Optical communication system and optical communication method

Abstract

To improve communication quality in an optical communication system.SOLUTION: An optical communication system is an optical communication system that is used for mobile communication and transmits and receives RF signals to and from a communication terminal, and includes a master station device and a slave station device that transmit and receive optical signals including analog signals. At least one of the master station device and the slave station device transmits and receives the optical signals within a same housing. The master station device transmits a downstream optical signal including a first analog signal in a first frequency band to the slave station device. The slave station device acquires the first analog signal from the received downstream optical signal and transmits a downstream RF signal based on the acquired first analog signal to the communication terminal. The slave station device transmits to the master station device an upstream optical signal including a second analog signal that is based on an upstream RF signal received from the communication terminal and is in a second frequency band different from the first frequency band. At least one of the first analog signal and the second analog signal is a signal in an intermediate frequency band.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to an optical communication system and an optical communication method. [Background technology]

[0002] Conventionally, technologies have been developed for optically modulating and transmitting analog signals. For example, Non-Patent Document 1 (Yoshihiro Imasa, "Basics and Use of RoF Devices," RF World, CQ Publishing Co., Ltd., October 29, 2011, No. 16, pp. 107-108) discloses an optical communication system using RoF (Radio over Fiber) technology. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Yoshihiro Imasu, "The Fundamentals and Use of RoF Devices", RF World, CQ Publishing Co., Ltd., October 29, 2011, No. 16, p. 107-108 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for a technique that goes beyond the technique described in Non-Patent Document 1 and that is capable of improving communication quality in optical communication systems.

[0005] The present disclosure has been made to solve the above-mentioned problems, and has as its object to provide an optical communication system and an optical communication method capable of improving communication quality in the optical communication system. [Means for solving the problem]

[0006] The optical communication system disclosed herein is an optical communication system used for mobile communication, which transmits and receives RF (Radio Frequency) signals with a communication terminal, and includes a master station device and a slave station device which transmit and receive optical signals including analog signals, and at least one of the master station device and the slave station device transmits and receives the optical signals within the same housing, the master station device transmits a downstream optical signal, which is the optical signal including a first analog signal in a first frequency band, to the slave station device, the slave station device acquires the first analog signal from the downstream optical signal received from the master station device and transmits to the communication terminal a downstream RF signal, which is the RF signal based on the acquired first analog signal, and the slave station device transmits to the master station device an upstream optical signal, which is the optical signal including the second analog signal in a second frequency band different from the first frequency band, and at least one of the first analog signal and the second analog signal is a signal in an intermediate frequency band.

[0007] One aspect of the present disclosure may be realized not only as a master station device having such a characteristic processing unit, but also as an optical communication method having such characteristic processing steps, or as a program for causing a computer to execute such steps. Furthermore, one aspect of the present disclosure may be realized as a semiconductor integrated circuit that realizes part or all of the master station device.

[0008] 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 having such characteristic processing steps, or as a program for causing a computer to execute such steps. Furthermore, one aspect of the present disclosure may be realized as a semiconductor integrated circuit that realizes part or all of the slave station device. Effect of the Invention

[0009] According to the present disclosure, it is possible to improve communication quality in an optical communication system. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram illustrating a configuration of an optical communication system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating a level of transmission noise generated from a downstream signal processing circuit in a master station device according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram illustrating a configuration of a master station device according to an embodiment of the present disclosure. [Figure 4] FIG. 4 is a diagram illustrating a configuration of a slave station device according to an embodiment of the present disclosure. [Diagram 5] FIG. 5 is a diagram illustrating an example of a frequency spectrum of a signal before attenuation by a BPF in a slave station device according to an embodiment of the present disclosure. [Figure 6] FIG. 6 is a diagram illustrating an example of a frequency spectrum of a signal after being amplified by an amplifier in a slave station device according to an embodiment of the present disclosure. [Figure 7] FIG. 7 is a diagram illustrating an example of a communication sequence in the optical communication system according to the embodiment of the present disclosure. [Figure 8] FIG. 8 is a diagram illustrating a configuration of a slave station device according to a modified example of the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] First, the contents of the embodiments of the present disclosure will be listed and described.

