Optical communication system, terminal device, and base station device

Abstract

This optical communication system comprises a base station device and a terminal device that performs optical communication with the base station device. At least one of the base station device and the terminal device performs a connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device in such a way that the communication quality of the optical communication in an uplink is prioritized over the communication quality of the optical communication in a downlink.

Description

Optical communication system, terminal device, and base station device

[0001] The present disclosure relates to an optical communication system, a terminal device, and a base station device.

[0002] For example, optical communication systems that use light (particularly visible light) as a transmission medium for underwater communication are known. Because light has high directivity, conventional optical communication systems generally perform one-to-one communication between the transmitting and receiving sides, with the transmitting and receiving sides facing each other, under the assumption that the optical communication devices on each side are fixed.

[0003] Japanese Patent Application Publication No. 4-103232

[0004] According to a first aspect, an optical communication system includes a base station device and a terminal device that performs optical communication with the base station device, wherein at least one of the base station device and the terminal device performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize communication quality of the optical communication in an uplink over communication quality of the optical communication in a downlink.

[0005] A terminal device according to the second aspect includes an optical communication unit that performs optical communication with a base station device, and a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in the uplink over the communication quality of the optical communication in the downlink.

[0006] A base station device according to a third aspect includes an optical communication unit that performs optical communication with a terminal device, and a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in the uplink over the communication quality of the optical communication in the downlink.

[0007] An optical communication system according to a fourth aspect is an optical communication system for performing optical communication between a base station device and a terminal device, and includes a plurality of base station devices arranged three-dimensionally underwater at intervals in the horizontal and vertical directions, wherein the communication areas formed by each of the plurality of base station devices underwater constitute an optical communication coverage area in the optical communication system.

[0008] 1 is a diagram illustrating an example of the configuration of an optical communication system according to an embodiment. A diagram schematically illustrating a transmission operation in an uplink (UL) of a terminal device according to an embodiment. A diagram illustrating an example of the block configuration of a base station device according to an embodiment. A diagram illustrating an example of the external configuration of a base station device according to an embodiment. A diagram illustrating a first modified example of the external configuration of a base station device according to an embodiment. A diagram illustrating a second modified example of the external configuration of a base station device according to an embodiment. A diagram illustrating an example of the block configuration of a terminal device according to an embodiment. A diagram illustrating an example of the external configuration of a terminal device according to an embodiment. A diagram illustrating a first modified example of the external configuration of a terminal device according to an embodiment. A diagram illustrating a second modified example of the external configuration of a terminal device according to an embodiment. A diagram illustrating downlink (DL) communication as an example of optical communication according to an embodiment. A diagram illustrating an example of the configuration of a communication frame used in an optical communication system according to an embodiment. A diagram illustrating the influence of solar noise in an optical communication system according to an embodiment. A diagram illustrating the influence of ambient light in an optical communication system according to an embodiment. A diagram illustrating an estimation operation of UL communication quality performed by a terminal device according to an embodiment. A diagram illustrating an operation of selecting an optical communication unit for noise estimation in a terminal device according to an embodiment. A diagram illustrating an example of an operation flow in a terminal device according to the first embodiment. A diagram illustrating an operation according to a first modified example of the first embodiment. A diagram illustrating an operation according to a second modified example of the first embodiment. FIG. 1 is a diagram showing an example of an operation flow in a terminal device according to a second modified example of the first embodiment. FIG. 2 is a diagram showing an example of an operation sequence of an optical communication system 1 according to a third modified example of the first embodiment. FIG. 3 is a diagram showing an example of an operation sequence of an optical communication system according to a second modified example. FIG. 4 is a diagram showing an example of an operation sequence of an optical communication system according to a modified example of the second embodiment. FIG. 5 is a diagram showing an example of the configuration of an optical communication system according to a third embodiment. FIG. 6 is a diagram showing an example of the configuration of a base station group according to the third embodiment. FIG. 7 is a diagram for explaining base station design of an optical communication system according to the third embodiment. FIG. 8 is a diagram for explaining base station design of an optical communication system according to the third embodiment. FIG. 9 is a diagram for explaining base station design of an optical communication system according to the third embodiment.10 is a diagram for explaining a response to movement of a base station device in the horizontal direction according to the third embodiment. FIG. 11 is a diagram for explaining an example of the configuration of functional blocks of a control device according to the third embodiment. FIG. 12 is a diagram for explaining an operation of specifying the communication distance of optical communication of a base station device according to the third embodiment. FIG. 13 is a diagram for explaining an operation of calculating the base station distance according to the third embodiment. FIG. 14 is a diagram for explaining a blind zone adjustment amount in the vertical direction according to the third embodiment. FIG. 15 is a diagram for explaining a blind zone adjustment amount in the horizontal direction according to the third embodiment. FIG. 16 is a diagram for explaining an example of a flow at the time of initial installation of each base station device according to the third embodiment. FIG. 17 is a diagram for explaining an operation according to a first modified example of the third embodiment. FIG. 18 is a diagram for explaining an operation according to a first modified example of the third embodiment. FIG. 19 is a diagram for explaining a first setting pattern of the base station distance according to the first modified example of the third embodiment. FIG. 19 is a diagram for explaining a second setting pattern of the base station distance according to the first modified example of the third embodiment. FIG. 19 is a diagram for explaining an example of the configuration of a control device according to the first modified example of the third embodiment. FIG. 19 is a diagram for explaining a third setting pattern of the base station distance according to the first modified example of the third embodiment. FIG. 19 is a diagram for explaining an operation example of an optical communication system according to the second modified example of the third embodiment. FIG. 19 is a diagram for explaining an operation example of an optical communication system according to the third modified example of the third embodiment.

[0009] In future optical communication systems, it is expected that optical communication between a plurality of terminal devices and a base station device will be realized, similar to radio wave-based wireless communication on land.

[0010] Therefore, the present disclosure provides an optical communication system, a terminal device, and a base station device that enable appropriate optical communication between a terminal device and a base station device.

[0011] An optical communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0012] The optical communication system according to the embodiment is a system that performs optical communication using visible light as an example of light. However, the optical communication system may be a system that performs optical communication using light other than visible light, for example, infrared light. Furthermore, the optical communication system according to the embodiment is a system that performs optical communication underwater. However, the optical communication system is not limited to a system that performs optical communication underwater, and may be a system that performs optical communication in space, for example.

[0013] First Embodiment First, an optical communication system according to a first embodiment will be described.

[0014] In future optical communication systems, it is expected that optical communication between multiple terminal devices and base station devices will be realized, similar to radio wave wireless communication on land. Under such assumptions, it is desirable to realize connection control that appropriately establishes and / or maintains optical communication connections between terminal devices and base station devices.

[0015] In radio-wave wireless communication, connection control is performed based on the reception strength of downlink (DL) radio waves received by a terminal device from a base station device. However, such connection control that prioritizes downlink communication quality may cause a concern that a terminal device may not be able to establish and / or maintain an optical communication connection with an appropriate base station device in an optical communication system.

[0016] In the first embodiment, an optical communication system, a terminal device, and a base station device that are capable of appropriately establishing and / or maintaining an optical communication connection will be described.

[0017] (Configuration example of optical communication system) Fig. 1 is a diagram showing a configuration example of an optical communication system 1 according to this embodiment. The optical communication system 1 has a terminal device 100 and a plurality of base station devices 200 (200a to 200f). However, the number of terminal devices 100 and the number of base station devices 200 are not limited to the example shown in the figure.

[0018] The terminal device 100 is an example of an optical communication device. Each of the base station devices 200 is another example of an optical communication device. The terminal device 100 and each of the multiple base station devices 200 have multiple optical communication units whose optical axes (from another perspective, the directivity of optical communication) are oriented in different directions. This allows the terminal device 100 and each of the multiple base station devices 200 to use light as a transmission medium and perform optical communication in various ways (all directions) using the multiple optical communication units.

[0019] For each terminal device 100 connected to the base station device 200, the base station device 200 selects its own optical communication unit corresponding to the direction of the terminal device 100 and uses the selected optical communication unit to perform optical communication with the terminal device 100. Similarly, the terminal device 100 selects its own optical communication unit corresponding to the direction of the base station device 200 that is its serving base station (the base station device to which it is connected) and performs optical communication with the base station device 200 using the selected optical communication unit.

[0020] In order to form a wide underwater communication area independent of the position or orientation of the terminal device 100, multiple base station devices 200 are arranged three-dimensionally underwater. Each base station device 200 may be temporarily installed, for example, for the period during which underwater investigations are conducted using the terminal device 100. In Fig. 1, the communication area of ​​each base station device 200 is indicated by a dashed line. The communication area of ​​each base station device 200 is also called a cell.

[0021] Each of the base station devices 200a and 200b is located near the water surface and is fixed to a buoy, for example. Each of the base station devices 200a and 200b has a hemispherical housing, and a plurality of optical communication units are arranged in an array on the surface of the hemispherical housing. Each of the base station devices 200a and 200b is communicatively connected to the network 10 via a backhaul line. The backhaul line may be a wireless line or a wired line. In order to efficiently secure a communication area underwater, the base station devices 200a and 200b are installed a predetermined distance apart from each other.

[0022] Base station device 200c is suspended from base station device 200a via a rope and / or cable (hereinafter referred to as "cable, etc."). Base station device 200e is suspended from base station device 200c via a cable, etc. Similarly, base station device 200d is suspended from base station device 200b adjacent to base station device 200a via a cable, etc. Base station device 200f is suspended from base station device 200d via a cable, etc. Each of base station devices 200c, 200d, 200e, and 200f has a spherical housing, and a plurality of optical communication units are arranged in an array on the surface of the spherical housing.

[0023] The terminal device 100 is underwater. The terminal device 100 is configured to be movable underwater. For example, the terminal device 100 may be a self-propelled terminal device 100 such as an underwater robot or an underwater drone. The terminal device 100 connects to one of the base station devices 200 and performs optical communication with the connected base station device 200 (serving base station).

[0024] The terminal device 100 may include a sensor such as an image sensor and generate sensor data. For example, each terminal device 100 may transmit uplink (UL) data including the sensor data to the base station device 200 (serving base station) via optical communication. The terminal device 100 may receive downlink (DL) data including instruction data from the base station device 200 (serving base station) via optical communication. The terminal device 100 may move and perform a sensing operation (such as photographing) based on the instruction data.

[0025] In this embodiment, a scenario is assumed in which a terminal device 100 such as an underwater drone uploads large amounts of data such as video data to the network 10 via a base station device 200. In such a scenario, it is desirable to improve the communication quality of UL optical communication over that of DL optical communication.

[0026] Each base station device 200 may transmit its own unique synchronization optical signal and / or reference optical signal in all directions from all optical communication units. The terminal device 100 may identify the direction of the base station device 200 based on these optical signals, identify its own optical communication unit corresponding to that direction, and perform optical communication with the base station device 200 using the identified optical communication unit.

[0027] FIG. 2 is a diagram schematically showing a transmission operation in the UL of the terminal device 100 according to this embodiment.

[0028] In the terminal device 100, for example, a plurality of optical communication units 101 (optical communication units 101a, 101b, ...) are arranged inside a transparent housing 150, and the optical communication units 101 perform optical communication with the base station device 200 via the housing 150. The plurality of optical communication units 101 are arranged in an array along the curved inner surface 2a of the housing 150, with their optical axes facing in different directions. For example, the optical axis of each optical communication unit 101 is directed in the normal direction to the curved surface of the housing 150. Light has high directionality, and such a configuration makes it possible to perform optical communication in various directions.

[0029] 3 is a diagram showing an example of a block configuration of a base station device 200 according to this embodiment. The base station device 200 includes a plurality of optical communication units 201 (201#0, 201#1, ...), a control unit 230, and a backhaul communication unit 240. The base station device 200 may include a battery for supplying power necessary for the operation of the base station device 200.

[0030] The multiple optical communication units 201 are arranged with the directivity (optical axis) of optical communication facing in different directions. Each optical communication unit 201 performs optical communication (visible light communication in this embodiment) with the terminal device 100 under the control of the control unit 230. Each optical communication unit 201 has a light receiving unit 210 and a light emitting unit 220. Since each optical communication unit 201 has the same configuration, the configuration of optical communication unit 201#0 will be described here.

[0031] The light receiving unit 210#0 of the optical communication unit 201#0 receives an optical signal (in this embodiment, a visible light signal) from the terminal device 100 and outputs the received signal to the control unit 230. The light receiving unit 210#0 has at least one light receiving element 211#0 and a receiver 212#0. The light receiving element 211#0 may include a photodiode (PD) and its peripheral circuitry. The light receiving element 211#0 receives the optical signal, converts the received optical signal into an electrical signal (received signal), and outputs the received signal to the receiver 212#0. The optical axis of the light receiving element 211#0 is oriented in a predetermined direction different from the optical axis of the other light receiving elements 211 (e.g., light receiving element 211#1). The receiver 212#0 may be configured with an FPGA (Field Programmable Gate Array) and / or a SoC (System-on-a-chip). The receiver 212#0 converts the received signal output by the light receiving element 211#0, performs signal processing on the converted received signal, and outputs the processed signal to the control unit 230. At least a portion of the receiver 212#0 may be integrated with another receiver 212 (for example, the receiver 212#1) or with the transmitter 222.

