Visible-light communication system and terminal device

Abstract

This terminal device comprises a plurality of visible-light communication units including a visible-light communication unit and a visible-light communication unit, and a control unit for controlling the plurality of visible-light communication units. Each of the plurality of visible-light communication units has directivity in respectively different directions. The control unit exercises simultaneous communication control so that a visible-light communication unit performs visible-light communication with a base station device while a visible-light communication unit performs visible-light communication with a base station device.

Description

Visible light communication system and terminal device

[0001] The present disclosure relates to a visible light communication system and a terminal device.

[0002] For example, visible light communication, which uses visible light as a transmission medium for underwater communication, is known. Because visible light has high directionality, conventional visible light communication generally involves communication between a transmitter and a receiver facing each other, under the assumption that the transmitter and receiver of the visible light signal are fixed.

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

[0004] A visible light communication system according to a first aspect is a system for performing visible light communication between a terminal device and a base station device. The terminal device includes a plurality of visible light communication units, including a first visible light communication unit and a second visible light communication unit, and a control unit that controls the plurality of visible light communication units. The plurality of visible light communication units each have directivity in a different direction. The control unit performs simultaneous communication control so that the first visible light communication unit performs visible light communication with a first base station device, while the second visible light communication unit performs visible light communication with a second base station device.

[0005] A terminal device according to a second aspect is a device that performs visible light communication with a base station device. The terminal device includes multiple visible light communication units, including a first visible light communication unit and a second visible light communication unit, and a control unit that controls the multiple visible light communication units. The multiple visible light communication units each have directivity in a different direction. The control unit performs simultaneous communication control so that the first visible light communication unit performs visible light communication with a first base station device, while the second visible light communication unit performs visible light communication with a second base station device.

[0006] 1 is a diagram illustrating a configuration of a visible light communication system according to an embodiment. FIG. 2 is a diagram illustrating an operation scenario in a visible light communication system according to an embodiment. FIG. 3 is a diagram illustrating an operation scenario in a visible light communication system according to an embodiment. FIG. 4 is a diagram illustrating a configuration of a terminal device according to an embodiment. FIG. 5 is a diagram illustrating an example of association information according to an embodiment. FIG. 6 is a diagram illustrating an example of a format of a report visible light signal according to an embodiment. FIG. 7 is a diagram illustrating an example of an external configuration of a terminal device according to an embodiment. FIG. 8 is a diagram illustrating a configuration of a base station device according to an embodiment. FIG. 9 is a diagram illustrating an example of an external configuration of a base station device according to an embodiment. FIG. 10 is a diagram illustrating an operation example of a visible light communication system according to a first embodiment. FIG. 11 is a diagram illustrating a modification of the first embodiment. FIG. 12 is a diagram illustrating an operation scenario in a visible light communication system according to a second embodiment. FIG. 13 is a diagram illustrating a specific example of a combining process (buffer combining process) in a base station device according to the second embodiment. FIG. 14 is a diagram illustrating a specific example of a combining process (buffer combining process) in a base station device according to the second embodiment. FIG. 15 is a diagram illustrating an operation example of a visible light communication system according to a modification of the second embodiment. FIG. 16 is a diagram illustrating an operation example of a visible light communication system according to a modification of the second embodiment. FIG. 17 is a diagram illustrating a configuration of a visible light communication system according to another embodiment. FIG. 18 is a diagram illustrating a configuration of a visible light communication system according to another embodiment. FIG. 19 is a diagram illustrating an example of an external configuration of a terminal device according to another embodiment.

[0007] In a visible light communication system, it is desirable to enable a terminal device to simultaneously communicate with multiple base station devices (i.e., multiple base station communication), as in general cellular communication. However, unlike radio waves, which are the transmission medium for general cellular communication, visible light has high directionality, making it difficult to realize multiple base station communication in a visible light communication system.

[0008] Therefore, an object of the present disclosure is to make it possible to realize communication between multiple base stations while using visible light as a transmission medium.

[0009] A communication device according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0010] (1) Overview of the embodiment

[0011] (1.1) A visible light communication system according to a first aspect is a system for performing visible light communication between a terminal device and a base station device. The terminal device includes a plurality of visible light communication units, including a first visible light communication unit and a second visible light communication unit, and a control unit that controls the plurality of visible light communication units. The plurality of visible light communication units each have directivity in a different direction. The control unit performs simultaneous communication control such that the first visible light communication unit performs visible light communication with a first base station device, while the second visible light communication unit performs visible light communication with a second base station device.

[0012] In this way, the multiple visible light communication units of the terminal device each have directivity in a different direction, allowing the terminal device to perform visible light communication in various directions. The control unit of the terminal device then controls simultaneous communication so that the first visible light communication unit performs visible light communication with the first base station device while the second visible light communication unit performs visible light communication with the second base station device, allowing the terminal device to perform simultaneous communication with the first base station device and the second base station device (multiple base station communication). Thus, a visible light communication system that can achieve multiple base station communication while using visible light as a transmission medium can be provided.

[0013] (1.2) A visible light communication system according to a second aspect is the visible light communication system according to the first aspect, wherein each of the plurality of visible light communication units includes at least one light-emitting element, at least one light-receiving element, and a transceiver that performs transmission and reception processing of visible light signals using the light-emitting element and the light-receiving element.

[0014] This enables each visible light communication unit of the terminal device to perform visible light communication independently of other visible light communication units, thereby enabling visible light communication (multiple base station communication) using multiple visible light communication units simultaneously.

[0015] (1.3) A visible light communication system according to a third aspect is the visible light communication system according to the first or second aspect, wherein the control unit performs measurement processing on pilot visible light signals received by the plurality of visible light communication units from each base station device when the first visible light communication unit is performing visible light communication with the first base station device.

[0016] This makes it possible to detect handover candidates and determine whether or not to execute a handover.

[0017] (1.4) A visible light communication system according to a fourth aspect is the visible light communication system according to the third aspect, wherein the control unit performs the measurement process in response to a trigger condition set by the first base station device being satisfied or in response to detection of movement of the terminal device.

[0018] This allows the measurement process to be performed at an appropriate timing.

[0019] (1.5) A visible light communication system according to a fifth aspect is the visible light communication system according to the third or fourth aspect, wherein the pilot visible light signal is a visible light signal including a pilot signal sequence, and each of the base station devices includes in the pilot visible light signal of its own base station device the pilot signal sequence that is different from the pilot signal sequence used by base station devices surrounding the own base station device.

[0020] This allows the terminal device to distinguish each base station device from other base station devices based on the pilot signal sequence.

[0021] (1.6) A visible light communication system according to a sixth aspect is the visible light communication system according to any one of the third to fifth aspects, wherein the control unit controls the first visible light communication unit to transmit to the first base station device a report visible light signal including a measurement result for a pilot visible light signal of each of the base station devices.

[0022] This allows the first base station device in communication with the terminal device to grasp the reception status of the terminal device from each base station device.

[0023] (1.7) A visible light communication system according to a seventh aspect is the visible light communication system according to the sixth aspect, wherein the control unit controls the first visible light communication unit to transmit the report visible light signal to the first base station device in response to the measurement result satisfying a threshold condition or periodically.

[0024] This enables the terminal device to transmit a report visible light signal to the first base station device at an appropriate timing.

[0025] (1.8) A visible light communication system according to an eighth aspect is the visible light communication system according to the sixth or seventh aspect, wherein the plurality of visible light communication units receive an alert visible light signal from each of the base station devices. The alert visible light signal includes information indicating at least one of the attitude and shaking of the base station device that transmitted the alert visible light signal. The control unit corrects the measurement result in accordance with the information included in the alert visible light signal.

[0026] This makes it possible to reflect the base station status, such as the posture and shaking of each base station device, in the reported visible light signal, making it easier to determine a base station device that can perform visible light communication stably as the target base station (second base station device) for multiple base station communication.

[0027] (1.9) A visible light communication system according to a ninth aspect is the visible light communication system according to any one of the sixth to eighth aspects, wherein the control unit further includes, in the reporting visible light signal, information indicating whether the terminal device is capable of simultaneous communication with the first visible light communication unit for each base station device other than the first base station device.

[0028] This allows the first base station device in communication with the terminal device to appropriately determine other base station devices available for multi-base station communication.

[0029] (1.10) A visible light communication system according to a tenth aspect is the visible light communication system according to any one of the sixth to ninth aspects, wherein the control unit further includes information indicating a movement state of the terminal device in the reporting visible light signal.

