Optical communication system, parent station device, and optical communication method

Abstract

This optical communication system comprises a parent station device and a child station device that transmits and receives a wireless signal via an antenna. The parent station device acquires control information for controlling transmission operation of the wireless signal in the child station device, said control information being generated on the basis of a captured image of a target area including a part or all of the transmission / reception range of the wireless signal in the child station device. The parent station device transmits an optical signal including an analog main signal and a digital signal containing the acquired control information to the child station device. The child station device acquires the control information from the digital signal included in the optical signal received from the parent station device and switches the content of the transmission operation of the wireless signal in accordance with the acquired control information.

Description

Optical communication system, master station device, and optical communication method

[0001] This application claims priority based on Japanese Patent Application No. 2023-107472, filed on June 29, 2023, the disclosure of which is incorporated herein in its entirety by reference.

[0002] Patent Document 1 (JP 2016-225864 A) discloses the following cooperative communication system: That is, the cooperative communication system is a cooperative communication system in which a transmission system transmits communication between a first communication device and a second communication device of a communication system, and the transmission system includes an information acquisition unit that acquires state transition information that indicates a transition of a state of activation or deactivation of a communication function of the first communication device, and a state control unit that controls the activation or deactivation state of the transmission system based on the state transition information.

[0003] JP 2016-225864 A JP 2017-46050 A

[0004] The optical communication system disclosed herein includes a master station device and a slave station device that transmits and receives radio signals via an antenna, wherein the master station device acquires control information for controlling the transmission operation of the radio signals in the slave station device, the control information being generated based on an image of a target area that includes part or all of the transmission and reception range of the radio signals in the slave station device, and transmits an optical signal including a digital signal and an analog main signal that includes the acquired control information to the slave station device, and the slave station device acquires the control information from a digital signal included in the optical signal received from the master station device and switches the content of the transmission operation of the radio signals in accordance with the acquired control information.

[0005] One aspect of the present disclosure can be realized not only as an optical communication system including such a characteristic processing unit, but also as a program for causing a computer to execute the steps of such a characteristic processing.

[0006] One aspect of the present disclosure may be realized not only as a master station device having such a characteristic processing unit, but also as a method having such characteristic processing steps, or as a program for causing a computer to execute such steps. Furthermore, one aspect of the present disclosure may be realized as a semiconductor integrated circuit that realizes part or all of the master station device.

[0007] FIG. 1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating configurations of a master station device, a slave station device, and a central processing unit in the optical communication system according to the first embodiment of the present disclosure. FIG. 3 is a diagram illustrating a correspondence table stored in a storage unit in the central processing unit of the optical communication system according to the first embodiment of the present disclosure. FIG. 4 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device and an imaging area of ​​a camera in the optical communication system according to the first embodiment of the present disclosure. FIG. 5 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device and an imaging area of ​​a camera in the optical communication system according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 7 is a diagram illustrating a configuration of an optical communication system according to a modification of the first embodiment of the present disclosure. FIG. 8 is a diagram illustrating a configuration of a relay station device in the optical communication system according to a modification of the first embodiment of the present disclosure. FIG. 9 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. 10 is a diagram illustrating a configuration of a master station device, a slave station device, and a central processing unit in an optical communication system according to a second embodiment of the present disclosure. FIG. 11 is a diagram illustrating an example of a communication sequence in the optical communication system according to the second embodiment of the present disclosure.

[0008] Conventionally, techniques have been developed to improve communication performance in optical communication systems.

[0009] [Problem to be Solved by the Present Disclosure] There is a need for a technology that goes beyond the technologies described in Patent Documents 1 and 2 and that can achieve excellent functionality regarding transmission control of wireless signals in an optical communication system.

[0010] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide an optical communication system, a master station device, and an optical communication method that can realize excellent functions related to the transmission control of wireless signals in an optical communication system.

[0011] Effect of the Present Disclosure According to the present disclosure, it is possible to realize an excellent function for controlling the transmission of radio signals in an optical communication system.

[0012] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0013] (1) An optical communication system according to an embodiment of the present disclosure includes a master station device and a slave station device that transmits and receives radio signals via an antenna, wherein the master station device acquires control information for controlling the transmission operation of the radio signals in the slave station device, the control information being generated based on an image of a target area that includes part or all of the transmission and reception range of the radio signals in the slave station device, and transmits an optical signal including a digital signal and an analog main signal that includes the acquired control information to the slave station device, and the slave station device acquires the control information from a digital signal included in the optical signal received from the master station device and switches the content of the transmission operation of the radio signals in accordance with the acquired control information.

[0014] In this way, the master station device transmits control information generated based on an image of a target area including the transmission and reception range of the wireless signal at the slave station device, the control information being included in an optical signal together with a main signal, and the slave station device switches the content of the wireless signal transmission operation in accordance with the control information. This configuration makes it possible to appropriately control the content of the wireless signal transmission operation at the slave station device, for example, depending on the number of communication terminals estimated to be present within the transmission and reception range of the wireless signal at the slave station device. Therefore, excellent functionality for wireless signal transmission control in an optical communication system can be realized.

[0015] (2) In the above (1), the parent station device may acquire sleep control information, which is the control information for controlling the suspension or execution of the transmission operation of the radio signal in the child station device, and transmit an optical signal including a digital signal and an analog main signal including the acquired sleep control information to the child station device. The child station device may acquire the sleep control information from a digital signal included in the optical signal received from the parent station device, and switch between suspension and execution of the transmission operation of the radio signal in accordance with the acquired sleep control information.

[0016] With this configuration, for example, it is possible to realize simple sleep control that switches between stopping and starting the transmission of wireless signals depending on the number of communication terminals estimated to be present within the transmission and reception range of the wireless signals of the slave station device. Also, for example, when there are only a few communication terminals connected to the slave station device, power consumption can be reduced by transitioning the slave station device to the sleep state.

[0017] (3) In the above (1) or (2), the parent station device may acquire beamforming information, which is the control information for controlling the transmission and reception range of the wireless signal in the child station device, and transmit an optical signal including a digital signal containing the acquired beamforming information and an analog main signal to the child station device. The child station device may acquire the beamforming information from a digital signal contained in the optical signal received from the parent station device, and change the transmission and reception range of the wireless signal in accordance with the acquired beamforming information.

[0018] With this configuration, for example, it is possible to improve the throughput of a communication terminal communicatively connected to a slave station device while suppressing an increase in power consumption in the slave station device.

[0019] (4) In any of (1) to (3) above, the parent station device may acquire power control information, which is the control information for controlling the transmission power of the radio signal in the child station device, and transmit an optical signal including a digital signal and an analog main signal, including the acquired power control information, to the child station device; and the child station device may acquire the power control information from a digital signal included in the optical signal received from the parent station device, and change the transmission power of the radio signal in accordance with the acquired power control information.

[0020] With this configuration, for example, when there are only a few communication terminals estimated to be present within the transmission and reception range of a radio signal from a slave station device, power consumption can be reduced by reducing the transmission power of the radio signal from the slave station device.

[0021] (5) In any of (1) to (4) above, the slave station device may acquire imaging information indicating the captured image and transmit to the master station device an optical signal including a digital signal containing the acquired imaging information and an analog main signal, and the master station device may acquire the imaging information from a digital signal contained in the optical signal received from the slave station device and acquire the control information generated based on the acquired imaging information.

[0022] With this configuration, for example, imaging information generated by an imaging device provided corresponding to a slave station device can be transmitted to the master station device by optical communication without using a dedicated network.

[0023] (6) In any one of (1) to (5) above, the master station device may acquire the control information generated further based on the reception strength of a radio signal at the slave station device.

[0024] With this configuration, it is possible to control the content of the radio signal transmission operation in the slave station device in accordance with a more accurate number of communication terminals present within the transmission and reception range of the radio signal.

