Optical communication system

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

Technical Field

[0006] , , ,

[0004] , , ,

[0005] ,

[0001] The present disclosure relates to an optical communication system.

Background Art

[0002] For example, in underwater communication, an optical communication system that uses light (especially visible light) as a transmission medium is known. Since light has high directivity, in a conventional optical communication system, it is common to perform one-to-one communication with the transmission side and the reception side facing each other on the premise that each optical communication device on the transmission side and the reception side is fixed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0004] The optical communication system according to the first aspect includes 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 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.

[0005] The 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] The base station device according to the third embodiment 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 on the uplink over the communication quality of the optical communication on the downlink.

[0007] The optical communication system according to the fourth embodiment is an optical communication system that performs optical communication between a base station device and a terminal device, and comprises a plurality of base station devices arranged three-dimensionally in water at intervals in the horizontal and vertical directions. The communication area formed in the water by each of the plurality of base station devices constitutes the optical communication coverage area in the optical communication system. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram showing an example configuration of an optical communication system according to the embodiment. [Figure 2] This diagram schematically illustrates the transmission operation on the uplink (UL) of the terminal device according to the embodiment. [Figure 3] This figure shows an example of the block configuration of a base station device according to the embodiment. [Figure 4] This figure shows an example of the external configuration of a base station device according to the present invention. [Figure 5] This figure shows a first modified example of the external configuration of the base station device according to the embodiment. [Figure 6] This figure shows a second example of the external configuration of the base station device according to the embodiment. [Figure 7] This figure shows an example of the block configuration of a terminal device according to an embodiment. [Figure 8] This figure shows an example of the external configuration of a terminal device according to the embodiment. [Figure 9] This figure shows a first modified example of the external configuration of the terminal device according to the embodiment. [Figure 10] This figure shows a second example of the external configuration of the terminal device according to the embodiment. [Figure 11]It is a diagram showing downlink (DL) communication as an example of optical communication according to an embodiment. [Figure 12] It is a diagram showing a configuration example of a communication frame used in an optical communication system according to an embodiment. [Figure 13] It is a diagram for explaining the influence of sunlight noise in an optical communication system according to an embodiment. [Figure 14] It is a diagram for explaining the influence of ambient light in an optical communication system according to an embodiment. [Figure 15] It is a diagram for explaining the estimation operation of UL communication quality performed by a terminal device according to an embodiment. [Figure 16] It is a diagram for explaining the operation of selecting an optical communication unit for noise estimation in a terminal device according to an embodiment. [Figure 17] It is a diagram showing an example of an operation flow in a terminal device according to the first embodiment. [Figure 18] It is a diagram for explaining the operation according to the first modification example of the first embodiment. [Figure 19] It is a diagram for explaining the operation according to the second modification example of the first embodiment. [Figure 20] It is a diagram showing an example of an operation flow in a terminal device according to the second modification example of the first embodiment. [Figure 21] It is a diagram showing an example of an operation sequence of an optical communication system 1 according to the third modification example of the first embodiment. [Figure 22] It is a diagram showing an example of an operation sequence of an optical communication system according to the second embodiment. [Figure 23] It is a diagram showing an example of an operation sequence of an optical communication system according to a modification example of the second embodiment. [Figure 24] It is a diagram showing a configuration example of an optical communication system according to the third embodiment. [Figure 25] It is a diagram showing a configuration example of a base station group according to the third embodiment. [Figure 26] It is a diagram for explaining the station placement design of an optical communication system according to the third embodiment. [Figure 27]This is a diagram for explaining the placement design of an optical communication system according to the third embodiment. [Figure 28] This is a diagram for explaining the placement design of an optical communication system according to the third embodiment. [Figure 29] This is a diagram for explaining the placement design of an optical communication system according to the third embodiment. [Figure 30] This is a diagram for explaining the response to the movement of the base station device in the horizontal direction according to the third embodiment. [Figure 31] This is a diagram showing a configuration example of the functional blocks of the control device according to the third embodiment. [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​This figure shows an example of the operation of an optical communication system according to the third modification of the third embodiment. [Modes for carrying out the invention]

[0009] In future optical communication systems, it is anticipated that optical communication between multiple terminal devices and base station devices will be realized, similar to radio wave wireless communication on land.

[0010] Therefore, this 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 drawings, identical 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 also be a system that performs optical communication using light other than visible light, such as 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 also be a system that performs optical communication in space, for example.

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

[0014] In future optical communication systems, it is assumed that optical communication between multiple terminal devices and base station devices will be realized, similar to radio wave wireless communication on land. Under these 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-based wireless communication, connection control is performed based on the received signal strength of the downlink (DL) radio waves received by the terminal device from the base station device. However, such connection control, which prioritizes downlink communication quality, raises concerns that in optical communication systems, the terminal device may not be able to establish and / or maintain an optical communication connection with a proper base station device.

[0016] In the first embodiment, an optical communication system, terminal equipment, and base station equipment that enable the proper establishment and / or maintenance of an optical communication connection will be described.

[0017] (Example of optical communication system configuration) Figure 1 shows an example configuration of the optical communication system 1 according to this embodiment. The optical communication system 1 includes 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.

[0018] Terminal device 100 is an example of an optical communication device. Each base station device 200 is another example of an optical communication device. Each of the terminal device 100 and the multiple base station devices 200 has multiple optical communication units with optical axes (or, from another perspective, the directivity of optical communication) oriented in different directions. As a result, each of the terminal device 100 and the multiple base station devices 200 can use multiple optical communication units to perform optical communication in various ways (omnidirectionally) while using light as the transmission medium.

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

[0020] To form a wide communication area underwater, independent of the position and 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 duration of underwater research using the terminal device 100. In Figure 1, the communication area of ​​each base station device 200 is shown by a dashed line. The communication area of ​​each base station device 200 is also referred to as a cell.

[0021] Each of the base station devices 200a and 200b is located near the water surface and is fixed, for example, to a buoy. 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 connected to the network 10 in a communicative manner 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 at a predetermined distance apart from each other.

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

[0023] The terminal device 100 is located underwater. The terminal device 100 is configured to be mobile underwater. For example, the terminal device 100 may be a self-propelled terminal device such as an underwater robot or 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 be equipped with sensors such as an image sensor and generate sensor data. For example, each terminal device 100 may transmit uplink (UL) data including 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 perform movement and sensing operations (such as taking pictures) based on the instruction data.

[0025] In this embodiment, we assume a scenario in which a terminal device 100, such as an underwater drone, uploads large-capacity 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's optical communication compared to that of DL's optical communication.

[0026] Each base station device 200 may transmit a synchronization optical signal and / or a reference optical signal unique to its device in all directions from its optical communication unit. 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] Figure 2 is a schematic diagram showing the transmission operation of the terminal device 100 in UL according to this embodiment.

[0028] In the terminal device 100, for example, multiple 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 multiple optical communication units 101 are arranged in an array along the curved inner surface 2a of the housing 150, and the optical axes of each are directed in different directions. For example, the optical axis of each optical communication unit 101 is directed in the direction normal to the curved surface of the housing 150. Although light has high directivity, this configuration makes it possible to perform optical communication in various directions.

[0029] (Example of base station equipment configuration) Figure 3 shows an example of the block configuration of the base station device 200 according to this embodiment. The base station device 200 has 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 have a battery to supply the power necessary for the operation of the base station device 200.

[0030] Multiple optical communication units 201 are arranged with their optical communication directionality (optical axis) 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 is configured similarly, 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 (visible light signal in this embodiment) 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 an 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 other light receiving elements 211 (for example, light receiving element 211#1). The receiver 212#0 may be configured by an FPGA (Field Programmable Gate Array) and / or a SoC (System-on-a-chip). Receiver 212#0 converts the received signal output by photodetector 211#0, performs signal processing on the converted received signal, and outputs it to control unit 230. At least a part of receiver 212#0 may be integrated with another receiver 212 (for example, receiver 212#1) or with transmitter 222.

