Opto-acoustic fusion-based air-sea cross-medium bidirectional communication system and method

Abstract

The application belongs to the technical field of air-sea cross-medium communication, and relates to an air-sea cross-medium bidirectional communication system and method based on photoacoustic fusion. The system comprises a dual-wavelength laser and a millimeter wave radar arranged on an air mobile platform, and a photoacoustic receiving device and a photoacoustic emitting device arranged on an underwater mobile platform. The dual-wavelength laser emits two-wavelength laser beams to the water surface, one laser beam breaks through the water surface to generate a downlink acoustic wave signal, and the other laser beam penetrates the water surface to transmit a downlink blue-green light wave signal. The photoacoustic receiving device receives the downlink acoustic wave signal and the downlink blue-green light wave signal. The photoacoustic emitting device emits an uplink blue-green light wave signal and an uplink acoustic wave signal to the water surface, and the uplink acoustic wave signal impacts the water surface to generate a microwave ripple. The millimeter wave radar emits a signal to the water surface to obtain a microwave ripple echo signal, and can also receive the uplink blue-green light wave signal. The application realizes air-sea cross-medium bidirectional communication, solves the communication blind area problem in the acoustic field near-field area, and improves the communication quality and reliability.

Description

Technical Field

[0001] This invention belongs to the field of air-sea cross-medium communication technology, specifically relating to an air-sea cross-medium bidirectional communication system and method based on optical-acoustic fusion. Background Technology

[0002] Laser communication has enormous potential in both military and civilian applications, and countries around the world, especially developed countries, attach great importance to it. Over the past half-century, laser communication has developed exceptionally rapidly. With the expansion of human activity areas, in marine environments, traditional underwater communication typically uses very low frequency (VLF) and super low frequency (SLF) electromagnetic waves. However, this method results in large-scale communication equipment, cumbersome systems, and low transmission rates, significantly limiting the effectiveness of information transmission. Meanwhile, high-frequency electromagnetic waves experience severe energy attenuation during underwater transmission, making them almost impossible to propagate through seawater.

[0003] Patent application number 202011445379.9 discloses a two-way optical-acoustic communication method for airborne and underwater mobile platforms. The airborne mobile platform transmits a signal beam through a free-space optical communication module, using laser-induced acoustic technology to excite the water surface to generate an underwater acoustic carrier signal. The underwater mobile platform receives the acoustic signal through an underwater sonar communication module, thus achieving downlink communication from the air to the underwater surface. However, when the beam excites the water surface to generate the underwater acoustic carrier signal, the characteristics of the resulting sound field are altered by the influence of sea waves, creating a certain blind zone in the near-field region of the sound field, making it difficult to achieve the communication objective. Furthermore, relying solely on laser-induced acoustic technology for underwater communication results in low reliability and is prone to packet loss and bit errors. Summary of the Invention

[0004] To address the shortcomings of related technologies, this invention provides an air-sea cross-medium bidirectional communication system and method based on photoacoustic fusion, aiming to realize air-sea cross-medium bidirectional communication and solve the communication blind zone problem in the near-field region of the sound field during laser-induced acoustic communication, thereby improving communication quality and reliability.

[0005] This invention provides an air-sea cross-medium two-way communication system based on photoacoustic fusion, comprising an airborne mobile platform on the sea surface, an underwater mobile platform in the seawater, a dual-wavelength laser and millimeter-wave radar mounted on the airborne mobile platform, and a photoacoustic receiving device and a photoacoustic transmitting device mounted on the underwater mobile platform; wherein...

[0006] The dual-wavelength laser is used to emit a first laser beam with a wavelength of 1064nm and a second laser beam with a wavelength of 532nm towards the water surface; the first laser beam enters the water and is focused on the water surface, causing the water medium to produce a photoacoustic effect and radiating a downward acoustic signal into the water; the second laser beam directly penetrates the water surface and enters the water, transmitting a downward blue-green light wave signal into the water.

[0007] The photoacoustic receiver is used to receive downlink acoustic signals and downlink blue-green light signals;

[0008] The photoacoustic emitting device is used to emit upward blue-green light wave signals and upward sound wave signals onto the water surface. The upward sound wave signals hit the water surface and generate ripples on the water surface.

[0009] Millimeter-wave radar is used to transmit frequency-modulated continuous wave radio frequency signals to the water surface to obtain echo signals of microwave ripples on the water surface; millimeter-wave radar also has a built-in blue-green light detection unit to receive uplink blue-green light wave signals.

[0010] In some embodiments, an airborne computer is also installed on the airborne maneuvering platform, and an underwater computer is also installed on the underwater maneuvering platform; the airborne computer is communicatively connected to a dual-wavelength laser to control the emission of the first and second laser beams; the airborne computer is communicatively connected to a millimeter-wave radar to process the echo signals and uplink blue-green light wave signals it receives; the underwater computer is communicatively connected to a photoacoustic receiver to process the downlink acoustic signals and downlink blue-green light wave signals it receives; and the underwater computer is communicatively connected to a photoacoustic transmitter to control the emission of uplink blue-green light wave signals and uplink acoustic signals.

[0011] In some embodiments, the photoacoustic emitting device includes a blue-green laser and a transmitting transducer. The blue-green laser is used to emit an upward blue-green light wave signal onto the water surface, and the transmitting transducer is used to convert the mechanical wave into a sound wave to emit an upward sound wave signal onto the water surface. The photoacoustic receiving device includes a blue-green light receiver and a receiving transducer. The blue-green light receiver is used to receive a downward blue-green light wave signal, and the receiving transducer is used to receive a downward sound wave signal.

