Wireless communication system

Abstract

To provide a wireless communication system that can expand a coverage area while reducing power consumption, radio equipment costs, and base station installation costs.SOLUTION: A wireless communication system includes a base station having an RU 410 that uses multiple antenna elements to emit beam-shaped radio waves with directivity in a fixed direction, and a radio wave scattering component 420 that scatters and reflects received radio waves. The RU 410 is installed on the floor of a building and emits a beam of radio waves toward the ceiling of the building. The radio wave scattering component 420 is installed on the ceiling side of the building and on an extension of the direction in which the beam-shaped radio waves are emitted.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a wireless communication system including a base station deployed indoors in a building.

Background Art

[0002] In recent years, wireless access systems have become widespread and are essential for leading a rich life. Looking back from the first generation to the fourth generation of mobile phones, technologies mainly for speeding up wireless communication have evolved. In the fifth generation, in addition to speeding up, ultra-low latency and a large number of simultaneous connections are required. To achieve these, broadbandization is effective, and since the frequency utilization situation is tight, from the fifth generation onwards, the use of high-frequency bands such as the millimeter wave band is effective. For example, in the fifth generation, the 28 GHz band close to the millimeter wave band is used.

[0003] However, as the frequency increases (i.e., the wavelength becomes shorter), for example, the reception area of a single planar antenna becomes smaller, so there is a problem that the propagation loss becomes larger compared to the microwave band. Also, when the propagation loss becomes larger, the coverage area per wireless device becomes smaller, leading to an increase in cost.

[0004] To solve this problem, beam forming (BF) technology is adopted in the fifth generation. The BF technology can obtain a sharp antenna directivity by arranging (arraying) a plurality of antennas and controlling the amplitude and phase of the transmission signals of each antenna element. Also, the radio wave propagation loss can be compensated by the antenna gain.

[0005] In the transmission BF, the phase of the transmission signal radiated from multiple antennas is controlled and spatially combined, so that in some places the phases of the radio waves radiated from each antenna are close to the same phase and the power is reinforced, and in other places the power is canceled out. As a result, a composite gain can be obtained in places where the power is reinforced, compensating for radio wave propagation loss and enabling long-distance transmission. Alternatively, the desired signal power to noise power ratio at the receiver increases, so high-speed transmission is possible by increasing the number of levels of quadrature amplitude modulation.

[0006] With reference to FIG. 1, the directivity when a narrow beam is formed by BF will be described. Here, an example is taken of a planar antenna, which is widely used in the microwave and millimeter wave bands. FIG. 1(a) is an example of one subarray (or one element), and the antenna beam has the directivity of a planar antenna. FIG. 1(b) is an example of four subarrays, and the directivity of the antenna beam is sharper than that of one subarray, and the combined power in the front direction is larger. FIG. 1(c) is an example of 16 subarrays, and the directivity of the antenna beam is even sharper, and the combined power in the front direction is also larger. FIG. 1(d) shows a 16 subarray, but is an example of a case where the phase of the transmission signal of each antenna element is different from that of FIG. 1(c), and the directivity of the antenna beam is controlled to face leftward rather than forward.

[0007] By making the antenna directivity sharper, it is possible to reduce interference with other wireless devices, and there is also the advantage that the frequency usage efficiency is improved. The principles of BF technology and directivity control methods are well-known technologies in many documents, so a detailed explanation is omitted. In addition, as shown in Patent Document 1, development of a hybrid BF that combines analog BF and digital BF is also underway.

[0008] There are several methods for receiving BF, such as maximizing the gain in the direction of arrival of the desired wave and minimizing the gain in the direction of arrival of the interference wave when combining the received signals of each antenna. It is also known that the reception performance can be improved by providing multiple antennas and performing spatial diversity. Various research and practical applications are also being conducted on algorithms that automatically select and execute the optimal method from the above receiving techniques according to changes in the propagation environment.

[0009] Another technology for solving the above problem is a distributed antenna system (DAS) that can be applied to base stations (gNodeB) of a fifth generation mobile communication system (5G system). FIG. 2 shows an example of the configuration of a distributed antenna system in a base station. A base station 100 connected to a core network includes a CU (Central Unit) 110, a plurality of DUs (Distributed Units) 120 connected to the CU 110, and a plurality of RUs (Radio Units) 130 connected to each of the DUs 120. The CU 110 is a centralized control device that mainly executes data processing and network control. The DU 120 is a unit that mainly executes radio signal processing. The RU 130 is a unit equivalent to the radio section of a general radio device, and is composed of an RF unit, an antenna, and the like.

