Terminal device, base station device, and wireless communication system

Abstract

The present invention comprises: a reception unit that receives, from a base station device, a first signal including change destination information in which a first cell and a second cell are cell change destination candidates, and a second signal including information relating to a cell change; and a switching unit for performing a first process of switching the serving cell from the third cell to the first cell in accordance with the information related to the cell change included in the second signal. When the first process fails, the switching unit performs a second process in which, when the second cell is selected as a change destination cell, a second configuration applied to the second cell is generated, and the second configuration is used to switch the serving cell to the second cell. And when a cell other than the cell change destination candidate included in the first signal is selected as a change destination cell, performing a reestablishment procedure of the first RRC connection using a third configuration applied to a third cell.

Description

Technical Field

[0001] This invention relates to a terminal device, a base station device, and a wireless communication system. Background Technology

[0002] Current networks are expanding to include wireless communication networks using mobile terminals (smartphones or feature phones). This expansion of wireless communication is demanding further increases in speed and capacity.

[0003] Within the Third Generation Partnership Project (3GPP), an international standardization project, technical research and standardization of cellular mobile communication systems are underway. For example, Evolved Terrestrial Radio Access (E-UTRA) has been standardized as Radio Access Technology (RAT) for 3.9G and 4G generations, and Evolved Packet Core (EPC) has been standardized as Core Network (CN) technology. Furthermore, New Radio (NR) has been standardized as 5G RAT, and 5G Core (5GC) has been standardized as Core Network technology. Further research and standardization of these technologies are ongoing.

[0004] For example, the following non-patent documents 1 to 11 describe technologies related to NR.

[0005] List of cited references

[0006] Non-patent literature

[0007] Non-patent document 1: 3GPP TS 38.300 NR Overview Specification

[0008] Non-Patent Document 2: 3GPP TS 38.211 NR PHY Channel and Modulation Specification

[0009] Non-patent document 3: 3GPP TS 38.321 NR MAC specification

[0010] Non-patent document 4: 3GPP TS 38.322 NR RLC specification

[0011] Non-patent document 5: 3GPP TS 38.323 NR PDCP specification

[0012] Non-patent document 6: 3GPP TS 37.324 NR SDAP specification

[0013] Non-patent document 7: 3GPP TS 38.304 NR RRC specification

[0014] Non-Patent Document 8: 3GPP TS38.331 NR Idle Mode and Inactive Mode Specification

[0015] Non-Patent Document 9: 3GPP RP-223520 "Revised WID for Further Enhancing NR Mobility"

[0016] Non-patent document 10: 3GPP R2-2211642 "Solutions for Cell Handover in LTM"

[0017] Non-patent document 11: 3GPP R2-2211795 "Discussion on Dynamic Cell Handover" Summary of the Invention

[0018] Technical issues

[0019] As one of the extended technologies, research has been conducted on technologies to improve mobility. One of the research projects is a technology called L1 / L2 triggered mobility (LTM), which aims to reduce latency during movement by changing the serving cell of the terminal device using Layer 1 and / or Layer 2 signals (Non-Patent Document 9).

[0020] However, the specific methods for LTM have not yet been defined in the standardized specifications. For example, in the event of a cell handover failure during LTM, the method for restoring the RRC connection has not yet been specified, taking into account security measures in the terminal device's processing.

[0021] Therefore, the purpose of this invention is to provide a base station device, a terminal device, and a wireless communication system capable of efficiently restoring the RRC connection.

[0022] Technical solution

[0023] One disclosure includes: a receiving unit that receives a first signal and a second signal from a base station device, the first signal including change destination information designating a first cell and a second cell as cell change destination candidates, and the second signal including information related to cell change; and a handover unit configured to perform a first process of handing a serving cell from a third cell to the first cell based on the cell change-related information included in the second signal, wherein, in the event that the first process fails, the handover unit performs a second process in which, when the second cell is selected as the change destination cell, a second configuration applied to the second cell is generated, and the serving cell is handed over to the second cell using the second configuration; and when a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, a first RRC connection re-establishment process is performed using a third configuration applied to the third cell.

[0024] One disclosure includes: a transmitting unit for transmitting a first signal and a second signal to a terminal device, the first signal including change destination information designating a first cell and a second cell as cell change destination candidates, and the second signal including information related to cell change; and a control unit for causing the terminal device to: perform a first process of switching the serving cell from a third cell to the first cell based on the cell change-related information included in the second signal; perform a second process if the first process fails; in the second process, when the second cell is selected as the change destination cell, generate a second configuration applied to the second cell and switch the serving cell to the second cell using the second configuration; and when a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, perform a first RRC connection re-establishment process using a third configuration applied to the third cell.

[0025] One disclosure is a wireless communication system comprising a base station device and a terminal device. The base station device transmits a first signal and a second signal to the terminal device. The first signal includes change destination information designating a first cell and a second cell as cell change destination candidates. The second signal includes information related to the cell change. The terminal device receives the first signal and the second signal. Based on the cell change-related information included in the second signal, it performs a first process of switching a serving cell from a third cell to the first cell. If the first process fails, it performs a second process. In the second process, when the second cell is selected as the change destination cell, a second configuration applied to the second cell is generated, and the serving cell is switched to the second cell using the second configuration. And when a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, a first RRC connection re-establishment process is performed using a third configuration applied to the third cell.

[0026] Technical effect

[0027] In one disclosure, when the terminal device performs mobility processing, it can perform communication that can efficiently resume processing RRC connections. Attached Figure Description

[0028] Figure 1 This is a diagram illustrating a configuration example of the communication system 10.

[0029] Figure 2 This is a diagram showing an example configuration of the base station device 200.

[0030] Figure 3 This is a diagram showing an example configuration of the terminal device 100.

[0031] Figure 4 This is a diagram illustrating an example of the U-Plane protocol stack.

[0032] Figure 5 This is a diagram illustrating an example of the C-Plane protocol stack.

[0033] Figure 6 This is a diagram illustrating an example of the message format for RRCReconfiguration.

[0034] Figure 7 This is a diagram illustrating an example configuration of a cell group in communication system 10.

[0035] Figure 8 This is a diagram illustrating an example of synchronized reconfiguration.

[0036] Figure 9 This is a diagram illustrating the handover process through four steps of random access.

[0037] Figure 10 This is a diagram showing an example of an LTM sequence.

[0038] Figure 11 This is a diagram illustrating an example of the sequence for cell handover failure detection and cell handover failure handling.

[0039] Figure 12 This is a diagram illustrating an example of a method for handling a handover failure in the first cell.

[0040] Figure 13 This is a diagram illustrating an example of a second cell handover failure handling method.

[0041] Figure 14 This is a diagram illustrating an example of a third-cell handover failure handling method.

[0042] Figure 15 This is a diagram illustrating an example of a method for handling handover failures in the fourth cell.

[0043] Figure 16 This is a diagram illustrating an example of processing based on a selected cell. Detailed Implementation

[0044] The embodiments described below will be described in detail with reference to the accompanying drawings. The problems and examples in this specification are merely exemplary and do not limit the claims of this application. Specifically, even if the expressions are different, as long as the expressions are technically equivalent, the technology of this application can be applied to different expressions and is not limited by the claims.

[0045] In this embodiment, the names and processing of each device, node, function, protocol, entity, signaling, message, parameter, etc., will be described for cases where the radio access technology is E-UTRA or NR and the core network is EPC or 5GC. However, these embodiments can also be used for other radio access technologies. The names of each node and entity in the embodiments can be different.

[0046] <Configuration Example of Communication System 10>

[0047] Figure 1 This is a diagram illustrating a configuration example of communication system 10. Communication system 10 includes terminal device 100, base station devices 200-1 and 200-2, and a core network 300. Communication system 10 can be a diagram of a wireless communication system in which terminal device 100 communicates with base station device 200-1 or base station device 200-2, or it can be a diagram of a wireless communication system in which terminal device 100 communicates with base station devices 200-1 and 200-2 via Multiple Radio Dual Connection (MR-DC), described later. For example, in the case of communication via MR-DC, base station device 200-1 is a primary base station device, and base station device 200-2 is a secondary base station device. Hereinafter, the primary base station device may be referred to as the primary node (MN), and the secondary base station device may be referred to as the secondary node (SN).

[0048] Terminal device 100 is wirelessly connected to one or both of base station devices 200-1 and 200-2, and performs wireless communication. The RAT providing the wireless connection is, for example, E-UTRA or NR. Terminal device 100 is a terminal device compatible with one or both of E-UTRA and NR.

[0049] Base station devices 200-1 and 200-2 (hereinafter, in some cases, collectively referred to as base station device 200) are communication devices wirelessly connected to terminal device 100 and performing wireless communication. Base station devices 200-1 and 200-2 are connected to each other, for example, via a wired connection and communicate with each other. Base station device 200 is connected to core network 300, for example, via a wired connection and performs communication. Base station device 200 is, for example, an eNodeB (eNB) providing E-UTRA as RAT or a gNodeB (gNB) providing NR as RAT.

[0050] Core Network 300 refers to a network corresponding to a specific generation. Core Network 300 could be, for example, 5GC for 5G standardization or EPC for 4G standardization.

[0051] The details of the MR-DC implemented in communication system 10 will be described later.

[0052] <Configuration Example of Base Station Device 200>

[0053] Figure 2 This is a diagram illustrating a configuration example of a base station device 200. The base station device 200 is a communication device or relay device, which includes a central processing unit (CPU) 210, a storage device 220, a memory 230, a wireless communication circuit 240, and a network interface 250.

[0054] Storage device 220 is an auxiliary storage device such as flash memory, hard disk drive (HDD), or solid-state drive (SSD) that stores programs and data. Storage device 220 stores wireless communication program 221 and base station side program 222.

[0055] Memory 230 is the area where programs stored in storage device 220 are loaded. Memory 230 can also be used as an area for storing program data.

[0056] The wireless communication circuit 240 is a circuit that is wirelessly connected to the terminal device 100 and performs communication. The base station device 200 receives signals transmitted from the terminal device 100 via, for example, the wireless communication circuit 240, and transmits signals to the terminal device 100.

[0057] Network interface (NI) 250 is a communication device, for example, connected to another base station device 200 and enabling communication between base stations. NI 250 is also a communication device, for example, connected to a core network 300 (constituting a communication device of the core network 300) and performing communication. For example, NI 250 is a network interface card (NIC). Base station device 200 receives signals from other communication devices via NI 250 and transmits signals to other communication devices.

[0058] CPU 210 is a processor that loads the program stored in storage device 220 onto memory 230, executes the loaded program, builds each unit, and implements each process.

[0059] CPU 210 executes wireless communication program 221 to perform wireless communication processing. Wireless communication processing is the process of wirelessly connecting to terminal device 100, performing wireless communication with terminal device 100, and relaying communication performed by terminal device 100 with another communication device.

[0060] CPU 210 executes base station-side program 222 to construct a second transmitting unit, a second receiving unit, and a second processing unit, and performs base station-side processing. When base station device 200 performs communication with terminal device 100 using MR-DC, the base station-side processing may include MR-DC master node processing and MR-DC slave node processing. In this case, MR-DC master node processing is the processing of performing control on the master node side within the MR-DC, and MR-DC slave node processing is the processing of performing control on the slave node side within the MR-DC. Base station device 200 performs communication corresponding to each type of MR-DC described later in the MR-DC master node processing and MR-DC slave node processing.

