CN104883140A - Digital predistortion device based on broadband radio frequency power amplifier - Google Patents

Abstract

The invention discloses a digital predistortion device based on a broadband radio frequency power amplifier, relates to the technical field of wireless communication, and overcomes the defects that the traditional digital predistortion method in the prior art requires a higher sampling rate of an ADC when being applied to a broadband communication system, so that the hardware cost of digital predistortion processing and the system power consumption are greatly increased. According to the digital predistortion device based on the broadband radio frequency power amplifier, the band-pass filter is added in the feedback channel and used for limiting the bandwidth of the radio frequency signal output by the broadband radio frequency power amplifier, so that the minimum bandwidth of the feedback radio frequency signal output by the band-pass filter is the bandwidth of the baseband signal input by the digital predistorter.

Description

Digital predistortion device based on broadband radio frequency power amplifier

technical field

The invention relates to the technical field of wireless communication, in particular to a digital pre-distortion device based on a broadband radio frequency power amplifier.

Background technique

With the continuous development of wireless communication technologies such as LTE-advanced and IEEE802.11ac, the use of complex modulation methods and wider signal bandwidths have become indispensable characteristics of transmitted signals, and these characteristics make the output behavior of RF power amplifiers become more complex. for complex. In the wireless communication transmission system, the nonlinear characteristic of the RF power amplifier not only brings distortion to the transmission signal, but also causes great waste to the energy consumption of the system. Therefore, research on digital predistortion technology for wideband radio frequency power amplifiers is particularly important.

Existing digital predistortion methods mainly perform linearization processing on narrowband signals. In a narrowband communication system, since the bandwidth of the input signal and the output signal of the RF power amplifier are relatively small compared with the sampling rate of the analog-to-digital converter (ADC), the traditional digital predistortion method is used, that is, the RF power amplifier It is feasible to capture the input signal and the output signal to calculate the compensation coefficient required for digital pre-distortion processing.

However, in broadband communication systems similar to LTE-advanced and IEEE802.11ac, since the input signal bandwidth of the RF power amplifier reaches 80MHz, the output signal bandwidth will be close to 400MHz due to the spectrum spread phenomenon of the power amplifier. Distortion method requires the analog-to-digital converter (ADC) to have a sampling rate close to 1GSPS (Gigabit Samples Per Second, that is, Gigabit Samples Per Second). It can be seen that when the traditional digital pre-distortion method is applied to a broadband communication system The sampling rate of the required ADC is relatively high, which greatly increases the hardware cost of the digital pre-distortion processing, and also significantly increases the power consumption of the system.

Contents of the invention

The invention provides a digital predistortion device based on a broadband radio frequency power amplifier, which can reduce the sampling rate of ADC in the process of digital predistortion processing, thereby reducing system power consumption and hardware cost required for digital predistortion processing.

The present invention provides a digital predistortion device based on a broadband radio frequency power amplifier. The device includes a forward channel and a feedback channel, wherein the forward channel includes a digital predistorter, a digital-to-analog converter, a radio frequency transmission module and a broadband A radio frequency power amplifier, the feedback channel includes a radio frequency receiving module, an analog-to-digital converter, and a coefficient calculation module, and the feedback channel also includes a bandpass filter and an equivalent nonlinear processing module, wherein the digital predistorter, respectively It is connected with the coefficient calculation module and the digital-to-analog converter, and is used to perform pre-distortion processing on the input forward baseband signal according to the compensation coefficient output by the coefficient calculation module, and convert the pre-distortion processed forward baseband signal to sent to said digital-to-analog converter;

The digital-to-analog converter is connected to the radio frequency transmission module, and is used to perform digital-to-analog conversion on the pre-distorted forward baseband signal to obtain a forward analog signal, and transmit the forward analog signal obtained through the digital-to-analog conversion to the radio frequency sending module;