[0025] (7) In the above (1), the optical communication system may further include a control information generating device that acquires the captured image from an imaging device provided corresponding to one or more of the slave station devices and generates sleep control information, which is control information for controlling the suspension or execution of a wireless signal transmission operation in the slave station devices, based on a detection result of a person appearing in the acquired captured image; the master station device may acquire the sleep control information generated by the control information generating device and transmit an optical signal including a digital signal and an analog main signal that includes the acquired sleep control information to the slave station devices; and the slave station device may acquire the sleep control information from a digital signal included in the optical signal received from the master station device and switch between suspension and execution of the wireless signal transmission operation in accordance with the acquired sleep control information.

[0026] With this configuration, it is possible to realize simple sleep control that switches between stopping and starting the transmission of wireless signals depending on the number of communication terminals estimated to be present within the transmission and reception range of the wireless signals of the slave station device, without complicating the processing in the master station device. Furthermore, for example, when there are only a few communication terminals connected to the slave station device, power consumption can be reduced by transitioning the slave station device to the sleep state.

[0027] (8) A master station device according to an embodiment of the present disclosure includes an acquisition unit that acquires control information for controlling the transmission operation of a wireless signal in a slave station device, the control information being generated based on an image of a target area that includes part or all of the transmission and reception range of a wireless signal in the slave station device, and a transmission unit that transmits an optical signal to the slave station device, the optical signal including a digital signal including the control information acquired by the acquisition unit and an analog main signal.

[0028] In this way, by acquiring control information generated based on an image of a target area including the transmission and reception range of a wireless signal at a slave station device, and including the acquired control information in an optical signal together with a main signal and transmitting the optical signal to the slave station device, it is possible to appropriately control the content of the wireless signal transmission operation at the slave station device, for example, depending on the number of communication terminals estimated to be present within the transmission and reception range of the wireless signal at the slave station device, thereby achieving excellent functionality for controlling the transmission of wireless signals in an optical communication system.

[0029] (9) An optical communication method according to an embodiment of the present disclosure is an optical communication method in an optical communication system including a master station device and a slave station device that transmits and receives radio signals via an antenna, the method including the steps of: the master station device acquiring control information for controlling a transmission operation of the radio signal in the slave station device, the control information being generated based on an image of a target area including part or all of the transmission and reception range of the radio signal in the slave station device; and transmitting an optical signal including a digital signal and an analog main signal including the acquired control information to the slave station device; and the slave station device acquiring the control information from a digital signal included in the optical signal received from the master station device; and switching the content of the transmission operation of the radio signal in accordance with the acquired control information.

[0030] In this way, the master station device transmits control information generated based on an image of a target area including the transmission and reception range of a wireless signal at the slave station device, the control information being included in an optical signal together with a main signal, and the slave station device switches the content of the wireless signal transmission operation in accordance with the control information. This method makes it possible to appropriately control the content of the wireless signal transmission operation at the slave station device, for example, depending on the number of communication terminals estimated to be present within the transmission and reception range of the wireless signal at the slave station device. Therefore, excellent functionality for wireless signal transmission control in an optical communication system can be realized.

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and their description will not be repeated. Furthermore, at least some of the embodiments described below may be combined in any manner.

[0032] First Embodiment [Configuration and Basic Operation] Fig. 1 is a diagram illustrating a configuration of an optical communication system according to a first embodiment of the present disclosure. Referring to Fig. 1, the optical communication system 501 includes a master station device 101, multiple slave station devices 201, a central processing unit 301, and multiple cameras 361. The central processing unit 301 is an example of a control information generating device. The camera 361 is an example of an imaging device. The optical communication system 501 may include one slave station device 201 or one camera 361.

[0033] Each slave station device 201 is assigned a slave station ID. The slave station device 201 is connected to an antenna 161. The slave station device 201 transmits and receives wireless signals to and from a communication terminal (not shown) via the antenna 161. The communication terminal may be a mobile communication terminal or a fixed communication terminal. For example, any of multiple slave station devices 201 in the optical communication system 501 are located within a range where they can be interchanged for transmitting and receiving wireless signals to and from the communication terminal. In other words, the multiple slave station devices 201 in the optical communication system 501 can transmit and receive wireless signals to and from communication terminals located within that range. For example, the optical communication system 501 is an analog radio over fiber (RoF) system and can be used for local 5G (5th Generation), small cells, and distributed antenna systems (DAS).

[0034] The slave station equipment 201 is connected to the master station equipment 101 via an optical fiber 191 and an optical splitter (not shown). The master station equipment 101 and the slave station equipment 201 transmit and receive optical signals including communication data via the optical fiber 191. Hereinafter, an optical signal transmitted from the master station equipment 101 to the slave station equipment 201 will also be referred to as a downstream optical signal, and an optical signal transmitted from the slave station equipment 201 to the master station equipment 101 will also be referred to as an upstream optical signal.

[0035] When the optical communication system 501 is applied to mobile wireless communication, for example, a TDD (Time Division Duplex) system is adopted for the mobile wireless communication. In this case, in the optical communication system 501, an upstream transmission period for transmitting communication data from the slave station device 201 to the master station device 101 and a downstream transmission period for transmitting communication data from the master station device 101 to the slave station device 201 are switched and alternately repeated.

[0036] More specifically, the master station device 101 receives an OFDM (Orthogonal Frequency Division Multiplexing) modulated millimeter-wave band RF (Radio Frequency) signal Srd containing communication data from a base station device (not shown). During a downstream transmission period, the master station device 101 transmits a downstream optical signal containing the received RF signal Srd to the slave station device 201 via the optical fiber 191. The RF signal Srd is an example of a main signal.

[0037] Each slave station device 201 receives a downstream optical signal from the master station device 101 via the optical fiber 191. Each slave station device 201 acquires an RF signal Srd from the received downstream optical signal and transmits the acquired RF signal Srd to a communication terminal (not shown) via a corresponding antenna 161.

[0038] Each slave station device 201 also receives an OFDM-modulated millimeter-wave RF signal Sru containing communication data from a communication terminal (not shown) via the corresponding antenna 161. During an upstream transmission period, each slave station device 201 transmits an upstream optical signal containing the received RF signal Sru to the master station device 101 via the optical fiber 191.

[0039] The master station 101 receives upstream optical signals from each slave station 201 via the optical fiber 191. The master station 101 acquires an RF signal Sru from the received upstream optical signals and transmits the acquired RF signal Sru to the base station.

[0040] The cameras 361 are provided corresponding to the multiple slave station devices 201. More specifically, the cameras 361 are provided for each of the multiple slave station devices 201 that are installed in close proximity to each other. The cameras 361 may also be provided for each slave station device 201. The cameras 361 generate captured images of an imaging area IA that includes part or all of the transmission and reception range of the RF signals Srd and Sru in the corresponding slave station device 201. The imaging area IA is an example of a target area. For example, in a space separated by walls, such as an underground passage or inside a building, the imaging area IA and the coverage area CE of the slave station device 201 can be similar to each other. The cameras 361 may also include a driving device for scanning the field of view.

[0041] The camera 361 generates captured images periodically or irregularly, and transmits the generated captured images and imaging information including the ID of the camera 361 to the central processing unit 301 via the network 351 .

[0042] The central processing unit 301 acquires a captured image from the camera 361. More specifically, the central processing unit 301 receives imaging information from the camera 361 via the network 351 and acquires the captured image from the received imaging information. Based on the acquired captured image, the central processing unit 301 generates control information for controlling the transmission operation of the RF signal Srd in the slave station device 201. For example, the central processing unit 301 generates the control information further based on the reception strength of the RF signal Sru in the slave station device 201.

[0043] The master station device 101 acquires control information generated by the central processing unit 301 based on the captured image of the imaging area IA, and transmits a downstream optical signal including a digital signal Sdd and an RF signal Srd, which include the acquired control information, to the slave station device 201. The slave station device 201 acquires the control information from the digital signal Sdd included in the downstream optical signal received from the master station device 101, and switches the content of the transmission operation of the RF signal Srd according to the acquired control information. Details of the processing in the master station device 101, the slave station device 201, and the central processing unit 301 will be described below.

