Acoustic compatible anti-interference method for harmonic waves

Abstract

The invention discloses an acoustic compatible anti-interference method for harmonic waves, which aims at the interference phenomenon that the emission main frequency and the emission harmonic waves of equipment A both exceed the detection threshold of equipment B. The method comprises the following steps: expanding the lower limit of the detection frequency band of underwater acoustic equipment B to the low-frequency cut-off frequency of the underwater acoustic equipment A; the equipment B judges whether the interference frequency fA passing through the detection threshold a0 in the working frequency band (FA-low-FA-high) of the equipment A and the frequency fB passing through the detection threshold a0 in the original working frequency band (FB-low-FB-high) of the equipment B are in a frequency multiplication harmonic relation, if yes, fB is determined to be harmonic interference, and the equipment B does not respond to the interference; if not, the fB is determined as a target signal, and the device B responds to the target signal. The invention provides an anti-interference measure aiming at the interference phenomenon that the emission main frequency and the emission harmonic wave of the equipment A both exceed the detection threshold of the equipment B, so that the equipment B can effectively treat the interference generated by the equipment A.

Description

Technical Field

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

[0002] In the field of underwater acoustic operations, underwater acoustic communication and positioning and navigation technologies are the core. In oceanographic research, a research ship and an underwater detector rely on it to transmit a large amount of deep-sea data, helping scientists to deeply understand the mysterious ocean world; in underwater security, different security devices achieve information interaction through underwater acoustic communication to closely monitor the underwater security situation; at the same time, in the field of ocean resource development, underwater mining equipment uses it to communicate smoothly with the sea surface operation platform to ensure the efficient progress of mining work. The positioning and navigation technology transmits information, detects targets, and performs positioning and navigation through specific frequency acoustic signals between devices. The acoustic signals are like messengers underwater, shuttling through the complex underwater environment, providing crucial support for various underwater operations and promoting the continuous development of the underwater acoustic operation field. However, the underwater environment is complex, and signal propagation is easily interfered by various factors, among which harmonic interference is a common problem. When underwater acoustic operation equipment works, it will generate harmonics, which may be coupled with the working frequencies of other equipment to cause interference. For example, when multiple devices work together, if the working frequencies of different devices are close or have a multiple-frequency relationship, the harmonic interference will be aggravated. Moreover, the particularity of the underwater environment, such as water temperature stratification, underwater terrain, etc., will make the propagation path of acoustic signals complex, further aggravating the impact of harmonic interference.

[0003] In actual application scenarios, there often occurs a situation where both the transmitting main frequency and the transmitting harmonics of device A exceed the detection threshold of device B. When device A works, its transmitting main frequency and the generated harmonics may conflict with the detection threshold of device B, resulting in a large amount of interference components mixed in the signal received by device B.

[0004] Currently, the equipment used in underwater acoustic operations has obvious deficiencies in dealing with this kind of harmonic interference. It seriously affects the detection accuracy of the target signal or the communication performance of the equipment, etc. In actual operation scenarios, the equipment often misjudges because it cannot accurately identify the interference signal, and mistakes the harmonic interference signal for the target signal for processing, which not only wastes system resources but also may cause delays in the operation process, operation errors, etc. At the same time, due to the increase in the background noise caused by harmonic interference, the receiving sensitivity of the equipment is greatly reduced. In some fine detection tasks with high requirements for signal quality, clear and accurate signal data cannot be obtained, affecting the reliability of the detection results. In addition, when multiple devices work together, due to the problem of harmonic interference not being effectively solved, the communication link between devices is often interrupted or data transmission errors occur, reducing the efficiency and coordination of the entire operation system, increasing the operation cost and time investment, and 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 acoustic compatibility anti-interference method for harmonics to solve the technical problem that signals are vulnerable to harmonic interference during underwater acoustic operations at present.

