Underwater optical wireless communication system and underwater optical wireless communication method

Abstract

An underwater optical wireless communication system (100) is provided with a first optical wireless communication device (1) and a plurality of second optical wireless communication devices (2). The first optical wireless communication device includes: a plurality of light-receiving / emitting units (10) having a first light-emitting unit (14) and a first light-receiving unit (15); and a first control unit (11) that, on the basis of whether two or more second optical wireless communication devices are positioned within each of a plurality of prescribed regions, performs control for switching between a first communication method in which communication is performed simultaneously with the plurality of second optical wireless communication devices and a second communication method in which communication is sequentially performed with the plurality of second optical wireless communication devices.

Description

Underwater optical wireless communication system and underwater optical wireless communication method

[0001] The present invention relates to an underwater optical wireless communication system and an underwater optical wireless communication method, and more particularly to an underwater optical wireless communication system and an underwater optical wireless communication method in which communication is performed between one underwater optical wireless communication device and a plurality of underwater optical wireless communication devices.

[0002] Conventionally, underwater wireless communication systems are known in which communication is performed between one underwater wireless communication device and multiple underwater wireless communication devices. Such underwater wireless communication systems are disclosed, for example, in JP 2018-70125 A. Also known are underwater optical wireless communication systems in which wireless communication using light is performed between underwater wireless communication devices. Such underwater optical wireless communication systems are disclosed, for example, in JP 2018-90017 A.

[0003] Japanese Patent Application Publication No. 2018-70125 discloses an underwater acoustic communication system including a single relay and multiple underwater vehicles. The relay disclosed in Japanese Patent Application Publication No. 2018-70125 includes acoustic communication means having a transmitter that transmits acoustic waves and a receiver that receives the acoustic waves. Each of the multiple underwater vehicles disclosed in Japanese Patent Application Publication No. 2018-70125 includes acoustic communication means having a transmitter that transmits acoustic waves and a receiver that receives the acoustic waves. In the configuration disclosed in Japanese Patent Application Publication No. 2018-70125, the single relay is configured to perform acoustic communication using acoustic waves with each of the multiple underwater vehicles.

[0004] It is generally known that communication using sound waves has a lower communication speed than communication using light or the like. Therefore, as disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2018-70125, communication using sound waves underwater has the disadvantage of slow communication speed. Therefore, the above-mentioned Japanese Patent Application Laid-Open No. 2018-90017 discloses a communication system for underwater drones, in which each of the multiple underwater drones is equipped with a transmitting and receiving antenna that transmits and receives wireless signals using light, such as visible light, and performs wireless communication using light underwater.

[0005] JP 2018-70125 A JP 2018-90017 A

[0006] In order to improve the communication speed in the configuration disclosed in JP 2018-70125 A, as disclosed in JP 2018-90017 A, when performing optical wireless communication, it is possible to efficiently communicate between a relay (first optical wireless communication device) and each of multiple underwater vehicles (second optical wireless communication devices) by simultaneously communicating between the first optical wireless communication device and each of the multiple second optical wireless communication devices. However, depending on the relative positions of the first optical wireless communication device and the multiple second optical wireless communication devices, there is a problem that interference may occur when communicating simultaneously. Furthermore, if communication is performed sequentially with each of the multiple second optical wireless communication devices regardless of the relative positions of the first optical wireless communication device and the multiple second optical wireless communication devices to avoid interference between the first optical wireless communication device and the multiple second optical wireless communication devices, there is a problem that communication takes a long time and communication efficiency is reduced.

[0007] The present invention has been made to solve the above-mentioned problems, and one object of the present invention is to provide an underwater optical wireless communication system and an underwater optical wireless communication method that can suppress interference between a first optical wireless communication device 1 and a plurality of second optical wireless communication devices 2 while suppressing a decrease in communication efficiency.

[0008] An underwater optical wireless communication system according to a first aspect of the present invention includes a first optical wireless communication device that communicates using light underwater, and a plurality of second optical wireless communication devices, each of which communicates using light underwater with the first optical wireless communication device. The first optical wireless communication device includes a plurality of light-emitting and light-receiving units, each of which has a first light-emitting unit and a first light-receiving unit, that irradiate light onto a corresponding one of a plurality of predetermined areas and receive light from the corresponding one of the plurality of predetermined areas, and a control unit that controls switching of the method of communication using light by the plurality of light-emitting and light-receiving units between a first communication method in which communication is performed simultaneously with a plurality of second optical wireless communication devices and a second communication method in which communication is performed sequentially with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices of the plurality of second optical wireless communication devices are located within each of the plurality of predetermined areas.

[0009] An underwater optical wireless communication method in a second aspect of the present invention is an underwater optical wireless communication method for communicating using light underwater between a first optical wireless communication device and each of a plurality of second optical wireless communication devices, and includes the steps of: acquiring the number of a plurality of second optical wireless communication devices located within each of a plurality of predetermined areas in which the first optical wireless communication device emits light; and switching the method of communication using light emitted from the first optical wireless communication device between a first communication method for communicating simultaneously with a plurality of second optical wireless communication devices and a second communication method for communicating sequentially with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices among the plurality of second optical wireless communication devices are located in each of the plurality of predetermined areas.

[0010] In an underwater optical wireless communication system according to a first aspect of the present invention and an underwater optical wireless communication method according to a second aspect, a communication method using light emitted from a first optical wireless communication device is switched between a first communication method in which simultaneous communication is performed with a plurality of second optical wireless communication devices and a second communication method in which sequential communication is performed with a plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices among a plurality of second optical wireless communication devices are located in each of a plurality of predetermined areas. As a result, when a plurality of second optical wireless communication devices are located in a single predetermined area, communication between the first optical wireless communication device and the plurality of second optical wireless communication devices can be performed using the second communication method in which sequential communication is performed with the plurality of second optical wireless communication devices, thereby preventing interference. Furthermore, when only one second optical wireless communication device is located in a predetermined area, communication between the first optical wireless communication device and the second optical wireless communication device can be performed using the first communication method in which simultaneous communication is performed. This prevents a decrease in efficiency of communication between the first optical wireless communication device and the second optical wireless communication device compared to when the second communication method using sequential communication is performed in all cases. As a result, when the first optical wireless communication device communicates with multiple second optical wireless communication devices located within multiple specified areas, it is possible to use both communication using the first communication method and communication using the second communication method, thereby enabling efficient communication between the first optical wireless communication device and the multiple second optical wireless communication devices while suppressing interference.

[0011] FIG. 1 is a schematic diagram showing the overall configuration of an underwater optical wireless communication system according to an embodiment. FIG. 2 is a block diagram showing the configuration of a first optical wireless communication device according to an embodiment. FIG. 3 is a block diagram showing the configuration of a second optical wireless communication device according to an embodiment. FIG. 4 is a block diagram for explaining a configuration in which a first optical wireless communication device according to an embodiment determines the position of a second optical wireless communication device. FIG. 5 is a graph for explaining a configuration in which a first optical wireless communication device according to an embodiment communicates with each of a plurality of second optical wireless communication devices using only a first communication method. FIG. 6 is a schematic diagram for explaining a configuration in which a first optical wireless communication device according to an embodiment uses both the first communication method and the second communication method when communicating with each of a plurality of second optical wireless communication devices. FIG. 7 is a schematic diagram for explaining a configuration in which a first optical wireless communication device according to an embodiment communicates with each of a plurality of second optical wireless communication devices using only the second communication method. FIG. 8 is a graph for explaining a configuration in which a first optical wireless communication device according to an embodiment switches the communication method with each of a plurality of second optical wireless communication devices. FIG. 1 is a schematic diagram illustrating a configuration in which a first control unit according to an embodiment controls a communication method when a second optical wireless communication device is located in an area where a first area and a second area overlap; FIG. 2 is a schematic diagram illustrating a configuration in which a first control unit according to an embodiment controls a communication method when a second optical wireless communication device is located in an area where first areas overlap; FIG. 3 is a schematic diagram illustrating a configuration in which a first control unit according to an embodiment controls a communication method when a second optical wireless communication device is located in an area where second areas overlap; FIG. 4 is a flowchart illustrating a process in which a first control unit according to an embodiment switches a communication method; FIG. 5 is a flowchart illustrating a process in which a first control unit according to an embodiment acquires the number of second optical wireless communication devices located in a predetermined area; and FIG. 6 is a flowchart illustrating a process in which a first control unit according to an embodiment switches a communication method for each predetermined area.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings.

