COMMUNICATION CONTROL METHOD, DONOR NODE, AND SYSTEM

Abstract

To provide a method for a relay node to smoothly perform handover or connection re-establishment from a source base station to a target base station.SOLUTION: In a cellular communication system, a communication control method includes a donor node (donor gNB 200-1) transmitting configuration information regarding connection established between a distributed unit of a relay node (IAB node 300) and the donor node, to another donor node (target gNB 200-2).SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a communication control method for use in a cellular communication system. [Background technology]

[0002] In the 3GPP (3rd Generation Partnership Project) (registered trademark, hereinafter the same), which is a standardization project for cellular communication systems, the introduction of a new relay node called an IAB (Integrated Access and Backhaul) node is being considered. One or more relay nodes are involved in communication between a base station and a user device, and relay this communication. Summary of the Invention

[0003] A communication control method according to a first aspect is a communication control method for performing handover or connection re-establishment of a relay node from a source base station to a target base station, and includes the source base station transmitting fronthaul setting information regarding a fronthaul connection established between a distributed unit of the relay node and the source base station to the target base station.

[0004] A communication control method according to a second aspect is a communication control method for performing handover of a parent relay node having a child relay node from a source base station to a target base station, and includes a step of transferring context information of the child relay node from the source base station to the target base station, and a step of the target base station transmitting an RRC (Radio Resource Control) reconfiguration message to the child relay node via the parent relay node based on the context information. [Brief description of the drawings]

[0005] [Figure 1] 1 is a diagram showing a configuration of a cellular communication system according to an embodiment; [Diagram 2]FIG. 2 is a diagram showing the relationship between IAB nodes, parent nodes, and child nodes. [Diagram 3] FIG. 2 is a diagram illustrating a configuration of a base station according to an embodiment. [Figure 4] FIG. 2 is a diagram illustrating a configuration of a relay node according to an embodiment. [Diagram 5] FIG. 2 is a diagram illustrating a configuration of a user device according to an embodiment. [Figure 6] FIG. 2 is a diagram illustrating a configuration of a protocol stack according to an embodiment. [Figure 7] FIG. 2 illustrates a protocol stack for the F1-U protocol. [Figure 8] FIG. 2 illustrates a protocol stack for the F1-C protocol. [Figure 9] FIG. 2 is a diagram illustrating the operation of a cellular communication system according to one embodiment. [Figure 10] FIG. 13 is a diagram illustrating the operation of the first modified example. [Figure 11] FIG. 13 is a diagram illustrating the operation of the second modified example. [Figure 12] FIG. 13 is a diagram illustrating the operation of the third modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The present disclosure aims to enable a relay node to smoothly perform a handover or connection re-establishment from a source base station to a target base station.

[0007] A cellular communication system according to an embodiment will now be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0008] (Configuration of Cellular Communication System) First, a configuration of a cellular communication system according to an embodiment will be described. Fig. 1 is a diagram showing a configuration of a cellular communication system 1 according to an embodiment.

[0009] The cellular communication system 1 is a fifth generation (5G) cellular communication system based on the 3GPP standard. Specifically, the wireless access method in the cellular communication system 1 is NR (New Radio), which is a 5G wireless access method. However, LTE (Long Term Evolution) may be applied at least partially to the cellular communication system 1.

[0010] As shown in Fig. 1, the cellular communication system 1 includes a 5G core network (5GC) 10, a user equipment (UE: User Equipment) 100, a base station (called a gNB) 200, and an IAB node 300. The IAB node 300 is an example of a relay node.

[0011] In the following, an example in which the base station is an NR base station is mainly described, but the base station may also be an LTE base station (i.e., an eNB).

[0012] The 5GC 10 has an Access and Mobility Management Function (AMF) 11 and a User Plane Function (UPF) 12. The AMF 11 is a device that performs various mobility controls for the UE 100. The AMF 11 manages information on the area in which the UE 100 is located by communicating with the UE 100 using Non-Access Stratum (NAS) signaling. The UPF 12 is a device that performs transfer control of user data.

[0013] Each gNB 200 is a fixed wireless communication node and manages one or more cells. A cell is used as a term indicating the smallest unit of a wireless communication area. A cell may be used as a term indicating a function or resource for performing wireless communication with a UE 100. One cell belongs to one carrier frequency.

[0014] Each gNB 200 is mutually connected to the 5GC 10 via an interface called an NG interface. In FIG. 1, two gNBs 200-1 and 200-2 connected to the 5GC 10 are illustrated.

[0015] Each gNB 200 is connected to other adjacent gNBs 200 via an inter-base station interface called an Xn interface. In FIG. 1, an example in which gNB 200-1 is connected to gNB 200-2 is shown.

[0016] Each gNB 200 may be divided into a central unit (CU) and a distributed unit (DU). The CU and the DU are connected to each other via an interface called an F1 interface. The F1 protocol is a communication protocol between the CU and the DU, and includes an F1-C protocol, which is a control plane protocol, and an F1-U protocol, which is a user plane protocol.

[0017] The cellular communication system 1 uses NR for backhaul and supports IAB, which enables wireless relay of NR access. The donor gNB 200-1 is a terminal node of the NR backhaul on the network side, and is a gNB 200 with additional functions that support IAB. The backhaul can be multi-hopped via multiple hops (i.e., multiple IAB nodes 300).

[0018] FIG. 1 illustrates an example in which IAB node 300-1 wirelessly connects to donor gNB 200-1, IAB node 300-2 wirelessly connects to IAB node 300-1, and the F1 protocol is transmitted over two backhaul hops.

[0019] The UE 100 is a mobile wireless communication device that performs wireless communication with a cell. The UE 100 may be any device that performs wireless communication with the gNB 200 or the IAB node 300. For example, the UE 100 is a mobile phone terminal, a tablet terminal, a laptop PC, a sensor or a device provided in a sensor, and / or a vehicle or a device provided in a vehicle. The UE 100 wirelessly connects to the IAB node 300 or the gNB 200 via an access link. FIG. 1 shows an example in which the UE 100 is wirelessly connected to the IAB node 300-2. The UE 100 indirectly communicates with the donor gNB 200-1 via the IAB node 300-2 and the IAB node 300-1.

