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

Abstract

This optical communication system comprises a master station device and slave station devices. The master station device generates a downlink optical signal including a first electric signal in which a plurality of first analog signals corresponding to a plurality of frequency bands are multiplexed, and transmits the downlink optical signal to the slave station devices. The slave station devices acquire the first electric signal from the downlink optical signal, and transmit downlink wireless signals based on the first electric signal. The slave station devices receive uplink wireless signals, and transmit, to the master station device, uplink optical signals including second electric signals based on the uplink wireless signals. The master station device acquires the second electric signals from the uplink optical signals, and acquires, from the second electric signals, a plurality of second analog signals corresponding to the plurality of frequency bands.

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. 2024-83721, 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 analog 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 analog signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, the slave station device acquires the first electrical signal from the downstream optical signal and transmits a downstream wireless signal based on the acquired first electrical signal, the slave station device receives an upstream wireless signal and generates an upstream optical signal including a second electrical signal based on the received upstream wireless signal and transmits the generated upstream optical signal to the master station device, and the master station device acquires the second electrical signal from the upstream optical signal and acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the acquired second electrical 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 correspondence table in a gain setting unit in a slave station device according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure. FIG. 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 master 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 master 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] The technologies described in Patent Documents 1 to 3 require a wide bandwidth to accommodate multiple telecommunications carriers, have low frequency utilization efficiency, and require many optical modules to transmit and receive optical signals.

[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 are capable of transmitting multiple communication signals in different frequency bands with a simple configuration.

[0012] Effect of the Present Disclosure According to the present disclosure, it is possible to transmit a plurality of communication signals in different frequency bands with a simple configuration.

[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 analog 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 analog signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, the slave station device acquires the first electrical signal from the downstream optical signal and transmits a downstream wireless signal based on the acquired first electrical signal, the slave station device receives an upstream wireless signal and generates an upstream optical signal including a second electrical signal based on the received upstream wireless signal and transmits the generated upstream optical signal to the master station device, and the master station device acquires the second electrical signal from the upstream optical signal and acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the acquired second electrical signal.

[0014] In this way, the configuration in which the master station transmits a downstream optical signal including a first electrical signal in which multiple first analog signals are multiplexed to the slave station can narrow the communication bandwidth compared to a configuration in which a downstream optical signal including a signal in which multiple digital signals are multiplexed, thereby reducing the number of optical modules required to transmit and receive optical signals. This makes it possible to build an optical communication system that can be shared and used by multiple telecommunications carriers using fewer optical modules and optical wavelength resources. Therefore, it is possible to transmit multiple communication signals in different frequency bands with a simple configuration.

[0015] (2) In the above (1), the parent station device may adjust the plurality of first analog signals so as to reduce the intensity difference between the plurality of first analog signals, and generate the first electrical signal in which the plurality of adjusted first analog signals are multiplexed.

[0016] With this configuration, it is possible to align the signal strength of each of the multiple frequency bands in the downstream radio signal transmitted by the slave station device via the antenna, and to reduce signal distortion of the downstream radio signal caused by optically modulating the first electrical signal.

[0017] (3) In the above (1) or (2), the base station device may generate the first electrical signal by multiplexing the first analog signals that have passed through a plurality of first filters, each corresponding to a plurality of frequency bands, the first filters having different passbands from one another, and the base station device may acquire the second analog signals using a plurality of second filters having different passbands from one another.

[0018] With this configuration, it is possible to reduce noise components in the downstream radio signal, and to extract the second analog signal of each frequency band from the second electrical signal contained in the upstream optical signal.

[0019] (4) In any of (1) to (3) above, the slave station device may adjust the intensity of the received upstream wireless signal using an amplification factor or an attenuation factor according to the intensity of the received upstream wireless signal, and generate the upstream optical signal including the second electrical signal based on the adjusted upstream wireless signal.

[0020] This configuration reduces the fluctuation range of the level of the second electrical signal generated in the slave station device and enables the generation of an upstream optical signal with good characteristics, thereby reducing signal distortion of the second electrical signal obtained from the upstream optical signal in the master station device, and thereby widening the reception dynamic range of the upstream wireless signal.

[0021] (5) In any of (1) to (4) above, the parent station device may receive the plurality of first analog signals and a plurality of pieces of control information for controlling the operation of the child station device from a plurality of base station devices, respectively; the parent station device may select one of the plurality of pieces of control information, generate a control signal including the selected control information, 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 operate in accordance with the control information included in the acquired control signal.

[0022] With this configuration, it is possible to stably control the operation of the slave station equipment in an optical communication system that can be shared and used by a plurality of communication carriers.

[0023] (6) In the above (5), the optical communication system may include a plurality of the slave station devices, and the master station device may generate the control signal further including identification information indicating the slave station device that is to be controlled using the control information.

[0024] With this configuration, in a distributed antenna system having a plurality of slave station devices, the operation of each slave station device can be controlled individually.

[0025] (7) In any of (1) to (6) above, the optical communication system may include a plurality of the slave station devices, and the plurality of slave station devices may each transmit a plurality of the upstream optical signals having different wavelengths to the master station device, and the master station device may acquire a plurality of the second electrical signals from the plurality of upstream optical signals, multiplex the acquired second electrical signals, and acquire the plurality of second analog signals from the multiplexed signals.