[0013] 1 to 12 , a configuration of an underwater optical wireless communication system 100 according to one embodiment and an underwater optical wireless communication method using the underwater optical wireless communication system 100 will be described. The underwater optical wireless communication system 100 according to this embodiment is used for inspecting structures installed underwater, such as offshore power generation facilities, aquaculture facilities, and submarine structures. The underwater optical wireless communication method according to this embodiment is an underwater optical wireless communication method in which a first optical wireless communication device 1 and each of a plurality of second optical wireless communication devices 2 communicate using light underwater when inspecting offshore power generation facilities, aquaculture facilities, submarine structures, etc.

[0014] As shown in FIG. 1 , the underwater optical wireless communication system 100 includes a first optical wireless communication device 1 and multiple second optical wireless communication devices 2. In the example shown in FIG. 1 , the underwater optical wireless communication system 100 includes one first optical wireless communication device 1 and three second optical wireless communication devices 2. Specifically, the underwater optical wireless communication system 100 includes one first optical wireless communication device 1, a second optical wireless communication device 2a, a second optical wireless communication device 2b, and a second optical wireless communication device 2c. The underwater optical wireless communication system 100 may include three or more second optical wireless communication devices 2. The underwater optical wireless communication system 100 is a system in which one first optical wireless communication device 1 and multiple second optical wireless communication devices 2 perform bidirectional communication. The underwater optical wireless communication system 100 may include, for example, one first optical wireless communication device 1 and 2 to 20 second optical wireless communication devices 2. The underwater optical wireless communication system 100 may also include multiple first optical wireless communication devices 1. When the underwater optical wireless communication system 100 includes a plurality of first optical wireless communication devices 1, each of the plurality of first optical wireless communication devices 1 performs bidirectional communication with a corresponding one of the plurality of second optical wireless communication devices 2.

[0015] The first optical wireless communication device 1 is configured to perform underwater optical communication. Specifically, the first optical wireless communication device 1 is configured to perform underwater optical communication by emitting light to a plurality of predetermined areas 30 and receiving light from the plurality of predetermined areas 30.

[0016] Furthermore, each of the second optical wireless communication devices 2 is configured to perform underwater optical wireless communication with the first optical wireless communication device 1. Specifically, each of the second optical wireless communication devices 2 is configured to emit light to a predetermined area 31 and receive light from the predetermined area 31, thereby performing underwater optical communication.

[0017] The underwater optical wireless communication system 100 according to this embodiment is configured to perform bidirectional communication using light, in which the second optical wireless communication device 2 receives light emitted by the first optical wireless communication device 1 to a plurality of predetermined areas 30, and the first optical wireless communication device 1 receives light emitted by the plurality of second optical wireless communication devices 2 to a predetermined area 31. That is, each of the plurality of predetermined areas 30 is an area in which communication with the first optical wireless communication device 1 is possible. Furthermore, the predetermined area 31 is an area in which communication with the second optical wireless communication device 2 is possible.

[0018] The detailed configuration of the first optical wireless communication device 1 and the detailed configuration of the second optical wireless communication device 2 will be described later.

[0019] 2, the first optical wireless communication device 1 includes a plurality of light receiving and emitting units 10 and a first control unit 11. In this embodiment, the first optical wireless communication device 1 further includes a first storage unit 12 and a communication unit 13. The first control unit 11 is an example of the "control unit" in the claims.

[0020] Each of the multiple light receiving and emitting units 10 has a first light emitter 14 and a first light receiving unit 15. The multiple light receiving and emitting units 10 are configured to emit light to corresponding areas of multiple predetermined areas 30 (see FIG. 1 ) and to receive light from corresponding areas of the multiple predetermined areas 30. In this embodiment, the first optical wireless communication device 1 has a first light receiving and emitting unit 10a, a second light receiving and emitting unit 10b, and a third light receiving and emitting unit 10c. The first light receiving and emitting unit 10a, the second light receiving and emitting unit 10b, and the third light receiving and emitting unit 10c have the same configuration as one another, except for their arrangement in the first optical wireless communication device 1. In this embodiment, each of the multiple light receiving and emitting units 10 includes a filter 16.

[0021] The first light-emitting unit 14 is configured to emit light of a predetermined wavelength. In this embodiment, the first light-emitting unit 14 is configured to emit light of any one of green, light blue, blue, and purple wavelength bands. The first light-emitting unit 14 includes, for example, a laser diode.

[0022] The first light receiving unit 15 is configured to receive light irradiated onto the light receiving and emitting unit 10. The first light receiving unit 15 is also configured to output a signal based on the received light to the first control unit 11. The first light receiving unit 15 includes, for example, a photomultiplier tube.

[0023] The filter 16 is disposed upstream of the first light receiving unit 15 on the path of light incident on the light receiving and emitting unit 10. That is, light that has passed through the filter 16 is incident on the first light receiving unit 15. The filter 16 is configured to selectively transmit light in a predetermined wavelength band. In this embodiment, the filter 16 is configured to selectively transmit light in the wavelength band of light emitted from the second optical wireless communication device 2 (see FIG. 1 ). The filter 16 includes, for example, a low-pass filter, a high-pass filter, a band-cut filter, or a filter that combines any of these.

[0024] In this embodiment, the first light-emitting unit 14 is housed in a first housing 17. The first light-receiving unit 15 and the filter 16 are housed in a second housing 18. A window (not shown) is provided in the first housing 17. The first housing 17 is made of a material that does not transmit light, such as a metal material. Therefore, the first housing 17 is configured so that light emitted from the first light-emitting unit 14 can be irradiated to the outside of the first optical wireless communication device 1 through the window.

[0025] The second housing 18 is provided with a window (not shown). The second housing 18 is made of a material that does not transmit light, such as a metal material. Therefore, the second housing 18 is configured to allow light emitted to the light receiving and emitting unit 10 to enter through the window. The filter 16 is disposed between the window and the first light receiving unit 15.

[0026] The first control unit 11 is configured to perform various controls of the first optical wireless communication device 1. The first control unit 11 is also configured to switch the communication method between the first optical wireless communication device 1 and the second optical wireless communication device 2. The first control unit 11 is configured with a processor such as a CPU (Central Processing Unit) or a circuit, and memories such as a ROM (Read Only Memory) and a RAM (Random Access Memory). Details of the configuration by which the first control unit 11 switches the communication method between the first optical wireless communication device 1 and the second optical wireless communication device 2 will be described later.

[0027] The first storage unit 12 is configured to store test information 50, which will be described later. The first storage unit 12 also stores various programs executed by the first control unit 11. The first storage unit 12 includes a non-volatile storage device, such as a hard disk drive (HDD) or a solid state drive (SSD).

[0028] The communication unit 13 is configured to be able to communicate with a communication device (not shown) provided on a mother ship (not shown) located on the sea surface or a communication device (not shown) provided on land. The communication unit 13 is connected to the communication device provided on the mother ship located on the sea surface or the communication device provided on land via a wired or wireless connection, and is configured to be able to communicate the inspection information 50.

[0029] 2, the first optical wireless communication device 1 includes three light receiving and emitting units 10. Therefore, the first optical wireless communication device 1 is configured to emit light to each of the predetermined area 30a (see FIG. 1), the predetermined area 30b (see FIG. 1), and the predetermined area 30c (see FIG. 1), and to receive light from each of the predetermined area 30a, the predetermined area 30b, and the predetermined area 30c.

[0030] 3 , each of the second optical wireless communication devices 2 includes a light receiving and emitting unit 20, a propulsion mechanism 21, and an inspection information acquiring unit 22. In this embodiment, each of the second optical wireless communication devices 2 further includes a second control unit 23 and a second storage unit 24.

[0031] The light receiving and emitting unit 20 includes a second light emitting unit 20a and a second light receiving unit 20b. The light receiving and emitting unit 20 also includes a filter 20c.

[0032] The second light-emitting unit 20a is configured to emit light toward a predetermined region 31 (see FIG. 1). In this embodiment, the second light-emitting unit 20a is configured to emit light in one of the wavelength bands of green, light blue, blue, and purple, for example, and in a wavelength band different from the light emitted by the first light-emitting unit 14 (see FIG. 2). The second light-emitting unit 20a includes, for example, a laser diode.

[0033] The second light receiving unit 20b is configured to receive light irradiated onto the light receiving and emitting unit 20. The second light receiving unit 20b is also configured to output a signal based on the received light to the second control unit 23. The second light receiving unit 20b includes, for example, a photomultiplier tube.

[0034] In this embodiment, each of the multiple second optical wireless communication devices 2 is configured to emit light from the second light-emitting unit 20a toward a predetermined area 31 (see Figure 1) and to communicate by having the second light-receiving unit 20b receive the light irradiated from the predetermined area 31.

