Wireless communication method and wireless communication device

Abstract

This wireless communication method for execution by a wireless communication device comprises: an inverse fast Fourier transform step in which an inverse fast Fourier transform is performed on a digital electric signal associated with a downlink wireless signal; a digital-to-analog conversion step in which the digital electric signal subjected to the inverse fast Fourier transform is converted into a first analog electric signal; an electrical-to-optical conversion step in which the first analog electric signal is converted into an optical signal; a step in which the optical signal is transmitted; an optical-to-electrical conversion step in which the transmitted optical signal is converted into a second analog electric signal; and a step in which a downlink wireless signal corresponding to the second analog electric signal is transmitted.

Description

[Technical field]

[0001] The present invention relates to a wireless communication method and a wireless communication device. [Background technology]

[0002] In order to popularize the fifth generation mobile communication system (hereinafter referred to as "5G") and local 5G, installation of base stations is being promoted in areas where wireless communication services are provided. A base station used for 5G and local 5G includes a centralized unit (CU), a distributed unit (DU), and a radio unit (RU) (see Non-Patent Document 1). In addition, multiple combinations of the centralized unit, distributed unit, and radio unit are defined (see Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Umesh et al., “O-RAN Fronthaul Specifications Overview,” NTT DOCOMO Technical Journal Vol. 27 No. 1 (Apr. 2019). [Non-Patent Document 2] NGMN (Next Generation Mobile Networks) Alliance, “NGMN Overview on 5G RAN Functional Decomposition,” 2018. Summary of the Invention [Problem to be solved by the invention]

[0004] 18 is a diagram showing a configuration example of a conventional 5G and local 5G wireless communication system. The wireless communication system includes a host device, an aggregation unit, a distribution unit, and one or more wireless units 200.

[0005] 18, wireless unit 200-1 is an existing wireless unit in an area where wireless communication services are provided. Wireless unit 200-1 performs wireless communication with wireless terminals (not shown) within coverage area 201-1 (cell).

[0006] 5G and local 5G use radio waves in the high frequency band (millimeter wave band) for communication. In general, the propagation distance of radio waves in the high frequency band is short. In addition, radio waves in the high frequency band have a high tendency to travel in a straight line. For these reasons, radio waves in the high frequency band are easily blocked by obstructions. When radio waves are blocked by obstructions, there may be areas where communication becomes difficult.

[0007] In FIG. 18, area 202 is an area where communication becomes difficult because part of the radio waves transmitted from wireless unit 200-1 is blocked by obstruction 110. Area 202 occurs in part of cover area 201-1 of wireless unit 200-1. In order to expand the area where wireless communication services are provided, a new wireless unit 200 is installed in addition to existing wireless unit 200. In FIG. 18, wireless unit 200-2 is newly installed. Wireless unit 200-2 performs wireless communication with a wireless terminal (not shown) in cover area 201-2 including area 202.

[0008] However, the conventional radio unit 200 is heavy and large because it includes a signal processing unit, a D / A conversion unit (digital-to-analog conversion unit), an A / D conversion unit (analog-to-digital conversion unit), and an antenna element. Also, the power consumption of the conventional radio unit 200 is large. For these reasons, it may not be possible to suppress the increase in equipment costs for expanding the area where wireless communication services are provided.

[0009] In view of the above circumstances, an object of the present invention is to provide a wireless communication method and a wireless communication device that can suppress an increase in equipment costs for expanding the area in which wireless communication services are provided. [Means for solving the problem]

[0010] One aspect of the present invention is a wireless communication method executed by a wireless communication device, the wireless communication method including an inverse fast Fourier transform step of performing an inverse fast Fourier transform on a digital electrical signal corresponding to a downlink wireless signal, a digital-to-analog conversion step of converting the inverse fast Fourier transformed digital electrical signal into a first analog electrical signal, an electrical-to-optical conversion step of converting the first analog electrical signal into an optical signal, a step of transmitting the optical signal, an optical-to-electrical conversion step of converting the transmitted optical signal into a second analog electrical signal, and a step of transmitting the downlink wireless signal in response to the second analog electrical signal.

[0011] One aspect of the present invention is a wireless communication device comprising an inverse fast Fourier transform unit that performs an inverse fast Fourier transform on a digital electrical signal corresponding to a downlink radio signal, a digital-to-analog conversion unit that converts the inverse fast Fourier transformed digital electrical signal into a first analog electrical signal, an electrical-to-optical conversion unit that converts the first analog electrical signal into an optical signal, an optical fiber that transmits the optical signal, an optical-to-electrical conversion unit that converts the transmitted optical signal into a second analog electrical signal, and an antenna element that transmits the downlink radio signal in response to the second analog electrical signal. Effect of the Invention

[0012] According to the present invention, it is possible to suppress an increase in equipment costs for expanding the area in which wireless communication services are provided. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system in each embodiment. [Diagram 2] 3 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in the first embodiment. FIG. [Diagram 3] 5A to 5C are diagrams illustrating an example of the operation of a wireless unit and an extension unit in the first embodiment. [Figure 4] 10 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in a modified example of the first embodiment. FIG. [Diagram 5]13 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in a second embodiment. FIG. [Figure 6] 13 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in a third embodiment. FIG. [Figure 7] 13 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in a fourth embodiment. FIG. [Figure 8] 13 is a diagram illustrating a configuration example of a wireless unit and an extension unit in a fifth embodiment. FIG. [Figure 9] 13 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in a sixth embodiment. FIG. [Figure 10] 13 is a diagram illustrating a configuration example of a wireless unit and an extension unit in the seventh embodiment. FIG. [Figure 11] 13 is a diagram illustrating a configuration example of a wireless unit and an extension unit in the eighth embodiment. FIG. [Figure 12] 13 is a diagram illustrating a configuration example of a wireless unit and an extension unit in the ninth embodiment. FIG. [Figure 13] 23 is a diagram illustrating a configuration example of a wireless unit and an extension unit in a tenth embodiment. FIG. [Figure 14] 23 is a diagram illustrating an example of the configuration of a wireless unit and an extension unit in an eleventh embodiment. FIG. [Figure 15] 23A to 23C are diagrams illustrating an example of the operation of the wireless unit and the extension unit in the eleventh embodiment. [Figure 16] FIG. 23 is a diagram illustrating a configuration example of a wireless unit and an extension unit in a modified example of the eleventh embodiment. [Figure 17] FIG. 2 is a diagram illustrating an example of a hardware configuration of a base station in each embodiment. [Figure 18] FIG. 1 is a diagram showing an example of the configuration of a conventional 5G and local 5G wireless communication system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the drawings. (overview) 1 is a diagram showing an example of the configuration of a wireless communication system 1 in each embodiment. The wireless communication system 1 includes a higher-level device 2 and a base station 3. The base station 3 includes a consolidation unit 4 (CU), a distribution unit 5 (DU), and a wireless unit 6 (RU).

