An acoustically compatible anti-interference method for harmonics

Abstract

The present invention discloses an acoustically compatible anti-interference method for harmonics. This method addresses interference caused by device A's primary transmission frequency and harmonics exceeding the detection threshold of device B. The method includes extending the lower limit of underwater acoustic device B's detection frequency band to the low-frequency cutoff frequency of underwater acoustic device A. Device B then determines whether an interference frequency fA exceeding the detection threshold a0 within device A's operating frequency band (FA-low to FA-high) is a harmonic of the frequency fB exceeding the detection threshold a0 within device B's original operating frequency band (FB-low to FB-high). If so, fB is determined to be harmonic interference, and device B does not respond to it. If not, fB is determined to be a target signal, and device B responds to it. This invention addresses interference caused by device A's primary transmission frequency and harmonics exceeding the detection threshold of device B by providing an anti-interference measure that enables device B to effectively mitigate the interference caused by device A.

Description

Technical Field

[0001] The present invention belongs to the technical field of acoustic compatibility design, and in particular relates to an acoustic compatibility anti-interference method for harmonics. Background Art

[0002] In the field of underwater acoustic operations, underwater acoustic communication and positioning and navigation technologies are core. In marine scientific research, underwater acoustic communication is used to transmit vast amounts of deep-sea data between research vessels and underwater detectors, helping scientists gain a deeper understanding of the mysterious ocean world. In underwater security, various security devices exchange information through underwater acoustic communication, closely monitoring underwater safety conditions. Furthermore, in marine resource development, underwater mining equipment relies on underwater acoustic communication to smoothly communicate with surface platforms, ensuring efficient mining operations. Positioning and navigation technologies use specific frequency acoustic signals between devices to transmit information, detect targets, and locate and navigate. These acoustic signals act as underwater messengers, navigating complex aquatic environments and providing crucial support for various underwater operations, driving the continuous advancement of the field. However, the complex underwater environment makes signal propagation susceptible to interference from various factors, with harmonic interference being a common problem. When underwater acoustic equipment operates, it generates harmonics, which can couple and interfere with the operating frequencies of other devices. For example, when multiple devices operate collaboratively, if the operating frequencies of different devices are close or have multiple frequencies, harmonic interference can be exacerbated. Moreover, the particularities of the underwater environment, such as water temperature stratification and underwater topography, will make the propagation path of the acoustic signal complex, further aggravating the impact of harmonic interference.

[0003] In actual applications, it's common for device A's transmitted main frequency and harmonics to exceed the detection threshold of device B. When device A is operating, its transmitted main frequency and generated harmonics may conflict with device B's detection threshold, causing the signal received by device B to be mixed with a large amount of interference.

[0004] Currently, the equipment used in underwater acoustic operations has obvious deficiencies in dealing with this type of harmonic interference. This seriously affects the equipment's detection accuracy of target signals or communication performance. In actual operation scenarios, the equipment often makes misjudgments due to its inability to accurately identify interference signals, mistakenly processing harmonic interference signals as target signals. This not only wastes system resources, but may also lead to problems such as delays in the operation process and operational errors. At the same time, the increase in background noise caused by harmonic interference significantly reduces the equipment's receiving sensitivity. In some fine detection tasks with high signal quality requirements, clear and accurate signal data cannot be obtained, affecting the reliability of the detection results. In addition, when multiple devices work together, the harmonic interference problem cannot be effectively resolved, and the communication links between devices are often interrupted or data transmission errors occur, reducing the efficiency and coordination of the entire operation system and increasing operation costs and time investment. There is an urgent need for a more effective anti-harmonic interference method to improve the performance and operation quality of underwater acoustic operation equipment. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an acoustically compatible anti-interference method for harmonics, so as to solve the technical problem that signals are easily interfered by harmonics during current underwater acoustic operations.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides an acoustic compatibility anti-interference method for harmonics, which targets the interference phenomenon where both the emission main frequency and emission harmonics of device A exceed the detection threshold of device B, including:

[0008] Extend the lower limit of the detection frequency band of underwater acoustic equipment B to the low-frequency cutoff frequency of underwater acoustic equipment A;

[0009] Device B determines the signal type by checking whether the interference frequency fA exceeding the detection threshold a0 within device A's operating frequency band (FA-low to FA-high) is a harmonic of the frequency fB exceeding the detection threshold a0 within device B's original operating frequency band (FB-low to FB-high). That is, by checking whether fB satisfies the following formula:

[0010]

[0011] If it is satisfied, fB is determined to be harmonic interference and device B does not respond to it;

[0012] If not, fB is determined to be the target signal and device B responds to it.

