Underwater optical wireless communication system

Abstract

The present invention aims to provide an underwater optical wireless communication system that can detect the location of a mobile station performing optical wireless communication underwater and allow the optical wireless communication device to automatically move along a cable or the like to a range where it can communicate with the mobile station. [Solution] The underwater optical wireless communication system according to the present invention comprises a waterproof leaky cable extended underwater, a mobile radio having an optical wireless communication device for performing optical wireless communication with a mobile station, an information acquisition device for acquiring location information of the mobile station and the mobile radio, and an analysis means for analyzing the positional relationship that enables the mobile radio and the mobile station to perform optical wireless communication based on the location information acquired by the information acquisition device. Furthermore, the mobile radio includes a transmitting and receiving means for transmitting and receiving signals transmitted through the leaky cable, and a mobile mechanism that moves along the leaky cable.

Description

Technical Field

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[0005]

[0001] The present invention relates to an underwater optical wireless communication system that performs optical wireless communication with a mobile station in water.

Background Art

[0002] Techniques for performing optical wireless communication in water have been developed. For example, Patent Document 1 discloses a technique for underwater communication between divers using signal light in water, and Patent Document 2 discloses a technique for an underwater visible light communication system in which an observation device and an underwater mobile body transmit and receive data using visible light in water.

[0003] In addition, Patent Document 3 discloses a remote control system for optically wirelessly controlling an underwater vehicle by an optical wireless transmitter connected to a cable. According to this remote control system, the length of the cable extended in water can be adjusted to bring the optical wireless transmitter closer to the vehicle, and the vehicle can be controlled optically wirelessly.

[0004] The above are examples of prior art related to optical wireless communication in water. However, as prior art related to the present invention separately from the technology related to optical wireless communication, Patent Document 4 discloses an underwater wireless connection service providing device in which a leaky cable covered with a waterproof sheath is laid in water, and a wireless device is brought close to or contacted with the leaky cable covered with this waterproof sheath, so that the wireless device can communicate with the leaky cable by electromagnetic waves. This technology is related to the leaky cable used in the present invention. In addition, Patent Documents 5 and 6 disclose technologies related to a moving mechanism that moves along a cable or the like used in the present invention.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] Applying the technologies disclosed in the aforementioned Patent Documents 1, 2, and 3, it is conceivable to construct an underwater optical wireless communication system that includes means for sending and receiving optical wireless communication devices connected to a cable, and for sending and extending this cable underwater, and for pulling it up. With this underwater optical wireless communication system, it is thought that the cable length can be adjusted underwater to bring the optical wireless communication device attached to the cable closer to a vehicle (mobile station), and optical wireless communication can be performed between the optical wireless communication device attached to the cable and the optical wireless communication device attached to the vehicle.

[0007] However, if the optical radio communication device on the cable and the optical radio communication device on the vessel are located in positions where optical radio communication is not possible, measures such as detecting the positions of both devices are necessary to adjust their positions so that optical radio communication can be performed. In addition, when adjusting the position of the optical radio communication device on the cable, it is necessary to unwind and rewind the cable that has been extended below the water surface in order to adjust the cable length.

[0008] Therefore, the object of the present invention is to provide an underwater optical wireless communication system that can detect the position of a mobile station performing optical wireless communication underwater and allow the optical wireless communication device to automatically move along a cable or the like to a range where it can communicate with the mobile station. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides the following underwater optical wireless communication system: (1) An underwater optical wireless communication system for performing optical wireless communication with a mobile station underwater, wherein the underwater optical wireless communication system comprises: a waterproof leaky cable extended underwater; a mobile radio having an optical wireless communication device for performing optical wireless communication with the mobile station; an information acquisition device for acquiring an optical wireless communication start request and position information between the mobile station and the mobile radio; and an analysis means for analyzing the positional relationship that enables the mobile radio and the mobile station to perform optical wireless communication based on the positional information acquired by the information acquisition device, wherein the mobile radio further includes a transmitting and receiving means for transmitting and receiving signals to transmit through the leaky cable; and a mobile mechanism that moves along the leaky cable, wherein the mobile radio receives signals of movement control steps created based on the analysis results of the analysis means via the leaky cable to adjust the position of the mobile radio, and transmits data for optical wireless communication performed with the mobile station via the leaky cable.

[0010] (2) The underwater optical wireless communication system according to (1), characterized in that it has a beacon that transmits location information of the mobile radio to the mobile station.