[0012] In some embodiments, the dual-wavelength laser includes two output ports for the emission of a first laser beam and a second laser beam, respectively. The aerial maneuvering platform is also equipped with a beam expander, a first reflector, and a long focal length focusing lens located on the output optical path of the first laser beam. The first laser beam passes through the beam expander, the first reflector, and the long focal length focusing lens in sequence before entering the water and focusing on the water surface to radiate a downward acoustic signal underwater. The aerial maneuvering platform is also equipped with a second reflector located on the output optical path of the second laser beam. The second laser beam passes through the second reflector and directly penetrates the water surface to enter the underwater environment.

[0013] In some embodiments, the airborne maneuvering platform is further equipped with a downlink communication encoding module. This module transmits four different repetition frequencies using a four-frequency BPSK signal modulation method to encode downlink communication information. An airborne computer is communicatively connected to the downlink communication encoding module to control a dual-wavelength laser based on the encoded downlink communication information. This causes the laser to emit a first laser beam and a second laser beam carrying the downlink encoded signal towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic wave signal carrying the downlink encoded signal. The underwater maneuvering platform is also equipped with an uplink communication encoding module. This module transmits four different repetition frequencies using a four-frequency BPSK signal modulation method to encode uplink communication information. An underwater computer is communicatively connected to the uplink communication encoding module to control a photoacoustic transmitting device based on the encoded uplink communication information. This causes the device to emit an uplink acoustic wave signal carrying the uplink encoded signal and an uplink blue-green light wave signal towards the water surface. The uplink acoustic wave signal impacts the water surface to generate ripples on the water surface carrying the uplink encoded signal.

[0014] In some embodiments, the dual-wavelength laser has a built-in modulator located in the optical path outside the resonant cavity of the dual-wavelength laser. When the laser beam emitted by the dual-wavelength laser passes through the modulator, the modulator changes the amplitude, phase and frequency of the laser beam by modulating the voltage to obtain a first laser beam and a second laser beam carrying downlink encoded signals.

[0015] This invention also provides a two-way air-sea cross-medium communication method based on photoacoustic fusion, which uses the aforementioned two-way air-sea cross-medium communication system based on photoacoustic fusion and includes the following steps:

[0016] The air-to-sea downlink communication steps are as follows: The downlink communication encoding module encodes the downlink communication information using a four-frequency BPSK signal modulation method, obtaining the encoded downlink communication information. The airborne computer then controls a dual-wavelength laser to emit a first laser beam with a wavelength of 1064nm and a second laser beam with a wavelength of 532nm towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic signal, which is received by a transducer, establishing the air-to-sea downlink acoustic channel. The second laser beam directly penetrates the water surface and transmits downlink blue-green light signals underwater. A blue-green light receiver receives the downlink blue-green light signals, establishing the air-to-sea downlink optical channel. The photoacoustic receiving device transmits the received downlink acoustic signal and downlink blue-green light wave signal to an underwater computer for demodulation, obtaining the demodulated downlink communication information and completing air-to-sea downlink communication. When the air-to-sea downlink communication step is applied to short-range air-to-sea downlink communication, downlink data transmission services within the blue-green light attenuation radius are completed using downlink blue-green light wave signals and downlink acoustic signals as carriers, respectively. When the air-to-sea downlink communication step is applied to medium-to-long-range air-to-sea downlink communication, downlink data transmission services outside the blue-green light attenuation radius are completed using downlink acoustic signals as carriers. The downlink blue-green light wave signal also plays a directional guiding role in air-to-sea downlink acoustic communication.

[0017] The sea-to-air uplink communication process is as follows: The uplink communication encoding module encodes the uplink communication information using a four-frequency BPSK signal modulation method, obtaining the encoded uplink communication information. The underwater computer then controls the transmitting transducer and blue-green laser to transmit uplink acoustic signals and uplink blue-green light signals to the water surface, respectively. The uplink acoustic signals impact the water surface, generating ripples. The millimeter-wave radar transmits frequency-modulated continuous wave radio frequency signals to the water surface to obtain the echo signals of the ripples, thus establishing the sea-to-air uplink acoustic channel. The uplink blue-green light signals are received by the blue-green light detection unit within the millimeter-wave radar, thus establishing the sea-to-air uplink optical channel. The millimeter-wave radar transmits the acquired echo signal and uplink blue-green light wave signal to an airborne computer for demodulation, obtaining the demodulated uplink communication information and completing the sea-to-air uplink communication. When the sea-to-air uplink communication step is applied to short-range sea-to-air uplink communication, the uplink blue-green light wave signal and the uplink acoustic wave signal are used as carriers to complete the uplink data transmission service within the blue-green light attenuation radius, respectively. When the sea-to-air uplink communication step is applied to long-range sea-to-air uplink communication, the uplink acoustic wave signal is used as the carrier to complete the uplink data transmission service outside the blue-green light attenuation radius. The uplink blue-green light wave signal also plays a directional guidance role in sea-to-air uplink acoustic wave communication.

