Frequency domain predistortion method for power amplifier

Abstract

The invention discloses a frequency domain predistortion method for a power amplifier, which relates to the technical field of power amplifiers, and comprises the following steps: firstly, acquiring an input signal and carrying out frequency domain predistortion processing to obtain an output signal; performing inverse Fourier transform, digital-to-analog conversion and frequency conversion on the output signal, and performing power amplification through a power amplifier; coupling back the output power amplifier signal, sequentially carrying out frequency conversion and analog-to-digital conversion, then sending the signal into a digital processor, and then carrying out frequency domain division on a sampling signal and an input signal to obtain a transfer function; performing frequency domain multiplication on the transfer function and the last output signal to obtain a frequency domain signal of the current output signal; performing inverse Fourier transform to obtain a corresponding time domain signal, performing digital-to-analog conversion and frequency conversion, and inputting the time domain signal into a power amplifier for power amplification; and repeating the steps, and continuously carrying out iteration. According to the invention, the nonlinear distortion problem of the power amplifier can be effectively solved, the cost and the implementation complexity are greatly reduced, and the practicability is very high.

Description

Technical Field

[0001] The present invention relates to the technical field of power amplifiers, and in particular to a frequency domain predistortion method for a power amplifier. Background Art

[0002] The power amplifier is a key component in radar detection, wireless communication and other equipment. Its main function is to amplify the milliwatt modulated signal to be amplified to a few watts to several kilowatts, so as to meet the radiation power requirements of the equipment. Usually the power amplifier works in the saturation amplification area to obtain the maximum peak transmission power and the highest working efficiency, but it also brings nonlinear distortion caused by the intermodulation of the power amplifier itself. In order to improve the efficiency of the use of the power amplifier and the spectrum utilization rate, digital pre-distortion technology is introduced. Digital pre-distortion technology has been widely studied because of its good correction performance and easy implementation. Digital pre-distortion technology is also often used in industry to complete the correction of the nonlinearity of the power amplifier. Digital pre-distortion refers to the distortion of the baseband signal according to the nonlinear characteristics of the power amplifier, and a pre-distortion signal complementary to the nonlinearity of the power amplifier is obtained. Ideally, the pre-distorter and the power amplifier are cascaded to obtain a linear output, thereby realizing the correction of the nonlinearity of the power amplifier.

[0003] The existing technology for implementing nonlinear correction of power amplifiers based on digital predistortion mainly includes: 1) using a lookup table, in which the amplitude and phase responses of the power amplifier are recorded as functions of the input power, and these responses are inverted to ensure the linearization function of the predistorter. When the predistortion is working, the input signal power is used as the address index, and the table lookup obtains the unique amplitude and phase information. Although the implementation is simple, it is arduous to test the amplitude and phase information of the power amplifier, and the amplitude and phase results are related to the conditions during the test. When the power amplifier is working normally, the amplitude and phase are not modified, resulting in poor linearity during actual operation; 2) based on Volterra The model of basis function, through the study of the power amplifier model of Volterra series, digital pre-distortion technology has been greatly developed, and a variety of digital pre-distortion implementation methods have been proposed. Most of them use the power amplifier output signal to couple to the frequency converter for processing, and then convert the signal into a digital signal through an analog-to-digital converter and send it to processing devices such as a digital signal processor. Through a specific pre-distortion algorithm, a feedback signal that can offset the nonlinear distortion is calculated, and after being superimposed with the signal to be transmitted, it is converted into an analog intermediate frequency signal through a digital-to-analog converter, and then sent to the power amplifier through an up-conversion channel, so that the linearity of the signal output by the power amplifier is improved. After modeling and simulating the nonlinearity of the power amplifier based on the Volterra series, it is proposed to achieve nonlinear distortion compensation for the power amplifier in the time domain through multiple iterative filtering algorithms, matrix operations and other methods. However, the algorithm used in this method is complex, the amount of calculation is large, and it is more difficult to implement; 3) Another more active digital pre-distortion method is to introduce neural network algorithms, machine learning, artificial intelligence and other algorithms into the research of digital pre-distortion of power amplifiers. For example, a simple neural network model based on different classification principles is proposed, which greatly reduces the computational complexity while ensuring the power amplifier modeling effect. Another example is to optimize the traditional direct learning structure to avoid the complex power amplifier modeling process, and use the pre-distorter output error instead of the power amplifier output error to update the pre-distorter coefficient. However, these algorithms require strong computing power as support, and the real-time requirements for the power amplifier when working are also challenges faced by intelligent algorithms such as neural networks.

