Visible light communication system and terminal device

Abstract

This terminal device comprises: a plurality of visible light communication units that include a visible light communication unit and another 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 directionality in mutually different directions. The control unit carries out switching control to switch from a state in which a visible light communication unit performs visible light communication with the base station device, to a state in which a visible light communication unit performs visible light communication with the base station device.

Description

[Technical Field]

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

[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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-103232 Summary of the Invention

[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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a diagram illustrating a configuration of a visible light communication system according to an embodiment. [Figure 2] FIG. 1 is a diagram illustrating an operation scenario in a visible light communication system according to an embodiment. [Figure 3] FIG. 1 is a diagram illustrating an operation scenario in a visible light communication system according to an embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a terminal device according to an embodiment. [Figure 5] FIG. 10 is a diagram illustrating an example of association information according to the embodiment. [Figure 6] FIG. 2 is a diagram illustrating an example of a format of a report visible light signal according to the embodiment. [Figure 7] FIG. 1 is a diagram illustrating an example of the external configuration of a terminal device according to an embodiment. [Figure 8] FIG. 1 is a diagram illustrating a configuration of a base station device according to an embodiment. [Figure 9] FIG. 1 is a diagram illustrating an example of the external configuration of a base station device according to an embodiment. [Figure 10] FIG. 2 is a diagram illustrating an example of the operation of the visible light communication system according to the first embodiment. [Figure 11] FIG. 10 is a diagram for explaining a modification of the first embodiment. [Figure 12] FIG. 10 is a diagram for explaining a modification of the first embodiment. [Figure 13] FIG. 10 is a diagram showing an operation scenario in a visible light communication system according to a second embodiment. [Figure 14] FIG. 10 is a diagram illustrating a specific example of a combining process (buffer combining process) in the base station device according to the second embodiment. [Figure 15] FIG. 10 is a diagram illustrating a specific example of a combining process (buffer combining process) in the base station device according to the second embodiment. [Figure 16] FIG. 10 is a diagram illustrating an example of the operation of the visible light communication system according to the second embodiment. [Figure 17]FIG. 10 is a diagram illustrating an example of the operation of a visible light communication system according to a modification of the second embodiment. [Figure 18] FIG. 10 is a diagram illustrating an example of the operation of a visible light communication system according to a modification of the second embodiment. [Figure 19] FIG. 10 is a diagram illustrating a configuration of a visible light communication system according to another embodiment. [Figure 20] FIG. 10 is a diagram illustrating a configuration of a visible light communication system according to another embodiment. [Figure 21] FIG. 10 is a diagram illustrating an example of the external configuration of a terminal device according to another embodiment. [Figure 22] FIG. 10 is a diagram illustrating an example of the external configuration of a terminal device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0007] In visible light communication systems, it is desirable to enable handover of mobile terminal devices between base station devices, 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 handover in visible light communication systems.

[0008] Therefore, an object of the present disclosure is to make it possible to realize handover 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 (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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device.

[0011] 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 performs switching control to switch from a state in which the first visible light communication unit performs visible light communication with the first base station device to a state in which the second visible light communication unit performs visible light communication with the second base station device, thereby enabling handover of the terminal device from the first base station device to the second base station device. Therefore, the visible light communication system according to the first aspect can provide a visible light communication system that uses visible light as a transmission medium and is capable of realizing handover.

[0012] (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.

[0013] This enables each visible light communication unit of the terminal device to perform visible light communication independently of the other visible light communication units, thereby enabling visible light communication using multiple visible light communication units simultaneously, for example.

[0014] (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.

[0015] This makes it possible to detect handover candidates and determine whether or not to execute a handover.

[0016] (1.4) A visible light communication system according to a fourth aspect is the visible light communication system according to the third aspect, in which the control unit performs the measurement processing 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.

[0017] This allows the measurement process to be performed at an appropriate timing.

[0018] (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 a pilot signal sequence that is different from the pilot signal sequences used by base station devices surrounding the own base station device.

