Relay device, control method, and program

Abstract

To provide a repeating device, a control method, and a program for efficiently changing a connection destination in a repeating system.SOLUTION: A repeating device included in a repeating route for relaying communication between a network and a terminal transmits a message to announce in advance a relay stop to other repeating devices connected to the repeating device on the opposite side of a network in the repeating route when the relay is scheduled to be stopped. Information on a second other repeating device connected to a repeating device on a network side in the repeating route and information indicating the scheduled time for stopping a relay is included in the message and sent.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a route setting control technique for relay transmission. [Background technology]

[0002] The Third Generation Partnership Project (3GPP) has standardized IAB (Integrated Access and Backhaul), which forms a backhaul line using a wireless access line (see Patent Document 1). In IAB, a relay device (IAB node) relays communications between a terminal connected to that relay device, or between another relay device further connected to that relay device, and a base station (IAB donor). By using IAB, it is possible to expand the coverage area at a lower cost than conventional wired communications using optical fiber or the like. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2019-534625 Summary of the Invention [Problem to be solved by the invention]

[0004] In IAB, radio link failures (RLFs) can occur between IAB donors and IAB nodes, or between IAB nodes themselves, due to node failures or changes in the radio environment. In such cases, normally operating IAB nodes can continue communication by searching for other IAB nodes and performing a reconnection process. However, such reconnection processes take time, and there are periods when IAB nodes cannot communicate. If such periods continue for a long time, the efficiency of the entire system deteriorates. [Means for solving the problem]

[0005] The present invention provides a technique for improving the efficiency of connection destination change processing in a relay system.

[0006] A relay device according to one aspect of the present invention is a relay device included in a relay path that relays communication between a network and a terminal, of Stop of If you have plans, In response to the time being a predetermined time before the scheduled time of stopping the relay, The relay device has a transmitting means for transmitting a message informing the relay device of the stop of relay to a first other relay device connected to the relay device on the opposite side of the network in the relay route. [Effects of the Invention]

[0007] According to the present invention, the connection destination in the relay system can be changed efficiently. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication network. [Figure 2] FIG. 2 is a diagram illustrating an example of the hardware configuration of an IAB node. [Figure 3] FIG. 10 is a diagram illustrating an example of a functional configuration of an IAB node. [Figure 4] FIG. 10 is a diagram illustrating an example of the configuration of a BAP PDU. [Figure 5] A diagram showing an example of the processing flow when an IAB node stops backhaul communication. [Figure 6] FIG. 10 is a diagram illustrating an example of the flow of processing in which an IAB node changes its parent node. [Figure 7] FIG. 1 illustrates an example of processing performed in a wireless communication network. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention claimed. Although multiple features are described in the embodiments, not all of these multiple features are necessarily essential to the invention, and multiple features may be combined arbitrarily. Furthermore, in the accompanying drawings, the same reference numerals are used to designate the same or similar components, and redundant explanations will be omitted.

[0010] (Network configuration) FIG. 1 illustrates an example of the configuration of a wireless communication network in this embodiment. This wireless communication network is configured based on IAB (Integrated Access and Backhaul) defined by the 3rd Generation Partnership Project (3GPP). In this wireless communication network, relay devices (IAB nodes 121-125) relay communications between base stations (IAB donors 111-112) and a terminal 141. Note that the arrangement / configuration of the communication devices (IAB donors 111-112, IAB nodes 121-125, and UE 141) in FIG. 1 is an example, and the following discussion can be applied to other arrangements / configurations. Furthermore, these communication devices are communication devices in a fifth-generation (5G) access network also called an NR (New Radio) access network, and the IAB donors 111-112 and IAB nodes 121-125 can also be called gNBs. Note that the following discussion can be applied to a configuration in which a network of another generation is used.