[0004] Therefore, there is an urgent need for a frequency domain predistortion method for power amplifiers to solve the problems existing in the current technology for implementing power amplifier nonlinear correction based on digital predistortion. Summary of the invention

[0005] In order to solve the above-mentioned deficiencies in the prior art, the present invention provides a frequency domain predistortion method for a power amplifier, comprising: S1. Get the input signal as , and order As the Fourier transform signal of the input signal, the input signal is subjected to frequency domain predistortion processing to obtain an output signal as follows: , and order A Fourier transform signal as the output signal; S2. The output signal is stored, and the output signal is subjected to inverse Fourier transform, digital-to-analog conversion and frequency conversion processing in sequence, and then transmitted to a power amplifier for power amplification, and the output power amplifier signal is collected; S3. After coupling, frequency conversion and analog-to-digital conversion of the power amplifier signal, the sampling signal is obtained as follows: , and order A Fourier transform signal as the sampling signal; S4. Using the first formula to divide the sampled signal and the input signal in the frequency domain, the transfer function obtained includes: is the transfer function; S5. Based on the stored output signal, multiplying the output signal and the transfer function using a second formula to obtain a first output signal includes: is the first output signal; S6. Use the first output signal as a new output signal, and execute steps S2 to S5 in a loop until the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

[0006] The present invention is implemented through the following technical scheme: the scheme first obtains the input signal, and performs frequency domain pre-distortion processing (i.e., performs Fourier transform) on the input signal to obtain the output signal, and then performs inverse Fourier transform, digital-to-analog conversion and frequency conversion processing on the output signal, and then sends it to the power amplifier for power amplification. Due to the nonlinear distortion caused by the intermodulation of the power amplifier itself, the output power amplifier signal also has nonlinear distortion at this time. The scheme couples the output power amplifier signal back, and sends it to the digital processor after frequency conversion processing and analog-to-digital conversion processing in sequence, and then performs frequency conversion on the sampled signal and the input signal. The transfer function is obtained by dividing the domain by the transfer function, which is then multiplied by the output signal stored last time in the frequency domain to obtain the frequency domain signal of the output signal this time, and then the inverse Fourier transform is performed to obtain the time domain signal after pre-distortion processing, and then after digital-to-analog conversion and frequency conversion processing, it is input into the power amplifier for power amplification, and the above steps are repeated and iterated continuously, so that the power amplifier signal output by the power amplifier continuously approaches the input signal, and the linearity of the power amplifier when working in the saturation working area is improved. Compared with the existing technology, the scheme has a small amount of calculation and a faster convergence speed, and can achieve the feasibility and controllability of the pre-distortion method.

[0007] As an optional technical solution, performing frequency domain predistortion processing on the input signal includes: Perform Fourier transform on the input signal, that is, .

[0008] As an optional technical solution, step S4 is specifically as follows: By combining the above equations and optimizing the first formula, we can obtain: for The modulus value, for The angle value of for The modulus value, for The angle value of for The modulus value, for The angle value of .

[0009] As an optional technical solution, step S5 and step S6 are specifically as follows: when When approaching infinity, the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

[0010] As an optional technical solution, the input signal is subjected to frequency domain pre-distortion processing, the output signal is stored, and the output signal is inverse Fourier transformed in sequence, all of which are implemented through a digital processor in a signal processing board; the output signal is subjected to digital-to-analog conversion processing, which is implemented through a digital-to-analog converter in the signal processing board.

[0011] As an optional technical solution, the frequency conversion processing of the output signal is implemented through an up-conversion channel in the frequency converter, and the frequency conversion processing of the power amplifier signal is implemented through a down-conversion channel in the frequency converter.

[0012] As an optional technical solution, based on an up-conversion channel in the frequency converter, the output signal is converted from an intermediate frequency signal to a radio frequency signal.

[0013] As an optional technical solution, based on the down-conversion channel in the frequency converter, the power amplifier signal is converted from a radio frequency signal to an intermediate frequency signal.

[0014] As an optional technical solution, the power amplifier signal is coupled through a power amplifier coupling channel in the power amplifier.

[0015] As an optional technical solution, the power amplifier signal is subjected to analog-to-digital conversion processing, which is achieved through an analog-to-digital converter in a signal processor board; the transfer function and the first output signal are calculated, which are both achieved through a digital processor in the signal processing board.