[0032] The light-emitting unit 220#0 of the optical communication unit 201#0 transmits an optical signal (visible light signal in this embodiment) 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 axis of 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 photodetector 211#0. The transmitter 222#0 may be configured by an FPGA and / or SoC. Transmitter 222#0 performs signal processing on the transmission signal output by control unit 230, converts the processed signal, and outputs it to light-emitting element 221#0. At least a part of transmitter 222#0 may be integrated with another transmitter 222 (for example, transmitter 222#1) or with receiver 212.

[0033] The control unit 230 controls the overall operation of the base station equipment 200. The operation of the base station equipment 200 described above and the operation of the base station equipment 200 described later may be controlled by the control unit 230. For example, the control unit 230 controls a plurality of 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 for 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, and decoding of digital signals. The CPU executes programs stored in memory and performs various processing. At least a part of the control unit 230 may be integrated with the receiver 212 or with the transmitter 222.

[0034] The backhaul communication unit 240 performs backhaul communication (wired communication and / or wireless communication) via the backhaul line under the control of the control unit 230. The backhaul communication unit 240 may have a network communication unit 241 that communicates with the network 10 (e.g., the 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 way, 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, prioritizing the communication quality of the optical communication on the uplink (UL) over the communication quality of the optical communication on the downlink (DL). Details of this connection control will be described later.

[0036] Figure 4 shows 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 terminal devices 100 in various directions.

[0038] Figure 5 shows a first modified example of the external configuration of the base station device 200 according to this embodiment.

[0039] The base station device 200 includes 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] Cables 262a and 262b may be made of optical fiber. Cable 262a is used for base station-to-base station communication with the upper adjacent base station, and cable 262b is used for base station-to-base station communication with the lower adjacent base station. The base station device 200 may relay data received from the upper adjacent base station via cable 262a to the lower adjacent base station via cable 262b. Alternatively, the base station device 200 may relay data received from the lower adjacent base station via cable 262b to the upper adjacent base station via 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 routed along the upper rope 261a, and the lower cable 262b is routed along the lower rope 261b. The optical communication section 201 on the surface of the housing 250 is positioned to avoid the hook portions 260a and 260b.

[0042] Figure 6 shows a second 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 includes 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 communication device 263 provided above the housing 250. The laser communication device 263 is used for inter-base station communication with an adjacent base station above.

[0044] (Example of terminal device configuration) Figure 7 shows an example of the block configuration of the 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 mechanical unit 140. The terminal device 100 may have a battery to supply the power necessary for the operation of the terminal device 100. The terminal device 100 may be equipped with a sensor such as an image sensor and generate sensor data.

[0045] Multiple optical communication units 101 are arranged with their optical communication directionality (optical axis) 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 is configured similarly, 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 (visible light signal in this embodiment) 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 an 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 other light receiving elements 111 (for example, light receiving element 111#1). The receiver 112#0 may be configured by 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 it to the control unit 130. At least a portion of receiver 112#0 may be integrated with another receiver 112 (for example, receiver 112#1) or with transmitter 122.

[0047] The light-emitting unit 120#0 of the optical communication unit 101#0 transmits an optical signal (visible light signal in this embodiment) 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 axis of 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 photodetector 111#0. The transmitter 122#0 may be configured by an FPGA and / or SoC. Transmitter 122#0 performs signal processing on the transmission signal output by control unit 130, converts the processed signal, and outputs it to light-emitting element 121#0. At least a part of transmitter 122#0 may be integrated with another transmitter 122 (for example, transmitter 122#1) or with receiver 112.

[0048] The control unit 130 controls the overall operation of the terminal device 100. The operation of the terminal device 100 described above and the operation of the terminal device 100 described later may be controlled by the control unit 130. For example, the control unit 130 controls a plurality of 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 for 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, and decoding of digital signals. The CPU executes programs stored in memory and performs various processes. At least a part of the control unit 130 may be integrated with the receiver 112 or with the transmitter 122.

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

[0050] In the terminal device 100 configured in this way, 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, prioritizing the communication quality of the optical communication on the uplink (UL) over the communication quality of the optical communication on the downlink (DL). Details of this connection control will be described later.

[0051] Figure 8 shows an example of the external configuration of the terminal device 100 according to this embodiment.

[0052] The terminal device 100 comprises an upper housing 150a, a lower housing 150b, and a mechanism 140 provided between housings 150a and 150b. Each of housings 150a and 150b is hemispherical, and the terminal device 100 as a whole forms a spherical shape. Each of 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. With this configuration, the terminal device 100 can perform optical communication with base station devices 200 in various directions.

[0053] Figure 9 shows a first example of a modified 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 140 provided between housings 150a and 150b. Each of housings 150a and 150b is hemispherical, and the terminal device 100 as a whole has a spherical shape. Each of 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.

[0055] Figure 10 shows a second example of the external configuration of the terminal device 100 according to this embodiment.

[0056] In this modified example, the terminal device 100 has a spherical housing 150 and a mechanism 140 connected to the housing 150 via a cable 160. The housing 150 is spherical. The housing 150 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.

[0057] (An example of optical communication) Figure 11 shows DL communication as an example of optical communication according to this embodiment. In the illustrated example, the cross-sections of the base station equipment 200 and the terminal equipment 100 are shown in a simplified manner for DL ​​communication.

[0058] In the base station device 200, multiple light-emitting units 220 are arranged such that as the distance between one light-emitting unit 220 and another light-emitting unit 220 increases, the angle between the optical axis of one light-emitting unit 220 and the optical axis of the other light-emitting unit 220 increases. For example, the angle between the optical axis of light-emitting unit 220#0 and the optical axis of light-emitting unit 220#2 which is not adjacent to light-emitting unit 220#0 is greater than the angle between the optical axis of light-emitting unit 220#0 and the optical axis of light-emitting unit 220#1 which 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 performs optical communication with the terminal device 100 using the light-emitting unit 220#4 (optical communication unit #4). 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] Figure 12 shows an example of the configuration of a communication frame used in the optical communication system 1 according to this embodiment. In the illustrated example, one communication frame is composed of 10 time slots, but the number of time slots that make up one communication frame is not limited to 10. Each time slot is composed of a predetermined number of symbol intervals.

[0061] In this frame configuration example, the communication frame consists of one synchronization slot (Sync.), one control slot (Ctrl.), four DL slots (DL slot) #0 to #3, and four UL slots (UL slot) #0 to #3. However, in scenarios where the amount of data in UL communication is greater than that of 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 reference optical signal specific to the base station device). 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 reference optical signal specific to the base station device may be transmitted in all slots other than the UL slot. The reference optical signal is used in the terminal device 100 to measure the received signal strength (reference signal strength) from the base station device 200.

[0063] A control slot (Ctrl.) is a time slot on which the base station device 200 transmits a control optical signal. The control optical signal includes scheduling information indicating, for example, the resource allocation (e.g., time slot allocation) of DL and UL. The terminal device 100 determines its own time slot allocation by receiving the control optical signal from the base station device 200, for example.

[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 DL data optical signals in each DL slot. Each DL slot may have a light-emitting element-specific reference signal (Ref.TxElement) and a data optical signal arranged in time division.

