Radio communication system and control method therefor

Abstract

To reduce resource consumption for a reference signal in an environment where communications are performed with a plurality of APs.SOLUTION: In a radio communication system, user equipment (UE) is configured connectable with a base station (BS) via a plurality of base station antennas (APs). Each of the plurality of APs transmits a downlink reference signal (DL_RS) periodically, and the plurality of APs include an AP that transmits the DL_RS in a first transmission period and an AP that transmits the DL_RS in a second transmission period. In a case where it is determined that a signal quality of a received DL_RS is lower than a predetermined quality, the UE transmits a beam management (BM) implementation instruction with the UE to a first AP that transmits the DL_RS. Each of the plurality of APs other than the first AP transmits a non-periodic DL_RS based on transmitting the BM implementation instruction from the UE to the first AP.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to beam control in wireless communication systems. [Background technology]

[0002] Currently, the Third Generation Partnership Project (3GPP (registered trademark)) is working on Beyond 5G and 6G (B5G / 6G), which are more advanced versions of 5G. In B5G / 6G, the application of "Cell-Free massive MIMO (CFmMIMO)" is being considered to achieve more comfortable wireless communication (Non-Patent Document 1). CFmMIMO provides a wireless environment that does away with the concept of cells by linking multiple base station antennas to individual user equipment (UE) and applying massive MIMO (mMIMO). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] KDDI, "B5G / 6G White Paper 2.0.1 Edition," October 2021, pages 36-39 Summary of the Invention [Problem to be solved by the invention]

[0004] In mMIMO, control for optimizing beams, called beam management (BM), is performed between the base station antenna and the user equipment. Specifically, the base station antenna periodically transmits reference signals, and the UE controls the beams formed by the base station antenna by feeding back information on the received reference signals.

[0005] Therefore, in CFmMIMO, where each UE communicates with multiple base station antennas, the UE needs to perform BM with multiple base station antennas. In addition, since the coverage of multiple base station antennas communicating with the UE overlaps with each other, the resources of the reference signals transmitted from each base station antenna need to be orthogonal to each other. Due to these requirements, CFmMIMO has the problem of increasing resource consumption for reference signals.

[0006] The present invention has been made in consideration of such problems, and has an object to provide a technique for reducing the amount of resources consumed for reference signals in an environment in which communication with multiple APs is performed. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, a wireless communication system according to the present invention has the following configuration. That is, in a wireless communication system configured so that a user equipment (UE) can be connected to a base station (BS) via a plurality of base station antennas (APs), Each of the plurality of APs is configured to periodically transmit a downlink reference signal (DL_RS), and the plurality of APs includes an AP that transmits the DL_RS in a first transmission period and an AP that transmits the DL_RS in a second transmission period different from the first transmission period; The UE is configured to, when determining that a signal quality of the received DL_RS is lower than a predetermined quality, transmit a beam management (BM) execution instruction between the UE and a first AP that transmitted the DL_RS; Each of the plurality of APs other than the first AP is configured to transmit a non-periodic DL_RS based on the BM implementation indication being transmitted from the UE to the first AP. Effect of the Invention

[0008] According to the present invention, it is possible to provide a technique for reducing the amount of resources consumed for reference signals in an environment in which communication is performed with a plurality of APs. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of a radio access network. [Diagram 2] FIG. 2 is a diagram illustrating a hardware configuration and a functional configuration of a central station. [Diagram 3] A diagram showing the hardware configuration and functional configuration of a UE. [Figure 4] FIG. 13 is a diagram illustrating transmission of reference signals from a plurality of APs. [Diagram 5] FIG. 13 is a diagram illustrating transmission of reference signals from a plurality of APs in an embodiment (in a steady state). [Figure 6] 10A to 10C are diagrams illustrating exemplary operations of each device when a BM implementation instruction is transmitted in an embodiment. [Figure 7] FIG. 2 is a signaling diagram according to an embodiment. [Figure 8] FIG. 11 is a signaling diagram in a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments will be described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims. Although the embodiments describe a number of features, not all of these features are essential to the invention, and the features may be combined in any manner. Furthermore, in the attached drawings, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

[0011] (First embodiment) As a first embodiment of the wireless communication device according to the present invention, a user equipment (UE) configured to be capable of simultaneous communication with a plurality of base station antennas will be described below. Note that the base station antennas are called access points (AP) or transmission / reception points (TRP), but will be referred to as APs below.

