Time delay estimation system and method for suppressing intermodulation and harmonic waves of short wave transmitter

Abstract

The invention discloses a time delay estimation system for suppressing intermodulation and harmonic waves of a short wave transmitter, which comprises a preprocessing module, a digital pre-distortion algorithm module, an up-conversion module, a digital-to-analog converter, a power amplifier, an analog-to-digital converter and a down-conversion module, and also discloses a time delay estimation method for suppressing intermodulation and harmonic waves of the short wave transmitter. Comprising the following steps of 1, performing amplitude alignment on a baseband signal and an output signal of a down-conversion module, 2, performing preliminary time delay alignment calculation by utilizing the baseband signal and the output signal, a real part or an imaginary part of the down-conversion module, and 3, performing time delay alignment calculation on the basis of the preliminary time delay alignment of the baseband signal and the output signal of the down-conversion module. And carrying out time delay alignment on the module value of the signal again. According to the method provided by the invention, the modeling of the digital pre-distortion model on intermodulation and harmonic waves is more accurate, so that the suppression of intermodulation and harmonic waves is realized, and the linearity of a short wave transmitter system is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of digital predistortion, and in particular relates to a time delay estimation system and method for suppressing intermodulation and harmonics of a shortwave transmitter. Background Art

[0002] In order to make the shortwave power amplifier have better output performance while removing the analog filter group, digital pre-distortion technology is used to suppress the intermodulation distortion and harmonic distortion of the shortwave power amplifier. Delay estimation of the input and output signals of the power amplifier is an important part of digital pre-distortion technology. The traditional delay estimation method is mainly aimed at suppressing intermodulation distortion. Its modeling is characterized by using terms such as the input signal multiplied by the input signal modulus value. The delay can be estimated by using the modulus value of the baseband signal, which does not require the real and imaginary parts of the input and output signals of the power amplifier to be strictly aligned. However, when digital pre-distortion technology is used for harmonic distortion suppression, its modeling needs to use the power series of the input signal to characterize the harmonics. It is proved that the delay alignment result of the real and imaginary parts of the input and output signals of the power amplifier will directly affect the characterization of the harmonic signal, and then affect the suppression effect of the harmonics. If only the real and imaginary parts of the power amplifier input and output signals are used for delay alignment, due to the nonlinearity of the power amplifier, the alignment result may not necessarily meet the alignment result of the power amplifier input and output signal modulus values, thereby affecting the digital pre-distortion model's representation of intermodulation distortion.

[0003] Therefore, there is an urgent need for a delay estimation method that can combine the modulus value and the real part (or imaginary part) of the input and output signals of the power amplifier. Summary of the invention

[0004] In order to solve the problems in the prior art, the present invention proposes a delay estimation system and method that combines the modulus value and its real part (or imaginary part) of the input and output signals of a power amplifier, thereby realizing the delay alignment of the input and output signals of the shortwave power amplifier, and further effectively using digital pre-distortion technology to suppress intermodulation distortion and harmonic distortion.

[0005] In a first aspect, the present invention provides a time delay estimation system for suppressing intermodulation and harmonics of a shortwave transmitter, comprising: a preprocessing module, a digital predistortion algorithm module, an up-conversion module, a digital-to-analog converter, a power amplifier, an analog-to-digital converter, and a down-conversion module, wherein a first input end of the preprocessing module is connected to a baseband signal, a second input end is connected to an output end of the down-conversion module, an output end of the preprocessing module is connected to a second input end of the digital predistortion algorithm module, and the preprocessing module is used to perform time delay alignment and amplitude alignment preprocessing operations on the baseband signal and the output signal of the down-conversion module;

[0006] The first input end of the digital pre-distortion algorithm module is connected to the baseband signal, the output end of the digital pre-distortion algorithm module is connected to the input end of the up-conversion module, and the digital pre-distortion algorithm module is used to train and generate a pre-distortion signal that can suppress harmonics and intermodulation;

[0007] The output end of the up-conversion module is connected to the input end of the digital-to-analog converter, and the up-conversion module is used to shift the frequency of the predistortion signal to a high frequency;

[0008] The output end of the digital-to-analog converter is connected to the input end of the power amplifier, and the digital-to-analog converter is used to convert the digital signal into an analog signal;

[0009] The output end of the power amplifier is connected to the input end of the analog-to-digital converter, and is used to amplify the power of the input signal of the power amplifier;

[0010] The output end of the analog-to-digital converter is connected to the input end of the down-conversion module, and the analog-to-digital converter is used to convert the analog signal into a digital signal;

[0011] The output end of the down-conversion module is connected to the second input end of the pre-processing module, and is used to shift the frequency of the collected output signal of the power amplifier to a low frequency.