[0013] Preferably, the method for extracting the frequency in the anti-interference measure specifically includes the following steps:

[0014] First, the received signal Perform DFT operation to obtain its power spectrum ;

[0015] Then perform background normalization processing, select the corresponding threshold to perform double detection judgment on the normalization result and DFT spectrum estimation result, and obtain All frequencies exceeding the threshold;

[0016] Finally, the spectrum characteristics of the narrowband signal are used to complete The frequencies of the component signals contained in are extracted.

[0017] Preferably, the steps of normalization processing are:

[0018] S1, the signal power spectrum The average of 2*N points centered at each frequency point is taken as the estimated mean of the power spectrum of each frequency point ;

[0019] S2. Determine the elimination threshold based on the estimated mean value ,in Take 3.2, is the average number of times the power spectrum of the input signal is calculated;

[0020] S3, the signal power spectrum and rejection threshold Compare, if less than, keep No change, on the contrary, Alternative ;

[0021] S4. The result after the elimination process is averaged with 2*N points centered at each frequency point as the estimated value μ of the power spectrum of each frequency point. k ;

[0022] S5, the signal power spectrum With estimated value Do calculations .

[0023] Preferably, the spectrum characteristics of the narrowband signal are used to complete In the frequency extraction process of the component signal contained in , a comparison method is used to find the frequency point corresponding to the maximum power in a preset area, wherein the criteria for determining the preset area include:

[0024] The frequency point number obtained by detection judgment is expressed as , the length is , using a recursive method to find the area for frequency extraction;

[0025] The conditions for determining the end position of the judgment area are:

[0026] Compare from the beginning of the region The adjacent frequency point number, The difference exceeds , The value of should be greater than 0;

[0027] The value selection principle is: The larger the value, the worse the resolution during frequency extraction and the stronger the ability to resist noise interference; conversely, the better the resolution, the worse the ability to resist noise interference.

[0028] Finally, the frequency point is selected based on the signal-to-noise ratio and minimum resolution requirements during operation.

[0029] The beneficial effects of the present invention are:

[0030] 1. The present invention addresses the interference phenomenon in which the emission harmonics of device A are within the operating frequency band of device B, and both the emission main frequency and emission harmonics of device A exceed the detection threshold of device B. An acoustically compatible anti-interference measure is proposed, which can be used by device B to mitigate the interference caused by device A.

[0031] Other advantages, objectives and features of the present invention will be described in the following description and will be apparent to those skilled in the art to some extent, or those skilled in the art can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the purpose, technical solutions and beneficial effects of the invention clearer, the present invention is described with the following drawings:

[0033] Figure 1 A flowchart of the steps of an acoustic compatibility anti-interference method for harmonics;

[0034] Figure 2 Schematic diagram of the relationship between the operating frequency bands of device A and device B of the present invention;

[0035] Figure 3 (ab) are schematic diagrams of the experimental deployment of the device A of the present invention on the lake;

[0036] Figure 4 This is a schematic diagram of the test deployment of the device B on the lake;

[0037] Figure 5 This is a schematic diagram of the receiving channel of device B of the present invention;

[0038] Figure 6 (ad) is the time domain waveform judgment diagram of the present invention;

[0039] Figure 7 This is a spectrum diagram during testing of the present invention;

[0040] Figure 8 This is a frequency extraction flow chart of the present invention;

[0041] Figure 9 Schematic diagram of the simulation conditions of the present invention. DETAILED DESCRIPTION

[0042] like Figure 1-9 As shown, the present invention provides an acoustically compatible anti-interference method for harmonics.

[0043] The present invention provides an acoustic compatibility anti-interference method for harmonics, which targets the interference phenomenon that the emission main frequency and emission harmonics of device A exceed the detection threshold of device B. Figure 1 ,include;

[0044] Extend the lower limit of the detection frequency band of underwater acoustic equipment B to the low-frequency cutoff frequency of underwater acoustic equipment A;

[0045] Device B determines the signal type by checking whether the interference frequency fA exceeding the detection threshold a0 within device A's operating frequency band (FA-low to FA-high) is a harmonic of the frequency fB exceeding the detection threshold a0 within device B's original operating frequency band (FB-low to FB-high). That is, by checking whether fB satisfies the following formula:

[0046]

[0047] If it is satisfied, fB is determined to be harmonic interference and device B does not respond to it;

[0048] If not, fB is determined to be the target signal and device B responds to it.

