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

Abstract

This optical communication system comprises: a master station device, and a slave station device for transmitting and receiving a radio signal via an antenna. The master station device: receives a plurality of first communication signals respectively corresponding to a plurality of frequency bands; generates a downlink optical signal including a first electric signal in which the plurality of first communication signals are multiplexed; and transmits the downlink optical signal to the slave station device. The slave station device: acquires the first electric signal from the downlink optical signal; extracts, from the first electric signal, first communication signals corresponding to a portion of the plurality of frequency bands; and transmits a downlink radio signal based on the extracted first communication signals.

Description

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

[0001] This application claims priority based on Japanese Patent Application No. 2024-83722, filed May 23, 2024, the disclosure of which is incorporated herein in its entirety by reference.

[0002] Patent Document 1 (JP 2022-185171 A) discloses the following communication relay system: That is, the communication relay system transmits signals related to wireless communication between a mobile station and base stations of multiple communication carriers that use different frequency bands, and includes a master unit that can send and receive signals to and from the base stations of the multiple communication carriers, and a slave unit that transmits signals between the master unit and also communicates wirelessly with the mobile station, and includes a timing detection unit that detects the timing of transmission and reception between the base station of each communication carrier and the mobile station, and a signal suppression unit that suppresses interference waves using a signal that is transmitted to the mobile station at a timing tailored to a desired communication carrier based on the timing detected by the timing detection unit for the signal received from the mobile station.

[0003] JP 2022-185171 A JP 2019-213014 A JP 2018-186353 A

[0004] The optical communication system disclosed herein includes a master station device and slave station devices that transmit and receive wireless signals via an antenna, wherein the master station device receives a plurality of first communication signals corresponding to a plurality of frequency bands from other devices, generates a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, and the slave station device acquires the first electrical signal from the downstream optical signal, performs a downstream extraction process to extract the first communication signal corresponding to a portion of the frequency bands from the acquired first electrical signal, and transmits a downstream wireless signal based on the extracted first communication signal.

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

[0006] Furthermore, 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 an optical communication method including such characteristic processing steps, or as a program for causing a computer to execute such steps. Furthermore, one aspect of the present disclosure may be realized as a semiconductor integrated circuit that realizes part or all of the master station device.

[0007] Furthermore, one aspect of the present disclosure may be realized not only as a slave station device having such a characteristic processing unit, but also as an optical communication method including 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 a slave 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 a configuration of a master station device in the optical communication system according to the first embodiment of the present disclosure. FIG. 3 is a diagram illustrating a configuration of a slave station device in the optical communication system according to the first embodiment of the present disclosure. FIG. 4 is a diagram illustrating an example of a downstream communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of an upstream communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. FIG. 7 is a diagram illustrating a configuration of a slave station device in the optical communication system according to the second embodiment of the present disclosure. FIG. 8 is a diagram illustrating a configuration of an optical communication system according to a third embodiment of the present disclosure. FIG. 9 is a diagram illustrating a configuration of a slave station device in the optical communication system according to the third embodiment of the present disclosure.

[0009] Conventionally, optical communication systems that can be shared and used by a plurality of communication carriers have been developed.

[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 to 3 and allows telecommunications carriers to flexibly select the use of slave station devices in an optical communication system used by multiple telecommunications carriers.

[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, a slave station device, and an optical communication method that enable a telecommunications carrier to flexibly select the slave station device to be used in an optical communication system used by multiple telecommunications carriers.

[0012] Effect of the Present Disclosure According to the present disclosure, in an optical communication system used by a plurality of communication carriers, the communication carriers can flexibly select which slave station devices to use.

[0013] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. (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 wireless signals via antennas, wherein the master station device receives a plurality of first communication signals corresponding to a plurality of frequency bands from other devices, generates a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, and the slave station device acquires the first electrical signal from the downstream optical signal and performs downstream extraction processing to extract the first communication signal corresponding to a portion of the frequency bands from the acquired first electrical signal, and transmits a downstream wireless signal based on the extracted first communication signal.

[0014] In this manner, by transmitting a downstream wireless signal based on a first communication signal extracted in the downstream extraction process from among a plurality of first communication signals corresponding to a plurality of frequency bands, it is possible to selectively transmit some of the plurality of first communication signals. Therefore, for example, in an optical communication system including a plurality of distributed slave station devices, it is possible to change the first communication signal to be wirelessly transmitted from among the plurality of first communication signals for each area where the slave station devices are installed, in response to requests from the telecommunications carriers. Furthermore, power consumption can be reduced compared to a configuration in which all first communication signals are transmitted. Therefore, in an optical communication system used by multiple telecommunications carriers, telecommunications carriers can flexibly select which slave station devices to use.

[0015] (2) In the above (1), the slave station device may receive an upstream wireless signal, perform an upstream extraction process to extract a second communication signal corresponding to the part of the frequency band from a signal based on the received upstream wireless signal, generate an upstream optical signal including the extracted second communication signal, and transmit the generated upstream optical signal to the master station device.

[0016] With this configuration, it is possible to reduce ingress noise in upstream communication and widen the reception dynamic range of the upstream wireless signal compared to a configuration in which an upstream optical signal including a signal based on the upstream wireless signal is transmitted to the parent station device without performing upstream extraction processing.

[0017] (3) In the above (1) or (2), the parent station device may generate a control signal indicating the first communication signal to be extracted in the downstream extraction process, and transmit the downstream optical signal further including the generated control signal to the child station device, and the child station device may further acquire the control signal from the downstream optical signal, and extract the first communication signal from the first electrical signal in accordance with the acquired control signal.

[0018] With this configuration, the first communication signal to be extracted in the slave station device can be easily set.

[0019] (4) In the above (2), in the uplink extraction process, the slave station device may extract the second communication signals corresponding to the partial frequency band, the communication quality of which satisfies a predetermined condition.

[0020] With this configuration, it is possible to selectively extract, for example, a second communication signal corresponding to the frequency band in which the upstream communication is being carried out, thereby reducing ingress noise in the upstream communication and widening the reception dynamic range of the upstream radio signal.

[0021] (5) A master station device according to an embodiment of the present disclosure is a master station device that transmits communication signals to slave station devices that transmit and receive wireless signals via an antenna, and includes: a receiver that receives from another device a plurality of first communication signals corresponding to a plurality of frequency bands, respectively; a first generator that generates a first electrical signal into which the plurality of first communication signals received by the receiver are multiplexed; a second generator that generates a control signal indicating which of the plurality of first communication signals is to be wirelessly transmitted by the slave station device; and an optical transmitter that generates a downstream optical signal including the first electrical signal generated by the first generator and the control signal generated by the second generator, and transmits the generated downstream optical signal to the slave station device.

[0022] In this manner, a control signal indicating a first communication signal to be wirelessly transmitted in a slave station device is generated, and a downstream optical signal including the control signal is transmitted to the slave station device. This configuration allows selective transmission of some of the multiple first communication signals. Therefore, for example, in an optical communication system including multiple distributed slave station devices, it is possible to change the first communication signal to be wirelessly transmitted among the multiple first communication signals for each area where the slave station devices are installed, depending on the needs of the telecommunications carrier. Furthermore, power consumption can be reduced compared to a configuration in which all first communication signals are transmitted. Therefore, in an optical communication system used by multiple telecommunications carriers, telecommunications carriers can flexibly select which slave station devices to use.

[0023] (6) A slave station device according to an embodiment of the present disclosure is a slave station device that transmits and receives wireless signals via an antenna, and includes an optical receiving unit that receives a downstream optical signal from a master station device and acquires, from the received downstream optical signal, a first electrical signal into which multiple first communication signals corresponding to multiple frequency bands are multiplexed; an extracting unit that performs a downstream extraction process to extract, from the first electrical signal acquired by the optical receiving unit, the first communication signals corresponding to some of the frequency bands; and a wireless transmitting unit that transmits a downstream wireless signal based on the first communication signals extracted by the extracting unit.

[0024] In this manner, by transmitting a downstream wireless signal based on a first communication signal extracted in the downstream extraction process from among a plurality of first communication signals corresponding to a plurality of frequency bands, it is possible to selectively transmit some of the plurality of first communication signals. Therefore, for example, in an optical communication system including a plurality of distributed slave station devices, it is possible to change the first communication signal to be wirelessly transmitted from among the plurality of first communication signals for each area where the slave station devices are installed, in response to requests from the telecommunications carriers. Furthermore, power consumption can be reduced compared to a configuration in which all first communication signals are transmitted. Therefore, in an optical communication system used by multiple telecommunications carriers, telecommunications carriers can flexibly select which slave station devices to use.

