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

Abstract

This optical communication system comprises: a master station device; and a plurality of slave station devices that each transmit and receive a radio signal via an antenna. The master station device generates control information for controlling radio signal transmission operations at the slave station devices on the basis of the radio signal reception strength at the slave station devices, and transmits, to the slave station devices, an optical signal that includes a digital signal including the generated control information, and an analog main signal. The slave station devices each acquire the control information from the digital signal included in the optical signal received from the master station device, and switch the contents of a radio signal transmission operation according to 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. 2023-107455, 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] Naoya Matsumoto and four others, "Study on congestion estimation system using RSSI," Multimedia, Distributed, Cooperative and Mobile (DICOMO2018) Symposium, July 2018, pp. 369-376

[0005] The optical communication system disclosed herein includes a master station device and slave station devices that transmit and receive radio signals via antennas, wherein the master station device generates control information for controlling the transmission operation of the radio signals in the slave station devices based on the reception strength of the radio signals in the slave station devices, and transmits an optical signal including a digital signal and an analog main signal that includes the generated control information to the slave station devices, and the slave station devices acquire the control information from the digital signal included in the optical signal received from the master station device and switch the content of the transmission operation of the radio signals in accordance with the acquired control information.

[0006] 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.

[0007] 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.

[0008] 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 and a slave station device 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 master station device 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 an arrangement of slave station devices 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 in the optical communication system according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of an RSSI table stored in a storage unit in the master station device of the optical communication system according to the first embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of RSSI values ​​stored in a storage unit in the master station device of the optical communication system according to the first embodiment of the present disclosure. FIG. 8 is a diagram illustrating an example of a coverage area of ​​a slave station device in the optical communication system according to the first embodiment of the present disclosure. FIG. 9 is a bird's-eye view showing an example of a coverage area of ​​a slave station device in an optical communication system according to a first embodiment of the present disclosure. FIG. 10 is a diagram showing an example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 11 is a diagram showing another example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 12 is a bird's-eye view showing another example of a coverage area of ​​a slave station device in the optical communication system according to the first embodiment of the present disclosure. FIG. 13 is a diagram showing another example of an RSSI table stored in a storage unit in the master station device of the optical communication system according to the first embodiment of the present disclosure. FIG. 14 is a diagram showing a configuration of an optical communication system according to a modification of the first embodiment of the present disclosure. FIG. 15 is a diagram showing a configuration of a relay station device in an optical communication system according to a modification of the first embodiment of the present disclosure. FIG. 16 is a diagram showing a configuration of an optical communication system according to a second embodiment of the present disclosure. FIG. 17 is a diagram showing configurations of a master station device and a slave station device in an optical communication system according to the second embodiment of the present disclosure. FIG. 18 is a diagram illustrating a classification table stored in a storage unit in a master station device of an optical communication system according to a second embodiment of the present disclosure.Fig. 19 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device in an optical communication system according to a second embodiment of the present disclosure. Fig. 20 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device in an optical communication system according to the second embodiment of the present disclosure. Fig. 21 is a diagram illustrating an example of a communication sequence in the optical communication system according to the second embodiment of the present disclosure.

[0009] Conventionally, techniques have been developed to improve communication performance in optical communication systems.

[0010] [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.

[0011] 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.

[0012] 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.

[0013] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0014] (1) An optical communication system according to an embodiment of the present disclosure includes a master station device and slave station devices that transmit and receive radio signals via antennas, wherein the master station device generates control information for controlling the transmission operation of the radio signals in the slave station devices based on the reception strength of the radio signals in the slave station devices, and transmits an optical signal including a digital signal and an analog main signal that includes the generated control information to the slave station devices, and the slave station devices acquire the control information from the digital signal included in the optical signal received from the master station device and switch the content of the transmission operation of the radio signals in accordance with the acquired control information.

[0015] In this way, the master station device generates control information based on the reception strength of the radio signal at the slave station device, includes the control information in an optical signal together with the main signal, and transmits the optical signal to the slave station device, and the slave station device switches the content of the radio signal transmission operation in accordance with the control information. This configuration makes it possible to appropriately control the content of the radio signal transmission operation in accordance with the reception status of the radio signal at the slave station device, thereby achieving excellent functionality for radio signal transmission control in an optical communication system.

[0016] (2) In the above (1), the parent station device may generate 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 that includes the generated 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.

[0017] This configuration allows for simple sleep control that switches between stopping and starting the transmission of radio signals depending on the reception status of the radio signals at the slave 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.

[0018] (3) In the above (1) or (2), when the reception strength of the radio signal at the first slave station device is equal to or greater than a predetermined value, the parent station device may determine a second slave station device that is the slave station device that covers the transmission and reception range of the radio signal by the first slave station device, the parent station device may generate beamforming information that is the control information for controlling the transmission and reception range of the radio signal at the second slave station device, and transmit an optical signal that includes a digital signal including the generated beamforming information and an analog main signal to the second slave station device, and the second slave station device may acquire the beamforming information from a digital signal included in the optical signal received from the parent station device, and change the transmission and reception range of the radio signal in accordance with the acquired beamforming information.

[0019] With this configuration, the transmission and reception range of the radio signal in the second slave station device can be changed depending on the reception status of the radio signal in the first slave station device. Therefore, for example, when there are many communication terminals that are communicatively connected to the first slave station device, the communication bandwidth of the first slave station device can be allocated to the second slave station device while suppressing an increase in power consumption in the second slave station device.

[0020] (4) In the above (3), the parent station device may determine the second child station device based on the reception strength of the radio signal transmitted by the first child station device at a child station device different from the first child station device.

[0021] With this configuration, the transmission and reception range of the first slave station device can be covered more reliably by using the second slave station device.

[0022] (5) In the above (1) or (2), the plurality of slave station devices may include a representative slave station device and dependent slave station devices different from the representative slave station device, and the master station device may generate the control information for controlling the transmission operation of the wireless signal in the dependent slave station devices, and transmit an optical signal including a digital signal containing the generated control information and an analog main signal to the dependent slave station devices.

[0023] With this configuration, for example, the minimum number of slave station devices required for the operation of the optical communication system can be kept running at all times as the representative slave station device, while the transmission operation of the radio signals in the dependent slave station devices can be controlled according to the reception status of the radio signals in the representative slave station device, thereby making it possible to further reduce power consumption according to the operation status of the optical communication system.

[0024] (6) In the above (5), the parent station device may increase or decrease the number of representative child station devices depending on the time period.

[0025] With this configuration, for example, it is possible to increase or decrease the number of slave station devices that are always running as representative slave station devices depending on the time period of increase or decrease in the number of communication terminals that are communicatively connected to the slave station devices, thereby reducing power consumption while maintaining stable communication depending on the increase or decrease in communication volume in the optical communication system.

[0026] (7) A master station device according to an embodiment of the present disclosure includes a control information generating unit that generates control information for controlling a transmission operation of a wireless signal in a plurality of slave station devices based on the reception strength of the wireless signal in the slave station devices, and a transmitting unit that transmits an optical signal to the slave station devices, the optical signal including a digital signal including the control information generated by the control information generating unit and an analog main signal.

[0027] In this way, by generating control information based on the reception strength of the radio signal at the slave station device and including the generated control information in an optical signal together with the main signal and transmitting the optical signal to the slave station device, it is possible to appropriately control the content of the transmission operation of the radio signal according to the reception status of the radio signal at the slave station device, thereby achieving excellent functionality for controlling the transmission of the radio signal in the optical communication system.