[0015] The base station 3 includes a consolidation unit 4, a distribution unit 5, and a radio unit 6. The radio unit 6 includes one or more extension units 7 (antenna units). The extension units 7 are arranged in multiple planes in the area where the wireless communication service is provided.

[0016] The higher-level device 2 and the aggregation unit 4 are connected to each other using a coaxial cable 8-1 (communication line). The aggregation unit 4 and the distribution unit 5 are connected to each other using a coaxial cable 8-2 (communication line). The distribution unit 5 and the wireless unit 6 are connected to each other using a coaxial cable 8-3 (communication line).

[0017] The radio unit 6 and the extension unit 7 are connected to each other using an optical fiber 9. That is, the extension unit 7 extends from the radio unit 6 via the optical fiber 9. The optical fiber 9 may be a single-core fiber having M cores (M is an integer equal to or greater than 1) or a multi-core fiber having M cores.

[0018] In Fig. 1, the wireless unit 6 and the extension unit 7-1 are connected by a point-to-point (PP) connection, for example. In Fig. 1, the two extension units 7-4 and the wireless unit 6 are connected by a passive optical network (PON), for example. In Fig. 1, the passive optical network includes an optical fiber 9-4 and an optical splitter 10 (branching unit). The passive optical network is, for example, a WDM-PON (Wavelength Division Multiplexing - Passive Optical Network) or a TDM-PON (Time Division Multiplexing - Passive Optical Network).

[0019] The higher-level device 2 outputs downstream data to a consolidation unit 4 (CU). The consolidation unit 4 generates a downstream stream (digital electrical signal) by performing predetermined signal processing (e.g., packetization) on the downstream data. The consolidation unit 4 outputs the downstream stream to a distribution unit 5 (DU). The distribution unit 5 generates M downstream streams (digital electrical signals associated with wireless signals) by performing predetermined signal processing (e.g., encoding) on ​​the downstream stream. The distribution unit 5 outputs the M downstream streams to a wireless unit 6.

[0020] In the wireless communication system 1, for example, radio waves in a high frequency band (millimeter wave band) are used for communication. Wireless communication services provided in the wireless communication system 1 are, for example, 5G and local 5G wireless communication services. A shield 100 may be present in an area where the wireless communication service of the wireless communication system 1 is provided. The shield 100 is, for example, a building. A coverage area 11 is a cell of the wireless unit 6.

[0021] The extension unit 7-n (n is an integer equal to or greater than 1) transmits a downstream wireless signal to a wireless terminal (not shown) located in the coverage area 12-n. The extension unit 7-n may receive an upstream wireless signal from a wireless terminal (not shown) located in the coverage area 12-n.

[0022] The shield 100 blocks a portion of the wireless signal of the wireless unit 6. Area 13 is an area where communication becomes difficult due to the shield 100 blocking a portion of the radio waves transmitted from the wireless unit 6. In FIG. 1, area 13 occurs in a portion of the coverage area 11 of the wireless unit 6. In FIG. 1, the extension 7-1 is installed above (at a high place) the shield 100 as an example. As a result, the extension 7-1 performs wireless communication with a wireless terminal (not shown) in the coverage area 12-1 including area 13.

[0023] The extension 7-n includes M antenna elements and M photoelectric conversion units. The extension 7-n does not need to include a signal processing unit that executes predetermined wireless front-end processing (e.g., frequency conversion processing) and the like. The extension 7-n may also include an amplifier that amplifies signal strength.

[0024] The wireless unit 6 transmits a downstream optical signal to the extension 7-n using analog Radio-over-Fiber (RoF). In the analog RoF, an optical signal that is intensity-modulated according to a wireless signal is transmitted through an optical fiber. The photoelectric conversion unit of the extension 7-n converts the downstream optical signal transmitted through the optical fiber 9 using the analog RoF into an analog electrical signal. The photoelectric conversion unit of the extension 7-n extracts a downstream wireless signal from the optical signal using optical-to-electrical conversion of the optical signal transmitted through the optical fiber 9. One or more antenna elements of the extension 7-n transmit the downstream wireless signal to a wireless terminal (not shown) within the coverage area 12. The wireless terminal (not shown) within the coverage area 12 separates M streams according to the downstream wireless signal by signal processing such as Multiple Input Multiple Output (MIMO) signal processing.

[0025] (First embodiment) Fig. 2 is a diagram showing a configuration example of the wireless unit 6a and the extension unit 7a-n in the first embodiment. The wireless unit 6a corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7a-n corresponds to the extension unit 7-n shown in Fig. 1. In the first embodiment, the wireless unit 6a and the extension unit 7a-n do not need to perform beamforming of downstream wireless signals.