[0019] This allows the terminal device to distinguish each base station device from other base station devices based on the pilot signal sequence.

[0020] (1.6) A visible light communication system according to a sixth aspect is the visible light communication system according to the fifth aspect, wherein each of the base station devices acquires the pilot signal sequence used in the base station device from a network.

[0021] This makes it possible to appropriately set pilot signal sequences in each base station device under the control of the network.

[0022] (1.7) A visible light communication system according to a seventh aspect is the visible light communication system according to the fifth aspect, in which each base station device acquires location information indicating the location of the base station device, and determines the pilot signal sequence to be used by the base station device based on the location information.

[0023] This allows each base station device to autonomously set its own pilot signal sequence that is different from the pilot signal sequences of other base station devices based on its own location.

[0024] (1.8) A visible light communication system according to an eighth aspect is a visible light communication system according to the fifth aspect, in which each base station device acquires the pilot signal sequence used by other base station devices from a terminal device connected to the base station device, and determines the pilot signal sequence to be used by the base station device based on the pilot signal sequence acquired from the terminal device.

[0025] This allows the base station device to recognize pilot signal sequences used by other base station devices with which inter-base station communication is not possible, and makes it possible for the base station device to autonomously set its own pilot signal sequence that is different from the pilot signal sequences of other base station devices.

[0026] (1.9) A visible light communication system according to a ninth aspect is a visible light communication system according to any one of the third to eighth 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 measurement results for pilot visible light signals of each of the base station devices.

[0027] 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.

[0028] (1.10) A visible light communication system according to a tenth aspect is the visible light communication system according to the ninth 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.

[0029] This enables the terminal device to transmit a report visible light signal to the first base station device at an appropriate timing.

[0030] (1.11) A visible light communication system according to an eleventh aspect is the visible light communication system according to the ninth or tenth 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.

[0031] This makes it possible to reflect the base station status, such as the attitude 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 stable visible light communication as the target base station (second base station device) for handover.

[0032] (1.12) A visible light communication system according to a twelfth aspect is a visible light communication system according to any one of the ninth to eleventh aspects, wherein the control unit further includes, in the reporting visible light signal, information indicating whether the visible light communication unit associated with a base station device other than the first base station device is the same as the first visible light communication unit.

[0033] This makes it possible to determine the base station device associated with the first visible light communication unit currently being used for visible light communication as the target base station (second base station device) for handover, thereby facilitating handover.

[0034] (1.13) A visible light communication system according to a thirteenth aspect is a visible light communication system according to a twelfth aspect, in which the first base station device preferentially selects, based on the reporting visible light signal, a base station device associated with a visible light communication unit different from the first visible light communication unit as the second base station device.

[0035] This allows the terminal device to smoothly perform handover using a visible light communication unit different from the first visible light communication unit currently being used for visible light communication.

[0036] (1.14) A visible light communication system according to a fourteenth aspect is a visible light communication system according to any one of the ninth to thirteenth aspects, wherein the control unit further includes information indicating the movement state of the terminal device in the reporting visible light signal.

[0037] This makes it easier to perform handover at an appropriate timing, taking into account the movement state of the terminal device.

[0038] (1.15) A visible light communication system according to a fifteenth aspect is a visible light communication system according to any one of the third to fourteenth 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.

[0039] This makes it possible to appropriately use a plurality of visible light communication units for each base station device.

[0040] (1.16) A visible light communication system according to a sixteenth aspect is the visible light communication system according to the fifteenth aspect, wherein the first visible light communication unit receives from the first base station an instruction visible light signal including a handover command designating the second base station, 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 based on the association information, and establishes communication with the second base station using the selected visible light communication unit.

[0041] This enables the terminal device to perform visible light communication with the second base station device using an appropriate visible light communication unit after handover.

[0042] (1.17) A visible light communication system according to a seventeenth aspect is the visible light communication system according to the fifteenth or sixteenth aspect, wherein the control unit updates the association information in response to detection of rotation of the terminal device.

[0043] 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.

[0044] (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, and the control unit updates the association information based on the attitude information.

