Communication device, control method, and program

Abstract

A communication device functions as a base station for performing cellular communication with a user equipment (UE). When the number of connections to the base station provided by the communication device itself reaches an upper limit of the number of connections, the communication device externally notifies information indicating that the upper limit of the number of connections has been reached.

Description

Technical Field

[0001] The present invention relates to a communication device, a control method, and a program for performing wireless communication. Background Art

[0002] The 3rd Generation Partnership Project (3GPP (registered trademark)) has formulated cellular communication standards. In the cellular communication standards in 3GPP (hereinafter referred to as "3GPP standards"), standardization of integrated access and backhaul (IAB) obtained by integrating an access line and a backhaul line is in progress (see Patent Document 1).

[0003] In IAB, the wireless resources used for the access line between the base station and the user terminal (user equipment (UE)) are also used for the backhaul line. For example, in IAB, wireless resources with millimeter wave bands (such as 28GHz bands) can be used. By using IAB, a relay device (IAB node) can relay the communication between the base station device (IAB donor) and the terminal device via a wireless line. Therefore, compared with the case of using a wired line such as an optical fiber, it is possible to expand the regional coverage inexpensively.

[0004] In cellular communications, there is known a notification technology in which a base station cell notifies a UE of access prohibition information to appropriately prohibit access to a base station cell whose functions can be restricted (Patent Document 2).

[0005] Citation List

[0006] Patent Literature

[0007] PTL 1: Japanese Patent Publication No. 2019-534625

[0008] PTL 2: Japanese Patent Publication No. 2019-36869 Summary of the invention

[0009] Technical issues

[0010] By the way, it is possible to newly use a vehicle-mounted relay device (hereinafter also referred to as "vehicle-mounted relay", "vehicle-mounted relay" or "mobile IAB") obtained by installing a relay device serving as an IAB node on a vehicle such as a bus, train or taxi. By using this vehicle-mounted relay, it is possible to expand the coverage area in urban areas.

[0011] On the other hand, when using an in-vehicle relay, various problems are considered to arise which are not solved using only the specifications of the cellular communication standard formulated up to Release 17 and assuming IAB nodes and fixed base stations to be fixedly installed at certain locations.

[0012] For example, since the vehicle-mounted relay is assumed to be installed on the vehicle, there is a possibility that the processing capacity of the vehicle-mounted relay is low compared to the processing capacity of the conventionally known fixedly installed IAB donor due to the reduction in weight and power consumption cost. The vehicle-mounted relay performs backhaul communication with the IAB node as the superior and the IAB donor while moving in the area. Therefore, compared with the conventionally known communication conditions in which base stations are fixedly installed based on the prediction of communication demand and these base stations cover the communication of UE, the vehicle-mounted relay has a characteristic that the communication demand changes dynamically according to the movement.

[0013] In view of these characteristics, in the present exemplary embodiment, it is possible to provide an upper limit on the number of connections to a base station represented by an in-vehicle relay to stably provide a communication service to a UE.

[0014] However, conventional cellular communication standards do not define a specific mechanism for giving a notification that the upper limit of the number of connections has been reached. Therefore, both the base station and the UE waste power and resources because the UE tries or retries to connect to the base station that has reached the upper limit of the number of connections.

[0015] The present invention is made in view of at least one of the above problems. As one aspect of the present invention, one of the purposes is to provide a mechanism for notifying the outside of information indicating that the upper limit of the number of connections has been reached in a base station. As another aspect of the present invention, one of the purposes is to increase the convenience of cellular communication.

[0016] Solution to the problem

[0017] In order to achieve at least one of the above-mentioned purposes, according to one aspect of the present invention, a communication device used as a base station for performing cellular communication with a user equipment (UE) includes a notification unit, and the notification unit is configured to notify the outside of information indicating that the upper limit of the number of connections has been reached when the number of connections with the base station reaches an upper limit of the number of connections.

[0018] Advantageous Effects of the Invention

[0019] According to one aspect of the present invention, information indicating that the upper limit of the number of connections has been reached in a base station can be notified to the outside. According to another aspect of the present invention, the convenience of cellular communication can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a diagram illustrating an example of a communication system.

[0021] Figure 2 is a diagram illustrating an example of a hardware configuration of an Integrated Access and Backhaul (IAB) node.

[0022] Figure 3 is a diagram illustrating an example of a functional configuration of an IAB node.

[0023] Figure 4 is a diagram illustrating an example of a functional configuration of a user equipment (UE).

[0024] Figure 5 is a sequence diagram illustrating the flow of connection processing in cellular communication.

[0025] Figure 6 is a diagram illustrating an example of control performed by an IAB node.

[0026] Figure 7 is a diagram illustrating an example of control performed by a UE.

[0027] Figure 8 is an example of a Radio Resource Control (RRC) Reject message.

[0028] Fig. 9 is a diagram illustrating an example of control performed by an IAB node according to the second exemplary embodiment.

[0029] Fig.10 is a diagram illustrating an example of control performed by a UE according to the second exemplary embodiment.

[0030] Fig.11 : is a diagram illustrating an example of notification information which an IAB node notifies to the outside.

[0031] Fig.12 is a schematic diagram illustrating switching of a connection destination in a communication system.

[0032] Fig.13 is an example of a sequence diagram illustrating exchange of information between devices according to the third exemplary embodiment.

[0033] Fig.14 is a diagram illustrating an example of control performed by an IAB node according to the third exemplary embodiment.

[0034] Fig.15 is a diagram illustrating an example of control performed by a UE according to the third exemplary embodiment. DETAILED DESCRIPTION

[0035] Exemplary embodiments for implementing the present invention will be described below with reference to the accompanying drawings. The following exemplary embodiments do not limit the invention according to the appended claims, and not all combinations of features described in the mobile implementation are essential to the method for solving the problem in the present invention.

[0036] <First Exemplary Embodiment>

[0037] First, refer to Figure 1, describing a mobile communication system according to the present exemplary embodiment. The mobile communication system according to the present exemplary embodiment includes a core network (CN) 10, an integrated access and backhaul (IAB) donor 100, wireless base stations 101 and 102 as IAB nodes, and user equipment (UE) 110 to 115. "UE" is an abbreviation of user equipment and is a communication terminal such as a smart phone or a personal computer. Each of the wireless base stations 101 and 102 as IAB nodes can be a vehicle-mounted wireless base station obtained by installing a relay device serving as an IAB node on a vehicle such as a bus, a train, or a taxi.

[0038] The wireless base stations 101 and 102 as IAB nodes are connected to the CN 10 via the IAB donor 100 as an upper node by establishing communication with the IAB donor 100 via a backhaul line using wireless resources based on fifth generation (5G) New Radio (NR).

[0039] The IAB node 101 as a wireless base station forms a cell 103 as a coverage area. The CN 10 and the IAB donor 100 perform various processes such as authentication of the UEs 110 to 115 as terminals, transmission control of data packets, and establishment of communication paths. For the purpose of illustration, Figure 1 A case is illustrated in which UEs 110 to 115 exist in a cell 103 and a total of four UEs (ie, UEs 110 to 113) are connected to an IAB node 101. An IAB node 102 as a radio base station forms a cell 104 as a coverage area.

[0040] In the present exemplary embodiment, in order to stably provide communication services to UEs, a configuration is adopted in which an upper limit on the number of connections with IAB nodes such as in-vehicle relays can be set for each of IAB nodes 101 and 102 as wireless base stations. Figure 1 The case where the maximum number of connections of UEs that can connect to IAB node 101 is set to four is illustrated. If the connecting UEs do not reach the upper limit of the number of connections, the IAB node cooperates with CN 10 and IAB donor 100 to establish a connection with the UE based on a connection request from the UE.

