Communication control method

Abstract

A communication control method according to one aspect of the present invention is used in a cellular communication system. This communication control method includes a step in which, in response to receiving a prescribed message from a source donor node, a mobile relay node that moves from the source donor node to a target donor node transmits, to the target donor node, an F1 setup request message requesting the establishment of an F1 connection. The prescribed message indicates either a new establishment request for an F1 connection to the target donor node, or a movement instruction to the target donor node.

Description

Communication Control Method

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

[0002] The Third Generation Partnership Project (3GPP), a standardization project for cellular communication systems, is considering the introduction of a new relay node called an Integrated Access and Backhaul (IAB) node (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] In addition, in NR in 3GPP, the aggregation node constituting the gNB is defined as a CU (Central Unit) and the distributed node is defined as a DU (Distributed Unit). The PDCP layer and above are installed in the CU, and the RLC layer and below are installed in the DU, and the interface between the CU and DU is specified as F1.

[0004] 3GPP TS 38.300 V17.1.0 (2022-06)

[0005] 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 comprising the steps of: a mobile relay node moving from a source donor node to a target donor node, in response to receiving a predetermined message from the source donor node, transmitting an F1 setup request message to the target donor node requesting establishment of an F1 connection, wherein the predetermined message is a message representing either a request to newly establish an F1 connection with the target donor node or a movement instruction to the target donor node.

[0006] 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 the step of, when a relay node is operating as a mobile relay node, broadcasting a system information block that does not include information indicating that the relay node supports other relay nodes.

[0007] 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 for IAB-MT RRC connection and NAS connection. FIG. 7 is a diagram illustrating an example protocol stack for the F1-U protocol. FIG. 8 is a diagram illustrating an example protocol stack for the F1-C protocol. FIGS. 9A and 9B are diagrams illustrating an example of movement of a mobile IAB node according to the first embodiment. FIG. 10 is a diagram illustrating an example operation according to the first embodiment. FIG. 11 is a diagram illustrating an example operation according to the second embodiment. FIG. 12 is a diagram illustrating an example of a traditional handover (top) and an example of group reconfiguration (bottom). Figure 13 illustrates a solution 1 for reducing service interruptions. Figure 14 illustrates a solution 2 for reducing service interruptions.

[0008] 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.

[0009] [First embodiment]

[0010] (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.

[0011] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system 1 according to an embodiment.

[0012] 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.

[0013] 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).

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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).

[0020] 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.

[0021] 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.

[0022] FIG. 2 is a diagram showing an example of the relationship between the IAB node 300, parent nodes, and child nodes.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] (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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] (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.

[0036] 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.

[0037] 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.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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."

[0051] 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.

[0052] (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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] In the following, the terms "migration" of a mobile IAB node and "handover" of a mobile IAB node may be used interchangeably.

[0057] In the following description, the mobile IAB node may be referred to as a "mobile IAB node." The mobile IAB node may also be referred to as a "migrating IAB node." In either case, the mobile IAB node may be referred to as a mobile IAB node.

[0058] (Partial and Full Movement) A migrating IAB node may move between donor nodes (IAB-donors) 200 .

[0059] 9(A) and 9(B) are diagrams illustrating an example of movement of the mobile IAB node 300M according to the first embodiment. 9(A) and 9(B) illustrate an example in which the mobile IAB node 300M moves from the source donor node 200-S to the target donor node 200-T.

[0060] Of these, FIG. 9A shows an example of partial migration, and FIG. 9B shows an example of full migration.

[0061] 9A, in partial mobility, IAB-DU#1 (and UE 100) of the mobile IAB node 300M is terminated in CU#1 (200-CU#1) of the source donor node 200-S, while IAB-MT of the mobile IAB node 300M is moved to CU#2 (200-CU#2) of the target donor node 200-T. Partial mobility refers to a state in which, for example, the connection of UE 100 under the mobile IAB node 300M remains in the source donor node 200-S via IAB-DU#1 of the mobile IAB node 300M.

