Master station device and optical communication method

Abstract

To transmit a control signal from a master station device to a slave station device while improving the utilization efficiency of a limited frequency band.SOLUTION: A master station device includes an acquisition unit that acquires a control signal for controlling a slave station device that transmits and receives RF (Radio Frequency) signals, a generation unit that generates a digital modulated signal including the control signal acquired by the acquisition unit, and a transmission unit that transmits an optical signal including the digital modulated signal generated by the generation unit and an analog main signal to the slave station device via an optical fiber.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a master station device and an optical communication method.

Background Art

[0002] Conventionally, a communication system including a slave station device that transmits and receives RF (Radio Frequency) signals to and from a communication terminal and a master station device has been developed. For example, Non-Patent Document 1 (Mesh Aneel, et al., "O-RAN fronthaul specification overview", NTT DOCOMO Technical Journal, NTT DOCOMO, Inc., January 2019, Vol. 27, No. 1, p. 43-55) discloses the fronthaul specification in a communication system.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Beyond the technology described in Non-Patent Document 1, it is desired to transmit a control signal from a master station device to a slave station device while improving the utilization efficiency of a limited frequency band.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a master station device and an optical communication method capable of transmitting a control signal from a master station device to a slave station device while improving the utilization efficiency of a limited frequency band.

Means for Solving the Problems

[0006] The master station device of the present disclosure includes an acquisition unit that acquires a control signal for controlling a slave station device that transmits and receives RF (Radio Frequency) signals, a generation unit that generates a digital modulation signal including the control signal acquired by the acquisition unit, and a transmission unit that transmits an optical signal including the digital modulation signal generated by the generation unit and an analog main signal to the slave station device via an optical fiber.

[0007] One aspect of the present disclosure can be realized not only as a master station device including such a characteristic processing unit, but also as a program for causing a computer to execute the steps of such characteristic processing. Further, one aspect of the present disclosure can be realized as a semiconductor integrated circuit that realizes part or all of the master station device, or can be realized as a system including the master station device.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to transmit a control signal from the master station device to the slave station device while improving the utilization efficiency of a limited frequency band.

Brief Description of the Drawings

[0009]

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DETAILED DESCRIPTION OF THE INVENTION

[0010] First, the contents of the embodiments of the present disclosure will be listed and described. (1) The master station device according to the embodiment of the present disclosure includes an acquisition unit that acquires a control signal for controlling a slave station device that transmits and receives RF signals, a generation unit that generates a digital modulation signal including the control signal acquired by the acquisition unit, and a transmission unit that transmits an optical signal including the digital modulation signal generated by the generation unit and an analog main signal to the slave station device via an optical fiber.

[0011] Thus, with a configuration in which a control signal is transmitted to the slave unit device using a digital modulation signal, for example, compared with a configuration in which a control signal is transmitted to the slave unit device using a digital signal, the bandwidth of the frequency band used for transmitting the control signal can be made smaller. Therefore, it is possible to transmit a control signal from the master unit device to the slave unit device while improving the utilization efficiency of the limited frequency band.

[0012] (2) In the above (1), the acquisition unit may acquire the control signal related to the transmission and reception of the RF signal via the antenna in the slave unit device.

[0013] With such a configuration, it is possible to transmit a control signal to the slave unit device using a narrow frequency band and control the transmission and reception of the RF signal in the slave unit device.

[0014] (3) In the above (2), the acquisition unit may acquire the control signal indicating the switching timing of the transmission and reception of the RF signal via the antenna.

[0015] With such a configuration, it is possible to transmit a control signal to the slave unit device using a narrow frequency band and control the switching of the transmission and reception of the RF signal in the slave unit device.

[0016] (4) In the above (3), the acquisition unit may acquire the binary control signal indicating the transmission period and reception period of the RF signal, and the generation unit may generate the digital modulation signal in which the carrier wave is modulated based on the control signal.

[0017] With such a configuration, it is possible to generate a digital modulation signal including a control signal for controlling the transmission period and reception period of the RF signal with a simple configuration.

[0018] (5) In the above (4), the acquisition unit may acquire the control signal whose value changes at a timing predetermined time before the timing at which the downlink period for downlink communication and the uplink period for uplink communication are switched, and the predetermined time may be equal to or longer than the time required for demodulating the digital modulation signal in the slave unit device.

[0019] With such a configuration, in the slave unit device, the timing at which the transmission period and the reception period should be switched can be acquired earlier than the timing at which the downlink period and the uplink period are switched. Therefore, in accordance with the timing at which the downlink period and the uplink period are switched, the transmission and reception of the RF signal in the slave unit device can be switched.

[0020] (6) In any one of the above (2) to (5), the acquisition unit may acquire the control signal indicating the transmission and reception range of the RF signal via the antenna.

[0021] With such a configuration, a control signal can be transmitted to the slave unit device using a narrow frequency band, and the transmission and reception range of the RF signal in the slave unit device can be controlled.

[0022] (7) In any one of the above (1) to (6), the generation unit may generate the digital modulation signal conforming to the FSK (Frequency Shift Keying) method.

[0023] In this way, with a configuration using the FSK method which is a single carrier modulation method, the bandwidth of the frequency band used for transmitting the control signal can be made smaller. Also, compared with a configuration using another single carrier modulation method, the control signal can be transmitted with a simpler configuration.

[0024] (8) The optical communication method of the present disclosure is an optical communication method in a master station device, and includes steps of acquiring a control signal for controlling a slave station device that transmits and receives RF signals, generating a digital modulation signal including the acquired control signal, and transmitting an optical signal including the generated digital modulation signal and an analog main signal to the slave station device via an optical fiber.

[0025] In this way, by using a digital modulation signal to transmit a control signal to a slave station device, for example, compared with a method of transmitting a control signal to a slave station device using a digital signal, the bandwidth of the frequency band used for transmitting the control signal can be made smaller. Therefore, while improving the utilization efficiency of the limited frequency band, the control signal can be transmitted from the master station device to the slave station device.

[0026] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their descriptions will not be repeated. Also, at least a part of the embodiments described below may be arbitrarily combined.

[0027] <First Embodiment> [Configuration and Basic Operation] FIG. 1 is a diagram showing the configuration of an optical communication system according to the first embodiment of the present disclosure. Referring to FIG. 1, the optical communication system 301 includes a master station device 101 and a slave station device 201. The master station device 101 is a central station in the optical communication system 301. The slave station device 201 is an outstation in the optical communication system 301. The master station device 101 and the slave station device 201 are connected to each other via an optical fiber 191. The slave station device 201 includes an antenna 161. The slave station device 201 transmits and receives RF signals to and from a communication terminal 121, which is a mobile terminal, via the antenna 161. Note that the optical communication system 301 may be configured to include a plurality of slave station devices 201. In this case, for example, the plurality of slave station devices 201 are connected to the master station device 101 via one optical fiber 191 and an optical coupler. Also, the communication terminal 121 is not limited to a mobile terminal and may be a fixed terminal.

