JP7739677B2 - Underwater communication systems and devices - Google Patents

Description

The present invention relates to a communication system or device for performing mutual communication in water such as seawater or a swimming pool, or for performing communication between underwater and abovewater.

Ultrasonic communication is primarily used as a wireless communication system for transmitting voice, images, data, etc. in fresh water, such as a swimming pool, or in seawater (hereinafter referred to as "underwater"). This is because electromagnetic waves are absorbed by water or seawater, resulting in severe radio wave attenuation in radio wave and current communications. Radio wave attenuation in water is approximately 1 dB/m at low frequencies, but the attenuation increases as the frequency increases. For example, at 100 MHz, the attenuation is known to be approximately 200 dB/m in fresh water and approximately 300 dB/m in seawater, limiting high-frequency communications to extremely short distances. However, while ultrasonic communication can ensure a certain transmission distance for radio waves (ultrasound), its data transmission performance is low. Currently used sonars and other similar systems have an average transmission rate of 100 Kbps or less, making them unsuitable for real-time video transmission, for example.

Most underwater video and image transmissions use wired cables rather than wireless communication to transmit video, audio, and various control signals between the transmitter of the underwater camera or search device and the receiver on the surface. However, such wired cable communication has drawbacks, such as the cable restricting the movement of the underwater search device and diver, making it difficult to move freely. In addition, there are problems with cable entanglement and cable connection failure, so there is a demand for wireless transmission of video, audio, and control signals.

To address these issues, Patent Document 1 discloses a technology for transmitting large volumes of data, such as video, underwater using laser light. While laser light communication has little light scattering during high-frequency transmission, enabling broadband, high-capacity communication, the strong directionality and convergence of single-wavelength coherent light necessitates pinpoint transmission and reception in underwater communications. While this laser light communication requires both the transmitter and receiver to be fixed, it is difficult to fix the underwater communication device and the communication device on a vessel or other surface at sea. Patent Document 1 therefore uses a movable optical lens to diffuse the laser light, allowing a certain degree of freedom in the range of motion of the transmitter and receiver. However, this movable optical lens is a special lens, which poses design challenges and is therefore unsatisfactory.

Furthermore, since the directivity and convergence of laser light are difficult points for underwater communications, a technology that uses diverging light rays is disclosed in Patent Document 2. Although the use of diverging light ensures greater freedom in transmission and reception irradiation compared to laser light, it only allows for slight misalignment of the optical axes of the transmitter and receiver, making it unsuitable for divers or explorers to communicate while taking videos or the like underwater.

Patent Document 3 also discloses an underwater communication technology using resonance communication as another method. This resonance communication requires a resonance coil for mutual communication between transmitter and receiver, which has drawbacks such as being large-scale and requiring large amounts of power. Furthermore, this method also requires that the transmitter and receiver devices be coaxial with each other, which limits the free movement area of divers and others underwater.

All of these methods either limit the freedom of underwater activity or are unsatisfactory in terms of communication speed and capacity, so there is a demand for more reliable, high-capacity, high-speed wireless communication, and in particular, there is a need for improvements in underwater communication systems that can smoothly transmit data signals such as video, audio, and control signals via wireless communication.

JP 2009-55408 A JP 2013-211731 A Japanese Patent Application Laid-Open No. 2019-176316

The present invention has been made in view of the above circumstances, and has an object to provide the following underwater wireless communication device and system.
(1) Underwater wireless communication device and system that can perform wireless communication between underwater and above water surface and wireless communication between underwater moving bodies more reliably. (2) Device and system that can transmit and receive large amounts of data at higher speeds in underwater wireless communication.

In order to solve the above-mentioned problems, the underwater communication system of the present invention is a communication means between a plurality of floats floating on the water surface and an underwater mobile body, wherein a float-side transceiver device is installed on the float, and the float-side transceiver device is connected to a control center or another float-side transceiver device by wire or wirelessly, the plurality of floats can be freely connected and detached from each other and can be expanded according to the range of movement of the underwater mobile body, and the underwater mobile body is installed with a mobile-side transceiver device facing the float, and is configured to perform optical communication including visible light communication or laser light communication with the float-side transceiver device.