[0035] The filter 20c is disposed upstream of the second light receiving unit 20b on the path of light incident on the light receiving and emitting unit 20. That is, light transmitted through the filter 20c is incident on the second light receiving unit 20b. The filter 20c is configured to selectively transmit light of a predetermined wavelength band. In this embodiment, the filter 20c is configured to selectively transmit light of the wavelength band of light emitted from the first light emitter 14 (see FIG. 2). The filter 20c includes, for example, a low-pass filter, a high-pass filter, a band-cut filter, or a filter that combines these.

[0036] In this embodiment, the second light emitter 20a is housed in a first housing 25. The second light receiver 20b and the filter 20c are housed in a second housing 26. The first housing 25 has a window (not shown). The first housing 25 is made of a material that does not transmit light, such as a metal material. Therefore, the first housing 25 is configured to allow light emitted from the second light emitter 20a to be irradiated to the outside through the window.

[0037] The second housing 26 is provided with a window (not shown). The second housing 26 is made of a material that does not transmit light, such as a metal material. Therefore, the second housing 26 is configured to allow light emitted to the light receiving and emitting unit 20 to enter through the window. The filter 20c is disposed between the window and the second light receiving unit 20b.

[0038] The propulsion mechanism 21 is configured to provide a propulsive force to the second optical wireless communication device 2 under the control of the second control unit 23. The propulsion mechanism 21 includes a propeller (not shown) and a drive source (not shown) that drives the propeller. The propulsion mechanism 21 may be a so-called screw mechanism that obtains propulsive force by rotating a propeller to paddle through water, or may be a so-called water jet propulsion mechanism that obtains propulsive force by ejecting a high-pressure water stream backward.

[0039] In this embodiment, the second optical wireless communication device 2 is a mobile body that can move underwater by a propulsion mechanism 21. Examples of the mobile body include an AUV (Autonomous Underwater Vehicle) and a ROV (Remotely Operated Vehicle) that is controlled by a person via a cable.

[0040] The inspection information acquisition unit 22 is configured to acquire inspection information 50 including at least an image of the inspection object. The inspection information acquisition unit 22 includes, for example, an optical camera. The inspection information acquisition unit 22 may also include sensors such as a magnetic sensor and a temperature sensor. When the inspection information acquisition unit 22 includes a magnetic sensor and a temperature sensor, the inspection information acquisition unit 22 may acquire magnetic information, temperature information, and the like as the inspection information 50 along with the image of the inspection object.

[0041] The second control unit 23 is configured to perform various controls of the second optical wireless communication device 2. The second control unit 23 is configured with a processor such as a CPU or a circuit, and memories such as a ROM and a RAM.

[0042] The second storage unit 24 stores various programs executed by the second control unit 23. The second storage unit 24 is also configured to store the examination information 50 acquired by the examination information acquisition unit 22. The second storage unit 24 includes, for example, a non-volatile storage device such as an HDD or an SSD.

[0043] In this embodiment, each of the second optical wireless communication devices 2 is a slave device that moves around the first optical wireless communication device 1 (see FIG. 2 ) and transmits inspection information 50 acquired by the inspection information acquisition unit 22 to the first optical wireless communication device 1 using light emitted from the second light emitter 20 a. The first optical wireless communication device 1 is also a master device that acquires the inspection information 50 from each of the multiple second optical wireless communication devices 2. In this embodiment, the first optical wireless communication device 1 is configured to transmit the acquired inspection information 50 to a communication device located on a mother ship or on land.

[0044] (Determining the Position of the Second Optical Wireless Communication Device) In this embodiment, since each of the multiple second optical wireless communication devices 2 is configured to be movable, when communication is performed between the first optical wireless communication device 1 and the second optical wireless communication device 2, the first control unit 11 (see FIG. 2 ) determines the position of each of the multiple second optical wireless communication devices 2. Specifically, as shown in FIG. 4 , the first control unit 11 is configured to emit, from the multiple first light-emitting units 14 to each of the multiple second optical wireless communication devices 2 in sequence, a determination signal light 40 that is used to determine the number of multiple second optical wireless communication devices 2 included in each of the multiple predetermined areas 30.

[0045] Furthermore, each of the second optical wireless communication devices 2 is configured to emit a response signal light 41 for responding to the first optical wireless communication device 1 when the second optical wireless communication device 2 receives the discrimination signal light 40 .

[0046] The discrimination signal light 40 emitted from the first optical wireless communication device 1 includes information for identifying the light-emitting target. The information for identifying the light-emitting target is, for example, an identification number uniquely assigned to each of the multiple second optical wireless communication devices 2. Each of the multiple second optical wireless communication devices 2 determines whether or not its own identification number is included in the received discrimination signal light 40. If its own identification number is included in the received discrimination signal light 40, the second optical wireless communication device 2 emits a response signal light 41. At that time, the second optical wireless communication device 2 includes its own identification number in the response signal light 41. This allows the first optical wireless communication device 1 to identify the second optical wireless communication device 2 that emitted the response signal light 41 based on the identification number included in the received response signal light 41.

[0047] As shown in graph 60 in Fig. 5, the first control unit 11 (see Fig. 4) is configured to control the plurality of light receiving and emitting units 10 (see Fig. 4) to sequentially emit the discrimination signal light 40 (see Fig. 4). In graph 60, the horizontal axis is a graph representing time.

[0048] The solid line 60a in the graph 60 indicates the period during which the first optical wireless communication device 1 (see FIG. 4) communicates with the second optical wireless communication device 2a (see FIG. 4). Specifically, the solid line 60a indicates the period during which the first light receiving and emitting unit 10a (see FIG. 4) waits to see whether it receives the response signal light 41a (see FIG. 4) from the second optical wireless communication device 2a after emitting the discrimination signal light 40a (see FIG. 4) to the second optical wireless communication device 2a.

[0049] The thick solid line 60b in the graph 60 indicates the period during which the first optical wireless communication device 1 communicates with the second optical wireless communication device 2b (see FIG. 4). Specifically, the thick solid line 60b indicates the period during which the first light receiving and emitting unit 10a waits to see whether it receives the response signal light 41b (see FIG. 4) from the second optical wireless communication device 2b after emitting the discrimination signal light 40a to the second optical wireless communication device 2b.

[0050] The dashed line 60c in the graph 60 indicates the period during which the first optical wireless communication device 1 communicates with the second optical wireless communication device 2c (see FIG. 4). Specifically, the dashed line 60c indicates the period during which the first light receiving and emitting unit 10a waits to see whether it receives the response signal light 41c (see FIG. 4) from the second optical wireless communication device 2c after emitting the discrimination signal light 40a to the second optical wireless communication device 2c.

[0051] In addition, the solid line 60d, the thick solid line 60e, and the dashed line 60f in the graph 60 each indicate a period of time during which the second light receiving / emitting unit 10b (see Figure 4) emits a discrimination signal light 40b (see Figure 4) to each of the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c, and then waits to see whether or not the response signal light 41a to the response signal light 41c are received from the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c.

[0052] In addition, the solid line 60g, the thick solid line 60h, and the dashed line 60i in the graph 60 each indicate a period of time during which the third light receiving / emitting unit 10c (see Figure 4) waits to see whether or not the response signal light 41a to the response signal light 41c are received from the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c, after emitting the discrimination signal light 40c (see Figure 4) to each of the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c.

[0053] That is, the first control unit 11 is configured to sequentially control the first light receiving and emitting unit 10a, the second light receiving and emitting unit 10b, and the third light receiving and emitting unit 10c to emit discrimination signal light 40, and each light receiving and emitting unit 10 receives response signal light 41 emitted from each of the multiple second optical wireless communication devices 2.

[0054] Referring again to Fig. 4, in the example shown in Fig. 4, the second optical wireless communication device 2a is located within the predetermined area 30a (see Fig. 1) and receives a discrimination signal light 40a emitted from the first light receiving and emitting unit 10a. Then, having received the discrimination signal light 40a, the second optical wireless communication device 2a emits a response signal light 41a from within the predetermined area 30a to the first light receiving and emitting unit 10a.

[0055] The first optical wireless communication device 1 determines that the second optical wireless communication device 2a is located within the predetermined area 30a by receiving the response signal light 41a at the first light receiving and emitting part 10a.

[0056] Note that the second optical wireless communication devices 2b and 2c are not located within the predetermined area 30a. Therefore, the second optical wireless communication devices 2b and 2c do not receive the discrimination signal light 40a emitted from the first light receiving and emitting unit 10a. Therefore, the second optical wireless communication devices 2b and 2c do not emit the response signal light 41b and the response signal light 41c to the first light receiving and emitting unit 10a. In other words, the first control unit 11 can determine the presence or absence and number of second optical wireless communication devices 2 located within the predetermined area 30, based on the response signal light 41 in response to the discrimination signal light 40 emitted from the first light receiving and emitting unit 10a.