[0012] (1) An optical communications system according to an embodiment of the present disclosure is an optical communications system used for mobile communications, which transmits and receives RF signals with a communication terminal, and includes a master station device and a slave station device which transmit and receive optical signals including analog signals, wherein at least one of the master station device and the slave station device transmit and receive the optical signals within the same housing, wherein the master station device transmits a downstream optical signal to the slave station device, which is the optical signal including a first analog signal in a first frequency band, wherein the slave station device acquires the first analog signal from the downstream optical signal received from the master station device and transmits to the communication terminal a downstream RF signal, which is the RF signal based on the acquired first analog signal, wherein the slave station device transmits to the master station device an upstream optical signal, which is the optical signal including the second analog signal in a second frequency band different from the first frequency band, wherein at least one of the first analog signal and the second analog signal is a signal in an intermediate frequency band.

[0013] In this manner, a downstream optical signal including a first analog signal in a first frequency band is transmitted from a master station to a slave station, and an upstream optical signal including a second analog signal in a second frequency band different from the first frequency band is transmitted from the slave station to a master station, so that even if noise having a frequency component of the first analog signal sneaks into the second analog signal, it is easy to separate the second analog signal from the noise, thereby reducing the effect of the noise on the second analog signal, and thus improving the communication quality in the optical communication system.

[0014] (2) In the above (1), at least one of the master station device and the slave station device may include a filter that attenuates frequency components of the second analog signal that are outside the second frequency band.

[0015] With such a configuration, it is possible to attenuate noise that has sneaked into the second analog signal, thereby suppressing the occurrence of spurious signals in downstream circuits, such as an ADC (Analog to Digital Converter) that digitally converts the second analog signal.

[0016] (3) In the above (2), at least one of the master station device and the slave station device may include an amplifier that amplifies the second analog signal that has passed through the filter.

[0017] With this configuration, it is possible to use a filter and an amplifier to amplify the second analog signal, which is weaker than the first analog signal, without amplifying noise that has sneaked into the second analog signal.

[0018] (4) In any of (1) to (3) above, the slave station device may include a frequency conversion unit that converts the first analog signal into the downlink RF signal in a third frequency band and converts the uplink RF signal in the third frequency band into the second analog signal.

[0019] With this configuration, while analog signals in different frequency bands are transmitted between the master station device and the slave station device, RF signals in the same frequency band can be transmitted and received between the communication terminals.

[0020] (5) In the above (4), the frequency of the second frequency band may be a frequency band that is N times the frequency of the first frequency band, and the frequency conversion unit may include a frequency conversion circuit that converts the frequency of the first analog signal by N times, where N is a number greater than zero.

[0021] With this configuration, it is possible to use a common local signal to convert a first analog signal into a downstream RF signal and to convert an upstream RF signal into a second analog signal.

[0022] (6) In any one of (1) to (3) above, the slave station device transmits and receives the RF signal in the same frequency band to and from the communication terminal.

[0023] With this configuration, it is possible to carry out both upstream and downstream communications with a communication terminal using a common frequency band, and in an optical communication system in which the use of a common frequency band is likely to result in significant degradation of communication quality due to the intrusion of the above-mentioned noise, it is possible to reduce the impact of the above-mentioned noise on the second analog signal.

[0024] (7) An optical communication method according to an embodiment of the present disclosure is an optical communication method in an optical communication system used for mobile communication, which transmits and receives an RF signal to and from a communication terminal, the optical communication system including a master station device and a slave station device which transmit and receive an optical signal including an analog signal, and at least one of the master station device and the slave station device transmits and receives the optical signal within the same housing, the optical communication method includes a step of the master station device transmitting a downstream optical signal, the optical signal including a first analog signal in a first frequency band, to the slave station device, and a step of the slave station device receiving an RF signal from the master station device. the slave station device transmitting to the master station an upstream optical signal, which is the optical signal including the second analog signal in a second frequency band different from the first frequency band, the second analog signal being based on the upstream RF signal, which is the RF signal received from the communication terminal, and at least one of the first analog signal and the second analog signal being a signal in an intermediate frequency band.

[0025] In this manner, by transmitting a downstream optical signal including a first analog signal in a first frequency band from a master station to a slave station, and transmitting an upstream optical signal including a second analog signal in a second frequency band different from the first frequency band from the slave station to a master station, even if noise having a frequency component of the first analog signal sneaks into the second analog signal, it becomes easy to separate the second analog signal from the noise, thereby reducing the effect of the noise on the second analog signal, and thus improving the communication quality in the optical communication system.