[0049] In a specific embodiment, the method for extracting the frequency in the anti-interference measure specifically includes the following steps:

[0050] First, the received signal Perform DFT operation to obtain its power spectrum ;

[0051] Then perform background normalization processing, select the corresponding threshold to perform double detection judgment on the normalization result and DFT spectrum estimation result, and obtain All frequencies exceeding the threshold;

[0052] Finally, the spectrum characteristics of the narrowband signal are used to complete The frequencies of the component signals contained in are extracted.

[0053] In a specific embodiment, the normalization process is as follows:

[0054] S1, the signal power spectrum The average of 2*N points centered at each frequency point is taken as the estimated mean of the power spectrum of each frequency point ;

[0055] S2. Determine the elimination threshold based on the estimated mean value ,in Take 3.2, is the average number of times the power spectrum of the input signal is calculated;

[0056] S3, the signal power spectrum and rejection threshold Compare, if less than, keep No change, on the contrary, Alternative ;

[0057] S4. The result after the elimination process is averaged with 2*N points centered at each frequency point as the estimated value μ of the power spectrum of each frequency point. k .

[0058] S5, the signal power spectrum With estimated value Do calculations .

[0059] In one embodiment, the spectral characteristics of the narrowband signal are used to perform In the frequency extraction process of the component signal contained in , a comparison method is used to find the frequency point corresponding to the maximum power in a preset area, wherein the criteria for determining the preset area include:

[0060] The frequency point number obtained by detection judgment is expressed as , the length is , using a recursive method to find the area for frequency extraction;

[0061] The conditions for determining the end position of the judgment area are:

[0062] Compare from the beginning of the region The adjacent frequency point number, The difference exceeds , The value of should be greater than 0;

[0063] The value selection principle is: The larger the value, the worse the resolution during frequency extraction and the stronger the ability to resist noise interference; conversely, the better the resolution, the worse the ability to resist noise interference.

[0064] Finally, the frequency point is selected based on the signal-to-noise ratio and minimum resolution requirements during operation.

[0065] The process of conducting lake experiments and research to verify the acoustic compatibility anti-interference method for harmonics provided by the present invention is as follows:

[0066] Design an acoustic compatibility lake test based on frequency extraction measurement method to analyze whether the anti-interference measures (acoustic compatibility design) are effective.

[0067] The specific plan is as follows: Taking the acoustic interference test of an active sonar (device A) on device B as an example, the acoustic compatibility test on the lake is introduced:

[0068] Among them, the operating frequency band of device A is relatively low, and its low-frequency and high-frequency cutoff frequencies are F A-low 、F A-high ; Device B has a higher operating frequency band, and its low-frequency and high-frequency cutoff frequencies are F B-low 、F B-high , where FB-low >F A-high , F B-high >2*F A-high , the relationship between the two devices' working frequency bands is as follows Figure 2 As shown, the frequencies are all above 10KHz.

[0069] Device A transmits a CW acoustic wave waveform, and its spectrum includes the in-band main frequency and out-of-band noise and harmonics. Device B operates in broadband noise and response modes. After entering the water, it begins emitting broadband noise and responds when the received acoustic wave exceeds its frequency domain detection threshold (hereinafter referred to as the "interference criterion") a0.

[0070] The acoustic compatibility test on the lake is as follows:

[0071] ①Construct an experimental environment on the lake.

[0072] Equipment A and equipment B are deployed to a certain depth underwater (the same as their designed normal operating depth) via a pontoon and a movable experimental ship respectively. The distance between the ships is the typical distance under normal working conditions of the two equipments and can be adjusted as needed. A standard water stop is placed near equipment B to synchronously receive the signal transmitted by equipment A for auxiliary shutdown and data verification. The experimental waters are 50-60 meters deep and open, with no obvious obstruction between the two equipments. The layout is shown as follows: Figure 3 (ab) shown.

[0073] ② Establish the transmitting and receiving conditions of the test equipment and determine the measuring points for conducting the test.