[0032] The light-emitting unit 220#0 of the optical communication unit 201#0 transmits an optical signal (in this embodiment, a visible light signal) to the terminal device 100 under the control of the control unit 230. The light-emitting unit 220#0 has at least one light-emitting element 221#0 and a transmitter 222#0. The light-emitting element 221#0 may include a laser diode (LD) or a light-emitting diode (LED) and its peripheral circuitry. The light-emitting element 221#0 converts an electrical signal (transmission signal) output by the transmitter 222#0 for optical communication into an optical signal and transmits the optical signal. The optical axis of the light-emitting element 221#0 is oriented in a predetermined direction different from the optical axes of the other light-emitting elements 221 (e.g., light-emitting element 221#1). However, the optical axis of the light-emitting element 221#0 is oriented in the same direction as the optical axis of the corresponding light-receiving element 211#0. The transmitter 222#0 may be configured using an FPGA and / or SoC. The transmitter 222#0 performs signal processing on the transmission signal output by the control unit 230, converts the processed signal, and outputs it to the light-emitting element 221#0. At least a part of the transmitter 222#0 may be integrated with another transmitter 222 (for example, the transmitter 222#1) or may be integrated with the receiver 212.

[0033] The control unit 230 controls the overall operation of the base station device 200. The operations of the base station device 200 described above and later may be controlled by the control unit 230. For example, the control unit 230 controls multiple optical communication units 201. The control unit 230 includes at least one processor 231 and at least one memory 232. The memory 232 stores programs executed by the processor 231 and information used in processing by the processor 231. The processor 231 may include a digital signal processor and a CPU (Central Processing Unit). The digital signal processor performs modulation / demodulation, encoding / decoding, etc. of digital signals. The CPU executes programs stored in the memory to perform various processes. At least a portion of the control unit 230 may be integrated with the receiver 212 or the transmitter 222.

[0034] The backhaul communication unit 240 performs backhaul communication (wired communication and / or wireless communication) via a backhaul line under the control of the control unit 230. The backhaul communication unit 240 may have a network communication unit 241 that performs communication with the network 10 (e.g., a core network) and an inter-base station communication unit 242 that performs inter-base station communication with adjacent base stations. For example, the network communication unit 241 receives data to be transmitted to the terminal device 100 from the network 10 and outputs the received data to the control unit 230. The network communication unit 241 also transmits data received by the optical communication unit 201 from the terminal device 100 to the network 10.

[0035] In the base station device 200 configured in this manner, the control unit 230 performs connection control to establish and / or maintain an optical communication connection between the terminal device 100 and the base station device 200 so as to prioritize the communication quality of optical communication in the uplink (UL) over the communication quality of optical communication in the downlink (DL). Details of such connection control will be described later.

[0036] FIG. 4 is a diagram showing an example of the external configuration of the base station device 200 according to this embodiment.

[0037] The base station device 200 has a spherical housing 250 and a plurality of optical communication units 201 arranged in an array on the curved surface of the housing 250. However, the housing 250 may be configured in a hemispherical shape. Each optical communication unit 201 is provided with a set of at least one light receiving element 211 and at least one light emitting element 221. With this configuration, the base station device 200 can perform optical communication with the terminal devices 100 in various directions.

[0038] FIG. 5 is a diagram showing a first modified example of the external configuration of the base station device 200 according to this embodiment.

[0039] The base station device 200 has a hook portion 260a provided at the upper end of the housing 250, a hook portion 260b provided at the lower end of the housing 250, a cable 262a extending upward from the housing 250, and a cable 262b extending downward from the housing 250.

[0040] The cables 262a and 262b may be configured with optical fibers. The cable 262a is used for inter-base station communication with an adjacent base station on the upper side, and the cable 262b is used for inter-base station communication with an adjacent base station on the lower side. The base station device 200 may relay data received from an adjacent base station on the upper side via the cable 262a to an adjacent base station on the lower side via the cable 262b. The base station device 200 may also relay data received from an adjacent base station on the lower side via the cable 262b to an adjacent base station on the upper side via the cable 262a.

[0041] A rope 261a is attached to the upper hook portion 260a, and a rope 261b is attached to the lower hook portion 260b. The upper cable 262a is arranged along the upper rope 261a, and the lower cable 262b is arranged along the lower rope 261b. The optical communication unit 201 on the surface of the housing 250 is positioned so as to avoid the hook portions 260a and 260b.

[0042] FIG. 6 is a diagram showing a second modified example of the external configuration of the base station device 200 according to this embodiment.

[0043] In this modified example, the base station device 200 has a hook portion 260a provided at the upper end of the housing 250, a hook portion 260b provided at the lower end of the housing 250, and a laser communicator 263 provided above the housing 250. The laser communicator 263 is used for inter-base station communication with the adjacent base station above.

[0044] (Configuration Example of Terminal Device) Fig. 7 is a diagram showing a block configuration example of a terminal device 100 according to this embodiment. The terminal device 100 has a plurality of optical communication units 101 (101#0, 101#1, ...), a control unit 130, and a mechanism unit 140. The terminal device 100 may have a battery for supplying power necessary for the operation of the terminal device 100. The terminal device 100 may also have a sensor such as an image sensor and generate sensor data.

[0045] The multiple optical communication units 101 are arranged with their optical communication directivities (optical axes) facing in different directions. Each optical communication unit 101 performs optical communication (visible light communication in this embodiment) with the base station device 200 under the control of the control unit 130. Each optical communication unit 101 has a light receiving unit 110 and a light emitting unit 120. Since each optical communication unit 101 has the same configuration, the configuration of optical communication unit 101#0 will be described here.

[0046] The light receiving unit 110#0 of the optical communication unit 101#0 receives an optical signal (in this embodiment, a visible light signal) from the base station device 200 and outputs the received signal to the control unit 130. The light receiving unit 110#0 has at least one light receiving element 111#0 and a receiver 112#0. The light receiving element 111#0 may include a photodiode (PD) and its peripheral circuitry. The light receiving element 111#0 receives the optical signal, converts the received optical signal into an electrical signal (received signal), and outputs the received signal to the receiver 112#0. The optical axis of the light receiving element 111#0 is oriented in a predetermined direction different from the optical axis of the other light receiving elements 111 (e.g., light receiving element 111#1). The receiver 112#0 may be configured using an FPGA and / or SoC. The receiver 112#0 converts the received signal output by the light receiving element 111#0, performs signal processing on the converted received signal, and outputs the processed signal to the control unit 130. At least a part of the receiver 112#0 may be integrated with another receiver 112 (for example, the receiver 112#1) or with the transmitter 122.

[0047] The light-emitting unit 120#0 of the optical communication unit 101#0 transmits an optical signal (in this embodiment, a visible light signal) to the base station device 200 under the control of the control unit 130. The light-emitting unit 120#0 has at least one light-emitting element 121#0 and a transmitter 122#0. The light-emitting element 121#0 may include a laser diode (LD) or a light-emitting diode (LED) and its peripheral circuitry. The light-emitting element 121#0 converts an electrical signal (transmission signal) output by the transmitter 122#0 for optical communication into an optical signal and transmits the optical signal. The optical axis of the light-emitting element 121#0 is oriented in a predetermined direction different from the optical axes of the other light-emitting elements 121 (e.g., light-emitting element 121#1). However, the optical axis of the light-emitting element 121#0 is oriented in the same direction as the optical axis of the corresponding light-receiving element 111#0. The transmitter 122#0 may be configured using an FPGA and / or SoC. The transmitter 122#0 performs signal processing on the transmission signal output by the control unit 130, converts the processed signal, and outputs it to the light-emitting element 121#0. At least a part of the transmitter 122#0 may be integrated with another transmitter 122 (for example, the transmitter 122#1) or with the receiver 112.

[0048] The control unit 130 controls the overall operation of the terminal device 100. The operations of the terminal device 100 described above and later may be operations controlled by the control unit 130. For example, the control unit 130 controls multiple optical communication units 101. The control unit 130 includes at least one processor 131 and at least one memory 132. The memory 132 stores programs executed by the processor 131 and information used in processing by the processor 131. The processor 131 may include a digital signal processor and a CPU. The digital signal processor performs modulation / demodulation, encoding / decoding, etc. of digital signals. The CPU executes programs stored in the memory to perform various processes. At least a portion of the control unit 130 may be integrated with the receiver 112 or the transmitter 122.

[0049] The mechanical unit 140 includes a movement mechanism that moves the terminal device 100 under the control of the control unit 130. The movement mechanism includes, for example, a motor and a screw connected to the rotation shaft of the motor. The mechanical unit 140 may also include an arm or the like used for underwater work.

[0050] In the terminal device 100 configured in this manner, the control unit 130 performs connection control to establish and / or maintain an optical communication connection between the terminal device 100 and the base station device 200 so as to prioritize the communication quality of optical communication in the uplink (UL) over the communication quality of optical communication in the downlink (DL). Details of such connection control will be described later.

[0051] FIG. 8 is a diagram showing an example of the external configuration of the terminal device 100 according to this embodiment.

[0052] The terminal device 100 has an upper housing 150a, a lower housing 150b, and a mechanism unit 140 provided between the housings 150a and 150b. The housings 150a and 150b are each hemispherical, giving the terminal device 100 a spherical shape as a whole. Each of the housings 150a and 150b has a plurality of optical communication units 101 distributed on its surface. Each optical communication unit 101 is provided with a set of at least one light receiving element 111 and at least one light emitting element 121. This configuration enables the terminal device 100 to perform optical communication with the base station device 200 in various directions.

[0053] FIG. 9 is a diagram showing a first modified example of the external configuration of the terminal device 100 according to this embodiment.

[0054] In this modified example, the terminal device 100 has a left housing 150a, a right housing 150b, and a mechanism unit 140 provided between the housings 150a and 150b. The housings 150a and 150b are each hemispherical, and the terminal device 100 as a whole has a spherical shape. The housings 150a and 150b each have a plurality of optical communication units 101 distributed on their surfaces. Each optical communication unit 101 is provided with a set of at least one light receiving element 111 and at least one light emitting element 121.

[0055] FIG. 10 is a diagram showing a second modified example of the external configuration of the terminal device 100 according to this embodiment.

[0056] In this modified example, terminal device 100 has a spherical housing 150 and a mechanism unit 140 connected to housing 150 via a cable 160. Housing 150 is spherical. Housing 150 has a plurality of optical communication units 101 distributed over its surface. Each optical communication unit 101 is provided with a set of at least one light receiving element 111 and at least one light emitting element 121.

[0057] 11 is a diagram illustrating DL communication as an example of optical communication according to this embodiment. In the illustrated example, a cross section of a base station device 200 and a cross section of a terminal device 100 are simply illustrated for DL ​​communication.

[0058] In the base station device 200, the multiple light-emitting units 220 are arranged so that the angle formed between the optical axis of one light-emitting unit 220 and the optical axis of another light-emitting unit 220 increases as the distance between the light-emitting unit 220 and another light-emitting unit 220 increases. For example, the angle formed between the optical axis of light-emitting unit 220#0 and the optical axis of light-emitting unit 220#2 that is not adjacent to light-emitting unit 220#0 is larger than the angle formed between the optical axis of light-emitting unit 220#0 and the optical axis of light-emitting unit 220#1 that is adjacent to light-emitting unit 220#0.

[0059] The base station device 200 associates the light-emitting unit 220#4 (optical communication unit #4) corresponding to the direction in which the terminal device 100 is located with the terminal device 100, and uses the light-emitting unit 220#4 (optical communication unit #4) to perform optical communication with the terminal device 100. The terminal device 100 associates the light-receiving unit 110#0 (optical communication unit #0) corresponding to the direction in which the base station device 200 is located with the base station device 200, and performs optical communication with the base station device 200 using the light-receiving unit 110#0 (optical communication unit #0).

[0060] 12 is a diagram showing an example of the configuration of a communication frame used in the optical communication system 1 according to this embodiment. In the example shown, one communication frame is made up of 10 time slots, but the number of time slots making up one communication frame is not limited to 10. Each time slot is made up of a predetermined number of symbol intervals.

[0061] In this frame configuration example, the communication frame is composed of one synchronization slot (Sync.), one control slot (Ctrl.), four DL slots (DL slots) #0 to #3, and four UL slots (UL slots) #0 to #3. However, in a scenario where the amount of data in UL communication is greater than that in DL communication, the number of UL slots in the communication frame may be greater than the number of DL slots.

