COMMUNICATION CONTROL METHOD, TARGET DONOR NODE, AND MOBILE RELAY NODE

Abstract

A communication control method according to one aspect is used in a cellular communication system. The communication control method includes a step in which a mobile relay node transmits, to a target donor node, an F1 setup request message including a first physical cell ID used in the mobile relay node. In addition, the communication control method includes a step in which, in response to receiving the F1 setup request message, the target donor node transmits a PCI request message including the first physical cell ID to an adjacent donor node, which is adjacent to the target donor node and is not a source donor node, in order to inquire whether the first physical cell ID is available.

Description

Communication Control Method

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

[0002] In 3GPP (Third Generation Partnership Project) (registered trademark, the same applies hereinafter), 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 (see, for example, Non-Patent Document 1). One or more relay nodes intervene in communication between a base station and a user device and relay this communication.

[0003] 3GPP TS 38.300 V17.1.0 (2022-06)

[0004] A communication control method according to a first aspect is a communication control method for use in a cellular communication system, the communication control method including a step of transmitting, by a mobile relay node, an F1 setup request message including a first physical cell ID used by the mobile relay node to a target donor node, and a step of transmitting, by the target donor node in response to receiving the F1 setup request message, a PCI request message including the first physical cell ID to an adjacent donor node adjacent to the target donor node and other than the source donor node, to inquire whether the first physical cell ID is usable.

[0005] A communication control method according to a second aspect is a communication control method for use in a cellular communication system, the communication control method comprising: a step of transmitting, by a mobile relay node, an F1 setup request message including a first physical cell ID to be used by the mobile relay node to a target donor node; and a step of transmitting, by the target donor node in response to receiving the F1 setup request message, a serving cell information request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than the source donor node, requesting provision of the physical cell ID to be used by the neighboring donor node.

[0006] A communication control method according to a third aspect is a communication control method for use in a cellular communication system, the communication control method including a step of transmitting, by a mobile relay node, an F1 setup request message including first PRACH (Physical Random Access Channel) resources to a target donor node to be used by the mobile relay node, and a step of transmitting, by the target donor node, in response to receiving the F1 setup request message, a PRACH request message including the first PRACH resources to a neighboring donor node neighboring the target donor node but other than the source donor node, to inquire whether the first PRACH resources are available for use.

[0007] A communication control method according to a fourth aspect is a communication control method for use in a cellular communication system, the communication control method comprising: a step of transmitting, by a mobile relay node, an F1 setup request message including a first PRACH resource to be used by the mobile relay node to a target donor node; and a step of transmitting, by the target donor node in response to receiving the F1 setup request message, a serving cell information request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than the source donor node, requesting provision of a PRACH resource to be used by the neighboring donor node.

[0008] FIG. 1 is a diagram illustrating an example configuration of a cellular communication system according to one embodiment. FIG. 2 is a diagram illustrating the relationship between an IAB node, parent nodes, and child nodes. FIG. 3 is a diagram illustrating an example configuration of a gNB (base station) according to one embodiment. FIG. 4 is a diagram illustrating an example configuration of an IAB node (relay node) according to one embodiment. FIG. 5 is a diagram illustrating an example configuration of a UE (user equipment) according to one embodiment. FIG. 6 is a diagram illustrating an example protocol stack related to IAB-MT RRC connection and NAS connection. FIG. 7 is a diagram illustrating an example protocol stack related to the F1-U protocol. FIG. 8 is a diagram illustrating an example protocol stack related to the F1-C protocol. FIGS. 9(A) and 9(B) are diagrams illustrating an example of complete movement according to the first embodiment. FIGS. 10(A) and 10(B) are diagrams illustrating an example of complete movement according to the first embodiment. FIG. 11 is a diagram illustrating an example operation according to the first embodiment. FIG. 12 is a diagram illustrating another example operation according to the first embodiment.

[0009] The present disclosure provides a communication control method that enables a mobile relay node to appropriately communicate with user equipments under its control.

[0010] A cellular communication system according to an embodiment will 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.

[0011] [First embodiment]

[0012] (Configuration of Cellular Communication System) An example configuration of a cellular communication system according to one embodiment will be described. The cellular communication system 1 according to one embodiment is a 3GPP 5G system. Specifically, the radio access method in the cellular communication system 1 is NR (New Radio), which is a 5G radio access method. However, LTE (Long Term Evolution) may be applied at least in part to the cellular communication system 1. Furthermore, future cellular communication systems such as 6G may also be applied to the cellular communication system 1.

[0013] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system 1 according to an embodiment.

[0014] 1, the cellular communication system 1 includes a 5G core network (5GC) 10, user equipment (UE) 100, base station devices (hereinafter sometimes referred to as "base stations") 200-1 and 200-2, and IAB nodes 300-1 and 300-2. The base station 200 may be referred to as a gNB.

[0015] In the following, we will mainly describe an example in which base station 200 is an NR base station, but base station 200 may also be an LTE base station (i.e., eNB).

[0016] In the following, base stations 200-1 and 200-2 may be referred to as gNB 200 (or base station 200), and IAB nodes 300-1 and 300-2 may be referred to as IAB node 300.

[0017] 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 about 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, etc.

[0018] 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 also 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. Hereinafter, there may be cases where a cell and a base station are used interchangeably.

[0019] Each gNB 200 is interconnected with 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.

[0020] Each gNB 200 may be divided into a central unit (CU) and a distributed unit (DU). The CU and DU are connected to each other via an interface called an F1 interface. The F1 protocol is a communication protocol between the CU and DU, and includes the F1-C protocol, which is a control plane protocol, and the F1-U protocol, which is a user plane protocol.

[0021] The cellular communication system 1 supports IAB, which enables wireless relay of NR access using NR for backhaul. The donor gNB 200-1 (or donor node, hereinafter sometimes referred to as the "donor node") is the terminal node of the NR backhaul on the network side and is a donor base station with additional functions that support IAB. The backhaul can be multi-hopped via multiple hops (i.e., multiple IAB nodes 300).

[0022] FIG. 1 shows an example in which IAB node 300-1 wirelessly connects with donor node 200-1, IAB node 300-2 wirelessly connects with IAB node 300-1, and the F1 protocol is transmitted over two backhaul hops.

[0023] 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 and / or a tablet terminal, a laptop PC, a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle, or an aircraft or a device provided in an aircraft. 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 node 200-1 via the IAB node 300-2 and the IAB node 300-1.

[0024] FIG. 2 is a diagram showing an example of the relationship between the IAB node 300, parent nodes, and child nodes.

[0025] 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.

[0026] An adjacent node (i.e., an upper node) on the NR Uu radio interface of the IAB-MT is called a parent node. The parent node is the parent IAB node or the DU of the donor node 200. The radio link between the IAB-MT and the parent node is called a backhaul link (BH link). FIG. 2 shows an example in which the parent nodes of the IAB node 300 are IAB nodes 300-P1 and 300-P2. The direction toward the parent node is called upstream. From the perspective of the UE 100, the upper node of the UE 100 may correspond to the parent node.

