Communication Control Method

Abstract

A communication control method according to an aspect is used in a cellular communication system. The communication control method comprises a step of a base station transmitting, to user equipment, a conditional reconfiguration that includes permission information indicating whether connection by RACH-less handover is permitted for each target cell.

Description

[Technical Field]

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

[0002] In the 3GPP (Third Generation Partnership Project), 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. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP TS 38.300 V17.1.0(2022-06) Summary of the Invention

[0004] A communication control method according to a first aspect is a communication control method for use in a cellular communication system, comprising a step of transmitting, from a base station to a user equipment, a conditional reconfiguration including permission information indicating whether connection via RACH-less handover is permitted for each target cell.

[0005] A communication control method according to a second aspect is a communication control method used in a cellular communication system. The communication control method includes a step in which a donor node transmits, to a user equipment under a mobile relay node, a conditional reconfiguration including an execution condition to be executed upon receiving an execution instruction. The communication control method also includes a step in which the donor node transmits, to the mobile relay node, a transmission instruction instructing the mobile relay node to transmit the execution instruction. The communication control method further includes a step in which the mobile relay node transmits, in response to receiving the transmission instruction, the execution instruction to the user equipment.

[0006] A communication control method according to a third aspect is a communication control method used in a cellular communication system. The communication control method includes a step of a donor node transmitting a first message to a mobile relay node, the first message including common settings common to multiple user equipments under the mobile relay node. The communication control method also includes a step of the donor node transmitting a second message to the mobile relay node, the second message including individual settings for each user equipment under the mobile relay node. The communication control method further includes a step of the mobile relay node transmitting an RRC reconfiguration message including the common settings and the individual settings to each user equipment. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the relationship between IAB nodes, parent nodes, and child nodes. [Figure 3] FIG. 3 is a diagram illustrating an example configuration of a gNB (base station) according to an embodiment. [Figure 4] FIG. 4 is a diagram illustrating an example of the configuration of an IAB node (relay node) according to an embodiment. [Figure 5] FIG. 5 is a diagram illustrating an example of the configuration of a UE (user equipment) according to an embodiment. [Figure 6] FIG. 6 is a diagram illustrating an example of a protocol stack related to an RRC connection and a NAS connection of an IAB-MT. [Figure 7] FIG. 7 is a diagram illustrating an example of a protocol stack for the F1-U protocol. [Figure 8] FIG. 8 is a diagram illustrating an example of a protocol stack for the F1-C protocol. [Figure 9] FIG. 9 is a diagram illustrating an example of operation according to the first embodiment. [Figure 10] FIG. 10 is a diagram illustrating another example of operation according to the first embodiment. [Figure 11] FIG. 11 is a diagram illustrating an example of the operation of Solution 2 according to the second embodiment. [Figure 12] FIG. 12 is a diagram illustrating an example of operation according to the second embodiment. [Figure 13] FIG. 13 is a diagram illustrating another example of operation according to the second embodiment. [Figure 14] 14(A) and 14(B) are diagrams illustrating an example of a group handover operation according to the third embodiment. [Figure 15] FIG. 15 is a diagram illustrating an example of operation according to the third embodiment. [Figure 16] FIG. 16 is a diagram illustrating another example of operation according to the third embodiment. [Figure 17] FIG. 17 shows an example of a traditional handover (top) and an example of a group reconfiguration (bottom). [Figure 18] FIG. 18 illustrates Solution 1 for reducing service interruptions. [Figure 19] FIG. 19 illustrates Solution 2 for reducing service interruptions. DETAILED DESCRIPTION OF THE INVENTION

[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] (Configuration of a cellular communication system) An example of the configuration of a cellular communication system according to an embodiment will be described. The cellular communication system 1 according to an 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 partially to the cellular communication system 1. Furthermore, future cellular communication systems such as 6G may also be applied to the cellular communication system 1.

[0010] FIG. 1 is a diagram showing an example of the configuration of a cellular communication system 1 according to an embodiment.

[0011] 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.

[0012] In the following, an example in which base station 200 is an NR base station will be mainly described, but base station 200 may also be an LTE base station (i.e., an eNB).

[0013] In the following, the base stations 200-1 and 200-2 may be referred to as gNB 200 (or base station 200), and the IAB nodes 300-1 and 300-2 may be referred to as IAB node 300.

[0014] 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.

[0015] 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. In the following, there may be cases where a cell and a base station are used interchangeably.

[0016] Each gNB 200 is interconnected with the 5GC 10 via an interface called an NG interface. Figure 1 illustrates two gNBs, gNB 200-1 and gNB 200-2, connected to the 5GC 10.

[0017] Each gNB 200 may be divided into a central unit (CU) and distributed units (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 an F1-C protocol, which is a control plane protocol, and an F1-U protocol, which is a user plane protocol.

[0018] 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 functionality to support IAB. The backhaul can be multi-hop via multiple hops (i.e., multiple IAB nodes 300).

[0019] FIG. 1 illustrates 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.

[0020] 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 may be a mobile phone terminal and / or a tablet terminal, a laptop computer, 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 is wirelessly connected 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.

[0021] FIG. 2 is a diagram showing an example of the relationship between an IAB node 300, parent nodes, and child nodes.

[0022] 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.

[0023] 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 DU of the parent IAB node or 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.

[0024] Adjacent nodes (i.e., lower nodes) on the NR access interface of the IAB-DU are called child nodes. The IAB-DU manages a 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. While FIG. 2 shows an example in which the child nodes of the IAB node 300 are IAB nodes 300-C1 to 300-C3, the child nodes of the IAB node 300 may also include the UE 100. The direction toward the child nodes is called downstream.

[0025] 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 centrally manages, for example, resources, 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.

[0026] (Base station configuration) Next, a 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 radio communication unit 210, a network communication unit 220, and a control unit 230.

[0027] 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 types of reception 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 types of transmission 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.

[0028] 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 types of reception 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 types of transmission 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.

[0029] 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 described below.

[0030] (Relay node configuration) Next, the configuration of the IAB node 300, which is a relay node (or relay node device; hereinafter, sometimes referred to as a "relay node") according to the 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.

[0031] 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.

[0032] 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 radio 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 radio signal, and transmits the signal from the antenna.

[0033] 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.

[0034] (Configuration of user device) Next, a description will be given of a configuration of a UE 100 which is a user equipment according to the embodiment. Fig. 5 is a diagram showing an example of the configuration of the UE 100. As shown in Fig. 5, the UE 100 includes a radio communication unit 110 and a control unit 120.

