IAB donor, control method, program, and control device

Abstract

To appropriately set a communication path for relaying communication of UE.SOLUTION: A control device of a wireless communication system including relay devices that relay communication between a base station and a terminal determines whether to change a first communication path based on the number of terminals connected to the relay devices included in the first communication path, regarding the first communication path starting from the base station and including a first relay device and a second relay device directly connected to the first relay device on a downstream side of the first relay device, and when it is determined that the first communication path is changed, changes the connection destination of the second relay device from the first relay device to a third relay device or the base station, and sets a second communication path.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] ]] The present invention relates to a technology for setting a relay communication path.

Background Art

[0002] In the Third Generation Partnership Project (3GPP), the standardization of Integrated Access and Backhaul (IAB), which integrates an access line and a backhaul line, is in progress (see Patent Document 1). In IAB, the radio resources used for the access line between the base station and the user equipment (UE) are also used for the backhaul line. For example, in IAB, radio resources in the millimeter wave band such as the 28 GHz band 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 by a wireless line, and the area coverage can be expanded at a lower cost compared with the case of using a wired line such as an optical fiber.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In IAB, it is important that a communication path is appropriately set to relay the communication of the UE.

Means for Solving the Problems

[0005] An IAB donor according to one aspect of the present invention is a wireless communication system using IAB (Integrated Access and Backhaul) technology as defined by the Third Generation Partnership Project (3GPP), comprising at least one IAB node that relays communication between a core network and terminals, and an IAB donor that relays communication between the IAB node and the core network, wherein the IAB donor of the wireless communication system comprises identification means for identifying the number of terminals connected to the IAB nodes under the IAB donor, based at least on communication with the IAB nodes under its control. The system includes: determination means for determining whether to change the communication path based at least on the number of terminals connected on a first communication path including the IAB donor, a first IAB node under the IAB donor, and a second IAB node under the first IAB node; and setting means for changing the connection destination of the second IAB node to a third IAB node that constitutes a different communication path from the first communication path, and setting a second communication path for relaying communication between the second IAB node and the terminals under the second IAB node and the IAB donor via the third IAB node. Yes Furthermore, a maximum number of terminals is set for each IAB node under the IAB donor, and if the total number of terminals connected to the first IAB node and the total number of terminals connected to one or more IAB nodes downstream of the first IAB node in the first communication path exceeds the maximum number of terminals set for the first IAB node, the determination means determines that the communication path should be changed. do. [Effects of the Invention]

[0006] According to the present invention, a communication path for relaying UE communications can be appropriately configured. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram showing an example configuration of a wireless communication system. [Figure 2] This figure shows an example of an IAB donor hardware configuration. [Figure 3] This figure shows an example of the functional configuration of an IAB donor. [Figure 4] This figure shows an example of the information used to switch the connection destination of an IAB node. [Figure 5] This diagram shows an example of the processing flow performed in a wireless communication system. [Figure 6] This figure shows an example of the processing flow performed by an IAB donor. [Figure 7] This diagram illustrates an example of the relationship between the number of hops from an IAB donor and the maximum capacity of a UE (Union Engineer). [Figure 8] This figure shows an example of the processing flow performed by an IAB donor. [Modes for carrying out the invention]

[0008] 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.

[0009] (System Configuration) Figure 1 shows an example of the configuration of the wireless communication system according to this embodiment. This wireless communication system is a relay communication system using IAB (Integrated Access and Backhaul) as defined in the cellular communication standard of the Third Generation Partnership Project (3GPP). The IAB includes IAB donors 102 and 108 connected to the core network 101. IAB donors 102 and 108 function as base station devices and establish wireless connections with the terminal function (Mobile Termination) of the IAB node. Then, IAB donors 102 and 108 are configured using BAP (Backhaul Adaptation Protocol), enabling the IAB node to function as a relay device. For example, IAB donor 102 is connected to IAB node 103 and IAB node 105, and communication paths are set up via IAB donor 102 and IAB node 103, and via IAB donor 102 and IAB node 105. Furthermore, an IAB node 109 is connected to the IAB donor 108, and a communication path is established via the IAB donor 108 and the IAB node 109.

[0010] An IAB node can connect to other IAB nodes that are directly or indirectly connected to an IAB donor. In this case, communication between the IAB node and the IAB donor will take place via other IAB nodes. For example, IAB node 104 can establish a connection with IAB donor 102 and set up a communication path via IAB node 103. Similarly, IAB node 106 can establish a connection with IAB donor 102 via IAB node 105, and IAB node 110 can connect to IAB donor 108 via IAB node 109. Furthermore, IAB node 107 can, for example, connect to IAB node 104 to establish a communication path to IAB donor 102. IAB node 107 may also be configured to connect simultaneously with IAB node 106 and IAB node 105 in addition to IAB node 104, for example, using Dual Connectivity.

[0011] In this embodiment, a node that is directly connected to an IAB node on the side of the established communication path that is closer to the core network 101 is called a parent node. Conversely, a node that is directly connected to an IAB node on the side of the communication path that is further away from the core network 101 is called a child node. For example, the parent node of IAB node 104 is IAB node 103, and the child node of IAB node 104 is IAB node 107. Similarly, from the perspective of IAB node 109, IAB donor 108 is the parent node, and IAB node 110 is the child node. As described above, in the wireless communication system according to this embodiment, a tree-structured relay network is formed starting from the IAB donor.

[0012] Furthermore, IAB nodes (and potentially IAB donors) handle not only backhaul communication but also access line communication. For example, an IAB node uses an antenna shared with or separately provided for the access line to form a cell, establish an access line with a terminal (UE), and provide communication services. For example, IAB node 104 forms cell 111, IAB node 106 forms cell 112, and IAB node 107 forms cell 113. Similarly, other IAB nodes (and potentially IAB donors) can also form cells, establish connections with UEs, and provide communication services. In addition, each IAB node (and potentially IAB donor) can communicate by forming a predetermined number of beams, or by forming an appropriate beam for each UE. Furthermore, each IAB node receives data (control data and user data) destined for the connected UE from the parent node and transmits it to that UE. Similarly, an IAB node forwards data received from the connected UE to the parent node. This enables communication between the IAB donor, which functions as a base station, and the UE. The IAB donor and IAB node may provide the access line in the same frequency band as the backhaul line, or in a different frequency band than the backhaul line.