[0026] With this configuration, in a distributed antenna system that can be shared and used by multiple telecommunications carriers, second electrical signals based on uplink radio signals received at each slave station device can be aggregated, and second analog signals in each frequency band can be provided to each telecommunications carrier without omission.

[0027] (8) A parent station device according to an embodiment of the present disclosure includes a receiving unit that receives from another device a plurality of first analog signals corresponding to a plurality of frequency bands, respectively; a generating unit that generates a first electrical signal into which the plurality of first analog signals received by the receiving unit are multiplexed; an optical transmitting unit that generates a downstream optical signal including the first electrical signal generated by the generating unit and transmits the generated downstream optical signal to a child station device; an optical receiving unit that receives an upstream optical signal from the child station device and acquires a second electrical signal from the received upstream optical signal; and an acquiring unit that acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the second electrical signal acquired by the optical receiving unit.

[0028] In this way, by transmitting a downstream optical signal including a first electrical signal in which multiple first analog signals are multiplexed to a slave station device, the communication bandwidth can be narrowed compared to a configuration in which a downstream optical signal including a signal in which multiple digital signals are multiplexed, and therefore the number of optical modules required to transmit and receive optical signals can be reduced. This makes it possible to build an optical communication system that can be shared and used by multiple telecommunications carriers using fewer optical modules and optical wavelength resources. Therefore, it is possible to transmit multiple communication signals in different frequency bands with a simple configuration.

[0029] (9) 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 analog signals corresponding to multiple frequency bands are multiplexed; a wireless transmitting unit that transmits a downstream wireless signal based on the first electrical signal acquired by the optical receiving unit; a wireless receiving unit that receives an upstream wireless signal; and an optical transmitting unit that generates an upstream optical signal including a second electrical signal based on the upstream wireless signal received by the wireless receiving unit and transmits the generated upstream optical signal to the master station device.

[0030] In this way, by acquiring a first electrical signal in which multiple first analog signals are multiplexed from a downstream optical signal received from a master station and transmitting a downstream wireless signal based on the acquired first electrical signal, the communication bandwidth can be narrowed compared to a configuration in which a downstream optical signal including a signal in which multiple digital signals are multiplexed is received from a master station, thereby reducing the number of optical modules required to transmit and receive optical signals. This makes it possible to build an optical communication system that can be shared and used by multiple telecommunications carriers using fewer optical modules and optical wavelength resources. Therefore, it is possible to transmit multiple communication signals in different frequency bands with a simple configuration.

[0031] (10) 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 analog 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 analog signals are multiplexed, and transmitting the generated downstream optical signal to the slave station device; the slave station device acquiring the first electrical signal from the downstream optical signal and transmitting a downstream wireless signal based on the acquired first electrical signal; the slave station device receiving an upstream wireless signal, generating an upstream optical signal including a second electrical signal based on the received upstream wireless signal, and transmitting the generated upstream optical signal to the master station device; and the steps of the master station device acquiring the second electrical signal from the upstream optical signal and acquiring a plurality of second analog signals corresponding to a plurality of frequency bands from the acquired second electrical signal.

[0032] In this way, the method in which the master station transmits a downstream optical signal including a first electrical signal in which multiple first analog signals are multiplexed to the slave station can narrow the communication bandwidth compared to the method in which a downstream optical signal including a signal in which multiple digital signals are multiplexed, thereby reducing the number of optical modules required to transmit and receive optical signals. This makes it possible to build an optical communication system that can be shared and used by multiple telecommunications carriers using fewer optical modules and optical wavelength resources. Therefore, it is possible to transmit multiple communication signals in different frequency bands with a simple configuration.

[0033] 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.

[0034] 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. The transmission line 181 is, for example, a coaxial cable. The base station devices 301A, 301B, 301C, and 301D are provided in base stations of different telecommunications carriers. Hereinafter, each of the base station devices 301A, 301B, 301C, and 301D will also be referred to as a base station device 301.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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 analog signal. The RF signals SdA, SdB, SdC, and SdD are Sub6 band signals corresponding to different frequency bands FbA, FbB, FbC, and FbD, respectively. Note that a part of the frequency band of the RF signal Sd may overlap a part of the frequency band of another RF signal Sd. Furthermore, the RF signal Sd may be a millimeter wave signal.

[0040] The master station device 101 generates a downstream optical signal including an RF signal Md in which the received RF signals SdA, SdB, SdC, and SdD are multiplexed, 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 and an example of a downstream wireless signal.

[0041] 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.

[0042] 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 and an example of a second electrical signal.

[0043] The master station device 101 receives an upstream optical signal from each slave station device 201 via an 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 analog 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 part of the frequency band of the RF signal Su may overlap part of the frequency band of another RF signal Su. The RF signal Su may also be a millimeter wave 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.

[0044] 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.

[0045] (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 generator. The upstream processing unit 20 is an example of an acquirer. The optical transceiver unit 30 is an example of an optical transmitter and an example of an optical receiver.

[0046] 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. The BPF 11 is an example of a first filter.

[0047] 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. The BPF 22 is an example of a second filter.

[0048] 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.