[0011] The IAB donors 111-112 control relay communications by the IAB nodes 121-122 directly connected to the donors themselves and by other IAB nodes 123-125 connected downstream of the IAB nodes. The IAB donors 111-112 are connected to the core network 101. It can be said that the IAB donors 111-112 provide the IAB nodes 121-125 with connections to the core network 101. In this embodiment, communications between the IAB donors 111-112 and the IAB nodes 121-125 and the core network 101 are referred to as backhaul communications. In this embodiment, of two nodes directly connected in a communication path formed by relaying, the node closer to the core network 101 is referred to as a parent node, and the node farther from the core network 101 is referred to as a child node. For example, the IAB donor 111 is the parent node of the IAB node 121, and the IAB node 121 is the child node of the IAB donor 111. Furthermore, IAB node 122 is a child node of IAB donor 112 and also a parent node of IAB node 123. Similarly, IAB node 122 is a child node of IAB node 122 and also a parent node of IAB node 124. Note that although the example in FIG. 1 shows a configuration in which one child node is connected to one parent node, two or more child nodes may be connected to one parent node.

[0012] IAB donors 111-112 operate as radio base stations in a cellular communication system. IAB nodes 121-125 relay communications between IAB donors 111-112. As a result, a terminal (e.g., terminal 141) connected to IAB nodes 121-125 can perform radio communications under the control of IAB donors 111-112. That is, IAB nodes 121-125 also operate as base stations from the terminal's perspective. Note that FIG. 1 illustrates an example in which terminal 141 is located within the range of cell 131 provided by IAB node 125, and connects to core network 101 via IAB nodes 122-125 and IAB donor 112.

[0013] In such a wireless communication network, nodes (IAB donors and IAB nodes) are connected wirelessly, and therefore a radio link failure (RLF) may occur due to changes in the wireless environment or node outages. This RLF is called a backhaul radio link failure (BH RLF). When an IAB node detects a BH RLF, it notifies its child nodes that a BH RLF has occurred. For example, if a failure occurs in IAB node 122 and wireless communication becomes impossible, IAB node 123 detects the wireless failure and notifies IAB node 124 of the BH RLF. Furthermore, when an IAB node receives a BH RLF from a parent node, if the node has a child node, it notifies the child node of the BH RLF. For example, when IAB node 124 receives a BH RLF, it transmits a BH RLF to IAB node 125. When each IAB node receives a BH RLF, it selects one device from the surrounding IAB nodes or IAB donors and performs a reconnection process to continue backhaul communication.

[0014] Here, the IAB node 124 is assumed to be a mobile communication device, such as a drone or a vehicle such as a relay van. For example, in the event of a disaster, such a communication device can be moved to an area where communication services cannot be provided by operational communication devices alone, and operated as an IAB node, thereby providing communication services in that area. In one example, it is assumed that the IAB node 125 is participating in a wireless communication network with the IAB node 123 as its parent node, and the IAB node 124 begins operating in the wireless communication network. In this embodiment, it is assumed that the IAB node 124 observes signals transmitted from, for example, a surrounding IAB donor or IAB node, and connects to the IAB node 123 as a child node of the IAB node 123. It is also assumed that the IAB node 125 has switched its parent node from the IAB node 123 to the IAB node 124. For example, IAB node 125 may switch the parent node to IAB node 124 if the communication quality of the signal from IAB node 124 is better than the communication quality, such as the radio wave strength, of the signal from IAB node 123. In addition, IAB donor 112 may instruct IAB node 125 to switch the parent node to IAB node 124 based on the frequency band (frequency utilization rate) used by IAB node 123 and the processing load.

[0015] In this embodiment, it is assumed that the IAB node 124 leaves the wireless communication network after a certain period of time has elapsed since joining the wireless communication network. In other words, it is assumed that the IAB node 124 has previously decided to cease functioning as an IAB node. In this case, when the IAB node 124 leaves the wireless communication network after the certain period of time has elapsed, an RLF occurs, similar to when the IAB node 124 fails. However, the interruption of communication by the IAB node 124 is planned, and it is inefficient to perform the same procedure as when a conventional RLF occurs. For this reason, in this embodiment, the IAB node 124 transmits a relay stop notice message to its child node, the IAB node 125, indicating that it plans to cease communication as an IAB node. This allows the IAB node 125 to recognize that a communication interruption with the IAB node 124 is planned, and to, for example, identify an IAB node or IAB donor to which it will reconnect in advance and connect to the identified destination before or immediately after the RLF occurs. This allows the duration of the disconnection to be shortened by, for example, changing the destination immediately before or after the planned RLF occurs. IAB node 124 may determine to stop communication based on the state of its own device, and transmit a message announcing the stop to IAB node 125. For example, IAB node 124 may determine the time to stop communication based on the remaining battery power of its own device, and transmit a relay stop notice message accordingly.

