Terminal device, base station device, and wireless communication system

Abstract

This terminal device includes a reception unit and a processing unit. The reception unit receives, from a base station device, a first signal instructing cell switching from a first cell serving as a serving cell to a second cell serving as an LTM candidate cell. The processing unit performs processing for determining whether the condition is a first condition or a second condition. When having determined that the condition is the first condition, the processing unit performs first processing that is protocol processing accompanying inter-base station device cell switching, and when having determined that the condition is the second condition, the processing unit performs second processing that is protocol processing accompanying intra-base station device cell switching.

Description

Terminal device, base station device, and wireless communication system

[0001] The present invention relates to a terminal device, a base station device, and a wireless communication system.

[0002] In the current network, the network of wireless communication using mobile terminals (smartphones, feature phones, etc.) is expanding. In the expansion of wireless communication, further higher speed and larger capacity are required.

[0003] In the 3rd Generation Partnership Project (3GPP: 3rd Generation Partnership Project (registered trademark)), which is an international standardization project, technical studies and standard setting for cellular mobile communication systems are being carried out. For example, as the radio access technology (RAT) for the 3.9th generation (3.9G) and the 4th generation (4G), E-UTRA (Evolved Terrestrial Radio Access) has been standardized, and as the core network (CN) technology, EPC (Evolved Packet Core) has been standardized. Also, as the RAT for the 5th generation (5G), NR (New Radio) has been standardized, and as the core network technology, 5GC (5G Core) has been standardized. Also, currently, these extended technologies are continuously being studied and standardized.

[0004] Technologies related to the NR or 5G system are described, for example, in Non-Patent Documents 1 to Non-Patent Documents 11 below.

[0005] 3GPP TS38.300 v18.0.0 NR Overview Specification 3GPP TS38.211 v18.0.0 NR PHY Channel and Modulation Specification 3GPP TS38.321 v18.0.0 NR MAC Specification 3GPP TS38.322 v18.0.0 NR RLC Specification 3GPP TS38.323 v18.0.0 NR PDCP Specification 3GPP TS37.324 v18.0.0 NR SDAP Specification 3GPP TS38.304 v18.0.0 NR Idle Mode and Inactive Mode Specification 3GPP TS38.331 v18.1.0 NR RRC Specification 3GPP RP-223520 "Revised WID on Further NR mobility enhancements" 3GPP RP-241515 "Revised Work Item: NR mobility enhancements" Phase 4" 3GPP TS33.501 v18.4.0 5G System Security Specification

[0006] As one of the advanced technologies, technical studies are being conducted on improving mobility. One of the items under consideration is the specification of a technology called LTM (L1 / L2-triggered mobility), which aims to reduce latency in mobility by having base station equipment switch serving cells of terminal devices using Layer 1 and / or Layer 2 signals instead of Layer 3 signals such as RRC (Radio Resource Control) messages. This specification was defined in Rel-18 (Non-Patent Literature 9). Furthermore, the LTM in Rel-18, which only supported cell switching within a Centralized Unit (CU) (intra-CU), will be further extended to include cell switching between CUs (inter-CU), and the specification for LTM will be defined in Rel-19 (Non-Patent Literature 10).

[0007] However, the specific method for LTM that supports cell switching both within and between CUs has not been determined in the standard specifications. For example, the specification for how to achieve cell switching between multiple LTM candidate cells that support cell switching both within and between CUs without reconfiguring via RRC messages has not been determined. Furthermore, the specification for how terminal devices handle cell switching when inter-CU LTM fails has not been determined. In addition, the specific method for LTM that supports cell switching both within and between CUs when DC (Dual Connectivity) is set on the terminal device has not been determined in the standard specifications.

[0008] Therefore, one disclosure aims to provide a base station device, terminal device, and wireless communication system that enable flexible cell switching that supports cell switching both within and between CUs.

[0009] One disclosure is a terminal device comprising: a receiving unit that receives a first signal instructing cell switching from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that performs a process to determine whether the first condition or the second condition is met. If the processing unit determines that the first condition is met, it performs a first process, which is protocol processing associated with cell switching between base station devices; and if the processing unit determines that the second condition is met, it performs a second process, which is protocol processing associated with cell switching within a base station device.

[0010] Another disclosure is a base station device comprising: a transmitting unit that transmits a first signal to a terminal device that instructs the terminal device to switch cells from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that causes the terminal device to perform a process to determine whether the first condition or the second condition is met. If the processing unit determines that the first condition is met, it causes the terminal device to perform a first process, which is a protocol process associated with cell switching between base station devices; and if the processing unit determines that the second condition is met, it causes the terminal device to perform a second process, which is a protocol process associated with cell switching within a base station device.

[0011] Another disclosure is a wireless communication system comprising: a base station device that transmits a first signal instructing a cell switch from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a terminal device that receives the first signal and performs processing to determine whether the first condition or the second condition is met. The terminal device performs a first process, which is protocol processing associated with cell switching between base station devices, if it determines that the first condition is met, and a second process, which is protocol processing associated with cell switching within a base station device, if it determines that the second condition is met.

[0012] One disclosure indicates that when a terminal device with a DC configured performs mobility processing, it becomes possible to perform communication that processes Layer 2 protocol processing according to the switching status of each wireless bearer.

[0013] Figure 1 shows an example configuration of the communication system 10. Figure 2 shows an example configuration of the base station device 200. Figure 3 shows an example configuration of the terminal device 100. Figure 4 shows an example of the U-Plane protocol stack. Figure 5 shows an example of the C-Plane protocol stack. Figure 6 shows an example of the RRCReconfiguration message format. Figure 7 shows an example of the configuration of the cell group of the communication system 10. Figure 8 shows an example of synchronized reconfiguration. Figure 9 shows an example of parameters related to the LTM included in the RRCReconfiguration message. Figure 10 shows an example of the sequence of the LTM within the CU. Figure 11 shows an example of the sequence of cell switching failure detection and cell switching failure processing. Figure 12 shows an example of a subsequent cell switching method corresponding to within and between CUs.

[0014] Hereinafter, this embodiment will be described in detail with reference to the drawings. The problems and embodiments described herein are examples only and do not limit the scope of the rights of this application. In particular, even if the wording differs, if the technical aspects are equivalent, the technology of this application can be applied even with different wording, and the scope of the rights is not limited.

[0015] Furthermore, in this embodiment, the names and processing of each device, node, function, protocol, entity, signaling, message, parameter, etc., when the wireless access technology is E-UTRA or NR, and the core network is EPC or 5GC will be described, but this embodiment may be used with other wireless access technologies. The names of each node and entity in each embodiment may be different.

[0016] <Example Configuration of Communication System 10> Figure 1 shows an example configuration of communication system 10. Communication system 10 includes a terminal device 100, base station devices 200-1 and 200-2, and a core network 300. Communication system 10 may be a wireless communication system in which terminal device 100 communicates with base station device 200-1 or base station device 200-2, or it may be a wireless communication system in which terminal device 100 communicates with base station devices 200-1 and base station devices 200-2 using MR-DC (Multi Radio Dual Connectivity) as described later. When communication is performed using MR-DC, for example, base station device 200-1 is the master base station device, and base station device 200-2 is the secondary base station device. Hereafter, the master base station device may be called MN (Master Node), and the secondary base station device may be called SN (Secondary Node). Note that MR-DC may also be simply called DC.

[0017] Terminal device 100 wirelessly connects to one or both of base station devices 200-1 and 200-2 to perform wireless communication. The RAT providing the wireless connection is, for example, E-UTRA or NR. Terminal device 100 is a terminal device that supports either or both of E-UTRA and NR.

[0018] Base station devices 200-1 and 200-2 (hereinafter sometimes referred to as base station device 200) are communication devices that wirelessly connect to terminal device 100 and perform wireless communication. Base station devices 200-1 and 200-2 may also communicate with each other, for example, by wired connections. Base station device 200 may also communicate with core network 300, for example, by wired connections. Base station device 200 is, for example, an eNodeB (eNB) that provides E-UTRA as RAT, or a gNodeB (gNB) that provides NR as RAT. Note that one base station device may consist of one CU (Centralized Unit) and one or more DUs (Distributed Units). The CU may have functions such as RRC (Radio Resource Control), SDAP (Service Data Adaptation Protocol), and PDCP (Packet Data Convergence Protocol), which are part of the protocol stack described later. Furthermore, the CU may have interface functions between base station devices and between base station devices and the core network. The DU may have functions such as RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical) from the protocol stack described later.

[0019] The core network 300 is a network corresponding to a particular generation. For example, the core network 300 is 5GC, which is a core network standardized for 5G, or EPC, which is a core network standardized for 4G.

[0020] Details of the MR-DC implemented in the communication system 10 will be described later.

[0021] <Example Configuration of Base Station Device 200> Figure 2 is a diagram showing an example configuration of base station device 200. Base station device 200 is a communication device or relay device having a CPU (Central Processing Unit) 210, storage 220, memory 230, wireless communication circuit 240, and network interface (NI (Network Interface)) 250.

[0022] Storage 220 is an auxiliary storage device such as flash memory, HDD (Hard Disk Drive), or SSD (Solid State Drive) that stores programs and data. Storage 220 stores the wireless communication program 221 and the base station side program 222.

[0023] Memory 230 is an area for loading programs stored in storage 220. Memory 230 may also be used as an area for programs to store data.

[0024] The wireless communication circuit 240 is a circuit that wirelessly connects to the terminal device 100 and performs communication. The base station device 200, for example, receives signals transmitted from the terminal device 100 via the wireless communication circuit 240 and transmits signals to the terminal device 100.

[0025] NI250 is a communication device that, for example, connects to other base station equipment 200 to realize inter-base station communication. NI250 is also a communication device that, for example, connects to and communicates with a core network 300 (communication devices constituting the core network 300). NI250 is, for example, a NIC (Network Interface Card). Base station equipment 200 receives signals from other communication devices and transmits signals to other communication devices via NI250.

[0026] The CPU 210 is a processor that loads programs stored in the storage 220 into the memory 230, executes the loaded programs, builds each part, and performs each process.

[0027] The CPU 210 performs wireless communication processing by executing the wireless communication program 221. Wireless communication processing involves wirelessly connecting with the terminal device 100, communicating wirelessly with the terminal device 100, and relaying communications between the terminal device 100 and other communication devices.

[0028] The CPU 210 constructs the second transmission unit, the second reception unit, and the second processing unit by executing the base station-side program 222, and performs base station-side processing. When the base station device 200 communicates with the terminal device 100 using MR-DC, the base station-side processing may include MR-DC master node processing and MR-DC secondary node processing. In this case, MR-DC master node processing is processing that controls the master node side in MR-DC, and MR-DC secondary node processing is processing that controls the secondary node side in MR-DC. In MR-DC master node processing and MR-DC secondary node processing, the base station device 200 performs communication corresponding to each type of MR-DC described later.

[0029] <Example of Terminal Device 100 Configuration> Figure 3 is a diagram showing an example of the configuration of terminal device 100. Terminal device 100 is a communication device having a CPU 110, storage 120, memory 130, and wireless communication circuit 140.

[0030] Storage 120 is an auxiliary storage device such as flash memory, HDD, or SSD that stores programs and data. Storage 120 stores the wireless communication program 121 and the terminal-side program 122.

[0031] Memory 130 is an area for loading programs stored in storage 120. Memory 130 may also be used as an area for programs to store data.

[0032] The wireless communication circuit 140 is a circuit that wirelessly connects to and communicates with the base station device 200. The terminal device 100, for example, receives signals transmitted from the base station device 200 via the wireless communication circuit 140 and transmits signals to the base station device 200. The wireless communication circuit 140 is, for example, a network card that supports wireless connection.

[0033] The CPU 110 is a processor that loads programs stored in the storage 120 into the memory 130, executes the loaded programs, constructs each part, and performs each process.

[0034] The CPU 110 performs terminal-side wireless communication processing by executing the wireless communication program 121. Terminal-side wireless communication processing involves wirelessly connecting with the base station device 200 and communicating wirelessly with the base station device 200, or communicating with other communication devices via the base station device 200.

[0035] The CPU 110 constructs the transmitting unit, receiving unit, and processing unit by executing the terminal-side program 122, and performs terminal-side processing. When the terminal device 100 communicates with the base station device 200 using MR-DC, the terminal-side processing may include terminal-side MR-DC processing. In this case, the terminal-side MR-DC processing is the processing that controls communication in MR-DC. In the terminal-side MR-DC processing, the terminal device 100 performs communication corresponding to each type of MR-DC described later.

[0036] <Protocol Stack> An example of the protocol stack of the communication system 10 will be explained. In the communication system 10, a series of protocols for sending and receiving data, shown in a hierarchical structure, is called a protocol stack. In the following example, the case where the base station equipment 200 is eNB or gNB, and the core network 300 is EPC or 5GC will be explained. In addition, the terminal equipment 100 (UE: User Equipment) will support either E-UTRA or NR, or both.

[0037] The following describes the U-Plane (User Plane), C-Plane (Control Plane), and their protocol stacks. The U-Plane is used, for example, to send and receive user data in communication. The C-Plane is used, for example, to send and receive control signals (messages) in communication. In each embodiment, unless otherwise specifically mentioned, "data" refers to either user data, control signals (messages), or both.

[0038] Figure 4 shows an example of the U-Plane protocol stack when the core network 300 is 5GC. Figure 5 shows an example of the C-Plane protocol stack when the core network 300 is 5GC. In Figures 4 and 5, PHY (PHYsical), MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol), SDAP (Service Data Adaptation Protocol), RRC (Radio Resource Control), and NAS (Non Access Stratum) are the names of the layers. Hereafter, PHY, MAC, RLC, PDCP, SDAP, RRC, and NAS may be referred to as the PHY layer, MAC layer, RLC layer, PDCP layer, SDAP layer, RRC layer, and NAS layer, respectively. Furthermore, MAC, RLC, PDCP, and SDAP may be referred to as the MAC sublayer, RLC sublayer, PDCP sublayer, and SDAP sublayer, respectively. Also, MAC, RLC, PDCP, and SDAP may be referred to as the MAC entity, RLC entity, PDCP entity, and SDAP entity, respectively. Note that when the core network 300 is an EPC, the U-Plane protocol stack will be the protocol stack without SDAP as shown in Figure 4. That is, it will be a protocol stack consisting of PHY, MAC, RLC, and PDCP. Also, when the core network 300 is an EPC, the C-Plane protocol stack will have NAS in the AMF (Access and Mobility Management Function) as shown in Figure 5, while NAS will be in the MME (Mobility Management Entity).

[0039] The functions of each layer may be common or different depending on whether RAT is E-UTRA or NR. In the following explanation, unless otherwise specified, the functions are common to both E-UTRA and NR.