[0062] On the other hand, as shown in Figure 9 (B), in the case of total movement, the connection of the mobile IAB node 300M (and the UE 100) moves from CU #1 (200-CU #1) of the source donor node 200-S to CU #2 (200-CU #2) of the target donor node 200-T. Total movement refers to, for example, a state in which the connection of the UE 100 moves to the target donor node 200-T via IAB-DU #2 of the mobile IAB node 300M.

[0063] Here, to realize the whole mobility, it is necessary that IAB-DU#2 is logically established in the mobile IAB node 300M and that an F1 connection is established between the IAB-DU#2 and CU#2 (200-CU#2) of the target donor node 200-T. This is because the UE 100 can exchange various messages with the target donor node 200-T via the IAB-DU#2.

[0064] In order for an F1 connection to be established between IAB-DU#2 and CU#2 (200-CU#2) of target donor node 200-T, an F1 setup request (F1 SETUP REQUEST) must be sent from mobile IAB node 300M to CU#2 (200-CU#2) of target donor node 200-T.

[0065] However, the mobile IAB node 300M does not know when to transmit the F1 setup request. If the F1 setup request is not transmitted at an appropriate time, the F1 connection with the target donor node 200-T cannot be established, and the entire movement may not be able to be performed. Therefore, the UE 100 under the mobile IAB node 300M may not be able to properly connect to the network.

[0066] Therefore, the first embodiment aims to enable the UE 100 to properly connect to the network.

[0067] In the first embodiment, a source donor node (e.g., source donor node 200-S) sends a request to a mobile relay node (e.g., a mobile IAB node) moving from the source donor node to a target donor node (e.g., target donor node 200-T) to establish a new F1 connection to the target donor node.

[0068] As a result, for example, the mobile IAB node 300M only needs to transmit an F1 setup request message in response to receiving a new establishment request from the source donor node 200-S, and can transmit the message at the appropriate timing. Therefore, the mobile IAB node 300M can establish an F1 connection via IAB-DU#2 at the appropriate timing and perform overall mobility. Therefore, the UE 100 can connect to the network via the IAB-DU#2, and can connect to the network at the appropriate timing.

[0069] (Operation Example According to First Embodiment) FIG. 10 is a diagram illustrating an operation example according to the first embodiment.

[0070] 10 illustrates an example in which a mobile IAB node 300M moves from a source donor node 200-S to a target donor node 200-T, thereby executing a full migration. The source donor node 200-S may be configured with CU#1 (200-CU#1) and DU#1 (200-DU#1) of the source donor node 200-S shown in FIG. 9B. The target donor node 200-T may also be configured with CU#2 (200-CU#2) and DU#2 (200-DU#2) of the target donor node 200-T shown in FIG. 9B.

[0071] 10, in step S10, the source donor node 200-S determines the migration of the mobile IAB node 300M. The CU of the source donor node 200-S may determine the migration in response to receiving a measurement report from the IAB-MT of the mobile IAB node 300M via the DU of the source donor node 200-S.

[0072] In step S11, the source donor node 200-S transmits a handover request (HANDOVER REQUEST) message for the mobile IAB node 300M to the target donor node 200-T. The source donor node 200-S may transmit an execution request requesting that the mobile IAB node 300M perform a full migration by including it in the message. Alternatively, the source donor node 200-S may transmit information indicating whether or not the mobile IAB node 300M will perform a full migration by including it in the message. Alternatively, the source donor node 200-S may transmit an execution request requesting that the mobile IAB node 300M perform a partial migration by including it in the message. Alternatively, the source donor node 200-S may transmit information indicating whether or not the mobile IAB node 300M will perform a partial migration by including it in the message. For example, the CU of the source donor node 200-S sends the handover request message, which is an Xn message, to the CU of the target donor node 200-T.

[0073] In step S12, the target donor node 200-T decides to accept the handover based on the handover request message. Also, the target donor node 200-T decides to perform a full migration. For example, the CU of the target donor node 200-T decides to accept the handover and perform a full migration in response to receiving the handover request message.

