Communication device and communication system

Abstract

One aspect of the present invention relates to a communication device including: a spreading unit for performing, using a spreading code, a spreading process on a control signal used when transmitting a wireless signal that is a main signal; a combining unit for electrically combining the main signal and the spread control signal; and an electro-optical converter for externally modulating light with the combined electrical signal and outputting the modulated optical signal to a transmission device.

Description

Communication device and communication system

[0001] The present invention relates to the technology of communication devices and communication systems.

[0002] Although attention has been paid to the millimeter-wave band capable of high-speed transmission, due to large propagation loss, it is necessary to deploy radio base stations at high density. Therefore, studies are underway to flexibly and economically deploy radio areas by dividing the radio base station function into an aggregation station and a remote station and applying analog RoF (Radio-over-Fiber) to simplify the remote station. Note that analog RoF is a technology that intensity-modulates an optical signal with a radio signal and transmits an optical signal in the form of a radio signal over an optical fiber, and is a technology that extracts the original radio signal only by performing optoelectronic conversion of the transmitted optical signal. Also, in an analog RoF system, since the number of wavelength resources that can be transmitted in one optical fiber is limited, it is required to suppress the number of wavelengths used for one remote station as much as possible to realize communication. In contrast, the SCM (Subcarrier multiplexing) method is generally known as a communication method capable of transmitting a main signal and a control signal with one wavelength (see, for example, Non-Patent Document 1).

[0003] For example, when the transmission method is SCM (Subcarrier multiplexing), the main signal and the control signal are electrically multiplexed and then modulated by an optical modulator for transmission. The main signal is an analog signal, and the control signal is a digital baseband signal.

[0004] Y. Yamamoto et al., “Experimental results of multiplexing transmission of 256-QAM 5G NR signal with control signal by SCM over 20-km analog RoF link”, Optics Communications, Vol.570, Available online 11 July 2024

[0005] However, in the conventional technology, as shown in Figure 10, the nonlinearity of the electro-optical converter 902 caused intermodulation distortion (IMD) when the amplitude of the electrical signal input to the optical modulator was large, resulting in a problem where the quality of the analog main signal, which has low noise immunity, deteriorated. Figure 10 is a diagram illustrating the distortion due to nonlinearity in the conventional communication device. In Figure 10, graph g901 is an example of the spectrum of the analog main signal input to the combining unit 901 of the aggregation station, graph g902 is an example of the spectrum of the digital control signal input to the combining unit 901, and graph g903 is an example of the spectrum when the analog main signal and control signal input from the combining unit 901 to the electro-optical converter 902 are combined. In graphs g901 to g903, the horizontal axis is frequency (Freq), and the vertical axis is signal power. Also, the symbol g910 is a diagram illustrating the nonlinearity of the electro-optical converter 902. The region indicated by code g911 represents a nonlinear region, waveform g912 is an example of an electrical signal, and waveform g913 is an example of an optically modulated signal. When the amplitude of an electrical signal falls within the nonlinear region, as in waveform g913, distortion occurs in the modulated optical signal, as in waveform g913. In view of the above circumstances, the present invention aims to provide a technology that can suppress the deterioration of communication quality due to IMD occurring between the main signal and the control signal.

[0006] One aspect of the present invention is a communication device comprising: a diffusion unit that performs diffusion processing on a control signal used when radiating a main signal, which is a wireless signal, using a diffusion code; a synthesis unit that electrically combines the main signal and the diffused control signal; and an electro-optic converter that externally modulates light with the synthesized electrical signal and outputs the modulated optical modulation signal to a transmitting device.

[0007] One aspect of the present invention is a communication system comprising a communication device and a transmitting device, wherein the communication device comprises a diffusion unit that performs diffusion processing using a diffusion code on a control signal used when radiating a main signal which is a wireless signal, a combining unit that electrically combines the main signal and the diffused control signal, and an electro-optical converter that externally modulates light with the combined electrical signal and outputs the modulated optical modulation signal to the transmitting device, and the transmitting device comprises an optical-electrical converter that directly detects the optical modulation signal input from the communication device and converts it into an electrical signal, an inverse diffusion unit that performs inverse diffusion processing on the electrical signal using the diffusion code, a control unit that demodulates the control signal input from the inverse diffusion unit, and an antenna that radiates the main signal output by the optical-electrical converter based on the demodulated control signal.