[0020] FIG. 2 is a diagram showing the relationship between the IAB node 300, parent nodes, and child nodes.

[0021] As shown in FIG. 2, each IAB node 300 has an IAB-DU corresponding to a base station function unit and an IAB-MT (Mobile Termination) corresponding to a user equipment function unit.

[0022] The neighboring node (i.e., upper node) on the NR Uu radio interface of the IAB-MT is called a parent node. The parent node is a parent IAB node or a DU of the donor gNB 200. The radio link between the IAB-MT and the parent node is called a backhaul link. In FIG. 2, an example is shown in which the parent nodes of the IAB node 300 are IAB nodes 300P1 and 300P2. The direction toward the parent node is called upstream.

[0023] Adjacent nodes (i.e., lower nodes) on the NR access interface of the IAB-DU are called child nodes. The IAB-DU manages cells, similar to the gNB 200. The IAB-DU terminates the NR Uu radio interface to the UE 100 and the lower IAB nodes. The IAB-DU supports the F1 protocol to the CU of the donor gNB 200-1. In FIG. 2, an example is shown in which the child nodes of the IAB node 300 are IAB nodes 300C1 to 300C3. The direction toward the child nodes is called downstream.

[0024] (Base station configuration) Next, a configuration of the gNB 200, which is a base station according to an embodiment, will be described. Fig. 3 is a diagram showing the configuration of the gNB 200. As shown in Fig. 3, the gNB 200 has a wireless communication unit 210, a network communication unit 220, and a control unit 230.

[0025] The wireless communication unit 210 performs wireless communication with the UE 100 and wireless communication with the IAB node 300. The wireless communication unit 210 has a receiving unit 211 and a transmitting unit 212. The receiving unit 211 performs various receptions under the control of the control unit 230. The receiving unit 211 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 230. The transmitting unit 212 performs various transmissions under the control of the control unit 230. The transmitting unit 212 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 230 into a wireless signal, and transmits the signal from the antenna.

[0026] The network communication unit 220 performs wired communication (or wireless communication) with the 5GC10 and wired communication (or wireless communication) with other adjacent gNBs 200. The network communication unit 220 has a receiving unit 221 and a transmitting unit 222. The receiving unit 221 performs various receptions under the control of the control unit 230. The receiving unit 221 receives a signal from the outside and outputs the received signal to the control unit 230. The transmitting unit 222 performs various transmissions under the control of the control unit 230. The transmitting unit 222 transmits the transmission signal output by the control unit 230 to the outside.

[0027] The control unit 230 performs various controls in the gNB 200. The control unit 230 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processing. The processor performs processing of each layer, which will be described later.

[0028] (Configuration of relay node) Next, a configuration of the IAB node 300, which is a relay node according to an embodiment, will be described. Fig. 4 is a diagram showing the configuration of the IAB node 300. As shown in Fig. 4, the IAB node 300 has a wireless communication unit 310 and a control unit 320. The IAB node 300 may have a plurality of wireless communication units 310.

[0029] The wireless communication unit 310 performs wireless communication (BH link) with the gNB 200 and wireless communication (access link) with the UE 100. The wireless communication unit 310 for BH link communication and the wireless communication unit 310 for access link communication may be provided separately.

[0030] The wireless communication unit 310 has a receiving unit 311 and a transmitting unit 312. The receiving unit 311 performs various receptions under the control of the control unit 320. The receiving unit 311 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal), and outputs the signal to the control unit 320. The transmitting unit 312 performs various transmissions under the control of the control unit 320. The transmitting unit 312 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 320 into a wireless signal, and transmits the signal from the antenna.

[0031] The control unit 320 performs various controls in the IAB node 300. The control unit 320 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processing. The processor performs processing of each layer, which will be described later.

[0032] (Configuration of user device) Next, a configuration of a UE 100 which is a user device according to an embodiment will be described. Fig. 5 is a diagram showing the configuration of the UE 100. As shown in Fig. 5, the UE 100 includes a radio communication unit 110 and a control unit 120.

[0033] The wireless communication unit 110 performs wireless communication in an access link, that is, wireless communication with the gNB 200 and wireless communication with the IAB node 300. The wireless communication unit 110 may also perform wireless communication in a side link, that is, wireless communication with another UE 100. The wireless communication unit 110 has a receiving unit 111 and a transmitting unit 112. The receiving unit 111 performs various receptions under the control of the control unit 120. The receiving unit 111 includes an antenna, and converts a wireless signal received by the antenna into a baseband signal (received signal) and outputs the signal to the control unit 120. The transmitting unit 112 performs various transmissions under the control of the control unit 120. The transmitting unit 112 includes an antenna, and converts a baseband signal (transmitted signal) output by the control unit 120 into a wireless signal and transmits the signal from the antenna.

[0034] The control unit 120 performs various controls in the UE 100. The control unit 120 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processing. The processor performs processing of each layer, which will be described later.

[0035] (Protocol stack configuration) Next, a configuration of a protocol stack according to an embodiment will be described below. Fig. 6 is a diagram showing a protocol stack related to an RRC connection and a NAS connection of an IAB-MT.

[0036] As shown in FIG. 6, the IAB-MT of IAB node 300-2 has a physical (PHY) layer, a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, a Packet Data Convergence Protocol (PDCP) layer, a Radio Resource Control (RRC) layer, and a Non-Access Stratum (NAS) layer.

[0037] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the IAB-MT of the IAB node 300-2 and the PHY layer of the IAB-DU of the IAB node 300-1 via a physical channel.

[0038] The MAC layer performs data priority control, retransmission processing using hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of the IAB-MT of IAB node 300-2 and the MAC layer of the IAB-DU of IAB node 300-1 via a transport channel. The MAC layer of the IAB-DU includes a scheduler. The scheduler determines the transport format (transport block size, modulation and coding scheme (MCS)) and the assigned resource blocks for uplink and downlink.

[0039] The RLC layer transmits data to the RLC layer on the receiving side by utilizing the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the IAB-MT of the IAB node 300-2 and the RLC layer of the IAB-DU of the IAB node 300-1 via a logical channel.