[0006] To achieve the above purpose, the present invention provides the following technical solutions: An acoustic compatibility anti-interference method for harmonics provided by the present invention, aiming at the interference phenomenon that both the transmission main frequency and the transmission harmonics of device A exceed the detection threshold of device B, includes: Extend the lower limit of the detection frequency band of underwater acoustic device B to the low-frequency cut-off frequency of underwater acoustic device A; Device B determines whether the interference frequency fA exceeding the detection threshold a0 within the working frequency band of device A (FA-low~FA-high) and the frequency fB exceeding the detection threshold a0 within the original working frequency band of device B (FB-low~FB-high) are in a multiple-frequency harmonic relationship, that is, determines the signal type by judging whether fB satisfies the following formula: If it is satisfied, it is determined that fB is harmonic interference, and device B does not respond to it; If it is not satisfied, it is determined that fB is the target signal, and device B responds to it.

[0007] Preferably, the method for extracting frequencies in the anti-interference measures specifically includes the following steps: First, perform DFT operation on the received signal to obtain its power spectrum ; Then perform background normalization processing, select the corresponding threshold to perform double detection and decision on the normalization result and the DFT spectrum estimation result, and obtain all the frequencies exceeding the threshold in; Finally, use the spectral characteristics of narrowband signals to complete the frequency extraction of the component signals included in.

[0008] Preferably, the steps of normalization processing are: S1. Take the average of 2*N points centered on each frequency point of the signal power spectrum as the estimated mean value of the power spectrum of each frequency point ; S2. Determine the rejection threshold according to the estimated mean value result, where take 3.2, is the average number of times when calculating the power spectrum of the input signal; S3. Compare the signal power spectrum with the rejection threshold Compare. If it is less, then keep unchanged. Otherwise, replace ; S4. Take the average of 2*N points centered on each frequency point from the result after the rejection process as the estimated value μ of the power spectrum of each frequency point k ; S5. Perform an operation on the signal power spectrum and the estimated value .

[0009] Preferably, use the spectral characteristics of the narrowband signal to complete During the process of extracting the frequencies of the component signals included in, use the comparison method to find the frequency point corresponding to the maximum power within the preset region. Among them, the determination criteria for the preset region include: Express the frequency point number obtained by the detection decision as , with a length of , and use the recursive method to find the region for frequency extraction; The condition for the end position of the decision region is: Start comparing from the starting position of the region the adjacent frequency point numbers in, the difference exceeds , the value of should be greater than 0; Its value principle is: The larger, the worse the resolution during frequency extraction and the stronger the anti-noise interference ability; otherwise, the better the resolution and the worse the anti-noise interference ability; Finally, select the frequency point by preference according to the signal-to-noise ratio during operation and the minimum resolution requirement.

[0010] The beneficial effects of the present invention are as follows: 1. In view of the interference phenomenon that the transmission harmonics of device A are within the working frequency band of device B, and both the transmission main frequency and transmission harmonics of device A exceed the detection threshold of device B, the present invention proposes an acoustic compatibility anti-interference measure, which can be used for device B to control the interference generated by device A to it.

[0011] Other advantages, objectives, and features of the present invention will be described in the subsequent specification, and to some extent will be obvious to those skilled in the art, or those skilled in the art can obtain teachings from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to make the objectives, technical solutions, and beneficial effects of the invention clearer, the present invention provides the following drawings for illustration: ​Figure 1 A flowchart of the steps of an acoustic compatibility anti-interference method for harmonics; Figure 2 Schematic diagram of the relationship between the operating frequency bands of device A and device B of the present invention; Figure 3 (ab) are schematic diagrams of the experimental deployment of the device A of the present invention on the lake; Figure 4 This is a schematic diagram of the test deployment of the device B on the lake; Figure 5 This is a schematic diagram of the receiving channel of device B of the present invention; Figure 6 (ad) is the time domain waveform judgment diagram of the present invention; Figure 7 This is a spectrum diagram during testing of the present invention; Figure 8 This is a frequency extraction flow chart of the present invention; Figure 9 Schematic diagram of the simulation conditions of the present invention. DETAILED DESCRIPTION

[0013] like Figure 1-9 As shown, the present invention provides an acoustically compatible anti-interference method for harmonics.

