Analog rof system, master station device, slave station device, and optical communication method

Abstract

This analog RoF system comprises a master station device and a slave station device that performs transmission and reception of a radio signal via an antenna. The master station device generates control information that is used for controlling transmission and reception operations for the radio signal, and transmits an optical signal, which includes a first digital signal including the generated control information and an analog main signal, to the slave station device via an optical fiber. The slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs a process of switching between the transmission operation and the reception operation for the radio signal via the antenna, on the basis of the acquired control information.

Description

Analog RoF system, master station device, slave station device, and optical communication method

[0001] The present disclosure relates to an analog Radio over Fiber (RoF) system, a master station device, a slave station device, and an optical communication method. This application claims priority based on Japanese Patent Application No. 2022-166626, filed on October 18, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] Patent Literature 1 (JP 2016-158062 A) discloses the following communication device. That is, the communication device includes a packet receiving unit that receives a packet in which a divided continuous signal is stored, a signal holding unit that receives and holds a received continuous signal that is a continuous signal stored in the packet received by the packet receiving unit, a transmission timing control unit that, when the packet receiving unit receives a packet that is different from a packet subsequent to a previously received packet, instructs the signal holding unit to output the received continuous signal at timing determined based on a timestamp inserted in the header of the currently received packet, and, when the packet receiving unit receives a packet subsequent to the previously received packet, instructs the signal holding unit to output the received continuous signal at timing determined in advance based on the size of the divided continuous signal, and a continuous signal transmitting unit that transmits the continuous signal output from the signal holding unit to a continuous signal transmission network.

[0003] Furthermore, Patent Document 2 (Japanese Patent Laid-Open Publication No. 2007-166278) discloses the following wireless communication system. That is, the wireless communication system is a wireless communication system consisting of a master station device, slave station devices, a network connecting the master station device and the slave station devices, and wireless terminals, wherein the master station device comprises a wireless modulation circuit that modulates data, a wireless demodulation circuit that demodulates data, and a processing unit that packetizes digital wireless signals input from the wireless modulation circuit and transmits them to the network, as well as receives packets from the network, converts the received packets into digital wireless signals and transfers them to the wireless demodulation circuit, and the slave station device comprises a wireless transmission circuit that transmits wireless signals to the wireless terminal, a wireless reception circuit that receives wireless signals from the wireless terminal, and a processing unit that packetizes digital wireless signals input from the wireless reception circuit and transmits them to the network, as well as receives packets from the network, extracts digital wireless signals from the received packets and transfers them to the wireless transmission circuit, and the processing units of the master station device and the slave station devices synchronize the time and clock frequency of the master station device and the slave station devices, and add time information to packets to be transmitted through the network and transmit digital wireless signals.

[0004] JP 2016-158062 A JP 2007-166278 A

[0005] The analog RoF system of the present disclosure includes a master station device and slave station devices that transmit and receive radio signals via an antenna, wherein the master station device generates control information used to control the transmission and reception operations of the radio signals, and transmits an optical signal that includes a first digital signal and an analog main signal to the slave station device via an optical fiber, and the slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs switching processing between the transmission and reception operations of the radio signals via the antenna based on the acquired control information.

[0006] The master station device of the present disclosure includes a control information generating unit that generates control information used to control the transmission and reception of radio signals by slave station devices via antennas, and a transmitting unit that transmits an optical signal that includes a digital signal including the control information generated by the control information generating unit and an analog main signal to the slave station device via an optical fiber.

[0007] The slave station device of the present disclosure includes a wireless transceiver unit that transmits and receives wireless signals via an antenna, a receiver unit that receives an optical signal from a master station device via an optical fiber, the optical signal including a digital signal including control information and an analog main signal, an acquisition unit that acquires the control information from the digital signal included in the optical signal received by the receiver unit, and a control unit that performs switching processing between the wireless transceiver unit's transmission operation and reception operation via the antenna based on the control information acquired by the acquisition unit.

[0008] The optical communication method disclosed herein is an optical communication method in an analog RoF system including a master station device and slave station devices that transmit and receive radio signals via an antenna, and includes the steps of: the master station device generating control information used to control the transmission and reception operations of the radio signals; and transmitting an optical signal including a first digital signal and an analog main signal, the first digital signal including the generated control information, to the slave station device via an optical fiber; and the slave station device acquiring the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performing a switching process between the transmission operation and the reception operation of the radio signals via the antenna based on the acquired control information.

[0009] 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.

[0010] 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.

[0011] FIG. 1 is a diagram illustrating a configuration of an analog RoF system according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of a time chart of a communication frame in a mobile wireless communication system. FIG. 3 is a diagram illustrating a configuration of a master station device according to the first embodiment of the present disclosure. FIG. 4 is a diagram illustrating a configuration of a slave station device according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of a TDD signal transmitted by a base station device according to the first embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of a TDD signal generated by a TDD processing unit in a slave station device according to the first embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of a communication sequence in the analog RoF system according to the first embodiment of the present disclosure. FIG. 8 is a diagram illustrating a configuration of an analog RoF system according to a second embodiment of the present disclosure. FIG. 9 is a diagram illustrating a configuration of a master station device according to the second embodiment of the present disclosure. FIG. 10 is a diagram illustrating an example of a correspondence table held by an information storage unit in a master station device according to the second embodiment of the present disclosure. FIG. 11 is a diagram illustrating a configuration of a slave station device according to the second embodiment of the present disclosure. FIG. 12 is a diagram illustrating a configuration of an analog RoF system according to a third embodiment of the present disclosure. Fig. 13 is a diagram illustrating a configuration of a master station device according to a third embodiment of the present disclosure. Fig. 14 is a diagram illustrating a configuration of a slave station device according to the third embodiment of the present disclosure. Fig. 15 is a diagram illustrating an example of a communication sequence in an analog RoF system according to the third embodiment of the present disclosure.

[0012] Conventionally, techniques have been developed to improve communication performance in optical communication systems.

[0013] [Problem to be Solved by the Present Disclosure] There is a need for a technology that goes beyond the technologies described in Patent Documents 1 and 2 and that can realize TDD (Time Division Duplex) with a simple configuration in an analog RoF system that includes a master station device and a slave station device.

[0014] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide an analog RoF system including a master station device and a slave station device, which is capable of realizing TDD with a simple configuration, a master station device, a slave station device, and an optical communication method.

[0015] Effect of the Present Disclosure According to the present disclosure, it is possible to realize TDD with a simple configuration in an analog RoF system including a master station device and a slave station device.

[0016] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0017] (1) An analog RoF system according to an embodiment of the present disclosure includes a master station device and a slave station device that transmits and receives radio signals via an antenna. The master station device generates control information used to control the transmission and reception of the radio signals, and transmits an optical signal including a first digital signal and an analog main signal to the slave station device via an optical fiber. The slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs switching processing between the transmission and reception of the radio signals via the antenna based on the acquired control information.

[0018] In this way, the master station transmits a downstream optical signal including a first digital signal and a main signal to the slave station via an optical fiber, and the slave station acquires control information from the first digital signal included in the downstream optical signal and performs switching processing between transmission and reception of the radio signal. This configuration enables switching processing between transmission and reception without requiring the slave station to perform detailed calculation processing for determining the timing of switching between transmission and reception. Therefore, in an analog RoF system including a master station and a slave station, TDD can be realized with a simple configuration.

[0019] (2) In the above (1), the master station device may be connected between the base station device and the slave station device, and the master station device may receive a pattern signal indicating an uplink communication period and a downlink communication period in TDD from the base station device, and may generate the control information based on the received pattern signal.

[0020] With this configuration, the master station can generate control information through simple processing, and the slave station can perform transmission / reception switching processing in synchronization with the uplink communication period and downlink communication period set in the base station. Furthermore, if the downlink communication period and uplink communication period are changed by the base station, the master station can transmit control information reflecting the changes to the slave station, thereby changing the switching processing in the slave station. This allows for flexible response to changes in the downlink communication period and uplink communication period.