[0041] By the way, conventional cellular communication standards do not define a mechanism for appropriately giving a notification of reaching the upper limit of the number of connections. In this exemplary embodiment, in order to prevent the IAB node and the UE from wasting power and resources due to the UE trying or retrying to connect to the IAB node that has reached the upper limit of the number of connections, a mechanism for giving a notification of this information is provided.

[0042] Give a more specific description. Figure 1In the state where four UEs are connected to the IAB node 101 as shown in FIG, if the fifth and subsequent UEs 114 and 115 attempt to connect to the IAB node 101, since the maximum number of connections (four) has been reached in the IAB node, control is performed to prevent the establishment of the connection. Then, in the case where these connections are not established, the UEs for which the connection is not established are notified that the reason for the connection failure is the state in which the maximum number of connections has been reached. Through this process, it is possible to prevent unnecessary connections from being retried.

[0043] A specific configuration for realizing this processing will be described below.

[0044] <Hardware Configuration>

[0045] refer to Figure 2 , describing the hardware configuration of the IAB node 101. Figure 2 is a block diagram illustrating an example of a hardware configuration of the IAB node 101 .

[0046] The IAB node 101 includes a control unit 202, a storage unit 203, a wireless communication unit 204, an antenna control unit 205, an antenna 206, and an operation unit 207. Although a phased array antenna is assumed as the antenna, the present invention is not limited thereto.

[0047] The storage unit 203 includes one or more memories such as a read-only memory (ROM) and a random access memory (RAM). The storage unit 203 stores computer programs for performing various operations described below, communication parameters for wireless communication, and management information about UEs connected to the IAB node. The storage unit 203 is also used as a temporary storage area (work area) for data to be transmitted from the IAB node to each UE via the IAB donor 100 and the CN 10.

[0048] As the storage unit 203, a storage medium such as a hard disk or a nonvolatile memory may be used in addition to memories such as ROM and RAM. Alternatively, the storage unit 203 may include a plurality of memories.

[0049] The control unit 202 includes one or more processors, such as a central processing unit (CPU) and a microprocessor unit (MPU), and controls the entire IAB node 101 by executing a computer program loaded into a RAM as a storage unit 203. The control unit 202 can control the entire IAB node 101 through the cooperation of the computer program stored in the storage unit 203 and an operating system (OS).

[0050] The processing performed by the control unit 202 described with reference to the flowchart described below is also realized by executing a computer program loaded into the RAM as the storage unit 203. The processing described with reference to the flowchart described below can also be realized using a hardware circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). The processing described with reference to the flowchart described below can also be realized by the cooperation of the hardware circuit and a processor such as a CPU and an MPU.

[0051] The wireless communication unit 204 is a module that cooperates with the control unit 202, the antenna control unit 205, and the antenna 206 to perform transmission and reception through cellular communications based on Long Term Evolution (LTE) and 5G NR that conform to the 3rd Generation Partnership Project (3GPP) standard. Although in this exemplary embodiment, the case where the communication unit 204 supports wireless communications that conform to LTE and 5G NR is described, the present invention is not limited to this. For example, the communication unit 204 can support wireless communications that conform to the sixth generation (6G) and Beyond 5G, which are successor standards to 5G NR. The wireless communication unit 204 also has a measurement function for measuring the communication status with each UE or each base station.

[0052] The antenna control unit 205 controls the directivity of the antenna 206 , transmits a wireless signal generated by the wireless communication unit 204 to the UE using a technique such as beamforming or multiple-input multiple-output (MIMO), or receives a wireless signal transmitted from the UE and transmits the wireless signal to the wireless communication unit 204 .

[0053] The operation unit 207 includes a touch panel that can detect a user's touch operation and a display panel that displays various screens. The operation unit 207 serves as a display unit that displays information and a receiving unit that receives instructions from the user. The control unit 202 cooperates with the operation unit 207 to display a setting screen for performing various settings of the IAB node. The user can input a desired operation instruction to the IAB node 101 by performing a touch operation on the operation unit 207 using an object such as a finger. The display unit may be an external display device separated from the IAB node, or the receiving unit may be an input device such as a keyboard and a mouse.

[0054] The hardware configurations of the IAB donor 100, the IAB node 102, and the UEs 110 to 115 are similar to that of the IAB node 101, and thus will not be described.

[0055] <Software Configuration>

[0056] Next, refer to Figure 3 , describing the functional configuration of each of the IAB nodes 101 and 102. Figure 3The functional units shown in exemplify software components. The functional units are implemented by the processor of the control unit 202 executing a computer program stored in the storage unit 203 for implementing the functional units.

[0057] The signal processing unit 302 cooperates with the wireless communication unit 204 to transmit data obtained by decoding a signal of cellular communication compliant with 5G or LTE received by the wireless communication unit 204 to another functional unit. The processing unit 302 also cooperates with the wireless communication unit 204 to transmit a signal compliant with 5G or LTE obtained by encoding and modulating data as a transmission target requested by another functional unit to the outside.

[0058] The data storage unit 304 manages system information such as cell information, communication parameters, and setting information for communication for causing the device to operate as an IAB node, and saves the system information in the storage unit 203. The storage unit 304 updates the setting information managed by the storage unit 304 itself based on a change request from another functional unit, or provides the setting information managed by the storage unit 304 itself to another functional unit based on a setting reference request from another functional unit. The storage unit 304 also manages information indicating an upper limit on the number of connections indicating an upper limit on the number of UEs that can be connected to the IAB node 101.

[0059] The setting control unit 303 cooperates with the operation unit 207 and the storage unit 304 to perform a change process for changing the setting stored in the storage unit 304. The setting control unit 303 generates a setting screen including display items such as an entry field for changing the upper limit of the number of connections of the UE and displays the setting screen on the operation unit 207. If the user provides an input to the entry field displayed on the setting screen and the setting control unit 303 determines that a user operation for changing the upper limit of the number of UEs that can be connected is received, the setting control unit 303 sends a change request for updating the upper limit of the number of connections managed by the storage unit 304 using the value input to the entry field to the storage unit 304. The storage unit 304 that has received the change request updates the upper limit of the number of connections. Although the case where the upper limit of the number of connections is updated via the operation unit of the IAB node has been described as an example in the present exemplary embodiment, the present invention is not limited thereto. For example, a configuration in which an instruction to change the upper limit of the number of connections is received from the coordinator on the CN 10 or the IAB donor 100 that performs overall control of the IAB communication, and the upper limit of the number of connections is updated based on this instruction can also be adopted.

[0060] The connection control unit 305 cooperates with the signal processing unit 302 and the wireless communication unit 204 to perform various processes for establishing and disconnecting connections with the UE and the IAB donor. The control unit 305 generates and sends a Radio Resource Control (RRC) message for exchanging information about the wireless connection with the UE and a Backhaul Adaptation Protocol (BAP) message for exchanging information between the IAB node and the donor. "BAP" is an abbreviation for Backhaul Adaptation Protocol and is a protocol for routing data between nodes. The control unit 305 also analyzes messages received from the outside, generates a UE context necessary to maintain a connection with the UE, and transmits the UE context to the connection management unit 306. According to the occurrence of the disconnection process, the control unit 305 also requests the connection management unit 306 to release unnecessary UE contexts. The connection management unit 306 performs overall management of information about the currently connected UE, such as the UE context of the UE being connected under the control of the connection management unit 306 itself, and the number of currently connected UEs.