[0018] In some embodiments, during short-range air-to-sea downlink communication, the optical carrier information carried by the downlink blue-green light wave signal and the acoustic carrier information carried by the downlink acoustic wave signal are cross-checked. During short-range sea-to-air uplink communication, the optical carrier information carried by the uplink blue-green light wave signal and the acoustic carrier information carried by the uplink acoustic wave signal are cross-checked. When the sender encodes the same information onto the optical carrier and acoustic carrier, the cross-check operation is used to perform packet loss and bit error checking to minimize the packet loss rate and bit error rate. When the sender modulates different information onto the optical carrier and acoustic carrier, the cross-check operation is used to perform data restoration.

[0019] In some embodiments, when the downlink blue-green light wave signal is used as the carrier, the sender and receiver are connected through an air-to-sea downlink optical channel and use the same operating wavelength, communication protocol and encryption scheme; when the uplink blue-green light wave signal is used as the carrier, the sender and receiver are connected through a sea-to-air uplink optical channel and use the same operating wavelength, communication protocol and encryption scheme.

[0020] In some embodiments, when the downlink or uplink blue-green light wave signal is used as the carrier, data transmission services within the blue-green light attenuation radius are completed through precise tracking, communication signal transmission, and weak signal analysis.

[0021] Based on the above technical solutions, the air-sea cross-medium bidirectional communication system and method based on photoacoustic fusion in the embodiments of the present invention realizes air-sea cross-medium bidirectional communication based on photoacoustic fusion, solves the communication blind zone problem in the near field of the sound field when relying solely on laser-induced acoustic communication, improves the quality and reliability of air-sea cross-medium bidirectional communication, and reduces the communication error rate and packet loss rate. Attached Figure Description

[0022] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0023] Figure 1 This is a schematic diagram of the air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to the present invention;

[0024] Figure 2 This is a schematic diagram illustrating the principle of the air-sea cross-medium bidirectional communication method based on photoacoustic fusion during uplink communication according to the present invention.

[0025] Figure 3 This is a schematic diagram illustrating the principle of the air-sea cross-medium bidirectional communication method based on photoacoustic fusion in the downlink communication of the present invention.

[0026] Figure 4 This is a schematic diagram of the modulation and demodulation process;

[0027] Figure 5 Schematic diagram of BPSK modulation principle;

[0028] Figure 6 Schematic diagram of BPSK modulation and demodulation principle;

[0029] Figure 7 This is a schematic diagram of the simulated transmission information code;

[0030] Figure 8 This is a schematic diagram of a carrier signal;

[0031] Figure 9 A schematic diagram of a 2BPSK modulated signal;

[0032] Figure 10 This is a schematic diagram of the demodulated signal. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] In the description of this invention, it should be understood that the terms "center", "lateral", "longitudinal", "upper", "lower", "top", "bottom", "inner", "outer", "front", "rear", "vertical", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] The terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] refer to Figures 1-3 As shown, this invention provides an air-sea cross-medium two-way communication system based on photoacoustic fusion, including an airborne mobile platform located on the sea surface, an underwater mobile platform located in the seawater, a dual-wavelength laser and millimeter-wave radar installed on the airborne mobile platform, and a photoacoustic receiving device and a photoacoustic transmitting device installed on the underwater mobile platform. It is understood that both the airborne mobile platform and the underwater mobile platform are mobile.

[0038] A dual-wavelength laser is used to emit two laser beams of different wavelengths towards the water surface; the first laser beam has a wavelength of 1064 nm, and the second laser beam has a wavelength of 532 nm. The first laser beam with a wavelength of 1064 nm is injected into the water and focused at the water surface, causing a photoacoustic effect in the water medium and radiating a downward acoustic signal underwater. Specifically, the energy density at the focal point of the first laser beam is much greater than the dielectric breakdown threshold of water, which can cause photoacoustic effects such as thermal expansion, vaporization, and dielectric breakdown in the water medium, realizing photoacoustic conversion, generating a sound field, and then radiating sound waves underwater, thus achieving the laser-induced acoustic effect. It can be further explained that by using laser-induced acoustic technology, the difficulties of high-frequency electromagnetic waves being unable to propagate in water and the large attenuation of sound waves propagating across media in the air and sea can be overcome. Since the signal attenuation of sound waves is small and the transmission distance is long when transmitted underwater, sound waves are very suitable for underwater communication. However, because laser-induced acoustic is affected by sea waves, a communication blind zone is created in the near-field region of the sound field, and the bit error rate is high when communicating in the near-field region of the sound field. A second laser beam with a wavelength of 532nm directly penetrates the water surface and enters the underwater environment, transmitting downlink blue-green light wave signals. This further illustrates that blue-green light communication operates at frequencies concentrated around 1000THz, offering wide bandwidth, strong information transmission capabilities, high coding rates, and strong anti-interference capabilities. Therefore, blue-green light experiences very low energy loss during transmission, whether in the air or seawater, reducing the transmission frequency and increasing the determinism and reliability of communication. Since the underwater transmission distance of blue-green light waves is shorter than that of sound waves, blue-green light waves are more suitable for short-range communication, i.e., communication within the blue-green light attenuation radius. An optoacoustic receiving device is used to receive downlink acoustic signals and downlink blue-green light wave signals. Specifically, the optoacoustic receiving device receives the downlink acoustic signal generated by the first laser beam. Utilizing the advantages of underwater sound wave transmission, it can effectively achieve long-distance downlink communication between air and sea with high reliability. The photoacoustic receiver receives the downlink blue-green light wave signal generated by the second laser beam. Utilizing the advantages of blue-green light wave transmission in air and sea, it effectively achieves short-range (within the blue-green light attenuation radius) downlink communication between air and sea with high reliability, thus perfectly solving the communication blind zone problem in the near-field region of the acoustic field. Furthermore, the downlink blue-green light wave signal can provide directional guidance for air-to-sea downlink acoustic communication. Therefore, by using a dual-wavelength laser and photoacoustic receiver, air-to-sea cross-medium downlink communication can be achieved, solving the communication blind zone problem in the near-field region of the acoustic field when relying solely on laser-induced acoustic communication. This enables full-range air-to-sea downlink communication, improving the quality and reliability of air-to-sea downlink communication and reducing the packet loss rate.