[0025] (7) An optical communication method according to an embodiment of the present disclosure is an optical communication method in an optical communication system including a master station device and a slave station device that transmits and receives wireless signals via an antenna, the method including the steps of: the master station device receiving a plurality of first communication signals corresponding to a plurality of frequency bands from another device, generating a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmitting the generated downstream optical signal to the slave station device; and the steps of the slave station device acquiring the first electrical signal from the downstream optical signal, performing a downstream extraction process to extract the first communication signal corresponding to a portion of the frequency bands from the acquired first electrical signal, and transmitting a downstream wireless signal based on the extracted first communication signal.

[0026] In this way, by using a method for transmitting a downstream wireless signal based on a first communication signal extracted in the downstream extraction process from among a plurality of first communication signals corresponding to a plurality of frequency bands, it is possible to selectively transmit some of the plurality of first communication signals. Therefore, for example, in an optical communication system including a plurality of distributed slave station devices, it is possible to change the first communication signal to be wirelessly transmitted from among the plurality of first communication signals for each area where the slave station devices are installed, in response to requests from the telecommunications carrier. Furthermore, compared to a method for transmitting all first communication signals, it is possible to reduce power consumption. Therefore, in an optical communication system used by multiple telecommunications carriers, telecommunications carriers can flexibly select which slave station devices to use.

[0027] 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.

[0028] 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, an optical communication system 401 includes a master station device 101 and multiple slave station devices 201. The master station device 101 and the multiple slave station devices 201 are connected in a one-to-multiple configuration via an optical fiber 191 and an optical splitter (not shown). The master station device 101 is connected to base station devices 301A, 301B, 301C, and 301D via a transmission line 181, and is connected to a control device 311 via a transmission line 171. The transmission lines 171 and 181 are, for example, coaxial cables. The base station devices 301A, 301B, 301C, and 301D are provided in the base stations of communication carriers OpA, OpB, OpC, and OpD, respectively. Hereinafter, each of the base station devices 301A, 301B, 301C, and 301D will also be referred to as a base station device 301, and each of the communication operators OpA, OpB, OpC, and OpD will also be referred to as a communication operator Op.

[0029] Each slave station device 201 includes an antenna 211. The antennas 211 are arranged at intervals. More specifically, the antennas 211 are arranged spatially dispersed. The optical communication system 401 is a distributed antenna system.

[0030] The slave station device 201 transmits and receives wireless signals, i.e., RF (Radio Frequency) signals, to and from a communication terminal (not shown) via an antenna 211. The communication terminal may be a mobile terminal or a fixed terminal.

[0031] The master station device 101 and the slave station device 201 transmit and receive optical signals, including analog signals, via the optical fiber 191. Hereinafter, an optical signal transmitted from the master station device 101 to the slave station device 201 will also be referred to as a downstream optical signal, and an optical signal transmitted from the slave station device 201 to the master station device 101 will also be referred to as an upstream optical signal.

[0032] For example, the optical communication system 401 is used as a fronthaul in a mobile communication system conforming to the TDD (Time Division Duplex) method. In this case, in the optical communication system 401, a downlink period Pd for downlink communication in which the slave station device 201 transmits an RF signal to a communication terminal and an uplink period Pu for uplink communication in which the slave station device 201 receives an RF signal from the communication terminal are alternately switched and repeated.

[0033] More specifically, the master station device 101 receives RF signals SdA, SdB, SdC, and SdD containing communication data from the base station devices 301A, 301B, 301C, and 301D via the corresponding transmission lines 181. For example, the RF signals SdA, SdB, SdC, and SdD are signals modulated using Orthogonal Frequency Division Multiplex (OFDM). Hereinafter, each of the RF signals SdA, SdB, SdC, and SdD will also be referred to as RF signal Sd. The RF signal Sd is an example of a first communication signal. The RF signals SdA, SdB, SdC, and SdD are Sub6 band signals corresponding to different frequency bands FbA, FbB, FbC, and FbD, respectively. Hereinafter, each of the frequency bands FbA, FbB, FbC, and FbD will also be referred to as a frequency band Fb. Note that a portion of the frequency band Fb may overlap with a portion of another frequency band Fb. Furthermore, the RF signal Sd may be a millimeter wave signal.

[0034] The master station device 101 generates a downstream optical signal including an RF signal Md multiplexed with the received RF signal Sd, and transmits the generated downstream optical signal to each slave station device 201 via the optical fiber 191. The RF signal Md is an example of a first electrical signal.

[0035] Each slave station device 201 receives a downstream optical signal from the master station device 101 via the optical fiber 191 and acquires an RF signal Md from the received downstream optical signal. During the downstream period Pd, each slave station device 201 transmits the acquired RF signal Md to the communication terminal via the antenna 211. Here, in the optical communication system 401, it is permitted that the signal strengths of the frequency bands FbA, FbB, FbC, and FbD in the RF signal Md transmitted by the slave station device 201 via the antenna 211 are different from the strengths of the RF signals SdA, SdB, SdC, and SdD transmitted to the master station device 101 by the base station devices 301A, 301B, 301C, and 301D, respectively.

[0036] Furthermore, each slave station device 201 receives an RF signal Mu containing communication data from the communication terminal during the upstream period Pu. Each slave station device 201 generates an upstream optical signal containing the received RF signal Mu and transmits the generated upstream optical signal to the master station device 101 via the optical fiber 191. The RF signal Mu is an example of an upstream wireless signal.

[0037] The master station device 101 receives upstream optical signals from each slave station device 201 via the optical fiber 191. The master station device 101 acquires an RF signal Mu from the received upstream optical signal, and acquires RF signals SuA, SuB, SuC, and SuD from the acquired RF signal Mu. For example, the RF signals SuA, SuB, SuC, and SuD are OFDM-modulated signals. Hereinafter, each of the RF signals SuA, SuB, SuC, and SuD will also be referred to as an RF signal Su. The RF signal Su is an example of a second communication signal. The RF signals SuA, SuB, SuC, and SuD are Sub6 band signals corresponding to different frequency bands FbA, FbB, FbC, and FbD, respectively. Note that the RF signal Su may be a millimeter wave band signal. Furthermore, the frequency bands of the RF signals SuA, SuB, SuC, and SuD may be different from the frequency bands of the RF signals SdA, SdB, SdC, and SdD, respectively.

[0038] The master station device 101 transmits the acquired RF signals SuA, SuB, SuC, and SuD via the corresponding transmission lines 181 to the base station devices 301A, 301B, 301C, and 301D, respectively.

[0039] [Problem] In an optical communication system 401 used by a plurality of communication carriers, a technique is desired that allows the communication carriers to flexibly select which slave station devices 201 to use.

[0040] More specifically, in the optical communication system 401, the combination of carriers that use the slave station equipment 201 as an RU (Radio Unit) may differ for each slave station equipment 201 in accordance with the service contracts of the carriers.

[0041] Therefore, a technology is desired that enables the slave station device 201 to transmit an RF signal in which RF signals Sd corresponding to some of the multiple telecommunications carriers are selectively multiplexed, and to transmit an upstream optical signal including the RF signals corresponding to those some of the telecommunications carriers to the master station device 101.

[0042] Therefore, the optical communication system 401 according to the first embodiment of the present disclosure solves the above problem by adopting the following configuration.

[0043] (Configuration of Master Station Device and Slave Station Device) Fig. 2 is a diagram showing the configuration of a master 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 downstream processing unit 10, an upstream processing unit 20, and an optical transceiver unit 30. The downstream processing unit 10 is an example of a receiver and an example of a first generator. The optical transceiver unit 30 is an example of a second generator and an example of an optical transmitter.

[0044] The downstream processing unit 10 includes band pass filters (BPFs) 11A, 11B, 11C, and 11D, amplifiers 12A, 12B, 12C, and 12D, and a multiplexer 13. The BPFs 11A, 11B, 11C, and 11D are filters corresponding to frequency bands FbA, FbB, FbC, and FbD, respectively, and have different pass bands. Hereinafter, each of the BPFs 11A, 11B, 11C, and 11D will also be referred to as BPF 11, and each of the amplifiers 12A, 12B, 12C, and 12D will also be referred to as amplifier 12.

[0045] The upstream processing unit 20 includes a distributor 21, BPFs 22A, 22B, 22C, and 22D, and amplifiers 23A, 23B, 23C, and 23D. The BPFs 22A, 22B, 22C, and 22D are filters corresponding to the frequency bands FbA, FbB, FbC, and FbD, respectively, and have different passbands. Hereinafter, each of the BPFs 22A, 22B, 22C, and 22D will also be referred to as a BPF 22, and each of the amplifiers 23A, 23B, 23C, and 23D will also be referred to as an amplifier 23.