[0021] (3) In the above (2), the parent station device may generate a switching pattern for the transmission and reception operation of the wireless signal based on the pattern signal, and generate the control information including the generated switching pattern and the start timing of the switching process using the switching pattern.

[0022] With this configuration, for example, the start timing can be set taking into consideration the transmission delay of control information between the master station equipment and the slave station equipment, and stable switching processing can be performed in the slave station equipment.

[0023] (4) In the above (2), the parent station device and the child station device may retain correspondence information indicating the correspondence between the type of the pattern signal and identification information of the pattern signal, and the parent station device may refer to the correspondence information to acquire the identification information corresponding to the pattern signal received from the base station device, and generate the control information including the acquired identification information and the start timing of the switching process using the identification information.

[0024] With this configuration, compared to a configuration in which control information including a switching pattern for transmitting and receiving wireless signals is transmitted from a parent station device to a child station device, the parent station device can notify the child station device of the uplink communication period and the downlink communication period set in the base station device with a simpler configuration.

[0025] (5) In the above (3) or (4), the analog RoF system may include a plurality of the slave station devices, and the master station device may generate the control information including the start timing that differs for each of the slave station devices.

[0026] With this configuration, it is possible to set the start timing taking into consideration the processing delay that differs for each slave station device, for example, and therefore to suppress interference between radio signals transmitted via the antennas of the slave station devices.

[0027] (6) In any of the above (3) to (5), the slave station device may correct the start timing included in the control information, and start the switching process based on the control information at the corrected start timing.

[0028] With this configuration, the start timing can be corrected to a more appropriate timing based on the actual transmission delay of the control information received at the slave station equipment, and stable switching processing can be performed at the slave station equipment.

[0029] (7) In any of (1) to (6) above, the slave station device may receive pattern information indicating an upstream communication period and a downstream communication period in TDD from a device other than the master station device outside the slave station device, generate a second digital signal including the received pattern information, and transmit an optical signal including the generated second digital signal and an analog main signal to the master station device via the optical fiber, and the master station device may obtain the pattern information from the second digital signal included in the optical signal received from the slave station device via the optical fiber, and generate the control information reflecting the content of the obtained pattern information.

[0030] With this configuration, for example, when the downlink communication period and the uplink communication period in TDD adopted in a mobile wireless communication system are changed depending on the communication status of a mobile communication terminal, it is possible to flexibly respond to changes in the downlink communication period and the uplink communication period.

[0031] (8) A master station device according to an embodiment of the present disclosure includes a control information generating unit that generates control information used to control the transmission and reception of radio signals by a slave station device via an antenna, and a transmitting unit that transmits an optical signal that includes a digital signal including the control information generated by the control information generating unit and an analog main signal to the slave station device via an optical fiber.

[0032] In this way, by transmitting a digital signal including control information and a downstream optical signal including a main signal to a slave station device via an optical fiber, the slave station device can perform a switching process between transmission and reception of radio signals without performing detailed calculations to determine the timing of the switching between transmission and reception of radio signals. Therefore, in an analog RoF system including a master station device and a slave station device, TDD can be realized with a simple configuration.

[0033] (9) A slave station device according to an embodiment of the present disclosure includes a wireless transceiver unit that transmits and receives wireless signals via an antenna, a receiver unit that receives an optical signal from a master station device via an optical fiber, the optical signal including a digital signal including control information and an analog main signal, an acquirer unit that acquires the control information from the digital signal included in the optical signal received by the receiver unit, and a controller that performs switching processing between transmitting and receiving wireless signals via the antenna by the wireless transceiver unit based on the control information acquired by the acquirer.

[0034] In this way, by using a configuration in which control information is acquired from a digital signal included in an optical signal and switching between transmission and reception of radio signals is performed, it is possible to perform switching between transmission and reception without performing detailed calculations to determine the timing of switching between transmission and reception of radio signals. Therefore, in an analog RoF system including a master station device and a slave station device, TDD can be achieved with a simple configuration.

[0035] (10) A communication method according to an embodiment of the present disclosure is an optical communication method in an analog RoF system including a master station device and slave station devices that transmit and receive radio signals via an antenna, the method including: a step in which the master station device generates control information used to control the transmission and reception operations of the radio signals, and transmits an optical signal that includes a first digital signal and an analog main signal, the first digital signal including the generated control information, to the slave station device via an optical fiber; and a step in which the slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs a switching process between the transmission operation and the reception operation of the radio signals via the antenna based on the acquired control information.

[0036] In this way, the master station transmits a downstream optical signal including a first digital signal and a main signal to the slave station via an optical fiber, and the slave station acquires control information from the first digital signal included in the downstream optical signal and switches between transmission and reception of the radio signal. This method enables the slave station to switch between transmission and reception without performing detailed calculations or the like to determine the timing of switching between transmission and reception. Therefore, in an analog RoF system including a master station and a slave station, TDD can be realized with a simple configuration.

[0037] 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.

[0038] First Embodiment [Configuration and Basic Operation] Fig. 1 is a diagram showing the configuration of an analog RoF system according to a first embodiment of the present disclosure. Referring to Fig. 1, the analog RoF system 301 includes a master station device 101 and multiple slave station devices 201. One slave station device 201 is representatively shown in Fig. 1. The master station device 101 and the slave station devices 201 are connected to each other via an optical fiber 191. The master station device 101 is connected between a base station device 111 and the slave station devices 201. The master station device 101 and the multiple slave station devices 201 may be connected via the optical fiber 191 and an optical coupler. Alternatively, the analog RoF system 301 may be configured to include only one slave station device 201.

[0039] The master station device 101 and the slave station device 201 transmit and receive optical signals including communication data generated in the base station device 111 via the optical fiber 191. Hereinafter, the 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 the 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.

[0040] The analog RoF system 301 is used in a mobile wireless communication system that employs TDD. For example, the analog RoF system 301 is used in a mobile fronthaul in a fifth-generation mobile communication system (hereinafter also referred to as 5G) that employs TDD, and in local 5G.

[0041] 2 is a diagram showing an example of a time chart of a communication frame in a mobile wireless communication system. Referring to FIG. 2, in TDD, a communication frame F consisting of ten subframes SF#0 to SF#9 is repeated. Each subframe SF includes two time slots S. For example, the duration of one communication frame F is 10 milliseconds, the duration of one subframe SF is 1 millisecond, and the duration of one time slot S is 0.5 milliseconds.

[0042] The time slot S is assigned one of the following: an upstream communication slot US constituting an upstream communication period UP in TDD, a downstream communication slot DS constituting a downstream communication period DP in TDD, and a special slot SS which is a period for switching between the upstream communication period UP and the downstream communication period DP. The upstream communication period UP and the downstream communication period DP are alternately repeated.

[0043] In the example shown in Figure 2, downlink communication slots DS are assigned to time slots S#0 and S#1 in subframe SF#0 and time slots S#2 and S#3 in subframe SF#1. Special slot SS is assigned to the first time slot S#4 in subframe SF#2. Uplink communication slots US are assigned to the second time slot S#5 in subframe SF#2, time slots S#6 and S#7 in subframe SF#3, and the first time slot S#8 in subframe SF#4. Special slot SS is assigned to the second time slot S#9 in subframe SF#4. Downlink communication slots DS are assigned to time slots S#10 and S#11 in subframe SF#5 and time slots S#12 and S#13 in subframe SF#6. Special slot SS is assigned to the first time slot S#14 in subframe SF#7. The second time slot S#15 in subframe SF#7, the time slots S#16 and S#17 in subframe SF#8, and the first time slot S#18 in subframe SF#9 are assigned as upstream communication slots US. The second time slot S#19 in subframe SF#9 is assigned as special slot SS.

[0044] In the analog RoF system 301, the slave station device 201 transmits communication data to the master station device 101 during an upstream communication period UP, and the master station device 101 transmits communication data to the slave station device 201 during a downstream communication period DP.

