Wireless communication system and its control method

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 a wireless communication system.

Background Art

[0002] Currently, studies on Beyond 5G and 6G (B5G / 6G), which are further advanced versions of 5G that are continuously being developed in the 3rd Generation Partnership Project (3GPP (registered trademark)), have begun. In B5G / 6G, applying "Cell-Free massive MIMO (CFmMIMO)" to achieve more comfortable wireless communication has been studied (Non-Patent Document 1). CFmMIMO provides a wireless environment without the concept of cells by applying massive MIMO (mMIMO) with multiple base station antennas coordinated for each individual user equipment (UE).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In mMIMO, control for beam optimization called beam management (BM) is performed between the base station antenna and the user equipment. Specifically, the base station antenna periodically transmits a reference signal, and the UE feeds back information regarding the received reference signal to control the beam formed by the base station antenna.

[0005] Therefore, in CFmMIMO, where each UE communicates with multiple base station antennas, the UE needs to perform data building (BM) with multiple base station antennas. Furthermore, since the coverage of the multiple base station antennas communicating with the UE overlaps, the resources for the reference signal transmitted from each base station antenna must be orthogonal to each other. These requirements lead to a challenge in CFmMIMO: increased resource consumption for the reference signal.

[0006] This invention has been made in view of these problems and aims to provide a technology that reduces resource consumption for reference signals in an environment where multiple APs communicate with each other. [Means for solving the problem]

[0007] To solve the above-mentioned problems, the wireless communication system according to the present invention has the following configuration. That is, in a wireless communication system configured so that a user device (UE) can connect to a base station (BS) via multiple 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 DL_RS in a first transmission cycle and an AP that transmits DL_RS in a second transmission cycle different from the first transmission cycle. The UE is configured to send a beam management (BM) instruction to the first AP that transmitted the DL_RS if it determines that the signal quality of the received DL_RS is lower than a predetermined quality. Each of the multiple APs other than the first AP is configured to send an irregular DL_RS based on the fact that the BM implementation instruction has been sent from the UE to the first AP. [Effects of the Invention]

[0008] According to the present invention, a technology can be provided to reduce resource consumption for reference signals in an environment where communication is performed with multiple APs. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing the configuration of a wireless access network. [Figure 2] This diagram shows the hardware and functional configuration of the aggregation station. [Figure 3] This diagram shows the hardware and functional configuration of the UE. [Figure 4] This diagram illustrates the transmission of reference signals from multiple access points (APs). [Figure 5] This figure illustrates the transmission of reference signals from multiple APs in the embodiment (steady state). [Figure 6] This diagram illustrates the operation of each device when a BM implementation instruction is transmitted in the embodiment. [Figure 7] This is a signaling diagram in an embodiment. [Figure 8] This is a signaling diagram in a modified example. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] (First Embodiment) As a first embodiment of the wireless communication device according to the present invention, a user device (UE) configured to enable simultaneous communication with multiple base station antennas will be described below as an example. Note that base station antennas are also called access points (APs) or transceiver points (TRPs), but will be referred to as APs below.

[0012] <Wireless access network configuration> FIG. 1 is a diagram exemplarily showing the configuration of a radio access network (RAN) 100 part in a wireless communication system. This wireless communication system is a cellular communication system configured in accordance with a cellular communication standard such as the fifth generation (5G), for example. In FIG. 1, only the RAN 100 part is shown, and one base station (BS, gNB) 110 and a plurality of user devices (UE) 120 are shown in a simplified manner.

[0013] RAN 100 includes a base station 110 and one or more UEs 120. The base station 110 includes a plurality of base station antennas (AP) 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 communication using massive MIMO (mMIMO) is possible.

[0014] It is assumed that the aggregation station 111 corresponds to a CU (Central Unit) and is configured to integrally control a plurality of APs 112. Also, each AP 112 corresponds to one including a DU (Distributed Unit) and a RU (Radio Unit), and is configured to perform beam management (including controls such as MIMO and beamforming) in response to control from the aggregation station 111. However, a part or all of the functions of the DU may be configured to be provided in the aggregation station 111. As described above, the UE 120 is configured to communicate with a plurality of APs 112 simultaneously and perform communication using mMIMO with each AP 112.