[0013] An IAB node can switch to a different IAB donor or other IAB node. For example, an IAB node may switch to another node if a Backhaul Radio Link Failure (BH RLF) occurs in the radio link with the other node it is connected to. For instance, if a BH RLF occurs, an IAB node can search for and connect to another available IAB node or IAB donor, establishing a new IAB communication path. This allows the provision of communication services to the connected UE to continue even if the radio quality of the IAB backhaul line becomes insufficient for any reason. Note that BH RLF is just one example, and communication paths may be switched for other reasons. An IAB node may also change its communication path in response to a predetermined event, such as when the radio quality with other unconnected IAB nodes becomes at a predetermined level or higher than the radio quality with the connected parent node, as in a normal handover.

[0014] Here, it is assumed that each IAB node has a limited number of UEs it can handle, based on factors such as the wireless quality in the communication path to the IAB donor connected via a parent node, and the processing capacity of the IAB node itself. For example, if the wireless quality is insufficient in part of the communication path, the number of UEs that can be handled will be less than when the wireless quality is good. The number of UEs that can be handled also fluctuates depending on the amount of physical resources such as baseband processing and RF processing. Note that the "number of UEs that can be handled" here includes the total number of child nodes and UEs connected further downstream. In other words, upstream IAB nodes connected closer to the IAB donor in the communication path need to relay not only the communication of UEs connected to their own device, but also the communication of UEs connected to downstream IAB nodes such as child nodes. For this reason, even if the number of UEs directly connected to an IAB node does not exceed the number of connections allowed by the device, an IAB node may not be able to provide communication services to UEs depending on the number of UEs connected to downstream IAB nodes. Therefore, in this embodiment, control devices such as IAB donors and control nodes in the core network 101 determine the communication path to be set considering the allowable number of UEs at each IAB node. The following describes the case where this control device is an IAB donor. The "allowable number of UEs" of an IAB node refers to the maximum number of UEs connected to that IAB node and the total number of UEs connected to child nodes or downstream nodes. In addition, the allowable number of UEs here may be a number that, in one example, could result in communication of sufficient quality becoming impossible if more UEs are connected, but it may be set to a number that would not immediately prevent communication. In addition to or instead of the allowable number of UEs, the communication path may be determined based on other criteria such as allowable total throughput or allowable bandwidth. That is, the communication path may be determined so that the total throughput or bandwidth required for communication of UEs connected to each IAB node and its downstream IAB nodes does not exceed the allowable amount.

[0015] (Device configuration) Fig. 2 shows an example of the hardware configuration of an IAB donor (control device). The IAB donor has, for example, a control unit 201, a storage unit 202, a wireless communication unit 203, an antenna control unit 204, and an antenna 205. Note that these configurations are just examples, and the IAB donor (control device) may further include other hardware configurations, or may not include at least a part of the configurations shown in Fig. 2. Also, the IAB donor (control device) may further include configurations not included in Fig. 2. For example, although the IAB donor has a wireless communication unit 203, an antenna control unit 204, and an antenna 205, when a control device arranged in the core network 101 is used, a wired communication unit and an interface therefor may be included instead of these hardware components.

[0016] The control unit 201 is configured to include one or more processors such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). Note that the control unit 201 may include an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), an ASIC (Application Specific Integrated Circuit), etc. The control unit 201 can be configured to control the entire IAB donor device and execute the processes described later, for example, by executing a computer program stored in the storage unit 202. The storage unit 202 is configured to include one or more memories such as a ROM (Read Only Memory) or a RAM (Random Access Memory), and a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). Note that these are just examples, and the storage unit 202 may have any device configuration capable of storing information. The storage unit 202 is configured to store, for example, a computer program corresponding to the control process executed by the control unit 201 and various types of information (cell information, connected terminal information, IAB routing information, etc.) used in the control process.

[0017] The wireless communication unit 203 executes various processes related to cellular communication such as LTE (Long-Term Evolution) compliant with the 3GPP standard and the 5th generation (5G) cellular communication standard. The wireless communication unit 203 is configured to include, for example, a circuit for control processing for executing communication processing such as a baseband chip and an RF (radio frequency) chip. The antenna control unit 204 controls the antenna 205 to transmit the electrical signal generated by the wireless communication unit 203 as a wireless signal and to detect a wireless signal arriving from outside the IAB donor to obtain an electrical signal. The antenna control unit 204, for example, determines an antenna weight so as to form a beam toward a counterpart device at the connection destination such as an IAB node, and can apply the antenna weight to a signal transmitted from the antenna 205 or a signal received at the antenna 205. The antenna 205 is an antenna configured to include one or more antenna elements designed to transmit radio waves in a frequency band corresponding to the wireless communication system to which the wireless communication unit 203 conforms and to receive radio waves in that frequency band from the outside. Note that the antenna 205 can be configured to be able to form a beam having a high gain in a predetermined direction and a low gain in other directions using a plurality of antenna elements. Note that the control for the beam formation can be performed by the antenna control unit 204.

[0018] Next, an example of the functional configuration of an IAB donor (control device) will be explained using Figure 3. The IAB donor (control device) includes, for example, a signal transmission unit 301, a signal reception unit 302, a data storage unit 303, a connection control unit 304, an RRC processing unit 305, a notification signal control unit 306, a UE connection count confirmation unit 307, a connection destination determination unit 308, and a connection destination notification unit 309. Note that these functional units are just examples, and some of their functions may be omitted, or functions different from those shown in Figure 3 may be added. Furthermore, a single functional unit may be provided that integrates two or more of the functions shown in Figure 3, or a function shown as a single functional unit in Figure 3 may be divided into multiple functional units. The functional unit shown in Figure 3 can be implemented, for example, by the control unit 201 executing a program stored in the storage unit 202. In addition, at least some functions may be implemented using dedicated hardware, such as functions pre-built into the wireless communication unit 203. Furthermore, some functions may be realized through cooperation between the IAB donor and the IAB node.

