Laser-induced sound-air-water cross-medium communication method and device based on phased array beam forming

Abstract

The invention belongs to the technical field of cross-medium communication, and particularly relates to a laser-induced sound-air-water cross-medium communication method and device based on phased array beam forming. Establishing a space coordinate system and acquiring an underwater target position; constructing a virtual sound source array according to the target orientation and calculating a geometric wave path difference; calculating the triggering time delay amount of each array unit by using a real time delay algorithm; coding the communication data into a pulse modulation signal and applying corresponding time domain offset; and the pulse laser array is driven to emit a plurality of laser pulses with accurate time sequence differences to the water-gas interface. The broadband sound waves excited by the laser pulses achieve time domain wavefront alignment and coherent superposition in the target direction, and high-directivity synthetic sound beams are formed. According to the flexible dynamic adjustment mechanism, the communication link can still be kept stable in a complex marine environment and under a target maneuvering condition, and accurate recovery of the communication data flow to be transmitted is effectively guaranteed.

Description

Technical Field

[0001] This application belongs to the field of cross-medium communication technology, specifically relating to a laser-induced acoustic air-water cross-medium communication method and device based on phased array beamforming. Background Technology

[0002] Traditional radio waves attenuate significantly in water, making long-distance transmission difficult. While sound waves are the primary carrier of underwater information transmission, they suffer from limitations such as narrow bandwidth, low data rate, and severe multipath effects. In recent years, air-to-water communication schemes based on laser-induced acoustic technology have attracted widespread attention. This technology uses high-energy laser pulses to irradiate the water surface to generate sound waves, thereby enabling information to travel from the air to the underwater environment.

[0003] However, existing laser-induced acoustic communication technologies mostly employ single-point laser focusing or simple laser array scanning, resulting in acoustic waves that typically exhibit omnidirectional diffusion or are difficult to control precisely. This leads to low energy utilization and makes it difficult to establish effective high signal-to-noise ratio communication links over long distances. To improve communication distance and anti-interference capabilities, acoustic beamforming technology is crucial. However, in air-water cross-medium scenarios, the "source" of the acoustic wave is not a fixed physical transducer, but rather a transient optical breakdown point (i.e., photoacoustic conversion point) located on the dynamic water surface. This makes it difficult to directly apply traditional beamforming methods based on fixed arrays.

[0004] Specifically, the main challenges faced by existing technologies include: first, the difficulty in dynamically adjusting the strike distribution of airborne lasers based on the real-time position of underwater moving targets to construct a virtual sound source array that meets phase matching requirements; second, due to the significant differences in the physical properties of the media used for laser transmission in air and sound wave transmission in water, the microsecond-level delay of light propagation and the millisecond-level delay of sound propagation are difficult to synchronize precisely. If only the path difference is considered while ignoring the effects of optical travel delay and emission geometry, the phase of the sound waves arriving at the target will be disordered, making it impossible to form a directional high-gain sound beam, which seriously affects the quality of communication data recovery. Therefore, how to accurately construct a virtual sound source array and achieve precise delay control of the optical-acoustic dual-medium transmission path is an urgent problem to be solved to improve the performance of air-to-water laser-induced acoustic communication. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming, comprising: A three-dimensional spatial coordinate system is established with the geometric center or a predetermined reference point of the predetermined photoacoustic conversion region on the water-air interface as the origin; under this coordinate system, the three-dimensional position coordinates of each laser emitting unit in the air are obtained, and the real-time position vector of the underwater target receiver is obtained. Based on the position vector of the target receiver and the preset beamwidth index, the number of photoacoustic conversion points projected on the water-air interface and their two-dimensional spatial distribution coordinates in the coordinate system are determined, thereby constructing a virtual sound source array. Obtain the sound wave propagation speed parameters in the current water environment as the reference constants for beamforming calculations; Based on the spatial geometric distance between each photoacoustic conversion point in the virtual sound source array and the underwater target receiver, and taking one of the photoacoustic conversion points or virtual points as a reference, the sound path difference of each of the other photoacoustic conversion points relative to the reference reference is calculated. Based on the broadband pulse characteristics of laser-induced acoustic signals, the acoustic propagation delay component corresponding to each photoacoustic conversion point is calculated using a true time delay algorithm according to the ratio of the acoustic path difference to the acoustic wave propagation speed parameter. The system receives the communication data stream to be transmitted and encodes it into a laser pulse modulation signal. Based on a unified global clock reference, it calculates the total trigger time delay, which includes the acoustic propagation delay component and the optical propagation delay component determined based on the emission geometry. It then performs independent time-domain offset processing on each modulation signal. Using the signal after time-domain offset processing, a pulsed laser array is driven under global clock synchronization control to precisely control the excitation time of each laser unit. Multiple laser pulses are emitted and incident on the water-air interface. At the interface, broadband acoustic pulses are excited through photoacoustic effect, so that the broadband acoustic pulses generated at each photoacoustic conversion point achieve wavefront alignment and coherent superposition in the time domain when they propagate to the target receiving end, forming a high-gain synthetic acoustic beam pointing to the target receiving end. At the target receiving end, the high-gain synthesized sound beam is picked up using an underwater acoustic transducer, and the received sound signal is filtered and demodulated to recover the communication data stream.

