Optical communication systems, base station equipment, and terminal equipment

Abstract

This optical communication system performs optical communication, which is wireless communication employing light, underwater, and is provided with: a base station device that forms a cell underwater; and a terminal device that performs the optical communication with the base station device in the cell. At least one of the base station device and the terminal device performs the optical communication with time diversity applied thereto, said time diversity involving the repetition, at predetermined time intervals, of optical signal transmission corresponding to the same transmission information.

Description

[[Technical Field]]

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

[0002] For example, in underwater communication, an optical communication system is known that performs wireless communication (also simply referred to as "optical communication") using light, in particular visible light, as a transmission medium. Since light has high directivity, in conventional optical communication systems, under the premise that the optical communication apparatuses on the transmitting side and the receiving side are fixed, it is common to perform one-to-one optical communication with the transmitting side and the receiving side facing each other.

[0003] In the future, it is expected that cellular operation will be realized in optical communication systems, in which a coverage area is divided into small areas called cells, and a base station apparatus that manages a cell performs optical communication with a terminal apparatus within the cell. Such an optical communication system is also referred to as a cellular optical communication system. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Patent Application Laid-Open No. 4-103232 [[Summary of the Invention]]

[0005] An optical communication system according to a first aspect is an optical communication system that performs optical communication, which is wireless communication using light, underwater, comprising: a base station apparatus that forms a cell underwater; and a terminal apparatus that performs the optical communication with the base station apparatus in the cell. At least one of the base station apparatus and the terminal apparatus performs the optical communication to which time diversity is applied, in which optical signal transmission corresponding to the same transmission information is repeatedly performed at predetermined time intervals.

[0006] A base station device according to the second embodiment is a base station device that forms a cell in water, comprising: an optical communication unit that performs optical communication, which is wireless communication using light, with terminal devices in the cell; and a control unit that controls the optical communication unit to apply time diversity, which is the repeated transmission of optical signals corresponding to the same transmission information at predetermined time intervals, to the optical communication.

[0007] A terminal device according to the third embodiment is a terminal device that performs optical communication, which is wireless communication by light, underwater, and comprises an optical communication unit that performs optical communication with a base station device in a cell formed by the base station device underwater, and a control unit that controls the optical communication unit to apply time diversity, which is the repeated transmission of optical signals corresponding to the same transmission information at predetermined time intervals, to the optical communication. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows an example of the configuration of an optical communication system according to the embodiment. [Figure 2] This figure shows another example of the configuration of the optical communication system according to the embodiment. [Figure 3] This figure shows an example of the configuration of a communication frame used in the optical communication system according to the embodiment. [Figure 4] This figure shows an example configuration of a base station device according to the embodiment. [Figure 5] This figure shows an example of the external configuration of a base station device according to the present invention. [Figure 6] This figure shows an example configuration of a terminal device according to the embodiment. [Figure 7] This figure shows an example of the external configuration of a terminal device according to the embodiment. [Figure 8] This is a diagram illustrating spatial multiplexing according to an embodiment. [Figure 9] This is a diagram illustrating the composite transmission according to the embodiment. [Figure 10] This is a diagram to explain caustics. [Figure 11] This figure shows the spatial distribution of light intensity (illuminance) in water. [Figure 12] This figure shows the temporal distribution of light intensity (illuminance) at a single point in the water. [Figure 13] This figure shows an example of a communication sequence when time diversity according to the embodiment is applied to downlink (DL) optical communication. [Figure 14] This figure shows an example of a communication sequence when applying time diversity to uplink (UL) optical communication. [Figure 15] This figure shows an example of time diversity control based on wind speed parameter values ​​according to the embodiment. [Figure 16] This figure shows an example of time diversity control based on wave state parameter values ​​according to the embodiment. [Figure 17] This figure shows an example of time diversity control based on illuminance parameter values ​​according to the embodiment. [Figure 18] This figure shows an example of time diversity control based on the incident angle parameter value according to the embodiment. [Figure 19] This figure shows an example of time diversity control based on water depth parameter values ​​according to the embodiment. [Figure 20] This figure shows an example of time diversity control based on the orientation of light-emitting and receiving elements of a base station device according to an embodiment. [Figure 21] This figure shows an example of time diversity control based on the orientation of the light-emitting and receiving elements of a terminal device according to an embodiment. [Figure 22] This figure shows a first embodiment of a method for notifying time diversity information according to an embodiment. [Figure 23] This figure shows a second embodiment of the method for notifying time diversity information according to the embodiment. [Figure 24] This figure shows a third embodiment of the method for notifying time diversity information according to the embodiment. [Figure 25] This figure shows an example of a change in the external configuration of the optical communication device according to the embodiment. [Figure 26]FIG. 11 is a diagram illustrating a modification example of an external configuration of an optical communication device according to an embodiment.

Mode for Carrying Out the Invention

[0009] In an optical communication system, sunlight acts as an inhibitory factor having an extremely large influence. In particular, in an optical communication system that performs optical communication under water, a lattice pattern of light derived from sunlight called caustics is generated in water under the influence of the gradient distribution of a water surface. In portions corresponding to lattice points in this lattice pattern, sunlight with higher intensity compared to the surrounding area is concentrated, and large noise for optical communication is instantaneously generated. Therefore, in an optical communication system that performs optical communication under water, there is a problem that it is difficult to properly perform optical communication due to the influence of sunlight noise caused by caustics.

[0010] Accordingly, an object of the present disclosure is to properly perform optical communication under water.

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

[0012] The optical communication system according to the embodiment is a system that performs optical communication using visible light as an example of light. However, the optical communication system may be a system that performs optical communication using light other than visible light, for example, infrared light. In addition, the optical communication system according to the embodiment is a system that performs optical communication under water. Optical communication under water refers to, for example, optical communication in the ocean, a lake, a river, or the like. In the following embodiments, an optical communication system that performs optical communication in the ocean (under the sea) is mainly assumed.

[0013] (1) Configuration Example of Optical Communication System First, a configuration example of an optical communication system according to an embodiment will be described. FIG. 1 is a diagram illustrating an example of a configuration of an optical communication system 1.

[0014] In optical communication system 1, the coverage area is divided into small regions called cells, and a base station device 200 that manages the cells performs optical communication with terminal devices 100 within those cells. In the illustrated example, optical communication system 1 has multiple terminal devices 100 (100a and 100b) and a base station device 200. However, the number of terminal devices 100 and the number of base station devices 200 are not limited to the illustrated example.

[0015] Each terminal device 100 is an example of an optical communication device. Each terminal device 100 is located underwater. Each terminal device 100 is configured to be mobile underwater. For example, each terminal device 100 may be a self-propelled device such as an underwater robot or underwater drone. The terminal device 100 connects to a base station device 200 that manages the cell in which it is located (also referred to as a "serving cell") and performs optical communication with the base station device 200 to which it is connected (also referred to as a "serving base station").

[0016] Each terminal device 100 has multiple light-emitting and light-receiving units whose optical axes (or, from another perspective, the directivity of optical communication) are oriented in different directions. Each light-emitting and light-receiving unit includes at least one light-emitting element and at least one light-receiving element. This allows each terminal device 100 to perform optical communication in various directions using multiple light-emitting and light-receiving units while using light as the transmission medium.

[0017] Each terminal device 100 may be equipped with a sensor 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 via optical communication. Each terminal device 100 may receive downlink (DL) data including instruction data from the base station device 200 via optical communication. Based on the instruction data, the terminal device 100 may perform movement and sensing operations (such as taking pictures).

[0018] The base station device 200 is another example of an optical communication device. Multiple base station devices 200 may be installed at horizontal intervals to create a wide coverage area underwater. The base station devices 200 may be installed temporarily, for example, during the period of underwater surveys using each terminal device 100. In Figure 1, the communication area of ​​each base station device 200, which is called a cell, is shown by a dashed line.

[0019] The base station device 200 has, for example, a floating member and is located near the water surface. The base station device 200 is communicably connected to the network 10 via a backhaul line. The backhaul line may be a wireless line. The backhaul line may be a wired line. The network 10 may include the Internet. The base station device 200 may perform inter-base station communication with other base station devices via the network 10.