[0028] The master station device 101 and the slave station device 201 transmit and receive an optical signal including an analog signal via the optical fiber 191. Hereinafter, the optical signal transmitted from the master station device 101 to the slave station device 201 is also referred to as a downstream optical signal, and the optical signal transmitted from the slave station device 201 to the master station device 101 is also referred to as an upstream optical signal.

[0029] For example, the optical communication system 301 is used as a fronthaul in a mobile communication system that follows the TDD (Time Division Duplex) method. In this case, in the optical communication system 301, the downstream period Pd for the slave station device 201 to perform downstream communication for transmitting an RF signal to the communication terminal 121 and the upstream period Pu for the slave station device 201 to perform upstream communication for receiving an RF signal from the communication terminal 121 are switched and repeatedly alternated.

[0030] More specifically, the master station device 101 receives a digital signal including communication data from the base station device 111, and generates an analog signal SId in the IF (Intermediate Frequency) band, for example, by performing analog conversion on the received digital signal. The master station device 101 transmits a downstream optical signal including the generated analog signal SId to the slave station device 201 via the optical fiber 191. The analog signal SId is an example of a main signal.

[0031] The slave station device 201 receives a downstream optical signal from the master station device 101 via the optical fiber 191. The slave station device 201 acquires the analog signal SId from the received downstream optical signal, and generates an RF signal SRd by performing frequency conversion on the acquired analog signal SId. The slave station device 201 transmits the generated RF signal SRd to the communication terminal 121 via the antenna 161 in the downstream period Pd.

[0032] Also, in the uplink period Pu, the slave station device 201 receives an RF signal SRu including communication data from the communication terminal 121. The slave station device 201 generates, for example, an analog signal SIu in the IF band by frequency-converting the RF signal SRu received from the communication terminal 121. The slave station device 201 transmits an uplink optical signal including the generated analog signal SIu to the master station device 101 via the optical fiber 191.

[0033] The master station device 101 receives an uplink optical signal from the slave station device 201 via the optical fiber 191. The master station device 101 acquires the analog signal SIu from the received uplink optical signal, generates a digital signal by digitally converting the acquired analog signal SIu, and transmits the generated digital signal to the base station device 111.

[0034] [Problem] The master station device 101 transmits a control signal Sc for controlling the slave station device 201 to the slave station device 201. In the optical communication system 301, it is desirable to transmit the control signal Sc from the master station device 101 to the slave station device 201 while improving the utilization efficiency of the limited frequency band.

[0035] For example, in a conventional optical communication system, the master station device generates a control signal Scc which is a control signal Sc including a frame conforming to PTP (Precision Time Protocol), and includes the generated control signal Scc in a downlink optical signal and transmits it to the slave station device via an optical fiber.

[0036] FIG. 2 is a diagram schematically showing the frequency band used for transmitting a signal from the master station device to the slave station device in an optical communication system according to a comparative example. FIG. 2 shows a frequency band Fr1 used for transmitting the analog signal SId and a frequency band Frc used for transmitting the control signal Scc. In FIG. 2, the horizontal axis represents frequency [GHz], and the vertical axis represents power.

[0037] When transmitting the control signal Scc to the slave station device by including it in the downlink optical signal with reference to FIG. 2, there is a case where the frequency bands Fr1 and Fr2 overlap, and the communication quality in the optical communication system may deteriorate.

[0038] In this case, in order to suppress the deterioration of communication quality, it is necessary to set the frequency band Fr1 used for transmitting the analog signal SId to a higher frequency side, or to perform band limiting of the frequency band Frc using an LPF (Low Pass Filter).

[0039] Therefore, the optical communication system 301 according to the embodiment of the present disclosure solves the above problems with the following configuration.

[0040] (Master station device and slave station device) FIG. 3 is a diagram showing the configurations of the master station device and the slave station device in the optical communication system according to the first embodiment of the present disclosure.

[0041] Referring to FIG. 3, the master station device 101 includes an AD / DA (Analog to Digital / Digital to Analog) conversion unit 11, a frequency conversion unit 12, a modulation signal generation unit 13, a multiplexer 14, and an optical transceiver 15. The modulation signal generation unit 13 is an example of an acquisition unit and also an example of a generation unit. The optical transceiver 15 is an example of a transmission unit. Part or all of the modulation signal generation unit 13 is realized by, for example, a processing circuit (Circuitry) including one or more processors.

[0042] The slave station device 201 includes an optical transceiver 21, a multiplexer 22, a frequency conversion unit 23, an RF transceiver 24, a demodulation unit 25, a switching unit 26, and an antenna 161. Part or all of the demodulation unit 25 and the switching unit 26 are realized by, for example, a processing circuit (Circuitry) including one or more processors.

[0043] (Uplink communication) The RF transceiver 24 in the slave station device 201 receives the RF signal SRu from the communication terminal 121 via the antenna 161. The RF transceiver 24 outputs the received RF signal SRu to the frequency conversion unit 23.

[0044] The frequency conversion unit 23 generates an analog signal SIu by frequency-converting the RF signal SRu received from the RF transceiver 24 and outputs it to the multiplexer 22.

[0045] The multiplexer 22 outputs the analog signal SIu received from the frequency conversion unit 23 to the optical transceiver 21.

[0046] The optical transceiver 21 transmits an upstream optical signal including the analog signal SIu received from the multiplexer 22 to the master station device 101 via the optical fiber 191. More specifically, the optical transceiver 21 receives the analog signal SIu from the multiplexer 22 and generates an upstream optical signal with a wavelength λu in which the received analog signal SIu is optically modulated. The optical transceiver 21 transmits the generated upstream optical signal to the master station device 101 via the optical fiber 191.

[0047] The optical transceiver 15 in the master station device 101 receives an upstream optical signal from the slave station device 201 via the optical fiber 191. The optical transceiver 15 generates an analog signal SIu, which is an electrical signal at a level corresponding to the intensity of the received upstream optical signal, and outputs it to the multiplexer 14.

[0048] The multiplexer 14 outputs the analog signal SIu received from the optical transceiver 15 to the frequency conversion unit 12.

[0049] The frequency conversion unit 12 generates, for example, an analog signal SBu in the baseband band by frequency-converting the analog signal SIu received from the multiplexer 14, and outputs the generated analog signal SBu to the AD / DA conversion unit 11.

[0050] The AD / DA conversion unit 11 generates a digital signal by digitally converting the analog signal SBu received from the frequency conversion unit 12, and transmits the generated digital signal to the base station device 111.

[0051] (Downlink communication) The AD / DA conversion unit 11 in the master station device 101 receives a digital signal including communication data from the base station device 111. The AD / DA conversion unit 11 generates an analog signal SBd by analog-converting the received digital signal, and outputs the generated analog signal SBd to the frequency conversion unit 12.

[0052] The frequency conversion unit 12 generates an analog signal SId by frequency-converting the analog signal SBd received from the AD / DA conversion unit 11, and outputs the generated analog signal SId to the multiplexer 14.