[0045] More specifically, the master station device 101 receives an Orthogonal Frequency Division Multiplexing (OFDM) modulated analog signal containing communication data from the base station device 111. The master station device 101 generates an intermediate frequency (IF) signal Fa by frequency-converting the received analog signal. The IF signal Fa is an example of a main signal. During a downstream communication period DP, the master station device 101 transmits a downstream optical signal containing the generated IF signal Fa to the slave station device 201 via the optical fiber 191.

[0046] The slave station device 201 transmits and receives RF (Radio Frequency) signals via the switch device 151 and the antenna 161. More specifically, the slave station device 201 receives downstream optical signals from the master station device 101 via the optical fiber 191. The slave station device 201 then acquires an IF signal Fa from the received downstream optical signal, and transmits a millimeter-waveband RF signal based on the acquired IF signal Fa via the switch device 151 and the antenna 161.

[0047] The slave station device 201 also receives an OFDM-modulated millimeter-wave RF signal containing communication data from a mobile communication terminal (not shown) via the antenna 161 and the switch device 151, and generates an IF signal Fb by frequency-converting the received RF signal. During an upstream communication period UP, the slave station device 201 transmits an upstream optical signal containing the generated IF signal Fb to the master station device 101 via the optical fiber 191.

[0048] The master station device 101 receives an upstream optical signal from the slave station device 201 via the optical fiber 191. The master station device 101 acquires an IF signal Fb from the received upstream optical signal and transmits a signal based on the acquired IF signal Fb to the base station device 111.

[0049] The slave station device 201 transmits a TDD signal Std2 to the switch device 151 to control the state of the switch device 151. In accordance with the TDD signal Std2 received from the slave station device 201, the switch device 151 switches between a transmission state in which the antenna 161 is connected to an RF signal transmission circuit in the slave station device 201 and a reception state in which the antenna 161 is connected to an RF signal reception circuit in the slave station device 201.

[0050] 3 is a diagram illustrating a configuration of a master station device according to a first embodiment of the present disclosure. Referring to FIG. 3, the master station device 101 includes a synchronization processing unit 11, a TDD processing unit 12, a frame processing unit 13, a frequency conversion unit 14, a multiplexing unit 15, a demultiplexing unit 16, an optical modulation unit 17, an optical demodulation unit 18, and an optical coupler CP1. The TDD processing unit 12 is an example of a control information generation unit. The optical modulation unit 17 is an example of a transmission unit.

[0051] The synchronization processing unit 11 receives a reference clock from, for example, an oscillator external or internal to the master station device 101, and generates a local clock CL1 by dividing or multiplying the received reference clock. The synchronization processing unit 11 counts up in accordance with the timing of the generated local clock CL1 and holds the count value. Each unit in the master station device 101 operates based on the local clock CL1.

[0052] The synchronization processing unit 11 receives a reference signal from the base station device 111. For example, the synchronization processing unit 11 receives a clock signal, a Global Navigation Satellite System (GNSS) signal, or a grand master clock signal from the base station device 111 as the reference signal. The synchronization processing unit 11 performs base station synchronization processing to synchronize the count value of the local clock CL1 with the base station device 111 based on the received reference signal. For example, if the wiring between the base station device 111 and the master station device 101 is short, the synchronization processing unit 11 performs base station synchronization processing based on the reference signal without considering transmission delay of the reference signal between the base station device 111 and the master station device 101.

[0053] The frame processing unit 13 generates an Ethernet® frame addressed to the slave station equipment 201, the payload of which contains information to be transmitted to the slave station equipment 201. The frame processing unit 13 outputs a digital signal Da including the generated Ethernet frame to the multiplexing unit 15.

[0054] The frequency converter 14 receives an OFDM-modulated analog signal including communication data from the base station device 111. The frequency converter 14 may be configured to receive an RF band analog signal or a baseband analog signal. The frequency converter 14 up-converts or down-converts the received analog signal to generate an IF signal Fa, and outputs the generated IF signal Fa to the multiplexer 15.

[0055] The multiplexing unit 15 frequency-multiplexes the digital signal Da received from the frame processing unit 13 and the IF signal Fa received from the frequency conversion unit 14. The multiplexing unit 15 generates an electrical signal in which the digital signal Da and the IF signal Fa are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 17.

[0056] The optical modulation unit 17 receives the electrical signal from the multiplexing unit 15 and generates a downstream optical signal having a wavelength λ1 by optically modulating the received electrical signal. The optical modulation unit 17 outputs the downstream optical signal to the optical fiber 191 via the optical coupler CP1 during a downstream communication period DP.

[0057] In this way, by generating the digital signal Da and the IF signal Fa in different units and transmitting a downstream optical signal including the generated digital signal Da and IF signal Fa to the slave station device 201, it is possible to suppress degradation in the signal quality of the IF signal Fa and transmission delays of the IF signal Fa.

[0058] The master station device 101 may be configured to receive the IF signal Fa from the base station device 111 and transmit a downstream optical signal including the received IF signal Fa to the slave station device 201 via the optical fiber 191. More specifically, the master station device 101 may be configured without the frequency conversion unit 14. In this case, the multiplexing unit 15 receives the IF signal Fa from the base station device 111 and frequency-multiplexes the digital signal Da received from the frame processing unit 13 and the IF signal Fa received from the base station device 111.

[0059] 4 is a diagram illustrating a configuration of a slave station device according to the first embodiment of the present disclosure. Referring to FIG. 4, the slave station device 201 includes a synchronization processing unit 21, a TDD processing unit 22, a frame processing unit 23, an RF transceiver unit 24, a demultiplexer 25, a multiplexer 26, an optical demodulator 27, an optical modulator 28, and an optical coupler CP2. The RF transceiver unit 24 is an example of a wireless transceiver unit. The RF transceiver unit 24 includes a receiving circuit (not shown) that receives an RF signal and a transmitting circuit (not shown) that transmits the RF signal. The optical demodulator 27 is an example of a receiving unit. The frame processing unit 23 is an example of an acquiring unit. The TDD processing unit 22 is an example of a control unit.

[0060] The synchronization processing unit 21 receives a reference clock from, for example, an oscillator external or internal to the slave station equipment 201, and generates a local clock CL2 by dividing or multiplying the received reference clock. The synchronization processing unit 21 counts up in accordance with the timing of the generated local clock CL2 and holds the count value. Each unit in the slave station equipment 201 operates based on the local clock CL2. The frequency setting of the local clock CL2 is the same as that of the local clock CL1 in the master station equipment 101.

[0061] The optical demodulator 27 receives a downstream optical signal from the parent station 101 via the optical fiber 191 and the optical coupler CP2, and generates an electrical signal based on the received downstream optical signal. More specifically, the optical demodulator 27 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 25.

[0062] The separator 25 receives the electrical signal from the optical demodulator 27, separates the received electrical signal into an IF signal Fa and a digital signal Da, and outputs the IF signal Fa to the RF transceiver 24 and the digital signal Da to the frame processor 23. For example, the separator 25 is a diplexer configured with an HPF (High Pass Filter) and an LPF. The separator 25 outputs frequency components of the electrical signal received from the optical demodulator 27 that are equal to or greater than a frequency Fx as the IF signal Fa to the RF transceiver 24, and outputs frequency components that are less than the frequency Fx as the digital signal Da to the frame processor 23. Here, the frequency Fx is lower than the center frequency of the IF signal Fa.

[0063] For example, the RF transceiver 24 amplifies the IF signal Fa received from the separator 25. The RF transceiver 24 generates an RF signal by up-converting the amplified IF signal Fa, and outputs the generated RF signal to the antenna 161 via the switch device 151.

[0064] The frame processing unit 23 receives the digital signal Da from the separation unit 25 and acquires an Ethernet frame from the received digital signal Da. If the destination MAC address included in the acquired Ethernet frame does not match the MAC address of the slave station device 201, the frame processing unit 23 discards the Ethernet frame. On the other hand, if the destination MAC address included in the acquired Ethernet frame matches the MAC address of the slave station device 201, the frame processing unit 23 acquires information from the payload of the Ethernet frame.

