Active sonar anti-reverberation technology

Abstract

The invention discloses an active sonar anti-reverberation technology, and the technology is characterized in that the technology comprises an active sonar which employs the waveform of a fuzzy function for the anti-reverberation of an emission signal of the active sonar; and the active sonar adopts waveforms for transmitting different types of fuzzy functions in turn or simultaneously transmitting waveforms for transmitting different types of fuzzy functions. The invention relates to the technical field of active sonar, in particular to an active sonar anti-reverberation technology. The technical problem to be solved by the invention is to provide an active sonar anti-reverberation technology, and the waveform of a drawing pin type fuzzy function is used as an emission signal of an active sonar to improve the detection performance of a target under a reverberation background.

Description

Technical Field

[0001] The present invention relates to the technical field of active sonar, and more specifically, to an active sonar anti-reverberation technique. Background Art

[0002] With the development of submarine vibration and noise reduction technology, the noise of submarines is getting lower and lower, and it is very difficult for passive sonar to detect quiet submarines. Active sonar must be used to detect quiet submarines. The ambiguity function is an important tool for studying the time (range) and frequency resolution of active sonar.

[0003] The ambiguity function is defined as: (3); Where: is the time delay; is the frequency; is the complex envelope of the signal; is the time; The working waveforms used in existing active sonars are long continuous wave (CW) pulses, short CW pulses, linearly frequency modulated pulses, and hyperbolic frequency modulated pulses; their ambiguity functions are respectively of the knife-edge type (as shown in Figure 4 ) and the oblique knife-edge type (as shown in Figure 5 ).

[0004] From the perspective of anti-reverberation, the anti-reverberation capabilities of these working waveforms all have defects. Long continuous wave (CW) pulses and short CW pulses have only one-dimensional range or frequency resolution dimensions. The range and frequency resolutions of linearly frequency modulated pulses and hyperbolic frequency modulated pulses are highly coupled. An important technical index for evaluating anti-reverberation performance is the ambiguity area, and the smaller the ambiguity area, the better: (4); Where: is the mean square pulse width, is the mean square bandwidth, is the linear frequency modulation coefficient. For an energy-normalized signal there is: (5); (6); For an energy-normalized signal the corresponding Fourier transform is , and the mean square bandwidth is defined as: (7); (8); Where: is the frequency; As can be seen from equation (4), to reduce the ambiguity area, there must be no frequency modulation coefficient first. Therefore, if we want to suppress reverberation, we cannot use linear frequency modulation signals. In addition, to reduce the ambiguity area, we must also increase the product of while the CW pulse where are the pulse width and bandwidth of the CW pulse respectively. Therefore, the anti-reverberation performance is also not good.

[0005] Therefore, if we want to improve the anti-reverberation performance, we must use signals with a large time-bandwidth product other than linear frequency modulation signals. Then such a signal can only be a waveform with a thumbtack-shaped ambiguity function. SUMMARY OF THE INVENTION

[0006] The technical problem to be solved by the present invention is to provide an active sonar anti-reverberation technology, which uses a waveform with a thumbtack-shaped ambiguity function as the transmission signal of the active sonar to improve the detection performance of the target under the reverberation background.

[0007] The present invention adopts the following technical solutions to achieve the invention purpose: An active sonar anti-reverberation technology, characterized by including: an active sonar, the active sonar uses a waveform of an ambiguity function as the transmission signal of the active sonar to anti-reverberate; the active sonar alternately transmits waveforms of different types of ambiguity functions or simultaneously transmits waveforms of different types of ambiguity functions.

[0008] As a further limitation of this technical solution, the ambiguity function is a thumbtack-shaped ambiguity function.

[0009] As a further limitation of this technical solution, the thumbtack-shaped ambiguity function waveforms mainly include Barker codes and pseudo-random sequences.

[0010] As a further limitation of this technical solution, the characteristic of the Barker code is that the non-cyclic autocorrelation function value can only be 1, -1 or zero. Therefore, for a Barker code with a code length of the main-to-side lobe ratio of the autocorrelation function is ; The m-sequence is a pseudo-random sequence with the largest period, and the cyclic autocorrelation side lobe is always -1, and the period or code length where is a positive integer; The active sonar requires a working waveform with a low side lobe of the non-cyclic autocorrelation function. When its non-cyclic autocorrelation function main-to-side lobe ratio is approximately When the code length is long, the main-to-side lobe ratio of the m-sequence meets the requirements of the active sonar transmission waveform.

[0011] As a further limitation of this technical solution, the pseudo-random sequence is an L-sequence (also known as a binary quadratic residue sequence); Decision criterion: is an odd prime number, is a positive integer relatively prime to If the congruence equation has integer solutions, then the integer is a quadratic residue modulo ; otherwise is a non - quadratic residue modulo ; Define the Legendre symbol: (1); When the value is 1, is a quadratic residue modulo ; When the value is - 1, is a non - quadratic residue modulo ; Define an L - sequence of prime type with length . The autocorrelation function property of the L - sequence defined in this way is the same as that of the m - sequence, always being - 1. Let the periodic sequence of the L - sequence be , and takes values according to the following rule: (2). As a further limitation of this technical solution, the active sonar includes a transmitting system, a receiving system, and a display and control console. The transmitting system includes a signal source, a transmitter, and a transmitting transducer, which are electrically connected in sequence. The receiving system includes a receiving array, a receiver, an A / D converter, and a signal processor, which are electrically connected in sequence. The receiving array is electrically connected to the receiver, and the signal source is electrically connected to the receiver and the A / D converter.