[0011] (3) The underwater optical wireless communication system according to (1) to (2) above, characterized by comprising a plurality of the mobile wireless devices. [Effects of the Invention]

[0012] According to the present invention, even if an optical wireless communication device attached to a cable is located in a position where it cannot communicate with a mobile station via optical wireless communication underwater, the optical wireless communication device can move along the cable to a range where optical wireless communication is possible and communicate with the mobile station via optical wireless communication. In this case, since the optical wireless communication device moves along the cable, there is no need to feed out and reel in the cable in order to move the optical wireless communication device underwater. [Brief explanation of the drawing]

[0013] [Figure 1]It is a block diagram of an underwater optical wireless communication system according to the first embodiment. [Figure 2] It is a schematic diagram showing an example of an underwater optical wireless communication system according to the first embodiment. [Figure 3] It is a perspective view showing an antenna and a leaky cable. [Figure 4] It is a schematic diagram showing an example of a moving mechanism. [Figure 5] It is a schematic diagram showing an example of applying the underwater optical wireless communication system according to the first embodiment. [Figure 6] It is a schematic diagram showing an example in which a part of the underwater optical wireless communication system according to the first embodiment is changed. [Figure 7] It is a schematic diagram showing an example of an underwater optical wireless communication system according to the second embodiment. [Figure 8] It is a schematic diagram showing an example in which a part of the underwater optical wireless communication system according to the second embodiment is changed.

Mode for Carrying Out the Invention

[0014] Embodiments of the present invention will be described below with reference to the accompanying drawings. The drawings are schematic or simplified for explaining the content of the invention, and the shapes and dimensional ratios of each part disclosed in the drawings are different from the actual ones.

[0015] (First Embodiment) The first embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram of the underwater optical wireless communication system of the present invention, and FIG. 2 is a schematic diagram showing the outline of the underwater optical wireless communication system. In FIGS. 1 and 2, the controller 1 and components other than a part of the start end side connected to the controller 1 of the leaky cable 2 are provided underwater or on the water surface. As shown in FIG. 2, one end of the leaky cable 2 is connected to the controller 1, the leaky cable 2 extends vertically underwater, and a terminating resistor 3 is connected to the other end of the extended leaky cable 2.

[0016] The leakage cable 2 is provided on a cable reel, for example, so that it can be fed out and wound up. When using the underwater optical wireless communication system, the leakage cable 2 may be fed out from the cable reel into the water for extension. Also, in a situation where the leakage cable 2 is likely to be washed away by water flow or the like, in order to keep it stable at a fixed position, a weight may be suspended at the portion where the terminating resistor 3 is connected, or a wire may be extended from the portion where the terminating resistor 3 is connected to the bottom of the water, and an anchor may be provided at the tip of the wire.

[0017] The controller 1 has a function of controlling the entire underwater optical wireless communication system, and in addition to the functions of transmitting and receiving signals, it includes a computer or the like required for control, and includes an analysis means for processing the data acquired via the mobile radio 4 and the information acquisition device 7 described later. In FIG. 2, the controller 1 is placed on a floating body such as a ship, but the place where the controller 1 is installed may also be on land.

[0018] The leakage cable 2 has a function of radiating the signal to be transmitted as electromagnetic waves from the side surface of the leakage cable 2, and a function of receiving wireless signals due to electromagnetic waves transmitted from the outside from the side surface of the leakage cable 2. Examples of the leakage cable 2 used in the present invention include those in which a waterproof sheath is applied to a leakage coaxial cable as disclosed in Patent Document 4. This leakage coaxial cable has a configuration of a shield cable in which holes (slots) for leaking electromagnetic waves are provided in a shield (outer conductor) at a constant period. As an example of the leakage cable 2 in the present invention, a waterproof sheath is covered on the outer periphery of such a shield cable via an air layer, and it has waterproof properties. Note that the leakage cable used in the underwater optical wireless communication system of the present invention is not limited to the configuration disclosed in Patent Document 4 as long as it can output and input electromagnetic waves from the side surface of the cable, has waterproof properties, can ensure insulation in water, and can be used safely.

[0019] The leaky cable 2 is equipped with a mobile radio 4 that can move along the leaky cable 2. The mobile radio 4 is equipped with a transmitting and receiving means for transmitting and receiving radio signals as electromagnetic waves to and from the leaky cable 2. This transmitting and receiving means includes an antenna section 41 and a radio section 42 that performs modulation, demodulation, amplification, etc., of electrical signals. The mobile radio 4 also has a control device 43 and a mobile mechanism 44, and these control device 43 and mobile mechanism 44 allow it to move vertically along the leaky cable 2 (see Figures 1 and 2).