[0074] In step S13, the target donor node 200-T transmits a handover request acknowledgement (HANDOVER REQUEST ACKNOWLEDGE) message to the source donor node 200-S. For example, in response to the CU of the target donor node 200-T deciding to accept the handover (step S12), the CU transmits the message, which is an Xn message, to the CU of the source donor node 200-S.

[0075] The handover request acknowledgement message includes an RRC reconfiguration message for the mobile IAB node 300M. The RRC reconfiguration message may include information requesting new establishment of an F1 connection. Alternatively, the RRC reconfiguration message may include information indicating execution of a full migration. Note that the RRC reconfiguration message functions as, for example, a handover command instructing a handover for the mobile IAB node 300M.

[0076] In step S14, the source donor node 200-S may transmit a request to establish a new F1 connection to the mobile IAB node 300M. For example, in response to receiving the handover request acknowledgement message (step S13), the CU of the source donor node 200-S generates an F1 message including a request to establish a new F1 connection and transmits the generated F1 message to the IAB-DU of the mobile IAB node 300M. The CU of the source donor node 200-S may transmit the F1 message before the decision to move of the mobile IAB node 300M (step S10). The CU of the source donor node 200-S may transmit the F1 message immediately after the decision to move. Note that the new establishment request may be transmitted by being included in the RRC reconfiguration message transmitted in step S13 described above and step S15 described below. In this case, step S14 may be omitted.

[0077] In step S15, the source donor node 200-S transmits the RRC reconfiguration message included in the handover request acknowledgement message (step S13) to the mobile IAB node 300M. For example, the following processing is performed. That is, the CU of the source donor node 200-S extracts the RRC reconfiguration message from the handover request acknowledgement message received in step S13 and transmits an F1 message including the RRC reconfiguration message to the DU of the source donor node 200-S. Then, the DU of the source donor node 200-S extracts the RRC reconfiguration message from the F1 message and transmits the RRC reconfiguration message to the IAB-MT of the mobile IAB node 300M. The RRC reconfiguration message may be a request to establish a new F1 connection with the target donor node 200-T. Alternatively, the RRC reconfiguration message may include information indicating a request to establish a new F1 connection with the target donor node 200-T. When the AS layer receives the request to establish a new F1 connection, it may notify the upper layer (F1AP layer) of the request.

[0078] In step S16, the mobile IAB node 300M recognizes that a new F1 connection needs to be established with the target donor node 200-T by receiving either an F1 message (step S14) containing a request to establish a new F1 connection or an RRC reconfiguration message (step S15).

[0079] Then, the mobile IAB node 300M transmits an F1 setup request (F1 SETUP REQUEST) message requesting the establishment of the F1 connection to the target donor node 200-T. That is, the mobile IAB node 300M transmits the F1 setup request message in response to receiving the request to establish a new F1 connection (step S14 or step S15). For example, the IAB-DU of the mobile IAB node 300M transmits the F1 setup request message to the CU of the target donor node 200-T. The mobile IAB node 300M may transmit the F1 setup request message via the source donor node 200-S.

[0080] In step S17, the mobile IAB node 300M establishes a new F1 connection with the target donor node 200-T. As a result, the mobile IAB node 300M enters a state in which "IAB-DU#2" shown in FIG. 9B exists. Then, the mobile IAB node 300M establishes an F1 connection with the CU of the target donor node 200-T via "IAB-DU#2," and is thus able to perform overall migration.

[0081] When the entire movement is completed, the mobile IAB node 300M performs processing to discard the F1 connection with the source donor node 200-S. The F1 connection is, for example, the F1 connection from "IAB-DU#1" to CU#1 (200-CU#1) of the source donor node 200-S, as shown in FIG. 9B. The entire movement may be completed when handover of all UEs 100 under the mobile IAB node 300M is completed.

[0082] In step S18, the F1 connection may be torn down by the source donor node 200-S transmitting a request to torn down the F1 connection to the mobile IAB node 300M. For example, the CU of the source donor node 200-S transmits an F1 message including a request to torn down the F1 connection to the IAB-DU of the mobile IAB node 300M.