[0019] The signal receiving unit 301 and the signal transmitting unit 302 perform processing to transmit and receive radio signals with the UE in accordance with 3GPP cellular communication standards such as LTE and 5G. The data storage unit 303 performs processing to store and retain software (computer programs) executed on the IAB donor, IAB routing information, and information about connected UEs. The data storage unit 303 can also store general information related to communication control, such as PLMN (Public Land Mobile Network Identity), which is an identifier that identifies the telecommunications carrier. The connection control unit 304 performs processing related to the connection and disconnection of UEs to the cellular network, such as the communication of radio resource control (RRC) messages between the UE and the core network. The RRC processing unit 305 performs RRC processing, such as requesting the establishment and release of RRC connections. When the first IAB node under its control hands over to another IAB donor or a second IAB node under that other IAB donor, the RRC processing unit 305 can send a handover message to the UE connected to the first IAB node. Furthermore, the RRC processing unit 305 may also send a handover message to the UE currently connected to the first IAB node when the first IAB node is handed over from another IAB donor or a second IAB node under its control and connected to the device. That is, when a connected IAB node is connected to another IAB donor, the RRC processing unit 305 performs processing to release the RRC connection with the UE currently connected to that IAB node, because the IAB donor to which the UE is connected will also change. In addition, when an unconnected first IAB node is handed over to the device or a second IAB node under its control, the RRC processing unit 305 performs processing to establish an RRC connection for the UE currently connected to that first IAB node.

[0020] The notification signal control unit 306 periodically transmits notification signals such as synchronization signals (SS) and physical broadcast channels (PBCH) to the surrounding area using predetermined frequency resources for each cell provided by the device. The notification signal control unit 306 can also determine, for example, the radio resources to be used for transmitting SS / PBCH at each of the IAB nodes connected under its control, and control the transmission of notification signals using those radio resources. MTs of UEs and IAB nodes within range of the notification signal can recognize IAB donors or IAB nodes connected to those IAB donors in the vicinity of the device based on the notification signal. The MTs of UEs and IAB nodes can then perform connection processing to surrounding IAB donors or other IAB nodes based on the received notification signal.

[0021] The UE connection count verification unit 307 checks the number of UEs connected to each IAB node connected to its own device and to other IAB nodes connected downstream. In the procedure when a UE connects to each IAB node, the UE connection count verification unit 307 can recognize which IAB node the UE is connected to, for example, based on the communication path identifier included in the signal transmitted from the IAB node. The UE connection count verification unit 307 then stores the number of UEs connected to each IAB node in the data storage unit 303 and can check the number of UEs currently connected to each IAB node based on the stored information. The UE connection count verification unit 307 can also obtain the allowable capacity of each IAB node when establishing a connection and communication path with each IAB node and store it in the data storage unit 303. Furthermore, the UE connection count verification unit 307 can identify the IAB nodes included in each communication path when setting up the establishment of a communication path. Therefore, the UE connection count verification unit 307 can calculate the total number of UEs connected to each IAB node included in a given communication path, including that IAB node and the IAB nodes downstream from it, and determine whether that total number exceeds the allowable capacity.

[0022] The connection destination determination unit 308 determines the connection destination of an IAB node in a communication path if the number of UEs connected to that IAB node and other downstream IAB nodes exceeds the allowable capacity. For example, the connection destination determination unit 308 may determine that it will switch the connection destination of the IAB node to which the UE is connected, or the connection destination of an upstream IAB node. The connection destination determination unit 308 may, for example, establish a new communication path by connecting the IAB node to which the UE is connected to another IAB node, and then determine whether there are more IAB nodes than the allowable capacity in that new communication path. If it is possible to set up a new communication path in which there are no IAB nodes that exceed the allowable capacity, the connection destination determination unit 308 may decide to change the connection destination of one of the IAB nodes to set up that new communication path. The connection destination notification unit 309 notifies the IAB node whose connection destination is to be changed, as determined by the connection destination determination unit 308, that the connection destination should be changed and provides information indicating the IAB node of the changed connection destination.

[0023] (Communication processing flow) Next, an example of the processing flow performed in the wireless communication system described above will be explained. In the following explanation, we will focus only on IAB donor 102 and IAB nodes 103-107 of the system shown in Figure 1. Note that IAB node 107 is connected to IAB node 104, and a communication path is formed that includes IAB donor 102, IAB node 103, IAB node 104, and IAB node 107. It is also assumed that another communication path is formed that includes IAB donor 102, IAB node 105, and IAB node 106.

[0024] <Processing Example 1> This example describes the case where the number of UEs that can be accommodated at each IAB node (i.e., the maximum total number of UEs connected to each IAB node and other downstream IAB nodes) is set. In this example, IAB node 104 can be connected to IAB node 105 in addition to IAB node 103, and IAB node 107 can be connected to IAB node 105 or IAB node 106 in addition to IAB node 104. Also, IAB node 106 can be connected to IAB node 103 in addition to IAB node 105. The devices that each IAB node can connect to are identified in advance, for example, by measuring the surrounding wireless environment with the MT of each IAB node and determining the results of that measurement. This can be done in the same way as the conventional process of determining the cell to be measured for the UE.

[0025] The allowable capacity of each IAB node is assumed to be 12 for IAB node 103, 8 for IAB node 104, 20 for IAB node 105, 12 for IAB node 106, and 5 for IAB node 103. Furthermore, it is assumed that there are 4 UEs connected in cell 111 formed by IAB node 104, and 6 UEs connected in cell 112 formed by IAB node 106. And that there are 4 UEs connected in cell 113 formed by IAB node 107, and that UE 121 is attempting to connect. Note that IAB node 104 has 4 UEs connected to itself, and there are also 4 UEs connected to IAB node 107 which is connected downstream, so the total number of UEs accommodated by IAB node 104 is 8. On the other hand, since there are no other IAB nodes connected downstream to IAB node 107, the only UEs it accommodates are the 4 UEs connected to itself. A table summarizing this information is shown in Figure 4.