[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 the description thereof will not be repeated. In addition, at least some of the embodiments described below may be arbitrarily combined.

[0027] [Configuration and basic operation] FIG. 1 is a diagram illustrating a configuration of an optical communication system according to an 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 and the slave station device 201 are connected to each other via an optical fiber 191. The optical communication system 301 is used as a fronthaul for mobile communication. The optical communication system 301 transmits and receives RF signals to and from a communication terminal 121. The optical communication system 301 may 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. 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 optical signals including analog signals via one optical fiber 191. Hereinafter, an 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 an 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 master station device 101 receives a digital signal including communication data from the base station device 111. The master station device 101 converts the received digital signal into an analog signal SAd, for example, in the IF (Intermediate Frequency) band, and transmits a downstream optical signal including the generated analog signal SAd to the slave station device 201 via the optical fiber 191.

[0030] 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 an analog signal SAd from the downstream optical signal received from the master station device 101, and generates an RF signal SRd of a frequency band fb3 by frequency-converting the acquired analog signal SAd, and transmits the RF signal SRd to the communication terminal 121. The RF signal SRd is an example of a downstream RF signal. The frequency band fb3 is an example of a third frequency band.

[0031] The slave station device 201 also receives an RF signal SRu of the frequency band fb3 including communication data from the communication terminal 121. The RF signal SRu is an example of an upstream RF signal. The slave station device 201 generates, for example, an analog signal SAu in the IF band by frequency-converting the RF signal SRu received from the communication terminal 121, and transmits an upstream optical signal including the generated analog signal SAu to the master station device 101 via the optical fiber 191.

[0032] 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 analog signal SAu from the received upstream optical signal, generates a digital signal by digitally converting the acquired analog signal SAu, and transmits the generated digital signal to the base station device 111.

[0033] [assignment] In the optical communication system 301, crosstalk may occur in the master station 101 and the slave station 201, causing noise caused by the analog signal SAd to leak into the analog signal SAu.

[0034] More specifically, the master station 101 includes a downstream signal processing circuit that amplifies the analog signal SAd, etc. The downstream signal processing circuit generates transmission noise TN, which is noise having the frequency component of the analog signal SAd.

[0035] Fig. 2 is a diagram showing the level of transmission noise generated from a downstream signal processing circuit in a master station device according to an embodiment of the present disclosure. In Fig. 2, the horizontal axis is frequency [Hz], and the vertical axis is power [dBm]. The dashed line in Fig. 2 indicates the level of transmission noise TN when the downstream signal processing circuit in the master station device 101 is stopped. The solid line in Fig. 2 indicates the level of transmission noise TN when the downstream signal processing circuit in the master station device 101 is started.

[0036] 2, when the downstream signal processing circuit in the master station 101 is started, transmission noise TN is generated. For example, the transmission noise TN constantly leaks out from the downstream signal processing circuit even when the downstream signal processing circuit is not processing the analog signal SAd. In the master station 101, the transmission noise TN generated from the downstream signal processing circuit may sneak into the analog signal SAu, thereby degrading the communication quality in the optical communication system.

[0037] Similarly, the slave station device 201 also includes a downstream signal processing circuit. In the slave station device 201, transmission noise TN generated from the downstream signal processing circuit may sneak into the analog signal SAu, thereby degrading the communication quality in the optical communication system.

[0038] Therefore, the optical communication system 301 according to the embodiment of the present disclosure solves the above problem by adopting the following configuration.

[0039] (Master and slave station devices) Fig. 3 is a diagram showing a configuration of a master station device according to an embodiment of the present disclosure. Referring to Fig. 3, the master station device 101 includes a transceiver unit 11, a digital to analog converter (DAC) 12, a low pass filter (LPF) 13, amplifiers 14 and 17, an optical modulator unit 15, an optical demodulator unit 16, a band pass filter (BPF) 18, an ADC 19, and an optical coupler CP1. The DAC 12, the LPF 13, and the amplifier 14 constitute at least a part of a downstream signal processing circuit.