[0083] In step S19, the target donor node 200-T may transmit a request to tear down the F1 connection. In this case, an F1 message including a request to tear down the F1 connection may also be transmitted. For example, the CU of the target donor node 200-T transmits an F1 message including a request to tear down the F1 connection to the IAB-DU of the mobile IAB node 300M. The CU of the target donor node 200-T may transmit an F1 message including information indicating the completion of the entire migration instead of a request to tear down the F1 connection.

[0084] In step S20, the mobile IAB node 300M determines that the entire movement is complete when all UE contexts are lost (or all UE contexts are released) in the F1 connection (F1 entity) connected to the source donor node 200-S. Then, the mobile IAB node 300M transmits an F1 REMOVE REQUEST message to the source donor node 200-S to request the removal of the F1 connection.

[0085] The mobile IAB node 300M may send an F1 discard request message in response to receiving either a request to discard the F1 connection from the source donor node 200-S (step S18) or a request to discard the F1 connection from the target donor node 200-T (step S19).

[0086] In this way, the mobile IAB node 300M transmits an F1 discard request message in response to receiving a request to discard the F1 connection to the source donor node 200-S from the source donor node 200-S or the target donor node 200-T. Therefore, the mobile IAB node 300M can transmit the F1 discard request message to the source donor node 200-S at an appropriate timing.

[0087] Second Embodiment Next, a second embodiment will be described.

[0088] 3GPP proposes that mobile IAB node 300M should not be connected to IAB node 300 as a child node or grandchild node, but should be connected only to UE 100. This is because if IAB node 300 connects to mobile IAB node 300M as a child node or grandchild node, it is expected that control of not only the IAB node but also the UEs under the IAB node will become complicated.

[0089] Here, there is a problem as to how to connect only UE 100 to mobile IAB node 300M.

[0090] The purpose of the second embodiment is to enable only UE 100 to connect to the mobile IAB node 300M, thereby enabling UE 100 to properly connect to the network.

[0091] Therefore, in the second embodiment, when the IAB node 300 operates as the mobile IAB node 300M, the IAB node 300 does not set IAB support information (iab-Support IE), which is an information element indicating that the IAB node is supported, in the SIB 1. In other words, the IAB node 300 broadcasts an SIB 1 that does not include the IAB support information.

[0092] Specifically, when a relay node (e.g., IAB node 300) is operating as a mobile relay node (e.g., mobile IAB node 300M), it broadcasts a system information block (e.g., SIB1) that does not include information indicating that it supports other relay nodes (e.g., IAB support information).

[0093] As a result, the IAB-MT of the IAB node 300 that received the SIB1 recognizes that the IAB node that broadcast the SIB1 (or the cell that broadcast the SIB1) does not support IAB nodes. Therefore, the IAB-MT of the IAB node 300 that received the SIB1 does not perform a connection process (e.g., a cell selection procedure or a cell reselection procedure) with the IAB node that broadcast the SIB1.

[0094] Furthermore, even if the IAB support information is not included in the SIB, the UE 100 that receives the SIB 1 does not have its own connection to the IAB node 300 restricted because the IAB support information is an information element for the IAB node 300.

[0095] Therefore, the IAB node 300 operating as the mobile IAB node 300M does not have other IAB nodes as child nodes or grandchild nodes, but has only the UE 100. Therefore, the UE 100 under the control of the mobile IAB node 300M can properly connect to the network.

[0096] (Example of Operation According to Second Embodiment) Next, an example of operation according to the second embodiment will be described.

[0097] FIG. 11 is a diagram illustrating an example of operation according to the second embodiment.

[0098] 11, in step S30, the IAB node 300-1 determines that it is operating as the mobile IAB node 300M. The IAB node 300-1 determines that it is operating as the mobile IAB node 300M, for example, in the following manner.

[0099] First, IAB node 300-1 may determine that it is operating as mobile IAB node 300M because it is moving. IAB node 300-1 may determine that it is moving based on the detection result of an acceleration sensor or a Global Navigation Satellite System (GNSS) reception signal received by a GNSS reception unit.

