Communication device, mobile communication system, control method, and program

Abstract

To perform efficient communication using backup IAB nodes.SOLUTION: A communication device that operates as an IAB donor that communicates with a first IAB node in a mobile communication system includes detection means for detecting a second IAB node different from the first IAB node, and transmitting means for transmitting a handover request for user equipment connected to the first IAB node to hand over to the second IAB node in response to the detection of the second IAB node by the detection means.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to load distribution processing of communication in a mobile communication system.

Background Art

[0002] In 3GPP (Registered Trademark) (3rd Generation Partnership Project), the standardization of IAB (Integrated Access and Backhaul) as a communication technology for backhaul is in progress. IAB is a technology that simultaneously uses access communication between a base station and a user equipment (UE: User Equipment) as backhaul communication (Patent Document 1). For IAB, for example, millimeter-wave wireless communication such as the 28 GHz band is used.

[0003] In backhaul communication using the IAB technology, a relay device called an IAB node relays communication from a base station called an IAB donor by millimeter-wave communication. By using IAB, it is possible to expand the area coverage at a lower cost compared to conventional wired communication using optical fibers or the like.

[0004] Also, in a communication system, a technique has been proposed in which when a UE monitors the radio link status and a problem occurs, it notifies the base station of a failure, and the base station that receives the notification makes a handover request to the UE as necessary (Patent Document 2).

[0005] When using IAB, in backhaul communication, the UE periodically notifies the base station of surrounding environment information (such as radio wave intensity information between IAB nodes existing in the vicinity). The base station that receives the surrounding environment information from the UE makes a handover request to other IAB nodes for the user equipment as necessary.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] Incidentally, in situations where a large number of UEs are concentrated (such as events in stadiums, large-scale offline events, or disaster sites), the surrounding IAB nodes to which these UEs are connected may become overloaded. Also, if relay stations become non-functional due to a disaster, the remaining relay stations may become relatively overloaded.

[0008] In such cases, to reduce the load on the IAB node, an IAB node that can be mounted on a vehicle or similar vehicle and used as a temporary relay station (hereinafter referred to as a "backup IAB node") may be installed. In this case, it is necessary to properly balance the load between the heavily loaded IAB node and the backup IAB node.

[0009] However, with conventional handover technology, a handover is basically only performed when the UE's connection to the currently connected IAB node is disconnected, or when the base station determines it is necessary based on the surrounding environment information collected from the UE. Under the aforementioned circumstances, since the signal strength between the UE and the IAB node is not reduced, a disconnection is not detected. In addition, congestion can cause a significant delay in the notification of surrounding environment information from the UE to the base station. Therefore, there has been a challenge in that it is difficult to perform rapid load balancing using backup IAB nodes.

[0010] This invention has been made in view of these problems and aims to provide a technology that enables more efficient communication. [Means for solving the problem]

[0011] To solve the above-mentioned problems, the communication device according to the present invention has the following configuration. That is, the communication device that operates as an IAB donor communicating with a first IAB (Integrated Access and Backhaul) node in a mobile communication system is A detection means for detecting a second IAB node different from the first IAB node, In response to the detection of the second IAB node by the detection means, a transmission means transmits a handover request for a user device connected to the first IAB node to hand over to the second IAB node. Equipped with 、 The detection means detects the second IAB node by receiving notification information indicating the presence of the second IAB node, The notification information includes first information indicating that the second IAB node is an IAB node installed as a backup node for the first IAB node. . [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a technology that enables more efficient communication. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram showing the hardware configuration of a communication device. [Figure 2] This is a block diagram showing the functional configuration of a communication device. [Figure 3A] This diagram shows the system configuration before load balancing. [Figure 3B] This diagram shows the system configuration after load balancing. [Figure 4] This diagram shows a typical handover sequence. [Figure 5] This figure shows the handover sequence in the first embodiment. [Figure 6A] This shows a general flowchart of the operations of an IAB donor related to the reception of notification information. [Figure 6B] This shows a general flowchart of the operations performed by an IAB donor regarding the reception of surrounding environment information notifications. [Figure 7]It is an operation flowchart of an IAB donor in the first embodiment. [Figure 8] It is a diagram showing a handover sequence in the second embodiment. [Figure 9] It is an operation flowchart of an IAB donor in the second embodiment. [Figure 10] It is an operation flowchart of a UE in the second embodiment. [Figure 11] It is a diagram showing a handover sequence in a modification.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations are denoted by the same reference numerals, and duplicate descriptions are omitted.