[0062] The synchronization slot (Sync.) is a time slot in which the base station device 200 transmits a synchronization optical signal (and a base station device-specific reference optical signal). The terminal device 100 identifies the base station device 200 by the synchronization optical signal received from the base station device 200, and establishes or maintains synchronization with the base station device 200 using the synchronization optical signal. Note that the base station device-specific reference optical signal may be transmitted in all slots except for the UL slot. The reference optical signal is used by the terminal device 100 to measure the reception strength (reference signal strength) from the base station device 200.

[0063] The control slot (Ctrl.) is a time slot in which the base station device 200 transmits a control optical signal. The control optical signal includes, for example, scheduling information indicating DL and UL resource allocation (for example, time slot allocation). The terminal device 100, for example, knows its own time slot allocation from the control optical signal received from the base station device 200.

[0064] DL slots #0 to #3 constitute a DL communication period. The base station device 200 assigns each of DL slots #0 to #3 to one or more terminal devices 100. The base station device 200 transmits a DL data optical signal in each DL slot. A reference signal (Ref. TxElement) specific to the light-emitting element and a data optical signal may be allocated in a time-division manner in each DL slot.

[0065] UL slots #0 to #3 constitute a UL communication period. The base station device 200 allocates each of the UL slots #0 to #3 to one or more terminal devices 100. The terminal devices 100 transmit UL data optical signals in the allocated UL slots.

[0066] The base station device 200 can simultaneously communicate with multiple terminal devices 100 located in different directions. Specifically, the base station device 200 can spatially multiplex multiple terminal devices 100 located in different directions. Therefore, the base station device 200 may allocate one DL slot or one UL slot to multiple terminal devices 100.

[0067] 13 to 17, the operation of the optical communication system 1 according to this embodiment will be described. In the optical communication system 1 according to this embodiment, in order to accommodate applications that place too much emphasis on UL communication, such as video uploading, a destination base station (serving base station) is selected and an optical communication connection is maintained under conditions where UL communication is good. Specifically, the terminal device 100 estimates the UL communication quality of the base station device 200, and the terminal device 100 selects a base station device 200 that is suitable for conditions where UL communication is good, and establishes an optical communication connection with the selected base station device 200.

[0068] Conventionally, in radio communication using radio waves on land, since it is difficult for a discrepancy in communication quality to occur between DL communication and UL communication, connection control is performed based on the reception strength of DL radio waves received by the terminal device 100 from the base station device 200. In other words, the terminal device 100 establishes a connection with the base station device 200 that is the source of the reference signal with the highest DL reception strength.

[0069] On the other hand, in optical communications, there exists noise, such as sunlight noise, that has a significant effect on light receiving units in specific directions. Therefore, UL communication quality cannot be accurately estimated based on DL reception intensity alone. Specifically, because light is highly directional (straight-line), it is expected that reception conditions will differ at light receiving units in different locations due to the influence of sunlight noise and / or ambient light. Therefore, if connection control similar to that used in radio wave-based wireless communications on land is performed in the optical communication system 1, there is a risk that the terminal device 100 will connect to a base station device 200 with poor UL communication quality. In the following, sunlight and / or ambient light will be collectively referred to as "ambient light."

[0070] FIG. 13 is a diagram for explaining the influence of sunlight noise in the optical communication system 1 according to this embodiment.

[0071] In the illustrated example, a base station device 200a and a base station device 200b located below the base station device 200a are underwater. The distance between the terminal device 100 and the base station device 200a is equal to the distance between the terminal device 100 and the base station device 200b. Sunlight is incident on the terminal device 100 and each base station device 200 from above.

[0072] The terminal device 100 transmits an UL optical signal from its own optical communication unit 101a, which corresponds to the direction of the base station device 200a, and the base station device 200a receives the UL optical signal from its own optical communication unit 201a, which corresponds to the direction of the terminal device 100. Also, the terminal device 100 transmits an UL optical signal from its own optical communication unit 101b, which corresponds to the direction of the base station device 200b, and the base station device 200b receives the UL optical signal from its own optical communication unit 201b, which corresponds to the direction of the terminal device 100.

[0073] Since the distance between the terminal device 100 and each base station device 200a is equal, in the absence of solar noise, it can be assumed that the communication quality of the UL optical signal received by the optical communication unit 201a of the base station device 200a is equal to the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b.

[0074] However, because the optical axis of the optical communication unit 201b of the base station device 200b is oriented diagonally upward, sunlight enters as a noise signal. This causes a deterioration in the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b. In contrast, because the optical axis of the optical communication unit 201a of the base station device 200a is oriented diagonally downward, sunlight does not enter as a noise signal, and the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b does not deteriorate. Therefore, when prioritizing UL communication, it is preferable that the terminal device 100 connect to the base station device 200a rather than the base station device 200b.

[0075] FIG. 14 is a diagram for explaining the influence of ambient light in the optical communication system 1 according to this embodiment.

[0076] In the illustrated example, the base station device 200a and the base station device 200b located to the right of the base station device 200a are both underwater. The distance between the terminal device 100 and the base station device 200a is equal to the distance between the terminal device 100 and the base station device 200b. Light (ambient light) from a light source located diagonally above and to the right of the base station device 200b is incident on the terminal device 100 and each base station device 200. The light source is assumed to be underwater, but may be located above the water surface.

[0077] The terminal device 100 transmits an UL optical signal from its own optical communication unit 101a, which corresponds to the direction of the base station device 200a, and the base station device 200a receives the UL optical signal from its own optical communication unit 201a, which corresponds to the direction of the terminal device 100. Also, the terminal device 100 transmits an UL optical signal from its own optical communication unit 101b, which corresponds to the direction of the base station device 200b, and the base station device 200b receives the UL optical signal from its own optical communication unit 201b, which corresponds to the direction of the terminal device 100.

[0078] Since the distance between the terminal device 100 and each base station device 200a is equal, in the absence of solar noise, it can be assumed that the communication quality of the UL optical signal received by the optical communication unit 201a of the base station device 200a is equal to the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b.

[0079] However, because the optical axis of the optical communication unit 201a of the base station device 200a faces to the right, ambient light from the light source enters as a noise signal. This causes a deterioration in the communication quality of the UL optical signal received by the optical communication unit 201a of the base station device 200a. In contrast, because the optical axis of the optical communication unit 201b of the base station device 200b faces to the left, ambient light does not enter as a noise signal, and the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b does not deteriorate. Therefore, when prioritizing UL communication, it is preferable for the terminal device 100 to connect to the base station device 200b rather than the base station device 200a.

[0080] In this embodiment, the control unit 130 of the terminal device 100 estimates UL communication quality, which is the reception quality of the UL optical signal received by the base station device 200 from the terminal device 100, and uses the estimated UL communication quality for connection control. Here, the control unit 130 of the terminal device 100 estimates the UL communication quality based on the reception conditions of its own multiple optical communication units 101. Then, the control unit 130 of the terminal device 100 estimates the UL communication quality for each of the multiple base station devices 200, selects from the multiple base station devices 200 a base station device 200 whose UL communication quality satisfies a predetermined criterion, and attempts to connect to the selected base station device 200. In this embodiment, the predetermined criterion is a condition that the UL communication quality is the highest among the multiple base station devices 200. However, the predetermined criterion may also be a condition that the UL communication quality is higher than a threshold.

[0081] FIG. 15 is a diagram for explaining the operation of estimating UL communication quality performed by the terminal device 100 according to this embodiment.

[0082] The optical communication unit 101a (light receiving unit 110) of the terminal device 100 receives a DL optical signal, specifically a reference optical signal, from the optical communication unit 201a (light emitting unit 220) of the base station device 200. The control unit 130 of the terminal device 100 measures the reference signal strength, which is the reception strength of the reference optical signal in the optical communication unit 101a (first optical communication unit) that receives the reference optical signal from the base station device 200. The optical communication unit 101a is an optical communication unit that is scheduled to be used for optical communication with the base station device 200.

[0083] Furthermore, the control unit 130 of the terminal device 100 estimates the ambient optical noise intensity, which is the received intensity of ambient light at the base station device 200, based on the received intensity at an optical communication unit 101b (second optical communication unit) different from the optical communication unit 101a. The optical communication unit 101b is an optical communication unit 101 whose optical axis is oriented in the opposite direction to the direction in which the optical axis of the optical communication unit 101a is oriented. Since it can be assumed that the ambient light incident on the optical communication unit 101b (light receiving unit 110) is also incident on the optical communication unit 201a (light receiving unit 210) of the base station device 200, it is possible to estimate the received intensity at the optical communication unit 101b on the opposite side of the optical communication unit 101a as the ambient optical noise intensity.

[0084] Then, the control unit 130 of the terminal device 100 estimates the UL communication quality with the base station device 200 based on the reference signal strength measured using the optical communication unit 101a and the ambient optical noise strength estimated using the optical communication unit 101b. The UL communication quality is calculated, for example, by the following formula (1): "UL communication quality" = "reference signal strength" - "ambient optical noise strength".

[0085] In this way, when estimating the ambient optical noise in the optical communication unit 201a (light receiving unit 210) of the base station device 200 that is a connection candidate, the terminal device 100 uses the ambient optical noise intensity measured by the optical communication unit 101b (light receiving unit 110) of the terminal device 100 that faces the same direction as the optical communication unit 201a (light receiving unit 210) of the base station device 200 as an estimated value of the ambient optical noise received by the optical communication unit 201a (light receiving unit 210) of the base station device 200. In this way, the terminal device 100 can compare the UL communication quality of each surrounding base station device 200 before attempting a connection, and select the base station device 200 to connect to.

[0086] 16 is a diagram for explaining the operation of selecting the optical communication unit 101 (light receiving unit 110) for noise estimation in the terminal device 100 according to this embodiment. In the illustrated example, the number of optical communication units 101 in the terminal device 100 is smaller than the number of optical communication units 101 in the terminal device 100 shown in FIG.

[0087] The control unit 130 of the terminal device 100 pre-registers optical communication units 101 (light receiving units 110) whose optical axes are directed in opposite directions as pairs, and selects the optical communication unit 101 (light receiving unit 110) that is paired with the optical communication unit 101 (light receiving unit 110) that received the reference optical signal for noise estimation.

[0088] In the illustrated example, the optical communication unit 101 (light receiving unit 110) #0 and the optical communication unit 101 (light receiving unit 110) #0' are registered as a pair. Similarly, the optical communication unit 101 (light receiving unit 110) #1 and the optical communication unit 101 (light receiving unit 110) #1' are registered as a pair, the optical communication unit 101 (light receiving unit 110) #2 and the optical communication unit 101 (light receiving unit 110) #2' are registered as a pair, and the optical communication unit 101 (light receiving unit 110) #3 and the optical communication unit 101 (light receiving unit 110) #3' are registered as a pair. , the optical communication unit 101 (light receiving unit 110) #4 and the optical communication unit 101 (light receiving unit 110) #4' are registered as a pair, the optical communication unit 101 (light receiving unit 110) #5 and the optical communication unit 101 (light receiving unit 110) #5' are registered as a pair, and the optical communication unit 101 (light receiving unit 110) #6 and the optical communication unit 101 (light receiving unit 110) #6' are registered as a pair.

[0089] FIG. 17 is a diagram showing an example of an operation flow in the terminal device 100 according to this embodiment.

[0090] In step S1 , the control unit 130 of the terminal device 100 measures the reference signal intensity in the optical communication unit 101 a that receives the reference optical signal from the base station device 200 .

[0091] In step S2, the control unit 130 of the terminal device 100 measures the reception strength of the optical communication unit 101b opposite (i.e., paired with) the optical communication unit 101a that receives the reference optical signal from the base station device 200.

[0092] In step S3, the control unit 130 of the terminal device 100 estimates the ambient optical noise intensity at the base station device 200 based on the reception intensity measured in step S2. In this embodiment, the reception intensity measured in step S2 may be directly estimated as the ambient optical noise intensity at the base station device 200.

[0093] In step S4, the control unit 130 of the terminal device 100 estimates the UL communication quality using the reference signal strength measured in step S1 and the ambient optical noise strength estimated in step S3, using the above-mentioned formula (1).

[0094] In step S5, the control unit 130 of the terminal device 100 determines whether there is another optical communication unit 101 that receives a reference optical signal from another base station device 200. That is, the control unit 130 of the terminal device 100 determines whether there is another candidate base station. If the determination in step S5 is YES, the control unit 130 of the terminal device 100 estimates the UL communication quality for the other base station device 200 (steps S1 to S4). In this way, the control unit 130 of the terminal device 100 estimates the UL communication quality for each of the multiple candidate base station devices 200.