[0100] Second, IAB node 300-1 may determine that it is operating as mobile IAB node 300M if it has been authorized by the core network (CN) to operate as mobile IAB node 300M. IAB node 300-1 may determine that authorization has been granted by receiving a message including information indicating the authorization from AMF 11 or the like.

[0101] Third, the IAB node 300-1 may determine that it is operating as the mobile IAB node 300M if it has been authorized by the donor node 200 to operate as the mobile IAB node 300M. The IAB node 300-1 may determine that authorization has been granted by receiving a message including information indicating the authorization from the donor node 200. Alternatively, the IAB node 300-1 may determine that it has been implicitly authorized as the mobile IAB node 300M by having settings specific to the mobile IAB node 300M configured by the donor node 200.

[0102] In addition, if the IAB node 300 is permitted to operate as the mobile IAB node 300M in the upper layer, the IAB node 300 may output the permission to the AS layer.

[0103] In step S31, if the IAB node 300-1 is operating as the mobile IAB node 300M, it does not transmit IAB support information. That is, the IAB node 300-1 broadcasts an SIB1 that does not include IAB support information. The IAB node 300-1 may broadcast a system information block (e.g., SIB1) that includes information indicating that the IAB node 300-1 is the mobile IAB node 300M. Alternatively, the IAB node 300-1 may broadcast a system information block (e.g., SIB1) that includes information indicating that the IAB node 300-1 is not an intermediate IAB node 300S.

[0104] The other IAB node 300-2 that received SIB1 excludes the cell of the IAB node 300-1 that broadcast SIB1 (step S31) from the candidate cells for the cell selection procedure or cell reselection procedure. As a result, the other IAB node 300-2 does not connect to the IAB node 300-1 that broadcast SIB1.

[0105] As used in this disclosure, the terms "based on" and "depending on" 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." Furthermore, the terms "include" and "comprise" 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. Furthermore, 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.

[0106] The above describes the embodiments in detail with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes can be made within the scope that does not deviate from the gist of the invention.

[0107] This application claims priority to U.S. Provisional Application No. 63 / 395,944 (filed August 8, 2022), the entire contents of which are incorporated herein by reference.

[0108] (Appendix 1)

[0109] (Supplementary Note 1) A communication control method for use in a cellular communication system, comprising a step in which a source donor node transmits a request for new establishment of an F1 connection to a target donor node to a mobile relay node moving from the source donor node to the target donor node.

[0110] (Supplementary Note 2) The communication control method according to Supplementary Note 1, further comprising a step of the mobile relay node, in response to receiving the new establishment request, sending an F1 setup request message to the target donor node requesting to establish the F1 connection.

[0111] (Supplementary Note 3) The communication control method according to Supplementary Note 1 or Supplementary Note 2, further comprising a step of the source donor node sending an execution request to the target donor node requesting that the mobile relay node perform a full migration, wherein the full migration is a state in which the connection of the mobile relay node has moved from a control unit (CU) of the source donor node to a control unit (CU) of the target donor node.

[0112] (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 source donor node or the target donor node sending a request to the mobile relay node to discard the F1 connection to the source donor node.

[0113] (Supplementary Note 5) The communication control method according to any one of Supplementary Notes 1 to 4, further comprising the step of: in response to receiving the discard request, the mobile relay node transmitting an F1 discard request message to the source donor node, requesting discard of the F1 connection to the source donor node.

[0114] (Supplementary Note 6) A communication control method for use in a cellular communication system, comprising: when a relay node operates as a mobile relay node, broadcasting a system information block that does not include information indicating that it supports other relay nodes.

[0115] (Supplementary Note 7) The communication control method according to Supplementary Note 6, wherein the step of reporting includes a step of the relay node reporting the system information block including information indicating that the relay node is the mobile relay node.