[0028] (8) An optical communication system according to an embodiment of the present disclosure is an optical communication method in an optical communication system including a master station device and slave station devices that transmit and receive radio signals via antennas, the method including the steps of: the master station device generating control information for controlling the transmission operation of the radio signals in the slave station devices based on the reception strength of the radio signals in the slave station devices; and transmitting an optical signal including a digital signal and an analog main signal that includes the generated control information to the slave station devices; and the slave station device acquiring the control information from the digital signal included in the optical signal received from the master station device; and switching the content of the transmission operation of the radio signals in accordance with the acquired control information.

[0029] In this way, the master station device generates control information based on the reception strength of the radio signal at the slave station device, includes the control information in an optical signal together with the main signal, and transmits the optical signal to the slave station device, and the slave station device switches the content of the radio signal transmission operation in accordance with the control information. This method makes it possible to appropriately control the content of the radio signal transmission operation in accordance with the reception status of the radio signal at the slave station device, thereby achieving excellent functionality for radio signal transmission control in an optical communication system.

[0030] 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.

[0031] 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 401 includes a master station device 101 and multiple slave station devices 201. Each slave station device 201 is assigned a slave station ID. The slave station devices 201 are connected to an antenna 161. The slave station devices 201 transmit and receive 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 401 are located within a range where they can be interchanged for transmitting and receiving wireless signals to and from the communication terminal. That is, the multiple slave station devices 201 in the optical communication system 401 can transmit and receive wireless signals to and from communication terminals located within that range. For example, the optical communication system 401 is an analog Radio over Fiber (RoF) system, and can be used for local 5th Generation (5G), small cells, and distributed antenna systems (DAS).

[0032] 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.

[0033] When the optical communication system 401 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 401, 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Furthermore, the master station device 101 generates control information for controlling the transmission operation of the RF signal Srd in each slave station device 201 based on the reception strength of the RF signal Sru in that slave station device 201, and transmits a digital signal Sdd including the generated control information and a downstream optical signal including the RF signal Srd to that 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 in accordance with the acquired control information. Details of the processing in the master station device 101 and the slave station device 201 will be described below.

[0039] (Master Station Device and Slave Station Device) FIG. 2 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a first embodiment of the present disclosure. Referring to FIG. 2 , 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, a control information generation unit 17, a storage unit 18, and an optical coupler 19. The optical modulation unit 15 is an example of a transmission unit. The digital processing unit 11, the analog processing unit 12, and the control information generation unit 17 are all or partly realized by a processing circuit including one or more processors, for example. The storage unit 18 is, for example, a non-volatile memory included in the processing circuit.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] The digital processing unit 21 receives the RSSI value from the monitor unit 28 and generates a frame Fu including the received RSSI value and the slave station ID of the slave station device 201. The digital processing unit 21 generates a digital signal Sdu including the frame Fu and outputs the generated digital signal Sdu to the multiplexer 23.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] The analog processing unit 12 outputs the RF signal Sru received from the separation unit 14 to the base station device.

[0050] The digital processing unit 11 receives the digital signal Sdu from the separation unit 14 and acquires a frame Fu from the received digital signal Sdu. The digital processing unit 11 acquires the slave station ID and RSSI value of the slave station device 201 from the frame Fu. The digital processing unit 11 stores the acquired RSSI value in the storage unit 18 in association with the slave station ID of the slave station device 201.

[0051] The control information generator 17 generates control information for controlling the transmission operation of the RF signal Srd in the slave station devices 201 based on the reception strength of the RF signal Sru in the multiple slave station devices 201, and transmits the generated control information to the slave station devices 201. More specifically, the control information generator 17 periodically or irregularly generates control information addressed to the slave station devices 201 based on the RSSI value in the storage unit 18, for controlling the transmission operation of the RF signal Srd in the slave station devices 201. The control information generator 17 outputs the generated control information to the digital processing unit 11.

[0052] The digital processing unit 11 receives control information from the control information generating unit 17 and generates a frame Fd including the received control information. The digital processing unit 11 generates a digital signal Sdd including the frame Fd and outputs the generated digital signal Sdd to the multiplexing unit 13.

[0053] The analog processing unit 12 receives an OFDM-modulated millimeter wave RF signal Srd containing communication data from the base station device 10. The analog processing unit 22 outputs the received RF signal Srd to the multiplexing unit 13.

[0054] 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.

[0055] The optical modulator 15 transmits a downstream optical signal including a digital signal Sdd containing control information generated by the control information generator 17 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 having a 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.

[0056] 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.

[0057] 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.

[0058] 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 .

[0059] 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.

[0060] 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.

[0061] (Control Example 1: Sleep Control) The master station device 101 generates 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 generated sleep control information and a downstream optical signal including the RF signal Srd.

[0062] 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.

[0063] When the optical communication system 401 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 connected to the slave station equipment 201. Therefore, when the optical communication system 401 is in operation, it is desirable to transition slave station equipment 201 that is not connected to any communication terminals or that is connected to only a small number of communication terminals into a sleep state, thereby reducing power consumption and noise in upstream communication.

[0064] 3 is a diagram illustrating a correspondence table stored in a storage unit in a master station device in the optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 3 , the storage unit 18 in the master station device 101 stores a correspondence table T1 indicating correspondence relationships between slave station IDs of slave station devices 201, RSSI values, and operating states of the slave station devices 201. The operating states in the correspondence table T1 are either an active state or a sleep state. "ID_A," "ID_B," "ID_C," "ID_D," "ID_E," "ID_F," and "ID_G" are assumed to be the slave station IDs of slave station devices 201A, 201B, 201C, 201D, 201E, 201F, and 201G, which are slave station devices 201, respectively.

[0065] For example, when the digital processing unit 11 acquires the slave station ID and RSSI value of the slave station device 201 from the frame Fu, it updates the correspondence table T1 in the storage unit 18 using the acquired RSSI value and slave station ID.

[0066] The control information generator 17 performs switching control to switch the slave station equipment 201 between an active state and a sleep state based on the RSSI value of the slave station equipment 201 .

[0067] More specifically, the control information generator 17 compares the RSSI value corresponding to the activated slave station device 201 with a predetermined threshold value ThA by referring to the correspondence table T1 in the storage unit 18. If any RSSI value corresponding to the activated slave station device 201 is continuously equal to or less than the threshold value ThA for a certain period of time, the control information generator 17 controls the slave station device 201 corresponding to that RSSI value to transition from the activated state to the sleep state.

[0068] Specifically, the control information generator 17 acquires a slave station ID corresponding to the RSSI value from the correspondence table T1. The control information generator 17 generates sleep transition information including the acquired slave station ID and outputs the generated sleep transition information to the digital processing unit 11. The sleep transition information is an example of sleep control information. The control information generator 17 also changes the operating state corresponding to the slave station ID in the correspondence table T1 from an active state to a sleep state.

[0069] The digital processing unit 21 in each slave station device 201 in the optical communication system 401 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.

[0070] 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.

[0071] Furthermore, the control information generator 17 in the master station device 101 compares the RSSI value corresponding to the slave station device 201 in the sleep state with a predetermined threshold value ThB by referring to the correspondence table T1 in the storage unit 18. If any RSSI value corresponding to the slave station device 201 in the sleep state is continuously equal to or greater than the threshold value ThB for a certain period of time, the control information generator 17 controls the slave station device 201 corresponding to that RSSI value to transition from the sleep state to the wake-up state.

[0072] Specifically, the control information generator 17 acquires a slave station ID corresponding to the RSSI value from the correspondence table T1. The control information generator 17 generates sleep wake-up information including the acquired slave station ID and outputs the generated sleep wake-up information to the digital processing unit 11. The sleep wake-up information is an example of sleep control information. The control information generator 17 also changes the operating state corresponding to the slave station ID in the correspondence table T1 from a sleep state to an active state.

[0073] The digital processing unit 21 in each slave station device 201 in the optical communication system 401 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.

