Underwater acoustic communication signal enhancement method
By using ultra-short baseline matrix and conjugation method to measure the phase difference for signal correction and merging on small unmanned platforms, the problem of low signal-to-noise ratio of water-to-sound communication in small unmanned platforms is solved, and the performance of water-to-sound communication is improved.
Patent Information
- Application Number
- CN202411909780.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-24
- Publication Date
- 2025-03-28
AI Technical Summary
Due to the limited space size of small unmanned platforms, it is difficult to obtain high array gain, resulting in low signal-to-noise ratio of water-acoustic communication, affecting reliable water-acoustic communication.
The ultra-short baseline matrix is used to receive the water acoustic communication signal, measure the phase difference of each array element through the conjugation method, and perform phase correction and merging to improve the signal-to-noise ratio of the water acoustic communication signal.
It effectively improves the signal-to-noise ratio of water acoustic communication signals, improves the water acoustic communication performance of small unmanned platforms, realizes the sharing of sound matrix, simplifies the method, and has good practical value.
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Figure CN119727942A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of underwater acoustic communication, and mainly relates to an underwater acoustic communication signal enhancement method. Background Art
[0002] Underwater acoustic communication and positioning technology provides technical support for improving the collaborative capabilities of underwater unmanned platforms. Large unmanned platforms (such as UUVs above the ton level) are usually equipped with communication sonars and inertial navigation systems. They use their own large-aperture acoustic arrays to obtain high array gain, ensure a high signal-to-noise ratio for underwater acoustic communication, and are more likely to achieve reliable underwater acoustic communication. They use inertial navigation systems to achieve high-precision self-positioning functions. Due to limited space size, small unmanned platforms (such as small UUVs, underwater gliders, etc.) are generally equipped with small communication sonars and baseline positioning systems for underwater acoustic communication and positioning. Due to the small aperture of the array, it is difficult to obtain array gain, which limits the communication signal-to-noise ratio and brings technical challenges to reliable underwater acoustic communication. In the marine environment, the transmission conditions of the underwater acoustic channel are complex, with inherent time-space-frequency variations and narrowband, strong multipath, and long-delay transmission characteristics. The noise of the unmanned platform navigation further exacerbates the complexity of the channel. How to improve the underwater acoustic communication performance of small unmanned platforms has always been a long-term concern in the field of underwater acoustic communication technology. Summary of the invention
[0003] The present invention aims at the problem of how to improve the underwater acoustic communication performance of a small unmanned platform, and proposes a method for enhancing underwater acoustic communication signals. The method uses the underwater acoustic communication signals received by the ultra-short baseline array installed on the unmanned platform, adopts the conjugate method to measure the phase difference of each array element, and uses the measured phase difference to perform phase correction and merging on the signals of each array element, thereby improving the signal-to-noise ratio of the underwater acoustic communication signal, and further improving the performance of the underwater acoustic communication. The method is simple to implement and has good practical value.
[0004] The objective of the present invention is achieved through the following technical solution: A method for enhancing underwater acoustic communication signals, comprising the following steps:
[0005] Step 1: Intercepting underwater acoustic communication signals: Obtain the starting time of the underwater acoustic communication signal through frame synchronization processing, and intercept the coded signal of the entire frame according to the frame format agreed upon by the sender and the receiver;
[0006] Step 2, phase difference measurement: perform complex band shift processing on the coded signal of each element of the ultra-short baseline to obtain the baseband signal of the coded signal, take any one of the elements as the reference element, perform conjugate point multiplication of the baseband signal of the other elements with the baseband signal of the reference element and then add them up, take the phase of the accumulated complex value, and measure the phase difference with the baseband signal of the element;
[0007] Step 3: Underwater acoustic communication signal enhancement: Use the measured phase difference to perform phase correction on the baseband signals of each element except the reference element. The corrected baseband signals are superimposed on the baseband signal of the reference element to achieve underwater acoustic communication signal enhancement.
[0008] The beneficial effects of the present invention are as follows: the present invention proposes a method for enhancing underwater acoustic communication signals, which makes full use of the underwater acoustic communication signals received by the ultra-short baseline array installed on a small unmanned platform, firstly adopts the conjugate method to measure the phase difference of each array element, and then uses the measured phase difference to perform phase correction and phase merging on the signals of each array element, thereby improving the signal-to-noise ratio of the underwater acoustic communication signal. The ultra-short baseline array is usually used for underwater positioning of small unmanned platforms. This method realizes the sharing of acoustic arrays, effectively improves the performance of underwater acoustic communication, is simple to implement, and has good practical value. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art or ordinary technicians, other drawings can be obtained based on these drawings without paying creative work.