[0040] The PDCP layer performs header compression / decompression and encryption / decryption. Data and control information are transmitted between the PDCP layer of the IAB-MT of the IAB node 300-2 and the PDCP layer of the donor gNB 200-1 via a radio bearer.

[0041] The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. RRC signaling for various settings is transmitted between the RRC layer of the IAB-MT of the IAB node 300-2 and the RRC layer of the donor gNB 200-1. When there is an RRC connection with the donor gNB 200-1, the IAB-MT is in the RRC connected mode. When there is no RRC connection with the donor gNB 200-1, the IAB-MT is in the RRC idle mode.

[0042] The NAS layer, which is located above the RRC layer, performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the IAB-MT of the IAB node 300-2 and the AMF 11.

[0043] Fig. 7 is a diagram showing a protocol stack for the F1-U protocol. Fig. 8 is a diagram showing a protocol stack for the F1-C protocol. Here, an example is shown in which the donor gNB 200-1 is divided into a CU and a DU.

[0044] As shown in Fig. 7, each of the IAB-MT of the IAB node 300-2, the IAB-DU of the IAB node 300-1, the IAB-MT of the IAB node 300-1, and the DU of the donor gNB 200-1 has a BAP (Backhaul Adaptation Protocol) layer as a layer above the RLC layer. The BAP layer is a layer that performs routing processing and bearer mapping / demapping processing. In the backhaul, the IP layer is transmitted through the BAP layer, enabling routing in multiple hops.

[0045] In each backhaul link, PDUs (Protocol Data Units) of the BAP layer are transmitted by a backhaul RLC channel (BH NR RLC channel). By configuring multiple backhaul RLC channels in each BH link, traffic prioritization and QoS control are possible. The association between BAP PDUs and backhaul RLC channels is performed by the BAP layer of each IAB node 300 and the BAP layer of the donor gNB 200-1.

[0046] As shown in FIG. 8, the protocol stack of the F1-C protocol has an F1AP layer and an SCTP layer instead of the GTP-U layer and UDP layer shown in FIG.

[0047] (Operation of a Cellular Communication System) Next, an operation of the cellular communication system 1 according to an embodiment will be described. This operation is an operation for performing handover of the IAB node 300 from a source gNB 200-1 (source base station) to a target gNB 200-2 (target base station).

[0048] In the following, an example will be described in which a child node IAB node 300-2 (hereinafter referred to as "child IAB node 300-2") is connected to a parent node IAB node 300-1 (hereinafter referred to as "parent IAB node 300-1"), and handover of the child IAB node 300-2 is performed together with handover of the parent IAB node 300-1. However, this operation may be an operation in which handover of only one IAB node 300 is performed from a source gNB 200-1 (source base station) to a target gNB 200-2 (target base station).

[0049] Fig. 9 is a diagram showing the operation of the cellular communication system 1 according to one embodiment. In Fig. 9, non-essential steps are shown with dashed lines.

[0050] 9, in step S101, an F1 interface connection (hereinafter referred to as "F1 connection") and an RRC connection are established between the child IAB node 300-2 and the source gNB 200-1. In addition, in step S102, an F1 connection and an RRC connection are established between the parent IAB node 300-1 and the source gNB 200-1. The F1 connection is an example of a fronthaul connection.

[0051] In step S103, the IAB-MT of the parent IAB node 300-1 transmits a measurement report including a measurement result of a radio condition to the source gNB 200-1. The measurement report is included in a message of the RRC layer.

[0052] In step S104, the RRC layer of the source gNB 200-1 decides to handover the parent IAB node 300-1 to the target gNB 200-2 based on the measurement report from the parent IAB node 300-1.

[0053] In step S105, the source gNB 200-1 transmits a handover request (HO Request) requesting handover of the parent IAB node 300-1 to the target gNB 200-2 via the Xn interface, which is an inter-base station interface.

[0054] In step S106, the target gNB 200-2 performs admission control to determine whether or not handover of the parent IAB node 300-1 is possible based on the handover request from the source gNB 200-1. Here, the description will proceed on the assumption that the handover is possible. The target gNB 200-2 modifies the RRC context information included in the handover request as necessary.

[0055] In step S107, the target gNB200-2 sends a handover response (HO Response) to the source gNB200-1 via the Xn interface.

[0056] In step S108, the source gNB 200-1 sends an F1 Removal Request to the child IAB node 300-2, requesting removal of the F1 connection, via the F1 interface between the child IAB node 300-2 and the source gNB 200-1.

[0057] Here, the source gNB 200-1 transmits an F1 deletion request to the child IAB node 300-2, which is farther from the source gNB 200-1 in the IAB topology, rather than to the parent IAB node 300-1, which is closer to the source gNB 200-1 in the IAB topology. This is because if the F1 connection of the parent IAB node 300-1 is deleted first, the IAB-DU of the parent IAB node 300-1 may stop functioning, making it impossible to continue providing service to the child IAB node 300-2.

[0058] In step S109, in response to receiving the F1 removal request, the child IAB node 300-2 transmits an F1 removal response to the source gNB 200-1 via the F1 interface between the child IAB node 300-2 and the source gNB 200-1.

[0059] In step S110, the source gNB 200-1 sends an RRC message (RRC de-activation) to the child IAB node 300-2 requesting RRC deactivation or suspend.

[0060] In step S111, the IAB-DU of the child IAB node 300-2 stops the service (Service stop).

[0061] In step S112, the source gNB 200-1 sends an F1 Removal Request to the parent IAB node 300-1, requesting removal of the F1 connection, via the F1 interface between the parent IAB node 300-1 and the source gNB 200-1.

[0062] In step S113, in response to receiving the F1 removal request, the parent IAB node 300-1 transmits an F1 removal response to the source gNB 200-1 via the F1 interface between the parent IAB node 300-1 and the source gNB 200-1.

[0063] In step S114, the IAB-DU of the parent IAB node 300-1 stops the service (Service stop).

[0064] Thus, in the handover operation according to one embodiment, the F1 connection is deleted before executing the handover procedure (RRC handover) in the RRC layer.