[0015] (First Embodiment) As a first embodiment of a communication device according to the present invention, a communication device that operates as a base station and an IAB donor in a mobile communication system will be described below as an example. The mobile communication system is, for example, a fifth-generation (5G) mobile communication system. One or more IAB nodes are connected to the IAB donor, and the UE communicates with the IAB donor via an IAB node that is a relay node. The IAB node can be a RAN (Radio Access Network) node that supports both an NR (New Radio) access link and an NR backhaul link.

[0016] <Device Configuration> Figure 1 is a block diagram showing an example of the hardware configuration of a communication device that functions as an IAB donor or IAB node. The communication device 101 includes a control unit 102, a storage unit 103, a wireless communication unit 104, and an antenna control unit 105. The control unit 102 controls the entire device by executing a control program stored in the storage unit 103. The storage unit 103 stores the control program executed by the control unit 102 and various information used for control (cell information, connected terminal information, IAB routing information, etc.). Various operations described later are realized by the control unit 102 executing the control program stored in the storage unit 103. The wireless communication unit 104 performs cellular network communication such as LTE and 5G in accordance with the 3GPP standard. The antenna control unit 105 controls the antenna for wireless communication performed by the wireless communication unit 104.

[0017] Figure 2 is a block diagram showing an example of the software function configuration of a communication device that functions as an IAB donor or IAB node. The communication device function 201 includes a signal transmission unit 202, a signal reception unit 203, a data storage unit 204, a connection control unit 205, a broadcast information detection unit 206, a handover request unit 207, and a broadcast information generation unit 208. The signal transmission unit 202 and the signal reception unit 203 perform cellular network communication such as LTE and 5G in accordance with 3GPP standards with other devices (such as UEs). The data storage unit 204 stores and holds software programs, as well as IAB routing information and information about connected terminals.

[0018] The connection control unit 205 controls the wireless communication performed by the wireless communication unit 104. The detection unit 206 detects broadcast information from nearby IAB nodes. The handover request unit 207 sends a wireless resource control (RRC) message to the UE to request a handover. The broadcast information generation unit 208 broadcasts a signal indicating the presence of its own device (communication device 101, which is an IAB node).

[0019] <System Configuration and General Operation> Figures 3A and 3B illustrate the system configuration, particularly illustrating the state before and after the UE handover associated with the load balancing process described later.

[0020] IAB donor 311 has IAB nodes 301-306 under its control and is configured to establish the communication path shown in route 320 between the donor and the multiple nodes.

[0021] In a large event venue 330, numerous UE400s are densely packed together, forming a UE group 331. The numerous UE400s included in UE group 331 are basically connected to the nearest (best-sounding) IAB node, IAB node 306. As a result, IAB node 306 is under extremely high load. In such cases, as shown in Figure 3B, a backup IAB node (e.g., an in-vehicle IAB node) 307 may be installed to increase communication capacity and distribute the load at the event venue 330.

[0022] In this situation, there is a need to quickly distribute the load from the heavily loaded IAB node 306 to the backup IAB node 307. However, under the current 3GPP standard, a handover is only performed if the connection between each UE and the IAB node is disconnected, or if the UE determines that an IAB donor is necessary based on the surrounding environment information collected from the UE.

[0023] In the latter case, a handover led by the IAB donor, each UE collects surrounding environment information and notifies the IAB donor 311 of this information, which is then analyzed by the IAB donor 311. If the IAB donor 311 determines that it is better to hand over the UE to another IAB node, it notifies the UE of a request to reconfigure the RRC connection (RRC Reconfiguration message). The format of the RRC Reconfiguration message is specified in 3GPP TR 38.331 6.2.2. After this process, the handover of the UE to another IAB node begins.

[0024] Thus, under the current 3GPP standard, even if a backup IAB node is deployed, it is not possible to quickly hand over the UE. In other words, it is necessary to wait for the UE to disconnect or for a decision to be made by the IAB donor. Furthermore, since the IAB donor receives notifications of surrounding environment information from each UE via the IAB node, there is a high possibility that notifications of surrounding environment information from each UE will be delayed if the IAB node being used is under heavy load.

[0025] Therefore, in this embodiment, we will describe a configuration in which the IAB donor hands over the UE from the high-load IAB node to the backup IAB node regardless of whether or not it has received notification of surrounding environment information from the UE (without waiting for the reception to be completed). In particular, we will describe the operation of the system when the backup IAB node 307 is newly installed in the event venue 330 (Figure 3B) in a situation where the UE 400 has established a communication path with the IAB donor 311 via the IAB node 306 (Figure 3A).