[0027] Adjacent nodes (i.e., lower nodes) on the NR access interface of the IAB-DU are called child nodes. The IAB-DU manages the cell, similar to the gNB 200. The IAB-DU terminates the NR Uu radio interface to the UE 100 and lower IAB nodes. The IAB-DU supports the F1 protocol to the CU of the donor node 200-1. In FIG. 2, an example is shown in which the child nodes of the IAB node 300 are IAB nodes 300-C1 to 300-C3, but the child nodes of the IAB node 300 may also include the UE 100. The direction toward the child nodes is called downstream.

[0028] Furthermore, all IAB nodes 300 connected to the donor node 200 via one or more hops form a directed acyclic graph (DAG) topology (hereinafter sometimes referred to as "topology") with the donor node 200 as the root. In this topology, as shown in FIG. 2, adjacent nodes on the IAB-DU interface are child nodes, and adjacent nodes on the IAB-MT interface are parent nodes. The donor node 200 centralizes, for example, resource, topology, and route management of the IAB topology. The donor node 200 is a gNB that provides network access to the UE 100 via a network of backhaul links and access links.

[0029] (Configuration of base station) Next, the configuration of the gNB 200, which is a base station according to the embodiment, will be described. Fig. 3 is a diagram showing an example 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.

[0030] 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 (down-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 (up-converts) a baseband signal (transmitted signal) output by the control unit 230 into a wireless signal, and transmits the signal from the antenna.

[0031] 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.

[0032] 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 processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs processing of each layer, which will be described later. Note that the control unit 230 may perform each process or operation in the gNB 200 in each of the embodiments shown below.

[0033] (Configuration of Relay Node) Next, a configuration of an IAB node 300, which is a relay node (or relay node device; hereinafter, may be referred to as a "relay node") according to an embodiment, will be described. FIG. 4 is a diagram showing an example 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 multiple wireless communication units 310.

[0034] 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.

[0035] The wireless communication unit 310 has a receiving unit 311 and a transmitting unit 312. The receiving unit 311 performs various types of reception under the control of the control unit 320. The receiving unit 311 includes an antenna, and converts (down-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 types of transmission under the control of the control unit 320. The transmitting unit 312 includes an antenna, and converts (up-converts) a baseband signal (transmitted signal) output by the control unit 320 into a wireless signal, and transmits the signal from the antenna.

[0036] 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 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 processes. The processor performs processing of each layer, which will be described later. Note that the control unit 320 may perform each process or operation in the IAB node 300 in each of the embodiments described below.

[0037] (Configuration of User Device) Next, a configuration of the UE 100, which is a user device according to the embodiment, will be described. Fig. 5 is a diagram showing an example configuration of the UE 100. As shown in Fig. 5, the UE 100 includes a radio communication unit 110 and a control unit 120.

[0038] The wireless communication unit 110 performs wireless communication in an access link, i.e., 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, i.e., wireless communication with other UEs 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 (down-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 (up-converts) a baseband signal (transmitted signal) output by the control unit 120 into a wireless signal, and transmits the signal from the antenna.

[0039] 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 processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation, encoding / decoding, etc. of baseband signals. The CPU executes programs stored in the memory to perform various processes. The processor performs processing of each layer, which will be described later. Note that the control unit 120 may be configured to perform each process in the UE 100 in each of the embodiments described below.

[0040] (Protocol Stack Configuration) Next, a description will be given of the configuration of a protocol stack according to the embodiment. Fig. 6 is a diagram showing an example of a protocol stack related to an IAB-MT RRC connection and a NAS connection.

[0041] 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.

[0042] 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 IAB node 300-2 and the PHY layer of the IAB-DU of IAB node 300-1 via a physical channel.

[0043] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (HARQ), random access procedures, etc. Data and control information are transmitted via transport channels 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. The MAC layer of the IAB-DU includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the allocated resource blocks.

[0044] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of the IAB-MT of IAB node 300-2 and the RLC layer of the IAB-DU of IAB node 300-1 via logical channels.

[0045] 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 node 200 via a radio bearer.

[0046] The RRC layer controls logical channels, transport channels, and physical channels in response 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 node 200. When there is an RRC connection with the donor node 200, the IAB-MT is in an RRC connected state. When there is no RRC connection with the donor node 200, the IAB-MT is in an RRC idle state.

[0047] The NAS layer, which is positioned 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.

[0048] Figure 7 shows a protocol stack for the F1-U protocol. Figure 8 shows a protocol stack for the F1-C protocol. Here, an example is shown in which the donor node 200 is divided into a CU and a DU.

[0049] As shown in Figure 7, the IAB-MT of IAB node 300-2, the IAB-DU of IAB node 300-1, the IAB-MT of IAB node 300-1, and the DU of donor node 200 each have a BAP (Backhaul Adaptation Protocol) 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 via the BAP layer, enabling routing over multiple hops.

[0050] 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 (Quality of Service) 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 node 200.

[0051] 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.

[0052] In the following, the processing or operations performed by the IAB-DU and IAB-MT of the IAB may be simply described as the processing or operations of the "IAB." For example, the transmission of a BAP layer message from the IAB-DU of IAB node 300-1 to the IAB-MT of IAB node 300-2 will be described as the IAB node 300-1 sending the message to IAB node 300-2. In addition, the processing or operations of the DU or CU of the donor node 200 may also be simply described as the processing or operations of the "donor node."

[0053] Also, the upstream direction and the uplink (UL) direction may be used interchangeably, and the downstream direction and the downlink (DL) direction may be used interchangeably.

[0054] (Mobile IAB Node) Currently, 3GPP has begun discussions toward the introduction of mobile IAB nodes. A mobile IAB node is, for example, an IAB node that is moving. A mobile IAB node may be an IAB node that is capable of moving. Alternatively, a mobile IAB node may be an IAB node that is currently stationary but is certain to move in the future (or is expected to move in the future).

[0055] The mobile IAB node enables, for example, a UE 100 under the mobile IAB node to receive services from the mobile IAB node while moving in accordance with the movement of the mobile IAB node. For example, a case is envisioned in which a user (or UE 100) on a vehicle receives services via a mobile IAB node installed on the vehicle.

[0056] On the other hand, in contrast to mobile IAB nodes, there are also IAB nodes that do not move. Such IAB nodes are sometimes referred to as intermediate IAB nodes. An intermediate IAB node is, for example, an IAB node that does not move. Alternatively, the intermediate IAB node may be a stationary IAB node. Alternatively, the intermediate IAB node may be an IAB node that remains stationary (or does not move) and remains installed at its installation location. Alternatively, the intermediate IAB node may be a stationary IAB node that does not move. The intermediate IAB node may also be a fixed IAB node.