The radio frequency sending module is connected with the broadband radio frequency power amplifier, and is used for up-converting the forward analog signal to obtain a forward radio frequency signal, and sending the forward radio frequency signal to the broadband radio frequency power amplifier ;

The broadband radio frequency power amplifier is used to amplify the forward radio frequency signal output by the radio frequency transmission module;

The band-pass filter is connected to the radio frequency receiving module, and is used to filter the forward radio frequency signal output by the broadband radio frequency power amplifier coupled to the feedback channel to obtain a feedback radio frequency signal, and transfer the feedback The radio frequency signal is sent to the radio frequency receiving module, wherein the minimum bandwidth of the feedback radio frequency signal is the bandwidth of the forward baseband signal input by the digital predistorter;

The radio frequency receiving module is connected to the analog-to-digital converter, and is used for down-converting the feedback radio frequency signal to obtain a feedback analog signal, and sending the feedback analog signal to the analog-to-digital converter;

The analog-to-digital converter is connected to the coefficient calculation module, and is used to perform analog-to-digital conversion on the feedback analog signal output by the radio frequency receiving module to obtain a feedback baseband signal;

The coefficient calculation module is respectively connected with the analog-to-digital converter, the equivalent nonlinear processing module and the digital predistorter, and is used to output the feedback baseband signal according to the analog-to-digital converter and the etc. Calculate the compensation coefficient of the digital pre-distortion based on the equivalent baseband signal output by the effective nonlinear processing module, and send the compensation coefficient of the digital pre-distortion to the digital pre-distorter until the output signal of the broadband radio frequency power amplifier meets the system requirements ;

The equivalent nonlinear processing module is configured to perform equivalent nonlinear processing on the forward baseband signal input by the digital predistorter to obtain an equivalent baseband signal.

Optionally, the coefficient calculation module is configured to obtain an error function capable of characterizing the nonlinear characteristics of the power amplifier according to the feedback baseband signal output by the analog-to-digital converter and the equivalent baseband signal output by the equivalent nonlinear processing module , calculating a compensation coefficient of the digital predistortion by using the error function, and sending the calculated compensation coefficient to the digital predistorter.

Optionally, the forward channel further includes an acquisition module, wherein the acquisition module is respectively connected to the digital predistorter and the equivalent nonlinear processing module, and is used to acquire The forward baseband signal of the distorter, and send the collected forward baseband signal to the digital predistorter and the equivalent nonlinear processing module.

The digital predistortion device based on the broadband radio frequency power amplifier provided by the present invention adds a bandpass filter in the feedback channel, and the bandpass filter is used to limit the bandwidth of the radio frequency signal output by the broadband radiofrequency power amplifier, so that The minimum bandwidth of the feedback radio frequency signal output by the bandpass filter is the bandwidth of the baseband signal input by the digital predistorter; at the same time, by adding an equivalent nonlinear processing module in the feedback channel, the used for digital The forward baseband signal input by the predistorter is subjected to equivalent non-linear processing to obtain an equivalent baseband signal. Compared with the existing technology, on the one hand, it can reduce the sampling rate of the analog-to-digital converter in the digital pre-distortion process, and avoid spectrum aliasing, so as to ensure that the broadband communication system can use a lower sampling rate for broadband radio frequency The RF signal output by the power amplifier is sampled, thereby reducing the system power consumption and the hardware cost required for digital pre-distortion processing; on the other hand, it can obtain the nonlinearity of the broadband RF power amplifier through the equivalent pre-distortion input signal and feedback signal characteristics, so that the same linearization effect as the traditional digital predistortion method can be achieved.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is the structural representation of an embodiment of the digital predistortion device based on the broadband radio frequency power amplifier of the present invention;

Fig. 2 is the polynomial functional block diagram of equivalent nonlinear processing module described in the present invention;

Fig. 3 is a functional block diagram of the look-up table of the equivalent nonlinear processing module in the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

As shown in Figure 1, an embodiment of the present invention provides a digital predistortion device based on a broadband radio frequency power amplifier, the device forward channel and feedback channel, wherein the forward channel includes a digital predistorter 1, a digital-to-analog Converter 2, radio frequency transmission module 3 and broadband radio frequency power amplifier 4, the feedback channel includes bandpass filter 5, radio frequency reception module 6, analog-to-digital converter 7, coefficient calculation module 8 and equivalent nonlinear processing module 9.