[0035] The radio communication unit 110 performs radio communication in the access link, i.e., radio communication with the gNB 200 and radio communication with the IAB node 300. The radio communication unit 110 may also perform radio communication in the side link, i.e., radio communication with another UE 100. The radio 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 radio 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 radio signal, and transmits the signal from the antenna.

[0036] The control unit 120 performs various controls in the UE 100. The control unit 120 includes at least one memory and at least one processor electrically connected to the memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processing. The processor performs processing of each layer, which will be described later. Note that the control unit 120 may perform each processing in the UE 100 in each of the embodiments described below.

[0037] (Protocol stack configuration) Next, a configuration of a protocol stack according to an embodiment will be described. Fig. 6 is a diagram showing an example of a protocol stack related to an RRC connection and a NAS connection of an IAB-MT.

[0038] 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.

[0039] 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.

[0040] 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 between the MAC layer of the IAB-MT in IAB node 300-2 and the MAC layer of the IAB-DU in IAB node 300-1 via a transport channel. The MAC layer of the IAB-DU includes a scheduler, which determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the allocated resource blocks.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Figure 7 is a diagram showing a protocol stack for the F1-U protocol. Figure 8 is a diagram showing 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.

[0046] 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.

[0047] In each backhaul link, PDUs (Protocol Data Units) of the BAP layer are transmitted via a backhaul RLC channel (BH NR RLC channel). Configuring multiple backhaul RLC channels in each BH link enables traffic prioritization and Quality of Service (QoS) control. 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.

[0048] 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.

[0049] In the following, the processing or operations performed by the IAB-DU and IAB-MT of the IAB may be simply referred to 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 be simply referred to as the processing or operations of the "donor node."

[0050] 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.

[0051] (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).

[0052] 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 along 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.

[0053] On the other hand, in contrast to mobile IAB nodes, there are also IAB nodes that do not move. Such IAB nodes may be 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 be a fixed IAB node.

[0054] A mobile IAB node can also connect to an intermediate IAB node. A mobile IAB node can also connect to a donor node. On the other hand, a mobile IAB node can change its connection destination due to movement (migration or handover). The connection source may be an intermediate IAB node. The connection source may be a donor node. The connection destination may be an intermediate IAB node. The connection destination may be a donor node.

[0055] In the following, the terms "migration of a mobile IAB node" and "handover of a mobile IAB node" may be used interchangeably.

[0056] (RACH-less handover) 3GPP specifies RACH-less handover (RACH-less HO) (for example, 3GPP TS 36.300 V14.13.0 (2020-12)). RACH-less handover is a handover that skips the random access procedure. In RACH-less handover, for example, the following process is performed.

[0057] That is, the UE 100 for which the RACH-less handover is configured receives an RRC connection reconfiguration (RRCConnectionReconfiguration) message from the source cell. Then, the UE 100 synchronizes with the target cell included in the RRC connection reconfiguration message without performing a random access (RACH) procedure. After that, the UE 100 transmits an RRC connection reconfiguration complete (RRCConnectionReconfigurationComplete) message to the target cell using the uplink resource included in the RRC connection reconfiguration message, and ends the handover procedure.

[0058] In the RACH-less handover, the random access procedure is skipped, and therefore, the UE 100 can improve the delay in the execution time of the handover compared to the case where the random access procedure is executed.

[0059] (Conditional Handover) In a typical handover, the UE 100 reports measurements of the radio conditions of the serving cell and / or neighboring cells to the gNB 200, and the gNB 200 determines a handover to the neighboring cell based on this report and transmits a handover command to the UE 100. For this reason, in a typical handover, if the radio conditions of the serving cell suddenly deteriorate, communication may be interrupted before the handover is executed.

[0060] In contrast, in the conditional handover, when a preset trigger condition is satisfied, the UE 100 can autonomously execute handover to a candidate cell corresponding to the trigger condition, thereby solving problems such as communication interruption that occur in general handover.

[0061] Conditional handover is configured by conditional reconfiguration. The conditional reconfiguration is one of the information elements (IEs) included in an RRC reconfiguration message. The conditional reconfiguration is configured, for example, by transmitting an RRC reconfiguration message from the CU of the donor node 200 to the IAB-MT of the IAB node 300 and the UE 100. The conditional reconfiguration includes candidate cells and execution conditions used in the conditional handover. The execution conditions include one or more trigger conditions. When the trigger condition is satisfied, the IAB-MT of the IAB node 300 and the UE 100 start executing a handover to the candidate cell.

[0062] (Communication control method according to the first embodiment) There are cases where a mobile IAB node causes all UEs 100 under the mobile IAB node to perform handover simultaneously by performing its own handover.

[0063] A handover of the mobile IAB node itself changes the cell ID of the cell to which the mobile IAB node is connected. Since the cell ID to which the mobile IAB node is connected changes due to a handover, it is considered that management of the UE 100 under the mobile IAB node will be easier if the cell ID to which the UE 100 under the mobile IAB node is connected is also changed. Therefore, the above-mentioned case is assumed.

[0064] In such a case, if the distance (or location) of a UE 100 under a mobile IAB node to the mobile IAB node does not change, it is possible to shorten the execution time of the handover procedure by having the UE 100 perform a RACH-less handover.

[0065] Generally, the CU performs the RRC configuration, while the DU manages the cell.

[0066] For example, the DU of the gNB 200 (or donor node) may know which cells have the same timing advance (TA) value among the cells managed by the DU. Also, for example, the IAB-DU of the mobile IAB node may know the distance from the subordinate UE 100, as described above.

[0067] However, since the CU (the CU of the gNB 200 or the CU of the donor node 200) does not know the status of the cell, it may not be able to properly configure the RACH-less handover for the UE 100. In this case, the UE 100 cannot properly connect to the network.

[0068] Therefore, the first embodiment aims to enable the UE 100 to properly connect to the network.

[0069] Therefore, in the first embodiment, a base station (e.g., gNB200 or donor node 200) transmits a conditional reconfiguration to a user equipment (e.g., UE100 under gNB200 or UE100 under mobile IAB node 300M) including permission information indicating whether connection via RACH-less handover is permitted for each target cell.

[0070] This allows the UE 100 to determine which target cell to connect to for RACH-less handover during handover. Therefore, if the target cell allows connection by RACH-less handover, the UE 100 can execute RACH-less handover to the target cell. Therefore, the UE 100 can be properly connected to the network.

