _i (step S201). That is, in step S201, output frequency characteristics are compensated for the _M transmission signals S _{1 to} S _M.

The nonlinear characteristic compensator 212 receives a signal having a center frequency ω _m (m = 1,..., M) whose output frequency characteristics have been compensated by the output frequency characteristic compensators 203-1 to 203-M. The nonlinear characteristic compensation unit 212 compensates for the frequency component of the output signal corresponding to the frequency ω _l (l = 1,..., L) to be compensated, so that the compensation signal X ′ (ω _p ) ( p = 1,..., P; P ≠ M), and the calculated compensation signal X ′ (ω _p ) is output to the input frequency characteristic compensation units 201-1 to 201-P (step S202).

The input frequency characteristic compensator 201-i (i = 1,..., P) receives the compensation signal X ′ (ω _i ) from the nonlinear characteristic compensator 212. Input frequency characteristic compensator 201-i is 'in accordance with the frequency band of the (omega _i), the compensation signal X' input compensation signal X to compensate for the input frequency characteristic of the linear element 501 with respect to (ω _i). The input frequency characteristic compensation unit 201-i outputs the signal obtained by the compensation to the digital-analog converter 300-i (Step S203), and ends the distortion compensation process. That is, the input frequency characteristic compensators 201-1 to 201-P compensate the input frequency characteristics of the P compensation signals.
Thus, the accuracy of compensation can be improved by adding a compensation signal corresponding to a frequency other than the frequencies of the transmission signals S _{1 to} S _M.

Further, when the power level of the compensation signal calculated in step S202 is equal to or lower than a predetermined threshold Th ₅ , the output of the compensation signal may be stopped. Thereby, the calculation amount in the input frequency characteristic compensation units 201-1 to 201-P can be reduced, the operation amount of the digital-analog converters 300-1 to 300-P can be reduced, and the power consumption can be suppressed. Note that in the case of a configuration in which a signal is converted into an analog after the compensation signal is combined (for example, the configuration in FIG. 6), the calculation in the combiner 400 can be reduced. It may further limit the subject of the determination to stop the compensation signal output only to the compensation signal corresponding to a frequency other than the frequency of the transmission signal S ₁ to S _M, for example. As a result, it is possible to suppress the generation of unnecessary waves while protecting the output of the compensation signal for the transmission signal with low transmission power and suppressing an increase in the amount of calculation due to the addition of the compensation signal.

(Third embodiment)
FIG. 9 is a schematic block diagram illustrating a configuration of the transmitter 30 according to the third embodiment. As shown in the figure, the transmitter 30 includes a signal generator 120, a distortion compensator 220, digital-analog converters 300-1 to 300-M, and up-converters 800-1 to 800-M. A device 400, an amplifier 500, and an antenna 600 are provided. In the transmitter 30, the same components as those of the transmitter 10 (FIG. 1) in the second embodiment are denoted by the same reference numerals, and description thereof is omitted.

Signal generator 120, the intermediate signal s ₁ for generating an intermediate signal s ₁ ~s _M intermediate frequency band proportional relationship between the frequencies of the transmission signals S ₁ to S _M are maintained in a radio frequency band, to produce ˜s _M is output to the distortion compensator 220. The intermediate frequency band is, for example, 1 MHz and 2 MHz when the radio frequency band is 1 GHz and 2 GHz. The intermediate signals s _{1 to} s _M are signals including information to be transmitted, similar to the transmission signals S _{1 to} S _M.

The distortion compensation unit 220 includes output frequency characteristic compensation units 223-1 to 223 -M, a nonlinear characteristic compensation unit 222, and input frequency characteristic compensation units 221-1 to 221 -M.
Output frequency characteristic compensation unit 223-i (i = 1, ..., M) , to the intermediate signal _{s i} to the signal generating unit 120 has generated, the frequency band of the transmission signal _{S i} corresponding to the intermediate signal _{s i B i} Compensation corresponding to the output frequency characteristic of the linear element 503 is performed. That is, the output frequency characteristic compensation unit 223-i performs compensation for the intermediate signal s _i by the inverse characteristic of the output frequency characteristic of the linear element 503 in the frequency band B _i . The output frequency characteristic compensation unit 223-i outputs a signal obtained by the compensation to the nonlinear characteristic compensation unit 222.