[0012] <Radio access network configuration> 1 is a diagram illustrating an example of the configuration of a radio access network (RAN) 100 in a wireless communication system. This wireless communication system is a cellular communication system configured in compliance with a cellular communication standard such as the fifth generation (5G). In FIG. 1, only the RAN 100 is illustrated, and one base station (BS, gNB) 110 and multiple user equipments (UE) 120 are illustrated in a simplified manner.

[0013] The RAN 100 includes a base station 110 and one or more UEs 120. The base station 110 includes a plurality of base station antennas (APs) 112 and an aggregation station 111, and the aggregation station 111 controls the plurality of APs 112 to control communication with each UE 120. Here, each AP 112 includes an antenna with a multiple-input multiple-output (MIMO) configuration, and is capable of communication using massive MIMO (mMIMO).

[0014] The central station 111 corresponds to a CU (Central Unit) and is configured to integrally control a plurality of APs 112. Each AP 112 corresponds to a DU (Distributed Unit) and a RU (Radio Unit) and is configured to perform beam management (including control of MIMO, beamforming, etc.) according to control from the central station 111. However, the central station 111 may be configured to have some or all of the functions of the DU. As described above, the UE 120 is configured to be able to simultaneously communicate with a plurality of APs 112 and to communicate with each AP 112 using mMIMO.

[0015] <Hardware and functional configuration of the aggregation station 111> Fig. 2(a) is a diagram showing a hardware configuration of the central station 111. As described above, the central station 111 is a component of the BS 110, and corresponds to a CU. Note that Fig. 2(a) shows only the configuration particularly related to this embodiment, and other various configurations that the central station 111 may have are omitted from the illustration.

[0016] In one example, the aggregation station 111 includes a processor 201, a ROM 202, a RAM 203, a storage device 204, a first communication circuit 205, and a second communication circuit 206. The processor 201 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and reads and executes programs stored in the ROM 202 or the storage device 204 to perform the overall processing of the device and each process described below.

[0017] The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processes executed by the central station 111. The RAM 203 functions as a workspace when the processor 201 executes the programs, and is a random access memory that stores temporary information. The storage device 204 is, for example, a removable external storage device.

[0018] The first communication circuit 205 is a communication circuit for controlling the AP 112 and communicating with the UE 120. A part of the first communication circuit 205 may be configured as a DU and a RU. The communication between the aggregation station 111 and the UE 120 includes control plane and user plane communication, and the control plane communication includes non-access stratum (NAS) protocol and radio resource control (RRC) protocol communication. On the other hand, the second communication circuit 206 is a communication circuit for communicating with a core network (CN) (not shown). The communication between the aggregation station 111 and the CN includes control plane and user plane communication, and the control plane communication includes NAS protocol communication.

[0019] FIG. 2(b) is a diagram showing the functional configuration of the central station 111. The central station 111 has, for example, a first communication control unit 211, a second communication control unit 212, a control unit 213, and a storage unit 214 as its functions. Note that FIG. 2(b) shows only the configuration particularly related to this embodiment, and other various functions that the central station 111 may have are omitted. The functional blocks in FIG. 2(b) are shown in a schematic manner, and each functional block may be integrated and realized, or may be further subdivided. Each function in FIG. 2(b) may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage unit 204. Each function may be realized, for example, by a processor present inside the first communication circuit 205 or the second communication circuit 206 executing predetermined software.

[0020] The first communication control unit 401 controls wireless communication via the first communication circuit 205. Specifically, it controls the AP 112 to communicate with the UE 120, and controls the execution of control plane and user plane communications with the UE. The second communication control unit 402 controls communication via the second communication circuit 206. That is, it executes control plane and user plane communications with the CN.

[0021] Each AP112 communicates with the UE120 in the control plane and the user plane based on the control via the first communication control unit 401. In particular, in this embodiment, it is characterized in the part of controlling the transmission of the downlink reference signal (DL_RS) for the above-mentioned BM (including controls such as MIMO and beamforming) in the communication of the RRC protocol, which is the communication in the control plane in the RAN section. Details will be described later with reference to FIGS. 5 to 8, but the AP112 is configured to transmit the DL_RS periodically. However, the DL_RS may be different for different APs. Also, when receiving a BM request (BM_Request) from the UE120 or a downlink reference signal request (DL_RS_Request) from the aggregation station 111, it is configured to temporarily transmit the downlink reference signal (DL_RS) aperiodically.