[0016] (Device configuration) The configuration of an IAB node according to this embodiment will be described. Note that an IAB donor may also have a hardware configuration and functional configuration similar to the configuration of the IAB node described here. An example hardware configuration of an IAB node is shown in FIG. 2. The IAB node is configured to include, 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 the configuration in FIG. 2 is an example, and components not shown in FIG. 2 may be included in the IAB node, or at least a part of the components shown in FIG. 2 may be replaced with other components or omitted. Also, multiple components of the single component shown in FIG. 2 may be provided.

[0017] The control unit 201 includes one or more processors, such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit). The processor may be a processor other than a CPU or an MPU, such as an FPGA (Field Programmable Gate Array), a DSP (Digital Signal Processor), or an ASIC (Application Specific Integrated Circuit). The control unit 201 controls the entire device by executing a control program stored in the storage unit 202. The storage unit 202 includes one or more memories, such as a ROM (Read Only Memory) or a RAM (Random Access Memory). The storage unit 202 may also include a large-capacity storage device, such as a hard disk drive or a solid-state drive. The storage unit 202 stores various information, such as the control program executed by the control unit 201, information on cells and neighboring cells that the device configures, information on terminals connected to the device, and IAB routing information. The control unit 201 executes the control program stored in the storage unit 202 to perform various operations, which will be described later.

[0018] The wireless communication unit 203 performs wireless communication in accordance with a cellular communication standard such as Long Term Evolution (LTE) or 5G, which conforms to the 3GPP standard. The wireless communication unit 203 may be configured to perform wireless communication in accordance with a future cellular communication standard or a non-cellular standard. The antenna control unit 204 controls the antenna 205 to output a wireless signal for wireless communication by the wireless communication unit 203 and to receive an external wireless signal as an input. For example, when searching for an IAB donor or IAB node that is a candidate for a parent node, the antenna control unit 204 controls the antenna 205 to receive a signal with a beam having a wide beam width. Furthermore, when determining a device to connect to, the antenna control unit 204 controls the antenna 205 to form a beam having a narrow beam width toward the device. The antenna 205 may be an antenna having characteristics that enable communication in both a frequency band used for backhaul communication, such as the 28 GHz band, and a frequency band used for communication with a terminal. The antenna 205 may be an antenna array in which multiple antenna elements are arranged in an array.

[0019] Next, an example of the functional configuration of the IAB node will be described with reference to FIG. 3. Note that each function described below can be realized, for example, by the control unit 201 executing a program stored in the storage unit 202. Also, some or all of the functions described below may be implemented by dedicated hardware. Note that some or all of the functions described below may be replaced by other functional configurations or may be omitted. The IAB node has, as its functions, for example, a transmitter 301, a receiver 302, a connection controller 303, a broadcast information generator 304, a time information unit 305, a parent node change determiner 306, a backhaul PDU generator 307, and a backhaul PDU receiver 308.

[0020] The transmitter 301 transmits various signals (including frames and information) to other communication devices via the wireless communication unit 203. The receiver 302 receives various signals from other communication devices via the wireless communication unit 203. The connection controller 303 controls connections with other communication devices through communication using the transmitter 301 and the receiver 302. The connection controller 303 performs processing related to connection and disconnection with other communication devices, for example, by transmitting and receiving Radio Resource Control (RRC) messages using the transmitter 301 and the receiver 302. The broadcast information generator 304 generates broadcast information including system information related to the cell provided by the IAB node itself. This broadcast information is periodically transmitted by the transmitter 301. By receiving this broadcast information, other communication devices (other IAB nodes and terminals) recognize the presence of an IAB node in the vicinity of their own device and can perform connection processing to that IAB node.