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

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

[0067] (Example of operation of an optical communication system) The operation of the optical communication system 1 according to this embodiment will be described with reference to Figures 13 to 17. In the optical communication system 1 according to this embodiment, in order to support applications that heavily rely on UL communication, such as video uploads, the system selects the destination base station (serving base station) and maintains the optical communication connection under conditions that ensure good UL communication. 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 that ensure good UL communication, and establishes an optical communication connection to the selected base station device 200.

[0068] Conventionally, in radio wave wireless communication over land, there is little discrepancy in communication quality between DL communication and UL communication. Therefore, connection control is performed based on the received 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 received strength.

[0069] On the other hand, in optical communication, there is noise, such as sunlight noise, that has a significant impact on light-receiving parts in specific directions. Therefore, UL communication quality cannot be accurately estimated using DL reception strength alone. Specifically, because light has strong directionality (directivity), it is expected that reception conditions will differ at light-receiving parts located in different positions due to the influence of sunlight noise and / or ambient light. Therefore, if connection control in optical communication system 1 is performed in the same way as for radio wave wireless communication on land, 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] Figure 13 is a diagram illustrating the effect of solar noise on the optical communication system 1 according to this embodiment.

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

[0072] Terminal device 100 transmits a UL optical signal from its optical communication unit 101a corresponding to the direction of base station device 200a, and base station device 200a receives the UL optical signal with its optical communication unit 201a corresponding to the direction of terminal device 100. Furthermore, terminal device 100 transmits a UL optical signal from its optical communication unit 101b corresponding to the direction of base station device 200b, and base station device 200b receives the UL optical signal with its optical communication unit 201b corresponding to the direction of 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 base station device 200a is equal to the communication quality of the UL optical signal received by the optical communication unit 201b of 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 is incident as noise signals. As a result, the communication quality of the UL optical signal received by the optical communication unit 201b of the base station device 200b deteriorates. In contrast, because the optical axis of the optical communication unit 201a of the base station device 200a is oriented diagonally downward, sunlight is not incident as noise signals, 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 UL communication is important, it is preferable to connect the terminal device 100 to the base station device 200a rather than the base station device 200b.

[0075] Figure 14 is a diagram illustrating the influence of ambient light on the optical communication system 1 according to this embodiment.

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

[0077] Terminal device 100 transmits a UL optical signal from its optical communication unit 101a corresponding to the direction of base station device 200a, and base station device 200a receives the UL optical signal with its optical communication unit 201a corresponding to the direction of terminal device 100. Furthermore, terminal device 100 transmits a UL optical signal from its optical communication unit 101b corresponding to the direction of base station device 200b, and base station device 200b receives the UL optical signal with its optical communication unit 201b corresponding to the direction of 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 base station device 200a is equal to the communication quality of the UL optical signal received by the optical communication unit 201b of base station device 200b.

[0079] However, in the optical communication unit 201a of base station device 200a, the optical axis is oriented to the right, so ambient light from the light source is incident as noise signals. As a result, the communication quality of the UL optical signal received by the optical communication unit 201a of base station device 200a deteriorates. In contrast, in the optical communication unit 201b of base station device 200b, the optical axis is oriented to the left, so ambient light is not incident as noise signals, and the communication quality of the UL optical signal received by the optical communication unit 201b of base station device 200b does not deteriorate. Therefore, when UL communication is important, it is preferable to connect the terminal device 100 to base station device 200b rather than base station device 200a.

[0080] In this embodiment, the control unit 130 of the terminal device 100 estimates the 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 status of its 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 a base station device 200 from the multiple base station devices 200 whose UL communication quality meets a predetermined standard, and attempts to connect to the selected base station device 200. In this embodiment, the predetermined standard is the condition that the UL communication quality is the highest among the multiple base station devices 200. However, the predetermined standard may also be the condition that the UL communication quality is higher than a threshold.

[0081] Figure 15 is a diagram illustrating the UL communication quality estimation operation 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 intensity, which is the received intensity 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 the optical communication unit intended for use in optical communication with the base station device 200.

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

[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 light noise strength estimated using the optical communication unit 101b. The UL communication quality is, for example, "UL Communication Quality" = "Reference Signal Strength" - "Ambient Light Noise Strength" ... Equation (1) It is calculated by [this method].

[0085] In this way, when the terminal device 100 estimates the ambient light noise at the optical communication unit 201a (light receiving unit 210) of the base station device 200 that is a candidate for connection, it uses the ambient light noise intensity measured by the optical communication unit 101b (light receiving unit 110) of the terminal device 100, which is facing 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 light noise received by the optical communication unit 201a (light receiving unit 210) of the base station device 200. This allows the terminal device 100 to compare the UL communication quality of each surrounding base station device 200 before attempting to connect and select the base station device 200 to connect to.

[0086] Figure 16 is a diagram illustrating the operation of selecting an 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 less than the number of optical communication units 101 in the terminal device 100 shown in Figure 15.

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

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

[0089] Figure 17 shows an example of the 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 strength in the optical communication unit 101a that receives a reference optical signal from the base station device 200.

[0091] In step S2, the control unit 130 of the terminal device 100 measures the received signal strength at 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 light noise intensity at the base station device 200 based on the received signal strength measured in step S2. In this embodiment, the received signal strength measured in step S2 may be used directly as the ambient light 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 above-described equation (1) based on the reference signal strength measured in step S1 and the ambient light noise strength estimated in step S3.

[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 answer in step S5 is YES, the control unit 130 of the terminal device 100 estimates the UL communication quality for that 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 answer in step S5 is NO, in step S6, the control unit 130 of the terminal device 100 ranks the UL communication quality 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 results in step S6. For example, it 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 sending a connection request message to the base station device 200 and receiving a response message from the base station device 200. If the attempt to connect 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 example of modification of the first embodiment] The first modification example of the first embodiment will be explained, primarily focusing on the differences from the first embodiment described above. Figure 18 is a diagram illustrating the operation related to this modification example.

[0099] In the first embodiment described above, there is a possibility that a work light source 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 Figure 17. If ambient light measurement is performed with such light incident, the ambient light intensity incident on the base station device 200 may become excessively large, potentially leading to the incorrect selection of the appropriate base station device 200.

[0100] In this modified example, in order to eliminate the influence of such temporarily incident ambient light, instead of using instantaneous ambient light measurement results, the average intensity is calculated by taking measurements over 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 multiple measurements obtained by measuring the received intensity at the optical communication unit 101b on the opposite side (i.e., the pair) of 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 Figure 17). This makes it possible to select a base station device 200 suitable for UL communication without being affected by instantaneous ambient light.

[0101] Furthermore, this method may also be applied to the measurement of the reference signal strength in step S2 of Figure 17. That is, the control unit 130 of the terminal device 100 may measure the reference signal strength multiple times in the optical communication unit 101a that receives the reference optical signal from the base station device 200, and obtain the result of averaging the multiple measured values ​​as the reference signal strength.

[0102] [Second modification example of the first embodiment] The second modification of the first embodiment will be described primarily in terms of the differences from the first embodiment described above. This modification can be implemented in combination with the first embodiment or its modification. Figure 19 is a diagram illustrating the operation related to this modification.

[0103] Assume a situation where ambient light is constantly incident on a light-receiving unit 110 in a specific direction of the terminal device 100 (for example, the light-receiving unit 110 of the optical communication unit 101b). When estimating the ambient light noise intensity of the base station device 200 using the light-receiving unit 110 into which 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 of the estimated UL reception quality.

[0104] However, as shown in Figure 19, ambient light incident on the terminal device 100 may not reach the base station device 200 because the terminal device 100 itself acts as a shield. 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 measurements at the terminal device 100 may lead to an inability to correctly select a base station device 200 suitable for UL communication.

[0105] Figure 20 shows an example of the operation flow in the terminal device 100 according to this modified example. Here, we will explain the differences from the first embodiment described above.

