Digital pre-distortion method and system for spectrum derivation and harmonic growth of dual-frequency concurrent signals

Abstract

The application belongs to the field of signal linearization in parallel dual-frequency transmitter, and particularly relates to a digital pre-distortion method and system for spectrum derivation and harmonic proliferation of dual-frequency concurrent signals, comprising: synthesizing dual-frequency signals to obtain dual-frequency concurrent signals; inputting the dual-frequency concurrent signals into a power amplifier to obtain an output signal; modeling and constructing a power amplifier model by spectrum derivation and harmonic proliferation of the dual-frequency concurrent signals; collecting forward signals and feedback signals, and aligning the forward signals and the feedback signals by a signal frequency domain cross-correlation algorithm; estimating coefficients of an inverse model of the power amplifier model according to the aligned forward signals and feedback signals, and updating the estimated coefficients to a digital pre-distortion device; the application constructs a power amplifier model by accurately modeling high-order harmonics and intermodulation distortion of the dual-frequency concurrent signals, and updates the coefficients of the inverse model of the power amplifier model to the digital pre-distortion device in combination with a feedback mechanism; after the update, the digital pre-distortion device can effectively suppress harmonic derivation and spectrum pollution.

Description

Technical Field

[0001] This invention belongs to the field of signal linearization in parallel dual-frequency transmitters, specifically relating to a digital predistortion method and system for spectrum derivation and harmonic amplification of dual-frequency concurrent signals. Background Technology

[0002] In modern wireless communication systems, with the increasing scarcity of communication frequency band resources, improving spectrum utilization has become a key issue. Concurrent transmission of multi-band signals has gradually become an important means of enhancing system capacity and efficiency. However, in this transmission method, the nonlinear effects of the power amplifier (PA) can induce complex distortion phenomena, particularly harmonic derivation and cross-modulation distortion. These nonlinear effects can lead to a decline in communication system performance, affect signal transmission quality, and even cause interference to adjacent frequency bands.

[0003] Harmonic issues are a typical manifestation of the nonlinear effects of power amplifiers. Power amplifiers generate multiple harmonics when driven by high-power signals. These harmonic signals not only fall within the original signal frequency band but also extend to higher frequency ranges, causing spectrum pollution. This spectrum spreading phenomenon is particularly significant in the concurrent transmission of dual-frequency signals. In particular, the presence of higher-order harmonics can severely interfere with other communication signals, especially affecting the normal operation of adjacent channel communication systems.

[0004] Traditional single-frequency digital predistortion (DPD) technology aims to reduce nonlinear distortion by modeling the nonlinear characteristics of the power amplifier and correcting the input signal using predistortion techniques. However, single-frequency DPD technology struggles to effectively handle multi-frequency concurrent signals, especially the harmonic and cross-modulation distortion problems of dual-frequency signals. This is because the mutual influence of multiple frequency signals not only exacerbates the nonlinear effects of the power amplifier but also induces intermodulation distortion and harmonic amplification, posing a significant challenge to the stability of the communication system.

[0005] To address the nonlinear distortion problem in multi-frequency concurrent signals, a technique based on a two-dimensional predistortion (2-D DPD) model has been proposed in recent years. This technique, by simultaneously considering the nonlinear distortion and intermodulation effects of dual-frequency signals, can more effectively correct the nonlinear behavior of power amplifiers.

[0006] However, while two-dimensional predistortion models perform well in suppressing intermodulation distortion, their effect on suppressing higher harmonics is not significant. The complexity and spectral spread effect of higher harmonics pose a significant challenge to predistortion models, especially in communication systems with a wider frequency range, where the presence of higher harmonics has a significant impact on the overall system performance. Summary of the Invention

[0007] To address the aforementioned problems in the prior art, this invention employs a digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification, comprising: acquiring dual-frequency signals; inputting the dual-frequency signals into a trained digital predistorter to obtain predistorted dual-frequency signals; synthesizing the predistorted dual-frequency signals to obtain predistorted dual-frequency concurrent signals; and inputting the predistorted dual-frequency concurrent signals into a power amplifier PA to obtain an output signal. The training process of the digital predistorter includes:

[0008] S1. Acquire the dual-frequency signal, synthesize the dual-frequency signal to obtain the dual-frequency concurrent signal; input the dual-frequency concurrent signal into the power amplifier PA to obtain the output signal;

[0009] S2. A power amplifier model is constructed by modeling the spectral derivation and harmonic amplification of dual-frequency concurrent signals;

[0010] S3. Acquire the forward signal from the dual-frequency signal and the feedback signal from the output signal, and align the forward signal and the feedback signal using a signal frequency domain cross-correlation algorithm.

