Extension station, radio system, and communication method

Abstract

The present invention provides an extension station having a communication function among a signal processing function and the communication function provided in a radio communication device. The extension station includes: one or more light sources for outputting light of a predetermined wavelength; a plurality of conversion units for generating modulated signal light by modulating the light of the predetermined wavelength output from the one or more light sources; one or more polarization adjustment units for adjusting the polarization of the modulated signal light generated by at least one of the plurality of conversion units; and a multiplexing unit for multiplexing a plurality of optical signals including the modulated signal light of which the polarization has been adjusted by the polarization adjustment units and outputting the multiplexed optical signals to an aggregation station having a signal processing function.　

Description

Base station, wireless system and communication method

[0001] The present invention relates to a base station, a wireless system, and a communication method.

[0002] Traditionally, millimeter-wave bands have attracted attention due to their high-speed transmission capabilities, but due to the large propagation loss in millimeter-wave bands, wireless base stations must be deployed at high density. Studies are underway to develop a system using analog RoF (Radio over Fiber) that divides wireless base station functions into a central station (CS) and a remote radio unit (RRU), and aims to achieve flexible and economical wireless area deployment by deploying simple base stations.

[0003] In such systems, base stations are deployed at high density, and it is expected that communication will occur with user terminals located close to each other. In upstream communication from the base station to the central station, if the input power to the base station is large, the linear range of the optical modulator (E / O device) will be exceeded, and unwanted harmonics will be generated due to nonlinear distortion. This can cause degradation of signal quality, so it is necessary to widen the linear range of the E / O device.

[0004] FIG. 6 is a diagram illustrating E / O conversion. FIG. 6 shows the extinction curve characteristics of an E / O device. In E / O conversion, an electrical signal is converted into an optical signal by adjusting the bias voltage input to the E / O device. During this process, the bias voltage input to the E / O device is adjusted to use the linear region of the extinction curve. This can suppress degradation of signal quality. However, as the power of the input radio signal increases, it becomes necessary to use the nonlinear region of the extinction curve, which distorts the main radio signal during photoelectric conversion, resulting in degradation of signal quality.

[0005] In analog RoF systems, when the base station and user terminal are very close to each other, the extinction curve reaches a nonlinear region, distorting the output optical wireless signal. Assuming communication is performed using the main lobe with analog beamforming, the EIRP (Equivalent Isotropically Radiated Power, or Effective Isotropically Radiated Power) becomes very large, and it is thought that cases where the nonlinear region is reached will occur frequently. EIRP represents the power required when replacing an antenna with an isotropic antenna. Expanding the linear region of the extinction curve of an E / O device can expand the dynamic range of input power in uplink communication. Therefore, combining two E / O devices has been studied as a method for expanding the linear region of an E / O device (see, for example, Non-Patent Document 1).

[0006] In the method described in Non-Patent Document 1, two external modulators (E / O conversion units) with approximately the same extinction curve characteristics are prepared, and light is input from a single light source to each external modulator at a certain ratio. In the method described in Non-Patent Document 1, the linear region is expanded by offsetting the bias voltage of one external modulator with respect to the bias voltage of the other external modulator.

[0007] Jian Dai et al, “Optical Linearization for Intensity-modulated Analog Links Employing Equivalent Incoherent Combination Technique”, 2011.

[0008] In the method described in Non-Patent Document 1 above, it is necessary to connect the external modulators (Modulator #1 and Modulator #2 in the diagram of Non-Patent Document 1) and the receiver (Balanced Detection in the diagram of Non-Patent Document 1) with two optical fibers. In the wireless system shown in FIG. 7, the connection can be made with a single optical fiber. FIG. 7 is a diagram for solving the connection problem. The wireless system 1 shown in FIG. 7 includes a base station 2 and a central station 3. The base station 2 includes a light source 4, an optical splitter 5, two E / O conversion units 6-1 and 6-2, a driver 7, and an optical coupler 8. The central station 3 includes an O / E conversion unit 9.