[0065] The frame processing unit 23 also generates an Ethernet frame addressed to the master station device 101, the payload of which contains information to be transmitted to the master station device 101. The frame processing unit 23 outputs a digital signal Db including the generated Ethernet frame to the multiplexing unit 26.

[0066] The RF transceiver 24 receives an OFDM-modulated RF band analog signal containing communication data from a mobile communication terminal (not shown) via the antenna 161 and the switch device 151. The RF transceiver 24 down-converts the received analog signal to generate an IF signal Fb, and outputs the generated IF signal Fb to the multiplexer 26.

[0067] The multiplexing unit 26 frequency-multiplexes the digital signal Db received from the frame processing unit 23 and the IF signal Fb received from the RF transceiver unit 24. The multiplexing unit 26 generates an electrical signal in which the digital signal Db and the IF signal Fb are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 28.

[0068] The optical modulator 28 transmits an upstream optical signal including the digital signal Db and the IF signal Fb to the parent station 101 via the optical fiber 191. More specifically, the optical modulator 28 receives an electrical signal from the multiplexer 26 and generates an upstream optical signal with wavelength λ2 by optically modulating the received electrical signal. During an upstream communication period UP, the optical modulator 28 outputs the upstream optical signal to the optical fiber 191 via the optical coupler CP2.

[0069] 3 , the optical demodulator 18 in the master station 101 receives an upstream optical signal from the slave station 201 via the optical fiber 191 and the optical coupler CP1, and generates an electrical signal based on the received upstream optical signal. More specifically, the optical demodulator 18 generates an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs the electrical signal to the demultiplexer 16.

[0070] The separator 16 receives the electrical signal from the optical demodulator 18, separates the received electrical signal into an IF signal Fb and a digital signal Db, and outputs the IF signal Fb to the frequency converter 14 and the digital signal Db to the frame processor 13. For example, the separator 16 is a diplexer composed of an HPF and an LPF. The separator 16 outputs frequency components of the electrical signal received from the optical demodulator 18 that are equal to or greater than frequency Fy as an IF signal Fb to the frequency converter 14, and outputs frequency components that are less than frequency Fy as a digital signal Db to the frame processor 13. Here, frequency Fy is smaller than the center frequency of IF signal Fb.

[0071] For example, the frequency conversion unit 14 generates an RF signal by up-converting the IF signal Fb received from the separation unit 16, and transmits the generated RF signal to the base station device 111. Alternatively, the frequency conversion unit 14 generates a baseband signal by down-converting the IF signal Fb received from the separation unit 16, and transmits the generated baseband signal to the base station device 111. As described above, the master station device 101 may be configured without including the frequency conversion unit 14. In this case, the separation unit 16 transmits the IF signal Fb to the base station device 111.

[0072] The frame processing unit 13 receives the digital signal Db from the separation unit 16, obtains an Ethernet frame from the received digital signal Db, and obtains information from the payload of the Ethernet frame.

[0073] (Inter-station synchronization processing) The synchronization processing unit 11 in the parent station equipment 101 and the synchronization processing unit 21 in the child station equipment 201 perform inter-station synchronization processing to synchronize the count value of the local clock CL1 in the parent station equipment 101 with the count value of the local clock CL2 in the child station equipment 201, for example, at a synchronization processing timing according to a predetermined period.

[0074] More specifically, in the inter-station synchronization process, the synchronization processing unit 11 acquires the current count value of the local clock CL1, generates count information indicating the acquired count value, and outputs it to the frame processing unit 13.

[0075] The frame processing unit 13 receives the count information from the synchronization processing unit 11, generates an Ethernet frame addressed to the slave station equipment 201, with the received count information stored in its payload, and outputs a digital signal Da1 including the generated Ethernet frame to the multiplexing unit 15. The digital signal Da1 output by the frame processing unit 13 to the multiplexing unit 15 is frequency-multiplexed with the IF signal Fa by the multiplexing unit 15, and the digital signal Da1 is included in a downstream optical signal by the optical modulation unit 17 and transmitted to the slave station equipment 201.

[0076] 4 , the frame processing unit 23 in the slave station equipment 201 loops back the count information generated in the master station equipment 101 during inter-station synchronization processing. More specifically, the frame processing unit 23 acquires an Ethernet frame from the digital signal Da1 received from the demultiplexer 25 and acquires the count information from the payload of the Ethernet frame. The frame processing unit 23 generates an Ethernet frame addressed to the master station equipment 101, the payload of which contains the acquired count information, and outputs a digital signal Db1 including the generated Ethernet frame to the multiplexer 26. The digital signal Db1 output from the frame processing unit 23 to the multiplexer 26 is frequency-multiplexed with the IF signal Fb by the multiplexer 26, and the digital signal Db1 is then included in an upstream optical signal by the optical modulator 28 and transmitted to the master station equipment 101.

[0077] 3 , the frame processing unit 13 in the parent station device 101 receives the digital signal Db1 from the demultiplexer 25, acquires an Ethernet frame from the received digital signal Db1, and acquires count information from the payload of the Ethernet frame. The frame processing unit 13 outputs the acquired count information to the synchronization processing unit 11.

[0078] The synchronization processing unit 11 receives the count information from the frame processing unit 13 and calculates the difference between the count value indicated by the count information and the current count value of the local clock CL1 as the RTT (Round Trip Time) of the count information. The synchronization processing unit 11 also calculates half of the RTT as the transmission delay time DT between the parent station equipment 101 and the child station equipment 201.

[0079] After calculating the transmission delay time DT, the synchronization processing unit 11 acquires the current count value of the local clock CL1 and generates synchronization information including a synchronization time ST1, which is the value obtained by adding the transmission delay time DT to the acquired counter value. The synchronization processing unit 11 outputs the generated synchronization information to the frame processing unit 13.

[0080] The frame processing unit 13 receives the synchronization information from the synchronization processing unit 11, generates an Ethernet frame addressed to the slave station equipment 201, with the received synchronization information stored in its payload, and outputs a digital signal Da2 including the generated Ethernet frame to the multiplexing unit 15. The digital signal Da2 output by the frame processing unit 13 to the multiplexing unit 15 is frequency-multiplexed with the IF signal Fa by the multiplexing unit 15, and the digital signal Da2 is included in a downstream optical signal by the optical modulation unit 17 and transmitted to the slave station equipment 201.

[0081] 4 , the frame processing unit 23 in the slave station device 201 acquires an Ethernet frame from the digital signal Da2 received from the demultiplexer 25, and acquires synchronization information from the payload of the Ethernet frame. The frame processing unit 23 outputs the acquired synchronization information to the synchronization processing unit 21.

[0082] The synchronization processing unit 21 receives synchronization information from the frame processing unit 23 and updates the count value of the local clock CL2 based on the received synchronization information. That is, the synchronization processing unit 21 sets the count value of the local clock CL2 to the synchronization time ST1 included in the synchronization information. As a result, the count value of the local clock CL2 in the slave station equipment unit 201 is synchronized with the count value of the local clock CL2 in the master station equipment unit 101.

[0083] The synchronization processing unit 11 in the parent station equipment unit 101 and the synchronization processing unit 21 in the child station equipment unit 201 may be configured to synchronize the count value of the local clock CL1 and the count value of the local clock CL2 in accordance with IEEE 1588.

[0084] (Switching Process) Referring again to FIG. 1 , the parent station device 101 generates control information used to control the transmission and reception operations of the RF signal, and transmits a downstream optical signal including a digital signal Da3 containing the generated control information and an IF signal Fa to the child station device 201 via the optical fiber 191.

[0085] The slave station device 201 acquires control information from the digital signal Da3 contained in the downstream optical signal received from the master station device 101 via the optical fiber 191, and performs a switching process to switch between the transmission operation and the reception operation of the RF signal via the antenna 161 based on the acquired control information.