[0040] Furthermore, in each sublayer, the data provided from the upper layer and the data provided to the upper layer are called SDUs (Service Data Units). Specifically, the data provided to MAC, RLC, PDCP, and SDAP from the upper layer, and the data provided from MAC, RLC, PDCP, and SDAP to the upper layer are called MAC SDUs, RLC SDUs, PDCP SDUs, and SDAP SDUs, respectively.

[0041] Furthermore, within each sublayer, the data provided to and received from lower layers is called a PDU (Protocol Data Unit). Specifically, the data provided from MAC, RLC, PDCP, and SDAP to lower layers, and the data received from lower layers to MAC, RLC, PDCP, and SDAP are called MAC PDU, RLC PDU, PDCP PDU, and SDAP PDU, respectively. Additionally, RLC, PDCP, and SDAP have control PDUs, which are sometimes called control PDUs. To distinguish them from control PDUs, other PDUs are sometimes called data PDUs.

[0042] In Figure 4, the U-Plane consists of PHY, MAC, RLC, PDCP, and SDAP, and is terminated by terminal device 100 (UE) and base station device 200 (gNB).

[0043] This section describes an example of PHY functionality. PHY is a wireless physical layer that transmits control information and data between a terminal device 100 and a base station device 200 using a physical channel. The direction from the base station device 200 to the terminal device 100 is sometimes called the downlink (DL), and the direction from the terminal device 100 to the base station device 200 is sometimes called the uplink (UL). Within the terminal device 100 and the base station device 200, PHY is connected to the higher layer MAC via a transport channel, and data moves between PHY and MAC via the transport channel. In PHY, an RNTI (Radio Network Temporary Identifier) ​​is used to identify various control information.

[0044] An example of the functions of the MAC will be described. The MAC is the Medium Access Control layer, which performs functions such as mapping of transport channels and logical channels (LCHs), multiplexing and demultiplexing of MAC SDUs, scheduling reports (SRs), error correction through HARQ (Hybrid Automatic Repeat reQuest), and priority control. Within the terminal device 100 and the base station device 200, the MAC is connected to the upper layer RLC via a logical channel, and data moves between the MAC and the RLC via the logical channel. The logical channel may be identified by a logical channel identifier (LCID: Logical Channel identifier). Also, the base station device 200 controls the terminal device 100 using MAC control elements (CEs). Further, the terminal device 100 reports to the base station device 200 using MAC CEs, etc.

[0045] The RLC is the Radio Link Control layer, and there are three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). The RLC performs, on the transmitting side, transfer of PDUs, assignment of sequence numbers (in the case of UM and AM), segmentation of SDUs (in the case of UM and AM), and resegmentation (in the case of AM), and on the receiving side, reassembly of SDUs (in the case of UM and AM), duplicate detection (in the case of AM), discarding of SDUs (in the case of UM and AM). In addition, the RLC performs RLC re-establishment, etc. on both the transmitting and receiving sides. The segmented SDUs are called SDU segments. Also, the RLC has a data retransmission function and / or an automatic repeat request (ARQ) function (in the case of AM). In the case of E-UTRA RLC, there are also functions such as data concatenation on the transmitting side, reordering and in-order delivery functions on the receiving side.

[0046] PDCP is a Packet Data Convergence Protocol layer that performs functions such as data transfer in the U-Plane and C-Plane, PDCP sequence number management, header compression / decompression, encryption / decryption, integrity protection / integrity verification, timer-based SDU discard, PDCP re-establishment, PDCP data recovery, routing for split bearers, reordering, and in-order delivery. Note that in E-UTRA PDCP, functions such as timer-based SDU discard, reordering, and in-order delivery may be limited to cases such as that of split bearers described later.

[0047] SDAP is a Service Data Adaptation Protocol layer that performs functions such as mapping between QoS (Quality of Service) flows and the Data Radio Bearer (DRB) described later, and marking the QoS flow identifier (QFI) in downlink (DL) packets and uplink (UL) packets.

[0048] As the upper layer of the U-Plane, there are layers such as IP (Internet Protocol), TCP (Transmission Control Protocol), UDP (User Datagram Protocol), Ethernet (registered trademark), and applications. The layer including IP, TCP, UDP, Ethernet, etc. may be called the PDU layer. Also, IMS (IP Multimedia Subsystem) that performs session control may be included in the application layer.

[0049] In FIG. 5, the C-Plane of the AS (Access Stratum) is composed of PHY, MAC, RLC, PDCP, and RRC, and is terminated at the terminal device 100 and the base station device 200. Also, the C-Plane of the NAS is composed of NAS and is terminated between the terminal device 100 and the AMF which is a device of the core network 300. For PHY, MAC, RLC, and PDCP, it is the same as in the U-Plane.

[0050] The RRC performs functions such as broadcasting and paging system information (SI) related to the AS and NAS, establishing / maintaining / releasing RRC connections between terminal equipment 100 and base station equipment 200, adding / modifying / releasing carrier aggregation (CA), adding / modifying / releasing dual connectivity (DC), security functions including security key management, establishing / configuring / maintaining / releasing signaling radio bearers (SRB) and data radio bearers (DRB), mobility functions, QoS management functions, control of terminal equipment measurement reports and reporting, detection and recovery of radio link failures (RLF), and forwarding NAS messages. A radio link failure may include, for example, detection of a physical layer problem, random access failure, or the RRC reaching its maximum number of retransmissions.

[0051] NAS handles authentication, mobility management, and security control on the core network side.

[0052] <Channels> The channels used in the communication system 10 are described below. Examples of channels corresponding to NR are shown below, but the channels used are not limited to those shown. In addition, channels with the same name may be used for the same or similar purposes in RATs other than NR, such as E-UTRA.

[0053] <1. Physical Channel> The PBCH (Physical Broadcast Channel) is a channel used to transmit broadcast information from the base station equipment 200 to the terminal equipment 100.

[0054] The PDCCH (Physical Downlink Control Channel) is a channel used to transmit downlink control information (DCI) and other data from the base station equipment 200 to the terminal equipment 100.

[0055] PDSCH (Physical Downlink Shared Channel) is a channel used to transmit data from higher layers to terminal devices 100 from base station equipment 200.

[0056] PUCCH (Physical Uplink Control Channel) is a channel used to transmit uplink control information (UCI) and other data from the terminal device 100 to the base station device 200.

[0057] PUSCH (Physical Uplink Shared Channel) is a channel used to transmit data from higher layers to base station equipment 200 from terminal device 100.

[0058] PRACH (Physical Random Access Channel) is a channel used to transmit random access preambles and other information from terminal device 100 to base station device 200.

[0059] <2. Transport Channel> The BCH (Broadcast Channel) is mapped to the physical channel, the PBCH.

[0060] DL-SCH (Downlink Shared Channel) is mapped to the physical channel PDSCH.

[0061] The Paging Channel (PCH) is mapped to the physical channel, the PDSCH.

[0062] UL-SCH (Downlink Shared Channel) is mapped to the physical channel PUSCH.

[0063] RACH (Random Access Channel(s)) is mapped to the physical channel PRACH.

[0064] <3. Logical Channel> The BCCH (Broadcast Control Channel) is a downlink channel for broadcasting system information and is mapped to the transport channel BCH or DL-SCH.

[0065] The PCCH (Paging Control Channel) is a downlink channel for carrying paging messages and is mapped to the PCH of the transport channel.

[0066] CCCH (Common Control Channel) is a channel for transmitting control information (such as RRC messages) between a terminal device 100 and a base station device 200. It is used for terminal devices 100 that do not maintain (have) an RRC connection with the base station device 200. The downlink is mapped to the transport channel DL-SCH, and the uplink is mapped to the transport channel UL-SCH.

[0067] DCCH (Dedicated Control Channel) is a point-to-point bidirectional channel used to transmit dedicated control information (such as RRC messages) between a terminal device 100 and a base station device 200. It is used for terminal devices 100 that have an RRC connection with the base station device 200, with the downlink mapped to the transport channel DL-SCH and the uplink mapped to the transport channel UL-SCH.

[0068] DTCH (Dedicated Transport Channel) is a bidirectional channel dedicated to point-to-point terminals, transmitting user information (user data). The downlink is mapped to the DL-SCH transport channel, and the uplink is mapped to the UL-SCH transport channel.

[0069] The MCCH (MBS Control Channel) is a point-to-multipoint downlink channel used to transmit MBS (Multicast Broadcast Service) broadcast control information corresponding to one or more MTCHs (MBS Traffic Channels) from the base station equipment 200 to the terminal equipment 100. It is mapped to the DL-SCH transport channel.

[0070] MTCH is a point-to-multipoint downlink channel used to transmit MBS multicast session data or broadcast session data from base station equipment 200 to terminal equipment 100. It is mapped to the transport channel DL-SCH.

[0071] <RRC State (Mode)> The RRC state of the terminal device 100 refers to the state of the terminal device 100's RRC connection. The state in which the RRC connection with the base station device 200 has not been established is called RRC idle mode (RRC_IDLE). The state in which the RRC connection with the base station device 200 has been established is called RRC connected mode (RRC_CONNECTED). The state in which the RRC connection with the base station device 200 is temporarily suspended is called RRC inactive mode (RRC_INACTIVE). Note that if the core network 300 is EPC, the state in which the RRC connection with the base station device 200 is temporarily suspended is not called RRC inactive mode, but may be called by another name such as RRC suspension.

[0072] <RRC Messages> This section explains RRC messages. RRC messages are messages that contain information necessary for communication within a cell, and include MIBs (Master Information Blocks) and System Information Blocks (SIBs). Parameters included in RRC messages are sometimes called fields or information elements (IE).

[0073] Furthermore, RRC messages include messages related to the establishment of an RRC connection. For example, in the case of NR, messages related to the establishment of an RRC connection include the RRC Setup Request message (RRCSetupRequest), the RRC Setup message (RRCSetup), and the RRC Setup Complete message (RRCSetupComplete). Similarly, in the case of E-UTRA, messages related to the establishment of an RRC connection include the RRC Connection Setup Request message (RRCConnectionSetupRequest), the RRC Connection Setup message (RRCConnectionSetup), and the RRC Connection Setup Complete message (RRCConnectionSetupComplete).

[0074] Furthermore, RRC messages include messages related to the initial activation of Access Stratum (AS) security. Examples of messages related to the initial activation of AS security include security mode command messages (SecurityModeCommand).

[0075] Furthermore, RRC messages include messages related to the reconfiguration of RRC connections. For example, in the case of NR, messages related to the reconfiguration of RRC connections include RRCReconfiguration and RRCReconfigurationComplete. Similarly, in the case of E-UTRA, messages related to the reconfiguration of RRC connections include RRCConnectionReconfiguration and RRCConnectionReconfigurationComplete. Messages related to the reconfiguration of RRC connections perform actions such as establishing, setting, changing, and releasing wireless bearers, cell groups, etc., as well as synchronized reconfiguration, and establishing, setting, changing, and releasing measurement information.

[0076] After the initial activation of AS security, the terminal device 100 receives the first RRC reset message from the base station device 200, thereby obtaining all the necessary settings, or at least the minimum necessary settings, for communication (data communication) with the base station device 200 in the cell to which the terminal device 100 is connected. These all the necessary settings, or at least the minimum necessary settings, for communication (data communication) with the base station device 200 may be referred to as, for example, a complete configuration.

[0077] Furthermore, after the initial activation of the AS security of the terminal device 100, the base station device 200 can send an initial RRC reset message, and then another RRC reset message, to cause the terminal device 100 to update the settings necessary for communication (data communication) with the base station device 200. In this case, the base station device 200 sends the RRC reset message including the differential settings to the complete settings currently set on the terminal device 100. These differential settings are sometimes called delta settings. When the terminal device 100 receives an RRC reset message containing delta settings, it generates new settings by applying the delta settings to the complete settings currently in use.

[0078] Furthermore, RRC messages include messages related to the re-establishment of RRC connections. Messages related to the re-establishment of RRC connections include, for example, in the case of NR, the RRC Re-establishment Request message (RRCReestablishRequest), the RRC Re-establishment message (RRCReestablish), and the RRC Re-establishment Complete message (RRCReestablishComplete). Messages related to the establishment of RRC connections include, for example, in the case of E-UTRA, the RRC Connection Re-establishment Request message (RRCConnectionReestablishRequest), the RRC Connection Re-establishment message (RRCConnectionReestablish), and the RRC Connection Re-establishment Complete message (RRCConnectionReestablishComplete).

[0079] Furthermore, RRC messages also include messages regarding the release and suspension of RRC connections, messages regarding the resumption of RRC connections, messages regarding the capabilities of terminal devices, messages regarding terminal information, and messages regarding MCG failure information and SCG failure information.

[0080] In MR-DC, if the master node is an eNB, the eNB may configure the terminal device 100 by including the NR RRC messages and parameters received from the secondary node (gNB) as a container in the E-UTRA RRC message and sending it to the terminal device 100. The terminal device 100 may also include a completion message for the NR configuration as a container in the E-UTRA RRC message and send it to the master node (eNB).

[0081] Furthermore, in MR-DC, if the master node is a gNB, the gNB may configure the terminal device 100 by including the E-UTRA RRC messages and parameters received from the secondary node (eNB) as a container in the NR's RRC message and sending it to the terminal device 100. The terminal device 100 may also include a completion message for the E-UTRA configuration as a container in the NR's RRC message and send it to the master node (gNB).

[0082] Figure 6 shows an example of the RRC Reconfiguration message format. Format E1 is the RRC Reconfiguration parameters.

[0083] RRC Reconfiguration has the following parameters: radioBearerConfig, radioBearerConfig2, masterCellGroup, secondaryCellGroup, masterKeyUpdate, and sk-counter.

[0084] radioBearerConfig and radioBearerConfig2 are settings for an MN-terminated bearer or an SN-terminated bearer, including SRB settings, DRB settings, and security settings. SRB settings (DRB settings) include the SRB identifier (DRB identifier), PDCP settings, and parameters that instruct PDCP re-establishment. Security settings include a parameter (keyToUse) that indicates whether to use the master key or the secondary key.

[0085] masterCellGroup and secondaryCellGroup are MCG settings and SCG settings, respectively, and include cell group identifiers, RLC bearer settings, and SpCell settings. RLC bearer settings include logical channel identifiers, RLC settings, and the radio bearer identifier (SRB identifier or DRB identifier) ​​associated with the RLC bearer. SpCell settings include information necessary for synchronized reconfiguration.

[0086] masterKeyUpdate contains the information necessary for updating the master key.

[0087] sk-counter contains the information necessary for secondary key generation.

[0088] Format E11 is a diagram showing an example of the parameters of RadioBearerConfig included in RRCReconfiguration.

[0089] Format E12 is a diagram showing an example of CellGroupConfig parameters included in RRCReconfiguration.