[0020] The base station device 200 has multiple light-emitting and light-receiving units whose optical axes are oriented in different directions. Each light-emitting and light-receiving unit includes at least one light-emitting element and at least one photodetector. In the illustrated example, the base station device 200 has a hemispherical housing submerged in water, with multiple light-emitting and light-receiving units arranged in an array on the surface of the spherical housing. This allows the base station device 200 to perform optical communication in various directions using multiple light-emitting and light-receiving units while using light as the transmission medium.

[0021] The base station device 200 selects its own light-emitting / receiving unit corresponding to the direction of each terminal device 100 connected to it, and uses the selected unit to perform optical communication with the terminal device 100. Similarly, the terminal device 100 selects its own light-emitting / receiving unit corresponding to the direction of the base station device 200, which is its serving base station, and uses the selected unit to perform optical communication with the base station device 200.

[0022] The base station device 200 may also transmit a synchronization optical signal and / or a reference optical signal unique to its device from all light-emitting and receiving units in all directions. The terminal device 100 may identify the direction of the base station device 200 based on these optical signals, identify its own light-emitting and receiving unit corresponding to that direction, and perform optical communication with the base station device 200 using the identified light-emitting and receiving unit.

[0023] Thus, in the optical communication system 1, each of the terminal device 100 and the base station device 200 has multiple light-emitting and receiving units (multiple light-emitting and receiving units) arranged on its surface, and selectively uses the light-emitting and receiving unit corresponding to the direction of the communication partner. The base station device 200 transmits optical signals from multiple light-emitting units with different directivity to form a communication area (cell). The base station device 200 covers a wide area by selectively using the light-emitting and receiving unit corresponding to the direction of the terminal device 100 that has entered its cell.

[0024] Figure 2 shows another example of the configuration of optical communication system 1. Here, we will explain the differences between the configuration example in Figure 2 and the configuration example in Figure 1. In the configuration example in Figure 1, the base station equipment 200 was installed on the water surface. In contrast, in the configuration example in Figure 2, multiple base station equipment 200 are arranged three-dimensionally in the water.

[0025] Specifically, each of the base station devices 200a and 200b is located near the water surface and is fixed to, for example, a buoy (floating device). Each of the base station devices 200a and 200b has a hemispherical housing, and multiple light-receiving 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 via a backhaul line so as to be able to communicate.

[0026] 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.

[0027] Base station device 200c communicates with network 10 via base station device 200a, and base station device 200e communicates with network 10 via base station devices 200a and 200c. Similarly, base station device 200d communicates with network 10 via base station device 200b, and base station device 200f communicates with network 10 via base station devices 200b and 200d.

[0028] The base station device 200 may be installed on the seabed. In that case, the terminal device 100 moving underwater will perform optical communication with the base station device 200 located below (diagonally below) it. Alternatively, the base station device 200 may be installed on the underwater wall. In that case, the terminal device 100 will perform optical communication with the base station device 200 while moving vertically underwater.

[0029] Figure 3 shows an example of the configuration of a communication frame used in optical communication system 1. In the example shown, one communication frame consists of 10 time slots, but the number of time slots constituting one communication frame is not limited to 10. Each time slot consists of a predetermined number of symbol intervals.

[0030] 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.

[0031] 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 by the terminal device 100 to measure the light intensity received from the base station device 200.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Furthermore, intensity modulation direct detection (IM / DD) may be used for optical communication between the terminal device 100 and the base station device 200. In the IM / DD method, data transmission is performed using the intensity of light emitted by the light-emitting element on the transmitting side of the optical signal. The transmitting side transmits an optical signal whose intensity is modulated according to the data to be transmitted. The receiving side acquires the transmitted data by directly detecting the intensity of the received optical signal with a photodetector. One of the modulation methods used in the IM / DD method is subcarrier modulation. Subcarrier modulation is a method of transmitting data by controlling the intensity of light emitted from the light-emitting element in a sinusoidal shape and modulating the amplitude and / or phase of this sinusoidal wave (also called a "subcarrier"). In the optical communication system 1, orthogonal frequency division multiplexing (OFDM), a type of subcarrier modulation method, may also be used.

[0037] (2) Example of base station equipment configuration Next, an example of the configuration of a base station device 200 according to one embodiment will be described. Figure 4 is a diagram showing an example of the configuration of a base station device 200 according to one embodiment.

[0038] The base station device 200 includes a light-emitting unit 210, a light-receiving unit 220, a control unit 230, and a backhaul communication unit 240. The light-emitting unit 210 and the light-receiving unit 220 constitute the optical communication unit. The base station device 200 may have a battery to supply the power necessary for the operation of the base station device 200.

[0039] The light-emitting unit 210 transmits an optical signal to the terminal device 100 under the control of the control unit 230. The light-emitting unit 210 has a plurality of light-emitting elements 211 (211#0, 211#1, ...) and a transmitter 212. Each light-emitting element 211 may be a laser diode (LD) or a light-emitting diode (LED). In the following, an example in which each light-emitting element 211 is an LED will be mainly described. Each light-emitting element 211 converts an electrical signal (transmission signal) output by the transmitter 212 for optical communication into an optical signal and transmits the optical signal. The transmitter 212 may be composed of an FPGA (Field Programmable Gate Array) and / or a SoC (System-on-a-chip). The transmitter 212 performs signal processing on the transmission signal output by the control unit 230, converts the signal after signal processing, and outputs it to the light-emitting elements 211. In one embodiment, each of the plurality of light-emitting elements 211 has a different optical axis orientation. In other words, each of the multiple light-emitting elements 211 has a different direction of directivity (transmission directivity).

[0040] The light-receiving unit 220 receives an optical signal from the terminal device 100. The light-receiving unit 220 has a plurality of light-receiving elements 221 (221#0, 221#1, ...) and a receiver 222. Each light-receiving element 221 may be a photodiode (PD). Each light-receiving element 221 receives an optical signal, converts the received optical signal into an electrical signal (received signal), and outputs the received signal to the receiver 222. The receiver 222 may be configured by an FPGA and / or SoC. At least a part of the receiver 222 may be configured integrally with the transmitter 212. The receiver 222 converts the received signal output by the light-receiving elements 221, performs signal processing on the converted received signal, and outputs it to the control unit 230.

[0041] For example, a light-receiving element 221 is provided in a one-to-one pair with a light-emitting element 211. Here, the light-receiving element 221 has the same directionality (receiving directionality) as its corresponding light-emitting element 211. That is, multiple pairs of light-emitting elements 211 and light-receiving elements 221 each transmit optical signals in different directions and receive optical signals from different directions.

[0042] The control unit 230 controls the overall operation of the base station device 200. For example, the control unit 230 controls the light-emitting unit 210 and the light-receiving unit 220. The operation of the base station device 200 described above and the operation of the base station device 200 described later may be controlled by the control unit 230. 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 executes the programs stored in memory and performs various processes.

[0043] The base station device 200 may have a measurement unit 170 for acquiring communication environment parameters. The measurement unit 170 includes, for example, at least one of an anemometer, accelerometer, illuminometer, time meter (clock), and depth meter. In particular, when the base station device 200 is installed on the water surface (see, for example, the base station device 200 in Figure 1), at least a portion of the measurement unit 170 may be installed on a buoy (floating device). Alternatively, the light receiving unit 220 may be used as an illuminometer.

[0044] The backhaul communication unit 240 performs backhaul 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 (for example, the core network) and an inter-base station communication unit 242 that communicates with adjacent base stations.

[0045] The base station device 200 configured in this way forms a cell in water. The optical communication unit, composed of a light-emitting unit 210 and a light-receiving unit 220, performs optical communication, which is wireless communication using light, with the terminal device 100 in the cell. The control unit 230 controls the optical communication unit (light-emitting unit 210 and light-receiving unit 220) to apply time diversity to the optical communication, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals.

[0046] Figure 5 shows an example of the external configuration of a base station device 200 according to one embodiment.

[0047] The base station device 200 has a hemispherical optical communication unit 250 and a main body 260 connected to the optical communication unit 250. However, the base station device 200 may be configured to be spherical as a whole. The optical communication unit 250 has a plurality of dispersedly arranged light-receiving and light-emitting regions 251. Each light-receiving and light-emitting region 251 is provided with at least one pair of light-emitting element 211 and light-receiving element 221. This configuration makes it easy for the base station device 200 to perform optical communication with terminal devices 100 in various directions. In the illustrated example, the hemispherical optical communication unit 250 has a total of 19 light-receiving and light-emitting regions 251#0 to 251#18. That is, the base station device 200 has a total of 19 light-emitting elements 211#0 to 211#18 and a total of 19 light-receiving elements 221#0 to 221#18.