[0057] A mobile IAB node can also be connected to an intermediate IAB node. Also, a mobile IAB node can be connected to a donor node 200. A mobile IAB node can also change its connection destination due to movement (migration or handover). The connection source may be an intermediate IAB node. The connection source may be the donor node 200. Also, the connection destination may be an intermediate IAB node. The connection destination may be the donor node 200.

[0058] In the following, the terms "migration" of a mobile IAB node and "handover" of a mobile IAB node may be used interchangeably.

[0059] In the following description, a mobile IAB node may be referred to as a "mobile IAB node" or a "migrating IAB node." In either case, the mobile IAB node may be referred to as a mobile IAB node.

[0060] (Full Migration of a Mobile IAB Node) A mobile IAB node may move between donor nodes (IAB-donors) 200 .

[0061] 9(A) to 10(B) are diagrams showing an example of a procedure when the mobile IAB node 300M moves from the source donor node 200-S to the target donor node 200-T. The mobile IAB node 300M has a UE 100 under its control. The example of FIG. 9(A) shows an example in which the UE 100 is present in a cell range formed by IAB-DU#1 of the mobile IAB node 300M. The UE 100 can move together with the mobile IAB node 300M.

[0062] 9A shows an example of an initial condition. The IAB-DU#1 of the mobile IAB node 300M has established an F1 connection with the CU of the source donor node 200-S. The IAB-MT of the mobile IAB node 300M has established an RRC connection with the CU of the source donor node 200-S.

[0063] 9(B) shows an example in which the mobile IAB node 300M moves to the target donor node 200-T, resulting in a partial migration state with respect to the target donor node 200-T. As shown in FIG. 9(B), in partial migration, the IAB-DU #1 (and the UE 100) of the mobile IAB node 300M is terminated in the CU of the source donor node 200-S, while the IAB-MT of the mobile IAB node 300M has moved to the CU of the target donor node 200-T. The IAB-MT of the mobile IAB node 300M has established an RRC connection with the CU of the target donor node 200-T. In addition, the IAB-DU of the mobile IAB node 300M has established an F1 connection with the source donor node 200-S. Partial mobility refers to a state in which, for example, the connection of the UE 100 under the mobile IAB node 300M remains with the source donor node 200-S via the IAB-DU#1 of the mobile IAB node 300M.

[0064] 10A shows an example in which the mobile IAB node 300M subsequently enters a state of phase 1 of full migration with respect to the target donor node 200-T. In phase 1 of full migration, the UE 100 remains connected to the source donor node 200-S via IAB-DU#1, but a new IAB-DU#2 has established an F1 connection with the CU of the target donor node 200-T. Here, IAB-DU#1 and IAB-DU#2 may be logical IAB-DUs. One physical IAB-DU may include two logical IAB-DUs (IAB-DU#1 and IAB-DU#2).

[0065] 10(B) shows an example in which the mobile IAB node 300M subsequently enters a state of complete movement phase 2 with respect to the target donor node 200-T. In the complete movement phase 2, the connection of the mobile IAB node 300M (and the UE 100) has moved from the CU of the source donor node 200-S to the CU of the target donor node 200-T. Complete movement refers to, for example, a state in which the connection of the UE 100 has moved to the target donor node 200-T via IAB-DU #2 of the mobile IAB node 300M.

[0066] Note that movement between CUs using two DUs (IAB-DU #1 and IAB-DU #2) by the mobile IAB node 300M may be referred to as a “dual DU approach.” For example, the dual DU approach is performed when the UE 100 moves from one CU and DU to another CU and DU.

[0067] (Communication Control Method According to First Embodiment) A physical cell ID (PCI) is an identifier used to identify a cell. Regarding PCI, a problem called PCI collision may occur.

[0068] For example, when a UE located between adjacent cells measures the radio wave strength of one cell, assume that the same PCI is used between the adjacent cells. In such a case, the UE 100 is supposed to measure the radio wave strength of the radio signal from one cell, but may measure the radio wave strength by adding up the two radio signals from the other cell as a radio signal from the same cell. For this reason, the UE may select an inappropriate cell during cell search and start synchronization with the cell, or may transmit an inappropriate measurement report, thereby performing handover to another cell that is not the correct target cell.

[0069] The problem caused by using the same PCI between different cells is sometimes called a “PCI collision.” In general, it is possible to avoid PCI collision by configuring cells so that the same PCI is not used for a given cell and its neighboring cell.

[0070] On the other hand, as described above, the mobile IAB node 300M may move between donor nodes 200. Due to movement of the mobile IAB node 300M (for example, complete movement), the PCI used in the cell under the mobile IAB node 300M may be the same as or overlap with the PCI used in the cell under the destination donor node 200. In this case, the UE 100 under the mobile IAB node 300M may not be able to distinguish between the IAB-DU of the mobile IAB node 300M and the DU of the donor node 200, and a PCI collision may occur.

[0071] In contrast, for example, it is conceivable to divide the "1024" PCIs used in NR into PCIs dedicated to mobile IAB nodes and PCIs for other purposes (e.g., fixed cells or macro cells). However, even if, for example, "512" PCIs are assigned to PCIs dedicated to mobile IABs, only "512" PCIs would physically exist. Therefore, if a unique (global) PCI were assigned to each mobile IAB node 300M, only "512" cells could be accommodated as cells for mobile IAB nodes. Furthermore, if a unique (global) PCI is not assigned to each mobile IAB node 300M (i.e., if PCIs are repeatedly assigned), there would be only "512" PCIs, and therefore PCI collisions could occur when mobile IAB nodes 300M approach each other.

[0072] Therefore, the first embodiment aims to avoid PCI collisions in the mobile IAB node 300M, thereby enabling the mobile IAB node 300M to communicate appropriately with the UE 100 under its control.

[0073] Therefore, in the first embodiment, first, a mobile relay node (e.g., mobile IAB node 300M) transmits an F1 setup request message including a first physical cell ID to be used in the mobile relay node to a target donor node (e.g., target donor node 200-T). Second, in response to receiving the F1 setup request message, the target donor node transmits a request message including the first physical cell ID to a neighboring donor node adjacent to the target donor node other than the source donor node, in order to inquire whether the first physical cell ID can be used.

[0074] As a result, for example, an adjacent donor node can grasp the PCI used by the mobile IAB node 300M. Therefore, the adjacent donor node can prevent the mobile IAB node 300M from using a PCI that matches the PCI it uses, and can allow the mobile IAB node 300M to use a PCI that it does not use. This allows the mobile IAB node 300M to avoid PCI collisions with adjacent donor nodes. Therefore, even if the mobile IAB node 300M moves to the target donor node 200-T, it can properly communicate with the subordinate UE 100.

[0075] (Example of Operation According to First Embodiment) Next, an example of operation according to the first embodiment will be described.