[0044] (Master Station Device, Slave Station Device, and Central Processing Unit) Fig. 2 is a diagram illustrating configurations of a master station device, a slave station device, and a central processing unit in an optical communication system according to a first embodiment of the present disclosure. Referring to Fig. 2, the central processing unit 301 includes a transceiver 31, a control information generator 32, and a storage unit 33. The transceiver 31 and the control information generator 32 are partly or entirely realized by a processing circuit including one or more processors, for example. The storage unit 33 is, for example, a non-volatile memory included in the processing circuit.

[0045] The storage unit 33 stores camera information indicating the correspondence between the ID of the camera 361, the installation position of the camera 361, and the imaging area IA of the camera 361. The storage unit 33 also stores slave station information indicating the correspondence between the slave station ID of the slave station device 201, the installation position of the slave station device 201, and the coverage area CE of the slave station device 201.

[0046] The master station device 101 includes a digital processing unit 11, an analog processing unit 12, a multiplexing unit 13, a demultiplexing unit 14, an optical modulation unit 15, an optical demodulation unit 16, and an optical coupler 19. The digital processing unit 11 is an example of an acquisition unit. The optical modulation unit 15 is an example of a transmission unit. Some or all of the digital processing unit 11 and the analog processing unit 12 are realized, for example, by a processing circuit including one or more processors.

[0047] The digital processing unit 11 in the master station device 101 periodically or irregularly receives a reference signal from the base station device. Based on the received reference signal, the digital processing unit 11 performs synchronization processing to synchronize the count value of a counter (not shown) in the master station device 101 with that of the base station device.

[0048] The slave station device 201 includes a digital processing unit 21, an analog processing unit 22, a multiplexing unit 23, a demultiplexing unit 24, an optical modulation unit 25, an optical demodulation unit 26, a control information processing unit 27, a monitor unit 28, and an optical coupler 29. Some or all of the digital processing unit 21, the analog processing unit 22, the control information processing unit 27, and the monitor unit 28 are realized, for example, by a processing circuit including one or more processors.

[0049] The analog processing unit 22 in the slave station device 201 receives an OFDM-modulated millimeter wave band RF signal Sru containing communication data from a communication terminal (not shown) via the corresponding antenna 161. The analog processing unit 22 branches the received RF signal Sru and outputs the branched RF signal Sru to the multiplexing unit 23 and the monitor unit 28, respectively.

[0050] The monitor unit 28 periodically or irregularly acquires the reception strength of the RF signal Sru in the slave station device 201. More specifically, the monitor unit 28 calculates a received signal strength indicator (RSSI) that indicates the reception strength of the RF signal Sru in the analog processing unit 22, based on the RF signal Sru received from the analog processing unit 22. After calculating the RSSI, the monitor unit 28 outputs the RSSI value, which is the calculated value of the RSSI, to the digital processing unit 21.

[0051] The digital processing unit 21 receives the RSSI value from the monitor unit 28, generates reception strength information including the received RSSI value and the slave station ID of the slave station device 201, and generates a frame Fu1 in which the generated reception strength information is stored. The digital processing unit 21 generates a digital signal Sdu including the frame Fu1, and outputs the generated digital signal Sdu to the multiplexer 23.

[0052] The multiplexing unit 23 frequency-multiplexes the digital signal Sdu received from the digital processing unit 21 and the RF signal Sru received from the analog processing unit 22. The multiplexing unit 23 generates an electrical signal in which the digital signal Sdu and the RF signal Sru are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 25.

[0053] The optical modulation unit 25 receives the electrical signal from the multiplexing unit 23 and generates an upstream optical signal with wavelength λ1 by optically modulating the received electrical signal. During the upstream transmission period, the optical modulation unit 25 outputs the upstream optical signal to the optical fiber 191 via the optical coupler 29.

[0054] The optical demodulator 16 in the master station 101 receives an upstream optical signal from the slave station 201 via the optical fiber 191 and the optical coupler 19, and generates an electrical signal based on the received upstream optical signal. More specifically, the optical demodulator 16 generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal. The optical demodulator 16 outputs the generated electrical signal to the demultiplexer 14.

[0055] The separator 14 receives the electrical signal from the optical demodulator 16, separates the received electrical signal into an RF signal Sru and a digital signal Sdu, and outputs the RF signal Sru to the analog processor 12 and the digital signal Sdu to the digital processor 11. More specifically, the separator 14 is a diplexer configured, for example, with an HPF (High Pass Filter) and an LPF (Low Pass Filter). The separator 14 outputs frequency components of the electrical signal received from the optical demodulator 16 that are equal to or greater than a predetermined frequency F1 as the RF signal Sru to the analog processor 12, and outputs frequency components that are less than the frequency F1 to the digital processor 11 as the digital signal Sdu.

[0056] The analog processing unit 12 outputs the RF signal Sru received from the separation unit 14 to the base station device.

[0057] The digital processing unit 11 receives the digital signal Sdu from the separation unit 14 and acquires a frame Fu1 from the received digital signal Sdu. The digital processing unit 11 acquires reception strength information from the frame Fu1. The digital processing unit 11 transmits the acquired reception strength information to the central processing unit 301.

[0058] The transmitter / receiver 31 in the central processing unit 301 receives reception strength information from the master station device 101 and stores the received reception strength information in the storage unit 33. The transmitter / receiver 31 also receives imaging information from the camera 361 via the network 351 and stores the received imaging information in the storage unit 33.

[0059] The control information generator 32 periodically or irregularly generates control information for controlling the transmission operation of the RF signal Srd in the slave station device 201 based on the imaging information, reception strength information, camera information, and slave station information stored in the storage unit 33. For example, the control information generator 32 detects a person appearing in an image included in the imaging information, and generates control information based on the detection result, reception strength information, camera information, and slave station information. The control information generator 32 outputs the generated control information to the transmitter / receiver 31.

[0060] The transmitter / receiver 31 receives control information from the control information generator 32 and transmits the received control information to the master station device 101 .

[0061] The digital processing unit 11 in the master station device 101 acquires control information for controlling the transmission operation of the RF signal Srd in the slave station device 201, the control information being generated based on an image captured in an imaging area IA that includes part or all of the transmission and reception range of the RF signals Srd and Sru in the slave station device 201. More specifically, the digital processing unit 11 receives the control information from the central processing unit 301. The digital processing unit 11 generates a digital signal Sdd including a frame Fd in which the received control information is stored, and outputs the generated digital signal Sdd to the multiplexing unit 13.

[0062] The analog processing unit 12 receives an OFDM-modulated millimeter wave RF signal Srd containing communication data from the base station device, and outputs the received RF signal Srd to the multiplexing unit 13.

[0063] The multiplexing unit 13 frequency-multiplexes the digital signal Sdd received from the digital processing unit 11 and the RF signal Srd received from the analog processing unit 12. The multiplexing unit 13 generates an electrical signal in which the digital signal Sdd and the RF signal Srd are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 15.

[0064] The optical modulator 15 transmits a downstream optical signal including a digital signal Sdd containing control information acquired by the digital processing unit 11 and an RF signal Srd to the slave station equipment 201. More specifically, the optical modulator 15 receives an electrical signal from the multiplexer 13 and generates a downstream optical signal with wavelength λ2 by optically modulating the received electrical signal. During a downstream transmission period, the optical modulator 15 outputs the downstream optical signal to the optical fiber 191 via the optical coupler 19.

[0065] The optical demodulator 26 in the slave station device 201 receives the downstream optical signal from the master station device 101 via the optical fiber 191 and the optical coupler 29, and generates an electrical signal based on the received downstream optical signal. More specifically, the optical demodulator 26 generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal. The optical demodulator 26 outputs the generated electrical signal to the demultiplexer 24.