[0048] (3) Example of terminal device configuration Next, an example of the configuration of a terminal device 100 according to one embodiment will be described. Figure 6 is a diagram showing an example of the configuration of a terminal device 100 according to one embodiment.

[0049] The terminal device 100 includes a light-emitting unit 110, a light-receiving unit 120, and a control unit 130. The light-emitting unit 110 and the light-receiving unit 120 constitute an optical communication unit. The terminal device 100 may have a battery to supply the power necessary for its operation. The terminal device 100 may have a moving mechanism (e.g., a motor and a screw) used to move the terminal device 100.

[0050] The light-emitting unit 110 transmits an optical signal to the base station device 200 under the control of the control unit 130. The light-emitting unit 110 has a plurality of light-emitting elements 111 (111#0, 111#1, ...) and a transmitter 112. Each light-emitting element 111 may be a laser diode (LD) or a light-emitting diode (LED). In the following, an example in which each light-emitting element 211 is an LED will be mainly described. Each light-emitting element 111 converts an electrical signal (transmission signal) output by the transmitter 112 for optical communication into an optical signal and transmits the optical signal. The transmitter 112 may be composed of an FPGA and / or SoC. The transmitter 112 performs signal processing on the transmission signal output by the control unit 130, converts the signal after signal processing, and outputs it to the light-emitting elements 111. In one embodiment, each of the plurality of light-emitting elements 111 has a different optical axis orientation. That is, each of the plurality of light-emitting elements 111 has a different directionality (transmission directionality).

[0051] The light-receiving unit 120 receives an optical signal from the base station device 200. The light-receiving unit 120 has a plurality of light-receiving elements 121 (121#0, 121#1, ...) and a receiver 122. Each light-receiving element 121 may be a photodiode (PD). Each light-receiving element 121 receives an optical signal, converts the received optical signal into an electrical signal (received signal), and outputs the received signal to the receiver 122. The receiver 122 may be configured by an FPGA and / or SoC. At least a part of the receiver 122 may be configured integrally with the transmitter 112. The receiver 122 converts the received signal output by the light-receiving elements 121, performs signal processing on the converted received signal, and outputs it to the control unit 130.

[0052] For example, a light-receiving element 121 is provided in a one-to-one pair with a light-emitting element 111. Here, the light-receiving element 121 has the same directionality (receiving directionality) as its corresponding light-emitting element 111. That is, multiple pairs of light-emitting elements 111 and light-receiving elements 121 each transmit optical signals in different directions and receive optical signals from different directions.

[0053] The control unit 130 controls the overall operation of the terminal device 100. For example, the control unit 130 controls the light-emitting unit 110 and the light-receiving unit 120. 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. 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 executes the programs stored in the memory and performs various processes.

[0054] The terminal device 100 may have a measurement unit 170 for acquiring communication environment parameters. The measurement unit 170 may include, for example, at least one of an illuminance meter and a depth meter. However, the light receiving unit 120 may be used as an illuminance meter.

[0055] The terminal device 100 configured in this way performs optical communication, which is wireless communication using light, underwater. The optical communication unit, which consists of a light-emitting unit 110 and a light-receiving unit 120, performs optical communication with the base station device 200 in a cell formed by the base station device 200 underwater. The control unit 130 controls the optical communication unit (light-emitting unit 110 and light-receiving unit 120) to apply time diversity to the optical communication, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals.

[0056] Figure 7 shows an example of the external configuration of a terminal device 100 according to one embodiment.

[0057] The terminal device 100 has a hemispherical optical communication unit 150 and a main body 160 connected to the optical communication unit 150. However, the terminal device 100 may be configured to be spherical as a whole. The optical communication unit 150 has a plurality of dispersedly arranged light-receiving and light-emitting regions 151. Each light-receiving and light-emitting region 151 is provided with at least one pair of light-emitting element 111 and light-receiving element 121. This configuration makes it easy for the terminal device 100 to perform optical communication with base station devices 200 in various directions. In the illustrated example, the hemispherical optical communication unit 150 has a total of seven light-receiving and light-emitting regions 151#0 to 151#6. That is, the terminal device 100 has a total of seven light-emitting elements 111#0 to 111#6 and a total of seven light-receiving elements 121#0 to 121#6.

[0058] (4) An example of downlink transmission Next, an example of downlink transmission according to one embodiment will be described. The base station device 200 has a plurality of light-emitting elements 211 with different directivity. In downlink transmission, the base station device 200 may use the plurality of light-emitting elements 211 to perform spatial multiplexing transmission, which transmits data to different terminal devices 100, or composite transmission, which transmits the same data to the same terminal device 100.

[0059] Figure 8 is a diagram illustrating spatial multiplexing according to one embodiment. Figure 8 shows a simplified cross-section of the base station device 200. In the base station device 200, multiple light-emitting elements 211 are arranged such that as the distance between one light-emitting element 211 and another light-emitting element 211 increases, the angle between the optical axis of one light-emitting element 211 and the optical axis of the other light-emitting element 211 increases. The angle between the optical axis of light-emitting element 211#0 and the optical axis of light-emitting element 211#7 that is not adjacent to light-emitting element 211#0 is greater than the angle between the optical axis of light-emitting element 211#0 and the optical axis of light-emitting element 211#1 that is adjacent to light-emitting element 211#0.

[0060] In the illustrated example, the base station device 200 transmits an optical signal to terminal device 100a using light-emitting element 211#0, while simultaneously transmitting an optical signal to terminal device 100b using light-emitting element 211#7, whose optical axis is oriented in a different direction from that of light-emitting element 211#0. This spatially separates the transmission to terminal device 100a and the transmission to terminal device 100b, allowing simultaneous transmission while suppressing interference between them. This increases the number of terminal devices 100 that the base station device 200 can accommodate, thereby improving the system capacity of the optical communication system 1.

[0061] Figure 9 is a diagram illustrating a composite transmission according to one embodiment. Figure 9 shows a simplified cross-section of the base station equipment 200.

[0062] In the illustrated example, the base station device 200 transmits an optical signal to the terminal device 100 using the light-emitting element 211#1, while simultaneously transmitting the same optical signal to the same terminal device 100 using the light-emitting element 211#7, whose optical axis is oriented in a different direction than that of the light-emitting element 211#1. Since the optical signals transmitted by the light-emitting element 211#1 and the optical signals transmitted by the light-emitting element 211#7 are the same optical signals, they are partially combined and reinforce each other in water. As a result, it is possible to extend the communication range.

[0063] (5) Caustics and temporal diversity Next, caustics and temporal diversity according to one embodiment will be described. Figures 10 to 12 are diagrams illustrating caustics.

[0064] In Figure 10, sunlight rays are indicated by arrows, and the areas where sunlight rays are concentrated (concentration regions) are indicated by dashed circles. In optical communication system 1, sunlight is a very significant inhibiting factor. In particular, in optical communication system 1, which performs optical communication underwater, a grid pattern of sunlight-derived light called caustics is generated in the water due to the influence of the gradient distribution of the water surface. That is, caustics is a concentration phenomenon that occurs when sunlight is refracted at the water surface. At the grid points in the grid pattern, sunlight of a higher intensity is concentrated compared to the surrounding areas, and a large amount of noise (sunlight noise) is instantaneously generated in optical communication.

[0065] Figure 11 shows the spatial distribution of light intensity (illuminance) in water. Figure 12 shows the temporal distribution of light intensity (illuminance) at a single point in the water. For example, in shallow waters, caustics caused by wave motion due to refraction at the wavefront instantaneously generate a large amount of noise. In particular, in areas with relatively shallow water depth and / or calm waves (low wind speed), sunlight about 5 to 10 times the average is incident in a spot temporally and spatially, resulting in a large amount of noise.

[0066] In one embodiment, at least one of the base station device 200 and the terminal device 100 performs optical communication using time diversity, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals (also referred to as "time interval T"). For example, at least one of the base station device 200 and the terminal device 100 avoids the solar noise peak in time by using time diversity with a time interval T that is longer than the duration of the solar noise peak due to caustics shown in Figure 12, for example, a time interval T of 10 ms or more. This makes it possible to reduce the effects of solar noise due to caustics and perform optical communication appropriately in the optical communication system 1 that performs optical communication underwater.