[0076] 11 is a diagram illustrating an example of operation according to the first embodiment. FIG. 11 illustrates an example in which a mobile IAB node 300M performs a handover from a source donor node 200-S to a target donor node 200-T. Note that an adjacent donor node 200-TN refers to a donor node 200 adjacent to the target donor node 200-T, other than the source donor node 200-S.

[0077] 11, in step S10, the mobile IAB node 300M establishes an RRC connection with the source donor node 200-S and also establishes an F1 connection. For example, as in FIG. 9A, the IAB-DU of the mobile IAB node 300M establishes an RRC connection with the CU of the source donor node 200-S, and the IAB-MT of the mobile IAB node 300M establishes an F1 connection with the CU of the source donor node 200-S.

[0078] In step S11, the source donor node 200-S decides to hand over the mobile IAB node 300M to the target donor node 200-T.

[0079] In step S12, the source donor node 200-S transmits a handover request message to the target donor node 200-T. For example, the CU of the source donor node 200-S transmits a handover request (HANDOVER REQUEST) message, which is an XnAP message, to the CU of the target donor node 200-T.

[0080] In step S13, in response to receiving the handover request message, the target donor node 200-T transmits a handover request response message accepting the handover request to the source donor node 200-S. For example, in response to receiving the handover request (HANDOVER REQUEST) message, the CU of the target donor node 200-T transmits a handover request response (HANDOVER REQUEST ACKNOWLEDGEMENT) message to the CU of the source donor node 200-S.

[0081] In step S14, in response to receiving the handover request response message, the source donor node 200-S transmits an RRC message (RRC Reconfiguration message) to the mobile IAB node 300M. The RRC message includes information (ReconfigurationwithSync) for the mobile IAB node 300M to establish an RRC connection with the target donor node 200-T. For example, the CU of the source donor node 200-S transmits the RRC message to the IAB-MT of the mobile IAB node 300M.

[0082] In step S15, the mobile IAB node 300M establishes an RRC connection with the target donor node 200-T. For example, the IAB-MT of the mobile IAB node 300M establishes an RRC connection with the CU of the target donor node 200-T (for example, FIG. 9B).

[0083] In step S16, the mobile IAB node 300M transmits an F1 setup request message to the target donor node 200-T to establish an F1 connection. At this time, the mobile IAB node 300M transmits the F1 setup request message including the PCI (e.g., first physical cell ID) to be used (or to be used) in its own IAB-DU. The PCI may be in the form of a list. For example, the IAB-DU of the mobile IAB node 300M includes the PCI in the serving cell information included in the F1 setup request message and transmits it to the CU of the target donor node 200-T.

[0084] In step S17, in response to receiving the F1 setup request message, the target donor node 200-T transmits a PCI request (mIAB PCI Request) message including the PCI to be used in the mobile IAB node 300M to the adjacent donor node 200-TN. The PCI request message may be a message requesting that the PCI used in the mobile IAB node 300M also be used in the adjacent donor node 200-TN. Alternatively, the PCI request message may be a message inquiring whether the PCI used in the mobile IAB node 300M can be used in the adjacent donor node 200-TN. The target donor node 200-T extracts the PCI to be used in the mobile IAB node 300M from the F1 setup request message (step S16) and transmits a PCI request message including the PCI to the adjacent donor node 200-TN. For example, the CU of the target donor node 200-T transmits a PCI request message as an Xn message to the CU of the adjacent donor node 200-TN. If there are multiple adjacent donor nodes 200-TN, the CU of the target donor node 200-T transmits a PCI request message to the CU of each adjacent donor node 200-TN. The PCI included in the PCI request message may be in a list format.

[0085] In step S18, in response to receiving the PCI request message, the adjacent donor node 200-TN determines a PCI that can be used in the mobile IAB node 300M. For example, the available PCI is determined as follows.

[0086] That is, the adjacent donor node 200-TN compares or collates the PCI included in the PCI request message (e.g., the PCI used in the cell under the mobile IAB node 300M) with the PCI it uses (e.g., the PCI used in the cell under the adjacent donor node 200-TN or the cell under the IAB node 300 under the adjacent donor node 200-TN). The adjacent donor node 200-TN then determines a PCI that can be used by the mobile IAB node 300M depending on whether the PCI included in the PCI request message matches the PCI it uses. If the two PCIs match, the adjacent donor node 200-TN determines that the PCI used by the mobile IAB node 300M is not usable. This is because the PCI used by the mobile IAB node 300M is also used by the adjacent donor node 200-TN, causing a PCI collision. On the other hand, if the two PCIs do not match, the adjacent donor node 200-TN determines that the PCI used by the mobile IAB node 300M is usable. This is because the PCI used by the mobile IAB node 300M is not used by the adjacent donor node 200-TN, and no PCI collision occurs. If the PCIs are in list format, each PCI is compared. This process may be performed in the CU of the adjacent donor node 200-TN.

[0087] In step S19, the adjacent donor node 200-TN transmits a PCI request acknowledgement (mIAB PCI Request Acknowledgement) message, which is a response message to the PCI request message (step S17), to the target donor node 200-T. The PCI request acknowledgement message is a response message to the PCI request message (step S17). The PCI request acknowledgement message includes the determination result in step S18.

[0088] First, the PCI request response message may include an allowed PCI list (AllowedPCI list), which represents, for example, a list of PCIs (e.g., second physical cell IDs) that the mobile IAB node 300M can use for the neighboring donor node 200-TN.

[0089] Second, the PCI request response message may include an Exclude PCI list, which represents, for example, a list of unavailable PCIs (e.g., third physical cell IDs) that the mobile IAB node 300M cannot use for the adjacent donor node 200-TN.

[0090] Third, the PCI request response message may include information indicating that all PCIs included in the PCI request message are approved. The information may indicate that all PCIs used by the mobile IAB node 300M may be used for the adjacent donor node 200-TN.

[0091] Fourth, the PCI request response message may include information indicating that all PCIs included in the PCI request message are rejected. The information may indicate that none of the PCIs used by the mobile IAB node 300M can be used for the adjacent donor node 200-TN.

[0092] For example, the CU of the adjacent donor node 200-TN sends a PCI request message as an Xn message to the CU of the target donor node 200-T.

[0093] In step S20, in response to receiving the PCI request response message, the target donor node 200-T checks whether or not it is necessary to change the PCI (eg, first physical cell ID) used by the mobile IAB node 300M.