[0061] <Configuration Example of Terminal Device 100>

[0062] Figure 3 This is a diagram illustrating a configuration example of terminal device 100. Terminal device 100 is a communication device including CPU 110, storage device 120, memory 130, and wireless communication circuitry 140.

[0063] Storage device 120 is an auxiliary storage device such as flash memory, HDD, or SSD that stores programs and data. Storage device 120 stores terminal-side wireless communication program 121 and terminal-side program 122.

[0064] The memory 130 is the area where programs stored in the storage device 120 are loaded. Furthermore, the memory 130 can also be used as an area for storing program data.

[0065] The wireless communication circuit 140 is a circuit that is wirelessly connected to the base station device 200 and performs communication. The terminal device 100 receives signals transmitted from the base station device 200 via, for example, the wireless communication circuit 140, and transmits signals to the base station device 200. The wireless communication circuit 140 is, for example, a network interface card (NIC) that supports wireless connectivity.

[0066] CPU 110 is a processor that loads programs stored in storage device 120 into memory 130, executes the loaded programs, builds each unit, and implements each process.

[0067] The CPU 110 executes the terminal-side wireless communication program 121 to perform terminal-side wireless communication processing. The terminal-side wireless communication processing is the process of wirelessly connecting to the base station device 200 and performing wireless communication with the base station device 200 or performing communication with another communication device via the base station device 200.

[0068] CPU 110 executes terminal-side program 122 to construct a transmitting unit, a receiving unit, and a processing unit, and performs terminal-side processing. When terminal device 100 performs communication with base station device 200 using MR-DC, the terminal-side processing may include terminal-side MR-DC processing. In this case, terminal-side MR-DC processing is the process of controlling communication within the MR-DC. In terminal-side MR-DC processing, terminal device 100 performs communication corresponding to each type of MR-DC described later.

[0069] <Protocol Stack>

[0070] An example of the protocol stack of communication system 10 will be described. In communication system 10, the protocol stack is referred to as a layered structure representing a series of protocols used to perform data transmission and reception. In the following example, the case where base station device 200 is an eNB or gNB and core network 300 is an EPC or 5GC will be described. Furthermore, terminal device 100 (user equipment (UE)) corresponds to one or both of E-UTRA and NR.

[0071] The protocol stacks for the user plane (U-Plane) and control plane (C-Plane) will be described below. The U-Plane is used, for example, for sending and receiving user data in communication. The C-Plane is used, for example, for sending and receiving control signals (messages) in communication. It should be noted that in each implementation, unless specifically referred to as "user data," "control signals (messages)," etc., data refers to one or both of user data and control signals (messages).

[0072] Figure 4 This is a diagram illustrating an example of the U-Plane protocol stack when the core network 300 is 5GC. Figure 5 This is a diagram illustrating an example of the C-Plane protocol stack when the core network 300 is a 5GC. Figure 4 and Figure 5In this context, each of the Physical Layer (PHY), Medium Access Control (MAC), Radio Link Control (RLC), Packet Data Convergence Protocol (PDCP), Service Data Adaptation Protocol (SDAP), Radio Resource Control (RRC), and Non-Access Layer (NAS) indicates the name of the layer. Below, each of 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, or NAS layer. Each of MAC, RLC, PDCP, and SDAP may be referred to as the MAC sublayer, RLC sublayer, PDCP sublayer, and SDAP sublayer. Each of MAC, RLC, PDCP, and SDAP may be referred to as the MAC entity, RLC entity, PDCP entity, or SDAP entity. The protocol stack of U-Plane in the case of the core network 300 being an EPC is... Figure 4 The protocol stack in this case does not include SDAP. That is, the protocol stack in this scenario includes PHY, MAC, RLC, and PDCP. In the C-Plane protocol stack where the core network 300 is an EPC, NAS exists within the Mobility Management Entity (MME), while... Figure 5 In this context, NAS exists within the Access and Mobility Management Function (AMF).

[0073] Depending on whether the RAT is E-UTRA or NR, the functionality of each layer may be the same or different. In the following description, unless E-UTRA or NR is specified, the functionality is common to both E-UTRA and NR.

[0074] It should be noted that in each sub-layer, the data provided from the upper layer and the data provided to the upper layer are called Service Data Units (SDUs). That is, the data provided from the upper layer to MAC, RLC, PDCP, and SDAP, and the data provided from MAC, RLC, PDCP, and SDAP to the upper layer, are respectively called MAC SDU, RLC SDU, PDCP SDU, and SDAP SDU.

[0075] Within each sublayer, the data provided to and from the lower layer is called a Protocol Data Unit (PDU). Specifically, the data provided to the lower layer from MAC, RLC, PDCP, and SDAP, and the data provided from the lower layer to MAC, RLC, PDCP, and SDAP, are respectively called MAC PDU, RLC PDU, PDCP PDU, and SDAP PDU. Control PDUs reside in RLC, PDCP, and SDAP and can be referred to as control PDUs. To distinguish them from control PDUs, other PDUs can be called data PDUs.

[0076] exist Figure 4 In this context, U-Plane includes PHY, MAC, RLC, PDCP, and SDAP, and terminates at terminal device 100 (UE) and base station device 200 (gNB).

[0077] The following describes an example of PHY functionality. PHY is the radio physical layer and uses physical channels to transmit control information and data between terminal device 100 and base station device 200. The direction from base station device 200 to terminal device 100 is referred to as the downlink (DL), and the direction from terminal device 100 to base station device 200 is referred to as the uplink (UL). In both terminal device 100 and base station device 200, the PHY is connected to the MAC layer (the upper layer) via a transport channel, and data moves between the PHY and MAC via the transport channel. In the PHY, Radio Network Temporary Identifiers (RNTIs) are used to identify various control information.

[0078] The following describes an example of MAC functionality. The MAC is the Media Access Control layer and performs mapping between transport channels and logical channels (LCH), multiplexing and demultiplexing of MAC SDUs, scheduling reports (SR), error correction via Hybrid Automatic Repeat Request (HARQ), priority control, etc. In terminal device 100 and base station device 200, the MAC is connected to the upper-layer RLC via a logical channel, and data moves between the MAC and RLC via the logical channel. The logical channel can be identified by a Logical Channel Identifier (LCID). Base station device 200 uses a MAC Control Element (CE) to control terminal device 100. Terminal device 100 uses the MAC CE to perform reporting to base station device 200, etc.

[0079] RLC is the Radio Link Control layer and exists in three modes: Transparent Mode (TM), Unacknowledged Mode (UM), and Acknowledged Mode (AM). On the transmitting side, RLC performs PDU transmission, sequence number assignment (in UM and AM), SDU segmentation (in UM and AM), and resegmentation (in AM). On the receiving side, it performs SDU reassembly (in UM and AM), duplicate detection (in AM), and SDU discarding (in UM and AM). It also performs RLC re-establishment on both the transmitting and receiving sides. Segmented SDUs are called SDU segments. RLC has data retransmission capabilities and / or Automatic Repeat Request (ARQ) capabilities (in AM). In the case of E-UTRA RLC, additional functions include data concatenation on the transmitting side and reordering and in-order delivery on the receiving side.

[0080] PDCP is the packet data aggregation protocol layer, and it performs data transmission for U-Plane and C-Plane, PDCP sequence number management, header compression and decompression, encryption and decryption, integrity protection and integrity verification, timer-based SDU discarding, routing to segmented bearers, reordering, and sequential transmission. It should be noted that in E-UTRA PDCP, functions such as timer-based SDU discarding, reordering, and sequential transmission may be limited to the segmented bearer scenario described later.

[0081] SDAP is the Service Data Adaptation Protocol layer and performs the mapping between Quality of Service (QoS) flows and Data Radio Bearers (DRBs), which will be described later, thereby marking downlink (DL) packets and uplink (UL) packets with QoS Flow Identifiers (QFIs), etc.

[0082] Examples of upper layers of U-Plane include layers such as Internet Protocol (IP), Transmission Control Protocol (TCP), User Datagram Protocol (UDP), Ethernet (registered trademark), and application layers. Layers including IP, TCP, UDP, Ethernet, etc., can be referred to as PDU layers. The IP Multimedia Subsystem (IMS), which performs session control, can be included in the application layer.

[0083] exist Figure 5 In this architecture, the C-Plane of the Access Layer (AS) includes PHY, MAC, RLC, PDCP, and RRC, and terminates at terminal device 100 and base station device 200. The C-Plane of the NAS includes the NAS and terminates between terminal device 100 and the AMF, which serves as the core network 300. PHY, MAC, RLC, and PDCP are similar to those of the U-Plane.

[0084] RRC performs the following functions: broadcasting System Information (SI) related to AS and NAS; paging; establishing, maintaining, and releasing RRC connections between terminal device 100 and base station device 200; adding, modifying, and releasing carrier aggregation (CA); adding, modifying, and releasing dual connectivity (DC); security functions including security key management; establishing, configuring, maintaining, and releasing signaling radio bearers (SRB) and data radio bearers (DRB); mobility functions; QoS management functions; control of measurement reporting and uploading processes for terminal devices; detection and recovery of radio link failures (RLF); and transmission of NAS messages.

[0085] NAS performs authentication, mobility management, and security control on the core network side.

[0086] <channel>

[0087] The channels used in communication system 10 will be described below. Examples of channels corresponding to NR will be described below, but the channels to be used are not limited to the following. Channels with the same name may be used for the same or similar applications in RATs other than NR (e.g., E-UTRA).

[0088] <1. Physical Channel>

[0089] The Physical Broadcast Channel (PBCH) is a channel used to send broadcast information from the base station device 200 to the terminal device 100.

[0090] The Physical Downlink Control Channel (PDCCH) is a channel used to send downlink control information (DCI) from base station device 200 to terminal device 100.

[0091] The Physical Downlink Shared Channel (PDSCH) is a channel used for transmitting data from the base station device 200 to the terminal device 100 from the upper layer.

[0092] The Physical Uplink Control Channel (PUCCH) is a channel used to send uplink control information (UCI) and the like from the terminal device 100 to the base station device 200.

[0093] The Physical Uplink Shared Channel (PUSCH) is a channel used for transmitting data from the terminal device 100 to the base station device 200 from the upper layer.

[0094] The Physical Random Access Channel (PRACH) is a channel used to send random access preambles, etc., from terminal device 100 to base station device 200.

[0095] <2. Transmission Channel>

[0096] The broadcast channel (BCH) is mapped to the PBCH, which is the physical channel.

[0097] The downlink shared channel (DL-SCH) is mapped to the PDSCH, which is a physical channel.

[0098] The paging channel (PCH) is mapped to the PDSCH, which is the physical channel.

[0099] The downlink shared channel (UL-SCH) is mapped to the PUSCH, which is a physical channel.

[0100] The Random Access Channel (RACH) is mapped to the PRACH, which is a physical channel.