[0106] In this modified example, in step S11, the control unit 130 of the terminal device 100 determines whether the ambient light incident on the base station device 200 is in a shielded state, being blocked by the terminal device 100. If the control unit 130 of the terminal device 100 determines that it is in a shielded state (step S11: YES), in step S12, it 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 it is in a shielded state based on the fact that condition 1 (first condition) is met, which is that the ambient light noise intensity estimated in step S3 is equal to or greater than the first threshold, and at least the ambient light reception intensity at the optical communication unit 101 (first optical communication unit) used to measure the reference signal intensity in step S1 is less than the second threshold. In other words, the control unit 130 of the terminal device 100 determines that it is in a shielded state based on the fact that condition 1 is met, which is that the estimated ambient light noise is sufficiently large, but the ambient light noise at other light 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, the terminal device 100 as a whole is affected by the ambient light and can be considered not to be in a shielded state.

[0109] The control unit 130 of the terminal device 100 may determine that the device is in a shielded state if it determines that condition 1 is met and that at least one of the following conditions 2a and 2b is met.

[0110] Condition 2a: The distance between the terminal device 100 and the base station device 200 is sufficiently close. For example, the control unit 130 of the terminal device 100 may determine that condition 2a is met if the reference signal strength measured in step S1 is greater than a threshold, assuming that the distance between the terminal device 100 and the base station device 200 is sufficiently close. 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, the value obtained by subtracting the transmission power of the reference optical signal from the reference signal strength measured in step S1 may also be used as a value indicating the distance between the terminal device 100 and the base station device 200. The control unit 130 of the terminal device 100 determines that it is in a shielded state if condition 1 is met and the distance between the terminal device 100 and the base station device 200 is less than or equal to a threshold (i.e., condition 2a is met). Note that if the distance between the terminal device 100 and the base station device 200 is sufficiently close, it can be considered a state where it is easily in the shadow of the terminal device 100, i.e., a shielded state.

[0111] Condition 2b: The photodetector where large ambient light noise was measured is limited. For example, the control unit 130 of the terminal device 100 may determine that condition 2b is met if the noise intensity of the optical communication unit 101 (light receiving unit 110) surrounding 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. The control unit 130 of the terminal device 100 determines that it is in a shielded state if condition 1 is met and the received ambient light intensity of the optical communication unit 101 surrounding 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 (i.e., condition 2b is met).

[0112] If the control unit 130 of the terminal device 100 determines that a shielding condition exists, it uses a predetermined alternative value instead of the ambient light noise intensity estimated in step S3 (step S12). The predetermined alternative value may be the average or median value of the received intensity in each of the multiple optical communication units 101 of the terminal device 100.

[0113] Alternatively, the control unit 130 of the terminal device 100 may obtain 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 obtained from the base station device 200 as a predetermined substitute value. In that 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 unit 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 unit 210 of the base station device 200.

[0114] According to this modification example, even when ambient light from a specific direction enters the terminal device 100 and noise estimation is difficult, a base station device 200 suitable for UL communication can be selected.

[0115] [Third modification example of the first embodiment] The third modification of the first embodiment will be described primarily in terms of its differences from the first embodiment described above. This modification can be implemented in combination with the first embodiment or its modification.

[0116] If the transmission power of the reference optical signal differs for each base station device 200, estimating UL communication quality without considering the transmission power (specifically, calculating it using equation (1) above) may result in the terminal device 100 connecting to a base station device 200 with high transmission power but poor UL communication quality (a distant base station). 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 obtains information from the base station device 200 indicating the transmission power of the reference signal at 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 light noise strength using the following equation (2): "UL Communication Quality" = "Reference Signal Strength" - "Transmit Power" - "Ambient Light Noise Intensity" ... Equation (2) Then, 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, based on the calculated UL communication quality.

[0118] Figure 21 shows an example of the operation sequence of the optical communication system 1 related to this modification example.

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

[0120] In step S22, the base station device 200b transmits notification information indicating the transmission power of its reference optical signal. The terminal device 100 receives this notification 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 devices 200a and 200b using equation (2) described above, and determines the base station device 200 to connect to by comparing the UL communication quality. Here, we will continue the explanation assuming that the UL communication quality estimated for base station device 200a is higher than the UL communication quality estimated for base station device 200b.

[0124] In step S26, the terminal device 100 determines the base station device 200a as the connection destination and sends 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, the second embodiment will be described, primarily focusing on the differences from the first embodiment described above. This embodiment can be implemented in combination with the first embodiment or its modifications.

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

[0128] In the first embodiment described above, even if the terminal device 100 selects a base station device 200 with good UL communication quality and connects to it, there is a risk that the base station device 200 will perform control without considering UL priority 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 must not perform DL priority control on the terminal device 100 that has connected with UL priority, but rather perform control based on conditions that allow the connection to be maintained with UL priority.

[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 priority connection during the process of establishing a connection with the base station device 200. As a result, the base station device 200 recognizes that the terminal device 100 is performing a UL priority connection and is able to perform control to maintain the UL priority connection.

[0130] In this embodiment, the base station device 200 may notify the terminal device 100 whether or not it is capable of performing connection control that prioritizes UL communication quality. For example, the base station device 200 transmits notification information indicating that it is capable of performing connection control that prioritizes UL communication quality. As a result, the terminal device 100 can prioritize the base station device 200 capable of performing connection control that prioritizes UL communication quality when deciding on a connection destination.

[0131] Figure 22 shows an example of the 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 it is able to perform connection control prioritizing UL's communication quality. The terminal device 100 receives this 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 for the base station device 200 and determines the base station device 200 as the connection destination.

[0135] In step S34, the terminal device 100 sends a connection request message to the base station device 200, which includes information indicating that it is performing a UL priority connection. 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] [Example of modification of the second embodiment] The modifications to the second embodiment will be described primarily in terms of the differences from the second embodiment described above. These modifications can be implemented in combination with the embodiments or modifications thereof described above.

[0138] In this modified example, the base station device 200 configures the terminal device 100 to send a measurement report message to the base station device 200 that includes information indicating the estimated UL communication quality at the terminal device 100. Based on the measurement report message from the terminal device 100, the base station device 200 decides whether to hand over the terminal device 100 from its own base station device 200 to another base station device 200. This allows the base station device 200 to hand over the terminal device 100 to another base station device 200 with good UL communication quality.

[0139] The control unit 130 of the terminal device 100 may trigger the transmission of a measurement report message to the base station device 200 when the estimated UL communication quality satisfies predetermined trigger conditions. Such trigger conditions are: • The UL communication quality of the connected base station equipment 200 falls below the threshold. • The UL communication quality of the connected base station equipment 200 is worse than the UL communication quality of another base station equipment 200. - Apply a negative offset value for UL priority to the threshold used to compare with the DL communication quality of the connected base station equipment 200, and apply the lower threshold. Either of these is acceptable.

[0140] In this modified example, the base station device 200 may notify the other base station device 200 that the terminal device 100 is performing a UL priority connection during the handover process of the terminal device 100 from its own base station device 200 to another base station device 200. This allows the base station devices 200 to share UL priority connection information, enabling the receiving base station device 200 to continue the control necessary to maintain the UL priority connection.

[0141] Figure 23 shows an example of the operation sequence of the optical communication system 1 related to this modification example.

[0142] In step S41, the terminal device 100 establishes an optical communication connection with the base station device 200a using the method of the first embodiment or a modified version thereof described above. When the optical communication connection is established, the terminal device 100 notifies the base station device 200a that it is performing a UL priority connection.