[0026] The wireless unit 6a includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n (digital-analog conversion unit), and a first electric-to-optical conversion unit 62-n. The extension unit 7a-n includes M combinations (systems) of a first optical-to-electrical conversion unit 70-n and an antenna element 71-n. The extension unit 7a-n may include M amplifiers that amplify the intensity of an analog electric signal or an optical signal.

[0027] The first electro-optical conversion unit 62-n and the first opto-electrical conversion unit 70-n are connected to each other using an optical fiber 9-n. The optical fiber 9-n may be a single-core fiber having M cores or a multi-core fiber having M cores.

[0028] Next, an example of the operation of the wireless unit 6a and the extension unit 7a will be described. 3 is a diagram showing an example of the operation of the wireless unit 6a and the extension unit 7a in the first embodiment. The wireless unit 6a acquires M downstream streams (digital electrical signals associated with wireless signals) from the distribution unit 5.

[0029] Stream "#m" (m is an integer between 1 and M) is input to inverse fast Fourier transform unit 60-nm. For example, stream "#1" is input to inverse fast Fourier transform unit 60-n-1. For example, stream "#2" is input to inverse fast Fourier transform unit 60-n-2.

[0030] The inverse fast Fourier transform unit 60-nm performs an inverse fast Fourier transform (IFFT) on a digital electrical signal (stream "#m") associated with a downstream wireless signal. The inverse fast Fourier transform unit 60-nm outputs the inverse fast Fourier transformed digital electrical signal to the D / A conversion unit 61-nm (step S101).

[0031] The D / A conversion unit 61-nm converts the digital electrical signal that has been subjected to the inverse fast Fourier transform by the inverse fast Fourier transform unit 60-nm into a first analog electrical signal. The D / A conversion unit 61-nm outputs the first analog electrical signal to the first electro-optical conversion unit 62-nm (step S102).

[0032] The first electrical-to-optical conversion unit 62-nm converts the first analog electrical signal into an optical signal using electrical-to-optical conversion of the first analog electrical signal (step S103). The first electrical-to-optical conversion unit 62-nm transmits the optical signal through the optical fiber 9-nm. That is, the optical fiber 9-nm transmits an optical signal corresponding to the first analog electrical signal to the first optical-to-electrical conversion unit 70-nm (step S104).

[0033] The first photoelectric conversion unit 70-nm converts the optical signal transmitted by the optical fiber 9-nm into a second analog electric signal (step S105). The antenna element 71-nm emits a radio signal corresponding to the second analog electric signal converted by the first photoelectric conversion unit 70-nm (step S106). In this manner, the optical signal is transmitted using the analog RoF.

[0034] As described above, the inverse fast Fourier transform unit 60-nm performs an inverse fast Fourier transform on the digital electrical signal associated with the downstream wireless signal. The D / A conversion unit 61-nm (digital-analog conversion unit) converts the inverse fast Fourier transformed digital electrical signal into a first analog electrical signal. The first electrical-to-optical conversion unit 62-nm converts the first analog electrical signal into an optical signal. The optical fiber 9-nm transmits the optical signal to the first optical-to-electrical conversion unit 70-nm. The first optical-to-electrical conversion unit 70-nm converts the transmitted optical signal into a second analog electrical signal. The antenna element 71-nm transmits a downstream wireless signal corresponding to the second analog electrical signal.

[0035] This makes it possible to suppress increases in equipment costs for expanding the area in which wireless communication services are provided.

[0036] That is, conventionally, the radio unit and the antenna are integrated without being connected to each other by optical fiber, and correspond one-to-one. Furthermore, the conventional radio unit includes a radio front-end processing unit, a digital-to-analog conversion unit, and an analog-to-digital conversion unit. Conventionally, when the area where wireless communication services are provided is expanded, a large number of radio units need to be installed in the area where wireless communication services are provided, depending on the frequency characteristics such as the linearity and attenuation of millimeter waves. Furthermore, in the area where wireless communication services are provided, it may be difficult to install the radio units on high places such as walls, traffic lights, and street lights. Furthermore, the power consumption of the radio units may be high. For these reasons, there are problems such as increased capital investment costs.

[0037] In contrast, in the first embodiment, the wireless unit 6 and the extension unit 7 (antenna unit) are connected by an optical fiber 9. Moreover, the wireless unit 6 does not have to be integrated with the aggregation unit 4 and the distribution unit 5. In the first embodiment, it is not necessary to install a large number of wireless units 6 in the area where wireless communication services are provided, and it is sufficient to newly install a low-cost extension unit 7a in the service area, so that it is possible to suppress increases in capital investment costs. Moreover, the extension unit 7a is smaller and lighter than the wireless unit 6a. Therefore, the extension unit 7a can be easily installed in high places, on walls, traffic lights, street lights, etc. (places where installation is burdensome).

[0038] Moreover, the power consumption of the wireless unit 6a is low. Furthermore, since optical fiber 9 is used for signal transmission, the signal loss in the extension 7a is smaller than when a coaxial cable is used between the wireless unit and the extension.

[0039] (Modification of the first embodiment) The difference between the modified example of the first embodiment and the first embodiment is that a wavelength division multiplexed (WDM) optical signal is transmitted between the radio unit and the extension unit. The difference between the modified example of the first embodiment and the first embodiment will be mainly described.

[0040] Fig. 4 is a diagram showing a configuration example of radio unit b and extension unit 7b in a modified example of the first embodiment. Radio unit 6b corresponds to radio unit 6 shown in Fig. 1. Extension unit 7b-n corresponds to extension unit 7 shown in Fig. 1. Radio unit 6b and extension unit 7b-n are connected to each other using optical fiber 9. The number of optical fibers 9-n may be less than the number (M) of streams (digital electrical signals associated with radio signals). Optical fiber 9-n does not need to be a multi-core fiber having the same number of cores as the number of streams.