[0094] First, the target donor node 200-T checks whether it is necessary to change the PCI used by the mobile IAB node 300M, based on information included in the PCI request response message (such as the Allowed PCI list or the Exclude PCI list). For example, if the PCI request response message includes information indicating approval for all requests, the target donor node 200-T checks that there is no need to change the PCI. Furthermore, for example, if the PCI request response message includes the Allowed PCI list, the target donor node 200-T checks that the PCIs used by the mobile IAB node 300M should be changed to PCIs included in the list. Furthermore, for example, when the PCI request response message includes an Exclude PCI list, the target donor node 200-T confirms that the PCIs included in the list among the PCIs used by the mobile IAB node 300M are PCIs to be deleted, or confirms that the PCIs are to be changed to PCIs other than those included in the list. Furthermore, for example, when the PCI request response message includes information indicating that all PCIs are denied, the target donor node 200-T confirms that all PCIs used by the mobile IAB node 300M are PCIs to be deleted.

[0095] Second, the target donor node 200-T may compare or verify the PCIs used in its subordinate cells to determine whether a PCI change is necessary. For example, when the PCI request response message includes an Allowed PCI list, the target donor node 200-T may check whether the PCIs included in the list are also used by the target donor node 200-T, and if a PCI that the target donor node 200-T uses is included, delete the PCI. Alternatively, the target donor node 200-T may check that if the Allowed PCI list does not include a PCI that the target donor node uses, it does not need to change the PCIs included in the Allowed PCI list.

[0096] The process in step S20 may be performed in the CU of the target donor node 200-T.

[0097] In step S21, the target donor node 200-T transmits an F1 setup response message to the mobile IAB node 300M. The F1 setup response message may include a PCI after the change to the PCI used by the mobile IAB node 300M, depending on the confirmation result (step S20) in the target donor node 200-T. Specifically, the F1 setup response message may include the following information:

[0098] First, the F1 setup response message may include an additional PCI list (PCI To Be Added List), which includes a list of PCIs that are further available for use by the adjacent donor node 200-TN, for the PCIs used by the mobile IAB node 300M (step S16 or step S17).

[0099] Second, the F1 setup response message may include a modified PCI list (PCI To Be Modified List). For example, the modified PCI list includes, among the PCIs used by the mobile IAB node 300M (step S16 or step S17), PCIs that can be used for the adjacent donor node 200-TN after modification.

[0100] Third, the F1 setup response message may include a PCI to be removed list (PCI to be removed list). The PCI to be removed list includes PCIs to be removed as PCIs that cannot be used for the adjacent donor node 200-TN, among the PCIs used by the mobile IAB node 300M (step S16 or step S17).

[0101] Fourth, the F1 setup response message may include information linking (or combining) the PCI (e.g., old PCI) used by the mobile IAB node 300M with the changed PCI (e.g., new PCI) confirmed by the target donor node 200-T.

[0102] The target donor node 200-T can send an F1 setup response message to the mobile IAB node 300M including the changed PCI for the PCI used by the mobile IAB node 300M using an added PCI list, a changed PCI list, or a deleted PCI list, etc.

[0103] For example, the CU of the target donor node 200-T sends an F1 setup response message including an added PCI list, a changed PCI list, or a deleted PCI list to the IAB-DU of the mobile IAB node 300M.

[0104] In step S22, the mobile IAB node 300M changes the PCI in response to receiving the F1 setup response message. For example, the IAB-DU of the mobile IAB node 300M changes the PCI to be used by adding a PCI in accordance with the added PCI list. Also, for example, the IAB-DU of the mobile IAB node 300M changes the PCI to be used in accordance with the changed PCI list. Furthermore, for example, the IAB-DU of the mobile IAB node 300M changes the PCI to be used by deleting a PCI included in the deleted PCI list from the PCIs to be used in accordance with the deleted PCI list.

[0105] In step S23, the mobile IAB node 300M establishes an F1 connection to the target donor node 200-T.

[0106] Another Example of the First Embodiment Next, another example of the first embodiment will be described. In the other example of the first embodiment, differences from the first embodiment will be mainly described.

[0107] In the first embodiment, an example has been described in which the target donor node 200-T transmits the PCI used by the mobile IAB node 300M to the adjacent donor node 200-TN, but the present invention is not limited to this. For example, the target donor node 200-T may request the adjacent donor node 200-TN to provide the PCI used by the adjacent donor node 200-TN. In this case, the target donor node 200-T determines whether the PCI used by the mobile IAB node 300M can be used by the adjacent donor node 200-TN.

[0108] Specifically, first, a mobile relay node (e.g., mobile IAB node 300M) transmits an F1 Setup Request message including a first physical cell ID used by the mobile relay node. Second, in response to receiving the F1 Setup Request message, the target donor node transmits a Serving Cell Information Request message to a neighboring donor node (e.g., neighboring donor node 200-TN) adjacent to the target donor node but other than the source donor node, requesting provision of the physical cell ID used by the neighboring donor node.

[0109] As a result, the target donor node 200-T can transmit to the mobile IAB node 300M, among the PCIs used by the mobile IAB node 300M, PCIs other than the PCIs used by the adjacent donor node 200-TN, as PCIs usable by the mobile IAB node 300M. Therefore, in the cell subordinate to the mobile IAB node 300M, PCI collisions with the adjacent donor node 200-TN can be avoided. Therefore, the mobile IAB node 300M can appropriately communicate with the UE 100 subordinate to it.

[0110] 12 is a diagram showing another example of the operation of the first embodiment. In FIG. 12, the same processes as those in the first embodiment are denoted by the same reference numerals.

[0111] In step S30, in response to receiving the F1 setup request message (step S16), the target donor node 200-T transmits a serving cell information request message to the adjacent donor node 200-TN. The serving cell information request message is a message requesting the provision of a PCI to be used by the adjacent donor node 200-TN. The serving cell information request message may be a message requesting serving cell information used by the adjacent donor node 200-TN. For example, the CU of the target donor node 200-T transmits the serving cell information request message as an Xn message to the CU of the adjacent donor node 200-TN.

[0112] In step S31, in response to receiving the serving cell information request message, the adjacent donor node 200-TN lists the PCIs used by the adjacent donor node 200-TN.

[0113] In step S32, the adjacent donor node 200-TN transmits a serving cell information response message to the target donor node 200-T. The serving cell information response message is a response message to the serving cell information request message. The serving cell information response message includes the PCI (or a list of PCIs) used by the adjacent donor node 200-TN. The serving cell information response message may include an information element (Serving Cell Information) including the serving cell information, and the PCI may be included in the information element. For example, the CU of the adjacent donor node 200-TN transmits the serving cell information response message as an Xn message to the CU of the target donor node 200-T.

[0114] In step S33, in response to receiving the serving cell information response message, the target donor node 200-T confirms whether the PCI used by the mobile IAB node 300M needs to be changed. The confirmation itself may be the same as in the first embodiment (step S18 or step S20). The target donor node 200-T may confirm an available PCI for the mobile IAB node 300M by avoiding PCIs used by adjacent donor nodes 200-TN. As in the first embodiment, the target donor node 200-T may confirm an available PCI for the mobile IAB node 300M by comparing or collating the PCI (or PCI list) used by itself. Thereafter, as in the first embodiment, the target donor node 200-T transmits an F1 setup response message including an added PCI list, a changed PCI list, or a deleted PCI list to the mobile IAB node 300M (step S21).