[0074] The transmitting condition of device A is the same as that of its normal operating mode, where the transmitting waveform is CW. To facilitate the analysis of the interference value caused by device A to device B, device B operates in receive-only mode, that is, it does not transmit broadband noise. The test points of device B include the rear end of the receiving transducer, the rear end of the front-end amplifier, and the front end of the AD switch. The layout diagram of device B is shown in the figure below. Figure 4 As shown, the receiving channel diagram is as follows Figure 5 As shown in the figure, the data collector is used to collect the measuring point data.

[0075] ③ Data analysis and interference judgment.

[0076] At each measuring point of device B (behind the receiving transducer, behind the front-end amplifier, and before AD switching), collect the time domain waveform and spectrum of the data to determine whether interference occurs. If yes, take anti-interference measures:

[0077] The time domain waveform is as follows Figure 6 As shown in (ad), it is determined whether the waveform data of each measuring point is distorted, whether the amplitude exceeds the limiting voltage at the relevant position, and whether the channel is saturated.

[0078] Spectrum Figure 7As shown, the time domain waveform, LOFAR diagram, and maximum spectral level within the single-shot operating frequency band at measurement point 4 are determined. When the interference spectrum level received by device B within the operating frequency band during device A's transmission exceeds its interference criterion a0, it is determined that device A interferes with device B during transmission. In the LOFAR diagram, the warmer the color, the larger the amplitude.

[0079] The specific anti-interference measures are:

[0080] The lower limit of the detection frequency band is extended to the low-frequency cutoff frequency FA-low of device A. Device B determines whether the interference frequency fA exceeding the detection threshold a0 within the operating frequency band of device A (FA-low—FA-high) and the frequency fB exceeding the detection threshold a0 within the original operating frequency band of device B (FB-low—FB-high) are harmonics of the same frequency, that is, whether fB satisfies formula (1):

[0081]

[0082] If formula (1) is satisfied, it is harmonic interference. If not, it is the target signal of device B. It is determined whether fB should be interference. If it is interference, device B will not respond to it. If it is not interference, it will respond to it.

[0083] The frequency extraction method in anti-interference measures is as follows Figure 8 As shown, the specific steps are:

[0084] P1, receiving signal Perform DFT operation to obtain its power spectrum ;

[0085] P2, perform background normalization processing, the processing steps are:

[0086] S1, the signal power spectrum The average of 2*N points (2*N points are excluding 2*J+1 points including this point) centered at each frequency point is taken as the estimated mean of the power spectrum of each frequency point. ;

[0087] S2. Determine the elimination threshold based on the estimated mean value. ,in Take 3.2, is the average number of times the power spectrum of the input signal is calculated;

[0088] S3, the signal power spectrum and rejection threshold Compare, if less than, keep No change, on the contrary, Alternative ;

[0089] S4. The result after the elimination process is averaged with 2*N points centered at each frequency point as the estimated value of the power spectrum of each frequency point. .

[0090] S5, the signal power spectrum The second estimated mean result Do calculations ;

[0091] Select the corresponding threshold to perform double detection judgment on the normalized result and DFT spectrum estimation result, and obtain All frequencies exceeding the threshold;

[0092] P3, using the spectrum characteristics of narrowband signals, complete The frequencies of the component signals contained in are extracted.

[0093] Since the background normalization processing idea is that the size of the background noise at different frequencies varies greatly, and unknown signals must be detected under this background, the present invention uses the variation range of the energy of each frequency point to be detected within the frequency band to unify the energy of all frequency points to eliminate the huge differences between the energy values ​​of each frequency point, so that these values ​​are only related to the background near it, reducing the impact of inter-spectral leakage on frequency extraction.

[0094] The idea of ​​frequency extraction is to use the comparison method to select an area and find the frequency point corresponding to the maximum value of the power spectrum in the area. The specific selection steps are:

[0095] The frequency point number obtained by detection judgment is expressed as , the length is , using a recursive method to find the area for frequency extraction;

[0096] The condition for determining the end position of the area is to compare from the starting position of the area The adjacent frequency point number, The difference exceeds , The value of should be greater than 0;

[0097] The value selection principle is: The larger the value, the worse the resolution during frequency extraction, but the stronger the ability to resist noise interference; conversely, the better the resolution, the worse the ability to resist noise interference.