[0090] Format E13 is a diagram showing an example of the parameters for MaskerKeyUpdate included in RRCReconfiguration.

[0091] Format E111 is a diagram showing an example of the SRB-ToAddMod parameters included in RadioBearerConfig.

[0092] Format E112 is a diagram showing an example of the DRB-ToAddMod parameters included in RadioBearerConfig.

[0093] Format E113 is a diagram showing an example of SecurityConfig parameters included in RadioBearerConfig.

[0094] Format E121 is a diagram showing an example of the parameters of RLC-BearerConfig included in CellGroupConfig.

[0095] Format E122 is a diagram showing an example of the parameters of SpCellConfig included in CellGroupConfig.

[0096] <Wireless Bearer> An example of a wireless bearer in the communication system 10 will be described.

[0097] <1. Signaling Radio Bearer> A Signaling Radio Bearer (SRB) is a radio bearer used to transmit RRC messages and NAS messages.

[0098] SRB0 is a radio bearer for RRC messages using the CCCH logical channel.

[0099] SRB1 is a radio bearer for RRC and NAS messages using the DCCH logical channel, which is established before SRB2, described later, is established.

[0100] SRB2 is a wireless bearer for sending and receiving NAS messages and RRC messages containing logged measurement information, and uses the DCCH logical channel. The priority of SRB2 is lower than that of SRB1 and may be set by the base station equipment 200 after AS security has been activated.

[0101] SRB3 is a wireless bearer for RRC messages when EN-DC, NGEN-DC, or NR-DC is configured on the terminal device 100, and uses the DCCH logical channel. EN-DC, NGEN-DC, and NR-DC are types of MR-DC, and details of the MR-DC types will be described later.

[0102] <2. Data Radio Bearer> A Data Radio Bearer (DRB) is a radio bearer used to transmit user data.

[0103] <SRB and DRB Protocol Configuration> The protocol configuration of the SRB and DRB of the terminal device 100 will be explained below.

[0104] SRB0 does not have any PDCP entities and is composed of RLC bearers. The RLC bearers consist of RLC entities and MAC logical channels. The mode of the RLC entities in SRB0 is TM.

[0105] SRB1 and SRB2 each consist of one PDCP entity and one or more RLC bearers. The mode of the RLC entity is AM.

[0106] SRB3 consists of one PDCP entity and one RLC bearer. The mode of the RLC entity is AM.

[0107] A DRB consists of one PDCP entity and one or more RLC bearers. The mode of the RLC entity is either UM or AM. A DRB may be called a UM DBR if the RLC entity is UM, and an AM DRB if the RLC entity is AM. Furthermore, a DRB is associated with one SDAP if the core network 300 is 5GC, and with one EPS bearer (or EPS bearer identity) if the core network 300 is EPC.

[0108] Note that there is one MAC entity for each cell group, as will be explained later.

[0109] <Cells and Cell Groups> The cells and cell groups (CG) configured in the terminal device 100 will be explained below.

[0110] A cell group may consist of one Special Cell (SpCell). Alternatively, a cell group may consist of one SpCell and one or more Secondary Cells (SCells). Note that in a Master Cell Group (MCG), which will be discussed later, the SpCell may be referred to as a Primary Cell (PCell). Similarly, in a Secondary Cell Group (SCG), which will be discussed later, the SpCell may be referred to as a Primary SCG Cell (PSCell).

[0111] A PCell is a primary frequency cell used for establishing and re-establishing RRC connections. That is, when establishing or re-establishing an RRC connection, the cell selected by the terminal device 100 becomes the PCell. Also, when the base station device 200 requests a handover from the terminal device 100 (described later), the new PCell specified by the base station device 200 is used for random access.

[0112] SCell is a cell that provides additional radio resources in addition to SpCell when carrier aggregation (CA) is configured on the terminal device 100.

[0113] PSCell is the primary frequency cell on the SCG side. PSCell is specified by the base station equipment 200 and is used for random access when adding or changing PSCells in the SCG.

[0114] In addition, the cell used by the terminal device 100 in an RRC connection state to communicate with the base station device 200 is sometimes called a serving cell. If CA is not set, SpCell is the serving cell, and if CA is set, both SpCell and SCell are serving cells.

[0115] MCG is a CG that is used when DC (Dual Connectivity) is not set on the terminal device 100, or a CG that belongs to the master node (MN) when DC is set on the terminal device 100. DC is a technology in which the terminal device 100 wirelessly connects to a base station device 200 that is the master node and another base station device 200 that is the secondary node (SN), and performs wireless communication using the carriers (cell groups) of each base station device 200.

[0116] SCG is a CG belonging to a secondary node that is set up in addition to MCG when DC is set up on terminal device 100.

[0117] Figure 7 shows an example of the configuration of a cell group in the communication system 10. In Figure 7, the master node (MN) is base station equipment 200-1, and the secondary node (SN) is base station equipment 200-2. The master node is, for example, a base station equipment 200 that provides a C-Plane connection to the core network 300 in an MR-DC. The secondary node is, for example, a base station equipment 200 that does not provide C-Plane to the core network 300 in an MR-DC, but provides additional radio resources to the terminal equipment 100. In Figure 7, the MCG is, for example, composed of one PCell and two SCells. Also in Figure 7, the SCG is, for example, composed of one PSCell and two SCells.

[0118] Furthermore, the base station device 200 may set a BWP (BandWidth Part) for the cell to be set in the terminal device 100 and adjust it to use a limited frequency band from the entire frequency band of the cell. The BWP may consist of a portion of the frequency band of each cell. Also, multiple BWPs (for example, up to four) may be set for each cell. The BWP may be set by an RRC reset message. In each cell, the specification or switching of the BWP to be used may be done by an RRC reset message or by using DCI. <MR-DC Bearer Types> Bearer types in MR-DC will be explained below.Hereinafter, a configuration in which the PDCP is terminated at the master node and the PDCP is on the master node side may be called MN-terminated.Also, a configuration in which the PDCP is terminated at the secondary node and the PDCP is on the secondary node side may be called SN-terminated.Bearer types are classified into the following six types.

[0119] 1. An MN-terminated MCG bearer where the RLC bearer is located on the MCG side.

[0120] 2. A split bearer in which the RLC bearer is present in both the MCG and SCG in an MN-terminated state.

[0121] 3. MN-terminated, with the RLC bearer located on the SCG side, an SCG bearer.

[0122] 4. SN-terminated, with the RLC bearer located on the MCG side, an MCG bearer.

[0123] 5. A split bearer that is SN-terminated and has RLC bearers present in both the MCG and SCG.

[0124] 6. SN-terminated, with the RLC bearer located on the SCG side; SCG bearer.

[0125] The DRB consists of one of the six bearer types listed above.

[0126] SRB1 and SRB2 consist of either an MN-terminated MCG bearer or an MN-terminated Split bearer. When SRB1 and SRB2 consist of an MN-terminated Split bearer, they may be referred to as split SBR1 and split SBR2, respectively.

[0127] SBR3 consists of SN-terminated SCG bearers.

[0128] In addition, in the case of a Split Bearer, a Primary Path is set. The Primary Path indicates the base station device 200 to which the terminal device 100 (preferentially) transmits data in its initial state. The Primary Path is specified by the cell group (MCG, SCG) and LCH. The terminal device 100 transmits data to the base station device 200 of the Primary Path as long as the amount of uplink data transmitted does not exceed a threshold. If the threshold is exceeded, the terminal device 100 may transmit the data to either base station device 200.

[0129] Furthermore, the security keys used in PDCP differ depending on whether it is an MN-Terminated (master key) or an SN-Terminated (secondary key).

[0130] <Reconfiguration with Synchronization> This section describes reconfiguration with sync. Reconfiguration with sync is a procedure performed in the terminal device 100 by including a parameter (reconfigurationWithSync: hereafter sometimes referred to as the reconfiguration with sync parameter) indicating that reconfiguration with sync should be performed in the RRC reconfiguration message (RRCReconfiguration) that the base station device 200 sends to the terminal device 100.

[0131] Synchronized reset parameters are included separately under the parameters for MCG settings (hereinafter sometimes referred to as MCG setting parameters) and under the parameters for SCG settings (hereinafter sometimes referred to as SCG setting parameters). In other words, if they are included under the MCG setting parameters, it means synchronized reset of the MCG, and if they are included under the SCG setting parameters, it means synchronized reset of the SCG.

[0132] Synchronized reconfiguration is a procedure in which the terminal device 100 changes the SpCell, and includes operations such as random access to the new (target) SpCell, MAC reset, and PDCP data recovery (in the case of AM DRB).

[0133] The process when synchronized reset parameters are included under MCG setting parameters is sometimes called a handover. The process when synchronized reset parameters are included under SCG setting parameters is sometimes called a PSCell addition and / or PSCell change. The source PCell / PSCell is sometimes called the source PCell / source PSCell, and the target PCell / PSCell is sometimes called the target PCell / target PSCell. Since synchronized resets may involve CA (Computer Adapter), the term "serving cell" is sometimes used, referring to the source serving cell and target serving cell. Alternatively, "serving" may be omitted, and they are simply called source cell and target cell.

[0134] The terminal device 100 may generate the target cell settings by applying the delta settings included in the RRC reset message to the source cell settings.

[0135] Furthermore, synchronized reconfiguration may involve updating security keys. In this case, in addition to the above, PDCP re-establishment will be performed.

[0136] When a security key is updated, a new key is generated in the RRC of the terminal device 100, and the PDCP is re-established, thereby applying the new key to the PDCP.

[0137] Figure 8 shows an example of processing when the synchronized reset parameter is included under the parameter that sets the MCG. Note that Figure 8 shows an example of synchronized reset.

[0138] The synchronized reset parameters include settings for the target PCell, a new C-RNTI (Cell Radio Network Temporary Identifier), RACH settings, and a timer for detecting handover failures. The terminal device 100 performs random access (RA) on the target PCell according to the settings and changes the current source PCell to the target PCell (S1). Note that RACH can refer to a random access procedure in addition to a random access channel.

[0139] <Handover Failure Handling> If terminal device 100, which has received an RRC reset message containing synchronized reset parameters, fails to perform a handover within a certain period of time, the handover will be considered a failure. Failure to perform a handover within a certain period of time means that the timer for detecting handover failures, which starts when an RRC reset message containing synchronized reset parameters is received, expires before the handover is successful.

[0140] If the handover fails, the terminal device 100 reverts its settings to those used by the source PCell and performs the procedure to re-establish the RRC connection. When the terminal device 100's settings are reverted to those used by the source PCell, the values ​​of the state variables in each entity of each wireless bearer are also reverted to the values ​​used by the source (the values ​​immediately before the handover process).

[0141] In the RRC connection re-establishment procedure, the terminal device 100 performs cell selection, and if an NR cell is selected, it sends an RRC re-establishment request message (RRCReestablishmentRequest) to the base station device 200. The RRC re-establishment request message is sent through SRB0. Since there is no PDCP entity in SRB0, no PDCP security processing is performed on the RRC re-establishment request message. Also, when the terminal device 200 receives an RRC re-establishment message (RRCReestablishment), which is a response message to the RRC re-establishment request message, from the base station device 200, the security key of the terminal device 200 is updated.

[0142] <Conditional Handover> A Conditional Handover (CHO) is a handover that is performed (initially) by the terminal device 100 when one or more handover execution conditions are met. The terminal device 100 receives an RRC reset message containing conditional reset parameters from the base station device 200 and stores the conditional reset parameters. The conditional reset parameters include one or more pairs of setting parameters for a PCell target candidate, including synchronized reset parameters, and execution condition parameters for performing a handover to that PCell target candidate. The execution condition parameters include, for example, parameters related to measurement settings. When the terminal device 100 receives the conditional reset parameters, it starts measuring cells, and if any of the measured cells' PCells meet the execution conditions, it applies the setting parameters of the PCell target candidate of the PCell that meets the execution conditions and performs a conditional handover to that PCell. After the conditional handover is successful, the terminal device 100 releases the conditional reset parameters.

[0143] The conditional reset parameters may include one or more pairs of settings on the SCG side, i.e., setting parameters for a candidate PSCell change target, and execution condition parameters for performing the change to that candidate PSCell change target. When the terminal device 100 receives the conditional reset parameters from the SCG side, it starts measuring the execution conditions, and if the measurement result satisfies the execution conditions, it performs a Conditional PSCell Addition Change (CPAC).

[0144] Conditional handovers, like non-conditional handovers (which may hereafter be simply referred to as handovers), detect handover failures and perform post-handover failure processing. In the procedure for re-establishing the RRC connection after a conditional handover failure or handover failure, or in the procedure for re-establishing the RRC connection after a wireless link failure, if the selected cell is a candidate for PCell change destination, the terminal device 100 can attempt a handover by sending an RRC reset completion message instead of an RRC re-establishment request message to the base station device 200, thereby recovering the RRC connection. Note that the ability to send an RRC reset completion message instead of an RRC re-establishment request message to the base station device 200 when the cell selected by the terminal device 100 is a candidate for PCell change destination is limited to cases where the conditional reset attempt parameter (attemptCondReconfig), which permits this processing, is set in the terminal device 100.

[0145] Note that conditional handovers and unconditional handovers can be referred to simply as handovers without distinction.

[0146] <CU In-Unit LTM Cell Switching> This section describes an example of cell switching in L1 / L2 Triggered Mobility (LTM), as specified in Rel-18.

[0147] Figure 9 shows an example of parameters related to the LTM included in the RRCReconfiguration message (RRC reconfiguration message). Note that the parameters described in Figure 6 are omitted in Figure 9. Also, parameters other than the example shown in Figure 9 may be included in the RRC reconfiguration message. Furthermore, the parameter names are examples only and do not have to be exactly as shown.

[0148] Format E2 is a parameter of RRC Reconfiguration. RRC Reconfiguration includes ltm-Config, which represents the LTM settings. If ltm-Config is included in SetupRelease, a new LTM setting is configured or modified; if SetupRelease contains nothing, it means the LTM settings are released.

[0149] Format E21 is a parameter included in the LTM settings. ltm-ReferenceConfiguration is the reference setting described later. ltm-CandidateToAddModList is a list of LTM candidate cell settings. In other words, ltm-CandidateToAddModList is a list of LTM candidate cell settings and contains one or more LTM candidate cell settings. ltm-ServingCellNoResetID is an identifier used by the terminal device 100 to determine whether an L2 reset (Layer 2 reset) is necessary during cell switching, as described later. The initial value of ltm-ServingCellNoResetID or ltm-ServingCellNoResetID may be the group identifier of the serving cell, which the base station device 200 uses when sending an RRC reset message including the LTM setting to the terminal device 100 in step S1001, described later. ltm-ServingCellNoResetID is stored in the terminal device 100 as a value indicating the group identifier of the current serving cell. attemptLTM-Switch is a parameter that has the same meaning as the conditional reset attempt parameter (attemptCondReconfig) in conditional handover, and is a parameter that allows recovery of the RRC connection after cell switching failure, handover failure, or radio link failure.