[0030] This makes it easier to appropriately control communication between multiple base stations while taking into account the movement state of the terminal device.

[0031] (1.11) A visible light communication system according to an eleventh aspect is the visible light communication system according to the tenth aspect, wherein the control unit determines the moving state according to a reception status of pilot visible light signals in the plurality of visible light communication units.

[0032] This makes it easier to appropriately determine the movement state of the terminal device.

[0033] (1.12) A visible light communication system according to a twelfth aspect is the visible light communication system according to any one of the third to eleventh aspects, wherein the control unit generates association information that associates the visible light communication unit that received the pilot visible light signal with the base station device that transmitted the pilot visible light signal.

[0034] This makes it possible to appropriately use a plurality of visible light communication units for each base station device.

[0035] (1.13) A visible light communication system according to a thirteenth aspect is the visible light communication system according to the twelfth aspect, wherein the first visible light communication unit receives from the first base station device an instruction visible light signal including a communication instruction designating the second base station device. In response to receiving the instruction visible light signal, the control unit selects the visible light communication unit associated with the second base station device based on the association information, and establishes communication with the second base station device using the selected visible light communication unit.

[0036] This enables the terminal device to communicate with multiple base stations using an appropriate visible light communication unit.

[0037] (1.14) A visible light communication system according to a fourteenth aspect is the visible light communication system according to the thirteenth aspect, wherein the instruction visible light signal includes the communication instruction instructing the terminal device to transmit to the second base station device information that is the same as information that the terminal device transmits to the first base station device, and the control unit controls the first visible light communication unit and the second visible light communication unit in response to receiving the instruction visible light signal to transmit the same information to the first base station device and the second base station device.

[0038] This allows redundancy to be added to the information to be transmitted, thereby improving the quality of communication.

[0039] (1.15) A visible light communication system according to a fifteenth aspect is the visible light communication system according to the thirteenth aspect, wherein the instruction visible light signal includes the communication instruction instructing the terminal device to transmit information to the second base station device that is different from information to be transmitted from the terminal device to the first base station device, and the control unit controls the first visible light communication unit and the second visible light communication unit in response to reception of the instruction visible light signal to transmit the different information to the first base station device and the second base station device.

[0040] This allows two information streams to be transmitted simultaneously, improving communication speed.

[0041] (1.16) A visible light communication system according to a sixteenth aspect is the visible light communication system according to the fourteenth or fifteenth aspect, wherein the second base station device transfers information received by the second base station device from the terminal device to the first base station device. The first base station device performs a synthesis process on the information received by the first base station device from the terminal device and the information received by the first base station device from the second base station device.

[0042] This makes it possible to combine information transmitted to separate base station devices at a single base station device.

[0043] (1.17) A visible light communication system according to a seventeenth aspect is a visible light communication system according to any one of the twelfth to sixteenth aspects, wherein the control unit updates the association information in response to detection of rotation of the terminal device.

[0044] This makes it possible to appropriately update the association between the visible light communication unit and the base station device even if the terminal device rotates.

[0045] (1.18) A visible light communication system according to an eighteenth aspect is the visible light communication system according to the seventeenth aspect, wherein the terminal device further includes a sensor for generating attitude information of the terminal device. The control unit updates the association information based on the attitude information.

[0046] This makes it possible to appropriately update the association between the visible light communication unit and the base station device based on the attitude information, even if the terminal device rotates.

[0047] (1.19) A visible light communication system according to a 19th aspect is the visible light communication system according to the 17th aspect, wherein the control unit re-executes the measurement process in response to the detection of the rotation, and updates the association information in response to a result of the re-executed measurement process. The control unit may re-execute the measurement process in response to a change in the attitude information according to the 18th aspect, and update the association information in response to a result of the re-executed measurement process.

[0048] This makes it possible to appropriately update the association between the visible light communication unit and the base station device based on the measurement results of the pilot visible light signal, even if the terminal device rotates.

[0049] (1.20) A terminal device according to a twentieth aspect is a device that performs visible light communication with a base station device. The terminal device includes multiple visible light communication units including a first visible light communication unit and a second visible light communication unit, and a control unit that controls the multiple visible light communication units. The multiple visible light communication units each have directivity in a different direction. The control unit performs simultaneous communication control so that the first visible light communication unit performs visible light communication with a first base station device, while the second visible light communication unit performs visible light communication with a second base station device.

[0050] (2) First Embodiment First, a first embodiment will be described. The visible light communication system according to the first embodiment is a communication system that performs underwater visible light communication. In the following, underwater visible light communication is mainly assumed to be undersea visible light communication, but underwater visible light communication may also be visible light communication in lakes or rivers. Note that the visible light communication system according to the first embodiment is not limited to underwater visible light communication, and may also be applied to visible light communication on land (or in space).

[0051] (2.1) Configuration of Visible Light Communication System FIG. 1 is a diagram showing the configuration of a visible light communication system 1 according to the first embodiment. The visible light communication system 1 has a terminal device 100 and multiple base station devices 200. In FIG. 1, three base station devices 200 (200A, 200B, 200C) are shown as an example of the multiple base station devices 200, but the number of base station devices 200 may be two or four or more. Furthermore, although one terminal device 100 is shown as an example, the number of terminal devices 100 may be two or more.

[0052] In the example of FIG. 1 , each base station device 200 is located on the water surface. For example, each base station device 200 is fixed to a buoy. Each base station device 200 is connected to the network via a backhaul line. The backhaul line may be a wireless line or a wired line. In order to efficiently secure a communication area underwater, each base station device 200 is installed at a predetermined distance from adjacent other base station devices 200. Each base station device 200 may be installed temporarily, for example, for the period during which underwater surveys are conducted using the terminal device 100.

[0053] The terminal device 100 is underwater. The terminal device 100 is performing visible light communication (specifically, underwater visible light communication) with the base station device 200A. That is, the base station device 200A is the serving base station for the terminal device 100. The terminal device 100 transmits uplink data to the base station device 200A by visible light communication. The terminal device 100 also receives downlink data from the base station device 200A by visible light communication. The terminal device 100 is configured to be able to move underwater. The terminal device 100 moving underwater performs visible light communication with the base station device 200 located above (including diagonally above) itself.

[0054] In the first embodiment, in such a visible light communication system 1, it is possible for a mobile terminal device 100 to perform handover between base station devices 200. As shown in Fig. 2 , the terminal device 100 moves closer to the base station device 200B while performing visible light communication with the base station device 200A. In this case, the base station device 200A determines the base station device 200B as a target base station for handover based on the reported visible light signal from the terminal device 100, and controls the base station device 200B to perform handover of the terminal device 100. As a result, as shown in Fig. 3 , the terminal device 100 establishes visible light communication with the base station device 200B and performs visible light communication with the base station device 200B.

[0055] Each base station device 200 transmits a pilot visible light signal including a pilot signal sequence different from the pilot signal sequence used by adjacent base station devices 200. The pilot visible light signal is a visible light signal used by the terminal device 100 to discover the base station device 200, synchronize with the base station device 200, and measure the base station device 200. The pilot visible light signal may include a synchronization visible light signal and a reference visible light signal. The synchronization visible light signal is a visible light signal used by the terminal device 100 to discover and synchronize with the base station device 200. The synchronization visible light signal may be configured to be able to identify the identifier (ID) of the base station device 200 that is the transmission source. The reference visible light signal is a visible light signal used by the terminal device 100 to measure the base station device 200.

[0056] (2.2) Configuration of the Terminal Device FIG. 4 is a diagram showing the configuration of the terminal device 100 according to the first embodiment. The terminal device 100 has a plurality of visible light communication units 10 (10_1, 10_2, ...) and a control unit 110. The terminal device 100 may have a sensor 120. The terminal device 100 may have a movement mechanism (e.g., a motor and a screw) used to move the terminal device 100. The terminal device 100 may have a battery for supplying power necessary for the operation of the terminal device 100.

[0057] The multiple visible light communication units 10 each have directivity in a different direction. That is, the multiple visible light communication units 10 each transmit visible light signals in a different direction and receive visible light signals from a different direction. Each visible light communication unit 10 has at least one light-emitting element 101, at least one light-receiving element 102, and a transceiver 103. For example, visible light communication unit 10_1 has at least one light-emitting element 101_1, at least one light-receiving element 102_1, and a transceiver 103_1.