[0061] The connection control unit 305 refers to the information on the upper limit of the number of connections managed by the storage unit 304 and the number of UEs being connected managed by the management unit 306. If the connection control unit 305 receives a connection request from the UE, the connection control unit 305 determines whether the upper limit of the number of connections has been reached in the connection control unit 305 itself. If the upper limit of the number of connections has been reached, the connection control unit 305 generates a message rejecting the connection request and notifies the UE of the message. In the present exemplary embodiment, the connection control unit 305 includes information indicating that the cause of the connection failure is a state in which the maximum number of connections has been reached in the notification. The details will be described with reference to the flowchart described below.

[0062] In addition, based on the congestion state caused by the traffic load or the device state such as the state where the base station stops due to a failure, the control unit 305 can also determine whether to accept or reject the connection request from the UE, and perform processing according to the determination. The control unit 305 also has the function of performing admission control, managing the state, and notifying the surrounding of the surrounding cell information.

[0063] As described above, the control unit 305 and the management unit 306 provide functions related to so-called Radio Resource Management (RRM) and RRC. The software configuration of the IAB node 102 is similar to that of the IAB node 101. The software configuration of the IAB donor 100 is different from that of the IAB node 101 in that, in addition to the configuration of the IAB node 101, the IAB donor 100 also includes a functional unit for communicating with a CN such as the CN 10.

[0064] The collection unit 307 cooperates with the signal processing unit 302 and the wireless communication unit 204 to receive a signal transmitted from an IAB donor, an IAB node or a fixed base station adjacent to the IAB node 101 and collects and manages information about surrounding base stations. At this time, the collection unit 307 also measures the quality such as the received signal strength of the signal and stores the measured quality in association with the information about the surrounding base stations. The information is appropriately referenced by the control unit 305. Based on the referenced information, the control unit 305 determines whether it is necessary to perform a handover process, or generates various messages for causing a handover process.

[0065] Based on the system information managed by the storage unit 304, the notification control unit 308 generates information to be sent using a physical broadcast channel (PBCH) block that notifies the UE of the minimum information that the UE must first read after searching for a cell. The notification control unit 308 also generates information to be sent using a system information block (SIB) that notifies the outside of other system information. The notification control unit 308 also cooperates with the signal processing unit 302, the wireless communication unit 204, and the antenna control unit 205 to send an SS / PBCH block including a PBCH as channel notification information and a SIB that stores system information to be notified to the UE at a constant transmission period to the outside. The SS / PBCH block, which is a collection of various synchronization information including PBCH and SIB, is also called a "Synchronization Signal Block (SSB)".

[0066] Next, a functional configuration of each of UEs 110 to 115 is described. Figure 4 The functional units shown in exemplify software components. The functional units are implemented by the processor of the control unit 202 of each UE executing a computer program for implementing the functional units stored in the storage unit 203 of the UE.

[0067] The signal processing unit 402 cooperates with the wireless communication unit 204 of the UE to transmit, to another functional unit, data obtained by decoding a signal of cellular communication compliant with 5G NR or LTE that is transmitted from a base station and received by the wireless communication unit 204 of the UE. The processing unit 402 also cooperates with the wireless communication unit 204 of the UE to transmit, to an external base station, a signal compliant with 5G NR or LTE that is obtained by encoding and modulating data as a transmission target requested by another functional unit.

[0068] The data storage unit 404 manages connection parameters for use in connection with a base station and setting information for communication, and saves the connection parameters and setting information in the storage unit 203 of the UE. The data storage unit 404 also updates the setting information managed by the data storage unit 404 itself based on a change request from another functional unit, or provides the setting information managed by the data storage unit 404 itself to another functional unit based on a setting reference request from another functional unit. The storage unit 404 manages and stores the public land mobile network (PLMN) and contract information for identifying the operator (telecommunication operator) of the connection destination.

[0069] The collection unit 407 cooperates with the signal processing unit 402 and the wireless communication unit 204 of the UE to receive a signal transmitted from an IAB donor, an IAB node or a fixed base station adjacent to the UE and collects and manages information about surrounding base stations. At this time, the collection unit 407 also measures the quality such as the received signal strength of the signal and stores the measured quality in association with the information about surrounding base stations. This information is appropriately referenced by the connection control unit 405.

[0070] The connection control unit 405 refers to the information managed by the collection unit 407 and the information managed by the storage unit 404, and performs a selection process for selecting a base station as a connection destination and a determination process for determining whether to request the base station to perform a handover process. Specifically, among the base stations of the operator as the target of connection identified based on the contract information and the PLMN, the control unit 405 selects a base station whose received signal strength of a signal transmitted from the base station exceeds a predetermined threshold and whose received signal strength is high as the connection destination.

[0071] The control unit 405 sends a connection request to the base station selected as the connection destination, and attempts to connect to the base station such as the IAB node 101 or 102. As an example, a case where the control unit 405 is connected to the IAB node 101 is described. If the connection with the IAB node 101 is completed as a result of the connection attempt, the UE can communicate with an external device and a web server on the Internet via the IAB node 101, the IAB donor 100, and the CN 10.

[0072] <Connection establishment process>

[0073] Next, refer to Figure 5 , describing a method for avoiding retries according to the present exemplary embodiment. Figure 5 The sequence diagram in illustrates control of the apparatus in a case where the UE makes a connection request to a base station that is a connection destination candidate. Figure 5 Control in a case where the UEs being connected to the IAB node 101 have reached the upper limit of the number of connections is illustrated.

[0074] First, in step S500, the UE sends an RRC Setup Request message requesting the IAB node 101 to set up a connection.

[0075] In step S501, the IAB node 101 that has received the RRC setup request message determines whether to allow or reject the connection based on the upper limit of the number of connections and the number of currently connected UEs. If it is determined to allow the connection, the IAB donor 100, the CN 10, and the UE exchange information using RRC messages and BAP messages (not shown), whereby the IAB node 101 establishes a connection with the UE. For example, this connection follows the UE connection establishment process described in Section 9.2.1.3 of TS 38.300 formulated by 3GPP.

[0076] On the other hand, if it is determined that the connection is allowed, then in step S502, the IAB node 101 sends an RRC Reject message including a parameter indicating the reason why the connection is impossible to the UE. The parameter includes information indicating that the connection is not made because the upper limit of the number of connections is reached. The RRC Reject message may also include information indicating a base station as a connection candidate. The details will be described below.

[0077] In step S503, the UE that has received the RRC reject message transmitted from the IAB node 101 in step S502 performs a determination process for determining a connection destination. If the RRC reject message does not indicate a reason why the connection is impossible, the UE performs a retry process for retrying to connect to the IAB node 101. If the retry fails multiple times, the UE abandons the connection to the IAB node and attempts to connect to another IAB node or base station. On the other hand, if the RRC reject message indicates a reason why the connection is impossible and indicates information indicating that the connection is not made, the UE determines that another IAB node or base station is a connection destination. A description is given under the assumption that the IAB node 102 is selected.

[0078] If the connection destination is determined in the process of step S503 , then in step S504 , the UE transmits an RRC setup request message to the IAB node 102 .

[0079] The IAB node 102 that has received the RRC setup request message performs a determination process (not shown) to determine whether to allow or reject the connection. This determination is similar to the determination in step S5501. This sequence diagram illustrates a case where it is determined that the connection is allowed. If it is determined that the connection is allowed, then in step S505, the IAB node 102 sends an RRC setup (RRC Setup) message to the UE that has requested the connection. In step S506, the UE that has received the RRC setup message sends an RRC setup complete (RRC Setup Complete) message to the IAB node 102.

