A clutter low false alarm rate noise interference identification method and system

Abstract

The application discloses a clutter low false alarm rate noise jamming identification method and system, and the method comprises the following steps: judging whether the radar is possibly interfered by noise according to whether the average amplitude of the amplitude envelope of the baseband complex signal exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding time length; judging whether the radar is possibly interfered by noise according to whether the average amplitude of the amplitude envelope of the baseband complex signal before and after pulse compression processing exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding time length; after judging that the radar is possibly interfered by noise, the modulus of the pulse compression result is calculated, the modulus value is transformed to the frequency domain, and whether the radar is interfered by noise is judged by judging whether the amplitude of the zero-frequency component in the frequency domain is greater than the preset threshold. The application realizes real-time detection and identification of noise jamming, reduces the false alarm of interference detection caused by clutter, and provides a decision basis for the radar to take effective anti-jamming measures in time.

Description

Technical Field

[0001] This invention belongs to the field of radar anti-jamming, and particularly relates to a method and system for identifying noise interference with low false alarm rate in clutter. Background Technology

[0002] The development of modern electronic countermeasures technology has made the electromagnetic environment faced by radar increasingly complex. Various high-tech means and equipment for countering radar are constantly emerging, leading to an increasingly complex and deteriorating radar operating environment. Electronic interference, as one of the four major threats to radar, poses the most significant threat to military radar due to its diverse forms, flexible use, and strong countermeasure capabilities.

[0003] Noise jamming is one of the most common types of active jamming faced by radar. It is characterized by raising the radar echo noise floor, reducing the target echo signal-to-noise ratio, and even completely submerging the target in noise, making it undetectable by the radar. Noise jamming is extremely easy for jammers to implement, hence its widespread use in various types of jammers.

[0004] In the process of radar anti-jamming, interference perception includes the detection of interference and the identification of interference types; interference suppression refers to taking appropriate anti-jamming measures manually or adaptively based on the interference perception results; interference perception is a prerequisite for interference suppression.

[0005] Existing noise interference detection and identification methods are computationally complex, making them difficult to widely apply in equipment; they are also susceptible to clutter, leading to false alarms. Radars struggle to accurately detect whether they are under noise interference, resulting in a failure to automatically or promptly alert operators to take anti-jamming measures. In such situations, radars are highly prone to missed alarms, meaning targets can be effectively protected by self-defense jammers, allowing them to successfully penetrate defenses and potentially resulting in devastating close-range attacks on the radar system. Summary of the Invention

[0006] To address the above problems, this invention proposes a method for identifying low false alarm rate noise interference in clutter, comprising the following steps:

[0007] The radar transmits a linear frequency modulated signal;

[0008] The radar echo signal is preprocessed to obtain the baseband complex signal. The amplitude envelope of the baseband complex signal is calculated. Based on whether the average amplitude of the amplitude envelope of the baseband complex signal exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding duration, it is determined whether the radar may be subject to noise interference.

[0009] If the average amplitude of the baseband complex signal's amplitude envelope does not exceed the corresponding threshold and the duration of the amplitude envelope does not exceed the corresponding duration, then the radar is not affected by noise interference.

[0010] If the average amplitude of the baseband complex signal's amplitude envelope exceeds the corresponding threshold or the duration of the amplitude envelope is greater than the corresponding duration, the radar may be subject to noise interference. The baseband complex signal is then subjected to pulse compression processing to obtain the pulse compression result. Based on whether the average amplitude of the baseband complex signal's amplitude envelope exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding duration before and after pulse compression processing, it is determined whether the radar may be subject to noise interference.

[0011] If the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression processing does not exceed the corresponding threshold and the duration of the amplitude envelope is not greater than the corresponding duration, then the radar is not affected by noise interference.

[0012] If the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression exceeds the corresponding threshold or the duration of the amplitude envelope is greater than the corresponding duration, the radar may be subject to noise interference. The modulus of the pulse compression result is calculated and its modulus value is transformed to the frequency domain. By judging whether the amplitude of the zero-frequency component in the frequency domain is greater than the preset threshold, it can be determined whether the radar is subject to noise interference.

[0013] If the amplitude of the zero-frequency component in the frequency domain is less than or equal to a preset threshold, the radar is not affected by noise interference; if the amplitude of the zero-frequency component in the frequency domain is greater than the preset threshold, the radar is affected by noise interference.

[0014] Furthermore, the preprocessing of the radar echo signal includes amplification, down-conversion, sampling, and quadrature dual-channel processing of the echo signal.

