Relay device, communication device, control method, and storage medium for performing switching processing of a relay device

Abstract

A relay device that relays communication between a base station device and a communication device connected to the base station device. The relay device performs control when switching itself to another base station device so that the signal for switching the communication device is retained during the period when the switching of the relay device is unsuccessful. The signal is sent / received between the communication device and the base station device.

Description

Technical Field

[0001] The present invention relates to a switching technology of a relay device that relays communication between a base station device and a terminal device. Background Art

[0002] In the 3rd Generation Partnership Project (3GPP), a technology for applying a method for enabling a terminal device to access a network to a backhaul link and making the method useful has been explored (see non-patent document 1). The technology is called "Integrated Access and Backhaul (IAB)". For example, a relay device called an "IAB node" establishes a connection with a 5G base station device (IAB donor) using a wireless link. At this time, the IAB node can be directly connected to the IAB donor node by establishing a wireless link, or the IAB node can be indirectly connected to the IAB donor node by establishing a wireless link with another IAB node that is directly or indirectly connected to the IAB donor node. At this time, the IAB node serves as a terminal device connected to the base station device, thereby establishing a wireless connection with the above-mentioned other devices (upstream devices) on the IAB donor node side. In addition, after the connection with the IAB donor node has been established, the IAB node can establish a connection with another IAB node or a terminal device to be connected to the IAB donor node. In this case, the IAB node operates in a manner similar to a base station device and establishes a wireless connection with a terminal device or another IAB node (downstream device) operating as a terminal device. In this way, the IAB node has a terminal function (MT, mobile terminal) and a function for performing operations similar to those of a base station device (DU, distributed unit), and can relay communications between upstream devices and downstream devices using these functions.

[0003] Prior art literature

[0004] Non-patent literature

[0005] Non-patent document 1: 3GPP, TR38.874, V16.0.0, December 2018

[0006] Non-patent document 2: 3GPP, RP-193251, December 2019 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In 3GPP Release 17, it has been proposed to start considering a topology change technology that is accompanied by the switching of an IAB host node (i.e., the connection destination of the IAB node) (Non-Patent Document 2). With this technology, when an IAB node installed in a movable object (such as a train or bus) moves, the communication of the IAB host node itself and the communication of another device connected to the IAB host node can be maintained.

[0009] Means used to solve problems

[0010] The present invention provides a technique for making the processing performed when an IAB node switches its connection destination (ie, IAB host node) more efficient.

[0011] A relay device according to one aspect of the present invention relays communication between a base station device and a communication device connected to the base station device, wherein the relay device has: a control unit that performs control when the relay device switches to another base station device so that the signal for switching the communication device is retained for sending / receiving between the communication device and the base station device during the period when the switching of the relay device is unsuccessful.

[0012] According to another aspect of the present invention, a communication device is connected to a base station device via a relay device, wherein the communication device comprises: a sending unit which, in a case where the relay device switches to another base station device, sends a second signal for switching the communication device to the relay device after receiving a first signal related to the switching of the communication device; and a retaining unit which retains the sending of the second signal until information is received from the relay device indicating that a condition for releasing the reservation of the sending / receiving of the signal for switching the communication device is satisfied.

[0013] Effects of the Invention

[0014] According to the present invention, it is possible to improve the efficiency of the process performed when an IAB node switches its connection destination (ie, IAB host node).

[0015] Other features and advantages of the present invention will be apparent from the following description made in conjunction with the accompanying drawings.In addition, in the accompanying drawings, the same reference numerals represent the same or similar structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0017] Figure 1 is a diagram showing an example configuration of a wireless communication system.

[0018] Figure 2 is a diagram showing an example hardware configuration of an IAB node and a communication device connected downstream of the IAB node.

[0019] Figure 3 is a diagram showing an example functional configuration of an IAB node.

[0020] Figure 4 FIG. 1 is a diagram showing an example functional configuration of a communication device connected downstream of an IAB node.

[0021] Figure 5 is a diagram showing an example of a process flow performed by a wireless communication system. DETAILED DESCRIPTION

[0022] The embodiments will be described in detail below with reference to the accompanying drawings. In addition, the following embodiments are not intended to limit the inventions involved in the claims, and do not limit the inventions that require the combination of all the features described in the embodiments. Two or more of the multiple features described in the embodiments may be appropriately combined. In addition, the same reference numerals are given to the same or similar structures, and their repeated descriptions are omitted.