[0012] In a second aspect, the present invention further provides a delay estimation method for suppressing intermodulation and harmonics of a shortwave transmitter, comprising the following steps:

[0013] Step 1: Align the amplitude of the baseband signal and the output signal of the down-conversion module.

[0014] Step 2: Perform preliminary delay alignment calculation using the baseband signal and the output signal, real part or imaginary part of the down-conversion module.

[0015] Step 3: Based on the preliminary delay alignment of the baseband signal and the output signal of the down-conversion module, the module value of the signal is delayed again.

[0016] Furthermore, in step 2, the baseband signal and the real part of the output signal of the down-conversion module are preliminarily aligned with each other using the following calculation function:

[0017]

[0018] Wherein, real(u(n)) is the real part of the baseband signal, R(τ) is the delay function, real(y(n)) is the real part of the output signal of the down-conversion module, [0,N] is the interval of the initial estimated delay position, and N is not less than the period of real(u(n)).

[0019] Furthermore, τ corresponding to the minimum R(τ) is the initially estimated time delay, denoted as τ0, and the starting point of the output signal y(n) of the down-conversion module is set to τ0, thus completing the initial time delay alignment with the baseband signal u(n).

[0020] Further, the delay function R(τ) is calculated by using the imaginary part of the baseband signal and the imaginary part of the output signal of the down-conversion module or by using the baseband signal and the output signal of the down-conversion module.

[0021] Furthermore, in step 3, based on the preliminary delay alignment of the baseband signal and the output signal of the down-conversion module, the module value of the signal is again delayed aligned using the following calculation function:

[0022]

[0023] Wherein, y1(n) represents the output signal of the down-conversion module after the preliminary delay alignment in step 2, abs(u(n)) is the modulus of the baseband signal, abs(y1(n)) is the modulus of y1(n), [N0, N1] is the interval for further estimating the delay position, the value of (N1-N0) is equal to the period of abs(u(n)), and R1(τ) is the delay function.

[0024] Furthermore, τ corresponding to the minimum R1(τ) is the further estimated time delay, denoted as τ1, τ0+τ1-N0 is the further estimated time delay position, and the starting point of the down-conversion module output signal y(n) is set to τ0+τ1-N0, thus completing the re-delay alignment with the baseband signal u(n).

[0025] Furthermore, to align the baseband signal u(n) with the output signal y(n) of the down-conversion module, the sequence length of real(y(n)) is required to be smaller than the sequence length of real(u(n)), and the sequence length of abs(y1(n)) is required to be smaller than the sequence length of abs(u(n)).

[0026] Furthermore, in step 1, before amplitude alignment is performed, a low-pass filter is used to filter out the DC and harmonics of the output signal of the down-conversion module.

[0027] Compared with the prior art, the delay estimation method provided by the present invention, which combines the modulus and the real part (or imaginary part) of the power amplifier input and output signals, can be applied to the suppression algorithm of intermodulation and harmonics on the baseband signal based on digital predistortion technology, so that the digital predistortion model can model intermodulation and harmonics more accurately, thereby achieving suppression of intermodulation and harmonics and improving the linearity of the shortwave transmitter system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1It is a structural schematic diagram of a time delay estimation system for suppressing intermodulation and harmonics of a shortwave transmitter according to the present invention;

[0029] Figure 2 is a time domain diagram of the real part of the baseband signal and the output signal of the down-conversion module after preliminary delay alignment in an embodiment of the present invention;

[0030] Figure 3 is a time domain diagram of the imaginary part of the baseband signal and the output signal of the down-conversion module after preliminary delay alignment in an embodiment of the present invention;

[0031] Figure 4 It is a time domain diagram of the modulus value of the baseband signal and the output signal of the down-conversion module after preliminary delay alignment in an embodiment of the present invention;