[0101] <3. Logical Channel>

[0102] The Broadcast Control Channel (BCCH) is a downlink channel used to broadcast system information and is mapped to the BCH or DL-SCH of the transport channel.

[0103] The paging control channel (PCCH) is a downlink channel for carrying paging messages and is mapped to the PCH of the transport channel.

[0104] The common control channel (CCCH) is a channel for transmitting control information (such as RRC messages) between the terminal device 100 and the base station device 200, and is a channel for the terminal device 100 that does not maintain an RRC connection (does not have an RRC connection) with the base station device 200. The downlink is mapped to the DL-SCH of the transport channel, and the uplink is mapped to the UL-SCH of the transport channel.

[0105] The dedicated control channel (DCCH) is a point-to-point two-way channel for transmitting dedicated control information (such as RRC messages) between the terminal device 100 and the base station device 200, and is used for the terminal device 100 that has an RRC connection with the base station device 200. The downlink is mapped to the DL-SCH of the transport channel, and the uplink is mapped to the UL-SCH of the transport channel.

[0106] The dedicated transport channel (DTCH) is a point-to-point terminal dedicated two-way channel for transmitting user information (user data). The downlink is mapped to the DL-SCH of the transport channel, and the uplink is mapped to the UL-SCH of the transport channel.

[0107] The MBS control channel (MCCH) is a point-to-multipoint downlink channel and is used to transmit multicast broadcast service (MBS) broadcast control information corresponding to one or more MBS traffic channels (MTCH) from the base station device 200 to the terminal device 100. The downlink is mapped to the DL-SCH of the transport channel.

[0108] The MTCH is a point-to-multipoint downlink channel and is used to transmit multicast session data or broadcast session data of MBS from the base station device 200 to the terminal device 100. The downlink is mapped to the DL-SCH of the transport channel.

[0109] <RRC state (mode)>

[0110] The RRC state of the terminal device 100 is a state related to the RRC connection of the terminal device 100. The state in which no RRC connection with the base station device 200 is established is called the RRC idle mode (RRC_IDLE). The state in which an RRC connection with the base station device 200 is established is called the RRC connected mode (RRC_CONNECTED). The state in which the RRC connection with the base station device 200 is temporarily stopped (paused) is called the RRC inactive mode (RRC_INACTIVE). In the case where the core network 300 is an EPC, the state in which the RRC connection with the base station device 200 is temporarily stopped is not called the RRC inactive mode and may be called other names such as RRC suspension.

[0111] <RRC message>

[0112] The RRC messages will be described. RRC messages are messages that include information required for communication in a cell, including a master information block (MIB), a set of system information blocks (SIB), etc. The parameters included in the RRC messages may be called fields or information elements (IEs).

[0113] RRC messages include messages related to RRC connection establishment. In the case of NR, examples of messages related to the establishment of an RRC connection include an RRC setup request message (RRCSetupRequest), an RRC setup message (RRCSetup), and an RRC setup complete message (RRCSetupComplete). In the case of E-UTRA, examples of messages related to the establishment of an RRC connection include an RRC connection establishment request message (RRCConnectionSetupRequest), an RRC connection establishment message (RRCConnectionSetup), and an RRC connection establishment complete message (RRCConnectionSetupComplete).

[0114] 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 a security mode command message (SecurityModeCommand).

[0115] RRC messages include messages related to the reconfiguration of RRC connections. In the case of NR, examples of RRC connection reconfiguration-related messages include the RRC Reconfiguration message (RRCReconfiguration) and the RRC Reconfiguration Complete message (RRCReconfigurationComplete). In the case of E-UTRA, examples of RRC connection reconfiguration-related messages include the RRC Connection Reconfiguration message (RRCConnectionReconfiguration) and the RRC Connection Reconfiguration Complete message (RRCConnectionReconfigurationComplete). RRC connection reconfiguration-related messages perform the establishment, configuration, modification, and release of radio bearers, cell groups, etc., as described later, as well as synchronization reconfiguration, and also perform the establishment, configuration, modification, and release of measurement information, etc.

[0116] After performing the initial activation of AS security, terminal device 100 receives a first RRC reconfiguration message from base station device 200 to obtain all or all minimum necessary configurations required for communication (data communication) with base station device 200 in the cell to which terminal device 100 is connected. All or all minimum necessary configurations required for communication (data communication) with base station device 200 may be referred to as, for example, a complete configuration.

[0117] After the initial activation of AS security in terminal device 100, base station device 200 may send a first RRC reconfiguration message, further send another RRC reconfiguration message, and cause terminal device 100 to update the configuration required for communication (data communication) with base station device 200. In this case, base station device 200 includes a configuration different from the complete configuration currently configured in terminal device 100 in the RRC reconfiguration message and sends the RRC reconfiguration message. The differing configuration may be referred to as the incremental configuration. When receiving an RRC reconfiguration message including the incremental configuration, terminal device 100 generates a new setting by applying the incremental configuration to the currently used complete configuration.

[0118] In addition, RRC messages include messages related to RRC connection re-establishment. In the NR case, examples of messages related to RRC connection re-establishment include: RRC Reestablish Request, RRC Reestablish, and RRC Reestablish Complete. In the E-UTRA case, examples of messages related to RRC connection establishment include: RRC Connection Reestablish Request, RRC Connection Reestablish, and RRC Connection Reestablish Complete.

[0119] RRC messages also include messages related to the release or suspension of RRC connections, messages related to the restoration of RRC connections, messages related to the capabilities of the terminal device, messages related to terminal information, and messages related to MCG or SCG fault information.

[0120] In MR-DC, when the primary node is an eNB, the eNB can include the NR RRC message or parameters received from the gNB (as a secondary node) as a container in an E-UTRA RRC message and send it to the terminal device 100, thereby allowing NR-related configuration to be performed in the terminal device 100. The terminal device 100 can also include the completion message of the NR-related configuration as a container in an E-UTRA RRC message and send it to the eNB (as the primary node).

[0121] In MR-DC, when the master node is a gNB, the gNB can include the E-UTRA RRC message and parameters received from the eNB (which is the secondary node) as a container in an NR RRC message and send it to the terminal device 100, allowing E-UTRA-related configuration to be performed in the terminal device 100. The terminal device 100 can also include the completion message of the E-UTRA-related configuration as a container in an NR RRC message and send it to the gNB (which is the master node).

[0122] Figure 6 This is a diagram illustrating an example of the message format for RRCReconfiguration. Format E1 represents the parameters for RRC reconfiguration.

[0123] RRCReconfiguration takes radioBearerConfig, radioBearerConfig2, masterCellGroup, secondaryCellGroup, masterKeyUpdate, and sk-counter as parameters.

[0124] radioBearerConfig and radioBearerConfig2 are configurations related to the MN or SN termination bearer, and include SRB configuration, DRB configuration, security configuration, etc. SRB configuration (DRB configuration) includes the SRB identifier (DRB identifier), PDCP configuration, parameters indicating PDCP re-establishment, etc. Security configuration includes parameters indicating whether to use a master key or a secondary key (keyToUse).

[0125] `masterCellGroup` and `secondaryCellGroup` are the MCG and SCG configurations, respectively, and include cell group identifiers, RLC bearer configurations, and SpCell configurations. RLC bearer configurations include logical channel identifiers, RLC configurations, and radio bearer identifiers associated with the RLC bearer (SRB identifiers or DRB identifiers). SpCell configurations include information required for synchronization reconfiguration.

[0126] masterKeyUpdate includes the information needed to update the master key.

[0127] sk-counter contains the information needed to generate the secondary key.

[0128] Format E11 is a diagram showing an example of the parameters included in RadioBearerConfig within RRCReconfiguration.

[0129] Format E12 is a diagram showing an example of the parameters included in CellGroupConfig in RRCReconfiguration.

[0130] Format E111 is a diagram showing an example of the parameters included in RadioBearerConfig for SRB-ToAddMod.

[0131] Format E112 is a diagram showing an example of the parameters included in RadioBearerConfig for DRB-ToAddMod.

[0132] Format E113 is a diagram showing an example of the parameters of SecurityConig included in RadioBearerConfig.

[0133] Format E121 is a diagram showing an example of the parameters of RLC-BearerConfig included in CellGroupConfig.

[0134] Format E122 is a diagram showing an example of the parameters of SpCellConfig included in CellGroupConfig.

[0135] <Radio bearer>

[0136] Examples of radio bearers of the communication system 10 will be described.

[0137] <1. Signaling radio bearer>

[0138] A signaling radio bearer (SRB) is a radio bearer for transmitting RRC messages and NAS messages.

[0139] SRB0 is a radio bearer for RRC messages using the CCCH logical channel.

[0140] SRB1 is a radio bearer for RRC messages and NAS messages using the DCCH logical channel, and is established before the establishment of SRB2 described later. [[ID="26"]]

[0141] SRB2 is a radio bearer for RRC messages and NAS messages including measurement information of the logged history, and uses the DCCH logical channel. The priority of SRB2 is lower than that of SRB1, and SRB2 can be configured by the base station device 200 after AS security activation.

[0142] SRB3 is a radio bearer for RRC messages in the case where the terminal device 100 configures EN-DC, NGEN-DC or NR-DC, and uses the DCCH logical channel. It should be noted that EN-DC, NGEN-DC and NR-DC are types of MR-DC, and the details of the MR-DC type will be described later.

[0143] <2. Data radio bearer>

[0144] A data radio bearer (DRB) is a radio bearer for transmitting user data.

[0145] <Protocol configuration of SRB and DRB>

[0146] The protocol configuration of SRB and DRB of the terminal device 100 will be described.

[0147] There is no PDCP entity in SRB0, and SRB0 is configured with an RLC bearer. The RLC bearer includes an RLC entity and a MAC logical channel. The mode of the RLC entity in SRB0 is TM.

[0148] Each of SRB1 and SRB2 includes a PDCP entity and one or more RLC bearers. The mode of the RLC entity is AM.

[0149] SRB3 consists of a PDCP entity and an RLC bearer. The RLC entity is in AM mode.

[0150] A DRB consists of a PDCP entity and one or more RLC bearers. The RLC entity's mode is UM or AM. When the RLC entity is UM, the DRB may be called a UM DBR, and when the RLC entity is AM, the DBR may be called an AM DRB. A DRB is associated with an SDAP when the core network 300 is 5GC, and with an EPS bearer (or EPS bearer identifier (EPS bearer identifier)) when the core network 300 is EPC.

[0151] It should be noted that it is assumed that there is one MAC entity for each cell group, which will be described later.

[0152] <Neighborhood and Neighborhood Group>

[0153] The cells and cell groups (CGs) configured in the terminal device 100 will be described.

[0154] A cell group may include a special cell (SpCell). A cell group may include one SpCell and one or more secondary cells (SCells). It should be noted that the SpCell within the primary cell group (MCG) described later may be referred to as the primary cell (PCell). The SpCell within the secondary cell group (SCG) described later may be referred to as the primary SCG cell (PSCell).

[0155] A PCell is a cell on the primary frequency and is used to establish or re-establish an RRC connection. That is, when establishing or re-establishing an RRC connection, the cell selected by the terminal device 100 is used as the PCell. When the base station device 200 requests handover to the terminal device 100 (described later), the new PCell specified by the base station device 200 is used for random access.