[0049] 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 and a front-end unit 50. The optical transceiver 40 is an example of an optical receiver and an example of an optical transmitter. The front-end unit 50 is an example of a wireless transmitter and an example of a wireless receiver.

[0050] The optical transceiver 40 includes an optical coupler 41, an optical demodulator 42, a separator 43, switches 44 and 45, a multiplexer 46, an optical modulator 47, and a controller 48. The switch 44 has a first end connected to the front end 50, a second end connected to the separator 43, and a third end connected to a termination resistor (not shown). The switch 45 has a first end connected to the front end 50, a second end connected to the multiplexer 46, and a third end connected to a termination resistor (not shown). The switches 44 and 45 are capable of switching the terminal connected to the first end between the second end and the third end. For example, in the initial state, the switches 44 and 45 have their first and second ends connected.

[0051] The front-end unit 50 includes a BPF 51, an amplifier unit 52, an RF transceiver unit 53, an amplifier unit 54, a gain setting unit 55, and an antenna 211. Some or all of the functions of the control unit 48 and the gain setting unit 55 are realized by, for example, a processing circuit including one or more processors.

[0052] (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.

[0053] 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.

[0054] 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 the signal distortion of the RF signal Md.

[0055] The multiplexing unit 13 generates an RF signal Md that is a multiplexed version of the RF signals SdA, SdB, SdC, and SdD that have passed through the BPFs 11A, 11B, 11C, and 11D and been amplified by the amplifiers 12A, 12B, 12C, and 12D. More specifically, the multiplexing unit 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 transceiver 30.

[0056] The optical transceiver 30 generates a downstream optical signal including the RF signal Md generated by the downstream processing unit 10, and transmits the generated downstream optical signal to each slave station device 201. For example, the optical transceiver 30 transmits to the slave station device 201 a downstream optical signal that further includes a digital signal Sdd that includes control information for controlling the operation of the slave station device 201.

[0057] More specifically, the control unit 36 ​​in the optical transceiver 30 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 the uplink period Pu and the downlink period Pd, and synchronization information indicating a reference clock signal.

[0058] 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. Then, the control unit 36 ​​generates a digital signal Sdd including the selected control information. The digital signal Sdd is an example of a control signal.

[0059] For example, the control unit 36 ​​generates a digital signal Sdd that further includes identification information indicating the slave station device 201 that is the target of control using the control information. More specifically, the control unit 36 ​​generates a digital signal Sdd that further includes identification information indicating the ID of the slave station device 201 that is the target of control. The control unit 36 ​​outputs the generated digital signal Sdd to the multiplexing unit 31.

[0060] 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.

[0061] 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.

[0062] 3 , in the slave station device 201, the optical transceiver 40 receives a downstream optical signal from the master station device 101 and acquires an RF signal Md from the received downstream optical signal. For example, the optical transceiver 40 further acquires a digital signal Sdd from the downstream optical signal. Each unit in the slave station device 201 operates in accordance with control information included in the digital signal Sdd.

[0063] 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.

[0064] 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 front end unit 50 via the switch 44, and also outputs the separated digital signal Sdd to the control unit 48.

[0065] The front end unit 50 transmits the RF signal Md acquired by the optical transceiver 40. More specifically, in the front end unit 50, the BPF 51 receives the RF signal Md from the separator 43 and attenuates components outside a predetermined passband in the received RF signal Md.

[0066] The amplifier 52 amplifies the RF signal Md that has passed through the BPF 51 , and outputs the amplified RF signal Md to the RF transmitter / receiver 53 .

[0067] The control unit 48 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 53. More specifically, based on the TDD information and synchronization information, the control unit 48 generates a TDD switching signal for switching between the transmission and reception of RF signals by the RF transceiver unit 53, and outputs the generated TDD switching signal to the RF transceiver unit 53.

[0068] In accordance with the TDD switching signal received from the control unit 48, the RF transceiver unit 53 transmits the RF signal Md received from the amplifier unit 52 to the communication terminal via the antenna 211 during the downlink period Pd.

[0069] (Uplink Communication) The front-end unit 50 receives the RF signal Mu. More specifically, the RF transceiver unit 53 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 48. The RF transceiver unit 53 outputs the received RF signal Mu to the amplifier unit 54 and the gain setting unit 55.

[0070] 4 is a diagram illustrating an example of a correspondence table in a gain setting unit in the slave station device according to the first embodiment of the present disclosure. Referring to FIG. 4, the gain setting unit 55 stores a correspondence table T1 indicating a correspondence relationship between an average power AP of an RF signal Mu in frequency bands FbA, FbB, FbC, and FbD and a gain setting value GV of the amplifier 54.

[0071] The gain setting unit 55 receives the RF signal Mu from the RF transceiver unit 53 and calculates the average power AP of the RF signal Mu in the frequency bands FbA, FbB, FbC, and FbD. The gain setting unit 55 references the correspondence table T1 and obtains a gain setting value GV corresponding to the calculated average power AP. The gain setting unit 55 sets the gain of the amplifier unit 54 to the obtained gain setting value GV.