[0006] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, wherein: determining the number of photoacoustic conversion points and their two-dimensional spatial distribution coordinates includes: The beam scanning pointing angle is calculated based on the position vector of the target receiver. According to the preset beamwidth index and the center frequency of the laser-induced acoustic signal, the effective aperture size required for the virtual sound source array is calculated and determined by using the inverse relationship between the beamwidth and the array aperture, combined with the beam factor constant related to the propagation speed of sound waves in water and the array geometry. Under the constraint that the element spacing is less than half the wavelength of the sound wave, the number of photoacoustic conversion points projected on the water-air interface and the two-dimensional plane coordinates of each point are calculated according to the effective aperture size.

[0007] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, the two-dimensional spatial distribution coordinate system of the virtual sound source array is configured into one of the following topologies based on communication scanning requirements: Uniform Linear Array (ULA) is configured to respond to the requirements of single-dimensional sector scanning, with each photoacoustic conversion point arranged at equal intervals along a straight line; The uniform circular array (UCA) is configured to respond to the requirements of omnidirectional horizontal scanning, with each photoacoustic conversion point evenly distributed on a circle centered on the target azimuth projection point. An irregular sparse random array is configured to respond to the requirements of grating lobe suppression and aperture expansion, with the spacing between each photoacoustic conversion point following a preset probability density function distribution.

[0008] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, wherein: obtaining the sound wave propagation speed parameters in the current water environment includes: The environmental parameters of the current water area are obtained and calculated using the empirical formula for underwater acoustic velocity. The sound velocity was measured in the current water area using a sound velocity measuring device. Access the data by calling a pre-set hydrological database or historical sound velocity profile data.

[0009] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, wherein: calculating the acoustic path difference of each photoacoustic conversion point relative to a reference reference includes: Based on the determined three-dimensional coordinates of each optical-acoustic conversion point and the obtained three-dimensional coordinates of the target receiver, the geometric path difference of each point is obtained by using the Euclidean distance calculation rule, comparing the physical distances of each optical conversion point, determining the maximum physical distance or selecting a reference distance.

[0010] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, the calculation of the acoustic propagation delay component corresponding to each photoacoustic conversion point includes: The total trigger time delay of the i-th photoacoustic conversion point in the true delay sequence is equal to the sum of the acoustic propagation delay component and the optical propagation delay component; The acoustic propagation time delay component is determined by dividing the geometric path difference by the sound wave propagation speed parameter; The optical propagation delay component is determined by dividing the optical path distance from the laser emitting unit corresponding to the photoacoustic conversion point to the water-air interface by the speed of light.

[0011] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, the step of performing independent time-domain offset processing on each modulation signal includes: A digital modulation method based on pulse time-domain characteristics is used to encode the communication data stream to be transmitted into a standard baseband pulse sequence; The baseband pulse sequence is copied multiple times to generate N parallel signals, which are equal to the number of photoacoustic conversion points in the virtual sound source array. The calculated total trigger time delay, including acoustic and optical delays, is applied to the corresponding i-th parallel signal, so that the trigger time of each laser pulse in the i-th parallel signal is delayed relative to the global reference time, thereby generating N-way drive control signals containing beam pointing information.