[0032] Figure 5 is a time domain diagram of the modulus value of the baseband signal and the output signal of the down-conversion module after further delay alignment in an embodiment of the present invention;

[0033] Figure 6 is a spectrum comparison diagram of the power amplifier output signal before and after the predistortion processing according to the embodiment of the present invention;

[0034] Among them, digital pre-distortion algorithm module - DPD; digital-to-analog converter - DAC; power amplifier - PA, analog-to-digital converter - ADC. DETAILED DESCRIPTION

[0035] The present invention is further explained below in conjunction with the drawings and specific embodiments of the specification. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0036] According to the embodiment of the present invention, in combination with the appended claims of the present invention, Figure 1 The present invention provides a structural schematic diagram of a time delay estimation system for suppressing intermodulation and harmonics of a shortwave transmitter, including: a preprocessing module, a digital predistortion algorithm module DPD, an up-conversion module, a digital-to-analog converter DAC, a power amplifier PA, an analog-to-digital converter ADC and a down-conversion module.

[0037] According to an embodiment of the present invention, the first input end of the preprocessing module is connected to the baseband signal, the second input end is connected to the output end of the down-conversion module, the output end of the preprocessing module is connected to the second input end of the digital predistortion algorithm module DPD, and the preprocessing module is used to perform delay alignment and amplitude alignment preprocessing operations on the baseband signal and the output signal of the down-conversion module.

[0038] According to an embodiment of the present invention, a first input end of the digital predistortion algorithm module DPD is connected to a baseband signal, an output end of the digital predistortion algorithm module DPD is connected to an input end of an up-conversion module, and the digital predistortion algorithm module DPD is used to train and generate a predistortion signal that can suppress harmonics and intermodulation.

[0039] According to an embodiment of the present invention, the input end of the up-conversion module is connected to the output end of the digital pre-distortion algorithm module DPD, the output end of the up-conversion module is connected to the input end of the digital-to-analog converter DAC, and the up-conversion module is used to move the pre-distortion signal frequency to a high frequency.

[0040] According to an embodiment of the present invention, an output end of the digital-to-analog converter DAC is connected to an input end of the power amplifier PA, and the digital-to-analog converter DAC is used to convert a digital signal into an analog signal.

[0041] According to an embodiment of the present invention, the output end of the power amplifier PA is connected to the input end of the analog-to-digital converter ADC, so as to amplify the power of the input signal of the power amplifier PA.

[0042] According to an embodiment of the present invention, the output end of the analog-to-digital converter ADC is connected to the input end of the down-conversion module, and the analog-to-digital converter ADC is used to convert an analog signal into a digital signal.

[0043] According to an embodiment of the present invention, the output end of the down-conversion module is connected to the second input end of the pre-processing module, and the down-conversion module is used to shift the frequency of the collected output signal of the power amplifier PA to a low frequency.

[0044] According to an embodiment of the present invention, the present invention provides a delay estimation method for suppressing intermodulation and harmonics of a shortwave transmitter, comprising the following steps:

[0045] Step 1: align the amplitudes of the baseband signal and the output signal of the down-conversion module.

[0046] Before amplitude alignment, a low-pass filter can be used to filter out the DC and harmonics of the output signal of the down-conversion module to improve the accuracy of delay estimation.

[0047] Step 2: Perform preliminary delay alignment calculation using the baseband signal and the output signal, real part or imaginary part of the down-conversion module.

[0048] The delay function R(τ) is calculated using the following formula, where real(u(n)) is the real part of the baseband signal. The sequence length of real(u(n)) is recommended to be greater than one cycle of real(u(n)). real(y(n)) is the real part of the output signal of the down-conversion module. The sequence length of real(y(n)) is at least the length of the real(u(n)) sequence plus N. [0,N] is the interval where the delay position is initially estimated, and N should not be less than the cycle of real(u(n)). The τ corresponding to the minimum R(τ) is the initially estimated delay, denoted as τ0. Setting the starting point of the down-conversion module output signal y(n) to τ0 can achieve initial delay alignment with the baseband signal u(n).

[0049]

[0050] The delay function R(τ) can also be calculated using the imaginary part of the baseband signal and the imaginary part of the down-conversion module output signal, or directly using the baseband signal and the down-conversion module output signal. In the calculation, real(u(n)) can also be expressed as the baseband signal or the imaginary part of the baseband signal; real(y(n)) can also be expressed as the down-conversion module output signal or the imaginary part of the down-conversion module output signal.