[0014] 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; 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 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: 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.

[0015] In a specific embodiment, the method for extracting the frequency in the anti-interference measure specifically includes the following steps: First, the received signal Perform DFT operation to obtain its power spectrum ; 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 in Finally, utilize the spectral characteristics of the narrowband signal to complete the frequency extraction of the component signals contained in

[0016] In a specific embodiment, the steps of the normalization process are as follows: S1. Take the average of 2*N points centered on each frequency point of the signal power spectrum as the estimated mean of the power spectrum of each frequency point ; S2. Determine the rejection threshold according to the result of the estimated mean , where take 3.2, which is the average number of times when calculating the power spectrum of the input signal; S3. Compare the signal power spectrum with the rejection threshold . If it is less, keep it unchanged. Otherwise, substitute ; S4. Take the average of 2*N points centered on each frequency point of the result after the rejection process as the estimated value μ of the power spectrum of each frequency point k .

[0017] S5. Perform an operation on the signal power spectrum and the estimated value .

[0018] In a specific embodiment, when using the spectral characteristics of the narrowband signal to complete the frequency extraction of the component signals contained in, use the comparison method to find the frequency point corresponding to the maximum power within the preset region. Among them, the determination criteria for the preset region include: Express the frequency point number obtained by the detection decision as , with a length of , and use the recursive method to find the region for frequency extraction; The condition for the end position of the decision region is: Start comparing from the starting position of the region the adjacent frequency point numbers in , and the difference exceeds , and the value of should be greater than 0; The larger the Finally, the frequency points are optimally selected based on the signal-to-noise ratio during operation and the minimum resolution requirement.

[0019] For the method for acoustic compatibility anti-interference against harmonics provided by the present invention, the process of conducting a lake experiment for verification is as follows: Design an acoustic compatibility lake experiment, and based on the frequency extraction measurement method, analyze whether the anti-interference measures (acoustic compatibility design) are effective.

[0020] The specific scheme is as follows: Taking the acoustic interference experiment of an active sonar (Device A) on a Device B as an example, introduce the acoustic compatibility lake experiment situation: Among them, the operating frequency band of Device A is relatively low, and its low-frequency and high-frequency cut-off frequencies are F A-low and F A-high respectively; the operating frequency band of Device B is relatively high, and its low-frequency and high-frequency cut-off frequencies are F B-low and F B-high respectively, where F B-low > F A-high , F B-high > 2 * F A-high , and the relationship between the operating frequency bands of the two devices is as shown in Figure 2 , and the frequencies are all above 10 KHz.

[0021] The acoustic wave waveform emitted by Device A is a CW signal, and its emission spectrum includes in-band main frequency, out-of-band clutter, harmonics, etc.; Device B has working modes such as broadband noise and response; after entering the water, it starts to emit broadband noise, and when the received acoustic wave exceeds its frequency domain detection threshold (hereinafter referred to as "interference criterion") a0, it will respond to it.

[0022] The acoustic compatibility lake experiment is as follows: ① Construct a lake experiment environment.

[0023] Device A and Device B are respectively placed to a certain depth underwater (the same as their designed normal working depth) through a pontoon and a movable experimental ship. The distance between the ships is the typical distance under the normal working conditions of the two devices, which can be adjusted as needed. A standard water stopper is suspended near Device B to synchronously receive the signal emitted by Device A, which is used for auxiliary switching and data verification, etc.; the depth of the experimental water area is 50 - 60 meters, the experimental water area is open, and there is no obvious obstruction between the two devices. The layout schematic is as shown in Figure 3 (a - b).

[0024] ② Formulate the emission and reception working conditions of the participating devices, determine the measurement points and conduct the experiment.

[0025] The transmission condition of Device A is the same as that in its normal working mode, where the transmission waveform is in the form of CW. To facilitate the analysis of the interference magnitude generated by Device A on Device B, Device B operates in a receive-only mode, that is, it does not emit broadband noise; the test points of Device B include the back end of the receiving transducer, the back end of the preamplifier, and before the AD conversion, etc. The layout schematic diagram of Device B is as shown in Figure 4 shown, and the schematic diagram of the receiving channel is as shown in Figure 5 shown, and a data collector is used to collect the data at the measuring points.

