Digital pre-distortion and dispersion compensation method for frequency hopping communication system

Abstract

The invention belongs to the technical field of communication engineering, and relates to a digital pre-distortion and dispersion compensation method for a frequency hopping communication system, which comprises the following steps: generating S frequency mixing signals xs (n), s belongs to (1, S), respectively inputting the signals xs (n) into the frequency hopping communication system, and collecting a power amplifier forward signal zs (n), a power amplifier output signal mu s (n) and a system feedback signal vs (n) of the signals xs (n) in the frequency hopping communication system; calculating a group delay residual equalization signal rs (n) according to the signals vs (n) and mu s (n); performing time alignment on the signals rs (n) and zs (n) to obtain a time alignment signal rs' (n); estimating a predistortion coefficient according to the signals xs (n) and rs' (n), and updating the coefficient to a digital predistorter to obtain an updated frequency hopping communication system; inputting the frequency mixing signal into the updated frequency hopping communication system to obtain an output signal subjected to predistortion and dispersion compensation; according to the invention, mathematical modeling is carried out on the nonlinear behavior of the power amplifier under the excitation of the broadband signal with fast frequency hopping, and a method of combining digital pre-distortion and dispersion compensation is adopted, so that signal distortion caused by nonlinearity of the power amplifier can be accurately compensated, and the signal quality is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of communication engineering, and in particular relates to a digital predistortion and dispersion compensation method for a frequency hopping communication system. Background Art

[0002] In the field of modern communications, frequency hopping communication systems are widely used due to their good anti-interference ability and confidentiality. However, as a key component in frequency hopping communication systems, the nonlinear characteristics of power amplifiers bring many challenges to the system.

[0003] Traditional power amplifiers operate at a relatively fixed frequency and power range, and their design is relatively simple. However, in frequency hopping communications, as frequency hopping proceeds, the power amplifier needs to quickly switch its operating state at different frequencies. Due to its nonlinear characteristics, the signal will produce spectrum regeneration, which will not only expand the signal spectrum, invade adjacent channels, and cause adjacent channel interference, but also cause intermodulation distortion, generate new frequency components, and interfere with the original signal. For example, when two or more signals of different frequencies pass through a nonlinear power amplifier, intermodulation products such as sum frequency and difference frequency will be generated. These intermodulation products may fall into the signal frequency band, resulting in a serious degradation of signal quality.

[0004] Some existing compensation methods, such as analog pre-distortion technology, can improve the linearity of power amplifiers to a certain extent, but they have problems such as poor stability, limited accuracy, and difficulty in adapting to rapid frequency changes in frequency hopping systems. Although digital pre-distortion technology has the advantages of high flexibility and easy implementation, when applied in frequency hopping communication systems, the traditional digital pre-distortion method is difficult to achieve ideal compensation effects when facing broadband frequency hopping signals. On the one hand, it is difficult to quickly and accurately obtain the nonlinear characteristics of the power amplifier at each frequency point during the rapid frequency switching process, resulting in the inability to adjust the pre-distortion parameters in a timely and accurate manner; on the other hand, when processing broadband signals, traditional methods are difficult to effectively deal with the different degrees of nonlinearity of different frequency components within the signal bandwidth.

[0005] In addition, the dispersion problem in frequency hopping communication systems cannot be ignored. During the transmission of signals, due to factors such as the frequency selectivity of the transmission medium, group delay distortion will occur, causing signal components of different frequencies to arrive at the receiving end at different times, further affecting signal synchronization and quality. Existing dispersion compensation methods are often independent of power amplifier nonlinear compensation methods, lack effective collaborative design, and cannot fully solve the signal distortion problem in frequency hopping communication systems.