[0150] Format E211 is a parameter included in the LTM candidate cell setting list. LTM-Candidate is the LTM candidate cell setting. ltm-CandidateId included in the LTM candidate cell setting is an identifier or index that uniquely identifies one or more LTM candidate cell settings within the terminal device 100. ltm-CandidateConfig is a parameter for generating the settings used at the cell switching destination (target), and includes some of the RRCReconfiguration parameters described in Figure 6. ltm-CandidateConfig may be a complete setting or a delta setting, as will be described later. ltm-CandidateConfig may consist of parameters included in the RRC reconfiguration message. ltm-NoResetID is an identifier used by the terminal device 100 to determine whether an L2 reset (Layer 2 reset) is necessary during cell switching, as described later. ltm-NoResetID may be a group identifier for LTM candidate cells. Different values ​​may be assigned to ltm-NoResetID for each DU (Distributed Unit). For example, '1' may be set for all LTM candidate cells under DU1, while '2' may be set for all LTM candidate cells under DU2.

[0151] Figure 10 shows an example of a sequence of LTMs within a CU.

[0152] The base station device 200 sends an RRC reset message to the terminal device 100 that includes one or more cell change destination candidate settings (target cell candidate settings) (S1001).

[0153] When terminal device 100 receives an RRC reset message (S1001), it stores the LTM setting information (including the settings for candidate cell change destinations) contained in the received message. Terminal device 100 may also store the value of ltm-ServingCellNoResetID included in the LTM setting in a variable that indicates the group identifier of the current serving cell.

[0154] The candidate cell change destinations may be, for example, PCell only, or they may also include SCell. Each candidate cell change destination only needs to be uniquely identifiable within the terminal device 100 using an index (ltm-CandidateId). Furthermore, the candidate cell change destination settings do not need to include parameters indicating security key updates. That is, the security key provided by LTM does not need to be updated. Also, the candidate cell change destination settings may include parameters similar to those for synchronized reconfiguration parameters.

[0155] Furthermore, the terminal device 100 may retain the settings of the candidate cell change destinations received and stored in step S1001, instead of releasing them after the successful cell switch described later. In this case, the retained settings of the candidate cell change destinations may be used for subsequent cell switches. However, when retaining the settings of the candidate cell change destinations and using them for subsequent cell switches, it may not be possible to set the settings of the candidate cell change destinations to delta settings and apply the delta settings to the source settings to generate the target cell settings. This phenomenon occurs because the source settings differ depending on the order in which the cells are changed by the cell switch.

[0156] Therefore, in step S1001, the RRC reset message may include a reference setting in addition to, or as part of, the setting of the cell destination candidate. The reference setting is used, for example, to complete the settings to be used at the cell switching destination (target). When the RRC reset message includes a reference setting, the settings for each cell destination candidate included in the RRC reset message may be differential settings (delta settings) from the reference setting. In other words, the terminal device 100 can generate the settings to be used at the cell switching destination (target), i.e., the complete settings to be used at the cell switching destination, from the reference setting and the settings of the cell destination candidate (delta settings). For example, in step S1002 described later, when the terminal device 100 receives a cell switching signal from the base station device 200 to cell X, which is a cell switching destination candidate, it generates the settings to be used at cell X by applying the settings of cell X to the reference setting.

[0157] Furthermore, in step S1001, the RRC reset message may not include reference settings. If the RRC reset message does not include reference settings, the settings for each candidate cell destination included in the RRC reset message are, for example, complete settings. In other words, the terminal device 100 can generate the settings to be used at the cell destination (target) by replacing the settings used in the current cell with the settings of the candidate cell destination. For example, in step S1002, described later, when the terminal device 100 receives a cell switching signal from the base station device 200 to cell X, which is a candidate cell destination, it generates the settings to be used at cell X by replacing the settings of the current cell with the settings of cell X. However, if the settings for the candidate cell destination are complete settings, some settings do not need to be included. Some settings include, for example, settings that are not changed by cell switching (fixed settings). Settings that do not change by cell switching (fixed settings) include, for example, some or all of the wireless bearer settings. In this case, when the terminal device 100 receives a cell switching signal from the base station device 200 to cell X, which is a candidate cell to switch to, it generates the settings to be used in cell X by replacing the current cell settings, except for fixed settings, with the settings of cell X.

[0158] Furthermore, whether or not the RRC reset message includes reference settings, the terminal device 100 does not need to reset some or all of the values ​​of state variables, timers, etc. used in each entity (SDAP entity, PDCP entity, RLC entity, MAC entity, etc.) to their initial state when generating settings to be used at the cell switching destination. Also, the terminal device 100 does not need to discard some or all of the buffers in each entity. In other words, the terminal device 100 can retain some or all of the values ​​of state variables, timers, etc. used in each entity. Also, the terminal device 100 may retain some or all of the buffers in each entity.

[0159] The base station device 200 transmits a cell switching signal to the terminal device 100 to switch the serving cell of the terminal device 100 from the current serving cell to one of the candidate cell change destinations (S1002).

[0160] The terminal device 100 receives a cell switching signal in the current serving cell (S1002). For example, MAC CE may be used as the cell switching signal. Alternatively, a physical layer signal such as DCI may be used as the cell switching signal.

[0161] The cell switching signal includes at least an index (ltm-CandidateId). The terminal device 100 applies the settings of the cell change destination (let's call it cell X) specified by the received cell switching signal. Cell X may consist only of PCell, or only of PSCell, or of PCell or PSCell and one or more SCell.

[0162] The terminal device 100 performs a 4-step or 2-step CFRA (Contention-Free Random Access) or CBRA (Contention-Based Random Access) with the base station device 200 in cell X, according to the settings of cell X (S1003). Furthermore, if, for example, the settings of cell X include a parameter indicating that RACH-less cell switching will be performed, or if early TA acquisition described later is performed, the random access processing in step S1003 will not be executed. Also, the terminal device 100 will not perform an L2 reset if the ltm-NoResetID of cell X is the same as ltm-ServingCellNoResetID or a variable indicating the group identifier of the current serving cell. Furthermore, if the terminal device 100 finds that the ltm-NoResetID of cell X is not the same as the ltm-ServingCellNoResetID or a variable indicating the group identifier of the current serving cell, it performs an L2 reset and overwrites the ltm-ServingCellNoResetID or the variable indicating the group identifier of the current serving cell with the ltm-NoResetID of cell X. An L2 reset is, for example, RLC re-establishment. Another example of an L2 reset is PDCP data recovery.

[0163] The terminal device 100 transmits a notification to the base station device 200 indicating that it has switched cells in cell X (S1004). This notification corresponds to the RRC reset completion message in a handover or conditional handover. The notification indicating that it has switched cells may use an RRC message such as the RRC reset completion message, or it may use MAC CE. Alternatively, the notification indicating that it has switched cells may use a physical signal such as UCI.

[0164] Furthermore, the notification indicating that a cell has been switched may include at least the identifier of cell X in terminal device 100. Note that if a two-step CFRA or CFRA was performed in step S1003, the notification indicating that a cell has been switched is sent before receiving the random access response in step S1003. In addition, uplink data generated by the DRB may be sent along with the notification indicating that a cell has been switched.

[0165] If a 4-step or 2-step CBRA is performed in step S1003, or if a RACH-less cell switchover is performed, the base station device 200 transmits a signal to the terminal device 100 that includes a conflict resolution signal or information indicating that the notification transmitted from the terminal device 100 in step S1004 has been successfully received (hereinafter sometimes referred to as reception success information).

[0166] Furthermore, the terminal device 100 receives, for example, a conflict resolution signal or a signal containing reception success information in cell X. The conflict resolution signal or reception success information may include at least an identifier in cell X of the terminal device 100.

[0167] The timing of successful cell switching may be the same as that of successful handover in handover or conditional handover. That is, in the case of cell switching using a 4-step or 2-step CFRA, cell switching is successful when a random access response is received. Also, in the case of cell switching using a 4-step or 2-step CBRA, or RACH-less cell switching, cell switching is successful when the processing in step S1004 is completed. If the timing of successful cell switching is the same as that of successful handover in handover or conditional handover, then, as with handover or conditional handover, in cell switching using a 4-step CFRA, no notification indicating that the cell has been switched, nor any uplink data generated by the DRB, will be transmitted before the cell switching is successful. However, in the case of cell switching using a 4-step CBRA, cell switching using a 2-step CFRA or CBRA, and RACH-less cell switching, a notification indicating that the cell has been switched will be transmitted before the cell switching is successful. Furthermore, uplink data generated by the DRB may be transmitted along with a notification indicating that the cell has been switched.

[0168] Furthermore, after executing step S1001 and before the cell switching signal is transmitted in step S1002, the terminal device 100 may perform downlink synchronization and / or uplink synchronization with one or more cell switching candidates. The base station device 200 may measure the Timing Advance (TA) of each of the one or more cell switching candidates of the terminal device 100 during uplink synchronization. Uplink synchronization may be performed by instructing the terminal device 100 to transmit a random access preamble. The base station device 200 may instruct the terminal device 100 to transmit a different random access preamble to each of the one or more cell switching candidates, or it may instruct it to transmit a common random access preamble to a group of cell switching candidates. The TA measured by the base station device 200 may be transmitted to the terminal device 100 using a random access response (RAR), or it may be transmitted to the terminal device 100 using the cell switching signal in step S1002. In this manner, performing uplink synchronization between the time the terminal device 100 executes step S1001 and the time the cell switching signal is sent in step S1002 is sometimes referred to as early TA measurement or early TA acquisition.

[0169] Note that "cell switching" may be rephrased as "LTM" or "LTM cell switching." Furthermore, "cell switching" may be replaced with other terms that represent LTM-based cell switching. Hereafter, "cell switching" and "cell change" may be treated as synonymous.

[0170] Furthermore, in this embodiment, unless otherwise specified, the cell switching will be MCG cell switching.

[0171] Furthermore, in the LTM settings, the setting of candidate cells for MCG cell changes may include a synchronized reset parameter under the MCG setting parameter. Similarly, in the LTM settings, the setting of candidate cells for SCG cell changes may include a synchronized reset parameter under the SCG setting parameter. Therefore, MCG cell switching can be referred to as handover. Also, SCG cell switching can be referred to as PSCell change.

[0172] <LTM Cell Switching Failure Handling> If LTM cell switching fails, the RRC connection re-establishment procedure may be executed, similar to the handover failure handling and conditional handover failure handling.

[0173] Figure 11 shows an example of the sequence for detecting cell switching failure and processing cell switching failure. The processes in steps S1001 and S1002 in Figure 11 are the same as those in steps S1001 and S1002 in Figure 10, so their explanation is omitted.

[0174] When the terminal device 100 receives a cell switching signal (S1002), it starts a timer to detect a cell switching failure (S1101) and starts the cell switching process to the cell specified by the received cell switching signal (let's call it cell X) (not shown).

[0175] If the cell switchover is successful before the timer expires, the terminal device 100 stops the timer (not shown). On the other hand, if the timer expires, the terminal device 100 detects that the cell switchover to cell X has failed (S1102).

[0176] When the terminal device 100 detects a cell switching failure (S1102), it performs a cell switching failure process (S1103). In the cell switching failure process, the terminal device 100 may revert its settings to the settings used by source PCell and perform the procedure to re-establish the RRC connection.

[0177] In the RRC connection re-establishment procedure, cell selection is performed. If the cell selected during cell selection is one of the LTM candidate cells, the terminal device 100 can autonomously perform an LTM cell switch to this selected cell. This is called fast LTM recovery or fast recovery. When fast LTM recovery is performed, the terminal device 100 initiates cell switching. Note that the terminal device 100 performs fast LTM recovery only if the LTM settings include a parameter indicating that fast LTM recovery should be performed. Note that fast recovery is not limited to LTM. Fast recovery is also performed in CHO, for example. In other words, fast recovery is when, during the cell selection in the RRC connection re-establishment procedure after a cell switch or handover failure, the terminal device 100 autonomously performs a cell switch or handover to the selected cell if it is one of the candidate cells set in the terminal device 100.

[0178] <Updating AS Security Keys During Handover> AS security processing is performed in the PDCP entities of wireless bearers other than SRB0, using the encryption key and integrity protection key generated by RRC. AS security processing consists of encryption and integrity protection, which are performed using the encryption key and integrity protection key, respectively. The encryption key and integrity protection key are generated separately for SRB and DRB, and the encryption key for SRB is called KRRCenc, the integrity protection key for SRB is called KRRCint, the encryption key for DRB is called KUPenc, and the integrity protection key for DRB is called KUPint. The encryption key and integrity protection key used in SRBs other than SRB0 and DRB are generated from a security key called KgNB. A common KgNB is generated in both the base station equipment 200 and the terminal equipment 100. Hereafter, unless otherwise specified, KgNB will be referred to as the security key.

[0179] In the case of a handover within a base station device or CU, security key updating is optional. That is, the base station device 200 may or may not instruct the terminal device 100 to update the security key. However, in the case of a handover between base stations or between CUs, security key updating is mandatory. That is, the base station device 200 instructs the terminal device 100 to update the security key.

[0180] The method for updating the security key is described below. When a security key update is necessary, the base station device 200 sends an RRC reset message to the terminal device 100 that includes the MasterKeyUpdate parameter (master key update parameter) shown in format E13 of Figure 6. The master key update parameter includes either keySetChangeIndicator (key set change instruction) or nextHopChainingCount (NCC). The key set change instruction is information indicating true or false, and NCC is a non-negative integer. The initial value of NCC is zero ('0'), and the terminal device 100 stores NCC=0 in its initial state.

[0181] If the key set change instruction in the master key update parameter is set to "true", the terminal device 100 generates a new KgNB from the NAS security key (called KAMF) of the terminal device 100.

[0182] Furthermore, if the key set change instruction in the master key update parameter is not set to "true," i.e., if it is set to "false," the terminal device 100 generates a new key according to the NCC value of the master key update parameter. In this case, the terminal device 100 generates a new key using the original key information and the target cell information. If the NCC value of the master key update parameter is the same as the NCC value stored in the terminal device 100 or the NCC value previously received from the base station device 200, the terminal device 100 generates a security key using the currently used KgNB as the original key information. This is called horizontal derivation. Also, if the NCC value of the master key update parameter is different from the NCC value stored in the terminal device 100 or the NCC value previously received from the base station device 200, the terminal device 100 generates a new security key using the NH (Next Hop) corresponding to the received NCC value as the original key information. This is called vertical derivation. The target cell information used when generating a new security key includes, for example, the Physical Cell Identity (PCI) and the Absolute Radio Frequency Channel Number (ARFCN).