[0022] The control unit 403 comprehensively controls the operation of the entire aggregation station 111 (or the entire BS110). The storage unit 404 stores various information used when the first communication control unit 401, the second communication control unit 402, and the control unit 403 perform operations.

[0023] <Hardware Configuration and Functional Configuration of UE120> FIG. 3(a) is a diagram showing the hardware configuration of the UE120. Here, a smartphone is assumed as the UE120, but other forms of devices (for example, IoT devices) may also be used. Note that FIG. 3(a) shows only the configurations particularly related to this embodiment, and illustration of other various configurations that the UE120 may have is omitted.

[0024] In one example, the UE 120 includes a processor 301, a ROM 302, a RAM 303, a storage device 304, a communication circuit 305, and a touch screen 306. The processor 301 is a computer including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and reads and executes programs stored in the ROM 302 or the storage device 304 to perform the overall processing of the device and each process described below.

[0025] The ROM 302 is a read-only memory that stores information such as programs related to processes executed by the UE 120 and various parameters. The RAM 303 functions as a workspace when the processor 301 executes a program, and is a random access memory that stores temporary information. The storage device 304 is, for example, a removable external storage device.

[0026] The communication circuit 305 is configured by a circuit for wireless communication conforming to a predetermined communication standard. In the following description, the predetermined communication standard will be described using the 5G standard, particularly mMIMO, as an example, but any communication standard used in the system configuration shown in FIG. 1 can be applied.

[0027] The touch screen 306 is, for example, a touch panel display, and is a component that combines a display unit for providing information to the user and a reception unit for receiving instructions from the user through touch operations.

[0028] Fig. 3(b) is a diagram showing a functional configuration of the UE 120. The UE 120 has, as its functions, for example, a communication control unit 311, an information processing unit 312, a control unit 313, and a storage unit 314. Note that Fig. 3(b) shows only the configuration particularly related to the present embodiment, and various other functions that the UE 120 may have are omitted from the illustration. For example, if the UE 120 is a smartphone, it naturally has other functions such as various input functions (touch panel, GPS receiver, camera, microphone) and various output functions (display, vibration, speaker, etc.).

[0029] Moreover, the functional blocks in Fig. 3(b) are shown in a schematic manner, and each functional block may be realized as an integrated unit, or may be further subdivided. Each function in Fig. 3(b) may be realized, for example, by the processor 301 executing a program stored in the ROM 302 or the storage device 304. Each function may also be realized, for example, by a processor present in the communication circuit 305 executing predetermined software.

[0030] The communication control unit 311 controls wireless communication via the communication circuit 305. Specifically, it controls the execution of control plane and user plane communication with the BS 110 (the central station 111 and one or more APs 112). In particular, this embodiment is characterized by a part that receives and processes the periodic DL_RS and the non-periodic DL_RS for the BM described above. In addition, when the information processing unit 312 determines that the quality of the wireless connection with one or more APs 112 currently connected has deteriorated, it transmits a BM request (BM_Request) to the AP to trigger the execution of the BM. Furthermore, although not described in detail here, the communication control unit 311 performs initial access to connect (attach) to the BS 110 and executes handover to another BS 110 according to a standard.

[0031] The information processing unit 312 executes various processes based on requests from the communication control unit 311. For example, the information processing unit 312 generates a measurement (reception result) report for the DL_RS received by the communication control unit 311 from the AP 112, and transmits the report to the AP via the communication control unit 311. Also, based on the reception result for the DL_RS, the information processing unit 312 determines whether or not to transmit a BM request (BM_Request) to the AP 112, and notifies the communication control unit 311.

[0032] The control unit 313 centrally controls the operation of the entire UE 120. The storage unit 314 stores various information used when the communication control unit 311, the information processing unit 312, and the control unit 313 perform their operations.

[0033] <System Operation> First, with reference to Fig. 4, transmission of a reference signal (DL_RS) in an environment in which communication is performed with multiple base station antennas (APs) will be described. Then, with reference to Figs. 5 to 8, an implementation example for reducing transmission of DL_RS will be described. Note that Figs. 4 to 8 show a case in which one UE is connected to four APs (AP#0 to AP#3), but a configuration in which one UE is connected to another number of APs may also be used. Also, the number of APs connected to each UE may vary.

[0034] <Reference signal transmission (conventional example)> Fig. 4 shows a conventional example of transmitting a reference signal when one UE is connected to four APs. The one UE and the four APs are geographically located as shown in Fig. 4(a).