[0057] Similarly to the first light-receiving and light-emitting unit 10a, the second light-receiving and light-emitting unit 10b emits a discrimination signal light 40b toward the predetermined region 30b (see FIG. 1) and determines the presence and number of second optical wireless communication devices 2 located within the predetermined region 30b based on which of the response signal lights 41a to 41c it receives. In the example shown in FIG. 4, because the second optical wireless communication device 2b is located within the predetermined region 30b, the discrimination signal light 40b emitted from the second light-receiving and light-emitting unit 10b is received by the second optical wireless communication device 2b. Furthermore, upon receiving the discrimination signal light 40b, the second optical wireless communication device 2b emits a response signal light 41b toward the second light-receiving and light-emitting unit 10b. As a result, the first control unit 11 determines that the second optical wireless communication device 2b is located within the predetermined region 30b.

[0058] Similarly to the first and second light-receiving and -emitting units 10a and 10b, the third light-receiving and -emitting unit 10c also emits a discrimination signal light 40c toward the predetermined region 30c (see FIG. 1 ) and determines the presence and number of second optical wireless communication devices 2 located within the predetermined region 30c based on which of the response signal lights 41a to 41c it receives. In the example shown in FIG. 4 , because the second optical wireless communication device 2c is located within the predetermined region 30c, the discrimination signal light 40c emitted from the third light-receiving and -emitting unit 10c is received by the second optical wireless communication device 2c. Furthermore, upon receiving the discrimination signal light 40c, the second optical wireless communication device 2c emits a response signal light 41c toward the third light-receiving and -emitting unit 10c. As a result, the first control unit 11 determines that the second optical wireless communication device 2c is located within the predetermined region 30c.

[0059] In this embodiment, each of the second optical wireless communication devices 2 includes a propulsion mechanism 21 (see FIG. 3 ) and is configured to be movable underwater. Furthermore, the relative positions of the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2 may change if either the first optical wireless communication device 1 or the second optical wireless communication device 2 is swept away by ocean currents or the like.

[0060] Therefore, the first control unit 11 is configured to control the plurality of first light-emitting units 14 to emit discrimination signal light 40 sequentially to each of the plurality of second optical wireless communication devices 2 at predetermined time intervals, and to control the plurality of first light-receiving units 15 to receive response signal light 41 from each of the plurality of second optical wireless communication devices 2 at predetermined time intervals. The predetermined time interval is, for example, one second.

[0061] Furthermore, when the relative positions of the first optical wireless communication device 1 and the plurality of second optical wireless communication devices 2 change, interference may occur in communication between the first optical wireless communication device 1 and each of the plurality of second optical wireless communication devices 2. Therefore, in this embodiment, the first control unit 11 is configured to switch the communication method between the first optical wireless communication device 1 and each of the plurality of second optical wireless communication devices 2 based on the relative positions of the first optical wireless communication device 1 and the plurality of second optical wireless communication devices 2.

[0062] (Communication Using Only the First Communication Method) First, a configuration in which the first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 communicate using only the first communication method will be described with reference to Fig. 6. The first communication method is a method in which the first optical wireless communication device 1 communicates simultaneously with the multiple second optical wireless communication devices 2.

[0063] 6 illustrates a state in which each of the second optical wireless communication devices 2 is located in a different area among a plurality of predetermined areas 30. Specifically, the second optical wireless communication device 2a is located in the predetermined area 30a, the second optical wireless communication device 2b is located in the predetermined area 30b, and the second optical wireless communication device 2c is located in the predetermined area 30c. In this embodiment, a first area 32 is defined as an area among the plurality of predetermined areas 30 in which any one of the second optical wireless communication devices 2 is located. The predetermined area 30a, the predetermined area 30b, and the predetermined area 30c illustrated in FIG. 6 are all first areas 32.

[0064] 6, when the second optical wireless communication devices 2 are located in different areas, the first optical wireless communication device 1 simultaneously communicates with each of the second optical wireless communication devices 2a to 2c. That is, communication using the first light receiving and emitting unit 10a, communication using the second light receiving and emitting unit 10b, and communication using the third light receiving and emitting unit 10c are simultaneously performed.

[0065] (Communication Using First and Second Communication Methods Together) Next, a configuration in which the first optical wireless communication device 1 and multiple second optical wireless communication devices 2 communicate using the first and second communication methods together will be described with reference to Fig. 7. The second communication method is a method in which the first optical wireless communication device 1 communicates sequentially with each of the multiple second optical wireless communication devices 2.

[0066] In the example shown in Fig. 7, the second optical wireless communication device 2a and the second optical wireless communication device 2b are located within the predetermined region 30a, and the second optical wireless communication device 2c is located within the predetermined region 30c. This state may occur, for example, when the second optical wireless communication device 2b moves from the state shown in Fig. 6 to the predetermined region 30a. In this embodiment, a region among the plurality of predetermined regions 30 in which two or more second optical wireless communication devices 2 out of the plurality of second optical wireless communication devices 2 are located is defined as a second region 33. In the example shown in Fig. 7, the predetermined region 30a is the second region 33. In the example shown in Fig. 7, the predetermined region 30c is the first region 32.

[0067] 7, when two second optical wireless communication devices 2 are located within one predetermined area 30a, the first optical wireless communication device 1 cannot communicate with the second optical wireless communication device 2a and the second optical wireless communication device 2b simultaneously within the predetermined area 30a. On the other hand, either the second optical wireless communication device 2a or the second optical wireless communication device 2b located within the predetermined area 30a can communicate with the second optical wireless communication device 2c located within the predetermined area 30c simultaneously.

[0068] Therefore, in this embodiment, the first control unit 11 (see FIG. 2 ) is configured to control the multiple light receiving and emitting units 10 (see FIG. 2 ) to communicate with the second optical wireless communication devices 2 using the first communication method when communicating with the second optical wireless communication devices 2 in the first area 32. Furthermore, the first control unit 11 is configured to control the multiple light receiving and emitting units 10 to communicate with each of the multiple second optical wireless communication devices 2 sequentially using the second communication method when communicating with each of the second optical wireless communication devices 2 in the second area 33.

[0069] In the example shown in Figure 7, the first control unit 11 controls the first light receiving and emitting unit 10a so that communication by the first light receiving and emitting unit 10a is performed using the second communication method, and controls the third light receiving and emitting unit 10c so that communication by the third light receiving and emitting unit 10c is performed using the first communication method.

[0070] In this embodiment, when communicating with a second optical wireless communication device 2 located in the first region 32, the first control unit 11 is configured to control the multiple light receiving and emitting units 10 to communicate using a space division method as the first communication method, in which communication is performed simultaneously with second optical wireless communication devices 2 located in different regions. Furthermore, when communicating with each of the multiple second optical wireless communication devices 2 located in the second region 33, the first control unit 11 is configured to control the multiple light receiving and emitting units 10 to communicate using a time division method as the second communication method, in which communication is performed sequentially with each of the multiple second optical wireless communication devices 2 located in one region.

[0071] (Communication Using Only the Second Communication Method) Next, with reference to FIG. 8, a configuration in which the first optical wireless communication device 1 and each of the plurality of second optical wireless communication devices 2 communicate using only the second communication method will be described.

[0072] In the example shown in Fig. 8, the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c are all located within the predetermined area 30a. This state occurs when the second optical wireless communication device 2b and the second optical wireless communication device 2c each move into the predetermined area 30a from the state shown in Fig. 6. The state shown in Fig. 8 also occurs when the second optical wireless communication device 2c moves into the predetermined area 30a from the state shown in Fig. 7.

[0073] As shown in Figure 8, when multiple second optical wireless communication devices 2 are located only within one specified area 30a (second area 33), the first control unit 11 (see Figure 2) communicates with each of the second optical wireless communication devices 2a, 2b, and 2c located within the specified area 30a using only the second communication method.

[0074] In this embodiment, each of the multiple second optical wireless communication devices 2 has a propulsion mechanism 21 (see FIG. 3 ). Therefore, each of the multiple second optical wireless communication devices 2 can move freely. As each of the multiple second optical wireless communication devices 2 moves, multiple second optical wireless communication devices 2 may be located within one predetermined area 30, as shown in FIG. 8 . In this case, when communication is performed with a second optical wireless communication device 2 located within one predetermined area 30 using the first communication method, interference occurs.

