Communication device

Abstract

Provided is a communication device composed of a first communication device that has a signal processing function, and at least one second communication device that is connected to the first communication device via an optical transmission line and that has a communication function, wherein: the first communication device comprises a frequency multiplexing unit that generates a multiplexed signal by frequency multiplexing signals having differing intermediate frequency bands and at least one local signal having a frequency, and a first conversion unit that converts the multiplexed signal generated by the frequency multiplexing unit to an optical signal and outputs the optical signal; and the second communication device comprises a second conversion unit that converts the optical signal output from the first communication device to the multiplexed signal, and a plurality of mixers that, with respect to the signals having differing intermediate frequency bands included in the multiplexed signal, generate signals having differing radio frequencies by using the local signal multiplied by differing multiplication factors.　

Description

Communication device

[0001] This invention relates to a communication device.

[0002] A communication system has been proposed that divides the functions of a radio base station into a central station (CS) and a remote radio unit (RRU), and applies analog RoF (Radio-over-Fiber) between the central station and the remote radio unit. In a communication system that applies analog RoF, the signal processing function of the radio base station is separated into the central station and the antenna function into the remote radio unit. In this way, a communication system that applies analog RoF can simplify the remote radio unit, allowing for flexible and economical deployment of the radio area.

[0003] Conventionally, in communication systems using analog RoF, there are two methods for multiplexing and transmitting multiple signals: Wavelength Division Multiplexing (WDM) and Sub-Carrier Multiplexing (SCM). Sub-carrier multiplexing, in particular, is highly efficient because it uses the same wavelength for transmission. Therefore, it is an effective method for multiplexing multiple signals.

[0004] Examples of use cases for multiplexing and transmitting multiple signals include sharing communication equipment among multiple operators or among multiple systems (see, for example, Non-Patent Document 1). However, it is known that when multiple frequency-multiplexed signals are optically modulated, intermodulation distortion occurs due to the nonlinearity of optical modulators and optical fiber transmission (see, for example, Non-Patent Document 2).

[0005] Xiao Li, Chunlei Hu, Weiliang Xie, “Research on 5G Shared Network Access Residency Strategy”, 2022 IEEE International Symposium on Broadband Multimedia Systems and Broadcasting (BMSB), July 2022.Keisuke Hayasaka, Takeshi Higashino, Katsutoshi Tsukamoto and Shozo Komaki, “A Theoretical Estimation of IMD on Heterogeneous OFDM Service over SCM RoF Link”, 2011 International Topical Meeting on Microwave Photonics jointly held with the 2011 Asia-Pacific Microwave Photonics Conference, December 2011.

[0006] In communication systems using analog RoF, when subcarrier multiplexing is employed, multiple radio signals are transmitted side-by-side on adjacent channels. As a result, not only the distortion components of the own signal but also the distortion components of adjacent channels leak into the own channel, leading to a significant increase in intermodulation distortion. Consequently, there is a problem of signal quality degradation. This problem arises in communication systems that employ analog transmission technologies such as IF-over-Fiber (IFoF), which transmits IF (Intermediate Frequency) signals via analog RoF between a central station and an outpost, and RF-over-Fiber (RFoF), which transmits RF (Radio Frequency) signals via analog RoF.

[0007] In view of the above circumstances, the present invention aims to provide a technology that can reduce the effects of intermodulation distortion even when multiple signals are transmitted via subcarrier multiplexing.

[0008] One aspect of the present invention is a communication device comprising a first communication device having a signal processing function and one or more second communication devices having a communication function and connected to the first communication device via an optical transmission path, wherein the first communication device includes a frequency multiplexing unit that generates a multiplexed signal by frequency multiplexing signals of different intermediate frequency bands and local signals of one or more frequencies, and a first conversion unit that converts the multiplexed signal generated by the frequency multiplexing unit into an optical signal and outputs it, and the second communication device includes a second conversion unit that converts the optical signal output from the first communication device into the multiplexed signal, and a plurality of mixers that generate signals of different radio frequencies using local signals that have been multiplied by different multipliers with respect to signals of different intermediate frequency bands included in the multiplexed signal.