[0080] Next, the IAB node 102 having received the RRC setup complete message performs a setup process for setting up cellular communication in which the UE cooperates with the IAB donor and the CN 10, which are upper nodes of the IAB node 102. Although the IAB donor is not illustrated in the present exemplary embodiment due to space limitations, the IAB node and the IAB donor cooperate with each other to exchange data with the CN 10.

[0081] The UE that has established a connection with the IAB node 102 sends a non-access stratum (NAS) message (not shown) to the IAB node 102. Next, in step S507, the IAB node 102 sends an initial UE message (Initial UE Message) including the NAS message from the UE to the CN 10. Then, in step S508, the IAB node 102 uses downlink NAS transport (Downlink NAS Transport) to exchange information required for setting. In step S509, the IAB node 102 uses DL information transfer (DL Information Transfer) to exchange information required for setting. In addition, in step S510, the IAB node 102 uses UL information transfer (UL Information Transfer) to exchange information required for setting. In step S511, the IAB node 102 uses uplink NAS transport (Uplink NAS Transport) to exchange information required for setting.

[0082] Next, in step S512, the CN 10 sends an Initial Context Setup Request including a protocol data unit (PDU) session context, UE radio functions, and UE security to the IAB node 102. Parameters for managing the connection state with the UE represented by this context are appropriately managed by the connection management unit 306. Next, in step S513, the IAB node 102 sends a Security Mode Command to the UE. The UE that has received the Security Mode Command updates the security algorithm used for communication and the key used for encrypted communication. If the update is completed, then in step S514, the UE sends a Security Mode Complete to the IAB node 102. Through these processes, data flowing through the cellular communication network can be encrypted and decrypted. Therefore, secure communication can be performed.

[0083] In step S515, the IAB node 102 having received the security mode completion message sends an RRC reconfiguration message to the UE.

[0084] The UE that has received the RRC reconfiguration message performs the processing required for the setting of the configuration such as the configuration of the radio bearer (Radio Bearer) according to this configuration. If the configuration is completed, then in step S516, the UE sends an RRC reconfiguration complete (RRC Reconfiguration Complete) message to the IAB node 102. Through the above processing, the signal radio bearer (Signal Radio Bearer, SRB) 2 and the data radio bearer (Data Radio Bearer, DRB) of the UE can be set.

[0085] Finally, in step S517, the IAB node 102 uses an Initial Context Setup Response to notify the CN 10 that the setup process is complete.

[0086] Through the above processing, the setting is completed. If the setting is completed, then in step S518, the UE can communicate downlink user plane data with CN 10 via IAB node 102 and IAB donor 100. In step S519, the UE can communicate uplink user plane data with CN 10 via IAB node 102 and IAB donor 100.

[0087] Next, refer to Figure 6 , a description is given of a determination process for determining a connection in an IAB node that has received a connection request. Figure 6The flowchart in the selectively illustrates the processing of handling the connection request in the IAB node. The processing shown in the flowchart is implemented by the control unit 202 of the IAB node executing the program. In the case of explicitly indicating what processing is to be performed, the reference Figure 3 The functional units described are given as the main body of the description.

[0088] In step S600, the signal processing unit 302 and the connection control unit 305 cooperate to receive a connection request from the UE. If the signal processing unit 302 and the connection control unit 305 receive a connection request, the process proceeds to step S601.

[0089] Next, in step S601, the connection control unit 305 determines whether the number of UEs being connected has reached the upper limit of the number of connections, based on the number of connections indicating the number of currently connected UEs managed by the connection management unit 305 and the information on the upper limit of the number of connections managed by the setting control unit 303. If it is determined that the number of UEs being connected has reached the upper limit of the number of connections, the process proceeds to step S602. If it is determined that the number of UEs being connected has not reached the upper limit of the number of connections, the process proceeds to step S603.

[0090] In step S602, the connection control unit 305 cooperates with the signal processing unit 302 to send an RRC reject message including a parameter indicating a reason why the connection is impossible to the UE from which the connection request was received in step S601. Figure 8 , describing the RRC reject message sent in step S602. Figure 8 An example of an RRC reject message is illustrated.

[0091] Figure 8 The message in is an RRC reject message obtained by extending the message format of the RRC reject described in Section 6.2.2 of 3GPP TS 38.331. Figure 8 In the , the format of the message is indicated by a notation based on Abstract Syntax Notation One (ASN.1).

[0092] In the present exemplary embodiment, a structure of "Reason of NonAccess-IEs" listing information indicating the reason why connection is impossible and prompt information in the case where connection is impossible is added to the structure member of "RRC Reject-IEs." "IE" is an abbreviation of Infomation Elements and means an information element to be included in a message.

[0093] First, information indicating the reason why connection is impossible is stored in "Detail Reason of NonAccess". In this area, information indicating the reason why connection is impossible, such as "exceeding the upper limit of the number of UEs", "congestion period", or "base station stop period" is stored. "Exceeding the upper limit of the number of UEs" is information indicating that connection cannot be made because the number of UEs being connected has reached the upper limit of the number of connections. "Congestion period" is information indicating that connection cannot be made because congestion is occurring. Based on the ensuring status of the communication band in the admission control or the occurrence of errors in the communication path, the connection control unit 305 determines whether congestion is occurring. If it is determined that congestion is occurring, the connection control unit 305 stores information indicating that congestion is occurring. If it is not determined that congestion is occurring, the connection control unit 305 does not store information indicating that congestion is occurring.

[0094] "Base station stop period" is information indicating that the service is being stopped because normal communication cannot be provided by the base station due to a certain problem. The value actually stored may be a numerical value predefined in association with this information. For example, two bits are secured as a bit sequence corresponding to "Detail Reason of NonAccess". Then, "0b00" is associated with "exceeding the upper limit of the number of UEs", "0b01" is associated with "congestion period", "0b10" is associated with "base station stop period", and "0b11" is associated with a reserved value, thereby transmitting information about the reason why connection is impossible between devices.

[0095] The subsequent information included in the "Reason of NonAccess-IEs" is prompt information in the case where connection is impossible. "Candidate gNB" is information indicating a base station that is a connection candidate. In "Candidate gNB", the identifier (ID) of the base station to be a connection candidate is stored. In "UE number in Cell", the number of UEs present within the range of the cell is stored. In "connected UE number", the number of UEs that are being connected to the IAB node is stored. In "non-connected UE number", the number of UEs that are not connected to the IAB node within the range of the cell is stored. Although the case of including the prompt information is described as an example in the present exemplary embodiment, whether the prompt information is to be provided may vary based on the setting of the base station.

[0096] For example, the base station may also be configured not to provide prompt information.

[0097] Description Back to Figure 6. In step S603, the connection control unit 305 cooperates with the components to perform a connection process for connecting to the UE, thereby causing the UE to join the CN 10. At this time, the connection control unit 305 performs a process of transferring the context of the UE to the connection management unit 306. The management unit 306 updates the management of the number of connections indicating the number of terminals currently connected to the IA node. The number of connections is updated by incrementing a value indicating the number of connections currently connected to the IAB node. Although not illustrated due to space limitations, if the number of UEs being connected decreases according to disconnection, the number of connections is updated by decrementing a value indicating the number of connections.

[0098] Next, in step S604, the connection control unit 305 determines whether the number of UEs being connected has reached the upper limit of the number of connections, based on the number of connections indicating the number of currently connected UEs managed by the connection management unit 306 and the information on the upper limit of the number of connections managed by the setting control unit 303. If it is determined that the upper limit of the number of connections has been reached, the process proceeds to step S605. If it is not determined that the upper limit of the number of connections has been reached (that is, the upper limit of the number of connections has not been reached), a series of operations in the process of handling a connection request ends.