[0010] Figure 1 It is a schematic diagram of the frame format of the underwater acoustic communication signal in the present invention.
[0011] Figure 2 This is a block diagram of underwater acoustic communication signal enhancement in the present invention. DETAILED DESCRIPTION
[0012] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.
[0013] Figure 1The frame format commonly used in underwater acoustic communication signals is given. The communication signal frame is formed in the form of a frame synchronization signal followed by a communication gap, a communication coding signal, and a communication gap. The frame synchronization signal is mainly used for time and frequency synchronization. Generally, a broadband signal with a certain time length is used to ensure the accuracy of time synchronization and have a certain processing gain to improve the probability of synchronization signal capture. In some cases, the frame synchronization signal is also multiplexed as a pilot signal for channel estimation. The communication gap is used to prevent the frame synchronization signal from interfering with the communication coding signal due to the multipath effect, or to prevent the communication coding signal from interfering with the frame synchronization signal due to the multipath effect. Generally, the time length of the communication gap should be greater than the maximum multipath time extension length of the channel. The communication coding signal is used to carry the transmitted information. In order to achieve the purpose of communication concealment, some underwater acoustic communication systems weaken the time domain characteristics of the signal. The time length of the communication gap is 0, that is, the frame synchronization directly follows the communication coding signal. The present invention is applicable to such communication signals with the frame synchronization signal as the leader.
[0014] Assume that the number of primitives of the ultra-short baseline is I, numbered 1, 2, ..., I, and any primitive can be selected as the reference primitive. For the convenience of description and without loss of generality, primitive No. 1 is selected as the reference primitive. Figure 2 The block diagram of underwater acoustic communication signal enhancement is given.
[0015] The first step is to perform frame synchronization. The received signal of the reference element is subjected to sliding correlation or matched filtering processing with a copy of the local frame synchronization signal. The starting time of the frame synchronization signal is obtained by finding the position of the correlation peak or the matched filtering peak. According to the frame format of the communication signal, the communication coding signal of the current frame of each element is intercepted.
[0016] In the second step, the intercepted communication coded signal is mixed, low-pass filtered and extracted in sequence to complete the transfer of the communication coded signal from the passband to the baseband. The underwater acoustic multipath channel is modeled as a tapped delay line model. The communication coded baseband signal y received by each primitive is i (n) can be expressed as:
[0017]
[0018] In the above formula, h i (n) is the channel impulse response function between the transmitter and the i-th primitive, is the phase of the communication baseband signal received by the i-th element, s(n) is the baseband envelope signal of the coded signal, and w i (n) is the baseband noise received by element i, Δ i , are the Doppler compression factor and frequency deviation, respectively, c is the center frequency, d i is the sound path difference between primitive number i and the reference primitive number, T sych 、T gap, T are the time lengths of the frame synchronization signal, communication gap and code element respectively.
[0019] The third step is to perform conjugate point multiplication of the baseband signal of the i-th primitive with the baseband signal of the reference primitive and then add them together to measure the phase difference with the primitive baseband signal, which is calculated as follows:
[0020]
[0021] In the above formula, (·) * is the conjugate operation, T code is the length of the coded signal, is the phase difference between each primitive and the reference primitive, z i is a quantity related to noise, which can be expressed as:
[0022]
[0023] Since the distance between each element of the ultra-short baseline is very small, the distance between the transmitter and element No. i is h. i (n), Δ i Approximately the same, indicating that x i (n)≈x0(n), the noise of each primitive w i (n) are independent of each other, and w i (n) and x i (n) are independent of each other, so z in formula (2) i The first term can be ignored, and the measured phase difference is:
[0024]
[0025] |·| is the complex modulus operation.
[0026] The fourth step is to use the measured phase to complete the phase difference correction of formula (1), and combine the primitive signals to achieve underwater acoustic communication signal enhancement, which is expressed as follows:
[0027]
[0028] Since the distance between each primitive in the ultra-short baseline is very small, each primitive x i (n) The above formula can be further written as:
[0029]
[0030] It can be seen from formula (6) that after phase difference correction and merging of each primitive signal, the communication signal amplitude is 1 times the original one. Since each primitive noise is independent, the noise after merging is not increased, so the underwater acoustic communication signal is significantly enhanced.