[0016] One or more technical solutions provided by the present invention have at least the following technical effects or advantages: The present invention provides a frequency domain predistortion method for a power amplifier, which realizes digital predistortion in the frequency domain. By coupling the power amplifier signal and adopting the transfer function, it continuously iterates so that the output signal of the power amplifier continuously approaches the input signal. Compared with the prior art, the amount of calculation is greatly reduced, the convergence speed is faster, the hardware computing power required for the algorithm is reduced, and the cost and implementation complexity are also greatly reduced, and the method has strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of the present invention, and do not constitute a limitation on the embodiments of the present invention; Figure 1 It is a flow chart of a frequency domain predistortion method for a power amplifier in the present invention; Figure 2 It is a working principle diagram of a frequency domain predistortion method for a power amplifier in the present invention. DETAILED DESCRIPTION

[0018] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0019] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those within the scope of this description. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0020] Example Please refer to Figure 1 and Figure 2 , Figure 1 is a flow chart of a frequency domain predistortion method for a power amplifier in the present invention, Figure 2 The present invention summarizes a working principle diagram of a frequency domain predistortion method for a power amplifier, including: S1. Get the input signal as , and order As the Fourier transform signal of the input signal, the input signal is subjected to frequency domain predistortion processing to obtain an output signal as follows: , and order A Fourier transform signal as the output signal; S2. The output signal is stored, and the output signal is subjected to inverse Fourier transform, digital-to-analog conversion and frequency conversion processing in sequence, and then transmitted to a power amplifier for power amplification, and the output power amplifier signal is collected; S3. After coupling, frequency conversion and analog-to-digital conversion of the power amplifier signal, the sampling signal is obtained as follows: , and order A Fourier transform signal as the sampling signal; S4. Using the first formula to divide the sampled signal and the input signal in the frequency domain, the transfer function obtained includes: is the transfer function; S5. Based on the stored output signal, multiplying the output signal and the transfer function using a second formula to obtain a first output signal includes: is the new output signal; S6. Use the first output signal as a new output signal, and execute steps S2 to S5 in a loop until the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

[0021] The specific embodiments of the present invention are as follows: This embodiment includes a signal processing board, a frequency converter and a power amplifier, the signal processing board includes a digital processor, a digital-to-analog converter and an analog-to-digital converter, the frequency converter includes an up-conversion channel and a down-conversion channel, and the power amplifier includes a power amplifier coupling channel; S1. Get the input signal as , and order As the Fourier transform signal of the input signal, the digital processor in the signal processing board performs Fourier transform processing on the input signal to obtain the output signal: , and order As the Fourier transform signal of the output signal, wherein, .

[0022] S2. The output signal is stored by a digital processor, and the output signal is subjected to inverse Fourier transform by a digital processor and digital-to-analog conversion by a digital-to-analog converter, and then the frequency is converted by a frequency converter (the intermediate frequency signal is converted into a radio frequency signal), and then the signal is transmitted to a power amplifier for power amplification, and the output power amplifier signal is collected; S3. The power amplifier signal is coupled back through the power amplifier coupling channel in the power amplifier, and the coupled power amplifier signal is frequency-converted through the down-conversion channel in the frequency converter (the RF signal is converted into an intermediate frequency signal), and the analog-to-digital converter is used to perform analog-to-digital conversion to obtain a sampling signal: , and order A Fourier transform signal as the sampling signal; S4. Using the first formula to divide the sampled signal and the input signal in the frequency domain, the transfer function obtained includes: is the transfer function; By combining the above equations and optimizing the first formula, we can obtain: for The modulus value, for The angle value of for The modulus value, for The angle value of for The modulus value, for The argument value of S5. Based on the stored output signal, multiplying the output signal and the transfer function using a second formula to obtain a first output signal includes: is the first output signal; S6. Take the first output signal as a new output signal, and repeat steps S2 to S5 until the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum; that is, when When approaching infinity, the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

[0023] Further, performing frequency domain predistortion processing on the input signal includes: Perform Fourier transform on the input signal, that is, .

[0024] Furthermore, step S4 is specifically as follows: By combining the above equations and optimizing the first formula, we can obtain: for The modulus value, for The angle value of for The modulus value, for The angle value of for The modulus value, for The angle value of .

[0025] Furthermore, step S5 and step S6 are specifically as follows: when When approaching infinity, the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

[0026] Furthermore, the input signal is subjected to frequency domain predistortion processing, the output signal is stored, and the output signal is inverse Fourier transformed in sequence, all of which are implemented through the digital processor in the signal processing board; the output signal is subjected to digital-to-analog conversion processing, which is implemented through the digital-to-analog converter in the signal processing board.

[0027] Furthermore, the frequency conversion processing of the output signal is implemented through an up-conversion channel in the frequency converter, and the frequency conversion processing of the power amplifier signal is implemented through a down-conversion channel in the frequency converter.

[0028] Furthermore, based on the up-conversion channel in the frequency converter, the output signal is converted from an intermediate frequency signal to a radio frequency signal.

[0029] Furthermore, based on the down-conversion channel in the frequency converter, the power amplifier signal is converted from a radio frequency signal to an intermediate frequency signal.

[0030] Furthermore, the power amplifier signal is coupled through a power amplifier coupling channel in the power amplifier.