[0009] The light output from the light source 4 is split by the optical splitter 5 and input to two E / O conversion units 6-1 and 6-2 (with approximately the same extinction curve characteristics). A driver 7 distributes the electrical signal to the E / O conversion units 6-1 and 6-2. The two E / O conversion units 6-1 and 6-2 generate optical modulated signals based on the light split by the optical splitter 5 and the electrical signal distributed by the driver 7. The optical modulated signals output from the two E / O conversion units 6-1 and 6-2 are combined by an optical coupler 8. Simply combining the signals in this manner by the optical coupler 8 results in a combination of coherent light. Therefore, if square-law detection is performed in the O / E conversion unit 9 of the central station 3 in this state, the optical modulated signals will cause multipath interference, significantly degrading the transmission signal quality. This poses a problem: the linearity of the E / O conversion unit cannot be improved.

[0010] In view of the above circumstances, an object of the present invention is to provide a technique capable of improving the linearity of an E / O conversion section in a system in which devices are connected by a single optical transmission line.

[0011] One aspect of the present invention is a remote station having a communication function among the signal processing functions and communication functions of a wireless communication device, and comprising: one or more light sources that output light of a predetermined wavelength; a plurality of conversion units that generate modulated signal light by modulating the light of the predetermined wavelength output from the one or more light sources; one or more polarization adjustment units that adjust the polarization of the modulated signal light generated by at least any of the plurality of conversion units; and a multiplexing unit that multiplexes a plurality of optical signals including the modulated signal light whose polarization has been adjusted by the polarization adjustment units, and outputs the multiplexed optical signals to a central station having the signal processing function.

[0012] One aspect of the present invention is a wireless system comprising: a central station having the signal processing function of the signal processing function and communication function of a wireless communication device; and one or more base stations having the communication function, wherein the one or more base stations comprise one or more light sources that output light of a predetermined wavelength; a plurality of conversion units that generate modulated signal light by modulating the light of the predetermined wavelength output from the one or more light sources; one or more polarization adjustment units that adjust the polarization of the modulated signal light generated by at least any of the plurality of conversion units; and a multiplexing unit that combines a plurality of optical signals including the modulated signal light whose polarization has been adjusted by the polarization adjustment unit, and outputs the combined optical signals to the central station having the signal processing function, and the central station comprises a conversion unit that converts the combined wave combined by the one or more base stations into an electrical signal.

[0013] One aspect of the present invention is a communication method performed by a base station having the signal processing function and communication function of a wireless communication device, which communication method adjusts the polarization of the modulated signal light generated by at least one of a plurality of conversion units that generate modulated signal light by modulating light of a predetermined wavelength output from one or more light sources that output light of the predetermined wavelength, and combines a plurality of optical signals including the modulated signal light whose polarization has been adjusted, and outputs the combined signal to a central station having the signal processing function.

[0014] According to the present invention, it is possible to improve the linearity of the E / O conversion section in a system in which devices are connected by a single optical transmission line.

[0015] FIG. 1 is a diagram illustrating an example of the configuration of a wireless system in a first embodiment. FIG. 2 is a sequence diagram illustrating a processing flow of the wireless system in the first embodiment. FIG. 3 is a diagram illustrating an example of the configuration of a wireless system in a second embodiment. FIG. 4 is a diagram illustrating an example of the configuration of a wireless system in a third embodiment. FIG. 5 is a diagram illustrating an example of wavelength allocation. FIG. 6 is a diagram for explaining E / O conversion. FIG. 7 is a diagram for connecting problems.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] First Embodiment FIG. 1 is a diagram illustrating an example configuration of a wireless system 100 according to a first embodiment. The wireless system 100 includes one or more base stations 10 and a central station 20. The one or more base stations 10 and the central station 20 are connected via an optical transmission path 30. The optical transmission path 30 is an optical fiber. In the following description, an example in which there is one base station 10 will be described; however, there may be multiple base stations 10. In this configuration, the connection between one central station 20 and multiple base stations 10 may be a single star type or a passive double star type (including cascade). In the passive double star type, an optical multiplexer / demultiplexer, an optical coupler, or a splitter may be used to connect multiple base stations 10 and one central station 20. One or more base stations 10 and the central station 20 constitute a single base station. Specifically, one or more base stations 10 have a communication function that is a function that is obtained by separating the signal processing function and communication function that a base station has, and the central station 20 has a signal processing function that is a function that is obtained by separating the signal processing function and communication function that a base station has.