[0010] A distributed antenna system as shown in Fig. 2 can obtain economic benefits by centrally controlling multiple DUs 120 with one CU 110. In Fig. 2, one RU 130 is connected to one DU 120, but multiple RUs 130 may be connected to one DU 120. In the distributed antenna system of Fig. 2, multiple RUs 130 under the DU 120 are used for wireless communication with different mobile stations. The architecture of the 5G system is specified as O-RAN (Open Radio Access Network), for example (see Non-Patent Document 1, for example).

[0011] Fig. 3 shows another example of the configuration of a distributed antenna system in a base station. A base station 200 connected to a core network includes a CU 210 and multiple DUs 220 connected to the CU 210. The CU 210 is a centralized control device that mainly performs data processing and network control. The DU 220 is a unit that mainly performs wireless signal processing, and is composed of an RF unit, an antenna, and the like. The DU 220 in Fig. 3 is an expression that includes the RU 130 in Fig. 2 (for example, see Non-Patent Document 2).

[0012] Fig. 4 shows a configuration example of the DU 220 in the distributed antenna system of Fig. 3. Fig. 5 shows an arrangement example of the DU 220 in the distributed antenna system of Fig. 3. As shown in Fig. 4 and Fig. 5, the DU 220 includes a BBU (Base Band Unit) 230 and a plurality of RUs (Radio Units) 240 connected to the BBU 230. In the distributed antenna system of Fig. 2, the plurality of RUs 130 under the DU 120 are used for wireless communication with different mobile stations, whereas in the distributed antenna system of Fig. 3, the plurality of RUs 240 under the DU 220 are used for wireless communication with the same mobile station, as described later.

[0013] The BBU 230 is a unit that centralizes baseband signal processing and control of the distributed antenna system. The RU 240 is a unit that corresponds to the radio section of a general radio device, and is composed of an RF unit, an antenna, and the like. In this example, multiple RUs 240 are arranged at intervals so as to complement each other's coverage areas 242. The CU 210 and the BBU 230, and the BBU 230 and the RU 240 are connected by connection cables 250 such as optical fibers.

[0014] RU240 includes a transmitting / receiving antenna, a power amplifier, an LNA (Low Noise Amplifier), a frequency filter, a D / A (Digital to Analog) converter, an A / D (Analog to Digital) converter, an OFDM (Orthogonal Frequency Division Multiplexing) modulator, an OFDM demodulator, an O / E (Optical to Electronic) converter, and an E / O (Electronic to Optical) converter.

[0015] The BBU 230 distributes the downlink signal transmitted from the CU 210 to the multiple RUs 240. Each of the multiple RUs 240 transmits the same downlink signal distributed from the BBU 230 from a transmitting / receiving antenna. The BBU 230 also receives the uplink signals transmitted from each of the multiple RUs 240 and combines them. The uplink signals transmitted from the multiple RUs 240 generally differ depending on the positional relationship between the mobile station with which the communication is made and the RU 240, the radio wave environment, noise, etc. The BBU 230 transmits the combined uplink signal to the CU 210.

[0016] By connecting multiple RUs 240 to the BBU 230 and controlling them centrally, the coverage area of ​​the base station can be expanded. In addition, since the number of BBUs 230 can be kept relatively small compared to the size of the coverage area, this is economical. Since the purpose of the distributed antenna system is to expand the coverage area, the signals distributed from the BBU 230 to each RU 240 and transmitted from the antenna of each RU 240 are the same for all RUs 240 connected to the BBU 230. On the other hand, the signals received by the antenna of each RU 240 and aggregated at the BBU 230 are different for each RU 240, and are synthesized at the BBU 230 and transmitted to the CU 210. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] JP 2018-107594 A [Non-patent literature]

[0018] [Non-Patent Document 1] Umesh Anil et al., "O-RAN Fronthaul Specifications Overview," NTT DOCOMO Technical Journal Vol. 27 No. 1, April 2019, pp. 43-55 [Non-Patent Document 2] Umesh Anil et al., "5G Radio Access Network Standardization Trends," NTT DOCOMO Technical Journal Vol. 25 No. 3, October 2017, pp. 33-43 Summary of the Invention [Problem to be solved by the invention]

[0019] In the millimeter wave band, the transmission loss from an outdoor radio device to the inside of a building (i.e., indoors) is larger than in the microwave band, and the area in which radio waves can be received is smaller. For this reason, it is necessary to expand the indoor coverage area using a distributed antenna system or the like. However, when building a distributed antenna system with radio devices equipped with BF functionality, there is a problem that the maximum area expansion effect and maximum wireless communication performance are not necessarily obtained because the sharply directional antenna beam is dynamically controlled. There is also the problem that there are restrictions on the installation of wireless antenna units.