[0023] (System Configuration)

[0024] Figure 1 : represents an example configuration of a wireless communication system according to the present embodiment. The wireless communication system according to the present embodiment is a relay transmission system based on the integrated access and backhaul (IAB) specified in 3GPP, and is composed of an IAB host node 101 and an IAB node 111. The IAB node 111 is a relay device that relays communication between the IAB host node 101 and the terminal device 121 or between the terminal device 122. That is, the terminal device 121 or the terminal device 122 is connected to the IAB host node 101 via the IAB node 111. In addition, it can be interpreted that the IAB host node is used as a base station device and the IAB node is used as a relay device. In the present embodiment, due to the movement of the IAB node 111, the decrease in the communication quality with the IAB host node 101 connected to the IAB node 111, etc., the connection with the IAB host node 101 is switched to the connection with another IAB host node (i.e., the IAB host node 102) (switching is performed).

[0025] The terminal device 121 and the terminal device 122 are connected to the IAB host node 101 via the IAB node 111. Therefore, according to the switching of the IAB node 111 to the IAB host node 102, the terminal device 121 and the terminal device 122 also need to change the processing of the connection destination. Therefore, the IAB host node 101 generates a control signal for the switching of the IAB node 111 and a control signal for the switching of the communication device (terminal device or other IAB node) connected to the downstream of the IAB node 111, respectively, and sends the generated control signal to the IAB host node 102 as the switching destination. In addition, for example, the control signal for the switching of each of the terminal devices (IAB node 111, terminal device 121 and terminal device 122) may include identification information (ID) and name of the terminal device and information on the connection parameters used by the device. In addition, the control signal corresponds to a handover request (HANDOVER REQUEST) message, which is sent from the base station device as the handover source to the base station device as the handover destination. In addition, after sending the control signal, the IAB host node 101 may delete information about the IAB node 111 and the communication device (terminal device or other IAB node) connected downstream of the IAB node 111 .

[0026] In addition, the above-mentioned identification information (ID) can be an identifier assigned by the base station device to each of the terminal device and the IAB node, that is, a ReestabUE-identification derived (for example, calculated) from a cell radio network temporary identifier (C-RNTI, Cell Radio Network Temporary Identifier) ​​or C-RNTI and a physical layer cell identification (PhysCell ID). In addition, if the communication device connected to the downstream of the IAB node 111 is an IAB node, the global NG-RAN node ID or IP address assigned to the IAB node (as a 5G radio access network node) can be used as the identification information (ID).

[0027] Upon receiving the control signal for the switching of the IAB node 111, the terminal device 121, and the terminal device 122, the IAB host node 102 as the switching destination sends a response signal to each control signal to the IAB host node 101. The "response signal" mentioned herein may include information about connection parameters to be used by the IAB node and the terminal device after the switching and determined, for example, based on the connection parameters already used by the node or device. In addition, the response signal may correspond to a handover request confirmation (HANDOVER REQUEST ACKNOWLEDGE) message, which is sent from the base station device as the switching destination to the base station device as the switching source in the existing method.

[0028] Upon receiving the response signal, the IAB host node 101 sends a control signal for switching the IAB node 111 and a control signal for switching a communication device connected to the downstream of the IAB node 111 to the IAB node 111. In addition, for example, the control signal for switching here corresponds to an existing RRC reconfiguration message. Here, the control signal for the IAB node 111 may include information indicating a process (e.g., a random access process) required for establishing synchronization with the connection destination (IAB host node 102) to be switched.

[0029] On the other hand, the partner device to which the communication device connected downstream of the IAB node 111 is directly connected (for example, the IAB node 111 for the terminal device 121 and the terminal device 122) has not changed, so the control signal for these devices can include information indicating that the synchronization establishment process is not required. Therefore, upon receiving the control signal, each of the communication devices connected downstream of the IAB node 111 sends a response message (RRC Reconfiguration Complete (RRCReconfigurationComplete) message) to the IAB node 111 without performing random access processing, etc., and receives a processing response in response to the message, so it can be determined that the handover is successful. At this time, the control signal received by each of the devices via the IAB node 111 includes information about the connection parameters for connecting to the IAB host node 102, so a state can be reached based on which it can be determined that the connection with the IAB host node 102 has been established.

