阅读说明：本技术 一种多制式同频干扰抵消方法 (Multi-system same-frequency interference cancellation method ) 是由 贺荣华 涂世龙 万坚 李翔 于 2020-04-28 设计创作，主要内容包括：本发明公开了一种多制式同频干扰抵消方法,包括以下步骤：检测干扰信号的有无,对连续信号和突发信号均能适应,采用滑动双窗法进行干扰的检测,判定干扰的有无,在有干扰的情况下记录干扰的起始位置和结束位置；对干扰的参数进行初始估计,参数包括信道传输的时延、频偏和幅相,利用估计到的参数完成两路信号对准和频偏的校正；将幅相估计的结果作为自适应滤波器的初值,采用多态LMS跟踪环路算法实现干扰的抵消。本发明支持多种不同样式的干扰,包括各种调制信号、单音、噪声调频等,可应用于多种干扰场景中；对于不同的干扰样式具有普适性。(The invention discloses a multi-system same frequency interference cancellation method, which comprises the following steps: detecting whether an interference signal exists or not, adapting to both continuous signals and burst signals, detecting the interference by adopting a sliding double-window method, judging whether the interference exists or not, and recording the initial position and the end position of the interference under the condition of the interference; initially estimating interference parameters, wherein the parameters comprise time delay, frequency offset and amplitude phase of channel transmission, and completing alignment of two paths of signals and correction of frequency offset by using the estimated parameters; and taking the result of the amplitude-phase estimation as an initial value of the adaptive filter, and adopting a polymorphic LMS tracking loop algorithm to realize the interference cancellation. The invention supports various interferences with different styles, including various modulation signals, single tone, noise frequency modulation and the like, and can be applied to various interference scenes; and the method has universality for different interference patterns.)

1. A multi-system same-frequency interference cancellation method is characterized by comprising the following steps:

s1: an interference detection step, namely detecting whether an interference signal exists or not, adapting to both continuous signals and burst signals, detecting the interference by adopting a sliding double-window method, judging whether the interference exists or not, and recording the initial position and the end position of the interference under the condition of the interference;

s2: a parameter initial estimation step, in which after the interference is detected in step S1, initial estimation is performed on interference parameters, the parameters include time delay, frequency offset and amplitude phase of channel transmission, and the estimated parameters are used to complete alignment of two paths of signals and correction of frequency offset;

s3: and a multi-state adaptive interference cancellation step, namely, on the basis of the step S2, the result of the amplitude-phase estimation is used as an initial value of the adaptive filter, and the multi-state LMS tracking loop algorithm is adopted to realize the interference cancellation.

2. The method according to claim 1, wherein the interference detection by the sliding dual window method in step S1 is as follows:

adopting sliding double-window method burst detection, starting or stopping the self-adaptive canceller under the guidance of a detection result, and enabling the canceller to work only in the time period when interference occurs, and outputting directly without interference;

the sliding double-window method detects the start and stop of a signal by comparing the signal energy in two adjacent time windows; that is, two adjacent windows with a length of L are assumed and are respectively referred to as windows a and B; when two windows slide on the received signal, the energy falling into the two windows is E_AAnd E_B：

S 'in the above formula'₁Representing a signal sample point sequence, n is a related starting point, and k represents a sample point index in a related window;

during detection, the window A and the window B start to slide; when both windows contain only noise energy, E_AAnd E_BAre constant, their ratio m is also constant, i.e. m equals 1; the two windows continue to slide, the burst signal gradually enters the window B, the energy of the window B is gradually increased, the window A only contains noise at the moment, and the energy ratio of the two windows is gradually increased; when the window B just contains all burst signals, the window A still only contains all noise energy, the ratio m of the two windows reaches the maximum, and the window B corresponds to the starting moment of the burst signals; then, the window A also gradually contains burst signals, and the energy ratio m of the two windows gradually falls back to 1; when window B contains noise energy, m continues to decrease; when the window B just contains noise, the window A contains burst signals, and the ratio m of the two windows reaches the minimum, the end time of the corresponding burst signals is reached.