[0031] Furthermore, the power amplifier signal is subjected to analog-to-digital conversion processing, which is achieved through an analog-to-digital converter in a signal processor board; and the transfer function and the first output signal are calculated, which are both achieved through a digital processor in the signal processing board.

[0032] Among them, this embodiment realizes digital pre-distortion in the frequency domain. The processing algorithm is an iterative method, which makes the output signal of the power amplifier approach the input signal continuously. The signal output by the power amplifier is coupled back and converted into an intermediate frequency signal after passing through a down-conversion receiver. The signal is connected to the analog-to-digital converter in the signal processing board for collection and then sent to the digital processor. The digital processor divides the collected signal and the input signal in the frequency domain to obtain a transfer function. The transfer function is multiplied by the previous output signal in the frequency domain to obtain a frequency domain signal of the current output signal, and then the digital frequency domain signal is inverse Fourier transformed to obtain the pre-distortion. The time domain signal after the transformation is converted, and then the digital analog converter in the signal processing board performs digital-to-analog conversion and outputs it, and the up-conversion channel in the frequency converter converts the intermediate frequency signal to a radio frequency signal for transmission, and then amplifies it through the power amplifier. After infinite iterations, the spectrum of the output signal of the power amplifier is consistent with the spectrum of the input signal. Since the signal processing process uses complex operations, the spectrum of the signal coupled back by the power amplifier is equal to the spectrum of the input signal, that is, the two signals are equal in the time domain, and the signal output by the power amplifier is not distorted, thereby solving the nonlinear distortion problem of the power amplifier. This embodiment uses a frequency domain digital pre-distortion processing method. Compared with the prior art, the amount of calculation is greatly reduced, the required hardware computing power is reduced, and the cost and implementation complexity are also greatly reduced. It has strong practicality and can effectively solve the nonlinear distortion problem of the power amplifier.

[0033] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0034] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A frequency domain predistortion method for a power amplifier, characterized in that: include: S1. Get the input signal as , and order As the Fourier transform signal of the input signal, the input signal is subjected to frequency domain predistortion processing to obtain an output signal as follows: , and order A Fourier transform signal as the output signal; S2. The output signal is stored, and the output signal is subjected to inverse Fourier transform, digital-to-analog conversion and frequency conversion processing in sequence, and then transmitted to a power amplifier for power amplification, and the output power amplifier signal is collected; S3. After coupling, frequency conversion and analog-to-digital conversion of the power amplifier signal, the sampling signal is obtained as follows: , and order A Fourier transform signal as the sampling signal; S4. Using the first formula to divide the sampled signal and the input signal in the frequency domain, the transfer function obtained includes: is the transfer function; S5. Based on the stored output signal, multiplying the output signal and the transfer function using a second formula to obtain a first output signal includes: is the first output signal; S6. Use the first output signal as a new output signal, and execute steps S2 to S5 in a loop until the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

2. A frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: Performing frequency domain predistortion processing on the input signal includes: Perform Fourier transform on the input signal, that is, .

3. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: Step S4 is specifically as follows: By combining the above equations and optimizing the first formula, we can obtain: for The modulus value, for The angle value of for The modulus value, for The angle value of for The modulus value, for The angle value of .

4. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: Step S5 and step S6 are specifically as follows: when When approaching infinity, the power amplifier signal output by the power amplifier is consistent with the input signal in frequency spectrum.

5. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: The input signal is subjected to frequency domain predistortion processing, the output signal is stored, and the output signal is subjected to inverse Fourier transform in sequence, all of which are realized by the digital processor in the signal processing board; the output signal is subjected to digital-to-analog conversion processing, which is realized by the digital-to-analog converter in the signal processing board.

6. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: The frequency conversion processing of the output signal is realized through an up-conversion channel in the frequency converter, and the frequency conversion processing of the power amplifier signal is realized through a down-conversion channel in the frequency converter.

7. A frequency domain predistortion method for a power amplifier according to claim 6, characterized in that: Based on the up-conversion channel in the frequency converter, the output signal is converted from an intermediate frequency signal to a radio frequency signal.

8. The frequency domain predistortion method for a power amplifier according to claim 6, characterized in that: Based on the down-conversion channel in the frequency converter, the power amplifier signal is converted from a radio frequency signal to an intermediate frequency signal.

9. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: The power amplifier signal is coupled through a power amplifier coupling channel in the power amplifier.

10. The frequency domain predistortion method for a power amplifier according to claim 1, characterized in that: The power amplifier signal is subjected to analog-to-digital conversion processing, which is realized by an analog-to-digital converter in a signal processor board; the transfer function and the first output signal are calculated, which are both realized by a digital processor in the signal processing board.

Images