[0021] The time information unit 305 acquires time information via the network and executes timer processing until a predetermined time. The parent node change determination unit 306 determines whether to change the parent node in backhaul communication. As described above, a parent node is a node that exists closer to the core network than the device itself on the communication path for backhaul communication and to which the device itself is directly connected. The parent node change determination unit 306 may decide to change the parent node when it detects a deterioration in wireless quality in the link between the device itself and the parent node, or when it detects a BH RLF in that link or in a link further upstream (on the core network side). The parent node change determination unit 306 may also change the parent node based on a specific instruction from the IAB donor indicating that the parent node should be changed.

[0022] The backhaul PDU generation unit 307 generates a PDU (Protocol Data Unit) to be transmitted and received between communication devices (IAB donors and other IAB nodes) in backhaul communication. This PDU is based on the Backhaul Adaptation Protocol (BAP) and is also called a BAP PDU. Data transfer and notification of control messages for backhaul communication are performed using this BAP PDU, and the BAP PDU is transmitted to other communication devices by the transmitter 301. The backhaul PDU receiver 308 receives a BAP PDU from another communication device via the receiver 302 and analyzes the received BAP PDU to obtain the included information. An example of the configuration of a BAP PDU is shown in FIG. 4. As shown in FIG. 4, the BAP PDU is configured to include, for example, a D / C field 401, a PDU type field 402, a Reserved field 403, and an Options field 404. The D / C field 401 is a 1-bit field, and when the value is set to "0", it indicates that the BAP PDU is a control message, and when the value is set to "1", it indicates that the BAP PDU is data. The PDU type field 402 is made up of 4 bits and indicates the type of control message. For example, when the value is set to "0011", it indicates that this control message is a BH RLF. The reserved field 403 is an unused reserved area. The option field 404 is a field that stores additional information. The fields from the second octet onwards of the BAP PDU are used as the option field 404.

[0023] In this embodiment, when an IAB node decides to stop backhaul communication prior to the stoppage, the backhaul PDU generation unit 307 generates a BAP PDU that notifies the relay stop. This BAP PDU that notifies the relay stop will be referred to hereinafter as a relay stop notice message. Because the relay stop notice message is a control message, the D / C field 401 is set to “0,” and the PDU type field 402 is set to a value indicating a relay stop notice message. The value indicating this relay stop notice message may be, for example, “0100,” but may be any other value as long as it does not overlap with values ​​of other PDU types. In this embodiment, for example, information indicating a parent node to which the IAB node that transmitted this relay stop notice message is connected may be stored in the option field 404 as additional information. Note that this is just an example, and a relay stop notice message containing other appropriate information may also be formed. For example, the IAB node may store the scheduled time at which the backhaul communication will be stopped in the option field 404 as additional information.

[0024] (Processing flow) Next, an example of the flow of processing executed by the IAB node will be described. Note that, in one example, each processing described below can be realized by the control unit 201 executing a program stored in the storage unit 202. Also, a part or all of each processing described below may be performed by dedicated hardware.

[0025] 5 shows an example of a process flow for the IAB node 124 to stop backhaul communication. This process is initiated, for example, when the IAB node 124 joins a wireless communication network that performs backhaul communication. This process may be repeatedly executed, for example, at regular time intervals. This process may be executed not only by the IAB node 124 but also by any communication device that can join a wireless communication network such as that shown in FIG. 1, operate as an IAB node, and perform an operation to stop backhaul communication.