[0066] The separator 24 receives the electrical signal from the optical demodulator 26, separates the received electrical signal into an RF signal Srd and a digital signal Sdd, and outputs the RF signal Srd to the analog processor 22 and the digital signal Sdd to the digital processor 21. More specifically, the separator 24 is a diplexer configured, for example, with an HPF and an LPF. The separator 24 outputs frequency components of the electrical signal received from the optical demodulator 26 that are equal to or greater than a predetermined frequency F2 as the RF signal Srd to the analog processor 22, and outputs frequency components that are less than the frequency F2 to the digital processor 21 as the digital signal Sdd.

[0067] The analog processing unit 22 amplifies the RF signal Srd received from the separation unit 24 and outputs the amplified RF signal Srd to the antenna 161 .

[0068] The digital processing unit 21 in the slave station device 201 receives the digital signal Sdd from the separation unit 24, extracts a frame Fd from the received digital signal Sdd, and extracts control information from the frame Fd. The digital processing unit 21 outputs the extracted control information to the control information processing unit 27.

[0069] The control information processing unit 27 receives control information from the digital processing unit 21 and switches the content of the transmission operation of the RF signal Srd in the slave station equipment unit 201 in accordance with the received control information.

[0070] (Control Example 1: Sleep Control) The master station device 101 acquires sleep control information, which is control information for controlling the suspension or execution of the transmission operation of the RF signal Srd in the slave station device 201. The master station device 101 transmits, to the slave station device 201, a digital signal Sdd including the acquired sleep control information and a downstream optical signal including the RF signal Srd.

[0071] The slave station device 201 acquires sleep control information from the digital signal Sdd included in the downstream optical signal received from the master station device 101, and switches between stopping and starting the transmission operation of the RF signal Srd in accordance with the acquired sleep control information.

[0072] Here, when the optical communication system 501 is designed, the slave station equipment 201 is arranged in a redundant manner so that normal communication can be performed even when a large number of communication terminals are communicatively connected to the slave station equipment 201. Therefore, when the optical communication system 501 is in operation, it is desirable to transition slave station equipment 201 that is not communicatively connected to a communication terminal or that is communicatively connected to a small number of communication terminals into a sleep state, thereby reducing power consumption and noise in upstream communication.

[0073] 3 is a diagram illustrating a correspondence table stored in a storage unit in a central processing unit of the optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 3 , the storage unit 33 in the central processing unit 301 stores a correspondence table T1 indicating correspondence relationships between the slave station ID of a slave station device 201, the area population Nce, which is the number of people present in the coverage area CE of the slave station device 201, the RSSI value, and the operating state of the slave station device 201. The operating state in the correspondence table T1 is either an active state or a sleep state. Let "ID_A," "ID_B," "ID_C," "ID_D," "ID_E," "ID_F," and "ID_G" be the slave station IDs of the slave station devices 201A, 201B, 201C, 201D, 201E, 201F, and 201G, which are the slave station devices 201, respectively.

[0074] For example, when the transmitting / receiving unit 31 stores reception strength information in the storage unit 33, the control information generating unit 32 in the central processing unit 301 updates the correspondence table T1 using the RSSI value and the slave station ID included in the reception strength information.

[0075] Furthermore, for example, when the transmitting / receiving unit 31 stores imaging information in the storage unit 33, the control information generating unit 32 detects people appearing in the captured image included in the imaging information. The control information generating unit 32 calculates the number of people in the area Nce based on the detection result of the people appearing in the captured image, the camera information, and the slave station information, and updates the correspondence table T1 using the calculated number of people in the area Nce.

[0076] The control information generator 32 performs switching control to switch the slave station device 201 between the active state and the sleep state based on the area resident count Nce and the RSSI value corresponding to the slave station device 201.

[0077] More specifically, the control information generator 32 refers to the correspondence table T1 in the storage unit 33, compares the area number of people Nce corresponding to an activated slave station device 201 with a predetermined threshold ThA1, and compares the RSSI value corresponding to the activated slave station device 201 with a predetermined threshold ThA2. For example, the threshold ThA1 is "1," and the threshold ThA2 is "-80 dBm." If there is an activated slave station device 201 whose area number of people Nce is continuously less than the threshold ThA1 for a certain period of time or whose RSSI value is continuously less than the threshold ThA2 for a certain period of time, the control information generator 32 controls the slave station device 201 to transition from the activated state to the sleep state.

[0078] Specifically, the control information generator 32 acquires a slave station ID corresponding to the slave station device 201 from the correspondence table T1. The control information generator 32 generates sleep transition information including the acquired slave station ID and outputs the generated sleep transition information to the transmitter / receiver 31. The sleep transition information is an example of sleep control information. The control information generator 32 also changes the operating state corresponding to the slave station ID in the correspondence table T1 from an active state to a sleep state.

[0079] The transmitter / receiver 31 receives the sleep transition information from the control information generator 32 and transmits the received sleep transition information to the master station device 101 .

[0080] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires sleep transition information from the frame Fd. If the acquired sleep transition information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the sleep transition information to the control information processing unit 27.

[0081] The control information processing unit 27 receives sleep transition information from the digital processing unit 21 and performs processing to transition to a sleep state in accordance with the received sleep transition information. Specifically, the control information processing unit 27 transitions units other than the control information transmission / reception system and the RF signal Sru reception system to a sleep state. That is, the control information processing unit 27 stops the analog processing unit 22 from outputting the RF signal Srd to the antenna 161 and the analog processing unit 22 from outputting the RF signal Sru to the multiplexing unit 23.

[0082] Furthermore, the control information generator 32 in the central processing unit 301 references the correspondence table T1 in the storage unit 33, compares the area population Nce corresponding to a slave station device 201 in the sleep state with a predetermined threshold ThB1, and compares the RSSI value corresponding to the slave station device 201 with a predetermined threshold ThB2. For example, the threshold ThB1 is "2," and the threshold ThB2 is "-75 dBm." Note that the threshold ThB1 may be the same value as the threshold ThA1, and the threshold ThB2 may be the same value as the threshold ThA2. If there is a slave station device 201 in the wake-up state whose area population Nce is equal to or greater than the threshold ThB1 for a certain period of time or whose RSSI value is equal to or greater than the threshold ThB2 for a certain period of time, the control information generator 32 controls the slave station device 201 to transition from the sleep state to the wake-up state.

[0083] Specifically, the control information generator 32 acquires a slave station ID corresponding to the slave station device 201 from the correspondence table T1. The control information generator 32 generates sleep wake-up information including the acquired slave station ID and outputs the generated sleep wake-up information to the transmitter / receiver 31. The sleep wake-up information is an example of sleep control information. The control information generator 32 also changes the operating state corresponding to the slave station ID in the correspondence table T1 from a sleep state to an active state.

[0084] The transmitter / receiver 31 receives the sleep release information from the control information generator 32 and transmits the received sleep release information to the master station device 101 .

[0085] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires sleep release information from the frame Fd. If the acquired sleep release information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the sleep release information to the control information processing unit 27.

[0086] The control information processing unit 27 receives the sleep release information from the digital processing unit 21 and performs processing to release the sleep state in accordance with the received sleep release information. Specifically, the control information processing unit 27 starts the analog processing unit 22 outputting the RF signal Srd to the antenna 161 and the analog processing unit 22 outputting the RF signal Sru to the multiplexing unit 23.

[0087] Here, if the area number of people Nce in the coverage area CE of the slave station device 201 is zero, it can be estimated that there are zero communication terminals present in the coverage area CE. Furthermore, the proportion of people carrying communication terminals has increased in recent years, and people appearing in a captured image can be assumed to be carrying communication terminals. Therefore, by performing the above-described switching control based on the area number of people Nce, sleep control can be performed according to the number of communication terminals present in the coverage area CE. Furthermore, by performing switching control based additionally on the RSSI value, sleep control can be performed according to a more accurate number of communication terminals present in the coverage area CE, even when, for example, a person is not visible in the captured image due to an obstruction, or when a person not carrying a communication terminal is present in the coverage area CE.