[0012] Compared with the prior art, the advantages and positive effects of the present invention are as follows: This technology improves the detection performance of targets under reverberation background, and uses two - dimensional joint resolution of distance and frequency to enhance the detection performance of targets under reverberation background. This technology improves the resolution ability of targets. When there are multiple targets in the same beam, two - dimensional resolution of distance and frequency can be used to improve the resolution ability of multiple targets and the performance of target batch numbering. This technology improves the measurement accuracy of the distance and radial velocity of the active sonar.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a schematic diagram of the thumbtack - type ambiguity function graph of the present invention.

[0015] Figure 2 FIG. is the autocorrelation function of the Barker code of the present invention.

[0016] ​Figure 3 This is the block diagram of the active sonar of the present invention.

[0017] Figure 4 This is the knife-edge type ambiguity function graph of the present invention.

[0018] Figure 5 This is the inclined knife-edge type ambiguity function graph of the present invention. Specific embodiments

[0019] The following combines the accompanying drawings to describe in detail a specific embodiment of the present invention. However, it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0020] The present invention includes: an active sonar, and the active sonar uses the waveform of the ambiguity function as the transmitted signal of the active sonar to resist reverberation; the active sonar alternately transmits waveforms of different types of ambiguity functions or simultaneously transmits waveforms of different types of ambiguity functions.

[0021] An active sonar is a general term for various sonars that actively transmit underwater acoustic signals and obtain target parameters from the echo reflected by underwater targets. Its operation is based on the principle of sound wave propagation and reflection. First, the sonar transmitter generates an electrical signal, and then through the transducer array, the electrical signal is converted into an acoustic signal and transmitted into the seawater. When the acoustic signal propagates in the water and encounters a target (such as a submarine, fish school, seabed terrain, etc.), it will be reflected back. The reflected acoustic signal is received by the transducer and then converted back into an electrical signal, which is amplified and processed by the receiver. Finally, the processed signal is displayed on the fluorescent screen of the display, thereby realizing the detection and positioning of underwater targets.

[0022] The transmitted waveform of the thumbtack type ambiguity function can be used together with waveforms of other types of ambiguity functions, and can be alternately transmitted or simultaneously transmitted with waveforms of other types of ambiguity functions. Alternate transmission can be: the thumbtack type ambiguity function waveform and the knife-edge type ambiguity function waveform are alternately transmitted, the thumbtack type ambiguity function waveform and the inclined knife-edge type ambiguity function waveform are alternately transmitted, and the thumbtack type ambiguity function waveform, the knife-edge type ambiguity function, and the inclined knife-edge type ambiguity function are alternately transmitted. Simultaneous transmission can be: the thumbtack type ambiguity function waveform and the knife-edge type ambiguity function waveform are simultaneously transmitted, the thumbtack type ambiguity function waveform and the inclined knife-edge type ambiguity function waveform are simultaneously transmitted, and the thumbtack type ambiguity function waveform, the knife-edge type ambiguity function, and the inclined knife-edge type ambiguity function are simultaneously transmitted.

[0023] The ambiguity function is a thumbtack type ambiguity function.

[0024] The thumbtack-shaped ambiguity function refers to an ambiguity function graph that has a sharp central peak at the origin, while the sidelobes are relatively flat and evenly distributed, forming a relatively high plateau, making the entire ambiguity function graph resemble the shape of a thumbtack. It can provide the characteristics of high resolution and low sidelobes, so it is often used in radar systems that require precise detection and positioning of targets.

[0025] The autocorrelation function of the Barker code has relatively small values (usually 0 or ±1) at its non-zero delays, and reaches the maximum value (i.e., the sequence length n) at zero delay. This characteristic enables the Barker code to provide better synchronization performance and anti-noise ability in the transmission and reception of synchronization signals.

[0026] L-sequences generally refer to training sequences used for synchronization. For example, L-STF (Short Training Field) and L-LTF (Long Training Field) are used for the synchronization of OFDM signals in the IEEE 802.11ac protocol. These sequences help the receiving end find the starting point of the OFDM symbol, so as to correctly perform FFT (Fast Fourier Transform) to recover the original signal.

[0027] The waveforms of the thumbtack-shaped ambiguity function mainly include Barker codes and pseudo-random sequences (such as m-sequences and L-sequences, etc.), but are not limited to Barker codes and pseudo-random sequences. Any waveform of the thumbtack-shaped ambiguity function can be used as a waveform for suppressing reverberation.