[0006] In summary, the existing digital pre-distortion method is difficult to achieve an ideal compensation effect when facing broadband frequency hopping signals, and the existing dispersion compensation method is often independent of the digital pre-distortion method and cannot fully solve the signal distortion problem in the frequency hopping communication system. Summary of the invention

[0007] In order to solve the above-mentioned prior art problems, the present invention adopts a digital predistortion and dispersion compensation method for a frequency hopping communication system, the frequency hopping communication system comprising: a digital predistorter, the digital predistortion and dispersion compensation method comprising:

[0008] S1, generate S mixing signals x with different carrier frequencies s (n),s∈(1,S), input the mixed signals of different carrier frequencies into the frequency hopping communication system respectively, and collect the forward signal z of the power amplifier of the mixed signals of different carrier frequencies in the frequency hopping communication system s (n), amplifier output signal μ s (n), system feedback signal v s (n); where s is the index of the mixing signal;

[0009] S2, according to the system feedback signal v s (n) and the amplifier output signal μ s (n) Calculate the group delay residual equalization signal r s (n);

[0010] S3, equalize the group delay residual signal r s (n) and the amplifier forward signal z s (n) Perform time alignment to obtain the time alignment signal r s '(n);

[0011] S4, according to the mixing signal x of different carrier frequencies s (n) and the time-aligned signal r s '(n) estimating predistortion coefficients corresponding to different carrier frequencies, and updating the predistortion coefficients corresponding to different carrier frequencies into a digital predistorter of a frequency hopping communication system to obtain an updated frequency hopping communication system;

[0012] S5. Obtain a predistorted and dispersion compensated output signal according to the updated frequency hopping communication system.

[0013] The beneficial effects of the present invention are as follows:

[0014] 1. Effectively compensate for signal distortion: The present invention adopts a method that combines digital pre-distortion with dispersion compensation, which can comprehensively and accurately compensate for signal distortion caused by power amplifier nonlinearity and transmission medium. This enables the signal to maintain good waveform integrity during transmission, reduces signal distortion, and thus improves signal quality.

[0015] 2. Improve frequency adaptability: The present invention generates mixing signals of different carrier frequencies, and mathematically models the nonlinear behavior of the power amplifier under the excitation of the fast-hopping broadband signal according to the power amplifier forward signal, power amplifier output signal and system feedback signal of the mixing signals of different carrier frequencies in the frequency-hopping communication system, and calculates the predistortion coefficient of the mixing signal of each carrier frequency based on the modeling result, thereby realizing cross-frequency and dynamically changing nonlinear compensation. This method solves the adaptability problem of traditional methods in frequency changes, ensures that signals at different frequency points in the frequency-hopping communication system can be effectively predistorted, and further stabilizes the signal quality.

[0016] 3. Reduce hardware requirements: The digital predistortion and dispersion compensation method of the present invention reduces the dependence on hardware performance to a certain extent, and can avoid excessively increasing the complexity and cost of hardware equipment such as power amplifiers in order to achieve the same signal quality, thereby reducing hardware requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flow chart of a digital predistortion and dispersion compensation method for a frequency hopping communication system provided by an embodiment of the present invention;

[0018] Figure 2 It is a system block diagram of a digital predistortion and dispersion compensation method for a frequency hopping communication system provided by an embodiment of the present invention;

[0019] Figure 3 It is a block diagram of a group delay residual equalization model of a frequency hopping communication system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, the present invention adopts a digital predistortion and dispersion compensation method for a frequency hopping communication system, the frequency hopping communication system comprises: a digital predistorter, and the digital predistortion and dispersion compensation method comprises:

[0022] S1, generate S mixing signals x with different carrier frequencies s (n),s∈(1,S), input the mixed signals of different carrier frequencies into the frequency hopping communication system respectively, and collect the forward signal z of the power amplifier of the mixed signals of different carrier frequencies in the frequency hopping communication system s(n), amplifier output signal μ s (n), system feedback signal v s (n); where s is the index of the mixing signal; the amplifier forward signal z s (n) and the amplifier output signal μ s (n) are the signals collected from the input and output signals of the power amplifier of the frequency hopping communication system, and the system feedback signal v s (n) is a signal collected from the final output signal of the frequency hopping communication system;

[0023] Generating mixing signals with different carrier frequencies includes: generating an I-channel baseband signal and a Q-channel baseband signal; performing up-conversion on the I-channel baseband signals and the Q-channel baseband signals at different frequencies, respectively, and synthesizing the up-converted I-channel baseband signals and the Q-channel baseband signals to obtain mixing signals x1(n)…x S (n); where S is the number of frequency hopping points for up-conversion and n is the time variable of the signal.