In addition, this underwater wireless communication system can be configured so that the multiple float-side transceivers can communicate with the float-side transceiver that transmits the strongest signal from the mobile-side transceiver.

In addition, this underwater wireless communication system can also be configured so that the mobile-side transceiver device is placed near the diver or near a camera or audio microphone owned by the diver, and is controlled to maintain horizontal movement using a direction control device with a gravity gyrocompass.

In addition, this underwater wireless communication system can be configured so that video signals, audio signals, or data signals from the underwater vehicle are relayed through the vehicle-side transceiver device possessed by the underwater vehicle or the diver, and communicated with the float-side transceiver device or another vehicle-side transceiver device.

According to the present invention, by arranging a plurality of detachably connected surface floats in an area covering the underwater moving body, an appropriate communication range with the underwater moving body can be secured, and more reliable wireless communication can be achieved using optical communication such as visible light communication or laser light communication. In addition, the float-side transmitting/receiving device and the underwater moving body-side transmitting/receiving device can be equipped with parabolic antennas to improve reception sensitivity, and a gyrocompass can be used to control the transmitting and receiving directions of the transmitting and receiving devices to the appropriate direction, thereby enabling more reliable communication.

1 is an explanatory diagram showing the configuration of a communication system for an underwater moving body according to the present invention; 1 is an explanatory diagram showing an example of an underwater vehicle drone according to the present invention. FIG. 1 is a block diagram illustrating an example of the configuration of an underwater communication system according to the present invention. 1 is an explanatory diagram showing an example of an expanded configuration of a float according to the present invention. FIG. 3 is an explanatory diagram showing an example of the configuration of a direction control means according to the present invention; FIG. 1 is an explanatory diagram showing an example of the configuration of a receiving parabolic reflector according to the present invention; 1 is an explanatory diagram showing an example of the configuration of a receiving offset parabolic reflector according to the present invention;

Hereinafter, embodiments of a communication device and system for communication with an underwater vehicle according to the present invention will be described in detail with reference to the drawings. Note that any explanatory diagrams and drawings described in the following examples are drawn as outlines or schematic diagrams for the purpose of explaining the present invention, and the actual dimensions and shapes are not particularly limited. Furthermore, the system configuration, dimensions, materials, shapes, relative positions, and use examples used in the examples are not intended to limit the technical scope of the invention to those alone, unless otherwise specified.

FIG. 1 is an explanatory diagram showing the configuration of a communication system for underwater vehicles according to the present invention. A float (floating body) 1 is placed on the water surface and is equipped with a transceiver 2 for optical communication. The float 1 has multiple transceivers 2, each equipped with a transmitting element 3 and a receiving element 4, built into its underwater side. Each transceiver 2 transmits and receives signals using the transmitting element 3 and the receiving element 4, and is also equipped with an antenna 5 for wireless communication with a control center, such as a base station on land or on the water (on a ship), or with other float-side transceivers. Because communication between this float-side transceiver and the control center or other float-side transceivers is performed on the water surface, any broadband wireless or wired communication, not limited to optical communication, can be used.

The float 1 is connected to a fixed object or a vessel 20 on the water by passing a connecting buoy rope 6 through a perforated buoy, and is configured to be moored in a predetermined position by an anchor buoy 7. It is possible to prepare a plurality of such floats 1 and connect and expand them, or they may be connected to each other by the connecting buoy rope 6. A solar panel 22 is also installed on the float 1 for power supply. For short-term use, it is sufficient to power the float with a battery built into each transmitter/receiver, and the solar panel 22 may be installed as needed.

Underwater, a diver 8 and a camera 9 operated by the diver are positioned below multiple floats 1, and an underwater drone 10 is located near the diver, exploring or swimming underwater. The underwater drone 10 is equipped with a transmitter/receiver 11, with its transmitter element 12 and receiver element 13 located exposed on the top of the underwater drone 10 and facing toward the water surface. Figure 2 shows the underwater drone 10 from the front, and the drone can be propelled up, down, left, and right by controlling four propeller fans 14, 15, 16, and 17. The drone is also equipped with a horizontal stabilizer 18 to ensure stable horizontal movement. The underwater drone 10 is equipped with the transmitter/receiver 11, and the transmitter element 12 and receiver element 13 are located on the top of the drone 10 body.