[0088] (Control Example 2: Transmission Power Control) The master station device 101 acquires power control information, which is control information for controlling the transmission power of the RF signal Srd in the slave station device 201. The master station device 101 transmits, to the slave station device 201, a digital signal Sdd including the acquired power control information and a downstream optical signal including the RF signal Srd.

[0089] The slave station device 201 acquires power control information from the digital signal Sdd included in the downstream optical signal received from the master station device 101, and changes the transmission power of the RF signal Srd in accordance with the acquired power control information.

[0090] For example, the control information generator 32 in the central processing unit 301 performs adjustment control to adjust the transmission power of the RF signal Srd in the slave station device 201 based on the area population Nce and the RSSI value corresponding to the slave station device 201.

[0091] More specifically, the control information generator 32 refers to the correspondence table T1 in the storage unit 33, compares the number of people in the area Nce corresponding to an activated slave station device 201 with a predetermined threshold ThC1, and compares the RSSI value corresponding to the activated slave station device 201 with a predetermined threshold ThC2. If there is an activated slave station device 201 whose number of people in the area Nce is continuously less than the threshold ThC1 for a certain period of time or whose RSSI value is continuously less than the threshold ThC2 for a certain period of time, the control information generator 32 performs control to reduce the transmission power of the RF signal Srd from the activated slave station device 201.

[0092] Specifically, the control information generator 32 acquires a slave station ID corresponding to the slave station device 201 from the correspondence table T1. The control information generator 32 generates power reduction information including the acquired slave station ID, and outputs the generated power reduction information to the transmitter / receiver 31. The power reduction information is an example of power control information.

[0093] The transmitter / receiver 31 receives the power reduction information from the control information generator 32 and transmits the received power reduction information to the master station device 101 .

[0094] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires power reduction information from the frame Fd. If the acquired power reduction information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the power reduction information to the control information processing unit 27.

[0095] The control information processing unit 27 receives the power reduction information from the digital processing unit 21 and performs processing to reduce the transmission power of the RF signal Srd in accordance with the received power reduction information.

[0096] Furthermore, the control information generator 32 in the central processing unit 301 refers to the correspondence table T1 in the storage unit 33, compares the area number Nce corresponding to an activated slave station device 201 with a predetermined threshold ThD1, and compares the RSSI value corresponding to the activated slave station device 201 with a predetermined threshold ThD2. The threshold ThD1 may be the same as the threshold ThC1, and the threshold ThD2 may be the same as the threshold ThC2. If there is an activated slave station device 201 whose area number Nce is equal to or greater than the threshold ThD1 for a certain period of time or whose RSSI value is equal to or greater than the threshold ThD2 for a certain period of time, the control information generator 32 performs control to increase the transmission power of the RF signal Srd from the activated slave station device 201.

[0097] Specifically, the control information generator 32 acquires a slave station ID corresponding to the slave station device 201 from the correspondence table T1. The control information generator 32 generates power increase information including the acquired slave station ID, and outputs the generated power increase information to the transmitter / receiver 31. The power increase information is an example of power control information.

[0098] The transmitter / receiver 31 receives the power increase information from the control information generator 32 and transmits the received power increase information to the master station device 101 .

[0099] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires power increase information from the frame Fd. If the acquired power increase information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the power increase information to the control information processing unit 27.

[0100] The control information processing unit 27 receives the power increase information from the digital processing unit 21 and performs processing to increase the transmission power of the RF signal Srd in accordance with the received power increase information.

[0101] (Control Example 3: Beamforming Control) The master station device 101 acquires beamforming control information, which is control information for controlling the transmission and reception ranges of the RF signals Sru and Srd in the slave station device 201. The master station device 101 transmits, to the slave station device 201, a digital signal Sdd including the acquired beamforming control information and a downstream optical signal including the RF signal Srd.

[0102] The slave station device 201 acquires beamforming control information from the digital signal Sdd included in the downstream optical signal received from the master station device 101, and changes the transmission and reception range of the RF signals Sru and Srd in accordance with the acquired beamforming control information.

[0103] 4 is an overhead view illustrating an example of a coverage area of ​​a slave station device 201 and an imaging area of ​​a camera in the optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 4, the coverage area CE of the slave station device 201 is a reception range of the RF signal Sru and a transmission range of the RF signal Srd in the slave station device 201. For example, in a plan view, the coverage area CE of the slave station device 201 is a circular area centered on the position of the slave station device 201.

[0104] When the imaging information is stored in the memory unit 33 by the transmitter / receiver unit 31, the control information generator 32 detects the target position, which is the position where the person DT is located, in the coverage area CE of the slave station device 201 based on the captured image contained in the imaging information, as well as the camera information and slave station information in the memory unit 33.

[0105] When the control information generator 32 detects a target position in the coverage area CE of the slave station device 201, the control information generator 32 performs control to change the coverage area CE of the slave station device 201 based on the detected target position.

[0106] More specifically, the control information generator 32 generates beamforming setting information including the slave station ID of the slave station device 201 and the position coordinates of the target position, and outputs the generated sleep transition information to the transmitter / receiver 31. The beamforming setting information is an example of beamforming control information.

[0107] The transmitter / receiver 31 receives the beamforming setting information from the control information generator 32 and transmits the received beamforming setting information to the master station device 101 .

[0108] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires beamforming setting information from the frame Fd. If the acquired beamforming setting information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the beamforming setting information to the control information processing unit 27.

[0109] FIG. 5 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device and an imaging area of ​​a camera in the optical communication system according to the first embodiment of the present disclosure.

[0110] 5 , the control information processing unit 27 receives beamforming setting information from the digital processing unit 21 and, in accordance with the received beamforming setting information, changes the transmission / reception range of the RF signals Sru and Srd by the antenna 161, i.e., the coverage area CE, to a coverage area CEs, for example, within a range that does not increase power consumption in the slave station device 201. More specifically, the control information processing unit 27 uses beamforming technology to make the beam width of the RF signals Sru and Srd elongated, or to perform sweep control in a sweep region that includes the position coordinates indicated by the beamforming setting information. This makes it possible to form a more desirable coverage area CE in situations where many people gather, such as during a disaster.

[0111] In addition, when the control information generation unit 32 in the central processing unit 301 detects, based on the captured image, camera information, and slave station information, that a person DT who was present in the coverage area CE of the slave station device 201 has moved outside the coverage area CE, it performs control to return the coverage area CE of the slave station device 201 to its original state.

[0112] More specifically, the control information generator 32 generates beamforming cancellation information including the slave station ID of the slave station device 201. The control information generator 32 outputs the generated beamforming cancellation information to the transmitter / receiver 31. The beamforming cancellation information is an example of beamforming control information.

[0113] The transmitter / receiver 31 receives the beamforming cancellation information from the control information generator 32 and transmits the received beamforming cancellation information to the master station device 101 .

[0114] The digital processing unit 21 in each slave station device 201 in the optical communication system 501 receives the digital signal Sdd from the demultiplexer 24, acquires a frame Fd from the received digital signal Sdd, and acquires beamforming cancellation information from the frame Fd. If the acquired beamforming cancellation information includes the slave station ID of the slave station device 201, the digital processing unit 21 outputs the beamforming cancellation information to the control information processing unit 27.

[0115] The control information processing unit 27 receives the beamforming cancellation information from the digital processing unit 21 and, in accordance with the beamforming cancellation information, restores the transmission and reception range of the RF signals Sru and Srd by the antenna 161. That is, the control information processing unit 27 changes the coverage area CEs to the coverage area CE.

[0116] [Operation Flow] FIG. 6 is a diagram illustrating an example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure.