[0018] Between the base station 10 and the central station 20, transmission is performed using analog RoF, which transmits radio signals using optical fiber. The base station 10 is an RRU, and the central station 20 is a CS. In the following description, the upstream direction is the direction from the base station 10 to the central station 20, and the downstream direction is the direction from the central station 20 to the base station 10.

[0019] Next, the specific configuration of the base station 10 and the central station 20 will be described. Note that Fig. 1 shows only the functional units of the functional configuration of the base station 10 and the central station 20 that are necessary for explaining the present invention. First, the specific configuration of the base station 10 will be described. The base station 10 includes a light source 11, an optical splitter 12, two E / O conversion units 13-1 and 13-2, a driver 14, a polarization adjustment unit 15, and an optical coupler 16.

[0020] The light source 11 emits light of a certain wavelength (for example, wavelength λ １ ) light. The optical splitter 12 splits the light output from the light source 11. The splitting ratio of the optical splitter 12 may be adjusted as necessary. The E / O conversion units 13-1 and 13-2 receive bias voltages Vb1 and Vb2, the light split by the optical splitter 12, and an electrical signal output from the driver 14. The E / O conversion units 13-1 and 13-2 use the input bias voltages Vb1 and Vb2 and the electrical signal to modulate the light and generate an optical signal of a certain wavelength (modulated signal light). The E / O conversion units 13-1 and 13-2 receive a light signal of a wavelength λ １ Since the light having the wavelength λ is input, the wavelength of the optically modulated signal output from the E / O conversion units 13-1 and 13-2 by external modulation is also λ １ When a wavelength shifter is built into the E / O conversion units 13-1 and 13-2, the wavelength of the optical modulation signal output from the E / O conversion units 13-1 and 13-2 by external modulation is λ １ The E / O conversion units 13-1 and 13-2 are one aspect of the conversion unit.

[0021] Here, the E / O conversion units 13-1 and 13-2 convert the wavelength λ １ Hereinafter, the E / O conversion unit 13-1 generates an optical signal having a wavelength λ １ The optical signal of wavelength λ generated by the E / O conversion unit 13-2 is referred to as a first optical signal. １ The optical signal is referred to as a second optical signal.

[0022] The driver 14 receives an electrical signal based on a radio signal transmitted from a user terminal, which is a communication partner, and distributes the received electrical signal to the E / O conversion units 13-1 and 13-2. The polarization adjustment unit 15 adjusts the polarization of the second optical signal generated by the E / O conversion unit 13-2. For example, the polarization adjustment unit 15 adjusts the polarization of the second optical signal so that the polarization state of the first optical signal generated by the E / O conversion unit 13-1 and the polarization state of the second optical signal generated by the E / O conversion unit 13-2 are orthogonal to each other.

[0023] While FIG. 1 illustrates a configuration in which the polarization adjustment unit 15 is provided on the E / O conversion unit 13-2 side, the polarization adjustment unit 15 may be provided on the E / O conversion unit 13-1 side, or may be provided on both the E / O conversion unit 13-1 and the E / O conversion unit 13-2. This also applies to the following embodiments. That is, the base station 10 only needs to include a polarization adjustment unit 15 on the output side of at least one of the two E / O conversion units 13-1 and 13-2. When there are multiple polarization adjustment units 15 and each is provided on the E / O conversion unit 13-1 and the E / O conversion unit 13-2, the polarization adjustment unit 15 connected to the E / O conversion unit 13-1 adjusts the polarization of the first optical signal generated by the E / O conversion unit 13-1, and the polarization adjustment unit 15 connected to the E / O conversion unit 13-2 adjusts the polarization of the second optical signal generated by the E / O conversion unit 13-2.