The nonlinear characteristic compensator 222 amplifies unnecessary waves including harmonics, intermodulation distortion, and intermodulation distortion generated in the nonlinear element 502 with respect to the signals input from the output frequency characteristic compensation units 223-1 to 223 -M. At 500, compensation signals in the intermediate frequency band corresponding to the frequency bands B _{1 to} B _M to be suppressed are calculated. That is, the nonlinear characteristic compensation unit 222 performs nonlinear characteristic compensation on the signals input from the output frequency characteristic compensation units 223-1 to 223 -M while maintaining the intermediate frequency band signal, and is obtained by compensation. The intermediate frequency band compensation signal is output to the input frequency characteristic compensation units 221-1 to 221-M.

The input frequency characteristic compensation unit 221-i (i = 1,..., M) receives the input frequency characteristic of the linear element 501 in the frequency band B _{i with} respect to the compensation signal in the intermediate frequency band input from the nonlinear characteristic compensation unit 222. Compensation corresponding to. The input frequency characteristic compensation unit 221-i (i = 1,..., M) outputs a compensation signal obtained by compensation of the input frequency characteristic and in the intermediate frequency band to the digital-analog converter 300-i. To do.

  The up-converter 800-i (i = 1,..., M) performs frequency conversion from the intermediate frequency band to the radio frequency band, and synthesizes the compensation signal converted into an analog signal by the digital-analog converter 300-i. Output to the device 400.

As described above, the transmitter 30 in the present embodiment performs the compensation for the output frequency characteristic, the nonlinear characteristic, and the input frequency characteristic in the intermediate frequency band having a frequency lower than the radio frequency band in the first and second implementations. It differs from the transmitters 10 and 20 in the form. Another implementation is that it includes up-converters 800-1 to 800-M for converting a compensation signal obtained by compensation for output frequency characteristics, nonlinear characteristics, and input frequency characteristics into signals in a radio frequency band. It differs from the transmitters 10 and 20 in the form.
Note that the distortion compensation processing performed by the distortion compensation unit 220 is the same as the distortion compensation processing in the first embodiment except that the frequency band of the target signal is different, and thus description thereof is omitted.

  In the transmitter 10 in the first embodiment or the transmitter 20 in the second embodiment, the transmission signal input to the distortion compensation unit 200 is a radio frequency band signal and outputs a radio frequency band compensation signal. . However, in the digital-analog converters 300-1 to 300-M, the compensation signal in the radio frequency band may not be correctly converted into analog depending on the sampling rate. In such a case, there is a possibility that unnecessary waves generated in the amplifier 500 cannot be sufficiently suppressed. On the other hand, since the transmitter 30 in this embodiment is analogized as a compensation signal in the intermediate frequency band that is a low frequency, the compensation signal can be correctly analogized. Thereby, the transmitter 30 can suppress unnecessary waves generated in the amplifier 500 regardless of the sampling rate of the digital-analog converters 300-1 to 300-M.

  In addition, a digital-analog converter that converts a radio frequency band signal into analog is generally more expensive and consumes higher power than a digital-analog converter that converts a low frequency band signal into analog. Therefore, by converting the compensation signal into a signal in the intermediate frequency band and mounting the transmitter using a digital-analog converter with a low sampling rate, the manufacturing cost and power consumption of the transmitter can be reduced.

  As described in the above embodiments, the transmitters 10, 11, 20, and 30 limit interference waves such as harmonics and mixer spurious signals within the transmission band by calculating a compensation signal in the distortion compensation process. Without being able to suppress it. Further, when modeling the amplifier 500, it is possible to compensate for the non-linear characteristic without depending on the frequency characteristic by dividing the input frequency characteristic, the non-linear characteristic, and the output frequency characteristic, thereby reducing the calculation complexity. Thus, it is possible to simultaneously compensate for non-linear distortion in a plurality of bands.