[0143] In step S42, the base station device 200a sends configuration information (Meas. Config) to the terminal device 100 that configures the transmission of measurement report messages. The terminal device 100 receives the configuration information. The configuration information may include information that configures the trigger conditions related to the UL communication quality described above. The configuration information may also include information that configures the inclusion of 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 described above.

[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 described above.

[0146] In step S45, the terminal device 100 sends a Meas. Report message to the base station device 200a. The base station device 200a receives the Meas. Report message. The terminal device 100 may also send a Meas. Report message if the trigger condition set in step S42 is met. The terminal device 100 may include the UL communication quality estimated in steps S43 and S44 in the Meas. Report message.

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

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

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

[0150] (Example of optical communication system configuration) Figure 24 shows an example configuration of the 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 comprises a terminal device 100 and a plurality of base station devices 200.

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

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

[0153] The base station devices 200(0,0,0) to 200(2,2,2) constitute a group of base stations 300 arranged at intervals in the horizontal direction (see Figure 25). Each group of base stations 300 includes a group of base station devices 200 arranged vertically (in the illustrated example, three base station devices 200). In each group of base stations 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 member 264 is a member that can be wound up and unwound, for example, the rope 261 and / or cable 262 described above. The rope 261 may be a wire rope. Below, an example in which the connecting member 264 includes a wire rope will be mainly described.

[0154] Figure 25 shows an example of the 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) arranged at vertical intervals, and connecting members 264 that are provided between base station devices 200 whose communication areas are adjacent in the vertical direction and that connect the base station devices 200 vertically. 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. Base station device 200b is suspended from base station device 200a by a connecting member 264b. Base station device 200c is suspended from base station device 200b by a connecting member 264c. With this configuration, even if there are no walls or other structures in the water, the base station devices 200 can be efficiently arranged horizontally in the water.

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

[0156] In each base station group 300, the base station device 200c located at the deepest point 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 has sufficient weight, the weight member 320 may be unnecessary.

[0157] Each base station device 200 (base station devices 200a to 200c) is provided with an adjustment mechanism 265 at its top for winding in and unwinding the connecting member 264. The adjustment mechanism 265 may be an electric winch. . tone The adjustment mechanism 265 allows for adjustment of the vertical distance between base stations.

[0158] Specifically, the upper part of the base station device 200a is provided with an adjustment mechanism 265a for winding up and unwinding the connecting member 264a. The adjustment mechanism 265a may be controlled by the control unit 230 of the base station device 200a. The upper part of the base station device 200b is provided with an adjustment mechanism 265b for winding up and unwinding the connecting member 264b. The adjustment mechanism 265b may be controlled by the control unit 230 of the base station device 200b. The upper part of the base station device 200c is provided with an adjustment mechanism 265c for winding up and unwinding the connecting member 264c. 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 on the upper part of each base station device 200, but may also be provided on the lower part of each base station device 200. Furthermore, the configuration is not limited to making the connecting member 264 retractable and retractable, but a sliding mechanism as the adjustment mechanism 265 may be provided on the connecting member 264, making the connecting member 264 retractable. Alternatively, the connecting member 264 may be continuously provided vertically so as to pass through the center of each base station device 200, and the base station device 200 may be moved vertically by moving (sliding) on ​​the connecting member 264. In that case, the sliding mechanism as the adjustment mechanism may be provided inside the base station device 200.

[0160] The floating member 310 may have a moving mechanism 311 for moving the base station group 300 horizontally. The moving mechanism 311 may include a motor and a screw, etc. When the floating member 310 moves across the water surface by the moving mechanism 311, the base station group 300 (base station devices 200a to 200c) moves horizontally in accordance with the movement of the floating member 310. The moving 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] If the base station group 300 has a weight member 320, the weight member 320 may have a moving mechanism 321 for moving the base station group 300 horizontally. The moving mechanism 321 may include a motor and crawlers (caterpillars), etc. When the weight member 320 moves along the bottom of the water by the moving mechanism 321, the base station group 300 (base station devices 200a to 200c) moves horizontally in accordance with the movement of the weight member 320. The moving 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, vertically adjacent pairs of base station devices can communicate with each other via a connecting member 264 (cable) that connects the pairs. For example, the pair of base station devices 200a and 200b can communicate via the connecting member 264b. The pair of base station devices 200b and 200c can communicate via the connecting member 264c. Alternatively, instead of communication between base stations via the connecting member 264 (cable), the laser communication device 263 described above may be used to perform communication between base stations (see Figure 6).

[0163] The base station group 300 performs backhaul communication with the network 10. For example, base station device 200a may perform wireless communication with the network 10 using radio waves. However, since radio waves are greatly attenuated in water, it may be inappropriate to install an antenna on the base station device 200a underwater. For this reason, in the illustrated example, the antenna 312 of the network communication unit 241 (see Figure 3) of the base station device 200a is installed 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 installed on the base station device 200a.

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

[0165] (Placement design for optical communication systems) Figures 26 to 29 are diagrams illustrating the site layout design of the optical communication system 1 according to this embodiment.

[0166] Conventional communication systems that use radio waves for wireless communication on land have a two-dimensional coverage area in the horizontal direction. In addition, in the site design of conventional communication systems, base station equipment is arranged so that the coverage area is filled with communication areas in the shape of a regular hexagon, called a cell.

[0167] In contrast, in the optical communication system 1 according to this embodiment, as shown in Figures 26 and 27, the base station design is performed by considering the communication area formed by each of the multiple base station devices 200 as a cube. Specifically, the multiple base station devices 200 are arranged in water so as to fill the coverage area by arranging the cube-shaped communication areas in the horizontal and vertical directions.

[0168] As shown in Figure 26, assuming that the actual communication area of ​​the base station device 200 is a sphere with radius "r", the virtual communication area of ​​each base station device 200 is such that the length of one side "a" is

number

[0169] As a result, as shown in Figure 27, the distances between base stations in the horizontal and vertical directions are:

number

[0170] The base station equipment 200, positioned underwater, is expected to move due to the effects of waves and ocean currents. When the base station equipment 200 moves, coverage holes (i.e., dead zones) may occur within the coverage area. As shown in Figure 28, the points where the vertices of each cubic communication area overlap are where the edges of the actual communication areas of each base station equipment 200 converge, and these can become areas with extremely poor communication conditions. Therefore, when the base station equipment 200 moves, the points where the vertices of each cubic communication area overlap are likely to become coverage holes.

[0171] In this embodiment, as shown in Figure 29, when arranging the communication area of ​​each base station device 200 as a cube, the base station devices 200 are offset from each other so that the vertices of the cubes do not overlap as much as possible. Specifically, in two adjacent cubic communication areas in the horizontal or vertical direction, multiple base station devices 200 are placed in the water such that the vertices of one cubic communication area do not overlap with the vertices of the other cubic communication area. As a result, the base station devices 200 can be arranged so that the vertices (edges of the communication areas) do not become densely packed, making it less likely for dead zones to occur even when the base station devices 200 are moved.

[0172] In the illustrated example, in two horizontally adjacent cubic communication areas, the base station equipment 200 responsible for one cubic communication area is positioned with a predetermined amount of vertical (and / or horizontal) offset from the base station equipment 200 responsible for the other cubic communication area. This vertical offset is also referred to as the dead 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 positioned offset by a predetermined amount 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 positioned 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 direction of the shift can be any direction in three dimensions; the goal is simply to arrange the cubic communication areas without any gaps after the shift. Alternatively, each cubic communication area should be positioned so that its vertices overlap with only one of its adjacent cubic communication areas.

[0176] Furthermore, the installation of each base station device 200 underwater may be performed by a worker. After each base station device 200 is installed underwater, each base station device 200 may autonomously adjust the distance between base stations, taking into account the communication environment. Such autonomous adjustment operations will be described later.