[0117] Referring to FIG. 6, first, the slave station device 201 periodically or irregularly calculates an RSSI indicating the reception strength of the RF signal Sru, and generates reception strength information including the calculated RSSI value and the slave station ID (step S11).

[0118] Next, the slave station device 201 generates a digital signal Sdu including the reception intensity information, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S12).

[0119] Next, the master station 101 acquires reception intensity information from the upstream optical signal received from the slave station 201, and transmits the acquired reception intensity information to the central processing unit 301 (step S13).

[0120] Furthermore, the central processing unit 301 receives imaging information from the camera 361 via the network 351, and acquires a captured image from the received imaging information (step S14).

[0121] Next, based on the captured image and the reception strength information, the central processing unit 301 generates control information for controlling the transmission operation of the RF signal Srd in the slave station device 201. More specifically, the central processing unit 301 generates sleep control information, power control information, or beamforming control information as the control information (step S15).

[0122] Next, the central processing unit 301 transmits the generated control information to the master station device 101 (step S16).

[0123] Next, the master station 101 transmits a downstream optical signal including the digital signal Sdd containing the control information received from the central processing unit 301 and the RF signal Srd to the slave station 201 (step S17).

[0124] Next, the slave station device 201 acquires control information from the downstream optical signal received from the master station device 101, and switches the content of the transmission operation of the RF signal Srd in accordance with the acquired control information (step S18).

[0125] In addition, in the central processing unit 301 according to the first embodiment of the present disclosure, the control information generating unit 32 may be configured to be capable of performing the above-mentioned control examples 1, 2, and 3, or may be configured not to perform some of control examples 1, 2, and 3.

[0126] Furthermore, in the central processing unit 301 according to the first embodiment of the present disclosure, the control information generator 32 is configured to generate control information based on the detection result of a person appearing in a captured image included in the imaging information, reception strength information, camera information, and slave station information, but this is not limited to this. The control information generator 32 may be configured to generate control information based on the detection result of a communication device such as a robot appearing in a captured image included in the imaging information, reception strength information, camera information, and slave station information.

[0127] Furthermore, in the central processing unit 301 according to the first embodiment of the present disclosure, the control information generator 32 is configured to generate control information based on imaging information, reception strength information, camera information, and slave station information. However, this is not limited to this. The control information generator 32 may be configured to generate control information based on the detection results of a human presence sensor that detects the presence of a person in a detection area including part or all of the coverage area CE, instead of or in addition to reception strength information. Furthermore, the control information generator 32 may be configured to generate control information for the slave station device 201 based on the throughput of a communication terminal communicating with the slave station device 201, instead of or in addition to reception strength information. Furthermore, the control information generator 32 may be configured to generate control information based on imaging information, camera information, and slave station information, without using reception strength information. In addition, the control information generation unit 32 may be configured to generate control information for improving the throughput of the communication terminal communicating with the slave station device 201 by analyzing the captured image and the throughput of the communication terminal communicating with the slave station device 201 using data analysis techniques such as machine learning.

[0128] Furthermore, although the optical communication system 501 according to the first embodiment of the present disclosure is configured to include multiple cameras 361, this is not limiting. The optical communication system 501 may be configured to include multiple LiDARs (Light Detection and Ranging) instead of the multiple cameras 361. The LiDAR is an example of an imaging device. The LiDAR generates point cloud data of a sensing region including part or all of the coverage area CE of the slave station device 201, and transmits the generated point cloud data and sensing information including the ID of the LiDAR to the central processing unit 301 via the network 351. The point cloud data is an example of a captured image. In this case, the control information generator 32 generates control information based on the sensing information instead of the imaging information.

[0129] Furthermore, the optical communication system 501 may be configured to include a plurality of motion sensors instead of the plurality of cameras 361. The motion sensors generate detection information indicating detection results in a sensing region including part or all of the coverage area CE of the slave station device 201, and transmit the generated detection information and sensing information including the ID of the motion sensor to the central processing unit 301 via the network 351. In this case, the control information generator 32 generates control information based on the sensing information instead of the imaging information.

[0130] Furthermore, in the optical communication system 501 according to the first embodiment of the present disclosure, the control information generator 32 in the central processing unit 301 generates the control information. However, this is not limiting. Instead of the central processing unit 301, the master station 101 may generate the control information as a control information generator. That is, instead of the central processing unit 301, the master station 101 may include the control information generator 32. In this case, the transmitter / receiver 31 in the central processing unit 301 receives imaging information from the camera 361 via the network 351 and transmits the received imaging information to the master station 101. The master station 101 then acquires the control information by generating the control information. More specifically, the control information generator 32 in the master station 101 generates the control information based on the imaging information received from the central processing unit 301, the reception intensity information, camera information, and slave station information acquired from frame Fu1. The central processing unit 301 may be installed within the master station 101.

[0131] Although the optical communication system 501 according to the first embodiment of the present disclosure is described as an analog RoF system, the present invention is not limited to this. The optical communication system 501 may be an IFoF (Intermediate Frequency over Fiber) system. In this case, the analog processing unit 12 in the master station 101 generates an IF (Intermediate Frequency) signal by frequency-converting an RF signal Srd received from a base station device and outputs the generated IF signal to the multiplexing unit 13. Alternatively, the analog processing unit 12 receives an IF signal from the base station device and outputs the received IF signal to the multiplexing unit 13.

[0132] The multiplexing unit 13 frequency-multiplexes the digital signal Sdd received from the digital processing unit 11 and the IF signal received from the analog processing unit 12. The multiplexing unit 13 generates an electrical signal in which the digital signal Sdd and the IF signal are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 15.

[0133] Similarly, the analog processing unit 22 in the slave station device 201 generates an IF signal by frequency converting the RF signal Sru received from the communication terminal via the antenna 161, branches the generated IF signal, and outputs the branched IF signal to the multiplexing unit 23 and the monitor unit 28, respectively.

[0134] The multiplexing unit 23 frequency-multiplexes the digital signal Sdu received from the digital processing unit 21 and the IF signal received from the analog processing unit 22. The multiplexing unit 23 generates an electrical signal in which the digital signal Sdu and the IF signal are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 25.

[0135] 7 is a diagram illustrating a configuration of an optical communication system according to a modification of the first embodiment of the present disclosure. Referring to FIG. 7 , the optical communication system 501A further includes a relay station 401 in addition to the optical communication system 501. The relay station 401 is connected to the master station 101 via an optical fiber 191 and an optical splitter (not shown). Some of the slave station devices 201 in the optical communication system 501A are connected to the relay station 401 via the optical fiber 191. Note that the optical communication system 501A may be configured to include multiple relay station devices 401. Alternatively, all of the slave station devices 201 in the optical communication system 501A may be connected to the relay station 401 via the optical fiber 191.

[0136] 8 is a diagram illustrating a configuration of a relay station device in an optical communication system according to a modification of the first embodiment of the present disclosure. Referring to FIG. 8, a relay station device 401 includes optical couplers 41 and 48, optical demodulators 42A and 42B, separators 43A and 43B, amplifiers 44A and 44B, digital processors 45A and 45B, multiplexers 46A and 46B, and optical modulators 47A and 47B. The amplifiers 44A and 44B may be linear amplifiers or AGC (Automatic Gain Control) amplifiers.

[0137] The optical demodulator 42A receives a downstream optical signal from the parent station 101 via the optical fiber 191 and the optical coupler 41, and generates an electrical signal based on the received downstream optical signal. More specifically, the optical demodulator 42A generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal. The optical demodulator 42A outputs the generated electrical signal to the demultiplexer 43A.

[0138] The separator 43A receives the electrical signal from the optical demodulator 42A, separates the received electrical signal into an RF signal Srd and a digital signal Sdd, and outputs the RF signal Srd to the amplifier 44A and the digital signal Sdd to the digital processing unit 45A. More specifically, the separator 43A outputs frequency components of the electrical signal received from the optical demodulator 42A that are equal to or greater than a predetermined frequency F2 as the RF signal Srd to the amplifier 44A, and outputs frequency components that are less than the frequency F2 to the digital processing unit 45A as the digital signal Sdd.