[0058] The light emitting element 101 may be a laser diode or a light emitting diode. The light emitting element 101 converts an electrical signal (transmission signal) output by the transceiver 103 for visible light communication into a visible light signal and transmits the visible light signal.

[0059] The light receiving element 102 may be a photodiode. The light receiving element 102 receives a visible light signal, converts the received visible light signal into an electrical signal (received signal), and outputs the received signal to the transceiver 103.

[0060] The transceiver 103 may be a field-programmable gate array (FPGA) and / or a system on a chip (SoC). The transceiver 103 includes a transmitter that performs signal processing on a transmission signal output by the control unit 110 and converts the processed signal. The transceiver 103 includes a receiver that converts a reception signal output by the light receiving element 102, performs signal processing on the converted reception signal, and outputs the signal to the control unit 110.

[0061] In this way, since multiple visible light communication units 10 each have directivity in different directions and each visible light communication unit 10 is equipped with an independent transceiver 103, the terminal device 100 can simultaneously perform visible light communication in various directions.

[0062] The control unit 110 controls the overall operation of the terminal device 100. For example, the control unit 110 controls each visible light communication unit 10. The control unit 110 includes at least one processor 111 and at least one memory 112. The memory 112 stores programs executed by the processor 111 and information used in processing by the processor 111. The processor 111 may include a digital signal processor and a CPU (Central Processing Unit). The digital signal processor performs modulation / demodulation and encoding / decoding of digital signals. The CPU executes programs stored in the memory to perform various processes.

[0063] The sensor 120 detects parameters indicating the state of the terminal device 100 (for example, the attitude and / or the movement speed of the terminal device 100) and outputs the detection result to the control unit 110. The sensor 120 may include an acceleration sensor and / or a gyro sensor.

[0064] The terminal device 100 configured in this manner includes a plurality of visible light communication units 10, including a visible light communication unit 10_1 and a visible light communication unit 10_2, and a control unit 110 that controls the plurality of visible light communication units 10. The plurality of visible light communication units 10 each have directivity in a different direction. In the first embodiment, the control unit 110 performs switching control so that the visible light communication unit 10_1 switches from a state in which it performs visible light communication with the base station device 200A to a state in which it performs visible light communication with the base station device 200B. This enables handover of the terminal device 100 from the base station device 200A to the base station device 200B.

[0065] When visible light communication unit 10_1 is performing visible light communication with base station device 200A, control unit 110 performs measurement processing on pilot visible light signals received by multiple visible light communication units 10 from each base station device 200. For example, control unit 110 controls visible light communication units 10 to measure the received signal strength (i.e., pilot received power) of the pilot visible light signal. Control unit 110 manages the measurement results for the pilot visible light signals in association with the ID of base station device 200 that is the source of the pilot visible light signal. Here, control unit 110 may perform measurement processing in response to a trigger condition set by base station device 200A being satisfied or in response to detection of movement of terminal device 100.

[0066] The control unit 110 generates association information that associates a visible light communication unit 10 that has received a pilot visible light signal with a base station device 200 that transmitted the pilot visible light signal. Fig. 5 is a diagram showing an example of the association information. The association information is information that associates a visible light communication unit 10 with a base station device 200. In the example of Fig. 5, visible light communication unit 10_1 is associated with ID "#1" of base station device 200A, visible light communication unit 10_2 is associated with ID "#2" of base station device 200B, and visible light communication unit 10_3 is associated with ID "#3" of base station device 200C.

[0067] The control unit 110 controls the visible light communication unit 10_1 to transmit to the base station device 200A a report visible light signal including a measurement result for the pilot visible light signal of each base station device 200. Here, the control unit 110 may control the visible light communication unit 10_1 to transmit to the base station device 200A the report visible light signal in response to the measurement result satisfying a threshold condition or periodically. The report visible light signal may be referred to as an optical reception intensity measurement report.

[0068] The multiple visible light communication units 10 may receive an alert visible light signal from each base station device 200. The alert visible light signal includes information indicating at least one of the attitude (tilt) and shaking (i.e., the base station state) of the base station device 200 that is the source of the alert visible light signal. The control unit 110 corrects the measurement result (pilot reception power) according to the information included in the alert visible light signal.

[0069] For example, if each base station device 200 is shaking, it is expected that the propagation environment between each base station device 200 and the terminal device 100 will fluctuate significantly. Therefore, when measuring the optical reception intensity from each base station device 200, the control unit 110 takes into account the base station state (posture, whether there is shaking, etc.) of each base station device 200 and corrects the measurement result. For example, the optical reception intensity observed over a period roughly equivalent to the shaking cycle of the base station device 200 is averaged and treated as one sample, and the result of taking a weighted average with samples from a certain past period is reported to the base station device 200A.

[0070] The control unit 110 may further include, in the report visible light signal, information indicating whether a visible light communication unit 10 associated with a base station device 200 other than base station device 200A is the same as visible light communication unit 10_1. FIG. 6 is a diagram showing an example of the format of the report visible light signal. In the example of FIG. 6, the report visible light signal includes, for each measured base station device 200, the ID of that base station device 200, a measurement result for the pilot visible light signal of that base station device 200, and information indicating whether that base station device 200 is associated with a visible light communication unit 10 different from the visible light communication unit 10 (in this example, visible light communication unit 10_1) used for communication with the serving base station (hereinafter referred to as "simultaneous communication availability information").

[0071] Here, when the base station device 200 is associated with a visible light communication unit 10 different from the visible light communication unit 10 (in this example, the visible light communication unit 10_1) used for communication with the serving base station, the terminal device 100 can simultaneously perform visible light communication with the serving base station and visible light communication with the base station device 200, thereby enabling smooth handover to the base station device 200. The simultaneous communication availability information may be preference information indicating a base station device 200 with which the terminal device 100 can simultaneously communicate as the base station device 200 desired as the target base station for handover.

[0072] The control unit 110 may further include information (movement information) indicating the movement state of the terminal device 100 in the report visible light signal. This makes it easier for the serving base station to perform handover at appropriate timing, taking into account the movement state of the terminal device 100. The control unit 110 may determine the movement state of the terminal device 100 according to the reception status of the pilot visible light signals at the multiple visible light communication units 10. For example, the control unit 110 may determine that the terminal device 100 is moving when the light receiving element 102 with the highest optical reception intensity changes within a short period of time.

[0073] For example, for a terminal device 100 that can be determined to be moving at a speed equal to or greater than a certain threshold, it is preferable to initiate handover at an earlier stage than usual. Therefore, when the terminal device 100 is moving in a generally constant direction at a speed equal to or greater than the threshold, the control unit 110 adds movement information of the terminal device 100 to the optical reception intensity measurement report. The movement information may be a value indicating the movement speed of the terminal device 100. Alternatively, the movement information may be an index indicating the degree of the movement speed of the terminal device 100 (e.g., low speed, medium speed, high speed). Alternatively, the movement information may be flag information indicating that the terminal device 100 is moving (particularly, moving).

[0074] The control unit 110 may determine the movement state of the terminal device 100 using at least one of the number of handovers within a predetermined time period and the detection results of the sensor 120 (e.g., an inertial sensor such as an acceleration sensor). In addition to these determination indicators, the control unit 110 may determine the movement state of the terminal device 100 based on the reception status of pilot visible light signals at multiple visible light communication units 10. For example, when the base station device 200 is shaking and / or the terminal device 100 is shaking or rotating, it is preferable to determine the movement state based on multiple indicators rather than a single indicator. For example, when the terminal device 100 performs measurements taking into account the shaking of the base station device 200 in addition to the number of handovers and inertial sensor information, if the light receiving element with the highest optical reception intensity in the measurement sample changes within a short period of time, it can be determined that the terminal device 100 is moving in the direction in which the light receiving element with the highest optical reception intensity has changed.

[0075] In the first embodiment, visible light communication unit 10_1 receives an instruction visible light signal including a handover command specifying base station device 200B, which is the target base station for handover, from base station device 200A, which is the serving base station. In response to receiving the instruction visible light signal, control unit 110 selects a visible light communication unit 10 associated with base station device 200B based on the association information (see FIG. 5 ) and establishes communication with base station device 200B using the selected visible light communication unit 10 (visible light communication unit 10_2 in this example). This enables terminal device 100 to perform visible light communication with base station device 200B using an appropriate visible light communication unit 10 (visible light communication unit 10_2 in this example) after handover.

