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

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

[0004] A communication control method according to a first aspect is a communication control method for use in a cellular communication system, the communication control method comprising: a base station transmitting, 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 (UE) under a mobile relay node, a conditional reconfiguration including an execution condition for execution in response to an execution instruction received from the donor node. 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 served by 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 served by 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.

[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 related to IAB-MT RRC connection and NAS connection. FIG. 7 is a diagram illustrating an example protocol stack related to the F1-U protocol. FIG. 8 is a diagram illustrating an example protocol stack related to the F1-C protocol. FIG. 9 is a diagram illustrating an example operation according to the first embodiment. FIG. 10 is a diagram illustrating another example operation according to the first embodiment. FIG. 11 is a diagram illustrating an example operation of Solution 2 according to the second embodiment. FIG. 12 is a diagram illustrating an example operation according to the second embodiment. FIG. 13 is a diagram illustrating another example operation according to the second embodiment. Figures 14(A) and 14(B) are diagrams illustrating an example of group handover operations according to the third embodiment. Figure 15 is a diagram illustrating an example of operations according to the third embodiment. Figure 16 is a diagram illustrating another example of operations according to the third embodiment. Figure 17 is a diagram illustrating an example of traditional handover (top) and an example of group reconfiguration (bottom). Figure 18 is a diagram illustrating Solution 1 for reducing service interruptions. Figure 19 is a diagram illustrating 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] (Configuration of cellular communication system) An example configuration of a cellular communication system according to one embodiment will be described. A 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 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, 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).

[0013] 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.

[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. Hereinafter, 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. In FIG. 1, two gNBs 200-1 and 200-2 connected to the 5GC 10 are illustrated.

[0017] 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.

[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 functions that support IAB. The backhaul can be multi-hopped via multiple hops (i.e., multiple IAB nodes 300).

[0019] 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.

[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 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.

[0021] FIG. 2 is a diagram showing an example of the relationship between the 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 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.

[0024] 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.

[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 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.

[0026] (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.

[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 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.

[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 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.

[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 shown below.

[0030] (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.

[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 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.

[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 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.

[0035] 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.

[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 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.

[0037] (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.

[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 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.

[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 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.

[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 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.

[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 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."

[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 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.

[0053] 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.

[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 source of the connection may be an intermediate IAB node. The source of the connection may be a donor node. The destination of the connection may be an intermediate IAB node. The destination of the connection 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. Thereafter, the UE 100 uses the uplink resources included in the RRC connection reconfiguration message to transmit an RRC connection reconfiguration complete (RRCConnectionReconfigurationComplete) message to the target cell, thereby completing the handover procedure.

[0058] In the RACH-less handover, the random access procedure is skipped, and therefore, in the UE 100, it is possible to 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, UE 100 reports measurements of the radio conditions of the serving cell and / or neighboring cells to gNB 200, and based on this report, gNB 200 decides to handover to the neighboring cell and transmits a handover instruction to UE 100. For this reason, if the radio conditions of the serving cell suddenly deteriorate, a typical handover may result in communication being interrupted before the handover is performed.

[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. Therefore, it is possible to solve problems such as communication interruption 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 First Embodiment) There is a case where a mobile IAB node causes all UEs 100 under the mobile IAB node to perform handover simultaneously by performing a handover of the mobile IAB node itself.

[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. For this reason, the above-described case is assumed.

[0064] In such a case, if the distance (or location) of UE 100 under the 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 UE 100 perform a RACH-less handover.

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

[0066] For example, the DU of the gNB 200 (or donor node) may know the cells that 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 (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 possible to properly set 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] As a result, the UE 100 can determine which target cell to connect to in order to perform a RACH-less handover during handover. Therefore, if the target cell allows connection by a RACH-less handover, the UE 100 can perform a RACH-less handover to the target cell. Therefore, the UE 100 can be appropriately connected to the network.

[0071] (Operation Example According to First Embodiment) Fig. 9 is a diagram illustrating an operation example 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 illustrates an example in which UE 100 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 subordinate to 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 has the capability to perform 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. Note that, 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 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 a source cell to a 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 combination information. The IAB-DU of the mobile IAB node 300M may grasp a combination of cells in which the TA value is the same from the history of past handovers of the subordinate UEs 100.

[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 is handed over 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 executes the 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 RRC Reconfiguration 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, based on the combination information (step S11), a cell to be combined as a target cell permitted for connection via RACH-less handover. 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] Secondly, when the permission information indicates that connection by RACH-less handover is permitted, it may indicate that execution of RACH-less handover is instructed to the target cell. Alternatively, it 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, it 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 confirms 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 confirms 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 a 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 First Embodiment) In the first embodiment, an example in which conditional reconfiguration is configured between the donor node 200, the mobile IAB node 300M, and the UE 100 has been described. 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] 10 is a diagram showing another example of operation according to the first embodiment. The example shown in FIG. 10 shows an example in which UE100 performs a conditional handover from a source cell managed by a DU of gNB200 to a target cell managed by the DU of gNB200.