[0095] If the result of step S5 is NO, in step S6, the control unit 130 of the terminal device 100 ranks the UL communication qualities of each of the multiple candidate base station devices 200 (i.e., ranks them in descending order of UL communication quality).

[0096] In step S7, the control unit 130 of the terminal device 100 determines (selects) the base station device 200 to connect to based on the ranking result of step S6. For example, the control unit 130 determines the base station device 200 with the highest UL communication quality as the connection destination.

[0097] In step S8, the control unit 130 of the terminal device 100 attempts to connect to the base station device 200 determined in step S7. For example, the terminal device 100 establishes an optical communication connection with the base station device 200 by transmitting a connection request message to the base station device 200 and receiving a response message from the base station device 200. Note that if the connection attempt to the base station device 200 fails, the control unit 130 of the terminal device 100 may select the second-ranked base station device 200 and attempt to connect to that base station device 200.

[0098] [First Modification of First Embodiment] A first modification of the first embodiment will be described, focusing on differences from the first embodiment described above. Fig. 18 is a diagram for explaining the operation of this modification.

[0099] In the first embodiment described above, there is a possibility that a light source for work such as an underwater drone or transmitted light from other visible light communications may be incident during the ambient light measurement in step S2 of Fig. 17. If ambient light measurement is performed in a state where such light is incident, the intensity of the ambient light incident on the base station device 200 may become excessively large, which may result in an erroneous selection of an appropriate base station device 200.

[0100] In this modification, to eliminate the influence of such transient ambient light, instead of using instantaneous ambient light measurement results, the average intensity is calculated by measuring for a certain period of time, and this value is used for noise estimation. That is, the control unit 130 of the terminal device 100 estimates the ambient light noise intensity by averaging the multiple measurements obtained by measuring the reception intensity of the optical communication unit 101b opposite (i.e., paired with) the optical communication unit 101a that receives the reference optical signal from the base station device 200 multiple times within a predetermined period (step S3 in FIG. 17). This makes it possible to select a base station device 200 suitable for UL communication without being affected by instantaneous ambient light.

[0101] Note that such a technique may be applied to the measurement of the reference signal strength in step S2 of Fig. 17. That is, the control unit 130 of the terminal device 100 may measure the reference signal strength in the optical communication unit 101a that receives the reference optical signal from the base station device 200 multiple times, and may acquire the average of the multiple measurement values ​​as the reference signal strength.

[0102] [Second Modification of First Embodiment] A second modification of the first embodiment will be described, focusing on differences from the first embodiment. This modification can be implemented in combination with the first embodiment or its modifications. Figure 19 is a diagram for explaining the operation of this modification.

[0103] Assume a situation in which ambient light is constantly incident on the light receiving unit 110 (e.g., the light receiving unit 110 of the optical communication unit 101b) in a specific direction of the terminal device 100. When the ambient light noise intensity of the base station device 200 is estimated using the light receiving unit 110 to which the ambient light is incident, the estimated ambient light noise intensity usually increases due to the influence of the incident ambient light, resulting in a deterioration in the estimated UL reception quality.

[0104] However, as shown in Fig. 19 , the terminal device 100 itself may block the ambient light incident on the terminal device 100, preventing it from reaching the base station device 200. As a result, the actual UL reception quality of the base station device 200 may be better than the estimated ambient light noise intensity. In this case, estimating the UL reception quality based on the measurement value in the terminal device 100 may result in an inability to correctly select a base station device 200 suitable for UL communication.

[0105] 20 is a diagram showing an example of an operation flow in the terminal device 100 according to this modified example. Here, differences from the first embodiment described above will be described.

[0106] In this modified example, in step S11, the control unit 130 of the terminal device 100 determines whether the terminal device 100 is in a blocked state, in which ambient light incident on the base station device 200 is blocked by the terminal device 100. If the control unit 130 of the terminal device 100 determines that the terminal device 100 is in a blocked state (step S11: YES), in step S12, the control unit 130 corrects the ambient light noise intensity estimated in step S3 to a predetermined alternative value.

[0107] For example, the control unit 130 of the terminal device 100 determines that the terminal device 100 is in an obstructed state based on whether condition 1 (first condition) is satisfied, that is, the ambient light noise intensity estimated in step S3 is equal to or greater than a first threshold value, and the received intensity of ambient light at least in the optical communication unit 101 (first optical communication unit) used to measure the reference signal intensity in step S1 is less than a second threshold value. In other words, the control unit 130 of the terminal device 100 determines that the terminal device 100 is in an obstructed state based on whether condition 1 is satisfied, that is, the estimated ambient light noise is sufficiently large, but the ambient light noise in the other optical receiving units is sufficiently small.

[0108] Here, the optical communication unit 101 (first optical communication unit) used to measure the reference signal strength in step S1 is the optical communication unit 101 on the opposite side of the optical communication unit 101 (second optical communication unit) used to estimate the ambient light noise strength in step S3. When the optical communication unit 101 (first optical communication unit) receives ambient light other than the reference optical signal, it means that the terminal device 100 is entirely affected by the ambient light, and it can be considered not to be in a blocked state.

[0109] The control unit 130 of the terminal device 100 may determine that the terminal device 100 is in an obstructed state when it determines that Condition 1 is satisfied and also determines that at least one of the following Conditions 2a and 2b is satisfied.

[0110] Condition 2a: The distance between the terminal device 100 and the base station device 200 is sufficiently close For example, if the reference signal strength measured in step S1 is greater than a threshold, the control unit 130 of the terminal device 100 may consider that the distance between the terminal device 100 and the base station device 200 is sufficiently close and determine that condition 2a is satisfied. Here, the control unit 130 of the terminal device 100 uses the reference signal strength measured in step S1 as a value indicating the distance between the terminal device 100 and the base station device 200. However, as described later, a value obtained by subtracting the transmission power of the reference optical signal from the reference signal strength measured in step S1 may be used as a value indicating the distance between the terminal device 100 and the base station device 200. If condition 1 is satisfied and the distance between the terminal device 100 and the base station device 200 is equal to or less than a threshold (i.e., condition 2a is satisfied), the control unit 130 of the terminal device 100 determines that the terminal device 100 is in a shielded state. When the distance between the terminal device 100 and the base station device 200 is sufficiently short, it can be considered that the terminal device 100 is likely to be in the shadow of the terminal device 100, that is, it is in an obstructed state.

[0111] Condition 2b: Light receiving units where large ambient light noise is measured are limited For example, the control unit 130 of the terminal device 100 may determine that condition 2b is satisfied if the noise intensity of the optical communication units 101 (light receiving units 110) around the optical communication unit 101 (second optical communication unit) used to estimate the ambient light noise intensity in step S3 is smaller than a threshold value. The control unit 130 of the terminal device 100 determines that the terminal device 100 is in an obstructed state if condition 1 is satisfied and the received intensity of ambient light in the optical communication units 101 around the optical communication unit 101 (second optical communication unit) used to estimate the ambient light noise intensity in step S3 is less than a threshold value (i.e., condition 2b is satisfied).

[0112] If the terminal device 100 determines that the optical communication unit 101 is in an obstructed state, the control unit 130 of the terminal device 100 uses a predetermined substitute value instead of the ambient light noise intensity estimated in step S3 (step S12). The predetermined substitute value may be the average or median of the reception intensity of each of the optical communication units 101 of the terminal device 100.

[0113] Alternatively, the control unit 130 of the terminal device 100 may acquire the ambient light noise intensity derived by the base station device 200 from the base station device 200 and use the ambient light noise intensity acquired from the base station device 200 as a predetermined substitute value. In this case, the base station device 200 notifies the terminal device 100 of the ambient light noise intensity information by broadcast. Here, the ambient light noise intensity derived by the base station device 200 may be, for example, the average value of the ambient light intensity measured by the available light receiving units 210 of the base station device 200. The ambient light noise intensity derived by the base station device 200 may also be the average value of the ambient light intensity measured for each group (area) of the light receiving units 210 of the base station device 200.

[0114] According to this modification, even when ambient light is incident on the terminal device 100 from a specific direction and noise estimation is difficult, it is possible to select a base station device 200 suitable for UL communication.

[0115] [Third Modification of First Embodiment] A third modification of the first embodiment will be described, focusing on differences from the first embodiment described above. This modification can be implemented in combination with the first embodiment or its modifications.

[0116] If the transmission power of the reference optical signal differs for each base station device 200, estimating the UL communication quality (specifically, calculating using the above-described formula (1)) without taking the transmission power into consideration may result in the terminal device 100 connecting to a (distant) base station device 200 that has high transmission power but poor UL communication quality. Therefore, in this modified example, the base station device 200 transmits the transmission power of the reference optical signal as broadcast information. The control unit 130 of the terminal device 100 acquires information indicating the transmission power of the reference signal at the base station device 200 from the base station device 200.

[0117] The control unit 130 of the terminal device 100 calculates the UL communication quality from the reference signal strength, transmission power, and ambient optical noise strength using the following equation (2): "UL communication quality" = "reference signal strength" - "transmission power" - "ambient optical noise strength" ... equation (2) Then, based on the calculated UL communication quality, the control unit 130 of the terminal device 100 determines the base station device 200 to connect to in the same manner as in the first embodiment described above.

[0118] FIG. 21 is a diagram showing an example of an operation sequence of the optical communication system 1 according to this modified example.

[0119] In step S21, the base station device 200a transmits broadcast information indicating the transmission power of its own reference optical signal. The terminal device 100 receives the broadcast information. Here, it is assumed that the transmission power is a small value.

[0120] In step S22, the base station device 200b transmits broadcast information indicating the transmission power of its own reference optical signal. The terminal device 100 receives the broadcast information. Here, it is assumed that the transmission power is a large value.

[0121] In step S23, the base station device 200a transmits a reference optical signal. The terminal device 100 receives the reference optical signal and measures the reference signal strength.

[0122] In step S24, the base station device 200b transmits a reference optical signal. The terminal device 100 receives the reference optical signal and measures the reference signal strength.

[0123] In step S25, the terminal device 100 estimates the UL communication quality for each of the base station device 200a and the base station device 200b using the above-described formula (2), and compares the UL communication qualities to determine the connection destination base station device 200. Here, the explanation will continue assuming that the UL communication quality estimated for the base station device 200a is higher than the UL communication quality estimated for the base station device 200b.

[0124] In step S26, the terminal device 100 determines the base station device 200a as the connection destination and transmits a connection request message to the base station device 200a. The base station device 200a receives the connection request message.

[0125] As a result, in step S27, the terminal device 100 establishes an optical communication connection with the base station device 200a.

[0126] Second Embodiment Next, a second embodiment will be described, focusing mainly on the differences from the first embodiment described above. This embodiment can be implemented in combination with the first embodiment described above or a modified example thereof.

[0127] In the above-described first embodiment, as an example of connection control, an operation for establishing an optical communication connection between the terminal device 100 and the base station device 200 has been mainly described. In the second embodiment, as an example of connection control, an operation for maintaining an optical communication connection between the terminal device 100 and the base station device 200 will be mainly described.

[0128] According to the first embodiment described above, even if the terminal device 100 selects and connects to a base station device 200 with good UL communication quality, there is a risk that the base station device 200 may perform control without considering the UL-prioritized connection. As a result, the base station device 200 may hand over the terminal device 100 to another base station device 200 with poor UL communication quality. Therefore, the base station device 200 needs to perform control based on conditions that allow the UL-prioritized connection to be maintained for the terminal device 100 that has connected with UL priority, rather than performing DL-prioritized control.

[0129] In this embodiment, the control unit 130 of the terminal device 100 notifies the base station device 200 that the terminal device 100 is performing a UL-preferred connection in the process of establishing a connection with the base station device 200. This allows the base station device 200 to recognize that the terminal device 100 is performing a UL-preferred connection, and to perform control to maintain the UL-preferred connection.

[0130] In this embodiment, the base station device 200 may notify the terminal device 100 of whether the base station device 200 is capable of performing connection control that prioritizes UL communication quality. For example, the base station device 200 transmits notification information indicating that the base station device 200 is capable of performing connection control that prioritizes UL communication quality. This allows the terminal device 100 to preferentially determine, as a connection destination, a base station device 200 that is capable of performing connection control that prioritizes UL communication quality.

[0131] FIG. 22 is a diagram showing an example of an operation sequence of the optical communication system 1 according to this embodiment.

[0132] In step S31, the base station device 200 transmits notification information indicating that the base station device 200 is capable of performing connection control that prioritizes UL communication quality. The terminal device 100 receives the notification information.

[0133] In step S32, the base station device 200 transmits a reference optical signal. The terminal device 100 receives the reference optical signal and measures the reference signal strength.

[0134] In step S33, the terminal device 100 estimates the UL communication quality of the base station device 200 and determines the base station device 200 as the connection destination.

[0135] In step S34, the terminal device 100 transmits a connection request message including information indicating that a UL prioritized connection is being performed to the base station device 200. The base station device 200 receives the connection request message.