The transmitting/receiving device (mobile-side transmitting/receiving device) 11 and transmitting/receiving elements 12, 13 are controlled by a direction control means 30 so that signals can be constantly transmitted upward even while the underwater drone 10 is moving. This direction control means 30 is performed by gyrocompass direction control, as will be described in detail later. A drone camera 19 is installed on the front of the drone 10 so that underwater images can be transmitted upward (to the water surface) from the drone-side transmitting/receiving device 11. This drone camera 19 is controlled by a data signal from a base station or center using the underwater communication system of the present invention.

In addition, image signals captured by the camera 9 owned by the diver 8, audio signals from the diver, and data signals such as the diver's vital signs can be sent to the transceiver 11 of the drone 10 via a short-range communication device installed in the camera 9 or on the diver's back, and then transmitted to the transceiver 2 on the float on the water via the transceiver 11 of the drone 10. Possible short-range communication devices in this case include Bluetooth and Wi-Fi (registered trademark), but this is limited to when the drone 10 and the diver camera 9 are located close to each other. For this reason, it is desirable to install a transceiver on the drone 10 above the camera 9 owned by the diver 8 so that the transceiver can communicate directly with the transceiver 2 on the float 1.

Here, in order for the float-side transmitter/receiver (float-side transmitter/receiver) 2 and the drone-side transmitter/receiver (mobile-side transmitter/receiver) 11 to transmit (transmit and receive) signals such as video, audio, and data, a bandwidth and transmission speed sufficient for transmitting video signals is required. In underwater communications, as mentioned above, electromagnetic radio wave communication has a high degree of attenuation, making radio wave transmission over a distance of several meters more difficult, especially at higher frequencies, and is therefore not suitable for transmitting video signals. Therefore, optical communications such as visible light communications or laser light communications, which enable large-capacity communications and high transmission speeds, are used.

When using visible light communication, the development of silicon photodiodes (Si-PDs), avalanche photodiodes (APDs), silicon photomultipliers (Si-PMs), and other light-receiving elements has increased the light sensitivity to detect ultra-weak light at the photon level, making communication possible even with extremely weak light levels as long as visible light is available on the transmitting side. It is also known that carrier-band transmission using visible light can achieve high-speed transmissions of up to several hundred Mbps, and high-speed (several hundred Mbps) and highly sensitive (long-distance) communication is possible even underwater, provided there are no obstacles, debris, or turbidity that block the light.

A possible configuration for visible light communication is a visible light transceiver as shown in the block circuit of Fig. 3. This type of visible light transceiver is similar on both the float side and the mobile body side, and signals transmitted from the float side include control signals (data signals) for the drone 10 underwater and audio signals for conversation with the diver 8, while signals transmitted from the mobile body side include underwater video and audio signals and data signals such as the diver's vital signs.

Input signals 31, such as video, audio, and data control signals from the transmitting side, are sent to received data processing means 33 via interface means (or input/output means) 32. The interface means 32 can be a variety of interfaces depending on the type of input signal, such as USB (Universal Serial Bus), Ethernet, HDMI (High Definition Multimedia Interface), or SDI (Serial Digital Interface), and performs signal processing in accordance with these input signals. The received data processing means 33 packetizes the input signal using a framing circuit and provides it to modulation means 34, which then modulates it using a carrier wave. This modulation method can be any method, such as QAM (Quadrature Amplitude Modulation), QSPK (Quadrature Phase Shift Keying), or OFDM (Orthogonal Frequency Division Multiplexing), or a combination thereof.

The data signal modulated by the modulation means 34 is converted to analog by a DA conversion means 35 and superimposed on an LED light emission signal by a dimming control means 36 and an LED driving means 37, which drive an LED (Light Emitting Diode), a visible light communication transmitting element, and transmitted from a light emitting element (LED) 38. The LED light emission frequency is preferably around 500 nm. This is because the higher the frequency, the greater the light absorption by water molecules, particularly at wavelengths longer than 600 nm. In the case of seawater, for example, the absorption characteristics of microorganisms, plankton, turbid water, etc. affect the signal, so a wavelength band of 500 nm (green-blue) is selected in consideration of absorption in the short wavelength band at 400 nm.