[0088] As in the first embodiment, UE100 may transmit RACH-less handover capability information to the CU of gNB200 (step S15). In this case, UE100 transmits an RRC message including the RACH-less handover capability information to the DU of gNB200, and the DU of gNB200 may transmit an F1 message including the RRC message to the CU of gNB200.

[0089] Then, the DU of the gNB200 transmits the combination information (including the F1 message) to the CU of the gNB200 (step S16). The combination information includes a combination of cells capable of RACH-less handover, as in the first embodiment.

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

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

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

[0093] (Another Example 3 According to First Embodiment) In the first embodiment, an example of the mobile IAB node 300M has been described. However, for example, instead of the mobile IAB node 300M, 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. For example, in FIG. 9 , this can be implemented by replacing the mobile IAB node 300M with the intermediate IAB node 300S.

[0094] (Another Example 4 According to the First Embodiment) In Another Example 2 according to the first embodiment, an example implemented between the gNB 200 and the UE 100 has been described. However, it is also possible to implement, for example, between the donor node 200 and the mobile IAB node 300M. For example, in FIG. 10, this can be implemented by replacing the gNB 200 with the donor node 200 and the UE 100 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 reconfiguration including permission information based on the combination information, and transmits the conditional reconfiguration 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, a case has been described in which, 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 RRC reconfiguration message to each of the subordinate UEs 100 in order to instruct the UEs 100 to execute a 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 service interruptions 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 specified.

[0100] 11 is a diagram showing an example of the operation of Solution 2 (Solution 2 for reduction of service interruption). In the example shown in Fig. 11, 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 IAB node 300, 300-C, and 300-GC is performed. Since the RRC reconfiguration message is transmitted to each IAB node 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 UEs 100 subordinate to each IAB node 300, 300-C, and 300-GC.

[0102] As shown in Fig. 11, Solution 2 suspends the execution of the RRC reconfiguration message 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 the relationship between the mobile IAB node 300M and the subordinate UE 100 is considered, 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 for 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 to be executed 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 Second Embodiment) FIG. 12 is a diagram showing an operation example according to the second embodiment.

[0112] 12 illustrates 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 illustrates an example in which the subordinate UE 100 is also 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 UE 100 with conditional reconfiguration. For example, the CU of the donor node 200 generates an RRC message (e.g., an RRC reconfiguration (HO command) message) including the conditional reconfiguration, and transmits an F1 message including the RRRC 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 configuration. 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-described 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 a transmission instruction to the IAB-DU of the mobile IAB node 300M.

[0117] Second, the transmission instruction may include a UE identifier of the UE 100 to which the transmission instruction is to be transmitted. The transmission instruction may also include an identifier (conditional reconfiguration identifier) ​​of the conditional reconfiguration to which the transmission instruction is to be transmitted. The identifier represents, for example, information indicating 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 indicating an immediate transmission of the execution instruction. Alternatively, the transmission instruction may include an instruction indicating an execution instruction to be transmitted when a conditional handover is performed. Alternatively, the transmission instruction may include an instruction indicating an execution instruction to be transmitted when a handover is performed. Alternatively, the transmission instruction may include an instruction indicating an execution instruction to be transmitted when an RRC reconfiguration complete (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 (conditional reconfiguration identifier) ​​of the conditional reconfiguration to be performed. The identifier may represent, for example, information indicating whether at least one of a plurality of conditional reconfigurations should be performed. Alternatively, the execution instruction may include an entry number of a list in the conditional reconfiguration to be performed.

[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 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 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 operation example shown in FIG. 12 can be implemented by replacing the mobile IAB node 300M with the intermediate IAB node 300S.

[0123] (Another example 2 according to the second embodiment) In addition, 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] As shown in Figure 13, the CU of the gNB 200 configures the conditional reconfiguration for the UE 100, as in the second embodiment (step S25). As in the second embodiment, at least one of the entries included in the conditional reconfiguration includes an execution condition of "executing by execution instruction." 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, as in the second embodiment, and executes handover to the target cell (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 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 donor node (Source IAB-donor) 200-S transmits an RRC reconfiguration 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 is not limited to Rel-18-only UEs 100, but also allows connection of UEs 100 of Rel-17 or earlier. 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 a mobile IAB node 300M receives a common setting common to the group and an individual setting for each UE from a donor node, 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 a 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 a message is transmitted to each UE as shown in Fig. 14(A).

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

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

[0139] The example shown in Figure 15 illustrates an example in which a mobile IAB node 300M is handed over from a source donor node (Source IAB-donor) 200-S to a target donor node (Target IAB-donor) 200-T. Also, the example shown in Figure 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 represents 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 a second message.

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

[0146] In step S32, the IAB-DU of the mobile IAB node 300M combines the common settings and the individual settings to generate an RRC reconfiguration message including the common settings and the individual settings. This 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 belonging 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 donor node (Target IAB-donor) 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 mobile IAB node 300M has been described, but this is not limited to this. For example, a group handover may also be performed in the UE 100 under 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 gNB 200 form a UE group and group handover is performed among the UEs 100-1, ..., 100-n.