[0012] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, wherein: forming a high-gain synthesized acoustic beam pointing towards the target receiver includes: The driving circuit responds to the signal after the time domain shift and triggers the pulsed laser array to emit multiple laser pulses. The laser pulses are incident on the water-air interface and are excited by the photoacoustic conversion effect to generate multiple broadband acoustic pressure waves. Multiple broadband acoustic pressure waves propagate in the water medium. Due to the pre-applied trigger time delay of each signal to compensate for the difference in the physical propagation path, the acoustic wave components achieve phase alignment and in-phase superposition in the time domain when they reach the target receiving end, forming a high-gain synthetic sound field.

[0013] As a preferred embodiment of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming described in this invention, wherein: the recovery of the communication data stream includes: The electrical signal output from the underwater acoustic transducer is subjected to bandpass filtering. The filtered signal is processed using relevant detection algorithms or preamble acquisition algorithms to extract symbol timing information and establish communication frame synchronization. Based on the established communication frame synchronization, the signal is reverse-mapped to recover the binary communication data stream.

[0014] In a second aspect, the present invention provides a laser-induced acoustic air-to-water cross-medium communication device based on phased array beamforming, comprising: an air-to-air transmitting subsystem and an underwater receiving subsystem; The airborne transmission subsystem includes: a collaborative sensing module, a main control unit, a drive circuit, a pulsed laser array, and an optical projection component; The underwater receiving subsystem includes: an underwater acoustic transducer and a signal processing terminal.

[0015] This application provides a laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming, which has the following advantages compared with the prior art: Firstly, by acquiring the real-time position vector of the underwater target receiver and the preset beamwidth index, the number of photoacoustic conversion points and their two-dimensional spatial distribution coordinates were determined, thus constructing a "virtual sound source array." Combining a true time-delay algorithm with the calculation of the path difference at each conversion point, the system can precisely control the phase relationship of the excited sound waves at each point, allowing the dispersed sound wave energy to be superimposed in phase at the target receiver, forming a high-gain synthesized sound beam pointing towards the target. This coherent synthesis mechanism greatly improves the spatial utilization of acoustic energy and effectively overcomes the shortcomings of traditional laser-induced sound energy divergence.

[0016] Secondly, this invention innovatively incorporates both the "acoustic propagation delay component" and the "optical propagation delay component determined based on the emission geometry" into the calculation of the total trigger time delay. By utilizing a unified global clock reference and performing independent time-domain offset processing on each laser pulse modulation signal, it accurately compensates for the optical flight time from the airborne laser emission unit to the photoacoustic conversion point on the water surface, as well as the acoustic propagation time from the water surface to the underwater target. This end-to-end time delay calibration mechanism solves the phase mismatch problem caused by airborne platform jitter, target movement, or changes in geometric configuration, ensuring that the synthesized sound beam always accurately locks onto the moving target.

[0017] Third, by acquiring the three-dimensional position of the airborne laser emitting unit and the real-time position vector of the underwater target, the system can dynamically adjust the configuration of the virtual sound source array. This means that regardless of the movement of the underwater target, the system can recalculate the sound path difference and trigger delay based on the latest position coordinates, thereby changing the direction and coverage of the sound beam in real time (determined by the beamwidth index). This flexible dynamic adjustment mechanism ensures that the communication link remains stable even in complex marine environments and under maneuvering target conditions, effectively guaranteeing the accurate recovery of the communication data stream to be transmitted. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Figure 1 This is an overall flowchart of a laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming.

[0019] Figure 2 This is a schematic diagram of a laser-induced acoustic air-to-water cross-medium communication device based on phased array beamforming. Detailed Implementation

[0020] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0021] Example 1, as Figure 1 The image shows the first embodiment of the present invention, which provides a laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming, comprising: S1: Establish a three-dimensional spatial coordinate system with the geometric center or a predetermined reference point of the predetermined photoacoustic conversion region on the water-air interface as the origin; under this coordinate system, obtain the three-dimensional position coordinates of each laser emitting unit in the air and obtain the real-time position vector of the underwater target receiver.

[0022] It should be noted that a three-dimensional Cartesian coordinate system is established with the geometric center of the predetermined photoacoustic conversion region at the water-air interface as the origin O(0,0,0). The coordinates of the transmitting end are obtained: using the RTK-GPS and attitude sensors mounted on the UAV, the three-dimensional coordinates (X, Y, X, Y) of the i-th laser transmitting unit in the air are obtained. i ,Y i H i ); where H i The altitude is represented by the real-time position vector r of the underwater target receiver. t =(x t ,y t ,z t ), where z t <0 indicates water depth.