[0183] On the other hand, when the base station device 200 sends an RRC reset message containing master key update parameters to the terminal device 100, if it is instructed by the AMF, a node in the core network, to use the new KgNB generated by the AMF, it sets the key set change instruction to "true". If the base station device 200 is not instructed by the AMF to use the new KgNB generated by the AMF, it sets the key set change instruction to "false". The base station device 200 also determines the value of NCC based on whether or not it has used the new NCC and NH pair issued by the AMF for the terminal device 100. If the new NCC and NH pair has not been used, it sets the value of this new NCC as the NCC. If the new NCC and NH pair has already been used, it sets the value of the NCC as it was last time. The value of NCC increases by 1 each time a new NCC and NH pair is issued by the AMF. Furthermore, when terminal device 100 performs a handover from one base station device 200 (referred to as base station device 200-A) to another base station device 200 (referred to as base station device 200-B), and base station device 200-B sends a path switch request to AMF for this terminal device 100, AMF issues a new NCC and NH pair for this terminal device 100 and sends it to base station device 200-B.

[0184] <SN-side security key in MR-DC> When a DC is configured on terminal device 100, it is necessary to generate an SN-side security key. The SN-side security key will be explained using Figure 6. The SN-side security key, S-KgNB, is generated from the MN-side security key, KgNB. Specifically, S-KgNB is generated from KgNB and a parameter called SK-Counter (or sk-counter) (shown in E1 in Figure 6). SK-Counter is a non-negative integer. In addition, the SN-side encryption key for SRB, the SRB integrity protection key, the DRB encryption key, and the DRB integrity protection key are generated from S-KgNB.

[0185] Hereafter, the security key on the MN side may be referred to as the master key, and the security key on the SN side as the secondary key. The master key is applied to MN-terminated radio bearers, and the secondary key is applied to SN-terminated radio bearers. The base station device 200 uses a parameter called keyToUse (shown in E113 in Figure 6) to indicate whether the PDCP entity of the DRB set in the terminal device 100 resides on the MN or SN side. The terminal device 100 can determine that the PDCP entity on the base station device 200 side resides on the MN side, i.e., that it is an MN-terminated DRB, when the keyToUse parameter is set to master. Furthermore, the terminal device 100 can determine that a DRB with the keyToUse parameter set to secondary has a PDCP entity on the base station device 200 on the SN side, i.e., it is an SN-terminated DRB. [Embodiments] The following describes each embodiment.

[0186] <Subsequent Cell Switching within and between CUs> The LTM specified in Rel-18 targets cell switching within a CU and does not support security key updates. However, security key updates may be required for cell switching between CUs, which is within the scope of Rel-19.

[0187] In CHO, if the target PCell belongs to a different CU, the configuration parameters for the PCell change target candidate must include a parameter indicating the update of the security key, i.e., the master key update parameter (masterKeyUpdate parameter). Therefore, even in the case of CHO between CUs, the security key is updated according to the master key update parameter. In CHO, after the CHO is executed, the terminal device 100 releases the CHO settings, and the base station device 200 newly configures the CHO settings for the terminal device 100. Therefore, even after CHO between CUs has been executed, CHO can be performed in a way that supports both intra-CU and inter-CU operations by setting a new PCell change target candidate via the RRC reset message. However, when performing subsequent cell switching, the LTM candidate cell settings are not updated via the RRC reset message, so a method is needed to appropriately update the security key for the terminal device 100.

[0188] Furthermore, when MR-DC (hereinafter referred to as DC) is configured on terminal device 100, updating the security key on the SN side is essential if the security key on the MN side is updated. In other words, when DC is configured on terminal device 100, if cell switching occurs between CUs in the MN, a method is needed to appropriately update the security key on the MN side and the security key on the SN side on terminal device 100.

[0189] From now on, when the term "security key" is used without specifying whether it is on the MN side or SN side, it will refer to the security key on the MN side.

[0190] <Subsequent Cell Switching Method 1 for Within and Between CUs> The first example of a subsequent cell switching method for within and between CUs is that it does not support subsequent cell switching after inter-CU cell switching. For example, the base station device 200 sends a cell switching signal to the terminal device 100 and causes the terminal device 100 to perform inter-CU cell switching. Before sending the next cell switching signal to this terminal device, the base station device 200 receives an RRC message and changes the settings related to cell switching.

[0191] When the base station device 200 performs LTM settings on the terminal device 100, for example, it does not include the master key update parameter when setting up LTM candidate cells that belong to the same CU as the CU to which the terminal device 100's current serving cell belongs, but it does include the master key update parameter when setting up LTM candidate cells that belong to a different CU than the CU to which the terminal device 100's current serving cell belongs.

[0192] When the terminal device 100 performs cell switching, if the target LTM candidate cell settings include master key update parameters, it deletes some or all of the parameters related to the LTM settings after the cell switching is successful. The parameters to be deleted include, for example, at least the list of LTM candidate cell settings. The parameters to be deleted also include, for example, settings related to SN. The settings related to SN include, for example, the SRB3 settings, the SN-terminated DRB settings, and some or all of the SCG settings. The terminal device 100 may also change the SCG bearer and / or split bearer to an MCG bearer. After inter-CU LTM cell switching, the base station device 200 gives the terminal device 100, for example, a new LTM setting or updates the LTM setting. This allows the terminal device 100 to perform cell switching again, corresponding to within CUs and between CUs.

[0193] Furthermore, another example of the first example of a subsequent cell switching method corresponding to within and between CUs will be described. When the base station device 200 performs LTM settings on the terminal device 100, for example, the master key update parameter is not included in the LTM candidate cell settings, but is included outside of the LTM candidate cell settings. Furthermore, when the terminal device 100 performs cell switching, the base station device 200 includes a parameter that allows the terminal device 100 to determine whether it is a cell switching within a CU or a cell switching between CUs. Determining whether it is a cell switching within a CU or a cell switching between CUs on the terminal device 100 side can be rephrased as determining whether a security key update is necessary on the terminal device 100 side. The parameter that allows the terminal device 100 to determine whether it is a cell switching within a CU or a cell switching between CUs may be, for example, a group identifier set for each LTM candidate cell, as described later. This process is an example of the process in step S1201 in Figure 12, which will be described later.

[0194] Next, the base station device 200 transmits a cell switching signal to the terminal device 100. This process is an example of the process in step S1202 in Figure 12, which will be described later.

[0195] When the terminal device 100 determines that it is to perform inter-CU cell switching, it updates the master key according to the master key update parameters and performs inter-CU cell switching. This process is an example of the process from steps S1203 to S1206 in Figure 12, which will be described later.

[0196] After the terminal device 100 successfully switches between CU cells, the base station device 200 sends an RRC message to the terminal device 100 to update the settings of the terminal device 100's master key update parameters. The base station device 200 does not send a cell switching signal to the terminal device 100 until the update of the terminal device 100's master key update parameters is successful.

[0197] Furthermore, after successful cell switching, the terminal device 100 does not release some or all of the parameters related to the LTM settings. In this case, for example, the base station device 200 updates the LTM settings and / or SN settings to the terminal device 100, allowing the terminal device 100 to perform cell switching again, corresponding to within and between CUs.

[0198] <Subsequent Cell Switching Method 2 for Within and Between CUs> A second example of a subsequent cell switching method for within and between CUs will be explained using Figure 12. Figure 12 is a diagram showing an example of a subsequent cell switching method for within and between CUs. Note that the method explained using Figure 12 may be performed in addition to some or all of the processes of the in-CU LTM cell switching process explained using Figure 10. Note that the example explained using Figure 12 is an explanation when the CU is an MN, but the same procedure may be applied when the CU is an SN. Also, when DC is set on the terminal device 100, the base station device corresponding to SN is not shown in Figure 12. Note that the process from step S1203 onwards may also be applied when the terminal device 100 performs fast LTM recovery.

[0199] The base station device 200 sends an RRC reset message to the terminal device 100, including parameters related to the LTM (S1201). The parameters related to the LTM include, for example, an LTM setting that includes one or more settings for LTM candidate cells (settings for target candidate cells). When the terminal device 100 receives the RRC reset message, it stores the LTM setting included in the received message. When storing the LTM setting, some or all of the parameters included in the LTM setting may be stored as variables of the terminal device 100. Hereafter, when describing parameters, it may refer to the parameters stored as variables of the terminal device 100, rather than the parameters included in the RRC reset message. The base station device 200 also sets different reference configuration parameters (ltm-ReferenceConfiguration) for each CU, for example. When setting different reference configuration parameters for each CU, for example, it sets a parameter to indicate which CU the reference configuration parameter is related to. The parameter to indicate which CU the reference configuration parameter is related to is, for example, the security update-free identifier parameter described later.

[0200] Here, the parameters related to LTM included in the RRC reset message may include parameters other than those explained using Figure 9.

[0201] The parameters related to LTM other than those explained using Figure 9, included in the RRC reset message, are, for example, parameters that allow terminal device 100 to determine whether or not a security key update is necessary when terminal device 100 performs cell switching. The parameter that allows terminal device 100 to determine whether or not a security key update is necessary may be, for example, a group identifier set for each LTM candidate cell. Here, for example, the group identifier set for each LTM candidate cell, which is used as a parameter that allows terminal device 100 to determine whether or not a security key update is necessary, will be called the security update-free identifier parameter. The security update-free identifier parameter may be an identifier included in each LTM candidate cell setting, separate from ltm-NoResetID included in the LTM candidate cell setting (LTM-Candidate) in format E211 of Figure 9. Different values ​​may be assigned to the security update-free identifier parameter for each CU. For example, security update-free identifier parameter '1' may be set for all LTM candidate cells under CU1, and security update-free identifier parameter '2' may be set for all LTM candidate cells under CU2. When the terminal device 100 performs cell switching, if the value of the security update-free identifier parameter included in the target LTM candidate cell settings is the same as the value of the security update-free identifier parameter of the current serving cell, or the value stored in the terminal device 100 as the security update-free identifier parameter of the current serving cell, it determines that a security key update is not necessary; otherwise, it determines that a security key update is necessary. In addition, the initial value of the security update-free identifier parameter of the current serving cell may be set separately from the security update-free identifier parameter. The initial value of the security update-free identifier parameter of the current serving cell may be an identifier included under the LTM settings, separate from ltm-ServingCellNoResetID included in the LTM settings (LTM-Config) in format E21 of Figure 9. Note that the security update-free parameter may have a different name, such as a security cell set identifier.

[0202] Another method for setting a parameter that allows the terminal device 100 to determine whether or not a security key update is necessary when the terminal device 100 performs cell switching (a method that does not use the security update unnecessary identifier parameter mentioned above) is to further group the ltm-NoResetID included in the LTM candidate cell settings in format E211 in Figure 9 as a security update unnecessary group. For example, suppose that the LTM candidate cell with ltm-NoResetID='1' set and the LTM candidate cell with ltm-NoResetID='2' set are both cells under CU1, and that the LTM candidate cell with ltm-NoResetID='3' set and the LTM candidate cell with ltm-NoResetID='4' set are both cells under CU2. In this case, for example, ltm-NoResetID '1' and '2' are set to security update-free group 1, and ltm-NoResetID '3' and '4' are set to security update-free group 2. Security update-free groups may be included in, for example, the security update-free group parameter. The security update-free group parameter may include security update-free groups consisting of a security update-free group identifier and a list of ltm-NoResetIDs. The security update-free group parameter may be included under, for example, the LTM settings (LTM-Config). When the terminal device 100 performs a cell switch, if the value of the security update-free group identifier of the security update-free group to which the ltm-NoResetID included in the target LTM candidate cell settings belongs is the same as the group identifier of the current serving cell (ltm-ServingCellNoResetID), or the value of the security update-free group identifier of the security update-free group to which the identifier stored in the terminal device 100 as the group identifier of the current serving cell belongs, the terminal device 100 determines that a security key update is not necessary; otherwise, it determines that a security key update is necessary. Note that instead of using ltm-NoResetID, for example, ltm-CandidateId may be used to classify the security update-free group.

[0203] Furthermore, there may be other methods for setting parameters that allow the terminal device 100 to determine whether or not a security key update is necessary when the terminal device 100 performs a cell switch. Also, the names of the security update-free identifier parameter and the security update-free group parameter mentioned above may be referred to by different names.

[0204] Furthermore, parameters related to LTM other than those explained using Figure 9, included in the RRC reset message, are, for example, parameters indicating the key generation method when updating security keys. The parameter indicating the key generation method may be, for example, a parameter that specifies either "horizontal generation" or "vertical generation". Also, if, for example, the parameter indicating the key generation method when updating security keys is not included, it may mean that vertical generation will be performed.

[0205] Furthermore, parameters related to the LTM other than those explained using Figure 9, which are included in the RRC reset message, are, for example, the key set change instruction parameter or NCC used for generating security keys. When the terminal device 100 updates the security key, if, for example, the key set change instruction parameter is set, it generates a new KgNB. Also, when the terminal device 100 updates the security key, if, for example, NCC is included, it determines whether to generate horizontally or vertically based on the value of this NCC and generates the master key.

[0206] Furthermore, parameters related to LTM other than those explained using Figure 9, which are included in the RRC reset message, include, for example, the list of NCCs used to generate security keys. When the terminal device 100 performs vertical generation of a security key, it generates a new security key using, for example, the NH corresponding to the value of the first NCC in the configured list of NCCs as the source key information. For example, once the generation of the new security key is complete, the terminal device 100 may remove the NCC corresponding to the NH used as the source key information from the list of NCCs. Note that removing from the list of NCCs means, for example, removing it from the list of NCCs stored as a variable of the terminal device 100. Parameters indicating the key generation method when updating security keys are included, for example, directly under the LTM settings (within E21 in Figure 9).

[0207] Furthermore, parameters related to the LTM other than those explained using Figure 9, which are included in the RRC reset message, are parameters that indicate that the security keys on the MN side and / or SN side will be updated according to the information contained in the cell switching signal or other signals. The parameters that indicate that the security keys on the MN side and / or SN side will be updated according to the information contained in the cell switching signal or other signals are included, for example, directly below the LTM setting (within E21 in Figure 9).

[0208] Furthermore, parameters related to LTM other than those explained using Figure 9, which are included in the RRC reset message, are parameters necessary for the secondary key generation method when updating the secondary key, for example. The parameters necessary for the secondary key generation method are, for example, SK-Counters. SK-Counters are set, for example, as a list of SK-Counters. When the terminal device 100 updates the secondary key, it generates a new secondary key using, for example, the SK-Counter at the top of the set list of SK-Counters. When the generation of the new secondary key is complete, the terminal device 100 may, for example, remove the used SK-Counter from the list of SK-Counters. Removing from the list of SK-Counters means, for example, removing it from the list of SK-Counters stored as a variable of the terminal device 100. The list of SK-Counters is located, for example, directly under the LTM settings (within E21 in Figure 9). Each SK-Counter in the list may be assigned a different index or identifier.