The modulated signal superimposed on the LED light emission signal is transmitted from a light emitting element (LED) 38 and received by an opposing light receiving element 39. As mentioned above, Si-PD, APD, Si-PM, etc. can be used for the light receiving element 39, but by selecting an element having high sensitivity characteristics in the vicinity of 500 nm, which is the emission frequency of the light emitting element 38, and using an APD array element in which multiple APDs are arranged side by side, it is known that it is possible to detect weak light with an irradiance of about 10 ⁻¹⁶ W/mm ² (equivalent to 10 ⁻⁶ to 10 ⁻⁸ lx), and reception with an extremely good noise ratio (S/N ratio) can be achieved.

The modulated signal received by the light receiving element 39 is extracted by signal extraction means 40, which is composed of a filter, amplified by an RF amplifier 41, band equalized, converted to digital form by an A-D conversion means 42, and sent to demodulation means 43. The demodulation means 43 demodulates the signal according to the modulation method (QAM, QSPK, OFDM, etc.) used by the transmitting device, and extracts a data signal. The extracted data signal is processed by data processing means 44 to correspond to the video, audio, or data format to be reproduced, and is provided to interface 45. The interface 45 is provided with interface circuits and terminals corresponding to terminal devices such as a monitor display, television receiver, speaker, and PC, and provides an output signal to output means 46.

In each block in FIG. 3, signal processing for transmitting and receiving digital signals, modulation and demodulation means, interface means, etc. is performed by a CPU, memory, registers, etc., but these are not shown here along with the power supply circuit.

A plurality of transmitter/receivers 2 as described above are arranged in cooperation on the float 1 side, and signals received by any of the float-side transmitter/receivers are transmitted by wireless or wired communication to a control center such as a base station on land or on water (on a ship) via antenna 5. The base station or control center outputs the received video, audio, or data signals on a video monitor, audio player, recorder, computer, etc., and transmits the video, audio, and data signals from the base station side to the mobile body-side transmitter/receiver 11 via antenna 5 and float-side transmitter/receiver 2.

To utilize the underwater communication of the present invention, the float 1 is arranged to cover as much of the movement range of the drone 10 or diver 8 as possible. Multiple float-side transceivers 2 are installed on the float 1, so that any of the float-side transceivers 2 can receive signals from the mobile-body transceiver 11 even while the mobile body is moving around. In this case, only the float-side transceiver 2 with the highest reception sensitivity can function as a receiver, or the received signals of multiple float-side transceivers 2 that receive signals from the mobile-body transceiver 11 can be combined and used. The method to be used can be switched based on the reception environment and noise level.

It is also possible to connect multiple floats each equipped with multiple transmitter/receivers to extend the range of movement of drones, divers, and other mobile objects. Figure 4 is an explanatory diagram showing an example of an expanded configuration of a float according to the present invention. Four float-side transmitter/receivers 51, 52, 53, and 54 are arranged on a float 50, each equipped with a transmitter element 3 and a receiver element 4 facing the water surface. The approximately square float 50 is provided with connecting means 55 on all four sides so that the floats can be connected and expanded. These connecting means 55 may be capable of directly fitting the floats together or may be capable of connecting them at a certain distance, like a float buoy. Regardless of the connecting means, several floats each equipped with multiple transmitter/receivers can be connected to each other depending on the range of movement of the mobile object, such as a drone or diver, to expand the range of movement and enable communication with underwater mobile objects. Figure 4 shows how multiple such floats 56, 57, and 58 are connected to form an expanded float combination 59.

When the float combination unit 59 is used in a pool or the like, it is connected to a fixed object with the buoy rope 6 in Fig. 1 and secured to an anchor buoy 7 or the like. When it is used for underwater exploration or communication with divers, it is moved to an exploration point or diving point by boat or ship, and floats are combined to form the float combination unit 59 so as to cover the range of movement of the underwater mobile object, which is an underwater drone or diver, and it is moored to the boat or the like for use.