[0072] Referring back to FIG. 3 , the amplifier 54 amplifies the RF signal Mu received from the RF transceiver 53. For example, the amplifier 54 amplifies the RF signal Mu with an amplification factor corresponding to the strength of the RF signal Mu. More specifically, the amplifier 54 amplifies the RF signal Mu with a gain set by the gain setting unit 55. This reduces the fluctuation range of the level of the RF signal Mu depending on the number of communication terminals communicating via the antenna 211 and the distance between the antenna 211 and the communication terminals, and adjusts the level of the RF signal Mu to a range in which the optical modulator 47 operates with good characteristics. This reduces signal distortion of the RF signal Mu acquired from the upstream optical signal in the master station 101. This widens the reception dynamic range of the RF signal Mu. The amplifier 54 outputs the amplified RF signal Mu to the optical transceiver 40.

[0073] The optical transceiver 40 generates an upstream optical signal including the RF signal Mu received by the front end unit 50, and transmits the generated upstream optical signal to the parent station 101. For example, the optical transceiver 40 generates an upstream optical signal including the RF signal Mu amplified by the amplifier 54.

[0074] More specifically, the control unit 48 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 46 .

[0075] The multiplexing unit 46 generates an electrical signal in which the RF signal Mu received from the front end unit 50 via the switch 45 and the digital signal Sdu received from the control unit 48 are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 47 .

[0076] The optical modulator 47 is an EO element that has linear conversion characteristics over a wide frequency bandwidth. The optical modulator 47 receives the electrical signal from the multiplexer 46 and generates an upstream optical signal by optically modulating the received electrical signal. The optical modulator 47 transmits the upstream optical signal to the parent station 101 via the optical coupler 41 and the optical fiber 191.

[0077] 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 47 in each slave station device 201 generates upstream optical signals having different wavelengths and transmits them to the master station device 101.

[0078] 2 , in the master station device 101, the optical transceiver 30 receives upstream optical signals from the slave station devices 201 and acquires RF signals Mu from the received upstream optical signals. For example, the optical transceiver 30 receives multiple upstream optical signals from multiple slave station devices 201, acquires multiple RF signals Mu from the received upstream optical signals, and multiplexes the acquired RF signals Mu.

[0079] 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.

[0080] Each separator 34 separates the RF signal Mu and 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 to the multiplexer 35, and also outputs the separated digital signal Sdu to the controller 36.

[0081] 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.

[0082] The multiplexer 35 multiplexes the RF signals Mu received from the demultiplexers 34 to generate a multiplexed RF signal Mum, and outputs the generated multiplexed RF signal Mum to the upstream processor 20 .

[0083] The upstream processing unit 20 acquires RF signals SuA, SuB, SuC, and SuD from the RF signal Mu 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] (Stopping and Resuming Operation of a Slave Station Device) For example, in the master station device 101, the control unit 36 ​​receives, as control information, stop information indicating which slave station device 201 should stop transmitting and receiving RF signals from the base station device 301. The control unit 36 ​​generates a digital signal Sdd that further includes the stop information, and outputs the generated digital signal Sdd to the multiplexer 31.

[0088] Referring again to FIG. 3 , in the slave station device 201, the control unit 48 in the optical transceiver unit 40 acquires stop information from the digital signal Sdd received from the separator unit 43, and performs processing to stop transmission and reception of RF signals in the slave station device 201 based on the acquired stop information.

[0089] More specifically, the control unit 48 generates a switching signal for disconnecting the connection between the optical transceiver unit 40 and the front-end unit 50 , and outputs the generated switching signal to the switches 44 and 45 .

[0090] The switches 44 and 45 receive a switching signal from the control unit 48 and release the connection between the optical transceiver unit 40 and the front end unit 50 in accordance with the received switching signal. More specifically, the switch 44 switches from a state in which a first end connected to the front end unit 50 and a second end connected to the demultiplexer 43 are connected to a state in which the first end and a third end connected to the termination resistor are connected. Furthermore, the switch 45 switches from a state in which a first end connected to the front end unit 50 and a second end connected to the multiplexer 46 are connected to a state in which the first end and a third end connected to the termination resistor are connected.

[0091] 2 , for example, in the master station device 101, the control unit 36 ​​receives, as control information, start information indicating the slave station device 201 that should resume transmission and reception of RF signals from the base station device 301. The control unit 36 ​​generates a digital signal Sdd that further includes the start information, and outputs the generated digital signal Sdd to the multiplexing unit 31.

[0092] Referring again to FIG. 3 , in the slave station device 201, the control unit 48 in the optical transceiver unit 40 acquires start information from the digital signal Sdd received from the separator 43, and performs processing to stop transmission and reception of RF signals in the slave station device 201 based on the acquired start information.

[0093] More specifically, the control unit 48 generates a switching signal for connecting the optical transceiver unit 40 and the front-end unit 50 , and outputs the generated switching signal to the switches 44 and 45 .

[0094] The switches 44 and 45 receive a switching signal from the control unit 48 and connect the optical transceiver unit 40 and the front end unit 50 in accordance with the received switching signal. More specifically, the switch 44 switches from a state in which a first end connected to the front end unit 50 and a third end connected to the termination resistor are connected to a state in which the first end and a second end connected to the separation unit 43 are connected. Furthermore, the switch 45 switches from a state in which a first end connected to the front end unit 50 and a third end connected to the termination resistor are connected to a state in which the first end and a second end connected to the multiplexer unit 46 are connected.