[0026] If another UE 121 is connected to IAB node 107, the number of UEs accommodated by IAB nodes 103 and 104 will become 9, and the number of UEs accommodated by IAB node 107 will become 5. In this case, the number of UEs accommodated by IAB node 107 will not exceed the allowable capacity, but the number of UEs accommodated by IAB node 104 will exceed the allowable capacity. Therefore, IAB donor 102 can determine whether or not to switch the connection destination of IAB node 107. That is, because the number of UEs accommodated by IAB node 104 has exceeded the allowable capacity, a change in the connection destination of a child node of IAB node 104 or an IAB node further downstream (in this case, IAB node 107) is determined. In this example, it is determined whether or not IAB node 107 should change its connection to IAB node 106 or IAB node 105, which are candidate connection destinations other than the currently connected IAB node 104. According to Figure 4, IAB node 106 has a capacity of 12 devices and currently houses 6 UEs. When IAB node 107, to which UE 121 is connected, is connected, the number of UEs connected to IAB node 107 at that time is 5, so the number of UEs housed in IAB node 106 becomes 11, which is within the capacity limit. Similarly, IAB node 105 has a capacity of 20 devices and currently houses 6 UEs, so even if IAB node 107 is connected to IAB node 106, the number of UEs housed will remain within the capacity limit. Likewise, if IAB node 107 is connected to IAB node 105, the number of UEs housed will remain within the capacity limit. For these reasons, IAB donor 102 can decide to switch the connection destination of IAB node 107 to either IAB node 106 or IAB node 105.

[0027] Furthermore, if IAB node 107 supports Dual Connectivity, IAB donor 102 may decide to increase the number of connections for IAB node 107 rather than switching the connection destinations. That is, IAB donor 102 may decide that IAB node 107 will connect to IAB node 106 and IAB node 105 while maintaining its connection with IAB node 104. In this case, IAB donor 102 may decide, for example, whether each UE connected to IAB node 107 should communicate using route 1 via IAB node 104 or route 2 via IAB node 106 and IAB node 105. This is just one example, and UEs do not necessarily have to be fixedly associated with routes. For example, a predetermined percentage of the communication of UEs connected to IAB node 107 may be conducted using route 2. For example, IAB donor 102 may decide to handle communication for 3 UEs via route 1 and communication for 2 UEs via route 2, and share this configuration information with IAB node 107. In this case, for example, the number of UEs accommodated by IAB node 104 may be counted as 3, and the number of UEs accommodated by IAB node 106 or IAB 105 may be counted as 2.

[0028] An example of the processing flow in a wireless communication system will be explained using Figure 5. For the sake of simplicity, it will be assumed that IAB node 107 can be connected to either IAB node 104 or IAB node 106, and the connection to IAB node 105 will not be considered. First, a first communication path is formed starting from IAB donor 102, including IAB donor 102, IAB node 103, and IAB node 104, and a second communication path is formed including IAB donor 102, IAB node 105, and IAB node 106 (S501). For the first communication path, the connection between IAB donor 102 and IAB node 103 is established and the communication path is set, and the connection between IAB node 103 and IAB node 104 is established and the communication path is set. Furthermore, for the second communication path, a connection is established and a communication path is set between IAB donor 102 and IAB node 105, and a connection is established and a communication path is set between IAB node 105 and IAB node 106. With the first and second communication paths thus formed, IAB node 107 then connects to IAB node 104 in order to connect to the first communication path. IAB node 107 receives, for example, broadcast signals (synchronization signals and physical broadcast channels, SS / PBCH) arriving from IAB node 104 and IAB node 106 (S502, S503).

[0029] IAB node 107 establishes downlink synchronization based on the synchronization signal and obtains basic system information via PBCH. Here, it is assumed that IAB node 107 has decided to connect to IAB node 104 based on, for example, the received strength of the broadcast signal. In this case, IAB node 107 performs a random access procedure (RACH process) with IAB node 104 (S504). That is, IAB node 107 establishes uplink synchronization by sending a random access preamble to the IAB node and receiving a random access response containing information specifying the transmission timing. Then, IAB node 107 establishes a connection at the RRC layer (S505) and becomes able to communicate with IAB node 104. Then, IAB donor 107 performs a communication path setting process via BAP with IAB donor 102, thereby establishing a communication path connected in the order of IAB donor 102, IAB node 103, IAB node 104, and IAB node 107 (S506). The detailed procedures for establishing the connection and configuring the communication path are the same as for establishing a connection and configuring the communication path for a normal IAB node, so they will not be explained here. Once this configuration is complete, IAB donor 102 will be able to manage the communication path including IAB node 107. In addition, with this configuration, IAB node 107 will be able to function as a relay device that relays the communication of IAB donor 102 and establish a connection with the UE.

[0030] Subsequently, for example, after four UEs have connected to IAB node 107, UE 121 enters cell 113 formed by IAB node 107 and establishes a connection with IAB node 107 (S507). When UE 121 actually establishes the connection, it performs connection processing with IAB donor 102 via IAB node 107. At this time, IAB node 107 transfers data including identification information to identify the communication path between IAB node 107 and IAB donor 102. Therefore, IAB donor 102 can recognize that UE 121 is connecting to IAB node 107. IAB donor 102 determines, upon UE 121's connection, whether the number of UEs currently accommodated in the communication path currently associated with IAB node 107 exceeds the allowable capacity of the IAB node. Then, if there is a first IAB node where the number of UEs being accommodated exceeds the allowable capacity, IAB donor 102 determines to switch the connection destination of the second IAB node downstream of that IAB node. Then, for example, as described above, IAB donor 102 decides to set the connection destination of IAB node 107 to IAB node 106 and sends a connection destination switching instruction containing the information of the new connection destination to IAB node 107 (S509). The information of the new connection destination may be, for example, a cell identifier configured by IAB node 106.

[0031] When IAB node 107 receives a connection switching instruction from IAB donor 102, it performs a RACH process with IAB node 106 to establish synchronization (S510) and establishes an RRC connection (S511) based on that instruction. At this time, IAB node 107 may disconnect from IAB node 104. In other words, the MT of IAB node 107 may perform a handover to switch the connected IAB node. Subsequently, IAB node 107 performs a communication path setting process using BAP with IAB donor 102, thereby establishing a communication path connected in the order of IAB donor 102, IAB node 105, IAB node 106, and IAB node 107 (S512). Because this process is performed, there are no IAB nodes accommodating more UEs than the allowable capacity, making it possible to prevent some IAB nodes from becoming overloaded and resulting in insufficient communication quality.

[0032] In the example above, we discussed whether or not to change the connection destination of IAB node 107. However, if IAB node 107 supports Dual Connectivity, for example, an additional connection destination may be added. In other words, for IAB nodes that can connect to two or more destinations in parallel, the connection destination may be changed or an additional connection destination may be added.

[0033] Next, the processing flow executed by the IAB donor 102 in S509 will be explained using Figure 6. The processing in Figure 6 can be realized, for example, by the control unit 201 of the IAB donor 102 executing a program stored in the memory unit 202. Note that this is just one example, and predetermined hardware on which the processing in Figure 6 is implemented may be used.