[0035] Each AP periodically transmits a downlink reference signal (DL_RS), and the UE controls the beam (BM) formed by each AP by feeding back information on the received DL_RS. The DL_RS in each AP is the same, and the frequency of transmission is the same. Figure 4(b) shows a situation in which the UE receives the DL_RS periodically transmitted from each AP. From Figures 4(a) and 4(b), it can be seen that the following issues exist when applied to a configuration in which a large number of APs are geographically densely arranged, such as Cell-Free massive MIMO (CFmMIMO): · Because a UE communicates with multiple APs simultaneously, reference signals are transmitted to the UE from many APs, which increases the resources consumed to transmit the reference signals. · Because the coverage of each AP overlaps, the resources of the reference signals transmitted from each AP must be orthogonal.

[0036] <Outline of this embodiment> Therefore, in this embodiment, in order to reduce resources consumed in transmitting reference signals, control as shown in Figs. 5 and 6 is performed to reduce the number / frequency of reference signal transmissions.

[0037] Fig. 5 is a diagram for explaining transmission of reference signals from multiple APs in an embodiment. As shown in the figure, AP#0 has the same transmission cycle as in the past, but AP#1 to AP#3 are configured to have a transmission cycle three times that of AP#0 (i.e., the transmission frequency is 1 / 3). Comparing Fig. 4(b) with Fig. 5, it can be seen that this configuration reduces the number of reference signal transmissions (i.e., resources consumed) by half during normal operation (a state in which the radio wave quality at the UE does not change).

[0038] In this example, the transmission periods of AP#1 to AP#3 are all three times longer (transmission frequency is 1 / 3), but AP#1 to AP#3 may have different transmission periods (transmission frequencies). In addition, the transmission period may be other than three times longer. For example, the transmission period of the reference signal may be determined according to the following criteria. - Transmission cycle that reduces the resource consumption of reference signals by a certain percentage (XX%) - Transmission cycle that can be transmitted using a given transmission resource -Transmission period according to the ratio of received signal power to other APs

[0039] Also, the AP (AP#0 in FIG. 5) that transmits the reference signal at the same transmission cycle as before may be selected arbitrarily. However, for example, the AP that will lengthen the transmission cycle of the reference signal (reduce the transmission frequency) may be selected based on the following criteria, and the AP with the lowest priority as the AP that will lengthen the transmission cycle may be determined as the AP that will transmit the reference signal at the same transmission cycle as before. In other words, it may be utilized that an AP with a relatively low received signal power has less impact on UEs than an AP with a relatively high received signal power, and therefore it is easy to reduce the transmission frequency of the reference signal. -APs with the lowest received signal power -AP with received signal power strength below a certain level (XX [dBm]) -APs whose received signal power strength is lower than the maximum AP by a certain power (XX [dBi]) or more

[0040] However, in the configuration shown in Fig. 5, the frequency with which BM can be performed for AP #1 to AP #3 is 1 / 3. Therefore, when the radio wave quality at the UE changes suddenly (e.g., when the UE moves), the frequency with which BM is performed may not be able to keep up with the rate of change in the radio wave quality. Therefore, in this embodiment, when a BM performance instruction is transmitted from the UE, a temporary reference signal is transmitted from the AP. Note that the temporary reference signal is a non-periodic reference signal that is transmitted separately in addition to the periodic reference signal shown in Fig. 5.

[0041] FIG. 6 is a diagram illustrating an example of the operation of each device when a BM implementation instruction is transmitted in the embodiment. (S601) Each AP (AP#0 to AP#3 in FIG. 6) transmits a (periodic) DL_RS as shown in FIG. (S602) When the UE determines that the quality of the (periodic) DL_RS of a certain AP (AP#0 in FIG. 6) has deteriorated due to the movement of the UE, the UE instructs the AP to perform BM (beam update). (S603) The AP (AP#0 in FIG. 6) that received the instruction to perform BM (beam update) instructs other APs to transmit DL_RS (non-periodic). However, it is not necessary to instruct the AP that transmitted DL_RS most recently to transmit DL_RS (non-periodic). (S604) The other APs (AP#2 and AP#3 in FIG. 6) that have received the instruction to transmit the DL_RS transmit the (non-periodic) DL_RS while beam sweeping. (S605) The UE measures (non-periodic) DL_RS received from other APs (AP#2 and AP#3 in FIG. 6) and determines the respective reception results. (S606) The UE instructs the AP (AP#3 in FIG. 6) for which quality degradation has been determined to occur to perform BM. If there is no problem with the reception result, the UE does not instruct the AP to perform BM (=maintain the current beam).

