Terminal and communication method

Abstract

To improve security in LTM (Lower layer Triggered Mobility).SOLUTION: A terminal includes a control unit that detects a handover failure while performing LTM (Lower layer Triggered Mobility), and a transmitting unit that sends a base station a message reporting the handover failure and including information indicating that the failure is related to security.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a terminal and a communication method in a communication system. [Background technology]

[0002] 3GPP (registered trademark) (3rd Generation Partnership Project) is currently studying a wireless communication system called 5G or NR (New Radio) (hereinafter, this wireless communication system will be referred to as "5G" or "NR") in order to achieve even larger system capacity, even faster data transmission speeds, and even lower latency in wireless sections. Various wireless technologies are being studied for 5G to meet the requirements of achieving a throughput of 10 Gbps or more while reducing latency in wireless sections to 1 ms or less.

[0003] In NR, a network architecture is being considered that includes 5GC (5G Core Network), which corresponds to EPC (Evolved Packet Core), which is the core network in the network architecture of LTE (Long Term Evolution), and NG-RAN (Next Generation - Radio Access Network), which corresponds to E-UTRAN (Evolved Universal Terrestrial Radio Access Network), which is the RAN (Radio Access Network) in the network architecture of LTE (e.g., Non-Patent Document 1).

[0004] In addition, Release 19 is expected to include enhanced mobility features, such as inter-CU (inter-Central Unit) LTM (Lower layer Triggered Mobility) and functionality expansion to support cases where LTM is performed while maintaining DC (Dual connectivity) (see, for example, Non-Patent Document 2).

[0005] Additionally, MDT (Minimization of Drive Test) and SON (Self-Organizing Networks) are being investigated. For example, inter-CU-LTM and intra-CU conditional LTM are being considered as enhancements to MRO (Mobility Robustness Optimization). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP TS 23.501 V18.8.0 (2024-12) [Non-patent document 2] 3GPP TSG-RAN Meeting #101 RP-232618, Bengaluru, India, 11-15 September 2023 [Non-patent document 3] 3GPP TS 38.401 V18.4.0 (2024-12) [Non-patent document 4] 3GPP TS 38.331 V18.4.0 (2024-12) Summary of the Invention [Problem to be solved by the invention]

[0007] The cell switch command in LTM includes an NCC (NH (Next hop) chaining counter) value. However, since the cell switch command in LTM is sent on an unsecured layer, it may be subject to tampering.

[0008] The present invention has been made in view of the above points, and has an object to improve security in LTM (Lower layer Triggered Mobility). [Means for solving the problem]

[0009] According to the disclosed technology, a terminal is provided that has a control unit that detects a handover failure while executing LTM (Lower layer Triggered Mobility), and a transmission unit that transmits a message reporting the handover failure to a base station, the message including information indicating that the failure is security-related. [Effects of the Invention]

[0010] According to the disclosed technology, it is possible to improve security in LTM (Lower layer Triggered Mobility). [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram illustrating an example of a communication system. [Figure 2] FIG. 1 is a diagram illustrating an example of a communication system in a roaming environment. [Figure 3] FIG. 10 is a sequence diagram illustrating an example (1) of inter-DU-LTM. [Figure 4] FIG. 10 is a sequence diagram illustrating an example (2) of inter-DU-LTM. [Figure 5] FIG. 1 is a diagram illustrating an example of MAC-CE in an embodiment of the present invention. [Figure 6] FIG. 4 is a sequence diagram illustrating an example (1) of a UE report according to an embodiment of the present invention. [Figure 7] FIG. 10 is a sequence diagram illustrating an example (2) of a UE report according to an embodiment of the present invention. [Figure 8] 2 is a diagram illustrating an example of a functional configuration of a base station 10 and a network node 30 according to an embodiment of the present invention. [Figure 9] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal 20 according to the embodiment of the present invention. [Figure 10] 1 is a diagram illustrating an example of a hardware configuration of a base station 10 and a terminal 20 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the embodiment described below is an example, and the embodiment to which the present invention is applied is not limited to the following embodiment.

[0013] In the operation of the wireless communication system according to the embodiment of the present invention, existing technologies are used as appropriate. However, the existing technologies are, for example, but not limited to, the existing LTE. Furthermore, the term "LTE" used in this specification has a broad meaning including LTE-Advanced, a system subsequent to LTE-Advanced (e.g., NR), or a wireless LAN (Local Area Network), unless otherwise specified.