[0046] The optical transceiver 30 includes a multiplexer 31, an optical modulator 32, multiple optical demodulators 33, multiple demultiplexers 34, a combiner 35, a controller 36, and an optical coupler 37. Some or all of the functions of the controller 36 are implemented by, for example, a processing circuit including one or more processors. For example, the optical demodulator 33 and the demultiplexer 34 are provided corresponding to each slave station device 201. The optical coupler 37 is connected to the multiple slave station devices 201 in the optical communication system 401 via optical fibers 191.

[0047] 3 is a diagram illustrating a configuration of a slave station device in an optical communication system according to a first embodiment of the present disclosure. Referring to FIG. 3, the slave station device 201 includes an optical transceiver 40, extractors 50 and 60, and a front-end 70. The optical transceiver 40 is an example of an optical receiver. The front-end 70 is an example of a wireless transmitter.

[0048] The optical transceiver 40 includes an optical coupler 41, an optical demodulator 42, a separator 43, a multiplexer 44, an optical modulator 45, and a controller 46. Some or all of the functions of the controller 46 are implemented by, for example, a processing circuit including one or more processors. The optical transceiver 40 receives a downstream optical signal from the master station 101 and acquires an RF signal Md from the received downstream optical signal.

[0049] The extraction unit 50 includes a distribution unit 51, BPFs 52A, 52B, 52C, and 52D, switches 53A, 53B, 53C, and 53D, and a multiplexing unit 54. Hereinafter, each of the BPFs 52A, 52B, 52C, and 52D will also be referred to as a BPF 52, and each of the switches 53A, 53B, 53C, and 53D will also be referred to as a switch 53. The switches 53A, 53B, 53C, and 53D each have a first end connected to the multiplexing unit 54, a second end connected to the BPFs 52A, 52B, 52C, and 52D, and a third end connected to a termination resistor (not shown). The switch 53 is capable of switching between the second end and the third end and the terminal connected to the first end. For example, in the initial state, the switch 53 has the first end and the second end connected.

[0050] The extraction unit 50 is capable of performing a downstream extraction process to extract an RF signal Sd corresponding to some of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Md acquired by the optical transceiver 40. Details of the downstream extraction process performed by the extraction unit 50 will be described later.

[0051] The front end unit 70 includes a BPF 71, an amplifier unit 72, an RF transceiver unit 73, an amplifier unit 74, and an antenna 211. The front end unit 70 receives the RF signal Mu via the antenna 211.

[0052] The extraction unit 60 includes a distribution unit 61, BPFs 62A, 62B, 62C, and 62D, switches 63A, 63B, 63C, and 63D, and a multiplexing unit 64. Hereinafter, each of the BPFs 62A, 62B, 62C, and 62D will also be referred to as a BPF 62, and each of the switches 63A, 63B, 63C, and 63D will also be referred to as a switch 63. The switches 63A, 63B, 63C, and 63D each have a first end connected to the multiplexing unit 64, a second end connected to the BPFs 62A, 62B, 62C, and 62D, and a third end connected to a termination resistor (not shown). The switch 63 is capable of switching between the second end and the third end and the terminal connected to the first end. For example, in the initial state, the switch 63 has the first end and the second end connected.

[0053] The extraction unit 60 is capable of performing an uplink extraction process to extract an RF signal Su corresponding to some of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Mu received by the front end unit 70. The uplink extraction process performed by the extraction unit 60 will be described in detail later.

[0054] The passbands of the BPFs 11, 22, 52, and 62 provided corresponding to the common base station device 301 may be the same as or different from one another.

[0055] For example, the multiple slave station devices 201 provided in the optical communication system 401 include a slave station device 201A that is a slave station device 201 used by all telecommunications carriers Op, and a slave station device 201B that is a slave station device 201 used by telecommunications carriers OpA, OpB, and OpC excluding telecommunications carrier OpD.

[0056] The slave station device 201B acquires an RF signal Md from the downstream optical signal and performs downstream extraction processing to extract, from the acquired RF signal Md, RF signals SdA, SdB, and SdC corresponding to the frequency bands FbA, FbB, and FbC, respectively, of the frequency bands FbA, FbB, FbC, and FbD. Instead of the RF signal Md, the slave station device 201B transmits an RF signal Mdex based on the extracted RF signals SdA, SdB, and SdC. The RF signal Mdex is an example of a downstream wireless signal.

[0057] The slave station device 201B also performs upstream extraction processing to extract RF signals SuA, SuB, and SuC corresponding to the frequency bands FbA, FbB, and FbC, respectively, from the signal based on the received RF signal Mu. The slave station device 201B generates an upstream optical signal including the extracted RF signals SuA, SuB, and SuC instead of the RF signal Mu, and transmits the generated upstream optical signal to the master station device 101.

[0058] (Processing of the parent station device 101 in downstream communication) Referring again to Figure 2, in the parent station device 101, the downstream processing unit 10 receives RF signals SdA, SdB, SdC, and SdD from the base station devices 301A, 301B, 301C, and 301D via the corresponding transmission lines 181, respectively, and generates an RF signal Md in which the received RF signals SdA, SdB, SdC, and SdD are multiplexed.

[0059] More specifically, BPFs 11A, 11B, 11C, and 11D receive RF signals SdA, SdB, SdC, and SdD from base station devices 301A, 301B, 301C, and 301D, respectively. BPF 11A attenuates frequency components outside frequency band FbA in the received RF signal SdA. BPF 11B attenuates frequency components outside frequency band FbB in the received RF signal SdB. BPF 11C attenuates frequency components outside frequency band FbC in the received RF signal SdC. BPF 11D attenuates frequency components outside frequency band FbD in the received RF signal SdD. Note that part of the passband of one BPF 11 may overlap part of the passband of another BPF 11.

[0060] The amplifiers 12A, 12B, 12C, and 12D amplify the RF signals SdA, SdB, SdC, and SdD that have passed through the BPFs 11A, 11B, 11C, and 11D, respectively, by their respective predetermined gains and output the amplified RF signals SdA, SdB, SdC, and SdD to the multiplexer 13. For example, the amplifier 12 adjusts the RF signals SdA, SdB, SdC, and SdD so that the intensity difference between the RF signals SdA, SdB, SdC, and SdD is small. More specifically, the gain of each amplifier 12 is set in advance according to the level of the RF signals SdA, SdB, SdC, and SdD transmitted by the base station device 301 so that the intensity difference between the amplified RF signals SdA, SdB, SdC, and SdD is equal to or less than a predetermined value. This makes it possible to equalize the intensities of the RF signals SdA, SdB, SdC, and SdD transmitted via the antenna 211 in the slave station device 201, and also to reduce signal distortion of the RF signal Md.

[0061] The multiplexer 13 generates an RF signal Md by multiplexing the RF signals SdA, SdB, SdC, and SdD received from the amplifiers 12 , and outputs the generated RF signal Md to the optical transmitter / receiver 30 .

[0062] The master station device 101 generates a digital signal Sdd indicating the RF signals Sd and Su to be extracted in the downstream extraction process by the slave station device 201B, and transmits a downstream optical signal including the generated digital signal Sdd and RF signal Md to the slave station device 201B. That is, the optical transceiver 30 generates a digital signal Sdd indicating the RF signal Sd to be wirelessly transmitted by the slave station device 201B from the RF signals SdA, SdB, SdC, and SdD. The optical transceiver 30 generates a downstream optical signal including the RF signal Md and the digital signal Sdd, and transmits the generated downstream optical signal to the slave station device 201B. The digital signal Sdd is an example of a control signal.

[0063] More specifically, the control unit 36 ​​in the optical transceiver 30 receives usage information indicating that the communication service provider OpD does not use the slave station device 201B from the control device 311. The control unit 36 ​​generates extraction information indicating the RF signal Sd to be extracted in the downstream extraction process and the RF signal Su to be extracted in the upstream extraction process by the slave station device 201B, based on the usage information received from the control device 311. Specifically, the control unit 36 ​​generates extraction information indicating that the RF signals SdA, SdB, SdC, SuA, SuB, and SuC are to be extracted, including the ID of the slave station device 201B.

[0064] The control unit 36 ​​also receives control information for controlling the operation of the slave station device 201 from each base station device 301. For example, the control information received from each base station device 301 includes TDD information indicating an uplink period Pu and a downlink period Pd, and synchronization information indicating a reference clock signal.