[0075] Furthermore, depending on the positional relationship between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2, there are cases where the first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 can communicate simultaneously as shown in Fig. 6 , and cases where they cannot communicate simultaneously as shown in Figs. 7 and 8 . Therefore, in this embodiment, the first control unit 11 is configured to control switching of the communication method using light by the multiple light receiving and emitting units 10 based on the positions of the multiple second optical wireless communication devices 2 relative to the multiple predetermined areas 30. Specifically, the first control unit 11 is configured to control switching of the communication method using light by the multiple light receiving and emitting units 10 between a first communication method in which communication is performed simultaneously with the multiple second optical wireless communication devices 2 and a second communication method in which communication is performed sequentially with the multiple second optical wireless communication devices 2, based on whether two or more second optical wireless communication devices 2 out of the multiple second optical wireless communication devices 2 are located within each of the multiple predetermined areas 30.

[0076] A configuration in which the first control unit 11 (see FIG. 2) switches the communication method will be described with reference to a graph 61 shown in Fig. 9. In the graph 61, the horizontal axis represents time.

[0077] Graph 61 shown in Figure 9 shows a configuration in which the first control unit 11 switches the communication method when, for example, the positional relationship between the first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 changes from the state shown in Figure 6, through the state shown in Figure 7, to the state shown in Figure 8 due to the movement of the multiple second optical wireless communication devices 2.

[0078] As shown in graph 61, up until time t1, the second optical wireless communication devices 2a to 2c are located in the predetermined areas 30a to 30c, respectively, as shown in Fig. 6. Thereafter, at time t1, the second optical wireless communication device 2b moves into the predetermined area 30a, and the second optical wireless communication device 2a and the second optical wireless communication device 2b are located within the predetermined area 30a, and the second optical wireless communication device 2c is located within the predetermined area 30c, as shown in Fig. 7. Then, at time t2, the second optical wireless communication device 2c moves into the predetermined area 30a, and all of the second optical wireless communication devices 2a to 2c are located within the predetermined area 30a, as shown in Fig. 8.

[0079] Until time t1, each second optical wireless communication device 2 is located in a different predetermined area 30, and therefore the first control unit 11 controls each of the first light receiving and emitting unit 10a (see Figure 2), the second light receiving and emitting unit 10b (see Figure 2), and the third light receiving and emitting unit 10c (see Figure 2) to communicate using the first communication method.

[0080] At time t1, the second optical wireless communication device 2a and the second optical wireless communication device 2b are located within the predetermined area 30a, so the first control unit 11 switches the communication method used by the first light receiving and emitting unit 10a from the first communication method to the second communication method. The first control unit 11 also stops communication by the second light receiving and emitting unit 10b. Note that the second optical wireless communication device 2c, located within the predetermined area 30c, does not move, so the first control unit 11 does not change the communication method used by the third light receiving and emitting unit 10c.

[0081] After that, at time t2, the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c are all located within the predetermined area 30a, so the first control unit 11 stops communication by the third light receiving and emitting unit 10c. The first control unit 11 also switches the communication method by the first light receiving and emitting unit 10a to a method of communicating with the three second optical wireless communication devices 2 using the second communication method.

[0082] (Configuration when second optical wireless communication device is located in an area where predetermined areas overlap) Here, as shown in Fig. 10 , there is a case where one of the plurality of second optical wireless communication devices 2 moves into an overlapping area 34, which is an area where a plurality of predetermined areas 30 overlap. The example shown in Fig. 10 shows a state in which the second optical wireless communication device 2c has moved into the overlapping area 34, where the predetermined area 30a and the predetermined area 30b overlap.

[0083] In this case, the second optical wireless communication device 2c is able to receive and emit light with the first light receiving and emitting unit 10a and the second light receiving and emitting unit 10b. In the example shown in Fig. 10, three second optical wireless communication devices 2 are located within the predetermined area 30a, and one second optical wireless communication device 2 is located within the predetermined area 30b. That is, the overlapping area 34 shown in Fig. 10 is an area where the first area 32 and the second area 33 overlap. In this case, the first control unit 11 is configured to control the light receiving and emitting unit 10 to switch the communication method with the multiple second optical wireless communication devices 2 to the second communication method.

[0084] For example, the first control unit 11 is configured to control the first light receiving and emitting unit 10a to sequentially communicate with each of the second optical wireless communication devices 2a, 2b, and 2c. The first control unit 11 may also be configured to communicate with the second optical wireless communication devices 2a and 2b according to a second communication method using the first light receiving and emitting unit 10a, and to communicate with the second optical wireless communication device 2c according to a second communication method using the second light receiving and emitting unit 10b.

[0085] Furthermore, as shown in FIG. 11, when the second optical wireless communication device 2c moves into an overlapping area 34 where the predetermined area 30b, which is the first area 32, and the predetermined area 30c, which is the first area 32, overlap, the first control unit 11 controls either the second light receiving and emitting unit 10b or the third light receiving and emitting unit 10c to communicate with the second optical wireless communication device 2c by switching them to the first communication method.

[0086] 12 , when the second optical wireless communication device 2b moves into an overlapping region 34 where the predetermined region 30a, which is the second region 33, and the predetermined region 30b, which is the second region 33, overlap, the first control unit 11 is configured to communicate with the second optical wireless communication device 2a and the second optical wireless communication device 2b by switching the communication method by the first light receiving and emitting unit 10a to the second communication method, and to communicate with the second optical wireless communication device 2c by switching the communication method by the second light receiving and emitting unit 10b to the second communication method. Note that the first control unit 11 may be configured to communicate with the second optical wireless communication device 2a by switching the communication method by the first light receiving and emitting unit 10a to the second communication method, and to communicate with the second optical wireless communication device 2b and the second optical wireless communication device 2c by switching the communication method by the second light receiving and emitting unit 10b to the second communication method.

[0087] When the second optical wireless communication device 2 is located in the overlapping region 34, the communication method of which light-emitting and receiving unit 10 (see FIG. 2 ) is to be switched may be determined, for example, based on a preset priority order. For example, if the priority order is set so that the first light-emitting and receiving unit 10a has the highest priority, followed by the second light-emitting and receiving unit 10b and the third light-emitting and receiving unit 10c, in the example shown in FIG. 10 , the first control unit 11 controls the first light-emitting and receiving unit 10a to switch to the second communication method and to stop communication between the second light-emitting and receiving unit 10b and the third light-emitting and receiving unit 10c. In addition, in the example shown in FIG. 11 , the first control unit 11 controls the communication method of the second light-emitting and receiving unit 10b to switch to the first communication method. In addition, in the example shown in Figure 12, the first control unit 11 communicates with the second optical wireless communication device 2a and the second optical wireless communication device 2b by switching to a second communication method using the communication method of the first light receiving and emitting unit 10a, and communicates with the second optical wireless communication device 2c by switching the communication method of the second light receiving and emitting unit 10b to the second communication method.

[0088] (Communication Method Switching Process) Next, the process of switching the communication method performed by the first control unit 11 (see FIG. 2) will be described with reference to Fig. 13. The process of switching the communication method performed by the first control unit 11 is performed when any one of the plurality of second optical wireless communication devices 2 (see FIG. 1) moves to a different predetermined area 30 (see FIG. 1).

[0089] In step 101, the first control unit 11 acquires the number of second optical wireless communication devices 2 located in each of the plurality of predetermined regions 30 (see FIG. 1) into which the first optical wireless communication device 1 (see FIG. 1) emits light. Details of the process by which the first control unit 11 acquires the number of second optical wireless communication devices 2 located in each of the plurality of predetermined regions 30 will be described later.

[0090] In step 102, the first control unit 11 switches the communication method using light emitted from the first optical wireless communication device 1 between a first communication method in which communication is performed simultaneously with the plurality of second optical wireless communication devices 2 and a second communication method in which communication is performed sequentially with the plurality of second optical wireless communication devices 2, based on whether two or more second optical wireless communication devices 2 out of the plurality of second optical wireless communication devices 2 are located in each of the plurality of predetermined areas 30. Then, the processing ends. Details of the process in which the first control unit 11 switches the communication method between the first communication method and the second communication method will be described later.

[0091] (Process for obtaining the number of second optical wireless communication devices within a specified area) Next, referring to Figure 14, we will explain the process in which the first control unit 11 (see Figure 2) obtains the number of multiple second optical wireless communication devices 2 (see Figure 1) located within each of multiple specified areas 30 (see Figure 1).

[0092] In step 101a, the first control unit 11 emits a discrimination signal light 40 (see FIG. 4 ). Specifically, the first control unit 11 controls the multiple light receiving and emitting units 10 (see FIG. 2 ) to emit the discrimination signal light 40. In this embodiment, the first control unit 11 controls the light receiving and emitting units 10 to emit the discrimination signal light 40 at predetermined time intervals for all of the multiple second optical wireless communication devices 2 included in the underwater optical wireless communication system 100 (see FIG. 1 ). Specifically, the first control unit 11 controls the light receiving and emitting units 10 to emit a discrimination signal light 40a (see FIG. 4 ), a discrimination signal light 40b (see FIG. 4 ), and a discrimination signal light 40c (see FIG. 4 ) for the second optical wireless communication device 2a (see FIG. 4 ), the second optical wireless communication device 2b (see FIG. 4 ), and the second optical wireless communication device 2c (see FIG. 4 ), respectively.