[0074] 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 causes the analog processing unit 22 to start outputting the RF signal Srd to the antenna 161.

[0075] For example, the storage unit 18 in the master station device 101 stores a sleep database for the time period when the slave station device 201 is in a sleep state. When the control information generator 17 transitions the slave station device 201 from an active state to a sleep state and then transitions the slave station device 201 from the sleep state to an active state, the control information generator 17 adds the time period during which the slave station device 201 was in the sleep state to the sleep database in the storage unit 18.

[0076] The control information generator 17 performs switching control to switch the slave station equipment 201 between the awake state and the sleep state, further based on the sleep database in the storage unit 18. More specifically, the control information generator 17 switches more slave station equipment 201 to the sleep state based on the sleep database during time periods when there are fewer communication terminals located near the slave station equipment 201, such as late at night or early in the morning. Specifically, the control information generator 17 determines which slave station equipment 201 to transition from the awake state to the sleep state during those time periods using a threshold value ThAs that is greater than the threshold value ThA, instead of the threshold value ThA.

[0077] 4 is a bird's-eye view illustrating an example of an arrangement of slave station devices in an optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 4, for example, an optical communication system 401 includes slave station devices 201A, 201B, 201C, 201D, 201E, 201F, and 201G, which are slave station devices 201.

[0078] 5 is a bird's-eye view illustrating an example of coverage areas of slave station devices in an optical communication system according to the first embodiment of the present disclosure, which illustrates coverage areas CEA, CEB, CEC, CED, CEE, CEF, and CEG, which are the coverage area CE of slave station devices 201A, 201B, 201C, 201D, 201E, 201F, and 201G.

[0079] 5 , the coverage area CE of the slave station device 201 is the reception range of the RF signal Sru and the transmission range of the RF signal Srd by the slave station device 201. For example, the coverage area CE of the slave station device 201 is a circular range centered on the position of the slave station device 201.

[0080] 6 is a diagram illustrating an example of an RSSI table stored in a storage unit in a master station device 101 of the optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 6, the storage unit 18 in the master station device 101 stores in advance an RSSI table T2 indicating a correspondence relationship between a slave station device 201 transmitting an RF signal and an RSSI value indicating the reception strength of the RF signal at another slave station device 201.

[0081] For example, when the optical communication system 401 is started up or a slave station device 201 is added to the optical communication system 401, the control information generator 17 in the master station device 101 executes an RSSI acquisition sequence to acquire RSSI values ​​indicating the reception strength of RF signals transmitted by the slave station devices 201 at the other slave station devices 201, and creates an RSSI table T2 based on the acquired RSSI values. As an example, the control information generator 17 executes the RSSI acquisition sequence during times when there are few communication terminals located near the slave station devices 201, such as late at night or early in the morning.

[0082] More specifically, the control information generator 17 allocates non-overlapping transmission periods to each slave station device 201 in the optical communication system 401. The control information generator 17 outputs transmission information indicating the transmission periods allocated to each slave station device 201 to the digital processing unit 11. The transmission information is an example of control information. The control information generator 17 may output transmission information to the digital processing unit 11 that further includes designation of the intensity and frequency of the RF signal to be transmitted by each slave station device 201 during the transmission period. In this case, the control information generator 17 may cause each slave station device 201 to output RF signals of different frequencies, or may cause each slave station device 201 to output RF signals of different intensities.

[0083] 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 transmission information from the frame Fd. The digital processing unit 21 outputs the extracted transmission information to the control information processing unit 27.

[0084] In accordance with the transmission information, the control information processing unit 27 in the slave station device 201 causes the analog processing unit 22 to output the RF signal Srd to the antenna 161 during the transmission period assigned to that slave station device 201, and causes the analog processing unit 22 to stop outputting the RF signal Srd to the antenna 161 during the transmission period assigned to another slave station device 201.

[0085] During the transmission period allocated to the other slave station device 201, the monitor unit 28 receives the RF signal Sru from the analog processing unit 22, calculates an RSSI indicating the reception strength of the RF signal Sru at the analog processing unit 22, and outputs the RSSI value to the digital processing unit 21.

[0086] The digital processing unit 11 in the master station device 101 receives the digital signal Sdu from the separator 14 and acquires a frame Fu from the received digital signal Sdu. The digital processing unit 11 acquires the slave station ID and RSSI value of the slave station device 201 from the frame Fu. The digital processing unit 11 stores the acquired RSSI value in the storage unit 18 in association with the slave station ID of the slave station device 201.

[0087] The control information generator 17 creates the RSSI table T2 based on the RSSI values ​​stored in the storage unit 18 by the digital processing unit 11 in the RSSI acquisition sequence. For example, the control information generator 17 executes the RSSI acquisition sequence multiple times and creates the RSSI table T2 based on the average value of the acquired RSSI values. The control information generator 17 stores the created RSSI table T2 in the storage unit 18. The control information generator 17 may create the RSSI table T2 indicating the RSSI values ​​of all the slave station devices 201 in the optical communication system 401, or may create the RSSI table T2 indicating the RSSI values ​​of some of the slave station devices 201 in the optical communication system 401.

[0088] For example, if the RSSI value indicating the reception strength at another slave station device 201 of an RF signal transmitted by the slave station device 201 in the RSSI table T2 is −65 dBm or higher, the control information generator 17 determines that the other slave station device 201 is a slave station device 201 that can cover the coverage area CE of the slave station device 201. Specifically, the control information generator 17 determines that the slave station devices 201B and 201C are slave station devices 201 that can cover the coverage area CEA of the slave station device 201A, and that the slave station devices 201A, 201C, 201D, and 201F are slave station devices 201 that can cover the coverage area CEB of the slave station device 201B in the RSSI table T2.

[0089] (Control Example 2: Beamforming Control) When the reception strength of the RF signal Sru at the slave station device 201 is equal to or greater than a predetermined value, the master station device 101 determines another slave station device 201 that covers the transmission and reception range of the RF signal from the slave station device 201 .

[0090] The parent station device 101 generates beamforming information, which is control information for controlling the transmission and reception range of the RF signal in the determined other child station device 201, and transmits a downstream optical signal including a digital signal Sdd containing the generated beamforming information and an RF signal Srd to the other child station device 201.

[0091] The other slave station device 201 acquires beamforming 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 signal in accordance with the acquired beamforming information.

[0092] 7 is a diagram illustrating an example of RSSI values ​​stored in a storage unit in a master station device in an optical communication system according to a first embodiment of the present disclosure. Referring to FIG. 7 , the control information generator 17 periodically or irregularly compares the RSSI value of each slave station device 201 stored in the storage unit 18 with a predetermined threshold ThC. If a slave station device 201 has an RSSI value that is continuously equal to or greater than the threshold ThC for a certain period of time, the control information generator 17 determines that the slave station device 201 is a congested slave station device, i.e., a slave station device 201 in which a large number of communication terminals are present in the corresponding coverage area CE. For example, the threshold ThC is −50 dBm. In this case, the control information generator 17 determines that the slave station devices 201A, 201B, 201C, and 201D are congested slave station devices.

[0093] 8 is an overhead view illustrating an example of coverage areas of slave station devices in the optical communication system according to the first embodiment of the present disclosure. Fig. 8 illustrates a congested area CEZ, which is an outer edge of the coverage areas CEA, CEB, CEC, and CED of slave station devices 201A, 201B, 201C, and 201D, which are congested slave station devices, and coverage areas CEE, CEF, and CEG.

[0094] 6 and 8, the control information generator 17 determines, based on the RSSI table T2, other slave station devices 201 that cover the coverage areas CEA, CEB, CEC, and CED of the congested slave station devices 201A, 201B, 201C, and 201D.