[0034] When IAB donor 102 connects to UE 121 via IAB node 107, it receives UE connection information indicating that UE 121 will be connected to IAB node 107 (S601). Then, IAB donor 102 determines whether there is an IAB node in the communication path to which IAB node 107 belongs that can accommodate more UEs than the allowed number (S602). If no such IAB node exists (NO in S602), IAB donor 102 terminates the process and accepts the connection of UE 121 on the current communication path, communicating with UE 121 via IAB node 107. On the other hand, if such an IAB node exists (YES in S602), IAB donor 102 performs initial setup for selecting the destination for switching the connection (S603). In the initial settings, for an IAB node whose connection destination is changed, the number of candidate destinations for switching the connection is set to "N", the candidate destinations for switching the connection are sorted in order of signal strength (wireless quality), and the following processing is performed starting from the n=1 candidate. In this case, the only candidate destination for switching the connection of IAB node 107 is IAB node 106. That is, according to the information in Figure 4, IAB node 107 can connect to IAB node 104 and IAB node 106, and is currently connected to IAB node 104. Therefore, the only candidate destination after the change is IAB node 106. For this reason, when N is set to 1 and the connection destination of IAB node 107 is changed to IAB node 106, it is determined whether all UEs can be accommodated in the communication path between IAB node 107 and IAB donor 102.

[0035] The IAB node whose connection destination is changed could be IAB node 107 to which UE121 is connected, but it could also be a child IAB node of an IAB node that accommodates more UEs than its allowable capacity, or an IAB node further downstream. In this case, if there are multiple candidate IAB nodes whose connection destination is changed, the processing from S603 onwards may be executed for each of those multiple IAB nodes, and it may be decided to switch the connection destination of one of the IAB nodes. For example, it may be decided to prioritize switching the connection destination of a downstream IAB node.

[0036] In S604, IAB donor 102 determines whether the allowable capacity of the IAB node of the candidate destination for the nth connection exceeds the allowable capacity in response to the switchover of IAB node 107. That is, IAB donor 102 determines whether the allowable capacity of the candidate destination is greater than or equal to the sum of the number of UEs currently accommodated by the candidate destination and the number of UEs currently accommodated by IAB node 107 (S604). If the number of UEs exceeding the allowable capacity would be accommodated (NO in S604), IAB donor 102 decides not to connect IAB node 107 to that candidate destination. Then, IAB donor 102 increments parameter n and moves on to processing the next candidate destination (S608). At this point, if parameter n exceeds N, which is the number of candidate destinations, and there are no further candidate destinations (YES in S609), IAB donor 102 terminates the process. On the other hand, if IAB donor 102 has a candidate for the next switchover destination (NO in S609), it returns to S604 and performs the judgment process described above. If it is determined in S609 that there is no candidate for the next switchover destination, the switchover destination for the connection of IAB node 107 will not be changed, and the number of UEs accommodated by IAB node 104 will remain above the allowable capacity. For this reason, IAB donor 102 may take measures such as handing over UEs connected to IAB node 104 or IAB node 107 to other IAB nodes to prevent the number of UEs accommodated by IAB node 104 from exceeding the allowable capacity. In such a case, UEs connected to IAB node 104 or IAB node 107 may be notified that the current communication path has more UEs than the allowable capacity.

[0037] When the connection destination of IAB node 107 is switched, IAB donor 102 performs the same process for the parent node of the candidate destination if the number of UEs accommodated at that candidate destination does not exceed the allowable capacity (YES in S604). First, IAB donor 102 determines whether a parent node exists among the candidate destinations for the switchover of IAB node 107 (S605). If there is no parent node among the candidate destinations for the switchover, even if the connection destination of IAB node 107 is changed to the candidate destination, there will be no IAB node in the changed communication path where the number of UEs being accommodated exceeds the allowable capacity. Therefore, IAB donor 102 notifies IAB node 107 to connect to the IAB node of the candidate destination (S610) and terminates the process. IAB node 107 then changes its connection destination according to the notification. On the other hand, if a parent node exists for the candidate to be switched to (YES in S605), IAB donor 102 determines whether the number of UEs currently connected to that parent node will exceed the allowable capacity if IAB node 107 is connected to that candidate (S606). Then, if the number of UEs currently connected to the parent node does not exceed the allowable capacity (YES in S606), IAB donor 102 makes the same determination for the parent node's further parent node (S607). By repeating this procedure, it can be confirmed that the number of UEs currently connected to all IAB nodes included in the communication path to which the candidate to be switched to IAB node 107 belongs does not exceed the allowable capacity. Then, if connecting IAB node 107 to the candidate to be switched to would cause the number of UEs currently connected to any IAB node in the communication path to exceed the allowable capacity (NO in S606), IAB donor 102 determines not to connect IAB node 107 to that candidate. In this case, IAB donor 102 changes the candidate for the connection switching destination (S608) and repeats the same process as described above.

[0038] For example, a candidate for switching the connection of IAB node 107 is IAB node 106. As shown in Figure 4, before IAB node 107 is connected, IAB node 106 has 6 UEs. When IAB node 107 is connected to IAB node 106, IAB node 106 will also accommodate the 5 UEs connected to IAB node 107, so the number of UEs it has will be 11. Since this number of UEs does not exceed the allowable capacity of IAB node 106, which is 12 (YES in S604), the processing for IAB node 105, the parent node of IAB node 106, is then performed (S606). Currently, IAB node 105 has 6 UEs, and when IAB node 107 is connected to IAB node 106, the number of UEs it has will be 11. Furthermore, the number of UEs currently connected does not exceed the allowable capacity of IAB node 105, which is 20 (YES in S606). Here, IAB node 105 is connected to IAB donor 102, and there is no parent IAB node (NO in S605). Therefore, even if IAB node 107 connects to IAB node 106, it can be confirmed that the number of UEs currently connected does not exceed the allowable capacity at all IAB nodes included in the communication path after the connection. As a result, IAB donor 102 can decide to switch the connection destination of IAB node 107 from IAB node 104 to IAB node 106.