[0065] The control unit 36 ​​selects one of the pieces of control information received from each base station device 301. As an example, in the initial state, the control unit 36 ​​selects the control information received from the base station device 301A, and when the arrival of the control information from the base station device 301A stops, the control unit 36 ​​selects the control information received from another base station device 301.

[0066] The control unit 36 ​​generates a digital signal Sdd including the generated extracted information and the selected control information, and outputs the generated digital signal Sdd to the multiplexing unit 31 .

[0067] The multiplexing unit 31 generates an electrical signal in which the RF signal Md received from the downlink processing unit 10 and the digital signal Sdd received from the control unit 36 ​​are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 32. Note that, for example, an LPF (Low Pass Filter) may be provided between the control unit 36 ​​and the multiplexing unit 31.

[0068] The optical modulator 32 is an EO element having linear conversion characteristics over a wide frequency bandwidth. The optical modulator 32 receives the electrical signal from the multiplexer 31 and generates a downstream optical signal by optically modulating the received electrical signal. The optical modulator 32 transmits the downstream optical signal to each slave station device 201 via the optical coupler 37 and the optical fiber 191.

[0069] (Processing of the slave station device 201A in downstream communication) Referring back to FIG. 3, the optical transceiver 40 in the slave station device 201A receives a downstream optical signal from the master station device 101, and acquires the RF signal Md and the digital signal Sdd from the received downstream optical signal.

[0070] More specifically, the optical demodulator 42 receives a downstream optical signal from the parent station 101 via the optical fiber 191 and the optical coupler 41. The optical demodulator 42 generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal and outputs the electrical signal to the separator 43.

[0071] The separator 43 separates the RF signal Md and the digital signal Sdd contained in the electrical signal received from the optical demodulator 42. The separator 43 outputs the separated RF signal Md to the extractor 50, and also outputs the separated digital signal Sdd to the controller 46.

[0072] The control unit 46 acquires TDD information and synchronization information, which are control information, from the digital signal Sdd received from the demultiplexer 43, and, based on the acquired TDD information and synchronization information, switches between the transmission and reception of RF signals by the RF transceiver unit 73. More specifically, based on the TDD information and synchronization information, the control unit 46 generates a TDD switching signal for switching between the transmission and reception of RF signals by the RF transceiver unit 73, and outputs the generated TDD switching signal to the RF transceiver unit 73.

[0073] The control unit 46 also acquires extraction information from the digital signal Sdd received from the separation unit 43. The control unit 46 discards the acquired extraction information because the ID included in the acquired extraction information does not match the ID of the slave station device 201A.

[0074] In the extraction unit 50, the distribution unit 51 receives the RF signal Md from the optical transmission / reception unit 40 and distributes the received RF signal Md to BPFs 52A, 52B, 52C, and 52D.

[0075] The BPF 52A attenuates frequency components outside the frequency band FbA in the RF signal Md received from the distribution unit 51. The BPF 52B attenuates frequency components outside the frequency band FbB in the RF signal Md received from the distribution unit 51. The BPF 52C attenuates frequency components outside the frequency band FbC in the RF signal Md received from the distribution unit 51. The BPF 52D attenuates frequency components outside the frequency band FbD in the RF signal Md received from the distribution unit 51. Note that part of the pass band of one BPF 52 may overlap part of the pass band of another BPF 52.

[0076] The multiplexing unit 54 receives the RF signal SdA, which is a signal that has passed through the BPF 52A, via the switch 53A, the RF signal SdB, which is a signal that has passed through the BPF 52B, via the switch 53B, the RF signal SdC, which is a signal that has passed through the BPF 52C, via the switch 53C, and the RF signal SdD, which is a signal that has passed through the BPF 52D, via the switch 53D. The multiplexing unit 54 generates the RF signal Md by multiplexing the received RF signals SdA, SdB, SdC, and SdD, and outputs the generated RF signal Md to the front end unit 70.

[0077] The front end unit 70 in the slave station device 201A transmits the RF signal Md received from the extraction unit 50. More specifically, in the front end unit 70, the BPF 71 receives the RF signal Md from the extraction unit 50 and attenuates components outside a predetermined passband in the received RF signal Md.

[0078] The amplifier 72 amplifies the RF signal Md that has passed through the BPF 71 , and outputs the amplified RF signal Md to the RF transmitter / receiver 73 .

[0079] In accordance with the TDD switching signal received from the control unit 46, the RF transceiver unit 73 transmits the RF signal Md received from the amplifier unit 72 to the communication terminal via the antenna 211 during the downlink period Pd.

[0080] (Processing of the slave station device 201B in downstream communication) Compared to the slave station device 201A, the slave station device 201B extracts RF signals SdA, SdB, and SdC from the RF signal Md in accordance with the digital signal Sdd.

[0081] More specifically, the optical transceiver 40 in the slave station device 201B, like the optical transceiver 40 in the slave station device 201A, receives a downstream optical signal from the master station device 101 and acquires the RF signal Md and the digital signal Sdd from the received downstream optical signal.

[0082] The control unit 46 in the slave station device 201B receives the digital signal Sdd from the separation unit 43 and acquires extraction information from the received digital signal Sdd. Because the ID included in the acquired extraction information matches the ID of the slave station device 201B, the control unit 46 performs processing to stop the transmission of the RF signal SdD and the transmission of the RF signal SuD to the master station device 101 based on the acquired extraction information. More specifically, the control unit 46 generates a switching signal Soff to disconnect the connection between the BPF 52B and the multiplexer 54 and the connection between the BPF 62B and the multiplexer 64, and outputs the generated switching signal Soff to the extraction units 50 and 60.

[0083] Compared to the extraction unit 50 in the slave station device 201A, the extraction unit 50 in the slave station device 201B performs downstream extraction processing to extract RF signals SdA, SdB, and SdC corresponding to the frequency bands FbA, FbB, and FbC, respectively, of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Md acquired by the optical transceiver unit 40.

[0084] More specifically, the switch 53D in the extraction unit 50 receives a switching signal Soff from the control unit 46 and, in accordance with the received switching signal Soff, disconnects the connection between the BPF 52D and the multiplexing unit 54. That is, the switch 53D switches from an ON state in which a first end connected to the multiplexing unit 54 and a second end connected to the BPF 52D are connected to an OFF state in which the first end and a third end connected to the termination resistor are connected.

[0085] The multiplexing unit 54 receives the RF signals SdA, SdB, and SdC via the switches 53A, 53B, and 53C, respectively. The multiplexing unit 54 generates an RF signal Mdex by multiplexing the received RF signals SdA, SdB, and SdC, and outputs the generated RF signal Mdex to the front end unit 70.

[0086] Compared to the front end unit 70 in the slave station device 201A, the front end unit 70 in the slave station device 201B transmits an RF signal Mdex based on the RF signals SdA, SdC, and SdD extracted by the extraction unit 50. More specifically, in the front end unit 70, the BPF 71 receives the RF signal Mdex from the extraction unit 50 and attenuates components outside a predetermined passband in the received RF signal Mdex.

[0087] The amplifier 72 amplifies the RF signal Mdex that has passed through the BPF 71 , and outputs the amplified RF signal Mdex to the RF transceiver 73 .

[0088] In accordance with the TDD switching signal received from the control unit 46, the RF transceiver unit 73 transmits the RF signal Mdex received from the amplifier unit 72 to the communication terminal via the antenna 211 during the downlink period Pd.

[0089] (Processing of the slave station device 201A in upstream communication) The front end unit 70 in the slave station device 201A receives the RF signal Mu and outputs the received RF signal Mu to the extraction unit 60.

[0090] More specifically, the RF transceiver 73 in the front end unit 70 receives the RF signal Mu from the communication terminal via the antenna 211 during the uplink period Pu in accordance with the TDD switching signal received from the control unit 46. The RF transceiver 73 outputs the received RF signal Mu to the amplifier 74.

[0091] Amplifying unit 74 amplifies RF signal Mu received from RF transmitting / receiving unit 73 and outputs the amplified RF signal Mu to extracting unit 60 .

[0092] In the extraction unit 60, the distribution unit 61 receives the RF signal Mu from the RF transmission / reception unit 73 and distributes the received RF signal Mu to the BPFs 62A, 62B, 62C, and 62D.