[0030] However, the communication device connected to the downstream of the IAB node 111 can maintain the connection with the IAB node 111 as it is, but there is a case where the IAB node 111 cannot establish a connection with the IAB host node 102. That is, there is a case where the IAB node 111 fails in handover (e.g., random access). At this time, the IAB node 111 may perform a process for reconnecting with another IAB host node (or another IAB node that relays communication with the IAB host node) to establish a connection. In this case, the IAB host node that is the reconnection destination of the IAB node 111 and the IAB host node that is considered to be connected to the communication device connected to the downstream of the IAB node 111 may be different. Due to this mismatch, there is a case where the IAB node 111 cannot properly maintain the function of the relay device, such as a connection parameter mismatch occurs.

[0031] In view of this situation, when receiving the first control signal for the switching of the IAB node 111 and the second control signal for the communication device connected to the downstream of the IAB node 111 from the IAB host node 101 as the switching source, the IAB node 111 according to the present embodiment retains the forwarding of the second control signal. When retaining the forwarding of the second control signal, the IAB node 111 performs a process for switching to the IAB host node 102 as the switching destination. Here, the IAB node 111 needs to establish a synchronization process to perform a random access process (sending a random access preamble / receiving a random access response). In addition, the random access process described herein may be a four-step random access process or a two-step random access process. In addition, the "random access" described herein may be a contention-based random access (CBRA) or a non-contention-based random access (CFRA). After performing the random access process and establishing a connection with the IAB host node 102 as the switching destination, the IAB node 111 sends the second control signal that is retained to be forwarded to the communication device connected to the downstream of the IAB node 111. Therefore, after the IAB node 111 successfully performs the handover, a control signal for handover of the communication device connected to the downstream of the IAB node 111 is transmitted, thereby preventing a mismatch between the IAB host node as the connection destination of the IAB node 111 and the IAB host node as the connection destination of the communication device connected to its downstream. In addition, if the handover fails, the IAB node 111 may discard the second control signal. In this case, after reestablishing the connection, the IAB node 111 may perform a handover process of the downstream communication device.

[0032] In addition, the IAB node 111 can recognize that the handover is successful by receiving a random access response from a base station device as a handover destination, or can also recognize that the handover is successful by receiving a contention resolution. In addition, the IAB node 111 can recognize that the handover has failed when a timer started at the start of the handover process expires or when the number of times a random access preamble is sent exceeds a predetermined value.

[0033] In addition, if the handover is successful, the IAB node 111 may forward the retained second control signal after the path setting and the like for relay transmission are completed between the IAB node 111 and the IAB host node 102 which is the handover destination of the IAB node 111. A configuration may be adopted in which, for example, the retained second control signal is forwarded after the F1 interface is established.

[0034] In addition, for example, the IAB node 111 may send the second control signals without retaining them, receive the third control signal sent from the downstream communication device in response to the second control signal, and attempt to switch before sending the response signal after receiving the third control signal. When receiving the third control signal, if the switch is successful, the IAB node 111 may send a response signal to the device that has sent the third control signal. On the other hand, when receiving the third control signal, if the switch is not successful, the IAB node 111 may retain the sending of the response signal. In this case, the IAB node 111 may send the response signal after successfully performing the switch. In addition, the third control signal may be an RRC reconfiguration complete (RRCReconfigurationComplete) message, and the response signal may be an RLC ACK. In addition, "RLC" is an acronym for Radio Link Control, and "RLC ACK" is an affirmative response of the RLC layer.

[0035] A case has been described in which, in the above-mentioned process, the IAB node 111 reserves sending a predetermined control signal (e.g., an RRC reconfiguration message) for handover of a downstream communication device. In contrast, the IAB node 111 may reserve sending a predetermined control signal (e.g., an RRC reconfiguration completion message) to a communication device downstream of the IAB node 111 until the handover is successfully performed. In this case, when the handover is completed, the IAB node 111 may notify the communication device connected downstream of the IAB node 111 of information indicating that the handover has been successful. In addition, the information may be notified after the IAB node 111 completes the setting related to the relay path. That is, the IAB node 111 may notify the downstream communication device of information indicating that the condition for the reservation of the transmission / reception of the handover of the communication device connected downstream of the IAB node 111 is satisfied. Then, the communication device connected downstream of the IAB node 111 sends a predetermined signal to the IAB node 111 according to the information notified indicating that the handover is successful. On the other hand, if the handover is not successful, the IAB node 111 may notify the communication device connected downstream of the IAB node 111 of information indicating that the handover has failed. Then, the communication device connected downstream of the IAB node 111 may discard the predetermined control signal for handover received from the IAB node 111 according to the information notified indicating the handover failure.