[0014] Furthermore, in the embodiments of the present invention, when radio parameters etc. are "configured," it may mean that predetermined values ​​are pre-configured, or that radio parameters notified from the network node 30 or the terminal 20 are set.

[0015] Fig. 1 is a diagram illustrating an example of a communication system. As shown in Fig. 1, the communication system is composed of a UE, which is a terminal 20, and multiple network nodes 30. Hereinafter, it is assumed that one network node 30 corresponds to each function, but multiple functions may be realized by one network node 30, or multiple network nodes 30 may realize one function. Furthermore, the "connection" described below may be a logical connection or a physical connection.

[0016] The RAN (Radio Access Network) is a network node 30 having a radio access function, which may include a base station 10, and is connected to a UE, an AMF (Access and Mobility Management Function), and a UPF (User plane function). The AMF is a network node 30 having functions such as terminating the RAN interface, terminating the NAS (Non-Access Stratum), and performing registration management, connection management, reachability management, and mobility management. The UPF is a network node 30 having functions such as a PDU (Protocol Data Unit) session point to the outside that interconnects with a DN (Data Network), packet routing and forwarding, and user plane QoS (Quality of Service) handling. The UPF and the DN constitute a network slice. In the wireless communication network according to the embodiment of the present invention, multiple network slices are constructed.

[0017] The AMF is connected to the UE, RAN, SMF (Session Management function), NSSF (Network Slice Selection Function), NEF (Network Exposure Function), NRF (Network Repository Function), UDM (Unified Data Management), AUSF (Authentication Server Function), PCF (Policy Control Function), and AF (Application Function). The AMF, SMF, NSSF, NEF, NRF, UDM, AUSF, PCF, and AF are network nodes 30 that are interconnected via interfaces based on their respective services: Namf, Nsmf, Nnssf, Nnef, Nnrf, Nudm, Nausf, Npcf, and Naf.

[0018] The SMF is a network node 30 that has functions such as session management, UE IP (Internet Protocol) address allocation and management, DHCP (Dynamic Host Configuration Protocol) function, ARP (Address Resolution Protocol) proxy, and roaming function. The NEF is a network node 30 that has a function of notifying other NFs (Network Functions) of capabilities and events. The NSSF is a network node 30 that has functions such as selecting a network slice to which a UE connects, determining allowed NSSAIs (Network Slice Selection Assistance Information), determining the NSSAI to be configured, and determining the AMF set to which the UE connects. The PCF is a network node 30 that has a function of controlling network policies. The AF is a network node 30 that has a function of controlling application servers. The NRF is a network node 30 that has a function of discovering NF instances that provide services. The UDM is a network node 30 that manages subscriber data and authentication data. The UDM is connected to a UDR (User Data Repository) that stores the data.

[0019] Fig. 2 is a diagram illustrating an example of a communication system in a roaming environment. As shown in Fig. 2, the network is composed of a UE, which is a terminal 20, and multiple network nodes 30. Hereinafter, it is assumed that one network node 30 corresponds to each function, but multiple functions may be realized by one network node 30, or multiple network nodes 30 may realize one function. Furthermore, the "connection" described below may be a logical connection or a physical connection.

[0020] The RAN is a network node 30 having a radio access function, and is connected to the UE, the AMF, and the UPF. The AMF is a network node 30 having functions such as RAN interface termination, NAS termination, registration management, connection management, reachability management, and mobility management. The UPF is a network node 30 having functions such as a PDU session point to the outside that interconnects with the DN, packet routing and forwarding, and user plane QoS handling. The UPF and the DN constitute a network slice. In the wireless communication network according to the embodiment of the present invention, multiple network slices are constructed.

[0021] The AMF is connected to the UE, RAN, SMF, NSSF, NEF, NRF, UDM, AUSF, PCF, AF, and SEPP (Security Edge Protection Proxy). The AMF, SMF, NSSF, NEF, NRF, UDM, AUSF, PCF, and AF are network nodes 30 that are interconnected via their respective service-based interfaces, Namf, Nsmf, Nnssf, Nnef, Nnrf, Nudm, Nausf, Npcf, and Naf.