[0020] According to the configuration described above, the control signal transmitted from the controller 1 is transmitted by the leakage cable 2, radiating as electromagnetic waves from the side of the leakage cable 2, and the radiated control signal is received by the antenna unit 41 of the mobile radio 4. The received control signal is then demodulated and processed by the radio unit 42 before being sent to the control device 43. The control device 43 determines whether the control signal is a signal to control the mobile mechanism 44, and based on this control signal, the mobile mechanism 44 is controlled, allowing the mobile radio 4 to move along the leakage cable 2.

[0021] Furthermore, the mobile radio 4 includes an optical radio communication device 5A that communicates with the underwater mobile station 8 via optical radio, and a beacon 6 that can transmit location information of the mobile radio 4 to the mobile station 8 over long distances using sound waves or optical signals. The optical radio communication device 5A has the function of converting optical signals into electrical signals and electrical signals into optical signals using an optical media converter, and transmitting and receiving optical signals.

[0022] Therefore, the electrical signal received by the antenna unit 41 of the mobile radio 4 from the leaky cable 2 via radio waves is sent to the control device 43 via the radio unit 42. The control device 43 determines that the received electrical signal is an electrical signal to be transmitted to the mobile station 8 and sends this electrical signal to the optical radio communication device 5A. The optical media converter in the optical radio communication device 5A converts the electrical signal into an optical signal such as visible light and transmits it to the mobile station 8. In addition, the optical media converter in the optical radio communication device 5A receives an optical signal such as visible light from the mobile station 8 and converts it into an electrical signal, which can then be transmitted to the leaky cable 2 as a radio wave signal via the control device 43, radio unit 42, and antenna unit 41.

[0023] Furthermore, the optical wireless communication device 5A has a function (automatic tracking function) that tracks the mobile station while photographing it with a camera or the like, as disclosed in Patent Document 3, in order to perform highly directional optical wireless communication with the optical wireless communication device 5B installed in the mobile station 8, which will be described later. This tracking function allows the direction in which the light receiving unit and light transmitting unit of the optical wireless communication device 5A are facing to be aligned with the mobile station 8.

[0024] To describe the mobile station 8, it consists of an optical radio communication device 5A of the mobile radio 4, an optical radio communication device 5B for conducting optical radio communication underwater, and an unmanned submersible, diver, etc., that has means to detect the beacon signal transmitted from the mobile radio 4 and determine the location of the beacon signal transmission. As mentioned above, the optical radio communication conducted between the optical radio communication device 5A and the optical radio communication device 5B is highly directional, has a high communication speed, and enables large-capacity data communication over relatively short distances.

[0025] Therefore, the optical radio communication device 5B installed in the mobile station 8 has the same function as the optical radio communication device 5A, for example, to track the mobile radio 4 while photographing it with a camera. In other words, by using the function of tracking each other, the optical axes of the light transmitting unit of the optical radio communication device 5A and the light receiving unit of the optical radio communication device 5B, and the optical axes of the light receiving unit of the optical radio communication device 5A and the light transmitting unit of the optical radio communication device 5B, do not become misaligned, and the respective light transmitting and receiving units face each other precisely, making it possible to perform highly directional optical radio communication.

[0026] Furthermore, the unmanned submersible used as mobile station 8 can be either an autonomous or remotely operated unmanned submersible, as long as it has the ability to detect the transmission location of a beacon signal and move to that location. Although not shown in the diagram, mobile station 8 is equipped with a transmitter that transmits a signal requesting the start of optical wireless communication to the information acquisition device 7 of the underwater optical wireless communication system using light or sound waves, and the signal requesting the start of communication transmitted to the information acquisition device 7 is transmitted to the controller 1. In addition, the position information of mobile station 8 may also be transmitted to the controller 1 via the information acquisition device 7 of the underwater optical wireless communication system using this transmitter.

[0027] The signal transmitted from the transmitter of the mobile station 8 is transmitted over a wide area and long distance, and even when the mobile station 8 is located in an area where optical wireless communication devices 5A and 5B cannot perform optical wireless communication, the signal transmitted from the transmitter of the mobile station 8 needs to reach the information acquisition device 7. In other words, when the mobile station 8 is located in an area where optical wireless communication devices 5A and 5B cannot perform optical wireless communication, and a signal requesting the start of optical wireless communication is transmitted from the transmitter of the mobile station 8, this start request signal reaches the controller 1 via the information acquisition device 7. The controller 1 then adjusts the position of the mobile radio 4 so that it is within range of optical wireless communication devices 5A and 5B.