[0008] This invention makes it possible to suppress the deterioration of communication quality caused by IMD between the main signal and the control signal.

[0009] This figure shows an example configuration of the communication system of the first embodiment. This figure shows an example of the signal spectrum of each part in the communication system of the first embodiment. This is a sequence diagram of the processing of the communication system of the first embodiment. This figure shows a schematic of an example hardware configuration of the communication processing device applied to the embodiment. This figure shows an example configuration of the communication system of the second embodiment. This figure shows an example configuration of the aggregation station of the second embodiment. This figure shows an example configuration of the communication system of the third embodiment. This figure shows an example configuration of the aggregation station of the third embodiment. This figure shows an example configuration of the shared extension station of the third embodiment. This figure is for explaining nonlinear distortion in conventional communication devices.

[0010] Embodiments of the present invention will be described in detail with reference to the drawings.

[0011] <First Embodiment> Figure 1 shows an example of the configuration of the communication system of this embodiment. The communication system 1 includes, for example, a central station 2 and an outpost station 3 (transmitting device). The central station 2 and the outpost station 3 are connected by a transmission path 4 (for example, an optical fiber). The central station 2 includes, for example, a wireless signal processing unit 21, a processing delay compensation unit 22, a spectrum spread unit 23 (spreading unit), a combining unit 24, and an electro-optical converter 25. The outpost station 3 includes, for example, an optical-electrical converter 31, a separation unit 32, a spectrum despreading unit 33 (despreading unit), a control unit 34, and an antenna 35.

[0012] (Aggregation Station) The radio signal processing unit 21 generates the analog main signal, which is the radio signal, and the control signal (digital) used when radiating the radio signal from the transmission station 3. The radio signal processing unit 21 outputs the control signal to the spread spectrum unit 23 via the processing delay compensation unit 22. The radio signal processing unit 21 outputs the analog main signal to the combining unit 24.

[0013] The processing delay compensation unit 22 performs spectral spread processing using a spreading code on the transmitting side. The processing delay compensation unit 22 also extracts the baseband signal, which is the control signal, using a despreading code on the receiving side, and adjusts the transmission timing of the analog main signal, taking into account the delay until demodulation and control are applied.

[0014] The spread spectrum unit 23 performs spread spectrum processing on the control signal input from the wireless signal processing unit 21 using a spreading code. In spread spectrum processing, the signal is spread using a spreading code to a wider frequency band than the original signal's frequency band. The processing delay compensation unit 22 outputs the spread spectrum controlled signal to the synthesis unit 24.

[0015] The combining unit 24 electrically combines the analog main signal input from the wireless signal processing unit 21 and the control signal spread by the spread spectrum unit 23.

[0016] The electro-optic converter 25 modulates light externally using an electrical signal input from the synthesis unit 24. The electro-optic converter 25 outputs the modulated optical modulation signal to the transmission line 4.

[0017] (Output unit) The optical-electric converter 31 directly detects the optically modulated signal input from the transmission line 4 and converts it into an electrical signal, and outputs the converted electrical signal to the separation unit 32.

[0018] The separation unit 32 electrically separates the electrical signal input from the photoelectric converter 31 and outputs it to the antenna 35 and the spectral despreader 33.

[0019] The spectral despreading unit 33 performs spectral despreading on the electrical signal input from the separation unit 32 using the spreading code used in spectral spreading processing at the aggregation station 2. The spectral despreading unit 33 outputs the spectrally despreaded electrical signal to the control unit 34.

[0020] The control unit 34 demodulates the control signals input from the despread spectrum unit 33 and outputs the demodulated control signals to the antenna 35.

[0021] The antenna 35 radiates an analog main signal input separately from the separation unit 32 based on a control signal input from the control unit 34.

[0022] (Signal Spectra Examples of Each Part) Figure 2 shows examples of signal spectra of each part in the communication system of this embodiment. Graph g21 is an example of the spectrum of the radio signal (analog) output by the radio signal processing unit 21 to the combining unit 24. Graph g22 is an example of the spectrum of the control signal (digital) input to the spread spectrum unit 23. Graph g23 is an example of the spectrum of the control signal spread by the spread spectrum unit 23. Graph g24 is an example of the spectrum of the signal electrically combined by the combining unit 24 of the radio signal (analog) (g25) and the spread spectrum control signal (digital) (g26). In graphs g21 to g23, the horizontal axis is frequency and the vertical axis is signal power.