[0040] Fig. 4 is a diagram showing a configuration of a slave station device according to an embodiment of the present disclosure. Referring to Fig. 4, the slave station device 201 includes an optical demodulator 21, an optical modulator 22, an antenna 23, a frequency converter 30, and an optical coupler CP2. The frequency converter 30 includes a frequency conversion circuit 31, amplifiers 32, 34, 37, and 39, mixers M1 and M2, a local oscillator LO1, BPFs 33, 36, and 38, and a transceiver 35. The amplifier 32 constitutes at least a part of a downstream signal processing circuit.

[0041] 3 and 4, the master station device 101 transmits a downstream optical signal including an IF signal SId of a frequency band fb1 to the slave station device 201. The frequency band fb1 is an example of a first frequency band. The IF signal SId is an example of a first analog signal.

[0042] For example, the slave station device 201 transmits and receives RF signals in the same frequency band to and from the communication terminal 121. More specifically, the slave station device 201 acquires an IF signal SId from the downstream optical signal received from the master station device 101, and generates an RF signal SRd in the frequency band fb3 by frequency-converting the acquired IF signal SId, and transmits the RF signal SRd to the communication terminal 121. The frequency of the RF signal SRd is, for example, 28 GHz.

[0043] The slave station device 201 also receives an RF signal SRu of a frequency band fb3 from the communication terminal 121. The slave station device 201 generates an IF signal SIu of a frequency band fb2 by frequency-converting the received RF signal SRu, and transmits an upstream optical signal including the generated IF signal SIu to the master station device 101. The frequency band fb2 is a frequency band different from the frequency band fb1. The frequency band fb2 is an example of a second frequency band. The IF signal SIu is an example of a second analog signal. The frequency of the RF signal SRu is, for example, 28 GHz. That is, the slave station device 201 performs frequency conversion of the IF signal SId and frequency conversion of the RF signal SRu to match the frequency of the RF signal SRu and to make the frequency of the IF signal SIu different from the frequency of the IF signal SId.

[0044] In the master station device 101 and the slave station device 201, signal processing for downstream communication and signal processing for upstream communication are performed in separate housings. That is, in the master station device 101 and the slave station device 201, transmission and reception of optical signals are performed in the same housing. For example, each unit in the master station device 101 is provided in the same housing and on the same board or in the same module. Also, each unit in the slave station device 201 is provided in the same housing and on the same board or in the same module. Note that in either the master station device 101 or the slave station device 201, signal processing for downstream communication and signal processing for upstream communication may be configured to be performed in separate housings.

[0045] The frequency of the frequency band fb2 is N times the frequency of the frequency band fb1, where N is a number greater than zero. As an example, the frequency of the frequency band fb2 is twice the frequency of the frequency band fb1. More specifically, the frequency of the carrier wave of the IF signal SIu is twice the frequency of the carrier wave of the IF signal SId.

[0046] (Downstream communication) The transmitting / receiving unit 11 receives a digital signal including communication data from the base station device 111. The transmitting / receiving unit 11 outputs the received digital signal to the DAC 12.

[0047] The DAC 12 generates an IF signal SId that is an analog signal SAd in the frequency band fb1 by converting the digital signal received from the transmission / reception unit 11 into an analog signal, and outputs the generated IF signal SId to the LPF 13. The frequency of the IF signal SId is, for example, 2 GHz.

[0048] The LPF 13 attenuates, of the frequency components of the IF signal SId received from the DAC 12, components outside a predetermined passband.

[0049] The amplifier 14 amplifies the IF signal SId that has passed through the LPF 13 , and outputs the amplified IF signal SId to the optical modulation section 15 .

[0050] The optical modulation unit 15 receives the IF signal SId from the amplifier 14 and generates a downstream optical signal having a wavelength λ1 by optically modulating the received IF signal SId. The optical modulation unit 15 outputs the generated downstream optical signal to the optical fiber 191 via the optical coupler CP1.

[0051] The optical demodulator 27 in the slave station 201 receives a downstream optical signal from the master station 101 via the optical fiber 191 and the optical coupler CP2, and outputs to the frequency converter 30 an IF signal SId, which is an electrical signal at a level corresponding to the intensity of the received downstream optical signal.

[0052] The frequency conversion unit 30 converts the IF signal SId into an RF signal SRd in a frequency band fb3. For example, a frequency conversion circuit 31 in the frequency conversion unit 30 converts the frequency of the IF signal SId to double. More specifically, the frequency conversion circuit 31 is a multiplication circuit that doubles the frequency of the signal received from the optical demodulation unit 27. The frequency conversion circuit 31 outputs the 4 GHz IF signal SId after frequency conversion to the amplifier 32.