[0076] 7 is a diagram showing an example of the external configuration of the terminal device 100 according to the first embodiment. The terminal device 100 has a hemispherical light-emitting and receiving unit 150 and a main body 160 connected to the light-emitting and receiving unit 150. The light-emitting and receiving unit 150 has a plurality of light-emitting and receiving areas 151 that are dispersedly arranged. Each light-emitting and receiving area 151 is provided with a set of one light-emitting element 101 and one light-receiving element 102.

[0077] 7, the hemispherical light-emitting and receiving unit 150 has a total of seven light-emitting and receiving areas 151, 151#0 to 151#6. For example, the group of light-emitting and receiving areas 151#0 to 151#2 constitutes part of the visible light communication unit 10_1. The group of light-emitting and receiving areas 151#3 and 151#4 constitutes part of the visible light communication unit 10_2. The group of light-emitting and receiving areas 151#5 and 151#6 constitutes part of the visible light communication unit 10_3.

[0078] (2.3) Configuration of Base Station Device FIG. 8 is a diagram showing the configuration of the base station device 200 according to the first embodiment. The base station device 200 includes a plurality of visible light communication units 20 (20_1, 20_2, ...), a control unit 210, and a backhaul communication unit 220. The base station device 200 may include a sensor 230 and a GNSS (Global Navigation Satellite System) positioning unit 240. The base station device 200 may include a battery for supplying power necessary for the operation of the base station device 200.

[0079] The multiple visible light communication units 20 each have directivity in a different direction. That is, the multiple visible light communication units 20 each transmit visible light signals in a different direction and receive visible light signals from a different direction. Each visible light communication unit 20 has at least one light-emitting element 201, at least one light-receiving element 202, and a transceiver 203. For example, visible light communication unit 20_1 has at least one light-emitting element 201_1, at least one light-receiving element 202_1, and a transceiver 203_1.

[0080] The light emitting element 201 may be a laser diode or a light emitting diode. The light emitting element 201 converts an electrical signal (transmission signal) output by the transceiver 203 for visible light communication into a visible light signal, and transmits the visible light signal.

[0081] The light receiving element 202 may be a photodiode. The light receiving element 202 receives a visible light signal, converts the received visible light signal into an electrical signal (received signal), and outputs the received signal to the transceiver 203.

[0082] The transceiver 203 may be an FPGA and / or an SoC. The transceiver 203 includes a transmitter that performs signal processing on a transmission signal output by the control unit 210 and converts the processed signal. The transceiver 203 includes a receiver that converts a reception signal output by the light receiving element 202, performs signal processing on the converted reception signal, and outputs the signal to the control unit 210.

[0083] In this way, since multiple visible light communication units 20 each have directivity in a different direction and each visible light communication unit 20 is equipped with an independent transceiver 203, the base station device 200 can simultaneously perform visible light communication in various directions.

[0084] The control unit 210 controls the overall operation of the base station device 200. For example, the control unit 210 controls each visible light communication unit 20. The control unit 210 includes at least one processor 211 and at least one memory 212. The memory 212 stores programs executed by the processor 211 and information used in processing by the processor 211. The processor 211 may include a digital signal processor and a CPU. The digital signal processor performs modulation / demodulation and encoding / decoding of digital signals. The CPU executes programs stored in the memory to perform various processes.

[0085] The backhaul communication unit 220 performs backhaul communication via a backhaul line under the control of the control unit 210. The backhaul communication unit 220 may include a network communication unit 221 that performs communication with a network (e.g., a core network) and an inter-base station communication unit 222 that performs inter-base station communication with adjacent base stations.

[0086] The sensor 230 detects parameters indicating the state of the base station device 200 (for example, the attitude and / or shaking of the base station device 200) and outputs the detection result to the control unit 210. The sensor 230 may include an acceleration sensor and / or a gyro sensor.

[0087] The GNSS positioning unit 240 performs positioning by receiving satellite signals from positioning satellites, acquires position information (coordinate information) indicating the position of the base station device 200 , and outputs the position information to the control unit 210 .

[0088] In the base station device 200 configured in this manner, the control unit 210 controls each visible light communication unit 20 to transmit a pilot visible light signal. The pilot visible light signal is a visible light signal including a pilot signal sequence. The control unit 210 includes in the pilot visible light signal of the base station device 200 a pilot signal sequence that is different from the pilot signal sequences used by neighboring base station devices 200. This allows the terminal device 100 to distinguish each base station device 200 from other base station devices 200 based on the pilot signal sequence.

[0089] For example, the control unit 210 acquires a pilot signal sequence to be used in the base station device 200 from the network using the backhaul communication unit 220. The control unit 210 may acquire the pilot signal sequence from the network when the base station device 200 is installed. At this time, the network assigns a pilot signal sequence to the base station device 200 that is different from that of neighboring base stations, based on coordinate information of the base station device 200 at the time of installation.

[0090] The control unit 210 may determine the pilot signal sequence to be used by the base station device 200 based on location information (coordinate information) indicating the location of the base station device 200. For example, when GNSS location information is used, the control unit 210 determines the pilot signal sequence based on a value to the fourth or fifth decimal point that represents an accuracy of 1 to 10 meters. However, if the installation intervals between the base station devices 200 are short, the same pilot signal sequence may be determined between adjacent base stations. Therefore, the pilot signal sequence may be determined based on time information indicating the timing when the base station device 200 was installed (for example, time information when the power was turned on) in addition to the location information.

[0091] The control unit 210 may acquire pilot signal sequences used by other base station devices 200 from terminal devices 100 connected to the base station device 200, and may determine a pilot signal sequence to be used by the base station device 200 based on the pilot signal sequence acquired from the terminal device 100. For example, in response to an instruction (request) from the base station device 200, the terminal device 100 reports the pilot signal sequence of each pilot visible light signal received by the terminal device 100 to the base station device 200. The control unit 210 may determine a pilot signal sequence different from the pilot signal sequence reported from the terminal device 100 as the pilot signal sequence to be used by the base station device 200.

[0092] Furthermore, the control unit 210 may control each visible light communication unit 20 to transmit an alarm visible light signal. The alarm visible light signal includes information indicating at least one of the attitude (tilt) and shaking (i.e., the base station state) of the base station device 200. The control unit 210 can generate such information on the base station state based on the detection result of the sensor 230.

[0093] One of the visible light communication units 20 receives from the terminal device 100 a report visible light signal (optical reception intensity measurement report) including measurement results for the pilot visible light signal of each base station device 200. The report visible light signal may include the simultaneous communication availability information described above. Based on the report visible light signal, the control unit 210 may preferentially select another base station device 200 with which the terminal device 100 can simultaneously communicate as a target base station device for handover. The report visible light signal may include the movement information described above. Based on the movement information, the control unit 210 may determine a handover at a timing appropriate for the movement state of the terminal device 100. For example, the control unit 210 may initiate a handover earlier than usual for a terminal device 100 that is determined to be moving at a speed equal to or greater than a certain threshold. The control unit 210 controls the visible light communication unit 20 to transmit to the terminal device 100 an instruction visible light signal including a handover command specifying the base station device 200B, which is the target base station.

[0094] FIG. 9 is a diagram illustrating an example of the external configuration of a base station device 200 according to the first embodiment. The base station device 200 includes a hemispherical light-emitting and receiving unit 250 and a main body 260 connected to the light-emitting and receiving unit 250. The light-emitting and receiving unit 250 includes a plurality of light-emitting and receiving areas 251 that are dispersedly arranged. Each light-emitting and receiving area 251 includes a set of one light-emitting element 201 and one light-receiving element 202. In the example of FIG. 9, the hemispherical light-emitting and receiving unit 250 includes a total of 19 light-emitting and receiving areas 251, ie, light-emitting and receiving areas 251#0 to 251#18. Each group of two or three adjacent light-emitting and receiving areas 251 constitutes a part of one visible light communication unit 20.

[0095] (2.4) Example of Operation of Visible Light Communication System FIG. 10 is a diagram showing an example of operation of the visible light communication system 1 according to the first embodiment.

[0096] In step S100, the terminal device 100 performs visible light communication with the base station device 200A, which is the serving base station, and transmits and receives data to and from the base station device 200A.