[0015] <Hardware Configuration and Functional Configuration of Aggregation Station 111> FIG. 2(a) is a diagram showing the hardware configuration of the aggregation station 111. As described above, the aggregation station 111 is a component of the BS 110 and corresponds to the CU. In FIG. 2(a), only the configuration particularly related to this embodiment is shown, and illustration of various other configurations that the aggregation station 111 may have is omitted.

[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 and the storage device 204 to execute the overall processing of the device and each of the processes described below.

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

[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 can 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 communications. The control plane communication includes non-access stratum (NAS) protocol and radio resource control (RRC) protocol communications. 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 communications. The control plane communication includes NAS protocol communication.

[0019] Figure 2(b) shows the functional configuration of the aggregation station 111. The aggregation 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. Note that Figure 2(b) shows only the configuration particularly relevant to this embodiment, and other various functions that the aggregation station 111 may have are not shown. Also, the functional blocks in Figure 2(b) are shown schematically, and each functional block may be implemented as an integrated unit or further subdivided. Furthermore, each function in Figure 2(b) may be implemented, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204. Alternatively, it may be implemented, for example, by a processor located 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 AP112 to communicate with UE120 and controls the execution of control plane and user plane communication with UE. The second communication control unit 402 controls communication via the second communication circuit 206. That is, it executes control plane and user plane communication with 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 that controls 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 of 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 receiving 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 operations of the entire aggregation station 111 (or the entire BS110). The storage unit 404 stores various types of 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 in FIG. 3(a), only the configurations particularly related to this embodiment are shown, and other various configurations that the UE120 may have are omitted from the illustration.

[0024] In one example, the UE120 is comprised of a processor 301, ROM 302, RAM 303, storage device 304, communication circuit 305, and touchscreen 306. The processor 301 is a computer comprised of one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application-Specific Integrated Circuit), and performs the overall processing of the device and the individual processing described later by reading and executing programs stored in the ROM 302 and storage device 304.

[0025] ROM302 is a read-only memory that stores information such as programs and various parameters related to the processing performed by UE120. RAM303 functions as a workspace for the processor 301 when executing programs and is a random access memory that stores temporary information. Storage device 304 is composed of, for example, a removable external storage device.

[0026] The communication circuit 305 is composed of a wireless communication circuit compliant with a predetermined communication standard. In the following description, the 5G standard, particularly mMIMO, will be used as an example of the predetermined communication standard, but any communication standard used in a system configuration like the one shown in Figure 1 can be applied.

[0027] The touchscreen 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 via touch operation.

[0028] Figure 3(b) shows the functional configuration of the UE120. The UE120 has, for example, a communication control unit 311, an information processing unit 312, a control unit 313, and a storage unit 314. Note that Figure 3(b) shows only the configuration particularly relevant to this embodiment, and various other functions that the UE120 may have are not shown. For example, if the UE120 is a smartphone, it will naturally have other functions such as various input functions (touch panel, GPS receiver, camera, microphone) and various output functions (display, vibration, speaker, etc.).

[0029] Furthermore, the functional blocks in Figure 3(b) are schematic representations, and each functional block may be implemented as an integrated unit or further subdivided. Also, each function in Figure 3(b) may be implemented, for example, by the processor 301 executing a program stored in the ROM 302 or the storage device 304. Alternatively, it may be implemented, for example, by a processor located inside 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 between the BS110 (aggregation station 111 and one or more AP112). In particular, this embodiment is characterized by the part that receives and processes periodic DL_RS and irregular DL_RS for the BM described above. Furthermore, if the information processing unit 312 determines that the quality of the wireless connection with one or more AP112 currently connected has deteriorated, it sends a BM request (BM_Request) to the AP to trigger the execution of BM. In addition, although not described in detail here, the communication control unit 311 performs initial access and connects to (attaches to) the BS110 or performs handover to other BS110s in accordance with the standard.

[0031] The information processing unit 312 performs various processes based on requests from the communication control unit 311. For example, it generates a measurement (reception result) report for DL_RS received by the communication control unit 311 from AP112 and sends it to AP via the communication control unit 311. It also decides whether or not to send a BM request (BM_Request) to AP112 based on the reception result for DL_RS and notifies the communication control unit 311.