[0041] The wireless unit 6b includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6b further includes a multiplexer 63. The extension unit 7b-n includes M combinations (systems) of a first optical-electrical conversion unit 70-n and an antenna element 71-n. The extension unit 7b-n further includes a demultiplexer 72. The extension unit 7b-n may include M amplifiers that amplify the intensity of an analog electrical signal or an optical signal.

[0042] The first electro-optical converters 62-n convert the first analog electrical signals into optical signals having different wavelengths. The multiplexer 63 generates a wavelength division multiplexed optical signal by multiplexing the optical signals having different wavelengths. The optical fiber 9 transmits the wavelength division multiplexed optical signal to the demultiplexer 72.

[0043] The demultiplexer 72 demultiplexes the wavelength division multiplexed optical signal into multiple optical signals having different wavelengths. The demultiplexer 72 outputs the M optical signals having different wavelengths to the M first opto-electrical conversion units 70-n. The M first opto-electrical conversion units 70-n convert the transmitted optical signals into second analog electrical signals having a predetermined wavelength. The antenna element 71-nm transmits a downstream radio signal corresponding to the second analog electrical signal.

[0044] As described above, the multiplexer 63 generates a wavelength division multiplexed optical signal by multiplexing a plurality of optical signals having different wavelengths. The optical fiber 9 transmits the wavelength division multiplexed optical signal to the demultiplexer 72. The demultiplexer 72 demultiplexes the wavelength division multiplexed optical signal into a plurality of optical signals having different wavelengths. This makes it possible to reduce the number of optical fibers 9-n.

[0045] Second embodiment The second embodiment differs from the first embodiment in that the radio unit executes control of digital beamforming. The second embodiment will be described focusing on the differences from the first embodiment.

[0046] Fig. 5 is a diagram showing a configuration example of a wireless unit 6c and extension units 7a-n in the second embodiment. The wireless unit 6c corresponds to the wireless unit 6 shown in Fig. 1. The extension units 7a-n correspond to the extension units 7-n shown in Fig. 1. In the second embodiment, the wireless unit 6c performs digital beamforming of a downstream wireless signal.

[0047] The wireless unit 6c includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6c further includes a digital beam control unit 64 in the upstream direction (dispersion unit side) of the inverse fast Fourier transform unit 60-n. The extension unit 7a-n includes M combinations (systems) of a first optical-electrical conversion unit 70-n and an antenna element 71-n. The extension unit 7a-n may include M amplifiers that amplify the intensity of an analog electrical signal or an optical signal.

[0048] The first electro-optical conversion unit 62-n and the first opto-electrical conversion unit 70-n are connected to each other using an optical fiber 9-n. The optical fiber 9-n may be a single-core fiber having M cores or a multi-core fiber having M cores.

[0049] The wireless unit 6c may further include a multiplexer 63. The extension units 7a-n may further include a demultiplexer 72. In these cases, the number of optical fibers 9-n may be less than the number of streams. The optical fiber 9 does not need to be a multi-core fiber having the same number of cores as the number of streams.

[0050] The digital beam control unit 64 acquires a predetermined number of downstream streams from the distribution unit 5. The predetermined number of downstream streams are digital electrical signals associated with M wireless signals. The digital beam control unit 64 executes digital beamforming control on the digital electrical signals associated with the M wireless signals. For example, the digital beam control unit 64 adjusts the phase of the digital electrical signals associated with the wireless signals. The stream "#m" on which the digital beamforming control has been executed is input to the inverse fast Fourier transform unit 60-nm.

[0051] As described above, the digital beam control unit 64 adjusts the phase of one or more downstream streams (digital electrical signals associated with wireless signals), thereby making it possible to perform digital beamforming.

[0052] Third embodiment The third embodiment differs from the first embodiment in that analog beamforming control is executed. More specifically, the third embodiment differs from the first embodiment in that analog beamforming control is executed between a D / A conversion unit of a wireless unit and a first electro-optical conversion unit of a wireless unit. The third embodiment will be described focusing on the differences from the first embodiment.

[0053] Fig. 6 is a diagram showing a configuration example of a wireless unit 6d and extension units 7a-n in the third embodiment. The wireless unit 6d corresponds to the wireless unit 6 shown in Fig. 1. The extension units 7a-n correspond to the extension units 7-n shown in Fig. 1. In the third embodiment, the wireless unit 6d performs analog beamforming of a downstream wireless signal.

[0054] The wireless unit 6d includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6d further includes a first analog beam control unit 65 between the D / A conversion unit 61-n and the first electro-optical conversion unit 62-n.

[0055] The wireless unit 6d may further include a multiplexer 63. The extension unit 7a-n may further include a demultiplexer 72. In these cases, the number of optical fibers 9-n may be less than the number of streams (M). The optical fibers 9-n do not need to be multi-core fibers having the same number of cores as the number of streams.

[0056] The first analog beam control unit 65 executes analog beamforming in the high frequency electric signal domain (RF (Radio Frequency) domain). That is, the first analog beam control unit 65 adjusts the phase of each of the first analog electric signals output from the multiple D / A conversion units 61-n. The first analog beam control unit 65 outputs each of the first analog electric signals with the phase adjusted to the multiple first electro-optical conversion units 62-n.

[0057] As described above, the first analog beam control unit 65 adjusts the phase of each of the first analog electrical signals output from the multiple D / A conversion units 61. This makes it possible to perform analog beamforming.

[0058] (Fourth embodiment) The fourth embodiment differs from the third embodiment in that analog beamforming control is executed between the first electric-to-optical conversion unit of the wireless unit and the first optical-to-electrical conversion unit of the extension unit. The fourth embodiment will be described focusing on the differences from the third embodiment.

[0059] Fig. 7 is a diagram showing a configuration example of a wireless unit 6e and extension units 7a-n in the fourth embodiment. The wireless unit 6e corresponds to the wireless unit 6 shown in Fig. 1. The extension units 7a-n correspond to the extension units 7-n shown in Fig. 1. In the fourth embodiment, the wireless unit 6e performs analog beamforming of a downstream wireless signal.