[0023] Graph g31 shows an example of the spectrum of an electrical signal input to the despreadspectral unit 33. Graph g32 shows an example of the spectrum of the main signal (g34) and control signal (digital) (g33) despreadspectralized by the despreadspectral unit 33. Graph g35 shows an example of the spectrum of the radio signal (analog) separated by the separation unit 32 and input to the antenna 35, and the spreadspectralized control signal. In graphs g31, g32, and g35, the horizontal axis represents frequency and the vertical axis represents signal power.

[0024] (Processing Procedure) Next, an example of the processing procedure performed by the aggregation station 2 and the branch station 3 will be described. Figure 3 is a sequence diagram of the processing of the communication system in this embodiment.

[0025] (Step S1) The wireless signal processing unit 21 of the aggregation station 2 generates a control signal (digital).

[0026] (Step S2) The spread spectrum unit 23 of the aggregation station 2 performs spread spectrum processing on the control signal using a spread code.

[0027] (Step S3) The combining unit 24 of the aggregation station 2 electrically combines the analog main signal input from the radio signal processing unit 21 and the spread spectrum control signal.

[0028] (Step S4) The electro-optic converter 25 of the aggregation station 2 modulates light externally with the electrical signal input from the combining unit 24 and outputs the modulated optical modulation signal to the transmission line 4.

[0029] (Step S5) The optical-electric converter 31 of the extension station 3 acquires the optically modulated signal input from the transmission line 4, and directly detects the acquired optically modulated signal to convert it into an electrical signal.

[0030] (Step S6) The separation unit 32 of the extension station 3 electrically separates the electrical signal input from the photoelectric converter 31.

[0031] (Step S7) The spectral dediffusion unit 33 of the projection station 3 performs spectral dediffusion processing on the electrical signal input from the separation unit 32 using a diffusion code.

[0032] (Step S8) The antenna 35 of the extension station 3 radiates an analog main signal input separately from the separation unit 32 based on the control signal.

[0033] Furthermore, some of the functional units of the aggregation station 2 and some of the functional units of the extension station 3 are configured using a processor such as a CPU (Central Processing Unit) and memory. Some of the functional units of the aggregation station 2 function, for example, as a radio signal processing unit 21, a processing delay compensation unit 22, a spread spectrum unit 23, and a combining unit 24, when the processor executes a program. Some of the functional units of the extension station 3 function, for example, as a separation unit 32, a despread spectrum unit 233, and a control unit 34, when the processor executes a program. Furthermore, all or part of the functions of some of the functional units of the aggregation station 2 and some of the functional units of the extension station 3 may be implemented using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The above program may be recorded on a computer-readable recording medium. Computer-readable recording media include, for example, portable media such as flexible disks, magneto-optical disks, ROMs, CD-ROMs, semiconductor memory devices (e.g., SSDs: Solid State Drives), and memory devices such as hard disks and semiconductor memory devices built into computer systems. The above program may be transmitted via a telecommunications line.

[0034] Figure 4 is a schematic diagram of an example hardware configuration of a communication processing device applied to this embodiment. The communication processing device 6 includes, for example, a processor 601, a main memory 602, a communication interface 603, an auxiliary storage device 604, an input / output interface 605, and an internal bus 606. The processor 601, the main memory 602, the communication interface 603, the auxiliary storage device 604, and the input / output interface 605 are connected to each other via the internal bus 606 so as to be able to communicate with each other. The communication processing device 6 may be applied, for example, to some functional units of a consolidation station 2 or to some functional units of an extension station 3. In this case, the radio signal processing unit 21, processing delay compensation unit 22, spectrum spread unit 23, and synthesis unit 24 of the consolidation station 2 may be configured using the processor 601, the main memory 602, and the auxiliary storage device 604. Also, the separation unit 32, spectrum despread unit 233, and control unit 34 of the extension station 3 may be configured using the processor 601, the main memory 602, and the auxiliary storage device 604. Furthermore, if the aggregation station 2 or the branch station 3 is equipped with a storage unit, the storage unit may be configured using, for example, a main memory device 602 and an auxiliary storage device 604.