[0071] (Operation example according to the first embodiment) Fig. 9 is a diagram illustrating an example of operation according to the first embodiment. In the example illustrated in Fig. 9, UE 100 is a UE under the control of mobile IAB node 300M, and is handed over in conjunction with handover of mobile IAB node 300M.

[0072] In this case, for the UE 100, the source cell is the cell to which the mobile IAB node 300M was connected before the handover (for example, a cell managed by the DU of the donor node 200). Also, for the UE 100, the target cell is the cell to which the mobile IAB node 300M is connected by the handover (for example, it may be a cell managed by the DU of the donor node 200. The target cell may also be a cell managed by the IAB-DU of the intermediate IAB node 300S under the DU).

[0073] As shown in Fig. 9, in step S10, the UE 100 may transmit RACH-less handover capability information indicating that the UE 100 is capable of performing a RACH-less handover to a CU (IAB-donor-CU) of the donor node 200. The RACH-less handover capability information may be information indicating that the UE 100 supports a RACH-less handover. The UE 100 may transmit an RRC message including the RACH-less handover capability information to the IAB-DU of the mobile IAB node 300M. Then, the IAB-DU of the mobile IAB node 300M may transmit an F1 message including the RRC message to the CU of the donor node 200.

[0074] In step S11, the IAB-DU of the mobile IAB node 300M transmits combination information indicating a combination of cells that are capable of RACH-less handover among the cells that it manages to the CU of the donor node 200. The IAB-DU of the mobile IAB node 300M may transmit an F1 message including the combination information to the CU of the donor node 200. Prior to step S11, the CU of the donor node 200 may request the combination information from the mobile IAB node 300M. In this case, the CU of the donor node 200 may transmit an F1 message including the request for the combination information to the IAB-DU of the mobile IAB node 300M.

[0075] First, the cell pair may be geographically co-located cells, such as when the source cell and the target cell are physically the same, or when the UE 100 moves due to a handover of the mobile IAB node 300M, but the location of the UE 100 relative to the mobile IAB node 300M remains the same.

[0076] Secondly, the combination of cells may be a combination of cells in which the timing advance (TA) value is the same between the first cell and the second cell. When the UE 100 moves from the source cell to the target cell, if the distance from the source cell to the UE 100 and the distance from the target cell to the UE 100 are the same, the TA values ​​will be the same. Such a combination of source cells and target cells may be represented in the combination information. The IAB-DU of the mobile IAB node 300M may know a combination of cells in which the TA value is the same from the past handover history of the UE 100 subordinate thereto.

[0077] Third, the combination of cells may be a combination of cells before and after a change due to a handover of the mobile IAB node 300M. For example, when the mobile IAB node 300M performs a handover from a first cell to a second cell, the combination of the first cell and the second cell may be a combination of cells that allows a RACH-less handover.

[0078] The combination information may include the above cell combinations in a list format, and the cell combinations may be represented by a combination of the cell IDs of the cells.

[0079] The combination information may include, for each combination of cells, a TA value to be applied when the UE 100 performs a RACH-less handover. Alternatively, the TA value may be transmitted separately from the combination information.

[0080] In step S12, the CU of the donor node 200 configures conditional reconfiguration for the UE 100. For example, the CU of the donor node 200 generates an RRC message (e.g., an RRCReconfiguration message) including the conditional reconfiguration based on the combination information, and transmits an F1 message including (or encapsulating) the RRC message to the IAB-DU of the mobile IAB node 300M. The IAB-DU of the mobile IAB node 300M extracts the RRC message from the F1 message and transmits the RRC message to the UE 100.

[0081] The conditional reconfiguration includes permission information indicating whether a connection via RACH-less handover is permitted for each target cell. The permission information may indicate whether execution of RACH-less handover is permitted for each target cell.

[0082] First, the CU of the donor node 200 may determine a cell to be combined as a target cell permitted for connection via RACH-less handover based on the combination information (step S11). Alternatively, the CU of the donor node 200 may determine a cell not included in the combination information as a target cell not permitted for connection via RACH-less handover. Alternatively, when the CU of the donor node 200 determines, based on the combination information, that the TA value of the target cell is the same as the TA value of the source cell, it may permit connection via RACH-less handover to the target cell.

[0083] Second, when the permission information indicates that connection by RACH-less handover is permitted, the permission information may indicate that execution of RACH-less handover is instructed to the target cell. Alternatively, the permission information may indicate that execution of RACH-less handover is implicitly instructed by not including a PRACH resource specific to UE 100 in the conditional reconfiguration. Alternatively, the permission information may indicate that execution of RACH-less handover is instructed by including a radio resource (PUSCH resource) for UE 100 to transmit an RRC reconfiguration complete (RRCReconfigurationComplete) message to the target cell in the conditional reconfiguration.

[0084] In step S13, UE 100 performs conditional reconfiguration when the trigger condition for conditional reconfiguration is satisfied. At this time, UE 100 checks whether connection via RACH-less handover to the target cell is permitted based on the permission information. When UE 100 checks that connection via RACH-less handover to the target cell is permitted, UE 100 performs RACH-less handover to the target cell and connects to the target cell. On the other hand, when UE 100 checks that connection via RACH-less handover to the target cell is not permitted, UE 100 performs a random access procedure to the target cell and connects to the target cell.

[0085] (Another example 1 according to the first embodiment) In the first embodiment, an example in which the permission information is included in the conditional reconfiguration has been described, but the present invention is not limited to this. For example, the permission information may be included in an RRC reconfiguration message for executing a normal handover instead of a conditional handover. In this case, the CU of the donor node 200 generates an RRC reconfiguration message including the permission information based on the combination information (step S11) and transmits an F1 message including the RRC reconfiguration message to the IAB-DU of the mobile IAB node 300M. Then, the IAB-DU of the mobile IAB node 300M transmits the RRC reconfiguration message to the UE 100. In response to receiving the RRC reconfiguration message, the UE 100 executes a normal handover procedure instead of a conditional handover. At this time, the UE 100 checks whether or not RACH-less handover is possible for the target cell based on the permission information, as in the first embodiment, and performs the subsequent processing.

[0086] (Another example 2 according to the first embodiment) In the first embodiment, an example has been described in which conditional reconfiguration is configured between the donor node 200, the mobile IAB node 300M, and the UE 100. However, the present invention is not limited to this. For example, conditional reconfiguration may be configured between the gNB 200 and the UE 100.