The digital predistorter 1 is connected to the coefficient calculation module 8 and the digital-to-analog converter 2 respectively, and is used to perform predistortion processing on the input forward baseband signal according to the compensation coefficient output by the coefficient calculation module 8 , and send the pre-distorted forward baseband signal to the digital-to-analog converter 2;

In this embodiment, the power amplifier model of the digital predistorter 1 adopts a memory polynomial model, and its output signal is expressed as In the formula, x(n) represents the pre-distortion input signal, y(n) represents the pre-distortion output signal, a _kq represents the coefficient of pre-distortion processing, where Q represents the memory depth, and K represents the polynomial order. It should be noted that the memory polynomial model used in this embodiment is only one of the power amplifier models, and the main content of the present invention is not limited to memory polynomials, but also includes other power amplifier models based on polynomial forms.

The digital-to-analog converter 2 is connected to the radio frequency transmission module 3, and is used to perform digital-to-analog conversion on the pre-distorted forward baseband signal to obtain a forward analog signal, and convert the forward analog signal obtained through the digital-to-analog conversion The signal is sent to the radio frequency sending module;

The radio frequency sending module 3 is connected with the broadband radio frequency power amplifier 4, and is used for up-converting the forward analog signal to obtain a forward radio frequency signal, and sending the forward radio frequency signal to the broadband radio frequency power amplifier 4;

The broadband radio frequency power amplifier 4 is configured to amplify the forward radio frequency signal output by the radio frequency transmission module 3;

The bandpass filter 5 is connected to the radio frequency receiving module 6, and is used to filter the forward radio frequency signal output by the broadband radio frequency power amplifier 4 coupled to the feedback channel to obtain a feedback radio frequency signal, and The feedback radio frequency signal is sent to the radio frequency receiving module 6, wherein the minimum bandwidth of the feedback radio frequency signal is the bandwidth of the forward baseband signal input by the digital predistorter 1;

The radio frequency receiving module 6 is connected with the analog-to-digital converter 7, and is used for down-converting the feedback radio frequency signal to obtain a feedback analog signal, and sending the feedback analog signal to the analog-to-digital converter 7 ;

The analog-to-digital converter 7 is connected to the coefficient calculation module 8, and is used to perform analog-to-digital conversion on the feedback analog signal output by the radio frequency receiving module 6 to obtain a feedback baseband signal;

The coefficient calculation module 8 is respectively connected with the analog-to-digital converter 7, the equivalent nonlinear processing module 9 and the digital predistorter 1, and is used for feedback baseband output according to the analog-to-digital converter 7 signal and the equivalent baseband signal output by the equivalent nonlinear processing module 9 to calculate the compensation coefficient of the digital pre-distortion, and send the compensation coefficient of the digital pre-distortion to the digital pre-distorter 1 until the wideband radio frequency power The output signal of the amplifier 4 meets the system requirements;

Further, the coefficient calculating module 8 calculates the coefficients in the digital predistorter according to the collected data. In traditional methods, an indirect structure is generally used to calculate the predistortion coefficients. The basic basis is that there is only the influence of the characteristics of the power amplifier between the output signal of the predistorter and the feedback signal, so as to ensure that the difference between the output signal of the digital predistorter and the feedback signal can correctly reflect the nonlinear characteristics of the power amplifier. In the present invention, a band-pass filter is introduced in the feedback loop, which destroys the relationship between the predistortion output signal and the feedback signal. Between the input signal and the feedback signal of the digital predistorter, the influence of the band-pass filter is relatively small, and the influence of the power amplifier is dominant. It can be considered that the difference between the two reflects the nonlinear characteristics of the power amplifier. Therefore, the present invention adopts a direct structure digital predistortion system.