[0095] More specifically, the control information generator 17 determines that there is no slave station device 201 that can cover the coverage area CE of the slave station device 201A, because the RSSI values ​​in the RSSI table T2 indicating the reception strength of the RF signal transmitted by the slave station device 201A, which is the congested slave station device, at the slave station devices 201E, 201F, and 201G other than the congested slave station device are all less than −65 dBm.

[0096] Furthermore, the control information generator 17 determines that there is no slave station device 201 that can cover the coverage area CE of the slave station device 201C, because the RSSI values ​​in the RSSI table T2 indicating the reception strength of the RF signal transmitted by the slave station device 201C, which is a congested slave station device, at the slave station devices 201E, 201F, and 201G other than the congested slave station device are all less than −65 dBm.

[0097] Furthermore, the control information generator 17 determines that there is no slave station device 201 that can cover the coverage area CE of the slave station device 201D, because the RSSI values ​​in the RSSI table T2 indicating the reception strength of the RF signal transmitted by the slave station device 201D, which is the congested slave station device, at the slave station devices 201E, 201F, and 201G other than the congested slave station device are all less than −65 dBm.

[0098] On the other hand, the control information generator 17 determines that the slave station device 201F is capable of covering the coverage area CEB of the slave station device 201B because the RSSI value indicating the reception strength at the slave station device 201F of the RF signal transmitted by the slave station device 201B, which is the congested slave station device, in the RSSI table T2 is −51 dBm, i.e., −65 dBm or greater. The slave station device 201B is an example of a first slave station device, and the slave station device 201F is an example of a second slave station device.

[0099] In this case, the control information generator 17 compares the RSSI value of the slave station device 201F stored in the storage unit 18 with a predetermined threshold value ThD. If the RSSI value of the slave station device 201F is continuously less than the threshold value ThD for a certain period of time, the control information generator 17 determines that the slave station device 201F has sufficient communication bandwidth. Then, the control information generator 17 performs control to change the coverage area CEF of the slave station device 201F.

[0100] More specifically, the control information generator 17 performs control to change the coverage area CEF of the slave station device 201F. Specifically, the control information generator 17 generates beamforming setting information including the slave station ID of the slave station device 201F, which indicates the range of the coverage area CEB to be covered. The control information generator 17 outputs the generated beamforming setting information to the digital processing unit 11. The beamforming setting information is an example of beamforming information. Note that, when the slave station device 201F is in a sleep state, the control information generator 17 transitions the slave station device 201F from the awake state to the sleep state in accordance with the above-described control example 1, prior to control to change the coverage area CEF of the slave station device 201F.

[0101] The digital processing unit 21 in the slave station device 201F receives the digital signal Sdd from the separation unit 24, acquires a frame Fd from the received digital signal Sdd, and acquires beamforming setting information from the frame Fd. The digital processing unit 21 outputs the acquired beamforming setting information to the control information processing unit 27.

[0102] 9 is a bird's-eye view illustrating an example of a coverage area of ​​a slave station device in an optical communication system according to the first embodiment of the present disclosure, showing a congested area CEZ, coverage areas CEF and CEG, and a coverage area CEFs.

[0103] 9 , for example, the control information processing unit 27 in the slave station device 201F receives beamforming setting information from the digital processing unit 21 and, in accordance with the beamforming setting information, changes the transmission / reception range of the RF signals Sru and Srd by the antenna 161 within a range that does not increase power consumption in the slave station device 201F. For example, the control information processing unit 27 changes the coverage area CEF to the coverage area CEFs in accordance with the beamforming setting information. More specifically, the control information processing unit 27 uses beamforming technology to make the beam widths of the RF signals Sru and Srd elongated or to perform sweep control.

[0104] Furthermore, the control information generator 17 in the master station device 101 compares the RSSI value of each slave station device 201 stored in the storage unit 18 with a threshold value ThC. If the RSSI value of the slave station device 201B is continuously less than the threshold value ThC for a certain period of time, the control information generator 17 determines that the slave station device 201B is no longer a congested slave station device. In this case, the control information generator 17 performs control to restore the coverage area CEF of the slave station device 201F to its original state. Specifically, the control information generator 17 generates beamforming cancellation information including the slave station ID of the slave station device 201F. The control information generator 17 outputs the generated beamforming cancellation information to the digital processing unit 11. The beamforming cancellation information is an example of beamforming information.

[0105] The digital processing unit 21 in the slave station device 201F receives the digital signal Sdd from the separation unit 24, acquires a frame Fd from the received digital signal Sdd, and acquires beamforming cancellation information from the frame Fd. The digital processing unit 21 outputs the acquired beamforming cancellation information to the control information processing unit 27.

[0106] The control information processing unit 27 receives the beamforming cancellation information from the digital processing unit 21 and restores the transmission and reception range of the RF signals Sru and Srd by the antenna 161 to the original range in accordance with the beamforming cancellation information.

[0107] On the other hand, when the control information generator 17 in the master station device 101 determines that the slave station device 201F has become a congested slave station device in addition to the slave station devices 201A, 201B, 201C, and 201D based on the comparison result between the RSSI value of each slave station device 201 stored in the storage unit 18 and the threshold value ThC, the control information generator 17 determines, based on the RSSI table T2, another slave station device 201 that covers the coverage area CEF of the slave station device 201F. Then, the control information generator 17 performs control to change the coverage area CE of the determined slave station device 201.

[0108] [Operation Flow] Fig. 10 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. 10 illustrates the sequence of the above-described control example 1.

[0109] Referring to FIG. 10, first, the slave station device 201 calculates an RSSI indicating the reception strength of the RF signal Sru (step S11).

[0110] Next, the slave station device 201 generates a digital signal Sdu including the RSSI value, 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).

[0111] Next, the master station device 101 acquires an RSSI value from the upstream optical signal received from the slave station device 201 and compares the acquired RSSI value with thresholds ThA and ThB. If the RSSI value is continuously equal to or less than the threshold value ThA for a certain period of time, the master station device 101 generates sleep transition information including a slave station ID corresponding to the RSSI value (step S13).

[0112] Next, the master station 101 transmits a downstream optical signal including the digital signal Sdd containing the sleep transition information and the RF signal Srd to the slave station 201 (step S14).

[0113] Next, the slave station device 201 acquires sleep transition information from the downstream optical signal received from the master station device 101, and transitions to a sleep state in accordance with the acquired sleep transition information (step S15).

[0114] Next, the slave station device 201 calculates the RSSI indicating the reception strength of the RF signal Sru (step S16).

[0115] Next, the slave station device 201 generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S17).

[0116] Next, the master station device 101 acquires an RSSI value from the upstream optical signal received from the slave station device 201 and compares the acquired RSSI value with thresholds ThA and ThB. If the RSSI value is continuously equal to or greater than the threshold value ThB for a certain period of time, the master station device 101 generates sleep wake-up information including the slave station ID corresponding to the RSSI value (step S18).

[0117] Next, the master station device 101 transmits a downstream optical signal including the digital signal Sdd containing the sleep release information and the RF signal Srd to the slave station device 201 (step S19).

[0118] Next, the slave station device 201 acquires sleep release information from the downstream optical signal received from the master station device 101, and releases the sleep state in accordance with the acquired sleep transition information (step S20).

[0119] 11 is a diagram illustrating another example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure, showing the sequence of the above-described control example 2.

[0120] Referring to FIG. 11, first, the slave station device 201B calculates an RSSI indicating the reception strength of the RF signal Sru (step S31).

[0121] Next, the slave station device 201B generates a digital signal Sdu including the RSSI value, 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).

[0122] Next, the slave station device 201F calculates the RSSI indicating the reception strength of the RF signal Sru (step S33).