[0039] Furthermore, IAB donor 102 may decide to connect IAB node 107 to IAB node 106 while maintaining the connection with IAB node 104. Then, IAB donor 102 may specify some UEs so that their communications are routed through IAB node 106. Alternatively, IAB donor 102 may configure IAB node 107 to route some of its communications through IAB node 106 without specifying any UEs. In this case, IAB donor 102 may instruct IAB node 107 to forward some of its communications to IAB node 106 in the uplink communications.

[0040] As described above, the IAB donor 102 can appropriately configure the communication path based on the relationship between the allowable number of UEs set for each IAB node and the number of UEs currently connected. This makes it possible to suppress an excessive increase in communication processing load due to an increase in the number of UEs connected to the IAB node, and enables the provision of communication services to UEs using a communication path with a good communication environment.

[0041] <Processing Example 2> Processing Example 1 described the case where the number of UEs that can be accommodated is set individually in advance for each IAB node. This processing example describes the processing flow when the number of UEs that can be accommodated for each IAB node is set according to the number of hops from the IAB donor. In other words, in this processing example, the number of UEs that can be accommodated for each IAB node is not predetermined, and the number of UEs that can be accommodated is determined according to the number of hops from the IAB donor when the communication path is established. The number of hops is counted as follows: an IAB node directly connected to the IAB donor is 1 hop, an IAB node connected to another IAB node connected by that 1 hop is 2 hops, and so on. In this processing example, the more hops there are, the lower the number of UEs that can be accommodated. That is, IAB nodes that are connected closer to the IAB donor in the communication path have a higher number of UEs that can be accommodated. This is because the IAB node furthest from the IAB donor only needs to process the communication of the UE directly connected to that IAB node, but IAB nodes closer to the IAB donor need to process the communication of UEs connected to downstream IAB nodes as well. When the maximum number of UEs (UEs) accommodated is determined in this way, an IAB node can increase its capacity by connecting to an upstream IAB node or IAB donor. For example, if the number of UEs accommodated by an IAB node exceeds its maximum capacity, the number of UEs can be reduced to below the maximum capacity by switching the connection to an upstream IAB node or IAB donor.

[0042] Figure 7 shows the relationship between the number of hops and the allowable capacity in this processing example. Here, the allowable capacity of the first IAB node, which is wirelessly connected to the IAB donor, is set to 12 units, and the allowable capacity of the second IAB node, which is wirelessly connected to the first IAB node, is set to 8 units. In addition, the allowable capacity of the third IAB node, which is wirelessly connected to the second IAB node, is set to 4 units. In the example in Figure 1, the allowable capacity of IAB nodes 103 and 105, which are directly connected to the IAB donor 102, is set to 12 units, and the allowable capacity of IAB nodes 104 and 106, which are connected to those IAB nodes, is set to 8 units. Also, since IAB node 107 is connected to IAB node 104, its allowable capacity is set to 4 units.

[0043] Here, as shown in Figure 1, four UEs are connected to IAB node 104, six to IAB node 106, and four to IAB node 107, and UE 121 is newly connected to IAB node 107. In this case, since IAB node 107 has a maximum capacity of four UEs when connected to IAB node 104, the number of UEs accommodated by UE 121 will exceed the maximum capacity. In this example, in such a case, IAB node 107 switches its connection destination to, for example, IAB node 105. By directly connecting to IAB node 105, the number of hops to IAB donor 102 becomes two, and the maximum capacity can be increased to eight. In this way, even if the number of connected UEs increases due to the connection of UE 121, IAB node 107 can keep the number of UEs accommodated below the maximum capacity.

[0044] An example of the processing flow in this case will be explained using Figure 8. The processing in Figure 8, like the processing in Figure 6, can be realized, for example, by the control unit 201 of the IAB donor 102 executing a program stored in the memory unit 202. Note that this is just one example, and a predetermined hardware on which the processing in Figure 8 is implemented may be used. Steps S801 to S803 are the same as steps S601 to S603 in Figure 6.

[0045] In S804, IAB donor 102 identifies the maximum number of UEs that can be accommodated when the IAB node switching its connection destination connects to the nth candidate destination, and determines whether the number of currently accommodated UEs is less than or equal to that maximum number. For example, IAB donor 102 manages information indicating how each IAB node is connected and what communication paths are established. Therefore, IAB donor 102 can identify the maximum number of UEs that can be accommodated by IAB node 107 after the connection destination switch as the number of hops obtained by adding 1 to the number of hops from IAB donor 102 to the candidate destination destination of IAB node 107. Here, IAB node 105 and IAB node 106 are candidates destination destinations for IAB node 107, which is currently connected to IAB node 104. If IAB node 107 is connected to IAB node 106, there is no change in the number of hops before and after the connection destination switch. Therefore, IAB donor 102 may determine that IAB node 106 is unsuitable as a connection switching destination for IAB node 107. On the other hand, IAB donor 102 can determine that if IAB node 107 connects to IAB node 105, the number of hops decreases by 1 from before the connection switching, thus increasing the number of devices that can be accommodated. Then, IAB donor 102 can determine that IAB node 105 is suitable as a connection switching destination because the number of UEs currently accommodated by IAB node 107 (5 devices) does not exceed the number of devices that can be accommodated if the connection destination is switched to IAB node 105 (8 devices). In this way, IAB donor 102 identifies another IAB node that is suitable as a connection switching destination for IAB node 107 in S804.

[0046] As described above, IAB donor 102 determines that IAB node 105 is a suitable candidate for switching the connection (YES in S804). In this case, IAB donor 102 then determines whether the number of UEs accommodated at the candidate IAB node 105 when IAB node 107 is connected exceeds the allowable capacity (S806). This determination is then repeated for IAB nodes upstream of the IAB node determined to be a suitable candidate in S804. IAB donor 102 may then decide to connect IAB node 107 to the candidate IAB node if there are no IAB nodes in the communication path that would accommodate more UEs than the allowable capacity when IAB node 107 switches the connection. The processing in S805-S810 is the same as S605-S610 in Figure 6.

[0047] As described above, the IAB donor 102 can configure the communication path so that it accommodates a number of UEs that does not exceed the allowable capacity corresponding to the number of hops of the IAB node. This suppresses an excessive increase in communication processing load due to an increase in the number of UEs connected to the IAB node, and enables the provision of communication services to UEs using a communication path with a good communication environment. In the example above, the example of switching the connection destination of IAB node 107 to IAB node 105 was described, but for example, if IAB node 107 can connect to IAB node 103, the connection destination may be set to IAB node 103. In this case as well, since the number of hops of IAB node 107 becomes 2 from 3, the number of UEs accommodated by IAB node 107 can be kept below the allowable capacity. In another example, if IAB node 104 can connect to IAB donor 102, the connection destination of IAB node 104 may be switched to IAB donor 102 in response to the number of UEs that IAB node 107 has accommodated exceeding the allowable capacity.