[0035] As described above, in this embodiment, the control signal, which is a digital signal, is processed using a spreading code in the aggregation station 2. Then, in this embodiment, the control signal is extracted in the extension station 3 by using a despreading code.

[0036] As a result, according to this embodiment, the control signal undergoes spectral spread before being multiplexed with the main signal, resulting in a state that can be considered noise. Therefore, it becomes possible to suppress degradation of transmission quality without having to adjust the level of the analog main signal (wireless signal) with high precision in consideration of the input level of the control signal. Thus, according to this embodiment, when SCM transmission is performed with one wavelength on each side for communication between the aggregation station 2 and the extension station 3, it is possible to suppress degradation of communication quality due to IMD occurring between the main signal and the control signal.

[0037] (Variations) The radio signal processing unit 21 of the aggregation station 2 may include, for example, one of the following as a control signal: a BF (Beamforming) signal, a TDD (Time Division Duplex) signal, or a CLK signal (in the case of IFoF (Intermediate Frequency over Fiber)). The control signal may also include information on the spreading code used for spread spectrum. Alternatively, the control signal may be an analog signal, not limited to a digital signal (for example, an LO (Local Oscillator) used for frequency conversion). The LO, for example, has the function of generating a CW (Continuous Wave) signal based on a reference clock signal. The radio signal processing unit 21 may also send the main signal and control signal in advance, taking into account the transmission delay of the optical fiber.

[0038] Furthermore, the spread spectrum unit 23 of the aggregation station 2 may use a PN (Pseudo Random Noise) code as the spread spectrum code. A PN code is a digital signal in which bits of 1 and 0 are arranged almost randomly. The spread spectrum code used for spread spectrum processing may be communicated to the outgoing station 3 in advance, or it may be transmitted included in the control signal. The spread spectrum method used may be either direct spread spectrum (DS) or frequency hopping (FH).

[0039] Alternatively, the combining unit 24 of the aggregation station 2 may adjust the level of each input signal before combining them.

[0040] Furthermore, the electro-optical converter 25 of the aggregation station 2 may use an MZM (Mach-Zehner type optical intensity modulator), an EAM (electric field absorption modulator (EA modulator)), or a DML (directly modulated laser) as the modulator.

[0041] Further, the photoelectric converter 31 of the outrigger 3 may be a PD (Photo Diode) used as a photoelectric converter, which may be a pin-PD (PIN type photodiode), a UTC-PD, or an avalanche PD. The UTC-PD is a PD composed of a narrow bandgap optical absorption layer doped with a p-type and a carrier traveling layer of a wide bandgap that is undoped or doped with an n-type at a low concentration. The avalanche PD is a PD that accelerates carriers (electrons and holes) in a high electric field under reverse bias, excites (ionizes) electrons from the valence band to the conduction band by collision ionization, and performs avalanche amplification.

[0042] Further, the separation unit 32 of the outrigger 3 may have an unequal branching (for example, 1:9) as the separation ratio when electrically separating. The separation unit 32 may also include an electrical amplification unit. The separation unit 32 may also include a frequency filter.

[0043] Further, the spectral inverse diffusion unit 33 of the outrigger 3 may use, for example, a PN code as a spreading code. The spreading code used for the spectral spreading process may be transmitted to the outrigger side in advance, or may be transmitted included in a control signal. The method used for spectral spreading may be a direct spreading (DS) method or a frequency hopping (FH) method.

[0044] Further, the control unit 34 of the outrigger 3 may adjust the level for each input signal and then perform synthesis.

[0045] Further, the antenna 35 of the outrigger 3 may include an electrical amplification unit, a BFIC (beamforming integrated circuit), a frequency converter, a TDD switch, etc.