[0156] SCell is a cell that provides additional radio resources in addition to SpCell when carrier aggregation (CA) is configured in terminal device 100.

[0157] A PSCell is a cell on the primary frequency of the SCG. The PSCell is designated by the base station device 200 and is used for random access when adding or changing PSCells within the SCG.

[0158] It should be noted that the cell used by terminal device 100 to communicate with base station device 200 in RRC connection state can also be called the serving cell. In the absence of CA configuration, SpCell is used as the serving cell; and in the presence of CA configuration, both SpCell and SCell are used as serving cells.

[0159] When dual connectivity (DC) is not configured in terminal device 100, MCG is CG; and when DC is configured in terminal device 100, MCG is CG belonging to the master node (MN). DC is a technology in which terminal device 100 wirelessly connects to base station device 200 as the master node and base station device 200 as the secondary node (SN) and performs wireless communication using the carriers (cell groups) of the respective base station devices 200.

[0160] SCG is a CG that is configured as an auxiliary node in addition to MCG when DC is configured in terminal device 100.

[0161] Figure 7 This is a diagram illustrating an example configuration of a cell group in communication system 10. Figure 7 In this configuration, the primary node (MN) is base station device 200-1, and the secondary node (SN) is base station device 200-2. The primary node is base station device 200 that provides C-Plane connectivity to the core network 300 in the DC. The secondary node is base station device 200 in the MR-DC that does not provide C-Plane connectivity to the core network 300 but provides additional radio resources to the terminal device 100. Figure 7 In this context, the MCG comprises one PCell and two SCells. Figure 7 In this context, the SCG consists of one PSCell and two SCells.

[0162] Base station device 200 can configure a bandwidth portion (BWP) in a cell to be configured in terminal device 100, and can adjust the cell to use a limited frequency bandwidth across the entire frequency band of the cell. The BWP can be configured based on a portion of the frequency bandwidth of each cell's frequency band. Multiple (e.g., up to four) BWPs can be configured in each cell. BWPs can be configured via RRC reconfiguration messages. In each cell, the BWP to be used can be specified or switched via RRC reconfiguration messages or by using DCI.

[0163] <Synchronous Reconfiguration>

[0164] Synchronization reconfiguration will be described. Synchronization reconfiguration (reconfiguration with synchronization / reconfiguration with sync) refers to the process performed in terminal device 100 by including parameters (reconfigurationWithSync: (hereinafter sometimes referred to as synchronization reconfiguration parameters) indicating that synchronization reconfiguration should be performed) in the RRC reconfiguration message (RRCReconfiguration) sent from base station device 200 to terminal device 100.

[0165] Synchronous reconfiguration parameters are included under parameters for MCG configuration (hereinafter sometimes referred to as MCG configuration parameters) and parameters for SCG configuration (hereinafter sometimes referred to as SCG configuration parameters), respectively. That is, synchronous reconfiguration refers to synchronous reconfiguration of the MCG when the parameter is included in the MCG configuration parameters, and synchronous reconfiguration of the SCG when the parameter is included in the SCG configuration parameters.

[0166] Synchronous reconfiguration is the process by which terminal device 100 changes the SpCell, and includes operations such as randomly accessing a new (changed destination, target) SpCell, MAC reset, and PDCP data recovery (in the case of AM DRB).

[0167] The process when the MCG configuration parameters include synchronization reconfiguration parameters can be referred to as handover. The process when the SCG configuration parameters include synchronization reconfiguration parameters can be referred to as PSCell addition and / or PSCell change. The PCell / PSCell before the change can be referred to as the source PCell / source PSCell, and the PCell / PSCell after the change can be referred to as the target PCell / target PSCell. Since synchronization reconfiguration may involve CA, the term "serving cell" can be used to refer to both the source serving cell and the target serving cell. The term "serving" can be omitted to refer to the source cell and the target cell.

[0168] Terminal device 100 can generate the configuration of the target cell by applying the incremental configuration included in the RRC reconfiguration message to the configuration of the source cell.

[0169] Synchronous reconfiguration may involve changing the security key. In this case, in addition to the above, a PDCP re-establishment is also performed.

[0170] When the security key changes, the RRC of the terminal device 100 generates a new key and re-establishes the PDCP so that the new key is applied to the PDCP.

[0171] Figure 8This diagram illustrates an example of the process when synchronization reconfiguration parameters are included in the parameters used to configure the MCG. Synchronization reconfiguration parameters include settings such as the target PCell configuration, the new cell radio network temporary identifier (C-RNTI), RACH configuration, and a timer for detecting handover failure. Terminal device 100 performs random access (RA) in the target PCell according to the configuration and changes the current source PCell to the target PCell (S1).

[0172] Random access during the handover period

[0173] Random access during handover includes contention-free random access (CFRA, i.e., random access without contention) and contention-based random access. Contention-based random access (CBRA) exists, and random access can be performed in a four-step process or a two-step process.

[0174] Figure 9 This is a diagram illustrating the handover process through four steps of random access. Figure 9 (A) illustrates the handover process via a four-step CFRA, and Figure 9 (B) illustrates the handover process via a four-step CBRA.

[0175] will describe Figure 9 (A) sequence.

[0176] The base station device 200 sends an RRC reconfiguration message, which includes synchronization reconfiguration parameters, to the terminal device 100 (S901).

[0177] When the synchronization reconfiguration parameters include a four-step CFRA configuration and a reference signal with a Reference Signal Received Power (RSRP) equal to or greater than a threshold exists among the reference signals specified in the four-step CFRA configuration, the terminal device 100 uses four-step CFRA to perform handover. When the synchronization reconfiguration parameters include a two-step CFRA configuration and a reference signal with an RSRP equal to or greater than a threshold exists among the reference signals specified in the two-step CFRA configuration, the terminal device 100 uses two-step CFRA to perform handover. Furthermore, when the synchronization reconfiguration parameters do not include either a four-step CFRA configuration or a two-step CFRA configuration, or when the synchronization reconfiguration parameters include either a four-step CFRA configuration or a two-step CFRA configuration but no reference signal with an RSRP equal to or greater than a threshold exists among the reference signals specified in the four-step CFRA configuration or the two-step CFRA configuration, the terminal device 100 performs either four-step CBRA or two-step CBRA.

[0178] Terminal device 100 sends the random access preamble (RA preamble) to base station device 200 on the target PCell (S902).

[0179] When the random access preamble is received (S902), the base station device 200 sends a random access response (RA response) (S903).

[0180] In the case of CFRA, the preamble is included in the CFRA configuration, and therefore contention resolution is not required. Thus, when the terminal device 100 receives the random access response on the target PCell, the handover is successful.

[0181] When a random access response is received (S903), the terminal device 100 sends an RRC reconfiguration complete message to the base station device 200 on the target serving cell. This message is a response message to the RRC reconfiguration message (S904).

[0182] Next, we will describe Figure 9 (B) sequence.

[0183] The base station device 200 sends an RRC reconfiguration message including synchronization reconfiguration parameters to the terminal device 100 (S905). Since the synchronization reconfiguration parameters do not include CFRA configuration, the terminal device 100 uses CBRA to perform the handover (two-step or four-step).

[0184] Terminal device 100 sends a random access preamble to base station device 200 on the target PCell (S906).

[0185] When the random access preamble is received (S906), the base station device 200 sends a random access response (S907).

[0186] In the case of CBRA, since an arbitrary random access preamble is used, there is a possibility of contention with the random access preamble sent by another terminal device. Therefore, when terminal device 100 receives the random access response (S907), the handover is not yet considered successful.

[0187] When a random access response is received (S907), the terminal device 100 sends an RRC reconfiguration complete message to the base station device 200 on the target serving cell (S908).

[0188] When the RRC reconfiguration complete message is received (S907), the base station device 200 sends the contention-resolved MAC CE to the terminal device 100 on the target serving cell (S908).

[0189] In the case of CBRA, when the terminal device 100 receives the MAC CE indicating contention resolution, the handover is successful (S908).

[0190] In a handover using the four-step CFRA, the RRC reconfiguration completion message (S904) is sent after the handover is successful. However, in a handover using the four-step CBRA, the RRC reconfiguration completion message (S908) is sent before the handover is successful.

[0191] If the uplink resources allocated in step S907 are sufficiently large, in step S908, the terminal device 100 can not only send the RRC reconfiguration completion message, but also send the uplink data generated on the DRB. That is, in the handover using the four-step CBRA, there is a possibility that the uplink data generated on the DRB may be sent before the handover is successful.

[0192] In the case of handover using two-step random access, in both CBRA and CFRA, after sending the random access preamble in step S902 and before receiving the random access response in step S903, the terminal device 100 sends an RRC reconfiguration complete message in step S904. In handover using two-step random access, in either CFRA or CBRA, since the RRC configuration complete message is sent before successful handover, there is a possibility that uplink data generated on the DRB may be sent before successful handover.

[0193] In E-UTRA, a RACH-free handover can be performed as a handover that does not involve random access. In a RACH-free handover, an RRC reconfiguration complete message is sent to the base station device 200 of the target serving cell without performing random access, and the handover is successful when a MAC CE indicating contention resolution is received from the base station device 200 of the target serving cell. In a RACH-free handover, since the RRC reconfiguration complete message is sent before the handover is successful, there is a possibility that uplink data generated on the DRB may be sent before the handover is successful.

[0194] Handling of Transfer Failures

[0195] If the handover fails within a certain period of time after receiving an RRC reconfiguration message including synchronization reconfiguration parameters, the handover is considered to have failed. The failure to handover within a certain period corresponds to the timeout of a handover failure detection timer started upon receiving the RRC reconfiguration message including synchronization reconfiguration parameters before successful handover.

[0196] In the event of a handover failure, terminal device 100 will restore the configuration to the configuration used in the source PCell and perform an RRC connection re-establishment procedure. When restoring to the configuration used in the source PCell, the values ​​of the state variables in each entity of each radio bearer will also be restored to the values ​​used in the source (values ​​prior to the handover process).

[0197] During the RRC connection re-establishment process, terminal device 100 performs cell selection and, if an NR cell is selected, sends an RRC Reestablishment Request message (RRCReestablishmentRequest) to base station device 200. The RRC Reestablishment Request message is sent via SRB0. Since there is no PDCP entity in SRB0, PDCP security processing is not performed on the RRC Reestablishment Request message. When an RRC Reestablishment message (RRCReestablishment) is received from base station device 200 as a response to the RRC Reestablishment Request message, the security key of terminal device 200 is updated.

[0198] <Conditional Transfer>

[0199] Conditional handover (CHO) is a handover initiated by terminal device 100 when one or more handover execution conditions are met. Terminal device 100 receives an RRC reconfiguration message including conditional reconfiguration parameters from base station device 200 and stores these parameters. The conditional reconfiguration parameters include one or more pairs of configuration parameters (including synchronization reconfiguration parameters) for PCell change destination candidates and execution condition parameters for performing handover to the PCell change destination candidate. Execution condition parameters include, for example, parameters related to measurement configuration. Upon receiving the conditional reconfiguration parameters, terminal device 100 begins performing measurements on the cell and, if the execution conditions are met in any PCell of the measured cell, applies the configuration parameters of the PCell change destination candidate for the PCell that meets the execution conditions, and performs a conditional handover to the PCell. Terminal device 100 releases the conditional reconfiguration parameters after successful conditional handover.