[0060] The wireless unit 6e includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6e further includes a second analog beam control unit 66 in the downstream direction (toward the extension unit) relative to the first electro-optical conversion unit 62-n.

[0061] The wireless unit 6e may further include a multiplexer 63. The extension unit 7a-n may further include a demultiplexer 72. In these cases, the number of optical fibers 9-n may be less than the number of streams (M). The optical fibers 9-n do not need to be multi-core fibers having the same number of cores as the number of streams.

[0062] The second analog beam control unit 66 performs analog beamforming in the high-frequency optical signal domain (RF domain). That is, the second analog beam control unit 66 adjusts the phase of each optical signal output from the first electro-optical conversion units 62-n. The second analog beam control unit 66 outputs each phase-adjusted optical signal to the first optical-electrical conversion units 70-n via the optical fiber 9-n.

[0063] As described above, the second analog beam control unit 66 adjusts the phase of each optical signal output from the plurality of first electro-optical conversion units 62. This makes it possible to perform analog beamforming.

[0064] Fifth embodiment The fifth embodiment differs from the first embodiment in that the extension unit executes control of analog beamforming. More specifically, the fifth embodiment differs from the first embodiment in that control of analog beamforming is executed between a first photoelectric conversion unit and an antenna element. The fifth embodiment will be described focusing on the differences from the first embodiment.

[0065] Fig. 8 is a diagram showing a configuration example of a wireless unit 6a and an extension unit 7c-n in the fifth embodiment. The wireless unit 6a corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7c-n corresponds to the extension unit 7-n shown in Fig. 1. In the fifth embodiment, the extension unit 7c-n performs analog beamforming of a downstream wireless signal.

[0066] The extension 7c-n includes M combinations (systems) of the first photoelectric conversion units 70-n and the antenna elements 71-n. The extension 7c-n further includes a third analog beam control unit 73 between the first photoelectric conversion units 70-n and the antenna elements 71-n. The extension 7c-n may include M amplifiers that amplify the intensity of the analog electrical signal or optical signal.

[0067] The wireless unit 6a includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6a may further include a multiplexer 63. The extension unit 7c-n may further include a demultiplexer 72. In these cases, the number of optical fibers 9-n may be less than the number of streams. The optical fiber 9 does not need to be a multi-core fiber having the same number of cores as the streams.

[0068] The third analog beam control unit 73 executes analog beamforming in the high frequency electric signal domain (RF domain). That is, the third analog beam control unit 73 adjusts the phase of each of the second analog electric signals output from the plurality of first photoelectric conversion units 70-n. The third analog beam control unit 73 may periodically change the amount of phase adjustment. In this way, the third analog beam control unit 73 periodically changes the transmission direction of the downlink radio signal (beam).

[0069] The radio unit 6a may include a control unit that generates control information. The third analog beam control unit 73 may execute analog beamforming based on the control information transmitted from the radio unit 6a. The optical fiber 9 may transmit the control information superimposed on the main signal and the main signal. The control information may be transmitted from the radio unit 6a using a path (a communication line for control) other than the optical fiber 9 (path of the main signal). The third analog beam control unit 73 outputs each of the second analog electric signals, the phase of which has been adjusted, to the plurality of antenna elements 71-n.

[0070] As described above, the third analog beam control unit 73 adjusts the phase of each of the second analog electrical signals output from the plurality of first photoelectric conversion units 70. This makes it possible to perform analog beamforming.

[0071] Sixth embodiment The sixth embodiment differs from the fifth embodiment in that analog beamforming control is executed between the first photoelectric conversion unit of the extension unit and the first electro-optical conversion unit of the wireless unit. The sixth embodiment will be described focusing on the differences from the fifth embodiment.

[0072] Fig. 9 is a diagram showing a configuration example of a wireless unit 6a and an extension unit 7d-n in the sixth embodiment. The wireless unit 6a corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7d-n corresponds to the extension unit 7-n shown in Fig. 1. In the sixth embodiment, the extension unit 7d-n performs analog beamforming of a downstream wireless signal.

[0073] The extension 7d-n includes M combinations (systems) of the first photoelectric conversion units 70-n and the antenna elements 71-n. The extension 7d-n further includes a fourth analog beam control unit 74 in the upstream direction (wireless unit side) of the first photoelectric conversion units 70-n. The extension 7d-n may include M amplifiers that amplify the intensity of the analog electrical signal or optical signal.

[0074] The wireless unit 6a may further include a multiplexer 63. The extension unit 7d-n may further include a demultiplexer 72. In these cases, the number of optical fibers 9-n may be less than the number of streams. The optical fiber 9 does not need to be a multi-core fiber having the same number of cores as the number of streams.

[0075] The fourth analog beam control section 74 performs analog beamforming in the high-frequency optical signal domain (RF domain). That is, the fourth analog beam control section 74 adjusts the phase of each optical signal output from the first electro-optical conversion sections 62-n. The fourth analog beam control section 74 outputs each optical signal with the adjusted phase to the first optical-electrical conversion sections 70-n.

[0076] As described above, the fourth analog beam control unit 74 adjusts the phase of each optical signal output from the optical fiber 9-n, which is a single-core fiber having M cores. The fourth analog beam control unit 74 may adjust the phase of each optical signal output from the optical fiber 9-n, which is a multi-core fiber having M cores. This makes it possible to perform analog beamforming.

[0077] Seventh embodiment The seventh embodiment is a combination of the second and third embodiments. In the seventh embodiment, the differences from the second and third embodiments will be mainly described.

[0078] Fig. 10 is a diagram showing a configuration example of the radio unit 6f and the extension unit 7a-n in the seventh embodiment. The radio unit 6f corresponds to the radio unit 6 shown in Fig. 1. The extension unit 7a-n corresponds to the extension unit 7-n shown in Fig. 1. In the seventh embodiment, the radio unit 6f performs digital beamforming and analog beamforming on the downlink radio signal. That is, the radio unit 6f performs hybrid beamforming on the downlink radio signal.