[0028] Next, the specific configuration and operation of the leaky cable 2 and the mobile radio 4 for wireless communication will be described in more detail. Regarding the configuration of the mobile radio 4, as described above, the mobile radio 4 comprises an antenna unit 41, a radio unit 42, a control device 43, and a mobile mechanism 44. The antenna unit 41 is for performing electromagnetic wireless communication on the side of the leaky cable 2, and the antenna 41a is fixed to the hollow part of a hollow cylindrical body 41b (see Figure 3). The cylindrical body 41b comprises a body and a flange, and the body is made of a material (dielectric) that is transparent to electromagnetic waves. As shown in Figure 3, the cylindrical body 41b is attached to a pipe 41c that extends through the flange into the hollow part, and the antenna 41a is fixed to the pipe 41c in the hollow part of the cylindrical body 41b. One end of the cable 41d is connected to this antenna 41a, and the other end of the cable 41d is connected to the radio unit 42 of the mobile radio 4 after passing through the inside of the pipe 41c. Furthermore, the body of the cylindrical body 41b is positioned to be indirectly or directly in contact with the side of the leaky cable 2.

[0029] Here, as shown in Figure 3(a), for example, a rotating ring 41e is provided on the body of the cylindrical body 41b so as to rotate around the body, and the rotating ring 41e is moved while in contact with the longitudinal side of the leaky cable 2. As a result, the rotating ring 41e rotates as the cylindrical body 41b moves while in contact with the longitudinal side of the leaky cable 2, thereby reducing friction at the contact surface between the cylindrical body 41b and the leaky cable 2. The material of the rotating ring 41e is transparent to electromagnetic waves, similar to the material of the body of the cylindrical body 41b.

[0030] Alternatively, as shown in Figure 3(b), a rotating ring may be omitted, and for example, a cylindrical body 41b may be attached around the pipe 41c via a waterproof bearing 41f, so that the cylindrical body 41b rotates around the pipe 41c with the pipe 41c as the axis of rotation. In this case, the cylindrical body 41b rotates around the pipe 41c, but the antenna 41a remains fixed to the pipe 41c without rotating. With such a configuration, the body of the cylindrical body 41b can move while rotating in direct contact with the longitudinal side of the leaky cable 2, thereby reducing friction at the contact surface between the cylindrical body 41b and the leaky cable 2.

[0031] With the above configuration, the cylindrical body 41b moves while in contact with the longitudinal direction of the side surface of the leaky cable 2, and the antenna 41a fixed to the hollow part of the cylindrical body 41b moves along the leaky cable 2 while maintaining a constant orientation and a constant distance from the side surface of the leaky cable 2. Furthermore, the cylindrical body 41b and the pipe 41c are watertight, and the antenna 41a and cable 41d fixed to the hollow part of the cylindrical body 41b can transmit and receive electromagnetic signals to and from the leaky cable 2 via the contact surface between the side surface of the leaky cable 2 and the body of the cylindrical body 41b without being immersed in water. Therefore, electromagnetic transmission and reception can be performed underwater with the influence of water minimized.

[0032] Next, the configuration and operation of the mobile mechanism 44 provided in the mobile radio 4 will be described. The mobile mechanism 44 moves by sandwiching the leaky cable 2 between two drive rollers 44a, as shown in Figure 4, for example, and rotating the drive rollers 44a, thereby generating frictional force at the contact surface between the drive rollers 44a and the leaky cable 2. Although not shown, the drive rollers 44a are rotated by a drive mechanism such as a waterproof motor powered by a battery. Since one drive mechanism rotates one drive roller 44a, two drive mechanisms are provided. These two drive mechanisms are synchronized, and the two drive rollers 44a rotate in sync. Furthermore, the two drive mechanisms are controlled by the control device 43 based on control signals transmitted from the controller 1.

[0033] Similar mobile mechanisms to those described above are disclosed, for example, in Patent Documents 5 and 6. Although the mobile mechanisms disclosed in Patent Documents 5 and 6 are not for underwater use, their basic principles and configurations are similar to the mobile mechanisms used in the present invention described above. Furthermore, the mobile mechanisms used in the present invention can be applied to any device that can move along a cable or the like underwater, and are not limited to configurations similar to those in Patent Documents 5 and 6. In addition, the mobile radio 4, including the mobile mechanism 44, must be waterproof as a whole and have a configuration that allows for stable operation underwater.