[0065] However, if the old F1 connection is automatically deleted when a later RRC handover is performed, the process of deleting the F1 connection (i.e., steps S108 to S114) is not necessary. Under such an assumption, the RRC layer of each IAB node 300 may notify the F1AP layer of its own IAB node 300 of the completion of the handover or a request to delete the F1 connection when the RRC handover is completed (RRC Reconfiguration Complete).

[0066] In step S115, the source gNB 200-1 transmits an RRC message (RRC Reconfiguration) equivalent to a handover command (Handover Command) instructing a handover to the target gNB 200-2 to the parent IAB node 300-1. In response to receiving the RRC Reconfiguration message, the IAB-MT of the parent IAB node 300-1 performs a backhaul RLC channel reestablishment (BH RLC CH Reestablishment) and a routing update (Routing Update). The source gNB 200-1 may include an indicator to delete the F1 connection in the RRC message equivalent to the handover command. The RRC entity (IAB-MT) that receives the indicator may notify the F1 entity that it has received the indicator for deleting the F1 connection.

[0067] In step S116, the IAB-MT of the parent IAB node 300-1 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. This completes the handover procedure in the RRC layer of the parent IAB node 300-1. In addition, the RRC message may indicate completion of the F1 connection removal. The F1 entity may notify the RRC entity that the F1 connection removal is completed, and the RRC entity may transmit the RRC message based on the notification. Furthermore, when the RRC reconfiguration is completed (or when the transmission of the RRC message is completed), the RRC entity may notify the F1 entity that the handover is completed. The notification triggers an F1 setup request (S118) to be described later. That is, the F1 entity that receives the notification transmits an F1 setup request.

[0068] In step S117, the target gNB 200-2 transmits a message (UE Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the context information of the parent IAB node 300-1. Note that this message may not be transmitted in this step, but may be transmitted after this procedure is completed, i.e., after step S129.

[0069] In step S118, the parent IAB node 300-1 sends an F1 message (F1 Setup Request) to the target gNB 200-2 requesting setup of an F1 connection between the target gNB 200-2 and the parent IAB node 300-1.

[0070] In step S119, the target gNB 200-2 transmits an F1 message (F1 Setup Response) to the parent IAB node 300-1 indicating the setup of an F1 connection between the target gNB 200-2 and the parent IAB node 300-1. Steps S118 and S119 result in the setup of an F1 connection between the target gNB 200-2 and the parent IAB node 300-1, and the setup of an IAB-DU of the parent IAB node 300-1.

[0071] In step S120, the IAB-DU of parent IAB node 300-1 resumes providing the service.

[0072] By the processing of steps S115 to S119, an F1 connection and an RRC connection between the target gNB 200-2 and the parent IAB node 300-1 are established (step S121).

[0073] In step S122, the source gNB 200-1 transfers the context information of the child IAB node 300-2 to the target gNB 200-2 via the Xn interface (Child Context Transfer). The target gNB 200-2 modifies the context information of the child IAB node 300-2 as necessary.

[0074] In step S123, the target gNB 200-2 sends an RRC reconfiguration message (RRC Re-activation) to the child IAB node 300-2, requesting RRC activation or restoration, based on the context information of the child IAB node 300-2.

[0075] In step S124, the IAB-MT of the child IAB node 300-2 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. Through the processing of steps S122 to S124, handover from the source gNB 200-1 to the target gNB 200-2 is performed in the RRC layer of the child IAB node 300-2. In addition, the RRC message may indicate completion of the F1 connection removal. The F1 entity may notify the RRC entity that the F1 connection removal is completed, and the RRC entity may transmit the RRC message based on the notification. Furthermore, when the RRC reconfiguration is completed (or when the transmission of the RRC message is completed), the RRC entity may notify the F1 entity that the handover is completed. The notification triggers an F1 setup request (S126) to be described later. That is, the F1 entity that receives the notification transmits an F1 setup request.

[0076] In step S125, the target gNB 200-2 sends a message (UE Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the context information of the child IAB node 300-2.

[0077] In step S126, the child IAB node 300-2 sends an F1 message (F1 Setup Request) to the target gNB 200-2 requesting setup of an F1 connection between the target gNB 200-2 and the child IAB node 300-2.

[0078] In step S127, the target gNB 200-2 transmits an F1 message (F1 Setup Response) to the child IAB node 300-2 indicating the setup of the F1 connection between the target gNB 200-2 and the child IAB node 300-2. Steps S126 and S127 result in the setup of the F1 connection between the target gNB 200-2 and the child IAB node 300-2, and the setup of the IAB-DU of the child IAB node 300-2.

[0079] In step S128, the IAB-DU of the child IAB node 300-2 resumes providing the service.

[0080] By the processing of steps S122 to S127, an F1 connection and an RRC connection between the target gNB 200-2 and the child IAB node 300-2 are established (step S129).

[0081] (Example of Modification of Cellular Communication System Operation) Although the operation according to the embodiment described above (see FIG. 9) can smoothly perform the handover of the IAB node 300, it causes a service interruption during the handover of the parent IAB node 300-1 and requires a relatively large amount of signaling. In the following, a method for performing a more efficient handover (or RRC re-establishment) will be described.

[0082] The communication control method according to the modified example is a method for performing a relay node handover or a connection re-establishment from a source gNB 200-1 to a target gNB 200-2. The communication control method includes a step of transmitting fronthaul configuration information related to an F1 connection (fronthaul connection) established between an IAB-DU of an IAB node 300 and a source gNB 200-1 from the source gNB 200-1 to the target gNB 200-2. Hereinafter, such fronthaul configuration information is referred to as F1 context information.

[0083] In this manner, by transmitting F1 context information from source gNB 200-1 to target gNB 200-2, relocation of the F1 connection of the IAB-DU of IAB node 300 from source gNB 200-1 to target gNB 200-2 is facilitated.

[0084] (1) Change Example 1 Fig. 10 is a diagram showing the operation of Modification Example 1. In Fig. 10, non-essential steps are shown with dashed lines.

[0085] 10, in step S201, an F1 connection and an RRC connection are established between the child IAB node 300-2 and the source gNB 200-1. In addition, in step S202, an F1 connection and an RRC connection are established between the parent IAB node 300-1 and the source gNB 200-1.