[0200] The conditional reconfiguration parameters may include one or more pairs of SCG-side configurations, namely, configuration parameters for the PSCell change destination candidate and execution condition parameters for performing a change to the PSCell change destination candidate. Upon receiving the conditional reconfiguration parameters from the SCG side, the terminal device 100 begins measuring the execution conditions and performs a conditional PSCell change (CPC) if the measurement results meet the execution conditions.

[0201] In conditional handover, a handover failure is detected in a similar manner to unconditional handover (hereinafter, in some cases simply referred to as handover), and the processing after the handover failure is performed. During the RRC connection re-establishment process after a conditional handover failure or a handover failure, when the selected cell is a candidate for the PCell change destination, the terminal device 100 sends an RRC reconfiguration complete message to the base station device 200 to attempt a handover instead of sending an RRC re-establishment request message, and the RRC connection can be restored. When the cell selected by the terminal device 100 is a candidate for the PCell change destination, the RRC reconfiguration complete message can be sent to the base station device 200 only when the conditional reconfiguration attempt parameter (attemptCondReconfig), which is configured as a parameter allowed for processing in the terminal device 100, instead of sending the RRC re-establishment request message to the base station device 200.

[0202] <AS Security and Key Stream>

[0203] The processing of AS security is performed in the PDCP entity of the radio bearer other than SRB0 by using the security keys (encryption key, integrity protection key) generated by RRC. The AS security processing includes encryption (encryption / ciphering) and integrity protection, which are performed using the encryption key and the integrity protection key, respectively.

[0204] When a PDCP SDU is received from the upper layer, the PDCP entity of each radio bearer performs AS security processing on the received PDCP SDU by using an input called a key stream. The key stream includes four elements, for example, KEY, COUNT, BEARER, and DIRECTION.

[0205] KEY indicates, for example, the security key.

[0206] COUNT is one of the state variables of the PDCP entity and indicates, for example, a sequence number. The initial value of the COUNT value is '0', and each time a PDCP PDU is passed to the lower layer, the COUNT value is incremented by 1. The maximum value of the COUNT value is, for example, the value obtained by subtracting 1 from 2 to the 32nd power, that is, '4294967295'.

[0207] BEARER indicates, for example, the value of the radio bearer identifier. DIRECTION indicates the uplink or downlink, '0' indicates the uplink, and '1' indicates the downlink.

[0208] In AS security, from a security perspective, reusing the key stream (key stream reuse) is prohibited. For example, in the terminal device 100, when transmitting data from a certain radio bearer, unless the security key is updated, it is prohibited to use the COUNT value that has been used in the past in that radio bearer to perform AS security processing.

[0209] It should be noted that the definition of the term "key stream" may vary slightly depending on the specification. In this embodiment, the key stream will be described as four elements, KEY, COUNT, BEARER, and DIRECTION.

[0210] [Embodiment]

[0211] In the following, each embodiment will be described.

[0212] <L1 / L2 Triggered Mobility>

[0213] An overview of L1 / L2 triggered mobility (LTM) currently under the specification will be described.

[0214] Figure 10 It is a diagram showing an example of the LTM sequence.

[0215] The base station device 200 sends an RRC reconfiguration message to the terminal device 100, which includes one or more configurations of the cell change destination candidate (configuration of the target cell candidate) (S1001).

[0216] When receiving the RRC reconfiguration message (S1001), the terminal device 100 stores the information included in the received message (including the cell change destination candidate).

[0217] It should be noted that the cell change destination candidate may be, for example, only the PCell or may include the SCell. Each configuration of the cell change destination candidate only needs to be able to be uniquely specified in the terminal device 100 using an index. The configuration of the cell change destination candidate does not include a parameter indicating a security key update. That is, the security key used in LTM is not updated. The configuration of the cell change destination candidate may include parameters similar to the synchronization reconfiguration parameters.

[0218] Terminal device 100 may retain the configuration of the cell change destination candidate received and stored in step S1001, and will not release the configuration after a successful cell handover, as described later. In this case, the saved configuration of the cell change destination candidate can be used for cell handover (subsequent sell handover). However, if the configuration of the cell change destination candidate is retained and used for subsequent cell handover, the configuration of the cell change destination candidate may not be configured as an incremental configuration, and the incremental configuration may not be applied to the source configuration to generate the configuration of the target cell. This occurs because the source configuration differs depending on the cell order changed due to the cell handover.

[0219] Therefore, in step S1001, in addition to the configuration of the cell change destination candidate, or as part of the configuration of the cell change destination candidate, the RRC reconfiguration message may also include a reference configuration. The reference configuration is, for example, a complete configuration. When a reference configuration is included in the RRC reconfiguration message, the configuration of each cell change destination candidate included in the RRC reconfiguration message may be a different configuration from the reference configuration (incremental configuration). That is, the terminal device 100 can generate the configuration used in the cell handover destination (target) based on the reference configuration and the configuration of the cell change destination candidate (incremental configuration). For example, when a cell handover signal to cell X, which is a cell change destination candidate, is received from the base station device 200 in step S1002, described later, the terminal device 100 generates the configuration used in cell X by applying the configuration of cell X to the reference configuration.

[0220] In step S1001, the RRC reconfiguration message may not include a reference configuration. When the reference configuration is not included in the RRC reconfiguration message, the configuration included in each cell change destination candidate in the RRC reconfiguration message is, for example, a complete configuration. That is, the terminal device 100 can generate the configuration used in the cell handover destination (target) by replacing the configuration used in the current cell with the configuration of the cell change destination candidate. For example, when a cell handover signal to cell X, which is a cell change destination candidate, is received from the base station device 200 in step S1002, described later, the terminal device 100 generates the configuration used in cell X by replacing the current configuration of the cell with the configuration of cell X. However, when the configuration of the cell change destination candidate is a complete configuration, certain configurations may not be included. Some configurations include, for example, configurations that do not change due to cell handover (fixed configurations). Configurations that do not change due to cell handover (fixed configurations) include, for example, some or all radio bearer configurations. In this case, when the base station device 200 receives a cell handover signal to cell X, which is a candidate for cell change destination, the terminal device 100 generates the configuration used in cell X by replacing the current configuration of the cell with the configuration of cell X other than the fixed configuration.

[0221] Regardless of whether the RRC reconfiguration message includes a reference configuration, the terminal device 100 does not need to return some or all 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 the configuration used in the cell handover destination. The terminal device 100 does not need to discard some or all buffers in each entity. That is, the terminal device 100 can retain some or all values ​​of state variables, timers, etc. used by each entity. The terminal device 100 can retain some or all buffers in each entity.

[0222] The base station device 200 sends a cell handover signal to the terminal device 100 (S1002) to enable the terminal device 100 to switch its serving cell from the current serving cell to one of the cell change destination candidates.

[0223] Terminal device 100 receives a cell handover signal in the current serving cell (S1002). For example, MAC CE is used as the cell handover signal. Alternatively, a physical layer signal such as DCI can be used as the cell handover signal.

[0224] The cell handover signal includes at least an index. Terminal device 100 applies the configuration of the cell change destination candidate (referred to as cell X) specified by the received cell handover signal. It should be noted that cell X may include only PCell, or may include PCell and one or more SCells.

[0225] Depending on the configuration of cell X, terminal device 100 and base station device 200 in cell X perform a four-step or two-step CFRA or CBRA (S1003). Furthermore, if the configuration of cell X includes parameters indicating that a cell handover without RACH is to be performed, the processing in step S1003 is not performed.

[0226] Terminal device 100 sends a notification indicating that the cell has been handed over to base station device 200 in cell X (S1004). This notification corresponds to an RRC reconfiguration completion message in handover or conditional handover. For the notification indicating that the cell has been handed over, an RRC message such as an RRC reconfiguration completion message can be used, or a MAC CE can be used. For the notification indicating that the cell has been handed over, a physical signal such as UCI can be used.

[0227] The notification indicating that a cell has been handed over may include at least the identifier of the terminal device 100 in cell X. In the case of performing a two-step CFRA or CFRA in step S1003, the notification indicating that a cell has been handed over is sent before receiving the random access response in step S1003. The uplink data generated in the DRB may be sent together with the notification indicating that a cell has been handed over.

[0228] In step S1003, when performing a four-step or two-step CBRA or when performing a cell handover without RACH, the base station device 200 sends a contention resolution signal to the terminal device 100 (S1005).

[0229] For example, terminal device 100 receives a contention resolution signal in cell X (S1005). The contention resolution signal may include at least the identifier of terminal device 100 in cell X.

[0230] The timing of a successful cell handover can be similar to that of a successful handover in a transfer or conditional handover. That is, in the case of a cell handover using four-step or two-step CFRA, the handover is successful upon receiving a random access response. Furthermore, in the case of a cell handover using four-step or two-step CBRA or without RACH, the handover is successful during contention resolution. In cases where the timing of a successful cell handover is similar to that of a successful handover in a transfer or conditional handover, similar to a transfer in a transfer or conditional handover, in a cell handover using four-step CFRA, neither a notification indicating that the cell has been handed over nor uplink data generated in the DRB is sent before the cell handover is successful. However, in cases of a cell handover using four-step CBRA, a cell handover using two-step CFRA or CBRA, and a cell handover without RACH, a notification indicating that the cell has been handed over can be sent before the cell handover is successful, and the uplink data generated in the DRB can be sent along with this notification.

[0231] Terminal device 100 may perform downlink synchronization and / or uplink synchronization with one or more cell change destination candidates after executing step S1001 and before sending a cell handover signal in step S1002. Base station device 200 may measure the timing advance (TA) of one or more cell change destination candidates of terminal device 100 during uplink synchronization. Uplink synchronization may be performed by instructing base station device 200 to send a random access preamble. Base station device 200 may instruct terminal device 100 to send different random access preambles to one or more cell change destination candidates, or may instruct a group of multiple cell change destination candidates to send a common random access preamble. The TA measured by base station device 200 may be sent to terminal device 100 using a random access response (RAR), or may be sent to terminal device 100 using a cell handover signal in step S1002. In this manner, performing uplink synchronization after terminal device 100 executes step S1001 and before sending a cell handover signal in step S1002 may be referred to as early TA measurement or early TA acquisition.

[0232] It should be noted that cell handover can be interpreted as LTM. Cell handover can also be interpreted as another term indicating a cell handover performed by LTM. In the following text, cell handover and cell change can be considered as the same term.

[0233] <Cell handover failure handling>

[0234] In the event of a cell handover failure, the RRC connection re-establishment process can be performed in a manner similar to certain handover failure handling or conditional handover failure handling.

[0235] Figure 11 This is a diagram illustrating an example of the sequence for cell handover failure detection and cell handover failure handling. Figure 11 The processing of steps 1001 and 1002 is similar to Figure 10 The processing of steps 1001 and 1002 in the process.