[0022] The SMF is a network node 30 having functions such as session management, UE IP address allocation and management, DHCP function, ARP proxy, and roaming function. The NEF is a network node 30 having a function of notifying other NFs of capabilities and events. The NSSF is a network node 30 having functions such as selecting a network slice to which a UE connects, determining an allowed NSSAI, determining an NSSAI to be configured, and determining an AMF set to which a UE connects. The PCF is a network node 30 having a function of controlling network policies. The AF is a network node 30 having a function of controlling application servers. The NRF is a network node 30 having a function of discovering NF instances that provide services. The SEPP is a non-transparent proxy that filters control plane messages between PLMNs (Public Land Mobile Networks). The vSEPP shown in Figure 2 is the SEPP in the visited network, and the hSEPP is the SEPP in the home network.

[0023] As shown in Figure 2, a UE is in a roaming environment connected to a RAN and an AMF in a Visited PLMN (VPLMN). The VPLMN and a Home PLMN (HPLMN) are connected via a vSEPP and an hSEPP. The UE can communicate with a UDM in the HPLMN via the AMF in the VPLMN, for example.

[0024] In addition, in an NG-RAN (Next Generation Radio Access Network), a gNB, which is a RAN node, may have an architecture separated into a gNB-CU (Central Unit) and a gNB-DU (Distributed Unit). One gNB-CU may accommodate multiple gNB-DUs, and one gNB-DU may accommodate multiple cells.

[0025] To enhance mobility, functional extensions are being considered to support inter-CU-LTM, cases where LTM is performed while maintaining DC, and LTM where the UE performs cell switching on its own device (conditional LTM).

[0026] In conventional LTM, the network triggers cell switching. Only intra-CU-LTM in non-DC mode and intra-SN (Secondary Node) PSCell LTM without MN (Master Node) involvement in DC mode were supported.

[0027] 3 is a sequence diagram for explaining an example (1) of inter-DU-LTM (see Non-Patent Document 3). In step S101, the UE and source DU, and the source DU and CU transmit and receive user data. In step S102, Layer 3 measurement control and reporting are performed.

[0028] In step S103, the CU determines the LTM configuration. In step S104, the CU sends a UE context setup request to the candidate DU. In step S105, the candidate DU sends a UE context setup response to the CU. In step S106, the CU sends a UE context modification request to the source DU. In step S107, the source DU sends a UE context modification response to the CU.

[0029] In step S108, the CU may send a UE context modification request to the candidate DU. In step S109, the candidate DU may send a UE context modification response to the CU. In step S110, the CU sends a DL RRC message transfer including RRCReconfiguration to the source DU. In step S111, the source DU sends RRCReconfiguration to the UE. In step S112, the UE sends RRCReconfigurationComplete to the source DU. In step S113, the source DU sends a UL RRC message transfer including RRCReconfigurationComplete to the CU.

[0030] In step S114, the UE may perform early TA acquisition. In step S115, the candidate DU may forward the TA information to the CU. In step S116, the CU may forward the TA information to the source DU.

[0031] 4 is a sequence diagram for explaining an example (2) of inter-DU-LTM. In step S117, the UE transmits an L1 measurement report to the source DU. In step S118, the source DU determines an LTM cell switch. In step S119, the source DU transmits a cell switch command to the UE.

[0032] In step S120, the source DU sends a cell switch notification including the target cell ID and the TCI state ID to the CU. In step S121, the CU sends a cell switch notification including the target cell ID and the TCI state ID to the candidate DU. In step S122, the source DU may send a DL data delivery status to the CU.

[0033] In step S123, the DU detects UE access. In step S124, the candidate DU sends an access status including the target cell ID to the CU. In step S125, the UE sends an RRCReconfigurationComplete to the candidate DU. In step S126, the candidate DU sends an UL RRC message transfer including an RRCReconfigurationComplete to the CU.

[0034] In step S127, the CU may send a UE context release command to the source DU, causing the provisioning cell to be released. In step S128, the source DU may send a UE context release to the CU. In step S129, the UE and candidate DU, and the candidate DU and CU transmit and receive user data.

[0035] Note that steps S103 to S112 may be called LTM preparation.