[0015] Furthermore, the corresponding threshold is a fixed value VT0, which is determined by whether the average amplitude of the baseband complex signal amplitude envelope exceeds the corresponding threshold and whether the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression processing exceeds the corresponding threshold. The fixed value VT0 is equal to the radar echo noise floor plus a fixed value.

[0016] Furthermore, the pulse width TT0 of the radar transmitted signal is determined by whether the amplitude envelope duration of the baseband complex signal is greater than the corresponding duration and whether the amplitude envelope duration of the baseband complex signal before and after pulse compression processing is greater than the corresponding duration.

[0017] Furthermore, the modulus of the pulse compression result is calculated and its modulus value is transformed to the frequency domain, including the following steps:

[0018] The pulse compression result is represented by s1(t);

[0019] The modulus value obtained after calculating the modulus of the pulse compression result s1(t) is windowed.

[0020] The signal obtained after windowing is transformed to the frequency domain using FFT and then normalized according to the number of FFT points to obtain the frequency domain spectrum result S(f).

[0021] Furthermore, the windowing process specifically involves multiplying the modulus value obtained by modulating the pulse compression result s1(t) point by point with a window function of the same length.

[0022] Furthermore, the method for obtaining the preset threshold is as follows:

[0023] Based on the radar echo noise baseline, a fixed value is added as the noise interference detection threshold VT; this noise interference detection threshold VT is the preset threshold.

[0024] The present invention also provides a noise interference identification system with low false alarm rate in clutter, characterized in that the system identifies radar noise interference according to any of the above methods.

[0025] Compared with the prior art, the advantages of this invention are as follows:

[0026] The efficient and real-time noise interference detection and identification method provided by this invention can provide real-time alerts on whether the radar is under noise interference, while effectively suppressing false alarms caused by clutter interference detection. It ensures that the radar can automatically or manually activate the anti-noise interference function when it receives noise interference, enabling the radar to continuously and effectively detect targets carrying high-performance jammers that release noise interference, and better support the radar in improving its information security capabilities in complex electromagnetic environments. Attached Figure Description

[0027] Figure 1 This is a flowchart of the low-level virtual warning noise interference identification method in clutter according to an embodiment of the present invention.

[0028] Figure 2 This is a display diagram showing the variation of the amplitude of a typical radar baseband echo complex signal with the range cell when there is no noise interference.

[0029] Figure 3 When there is no noise interference, Figure 2 The graph shows how the amplitude of the echo signal changes with the distance unit after pulse compression processing.

[0030] Figure 4 This is the result obtained by processing the radar echo, which is not affected by noise, using the method of this embodiment.

[0031] Figure 5 This is a display diagram showing how the amplitude of a typical radar baseband echo complex signal varies with the range cell when subjected to noise interference.

[0032] Figure 6 When subject to noise interference, Figure 2 The graph shows how the amplitude of the echo signal changes with the distance unit after pulse compression processing.

[0033] Figure 7 This is the result obtained by processing the radar echo under noise interference in the application example using the method of this embodiment. Detailed Implementation

[0034] To address the computational complexity and susceptibility to clutter-induced false alarms in current noise interference detection methods, a new noise interference identification method with low false alarm rates in clutter is proposed. Utilizing the time-domain characteristics of radar echoes affected by noise, the method first calculates the envelope of the signal before and after pulse compression, comparing the envelope with the transmitted pulse width to preliminarily determine the presence of noise interference. Then, the amplitude distribution of the radar baseband echo data over time is transformed to the frequency domain, and its spectral characteristics are statistically analyzed. Based on the statistical results, the presence of noise interference signals in the radar echo is determined. By combining these two methods, real-time detection and identification of noise interference are achieved, while simultaneously reducing false alarms caused by clutter. This provides a basis for timely and effective anti-interference measures for the radar, demonstrating significant innovative value and practical significance.

[0035] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0037] This embodiment provides a method for identifying noise interference with a low false alarm rate in clutter, specifically including the following steps:

[0038] Step 1: The radar transmits a linear frequency modulated signal to search and detect a certain airspace. After the echo signal is amplified, down-converted, sampled, and processed by orthogonal dual channels, the baseband complex signal s(t) is obtained.

[0039] Step 2: The baseband complex signal s(t) obtained in Step 1 is processed by the interference detection and identification branch to calculate its amplitude envelope. If the average amplitude of the amplitude envelope is greater than a certain value V... T0 (V T0 If the noise level is equal to the radar echo noise floor plus a fixed value, and the duration is greater than the pulse width of the transmitted signal, then proceed to step 3; otherwise, directly determine that the radar is not affected by noise.