[0026] ③ Data analysis and interference judgment.

[0027] At each measuring point of Device B (the back end of the receiving transducer, the back end of the preamplifier, and before the AD conversion), the time-domain waveform and spectrum of the collected data are used to judge whether interference occurs. If the judgment result is yes, anti-interference measures are taken: Among them, the time-domain waveform is as shown in Figure 6 (a - d), and it is judged whether the waveform data at each measuring point is distorted, whether the amplitude exceeds the limiting voltage at the relevant position, and whether the channel is saturated.

[0028] The spectrum is as shown in Figure 7 shown. By judging the time-domain waveform, LOFAR diagram, and the maximum spectral level within the single-shot working frequency band at measuring point 4, it is found that when Device A transmits, if the interference spectral level received within the working frequency band of Device B exceeds its interference criterion a0, it is determined that Device A generates interference to Device B during transmission; among them, in the LOFAR diagram, the warmer the color tone, the larger the amplitude.

[0029] The specific anti-interference measures are as follows: The lower limit of the detection frequency band is extended to the low-frequency cut-off frequency FA-low of Device A. Device B judges whether the interference frequency fA that passes the detection threshold a0 within the working frequency band of Device A (FA-low - FA-high) and the frequency fB that passes the detection threshold a0 within the original working frequency band of Device B (FB-low - FB-high) are in a multiple-frequency harmonic relationship, that is, to judge whether fB satisfies formula (1): If it satisfies formula (1), it is harmonic interference. If it does not satisfy, it is the target signal of Device B. It is judged 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.

[0030] The method for extracting frequencies in the anti-interference measures is as shown in Figure 8 shown, and the specific steps are as follows: P1. Perform DFT operation on the received signal to obtain its power spectrum ; P2. Perform background normalization processing, and the processing steps are as follows: S1. The signal power spectrum Take the average of 2*N points centered on each frequency point (the 2*N points are the points obtained by removing 2*J + 1 points including this point) as the estimated mean of the power spectrum of each frequency point. ; S2. Determine the rejection threshold according to the estimated mean result, , where Take 3.2, which is the average number of times when calculating the power spectrum of the input signal; S3. Compare the signal power spectrum with the rejection threshold . If it is less, keep unchanged. Otherwise, replace ; S4. Take the average of 2*N points centered on each frequency point of the result after the rejection process as the estimated value of the power spectrum of each frequency point .

[0031] S5. Perform an operation on the signal power spectrum and the result of the second estimated mean ; Select the corresponding threshold to perform double detection and decision on the normalized result and the DFT spectrum estimation result to obtain all the frequencies exceeding the threshold in ; P3. Utilize the spectral characteristics of the narrowband signal to complete the frequency extraction of the component signals included in

[0032] Since the idea of background normalization processing has a large difference in the magnitude of background noise at different frequencies, and it is necessary to detect unknown signals under this background, the present invention uses the variation range of the energy of each frequency point to be detected in the frequency band range to uniformly plan all the frequency point energies, so as to eliminate the huge difference between the energy values of each frequency point, making these values only related to the background near it and reducing the influence of spectral leakage on frequency extraction.

[0033] The idea of frequency extraction is to use the comparison method to select a region and find the frequency point corresponding to the maximum power spectrum within the region. The specific selection steps are as follows: Express the frequency point numbers obtained by the detection and decision as , with a length of , and use the recursive method to find the region for frequency extraction; The condition for the end position of the decision region is to compare the adjacent frequency point numbers in starting from the start position of the region, the difference exceeds , and the value of should be greater than 0; Its value-taking principle is as follows: The larger it is, the worse the resolution during frequency extraction, but the stronger the anti-noise interference ability; conversely, the better the resolution and the worse the anti-noise interference ability.