[0087] Fig. 10 is a diagram illustrating another example of operation according to the first embodiment. The example illustrated in Fig. 10 illustrates an example in which the UE 100 executes a conditional handover from a source cell managed by a DU of the gNB 200 to a target cell managed by the DU of the gNB 200.

[0088] As in the first embodiment, the UE 100 may transmit the RACH-less handover capability information to the CU of the gNB 200 (step S15). In this case, the UE 100 may transmit an RRC message including the RACH-less handover capability information to the DU of the gNB 200, and the DU of the gNB 200 may transmit an F1 message including the RRC message to the CU of the gNB 200.

[0089] Then, the DU of the gNB 200 transmits (an F1 message including) the combination information to the CU of the gNB 200 (step S16). The combination information includes a combination of cells for which RACH-less handover is possible, as in the first embodiment.

[0090] The CU of the gNB200 generates a conditional reconfiguration including permission information based on the combination information, and transmits the conditional reconfiguration to the UE100 (step S17). The CU of the gNB200 may generate an RRC message including the conditional reconfiguration, and transmit an F1 message including the RRC message to the DU of the gNB200. The DU of the gNB200 may extract the RRC message from the F1 message, and transmit the RRC message to the UE100.

[0091] Then, when the trigger condition is satisfied, UE 100 performs conditional reconfiguration and executes conditional handover (step S18). When UE 100 confirms that the target cell is permitted to connect for RACH-less handover based on the permission information, UE 100 executes RACH-less handover to the target cell. On the other hand, when UE 100 confirms that the target cell is not permitted to connect for RACH-less handover based on the permission information, UE 100 executes a random access procedure to the target cell.

[0092] In the case of FIG. 10, similarly to the first embodiment, the UE 100 can connect to the target cell, and therefore can appropriately connect to the network.

[0093] (Another example 3 according to the first embodiment) In the first embodiment, an example of the mobile IAB node 300M has been described, but for example, an IAB node (an intermediate IAB node 300S or an access IAB node. The access IAB node is an IAB node serving the UE 100) can also be used instead of the mobile IAB node 300M. For example, in FIG. 9, the mobile IAB node 300M can be replaced with the intermediate IAB node 300S.

[0094] (Another example 4 according to the first embodiment) In Alternative Example 2 according to the first embodiment, an example implemented between the gNB 200 and the UE 100 has been described, but it is also possible to implement it between the donor node 200 and the mobile IAB node 300M, for example. For example, in FIG. 10, the gNB 200 is replaced with the donor node 200, and the UE 100 ofThis can be implemented by replacing it with the mobile IAB node 300M. In this case, the DU of the donor node 200 transmits combination information to the CU of the donor node 200 (step S16). Then, the CU of the donor node 200 generates a conditional resetting including permission information based on the combination information, and transmits the conditional resetting to the IAB-MT of the mobile IAB node 300M (step S17).

[0095] [Second embodiment] Next, a second embodiment will be described.

[0096] In the first embodiment, there has been described a case where, when the mobile IAB node 300M performs a handover, all of the subordinate UEs 100 are handed over at the same time.

[0097] In such a case, the mobile IAB node 300M may simultaneously transmit an RRCReconfiguration message to each of the subordinate UEs 100 in order to instruct the execution of handover.

[0098] However, when the mobile IAB node 300M transmits the message simultaneously, the load on radio resources in the downlink direction increases compared to when the message is not transmitted, because the message is transmitted individually to each UE 100. Furthermore, the simultaneous transmission of the message may cause an interruption of service in the UEs 100 subordinate to the mobile IAB node 300M.

[0099] Therefore, 3GPP has proposed two solutions for reducing service interruptions ("Solution 1 for reduction of service interruption" and "Solution 2 for reduction of service interruption"), of which Solution 1 has been standardized.

[0100] Fig. 11 is a diagram illustrating an example of the operation of Solution 2 (Solution 2 for reduction of service interruption). The example illustrated in Fig. 11 illustrates an example in which the CU (IAB-donor-CU) of the donor node 200 transmits an RRC reconfiguration message to the IAB node 300, its child node 300-C, and its grandchild node 300-GC, and the IAB node 300, the child node 300-C, and the grandchild node 300-GC perform handover.

[0101] In both of the two solutions, the CU of the donor node 200 transmits an RRC reconfiguration message before handover of each of the IAB nodes 300, 300-C, and 300-GC is performed. Since the RRC reconfiguration message is transmitted to each of the IAB nodes 300, 300-C, and 300-GC in advance, load distribution can be achieved compared to when the messages are transmitted simultaneously. Furthermore, load distribution can reduce service interruptions for the UEs 100 subordinate to each of the IAB nodes 300, 300-C, and 300-GC.

[0102] As shown in Fig. 11, Solution 2 is a solution in which the execution of the RRC reconfiguration message is suspended in the IAB-MT of the child node. In this case, the IAB-MT of the child node starts the execution of the message upon receiving an indication from the DU of the parent node (i.e., the IAB node).

[0103] On the other hand, in Solution 1, the transmission of the RRC reconfiguration message is held (or buffered) in the IAB-DU of the parent IAB node, and in Solution 1, the held message is transmitted when a certain condition is met.

[0104] In the second embodiment, attention is focused on Solution 2. Regarding Solution 2, when viewed from the perspective of the relationship between the mobile IAB node 300M and the subordinate UE 100, for example, it is as follows.

[0105] That is, the CU of the donor node 200 transmits an RRC reconfiguration message to the UE 100 under the control of the mobile IAB node 300M. Then, the DU of the mobile IAB node 300M transmits an execution instruction ("Indication" shown in FIG. 11) to the UE 100. Upon receiving the execution instruction, the UE 100 starts executing the RRC reconfiguration message.

[0106] However, the DU of the mobile IAB node 300M does not know when to transmit the execution instruction ("Indication" shown in FIG. 11). If the timing of transmitting the execution instruction is inappropriate, the UE 100 cannot properly connect to the target cell. Therefore, the UE 100 may not properly connect to the network.

[0107] Therefore, in the second embodiment, similarly to the first embodiment, an object is to enable the UE 100 to be appropriately connected to the network.

[0108] In the second embodiment, the CU of the donor node 200 configures the UE 100 with a conditional reconfiguration, and then transmits an instruction to transmit an execution instruction to the mobile IAB node 300M. Then, in response to receiving the transmission instruction, the mobile IAB node 300M transmits an execution instruction to the UE 100. Upon receiving the execution instruction, the UE 100 starts executing the conditional reconfiguration.