[0026] Below, we will first describe the general operation of an IAB donor-led handover according to the 3GPP standard, referring to Figures 4, 6A, and 6B. Next, we will describe the operation of an IAB donor-led handover in the first embodiment, referring to Figures 5 and 7.

[0027] <Typical handover operation according to 3GPP standards> Figure 4 shows a typical sequence of handovers led by an IAB donor. Specifically, it involves determining whether a handover of the UE is necessary based on the surrounding environment information notified by the UE, and then proceeding to hand over to the UE if necessary.

[0028] In S401, UE400 sends surrounding environment information to IAB node 306 in order to notify IAB donor 311 of its surrounding environment information. Surrounding environment information includes, for example, RSSI information between IAB nodes present around the UE. In S402, IAB node 306 sends (forwards) the received surrounding environment information to IAB donor 311.

[0029] In S403, IAB donor 311, based on the surrounding environment information notified by UE400, sends a handover notification to IAB node 306 in order to notify the originating UE400 of the handover notification if necessary. This notification uses the RRC Reconfiguration message defined in the 3GPP standard. In S404, IAB node 306 sends (forwards) the received handover notification to UE400.

[0030] In S405, upon receiving a handover notification, UE400 performs synchronization establishment and RACH (Random Access Channel) processing with IAB node 307 and connects to IAB node 307. Synchronization establishment and RACH processing are defined in the 3GPP standard and are performed when the UE makes its initial connection to the IAB node. Specifically, this process involves synchronization between the UE and the IAB node, as well as frequency determination processing for RACH (Random Access Channel), to establish link synchronization between the UE and the IAB node.

[0031] In S406, UE400 sends a handover completion notification to IAB node 306 in order to notify IAB donor 311 that the handover is complete. This notification uses the RRC Reconfiguration Complete message as defined in the 3GPP standard. In S407, IAB node 306 sends (forwards) the received handover completion notification to IAB donor 311.

[0032] Figure 6A shows a typical operation flowchart for an IAB donor related to the reception of broadcast information. Figure 6B shows a typical operation flowchart for an IAB donor related to the reception of ambient environment information notifications. These waiting processes are not sequential; processing is carried out sequentially according to the received content. Typically, an IAB donor waits to detect broadcast information from IAB nodes connecting to its network and to receive ambient environment information notified by UEs under the network (F600).

[0033] In F601, the IAB donor determines whether or not it has detected broadcast information from the IAB node. If it has detected information, it proceeds to F602; otherwise, it returns to F600.

[0034] In F602, the IAB donor performs integration processing into its own network, such as reconstructing path information, to make the IAB node that transmitted the detected broadcast information available on its own network. After that, it returns to F600, but if there is an instruction to end the reception waiting period, for example, the process will terminate.

[0035] In F603, the IAB donor determines whether or not it has received a notification of surrounding environment information from the UE (via the IAB node). If it has received it, it proceeds to F604; otherwise, it returns to F600.

[0036] In F604, the IAB donor checks the contents of the surrounding environment information notification and determines whether a handover is required for the UE that sent the notification. If a handover is required, the process proceeds to F605; otherwise, it returns to F600.

[0037] In F605, the IAB donor sends a handover notification to the UE (via the IAB node).

[0038] <Handover operation in the first embodiment> Figure 5 shows the handover sequence led by the IAB donor in the first embodiment. In this sequence, IAB node 308 is defined as the high-load IAB node (corresponding to IAB node 306), and IAB node 309 is defined as the backup IAB node (corresponding to IAB node 307).

[0039] UE400 has established a communication path with IAB donor 311 via IAB node 308. IAB node 309 will be newly installed to distribute the load on IAB node 308.

[0040] In S501, IAB node 309 transmits notification information via a beacon or a dedicated message to announce its presence. At this time, the notification information may include "I am an IAB node installed as a backup" or "I am an IAB node installed as a backup for IAB node 308".

[0041] Broadcast information is broadcast in accordance with the 3GPP standard (section 9.3.1 of 3GPP TS 38.413), specifically according to the broadcast information format defined in RadioNetworkLayer. This format is capable of broadcasting up to 256 types of information, and the aforementioned broadcast information is added to the reserved or free areas in the current standard to perform the broadcast.