[0098] Conduct a simulation test on the effect of anti-interference measures. The simulation conditions are as follows:

[0099] Device A: emits CW interference with a frequency of F1 and a spectrum level of Af1, and a second harmonic of F2 and a spectrum level of Af2. 、F2=2*F1,F1 10kHz.

[0100] Device B: Broadband noise is emitted normally, serving as the background noise for its operation. The spectrum level is A0, and the detection spectrum level threshold amplitude is a0.

[0101] The homing signal is the target signal of device B, which is detected and responded to, with a frequency of F3 and a spectral level of Af3.

[0102] in 、F3=F2+300Hz,Af1=Af2 Af3 A, such as Figure 9 shown.

[0103] Using the above frequency measurement method, the frequencies exceeding the detection threshold a0 in the frequency band of device B are measured as f1=F1+100Hz, f2=F2+79Hz, and f3=F3+94Hz, respectively. Formula (1) is used to determine whether f2 and f1 satisfy the second harmonic relationship.

[0104] According to the above anti-interference measures, device B regards f2 as interference and does not respond, but regards f3 as a beneficial homing signal and responds.

[0105] The simulation results show that the anti-interference measures proposed in the present invention can be used by device B to manage the interference caused by device A.

[0106] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. An acoustic compatibility anti-interference method for harmonics, targeting the interference phenomenon where both the emission main frequency and emission harmonics of device A exceed the detection threshold of device B, characterized in that: include; Extend the lower limit of the detection frequency band of underwater acoustic equipment B to the low-frequency cutoff frequency of underwater acoustic equipment A; Device B determines the signal type by determining whether the interference frequency fA exceeding the detection threshold a0 within the operating frequency band of device A is a harmonic of the frequency fB exceeding the detection threshold a0 within the original operating frequency band of device B. The operating frequency band of device A is FA-low to FA-high, and the original operating frequency band of device B is FB-low to FB-high. That is, the signal type is determined by determining whether fB satisfies the following formula: (2-1%)×fA <fB<(2+1%)×fA If it is satisfied, fB is determined to be harmonic interference and device B does not respond to it; If not, fB is determined to be the target signal and device B responds to it.

2. The method for acoustic compatibility and anti-interference of harmonics according to claim 1, characterized in that: The method for extracting the frequency in the anti-interference measure specifically includes the following steps: First, the received signal X (t) Perform DFT operation to obtain its power spectrum x k ; Then perform background normalization processing, select the corresponding threshold to perform double detection judgment on the normalization result and DFT spectrum estimation result, and obtain x k All frequencies exceeding the threshold; Finally, the spectrum characteristics of the narrowband signal are used to complete X (t) The frequencies of the component signals contained in are extracted.

3. The acoustic compatibility anti-interference method for harmonics according to claim 2, characterized in that: The steps of the normalization process are: S1, the signal power spectrum x k The average of 2*N points centered at each frequency point is taken as the estimated mean of the power spectrum of each frequency point S2. Determine the elimination threshold based on the estimated mean value Where c is 3.2, M is the average number of times the input signal power spectrum is calculated; S3, the signal power spectrum x k and the rejection threshold T k Compare, if less than, keep x k No change, on the contrary, Replace x k ; S4. The result after the elimination process is averaged with 2*N points centered at each frequency point as the estimated value μ of the power spectrum of each frequency point. k ; S5, the signal power spectrum x k With the estimated value μ k Perform operation x k / μ k .

4. The method for acoustic compatibility and anti-interference of harmonics according to claim 3, characterized in that: Complete X using the spectrum characteristics of narrowband signals (t) In the frequency extraction process of the component signal contained in , a comparison method is used to find the frequency point corresponding to the maximum power in a preset area, wherein the criteria for determining the preset area include: The frequency point number obtained by the detection judgment is expressed as Nf, the length is L, and the area for frequency extraction is found by recursive method; The conditions for determining the end position of the judgment area are: Compare the numbers of adjacent frequency points in Nf starting from the starting position of the region. If the difference between Nf(k-1) and Nf(k) exceeds Nk, the value of Nk should be greater than 0. The principle of its value selection is: the larger the Nk is, the worse the resolution is during frequency extraction and the stronger the anti-noise interference capability is; conversely, the better the resolution is, the worse the anti-noise interference capability is. Finally, the frequency point is selected based on the signal-to-noise ratio and minimum resolution requirements during operation.

Images