[0136] As a result, in step S35, the terminal device 100 establishes an optical communication connection with the base station device 200.

[0137] [Modification of Second Embodiment] A modification of the second embodiment will be described, focusing on differences from the second embodiment described above. This modification can be implemented in combination with the above-described embodiment or its modifications.

[0138] In this modified example, the base station device 200 configures the terminal device 100 to transmit to the base station device 200 a measurement report message including information indicating the UL communication quality estimated by the terminal device 100. The base station device 200 determines handover of the terminal device 100 from the base station device 200 to another base station device 200 based on the measurement report message from the terminal device 100. This enables the base station device 200 to handover the terminal device 100 to another base station device 200 with good UL communication quality.

[0139] When the estimated UL communication quality satisfies a predetermined trigger condition, the control unit 130 of the terminal device 100 may trigger transmission of a measurement report message to the base station device 200. Such a trigger condition may be any of the following: the UL communication quality of the destination base station device 200 falls below a threshold; the UL communication quality of the destination base station device 200 is deteriorated compared with the UL communication quality of another base station device 200; or a negative offset value for UL priority is applied to a threshold to be compared with the DL communication quality of the destination base station device 200, thereby applying a lower threshold.

[0140] In this modification, in the handover process of the terminal device 100 from its own base station device 200 to another base station device 200, the base station device 200 may notify the other base station device 200 that the terminal device 100 is performing a UL-preferred connection. This allows UL-preferred connection information to be shared between the base station devices 200, so that the control for maintaining the UL-preferred connection can be continued at the handover destination base station device 200.

[0141] FIG. 23 is a diagram showing an example of an operation sequence of the optical communication system 1 according to this modified example.

[0142] In step S41, the terminal device 100 establishes an optical communication connection with the base station device 200a by the method of the first embodiment or its modification. When the optical communication connection is established, the terminal device 100 notifies the base station device 200a that an UL prioritized connection is being established.

[0143] In step S42, the base station device 200a transmits configuration information (Meas. Config) for configuring transmission of a measurement report message to the terminal device 100. The terminal device 100 receives the configuration information. The configuration information may include information for configuring a trigger condition related to the above-mentioned UL communication quality. The configuration information may include information for configuring inclusion of the UL communication quality in the measurement report message.

[0144] In step S43, the base station device 200a transmits a reference optical signal. The terminal device 100 receives the reference optical signal, measures the reference signal strength, and estimates the UL communication quality of the base station device 200a by the method of the first embodiment or its modification.

[0145] In step S44, the base station device 200b transmits a reference optical signal. The terminal device 100 receives the reference optical signal, measures the reference signal strength, and estimates the UL communication quality of the base station device 200b by the method of the first embodiment or its modification.

[0146] In step S45, the terminal device 100 transmits a measurement report message (Meas. Report) to the base station device 200a. The base station device 200a receives the measurement report message. The terminal device 100 may transmit the measurement report message in response to the trigger condition set in step S42 being satisfied. The terminal device 100 may include the UL communication quality estimated in steps S43 and S44 in the measurement report message.

[0147] In step S46, the base station device 200a determines to hand over (HO) the terminal device 100 to the base station device 200b based on the measurement report message of step S45.

[0148] In step S47, the base station device 200a transmits HO information including information that the terminal device 100 is performing UL prioritized connection to the base station device 200b via inter-base station communication. The base station device 200b receives the HO information. The base station device 200a may transmit an HO request message including the HO information to the base station device 200b. As a result, HO of the terminal device 100 from the base station device 200a to the base station device 200b is performed.

[0149] [Third Embodiment] Next, a third embodiment will be described, focusing on differences from the above-described embodiments. This embodiment relates to details of the three-dimensional arrangement of the base station device 200 (see, for example, FIG. 1 ). This embodiment can be implemented in combination with the above-described embodiments or their modifications.

[0150] 24 is a diagram showing a configuration example of an optical communication system 1 according to this embodiment. As described above, the optical communication system 1 is an optical communication system that performs optical communication between a base station device 200 and a terminal device 100, and includes the terminal device 100 and a plurality of base station devices 200.

[0151] 24, the optical communication system 1 according to this embodiment has a plurality of base station devices 200 arranged three-dimensionally underwater at intervals in the horizontal and vertical directions. The communication areas formed underwater by each of the plurality of base station devices 200 constitute the optical communication coverage areas of the optical communication system 1. This makes it possible to form a wide coverage area underwater regardless of the position or orientation of the terminal device 100.

[0152] In the illustrated example, three base station devices 200 are arranged in each of the x and y directions, which are horizontal directions and perpendicular to each other, and three base station devices 200 are arranged in each of the z directions, which are vertical directions (depth directions), for a total of 27 base station devices 200 arranged underwater. In the illustrated example, the distances between the base station devices 200 (also referred to as "inter-base station distances") are equal. In FIG. 24 , in the three-dimensional coordinate space (x, y, z) of the x, y, and z directions, the base station device 200 located at the origin (0, 0, 0) is represented as base station device 200 (0, 0, 0), and other base stations are represented similarly.

[0153] Base station device 200 (0,0,0) to base station device 200 (2,2,2) constitute a plurality of base station groups 300 arranged at intervals in the horizontal direction (see FIG. 25 ). Each base station group 300 includes a plurality of base station devices 200 (three base station devices 200 in the illustrated example) arranged in the vertical direction. In each base station group 300, base station devices 200 whose communication areas are adjacent in the vertical direction are connected by connecting members 264. In this embodiment, the connecting members 264 are members that can be wound and unwound, such as the rope 261 and / or cable 262 described above. The rope 261 may be a wire rope. The following mainly describes an example in which the connecting members 264 include a wire rope.

[0154] FIG. 25 is a diagram illustrating an example configuration of a base station group 300. Each base station group 300 includes two or more base station devices 200 (three base station devices 200 in the illustrated example) spaced apart in the vertical direction, and a connecting member 264 whose communication area is provided between vertically adjacent base station devices 200 and vertically connects the base station devices 200. In the illustrated example, the base station device 200a closest to the water surface is suspended from a floating member (buoy) 310 on the water surface by a connecting member 264a. The base station device 200b is suspended from the base station device 200a by a connecting member 264b. The base station device 200c is suspended from the base station device 200b by a connecting member 264c. This configuration allows the base station devices 200 to be efficiently arranged in the water in a horizontal line, even if there are no walls or other structures underwater.

[0155] However, the base station device 200a may be integrated with the floating member 310 and placed on the water surface. In this case, the base station device 200a may have a hemispherical configuration instead of a spherical configuration (see FIG. 1).

[0156] In each base station group 300, the base station device 200c located at the deepest position may be connected to a weight member 320 at the bottom of the water via a connecting member 264d. However, if each base station device 200c is sufficiently heavy, the weight member 320 may not be necessary.

[0157] An adjustment mechanism 265 that winds up and pulls out the connecting member 264 is provided at the top of each base station device 200 (base station device 200a to base station device 200c). The adjustment mechanism 265 may be an electric winch. The adjustment mechanism 265 can adjust the vertical distance between the base stations.

[0158] Specifically, an adjustment mechanism 265a that winds up and unwinds the connecting member 264a is provided on the upper part of the base station device 200a. The adjustment mechanism 265a may be controlled by the control unit 230 of the base station device 200a. An adjustment mechanism 265b that winds up and unwinds the connecting member 264b is provided on the upper part of the base station device 200b. The adjustment mechanism 265b may be controlled by the control unit 230 of the base station device 200b. An adjustment mechanism 265c that winds up and unwinds the connecting member 264c is provided on the upper part of the base station device 200c. The adjustment mechanism 265c may be controlled by the control unit 230 of the base station device 200c.

[0159] However, the configuration is not limited to providing the adjustment mechanism 265 at the top of each base station device 200, and the adjustment mechanism 265 may be provided at the bottom of each base station device 200. Furthermore, the configuration is not limited to the coupling member 264 being capable of being wound up and pulled out, and a sliding mechanism serving as the adjustment mechanism 265 may be provided on the coupling member 264, making the coupling member 264 extendable and retractable. Alternatively, the coupling member 264 may be provided continuously in the vertical direction so as to penetrate the center of each base station device 200, and the base station device 200 may move (slide) on the coupling member 264 to move the base station device 200 in the vertical direction. In this case, the sliding mechanism serving as the adjustment mechanism may be provided inside the base station device 200.

[0160] The floating member 310 may have a movement mechanism 311 for moving the base station group 300 in the horizontal direction. The movement mechanism 311 may be configured to include a motor, a screw, and the like. When the floating member 310 moves on the water surface by the movement mechanism 311, the base station group 300 (base station devices 200a to 200c) moves in the horizontal direction in accordance with the movement of the floating member 310. The movement mechanism 311 may be controlled by the control unit 230 of the base station device 200a, for example, via a connecting member 264a (cable).

[0161] When the base station group 300 includes a weight member 320, the weight member 320 may include a movement mechanism 321 for moving the base station group 300 in the horizontal direction. The movement mechanism 321 may include a motor, a crawler (caterpillar), and the like. When the weight member 320 moves on the bottom of the water by the movement mechanism 321, the base station group 300 (base station device 200a to base station device 200c) moves in the horizontal direction in accordance with the movement of the weight member 320. The movement mechanism 321 may be controlled by the control unit 230 of the base station device 200c, for example, via a connecting member 264d (cable).

[0162] In each base station group 300, pairs of vertically adjacent base station devices can perform backhaul communication between the base stations via a connecting member 264 (cable) connecting the pair of base station devices. For example, the pair of base station device 200a and base station device 200b can communicate via connecting member 264b. The pair of base station device 200b and base station device 200c can communicate via connecting member 264c. Alternatively, instead of inter-base station communication via the connecting member 264 (cable), inter-base station communication may be performed using the above-mentioned laser communication device 263 (see FIG. 6).

[0163] The base station group 300 performs backhaul communication with the network 10. For example, the base station device 200a may perform wireless radio wave communication with the network 10. However, because radio waves are significantly attenuated underwater, it may be inappropriate to provide an antenna in the underwater base station device 200a. Therefore, in the illustrated example, the antenna 312 of the network communication unit 241 (see FIG. 3 ) of the base station device 200a is provided on the floating member 310. However, if the base station device 200a is placed on the water surface, the antenna 312 for backhaul communication can be provided in the base station device 200a.

[0164] The base station device 200a performs direct backhaul communication with the network 10. The base station device 200b performs indirect backhaul communication with the network 10 via the base station device 200a. The base station device 200c performs indirect backhaul communication with the network 10 via the base station device 200a and the base station device 200b.

[0165] (Location Design of Optical Communication System) FIGS. 26 to 29 are diagrams for explaining location design of the optical communication system 1 according to this embodiment.

[0166] In conventional communication systems that use radio waves for wireless communication on land, a two-dimensional coverage area is configured in the horizontal direction. In addition, in station placement design for conventional communication systems, base station devices are placed so that the coverage area is filled with regular hexagonal communication areas called cells.

[0167] In contrast to this, in the optical communication system 1 according to this embodiment, as shown in Figures 26 and 27, station placement design is performed by regarding the communication area formed by each of the multiple base station devices 200 as a cube. Specifically, the multiple base station devices 200 are placed underwater so that the cubic communication areas are arranged horizontally and vertically to fill the coverage area.

[0168] As shown in FIG. 26, if we assume that the actual communication area of ​​the base station device 200 is a sphere with a radius "r", the virtual communication area of ​​each base station device 200 has a side length "a" of The base station device 200 is arranged so that such cubic communication areas are arranged horizontally and vertically to fill the coverage area. Note that "r" is the communicable distance (also referred to as "communication distance") of the base station device 200. For example, the communication distance is the distance at which a reference signal transmitted by the base station device 200 can be received with a predetermined strength or higher.

[0169] As a result, as shown in FIG. 27, the distance between the base stations in the horizontal and vertical directions is By setting the base station distance in this manner and arranging a plurality of base station devices 200 underwater, a wide coverage area can be efficiently covered by the plurality of base station devices 200.

[0170] It is expected that the base station device 200 deployed underwater will move due to the influence of waves and ocean currents. When the base station device 200 moves, coverage holes (i.e., blind zones) may occur within the coverage area. As shown in FIG. 28 , the points where the vertices of the cubic communication areas overlap are the points where the edges of the actual communication areas of the base station devices 200 are concentrated, and may be areas with extremely poor communication conditions. Therefore, when the base station device 200 moves, the points where the vertices of the cubic communication areas overlap are likely to become coverage holes.

