A single vector sensor based method for underwater acoustic OFDM source localization

Abstract

This invention relates to the field of underwater acoustic positioning technology and discloses an underwater acoustic OFDM source positioning method based on a single vector sensor. By integrating positioning functionality into the underwater acoustic communication system, it aims to achieve efficient utilization of underwater time / frequency / space resources and promote the development of miniaturized, low-power devices. This method first establishes a frequency domain input-output model of the pilot subcarrier based on shallow water multipath acoustic channels. Then, utilizing the analytical structure of the sound field and the inherent directivity of the vector sensor, it employs the matched field principle to achieve three-dimensional positioning of the sound source. The underwater acoustic OFDM source positioning method based on a single vector sensor provided by this invention has the advantages of high integration, lightweight design, and portability. It can achieve sound source positioning while performing OFDM communication, improving the overall system operating efficiency and azimuth information update frequency. Furthermore, by fully utilizing sound field information and pilot subcarriers, it improves positioning accuracy.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic positioning technology, and in particular to an underwater acoustic OFDM source positioning method based on a single vector sensor. Background Technology

[0002] The underwater acoustic communication and positioning integration aims to achieve deep integration of communication and positioning functions based on a single signal, making fuller use of the time / frequency / spatial resources of the underwater acoustic channel: (1) In the time domain, the integration technology avoids the time-division communication and positioning system, and the two functions can be implemented in parallel at the receiving end, improving the overall operating efficiency of the system; (2) In the frequency domain, unlike the traditional communication and positioning frequency division implementation method, the integration technology integrates the two functions based on the dual-function waveform in the same frequency band, realizing the efficient use of spectrum resources; (3) In the spatial domain, the integration technology does not require beam splitting to realize communication and positioning functions, and the spatial processing is simpler and more practical. For the above reasons, the underwater acoustic communication and positioning integration technology is easy to integrate into hardware, which is in line with the development needs of low power consumption, miniaturization and long self-sustainability of underwater unmanned equipment.

[0003] Due to the use of a near-ultra-short baseline deployment, the device aperture is severely limited, making wide-area sampling of the monitoring space impossible. Therefore, the perception and utilization of wavefield information becomes crucial. To address this, this invention uses an acoustic vector sensor (AVS) as the signal receiving device, which incorporates a scalar sound pressure channel and a particle velocity acquisition channel, providing a more detailed sound field depiction. Consequently, compact single-vector systems have been widely studied in underwater acoustic positioning and communication fields, demonstrating the enormous application potential of a single AVS in integrated communication and positioning systems.

[0004] However, given the current limited availability of relevant technical solutions, this invention proposes an underwater acoustic orthogonal frequency division multiplexing (OFDM) source localization method based on a single vector sensor. The multiple subcarriers included in OFDM not only enable efficient data transmission but also ensure positioning accuracy. Summary of the Invention

[0005] To address the technical problem of underwater acoustic OFDM source localization based on a single AVS, this invention provides an underwater acoustic OFDM source localization method based on a single vector sensor.

[0006] The underwater acoustic OFDM source localization method based on a single vector sensor provided by this invention includes the following steps:

[0007] S1. A three-path propagation channel model for shallow water scenarios is formulated using ray acoustics, characterized by time delay factor, attenuation coefficient, and direction of arrival parameters.

[0008] S2. Based on the OFDM communication system, construct a multi-channel frequency domain input-output model for AVS for pilot subcarriers;

[0009] S3. Reveal the functional relationship between the observation model and the source location, and realize source localization through the matching field principle.

[0010] Preferably, the three-path propagation channel model in the shallow water scenario includes sound paths reflected from the sea surface, direct path, and reflected from the seabed. In cylindrical coordinates, it is assumed that the sound source is located at (r, θ, z), and the AVS receiver is located on the z-axis with coordinates... It consists of a sound pressure sensor and two sensors pointing to... x axis, y The particle velocity sensor consists of an axis, and its manifold with respect to the far-field signal is as follows: ,in It is the pitch angle.

[0011] Preferably, the channel impulse response for constructing the acoustic pressure sensor channel is:

[0012]

[0013] in Let be the attenuation coefficient. Assume the seawater-air interface satisfies the absolutely soft boundary condition, and the sound wave satisfies spherical attenuation: ,here r Given the seabed reflection coefficient, channel impulse responses corresponding to the x-axis and y-axis vibration velocity channels are constructed based on the corresponding pitch angles:

[0014] .

[0015] Preferably, consider the OFDM signal waveform:

[0016]

[0017] in To perform the real part operation, and These represent the indices of the data subcarriers and the pilot subcarriers, respectively. and These represent the symbol duration and the cyclic prefix duration, respectively (which should be greater than the maximum channel delay spread). and The first indivual( n =1,2,…, N The transmission symbols and operating frequencies of the subcarriers. The carrier frequency; combined with the transmitted OFDM signal. and channel impulse response The time-domain received signal corresponding to the sound pressure channel is obtained:

[0018]

[0019] in To observe the noise, OFDM demodulation is performed, and both sides of the frequency domain input-output equation for the pilot subcarrier are divided by the same value. ,have

[0020]

[0021] in For the number of pilot subcarriers, , It is by The column vector formed This is frequency domain noise.