[0177] (Responding to horizontal movement of base station equipment) As described above, vertically adjacent base station devices 200 are physically connected via connecting members 264, but horizontally adjacent base station devices 200 are not physically connected via connecting members 264. Therefore, base station devices 200 are difficult to move vertically, but are easily moved horizontally due to the influence of waves and ocean currents.

[0178] Figure 30 is a diagram illustrating how the base station equipment 200 responds to movement in the horizontal direction.

[0179] In this embodiment, multiple base station devices 200 are arranged in water such that the horizontal distance between base stations is narrower than the vertical distance between base stations by a predetermined distance "Δ". This predetermined distance Δ is also referred to as the horizontal adjustment amount. Specifically, assuming that the vertical distance between base stations is "a", the horizontal distance between base stations is "a-Δ". By arranging each base station device 200 in this way, the overlapping area of ​​the communication areas of each base station device 200 in the horizontal direction can be increased, making it less likely for dead zones to occur even if each base station device 200 moves horizontally.

[0180] The horizontal adjustment amount Δ may be set based on environmental parameters that indicate at least one of the wave height, wind speed on the water, and water flow speed in the coverage area of ​​the optical communication system 1. For example, the larger the value of the environmental parameter, the larger the horizontal adjustment amount Δ may be. 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 the distance between base stations considering the communication environment) In underwater optical communication, the communication distance is expected to vary depending on the location (sea area / water body) and time due to the effects of water turbidity and solar noise. Therefore, when arranging the base station equipment 200, it is desirable to appropriately determine and set the communication distance of the base station equipment 200 and the distance between base stations based on environmental information (environmental parameters) such as turbidity and solar noise.

[0182] Figure 31 shows an example of the configuration of a functional block of a control device 400 for determining and setting the communication distance of the base station equipment 200 and the distance between base stations.

[0183] The control device 400 may be composed of the control units 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 a plurality of base station devices 200 may have the functions of the control device 400, and that 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 that 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 range and inter-base station distance of each base station device 200 when the base station device 200 is initially installed underwater. The control device 400 may also determine and set to periodically update the communication range and inter-base station distance of each base station device 200 after the initial installation underwater.

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

[0186] The communication distance determination unit 410 determines the communication distance of the optical communication between the base station devices 200 constituting the base station device pair by performing optical communication between base station device pairs whose communication areas are adjacent in the vertical direction.

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

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

[0189] The base station distance setting unit 420 sets the horizontal and vertical base station distances based on the communication distance "r" determined by the communication distance determination unit 410. Figure 33 is a diagram illustrating the calculation operation of the base station distance. As described above, the base station distance "a" is,

number

[0190] Furthermore, the base station distance setting unit 420 also considers the base station radius "z" when setting the wire length "x". x = a - 2z It may also be calculated and set by the following method.

[0191] Furthermore, the base station distance setting unit 420 also takes into account a correction value "y" corresponding to the height of the adjustment mechanism 265, and sets the wire length "x" accordingly. x = a - 2z - y It may also be calculated and set by the following method.

[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 correspond to the horizontal movement of the base station equipment 200. The horizontal adjustment amount determination unit 430 determines the horizontal adjustment amount Δ based on environmental parameters that indicate at least one of the wave height, wind strength on the water, and water flow speed in the coverage area of ​​the optical communication system 1 (see Figure 30). The horizontal adjustment amount determination unit 430 may acquire these environmental parameters using sensors provided on the base station equipment 200 or the floating member 310, or it may acquire these environmental parameters from a server device that manages environmental parameters. As a result, the horizontal distance between base stations is set to "a-Δ".

[0194] The dead zone adjustment amount determination unit 440 determines a dead zone adjustment amount (shift amount) α to position the base station equipment 200 so that the vertices of each cubic communication area are not densely packed together. The dead zone adjustment amount determination unit 440 may determine the dead zone adjustment amount α based on environmental parameters in the same manner as the horizontal adjustment amount determination unit 430.

[0195] Figure 34 is a diagram illustrating the vertical dead zone adjustment amount α. In the illustrated example, each base station device 200 is positioned such that there is a vertical displacement of α between horizontally adjacent base station devices. 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 it is vertically displacement of α.

[0196] Figure 35 is a diagram illustrating the amount of dead zone adjustment α in the horizontal direction. In the illustrated example, each base station device 200 is positioned such that there is a positional shift of α in the x direction between adjacent base station devices in the y direction. For example, the positional shift of α in the horizontal direction is adjusted by 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 control unit 450 adjusts the position of the base station equipment 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 dead zone adjustment amount α in the vertical direction.

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

[0199] Figure 36 shows an example of the initial setup flow for each base station device 200.

[0200] In step S51, the communication distance determination unit 410 determines the communication distance (radius "r") of the optical communication between the base station devices 200 constituting the base station device pair by performing optical communication between base station device pairs whose communication areas are adjacent in the vertical direction.

[0201] In step S52, the base station distance setting unit 420 sets the horizontal and vertical base station distances "a" based on the communication distance "r" determined by the communication distance determination unit 410. For example, the base station distance setting unit 420 notifies each base station device 200 of the base station distance "a", and each base station device 200 can adjust the vertical base station distance by adjusting the wire length using the adjustment mechanism 265.

[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 flow speed in the coverage area of ​​the optical communication system 1, and calculates the horizontal distance between base stations "a-Δ". For example, the 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 distance between base stations by moving the floating member 310 and / or weight member 320 using the moving mechanism 311 and / or moving mechanism 321.

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

[0204] [Example of the first modification of the third embodiment] Figure 37 illustrates the operation of the first modification example of the third embodiment.

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

[0206] If the distance between base stations is set without considering the differences in communication distance "r" for each of the 200 base station devices, there is a risk of dead zones occurring within the coverage area. Therefore, in this modified example, the system is designed to accommodate the differences in communication distance "r" for each of the 200 base station devices.

[0207] In this modified example, the communication distance determination unit 410 determines the communication distance for each of the multiple base station device pairs by performing optical communication between multiple base station device pairs whose communication areas are adjacent in the vertical direction. Then, the communication distance determination unit 410 determines the shortest communication distance among the communication distances determined for each of the multiple base station device pairs. In the illustrated example, the communication distance determination unit 410 determines the communication distance "r'" as the shortest communication distance. The base station distance setting unit 420 sets the base station distance, at least in the horizontal direction, based on the shortest communication distance "r'" determined by the communication distance determination unit 410.

[0208] Figure 38 shows the first setting pattern for the distance between base stations in this modification example. In this setting pattern, the base station distance setting unit 420 sets the distance between base stations in the horizontal and vertical directions based on the shortest communication distance "r'". Specifically, the base station distance setting unit 420 sets the distance between base stations in the horizontal and vertical directions,

number

[0209] Figure 39 shows a second setting pattern for the distance between base stations in this modification example. In this setting pattern, the base station distance setting unit 420 sets the distance between base stations only in the horizontal direction based on the shortest communication distance "r'", and sets the distance between base stations in the vertical direction based on the communication distance "r" of each base station device pair consisting of vertically adjacent base station devices 200. For example, the vertical distance between base station devices 200a and 200b is set based on the communication distance r specified between base station devices 200a and 200b. Similarly, the vertical distance between base station devices 200b and 200c is set based on the communication distance r specified between base station devices 200b and 200c. Thus, in this setting pattern, the base station distance setting unit 420 reduces the distance between base stations only in the horizontal direction based on the shortest communication distance, and prevents the vertical distance between base stations from being reduced by setting it based on the communication distance for each base station device pair.

[0210] However, in both the first and second setting patterns, reducing the horizontal distance between base stations may cause interference between horizontally adjacent base station devices 200. Figure 40 shows an example configuration of the 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 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.