[0053] Amplifier 32 amplifies IF signal SId received from frequency conversion circuit 31, and outputs the amplified IF signal SId to mixer M1.

[0054] For example, a local oscillator LO1 outputs a 24 GHz local signal to mixers M1 and M2.

[0055] Mixer M1 multiplies the 4 GHz IF signal SId received from amplifier 32 by the 24 GHz local signal received from local oscillator LO1 to generate an RF signal SRd of 28 GHz and output it to BPF 33.

[0056] BPF 33 attenuates frequency components outside a predetermined passband of RF signal SRd received from mixer M1.

[0057] The amplifier 34 amplifies the RF signal SRd that has passed through the BPF 33, and outputs the amplified RF signal SRd to the transceiver unit 35.

[0058] For example, the transmitting / receiving unit 35 includes a circulator. The transmitting / receiving unit 35 transmits the RF signal SRd received from the amplifier 34 to the communication terminal 121 via the BPF 36 and the antenna 23. More specifically, the transmitting / receiving unit 35 outputs the RF signal SRd received from the amplifier 34 to the BPF 36.

[0059] The BPF 36 is a filter for blocking unwanted waves and removing interference waves. The BPF 36 attenuates components outside a predetermined passband among the frequency components of the RF signal SRd received from the transceiver 35. The RF signal SRd that has passed through the BPF 36 is transmitted via the antenna 23.

[0060] (Upstream communication) The frequency conversion unit 30 converts the RF signal SRu of the frequency band fb3 into an IF signal SIu. More specifically, the transmission / reception unit 35 in the frequency conversion unit 30 receives the RF signal SRu from the communication terminal 121 via the antenna 23 and the BPF 36. The frequency of the RF signal SRd is, for example, 28 GHz. The transmission / reception unit 35 outputs the received RF signal SRu to the amplifier 37.

[0061] Amplifier 37 amplifies RF signal SRu received from transceiver unit 35, and outputs the amplified RF signal SRu to mixer M2.

[0062] Mixer M2 multiplies the 28 GHz RF signal SRu received from amplifier 37 by the 24 GHz local signal received from local oscillator LO1 to generate a 4 GHz IF signal SIu and output it to BPF38.

[0063] Fig. 5 is a diagram illustrating an example of a frequency spectrum of a signal before attenuation by the BPF in a slave station device according to an embodiment of the present disclosure. Fig. 5 illustrates a frequency spectrum of a signal before attenuation by the BPF 38. Referring to Fig. 5, a transmission noise TN having a frequency component of the IF signal SId may sneak into the 4 GHz IF signal SIu output from the mixer M2 to the BPF 38.

[0064] BPF38 attenuates frequency components of IF signal SIu received from mixer M2 other than frequency band fb2.

[0065] The amplifier 39 amplifies the IF signal SIu that has passed through the BPF 38 , and outputs the amplified IF signal SIu to the optical modulation section 22 .

[0066] Fig. 6 is a diagram illustrating an example of a frequency spectrum of a signal after amplification by an amplifier in a slave station device according to an embodiment of the present disclosure. Fig. 6 illustrates a frequency spectrum of a signal after amplification by an amplifier 39. Referring to Fig. 6, the BPF 38 attenuates the transmission noise TN that has entered the IF signal SIu. Furthermore, the amplifier 39 amplifies the IF signal SIu. Therefore, the BPF 38 and the amplifier 39 can amplify the IF signal SIu while attenuating the transmission noise TN.

[0067] 3 and 4 again, the optical modulation unit 22 receives the IF signal SIu from the amplifier 39 and generates an upstream optical signal with a wavelength λ2 by optically modulating the received IF signal SIu. The optical modulation unit 22 outputs the generated upstream optical signal to the optical fiber 191 via the optical coupler CP2.

[0068] The optical demodulator 16 in the master station 101 receives an upstream optical signal from the slave station 201 via the optical fiber 191 and the optical coupler CP1, and outputs to the amplifier 17 an IF signal SIu which is an electrical signal at a level corresponding to the intensity of the received upstream optical signal.

[0069] The amplifier 17 amplifies the IF signal SIu received from the optical demodulator 16 , and outputs the amplified IF signal SIu to the BPF 18 .