[0051] Step three, based on the preliminary delay alignment of the baseband signal and the output signal of the down-conversion module, the module value of the signal is again delayed aligned.

[0052] The delay function R1(τ) is calculated using the following formula, where y1(n) represents the output signal of the down-conversion module after the preliminary delay alignment in step 2, abs(u(n) is the modulus of the baseband signal, the sequence length of abs(u(n)) is recommended to be one period of abs(u(n)), abs(y1(n)) is the modulus of y1(n), the sequence length of abs(y1(n)) is at least the sequence length of abs(u(n)) plus the period of abs(u(n)), [N0, N1] is the interval where the delay position is further estimated, and the value of (N1-N0) is equal to the period of abs(u(n)). The τ corresponding to the minimum R1(τ) is the further estimated delay, denoted as τ1. τ0+τ1-N0 is the further estimated delay position. By setting the starting point of the down-conversion module output signal y(n) to τ0+τ1-N0, further delay alignment with the baseband signal u(n) can be achieved.

[0053]

[0054] According to an embodiment of the present invention, the baseband signal u(n) can also be aligned with the down-conversion module output signal y(n), which requires that the sequence length of real(y(n)) is smaller than the sequence length of real(u(n)), and the sequence length of abs(y1(n)) is smaller than the sequence length of abs(u(n)).

[0055] According to the embodiment of the present invention, the delay functions R(τ) and R1(τ) may adopt other methods having the same effect besides the above formulas.

[0056] In order to highlight that the system and method of the present invention are superior to the prior art in suppressing intermodulation and harmonics, the following experiment is used to further illustrate the invention.

[0057] According to an embodiment of the present invention, in the experiment, the generation of the baseband signal and the implementation of the digital pre-distortion algorithm are both completed in MATLAB. The baseband signal is a dual-tone signal with a 12kHz interval, a carrier frequency of 3MHz, and a sampling of 15MHz. The input signal is downloaded to a vector signal generator (ESG4438C) and then injected into a power amplifier PA. The output signal of the power amplifier PA is attenuated and then captured by a spectrum analyzer.

[0058] According to an embodiment of the present invention, a delay estimation method for suppressing intermodulation and harmonics of a shortwave transmitter comprises the following steps:

[0059] Step 1: Amplitude align the baseband signal and the output signal of the down-conversion module;

[0060] Step 2: Perform preliminary delay alignment using the real part (or imaginary part) of the baseband signal and the output signal of the down-conversion module.

[0061] The delay function R(τ) can be calculated using the following formula, where real(u(n) is the real part of the baseband signal, the sequence length is 15000, real(y(n) is the real part of the output signal of the down-conversion module, the sequence length is 30000, [0,N] is the interval of the initial estimated delay position, and the value of N is 15000. The τ corresponding to the minimum R(τ) is the initial estimated delay, denoted as τ0. Setting the starting point of the output signal y(n) of the down-conversion module to τ0 can achieve initial delay alignment with the baseband signal u(n).

[0062]

[0063] After the initial delay alignment, the real part, imaginary part, and modulus of the baseband signal and the down-conversion module output signal are as follows: Figure 2 , Figure 3 , Figure 4 As shown, the main observation Figure 4,From this we can see that after the initial delay alignment, the alignment result of the modulus still has a certain time deviation, and the ,main observation area is the area with smaller amplitude value.

[0064] Step 3: Based on step 2, further delay alignment is performed using the modulus value of the baseband signal and the output signal of the down-conversion module.

[0065] The delay function R1(τ) can be calculated using the following formula, where y1(n) represents the output signal of the down-conversion module after the preliminary delay alignment in step 2, abs(u(n) is the modulus of the baseband signal, the sequence length is 1250, abs(y1(n) is the modulus of y1(n), the sequence length is 2500, [N0, N1] is the interval for further estimating the delay position, and the value of (N1-N0) is 1250. The τ corresponding to the minimum R1(τ) is the further estimated delay, denoted as τ1. τ0+τ1-N0 is the further estimated delay position. Setting the starting point of the down-conversion module output signal y(n) to τ0+τ1-N0 can achieve further delay alignment with the baseband signal u(n).