[0099] In step S605, the connection control unit 305 cooperates with the signal processing unit 302 to notify the upper node that the upper limit of the number of connections has been reached. For example, the upper node is the IAB donor 100. This notification can be given using a BAP message. In addition, the connection control unit 305 can cooperate with the signal processing unit 302 to use a BAP message to notify the upper node of information indicating the radio wave conditions of the surrounding communication devices and information about the UE being connected to the base station. The information notified to the IAB donor 100 using this BAP message is used to control the load distribution of the IAB donor. The IAB donor 100 can also be configured to further notify the CN 10 of each piece of information notified to the IAB donor 100. The pieces of information notified to the IAB donor 100 are notified to the coordinator that performs overall management of communications via the cellular network on the CN 10, and the pieces of information are used to control the load distribution of the entire cellular communication network.

[0100] Through the above-mentioned processing, the reason why the connection is impossible can be notified to the UE.

[0101] By notifying the upper node that the upper limit of the number of connections has been reached, this information can also be immediately notified to the IAB donor 100 and the CN 10. This information can be appropriately utilized to control load distribution.

[0102] Next, refer to Figure 7 A description is given of the control of a UE which has received a message including a reason why connection is not possible, in accordance with the flowchart in FIG. Figure 7 The flowchart in the figure selectively illustrates the process of handling the connection request in the UE. The process shown in the flowchart is implemented by the control unit 202 of the UE executing the program. In the case of explicitly indicating what process is to be performed, the reference Figure 4 The functional units described are given as the main body of the description.

[0103] In step S700, the connection control unit 405 cooperates with the signal processing unit 402 to receive the RRC rejection message. If the reception is completed, the process proceeds to step S701. In step S701, the connection control unit 405 cancels the connection with the base station from which the notification is received. Then, the process proceeds to step S702. In step S702, the connection control unit 405 cooperates with the collection unit 407 to determine whether the connection candidate station notified by the base station to the connection control unit 405 satisfies the connection condition. Specifically, if the base station does not notify the connection candidate station to the connection control unit 405, or if the communication quality of the connection candidate station notified to the connection control unit 405 is less than or equal to the threshold, it is determined that the connection condition is not satisfied. Then, the process proceeds to step S704.

[0104] On the other hand, if the base station notifies the connection control unit 405 of the connection candidate station, and the communication quality of the connection candidate station notified to the connection control unit 405 is excellent, it is determined that the connection condition is satisfied. Then, the process proceeds to step S703.

[0105] In step S703 , the connection control unit 405 attempts to connect to a connection candidate station.

[0106] On the other hand, in step S704, the connection control unit 405 determines as a connection destination a base station that is a surrounding base station collected by the collection unit 407 and has the maximum received radio wave intensity among the base stations whose received radio wave intensity is greater than a predetermined threshold value. Then, the connection control unit 405 attempts to connect to the determined connection destination. After excluding from the connection destination candidates the base station that has notified the connection control unit 405 of the reason why the connection is impossible in the notification in step S700, the connection control unit 405 determines the connection destination. Control may be performed so that the information indicating the reason why the connection is impossible is not notified to the connection control unit 405 and only the base station that the connection is impossible is not excluded from the connection destination candidates until the number of retries in the base station reaches a predetermined number of times. Through the above-mentioned processing, if the base station notifies the connection control unit 405 of the information indicating that the connection is impossible, particularly the information indicating that the upper limit of the number of connections has been reached, it is possible to prevent retrying to connect to the base station that has sent this notification.

[0107] refer to Fig.12 , describing the result of changing the base station as the connection destination. Fig.12 is a schematic diagram illustrating a change in a connection destination. Figure 1 Similarly, a case is illustrated in which UEs 110 to 115 exist in the cell 103 of the IAB node 101 and a total of four UEs (i.e., UEs 110 to 113) are connected to the IAB node 101. If UE 114 or 115 makes a connection request in this state, the IAB node 101 rejects the connection. At this time, the IAB node 101 sends an RRC reject message rejecting the connection by including information indicating that the upper limit of the number of connections has been reached in the RRC reject message as a reason why the connection is impossible.

[0108] The IAB node 101 also transmits an RRC reject message including information on the IAB node 102 as information indicating a connection destination candidate.

[0109] As a result, UE 114 or 115 performs Figure 7 . As indicated by cell area 1201, UEs 114 and 115 are located in the coverage area of ​​IAB node 102. Therefore, it is determined that the connection condition is also satisfied in terms of communication quality. Then, in cell area 1201 and cell area 1202, UEs 114 and 115 can try to connect to IAB node 102 as a connection candidate and switch the base station as the connection destination.

[0110] <Second Exemplary Embodiment>

[0111] In the first exemplary embodiment, a description has been given of a mechanism for notifying the outside of information indicating that the upper limit of the number of connections has been reached using an RRC reject message and a BAP message. In the second exemplary embodiment, in addition to the processing described in the first exemplary embodiment, a description is given of a mechanism for notifying the outside of information indicating that the upper limit of the number of connections has been reached using notification information notified by the IAB node.

[0112] The hardware configuration and software configuration of the device are similar to those in the first embodiment, so they are not described. In this exemplary embodiment, the SIB described in the first exemplary embodiment is notified to the outside by including information indicating that the upper limit of the number of connections has been reached in the SIB. A specific description is given below.

[0113] First, refer to Fig. 9 and Fig.11 , a description is given of a determination process for determining a connection in an IAB node that has received a connection request. Fig. 9The flowchart in the selectively illustrates the notification process for notifying the SIB to the outside that is periodically performed by the IAB node. The process shown in the flowchart is implemented by the control unit 202 of the IAB node executing the program. In the case of explicitly indicating what to perform the process, the reference Figure 3 The functional units described are given as the main body of the description.

[0114] In step S901, the control unit 308 determines whether the number of UEs being connected has reached the upper limit of the number of connections, based on the number of connections indicating the number of currently connected UEs managed by the connection management unit 306 and the information on the upper limit of the number of connections managed by the setting control unit 303. If it is determined that the upper limit of the number of connections has been reached, the process proceeds to step S902. If it is not determined that the upper limit of the number of connections has been reached, the process proceeds to step S903.

[0115] In step S902, the notification control unit 308 generates notification information including information indicating that the upper limit of the connection has been reached. Next, the notification control unit 308 cooperates with the signal processing unit 302, the wireless communication unit 204, and the antenna control unit 205 to generate SIB and PBCH including the generated notification information, and transmits the SIB and PBCH to the outside as SS / PBCH blocks. Fig.11 , describes the specific content of the SIB. In this exemplary embodiment, as an example, information indicating that the upper limit of the connection is reached is stored in System Information Block Type 1 (SIB1).

[0116] refer to Fig.11 , gives a description of the information that SIB1 notifies to the outside. Fig.11 In , the format of the notification information is indicated by notation based on ASN.1. In the present exemplary embodiment, notification of information indicating that the upper limit of the number of connections is reached is given by extending a part of the notification information based on SIB1 described in TS 38.331 V17.1.0.

[0117] Specifically, a structure of "Reason of NonAccess-IEs" is added to the structure member of "uac-BarringInfo-v1700" in which information indicating the reason why connection is impossible and prompt information when connection is impossible are listed in the structure member. The information included in this structure is similar to the information in the first exemplary embodiment, and includes information indicating that the upper limit of the number of connections has been reached. That is, a notification of the information about "Detail Reason of NonAccess" described in the first exemplary embodiment is given, thereby enabling a notification of information indicating whether the upper limit of the connection has been reached. A configuration in which only a bit sequence of "Detail Reason of NonAccess" is added and a notification is given using SIB1.