[0042] In S502, IAB donor 311, upon detecting broadcast information from IAB node 309, performs an IAB node check. This check determines whether the detected IAB node is available as a backup IAB node for IAB node 308.

[0043] For example, the location information of IAB node 308 and IAB node 309 can be used to determine whether the two IAB nodes are located in a position where they can be used as backup IAB nodes based on their relative positions. Alternatively, it may be determined whether the broadcast information includes information such as "I am an IAB node installed as a backup" or "I am an IAB node installed as a backup for IAB node 308".

[0044] In S503, the IAB donor 311 performs a determination process to select one or more UEs to be handed over. In other words, it is a process to select one or more UEs from among those connected to the high-load IAB node to be handed over to the backup IAB node. This determination process is performed if the aforementioned judgment process determines that it is acceptable to load balance the UEs connected to the high-load IAB node to the backup IAB node.

[0045] For example, the number of UEs connected to a high-load IAB node (e.g., whether it exceeds a separately defined threshold) or weighting based on the bandwidth usage of the UEs targeted for handover can be used to determine which UEs will be handovered, thereby effectively distributing the load and selecting one or more UEs to be handovered. For example, the number of UEs exceeding the threshold can be randomly selected and designated as handover targets. Alternatively, one or more UEs may be selected based on the bandwidth usage of each UE (the load ratio for each UE on the high-load IAB node), for example, in descending order of bandwidth usage.

[0046] In S504, IAB donor 311 sends a handover notification to IAB node 308 to notify the UE configured for handover. This notification uses the RRC Reconfiguration message defined in the 3GPP standard. Specifically, it uses a dedicatedSIB1-Delivery message in the defined format and specifies the ID of the IAB node 309 to which the reconnection will take place. Alternatively, a new definition specifically for this notification may be added to the RRC Reconfiguration message field. In S505, IAB node 308 sends (forwards) the received handover notification to UE 400.

[0047] Upon receiving the handover notification, UE400 performs a handover to the designated IAB node 309. Subsequent processing (S506-S508) is the same as a typical handover operation according to the 3GPP standard (S405-S407).

[0048] Figure 7 shows the operation flowchart of the IAB donor in the first embodiment. Here, the IAB donor is waiting to receive notification information from IAB nodes connected to its network.

[0049] In F701, the IAB donor detects broadcast information from the IAB node. The following explanation assumes that broadcast information has been detected.

[0050] In F702, the IAB donor performs the process of integrating the IAB node that transmitted the detected notification information into its own network (this process is the same as in F602).

[0051] In F703, the IAB donor performs a load check to determine if there are any IAB nodes on the network (among one or more IAB nodes under the IAB donor) that are experiencing a high load. If it determines that such nodes exist, it proceeds to F704; otherwise, it terminates.

[0052] As a criterion for determination, for example, thresholds for processing load and traffic congestion rate are used to detect IAB nodes that frequently experience high load conditions or congestion as high-load IAB nodes.

[0053] In F704, the IAB donor determines whether the IAB node that transmitted the notification information detected in F701 is available as a backup IAB node for a high-load IAB node. If it is determined to be available as a backup IAB node, the process proceeds to F705; otherwise, the process terminates.

[0054] For example, the location information of the high-load IAB node and the location information of the detected IAB node can be used to determine whether the two IAB nodes are located in a position where they can be used as backup IAB nodes based on their relative positions. Alternatively, it may be determined whether the broadcast information detected by F701 contains information such as "this IAB node was installed as a backup" or "this IAB node was installed as a backup for a specific high-load IAB node."

[0055] In F705, the IAB donor performs the process of determining which UEs will be subject to handover. In other words, it determines which UEs connected to a high-load IAB node will be subject to handover.

[0056] This determination process is performed to ensure that UEs connected to a high-load IAB node are properly handed over to a backup IAB node. For example, the determination is made using factors such as "the number of UEs connected to the high-load IAB node (e.g., whether it exceeds a separately defined threshold)" or "weighting based on the amount of bandwidth used by the UEs to be handed over," and one or more UEs that can effectively distribute the load are set as targets for handover.

[0057] In F706, the IAB donor sends a handover notification to one or more UEs determined in F705. This notification uses the RRC Reconfiguration message defined in the 3GPP standard. Specifically, it uses a dedicatedSIB1-Delivery message in the defined format, specifying the ID of the backup IAB node to which the reconnection will take place. Alternatively, a new definition specifically for this notification may be added to the RRC Reconfiguration message field.