[0053] The modulation signal generation unit 13 generates a control signal Cs for controlling the slave station device 201. For example, the modulation signal generation unit 13 generates a control signal Cs regarding the transmission and reception of the RF signals SRd and SRu via the antenna 161 in the slave station device 201. As an example, the modulation signal generation unit 13 generates a transmission / reception switching signal Csw which is a control signal Cs indicating the switching timing of the transmission and reception of the RF signal via the antenna 161. Note that the modulation signal generation unit 13 may be configured to receive the transmission / reception switching signal Csw from the base station device 111 instead of generating the transmission / reception switching signal Csw.

[0054] FIG. 4 is a diagram showing an example of a transmission / reception switching signal transmitted from the master station device to the slave station device in the optical communication system according to the first embodiment of the present disclosure. In FIG. 4, the horizontal axis represents time, and the vertical axis represents voltage.

[0055] Referring to FIG. 4, the modulation signal generation unit 13 generates a binary transmission / reception switching signal Csw indicating the transmission period PH of the RF signal SRd and the reception period PL of the RF signal SRu. More specifically, the modulation signal generation unit 13 generates a transmission / reception switching signal Csw that becomes a high-level voltage VH during the transmission period PH corresponding to the downlink period Pd and becomes a low-level voltage VL during the reception period PL corresponding to the uplink period Pu. The transmission / reception switching signal Csw is a logic signal corresponding to the transmission period PH and the reception period PL with voltages VH and VL, respectively. The data rate of the transmission / reception switching signal Csw is very low, for example, 16 kilobits per second or less.

[0056] The modulation signal generation unit 13 generates a digital modulation signal Sf1 including the transmission / reception switching signal Csw. For example, a digital modulation signal Sf1 in which a carrier wave is modulated based on the transmission / reception switching signal Csw is generated. As an example, the modulation signal generation unit 13 generates a digital modulation signal Sf1 according to a modulation method using a single carrier wave. That is, the modulation signal generation unit 13 generates a digital modulation signal Sf1 in which a carrier wave is discontinuously modulated based on the transmission / reception switching signal Csw according to the single carrier modulation method.

[0057] For example, the modulation signal generation unit 13 generates a digital modulation signal Sf1 according to the FSK method. More specifically, the modulation signal generation unit 13 includes a voltage-controlled oscillator that outputs a sine wave with a frequency fH when receiving the voltage VH and outputs a sine wave with a frequency fL when receiving the voltage VL. Here, it is assumed that fL < fH. The modulation signal generation unit 13 generates a digital modulation signal Sf1 that becomes the frequency fH during the transmission period PH and becomes the frequency fL during the reception period PL by applying the transmission / reception switching signal Csw to the voltage-controlled oscillator. The modulation signal generation unit 13 outputs the generated digital modulation signal Sf1 to the multiplexer 14.

[0058] Referring again to FIG. 3, the multiplexer 14 frequency-division multiplexes the digital modulation signal Sf1 received from the modulation signal generation unit 13 and the analog signal SId received from the frequency conversion unit 12. The multiplexer 14 generates an electrical signal M1 in which the digital modulation signal Sf1 and the analog signal SId are frequency-division multiplexed, and outputs the electrical signal M1 to the optical transceiver unit 15.

[0059] The optical transceiver unit 15 transmits a downstream optical signal including the digital modulation signal Sf1 and the analog signal SId generated by the modulation signal generation unit 13 to the slave station device 201 via the optical fiber 191. More specifically, the optical transceiver unit 15 receives the electrical signal M1 from the multiplexer 14, and generates a downstream optical signal having a wavelength λd in which the received electrical signal M1 is optically modulated. The optical transceiver unit 15 transmits the generated downstream optical signal to the slave station device 201 via the optical fiber 191.

[0060] The optical transceiver unit 21 in the slave station device 201 receives a downstream optical signal from the master station device 101 via the optical fiber 191. The optical transceiver unit 21 generates an electrical signal M1 having a level corresponding to the intensity of the received downstream optical signal, and outputs the electrical signal M1 to the multiplexer 22.

[0061] The multiplexer 22 separates the digital modulation signal Sf1 and the analog signal SId included in the electrical signal M1 received from the optical transceiver unit 21. The multiplexer 22 outputs the separated analog signal SId to the frequency conversion unit 23, and outputs the separated digital modulation signal Sf1 to the demodulation unit 25.

[0062] The frequency conversion unit 23 generates an RF signal SRd by frequency-converting the analog signal SId received from the multiplexer 22, and outputs the RF signal SRd to the RF transceiver unit 24.

[0063] The RF transceiver unit 24 transmits the RF signal SRd received from the frequency conversion unit 23 to the communication terminal 121 via the antenna 161. The RF transceiver unit 24 can switch between a reception state in which the RF signal SRu is received from the communication terminal 121 via the antenna 161 and a transmission state in which the RF signal SRd is transmitted to the communication terminal 121 via the antenna 161.

[0064] (Switching of RF signal transmission and reception) The demodulation unit 25 demodulates the digital modulation signal Sf1 received from the multiplexer 22. For example, the demodulation unit 25 obtains the transmission / reception switching signal Csw from the digital modulation signal Sf1 by performing delayed detection of the digital modulation signal Sf1.

[0065] More specifically, the demodulation unit 25 includes a delayed detection circuit (not shown) that obtains the transmission / reception switching signal Csw from the digital modulation signal Sf1. The delayed detection circuit includes a BPF (Band Pass Filter), a delay circuit, a multiplication circuit, an LPF (Low Pass Filter), and a monitoring unit.

[0066] In the delayed detection circuit, the BPF attenuates frequency components outside a predetermined passband in the digital modulation signal Sf1 received from the multiplexer 22. The delay circuit generates a delayed signal obtained by delaying the digital modulation signal Sf1 that has passed through the BPF by one bit, that is, by one of the transmission period PH or the reception period PL. The multiplication circuit generates a multiplication signal obtained by multiplying the digital modulation signal Sf1 that has passed through the BPF and the delayed signal generated by the delay circuit. The LPF attenuates harmonic components in the multiplication signal generated by the multiplication circuit. The monitoring unit monitors the phase of the multiplication signal that has passed through the LPF, and generates a demodulation signal based on the phase monitoring result and outputs it to the switching unit 26. More specifically, the monitoring unit generates a demodulation signal whose level switches from the voltage VL to the voltage VH at the timing when the phase of the multiplication signal advances, and whose level switches from the voltage VH to the voltage VL at the timing when the phase of the multiplication signal lags. The monitoring unit outputs the demodulation signal to the switching unit 26 as the transmission / reception switching signal Csw.

[0067] The switching unit 26 alternately switches between the reception state and the transmission state in the RF transceiver unit 24 such that the RF transceiver unit 24 is in the transmission state during the transmission period PH and in the reception state during the reception period PL according to the transmission / reception switching signal Csw received from the demodulation unit 25. More specifically, the switching unit 26 detects a change in the level of the transmission / reception switching signal Csw by comparing the level of the transmission / reception switching signal Csw received from the demodulation unit 25 with a predetermined threshold value.