[0040] Step 3: Perform pulse compression processing on the baseband complex signal s(t) obtained in Step 1 to obtain the pulse compression result s1(t), and calculate its amplitude envelope.

[0041] Step 4: If the average amplitude of the echo signal amplitude envelope is greater than the threshold V before and after pulse compression. T0 Furthermore, the duration of the amplitude envelope is greater than the pulse width T of the transmitted signal. T0 If so, proceed to step 5; otherwise, indicate that the radar has not received noise interference.

[0042] Step 5: Calculate the modulus of the pulse compression result s1(t) obtained in Step 3;

[0043] Step 6: Apply windowing to the modulus obtained in Step 6, that is, multiply it point by point with a window function of the same length;

[0044] Step 7: The signal obtained in Step 7 is transformed to the frequency domain using Fast Fourier Transform (FFT) and normalized according to the number of FFT points to obtain the frequency domain spectrum result S(f).

[0045] Step 8: Add a fixed value to the radar echo noise baseline as the noise interference detection threshold V. T ;

[0046] Step 9: Take the amplitude of the zero-frequency component from Step 8 and compare it with the noise detection threshold. If it is less than the noise threshold, the radar is considered not to be affected by noise interference; otherwise, the radar is considered to be affected by noise interference.

[0047] The fundamental reason why this invention can be used to detect noise interference is that by transforming the amplitude of the echo signal to the frequency domain, the overall amplitude of the echo in the time domain is evaluated by the amplitude of the zero-frequency component. When the radar is affected by noise interference, causing the amplitude of all or part of the range segment to be too high, the amplitude of the zero-frequency component in the frequency domain increases accordingly. If the radar is affected by patchy clutter interference, the amplitude of the zero-frequency component in the frequency domain increases only to a limited extent because the amplitude of other range cells does not increase.

[0048] This embodiment also provides a noise interference identification system with low false alarm rate in clutter, wherein the system identifies radar noise interference according to the above method.

[0049] One specific application of this embodiment is as follows: applied to radars subjected to noise interference, taking the measured data recorded when the radar counters a self-defense jamming source (releasing noise interference) as an example to introduce the method of this embodiment.

[0050] (1) In a certain test, a radar was operating in search mode and transmitting a linear frequency modulated signal. The self-defense jammer carried by the target was not powered on, and the radar was not subjected to noise or other interference. The amplitude of the radar baseband echo complex signal is shown below. Figure 2As shown, it can be seen that the amplitude increases at distances of 1–140 and 420–590 units; the result of pulse compression processing of this frame of echo data is as follows. Figure 3 As shown, in summary Figure 1 and Figure 2 It can be seen that sheet-like clutter exists at distances of 1–140 and 420–590 from the unit.

[0051] (2) Figure 2 The data is processed using steps 2 and 3 of this embodiment of the invention, while a detection threshold V is set. T0 Add 10 dB to the radar echo noise floor and perform step 4 processing. The result is that the average amplitude of the echo signal amplitude envelope in this frame is greater than the threshold V. T 0, and the duration of the amplitude envelope is greater than the pulse width T of the transmitted signal. T 0;

[0052] (3) Figure 3 The data is processed in steps 5, 6, and 7 to obtain the following results: Figure 4 The results shown here indicate that the noise detection threshold V is set. T It is 45dB, which shows that Figure 4 The amplitude of the mid-zero frequency component is less than the threshold V. T If so, the detection result of the radar is not affected by noise interference will be given.

[0053] (4) In the same test, a radar was operating in search mode and transmitting a linear frequency modulated signal. A self-defense jammer carried by the target was activated, and the radar was subjected to noise and other interference. The amplitude of the radar baseband echo complex signal is shown below. Figure 5 As shown, it can be seen that the echo amplitude increases across the entire range at this time; the result of pulse compression processing on this frame of echo data is as follows. Figure 6 As shown, in summary Figure 1 and Figure 2 It can be seen that the radar is subject to noise interference across all ranges.

[0054] (5) Figure 5 The data is processed using steps 2 and 3 of this embodiment of the invention, while a detection threshold V is set. T0 Add 10 dB to the radar echo noise floor and perform step 4 processing. The result is that the average amplitude of the echo signal amplitude envelope in this frame is greater than the threshold V. T 0, and the duration of the amplitude envelope is greater than the pulse width T of the transmitted signal. T 0;

[0055] (6) Figure 6 The data is processed in steps 5, 6, and 7 to obtain the following results: Figure 7 The results shown here indicate that the noise detection threshold V is set. T It is 45dB, which shows that Figure 4The amplitude of the mid-zero frequency component is less than the threshold V. T This will give the detection results of radar interference caused by noise.