[0039] The photoacoustic transmitter is used to emit uplink blue-green light wave signals and uplink acoustic wave signals towards the water surface; the uplink acoustic wave signal impacts the water surface, generating ripples; the uplink blue-green light wave signal is transmitted towards the water surface. The millimeter-wave radar is used to emit frequency-modulated continuous wave radio frequency signals towards the water surface to obtain echo signals from the ripples; that is, the millimeter-wave radar actively emits a radar electromagnetic beam to scan the water surface, and the radar electromagnetic beam modulates the ripple information on the water surface to form an echo signal, thereby achieving cross-medium uplink communication between sea and air. To further explain, in terms of uplink communication, traditional methods for measuring water surface ripples often employ Doppler vibration measurement. However, since water is a flowing medium, the reflected light received by Doppler equipment is weak, resulting in a high communication error rate. In contrast, millimeter-wave radar, with a wavelength range of 1mm-10mm, has higher frequency and resolution, better anti-interference capabilities, and can overcome the problem of water surface reflection. It has a natural advantage in detecting and tracking water surface ripples, offering high communication quality and a low error rate. Moreover, millimeter-wave radar can overcome the influence of weather conditions such as fog, rain, snow, and clouds, enabling all-weather detection, and its energy consumption and cost are both lower. Millimeter-wave radar also incorporates a built-in blue-green light detection unit. This unit receives uplink blue-green light signals and leverages the advantages of blue-green light transmission in air and sea to effectively achieve short-range (within the blue-green light attenuation radius) uplink communication between sea and air with high reliability. This creates redundant information for short-range sea-to-air uplink communication, serving as an effective supplement to improve its quality. Furthermore, the uplink blue-green light signal can provide directional guidance for sea-to-air uplink acoustic communication. Therefore, by combining millimeter-wave radar and photoacoustic transmitters, cross-medium sea-to-air uplink communication can be achieved, improving its quality and reducing error rates and packet loss rates.

[0040] The above illustrative embodiments, by setting up dual-wavelength lasers and millimeter-wave radars on airborne mobile platforms and photoacoustic receiving and transmitting devices on underwater mobile platforms, can realize two-way air-sea cross-medium communication based on photoacoustic fusion. They can also solve the communication blind zone problem in the near-field region of the sound field when relying solely on laser-induced acoustic communication, and can improve communication quality and reliability, reduce communication error rate and packet loss rate, providing a new approach for large-scale, highly reliable underwater communication.

[0041] In some embodiments, an airborne computer is also installed on the airborne maneuvering platform, and an underwater computer is also installed on the underwater maneuvering platform. The airborne computer is communicatively connected to a dual-wavelength laser to control the emission of the first and second laser beams; the airborne computer is also communicatively connected to a millimeter-wave radar to process the received echo signals and uplink blue-green light wave signals, and demodulates the sea-to-air uplink communication information through a demodulation module. The underwater computer is communicatively connected to an photoacoustic receiver to process the received downlink acoustic signals and downlink blue-green light wave signals, and demodulates the air-to-sea downlink communication information through a demodulation module; the underwater computer is also communicatively connected to an photoacoustic transmitter to control the emission of the uplink blue-green light wave signals and uplink acoustic signals.

[0042] In some embodiments, the photoacoustic emitting device includes a blue-green laser and a transmitting transducer. The blue-green laser emits an uplink blue-green light wave signal towards the water surface, and the transmitting transducer converts the mechanical wave into a sound wave to emit an uplink acoustic wave signal towards the water surface. The uplink acoustic wave signal impacts the water surface, generating ripples on the water surface. Further, the uplink blue-green light wave signal can serve as a direction guide for acoustic communication. When the uplink blue-green light wave signal is guided into the acoustic field range of the transmitting transducer, a millimeter-wave radar with a built-in blue-green light detection unit emits a frequency-modulated continuous wave radio frequency signal towards the water surface. After reflection from the water surface, an echo signal carrying ripple vibration information is obtained. The echo signal is then processed by an airborne computer to obtain the information transmitted by the uplink acoustic wave signal. When the millimeter-wave radar is within the blue-green light attenuation radius, the blue-green light detection unit receives the uplink blue-green light wave signal, and the airborne computer processes the signal to obtain the information transmitted by the uplink blue-green light wave signal. This process yields sea-to-air uplink communication information. The photoacoustic receiving device includes a blue-green light receiver and a receiving transducer; the receiving transducer is used to receive downlink acoustic wave signals, and then the underwater computer processes the signals to obtain the information transmitted by the downlink acoustic wave signals; the blue-green light receiver is used to receive downlink blue-green light wave signals, and then the underwater computer processes the signals to obtain the information transmitted by the downlink acoustic wave signals; thus, air-to-sea downlink communication information is obtained.