The underwater drone 10, which is a mobile body, receives drone control signals as data signals from a base station or control center to control the course, direction, speed, etc. of the underwater drone 10. These data signals can also be used as control signals for attitude control and image capture control of the photographic camera attached to the drone 10. The underwater drone 10 basically maintains horizontal movement so that it can communicate with the float 1 or float combination 59 on the water. However, it is not always horizontal during movement, and the light-emitting element 12 and light-receiving element 13 of the drone-side transmitter/receiver device 11 are not necessarily pointed toward the float 1 or float combination 59. Therefore, the mobile-side transmitter/receiver device 11 is equipped with direction control means 30, which controls the transmitter/receiver elements 12 and 13 to always point upward or in a specified direction.

FIG. 5 is an explanatory diagram showing an example configuration of the direction control means 30. Direction control and direction detection utilize a gyrocompass 61. The gyro moment of the gyroscope in the gyrocompass 61 is used to detect the X-axis (horizontal) or Y-axis (vertical) direction relative to the geomagnetic field. The X-axis tilt detection circuit 62 and the Y-axis tilt detection circuit 63 convert the degree of directional tilt relative to the geomagnetic field into electrical signals, which are then sent as X-axis and Y-axis control signals to the X-axis (horizontal) correction drive circuit 64 and the Y-axis (vertical) correction drive circuit 65. Each drive circuit drives the X-axis control micromotor 66 and the Y-axis control micromotor 67 to control the direction control plate 68 so that it always faces a specific direction (horizontal). The direction control plate 68 engages with a yoke member 69 and is controlled in the X-axis direction by the X-axis micromotor 66, while the Y-axis micromotor 67 engages with the yoke member 69 and controls the Y-axis direction.

The transmitting/receiving device 11 on the mobile body is engaged with the direction control plate 68, and can always orient the transmitting/receiving elements (light emitting element 12 and light receiving element 13) horizontally or in a predetermined direction toward the float 1 and float combination 59, even while the mobile drone 10 is moving. In addition, such directional tilt detection by the gyrocompass can be used for attitude control and automatic horizontal movement of the underwater drone 10, or can be applied to maintaining the shooting direction of the camera 19 mounted on the underwater drone 10 or preventing vibration and camera shake, or can be used for both purposes.

The underwater communication in the above-described first embodiment assumes visible light communication using LEDs as light-emitting elements, and in this method, 16QAM modulation enables transmission and reception of video signals at a bandwidth of 100 Mbps at distances of 50 m or more in fresh water such as a pool. To extend the underwater movement range or increase the communication distance, more float combinations 59 in the first embodiment are required, and a larger number of transmitter/receivers 2 or transmitter elements 3 and receiver elements 4 are required. Therefore, in the second embodiment, a transmitter/receiver system is provided that covers a wide area with fewer transmitter/receivers.

In the second embodiment, a parabolic reflector is used to focus light over a wider area onto the light receiving element 4, which is the receiving element. Fig. 6 is an explanatory diagram showing an example of the configuration of the receiving parabolic reflector used in four transmitting and receiving devices 71, 72, 73, and 74 on a float 70. The transmitting element (light emitting element) 75 of the float 70 is disposed in the center of the float 70, and the receiving element (light receiving element) 76 of the receiving device 71 inside the float 70 is disposed at the focal point of a parabolic reflector 77. The other receiving devices 72, 73, and 74 have the same configuration as the receiving device 71, and each have a parabolic reflector and a receiving element (light receiving element) at its focal point.

Figure 7 shows a cross-sectional view of the parabolic reflector 77. The parabolic shape has an offset axis, allowing for a wider range of light reception and a thinner configuration. The light receiving element 76 is located at the focus of the offset parabolic shape and collects and captures the received light captured by the reflecting mirror surface 77. By using such a parabolic reflector, it is possible to replace the number of light receiving elements corresponding to the size and surface of the parabola with a single light receiving element. Furthermore, such a parabolic reflector allows for pinpoint transmission and reception, and allows for maintaining reception sensitivity even when the light reception range changes, making it possible to construct an underwater visible light system that is resistant to communication interruptions.