[0109] Specifically, first, a donor node (e.g., donor node 200) transmits a conditional reconfiguration including an execution condition for execution upon receiving the execution instruction to a user equipment (e.g., UE 100) under a mobile relay node (e.g., mobile IAB node 300M). Second, the donor node transmits a transmission instruction to the mobile relay node to instruct the mobile relay node to transmit the execution instruction. Third, in response to receiving the transmission instruction, the mobile relay node transmits the execution instruction to the user equipment.

[0110] As a result, for example, the mobile IAB node 300M can receive a transmission instruction from the donor node 200 and transmit an execution instruction to the UE 100, and can therefore transmit the execution instruction to the UE 100 at an appropriate timing. Therefore, the UE 100 can perform conditional reconfiguration at an appropriate timing and perform handover to the target cell. Therefore, the UE 100 can be appropriately connected to the network.

[0111] (Operation example according to the second embodiment) FIG. 12 is a diagram illustrating an example of operation according to the second embodiment.

[0112] 12 shows an example in which the mobile IAB node 300M is handed over from the source parent node (Source Parent) 300-S to the target parent node (Target Parent) 300-T. Also, FIG. 12 shows an example in which the subordinate UE 100 is handed over in conjunction with the handover of the mobile IAB node 300M. The source parent node 300-S and the target parent node 300-T may be intermediate IAB nodes 300S subordinate to the donor node 200.

[0113] 12, in step S20, the CU of the donor node 200 configures the conditional reconfiguration to the UE 100. For example, the CU of the donor node 200 generates an RRC message (for example, an RRC reconfiguration (HO command) message) including the conditional reconfiguration, Applicable R The IAB node 300M transmits an F1 message including the RRC message to the IAB-DU of the mobile IAB node 300M. The IAB-DU of the mobile IAB node 300M extracts the RRC message including the conditional reconfiguration from the F1 message and transmits the RRC message to the UE 100.

[0114] The conditional reconfiguration may include multiple entries, with each entry representing a single setting. At least one of the multiple entries includes an execution condition of "execute by execution instruction" (or "execute when an execution instruction is received"). As a result, the UE 100 does not start execution of the execution condition even when it receives the conditional reconfiguration, but starts execution upon receiving an execution instruction from the mobile IAB node 300M, thereby enabling operation corresponding to the above-mentioned solution 2.

[0115] In step S21, the CU of the donor node 200 transmits an instruction to transmit an execution instruction to the IAB-DU of the mobile IAB node 300M.

[0116] First, the CU of the donor node 200 may generate an RRC message including a transmission instruction and transmit an F1 message including the RRC message to the IAB-DU of the mobile IAB node 300M. Alternatively, the CU of the donor node 200 may transmit an F1 message including the transmission instruction to the IAB-DU of the mobile IAB node 300M.

[0117] Second, the transmission instruction may include a UE identifier of UE 100 to which the transmission instruction is to be transmitted. The transmission instruction may also include an identifier (conditional reconfiguration identifier) ​​of a conditional reconfiguration to which the transmission instruction is to be transmitted. The identifier represents, for example, information instructing whether at least one of a plurality of conditional reconfigurations is to be the transmission target. Alternatively, the transmission instruction may include an entry number of a list in the conditional reconfiguration to which the transmission instruction is to be transmitted.

[0118] Third, the transmission instruction may include an instruction to immediately transmit the execution instruction. Alternatively, the transmission instruction may include an instruction to transmit the execution instruction when a conditional handover is performed. Alternatively, the transmission instruction may include an instruction to transmit the execution instruction when a handover is performed. Alternatively, the transmission instruction may include an instruction to transmit the execution instruction when an RRCReconfigurationComplete message is transmitted.

[0119] In step S22, the IAB-DU of the mobile IAB node 300M transmits an execution instruction to the UE 100. For example, the IAB-DU of the mobile IAB node 300M transmits an execution instruction for the conditional reconfiguration specified in the transmission instruction to the UE 100 specified in the transmission instruction (step S21).

[0120] The execution instruction may be transmitted in a MAC control element (MAC CE). The execution instruction may be transmitted in a BAP Control PDU. The execution instruction may also include an identifier of a conditional reconfiguration to be executed (conditional reconfiguration identifier). The identifier may represent, for example, information indicating whether at least one of a plurality of conditional reconfigurations should be executed. Alternatively, the execution instruction may include an entry number of a list in the conditional reconfiguration to be executed.

[0121] In step S23, the UE 100 performs the specified conditional reconfiguration and executes handover to the target cell.

[0122] (Another example 1 according to the second embodiment) In the second embodiment, the mobile IAB node 300M has been described, but the present invention is not limited to this. For example, the present invention can be implemented using an intermediate IAB node 300S instead of the mobile IAB node 300M. In this case, the UE 100 under the control of the intermediate IAB node 300S can execute conditional reconfiguration to execute handover from a serving cell managed by the intermediate IAB node 300S to a target cell managed by the intermediate IAB node 300S (or a target cell managed by another intermediate IAB node 300S). For example, in FIG. 12, the mobile IAB node 300M can be replaced with the intermediate IAB node 300S to implement the operation example shown in FIG. 12.

[0123] (Another example 2 according to the second embodiment) In the second embodiment, an example in which conditional reconfiguration is configured between the UE 100, the mobile IAB node 300M, and the donor node 200 has been described, but the present invention is not limited to this. For example, the conditional reconfiguration described in the second embodiment can also be applied between the UE 100 and the gNB 200.

[0124] FIG. 13 is a diagram illustrating another example of operation according to the second embodiment.

[0125] 13, the CU of the gNB 200 configures the UE 100 with conditional reconfiguration (step S25), similar to the second embodiment. At least one of the entries included in the conditional reconfiguration includes an execution condition of "execute by execution instruction," similar to the second embodiment. As in the second embodiment, the UE 100 does not immediately execute the entry even if the conditional reconfiguration is configured, but waits until it receives an execution instruction.

[0126] Then, the CU of the gNB 200 transmits an instruction to transmit the execution instruction to the DU of the gNB 200 (step S26). The content of the transmission instruction and the information included in the transmission instruction may also be the same as in the second embodiment.