  Here, nonlinear characteristic compensation in the case where the frequency band of the transmission signal has an integer multiple relationship and the harmonics are dominant among the unwanted waves superimposed on other frequency signals when transmitting each transmission signal simultaneously The calculation of the compensation signal by the unit 202 will be described. The same applies to the nonlinear characteristic compensator 212 in the second embodiment and the nonlinear characteristic compensator 222 in the third embodiment.

As an example, a transmission signal X ₁ (ω) having a center frequency ω, amplitude A ₁ and phase φ ₁ and a transmission signal X ₂ (3ω) having a center frequency 3ω, amplitude A ₂ and phase φ ₂ are transmitted simultaneously. The calculation method of the compensation signal X ′ ₁ (ω) of the amplitude A ′ ₁ phase φ ′ ₁ and the compensation signal X ′ ₂ (3ω) of the amplitude A ′ ₂ phase φ ′ ₂ by the nonlinear characteristic compensation unit 202 will be described.

  When the fifth-order nonlinear simultaneous equations for the transmission signal and the compensation signal are established using the equations (10) and (11), the following equations (13) and (14) are obtained.

  Here, in the terms of the simultaneous equations of the equations (13) and (14), if only the harmonic component is dominant as an unnecessary wave, the intermodulation distortion component and the intermodulation distortion component are omitted. Thus, the following equations (15) and (16) can be arranged as equations of only the fundamental wave component and the harmonic component.

  Substituting the amplitude and phase of the transmission signal and the amplitude and phase of the compensation signal into the equations (15) and (16), the following equations (17) and (18) are obtained.

At this time, assuming that the complex coefficients indicated by the first, third, and fifth order kernel functions are obtained in advance, the compensation signal X ′ ₁ (ω) of the amplitude A ′ ₁ and the phase φ ′ ₁ is obtained from Expression (17). Can be requested. By substituting the compensation signal X ′ ₁ (ω) into the equation (18), the compensation signal X ′ ₂ (3ω) having the amplitude A ′ ₂ and the phase φ ′ ₂ can be obtained.

  As described above, when the harmonic component is considered to be dominant in the unnecessary wave due to the nonlinear distortion generated when the M transmission signals having the center frequency of the integer multiple are simultaneously transmitted, the lowest frequency compensation is performed. By calculating in order from the signal, the amount of calculation of Expression (11) can be reduced, and the calculation can be simplified.

  Furthermore, in order to improve the accuracy of the compensation signal by reflecting the intermodulation distortion component and the intermodulation distortion component omitted so far, an iterative method using the compensation signal calculated only from the fundamental wave component and the harmonic component as an initial value. May be used. Thereby, the accuracy of the compensation signal can be improved, and unnecessary waves can be further suppressed.

  Note that a program for realizing the functions of the distortion compensation unit or transmitter in the present invention is recorded on a computer-readable recording medium, and the program recorded on the recording medium is read into a computer system and executed. Thus, distortion compensation processing may be performed. Here, the “computer system” includes an OS and hardware such as peripheral devices. The “computer system” includes a WWW system having a homepage providing environment (or display environment). The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may be for realizing a part of the functions described above. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer system, and what is called a difference file (difference program) may be sufficient.

DESCRIPTION OF SYMBOLS 10, 11, 20, 30 ... Transmitter 100, 120 ... Signal generation part 200,210,220 ... Distortion compensation part 201-1,201-M, 201-P, 221-1,221-M ... Input frequency characteristic compensation Units 202, 212, 222... Nonlinear characteristic compensation units 203-1, 203-M, 223-1, 223-M... Output frequency characteristic compensation units 300, 300-1, 300-M, 300-P. 400: Synthesizer 500 ... Amplifier 501,503 ... Linear element 502 ... Nonlinear element 600,600-1,600-L ... Antenna 700,700-1,700-L ... Band limiter 800-1,800-M ... Upconverter