[0026] In the process of FIG. 5, the IAB node 124 determines whether it plans to stop backhaul communication within a predetermined time from the current time (S501). The IAB node 124 measures, for example, the elapsed time since joining the wireless communication network such as that of FIG. 1 using the time information unit 305, and determines whether it is the predetermined time (e.g., 5 minutes) before stopping the backhaul communication. That is, the IAB node 124 may determine whether it is the predetermined time before stopping the backhaul communication by determining whether a time obtained by subtracting a predetermined time from a set time (e.g., 2 hours) has elapsed. Then, when it is determined that the backhaul communication will be stopped within the predetermined time (YES in S501), the IAB node 124 proceeds to the process of S502. Note that, after determining that it will stop backhaul communication within the predetermined time, if the IAB node 124 receives a new connection request from another IAB node or a terminal, the IAB node 124 may reject the connection request. Furthermore, the IAB node 124 may set a second predetermined time for determining whether to reject a new connection request, separate from the first predetermined time used in the determination of S501. That is, for example, after it is determined in S501 that backhaul communication will be stopped within the first predetermined time, the IAB node 124 may accept new connection requests until the time remaining until the backhaul communication is stopped reaches the second predetermined time. Furthermore, for example, before it is determined in S501 that backhaul communication will be stopped within the first predetermined time, the IAB node 124 may stop accepting new connection requests when the time remaining until the backhaul communication is stopped reaches the second predetermined time.

[0027] Although the above example uses five minutes as an example of the predetermined time, other values ​​may be used. In the above example, the IAB node 124 determines whether the predetermined time for stopping backhaul communication has arrived based on the elapsed time since joining the wireless communication network. However, this is not limiting. For example, the IAB node 124 may determine whether the predetermined time for stopping backhaul communication has arrived by determining whether the time for stopping backhaul communication is set in advance by a network operator or the like and determining whether the time remaining until that time is equal to or less than the predetermined time. The IAB node 124 may also be configured to estimate the length of time for which backhaul communication can be performed based on, for example, the remaining battery capacity available for communication. In this case, the IAB node 124 may determine to stop backhaul communication within the predetermined time if the estimated time is equal to or less than the predetermined time.

[0028] When the predetermined time until the stop of backhaul communication is reached, the IAB node 124 generates a relay stop notice message in the backhaul PDU generation unit 307 (S502). The relay stop notice message is, for example, a BAP PDU in which the D / C field 401 is set to "0" and the PDU type field 402 is set to "0100" as described above. Then, the IAB node 124 sets information indicating the parent node to which the IAB node 124 is currently connected in the option field 404 of the relay stop notice message generated in S502 in the backhaul PDU generation unit 307 (S503). The information indicating the parent node may be, for example, a gNB ID included in the broadcast information transmitted from the parent node. Here, the IAB node 124 stores information indicating the IAB node 123 in the option field 404 of the relay stop notice message. Then, the IAB node 124 transmits the generated relay stop notice message to the child node via the transmission unit 301 (S504). Here, IAB node 124 transmits a relay stop notice message to IAB node 125. Then, IAB node 124 stops the backhaul communication in response to the arrival of the scheduled time for stopping the backhaul communication based on the elapsed time measured in time information unit 305 (S505).

[0029] In this way, IAB node 124 stops backhaul communication after transmitting a relay stop notice message to the child node. This allows the child node to recognize that the wireless link with IAB node 124 will be disconnected after a predetermined time, and the child node (IAB node 125) can, for example, perform measurements for connection to the parent node of IAB node 124 or change the connection destination. Note that, although the above example shows an example in which the relay stop notice message is transmitted by a BAP PDU, the relay stop notice message may be output as broadcast information without specifying a destination.

[0030] Next, an example of the flow of a process in which the IAB node 125 changes the parent node will be described with reference to Figure 6. This process is initiated, for example, when the IAB node 125 receives a BAP PDU indicating a BH RLF or a relay stop notice message. Note that the IAB node 125 may receive other control messages in which the D / C field 401 is set to "0." In such cases, the IAB node 125 may be configured to perform processing according to the type of the message and not execute the process of Figure 6. This process may be executed not only by the IAB node 125, but also by any communication device that can participate in a wireless communication network such as that of Figure 1 and operate as an IAB node.