[0023] S2: Based on the position vector of the target receiver and the preset beamwidth index, determine the number of photoacoustic conversion points projected on the water-air interface and their two-dimensional spatial distribution coordinates in the coordinate system, thereby constructing a virtual sound source array.

[0024] It should be noted that the beam scanning pointing angle is calculated based on the position vector of the target receiver; according to the preset beamwidth index and the center frequency of the laser-induced acoustic signal, the effective aperture size required for the virtual sound source array is calculated and determined by using the inverse relationship between the beamwidth and the array aperture, combined with the propagation speed of sound waves in the water medium and the beam factor constant related to the array geometry; subsequently, under the constraint that the element spacing is less than half the wavelength of the sound wave, the number of photoacoustic conversion points projected on the water-air interface and the two-dimensional plane coordinates of each point are calculated based on the effective aperture size.

[0025] Preferably, the beam scanning pointing angle is calculated based on the position vector of the target receiver; and the beamwidth index θ is used as a preset reference. BW(Unit: radians) and the center frequency f0 of the laser-induced acoustic signal, the effective aperture size L required for the virtual sound source array is determined using an aperture estimation formula, which is:

[0026] Where c is the speed of sound in water, and K is the beam factor constant related to the array geometry and weighting function; Subsequently, under the constraint that the element spacing is less than half the wavelength of the sound wave, the number N of photoacoustic conversion points projected onto the water-air interface and the two-dimensional plane coordinates of each point are calculated based on the effective aperture size L, so that the main lobe direction of the constructed virtual sound source array is aligned with the beam scanning pointing angle.

[0027] Furthermore, the two-dimensional spatial coordinate system of the virtual sound source array is configured into one of the following topologies based on communication scanning requirements: Uniform Linear Array (ULA) is configured to respond to the requirements of single-dimensional sector scanning, with each photoacoustic conversion point arranged at equal intervals along a straight line; The uniform circular array (UCA) is configured to respond to the requirements of omnidirectional horizontal scanning, with each photoacoustic conversion point evenly distributed on a circle centered on the target azimuth projection point. An irregular sparse random array is configured to respond to the requirements of grating lobe suppression and aperture expansion, with the spacing between each photoacoustic conversion point following a preset probability density function distribution.

[0028] In this embodiment, the aim is to determine the distribution of photoacoustic conversion points on the water surface. Assuming the communication requirement is sector scanning, this embodiment uses a uniform linear array (ULA) topology. Based on a preset beamwidth θ... BW (For example, 5°), the effective aperture is calculated using the inverse relationship between beamwidth and aperture, expressed as:

[0029] Where c is the speed of sound in water, and f0 is the center frequency of laser-induced acoustics (e.g., 100 kHz). If θ BW =5°, then L≈0.3 meters is calculated. To avoid the grating lobe effect, the spacing d between adjacent photoacoustic conversion points must satisfy the following constraint:

[0030] Based on this calculation, the required number of array elements N== L / d +1. Determine the three-dimensional coordinates (x, y) of N photoacoustic conversion points on the water surface. i ,y i ,z i ), where z i ≡0.

[0031] Furthermore, Uniform Linear Array (ULA): best suited for one-dimensional / sector scanning tasks. When the communication target moves within a fixed plane, ULA can achieve beam reciprocating scanning in the simplest and most efficient way. Therefore, ULA is selected in embodiments requiring "sector scanning".

[0032] Uniform Circular Array (UCA): Primarily used for 360° omnidirectional horizontal scanning. When it is necessary to cover the entire horizontal plane without blind spots, or when the target may come from any direction, UCA is the best choice due to the uniformity of its radiation pattern.

[0033] Irregular sparse arrays: designed to meet specific requirements for high quality and high security. Their main objectives are to suppress grating lobes (reduce bypass interference) and expand the effective aperture (forming a narrower, more concentrated beam).

[0034] S3: Obtain the sound wave propagation speed parameters in the current water environment as a reference constant for beamforming calculation.

[0035] It should be noted that the sound wave propagation speed parameter is obtained through one or a combination of the following methods: Method 1: Obtain the environmental parameters of the current water area, which include at least temperature, salinity, and depth, and calculate them using the empirical formula for underwater acoustic velocity; Method 2: Obtained by actual measurement in the current water area using sound velocity measuring equipment; Method 3: Obtain by calling a pre-set hydrological database or historical sound velocity profile data.