[0046] <Second Embodiment>In the first embodiment, an example where there is one relay station 3 was described. In this embodiment, a configuration example and a processing example when there are a plurality of relay stations 3 will be described. FIG. 5 is a diagram showing a configuration example of the communication system of this embodiment. The communication system 1A includes, for example, an aggregation station 2A, N (N is an integer of 2 or more) relay stations 3A (3A-1,..., 3A-N) (transmission devices), and an optical splitter 5. The aggregation station 2A and the optical splitter 5 are connected via a transmission line 4 which is, for example, an optical fiber. Also, the optical splitter 5 and the relay stations 3A (3A-1,..., 3A-N) are connected via a transmission line 4 which is, for example, an optical fiber.

[0047] FIG. 6 is a diagram showing a configuration example of the aggregation station of this embodiment. The aggregation station 2A includes, for example, a radio signal processing unit 21A, N spectrum spreading units 23 (23-1,..., 23-N) (spreading units), N combining units 24 (24-1,..., 24-N), N electro-optical converters 25 (25-1,..., 25-N), and an optical combining unit 26. Note that the aggregation station 2A may include a processing delay compensation unit 22 (22-1,..., 22-N) between the radio signal processing unit 21A and the N spectrum spreading units 23 (23-1,..., 23-N).

[0048] (Aggregation Station) The radio signal processing unit 21A generates N radio signals which are analog main signals and N control signals (digital) used when radiating these signals from the relay stations 3A. The radio signal processing unit 21A outputs the first analog main signal to the Nth analog main signal to the combining units 24-1 to 24-N respectively. The radio signal processing unit 21A outputs the first control signal to the Nth control signal to the spectrum spreading units 23-1 to 23-N respectively. Note that the signals actually flowing as the first analog main signal to the Nth analog main signal may be freely changed. (For example, if all are the same signal, it becomes an SFN (Single frequency network) configuration). Also, the content of the first control signal to the Nth control signal may be freely changed.

[0049] The spread spectrum unit 23-n (where n is an integer from 1 to N) performs spread spectrum processing on the nth control signal input from the wireless signal processing unit 21A using the nth spread code. The spread spectrum unit 23-n outputs the spread spectrum-processed nth control signal to the synthesis unit 24-n.

[0050] The combining unit 24-n electrically combines the nth analog main signal input from the wireless signal processing unit 21A with the nth control signal spread by the spread spectrum unit 23-n.

[0051] The electro-optic converter 25-n modulates light externally using an electrical signal input from the synthesis unit-n, and outputs the modulated optical modulation signal to the photosynthesis unit 26.

[0052] The photosynthesis unit 26 wavelength-multiplexes the optically modulated signals input from each of the electro-optical converters 25-1 to 25-N. The photosynthesis unit 26 outputs the wavelength-multiplexed optically modulated signal to the transmission line 4. Alternatively, instead of using the optical multiplexing unit, each extension station may be connected to the optical fiber in a single-star configuration.

[0053] (Optical Splitter) The optical splitter 5 splits the wavelength-division multiplexed optical modulation signal input from the transmission line 4 into as many branches as there are connected extension stations 3A, and outputs each of the branched wavelength-division multiplexed optical modulation signals to extension stations 3A-1 to 3A-N. The optical splitter 5 is installed, for example, at a relay point. An optical demultiplexer may also be used at the relay point. The optical demultiplexer demultiplexes a specific wavelength from the optical modulation signal input from the transmission line 4 and outputs it to the optical-electric converter 31 (31-1, ..., 31-N). An optical multiplexer may also be used at the relay point, or an optical splitter may be used if the wavelengths are different on the upper and lower ends. Furthermore, if a wavelength multiplexer is used instead of an optical splitter at the relay point, an optical circulator may be used as the optical demultiplexer, or the wavelength multiplexer may be omitted altogether.

[0054] (Extended Stations) Each of the extended stations 3A-1 to 3A-N is equipped with an optical-electric converter 31 (31-1, ..., 31-N), a separation unit 32 (32-1, ..., 32-N), a spectral dediffusion unit 33 (33-1, ..., 33-N) (dediffusion unit), a control unit 34 (34-1, ..., 34-N), an antenna 35 (35-1, ..., 35-N), and an optical demultiplexer 37 (37-1, ..., 37-N).

[0055] The optical demultiplexer 37-n of the extension station 3A-n extracts only the wavelength intended for the nth station from the light reaching the extension station 3A-n, since all of the light from the N stations is received from that light, and outputs the extracted optical signal to the photoelectric converter 31-n.