[0024] The optical coupler 16 multiplexes the first optical signal generated by the E / O conversion unit 13-1 and the second optical signal whose polarization has been adjusted by the polarization adjustment unit 15. The polarization states of the multiplexed optical signals in the optical coupler 16 are adjusted to be orthogonal to each other. Therefore, the composite wave after being multiplexed by the optical coupler 16 becomes an incoherent optical signal. The optical coupler 16 is one aspect of a multiplexing unit.

[0025] Next, the configuration of the central station 20 will be described. The central station 20 includes an O / E converter 21. The O / E converter 21 receives the composite wave transmitted over the optical transmission path 30 as input. The O / E converter 21 converts the input composite wave into an electrical signal by performing square-law detection. As described above, an incoherent optical signal is output from the base station 10. Therefore, even if square-law detection is performed in the O / E converter 21, multipath interference does not occur between the optical signals.

[0026] 2 is a sequence diagram showing the flow of processing in the wireless system 100 according to the first embodiment. １ The light source 11 outputs light of wavelength λ １ The light having wavelength λ 1 is split by the optical splitter 12 (step S102). １ The light is input to the E / O conversion units 13-1 and 13-2. The driver 14 inputs an electrical signal based on a wireless signal transmitted from a user terminal and distributes the input electrical signal to the E / O conversion units 13-1 and 13-2. At this time, the driver 14 inputs the same power as the input power to the E / O conversion units 13-1 and 13-2. This drives the E / O conversion units 13-1 and 13-2.

[0027] The E / O converters 13-1 and 13-2 convert the wavelength λ output from the light source 11 into a sine wave using the input bias voltages Vb1 and Vb2 and the electrical signal. １ By modulating the light of wavelength λ １ The E / O conversion unit 13-1 generates an optical signal of wavelength λ 1 output from the light source 11 using, for example, the input bias voltage Vb1 and the electrical signal. １ By modulating the light of wavelength λ １ The E / O conversion unit 13-1 outputs the generated first optical signal to the optical coupler 16. The E / O conversion unit 13-2 converts, for example, an optical signal of wavelength λ 1 output from the light source 11 using the input bias voltage Vb2 and an electrical signal. １ By modulating the light of wavelength λ １The E / O conversion unit 13-2 outputs the generated second optical signal to the polarization adjustment unit 15.

[0028] The polarization adjustment unit 15 adjusts the polarization of the second optical signal output from the E / O conversion unit 13-2 (step S104). The polarization adjustment unit 15 adjusts the polarization of the second optical signal so that the polarization state of the first optical signal and the polarization state of the second optical signal are orthogonal to each other, so that they become orthogonal polarization states in the O / E conversion unit 21 of the central station 20. The polarization adjustment unit 15 outputs the polarization-adjusted second optical signal to the optical coupler 16.

[0029] The optical coupler 16 combines the first optical signal output from the E / O conversion unit 13-1 with the polarization-adjusted second optical signal output from the polarization adjustment unit 15 (step S105). As a result, the optical coupler 16 generates a combined wave. The optical coupler 16 outputs the generated combined wave to the optical transmission line 30 (step S106). The combined wave propagated through the optical transmission line 30 is input to the O / E conversion unit 21 of the central station 20. The O / E conversion unit 21 converts the input combined wave into an electrical signal by square-law detection (step S107).

[0030] The wireless system 100 configured as described above includes a light source 11 that outputs light of a predetermined wavelength, a plurality of E / O conversion units 13-1, 13-2 that generate modulated signal light by modulating the light of the predetermined wavelength output from the light source 11, a polarization adjustment unit 15 that adjusts the polarization of the modulated signal light generated by at least one of the plurality of E / O conversion units 13-1, 13-2, and an optical coupler 16 that combines a plurality of optical signals including the modulated signal light whose polarization has been adjusted by the polarization adjustment unit 15, and outputs the combined optical signals to the aggregation station 20.