[0139] The amplifier 44A amplifies the RF signal Srd received from the separator 43A and outputs the amplified RF signal Srd to the multiplexer 46A.

[0140] The digital processing unit 45A outputs the digital signal Sdd received from the separating unit 43A to the multiplexing unit 46A.

[0141] The multiplexing unit 46A frequency-multiplexes the digital signal Sdd received from the digital processing unit 45A and the RF signal Srd received from the amplifier unit 44A. The multiplexing unit 46A generates an electrical signal in which the digital signal Sdd and the RF signal Srd are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 47A.

[0142] The optical modulation unit 47A receives the electrical signal from the multiplexing unit 46A and generates a downstream optical signal with wavelength λ2 by optically modulating the received electrical signal. The optical modulation unit 47A outputs the generated downstream optical signal to the optical fiber 191 via the optical coupler 48.

[0143] The optical demodulator 42B receives an upstream optical signal from the slave station device 201 via the optical fiber 191 and the optical coupler 48, and generates an electrical signal based on the received upstream optical signal. More specifically, the optical demodulator 42B generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal. The optical demodulator 42B outputs the generated electrical signal to the demultiplexer 43B.

[0144] The separator 43B receives the electrical signal from the optical demodulator 42B, separates the received electrical signal into an RF signal Sru and a digital signal Sdu, and outputs the RF signal Sru to the amplifier 44B and the digital signal Sdu to the digital processing unit 45B. More specifically, the separator 43B outputs frequency components of the electrical signal received from the optical demodulator 42B that are equal to or greater than a predetermined frequency F1 as the RF signal Sru to the amplifier 44B, and outputs frequency components that are less than the frequency F1 to the digital processing unit 45B as the digital signal Sdu.

[0145] The amplifier 44B amplifies the RF signal Sru received from the separator 43B and outputs the amplified RF signal Sru to the multiplexer 46B.

[0146] The digital processing unit 45B outputs the digital signal Sdu received from the demultiplexing unit 43B to the multiplexing unit 46B.

[0147] The multiplexing unit 46B frequency-multiplexes the digital signal Sdu received from the digital processing unit 45B and the RF signal Sru received from the amplifier unit 44B. The multiplexing unit 46B generates an electrical signal in which the digital signal Sdu and the RF signal Sru are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 47B.

[0148] The optical modulator 47B receives the electrical signal from the multiplexer 46B and generates an upstream optical signal with wavelength λ1 by optically modulating the received electrical signal. The optical modulator 47B outputs the generated upstream optical signal to the optical fiber 191 via the optical coupler 41.

[0149] In the optical communication system 501A, the master station 101 and the slave station 201 may be configured to transmit and receive wavelength-multiplexed optical signals. In this case, the use of the relay station 401 allows for more flexible setting of the wavelength of the optical signal, making it possible to realize the optical communication system 501A equipped with a larger number of slave station 201.

[0150] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0151] Second Embodiment [Configuration and Basic Operation] In comparison with the optical communication system 501 according to the first embodiment, this embodiment relates to an optical communication system 502 in which imaging information is transmitted via an optical fiber 191. Other than the contents described below, the optical communication system 502 is the same as the optical communication system 501 according to the first embodiment.

[0152] 9 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. Compared to the optical communication system 501, the optical communication system 502 includes a slave station device 202 instead of the slave station device 201.

[0153] The camera 361 is provided corresponding to each slave station equipment 202. More specifically, the camera 361 is provided for each slave station equipment 202. Note that the camera 361 may be provided for each of a plurality of slave station equipment 202 that are installed in close locations.

[0154] The camera 361 generates captured images periodically or irregularly, and transmits the generated captured images and imaging information including the ID of the camera 361 to the corresponding slave station device 202 .

[0155] The slave station device 202 acquires imaging information indicating the captured image and transmits an upstream optical signal including a digital signal Sdu containing the acquired imaging information and an RF signal Sru to the master station device 101. The master station device 101 acquires the imaging information from the digital signal Sdu contained in the upstream optical signal received from the slave station device 202, and acquires control information generated based on the acquired imaging information.

[0156] 10 is a diagram illustrating the configurations of a master station device, a slave station device, and a central processing unit in an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 10, the slave station device 202 includes a digital processing unit 51 instead of the digital processing unit 21 in the slave station device 201.

[0157] The digital processing unit 51 generates a digital signal Sdu including a frame Fu1 in which reception intensity information is stored, and outputs the generated digital signal Sdu to the multiplexing unit 23 .

[0158] The digital processing unit 51 also receives imaging information from the camera 361 and generates a frame Fu2 in which the received imaging information is stored. The digital processing unit 51 generates a digital signal Sdu including the frame Fu2 and outputs the generated digital signal Sdu to the multiplexing unit 23.

[0159] The multiplexing unit 23 frequency-multiplexes the digital signal Sdu received from the digital processing unit 51 and the RF signal Sru received from the analog processing unit 22. The multiplexing unit 23 generates an electrical signal in which the digital signal Sdu and the RF signal Sru are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 25.

[0160] The optical modulation unit 25 receives the electrical signal from the multiplexing unit 23 and generates an upstream optical signal with wavelength λ1 by optically modulating the received electrical signal. During the upstream transmission period, the optical modulation unit 25 outputs the upstream optical signal to the optical fiber 191 via the optical coupler 29.

[0161] The optical demodulator 16 in the master station 101 receives an upstream optical signal from the slave station 202 via the optical fiber 191 and the optical coupler 19, and generates an electrical signal based on the received upstream optical signal. More specifically, the optical demodulator 16 generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal. The optical demodulator 16 outputs the generated electrical signal to the demultiplexer 14.

[0162] The separation unit 14 receives an electrical signal from the optical demodulation unit 16, separates the received electrical signal into an RF signal Sru and a digital signal Sdu, and outputs the RF signal Sru to the analog processing unit 12 and the digital signal Sdu to the digital processing unit 11.

[0163] The digital processing unit 11 receives the digital signal Sdu from the separation unit 14 and acquires a frame Fu1 from the received digital signal Sdu. The digital processing unit 11 acquires reception strength information from the frame Fu1. The digital processing unit 11 transmits the acquired reception strength information to the central processing unit 301.

[0164] The digital processing unit 11 also receives the digital signal Sdu from the separation unit 14 and acquires a frame Fu2 from the received digital signal Sdu. The digital processing unit 11 acquires imaging information from the frame Fu2. The digital processing unit 11 transmits the acquired imaging information to the central processing unit 301.

[0165] The transmitter / receiver 31 in the central processing unit 301 receives reception strength information from the master station device 101 and stores the received reception strength information in the storage unit 33. The transmitter / receiver 31 also receives imaging information from the master station device 101 and stores the received imaging information in the storage unit 33.

[0166] The control information generator 32 periodically or irregularly generates control information for controlling the transmission operation of the RF signal Srd in the slave station device 202 based on the imaging information, reception strength information, camera information, and slave station information stored in the storage unit 33. The control information generator 32 outputs the generated control information to the transmitter / receiver 31.

[0167] The transmitter / receiver 31 receives control information from the control information generator 32 and transmits the received control information to the master station device 101 .

[0168] [Operation Flow] FIG. 11 is a diagram illustrating an example of a communication sequence in the optical communication system according to the second embodiment of the present disclosure.

[0169] Referring to FIG. 11, first, the slave station device 202 periodically or irregularly calculates an RSSI indicating the reception strength of the RF signal Sru, and generates reception strength information including the calculated RSSI value and the slave station ID (step S31).

[0170] Next, the slave station device 202 generates a digital signal Sdu including the reception intensity information, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S32).