The equivalent nonlinear processing module 9 is configured to perform equivalent nonlinear processing on the forward baseband signal input by the digital predistorter 1 to obtain an equivalent baseband signal.

In the traditional digital predistortion processing system, the equivalent nonlinear processing module generally adopts the same model as the digital predistorter to generate the equivalent baseband signal, but in the present invention, the coefficient calculation of the digital predistorter adopts The direct structure operation introduces a band-pass filter on the feedback loop at the same time, so in order to eliminate these effects, a low-pass filter needs to be introduced in the equivalent processing module.

Specifically, polynomial function forms and lookup table forms can be used in the realization of equivalent nonlinear processing modules. The polynomial function form is designed based on the mathematical logic module, as shown in Figure 2. The form of the lookup table uses the amplitude of the input signal as the address index of the predistortion coefficient, as shown in FIG. 3 .

As shown in FIG. 2 , taking polynomial implementation as an example, a schematic structural diagram of the equivalent nonlinear processing module 9 of the present invention is given. where the signal z(n) is expressed as In the formula, x(n) represents the baseband input signal, z(n) represents the intermediate output signal of the equivalent nonlinear processing module, where Q represents the memory depth, K represents the polynomial order, and the values of Q and K are respectively related to the digital predistortion processing The values of memory depth and polynomial order in device 1 are the same. The signal z(n) then enters the low-pass filter. In order to eliminate the influence of the band-pass filter on the calculation of the coefficients of the digital predistorter, the transmission bandwidth of the low-pass filter is the same as that of the band-pass filter 5, and its in-band characteristic is the same as that of the band-pass filter The in-band characteristics of filter 5 remain consistent. In Fig. 2, for the simplicity of the graphical representation, only the structural schematic diagram of the equivalent nonlinear processing module when the memory depth Q is 0 is given. Generally, it can also be 3 or 6, etc., depending on the digital pre-set Value of Q in Distortion Processor 1.

As shown in FIG. 3 , taking the implementation of the lookup table as an example, a schematic structural diagram of the equivalent nonlinear processing module 9 of the present invention is given. The specific lookup table can be expressed as x(n) represents the baseband input signal, K represents the polynomial order, and the values of Q and K are respectively the same as the memory depth and the polynomial order in the digital predistortion processor 1 . The signal then enters the low-pass filter. In order to eliminate the influence of the band-pass filter on the calculation of the coefficients of the digital predistorter, the transmission bandwidth of the low-pass filter is the same as that of the band-pass filter 5, and its in-band characteristic is the same as that of the band-pass filter 5. The in-band characteristics remain the same. In Fig. 3, for the simplicity of the graphical representation, only the structural schematic diagram of the equivalent nonlinear processing module when the memory depth Q is 0 is given. Generally, it can also be 3 or 6, etc., depending on the digital preset Value of Q in Distortion Processor 1.

The digital predistortion device based on the broadband radio frequency power amplifier provided by the present invention adds a bandpass filter in the feedback channel, and the bandpass filter is used to limit the bandwidth of the radio frequency signal output by the broadband radiofrequency power amplifier, so that The minimum bandwidth of the feedback radio frequency signal output by the bandpass filter is the bandwidth of the baseband signal input by the digital predistorter; at the same time, by adding an equivalent nonlinear processing module in the feedback channel, the used for digital The forward baseband signal input by the predistorter is subjected to equivalent non-linear processing to obtain an equivalent baseband signal. Compared with the existing technology, on the one hand, it can reduce the sampling rate of the analog-to-digital converter in the digital pre-distortion process, and avoid spectrum aliasing, so as to ensure that the broadband communication system can use a lower sampling rate for broadband radio frequency The RF signal output by the power amplifier is sampled, thereby reducing the system power consumption and the hardware cost required for digital pre-distortion processing; on the other hand, it can obtain the nonlinearity of the broadband RF power amplifier through the equivalent pre-distortion input signal and feedback signal characteristics, so that the same linearization effect as the traditional digital predistortion method can be achieved.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (3)