[0031] As a result, the polarization of the multiple optical signals contained in the composite wave received by the central station 20 is adjusted. Therefore, the composite wave received by the central station 20 becomes an incoherent composite wave. This reduces the possibility of multipath interference occurring when square-law detection is performed in the central station 20. Therefore, it is possible to suppress degradation of transmission signal quality. Furthermore, it is possible to improve the linearity of the E / O conversion units 13-1 and 13-2 using a single optical fiber link. As a result, it is possible to expand the input power dynamic range to the E / O conversion units 13-1 and 13-2.

[0032] The polarization adjustment unit 15 adjusts the polarization of the modulated signal light so that the polarizations of the modulated signal light generated by each of the multiple E / O conversion units 13-1 and 13-2 are orthogonal. As a result, the polarizations of the multiple optical signals included in the composite wave received by the aggregation station 20 are orthogonal. Therefore, multipath interference does not occur when square-law detection is performed in the aggregation station 20. This makes it possible to suppress degradation of transmission signal quality. Furthermore, it is possible to improve the linearity of the E / O conversion units 13-1 and 13-2 using a single optical fiber link. As a result, it is possible to expand the input power dynamic range to the E / O conversion units 13-1 and 13-2.

[0033] Second Embodiment In a second embodiment, a configuration will be described in which a polarization adjustment unit provided in a base station is controlled based on a control signal transmitted from a central station.

[0034] 3 is a diagram showing an example configuration of a wireless system 100a according to the second embodiment. The wireless system 100a includes one or more base stations 10a and a central station 20a. The one or more base stations 10a and the central station 20a are connected via an optical transmission path 30. In the following description, an example in which there is one base station 10a will be described, but the number of base stations 10a may be multiple. The one or more base stations 10a and the central station 20a form a single base station. Specifically, the one or more base stations 10a have a communication function that is a function obtained by separating the signal processing function and communication function provided in a base station, and the central station 20a has a signal processing function that is a function obtained by separating the signal processing function and communication function provided in a base station.

[0035] Next, the specific configuration of the base station 10a and the central station 20a will be described. Note that Fig. 2 shows only the functional units of the base station 10a and the central station 20a that are necessary for explaining the present invention. First, the specific configuration of the base station 10a will be described. The base station 10a includes a light source 11, an optical splitter 12, two E / O conversion units 13-1 and 13-2, a driver 14, a polarization adjustment unit 15, an optical coupler 16, a wavelength multiplexer / demultiplexer 17, an O / E conversion unit 18, and a control unit 19.

[0036] The base station 10a differs in configuration from the base station 10 in that it further includes a wavelength multiplexer / demultiplexer 17, an O / E converter 18, and a control unit 19. The other configurations of the base station 10a are the same as those of the base station 10. The following description will focus on the differences from the base station 10.

[0037] The wavelength multiplexer / demultiplexer 17 multiplexes or demultiplexes the input optical signal. ... For example, the wavelength multiplexer / demultiplexer 17 multiplexes or demultiplexes the composite wave (for example, wavelength λ) output from the optical coupler 16. １ The wavelength division multiplexer 17 outputs a composite wave of wavelength λ 1 transmitted from the central station 20 a to the optical transmission line 30. ２ The optical signal is output to the O / E converter 18 .

[0038] The O / E converter 18 converts the optical signal output from the wavelength multiplexer / demultiplexer 17 into an electrical signal. This makes it possible to restore the control signal transmitted from the central station 20a. The controller 19 controls the polarization adjuster 15 based on the control signal obtained by the O / E converter 18. The controller 19 controls the polarization adjuster 15 so as to adjust the polarization state by the adjustment amount instructed by the control signal. This makes it possible to change the polarization state to the state instructed by the control signal.

[0039] Next, the configuration of the central station 20a will be described. The central station 20a includes an O / E converter 21, a wavelength multiplexer / demultiplexer 22, a control unit 23, and an E / O converter 24. The central station 20a differs in configuration from the central station 20 in that it further includes the wavelength multiplexer / demultiplexer 22, the control unit 23, and the E / O converter 24. The central station 20a is otherwise similar in configuration to the central station 20. The following description will focus on the differences from the central station 20.