[0034] The configuration and operation of the controller 1, leakage cable 2, and mobile radio 4 have been described above. Next, the configuration and operation of the information acquisition device 7 and analysis means of the underwater optical wireless communication system of the present invention will be described. The information acquisition device 7 can acquire a request from the mobile station 8 to initiate optical wireless communication, and can acquire the location information of the mobile radio 4 and the mobile station 8. As mentioned above, in order to acquire a request from the mobile station 8 to initiate optical wireless communication, a method is needed that can transmit and receive signals over a wider area and longer distance than the optical wireless communication conducted between the optical wireless communication device 5A and the optical wireless communication device 5B. In addition, a method is needed that can acquire the location information of the mobile radio 4 and the mobile station 8 over a wider area and longer distance.

[0035] Regarding the specific method by which the information acquisition device 7 receives a request from the mobile station 8 to initiate optical wireless communication and acquires the position information of the mobile radio 4 and the mobile station 8, an example is the use of an underwater sonar. The underwater sonar can be operated in an active or passive manner. In the active method, the sonar emits sound waves (ultrasonic waves) and detects the sound waves (ultrasonic waves) reflected from the mobile radio and mobile station, detecting their positions from the reflected sound wave data. In the passive method, the mobile radio and mobile station are equipped with sound wave transmitters, and the sonar captures the sound waves (ultrasonic waves) emitted by these transmitters, detecting their positions from the sound wave data. The choice between the active and passive methods depends on the situation in which the underwater optical wireless communication system is implemented, but both active and passive methods may be used in combination depending on the circumstances.

[0036] Furthermore, to more reliably identify the mobile radio and the mobile station, it is preferable to have the mobile radio and the mobile station each emit identification signals via sound waves from their respective sound wave transmitters, and for the underwater sonar to detect these sound waves. With this method, it is also possible to transmit data such as the water depth where the mobile radio and the mobile station are located to the underwater sonar, or to transmit a signal requesting the start of optical radio communication from the mobile station to the underwater sonar.

[0037] Another method of acquiring information is to use a photographic device as the information acquisition device 7. For example, a photographic device can be used to photograph the mobile radio 4 and the mobile station 8, and detect the direction and distance between the mobile radio 4 and the mobile station 8 from the captured image. With this photographic device, the positional information of the mobile radio 4 and the mobile station 8 can be acquired from the captured image. Furthermore, regarding the request to initiate optical radio communication from the mobile station 8, for example, the mobile station 8 may be equipped with a light emitter, and the optical signal transmitted by this emitter can be acquired from the captured image. In addition to the photographic device described above, the information acquisition device 7 may receive the optical signal transmitted by the mobile station 8 using an optical receiver that can detect signals transmitted by the mobile station 8 over a wide area.

[0038] The information acquisition device 7 is positioned to have a clear line of sight to the mobile radio 4 and mobile station 8, whether using an underwater sonar or a camera. Specifically, it is preferable to install it near the water surface so that it can overlook the entire leaky cable 2 and the surrounding area where the mobile station 8 is located. It is also considered useful to install multiple information acquisition devices 7 in different locations to acquire and analyze more data from multiple positions. Furthermore, it is considered useful to equip the information acquisition device 7 with means to move on the water surface and underwater, so that its position can be adjusted to always have a clear line of sight to the mobile radio 4 and mobile station 8.

[0039] The positional information of the mobile radio 4 and mobile station 8 obtained from the information acquisition device 7 described above is analyzed by the analysis means of the controller 1, and it is determined whether optical wireless communication is possible between the mobile radio 4 and mobile station 8 based on their positional relationship. The method of determination involves analyzing sound wave data or captured image data indicating the locations of the mobile radio 4 and mobile station 8 using a computer in the controller 1 to identify the positions of the mobile radio 4 and mobile station 8, determining the distance between the mobile radio 4 and mobile station 8, and taking into account data such as water transparency, to determine whether the distance is within which the light for optical wireless communication can reach. In addition to the distance between the mobile radio 4 and mobile station 8, it is also determined whether there are any obstructions that would hinder the transmission of light between them by analyzing the sound wave data or captured image data, etc.

[0040] For example, if the computer determines that optical wireless communication is not possible because the distance between the mobile radio 4 and the mobile station 8 is too long for light to reach, or because there is an obstruction between the mobile radio 4 and the mobile station 8 blocking the light, a step for movement control is created to move the mobile radio 4 to a range where optical wireless communication can be performed. Then, a control signal based on the step created by the computer is transmitted from the controller 1 to the leaky cable 2, and the mobile radio 4 moves along the leaky cable 2 to a range where optical wireless communication with the mobile station 8 can be performed according to this control signal.