[0079] For comparison, an example of conventional hybrid beamforming is shown in Reference 1 (Suyama et al., "5G Multi-Antenna Technology," NTT DOCOMO Technical Journal Vol. 23 No. 4 (2016)).

[0080] The radio unit 6f includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The radio unit 6f further includes a digital beam control unit 64 in the upstream direction (dispersion unit side) relative to the inverse fast Fourier transform unit 60-n. The radio unit 6f further includes a first analog beam control unit 65 between the D / A conversion unit 61-n and the first electro-optical conversion unit 62-n.

[0081] As described above, the digital beam control unit 64 adjusts the phase of one or more downstream streams (digital electrical signals associated with wireless signals). The first analog beam control unit 65 adjusts the phase of each of the first analog electrical signals output from the multiple D / A conversion units 61. This makes it possible to perform hybrid beamforming.

[0082] Eighth embodiment The eighth embodiment is a combination of the second embodiment and the fourth embodiment. In the eighth embodiment, the differences from the second embodiment and the differences from the fourth embodiment will be mainly described.

[0083] Fig. 11 is a diagram showing a configuration example of a radio unit 6g and extension units 7a-n in the eighth embodiment. The radio unit 6g corresponds to the radio unit 6 shown in Fig. 1. The extension units 7a-n correspond to the extension units 7-n shown in Fig. 1. In the eighth embodiment, the radio unit 6g performs digital beamforming and analog beamforming on downlink wireless signals. That is, the radio unit 6g performs hybrid beamforming on downlink wireless signals.

[0084] The wireless unit 6g includes M combinations (systems) of an inverse fast Fourier transform unit 60-n, a D / A conversion unit 61-n, and a first electro-optical conversion unit 62-n. The wireless unit 6g further includes a digital beam control unit 64 in the upstream direction (dispersion unit side) relative to the inverse fast Fourier transform unit 60-n. The wireless unit 6g further includes a second analog beam control unit 66 in the downstream direction (extension unit side) relative to the first electro-optical conversion unit 62-n.

[0085] As described above, the digital beam control unit 64 adjusts the phase of one or more downstream streams (digital electrical signals associated with wireless signals). The second analog beam control unit 66 adjusts the phase of each optical signal output from the multiple first electro-optical conversion units 62-n. This makes it possible to perform hybrid beamforming. Ninth embodiment The ninth embodiment is a combination of the second embodiment and the fifth embodiment. In the ninth embodiment, the differences from the second embodiment and the fifth embodiment will be mainly described.

[0086] Fig. 12 is a diagram showing a configuration example of the wireless unit 6c and the extension unit 7c-n in the ninth embodiment. The wireless unit 6c corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7c-n corresponds to the extension unit 7-n shown in Fig. 1. In the ninth embodiment, the wireless unit 6c performs digital beamforming on the downstream wireless signal. The extension unit 7c-n performs analog beamforming on the downstream wireless signal. That is, the wireless unit 6c and the extension unit 7c-n perform hybrid beamforming on the downstream wireless signal.

[0087] As described above, the digital beam control unit 64 adjusts the phase of one or more downstream streams (digital electrical signals associated with wireless signals). The third analog beam control unit 73 adjusts the phase of each of the second analog electrical signals output from the multiple first photoelectric conversion units 70-n. The third analog beam control unit 73 may perform analog beamforming based on control information transmitted from the digital beam control unit 64. This makes it possible to perform hybrid beamforming.

[0088] Tenth embodiment The tenth embodiment is a combination of the second embodiment and the sixth embodiment. In the tenth embodiment, the differences from the second embodiment and the sixth embodiment will be mainly described.

[0089] Fig. 13 is a diagram showing a configuration example of the wireless unit 6c and the extension unit 7d-n in the tenth embodiment. The wireless unit 6c corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7d-n corresponds to the extension unit 7-n shown in Fig. 1. In the tenth embodiment, the wireless unit 6c performs digital beamforming on the downstream wireless signal. The extension unit 7d-n performs analog beamforming on the downstream wireless signal. That is, the wireless unit 6c and the extension unit 7d-n perform hybrid beamforming on the downstream wireless signal.

[0090] As described above, the digital beam control unit 64 adjusts the phase of one or more downstream streams (digital electrical signals associated with wireless signals). The fourth analog beam control unit 74 adjusts the phase of each optical signal output from the multiple first electro-optical conversion units 62-n. The fourth analog beam control unit 74 may perform analog beamforming based on control information transmitted from the digital beam control unit 64. This makes it possible to perform hybrid beamforming.

[0091] Eleventh embodiment The eleventh embodiment differs from the first embodiment in that the extension unit transmits an upstream optical signal to the wireless unit. The eleventh embodiment will be described focusing on the differences from the first embodiment.

[0092] In the eleventh embodiment, the extension unit 7 shown in FIG. 1 transmits an optical signal corresponding to an upstream wireless signal to the wireless unit 6 by using an analog RoF. The wireless unit 6 outputs M upstream streams corresponding to the optical signal to the distribution unit 5. The distribution unit 5 generates an upstream stream by performing predetermined signal processing (e.g., decoding) on ​​the M upstream streams (digital electrical signals associated with the wireless signals). The aggregation unit 4 acquires the upstream stream from the distribution unit 5 (DU). The aggregation unit 4 generates upstream data by performing predetermined signal processing on the upstream stream (digital electrical signal). The higher-level device 2 acquires the upstream data from the aggregation unit 4 (CU).