[0070] The BPF 18 attenuates components other than the frequency band fb2 among the frequency components of the IF signal SIu received from the amplifier 17. More specifically, the BPF 18 attenuates the transmission noise TN that has sneaked into the IF signal SIu, similar to the BPF 38 in the slave station device 201. Therefore, the amplifier 17 and the BPF 18 can amplify the IF signal SIu while attenuating the transmission noise TN.

[0071] The ADC 19 generates a digital signal by digitally converting the IF signal SIu that has passed through the BPF 18 , and outputs the generated digital signal to the transmission / reception unit 11 .

[0072] The transceiver unit 11 transmits the digital signal received from the ADC 19 to the base station device 111 .

[0073] [Operation flow] FIG. 7 is a diagram illustrating an example of a communication sequence in the optical communication system according to the embodiment of the present disclosure.

[0074] 7, first, the master station device 101 generates an IF signal SId of the frequency band fb1 by analog-converting a digital signal received from the base station device 111 (step S11).

[0075] Next, the master station 101 generates a downstream optical signal including the IF signal SId (step S12).

[0076] Next, the master station 101 transmits the generated downstream optical signal to the slave station 201 via the optical fiber 191 (step S13).

[0077] 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 IF signal SId from the received downstream optical signal (step S14).

[0078] Next, the slave station device 201 generates an RF signal SRd by frequency-converting the acquired IF signal SId (step S15).

[0079] Next, the slave station device 201 transmits the generated RF signal SRd to the communication terminal 121 via the antenna 23 (step S16).

[0080] Next, the slave station device 201 receives the RF signal SRu from the communication terminal 121 via the antenna 23 (step S17).

[0081] Furthermore, the slave station device 201 generates an IF signal SIu by frequency-converting the received RF signal SRu (step S18).

[0082] Next, the slave station device 201 generates an upstream optical signal including the IF signal SIu (step S19).

[0083] Next, the slave station device 201 transmits the generated upstream optical signal to the master station device 101 via the optical fiber 191 (step S20).

[0084] Next, the master station device 101 receives an upstream optical signal from the slave station device 201 via the optical fiber 191, and acquires an IF signal SIu from the received upstream optical signal (step S21).

[0085] Next, the master station device 101 generates a digital signal by digitally converting the acquired IF signal SIu, and transmits the generated digital signal to the base station device 111 (step S22).

[0086] In the optical communication system 301 according to the embodiment of the present disclosure, the slave station device 201 is configured to include the frequency conversion circuit 31, which is a multiplication circuit, but the present invention is not limited to this. The frequency conversion circuit 31 may be a frequency division circuit. For example, the frequency of the frequency band fb2 is half the frequency of the frequency band fb1. In this case, the master station device 101 transmits a downstream optical signal including an IF signal SId of, for example, 8 GHz to the slave station device 201 via the optical fiber 191. For example, the frequency conversion circuit 31 in the slave station device 201 is a frequency division circuit that converts the frequency of a signal received from the optical demodulation unit 27 to 1 / 2. The frequency conversion circuit 31 receives the IF signal SId of 8 GHz from the optical demodulation unit 27 and outputs the IF signal SId of 4 GHz after frequency conversion to the amplifier 32.

[0087] In addition, in the optical communication system 301 according to the embodiment of the present disclosure, the parent station device 101 is configured to transmit a downstream optical signal including an IF signal SId to the child station device 201, and the child station device 201 transmits an upstream optical signal including an IF signal SIu to the parent station device 101, but this is not limited to the above.

[0088] For example, the master station device 101 may be configured to transmit a downstream optical signal including an RF signal SRd to the slave station device 201 instead of the IF signal SId. In this case, the slave station device 201 acquires an 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. In this case, the frequency conversion unit 30 in the slave station device 201 includes a mixer M2 for converting the RF signal SRu into an IF signal SIu, but does not include a mixer M1 for converting the IF signal SId into an RF signal SRd.

[0089] Also, for example, the slave station device 201 may be configured to transmit an upstream optical signal including an RF signal SRu to the master station device 101 instead of the IF signal SIu. 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. In this case, the frequency conversion unit 30 in the slave station device 201 includes a mixer M1 for converting the IF signal SId to an RF signal SRd, but does not include a mixer M2 for converting the RF signal SRu to an IF signal SIu.