[0011] S4. Estimate the coefficients of the inverse model of the power amplifier model based on the aligned forward and feedback signals, update the estimated coefficients to the digital predistorter, and obtain the trained digital predistorter.

[0012] The advantages and beneficial effects of this invention are as follows:

[0013] Compared with traditional predistortion methods, this invention constructs a power amplifier model by accurately modeling the high-order harmonics and intermodulation distortion of dual-frequency concurrent signals, estimates the coefficients of the inverse model of the power amplifier model, and updates the coefficients of the inverse model of the power amplifier model to the digital predistorter by combining a feedback mechanism. After the update, the digital predistorter can effectively suppress harmonic derivation and spectrum pollution, making the output signal after PA closer to the ideal state, significantly improving the transmission performance of multi-band communication systems, and meeting the needs of modern wireless communication for efficient and reliable signal transmission. Attached Figure Description

[0014] Figure 1 This is a flowchart of the digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification provided in an embodiment of the present invention;

[0015] Figure 2 This is a block diagram of a digital predistortion system for dual-frequency concurrent signal spectrum derivation and harmonic amplification provided in an embodiment of the present invention;

[0016] Figure 3 This is a flowchart of aligning the forward and feedback signals using a signal frequency domain cross-correlation algorithm provided in an embodiment of the present invention;

[0017] Figure 4This is a comparison chart of the upper-band power density spectrum after three digital predistortion methods provided in the embodiments of the present invention;

[0018] Figure 5 This is a comparison chart of the lower frequency band power density spectrum after three digital predistortion methods provided in the embodiments of the present invention;

[0019] Figure 6 This is a schematic diagram of harmonic and out-of-band intermodulation suppression provided in an embodiment of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, this invention employs a digital predistortion method for dual-frequency concurrent signal power amplifier spectrum derivation and harmonic amplification, comprising: acquiring dual-frequency signals; inputting the dual-frequency signals into a trained digital predistorter to obtain predistorted dual-frequency signals; synthesizing the predistorted dual-frequency signals to obtain predistorted dual-frequency concurrent signals; and inputting the predistorted dual-frequency concurrent signals into a power amplifier PA to obtain an output signal. The training process of the digital predistorter includes:

[0022] S1. Acquire the dual-frequency signal, synthesize the dual-frequency signal to obtain the dual-frequency concurrent signal; input the dual-frequency concurrent signal into the power amplifier PA to obtain the output signal;

[0023] Acquiring dual-frequency signals includes:

[0024] Initial upper band signal obtained using DDS (Direct Digital Synthesis) technology and initial lower frequency band signal , for signal and signal The signals are converted to higher frequencies to obtain the upper frequency band signal. and lower frequency band signals ;

[0025] Acquiring the initial upper frequency band signal and the initial lower frequency band signal includes:

[0026] The DDS includes a phase accumulator and a triangular ROM. The DDS generates a control frequency word CF and uses the control frequency word CF as the address value of the triangular ROM. The control frequency word CF carries the frequency information of the signal, the resolution of the frequency adjustment, and the phase increment. The output frequency of the triangular ROM is determined by the following relationship.

[0027]

[0028] in, To output frequency signal, This is the clock frequency of the DDS. This represents the bit width of the phase accumulator.

[0029] The signal frequency conversion for the initial upper frequency band signal and the initial lower frequency band signal includes:

[0030] The center frequencies of the frequency converters are respectively , Multiply the initial upper frequency band signal and the initial lower frequency band signal by their respective center frequencies. , From the sine and cosine signal sequences, the upper frequency band signal is obtained. and lower frequency band signals :

[0031]

[0032] in, The sampling time interval between the initial upper frequency band signal and the initial lower frequency band signal. Let j be the time variable of the signal, and j be the imaginary unit.

[0033] Synthesizing dual-frequency signals includes:

[0034] Signal and signal Convert to analog signal to obtain analog signal and analog signals , analog signal and analog signals The signals are synthesized to obtain dual-frequency concurrent signals. ;in, The time variable of the signal.