[0036] Preferably, the sound wave propagation speed parameter c is calculated based on the current water temperature T, salinity S, and depth D using an empirical formula for the speed of sound. The empirical formula for the speed of sound is:

[0037] Where c is in meters per second, T is in degrees Celsius, S is in parts per thousand, and D is in meters.

[0038] Furthermore, in this embodiment of the application, to ensure beam pointing accuracy, it is necessary to obtain the precise speed of sound c. This embodiment adopts "Method 1," that is, calculation through environmental parameters. The speed of sound c calculated by this formula will serve as the reference constant for time delay calculation in the subsequent step S5.

[0039] S4: Based on the spatial geometric distance between each photoacoustic conversion point in the virtual sound source array and the underwater target receiver, using one of the photoacoustic conversion points or virtual points as a reference, calculate the sound path difference of each of the other photoacoustic conversion points relative to the reference reference.

[0040] It should be noted that the physical distance of each photoacoustic conversion point is calculated based on the three-dimensional coordinates of each photoacoustic conversion point determined in step S2 and the three-dimensional coordinates of the target receiver obtained in step S1, using the Euclidean distance calculation rule; then, by comparing the physical distances of each photoacoustic conversion point, the maximum physical distance or a selected reference distance is determined, and the geometric path difference of each point is obtained.

[0041] Furthermore, the physical distance d between each photoacoustic conversion point is calculated. i The following geometric formula is used:

[0042] Among them, (x i ,y i ,z i (x) represents the coordinates of the i-th photoacoustic conversion determined in step S2 in the three-dimensional coordinate system. t ,y t ,z t () represents the real-time location coordinates of the target receiver obtained in step S1; Furthermore, the maximum physical distance is determined by traversing all N photoacoustic conversion points. And obtain the geometric path difference at the i-th point. .

[0043] S5: Based on the broadband pulse characteristics of the laser-induced acoustic signal, the acoustic propagation delay component corresponding to each photoacoustic conversion point is calculated using the true time delay algorithm according to the ratio of the acoustic path difference to the acoustic wave propagation speed parameter.

[0044] It should be noted that the total trigger time delay of the i-th photoacoustic conversion point in the true time delay sequence is equal to the sum of the acoustic propagation delay component and the optical propagation delay component; wherein, the acoustic propagation delay component is determined by dividing the geometric acoustic path difference by the acoustic wave propagation speed parameter; the optical propagation delay component is determined by dividing the optical path distance from the laser emitting unit corresponding to the photoacoustic conversion point to the water-air interface by the speed of light.

[0045] Furthermore, the total trigger time delay of the i-th photoacoustic conversion point in the true delay sequence The following physical relationship must be satisfied:

[0046] in, To calculate the geometric path difference, is the optical propagation delay component used to compensate for optical path difference in the air; c is the sound wave propagation speed parameter; The calculation accuracy is better than one-tenth of the laser pulse width to ensure the coherent superposition efficiency of broadband signals. This represents the total trigger time delay at the i-th photoacoustic conversion point.

[0047] Furthermore, the acoustic propagation time delay component is calculated using the obtained precise sound velocity c and the calculated sound path difference:

[0048] in, Let represent the acoustic propagation time delay component at the i-th photoacoustic conversion point, indicating that this component is used to compensate for the phase difference caused by the different propagation path lengths of sound waves in water.

[0049] S6: Receive the communication data stream to be transmitted and encode it into a laser pulse modulation signal; based on a unified global clock reference, calculate the total trigger time delay including the acoustic propagation delay component and the optical propagation delay component determined based on the emission geometry, and perform independent time-domain offset processing on each modulation signal.

[0050] It should be noted that a digital modulation method based on pulse time-domain characteristics is used to encode the communication data stream to be transmitted into a standard baseband pulse sequence; the modulation method includes, but is not limited to, pulse position modulation (PPM), on / off keying modulation (OOK), pulse interval modulation (PIM), or pulse width modulation (PWM). The baseband pulse sequence is copied in multiple ways to generate N parallel signals, which are equal to the number of photoacoustic conversion points in the virtual sound source array. The calculated total trigger time delay, including acoustic and optical delays, is applied to the corresponding i-th parallel signal, so that the trigger time of each laser pulse in the signal lags behind the global reference time, thereby generating N drive control signals containing beam pointing information.