[0093] The BPF 62A attenuates frequency components outside the frequency band FbA in the RF signal Mu received from the distribution unit 61. The BPF 62B attenuates frequency components outside the frequency band FbB in the RF signal Mu received from the distribution unit 61. The BPF 62C attenuates frequency components outside the frequency band FbC in the RF signal Mu received from the distribution unit 61. The BPF 62D attenuates frequency components outside the frequency band FbD in the RF signal Mu received from the distribution unit 61. Note that part of the pass band of one BPF 62 may overlap part of the pass band of another BPF 62.

[0094] The multiplexing unit 64 receives an RF signal SuA that has passed through the BPF 62A via a switch 63A, an RF signal SuB that has passed through the BPF 62B via a switch 63B, an RF signal SuC that has passed through the BPF 62C via a switch 63C, and an RF signal SuD that has passed through the BPF 62D via a switch 63D. The multiplexing unit 64 generates an RF signal Mu by multiplexing the received RF signals SuA, SuB, SuC, and SuD, and outputs the generated RF signal Mu to the optical transceiver 40.

[0095] The optical transceiver 40 in the slave station device 201 A generates an upstream optical signal including the RF signal Mu received from the extractor 60 , and transmits the generated upstream optical signal to the master station device 101 .

[0096] More specifically, the control unit 46 generates a digital signal Sdu including the monitored results such as the temperature of the slave station equipment 201 , and outputs the generated digital signal Sdu to the multiplexing unit 44 .

[0097] The multiplexing unit 44 generates an electrical signal in which the RF signal Mu received from the extraction unit 60 and the digital signal Sdu received from the control unit 46 are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 45 .

[0098] The optical modulator 45 is an EO element having linear conversion characteristics over a wide frequency bandwidth. The optical modulator 45 receives the electrical signal from the multiplexer 44 and generates an upstream optical signal by optically modulating the received electrical signal. The optical modulator 45 transmits the upstream optical signal to the parent station 101 via the optical coupler 41 and the optical fiber 191.

[0099] For example, multiple slave station devices 201 each transmit multiple upstream optical signals having different wavelengths to the master station device 101. More specifically, the optical modulation unit 45 in each slave station device 201 generates upstream optical signals having different wavelengths and transmits them to the master station device 101.

[0100] (Processing of the slave station device 201B in upstream communication) The front end unit 70 in the slave station device 201B receives the RF signal Mu and outputs the received RF signal Mu to the extraction unit 60, similar to the front end unit 70 in the slave station device 201A.

[0101] Compared to the extraction unit 60 in the slave station device 201A, the extraction unit 60 in the slave station device 201B performs an upstream extraction process to extract RF signals SuA, SuB, and SuC corresponding to the frequency bands FbA, FbB, and FbC, respectively, of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Mu received by the front end unit 70.

[0102] More specifically, the switch 63D in the extraction unit 60 receives a switching signal Soff from the control unit 46 and, in accordance with the received switching signal Soff, disconnects the connection between the BPF 62D and the multiplexing unit 64. That is, the switch 63D switches from an ON state in which a first end connected to the multiplexing unit 64 and a second end connected to the BPF 62D are connected to an OFF state in which the first end and a third end connected to the termination resistor are connected.

[0103] The multiplexing unit 64 receives the RF signals SuA, SuB, and SuC via the switches 63A, 63B, and 63C, respectively. The multiplexing unit 64 generates an RF signal Muex by multiplexing the received RF signals SuA, SuB, and SuC, and outputs the generated RF signal Muex to the optical transceiver 40.

[0104] Compared to the optical transceiver 40 in the slave station device 201A, the optical transceiver 40 in the slave station device 201B generates an upstream optical signal including the RF signal Muex extracted by the extraction unit 60 and transmits the generated upstream optical signal to the master station device 101.

[0105] More specifically, the multiplexing unit 44 generates an electrical signal in which the RF signal Muex received from the extraction unit 60 and the digital signal Sdu received from the control unit 46 are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 45 .

[0106] The optical modulation unit 45 receives the electrical signal from the multiplexing unit 44, optically modulates the received electrical signal to generate an upstream optical signal, and transmits the generated upstream optical signal to the parent station 101 via the optical coupler 41 and the optical fiber 191.

[0107] 2 , in the parent station device 101, the optical transceiver 30 receives upstream optical signals from one or more slave station devices 201A and acquires an RF signal Mu from the received upstream optical signals. The optical transceiver 30 also receives upstream optical signals from one or more slave station devices 201B and acquires an RF signal Muex from the received upstream optical signals. The optical transceiver 30 multiplexes the acquired RF signals Mu and Muex. Note that the optical transceiver 30 may also receive upstream signals from slave station devices 201 other than the slave station devices 201A and 201B and acquire, from the received upstream optical signals, a signal including one or more RF signals Su in a combination different from the RF signals Mu and Muex.

[0108] More specifically, each optical demodulator 33 receives an upstream optical signal from a corresponding slave station device 201 via an optical fiber 191 and an optical coupler 37. Each optical demodulator 33 is an optical emitter (OE) element that converts upstream optical signals of different wavelengths into electrical signals. Each optical demodulator 33 generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal and outputs it to the corresponding separator 34.

[0109] Each separator 34 separates the RF signal Mu or RF signal Muex from the digital signal Sdu contained in the electrical signal received from the corresponding optical demodulator 33. Each separator 34 outputs the separated RF signal Mu or RF signal Muex to the multiplexer 35, and also outputs the separated digital signal Sdu to the controller 36.

[0110] The control unit 36 ​​acquires the monitoring results from the digital signals Sdu received from each demultiplexer 34, and processes the acquired monitoring results. Note that the control unit 36 ​​may transmit the acquired monitoring results to the base station device 301.

[0111] The multiplexer 35 multiplexes the RF signals Mu and Muex received from the demultiplexer 34 to generate a multiplexed RF signal Mum, and outputs the generated multiplexed RF signal Mum to the upstream processor 20 .

[0112] The upstream processing unit 20 acquires RF signals SuA, SuB, SuC, and SuD from the RF signals Mu and Muex acquired by the optical transceiver unit 30. For example, the upstream processing unit 20 uses four BPFs 22 to acquire RF signals SuA, SuB, SuC, and SuD from the multiplexed RF signal Mum.

[0113] More specifically, in the upstream processing unit 20, the distributor 21 receives the multiplexed RF signal Mum from the optical transceiver 30 and distributes the received multiplexed RF signal Mum to the BPFs 22A, 22B, 22C, and 22D.

[0114] The BPF 22A attenuates frequency components outside the frequency band FbA in the multiplexed RF signal Mum received from the distribution unit 21. The BPF 22B attenuates frequency components outside the frequency band FbB in the multiplexed RF signal Mum received from the distribution unit 21. The BPF 22C attenuates frequency components outside the frequency band FbC in the multiplexed RF signal Mum received from the distribution unit 21. The BPF 22D attenuates frequency components outside the frequency band FbD in the multiplexed RF signal Mum received from the distribution unit 21. Note that part of the pass band of one BPF 22 may overlap part of the pass band of another BPF 22.

[0115] The amplifier 23A amplifies the RF signal SuA, which is the signal that has passed through the BPF 22A, by a predetermined gain and transmits the amplified RF signal SuA to the base station device 301A. The amplifier 23B amplifies the RF signal SuB, which is the signal that has passed through the BPF 22B, by a predetermined gain and transmits the amplified RF signal SuB to the base station device 301B. The amplifier 23C amplifies the RF signal SuC, which is the signal that has passed through the BPF 22C, by a predetermined gain and transmits the amplified RF signal SuC to the base station device 301C. The amplifier 23D amplifies the RF signal SuD, which is the signal that has passed through the BPF 22D, by a predetermined gain and transmits the amplified RF signal SuD to the base station device 301D.

[0116] 4 is a diagram illustrating an example of a downstream communication sequence in the optical communication system according to the first embodiment of the present disclosure. In FIG. 4, the slave station device 201B of the slave station devices 201 is representatively illustrated.

[0117] Referring to FIG. 4, first, the master station device 101 generates extraction information indicating the RF signals Sd and Su to be extracted in the downlink extraction process and the uplink extraction process by the slave station device 201B, based on the usage information received from the control device 311 (step S11).

[0118] Next, each base station device 301 transmits the RF signal Sd and the control information to the master station device 101 via the corresponding transmission line 181 (step S12).

[0119] Next, the master station 101 amplifies the received RF signals SdA, SdB, SdC, and SdD, and generates an RF signal Md in which the amplified RF signals SdA, SdB, SdC, and SdD are multiplexed (step S13).

[0120] Next, the master station device 101 generates a digital signal Sdd including the extraction information and the control information (step S14).