[0056] The present invention provides a highly efficient and real-time method and system for identifying low-level clutter noise interference with early warning capabilities. This system can provide real-time alerts to whether a radar is under noise interference, while effectively suppressing false alarms caused by clutter. It ensures that the radar can automatically or manually activate anti-noise interference functions when it receives noise interference, enabling the radar to continuously and effectively detect targets carrying high-performance jammers that emit noise interference. This better supports the radar's ability to enhance information security in complex electromagnetic environments.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for identifying low false alarm rate noise interference in clutter, characterized in that, Includes the following steps: The radar transmits a linear frequency modulated signal; The radar echo signal is preprocessed to obtain the baseband complex signal. The amplitude envelope of the baseband complex signal is calculated. Based on whether the average amplitude of the amplitude envelope of the baseband complex signal exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding duration, it is determined whether the radar may be subject to noise interference. If the average amplitude of the baseband complex signal's amplitude envelope does not exceed the corresponding threshold and the duration of the amplitude envelope does not exceed the corresponding duration, then the radar is not affected by noise interference. If the average amplitude of the baseband complex signal's amplitude envelope exceeds the corresponding threshold or the duration of the amplitude envelope is greater than the corresponding duration, the radar may be subject to noise interference. Pulse compression processing is performed on the baseband complex signal to obtain the pulse compression result. Based on whether the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression processing exceeds the corresponding threshold or whether the duration of the amplitude envelope is greater than the corresponding duration, it can be determined whether the radar may be subject to noise interference. If the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression processing does not exceed the corresponding threshold and the duration of the amplitude envelope is not greater than the corresponding duration, then the radar is not affected by noise interference. If the average amplitude of the baseband complex signal amplitude envelope before and after pulse compression exceeds the corresponding threshold or the duration of the amplitude envelope is greater than the corresponding duration, the radar may be subject to noise interference. The modulus of the pulse compression result is calculated and its modulus value is transformed to the frequency domain. By judging whether the amplitude of the zero-frequency component in the frequency domain is greater than the preset threshold, it can be determined whether the radar is subject to noise interference. If the amplitude of the zero-frequency component in the frequency domain is less than or equal to a preset threshold, the radar is not affected by noise interference; if the amplitude of the zero-frequency component in the frequency domain is greater than the preset threshold, the radar is affected by noise interference.

2. The method for identifying low false alarm rate noise interference in clutter according to claim 1, characterized in that, The preprocessing of radar echo signals includes amplification, down-conversion, sampling, and quadrature dual-channel processing of the echo signals.

3. The method for identifying low false alarm rate noise interference in clutter according to claim 1, characterized in that, The threshold is a fixed value V, which is determined based on whether the average amplitude of the baseband complex signal's amplitude envelope exceeds a corresponding threshold and whether the average amplitude of the baseband complex signal's amplitude envelope before and after pulse compression processing exceeds a corresponding threshold. T0 constant value V T0 It equals the radar echo noise floor plus a fixed value.

4. The method for identifying low false alarm rate noise interference in clutter according to claim 1, characterized in that, The criteria for determining whether the amplitude envelope duration of the baseband complex signal is greater than a corresponding duration, and whether the amplitude envelope duration of the baseband complex signal before and after pulse compression processing is greater than a corresponding duration, wherein the corresponding duration is the pulse width T of the radar transmitted signal. T0 .

5. The method for identifying low false alarm rate noise interference in clutter according to claim 1, characterized in that, The modulus of the pulse compression result is calculated, and its modulus value is transformed to the frequency domain, including the following steps: The pulse compression result is represented by s1(t); The modulus value obtained after calculating the modulus of the pulse compression result s1(t) is windowed. The signal obtained after windowing is transformed to the frequency domain using FFT and then normalized according to the number of FFT points to obtain the frequency domain spectrum result S(f).

6. The method for identifying low false alarm rate noise interference in clutter according to claim 5, characterized in that, The windowing process specifically involves multiplying the modulus value obtained by taking the modulus of the pulse compression result s1(t) by a window function of the same length point by point.

7. The method for identifying low false alarm rate noise interference in clutter according to claim 1, characterized in that, The method for obtaining the preset threshold is as follows: A fixed value is added to the radar echo noise baseline as a noise interference detection threshold V. T The noise interference detection threshold V T This is the preset threshold.

8. A noise interference identification system with low false alarm rate in clutter, characterized in that, The system performs radar noise interference identification according to the method described in any one of claims 1-7.

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