[0043] refer to Figure 1As shown, in some embodiments, the dual-wavelength laser includes two output ports for the emission of a first laser beam and a second laser beam, respectively. The aerial maneuvering platform is also equipped with a beam expander, a first reflector, and a long-focal-length focusing lens located on the emission path of the first laser beam. The first laser beam passes through the beam expander, the first reflector, and the long-focal-length focusing lens sequentially before entering the water and focusing at the water surface, causing a photoacoustic effect in the water medium and radiating a downward acoustic signal underwater, thus achieving laser-induced acoustic effects. The aerial maneuvering platform is also equipped with a second reflector located on the emission path of the second laser beam. After being reflected by the second reflector, the second laser beam directly penetrates the water surface and enters the water, transmitting a downward blue-green light wave signal underwater, thus achieving underwater transmission of the blue-green light wave across the air-sea interface.

[0044] In some embodiments, the airborne maneuvering platform is further equipped with a downlink communication encoding module. This module transmits four different repetition frequencies using a four-frequency BPSK signal modulation method to encode downlink communication information. An airborne computer communicates with the downlink communication encoding module to control a dual-wavelength laser based on the encoded downlink communication information. This laser emits a first laser beam and a second laser beam carrying the downlink encoded signal towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic wave signal carrying the downlink encoded signal. The underwater maneuvering platform is also equipped with an uplink communication encoding module. This module transmits four different repetition frequencies using a four-frequency BPSK signal modulation method to encode uplink communication information. An underwater computer communicates with the uplink communication encoding module to control a photoacoustic transmitting device based on the encoded uplink communication information. This device emits an uplink acoustic wave signal carrying the uplink encoded signal and an uplink blue-green light wave signal towards the water surface. The uplink acoustic wave signal impacts the water surface to generate ripples on the water surface carrying the uplink encoded signal.

[0045] refer to Figures 4-10 The following is a brief explanation of the four-frequency BPSK signal modulation process:

[0046] BPSK uses carrier phase changes to transmit information. The BPSK waveform can be represented as:

[0047] s(t)=Acos(2πf c t+πd k )

[0048] Where, d k The data to be transmitted is {0, 1}. BPSK modulation is achieved by changing the carrier phase. In BPSK modulation, binary data is encoded as a sequence of 0s and 1s, where 1 represents a 180-degree phase change in the sine wave, and 0 represents that the phase remains unchanged. Thus, phase changes in the modulated signal can transmit binary data. The process is as follows:

[0049] Modulation step one: Convert binary data into a 01 sequence;

[0050] Modulation step two: Generate a sinusoidal carrier signal with a fixed frequency;

[0051] Modulation step three: Multiply the 01 sequence with the carrier signal to obtain the modulated signal;

[0052] Modulation step four: Send the modulated signal.

[0053] BPSK demodulation is the process of converting the received modulated signal back into binary. The demodulator determines the 1s and 0s in the original data by detecting phase changes in the received signal, as follows:

[0054] Demodulation step one: Receive the modulated signal;

[0055] Demodulation step two: Generate a sinusoidal carrier signal with the same frequency as the transmitter;

[0056] Demodulation step three: Multiply the received signal with the carrier signal to obtain the demodulated signal;

[0057] Demodulation step four: Determine the 1s and 0s in the original data by detecting the phase change of the demodulated signal.

[0058] In marine communication channels, the theoretical bit error rate of BPSK is:

[0059]

[0060] Compared to the previous 2FSK modulation method, the four-frequency BPSK signal modulation method in this embodiment improves the effective utilization rate of communication codes and shortens the transmission time of communication coding units while ensuring normal code transmission. Furthermore, for dual-wavelength lasers, the presence or absence of laser pulses is represented as binary codes. This modulation method avoids the risk of signal decryption errors caused by the underwater photoacoustic receiver not receiving signals due to different locations. It has advantages such as high bandwidth efficiency, strong anti-interference ability, high reliability, and easy detection.

[0061] In some embodiments, the dual-wavelength laser has a built-in modulator located in the optical path outside the resonant cavity of the dual-wavelength laser. When the laser beam emitted by the dual-wavelength laser passes through the modulator, the modulator changes the amplitude, phase and frequency of the laser beam by modulating the voltage to obtain a first laser beam and a second laser beam carrying downlink coded signals.

[0062] refer to Figures 1-10As shown, this invention also provides a two-way air-sea cross-medium communication method based on photoacoustic fusion, employing the aforementioned two-way air-sea cross-medium communication system based on photoacoustic fusion, including an air-to-sea downlink communication step and a sea-to-air uplink communication step. It is understood that in the air-to-sea downlink communication step, the airborne mobile platform is the sender of downlink communication information, and the underwater mobile platform is the receiver of downlink communication information; in the sea-to-air uplink communication step, the underwater mobile platform is the sender of uplink communication information, and the airborne mobile platform is the receiver of uplink communication information.