[0127] In response to receiving the transmission instruction, the DU of the gNB 200 transmits an execution instruction to the UE 100 (step S27). Upon receiving the execution instruction, the UE 100 starts the instructed execution condition and executes handover to the target cell, as in the second embodiment (step S28).

[0128] [Third embodiment] Next, a third embodiment will be described.

[0129] Currently, 3GPP is planning to study group handover of the mobile IAB node 300M. A group handover is a handover that is performed simultaneously by a group of multiple UEs 100. In the group handover of the mobile IAB node 300M, the mobile IAB node 300M is also included in the group and is a target of the handover.

[0130] 14(A) and 14(B) are diagrams illustrating an example of a group handover operation according to the third embodiment. Of these, Fig. 14(A) illustrates an example in which a source IAB-donor node 200-S transmits an RRCReconfiguration message, which is a handover command, to each of the UEs 100-1, ..., 100-n and the mobile IAB node 300M.

[0131] On the other hand, in FIG. 14(B), the source donor node 200-S transmits a group reconfiguration message (including an F1 message) to the mobile IAB node 300M. The group reconfiguration message includes, for example, group handover configuration information. The group reconfiguration message is, for example, a message indicating an instruction for group handover. The mobile IAB node 300M transmits the group reconfiguration message to each of the UEs 100-1, ..., 100-n.

[0132] In the example shown in FIG. 14(B), group handover configuration information is transmitted from the source donor node 200-S to the mobile IAB node 300M by a single F1 message. Compared to the case where an individual message (F1 message) is transmitted from the source donor node 200-S to the mobile IAB node 300M for each UE 100-1, ..., 100-n (FIG. 14(A)), a single F1 message can be used to configure group handover for multiple UEs 100-1, ..., 100-n. Therefore, in the example shown in FIG. 14(B), the load of F1 signaling can be reduced compared to the example shown in FIG. 14(A). In particular, with regard to IAB, since F1 signaling is also wireless, it is considered effective to reduce the load of F1 signaling compared to when it is performed via a wired connection.

[0133] On the other hand, it is assumed that the mobile IAB node 300M allows connection of UEs 100 of Rel-17 or earlier, not just UEs 100 exclusive to Rel-18. Therefore, it is desirable that at least the mobile IAB node 300M transmits an RRC reconfiguration message that can be received by UEs 100 of Rel-17 or earlier, rather than a new RRC reconfiguration message for group handover.

[0134] Therefore, in the third embodiment, an example is described in which, when the mobile IAB node 300M receives a common setting common to the group and an individual setting for each UE from the donor node, it combines these and transmits an RRC reconfiguration message to each UE 100 that can also be received by UEs 100 prior to Rel-17.

[0135] Specifically, first, a donor node (e.g., source donor node 200-S) transmits a first message including common settings common to multiple user equipments (e.g., UEs 100) under the mobile relay node (e.g., mobile IAB node 300M) to the mobile relay node. Second, the donor node transmits a second message including individual settings for each user equipment under the mobile relay node to the mobile relay node. Third, the mobile relay node transmits an RRC reconfiguration message including the common settings and individual settings to each user equipment.

[0136] As a result, for example, a message including a common setting can be used to set the common setting for the UEs 100 in the group by one message. Therefore, in the second embodiment, it is possible to reduce F1 signaling compared to the case where each message is transmitted for each UE as shown in Fig. 14(A).

[0137] Furthermore, for example, an RRC reconfiguration message that can be received by UE 100 before Re-17 is used as the message transmitted to UE 100. Therefore, UE 100 before Re-17 can also be appropriately connected to the target cell by group handover. Therefore, UE 100 can be appropriately connected to the network as in the first embodiment.

[0138] (Operation example according to the third embodiment) FIG. 15 is a diagram illustrating an example of operation according to the third embodiment.

[0139] The example shown in Fig. 15 illustrates an example in which a mobile IAB node 300M is handed over from a source IAB-donor node 200-S to a target IAB-donor node 200-T. Also, the example shown in Fig. 14 illustrates an example in which UEs 100-1, ..., 100-n under the mobile IAB node 300M also form a single group and perform a group handover in conjunction with the handover of the mobile IAB node 300M. Hereinafter, a group formed by a plurality of UEs 100-1, ..., 100-n and in which a group handover is performed may be referred to as a "UE group."

[0140] As shown in FIG. 15, in step S30, the CU of the source donor node 200-S transmits the common configuration of the UE group to the IAB-DU of the mobile IAB node 300M.

[0141] First, the CU of the source donor node 200-S may generate an RRC message (e.g., an RRC reconfiguration message) including the common configuration and transmit an F1 message including the RRC message to the mobile IAB node 300M. Alternatively, the CU of the source donor node 200-S may transmit an F1 message including the common configuration to the mobile IAB node 300M. In either case, the F1 message is an example of a first message.

[0142] Second, the common configuration includes a configuration that is common to the UEs 100-1, ..., 100-n that belong to a UE group. The configuration may be a configuration value itself. The configuration may be expressed as an information element (IE). A message including the common configuration may include a UE group identifier that indicates an identifier of the UE group. Furthermore, a message including the common configuration may include a list of UE identifiers of the UEs 100 that belong to the UE group. The UE group identifier and / or the list of UE identifiers may be included in the common configuration.

[0143] In step S31, the CU of the source donor node 200-S transmits individual settings for the UE group to the IAB-DU of the mobile IAB node 300M.

[0144] First, the CU of the source donor node 200-S may generate an RRC message (e.g., an RRC reconfiguration message) including the personalized configuration and transmit an F1 message including the RRC message to the mobile IAB node 300M. Alternatively, the CU of the source donor node 200-S may transmit an F1 message including the personalized configuration to the mobile IAB node 300M. In either case, the F1 message is an example of the second message.

[0145] Second, the individual configuration includes individual configuration for each UE 100-1, ..., 100-n belonging to the UE group. The configuration may be a setting value itself. The configuration may be expressed as an information element (IE). A message including the individual configuration includes a UE identifier of the UE 100 belonging to the UE group. The UE identifier indicates the UE 100 that is the target of the individual configuration. The UE identifier may be included in the individual configuration.

[0146] In step S32, the IAB-DU of the mobile IAB node 300M combines the common configuration and the individual configuration to generate an RRC reconfiguration message including the common configuration and the individual configuration. The RRC reconfiguration message is an RRC reconfiguration message that can also be received by UEs 100 prior to Rel-17.