[0020] The first problem in the conventional method will be described with reference to Fig. 6. The figure shows an example in which the RU 240 is installed on the wall 310 of a building. The RU 240 has a BF function, which increases the propagation distance of radio waves, but sharpens the directivity of the antenna beam. Therefore, if an obstruction (e.g., a pillar 320) is present, the radio waves are blocked by the obstruction and cannot reach beyond the obstruction, and since millimeter waves are difficult to diffract, a dead zone 340 occurs within the planned coverage area 330. In particular, the height at which the RU 240 is installed indoors is limited by the height of the building's walls and ceiling, so that when the beam is directed far away, the angle between the floor and the beam becomes small, and the radio waves are blocked even by relatively low obstructions such as people.

[0021] The second problem in the conventional method will be described with reference to FIG. 7. The figure shows an example in which the RU240 is installed on the ceiling 350 of a building. In many cases, the obstruction is in contact with the floor, and the RU240 installed on the ceiling has a nearly line-of-sight environment, so the first problem is solved. However, despite the ability to propagate radio waves over long distances using BF, the installation height is limited by the height of the ceiling indoors, so the coverage area 330 becomes small. For example, if the directivity half-width of a planar antenna is calculated as a general 90°, the coverage area 330 will be limited to a circle with a radius equal to the installation height (h). Thus, the configuration in which the RU240 with BF function is installed on the ceiling has a significantly low performance relative to the cost.

[0022] The present invention has been made in consideration of the above-described conventional circumstances, and aims to provide a wireless communication system that can expand the coverage area while suppressing power consumption, reducing radio equipment costs, and reducing base station construction costs. [Means for solving the problem]

[0023] In order to achieve the above object, a wireless communication system according to the present invention is configured as follows. That is, in a wireless communication system equipped with a base station deployed inside a building, the base station has a wireless antenna unit that uses multiple antenna elements to emit beam-shaped radio waves having directionality in a fixed direction, and a radio wave scattering component that scatters and reflects the received radio waves, the wireless antenna unit is installed on the floor side of the building and emits beam-shaped radio waves toward the ceiling of the building, and the radio wave scattering component is installed on the ceiling side of the building on an extension of the direction in which the beam-shaped radio waves are emitted.

[0024] As an example, the wireless antenna unit is installed on the top surface of an object on the floor side of a building. As another example, the wireless antenna unit is installed on the floor surface of a building. The wireless antenna unit may be installed, for example, so as to emit a beam-shaped radio wave directly upward. The length of the wiring electrically connecting the antenna element and other electrical components may be the same for all antenna elements.

[0025] The wireless communication system may also include a plurality of wireless antenna units and radio wave scattering components. In this case, the wireless communication system may further include another wireless antenna unit that uses a plurality of antenna elements to emit a beam-shaped radio wave having directivity in any direction, and this another wireless antenna unit may be installed on the ceiling side of the building and emit the beam-shaped radio wave toward the floor of the building. Effect of the Invention

[0026] According to the present invention, it is possible to provide a wireless communication system that can expand the coverage area while suppressing power consumption, reducing the cost of wireless devices, and reducing the cost of installing base stations. [Brief description of the drawings]