[0209] Furthermore, the SK-Counter is set, for example, under the LTM candidate cell setting (LTM-Candidate, E211 in Figure 9). When the terminal device 100 updates the secondary key, it generates a new secondary key using the SK-Counter included in the target LTM candidate cell setting. Note that the SK-Counter included in the LTM candidate cell setting may also be a list of SK-Counters.

[0210] Furthermore, some or all of the LTM-related parameters included in the RRC reset message, other than those explained using Figure 9, do not necessarily need to be included as LTM-related parameters.

[0211] When terminal device 100 receives an RRC reset message, it stores the parameters related to LTM included in the received message. If the LTM setting includes an initial value for the security update-free identifier parameter of the current serving cell, terminal device 100 may store this value as the value indicating the security update-free identifier parameter of the current serving cell.

[0212] The base station device 200 transmits a cell switching signal to the terminal device 100 to switch the serving cell of the terminal device 100 from the current serving cell to one of the LTM candidate cells, thereby initiating cell switching in the terminal device 100 (S1202). Note that the cell switching signal is, for example, an MCG cell switching signal. Alternatively, the cell switching signal may be an SCG cell switching signal.

[0213] Upon receiving a cell switching signal, the terminal device 100, whose cell switching has been activated, determines whether or not a security key update is required for cell switching to the target cell (S1203). For example, the determination of whether or not a security key update is required may be made using parameters that the terminal device 100 can use to determine whether or not a security key update is required. Alternatively, the determination of whether or not a security key update is required may be made based on information contained in the cell switching signal, or information contained in other signals sent simultaneously from the base station device 200. Furthermore, the determination of whether or not a security key update is required may be rephrased as the determination of whether or not it is an inter-CU LTM cell switch or an intra-CU LTM cell switch. That is, the determination that a security key update is required may be the same as the determination that it is an inter-CU LTM cell switch. Similarly, the determination that a security key update is not required may be the same as the determination that it is an intra-CU LTM cell switch. Note that inter-CU LTM cell switching is an example of the first condition, and intra-CU LTM cell switching is an example of the second condition. In short, the first condition indicates that cell switching is performed between CUs, and the second condition indicates that cell switching is performed within the same CU.

[0214] If step S1203 is an MCG cell switchover and it is determined that updating the security key is unnecessary, the terminal device 100 performs, for example, a cell switchover process within the CU. Also, if it is an SCG cell switchover and it is determined that updating the security key on the SN side is unnecessary, the terminal device 100 performs, for example, a cell switchover process within the CU. If it is an MCG cell switchover and it is determined in step S1203 that updating the security key is necessary, the terminal device 100 performs, for example, a cell switchover process between the MN side and the CU. Also, if it is an MCG cell switchover and it is determined in step S1203 that a security key is necessary, and if DC is set on the terminal device 100, the terminal device 100 performs, for example, a cell switchover process between the MN side and the CU, as well as processing related to the SN setting. Also, if it is an SCG cell switchover and it is determined in step S1203 that updating the security key on the SN side is necessary, the terminal device 100 performs, for example, processing related to the SN setting (S1204).

[0215] Now, let's explain the cell switching process within the CU.

[0216] For example, the terminal device 100 applies the master key or secondary key set in the terminal device 100 to some or all of the PDCP entities of DRBs that are set in the terminal device 100 or included in the target cell settings, where the PDCP termination point is different from the PDCP termination point in the serving cell before cell switching, according to the keyToUse parameter.

[0217] Among the DRBs set in terminal device 100 or included in the target cell settings, a DRB whose PDCP termination point is different from the PDCP termination point in the serving cell before cell switching is, for example, a DRB that has been changed from an MN-terminated bearer to an SN-terminated bearer in an LTM cell switching. Also, among the DRBs set in terminal device 100 or included in the target cell settings, a DRB whose PDCP termination point is different from the PDCP termination point in the serving cell before cell switching is, for example, a DRB that has been changed from an SN-terminated bearer to an MN-terminated bearer in an LTM cell switching. Furthermore, among the DRBs set in the terminal device 100 or included in the target cell settings, a DRB whose PDCP termination point differs from the PDCP termination point in the serving cell before cell switching is, for example, a DRB whose keyToUse parameter included in the target cell settings differs from the keyToUse parameter set in the serving cell before cell switching. Also, the settings in the serving cell before cell switching refer to, for example, the current settings of the terminal device 100.

[0218] Furthermore, the process of applying the master key or secondary key set in the terminal device 100 according to the keyToUse parameter is, for example, the process of applying the master key to a DRB that has been changed to an MN-terminated bearer, and for example, the process of applying the secondary key to a DRB that has been changed to an SN-terminated bearer. In this process, for example, if the terminal device 100 does not have a parameter (cipheringDisabled) set that means deactivating encryption, the terminal device 100 sets the encryption algorithm and / or encryption key for the DRB to the PDCP of the corresponding DRB (some or all of the DRBs set in the terminal device 100 or included in the target cell settings, whose PDCP termination point is different from the PDCP termination point in the serving cell before cell switching). Furthermore, in this process, if, for example, a parameter (integrityProtection) indicating that integrity protection should be applied to the terminal device 100 is set, the terminal device 100 sets the integrity protection algorithm and / or the integrity key for the DRB for the corresponding DRB PDCP entity. Also in this process, the terminal device 100, for example, initiates PDCP re-establishment for the corresponding DRB PDCP entity. Also in this process, the terminal device 100, for example, initiates RLC re-establishment for some or all RLC entities associated with the DRB PDCP entity for which the DRB encryption key and / or DRB integrity key have been set.

[0219] Furthermore, for some or all of the DRBs configured in terminal device 100 or included in the target cell configuration whose PDCP termination point differs from the PDCP termination point in the serving cell before cell switching, the process of applying the master key or secondary key configured in terminal device 100 to the PDCP entities according to the keyToUse parameter may be performed during cell switching, regardless of whether or not the master key needs to be updated.

[0220] Next, the terminal device 100 determines, for example, whether the cell switching is between DUs (Distributed Units) or within a DU. To determine whether it is between DUs or within a DU, the terminal device compares the value of the ltm-ServingCellNoResetID parameter with the value of the ltm-NoResetID parameter included in the target cell settings. If the values ​​are different, it is determined to be a cell switching between DUs; if they are the same, it is determined to be a cell switching within a DU.

[0221] If terminal device 100 determines that a cell switchover has occurred between DUs, terminal device 100 initiates RLC re-establishment for some or all RLC entities associated with the cell group on the side where the cell switchover was initiated, for wireless bearers configured in terminal device 100 or included in the target cell configuration whose PDCP termination point is the same as the PDCP termination point in the serving cell before the cell switchover. Subsequently, terminal device 100 initiates PDCP recovery for some or all AM DRBs for which RLC re-establishment was initiated, among wireless bearers configured in terminal device 100 or included in the target cell configuration whose PDCP termination point is the same as the PDCP termination point in the serving cell before the cell switchover. Furthermore, the terminal device 100 initiates PDCP recovery for some or all AM DRBs whose RLC entities have been released, among the wireless bearers configured in the terminal device 100 or included in the target cell configuration, whose PDCP termination point is the same as the PDCP termination point in the serving cell before cell switching.

[0222] The cell group on which the cell switchover was initiated is the MCG if the cell switchover was initiated on the MCG side, and the SCG if the cell switchover was initiated on the SCG side. Furthermore, among the wireless bearers set in terminal device 100 or included in the target cell settings, a wireless bearer whose PDCP termination point is the same as the PDCP termination point in the serving cell before the cell switchover is, for example, a DRB whose keyToUse parameter included in the target cell settings is the same as the keyToUse parameter in the serving cell settings before the cell switchover. Among the wireless bearers set in terminal device 100 or included in the target cell settings, a wireless bearer whose PDCP termination point is the same as the PDCP termination point in the serving cell before the cell switchover is, for example, an SRB. Also, the settings in the serving cell before the cell switchover are, for example, the current settings of terminal device 100. Furthermore, an AM DRB in which an RLC entity has been released is, for example, an AM DRB in which the bearer type of the RLC bearer associated with the AM DRB's PDCP has changed from a split bearer to an MCG bearer or an SCG bearer due to a cell switch. Also, an AM DRB in which an RLC entity has been released is, for example, an AM DRB in which the bearer type of the RLC bearer associated with the AM DRB's PDCP has changed from an MCG bearer to an SCG bearer, or from an SCG bearer to an MCG bearer, due to a cell switch. Furthermore, "the RLC entity has been released" can be rephrased as "the RLC bearer has been released."

[0223] Note that cell switching between DUs is an example of the third condition. In short, the third condition indicates that cell switching is being performed between DUs.

[0224] Next, we will explain the cell switching process between MN-side CUs.

[0225] The method for updating the security key is, for example, a method using the parameters that indicate the key generation method described in step S1201, and updating the key using the method described in step S1201. For example, if the terminal device 100 does not have a list of NCCs set, and vertical generation is performed, the terminal device 100 adds 1 to the NCC it possesses or the NCC used in the previous security key update, and uses the NH corresponding to this value as the base key information to perform the security key update. Vertical generation is an example of the first generation method. In the first generation method, a security key is generated using a first key corresponding to a first value (for example, a value corresponding to the NCC). When performing horizontal generation, the terminal device 100 generates a security key using the currently used KgNB as the base key information. Horizontal key generation is an example of the second generation method. In the second generation method, a security key is generated using a second key corresponding to a second value (for example, a value corresponding to the currently used KgNB). Furthermore, if the base station device 200 needs to allow the terminal device 100 to use a security key generated from KAMF, it will include a master key update parameter in the RRC reset message, set the key set change instruction to "true", and send it to the terminal device 100. In this case, the RRC reset message may also include a parameter for updating the LTM settings.

[0226] Furthermore, the method for updating the security key is, for example, a method of updating it according to information contained in the cell switching signal, or information contained in other signals sent from the base station device 200 simultaneously with the cell switching signal. The process of determining whether or not a security key update is necessary, and / or using information contained in the cell switching signal, or information contained in other signals sent from the base station device 200 simultaneously with the cell switching signal, in determining whether or not a security key update is necessary, may be performed if the terminal device 100 is set with a parameter indicating that the MN side and / or SN side security keys should be updated according to the information contained in the cell switching signal, or information contained in other signals as described above.

[0227] The information included in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, includes, for example, a parameter indicating whether or not a security key update is required, and / or a parameter indicating how to update the security key.

[0228] For example, the information included in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, includes only a parameter indicating whether or not a security key update is required. If the parameter indicating whether or not a security key update is required indicates that a security key update is required, the terminal device 100 updates the security key, for example, according to the parameter indicating the key generation method described above.

[0229] Furthermore, information included in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, includes some or all of the information of the key set change instruction and NCC, which are master key update parameters included in the RRC reset message, as parameters indicating how to update the security key. The terminal device 100 updates the security key, for example, according to these parameters indicating how to update the security key.

[0230] Furthermore, information included in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, includes parameters indicating whether a security key update is necessary and / or how to update the security key, using numerical information such as '0' for no security update, '1' for horizontal generation, '2' for vertical generation, and '3' for key set change instruction = "true". If a security key update is necessary, the terminal device 100 updates the security key, for example, according to the parameters indicating how to update the security key.

[0231] Furthermore, if the information included in the cell switching signal described above, or other signals sent from the base station device 200 simultaneously with the cell switching signal, does not include information regarding the key set change instruction, and the base station device 200 needs to allow the terminal device 100 to use a security key generated from KAMF, the RRC reset message includes a master key update parameter, sets the key set change instruction to "true," and sends it to the terminal device 100. In this case, the RRC reset message may also include a parameter for updating the LTM setting. Additionally, the information included in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, may include other information, such as information indicating which reference setting to apply.

[0232] The terminal device 100 generates an encryption key for the SRB, an integrity protection key for the SRB, an encryption key for the DRB, and an integrity protection key for the DRB from the updated security key, and applies these to the PDCP entities of MN-terminated wireless bearers among the wireless bearers set in the terminal device 100 or included in the target cell settings (LTM candidate cell settings that will be the cell switching destination). In this process, if the terminal device 100 does not have a parameter (cipheringDisabled) set that means deactivating encryption, the terminal device 100 sets the encryption algorithm and / or the generated encryption key for the DRB to the PDCP of the corresponding DRB (some or all MN-terminated DRBs set in the terminal device 100 or included in the target cell settings). Furthermore, in this process, if, for example, a parameter (integrityProtection) indicating the application of integrity protection to the terminal device 100 is set, the terminal device 100 sets the integrity protection algorithm and / or the generated integrity key for the DRB to the PDCP entity of the corresponding DRB. Furthermore, in this process, the terminal device 100, for example, initiates PDCP re-establishment for the PDCP entity of the corresponding DRB. Furthermore, in this process, the terminal device 100 sets the encryption algorithm and / or the generated encryption key for the SRB to the PDCP entity of the corresponding SRB (some or all MN-terminated SRBs set in the terminal device 100 or included in the target cell settings). Furthermore, in this process, the terminal device 100 sets the integrity protection algorithm and / or the generated integrity key for the SRB to the PDCP entity of the corresponding SRB. Furthermore, in this process, the terminal device 100 initiates PDCP re-establishment for the corresponding SRB PDCP entity, for example, for which the SRB encryption key and / or SRB integrity key have been set. Note that an MN-terminated SRB is, for example, SRB1. Another example of an MN-terminated SRB is SRB2.In addition, during this process, the terminal device 100 initiates RLC re-establishment for some or all of the RLC bearers associated with the PDCP entities of the relevant DRB and SRB.

[0233] Next, we will explain the process related to setting up the SN.

[0234] The process related to SN settings includes, for example, updating and applying the secondary key. Terminal device 100 determines that a secondary key update is necessary when, for example, DC is set, and it is an MCG cell switchover, and the master key has been updated. Also, terminal device 100 determines that a secondary key update is necessary when, for example, it is an SCG cell switchover and it is performing a cell switchover between SNs.

[0235] The method for updating the secondary key is, for example, the method used when updating the secondary key as described in step S1201, using the parameters necessary for the secondary key generation method and updating it in the manner described in step S1201.

[0236] Furthermore, the method for updating the secondary key is, for example, a method of updating it according to information contained in the cell switching signal, or information contained in other signals sent from the base station device 200 simultaneously with the cell switching signal. The process of using information contained in the cell switching signal, or information contained in other signals sent from the base station device 200 simultaneously with the cell switching signal, as the method for updating the secondary key may be performed if the terminal device 100 is configured with a parameter indicating that it will update the MN side and / or SN side security keys according to the information contained in the cell switching signal, or information contained in other signals.