[0093] Fig. 14 is a diagram showing a configuration example of the wireless unit 6h and the extension unit 7e-n in the eleventh embodiment. The wireless unit 6h corresponds to the wireless unit 6 shown in Fig. 1. The extension unit 7e-n corresponds to the extension unit 7-n shown in Fig. 1. In the eleventh embodiment, the wireless unit 6h and the extension unit 7e-n do not need to perform beamforming of the upstream wireless signal. The extension unit 7e-n transmits the upstream optical signal to the wireless unit 6h by using an analog RoF.

[0094] The wireless unit 6h includes M combinations (systems) of a second optical-electrical conversion unit 67-n, an A / D conversion unit 68-n (analog-digital conversion unit), and a fast Fourier transform unit 69-n. The extension unit 7e-n includes M combinations (systems) of an antenna element 71-n and a second optical-electrical conversion unit 75-n. The extension unit 7e-n may include M amplifiers that amplify the intensity of an analog electrical signal or an optical signal.

[0095] The second electro-optical conversion unit 75-n and the second opto-electrical conversion unit 67-n are connected to each other using an optical fiber 9-n. The optical fiber 9-n may be a single-core fiber having M cores or a multi-core fiber having M cores.

[0096] Next, an example of the operation of the wireless unit 6h and the extension unit 7e-n will be described. 15 is a diagram showing an example of the operation of the wireless unit 6h and the extension unit 7e-n in the 11th embodiment. The extension unit 7e-n uses M antenna elements 71 to obtain an upstream wireless signal from a wireless terminal (not shown).

[0097] The antenna element 71-nm converts the upstream radio signal into a third analog electrical signal. The antenna element 71-nm outputs the third analog electrical signal corresponding to the upstream radio signal to the second electrical-to-optical converter 75-nm (step S201). The second electrical-to-optical converter 75-nm converts the third analog electrical signal into an optical signal (step S202).

[0098] The optical fiber 9-nm optically transmits the signal converted by the second electro-optical conversion unit 75-nm to the second opto-electrical conversion unit 67-nm (step S203). The second opto-electrical conversion unit 67-nm converts the transmitted optical signal into a fourth analog electrical signal. The second opto-electrical conversion unit 67-nm transmits the fourth analog electrical signal to the A / D conversion unit 68-nm (step S204).

[0099] The A / D conversion unit 68-nm converts the fourth analog electrical signal into a digital electrical signal. In this way, the extension unit 7e-n transmits an upstream optical signal to the wireless unit 6h using the analog RoF. The A / D conversion unit 68-nm outputs a digital electrical signal corresponding to the fourth analog electrical signal to the fast Fourier transform unit 69-nm (step S205). The fast Fourier transform unit 69-nm executes a fast Fourier transform (FFT) on the digital electrical signal corresponding to the fourth analog electrical signal. The fast Fourier transform unit 69-nm outputs the digital electrical signal subjected to the fast Fourier transform to the dispersing unit 5 (step S206).

[0100] As described above, the antenna element 71-nm converts the upstream radio signal into a third analog electrical signal. The second electrical-to-optical converter 75-nm converts the third analog electrical signal into an optical signal. The optical fiber 9-nm optically transmits the signal converted by the second electrical-to-optical converter 75-nm to the second optical-to-electrical converter 67-nm. The second optical-to-electrical converter 67-nm converts the transmitted optical signal into a fourth analog electrical signal. The A / D converter 68-nm converts the fourth analog electrical signal into a digital electrical signal. The fast Fourier transformer 69-nm performs a fast Fourier transform on the digital electrical signal corresponding to the fourth analog electrical signal.

[0101] This makes it possible to suppress increases in equipment costs for expanding the area in which wireless communication services are provided.

[0102] (Modification of the eleventh embodiment) The modification of the 11th embodiment differs from the 11th embodiment in that a wavelength division multiplexed optical signal is transmitted between the radio unit and the extension unit. The modification of the 11th embodiment will be described focusing on the differences from the 11th embodiment.

[0103] Fig. 16 is a diagram showing a configuration example of a radio unit 6i and an extension unit 7f in a modification of the eleventh embodiment. The radio unit 6i corresponds to the radio unit 6 shown in Fig. 1. The extension unit 7f-n corresponds to the extension unit 7 shown in Fig. 1. The radio unit 6i and the extension unit 7f-n are connected to each other using optical fibers 9. The number of optical fibers 9-n may be less than the number (M) of streams (digital electrical signals associated with radio signals). The optical fibers 9-n do not need to be multi-core fibers having the same number of cores as the number of streams.

[0104] The wireless unit 6i includes M combinations (systems) of a second photoelectric conversion unit 67-n, an A / D conversion unit 68-n (analog-to-digital conversion unit), and a fast Fourier transform unit 69-n. The wireless unit 6i further includes a demultiplexer 77.

[0105] The extension 7e-n includes M combinations (systems) of antenna elements 71-n and second electro-optical converters 75-n. The extension 7f-n further includes a multiplexer 76. The extension 7e-n may include M amplifiers for amplifying the intensity of analog electrical signals or optical signals.

[0106] The second electro-optical converters 75-n convert the third analog electrical signals into optical signals having different wavelengths. The multiplexer 76 generates a wavelength division multiplexed optical signal by multiplexing the optical signals having different wavelengths. The optical fiber 9 transmits the wavelength division multiplexed optical signal to the demultiplexer 77.

[0107] The demultiplexer 77 demultiplexes the wavelength division multiplexed optical signal into multiple optical signals having different wavelengths. The demultiplexer 77 outputs the M optical signals having different wavelengths to the M second opto-electrical conversion units 67-n. The M second opto-electrical conversion units 67-n convert the transmitted optical signals into fourth analog electrical signals having a predetermined wavelength. The A / D conversion unit 68-nm converts the fourth analog electrical signal into a digital electrical signal. The fast Fourier transform unit 69-nm performs a fast Fourier transform on the digital electrical signal corresponding to the fourth analog electrical signal.