[0032] The control unit 313 oversees and controls the operation of the entire UE120. The memory unit 314 stores various information used when the communication control unit 311, information processing unit 312, and control unit 313 operate.

[0033] <System Operation> First, referring to Figure 4, we will explain the transmission of the reference signal (DL_RS) in an environment where communication is performed with multiple base station antennas (APs). Then, referring to Figures 5 to 8, we will explain examples of how to reduce DL_RS transmission. Note that Figures 4 to 8 show the case where one UE is connected to four APs (AP#0 to AP#3), but configurations with other numbers of APs are also possible. Also, the number of APs connected to each UE may vary.

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

[0035] Each AP periodically transmits a downlink reference signal (DL_RS), and the UE controls the beam formed by each AP by feeding back information about the received DL_RS. The DL_RS for each AP is the same, and the transmission frequency is the same. Figure 4(b) shows the situation where the UE receives the DL_RS transmitted periodically from each AP. From Figures 4(a) and 4(b), it can be seen that when applied to a configuration where a large number of APs are geographically densely deployed, such as Cell-Free Massive MIMO (CFmMIMO), the following challenges exist: Since the UE communicates with multiple APs simultaneously, reference signals are sent to the UE from numerous APs, increasing the resources consumed by transmitting these reference signals. Since the coverage of each AP is superimposed, the resources of the reference signal transmitted from each AP must be orthogonal.

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

[0037] Figure 5 illustrates the transmission of reference signals from multiple APs in the embodiment. As shown, AP#0 has the same transmission cycle as conventional systems, but AP#1 to AP#3 are configured to have three times the transmission cycle of AP#0 (i.e., a transmission frequency of 1 / 3). Comparing Figure 4(b) and Figure 5, it can be seen that this configuration reduces the number of reference signal transmissions (i.e., resources consumed) by half during steady-state operation (when the radio wave quality at the UE does not change).

[0038] Note that here, the transmission cycles of AP#1 to AP#3 are all set to 3 times (transmission frequency is 1 / 3), but different transmission cycles (transmission frequencies) may be used for AP#1 to AP#3. Furthermore, transmission cycles other than 3 times may also be used. For example, the transmission cycle of the reference signal can be determined based on the following criteria. • Transmission cycle that reduces the resource consumption of the reference signal by a predetermined percentage (XX%). • Transmission cycles that can be transmitted using the designated transmission resources • Transmission cycle determined by the ratio of received signal power to other APs

[0039] Furthermore, APs that transmit the reference signal at the same transmission cycle as before (AP#0 in Figure 5) can be arbitrarily selected. However, for example, it is advisable to select APs that lengthen the transmission cycle of the reference signal (reduce the transmission frequency) based on the following criteria, and then determine the AP with the lowest priority as an AP that lengthens the transmission cycle to be the AP that transmits the reference signal at the same transmission cycle as before. In other words, APs with relatively low received signal power have less impact on the UE compared to APs with relatively high power, and therefore it is easier to reduce the transmission frequency of the reference signal. • APs with lower ranking in received signal power strength • APs whose received signal power strength is below a predetermined strength (XX [dBm]) • APs whose received signal power strength is at least XX [dBi] less than the maximum AP.

[0040] However, in the configuration shown in Figure 5, the frequency at which BM can be performed for AP#1 to AP#3 is reduced to 1 / 3. Therefore, if the radio wave quality at the UE changes rapidly (e.g., the UE moves), the frequency of BM implementation may not be able to keep up with the rate of change in radio wave quality. To address this, in this embodiment, when a BM implementation instruction is transmitted from the UE, the AP is configured to transmit an extraordinary reference signal. The extraordinary reference signal is an aperiodic reference signal transmitted separately in addition to the periodic reference signal shown in Figure 5.