[0027] [Figure 1] 1A and 1B are diagrams illustrating examples of a planar antenna and beamforming directivity. [Diagram 2] FIG. 1 is a diagram illustrating a configuration example of a distributed antenna system. [Diagram 3] FIG. 11 is a diagram illustrating another configuration example of a distributed antenna system. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of a DU in the distributed antenna system of FIG. [Diagram 5] FIG. 4 is a diagram illustrating an example of an arrangement of DUs in the distributed antenna system of FIG. [Figure 6] FIG. 1 is a diagram illustrating an example of a first problem in a conventional method. [Figure 7] FIG. 11 is a diagram illustrating an example of a second problem in the conventional method. [Figure 8]1 is a diagram illustrating an example of the configuration of a wireless communication system according to a first embodiment of the present invention. [Figure 9] FIG. 9 is a diagram illustrating an example of the configuration of an RU in the wireless communication system of FIG. [Figure 10] 9 is a diagram illustrating an example of the configuration of an antenna included in an RU in the wireless communication system of FIG. 8. [Figure 11] FIG. 11 is a diagram illustrating an example of the configuration of a wireless communication system according to a second embodiment of the present invention. [Figure 12] 12 is a diagram illustrating an example of functional division of a base station in the wireless communication system illustrated in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] A wireless communication system according to an embodiment of the present invention will be described with reference to the drawings. (First embodiment) FIG. 8 shows a configuration example of a wireless communication system according to a first embodiment of the present invention. A base station in the wireless communication system according to the first embodiment is based on the configuration of the base station shown in FIG. 2 and is deployed indoors in a building. Since the area expansion that is the subject of the present invention is mainly performed by the RU and the problem that the present invention is to solve is related to the RU, FIG. 8 focuses on the area expansion beyond the DU 120. The wireless communication system of this example includes a base station having an RU 410 and a radio wave scattering component 420. Although FIG. 8 shows one RU 410 and one radio wave scattering component 420, multiple sets of the RU 410 and the radio wave scattering component 420 may be included.

[0029] The RU 410 is a unit having an antenna that emits a beam-shaped radio wave having a directionality in a fixed direction using multiple antenna elements, and does not have a BF function. The RU 410 is installed on the floor side of a building, and is capable of emitting a beam-shaped radio wave toward the ceiling of the building and receiving radio waves from the ceiling side. In FIG. 8, the RU 410 is placed on an object 360 placed on the floor surface, and emits a beam-shaped radio wave directly upward. The object 360 is, for example, a stand, a desk, a table, etc., and the RU 410 is placed on the upper surface of the object 360. It is desirable not to place an obstruction between the RU 410 and the radio wave scattering component 420 so that they are in a line-of-sight environment. The RU 410 is connected to the DU 120 shown in FIG. 2 through a connection cable 250.

[0030] The radio wave scattering component 420 is a component that has the effect of scattering and reflecting received radio waves. The radio wave scattering component 420 is installed on the ceiling side of the building and on an extension of the direction in which the beam-shaped radio waves emitted from the RU 410 are emitted. In Fig. 8, the RU 410 emits beam-shaped radio waves directly upward, so the radio wave scattering component 420 is installed on the ceiling directly above the RU 410. The beam-shaped radio waves emitted in the ceiling direction from the floor-side RU 410 are scattered and reflected toward the floor by the ceiling-side radio wave scattering component 420, thereby achieving the effect of expanding the coverage area of ​​the RU 410.

[0031] The operation of the wireless communication system according to the first embodiment will be described. First, the downlink in which a wireless signal is transmitted from a base station to a mobile station (such as a smartphone) will be described. In the downlink, a signal for the mobile station is input from the DU 120 to the RU 410 of the base station through the connection cable 250. The RU 410 converts the input signal into a wireless signal and transmits it by a radio wave beam emitted toward the ceiling. The radio wave from the RU 410 is reflected toward the floor by the radio wave scattering component 420. The radio wave scattering component 420 has the effect of scattering the radio wave when reflecting it. As an effect of this radio wave scattering effect, it is possible to expand the area where the radio wave from the RU 410 reaches.

[0032] Next, an uplink in which a radio signal is transmitted from a mobile station to a base station will be described. In the uplink, the mobile station transmits a radio signal to the base station in the direction of arrival of the downlink radio signal, that is, in the direction of the radio wave scattering component 420. Radio waves from the mobile station are reflected toward the floor by the radio wave scattering component 402. As described above, the radio wave scattering component 420 has the effect of scattering radio waves when reflecting them. Therefore, a part of the radio waves from the mobile station reaches the RU 410 and is received by the RU 410. The RU 410 converts the received radio signal into a digital signal, an optical signal, or the like, and outputs it to the DU 120 via the connection cable 250.