[0115] Second Embodiment Next, a second embodiment will be described, focusing on the differences from the first embodiment.

[0116] In the first embodiment, an embodiment for avoiding PCI collisions has been described, but the present invention is not limited to this. For example, the present invention can also be applied to avoiding collisions of PRACH resources instead of PCI collisions.

[0117] The PRACH resource is, for example, a resource used by a UE 100 under a mobile IAB node 300M to transmit a PRACH preamble signal that the UE 100 first transmits to the mobile IAB node 300M when the UE 100 performs a random access procedure with the mobile IAB node 300M.

[0118] For example, when the mobile IAB node 300M moves between donor nodes 200, the PRACH resource used in the cell under the mobile IAB node 300M and the PRACH resource used in the cell under the donor node 200 may be the same resource. In this case, if a UE 100-1 under the mobile IAB node 300M and a UE 100-2 under the donor node 200 simultaneously execute a random access procedure, the two UEs 100-1 and 100-2 may fail the random access procedure because they use the same PRACH resource. Therefore, the mobile IAB node 300M may not be able to properly communicate with the UE 100-1 under its control.

[0119] Therefore, the second embodiment aims to avoid collision of PRACH resources and enable the mobile IAB node 300M to appropriately communicate with the UE 100 under its control.

[0120] Therefore, in the second embodiment, first, a mobile relay node (e.g., mobile IAB node 300M) transmits an F1 setup request message including a first PRACH resource to be used by the mobile relay node to a target donor node (e.g., target donor node 200-T). Second, in response to receiving the F1 setup request message, the target donor node transmits a PRACH request message including the first PRACH resource to a neighboring donor node (e.g., neighboring donor node 200-TN) adjacent to the target donor node but other than the source donor node, in order to inquire whether the first PRACH resource is available for use.

[0121] This allows the adjacent donor node 200-TN to grasp the PRACH resources used by the mobile IAB node 300M. Therefore, the adjacent donor node 200-TN can prevent the use of resources among the PRACH resources that match the PRACH resources it uses, and can allow the use of resources that do not match the PRACH resources it uses. This allows the mobile IAB node 300M to avoid PRACH resource collisions between the UE 100-1 under the mobile IAB node 300M and the UE 100-2 under the adjacent donor node 200-TN, and to appropriately execute random access procedures with each other. Therefore, the mobile IAB node 300M can appropriately communicate with the UE 100-1 under its control.

[0122] The operation example according to the second embodiment can be implemented by replacing PCI (or PCI list) with PRACH resource (or PRACH resource list) in Fig. 11. For example, the steps in Fig. 11 can be replaced as follows:

[0123] (Step S16) In step S16, the F1 setup request message includes a PRACH resource (for example, a first PRACH resource) to be used by the mobile IAB node 300M.

[0124] (Step S17) In step S17, instead of the PCI request message, a PRACH request (mIAB PRACH Request) message is transmitted from the target donor node 200-T to the adjacent donor node 200-TN. The PRACH request message may be a message requesting that the PRACH resources used by the mobile IAB node 300M be also used by the adjacent donor node 200-TN. Alternatively, the PRACH request message may be a message inquiring whether the PRACH resources used by the mobile IAB node 300M are also usable by the adjacent donor node 200-TN. The PRACH request message includes (a list of) the PRACH resources to be used by the mobile IAB node 300M. Note that the PRACH request message may also be an Xn message.

[0125] (Step S18) In step S18, the adjacent donor node 200-TN determines PRACH resources available for use by the mobile IAB node 300M. The adjacent donor node 200-TN may compare or collate the PRACH resources included in the PRACH request message with the PRACH resources it is using and determine whether they match.

[0126] (Step S19) In step S19, the neighboring donor node 200-TN transmits a PRACH request acknowledgement (mIAB PRACH Request Acknowledge) message, which is a response message to the PRACH request message, to the target donor node. The PRACH request acknowledgement message includes PRACH resources (e.g., second PRACH resources) available for use by the mobile IAB node 300M. Specifically, the PRACH request acknowledgement message may include an allowed PRACH list representing a list of PRACH resources available for use by the mobile IAB node 300M. Alternatively, the PRACH request acknowledgement message may include an excluded PRACH list representing a list of PRACH resources unavailable for use by the mobile IAB node 300M. Alternatively, the PRACH request response message may include information indicating approval of all PRACH resources included in the PRACH request message. Alternatively, the PRACH request response message may include information indicating denial of all PRACH resources included in the PRACH request message (or that none of them can be used). Alternatively, the PRACH request response message may include information linking the PRACH resources used by the mobile IAB node 300M with the changed PRACH resources confirmed by the target donor node 200-T. Note that the PRACH request response message may also be an Xn message.

[0127] (Step S20) In step S20, in response to receiving the PRACH request response message, the target donor node 200-T confirms whether or not it is necessary to change the PRACH resources used by the mobile IAB node 300M. The target donor node 200-T may confirm this based on information included in the PRACH request response message (such as the Allowed PRACH list or the Exclude PRACH list). Furthermore, the target donor node 200-T may confirm whether or not it is necessary to change the PRACH resources by comparing or collating the PRACH resources used in its subordinate cells.

[0128] (Step S21) In step S21, the target donor node 200-T transmits an F1 setup response message to the mobile IAB node 300M. The F1 setup response message may include PRACH resources after changes to the PRACH resources used by the mobile IAB node 300M, depending on the confirmation result (step S20) in the target donor node 200-T. Specifically, the F1 setup response message may include an additional PRACH list (PRACH To Be Added List) including PRACH resources that are further available for use in the mobile IAB node 300M for the neighboring donor node 200-TN. Alternatively, the F1 setup response message may include a modified PRACH list (PRACH To Be Modified List) including modified PRACH resources that are usable for adjacent donor nodes 200-TN for the PRACH resources used by the mobile IAB node 300M. Alternatively, the F1 setup response message may include a removed PRACH list (PRACH To Be Remove List) including PRACHs that cannot be used by the mobile IAB node 300M for adjacent donor nodes 200-TN.

[0129] (Step S22) In step S22, the mobile IAB node 300M changes the PRACH resources in accordance with the list included in the F1 setup response message.

[0130] Another Example of the Second Embodiment Next, another example of the second embodiment will be described. The other example of the second embodiment will be described mainly focusing on the differences from the second embodiment.

[0131] In another example of the first embodiment, the target donor node 200-T requests the adjacent donor node 200-TN to provide a PCI list used by the adjacent donor node 200-TN. This is also applicable to the second embodiment regarding PRACH resource collisions.