[0041] Figure 6 is a diagram illustrating the operation of each device when a BM implementation instruction is transmitted in the embodiment. (S601) Each AP (AP#0 to AP#3 in Figure 6) sends (periodic) DL_RS as shown in Figure 5. (S602). If a (periodic) degradation of DL_RS quality is detected at a certain AP (AP#0 in Figure 6) in the UE due to the movement of the UE, the UE instructs the AP to perform a beam refresh (BM). (S603). An AP (AP#0 in Figure 6) that receives a BM (beam refresh) instruction instructs other APs to send (irregular) DL_RS. However, it is not necessary to instruct an AP that has recently sent DL_RS to send (irregular) DL_RS. (S604) Other APs (AP#2 and AP#3 in Figure 6) that have received a DL_RS transmission instruction transmit (irregular) DL_RS while beam sweeping. (S605).UE measures the (irregular) DL_RS received from other APs (AP#2 and AP#3 in Figure 6) and determines the reception result for each. (S606).UE instructs AP (AP#3 in Figure 6) that has been judged to have degraded quality to perform a beam check. If there are no problems with the reception results, BM is not instructed (= the current beam is maintained).

[0042] <Example of a control sequence in Figure 6> Below, an example of a sequence corresponding to the control in Figure 6 described above will be explained with reference to Figure 7. Furthermore, an example of a modified sequence will be explained with reference to Figure 8. Note that in the explanations of Figures 7 and 8, the actions performed by the AP refer to the actions performed by the aggregation station 111 or the AP controlled by the aggregation station 111.

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

[0044] In S601, each AP (AP#0 and AP#1 at the timing shown for S601 in Figure 7) sends DL_RS(Periodic).

[0045] In S602, if the UE determines that the DL_RS (Periodic) quality has deteriorated from AP#0 due to the UE's relocation or other reasons, it sends a measurement report (Report) to AP#0 and instructs it to perform a BM (BM Request). AP#0 then performs a BM with the UE.

[0046] In S603, (triggered by the receipt of the BM implementation instruction mentioned above), AP#0 instructs the other APs to send DL_RS (Aperiodic). However, as mentioned above, AP#1 has already sent DL_RS in the immediate vicinity (at the timing shown in S601), so in S603, AP#2 and AP#3 are instructed to send DL_RS (Aperiodic).

[0047] In S604, AP#2 and AP#3 each transmit DL_RS(Aperiodic) while performing a beam sweep. The resources for transmitting DL_RS(Aperiodic) are configured in advance (decided and shared between the UE and APs). In S605, the UE measures the DL_RS(Aperiodic) received from AP#2 and AP#3 and determines the reception result for each.

[0048] In S606, the UE sends measurement reports to AP#2 and AP#3. If AP#3 is found to have a quality degradation, a BM request is also sent. In other words, only the measurement report is sent to AP#2, where no problems are found in the reception results.

[0049] Figure 8 is a signaling diagram in a modified example. Similar to Figure 7, the UE is connected to four APs (AP#0 to AP#3), and DL_RS (Periodic) is transmitted from each AP (AP#0 to AP#3) as shown in Figure 5. The main difference from Figure 7 is in the S603 section.

[0050] First, when the UE connects to the four APs (AP#0 to AP#3), one of the APs (AP#0 in Figure 8) pre-notifies the UE and the other APs (AP#1 to AP#3) of information regarding the physical uplink control channel (PUCCH) resource used to send BM execution requests (BM_Request), and this information is shared among the devices. Then, AP#0 to AP#3 each begin monitoring the BM execution requests (BM_Request) sent from the UE.

[0051] In S601, each AP (AP#0 and AP#1 at the timing shown for S601 in Figure 7) sends DL_RS(Periodic).

[0052] In S602, if the UE determines that the DL_RS (Periodic) quality has deteriorated from AP#0 due to the UE's relocation or other reasons, it sends a measurement report (Report) to AP#0 and instructs it to perform a BM (BM Request). AP#0 then performs a BM with the UE.

[0053] In S603-2, AP#1 to AP#3 detect the transmission of the BM execution instruction in S601. That is, as mentioned above, AP#1 to AP#3 know and monitor the information of the PUCCH resource that the UE uses to send the BM execution instruction (BM_Request), so they are able to detect the transmission of the BM execution instruction in S601.

[0054] In S604, AP#2 and AP#3 each transmit DL_RS (Aperiodic) while beam sweeping. As mentioned above, AP#1 transmits DL_RS most 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). The resources for transmitting DL_RS (Aperiodic) are configured in advance (decided and shared between the UE and APs). In S605, the UE measures the DL_RS (Aperiodic) received from AP#2 and AP#3 and determines the reception result for each.