[0022] Preferably, the following fitting problem is constructed based on the matching field theory:

[0023]

[0024] Furthermore, for ease of calculation, the above equation can be solved through the following two iterative steps:

[0025]

[0026] in Indicates the first The estimated value of the parameter in parentheses in the next iteration.

[0027] Preferably, considering the iterative initialization problem, since the three transmission paths have the same horizontal angle... i The horizontal directivity of AVS can be used to obtain i A rough estimate:

[0028] .

[0029] Compared with related technologies, the underwater acoustic OFDM source localization method based on a single vector sensor provided by this invention has the following advantages:

[0030] Compared with existing long baseline and (ultra) short baseline positioning schemes, the single AVS underwater acoustic positioning scheme proposed in this invention has the advantages of high integration, lightweight and portability, and has the ability to be installed on small underwater unmanned platforms, and further reduces the data processing burden.

[0031] The proposed solution can achieve sound source localization while performing OFDM communication. Compared with the existing time-division communication and positioning system, the overall system operation efficiency is higher and the orientation information is updated more frequently.

[0032] The proposed method fully utilizes acoustic field information and pilot subcarriers, achieving higher positioning accuracy compared to existing methods. Attached Figure Description

[0033] Figure 1 The output results of the proposed matched-field localization method and the traditional angle-time delay localization method are shown in the figure under the same conditions.

[0034] Figure 2 This is a schematic diagram of the integrated communication and positioning scenario in this invention. Detailed Implementation

[0035] The following description, in conjunction with the accompanying drawings and embodiments, further illustrates the underwater acoustic OFDM source localization method based on a single vector sensor proposed in this invention.

[0036] (1) Consider as Figure 2 The diagram shows a typical shallow water channel where the seabed and surface are flat, and the water depth is... The speed of sound is constant. Therefore, sound rays propagate in a straight line and undergo specular reflection at the boundary, resulting in a three-path transmission structure, including sea surface reflection, direct sound, and seabed radiating sound path. Relevant parameters are indicated by subscripts later. mark.

[0037] (2) In cylindrical coordinates, assume the sound source is located at p= ( i , R , Z t ),in i It is a horizontal angle. Horizontal distance The height is [not specified]. The AVS receiver is located at [not specified]. z The axis, coordinates are It consists of a sound pressure sensor and two sensors pointing to... x axis, y The particle velocity sensor consists of an axis, and its manifold with respect to the far-field signal is as follows: ,in It is the pitch angle.

[0038] (3) Order For the signal transmission distance on different paths, there are

[0039] (1)

[0040] (4) Accordingly, the absolute delay of signal transmission can be expressed as Assume the transmitted signal includes a timestamp. The transmitting and receiving ends synchronize their times, and the receiving end obtains an estimated arrival time through coarse synchronization. Then the time offset is .

[0041] (5) Based on Figure 2 The acoustic field structure, the incident elevation angle of the signal at the receiving end can be expressed as:

[0042] (2)

[0043] in It is the arctangent function in the four quadrants.

[0044] (6) The channel impulse response for constructing the acoustic pressure sensor channel is as follows:

[0045] (3)

[0046] in Let be the attenuation coefficient. Assume the seawater-air interface satisfies the absolutely soft boundary condition, and the sound wave satisfies spherical attenuation: ,here r Let be the seabed reflection coefficient. Similarly, based on the pitch angle in equation (2), a coefficient corresponding to can be constructed. x axis, y Channel impulse response of the shaft velocity channel:

[0047] (4)

[0048] (7) Consider the OFDM signal waveform:

[0049] (5)

[0050] in To perform the real part operation, and These represent the indices of the data subcarriers and the pilot subcarriers, respectively. and These represent the symbol duration and the cyclic prefix duration, respectively (which should be greater than the maximum channel delay spread). and The first indivual( n =1,2,…, N The transmission symbols and operating frequencies of the subcarriers. For carrier frequency.

[0051] (8) Combine the transmitted OFDM signal and channel impulse response The time-domain received signal corresponding to the sound pressure channel is obtained:

[0052] (6)

[0053] in To observe the noise, OFDM demodulation is performed, and both sides of the frequency domain input-output equation for the pilot subcarrier are divided by the same factor. ,have

[0054] (7)

[0055] in For the number of pilot subcarriers, , It is by The column vector formed This is frequency domain noise.

[0056] (9) To x axis, y The shaft vibration velocity channel is processed similarly to obtain... Stacking get

[0057] (8)

[0058] definition This can be expressed as follows:

[0059] (9)

[0060] In the above formula, ,for , ,also, .

[0061] (10) Note that in the absence of noise, The specific representation is predictable. and They are respectively and The function is given. Therefore, based on matched field theory, the following fitting problem is constructed:

[0062] (10)

[0063] (11) For ease of calculation, the solution to equation (10) can be completed through the following two iterative steps:

[0064] (11)

[0065] in Indicates the first The estimated value of the parameter in parentheses in the next iteration.