[0097] In step S101, the base station device 200A may transmit a configuration visible light signal including measurement configuration information to the terminal device 100. The measurement configuration information includes various configuration parameters related to measurements in the terminal device 100 and reporting of measurement results to the base station device 200A. For example, the measurement configuration information includes at least one of a parameter for setting a measurement trigger, a parameter for setting a measurement period, a parameter for setting visible light to be measured (color of visible light), and a parameter for setting a measurement report trigger.

[0098] Here, the measurement trigger is a trigger for starting measurement of the pilot signal strength in synchronization with the base station device 200, and the terminal device 100 starts receiving light in all directions when a measurement trigger condition is satisfied. For example, the measurement trigger may be when the reception strength of the serving base station (base station device 200A) falls below a threshold. The measurement trigger may be determined by the terminal device 100. For example, the terminal device 100 may start the measurement process in response to detecting that it is moving in a specific direction based on the detection result of the sensor 120 and / or the reception state of the pilot visible light signal in the visible light communication unit 10 used for visible light communication.

[0099] In step S102, base station device 200B transmits a pilot visible light signal, in step S103, base station device 200C transmits a pilot visible light signal, and in step S104, base station device 200A transmits a pilot visible light signal.

[0100] In step S105, the terminal device 100 receives pilot visible light signals from each of the base station devices 200A to 200C, and performs measurement processing (reception intensity measurement) on each pilot visible light signal.

[0101] In step S106, the terminal device 100 generates association information that associates the visible light communication unit 10 that received the pilot visible light signal with the base station device 200 that transmitted the pilot visible light signal.

[0102] In step S107, base station device 200B may transmit an advisory visible light signal. In step S108, base station device 200C may transmit an advisory visible light signal. In step S109, base station device 200A may transmit an advisory visible light signal.

[0103] In step S110, the terminal device 100 receives an alarm visible light signal from each of the base station devices 200A to 200C, acquires base station status information contained in each alarm visible light signal, and may correct the reception strength measurement of each base station device 200 based on the acquired base station status information.

[0104] In step S111, the terminal device 100 may acquire movement information indicating its own movement state.

[0105] In step S112, the terminal device 100 transmits a report visible light signal including the pilot reception strength of each base station device 200 to the base station device 200A. The terminal device 100 may transmit movement information by including it in the report visible light signal. Here, the terminal device 100 may transmit the report visible light signal to the base station device 200A when at least one of the pilot reception strength of the serving base station (base station device 200A) and the pilot reception strength of the neighboring base stations (base station device 200B, base station device 200C) satisfies a threshold condition. The threshold may be set in the terminal device 100 by the serving base station (base station device 200A). Alternatively, the terminal device 100 may determine the threshold.

[0106] In step S113, the base station device 200A makes a handover determination based on the reported visible light signal from the terminal device 100. Here, the description will continue assuming that the base station device 200A has determined the base station device 200B as the target base station.

[0107] In steps S114 and S115, the base station device 200A may perform communication for handover preparation with the base station device 200B via backhaul communication. For example, in step S114, the base station device 200A may transmit a handover request including information about the terminal device 100 to the base station device 200B. In step S115, the base station device 200B may transmit an acknowledgement notification (ACK) in response to the handover request to the base station device 200A.

[0108] In step S116, the base station device 200A transmits to the terminal device 100 an instruction visible light signal including a handover command specifying the base station device 200B.

[0109] In step S117, the terminal device 100 may transmit an acknowledgement notice for the instruction visible light signal to the base station device 200A. In step S118, the base station device 200A may transmit, via backhaul communication, a completion notice indicating that handover preparation has been completed to the base station device 200B.

[0110] In step S119, the terminal device 100 selects the visible light communication unit 10 associated with the base station device 200B, which is the target base station, based on the association information, and establishes communication with the base station device 200B.

[0111] In step S120, the base station device 200B may transmit an instruction visible light signal to the terminal device 100 to instruct it to transmit an uplink.

[0112] In step S121, the terminal device 100 transmits and receives data to and from the base station device 200B through visible light communication. The terminal device 100 may terminate the visible light communication with the base station device 200A. Alternatively, the terminal device 100 may continue the visible light communication with the base station device 200A and perform simultaneous communication (multiple base station communication) with the base station devices 200A and 200B. Details of the operation of performing multiple base station communication will be described in the second embodiment.

[0113] (2.5) Modification of the First Embodiment Next, a modification of the first embodiment will be described. As shown in Fig. 11 , when the terminal device 100 rotates in water, it is necessary to update the correspondence between the visible light communication unit 10 of the terminal device 100 and the base station device 200. In this modification, the control unit 110 of the terminal device 100 updates the correspondence information in response to detection of rotation of the terminal device 100.

[0114] The terminal device 100 includes a sensor 120 for generating attitude information of the terminal device 100. The control unit 110 of the terminal device 100 updates the association information based on the attitude information. For example, as shown in FIG. 12 , assume that before the terminal device 100 rotates, the light receiving and emitting area 151#1 of the terminal device 100 receives a pilot visible light signal from the base station device 200#1, and the visible light communication unit 10_1 to which the light receiving and emitting area 151#1 belongs is associated with the base station device 200#1. The control unit 110 of the terminal device 100 detects its own rotation amount φ from the detection result (attitude information) of the sensor 120, and updates the association information based on the rotation amount φ. As a result, after the terminal device 100 rotates, the visible light communication unit 10_3 to which the light receiving and emitting area 151#5 belongs is associated with the base station device 200#1.

[0115] Alternatively, the control unit 110 of the terminal device 100 may re-execute the measurement process of the pilot visible light signal in response to the detection of rotation (and / or a change in attitude information) and update the association information in response to the result of the re-executed measurement process. That is, the terminal device 100 receives pilot visible light signals from each base station device 200 and updates the association information so as to associate the visible light communication unit 10 that received the pilot visible light signal with the base station device 200 that transmitted the pilot visible light signal. When the terminal device 100 continuously rotates, the control unit 110 of the terminal device 100 may shorten the measurement period for the pilot visible light signal from the reference period.

[0116] This modified example can also be applied to the second embodiment described later.

[0117] (3) Second Embodiment Next, the second embodiment will be described, focusing on the differences from the first embodiment and its modifications. The configurations of the visible light communication system 1, the terminal device 100, and the base station device 200 according to the second embodiment are the same as those of the first embodiment.

[0118] In the second embodiment, as shown in FIG. 13 , the terminal device 100 is capable of simultaneous communication with a plurality of base station devices 200 (base station devices 200A and 200B) (i.e., multiple base station communication). As shown in FIG. 4 , the terminal device 100 according to the second embodiment includes a plurality of visible light communication units 10, each including a visible light communication unit 10_1 and a visible light communication unit 10_2, and a control unit 110 that controls the plurality of visible light communication units 10. The plurality of visible light communication units 10 each have directivity in a different direction. The control unit 110 performs simultaneous communication control such that the visible light communication unit 10_1 performs visible light communication with the base station device 200A, while the visible light communication unit 10_2 performs visible light communication with the base station device 200B. This enables the terminal device 100 to perform simultaneous communication with the base station device 200A and the base station device 200B (multiple base station communication).

[0119] Such multi-base station communication may be performed when handing over the terminal device 100 from the base station device 200A to the base station device 200B. For example, the terminal device 100 located at the edge of the communication area of ​​the base station device 200A performs multi-base station communication, and maintains communication connections with both the base station devices 200A and 200B until it is determined that the terminal device 100 has completely moved under the control of the base station device 200B, which is the handover destination. This minimizes the possibility of communication interruptions and improves communication quality. In the following second embodiment, multi-base station communication in the uplink will be mainly described, but multi-base station communication in the downlink may also be performed.

[0120] In the second embodiment, the control unit 110 of the terminal device 100 includes, in the report visible light signal, information indicating whether or not simultaneous communication is possible while the terminal device 100 is communicating with the visible light communication unit 10_1 for each base station device 200 other than the base station device 200A (simultaneous communication possibility information) (see FIG. 6 ). This enables the base station device 200A communicating with the terminal device 100 to appropriately determine other base station devices 200 available for multi-base station communication.

[0121] In the second embodiment, the control unit 110 of the terminal device 100 includes in the report visible light signal movement information indicating the movement state of the terminal device 100. If the terminal device 100 is stationary or moving at a low speed, it is preferable to continue the multi-base station communication even after handover, but if the terminal device 100 is moving at a speed equal to or greater than a certain threshold, it is preferable to terminate the multi-base station communication at the time of handover. Including the movement state in the report visible light signal allows the base station device 200A to make such a determination appropriately.