3. The method according to claim 2, wherein in step S2, the specific content of initial estimation of the time delay is as follows:

the method used for initial estimation of the delay is differential correlation, i.e.,

respectively differentiating the reference interference and the aliasing signal to obtain

d_r(n)＝r(n)conj(r(n-τ))；

In the above formula, d_rAs a result of the difference in the interfering signals,n is a sampling point index, r is an interference signal s'₁For aliasing signals, tau is a difference interval, and the over-sampling multiple of the interference signal is taken for re-correlation to obtain

In the above formula, E represents the average value,the peak value obtained by correlation, m is the position of correlation calculation, and N is the data volume of correlation calculation; - τ_max≤m≤τ_max，τ_maxDetermining the maximum delay deviation which can be tolerated by the canceller for the size of the time window of the correlation search;

performing sliding correlation on the aliasing signal and the reference signal in a set time window, searching the maximum value of a correlation peak, and recording the position to obtain the relative time delay of the aliasing signal and the reference signal; because the reference signal is a local input and the aliasing signal is a signal transmitted through a physical channel, the accurate channel delay can be obtained through the relative delay.

4. The method according to claim 3, wherein in step S2, the specific content of the initial estimation of the frequency difference is as follows:

establishing a signal receiving model

WhereinThe time delay of the previously estimated integer sample point; if the target signal and the noise in r (n) are ignored, y (n) is a single-frequency signal, and the frequency of the single-frequency signal is the frequency difference of the interference signals of the two channels; frequency difference estimation is realized through FFT; that is to say that the first and second electrodes,

z(n)＝abs(FFT(y(n)，L))

z(k)＝max(z(n))

in the above formula, z (n) is the amplitude obtained after FFT calculation, L is the length of FFT calculation, and when n is k, the peak z of the spectrum is obtained_k(ii) a Only the frequency corresponding to the peak value needs to be calculated, namely the frequency difference; carrying out parabolic fitting by utilizing the peak value and the points on the left side and the right side; variables a and b are set respectively, and the values are calculated by the following formulas

Obtaining the distance tau between k and the fitted peak value as-b/2 a, and calculating a final frequency offset value on the basis of the distance tau;

in the above formula, F_sIs the sampling rate of the signal.

5. The method according to claim 4, wherein in step S2, the content of the initial estimation of amplitude and phase is as follows:

correlating the two signals to obtain

In the above formula, m is the relevant position; taking the maximum value of the correlation peak, wherein the correlation value is the amplitude-phase difference between the two paths of signals;

computingCarrying out parabolic fitting on the three correlation values;

and obtaining the estimation of the time delay of the fractional sampling point.

6. The multi-system co-channel interference cancellation method according to claim 5, wherein in step S3, the specific content of interference cancellation implemented by using the polymorphic LMS tracking loop algorithm is as follows:

waiting for a link; that is, when no interference is detected, the filter does not operate;

counteracting a link; that is, the first interference is detected, the filter coefficient is initialized, the operation is started, and the coefficient is updated iteratively;

keeping a link; that is, after the interference disappears, the filter coefficient is kept and the next interference is waited for; after the interference occurs, counting the offset state again, and updating the coefficient in an iterative manner;

resetting; that is, if there is no interference for a long time, the timeout condition is reached, i.e., the filter coefficient is reset, and the standby state is entered again.

7. The method according to claim 4, wherein in step S2, after the initial estimation of the frequency difference is completed, the step of calculating the estimated error of the frequency difference is further performed, specifically as follows:

introducing a phase-locked loop, wherein a structure of a second-order phase-locked loop, namely a closed-loop structure of a phase discriminator, a loop filter and a voltage-controlled oscillator, is adopted, and two inputs of the phase discriminator are respectively a main channel received signal and reconstruction interference; setting the output phase of the voltage-controlled oscillator at n time toThen the interference is reconstructed asThe phase error output by the phase detector can then be simply obtained by correlation of the received waveforms of the main and auxiliary channels, as follows:

in the above formula, r (n) is an interference signal, m represents the position of the correlation, and l is the size of the time window selected when the correlation is performed.