[0031] In summary, the present invention only needs to perform operations such as conjugate point multiplication and accumulation, phase correction and merging to achieve effective underwater acoustic communication signal enhancement, and the method is simple and effective. Generally speaking, the communication coding signal lasts the longest in the signal frame. As can be seen from formula (2), since the coding signal has a longer time and a larger gain, even if there is a certain synchronization error, the effect on the phase measurement is small. Therefore, the present invention does not have strict requirements on the time synchronization of underwater acoustic communication and has good applicability.
[0032] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.
Claims
1. A method for enhancing underwater acoustic communication signals, characterized in that: The steps include: Step 1: Intercepting underwater acoustic communication signals: Obtain the starting time of the underwater acoustic communication signal through frame synchronization processing, and intercept the coded signal of the entire frame according to the frame format agreed upon by the sender and the receiver; Step 2, phase difference measurement: perform complex band shift processing on the coded signal of each element of the ultra-short baseline to obtain the baseband signal of the coded signal, take any one of the elements as the reference element, perform conjugate point multiplication of the baseband signal of the other elements with the baseband signal of the reference element and then add them up, take the phase of the accumulated complex value, and measure the phase difference with the baseband signal of the element; Step 3: Underwater acoustic communication signal enhancement: Use the measured phase difference to perform phase correction on the baseband signals of each element except the reference element. The corrected baseband signals are superimposed on the baseband signal of the reference element to achieve underwater acoustic communication signal enhancement.
2. The method for enhancing underwater acoustic communication signals according to claim 1, characterized in that: In the step 1, it is assumed that the number of primitives of the ultra-short baseline is I, numbered 1, 2, ..., I, and any primitive is selected as the reference primitive; frame synchronization is performed, and the received signal of the reference primitive is subjected to sliding correlation or matched filtering processing with a copy of the local frame synchronization signal, and the starting time of the frame synchronization signal is obtained by finding the position of the correlation peak or the matched filtering peak, and the communication coding signal of the current frame of each primitive is intercepted according to the frame format of the communication signal.
3. The method for enhancing underwater acoustic communication signals according to claim 2, characterized in that: In step 2, the intercepted communication coding signal is mixed, low-pass filtered and extracted in sequence to complete the transfer of the communication coding signal from the passband to the baseband. The underwater acoustic multipath channel is modeled as a tapped delay line model. The communication coding baseband signal y received by each primitive is i (n) is expressed as: In the above formula, h i (n) is the channel impulse response function between the transmitter and the i-th primitive, is the phase of the communication baseband signal received by the i-th element, s(n) is the baseband envelope signal of the coded signal, and w i (n) is the baseband noise received by element i, Δ i , are the Doppler compression factor and frequency deviation, respectively, c is the center frequency, d i is the sound path difference between primitive number i and the reference primitive number, T sych , T gap , T are the time lengths of the frame synchronization signal, communication gap and code element respectively.
4. The method for enhancing underwater acoustic communication signals according to claim 3, characterized in that: In step 2, the baseband signal of the i-th primitive is conjugate-point-multiplied with the baseband signal of the reference primitive respectively and then accumulated, and the phase difference with the primitive baseband signal is measured, which is calculated as follows: In the above formula, (·) * is the conjugate operation, T code is the length of the coded signal, is the phase difference between each primitive and the reference primitive, n i is a quantity related to noise, expressed as: The distance between each element of the ultra-short baseline is very small, and the distance between the transmitter and element No. i is h. i (n), Δ i Approximately the same, indicating that x i (n)≈x0(n), the noise of each primitive w i (n) are independent of each other, and w i (n) and x i (n) are independent of each other, and z in formula (2) i If the first term is ignored, the measured phase difference is: |·| is the complex modulus operation.
5. The method for enhancing underwater acoustic communication signals according to claim 4, characterized in that: In step 3, the measured phase is used to correct the phase difference in equation (1), and each primitive signal is combined to enhance the underwater acoustic communication signal, which is expressed as follows: The distance between each primitive in the ultra-short baseline is very small, and each primitive x i (n) The above formula is further written as: After phase difference correction and merging of each elementary signal, the communication signal amplitude is 1 times of the original one.