[0086] In step S203, the IAB-MT of the parent IAB node 300-1 transmits a measurement report including a measurement result of a radio condition to the source gNB 200-1. The measurement report is included in a message of the RRC layer.

[0087] In step S204, the RRC layer of the source gNB 200-1 decides on handover and F1 relocation of the parent IAB node 300-1 to the target gNB 200-2 based on the measurement report from the parent IAB node 300-1 (RRC HO & F1 Relocation decision).

[0088] In step S205, the source gNB 200-1 transmits a request message (F1 Relocation Request) to the target gNB 200-2 via the Xn interface. This request message is a message for requesting relocation of the F1 connection from the source gNB 200-1 to the target gNB 200-2, and includes F1 context information (fronthaul configuration information).

[0089] The request message (F1 Relocation Request) includes at least one of the following pieces of information A to C.

[0090] A) F1 context information of parent IAB node 300-1 The F1 context information of the parent IAB node 300-1 includes at least one of the following pieces of information A1 to A7.

[0091] A1) Transaction ID A2) gNB-CU name (human-readable name) A3) List of cell information for IAB-DU to be activated Each entry in the list includes at least one of the following: cell ID (NR CGI, NR PCI), system information (SIB held by the CU), and PLMN list. A4) gNB RRC version A5) Identifier of parent IAB node 300-1 (DU and MT) The identifier of the parent IAB node 300-1 may be a transaction ID and / or a C-RNTI. The identifier of the parent IAB node 300-1 is used to determine whether the IAB node 300 connecting to the target gNB 200-2 is a target of this relocation process. A6) IP address of parent IAB node 300-1 (DU) Assuming that the IP address of the parent IAB node 300-1 will not change even after the handover, the target gNB 200-2 can utilize this IP address by transmitting it to the target gNB 200-2. A7) F1 setting information associated with UE 100 This F1 configuration information includes at least one of the following: F1AP ID, RRC-related configuration, DRX configuration, bearer configuration (QoS, S-NSSAI, TNL configuration, etc.), and serving PLMN·AMBR configuration.

[0092] B) F1 context information of child IAB node 300-2 The F1 context information of the child IAB node 300-2 includes information similar to that of A1 to A7 above. However, the parent IAB node 300-1 in A1 to A7 above is replaced with the child IAB node 300-2. When the F1 context information of the child IAB node 300-2 is also transferred from the source gNB 200-1 to the target gNB 200-2, it becomes possible to perform the F1 rearrangement of the parent IAB node 300-1 and the F1 rearrangement of the child IAB node 300-2 together.

[0093] C) RRC context information of parent IAB node 300-1 and RRC context information of child IAB node 300-2 The F1 context information is context information related to the IAB-DU, whereas the RRC context information is context information related to the IAB-MT. In addition, the F1 context information is used for relocation of the F1 connection, whereas the RRC context information is used for switching (i.e., handover) of the RRC connection. The RRC context information may be referred to as UE context information.

[0094] This operation sequence shows an example in which both F1 context information and RRC context information are included in one request message (F1 Relocation Request). However, this operation sequence may be an operation in which a handover request message (HO Request) including RRC context information and a request message (F1 Relocation Request) including F1 context information are separately transmitted and received.

[0095] In step S206, the target gNB 200-2 performs admission control to determine whether or not handover between the parent IAB node 300-1 and the child IAB node 300-2 is possible, based on the request message from the source gNB 200-1. Here, the description will proceed on the assumption that handover is possible. The target gNB 200-2 modifies the F1 context information and the RRC context information included in the request message as necessary.

[0096] In step S207, in response to receiving the request message, the target gNB 200-2 transmits a response message (F1 Relocation Response) to the request message to the source gNB 200-1 via the Xn interface. The response message includes at least one of F1 information (fronthaul modification information) indicating modification contents to the F1 setting information, RRC information indicating modification contents to the RRC setting information, and the IP address of the target gNB 200-2. The RRC information may be included in a handover command.

[0097] The response message (F1 Relocation Response) includes at least one of the F1 context information of the parent IAB node 300-1 and the F1 context information of the child IAB node 300-2. The target gNB 200-2 may include the F1 context information corresponding to the changed part in the response message only when there is a change in the F1 context information from the source gNB 200-1. For example, it is desirable that the Cell ID of the IAB-DU does not change before and after the F1 relocation. However, when the IAB node 300 is movable, the cell ID may be changed at the moving destination.

[0098] The response message (F1 Relocation Response) includes at least one of a handover command (RRC information) of the parent IAB node 300-1 and a handover command (RRC information) of the child IAB node 300-2.

[0099] The response message (F1 Relocation Response) may include an IP address of the IAB-DU of the parent IAB node 300-1, which may be an IP address determined or selected by the target gNB 200-2.

[0100] The response message (F1 Relocation Response) may include the IP address of the target gNB 200-2. This IP address may be included in the handover command.

[0101] In step S208, in response to receiving the response message (F1 Relocation Response), the source gNB 200-1 sends an F1 relocation message (F1 Relocation) including information for the child IAB node 300-2 in the response message to the child IAB node 300-2 via the F1 connection between the IAB-DU of the child IAB node 300-2 and the source gNB 200-1.

[0102] The F1 relocation message (F1 Relocation) includes at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the child IAB node 300-2. However, at least one of the IP address of the target gNB 200-2 and the new IP address of the child IAB node 300-2 may be included in the RRC Reconfiguration (handover command) of step S210 described later.

[0103] The source gNB 200-1 sends an F1 relocation message (F1 Relocation) to the child IAB node 300-2, which is farther from the source gNB 200-1 in the IAB topology, rather than to the parent IAB node 300-1, which is closer to the source gNB 200-1 in the IAB topology.

[0104] In addition, the source gNB 200-1 transmits an F1 relocation message (F1 Relocation) to the child IAB node 300-2 before transmitting an RRC Reconfiguration (handover command) to the child IAB node 300-2 (step S210).

[0105] In addition, when the child IAB node 300-2 receives uplink data from a child node or UE 100 while processing F1 relocation (i.e., when the child IAB node 300-2 has not notified the target gNB 200-2 of the completion of F1 relocation), the child IAB node 300-2 may buffer the data and transfer the data to the target gNB 200-2 after the F1 relocation to the target gNB 200-2 is completed.