[0123] Next, the slave station device 201F generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S34).

[0124] Next, the master station device 101 acquires an RSSI value from the upstream optical signal received from the slave station device 201, and compares the acquired RSSI value with a threshold value ThC. For example, since the RSSI value of the slave station device 201B is continuously equal to or greater than the threshold value ThC for a certain period of time, the master station device 101 determines that the slave station device 201B is a congested slave station device (step S35).

[0125] Next, the master station device 101 determines, based on the RSSI table T2, that the slave station device 201F can cover the coverage area CEB of the slave station device 201B. The master station device 101 generates beamforming setting information including the slave station ID of the slave station device 201F, which indicates the range of the coverage area CEB to be covered (step S36).

[0126] Next, the master station device 101 transmits a downstream optical signal including a digital signal Sdd containing beamforming setting information and an RF signal Srd to the slave station device 201 (step S37).

[0127] Next, the slave station device 201F acquires beamforming setting information from 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 by the antenna 161 in accordance with the acquired beamforming setting information (step S38).

[0128] Next, the slave station device 201B calculates the RSSI indicating the reception strength of the RF signal Sru (step S39).

[0129] Next, the slave station device 201B generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S40).

[0130] Next, the slave station device 201F calculates the RSSI indicating the reception strength of the RF signal Sru (step S41).

[0131] Next, the slave station device 201F generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 101 (step S42).

[0132] Next, the master station device 101 acquires an RSSI value from the upstream optical signal received from the slave station device 201, and compares the acquired RSSI value with a threshold value ThC. For example, the master station device 101 determines that the slave station device 201B is no longer a congested slave station device because the RSSI value of the slave station device 201B is continuously less than the threshold value ThC for a certain period of time (step S43).

[0133] Next, the master station device 101 generates beamforming cancellation information including the slave station ID of the slave station device 201F (step S44).

[0134] Next, the master station device 101 transmits a downstream optical signal including the digital signal Sdd containing the beamforming cancellation information and the RF signal Srd to the slave station device 201 (step S45).

[0135] Next, the slave station device 201F acquires beamforming cancellation information from the downstream optical signal received from the master station device 101, and restores the transmission and reception range of the RF signals Sru and Srd by the antenna 161 to the original range in accordance with the acquired beamforming cancellation information (step S46).

[0136] In the master station device 101 according to the first embodiment of the present disclosure, the control information generator 17 is configured to determine whether a slave station device is congested based on the comparison result between the RSSI value and the threshold value ThC, but this is not limited to this. The control information generator 17 may estimate the number of communication terminals communicatively connected to the slave station device 201 using the technology described in Non-Patent Document 1, and determine whether a slave station device is congested based on the estimation result.

[0137] In the parent station device 101 according to the first embodiment of the present disclosure, the control information generator 17 is configured to perform the above-described control example 1 and control example 2, but this is not limiting. The control information generator 17 may be configured not to perform either control example 1 or control example 2.

[0138] In the master station device 101 according to the first embodiment of the present disclosure, the control information generator 17 is configured to control the slave station device 201 to transition from an active state to a sleep state in the above-described control example 1, but the present invention is not limited to this. Instead of controlling the slave station device 201 to transition from an active state to a sleep state, the control information generator 17 may be configured to control the slave station device 201 to reduce the signal strength of the RF signal Srd.

[0139] In addition, in the master station device 101 according to the first embodiment of the present disclosure, the control information generator 17 is configured to determine the other slave station devices 201 that cover the coverage area CE of the congested slave station device based on the RSSI table T2, but this is not limiting. The control information generator 17 may be configured to determine the other slave station devices 201 that cover the coverage area CE of the congested slave station device based on, for example, the location of the slave station device 201 without using the RSSI table T2.

[0140] Furthermore, although the slave station devices 201 according to the first embodiment of the present disclosure are configured to include the monitor unit 28, this is not limiting. Some of the slave station devices 201 in the optical communication system 401 may be configured not to include the monitor unit 28. In other words, some of the slave station devices 201 in the optical communication system 401 may be configured not to notify the master station device 101 of the RSSI value.

[0141] Although the optical communication system 401 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 401 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.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In addition, in the optical communication system 401 according to the first embodiment of the present disclosure, the coverage area CE of the slave station device 201 is a circular range centered on the position of the slave station device 201, but this is not limited to this.

[0146] 12 is an overhead view showing another example of the coverage areas of the slave station devices in the optical communication system according to the first embodiment of the present disclosure. Fig. 12 shows coverage areas CEAx, CEBx, CECx, CEDx, CEEx, CEFx, and CEGx, which are the coverage areas CE of the slave station devices 201A, 201B, 201C, 201D, 201E, 201F, and 201G. Referring to Fig. 12, the coverage area CE of the slave station device 201 may be an elongated range extending from the position of the slave station device 201.

[0147] In this case, for example, since the slave station device 201B is located outside the coverage area CEAx of the slave station device 201A, the reception strength of the RF signal transmitted by the slave station device 201A at the slave station device 201B is low. On the other hand, the coverage areas CEAx and CEBx include overlapping portions, and the slave station devices 201A and 201B can transmit and receive RF signals to and from communication terminals located in the overlapping portions. Therefore, the slave station device 201B can cover the overlapping portion in the coverage area CEAx of the slave station device 201A, and the slave station device 201A can cover the overlapping portion in the coverage area CEBx of the slave station device 201B.

[0148] 13 is a diagram illustrating another example of an RSSI table stored in a storage unit in a master station device of the optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 13, the storage unit 18 in the master station device 101 stores an RSSI table T2x indicating a correspondence relationship between points P1, P2, P3, P4, P5, and P6, which are points P where measurement terminals are installed, and RSSI values ​​indicating the reception strength at the measurement terminals of RF signals transmitted from slave station devices 201.

[0149] The control information generator 17 in the master station 101 generates an RSSI table T2x instead of or in addition to the RSSI table T2. The control information generator 17 stores the generated RSSI table T2x in the storage unit 18.

[0150] More specifically, as described above, the control information generator 17 outputs the transmission information to the digital processor 11 in the RSSI acquisition sequence.

[0151] 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 transmission information from the frame Fd. The digital processing unit 21 outputs the extracted transmission information to the control information processing unit 27.

[0152] The control information processing unit 27 in the slave station device 201 causes the analog processing unit 22 to output an RF signal Srd to the antenna 161 while changing the coverage area CE using beamforming technology during the transmission period assigned to the slave station device 201 in accordance with the transmission information, and causes the analog processing unit 22 to stop outputting the RF signal Srd to the antenna 161 during the transmission period assigned to another slave station device 201.

[0153] The control information generator 17 in the master station device 101 acquires, for example, via a network (not shown), RSSI values ​​indicating the reception strength of the RF signal Srd at each measurement terminal provided at points P1, P2, P3, P4, P5, and P6 shown in Fig. 12. The control information generator 17 creates an RSSI table T2x based on the maximum RSSI value during the transmission period allocated to each slave station device 201.

[0154] For example, the control information generator 17 determines that multiple slave station devices 201 that have RSSI values ​​of -50 dBm or greater corresponding to the same point P in the RSSI table T2x can mutually cover the coverage area CE. Specifically, the control information generator 17 determines that the slave station devices 201A and 201B can mutually cover the coverage area CE because the RSSI value corresponding to point P1 is -50 dBm in the RSSI table T2x. For example, the control information generator 17 determines other slave station devices 201 that cover the coverage area CE of the congested slave station device based on the RSSI table T2x in addition to the RSSI table T2.