[0116] (Addendum 2) 1. Introduction RAN#94e approved a new work item on mobility IAB, the WID of which was revised in RAN#96 as follows:

[0117] The detailed goals of this work item are as follows: ・Define transition / topology adaptation procedures to enable IAB node mobility. This includes inter-donor transition (full transition) of entire mobile IAB nodes. ・Enhance mobility for IAB nodes and their served UEs. This includes aspects related to group mobility. There are no optimizations targeted at surrounding UEs. Note: The solution should avoid touching on topics already discussed in Rel-17 or topics excluded from Rel-17, except for enhancements specific to IAB node mobility. ・Mitigate interference due to IAB node mobility, for example, avoid collisions of reference and control signals (e.g., PCI, RACH). Note: At the start of the work, RAN3 and RAN2 should discuss potential complications between scenarios where a mobile IAB node connects to a stationary (intermediate) IAB node and scenarios where a mobile IAB node connects directly to an IAB donor.

[0118] The following principles should be respected: - Mobile IAB nodes must be able to serve legacy UEs. - Solutions providing mobile IAB optimization may require Rel-18 UE extensions, but only if such extensions are backward compatible.

[0119] One of the key challenges in Rel-18 is how to efficiently perform handovers of multiple descendant UEs during the transition of a mobile IAB node. In this appendix, an initial discussion on mobility enhancements for mobile IABs from the perspective of UE handover is provided.

[0120] 2. Discussion 2.1 Group Reconfiguration Group UE mobility is expected as one of the possible enhancements of mobile IAB, because when a mobile IAB node moves to a new IAB donor, many UEs need to be handed over simultaneously.

[0121] In the current specification, handover is indicated by dedicated signaling, i.e., RRC reconfiguration and synchronization. This means that multiple individual messages are sent simultaneously to each UE. Therefore, to reduce the signaling overhead and delay, group reconfiguration is a possible candidate, which is expected to reconfigure multiple UEs with one message.

[0122] Group reconfiguration has already been discussed in Rel-17 MBS as "Common RRC Architecture" and the following summary is provided:

[0123] Summary of Common RRC Structure Conclusion The majority of the panel, 16 to 5, agreed that a common RRC configuration is not feasible. From the presenters' perspective, there appear to be no technical limitations that prevent it, but there appears to be significant opposition to doing so. The general understanding is that adopting a common RRC structure would increase overhead for Uu signaling, but would provide benefits for F1 / E1 signaling. However, given the industry's position, it is suggested that the current RRC signaling structure be maintained.

[0124] Proposal 2: Maintain the current CRRRC structure and do not move forward with a common RRC structure (i.e., no impact on RRCCR).

[0125] The point is that UEs need to receive individual RRC reconfiguration, and in addition they need to receive group RRC reconfiguration. Therefore, there was a common view in MBS that there is little benefit (or even disadvantage) to Uu signaling, but there may be some benefit to F1 / E1 signaling. As a result, RAN2 decided to maintain the current structure, i.e., only individual RRC reconfiguration.

[0126] In case P2, RAN2 assumes that if agreed, RRC will continue to use the dedicated UE configuration.

[0127] Similar concerns apply to mobile IAB: different UEs have different configurations, and one group reconfiguration cannot handle the different configurations of different UEs. Although F1 signal reduction is also more useful for mobile IAB than for MBS, access link signal reduction is still more important since the backhaul link is typically assumed to be over FR2.

[0128] Since the WID clearly states that "solutions should avoid touching on areas where Rel-17 discussions have already taken place and the topic has been excluded from Rel-17, except for improvements specific to IAB node mobility," RAN2 does not need to reopen group reconfiguration (or common RRC structure) in Rel-18 mobile IAB, at least from RAN2's point of view.

[0129] Proposal 1: RAN2 should agree to continue using only individual RRC reconfiguration for UE handovers involving the movement of mobile IAB nodes.

[0130] 2.2 Handover for Legacy UE As indicated in the WID (Work Item Description), "Mobile IAB nodes need to support legacy UEs." Therefore, RAN2 should consider handover methods for legacy UEs.

[0131] RAN3 had two solutions for reducing service interruption during inter-donor IAB node migration in Rel-17, among which solution 1 is shown in Figure 12 below.

[0132] In Solution 1, the IAB-DU withholds the RRC reconfiguration message to the child node upon handover completion. RAN2 concluded that both solutions require further discussion, but determined that Solution 1 has less overall impact than Solution 2.