[0108] As described above, the multiplexer 76 generates a wavelength division multiplexed optical signal by multiplexing a plurality of optical signals having different wavelengths. The optical fiber 9 transmits the wavelength division multiplexed optical signal to the demultiplexer 77. The demultiplexer 77 demultiplexes the wavelength division multiplexed optical signal into a plurality of optical signals having different wavelengths. This makes it possible to reduce the number of optical fibers 9-n.

[0109] In the second to tenth embodiments, similarly to the eleventh embodiment, the optical fiber 9 may transmit an upstream optical signal.

[0110] When the optical fiber 9 transmits an upstream optical signal, each of the radio units shown in the second to tenth embodiments includes the above-mentioned fast Fourier transform unit instead of the above-mentioned inverse fast Fourier transform unit. The radio unit includes the above-mentioned A / D conversion unit instead of the above-mentioned D / A conversion unit. The radio unit includes the above-mentioned second optical-electrical conversion unit instead of the above-mentioned first optical-electrical conversion unit.

[0111] When the optical fiber 9 transmits an upstream optical signal, each of the extension parts shown in the second to tenth embodiments includes the above-mentioned second electro-optical conversion part instead of the above-mentioned first opto-electrical conversion part.

[0112] (Hardware configuration example) 17 is a diagram showing an example of a hardware configuration of a base station 3 (wireless communication device) in each embodiment. Some or all of the functional units of the base station 3 are realized as software by a processor 111 such as a CPU (Central Processing Unit) executing a program stored in a storage device 113 having a non-volatile recording medium (non-transient recording medium) and a memory 112. The program may be recorded in a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM (Read Only Memory), a CD-ROM (Compact Disc Read Only Memory), or a non-transient recording medium such as a storage device built into a computer system, such as a hard disk.

[0113] Some or all of the functional units of base station 3 may be realized using hardware including electronic circuits (electronic circuits or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0114] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and designs that do not deviate from the gist of the present invention are also included. [Industrial Applicability]

[0115] The present invention is applicable to wireless communication systems. [Explanation of symbols]

[0116] 1...wireless communication system, 2...high-level device, 3...base station, 4...aggregation unit, 5...dispersion unit, 6, 5a, 6b, 6c, 6d, 6e, 6f, 6g, 6h, 6i...radio unit, 7, 7a, 7b, 7c, 7d, 7e, 7f...extension unit, 8...coaxial cable, 9...optical fiber, 10...optical splitter, 11...coverage area, 12...coverage area, 13...area, 60...inverse fast Fourier transform, 61...D / A conversion unit, 62...first electro-optical conversion unit, 63...multiplexer, 64...digital beam control unit, 65...first analog beam control unit, 66...second analog beam control unit, 67...second photoelectric conversion unit, 68...A / D conversion unit, 69...fast Fourier transform, 70...first photoelectric conversion unit, 71...antenna element, 72...splitting filter, 73...third analog beam control unit, 74...fourth analog beam control unit, 75...second photoelectric conversion unit, 76...multiplexer, 77...splitting filter, 100...shield, 110...shield, 111...processor, 112...memory, 113...storage device, 200...radio unit, 201...coverage area, 202...area

Claims

1. A wireless communication method executed by a wireless communication device, comprising: an inverse fast Fourier transform step of performing an inverse fast Fourier transform on a digital electrical signal associated with the downstream wireless signal; a digital-to-analog conversion step of converting the inverse fast Fourier transformed digital electrical signal into a first analog electrical signal; an electrical-to-optical conversion step of converting the first analog electrical signal into an optical signal; transmitting the optical signal; an opto-electrical conversion step of converting the transmitted optical signal into a second analog electrical signal; transmitting the downstream radio signal in response to the second analog electrical signal; Including, Each of the first analog electrical signal and the second analog electrical signal is an electrical signal in a high frequency band. A wireless communication method.

2. a multiplexing step of multiplexing a plurality of the optical signals having different wavelengths to generate the optical signal that is wavelength division multiplexed; a demultiplexing step of demultiplexing the wavelength division multiplexed optical signal into a plurality of optical signals having mutually different wavelengths; Further comprising: In the step of transmitting the optical signal, an optical fiber transmits the optical signal which is wavelength division multiplexed. The wireless communication method according to claim 1 .

3. and further comprising a digital beam control step of adjusting a phase of the digital electrical signal. The wireless communication method according to claim 1 or 2.

4. further comprising an analog beam control step of adjusting a phase of the optical signal, the first analog electrical signal, or the second analog electrical signal. The wireless communication method according to any one of claims 1 to 3.

5. an inverse fast Fourier transform unit that performs an inverse fast Fourier transform on a digital electrical signal associated with a downstream wireless signal; a digital-to-analog converter that converts the inverse fast Fourier transformed digital electrical signal into a first analog electrical signal; an electrical-to-optical converter that converts the first analog electrical signal into an optical signal; an optical fiber for transmitting the optical signal; an opto-electrical conversion unit that converts the transmitted optical signal into a second analog electrical signal; an antenna element for transmitting the downstream radio signal in response to the second analog electrical signal; Equipped with Each of the first analog electrical signal and the second analog electrical signal is an electrical signal in a high frequency band. Wireless communication device.

6. a multiplexer that multiplexes a plurality of the optical signals having different wavelengths to generate a wavelength division multiplexed optical signal; a demultiplexer that demultiplexes the wavelength division multiplexed optical signal into a plurality of optical signals having mutually different wavelengths; Further comprising: the optical fiber transmits the optical signal which is wavelength division multiplexed; 6. The wireless communication device according to claim 5.

7. Further comprising a digital beam control unit for adjusting a phase of the digital electrical signal.

7. The wireless communication device according to claim 5 or 6.

8. further comprising an analog beam control unit that adjusts a phase of the optical signal, the first analog electrical signal, or the second analog electrical signal; A wireless communication device according to any one of claims 5 to 7.

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