Underwater sound OFDM (Orthogonal Frequency Division Multiplexing) information source positioning method based on single vector sensor

Abstract

The invention relates to the technical field of underwater acoustic positioning, discloses an underwater acoustic OFDM (Orthogonal Frequency Division Multiplexing) information source positioning method based on a single vector sensor, and aims to realize efficient utilization of underwater time / frequency / space resources and promote development of miniaturized and low-energy-consumption equipment by integrating a positioning function into an underwater acoustic communication system. The method comprises the following steps: firstly, establishing a frequency domain input-output model of a pilot frequency subcarrier based on a shallow water multipath sound channel, and then realizing three-dimensional positioning of a sound source by utilizing an analytic structure of a sound field and inherent directivity of a vector sensor and adopting a matching field principle. The underwater sound OFDM information source positioning method based on the single vector sensor provided by the invention has the advantages of high integration, light weight and portability, can realize sound source positioning while OFDM communication is carried out, improves the overall operation efficiency and azimuth information updating frequency of the system, and improves the positioning precision by fully utilizing sound field information and pilot frequency subcarriers.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater acoustic positioning, and in particular to an underwater acoustic OFDM source localization method based on a single vector sensor. Background Technique

[0002] Underwater acoustic communication and positioning integration aims to deeply integrate communication and positioning functions based on a single signal, and will make more full 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 realized in parallel at the receiving end, improving the overall operation efficiency of the system; (2) In the frequency domain, different from the traditional communication and positioning frequency division implementation methods, the integration technology integrates the two functions based on a dual-functional waveform in the same frequency band, realizing the efficient utilization of spectrum resources; (3) In the spatial domain, the integration technology does not require sub-beams to realize communication and positioning functions, and the spatial domain processing is more simple and practical. For the above reasons, the underwater acoustic communication and positioning integration technology is convenient for hardware integration and is in line with the development requirements of underwater unmanned equipment for low power consumption, miniaturization, and long self-sustaining.

[0003] Due to the adoption of a form similar to the ultra-short baseline deployment, the aperture of the equipment will be severely restricted, and it is impossible to achieve wide-area sampling of the monitoring space. At this time, the perception and utilization of wave field information will be crucial. Therefore, the present invention uses an acoustic vector sensor (AVS) as the signal receiving device, which contains a scalar sound pressure channel and a particle velocity acquisition channel, and will provide a more delicate sound field description. Therefore, the compact single vector system has been widely studied in the fields of underwater acoustic positioning and communication, which shows the great application prospects of the single AVS in the communication and positioning integration system.

[0004] However, in view of the current very limited related technical solutions, the present invention proposes an underwater acoustic orthogonal frequency division multiplexing (OFDM) source localization method based on a single vector sensor, where the multiple subcarriers included in OFDM provide guarantee for positioning accuracy while realizing efficient data transmission. Summary of the Invention

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

[0006] The underwater acoustic OFDM source localization method provided by the present invention includes the following steps:

[0007] S1. Adopt ray acoustics to formulate a three-path propagation channel model in a shallow water scenario, which is characterized by a time delay factor, an attenuation coefficient, and a direction of arrival parameter;

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

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

[0010] Preferably, the three-path propagation channel model in the shallow water scenario includes the sea surface reflection, direct wave, and seabed reflection sound paths. In the cylindrical coordinate system, assuming the sound source is located at (r, θ, z) and the AVS receiver is located on the z-axis with the coordinate Z r , which consists of a sound pressure sensor and two particle velocity sensors respectively pointing to the x-axis and y-axis. Its manifold for the far-field signal is c(θ, φ) = [1, cosθsinφ, sinθsinφ] T , where φ is the pitch angle.

[0011] Preferably, the channel impulse response of the constructed sound pressure sensor channel is:

[0012]

[0013] where is the attenuation coefficient. Assuming that the seawater-air interface satisfies the absolute soft boundary condition and the sound wave satisfies spherical attenuation: α1 = -1 / L1, α2 = 1 / L2, α3 = ρ / L3, where ρ is the seabed reflection coefficient, construct the channel impulse responses corresponding to the x-axis and y-axis velocity channels based on the corresponding pitch angles:

[0014]

[0015] Preferably, consider the OFDM signal waveform:

[0016]

[0017] where is the real part operation, and respectively represent the indices of the data subcarrier and the pilot subcarrier, T and T cp respectively represent the symbol duration and the cyclic prefix duration (which should be greater than the maximum channel delay spread), s[n] and f n = f c +(n - 1) / T are respectively the transmission symbol and the operating frequency of the nth (n = 1, 2, 1 / 4, N) subcarrier, f c is the carrier frequency; combining the transmitted OFDM signal and the channel impulse response h p (t), obtain the time-domain received signal corresponding to the sound pressure channel:

[0018]

[0019] where w p (t) is the observation noise; perform OFDM demodulation, and divide both ends of the frequency-domain input-output equation of the pilot subcarriers by There is

[0020]

[0021] where P is the number of pilot subcarriers, a (∈ l ) is a column vector composed of n p is the frequency-domain noise.