[0132] That is, in another example of the second embodiment, an example will be described in which the target donor node 200-T requests the adjacent donor node 200-TN to provide the PRACH resource that the adjacent donor node 200-TN is using.

[0133] Specifically, first, a mobile relay node (e.g., mobile IAB node 300M) transmits an F1 setup request message including a first PRACH resource to be used at the mobile relay node to a target donor node (e.g., target donor node 200-T). Second, in response to receiving the F1 setup request message, the target donor node transmits a serving cell information request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than the source donor node, requesting the provision of a PRACH resource to be used at the neighboring donor node.

[0134] As a result, the target donor node 200-T can transmit to the mobile IAB node 300M, among the PRACH resources used by the mobile IAB node 300M, resources other than the PRACH resources used by the adjacent donor node 200-TN, as PRACH resources usable by the mobile IAB node 300M. Therefore, for example, different PRACH resources are used in the cell under the control of the mobile IAB node 300M and the cell under the control of the adjacent donor node 200-TN, thereby avoiding collision of PRACH resources. Therefore, the mobile IAB node 300M can appropriately communicate with the UE 100 under its control.

[0135] Another example of the operation of the second embodiment can be implemented by replacing the PCI (or PCI list) with the PRACH (or PRACH list) in the another example of the operation of the first embodiment (FIG. 12).

[0136] (Step S30) In step S30 of FIG. 12, the target donor node 200-T transmits a serving cell information request message requesting the provision of PRACH resources to the adjacent donor node 200-TN.

[0137] (Step S31) In step S31, in response to receiving the serving cell information request message, the adjacent donor node 200-TN lists the PRACH resources being used by the adjacent donor node 200-TN.

[0138] (Step S32) In step S32, the adjacent donor node 200-TN transmits a serving cell information response message to the target donor node 200-T. The serving cell information response message includes the PRACH (or a list of PRACHs) used by the adjacent donor node 200-TN.

[0139] (Step S33) In step S33, the target donor node 200-T confirms whether or not it is necessary to change the PRACH resources used by the mobile IAB node 300M. The target donor node 200-T may confirm available PRACH resources by avoiding PRACH resources used by the adjacent donor node 200-TN for the PRACH resources used by the mobile IAB node 300M. The target donor node 200-T may confirm available PRACH resources for the mobile IAB node 300M by comparing or collating the PRACH resources with the PRACH resources used by the target donor node 200-T itself.

[0140] [Other Embodiments] The above-described operational flows are not limited to being implemented independently, but can be implemented by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow. In each flow, it is not necessary to execute all steps, and only some steps may be executed.

[0141] In the above-described embodiments and examples, an example in which the base station is an NR base station (gNB) has been described, but the base station may be an LTE base station (eNB) or a 6G base station. The base station may also be a relay node such as an IAB (Integrated Access and Backhaul) node. The base station may also be a DU of the IAB node. The UE 100 may also be an MT (Mobile Termination) of the IAB node.

[0142] Also, the term "network node" primarily refers to a base station, but may also refer to a device in the core network or part of a base station (CU, DU, or RU).

[0143] A program that causes a computer to execute each process performed by the UE 100 or the gNB 200 may be provided. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0144] In addition, circuits that perform each process performed by UE100 or gNB200 may be integrated, and at least a portion of UE100 or gNB200 may be configured as a semiconductor integrated circuit (chip set, SoC: System on a chip).

[0145] As used in this disclosure, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." The terms "include," "comprise," and variations thereof do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Additionally, the term "or," as used in this disclosure, is not intended to mean an exclusive or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used herein as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0146] Although one embodiment has been described in detail above with reference to the drawings, the specific configuration is not limited to the above, and various design changes can be made within the scope of the gist. Furthermore, the embodiments, operation examples, and processes can be appropriately combined within the scope of not being inconsistent.

[0147] This application claims priority from Japanese Patent Application No. 2022-155349 (filed September 28, 2022), the entire contents of which are incorporated herein by reference.

[0148] (Supplementary Note) (Supplementary Note 1) A communication control method used in a cellular communication system, comprising: a step of a mobile relay node transmitting an F1 setup request message including a first physical cell ID used in the mobile relay node to a target donor node; and a step of the target donor node, in response to receiving the F1 setup request message, transmitting a PCI request message including the first physical cell ID to an adjacent donor node adjacent to the target donor node, the adjacent donor node being other than a source donor node, to inquire whether the first physical cell ID is usable.

[0149] (Supplementary Note 2) The communication control method according to Supplementary Note 1, further comprising the step of: the neighboring donor node determining a second physical cell ID usable by the mobile relay node in response to receiving the PCI request message.

[0150] (Supplementary Note 3) The communication control method according to Supplementary Note 1 or Supplementary Note 2, wherein the determining step includes a step of determining the second physical cell ID by the adjacent donor node depending on whether a physical cell ID used by the adjacent donor node matches the first physical cell ID.

[0151] (Supplementary Note 4) The communication control method according to any one of Supplementary Note 1 to Supplementary Note 3, further comprising the step of: the adjacent donor node transmitting a PCI request response message including the second physical cell ID to the target donor node.

[0152] (Supplementary Note 5) The communication control method according to any one of Supplementary Notes 1 to 4, wherein the step of transmitting the PCI request response message includes a step of the adjacent donor node transmitting the PCI request response message to the target donor node, the PCI request response message including a third physical cell ID that is unusable by the mobile relay node.

[0153] (Supplementary Note 6) The communication control method according to any one of Supplementary Notes 1 to 5, further comprising the step of: the target donor node transmitting an F1 setup response message to the mobile relay node, the F1 setup response message including a changed physical cell ID for the first physical cell ID.

[0154] (Supplementary Note 7) A communication control method used in a cellular communication system, comprising: a step of a mobile relay node transmitting an F1 setup request message including a first physical cell ID to be used in the mobile relay node to a target donor node; and a step of the target donor node, in response to receiving the F1 setup request message, transmitting a serving cell information request message to an adjacent donor node adjacent to the target donor node, the adjacent donor node being other than a source donor node, requesting the provision of a physical cell ID to be used in the adjacent donor node.

[0155] (Supplementary Note 8) The communication control method according to Supplementary Note 7, further comprising a step of transmitting, to the target donor node, a serving cell information response message including the physical cell ID used by the adjacent donor node in response to receiving the serving cell information request message.

[0156] (Supplementary Note 9) A communication control method used in a cellular communication system, comprising: a step of transmitting, by a mobile relay node, to a target donor node, an F1 setup request message including a first PRACH resource to be used by the mobile relay node; and a step of transmitting, by the target donor node, in response to receiving the F1 setup request message, a PRACH request message including the first PRACH resource to an adjacent donor node adjacent to the target donor node, the adjacent donor node being other than a source donor node, to inquire whether the first PRACH resource is available for use.

