JP7681549B2 - Wireless communication system - Google Patents

Description

The present invention relates to a wireless communication system equipped with a base station installed inside a building.

In recent years, wireless access systems have become widespread and indispensable for leading a rich life. Looking back at the first through fourth generation of mobile phones, technology has evolved primarily to increase the speed of wireless communication. For the fifth generation, in addition to higher speeds, ultra-low latency and multiple simultaneous connections are required. In order to achieve this, broadband is effective, and since frequency usage is tight, the use of high frequency bands such as millimeter wave bands will be effective from the fifth generation onwards. For example, the fifth generation uses the 28 GHz band, which is close to the millimeter wave band.

However, as the frequency increases (i.e., the wavelength becomes shorter), the receiving area of a single planar antenna, for example, becomes smaller, which creates the problem of greater propagation loss compared to the microwave band. Furthermore, as propagation loss increases, the coverage area per wireless device becomes smaller, which leads to increased costs.

To solve this problem, the fifth generation will adopt beamforming (BF) technology. BF technology arranges multiple antennas (array) and controls the amplitude and phase of the transmission signal of each antenna element to obtain sharp antenna directivity. In addition, the antenna gain can compensate for radio wave propagation loss.

In the transmission BF, the phase of the transmission signals 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 cancelled 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 is increased, making high-speed transmission possible by increasing the number of multi-levels of quadrature amplitude modulation.

With reference to Figure 1, the directivity when a narrow beam is formed by BF will be explained. Here, the example is a planar antenna, which is widely used in the microwave and millimeter wave bands. Figure 1(a) is an example of one subarray (or one element), and the antenna beam has the directivity of a planar antenna. Figure 1(b) is an example of four subarrays, and compared to one subarray, the directivity of the antenna beam is sharper and the combined power in the front direction is greater. Figure 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 greater. Figure 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 Figure 1(c), and the directivity of the antenna beam is controlled to face to the left rather than the front.

Sharpening the antenna directivity has the advantage of reducing interference with other wireless devices and improving frequency utilization efficiency. The principles of BF technology and directivity control methods are well-known technologies in many documents, so a detailed explanation will be omitted. In addition, as shown in Patent Document 1, development is also underway on hybrid BF, which combines analog BF and digital BF.

When combining the received signals from each antenna, the receiving BF can be maximised to maximize the gain in the direction of arrival of the desired wave, or minimised to minimize the gain in the direction of arrival of the interference wave. It is also known that reception performance can be improved by providing multiple antennas and implementing spatial diversity. Various research and practical applications are also being conducted on algorithms that automatically select and execute the most suitable method from the above receiving techniques in response to changes in the propagation environment.

Another technology that solves the above problems is a distributed antenna system (DAS) that can be applied to base stations (gNodeB) of the fifth generation mobile communication system (5G system). Figure 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, multiple DUs (Distributed Units) 120 connected to the CU 110, and multiple RUs (Radio Units) 130 connected to each DU 120. The CU 110 is a centralized control device that mainly performs data processing and network control. The DU 120 is a unit that mainly performs radio signal processing. The RU 130 is a unit that corresponds to the radio section of a general radio device and is composed of an RF unit, an antenna, etc.

The distributed antenna system 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 shown in FIG. 2, the multiple RUs 130 under the DU 120 are used for wireless communication with different mobile stations. The architecture of the 5G system is specified, for example, as O-RAN (Open Radio Access Network) (see, for example, Non-Patent Document 1).

Figure 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 comprises 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, etc. The DU 220 in Figure 3 is an expression that includes the RU 130 in Figure 2 (see, for example, non-patent document 2).

Figure 4 shows an example of the configuration of DU220 in the distributed antenna system of Figure 3. Figure 5 shows an example of the arrangement of DU220 in the distributed antenna system of Figure 3. As shown in Figures 4 and 5, DU220 includes BBU (Base Band Unit) 230 and multiple RUs (Radio Units) 240 connected to BBU230. In the distributed antenna system of Figure 2, multiple RUs 130 under DU120 are used for wireless communication with different mobile stations, whereas in the distributed antenna system of Figure 3, multiple RUs 240 under DU220 are used for wireless communication with the same mobile station, as described below.

The BBU 230 is a unit that centralizes baseband signal processing and control of the distributed antenna system. The RU 240 is a unit equivalent to the radio section of a typical radio, and is composed of an RF unit, an antenna, and the like. In this example, multiple RUs 240 are spaced apart from each other so that they 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.

The RU 240 has 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.

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 its 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.

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, the number of BBUs 230 can be kept relatively small compared to the size of the coverage area, which 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 in the BBU 230 are different for each RU 240, and are synthesized in the BBU 230 and transmitted to the CU 210.

