An interference detection and estimation method and system based on communication signal spectrum cancellation

Abstract

The present invention discloses an interference detection and estimation method and system based on communication signal spectrum cancellation. The method includes the following steps: obtaining the actual power spectrum of a communication signal; calculating the theoretical power spectrum of the communication signal according to prior information, and subtracting the actual power spectrum from the theoretical power spectrum to obtain a first power spectrum; performing interference detection on the first power spectrum to obtain an interference signal power spectrum; estimating interference signal parameters according to the interference signal power spectrum; and performing direction finding according to the power estimation value of the interference signal parameters. Compared with the prior art, the present invention can obtain a power spectrum that only retains interference information, thereby obtaining accurate results of interference signal parameter estimation and interference source positioning.

Description

Technical Field

[0001] The present invention relates to the field of signal processing, and in particular to an interference detection and estimation method and system based on communication signal spectrum cancellation. Background Art

[0002] In current satellite communication and telemetry processes, it is extremely vulnerable to malicious interference. It has become an urgent need to perform interference detection and parameter estimation on signals and further make countermeasures. Thus, various interference detection technologies have emerged. Patent CN105933032A discloses a frequency-domain anti-interference algorithm under enhanced power background, which uses the symmetry of the navigation signal itself to cancel the signal on the left and right of itself. After canceling the signal, the traditional CME algorithm can be used to estimate the adaptive interference detection threshold. This method uses the traditional threshold-based interference detection technology, but the traditional threshold-based interference detection technology cannot accurately estimate the power of the signal. And accurately estimating the power of the signal can perform amplitude comparison direction finding on the interference, further locate the interference source and counter it. Therefore, there is an urgent need for a method that can obtain accurate interference detection and estimation results. Summary of the Invention

[0003] The technical problem to be solved by the present invention lies in: aiming at the technical problems existing in the prior art, the present invention provides an interference detection and estimation method and system based on communication signal spectrum cancellation, which can accurately locate the interference source.

[0004] To solve the above technical problem, the technical solution proposed by the present invention is:

[0005] An interference detection and estimation method based on communication signal spectrum cancellation, comprising the following steps:

[0006] Obtain the actual power spectrum of the communication signal;

[0007] Calculate the theoretical power spectrum of the communication signal according to the prior information, and subtract the actual power spectrum from the theoretical power spectrum to obtain the first power spectrum;

[0008] Perform interference detection on the first power spectrum to obtain the interference signal power spectrum;

[0009] Estimate the interference signal parameters according to the interference signal power spectrum;

[0010] Perform direction finding according to the estimated value of the interference power in the interference signal parameters.

[0011] Furthermore, if the communication signal is a data transmission signal, the prior information includes the modulation type, the preset signal carrier frequency, and the preset symbol rate. The expression for calculating the theoretical power spectrum of the communication signal according to the prior information is:

[0012] P BPSK$(f)=|T s Sa(fT s )| 2

[0013] In the above formula, T s is the symbol period of the preset symbol rate, and f is the frequency of the preset signal carrier frequency.

[0014] Furthermore, if the communication signal is a telemetry signal, the prior information includes the modulation type, the preset signal carrier frequency, the preset symbol rate, and the subcarrier characteristics. The steps of calculating the theoretical power spectrum of the communication signal according to the prior information include:

[0015] Calculate the power spectrum of the subcarrier modulation signal, and the expression is as follows:

[0016]

[0017]

[0018] In the above formula, A is the preset power value modulation coefficient, T s is the symbol period of the preset symbol rate, f is the frequency of the preset signal carrier frequency, and f sub is the subcarrier frequency of the subcarrier characteristics;

[0019] After adding the power spectrum of the subcarrier modulation signal to the preset single-carrier power spectrum, set the single-spectrum peak power value at the target position to obtain the theoretical power spectrum of the communication signal.