[0237] The information contained in the cell switching signal, or other signals sent from the base station device 200 simultaneously with the cell switching signal, includes, for example, a parameter indicating whether a secondary key update is required, and / or a parameter necessary for the secondary key generation method. The parameter necessary for the secondary key generation method may be, for example, an SK-Counter. The terminal device 100 updates the secondary key using, for example, an SK-Counter contained in the information contained in the cell switching signal, or in other signals sent from the base station device 200 simultaneously with the cell switching signal. The parameter necessary for the secondary key generation method may also be, for example, an index or identifier indicating which SK-Counter from the list of SK-Counters set in the terminal device 100 is being used. The terminal device 100 updates the secondary key using, for example, an SK-Counter corresponding to the index or identifier contained in the information contained in the cell switching signal, or in other signals sent from the base station device 200 simultaneously with the cell switching signal.

[0238] The terminal device 100 generates an encryption key for the SRB, an integrity protection key for the SRB, an encryption key for the DRB, and an integrity protection key for the DRB from the updated secondary key, and applies these to the PDC entities of SN-terminated wireless bearers among the wireless bearers set in the terminal device 100 or included in the target cell settings, or included in the target cell settings (LTM candidate cell settings for cell switching destinations). In this process, for example, if the terminal device 100 does not have a parameter (cipheringDisabled) set that means deactivating encryption, the terminal device 100 sets the encryption algorithm and / or the generated encryption key for the DRB to the PDCP of the corresponding DRB (some or all of the SN-terminated DRBs set in the terminal device 100 or included in the target cell settings). Furthermore, in this process, if, for example, a parameter (integrityProtection) indicating that integrity protection should be applied to the terminal device 100 is set, the terminal device 100 sets the integrity protection algorithm and / or the generated integrity key for the DRB to the PDCP entity of the corresponding DRB. Furthermore, in this process, the terminal device 100 initiates PDCP re-establishment for the corresponding DRB to the PDCP entity of the corresponding DRB. Furthermore, in this process, the terminal device 100 sets the encryption algorithm and / or the generated encryption key for the SRB to the PDCP entity of the corresponding SRB (some or all SN-terminated SRBs set on the terminal device 100 or included in the target cell settings). Furthermore, in this process, the terminal device 100 sets the integrity protection algorithm and / or the generated integrity key for the SRB to the PDCP entity of the corresponding SRB. Furthermore, in this process, the terminal device 100 initiates a PDCP re-establishment for the corresponding SRB's PDCP entity. The SN-terminated SRB is, for example, SRB3.In addition, during this process, the terminal device 100 initiates RLC re-establishment for some or all of the RLC bearers associated with the PDCP entities of the relevant DRB and SRB.

[0239] Furthermore, when the terminal device 100 performs a process to update and apply a secondary key due to a cell switchover in the SCG, it applies the master key set in the terminal device 100 to the PDCP entities of some or all of the MN-terminated DRBs that are set in the terminal device 100 or included in the target cell settings, whose bearer type in the serving cell before the cell switchover is SN-terminated. In this process, for example, if the terminal device 100 does not have a parameter (cipheringDisabled) set that means deactivating encryption, it sets the encryption algorithm and / or encryption key for the DRB to the PDCP entities of the corresponding DRBs (some or all of the MN-terminated DRBs that are set in the terminal device 100 or included in the target cell settings, whose bearer type in the serving cell before the cell switchover is SN-terminated). Furthermore, in this process, if, for example, a parameter (integrityProtection) indicating that integrity protection should be applied to the terminal device 100 is set, the terminal device 100 sets the integrity protection algorithm and / or integrity key for the DRB for the corresponding DRB PDCP entity. Also in this process, the terminal device 100, for example, initiates PDCP re-establishment for the corresponding DRB PDCP entity. Also in this process, the terminal device 100, for example, initiates RLC re-establishment for some or all RLC bearer RLC entities associated with the corresponding DRB PDCP entity. Furthermore, among the MN-terminated DRBs set in the terminal device 100 or included in the target cell settings, a DRB whose bearer type in the serving cell before cell switching is SN-terminated is, for example, a DRB whose keyToUse parameter included in the target cell settings is different from the keyToUse parameter set in the serving cell before cell switching. Also, the settings in the serving cell before cell switching refer to, for example, the current settings of the terminal device 100.

[0240] Furthermore, when the terminal device 100 performs a process to update and apply secondary keys due to SCG cell switching, for example, it initiates RLC re-establishment for some or all of the RLC entities of MN-terminated wireless bearers, which are configured in the terminal device 100 or included in the target cell settings, and whose bearer type in the serving cell before cell switching was MN-terminated, that are linked to the SCG side. Furthermore, when the terminal device 100 performs a process to update and apply secondary keys due to SCG cell switching, for example, it initiates PDCP recovery for some or all of the AM DRBs for which RLC re-establishment has been initiated, which are MN-terminated wireless bearers, which are configured in the terminal device 100 or included in the target cell settings, and whose bearer type in the serving cell before cell switching was MN-terminated. Furthermore, when the terminal device 100 performs the process of updating and applying the secondary key due to the SCG cell switching, for example, it activates PDCP recovery for some or all of the AM DRBs whose RLC entities have been released among the MN-terminated wireless bearers that are set in the terminal device 100 or included in the target cell settings, and whose bearer type in the serving cell before the cell switching was MN-terminated.

[0241] Furthermore, among the MN-terminated wireless bearers set in terminal device 100 or included in the target cell settings, a wireless bearer whose bearer type in the serving cell before cell switching is MN-terminated is, for example, a DRB whose keyToUse parameter included in the target cell settings is the same as the keyToUse parameter in the settings of the serving cell before cell switching. Furthermore, among the MN-terminated wireless bearers set in terminal device 100 or included in the target cell settings, a wireless bearer whose bearer type in the serving cell before cell switching is MN-terminated is, for example, an SRB. Also, the settings in the serving cell before cell switching are, for example, the current settings of terminal device 100. Furthermore, an AM DRB in which an RLC entity has been released is, for example, an AM DRB in which the bearer type of the RLC bearer associated with the AM DRB's PDCP has changed from a split bearer to an MCG bearer or an SCG bearer due to a cell switch. Also, an AM DRB in which an RLC entity has been released is, for example, an AM DRB in which the bearer type of the RLC bearer associated with the AM DRB's PDCP has changed from an MCG bearer to an SCG bearer, or from an SCG bearer to an MCG bearer, due to a cell switch. Furthermore, "the RLC entity has been released" can be rephrased as "the RLC bearer has been released."

[0242] Furthermore, the processing related to SN settings includes, for example, the processing of releasing SN-related settings. Releasing SN-related settings includes, for example, releasing SRB3, releasing the SN-terminated DRB, and some or all of the SCG settings. Releasing SN-related settings also includes, for example, the resolution of the SCG bearer. Releasing SN-related settings also includes, for example, changing the SCG bearer and / or split bearer to an MCG bearer. Note that the processing of releasing SN-related settings includes, for example, the release of SN-related settings included in the reference settings stored as variables in the terminal device 100. Furthermore, the processing of releasing SN-related settings includes, for example, the release of SN-related settings included in the LTM candidate cell settings stored as variables in the terminal device 100.

[0243] Furthermore, an MN-terminated wireless bearer may be a wireless bearer with the keyToUse parameter set to master. Similarly, an SN-terminated wireless bearer may be a wireless bearer with the keyToUse parameter set to secondary.

[0244] The terminal device 100 performs cell switching to the target cell (S1205).

[0245] After switching to the target cell, the terminal device 100 sends an RRC reset completion message (S1206). The terminal device 100 may include the NCC value used when generating the security key in the RRC reset completion message. The terminal device 100 may also include the SK-Counter information used when generating the secondary key in the RRC reset completion message. The terminal device 100 does not release the LTM settings and / or LTM candidate cell settings received and stored in step S1201, but retains them. The retained LTM settings and / or LTM candidate cell settings are used for subsequent LTM cell switching. When an inter-CU LTM cell switch is performed, the terminal device 100 sends an RRC reset completion message to the base station device 200 to which the target cell belongs.

[0246] Furthermore, if the terminal device 100 is set to "horizontal generation" by the parameter indicating the key generation method described above, and performs a cell switch to the target cell after updating the security key using horizontal generation, it may, for example, immediately after successfully switching to the target cell, vertically generate a security key with the same cell as the target cell and autonomously switch to the same cell. The terminal device 100 that has switched to the same cell sends, for example, an RRC reset completion message. In this case, the RRC reset completion message may include the NCC value used when generating the security key. In this case, the terminal device 100 and the base station device 200 will not send or receive RRC messages using DCCH other than user data and / or the RRC reset completion message from the time the terminal device 100 updates the security key using horizontal generation and starts switching to the target cell until the process of vertically generating a security key in the target cell and autonomously switching to the same cell is successfully completed.

[0247] Furthermore, if the terminal device 100 updates the security key using horizontal generation during cell switching to a target cell, the base station device 200 may, for example, send an RRC reset message including master key update parameters to the terminal device 100, causing the terminal device 100 to perform an in-CU handover that includes updating the security key using vertical generation.

[0248] Furthermore, if the terminal device 100 updates the security key using horizontal generation during cell switching to a target cell, the base station device 200 may change the RRC reset message to include the master key update parameter and use the cell switching signal or a signal other than the cell switching signal to cause the terminal device 100 to perform an in-CU handover that includes updating the security key using vertical generation. The base station device 200 may also perform this process if it has set a parameter in the terminal device 100 that indicates updating the security keys on the MN side and / or SN side according to the information contained in the cell switching signal or other signals.

[0249] These processes are necessary to ensure that the security key update using horizontal generation is performed consistently during the next inter-CU cell switching of the terminal device 100.

[0250] The cell switching signal and / or other signals sent from the base station device 200 simultaneously with the cell switching signal in step S1203 (hereinafter referred to as signal A), and / or signals other than the cell switching signal for performing an in-CU handover accompanied by security key updates (hereinafter referred to as signal B) may be MAC CE, RRC messages, or DCI. If the cell switching signal is an RRC message, for example, it is an RRC message dedicated to cell switching. An RRC message dedicated to cell switching is, for example, an RRC message containing information necessary for cell switching. Also, if signal A is an RRC message, for example, it is a dedicated RRC message for notifying how to update the security key. An RRC message dedicated to notifying how to update the security key is, for example, an RRC message containing information necessary for notifying how to update the security key, as explained in step S1203. Also, if signal B is an RRC message, for example, it is a dedicated RRC message for performing an in-CU handover accompanied by security key updates. A dedicated RRC message for initiating an internal CU handover that involves updating security keys is, for example, an RRC message that contains the information necessary to initiate an internal CU handover that involves updating security keys.

[0251] Furthermore, the cell switching signal and / or signal A and / or signal B may be subjected to integrity protection / verification. To perform integrity protection / verification, for example, a MAC-I (Message Authentication Code for Integrity) is added to the cell switching signal and / or signal A and / or signal B. The input value used to generate the MAC-I is a defined value, for example, "all binary '1'". If the cell switching signal and / or signal A and / or signal B are MAC CEs, integrity verification may be performed at the MAC layer or at a higher layer. If integrity verification is performed at a higher layer, for example, the MAC entity forwards the received cell switching signal to the higher layer. Also, if integrity verification is performed at a higher layer, for example, the higher layer notifies the MAC layer, which is a lower layer, of the result of the integrity verification. Note that a higher layer may be, for example, the PDCP layer. Another higher layer may be, for example, the RRC layer.

[0252] Furthermore, before setting parameters related to the LTM to the terminal device 100 in step S1201, the base station device 200 transmits, for example, NCC information used by the terminal device when performing inter-CU LTM cell switching, along with the information of the terminal device 100, to a different CU (base station device) to which the LTM candidate cell belongs.

[0253] Furthermore, when terminal device 100 performs an inter-CU LTM cell switchover, base station device 200 may, after successfully receiving the RRC reset completion message in step S1206, notify all or some of the CUs to which the LTM candidate cell set in terminal device 100 belongs of the latest security key information of terminal device 100. The latest security key information of terminal device 100 is, for example, the security key information updated by terminal device 100 during an inter-CU LTM cell switchover. Also, after notifying all or some of the CUs to which the LTM candidate cell set in terminal device 100 belongs of the latest security key information of terminal device 100, base station device 200 may receive from the notified CU the information necessary for terminal device 100 to update the security key used when performing an inter-CU LTM cell switchover to the notified CU. The information necessary for updating the security key is, for example, NCC.

[0254] In the second example of the subsequent cell switching method corresponding to within and between CUs, an upper limit may be set on the number of CUs to which the LTM candidate cells set in the terminal device 100 belong. For example, the number of CUs to which the LTM candidate cells set in the terminal device 100 belong may be limited to two, four, six, or eight.

[0255] <Fast LTM Recovery within and between CUs> In cell switching or handovers involving security key updates or PDCP termination point changes, or in handovers (mobility) to RATs other than NR, the terminal device 100 and base station device 200 may erase values ​​and data used in the source cell due to the re-establishment of PDCP entities and RLC entities. Recovering erased values ​​and data after they have been erased presents implementation challenges. Therefore, after a cell switching or handover involving security key updates or PDCP termination point changes, or in handovers (mobility) to RATs other than NR fails, returning to the source cell settings and performing fast LTM recovery without further security key changes presents implementation challenges and should be avoided.

[0256] This explains method 1 for avoiding fast LTM recovery after data erasure.

[0257] If cell switching fails, the terminal device 100 performs RRC connection reconnection. In the RRC connection reconnection, cell selection is performed, and if at least all of the following conditions (1) to (4) are met, the terminal device 100 performs fast LTM recovery for the selected cell. If some or all of the following conditions (1) to (4) are not met, fast LTM recovery is not performed.

[0258] (1) A parameter indicating that fast LTM recovery should be performed (a parameter named attemptLTM-Switch) is set.

[0259] (2) The selected cell is one of the LTM candidate cells. (3) The failed cell switch or failed handover (MCG synchronized reconfiguration) did not involve a security key update.

[0260] (4) This is not a means of reconnecting the RRC connection that was activated due to a failure of handover (mobility) to a RAT other than NR.

[0261] Furthermore, terminal device 100 will perform fast LTM recovery if a parameter indicating that it will perform fast LTM recovery is set, regardless of, for example, after a failure in inter-CU LTM cell switching, or after a failure in handover (MCG synchronization reset) accompanied by security key updates, or after a failure in handover (mobility) to a RAT other than NR, and the selected cell is an LTM candidate cell, and the CU to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs.

[0262] This explains method number two for avoiding fast LTM recovery after data erasure.