[0095] [Operation Flow] FIG. 5 is a diagram illustrating an example of a communication sequence in the optical communication system according to the first embodiment of the present disclosure.

[0096] Referring to FIG. 5, first, each base station device 301 transmits an RF signal Sd and control information to the master station device 101 via the corresponding transmission line 181 (step S11).

[0097] Next, the parent station device 101 amplifies the RF signals SdA, SdB, SdC, and SdD at a predetermined amplification factor so that the intensity difference between the RF signals SdA, SdB, SdC, and SdD that have passed through the BPFs 11A, 11B, 11C, and 11D is equal to or less than a predetermined value (step S12).

[0098] Next, the master station device 101 generates an RF signal Md in which the amplified RF signals SdA, SdB, SdC, and SdD are multiplexed (step S13).

[0099] Next, the master station 101 generates a downstream optical signal including the RF signal Md and the digital signal Sdd including control information (step S14).

[0100] Next, the master station device 101 transmits the generated downstream optical signal to each slave station device 201 via the optical fiber 191 (step S15).

[0101] Next, each slave station device 201 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 S16).

[0102] Next, each slave station device 201 amplifies the RF signal Md that has passed through the BPF 51, and transmits the amplified RF signal Md to the communication terminal via the antenna 211 during the downlink period Pd (step S17).

[0103] Next, each slave station device 201 receives the RF signal Mu from the communication terminal via the antenna 211 during the uplink period Pu (step S18).

[0104] Next, each slave station device 201 amplifies the RF signal Mu with an amplification factor corresponding to the strength of the RF signal Mu (step S19).

[0105] Next, each slave station device 201 generates an upstream optical signal including the amplified RF signal Mu and a digital signal Sdu including control information (step S20).

[0106] Next, each slave station device 201 transmits the generated upstream optical signal to the master station device 101 via the optical fiber 191 (step S21).

[0107] Next, the master station device 101 receives the upstream optical signals from each slave station device 201 via the optical fiber 191, and acquires the RF signal Mu and the digital signal Sdu from the received upstream optical signals (step S22).

[0108] Next, the master station device 101 generates a multiplexed RF signal Mum by multiplexing the acquired RF signals Mu (step S23).

[0109] Next, the master station device 101 acquires the RF signals SuA, SuB, SuC, and SuD from the multiplexed RF signal Mum using the four BPFs 22 (step S24).

[0110] 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 S25).

[0111] 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.

[0112] 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.

[0113] 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, generates an RF signal Md by frequency-converting the acquired analog signal, and transmits the generated RF signal Md via the antenna 211. The slave station device 201 also receives an RF signal Mu via the antenna, frequency-converts the received RF signal Mu to generate an analog signal in the IF band, 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 101 acquires an analog signal from the received upstream optical signal and transmits the acquired analog signal to the base station 301 .

[0114] Furthermore, in the master station device 101 according to the first embodiment of the present disclosure, the downlink processing unit 10 is configured to include the amplifier unit 12, but this is not limited to this. The downlink processing unit 10 may be configured to include an attenuation unit that attenuates the RF signal Sd, instead of the amplifier unit 12. In this case, for example, the attenuation rate of the attenuation unit is set in advance according to the levels of the RF signals SdA, SdB, SdC, and SdD transmitted by the base station device 301 so that the intensity difference between the attenuated RF signals SdA, SdB, SdC, and SdD is equal to or less than a predetermined value.

[0115] Furthermore, in the master station device 101 according to the first embodiment of the present disclosure, the gain of the amplifier 12 is configured to be set in advance in accordance with the levels 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, but this is not limitative. The gain of each amplifier 12 may be set to a common value regardless of the levels of the RF signals SdA, SdB, SdC, and SdD transmitted by the base station device 301.

[0116] Furthermore, in the master station device 101 according to the first embodiment of the present disclosure, the downlink processing unit 10 is configured to include the BPF 11, but this is not limited to this. The downlink processing unit 10 may be configured not to include the BPF 11. In this case, the amplifiers 12A, 12B, 12C, and 12D receive RF signals SdA, SdB, SdC, and SdD from the base station devices 301A, 301B, 301C, and 301D, respectively, amplify the received RF signals SdA, SdB, SdC, and SdD, and output the amplified RF signals SdA, SdB, SdC, and SdD to the multiplexer 13.

[0117] Furthermore, in the master station device 101 according to the first embodiment of the present disclosure, the optical transceiver 30 is configured to include one optical modulator 32, but this is not limiting. The optical transceiver 30 may be configured to include multiple optical modulators 32 corresponding to multiple slave station devices 201, respectively. In this case, each optical modulator 32 receives an electrical signal from the multiplexer 31, generates downstream optical signals having different wavelengths, and transmits the generated downstream optical signals to the corresponding slave station device 201 via the optical coupler 37 and the optical fiber 191. In other words, the master station device 101 may be configured to perform wavelength multiplexing communication for downstream communication.

[0118] In addition, 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 identification information indicating the ID of the slave station device 201 to be controlled, but this is not limited to this. The control unit 36 ​​may also be configured to generate the digital signal Sdd without including identification information.