[0122] In the second embodiment, visible light communication unit 10_1 of terminal device 100 receives from base station device 200A an instruction visible light signal including a communication instruction specifying base station device 200B. In response to receiving the instruction visible light signal, control unit 110 of terminal device 100 selects a visible light communication unit 10 associated with base station device 200B based on the association information (see FIG. 5 ), and establishes communication with base station device 200B using the selected visible light communication unit 10. This enables terminal device 100 to communicate with multiple base stations using an appropriate visible light communication unit 10.

[0123] In the second embodiment, the instruction visible light signal may include a communication instruction instructing terminal device 100 to transmit the same information to base station device 200B as the information transmitted from terminal device 100 to base station device 200A. In response to receiving the instruction visible light signal, control unit 110 of terminal device 100 controls visible light communication unit 10_1 and visible light communication unit 10_2 to transmit the same information to base station device 200A and base station device 200B. This makes it possible to provide redundancy to the transmitted information, thereby improving communication quality.

[0124] Alternatively, the instruction visible light signal may include a communication instruction instructing terminal device 100 to transmit information different from the information transmitted from terminal device 100 to base station device 200A to base station device 200B. In response to receiving the instruction visible light signal, control unit 110 of terminal device 100 controls visible light communication unit 10_1 and visible light communication unit 10_2 to transmit different information to base station device 200A and base station device 200B. This enables simultaneous transmission of two information streams, thereby improving communication speed. Furthermore, since the coding rate for achieving a desired throughput can be lowered, error correction capability can also be improved.

[0125] In the second embodiment, the base station device 200B transfers to the base station device 200A information that the base station device 200B receives from the terminal device 100. The base station device 200A performs a synthesis process on the information that the base station device 200A receives from the terminal device 100 and the information that the base station device 200A receives from the base station device 200B. This makes it possible to synthesize information transmitted to separate base station devices 200 at a single base station device 200.

[0126] 14 and 15 are diagrams showing a specific example of the combining process (buffer combining process) in the base station device 200 A. Fig. 14 shows the operation when the terminal device 100 transmits the same information (the same data packet) to the base station device 200 A and the base station device 200 B.

[0127] 14, the buffer of the base station device 200A is empty in STEP 1. For example, the buffer is a layer 2 (L2) buffer.

[0128] In STEP 2, the base station device 200A receives a data packet (SN1) addressed to itself from the terminal device 100. Here, SN means the sequence number of the data packet. Since the data packet of SN1 is the first data packet and does not require packet order control, the base station device 200A passes the data packet of SN1 in the buffer to a higher layer.

[0129] In STEP 3, the base station device 200A receives from the base station device 200B a data packet (SN1) addressed to the base station device 200B from the terminal device 100. Because the data packet of SN1 has already been received, the base station device 200A discards the data packet of SN1 received from the base station device 200B.

[0130] In STEP 4, the base station device 200A receives a data packet (SN3) addressed to itself from the terminal device 100. It is assumed that the data packet of SN2 from the terminal device 100 to the base station device 200A is delayed, for example, in a lower layer. Because the base station device 200A has not yet received the data packet of SN2, it holds the data packet of SN3 in a buffer and waits for the arrival of the data packet of SN2.

[0131] In STEP 5, the base station device 200A receives from the base station device 200B a data packet (SN2) addressed to the base station device 200B from the terminal device 100. The base station device 200A stores the data packet of SN2 in SN order.

[0132] In STEP 6, the base station device 200A receives a data packet (SN2) addressed to itself from the terminal device 100. Because the data packet of SN2 has already been received, the base station device 200A discards the data packet of SN2. The base station device 200A passes the received data packet of SN2 and the data packet of SN3 to an upper layer.

[0133] 15 shows the operation when the terminal device 100 transmits different information (different data packets) to the base station device 200A and the base station device 200B. For example, the terminal device 100 transmits data packets with odd-numbered SNs to the base station device 200A and transmits data packets with even-numbered SNs to the base station device 200B.

[0134] 15, the buffer of the base station device 200A is empty in STEP 1. For example, the buffer is a layer 2 (L2) buffer.

[0135] In STEP 2, the base station device 200A receives a data packet (SN1) addressed to itself from the terminal device 100. Since the data packet of SN1 is the first data packet and does not require packet order control, the base station device 200A passes the data packet of SN1 in the buffer to an upper layer.

[0136] In STEP 3, the base station device 200A receives a data packet (SN3) addressed to itself from the terminal device 100. It is assumed that the data packet of SN2 from the terminal device 100 has been delayed in a lower layer of the base station device 200B, for example. Because the base station device 200A has not yet received the data packet of SN2, it holds the data packet of SN3 in a buffer and waits for the arrival of the data packet of SN2.

[0137] In STEP 4, the base station device 200A receives from the base station device 200B a data packet (SN4) addressed to the base station device 200B from the terminal device 100. The base station device 200A also receives a data packet (SN5) addressed to itself from the terminal device 100. However, because the base station device 200A has not yet received the data packet of SN2, it holds the data packet of SN4 and the data packet of SN5 in a buffer and waits for the arrival of the data packet of SN2.

[0138] In STEP 5, the base station device 200A receives from the base station device 200B a data packet (SN2) addressed to the base station device 200B from the terminal device 100. The base station device 200A also receives a data packet (SN7) addressed to itself from the terminal device 100. The base station device 200A stores the data packet of SN2 in SN order.

[0139] In STEP 6, the base station device 200A passes each of the data packets SN2 to SN5 to an upper layer.

[0140] In this way, in uplink multi-base station communication, buffer combining processing is performed by the base station device 200 A. In downlink multi-base station communication, the terminal device 100 receives the same or different data packets from the base station devices 200 A and 200 A, and performs buffer combining processing in the terminal device 100.

[0141] FIG. 16 is a diagram showing an example of the operation of the visible light communication system 1 according to the second embodiment.

[0142] As shown in FIG. 16, the operations from steps S100 to S112 are the same as those in the first embodiment.

[0143] In step S200, base station device 200A determines whether to perform multi-base station communication based on the reported visible light signal from terminal device 100. For example, base station device 200A identifies other base station devices 200 that can be used for multi-base station communication based on simultaneous communication availability information included in the reported visible light signal. Here, the description will continue assuming that base station device 200A has determined base station device 200B as the target base station for the multi-base station communication.

[0144] In step S201, the base station device 200A transmits a multi-base station communication request including information about the terminal device 100 to the base station device 200B via backhaul communication.

[0145] In step S202, the base station device 200B transmits an acknowledgement notification (ACK) in response to the multi-base station communication request to the base station device 200A.

[0146] In step S203, base station device 200A transmits to terminal device 100 an instruction visible light signal including a multi-base station communication instruction specifying base station device 200B.

[0147] In step S204, the terminal device 100 may transmit an acknowledgement notice for the indication visible light signal to the base station device 200A.

[0148] In step S205, the base station device 200A may transmit an instruction visible light signal to the terminal device 100 to instruct the terminal device 100 to perform uplink transmission.

[0149] In step S206, the terminal device 100 selects, based on the association information, the visible light communication unit 10 associated with the base station device 200B, which is the target base station for the multi-base station communication, and establishes communication with the base station device 200B.

[0150] In steps S207 and S208, the terminal device 100 transmits data (the same data or different data) to the base station devices 200A and 200B by visible light communication.

[0151] In step S209, the base station device 200B transfers the data received from the terminal device 100 to the base station device 200A via backhaul communication.

[0152] In step S210, the base station device 200A performs a synthesis process on the data received from the terminal device 100 and the data received from the base station device 200B.

[0153] (3.1) Modification of the Second Embodiment Next, a modification of the second embodiment will be described, focusing on the differences from the second embodiment. In this modification, multi-base station communication is performed during handover and terminated after the handover is completed. In addition, the combining process is performed on the base station device 200B side.

[0154] 17 and 18 are diagrams showing an example of the operation of the visible light communication system 1 according to the modified example of the second embodiment.

[0155] As shown in FIG. 17, the operations from steps S100 to S112 are the same as those in the first embodiment.

[0156] In step S300, the base station device 200A determines whether to perform handover and multi-base station communication based on the reported visible light signal from the terminal device 100. Here, the explanation will be continued assuming that the base station device 200A has determined the base station device 200B as the target base station for handover and multi-base station communication.

[0157] In step S301, the base station device 200A transmits, via backhaul communication, to the base station device 200B, a request message including information about the terminal device 100. The request message includes a handover request and a multi-base station communication request.