[0058] Note that the order of F701 to F706 is not limited to that described above. For example, the processing order of F703 and F704 may be changed. Also, if the notification information detected in F701 includes information that "this IAB node was installed as a backup for a specific high-load IAB node," then that IAB node may be considered to have been installed intentionally. In other words, it may be considered to have been installed as a backup IAB node not limited to load balancing for a high-load IAB node. In this case, even if a high-load IAB node could not be detected on the network in F703, a handover notification (F705, F706) may be sent to the UE.

[0059] As described above, according to the first embodiment, when a new IAB node is detected and predetermined conditions are met, an IAB donor-led handover is performed. Here, the predetermined conditions are that one or more existing IAB nodes are under heavy load, and the new IAB node is available as a backup for the heavy-load IAB node. In other words, one or more UEs are handed over from the heavy-load IAB node to the backup IAB node without waiting for UE disconnection detection or notification of surrounding environment information from the UE.

[0060] This control system enables rapid handover of UEs when a new IAB node is installed in a situation where many UEs are densely clustered, allowing for effective communication load balancing.

[0061] (Second Embodiment) In the second embodiment, in addition to the operation in the first embodiment, a configuration is described in which a UE that receives a handover notification from the IAB donor checks whether a handover is possible. This configuration is intended, for example, when it is desired to limit the UEs that can connect to the backup IAB node to those used by event participants. Note that the device configuration, system configuration, and the operation of the IAB donor and IAB node are the same as in the first embodiment (Figures 1 to 3B, 5, and 7), so a description is omitted.

[0062] <Handover operation in the second embodiment> Figure 8 shows the handover sequence led by the IAB donor in the second embodiment. In this sequence, as in the first embodiment, IAB node 308 is defined as the high-load IAB node (corresponding to IAB node 306), and IAB node 309 is defined as the backup IAB node (corresponding to IAB node 307).

[0063] UE400 establishes a communication path with IAB donor 311 via IAB node 308. IAB node 309 is newly installed to distribute the load on IAB node 308. The processing in S801-S803 is the same as in the first embodiment (S501-S503), so the explanation is omitted.

[0064] In S804, IAB donor 311 sends a handover notification to IAB node 308 in order to notify UE400, which has been set as the handover target, of the handover. In S805, IAB node 308 sends (forwards) the received handover notification to UE400.

[0065] This notification uses the RRC Reconfiguration message defined in the 3GPP standard. Specifically, it uses a dedicatedSIB1-Delivery message in the defined format, specifying the ID of the IAB node 309 to which the reconnection will take place. Alternatively, a new definition specifically for this notification may be added to the RRC Reconfiguration message field. For example, information indicating "handover to backup node" can be added as part of the new definition. By adding this information, the UE receiving the handover notification will know that this handover is to a backup IAB node.

[0066] In S806, upon receiving a handover notification, UE400 checks whether a handover to the designated backup IAB node (in this case, IAB node 309) is possible.

[0067] If S806 determines that a handover is not possible (check failed), then in S807 and S808, UE400 will notify IAB donor 311 of the handover failure via IAB node 308. There are several ways to notify the IAB donor of this message; for example, one method is to include the handover failure information within the RRC Reconfiguration Complete message. Alternatively, it is possible to create a new RRC message specifically for this message.

[0068] If S806 determines that a handover is possible (check OK), UE400 performs a handover to the designated IAB node 309. The process in this case (S809-S811) is the same as the general handover operation according to the 3GPP standard (S405-S407).

[0069] Figure 9 shows the operation flowchart of the IAB donor in the second embodiment. Note that the processes other than F906 are the same as in the first embodiment (F701 to F705), so their explanation is omitted.

[0070] In F906, the IAB donor sends a handover notification to one or more UEs determined in F905. This notification uses the RRC Reconfiguration message defined in the 3GPP standard. Here, a new definition will be added to the RRC Reconfiguration message field to indicate that it is a "handover to a backup node".

[0071] Note that the order of F901 to F906 is not limited to the one described above. For example, the processing order of F903 and F904 can be changed.

[0072] Figure 10 shows the operation flowchart of the UE in the second embodiment. This flowchart is written assuming that the UE has received a handover notification.

[0073] In F1001, the UE receives a handover notification from the IAB donor.