Technical Field

The invention belongs to the technical field of military communication anti-interference and communication countermeasure, and particularly relates to a multi-system same-frequency interference cancellation method.

Background

In the prior art, the field of military communication anti-interference and communication countermeasure solves the problem of eliminating common-frequency intentional or unintentional interference when own party communicates. The problem of co-frequency interference widely exists in communication, such as the problem of coupling interference of transmitted signals in a co-frequency full duplex communication system, the problem of mutual interference among multiple transceivers in the same communication platform, the problem of eliminating interference signals transmitted by the own party in communication countermeasure, and the like, research organizations and various companies at home and abroad conduct extensive research on the problem, and some patents also exist in the field at present.

For example, the chinese patent discloses a system and method for canceling simultaneous same-frequency self-interference of large transmission power in a multipath environment. The patent mainly processes interference at a radio frequency end, adopts a two-stage interference cancellation method, and obtains an original signal by subtracting an output radio frequency signal and an interference reconstruction signal. The method is mainly suitable for a simultaneous same-frequency system, and the interference pattern is only limited to a continuous signal waveform and is not suitable for counteracting the burst interference.

For example, the chinese patent discloses a method, an apparatus and a system for canceling co-channel interference. The method is mainly applied to the field of microwave communication, and is mainly used for offsetting an interference signal formed by a local transmitting terminal to a local receiving terminal, acquiring the local transmitting signal through a coupler, enabling a coupling signal to pass through an analog interference channel composed of an attenuator, an amplifier, a phase shifter, a time delay line and the like, adjusting the phase to be an odd multiple of 180 degrees different from the interference signal, and then outputting the odd multiple to the receiving terminal through the coupler, thereby realizing the offset of the interference signal. The key point of the method lies in the design of an analog interference channel, which is not suitable for the interference cancellation of digital signals and is also not suitable for the cancellation of burst interference.

That is, the existing interference cancellation method is only suitable for interference cancellation of continuous signals, and for different interference patterns, especially for a sudden interference scenario, the existing method cannot be applied, and has certain limitations in application scenarios.

Therefore, a multi-system co-channel interference cancellation method is urgently needed to be researched.

Disclosure of Invention

The invention aims to provide a multi-system same-frequency interference cancellation method, which is used for solving one of the technical problems in the prior art, such as: the existing interference cancellation method is only suitable for interference cancellation of continuous signals, and for different interference patterns, especially for a scene of burst interference, the existing technical method cannot be suitable, and has certain limitation in an application scene. The invention aims to provide a multi-system same-frequency interference cancellation method, which can effectively cancel interference in different forms such as continuous interference, burst interference and the like and interference in different forms such as modulation signals, single tone interference, noise frequency modulation interference and the like. The method is high in practicability, tests are conducted under different practical interference backgrounds, and interference can be effectively eliminated. The key points of the method comprise: 1. the method for multi-state self-adaptive interference cancellation is provided, and has universality for different interference patterns; 2. the frequency tracking problem under the condition of large frequency offset of an actual signal is solved by adopting differential correlation and phase-locked loop tracking technologies; 3. an efficient detection technology is added for the burst interference, the work of the self-adaptive filter is guided through a detection result, and the canceller does not work when the interference does not exist, so that the rapid convergence of the burst interference cancellation is ensured; 4. the synchronization and channel parameter fitting technology aiming at the burst interference is provided, and the high-precision initial estimation of the burst interference parameters is realized.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a multi-system same-frequency interference cancellation method comprises the following steps:

s1: an interference detection step, namely detecting whether an interference signal exists or not, adapting to both continuous signals and burst signals, detecting the interference by adopting a sliding double-window method, judging whether the interference exists or not, and recording the initial position and the end position of the interference under the condition of the interference;

s2: a parameter initial estimation step, in which after the interference is detected in step S1, initial estimation is performed on interference parameters, the parameters include time delay, frequency offset and amplitude phase of channel transmission, and the estimated parameters are used to complete alignment of two paths of signals and correction of frequency offset;

s3: and a multi-state adaptive interference cancellation step, namely, on the basis of the step S2, the result of the amplitude-phase estimation is used as an initial value of the adaptive filter, and the multi-state LMS tracking loop algorithm is adopted to realize the interference cancellation.

Further, the specific content of the detection of the interference by the sliding dual-window method in step S1 is as follows:

adopting sliding double-window method burst detection, starting or stopping the self-adaptive canceller under the guidance of a detection result, and enabling the canceller to work only in the time period when interference occurs, and outputting directly without interference;

the sliding double-window method detects the start and stop of a signal by comparing the signal energy in two adjacent time windows; that is, two adjacent windows with a length of L are assumed and are respectively referred to as windows a and B; when two windows slide on the received signal, the energy falling into the two windows is E_AAnd E_B：

S 'in the above formula'₁Representing a signal sample point sequence, n is a related starting point, and k represents a sample point index in a related window;

during detection, the window A and the window B start to slide; when both windows contain only noise energy, E_AAnd E_BAre constant, their ratio m is also constant, i.e. m equals 1; the two windows continue to slide, the burst signal gradually enters the window B, the energy of the window B is gradually increased, the window A only contains noise at the moment, and the energy ratio of the two windows is gradually increased; when the window B just contains all burst signals, the window A still only contains all noise energy, the ratio m of the two windows reaches the maximum, and the window B corresponds to the starting moment of the burst signals; then, the window A also gradually contains burst signals, and the energy ratio m of the two windows gradually falls back to 1; when window B contains noise energy, m continues to decrease; when the window B just contains noise, the window A contains burst signals, and the ratio m of the two windows reaches the minimum, the end time of the corresponding burst signals is reached.

Further, in step S2, the specific content of the initial estimation of the time delay is as follows:

the method used for initial estimation of the delay is differential correlation, i.e.,

respectively differentiating the reference interference and the aliasing signal to obtain

d_r(n)＝r(n)conj(r(n-τ))；

In the above formula, d_rAs a result of the difference in the interfering signals,n is a sampling point index, r is an interference signal s'₁For aliasing signals, tau is a difference interval, and the over-sampling multiple of the interference signal is taken for re-correlation to obtain

In the above formula, E represents the average value,the peak value obtained by correlation, m is the position of correlation calculation, and N is the data volume of correlation calculation; - τ_max≤m≤τ_max，τ_maxDetermining the maximum delay deviation which can be tolerated by the canceller for the size of the time window of the correlation search;

performing sliding correlation on the aliasing signal and the reference signal in a set time window, searching the maximum value of a correlation peak, and recording the position to obtain the relative time delay of the aliasing signal and the reference signal; because the reference signal is a local input and the aliasing signal is a signal transmitted through a physical channel, the accurate channel delay can be obtained through the relative delay.

Further, the specific content of the initial estimation of the frequency difference is as follows:

establishing a signal receiving model

WhereinThe time delay of the previously estimated integer sample point; if the target signal and the noise in r (n) are ignored, y (n) is a single-frequency signal, and the frequency of the single-frequency signal is the frequency difference of the interference signals of the two channels; frequency difference estimation is realized through FFT; that is to say that the first and second electrodes,

z(n)＝abs(FFT(y(n)，L))

z(k)＝max(z(n))

in the above formula, z (n) is the amplitude obtained after FFT calculation, L is the length of FFT calculation, and when n is k, the peak z of the spectrum is obtained_k(ii) a Only the frequency corresponding to the peak value needs to be calculated, namely the frequency difference; carrying out parabolic fitting by utilizing the peak value and the points on the left side and the right side; variables a and b are set respectively, and the values are calculated by the following formulas

Obtaining the distance tau between k and the fitted peak value as-b/2 a, and calculating a final frequency offset value on the basis of the distance tau;

in the above formula, F_sIs the sampling rate of the signal.