[0040] The wavelength multiplexer / demultiplexer 22 multiplexes or demultiplexes the input optical signal. １ The wavelength multiplexer / demultiplexer 22 outputs, for example, a composite wave of wavelengths λ 1 and λ 2 output from the E / O converter 24 to the O / E converter 21. ２ The optical signal is output to the optical transmission line 30.

[0041] The control unit 23 monitors the polarization state of the light input to the O / E conversion unit 21 or monitors the quality of the electrical signal after O / E conversion. Based on the monitoring result, the control unit 23 generates a control signal for controlling the polarization adjustment unit 15 provided in the base station 10a. For example, if monitoring the polarization state of the light input to the O / E conversion unit 21 indicates that multipath interference may occur or if multipath interference has occurred, the control unit 23 may generate a control signal including information indicating an adjustment amount for adjusting the polarization state of the optical signal. Note that the information included in the control signal may not be information indicating the adjustment amount, but may instead be information indicating the occurrence of multipath interference, for example.

[0042] The E / O converter 24 converts the control signal generated by the controller 23 into an optical signal having a wavelength λ ２ The E / O conversion unit 24 converts the optical signal into an optical signal of wavelength λ ２ The optical signal is output to the optical transmission line 30 via the wavelength multiplexer / demultiplexer 22 .

[0043] According to the wireless system 100a configured as above, it is possible to obtain the same effects as those of the first embodiment.

[0044] Furthermore, in the wireless system 100a, the base station 10a includes a control unit 19 that controls the polarization of the polarization adjustment unit 15 based on a control signal transmitted from the central station 20a. The polarization adjustment unit 15 adjusts the polarization of the modulated signal light according to the control of the control unit 19. This enables more appropriate polarization control, thereby improving the linearity of the E / O conversion unit.

[0045] (Variation 1) In the above-described configuration, the control signal is converted into an optical signal as a method for transmitting the control signal, but the method for transmitting the control signal is not limited to this. For example, a control line for transmitting an electrical signal may be provided between the base station 10a and the central station 20a, and the control unit 23 may transmit the generated control signal to the base station 10a via the control line. In this case, the base station 10a may not have the O / E conversion unit 18, and the central station 20a may not have the E / O conversion unit 24. Also, in the above-described configuration, only the control signal may be converted into an optical signal. ２ However, the main signal may be transmitted by subcarrier multiplexing, or a separate wavelength may be prepared for main signal transmission and WDM (Wavelength Division Multiplexing) may be used.

[0046] Third Embodiment In the first and second embodiments, a configuration was described in which light output from one light source was split by an optical splitter and input to each E / O conversion unit. In the third embodiment, a configuration will be described in which a base station is provided with multiple light sources, and light input to each E / O conversion unit is output from different light sources.

[0047] 4 is a diagram showing an example configuration of a wireless system 100b according to the third embodiment. The wireless system 100b includes one or more base stations 10b and a central station 20. The one or more base stations 10b and the central station 20 are connected via an optical transmission path 30. In the following description, an example in which there is one base station 10b will be described, but the number of base stations 10b may be multiple. The one or more base stations 10b and the central station 20 form a single base station. Specifically, the one or more base stations 10b have a communication function that is a function obtained by separating the signal processing function and communication function provided in a base station, and the central station 20 has a signal processing function that is a function obtained by separating the signal processing function and communication function provided in a base station.

[0048] Next, the specific configurations of the base station 10b and the central station 20 will be described. Note that Fig. 4 shows only the functional units of the functional configurations of the base station 10b and the central station 20 that are necessary for explaining the present invention. The configuration of the central station 20 is the same as that of the first embodiment, so a description thereof will be omitted. The specific configuration of the base station 10b will be described. The base station 10b includes two light sources 11-1 and 11-2, two E / O conversion units 13-1 and 13-2, a driver 14, a polarization adjustment unit 15, and an optical coupler 16.