[0028] The characteristic of the Barker code is that the values of the non-cyclic autocorrelation function can only be 1, -1 or zero. Therefore, the main-to-side lobe ratio of the autocorrelation function of the Barker code with a code length of is Figure 4 Give the autocorrelation function of the Barker code with a code length of 7 (+++---+-); The m-sequence is a pseudo-random sequence with the largest period, and the cyclic autocorrelation sidelobes are constantly -1, and the period or code length , where is a positive integer; The active sonar requires a working waveform with low sidelobes of the non-cyclic autocorrelation function. When , its non-cyclic autocorrelation function main-to-side lobe ratio is approximately , when the code length is relatively long, the main-to-side lobe ratio of the m-sequence meets the requirements of the active sonar transmission waveform, and usually requires the main-to-side lobe ratio to be greater than 30 dB.

[0029] The pseudo-random sequence is an L-sequence (also known as a binary quadratic residue sequence); Decision criterion: is an odd prime number, is a positive integer relatively prime to , if has an integer solution (i.e., can be divisible by ), then the integer is a quadratic residue modulo , otherwise is a non - quadratic residue modulo ; Define the Legendre symbol: (1); When the value is 1, is a quadratic residue modulo ; When the value is - 1, is a non - quadratic residue modulo ; Define an L - sequence of prime length . The autocorrelation function property of the L - sequence defined in this way is the same as that of the m - sequence, always being - 1. Let the L - sequence be a periodic sequence , and takes values according to the following rule: (2).

[0030] The active sonar includes a transmitting system, a receiving system and a display and control console. The transmitting system includes a signal source, a transmitter and a transmitting transducer. The signal source, the transmitter and the transmitting transducer are electrically connected in sequence. The receiving system includes a receiving array, a receiver, an A / D converter and a signal processor. The receiver, the A / D converter and the signal processor are electrically connected in sequence. The receiving array is electrically connected to the receiver, and the signal source is electrically connected to the receiver and the A / D converter.

[0031] The signal source generates the waveform of a thumbtack - type ambiguity function. The transmitter amplifies the signal, and the transmitting transducer converts the electrical signal into an acoustic signal. If phased transmission is required, the signal source needs to generate a set of transmission signals, which are amplified by the transmitter respectively and then fed to the transmitting array. The receiving array converts the acoustic signal into an electrical signal, and the receiver realizes signal amplification and conditioning. The A / D converter completes analog - to - digital conversion, and the signal processor completes beamforming and matched filtering processing of the received signal to obtain two - dimensional resolution of distance and frequency, and completes signal detection and two - dimensional measurement of distance and frequency.

[0032] The above - disclosed are only specific embodiments of the present invention. However, the present invention is not limited thereto, and any changes that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. An active sonar anti-reverberation technology, characterized in that Including: An active sonar, wherein the active sonar uses the waveform of a ambiguity function as the transmitted signal of the active sonar to anti-reverberation; The active sonar alternately transmits waveforms of different types of ambiguity functions or simultaneously transmits waveforms of different types of ambiguity functions.

2. The active sonar anti-reverberation technology according to claim 1, characterized in that: The ambiguity function is a thumbtack-shaped ambiguity function.

3. The active sonar anti-reverberation technology according to claim 2, characterized in that: The waveforms of the thumbtack-shaped ambiguity function mainly include Barker codes and pseudo-random sequences.

4. The active sonar anti-reverberation technology according to claim 3, characterized in that: The characteristic of Barker code is that the non-cyclic autocorrelation function values can only be 1, -1 or zero. Therefore, for a Barker code with a code length of , the main-to-side lobe ratio of its autocorrelation function is ; The m-sequence is a pseudo-random sequence with the maximum period, and its cyclic autocorrelation sidelobes are always -1, and the period or code length , where is a positive integer; The active sonar requires a working waveform with a non-cyclic autocorrelation function having low sidelobes. When the main-to-sidelobe ratio of its non-cyclic autocorrelation function is approximately . When the code length is long, the main-to-sidelobe ratio of the m-sequence meets the requirements of the active sonar transmission waveform.

5. The active sonar anti-reverberation technology according to claim 4, wherein: The pseudo-random sequence is an L-sequence; Decision criterion: is an odd prime number, is a positive integer relatively prime to and if has an integer solution, then the integer is a quadratic residue modulo otherwise is a non - quadratic residue modulo ; Define the Legendre symbol: （1）； When the value is 1, is a quadratic residue modulo ; When the value is -1, is a non-quadratic residue modulo ; Define the length as type prime number L-sequence. The property of the cyclic autocorrelation function of the L-sequence defined in this way is the same as that of the m-sequence, always being -1. Let the L-sequence periodic sequence be , and takes values according to the following rules: （2）。 6. The active sonar anti-reverberation technology according to claim 1, characterized in that: The active sonar includes a transmitting system, a receiving system and a display and control console. The transmitting system includes a signal source, a transmitter and a transmitting transducer. The signal source, the transmitter and the transmitting transducer are electrically connected in sequence. The receiving system includes a receiving array, a receiver, an A / D converter and a signal processor. The receiver, the A / D converter and the signal processor are electrically connected in sequence. The receiving array is electrically connected to the receiver. The signal source is electrically connected to the receiver and the A / D converter.

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