[0067] Time diversity may also be repetition, in which the same optical signal (e.g., the same data optical signal and / or the same control optical signal) is repeatedly transmitted at time intervals T. The transmitting side may repeatedly transmit the same optical signal at time intervals T for a predetermined number of times. The transmitting side may repeatedly transmit the same optical signal at time intervals T until it receives an acknowledgment (Ack) from the receiving side. The receiving side may hold the decoding result of a failed reception (specifically, decoding) and perform a synthesis process to combine it with the decoding result of the next optical signal received.

[0068] Alternatively, time diversity may be a Hybrid Automatic Repeat Request (HARQ) that repeatedly transmits a data optical signal containing the same data (and different redundant bits) at time intervals T. The transmitter may repeatedly transmit a data optical signal containing the same data (and different redundant bits) at time intervals T until it receives an Ack from the receiver. The receiver may hold the decoded result of a failed reception (specifically, decoding) and perform a synthesis process to combine it with the decoded result it holds for the next optical signal received.

[0069] Figure 13 shows an example of a communication sequence when time diversity is applied to downlink (DL) optical communication. While time diversity may also be applied to the transmission of control optical signals, here we will describe an example of applying time diversity to the transmission of data optical signals.

[0070] In step S11, the base station device 200 transmits a data optical signal to the terminal device 100. The terminal device 100 receives the data optical signal from the base station device 200. Here, let's assume that the terminal device 100 fails to decode the data optical signal from the base station device 200 due to solar noise caused by caustics (step S12).

[0071] In step S13, the base station device 200 transmits the same data optical signal to the terminal device 100 as the data optical signal transmitted in step S11, after a time interval T has elapsed since step S11. The terminal device 100 receives the data optical signal from the base station device 200. At this point, the influence of solar noise due to caustics is small, and the terminal device 100 successfully decodes the data optical signal from the base station device 200 (step S14).

[0072] In step S15, the terminal device 100 transmits a control optical signal to the base station device 200 that includes an Ack indicating that it successfully decoded the data optical signal in step S14. Upon receiving the control optical signal (Ack) from the terminal device 100, the base station device 200 stops repeatedly transmitting the same data optical signal (step S16).

[0073] Figure 14 shows an example of a communication sequence when time diversity is applied to uplink (UL) optical communication. While time diversity may also be applied to the transmission of control optical signals, here we will describe an example of applying time diversity to the transmission of data optical signals.

[0074] In step S21, the terminal device 100 transmits a data optical signal to the base station device 200. The base station device 200 receives the data optical signal from the terminal device 100. Here, let's assume that the base station device 200 fails to decode the data optical signal from the terminal device 100 due to solar noise caused by caustics (step S22).

[0075] In step S23, the terminal device 100 transmits the same data optical signal to the base station device 200 as the data optical signal transmitted in step S21, after a time interval T has elapsed since step S21. The base station device 200 receives the data optical signal from the terminal device 100. At this point, the influence of solar noise due to caustics is small, and the base station device 200 successfully decodes the data optical signal from the terminal device 100 (step S24).

[0076] In step S25, the base station device 200 transmits a control optical signal to the terminal device 100 that includes an Ack indicating that it successfully decoded the data optical signal in step S24. Upon receiving the control optical signal (Ack) from the base station device 200, the terminal device 100 stops repeatedly transmitting the same data optical signal (step S26).

[0077] The following embodiment describes an example in which time diversity can be applied to both UL and DL. However, time diversity may be applied only to UL, or only to DL. Furthermore, the time interval T (predetermined time interval) for time diversity may be a common time interval for both UL and DL, or it may be a different time interval for UL and DL.

[0078] (6) Time diversity control Next, based on the time diversity described above, a time diversity control according to one embodiment will be explained.

[0079] At least one of the base station equipment 200 and the terminal equipment 100 (also simply referred to as the "optical communication equipment") acquires communication environment parameters related to caustics that affect the communication quality of optical communication, and controls time diversity based on said communication environment parameters. Specifically, the optical communication equipment estimates the frequency and / or intensity of instantaneous noise peaks caused by caustics based on the communication environment parameters and performs appropriate time diversity. This suppresses the degradation of communication quality due to noise peaks. However, if repeated transmission is performed at wide time intervals due to time diversity, it is disadvantageous in terms of the real-time nature of communication and / or the effective use of communication resources. Therefore, if the optical communication equipment estimates that the effect of caustics is not significant, it may not apply time diversity or may narrow the time interval T of time diversity.

[0080] Here, the communication environment parameters may be at least one of the following: a wind speed parameter indicating the wind speed on the water; a wave state parameter indicating the wave state (i.e., the degree of water surface sway); an illuminance parameter indicating the intensity of sunlight incident on the water surface; an incidence angle parameter indicating the angle of incidence of sunlight on the water surface; a water depth parameter indicating the water depth of the optical communication device; and an orientation parameter indicating the orientation of the photodetector and / or light-emitting element of the optical communication device used for optical communication. However, the communication environment parameters may be any parameters related to caustics that affect the communication quality of optical communication, and are not limited to these parameters. The optical communication device may perform time diversity control using only one of these multiple parameters. The optical communication device may perform time diversity control using a combination of two or more parameters.

[0081] For example, optical communication equipment determines whether or not to apply time diversity to optical communication based on communication environment parameters. This makes it possible to not apply time diversity when the effects of caustics are estimated to be insignificant, thereby ensuring the real-time nature of communication and making efficient use of communication resources. On the other hand, optical communication equipment can apply time diversity when the effects of caustics are estimated to be significant, thereby mitigating the effects of solar noise caused by caustics and enabling proper optical communication.

[0082] The optical communication device may, instead of deciding whether or not to apply time diversity to optical communication based on communication environment parameters, or in addition to such a decision, determine the time interval T (predetermined time interval) of time diversity based on communication environment parameters. For example, the optical communication device may determine the time interval T of time diversity based on communication environment parameters, assuming that time diversity is always applied to optical communication. Alternatively, the optical communication device may decide to apply time diversity to optical communication based on communication environment parameters, and then further determine the time interval T of time diversity based on communication environment parameters. This makes it possible to narrow the time interval T, for example, when the effect of caustics is estimated to be insignificant, thereby ensuring the real-time nature of communication and making effective use of communication resources. On the other hand, when the effect of caustics is estimated to be significant, the optical communication device may, for example, not narrow the time interval T (may widen the time interval T), thereby reducing the effect of solar noise due to caustics and enabling proper optical communication.

[0083] The optical communication device acquires communication environment parameters based on at least one of the following: the output of a measuring unit installed on or above the water surface, information provided from the information providing device via the network 10, the output of a measuring unit 270 installed in the base station device 200, and the output of a measuring unit 170 installed in the terminal device 100. Here, the measuring unit installed on or above the water surface may be a measuring unit installed on a buoy (floating device). The measuring unit may use a solar power generation device (solar panel) installed on or above the water surface as an illuminometer. The information providing device may be a server connected to a wide area network (WAN) as the network 10. The information providing device may be a local computer connected to a narrow area network (LAN) as the network 10.

[0084] (6.1) An example of time diversity control based on wind speed and / or wave conditions Caustics are less likely to occur (i.e., solar noise peaks are less likely to occur) when the wind speed on the water is strong and / or when the degree of water surface sway (fluctuation) is high. Therefore, the optical communication device decides, based on at least one of the following: that the value of the wind speed parameter indicating wind speed is above a threshold, and that the value of the wave state parameter indicating wave state is above a threshold, whether to apply time diversity to optical communication, and whether to make the time interval T narrower than the reference time interval. The reference time interval may be a predetermined time interval (for example, a time interval of 10 ms or more). The reference time interval may be the time interval used during the previous transmission.

[0085] On the other hand, caustics are more likely to occur (i.e., solar noise peaks are more likely to occur) when the wind speed on the water is weak and / or the degree of water surface sway (fluctuation) is small. Therefore, the optical communication device may decide to apply time diversity to optical communication and to set the time interval T as a reference time interval (the time interval T may be wider than the reference time interval) based on at least one of the following: the value of the wind speed parameter indicating wind speed is below a threshold, and the value of the wave state parameter indicating wave state is below a threshold.