[0033] In both the downlink and the uplink, the radio waves are scattered by the radio wave scattering component 420, so that the received power is small even if the transmission power is the same as that of the conventional BF. Therefore, in this example, in order to supplement the power, the number of antenna elements of the RU 410 is increased to increase the antenna gain. Since passive antenna elements can be used, the increase in cost is minor. In addition, the directionality of the radio waves becomes stronger as the antenna elements are increased. In other words, the radio waves become narrower (i.e., the beam becomes narrower). For this reason, it becomes difficult for the BF to track the mobile station, but since the radio wave scattering component 420 of this example is fixedly installed, this is not a particular problem. In addition, this is more advantageous than increasing the number of power amplifiers and LNAs. Furthermore, it is possible to reduce power consumption.

[0034] Fig. 9 shows an example of the configuration of an RU 410 in a base station of the wireless communication system of this example. As shown in Fig. 9, the RU 410 has, as components, an O / E converter 501, a D / A converter 502, a frequency conversion section 503, a power amplifier (PA) 504, a TDD (Time Division Duplex) switch 505, an antenna 506, an LNA (Low Noise Amplifier) ​​507, a frequency conversion section 508, an A / D converter 509, and an E / O converter 510.

[0035] The signal from the DU 120 is converted from an optical signal to an electrical signal by an O / E converter 501. A D / A converter 502 converts the digital signal obtained by the O / E conversion into an analog signal. A frequency conversion unit 503 frequency converts the IF signal obtained by the D / A conversion into an RF signal. A power amplifier 504 amplifies the power of the RF signal after frequency conversion. A TDD switch 505 switches the path between the downlink (transmission) and the uplink (reception). In the downlink, an RF signal is transmitted from an antenna 506.

[0036] In the uplink, an antenna 506 receives an RF signal from a mobile station. An LNA 507 amplifies the RF signal received by the antenna 506. A frequency converter 508 converts the amplified RF signal into an IF signal. An A / D converter 509 converts the frequency-converted IF signal from an analog signal to a digital signal. An E / O converter 510 converts the electrical signal obtained by the A / D conversion into an optical signal.

[0037] In FIG. 9, only the functional blocks necessary for simplicity of explanation are shown, but various elements well known to those skilled in the art, such as a bandpass filter, AGC (Automatic Gain Control), AFC (Automatic Frequency Control), etc., may be inserted between each of the components shown in the figure.

[0038] Fig. 10 shows an example of the configuration of an antenna 506 of the RU 410 in the base station of the wireless communication system of Fig. 8. The antenna 506 has a planar antenna structure as described with reference to Fig. 1. In the conventional method, in order to perform BF, it is necessary to supply transmission signals with different amplitudes and phases to each antenna element during transmission, and it is necessary to supply the signals of each antenna element independently to the BF section during reception. In addition, amplitude control and phase control for BF are required, and for example, when performing analog BF, it is necessary to provide an amplifier, a power attenuator, and a phase shifter. Alternatively, when performing digital BF, the same number of D / A converters and A / D converters as the number of antenna elements are required, which is an obstacle to miniaturization and cost reduction of radio equipment.

[0039] In contrast, in this example, since BF is not performed, amplitude control and phase control for BF are not required. Also, only one power amplifier or LNA may be used. As shown in FIG. 10, other electrical components such as amplifiers and LNAs and each antenna element (black squares in the figure) are electrically connected to each other by wiring of the same length, such as a microstrip line. In this way, when the length of the wiring connecting each antenna element to other electrical components is the same for all antenna elements (equal length wiring), the phases of the transmission signals of each antenna element match each other, so that the directivity of the radio waves is in the front direction (see FIG. 1(c)). The RU 410 and the radio wave scattering component 420 shown in FIG. 8 are arranged in a positional relationship such that the direction of the directivity of the radio waves from the RU 410 and the front direction of the radio wave scattering component 420 match. In other words, the RU 410 and the radio wave scattering component 420 are arranged to face each other directly.

[0040] Next, a specific example of the radio wave scattering component 420 will be described. As an example, the radio wave scattering component 420 is formed of a material that reflects radio waves, and the reflection surface has a convex shape. It is known that a convex mirror that reflects radio waves scatters radio waves. On the other hand, the incidence angle and reflection angle of a normal plane mirror are determined by physical laws, and radio waves that are perpendicularly incident on the mirror surface are reflected in the same direction. As another example, the radio wave scattering component 420 actively scatters radio waves by applying an embossed unevenness to a flat plate or the like formed of a material that reflects radio waves. It is known that radio waves of a target frequency can be scattered by adjusting the density of the unevenness according to the wavelength of the radio waves.