[0171] In this embodiment, as shown in Fig. 29, when the communication area of ​​each base station device 200 is regarded as a cube and arranged, the base station devices 200 are arranged with a shift so that the vertices of the cube do not overlap as much as possible. Specifically, in two cubic communication areas adjacent in the horizontal or vertical direction, multiple base station devices 200 are arranged underwater so that the vertices of one cubic communication area do not overlap the vertices of the other cubic communication area. This allows the base station devices 200 to be arranged so that the vertices (edges of the communication areas) are not crowded together, making it less likely that blind zones will occur even when the base station devices 200 move.

[0172] In the illustrated example, in two horizontally adjacent cubic communication areas, the base station device 200 responsible for one of the cubic communication areas is shifted by a predetermined amount in the vertical direction (and / or horizontal direction) relative to the base station device 200 responsible for the other cubic communication area. Such a vertical shift amount is also referred to as the blind zone adjustment amount α.

[0173] For example, base station devices 200(0,0,0) and 200(0,0,1) adjacent in the z direction and base station devices 200(1,0,0) and 200(1,0,1) adjacent in the z direction are adjacent in the x direction. Base station devices 200(1,0,0) and 200(1,0,1) are arranged with a predetermined offset in the z and y directions relative to base station devices 200(0,0,0) and 200(0,0,1).

[0174] Furthermore, for example, base station devices 200(0,0,0) and 200(0,0,1) adjacent in the z direction and base station devices 200(0,1,0) and 200(0,1,1) adjacent in the z direction are adjacent in the y direction. Base station devices 200(0,1,0) and 200(0,1,1) are arranged offset by a predetermined amount in the vertical direction (z direction) relative to base station devices 200(0,0,0) and 200(0,0,1).

[0175] The shift direction may be any three-dimensional direction, and the cubic communication areas may be arranged without gaps after the shift. In other words, each cubic communication area is arranged so that its vertex overlaps with only one of the adjacent cubic communication areas.

[0176] Furthermore, each base station device 200 may be installed underwater by a worker. After each base station device 200 is installed underwater, each base station device 200 may autonomously adjust the inter-base station distance in consideration of the communication environment. Such autonomous adjustment operation will be described later.

[0177] (Response to movement of base station devices in the horizontal direction) As described above, vertically adjacent base station devices 200 are physically connected via the connecting members 264, but horizontally adjacent base station devices 200 are not physically connected via the connecting members 264. Therefore, the base station devices 200 are unlikely to move vertically but are likely to move horizontally due to the influence of waves and ocean currents.

[0178] FIG. 30 is a diagram for explaining how to respond to movement of the base station device 200 in the horizontal direction.

[0179] In this embodiment, multiple base station devices 200 are arranged underwater so that the distance between base stations in the horizontal direction is narrower by a predetermined distance "Δ" than the distance between base stations in the vertical direction. This predetermined distance Δ is also referred to as the horizontal adjustment amount. Specifically, assuming that the distance between base stations in the vertical direction is "a", the distance between base stations in the horizontal direction is "a - Δ". By arranging the base station devices 200 in this manner, the overlapping area between the communication areas of the base station devices 200 in the horizontal direction can be increased, making it less likely that blind zones will occur even when the base station devices 200 move horizontally.

[0180] The horizontal adjustment amount Δ may be set based on an environmental parameter indicating at least one of the wave height, wind strength on the water, and water current speed in the coverage area of ​​the optical communication system 1. For example, the horizontal adjustment amount Δ may be increased as the value of the environmental parameter increases. The horizontal adjustment amount Δ may be determined by any of the base station devices 200 or by a base station management device (e.g., a server device) provided on the network 10.

[0181] (Adjustment of Inter-Base Station Distance Taking Communication Environment into Account) In underwater optical communication, it is expected that the communication distance will change depending on the location (sea area / water area) and time due to the influence of underwater turbidity and solar noise. Therefore, when arranging the base station device 200, it is desirable to appropriately determine and set the communication distance and inter-base station distance of the base station device 200 based on environmental information (environmental parameters) such as turbidity and solar noise.

[0182] FIG. 31 is a diagram showing an example of the functional block configuration of the control device 400 for determining and setting the communication distance and inter-base station distance of the base station device 200.

[0183] The control device 400 may be configured by the control unit 230 of each base station device 200. That is, each base station device 200 may have the functions of the control device 400. Alternatively, only a specific base station device 200 among the multiple base station devices 200 may have the functions of the control device 400, and the specific base station device 200 may determine and set the communication distance and inter-base station distance for the other base station devices 200. Alternatively, a base station management device (e.g., a server device) provided on the network 10 may have the functions of the control device 400, and the base station management device may determine and set the communication distance and inter-base station distance for each base station device 200.

[0184] The control device 400 may determine and set the communication distance and the inter-base station distance of the base station device 200 at the time of initial installation in water of each base station device 200. After initial installation in water of each base station device 200, the control device 400 may determine and set the communication distance and the inter-base station distance of the base station device 200 to be updated periodically.

[0185] The control device 400 has a communication distance determination unit 410, a base station distance setting unit 420, a horizontal adjustment amount determination unit 430, a blind zone adjustment amount determination unit 440, a vertical direction control unit 450 (first control unit), and a horizontal direction control unit 460 (second control unit).

[0186] The communication distance specifying unit 410 performs optical communication between a pair of base station devices whose communication areas are adjacent in the vertical direction, and specifies the communication distance of the optical communication between the base station devices 200 that make up the pair of base station devices.

[0187] FIG. 32 is a diagram illustrating the operation of determining the communication distance of optical communication of a base station device 200. As shown in FIG. 32, the upper base station device 200a and the lower base station device 200b form a base station device pair. The upper optical communication unit 201 (light emitter 220) of the base station device 200b transmits a reference optical signal upward. The lower optical communication unit 201 (light receiver 210) of the base station device 200a receives the reference optical signal. The control unit 230 of the base station device 200a measures the received intensity of the reference optical signal. The control unit 230 of the base station device 200b also uses the adjustment mechanism 265b to gradually increase the length (wire length in this embodiment) of the coupling member 264b between the base station devices 200a and 200b.

[0188] The communication distance determination unit 410 determines the wire length "x" when the reception strength measured by the base station device 200a falls below a threshold, and determines the communication distance (radius "r") based on the wire length "x." For example, if the radius of the base station is "z" and the correction value according to the height of the adjustment mechanism 265 is "y," and the base station center is taken as the starting point, the communication distance (radius "r") is calculated as follows: r = x + y + z, where "z" and "y" are predetermined fixed values.

[0189] The base station distance setting unit 420 sets the base station distances in the horizontal and vertical directions based on the communication distance "r" specified by the communication distance specifying unit 410. Fig. 33 is a diagram for explaining the operation of calculating the base station distance. As described above, the base station distance "a" is calculated by It is calculated as follows.

[0190] Furthermore, the base station distance setting unit 420 may also take into consideration the radius "z" of the base station and calculate and set the wire length "x" by the following equation: x=a-2z.

[0191] Furthermore, the base station distance setting unit 420 may also take into consideration a correction value "y" according to the height of the adjustment mechanism 265, and calculate and set the wire length "x" by the following equation: x=a-2z-y.

[0192] The base station distance setting unit 420 may notify each base station device 200 of the calculated and set base station distance "a" and / or wire length "x".

[0193] The horizontal adjustment amount determination unit 430 determines the horizontal adjustment amount Δ to accommodate movement of the base station device 200 in the horizontal direction. The horizontal adjustment amount determination unit 430 determines the horizontal adjustment amount Δ based on environmental parameters indicating at least one of the wave height, wind strength on the water, and water current speed in the coverage area of ​​the optical communication system 1 (see FIG. 30 ). The horizontal adjustment amount determination unit 430 may acquire the environmental parameters using a sensor provided on the base station device 200 or the buoyant member 310, or may acquire the environmental parameters from a server device that manages the environmental parameters. As a result, the horizontal inter-base station distance is set to "a-Δ".

[0194] The blind zone adjustment amount determination unit 440 determines the blind zone adjustment amount (shift amount) α for arranging the base station device 200 so that the vertices of each cubic communication area are not crowded together. The blind zone adjustment amount determination unit 440 may determine the blind zone adjustment amount α based on environmental parameters in the same manner as the horizontal adjustment amount determination unit 430.

[0195] 34 is a diagram illustrating the vertical blind zone adjustment amount α. In the illustrated example, the base station devices 200 are arranged so that the horizontally adjacent base station devices are shifted vertically by α. For example, the base station device 200 closest to the water surface in each base station group 300 is adjusted using the adjustment mechanism 265 so that its position is shifted vertically by α.

[0196] 35 is a diagram illustrating the horizontal blind zone adjustment amount α. In the illustrated example, the base station devices 200 are arranged so that the positions of adjacent base station devices in the y direction are shifted by α in the x direction. For example, the positions are adjusted to be shifted by α in the horizontal direction by using a moving mechanism 311 provided on the floating member 310 and / or a moving mechanism 321 provided on the weight member 320.

[0197] The vertical direction control unit 450 adjusts the position of the base station device 200 in the vertical direction by controlling the adjustment mechanism 265 based on the base station distance "a" (and / or wire length "x") set by the base station distance setting unit 420 and the blind zone adjustment amount α in the vertical direction.

[0198] The horizontal direction control unit 460 adjusts the position of the base station device 200 in the horizontal direction by controlling the moving mechanism 311 and / or the moving mechanism 321 based on the base station distance "a" set by the base station distance setting unit 420, the horizontal adjustment amount "Δ" determined by the horizontal adjustment amount determination unit 430, and the blind zone adjustment amount "α" in the horizontal direction.

[0199] FIG. 36 is a diagram showing an example of a flow at the time of initial installation of each base station device 200.

[0200] In step S51, the communication distance determination unit 410 performs optical communication between a pair of base station devices whose communication areas are vertically adjacent to each other, and thereby determines the communication distance (radius "r") of the optical communication between the base station devices 200 that make up the pair of base station devices.

[0201] In step S52, the inter-base station distance setting unit 420 sets the inter-base station distance "a" in each of the horizontal and vertical directions based on the communication distance "r" identified by the communication distance identification unit 410. For example, the inter-base station distance setting unit 420 notifies each base station device 200 of the inter-base station distance "a", and each base station device 200 adjusts the wire length using the adjustment mechanism 265, thereby adjusting the inter-base station distance in the vertical direction.

[0202] In step S53, the horizontal adjustment amount determination unit 430 determines the horizontal adjustment amount Δ based on environmental parameters (environmental information) indicating at least one of the wave height, wind strength on the water, and water current speed in the coverage area of ​​the optical communication system 1, and calculates the horizontal inter-base station distance "a-Δ". For example, the inter-base station distance setting unit 420 notifies each base station device 200 of the horizontal adjustment amount Δ, and each base station device 200 can adjust the horizontal inter-base station distance by moving the float member 310 and / or the weight member 320 using the moving mechanism 311 and / or the moving mechanism 321.

[0203] In step S54, the blind zone adjustment amount determination unit 440 determines the blind zone adjustment amount (shift amount) α for arranging the base station devices 200 so that the vertices of each cubic communication area are not crowded together. For example, the blind zone adjustment amount determination unit 440 notifies each base station device 200 of the blind zone adjustment amount α, and each base station device 200 can adjust the position of each base station device 200 in the vertical and horizontal directions using the adjustment mechanism 265 (and movement mechanisms 311, 321).

[0204] [First Modification of Third Embodiment] FIG. 37 is a diagram for explaining the operation according to a first modification of the third embodiment.

[0205] In the third embodiment described above, it was assumed that the communication distances "r" of the base station devices 200 were equal. However, for example, if the base station device 200 is located close to the bottom of the water, the turbidity may be high and the communication distance "r" may be short. In the illustrated example, the communication distance of the base station device 200a close to the water surface is "r", while the communication distance of the base station device 200c close to the bottom of the water is "r'". Here, the communication distance "r'" is shorter than the communication distance "r". Therefore, a dead zone (coverage hole) occurs outside the communication area of ​​the base station device 200c.

[0206] If the inter-base station distance is set without taking into consideration the difference in communication distance "r" between the base station devices 200, there is a risk of blind zones occurring within the coverage area. Therefore, in this modified example, the operation is adapted to be able to accommodate the difference in communication distance "r" between the base station devices 200.

[0207] In this modified example, the communication distance specifying unit 410 performs optical communication between a plurality of base station device pairs whose communication areas are adjacent in the vertical direction, and specifies the communication distance for each of the plurality of base station device pairs. Then, the communication distance specifying unit 410 specifies the shortest communication distance among the communication distances specified for each of the plurality of base station device pairs. In the illustrated example, the communication distance specifying unit 410 specifies communication distance "r'" as the shortest communication distance. The base station distance setting unit 420 sets at least the horizontal inter-base station distance based on the shortest communication distance "r'" specified by the communication distance specifying unit 410.