[0118] It is also possible to adopt a configuration in which only 1-bit flag information indicating whether the upper limit of the connection is reached is added to SIB1. For example, if the flag is "1", this indicates that the upper limit of the number of connections is reached. If the flag is "0", this indicates that the upper limit of the number of connections is not reached. In this case, in step S902, the notification control unit 308 may generate notification information in which "1" is set in the area storing the flag.

[0119] Description Back to Fig. 9 In step S903, the notification control unit 308 generates notification information that does not include information indicating that the upper limit of the connection has been reached. Next, the notification control unit 308 cooperates with the signal processing unit 302, the wireless communication unit 204, and the antenna control unit 205 to generate SIB and PBCH including the generated notification information, and transmits the SIB and PBCH to the outside as SS / PBCH blocks.

[0120] In this case, the notification control unit 308 generates notification information of the information element after "Detail Reason of NonAccess" that does not include "Reason of NonAccess-IEs". It is also possible to adopt a configuration in which notification of only 1-bit flag information indicating whether the upper limit of the connection is reached is given. In this case, the notification control unit 308 can generate notification information in which "0" is set in the area storing the 1-bit flag information indicating whether the upper limit of the connection is reached.

[0121] Through the above-described process, the IAB node can notify the outside of information indicating that the upper limit of the number of connections has been reached.

[0122] Next, refer to Fig.10 A description is given of the control of the UE according to the second exemplary embodiment by referring to the flowchart in FIG. Fig.10The flowchart in the figure selectively illustrates the process of searching for a base station and connecting to a base station when the UE is not connected to the base station or when the UE performs handover of the base station. The process shown in the flowchart is implemented by the control unit 202 of the UE executing the program. In the case of explicitly indicating what process is to be performed, the reference Figure 4 The functional units described are given as the main body of the description.

[0123] In step S1001, the collection unit 407 cooperates with the signal processing unit 402 and the control unit 202 and the communication unit 204 of the UE to search for surrounding base stations. Then, the collection unit 407 receives the signal of the SS / PBCH block transmitted from the surrounding base station found by the search, and also measures the quality such as the received signal strength of the signal. Next, the collection unit 407 stores the information about the base station included in the signal and the received signal strength in association with each other. The collection unit 407 analyzes each SIB1 and also stores information about whether the base station notifies the outside of the information indicating that the upper limit of the number of connections has been reached.

[0124] In step S1002, the connection control unit 405 generates a list on which the base stations found in step S1001 and the radio wave strengths are associated with each other. Then, the control unit 405 rearranges this list in ascending order, and also generates a list of connection destination candidates on which only base stations exceeding a predetermined threshold are extracted. Based on the PLMN stored in the UE itself at this time, base stations provided by operators that do not allow connection are also excluded from the candidate list.

[0125] Next, in step S1003, the connection control unit 405 selects a base station as a connection candidate from the list rearranged in ascending order. In the first selection, the control unit 405 sets the index indicating the reference destination on the list to 0 and selects the base station at the head of the list as a base station as a connection candidate.

[0126] The index is incremented by the process of step S1006. Therefore, in the second or subsequent selection, the base station stored at the position corresponding to the index value on the list is selected as the base station as the connection candidate.

[0127] In step S1004, the connection control unit 405 determines whether the base station as the connection candidate is a base station that notifies the outside of information indicating that the upper limit of the number of connections has been reached. If it is determined that the base station as the connection candidate is a base station that notifies the outside of information indicating that the upper limit of the number of connections has been reached, the connection control unit 405 does not attempt to connect to the base station as the connection candidate, and the process proceeds to step S1006. If it is determined that the base station as the connection candidate is not a base station that notifies the outside of information indicating that the upper limit of the number of connections has been reached, the process proceeds to step S1005.

[0128] In step S1005, the connection control unit 405 attempts to connect to the base station that is a connection candidate. The process of this connection is similar to the process described in the first exemplary embodiment.

[0129] On the other hand, in step S1006, the connection control unit 405 determines whether there is another connection destination candidate on the list. Specifically, the connection control unit 405 increments the index indicating the reference destination on the list and determines whether there is another connection destination candidate on the list. If it is determined that there is another connection destination candidate on the list, the process proceeds to step S1003. If it is determined that the list ends, and there is no connection destination candidate on the list that is not attempted to be connected, a series of processes ends.

[0130] Through the above-described processing, connection to a base station that notifies the outside of information indicating that the upper limit of the number of connections has been reached is not attempted, thereby preventing unnecessary connection processing from being performed.

[0131] Although the case where control is performed to determine whether to attempt a connection through the determination processing in step S1004 is described in the present exemplary embodiment, the present invention is not limited thereto. For example, as described below, a configuration may also be adopted in which a base station that notifies externally of information indicating that the upper limit of the number of connections has been reached is excluded from the extraction target when the extraction processing in step S1002 is performed. In this case, in step S1002, the connection control unit 405 may further perform an extraction processing for excluding from the list a base station that notifies externally of information indicating that the upper limit of the number of connections has been reached.

[0132] <Third Exemplary Embodiment>

[0133] In the first and second exemplary embodiments, a description of a method for preventing connection by giving a notification of information indicating that the upper limit of the number of connections has been reached. In the third exemplary embodiment, a mechanism is provided for stopping the sending of notification information for searching cells when a new UE makes a connection when the number of UEs being connected to the IAB node reaches the upper limit of the number of connections. With this mechanism, it is possible to prevent new UEs from attempting to connect to this IAB node. The specific control method is described below. The hardware configuration and software configuration of the IAB donor, a wireless base station such as an IAB node, and the UE are similar to those in the first and second exemplary embodiments, and therefore are not described. The differences from the first and second exemplary embodiments are mainly described.

[0134] First, refer to Fig.13 , a description is given of control for preventing attempts to make a connection according to the present exemplary embodiment. Fig.131 is a sequence diagram illustrating an example of control for preventing an attempt to make a connection according to a third exemplary embodiment. First, the precondition is described. UE 112 and 113 are UEs connected to a cellular communication network via IAB node 101. Therefore, in steps S1301 and S1302, UE 112 and 113 can communicate downlink user plane data with CN 10. In steps S1303 and S1304, UE 112 and 113 can communicate uplink user plane data with CN 10. Although not illustrated due to space limitations, other UEs are also connected to IAB node 101, and the UEs being connected to IAB node 101 in this state reach the "upper limit of the number of connections - 1". The subsequent processing is described using the case where UE 111 is newly connected to IAB node 101 as an example.

[0135] In step S1305a, UE 111 sends an RRC setup request message requesting IAB node 101 to set up a connection. In step S1305b, IAB node 101 having received the RRC setup request message performs the same operation as in the first exemplary embodiment. Figure 5 The UE connection establishment sequence (the connection process described in Section 9.2.1.3 of TS 38.300) is similar to step S505 in and the sequence in subsequent steps.

[0136] Next, in step S1306, based on the upper limit of the number of connections and the number of currently connected UEs, the IAB node 101 determines whether to stop periodically sending notification information for searching cells when a new UE is connected. Fig.14 The flowchart in describes the specific determination method of the IAB 101 node. The following sequence illustrates the processing in the case of stopping the periodic transmission of notification information for searching cells when a new UE makes a connection.

[0137] If it is determined to stop the periodic transmission of notification information for searching a cell, then in step S1307 , similarly to the second exemplary embodiment, the IAB node 101 uses the extended additional area of ​​SIB1 to notify UEs existing within the range of the cell that the notification signal is scheduled to be stopped.