[0041] The above describes the configuration and operation of the first embodiment of the underwater optical wireless communication system. Next, we will explain the procedure by which the mobile radio 4 and the mobile station 8 actually perform optical wireless communication using the underwater optical wireless communication system. For example, suppose that when it becomes necessary to perform optical wireless communication from the base station controller 1 to the mobile station 8, or when the controller 1 receives a request from the mobile station 8 to start optical wireless communication via the information acquisition device 7, the mobile radio 4 and the mobile station 8 are in a position where they cannot perform optical wireless communication. That is, this occurs when the distance between the mobile radio 4 and the mobile station 8 is long, or when there is an obstacle between the mobile radio 4 and the mobile station 8 that blocks light.

[0042] In such cases, as described above, a movement control step is created to move the mobile radio 4 to a range where optical wireless communication can be performed. Then, a control signal based on the step is transmitted from the controller 1 and transmitted to the leaky cable 2. As the control signal is transmitted through the leaky cable 2, it is radiated as electromagnetic waves from the side of the leaky cable 2, and these radiated electromagnetic waves are received by the antenna section 41 of the mobile radio 4. After the received control signal is processed such as demodulation by the radio section 42, it is sent to the control device 43. When the control device 43 determines that the signal sent to it is a control signal to control the movement of the mobile radio 4, the movement mechanism 44 of the mobile radio 4 is controlled based on this control signal, and the mobile radio 4 moves along the leaky cable 2.

[0043] After the mobile radio 4 moves to a position close to the mobile station 8, it transmits its location information to the mobile station 8 via a beacon signal such as ultrasound from the beacon 6. The mobile station 8 detects this ultrasonic or similar beacon signal and approaches the mobile radio 4 until it is within a suitable distance for optical wireless communication. In this way, the mobile radio 4 and the mobile station 8 move closer to each other, so that they are within range of each other for optical wireless communication.

[0044] The mobile radio 4 and mobile station 8, located within range of optical wireless communication, transmit and receive data via optical wireless communication using the functions of their respective optical wireless communication devices 5A and 5B. In this way, information from the base station controller 1 can be transmitted to the mobile station 8 via the leaky cable 2 and mobile radio 4, and information from the mobile station 8 can be transmitted to the controller 1 via the mobile radio 4 and leaky cable 2.

[0045] To describe the details of the optical wireless communication between the mobile radio 4 and the mobile station 8, for example, if there is a signal to be transmitted from the controller 1 to the mobile station 8, the signal is first transmitted from the controller 1 to the leaky cable 2. When the signal transmitted to the leaky cable 2 is received by the mobile radio 4 via radio waves, this received signal is converted into an optical signal, such as visible light, by an optical media converter or the like in the optical wireless communication device 5A. Then, the signal is transmitted by light from the optical wireless communication device 5A to the optical wireless communication device 5B of the mobile station 8 which is underwater.

[0046] Furthermore, if there is a signal to be transmitted from the mobile station 8 to the controller 1, the optical radio communication device 5B of the mobile station 8 transmits the optical signal to the optical radio communication device 5A of the mobile radio 4. The transmitted optical signal is converted from an optical signal to an electrical signal by an optical media converter or the like of the optical radio communication device 5A of the mobile radio 4. After being converted to an electrical signal in this way, it is transmitted from the mobile radio 4 to the leaky cable 2 as a radio wave signal.

[0047] The above describes the first embodiment of the present invention. Below, we will describe examples of applications of the underwater optical wireless communication system described above and examples of modifications to the configuration. First, we will explain an example of applying the underwater optical wireless communication system of the first embodiment to relay optical wireless communication. In the first embodiment, it is considered possible to relay optical wireless communication between multiple mobile stations by providing multiple mobile radios. Figure 5 shows an example in which two mobile radios 4 are provided on a leaky cable 2. In the example shown in Figure 5, if the information acquisition device 7 provided on the underwater optical wireless communication system captures the position information of the upper mobile station 8 and the lower mobile station 8 respectively, then a control signal for adjusting the positions of the upper mobile radio 4 and the lower mobile radio 4 is transmitted from the base station controller 1 to the upper mobile radio 4 and the lower mobile radio 4 via the leaky cable 2. The upper mobile radio 4 then moves to approach the upper mobile station 8, and the lower mobile radio 4 moves to approach the lower mobile station 8.

[0048] Once the positions of the two mobile radios 4 are determined, each of the two mobile radios 4 emits an ultrasonic or other beacon signal from its respective beacon 6. The two mobile stations 8 sense the beacon signals emitted from the respective beacons 6 of the two mobile radios 4, and the upper mobile station 8 moves to get closer to the upper mobile radio 4 which is closer to the upper mobile station 8, and the lower mobile station 8 moves to get closer to the lower mobile radio 4 which is closer to the lower mobile station 8. Then, each mobile radio 4 and mobile station 8 moves until they are within range of optical radio communication and transmit and receive signals using optical radio.