[0066] (12) Consider the iterative initialization problem, since the three transmission paths have the same horizontal angle. i The horizontal directivity of AVS can be used to obtain i A rough estimate:

[0067] (12)

[0068] Figure 1 shows the output results of the proposed matching field positioning method and the traditional angle-time delay positioning method under the same conditions. The simulation experiment was executed independently 50 times. The results show that the proposed method provides positioning results that are closer to the true value from a statistical perspective, and has higher accuracy.

[0069] Compared with related technologies, the underwater acoustic OFDM source localization method based on a single vector sensor provided by this invention has the following advantages:

[0070] The equipment used in this invention has the advantages of high integration, lightweight and portability, has the ability to be installed on underwater unmanned small platforms, and further reduces the data processing burden.

[0071] This invention can achieve sound source localization while performing OFDM communication. Compared with existing time-division communication and positioning systems, the overall system operation efficiency is higher and the orientation information is updated more frequently.

[0072] This invention achieves full utilization of sound field information and pilot subcarriers, resulting in higher positioning accuracy compared to existing methods.

[0073] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for locating underwater acoustic OFDM sources based on a single vector sensor, characterized in that, Includes the following steps: S1. A three-path propagation channel model for shallow water scenarios is formulated using ray acoustics, characterized by time delay factor, attenuation coefficient, and direction-of-arrival parameters. The three paths include sea surface reflection, direct arrival, and seabed reflection sound paths. The seabed and sea surface are flat, and the speed of sound is constant. c ,make For the signal transmission distance on different paths, there are ， In the cylindrical coordinate system, the sound source is located at p = (θ, R, Zt), and the AVS receiver, a sound vector sensor, is located on the z-axis with coordinates (0, 0, ...). H is the water depth; R is the horizontal distance between the sound source and the receiver; Zt is the height, corresponding to the vertical distance between the sound source and the seabed; S2. Based on the OFDM communication system, construct a multi-channel frequency domain input-output model for AVS for pilot subcarriers; S3. Reveal the functional relationship between the observation model and the source location, and realize source localization through the matched field principle; define , by stacking And thus obtained; The frequency domain measurement data of the three channels correspond to the sound pressure, the particle velocity collected by the particle velocity sensor aligned along the x-axis, and the particle velocity collected by the particle velocity sensor aligned along the y-axis, respectively. in, For the number of pilot subcarriers; The horizontal angle of the incident signal θ and pitch angle Time offset and source location p Related, can be considered as about p The function, Abbreviated as ; , The attenuation coefficient is... f c For carrier frequency; In the absence of noise The specific representation is predictable. and They are respectively and The function is used to construct the following fitting problem based on matching field theory: 。 2. The underwater acoustic OFDM source localization method based on a single vector sensor as described in claim 1, characterized in that, The AVS receiver consists of a sound pressure sensor and two sensors pointing to... x axis, y The particle velocity sensor consists of an axis, and its manifold with respect to the far-field signal is as follows: ,in The pitch angle, θ It is a horizontal angle.

3. The underwater acoustic OFDM source localization method based on a single vector sensor as described in claim 1, characterized in that, The channel impulse response for constructing the acoustic pressure sensor channel is as follows: in, The absolute time delay of signal transmission is assumed; assuming the seawater-air interface satisfies the absolutely soft boundary condition and the sound wave satisfies spherical attenuation: ,here ρ Given the seabed reflection coefficient, channel impulse responses corresponding to the x-axis and y-axis vibration velocity channels are constructed based on the corresponding pitch angles: 。 4. The underwater acoustic OFDM source localization method based on a single vector sensor as described in claim 1, characterized in that, Consider the OFDM signal waveform: in To perform the real part operation, and These represent the indices of the data subcarriers and the pilot subcarriers, respectively. and These represent the symbol duration and the cycle prefix duration, respectively. and The first The transmission symbols and operating frequencies of each subcarrier, among which n =1,2,…, N , The carrier frequency; combined with the transmitted OFDM signal. and channel impulse response The time-domain received signal corresponding to the sound pressure channel is obtained: in To observe the noise, OFDM demodulation is performed, and both sides of the frequency domain input-output equation for the pilot subcarrier are divided by the same value. ,have ， in, It is by The column vector formed This is frequency domain noise.

5. The underwater acoustic OFDM source localization method based on a single vector sensor as described in claim 1, characterized in that, Based on matched field theory, the following fitting problem is constructed: ， Furthermore, for ease of calculation, the above equation can be solved through the following two iterative steps: in Indicates the first The estimated value of the parameter in parentheses in the next iteration.

6. The underwater acoustic OFDM source localization method based on a single vector sensor as described in claim 1, characterized in that, Consider the iterative initialization problem, since the three transmission paths have the same horizontal angle. θ The horizontal directivity of AVS can be used to obtain θ A rough estimate: , This is an operation to extract the real part.

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