[0086] Figure 15 shows an example of time diversity control based on wind speed parameter values. Here, an example of time diversity control led by the base station device 200 is described. However, time diversity control based on wind speed parameter values ​​may also be led by the terminal device 100. In that case, the base station device 200 may notify the terminal device 100 of the wind speed parameter values, and the terminal device 100 may perform time diversity control based on the wind speed parameter values ​​obtained from the base station device 200.

[0087] In step S101, the base station device 200 acquires wind speed parameter values. For example, the base station device 200 acquires wind speed parameter values ​​using at least one of the following: an anemometer installed on the buoy, an anemometer installed on the base station device 200, and weather information provided via the network 10.

[0088] In step S102, the base station device 200 determines whether the wind speed parameter value obtained in step S101 is equal to or greater than a threshold.

[0089] If the wind speed parameter value is greater than or equal to a threshold (step S102: YES), in step S103, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0090] On the other hand, if the wind speed parameter value is less than the threshold (step S102: NO), in step S104, the base station device 200 decides to apply time diversity to optical communication or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0091] Figure 16 shows an example of time diversity control based on wave state parameter values. Here, an example of time diversity control led by the base station device 200 is described. However, time diversity control based on wave state parameter values ​​may also be led by the terminal device 100. In that case, the base station device 200 may notify the terminal device 100 of the wave state parameter values, and the terminal device 100 may perform time diversity control based on the wave state parameter values ​​obtained from the base station device 200.

[0092] In step S131, the base station device 200 acquires wave state parameter values. For example, the base station device 200 acquires wave state parameter values ​​using at least one of the following: an accelerometer installed on the buoy, an accelerometer installed on the base station device 200, and weather information (wave information) provided via the network 10.

[0093] In step S132, the base station device 200 determines whether the wave state parameter value obtained in step S131 is greater than or equal to a threshold.

[0094] If the wave state parameter value is greater than or equal to a threshold (step S132: YES), in step S133, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0095] On the other hand, if the wave state parameter value is less than the threshold (step S132: NO), in step S134, the base station device 200 decides to apply time diversity to optical communication or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0096] (6.2) An example of time diversity control based on weather and / or time of day When the weather is not sunny and the amount of solar radiation is low, and / or when the angle of solar radiation is shallow (close to horizontal) at sunrise or sunset, caustics are less likely to occur (i.e., solar noise peaks are less likely to occur). Therefore, the optical communication device decides whether to not apply time diversity to optical communication and to make the time interval T narrower than the standard time interval, based on at least one of the following: the value of the parameter indicating the intensity of sunlight incident on the water surface (illuminance parameter value) is below a threshold, and the value of the parameter indicating the angle of incidence of sunlight on the water surface (incidence angle parameter value) is below a threshold. The optical communication device may also decide not to apply time diversity to optical communication after sunset (including at night) because sunlight does not incident on the water surface.

[0097] On the other hand, when the weather is clear and the amount of solar radiation is high, and / or when the angle of solar radiation is deep (near vertical) at times other than sunrise and sunset (during the day), caustics are more likely to occur (i.e., solar noise peaks are more likely to occur). Therefore, the optical communication device may decide to apply time diversity to optical communication and to set the time interval T as a reference time interval (the time interval T may be wider than the reference time interval) based on at least one of the following: the illuminance parameter value is above a threshold, and the incident angle parameter value is above a threshold.

[0098] Figure 17 shows an example of time diversity control based on illuminance parameter values. Here, an example of time diversity control led by the base station device 200 is described. However, time diversity control based on illuminance parameter values ​​may also be led by the terminal device 100. In that case, the base station device 200 may notify the terminal device 100 of the illuminance parameter values, and the terminal device 100 may perform time diversity control based on the illuminance parameter values ​​obtained from the base station device 200.

[0099] In step S201, the base station device 200 acquires illuminance parameter values. For example, the base station device 200 acquires illuminance parameter values ​​using at least one of the following: an illuminance meter installed on a buoy or the base station device 200, a solar panel installed on or above the water surface, and weather information provided via the network 10.

[0100] In step S202, the base station device 200 determines whether the illuminance parameter value acquired in step S201 is less than a threshold.

[0101] If the illuminance parameter value is below the threshold (step S202: YES), in step S203, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0102] On the other hand, if the illuminance parameter value is above a threshold (step S202: NO), in step S204, the base station device 200 decides to apply time diversity to optical communication or to use the time interval T as the reference time interval (the time interval T may be made wider than the reference time interval).

[0103] Figure 18 shows an example of time diversity control based on the incident angle parameter value. Here, an example of time diversity control led by the base station device 200 is described. However, the terminal device 100 may also lead the time diversity control based on the incident angle parameter value. In that case, the base station device 200 may notify the terminal device 100 of the incident angle parameter value, and the terminal device 100 may perform time diversity control based on the incident angle parameter value obtained from the base station device 200.

[0104] In step S231, the base station device 200 acquires an incident angle parameter value. For example, the base station device 200 acquires the current time using at least one of the clock installed in the base station device 200 and the time information provided via the network 10, and acquires an incident angle parameter value corresponding to the current time.

[0105] In step S232, the base station device 200 determines whether the incident angle parameter value obtained in step S231 is less than a threshold.

[0106] If the incident angle parameter value is less than the threshold (step S232: YES), in step S233, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0107] On the other hand, if the incident angle parameter value is greater than or equal to a threshold (step S232: NO), in step S234, the base station device 200 decides to apply time diversity to optical communication or to use the time interval T as the reference time interval (the time interval T may be made wider than the reference time interval).

[0108] (6.3) An example of time diversity control based on water depth When the optical communication equipment is submerged in deep water (i.e., far from the water surface), it is less susceptible to caustics and less likely to generate solar noise peaks. Therefore, the optical communication equipment decides, based on whether the value of a parameter indicating the equipment's submerged depth (submerged depth parameter value) is above a threshold, to either not apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0109] On the other hand, when the optical communication equipment is in shallow water (i.e., close to the water surface), it is susceptible to caustics and prone to generating solar noise peaks. Therefore, the optical communication equipment may decide to apply time diversity to optical communication and to set the time interval T as a reference time interval (the time interval T may be wider than the reference time interval) based on the water depth parameter value being below a threshold.

[0110] Figure 19 shows an example of time diversity control based on water depth parameter values. Here, an example of time diversity control led by the base station device 200 is described. However, time diversity control based on water depth parameter values ​​may also be led by the terminal device 100. In that case, the base station device 200 may notify the terminal device 100 of the water depth parameter values, and the terminal device 100 may perform time diversity control based on the water depth parameter values ​​obtained from the base station device 200. Alternatively, the terminal device 100 may perform time diversity control based on water depth parameter values ​​obtained using a depth gauge installed in the terminal device 100.

[0111] In step S301, the base station device 200 acquires the water depth parameter value. For example, the base station device 200 acquires the water depth parameter value using at least one of the depth gauge installed on the base station device 200 and depth information pre-stored in the memory 232 of the base station device 200. Alternatively, the base station device 200 may acquire the water depth parameter value from the terminal device 100.

[0112] In step S302, the base station device 200 determines whether the water depth parameter value obtained in step S301 is equal to or greater than a threshold.

[0113] If the water depth parameter value is greater than or equal to a threshold (step S302: YES), in step S303, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval.

[0114] On the other hand, if the water depth parameter value is less than the threshold (step S302: NO), in step S304, the base station device 200 decides to apply time diversity to optical communication or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0115] (6.4) An example of time diversity control based on the orientation of light-emitting and receiving elements Here, we will explain assuming the configuration of optical communication system 1 as shown in Figure 2, that is, a configuration in which each optical communication device is capable of optical communication in all directions. When the orientation of the photodetector used by the optical communication device for optical communication is not upward (for example, when the photodetector is oriented downward or horizontally), it is less susceptible to caustics and less likely to generate solar noise peaks. Therefore, the optical communication device acquires the orientation (orientation parameter) of the photodetector used by its device for optical communication and, based on the fact that the orientation is not upward, decides at least one of the following: not to apply time diversity to optical communication, and to make the time interval T narrower than the reference time interval.

[0116] On the other hand, if the photodetector used by the optical communication device is oriented upward, it is susceptible to caustics and prone to generating solar noise peaks. Therefore, based on the fact that the photodetector used by the device is oriented upward, the optical communication device may decide to apply time diversity to the optical communication and to set the time interval T as a reference time interval (the time interval T may be wider than the reference time interval).