[0074] In F1002, the UE determines whether the handover notification contains information indicating a "handover to a backup node." If it does, it proceeds to F1003; otherwise, it proceeds to F1004. Note that if the IAB donor has sent a typical handover notification (according to the 3GPP standard) as shown in Figure 6B, the notification will not contain information indicating a "handover to a backup node."

[0075] In F1003, the UE assumes that the received handover notification is a handover notification to a backup IAB node. It then determines whether a handover to the specified backup IAB node is possible. If a handover is possible, it proceeds to F1004; if a handover is not possible, it proceeds to F1005.

[0076] One possible method for making this determination is to check whether the UE has previously passed a specific authentication (such as MAC address authentication or 802.1X authentication). For example, the UE could be configured to access an authentication site provided by the service provider in advance, and if authentication is successful, information indicating that authentication was successful could be saved in the system information. In this case, if the service provider has prepared a backup IAB node, the information including information that identifies the backup IAB node could also be saved. When performing the S806 check, the UE refers to this system information and decides whether a handover is possible based on the current authentication status.

[0077] Another example is a method for checking whether a backup IAB node actually exists within the connection range of the UE being handed over. In other words, conventional IAB donor-led handovers followed the surrounding environment information notification from the UE. That is, it was guaranteed that the surrounding environment information notification from the UE had reached the IAB donor and that a backup IAB node existed within the UE's connection range. However, in the second embodiment, this guarantee is not present, so such a check is envisioned.

[0078] Specific checking methods include, for example, checking whether the specified backup IAB node exists in the IAB node list generated by the UE after scanning the surrounding environment. Alternatively, the UE can scan the surrounding environment when it receives a handover request and check whether the specified backup IAB node exists.

[0079] In F1004, the UE performs the normal (3GPP standard) handover process. On the other hand, in F1005, the UE notifies the IAB donor that handover is not possible. Several methods are possible for notifying the IAB donor of this message. For example, one method is to include the handover failure information in the RRC Reconfiguration Complete message, or to create a new RRC message specifically for this message.

[0080] As explained above, according to the second embodiment, a UE that receives a handover notification checks whether a handover is possible. For example, if it is desired to limit the UEs that can connect to the backup IAB node to those used by event participants, the system checks whether the UE has passed specific authentication in advance to determine whether a handover is possible. Furthermore, even in situations where the presence of a backup IAB node within the UE's connection range cannot be guaranteed, it becomes possible to appropriately control load balancing.

[0081] (modified version) In the first and second embodiments, the process of determining the UE to be handed over was described as being performed by the IAB donor, but it may also be configured so that an existing (high-load) IAB node performs this process.

[0082] <Handover operation in a modified example> Figure 11 shows a handover sequence led by the IAB donor in a modified example. In this sequence, as in the first embodiment, IAB node 308 is defined as the high-load IAB node (corresponding to IAB node 306), and IAB node 309 is defined as the backup IAB node (corresponding to IAB node 307).

[0083] UE400 establishes a communication path with IAB donor 311 via IAB node 308. IAB node 309 is newly installed to distribute the load on IAB node 308. The processing in S1101-S1102 and S1106-S1108 is the same as in the first embodiment (S501-S502 and S506-S508), so the explanation is omitted.

[0084] In S1103, IAB donor 311 sends a handover notification to IAB node 308 to notify it of the request to initiate a UE handover. This notification uses the RRC Reconfiguration message defined in the 3GPP standard. However, at this point, although the request to initiate a handover is included, it does not specify which UE is to be handed over. Therefore, a new definition indicating the request to initiate a handover may be added to the message field.

[0085] In S1104, the IAB node 308 performs a determination process to identify one or more UEs to be handed over. This determination process is the same as the process performed by the IAB donor in the first and second embodiments (S503, S803).

[0086] In S1105, IAB node 308 sends (forwards) the handover notification received in S1103 to one or more UEs determined in S1104.

[0087] In addition, in S1104, the IAB node 308 may use the determination of whether the connected UE has passed a specific authentication. In this case, the IAB node 308 may be configured to obtain information from the IAB donor 311 regarding whether each UE has passed a specific authentication.

[0088] For example, the UE can be configured to access the authentication site provided by the service provider in advance, and if authentication is successful, it will save information indicating that authentication was successful in the system information. The UE will then include this information in the notification process for the IAB donor. At this time, if the service provider has prepared a backup IAB node, the information that identifies the backup IAB node may also be saved. For example, a new area for this information can be created within the MeasurementReport-IEs field in the MeasurementReport message, and the notification can be made from there.