[0035] S2. A power amplifier model is constructed by modeling the spectral derivation and harmonic amplification of dual-frequency concurrent signals;

[0036] The two-dimensional predistortion (2-D-DPD) model is improved by using the Volterra series model that preserves the characteristics of the dual-frequency predistortion signal. The improved 2-D-DPD model is then used to accurately model the higher harmonics and intermodulation distortion of the dual-frequency signal, resulting in the power amplifier model, including:

[0037]

[0038] in, , , These are the coefficients of the power amplifier model. Let k be the nonlinear order of the power amplifier model, k be the index of the nonlinear order, and l be the... The traversal values, Let d be the memory depth of the power amplifier model. The index represents the number of sampling periods of the signal delay. and They represent signals respectively. and The memory depth corresponding to the frequency band fitting. For memory depth index, Memory depth index, M represents the time delay term, I represents the harmonic order, and i represents the index of the harmonic order. and These represent the input signals of the power amplifier model, respectively. and These represent the output signals of the power amplifier model.

[0039] Preferably, I=3 (meaning that the third order is taken into account, including the first, second and third harmonics).

[0040] Preferably, K=5, Q=4, M=4.

[0041] S3. Acquire the forward signal from the dual-frequency signal and the feedback signal from the output signal, and align the forward signal and the feedback signal using a signal frequency domain cross-correlation algorithm.

[0042] In signal analog signal and analog signals The forward signals of the upper frequency band were collected separately. and the forward signal of the lower frequency band For the output signal Filtering is performed to obtain output signals in two frequency bands. The feedback signal from the upper frequency band is then collected from the output signals in both frequency bands. and feedback signal in the lower frequency band , Figure 3 This invention relates to a method for calculating signal delay parameters; specifically, it includes:

[0043] S31. Based on the Blackman window function Forward signals respectively and feedback signals Perform a Fast Fourier Transform (FFT) to obtain the forward signal. and feedback signals Frequency domain representation and ;

[0044]

[0045]

[0046]

[0047] Where N is the signal The discrete time length is denoted by m, where m is the index in the frequency domain.

[0048] S32. Based on frequency domain representation The conjugate complex number and frequency domain representation Calculate the forward signal and feedback signals Frequency domain cross-correlation :

[0049]

[0050] in, Frequency domain representation The conjugate of complex numbers.

[0051] S33, Frequency domain cross-correlation Perform an inverse Fourier transform (IFFT) to obtain the discrete-time signal. According to discrete-time signals Obtain the signal delay amount ;

[0052]

[0053] in, Indicates that The time variable n with the largest absolute value.

[0054] S34. Based on signal delay right Adjustments were made to obtain the same result as Time-domain aligned signals The alignment method is as follows;

[0055]

[0056] Forward signal and feedback signals The alignment method is the same.

[0057] S4. Estimate the coefficients of the inverse model of the power amplifier model based on the aligned forward and feedback signals, update the estimated coefficients to the digital predistorter, and obtain the trained digital predistorter.

[0058] The coefficients of the inverse model of the power amplifier model are estimated using the least squares estimation algorithm, including:

[0059] According to the forward signal and forward signal Construct the output matrix of the inverse model of the power amplifier model respectively. and output matrix ;

[0060] Based on the aligned feedback signal , And the input matrix of the inverse model of the power amplifier model. :

[0061] ,

[0062]

[0063]

[0064] in, Based on the model, the least squares estimation is used. Feedback signals and Similarly, the constructed input matrix... Based on the model, the least squares estimation is used. and feedback signals The constructed input matrix, Based on the model, the least squares estimation is used. and feedback signals The constructed input matrix, and Corresponding to feedback signals and Similarly, we can obtain .

[0065] Based on the output matrix and input matrix Estimate the coefficients of the inverse model of the power amplifier model. According to the output matrix and input matrix Estimate the coefficients of the inverse model of the power amplifier model. :

[0066]

[0067]

[0068]

[0069]

[0070] in, , , , , , These are the coefficients of the inverse model of the power amplifier model. , , , , , Coefficients , , , , , The coefficient matrix is ​​denoted by H, where H represents the conjugate transpose and -1 represents the inverse.

[0071] like Figure 2 As shown, a digital predistortion cancellation system for dual-frequency concurrent signal power amplifier spectrum derivation and harmonic amplification includes:

[0072] The system comprises a DDS, an upper-band signal processing module, a lower-band signal processing module, a synthesizer, a power amplifier (PA), and a DPD coefficient training module. The upper-band signal processing module includes a first signal conversion module, a first digital predistorter (DPD1), a first switch, a second switch, and a first digital-to-analog converter (DAC). The lower-band signal processing module includes a second signal conversion module, a second digital predistorter (DPD2), a third switch, a fourth switch, and a second digital-to-analog converter (DAC).