[0121] Next, the master station 101 generates a downstream optical signal including the RF signal Md and the digital signal Sdd (step S15).

[0122] Next, the master station device 101 transmits the generated downstream optical signal to each slave station device 201 via the optical fiber 191 (step S16).

[0123] Next, the slave station device 201B receives the downstream optical signal from the master station device 101 via the optical fiber 191, and acquires the RF signal Md and the digital signal Sdd from the received downstream optical signal (step S17).

[0124] Next, the slave station device 201B performs downstream extraction processing to extract the RF signals SdA, SdB, and SdC from the RF signal Md in accordance with the extraction information included in the digital signal Sdd (step S18).

[0125] Next, the slave station device 201B multiplexes the extracted RF signals SdA, SdB, and SdC to generate an RF signal Mdex (step S19).

[0126] Next, the slave station device 201B transmits the amplified RF signal Mdex to the communication terminal via the antenna 211 during the downlink period Pd (step S20).

[0127] 5 is a diagram illustrating an example of an upstream communication sequence in the optical communication system according to the first embodiment of the present disclosure, in which the slave station device 201B of the slave station devices 201 is representatively illustrated.

[0128] Referring to FIG. 5, first, the slave station device 201B receives an RF signal Mu from the communication terminal via the antenna 211 during an uplink period Pu (step S21).

[0129] Next, the slave station device 201B performs an upstream extraction process to extract the RF signals SuA, SuB, and SuC from the RF signal Mu in accordance with the extraction information included in the digital signal Sdd (step S22).

[0130] Next, the slave station device 201B multiplexes the extracted RF signals SuA, SuB, and SuC to generate an RF signal Muex (step S23).

[0131] Next, the slave station device 201B generates an upstream optical signal including the RF signal Muex and the digital signal Sdu including control information (step S24).

[0132] Next, the slave station device 201B transmits the generated upstream optical signal to the master station device 101 via the optical fiber 191 (step S25).

[0133] Next, the master station device 101 receives the upstream optical signal from the slave station device 201B via the optical fiber 191 and acquires the RF signal Muex and the digital signal Sdu from the received upstream optical signal. For example, the master station device 101 further receives the upstream optical signal from the slave station device 201A and acquires the RF signal Mu and the digital signal Sdu from the received upstream optical signal (step S26).

[0134] Next, the master station device 101 multiplexes the acquired RF signals Mu and Muex to generate a multiplexed RF signal Mum (step S27).

[0135] Next, the master station device 101 uses the four BPFs 22 to acquire the RF signals SuA, SuB, SuC, and SuD from the multiplexed RF signal Mum (step S28).

[0136] Next, the master station device 101 amplifies the acquired RF signals SuA, SuB, SuC, and SuD, and transmits the amplified RF signals SuA, SuB, SuC, and SuD to the base station devices 301A, 301B, 301C, and 301D, respectively (step S29).

[0137] Although the optical communication system 401 according to the first embodiment of the present disclosure is configured to include a plurality of slave station devices 201, the present disclosure is not limited to this. The optical communication system 401 may be configured to include a single slave station device 201.

[0138] Although the optical communication system 401 according to the first embodiment of the present disclosure includes a slave station device 201A used by all of the telecommunications carriers OpA, OpB, OpC, and OpD, this is not limiting. All of the slave station devices 201 in the optical communication system 401 may be slave station devices 201 not used by some of the telecommunications carriers. For example, if all of the slave station devices 201 in the optical communication system 401 are not used by a common telecommunications carrier, the control unit 36 ​​in the master station device 101 performs a process of turning off the power to the amplifiers 12 and 23 provided corresponding to the base station devices 301 of the common telecommunications carrier. Turning off the power to the amplifier 12 reduces noise components contained in the RF signal Md output from the downstream processing unit 10 to the optical transceiver 30. Turning off the power to the amplifier 23 prevents noise signals from being transmitted from the upstream processing unit 20 to the base station device 301.

[0139] Furthermore, in the optical communication system 401 according to the first embodiment of the present disclosure, the master station device 101 is configured to transmit and receive RF signals to and from the base station device 301. However, this is not limiting. The master station device 101 may be configured to transmit and receive analog signals in the intermediate frequency (IF) band to and from the base station device 301. In this case, the master station device 101 generates an RF signal Md by frequency-converting a received analog signal, and transmits a downstream optical signal including the generated RF signal Md to the slave station device 201 via the optical fiber 191. The master station device 101 also acquires an RF signal Mu from an upstream optical signal received from the slave station device 201, frequency-converts the acquired RF signal Mu to generate an analog signal in the IF band, and transmits the generated analog signal to the base station device 301.

[0140] Furthermore, in the optical communication system 401 according to the first embodiment of the present disclosure, the master station device 101 and the slave station device 201 are configured to transmit and receive optical signals including RF signals, but this is not limited thereto. The master station device 101 and the slave station device 201 may be configured to transmit and receive optical signals including analog signals in the IF band. More specifically, the master station device 101 receives an analog signal in the IF band from the base station device 301 and transmits a downstream optical signal including the received analog signal to the slave station device 201 via the optical fiber 191. The slave station device 201 acquires an analog signal from the received downstream optical signal, frequency-converts the acquired analog signal to generate an RF signal Md, extracts an RF signal Sd from the generated RF signal Md, and transmits an RF signal Mdex based on the extracted RF signal Sd via the antenna 211. The slave station device 201 also receives the RF signal Mu via the antenna, extracts the RF signal Su from the received RF signal Mu, generates an analog signal in the IF band by frequency-converting the extracted RF signal Su, and transmits an upstream optical signal including the generated analog signal to the master station device 101 via the optical fiber 191. The master station device 101 obtains an analog signal from the received upstream optical signal and transmits the obtained analog signal to the base station device 301.

[0141] Alternatively, the master station device 101 and the slave station device 201 may be configured to transmit and receive optical signals including digital signals instead of RF signals. More specifically, the master station device 101 receives digital signals including communication data from the base station device 301 and transmits downstream optical signals including the received digital signals to the slave station device 201 via the optical fiber 191. The slave station device 201 acquires the digital signals from the received downstream optical signals, generates analog signals by converting the acquired digital signals to analog, generates RF signals Md by frequency-converting the generated analog signals, extracts RF signals Sd from the generated RF signals Md, and transmits RF signals Mdex based on the extracted RF signals Sd via the antenna 211. The slave station device 201 also receives the RF signal Mu via the antenna, extracts the RF signal Su from the received RF signal Mu, generates an analog signal, for example, in the IF band, performs frequency conversion on the extracted RF signal Su, generates a digital signal by digitally converting the generated analog signal, and transmits an upstream optical signal including the generated digital signal to the master station device 101 via the optical fiber 191. The master station device 101 acquires the digital signal from the received upstream optical signal and transmits the acquired digital signal to the base station device 301.

[0142] Furthermore, in the master station device 101 according to the first embodiment of the present disclosure, the control unit 36 ​​is configured to generate the digital signal Sdd including the extracted information and the control information, but this is not limited to this. The control unit 36 ​​may be configured to generate a tone signal including the extracted information and the control information instead of the digital signal Sdd. In this case, the control unit 36 ​​may generate a tone signal with a different frequency for each slave station device 201 that is the target of control using the extracted information and the control information.

[0143] Furthermore, although the master station device 101 according to the first embodiment of the present disclosure is configured to transmit a downstream optical signal including the digital signal Sdd to the slave station device 201, this is not limiting. The master station device 101 may be configured to transmit a downstream optical signal not including the digital signal Sdd to the slave station device 201. In this case, for example, the slave station device 201 receives usage information from the control device 311 and performs downstream sampling processing and upstream sampling processing in accordance with the received usage information.

[0144] Furthermore, although the slave station device 201B according to the first embodiment of the present disclosure is configured to perform uplink extraction processing to extract the RF signal Su from the RF signal Mu, this is not limiting. The slave station device 201B may be configured to perform downlink extraction processing to extract the RF signal Sd from the RF signal Md, but not to perform uplink extraction processing to extract the RF signal Su from the RF signal Mu. In other words, the slave station device 201B may be configured without including the extraction unit 60.

[0145] In addition, in the slave station device 201 according to the first embodiment of the present disclosure, the RF transceiver unit 73 is configured to transmit the RF signal Md and receive the RF signal Mu via the common antenna 211, but this is not limiting. The RF transceiver unit 73 may be configured to transmit the RF signal Md via a first antenna and receive the RF signal Mu via a second antenna separate from the first antenna.

[0146] 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.