[0093] In step 101b, the first control unit 11 receives the response signal light 41 (see FIG. 4). Specifically, the first control unit 11 receives the response signal light 41a (see FIG. 4), the response signal light 41b (see FIG. 4), and the response signal light 41c (see FIG. 4) from the second optical wireless communication device 2a, the second optical wireless communication device 2b, and the second optical wireless communication device 2c, respectively, at predetermined time intervals. Note that each of the multiple second optical wireless communication devices 2 emits the response signal light 41 when it receives the discrimination signal light 40 emitted toward itself. Therefore, if the corresponding second optical wireless communication device 2 is not located within the predetermined region 30 into which the discrimination signal light 40 is emitted, the response signal light 41 is not emitted to the light receiving and emitting unit 10.

[0094] In step 101 c, the first control unit 11 obtains the number of second optical wireless communication devices 2 located within the predetermined area 30 based on the received response signal light 41 .

[0095] In step 101d, the first control unit 11 determines whether the number of second optical wireless communication devices 2 has been acquired in all of the predetermined areas 30. If the number of second optical wireless communication devices 2 has been acquired in all of the predetermined areas 30, the process proceeds to step 102. If the number of second optical wireless communication devices 2 has not been acquired in all of the predetermined areas 30, the process proceeds to step 101e.

[0096] In step 101e, the first control unit 11 switches the light receiving and emitting unit 10 that emits the discrimination signal light 40. That is, the first control unit 11 switches the predetermined area 30 from which the number of second optical wireless communication devices 2 is obtained. Then, the process proceeds to step 101a.

[0097] (Processing for Switching Communication Method for Each Predetermined Area) Next, with reference to FIG. 15, a process in which the first control unit 11 (see FIG. 2) switches the communication method for each predetermined area 30 (see FIG. 1) will be described.

[0098] In step 102a, the first control unit 11 acquires the number of second optical wireless communication devices 2 (see FIG. 3) located within the predetermined area 30 and the communication method of the light receiving and emitting unit 10 (see FIG. 2).

[0099] In step 102b, the first control unit 11 determines whether the communication method used by the light-emitting and receiving unit 10 is suitable. Specifically, when there is one second optical wireless communication device 2 located within the predetermined area, the first control unit 11 determines whether the communication method used by the light-emitting and receiving unit 10 is the first communication method. Furthermore, when there are two or more second optical wireless communication devices 2 located within the predetermined area 30, the first control unit 11 determines whether the communication method used by the light-emitting and receiving unit 10 is the second communication method. If the communication method used by the light-emitting and receiving unit 10 is suitable, the process proceeds to step 102f. If the communication method used by the light-emitting and receiving unit 10 is not suitable, the process proceeds to step 102c.

[0100] In step 102c, the first control unit 11 determines whether or not the number of second optical wireless communication devices 2 located within the predetermined area 30 is two or more. If the number of second optical wireless communication devices 2 located within the predetermined area 30 is two or more, the process proceeds to step 102d. If the number of second optical wireless communication devices 2 located within the predetermined area 30 is one, the process proceeds to step 102e.

[0101] In step 102d, the first control unit 11 switches the communication method of the light receiving and emitting unit 10 to the second communication method. After that, the process proceeds to step 102f.

[0102] Furthermore, if the process proceeds from step 102c to step 102e, in step 102e, the first control unit 11 switches the communication method of the light receiving and emitting unit 10 to the first communication method. After that, the process proceeds to step 102f.

[0103] In step 102f, the first control unit 11 determines whether or not it has confirmed whether the communication methods of all the light-emitting and receiving units 10 are suitable. If it has not confirmed whether or not the communication methods of all the light-emitting and receiving units 10 are suitable, the process proceeds to step 102g. If it has confirmed whether or not the communication methods of all the light-emitting and receiving units 10 are suitable, the process ends.

[0104] When the process proceeds from step 102f to step 102g, in step 102g, the first control unit 11 switches the light receiving and emitting unit 10 for checking the communication method, and then the process proceeds to step 102a.

[0105] (Effects of this embodiment) In this embodiment, the following effects can be obtained.

[0106] In this embodiment, as described above, the underwater optical wireless communication system 100 includes a first optical wireless communication device 1 that performs communication using light underwater, and a plurality of second optical wireless communication devices 2 that each perform wireless communication using light underwater with the first optical wireless communication device 1. The first optical wireless communication device 1 includes a plurality of light-emitting and receiving units 10, each having a first light-emitting unit 14 and a first light-receiving unit 15, that irradiate light onto a corresponding one of a plurality of predetermined areas 30 and receive light from the corresponding one of the plurality of predetermined areas 30, and a first control unit 11 that performs control to switch the method of communication using light by the plurality of light-emitting and receiving units 10 between a first communication method in which communication is performed simultaneously with a plurality of second optical wireless communication devices 2, and a second communication method in which communication is performed sequentially with the plurality of second optical wireless communication devices 2, based on whether two or more second optical wireless communication devices 2 out of the plurality of predetermined areas 30 are located within each of the plurality of predetermined areas 30.

[0107] As a result, when multiple second optical wireless communication devices 2 are located within one predetermined area 30, communication between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2 can be performed using the second communication method in which communication is performed sequentially with the multiple second optical wireless communication devices 2, thereby preventing interference. Furthermore, when only one second optical wireless communication device 2 is located within the predetermined area 30, communication between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2 can be performed using the first communication method in which communication is performed simultaneously. This prevents a decrease in the efficiency of communication between the first optical wireless communication device 1 and the second optical wireless communication device 2 compared to when the second communication method in which communication is performed sequentially is used in all cases. As a result, when the first optical wireless communication device 1 communicates with multiple second optical wireless communication devices 2 located within multiple predetermined areas 30, communication using the first communication method and communication using the second communication method can be used together. This prevents interference and a decrease in communication efficiency between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2.

[0108] Furthermore, in this embodiment, as described above, the underwater optical wireless communication method is an underwater optical wireless communication method for performing communication using light underwater between a first optical wireless communication device 1 and each of a plurality of second optical wireless communication devices 2, and includes the steps of: acquiring the number of a plurality of second optical wireless communication devices 2 located in each of a plurality of predetermined areas 30 in which the first optical wireless communication device 1 emits light; and switching the method of communication using light emitted from the first optical wireless communication device 1 between a first communication method for communicating simultaneously with a plurality of second optical wireless communication devices 2 and a second communication method for communicating sequentially with a plurality of second optical wireless communication devices 2, based on whether two or more second optical wireless communication devices 2 out of the plurality of second optical wireless communication devices 2 are located in each of the plurality of predetermined areas 30.

[0109] This makes it possible to provide an underwater optical wireless communication method that can suppress interference between the first optical wireless communication device 1 and multiple second optical wireless communication devices 2 while suppressing a decrease in communication efficiency, similar to the underwater optical wireless communication system 100.

[0110] Furthermore, in the above embodiment, the following additional effects can be obtained by configuring as follows.

[0111] That is, in the present embodiment, as described above, the first control unit 11 is configured to control the plurality of light receiving and emitting units 10 to communicate with the second optical wireless communication device 2 by the first communication method when communicating with a second optical wireless communication device 2 in the first region 32 where any one of the plurality of second optical wireless communication devices 2 is located within the region, and to control the plurality of light receiving and emitting units 10 to communicate sequentially with each of the plurality of second optical wireless communication devices 2 by the second communication method when communicating with each of the second optical wireless communication devices 2 in the second region 33 where two or more of the plurality of second optical wireless communication devices 2 are located within the region. This allows the first optical wireless communication device 1 to simultaneously communicate with the second optical wireless communication device 2 located within the first region 32 of the plurality of second optical wireless communication devices 2 by the first communication method, while sequentially communicating with each of the two or more second optical wireless communication devices 2 located within the second region 33 of the plurality of second optical wireless communication devices 2 by the second communication method. As a result, when communication is performed between the first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2, by using both the first communication method in the first area 32 and the second communication method in the second area 33, it is possible to easily prevent interference from occurring while also easily prevent a decrease in communication efficiency.