[0147] In addition, in the IAB-DU of the mobile IAB node 300M, if the same setting is included in the common setting and the individual setting, the individual setting may be given priority so that the same setting is not included in both the common setting and the individual setting.

[0148] Then, the IAB-DU of the mobile IAB node 300M transmits the generated RRC reconfiguration message to each of the UEs 100-1, . . . , 100-n that belong to the UE group.

[0149] Thereafter, in step S33, the IAB-MT of the mobile IAB node 300M and each of the UEs 100-1, . . . , 100-n transmit an RRC reconfiguration complete message to the target IAB-donor node 200-T, thereby completing the group handover.

[0150] (Another example 1 of the third embodiment) In the third embodiment, an example in which a group handover is performed in the UE 100 under the control of the mobile IAB node 300M has been described, but the present invention is not limited to this. For example, a group handover may also be performed in the UE 100 under the control of the gNB 200.

[0151] FIG. 16 is a diagram illustrating another example of operation according to the third embodiment.

[0152] Figure 16 shows an example in which UEs 100-1, ..., 100-n under the control of gNB 200 form a UE group, and group handover is performed among these UEs 100-1, ..., 100-n.

[0153] As shown in Fig. 16, the CU of the gNB200 transmits the common configuration to the DU of the gNB200 (step S35). As in the third embodiment, the CU of the gNB200 may generate an RRC message (e.g., an RRC reconfiguration message) including the common configuration and transmit an F1 message including the RRC message to the DU of the gNB200. Alternatively, as in the third embodiment, the CU of the gNB200 may transmit an F1 message including the common configuration to the DU of the gNB200. The common configuration itself may be the same as in the third operation example.

[0154] Further, the CU of the gNB200 transmits the individual configuration to the DU of the gNB200 (step S36). As in the third embodiment, the CU of the gNB200 may generate an RRC message (e.g., an RRC reconfiguration message) including the individual configuration and transmit an F1 message including the RRC message to the DU of the gNB200. Alternatively, as in the third embodiment, the CU of the gNB200 may transmit an F1 message including the individual configuration to the DU of the gNB200. The individual configuration itself may be the same as in the third embodiment.

[0155] Then, the DU of the gNB 200 combines the common setting and the individual setting, and transmits an RRC reconfiguration message including the common setting and the individual setting to each of the UEs 100-1, ..., 100-n (step S38). As in the third embodiment, the RRC reconfiguration message is an RRC reconfiguration message that can be received by UEs 100 of Rel-17 or earlier. Each of the UEs 100-1, ..., 100-n transmits an RRC reconfiguration complete message to the target cell, completing the handover (step S38).

[0156] [Other embodiments] A program may be provided that causes a computer to execute each process performed by the UE 100, the gNB 200, or the IAB node 300. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed 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, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0157] In addition, circuits that execute each process performed by UE100, gNB200, or IAB node 300 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).

[0158] 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.

[0159] 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 without departing from the spirit of the invention. Furthermore, the embodiments, operation examples, or processes can be combined as appropriate within a consistent range.

[0160] This application claims priority to U.S. Provisional Application No. 63 / 395940 (filed August 8, 2022), the entire contents of which are incorporated herein by reference.

[0161] (Appendix 1) (Appendix 1) A communication control method for use in a cellular communication system, comprising: a step of transmitting, by the base station, to the user equipment, a conditional reconfiguration including permission information indicating whether connection via RACH-less handover is permitted for each target cell; Communication control method.

[0162] (Appendix 2) The base station is a donor node, and the user equipment is a user equipment under a mobile relay node. 10. The communication control method according to claim 1.

[0163] (Appendix 3) The method further includes a step of transmitting, by the mobile relay node, combination information representing a combination of cells that can be connected by the RACH-less handover to the donor node; the step of transmitting the conditional reconfiguration includes a step of transmitting the conditional reconfiguration by the base station based on the combination information. 10. A communication control method according to claim 1 or 2.

[0164] (Appendix 4) The step of transmitting the combination information includes the step of the mobile relay node transmitting a timing advance value for each of the combinations. A communication control method according to any one of Supplementary Note 1 to Supplementary Note 3.

[0165] (Appendix 5) A communication control method for use in a cellular communication system, comprising: a step in which the donor node receives an execution instruction and transmits a conditional reconfiguration including an execution condition to be executed by the donor node to a user equipment under the mobile relay node; the donor node transmitting a transmission instruction to the mobile relay node to instruct the mobile relay node to transmit the execution instruction; and transmitting, by the mobile relay node, the execution instruction to the user equipment in response to receiving the transmission instruction. Communication control method.

[0166] (Appendix 6) The step of transmitting the execution instruction includes a step of transmitting the execution instruction including information indicating whether the mobile relay node should execute at least any of the conditional reconfigurations among the plurality of conditional reconfigurations. 6. The communication control method according to claim 5.

[0167] (Appendix 7) A communication control method for use in a cellular communication system, comprising: a donor node transmitting a first message to a mobile relay node, the first message including a common setting common to a plurality of user devices under the mobile relay node; the donor node transmitting a second message to the mobile relay node, the second message including individual settings for each of the user devices under the mobile relay node; the mobile relay node transmitting an RRC reconfiguration message including the common configuration and the individual configuration to each of the user equipments. Communication control method.

[0168] (Second Appendix) 1. Introduction RAN#94e approved a new work item on mobile IAB, the WID of which was revised in RAN#96 as follows:

[0169] The detailed goals of this work item are: Define migration / topology adaptation procedures to enable IAB node mobility, including inter-donor migration (full migration) of the entire mobile IAB node. Enhances mobility for IAB nodes and their served UEs. This includes aspects related to group mobility. There is no optimization targeted at surrounding UEs. Note: The resolution must not touch on topics that are already under discussion for Rel-17 or that are excluded from Rel-17, except for enhancements specific to IAB Node Mobility. · It is necessary to mitigate interference caused by the mobility of IAB nodes, for example, to avoid collisions of reference signals and control signals (PCI, RACH, etc.). Note: At the outset, 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.

[0170] The following principles should be respected: -Mobile IAB nodes must be able to serve legacy UEs. Solutions providing mobile IAB optimization may require Rel-18UE extensions, but only if such extensions are backward compatible.

[0171] One of the key challenges in Rel-18 is how to efficiently perform handovers of multiple descendant UEs during the migration of a mobile IAB node. In this appendix, an initial discussion on mobility enhancements for mobile IABs is provided from the perspective of UE handover.

[0172] 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.