[0147] Second Embodiment This embodiment relates to an optical communication system 402 that performs upstream extraction processing of an RF signal Su based additionally on the communication quality of the RF signal Su, as compared with the optical communication system 401 according to the first embodiment. Except for the contents described below, the optical communication system 402 is the same as the optical communication system 401 according to the first embodiment.

[0148] 6 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. Compared to the optical communication system 401, the optical communication system 402 includes a slave station device 202 instead of the slave station device 201.

[0149] For example, the multiple slave station devices 202 provided in the optical communication system 402 include a slave station device 202A that is a slave station device 202 used by all telecommunications carriers Op, and a slave station device 202B that is a slave station device 202 used by telecommunications carriers OpA, OpB, and OpC except for telecommunications carrier OpD.

[0150] (Configuration of Slave Station Device) Fig. 7 is a diagram illustrating the configuration of a slave station device in an optical communication system according to a second embodiment of the present disclosure. Referring to Fig. 7, compared to the slave station device 201, the slave station device 202 includes an extraction unit 80 instead of the extraction unit 60. Compared to the extraction unit 60, the extraction unit 80 further includes determination units 81A, 81B, 81C, and 81D. The determination units 81A, 81B, 81C, and 81D are provided corresponding to the BPFs 62A, 62B, 62C, and 62D, respectively, and also corresponding to the switches 63A, 63B, 63C, and 63D. Hereinafter, each of the determination units 81A, 81B, 81C, and 81D will also be referred to as a determination unit 81.

[0151] If the communication quality of the RF signal Su that has passed through the corresponding BPF 62 satisfies a predetermined condition, the determining unit 81 performs processing to stop transmission of the RF signal Su to the master station device 101 .

[0152] More specifically, the determination unit 81 receives the RF signal Su that has passed through the corresponding BPF 62. The determination unit 81 measures the signal strength of the received RF signal Su as an index of the communication quality of the RF signal Su at a determination timing according to a predetermined determination period Pj. If the signal strength of the RF signal Su is less than a predetermined threshold Th1, the determination unit 81 generates a switching signal Soff for disconnecting the corresponding BPF 62 and the multiplexer 64 and outputs the generated switching signal Soff to the corresponding switch 63.

[0153] When the switch 63 receives a switching signal Soff from the corresponding determination unit 81, it disconnects the corresponding BPF 62 and multiplexing unit 64 in accordance with the received switching signal Soff. That is, the switch 63 switches from an ON state in which a first end connected to the multiplexing unit 64 and a second end connected to the BPF 62 are connected to an OFF state in which the first end and a third end connected to the termination resistor are connected.

[0154] For example, the determination unit 81 outputs a switching signal Soff to the corresponding switch 63 to disconnect the corresponding BPF 62 and the multiplexer 64, and then measures the signal strength of the RF signal Su received from the corresponding BPF 62 at a determination timing according to the determination period Pj. If the signal strength of the RF signal Su is greater than a predetermined threshold Th2, the determination unit 81 generates a switching signal Son to connect the corresponding BPF 62 and the multiplexer 64, and outputs the generated switching signal Son to the corresponding switch 63. For example, the threshold Th2 is a value greater than the threshold Th1.

[0155] When the switch 63 receives a switching signal Son from the corresponding determination unit 81, it connects the corresponding BPF 62 and the multiplexing unit 64 in accordance with the received switching signal Son. That is, the switch 63 switches from an OFF state in which a first end connected to the multiplexing unit 64 and a third end connected to the termination resistor are connected to an ON state in which the first end and a second end connected to the BPF 62 are connected.

[0156] (Processing of slave station device 202B in uplink communication) In the uplink extraction process, the extraction unit 80 in the slave station device 202B extracts an RF signal Su whose communication quality satisfies a predetermined condition from among the RF signals SuA, SuB, and SuC corresponding to the frequency bands FbA, FbB, and FbC, respectively.

[0157] More specifically, the control unit 46 in the optical transceiver unit 40 of the slave station device 202B, like the control unit 46 in the optical transceiver unit 40 of the slave station device 201B, generates a switching signal Soff for disconnecting the connection between the BPF 62B and the multiplexer unit 64 based on the extraction information acquired from the digital signal Sdd, and outputs the generated switching signal Soff to the extraction unit 80.

[0158] The switch 63D in the extraction unit 80 receives a switching signal Soff from the control unit 46 and, in accordance with the received switching signal Soff, disconnects the connection between the BPF 62D and the multiplexing unit 64. That is, the switch 63D switches from an ON state in which a first end connected to the multiplexing unit 64 and a second end connected to the BPF 62D are connected to an OFF state in which the first end and a third end connected to the termination resistor are connected.

[0159] If the signal strength of the RF signal SuA that has passed through the BPF 62A is less than the threshold value Th1, the judgment unit 81A generates a switching signal Soff to disconnect the connection between the BPF 62A and the multiplexing unit 64, and outputs the generated switching signal Soff to the switch 63A.

[0160] In addition, if the signal strength of the RF signal SuB that has passed through the BPF 62B is less than the threshold value Th1, the judgment unit 81B generates a switching signal Soff to disconnect the connection between the BPF 62B and the multiplexing unit 64, and outputs the generated switching signal Soff to the switch 63B.

[0161] In addition, if the signal strength of the RF signal SuC that has passed through the BPF 62C is less than the threshold value Th1, the judgment unit 81C generates a switching signal Soff to disconnect the connection between the BPF 62C and the multiplexing unit 64, and outputs the generated switching signal Soff to the switch 63C.

[0162] The multiplexing unit 64 receives an RF signal Su, of the RF signals SuA, SuB, and SuC, whose signal strength is equal to or greater than the threshold value Th1, via the corresponding switch 63. That is, the multiplexing unit 64 receives the RF signal Su via a switch 63 that has not been switched to the off state by the switching signal Soff from the control unit 46 and that has not been switched to the off state by the switching signal Soff from the determination unit 81. The multiplexing unit 64 generates an RF signal Muex by multiplexing the received RF signals Su, and outputs the generated RF signal Muex to the optical transceiver 40.

[0163] In the optical communication system 402 according to the first embodiment of the present disclosure, the determination unit 81 in the extraction unit 80 of the slave station device 202 is configured to measure the signal strength of the RF signal Su as an index indicating the communication quality of the RF signal Su, but this is not limited to this. The determination unit 81 may be configured to measure the EVM (Error Vector Magnitude) of the RF signal Su instead of or in addition to the signal strength of the RF signal Su, or may be configured to measure the SNR (Signal-to-Noise Ratio) of the RF signal Su as an index indicating the communication quality of the RF signal Su.

[0164] 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.

[0165] Third Embodiment This embodiment relates to an optical communication system 403 that performs downstream sampling processing and upstream sampling processing using a tunable filter, in contrast to the optical communication system 401 according to the first embodiment. Except for the details described below, the optical communication system 403 is the same as the optical communication system 401 according to the first embodiment.

[0166] 8 is a diagram illustrating a configuration of an optical communication system according to a third embodiment of the present disclosure. Referring to FIG. 8, the optical communication system 403 includes a slave station device 203 instead of the slave station device 201, as compared with the optical communication system 401.

[0167] For example, the multiple slave station devices 203 provided in the optical communication system 403 include a slave station device 203A that is a slave station device 203 used by all telecommunications carriers Op, and a slave station device 203B that is a slave station device 203 used by telecommunications carriers OpA, OpB, and OpC except for telecommunications carrier OpD.

[0168] (Configuration of a Slave Station Device) Fig. 9 is a diagram illustrating the configuration of a slave station device in an optical communication system according to a third embodiment of the present disclosure. Referring to Fig. 9, compared to the slave station device 201, the slave station device 203 includes an optical transceiver 140 instead of the optical transceiver 40, an extractor 150 instead of the extractor 50, and an extractor 160 instead of the extractor 60. Compared to the optical transceiver 40, the optical transceiver 140 includes a control unit 141 instead of the control unit 46. Compared to the extractor 50, the extractor 150 includes a variable filter 151 instead of the distributor 51, BPF 52, switch 53, and multiplexer 54. Compared to the extractor 60, the extractor 160 includes a variable filter 161 instead of the distributor 61, BPF 62, switch 63, and multiplexer 64.

[0169] The variable filters 151 and 161 are BPFs whose pass bands Pb can be changed. For example, the variable filters 151 and 161 include a plurality of BPFs with different pass bands. For example, the pass band Pbin, which is the pass band Pb of the variable filters 151 and 161 in the initial state, includes frequency bands FbA, FbB, FbC, and FbD. The control unit 141 controls the pass band Pb of the variable filters 151 and 161.