[0133] Of course, UE handover can also be performed without Solution 1. However, similar to the Rel-17 IAB node problem, since handover of descendant UEs is involved, if Solution 1 is not applied, the UE will experience service interruption during the moving IAB node transition. Therefore, RAN2 needs to assume that Solution 1 for intra-donor transition is reused to reduce service interruption for legacy UEs during inter-donor moving IAB node transition.

[0134] Proposal 2: RAN2 should assume that Solution 1 for reducing service interruption during Rel-17 intra-donor IAB node transition can be reused for legacy UE handover.

[0135] 2.3 Conditional Reconfiguration If individual RRC reconfigurations are sent to the UE simultaneously, the load on radio resources may increase due to many RRC messages and corresponding responses. For load balancing, i.e., time domain distribution, conditional reconfiguration is considered useful because it allows the IAB donor to avoid sending many simultaneous messages by pre-reconfiguring the IAB node while it is moving. A similar solution exists in Solution 2 for reducing service interruptions in Rel-17.

[0136] Observation 1: Conditional reconfiguration can help IAB donors distribute RRC reconfiguration messages in the time domain.

[0137] Depending on how the mobile IAB-DU handles cells and partly at the discretion of RAN3, it may be necessary for the mobile IAB-DU to change cell IDs after a mobile IAB node transition, for example, if this is necessary to avoid PCI collisions in the target topology. In this case, the UE also needs to move from the old cell (the cell that is disappearing) to the new cell (the cell that is becoming available), but both cells are managed by the same mobile IAB-DU. For such "cell shifts," a conditional reconfiguration is considered more effective than a traditional HO command.

[0138] Observation 2: Conditional reconfiguration may work efficiently when the serving cell ID changes due to the transition of a mobile IAB node.

[0139] Considering the above examples (but not limited to them), improvements to conditional reconfiguration may be worth discussing in RAN2, for example, considering whether existing trigger conditions can be reused for mobile IABs.

[0140] Proposal 3: RAN2 should consider whether conditional reconfiguration to UEs can be enhanced to improve the mobility of mobile IAB nodes.

[0141] 2.4 RACH-less Handover In the current specification, the UE must first initiate a random access procedure upon receiving the HO command. However, if the target cell is the same as the source cell, i.e., the same IAB-DU serves both cells, only the cell IDs may differ. In this case, the timing advance is also the same for both cells, so PRACH transmission is not required. RAN2 should consider whether to specify RACH-less handover to improve the mobility of mobile IABs. Note that RACH-less handover only applies to Rel-18 UEs.

[0142] Proposal 4: RAN2 should consider whether RACH-less handover of Rel-18 UE is useful due to the movement of mobile IAB nodes.

[0143] 2.5 Lossless Handover During the study phase, the issue of packet loss due to hop-by-hop ARQ was discussed. This issue was observed when an IAB topology change was performed after a hop-by-hop hole link failure or when an inter-CU handover occurred. In Rel-16 / 17, this was not pursued as it was considered a rare case given the deployment assumption of fixed (stationary) IAB nodes.

[0144] In Rel-18 mobile IAB, if the mobile IAB node is always the access IAB node, such packet loss is still considered a rare case. The justification for WID states that the mobile IAB node has no descendant IAB nodes, i.e., it serves only UEs. Therefore, this assumption should be confirmed by RAN2.

[0145] Proposal 5: RAN2 should ensure that mobile IAB nodes are always access IAB nodes, and therefore ensure that packet loss due to hop-by-hop ARQ is a rare case in Rel-18 mobile IAB.

[0146] For general packet loss, the PDCP sublayer in the UE can handle data recovery in the same way as it does today, even in legacy handovers, so no enhancements are planned for lossless handover of UEs due to mobile IAB node movement.

[0147] Proposal 6: RAN2 should agree that existing UE PDCP data recovery can be used in lossless handover due to mobile IAB node movement, i.e. no improvement is necessary.

[0148] 2.6 Other Aspects WID states that mobile IAB nodes only support UEs.

[0149] A mobile IAB node has no child nodes, i.e. it needs to support only UEs.