[0208] 38 is a diagram showing a first setting pattern of the base station distance according to this modification. In this setting pattern, the base station distance setting unit 420 sets the base station distances in the horizontal and vertical directions based on the shortest communication distance "r'". Specifically, the base station distance setting unit 420 sets the base station distances in the horizontal and vertical directions based on the shortest communication distance "r'". However, in this setting pattern, the distance between base stations is uniformly reduced, so the communication area in the vertical direction, where no blind zones existed, also shrinks.

[0209] FIG. 39 is a diagram showing a second setting pattern for the inter-base station distance according to this modified example. In this setting pattern, the inter-base station distance setting unit 420 sets the inter-base station distance only in the horizontal direction based on the shortest communication distance "r'", and sets the inter-base station distance in the vertical direction for each pair of base station devices 200 adjacent in the vertical direction based on the communication distance "r" of the pair of base station devices. For example, the inter-base station distance in the vertical direction between base station device 200a and base station device 200b is set based on the communication distance r specified between base station device 200a and base station device 200b. Furthermore, the inter-base station distance in the vertical direction between base station device 200b and base station device 200c is set based on the communication distance r specified between base station device 200b and base station device 200c. In this way, in this setting pattern, the inter-base station distance setting unit 420 reduces the inter-base station distance based on the shortest communication distance only in the horizontal direction, and sets the inter-base station distance in the vertical direction based on the communication distance for each pair of base station devices, thereby preventing reduction.

[0210] However, in both the first setting pattern and the second setting pattern, reducing the horizontal inter-base station distance may cause interference between horizontally adjacent base station devices 200. Fig. 40 is a diagram showing an example configuration of a control device 400 according to this modified example. The control device 400 according to this modified example further includes a horizontal power adjustment unit 470 that sets the optical signal transmission power of a base station device 200 in the horizontal direction to be lower than the optical signal transmission power of the base station device 200 in the vertical direction.

[0211] FIG. 41 illustrates a third setting pattern for the inter-base station distance according to this modification. In this setting pattern, the inter-base station distance setting unit 420 sets the inter-base station distance only in the horizontal direction based on the shortest communication distance "r'", as in the second setting pattern described above. The inter-base station distance setting unit 420 sets the inter-base station distance in the vertical direction for each pair of base station devices 200 adjacent in the vertical direction based on the communication distance "r" of the pair of base station devices. For example, the inter-base station distance in the vertical direction between base station devices 200a and 200b is set based on the communication distance r specified between base station devices 200a and 200b. The inter-base station distance in the vertical direction between base station devices 200b and 200c is set based on the communication distance r specified between base station devices 200b and 200c. The horizontal power adjustment unit 470 sets the optical signal transmission power of the base station device 200 in the horizontal direction to be lower than the optical signal transmission power of the base station device 200 in the vertical direction. In the illustrated example, the base station device 200c, which is closest to the bottom of the water, has a short communication distance to begin with, and therefore no interference occurs between horizontally adjacent base station devices. Therefore, the optical signal transmission power of the base station device 200c in the horizontal direction is not reduced.

[0212] [Second Modification of Third Embodiment] As described above, the communication distance may vary depending on the location of the base station. Furthermore, depending on the purpose of underwater communication, it may be necessary to prioritize securing a wide communication area at a specific location and accept dead zones (coverage holes) at other locations. In this case, if a terminal device 100 to be remotely controlled, such as an underwater drone, moves into the dead zone, communication may be interrupted, potentially resulting in loss of control.

[0213] In this modified example, some of the base station devices 200, whose optical communication distance is shorter than that of the other base station devices 200, transmit an optical signal (also referred to as a "dead zone warning") notifying that there is a possibility that a coverage hole exists outside the communication area of ​​the some of the base station devices 200. Upon receiving the optical signal (dead zone warning), the terminal device 100 performs control to keep the terminal device 100 within the communication area, or to return the terminal device 100 to the communication area when it moves from the communication area to a coverage hole. This makes it possible to prevent communication interruptions between the terminal device 100 and the base station device 200.

[0214] 42 is a diagram showing an example of the operation of the optical communication system 1 according to this modification. In the illustrated example, the base station device 200 is not a base station device 200 that prioritizes securing a wide communication area, but rather has a shorter communication distance than the base station device 200.

[0215] In step S61, the base station device 200 broadcasts within its own communication area a message indicating that a dead zone may be occurring (a dead zone warning). However, the base station device 200 may also unicast the dead zone warning to the terminal device 100 that is communicating with the base station device 200. The terminal device 100 receives the dead zone warning from the base station device 200.

[0216] In step S62, the terminal device 100 performs predetermined control based on the blind zone warning. The predetermined control is control to keep the terminal device 100 within the communication area, or control to return the terminal device 100 to the communication area when it moves from the communication area to the blind zone. For example, the terminal device 100 may move toward the base station device 200 to avoid entering the blind zone. Alternatively, the terminal device 100 may perform control to return to the communication area by autonomous control when it enters the blind zone. For example, the terminal device 100 may store the direction of the base station device 200 and move in that direction when it enters the blind zone. When the terminal device 100 enters the blind zone, the terminal device 100 may limit or stop its movement speed to avoid moving too far into the blind zone. The terminal device 100 may transmit an inquiry signal to search for neighboring base stations, identify the direction of the neighboring base station, and move in that direction.

[0217] [Third Modification of Third Embodiment] It is conceivable that the communication area provided by the base station device 200 may be adaptively expanded or contracted depending on the time of day or the underwater environment. For example, the communication area may be reduced during the day and increased at night. Furthermore, the communication area may be reduced on sunny days and increased on cloudy days. Alternatively, it is conceivable that the communication area may be reduced in response to increased turbidity due to rainfall, or the horizontal communication area may be reduced in response to the effects of strong winds. When adjusting the distance between base stations in response to such a change in the communication area, depending on the position of the terminal device 100, it may be located in a blind zone after the adjustment, resulting in communication interruptions and loss of control.

[0218] In this modification, a target base station device 200 that changes the inter-base station distance in accordance with a change in its communication area among the plurality of base station devices 200 transmits a first optical signal (also referred to as a "communication area change notification") notifying the change. The terminal device 100 that receives the optical signal (communication area change notification) transmits a second optical signal to the target base station device 200 indicating whether or not to permit the change.

[0219] 43 is a diagram showing an example of operation of the optical communication system 1 according to this modification. In the example shown, the base station device 200 is a base station device 200 that generates a blind zone when the inter-base station distance is changed. Such a base station device 200 may be, for example, a base station device 200 that serves as the edge of the coverage area of ​​the optical communication system 1.

[0220] In step S71, the base station device 200 broadcasts a communication area change notification within its own communication area. However, the base station device 200 may also transmit the communication area change notification by unicast to the terminal device 100 that is communicating with the base station device 200. The terminal device 100 receives the communication area change notification from the base station device 200.

[0221] In step S72, the terminal device 100 determines whether or not to permit the change. If the terminal device 100 does not want the communication area to be changed because, for example, the terminal device 100 is working, the terminal device 100 determines to deny the change.

[0222] If it is determined that the change is permitted (step S72: YES), in step S73, the terminal device 100 performs the predetermined control as described above. In addition, the terminal device 100 may transmit an optical signal (permission notification) indicating that the change is permitted to the base station device 200.

[0223] On the other hand, if it is determined that the change is to be rejected (step S72: NO), in step S77, the terminal device 100 transmits an optical signal (rejection notice) indicating that the change is to be rejected to the base station device 200.

[0224] In step S75, the base station device 200 determines whether or not a rejection notification has been received from the terminal device 100. If it is determined that a rejection notification has not been received from the terminal device 100 (step S75: NO), in step S76, the base station device 200 changes the communication area (and changes the inter-base station distance).

[0225] On the other hand, if it is determined that a rejection notification has been received from the terminal device 100 (step S75: YES), in step S77, the base station device 200 waits for a certain period of time after sharing that information with the other base station devices 200. After the certain period of time has elapsed, the base station device 200 attempts to change the inter-base station distance again.

[0226] [Other Embodiments] In the above-described embodiment, an example has been described in which the terminal device 100 and the base station device 200 are configured in a spherical shape. However, the terminal device 100 and / or the base station device 200 may be configured in a polyhedron shape. In this case, each face of the polyhedron may constitute an optical communication unit, and a set of light-emitting elements and light-receiving elements may be arranged on each face. Alternatively, the terminal device 100 and / or the base station device 200 may be configured in a rod shape as a whole. For example, the terminal device 100 and / or the base station device 200 may form a prism, the side faces of the prism may constitute an optical communication unit, and a set of light-emitting elements and light-receiving elements may be arranged on each side face.

[0227] A program may be provided that causes a computer to execute each process performed by the terminal device 100, the base station device 200, or the control device 400. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the terminal device 100, the base station device 200, or the control device 400 may be integrated, and at least a portion of the terminal device 100, the base station device 200, or the control device 400 may be configured as a semiconductor integrated circuit (chip set, SoC).

[0228] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or including additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0229] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0230] [Appendix A] The following appendix will be given regarding the features of the above-described embodiment.

[0231] (Supplementary Note 1) An optical communication system comprising: a base station device; and a terminal device that performs optical communication with the base station device, wherein at least one of the base station device and the terminal device performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in an uplink over the communication quality of the optical communication in a downlink.

[0232] (Supplementary Note 2) The optical communication system according to Supplementary Note 1, wherein the terminal device includes a control unit that estimates uplink communication quality, which is a reception quality of an uplink optical signal received by the base station device from the terminal device, and the control unit uses the estimated uplink communication quality for the connection control.

[0233] (Supplementary Note 3) The optical communication system according to Supplementary Note 2, wherein the terminal device further comprises a plurality of optical communication units each having an optical axis directed in a different direction, and the control unit estimates the uplink communication quality based on reception conditions in the plurality of optical communication units.

[0234] (Supplementary Note 4) The optical communication system described in Supplementary Note 3, wherein the control unit measures a reference signal strength, which is the reception strength of the reference optical signal at a first optical communication unit that receives the reference optical signal from the base station device; estimates an ambient optical noise strength, which is the reception strength of ambient light at the base station device, based on the reception strength at a second optical communication unit different from the first optical communication unit; and estimates the uplink communication quality based on the reference signal strength and the ambient optical noise strength.

[0235] (Supplementary Note 5) The optical communication system according to Supplementary Note 4, wherein the second optical communication unit is an optical communication unit whose optical axis is oriented in a direction opposite to a direction in which the optical axis of the first optical communication unit is oriented.

[0236] (Supplementary Note 6) The optical communication system according to Supplementary Note 4 or 5, wherein the control unit estimates the ambient optical noise intensity by averaging a plurality of measurement values ​​obtained by measuring the reception intensity at the second optical communication unit a plurality of times within a predetermined period.

[0237] (Supplementary Note 7) The optical communication system described in any one of Supplementary Notes 4 to 6, wherein the control unit determines whether the ambient light incident on the base station device is in a blocked state where it is blocked by the terminal device, and if it is determined that the ambient light is in a blocked state, corrects the ambient light noise intensity to a predetermined alternative value.

[0238] (Supplementary Note 8) The optical communication system according to Supplementary Note 7, wherein the control unit determines that the optical communication system is in the blocked state based on whether a first condition is satisfied, that is, the ambient light noise intensity is equal to or greater than a first threshold value, and the received intensity of ambient light at least in the first optical communication unit is less than a second threshold value.

[0239] (Supplementary Note 9) The optical communication system according to Supplementary Note 8, wherein the control unit obtains a value indicating a distance between the terminal device and the base station device based on the reference signal strength, and determines that the blocking state exists based on the first condition being satisfied and the distance being equal to or less than a threshold.

[0240] (Supplementary Note 10) The optical communication system according to Supplementary Note 8, wherein the control unit determines that the optical communication system is in the blocked state based on the fact that the first condition is satisfied and that a received intensity of ambient light in an optical communication unit around the second optical communication unit is less than a threshold value.

[0241] (Supplementary Note 11) The optical communication system according to any one of Supplementary Notes 7 to 10, wherein the predetermined alternative value is an average value or a median value of the reception strength in each of the plurality of optical communication units.

[0242] (Supplementary Note 12) The optical communication system according to any one of Supplementary Notes 7 to 10, wherein the control unit acquires from the base station device the ambient optical noise intensity derived by the base station device, and the predetermined alternative value is the ambient optical noise intensity acquired from the base station device.

[0243] (Supplementary Note 13) The optical communication system according to any one of Supplementary Notes 4 to 12, wherein the control unit acquires information indicating a transmission power of the reference signal in the base station device from the base station device, and estimates the uplink communication quality based on the reference signal strength, the transmission power, and the ambient optical noise intensity.

[0244] (Supplementary Note 14) The optical communication system described in any one of Supplementary Notes 1 to 13, wherein the control unit estimates the uplink communication quality for each of a plurality of base station devices, selects a base station device from the plurality of base station devices whose uplink communication quality satisfies a predetermined standard, and attempts to connect to the selected base station device.