[0020] Furthermore, the steps of performing interference detection on the first power spectrum specifically include:

[0021] Calculate the mean value of the first power spectrum and the standard deviation Multiply the standard deviation by the preset weighting factor N, and then add the mean value to obtain the threshold estimate value

[0022] Traverse the first power spectrum and retain the spectrum points whose amplitude exceeds the threshold estimate value to obtain the interference signal power spectrum.

[0023] Furthermore, estimating the interference signal parameters according to the interference signal power spectrum includes the step of estimating the interference signal power, which specifically includes:

[0024] Square the interference signal in the time domain to obtain the interference signal level as the power estimate value, and the expression is as follows:

[0025]

[0026] In the above formula, N is the number of points of the fast Fourier transform, y(n) is the time-domain level of the interference signal, and P n,k is the value of the noise power spectrum in the power spectrum of the interference signal, and M is the data length of the noise power spectrum in the power spectrum of the interference signal.

[0027] Further, the steps of direction finding according to the power estimation value of the interference signal parameters specifically include:

[0028] Calculate the sum-difference ratios of the azimuth angles and elevation angles of each antenna element according to the sum-difference direction finding method;

[0029] Based on the direction pattern F(θ), establish an angle mapping table, and select the sum-difference ratio of the target antenna element to look up the table in the angle mapping table to obtain the incident angle of the interference signal of the target antenna element.

[0030] The present invention also proposes an interference detection and estimation system based on communication signal spectrum cancellation, including:

[0031] An interference perception module, configured to obtain the actual power spectrum of the communication signal, calculate the theoretical power spectrum of the communication signal according to prior information, subtract the actual power spectrum from the theoretical power spectrum to obtain a first power spectrum; perform interference detection on the first power spectrum to obtain the power spectrum of the interference signal; estimate the interference signal parameters according to the power spectrum of the interference signal;

[0032] A signal receiving module, configured to obtain the prior information of the communication signal;

[0033] A direction finding module, configured to perform direction finding according to the interference signal power estimation value in the interference signal parameters.

[0034] Compared with the prior art, the advantages of the present invention are as follows:

[0035] The present invention accurately reproduces the theoretical power spectrum of the communication signal by using prior information, subtracts the actual power spectrum of the communication signal from the theoretical power spectrum to obtain the interference signal after eliminating the communication signal, thereby providing accurate data basis for subsequent interference detection to estimate the interference signal power and using the interference signal power for direction finding and positioning, and finally obtaining an accurate interference source positioning result. Description of the Drawings

[0036] Figure 1 is the overall flowchart of the embodiment of the present invention.

[0037] Figure 2 is the theoretical power spectrum of the PSK modulation signal in the embodiment of the present invention.

[0038] Figure 3 is the schematic diagram of the sum-difference direction finding principle in the embodiment of the present invention.

[0039] Figure 4Schematic diagram of direction angle calculation in sum-difference direction finding according to an embodiment of the present invention. Detailed implementation manners

[0040] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0041] As Figure 1 shown, this embodiment proposes an interference detection and estimation system based on communication signal spectrum cancellation. First, the communication signal is eliminated, then the interference signal parameters are accurately estimated, and then the interference is located. It includes an interference perception module, a signal reception module, and a direction finding module (not shown in the figure). These functional modules are configured to execute an interference detection and estimation method based on communication signal spectrum cancellation, including the following steps:

[0042] S1) The interference perception module receives the power spectrum data after performing a fast Fourier transform on the communication signal, that is, obtains the actual power spectrum of the communication signal.

[0043] S2) The signal reception module obtains the prior information of the communication signal and sends it to the interference perception module. The interference perception module reproduces the power spectrum of the communication signal according to the prior information, and uses the reproduced power spectrum of the communication signal and the received signal power spectrum to eliminate the communication signal from the received signal, that is, calculates the theoretical power spectrum of the communication signal according to the prior information, and subtracts the actual power spectrum from the theoretical power spectrum to obtain a first power spectrum containing only the interference signal.