[0009] The present invention makes it possible to reduce the effects of intermodulation distortion even when multiple signals are transmitted via subcarrier multiplexing.

[0010] This figure shows an example of the configuration of a conventional communication system. This figure shows an example of the configuration of a communication system in an embodiment. This is a sequence diagram showing the processing flow of the communication system in an embodiment.

[0011] One embodiment of the present invention will be described below with reference to the drawings.

[0012] (Conventional Communication System) Before describing the contents of the present invention, the configuration of a conventional communication system will be described. Figure 1 is a diagram showing an example of the configuration of a conventional communication system S. The communication system S comprises an aggregation station 1 and an extension station 2. The aggregation station 1 and the extension station 2 constitute a single base station B. The aggregation station 1 has the signal processing function, which is one of the signal processing functions and communication functions provided by the base station B. The extension station 2 has the communication function, which is one of the signal processing functions and communication functions provided by the base station B. The aggregation station 1 and the extension station 2 are connected by an optical transmission path 3. The optical transmission path 3 is, for example, an optical fiber. The optical transmission path 3 may also be equipped with one or more optical amplifiers that amplify optical signals.

[0013] In FIG. 1, a configuration is shown in which one distribution station 2 is connected to the aggregation station 1. However, a plurality of distribution stations 2 may be connected to the aggregation station 1. When a plurality of distribution stations 2 are connected to the aggregation station 1, an optical splitter such as an optical coupler is provided between the aggregation station 1 and the distribution stations 2. In the communication system S, for example, the technology of analog RoF is used between the aggregation station 1 and the distribution stations 2.

[0014] [Configuration of Aggregation Station 1] The aggregation station 1 includes a signal processing unit 11, a frequency multiplexing unit 12, a LO 13, an IF unit 14, and an E / O unit 15. In FIG. 1, the aggregation station 1 includes N (N is an integer of 2 or more) signal processing units 11. Each signal processing unit 11 generates an electrical signal (for example, a main signal and a control signal). The frequency multiplexing unit 12 performs frequency multiplexing by arranging the electrical signals generated by each signal processing unit 11 at adjacent frequencies.

[0015] The LO 13 is a local oscillator that outputs a local signal of frequency f ＬＯ . The IF unit 14 converts the signal frequency-multiplexed by the frequency multiplexing unit 12 into a signal in the intermediate frequency band (hereinafter referred to as an "IF signal"). The E / O unit 15 converts the signal into an optical signal based on the local signal of frequency f ＬＯ output from the LO 13 and the IF signal converted by the IF unit 14. The optical signal converted by the E / O unit 15 is transmitted to the distribution station 2 via the optical transmission line 3.

[0016] [Configuration of Distribution Station 2] The distribution station 2 includes an O / E unit 21, a filter 22, a mixer 23, an antenna 24, and a multiplier 25. In FIG. 1, the distribution station 2 includes (N + 1) filters 22, N mixers 23, N antennas 24, and N multipliers 25. The O / E unit 21 detects the optical signal input via the optical transmission line 3 and converts it into an electrical signal. Each filter 22 is a band-pass filter for separating sub-carrier multiplexed signals. That is, each filter 22 is a filter for extracting a signal of a predetermined frequency. For example, the filter 22-i (1 ≤ i ≤ N) is a filter that can pass through the frequency band in which the electrical signal generated by the signal processing unit 11-i is arranged. The filter 22-(N + 1) has a frequency f ＬＯIt is a filter that extracts the local signal.