[0119] 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 control information, but this is not limited to this. The control unit 36 ​​may be configured to generate a tone signal including the control information instead of the digital signal Sdd. Furthermore, 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 control information.

[0120] Furthermore, in the slave station device 201 according to the first embodiment of the present disclosure, the front-end unit 50 includes the amplifier unit 54 and the gain setting unit 55, but this is not limiting. The front-end unit 50 may include an attenuation unit that attenuates the RF signal Mu and an attenuation factor setting unit that sets the attenuation factor of the attenuation unit, instead of the amplifier unit 54 and the gain setting unit 55. In this case, the attenuation factor setting unit obtains the attenuation factor setting value from a correspondence table that indicates the correspondence relationship between the average power AP and the attenuation factor setting value, and sets the attenuation factor of the attenuation unit to the obtained attenuation factor setting value.

[0121] In addition, in the slave station device 201 according to the first embodiment of the present disclosure, the gain setting unit 55 in the front-end unit 50 is configured to set the gain of the amplifier unit 54 to the gain setting value GV obtained from the correspondence table T1, but this is not limited to this. For example, the gain setting unit 55 may be configured to compare the average power AP with one or more thresholds and set the gain of the amplifier unit 54 to a value corresponding to the comparison result between the average power AP and the thresholds.

[0122] Furthermore, in the slave station device 201 according to the first embodiment of the present disclosure, the front-end unit 50 is configured to include the gain setting unit 55, but this is not limiting. The front-end unit 50 may be configured not to include the gain setting unit 55. In this case, the amplifier unit 54 amplifies the RF signal Mu received from the RF transceiver unit 53 by a predetermined gain.

[0123] In addition, in the slave station device 201 according to the first embodiment of the present disclosure, the optical transceiver 40 is configured to include the switches 44 and 45. However, this is not limitative. The optical transceiver 40 may be configured not to include the switches 44 and 45.

[0124] In addition, in the slave station device 201 according to the first embodiment of the present disclosure, the RF transceiver unit 53 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 53 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.

[0125] 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.

[0126] Second Embodiment This embodiment relates to an optical communication system 402 in which slave station devices 201 are grouped and connected to an optical fiber 191, 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.

[0127] 6 is a diagram illustrating a configuration of an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 6, compared to the optical communication system 401, the optical communication system 402 includes a master station device 102 instead of the master station device 101. The master station device 102 and a plurality of slave station devices 201A are connected in a one-to-many manner via an optical fiber 191A and an optical splitter (not shown). The master station device 102 and a plurality of slave station devices 201B are connected in a one-to-many manner via an optical fiber 191B and an optical splitter (not shown). The slave station devices 201A and 201A are examples of the slave station devices 201. The optical fibers 191A and 191B are examples of the optical fiber 191.

[0128] 7 is a diagram illustrating a configuration of a master station device in an optical communication system according to a second embodiment of the present disclosure. Referring to FIG. 7 , the master station device 102 includes multiple optical transceivers 30 compared to the master station device 101. More specifically, the master station device 102 includes optical transceivers 30A and 30B, which are the optical transceivers 30. The optical coupler 37 in the optical transceiver 30A is connected to multiple slave station devices 201A in the optical communication system 402 via an optical fiber 191A. The optical coupler 37 in the optical transceiver 30B is connected to multiple slave station devices 201B in the optical communication system 402 via an optical fiber 191B. The control unit 36 ​​of the optical transceivers 30A and 30B may be shared.

[0129] (Downstream Communication) 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. The downstream processing unit 10 distributes the generated RF signal Md to the optical transceivers 30A and 30B.

[0130] The optical transceiver 30A generates a downstream optical signal including the RF signal Md received from the downstream processor 10, and transmits the generated downstream optical signal to each slave station device 201A via the optical fiber 191A.

[0131] The optical transceiver 30B generates a downstream optical signal including the RF signal Md received from the downstream processor 10, and transmits the generated downstream optical signal to each slave station device 201B via an optical fiber 191B.

[0132] The optical transceiver 30A receives a plurality of upstream optical signals from a plurality of slave station devices 201A via the optical fiber 191A. The optical transceiver 30A acquires a plurality of RF signals Mu from the received upstream optical signals, multiplexes the acquired RF signals Mu to generate a multiplexed RF signal Mum, and outputs the generated multiplexed RF signal Mum to the upstream processing unit 20.

[0133] The optical transceiver 30B receives a plurality of upstream optical signals from a plurality of slave station devices 201B via the optical fiber 191B. The optical transceiver 30B acquires a plurality of RF signals Mu from the received upstream optical signals, multiplexes the acquired RF signals Mu to generate a multiplexed RF signal Mum, and outputs the generated multiplexed RF signal Mum to the upstream processing unit 20.

[0134] The upstream processing unit 20 multiplexes the multiplexed RF signal Mum received from the optical transceiver 30A with the multiplexed RF signal Mum received from the optical transceiver 30B, and obtains RF signals SuA, SuB, SuC, and SuD from the multiplexed signal. The upstream processing unit 20 transmits the obtained RF signals SuA, SuB, SuC, and SuD to the base station devices 301A, 301B, 301C, and 301D, respectively.