[0036] In the manner described above, in the case where the IAB node 111 fails in handover, it is possible to prevent a connection destination (IAB host node) mismatch from occurring due to a communication device connected downstream of the IAB node 111 determining that the handover is successful.

[0037] In addition, the IAB node 111 can control to prevent a new terminal device from starting the process of connecting to the IAB node 111 until the process of switching of the IAB node 111 itself is completed. The IAB node 111 can, for example, set information indicating that a connection to a cell cannot be made (e.g., cell access is prohibited (Cellbarred)) in a notification signal (e.g., System Information Block Type 1, etc.) sent by the IAB node 111 based on a control signal for switching (e.g., RRC reconfiguration message) received from the IAB host node 101 as the switching source. Therefore, it is possible to prevent the signaling performed to reconnect the terminal device from being wasted when the switching fails.

[0038] in addition, Figure 1The case where the IAB node 111 is directly connected to the IAB host node 101 or the IAB host node 102 is shown, but the IAB node 111 may also be connected to the IAB host node via another IAB node. In addition, the terminal device 121 or the terminal device 122 may be another IAB node. In addition, Figure 1 Only a few IAB host nodes, IAB nodes and terminal devices are shown, but there may be many more IAB host nodes, IAB nodes and terminal devices without loss of generality.

[0039] (Device Configuration)

[0040] Next, the configurations of the IAB node and the terminal device that perform processing such as described above will be described. Figure 2 204. An example hardware configuration of an IAB node or a terminal device is shown. As an example, the IAB node and the terminal device each include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. For example, in the IAB node and the terminal device, a computer-readable program is executed by the processor 201, and the computer-readable program implements the above-mentioned functions of the IAB node and the terminal device and is recorded in one of the ROM 202, the RAM 203, and the storage device 204. In addition, the processor 201 can be replaced with one or more processors, such as an ASIC (application-specific integrated circuit), an FPGA (field programmable gate array), and a DSP (digital signal processor).

[0041] For example, the processor 201 of the IAB node or terminal device controls the communication circuit 205 to communicate with the partner device (IAB host node, IAB node, terminal device, etc.). Figure 2 Schematic diagram showing an IAB node or terminal device including one communication circuit 205, but not limited thereto. For example, the IAB node may include a communication circuit for communicating with an IAB host node and a communication circuit for communicating with another IAB node and a terminal device. In addition, the terminal device may include a communication circuit for cellular communication and a communication circuit for communication in accordance with another wireless standard.

[0042] Figure 3 : represents an example functional configuration of an IAB node. For example, the IAB node is composed of a switching processing unit 301, a control data transmission control unit 302, and a control data retention control unit 303. In addition, the IAB node is configured to be able to perform the usual functions of the IAB node other than these (terminal functions and base station functions) as a matter of course. In addition, for example, a part or the entire functional configuration can be implemented by the processor 201 executing a program stored in the ROM 202 or the storage device 204. In addition, dedicated hardware for implementing the functional configuration can be prepared. In addition, for example, Figure 3The functional configuration in can also be realized by executing a dedicated program by a processor included in the communication circuit 205. In addition, Figure 3 Some functions in it, or can be replaced by another function with similar functions Figure 3 Function in .

[0043] When performing a handover accompanied by a change in the connection destination (i.e., the IAB host node) due to the movement of the IAB node, etc., the handover processing unit 301 performs various types of processing. For example, upon receiving an RRC reconfiguration message indicating the need for synchronization establishment processing from the IAB host node as the handover source, the handover processing unit 301 sends a random access preamble to the IAB host node as the designated handover destination. When a random access response is received from the IAB host node as the handover destination, the handover processing unit 301 sends an RRC reconfiguration completion message to the IAB host node as the handover destination, and completes the handover. In addition, the handover processing unit 301 can also perform subsequent settings (e.g., settings of relay paths) as a relay device.