[0022] Preferably, construct the following fitting problem based on the matched field theory:

[0023]

[0024] And for the convenience of calculation, the solution of the above formula can be completed by the following two-step alternating iteration:

[0025]

[0026] where (·) [i] represents the estimated value of the parameter in the parentheses in the i-th iteration.

[0027] Preferably, considering the iteration initialization problem, since the three transmission paths have the same horizontal angle θ, a rough estimate of θ can be obtained by using the horizontal directivity of the AVS:

[0028]

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

[0030] The single AVS underwater acoustic positioning scheme proposed by the present invention, compared with the existing long baseline, (ultra) short baseline positioning schemes, has the advantages of high integration, lightweight, and portability of the equipment used, has the ability to be installed on an underwater unmanned small platform, and further reduces the data processing burden;

[0031] The proposed scheme can achieve sound source localization while performing OFDM communication. Compared with the existing time-division communication and positioning systems, the overall operation efficiency of the system is higher, and the azimuth information update frequency is faster;

[0032] The proposed method realizes the full utilization of the sound field information and pilot subcarriers, and has higher positioning accuracy compared with the existing methods. Description of the Drawings

[0033] Figure 1 Output result graphs of the proposed matched-field localization method and the traditional angle-time delay localization method under the same conditions;

[0034] Figure 2 Schematic diagram of the communication and positioning integration scenario in the present invention. Detailed implementation manners

[0035] The following further describes a method for underwater acoustic OFDM signal source localization based on a single vector sensor proposed by the present invention in conjunction with the accompanying drawings and implementation manners.

[0036] (1) Consider a typical shallow water channel as shown in Figure 2 where the seabed and sea surface are flat, the water depth is H, and the sound speed is a constant c. Therefore, the sound ray propagates along a straight line and undergoes specular reflection at the boundary, generating a three-path transmission structure, including the sea surface reflection, direct, and seabed reflection sound paths. The relevant parameters are marked by the subscript l = 1, 2, 3 in the following text.

[0037] (2) In the cylindrical coordinate system, assume that the sound source is located at p = (θ, R, Z t ), where θ is the horizontal angle, R is the horizontal distance, and Z t is the height. The AVS receiver is located on the z-axis with the coordinate Z r and consists of a sound pressure sensor and two particle velocity sensors respectively pointing to the x-axis and y-axis. Its manifold with respect to the far-field signal is c(θ, φ) = [1, cosθsinφ, sinθsinφ] T , where φ is the elevation angle.

[0038] (3) Let L l , l = 1, 2, 3 be the signal transmission distances on different paths, and there is

[0039]

[0040] (4) Correspondingly, the absolute time delay of signal transmission can be expressed as t l = L l / c, l = 1, 2, 3. Assume that the transmitted signal contains a timestamp T s , and the time is synchronized between the transmitter and receiver. The receiver obtains a rough synchronization to estimate the arrival time T r , then the time offset is ∈ l = τ l + T s - T r , l = 1, 2, 3.

[0041] (5) Based on Figure 2 the sound field structure, the incident elevation angle of the received signal can be expressed as

[0042] φ1 = atan2(R, 2H - Z t -Z r ),

[0043] φ2 = atan2(R, Z t -Z r ),

[0044] φ3 = atan2(R, -Z t -Z r ), (2)

[0045] where atan2(·, ·) is the four - quadrant arctangent function.

[0046] (6) Construct the channel impulse response of the sound - pressure sensor channel as

[0047]

[0048] where is the attenuation coefficient. Assume that the sea - air interface satisfies the absolute - soft boundary condition, and the sound wave satisfies spherical attenuation: α1 = - 1 / L1, α2 = 1 / L2, α3 = ρ / L3, where ρ is the seabed reflection coefficient. Similarly, based on the pitch angles in Equation (2), the channel impulse responses corresponding to the x - axis and y - axis particle - velocity channels can be constructed:

[0049]

[0050] (7) Consider the OFDM signal waveform:

[0051]

[0052] where is the real - part operation, and respectively represent the indices of the data sub - carriers and the pilot sub - carriers, T and T cp respectively represent the symbol duration and the cyclic - prefix duration (which should be greater than the maximum channel delay spread), s[n] and f n = f c +(n - 1) / T are the transmission symbol and the operating frequency of the nth (n = 1, 2, 1 / 4, N) sub - carrier respectively, and f c is the carrier frequency.

[0053] (8) Combine the transmitted OFDM signal and the channel impulse response h p (t) to obtain the time - domain received signal corresponding to the sound - pressure channel:

[0054]

[0055] where w p(t) is the observation noise. Perform OFDM demodulation, and divide both ends of the frequency-domain input-output equation of the pilot subcarriers by There is

[0056]

[0057] where P is the number of pilot subcarriers, a (∈ l ) is a column vector composed of , and n p is the frequency-domain noise.