[0155] In the RSSI acquisition sequence, the control information generator 17 may acquire RSSI values ​​indicating the reception strength of the RF signal Srd at the measurement terminal when the installation position of the measurement terminal is changed, and determine the slave station devices 201 that can mutually cover the coverage area CE based on the analysis results of the correlation between the RSSI values ​​corresponding to each slave station device 201. In this way, it is possible to determine the slave station devices 201 that can mutually cover the coverage area CE, taking into account the increase or decrease in RSSI between the moving communication terminal and the slave station device 201.

[0156] Furthermore, after the optical communication system 401 starts operating, the control information generator 17 may analyze the time-varying information of the RSSI values ​​stored in the storage unit 18 by the digital processing unit 11 using a data analysis technique such as machine learning, and determine the slave station devices 201 that can mutually cover the coverage area CE based on the analysis results. Furthermore, the control information generator 17 may use a pre-created RSSI table T2 in analyzing the time-varying information of the RSSI values.

[0157] 14 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. 14 , an optical communication system 401A further includes a relay station device 301 compared to the optical communication system 401. The relay station device 301 is connected to the parent station device 101 via an optical fiber 191 and an optical splitter (not shown). Some of the slave station devices 201 in the optical communication system 401A are connected to the relay station device 301 via the optical fiber 191. Note that the optical communication system 401A may be configured to include multiple relay station devices 301. Alternatively, all of the slave station devices 201 in the optical communication system 401A may be connected to the relay station device 301 via the optical fiber 191.

[0158] 15 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. 15, a relay station device 301 includes optical couplers 31 and 38, optical demodulators 32A and 32B, separators 33A and 33B, amplifiers 34A and 34B, digital processors 35A and 35B, multiplexers 36A and 36B, and optical modulators 37A and 37B. The amplifiers 34A and 34B may be linear amplifiers or AGC (Automatic Gain Control) amplifiers.

[0159] The optical demodulator 32A receives a downstream optical signal from the parent station 101 via the optical fiber 191 and the optical coupler 31, and generates an electrical signal based on the received downstream optical signal. More specifically, the optical demodulator 32A generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal. The optical demodulator 32A outputs the generated electrical signal to the demultiplexer 33A.

[0160] The separator 33A receives the electrical signal from the optical demodulator 32A, separates the received electrical signal into an RF signal Srd and a digital signal Sdd, and outputs the RF signal Srd to the amplifier 34A and the digital signal Sdd to the digital processing unit 35A. More specifically, the separator 33A outputs frequency components of the electrical signal received from the optical demodulator 32A that are equal to or greater than a predetermined frequency F2 as the RF signal Srd to the amplifier 34A, and outputs frequency components that are less than the frequency F2 to the digital processing unit 35A as the digital signal Sdd.

[0161] Amplifying unit 34A amplifies RF signal Srd received from separating unit 33A, and outputs the amplified RF signal Srd to multiplexing unit 36A.

[0162] The digital processing unit 35A outputs the digital signal Sdd received from the separating unit 33A to the multiplexing unit 36A.

[0163] The multiplexing unit 36A frequency-multiplexes the digital signal Sdd received from the digital processing unit 35A and the RF signal Srd received from the amplification unit 34A. The multiplexing unit 36A 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 37A.

[0164] The optical modulation unit 37A receives the electrical signal from the multiplexing unit 36A and generates a downstream optical signal with wavelength λ2 by optically modulating the received electrical signal. The optical modulation unit 37A outputs the generated downstream optical signal to the optical fiber 191 via the optical coupler 38.

[0165] The optical demodulator 32B receives an upstream optical signal from the slave station device 201 via the optical fiber 191 and the optical coupler 38, and generates an electrical signal based on the received upstream optical signal. More specifically, the optical demodulator 32B generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal. The optical demodulator 32B outputs the generated electrical signal to the demultiplexer 33B.

[0166] The separator 33B receives the electrical signal from the optical demodulator 32B, separates the received electrical signal into an RF signal Sru and a digital signal Sdu, and outputs the RF signal Sru to the amplifier 34B and the digital signal Sdu to the digital processing unit 35B. More specifically, the separator 33B outputs frequency components of the electrical signal received from the optical demodulator 32B that are equal to or greater than a predetermined frequency F1 as the RF signal Sru to the amplifier 34B, and outputs frequency components that are less than the frequency F1 to the digital processing unit 35B as the digital signal Sdu.

[0167] Amplifying unit 34B amplifies RF signal Sru received from separating unit 33B, and outputs the amplified RF signal Sru to multiplexing unit 36B.

[0168] The digital processing unit 35B outputs the digital signal Sdu received from the demultiplexing unit 33B to the multiplexing unit 36B.

[0169] The multiplexing unit 36B frequency-multiplexes the digital signal Sdu received from the digital processing unit 35B and the RF signal Sru received from the amplification unit 34B. The multiplexing unit 36B 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 37B.

[0170] The optical modulator 37B receives the electrical signal from the multiplexer 36B and generates an upstream optical signal with wavelength λ1 by optically modulating the received electrical signal. The optical modulator 37B outputs the generated upstream optical signal to the optical fiber 191 via the optical coupler 31.

[0171] In the optical communication system 401A, 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 301 allows for more flexible setting of the wavelength of the optical signal, making it possible to realize the optical communication system 401A equipped with a larger number of slave station 201.

[0172] 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.

[0173] Second Embodiment [Configuration and Basic Operation] This embodiment relates to an optical communication system 402 that switches the content of the RF signal transmission operation in a representative slave station device among a plurality of slave station devices 201, as compared with the optical communication system 401 according to the first embodiment. Other than the content described below, the optical communication system 402 is the same as the optical communication system 401 according to the first embodiment.

[0174] 16 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 16, compared to the optical communication system 401, the optical communication system 402 includes a master station device 102 instead of the master station device 101.

[0175] 17 is a diagram illustrating the configurations of a master station device and a slave station device in an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 17, the master station device 102 further includes a determination unit 51 in comparison with the master station device 101.

[0176] For example, the storage unit 18 stores operational information indicating the time variation of the RSSI value of each slave station device 201, the power consumption of each slave station device 201, and the location of each slave station device 201. As described above, the storage unit 18 also stores a sleep database for the time period when the slave station device 201 is in a sleep state.

[0177] Based on the operation information and the sleep database in the storage unit 18, the determination unit 51 determines, among the multiple slave station devices 201, a representative slave station device that is a slave station device 201 that will not transition to a sleep state and a dependent slave station device that is a slave station device 201 capable of sleep control. The representative slave station device is a slave station device 201 that can cover the coverage area CE of the dependent slave station device. In other words, the coverage area CE of the dependent slave station device can be covered by the representative slave station device. For example, the determination unit 51 determines a smaller number of representative slave station devices that can cover the coverage area CE of the dependent slave station device, further based on the above-mentioned RSSI table T2. Note that the optical communication system 402 may be configured to include a slave station device 201 that is different from the representative slave station device and different from the dependent slave station devices, and that has a coverage area CE that is not covered by the representative slave station device.

[0178] 18 is a diagram illustrating a classification table stored in a storage unit in a master station device of an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 18 , for example, the determination unit 51 determines slave station devices 201A, 201C, and 201F as representative slave station devices and slave station devices 201B, 201D, and 201G as dependent slave station devices, creates a classification table T3 indicating the slave station IDs of the representative slave station devices and the slave station IDs of the dependent slave station devices, and stores the classification table T3 in the storage unit 18.

[0179] Instead of determining the representative slave station device and the dependent slave station devices, the determination unit 51 may receive the determination results of the representative slave station device and the dependent slave station devices from the administrator of the optical communication system 402, and create the classification table T3 based on the received determination results.