[0089] This allows IAB donors to identify event participant UEs based on surrounding environment information acquired before congestion. As a result, handover notifications to non-event participant UEs can be suppressed, reducing the overall number of messages in the system.

[0090] The disclosures herein include the following communication devices and programs, as well as mobile communication systems and control methods. (Item 1) A communication device that operates as an IAB donor communicating with a first IAB (Integrated Access and Backhaul) node in a mobile communication system, A detection means for detecting a second IAB node different from the first IAB node, In response to the detection of the second IAB node by the detection means, a transmission means transmits a handover request for a user device connected to the first IAB node to hand over to the second IAB node. A communication device characterized by comprising: (Item 2) The system further includes a determination means for determining whether the second IAB node is available for load balancing of the first IAB node. The communication device according to item 1, characterized in that the transmission means transmits the handover request when the determination means determines that the second IAB node is available for load balancing of the first IAB node. (Item 3) The system further includes load determination means for determining whether the first IAB node is under load above a predetermined threshold, The determination means determines whether the second IAB node is available for load balancing of the first IAB node, which has been determined by the load determination means to be under high load. A communication device as described in item 2, characterized by the features described herein. (Item 4) The aforementioned mobile communication system is a fifth-generation (5G) mobile communication system. The first and second IAB nodes support both backhaul links and access links. A communication device as described in any one of items 1 to 3, characterized by the above. (Item 5) The transmitting means transmits the handover request using a Radio Resource Control (RRC) message. A communication device as described in any one of items 1 to 4, characterized by the above. (Item 6) The transmission means transmits the handover request regardless of whether it has received notification of surrounding environment information from the user device connected to the first IAB node. A communication device as described in any one of items 1 to 5, characterized by the above. (Item 7) The detection means detects the second IAB node by receiving notification information indicating the presence of the second IAB node, The notification information includes first information indicating that the second IAB node is an IAB node installed as a backup node for the first IAB node. A communication device as described in any one of items 1 to 6, characterized by the above. (Item 8) If the notification information includes the first information, the transmission means includes in the handover request information indicating that it is a handover to a backup node. A communication device as described in item 7, characterized by the features described herein. (Item 9) The determination means determines, based on the location information of the first IAB node and the location information of the second IAB node, whether or not the second IAB node is available for load balancing of the first IAB node. A communication device as described in item 2, characterized by the features described herein. (Item 10) The detection means detects the second IAB node by receiving notification information indicating the presence of the second IAB node, The determination means determines whether the second IAB node is available for load balancing of the first IAB node, based on whether the notification information includes first information indicating that the second IAB node is an IAB node installed as a backup for the first IAB node. A communication device as described in item 2, characterized by the features described herein. (Item 11) The system further comprises a determination means for determining one or more user devices to be subject to handover in the aforementioned handover request, The transmission means transmits the handover request to the one or more user devices determined by the determination means. A communication device characterized by any one of items 1 to 10. (Item 12) The determination means, if the number of user devices connected to the first IAB node exceeds a threshold, determines that the number of user devices exceeding the threshold will be one or more user devices subject to handover. A communication device as described in item 11, characterized by the features described herein. (Item 13) The determination means determines one or more user devices to be subject to handover based on information on the amount of bandwidth used by each user device connected to the first IAB node. A communication device as described in item 11, characterized by the features described herein. (Item 14) The determination means determines one or more user devices to be subject to handover based on the authentication status of each user device connected to the first IAB node at a predetermined authentication site. A communication device as described in item 11, characterized by the features described herein. (Item 15) A program for operating a computer with a communications unit as a communications device as described in any one of items 1 through 14.

[0091] (Other examples) 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.

[0092] 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]

[0093] 101 Communication device; 102 Control unit; 103 Storage unit; 104 Wireless communication unit; 105 Antenna control unit; 201 Communication device function; 202 Signal transmission unit; 203 Signal reception unit; 204 Data storage unit; 205 Connection control unit; 206 Notification information detection unit; 207 Handover request unit; 208 Notification information generation unit

Claims

1. A communication device that operates as an IAB donor communicating with a first IAB (Integrated Access and Backhaul) node in a mobile communication system, A detection means for detecting a second IAB node different from the first IAB node, In response to the detection of the second IAB node by the detection means, a transmission means transmits a handover request for a user device connected to the first IAB node to hand over to the second IAB node. Equipped with, The detection means detects the second IAB node by receiving notification information indicating the presence of the second IAB node. The notification information includes first information indicating that the second IAB node is an IAB node installed as a backup node for the first IAB node. A communication device characterized by the following features.