[0017] Mixer 23 mixes the main signal output from filter 22 and the local signal with frequency M×f multiplied by M via multiplier 25 to convert the frequency. As a result, mixer 23 generates a signal in the RF band. For example, mixer 23-i mixes the signal extracted by filter 22-(N + 1) with the local signal of frequency M×f multiplied by M via multiplier 25-i and the main signal extracted by filter 22-i. ＬＯ The antenna 24 is provided in association with the mixer 23. The antenna 24 radiates the signal output from the associated mixer 23 into space as radio waves. The wireless method by the repeater station 2a is not particularly limited. ＬＯ and the main signal extracted by filter 22-i. The antenna 24 is provided in association with the mixer 23. The antenna 24 radiates the signal output from the associated mixer 23 into space as radio waves. The wireless method by the repeater station 2a is not particularly limited.

[0018] In the conventional communication system S shown in FIG. 1, the concentration station 1 performs frequency multiplexing by arranging the electrical signals generated by each signal processing unit 11 at adjacent frequencies in the frequency multiplexing unit 12, and converts the signal after frequency multiplexing into an optical signal by converting the signal whose frequency has been converted to an intermediate frequency. The signals are close to each other in the sidebands of the optical signal. Therefore, the inter-channel mutual phase distortion increases during the conversion from the electrical signal to the optical signal or during the transmission through the optical transmission line 3. Further, even after the conversion from the optical signal to the electrical signal by the repeater station 2, the signals are close to each other. Therefore, it is necessary to use a sharp filter 22 in the repeater station 2 to extract the components of each signal.

[0019] To solve the above problems, in this invention, the aggregation station 1 converts each electrical signal generated by the signal processing unit 11 into an IF signal of a different frequency and then frequency multiplexes it. This widens the spacing between signals (widens the guard band). Subsequently, the aggregation station 1 converts the frequency multiplexed signals from electrical signals to optical signals. As a result, each signal is spaced apart in the sidebands of the optical signal. Therefore, mutual phase distortion between adjacent channels can be reduced during conversion from electrical signals to optical signals and during transmission on the optical transmission line 3. Furthermore, the frequency spacing between signals is widened even after conversion from optical signals to electrical signals by the extension station 2. Therefore, the characteristics of the filter 22 can be relaxed at the extension station 2. The following describes a specific configuration for realizing the above processing.

[0020] (Embodiment) Figure 2 shows an example of the configuration of a communication system 100 in an embodiment. The communication system 100 comprises a central station 1a and an extension station 2a. The central station 1a and the extension station 2a constitute a single base station Ba (communication device). The central station 1a has the signal processing function, which is one of the signal processing functions and communication functions separated from the base station Ba. The extension station 2a has the communication function, which is one of the signal processing functions and communication functions separated from the base station Ba. The central station 1a and the extension station 2a are connected by an optical transmission path 3. The optical transmission path 3 is, for example, an optical fiber. The optical transmission path 3 may also be equipped with one or more optical amplifiers for amplifying optical signals.

[0021] Figure 2 shows a configuration in which one branch station 2a is connected to the aggregation station 1a, but multiple branch stations 2a may be connected to the aggregation station 1a. When multiple branch stations 2a are connected to the aggregation station 1a, an optical splitter such as an optical coupler is provided between the aggregation station 1a and the branch stations 2a. Alternatively, multiple branch stations 2a may be connected from the aggregation station 1a using multiple optical transmission paths. In the communication system 100, for example, analog RoF technology is used between the aggregation station 1a and the branch stations 2a.

[0022] [Configuration of Aggregation Station 1a] The aggregation station 1a includes a signal processing unit 11, a frequency multiplexing unit 12a, a LO 13, an IF unit 14a, and an E / O unit 15a. The aggregation station 1a is one aspect of the first communication device. Since the signal processing unit 11 and the LO 13 perform the same processes as those described in FIG. 1, their descriptions are omitted. In FIG. 2, the aggregation station 1a includes N signal processing units 11 and N IF units 14a. Each signal processing unit 11 generates an electrical signal. For example, the signal processing unit 11-i generates a signal with a frequency f ｉ corresponding to the operator i. As described above, in the case of a configuration where a plurality of remote stations 2a are connected from the aggregation station 1a using a plurality of optical transmission lines, the aggregation station 1a includes the same number of E / O units 15a as the remote stations 2a. In this case, the signal output from the frequency multiplexing unit 12a is branched and input to each E / O unit 15a.