[0051] It should be noted that step S6 is the core of cross-medium communication, performing dual delay compensation. First, the information to be transmitted is encoded using Pulse Position Modulation (PPM), mapping the binary data to the time position of the baseband pulse, considering the laser's flight time in air. The optical path length d from the i-th transmitting unit to the water surface landing point is calculated. optical,i :

[0052] The light propagation time delay component is:

[0053] Among them, c light ≈3×10 8 m / s, d optical,max The maximum optical path length. The total trigger delay ΔT of the i-th signal. i The main control unit is based on this ΔT iPerform independent time-domain offset processing on the i-th modulated signal, ΔT i =Δt sound,i +Δt light, .

[0054] S7: Using the signal after time-domain offset processing, the pulsed laser array is driven under the global clock synchronization control to precisely control the excitation time of each laser unit. Multiple laser pulses are emitted and incident on the water-air interface. At the interface, broadband acoustic pulses are excited through photoacoustic effect, so that the broadband acoustic pulses generated at each photoacoustic conversion point achieve wavefront alignment and coherent superposition in the time domain when they propagate to the target receiving end position, forming a high-gain synthetic acoustic beam pointing to the target receiving end.

[0055] It should be noted that the driving circuit responds to the signal after time-domain offset and triggers the pulsed laser array to emit multiple laser pulses; the laser pulses are incident on the water-air interface and excited by the photoacoustic conversion effect to generate multiple broadband acoustic pressure waves; Furthermore, multiple broadband acoustic pressure waves propagate in the water medium and superimpose at the target receiver location; the time-domain acoustic pressure waveform of their composite sound field... The following delay-summation beamforming formula is satisfied:

[0056] Among them, A i Let be the sound source intensity amplitude at the i-th photoacoustic conversion point. To normalize the sound source waveform, d i Let be the distance between the i-th photoacoustic conversion point and the underwater target receiver, and let c be the speed of sound. The trigger time delay amount; the trigger time delay amount It is configured to compensate for the physical propagation time difference in order to achieve phase-consistent superposition of the various acoustic wave components.

[0057] Multiple broadband acoustic pressure waves propagate in the water medium. Because the trigger time delay applied to each signal in advance compensates for the difference in the physical propagation path, the acoustic wave components achieve phase alignment and in-phase superposition in the time domain when they reach the target receiving end, thereby forming a high-gain synthetic sound field.

[0058] Furthermore, the driving circuit, under global clock synchronization, controls the pulsed laser array according to the delay amount ΔT. i Lasers are emitted, and each laser beam strikes the water surface, generating broadband sound waves. At the underwater target, the received composite sound pressure P(t) is:

[0059] ΔT i Substituting into the above formula, we can see that the distance term in the time parameter is canceled out, and the formula simplifies to:

[0060] The N-channel sound waves achieved wavefront alignment at the target location, and their amplitudes were coherently superimposed to form a high-gain narrow beam.

[0061] S8: At the target receiving end, the high-gain synthesized sound beam is picked up using an underwater acoustic transducer, and the received sound signal is filtered and demodulated to recover the communication data stream.

[0062] It should be noted that the electrical signal output by the underwater acoustic transducer is subjected to bandpass filtering, and the bandpass filtering is configured to filter out environmental noise and interference signals outside the passband frequency range. The filtered signal is processed using relevant detection algorithms or preamble acquisition algorithms to extract symbol timing information and establish communication frame synchronization. Based on the established communication frame synchronization, the signal is reverse-mapped according to the demodulation rules corresponding to the modulation method to recover the binary communication data stream.

[0063] Furthermore, the underwater acoustic transducer at the underwater target picks up the high-gain signal, which is then passed through a bandpass filter with a center frequency of f0 and a bandwidth of B to filter out low-frequency marine environmental noise. Envelope detection or cross-correlation is performed on the filtered signal to determine the pulse peak time, and the original binary communication data stream is recovered in reverse according to the PPM modulation rules.

[0064] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

[0065] Example 2, as Figure 2 The image shows an embodiment of a laser-induced acoustic air-to-water trans-medium communication medium based on phased array beamforming.