[0135] Although the master station device 102 according to the second embodiment of the present disclosure is configured to include the optical transceivers 30A and 30B, the present disclosure is not limited to this. The master station device 102 may be configured to include three or more optical transceivers 30.

[0136] In the optical communication system 402 according to the second embodiment of the present disclosure, the number of slave station devices 201 that can be connected to the master station device 102 can be increased compared to the optical communication system 401. Specifically, in the optical communication system 401, the number of slave station devices 201 that can be accommodated is approximately eight in order to prevent a decrease in the reception dynamic range of the RF signal Mu. In contrast, in the optical communication system 402, the number of slave station devices 201 that can be accommodated can be increased to approximately 16.

[0137] 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.

[0138] Third Embodiment This embodiment relates to an optical communication system 403 in which a master station device 103 and a slave station device 201 are connected one-to-one, as compared with the optical communication system 401 according to the first embodiment. The optical communication system 403 is the same as the optical communication system 401 according to the first embodiment except for the contents described below.

[0139] 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, compared to the optical communication system 401, the optical communication system 403 includes a master station device 103 instead of the master station device 101. The master station device 103 and the slave station devices 201 are connected one-to-one via an optical fiber 191.

[0140] 9 is a diagram illustrating a configuration of a master station 103 in an optical communication system according to a third embodiment of the present disclosure. Compared to the master station 101, the master station 103 includes an optical transceiver 60 instead of the optical transceiver 30.

[0141] Compared to the optical transceiver 30, the optical transceiver 60 includes a plurality of multiplexing units 64 instead of the multiplexing unit 31, a plurality of optical modulation units 65 instead of the optical modulation unit 32, a plurality of optical couplers 66 instead of the optical coupler 37, and further includes a distribution unit 61, a plurality of downstream amplification units 62, and a plurality of upstream amplification units 63. For example, the downstream amplification units 62, upstream amplification units 63, multiplexing units 64, optical modulation units 65, optical couplers 66, optical demodulation units 33, and separation units 34 are provided corresponding to the slave station equipment 201.

[0142] 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. The downstream processing unit 10 outputs the generated RF signal Md to the optical transceiver unit 60.

[0143] The distributor 61 receives the RF signal Md from the downstream processor 10 and distributes the received RF signal Md to each downstream amplifier 62 .

[0144] Each downstream amplifier 62 amplifies the RF signal Md received from the distributor 61 at a predetermined amplification factor, and outputs the amplified RF signal Md to the corresponding multiplexer 64 .

[0145] The control unit 36 ​​generates a digital signal Sdd including control information, and outputs the generated digital signal Sdd to each multiplexing unit 64 .

[0146] Each multiplexing unit 64 generates an electrical signal that is frequency-multiplexed from the RF signal Md received from the downstream amplifier unit 62 and the digital signal Sdd received from the control unit 36, and outputs the generated electrical signal to the corresponding optical modulation unit 65.

[0147] Each optical modulator 65 is an EO element that converts an electrical signal into a downstream optical signal of a different wavelength. Each optical modulator 65 receives an electrical signal from the corresponding multiplexer 64 and generates a downstream optical signal by optically modulating the received electrical signal. Each optical modulator 65 transmits the downstream optical signal to the corresponding slave station equipment 201 via the corresponding optical coupler 66 and optical fiber 191.

[0148] (Upstream Communication) Each optical demodulator 33 receives an upstream optical signal from a corresponding slave station device 201 via the optical fiber 191 and the corresponding optical coupler 66. Each optical demodulator 33 generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal and outputs the electrical signal to the corresponding separator 34.

[0149] Each separator 34 separates the RF signal Mu and 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 to the corresponding upstream amplifier 63, and also outputs the separated digital signal Sdu to the control unit 36.

[0150] Each upstream amplifier 63 amplifies the RF signal Mu received from the corresponding separator 34 at a predetermined amplification factor, and outputs the amplified RF signal Mu to the multiplexer 35 .

[0151] The multiplexer 35 generates a multiplexed RF signal Mum by multiplexing the RF signals Mu received from the upstream amplifiers 63 , and outputs the generated multiplexed RF signal Mum to the upstream processor 20 .

[0152] The upstream processing unit 20 acquires RF signals SuA, SuB, SuC, and SuD from the RF signal Mu acquired by the optical transceiver unit 60. The upstream processing unit 20 transmits the acquired RF signals SuA, SuB, SuC, and SuD to the base station devices 301A, 301B, 301C, and 301D, respectively.

[0153] In the optical communication system 403 according to the third embodiment of the present disclosure, it is possible to prevent a decrease in the intensity of an optical signal due to branching the optical signal, compared to the optical communication system 401 .

[0154] 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.

[0155] 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.

[0156] The above description includes the following additional features: [Supplementary Note 1] An optical communication system comprising: a master station device; and a plurality of slave station devices that transmit and receive wireless signals via antennas, wherein the master station device receives a plurality of first analog 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 analog signals are multiplexed, and transmits the generated downstream optical signal to the slave station device, the slave station device acquires the first electrical signal from the downstream optical signal and transmits a downstream wireless signal based on the acquired first electrical signal, the slave station device receives an upstream wireless signal and generates an upstream optical signal including a second electrical signal based on the received upstream wireless signal and transmits the generated upstream optical signal to the master station device, the master station device acquires the second electrical signal from the upstream optical signal and acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the acquired second electrical signal, and the master station device and the plurality of slave station devices are connected in a one-to-multiple configuration via optical fibers and an optical splitter.