[0073] The DDS generates upper-band and lower-band signals. The inputs of the upper-band signal processing module and the lower-band signal processing module are connected to the DDS to receive the upper-band and lower-band signals, respectively. The input of the synthesizer is connected to the outputs of the upper-band signal processing module and the lower-band signal processing module, respectively, to synthesize the signals output by the upper-band signal processing module and the lower-band signal processing module. The input of the power amplifier PA is connected to the output of the synthesizer to amplify the power of the synthesizer output signal. The input of the DPD coefficient training module is connected to the outputs of the power amplifier PA, the upper-band signal processing module, and the lower-band signal processing module, respectively. The output of the DPD coefficient training module is connected to DPD1 of the upper-band signal processing module and DPD2 of the lower-band signal processing module, respectively.

[0074] The first switch includes an input terminal, an output terminal 1, and an output terminal 2; the second switch includes an input terminal 1, an input terminal 2, and an output terminal; the output terminal of the first signal frequency conversion module is connected to the input terminal of the first switch; the output terminal 2 of the first switch is connected to the input terminal of the first digital predistorter DPD1; the output terminal of DPD1 is connected to the input terminal 2 of the second switch; the output terminal of the second switch is connected to the input terminal of the first digital-to-analog converter DAC; the output terminal 1 of the first switch is connected to the input terminal 1 of the second switch; the output terminal of the first digital-to-analog converter DAC is connected to the input terminal of the synthesizer.

[0075] The third switch includes an input terminal, an output terminal 1, and an output terminal 2; the fourth switch includes an input terminal 1, an input terminal 2, and an output terminal; the output terminal of the second signal frequency conversion module is connected to the input terminal of the third switch; the output terminal 2 of the third switch is connected to the input terminal of the second digital predistorter DPD2; the output terminal of DPD2 is connected to the input terminal 2 of the fourth switch; the output terminal of the fourth switch is connected to the input terminal of the second digital-to-analog converter DAC; the output terminal 1 of the third switch is connected to the input terminal 1 of the fourth switch; the output terminal of the second digital-to-analog converter DAC is connected to the input terminal of the synthesizer.

[0076] Before the digital predistorter is updated, the output terminal 1 of the first switch and the input terminal 1 of the second switch in the upper frequency band signal processing module are connected, and the output terminal 1 of the third switch and the input terminal 1 of the fourth switch in the lower frequency band signal processing module are connected; after the digital predistorter is updated, the output terminal 2 of the first switch and the input terminal 2 of the second switch in the upper frequency band signal processing module are connected, and the output terminal 2 of the third switch and the input terminal 2 of the fourth switch in the lower frequency band signal processing module are connected.

[0077] like Figure 4 , Figure 5 , Figure 6 As shown, the digital predistorter (HC-2-D-DPD) of the present invention outperforms other methods; wherein, No-DPD indicates that no digital predistorter is used, and 2-D-DPD indicates a two-dimensional predistortion model.

[0078] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Digital predistortion methods for dual-frequency concurrent signal spectrum derivation and harmonic amplification, including: The process involves acquiring a dual-frequency signal, inputting the dual-frequency signal into a trained digital predistorter to obtain a predistorted dual-frequency signal, synthesizing the predistorted dual-frequency signal to obtain a predistorted concurrent dual-frequency signal, and inputting the predistorted concurrent dual-frequency signal into a power amplifier PA to obtain an output signal. The training process of the digital predistorter includes: S1. Acquire the dual-frequency signal, synthesize the dual-frequency signal to obtain the dual-frequency concurrent signal; input the dual-frequency concurrent signal into the power amplifier PA to obtain the output signal; S2. A power amplifier model is constructed by modeling the spectral derivation and harmonic amplification of dual-frequency concurrent signals; The power amplifier model is as follows: ； in, , , , , , These are the coefficients of the power amplifier model. Let k be the nonlinear order of the power amplifier model, k be the index of the nonlinear order, and l be the... The traversal values, Let d be the memory depth of the power amplifier model. index, and They represent signals respectively. and The memory depth corresponding to the frequency band fitting. For memory depth index, Memory depth index, M represents the time delay term, I represents the harmonic order, and i represents the index of the harmonic order. and This represents the input signal of the power amplifier model. and This represents the output signal of the power amplifier model; S3. Acquire the forward signal from the dual-frequency signal and the feedback signal from the output signal, and align the forward signal and the feedback signal using a signal frequency domain cross-correlation algorithm. S4. Estimate the coefficients of the inverse model of the power amplifier model based on the aligned forward and feedback signals, update the estimated coefficients to the digital predistorter, and obtain the trained digital predistorter.