[0236] When a cell handover signal is received (S1002), the terminal device 100 starts a timer for detecting cell handover failure (S1101) and begins cell handover processing to the cell (referred to as cell X) specified by the received cell handover signal (not shown).

[0237] If the cell handover 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 handover to cell X has failed (S1102).

[0238] When a cell handover failure is detected (S1102), the terminal device 100 performs cell handover failure processing (S1103). In the cell handover failure processing, the terminal device 100 may restore the configuration used in the source PCell and perform the RRC connection re-establishment procedure.

[0239] Keystream reuse issues in cell handover failure handling

[0240] In LTM, during the RRC connection re-establishment process in cell handover failure handling, it has been proposed that if the selected cell is one of the cell change destination candidates, the RRC connection be restored in the same way as in the conditional handover case. That is, a cell handover to the selected cell is performed instead of sending an RRC re-establishment request message in the selected cell (e.g., Non-Patent Document 10 and Non-Patent Document 11).

[0241] However, when the selected cell is one of the cell change destination candidates in the RRC connection re-establishment process after a cell handover failure using four-step CBRA, a cell handover failure using two-step CFRA or CBRA, or a cell handover failure without RACH, processing the cell handover to the selected cell instead of sending the RRC re-establishment request message in the selected cell may lead to key stream reuse issues.

[0242] As described above, in cell handovers using four-step CBRA, two-step CFRA or CBRA, and cell handovers without RACH, uplink data may be sent along with a notification indicating that the cell has been handed over before the handover is successful. If the notification indicating that the cell has been handed over is an RRC message sent by an SRB other than SRB0 (e.g., SRB1), this RRC message undergoes processing, including security processing, in the PDCP entity of SRB1 and is sent via the lower layer as a PDCP data PDU. Assume that the COUNT value for security processing in the PDCP entity of the RRC message is, for example, n.

[0243] When uplink data is sent from a DRB (referred to as DRB1) along with a notification indicating that a cell has been handed over, the uplink data undergoes processing, including security processing, in the PDCP entity of DRB1 and is then sent via the lower layer as a PDCP data PDU. Assume the COUNT value used for the security processing of the uplink data (in the PDCP entity of the uplink data) is, for example, m.

[0244] In the event of a cell handover failure, terminal device 100 restores the configuration to that used in the source PCell and performs an RRC connection re-establishment procedure. When restoring to the configuration used in the source PCell, the values ​​of the state variables in each entity of each radio bearer are also restored to the values ​​used in the source, and therefore the COUNT value is restored to the state before the cell handover signal was received. During the RRC connection re-establishment procedure, if the selected cell is one of the cell change destination candidates and a cell handover to the selected cell is performed, terminal device 100 sends an RRC message in the cell as a notification indicating that the cell has been handed over. When the RRC message is sent, n is again used as the COUNT value in the security processing of the PDCP entity of SRB1. When DRB1 sends the first uplink message within the cell, m is again used as the COUNT value in the security processing of the PDCP entity of DRB1. In cell handover in LTM, the security key remains unchanged, and the same security key and the same COUNT value are used for the same direction (uplink) of the same radio bearer. That is, a key stream reuse problem may occur.

[0245] <Cell handover failure handling to avoid key stream reuse issues 1>

[0246] Figure 12 This is a diagram illustrating an example of a first cell handover failure handling method. The first cell handover failure handling method involves sending an RRC re-establishment request message to the base station device 200 in the selected NR cell when the cell selected by the terminal device 100 during the RRC connection re-establishment process is an NR cell, regardless of whether the NR cell is one of the cell change destination candidates.

[0247] Terminal device 100 detected a cell handover failure to cell X (S1102).

[0248] Next, the terminal device 100 restores the configuration to the configuration used in the source PCell and performs the RRC connection re-establishment procedure (S1201). In the case of restoring to the configuration used in the source PCell, the values ​​of the state variables in each entity of each radio bearer are also restored to the values ​​used in the source. Figure 11 The value at the time the cell handover signal is received in step S1002 (or the value before the cell handover signal is received). It should be noted that when performing the RRC connection re-establishment procedure, the terminal device 100 may release the stored configuration of the cell change destination candidate. In the case of releasing the stored configuration of the cell change destination candidate, the release process can be performed before the processing in step S1202, which will be described later.

[0249] During the RRC connection re-establishment process, terminal device 100 performs cell selection and selects, for example, an NR cell. Terminal device 100 sends an RRC re-establishment request message to base station device 200 in the selected NR cell (S1202).

[0250] During RRC connection re-establishment, if the selected cell is a RAT other than NR, the terminal device 100 switches to RRC idle mode. If a cell cannot be selected within a certain time period, the terminal device 100 switches to RRC idle mode.

[0251] <Cell handover failure handling to avoid key stream reuse issues 2>

[0252] Figure 13 This is a diagram illustrating an example of a second cell handover failure handling method. The second cell handover failure method involves, if the cell selected by the terminal device 100 is one of the cells that meets a second condition and at least a first condition is met during the RRC connection re-establishment process in the cell handover failure handling, applying the configuration of the cell change destination candidate for the selected cell and performing cell handover processing to the selected cell.

[0253] The second condition includes, for example, that the cell is a candidate cell change destination stored in the terminal device 100. Furthermore, the second condition includes, for example, that the cell is a cell permitted to restore RRC connection after a cell handover failure.

[0254] Cells permitted to restore RRC connections after a cell handover failure include, for example, candidate cells for cell change destinations stored in terminal device 100, and cells that belong to the same group as the cell that failed the handover (e.g., cell X). For example, whether a cell belongs to the same group as cell X is determined by a group identifier pre-configured in the configuration of the candidate cell change destinations.

[0255] Cells that can restore RRC connections after a cell handover failure include, for example, cells that are cell change destination candidates stored in terminal device 100, and the configuration of cell change destination candidate cells includes information indicating that RRC connections can be restored after a cell handover failure.

[0256] If the cell selected by the terminal device 100 is one of the cells that meets the second condition and at least meets the first condition, for example, if at least the first parameter is configured in the terminal device 100, the process of applying the cell change destination candidate configuration of the selected cell and performing cell handover on the selected cell can be executed.

[0257] Terminal device 100 detected a cell handover failure to cell X (S1102).

[0258] Next, terminal device 100 restores the configuration to the configuration used in the source PCell and performs the RRC connection re-establishment procedure (S1301). In the case of restoring to the configuration used in the source PCell, terminal device 100 restores the values ​​of the state variables in each entity of each radio bearer to the values ​​used in the source. Figure 11 The value at the time of receiving the cell handover signal in step S1002 or the value immediately preceding the receipt of the cell handover signal.

[0259] During the RRC connection re-establishment process, the terminal device 100 performs cell selection and performs processing based on the selected cell and the first condition (S1302).

[0260] The first condition is, for example, in Figure 11 After receiving the cell handover signal in step S1002, the cell handover process is performed in cell X through a four-step CFRA. That is, the configuration of the cell change destination candidate for cell X includes a four-step CFRA configuration.

[0261] The first condition could be, for example, in Figure 11After receiving the cell handover signal in step S1002, the cell handover process performed on cell X is carried out only through four-step CFRA. That is, the configuration of the cell change destination candidate of cell X includes four-step CFRA configuration, and there is a reference signal with RSRP equal to or greater than the threshold during the initial random access resource selection.

[0262] Furthermore, the first condition could be, for example, in Figure 11 After receiving the cell handover signal in step S1002, the cell handover process is performed in cell X through a four-step CFRA. That is, the configuration of the cell change destination candidate of cell X includes a four-step CFRA configuration, and this selection is the first cell selection after the cell handover failure is detected in step S1102.

[0263] The first condition could be, for example, in Figure 11 After receiving the cell handover signal in step S1002, the cell handover process performed in cell X is only performed through four-step CFRA. That is, the configuration of the cell change destination candidate of cell X includes four-step CFRA configuration. There is a reference signal with RSRP equal to or greater than the threshold during the initial random access resource selection, and this selection is the first cell selection after the cell handover failure is detected in step S1102.

[0264] The fact that only four-step CFRA cell handover processing is performed can be interpreted as performing four-step CFRA cell handover processing without sending the MAC PDU in the Message 3 (Msg3) buffer. The fact that only four-step CFRA cell handover processing is performed can also be interpreted as not performing four-step or two-step CBRA prior to the four-step CFRA cell handover processing.

[0265] Furthermore, the first condition could be, for example, in Figure 11 Between receiving the cell handover signal in step S1002 and detecting the cell handover failure in step S1102, PDCP data PDU is not sent from the terminal device 100 via the lower layer. That is, RRC messages are not sent from SRBs other than SRB0 and / or uplink data is not sent from DRBs.

[0266] Furthermore, the first condition could be, for example, in Figure 11 Between receiving the cell handover signal in step S1002 and detecting the cell handover failure in step S1102, the terminal device 100 does not send PDCP data PDUs via the lower layer. That is, RRC messages are not sent from SRBs other than SRB0 and / or uplink data is not sent from DRBs. This selection is the first cell selection after detecting the cell handover failure in step S1102.

[0267] Furthermore, the first condition could be, for example, in Figure 11 Between receiving the cell handover signal in step S1002 and detecting the cell handover failure in step S1102, the terminal device 100 only sends the first signal.

[0268] Furthermore, the first condition could be, for example, in Figure 11 Between receiving the cell handover signal in step S1002 and detecting the cell handover failure in step S1102, the terminal device 100 sends only a first signal, and this selection is the first cell selection after detecting the cell handover failure in step S1102.

[0269] The first signal is Figure 10 The notification sent in step S1004. The first signal may be, for example, a MAC CE. Alternatively, the first signal may be a physical layer signal.

[0270] Sending only the first signal from terminal device 100 may mean that terminal device 100 did not send a MAC SDU.

[0271] During RRC connection re-establishment, terminal device 100 performs cell selection. Terminal device 100 selects an NR cell, and if the NR cell is one of the cells satisfying the second condition (e.g., cell Y) and the first condition is also met, terminal device 100 applies the configuration of the cell change destination candidate to cell Y and performs cell handover processing to cell Y. It should be noted that cell handover processing to cell Y may be limited to cases where a first parameter is configured in terminal device 100. The first parameter is, for example, a parameter indicating, that if the cell selected in the cell handover failure processing is one of the cells satisfying the second condition and the first condition is also met, cell handover processing should be performed on that cell.

[0272] During the RRC connection re-establishment process, if the selected cell is an NR cell and meets some or all of the following conditions A to C, the terminal device 100 sends an RRC re-establishment request message to the base station device 200 in the selected cell. At this time, the terminal device 100 may release the stored configuration of the cell change destination candidate before sending the RRC re-establishment request message to the base station device 200.

[0273] Condition A: The selected community is not one of the communities that meet the second condition.

[0274] Condition B: The first condition was not met.

[0275] Condition C: The first parameter is not configured.

[0276] During the RRC connection re-establishment process, if the selected cell is a RAT cell other than NR, or if cell selection cannot be performed within a predetermined time, the terminal device 100 switches to RRC idle mode.