[0041] (Second Example) Fig. 11 shows an example of the configuration of a wireless communication system according to a second embodiment of the present invention. The second embodiment is an example in which the present invention is applied to the distributed antenna system of Figs. 3 to 5. In Fig. 11, three sets of RUs 410 and radio wave scattering components 420 are arranged in the same room of a building. These RUs 410 are connected to BBU 230 shown in Fig. 4 via connection cables 250. The number of sets of RUs 410 and radio wave scattering components 420 is arbitrary.

[0042] The RU 410 does not have a BF function, and is installed on an object 360 on the floor side of the building so that it can transmit radio waves in the direction of the ceiling and receive radio waves from the ceiling side. In addition, radio wave scattering components 420 that have the effect of scattering radio waves are installed on the ceiling. The same number of radio wave scattering components 420 as the number of RUs 410 (three in this example) are installed. The beam-shaped radio waves emitted from the floor-side RU 410 in the direction of the ceiling are scattered and reflected back to the floor side by the ceiling-side radio wave scattering components 420, thereby achieving the effect of expanding the coverage area of ​​the RU 410.

[0043] The set of RU 410 and radio wave scattering component 420 is installed at a certain interval so that the areas reached by radio waves scattered and reflected by each radio wave scattering component 420 complement each other to cover the entire room. The interval between the set of RU 410 and radio wave scattering component 420 may be determined according to the range over which the radio wave scattering component 420 scatters radio waves when reflecting them.

[0044] The BBU230 has an RU selection function that selects one of multiple RUs 410 to be used for wireless communication with a mobile station. The RU selection function can be realized by using BF control information used to control BF. The BF control information is originally used for control to select one of multiple BF patterns, but here it is used to select the RU 410 to be used for wireless communication with a mobile station. In other words, instead of selecting a BF pattern according to the BF control information, an operation to select an RU 410 is performed. Note that when a HUB (e.g., a switching hub) is interposed between the BBU230 and the RU 410, the HUB may be provided with the RU selection function.

[0045] The RU selection function is explained below. First, the interface between the DU and RU is explained. For example, in RRHs (Remote Radio Heads) up to the fourth generation, signal transmission between the CU and DU was mainly performed by RoF (Radio over Fiber). However, in 5G, the signal bandwidth is as wide as several hundred MHz, and the transmission capacity of optical fiber becomes huge and unrealistic. Therefore, a method is adopted to suppress the transmission capacity by optically transmitting the digital signal before OFDM modulation during transmission and the digital signal after OFDM demodulation during reception. In addition, since high frequency bands such as millimeter waves are used for the radio frequency of 5G, it is considered to perform BF using a multi-element antenna, and a signal related to BF is included as a control signal in the optically transmitted digital signal.

[0046] Next, the functional division of the base station function into CU and DU will be described. As an example of the architecture of the 5G system, there is O-RAN (Open Radio Access Network) as shown in Non-Patent Document 1, and the format of the control signal (C-plane) is specified in Split7 specified in the O-RAN specification. In the following, the functional division of the base station function into CU and DU will be described using the widely used interface "split7" of the O-RAN specification as an example, but is not limited to this.

[0047] FIG. 12 shows an example of functional split of a base station in the wireless communication system shown in FIG. 11. The functions of the base station include functions of RRC (Radio Resource Control) 601, PDCP (Packet Data Convergence Protocol) 602, RLC (Radio Link Control) 603, MAC (Medium Access Control) 604, PHY (PHYsical layer) 605, and RF (Radio Frequency) 606.

[0048] In O-RAN "split7", the function of PHY 605 is split. Among the split functions of PHY 605, the CU side is defined as PHY-high 605H, and the DU side is defined as PHY-low 605L. The functions of PHY-high 605H include, in the [downlink / uplink] expression, [encoding / decoding], [scrambling / descrambling], [modulation / demodulation], [layer mapping / equivalent processing, IDFT], [precoding / channel estimation], [resource element mapping / resource element demapping]. The functions of PHY-Low 605L include [transmit digital BF / receive digital BF], [IFFT / FFT]. The functions of RF 606 include [D / A conversion / A / D conversion], [transmit analog BF / receive analog BF].

[0049] PHY-high 605H and PHY-low 605L are connected by a connection cable 250. The U-plane (User-plane) in the interface of the connection cable 250 includes the mapped transmission data and the FFT (Fast Fourier Transform)ed received data. The C-plane (Control-plane) in the interface of the connection cable 250 includes a BeamID which is an example of BF control information. The BeamID is information for selecting one from a plurality of BF patterns preset in the RU.