[0045] 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.

[0046] (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. 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.

[0047] 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.

[0048] (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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device.

[0049] (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).

[0050] (2.1) Visible Light Communication System Configuration 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 includes a terminal device 100 and a plurality of base station devices 200. In FIG. 1, three base station devices 200 (200A, 200B, 200C) are shown as an example of the plurality of 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.

[0051] 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. 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.

[0052] 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 a 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.

[0053] In the first embodiment, in such a visible light communication system 1, it is possible for a mobile terminal device 100 to be handed over 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 hand over 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.

[0054] 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.

[0055] (2.2) Terminal Device Configuration 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 (for example, 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.

[0056] 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, the 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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, encoding / decoding, etc. of digital signals. The CPU executes programs stored in the memory to perform various processes.

[0062] The sensor 120 detects parameters indicating the state of the terminal device 100 (for example, the attitude and / or 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.

[0063] 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 have directivities in different directions. In the first embodiment, the control unit 110 performs switching control such 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.

[0064] 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 the plurality of visible light communication units 10 from each base station device 200. For example, control unit 110 controls the 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 on 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.

[0065] The control unit 110 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. Fig. 5 is a diagram showing an example of the association information. The association information is information that associates the visible light communication unit 10 with the base station device 200. In the example of Fig. 5, the visible light communication unit 10_1 is associated with the ID "#1" of the base station device 200A, the visible light communication unit 10_2 is associated with the ID "#2" of the base station device 200B, and the visible light communication unit 10_3 is associated with the ID "#3" of the base station device 200C.

[0066] Control unit 110 controls visible light communication unit 10_1 to transmit, to 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, control unit 110 may control visible light communication unit 10_1 to transmit, to 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.

[0067] The multiple visible light communication units 10 may receive a broadcast visible light signal from each base station device 200. The broadcast 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 broadcast visible light signal. The control unit 110 corrects the measurement result (pilot reception power) according to the information included in the broadcast visible light signal.

[0068] 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 of each base station device 200 (posture, whether there is shaking, etc.) and corrects the measurement result. For example, the terminal device 100 averages the optical reception intensity observed over a period roughly equivalent to the shaking cycle of the base station device 200, treats it as one sample, and reports the result of taking a weighted average with samples from a certain past period to the base station device 200A.

[0069] Control unit 110 may further include, in the report visible light signal, information indicating whether or not 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 or not 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").

[0070] 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 a base station device 200 desired as a target base station for handover.

[0071] 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 pilot visible light signals in 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.

[0072] 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 start 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 (for example, low speed, medium speed, high speed). Alternatively, the movement information may be flag information indicating that the terminal device 100 is moving (particularly, moving).

[0073] The control unit 110 may determine the moving state of the terminal device 100 using at least one of the number of handovers within a predetermined time period and the detection result of the sensor 120 (for example, an inertial sensor such as an acceleration sensor). In addition to these determination indicators, the control unit 110 may determine the moving 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 moving 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.

[0074] In the first embodiment, the visible light communication unit 10_1 receives an instruction visible light signal including a handover command specifying the base station device 200B, which is a target base station for handover, from the base station device 200A, which is a serving base station. In response to receiving the instruction visible light signal, the control unit 110 selects a visible light communication unit 10 associated with the base station device 200B based on the association information (see FIG. 5 ), and establishes communication with the base station device 200B using the selected visible light communication unit 10 (in this example, the visible light communication unit 10_2). This enables the terminal device 100 to perform visible light communication with the base station device 200B using an appropriate visible light communication unit 10 (in this example, the visible light communication unit 10_2) after the handover.

[0075] 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.

[0076] 7, the hemispherical light emitting and receiving unit 150 has a total of seven light emitting and receiving areas 151, ie, light emitting and receiving areas 151#0 to 151#6. For example, the group of light emitting and receiving areas 151#0 to 151#2 constitutes a part of visible light communication unit 10_1. The group of light emitting and receiving areas 151#3 and 151#4 constitutes a part of visible light communication unit 10_2. The group of light emitting and receiving areas 151#5 and 151#6 constitutes a part of visible light communication unit 10_3.