[0023] The IF unit 14a generates an IF signal that can be converted at a frequency generated from a local signal with a frequency f ＬＯ with different multiplication factors. For example, the IF unit 14a-i generates an IF signal with a frequency f ＩＦｉ based on the following formula (1). The IF unit 14a is one aspect of the frequency conversion unit.

[0024]

[0025] In formula (1), f ＲＦｉ represents the radio frequency for transmitting the electrical signal generated by the signal processing unit 11-i, and M ｉ represents the multiplication factor. Therefore, the IF unit 14a-1 generates an IF signal with a frequency f １ that can be converted at a frequency f ＬＯ generated by the multiplication factor M ＬＯ and the local signal with a frequency f ＩＦ１ . The IF unit 14a-N generates an IF signal with a frequency f Ｎ that can be converted at a frequency Nf ＬＯ generated by the multiplication factor M ＬＯ and the local signal with a frequency f ＩＦＮ .

[0026] The frequency multiplexing unit 12a multiplexes the frequencies f ＩＦ１ to f ＩＦＮEach IF signal and the frequency f output from LO13 ＬＯ The local signal is frequency-multiplexed. The E / O unit 15a converts the frequency-multiplexed signal by the frequency-multiplexing unit 12a into an optical signal. In this way, the signals generated by each signal processing unit 11 are transmitted as subcarriers using different intermediate frequency bands. As a result, guard bands are generated between the signals generated by each signal processing unit 11, which reduces the effects of intermodulation distortion during transmission in the optical transmission path 3.

[0027] [Configuration of the extension station 2a] The extension station 2a comprises an O / E unit 21, a filter 22a, a mixer 23, an antenna 24, and a frequency multiplier 25a. Note that the O / E unit 21 and the antenna 24 are the same as those described in Figure 1, so their explanation is omitted. In Figure 2, the extension station 2a comprises (N+1) filters 22a, N mixers 23, N antennas 24, and N frequency multipliers 25a. The extension station 2a is one embodiment of the second communication device.

[0028] Each filter 22a is a band-pass filter for separating subcarrier multiplexed signals. That is, each filter 22a is a filter for extracting signals of a predetermined frequency. For example, filter 22a-i is a filter for the frequency f converted by each IF unit 14a-i. ＩＦｉ This is a filter that can pass the IF signal. Filter 22a-(N+1) has a frequency f ＬＯ This is a filter that extracts the local signal.

[0029] The frequency multiplier 25a is installed between the filter 22a-(N+1) that outputs the local signal and the mixer 23. For example, the frequency multiplier 25a-i is installed between the filter 22a-(N+1) that outputs the local signal and the mixer 23-i. The frequency multiplier 25a-i takes the frequency f output from the filter 22a-(N+1) ＬＯ The local signal is multiplied by a predetermined number M ｉ The frequency is multiplied by a factor of 1. The frequency multiplier 25a-1 multiplies the frequency f output from filter 22a-(N+1), for example. ＬＯ The local signal multiplied by M １ Multiply by (M １The frequency multiplier 25a-2 multiplies the frequency f output from filter 22a-(N+1), for example. ＬＯ The local signal multiplied by M ２ Multiply by (M ２ The frequency multiplier 25a-N multiplies the frequency f output from filter 22a-(N+1), for example. ＬＯ The local signal multiplied by M Ｎ Multiply by (M Ｎ (Multiply by a factor of two.)

[0030] Mixer 23 mixes the main signal output from filter 22a with the local signal whose frequency has been multiplied by the frequency multiplier 25a to convert the frequency. This allows mixer 23 to generate an RF band signal. For example, mixer 23-i mixes the main signal output from filter 22a-i with the local signal whose frequency has been multiplied by the frequency multiplier 25a-i to convert the frequency. ｉ The doubled local signal is mixed with the local signal.