[0024] Up-converting the I and Q baseband signals respectively includes: multiplying the I and Q baseband signals with the local oscillator (LO) signal through a mixer; for the I and Q signals, two different LO signals are used respectively, and the two signals have the same frequency hopping frequency but a phase difference of 90° (i.e., orthogonal).

[0025] S2, according to the system feedback signal v s (n) and the amplifier output signal μ s (n) Calculate the group delay residual equalization signal r s (n);

[0026] The specific steps include:

[0027] like Figure 3 As shown, a group delay residual equalization model is constructed:

[0028] Where n is the time variable of the signal, M is the tap level of the filter of the group delay residual equalization model; d s,p and d s,M+p is the tap coefficient of the filter of the group delay residual equalization model, which is used to adjust the weights of different delay paths. i is the subscript index from 0 to M, T is the unit offset of time, and s 1 / T represents the Laplace transform;

[0029] According to the system feedback signal, the basis function matrix V is calculated using the LTI cascade network with a fixed delay interval of 1 / τ; wherein LTI is linear time invariant and 1 / τ is a time constant;

[0030] τ=B / f s

[0031] Where B is the acquired signal bandwidth, f s is the system sampling rate;

[0032] The matrix is ​​constructed as follows: s,N×1 =V s,N×(2M+1) d s,(2M+1)×1 , where N is the length of the signal, d s,(2M+1)×1 is the coefficient matrix of the group delay residual equalization model, V s,N×(2M+1) It is the basis function matrix generated according to the system feedback signal, and is generated in the following way;

[0033]

[0034] Calculate the coefficients of the group delay residual equalization model based on the basis function matrix V and the power amplifier output signal: s =(V s H V s ) - 1 V s H u s ; Among them, u s The output signal u is the power amplifier s (n) constructed matrix; directly put u s (n) Sort by time to form a column vector:

[0035]

[0036] The coefficients and the system feedback signal are input into a group delay residual equalization model to obtain a group delay residual equalization signal.

[0037] S3, equalize the group delay residual signal r s (n) and the amplifier forward signal z s (n) Perform time alignment to obtain the time alignment signal r s '(n);

[0038] The specific steps include:

[0039] Calculate the group delay residual equalization signal r s (n) and the amplifier forward signal z s The wavelet coefficient W of (n) s,r (j,k) and W s,z (j,k):

[0040]

[0041] ψ j,k (n) = 2 j / 2 ψ(2 j nk)

[0042] Where j is the signal r s (n) and z s (n) is the scale parameter, k is the signal r s (n) and z s The translation parameter of (n), ψ j,k (n) is a wavelet function with scale parameter j and translation parameter k, is j,k The complex conjugate of (n);

[0043] The scale parameter usually depends on the scale level of the wavelet transform used; in one embodiment, the minimum value j of the scale parameter is min Usually it is taken as 0, indicating the coarsest scale (the scale of the original signal), and the maximum value j max satisfy

[0044] According to the wavelet coefficient W x (j,k) and W y (j,k) Calculate the cross-correlation function in the wavelet domain Where δ is the Kronecker function, n and m are the time variables of the signal, 0≤n≤N-1, 0≤m≤N-1, and are defined as follows:

[0045]

[0046] Calculation The variable that reaches the maximum value Calculate the time delay based on the variable k0 According to the time delay Δn s For signal r s (n) is adjusted to obtain the time-aligned signal r'(n).