JP 2018-107594 A

Umesh Anil and 3 others, "O-RAN Fronthaul Specifications Overview," NTT DOCOMO Technical Journal Vol. 27 No. 1, April 2019, pp. 43-55 Umesh Anil and 4 others, "5G Radio Access Network Standardization Trends," NTT DOCOMO Technical Journal Vol. 25 No. 3, October 2017, pp. 33-43

Millimeter wave bands have a larger transmission loss from an outdoor radio device to the inside of a building (i.e., indoors) than microwave bands, resulting in a smaller area in which radio waves can be received. 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.

The first problem with the conventional method will be described with reference to FIG. 6. The figure shows an example in which RU 240 is installed on the wall 310 of a building. RU 240 has a BF function, which increases the propagation distance of radio waves, but sharpens the directivity of the antenna beam. Therefore, if there is an obstruction (e.g., a pillar 320), the radio waves are blocked by the obstruction and cannot reach beyond that point. In addition, millimeter waves are not easily diffracted, so a dead zone 340 occurs within the planned coverage area 330. In particular, the height at which RU 240 is installed indoors is limited by the height of the building's walls and ceiling, so if 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.

The second problem in the conventional method will be described with reference to FIG. 7. The figure shows an example in which 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 indoors is limited by the height of the ceiling, 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 of the installation height (h). In this way, a configuration in which RU240 with BF function is installed on the ceiling has significantly low performance relative to the cost.

The present invention has been made in consideration of the above-mentioned conventional circumstances, and aims to provide a wireless communication system that can expand the coverage area while suppressing power consumption, reducing the cost of radio equipment, and reducing the cost of constructing base stations.

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.

As one 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 to other electrical components may be, for example, the same for all antenna elements.

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 other wireless antenna unit may be installed on the ceiling side of the building and emit a beam-shaped radio wave toward the floor of the building.

The present invention provides a wireless communication system that can expand the coverage area while reducing power consumption, reducing the cost of radio equipment, and reducing the cost of installing base stations.

1A and 1B are diagrams illustrating examples of a planar antenna and beamforming directivity. FIG. 1 is a diagram illustrating a configuration example of a distributed antenna system. FIG. 11 is a diagram illustrating another configuration example of a distributed antenna system. A diagram showing an example of the configuration of a DU in the distributed antenna system of Figure 3. A diagram showing an example of DU placement in the distributed antenna system of Figure 3. FIG. 1 is a diagram illustrating an example of a first problem in a conventional method. FIG. 13 is a diagram illustrating an example of a second problem in the conventional method. 1 is a diagram illustrating an example of the configuration of a wireless communication system according to a first embodiment of the present invention. FIG. 9 is a diagram illustrating an example of the configuration of an RU in the wireless communication system of FIG. 8 . 9 is a diagram showing an example of the configuration of an antenna included in an RU in the wireless communication system of FIG. 8 . 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. 12 is a diagram showing an example of functional division of a base station in the wireless communication system shown in FIG. 11.

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 an example of the configuration 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, the system may include multiple sets of the RU 410 and the radio wave scattering component 420.

The RU 410 is a unit having an antenna that uses multiple antenna elements to emit a beam-shaped radio wave with a directionality in a fixed direction, 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 is configured to emit a beam-shaped radio wave directly upward. The object 360 is, for example, a mounting stand, desk, table, etc., and the RU 410 is placed on its upper surface. It is desirable not to place any 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.

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 upwards, 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 to the floor side by the ceiling-side radio wave scattering component 420, thereby achieving the effect of expanding the coverage area of the RU 410.

The operation of the wireless communication system according to the first embodiment will be described. First, the downlink for transmitting a wireless signal from a base station to a mobile station (e.g., 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 as a beam-shaped radio wave 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 that the radio wave from the RU 410 reaches.

Next, the uplink, which transmits a radio signal 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, i.e., 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 portion 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, optical signal, etc., and outputs it to the DU 120 via the connection cable 250.

In both the downlink and uplink, radio waves are scattered by the radio wave scattering component 420, so even if the transmission power is the same as that of a conventional BF, the received power is smaller. 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 in this example is fixedly installed, this is not a particular problem. It is also advantageous compared to increasing the power amplifiers and LNAs. Furthermore, it is possible to reduce power consumption.

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

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

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

In FIG. 9, only the necessary functional blocks are shown for the sake of simplicity, but various elements such as bandpass filters, AGC (Automatic Gain Control), and AFC (Automatic Frequency Control), which are well known to those skilled in the art, may be inserted between each of the components shown in the figure.

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

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 with wiring of the same length by microstrip lines or the like. 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 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.

Next, a specific example of the radio wave scattering component 420 will be described. As one example, the radio wave scattering component 420 is formed from a material that reflects radio waves, and the reflective surface has a convex shape. It is known that convex mirrors that reflect radio waves scatter radio waves. On the other hand, the angles of incidence and reflection of a normal flat mirror are determined by the laws of physics, 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 from a material that reflects radio waves. It is known that radio waves of a desired frequency can be scattered by adjusting the density of the unevenness according to the wavelength of the radio waves.

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 systems 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.