[0068] At the switching timing Tsw, which is the timing when the level of the transmission / reception switching signal Csw received from the demodulation unit 25 changes from the voltage VL to the voltage VH, the switching unit 26 outputs a transmission start instruction to the RF transceiver unit 24 for switching the RF transceiver unit 24 from the reception state to the transmission state. Also, at the switching timing Tsw, which is the timing when the level of the transmission / reception switching signal Csw received from the demodulation unit 25 changes from the voltage VH to the voltage VL, the switching unit 26 outputs a transmission stop instruction to the RF transceiver unit 24 for switching the RF transceiver unit 24 from the transmission state to the reception state.

[0069] When the RF transceiver unit 24 receives a transmission start instruction from the switching unit 26, it transitions from the reception state to the transmission state and starts outputting the RF signal SRd to the antenna 161. Also, when the RF transceiver unit 24 receives a transmission stop instruction from the switching unit 26, it transitions from the transmission state to the reception state and stops outputting the RF signal SRd to the antenna 161.

[0070] As described above, since the demodulation unit 25 performs delay detection using a delay signal obtained by delaying the digital modulation signal Sf1 by one bit, the change timing of the level of the transmission / reception switching signal Csw acquired by the demodulation unit 25 may be delayed by a time corresponding to one bit compared to the change timing of the level of the transmission / reception switching signal Csw generated by the modulation signal generation unit 13.

[0071] Therefore, the modulation signal generation unit 13 in the master station device 101 generates a transmission / reception switching signal Csw whose value changes at a timing a predetermined adjustment time Tw before the timing at which the downlink period Pd and the uplink period Pu are switched. The adjustment time Tw is set in consideration of the time required for demodulating the digital modulation signal Sf1 in the demodulation unit 25 of the slave station device 201, and is equal to or longer than the time required for demodulating the digital modulation signal Sf1. More specifically, the modulation signal generation unit 13 generates a transmission / reception switching signal Csw whose level changes at a timing one bit time earlier than the timing at which the downlink period Pd and the uplink period Pu are switched. Thereby, it is possible to switch the transmission and reception of the RF signal in the RF transceiver 24 at a switching timing Tsw closer to the timing at which the downlink period Pd and the uplink period Pu are switched.

[0072] Note that the frequency conversion unit 23 is not limited to a configuration capable of performing frequency conversion of the analog signal SId and frequency conversion of the RF signal SRu in parallel, and may be capable of switching between an up-conversion state in which the analog signal SId is frequency-converted to generate the RF signal SRd and a down-conversion state in which the RF signal SRu is frequency-converted to generate the analog signal SIu. In this case, in addition to outputting a transmission start instruction to the RF transceiver 24, the switching unit 26 may output an up-conversion instruction to the frequency conversion unit 23, and in addition to outputting a transmission stop instruction to the RF transceiver 24, may output a down-conversion instruction to the frequency conversion unit 23. When the frequency conversion unit 23 receives the up-conversion instruction received from the switching unit 26, it transitions from the down-conversion state to the up-conversion state and starts frequency conversion of the analog signal SId. Also, when the frequency conversion unit 23 receives the down-conversion instruction received from the switching unit 26, it transitions from the up-conversion state to the down-conversion state and starts frequency conversion of the RF signal SRu.

[0073] FIG. 5 is a diagram schematically showing a frequency band used for signal transmission from a master station device to a slave station device in an optical communication system according to the first embodiment of the present disclosure. FIG. 5 shows a frequency band Fr1 used for transmission of an analog signal SId and a frequency band Fr2 used for transmission of a transmission / reception switching signal Csw. In FIG. 5, the horizontal axis represents frequency [GHz], and the vertical axis represents power.

[0074] Referring to FIG. 5, the frequency band Fr2 has a smaller bandwidth than the frequency band Frc used for transmission of the control signal Scc described above and does not overlap with the frequency band Fr1. For example, the bandwidth of the frequency band Fr2 is several megahertz. Therefore, the transmission / reception switching signal Csw can be transmitted from the master station device 101 to the slave station device 201 without band-limiting the frequency band Fr2.

[0075] FIG. 6 is a diagram showing switching timing in an optical communication system according to the first embodiment of the present disclosure. In FIG. 6, the horizontal axis represents time.

[0076] Referring to FIG. 6, in the optical communication system 301, according to the standard defined by 3GPP (Third Generation Partnership Project) (registered trademark), the ON period Pon, which is the period during which the slave station device 201 should transmit the RF signal SRd, is provided for the entire downlink period Pd, and the OFF period Poff, which is the period during which the slave station device 201 should stop transmitting the RF signal SRd, is provided for a part of the uplink period Pu. Also, according to the standard defined by 3GPP, transition periods Pt1 from the OFF period Poff to the ON period Pon and Pt2 from the ON period Pon to the OFF period Poff are provided before and after the downlink period Pd. The transition periods Pt1 and Pt2 are, for example, 10 microseconds.

[0077] The deviation frequency fdev, which is half of the difference between the frequencies fH and fL in the digital modulation signal Sf1, and the data rate of the transmission / reception switching signal Csw are preset so that the variation in the switching timing Tsw falls within the transition periods Pt1 and Pt2.

[0078] By setting the deviation frequency fdev to a larger value, the variation in the switching timing Tsw becomes smaller, while the bandwidth of the frequency band Fr2 becomes larger.

[0079] Also, by setting the data rate of the transmission / reception switching signal Csw to a smaller value, the variation in the switching timing Tsw becomes smaller. On the other hand, the delay time due to the delay circuit increases, and the time required for demodulating the digital modulation signal Sf1 by the demodulation unit 25 becomes longer. Therefore, the delay amount of the switching timing Tsw with respect to the timing at which the downlink period Pd and the uplink period Pu are switched becomes larger.

[0080] [Sequence of Operations] FIG. 7 is a diagram showing an example of a communication sequence in an optical communication system according to the first embodiment of the present disclosure.

[0081] Referring to FIG. 7, first, the master station device 101 generates an analog signal SBd by analog-converting the digital signal received from the base station device 111, and generates an analog signal SId by frequency-converting the generated analog signal SBd (step S11).

[0082] Next, the master station device 101 generates a digital modulation signal Sf1 including the transmission / reception switching signal Csw (step S12).

[0083] Next, the master station device 101 transmits a downlink optical signal including the analog signal SId and the digital modulation signal Sf1 to the slave station device 201 (step S13).

[0084] Next, the slave station device 201 receives the downlink optical signal from the master station device 101 via the optical fiber 191, and acquires the analog signal SId and the digital modulation signal Sf1 from the received downlink optical signal (step S14).

[0085] Next, the slave station device 201 acquires a transmission / reception switching signal Csw from the digital modulation signal Sf1 (step S15).

[0086] Next, during the transmission period PH indicated by the transmission / reception switching signal Csw, the slave station device 201 transmits the RF signal SRd generated by frequency-converting the analog signal SId to the communication terminal 121 via the antenna 161 (step S16).

[0087] Next, during the reception period PL indicated by the transmission / reception switching signal Csw, the slave station device 201 receives the RF signal SRu from the communication terminal 121 via the antenna 161 (step S17).

[0088] Next, the slave station device 201 generates an analog signal SIu by frequency-converting the RF signal SRu (step S18).

[0089] Next, the slave station device 201 transmits the upstream optical signal including the analog signal SIu to the master station device 101 via the optical fiber 191 (step S19).