[0031] In this process, the IAB node 125 determines whether a BAP PDU received during communication indicates a BH RLF (S601). When the IAB node 125 receives a BAP PDU indicating a BH RLF (YES in S601), it recognizes that an RLF has occurred upstream from the IAB node 125 itself. For example, a BAP PDU indicating a BH RLF is received when an RLF is detected in the IAB node 124 due to a failure in the IAB node 123. In this case, the IAB node 125 determines whether a child node is connected to the IAB node 125 itself (S602). If a child node is present (YES in S602), the IAB node 125 generates and transmits a BH RLF message to the child node (S603). If a child node is not present (NO in S602), the IAB node 125 does not perform this process. Thereafter, the IAB node 125 selects one of the surrounding IAB nodes or IAB donors as parent node candidates and performs connection processing (S604). The IAB node 125 can recognize surrounding IAB nodes or IAB donors, for example, based on receivable broadcast information. When there are multiple surrounding IAB nodes or IAB donors, the IAB node 125 selects a device to connect to based on predetermined criteria, such as whether the received strength of the incoming radio waves is greater than a predetermined value or is the strongest, or whether the number of hops to the core network is small. The IAB node 125 then changes the parent node to the device connected in S604 (S605) and continues backhaul communication.

[0032] If the received BAP PDU is a relay stop notification message (NO in S601), the IAB node 125 determines whether the message contains information about the parent node (e.g., gNB ID) of the message sender (IAB node 124) (S606). If such information is not contained (NO in S606), the IAB node 125 proceeds to S604, where it selects one device from among the surrounding IAB nodes or IAB donors as parent node candidates and performs connection processing (S604). The IAB node 125 then changes the parent node to the device connected in S604 (S605) and continues backhaul communication. That is, if the gNB ID is not contained in the relay stop notification message, the IAB node 125 searches for parent node candidates and switches the parent node in response to receiving the message. Furthermore, if the information (gNB ID) of the parent node of the IAB node 124 is included (YES in S606), the IAB node 125 determines whether or not it is possible to connect to the node indicated by that information (S607). For example, the IAB node 125 can determine whether or not it is possible to connect to the node by determining whether or not the reception strength of a signal transmitted from the parent node of the IAB node 124 is equal to or greater than a predetermined level. Then, if the IAB node 125 determines that it is possible to connect to the node (YES in S607), it connects to the node (S608), changes the parent node to the device connected in S608 (S605), and continues backhaul communication.

[0033] As shown in Figure 6, when the IAB node 125 receives a relay stop notice message, it can change its connection destination without relaying the message, even if a child node is connected. This eliminates the need to change the connection in devices downstream from the IAB node 125 (away from the core network 101), thereby shortening the time it takes for each node to lose connection. Furthermore, if the IAB node 125 can connect to the parent node of the IAB node 124, there will be no change in the IAB donor 112 to which it is connected, eliminating the need to perform processing such as resetting the BAP address. This reduces the processing load, such as route resetting.

[0034] If the relay stop notice message includes information about the scheduled time when the IAB node 124 will stop backhaul communication, the IAB node 125 may execute a parent node change process so that the parent node change is completed by the scheduled time. This is merely an example, and it is also possible that, for example, a search for another communication device to be the new parent node is completed by the scheduled time. In this case, the parent node may be changed to the communication device that was previously searched for when the scheduled time arrives. Alternatively, the IAB node 125 may complete the change of the connection destination by the scheduled time, and then perform a relay path setting process for changing the parent node when the scheduled time arrives.

[0035] In a case where a relay stop notice message is transmitted, it is assumed that the IAB node 124 is not stopped and no RLF has occurred upstream at the time of S605. Therefore, if an RLF is expected to occur due to the relay stop of the IAB node 124, the IAB node 125 can change the parent node before the RLF actually occurs, thereby preventing a disruption of backhaul communication. Note that the IAB node 125 may not immediately perform a process to switch the parent node upon receiving the relay stop notice message, but may only search for parent node candidates and determine a connection destination. Then, for example, when the IAB node 125 detects an RLF due to the IAB node 124 stopping, the IAB node 125 may perform a process to connect to a predetermined connection destination node. This also shortens the period of disruption of backhaul communication compared to searching for connection destination candidates after an RLF occurs.

[0036] Next, an example of the flow of processing executed in the wireless communication network shown in Fig. 1 will be described with reference to Fig. 7. Fig. 7 shows an example of the flow of processing when IAB node 124 is scheduled to stop relaying in advance due to movement or the like, transmits a relay stop notice message to IAB node 125, and IAB node 125 switches its parent node. It is assumed that initially, IAB donor 112, IAB node 122, IAB node 123, IAB node 124, and IAB node 125 are connected in this order, and backhaul communication is performed between these nodes.