[0034] Carry out a simulation test on the effect of anti-interference measures. The simulation conditions are as follows: Device A: Transmits CW interference with a frequency of F1, a spectral level of Af1, a second harmonic of F2, and a spectral level of Af2. and F2 = 2 * F1, F1 10 kHz.

[0035] Device B: Normally transmits broadband noise, which is the background noise for its operation, with a spectral level of A0, and the detected spectral threshold amplitude is a0.

[0036] The homing signal is the target signal of Device B, and its detection and response have a frequency of F3 and a spectral level of Af3.

[0037] Where and F3 = F2 + 300 Hz, Af1 = Af2 Af3 A, as Figure 9 shown.

[0038] Using the above frequency measurement method, the frequencies exceeding the detection threshold a0 within the frequency band of Device B are measured as f1 = F1 + 100 Hz, f2 = F2 + 79 Hz, and f3 = F3 + 94 Hz respectively. Use formula (1) to determine that f2 and f1 satisfy the second harmonic relationship.

[0039] According to the above anti-interference measures, Device B regards f2 as interference and does not respond, and regards f3 as a beneficial homing signal and responds.

[0040] Through simulation verification, the anti-interference measures proposed by the present invention can be used for Device B to control the interference generated by Device A to it.

[0041] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit. 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, aiming at the interference phenomenon that both the main emission frequency and the emission harmonics of device A exceed the detection threshold of device B, characterized in that, including; extending the lower limit of the detection frequency band of the underwater acoustic device B to the low-frequency cut-off frequency of the underwater acoustic device A; By determining whether the interference frequency fA exceeding the detection threshold a0 within the operating frequency band of device A (FA-low to FA-high) and the frequency fB exceeding the detection threshold a0 within the original operating frequency band of device B (FB-low to FB-high) are in a multiple-frequency harmonic relationship, that is, by determining whether fB satisfies the following formula to determine the signal type: If it is satisfied, it is determined that fB is harmonic interference, and device B does not respond to it; If it is not satisfied, it is determined that fB is the target signal, and device B responds to it.

2. The acoustic compatibility anti-interference method for harmonics according to claim 1, characterized in that The method for extracting frequencies in the anti-interference measure specifically includes the following steps: First, perform DFT operation on the received signal to obtain its power spectrum ; Then perform background normalization processing, select the corresponding threshold to perform double detection and decision on the normalization result and the DFT spectrum estimation result, and obtain all the frequencies above the threshold in Finally, the frequency extraction of the component signals contained in is completed by using the spectral characteristics of the narrowband signal.

3. The acoustic compatibility anti-interference method for harmonics according to claim 2, wherein The steps of the normalization process are: S1. Take the signal power spectrum Take the average of 2*N points centered on each frequency point as the estimated mean of the power spectrum of each frequency point ; S2. Determine the rejection threshold according to the estimated mean result , where Take 3.2, which is the average number of times during the calculation of the input signal power spectrum; S3. Compare the signal power spectrum with the rejection threshold . If it is less, keep unchanged. Otherwise replace ; S4. Take the average of 2*N points centered on each frequency point from the result after the rejection process as the estimated value μ of the power spectrum for each frequency point. k ; S5. Calculate the operation of the signal power spectrum and the estimated value . .

4. The acoustic compatibility anti-interference method for harmonics according to claim 3, characterized in that, Complete the During the process of extracting the frequencies of the component signals included in, use the comparison method to find the frequency point corresponding to the maximum power within the preset region. Among them, the determination criteria for the preset region include: The frequency point number obtained by detection and decision is represented as , with a length of , and a recursive method is used to find the region for frequency extraction; The condition for the end position of the decision region is: Compare starting from the starting position of the region adjacent frequency point numbers in the difference exceeds , the value of should be greater than 0; The principle for its value is as follows: The larger it is, the worse the resolution during frequency extraction and the stronger the anti-noise interference ability; conversely, the better the resolution and the worse the anti-noise interference ability. Finally, select the frequency point by preference according to the signal-to-noise ratio during operation and the minimum resolution requirement.

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