[0090] Next, the master station device 101 receives the upstream optical signal from the slave station device 201 via the optical fiber 191, and acquires the analog signal SIu from the received upstream optical signal (step S20).

[0091] Next, the master station device 101 generates an analog signal SBu by frequency-converting the analog signal SIu, and transmits the digital signal obtained by digitally converting the generated analog signal SBu to the base station device 111 (step S21).

[0092] In the optical communication system 301 according to the first embodiment of the present disclosure, the master station device 101 transmits a downstream optical signal including the analog signal SId to the slave station device 201, and the slave station device 201 transmits an upstream optical signal including the analog signal SIu to the master station device 101. However, the present disclosure is not limited to this configuration. For example, the master station device 101 may be configured to transmit a downstream optical signal including the RF signal SRd instead of the analog signal SId to the slave station device 201. In this case, the slave station device 201 acquires the RF signal SRd from the downstream optical signal received from the master station device 101 and transmits the acquired RF signal SRd to the communication terminal 121. Further, for example, the slave station device 201 may be configured to transmit an upstream optical signal including the RF signal SRu instead of the analog signal SIu to the master station device 101. In this case, the master station device 101 acquires the RF signal SRu from the upstream optical signal received from the slave station device 201, generates a digital signal by digitally converting the acquired RF signal SRu, and transmits the generated digital signal to the base station device 111.

[0093] Also, in the master station device 101 according to the first embodiment of the present disclosure, the modulation signal generation unit 13 is configured to generate a control signal Sc related to the transmission and reception of the RF signals SRd and SRu via the antenna 161 in the slave station device 201. However, the present disclosure is not limited to this configuration. The modulation signal generation unit 13 may be configured to generate, for example, a control signal Sc for controlling the registers of the FPGA (Field-Programmable Gate Array) in the slave station device 201.

[0094] Also, in the master station device 101 according to the first embodiment of the present disclosure, the modulation signal generation unit 13 is configured to generate a binary transmission / reception switching signal Csw indicating the transmission period PH and the reception period PL. However, the present disclosure is not limited to this configuration. The modulation signal generation unit 13 may be configured to generate a pulse-shaped transmission / reception switching signal Csw that becomes high level at the switching timing Tsw.

[0095] Further, in the master station apparatus 101 according to the first embodiment of the present disclosure, the modulation signal generation unit 13 is configured to generate a transmission / reception switching signal Csw whose value changes at a timing before the adjustment time Tw from the timing at which the downlink period Pd and the uplink period Pu are switched. However, the present disclosure is not limited to this. The modulation signal generation unit 13 may be configured to generate a transmission / reception switching signal Csw whose value changes at the timing at which the downlink period Pd and the uplink period Pu are switched.

[0096] Further, in the master station apparatus 101 according to the first embodiment of the present disclosure, the modulation signal generation unit 13 is configured to generate a digital modulation signal Sf1 according to the FSK method. However, the present disclosure is not limited to this. The modulation signal generation unit 13 may be configured to generate a digital modulation signal according to a method other than the FSK method, such as the ASK (Amplitude Shift Keying) method. However, compared with the digital modulation signal according to the ASK method, the digital modulation signal Sf1 according to the FSK method can be easily distinguished from the state in which the digital modulation signal Sf1 is interrupted and the state in which the transmission / reception switching signal Csw included in the digital modulation signal Sf1 is at a low level in the demodulation unit 25 in the slave station apparatus 201.

[0097] Next, another embodiment of the present disclosure will be described with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and their description will not be repeated.

[0098] <Second Embodiment> This embodiment relates to an optical communication system 302 capable of controlling the transmission / reception range of RF signals SRd and SRu as compared with the optical communication system 301 according to the first embodiment. Except for the content described below, it is the same as the optical communication system 301 according to the first embodiment.

[0099] FIG. 8 is a diagram showing the configuration of an optical communication system according to the second embodiment of the present disclosure. Referring to FIG. 8, the optical communication system 302 includes a master station apparatus 102 instead of the master station apparatus 101 and a slave station apparatus 202 instead of the slave station apparatus 201 as compared with the optical communication system 301.

[0100] FIG. 9 is a diagram showing the configurations of the master station apparatus and the slave station apparatus in the optical communication system according to the second embodiment of the present disclosure.

[0101] Referring to FIG. 9, the master station apparatus 102 further includes a modulation signal generation unit 16 as compared with the master station apparatus 101. The modulation signal generation unit 16 is an example of an acquisition unit and an example of a generation unit. The slave station apparatus 202 further includes a demodulation unit 27 and a beam control unit 28 as compared with the slave station apparatus 201.

[0102] The slave station apparatus 202 can change the beam direction Db which is the transmission / reception range of the RF signals SRd and SRu. For example, the slave station apparatus 201 can change the beam direction Db among eight predetermined beam directions D1, D2, D3, D4, D5, D6, D7, and D8.

[0103] FIG. 10 is a diagram showing an example of the transmission / reception pattern of the RF signal of the slave station apparatus in the optical communication system according to the second embodiment of the present disclosure. In FIG. 10, the horizontal axis represents time.

[0104] Referring to FIG. 10, in the optical communication system 302, a downlink period Pd1 which is a downlink period Pd, an uplink period Pu1 which is an uplink period Pu, a downlink period Pd2 which is a downlink period Pd, and an uplink period Pu2 which is an uplink period Pu are switched in this order.

[0105] For example, in the downlink period Pd1, the slave station apparatus 202 transmits the RF signal SRd in the beam direction D1 in the first period Td11, transmits the RF signal SRd in the beam direction D2 in the second period Td12 following the first period Td11, transmits the RF signal SRd in the beam direction D3 in the third period Td13 following the second period Td12, and transmits the RF signal SRd in the beam direction D4 in the fourth period Td14 following the third period Td13.

[0106] Also, for example, in the uplink period Pu1, the slave station device 202 receives the RF signal SRu in the beam direction D2 in the first period Tu11, receives the RF signal SRu in the beam direction D4 in the second period Tu12 following the first period Tu11, receives the RF signal SRu in the beam direction D6 in the third period Tu13 following the second period Tu12, and receives the RF signal SRu in the beam direction D8 in the fourth period Tu14 following the third period Tu13.

[0107] Also, for example, in the downlink period Pd2, the slave station device 202 transmits the RF signal SRd in the beam direction D2 in the first period Td21, transmits the RF signal SRd in the beam direction D4 in the second period Td22 following the first period Td21, transmits the RF signal SRd in the beam direction D6 in the third period Td23 following the second period Td22, and transmits the RF signal SRd in the beam direction D8 in the fourth period Td24 following the third period Td23.

[0108] Also, for example, in the uplink period Pu2, the slave station device 202 receives the RF signal SRu in the beam direction D1 in the first period Tu21, receives the RF signal SRu in the beam direction D3 in the second period Tu22 following the first period Tu21, receives the RF signal SRu in the beam direction D5 in the third period Tu23 following the second period Tu22, and receives the RF signal SRu in the beam direction D7 in the fourth period Tu24 following the third period Tu23.