[0044] S3) The interference perception module performs interference detection on the first power spectrum after eliminating the communication signal to obtain a second power spectrum after threshold detection (hereinafter referred to as the interference signal power spectrum).

[0045] S4) The interference perception module estimates the interference signal parameters using the interference signal power spectrum, including the estimation of the frequency, bandwidth, and power of the interference signal.

[0046] S5) The direction finding module uses the power estimation value of the interference signal to perform direction finding and positioning on the interference signal.

[0047] In step S1) of this embodiment, obtaining the power spectrum data by performing a fast Fourier transform on the communication signal is a conventional technique in the art, and the related calculation process will not be elaborated here.

[0048] In step S2) of this embodiment, since common communication signals include data transmission signals and telemetry signals, there are the following two situations for calculating the theoretical power spectrum of the communication signal according to the prior information:

[0049] The data transmission signal generally adopts M-PSK modulation. At this time, the prior information includes the modulation type, the preset signal carrier frequency, and the preset symbol rate. After the interference perception module identifies the modulation type as M-PSK modulation, the theoretical power spectrum of the communication signal is calculated according to Equation (1):

[0050] P BPSK (f)=|T s Sa(fT s )| 2 (1)

[0051] In the above formula, T s is the symbol period of the preset symbol rate, and f is the frequency of the preset signal carrier frequency. The theoretical power spectrum of the PSK modulation signal calculated according to Equation (1) is as Figure 2 shown. It can be seen that the 3dB bandwidth is about 0.886 / T s , and the power within the 3dB bandwidth accounts for about 72.2% of the total power.

[0052] The telemetry signal is generally PCM-PSK-PM modulation. At this time, in addition to the modulation type, the preset signal carrier frequency, and the preset symbol rate, the prior information also includes the subcarrier characteristics. After the interference perception module identifies the modulation type as PCM-PSK-PM modulation, the power spectrum of the subcarrier PSK modulation signal is first calculated according to Equation (2) and Equation (3):

[0053]

[0054] In the formula, the definition of G D (f) is:

[0055]

[0056] In the above formula, A is the coefficient for adjusting the power value of the theoretical model, that is, the preset power value modulation coefficient, T s is the symbol period of the preset symbol rate, f is the frequency of the preset signal carrier frequency, f sub is the subcarrier frequency of the subcarrier characteristics. It has been verified that the power spectrum curve of the subcarrier PSK modulation signal basically coincides with the power spectrum of the simulation data without superimposed noise.

[0057] After obtaining the power spectrum of the subcarrier PSK modulation signal, the theoretical power spectrum of the PCM-PSK-PM modulation signal can be represented by adding the spectral peaks of the single-carrier power spectrum. The spectral peaks of the single-carrier power spectrum are at the five positions of the frequency f c is, f c ±2f sub 、f c ±4f sub f cis the preset signal center frequency. After adding the spectral peak of the subcarrier PSK modulation signal to the spectral peak of the single-carrier power spectrum, and then setting the power value of each single spectral peak according to the characteristics of the residual carrier band-pass filter, the theoretical power spectrum of the PCM-PSK-PM modulation signal can be obtained. Setting the power value of each single spectral peak according to the characteristics of the residual carrier band-pass filter is a commonly used technical means by those skilled in the art, and the specific setting process is not the key point protected by this solution, so it will not be elaborated here.

[0058] In step S3) of this embodiment, the step of performing interference detection on the first power spectrum specifically includes:

[0059] Calculating the threshold estimate value of the detection threshold In view of the fact that the communication signal contains Gaussian noise in the environment, and after these Gaussian noises pass through the discrete Fourier transform (i.e., the fast Fourier transform in step S1)), the data at each frequency point on the spectrum is independently and identically distributed. In theory, the amplitude of these frequency points and its transformed form of the amplitude can be used as statistics to calculate the detection threshold. Therefore, in practical applications, the detection threshold is usually directly determined by performing a histogram statistics on the spectrum data, including the following steps:

[0060] Calculating the mean value of the first power spectrum and the standard deviation The expressions are as follows:

[0061]

[0062]

[0063] In the above formula, X(k) is the power spectrum line of the first power spectrum, and M is the number of spectrum lines of the first power spectrum;

[0064] Multiplying the standard deviation by the weighting factor N, and then adding the mean value to obtain the threshold estimate value The expression is as follows:

[0065]

[0066] In the above formula, the weighting factor N is determined by the histogram statistics of the spectrum lines and usually takes 2;

[0067] Traversing the first power spectrum and retaining the spectral points whose amplitude exceeds the threshold estimate value to obtain the interference signal power spectrum.

[0068] In step S4) of this embodiment, the calculation process of estimating each interference signal parameter is as follows:

[0069] Carrier frequency estimation: Considering that the spectra of most modulation signals are symmetric, the carrier frequency can be calculated from the centroid of the spectrum:

[0070]

[0071] In the above formula, St is the starting point of the main lobe of the interference signal power spectrum, Ed is the ending point of the main lobe of the interference signal power spectrum, P i is the spectral value at position i of the interference signal power spectrum, and f i is the frequency scale at position i of the interference signal power spectrum;

[0072] Bandwidth estimation: For the estimation of the effective bandwidth of the interference signal, the 3dB bandwidth is usually considered as the effective bandwidth. Since the signal-to-noise ratios of different payloads are different, a unified metric cannot be used as the standard for bandwidth estimation. It is necessary to set the corresponding 3dB bandwidth estimation threshold Th_P i for different payloads. The 3dB bandwidth of the interference signal is:

[0073]

[0074] In the above formula, is the spectral line St_P at the starting point of the interference signal power spectrum i from the start to the spectral line Ed_p at the ending point i between which the number of spectral points W i exceeding the 3dB bandwidth estimation threshold Th_p D is the channel detection bandwidth, N FFT is the number of points of the fast Fourier transform, is the frequency resolution;

[0075] Power estimation: Square the interference signal in the time domain to obtain the interference signal level as the interference signal power estimation value. The expression is as follows:

[0076]

[0077] In the above formula, N is the number of points of the fast Fourier transform, y(n) is the interference signal level in the time domain, and P n,k is the value of the noise power spectrum in the interference signal power spectrum, and M is the data length of the noise power spectrum in the interference signal power spectrum.

[0078] In this embodiment, the direction finding module is composed of multiple antenna elements. As Figure 3 shown, near the focus of the reflector of each antenna element, a set of two receiving feeds is placed offset from the focus in the pitch and azimuth directions, and the pitch and direction angles are measured using the sum and difference direction finding method respectively. Step S5) of this embodiment is to perform direction finding according to the sum and difference direction finding method using the power estimation value of step S4), including the following steps:

[0079] Calculate the sum-difference ratios of the azimuth and elevation angles of each antenna element according to the sum-difference direction-finding method. As Figure 4 shown, in this embodiment, the classical amplitude sum-difference direction-finding method is adopted. In a plane of an angle, direction-finding is carried out by forming two identical and overlapping beam patterns F1(θ) and F2(θ) (F1(θ) and F2(θ) are the directivity functions of the two beams respectively). The included angle between the main beam direction of each beam and the equal-signal axis θ0 is θ k .

[0080] Denote the deviation angle of the incident signal relative to the equal-signal axis θ0 as δ. Then the signal voltages received by the two beams are respectively:

[0081] u1(δ) = K·F1(θ0 - δ) = K·F(-θ k -δ) = K·F(θ k +δ) (10)

[0082] u2(δ) = K·F2(θ0 - δ) = K·F(θ k -δ) (11)

[0083] Perform sum-difference processing through a monopulse comparator to obtain sum and difference signals:

[0084] ∑(δ) = u1(δ) + u2(δ) = K·F(θ k +δ) + K·F(θ k -δ) (12)