[0050] In this example, the BeamID is not used to select a BF pattern, but is used to select an RU 410. That is, the BeamID is associated in advance with an RUID, which is identification information for identifying each of the multiple RUs 410. Then, the RU 410 having the RUID corresponding to the BeamID specified in the control signal is selected as the RU that will perform wireless communication with the mobile station. The selected RU 410 does not switch the BF pattern according to the BeamID, but instead emits a beam-shaped radio wave with directionality in a fixed direction.

[0051] Therefore, the radio waves emitted from the selected RU 410 have the directionality shown in Fig. 8 regardless of the BeamID, and can cover a wide area. In addition, in the Beam search process, the mobile station selects the BeamID with the best wireless environment and transmits to the RU 410, but in reality, the wireless environment is almost the same for all BeamIDs, so it does not matter which one is selected. Therefore, there is no need to change the conventional wireless interface.

[0052] As described above, the wireless communication systems according to the first and second embodiments include a base station having RU 410 that uses multiple antenna elements to emit beam-shaped radio waves having directivity in a fixed direction, and radio wave scattering component 420 that scatters and reflects the received radio waves, with RU 410 installed on the floor side of a building and emitting beam-shaped radio waves toward the ceiling of the building, and radio wave scattering component 420 installed on the ceiling side of the building on an extension of the direction in which the beam-shaped radio waves are emitted. RU 410 corresponds to the wireless antenna unit according to the present invention, and radio wave scattering component 420 corresponds to the radio wave scattering component according to the present invention.

[0053] According to the wireless communication system having such a configuration, it is possible to expand the coverage area of ​​the base station by avoiding obstacles such as people and objects inside a building. In other words, this is one solution to the problem of radio wave obstruction caused by obstacles. In addition, since amplitude control and phase control for BF are not required, the cost of expanding the coverage area can be reduced. Also, one power amplifier and one LNA are sufficient. Also, by increasing the number of antenna elements of the wireless antenna unit (RU410), the antenna gain can be increased and the power can be increased, which is more advantageous than increasing the number of power amplifiers and LNAs.

[0054] In addition, when installing conventional wireless antenna units on the ceiling or wall, it was necessary to wire connection cables such as optical fibers and power sources in the ceiling or behind the wall, which increased the installation costs, but with this configuration, the wireless antenna unit can be installed on the floor side, and the radio wave scattering components on the ceiling side do not require a power source, reducing installation costs. Moreover, since it can be installed like modern PC LAN cables and hubs, it will contribute to the spread and expansion of wireless communication areas using high frequencies such as 5G.

[0055] In addition, while conventional maintenance work on wireless antenna units installed on the ceiling had to be performed at a high altitude, with this configuration, maintenance work can be performed on the ground (floor, etc.) In addition, adjustment of the beam-shaped radio waves emitted by the wireless antenna units and confirmation of the base station coverage area can also be performed solely on the ground. As described above, according to the wireless communication systems of the first and second embodiments, it is possible to expand the coverage area while suppressing power consumption, reducing the cost of wireless devices, and reducing the cost of installing base stations.

[0056] Here, in the above embodiment, the wireless antenna unit is installed on an object placed on the floor, but the wireless antenna unit can be installed at any position on the floor side, for example, the wireless antenna unit may be installed on the floor. However, when installing the wireless antenna unit on the floor, it is better to install it in a place where there is no (or little) foot traffic, since there is a possibility that the propagation of radio waves may be affected by foot traffic. Also, when installing the wireless antenna unit on an object placed on the floor, a separate configuration may be used in which only some of the components, such as the antenna components, are placed on the upper surface of the object, and the remaining components are placed on the lower surface or legs of the object.

[0057] The wireless antenna unit (or its installation position) may be designed to be easily visible. This allows the user of the mobile station to grasp the approximate center of the spot area, and by attempting wireless communication in the vicinity of the center, efficient wireless communication can be achieved. In addition, when the mobile station is held over the wireless antenna unit, the wireless antenna unit can be used exclusively, enabling high-speed wireless communication.

[0058] In the above embodiment, the radio wave beam is emitted directly upward from the radio antenna unit arranged on the floor side, but the directivity of the radio wave beam may be tilted relative to the directly upward direction. In this case, the radio wave scattering component may be installed on an extension of the direction in which the radio wave beam is emitted. However, using a radio antenna unit that emits radio waves in a directly upward direction makes it easier to adjust the positional relationship between the radio wave scattering component and the radio antenna unit.