[0112] Furthermore, in this embodiment, as described above, the first control unit 11 is configured to cause the multiple first light-emitting units 14 to sequentially emit, to each of the multiple second optical wireless communication devices 2, a discrimination signal light 40 used to determine the number of multiple second optical wireless communication devices 2 included in each of the multiple predetermined areas 30, and each of the multiple second optical wireless communication devices 2 is configured to emit a response signal light 41 for responding to the first optical wireless communication device 1 when receiving the discrimination signal light 40. As a result, when the response signal light 41 is emitted in a region of the multiple predetermined areas 30 where the first light-emitting unit 14 emitted the discrimination signal light 40, it can be determined that the second optical wireless communication device 2 is located in the region where the first light-emitting unit 14 emitted the discrimination signal light 40. Furthermore, if the response signal light 41 is not emitted in an area of ​​the plurality of predetermined areas 30 where the first light-emitting unit 14 has emitted the discrimination signal light 40, it can be determined that the second optical wireless communication device 2 is not located in the area of ​​the plurality of predetermined areas 30 where the first light-emitting unit 14 has emitted the discrimination signal light 40. As a result, it can be easily determined whether or not a second optical wireless communication device 2 is present and how many second optical wireless communication devices 2 are present in the area where each of the plurality of first light-emitting units 14 emits the discrimination signal light 40.

[0113] Furthermore, in this embodiment, as described above, the first control unit 11 is configured to control the multiple first light-emitting units 14 to emit discrimination signal light 40 sequentially to each of the multiple second optical wireless communication devices 2 at predetermined time intervals, and to control the multiple first light-receiving units 15 to receive response signal light 41 from each of the multiple second optical wireless communication devices 2 at predetermined time intervals. Thus, since the response signal light 41 is received from the area where the discrimination signal light 40 is emitted at predetermined time intervals, even if one of the multiple second optical wireless communication devices 2 moves, the area where the second optical wireless communication device 2 is located after the movement can be easily obtained. Therefore, even if one of the multiple second optical wireless communication devices 2 moves, the first control unit 11 can easily switch between the first communication method and the second communication method depending on the position of the second optical wireless communication device 2 after the movement. As a result, even if any of the multiple second optical wireless communication devices 2 moves, it is possible to prevent interference between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2 while also preventing a decrease in communication efficiency.

[0114] Furthermore, in this embodiment, as described above, each of the multiple second optical wireless communication devices 2 includes the second light-emitting unit 20 a, the second light-receiving unit 20 b, the propulsion mechanism 21, and the test information acquiring unit 22 that acquires test information 50 including at least an image of the test object, and is a slave device that moves around the first optical wireless communication device 1 and transmits the test information 50 acquired by the test information acquiring unit 22 to the first optical wireless communication device 1 using light emitted from the second light-emitting unit 20 a, and the first optical wireless communication device 1 is a master device that acquires the test information 50 from each of the multiple second optical wireless communication devices 2. This makes it possible to suppress interference and a decrease in communication efficiency when the test information 50 acquired by each of the multiple second optical wireless communication devices 2 that are slave devices is transmitted to the first optical wireless communication device 1 that is the master device.

[0115] Furthermore, in this embodiment, as described above, when communicating with a second optical wireless communication device 2 located within the first region 32, the first control unit 11 controls the multiple light receiving and emitting units 10 to communicate using a space division method as the first communication method, in which communication is performed simultaneously with second optical wireless communication devices 2 located within different regions. When communicating with each of the multiple second optical wireless communication devices 2 located within the second region 33, the first control unit 11 controls the multiple light receiving and emitting units 10 to communicate using a time division method as the second communication method, in which communication is performed sequentially with each of the multiple second optical wireless communication devices 2 located within a single region. As a result, when communication is performed using the space division method as the first communication method, the communication regions are different, so interference can be reliably suppressed even when one first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 communicate simultaneously. Furthermore, since one first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 can communicate simultaneously, efficient communication is achieved. Furthermore, when communication is performed using the time division method as the second communication method, communication is performed sequentially with each of the multiple second optical wireless communication devices 2 located in one area, thereby making it possible to prevent interference from occurring. As a result, by the first control unit 11 switching between the first communication method using the space division method and the second communication method using the time division method, it is possible to easily prevent interference from occurring between the first optical wireless communication device 1 and the multiple second optical wireless communication devices 2, and also to easily prevent a decrease in communication efficiency.

[0116] [Modifications] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the description of the above-mentioned embodiments, and further includes all modifications (modifications) within the meaning and scope of the claims.

[0117] For example, in the above embodiment, the first control unit 11 controls the multiple light receiving and emitting units 10 to sequentially communicate with each of the multiple second optical wireless communication devices 2 located within the second region 33. However, the present invention is not limited to this. For example, the first control unit may be configured to control the light receiving and emitting units 10 to communicate simultaneously with the multiple second optical wireless communication devices 2 located within the second region 33 as long as it communicates with the second optical wireless communication devices 2 located within the first region 32 using the first method and with the multiple second optical wireless communication devices 2 located within the second region 33 using the second method, as long as there is no interference with the multiple second optical wireless communication devices 2 located within the other predetermined region 30. For example, if the first optical wireless communication device 1 and each of the multiple second optical wireless communication devices 2 located within the predetermined region 30 are configured to communicate using pairs of light beams in different wavelength bands, the first control unit may be configured to control the light receiving and emitting units 10 to simultaneously communicate with each of the multiple second optical wireless communication devices 2 located within the second region 33.

[0118] Furthermore, in the above embodiment, an example of a configuration in which the first control unit 11 emits a discrimination signal light 40 from the first optical wireless communication device 1 to each of the multiple second optical wireless communication devices 2 and determines the number of second optical wireless communication devices 2 located in each of the multiple predetermined regions 30 based on the response signal light 41 from each of the multiple second optical wireless communication devices 2 has been described. However, the present invention is not limited to this. For example, the first control unit may be configured to determine the number of second optical wireless communication devices 2 located in each of the multiple predetermined regions 30 based on signal light spontaneously emitted from each of the multiple second optical wireless communication devices 2. However, in a configuration in which the first control unit determines the number of second optical wireless communication devices 2 located in each of the multiple predetermined regions 30 based on light spontaneously emitted from each of the multiple second optical wireless communication devices 2, interference may occur between the lights emitted from the second optical wireless communication devices 2. As a result, it may be difficult to determine the number of second optical wireless communication devices 2 located in each of the multiple predetermined regions 30. Therefore, it is preferable that the first control unit 11 is configured to emit a discrimination signal light 40 from the first optical wireless communication device 1 to each of the multiple second optical wireless communication devices 2, and to determine the number of second optical wireless communication devices 2 located within each of the multiple specified areas 30 based on the response signal light 41 from each of the multiple second optical wireless communication devices 2.

[0119] In the above embodiment, the first control unit 11 emits the discrimination signal light 40 sequentially to each of the plurality of second optical wireless communication devices 2 at predetermined time intervals, but the present invention is not limited to this. For example, the first control unit may be configured to control the light receiving and emitting unit 10 to emit the discrimination signal light 40 when, for example, communication between the first optical wireless communication device 1 and the second optical wireless communication device 2 is interrupted.

[0120] In the above embodiment, the first optical wireless communication device 1 is a master device and each of the second optical wireless communication devices 2 is a slave device. However, the present invention is not limited to this. The first optical wireless communication device 1 and the second optical wireless communication device 2 do not have to have a master-slave relationship. For example, each of the first optical wireless communication device 1 and the second optical wireless communication device 2 may be a master device.

[0121] Furthermore, in the above embodiment, an example has been described in which the first control unit 11 communicates using a space division method as the first communication method, but the present invention is not limited to this. For example, the first control unit 11 may be configured to communicate using a wavelength division method in which different light beams are emitted as the first communication method. In this case, simultaneous communication with multiple second optical wireless communication devices 2 can be performed, the number of which corresponds to the number of different wavelength bands. For example, if the wavelength bands of light emitted from the first light emitter 14 are blue and purple, the wavelength bands of light emitted from the second optical wireless communication device 2 can be green and light blue. This allows simultaneous communication between the first optical wireless communication device 1 and two second optical wireless communication devices 2, even when two second optical wireless communication devices 2 are located within the same predetermined area 30.

[0122] Furthermore, in the above embodiment, an example of a configuration in which the multiple light receiving and emitting units 10 are arranged on the same side of the first optical wireless communication device 1 has been shown, but the present invention is not limited to this. For example, the multiple light receiving and emitting units 10 may be arranged on the first optical wireless communication device 1 so as to emit light in different directions from each other. For example, the multiple light receiving and emitting units 10 may be arranged at predetermined intervals along the outer periphery of the first optical wireless communication device 1, and configured to emit light in different directions from each other.