[0077] (2.3) Base Station Equipment Configuration 8 is a diagram showing the configuration of a 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.

[0078] 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 a visible light signal in a different direction and receive a visible light signal 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, the 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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, encoding / decoding, etc. of digital signals. The CPU executes programs stored in the memory to perform various processes.

[0084] 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.

[0085] 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.

[0086] 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 itself, and outputs the position information to the control unit 210.

[0087] In the base station device 200 configured as described above, 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.

[0088] 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.

[0089] The control unit 210 may determine a 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 a 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 of 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.

[0090] 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.

[0091] 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 of the base station device 200 (i.e., the base station state). The control unit 210 can generate such information on the base station state based on the detection result of the sensor 230.

[0092] 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.

[0093] FIG. 9 is a diagram showing an example of the external configuration of the base station device 200 according to the first embodiment. The base station device 200 has 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 has a plurality of light-emitting and receiving areas 251 that are dispersedly arranged. Each light-emitting and receiving area 251 is provided with 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 has a total of 19 light-emitting and receiving areas 251, namely, 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.

[0094] (2.4) Example of operation of visible light communication system FIG. 10 is a diagram showing an example of the operation of the visible light communication system 1 according to the first embodiment.

[0095] 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.

[0096] 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 the visible light to be measured (color of visible light), and a parameter for setting a measurement report trigger.

[0097] Here, the measurement trigger is a trigger for starting measurement of 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 being used for visible light communication.

[0098] 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. In step S104, base station device 200A transmits a pilot visible light signal.

[0099] 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.

[0100] 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 is the source of the pilot visible light signal.

[0101] In step S107, base station device 200B may transmit an alert visible light signal. In step S108, base station device 200C may transmit an alert visible light signal. In step S109, base station device 200A may transmit an alert visible light signal.

[0102] In step S110, the terminal device 100 may receive an alarm visible light signal from each of the base station devices 200A to 200C, 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.

[0103] In step S111, the terminal device 100 may acquire movement information indicating its own movement state.

[0104] 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.

[0105] In step S113, the base station device 200A makes a handover decision 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.

[0106] In steps S114 and S115, the base station device 200A may perform communication for preparing for handover 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] In step S120, the base station device 200B may transmit to the terminal device 100 an instruction visible light signal instructing the terminal device 100 to perform uplink transmission.

[0111] 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.

[0112] (2.5) Modification of the First Embodiment Next, a modified example 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 relationship between the visible light communication unit 10 of the terminal device 100 and the base station device 200. In this modified example, the control unit 110 of the terminal device 100 updates the correspondence information in response to detection of rotation of the terminal device 100.

[0113] 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, it is assumed 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.

[0114] 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 detection of rotation (and / or 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.

[0115] This modified example can also be applied to the second embodiment described later.

[0116] (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.

[0117] In the second embodiment, as shown in FIG. 13, the terminal device 100 is enabled to perform 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 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 have directivities in different directions. 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).

[0118] 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 makes it possible to improve 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.

[0119] 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.

[0120] 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 for a terminal device 100 moving at a speed equal to or higher than a certain threshold, it is preferable to end the multi-base station communication at the time of handover. Including the movement state in the report visible light signal enables the base station device 200A to make such a determination appropriately.

[0121] In the second embodiment, the visible light communication unit 10_1 of the terminal device 100 receives from the base station device 200A an instruction visible light signal including a communication instruction specifying the base station device 200B. In response to receiving the instruction visible light signal, the control unit 110 of the terminal device 100 selects a visible light communication unit 10 associated with the base station device 200B based on the association information (see FIG. 5 ), and establishes communication with the base station device 200B using the selected visible light communication unit 10. This enables the terminal device 100 to perform multi-base station communication using an appropriate visible light communication unit 10.