[0037] In this process, the IAB node 124 determines whether it plans to stop backhaul communication within a predetermined time (S701). This determination process may also be performed by each IAB node and IAB donor. However, for devices that do not stop communication unless scheduled maintenance, for example, the device may be configured not to perform this determination process unless information such as scheduled maintenance is input. If the IAB node 124 determines that it plans to stop backhaul communication within the predetermined time, it transmits a relay stop notice message to its child node (IAB node 125) (S702).

[0038] When the IAB node 125 receives the relay stop notice message, the IAB node 125 determines whether communication with the IAB node 123 is possible, for example, based on information about the parent node (IAB node 123) of the IAB node 124 in the relay stop notice message. Furthermore, if the relay stop notice message does not include information about the parent node of the IAB node 124, the IAB node 125 may search for a surrounding IAB node or IAB donor that can set up a relay route to the core network. Here, as a result of either of these processes, the IAB node 125 determines to connect to the IAB node 123 and executes a connection process (S703). The IAB node 125 establishes downlink synchronization based on the synchronization signal transmitted from the IAB node 123, and further executes a random access process to establish uplink synchronization, etc. (S704). Furthermore, the IAB node 125 establishes a connection in the radio resource control (RRC) layer with the IAB node 123 (S705).

[0039] After establishing a connection with the IAB node 123, the IAB node 125 subsequently performs a process of updating relay route information between the IAB node 125 and the IAB donor 112. Through this setting process, the IAB donor 112 updates the information on the relay route between the IAB node 125 and the IAB donor 112 (S706). For example, the IAB donor 112 changes the relay route to the IAB node 125 from a relay route that passes through the IAB node 122, the IAB node 123, and the IAB node 124 to a relay route that passes only through the IAB node 122 and the IAB node 123. Thereafter, the IAB node 125 switches the backhaul communication that had been using the IAB node 124 as the parent node to backhaul communication that does not pass through the IAB node 124 but uses the IAB node 123 as the parent node (S707). Meanwhile, the IAB node 124 stops the backhaul communication after a predetermined time has elapsed (S708).

[0040] According to this embodiment, based on the schedule for the IAB node 124 to stop relaying, the child node of the IAB node 125 changes its connection destination and reconfigures the relay route before the scheduled time. This significantly reduces the time it takes for backhaul communication to be interrupted compared to switching the connection destination after an RLF occurs due to the IAB node 124 actually stopping relaying. Furthermore, a relay stop notice message is sent only to child nodes directly connected to the IAB node that stops relaying, and only the child nodes change their connection destinations, preventing other IAB nodes connected downstream from the child nodes from changing their connection destinations. This allows the relay route to be changed while minimizing the load associated with changing the connection destination. Furthermore, by connecting the IAB node to the parent node of the IAB node that stops relaying, processing such as setting a BAP address can be omitted, thereby reducing the processing load.

[0041] In the above embodiment, the process when an IAB node that is scheduled to stop relaying a relay communication path based on IAB exists has been described. However, similar processes can be performed in a relay transmission system that is not based on IAB. That is, in a general relay transmission system including two or more relay devices, when a first relay device plans to stop relaying, it can transmit a relay stop notice message to a second relay device connected to the network side (base station side) and the opposite side (terminal side). As described above, this allows the second relay device to change its connection destination before relaying is actually stopped in the first relay device. Therefore, the period during which the relay path is interrupted can be shortened compared to when the second relay device searches for and changes its connection destination after the first relay device stops relaying.

[0042] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0043] The invention is not limited to the above-described embodiments, and various changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the following claims are appended to apprise the public of the scope of the invention. [Explanation of symbols]

[0044] 301: Transmitter, 302: Receiver, 306: Parent node change decision unit, 307: Backhaul PDU generator, 308: Backhaul PDU receiver

Claims

1. A relay device included in a relay path that relays communication between a network and a terminal, A relay device characterized by having a transmitting means for transmitting a message informing a first other relay device connected to the relay device on the opposite side of the network on the relay route of the message when the relay is scheduled to be stopped, in response to the time being a predetermined time before the scheduled time of the relay being stopped.