[0211] Figure 41 shows a third setting pattern for the base station distance in this modification example. In this setting pattern, the base station distance setting unit 420 sets the base station distance only in the horizontal direction based on the shortest communication distance "r'", similar to the second setting pattern described above, and sets the vertical base station distance for each base station device pair consisting of vertically adjacent base station devices 200 based on the communication distance "r" of the base station device pair. For example, the vertical base station distance 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. Similarly, the vertical base station distance 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. Furthermore, 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 closest to the seabed has a short communication range and does not experience interference between adjacent base station devices in the horizontal direction, so the optical signal transmission power of the base station device 200 in the horizontal direction is not reduced.

[0212] [Example of the second modification of the third embodiment] As mentioned above, the communication range may vary depending on the base station location. Furthermore, depending on the purpose of underwater communication, it may be necessary to prioritize securing a wide communication area at a specific location and tolerate dead zones (coverage holes) at other locations. In that case, if a remotely controlled terminal device 100, such as an underwater drone, moves into a dead zone, communication may be interrupted, potentially leading to loss of control.

[0213] In this modified example, among the multiple base station devices 200, some base station devices 200 whose optical communication range is shorter than that of the other base station devices 200 transmit an optical signal (also referred to as a "dead zone warning") that indicates the possibility that the area outside the communication area of ​​those base station devices 200 is a coverage hole. Upon receiving the optical signal (dead zone warning), a terminal device 100 performs control to maintain the terminal device 100 within the communication area, or performs control to return the terminal device 100 to the communication area if it moves from the communication area to a coverage hole. This suppresses the occurrence of communication interruptions between the terminal device 100 and the base station devices 200.

[0214] Figure 42 shows an example of the operation of the optical communication system 1 according to this modified example. In the illustrated example, the base station equipment 200 is not a base station equipment 200 that prioritizes securing a wide communication area, but rather one that has a shorter communication range compared to the base station equipment 200.

[0215] In step S61, the base station device 200 broadcasts a message within its communication area indicating that there may be a dead zone (dead zone warning). However, the base station device 200 may also unicast the dead zone warning to the terminal device 100 with which it is communicating. 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 a dead zone alarm. This predetermined control is either a control to maintain the terminal device 100 within the communication area, or a control to return the terminal device 100 to the communication area when it moves from the communication area to a dead zone. For example, the terminal device 100 may move towards the base station device 200 to avoid entering a dead zone. Alternatively, the terminal device 100 may perform autonomous control to return to the communication area when it enters a dead 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 a dead zone. The terminal device 100 may limit or stop its movement speed when it enters a dead zone to avoid going too deep into the dead zone. The terminal device 100 may transmit an inquiry signal to search for an adjacent base station, identify the direction of the adjacent base station, and move in that direction.

[0217] [Example of the third modification of the third embodiment] It is envisioned that the communication area provided by the base station equipment 200 will be adaptively expanded or contracted in response to changes in the time of day and the underwater environment. For example, the communication area may be reduced during the day and increased at night. Alternatively, the communication area may be reduced on sunny days and increased on cloudy days. Or, 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 conjunction with such changes in the communication area, depending on the location of the terminal equipment 100, it may end up in a dead zone after the adjustment, potentially causing a communication interruption and leading to a loss of control.

[0218] In this example of modification, among the multiple base station devices 200, the target base station device 200 that changes the distance between base stations in accordance with the change in the communication area transmits a first optical signal (also referred to as a "communication area change notification") to notify 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] Figure 43 shows an example of the operation of the optical communication system 1 according to this modification example. In the illustrated example, the base station device 200 is assumed to be a base station device 200 that creates a dead zone when the distance between base stations is changed. Such a base station device 200 may be, for example, a base station device 200 that is responsible for 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 send a communication area change notification by unicast to the terminal device 100 with which it is communicating. 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 to permit the change. If the terminal device 100 does not want the communication area to be changed for reasons such as being in the middle of work, it determines to reject the change.

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

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

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

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

[0226] [Other embodiments] In the above-described embodiment, an example was given 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 polyhedral shape. In that case, each face of the polyhedron may constitute an optical communication section, 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 as a rod shape. For example, the terminal device 100 and / or the base station device 200 may constitute a rectangular prism, with the sides of the rectangular prism constituting an optical communication section, and a set of light-emitting elements and light-receiving elements may be arranged on each side.

[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 a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM. Furthermore, the 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 part of the terminal device 100, the base station device 200, or the control device 400 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0228] The phrases “based on” and “depending on / in response to” used in this disclosure do not mean “based solely on” or “depending solely on” unless otherwise specified. “Based on” means both “based solely on” and “at least partially on.” Similarly, “depending on” means both “at least partially on” and “at least partially on.” The terms “include,” “comprise,” and variations thereof do not mean that only the listed items are included; they mean that only the listed items may be included, or that additional items may be included in addition to the listed items. Furthermore, the term “or” used in this disclosure is not intended to mean exclusive OR. Additionally, any reference to elements using designations such as “first,” “second,” etc., 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 way to distinguish between two or more elements. Therefore, references to the first and second elements do not imply that only two elements may be adopted therein, or that the first element must precede the second element in any way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall be plural unless it is clearly indicated by the context that they are not.

[0229] Although the embodiments have been described in detail above with reference to the drawings, the specific configuration is not limited to those described above, and various design changes can be made without departing from the gist of the invention.

[0230] [Note A] The following is an addendum regarding the features of the embodiment described above.

[0231] (Note 1) Base station equipment and The system includes 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, prioritizing the communication quality of the optical communication on the uplink over the communication quality of the optical communication on the downlink. Optical communication system.

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

[0233] (Note 3) The terminal device further comprises a plurality of optical communication units, each with an optical axis oriented in a different direction. The control unit estimates the uplink communication quality based on the reception status of the plurality of optical communication units. The optical communication system described in Appendix 2.

[0234] (Note 4) The control unit, The first optical communication unit, which receives a reference optical signal from the base station device, measures the reference signal intensity, which is the received intensity of the reference optical signal. Based on the received intensity in the second optical communication unit, which is different from the first optical communication unit, the ambient light noise intensity, which is the received intensity of ambient light in the base station device, is estimated. The uplink communication quality is estimated based on the reference signal strength and the ambient light noise strength. The optical communication system described in Appendix 3.

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

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

[0237] (Supplementary Note 7) The control unit determines whether or not the ambient light incident on the base station device is in a shielding state where it is shielded by the terminal device, and when it is determined that the state is the shielding state, corrects the ambient light noise intensity to a predetermined alternative value. The optical communication system according to any one of Supplementary Notes 4 to 6.

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

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

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

[0241] (Supplementary Note 11) The predetermined alternative value is an average value or a median value of the reception intensities in each of the plurality of optical communication units. An optical communication system as described in any of the appendices 7 to 10.

[0242] (Note 12) The control unit, The ambient light noise intensity derived by the base station device is obtained from the base station device. The predetermined alternative value is the ambient light noise intensity obtained from the base station device. An optical communication system as described in any of the appendices 7 to 10.

[0243] (Note 13) The control unit, Information indicating the transmission power of the reference signal in the base station device is obtained from the base station device, The uplink communication quality is estimated based on the reference signal strength, the transmission power, and the ambient light noise intensity. An optical communication system as described in any of the appendices 4 through 12.

[0244] (Note 14) The control unit, The uplink communication quality is estimated for each of the multiple base station devices. A base station device whose uplink communication quality meets a predetermined standard is selected from among the multiple base station devices. Attempt to connect to the selected base station device. An optical communication system as described in any of the appendices 1 to 13.