[0109] The modulation signal generation unit 16 in the master station device 102 generates a beam control signal Cbm, which is a control signal Cs indicating the transmission and reception range of the RF signals SRd and SRu via the antenna 161. More specifically, the modulation signal generation unit 16 holds correspondence information indicating the correspondence relationship between the beam direction Db and the level of the beam control signal Cbm. Based on the correspondence information, the modulation signal generation unit 16 generates a beam control signal Cbm at a level indicating the beam direction Db in which the slave station device 202 should transmit and receive the RF signals SRd and SRu. Note that the modulation signal generation unit 16 may be configured to receive the beam control signal Cbm from the base station device 111 instead of generating the beam control signal Cbm.

[0110] FIG. 11 is a diagram showing an example of a beam control signal transmitted from a master station device to a slave station device in an optical communication system according to a second embodiment of the present disclosure. In FIG. 11, the horizontal axis represents time. FIG. 11 shows a beam control signal Cbm for controlling the slave station device 202 according to the transmission / reception pattern of the RF signal shown in FIG. 10.

[0111] Referring to FIG. 11, the modulation signal generation unit 16 generates a beam control signal Cbm that indicates the beam direction Db in the next uplink period Pu during the transmission period PH corresponding to the downlink period Pd, and indicates the beam direction Db in the next downlink period Pd during the reception period PL corresponding to the uplink period Pd. The data rate of the beam control signal Cbm is higher than the data rate of the transmission / reception switching signal Csw, for example, 16 times the data rate of the transmission / reception switching signal Csw.

[0112] The modulation signal generation unit 16 generates a digital modulation signal Sf2 including the beam control signal Cbm. For example, the modulation signal generation unit 16 generates a digital modulation signal Sf2 according to a modulation method using a single carrier. That is, the modulation signal generation unit 16 generates a digital modulation signal Sf2 in which the carrier is discontinuously modulated according to the single carrier modulation method. The modulation signal generation unit 16 generates a digital modulation signal Sf2 in a frequency band different from the frequency band of the digital modulation signal Sf1 generated by the modulation signal generation unit 13. The modulation signal generation unit 16 outputs the generated digital modulation signal Sf2 to the multiplexer 14.

[0113] Referring again to FIG. 9, the multiplexer 14 frequency-division multiplexes the digital modulation signals Sf1 and Sf2 received from the modulation signal generation units 13 and 16 and the analog signal SId received from the frequency conversion unit 12. The multiplexer 14 generates an electrical signal M2 in which the digital modulation signals Sf1 and Sf2 and the analog signal SId are frequency-division multiplexed and outputs it to the optical transceiver 15.

[0114] The optical transceiver unit 15 receives the electrical signal M2 from the multiplexer 14 and generates a downstream optical signal with a wavelength λd in which the received electrical signal M2 is optically modulated. The optical transceiver unit 15 transmits the generated downstream optical signal to the slave station device 202 via the optical fiber 191.

[0115] The optical transceiver unit 21 in the slave station device 202 receives the downstream optical signal from the master station device 102 via the optical fiber 191. The optical transceiver unit 21 generates an electrical signal M2 at a level corresponding to the intensity of the received downstream optical signal and outputs it to the multiplexer 22.

[0116] The multiplexer 22 separates the digital modulation signals Sf1, Sf2 and the analog signal SId included in the electrical signal M2 received from the optical transceiver unit 21. The multiplexer 22 outputs the separated analog signal SId to the frequency conversion unit 23, outputs the separated digital modulation signal Sf1 to the demodulation unit 25, and outputs the separated digital modulation signal Sf2 to the demodulation unit 27.

[0117] The demodulation unit 27 demodulates the digital modulation signal Sf2 received from the multiplexer 22. For example, the demodulation unit 27 obtains the beam control signal Cbm from the digital modulation signal Sf2 by performing delay detection of the digital modulation signal Sf2. The demodulation unit 27 outputs the obtained beam control signal Cbm to the beam control unit 28.

[0118] The beam control unit 28 switches the beam direction Db of the RF signal SRd transmitted in the RF transceiver unit 24 and the beam direction Db of the RF signal SRu received in the RF transceiver unit 24 according to the beam control signal Cbm received from the demodulation unit 27.

[0119] Note that in the optical communication system 302 according to the second embodiment of the present disclosure, the master station device 102 is configured to include the modulation signal generation unit 13, but is not limited thereto. The master station device 102 may be configured not to include the modulation signal generation unit 13. In this case, the slave station device 202 does not include the demodulation unit 25 and the switching unit 26.

[0120] Next, other embodiments of the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0121] <Third Embodiment> This embodiment relates to an optical communication system 303 that transmits and receives RF signals SRd and SRu using a plurality of antennas 161 as compared with the optical communication system 302 according to the second embodiment. Except for the content described below, it is the same as the optical communication system 302 according to the second embodiment.

[0122] FIG. 12 is a diagram showing the configuration of an optical communication system according to the third embodiment of the present disclosure. Referring to FIG. 12, the optical communication 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 as compared with the optical communication system 302. The slave station device 203 includes a plurality of antennas 161. As an example, the slave station device 203 includes antennas 161A and 161B which are antennas 161. The optical communication system 303 is an optical communication system that follows 2×2 MIMO (Multiple-Input and Multiple-Output) for transmitting two streams of communication data.

[0123] FIG. 13 is a diagram showing the configurations of the master station device and the slave station device in the optical communication system according to the third embodiment of the present disclosure.

[0124] Referring to FIG. 13, the master station device 103 includes a plurality of sets of an AD / DA conversion unit 11, a frequency conversion unit 12, and a modulation signal generation unit 16 as compared with the master station device 102. More specifically, the master station device 103 includes AD / DA conversion units 11A and 11B which are AD / DA conversion unit 11, frequency conversion units 12A and 12B which are frequency conversion unit 12, and modulation signal generation units 16A and 16B which are modulation signal generation unit 16.

[0125] The slave station device 203 includes a plurality of sets of a frequency conversion unit 23, an RF transceiver unit 24, a demodulation unit 27, and a beam control unit 28, as compared with the slave station device 202. More specifically, the slave station device 203 includes frequency conversion units 23A and 23B that are the frequency conversion unit 23, RF transceiver units 24A and 24B that are the RF transceiver unit 24, demodulation units 27A and 27B that are the demodulation unit 27, and beam control units 28A and 28B that are the beam control unit 28.

[0126] (Up-link communication) The RF transceiver unit 24A receives the RF signal SRuA from the communication terminal 121 via the antenna 161A. For example, the RF signal SRuA is an RF signal SRu with vertical polarization. The RF transceiver unit 24A outputs the received RF signal SRuA to the frequency conversion unit 23A.

[0127] The RF transceiver unit 24B receives the RF signal SRuB from the communication terminal 121 via the antenna 161B. For example, the RF signal SRuB is an RF signal SRu with horizontal polarization. The RF transceiver unit 24B outputs the received RF signal SRuB to the frequency conversion unit 23B.