[0059] In the above embodiment, a wireless antenna unit (RU410) is used that emits a beam-shaped radio wave having directivity in a fixed direction, but a conventional wireless antenna unit that uses multiple antenna elements to emit a beam-shaped radio wave having directivity in any direction may be added. In other words, a conventional wireless antenna unit may be installed on the ceiling side of a building, and the wireless antenna unit may emit a beam-shaped radio wave toward the floor of the building.

[0060] In the above embodiment, the present invention is applied to a distributed antenna system in which a base station in a wireless communication system has multiple wireless antenna units, but the present invention can also be applied to a case in which a base station has one wireless antenna unit. Even in this case, it is possible to suppress power consumption, reduce the cost of wireless devices, and reduce the cost of installing base stations while expanding the coverage area.

[0061] Although the embodiments of the present invention have been described above, the above embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take various other embodiments, and various modifications such as omissions and substitutions can be made without departing from the gist of the present invention. These embodiments and modifications are included in the scope and gist of the invention described in this specification, etc., and are included in the scope of the invention described in the claims and their equivalents.

[0062] Furthermore, the present invention can be provided not only as devices such as those described above or as a system composed of these devices, but also as methods executed by these devices, programs for causing a processor to realize the functions of these devices, and storage media for storing such programs in a computer-readable format. [Industrial Applicability]

[0063] The present invention can be used in a wireless communication system having a base station installed inside a building. [Explanation of symbols]

[0064] 100: base station, 110: CU, 120: DU, 130: RU, 200: base station, 210: CU, 220: DU, 230: BBU, 240: RU, 242: coverage area, 250: connection cable, 310: wall, 320: pillar, 330: coverage area, 340: blind zone, 350: ceiling, 360: object, 410: RU, 420: radio wave scattering component, 501: O / E converter, 502: D / A converter, 503: frequency conversion unit, 504: power amplifier, 505: TDD-SW, 506: antenna, 507: LNA, 508: frequency conversion unit, 509: A / D converter, 510: E / O converter, 601: RRC, 602:PDCP, 603:RLC, 604:MAC, 605H:PHY-high, 605L:PHY-Low, 606:RF

Claims

1. In a wireless communication system having a base station installed inside a building, a base station including a distributed unit having a plurality of radio antenna units that emits a beam-shaped radio wave having a directivity in a fixed direction using a plurality of antenna elements, and a central unit that outputs a control signal including identification information for beamforming to the distributed unit; a plurality of radio wave scattering components corresponding to the plurality of radio antenna units, respectively, for scattering and reflecting received radio waves; the wireless antenna unit is installed on a floor side of the building and emits the beam-shaped radio waves toward a ceiling of the building; the radio wave scattering component is installed on a ceiling side of the building and on an extension line of a direction in which the beam-shaped radio waves are emitted with respect to a corresponding radio antenna unit among the plurality of radio antenna units; At least one of the plurality of radio antenna units is previously associated with each of the beamforming identification information, A wireless communication system characterized in that the distributed unit uses the beamforming identification information contained in the control signal received from the central unit not to switch beamforming patterns, but to select a radio antenna unit from among the multiple radio antenna units that corresponds to the beamforming identification information, and the radio antenna unit selected from among the multiple radio antenna units emits the beam-shaped radio waves.

2. 2. The wireless communication system according to claim 1, A wireless communication system, characterized in that the wireless antenna unit is installed on an upper surface of an object located on the floor side of the building.

3. 2. The wireless communication system according to claim 1, The wireless communication system is characterized in that the wireless antenna unit is installed on a floor surface of the building.

4. 2. The wireless communication system according to claim 1, A wireless communication system, wherein the wireless antenna unit is installed so as to emit the beam-shaped radio waves directly upward.

5. 2. The wireless communication system according to claim 1, A wireless communication system, characterized in that the lengths of the wiring electrically connecting the antenna elements to other electrical components are the same for all of the antenna elements.

6. 2. The wireless communication system according to claim 1, Further comprising another radio antenna unit that uses a plurality of antenna elements to emit a beam-shaped radio wave having directivity in any direction; The other wireless antenna unit is installed on the ceiling side of the building and emits the beam-shaped radio waves toward a floor of the building.

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