[0245] (Supplementary Note 15) The optical communication system according to Supplementary Note 14, wherein the control unit notifies the selected base station device that the terminal device is performing an uplink prioritized connection in a process of establishing a connection to the selected base station device.

[0246] (Supplementary Note 16) The optical communication system according to any one of Supplementary Notes 1 to 15, wherein the base station device notifies the terminal device whether or not the base station device is capable of performing the connection control that prioritizes communication quality of the uplink.

[0247] (Supplementary Note 17) The optical communication system described in any one of Supplementary Notes 1 to 16, wherein the base station device configures the terminal device to transmit a measurement report message including information indicating the estimated uplink communication quality to the base station device, and determines handover of the terminal device from the base station device to another base station device based on the measurement report message from the terminal device.

[0248] (Supplementary Note 18) The optical communication system according to Supplementary Note 17, wherein the control unit of the terminal device triggers transmission of the measurement report message to the base station device in response to the estimated uplink communication quality satisfying a predetermined trigger condition.

[0249] (Supplementary Note 19) The optical communication system according to any one of Supplementary Notes 1 to 18, wherein, in a handover process of the terminal device from the base station device to another base station device, the base station device notifies the other base station device that the terminal device is performing an uplink prioritized connection.

[0250] (Supplementary Note 20) A terminal device comprising: an optical communication unit that performs optical communication with a base station device; and a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in an uplink over the communication quality of the optical communication in a downlink.

[0251] (Supplementary Note 21) A base station device comprising: an optical communication unit that performs optical communication with a terminal device; and a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in an uplink over the communication quality of the optical communication in a downlink.

[0252] [Appendix B] Additional notes will be given regarding other features of the above-described embodiment.

[0253] (Supplementary Note 1) An optical communication system for optical communication between a base station device and a terminal device, comprising a plurality of base station devices arranged three-dimensionally underwater at intervals in the horizontal and vertical directions, and a communication area formed underwater by each of the plurality of base station devices constituting a coverage area for optical communication in the optical communication system.

[0254] (Supplementary Note 2) The optical communication system described in Supplementary Note 1, wherein, when the communication area formed by each of the plurality of base station devices is considered to be cubic, the plurality of base station devices are arranged underwater so that the cubic communication areas are arranged horizontally and vertically to fill the coverage area.

[0255] (Supplementary Note 3) The optical communication system described in Supplementary Note 2, wherein the plurality of base station devices are arranged underwater in two horizontally or vertically adjacent cubic communication areas such that the vertices of one cubic communication area do not overlap with the vertices of the other cubic communication area.

[0256] (Supplementary Note 4) An optical communication system according to any one of Supplementary Notes 1 to 3, wherein the plurality of base station devices constitute a plurality of base station groups spaced apart in the horizontal direction, and each of the plurality of base station groups includes: two or more base station devices spaced apart in the vertical direction; and a connecting member provided between the base station devices whose communication areas are vertically adjacent, connecting the base station devices in the vertical direction.

[0257] (Supplementary Note 5) The optical communication system according to Supplementary Note 4, wherein the plurality of base station devices are arranged underwater so that a distance between the base stations in a horizontal direction is narrower than a distance between the base stations in a vertical direction by a predetermined distance.

[0258] (Supplementary Note 6) The optical communication system according to Supplementary Note 5, further comprising a determination unit that determines the predetermined distance based on an environmental parameter indicating at least one of a wave height, a wind strength on the water, and a water current speed in the coverage area.

[0259] (Supplementary Note 7) An optical communication system according to any one of Supplementary Notes 4 to 6, comprising: a specifying unit that specifies a communicable distance of optical communication between base station devices constituting the base station device pair by performing optical communication between the base station device pair whose communication areas are adjacent in the vertical direction; and a setting unit that sets the inter-base station distances in the horizontal and vertical directions based on the specified communicable distances.

[0260] (Supplementary Note 8) The optical communication system according to Supplementary Note 7, further comprising: an adjustment mechanism that adjusts a length of the connecting member; and a first control unit that controls the adjustment mechanism based on the set vertical inter-base station distance.

[0261] (Supplementary Note 9) The optical communication system according to Supplementary Note 7 or 8, further comprising: a movement mechanism for moving at least one of the plurality of base station groups in a horizontal direction; and a second control unit for controlling the movement mechanism based on the set vertical distance.

[0262] (Supplementary Note 10) The optical communication system described in any one of Supplementary Notes 7 to 9, wherein the identification unit identifies the communication distance for each of a plurality of base station device pairs whose communication areas are adjacent in the vertical direction by performing optical communication between the plurality of base station device pairs, and identifies the shortest communication distance among the communication distances identified for each of the plurality of base station device pairs, and the setting unit sets at least the horizontal inter-base station distance based on the identified shortest communication distance.

[0263] (Supplementary Note 11) The optical communication system according to Supplementary Note 10, further comprising a power adjustment unit that sets the optical signal transmission power of the base station device in the horizontal direction to be lower than the optical signal transmission power of the base station device in the vertical direction.

[0264] (Supplementary Note 12) An optical communication system according to any one of Supplementary Notes 1 to 11, wherein some of the base station devices, among the plurality of base station devices, have a shorter communication distance for optical communication than other base station devices, transmit an optical signal notifying that there is a possibility that there is a coverage hole outside the communication area of ​​the some of the base station devices, and a terminal device that receives the optical signal performs control to keep the terminal device within the communication area, or control to return the terminal device to the communication area when the terminal device moves from the communication area to the coverage hole.

[0265] (Supplementary Note 13) An optical communication system according to any one of Supplementary Notes 1 to 12, wherein a target base station device among the plurality of base station devices that changes the base station distance transmits a first optical signal notifying the change in the base station distance, and a terminal device that receives the optical signal transmits a second optical signal to the target base station device indicating whether or not to permit the change in the base station distance.

[0266] [Cross-reference to related applications] This application claims priority to Japanese Patent Application No. 2022-134686 (filed August 26, 2022) and Japanese Patent Application No. 2022-171108 (filed October 26, 2022), the entire contents of which are incorporated herein by reference.

[0267] 1: Optical communication system 2a: Inner surface 10: Network 100: Terminal device 101: Optical communication unit 110: Light receiving unit 111: Light receiving element 112: Receiver 120: Light emitting unit 121: Light emitting element 122: Transmitter 130: Control unit 131: Processor 132: Memory 140: Mechanical unit 150: Housing 160: Cable 200: Base station device 201: Optical communication unit 210: Light receiving unit 211: Light receiving element 212: Receiver 220: Light emitting unit 221: Light emitting element 222: Transmitter 230: Control unit 231: Processor 232: Memory 240: Backhaul communication unit 241: Network communication unit 242: Inter-base station communication unit 250: Housing 260: Hook portion 261: Rope 262: Cable 263: Laser communication device 264: Connection member 265: Adjustment mechanism 300: Base station group 310: Floating member 311: Moving mechanism 312: Antenna 320: Weight member 321: Moving mechanism 400: Control device 410: Communication distance determination unit 420: Base station distance setting unit 430: Horizontal direction adjustment amount determination unit 440: Blind zone adjustment amount determination unit 450: Vertical direction control unit 460: Horizontal direction control unit 470: Horizontal direction power adjustment unit

Claims

1. An optical communication system for performing optical communication between a base station device and a terminal device, comprising: A plurality of base station devices are arranged three-dimensionally underwater at intervals in horizontal and vertical directions, The communication area formed underwater by each of the plurality of base station devices constitutes a coverage area of ​​optical communication in the optical communication system. Optical communication system.

2. When the communication area formed by each of the plurality of base station devices is regarded as a cube, the plurality of base station devices are arranged underwater so that the cubic communication areas are arranged in the horizontal and vertical directions to fill the coverage area.

2. The optical communication system according to claim 1.

3. The plurality of base station devices constitute a plurality of base station groups arranged at intervals in a horizontal direction, Each of the plurality of base station groups two or more base station devices spaced apart in a vertical direction; The communication area is provided between adjacent base station devices in the vertical direction, and a connecting member that connects the base station devices in the vertical direction is included.

2. The optical communication system according to claim 1.

4. The plurality of base station devices are arranged underwater so that the distance between the base stations in the horizontal direction is narrower than the distance between the base stations in the vertical direction by a predetermined distance.

4. The optical communication system according to claim 3.

5. An identification unit that identifies a communication distance of optical communication between base station devices constituting a base station device pair by performing optical communication between the base station device pair whose communication areas are adjacent in a vertical direction; a setting unit that sets the base station distances in the horizontal and vertical directions based on the identified communication distance.

4. The optical communication system according to claim 3.

6. An adjustment mechanism for adjusting the length of the connecting member; a first control unit that controls the adjustment mechanism based on the set vertical inter-base station distance.

6. The optical communication system according to claim 5.

7. A movement mechanism for moving at least one of the plurality of base station groups in a horizontal direction; a second control unit that controls the mobile mechanism based on the set vertical inter-base station distance.

6. The optical communication system according to claim 5.

8. The identification unit, performing optical communication between a plurality of base station device pairs whose communication areas are adjacent in a vertical direction, thereby determining the communication distance for each of the plurality of base station device pairs; Identifying the shortest communication distance among the communication distances identified for each of the plurality of base station device pairs; The setting unit sets an inter-base station distance in at least a horizontal direction based on the identified shortest communication distance.

6. The optical communication system according to claim 5.

9. A power adjustment unit that sets the optical signal transmission power of a base station device in a horizontal direction to be lower than the optical signal transmission power of the base station device in a vertical direction.

9. The optical communication system according to claim 8.

10. Among the plurality of base station devices, some base station devices having a shorter communication distance for optical communication than the other base station devices transmit an optical signal notifying that there is a possibility that a coverage hole exists outside the communication area of ​​the some base station devices, The terminal device that receives the optical signal performs control to maintain the terminal device within the communication area, or performs control to return the terminal device to the communication area when the terminal device moves from the communication area to a coverage hole.

10. An optical communication system according to claim 1.

11. Among the plurality of base station devices, a target base station device that changes the base station distance transmits a first optical signal notifying the change in the base station distance; The terminal device that has received the optical signal transmits a second optical signal to the target base station device, the second optical signal indicating whether or not the change in the inter-base station distance is permitted.

10. An optical communication system according to claim 1.

12. A base station device, a terminal device that performs optical communication with the base station device, At least one of the base station device and the terminal device performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so as to prioritize the communication quality of the optical communication in the uplink over the communication quality of the optical communication in the downlink. Optical communication system.

13. the terminal device includes a control unit configured to estimate an uplink communication quality, which is a reception quality of an uplink optical signal received by the base station device from the terminal device; The control unit uses the estimated uplink communication quality for the connection control.

13. The optical communication system according to claim 12.

14. The terminal device further includes a plurality of optical communication units each having an optical axis oriented in a different direction; The control unit estimates the uplink communication quality based on reception conditions in the plurality of optical communication units.

14. The optical communication system according to claim 13.

15. The control unit is measuring a reference signal intensity, which is a reception intensity of the reference optical signal in a first optical communication unit that receives the reference optical signal from the base station device; estimating an ambient light noise intensity, which is a reception intensity of ambient light at the base station device, based on a reception intensity at a second optical communication unit different from the first optical communication unit; Estimating the uplink communication quality based on the reference signal strength and the ambient optical noise strength.

15. An optical communication system according to claim 14.

16. The control unit is Estimating the uplink communication quality for each of a plurality of base station devices; selecting a base station device whose uplink communication quality satisfies a predetermined standard from among the plurality of base station devices; Attempting to connect to the selected base station 16. An optical communication system according to any one of claims 12 to 15.

17. The base station device notifies the terminal device of whether or not the base station device can perform the connection control that prioritizes the communication quality of the uplink.

16. An optical communication system according to any one of claims 12 to 15.

18. The base station device, configuring the terminal device to transmit to the base station a measurement report message including information indicating the estimated uplink communication quality; Based on the measurement report message from the terminal device, a handover of the terminal device from the base station device to another base station device is determined.

16. An optical communication system according to any one of claims 12 to 15.

19. In a handover process of the terminal device from the base station device to another base station device, the base station device notifies the other base station device that the terminal device is performing an uplink prioritized connection.

16. An optical communication system according to any one of claims 12 to 15.

20. an optical communication unit for performing optical communication with a base station device; a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so that a communication quality of the optical communication in an uplink is prioritized over a communication quality of the optical communication in a downlink. Terminal device.

21. an optical communication unit for performing optical communication with a terminal device; a control unit that performs connection control to establish and / or maintain an optical communication connection between the terminal device and the base station device so that a communication quality of the optical communication in an uplink is prioritized over a communication quality of the optical communication in a downlink. Base station equipment.

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