1. the digital predistortion apparatus based on wide-band radio frequency power amplifier, described device comprises forward path and feedback path, wherein, described forward path comprises digital predistorter, digital to analog converter, radio frequency sending module and wide-band radio frequency power amplifier, described feedback path comprises Receiver Module, analog to digital converter and coefficients calculation block, it is characterized in that, described feedback path also comprises band pass filter and equivalent Nonlinear processing module, wherein

Described digital predistorter, be connected with described coefficients calculation block and described digital to analog converter respectively, the forward direction baseband signal of penalty coefficient to input for exporting according to described coefficients calculation block carries out pre-distortion, and the forward direction baseband signal through pre-distortion is sent to described digital to analog converter;

Described digital to analog converter, is connected with described radio frequency sending module, obtains forward simulation signal, and the forward simulation signal obtained through digital-to-analogue conversion is sent to described radio frequency sending module for carrying out digital-to-analogue conversion to the forward direction baseband signal through pre-distortion;

Described radio frequency sending module, is connected with described wide-band radio frequency power amplifier, for carrying out up-conversion to described forward simulation signal, obtains forward direction radiofrequency signal, and described forward direction radiofrequency signal is sent to described wide-band radio frequency power amplifier;

Described wide-band radio frequency power amplifier, the forward direction radiofrequency signal for exporting described radio frequency sending module carries out amplification process;

Described band pass filter, be connected with described Receiver Module, forward direction radiofrequency signal for exporting the described wide-band radio frequency power amplifier being coupled to described feedback path is carried out filtering process and is obtained feeding back radiofrequency signal, and described feedback radiofrequency signal is sent to described Receiver Module, wherein, the minimum bandwidth of described feedback radiofrequency signal is the bandwidth of the forward direction baseband signal of described digital predistorter input;

Described Receiver Module, is connected with described analog to digital converter, for carrying out down-conversion to described feedback radiofrequency signal, obtains feedback analog signal, and described feedback analog signal is sent to described analog to digital converter;

Described analog to digital converter, is connected with described coefficients calculation block, and the feedback analog signal for exporting described Receiver Module carries out analog-to-digital conversion and obtains feeding back baseband signal;

Described coefficients calculation block, be connected with described analog to digital converter, described equivalent Nonlinear processing module and described digital predistorter respectively, for the penalty coefficient of the Equivalent Base-Band calculated signals digital pre-distortion that the feedback baseband signal that exports according to described analog to digital converter and described equivalent Nonlinear processing module export, and the penalty coefficient of described digital pre-distortion is sent described digital predistorter, until the output signal of described wide-band radio frequency power amplifier meets system requirements;

Described equivalent Nonlinear processing module, the forward direction baseband signal for inputting described digital predistorter is carried out equivalent Nonlinear Processing and is obtained Equivalent Base-Band signal.

2. device according to claim 1, it is characterized in that, described coefficients calculation block, the Equivalent Base-Band signal exported for the feedback baseband signal that exports according to described analog to digital converter and described equivalent Nonlinear processing module obtains characterizing the error function of non-linearity of power amplifier characteristic, utilize described error function to calculate the penalty coefficient of described digital pre-distortion, and the described penalty coefficient calculated is sent to described digital predistorter.

3. device according to claim 1 and 2, it is characterized in that, described forward path also comprises acquisition module, wherein, described acquisition module, being connected with described digital predistorter and described equivalent Nonlinear processing module respectively, for gathering the forward direction baseband signal to described digital predistorter to be entered, and the described forward direction baseband signal collected being sent to described digital predistorter and described equivalent Nonlinear processing module.