[0090] That is, the slave station device 201 may be configured to perform at least one of frequency conversion from the IF signal SId to the RF signal SRd and frequency conversion from the RF signal SRu to the IF signal SIu.

[0091] In the optical communication system 301 according to the embodiment of the present disclosure, the slave station device 201 is configured to transmit and receive RF signals of the same frequency band with the communication terminal 121, but this is not limited thereto. The slave station device 201 may be configured to transmit an RF signal SRd of a frequency band fb3a to the communication terminal 121 and receive an RF signal SRu of a frequency band fb3b that at least partially overlaps with the frequency band fb3a from the communication terminal 121. That is, the slave station device 201 may be configured to transmit and receive RF signals in a frequency band including the same frequency. For example, the frequency band fb3a and the frequency band fb3b have the same center frequency and different bandwidths. Alternatively, the frequency band fb3a and the frequency band fb3b have different center frequencies and the difference between the center frequencies of the frequency bands fb3a and fb3b is smaller than 1 / 2 of the sum of the bandwidths of the frequency bands fb3a and fb3b.

[0092] In addition, in the optical communication system 301 according to the embodiment of the present disclosure, the master station device 101 is configured to include the BPF 18, but this is not limited thereto. The master station device 101 may be configured not to include the BPF 18.

[0093] In addition, in the optical communication system 301 according to the embodiment of the present disclosure, the slave station device 201 is configured to include the BPF 38, but this is not limited thereto. The slave station device 201 may be configured not to include the BPF 38.

[0094] In addition, in the optical communication system 301 according to the embodiment of the present disclosure, the master station 101 is configured to include the amplifier 17, but this is not limited to this. The master station 101 may be configured not to include the amplifier 17.

[0095] In addition, in the optical communication system 301 according to the embodiment of the present disclosure, the slave station device 201 is configured to include the amplifier 39, but this is not limited thereto. The slave station device 201 may be configured not to include the amplifier 39.

[0096] Fig. 8 is a diagram showing a configuration of a slave station device according to a modified example of the embodiment of the present disclosure. With reference to Fig. 8, compared to the slave station device 201, the slave station device 202 according to the modified example includes a frequency conversion unit 40 instead of the frequency conversion unit 30. Compared to the frequency conversion unit 30, the frequency conversion unit 40 does not include the frequency conversion circuit 31 and further includes a local oscillator LO2.

[0097] Amplifier 32 amplifies 2 GHz IF signal SId received from optical demodulator 21, and outputs the amplified IF signal SId to mixer M1.

[0098] For example, local oscillator LO2 outputs a 26 GHz local signal to mixer M1.

[0099] Mixer M1 multiplies the 2 GHz IF signal SId received from amplifier 32 by the 26 GHz local signal received from local oscillator LO1 to generate an RF signal SRd of 28 GHz and output it to BPF 33.

[0100] The above-described embodiments should be considered as illustrative and not restrictive in all respects. 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.

[0101] Each process (each function) of the above-mentioned embodiment is realized by a processing circuit (circuitry) including one or more processors. The above-mentioned processing circuit may be composed of 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 above-mentioned one or more processors. The above-mentioned one or more memories store programs (instructions) that cause the above-mentioned one or more processors to execute each of the above-mentioned processes. The above-mentioned one or more processors may execute each of the above-mentioned processes according to the programs read from the above-mentioned one or more memories, or may execute each of the above-mentioned processes according to a logic circuit designed in advance to execute each of the above-mentioned processes. The above-mentioned processors may be 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). The above-mentioned physically separated processors may execute each of the above-mentioned processes in cooperation with each other. For example, the processors mounted on each of a 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), the Internet, etc. The program may be installed in the memory from an external server device or the like via the network, 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 Disc Read Only Memory), or a semiconductor memory, and installed in the memory from the recording medium.