Claims (10)

A transmitter that simultaneously amplifies and transmits transmission signals in a plurality of frequency bands,
An amplifier for simultaneously amplifying a plurality of the transmission signals;
An output frequency characteristic compensator for compensating the output frequency characteristic for a plurality of input signals based on an amplifier model obtained by separating the amplifier into an input frequency characteristic, a non-linear characteristic, and an output frequency characteristic;
Based on the nonlinear characteristic of the amplifier model, a compensation signal for the signal obtained by the compensation by the output frequency characteristic compensation unit is calculated by solving a nonlinear simultaneous equation corresponding to the output of the amplifier in the plurality of frequency bands. A non-linear characteristic compensator to
An input frequency characteristic compensator for compensating the input frequency characteristic of the amplifier model with respect to a compensation signal calculated by the nonlinear characteristic compensator, and outputting a signal obtained by the compensation to the amplifier. Transmitter. The transmitter of claim 1, comprising:
The nonlinear characteristic compensator is
A transmitter for calculating a compensation signal for suppressing unnecessary waves generated in a frequency band of the transmission signal when solving the nonlinear simultaneous equations. The transmitter according to claim 1 or 2, wherein
The nonlinear characteristic compensator is
A transmitter characterized in that a compensation signal in a frequency band different from a frequency band of a signal obtained by compensation by the output frequency characteristic compensation unit is calculated. The transmitter according to any one of claims 1 to 3, wherein
The nonlinear characteristic compensator is
Of the calculated compensation signals, a compensation signal having a power level lower than a predetermined first threshold is not output. The transmitter according to any one of claims 1 to 4, wherein
The output frequency characteristic compensator does not perform compensation for an input signal whose power level is lower than a predetermined second threshold among the input signals. Alternatively, the nonlinear characteristic compensator is configured to solve the nonlinear simultaneous equations. In addition, regarding a signal having a power level lower than the second threshold among signals obtained by compensation by the output frequency characteristic compensation unit, a term of a predetermined order or more is regarded as 0. . The transmitter according to any one of claims 1 to 5, wherein
One or both of the output frequency characteristic compensation unit and the input frequency characteristic compensation unit are
The transmitter is characterized in that no compensation is performed when the difference between the maximum value and the minimum value of the gain in the frequency band of the input signal is equal to or smaller than a predetermined third threshold value. The transmitter according to any one of claims 1 to 6, wherein
The nonlinear characteristic compensator is
When the nonlinear simultaneous equations are solved, the transmitter is calculated in order from a compensation signal having a lower center frequency based on a harmonic component of the transmission signal. The transmitter according to claim 7, wherein
The nonlinear characteristic compensator is
A transmitter characterized in that a compensation signal reflecting intermodulation distortion or intermodulation distortion is calculated by an iterative method with compensation signals calculated in ascending order of center frequencies based on harmonic components of the transmission signal as initial values. The transmitter according to any one of claims 1 to 8, wherein
A frequency converter provided between the input frequency characteristic compensator and the amplifier, and frequency-converting a signal obtained by compensation by the input frequency characteristic compensator into a frequency band of the transmission signal and outputting the frequency to the amplifier. A transmitter further comprising: A distortion compensation method for compensating for distortion that occurs when a single amplifier amplifies signals in a plurality of frequency bands,
An output frequency characteristic compensation step for compensating the output frequency characteristic for a plurality of input signals based on an amplifier model obtained by separating the amplifier into an input frequency characteristic, a non-linear characteristic, and an output frequency characteristic.
Based on the nonlinear characteristic of the amplifier model, a compensation signal for the signal obtained by the compensation in the output frequency characteristic compensation step is calculated by solving a nonlinear simultaneous equation corresponding to the output of the amplifier in the plurality of frequency bands. Non-linear characteristic compensation step,
An input frequency compensation step of compensating the input frequency characteristic of the amplifier model with respect to a compensation signal calculated in the nonlinear characteristic compensation step.

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