[0128] The frequency conversion unit 23A generates an analog signal SIuA, which is an analog signal SIu with a frequency Bu1, by frequency-converting the RF signal SRuA received from the RF transceiver unit 24A, and outputs it to the multiplexer 22.

[0129] The frequency conversion unit 23B generates an analog signal SIuB, which is an analog signal SIu with a frequency Bu2, by frequency-converting the RF signal SRuB received from the RF transceiver unit 24B, and outputs it to the multiplexer 22.

[0130] The multiplexer 22 frequency-division multiplexes the analog signals SIuA and SIuB received from the frequency conversion units 23A and 23B. The multiplexer 22 generates an electrical signal M3 in which the analog signals SIuA and SIuB are frequency-division multiplexed, and outputs it to the optical transceiver unit 21.

[0131] The optical transceiver unit 21 receives the electrical signal M3 from the multiplexer 22 and generates an upstream optical signal with a wavelength λu in which the received electrical signal M3 is optically modulated. The optical transceiver unit 21 transmits the generated upstream optical signal to the master station device 103 via the optical fiber 191.

[0132] The optical transceiver unit 15 in the master station device 103 receives an upstream optical signal from the slave station device 203 via the optical fiber 191. The optical transceiver unit 15 generates an electrical signal M3 at a level corresponding to the intensity of the received upstream optical signal and outputs it to the multiplexer 14.

[0133] The multiplexer 14 separates the analog signals SIuA and SIuB included in the electrical signal M3 received from the optical transceiver unit 15. The multiplexer 14 outputs the separated analog signal SIuA to the frequency conversion unit 12A and outputs the separated analog signal SIuB to the frequency conversion unit 12B.

[0134] The frequency conversion unit 12A generates an analog signal SBuA by frequency-converting the analog signal SIuA received from the multiplexer 14, and outputs the generated analog signal SBuA to the AD / DA conversion unit 11A.

[0135] The frequency conversion unit 12B generates an analog signal SBuB by frequency-converting the analog signal SIuB received from the multiplexer 14, and outputs the generated analog signal SBuB to the AD / DA conversion unit 11B.

[0136] The AD / DA conversion unit 11A generates a digital signal by digitally converting the analog signal SBuA received from the frequency conversion unit 12A, and transmits the generated digital signal to the base station device 111.

[0137] The AD / DA conversion unit 11B generates a digital signal by digitally converting the analog signal SBuB received from the frequency conversion unit 12B, and transmits the generated digital signal to the base station device 111.

[0138] (Downlink communication) The AD / DA conversion unit 11A in the master station device 101 receives a digital signal including communication data for vertical polarization from the base station device 111. The AD / DA conversion unit 11A generates an analog signal SBdA, which is an analog signal SBd, by analog-converting the received digital signal, and outputs the generated analog signal SBdA to the frequency conversion unit 12A.

[0139] The AD / DA conversion unit 11B receives a digital signal including communication data for horizontal polarization from the base station device 111. The AD / DA conversion unit 11B generates an analog signal SBdB, which is an analog signal SBd, by analog-converting the received digital signal, and outputs the generated analog signal SBdB to the frequency conversion unit 12B.

[0140] The frequency conversion unit 12A generates an analog signal SIdA, which is an analog signal SId of frequency Bd1, by frequency-converting the analog signal SBdA received from the AD / DA conversion unit 11A, and outputs the generated analog signal SIdA to the multiplexer 14.

[0141] The frequency conversion unit 12B generates an analog signal SIdB, which is an analog signal SId of frequency Bd2, by frequency-converting the analog signal SBd received from the AD / DA conversion unit 11B, and outputs the generated analog signal SIdB to the multiplexer 14.

[0142] The modulation signal generation unit 16A generates a beam control signal CbmA, which is a beam control signal Cbm indicating the transmission / reception range of the RF signals SRd and SRu via the antenna 161A. The modulation signal generation unit 16A generates a digital modulation signal Sf2A, which is a digital modulation signal Sf2 including the beam control signal CbmA, and outputs the generated digital modulation signal Sf2A to the multiplexer 14.

[0143] The modulation signal generation unit 16B generates a beam control signal CbmB, which is a beam control signal Cbm indicating the transmission / reception range of the RF signals SRd and SRu via the antenna 161B. The modulation signal generation unit 16B generates a digital modulation signal Sf2B, which is a digital modulation signal Sf2 including the beam control signal CbmB, and outputs the generated digital modulation signal Sf2B to the multiplexer 14.

[0144] The multiplexer 14 frequency-division multiplexes the digital modulation signals Sf1, Sf2A, and Sf2B received from the modulation signal generation units 13, 16A, and 16B and the analog signals SIdA and SIdB received from the frequency conversion units 12A and 12B. The multiplexer 14 generates an electrical signal M4 in which the digital modulation signals Sf1, Sf2A, and Sf2B and the analog signals SIdA and SIdB are frequency-division multiplexed, and outputs the electrical signal M4 to the optical transceiver unit 15.

[0145] The optical transceiver unit 15 receives the electrical signal M4 from the multiplexer 14 and generates a downstream optical signal with a wavelength λd in which the received electrical signal M4 is optically modulated. The optical transceiver unit 15 transmits the generated downstream optical signal to the slave station device 203 via the optical fiber 191.

[0146] The optical transceiver unit 21 in the slave station device 203 receives the downstream optical signal from the master station device 103 via the optical fiber 191. The optical transceiver unit 21 generates an electrical signal M4 with a level corresponding to the intensity of the received downstream optical signal and outputs the electrical signal M4 to the multiplexer 22.

[0147] The multiplexer 22 separates the digital modulation signals Sf1, Sf2A, and Sf2B and the analog signals SIdA and SIdB included in the electrical signal M4 received from the optical transceiver unit 21. The multiplexer 22 outputs the separated analog signals SIdA and SIdB to the frequency conversion units 23A and 23B, respectively, outputs the separated digital modulation signal Sf1 to the demodulation unit 25, and outputs the separated digital modulation signals Sf2A and Sf2B to the demodulation units 27A and 27B, respectively.

[0148] The frequency conversion unit 23A generates an RF signal SRdA by frequency-converting the analog signal SIdA received from the multiplexer 22, and outputs it to the RF transceiver unit 24A.

[0149] The frequency conversion unit 23B generates an RF signal SRdB by frequency-converting the analog signal SIdB received from the multiplexer 22, and outputs it to the RF transceiver unit 24B.

[0150] The RF transceiver unit 24A transmits the RF signal SRdA received from the frequency conversion unit 23A to the communication terminal 121 via the antenna 161A. For example, the RF signal SRdA is an RF signal SRd with vertical polarization.

[0151] The RF transceiver unit 24B transmits the RF signal SRdB received from the frequency conversion unit 23B to the communication terminal 121 via the antenna 161B. For example, the RF signal SRdB is an RF signal SRd with horizontal polarization.

[0152] The demodulation unit 27A demodulates the digital modulation signal Sf2A received from the multiplexer 22. For example, the demodulation unit 27 performs delay detection of the digital modulation signal Sf2A to obtain a beam control signal CbmA from the digital modulation signal Sf2A. The demodulation unit 27A outputs the obtained beam control signal CbmA to the beam control unit 28A.