[0056] The optical-electric converter 31-n of the extension station 3A-n directly detects the optically modulated signal input from the optical splitter 5, converts it into an electrical signal, and outputs the converted electrical signal to the separation unit 32-n.

[0057] The separation unit 32-n of the extension station 3A-n electrically separates the electrical signal input from the photoelectric converter 31-n and outputs the separated signal to the antenna 35-n and the spectral despreader 33-n.

[0058] The spectral despreading unit 33-n of the extension station 3A-n performs spectral despreading on the electrical signal input from the separation unit-n using the nth spreading code used in spectral spread processing at the aggregation station 2A. The spectral despreading unit 33-n outputs the spectrally despreaded electrical signal to the control unit 34-n. The nth spreading code used in spectral despreading processing may be transmitted in advance from the aggregation station 2A, or it may be extracted from the nth control signal at the control unit 34-n and transmitted.

[0059] The control unit 34-n of the extension station 3A-n demodulates the nth control signal input from the spectral despreader 33-n and outputs the demodulated various control signals to the antenna 35-n.

[0060] The antenna 35-n of the extension station 3A-n radiates the nth analog main signal, which is input separately from the separation unit 32-n, based on the control signal input from the control unit 34-n.

[0061] As described above, according to this embodiment, even when outputting control signals and radio signals to multiple extension stations 3A, when SCM transmission is performed with one wavelength on each side for communication between the aggregation station 2A and the extension stations 3A, it is possible to suppress the deterioration of communication quality due to IMD occurring between the main signal and the control signal.

[0062] <Third Embodiment> In this embodiment, an example of a communication system that shares equipment will be described. Figure 7 is a diagram showing an example of the configuration of the communication system of this embodiment. The communication system 1B includes, for example, a carrier station 7, an aggregation station 2B, and a shared extension station 3B (transmitter). The aggregation station 2B and the shared extension station 3B are connected by a transmission line 4 (for example, an optical fiber). The carrier station 7 and the aggregation station 2B are connected by a transmission line 4 (for example, an optical fiber).

[0063] The operator stations 7 are stations operated by different operators, for example, a first operator station 71-1, a second operator station 71-2, and a third operator station 71-3. Each operator station 71 is equipped with a CD / DU 711 (711-1, 711-2, 711-3).

[0064] The CD / DU 711 processes the O-CU (centralized unit) and O-DU (distributed unit) of the O-RAN (a standard being considered for standardization by the O-RAN ALLIANCE) layer split. For example, in the case of the fifth-generation communication standard NR (a radio access technology specified by 3GPP® for fifth-generation mobile communication systems), it outputs an optical signal in the eCPRI (internal interface specification for radio base stations) format to an optical fiber. The nth operator station 71-n (where n is an integer from 1 to 3) includes in its output signal a signal containing the nth analog main signal and the nth control signal separated by the O-RU.

[0065] (Aggregation Station) Figure 8 shows an example of the configuration of the aggregation station in this embodiment. The aggregation station 2B includes, for example, a radio signal processing unit 21B, three spectrum spreading units 23B (23-1, 23B-2, 23B-3) (spreading unit), a combining unit 24B, and an electro-optical converter 25. The aggregation station 2B is operated by, for example, a business company.

[0066] The wireless signal processing unit 21B extracts the nth main signal and the nth control signal from the optical modulation signal input from the nth operator station 71-n (where n is an integer from 1 to 3). The wireless signal processing unit 21B outputs the extracted nth main signal to the combining unit 24B. The wireless signal processing unit 21B outputs the nth control signal to the spectrum spreading unit 23B-n. In Figure 8, an example is given in which optical modulation signals are input from the operator stations 71 of three operating companies, but it is possible to support any number of operator stations. Furthermore, the nth control signal output to the spectrum spreading unit 23B-n is not limited to the one extracted from the optical modulation signal input from the nth operator station 71, but may also include a control signal newly generated by the wireless signal processing unit 21B. Furthermore, the nth control signal may also include information on the spreading code used for spectrum spreading. Furthermore, the nth control signal is not limited to a digital signal but may also be an analog signal (for example, an LO used for frequency conversion). Furthermore, if the antenna is shared at the shared extension station 3B, the control signals may be unified and output.