[0122] In the second embodiment, the instruction visible light signal may include a communication instruction instructing terminal device 100 to transmit to base station device 200B the same information as that 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 units 10_1 and 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 information to be transmitted, thereby improving communication quality.

[0123] 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.

[0124] 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.

[0125] 14 and 15 are diagrams showing a specific example of combining processing (buffer combining processing) in base station device 200 A. Fig. 14 shows the operation when terminal device 100 transmits the same information (same data packet) to base station device 200 A and base station device 200 B.

[0126] 14, the buffer of the base station device 200A is empty in STEP 1. For example, the buffer is a layer 2 (L2) buffer.

[0127] 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 an upper layer.

[0128] 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 SN1 data packet has already been received, the base station device 200A discards the SN1 data packet received from the base station device 200B.

[0129] 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 SN2 data packet 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 SN2 data packet, it holds the SN3 data packet in a buffer and waits for the SN2 data packet to arrive.

[0130] 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 holds the data packet of SN2 in the order of the SNs.

[0131] In STEP 6, the base station device 200A receives a data packet (SN2) addressed to itself from the terminal device 100. Because the SN2 data packet has already been received, the base station device 200A discards the SN2 data packet. The base station device 200A passes the received SN2 data packet and SN3 data packet to an upper layer.

[0132] 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.

[0133] 15, the buffer of the base station device 200A is empty in STEP 1. For example, the buffer is a layer 2 (L2) buffer.

[0134] 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.

[0135] 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 SN2 data packet 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 SN2 data packet, it holds the SN3 data packet in a buffer and waits for the SN2 data packet to arrive.

[0136] 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.

[0137] 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 holds the data packet of SN2 in the order of the SNs.

[0138] In STEP 6, the base station device 200A passes each of the data packets of SN2 to SN5 to an upper layer.

[0139] In this way, in uplink multi-base station communication, buffer combining processing is performed by base station device 200A. In downlink multi-base station communication, terminal device 100 receives the same or different data packets from base station devices 200A and 200A, and buffer combining processing is performed by terminal device 100.

[0140] FIG. 16 is a diagram showing an example of the operation of the visible light communication system 1 according to the second embodiment.

[0141] As shown in FIG. 16, the operations in steps S100 to S112 are the same as those in the first embodiment described above.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In step S203, the base station device 200A transmits to the terminal device 100 an instruction visible light signal including a multi-base station communication instruction specifying the base station device 200B.

[0146] In step S204, the terminal device 100 may transmit an acknowledgement notification for the indication visible light signal to the base station device 200A.

[0147] In step S205, the base station device 200A may transmit to the terminal device 100 an instruction visible light signal instructing the terminal device 100 to perform uplink transmission.

[0148] 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 that is the target base station in the multi-base station communication, and establishes communication with the base station device 200B.

[0149] 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.

[0150] 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.

[0151] In step S210, the base station device 200A performs a combining process on the data received from the terminal device 100 and the data received from the base station device 200B.

[0152] (3.1) Modification of the Second Embodiment Next, a modified example of the second embodiment will be described, focusing on differences from the second embodiment. In this modified example, multi-base station communication is performed during handover and terminated after the handover is completed. Also, the combining process is performed on the base station device 200B side.

[0153] 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.

[0154] As shown in FIG. 17, the operations in steps S100 to S112 are the same as those in the first embodiment described above.

[0155] 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 description will continue 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.

[0156] 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.

[0157] In step S302, the base station device 200B transmits an acknowledgement (ACK) to the request message to the base station device 200A.

[0158] In step S303, the base station device 200A transmits an instruction visible light signal specifying the base station device 200B to the terminal device 100. The instruction visible light signal includes a handover command and a multi-base station communication instruction.

[0159] In step S304, the terminal device 100 may transmit an acknowledgement notification for the indication visible light signal to the base station device 200A.

[0160] 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.

[0161] In step S306, 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 handover and multi-base station communication, and establishes communication with the base station device 200B.

[0162] In step S307, the base station device 200B may transmit to the terminal device 100 an instruction visible light signal instructing the terminal device 100 to perform uplink transmission.