[0123] Furthermore, in the above embodiment, for convenience of explanation, the communication method switching process by the first control unit 11, the process of acquiring the number of second optical wireless communication devices 2 located in the predetermined area 30, and the communication method switching process for each predetermined area 30 have been described using a flow-driven flowchart in which the processes are performed in order according to a processing flow, but the present invention is not limited to this. In the present invention, the communication method switching process by the first control unit 11, the process of acquiring the number of second optical wireless communication devices 2 located in the predetermined area 30, and the communication method switching process for each predetermined area 30 may be performed by event-driven processing in which processing is performed on an event-by-event basis. In this case, the processes may be completely event-driven, or may be a combination of event-driven and flow-driven processes.

[0124] Aspects It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0125] (Item 1) An underwater optical wireless communication system comprising: a first optical wireless communication device that performs optical wireless communication underwater; and a plurality of second optical wireless communication devices, each performing optical wireless communication underwater with the first optical wireless communication device, wherein the first optical wireless communication device includes a plurality of light-emitting and light-receiving units, each having a first light-emitting unit and a first light-receiving unit, that irradiate light onto a corresponding one of a plurality of predetermined regions and receive light from the corresponding one of the plurality of predetermined regions; and a control unit that controls switching of a communication method using light by the plurality of light-emitting and light-receiving units between a first communication method in which communication is performed simultaneously with the plurality of second optical wireless communication devices and a second communication method in which communication is performed sequentially with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices among the plurality of second optical wireless communication devices are located within each of the plurality of predetermined regions.

[0126] (Item 2) The control unit is configured to control the plurality of light receiving and emitting units to communicate with the second optical wireless communication device by the first communication method when communicating with a second optical wireless communication device in a first region in which any one second optical wireless communication device of the plurality of second optical wireless communication devices is located, and to control the plurality of light receiving and emitting units to communicate with each of the plurality of second optical wireless communication devices by the second communication method when communicating with each of the second optical wireless communication devices in a second region in which two or more second optical wireless communication devices of the plurality of second optical wireless communication devices are located. The underwater optical wireless communication system according to item 1.

[0127] (Item 3) The underwater optical wireless communication system according to item 1 or 2, wherein the control unit is configured to emit, from the plurality of first light-emitting units to each of the plurality of second optical wireless communication devices in sequence, a discrimination signal light used to determine the number of the plurality of second optical wireless communication devices included in each of the plurality of predetermined areas, and each of the plurality of second optical wireless communication devices is configured to emit a response signal light for responding to the first optical wireless communication device when receiving the discrimination signal light.

[0128] (Item 4) The underwater optical wireless communication system according to Item 3, wherein the control unit is configured to control the first light-emitting units to emit the discrimination signal light sequentially to each of the second optical wireless communication devices at a predetermined time interval, and to control the first light-receiving units to receive the response signal light from each of the second optical wireless communication devices at a predetermined time interval.

[0129] (Item 5) The underwater optical wireless communication system according to Item 3 or 4, wherein each of the plurality of second optical wireless communication devices has a second light-emitting unit, a second light-receiving unit, a propulsion mechanism, and an inspection information acquiring unit that acquires inspection information including at least an image of an inspection target, and is a slave unit that moves around the first optical wireless communication device and transmits the inspection information acquired by the inspection information acquiring unit to the first optical wireless communication device using light emitted from the second light-emitting unit, and the first optical wireless communication device is a master unit that acquires the inspection information from each of the plurality of second optical wireless communication devices.

[0130] (Item 6) The control unit is configured to control the plurality of light receiving and emitting units to communicate, as the first communication method, by a space division method in which communication is simultaneously performed with second optical wireless communication devices located in different areas when communicating with a second optical wireless communication device located in the first area, and to control the plurality of light receiving and emitting units to communicate, as the second communication method, by a time division method in which communication is sequentially performed with each of the plurality of second optical wireless communication devices located in one area when communicating with each of the plurality of second optical wireless communication devices located in the second area. The underwater optical wireless communication system according to item 2.

[0131] (Item 7) An underwater optical wireless communication method for performing communication using light between a first optical wireless communication device and each of a plurality of second optical wireless communication devices underwater, comprising: a step of acquiring the number of the plurality of second optical wireless communication devices located within each of a plurality of predetermined areas into which the first optical wireless communication device emits light; and a step of switching a communication method using the light emitted from the first optical wireless communication device between a first communication method for simultaneously communicating with the plurality of second optical wireless communication devices and a second communication method for sequentially communicating with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices among the plurality of second optical wireless communication devices are located within each of the plurality of predetermined areas.

[0132] REFERENCE SIGNS LIST 1 First optical wireless communication device 2, 2a, 2b, 2c Multiple second optical wireless communication devices 10 Light receiving and emitting unit (multiple light receiving and emitting units) 11 First control unit (control unit) 14 First light emitting unit 15 First light receiving unit 20a Second light emitting unit 20b Second light receiving unit 21 Propulsion mechanism 22 Inspection information acquisition unit 30 Predetermined area (multiple predetermined areas) 40, 40a, 40b, 40c Discrimination signal light 41, 41a, 41b, 41c Response signal light 50 Inspection information 100 Underwater optical wireless communication system

Claims

1. An underwater optical wireless communication system comprising: a first optical wireless communication device that performs optical wireless communication underwater; and a plurality of second optical wireless communication devices, each of which performs optical wireless communication underwater with the first optical wireless communication device, wherein the first optical wireless communication device includes a plurality of light receiving and transmitting units, each of which has a first light emitting unit and a first light receiving unit, and which irradiates light onto a corresponding one of a plurality of predetermined regions and receives light from the corresponding one of the plurality of predetermined regions; and a control unit that controls switching of a communication method using light by the plurality of light receiving and transmitting units between a first communication method for simultaneously communicating with the plurality of second optical wireless communication devices and a second communication method for sequentially communicating with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices of the plurality of second optical wireless communication devices are located within each of the plurality of predetermined regions.

2. The underwater optical wireless communication system described in claim 1, wherein the control unit is configured to control the multiple light receiving and emitting units to communicate with the second optical wireless communication device by the first communication method when communicating with a second optical wireless communication device in a first region within which any one of the multiple second optical wireless communication devices is located, and to control the multiple light receiving and emitting units to communicate with each of the multiple second optical wireless communication devices sequentially by the second communication method when communicating with each of the second optical wireless communication devices in a second region within which two or more second optical wireless communication devices of the multiple second optical wireless communication devices are located.

3. The underwater optical wireless communication system described in claim 1, wherein the control unit is configured to emit, in sequence, from the multiple first light-emitting units to each of the multiple second optical wireless communication devices, a discrimination signal light used to discriminate the number of the multiple second optical wireless communication devices included in each of the multiple specified areas, and each of the multiple second optical wireless communication devices is configured to emit a response signal light for responding to the first optical wireless communication device when it receives the discrimination signal light.

4. The underwater optical wireless communication system described in claim 3, wherein the control unit is configured to control the multiple first light-emitting units to emit the discrimination signal light sequentially to each of the multiple second optical wireless communication devices at predetermined time intervals, and to control the multiple first light-receiving units to receive the response signal light from each of the multiple second optical wireless communication devices at predetermined time intervals.

5. The underwater optical wireless communication system described in claim 3, wherein each of the multiple second optical wireless communication devices has a second light emitter, a second light receiver, a propulsion mechanism, and an inspection information acquisition unit that acquires inspection information including at least an image of an inspection object, and is a slave unit that moves around the first optical wireless communication device and transmits the inspection information acquired by the inspection information acquisition unit to the first optical wireless communication device using light emitted from the second light emitter, and the first optical wireless communication device is a master unit that acquires the inspection information from each of the multiple second optical wireless communication devices.

6. The underwater optical wireless communication system described in claim 2, wherein the control unit is configured to control the multiple light receiving and emitting units to communicate, as the first communication method, by a space division method in which communication is performed simultaneously with second optical wireless communication devices located in different regions when communicating with a second optical wireless communication device located within the first region, and to control the multiple light receiving and emitting units to communicate, as the second communication method, by a time division method in which communication is performed sequentially with each of the multiple second optical wireless communication devices located within one region when communicating with each of the multiple second optical wireless communication devices located within the second region.

7. An underwater optical wireless communication method for performing communication using light between a first optical wireless communication device and each of a plurality of second optical wireless communication devices underwater, comprising the steps of: acquiring the number of the plurality of second optical wireless communication devices located within each of a plurality of predetermined areas in which the first optical wireless communication device emits light; and switching a communication method using the light emitted from the first optical wireless communication device between a first communication method for simultaneously communicating with the plurality of second optical wireless communication devices and a second communication method for sequentially communicating with the plurality of second optical wireless communication devices, based on whether two or more second optical wireless communication devices among the plurality of second optical wireless communication devices are located in each of the plurality of predetermined areas.

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