[0058] (9) Perform similar processing on the vibration velocity channels of the x-axis and y-axis to obtain z vx , z vy . Stack z p , z vx , z vy to obtain

[0059]

[0060] Define ∈ = [∈1, ∈2, ∈3], α = [α1, α2, α3], φ = [φ1, φ2, φ3], and the following expression can be obtained:

[0061]

[0062] In the above formula, For l = 1, 2, 3, In addition, ξ(α, ∈) = [ξ(α1, ∈1), ξ(α2, ∈2), ξ(α3, ∈3)] T .

[0063] (10) Note that in the case of no noise, The specific representation of is predictable. A(θ, φ, ∈) and ξ(α, ∈) are functions of p and (R, Z t ), respectively. For this reason, the following fitting problem is constructed based on the matched field theory:

[0064]

[0065] (11) For the convenience of calculation, the solution of equation (10) can be completed by the following two-step alternating iteration:

[0066]

[0067] where (·) [i] represents the estimated value of the parameter in the parentheses in the i-th iteration.

[0068] (12) Considering the iterative initialization problem, since the three transmission paths have the same horizontal angle θ, a rough estimate of θ can be obtained using the horizontal directivity of AVS:

[0069]

[0070] As Figure 1 shown, it shows the output results of the proposed matched-field localization method and the traditional angle-delay localization method under the same conditions. The simulation experiment was independently executed 50 times, and the results show that the proposed method provides a more accurate localization result closer to the true value at the statistical level.

[0071] Compared with the related technologies, the underwater acoustic OFDM source localization method based on a single vector sensor provided by the present invention has the following beneficial effects:

[0072] The equipment used in the present invention has the advantages of high integration, lightweight, and portability, has the ability to be installed on small underwater unmanned platforms, and further reduces the data processing burden;

[0073] The present invention can achieve sound source localization while performing OFDM communication. Compared with the existing time-division communication and localization systems, the overall operation efficiency of the system is higher, and the azimuth information update frequency is faster;

[0074] The present invention realizes the full utilization of the sound field information and pilot subcarriers, and has higher localization accuracy compared with the existing methods.

[0075] The above are only the embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the content of the specification and drawings of the present invention, or directly or indirectly applied to other related technical fields, shall be similarly included in the patent protection scope of the present invention.

Claims

1. A method for underwater acoustic OFDM source localization based on a single vector sensor, characterized in that: The following steps are involved: S1. Use ray acoustics to develop a three-path propagation channel model in shallow water scenarios, characterized by delay factor, attenuation coefficient, and direction of arrival parameters; S2. Based on the OFDM communication system, a multi-channel frequency domain input-output model of AVS is constructed for the pilot subcarriers; S3. Reveal the functional relationship between the observation model and the source orientation, and realize the source positioning through the matching field principle.

2. The underwater acoustic OFDM source localization method based on a single vector sensor according to claim 1, characterized in that: The three-path propagation channel model in the shallow water scenario includes the sea surface reflection, direct, and seabed reflection sound paths. In the cylindrical coordinate system, it is assumed that the sound source is located at (r, θ, z), and the AVS receiver is located on the z axis with coordinate Z r , which consists of a sound pressure sensor and two particle velocity sensors pointing to the x-axis and y-axis respectively. Its manifold for far-field signals is c(θ, φ) = [1, cosθsinφ, sinθsinφ] T , where φ is the pitch angle.

3. The underwater acoustic OFDM source localization method based on a single vector sensor as claimed in claim 1, characterized in that: The channel impulse response of the sound pressure sensor channel is: in is the attenuation coefficient. Assuming that the seawater-air interface satisfies the absolute soft boundary condition, the sound wave satisfies the spherical attenuation: α1 = -1 / L1, α2 = 1 / L2, α3 = ρ / L3, where ρ is the seabed reflection coefficient. Based on the corresponding pitch angle, the channel impulse response corresponding to the x-axis and y-axis velocity channels is constructed:

4. The underwater acoustic OFDM source localization method based on a single vector sensor as claimed in claim 1, characterized in that: Consider the OFDM signal waveform: in To take the real part operation, and The indices of data subcarriers and pilot subcarriers, T and T cp Respectively represent the symbol duration and cyclic prefix duration (should be greater than the maximum delay spread of the channel), s[n] and f n =f c +(n-1) / T respectively for the nth (n=1,2, 1 / 4,N) subcarrier transmission symbol and operating frequency, f c is the carrier frequency; combined with the transmitted OFDM signal and the channel impulse response h p (t), and obtain the time domain received signal corresponding to the sound pressure channel: where w p (t) is the observed noise; perform OFDM demodulation and divide both ends of the frequency domain input-output equation of the pilot subcarrier by have Where P is the number of pilot subcarriers, a(∈ l ) is The column vector, n p is the frequency domain noise.

5. The underwater acoustic OFDM source localization method based on a single vector sensor according to claim 1, characterized in that: Based on the matching field theory, the following fitting problem is constructed: And for the convenience of calculation, the solution of the above formula can be completed through the following two steps of alternating iteration: in(·) [i] represents the estimated value of the parameter in parentheses at the i-th iteration.

6. The underwater acoustic OFDM source localization method based on a single vector sensor according to claim 1, characterized in that: Considering 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 a rough estimate of θ:

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