[0106] In step S209, the child IAB node 300-2 sends a response message (F1 Relocation Acknowledge) indicating that it has received the F1 relocation message (or that it has started the F1 relocation process) to the source gNB 200-1 via the F1 connection between the IAB-DU of the child IAB node 300-2 and the source gNB 200-1.

[0107] In step S210, the source gNB 200-1 sends an RRC Reconfiguration (handover command), which is an RRC message instructing a handover to the target gNB 200-2, to the child IAB node 300-2.

[0108] In step S211, the source gNB 200-1 sends an F1 relocation message (F1 Relocation) including information for the parent IAB node 300-1 in the response message (F1 Relocation Acknowledge) to the parent IAB node 300-1 via the F1 connection between the IAB-DU of the parent IAB node 300-1 and the source gNB 200-1.

[0109] The F1 relocation message (F1 Relocation) includes at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the parent IAB node 300-1. However, at least one of the IP address of the target gNB 200-2 and the new IP address of the parent IAB node 300-1 may be included in the RRC Reconfiguration (handover command) of step S213 described later.

[0110] Here, the source gNB 200-1 transmits an F1 relocation message (F1 Relocation) to the parent IAB node 300-1 before transmitting an RRC Reconfiguration (handover command) to the parent IAB node 300-1 (step S213).

[0111] In addition, when the parent IAB node 300-1 receives uplink data from a child node or UE 100 while the F1 relocation is being processed (i.e., when the parent IAB node 300-1 has not notified the target gNB 200-2 of the completion of F1 relocation), the parent IAB node 300-1 may buffer the data and transfer the data to the target gNB 200-2 after the F1 relocation to the target gNB 200-2 is completed.

[0112] In step S212, the parent IAB node 300-1 transmits a response message (F1 Relocation Acknowledge) indicating that it has received the F1 relocation message (or that it will start the F1 relocation process) to the source gNB 200-1 via the F1 connection between the IAB-DU of the parent IAB node 300-1 and the source gNB 200-1. Note that step S212 is not a required step.

[0113] In step S213, the source gNB 200-1 sends an RRC Reconfiguration (handover command), which is an RRC message instructing a handover to the target gNB 200-2, to the parent IAB node 300-1.

[0114] In step S214, the IAB-MT of the parent IAB node 300-1 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. This completes the handover procedure in the RRC layer of the parent IAB node 300-1. At this time, the RRC entity may notify the F1 entity that the RRC reconfiguration has been completed. In other words, the notification may trigger an F1 relocation complete message (S215).

[0115] In step S215, the IAB-DU of the parent IAB node 300-1 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes F1 relocation of the parent IAB node 300-1. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the parent IAB node 300-1 (DU and MT).

[0116] In step S216, the target gNB 200-2 sends a message (UE Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the RRC context information of the parent IAB node 300-1.

[0117] In step S217, the target gNB 200-2 sends a message (F1 Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the F1 context information of the parent IAB node 300-1.

[0118] In this manner, by the processing of steps S211 to S217, rearrangement of the F1 connection of the parent IAB node 300-1 and handover at the RRC layer of the parent IAB node 300-1 are performed (step S218).

[0119] In step S219, the IAB-MT of the child IAB node 300-2 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. This completes the handover procedure in the RRC layer of the child IAB node 300-2. At this time, the RRC entity may notify the F1 entity that the RRC reconfiguration has been completed. In other words, the notification may trigger an F1 relocation complete message (S220).

[0120] In step S220, the IAB-DU of the child IAB node 300-2 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes the F1 relocation of the child IAB node 300-2. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the child IAB node 300-2 (DU and MT).

[0121] In step S221, the target gNB 200-2 sends a message (UE Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the RRC context information of the child IAB node 300-2.

[0122] In step S222, the target gNB 200-2 sends a message (F1 Context Release) to the source gNB 200-1 via the Xn interface to cause the source gNB 200-1 to release the F1 context information of the child IAB node 300-2.

[0123] In this manner, by the processes of steps S208 to S210 and steps S219 to S222, rearrangement of the F1 connection of child IAB node 300-2 and handover at the RRC layer of child IAB node 300-2 are performed (step S223).

[0124] According to modification example 1, by introducing a rearrangement process for F1 connection, the IAB node 300 can perform a handover from the source gNB 200-1 to the target gNB 200-2 while continuing the service.

[0125] (2) Change Example 2 Fig. 11 is a diagram showing the operation of Modification Example 2. In Fig. 11, non-essential steps are shown with dashed lines.

[0126] As shown in FIG. 11, the processes in steps S301 to S307 are similar to the processes in steps S101 to S107 in the above-described embodiment.

[0127] In step S308, the source gNB 200-1 transmits an RRC Reconfiguration (handover command), which is an RRC message instructing a handover to the target gNB 200-2, to the child IAB node 300-2. The source gNB 200-1 may include information indicating that the handover is between different gNBs 200 (different CUs) (Inter-CU HO Indication) in the RRC Reconfiguration (handover command).

[0128] In step S309, the source gNB 200-1 transmits an RRC Reconfiguration (handover command), which is an RRC message instructing a handover to the target gNB 200-2, to the parent IAB node 300-1. The source gNB 200-1 may include information indicating that the handover is between different gNBs 200 (different CUs) (Inter-CU HO Indication) in the RRC Reconfiguration (handover command).

[0129] In step S310, the IAB-MT of the parent IAB node 300-1 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. This completes the handover procedure in the RRC layer of the parent IAB node 300-1.

[0130] Here, the IAB-MT of the parent IAB node 300-1 may send a relocation request (F1 Relocation Request) in an RRC message (RRC Reconfiguration Complete) to request relocation of the F1 connection from the source gNB 200-1 to the target gNB 200-2.

[0131] In addition, the IAB-MT of the parent IAB node 300-1 may include the identifier (Source-donor ID) of the source gNB 200-1 or the identifier (Source Cell ID) of the source cell in an RRC message (RRC Reconfiguration Complete) and transmit it.

[0132] Furthermore, the IAB-MT of parent IAB node 300-1 may include its own node's IP address in an RRC message (RRC Reconfiguration Complete) and transmit it.

