Optical communication systems, terminal equipment, and base station equipment

Abstract

This enables the proper establishment and / or maintenance of optical communication connections. [Solution] The 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 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.

Description

Technical Field

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

Background Art

[0002] For example, in underwater communication, an optical communication system using 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

Problems to be Solved by the Invention

[0004] In future optical communication systems, it is assumed that optical communication between a plurality of terminal devices and a base station device will be realized, similar to radio communication using radio waves on land. Under such an assumption, it is desired to realize connection control for appropriately establishing and / or maintaining an optical communication connection between a terminal device and a base station device.

[0005] Here, in radio communication using radio waves, connection control based on the reception intensity of the downlink (DL) radio waves received by the terminal device from the base station device is performed. However, there is a concern that such connection control that prioritizes the quality of downlink communication may prevent the terminal device from appropriately establishing and / or maintaining an optical communication connection with an appropriate base station device in an optical communication system.

[0006] Therefore, an object of the present invention is to provide an optical communication system, a terminal device, and a base station device that can appropriately establish and / or maintain an optical communication connection. [Means for solving the problem]

[0007] The optical communication system according to the first embodiment 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 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.

[0008] The terminal device according to the second embodiment 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, prioritizing the communication quality of the optical communication in the uplink over the communication quality of the optical communication in the downlink.

[0009] 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. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide an optical communication system, terminal equipment, and base station equipment that enable the proper establishment and / or maintenance of an optical communication connection. [Brief explanation of the drawing]

[0011] [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]It is a diagram showing an example of the external configuration of a base station apparatus according to an embodiment. [Figure 5] It is a diagram showing a first modification example of the external configuration of a base station apparatus according to an embodiment. [Figure 6] It is a diagram showing a second modification example of the external configuration of a base station apparatus according to an embodiment. [Figure 7] It is a diagram showing an example of the block configuration of a terminal device according to an embodiment. [Figure 8] It is a diagram showing an example of the external configuration of a terminal device according to an embodiment. [Figure 9] It is a diagram showing a first modification example of the external configuration of a terminal device according to an embodiment. [Figure 10] It is a diagram showing a second modification example of the external configuration of a terminal device according to an 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 an example of the configuration 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 the operation sequence of the optical communication system 1 according to the third modification example of the first embodiment. [Figure 22] It is a diagram showing an example of the operation sequence of the optical communication system according to the second embodiment. [Figure 23] It is a diagram showing an example of the operation sequence of the optical communication system according to the modification example of the second embodiment.

Embodiment for Carrying out the Invention

[0012] The optical communication system according to the embodiment will be described while referring to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0013] The optical communication system according to the embodiment is a system that performs optical communication using visible light as an example of light. However, the optical communication system may be a system that performs optical communication using light other than visible light, such as infrared light. Also, the optical communication system according to the embodiment is a system that performs optical communication underwater. However, the optical communication system is not limited to a system that performs optical communication underwater, and may be, for example, a system that performs optical communication in space.

[0014] [First Embodiment] First, the optical communication system according to the first embodiment will be described.

[0015] (Configuration Example of Optical Communication System) FIG. 1 is a diagram showing a configuration example of the optical communication system 1 according to the present 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 illustrated example.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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).

[0022] 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.

[0023] 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.

[0024] 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.

[0025] Figure 2 is a schematic diagram showing the transmission operation of the terminal device 100 in UL according to this embodiment.

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Figure 4 shows an example of the external configuration of the base station device 200 according to this embodiment.

[0035] 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.

[0036] Figure 5 shows a first modified example of the external configuration of the base station device 200 according to this embodiment.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] Figure 6 shows a second example of the external configuration of the base station device 200 according to this embodiment.

[0041] 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.

[0042] (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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Figure 8 shows an example of the external configuration of the terminal device 100 according to this embodiment.

[0050] 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.

[0051] Figure 9 shows a first example of a modified external configuration of the terminal device 100 according to this embodiment.

[0052] 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.

[0053] Figure 11 shows a second example of the external configuration of the terminal device 100 according to this embodiment.

[0054] In this modified example, the terminal device 100 has a 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.

[0055] (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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] (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, 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.

[0066] 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.

[0067] 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".

[0068] Figure 13 is a diagram illustrating the effect of solar noise on the optical communication system 1 according to this embodiment.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] Figure 14 is a diagram illustrating the influence of ambient light on the optical communication system 1 according to this embodiment.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] Figure 15 is a diagram illustrating the UL communication quality estimation operation performed by the terminal device 100 according to this embodiment.

[0080] 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.

[0081] 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.

[0082] 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].

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] Figure 17 shows an example of the operation flow in the terminal device 100 according to this embodiment.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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).

[0094] 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.

[0095] 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.

[0096] [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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] [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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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 likely to be in the shadow of the terminal device 100, i.e., a shielded state.

[0109] 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).

[0110] 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.

[0111] 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.

[0112] 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.

[0113] [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.

[0114] 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.

[0115] 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.

[0116] Figure 21 shows an example of the operation sequence of the optical communication system 1 related to this modification example.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] As a result, in step S27, the terminal device 100 establishes an optical communication connection with the base station device 200a.