[0138] In steps S1308a to S1308c, each UE that is connected and has received this information returns a response indicating whether the notification signal can be stopped. In this exemplary embodiment, as an example, the case where UE 112 and 111 return acceptance and UE 113 returns non-acceptance is described. Fig.15The flowchart in describes the determination process for determining whether the notification signal can be stopped in each UE, so it is briefly described here. For example, a UE that is gradually moving away from the base station in the direction of the end of the coverage area of ​​the cell determines that information about the notification signal is needed. Then, the UE sends an RRC message including information indicating that the stop is not accepted (not accepted). The UE moving in such a direction is in a state where the received radio wave strength of the radio wave from the base station is weakened. Therefore, the UE needs notification information that is related to another base station and that the IAB node 101 notifies the outside for handover, and therefore returns non-acceptance to the notification of the notification of the stop.

[0139] In step S1310 , the IAB node 101 , which has received responses from all UEs being connected, stops sending the notification signal.

[0140] Next, in step S1311, the IAB node 101 performs processing of sending user plane (U-plane) data to the UE (e.g., UE 113) that has returned the non-acceptance as to whether the notification signal can be stopped by including information equivalent to the notification signal in the U-plane data. More specifically, the IAB node 101 includes information equivalent to the notification signal in the payload area of ​​the Service Data Adaptation Protocol (SDAP). The IAB node 101 also allocates bits for detecting the inclusion of data equivalent to the notification signal to the header area, thereby delivering to the UE that the SDAP includes information equivalent to the notification signal. The above-mentioned technology for sending information equivalent to the notification signal to the UE is merely an example and is not limited thereto. For example, the technology can also be modified so that a data frame including data equivalent to the notification signal in the header area is sent.

[0141] Next, a description is given of a sequence in which a peripheral UE connects to a base station after transmission of a notification signal is stopped. Assume a case where UE 114 moves to a coverage area of ​​IAB nodes 101 and 102. UE 114 attempts to refer to Fig.10 The search process and the connection process according to the second exemplary embodiment are described. At this time, the IAB node 101 stops the transmission of the notification signal at the timing of step S1310. Therefore, the UE 114 does not find the IAB node 101 in the search process. As a result, in steps S1312a and S1312b, the UE 114 detects the IAB node 102 as another IAB node as a base station to which the UE 114 can connect. Then, the UE 114 sends an RRC setup request message to the IAB node 102 and performs a connection establishment process.

[0142] If the connection establishment process is completed, then in steps S1314 and S1315 , UE 114 communicates downlink user plane data with CN 10 via IAB node 102 and IAB donor 100 .

[0143] Next, refer to Fig.14 , a description is given of a determination process related to stop of notification information in the IAB node according to the present exemplary embodiment. Fig.14 The flowchart in the selectively illustrates the control of the transmission of the notification signal periodically performed by the IAB node. The processing shown in the flowchart is implemented by the control unit 202 of the IAB node executing the program. In the case of explicitly indicating what processing is performed, the reference Figure 3 The functional units described are given as the main body of the description.

[0144] In step S1401, the control unit 308 determines whether the number of UEs being connected has reached the upper limit of the number of connections, based on the number of connections indicating the number of UEs currently connected managed by the connection management unit 306 and the information on the upper limit of the number of connections managed by the setting control unit 303. If it is determined that the upper limit of the number of connections has been reached, the process proceeds to step S1403. If it is not determined that the upper limit of the number of connections has been reached, the process proceeds to step S1402.

[0145] In step S1402, the notification control unit 308 generates notification information that does not include information indicating that the upper limit of the connection has been reached. Next, the notification control unit 308 cooperates with the signal processing unit 302, the wireless communication unit 204, and the antenna control unit 205 to generate SIB and PBCH including the generated notification information, and transmits the SIB and PBCH to the outside as SS / PBCH blocks. In this case, the notification control unit 308 generates and transmits the notification information that does not include the information in the second exemplary embodiment. Fig.11 Information about the information elements following "Detail Reason of NonAccess" in the "Reason of NonAccess-IEs" described.

[0146] On the other hand, in step S1403, the notification control unit 308 generates notification information including information indicating that the upper limit of the connection is reached and information indicating that the notification signal is scheduled to stop. Next, the notification control unit 308 cooperates with the signal processing unit 302, the wireless communication unit 204, and the antenna control unit 205 to generate SIB and PBCH including the generated notification information, and transmits the notification signal to the outside as an SS / PBCH block. Specifically, the notification control unit 308 further adds information such as "Pre-Notification-of-BCH Txstop" indicating that the notification signal is scheduled to stop to the reference signal in the second exemplary embodiment. Fig.11 "Reason of NonAccess-IEs" described in the documentation.

[0147] Next, in steps S1404 to S1406, the control unit 202 performs a process of waiting for a response to the advance notification message about the stop of the notification signal from all UEs being connected to the IAB node 102. In step S1404, based on whether a response is received from all UEs, the control unit 202 determines whether to repeat the response reception process. If a response is not received from all UEs, the control unit 202 determines to repeat the response reception process. Then, the process proceeds to step S1406. If a response is received from all UEs, it is determined that the response reception process is to be ended. Then, the process proceeds to step S1407.

[0148] In step S1405, the control unit 202 receives a response from the UE and also determines whether the response indicates acceptance. If the received response indicates acceptance of the stop of the notification signal, the control unit 202 records the reception of the response from this UE in the management list, and repeats the process of receiving a response from another UE and the determination process for determining whether a signal is received from all UEs being connected. This management list is used to determine whether a signal is received from all UEs being connected. On the other hand, if the received response indicates non-acceptance of the stop of the notification signal without acceptance, the process proceeds to step S1406. In step S1406, the control unit 202 sends U-plane data including information equivalent to the notification signal to the UE from which the response indicating non-acceptance is received, and also stores the UE as the UE to which the notification signal is sent.

[0149] Finally, in step S1407, the control unit 202 stops the transmission process for transmitting the notification signal, and a series of processes ends. Moreover, after stopping the transmission process for transmitting the notification signal, the control unit 202 periodically transmits U-plane data including information equivalent to the notification signal to the UE stored as the UE as the transmission target of the notification signal in step S1406. In the case where the number of connections changes from a state where the upper limit of the number of connections is reached to a state where the upper limit of the number of connections is not reached due to the exit of the UE, the control unit 202 stops notifying the information equivalent to the notification signal to the outside using the U-plane data and also resumes the transmission process for broadcasting the notification signal to the surrounding using the SIB.

[0150] Finally, reference Fig.15 A description is given of control of a UE that is being connected to an IAB node and has received a message including information indicating that a notification signal is scheduled to be stopped from the IAB node, according to a flowchart in FIG. Fig.15 The flowchart in the selectively illustrates the processing in the case where the UE receives information indicating that the notification signal is scheduled to be stopped from a base station such as an IAB node. The processing shown in the flowchart is implemented by the control unit 202 of the UE executing the program. In the case of explicitly indicating what to perform the processing, the reference Figure 4 The functional units described are given as the main body of the description.

[0151] In step S1501, the connection control unit 405 cooperates with the signal processing unit 402 to receive an SS / PBCH block message including information indicating that the notification signal is scheduled to be stopped. If the reception is completed, the process proceeds to step S1502. In step S1502, the connection control unit 405 determines whether the current state is a state in which the notification information received from the base station such as the IAB node in step S1501 needs to be updated. Specifically, based on the mobile state of the connection control unit 405 itself and the reception state of the radio wave from the base station, the connection control unit 405 determines whether the connection control unit 405 itself is moving in a direction away from the base station and whether the current situation is a situation in which the communication quality is expected to decline. If it is determined that the current situation is a situation in which the communication quality is expected to decline, the connection control unit 405 determines that the notification information needs to be updated. Then, the process proceeds to step S1504. On the other hand, if it is determined that the current situation is not a situation in which the communication quality is expected to decline, the connection control unit 405 determines that the notification information does not need to be updated. Then, the process proceeds to step S1503. The specific technique for determining whether the current state is a state in which notification information needs to be updated is not limited thereto.