[0049] To further elaborate on the transmission and reception of signals by optical radio between the mobile radio 4 and mobile station 8 described above, first, the signal transmitted by optical radio from the optical radio communication device 5B installed in the upper mobile station 8 is received by the optical radio communication device 5A installed in the upper mobile radio 4. The signal received as light is converted from an optical signal to an electrical signal by the optical media converter of the optical radio communication device 5A installed in the upper mobile radio 4 and transmitted as a radio wave to the leaky cable 2. The signal transmitted to the leaky cable 2 is first transmitted to the controller 1 via the leaky cable 2, and then, under the control of the controller 1, is transmitted further through the leaky cable 2 to the lower mobile radio 4, or is transmitted directly to the lower mobile radio 4 via the leaky cable 2 without going through the controller 1.

[0050] The signal transmitted by electrical signals to the lower mobile radio 4 is converted from an electrical signal to an optical signal by an optical media converter in the optical wireless communication device 5A installed in the lower mobile radio 4, and then transmitted to the optical wireless communication device 5B installed in the lower mobile station 8. In this way, it becomes possible to transmit signals from the upper mobile station 8 to the lower mobile station 8. Conversely, it is also possible to transmit signals from the lower mobile station 8 to the upper mobile station 8. As described above, as shown in Figure 5, even when the two mobile stations 8 are not in a position to see each other directly due to obstacles and therefore cannot transmit and receive signals directly by optical wireless communication, it is considered that optical wireless communication can be performed by relaying signals through the two mobile radios 4.

[0051] Next, we will describe an example in which the configuration of the first embodiment of the underwater optical wireless communication system described above has been partially modified. In the first embodiment described above, the leak cable 2 is extended so as to be lowered vertically into the water, but if the leak cable 2 is not strong enough, a wire rope 9 with sufficient strength may be extended along the leak cable 2 as shown in Figure 6. The moving mechanism 44 is configured so that the wire rope 9 is sandwiched between two drive rollers 44a instead of the leak cable 2. In this configuration, when the two drive rollers 44a are rotated, the mobile radio 4 moves along the wire rope 9 due to the frictional force at the contact surface between the drive rollers 44a and the wire rope 9, and at the same time moves along the leak cable 2. In this way, it is possible to modify the moving mechanism, which is part of the first embodiment, depending on the situation.

[0052] To describe another example of modification, the above-described embodiment uses a leaky coaxial cable, but it is also possible to include a leaky optical fiber in the leaky cable. Examples of leaky optical fibers include side-emitting optical fibers that transmit while leaking optical signals from the side of the optical fiber, and side-receiving optical fibers that receive optical signals from the side of the optical fiber. In this case, a light-emitting element or a light-receiving element is used instead of an antenna. It should be noted that the side-emitting optical fiber, side-receiving optical fiber, light-receiving element, and light-emitting element, like the other elements, must be waterproof. The above are examples of applications and modified configurations of the underwater optical wireless communication system of the present invention.

[0053] (Second Embodiment) A second embodiment of the present invention will be described below with reference to the accompanying drawings. In the first embodiment, the leak cable 2 was extended vertically underwater, but in the second embodiment, the leak cable 2 is extended horizontally underwater. That is, as shown in Figure 7, the leak cable 2, one end of which is connected to the controller 1, is initially lowered vertically below the water surface, and then bent by one of the guide rollers 10 at an appropriate water depth to be extended horizontally. The leak cable 2, which has been extended horizontally to an appropriate length, is then bent towards the water surface by the other guide roller 10 and pulled up vertically so that the other end of the leak cable 2 is brought out of the water surface, and a terminating resistor 3 is connected to this other end of the leak cable 2.

[0054] Furthermore, the leaky cable 2 is laid along the reinforcing wire rope 9. The guide roller 10 can be fixed to the wire rope 9, or, if the environment in which the leaky cable 2 is laid is a body of water enclosed by walls such as a rectangular swimming pool, it may be fixed to the wall of the pool. When fixing the guide roller 10 to the wall, it should be fixed at a distance from the wall so that the leaky cable 2 can maintain a certain distance from the wall. If the leaky cable 2 can withstand sufficient tension, it is also possible to lay the leaky cable 2 alone without the reinforcing wire rope 9. To prevent the laid leaky cable 2 from sagging or being subjected to excessive tension, a mechanism may be provided to feed out and pull in the leaky cable 2 in accordance with its tension.