2. The system further includes a determination means for determining whether the second IAB node is available for load balancing of the first IAB node. The communication device according to claim 1, wherein the transmission means transmits the handover request when the determination means determines that the second IAB node is available for load balancing of the first IAB node.

3. The system further includes load determination means for determining whether the first IAB node is under load above a predetermined threshold, The determination means determines whether the second IAB node is available for load balancing of the first IAB node, which has been determined by the load determination means to be under high load. The communication device according to feature 2.

4. The aforementioned mobile communication system is a fifth-generation (5G) mobile communication system. The first IAB node and the second IAB node support both backhaul links and access links. The communication device according to feature 1.

5. The transmitting means transmits the handover request using a Radio Resource Control (RRC) message. The communication device according to feature 1.

6. The transmission means transmits the handover request regardless of whether it has received notification of surrounding environment information from the user device connected to the first IAB node. The communication device according to feature 1.

7. If the notification information includes the first information, the transmission means includes in the handover request information indicating that it is a handover to a backup node. The communication device according to feature 1.

8. The determination means determines, based on the location information of the first IAB node and the location information of the second IAB node, whether or not the second IAB node is available for load balancing of the first IAB node. The communication device according to feature 2.

9. The determination means determines whether the second IAB node is available for load balancing of the first IAB node based on whether the notification information includes the first information. The communication device according to feature 2.

10. The system further comprises a determination means for determining one or more user devices to be subject to handover in the aforementioned handover request, The transmission means transmits the handover request to the one or more user devices determined by the determination means. The communication device according to feature 1.

11. The determination means, if the number of user devices connected to the first IAB node exceeds a threshold, determines that the number of user devices exceeding the threshold will be one or more user devices subject to handover. The communication device according to feature 10.

12. The determination means determines one or more user devices to be subject to handover based on information regarding the amount of bandwidth used by each user device connected to the first IAB node. The communication device according to feature 10.

13. The determination means determines one or more user devices to be subject to handover based on the authentication status of each user device connected to the first IAB node at a predetermined authentication site. The communication device according to feature 10.

14. A mobile communication system comprising a base station, a first relay node, and user equipment that communicates with the base station via the first relay node, The aforementioned base station is A detection means for detecting a second relay node different from the first relay node, In response to the detection of the second relay node by the detection means, a transmission means transmits a handover request for a user device connected to the first relay node to hand over to the second relay node. Equipped with, The aforementioned user equipment is Receiving means for receiving the handover request from the base station, A second determination means for determining whether a handover to the second relay node indicated by the handover request is possible, If the second determination means determines that a handover to the second relay node is impossible, a notification means notifies the base station of that fact, Equipped with, The detection means detects the second relay node by receiving notification information indicating the presence of the second relay node, The notification information includes first information indicating that the second relay node is a relay node installed as a backup node for the first relay node. A mobile communication system characterized by the following features.

15. A mobile communication system comprising a base station, a first relay node, and user equipment that communicates with the base station via the first relay node, The aforementioned base station is A detection means for detecting a second relay node different from the first relay node, In response to the detection of the second relay node by the detection means, a first transmission means transmits a first handover request to the first relay node for a user device connected to the first relay node to hand over to the second relay node. Equipped with, The first relay node is, Receiving means for receiving the first handover request from the base station, A determination means for determining one or more user devices to be subject to handover based on the first handover request, A second transmission means that transmits a second handover request instructing the one or more user devices determined by the determination means to hand over to the second relay node, Equipped with, The detection means detects the second relay node by receiving notification information indicating the presence of the second relay node, The notification information includes first information indicating that the second relay node is a relay node installed as a backup node for the first relay node. A mobile communication system characterized by the following features.

16. A method for controlling a communication device that operates as an IAB donor communicating with a first IAB node in a mobile communication system, A detection step for detecting a second IAB node that is different from the first IAB node, In response to the detection of the second IAB node by the detection step, a transmission step is performed in which a user device connected to the first IAB node transmits a handover request to the second IAB node. Includes, In the detection step, the second IAB node is detected by receiving notification information indicating the presence of the second IAB node. The notification information includes first information indicating that the second IAB node is an IAB node installed as a backup node for the first IAB node. A control method characterized by the following:

17. A program for operating a computer having a communication unit as a communication device according to any one of claims 1 to 13.

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