[0277] Terminal device 100 can be configured or designed to... Figure 11 No PDCP data PDU is transmitted between receiving the cell handover signal in step S1002 and detecting the cell handover failure in step S1102 (hereinafter sometimes referred to as transmission restriction configuration). Transmission restriction configuration is, for example, a configuration or design that uses only four-step CFRA for random access in cell handover processing. Using only four-step CFRA for random access in cell handover processing means that the configuration for each cell change destination candidate includes a four-step CFRA configuration.

[0278] Sending limit configuration is, for example, in Figure 10 In step S1004, notification is made using MAC CE or physical layer signaling, and uplink data generated in the DRB, etc., is not sent in step S1004. Not sending uplink data generated in the DRB, etc., for example means not sending MAC SDU.

[0279] When the application sends a restricted configuration, the process performed by the terminal device 100 in step S1302 is as follows.

[0280] During RRC connection re-establishment, terminal device 100 performs cell selection. If the selected cell is an NR cell and one of the cells that meets the second condition (e.g., cell Y), terminal device 100 applies the configuration of the cell change destination candidate for cell Y and performs cell handover processing to cell Y. It should be noted that the cell handover processing to cell Y may be limited to the case where the second parameter is configured in terminal device 100.

[0281] The second parameter is, for example, a parameter indicating that a cell handover process will be performed on the cell if the cell selected by the terminal device 100 in the cell handover failure handling is one of the cells that meets the second condition.

[0282] The second parameter could be, for example, an indication that the cell selected in the cell handover failure handling is one of the cells that meets the second condition, and that the selection is a parameter for performing cell handover handling on the cell in the case of the first cell selection after the cell handover failure is detected in step S1102.

[0283] When the application transmit restriction configuration is applied, during the RRC connection re-establishment process, if the cell selected by the terminal device 100 is an NR cell and meets some or all of the following conditions D and E, the terminal device 100 sends an RRC re-establishment request message to the base station device 200 in the selected cell. At this time, the terminal device 100 releases the stored configuration of the cell change destination candidate before sending the RRC re-establishment request message to the base station device 200.

[0284] Condition D: The selected cell is not one of the cells that meet the second condition.

[0285] Condition E: The first parameter is not configured.

[0286] During the RRC connection re-establishment process, if the selected cell is a RAT cell other than NR, or if cell selection cannot be performed within a predetermined time, the terminal device 100 switches to RRC idle mode.

[0287] <Cell handover failure handling to avoid key stream reuse issues 3>

[0288] Figure 14 This diagram illustrates an example of a third cell handover failure handling method. The third cell handover failure method involves, after the terminal device 100 detects a cell handover failure and restores its configuration to the configuration of the source PCell, retaining the values ​​of some or all state variables. During the RRC connection re-establishment process, if the cell selected by the terminal device 100 is an NR cell and is one of the cells satisfying the second condition, the configuration of the cell change destination candidate for the selected cell is applied, and cell handover processing to the selected cell is performed. If the terminal device 100 detects a cell handover failure as described above and restores its configuration to the configuration of the source PCell, for example, if at least the second parameter is configured in the terminal device 100, the process of retaining the values ​​of some or all state variables is performed. During the RRC connection re-establishment process, if the cell selected by the terminal device 100 is one of the cells satisfying the second condition, for example, if at least the second parameter is configured in the terminal device 100, the process of applying the configuration of the cell change destination candidate for the selected cell and performing cell handover to the selected cell is performed. When an RRC re-establishment request message is sent to a base station device 200 in a selected cell, the terminal device 100 restores the retained state variables to the configuration of the source PCell before sending the RRC re-establishment request message.

[0289] Terminal device 100 detected a cell handover failure to cell X (S1102).

[0290] Next, the terminal device 100 will restore the configuration to the configuration used in the source PCell and execute the RRC connection re-establishment procedure (S1401). In the case of restoring to the configuration used in the source PCell, the values ​​of some or all of the state variables in each entity of each radio bearer will be retained, and will not be restored to the values ​​used in the source PCell (in...). Figure 11 The values ​​of the state variables retained in step S1002 when the cell handover signal is received, or immediately before the cell handover signal is received. These retained state variables include, for example, the COUNT value in the PDCP entity. In the case of restoring to the configuration used in the source PCell, such as configuring the second parameter in terminal device 100, processing is performed to retain the values ​​of some or all of the state variables in each entity of each radio bearer.

[0291] Next, during the RRC connection re-establishment process, the terminal device 100 performs cell selection and performs processing based on the selected cell and the first condition (step S1402).

[0292] If the selected cell is an NR cell and one of the cells that meets the second condition (e.g., cell Y), the terminal device 100 applies the configuration of the cell change destination candidate for cell Y and performs cell handover processing to cell Y. It should be noted that the processing for cell Y is performed, for example, when the second parameter is configured in the terminal device 100.

[0293] The second parameter is, for example, a parameter indicating that a cell handover process will be performed on the cell if the cell selected by the terminal device 100 in the cell handover failure handling is one of the cells that meets the second condition.

[0294] The second parameter could be, for example, an indication that the cell selected in the cell handover failure handling is one of the cells that meets the second condition, and that the selection is a parameter for performing cell handover handling on the cell in the case of the first cell selection after the cell handover failure is detected in step S1102.

[0295] It should be noted that the values ​​of some or all of the state variables in each entity of each radio bearer are, for example, the values ​​of some or all of the state variables in each entity of each DRB.

[0296] During the RRC connection re-establishment process, if the selected cell is an NR cell and some or all of the following conditions F and G are met, the terminal device 100 sends an RRC re-establishment request message to the base station device 200 in the selected cell. At this time, the terminal device 100 releases the stored configuration of the cell change destination candidate before, for example, sending the RRC re-establishment request message to the base station device 200. Furthermore, at this time, for example, the terminal device 100 may restore the values ​​of the state variables retained in step S1401 to the values ​​used in the source PCell before sending the RRC re-establishment request message to the base station device 200. Figure 11 The value at the time the cell handover signal is received in step S1002 or the value immediately preceding the receipt of the cell handover signal. For example, if the second parameter is configured, the process of restoring the value of the state variable retained in step S1401 to the value used in the source before sending the RRC re-establishment request message to the base station device 200 is performed.

[0297] Condition F: The selected cell is not one of the cells that meets the second condition.

[0298] Condition G: No second parameter is configured.

[0299] During the RRC connection re-establishment process, if the selected cell is a RAT cell other than NR, or if cell selection cannot be performed within a predetermined time, the terminal device 100 switches to RRC idle mode.

[0300] <Cell handover failure handling to avoid key stream reuse issues 4>

[0301] Figure 15 This is a diagram illustrating an example of a method for handling handover failures in the fourth cell.

[0302] Terminal device 100 detected a cell handover failure to cell X (S1102).

[0303] Next, terminal device 100 executes the cell selection procedure (S1501). Terminal device 100 may stop some or all running timers before executing the cell selection procedure. Terminal device 100 may start timers to limit the execution time of the cell selection procedure to a certain period. Terminal device 100 may execute the cell selection procedure using the configuration of terminal device 100 in the event of a cell handover failure, without returning the configuration to the configuration of the source PCell.

[0304] When performing the cell selection process, and when returning the configuration to the source PCell, the terminal device 100 saves some or all values ​​of state variables, timers, etc. in each entity, as well as some or all buffers in each entity.

[0305] Without restoring the configuration to the original PCell configuration, terminal device 100 performs the cell selection process using the configuration of terminal device 100 in the event of a cell handover failure. When the configuration is returned to the original PCell configuration, terminal device 100 performs the cell selection process by saving some or all values ​​of state variables, timers, etc., in each entity, as well as some or all buffers. For example, the cell selection process is performed when either or both of the following conditions are met: a parameter indicating the execution of LTM is set in terminal device 100, or at least a second parameter is set in terminal device 100.

[0306] The cell selection process can be performed as part of the RRC connection re-establishment process, or it can be performed independently of the RRC connection re-establishment process. If at least the second parameter is not set, the terminal device 100 can perform the processes of steps S1604 and S1605, but not the process of step S1602, which will be described later.

[0307] Next, the terminal device 100 performs processing according to the selected cell (S1502).

[0308] Figure 16 This is a diagram illustrating an example of processing based on the selected cell in step S1502. The terminal device 100 begins processing based on the selected cell (S1601).

[0309] Terminal device 100 determines whether the selected cell is one of the cells that meets the second condition (S1602).

[0310] If the selected cell is one of the cells that meet the second condition (e.g., cell Y), the terminal device 100 performs a cell handover to the selected cell (cell Y) (S1603). If the selected cell is one of the cells that meet the second condition, for example, if either or both of the following conditions are met: the terminal device 100 has a parameter indicating the execution of LTM is set, or the terminal device 100 has at least a second parameter set, the cell handover process to the selected cell is performed.

[0311] The second parameter is, for example, a parameter indicating that if the selected cell in the cell handover failure handling is one of the cells that meets the second condition, cell handover handling shall be performed on that cell.

[0312] The second parameter could be, for example, an indication that the cell selected in the cell handover failure handling is one of the cells that meets the second condition, and that the selection is a parameter for performing cell handover handling on the cell in the case of the first cell selection after the cell handover failure is detected in step S1102.

[0313] When performing a cell handover to cell Y or before performing the handover, terminal device 100 may release a portion of the retained information. This portion of the retained information may include, for example, information obtained through early TA measurement or early TA acquisition. Information obtained through early TA measurement or early TA acquisition may include, for example, TA information and information including the value of the TA timer used for that TA.

[0314] When performing a cell handover to cell Y or before performing the handover, terminal device 100 may generate a configuration for cell Y. That is, when storing a reference configuration, terminal device 100 generates a configuration to be used in cell Y by applying the configuration of cell Y to be stored to the reference configuration. If no reference configuration is stored or the configuration of the cell change destination candidate to be stored is a complete configuration, terminal device 100 may generate a configuration to be used in cell Y by replacing the configuration used in the current cell with the configuration of cell Y to be stored, or by replacing the configuration used in the current cell with a configuration of cell Y to be stored other than the fixed configuration. In some cases, terminal device 100 does not return some or all values ​​of state variables, timers, etc., used by each entity (SDAP entity, PDCP entity, RLC entity, MAC entity, etc.) to their initial state when generating the configuration to be used in the cell handover destination. That is, terminal device 100 may retain some or all values ​​of state variables, timers, etc., used by each entity. In some cases, terminal device 100 does not need to discard some or all buffers in each entity when generating the configuration to be used in the cell handover destination. In other words, terminal device 100 can retain some or all values ​​of state variables, timers, etc., used by each entity. Terminal device 100 can retain some or all buffers in each entity.

[0315] When performing a cell handover to cell Y, terminal device 100 may use a four-step or two-step CFRA, a four-step or two-step CBRA, or no RACH to perform the cell handover. Terminal device 100 may determine which cell handover method to use (using a four-step or two-step CFRA, a four-step or two-step CBRA, or no RACH) based on the configuration of cell Y. When performing a cell handover to cell Y, terminal device 100 may use no RACH to perform the cell handover if a third condition is met. The third condition includes, for example, the terminal device 100 maintaining a valid TA for cell Y. A valid TA includes, for example, the TA timer used for that TA not having expired.