RU410 does not have a BF function, and is installed on 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 RU410 (three in this example) are installed. The beam-shaped radio waves emitted from RU410 on the floor side in the direction of the ceiling are scattered and reflected back to the floor side by radio wave scattering components 420 on the ceiling side, thereby achieving the effect of expanding the coverage area of RU410.

The sets of RUs 410 and radio wave scattering components 420 are installed at a certain distance apart so that the areas of reach of the radio waves scattered and reflected by each radio wave scattering component 420 complement each other to cover the entire room. The distance between the sets of RUs 410 and radio wave scattering components 420 may be determined according to the range over which the radio wave scattering components 420 scatter radio waves when reflecting them.

The BBU 230 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 the BF. The BF control information is originally used to control the selection of 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 if a HUB (e.g., a switching hub) is interposed between the BBU 230 and the RU 410, the RU selection function may be provided in the HUB.

The RU selection function will be described below. First, the interface between the DU and RU will be described. For example, in RRHs (Remote Radio Heads) up to the fourth generation, signal transmission between the CU and DU was mainly performed using 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 a digital signal before OFDM modulation during transmission and optically transmitting a 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.

Next, the functional division of base station functions into CU and DU will be explained. As an example of the architecture of a 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 Split 7 defined in the O-RAN specifications. Below, the functional division of base station functions into CU and DU will be explained using the widely used O-RAN specification interface "split 7" as an example, but is not limited to this.

Figure 12 shows an example of functional division of a base station in the wireless communication system shown in Figure 11. The functions of the base station include 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.

In O-RAN "split 7", the functions of PHY 605 are split. Of the split PHY 605 functions, 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 are, in the downlink/uplink representation, [encoding/decoding], [scrambling/descrambling], [modulation/demodulation], [layer mapping/equalization processing, IDFT], [precoding/channel estimation], and [resource element mapping/resource element demapping]. The functions of PHY-low 605L are [transmit digital BF/receive digital BF] and [IFFT/FFT]. The functions of RF 606 are [D/A conversion/A/D conversion] and [transmit analog BF/receive analog BF].

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 contains the mapped transmission data and the received data that has been subjected to FFT (Fast Fourier Transform). The C-plane (Control-plane) in the interface of the connection cable 250 contains the BeamID, which is an example of BF control information. The BeamID is information for selecting one of multiple BF patterns preset in the RU.

In this example, the BeamID is not used to select a BF pattern, but rather to select an RU410. In other words, the BeamID is pre-associated with an RUID, which is identification information that identifies each of the multiple RUs 410. Then, an RU410 having an RUID that corresponds to the BeamID specified in the control signal is selected as the RU that will perform wireless communication with the mobile station. The selected RU410 does not switch the BF pattern according to the BeamID, but instead emits a beam-shaped radio wave with directionality in a fixed direction.

Therefore, the radio waves emitted from the selected RU 410 have the directionality shown in Figure 8 regardless of the Beam ID, so a wide area can be covered. Also, in the Beam Search process, the mobile station selects the Beam ID with the best wireless environment and transmits to the RU 410, but in reality, the wireless environment is almost the same for all Beam IDs, so there is no problem with whichever is selected. For this reason, there is no need to change the conventional wireless interface.

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

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

In addition, when installing conventional wireless antenna units on ceilings or walls, it was necessary to wire connection cables such as optical fibers and power sources behind the ceiling or inside the walls, making installation costs high. However, with this configuration, the wireless antenna unit can be installed on the floor, and the radio wave scattering components on the ceiling do not require a power source, reducing installation costs. Moreover, because 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.

In addition, while conventional maintenance work on wireless antenna units installed on the ceiling had to be performed at a high altitude, this configuration allows maintenance work to 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 equipment, and reducing the cost of installing base stations.

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 anywhere on the floor, 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 with no (or little) foot traffic, since foot traffic may affect the propagation of radio waves. Also, when installing a 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 top surface of the object, and the remaining components are placed on the bottom surface or legs of the object.

The wireless antenna unit (or its installation position) may be designed to be easily visible. This allows the user of the mobile station to ascertain the approximate center of the spot area, and by attempting wireless communication in that vicinity, 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.

In addition, in the above embodiment, a radio wave beam is emitted directly upward from the radio antenna unit placed 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 beamed directly upward makes it easier to adjust the positional relationship between the radio wave scattering component and the radio antenna unit.

In addition, in the above embodiment, a wireless antenna unit (RU410) is used that emits a beam-shaped radio wave with directivity in a fixed direction, but a conventional wireless antenna unit that uses multiple antenna elements to emit a beam-shaped radio wave with 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.

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 cases in which a base station has only one wireless antenna unit. Even in this case, it is possible to expand the coverage area while suppressing power consumption, reducing radio equipment costs, and reducing base station construction costs.

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 their 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.

The present invention can be provided not only as the devices described above or as systems composed of these devices, but also as methods executed by these devices, programs for implementing the functions of these devices using a processor, and storage media for storing such programs in a computer-readable format.

The present invention can be used in wireless communication systems with base stations installed inside buildings.

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 (6)

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. 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. 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. 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. 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. 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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