[0152] Using only information related to the possibility of moving to the end of the coverage area of ​​the cell, such as the moving speed of the terminal itself, it can be determined whether the current state is a state in which notification information needs to be updated.

[0153] In step S1503, the connection control unit 405 transmits a message including an acceptance indicating that the stop of the notification signal is accepted to the base station such as the IAB node which is the transmission source of the notification signal. On the other hand, in step S1504, the connection control unit 405 transmits a message including a non-acceptance indicating that the stop of the notification signal is not accepted to the base station such as the IAB node which is the transmission source of the notification signal. The messages in steps S1503 and S1504 can be transmitted using RRC messages.

[0154] The UE that has once sent a message including an acceptance indicating the stop of accepting the notification signal may periodically perform a determination equivalent to the determination in step S1502, and send a request to the base station to start a transmission process for sending notification information using the U-plane according to the determination result. The IAB node that has received this request may periodically send U-plane data including information equivalent to the notification signal to the transmission source of the UE's request. Through this process, if the UE that once agreed to stop changes to a state where the notification information needs to be updated due to changes over time, it is possible to use the U-plane to provide the changed UE with information equivalent to the notification information.

[0155] Through the above processing, when the number of UEs currently connected to the IAB node reaches the upper limit of the number of connections, it is possible to stop notifying the outside of notification information used to search for cells when a new UE is connected. Therefore, it is possible to prevent a new UE from attempting to connect to the IAB node that has reached the upper limit of the number of connections. For a UE that is currently connected and cannot accept the stop of notification information, information equivalent to the notification information can be provided by unicast using data communication based on the U plane.

[0156] <Changes>

[0157] Although the first and second exemplary embodiments have described the case where the base station that notifies the information indicating that the upper limit of the number of connections has been reached is an IAB node or a mobile IAB node, the present invention is not limited to this. If the operation of the mobile IAB node and the temporary installation of the IAB node are common, the uncertainty increases with respect to the change in the communication load, and some measures may also be required in the fixed base station. For example, it is also possible that due to the movement of the mobile IAB node or the removal of the temporarily installed IAB node, the communication demand temporarily responsible for the mobile IAB node or the temporarily installed IAB node flows into the fixed base station. Based on this, a configuration can be adopted in which control is performed to also notify the fixed base station, the fixedly installed IAB node, and the fixedly installed IAB donor of the information indicating that the upper limit of the number of connections has been reached.

[0158] The disclosure of the present exemplary embodiment includes the following configurations.

[0159] <Other embodiments>

[0160] The present invention can also be implemented by supplying a program for implementing one or more functions of the above exemplary embodiments to a system or device via a network or storage medium, and causing one or more processors of a computer of the system or device to read and execute the program. The present invention can also be implemented by a circuit (e.g., ASIC or FPGA) for implementing one or more functions.

[0161] The present invention is not limited to the above-described embodiments, and various changes and modifications can be made within the spirit and scope of the present invention. Therefore, in order to make the public aware of the scope of the present invention, the following claims are made.

[0162] This application claims the benefit of Japanese Patent Application No. 2022-152857 filed on September 26, 2022 and Japanese Patent Application No. 2023-015589 filed on February 3, 2023, which are hereby incorporated herein by reference.

[0163] Description of reference symbols

[0164] 100IAB Donor

[0165] 101IAB Node

[0166] 110UE

[0167] 202 control unit.

Claims

1. A communication device, the communication device being used as a base station for performing cellular communication with a user equipment (UE), the communication device comprising: A notification unit configured to notify externally information indicating that the upper limit of the number of connections has been reached, when the number of connections with the base station has reached an upper limit of the number of connections. 2 . The communication device according to claim 1 , further comprising a setting unit configured to set an upper limit on the number of connections. 3 . The communication device according to claim 2 , wherein the setting unit sets an upper limit on the number of connections based on a user operation through a screen.

4. The communication device according to any one of claims 1 to 3, further comprising: a management unit configured to manage information about a UE being connected to the base station; as well as A determining unit is configured to determine whether the number of UEs being connected managed by the management unit has reached an upper limit of the number of connections.

5. The communication device according to any one of claims 1 to 4, wherein the notification unit notifies a UE that has attempted to connect to the base station that the upper limit of the number of connections has been reached by including information indicating that the upper limit of the number of connections has been reached in a radio resource control (RRC) message. 6 . The communication apparatus according to claim 5 , wherein the RRC message including the information indicating that the upper limit of the number of connections has been reached, which the notification unit notifies the UE, is an RRC reject message.

7. The communication device according to any one of claims 1 to 5, wherein the base station is an integrated access and backhaul (IAB) node that uses radio resources for a backhaul line of an integrated access and backhaul (IAB) donor, and The notification unit notifies the IAB donor of information indicating that an upper limit of the number of connections has been reached using a Backhaul Adaptation Protocol (BAP).

8. The communication device according to claim 7, wherein the notification unit notifies the IAB donor of information indicating radio wave conditions of surrounding communication devices and information about UE being connected to the base station together with information indicating that an upper limit of the number of connections has been reached using the BAP.

9. The communication device according to any one of claims 1 to 8, wherein the notification unit notifies the outside of information indicating that an upper limit of the number of connections has been reached using a synchronization signal block (SSB).

10. The communication device according to claim 9, wherein when the number of connections with the base station has not reached an upper limit on the number of connections, the information notified to the outside by the notification unit using the SSB does not include information indicating that the upper limit on the number of connections has been reached. 11 . The communication device according to claim 1 , wherein even when an upper limit of the number of connections has not been reached, when congestion is occurring, the notification unit notifies the outside of second information indicating that congestion is occurring.

12. A communication device for performing cellular communication, the communication device comprising: a measuring unit configured to measure radio wave strength of radio waves transmitted from surrounding base stations; as well as a connecting unit configured to connect to a base station satisfying a condition regarding radio wave strength, The connection unit does not attempt to connect to a base station that satisfies the condition regarding the radio wave strength, but notifies externally information indicating that an upper limit of connection has been reached.

13. The communication device according to claim 12, further comprising: A receiving unit, wherein the receiving unit is configured to receive notification information that the base station notifies to the outside using a synchronization signal block (SSB); as well as A determining unit is configured to determine whether the notification information received by the receiving unit includes information indicating that an upper limit of connections has been reached.

14. A control method for controlling communication, the control method comprising: In a case where the number of connections with a base station providing cellular communication reaches an upper limit of the number of connections, information indicating that the upper limit of the number of connections is reached is notified to the outside.

15. A control method for controlling a communication device performing cellular communication, the control method comprising: Measuring the radio wave strength of radio waves emitted from surrounding base stations; as well as Connect to a base station that meets the conditions regarding radio wave strength, An attempt in which connection is made to a base station satisfying the condition regarding the radio wave strength while information indicating that the upper limit of connection is reached is not notified to the outside is not made. 16 . A program for causing a computer to execute the control method according to claim 14 or 15 .

17. A communication device, the communication device acting as a base station for performing cellular communication with a user equipment (UE), the communication device comprising: a sending unit, the sending unit being configured to send notification information including at least information for searching for the base station to the outside using a synchronization signal block (SSB); as well as A control unit configured to perform control of stopping the transmission of the notification information from the transmission unit when the number of connections with the base station reaches an upper limit of the number of connections.

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