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

[0246] (Note 16) The base station device notifies the terminal device whether or not it is able to perform the connection control that prioritizes the communication quality of the uplink. An optical communication system as described in any of the appendices 1 to 15.

[0247] (Appendix 17) The base station device sets the terminal device to transmit a measurement report message including information indicating the estimated uplink communication quality to the base station device, and determines a 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. The optical communication system according to any one of Appendices 1 to 16.

[0248] (Appendix 18) 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. The optical communication system according to Appendix 17.

[0249] (Appendix 19) In the 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 uplink priority connection. The optical communication system according to any one of Appendices 1 to 18.

[0250] (Appendix 20) 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. Terminal device.

[0251] (Appendix 21) 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. Base station equipment.

[0252] [Note B] Further details regarding other features of the embodiments described above are provided below.

[0253] (Note 1) An optical communication system that performs optical communication between a base station device and a terminal device, It is equipped with multiple base station devices arranged in three dimensions in the water, spaced apart in the horizontal and vertical directions. Each of the aforementioned base station devices forms a communication area underwater, which constitutes the optical communication coverage area in the optical communication system. Optical communication system.

[0254] (Note 2) If the communication area formed by each of the multiple base station devices is considered to be cubic, the multiple base station devices are arranged in water such that the cubic communication areas are arranged horizontally and vertically to fill the coverage area. The optical communication system described in Appendix 1.

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

[0256] (Note 4) The aforementioned multiple base station devices constitute a group of multiple base stations arranged at intervals in the horizontal direction. Each of the aforementioned group of base stations is Two or more base station devices arranged at vertical intervals, The aforementioned communication area is provided between vertically adjacent base station devices, and includes a connecting member that vertically connects the base station devices. An optical communication system as described in any of the appendices 1 to 3.

[0257] (Note 5) The multiple base station devices are arranged in water such that the horizontal distance between base stations is narrower than the vertical distance between base stations by a predetermined distance. The optical communication system described in Appendix 4.

[0258] (Note 6) The system includes a determination unit that determines the predetermined distance based on environmental parameters indicating at least one of the following in the coverage area: wave height, wind strength on the water, and water flow speed. The optical communication system described in Appendix 5.

[0259] (Note 7) A specific unit that determines the communication range of the base station devices constituting the base station device pair by performing optical communication between base station device pairs adjacent in the vertical direction within the aforementioned communication area, The system includes a setting unit that sets the horizontal and vertical distances between base stations based on the specified communication range. An optical communication system as described in any of the appendices 4 to 6.

[0260] (Note 8) An adjustment mechanism for adjusting the length of the connecting member, The system includes a first control unit that controls the adjustment mechanism based on the set vertical distance between base stations. The optical communication system described in Appendix 7.

[0261] (Note 9) A moving mechanism for moving at least one of the aforementioned group of base stations in the horizontal direction, The system includes a second control unit that controls the movement mechanism based on the set vertical distance. The optical communication system described in Appendix 7 or 8.

[0262] (Note 10) The specified part is, By performing optical communication with multiple pairs of base station devices that are adjacent vertically in the aforementioned communication area, the communication range is determined for each of the multiple pairs of base station devices. From among the communication ranges identified for each of the aforementioned multiple base station device pairs, the shortest communication range is identified. The setting unit sets at least the horizontal distance between base stations based on the identified shortest possible communication distance. An optical communication system as described in any of the appendices 7 to 9.

[0263] (Note 11) The base station equipment includes a power adjustment unit that sets the optical signal transmission power in the horizontal direction to be lower than the optical signal transmission power in the vertical direction. The optical communication system described in Appendix 10.

[0264] (Note 12) Among the aforementioned multiple base station devices, some base station devices whose optical communication range is shorter than that of the other base station devices transmit an optical signal indicating that the area outside the communication area of ​​those base station devices may be a coverage hole. The terminal device that receives the optical signal performs control to keep the terminal device within the communication area, or performs control to return the terminal device to the communication area when it moves from the communication area to the coverage hole. An optical communication system as described in any of the appendices 1 to 11.

[0265] (Note 13) Of the aforementioned multiple base station devices, the base station device whose inter-base station distance is to be changed transmits a first optical signal to notify the change in the inter-base station distance. The terminal device that receives the optical signal transmits a second optical signal to the target base station device indicating whether or not to permit a change in the distance between base stations. An optical communication system as described in any of the appendices 1 to 12.

[0266] [Cross-references to related applications] This application claims priority to Japanese Patent Application No. 2022-134686 (filed on August 26, 2022) and Japanese Patent Application No. 2022-171108 (filed on October 26, 2022), and all of their contents are incorporated into the specification of this application. [Explanation of symbols]

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

Claims

1. An optical communication system that performs optical communication between a base station device and a terminal device, It is equipped with multiple base station devices arranged in three dimensions in the water, spaced apart in the horizontal and vertical directions. Each of the aforementioned base station devices forms a communication area underwater, which constitutes the optical communication coverage area in the optical communication system. Optical communication system.

2. If the communication area formed by each of the multiple base station devices is considered to be cubic, the multiple base station devices are arranged in water such that the cubic communication areas are arranged horizontally and vertically to fill the coverage area. The optical communication system according to claim 1.

3. The aforementioned multiple base station devices constitute a group of multiple base stations arranged at intervals in the horizontal direction. Each of the aforementioned group of base stations is Two or more base station devices arranged at a vertical distance from each other, The aforementioned communication area is provided between vertically adjacent base station devices, and includes a connecting member that vertically connects the base station devices. The optical communication system according to claim 1.

4. The multiple base station devices are arranged in water such that the horizontal distance between base stations is narrower than the vertical distance between base stations by a predetermined distance. The optical communication system according to claim 3.

5. A specific unit that determines the communication range of the base station devices constituting the base station device pair by performing optical communication between base station device pairs adjacent in the vertical direction within the aforementioned communication area, The system includes a setting unit that sets the horizontal and vertical distances between base stations based on the specified communication range. The optical communication system according to claim 3.

6. An adjustment mechanism for adjusting the length of the connecting member, The system includes a first control unit that controls the adjustment mechanism based on the set vertical distance between base stations. The optical communication system according to claim 5.

7. A moving mechanism for moving at least one of the aforementioned group of base stations in the horizontal direction, The system includes a second control unit that controls the mobile mechanism based on the set vertical distance between base stations. The optical communication system according to claim 5.

8. The specified part is, By performing optical communication with multiple pairs of base station devices that are vertically adjacent in the aforementioned communication area, the communication range is determined for each of the multiple pairs of base station devices. From among the communication ranges identified for each of the aforementioned multiple base station device pairs, the shortest communication range is identified. The setting unit sets at least the horizontal distance between base stations based on the identified shortest possible communication distance. The optical communication system according to claim 5.

9. The base station equipment includes a power adjustment unit that sets the optical signal transmission power in the horizontal direction to be lower than the optical signal transmission power in the vertical direction. The optical communication system according to claim 8.

10. Among the aforementioned multiple base station devices, some base station devices whose optical communication range is shorter than that of the other base station devices transmit an optical signal indicating that the area outside the communication area of ​​those base station devices may be a coverage hole. The terminal device that receives the optical signal performs control to keep the terminal device within the communication area, or performs control to return the terminal device to the communication area when it moves from the communication area to the coverage hole. The optical communication system according to any one of claims 1 to 9.

11. Of the aforementioned multiple base station devices, the base station device whose inter-base station distance is to be changed transmits a first optical signal to notify the change in the inter-base station distance. The terminal device that receives the first optical signal transmits a second optical signal to the target base station device indicating whether or not to permit a change in the distance between base stations. The optical communication system according to any one of claims 1 to 9.

Images