Furthermore, by installing a receiver using this parabolic reflector for focusing light not only on the float but also on the mobile body, as long as the installation space is sufficient, a more stable communication system can be constructed. Furthermore, to improve communication speed and capacity beyond that of the above-mentioned visible light communication, laser light communication can also be used. Laser light communication is typically considered unsuitable for communication with underwater mobile bodies because it is extremely directional compared to communication using visible light such as LEDs, and is therefore limited to pinpoint 1:1 transmission and reception. However, by widening the light receiving range using the float combination of the present invention or by using a parabolic reflector in the receiver to widen the light receiving range, laser light communication can also be made possible.

In the above description, underwater communication is assumed to be an optical communication system between the mobile underwater drone 10 and the float 1 or float combination 59 above the water surface. Voice communication with another underwater mobile object, a diver 8, or transmission of a video output signal from a camera 9 held by the diver can be transmitted to the drone 10 via short-range communication, with the drone's 10 transceiver serving as a relay. However, if the camera 9 itself has a built-in transceiver, underwater communication is also possible directly between the camera 9 and the float 1 or float combination 59 without the need for a relay via the drone 10. Alternatively, by installing a transceiver 21 on the equipment carried on the diver 8's back, the camera 9 output signal, diver audio signal, and diver vital data signal can be sent to the transceiver 21 of the diver 8 via short-range communication, allowing underwater communication between the diver 8 and the float 1 via the transceiver 21 on the diver's back. Furthermore, communication between mobile objects can also be performed via a relay via the float-side transceiver 2.

As described above, the underwater communication system of the present invention can be used for a wide variety of purposes, including underwater exploration, diver training, underwater photography, and underwater entertainment facilities. By deploying floats on the water surface within the required range for such purposes, an optical communication network can be established for underwater communications with underwater vehicles such as drones and divers within the range covered by the floats. This network can then be used by a control center to check the underwater situation via video and audio and to provide instructions for training and other purposes. While conventional divers and other vehicles could only respond using hand signals, the system can also be configured to transmit information such as responses to instructions and commands, images of training status, and vital signs of divers and workers via data. Furthermore, because the expandable floats can be deployed within the required range, a vessel or other vessel can simply navigate to the location where underwater exploration is required, couple the floats, and deploy them, enabling high-volume communication, such as video, in a more reliable communication environment, making the system extremely convenient.

The underwater communication system according to the present invention enables broadband, high-speed communication, which was previously difficult to achieve, and allows the construction of a more reliable underwater communication system, expanding the industrial applicability to a wide range of applications, including underwater exploration, underwater training and other educational purposes, underwater entertainment, and military use.

1 Float 2 Float-side transmitting/receiving device 3 Transmitting element (light-emitting element)
4. Receiving element (light receiving element)
5. Above-water antenna 6. Float buoy (connected buoy)
7 Anchor buoy 8 Diver 9 Diver camera 10 Drone 11 Mobile body side transmitting and receiving device 20 Ship 21 Diver side transmitting and receiving device 30 Direction control means 59 Float combination body 68 Direction control plate 77 Parabolic reflector

Claims (4)

A communication means between a plurality of floats floating on the water surface and an underwater moving body,
A float-side transmitting and receiving device is installed on the float,
The float-side transmitting and receiving device is connected to a control center or another float-side transmitting and receiving device by wire or wirelessly,
the plurality of floats are mutually connectable and detachable, and are expandable according to the range of movement of the underwater vehicle;
An underwater wireless communication system characterized in that the underwater mobile body is equipped with a mobile body-side transceiver device facing the float, and is configured to perform optical communication including visible light communication or laser light communication with the float-side transceiver device. 2. The underwater wireless communication system according to claim 1 , wherein the plurality of float-side transceivers are capable of communicating with the float-side transceiver having the strongest signal strength transmitted from the mobile-side transceiver. An underwater wireless communication system as described in either claim 1 or claim 2, characterized in that the mobile-side transmitting/ receiving device is placed near the diver or near a camera or audio microphone owned by the diver, and is controlled to maintain horizontal movement using a direction control device using a gravity gyrocompass. The underwater wireless communication system described in claim 3, characterized in that video signals, audio signals, or data signals from the underwater moving body are relayed through the moving body side transceiver device possessed by the underwater moving body or the diver, and communicated with the float side transceiver device or another moving body side transceiver device.