[0063] The specific steps of air-to-sea downlink communication are as follows: The downlink communication encoding module encodes the downlink communication information based on a four-frequency BPSK signal modulation method to obtain the encoded downlink communication information. The airborne computer then controls a dual-wavelength laser to emit a first laser beam with a wavelength of 1064nm and a second laser beam with a wavelength of 532nm towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic signal, which is received by a transducer, thus establishing an air-to-sea downlink acoustic channel. The second laser beam directly penetrates the water surface and transmits a downlink blue-green light wave signal underwater, which is received by a blue-green light receiver, thus establishing an air-to-sea downlink optical channel. As can be seen, the air-to-sea downlink acoustic channel and the air-to-sea downlink optical channel operate independently and do not affect each other. Both are directly connected or without repeaters, thereby improving communication convenience, efficiency, and timeliness. The photoacoustic receiving device transmits the received downlink acoustic signal and downlink blue-green light wave signal to an underwater computer for demodulation, obtaining the demodulated downlink communication information and completing the air-to-sea downlink communication.

[0064] When air-to-sea downlink communication steps are applied to short-range air-to-sea downlink communication, a hybrid optical-acoustic communication method is adopted. This means that two carriers are used simultaneously for information transmission. Downlink blue-green light wave signals and downlink acoustic wave signals are used as carriers to complete downlink data transmission services within the blue-green light attenuation radius. Furthermore, it can be understood that the blue-green light attenuation radius is far beyond the range of the near-field zone of the acoustic field in laser-induced acoustic communication. Therefore, within the near-field zone of the acoustic field, the results of downlink blue-green light wave communication are taken as the standard, while the results of downlink acoustic wave communication are only for reference. Outside the near-field zone of the acoustic field but within the blue-green light attenuation radius, the results of downlink blue-green light wave communication and downlink acoustic wave communication are used to form redundant information for short-range air-to-sea downlink communication. A redundancy information mutual verification mechanism can be adopted to reduce the packet loss rate and bit error rate of short-range air-to-sea downlink communication, thereby improving the quality of short-range air-to-sea downlink communication. When the air-to-sea downlink communication steps are applied to medium- and long-distance air-to-sea downlink communication, downlink data transmission services are completed with downlink acoustic signals as carriers, oriented towards areas outside the attenuation radius of blue-green light; the downlink blue-green light wave signals also play a directional guiding role in air-to-sea downlink acoustic communication.

[0065] The specific steps of sea-to-air uplink communication are as follows: The uplink communication encoding module encodes the uplink communication information based on a four-frequency BPSK signal modulation method to obtain the encoded uplink communication information. The underwater computer then controls the transmitting transducer and the blue-green laser to transmit uplink acoustic signals and uplink blue-green light signals to the water surface, respectively. The uplink acoustic signals impact the water surface, generating ripples. The millimeter-wave radar transmits frequency-modulated continuous wave radio frequency signals to the water surface to obtain the echo signals of the ripples, thus realizing the sea-to-air uplink acoustic channel. The uplink blue-green light wave signal is received by the blue-green light detection unit in the millimeter-wave radar, realizing the establishment of the sea-to-air uplink optical channel. It can be seen that the sea-to-air uplink acoustic channel and the sea-to-air uplink optical channel operate independently and do not affect each other. Both are directly connected or without relays, thereby improving the convenience, efficiency and timeliness of communication. The millimeter-wave radar transmits the obtained echo signal and uplink blue-green light wave signal to the airborne computer for demodulation, and obtains the demodulated uplink communication information, completing the sea-to-air uplink communication.

[0066] When the sea-to-air uplink communication steps are applied to short-range sea-to-air uplink communication, a hybrid optical-acoustic communication method is used. This involves simultaneously transmitting information using two carriers: uplink blue-green optical signals and uplink acoustic signals. Uplink data transmission within the blue-green light attenuation radius is completed using both carriers. The results of the uplink blue-green optical and acoustic communication form redundant information for short-range sea-to-air uplink communication. A redundancy information mutual verification mechanism can be used to reduce packet loss and bit error rates, thereby improving the quality of short-range sea-to-air uplink communication. When the sea-to-air uplink communication steps are applied to long-range sea-to-air uplink communication, the uplink acoustic signal is used as the carrier to complete uplink data transmission outside the blue-green light attenuation radius. The uplink blue-green optical signal also provides directional guidance for the sea-to-air uplink acoustic communication.

[0067] The above illustrative embodiments utilize photoacoustic fusion communication to achieve bidirectional air-sea cross-medium communication, solving the communication blind zone problem in the near-field region of the sound field when relying solely on laser-induced acoustic communication, improving the quality and reliability of bidirectional air-sea cross-medium communication, and reducing the communication error rate and packet loss rate.

[0068] In some embodiments, during short-range air-to-sea downlink communication, the optical carrier information carried by the downlink blue-green light wave signal and the acoustic carrier information carried by the downlink acoustic wave signal undergo mutual verification. During short-range sea-to-air uplink communication, the optical carrier information carried by the uplink blue-green light wave signal and the acoustic carrier information carried by the uplink acoustic wave signal undergo mutual verification. The mutual verification operation compares the two sets of information, confirms bit errors and packet loss, and verifies the final generated plaintext. When the sender compiles the same information onto the optical and acoustic carriers, the mutual verification operation performs packet loss and bit error checks to minimize the packet loss rate and bit error rate. When the sender modulates different information—that is, different fragments of the same information, the ciphertext and key of the same information, or the plaintext and checksum of the same information—on the optical and acoustic carriers, the mutual verification operation performs data restoration. This illustrative embodiment improves the reliability of short-range two-way air-to-sea cross-medium communication and reduces the packet loss rate and bit error rate through mutual verification.