[0086] 5 is a diagram illustrating an example of a TDD signal transmitted by a base station device according to the first embodiment of the present disclosure. Referring to FIG. 5, the base station device 111 continuously transmits a square-wave TDD signal Std1 indicating an uplink communication period UP and a downlink communication period DP in TDD to the master station device 101. The TDD signal Std1 is an example of a pattern signal.

[0087] As an example, the TDD signal Std1 is set to a high level in the downstream communication slot DS and set to a low level in the upstream communication slot US. For example, the TDD signal Std1 transitions from a high level to a low level at the timing of switching from the downstream communication slot DS to the special slot SS, and transitions from a low level to a high level at the timing of switching from the special slot SS to the downstream communication slot DS.

[0088] The TDD processing unit 12 in the master station device 101 receives the TDD signal Std1 from the base station device 111 and generates control information based on the received TDD signal Std1. As an example, the TDD processing unit 12 generates the control information at a generation timing according to a predetermined generation cycle Cy. For example, the length of the generation cycle Cy is 10 milliseconds, which corresponds to one cycle of the communication frame F. Note that the length of the generation cycle Cy may be a length equivalent to multiple cycles of the communication frame F.

[0089] For example, the TDD processing unit 12 determines the transition time tr, which is the timing when the TDD signal Std1 transitions from low level to high level, and the transition time tf, which is the timing when the TDD signal Std1 transitions from high level to low level.

[0090] More specifically, when the TDD processing unit 12 detects that the TDD signal Std1 has transitioned from a low level to a high level, it acquires the current count value of the local clock CL1 held by the synchronization processing unit 11 as transition time tr1, which is the first transition time tr. Next, when the TDD processing unit 12 detects that the TDD signal Std1 has transitioned from a high level to a low level, it acquires the current count value of the local clock CL1 held by the synchronization processing unit 11 as transition time tf1, which is the first transition time tf. Next, when the TDD processing unit 12 detects that the TDD signal Std1 has transitioned from a low level to a high level, it acquires the current count value of the local clock CL1 held by the synchronization processing unit 11 as transition time tr2, which is the second transition time tr. Next, when the TDD processing unit 12 detects that the TDD signal Std1 has transitioned from high level to low level, it acquires the current count value of the local clock CL1 held by the synchronization processing unit 11 as transition time tf2, which is the second transition time tf. Note that the TDD processing unit 12 may be configured to acquire absolute times instead of count values ​​as the transition times tr and tf.

[0091] The TDD processing unit 12 then generates a switching pattern for the transmission and reception of RF signals via the antenna 161 in the slave station device 201, including the transition times tr1, tf1, tr2, and tf2 determined in the immediately preceding 10 milliseconds.

[0092] After generating the switching pattern, the TDD processing unit 12 sets a start timing ts for the switching process using the switching pattern. As an example, the TDD processing unit 12 sets the start timing ts to a time obtained by adding a predetermined margin time Tm to the transition time tr1, which is the earliest time among the transition times tr1, tf1, tr2, and tf2. The margin time Tm is, for example, 10 milliseconds, which corresponds to one period of the communication frame F.

[0093] 3 , the TDD processing unit 12 generates a switching pattern and sets a start timing ts at a generation timing according to the generation cycle Cy, and generates control information including the generated switching pattern and start timing ts. For example, the TDD processing unit 12 generates control information including a different start timing ts for each slave station device 201. More specifically, the TDD processing unit 12 sets the start timing ts to which a different length of margin time Tm is added for each slave station device 201. The TDD processing unit 12 outputs the generated control information to the frame processing unit 13.

[0094] The frame processing unit 13 receives control information from the TDD processing unit 12, generates an Ethernet frame addressed to the slave station device 201 with the received control information stored in the payload, and outputs a digital signal Da3 including the generated Ethernet frame to the multiplexing unit 15.

[0095] The multiplexing unit 15 frequency-multiplexes the digital signal Da3 received from the frame processing unit 13 and the IF signal Fa received from the frequency conversion unit 14. The multiplexing unit 15 generates an electrical signal in which the digital signal Da3 and the IF signal Fa are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 17.

[0096] The optical modulator 17 transmits a downstream optical signal including the digital signal Da3 and the IF signal Fa to the slave station equipment 201 via the optical fiber 191. More specifically, the optical modulator 17 receives an electrical signal from the multiplexer 15 and generates a downstream optical signal by optically modulating the received electrical signal. The optical modulator 17 outputs the downstream optical signal to the optical fiber 191 via the optical coupler CP1 during a downstream communication period DP.

[0097] 4 , the optical demodulator 27 in the slave station device 201 receives a downstream optical signal including the digital signal Da3 and the IF signal Fa from the master station device 101 via the optical fiber 191. The optical demodulator 27 generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal and outputs the electrical signal to the demultiplexer 25.

[0098] The separation unit 25 receives an electrical signal from the optical demodulation unit 27, separates the received electrical signal into the IF signal Fa and the digital signal Da3, and outputs the IF signal Fa to the RF transceiver unit 24 and the digital signal Da3 to the frame processing unit 23.

[0099] The frame processing unit 23 acquires control information from the digital signal Da3 included in the downstream optical signal received by the optical modulation unit 17. More specifically, the frame processing unit 23 receives the digital signal Da3 from the demultiplexer 25, acquires an Ethernet frame from the received digital signal Da3, and acquires the control information from the payload of the Ethernet frame. The frame processing unit 23 outputs the acquired control information to the TDD processing unit 22.

[0100] The TDD processing unit 22 switches between the transmission and reception of RF signals by the RF transceiver unit 24 based on the control information acquired by the frame processing unit 23 .

[0101] 6 is a diagram illustrating an example of a TDD signal generated by a TDD processing unit in a slave station device according to the first embodiment of the present disclosure. Referring to FIG. 6, the TDD processing unit 22 receives control information from the frame processing unit 23, generates a TDD signal Std2 based on a switching pattern included in the received control information, and transmits the generated TDD signal Std2 to the switch device 151 at a start timing ts included in the control information.

[0102] Here, the length of the optical fiber 191 connecting the master station equipment 101 and the slave station equipment 201 is, for example, about 30 km, and a transmission delay corresponding to the length of the optical fiber 191 may occur between the master station equipment 101 and the slave station equipment 201. By setting the start timing ts in the master station equipment 101 to the time obtained by adding a margin time Tm to the transition time tr1, the slave station equipment 201 can receive control information before the set start timing ts and transmit the TDD signal Std2 to the switch equipment 151 at the start timing ts.

[0103] The switch device 151 connects the antenna 161 to the transmission circuit in the RF transceiver unit 24 while the TDD signal Std2 received from the slave station device 201 is at a high level, and connects the antenna 161 to the reception circuit in the RF transceiver unit 24 while the TDD signal Std2 received from the slave station device 201 is at a low level.

[0104] The TDD processing unit 22 may be configured to correct the start timing ts included in the control information and start the switching process based on the control information at the corrected start timing tsx. More specifically, the TDD processing unit 22 determines the start timing tsx by adding a delay time required for processing the control information to the start timing ts, and transmits the generated TDD signal Std2 to the switch device 151 at the determined start timing tsx.

[0105] [Operation Flow] Each device in the analog RoF system according to the embodiment of the present disclosure includes a computer including a memory, and a processing unit such as a CPU in the computer reads and executes a program including some or all of the steps in the following flowcharts and sequences from the memory. The programs for these devices can be installed externally. The programs for these devices are distributed in a state stored on a recording medium or via a communication line.

[0106] FIG. 7 is a diagram illustrating an example of a communication sequence in an analog RoF system according to the first embodiment of the present disclosure.

[0107] 7, first, the master station device 101 performs a base station synchronization process to synchronize the count value of the local clock CL1 with that of the base station device 111 (step S11).

[0108] Next, the parent station equipment 101 and the child station equipment 201 perform inter-station synchronization processing to synchronize the count value of the local clock CL1 in the parent station equipment 101 with the count value of the local clock CL2 in the child station equipment 201 at a synchronization processing timing according to a predetermined period (step S12).