[0158] In step S302, the base station device 200B transmits an acknowledgement (ACK) to the base station device 200A in response to the request message.

[0159] In step S303, base station device 200A transmits an instruction visible light signal specifying base station device 200B to terminal device 100. The instruction visible light signal includes a handover command and a multi-base station communication instruction.

[0160] In step S304, the terminal device 100 may transmit an acknowledgement notice for the indication visible light signal to the base station device 200A.

[0161] In step S305, the base station device 200A may transmit a completion notification indicating completion of preparation for handover to the base station device 200B via backhaul communication.

[0162] In step S306, based on the association information, the terminal device 100 selects the visible light communication unit 10 associated with the base station device 200B, which is the target base station for handover and multi-base station communication, and establishes communication with the base station device 200B.

[0163] In step S307, the base station device 200B may transmit an instruction visible light signal to the terminal device 100 to instruct it to transmit an uplink.

[0164] In steps S308 and S309, the terminal device 100 transmits data (the same data or different data) to the base station devices 200A and 200B by visible light communication.

[0165] In step S310, the base station device 200A transfers the data received from the terminal device 100 to the base station device 200B via backhaul communication.

[0166] In step S311, the base station device 200B performs a synthesis process on the data received from the terminal device 100 and the data received from the base station device 200A.

[0167] Thereafter, as shown in FIG. 18, in steps S320 and S321, the terminal device 100 performs multi-base station communication with the base station devices 200A and 200B, and transmits and receives data to and from the base station devices 200A and 200B.

[0168] In step S322, the base station device 200B transmits a pilot visible light signal.In step S323, the base station device 200A transmits a pilot visible light signal.

[0169] In step S324, the terminal device 100 receives pilot visible light signals from each of the base station devices 200A and 200B, and performs measurement processing (reception intensity measurement) on each pilot visible light signal.

[0170] In step S325, the base station device 200B may transmit a notice visible light signal.In step S326, the base station device 200A may transmit a notice visible light signal.

[0171] In step S327, the terminal device 100 may receive an alarm visible light signal from each of the base station devices 200A and 200B, acquire base station status information contained in each alarm visible light signal, and correct the reception strength measurement of each base station device 200 based on the acquired base station status information.

[0172] In step S328, the terminal device 100 may acquire movement information indicating its own movement state.

[0173] In step S329, the terminal device 100 transmits, to the base station device 200B, a report visible light signal including the pilot reception intensity of each base station device 200. The terminal device 100 may transmit movement information included in the report visible light signal.

[0174] In step S330, base station device 200B determines whether to terminate the multi-base station communication based on the reported visible light signal from terminal device 100. Here, the description will continue assuming that base station device 200B determines to terminate the multi-base station communication.

[0175] In step S331, the base station device 200B transmits a notification of the end of the multi-base station communication to the base station device 200A via backhaul communication.

[0176] In step S332, the base station device 200A transmits an acknowledgement notification in response to the notification of the end of the multi-base station communication to the base station device 200B via backhaul communication.

[0177] In step S333, the base station device 200B transmits an instruction to end the multi-base station communication to the terminal device 100.

[0178] In step S334, the terminal device 100 transmits an acknowledgement notification for the instruction to terminate the multi-base station communication to the base station device 200B.

[0179] (4) Other Embodiments In the above-described embodiment, an example has been described in which each base station device 200 is installed on the water surface. However, each base station device 200 may be installed on the bottom of the water as shown in FIG. 19 . A terminal device 100 moving underwater performs visible light communication with a base station device 200 located below it. Alternatively, each base station device 200 may be installed on a wall surface underwater as shown in FIG. 20 . The terminal device 100 performs visible light communication with the base station device 200 while moving vertically underwater.

[0180] In the above-described embodiment, an example has been described in which the light-emitting and receiving unit 150 of the terminal device 100 and the light-emitting and receiving unit 250 of the base station device 200 are configured in a hemispherical shape. However, the terminal device 100 may be configured as a sphere as a whole, as shown in FIG. 21 . For example, the terminal device 100 may be configured as a polyhedron, and each face of the polyhedron (or a region consisting of multiple adjacent faces) may constitute the visible light communication unit 10. The base station device 200 may also be configured as a sphere as a whole. Alternatively, the terminal device 100 may be configured as a rod as a whole, as shown in FIG. 22 . For example, the terminal device 100 may be configured as a prism, and the side surface of the prism may constitute the visible light communication unit 10. The base station device 200 may also be configured as a rod as a whole. That is, each of the terminal device 100 and the base station device 200 may have multiple visible light communication units capable of visible light communication in multiple directions.

[0181] In the above embodiment, an example has been described in which the decisions on handover and on multi-base station communication are made on the side of the base station device 200. However, the decisions on handover and on multi-base station communication may also be made on the side of the terminal device 100. In this case, without transmitting a report visible light signal from the terminal device 100 to the base station device 200, the control unit 110 of the terminal device 100 may make the decisions on handover and on multi-base station communication based on measurement results, etc., and notify the base station device 200 of the decision results.

[0182] The above-described operational flows are not limited to being implemented independently, but can also be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. Furthermore, the order of the steps in each of the above-described operational flows is merely an example, and the order of the steps may be changed as appropriate.

[0183] 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 the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. Furthermore, circuits that execute each process performed by the terminal device 100 or the base station device 200 may be integrated, and at least a portion of the terminal device 100 or the base station device 200 may be configured as a semiconductor integrated circuit (chip set, SoC).

[0184] As used in this disclosure, the terms "based on" and "depending on" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "based only on" and "at least in part on." Furthermore, "obtain" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may also mean including only the listed items or including additional items in addition to the listed items. Furthermore, as used in this disclosure, the term "or" is not intended to mean an exclusive or. Furthermore, any reference to an element using a designation such as "first," "second," etc., used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein, or that the first element must precede the second element in some way. In this disclosure, when articles are added by translation, such as a, an, and the in English, these articles are intended to include the plural unless the context clearly indicates otherwise.

[0185] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0186] This application claims priority from Japanese Patent Application No. 2022-068340 (filed April 18, 2022), the entire contents of which are incorporated herein by reference.

[0187] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0188] (1) A visible light communication system for performing visible light communication between a terminal device and a base station device, wherein the terminal device comprises: a plurality of visible light communication units including a first visible light communication unit and a second visible light communication unit; and a control unit that controls the plurality of visible light communication units, wherein the plurality of visible light communication units each have directivity in a different direction; and the control unit performs simultaneous communication control such that the first visible light communication unit performs visible light communication with a first base station device while the second visible light communication unit performs visible light communication with a second base station device.

[0189] (2) The visible light communication system according to (1), wherein each of the plurality of visible light communication units includes at least one light-emitting element, at least one light-receiving element, and a transceiver that performs transmission and reception processing of visible light signals using the light-emitting element and the light-receiving element.

[0190] (3) The visible light communication system according to (1) or (2), wherein the control unit performs measurement processing on pilot visible light signals received by the plurality of visible light communication units from each base station device when the first visible light communication unit is performing visible light communication with the first base station device.

[0191] (4) The visible light communication system according to (3), wherein the control unit performs the measurement process in response to a trigger condition set by the first base station device being satisfied or in response to detection of movement of the terminal device.

[0192] (5) The visible light communication system according to (3) or (4), wherein the pilot visible light signal is a visible light signal including a pilot signal sequence, and each base station device includes in the pilot visible light signal of its own base station device the pilot signal sequence that is different from the pilot signal sequence used by base station devices around its own base station device.

[0193] (6) The visible light communication system according to any one of (3) to (5), wherein the control unit controls the first visible light communication unit to transmit to the first base station device a report visible light signal including a measurement result for the pilot visible light signal of each of the base station devices.

[0194] (7) The visible light communication system according to (6), wherein the control unit controls the first visible light communication unit to transmit the report visible light signal to the first base station device in response to the measurement result satisfying a threshold condition or periodically.

[0195] (8) The visible light communication system according to (6) or (7), wherein the plurality of visible light communication units receive an alarm visible light signal from each of the base station devices, the alarm visible light signal includes information indicating at least one of the attitude and shaking of the base station device that has transmitted the alarm visible light signal, and the control unit corrects the measurement result according to the information included in the alarm visible light signal.