[0150] To ensure this restriction, the existing IAB support IE can be reused. That is, a mobile IAB node can prevent other IAB nodes from accessing the node and allow the UE to access the node by not setting this IE in SIB1. The question is how such a restriction should be described in the specification. A clear description in the Stage-2 specification would help avoid confusion in mobile IAB implementations.

[0151] Proposal 7: RAN2 should agree to state in the Stage-2 specification that when functioning as a mobile IAB node in this release, an IAB node should not set the IAB support IE in the SIB.

Claims

1. A communication control method for use in a cellular communication system, comprising: A source donor node transmits a request for establishing a new F1 connection to a first distributed unit (DU) of a mobile relay node moving from the source donor node to a target donor node; The F1 connection is established between a second DU of the mobile relay node and the target donor node. Communications control method.

2. and transmitting an F1 setup request message to the target donor node, requesting to establish the F1 connection, in response to receiving the new establishment request, by the second DU of the mobile relay node. The communication control method according to claim 1.

3. The source donor node further comprises sending a revocation request for the F1 connection to the source donor node to the first DU of the mobile relay node. The communication control method according to claim 1.

4. A donor node in a cellular communication system, comprising: A transmitter for transmitting a new establishment request for an F1 connection to a first DU of a mobile relay node moving from the donor node to another donor node, The F1 connection is established between a second DU of the mobile relay node and the other donor node. Donor node.

5. In response to receiving the new establishment request in the second DU of the mobile relay node, an F1 setup request message requesting the establishment of the F1 connection is transmitted to the other donor node. The donor node of claim 4 .

6. The transmitter transmits a discard request for the F1 connection to the donor node to the first DU of the mobile relay node. The donor node of claim 4 .

7. A mobile relay node of a cellular communication system, comprising: A first DU receiving a request for establishing a new F1 connection to the target donor node, the request being sent from the source donor node to the mobile relay node moving from the source donor node to the target donor node; A second DU; The F1 connection is established between the second DU of the mobile relay node and the target donor node. Mobile relay node.

8. In response to receiving the new establishment request, the second DU sends an F1 setup request message to the target donor node requesting to establish the F1 connection. The mobile relay node of claim 7.

9. The method of claim 8, further comprising: receiving, from the source donor node, a request to discard the F1 connection to the source donor node. The mobile relay node of claim 7.

10. A source donor node; A target donor node; A cellular communication system having a mobile relay node, The source donor node sends a request to a first DU of the mobile relay node moving from the source donor node to a target donor node to establish a new F1 connection to the target donor node; The F1 connection is established between a second DU of the mobile relay node and the target donor node. Cellular communication systems.

11. In response to receiving the new establishment request, the second DU of the mobile relay node sends an F1 setup request message to the target donor node requesting to establish the F1 connection.

11. The cellular communication system of claim 10.

12. The source donor node sends a discard request for the F1 connection to the source donor node to the first DU of the mobile relay node.

11. The cellular communication system of claim 10.

13. A method for transmitting a signal to a source donor node of a cellular communication system, comprising: sending a request for establishing a new F1 connection to the target donor node to a first DU of a mobile relay node moving from the source donor node to the target donor node; The F1 connection is established between a second DU of the mobile relay node and the target donor node. program. In response to receiving the new establishment request in the second DU of the mobile relay node, an F1 setup request message is sent to the target donor node requesting to establish the F1 connection. The program according to claim 13.

15. The method further comprises: transmitting a request to the first DU of the mobile relay node to discard the F1 connection to the source donor node. The program according to claim 13.

16. A source donor node chipset comprising: sending a request to a first DU of a mobile relay node moving from the source donor node to a target donor node to establish a new F1 connection to the target donor node; The F1 connection is established between a second DU of the mobile relay node and the target donor node. Chipset. In response to receiving the new establishment request, in the second DU of the mobile relay node, an F1 setup request message is sent to the target donor node requesting to establish the F1 connection.

17. The chipset of claim 16.

18. The method of claim 17, further comprising: sending a request to the first DU of the mobile relay node to tear down the F1 connection to the source donor node.

17. The chipset of claim 16.