[0044] When the IAB node performs a handover process, the control data transmission control unit 302 transmits control data for the handover of the communication device connected to the downstream of the IAB node itself. In addition, the control data may be an RRC reconfiguration message received from the IAB host node as the handover source. The control data may also be a response signal (RLC ACK) to the RRC reconfiguration completion message received from the communication device connected to the downstream of the IAB node. For example, the control data retention control unit 303 may perform control so that the transmission of the control data performed by the control data transmission control unit 302 is retained. For example, the control data retention control unit 303 may retain the transmission of the RRC reconfiguration message for the handover of the device connected to the downstream of the IAB node to the communication device until the handover of the IAB node itself is successfully performed. In addition, for example, the control data transmission control unit 302 may be configured to send the RRC reconfiguration message for the handover of the device connected to the downstream of the IAB node to the device, regardless of whether the handover of the IAB node itself is successful. In this case, the control data retention control unit 303 may retain the transmission of the response signal (RLC ACK) to the RRC reconfiguration completion message from the downstream communication device.

[0045] In addition, the control data retention control unit 303 may control so that the RRC reconfiguration completion message is retained to be sent to the downstream communication device until the IAB node successfully performs the handover. In this case, the control data transmission control unit 302 may be configured to send an RRC reconfiguration message for the handover of the device connected to the downstream of the IAB node to the communication device, regardless of whether the handover of the IAB node itself is successful. Then, the control data retention control unit 303 causes the control data transmission control unit 302 to check whether the handover processing unit 301 successfully performs the handover or fails, and controls the control data transmission control unit 302 to send information indicating the success or failure of the handover to the downstream communication device. In the case of notifying the downstream communication device of the information indicating the success of the handover, the RRC reconfiguration completion message is sent from the downstream communication device. In this case, the control data transmission control unit 302 sends an RLC ACK to the downstream communication device and ends the handover processing of the downstream communication device. On the other hand, if the information indicating the failure of the handover is notified to the downstream communication device, the downstream communication device discards the RRC reconfiguration message. In this case, the IAB node attempts to reconnect with another IAB host node, and upon successful reconnection of the IAB node, the downstream communication device also attempts to connect with the reconnection partner (ie, the IAB host node). In addition, the downstream communication device may perform a process for reconnecting with other devices other than the IAB node.

[0046] Figure 4 The following is an example functional configuration of a downstream communication device (terminal device or other IAB node) in the case where the downstream communication device retains the sending of the RRC reconfiguration complete message. For example, the device includes a control data sending / receiving unit 401 and a control data retention processing unit 402. In addition, the device is configured to be able to perform the functions of a normal terminal device or IAB node other than these. In addition, if the device is an IAB node, it also includes Figure 3 In addition, for example, a part or the entire functional configuration may be implemented by the processor 201 executing a program stored in the ROM 202 or the storage device 204. In addition, dedicated hardware for implementing the functional configuration may be prepared. In addition, for example, Figure 4 The functional configuration in can also be realized by executing a dedicated program by a processor included in the communication circuit 205. In addition, Figure 4 Some functions in it, or can be replaced by another function with similar functions Figure 4 Function in .

[0047] The control data transmission / reception unit 401 receives an RRC reconfiguration message from an upstream IAB node as control data for switching of the device including the control data transmission / reception unit 401. The control data retention processing unit 402 retains the transmission of the RRC reconfiguration completion message in response to the RRC reconfiguration message until a message indicating that the switching is successful is received after the RRC reconfiguration message. Then, the control data retention processing unit 402 releases the reserved transmission according to the reception of the message indicating that the control data transmission / reception unit 401 has successfully performed the switching, and outputs an instruction to send the RRC reconfiguration completion message to the control data transmission / reception unit 401. On the other hand, in the case where the control data transmission / reception unit 401 receives information indicating that the switching has failed, the control data retention processing unit 402 discards the previously received RRC reconfiguration message.