[0124] [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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] Figure 22 shows an example of the operation sequence of the optical communication system 1 according to this embodiment.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] As a result, in step S35, the terminal device 100 establishes an optical communication connection with the base station device 200.

[0135] [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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] Figure 23 shows an example of the operation sequence of the optical communication system 1 related to this modification example.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In step S45, 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 in step S45.

[0146] 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.

[0147] [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.

[0148] A program may be provided that causes a computer to execute each process performed by the terminal device 100 or the base station device 200. 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 or the base station device 200 may be integrated, and at least a part of the terminal device 100 or the base station device 200 may be configured as a semiconductor integrated circuit (chipset, SoC).

[0149] 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.

[0150] 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.

[0151] [Note] The following is an addendum regarding the features of the embodiment described above.

[0152] (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.

[0153] (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.

[0154] (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.

[0155] (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.

[0156] (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.

[0157] (Note 6) The control unit estimates the ambient light noise intensity by averaging multiple measurements obtained by measuring the received intensity in the second optical communication unit multiple times within a predetermined period. The optical communication system described in Appendix 4 or 5.

[0158] (Note 7) The control unit, It is determined whether the ambient light incident on the base station device is in a shielded state, where it is blocked by the terminal device. If the aforementioned shielding condition is determined, the ambient light noise intensity is corrected to a predetermined alternative value. An optical communication system as described in any of the appendices 4 to 6.

[0159] (Note 8) The control unit determines that the shielding state exists based on the first condition being met, which is that the ambient light noise intensity is equal to or greater than a first threshold, and at least the reception intensity of ambient light in the first optical communication unit is less than a second threshold. The optical communication system described in Appendix 7.

[0160] (Note 9) The control unit, Based on the reference signal strength, a value indicating the distance between the terminal device and the base station device is obtained. Based on the fact that the first condition is met and the distance is less than or equal to the threshold, it is determined that the shielding state exists. The optical communication system described in Appendix 8.

[0161] (Note 10) The control unit determines that the shielding state exists based on the fact that the first condition is met and the received ambient light intensity in the optical communication unit surrounding the second optical communication unit is below a threshold. The optical communication system described in Appendix 8.

[0162] (Note 11) The predetermined alternative value is the average or median value of the received intensity in each of the plurality of optical communication units. An optical communication system as described in any of the appendices 7 to 10.

[0163] (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.

[0164] (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.

[0165] (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.

[0166] (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.

[0167] (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.

[0168] (Note 17) The base station device is, The terminal device is configured to transmit a measurement report message containing information indicating the estimated uplink communication quality to the base station device. Based on the measurement report message from the terminal device, the handover of the terminal device from one base station device to another base station device is determined. An optical communication system as described in any of the appendices 1 to 16.

[0169] (Note 18) The control unit of the terminal device triggers the transmission of the measurement report message to the base station device when the estimated uplink communication quality satisfies a predetermined trigger condition. The optical communication system described in Appendix 17.

[0170] (Note 19) The base station device, in the handover process of the terminal device from the base station device to another base station device, notifies the other base station device that the terminal device is performing an uplink priority connection. An optical communication system as described in any of the appendices 1 through 18.

[0171] (Note 20) The optical communication unit performs optical communication with the base station equipment, The system includes 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, prioritizing the communication quality of the optical communication on the uplink over the communication quality of the optical communication on the downlink. Terminal device.

[0172] (Note 21) The optical communication unit performs optical communication with the terminal device, The system includes 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, prioritizing the communication quality of the optical communication on the uplink over the communication quality of the optical communication on the downlink. Base station equipment. [Explanation of symbols]

[0173] 1: Optical communication system 2a :Inner surface 10: Network 100: Terminal device 101: Optical Communications Department 101a: Optical Communications Department 101b: Optical Communication 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

Claims

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. 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 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 in the plurality of optical communication units. 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 aforementioned reference signal strength and the aforementioned ambient light noise strength. It is determined whether the ambient light incident on the base station device is in a shielded state, where it is blocked by the terminal device. If the aforementioned shielding condition is determined, the ambient light noise intensity is corrected to a predetermined alternative value. 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. Optical communication system.

2. 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. The optical communication system according to claim 1.

3. 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. The optical communication system according to claim 1.

4. 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 according to claim 3.

5. 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. The optical communication system according to any one of claims 1 to 4.

6. The base station device is, The terminal device is configured to transmit a measurement report message containing information indicating the estimated uplink communication quality to the base station device. Based on the measurement report message from the terminal device, the handover of the terminal device from one base station device to another base station device is determined. The optical communication system according to any one of claims 1 to 5.

7. The control unit of the terminal device triggers the transmission of the measurement report message to the base station device when the estimated uplink communication quality satisfies a predetermined trigger condition. The optical communication system according to claim 6.

8. The base station device, in the handover process of the terminal device from the base station device to another base station device, notifies the other base station device that the terminal device is performing an uplink priority connection. The optical communication system according to any one of claims 1 to 7.

9. The optical communication unit performs optical communication with the base station equipment, The system includes 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, prioritizing the communication quality of the optical communication on the uplink over the communication quality of the optical communication on the downlink. Terminal device.

10. The optical communication unit performs optical communication with the terminal device, The system includes 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, prioritizing the communication quality of the optical communication on the uplink over the communication quality of the optical communication on the downlink. Base station equipment.

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