[0196] (9) The visible light communication system according to any one of (6) to (8), wherein the control unit further includes, in the report visible light signal, information indicating whether or not simultaneous communication is possible while the terminal device is communicating with the first visible light communication unit, for each base station device other than the first base station device.

[0197] (10) The visible light communication system according to any one of (6) to (9), wherein the control unit further includes information indicating a movement state of the terminal device in the report visible light signal.

[0198] (11) The visible light communication system according to any one of (6) to (10) above, wherein the control unit determines the moving state depending on reception conditions of the pilot visible light signal in the plurality of visible light communication units.

[0199] (12) The visible light communication system according to any one of (6) to (11), wherein the control unit generates association information that associates the visible light communication unit that received the pilot visible light signal with the base station device that transmitted the pilot visible light signal.

[0200] (13) A visible light communication system according to any one of (6) to (12) above, wherein the first visible light communication unit receives an instruction visible light signal from the first base station device, the instruction visible light signal including a communication instruction specifying the second base station device, and the control unit, in response to receiving the instruction visible light signal, selects the visible light communication unit associated with the second base station device based on the association information, and establishes communication with the second base station device using the selected visible light communication unit.

[0201] (14) The visible light communication system described in (13) above, wherein the instruction visible light signal includes the communication instruction instructing the terminal device to transmit the same information as information transmitted from the terminal device to the first base station device to the second base station device, and the control unit controls the first visible light communication unit and the second visible light communication unit to transmit the same information to the first base station device and the second base station device in response to receiving the instruction visible light signal.

[0202] (15) The visible light communication system described in (13) or (14) above, wherein the instruction visible light signal includes the communication instruction instructing the terminal device to transmit information different from information transmitted from the terminal device to the first base station device to the second base station device, and the control unit controls the first visible light communication unit and the second visible light communication unit to transmit different information to the first base station device and the second base station device in response to receiving the instruction visible light signal.

[0203] (16) The second base station device transfers information received by the second base station device from the terminal device to the first base station device, and the first base station device performs a synthesis process on the information received by the first base station device from the terminal device and the information received by the first base station device from the second base station device. The visible light communication system described in any of (13) to (15) above.

[0204] (17) The visible light communication system according to any one of (12) to (16) above, wherein the control unit updates the association information in response to detection of rotation of the terminal device.

[0205] (18) The visible light communication system according to (17), wherein the terminal device further includes a sensor for generating attitude information of the terminal device, and the control unit updates the association information based on the attitude information.

[0206] (19) The visible light communication system according to (17) or (18), wherein the control unit re-executes the measurement process in response to the detection of the rotation, and updates the association information in response to a result of the re-executed measurement process.

[0207] (20) A terminal device that performs visible light communication with a base station device, comprising: a plurality of visible light communication units including a first visible light communication unit and a second visible light communication unit; and a control unit that controls the plurality of visible light communication units, wherein the plurality of visible light communication units each have directivity in a different direction; and the control unit performs simultaneous communication control so that the first visible light communication unit performs visible light communication with a first base station device while the second visible light communication unit performs visible light communication with a second base station device.

[0208] 1: Visible light communication system 10: Visible light communication unit 20: Visible light communication unit 100: Terminal device 101: Light-emitting element 102: Light-receiving element 103: Transceiver 110: Control unit 111: Processor 112: Memory 120: Sensor 150: Light-emitting and receiving unit 151: Light-emitting and receiving area 160: Main body unit 200: Base station device 201: Light-emitting element 202: Light-receiving element 203: Transceiver 210: Control unit 211: Processor 212: Memory 220: Backhaul communication unit 221: Network communication unit 222: Inter-base station communication unit 230: Sensor 240: GNSS positioning unit 250: Light-emitting and receiving unit 251: Light-emitting and receiving area 260: Main body unit

Claims

1. A visible light communication system for performing visible light communication between a terminal device and a base station device, The terminal device A plurality of visible light communication units including a first visible light communication unit and a second visible light communication unit; A control unit that controls the plurality of visible light communication units, The plurality of visible light communication units each have directivity in a different direction, The control unit performs simultaneous communication control such that the first visible light communication unit performs visible light communication with a first base station device while the second visible light communication unit performs visible light communication with a second base station device. Visible light communication system.

2. Each of the plurality of visible light communication units is At least one light emitting element; At least one light receiving element; a transceiver that performs transmission and reception processing of a visible light signal using the light emitting element and the light receiving element. The visible light communication system according to claim 1 .

3. The control unit performs a measurement process on pilot visible light signals received by the plurality of visible light communication units from each base station device in a state in which the first visible light communication unit is performing visible light communication with the first base station device. The visible light communication system according to claim 1 .

4. The control unit performs the measurement process in response to a trigger condition set by the first base station device being satisfied or in response to detection of movement of the terminal device. The visible light communication system according to claim 3 .

5. the pilot visible light signal is a visible light signal including a pilot signal sequence, Each of the base station devices includes, in the pilot visible light signal of the own base station device, the pilot signal sequence that is different from the pilot signal sequence used by the neighboring base station devices of the own base station device. The visible light communication system according to claim 3 .

6. The control unit controls the first visible light communication unit to transmit a report visible light signal including a measurement result for the pilot visible light signal of each of the base station devices to the first base station device. The visible light communication system according to claim 3 .

7. The control unit controls the first visible light communication unit to transmit the report visible light signal to the first base station device in response to the measurement result satisfying a threshold condition or periodically. The visible light communication system according to claim 6 .

8. the plurality of visible light communication units receive a notification visible light signal from each of the base station devices; the notification visible light signal includes information indicating at least one of an attitude and a shaking of a base station device that is a transmission source of the notification visible light signal, The control unit corrects the measurement result in accordance with the information included in the notification visible light signal. The visible light communication system according to claim 6 .

9. The control unit further includes, in the report visible light signal, information indicating whether or not each base station device other than the first base station device is associated with a visible light communication unit among the plurality of visible light communication units that is different from the first visible light communication unit. The visible light communication system according to claim 6 .

10. The control unit further includes information indicating a moving state of the terminal device in the report visible light signal. The visible light communication system according to claim 6 .

11. The control unit determines the moving state according to a reception state of the pilot visible light signal in the plurality of visible light communication units. The visible light communication system according to claim 10.

12. The control unit generates association information that associates the visible light communication unit that received the pilot visible light signal with the base station device that transmitted the pilot visible light signal. The visible light communication system according to claim 3 .

13. the first visible light communication unit receives an instruction visible light signal including a communication instruction designating the second base station device from the first base station device; The control unit is selecting the visible light communication unit associated with the second base station device based on the association information in response to receiving the instruction visible light signal; Establish communication with the second base station device using the selected visible light communication unit. The visible light communication system according to claim 12.

14. the instruction visible light signal includes the communication instruction for instructing the terminal device to transmit to the second base station device the same information as information to be transmitted from the terminal device to the first base station device, The control unit controls the first visible light communication unit and the second visible light communication unit in response to receiving the instruction visible light signal so as to transmit the same information to the first base station device and the second base station device. The visible light communication system according to claim 13.

15. the instruction visible light signal includes the communication instruction for instructing the terminal device to transmit information to the second base station device that is different from information transmitted from the terminal device to the first base station device, The control unit controls the first visible light communication unit and the second visible light communication unit to transmit different information to the first base station device and the second base station device in response to receiving the instruction visible light signal. The visible light communication system according to claim 13.

16. the second base station device forwards the information received by the second base station device from the terminal device to the first base station device; The first base station device performs a synthesis process on the information received by the first base station device from the terminal device and the information received by the first base station device from the second base station device.

16. A visible light communication system according to claim 14 or 15.

17. The control unit updates the association information in response to detection of rotation of the terminal device. The visible light communication system according to claim 12.

18. The terminal device further includes a sensor for generating attitude information of the terminal device, The control unit updates the association information based on the posture information.

18. A visible light communication system according to claim 17.

19. The control unit is re-performing the measurement process in response to the rotation being detected; The association information is updated according to the result of the re-executed measurement process.

18. A visible light communication system according to claim 17.

20. A terminal device that performs visible light communication with a base station device, A plurality of visible light communication units including a first visible light communication unit and a second visible light communication unit; A control unit that controls the plurality of visible light communication units, The plurality of visible light communication units each have directivity in a different direction, The control unit performs simultaneous communication control such that the first visible light communication unit performs visible light communication with a first base station device while the second visible light communication unit performs visible light communication with a second base station device. Terminal device.