[0109] Next, the parent station device 101 determines transition times tr1 and tr2, which are the times when the TDD signal Std1 received from the base station device 111 transitions from a low level to a high level, and transition times tf1 and tf2, which are the times when the TDD signal Std1 transitions from a high level to a low level, and generates control information that includes a switching pattern that includes the transition times tr1, tf1, tr2, and tf2, and a start timing ts (step S13).

[0110] Next, the master station device 101 generates an Ethernet frame addressed to the slave station device 201, the payload of which contains the generated control information, and generates a digital signal Da3 including the generated Ethernet frame (step S14).

[0111] Next, the master station 101 frequency-multiplexes the digital signal Da3 and the IF signal Fa, and transmits a downstream optical signal including the digital signal Da3 and the IF signal Fa to the slave station 201 via the optical fiber 191 (step S15).

[0112] Next, the slave station device 201 receives the downstream optical signal from the master station device 101 via the optical fiber 191, and acquires the digital signal Ds3 from the received downstream optical signal (step S16).

[0113] Next, the slave station device 201 acquires control information from the digital signal Ds3 (step S17).

[0114] Next, the slave station device 201 performs switching processing based on the acquired control information. More specifically, the slave station device 201 generates the TDD signal Std2 based on the switching pattern included in the control information, and transmits the TDD signal Std2 to the switch device 151 at the start timing ts included in the control information (step S18).

[0115] In the analog RoF system 301 according to the first embodiment of the present disclosure, the slave station device 201 is configured to transmit and receive RF signals via the switch device 151 and the antenna 161, but this is not limiting. The slave station device 201 may also be configured to include the switch device 151.

[0116] In the analog RoF system 301 including the master station device 101 and the slave station device 201, a technique that can realize TDD with a simple configuration is desired.

[0117] For example, in a mobile radio communication system that employs TDD, it is desirable to control the transmission timing of RF signals with high precision in order to suppress radio interference.

[0118] Furthermore, in a mobile wireless communication system using the millimeter wave band, for example, the coverage area of ​​the antenna 161 is small, so it is necessary to install a large number of slave station devices 201 and antennas 161 at high density. Therefore, in order to realize a mobile wireless communication system using the millimeter wave band with a low-cost and simple configuration, it is desirable to simplify the configuration of the slave station devices 201.

[0119] In contrast, in the analog RoF system 301 according to the first embodiment of the present disclosure, the master station device 101 generates control information used to control transmission and reception of an RF signal, and transmits a digital signal Ds3 including the generated control information and a downstream optical signal including an IF signal Fa to the slave station device 201 via the optical fiber 191. The slave station device 201 acquires the control information from the digital signal Ds3 included in the downstream optical signal received from the master station device 101 via the optical fiber 191, and performs switching processing between transmission and reception of an RF signal via the antenna 161 based on the acquired control information.

[0120] In this manner, the master station device 101 transmits a downstream optical signal including the digital signal Ds3 and the IF signal Fa to the slave station device 201 via the optical fiber 191, and the slave station device 201 acquires control information from the digital signal Ds3 included in the downstream optical signal and performs switching processing between transmitting and receiving operations of the RF signal via the antenna 161 based on the acquired control information. This configuration enables control information to be transmitted from the master station device 101 to the slave station device 201 via the optical fiber 191 and switching processing between transmitting and receiving operations in the slave station device 201. Therefore, in the analog RoF system 301 including the master station device 101 and the slave station device 201, TDD can be realized with a simple configuration.

[0121] Furthermore, by changing the content of the control information generated in the master station equipment 101, the content of the switching process between transmission and reception operations in the slave station equipment 201 can be flexibly changed.

[0122] 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.

[0123] Second Embodiment This embodiment relates to an analog RoF system 302 that transmits control information that further includes a configuration number indicating the type of TDD signal Std1, as compared with the analog RoF system 301 according to the first embodiment. Except for the content described below, the analog RoF system 302 is the same as the analog RoF system 301 according to the first embodiment.

[0124] 8 is a diagram illustrating a configuration of an analog RoF system according to a second embodiment of the present disclosure. Compared to the analog RoF system 301 illustrated in FIG. 1 , the analog RoF system 302 includes a master station device 102 instead of the master station device 101 and a slave station device 202 instead of the slave station device 201.

[0125] 9 is a diagram illustrating a configuration of a master station device according to a second embodiment of the present disclosure. Referring to FIG. 9, the master station device 102 is different from the master station device 101 illustrated in FIG. 3 in that it includes a TDD processing unit 32 instead of the TDD processing unit 12 and further includes an information storage unit 31.

[0126] 10 is a diagram illustrating an example of a correspondence table stored in an information storage unit in a master station device according to the second embodiment of the present disclosure. Referring to FIG. 10, the information storage unit 31 stores a correspondence table TB1 indicating the correspondence between the allocation pattern PT of the time slots S in a communication frame F and the configuration number, which is identification information for the TDD signal Std1. The correspondence table TB1 is an example of correspondence information. The pattern of the time slots S in the communication frame F indicates the type of the TDD signal Std1.

[0127] The correspondence table TB1 shows that the TDD signal Std1 having the configuration number "C1" corresponds to an allocation pattern PT in which four downstream communication slots DS and four upstream communication slots US alternate with a special slot SS in between. The correspondence table TB1 also shows that the TDD signal Std1 having the configuration number "C2" corresponds to an allocation pattern PT in which nine downstream communication slots DS and nine upstream communication slots US alternate with a special slot SS in between. The correspondence table TB1 also shows that the TDD signal Std1 having the configuration number "C3" corresponds to an allocation pattern PT in which four downstream communication slots DS and two upstream communication slots US alternate with a special slot SS in between. Furthermore, the correspondence table TB1 indicates that the TDD signal Std1 having the configuration number "C4" corresponds to an allocation pattern PT in which four upstream communication slots US and two downstream communication slots DS alternately repeat with a special slot SS sandwiched therebetween. The correspondence table TB1 also indicates that the TDD signal Std1 having the configuration number "C11" corresponds to an allocation pattern PT in which time slots S#3 to S#5 are changed from downstream communication slots DS to upstream communication slots US in the allocation pattern PT of the TDD signal Std1 having the configuration number "C2."

[0128] The correspondence table TB1 stored in the information storage unit 31 may be updated by a control device (not shown). When the correspondence table TB1 in the information storage unit 31 is updated, the master station device 102 transmits the updated correspondence table TB1 to the slave station device 202.

[0129] When the TDD processing unit 32 acquires the transition times tr and tf of the TDD signal Std1 received from the base station device 111, it generates a switching pattern including the acquired transition times tr and tf and sets the start timing ts.

[0130] Furthermore, the TDD processing unit 32 refers to the correspondence table TB1 in the information storage unit 31 and acquires the configuration number corresponding to the TDD signal Std1 received from the base station device 111. More specifically, the TDD processing unit 32 acquires the configuration number corresponding to the type of the TDD signal Std1 indicated by the acquired transition times tr and tf.

[0131] Then, the TDD processing unit 32 generates control information including the switching pattern, the start timing ts, and the acquired configuration number, and outputs the generated control information to the frame processing unit 13 .

[0132] The frame processing unit 13 receives control information from the TDD processing unit 32, generates an Ethernet frame addressed to the slave station device 201 with the received control information stored in the payload, and outputs a digital signal Da4 including the generated Ethernet frame to the multiplexing unit 15.

[0133] The multiplexing unit 15 frequency-multiplexes the digital signal Da4 received from the frame processing unit 13 and the IF signal Fa received from the frequency conversion unit 14. The multiplexing unit 15 generates an electrical signal in which the digital signal Da4 and the IF signal Fa are frequency-multiplexed, and outputs the electrical signal to the optical modulation unit 17.

[0134] The optical modulator 17 transmits a downstream optical signal including the digital signal Da4 and the IF signal Fa to the slave station equipment 202 via the optical fiber 191. More specifically, the optical modulator 17 receives an electrical signal from the multiplexer 15 and generates a downstream optical signal by optically modulating the received electrical signal. The optical modulator 17 outputs the downstream optical signal to the optical fiber 191 via the optical coupler CP1 during a downstream communication period DP.