[0048] (Processing Flow)

[0049] Next, we will refer to Figure 5 An example of a process flow performed by a wireless communication system is described. In addition, here, an example of processing in the case where the IAB node 111 retains the transmission of an RRC reconfiguration message from the start of handover until the setting related to the relay path is completed will be described. However, this is merely exemplary, and for example, after the handover is successfully performed, the IAB node 111 may retain the transmission of the RRC reconfiguration message before the setting related to the relay path is completed. In addition, the IAB node 111 may retain the transmission of the RLC ACK, or may cause the downstream communication device to retain the transmission of the RRC reconfiguration completion message.

[0050] In this process, first, the IAB host node 101 connected to the IAB node 111 determines that the IAB node 111 is to be switched, based on the decrease in the first wireless quality of the signal received by the IAB node 111 from the IAB host node 101, the second wireless quality of the signal received by the IAB node 111 from the IAB host node 102 exceeding the first wireless quality predetermined level, etc. Then, the IAB host node 101 determines the communication device connected to the downstream of the IAB node 111, generates a switching request message for the device and a switching request message for the IAB node 111, and sends the messages to the IAB host node 102 as the switching destination (step S501). The IAB host node 102 obtains information such as the connection parameters being used by the device from the switching request message for each device. Then, the IAB host node 102 determines the connection parameters to be used by the device after the switching, generates a switching request confirmation message containing the information for each device, and sends the message to the IAB host node 101 as the switching source (step S502).

[0051] Upon receiving the multiplexed handover request confirmation message, the IAB host node 101 generates an RRC reconfiguration message for the IAB node 111 and the communication device connected downstream of the IAB node 111 based on the received message, and sends the generated message to the IAB node 111 (steps S503 and S504). At this time, the RRC reconfiguration message for the IAB node 111 may indicate that a synchronization establishment process such as a random access process will be performed. On the other hand, the RRC reconfiguration message for the communication device connected downstream of the IAB node 111 may indicate that a synchronization establishment process such as a random access process will not be performed. In addition, Figure 5 In the example, “w sync” indicates that synchronization establishment processing is required, and “wo sync” indicates that synchronization establishment processing is not required.

[0052] In this example, even when an RRC reconfiguration message for a downstream communication device is received, the IAB node temporarily reserves forwarding messages to the downstream communication device. Next, the IAB node 111 first attempts to connect to the IAB host node 102 as the switching destination. Specifically, the IAB node 111 performs a random access process based on the RRC reconfiguration message for the IAB node 111 and establishes synchronization with the IAB host node 102 (steps S505 and S506). Then, the IAB node 111 sends an RRC reconfiguration completion message for the IAB node 111 itself to the IAB host node 102 as the switching destination (step S507), and completes the switching. Then, the IAB node 111 uses the IAB host node 102 to perform settings related to the relay path (step S508). For example, the IAB node 111 sends a request (F1 SETUP REQUEST) message for establishing an F1 interface to the IAB host node 102, and the IAB host node 102 sends a response (F1 SETUP RESPONSE) message to the request message to the IAB node 111. Then, a UE context setup request (UE CONTEXT SETUP REQUEST) and a UE context setup response (UE CONTEXT SETUP RESPONSE) are sent / received, and routing setup of the backhaul (BH) is performed.

[0053] When the settings related to the relay path are completed, the IAB node 111 sends the RRC reconfiguration message for the downstream communication device received in step S504 and retained for forwarding to the downstream communication device (steps S509, S511). Upon receiving the RRC reconfiguration completion message from the device, the IAB node 111 forwards the message to the IAB host node 102 (S510, S512). The handover between the IAB host node 102 and the downstream communication device is completed by sending / receiving the RRC reconfiguration completion message. In addition, a configuration may be adopted in which the IAB node 111 sends an RLC ACK (not shown) to the downstream communication device and completes the handover process, and the downstream communication device determines that the handover is successful based on the receipt of the RLC ACK.

[0054] In this way, in the present embodiment, when performing handover, the IAB node 111 reserves the transmission of messages to the communication devices connected downstream of the IAB node 111 itself, or causes these devices to reserve the transmission of messages, thereby preventing the downstream communication devices from completing the handover process early. Therefore, after the handover of the IAB node 111 on the upstream side is successfully performed, the handover process on the downstream side is completed, thereby preventing the occurrence of a situation where the IAB host node as the connection destination (in other words, connection parameters) between the IAB node 111 and the downstream communication devices are inconsistent.