[0031] (Operation) Figure 3 is a sequence diagram showing the processing flow of the communication system 100 in the embodiment. Each signal processing unit 11 of the aggregation station 1a generates an electrical signal (step S101). The signal processing unit 11-i outputs the generated electrical signal to the IF unit 14-i. The IF unit 14-i outputs the electrical signal from the signal processing unit 11-i to a different frequency f ＩＦｉ Convert to an IF signal (step S102). The IF section 14-i is converted to the frequency f ＩＦｉ The IF signal is output to the frequency multiplexing unit 12a. LO13 is at frequency f ＬＯ The local signal is output to the frequency multiplexing unit 12a.

[0032] The frequency multiplexing unit 12a receives the frequency f output from each IF unit 14-i (IF units 14-1 to 14-N). ＩＦｉ IF signal (frequency f ＩＦ１ ~f ＩＦＮ The IF signal and the frequency f output from LO13 ＬＯFrequency multiplexing is performed using the local signal (step S103). As a result, the frequency multiplexing unit 12a generates a multiplexed signal. The frequency multiplexing unit 12a outputs the generated multiplexed signal to the E / O unit 15a. The E / O unit 15a converts the multiplexed signal output from the frequency multiplexing unit 12a into an optical signal (step S104). The E / O unit 15a outputs the converted optical signal to the optical transmission line 3 (step S105). The optical signal output from the E / O unit 15a is input to the extension station 2a via the optical transmission line 3.

[0033] The O / E unit 21 of the extension station 2a converts the optical signal input via the optical transmission path 3 into an electrical signal (step S106). The converted electrical signal is the multiplexed signal output from the frequency multiplexing unit 12a, as described above. The O / E unit 21 outputs the converted electrical signal to filters 22a-1 to 22a-(N+1). Filters 22a-1 to 22a-(N+1) perform filtering on the electrical signal output from the O / E unit 21 (step S107).

[0034] Filter 22a-i, for example, uses the frequency f generated by the IF section 14a-i from the multiplexed signal. ＩＦｉ The IF signal is extracted. The frequency f extracted by filter 22a-i ＩＦｉ The IF signal is input to mixer 23-i. Filter 22a-(N+1) filters, for example, multiplexed signals to frequency f ＬＯ The local signal is extracted. The frequency f extracted by filter 22a-(N+1) ＬＯ The local signal is input to the frequency multiplier 25a-i. The frequency multiplier 25a-i receives the input frequency f ＬＯ The local signal M ｉ The signal is doubled and output to mixer 23-i (step S108).

[0035] Mixer 23-i processes the frequency f extracted by filter 22a-i. ＩＦｉ The IF signal and the frequency multiplier 25a-i are used to make the frequency M ｉ Doubled local signal (frequency M ｉ f ＬＯ The local signal of ( ) is mixed with (step S109). As a result, mixer 23-i has a frequency f ＲＦｉIt generates a signal of the frequency f. Mixer 23-i generates a signal of the frequency f. ＲＦｉ The signal is output to antenna 24-i. Antenna 24-i receives the frequency f output from mixer 23-i. ＲＦｉ The signal is radiated into space as radio waves (step S110). For example, antenna 24-1 has a frequency f ＲＦ１ The signal is radiated into space as radio waves, and antenna 24-N emits the signal at frequency f ＲＦＮ The signal is emitted into space as radio waves.

[0036] According to the communication system 100 configured as described above, the aggregation station 1a receives signals of different intermediate frequency bands and frequency f Ｌｏ The system includes a frequency multiplexing unit 12a that generates a multiplexed signal by frequency multiplexing with the local signal, and an E / O unit 15a that converts the multiplexed signal generated by the frequency multiplexing unit 12a into an optical signal and outputs it. The branch station 2a includes an O / E unit 21 that converts the optical signal output from the aggregation station 1a into a multiplexed signal, and a plurality of mixers 23 that generate signals of different radio frequencies using local signals that have been multiplied by different multipliers for signals of different intermediate frequency bands included in the multiplexed signal.