[0067] The spread spectrum unit 23B performs spread spectrum processing on the nth control signal input from the wireless signal processing unit 21B using the nth spread spectrum code. The spread spectrum unit 23B outputs the spread spectrum-processed nth control signal to the synthesis unit 24B. Code g51 shows an example of the spectrum of the third control signal input to the spread spectrum unit 23B-3, with frequency on the horizontal axis and power on the vertical axis.

[0068] The combining unit 24B electrically combines the first to third main signals input from the wireless signal processing unit 21B with the first to third control signals spread by the respective spread spectrum units 23B-1 to 23B-3. Code g52 is an example of the spectrum of the spread spectrum first to third control signals input to the combining unit 24B, with frequency on the horizontal axis and power on the vertical axis. Code g60 is an example of the spectrum obtained by electrically combining the spread spectrum first to third control signals output from the combining unit 24B with the first main signal g61 to the third main signal g63, with frequency on the horizontal axis and power on the vertical axis.

[0069] The electro-optic converter 25 modulates light externally using an electrical signal input from the synthesis unit 24B. The electro-optic converter 25 outputs the modulated optical modulation signal to the transmission line 4.

[0070] (Shared Extension Station) Figure 9 shows an example of the configuration of a shared extension station in the embodiment. The shared extension station 3B includes, for example, an optical-electric converter 31, a separation unit 32B, three spectral despreaders 33 (33-1, 33-2, 33-3) (despreaders), three control units 34 (34-1, 34-2, 34-3), three antennas 35 (35-1, 35-2, 35-3), and a main signal separation unit 36.

[0071] The optical-electric converter 31 directly detects the optically modulated signal input from the transmission line 4 and converts it into an electrical signal, and outputs the converted electrical signal to the separation unit 32.

[0072] The separation unit 32B electrically separates the electrical signal input from the photoelectric converter 31 and outputs the separated electrical signal to the main signal separation unit 36 ​​and the spectral despreading units 33-1 to 33-3.

[0073] The main signal separation unit 36 ​​electrically separates the electrical signal input from the separation unit 32B into first to third main signals, for example, using a frequency filter, and outputs each to the corresponding antenna 35. If the antenna 35 is shared, separation by frequency filtering may be omitted. The symbol g70 is an example of a spectrum in which the first main signal g61 to the third main signal g63 are electrically combined with the spectrally spread first to third control signals input to the main signal separation unit 36, with the horizontal axis being frequency and the vertical axis being power.

[0074] The spectral despreading unit 33-n performs spectral despreading on the electrical signal input from the separation unit 32B using the nth spreading code used in spectral spread processing at the aggregation station 2B. The spectral despreading unit 33-n outputs the spectrally despreaded electrical signal to the control unit 34-n. The nth spreading code used in spectral despreading processing may be transmitted in advance from the aggregation station 2B, or it may be extracted from the nth control signal at the control unit 34-n and transmitted.

[0075] The control unit 34-n demodulates the nth control signal input from the despread spectrum unit 33-n and outputs various control signals to the antenna 35-n. If an analog signal is used instead of a digital signal as the nth control signal, it may be output directly to the antenna 35-n without demodulation processing.

[0076] Antennas 35 (35-1, 35-2, 35-3) radiate the nth main signal, which is output by a separate separation unit 32B and input via a main signal separation unit 36, based on the nth control signal input from the control unit 34-n. Note that the three antennas 35-1 to 35-3 may be shared.

[0077] In the example described using Figures 7 to 9, an example with three operator stations 71 was explained, but the number of operator stations 71 may be two or four. In this case, the aggregation station 2B is equipped with a spectral spread unit 23B corresponding to the number of operator stations 71, and the shared extension station 3B is equipped with a spectral inverse spread unit 33 and a control unit 34 corresponding to the number of operator stations 71.

[0078] Furthermore, this embodiment can be applied not only when multiple operators share equipment, but also when the same operator wants to share equipment with different frequencies, or when the same operator wants to provide different services with the same equipment.

[0079] As described above, according to the configuration and processing of this embodiment, even in a configuration where equipment is shared, when SCM transmission is performed with one wavelength on each side for communication between the aggregation station 2B and the shared extension station 3B, it is possible to suppress the deterioration of communication quality due to IMD occurring between the main signal and the control signal.