[0117] Furthermore, the optical communication device may perform time diversity control separately for UL and DL. This makes it possible to optimize time diversity control for both UL and DL.

[0118] For example, base station equipment 200 may decide to apply time diversity to UL optical communication based on the fact that the orientation of the photodetector 221 of base station equipment 200 used for optical communication is upward. Base station equipment 200 may decide to apply time diversity to DL optical communication based on the fact that the orientation of the light-emitting element 211 of base station equipment 200 used for optical communication is downward (in this case, the orientation of the photodetector 121 of terminal equipment 100 used for optical communication is upward).

[0119] Furthermore, the terminal device 100 may decide to apply time diversity to DL optical communication based on the fact that the orientation of the photodetector 121 of the terminal device 100 used for optical communication is upward. The terminal device 100 may decide to apply time diversity to UL optical communication based on the fact that the orientation of the light-emitting element 111 of the terminal device 100 used for optical communication is downward (in this case, the orientation of the photodetector 221 of the base station device 200 used for optical communication is upward).

[0120] Figure 20 shows an example of time diversity control based on the orientation of the light-receiving and light-emitting elements of the base station device 200.

[0121] In step S401, the base station device 200 acquires the orientation of the light-receiving element 221 and / or light-emitting element 211 of the base station device 200 used for optical communication. For example, the base station device 200 identifies the light-receiving element 221 with the highest received intensity of the optical signal from the terminal device 100 and the light-emitting element 211 paired with the light-receiving element 221, and acquires the orientation of the identified light-receiving element 221 and the identified light-emitting element 211.

[0122] In step S402, the base station device 200 determines whether the orientation of the light-receiving element 221 identified in step S401 is upward.

[0123] If the orientation of the photodetector 221 identified in step S401 is not upward (step S402: NO), in step S403, the base station device 200 decides not to apply time diversity to optical communication or to make the time interval T narrower than the reference time interval for UL.

[0124] On the other hand, if the orientation of the photodetector 221 identified in step S401 is upward (step S402: YES), in step S404, the base station device 200 decides to apply time diversity to optical communication for UL or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0125] In step S405, the base station device 200 determines whether the orientation of the light-emitting element 211 identified in step S401 is downward.

[0126] If the orientation of the light-emitting element 211 identified in step S401 is not downward (step S405: NO), in step S406, the base station device 200 decides not to apply time diversity to optical communication for DL ​​or to make the time interval T narrower than the reference time interval.

[0127] On the other hand, if the orientation of the light-emitting element 211 identified in step S401 is downward (step S405: YES), in step S407, the base station device 200 decides to apply time diversity to optical communication for DL ​​or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0128] Figure 21 shows an example of time diversity control based on the orientation of the light-receiving and light-emitting elements of the terminal device 100.

[0129] In step S431, the terminal device 100 acquires the orientation of the light-receiving element 121 and / or light-emitting element 111 of the terminal device 100 used for optical communication. For example, the terminal device 100 identifies the light-receiving element 121 with the highest received intensity of the optical signal from the base station device 200 and the light-emitting element 111 paired with the light-receiving element 121, and acquires the orientation of the identified light-receiving element 121 and the identified light-emitting element 111.

[0130] In step S432, the terminal device 100 determines whether the orientation of the light-receiving element 121 identified in step S431 is upward.

[0131] If the orientation of the light-receiving element 121 identified in step S431 is not upward (step S432: NO), in step S433, the terminal device 100 decides not to apply time diversity to optical communication for DL, or to make the time interval T narrower than the reference time interval.

[0132] On the other hand, if the orientation of the light-receiving element 121 identified in step S431 is upward (step S432: YES), in step S434, the terminal device 100 decides to apply time diversity to optical communication for DL ​​or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0133] In step S435, the terminal device 100 determines whether the orientation of the light-emitting element 111 identified in step S431 is downward.

[0134] If the orientation of the light-emitting element 111 identified in step S431 is not downward (step S435: NO), in step S436, the terminal device 100 decides not to apply time diversity to optical communication for UL or to make the time interval T narrower than the reference time interval.

[0135] On the other hand, if the orientation of the light-emitting element 111 identified in step S431 is downward (step S435: YES), in step S437, the terminal device 100 decides to apply time diversity to optical communication for UL or to use the time interval T as the reference time interval (the time interval T may be wider than the reference time interval).

[0136] (7) Method of notifying time diversity information Next, assuming the time diversity control described above, the first to third embodiments of a method for notifying time diversity information according to one embodiment will be described. The first and second embodiments are embodiments in which the base station device 200 takes the lead in performing time diversity control, and the third embodiment is an embodiment in which the terminal device 100 takes the lead in performing time diversity control. In the following, the explanation will assume that optical communication is performed underwater as an example, but optical communication may also be assumed to be performed in a lake or river.

[0137] (7.1) First Embodiment In the first embodiment, the base station device 200 collectively decides whether or not to apply time diversity to optical communication and / or the time interval T of time diversity for each terminal device 100 within its cell. The base station device 200 then broadcasts (notifies) each terminal device 100 within its cell information indicating the decision.

[0138] Figure 22 shows a first embodiment of a method for notifying time diversity information.

[0139] In step S501, the base station equipment 200 determines whether time diversity is necessary (and / or the time interval T for time diversity).

[0140] For example, the base station device 200 may acquire wind speed information from an anemometer on a sea buoy or from weather information via the network 10, and determine that time diversity is unnecessary if the wind speed is above a threshold, and determine that time diversity is necessary if the wind speed is below the threshold.

[0141] The base station device 200 may acquire wave information from the accelerometer of a sea buoy or from weather information via the network 10, and determine that time diversity is unnecessary if the waves on the sea surface are above a threshold, or determine that time diversity is necessary if the waves on the sea surface are below a threshold.

[0142] The base station device 200 may obtain sunshine information from the illuminance meter on a sea buoy, the amount of solar panel power generated, or weather information via the network 10, and determine that time diversity is not necessary if the amount of sunshine at sea is below a threshold, or that time diversity is necessary if the amount of sunshine at sea is above a threshold.

[0143] The base station device 200 may obtain time information via its built-in clock or the network 10, and may decide that time diversity is not necessary if it is near sunrise / sunset or after sunset, or if it is during the daytime (when the sun is high in the sky).

[0144] The base station device 200 may acquire depth information of its own device using its depth meter or a preset at the time of installation, and may determine that time diversity is not necessary if the water depth of its own device is above a threshold, or determine that time diversity is necessary if the water depth of its own device is below the threshold.

[0145] If the base station equipment 200 divides cells according to direction, the base station equipment 200 may acquire information on the orientation of the light-receiving and light-emitting elements used for optical communication (direction information), determine that UL time diversity is required if the light-receiving element direction is upward, determine that DL time diversity is required if the light-emitting element direction is downward, and determine that time diversity is not required in all other cases.

[0146] If it is determined in step S501 that time diversity is necessary, in step S502, the base station device 200 broadcasts information indicating the determination (in this case, time diversity will be used) to each terminal device 100 within its own cell. In this case, the base station device 200 and each terminal device 100 perform optical communication with time diversity applied (step S503).

[0147] On the other hand, if it is determined in step S501 that time diversity is not necessary, in step S504, the base station device 200 broadcasts information indicating the decision (in this case, no use of time diversity) to each terminal device 100 within its own cell. In this case, the base station device 200 and each terminal device 100 perform optical communication without applying time diversity (step S505).

[0148] (7.2) Second Example In the second embodiment, the base station device 200 individually determines whether or not to apply time diversity to optical communication and / or the time interval T of time diversity for each terminal device 100 in the cell. The base station device 200 then transmits (notifies) information indicating the determined content to each terminal device 100 in the cell via unicast.

[0149] Figure 23 shows a second embodiment of the method for notifying time diversity information.

[0150] In step S531, the base station device 200 determines whether time diversity is necessary (and / or the time interval T for time diversity) for the terminal device 100a.

[0151] For example, the base station device 200 may, in addition to or instead of the determination method described in the first embodiment, acquire the direction of the light-receiving and light-emitting elements used for optical communication with the terminal device 100a, determine that UL time diversity is required if the light-receiving element direction is upward, determine that DL time diversity is required if the light-emitting element direction is downward, and determine that time diversity is not required in all other cases.