[0037] In this manner, at the aggregation station 1a, the multiplexed radio signals are subcarrier multiplexed using IF signals of different intermediate frequencies. This creates guard bands between the signals. Consequently, the spacing between signals becomes wider compared to the conventional communication system S. This makes it less likely for distortion components of signals placed at different frequencies to leak into the channel. As a result, the effect of intermodulation distortion is reduced. Therefore, even when multiple signals are transmitted using subcarrier multiplexing, it becomes possible to mitigate the effects of intermodulation distortion.

[0038] Furthermore, the communication system 100 converts IF signals of different intermediate frequencies from a common local signal to frequencies that can be generated at different frequency multiplication factors. This allows the local signal for frequency conversion to be shared. For example, when subcarrier multiplexing signals from different carriers, sharing the local signal between carriers eliminates the need to transmit a local signal for each carrier. This enables efficient use of the optical transmission bandwidth and a reduction in the functionality of the extension station 2a. In this embodiment, the process between different carriers was described as an example, but the present invention can be applied when transmitting multiple signals with different radio frequencies. Therefore, it may also be applied when operating at different frequencies within the same carrier or when providing different services within the same carrier.

[0039] Furthermore, in the communication system 100, as described above, the spacing between signals transmitted via subcarrier multiplexing becomes wider. This allows the requirements for the filter 22 used by the extension station 2a to extract signals of each frequency after conversion from optical signals to electrical signals to be relaxed compared to the conventional communication system S.

[0040] (Modification 1) Any optical fiber capable of transmitting optical signals may be used, such as a single-mode fiber, multi-mode fiber, multi-core fiber, or dispersion-shift fiber.

[0041] (Modification 2) The optical fiber transmission method used between the aggregation station 1a and the extension station 2a may be any of the RFoF or IFoF transmission methods.

[0042] (Modification 3) Control signals such as beamforming control signals may be multiplexed at the aggregation station 1a.

[0043] (Modification 4) The aggregation station 1a or the extension station 2a may be equipped with components such as amplifiers and switches, and functions such as beamforming.

[0044] (Modification 5) In the embodiments described above, the device referred to as "extended station" may also be called by terms such as RRU (Remote Radio Unit), RU (Radio Unit), Distributed Antenna (DA), slave unit, antenna, etc. In the embodiments described above, the device referred to as "aggregation station" may also be called by terms such as CS (Central Station), Base Station, CU (Central Unit), DU (Distributed Unit), RU (Radio Unit), master unit, etc. The signal processing unit 11 may also be a wireless device that has a connection port to an antenna. For example, it may be a device called a BBU (Base Band Unit) or RU (Radio Unit). In that case, the signal processing unit 11 may be located outside (in a different device) of the aggregation station 1a, and the aggregation station 1a only needs to have a connection port to the wireless device. The signal output from the wireless device may be a baseband signal, an IF signal of the wireless device's own intermediate frequency, or an RF signal. ＩＦｉ If the IF signal is output, the aggregation station 1a does not need to have the IF unit 14.

[0045] (Modification 6) In the above-described embodiment, the signal multiplexing method may be combined with other multiplexing techniques such as polarization multiplexing, mode multiplexing, or SDM (Space Division Multiplexing) using a multicore processor.

[0046] (Modification 7) In the embodiment described above, the aggregation station 1a may transmit local signals using different optical wavelengths. Alternatively, the aggregation station 1a may transmit signals from the signal processing unit 11 using several optical wavelengths.

[0047] (Modification 8) In the above-described embodiment, the extension station 2a may perform MIMO (Multi Input Multi Output) transmission using multiple antennas, or it may perform beamforming using multiple antennas.

[0048] (Modification 9) In the embodiment described above, the extension station 2a is shown to have the same number of antennas 24 as the signal processing units 11 provided in the aggregation station 1a. However, within the relative bandwidth of the antenna 24, signals corresponding to multiple signal processing units 11 may be transmitted and received from the same antenna 24. In other words, the extension station 2a may be configured to have fewer antennas 24 than the number of signal processing units 11 provided in the aggregation station 1a.