[0153] The demodulation unit 27B demodulates the digital modulation signal Sf2B received from the multiplexer 22. For example, the demodulation unit 27 performs delay detection of the digital modulation signal Sf2B to obtain a beam control signal CbmB from the digital modulation signal Sf2B. The demodulation unit 27B outputs the obtained beam control signal CbmB to the beam control unit 28B.

[0154] The beam control unit 28A switches the beam direction Db of the RF signal SRdA transmitted in the RF transceiver unit 24A and the beam direction Db of the RF signal SRuA received in the RF transceiver unit 24A according to the beam control signal CbmA received from the demodulation unit 27A.

[0155] The beam control unit 28B switches the beam direction Db of the RF signal SRdB transmitted in the RF transceiver unit 24B and the beam direction Db of the RF signal SRuB received in the RF transceiver unit 24B according to the beam control signal CbmB received from the demodulation unit 27B.

[0156] Note that although the optical communication system 303 according to the third embodiment of the present disclosure is an optical communication system that follows 2×2 MIMO, it is not limited thereto. The optical communication system 303 may be an optical communication system that follows MIMO using three or more antennas 161. For example, the optical communication system 303 may be an optical communication system that follows 8×8 MIMO for transmitting eight streams of communication data.

[0157] FIG. 14 is a diagram schematically showing the frequency bands used for signal transmission from the master station device to the slave station device in the optical communication system according to the third embodiment of the present disclosure. FIG. 14 shows the frequency bands Fr1A, Fr1B, Fr1C, Fr1D, Fr1E, Fr1F, Fr1G, Fr1H which are the frequency band Fr1, the frequency band Fr2, and the eight frequency bands Fr3 used for transmission of the beam control signal Cbm in the optical communication system 303 that follows 8×8 MIMO. In FIG. 14, the horizontal axis represents the frequency [GHz], and the vertical axis represents the power.

[0158] Referring to FIG. 14, the frequency band Fr1 has a bandwidth of, for example, 400 MHz and is arranged on the frequency axis with a 100 MHz guard band sandwiched in the range from 1 GHz to 5 GHz. Also, the frequency bands Fr2 and Fr3 are arranged on the frequency axis in the range of 1 GHz or less.

[0159] Thus, in the optical communication system 303, since the bandwidths of the frequency bands Fr2 and Fr3 are small, it is possible to transmit the transmission / reception switching signal Csw and the beam control signal Cbm from the master station device 103 to the slave station device 203 while transmitting a large number of streams of communication data.

[0160] The above-described embodiments should be considered illustrative in all respects and not restrictive. The scope of the present invention is defined by the scope of the claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the scope of the claims be included.

[0161] Each process (each function) of the above-described embodiment is realized by a processing circuit including one or more processors. The processing circuit may be configured by an integrated circuit or the like in which one or more memories, various analog circuits, and various digital circuits are combined in addition to the one or more processors. The one or more memories store a program (instruction) for causing the one or more processors to execute each of the above processes. The one or more processors may execute each of the above processes according to the program read from the one or more memories, or may execute each of the above processes according to a logic circuit designed in advance to execute each of the above processes. The processor may be various processors suitable for controlling a computer, 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 plurality of physically separated processors may cooperate with each other to execute each of the above processes. For example, the processors mounted on each of the plurality of physically separated computers may cooperate with each other via a network such as a LAN (Local Area Network), a WAN (Wide Area Network), and the Internet to execute each of the above processes. The program may be installed in the memory via the network from an external server device or the like, or may be distributed in a state stored in a recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), and a semiconductor memory, and may be installed in the memory from the recording medium.

[0162] The above description includes the features appended below. [Appendix 1] An acquisition unit that acquires a control signal for controlling a slave station device that transmits and receives RF signals, A generation unit that generates a digital modulation signal including the control signal acquired by the acquisition unit, A transmission unit that transmits an optical signal including the digital modulation signal generated by the generation unit and an analog main signal to the slave station device via an optical fiber, and The generation unit generates the digital modulation signal according to a modulation method using a single carrier wave, a master station device.

[0163] [Appendix 2] A processing circuit in the master station device, The processing circuit, Acquires a control signal for controlling a slave station device that transmits and receives RF signals, Generates a digital modulation signal including the acquired control signal, Transmits an optical signal including the generated digital modulation signal and an analog main signal to the slave station device via an optical fiber, a master station device.

Explanation of symbols

[0164] 11, 11A, 11B AD / DA conversion unit 12, 12A, 12B Frequency conversion unit 13 Modulation signal generation unit 14 Multiplexer 15 Optical transceiver 16, 16A, 16B Modulation signal generation unit 21 Optical transceiver 22 Multiplexer 23, 23A, 23B Frequency conversion unit 24, 24A, 24B RF transceiver 25 Demodulation unit 26 Switching unit 27, 27A, 27B Demodulation unit 28, 28A, 28B Beam control unit 101, 102, 103 Master station device 201, 202, 203 Slave station device 111 Base station device 121 Communication terminal 161, 161A, 161B antennas 191 optical fiber 301, 302, 303 optical communication systems Fr1, Fr1A, Fr1B, Fr1C, Fr1D, Fr1E, Fr1F, Fr1G, Fr1H, Fr2, Frc, frequency bands Csw transmission / reception switching signal Cbm beam control signal VH, VL voltages

Claims

1. An acquisition unit that acquires a control signal for controlling a slave unit device that transmits and receives RF (Radio Frequency) signals, A generation unit that generates a digital modulation signal including the control signal acquired by the acquisition unit, A master unit device comprising: a transmission unit that transmits, via an optical fiber, an optical signal including the digital modulation signal generated by the generation unit and an analog main signal to the slave unit device.

2. The master unit device according to claim 1, wherein the acquisition unit acquires the control signal related to transmission and reception of RF signals via an antenna in the slave unit device.

3. The master unit device according to claim 2, wherein the acquisition unit acquires the control signal indicating the switching timing of transmission and reception of RF signals via the antenna.

4. The acquisition unit acquires the binary control signal indicating the transmission period and reception period of the RF signal, The master unit device according to claim 3, wherein the generation unit generates the digital modulation signal in which a carrier wave is modulated based on the control signal.

5. The acquisition unit acquires the control signal whose value changes at a timing before a predetermined time from the timing when the downlink period for downlink communication and the uplink period for uplink communication are switched, The master unit device according to claim 4, wherein the predetermined time is equal to or longer than the time required for demodulating the digital modulation signal in the slave unit device.

6. The master unit device according to claim 2, wherein the acquisition unit acquires the control signal indicating the transmission and reception range of RF signals via the antenna.

7. The master unit device according to any one of claims 1 to 6, wherein the generation unit generates the digital modulation signal according to the FSK (Frequency Shift Keying) method.

8. An optical communication method in a master unit device, A step of obtaining a control signal for controlling a slave station device that transmits and receives RF signals; A step of generating a digital modulation signal including the obtained control signal; An optical communication method including a step of transmitting an optical signal including the generated digital modulation signal and an analog main signal to the slave station device via an optical fiber.

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