[0069] In some embodiments, when the downlink blue-green light wave signal is used as the carrier, the transmitter and receiver are connected via an air-to-sea downlink optical channel, using the same operating wavelength, communication protocol, and encryption scheme; when the uplink blue-green light wave signal is used as the carrier, the transmitter and receiver are connected via a sea-to-air uplink optical channel, using the same operating wavelength, communication protocol, and encryption scheme. It is understood that the system architecture includes, but is not limited to, light sources, modulators, filters, amplifiers, demodulators, weak signal detectors, tracking and aiming systems, etc., and is not limited to specific operating wavelengths, communication protocols, industry standards, or mounting platforms.

[0070] In some embodiments, when either the downlink or uplink blue-green light wave signal is used as the carrier, data transmission services within the blue-green light attenuation radius are completed through precise tracking, communication signal transmission, and weak signal analysis. When the downlink acoustic wave signal is used as the carrier, downlink data transmission services are completed through laser amplification, acoustic signal monitoring, and waveform analysis; when the uplink acoustic wave signal is used as the carrier, uplink data transmission services are completed through mechanical transduction amplification, water surface ripple signal detection, and waveform analysis.

[0071] In summary, the air-sea cross-medium bidirectional communication system and method based on photoacoustic fusion of the present invention realizes air-sea cross-medium bidirectional communication based on photoacoustic fusion by setting up a dual-wavelength laser and millimeter-wave radar on an airborne mobile platform and a photoacoustic receiving device and a photoacoustic transmitting device on an underwater mobile platform. It solves the communication blind zone problem in the near-field area of ​​the sound field when relying solely on laser-induced acoustic communication, improves the quality and reliability of air-sea cross-medium bidirectional communication, and reduces the communication error rate and packet loss rate, providing a new approach for large-scale, highly reliable underwater communication.

[0072] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A two-way air-sea communication system based on optical-acoustic fusion, characterized in that, This includes aerial mobile platforms located on the sea surface, underwater mobile platforms located in the seawater, dual-wavelength lasers and millimeter-wave radars mounted on the aerial mobile platforms, and photoacoustic receiving and transmitting devices mounted on the underwater mobile platforms; among them, The dual-wavelength laser is used to emit a first laser beam with a wavelength of 1064nm and a second laser beam with a wavelength of 532nm towards the water surface; the first laser beam enters the water and is focused on the water surface, causing the water medium to produce a photoacoustic effect and radiating a downward acoustic signal underwater; the second laser beam directly penetrates the water surface and enters the water underwater, transmitting a downward blue-green light wave signal underwater. The photoacoustic receiving device is used to receive the downlink acoustic signal and the downlink blue-green light wave signal; The photoacoustic emitting device is used to emit upward blue-green light wave signals and upward acoustic wave signals to the water surface. The upward acoustic wave signals hit the water surface and generate ripples on the water surface. The millimeter-wave radar is used to transmit frequency-modulated continuous wave radio frequency signals to the water surface to obtain the echo signal of the microwave ripples on the water surface; the millimeter-wave radar also has a built-in blue-green light detection unit for receiving the uplink blue-green light wave signal.

2. The air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to claim 1, characterized in that, The aerial mobile platform is also equipped with an airborne computer, and the underwater mobile platform is also equipped with an underwater computer. The airborne computer is communicatively connected to a dual-wavelength laser to control the emission of the first and second laser beams. The airborne computer is communicatively connected to a millimeter-wave radar to process the echo signals and uplink blue-green light wave signals it receives. The underwater computer is communicatively connected to a photoacoustic receiver to process the downlink acoustic signals and downlink blue-green light wave signals it receives. The underwater computer is communicatively connected to the photoacoustic transmitting device to regulate the transmission of uplink blue-green light wave signals and uplink acoustic wave signals.

3. The air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to claim 2, wherein the photoacoustic transmitting device includes a blue-green laser and a transmitting transducer, the blue-green laser being used to transmit uplink blue-green light wave signals to the water surface, and the transmitting transducer being used to convert mechanical waves into sound waves to transmit uplink sound wave signals to the water surface; the photoacoustic receiving device includes a blue-green light receiver and a receiving transducer, the blue-green light receiver being used to receive downlink blue-green light wave signals, and the receiving transducer being used to receive downlink sound wave signals.

4. The air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to claim 2, characterized in that, The dual-wavelength laser includes two output ports for the emission of the first laser beam and the second laser beam, respectively. The aerial maneuvering platform is also equipped with a beam expander, a first reflector, and a long focal length focusing lens located on the output optical path of the first laser beam. The first laser beam passes through the beam expander, the first reflector, and the long focal length focusing lens in sequence before entering the water and focusing on the water surface to radiate a downward acoustic signal underwater. The aerial maneuvering platform is also equipped with a second reflector located on the output optical path of the second laser beam. The second laser beam passes through the second reflector and directly penetrates the water surface to enter the underwater environment to radiate a downward blue-green light wave signal underwater.

5. The air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to claim 3, characterized in that, The aerial maneuvering platform is also equipped with a downlink communication encoding module. This module uses a four-frequency BPSK signal modulation method to transmit four different repetition frequencies to encode downlink communication information. The aerial computer is connected to the downlink communication encoding module to control a dual-wavelength laser based on the encoded downlink communication information. This causes the laser to emit a first laser beam and a second laser beam carrying the downlink encoded signal towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic wave signal carrying the downlink encoded signal. The underwater maneuvering platform is also equipped with an uplink communication encoding module. This module uses a four-frequency BPSK signal modulation method to transmit four different repetition frequencies to encode uplink communication information. The underwater computer is connected to the uplink communication encoding module to control a photoacoustic transmitting device based on the encoded uplink communication information. This device emits an uplink acoustic wave signal and an uplink blue-green light wave signal carrying the uplink encoded signal towards the water surface. The uplink acoustic wave signal impacts the water surface to generate ripples on the water surface carrying the uplink encoded signal.