[0163] 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.

[0164] 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.

[0165] In step S311, the base station device 200B performs a combining process on the data received from the terminal device 100 and the data received from the base station device 200A.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] In step S325, the base station device 200B may transmit a broadcast visible light signal. In step S326, the base station device 200A may transmit a broadcast visible light signal.

[0170] 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.

[0171] In step S328, the terminal device 100 may acquire movement information indicating its own movement state.

[0172] 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.

[0173] In step S330, base station device 200B determines whether to end 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 end the multi-base station communication.

[0174] 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.

[0175] 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.

[0176] In step S333, the base station device 200B transmits an instruction to end the multi-base station communication to the terminal device 100.

[0177] In step S334, the terminal device 100 transmits an acknowledgement notification for the instruction to end the multi-base station communication to the base station device 200B.

[0178] (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.

[0179] 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 in a spherical shape 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 configure the visible light communication unit 10. The base station device 200 may also be configured in a spherical shape as a whole. Alternatively, the terminal device 100 may be configured in a rod shape 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 configure the visible light communication unit 10. The base station device 200 may also be configured in a rod shape as a whole. That is, it is sufficient that each of the terminal device 100 and the base station device 200 has multiple visible light communication units capable of visible light communication in multiple directions.

[0180] In the above embodiment, an example has been described in which the decision to perform handover and the decision to perform multi-base station communication are made on the side of the base station device 200. However, the decision to perform handover and the decision to perform 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 decision to perform handover and the decision to perform multi-base station communication based on measurement results, etc., and notify the base station device 200 of the decision results.

[0181] 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.

[0182] 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 part of the terminal device 100 or the base station device 200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0183] 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, the term "or" as used in this disclosure is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, reference to first and second elements does not imply that only two elements may be employed therein or that the first element must precede the second element in some manner. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0184] 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.

[0185] This application claims priority from Japanese Patent Application No. 2022-068351 (filed April 18, 2022), the entire contents of which are incorporated herein by reference.

[0186] (Addendum) The following additional notes are about the features of the above-described embodiment.

[0187] (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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device. Visible light communication system.

[0188] (2) Each of the plurality of visible light communication units at least one light emitting element; at least one light receiving element; a transceiver that performs transmission and reception processing of visible light signals using the light-emitting element and the light-receiving element. A visible light communication system according to (1) above.

[0189] (3) 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 in a state where the first visible light communication unit is performing visible light communication with the first base station device. A visible light communication system according to (1) or (2) above.

[0190] (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 a movement of the terminal device being detected. A visible light communication system according to any one of (1) to (3) above.

[0191] (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 base station device, the pilot signal sequence that is different from the pilot signal sequence used by the base station devices around the base station device. A visible light communication system according to any one of (1) to (4) above.

[0192] (6) Each of the base station devices acquires the pilot signal sequence used in the base station device from a network. The visible light communication system according to (5) above.

[0193] (7) Each of the base station devices Acquire location information indicating the location of the base station device; The pilot signal sequence to be used in the base station device is determined based on the location information. A visible light communication system according to either (5) or (6) above.

[0194] (8) Each of the base station devices acquiring the pilot signal sequence used by another base station device from the terminal device connected to the base station device; The base station determines the pilot signal sequence to be used in its own base station based on the pilot signal sequence acquired from the terminal device. A visible light communication system according to any one of (5) to (7) above.

[0195] (9) 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. A visible light communication system according to any one of (5) to (8) above.

[0196] (10) 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 (9) above.

[0197] (11) the plurality of visible light communication units receive broadcast visible light signals from the respective 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 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. A visible light communication system according to any one of (9) and (10) above.

[0198] (12) The control unit further includes, in the report visible light signal, information indicating whether a visible light communication unit associated with a base station device other than the first base station device is the same as the first visible light communication unit. A visible light communication system according to any one of (9) to (11) above.

[0199] (13) The first base station device preferentially selects, as the second base station device, a base station device associated with the visible light communication unit different from the first visible light communication unit, based on the reported visible light signal. A visible light communication system according to any one of (9) to (12) above.