[0066] Example 1 is a schematic scheme of a laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming. It should be noted that the technical solution of this laser-induced acoustic air-to-water cross-medium communication device based on phased array beamforming is based on the same concept as the technical solution of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming in Example 1. Details not described in detail in the technical solution of the laser-induced acoustic air-to-water cross-medium communication device based on phased array beamforming in this example can be found in the description of the technical solution of the laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming in Example 1.

[0067] This embodiment also provides a laser-induced acoustic air-to-water cross-medium communication device based on phased array beamforming, including: an air-to-air transmitting subsystem and an underwater receiving subsystem; The air-launch subsystem is configured to be mounted on one or more collaboratively operating drones and other aerial flight platforms, including: The collaborative sensing module is configured to acquire the relative position information between each laser emitting unit. When multi-machine collaboration (distributed aperture) is adopted, UWB (ultra-wideband) wireless ranging technology is used to calculate the relative position vector between each UAV in real time and transmit the data back to the main control unit.

[0068] It should be noted that the collaborative sensing module is implemented using one or a combination of the following methods: Wired coordination mode: When each laser emitting unit is integrated on the same flight platform, the clock signal and position parameters are shared through the high-speed bus or fiber optic link inside the platform; Wireless coordination method: When each laser emitting unit is distributed across multiple flight platforms, a distributed self-organizing network is constructed using an ultra-wideband (UWB) wireless ranging communication module or a two-way laser time comparison module to calculate the relative position coordinates of each platform in real time and maintain nanosecond-level time synchronization.

[0069] The main control unit, serving as the core processor, is implemented using a high-performance FPGA (such as the Xilinx Kintex series). It integrates a beamforming algorithm module and a global clock synchronization control module. Beamforming algorithm module: configured to calculate the total delay, including acoustic propagation delay and optical propagation delay, based on the relative coordinates of the target and the relative positions of each laser emitting unit; Global clock synchronization control module: Configured to establish and maintain a unified time base. When multiple machines collaborate, the time synchronization accuracy of each subsystem is ensured through PTP (Precise Time Protocol) or bidirectional laser time comparison. The clock accuracy inside the FPGA is better than 5ns to meet the precise control of minute delay differences.

[0070] The driving circuit connects the main control unit and the pulsed laser array, and is configured to respond to the synchronous trigger sequence to drive each laser emitting unit to emit light synchronously with nanosecond-level precision. The pulsed laser array consists of multiple parallel laser emitting units configured to generate high-energy laser pulses, using a narrow pulse width (10ns level) near-infrared (1064nm) fiber laser. An optical projection component is configured to project or guide the laser pulses to a water-air interface to construct a virtual sound source array.

[0071] The underwater receiving subsystem includes: The underwater acoustic transducer is configured to sense underwater sound pressure signals and convert them into electrical signals; a broadband omnidirectional hydrophone is selected, with an operating frequency band covering the main energy level range of laser-induced acoustic signals (20kHz-100kHz).

[0072] The signal processing terminal is configured to amplify, filter, and demodulate electrical signals and output communication data; to perform bandpass filtering (to remove low-frequency sea wave noise) and ADC sampling on the received signal; and then to extract the signal peak value using a cross-correlation detection algorithm to recover the communication data.

[0073] The device in this embodiment, through the combination of the aforementioned hardware and algorithms, can achieve directional, long-distance, high-speed data transmission to specific underwater targets without the need for pre-installed underwater equipment.

[0074] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A laser-induced acoustic air-to-water cross-medium communication method based on phased array beamforming, characterized in that, include: Obtain the three-dimensional position coordinates of each laser emitting unit in the air, and obtain the real-time position vector of the underwater target receiver; Based on the real-time position vector of the underwater target receiver and the preset beamwidth index, the number of photoacoustic conversion points and the two-dimensional spatial distribution coordinates are determined, and a virtual sound source array is constructed. Obtain the sound wave propagation speed parameters in the current water environment as the reference constants for beamforming calculations; Based on the spatial geometric distance between each photoacoustic conversion point in the virtual sound source array and the underwater target receiver, the acoustic path difference of each photoacoustic conversion point relative to the reference reference is calculated. The acoustic propagation delay component corresponding to each photoacoustic conversion point is calculated using the true time delay algorithm. Receive the communication data stream to be transmitted and encode it into a laser pulse modulation signal; Based on a unified global clock reference, the total trigger time delay, including the acoustic propagation delay component and the optical propagation delay component determined by the transmission geometry, is calculated, and each modulation signal is subjected to independent time-domain offset processing. Using the signal after time-domain offset processing, a pulsed laser array is driven under global clock synchronization control to form a high-gain synthetic acoustic beam pointing towards the target receiver. At the underwater target receiver, a high-gain synthesized sound beam is picked up using an underwater acoustic transducer to recover the communication data stream.

2. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The determination of the number of photoacoustic conversion points and their two-dimensional spatial distribution coordinates includes: The beam scanning pointing angle is calculated based on the position vector of the target receiver. Based on the preset beamwidth index and the center frequency of the laser-induced acoustic signal, the effective aperture size required for the virtual sound source array is calculated and determined by utilizing the inverse relationship between beamwidth and array aperture, combined with the beam factor constant related to the propagation speed of sound waves in water and the array geometry. Under the constraint that the element spacing is less than half the wavelength of the sound wave, the number of photoacoustic conversion points projected onto the water-air interface and the two-dimensional plane coordinates of each point are calculated based on the effective aperture size.

3. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The virtual sound source array includes: a topology structure configured based on communication scanning requirements.

4. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The acquisition of sound wave propagation speed parameters in the current aquatic environment includes: The environmental parameters of the current water area are obtained and calculated using the empirical formula for underwater acoustic velocity.

5. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The calculation of the acoustic path difference of each photoacoustic conversion point relative to the reference reference includes: Based on the determined three-dimensional coordinates of each optical-acoustic conversion point and the obtained three-dimensional coordinates of the target receiver, the geometric path difference of each point is obtained by using the Euclidean distance calculation rule, comparing the physical distances of each optical conversion point, determining the maximum physical distance or selecting a reference distance.

6. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The calculation of the acoustic propagation time delay component corresponding to each photoacoustic conversion point includes: The total trigger time delay of the i-th photoacoustic conversion point in the true delay sequence is equal to the sum of the acoustic propagation delay component and the optical propagation delay component; The acoustic propagation time delay component is determined by dividing the geometric path difference by the sound wave propagation speed parameter; The optical propagation delay component is determined by dividing the optical path distance from the laser emitting unit corresponding to the photoacoustic conversion point to the water-air interface by the speed of light.

7. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, in, The independent time-domain offset processing for each modulated signal includes: A digital modulation method based on pulse time-domain characteristics is used to encode the communication data stream to be transmitted into a standard baseband pulse sequence; The baseband pulse sequence is copied multiple times to generate N parallel signals, which are equal to the number of photoacoustic conversion points in the virtual sound source array. The calculated total trigger time delay, including acoustic and optical delays, is applied to the corresponding i-th parallel signal, so that the trigger time of each laser pulse in the i-th parallel signal is delayed relative to the global reference time, thereby generating N-way drive control signals containing beam pointing information.

8. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The formation of a high-gain synthesized sound beam pointing towards the target receiver includes: The driving circuit responds to the signal after the time domain shift and triggers the pulsed laser array to emit multiple laser pulses. The laser pulses are incident on the water-air interface and are excited by the photoacoustic conversion effect to generate multiple broadband acoustic pressure waves. Multiple broadband acoustic pressure waves propagate in the water medium. Due to the pre-applied trigger time delay of each signal to compensate for the difference in the physical propagation path, the acoustic wave components achieve phase alignment and in-phase superposition in the time domain when they reach the target receiving end, forming a high-gain synthetic sound field.

9. The laser-induced acoustic air-to-water trans-medium communication method based on phased array beamforming as described in claim 1, characterized in that, The recovery of the communication data stream includes: The electrical signal output from the underwater acoustic transducer is subjected to bandpass filtering. The filtered signal is processed to extract symbol timing information and establish communication frame synchronization. Based on communication frame synchronization, the signal is reverse-mapped to recover the binary communication data stream.

10. A laser-induced acoustic air-to-water trans-medium communication device based on phased array beamforming as described in claim 1, characterized in that, include: Airborne launch subsystem and underwater receiving subsystem; The airborne transmission subsystem includes: a collaborative sensing module, a main control unit, a drive circuit, a pulsed laser array, and an optical projection component; The underwater receiving subsystem includes: an underwater acoustic transducer and a signal processing terminal.

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