[0049] The base station 10b differs in configuration from the base station 10 in that it has two light sources 11-1 and 11-2 and does not have the optical splitter 12. Other configurations of the base station 10b are the same as those of the base station 10. The following description will focus on the differences from the base station 10.

[0050] The light sources 11-1 and 11-2 are connected to different E / O conversion units 13-1 and 13-2. For example, the light source 11-1 is connected to the E / O conversion unit 13-1, and the light source 11-2 is connected to the E / O conversion unit 13-2. The light source 11-1 emits light of a certain wavelength (for example, wavelength λ １ The light source 11-2 outputs light of a certain wavelength (for example, wavelength λ １ ) to the E / O conversion unit 13-2.

[0051] In this way, the base station 10b in the third embodiment outputs light from different light sources 11-1 and 11-2 to be input to the E / O converters 13-1 and 13-2, respectively. １However, because the light sources 11-1 and 11-2 are not the same light source, it is difficult to achieve perfectly identical wavelengths due to manufacturing errors and other factors. If the wavelengths are slightly different, beat noise due to wavelength differences will occur if the polarizations do not match perfectly when square-law detection is performed by the O / E converter 21 of the central station 20. However, polarization control as shown in the second embodiment may be performed based on the beat noise component. In theory, beat noise will not occur if the polarizations are perfectly orthogonal. Therefore, the base station 10b may be equipped with a wavelength multiplexer / demultiplexer 17, an O / E converter 18, and a control unit 19 as shown in the second embodiment, and the central station 20 may be equipped with a wavelength multiplexer / demultiplexer 22, a control unit 23, and an E / O converter 24 as shown in the second embodiment.

[0052] According to the wireless system 100b configured as above, even in a configuration including a plurality of light sources, it is possible to obtain the same effects as those of the first embodiment.

[0053] (Variant) In the above-described configuration, the light sources 11-1 and 11-2 use the same wavelength, but the light sources 11-1 and 11-2 may use different wavelengths as long as the extinction curve characteristics have similar tendencies (the bias voltages corresponding to the linear and nonlinear regions are approximately the same).

[0054] (Modification 1 common to the first to third embodiments) The wireless systems 100, 100a, and 100b may use either TDD (Time Division Duplex) or FDD (Frequency Division Duplex). In the case of TDD, the timing of switching between uplink and downlink can be flexibly handled.

[0055] (Variant 2 common to the first to third embodiments) In the optical connection sections between the base stations 10, 10a, 10b and the central stations 20, 20a, and between the base stations 10, 10a, 10b, the type of connector end face may be any of flat, PC (Physical Contact), UPC (Ultra Physical Contact), and APC (Angled Physical Contact).

[0056] (Modification 3 common to the first to third embodiments) In the above embodiments, analog RoF has been described as an example, but the present invention can also be applied to analog IFoF (Intermediate Frequency over Fiber) by adding necessary components.

[0057] (Modification 4 common to the first to third embodiments) The base stations 10, 10a, and 10b may include a frequency converter and an amplifier. Furthermore, the base stations 10, 10a, and 10b may include a phased array antenna as an antenna and be capable of beam direction control. For TDD switch and beam direction control, the base stations 10, 10a, and 10b may include a control unit. The control unit of the base stations 10, 10a, and 10b may be controlled by a control signal from the central station 20 and 20a.

[0058] (Modification 5 common to the first to third embodiments) The control signal may be subcarrier-multiplexed together with the main signal onto one wavelength. The control signal (including, for example, a TDD signal) may be polarization-multiplexed onto an optical signal of one wavelength.

[0059] (Modification 6 common to the first to third embodiments) By adding an optical amplifier to the optical transmission line, it becomes possible to compensate for optical loss and increase the number of base station branches.

[0060] (Modification 7 common to the first to third embodiments) The present technology can be applied to a mobile fronthaul.