[0173] 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 latency, group reconfiguration is a possible candidate, which is expected to reconfigure multiple UEs with a single message.

[0174] Group reconfiguration was already discussed in Rel-17MBS as a "Common RRC Structure" and the following summary was provided:

[0175] Summary of common RRC structures 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 would 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.

[0176] Proposal 2: Maintain the current CRRRC structure and do not proceed with a common RRC structure (i.e., no impact on RRCCR).

[0177] The point is that UEs need to receive individual RRC reconfiguration and in addition group RRC reconfiguration, so there is little benefit to Uu signals in MBS. stomach( Although there was a common view that F1 / E1 signaling would be more of a disadvantage than a benefit, there may be some advantages to F1 / E1 signaling. As a result, RAN2 decided to keep the current structure, i.e., with only separate RRC reconfiguration.

[0178] For P2, RAN2 assumes that if agreed, RRC will continue to use the dedicated UE configuration.

[0179] 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, signal reduction on the access link is still more important since the backhaul link is generally assumed to be over FR2.

[0180] The WID clearly states that "solutions should avoid touching on areas where Rel-17 discussions have already taken place and where the topic has been excluded from Rel-17, except for improvements specific to IAB node mobility," so RAN2 does not need to reopen group reconfiguration (or a common RRC structure) in Rel-18 mobile IAB, at least from RAN2's perspective.

[0181] Proposal 1: RAN2 should agree to continue using only individual RRC reconfiguration for UE handovers due to movement of the mobile IAB node.

[0182] 2.2 Handover for Legacy UE As indicated in the WID (Work Item Description), "Mobile IAB nodes must support legacy UEs." Therefore, RAN2 should consider handover methods for legacy UEs.

[0183] RAN3 had two solutions for reducing service interruptions during inter-donor IAB node migration in Rel-17, among which solution 1 is shown in Figure 17.

[0184] 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 a lesser overall impact than Solution 2.

[0185] Of course, UE handover can also be performed without Solution 1. However, similar to the Rel-17 IAB node issue, since it involves the handover of descendant UEs, if Solution 1 is not applied, the UE will experience service interruption during the moving IAB node transition. Therefore, RAN2 must assume that Solution 1 for intra-donor transition is reused to reduce service interruption for legacy UEs during inter-donor moving IAB node transition.

[0186] Proposal 2: RAN2 should assume that Solution 1 for reducing service interruptions during intra-donor IAB node migration in Rel-17 can be reused for legacy UE handovers.

[0187] 2.3 Conditional Reset If individual RRC reconfigurations are sent to the UE simultaneously, the load on radio resources may increase due to the large number of 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 IAB nodes while they are moving. A similar solution exists in Solution 2 for reducing service interruptions in Rel-17.

[0188] Observation 1: Conditional reconfiguration may help IAB donors distribute RRC reconfiguration messages in the time domain.

[0189] Depending on how the mobile IAB-DU handles cells and partly at the discretion of RAN3, it is possible that the mobile IAB-DU may need to change its cell ID after a mobile IAB node transition. For example, this may be 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", conditional reconfiguration is considered to be more effective than the traditional HO command.

[0190] Observation 2: Conditional reconfiguration may work efficiently when the serving cell ID changes due to the migration of a mobile IAB node.

[0191] Considering (but not limited to) the above examples, improvements to conditional reconfiguration may be worth discussing in RAN2, such as whether existing trigger conditions can be reused for mobile IAB.

[0192] Proposal 3: RAN2 should consider whether conditional reconfiguration to UEs can be enhanced to improve the mobility of mobile IAB nodes.

[0193] 2.4 RACH-less handover In the current specification, the UE must first initiate the random access procedure when it receives 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 value Since the PRACH transmission is the same in both cells, 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 UE.

[0194] Proposal 4: RAN2 should consider whether RACH-less handover of Rel-18 UE is useful due to the movement of mobile IAB nodes.

[0195] 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 because it was considered a rare case assuming a deployment with fixed (stationary) IAB nodes.

[0196] 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 "a mobile IAB node has no descendant IAB nodes, i.e., only the UE is Serving Therefore, such an assumption should be confirmed by RAN2.

[0197] 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.

[0198] 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 the UE due to the movement of the mobile IAB node.

[0199] 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 required.

[0200] 2.6 Other aspects WID states that mobile IAB nodes only support UEs.

[0201] · A mobile IAB node must not have any child nodes, i.e. it must only support UEs.

[0202] To ensure this restriction, the existing IAB Support IE can be reused. That is, a mobile IAB node can prevent access by other IAB nodes and allow access by the UE by not setting this IE in SIB1. The question is how such a restriction is described in the specification. A clear description in the Stage-2 specification would help avoid confusion in mobile IAB implementations.

[0203] Proposal 7: RAN2 should agree to include in the Stage-2 specification that an IAB node should not set the IAB Support IE in its SIB when acting as a mobile IAB node in this release.

Claims

1. A communication control method for use in a cellular communication system, comprising: The base station transmits, to the user equipment, a conditional reconfiguration that enables a RACH (Random Access Channel)-less handover to be configured for each target cell; the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. Communication control method.

2. 1. A base station of a cellular communication system, comprising: a transmitter for transmitting a conditional reconfiguration capable of setting a RACH (Random Access Channel)-less handover for each target cell to a user equipment; the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. Base station.

3. A user equipment of a cellular communication system, comprising: a receiving unit that receives, from a base station, conditional reconfiguration that enables setting of a RACH (Random Access Channel)-less handover for each target cell; a control unit that executes the RACH-less handover in accordance with the conditional reconfiguration, the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. User equipment.

4. A cellular communication system having a user equipment and a base station, The base station transmits, to the user equipment, a conditional reconfiguration that enables setting of a RACH (Random Access Channel)-less handover for each target cell; the user terminal receives the conditional reconfiguration; the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. Cellular communication systems.

5. At the base station of the cellular communication system, causing the user equipment to execute a process of transmitting a conditional reconfiguration that enables the setting of a RACH (Random Access Channel)-less handover for each target cell; the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. program.

6. A base station chipset, comprising: transmitting a conditional reconfiguration to the user equipment, the conditional reconfiguration enabling a RACH (Random Access Channel)-less handover to be configured for each target cell; the conditional reconfiguration indicates a conditional handover configuration; Each of the target cells configured by the conditional reconfiguration is a cell formed by the base station or a cell formed by a base station other than the base station. Chipset.

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