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

[0154] Further, the CU of gNB200 transmits the individual setting to the DU of gNB200 (step S36). As in the third embodiment, the CU of gNB200 may generate an RRC message (e.g., an RRC reconfiguration message) including the individual setting and transmit an F1 message including the RRC message to the DU of gNB200. Alternatively, as in the third embodiment, the CU of gNB200 may transmit an F1 message including the individual setting to the DU of gNB200. The individual setting 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 UE 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 prior to Rel-17. Each UE 100-1, ..., 100-n transmits an RRC reconfiguration completion message to the target cell to complete 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, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0157] In addition, circuits that perform 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 (chipset, 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 / 395,940 (filed August 8, 2022), the entire contents of which are incorporated herein by reference.

[0161] (Supplementary Note 1) (Supplementary Note 1) A communication control method used in a cellular communication system, comprising: a step in which a base station transmits, to a user equipment, a conditional reconfiguration including permission information indicating whether or not connection via RACH-less handover is permitted for each target cell.

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

[0163] (Supplementary Note 3) The communication control method according to Supplementary Note 1 or Supplementary Note 2, further comprising a step in which the mobile relay node transmits, to the donor node, combination information representing a combination of cells to which connection by the RACH-less handover is possible, and the step of transmitting the conditional reconfiguration comprises a step in which the base station transmits the conditional reconfiguration based on the combination information.

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

[0165] (Supplementary Note 5) A communication control method used in a cellular communication system, comprising: a step in which a donor node transmits, to a user device under a mobile relay node, a conditional reconfiguration including an execution condition to be executed upon receiving an execution instruction; 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; and a step in which the mobile relay node transmits, in response to receiving the transmission instruction, the execution instruction to the user device.

[0166] (Supplementary Note 6) The communication control method according to Supplementary Note 5, wherein the step of transmitting the execution instruction includes a step of the mobile relay node transmitting the execution instruction including information indicating whether at least any of the plurality of conditional resets should be performed.

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

[0168] (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:

[0169] 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.

[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-18 UE 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 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.

[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 delay, group reconfiguration is a possible candidate, which is expected to reconfigure multiple UEs with one message.

[0174] Group reconfiguration has already been discussed in Rel-17 MBS as "Common RRC Architecture" and the following summary is provided:

[0175] 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.

[0176] Proposal 2: Maintain the current CRRRC structure and do not move forward 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 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.

[0178] In case 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, access link signal reduction is still more important since the backhaul link is typically assumed to be over FR2.

[0180] 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.

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

[0182] 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.

[0183] 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 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 less 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 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.

[0186] 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.

[0187] 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.

[0188] Observation 1: Conditional reconfiguration can 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, 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 may be more effective than a traditional HO command.

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

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

[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 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.

[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 as it was considered a rare case given the deployment assumption of 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 the mobile IAB node has no descendant IAB nodes, i.e., it serves only UEs. Therefore, this 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 UEs due to mobile IAB node movement.

[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 necessary.

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

[0201] A mobile IAB node has no child nodes, i.e. it needs to support only UEs.

[0202] 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.

[0203] 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: The base station transmits, to the user equipment, a conditional reconfiguration capable of setting a RACH (Random Access Channel)-less handover for each target cell. Communications control method.

2. The base station is a donor node, and the user equipment is a user equipment under a mobile relay node. The communication control method according to claim 1.

3. The mobile relay node further includes transmitting combination information indicating a combination of cells to which a connection can be made by the RACH-less handover to the donor node; and transmitting the conditional reconfiguration includes transmitting the conditional reconfiguration by the base station based on the combination information. The communication control method according to claim 2.

4. Transmitting the combination information includes the mobile relay node transmitting a timing advance value for each of the combinations. The communication control method according to claim 3.

5. A base station for a cellular communication system, comprising: A transmitter that transmits a conditional reconfiguration capable of setting a RACH (Random Access Channel)-less handover for each target cell to a user equipment. Base station.

6. A user equipment of a cellular communication system, comprising: A receiving unit that receives conditional reconfiguration from a base station, the conditional reconfiguration enabling a RACH-less handover to be configured for each target cell; a control unit that executes the RACH-less handover in accordance with the conditional reconfiguration; User equipment.

7. A cellular communication system having a user terminal and a base station, The base station transmits, to the user equipment, a conditional reconfiguration capable of setting a RACH (Random Access Channel)-less handover for each target cell; The user terminal receives the conditional reconfiguration. Cellular communication systems.

8. A base station of a cellular communication system, comprising: A process of transmitting a conditional reconfiguration enabling a RACH-less handover to be set for each target cell to the user equipment. program.

9. A base station chipset, comprising: transmitting a conditional reconfiguration capable of setting a RACH (Random Access Channel)-less handover for each target cell to the user equipment. Chipset.