[0042] <Example of control sequence in Fig. 6> An example of a sequence corresponding to the control in Fig. 6 will be described below with reference to Fig. 7. Also, an example of a sequence in a modified example will be described with reference to Fig. 8. Note that in the description of Fig. 7 and Fig. 8, the operation performed by the AP means that it is performed by the aggregate station 111 or an AP controlled by the aggregate station 111.

[0043] Fig. 7 is a signaling diagram in this embodiment. A UE is connected to four APs (AP#0 to AP#3), and each AP (AP#0 to AP#3) transmits DL_RS (Periodic) as shown in Fig. 5.

[0044] In S601, each AP (AP#0 and AP#1 at the timing shown in S601 in FIG. 7) transmits a DL_RS (Periodic).

[0045] In S602, when the UE determines that the quality of DL_RS (Periodic) from AP#0 has deteriorated due to the movement of the UE, the UE transmits a measurement report (Report) to AP#0 and instructs the AP#0 to perform BM (BM_Request). In addition, the AP#0 performs BM with the UE.

[0046] In S603, (triggered by receiving the above-mentioned BM implementation instruction), AP#0 instructs the other APs to transmit DL_RS(Aperiodic). However, as described above, AP#1 has recently transmitted DL_RS (at the timing shown in S601), so in S603, AP#2 and AP#3 are instructed to transmit DL_RS(Aperiodic).

[0047] In S604, AP#2 and AP#3 transmit DL_RS(Aperiodic) while beam sweeping. Note that resources for transmitting DL_RS(Aperiodic) are configured in advance (determined and shared between UE and AP). In S605, UE measures DL_RS(Aperiodic) received from AP#2 and AP#3 and judges the reception results of each.

[0048] In S606, the UE transmits a measurement report (Report) to each of AP#2 and AP#3. At this time, the UE also instructs AP#3, which has been determined to have deteriorated quality, to perform BM (BM_Request). In other words, only the measurement report (Report) is transmitted to AP#2, which has no problems with the reception result.

[0049] Fig. 8 is a signaling diagram in the modified example. As in Fig. 7, the UE is connected to four APs (AP#0 to AP#3), and each AP (AP#0 to AP#3) transmits DL_RS (Periodic) as shown in Fig. 5. The difference from Fig. 7 above is mainly in S603.

[0050] First, when a UE connects to four APs (AP#0 to AP#3), one of the APs (AP#0 in FIG. 8) notifies the UE and the other APs (AP#1 to AP#3) in advance of information regarding the physical uplink control channel (PUCCH) resources used to transmit a BM implementation instruction (BM_Request), which is then shared between the devices. Then, AP#0 to AP#3 each start monitoring the BM implementation instruction (BM_Request) transmitted from the UE.

[0051] In S601, each AP (AP#0 and AP#1 at the timing shown in S601 in FIG. 7) transmits a DL_RS (Periodic).

[0052] In S602, when the UE determines that the quality of DL_RS (Periodic) from AP#0 has deteriorated due to the movement of the UE, the UE transmits a measurement report (Report) to AP#0 and instructs the AP#0 to perform BM (BM_Request). In addition, the AP#0 performs BM with the UE.

[0053] In S603-2, AP#1 to AP#3 detect the transmission of the BM implementation instruction in S601. That is, as described above, AP#1 to AP#3 know and monitor the information of the PUCCH resource used by the UE to transmit the BM implementation instruction (BM_Request), and therefore detect the transmission of the BM implementation instruction in S601.

[0054] In S604, AP#2 and AP#3 transmit DL_RS(Aperiodic) while beam sweeping. As described above, AP#1 has transmitted DL_RS recently (at the timing shown in S601). Therefore, in S604, AP#1 does not transmit DL_RS(Aperiodic), and only AP#2 and AP#3 transmit DL_RS(Aperiodic). Note that resources for transmitting DL_RS(Aperiodic) are configured in advance (determined and shared between the UE and AP). In S605, the UE measures the DL_RS(Aperiodic) received from AP#2 and AP#3 and determines the reception results of each.

[0055] In S606, the UE transmits a measurement report (Report) to each of AP#2 and AP#3. At this time, the UE also instructs AP#3, which has been determined to have deteriorated quality, to perform BM (BM_Request). In other words, only the measurement report (Report) is transmitted to AP#2, which has no problems with the reception result.