[0170] (Processing of Slave Station Device 203B in Downstream Communication) The control unit 141 in the optical transceiver unit 140 of the slave station device 203B acquires extracted information from the digital signal Sdd, similar to the control unit 46 in the optical transceiver unit 40 of the slave station device 201B. Based on the acquired extracted information, the control unit 141 generates a setting signal Sset for setting the pass band Pb of the tunable filters 151, 161 to a pass band PbABC that includes the frequency bands FbA, FbB, and FbC but does not include the frequency band FbD, and outputs the generated setting signal Sset to the tunable filters 151, 161.

[0171] The extraction unit 150 in the slave station device 203B performs downstream extraction processing to extract RF signals SdA, SdB, and SdC corresponding to the frequency bands FbA, FbB, and FbC, respectively, of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Md acquired by the optical transceiver unit 140.

[0172] More specifically, the variable filter 151 in the extraction unit 150 receives the setting signal Sset from the control unit 141 and changes the pass band Pb from the pass band Pbin to the pass band PbABC in accordance with the received setting signal Sset. The variable filter 151 then attenuates frequency components outside the pass band PbABC in the RF signal Md received from the optical transceiver 40.

[0173] The front end unit 70 in the slave station device 203B transmits an RF signal Mdex based on the RF signals SdA, SdC, and SdD extracted by the extraction unit 150. More specifically, the front end unit 70 receives the RF signal Mdex, which is a signal that has passed through the variable filter 151, and transmits the received RF signal Mdex to the communication terminal via the antenna 211.

[0174] (Processing of slave station device 203B in uplink communication) The extraction unit 160 in the slave station device 203B performs uplink extraction processing to extract RF signals SuA, SuB, and SuC corresponding to the frequency bands FbA, FbB, and FbC, respectively, of the frequency bands FbA, FbB, FbC, and FbD from the RF signal Mu received by the front end unit 70.

[0175] More specifically, the variable filter 161 in the extraction unit 160 receives the setting signal Sset from the control unit 141 and changes the pass band Pb from the pass band Pbin to the pass band PbABC in accordance with the received setting signal Sset. The variable filter 161 then attenuates frequency components outside the pass band PbABC in the RF signal Md received from the optical transceiver 40.

[0176] The optical transceiver 140 in the slave station device 203B generates an upstream optical signal including the RF signal Muex extracted by the extractor 160, and transmits the generated upstream optical signal to the master station device 101. More specifically, the optical transceiver 140 receives the RF signal Muex, which is a signal that has passed through the tunable filter 161, generates an upstream optical signal including the received RF signal Muex, and transmits the generated upstream optical signal to the master station device 101.

[0177] In the slave station device 203 according to the third embodiment of the present disclosure, the control unit 141 is configured to output the setting signal Sset to the variable filters 151, 161 in the extraction units 150, 160 to set the pass band Pb of the variable filters 151, 161 to the pass band PbABC. However, this is not limited to this. The extraction units 150, 160 may not include the variable filters 151, 161, and the control unit 141 may not output the setting signal Sset. In this case, for example, the administrator of the optical communication system 403 may create a filter having the pass band PbABC using one or more BPFs having a pass band tuned in advance according to the frequency band Fb, and may place the created filter in the extraction units 150, 160.

[0178] 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.

[0179] 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.

[0180] The above description includes the following additional features: [Supplementary Note 1] An optical communication system comprising: a master station device; and slave station devices that transmit and receive wireless signals via an antenna, wherein the master station device receives a plurality of first communication signals corresponding to a plurality of frequency bands from another device, generates a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, wherein the slave station device acquires the first electrical signal from the downstream optical signal and performs downstream extraction processing to extract the first communication signal corresponding to a portion of the plurality of frequency bands from the acquired first electrical signal, and transmits a downstream wireless signal based on the extracted first communication signal, and wherein the slave station device performs the downstream extraction processing using a variable filter that can change a passband.

[0181] 10 Downstream processing unit 11, 11A, 11B, 11C, 11D BPF 12, 12A, 12B, 12C, 12D Amplification unit 13 Multiplexing unit 20 Upstream processing unit 21 Distribution unit 22, 22A, 22B, 22C, 22D BPF 23, 23A, 23B, 23C, 23D Amplification unit 30 Optical transmitting / receiving unit 31 Multiplexing unit 32 Optical modulation unit 33 Optical demodulation unit 34 Separation unit 35 Multiplexing unit 36 ​​Control unit 37 Optical coupler 40 Optical transmitting / receiving unit 41 Optical coupler 42 Optical demodulation unit 43 Separation unit 44 Multiplexing unit 45 Optical modulation unit 46 Control unit 50 Extraction unit 51 Distribution unit 52, 52A, 52B, 52C, 52D BPF 53, 53A, 53B, 53C, 53D Switch 54 Multiplexing section 60 Extraction section 61 Distribution section 62, 62A, 62B, 62C, 62D BPF 63, 63A, 63B, 63C, 63D Switch 64 Multiplexing section 70 Front end section 71 BPF 72 Amplification section 73 RF transmission / reception section 74 Amplification section 80 Extraction section 81, 81A, 81B, 82C, 81D Determination section 101 Master station device 140 Optical transmission / reception section 141 Control section 150 Extraction section 151 Tunable filter 160 Extraction section 161 Tunable filter 171, 181 Transmission line 191 Optical fiber 201, 202, 203 Slave station device 211 Antenna 301, 301A, 301B, 301C, 301D Base station device 311 Control device 401, 402, 403 Optical communication system

Claims

1. An optical communication system comprising: a master station device; and a slave station device that transmits and receives wireless signals via an antenna, wherein the master station device receives a plurality of first communication signals corresponding to a plurality of frequency bands from another device, generates a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, and the slave station device acquires the first electrical signal from the downstream optical signal, performs a downstream extraction process to extract the first communication signal corresponding to a portion of the frequency bands from the acquired first electrical signal, and transmits a downstream wireless signal based on the extracted first communication signal.

2. The optical communication system described in claim 1, wherein the slave station device receives an upstream wireless signal, performs an upstream extraction process to extract a second communication signal corresponding to the part of the frequency band from a signal based on the received upstream wireless signal, generates an upstream optical signal including the extracted second communication signal, and transmits the generated upstream optical signal to the master station device.

3. The optical communication system described in claim 1 or claim 2, wherein the parent station device generates a control signal indicating the first communication signal to be extracted in the downstream extraction process, and transmits the downstream optical signal further including the generated control signal to the child station device, and the child station device further acquires the control signal from the downstream optical signal and extracts the first communication signal from the first electrical signal in accordance with the acquired control signal.

4. The optical communication system according to claim 2, wherein, in the upstream extraction process, the slave station device extracts the second communication signals corresponding to the partial frequency band whose communication quality satisfies a predetermined condition.

5. A master station device that transmits communication signals to a slave station device that transmits and receives wireless signals via an antenna, comprising: a receiver that receives from another device a plurality of first communication signals corresponding to a plurality of frequency bands, respectively; a first generator that generates a first electrical signal into which the plurality of first communication signals received by the receiver are multiplexed; a second generator that generates a control signal indicating which of the plurality of first communication signals is to be wirelessly transmitted by the slave station device; and an optical transmitter that generates a downstream optical signal including the first electrical signal generated by the first generator and the control signal generated by the second generator, and transmits the generated downstream optical signal to the slave station device.

6. A slave station device that transmits and receives wireless signals via an antenna, comprising: an optical receiving unit that receives a downstream optical signal from a master station device and acquires, from the received downstream optical signal, a first electrical signal into which multiple first communication signals corresponding to multiple frequency bands are multiplexed; an extracting unit that performs downstream extraction processing to extract, from the first electrical signal acquired by the optical receiving unit, the first communication signals corresponding to some of the frequency bands; and a wireless transmitting unit that transmits a downstream wireless signal based on the first communication signals extracted by the extracting unit.

7. An optical communication method in an optical communication system having a master station device and a slave station device that transmits and receives radio signals via an antenna, comprising the steps of: the master station device receiving a plurality of first communication signals corresponding to a plurality of frequency bands from another device, generating a downstream optical signal including a first electrical signal into which the received plurality of first communication signals are multiplexed, and transmitting the generated downstream optical signal to the slave station device; and the slave station device acquiring the first electrical signal from the downstream optical signal, performing a downstream extraction process to extract the first communication signal corresponding to a portion of the frequency bands from the acquired first electrical signal, and transmitting a downstream radio signal based on the extracted first communication signal.

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