[0157] 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, 30A, 30B 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, 45 Switch 46 Multiplexing unit 47 Optical modulation unit 48 Control unit 50 Front end unit 51 BPF 52 Amplifying section 53 RF transmitting / receiving section 54 Amplifying section 55 Gain setting section 60 Optical transmitting / receiving section 61 Distribution section 62 Downstream amplifying section 63 Upstream amplifying section 64 Multiplexing section 65 Optical modulation section 66 Optical coupler 101, 102, 103 Master station device 181 Transmission line 191, 191A, 191B Optical fiber 201, 201A, 201B Slave station device 211 Antenna 301, 301A, 301B, 301C, 301D Base station device 401, 402, 403 Optical communication system T1 Correspondence table

Claims

1. An optical communications system comprising: a master station; and slave station devices that transmit and receive wireless signals via an antenna; wherein the master station receives a plurality of first analog 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 analog signals are multiplexed, and transmits the generated downstream optical signal to the slave station; the slave station device acquires the first electrical signal from the downstream optical signal and transmits a downstream wireless signal based on the acquired first electrical signal; the slave station device receives an upstream wireless signal and generates an upstream optical signal including a second electrical signal based on the received upstream wireless signal and transmits the generated upstream optical signal to the master station; and the master station acquires the second electrical signal from the upstream optical signal and acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the acquired second electrical signal.

2. The optical communication system according to claim 1, wherein the master station adjusts the plurality of first analog signals so that the intensity difference between the plurality of first analog signals is reduced, and generates the first electrical signal in which the plurality of adjusted first analog signals are multiplexed.

3. The optical communication system according to claim 1 or 2, wherein the master station device generates the first electrical signal by multiplexing the first analog signals that have passed through a plurality of first filters, each corresponding to a plurality of frequency bands, the first filters having mutually different passbands, and the master station device acquires the second analog signals using a plurality of second filters having mutually different passbands.

4. An optical communication system according to any one of claims 1 to 3, wherein the slave station device adjusts the intensity of the received upstream radio signal with an amplification factor or attenuation factor according to the intensity of the upstream radio signal, and generates the upstream optical signal including the second electrical signal based on the adjusted upstream radio signal.

5. An optical communication system according to any one of claims 1 to 4, wherein the parent station device receives the plurality of first analog signals and a plurality of pieces of control information for controlling the operation of the child station device from a plurality of base station devices, the parent station device selects one of the plurality of pieces of control information, generates a control signal including the selected control information, 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 operates in accordance with the control information included in the acquired control signal.

6. The optical communication system according to claim 5, wherein the optical communication system comprises a plurality of said slave station devices, and the master station device generates the control signal further including identification information indicating the slave station device that is to be controlled using the control information.

7. The optical communication system according to any one of claims 1 to 6, comprising a plurality of said slave station devices, each of said slave station devices transmitting a plurality of said upstream optical signals having mutually different wavelengths to said master station device, and said master station device respectively acquiring a plurality of said second electrical signals from said plurality of upstream optical signals, multiplexing said acquired second electrical signals, and acquiring said plurality of said second analog signals from the multiplexed signals.

8. A master station device comprising: a receiving unit that receives a plurality of first analog signals corresponding to a plurality of frequency bands from another device; a generating unit that generates a first electrical signal into which the plurality of first analog signals received by the receiving unit are multiplexed; an optical transmitting unit that generates a downstream optical signal including the first electrical signal generated by the generating unit and transmits the generated downstream optical signal to a slave station device; an optical receiving unit that receives an upstream optical signal from the slave station device and acquires a second electrical signal from the received upstream optical signal; and an acquiring unit that acquires a plurality of second analog signals corresponding to a plurality of frequency bands from the second electrical signal acquired by the optical receiving unit.

9. 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 a plurality of first analog signals corresponding to a plurality of frequency bands are multiplexed; a wireless transmitting unit that transmits a downstream wireless signal based on the first electrical signal acquired by the optical receiving unit; a wireless receiving unit that receives an upstream wireless signal; and an optical transmitting unit that generates an upstream optical signal including a second electrical signal based on the upstream wireless signal received by the wireless receiving unit and transmits the generated upstream optical signal to the master station device.

10. An optical communication method in an optical communication system having a master station and a slave station that transmits and receives radio signals via an antenna, comprising the steps of: the master station receiving a plurality of first analog 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 analog signals are multiplexed, and transmitting the generated downstream optical signal to the slave station; the slave station obtaining the first electrical signal from the downstream optical signal and transmitting a downstream radio signal based on the obtained first electrical signal; the slave station receiving an upstream radio signal, generating an upstream optical signal including a second electrical signal based on the received upstream radio signal, and transmitting the generated upstream optical signal to the master station; and the master station obtaining the second electrical signal from the upstream optical signal and obtaining a plurality of second analog signals corresponding to a plurality of frequency bands from the obtained second electrical signal.

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