[0047] S4, according to the mixing signal x of different carrier frequencies s (n) and the time-aligned signal r s '(n) estimating predistortion coefficients corresponding to different carrier frequencies, and updating the predistortion coefficients corresponding to different carrier frequencies into a digital predistorter of a frequency hopping communication system to obtain an updated frequency hopping communication system;

[0048] The input I-channel baseband signal and Q-channel baseband signal are the same set of data in one cycle, except that the carrier is the frequency hopping point with the subscript 1-S; then after mixing, x1(n)…x S (n) Mixing signal; The following operator matrix U can be formed by the memory polynomial model MP model: mp :

[0049]

[0050] All input signals are then combined into an operator matrix U as follows:

[0051]

[0052] Among them, x S (n) is the signal after the baseband signal is mixed through the frequency hopping point S, q represents the memory depth of the MP model, and k represents the nonlinear order of the MP model;

[0053] Construct the output matrix, which is the corresponding weighted average

[0054] The predistortion coefficients are obtained by the least squares method. Where c = [c1(L)…c1(0)c2(L)…c2(0)…c S (L)…c S (0)] T , L is the number of pre-distortion coefficients.

[0055] S5. Obtain a predistorted and dispersion compensated output signal according to the updated frequency hopping communication system.

[0056] Specifically, the updated frequency hopping communication system generates a mixing signal, and the updated frequency hopping communication system selects a corresponding predistortion coefficient according to the generated mixing signal, and finally the frequency hopping communication system outputs a predistorted and dispersion compensated output signal.

[0057] On the other hand, Figure 2 As shown, the present invention adopts a system based on the above-mentioned digital predistortion and dispersion compensation method for a frequency hopping communication system, comprising:

[0058] A baseband signal frequency hopping processing module, used to generate mixed signals of different carriers;

[0059] A frequency hopping communication system is used to process a mixing signal for generating different carriers; the frequency hopping communication system comprises: a digital predistorter;

[0060] A signal acquisition module, used for acquiring a power amplifier forward signal, a power amplifier output signal and a system feedback signal of a frequency hopping communication system through an analog-to-digital converter ADC;

[0061] A group delay equalization module, used for calculating a group delay residual equalization signal according to a system feedback signal and a power amplifier output signal;

[0062] Wavelet domain time alignment module, used to time align the group delay residual equalization signal and the power amplifier forward signal;

[0063] The DPD coefficient estimation module is used to estimate the predistortion coefficient according to the mixing signals and time alignment signals of different carriers, and update the predistortion coefficient to the digital predistorter of the frequency hopping communication system.

[0064] The frequency hopping communication system comprises: a first switch, a second switch, a DPD predistorter, a digital-to-analog converter DAC, a power amplifier PA and a subsequent processing module; the output end of the baseband signal frequency hopping processing module is connected to the output end of the first switch, the output end 1 of the first switch is connected to the input end of the DPD predistorter, the output end of the DPD predistorter is connected to the input end 1 of the second switch, the output end 2 of the first switch is connected to the input end 2 of the second switch, the output end of the second switch is connected to the input end of the DAC, the output end of the DAC is connected to the input end of the PA, and the output end of the PA is connected to the input end of the subsequent processing module.

[0065] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation modes 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 in the protection scope of the present invention.

Claims

1. A digital predistortion and dispersion compensation method for a frequency hopping communication system, the frequency hopping communication system comprising: A digital predistorter, characterized in that the digital predistortion and dispersion compensation method comprises: S1, generate S mixing signals x with different carrier frequencies s (n),s∈(1,S), input the mixed signals of different carrier frequencies into the frequency hopping communication system respectively, and collect the forward signal z of the power amplifier of the mixed signals of different carrier frequencies in the frequency hopping communication system s (n), amplifier output signal μ s (n), system feedback signal v s (n); where s is the index of the mixing signal; S2, according to the system feedback signal v s (n) and the amplifier output signal μ s (n) Calculate the group delay residual equalization signal r s (n); S3, equalize the group delay residual signal r s (n) and the amplifier forward signal z s (n) Perform time alignment to obtain the time alignment signal r s '(n); S4, according to the mixing signal x of different carrier frequencies s (n) and the time-aligned signal r s '(n) estimating predistortion coefficients corresponding to different carrier frequencies, and updating the predistortion coefficients corresponding to different carrier frequencies to a digital predistorter of a frequency hopping communication system to obtain an updated frequency hopping communication system; S5. Obtain a predistorted and dispersion compensated output signal according to the updated frequency hopping communication system.

2. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 1, characterized in that: Generating mixing signals with different carrier frequencies includes: generating an I-channel baseband signal and a Q-channel baseband signal; performing up-conversion of the I-channel baseband signals and the Q-channel baseband signals at different frequencies, and synthesizing the I-channel baseband signals and the Q-channel baseband signals after the up-conversion at the same frequency to obtain mixing signals x1(n)…x S (n); where S is the number of frequency hopping points for up-conversion and n is the time variable of the signal.

3. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 1, characterized in that: Calculating the group delay residual equalization signal according to the system feedback signal and the power amplifier output signal includes: constructing a group delay residual equalization model, calculating the basis function matrix using the LTI cascade network according to the system feedback signal; calculating the coefficients of the group delay residual equalization model according to the basis function matrix and the power amplifier output signal, inputting the coefficients and the system feedback signal into the group delay residual equalization model, and obtaining the group delay residual equalization signal r s (n); where LTI is linear time invariant.

4. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 3, characterized in that: The group delay residual equalization model includes: Where n is the time variable of the signal, M is the tap level of the filter of the group delay residual equalization model; d s,p and d s,M+p is the tap coefficient of the filter of the group delay residual equalization model, i is the subscript index from 0 to M, and T is the unit offset of time.

5. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 3, characterized in that: The coefficients of the group delay residual equalization model calculated based on the basis function matrix and the power amplifier output signal include: s =(V s H V s ) -1 V s H u s ; Where d is the coefficient matrix of the group delay residual equalization model corresponding to the sth mixing signal, u s The output signal u is the power amplifier s (n) The constructed matrix, V s is the basis function matrix corresponding to the s-th mixing signal. The superscript H represents the conjugate transpose, and the superscript -1 represents the inverse.

6. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 1, characterized in that: The time alignment of the group delay residual equalization signal and the power amplifier forward signal includes: respectively calculating the group delay residual equalization signal r s (n) and the amplifier forward signal z s The wavelet coefficient W of (n) s,r (j,k) and W s,z (j,k), according to the wavelet coefficient W s,r (j,k) and W s,z (j,k) Calculate the cross-correlation function in the wavelet domain Calculation The variable k0 reaches the maximum value, and the time delay Δn is calculated based on the variable k0 s ; According to the time delay Δn s For signal r s (n) is adjusted to obtain the time-aligned signal r s '(n); where j is the signal r s (n) and z s (n) is the scale parameter, k is the signal r s (n) and z s (n) is the translation parameter of 7. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 6, characterized in that: Cross-correlation function in wavelet domain Where δ is the Kronecker function, and n and m are the time variables of the signal.

8. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 1, characterized in that: Estimating the predistortion coefficients according to the mixing signals and the time-aligned signals of different carrier frequencies includes: constructing an operator matrix U according to the mixing signals of different carrier frequencies, constructing an output matrix according to the time-aligned signals; estimating the predistortion coefficients according to the output matrix and the operator matrix U.

9. The digital predistortion and dispersion compensation method for a frequency hopping communication system according to claim 1, characterized in that: Constructing the output matrix from the time-aligned signal includes: in, is the output matrix.

10. A system using the digital predistortion and dispersion compensation method for a frequency hopping communication system as claimed in claims 1 to 9, characterized in that: include: A baseband signal frequency hopping processing module, used to generate mixing signals with different carrier frequencies; A frequency hopping communication system for processing mixed signals that generate different carrier frequencies; The frequency hopping communication system includes: a digital predistorter; A signal acquisition module, used to acquire the power amplifier forward signal, power amplifier output signal and system feedback signal of the frequency hopping communication system; A group delay equalization module, used for calculating a group delay residual equalization signal according to a system feedback signal and a power amplifier output signal; Wavelet domain time alignment module, used to time align the group delay residual equalization signal and the power amplifier forward signal; The DPD coefficient estimation module is used to estimate the coefficients of the digital predistortion DPD according to the mixing signals and time alignment signals of different carrier frequencies, and update the coefficients of the digital predistortion to the digital predistorter of the frequency hopping communication system.

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