[0048] In this example, the allowable capacity may be set fixedly as shown in Figure 7, or it may be set dynamically. For example, suppose the allowable capacity of the first IAB node directly connected to the IAB donor is set to M1 units, and the number of UEs expected to be connected to each IAB node is set to L units. If the second IAB node directly connected to the first IAB node is K1 units, the allowable capacity M2 of the second IAB node can be calculated as (M1-L) / K1 (units). Also, if the number of third IAB nodes directly connected to the second IAB node is K2 units, the allowable capacity M3 of the third IAB node can be calculated as (M2-L) / K2 (units). For example, suppose the allowable capacity of the first IAB node is 30 units, and the number of UEs expected to be directly connected to each IAB node is 6 units. Here, if there is one second IAB node directly connected to the first IAB node, the allowable capacity of that second IAB node is (30-6) / 1 = 24 units. On the other hand, if there are two second IAB nodes, the allowable capacity of that second IAB node is (30-6) / 2 = 12 units, and if there are three second IAB nodes, the allowable capacity of that second IAB node is (30-6) / 3 = 8 units. Note that an IAB donor may set the allowable capacity of each IAB node according to the total number of IAB nodes connected under the directly connected IAB node. For example, suppose there is K1 second IAB node directly connected to the first IAB node and K2 third IAB nodes directly connected to the second IAB node downstream of the first IAB node directly connected to the IAB donor. In this case, the number of UEs that should be directly connected to each IAB node can be calculated as P1 = M1 / (K1+K2), which is the result of dividing the capacity of the first IAB node by (K1+K2). This value P1 then becomes the capacity of the third IAB node. Also, if the third IAB node is connected to the second IAB node by K2 units, the capacity of the second IAB node will be (K2+1)×P1(units). This is the value obtained by adding the number of UEs that should be accommodated via the third IAB node (K2×P1 units) to the number of P1 units that are directly connected to the second IAB node.Thus, the permissible capacity may be statically pre-set or dynamically set based on various criteria.

[0049] Furthermore, if the number of allowed devices is determined dynamically, a change in the connection destination of IAB node 107 may change the number of allowed devices for each IAB node at the new connection destination. Therefore, the connection destination of IAB node 107 may be determined in such a way that no IAB node exceeds its allowed number as a result of such a change.

[0050] Furthermore, in the processing examples described above, it was explained that if the number of UEs accommodated by any of the IAB nodes included in the communication path exceeds the allowable capacity when the connection destination of IAB node 107 is changed, IAB node 107 will not be connected to that communication path. However, for example, after changing the connection destination of IAB node 107, the connection destination of other IAB nodes included in the communication path at the changed connection destination may be changed so that the number of UEs accommodated by each IAB node in the communication path does not exceed the allowable capacity. Also, for example, if another IAB node is connected as a child node of IAB node 104 to which IAB node 107 is connected, the decision of whether or not to change the connection destination of that other IAB node may be made in the manner described above.

[0051] Furthermore, the above processing example described an example where the number of allowed devices is set individually for each IAB node, or for the number of hops in the communication path of each IAB node, but it is not limited to this. For example, the number of allowed devices may be set for each communication path. For example, in the configuration of Figure 1, the number of allowed devices may be set for the communication path including IAB nodes 103, 104, and 107, and the number of allowed devices may be set for the communication path including IAB nodes 105 and 106. When a new UE is connected to any IAB node, it is determined whether the total number of UEs connected to the communication path including that IAB node exceeds the number of allowed devices set for that communication path. If the number of connected UEs exceeds the number of allowed devices, the IAB donor 102 may identify a second IAB node to which the connection of the first IAB node to which the UE has been newly connected will be switched, and instruct the first IAB node to connect to the second IAB node. Furthermore, when IAB donor 102 instructs any IAB node to switch its connection destination, it updates the communication path information it manages.

[0052] In the processing example described above, we explained an example of confirming that the number of UEs accommodated at each IAB node does not exceed the allowable capacity, assuming that the IAB node 107 switches connections before the IAB node 107 switches its connection destination. However, this is not the only example. For example, it may be confirmed that the number of UEs accommodated at each IAB node does not exceed the allowable capacity after the IAB node 107 has switched connections. After the switch, the information of the child nodes of the connected IAB node is changed. The IAB donor receives a notification of the updated connection information, and the IAB donor may perform a determination process at each IAB node to see whether the number of UEs accommodated exceeds the allowable capacity. If the number of UEs accommodated exceeds the allowable capacity, the process of switching the connection destination of at least some of the IAB nodes may be performed.

[0053] In the above explanation, the IAB donor was described in a case where the number of allowed devices and the number of UEs in the communication path starting from the IAB node directly connected to the IAB donor were not considered, but rather the number of allowed devices and the number of UEs in the communication path starting from the IAB node directly connected to the IAB donor. In contrast, for example, the IAB donor's DU (Distributed Unit) may be treated as an IAB node directly connected to the IAB donor in the above explanation. That is, the IAB donor's CU (Central Unit) may be treated as a base station, and the IAB donor's DU may be treated as an IAB node directly connected to the IAB donor. In one example, IAB node 103 and IAB node 105 in Figure 1 may be composed of the IAB donor's DU.

[0054] As described above, in this embodiment, in an IAB-based relay communication system, the communication path can be configured so that the load on each relay device (IAB node) does not increase excessively beyond the maximum allowable load for that relay device. This makes it possible to relay communication between base stations (IAB donors) or the core network and terminals (UEs) in a sufficiently good environment. Although the above embodiment has described an IAB-based relay communication system, the above discussions are applicable to wireless relay communication systems that wirelessly relay communication between base stations and terminals using relay devices. For example, the above discussions are applicable to relaying communication between access points and stations in a wireless LAN (Local Area Network). Furthermore, although the above discussions are applied to, for example, fifth-generation (5G) cellular communication systems, they may also be applied to Long-Term Evolution (LTE) or cellular communication systems of generations later than 5G.