[0102] The above description includes the following additional features. [Appendix 1] An optical communication system used for mobile communication, which transmits and receives RF signals between a communication terminal, A master station and a slave station are provided for transmitting and receiving optical signals including analog signals, In at least one of the master station device and the slave station device, transmission and reception of the optical signal are performed within the same housing; the parent station device transmits a downstream optical signal, which is the optical signal including the first analog signal in a first frequency band, to the child station device; the slave station device acquires the first analog signal from the downstream optical signal received from the master station device, and transmits to the communication terminal a downstream RF signal that is the RF signal based on the acquired first analog signal; the slave station device transmits to the master station device an upstream optical signal, the optical signal including the second analog signal in a second frequency band different from the first frequency band, the second analog signal being based on an upstream RF signal, the RF signal received from the communication terminal; At least one of the first analog signal and the second analog signal is an intermediate frequency band signal; the slave station device performs at least one of frequency conversion from the first analog signal to the downlink RF signal and frequency conversion from the uplink RF signal to the second analog signal; the master station device and the slave station device transmit and receive the optical signal via a single optical fiber; An optical communication system, wherein the first frequency band and the second frequency band are IF bands. [Explanation of symbols]

[0103] 11 Transmitter / receiver 12 DAC 13 LPF 14 Amplifier 15 Optical modulation section 16 Optical demodulation section 17 Amplifier 18 BPF 19 ADC 21 Optical demodulation section 22 Optical modulation section 23 Antenna 30,40 Frequency conversion section 31 Frequency conversion circuit 32 Amplifier 33 BPF 34 Amplifier 35 Transmitter / receiver 36 BPF 37 Amplifier 38 BPF 39 Amplifier 101 Master station device 111 Base station equipment 121 Communication terminal 191 Optical Fiber 201 Slave station device 301 Optical Communication Systems CP1, CP2 Optical Coupler M1,M2 Mixer LO1,LO2 local oscillator TN Transmission Noise SId IF signal

Claims

1. An optical communication system used for mobile communication, which transmits and receives RF (Radio Frequency) signals between a communication terminal, A master station and a slave station are provided for transmitting and receiving optical signals including analog signals, In at least one of the master station device and the slave station device, transmission and reception of the optical signal are performed within the same housing; the parent station device transmits a downstream optical signal, which is the optical signal including the first analog signal in a first frequency band, to the child station device; the slave station device acquires the first analog signal from the downstream optical signal received from the master station device, and transmits a downstream RF signal, which is the RF signal based on the acquired first analog signal, to the communication terminal; the slave station device transmits to the master station device an upstream optical signal, the optical signal including the second analog signal in a second frequency band different from the first frequency band, the second analog signal being based on an upstream RF signal, the RF signal received from the communication terminal; An optical communication system, wherein at least one of the first analog signal and the second analog signal is an intermediate frequency band signal.

2. 2. The optical communication system according to claim 1, wherein at least one of the master station device and the slave station device includes a filter that attenuates frequency components of the second analog signal that are not in the second frequency band.

3. 3. The optical communication system according to claim 2, wherein at least one of the master station device and the slave station device includes an amplifier that amplifies the second analog signal that has passed through the filter.

4. 4. The optical communication system according to claim 1, wherein the slave station device includes a frequency conversion unit that converts the first analog signal into the downstream RF signal in a third frequency band and converts the upstream RF signal in the third frequency band into the second analog signal.

5. The frequency of the second frequency band is a frequency band that is N times the frequency of the first frequency band, 5. The optical communication system according to claim 4, wherein the frequency conversion section includes a frequency conversion circuit that converts the frequency of the first analog signal by N times. Here, N is a number greater than zero.

6. The optical communication system according to claim 1 , wherein the slave station device transmits and receives the RF signal in the same frequency band to and from the communication terminal.

7. An optical communication method in an optical communication system used for mobile communication, which transmits and receives RF signals between a communication terminal, comprising: the optical communication system includes a master station device and a slave station device for transmitting and receiving optical signals including analog signals; In at least one of the master station device and the slave station device, transmission and reception of the optical signal are performed within the same housing; The optical communication method includes: a step of transmitting a downstream optical signal, which is the optical signal including the first analog signal in a first frequency band, from the master station device to the slave station device; a step of the slave station device acquiring the first analog signal from the downstream optical signal received from the master station device, and transmitting a downstream RF signal, which is the RF signal based on the acquired first analog signal, to the communication terminal; the slave station device transmitting to the master station device an upstream optical signal, the optical signal including the second analog signal in a second frequency band different from the first frequency band, the second analog signal being based on an upstream RF signal, the RF signal received from the communication terminal; 13. An optical communication method, wherein at least one of the first analog signal and the second analog signal is an intermediate frequency band signal.

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