2. 2. The relay device according to claim 1, wherein the transmitting means transmits the message including information about a second other relay device connected to the relay device on the network side along the relay route.

3. 3. The relay device according to claim 1, wherein the transmitting means transmits the message including information indicating the scheduled time.

4. 4. The relay device according to claim 1, further comprising: a control unit that, when a connection request is received from a communication device or another relay device after the transmission unit has transmitted the message, prevents the connection request from being accepted.

5. 5. The relay device according to claim 1, wherein the relay device is an IAB node that performs relaying based on IAB (Integrated Access and Backhaul) defined by the Third Generation Partnership Project (3GPP).

6. 6. The relay device according to claim 5, wherein the transmitting means transmits, as the message, a Backhaul Adaptation Protocol (BAP) PDU in which a value indicating a notice of relay stop is set in a Protocol Data Unit (PDU) type field.

7. A relay device that is included in a relay path that relays communication between a network and a terminal, and is an IAB node that performs relay based on IAB (Integrated Access and Backhaul) defined by the Third Generation Partnership Project (3GPP), a receiving means for receiving a message informing of a relay stop from a first other relay device connected to the relay device on the network side along the relay route; a connection means for executing a process for connecting to a second other relay device connectable to the network before the first other relay device stops relaying based on the reception of the message; a transmitting means for, when receiving a Backhaul Radio Link Failure (BH RLF) from the first other relay device, transmitting the BH RLF to a third other relay device connected to the relay device on the opposite side of the network in the relay route, and, when receiving the message informing of the stop of relay, not transmitting the message to the third other relay device; A relay device comprising:

8. 8. The relay device according to claim 7, wherein the connection unit switches the connection destination from the first other relay device to the second other relay device before the first other relay device stops relaying.

9. 8. The relay device according to claim 7, wherein the connection means searches for the second other relay device before the first other relay device stops relaying, and switches the connection destination from the first other relay device to the second other relay device in response to the first other relay device stopping relaying.

10. 10. The relay device according to claim 7, wherein, when the message contains information about a communication device connected to the first other relay device on the network side of the relay route, the connection means treats the communication device as the second other communication device and executes processing for connection with the second other relay device.

11. 11. The relay device according to claim 10, wherein, when the message does not include information about a communication device connected to the first other relay device on the network side of the relay route, the connection means selects the second other communication device from among the other communication devices based on the reception strength of a signal transmitted from the other communication device.

12. 12. The relay device according to claim 7, wherein, when the message includes information indicating a scheduled time at which the first other relay device will stop relaying, the connection unit completes the processing by the scheduled time.

13. 13. The relay device according to claim 12, wherein the connection unit completes the process of establishing a connection with the second other relay device by the scheduled time.

14. 13. The relay device according to claim 12, wherein the connection unit completes the process of setting the relay route via the second other relay device by the scheduled time.

15. A control method executed by a relay device included in a relay path that relays communication between a network and a terminal, comprising: A control method characterized by including, when there is a schedule for stopping the relay, sending a message informing a first other relay device connected to the relay device on the opposite side of the network on the relay route of the message, when the time reaches a predetermined time before the scheduled time for stopping the relay.

16. A control method executed by a relay device that is included in a relay path that relays communication between a network and a terminal and is an IAB node that performs relay based on IAB (Integrated Access and Backhaul) defined by the Third Generation Partnership Project (3GPP), comprising: receiving a message informing of a relay stop from a first other relay device connected to the relay device on the network side along the relay path; Based on the reception of the message, before the first other relay device stops relaying, executing a process for connection with a second other relay device connectable to the network; When a Backhaul Radio Link Failure (BH RLF) is received from the first other relay device, the BH RLF is transmitted to a third other relay device connected to the relay device on the opposite side of the network in the relay path, and when the message informing the relay device of the stop of relay is received, the message is not transmitted to the third other relay device; A control method comprising:

17. A program for causing a computer to function as the relay device according to any one of claims 1 to 14.

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