[0133] In addition, the IAB-MT of the parent IAB node 300-1 may send at least one of the relocation request (F1 Relocation Request), the identifier of the source gNB 200-1 (Source-donor ID), the identifier of the source cell (Source Cell ID), and the IP address of the node itself in a message other than the RRC Reconfiguration Complete.

[0134] In step S311, the target gNB 200-2 sends a request message (F1 Context Fetch) to the source gNB 200-1 via the Xn interface to obtain F1 context information (fronthaul configuration information) of the parent IAB node 300-1.

[0135] In step S312, in response to receiving the request message, the source gNB 200-1 sends a notification message (F1 Context Fetch) including F1 context information of the parent IAB node 300-1 to the target gNB 200-2.

[0136] In step S313, the target gNB 200-2 sends an F1 relocation message (F1 Relocation) to the parent IAB node 300-1 via the F1 connection based on the F1 context information of the parent IAB node 300-1. The F1 relocation message (F1 Relocation) may include at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the parent IAB node 300-1.

[0137] In step S314, the IAB-DU of the parent IAB node 300-1 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes F1 relocation of the parent IAB node 300-1. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the parent IAB node 300-1 (DU and MT).

[0138] In this manner, by the processing of steps S309 to S314, rearrangement of the F1 connection of the parent IAB node 300-1 and handover at the RRC layer of the parent IAB node 300-1 are performed (step S315).

[0139] In step S316, the IAB-MT of the child IAB node 300-2 transmits an RRC message (RRC Reconfiguration Complete) indicating completion of the RRC reconfiguration to the target gNB 200-2. This completes the handover procedure in the RRC layer of the child IAB node 300-2.

[0140] Here, the IAB-MT of the child IAB node 300-2 may send a relocation request (F1 Relocation Request) in an RRC message (RRC Reconfiguration Complete) to request relocation of the F1 connection from the source gNB 200-1 to the target gNB 200-2.

[0141] In addition, the IAB-MT of the child IAB node 300-2 may include the identifier (Source-donor ID) of the source gNB 200-1 or the identifier (Source Cell ID) of the source cell in an RRC message (RRC Reconfiguration Complete) and transmit it.

[0142] Furthermore, the IAB-MT of child IAB node 300-2 may include its own node's IP address in an RRC message (RRC Reconfiguration Complete) and transmit the message.

[0143] In addition, the IAB-MT of the child IAB node 300-2 may transmit at least one of the relocation request (F1 Relocation Request), the identifier of the source gNB 200-1 (Source-donor ID), the identifier of the source cell (Source Cell ID), and the IP address of the node itself in a message other than the RRC Reconfiguration Complete.

[0144] In step S317, the target gNB200-2 sends a request message (F1 Context Fetch) to the source gNB200-1 via the Xn interface to obtain F1 context information (fronthaul configuration information) of the child IAB node 300-2.

[0145] In step S318, in response to receiving the request message, the source gNB200-1 sends a notification message (F1 Context Fetch) including F1 context information of the child IAB node 300-2 to the target gNB200-2.

[0146] In step S319, the target gNB 200-2 sends an F1 relocation message (F1 Relocation) to the child IAB node 300-2 via the F1 connection based on the F1 context information of the child IAB node 300-2. The F1 relocation message (F1 Relocation) may include at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the child IAB node 300-2.

[0147] In step S320, the IAB-DU of the child IAB node 300-2 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes the F1 relocation of the child IAB node 300-2. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the child IAB node 300-2 (DU and MT).

[0148] In this manner, by the processes of step S308 and steps S316 to S320, rearrangement of the F1 connection of child IAB node 300-2 and handover at the RRC layer of child IAB node 300-2 are performed (step S321).

[0149] (3) Change Example 3 12 is a diagram showing the operation of Modification Example 3. Modification Example 3 is an operation assuming connection re-establishment (RRC re-establishment) instead of handover.

[0150] 12, in step S401, an F1 connection and an RRC connection are established between the child IAB node 300-2 and the source gNB 200-1. In addition, in step S402, an F1 connection and an RRC connection are established between the parent IAB node 300-1 and the source gNB 200-1.

[0151] In step S403, the IAB-MT of the parent IAB node 300-1 detects a failure of the wireless backhaul link (BH RLF) between the source gNB 200-1 and the parent IAB node 300-1.

[0152] In step S404, in response to detecting the BH RLF, the IAB-MT of the parent IAB node 300-1 sends an RRC message (RRC Reestablishment Request) requesting RRC reestablishment to the target gNB 200-2.

[0153] In step S405, in response to receiving the RRC Reestablishment Request, the target gNB 200-2 sends an RRC message (RRC Reestablishment) indicating RRC reestablishment to the parent IAB node 300-1.

[0154] In step S406, in response to receiving the RRC Reestablishment, the IAB-MT of the parent IAB node 300-1 sends an RRC message (RRC Reestablishment Complete) indicating completion of RRC reestablishment to the target gNB 200-2.

[0155] Here, the IAB-MT of the parent IAB node 300-1 transmits an F1 relocation request by including it in the RRC Reestablishment Complete. This F1 relocation request may be information notifying that the parent IAB node 300-1 will connect as an IAB node.

[0156] In addition, the IAB-MT of the parent IAB node 300-1 may include the identifier (Source-donor ID) of the source gNB 200-1 or the identifier (Source Cell ID) of the source cell in an RRC message (RRC Reestablishment Complete) and transmit it.

[0157] Furthermore, the IAB-MT of the parent IAB node 300-1 may include the IP address of the node itself in an RRC message (RRC Reestablishment Complete) and transmit the message.

[0158] In step S407, the target gNB 200-2 decides to relocate the F1 connection of the parent IAB node 300-1 from the source gNB 200-1 to the target gNB 200-2 based on the information contained in the RRC Reestablishment Complete (F1 Relocation decision).

[0159] In step S408, the target gNB 200-2 sends a request message (F1 Context Fetch) to the source gNB 200-1 via the Xn interface to obtain F1 context information (fronthaul configuration information) of the parent IAB node 300-1.

[0160] In step S409, in response to receiving the request message, the source gNB 200-1 sends a notification message (F1 Context Fetch) including F1 context information of the parent IAB node 300-1 to the target gNB 200-2.