[0152] In step S532, the base station device 200 notifies the terminal device 100a of information indicating the content determined in step S531. In this case, the base station device 200 and the terminal device 100a perform optical communication with or without time diversity depending on the content determined in step S531 (step S533).

[0153] In step S534, the base station device 200 determines whether time diversity is necessary (and / or the time interval T for time diversity) for the terminal device 100b.

[0154] For example, the base station device 200 may, in addition to or instead of the determination method described in the first embodiment, acquire the direction of the light-receiving and light-emitting elements used for optical communication with the terminal device 100b, determine that UL time diversity is required if the light-receiving element direction is upward, determine that DL time diversity is required if the light-emitting element direction is downward, and determine that time diversity is not required in all other cases.

[0155] In step S535, the base station device 200 notifies the terminal device 100b of information indicating the content determined in step S534. In this case, the base station device 200 and the terminal device 100b perform optical communication with or without time diversity depending on the content determined in step S534 (step S536).

[0156] (7.3) Third Example In the third embodiment, each terminal device 100 determines whether or not to apply time diversity to optical communication and / or the time interval T of time diversity, and transmits information indicating the determined content to the base station device 200.

[0157] Figure 24 shows a third embodiment of the method for notifying time diversity information.

[0158] In step S551, the terminal device 100a determines whether time diversity is necessary (and / or the time interval T of time diversity).

[0159] For example, in addition to or instead of the determination method described in the first embodiment, the terminal device 100a may acquire information on the direction of the light-receiving and light-emitting elements used for optical communication with the base station device 200, and determine that DL time diversity is required if the light-receiving element direction is upward, that UL time diversity is required if the light-emitting element direction is downward, and that time diversity is not required in all other cases.

[0160] In step S552, terminal device 100a notifies base station device 200 of information indicating the content determined in step S551. In this case, base station device 200 and terminal device 100a perform optical communication with or without time diversity depending on the content determined in step S551 (step S553).

[0161] In step S554, the terminal device 100b determines whether time diversity is necessary (and / or the time interval T of time diversity).

[0162] For example, in addition to or instead of the determination method described in the first embodiment, the terminal device 100b may acquire information on the direction of the light-receiving and light-emitting elements used for optical communication with the base station device 200, and determine that DL time diversity is required if the light-receiving element direction is upward, that UL time diversity is required if the light-emitting element direction is downward, and that time diversity is not required in all other cases.

[0163] In step S555, terminal device 100b notifies base station device 200 of information indicating the content determined in step S554. In this case, base station device 200 and terminal device 100b perform optical communication with or without time diversity depending on the content determined in step S554 (step S556).

[0164] In this embodiment, the explanation was based on the premise that the base station device 200 accepts the content determined by the terminal device 100 (notification in steps S552 and S555). However, the base station device 200 may also reject the content determined by the terminal device 100. Under this premise, the base station device 200 may notify the terminal device 100 whether it accepts or rejects the content determined by the terminal device 100 (i.e., OK / NG). If it rejects the terminal device 100, the base station device 200 may notify the terminal device 100 of the time diversity information determined by its own device.

[0165] (8) Other embodiments In the above-described embodiment, an example was given in which the optical communication unit 150 of the terminal device 100 and the optical communication unit 250 of the base station device 200 are configured in a hemispherical or spherical shape. However, the terminal device 100 and / or the base station device 200 may be configured as a polyhedron (mirror ball shape) as shown in Figure 25. For example, the terminal device 100 and / or the base station device 200 may constitute a polyhedron, with each face (#0, #1,...) of the polyhedron constituting a light-receiving and light-emitting region, and at least one pair of light-emitting and light-receiving elements placed on each face. Alternatively, the terminal device 100 and / or the base station device 200 may be configured as a rod shape as shown in Figure 26. For example, the terminal device 100 and / or the base station device 200 may constitute a rectangular prism, with the sides (#0, #1,...) of the rectangular prism constituting a light-receiving and light-emitting region, and at least one pair of light-emitting and light-receiving elements placed on each side.

[0166] 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: System on a chip).

[0167] 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. The phrase "based on" means both "based solely on" and "at least partially on." Similarly, the phrase "depending on" means both "at least partially on" and "at least partially on." The terms "include," "comprise," and their variations do not mean that only the listed items are included, but that they may include only the listed items or may include additional items in addition to the listed items. Furthermore, the term "or" used in this disclosure is not intended to mean exclusive OR. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles are intended to include multiple items unless it is clearly indicated in the context that this is not the case.

[0168] 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.

[0169] This application claims priority to Japanese Patent Application No. 2023-060558 (filed on April 4, 2023), and all of its contents are incorporated into the specification of this application.

[0170] (9) Note The following is an addendum regarding the features of the embodiment described above.

[0171] (Note 1) An optical communication system (1) that performs optical wireless communication, which is wireless communication using light, underwater, A base station device (200) that forms a cell in water, The cell includes a terminal device (100) that performs optical communication with the base station device (200), At least one of the base station device (200) and the terminal device (100) performs optical communication that applies time diversity, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. Optical communication system (1).

[0172] (Note 2) At least one of the base station device (200) and the terminal device (100) is A communication environment parameter is obtained that is related to caustics, a light-gathering phenomenon caused by the refraction of sunlight at the water surface, and that affects the communication quality of the optical communication. Control the time diversity based on the aforementioned communication environment parameters. The optical communication system (1) described in Appendix 1.

[0173] (Note 3) At least one of the base station device (200) and the terminal device (100) determines whether or not to apply the time diversity to the optical communication based on the communication environment parameters. The optical communication system (1) described in Appendix 2.

[0174] (Note 4) At least one of the base station device (200) and the terminal device (100) determines the predetermined time interval based on the communication environment parameters. The optical communication system described in Appendix 2 or 3 (1).

[0175] (Note 5) At least one of the base station device (200) and the terminal device (100) acquires the communication environment parameters based on at least one of the following: the output of a measuring unit installed on or above the water surface, information provided via the network from an information providing device, the output of a measuring unit installed in the base station device (200), and the output of a measuring unit installed in the terminal device (100). An optical communication system (1) as described in any of Appendix 2 to 4.

[0176] (Note 6) The aforementioned communication environment parameters include at least one of the following: a parameter indicating wind speed on the water, and a parameter indicating wave conditions. An optical communication system (1) as described in any of Appendix 2 to 5.

[0177] (Note 7) At least one of the base station device (200) and the terminal device (100) determines, based on at least one of the following: that the value of the parameter indicating wind speed is above a threshold, and that the value of the parameter indicating wave state is above a threshold, whether to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system (1) described in Appendix 6.

[0178] (Note 8) The aforementioned communication environment parameters include at least one of the following: a parameter indicating the intensity of the sunlight incident on the water surface, and a parameter indicating the angle at which the sunlight is incident on the water surface. An optical communication system (1) as described in any of Appendix 2 to 7.

[0179] (Note 9) At least one of the base station device (200) and the terminal device (100) determines, based on at least one of the following: that the value of the parameter indicating the intensity is below a threshold, and that the value of the parameter indicating the incident angle is below a threshold, whether to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system (1) described in Appendix 8.

[0180] (Note 10) The aforementioned communication environment parameters include at least one of the parameters indicating the water depth of the base station device (200) and the parameters indicating the water depth of the terminal device (100). An optical communication system (1) as described in any of Appendix 2 to 9.

[0181] (Note 11) At least one of the base station device (200) and the terminal device (100) determines, based on whether the value of the parameter indicating the water depth is greater than or equal to a threshold, at least one of the following: not to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system (1) described in Appendix 10.

[0182] (Note 12) The communication environment parameters include at least one of the following: a parameter indicating the orientation of the light-receiving element and / or light-emitting element of the base station device (200) used for optical communication, and a parameter indicating the orientation of the light-receiving element and / or light-emitting element of the terminal device (100) used for optical communication. An optical communication system (1) as described in any of Appendix 2 to 11.

[0183] (Note 13) At least one of the base station device (200) and the terminal device (100) determines, based on the fact that the orientation of the light-receiving element is not upward, at least one of the following: not to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system (1) described in Appendix 12.