[0200] (14) The control unit further includes information indicating a movement state of the terminal device in the report visible light signal. A visible light communication system according to any one of (9) to (13) above.

[0201] (15) 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. A visible light communication system according to any one of (9) to (14) above.

[0202] (16) the first visible light communication unit receives, from the first base station, an instruction visible light signal including a handover command designating the second base station; The control unit selecting a 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. A visible light communication system according to any one of (9) to (15) above.

[0203] (17) The control unit updates the association information in response to detection of rotation of the terminal device. A visible light communication system according to any one of (9) to (16) above.

[0204] (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. A visible light communication system according to any one of (9) to (17) above.

[0205] (19) The control unit re-executing 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. A visible light communication system according to any one of (9) to (18) above.

[0206] (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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device. Terminal device. [Explanation of symbols]

[0207] 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: Transmitter / Receiver 110: Control unit 111: Processor 112: Memory 120: Sensor 150: Light receiving and emitting unit 151: Light receiving and emitting area 160: Main body 200:Base station equipment 201: Light-emitting element 202: Light receiving element 203: Transmitter / Receiver 210: Control unit 211: Processor 212: Memory 220: Backhaul communication unit 221: Network Communications Department 222: Base station communication unit 230: Sensor 240: GNSS positioning unit 250: Light receiving and emitting unit 251: Light receiving and emitting area 260: Main body

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 have directivities in different directions, and the control unit performs switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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. Visible light communication system.

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

3. 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 a movement of the terminal device being detected. The visible light communication system according to claim 1 .

4. 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 base station device, the pilot signal sequence that is different from the pilot signal sequence used by the base station devices around the base station device. The visible light communication system according to claim 1 .

5. Each of the base station devices acquires the pilot signal sequence used in the base station device from a network. The visible light communication system according to claim 4 .

6. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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 base station device, the pilot signal sequence that is different from the pilot signal sequence used by a neighboring base station device of the base station device; Each of the base station devices Acquire location information indicating the location of the base station device; The pilot signal sequence to be used in the base station device is determined based on the location information. Visible light communication system.

7. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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 base station device, the pilot signal sequence that is different from the pilot signal sequence used by a neighboring base station device of the base station device; Each of the base station devices acquiring the pilot signal sequence used by another base station device from the terminal device connected to the base station device; The base station determines the pilot signal sequence to be used in its own base station based on the pilot signal sequence acquired from the terminal device. Visible light communication system.

8. 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 1 .

9. 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 8 .

10. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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; the plurality of visible light communication units receive broadcast visible light signals from the respective 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 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. Visible light communication system.

11. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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; The control unit further includes, in the report visible light signal, information indicating whether a visible light communication unit associated with a base station device other than the first base station device is the same as the first visible light communication unit. Visible light communication system.

12. The first base station device preferentially selects, as the second base station device, a base station device associated with the visible light communication unit different from the first visible light communication unit, based on the report visible light signal. The visible light communication system according to claim 11.

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

14. the first visible light communication unit receives, from the first base station, an instruction visible light signal including a handover command designating the second base station; The control unit selecting a 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; Establishing communication with the second base station device using the selected visible light communication unit The visible light communication system according to claim 1 .

15. 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 1 .

16. 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. The visible light communication system according to claim 5 .

17. The control unit re-executing 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.

16. The visible light communication system according to claim 15.

18. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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. Terminal device.

19. 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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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; the plurality of visible light communication units receive broadcast visible light signals from the respective 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 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. Terminal device.

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 switching control to switch from a state in which the first visible light communication unit performs visible light communication with a first base station device to a state in which the second visible light communication unit performs visible light communication with a second base station device; 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 while the first visible light communication unit is performing visible light communication with the first base station device; 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; The control unit further includes, in the report visible light signal, information indicating whether a visible light communication unit associated with a base station device other than the first base station device is the same as the first visible light communication unit. Terminal device.

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