[0085] Δ(δ) = u1(δ) - u2(δ) = K·F(θ k +δ) - K·F(θ k -δ) (13)

[0086] In the above formula, K is a constant. When θ is very close to θ0 (that is, δ is very small), use the first-order Taylor formula to simplify the sum and difference signals to obtain:

[0087]

[0088] Divide the difference signal by the sum signal, and it can be known that:

[0089]

[0090] The two terms on the right side of the above formula are fixed values when the antenna beam pattern F(θ) is determined, and can be accurately obtained through estimation and measurement. Therefore, the difference-sum ratio is proportional to the angle difference δ. The positive or negative of the ratio reflects which antenna element the incident signal is closer to, and the absolute value of the ratio corresponds to the absolute value of the angle difference δ. Thus, the antenna element closest to the incident signal can be selected as the target element.

[0091] Finally, since the beam pattern is an inherent characteristic of the antenna, the pattern will be measured when the antenna leaves the factory. Therefore, an angle mapping table (also known as library building operation) is established based on the beam pattern F(θ) of the target antenna element. After calculating the incident angle of the interference signal on the target antenna element, by looking up the table in the angle mapping table, the deviation angle δ of the incident angle of the interference signal relative to the equal signal axis θ0 of the target antenna element can be obtained, and then the incident angle of the interference signal θ0 - δ can be obtained.

[0092] For calculating the incident angle of the interference signal on the target antenna element, based on the estimated value of the interference signal power obtained in the foregoing step S4) and the electromagnetic wave power received by the target antenna element, the incident angle of the interference signal on the target antenna element can be calculated. The related calculation process is a conventional method well-known to those skilled in the art and will not be elaborated here.

[0093] In summary, in the interference detection and estimation system based on communication signal spectrum cancellation of this embodiment, the interference perception module, the signal reception module, and the direction finding module are configured to execute the interference detection and estimation method based on communication signal spectrum cancellation, accurately reproduce the theoretical power spectrum of the communication signal using prior information, and subtract the actual power spectrum of the communication signal from the theoretical power spectrum to obtain the interference signal after canceling the communication signal, thereby providing accurate data basis for subsequent interference detection and estimation of the interference signal power and direction finding and positioning using the interference signal power, and finally obtaining an accurate interference source positioning result.

[0094] The above is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Therefore, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. An interference detection and estimation method based on communication signal spectrum cancellation, characterized in that Including the following steps: Obtain the actual power spectrum of the communication signal; Calculate the theoretical power spectrum of the communication signal according to the prior information, and subtract the actual power spectrum from the theoretical power spectrum to obtain the first power spectrum; Perform interference detection on the first power spectrum to obtain the interference signal power spectrum; Estimate the interference signal parameters according to the interference signal power spectrum, specifically including: Carrier frequency estimation: Obtained by calculating the centroid of the spectrum: In the above formula, St is the starting point of the main lobe of the interference signal power spectrum, and Ed is the ending point of the main lobe of the interference signal power spectrum. is the position of the interference signal power spectrum of the spectral value, is the position of the interference signal power spectrum of the frequency scale; Bandwidth Estimation: For the interfering signal The bandwidth is: In the above formula, is the spectral line at the starting point of the interference signal power spectrum from the starting point to the ending point spectral line the number of spectral points exceeding the bandwidth estimation threshold is, is the channel detection bandwidth, is the number of points of the fast Fourier transform, is the frequency resolution; Power estimation: Square the interference signal in the time domain to obtain the interference signal level, which is used as the interference signal power estimation value, and the expression is as follows: In the above formula, N is the number of points of the fast Fourier transform, is the time-domain level of the interference signal, is the value of the noise power spectrum in the power spectrum of the interference signal, and M is the data length of the noise power spectrum in the power spectrum of the interference signal; Perform direction finding according to the interference signal power estimation value in the interference signal parameters.