2. The digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification according to claim 1, characterized in that, Acquiring dual-frequency signals includes: acquiring the initial upper frequency band signal. and the initial lower frequency band signal , for signal and signal The signals are converted to higher frequencies to obtain the upper frequency band signal. and lower frequency band signals ;in, The time variable of the signal.

3. The digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification according to claim 2, characterized in that, The signal frequency conversion for the initial upper frequency band signal and the initial lower frequency band signal includes: ； in, The sampling time interval between the initial upper frequency band signal and the initial lower frequency band signal. , This is the center frequency of the frequency converter.

4. The digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification according to claim 1, characterized in that, Forward signals include: forward signals in the upper frequency band. and the forward signal of the lower frequency band The feedback signals include: feedback signals in the upper frequency band. and feedback signal in the lower frequency band ; forward signal Align with feedback signal include: S31. Based on the Blackman window function Forward signals respectively and feedback signals Perform a Fast Fourier Transform to obtain the forward signal. and feedback signals Frequency domain representation and ;in, Let m be the time variable of the signal, and m be the index in the frequency domain. S32. Based on frequency domain representation The conjugate complex number and frequency domain representation Calculate the forward signal and feedback signals Frequency domain cross-correlation ; S33, Frequency domain cross-correlation Perform an inverse Fourier transform to obtain the discrete-time signal. According to discrete-time signals Obtain the signal delay amount ; S34. Based on signal delay right Adjustments are made to obtain the signal from the forward signal. Aligned feedback signal ; Forward signal and feedback signals Alignment method and forward signal and feedback signals If the alignment method is consistent, then the result is the same as the forward signal. Aligned feedback signal .

5. The digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification according to claim 4, characterized in that, Based on discrete-time signals Obtain the signal delay amount include: ； in, Indicates that The time variable n with the largest absolute value.

6. The digital predistortion method for dual-frequency concurrent signal spectrum derivation and harmonic amplification according to claim 5, characterized in that, Estimating the coefficients of the inverse model of the power amplifier model includes: using a least squares estimation algorithm based on the forward signal. Forward signal Aligned feedback signal and the feedback signal after alignment Estimate the coefficients of the inverse model of the power amplifier model.

7. A digital predistortion elimination system employing the digital predistortion method as described in any one of claims 1 to 6, characterized in that, include: DDS, upper band signal processing module, lower band signal processing module, synthesizer, power amplifier PA, and DPD coefficient training module; Both the upper-band signal processing module and the lower-band signal processing module include digital predistorters; among them, DDS is a direct digital synthesizer. The DDS generates initial upper-band and lower-band signals. The inputs of the upper-band and lower-band signal processing modules are connected to the DDS. The inputs of the synthesizer are connected to the outputs of the upper-band and lower-band signal processing modules. The input of the power amplifier PA is connected to the output of the synthesizer. The input of the DPD coefficient training module is connected to the outputs of the power amplifier PA, the upper-band signal processing module, and the lower-band signal processing module. The output of the DPD coefficient training module is connected to the digital predistorter of the upper-band signal processing module and the digital predistorter of the lower-band signal processing module.

8. The digital predistortion elimination system according to claim 7, characterized in that, The upper frequency band signal processing module also includes: a signal conversion module, a first switch, a second switch, and a digital-to-analog converter (DAC); the first switch includes an input terminal, an output terminal 1, and an output terminal 2, and the second switch includes an input terminal 1, an input terminal 2, and an output terminal; the input terminal of the signal conversion module is connected to the input terminal of the first switch, the output terminal 2 of the first switch is connected to the input terminal of the digital predistorter (DPD), the output terminal of the DPD is connected to the input terminal 2 of the second switch, the output terminal of the second switch is connected to the input terminal of the DAC, and the output terminal 1 of the first switch is connected to the input terminal 1 of the second switch; the output terminal of the DAC is connected to the input terminal of the synthesizer; the structure of the lower frequency band signal processing module is the same as that of the upper frequency band signal processing module.

9. The digital predistortion elimination system according to claim 8, characterized in that, Before the digital predistorter is updated, the output terminal 1 and input terminal 1 of the switch in the upper frequency band signal processing module and the lower frequency band signal processing module are connected; after the digital predistorter is updated, the output terminal 2 and input terminal 2 of the switch in the upper frequency band signal processing module and the lower frequency band signal processing module are connected.

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