[0263] The terminal device 100 performs RRC connection reconnection means in the event of a cell switching failure, etc. In the RRC connection reconnection means, cell selection is performed, and if at least all of the following conditions (1) to (2) are met, the terminal device 100 performs fast LTM recovery for the selected cell. If some or all of the following conditions (1) to (2) are not met, fast LTM recovery is not performed.

[0264] (1) A parameter indicating that fast LTM recovery should be performed (a parameter named attemptLTM-Switch) is set.

[0265] (2) The selected cell is one of the LTM candidate cells, and the CU to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs.

[0266] Furthermore, the statement that the CU to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs means, for example, that the security update-free identifier parameter of the selected LTM candidate cell is different from the security update-free identifier parameter of the source cell. Also, the statement that the CU to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs means, for example, that the security update-free identifier parameter of the selected LTM candidate cell is different from the security update-free identifier parameter of the current serving cell.

[0267] This explains method number 3 for avoiding fast LTM recovery after data erasure.

[0268] The terminal device 100 performs RRC connection reconnection means if cell switching fails or if a wireless link failure is detected. In the RRC connection reconnection means, cell selection is performed, and if at least all of the following conditions (1) to (4) are met, the terminal device 100 performs fast LTM recovery for the selected cell. If some or all of the following conditions (1) to (4) are not met, fast LTM recovery is not performed.

[0269] (1) A parameter indicating that fast LTM recovery should be performed (a parameter named attemptLTM-Switch) is set.

[0270] (2) The selected cell is one of the LTM candidate cells.

[0271] (3) In the failed LTM cell switching process, there were no wireless bearers that underwent PDCP re-establishment.

[0272] (4) In the failed LTM cell switching process, there is a wireless bearer to which PDCP re-establishment has occurred, and the CU to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs.

[0273] This explains method number four for avoiding fast LTM recovery after data erasure.

[0274] The terminal device 100 performs RRC connection reconnection means if cell switching fails or if a wireless link failure is detected. In the RRC connection reconnection means, cell selection is performed, and if at least all of the following conditions (1) to (4) are met, the terminal device 100 performs fast LTM recovery for the selected cell. If some or all of the following conditions (1) to (4) are not met, fast LTM recovery is not performed.

[0275] (1) A parameter indicating that fast LTM recovery should be performed (a parameter named attemptLTM-Switch) is set.

[0276] (2) The selected cell is one of the LTM candidate cells.

[0277] (3) In the failed LTM cell switching process, there were no wireless bearers that underwent PDCP re-establishment.

[0278] (4) In a failed LTM cell switching process, the CU to which the selected LTM candidate cell belongs is the same as the CU to which the source cell belongs.

[0279] The statement that a wireless bearer underwent PDCP re-establishment during LTM cell switching means, for example, that the master key and / or secondary key were updated during the LTM cell switching process. It also means that a DRB (Distributed Rail Breaker) whose PDCP termination point was changed during the LTM cell switching process. Furthermore, a wireless bearer underwent PDCP re-establishment can be rephrased as a wireless bearer underwent both PDCP re-establishment and RLC re-establishment. Additionally, the statement that the CU (Control Unit) to which the selected LTM candidate cell belongs is different from the CU to which the source cell belongs means, for example, that the master key and / or secondary key were updated when performing an LTM cell switch to the selected LTM candidate cell. Furthermore, the statement that the CU to which the selected LTM candidate cell belongs is the same as the CU to which the source cell belongs means, for example, that when performing an LTM cell switch to the selected LTM candidate cell, the master key and / or secondary key are not updated. If the cell switch fails, the terminal device 100 will, for example, revert its settings to the settings used by the source cell or source PCell. When the terminal device 100 reverts its settings to the settings used by the source cell or source PCell, for example, it will retain the state variables of some or all of the PDCP entities configured in the terminal device 100. Some or all of the wireless bearers are, for example, SRBs associated with the MCG. For example, fast LTM recovery is not permitted after a fast LTM recovery has failed.

[0280] When performing fast LTM recovery, the terminal device 100 activates cell switching. Furthermore, when performing fast LTM recovery, the terminal device 100 follows some or all of the subsequent cell switching methods 1 and 2, corresponding to those within and between CUs, as explained using Figure 12. For example, when performing fast LTM recovery, the terminal device 100 determines whether a security key update is necessary for cell switching to the target cell, and if a security key update is necessary, it updates the security key.

[0281] Furthermore, the first and second examples of subsequent cell switching methods corresponding to within and between CUs, and the example of fast LTM recovery corresponding to within and between CUs, may also be applied to the case of conditional LTM. Conditional LTM is a process in which the terminal device 100 performs LTM cell switching based on the judgment of the terminal device 100 without receiving a cell switching signal from the base station device 200. That is, in step S1201 of Figure 12, the base station device 200 sets measurement conditions for the serving cell and / or candidate cell for the terminal device 100. If the set measurement conditions for the serving cell and / or candidate cell are met, the terminal device 100 performs LTM cell switching for the candidate cell that meets the measurement conditions.

[0282] This embodiment enables flexible communication that supports subsequent cell switching within and between CUs. Furthermore, it avoids fast LTM recovery after cell switching failures that involve security key updates, thus mitigating implementation challenges.

[0283] <Other> Although this embodiment was described using the LTM case, this embodiment can be applied to other technologies and methods. For example, the method for determining whether or not a security key update is necessary on the terminal device 100 side, the method for setting and / or notifying the security key update method, and the processing after cell switching or handover failure in this embodiment can be applied to methods such as CHO and CPAC, in which candidates for synchronized reset destinations are set.

[0284] The messages in the sequence described above may not be executed in order, or their order may be changed. Furthermore, some messages in the sequence may not be executed at all.

[0285] Furthermore, the functions and processes described for the terminal device 100 may also be those of the base station device 200. Similarly, the functions and processes described for the base station device 200 may also be those of the terminal device 100.

[0286] Furthermore, when the term "wireless bearer" is used without distinguishing between signaling wireless bearers and data wireless bearers, the wireless bearer may be a signaling wireless bearer, a data wireless bearer, or both.

[0287] Furthermore, "A can be replaced with B" and "A can be replaced with B" include not only the meaning of replacing A with B, but also the meaning of replacing B with A.

[0288] Furthermore, if condition "A" and condition "B" are contradictory, condition "B" may be expressed as an "other" condition of condition "A".

[0289] In summary, it is as follows:

[0290] (1) A terminal device comprising: a receiving unit that receives a first signal from a base station device instructing a cell switch from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that performs a process to determine whether the first condition or the second condition is met, wherein if the processing unit determines that the first condition is met, it performs a first process, which is a protocol process associated with cell switching between base station devices, and if the processing unit determines that the second condition is met, it performs a second process, which is a protocol process associated with cell switching within a base station device.

[0291] (2) The terminal device according to (1), wherein the first process includes, when the first signal instructs a cell switch for the master cell group, updating a first security key which is a security key associated with the master node and a second security key which is a security key for the secondary node, applying the first security key to the PDCP entity of the first wireless bearer associated with the first key among the wireless bearers included in the setting of the second cell, applying the second security key to the PDCP entity of the second wireless bearer associated with the second key, and re-establishing the PDCP entities of the first and second wireless bearers and re-establishing the RLC entities.

[0292] (3) The terminal device according to (2), wherein the first process includes, if the first signal instructs a cell switch for the secondary cell group, updating the second security key, applying the second security key to the PDCP entity of the third wireless bearer associated with the second security key among the wireless bearers included in the setting of the second cell, re-establishing the PDCP entity and RLC entity of the second wireless bearer, re-establishing the RLC entity of the fourth wireless bearer associated with the first security key, and performing PDCP entity recovery for the AM DRB from which the RLC entity has been re-established and for the AM DRB from which the RLC bearer has been released among the fourth wireless bearers.

[0293] (4) The second process includes the following steps for a fifth wireless bearer among the wireless bearers included in the second cell configuration, where the security key associated in the first cell configuration is the first security key and the security key associated in the second cell configuration is the second security key: applying the second security key to the PDCP entity of the fifth bearer, and re-establishing the PDCP entity and RLC entity of the fifth bearer; and the second process also includes the following steps for a sixth wireless bearer among the wireless bearers included in the second cell configuration, where the security key associated in the first cell configuration is the second security key and the security key associated in the second cell configuration is the first security key: The terminal device according to (2) or (3), further comprising the process of applying the first security key to the PDCP entity of the sixth bearer, and re-establishing the PDCP entity and RLC entity of the sixth bearer, wherein the second process determines whether the third condition is met for a seventh wireless bearer among the wireless bearers included in the second cell configuration, whose security key associated with the first cell configuration is the same as the security key associated with the second cell, and if the third condition is met, re-establishing the RLC entity for the wireless bearer among the sixth bearers that has an RLC bearer associated with the master cell group, and regardless of whether the third condition is met, recovering the PDCP entity for the AM DRB among the seventh wireless bearers for which the RLC entity has been re-established and for the AM DRB for which the RLC bearer has been released.

[0294] (5) The terminal device according to claim (2) or (3) or claim 4, wherein the third condition is cell switching between DUs.

[0295] (6) A base station device comprising: a transmitting unit that transmits a first signal instructing a terminal device to switch cells from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that causes the terminal device to perform a process to determine whether the first condition or the second condition is met, wherein if the terminal device determines that the first condition is met, the processing unit causes the terminal device to perform a first process, which is a protocol process associated with cell switching between base station devices; and if the terminal device determines that the second condition is met, the processing unit causes the terminal device to perform a second process, which is a protocol process associated with cell switching within a base station device.

[0296] (7) A wireless communication system comprising: a base station device that transmits a first signal instructing a cell switch from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a terminal device that receives the first signal and performs processing to determine whether the first condition or the second condition is met, wherein the terminal device performs a first process, which is protocol processing associated with cell switching between base station devices, if it determines that the first condition is met, and performs a second process, which is protocol processing associated with cell switching within a base station device, if it determines that the second condition is met.

[0297] Although each embodiment describes an example of the apparatus, the method of this disclosure is not limited to cellular phones, smartphones, tablet terminals, base station equipment, etc., but can be applied to other electronic devices, such as electronic devices mounted on automobiles, trains, airplanes, artificial satellites, etc., electronic devices mounted on drones, etc., robots, AV equipment, home appliances, office equipment, vending machines, other household equipment, industrial equipment, etc.

[0298] Furthermore, although E-UTRA and NR were used as wireless access technologies and EPC and 5GC as core networks in each embodiment, the methods of this disclosure are not limited to these. For example, the methods of this disclosure may be applied to wireless access technologies and networks of different generations, such as sixth-generation and seventh-generation.

[0299] Furthermore, the invention is not limited to the above-described embodiment and can be implemented with various modifications.

[0300] Furthermore, although each embodiment has been described in detail with reference to the drawings, the specific configuration is not limited to the disclosed drawings and described forms.

[0301] 10: Communication system 100: Terminal device 110: CPU 120: Storage 121: Wireless communication program 122: Terminal-side program 130: Memory 140: Wireless communication circuit 200: Base station device 210: CPU 220: Storage 221: Wireless communication program 222: Base station-side program 230: Memory 240: Wireless communication circuit 250: Network interface 300: Core network

Claims

1. A terminal device comprising: a receiving unit that receives a first signal from a base station device instructing a cell switch from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that performs a process to determine whether a first condition or a second condition is met, wherein the processing unit performs a first process, which is a protocol process associated with cell switching between base station devices, if it determines that the first condition is met, and performs a second process, which is a protocol process associated with cell switching within a base station device, if it determines that the second condition is met.

2. The terminal device according to claim 1, wherein the first process includes, if the first signal instructs a cell switching for the master cell group, updating a first security key which is a security key associated with the master node and a second security key which is a security key for the secondary node; applying the first security key to the PDCP entity of the first wireless bearer associated with the first key among the wireless bearers included in the setting of the second cell; applying the second security key to the PDCP entity of the second wireless bearer associated with the second key; and re-establishing the PDCP entities of the first and second wireless bearers and re-establishing the RLC entities.

3. The terminal device according to claim 2, wherein the first process includes, if the first signal instructs a cell switch for the secondary cell group, updating the second security key, applying the second security key to the PDCP entity of the third wireless bearer associated with the second security key among the wireless bearers included in the second cell configuration, re-establishing the PDCP entity and RLC entity of the second wireless bearer, re-establishing the RLC entity of the fourth wireless bearer associated with the first security key, and performing PDCP entity recovery for the AM DRB from which the RLC entity has been re-established and for the AM DRB from which the RLC bearer has been released among the fourth wireless bearers.

4. The second process includes, for a fifth wireless bearer among the wireless bearers included in the second cell configuration, the security key associated with the first cell configuration is the first security key, and the security key associated with the second cell configuration is the second security key, applying the second security key to the PDCP entity of the fifth wireless bearer, and re-establishing the PDCP entity and RLC entity of the fifth wireless bearer; the second process includes, for a sixth wireless bearer among the wireless bearers included in the second cell configuration, the security key associated with the first cell configuration is the second security key, and the security key associated with the second cell configuration is the first security key, applying the first security key to the PDCP entity of the sixth wireless bearer, and re-establishing the PDCP entity and RLC entity of the sixth wireless bearer; the second process includes, for a fifth wireless bearer among the wireless bearers included in the second cell configuration, The terminal device according to claim 2 or 3, comprising the process of determining whether a third condition is met for a seventh wireless bearer whose security key associated with the setting of the first cell and the security key associated with the second cell are the same; if the third condition is met, re-establishing the RLC entity for the wireless bearer among the sixth wireless bearers that has an RLC bearer associated with the master cell group; and regardless of whether the third condition is met, recovering the PDCP entity for the AM DRB among the seventh wireless bearers for which the RLC entity has been re-established and for the AM DRB from which the RLC bearer has been released.

5. The terminal device according to claim 4, wherein the third condition is cell switching between DUs.

6. A base station device comprising: a transmitting unit that transmits a first signal instructing a terminal device to switch cells from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a processing unit that causes the terminal device to perform a process to determine whether the first condition or the second condition is met, wherein if the terminal device determines that the first condition is met, the processing unit causes the terminal device to perform a first process, which is a protocol process associated with cell switching between base station devices; and if the terminal device determines that the second condition is met, the processing unit causes the terminal device to perform a second process, which is a protocol process associated with cell switching within a base station device.

7. A wireless communication system comprising: a base station device that transmits a first signal instructing a cell switch from a first cell, which is a serving cell, to a second cell, which is an LTM candidate cell; and a terminal device that receives the first signal and performs processing to determine whether a first condition or a second condition is met, wherein the terminal device performs a first process, which is protocol processing associated with cell switching between base station devices, if it determines that the first condition is met, and performs a second process, which is protocol processing associated with cell switching within a base station device, if it determines that the second condition is met.

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