2. The interference detection and estimation method based on communication signal spectrum cancellation according to claim 1, characterized in that, If the communication signal is a data transmission signal, the prior information includes the modulation type, the preset signal carrier frequency, and the preset symbol rate. The expression for calculating the theoretical power spectrum of the communication signal according to the prior information is: In the above formula, is the symbol period of the preset symbol rate, is the frequency of the preset signal carrier frequency.

3. The interference detection and estimation method based on communication signal spectrum cancellation according to claim 1, characterized in that If the communication signal is a telemetry signal, the prior information includes the modulation type, the preset signal carrier frequency, the preset symbol rate, and the subcarrier characteristics. The steps for calculating the theoretical power spectrum of the communication signal according to the prior information include: Calculate the subcarrier modulation signal power spectrum, and the expression is as follows: In the above formula, A is a preset power value modulation coefficient, is the symbol period of the preset symbol rate, is the frequency of the preset signal carrier frequency, is the subcarrier frequency of the subcarrier characteristic; After adding the subcarrier modulation signal power spectrum to the preset single-carrier power spectrum, set the single-spectrum peak power value at the target position to obtain the theoretical power spectrum of the communication signal.

4. The interference detection and estimation method based on communication signal spectrum cancellation according to claim 1, characterized in that, The steps for performing interference detection on the first power spectrum specifically include: Calculate the mean value of the first power spectrum and the standard deviation . Multiply the standard deviation by a preset weighting factor N, and then add the mean value to obtain a threshold estimate value ; Traverse the first power spectrum and retain the spectral points whose amplitudes exceed the threshold estimate value to obtain the power spectrum of the interference signal.

5. The interference detection and estimation method based on communication signal spectrum cancellation according to claim 1, wherein The steps for performing direction finding according to the interference signal power estimation value in the interference signal parameters specifically include: Calculate the sum-difference ratio of the azimuth and elevation angles of each antenna array element according to the sum-difference direction finding method, and select the target antenna array element according to the sum-difference ratio of the azimuth and elevation angles; Beam pattern based on the target antenna element Establish an angle mapping table; Calculate the incident angle of the interference signal of the target antenna array element according to the interference signal power estimation value and the electromagnetic wave power received by the target antenna array element, and look up the interference signal incident angle in the angle mapping table for the incident angle of the interference signal of the target antenna array element.

6. An interference detection and estimation system based on communication signal spectrum cancellation, characterized in that, Including: An interference perception module, configured to obtain the actual power spectrum of the communication signal, calculate the theoretical power spectrum of the communication signal according to the prior information, and subtract the actual power spectrum from the theoretical power spectrum to obtain the first power spectrum; Perform interference detection on the first power spectrum to obtain the interference signal power spectrum; Estimate the interference signal parameters according to the interference signal power spectrum, specifically including: Carrier frequency estimation: Obtained by calculating the centroid of the spectrum: In the above formula, St is the starting point of the main lobe of the interference signal power spectrum, and Ed is the ending point of the main lobe of the interference signal power spectrum. is the position of the interference signal power spectrum of the spectral value, is the position of the interference signal power spectrum of the frequency scale; Bandwidth Estimation: For the interfering signal The bandwidth is: In the above formula, is the spectral line at the starting point of the interference signal power spectrum from the starting spectral line to the ending spectral line the number of spectral points exceeding the bandwidth estimation threshold is, is the channel detection bandwidth, is the number of points of the fast Fourier transform, is the frequency resolution; Power estimation: Square the interference signal in the time domain to obtain the interference signal level, which is used as the interference signal power estimation value, and the expression is as follows: In the above formula, N is the number of points of the fast Fourier transform, is the time-domain level of the interference signal, is the value of the noise power spectrum in the power spectrum of the interference signal, and M is the data length of the noise power spectrum in the power spectrum of the interference signal; A signal reception module, configured to obtain the prior information of the communication signal; A direction finding module, configured to perform direction finding according to the interference signal power estimation value in the interference signal parameters.

Images