[0055] In S606, the UE sends measurement reports to AP#2 and AP#3. If AP#3 is found to have a quality degradation, a BM request is also sent. In other words, only the measurement report is sent to AP#2, where no problems are found in the reception results.

[0056] <Effects> By transmitting periodic reference signals (DL_RS) from each AP in the configuration shown in Figure 5 above, it is possible to reduce the amount of resources required to transmit DL_RS. In addition, by transmitting non-periodic reference signals (DL_RS) from each AP in the configuration shown in Figures 6 to 8 above, it becomes possible to perform BM at the appropriate timing.

[0057] As described above, according to the first embodiment, the frequency of periodic reference signals (DL_RS) transmitted from each AP is reduced, and irregular reference signals are transmitted from each AP triggered by the transmission of a BM implementation instruction (BM_Request) by the UE. This makes it possible to reduce the resource consumption for reference signals in an environment where communication is performed with multiple APs.

[0058] Furthermore, this invention makes it possible to provide a more comfortable wireless communication environment, for example, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0059] The invention is not limited to the embodiments described above, and various modifications and changes 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 configured such that user equipment (UE) can connect to a base station (BS) via multiple base station antennas (AP), 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 DL_RS in a first transmission cycle and an AP that transmits DL_RS in a second transmission cycle different from the first transmission cycle. The UE is configured to send a beam management (BM) instruction to the first AP that transmitted the DL_RS when it determines that the signal quality of the received DL_RS is lower than a predetermined quality. Each of the multiple APs other than the first AP is configured to send an irregular DL_RS based on the fact that the BM implementation instruction has been sent from the UE to the first AP. A wireless communication system characterized by the following features.

2. Among the multiple APs other than the first AP, the AP that sent DL_RS immediately before the BM implementation instruction will suppress the transmission of the non-periodic DL_RS. The wireless communication system according to claim 1.

3. The second transmission period is an integer multiple of the first transmission period. The wireless communication system according to claim 1.

4. The plurality of APs include two or more APs that transmit DL_RS in the second transmission cycle, and the timing at which each of the two or more APs transmits DL_RS is different from that of the others. The wireless communication system according to claim 3.

5. Information regarding the resources used for sending the aforementioned non-periodic DL_RS is shared between the UE and each AP. The wireless communication system according to claim 1.

6. Each of the multiple APs other than the first AP transmits the non-periodic DL_RS while beam sweeping. The wireless communication system according to claim 1.

7. The first AP is configured to notify the other APs that the BM implementation instruction has been sent from the UE to the first AP. Each of the multiple APs other than the first AP transmits the irregular DL_RS based on the notification from the first AP. The wireless communication system according to claim 1.

8. Information regarding the physical uplink control channel (PUCCH) resources used to transmit the aforementioned BM implementation instructions is shared between the UE and each AP. Each of the aforementioned APs is configured to monitor the PUCCH resource. The wireless communication system according to claim 1.

9. Each of the multiple APs other than the first AP transmits the non-periodic DL_RS based on the detection of the transmission of the BM implementation instruction by monitoring the PUCCH resource. The wireless communication system according to claim 8.

10. Each of the aforementioned APs is configured as a multi-input multi-output (MIMO) antenna. The wireless communication system according to claim 1.

11. The aforementioned multiple APs are configured to be controlled by a centralized station that operates as the CU (Central Unit) of the BS. The wireless communication system according to claim 1.

12. A control method for a wireless communication system configured such that a user device (UE) can connect to a base station (BS) via multiple base station antennas (APs), A first transmission step in which each of the plurality of APs periodically transmits a downlink reference signal (DL_RS), wherein the plurality of APs include an AP that transmits DL_RS in a first transmission cycle and an AP that transmits DL_RS in a second transmission cycle different from the first transmission cycle, The UE performs a first receiving step in which it receives DL_RS transmitted from the plurality of APs, A second transmission step in which the UE transmits a beam management (BM) instruction to a first AP that has transmitted a DL_RS whose signal quality has been determined to be lower than a predetermined quality, A third transmission step in which, based on the transmission of the BM implementation instruction from the UE to the first AP, each of the one or more APs other than the first AP included in the plurality of APs transmits an irregular DL_RS, including A control method characterized by the following:

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