[0171] Next, the master station device 101 acquires reception intensity information from the upstream optical signal received from the slave station device 202, and transmits the acquired reception intensity information to the central processing unit 301 (step S33).

[0172] The slave station device 202 also receives imaging information from the camera 361 (step S34).

[0173] Next, the slave station device 202 generates a digital signal Sdu including the imaging information, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S35).

[0174] Next, the master station device 101 acquires imaging information from the upstream optical signal received from the slave station device 202, and transmits the acquired imaging information to the central processing unit 301 (step S36).

[0175] Next, the central processing unit 301 generates control information for controlling the transmission operation of the RF signal Srd in the slave station device 202 based on the captured image and reception strength information received from the master station device 101. More specifically, the central processing unit 301 generates sleep control information, power control information, or beamforming control information as the control information (step S37).

[0176] Next, the central processing unit 301 transmits the generated control information to the master station device 101 (step S38).

[0177] Next, the master station 101 transmits a downstream optical signal including the digital signal Sdd containing the control information received from the central processing unit 301 and the RF signal Srd to the slave station 202 (step S39).

[0178] Next, the slave station device 202 acquires control information from the downstream optical signal received from the master station device 101, and switches the content of the transmission operation of the RF signal Srd in accordance with the acquired control information (step S40).

[0179] The above-described embodiments should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0180] Each process (each function) in the above-described embodiments is realized by a processing circuit (circuitry) including one or more processors. The processing circuit may be configured as an integrated circuit or the like that combines one or more memories, various analog circuits, and various digital circuits in addition to the one or more processors. The one or more memories store programs (instructions) that cause the one or more processors to execute each of the processes. The one or more processors may execute each of the processes according to the program read from the one or more memories, or may execute each of the processes according to a logic circuit designed in advance to execute each of the processes. The processor may be any of various processors suitable for computer control, such as a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit). Note that the physically separated processors may cooperate with each other to execute the processes. For example, the processors installed in the physically separated computers may cooperate with each other via a network such as a LAN (Local Area Network), a WAN (Wide Area Network), or the Internet to execute the processes. The program may be installed into the memory from an external server device or the like via the network, or may be distributed in a state stored on a recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), or a semiconductor memory, and then installed into the memory from the recording medium.

[0181] The above description includes the following additional features: [Supplementary Note 1] An optical communication system comprising: a master station device; and slave station devices that transmit and receive wireless signals via an antenna, wherein the master station device acquires control information for controlling a transmission operation of the wireless signals in the slave station devices, the control information being generated based on a captured image of a target area including part or all of a transmission and reception range of the wireless signals in the slave station devices, and transmits an optical signal including a digital signal and an analog main signal including the acquired control information to the slave station devices, the slave station devices acquire the control information from a digital signal included in the optical signal received from the master station device, and switch content of the transmission operation of the wireless signals in accordance with the acquired control information, the master station device acquires the control information generated based on a detection result of a person appearing in the captured image, and the optical communication system is an analog RoF system.

[0182] REFERENCE SIGNS LIST 11 Digital processing unit 12 Analog processing unit 13 Multiplexing unit 14 Separating unit 15 Optical modulation unit 16 Optical demodulation unit 19 Optical coupler 21, 51 Digital processing unit 22 Analog processing unit 23 Multiplexing unit 24 Separating unit 25 Optical modulation unit 26 Optical demodulation unit 27 Control information processing unit 28 Monitor unit 29 Optical coupler 31 Transmitting / receiving unit 32 Control information generating unit 33 Storage unit 41, 48 Optical coupler 42A, 42B Optical demodulation unit 43A, 43B Separating unit 44A, 44B Amplifying unit 45A, 45B Digital processing unit 46A, 46B Multiplexing unit 47A, 47B Optical modulation unit 101 Master station equipment 161 Antenna 191 Optical fiber 201, 202 Slave station equipment 301 Central processing unit 351 Network 361 Camera 401 Repeater station device 501, 501A, 502 Optical communication system IA Imaging area CE, CEs Coverage area DT Person T1 Correspondence table

Claims

1. The master station and It includes a substation that transmits and receives wireless signals via an antenna, The master station device acquires control information for controlling the transmission operation of the wireless signal in the slave station device, which is generated based on an image of a target area that includes part or all of the transmission and reception range of the wireless signal in the slave station device, and transmits a digital signal including the acquired control information and an optical signal including an analog main signal to the slave station device. The aforementioned slave station device acquires control information from the digital signal contained in the optical signal received from the master station device, and switches the content of the wireless signal transmission operation according to the acquired control information, in an optical communication system.

2. The master station device acquires sleep control information, which is control information for controlling the stopping or starting of the wireless signal transmission operation in the slave station device, and transmits an optical signal including a digital signal and an analog main signal, which includes the acquired sleep control information, to the slave station device. The optical communication system according to claim 1, wherein the slave station device acquires sleep control information from the digital signal included in the optical signal received from the master station device, and switches between stopping and executing the transmission operation of the wireless signal according to the acquired sleep control information.

3. The master station device acquires beamforming information, which is control information for controlling the transmission and reception range of the wireless signal in the slave station device, and transmits an optical signal, which includes a digital signal and an analog main signal, including the acquired beamforming information, to the slave station device. The optical communication system according to claim 1, wherein the slave station device acquires beamforming information from the digital signal contained in the optical signal received from the master station device, and changes the transmission and reception range of the wireless signal according to the acquired beamforming information.

4. The master station device acquires power control information, which is control information for controlling the transmission power of the wireless signal in the slave station device, and transmits a digital signal including the acquired power control information and an optical signal including an analog main signal to the slave station device. The optical communication system according to claim 1, wherein the slave station device acquires power control information from the digital signal included in the optical signal received from the master station device, and changes the transmission power of the wireless signal according to the acquired power control information.

5. The slave station device acquires imaging information indicating the captured image, and transmits an optical signal including a digital signal containing the acquired imaging information and an analog main signal to the master station device. The optical communication system according to any one of claims 1 to 4, wherein the master station device acquires imaging information from a digital signal included in the optical signal received from the slave station device, and acquires control information generated based on the acquired imaging information.

6. The optical communication system according to any one of claims 1 to 4, wherein the master station device acquires the control information generated based on the received strength of the radio signal in the slave station device.

7. The aforementioned optical communication system further, The system includes an imaging device provided in correspondence with one or more of the slave station devices, which acquires the captured image from the imaging device, and a control information generation device which generates sleep control information, which is control information for controlling the stopping or execution of the wireless signal transmission operation in the slave station device, based on the detection result of a person appearing in the acquired captured image. The master station device acquires the sleep control information generated by the control information generation device, and transmits a digital signal including the acquired sleep control information and an optical signal including an analog main signal to the slave station device. The optical communication system according to claim 1, wherein the slave station device acquires sleep control information from the digital signal included in the optical signal received from the master station device, and switches between stopping and executing the transmission operation of the wireless signal according to the acquired sleep control information.

8. An acquisition unit that acquires control information for controlling the transmission operation of wireless signals in a slave station device, which is generated based on an image of a target area that includes part or all of the transmission and reception range of wireless signals in the slave station device. A master station device comprising a transmitting unit that transmits to the slave station device an optical signal including a digital signal containing the control information acquired by the acquisition unit and an analog main signal.

9. An optical communication method in an optical communication system comprising a master station device and a slave station device that transmits and receives wireless signals via an antenna, The master station device acquires control information for controlling the transmission operation of the wireless signal in the slave station device, which is generated based on an image of a target area that includes part or all of the transmission and reception range of the wireless signal in the slave station device, and transmits an optical signal including a digital signal and an analog main signal, which includes the acquired control information, to the slave station device. An optical communication method comprising the steps of: the slave station device acquiring control information from a digital signal included in the optical signal received from the master station device, and switching the content of the transmission operation of the wireless signal according to the acquired control information.