[0056] <Effects> It is possible to reduce the amount of resources required for transmitting the DL_RS by transmitting a periodic reference signal (DL_RS) from each AP in the configuration shown in Fig. 5. In addition, it is possible to perform BM at an appropriate timing by transmitting a non-periodic reference signal (DL_RS) from each AP in the configuration shown in Fig. 6 to Fig. 8.

[0057] As described above, according to the first embodiment, the frequency of periodic reference signal (DL_RS) transmission from each AP is reduced, and non-periodic reference signal transmission is triggered by the transmission of a BM execution instruction (BM_Request) from the UE. This makes it possible to reduce the amount of resources consumed for reference signals in an environment in which communication is performed with multiple APs.

[0058] Furthermore, the present invention will make it possible to provide, for example, a more comfortable wireless communication environment, thereby contributing to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote industry, innovation and infrastructure."

[0059] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention. [Explanation of symbols]

[0060] 100 Radio Access Network (RAN); 110 Base Station (BS); 120 User Equipment (UE); 111 Aggregation Station; 112 Base Station Antenna (AP)

Claims

1. A wireless communication system in which a user equipment (UE) can be connected to a base station (BS) via a plurality of base station antennas (APs), Each of the plurality of APs is configured to periodically transmit a downlink reference signal (DL_RS), and the plurality of APs includes an AP that transmits the DL_RS in a first transmission period and an AP that transmits the DL_RS in a second transmission period different from the first transmission period; The UE is configured to transmit a beam management (BM) execution instruction between the UE and a first AP that transmitted the DL_RS when the UE determines that the signal quality of the DL_RS received is lower than a predetermined quality, Each of the plurality of APs other than the first AP is configured to transmit a non-periodic DL_RS based on the BM implementation instruction being transmitted from the UE to the first AP.

1. A wireless communication system comprising:

2. Among the plurality of APs other than the first AP, an AP that transmitted a DL_RS immediately before the BM implementation instruction suppresses transmission of the non-periodic DL_RS.

2. The wireless communication system according to claim 1 .

3. The second transmission period is an integer multiple of the first transmission period.

2. The wireless communication system according to claim 1 .

4. The plurality of APs include two or more APs that transmit the DL_RS in the second transmission period, and the timings at which the two or more APs transmit the DL_RS are different from each other.

4. The wireless communication system according to claim 3.

5. Information regarding resources used for transmitting the non-periodic DL_RS is shared between the UE and each AP.

2. The wireless communication system according to claim 1 .

6. Each of the plurality of APs other than the first AP transmits the non-periodic DL_RS while beam sweeping.

2. The wireless communication system according to claim 1 .

7. The first AP is configured to notify the plurality of APs other than the first AP that the BM implementation instruction has been transmitted from the UE to the first AP; Each of the plurality of APs other than the first AP transmits the non-periodic DL_RS based on the notification from the first AP.

2. The wireless communication system according to claim 1 .

8. Information regarding a physical uplink control channel (PUCCH) resource used for transmitting the BM implementation instruction is shared between the UE and each AP, Each of the plurality of APs is configured to monitor the PUCCH resource.

2. The wireless communication system according to claim 1 .

9. Each of the plurality of APs other than the first AP transmits the non-periodic DL_RS based on detection of the transmission of the BM implementation instruction by monitoring the PUCCH resource.

9. The wireless communication system according to claim 8.

10. Each of the multiple APs is configured as a multiple-input multiple-output (MIMO) antenna.

2. The wireless communication system according to claim 1 .

11. The plurality of APs are configured to be controlled by a central station that operates as a central unit (CU) of the BS.

2. The wireless communication system according to claim 1 .

12. A method for controlling a wireless communication system in which a user equipment (UE) is configured to be able to connect to a base station (BS) via a plurality of base station antennas (APs), comprising: a first transmission step in which each of the plurality of APs periodically transmits a downlink reference signal (DL_RS), the plurality of APs including an AP that transmits the DL_RS in a first transmission period and an AP that transmits the DL_RS in a second transmission period different from the first transmission period; A first reception step in which the UE receives DL_RSs transmitted from the plurality of APs; A second transmission step in which the UE transmits a beam management (BM) execution instruction between the UE and a first AP that has transmitted a DL_RS whose signal quality is determined to be lower than a predetermined quality; A third transmission step in which, based on the BM implementation instruction being transmitted from the UE to the first AP, each of one or more APs other than the first AP included in the plurality of APs transmits a non-periodic DL_RS; Includes A control method comprising:

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