[0157] (Supplementary Note 10) The communication control method according to Supplementary Note 9, further comprising the step of the neighbouring donor node transmitting a PRACH request response message to the target donor node, the PRACH request response message including second PRACH resources available at the mobile relay node.

[0158] (Supplementary Note 11) The communication control method according to Supplementary Note 9 or Supplementary Note 10, further comprising the step of the target donor node sending an F1 setup response message to the mobile relay node, the F1 setup response message including a PRACH resource after the change to the first PRACH resource.

[0159] (Supplementary Note 12) A communication control method used in a cellular communication system, comprising: a step of transmitting, by a mobile relay node, an F1 setup request message including a first PRACH resource to be used at the mobile relay node to a target donor node; and a step of transmitting, by the target donor node, in response to receiving the F1 setup request message, a serving cell information request message to an adjacent donor node adjacent to the target donor node, the adjacent donor node being other than a source donor node, requesting the provision of a PRACH resource to be used at the adjacent donor node.

[0160] (Supplementary Note 13) The communication control method according to Supplementary Note 12, further comprising the step of transmitting, by the neighboring donor node, a serving cell information response message including the PRACH resources used by the neighboring donor node to the target donor node in response to receiving the serving cell information request message.

[0161] 1: Cellular communication system 10: 5GC 100: UE 110: Wireless communication unit 120: Control unit 200: Donor node (gNB) 200-S: Source donor node 200-T: Target donor node 210: Wireless communication unit 230: Control unit 300: IAB node 300M: Mobile IAB node 310: Wireless communication unit 320: Control unit

Claims

1. A communication control method for use in a cellular communication system, comprising: sending, by the mobile relay node, an F1 Setup Request message to the target donor node, the F1 Setup Request message including a first physical cell ID for use at the mobile relay node; In response to receiving the F1 setup request message, the target donor node transmits a PCI request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than a source donor node, to inquire whether the first physical cell ID is available. Communications control method.

2. and determining, by the neighboring donor node in response to receiving the PCI request message, a second physical cell ID available for use by the mobile relay node. The communication control method according to claim 1.

3. The determining step includes determining the second physical cell ID by the adjacent donor node depending on whether a physical cell ID used by the adjacent donor node matches the first physical cell ID. The communication control method according to claim 2.

4. The neighboring donor node may further include transmitting a PCI request response message to the target donor node that includes the second physical cell ID. The communication control method according to claim 2.

5. Transmitting the PCI request response message includes the neighboring donor node transmitting the PCI request response message to the target donor node including a third physical cell ID that is unavailable to the mobile relay node.

5. The communication control method according to claim 4.

6. The target donor node may further include transmitting an F1 Setup Response message to the mobile relay node, the F1 Setup Response message including a changed physical cell ID for the first physical cell ID. The communication control method according to claim 2.

7. A communication control method for use in a cellular communication system, comprising: sending, by the mobile relay node, an F1 Setup Request message to the target donor node, the F1 Setup Request message including a first physical cell ID for use at the mobile relay node; In response to receiving the F1 setup request message, the target donor node transmits a serving cell information request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than the source donor node, requesting provision of a physical cell ID to be used by the neighboring donor node. Communications control method.

8. The neighboring donor node may further include, in response to receiving the serving cell information request message, transmitting a serving cell information response message including the physical cell ID used by the neighboring donor node to the target donor node. The communication control method according to claim 7.

9. A communication control method for use in a cellular communication system, comprising: sending, by the mobile relay node, an F1 Setup Request message to the target donor node, the F1 Setup Request message including a first Physical Random Access Channel (PRACH) resource for use at the mobile relay node; In response to receiving the F1 setup request message, the target donor node transmits a PRACH request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than a source donor node, the PRACH request message including the first PRACH resource to inquire whether the first PRACH resource is available. Communications control method.

10. and transmitting a PRACH request response message to the target donor node including a second PRACH resource available at the mobile relay node from the neighboring donor node. The communication control method according to claim 9.

11. The target donor node may further include transmitting an F1 setup response message to the mobile relay node, the F1 setup response message including a modified PRACH resource relative to the first PRACH resource. The communication control method according to claim 10.

12. A communication control method for use in a cellular communication system, comprising: sending, by the mobile relay node, an F1 Setup Request message to the target donor node, the F1 Setup Request message including a first Physical Random Access Channel (PRACH) resource for use at the mobile relay node; In response to receiving the F1 setup request message, the target donor node transmits a serving cell information request message to a neighboring donor node adjacent to the target donor node, the neighboring donor node being other than the source donor node, requesting provision of a PRACH resource to be used by the neighboring donor node. Communications control method.

13. The neighboring donor node may further include, in response to receiving the serving cell information request message, transmitting a serving cell information response message including the PRACH resource used by the neighboring donor node to the target donor node. The communication control method according to claim 12.

14. A target donor node for use in a cellular communication system, comprising: a receiver for receiving an F1 setup request message from a mobile relay node, the F1 setup request message including a first physical cell ID for use at the mobile relay node; a transmitter for transmitting a PCI request message including the first physical cell ID to an adjacent donor node adjacent to the target donor node other than a source donor node in response to receiving the F1 setup request message, in order to inquire whether the first physical cell ID is available. Target donor node.

15. A target donor node for use in a cellular communication system, comprising: a receiver for receiving an F1 setup request message from a mobile relay node, the F1 setup request message including a first physical cell ID for use at the mobile relay node; a transmitter that transmits a serving cell information request message to a neighboring donor node other than a source donor node that is adjacent to the target donor node in response to receiving the F1 setup request message, requesting provision of a physical cell ID to be used by the neighboring donor node. Target donor node.

16. A target donor node for use in a cellular communication system, comprising: a receiving unit for receiving an F1 setup request message including a first PRACH (Physical Random Access Channel) resource to be used in the mobile relay node from the mobile relay node; a transmitter for transmitting a PRACH request message including the first PRACH resource to a neighboring donor node other than a source donor node adjacent to the target donor node in response to receiving the F1 setup request message, in order to inquire whether the first PRACH resource is available. Target donor node.

17. A target donor node for use in a cellular communication system, comprising: a receiving unit for receiving an F1 setup request message including a first PRACH (Physical Random Access Channel) resource to be used in the mobile relay node from the mobile relay node; a transmitter that transmits a serving cell information request message to a neighboring donor node other than a source donor node that is neighboring the target donor node in response to receiving the F1 setup request message, requesting provision of a PRACH resource to be used by the neighboring donor node. Target donor node.

18. A mobile relay node for use in a cellular communications system, comprising: a transmitter for transmitting an F1 setup request message to a target donor node, the F1 setup request message including a first physical cell ID for use in the mobile relay node; Mobile relay node.

19. A mobile relay node for use in a cellular communications system, comprising: A transmitter for transmitting an F1 setup request message including a first PRACH (Physical Random Access Channel) resource to be used in the mobile relay node to a target donor node. Mobile relay node.