[0180] The master station device 102 generates control information for controlling the transmission operation of the RF signal Srd in a dependent slave station device among the multiple slave station devices 201, and transmits a digital signal Sdd including the generated control information and a downstream optical signal including the RF signal Srd to the dependent slave station device. The dependent slave station device acquires the control information from the digital signal Sdd included in the downstream optical signal received from the master station device 102, and switches the content of the transmission operation of the RF signal Srd in accordance with the acquired control information.

[0181] (Control Example 3: Sleep Control) The master station device 102 generates sleep control information, which is control information for controlling the suspension or execution of the transmission operation of the RF signal Srd in a dependent slave station device among the multiple slave station devices 201. The master station device 102 transmits a digital signal Sdd including the generated sleep control information and a downstream optical signal including the RF signal Srd to the dependent slave station device.

[0182] The dependent slave station device acquires sleep control information from the digital signal Sdd included in the downstream optical signal received from the master station device 102, and switches between stopping and starting the transmission operation of the RF signal Srd in accordance with the acquired sleep control information.

[0183] 19 is a bird's-eye view illustrating an example of coverage areas of slave station devices in an optical communication system according to the second embodiment of the present disclosure, which illustrate coverage areas CEA, CEC, and CEF of slave station devices 201A, 201C, and 201F, which are representative slave station devices.

[0184] 19 , for example, when the determination unit 51 stores the classification table T3 in the storage unit 18, the control information generation unit 17 in the master station device 102 controls the slave station devices 201B, 201D, and 201G, which are dependent slave station devices, to transition from an active state to a sleep state based on the classification table T3. Furthermore, the coverage areas CEA, CEC, and CEF of the slave station devices 201A, 201C, and 201F, which are representative slave station devices, have elongated shapes and are subject to sweep control.

[0185] For example, the control information generation unit 17 in the master station device 102 performs switching control to switch the slave station devices 201B, 201D, and 201G, which are dependent slave station devices, between an active state and a sleep state based on the RSSI values ​​of the representative slave station devices 201A, 201C, and 201F.

[0186] More specifically, the control information generator 17 refers to the correspondence table T1 in the storage unit 18 and compares the RSSI value corresponding to the representative slave station device with a predetermined threshold ThE. If any RSSI value corresponding to the representative slave station device is continuously equal to or greater than the threshold ThE for a certain period of time, the control information generator 17 determines that the communication bandwidth of the representative slave station device corresponding to that RSSI value is constrained. In other words, the control information generator 17 determines that communication with the communication terminal using only that representative slave station device is difficult. The control information generator 17 then controls dependent slave station devices located near the representative slave station device and having RSSI values ​​equal to or greater than the predetermined value to transition from a sleep state to an active state. As an example, if the RSSI value corresponding to the slave station device 201F is continuously greater than or equal to the threshold value ThE for a certain period of time, the control information generation unit 17 controls the slave station devices 201E and 201G, which are dependent slave station devices located near the slave station device 201A, to transition from a sleep state to an active state.

[0187] Specifically, the control information generator 17 generates sleep release information including the slave station IDs of the slave station devices 201E and 201G, and outputs the generated sleep release information to the digital processor 11.

[0188] The digital processing unit 21 in each of the slave station devices 201E and 201G receives the digital signal Sdd from the separation unit 24, extracts a frame Fd from the received digital signal Sdd, and extracts sleep release information from the frame Fd. The digital processing unit 21 outputs the extracted sleep release information to the control information processing unit 27.

[0189] 20 is an overhead view illustrating an example of coverage areas of slave station devices in an optical communication system according to a second embodiment of the present disclosure, including coverage areas CEA, CEC, and CEF and coverage areas CEE and CEG of slave station devices 201E and 201G, which are dependent slave station devices.

[0190] 20 , the control information processing unit 27 in each of the slave station devices 201E and 201G 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 causes the analog processing unit 22 to start outputting the RF signal Srd to the antenna 161.

[0191] The control information generator 17 in the master station device 102 also references the correspondence table T1 in the storage unit 18 and compares the RSSI value corresponding to the slave station device 201F with a predetermined threshold value ThF. If the RSSI value corresponding to the slave station device 201F is continuously less than the threshold value ThF for a certain period of time, the control information generator 17 determines that there is sufficient bandwidth for the slave station device 201F. In other words, the control information generator 17 determines that communication with the communication terminal is possible using only the slave station device 201F. In this case, the control information generator 17 confirms that the RSSI values ​​of the slave station devices 201E and 201G are less than the predetermined value, and controls the slave station devices 201E and 201G to transition from the active state to the sleep state.

[0192] Specifically, the control information generator 17 generates sleep transition information including the slave station IDs of the slave station devices 201E and 201G, and outputs the generated sleep transition information to the digital processor 11.

[0193] The digital processing unit 21 in each of the slave station devices 201E and 201G receives the digital signal Sdd from the separation unit 24, acquires a frame Fd from the received digital signal Sdd, and acquires sleep transition information from the frame Fd. The digital processing unit 21 outputs the acquired sleep transition information to the control information processing unit 27.

[0194] The control information processing unit 27 in each of the slave station devices 201E and 201G receives the 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 multiplexer 23.

[0195] When the control information generator 17 in the master station device 102 controls the slave station devices 201E and 201G to transition from the sleep state to the active state, the control information generator 17 may also control the slave station device 201F to have a smaller coverage area CEF. Specifically, the control information generator 17 generates reduction information including the slave station ID of the slave station device 201F. The control information generator 17 outputs the generated reduction information to the digital processing unit 11.

[0196] The digital processing unit 21 in the slave station device 201F receives the digital signal Sdd from the separation unit 24, acquires a frame Fd from the received digital signal Sdd, and acquires reduced information from the frame Fd. The digital processing unit 21 outputs the acquired reduced information to the control information processing unit 27.

[0197] The control information processing unit 27 in the slave station device 201F receives the reduction information from the digital processing unit 21 and reduces the transmission / reception range of the RF signals Sru and Srd by the antenna 161 in accordance with the received reduction information.

[0198] Furthermore, for example, the determination unit 51 in the master station device 102 increases or decreases the number of representative slave station devices depending on the time period. More specifically, the determination unit 51 uses data analysis techniques such as machine learning to analyze the operational information and sleep database in the storage unit 18 to detect congested time periods and congested areas where the number of communication terminals increases. During the detected congested time period, the determination unit 51 changes a dependent slave station device in the vicinity of the detected congested area to a representative slave station device. The congested time period is, for example, a time period when the RSSI values ​​of all slave station devices 201 are equal to or greater than a predetermined value. By changing a dependent slave station device to a representative slave station device based on the congested time period and congested area detected using machine learning, it is possible to reduce power consumption in the optical communication system 402 while maintaining stable communication.

[0199] The determination unit 51 also uses machine learning to analyze the operational information and sleep database in the storage unit 18 to detect quiet time periods and quiet areas where the number of communication terminals is low. During the detected quiet time periods, the determination unit 51 changes representative slave station devices in the vicinity of the detected quiet area to dependent slave station devices. The quiet time periods are, for example, time periods when the RSSI values ​​of all slave station devices 201 are less than a predetermined value. By changing the representative slave station device to a dependent slave station device based on the quiet time periods and quiet areas detected using machine learning, it is possible to reduce power consumption in the optical communication system 402 while maintaining stable communication.

[0200] [Operation Flow] Fig. 21 is a diagram illustrating an example of a communication sequence in the optical communication system according to the second embodiment of the present disclosure. Fig. 21 illustrates the sequence of the above-described control example 3.

[0201] 21 , first, the master station device 102 determines the representative slave station devices and the dependent slave station devices based on the operation information, the sleep database, and the RSSI table T2 in the storage unit 18. As an example, the master station device 102 determines the slave station devices 201A, 201C, and 201F as the representative slave station devices, and the slave station devices 201B, 201D, and 201G as the dependent slave station devices (step S51).