[0055] The present invention can also be realized by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be realized by a circuit (e.g., an ASIC) that implements one or more functions.

[0056] The invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, claims are attached to disclose the scope of the invention. [Explanation of symbols]

[0057] 102: IAB Donor, 103-107: IAB Node, 201: Control Unit, 202: Memory Unit, 307: UE Connection Count Confirmation Unit, 308: Connection Destination Determination Unit, 309: Connection Destination Notification Unit

Claims

1. A wireless communication system using Integrated Access and Backhaul (IAB) technology as defined by the Third Generation Partnership Project (3GPP), wherein the IAB donor of the wireless communication system includes at least one IAB node that relays communication between a core network and a terminal, and an IAB donor that relays communication between the IAB node and the core network, A means for identifying the number of terminals connected to the IAB nodes under the IAB donor, based at least on communication with the subordinate IAB nodes, A determination means for determining whether to change the communication path, based at least on the number of terminals connected on a first communication path including the IAB donor, a first IAB node under the IAB donor, and a second IAB node under the first IAB node, If the determination means determines that the communication path should be changed, the setting means changes the connection destination of the second IAB node to a third IAB node that constitutes a different communication path from the first communication path, and sets up a second communication path for relaying communication between the second IAB node and the terminals under the second IAB node and the IAB donor via the third IAB node. It has, An IAB donor characterized in that a maximum number of terminals is set for each IAB node under the IAB donor, and the determination means determines to change the communication path when the total number of terminals connected to the first IAB node and the number of terminals connected to one or more IAB nodes downstream of the first IAB node in the first communication path exceeds the maximum number of terminals set for the first IAB node.

2. The determination means further determines the changed connection destination, The IAB donor according to claim 1, characterized in that, before the second IAB node connects to the third IAB node, the determination means determines to connect the second IAB node to the third IAB node if, in each of the one or more IAB nodes, including the third IAB node, included in the second communication path that would be formed when the second IAB node is connected to the third IAB node, the total number of terminals connected to the IAB node and the total number of terminals connected to other IAB nodes connected downstream of the IAB node does not exceed the allowable capacity set for the IAB node.

3. The IAB donor according to claim 1, characterized in that the determination means determines whether the number of IAB nodes included in the second communication path exceeds the allowable capacity after the second communication path has been set by the setting means, and does not perform the determination before the second communication path has been set.

4. The IAB donor according to any one of claims 1 to 3, characterized in that the number of permissible devices is set based on the number of hops from the IAB donor to the IAB node in the communication path.

5. The determination means further determines the changed connection destination, The IAB donor according to claim 4, characterized in that the determination means determines that if the total number of terminals connected to the second IAB node and the total number of terminals connected to IAB nodes downstream of the second IAB node in the first communication path exceeds the allowable number of terminals set for the second IAB node, it selects an IAB node that constitutes a different communication path from the first communication path, such that the number of hops for the second IAB node decreases, as the third IAB node, and determines that the second IAB node should be connected directly below the selected third IAB node.

6. The IAB donor according to any one of claims 1 to 3, characterized in that the permitted capacity is set based on the number of IAB nodes connected downstream from the IAB donor.

7. The determination means further determines the changed connection destination, The IAB donor according to any one of claims 1 to 6, further comprising notification means for notifying terminals connected to the first IAB node or the second IAB node that more terminals than the allowable number are connected, if the determination means determines that there are no IAB donors or IAB nodes to be used as the new connection destination such that the total number of IAB nodes in any of the IAB nodes included in the second communication path does not exceed the allowable number of terminals set for that IAB node.

8. The determination means further determines the changed connection destination, The IAB donor according to claim 1, characterized in that, when a permissible number of devices is set for each communication path, and the total number of terminals connected to the relay device included in the first communication path exceeds the permissible number of devices, the determination means determines to change the first communication path by changing the connection destination of the second IAB node to a third IAB node on a second communication path different from the first communication path.

9. A wireless communication system using Integrated Access and Backhaul (IAB) technology as defined by the Third Generation Partnership Project (3GPP), comprising at least one IAB node that relays communication between a core network and a terminal, and an IAB donor that relays communication between the IAB node and the core network, wherein the IAB donor of the wireless communication system is controlled by a control method for controlling the IAB donor, A process of identifying the number of terminals connected to the IAB nodes under the IAB donor, based at least on communication with the subordinate IAB nodes, A determination step of determining whether to change the communication path based at least on the number of UEs (User Equipment) connected on a first communication path that includes the IAB donor, a first IAB node under the IAB donor, and a second IAB node under the first IAB node. If it is determined that the communication path should be changed, the connection destination of the second IAB node is changed to a third IAB node that constitutes a different communication path from the first communication path, and a setting step is performed to set up a second communication path for relaying communication between the second IAB node and the terminals under the second IAB node and the IAB donor via the third IAB node. Includes, A control method characterized in that a maximum number of terminals is set for each IAB node under the IAB donor, and if the total number of terminals connected to the first IAB node and the total number of terminals connected to one or more IAB nodes downstream of the first IAB node in the first communication path exceeds the maximum number of terminals set for the first IAB node, the determination step determines that the communication path should be changed.

10. A program for causing a computer to function as an IAB donor according to any one of claims 1 to 8.

11. A control device for a wireless communication system that includes a relay device for relaying communications between a base station and a terminal, A means for identifying the number of terminals connected to the relay devices under the control device, based at least on communication with the relay devices under the control device, A determination means for determining whether to change the communication path, based at least on the number of terminals connected on a first communication path including the base station, a first relay device under the base station, and a second relay device under the first relay device, If the determination means determines that the communication path should be changed, the change means changes the connection destination of the second relay device to a third IAB node that constitutes a different communication path from the first communication path. It has, A control device characterized in that a maximum number of terminals that can be accommodated is set for each relay device under the control device, and the determination means determines to change the communication path when the total number of terminals connected to the first relay device and the total number of terminals connected to one or more relay devices downstream of the first relay device in the first communication path exceeds the maximum number of terminals that can be accommodated set for the first relay device.

12. The control device according to claim 11, characterized in that the control device is located within the core network to which the base station is connected via a backhaul line.

13. The control device according to claim 11 or 12, characterized in that the base station is an IAB donor using IAB (Integrated Access and Backhaul) technology as defined by the Third Generation Partnership Project (3GPP).

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