[0049] (Modification 10) In the embodiments described above, a downlink was used as an example, but it can also be applied to an uplink.

[0050] (Modification 11) In the above-described embodiment, only a configuration in which the local signal output from the LO13 of the aggregation station 1a is used in the extension station 2a was shown. In contrast, the local signal output from the LO13 may also be used in the IF section 14a within the aggregation station 1a. In this configuration, the LO13 has a frequency f ＬＯ The local signal is output to each IF 14a in addition to the frequency multiplexing unit 12a. Each IF 14a generates a frequency f based on the local signal output from LO 13 and the signal output from the signal processing unit 11. ＩＦｉ The IF signal is generated. Also, the frequency f is set for each IF14a. ＬＯ When using the local signal, the aggregation station 1a is further equipped with a frequency multiplier, and the frequency f output from LO13 ＬＯ Alternatively, the local signal may be multiplied before being output to each IF14a.

[0051] In the above-described embodiment, some or all of the functional units of the aggregation station 1a and the extension station 2a are implemented as software by one or more processors, such as a CPU (Central Processing Unit), executing a program stored in a storage device and memory having a non-volatile recording medium (non-temporary recording medium). The program may be recorded on a computer-readable non-temporary recording medium. A computer-readable non-temporary recording medium is, for example, a portable medium such as a flexible disk, magneto-optical disk, ROM (Read Only Memory), CD-ROM (Compact Disc-ROM), or a storage device such as a hard disk built into a computer system.

[0052] Some or all of the functional units of the aggregation station 1a and the extension station 2a may be implemented using hardware including electronic circuits (or circuits) such as LSI (Large Scale Integrated Circuit), ASIC (Application Specific Integrated Circuit), PLD (Programmable Logic Device), or FPGA (Field Programmable Gate Array).

[0053] 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.

[0054] This invention can be applied to systems using RoF.

[0055] 1a...Aggregation station, 2a...Extended station, 3...Optical transmission line, 11, 11-1 to 11-N...Signal processing unit, 12a...Frequency multiplexing unit, 13...LO, 14a, 14a-1 to 14a-N...IF unit, 15a...E / O unit, 21...O / E unit, 22a, 22a-1 to 22a-(N+1)...Filter, 23, 23-1 to 23-N...Mixer, 24, 24-1 to 24-N...Antenna, 25a, 25a-1 to 25a-N...Frequency multiplier

Claims

1. A communication device comprising a first communication device having a signal processing function and one or more second communication devices connected to the first communication device via an optical transmission path and having a communication function, wherein the first communication device includes a frequency multiplexing unit that generates a multiplexed signal by frequency multiplexing signals of different intermediate frequency bands and local signals of one or more frequencies, and a first conversion unit that converts the multiplexed signal generated by the frequency multiplexing unit into an optical signal and outputs it, and the second communication device includes a second conversion unit that converts the optical signal output from the first communication device into the multiplexed signal, and a plurality of mixers that generate signals of different radio frequencies using local signals that have been multiplied by different multipliers for signals of different intermediate frequency bands included in the multiplexed signal.

2. The first communication device further comprises a plurality of frequency conversion units that convert a plurality of signals into signals of different intermediate frequency bands, wherein the plurality of frequency conversion units convert the plurality of signals into signals of different intermediate frequency bands that can be converted at frequencies generated from the local signal at different frequency multiplication factors, as described in claim 1.

3. The communication device according to claim 1 or 2, wherein the second communication device further comprises a plurality of filters for extracting signals of different intermediate frequency bands and the local signal from the multiplexed signal, and the plurality of mixers generate signals of different radio frequencies based on the signals of different intermediate frequency bands and the local signal extracted by the plurality of filters.

4. The communication device according to claim 3, further comprising a filter for extracting the local signal from among the plurality of filters and a plurality of frequency multipliers provided between the plurality of mixers for multiplying the frequency of the local signal by different multipliers.

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