[0184] (Note 14) The base station equipment (200) is Based on the fact that the orientation of the photodetector of the base station device (200) used for the optical communication is upward, it is decided to apply the time diversity to the optical communication of the uplink. Based on the fact that the light-emitting element of the base station device (200) used for the optical communication is oriented downward, it is decided to apply the time diversity to the optical communication of the downlink. The optical communication system (1) described in Appendix 13.

[0185] (Note 15) The terminal device (100) is Based on the fact that the orientation of the photodetector element of the terminal device (100) used for the optical communication is upward, it is decided to apply the time diversity to the optical communication of the downlink. Based on the fact that the light-emitting element of the terminal device (100) used for the optical communication is oriented downward, it is decided to apply the time diversity to the optical communication on the uplink. Optical communication system as described in Appendix 13 or 14 (1).

[0186] (Note 16) The base station equipment (200) is Whether or not to apply the aforementioned time diversity to the optical communication and / or the predetermined time interval is determined collectively for each terminal device (100) within the cell. Information indicating the determined content is broadcast to each terminal device (100) within the cell. An optical communication system (1) as described in any of Appendix 2 to 15.

[0187] (Note 17) The base station equipment (200) is Whether or not to apply the aforementioned time diversity to the optical communication and / or to determine the predetermined time interval individually for each terminal device (100) within the cell, Information indicating the determined content is transmitted via unicast to each terminal device (100) within the cell. An optical communication system (1) as described in any of Appendix 2 to 15.

[0188] (Note 18) The terminal device (100) is Whether or not to apply the aforementioned time diversity to the optical communication and / or to determine the predetermined time interval, The information indicating the determined content is transmitted to the base station device (200). An optical communication system (1) as described in any of Appendix 2 to 15.

[0189] (Note 19) A base station device (200) that forms a cell in water, Optical communication units (210, 220) that perform optical communication, which is wireless communication using light, with terminal devices (100) within the cell, The system includes a control unit (230) that controls the optical communication unit (210, 220) to apply time diversity to the optical communication, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. Base station equipment (200).

[0190] (Note 20) A terminal device (100) for performing optical communication, which is wireless communication using light, underwater, An optical communication unit (110, 120) that performs optical communication with the base station device (200) in a cell formed by the base station device (200) in water, The optical communication unit (110, 120) is controlled by a control unit (130) to control the optical communication unit (110, 120) to apply time diversity, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. Terminal device (100). [Explanation of Symbols]

[0191] 1: Optical communication system 10: Network 100: Terminal device 110: Light-emitting part 111: Light-emitting element 112: Transmitter 120: Light receiving part 121: Photodetector 122: Receiver 130: Control Unit 131: Processor 132: Memory 150: Optical Communications Department 151: Light-receiving area 160: Main body 170: Measurement Unit 200:Base station equipment 210: Light-emitting part 211: Light-emitting element 212: Transmitter 220: Light receiving section 221: Photodetector 222: Receiver 230: Control Unit 231: Processor 232: Memory 240: Backhaul Communications Department 241: Network Communications Department 242: Inter-base station communication unit 250: Optical Communications Department 251: Light-receiving area 260: Main body 270: Measurement Unit

Claims

1. An optical communication system that performs optical wireless communication, which is wireless communication using light, underwater, A base station device that forms a cell underwater, The cell 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 is The optical communication described above is performed using time diversity, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. A communication environment parameter is obtained that is related to caustics, a light-gathering phenomenon caused by the refraction of sunlight at the water surface, and that affects the communication quality of the optical communication. The time diversity is controlled based on the aforementioned communication environment parameters. Optical communication system.

2. At least one of the base station device and the terminal device determines whether or not to apply the time diversity to the optical communication based on the communication environment parameters. The optical communication system according to claim 1.

3. At least one of the base station device and the terminal device determines the predetermined time interval based on the communication environment parameters. The optical communication system according to claim 1.

4. At least one of the base station device and the terminal device acquires the communication environment parameters based on at least one of the following: the output of a measuring unit installed on or above the water surface, information provided via the network from an information providing device, the output of a measuring unit installed in the base station device, and the output of a measuring unit installed in the terminal device. The optical communication system according to claim 1.

5. The aforementioned communication environment parameters include at least one of the following: a parameter indicating wind speed on the water, and a parameter indicating wave conditions. The optical communication system according to any one of claims 1 to 4.

6. At least one of the base station device and the terminal device determines, based on at least one of the following: that the value of the parameter indicating wind speed is above a threshold, and that the value of the parameter indicating wave state is above a threshold, whether to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system according to claim 5.

7. The aforementioned communication environment parameters include at least one of the following: a parameter indicating the intensity of the sunlight incident on the water surface, and a parameter indicating the angle at which the sunlight is incident on the water surface. The optical communication system according to any one of claims 1 to 4.

8. At least one of the base station device and the terminal device determines, based on at least one of the following: that the value of the parameter indicating the intensity is below a threshold, and that the value of the parameter indicating the incident angle is below a threshold, whether to apply the time diversity to the optical communication, and whether to make the predetermined time interval narrower than the reference time interval. The optical communication system according to claim 7.

9. The aforementioned communication environment parameters include at least one of the parameters indicating the water depth of the base station equipment and the parameters indicating the water depth of the terminal equipment. The optical communication system according to any one of claims 1 to 4.

10. At least one of the base station device and the terminal device determines, based on whether the value of the parameter indicating the water depth is greater than or equal to a threshold, at least one of the following: not to apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system according to claim 9.

11. The communication environment parameters include at least one of the following: a parameter indicating the orientation of the photodetector and / or light-emitting element of the base station device used for optical communication, and a parameter indicating the orientation of the photodetector and / or light-emitting element of the terminal device used for optical communication. The optical communication system according to any one of claims 1 to 4.

12. At least one of the base station device and the terminal device decides, based on the orientation of the light-receiving element not being upward, to not apply the time diversity to the optical communication, and to make the predetermined time interval narrower than the reference time interval. The optical communication system according to claim 11.

13. The base station device is, Based on the fact that the orientation of the photodetector of the base station equipment used for the optical communication is upward, it is decided to apply the time diversity to the uplink optical communication. Based on the fact that the light-emitting element of the base station device used for the optical communication is oriented downward, it is decided to apply the time diversity to the optical communication of the downlink. The optical communication system according to claim 12.

14. The aforementioned terminal device is Based on the fact that the orientation of the photodetector of the terminal device used for the optical communication is upward, it is decided to apply the time diversity to the optical communication of the downlink. Based on the fact that the light-emitting element of the terminal device used for the optical communication is oriented downward, it is decided to apply the time diversity to the uplink optical communication. The optical communication system according to claim 12.

15. The base station device is, Whether or not to apply the aforementioned time diversity to the optical communication and / or the predetermined time interval is determined collectively for each terminal device within the cell, Information indicating the determined content is broadcast to each terminal device within the cell. The optical communication system according to any one of claims 1 to 4.

16. The base station device is, Whether or not to apply the aforementioned time diversity to the optical communication and / or to determine the predetermined time interval individually for each terminal device within the cell, Information indicating the determined content is transmitted via unicast to each terminal device within the cell. The optical communication system according to any one of claims 1 to 4.

17. The aforementioned terminal device is Whether or not to apply the aforementioned time diversity to the optical communication and / or to determine the predetermined time interval, Information indicating the determined content is transmitted to the base station device. The optical communication system according to any one of claims 1 to 4.

18. A base station device that forms a cell in water, An optical communication unit that performs optical communication, which is wireless communication using light, with terminal devices within the cell, The system includes a control unit that controls the optical communication unit to apply time diversity to the optical communication, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. The control unit, A communication environment parameter is obtained that is related to caustics, a light-gathering phenomenon caused by the refraction of sunlight at the water surface, and that affects the communication quality of the optical communication. The time diversity is controlled based on the aforementioned communication environment parameters. Base station equipment.

19. A terminal device for performing optical communication, which is wireless communication using light, underwater, An optical communication unit that performs optical communication with the base station device in a cell formed by the base station device in water, The system includes a control unit that controls the optical communication unit to apply time diversity to the optical communication, which involves repeatedly transmitting optical signals corresponding to the same transmission information at predetermined time intervals. The control unit, A communication environment parameter is obtained that is related to caustics, a light-gathering phenomenon caused by the refraction of sunlight at the water surface, and that affects the communication quality of the optical communication. The time diversity is controlled based on the aforementioned communication environment parameters. Terminal device.

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