[0066]

[0067] Further delay alignment results are as follows Figure 5 As shown, it can be seen that further delay alignment can better suppress Figure 4 After digital pre-distortion processing, the suppression effect of intermodulation and harmonics is as follows: Figure 6 As shown in the figure, it can be seen that after digital pre-distortion processing, intermodulation and harmonics can be well suppressed.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A time delay estimation system for suppressing intermodulation and harmonics of shortwave transmitters, characterized in that: include: Pre-processing module, digital pre-distortion algorithm module (DPD), up-conversion module, digital-to-analog converter (DAC), power amplifier (PA), analog-to-digital converter (ADC) and down-conversion module, The first input end of the preprocessing module is connected to the baseband signal, the second input end is connected to the output end of the down-conversion module, and the output end of the preprocessing module is connected to the second input end of the digital predistortion algorithm module (DPD). The first input end of the digital pre-distortion algorithm module (DPD) is connected to the baseband signal, and the output end of the digital pre-distortion algorithm module (DPD) is connected to the input end of the up-conversion module. The output end of the up-conversion module is connected to the input end of a digital-to-analog converter (DAC), The output end of the digital-to-analog converter (DAC) is connected to the input end of the power amplifier (PA), The output end of the power amplifier (PA) is connected to the input end of the analog-to-digital converter (ADC), The output end of the analog-to-digital converter (ADC) is connected to the input end of the down-conversion module; The output end of the down-conversion module is connected to the second input end of the pre-processing module.

2. A delay estimation method for suppressing intermodulation and harmonics of shortwave transmitters, characterized in that: The following steps are involved: Step 1: Align the amplitude of the baseband signal and the output signal of the down-conversion module. Step 2: Perform preliminary delay alignment calculation using the baseband signal and the output signal, real part or imaginary part of the down-conversion module. Step 3: Based on the preliminary delay alignment of the baseband signal and the output signal of the down-conversion module, the module value of the signal is delayed again.

3. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 2, characterized in that: In step 2, the baseband signal and the real part of the output signal of the down-conversion module are preliminarily aligned using the following calculation function: Wherein, real(u(n)) is the real part of the baseband signal, R(τ) is the delay function, real(y(n)) is the real part of the output signal of the down-conversion module, [0,N] is the interval of the initial estimated delay position, and N is not less than the period of real(u(n)).

4. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 3 is characterized in that: The τ corresponding to the minimum R(τ) is the initially estimated time delay, denoted as τ0. The starting point of the output signal y(n) of the down-conversion module is set to τ0, thus completing the initial time delay alignment with the baseband signal u(n).

5. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 3, characterized in that: The delay function R(τ) is calculated by using the imaginary part of the baseband signal and the imaginary part of the output signal of the down-conversion module or by using the baseband signal and the output signal of the down-conversion module.

6. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 2, characterized in that: In step 3, based on the preliminary delay alignment of the baseband signal and the output signal of the down-conversion module, the module value of the signal is re-delayed and aligned using the following calculation function: Wherein, y1(n) represents the output signal of the down-conversion module after the preliminary delay alignment in step 2, abs(u(n)) is the modulus of the baseband signal, abs(y1(n)) is the modulus of y1(n), [N0, N1] is the interval for further estimating the delay position, the value of (N1-N0) is equal to the period of abs(u(n)), and R1(τ) is the delay function.

7. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 6, characterized in that: τ corresponding to the minimum R1(τ) is the further estimated time delay, denoted as τ1, τ0+τ1-N0 is the further estimated time delay position, and the starting point of the down-conversion module output signal y(n) is set to τ0+τ1-N0, thus completing the re-delay alignment with the baseband signal u(n).

8. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 6, characterized in that: To align the baseband signal u(n) with the down-conversion module output signal y(n), the sequence length of real(y(n)) is required to be smaller than the sequence length of real(u(n)), and the sequence length of abs(y1(n)) is required to be smaller than the sequence length of abs(u(n)).

9. The delay estimation method for suppressing shortwave transmitter intermodulation and harmonics according to claim 2, characterized in that: Step 1 Before amplitude alignment, use a low-pass filter to filter out the DC and harmonics of the output signal of the down-conversion module.

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