[0080] In the embodiments described above, analog RoF (Radio over Fiber) was used as an example, but by adding the necessary components, it can also be applied to analog IFoF (Intermediate Frequency over Fiber). Furthermore, in the embodiments described above, the wavelength arrangement during optical fiber transmission may be ODSB (Double Sideband Modulation), OSSB (Single Sideband Modulation), or OCS (Carrier Suppression Modulation). Also, in the embodiments described above, the optical fiber that is the transmission path 4 may be SMF (Single Mode Fiber), MMF (Multimode Fiber), MCF (Multicore Fiber), or polarization-maintaining fiber.

[0081] In the embodiments described above, communication from the aggregation station to the extension station (downlink) is used as an example. However, by swapping components other than the radio processing unit and antenna and using them symmetrically, the system can also be applied to communication from the extension station to the aggregation station (uplink).

[0082] Furthermore, in each of the embodiments described above, the device referred to as "aggregation station" may be a device called "CS (Central Station)," "Base Station," "CU (Central Unit)," "DU (Distributed Unit)," "Radio Unit (RU)," "master unit," etc.

[0083] In each of the embodiments described above, the device referred to as "extended station" may be a device called "Remote Radio Unit (RRU)", "Radio Unit (RU)", "Distributed Antenna (DA)", "slave unit", "antenna", etc.

[0084] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention.

[0085] The present invention is applicable to communication devices, transceivers, optical communication devices, communication systems, mobile fronthaul, and the like.

[0086] 1, 1A, 1B... Communication system, 2, 2A, 2B... Aggregation station, 3, 3A, 3-1,..., 3-N, 3A-1,..., 3A-N... Outgoing station, 3B... Shared outgoing station, 4... Transmission line, 5... Optical branching device, 7, 7 1-1, 71-2, 71-3...Business operator station, 21, 21A, 21B...Radio signal processing unit, 22...Processing delay compensation unit, 23, 23-1,..., 23-N, 23B-1, 23B-2, 23B-3...Spectrum Torl diffusion section, 24, 24-1, ..., 24-N, 24B... Synthesis section, 25, 25-1, ..., 25-N... Electro-optic converter, 26... Photosynthesis section, 31... Photoelectric converter, 32, 32B... Separation section, 33, 33-1, 33-2, 33-3... Spectral dediffusion section, 34, 34-1, 34-2, 34-3... Control section, 35, 35-1, 35-2, 35-3... Antenna, 36... Main signal separation section, 37... Optical demultiplexer

Claims

1. A communication device comprising: a diffusion unit that performs diffusion processing using a diffusion code on a control signal used when radiating a main signal, which is a wireless signal; a combining unit that electrically combines the main signal and the diffused control signal; and an electro-optic converter that externally modulates light with the combined electrical signal and outputs the modulated optically modulated signal to a transmitting device.

2. The communication device according to claim 1, wherein the spreading code used for spreading processing is transmitted in advance to the transmitting device, or is transmitted to the transmitting device as part of the control signal.

3. The communication device according to claim 1, wherein the control signal includes one of the Beamforming signal, the TDD (Time Division Duplex) signal, the CLK signal, and the spreading code.

4. The communication device according to claim 1, wherein the spreading code is a PN (Pseudo Random Noise) code.

5. The communication device according to claim 1, wherein the combining unit adjusts the level of each input signal before combining them.

6. A communication system comprising a communication device and a transmitting device, wherein the communication device comprises: a diffusion unit that performs diffusion processing using a diffusion code on a control signal used when radiating a main signal which is a wireless signal; a combining unit that electrically combines the main signal and the diffused control signal; and an electro-optical converter that externally modulates light with the combined electrical signal and outputs the modulated optical modulation signal to the transmitting device, wherein the transmitting device comprises: an optical-electrical converter that directly detects the optical modulation signal input from the communication device and converts it into an electrical signal; a despreading unit that performs despreading processing on the electrical signal using the diffusion code; a control unit that demodulates the control signal input from the despreading unit; and an antenna that radiates the main signal output by the optical-electrical converter based on the demodulated control signal.

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