[0316] During or after a cell handover to cell Y, terminal device 100 sends a notification indicating that the cell handover has occurred. Figure 10(Processing of step S1004 in the process). The notification indicating that the cell has been handed over may include information indicating that the RRC connection has been restored after the cell handover failure. Information related to the uplink resources that sent the notification indicating that the cell has been handed over is included, for example, in the RAR, dynamically assigned by the base station device 200 after the cell handover, or included in the configuration of cell Y.

[0317] In step S1602, the terminal device 100 determines whether the selected cell is one of the cells that meet the second condition, and if the selected cell is not one of the cells that meet the second condition (No), the configuration is returned to the configuration of the source PCell (step S1604). At this time, the terminal device 100 may also return the values ​​of state variables, timers, etc. used in each entity to the values ​​specified in the source PCell.

[0318] Next, terminal device 100 re-establishes the RRC connection or switches to RRC idle mode (step S1605). For example, if the selected cell is an NR cell, terminal device 100 re-establishes the RRC connection. If the selected cell is an NR cell, terminal device 100 sends an RRC re-establishment request message to base station device 200 in the selected NR cell. At this time, terminal device 100 releases the stored configuration of the cell change destination candidate before, for example, sending the RRC re-establishment request message to base station device 200. If the selected cell is a RAT cell other than NR, or if cell selection cannot be performed within a predetermined time, terminal device 100 switches to RRC idle mode.

[0319] The processing in step S1605 is performed, for example, as part of the RRC connection re-establishment process. If the cell selection processing in step S1501 is performed separately from the RRC connection re-establishment process, the terminal device 100 does not need to perform the cell selection process during the RRC connection re-establishment process. The terminal device 100 may reset the MAC and suspend some or all radio bearers before performing the processing in step S1605. The suspended radio bearers do not need to include at least SRB0. The terminal device 100 may release some or all of the retained information before performing the processing in step S1605. The terminal device 100 may stop some or all of the running timers before performing the processing in step S1605.

[0320] Therefore, the terminal device 100 and the base station device 200 can avoid the problem of key stream reuse and perform secure communication in the cell handover failure handling of the terminal device 100.

[0321] In cell handover failure handling, the fact that the selected cell is one of the cell change destination candidates stored in the terminal device 100 includes, for example, the selected cell being one of the PCells of the cell change destination candidates stored in the terminal device 100. Figure 11 The selected cell is one of the PCells in the configuration of the cell change destination candidates received in step S1001. In the cell handover failure handling, even if the selected cell is one of the cells included in the cell change destination candidates stored in the terminal device 100, the selected cell may not be considered as one of the cell change destination candidates stored in the terminal device 100 if the selected cell is an SCell.

[0322] Similarly, in cell handover failure handling, the fact that the selected cell is one of the cells that meet the second condition includes, for example, the selected cell being one of the PCells of the cells that meet the second condition.

[0323] This embodiment describes the handling of LTM cell handover failure, but this embodiment can also be applied to other technologies. For example, this embodiment can be applied to the handling of handover (synchronization reconfiguration) failure in non-terrestrial networks (NTN).

[0324] Although the handling following a cell handover failure performed by LTM has been described in this embodiment, this embodiment can be applied to handling following a handover failure (synchronization reconfiguration). The signal received by the terminal device 100 from the base station device in step S1002 may be an RRC reconfiguration message including synchronization reconfiguration parameters. In this case, the handover target does not need to be a cell change destination candidate stored in the terminal device 100. In this case, the cell handover failure detection in step S1102 may be a handover failure detection. The terminal device 100 may perform the cell handover failure handling disclosed in this embodiment after the handover failure detection. When the terminal device 100 performs the cell handover failure handling disclosed in this embodiment after the handover failure detection, if the RRC reconfiguration message including the synchronization reconfiguration parameters does not include parameters indicating master key updates, a portion of the cell handover failure handling may be performed. This portion of the cell handover failure handling is, for example, the process of maintaining some or all values ​​of state variables when the configuration of the terminal device 100 is returned to the configuration of the source PCell.

[0325] <Other>

[0326] In some cases, some messages in the sequence described above may not be executed in order, or the order may be partially altered. Furthermore, some messages in the sequence may fail to be executed.

[0327] The functions and processes described as those of terminal device 100 may also be the functions and processes of base station device 200. Furthermore, the functions and processes described as those of base station device 200 may also be the functions and processes of terminal device 100.

[0328] When using the term "radio bearer" without distinguishing between signaling radio bearers and data radio bearers, a radio bearer can be a signaling radio bearer, a data radio bearer, or both.

[0329] The statement "A can be interpreted as B" is intended to encompass both interpreting A as B and interpreting B as A.

[0330] When condition "B" is the opposite of condition "A", condition "B" can be expressed as an "other" condition relative to condition "A".

[0331] In summary, you will receive the following information.

[0332] (1) A terminal device includes: a receiving unit that receives a first signal and a second signal from a base station device, the first signal including change destination information designating a first cell and a second cell as cell change destination candidates, the second signal including information related to cell change; and a handover unit that performs a first process of handing a serving cell from a third cell to the first cell based on the information related to the cell change included in the second signal, wherein if the first process fails, the handover unit performs a second process in which, when the second cell is selected as the change destination cell, a second configuration applied to the second cell is generated, and the serving cell is handed over to the second cell by using the second configuration, and when a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, a first RRC connection re-establishment process is performed by using a third configuration applied to the third cell.

[0333] (2) According to the terminal device described in (1), the first RRC connection re-establishment process does not include the cell selection process.

[0334] (3) According to the terminal device of (1), when the first signal includes a reference configuration, the switching unit generates the second configuration by using the reference configuration.

[0335] (4) In the terminal device according to (3), the handover unit generates the second configuration by using the configuration applied to the reference configuration in the cell change destination candidate.

[0336] (5) A base station apparatus includes: a transmitting unit, the transmitting unit being configured to transmit a first signal and a second signal to a terminal device, the first signal including change destination information designating a first cell and a second cell as cell change destination candidates, the second signal including information related to cell change; and a control unit, the control unit causing the terminal device to: perform a first process of switching a serving cell from a third cell to the first cell based on the information related to the cell change included in the second signal; perform a second process when the first process fails; generate a second configuration applied to the second cell when selecting the second cell as the change destination cell in the second process, and switch the serving cell to the second cell by using the second configuration; and perform a first RRC connection re-establishment process by using a third configuration applied to the third cell when selecting a cell other than the cell change destination candidate included in the first signal as the change destination cell.

[0337] (6) A wireless communication system includes a base station device and a terminal device, wherein the base station device: transmits a first signal and a second signal to the terminal device, the first signal including change destination information designating a first cell and a second cell as cell change destination candidates, and the second signal including information related to cell change; the terminal device: receives the first signal and the second signal; performs a first process of switching a serving cell from a third cell to the first cell based on the information related to the cell change included in the second signal; performs a second process if the first process fails; in the second process, when the second cell is selected as the change destination cell, generates a second configuration applied to the second cell, and switches the serving cell to the second cell by using the second configuration; and when a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, performs a first RRC connection re-establishment process by using a third configuration applied to the third cell.

[0338] Although examples of devices are described in each embodiment, the methods disclosed herein are not limited to cellular phones, smartphones, tablet terminals, base station devices, etc., and can also be applied to other electronic devices, such as electronic devices installed in automobiles, trains, airplanes, satellites, etc.; electronic devices installed in drones; robots; AV equipment; home appliances; office equipment; vending machines; other everyday devices; and industrial equipment.

[0339] In each implementation, E-UTRA and NR are described as radio access technologies, and EPC and 5GC are described as core networks; however, the methods of this disclosure are not limited to these. For example, the form of this disclosure can be applied to different generations of radio access technologies or networks, such as 6th or 7th generation.

[0340] This invention is not limited to the above embodiments, and various modifications can be made.

[0341] Although the embodiments have been described in detail with reference to the accompanying drawings, the specific configurations are not limited to those shown in the drawings and those described in the embodiments.

[0342] Explanation of reference numerals in the attached figures

[0343] 10: Communication System

[0344] 100: Terminal device

[0345] 110: CPU

[0346] 120: Storage device

[0347] 121: Wireless Communication Program

[0348] 122: Terminal-side program

[0349] 130: Memory

[0350] 140: Wireless communication circuit

[0351] 200: Base station equipment

[0352] 210: CPU

[0353] 220: Storage device

[0354] 221: Wireless Communication Program

[0355] 222: Base Station Side Procedure

[0356] 230: Memory

[0357] 240: Wireless communication circuit

[0358] 250: Network Interface

[0359] 300: Core Network

Claims

1. A terminal device, the terminal device comprising: The receiving unit receives a first signal and a second signal from the base station device. The first signal includes change destination information that designates the first cell and the second cell as candidates for cell change destination. The second signal includes information related to cell change. as well as A handover unit performs a first process of handing over the serving cell from the third cell to the first cell based on information related to the cell change included in the second signal. In the event that the first processing fails, the switching unit performs the second processing. In the second process, when the second cell is selected as the destination cell for the change, a second configuration applied to the second cell is generated, and the serving cell is switched to the second cell using the second configuration. When a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, the first RRC connection re-establishment process is performed by using the third configuration applied to the third cell.

2. The terminal device according to claim 1, wherein, The first RRC connection re-establishment process does not include a cell selection process.

3. The terminal device according to claim 1, wherein, If the first signal includes a reference configuration, the switching unit generates the second configuration by using the reference configuration.

4. The terminal device according to claim 3, wherein, The handover unit generates the second configuration by using the configuration applied to the reference configuration in the cell change destination candidate.

5. A base station apparatus, the base station apparatus comprising: The sending unit sends a first signal and a second signal to the terminal device. The first signal includes change destination information that designates the first cell and the second cell as candidates for cell change destination. The second signal includes information related to cell change. as well as The control unit enables the terminal device to: The first process of switching the serving cell from the third cell to the first cell is performed based on the information related to the cell change included in the second signal; If the first process fails, the second process is executed. In the second process, when the second cell is selected as the destination cell for the change, a second configuration is generated for the second cell, and the serving cell is switched to the second cell by using the second configuration; as well as When a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, the first RRC connection re-establishment process is performed by using the third configuration applied to the third cell.

6. A wireless communication system, the wireless communication system comprising a base station device and a terminal device, wherein, The base station device: The first signal and the second signal are sent to the terminal device. The first signal includes change destination information that designates the first cell and the second cell as candidates for cell change destination. The second signal includes information related to cell change. The terminal device: Receive the first signal and the second signal; The first process of switching the serving cell from the third cell to the first cell is performed based on the information related to the cell change included in the second signal; If the first process fails, the second process is executed; In the second process, when the second cell is selected as the destination cell for the change, a second configuration is generated for the second cell, and the serving cell is switched to the second cell by using the second configuration; as well as When a cell other than the cell change destination candidate included in the first signal is selected as the change destination cell, the first RRC connection re-establishment process is performed by using the third configuration applied to the third cell.

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