[0135] 11 is a diagram illustrating a configuration of a slave station device according to a second embodiment of the present disclosure. Referring to FIG. 11, compared to the slave station device 201 illustrated in FIG. 4, the slave station device 202 includes a TDD processing unit 42 instead of the TDD processing unit 22, and further includes an information storage unit 41.

[0136] The information storage unit 41, like the information storage unit 31 in the master station device 102, holds a correspondence table TB1.

[0137] The optical demodulation unit 27 receives a downstream optical signal including a digital signal Da4 and an IF signal Fa from the parent station device 101 via the optical fiber 191, generates an electrical signal at a level corresponding to the intensity of the received downstream optical signal, and outputs the electrical signal to the separation unit 25.

[0138] The separation unit 25 receives an electrical signal from the optical demodulation unit 27, separates the received electrical signal into the IF signal Fa and the digital signal Da4, outputs the IF signal Fa to the RF transceiver unit 24, and outputs the digital signal Da4 to the frame processing unit 23.

[0139] The frame processing unit 23 receives the digital signal Da4 from the demultiplexer 25, acquires an Ethernet frame from the received digital signal Da4, and acquires control information from the payload of the Ethernet frame. The frame processing unit 23 outputs the acquired control information to the TDD processing unit 42.

[0140] The TDD processing unit 42 receives control information from the frame processing unit 23 and acquires a configuration number from the received control information. The TDD processing unit 42 acquires an allocation pattern PT corresponding to the acquired configuration number by referring to the correspondence table TB1 in the information storage unit 41. The TDD processing unit 42 generates a TDD signal Std2 based on the acquired allocation pattern PT and transmits the generated TDD signal Std2 to the switch device 151 at the start timing ts included in the control information.

[0141] The TDD processing unit 42 may be configured to correct the start timing ts included in the control information and start the switching process based on the control information at the corrected start timing tsx. For example, the TDD processing unit 42 corrects the start timing ts included in the control information received from the frame processing unit 23 based on the acquired allocation pattern PT. More specifically, when the difference between the transition times tr and tf included in the control information and the transition times tr and tf estimated from the acquired allocation pattern PT is equal to or greater than a predetermined value, the TDD processing unit 42 corrects the start timing ts included in the control information so as to reduce the difference.

[0142] Furthermore, for example, the TDD processing unit 42 may be configured to perform error correction on the TDD signal Std2 generated based on the switching pattern, based on the acquired allocation pattern PT, or may be configured to perform distortion correction on the duty ratio of the generated TDD signal Std2.

[0143] In the analog RoF system 302 according to the second embodiment of the present disclosure, the TDD processing unit 32 in the master station device 102 is configured to acquire a configuration number corresponding to the TDD signal Std1 received from the base station device 111, but this is not limiting. The TDD processing unit 32 may be configured to receive a notification of the configuration number from the base station device 111. In this case, the TDD processing unit 32 generates control information including the notified configuration number and outputs it to the frame processing unit 23. In this case, the TDD processing unit 32 may be configured not to receive the TDD signal Std1 from the base station device 111.

[0144] 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.

[0145] <Third Embodiment> This embodiment relates to an analog RoF system 303 that generates control information based on pattern information received from a management device 171 in a mobile wireless communication system, as compared with the analog RoF system 302 according to the second embodiment. Except for the contents described below, the analog RoF system 303 is the same as the analog RoF system 302 according to the second embodiment.

[0146] 12 is a diagram illustrating a configuration of an analog RoF system according to a third embodiment of the present disclosure. Compared to the analog RoF system 302 illustrated in FIG. 8 , the analog RoF system 303 includes a master station device 103 instead of the master station device 102 and a slave station device 203 instead of the slave station device 202.

[0147] The slave station device 203 receives pattern information indicating an uplink communication period UP and a downlink communication period DP in TDD from a device other than the master station device 103 that is external to the slave station device 203. For example, the slave station device 203 receives the pattern information from a management device 171 in the mobile wireless communication system.

[0148] More specifically, the management device 171 may change a portion of the downlink communication period DP in TDD to an uplink communication period UP in some slave station devices 203, for example, in order to improve the link speed of uplink communication, depending on the communication status of the mobile communication terminal in the mobile wireless communication system. When changing a portion of the downlink communication period DP to an uplink communication period UP, the management device 171 generates pattern information including a configuration number corresponding to an allocation pattern PT of time slots S indicating the changed uplink communication period UP and downlink communication period DP. The management device 171 then generates a frame addressed to the slave station device 203 in which the generated pattern information is stored, and transmits an RF signal including the generated frame. Note that, in order to improve the link speed of downlink communication, the management device 171 may change a portion of the uplink communication period UP to a downlink communication period DP, and generate pattern information including a configuration number corresponding to the allocation pattern PT of time slots S indicating the changed uplink communication period UP and downlink communication period DP. The management device 171 may also be configured to transmit a frame including pattern information to the slave station device 203 via a wired transmission path.

[0149] 13 is a diagram illustrating a configuration of a master station device 103 according to a third embodiment of the present disclosure. Referring to FIG. 13, the master station device 103 includes a TDD processing unit 52 instead of the TDD processing unit 32 in the master station device 102 illustrated in FIG. 9 .

[0150] 14 is a diagram illustrating a configuration of a slave station device 203 according to a third embodiment of the present disclosure. Referring to FIG. 14, the slave station device 203 includes a TDD processing unit 62 instead of the TDD processing unit 42 in the slave station device 202 illustrated in FIG. 11 .

[0151] The TDD processing unit 62 receives an RF signal including pattern information from the management device 171 via the antenna 161 and the switch device 151. The TDD processing unit 62 acquires the pattern information from the received RF signal and outputs the acquired pattern information to the frame processing unit 23.

[0152] The frame processing unit 23 receives the pattern information from the TDD processing unit 62, generates an Ethernet frame addressed to the parent station 103, with the received pattern information stored in its payload, and outputs a digital signal Db2 including the generated Ethernet frame to the multiplexing unit 26. The digital signal Db2 is an example of a second digital signal. The digital signal Db2 output by the frame processing unit 23 to the multiplexing unit 26 is frequency-multiplexed with the IF signal Fb by the multiplexing unit 26, and the digital signal Db2 is then included in an upstream optical signal by the optical modulation unit 28 and transmitted to the parent station 103.

[0153] Referring again to Figure 13, the parent station device 103 acquires pattern information from the digital signal Db2 included in the upstream optical signal received from the child station device 203, and generates control information that reflects the contents of the acquired pattern information.

[0154] More specifically, the frame processing unit 13 in the parent station device 103 receives the digital signal Db2 from the demultiplexer 25, acquires an Ethernet frame from the received digital signal Db2, and acquires pattern information from the payload of the Ethernet frame. The frame processing unit 13 outputs the acquired pattern information to the TDD processing unit 52.

[0155] The TDD processing unit 52 receives the pattern information from the frame processing unit 13 and acquires a configuration number from the received pattern information. The TDD processing unit 52 references the correspondence table TB1 in the information storage unit 31 and acquires an allocation pattern PT corresponding to the acquired configuration number. The TDD processing unit 52 generates control information that reflects the acquired allocation pattern PT.

[0156] Referring again to FIG. 10 , for example, when the TDD processing unit 52 receives pattern information including the configuration number “C11” from the frame processing unit 13, it acquires the allocation pattern PT corresponding to the configuration number “C11” and determines whether the acquired allocation pattern PT is in a quasi-synchronous state with the TDD signal Std1 received from the base station device 111.

[0157] Specifically, if the acquired allocation pattern PT corresponds to a pattern in which part of the high-level period in the TDD signal Std1 has been changed to a low level, the TDD processing unit 52 determines that the acquired allocation pattern PT is in a quasi-synchronous state with the TDD signal Std1, generates control information including the configuration number "C11" and the start timing ts, and outputs the generated control information to the frame processing unit 13.