6. The air-sea cross-medium bidirectional communication system based on photoacoustic fusion according to claim 5, characterized in that, The dual-wavelength laser has a built-in modulator located in the optical path outside the resonant cavity of the dual-wavelength laser. When the laser beam emitted by the dual-wavelength laser passes through the modulator, the modulator changes the amplitude, phase and frequency of the laser beam by modulating the voltage to obtain a first laser beam and a second laser beam carrying downlink encoded signals.

7. A method for bidirectional air-sea communication across media based on optical-acoustic fusion, characterized in that, The air-sea cross-medium bidirectional communication system based on optical-acoustic fusion as described in claim 5 is used, including the following steps: The air-to-sea downlink communication steps are as follows: The downlink communication encoding module encodes the downlink communication information based on a four-frequency BPSK signal modulation method to obtain the encoded downlink communication information. The airborne computer then controls a dual-wavelength laser to emit a first laser beam with a wavelength of 1064nm and a second laser beam with a wavelength of 532nm towards the water surface. The first laser beam penetrates the water surface to generate a downlink acoustic signal, which is received by a transducer, thus establishing an air-to-sea downlink acoustic channel. The second laser beam directly penetrates the water surface and transmits a downlink blue-green light wave signal underwater, which is received by a blue-green light receiver, thus establishing an air-to-sea downlink optical channel. The photoacoustic receiving device transmits the received downlink acoustic signal and downlink blue-green light wave signal to an underwater computer for demodulation, obtaining demodulated downlink communication information and completing air-to-sea downlink communication. When the air-to-sea downlink communication step is applied to short-range air-to-sea downlink communication, downlink data transmission services within the blue-green light attenuation radius are completed using downlink blue-green light wave signals and downlink acoustic signals as carriers, respectively. When the air-to-sea downlink communication step is applied to medium-to-long-range air-to-sea downlink communication, downlink data transmission services outside the blue-green light attenuation radius are completed using downlink acoustic signals as carriers. The downlink blue-green light wave signal also plays a directional guiding role in air-to-sea downlink acoustic communication. The sea-to-air uplink communication process is as follows: The uplink communication encoding module encodes the uplink communication information based on a four-frequency BPSK signal modulation method to obtain the encoded uplink communication information. The underwater computer then controls the transmitting transducer and the blue-green laser to transmit uplink acoustic signals and uplink blue-green light wave signals to the water surface, respectively. The uplink acoustic signals impact the water surface, generating surface ripples. The millimeter-wave radar transmits frequency-modulated continuous wave radio frequency signals to the water surface to obtain the echo signals of the surface ripples, thus establishing the sea-to-air uplink acoustic channel. The uplink blue-green light wave signals are received by the blue-green light detection unit in the millimeter-wave radar, thus establishing the sea-to-air uplink optical channel. The millimeter-wave radar transmits the acquired echo signal and uplink blue-green light wave signal to an airborne computer for demodulation, obtaining the demodulated uplink communication information and completing the sea-to-air uplink communication. When the sea-to-air uplink communication step is applied to short-range sea-to-air uplink communication, the uplink blue-green light wave signal and the uplink acoustic wave signal are used as carriers to complete the uplink data transmission service within the blue-green light attenuation radius, respectively. When the sea-to-air uplink communication step is applied to long-range sea-to-air uplink communication, the uplink acoustic wave signal is used as the carrier to complete the uplink data transmission service outside the blue-green light attenuation radius. The uplink blue-green light wave signal also plays a directional guidance role in sea-to-air uplink acoustic wave communication.

8. The air-sea cross-medium bidirectional communication method based on photoacoustic fusion according to claim 7, characterized in that, During short-range air-to-sea downlink communication, the optical carrier information carried by the downlink blue-green light wave signal and the acoustic carrier information carried by the downlink acoustic wave signal undergo mutual verification. During short-range sea-to-air uplink communication, the optical carrier information carried by the uplink blue-green light wave signal and the acoustic carrier information carried by the uplink acoustic wave signal undergo mutual verification. When the sender encodes the same information onto the optical carrier and acoustic carrier, the mutual verification operation is used to perform packet loss and bit error checking to minimize the packet loss rate and bit error rate. When the sender modulates different information onto the optical carrier and acoustic carrier, the mutual verification operation is used to perform data restoration.

9. The air-sea cross-medium bidirectional communication method based on photoacoustic fusion according to claim 7, characterized in that, When the downlink blue-green light wave signal is used as the carrier, the sender and receiver are connected through an air-to-sea downlink optical channel and use the same operating wavelength, communication protocol and encryption scheme; when the uplink blue-green light wave signal is used as the carrier, the sender and receiver are connected through a sea-to-air uplink optical channel and use the same operating wavelength, communication protocol and encryption scheme.

10. The air-sea cross-medium bidirectional communication method based on photoacoustic fusion according to claim 7, characterized in that, When either the downlink or uplink blue-green light wave signal is used as the carrier, data transmission services within the blue-green light attenuation radius are completed through precise tracking, communication signal transmission, and weak signal analysis.

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