[0055] Furthermore, if the leakage cable 2 is difficult to bend, it may be routed horizontally via the communication cable 11 as shown in Figure 8. That is, one end of the communication cable 11 is connected to the controller 1, and this communication cable 11 is lowered vertically into the water, and one end of the leakage cable 2 is connected to the other end of the communication cable 11 by a connector 12. From this connection point, the leakage cable 2 is extended horizontally, and a terminating resistor 3 is connected to the other end of the leakage cable 2. When fixing the terminating resistor 3 and connector 12, they can be fixed with a wire rope 9 as described above, or, if laid in a pool, the terminating resistor 3 and connector 12 may be fixed at a distance from the wall so that the leakage cable 2 can be at a certain distance from the pool wall. The connector 12 described above has a configuration for connecting different types of cables, and this connector 12, along with the terminating resistor 3 and communication cable 11, all have preventative properties and can be used stably even underwater.

[0056] As described above, in the first embodiment, the mobile radio 4 moves vertically along the leaky cable 2, while in the second embodiment, the mobile radio 4 moves horizontally along the leaky cable 2. The mobile radio 4 moves horizontally along the leaky cable 2 by rotating the leaky cable 2 or wire rope 9 between two drive rollers 44a, as in the first embodiment, but any mechanism that can safely move horizontally underwater may be used.

[0057] Other than the basic operation described above, the first and second embodiments are almost identical. That is, the mobile radio 4 and the mobile station 8 communicate via optical wireless communication devices 5A and 5B, and the signals transmitted and received via this optical wireless communication are transmitted and received to the controller 1 via the leaky cable 2. Furthermore, by equipping the leaky cable 2 with multiple mobile radios 4, it is also possible to relay communication between multiple mobile stations 8. Figures 7 and 8 illustrate an environment in which the leaky cable 2 is laid, which is a body of water enclosed by walls like a rectangular swimming pool. Such an underwater optical wireless communication system installed in a pool is expected to be used, for example, in cruising experiments of unmanned submersibles.

[0058] Furthermore, although not disclosed in the specification and drawings, the first and second embodiments described above include control and drive batteries in the mobile radio, and also include, for example, a microprocessor, memory device, sensors, etc. In addition, the entire electrical system of the underwater optical wireless system of the present invention must be waterproof and water-resistant so that events such as electrical leakage do not occur under the environmental conditions in which the underwater optical wireless communication system is used. [Industrial applicability]

[0059] If the underwater optical wireless communication system of the present invention can be realized, even if the optical wireless communication device attached to the cable is in a position where it cannot communicate with the mobile station via optical wireless communication underwater, the optical wireless communication device will be able to move along the cable over a wide area to a range where optical wireless communication is possible and communicate with the mobile station via optical wireless communication. Furthermore, it will be possible to transmit, receive, and relay signals with multiple mobile stations. [Explanation of symbols]

[0060] 1: Controller, 2: Leakage cable, 2A: First leakage cable, 2B: Second leakage cable, 3: Termination resistor, 4: Mobile radio, 41: Antenna unit, 41a: Antenna, 41b: Cylindrical body, 41c: Pipe, 41d: Cable, 41e: Rotating ring, 41f: Waterproof bearing, 42: Radio unit, 43: Control device, 44: Moving mechanism, 44a: Drive roller, 5A, 5B: Optical radio communication device, 6: Beacon, 7: Information acquisition device, 8: Mobile station, 9: Wire rope, 10: Guide roller, 11: Communication cable, 12: Connector

Claims

1. An underwater optical wireless communication system for performing optical wireless communication with a mobile station underwater, wherein the underwater optical wireless communication system comprises a waterproof leaky cable extended underwater, a mobile radio having an optical wireless communication device for performing optical wireless communication with the mobile station, information acquisition means for acquiring optical wireless communication start requests and position information between the mobile station and the mobile radio, and analysis means for analyzing the positional relationship that enables the mobile radio and the mobile station to perform optical wireless communication based on the positional information acquired by the information acquisition device, wherein the mobile radio further includes transmitting and receiving means for transmitting and receiving signals to be transmitted through the leaky cable, and a mobile mechanism that moves along the leaky cable, wherein the mobile radio receives signals of movement control steps created based on the analysis results of the analysis means via the leaky cable to adjust the position of the mobile radio, and transmits optical wireless communication data to be performed with the mobile station via the leaky cable.

2. The underwater optical wireless communication system according to claim 1, characterized in that the information acquisition means has a beacon that transmits location information of the mobile radio to the mobile station.

3. The underwater optical wireless communication system according to claim 1 to 2, characterized in that a plurality of the aforementioned mobile radios are provided.

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