[0055] The present invention is not limited to the foregoing embodiments, and thus various changes / alterations may be made within the spirit of the present invention.

[0056] This application claims the benefit of Japanese Patent Application No. 2020-110808, filed on June 26, 2020, which is hereby incorporated by reference.

Claims

1. A relay device that relays communication between a base station device and a communication device connected to the base station device, wherein: The relay device comprises: a control unit that performs control, when the relay device switches to another base station device, so that transmission / reception of a signal for switching of the communication device between the communication device and the base station device is retained during a period in which the switching of the relay device is unsuccessful, The control unit performs control so as not to forward a signal for switching the communication device received from the base station device during a period in which the switching of the relay device is unsuccessful.

2. The relay device according to claim 1, wherein: The signal for the handover of the communication device is an RRC reconfiguration message.

3. A relay device that relays communication between a base station device and a communication device connected to the base station device, wherein: The relay device comprises: a control unit that performs control, when the relay device switches to another base station device, so that transmission / reception of a signal for switching of the communication device between the communication device and the base station device is retained during a period in which the switching of the relay device is unsuccessful, The signal for switching of the communication device is a response signal to a predetermined signal related to switching received from the communication device. The control unit performs control so that the response signal is not transmitted even if the predetermined signal is received while the switching of the relay device is unsuccessful.

4. The relay device according to claim 3, wherein: The response signal is RLC ACK.

5. The relay device according to claim 3, wherein: The predetermined signal is an RRC reconfiguration complete message.

6. The relay device according to claim 1 or 3, wherein: The control unit releases the hold of transmission / reception of a signal for handover of the communication device between the communication device and the base station device, based on completion of setting of the relay path between the relay device and the other base station device.

7. The relay device according to claim 1 or 3, wherein: The control unit determines that the handover is unsuccessful during a period from when the relay device starts the handover process until the relay device receives a random access response to a random access preamble transmitted to the other base station device for the handover.

8. A communication device connected to a base station device via a relay device, wherein: The communication device comprises: a sending unit, which, when the relay device switches to another base station device, sends a second signal for switching the communication device to the relay device after receiving a first signal related to the switching of the communication device; as well as a holding unit that holds the transmission of the second signal until receiving information from the relay device indicating that a condition for releasing the holding of the transmission / reception of the signal for switching the communication device is satisfied, The first signal is an RRC reconfiguration message, The second signal is an RRC reconfiguration complete message.

9. The communication device according to claim 8, wherein: The information indicating that the condition for releasing the suspension of transmission / reception of the signal for switching the communication device is satisfied is information indicating that the switching of the relay device is successful.

10. A control method, which is performed by a relay device that relays communication between a base station device and a communication device connected to the base station device, wherein: The control method has the following features: a control step in which, when the relay device switches to another base station device, control is performed so that transmission / reception of a signal for switching of the communication device between the communication device and the base station device is retained during a period in which the switching of the relay device is unsuccessful, In the control step, control is performed so that a signal for switching the communication device received from the base station device is not forwarded while the switching of the relay device is unsuccessful.

11. A control method, which is performed by a relay device that relays communication between a base station device and a communication device connected to the base station device, wherein: The control method has the following features: a control step in which, when the relay device switches to another base station device, control is performed so that transmission / reception of a signal for switching of the communication device between the communication device and the base station device is retained during a period in which the switching of the relay device is unsuccessful, The signal for switching of the communication device is a response signal to a predetermined signal related to switching received from the communication device. In the control step, control is performed so that the response signal is not transmitted even if the predetermined signal is received while the switching of the relay device is unsuccessful.

12. A control method, which is performed by a communication device connected to a base station device via a relay device, wherein: The communication device is configured to, when the relay device switches to another base station device, send a second signal for switching the communication device to the relay device after receiving a first signal related to the switching of the communication device, The control method includes holding transmission of the second signal until receiving information from the relay device indicating that a condition for releasing holding of transmission / reception of a signal for switching of the communication device is satisfied, The first signal is an RRC reconfiguration message, The second signal is an RRC reconfiguration complete message.

13. A storage medium storing a program, wherein: The program causes a computer to execute the control method according to any one of claims 10 to 12.

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