[0158] On the other hand, if the TDD processing unit 52 determines that the acquired allocation pattern PT is not in a quasi-synchronization state with the TDD signal Std1, it does not generate control information including the configuration number "C11".

[0159] The frame processing unit 13 receives the control information from the TDD processing unit 52, generates an Ethernet frame addressed to the slave station equipment 203, with the received control information stored in its payload, and outputs a digital signal Da3 including the generated Ethernet frame to the multiplexing unit 15. The digital signal Da1 output by the frame processing unit 13 to the multiplexing unit 15 is frequency-multiplexed with the IF signal Fa by the multiplexing unit 15, and the digital signal Da1 is then included in a downstream optical signal by the optical modulation unit 17 and transmitted to the slave station equipment 203.

[0160] 15 is a diagram illustrating an example of a communication sequence in an analog RoF system according to the third embodiment of the present disclosure. Referring to FIG. 15, the master station device 103 and the slave station device 203 perform steps S21 to S28 similar to steps S11 to S18 shown in FIG.

[0161] Next, the slave station device 203 receives the pattern information from the management device 171 in the mobile wireless communication system (step S29).

[0162] Next, the slave station device 203 generates an Ethernet frame addressed to the master station device 103, with the received pattern information stored in its payload, frequency-multiplexes the digital signal Db2 containing the generated Ethernet frame with the IF signal Fb, and transmits an upstream optical signal containing the digital signal Db2 and the IF signal Fb to the master station device 103 via the optical fiber 191 (step S30).

[0163] Next, the master station device 103 generates control information that reflects the content of the pattern information received from the slave station device 203 (step S31).

[0164] Next, the master station device 103 generates an Ethernet frame addressed to the slave station device 203, with the generated control information stored in its payload, and generates a digital signal Da3 including the generated Ethernet frame (step S32).

[0165] Next, the master station 103 frequency-multiplexes the digital signal Da3 and the IF signal Fa, and transmits a downstream optical signal including the digital signal Da3 and the IF signal Fa to the slave station 203 via the optical fiber 191 (step S33).

[0166] Next, the slave station equipment 203 receives the downstream optical signal from the master station equipment 103 via the optical fiber 191, and acquires the digital signal Ds3 from the received downstream optical signal (step S34).

[0167] Next, the slave station device 203 acquires control information from the digital signal Ds3 (step S35).

[0168] Next, the slave station device 203 performs switching processing based on the acquired control information. More specifically, the slave station device 203 generates the TDD signal Std2 based on the switching pattern included in the control information, and transmits the TDD signal Std2 to the switch device 151 at the start timing ts included in the control information (step S36).

[0169] In the analog RoF system 303 according to the third embodiment of the present disclosure, the TDD processing unit 52 in the master station device 103 is configured to generate control information including a configuration number when the allocation pattern PT corresponding to the configuration number included in the pattern information is quasi-synchronized with the TDD signal Std1. However, this is not limiting. The TDD processing unit 52 may be configured to generate a switching pattern including transition times tr and tf based on the allocation pattern PT corresponding to the configuration number included in the pattern information and the TDD signal Std1, and to generate control information including the generated switching pattern. In this case, the TDD processing unit 52 may generate a new switching pattern that involves changing the length of the time slot S.

[0170] 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.

[0171] 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.

[0172] The above description includes the following additional features: [Supplementary Note 1] An analog RoF system comprising: a master station device; and slave station devices that transmit and receive radio signals via an antenna, wherein the master station device generates control information used to control transmission and reception of the radio signals, and transmits an optical signal, including a first digital signal and an analog main signal, to the slave station device via an optical fiber, the slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs switching processing between transmission and reception of the radio signals via the antenna based on the acquired control information, and the master station device and the slave station devices perform inter-station synchronization processing to synchronize a count value of a local clock in the master station device with a count value of a local clock in the slave station device at a timing according to a predetermined period.

[0173] DESCRIPTION OF SYMBOLS 11 Synchronization processing unit 12, 32, 52 TDD processing unit 13 Frame processing unit 14 Frequency conversion unit 15 Multiplexing unit 16 Separation unit 17 Optical modulation unit 18 Optical demodulation unit 21 Synchronization processing unit 22, 42, 62 TDD processing unit 23 Frame processing unit 24 RF transceiver unit 25 Separation unit 26 Multiplexing unit 27 Optical demodulation unit 28 Optical modulation unit 31 Information storage unit 41 Information storage unit 101, 102, 103 Master station device 111 Base station device 151 Switch device 161 Antenna 171 Management device 191 Optical fiber 201, 202, 203 Slave station device 301, 302, 303 Analog RoF system CP1, CP2 Optical coupler TB1 Correspondence table

Claims

1. A master station device; a slave station device for transmitting and receiving wireless signals via an antenna, the master station device generates control information used to control a transmission and reception operation of the wireless signal, and transmits an optical signal including a first digital signal and an analog main signal, the first digital signal including the generated control information, to the slave station device via an optical fiber; The slave station device acquires the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performs switching processing of transmitting and receiving the radio signal via the antenna based on the acquired control information.

2. the master station device is connected between the base station device and the slave station device, 2. The analog RoF system according to claim 1, wherein the master station device receives a pattern signal indicating an uplink communication period and a downlink communication period in TDD (Time Division Duplex) from the base station device, and generates the control information based on the received pattern signal.

3. 3. The analog RoF system of claim 2, wherein the master station device generates a switching pattern for the transmission and reception operation of the wireless signal based on the pattern signal, and generates the control information including the generated switching pattern and a start timing of the switching process using the switching pattern.

4. the master station device and the slave station device each hold correspondence information indicating a correspondence relationship between a type of the pattern signal and identification information of the pattern signal; 3. The analog RoF system of claim 2, wherein the master station device refers to the correspondence information to acquire the identification information corresponding to the pattern signal received from the base station device, and generates the control information including the acquired identification information and a start timing of the switching process using the identification information.

5. The analog RoF system comprises: A plurality of the slave station devices are provided, The analog RoF system according to claim 3 or 4, wherein the master station device generates the control information including the start timing that differs for each of the slave station devices.

6. The analog RoF system according to claim 3 , wherein the slave station device corrects the start timing included in the control information, and starts the switching process based on the control information at the corrected start timing.

7. the slave station device receives pattern information indicating upstream communication periods and downstream communication periods in TDD from a device other than the master station device outside the slave station device, generates a second digital signal including the received pattern information, and transmits an optical signal including the generated second digital signal and an analog main signal to the master station device via the optical fiber; 2. The analog RoF system of claim 1, wherein the master station device acquires the pattern information from the second digital signal contained in the optical signal received from the slave station device via the optical fiber, and generates the control information reflecting the contents of the acquired pattern information.

8. a control information generating unit that generates control information used to control transmission and reception of radio signals by the slave station device via an antenna; a transmitter that transmits an optical signal including a digital signal including the control information generated by the control information generator and an analog main signal to the slave station equipment via an optical fiber.

9. a wireless transceiver unit for transmitting and receiving wireless signals via an antenna; a receiving unit that receives an optical signal including a digital signal including control information and an analog main signal from a master station via an optical fiber; an acquisition unit that acquires the control information from the digital signal included in the optical signal received by the receiving unit; a control unit that performs switching processing between a transmission operation and a reception operation of a radio signal via the antenna by the radio transceiver unit based on the control information acquired by the acquisition unit.

10. An optical communication method in an analog RoF system including a master station device and a slave station device that transmits and receives radio signals via an antenna, comprising: the master station device generating control information used to control a transmission / reception operation of the wireless signal, and transmitting an optical signal including a first digital signal and an analog main signal, the first digital signal including the generated control information, to the slave station device via an optical fiber; the slave station device acquiring the control information from the first digital signal included in the optical signal received from the master station device via the optical fiber, and performing a switching process of transmitting and receiving the radio signal via the antenna based on the acquired control information.