Further, the details of the initial estimation of the amplitude and phase are as follows:

correlating the two signals to obtain

In the above formula, m is the relevant position; taking the maximum value of the correlation peak, wherein the correlation value is the amplitude-phase difference between the two paths of signals;

computingCarrying out parabolic fitting on the three correlation values;

and obtaining the estimation of the time delay of the fractional sampling point.

Further, the specific content of implementing interference cancellation by using the polymorphic LMS tracking loop algorithm is as follows:

waiting for a link; that is, when no interference is detected, the filter does not operate;

counteracting a link; that is, the first interference is detected, the filter coefficient is initialized, the operation is started, and the coefficient is updated iteratively;

keeping a link; that is, after the interference disappears, the filter coefficient is kept and the next interference is waited for; after the interference occurs, counting the offset state again, and updating the coefficient in an iterative manner;

resetting; that is, if there is no interference for a long time, the timeout condition is reached, i.e., the filter coefficient is reset, and the standby state is entered again.

Further, after the initial estimation of the frequency difference is completed, a step of calculating a frequency difference estimation error is also performed, which specifically includes:

introducing a phase-locked loop, adopting a second-order phase-locked loop structure, namely a closed-loop structure of a phase detector, a loop filter and a voltage-controlled oscillator, wherein two phase detectors are arranged on the phase detectorThe inputs should be the main channel received signal and reconstructed interference, respectively; setting the output phase of the voltage-controlled oscillator at n time toThen the interference is reconstructed asThe phase error output by the phase detector can then be simply obtained by correlation of the received waveforms of the main and auxiliary channels, as follows:

in the above formula, r (n) is an interference signal, m represents the position of the correlation, and l is the size of the time window selected when the correlation is performed.

Compared with the prior art, the invention has the beneficial effects that:

1. the method supports various types of interference, including various modulation signals, single tone, noise frequency modulation and the like, and can be applied to various interference scenes; universal for different interference patterns;

2. the method is specially optimized for the burst interference, can quickly capture the burst interference, accurately estimate the interference parameters and solve the problem of quick convergence of the burst interference cancellation;

3. interference capture is carried out by adopting a waveform correlation method, so that the method can adapt to a wider range of interference-to-signal ratio;

4. the method adopts a differential correlation technology, and overcomes the problem of interference capture under the condition of large frequency offset;

5. a phase-locked loop is introduced into the self-adaptive offset loop, so that the problem of phase tracking during long-time operation is solved, and offset loss is reduced.

Drawings

FIG. 1 is a schematic workflow diagram of an embodiment of the present invention.

Fig. 2 is a schematic diagram of a burst detection process by a double window method according to an embodiment of the present invention.

Fig. 3 is a diagram of a frequency offset parabolic fit in accordance with an embodiment of the present invention.

FIG. 4 is a schematic diagram of a magnitude and phase estimation parabolic fit according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of the basic principle of adaptive interference cancellation according to an embodiment of the present invention.

Fig. 6 is a schematic diagram of an adaptive FIR filter structure according to an embodiment of the present invention.

FIG. 7 is a state transition diagram according to an embodiment of the present invention.

Fig. 8 is a schematic diagram of a second order pll according to an embodiment of the present invention.

Fig. 9 is a schematic diagram of an interference signal cancellation test according to an embodiment of the present invention.

Fig. 10 is a schematic diagram of an interference cancellation device corresponding to a multi-system co-channel interference cancellation method according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to fig. 1 to 10 of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.