[0061] (Modification 8 common to the first to third embodiments) The optical fiber used in each of the above-described embodiments may be a single-mode fiber (SMF), a multi-mode fiber (MMF), a multi-core fiber (MCF), or a holey-core fiber. When an optical amplifier is used, the optical amplifier may be a semiconductor optical amplifier (SOA) or an erbium-doped fiber amplifier (EDFA).

[0062] (Modification 9 common to the first to third embodiments) The wavelength allocation during transmission through an optical transmission line may be any of ODSB (Optical Double Side Band), OSSB (Optical Single Side Band), and OCS (Optical Carrier Suppression) as shown in Fig. 5. Fig. 5 is a diagram showing an example of wavelength allocation. Fig. 5A is a diagram showing an example of ODSB, Fig. 5B is a diagram showing an example of OSSB, and Fig. 5C is a diagram showing an example of OCS.

[0063] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0064] The present invention is applicable to techniques using analog RoF.

[0065] 10, 10a, 10b... base station, 11, 11-1, 11-2... light source, 12... optical splitter, 13, 13-1, 13-2, 24... E / O conversion unit, 14... driver, 15... polarization adjustment unit, 16... optical coupler, 17, 22... wavelength multiplexer / demultiplexer, 18, 21... O / E conversion unit, 19, 23... control unit, 20, 20a... central station, 100, 100a, 100b... wireless system

Claims

1. A remote station having the communication function among the signal processing function and the communication function provided in a wireless communication device, comprising: one or more light sources that output light of a predetermined wavelength; a plurality of conversion units that generate modulated signal light by modulating the light of the predetermined wavelength output from the one or more light sources; one or more polarization adjustment units that adjust the polarization of the modulated signal light generated by at least any one of the plurality of conversion units; and a multiplexing unit that multiplexes a plurality of optical signals including the modulated signal light whose polarization has been adjusted by the polarization adjustment unit and outputs the multiplexed optical signals to an aggregation station having the signal processing function.

2. The remote station according to claim 1, wherein the polarization adjustment unit adjusts the polarization of the modulated signal light so that the polarizations of the modulated signal lights generated by the respective plurality of conversion units are orthogonal to each other.

3. The remote station according to claim 1 or 2, further comprising a control unit that performs polarization control of the one or more polarization adjustment units based on a control signal transmitted from the aggregation station, wherein the one or more polarization adjustment units adjust the polarization of the modulated signal light according to the control of the control unit.

4. The remote station according to claim 1 or 2, wherein the one or more light sources are a plurality of light sources, and each of the plurality of light sources outputs light of a predetermined wavelength to a different conversion unit.

5. The remote station according to claim 1 or 2, wherein the one or more polarization adjustment units are a plurality of polarization adjustment units, and the plurality of polarization adjustment units adjust the polarization of the modulated signal light generated by different conversion units.

6. A wireless system comprising an aggregation station having the signal processing function among the signal processing function and the communication function provided in a wireless communication device, and one or more remote stations having the communication function, wherein the one or more remote stations comprise: one or more light sources that output light of a predetermined wavelength; a plurality of conversion units that generate modulated signal light by modulating the light of the predetermined wavelength output from the one or more light sources; one or more polarization adjustment units that adjust the polarization of the modulated signal light generated by at least any one of the plurality of conversion units; and a multiplexing unit that multiplexes a plurality of optical signals including the modulated signal light whose polarization has been adjusted by the polarization adjustment unit and outputs the multiplexed optical signals to the aggregation station having the signal processing function, and the aggregation station comprises a conversion unit that converts the combined wave multiplexed by the one or more remote stations into an electrical signal.

7. A communication method performed by an outstation having the communication function among the signal processing function and the communication function provided in a wireless communication device, the method including adjusting the polarization of modulation signal light generated by at least any one of a plurality of conversion units that generate the modulation signal light by modulating the light of a predetermined wavelength output from one or more light sources that output light of the predetermined wavelength, multiplexing a plurality of optical signals including the modulation signal light with the adjusted polarization, and outputting the multiplexed optical signals to an aggregation station having the signal processing function.

Images