[0161] In step S410, the target gNB 200-2 sends an F1 relocation message (F1 Relocation) to the parent IAB node 300-1 via the F1 connection based on the F1 context information of the parent IAB node 300-1. The F1 relocation message (F1 Relocation) may include at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the parent IAB node 300-1.

[0162] In step S411, the IAB-DU of the parent IAB node 300-1 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes F1 relocation of the parent IAB node 300-1. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the parent IAB node 300-1 (DU and MT).

[0163] In this manner, by the processing of steps S404 to S411, the F1 connection of the parent IAB node 300-1 is rearranged and re-established in the RRC layer of the parent IAB node 300-1 (step S412).

[0164] In step S413, the parent IAB node 300-1 notifies the child IAB node 300-2 that F1 relocation is complete. This notification may be a notification that RRC re-establishment is complete. Here, the BAP layer of the parent IAB node 300-1 may notify the completion of F1 relocation or the completion of RRC re-establishment using a BAP control PDU (Protocol Data Unit). Such a notification may be a type (another type) of BH RLF Indication, for example, a notification indicating "RLF Recovered with different donor".

[0165] In step S414, in response to the notification from the parent IAB node 300-1, the IAB-MT of the child IAB node 300-2 sends an RRC message (RRC Reestablishment Request) requesting RRC reestablishment to the target gNB 200-2.

[0166] In step S415, in response to receiving the RRC Reestablishment Request, the target gNB 200-2 sends an RRC message (RRC Reestablishment) indicating RRC reestablishment to the child IAB node 300-2.

[0167] In step S416, in response to receiving the RRC Reestablishment, the IAB-MT of the child IAB node 300-2 sends an RRC message (RRC Reestablishment Complete) indicating completion of RRC reestablishment to the target gNB 200-2.

[0168] Here, the IAB-MT of the child IAB node 300-2 transmits an F1 relocation request by including it in the RRC Reestablishment Complete. This F1 relocation request may be information notifying that the child IAB node 300-2 will connect as an IAB node.

[0169] In addition, the IAB-MT of the child IAB node 300-2 may include the identifier (Source-donor ID) of the source gNB 200-1 or the identifier (Source Cell ID) of the source cell in an RRC message (RRC Reestablishment Complete) and transmit it.

[0170] Furthermore, the IAB-MT of child IAB node 300-2 may include its own node's IP address in an RRC message (RRC Reestablishment Complete) and transmit the message.

[0171] In step S417, the target gNB200-2 sends a request message (F1 Context Fetch) to the source gNB200-1 via the Xn interface to obtain F1 context information (fronthaul configuration information) of the child IAB node 300-2.

[0172] In step S418, in response to receiving the request message, the source gNB200-1 sends a notification message (F1 Context Fetch) including F1 context information of the child IAB node 300-2 to the target gNB200-2.

[0173] In step S419, the target gNB 200-2 sends an F1 relocation message (F1 Relocation) to the child IAB node 300-2 via the F1 connection based on the F1 context information of the child IAB node 300-2. The F1 relocation message (F1 Relocation) may include at least one of the F1 context information, the IP address of the target gNB 200-2, and the new IP address of the child IAB node 300-2.

[0174] In step S420, the IAB-DU of the child IAB node 300-2 transmits an F1 message (F1 Relocation Complete) indicating completion of F1 relocation to the target gNB 200-2. This completes the F1 relocation of the child IAB node 300-2. This F1 message (F1 Relocation Complete) is transmitted to the IP address of the target gNB 200-2. This F1 message (F1 Relocation Complete) may include an identifier of the child IAB node 300-2 (DU and MT).

[0175] In this manner, by the processing of steps S414 to S420, the F1 connection of child IAB node 300-2 is rearranged and re-established in the RRC layer of child IAB node 300-2 (step S421).

[0176] (Other embodiments) In the above-described embodiment and modified example, an example in which the cellular communication system 1 is a 5G cellular communication system has been mainly described. However, the base station in the cellular communication system 1 may be an eNB, which is an LTE base station. Also, the core network in the cellular communication system 1 may be an EPC (Evolved Packet Core). Furthermore, the gNB may be connected to the EPC, the eNB may be connected to the 5GC, and the gNB and the eNB may be connected via an inter-base station interface (Xn interface, X2 interface).

[0177] A program may be provided that causes a computer to execute each process according to the above-described embodiment and modified example. The program may be recorded in a computer-readable medium. Using the computer-readable medium, it is possible to install the program in the computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM. A chipset may be provided that is configured by a memory that stores a program for executing each process performed by the UE 100, the gNB 200, or the IAB node 300, and a processor that executes the program stored in the memory.

[0178] This application claims priority to Japanese Patent Application No. 2020-083477 (filed May 11, 2020), the entire contents of which are incorporated herein by reference.

Claims

1. A communication control method for performing a handover of a relay node from a source base station to a target base station, comprising: The source base station sends a request message to the target base station, the request message including information regarding an F1 connection established between a distributed unit of the relay node and the source base station; The target base station transmits a response message to the source base station in response to the request message, The response message includes an IP address that the target base station assigns to the relay node. Communications control method.

2. A source base station included in a system for performing handover of a relay node from a source base station to a target base station, comprising: a sending unit for sending a request message to the target base station, the request message including information regarding an F1 connection established between the distributed unit of the relay node and the source base station; a receiving unit that receives a response message to the request message from the target base station, The response message includes an IP address that the target base station assigns to the relay node. Source base station.

3. A target base station included in a system for performing handover of a relay node from a source base station to a target base station, a receiving unit for receiving a request message from the source base station, the request message including information regarding an F1 connection established between the distributed unit of the relay node and the source base station; a transmission unit that transmits a response message to the source base station in response to the request message, The response message includes an IP address that the target base station assigns to the relay node. Target base station.

4. A system for performing handover of a relay node from a source base station to a target base station, comprising: The source base station sends a request message to the target base station, the request message including information about an F1 connection established between a distributed unit of the relay node and the source base station; The target base station transmits a response message to the source base station in response to the request message; The response message includes an IP address that the target base station assigns to the relay node. system.

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