[0202] Next, the master station device 102 generates sleep transition information including the slave station ID of the dependent slave station device (step S52).

[0203] Next, the master station 102 transmits a downstream optical signal including the digital signal Sdd containing the sleep transition information and the RF signal Srd to the dependent slave station (step S53).

[0204] Next, the dependent slave station devices 201E and 201G acquire sleep transition information from the downstream optical signal received from the master station device 102, and transition to the sleep state in accordance with the acquired sleep transition information (step S54).

[0205] Next, the slave station device 201F calculates the RSSI indicating the reception strength of the RF signal Sru (step S55).

[0206] Next, the slave station device 201F generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 102 (step S56).

[0207] Next, the slave station devices 201E and 201G calculate the RSSI indicating the reception strength of the RF signal Sru (step S57).

[0208] Next, the slave station devices 201E and 201G generate a digital signal Sdu including the RSSI value, and transmit an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 102 (step S58).

[0209] Next, the master station device 102 acquires an RSSI value from the upstream optical signal received from the slave station device 201F and compares the acquired RSSI value with thresholds ThE and ThF. If the RSSI value is continuously equal to or greater than the threshold ThE for a certain period of time, the master station device 102 determines that the communication bandwidth of the slave station device 201F is congested, and generates sleep wake-up information including the slave station IDs of the slave station devices 201E and 201G (step S59).

[0210] Next, the master station device 102 transmits a downstream optical signal including the digital signal Sdd containing the sleep release information and the RF signal Srd to the slave station device 201 (step S60).

[0211] Next, the slave station devices 201E and 201G acquire sleep release information from the downstream optical signal received from the master station device 102, and release the sleep state in accordance with the acquired sleep release information (step S61).

[0212] Next, the slave station device 201F calculates the RSSI indicating the reception strength of the RF signal Sru (step S62).

[0213] Next, the slave station device 201F generates a digital signal Sdu including the RSSI value, and transmits an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 102 (step S63).

[0214] Next, the slave station devices 201E and 201G calculate the RSSI indicating the reception strength of the RF signal Sru (step S64).

[0215] Next, the slave station devices 201E and 201G generate a digital signal Sdu including the RSSI value, and transmit an upstream optical signal including the generated digital signal Sdu and the RF signal Sru to the master station device 102 (step S65).

[0216] Next, the master station device 102 acquires an RSSI value from the upstream optical signal received from the slave station device 201F and compares the acquired RSSI value with thresholds ThE and ThF. If the RSSI value is continuously less than the threshold ThF for a certain period of time, the master station device 102 determines that the communication bandwidth of the slave station device 201F has become available, and generates sleep transition information including the slave station IDs of the slave station devices 201E and 201G (step S66).

[0217] Next, the master station 102 transmits a downstream optical signal including the digital signal Sdd containing the sleep transition information and the RF signal Srd to the slave station 201 (step S67).

[0218] Next, the slave station devices 201E and 201G acquire sleep transition information from the downstream optical signal received from the master station device 102, and transition to the sleep state in accordance with the acquired sleep transition information (step S68).

[0219] In the master station device 102 according to the second embodiment of the present disclosure, the control information generator 17 is configured to perform switching control to switch the dependent slave station devices 201B, 201D, and 201G between an active state and a sleep state based on the RSSI value of the representative slave station devices 201A, 201C, and 201F, but this is not limiting. The control information generator 17 may also acquire a throughput value of the communication terminal from the base station device, and perform switching control to switch the dependent slave station devices between an active state and a sleep state based on the acquired throughput value instead of or in addition to the RSSI value.

[0220] 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.

[0221] 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.

[0222] 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 radio signals via antennas, wherein the master station device generates control information for controlling a transmission operation of the radio signals in the slave station devices based on reception strength of the radio signals in the plurality of slave station devices, and transmits an optical signal including a digital signal and an analog main signal that includes the generated control information to the slave station devices, wherein 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 radio signals in accordance with the acquired control information, wherein the master station device generates the control information based on RSSI in the plurality of slave station devices, and wherein the optical communication system is an analog RoF system.

[0223] 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 17 Control information generation unit 18 Storage unit 19 Optical coupler 21 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, 38 Optical coupler 32A, 32B Optical demodulation unit 33A, 33B Separating unit 34A, 34B Amplifying unit 35A, 35B Digital processing unit 36A, 36B Multiplexing unit 37A, 37B Optical modulation unit 51 Determination unit 101, 102 Master station device 161 Antenna 191 Optical fiber 201, 201A, 201B, 201C, 201D, 201E, 201F, 201G slave station equipment 301 relay station equipment 401, 401A, 402 optical communication system CE, CEA, CEB, CEC, CED, CEE, CEF, CEG, CEFs coverage area CEZ congestion area T1 correspondence table T2 RSSI table T3 classification table

Claims

1. An optical communications system comprising: a master station device; and slave station devices that transmit and receive radio signals via an antenna; wherein the master station device generates control information for controlling the transmission operation of the radio signals in the slave station devices based on the reception strength of the radio signals in a plurality of the slave station devices, and transmits an optical signal including a digital signal and an analog main signal including the generated control information to the slave station devices; and 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 the content of the transmission operation of the radio signals in accordance with the acquired control information.

2. The optical communication system of claim 1, wherein the parent station device generates sleep control information, which is the control information for controlling the suspension or execution of radio signal transmission operation in the child station device, and transmits an optical signal including a digital signal and an analog main signal including the generated sleep control information to the child station device, and the child station device acquires the sleep control information from a digital signal included in the optical signal received from the parent station device, and switches between suspension and execution of the radio signal transmission operation in accordance with the acquired sleep control information.

3. The optical communication system described in claim 1 or claim 2, wherein when the receiving strength of the radio signal at the first slave station device is equal to or greater than a predetermined value, the parent station device determines a second slave station device that covers the transmission and reception range of the radio signal by the first slave station device, the parent station device generates beamforming information, which is the control information for controlling the transmission and reception range of the radio signal at the second slave station device, and transmits an optical signal including a digital signal containing the generated beamforming information and an analog main signal to the second slave station device, and the second slave station device acquires the beamforming information from a digital signal contained in the optical signal received from the parent station device, and changes the transmission and reception range of the radio signal in accordance with the acquired beamforming information.

4. The optical communication system according to claim 3, wherein the master station device determines the second slave station device based on the reception strength of the radio signal transmitted by the first slave station device at a slave station device different from the first slave station device.

5. An optical communication system as described in claim 1 or claim 2, wherein the multiple slave station devices include a representative slave station device and a dependent slave station device different from the representative slave station device, and the master station device generates the control information for controlling the transmission operation of radio signals in the dependent slave station devices, and transmits an optical signal including a digital signal and an analog main signal including the generated control information to the dependent slave station devices.

6. The optical communication system according to claim 5, wherein the master station increases or decreases the number of representative slave stations depending on the time period.

7. A master station device comprising: a control information generating unit that generates control information for controlling the transmission operation of radio signals in a plurality of slave station devices based on the reception strength of the radio signals in the slave station devices; and a transmitting unit that transmits an optical signal including a digital signal including the control information generated by the control information generating unit and an analog main signal to the slave station devices.

8. An optical communication method in an optical communication system having a master station device and slave station devices that transmit and receive radio signals via an antenna, comprising the steps of: the master station device generating control information for controlling a transmission operation of the radio signals in the slave station devices based on the reception strength of the radio signals in the slave station devices, and transmitting an optical signal including a digital signal and an analog main signal including the generated control information to the slave station devices; 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 signals in accordance with the acquired control information.

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