[0036] Additionally, MDT (Minimization of Drive Test) and SON (Self-Organizing Networks) are being considered. For example, inter-CULTM and intra-CU conditional LTM are being considered as enhancements to MRO (Mobility Robustness Optimization). Specifications for inter-node information exchange, including possible enhancements over existing interfaces, and UE reporting for enhanced mobility parameter tuning are also being considered.

[0037] FIG. 5 is a diagram illustrating an example of a MAC-CE in an embodiment of the present invention. FIG. 5 is an example of an LTM cell switch command MAC-CE. As shown in FIG. 5, the LTM cell switch command MAC-CE includes an NCC (NH (Next hop) chaining counter) value. If ltm-NoSecurityChangeID is configured for an LTM candidate associated with the target configuration ID in ltm-Config and the UE does not have a retained value of ltm-ServingCellNoSecurityChangeID, the NCC value field is included only for MAC entities associated with the MCG. Alternatively, if the value of ltm-NoSecurityChangeID included in an LTM candidate in ltm-Config is not equal to the retained ltm-ServingCellNoSecurityChangeID, the NCC value field is included only for MAC entities associated with the MCG. In other cases, this field is not included and the corresponding bits are three reserved bits.

[0038] Here, if the NCC value in the cell switch command MAC-CE is tampered with in the LTM, there is a risk that handover will fail because the MAC-CE is not protected by security. Specifically, if the NCC value in the MAC-CE is tampered with, the security key held by the UE and the security key held by the base station will no longer match, and the RRCReconfigurationComplete sent from the UE to the base station will no longer be decoded by the base station.

[0039] Therefore, in the event of an LTM failure, a handover failure, or an RLF (Radio Link Failure), the UE may record the NCC value used by the UE in an RLF report. In addition to the NCC value, the target cell ID and / or source cell ID where the handover failure occurred may be recorded in the RLF report. The UE may transmit the RLF report to the base station.

[0040] New security-related cause values ​​may be defined as the cause of the LTM failure. For example, the cause value for LTM failure may indicate "invalid NCC value" or "invalid security key."

[0041] The UE may record the NCC value notified by the LTM cell switch command MAC-CE in the RLF report.

[0042] When the network requests an RLF report in a UE information request, the UE may transmit the RLF report to the base station.

[0043] In the case of dual connectivity, the UE may perform an LTM or SCG change in the SCG, and an SCG failure may occur due to an invalid sk counter value used to derive security keys. In this case, the UE may report the sk counter value used by the UE to the MN by including it in an SCGFailureInfo message. The UE may also report the target primary secondary cell ID (PSCell ID) and / or source primary secondary cell ID to the MN by including it in the message. The UE may also report a new security-related cause value to the MN by including it in the message.

[0044] 6 is a sequence diagram for explaining an example (1) of a UE report in an embodiment of the present invention. In step S201, the terminal detects an RLF. Note that the terminal may be replaced with a UE, an IAB-MT, or a WAB-MT. Note that the RLF may be an RLF caused by a handover failure occurring in an LTM procedure.

[0045] In step S202, the terminal sends an RRC reconnection request (RRCR establishment Request) message to the base station. The base station may be replaced by a gNB, an IAB donor, or a backhaul gNB. In step S203, the base station sends an RRC reconnection (RRCR establishment) message to the terminal.

[0046] In step S204, the terminal sends an RRC reconnection complete (RRCR establishment complete) message to the base station. The RRC reconnection complete message may include information indicating whether an RLF report or a handover failure report is available. In step S205, if an RLF report or a handover failure report is available, the base station sends a UE information request message to the terminal.

[0047] In step S206, the terminal sends a UE information response message to the base station. The UE information response message may include an RLF report or a handover failure report. The RLF report or the handover failure report may include the used NCC value and / or a new failure cause value, for example, "NCC value is invalid."

[0048] In addition, information indicating whether an RLF report or a handover failure report is available may be reported from the terminal to the base station via an RRC setup complete (RRCSetupComplete) message, an RRC reconfiguration complete (RRCReconfigurationComplete) message, or an RRC recovery complete (RRCResumeComplete) message.

[0049] 7 is a sequence diagram illustrating an example (2) of a UE report in an embodiment of the present invention. In step S301, the terminal, MN, and SN detect an SCG conditional LTM failure. The LTM failure may be an RLF detection. In step S302, the terminal transmits SCG failure information (SCGFailureInfo) to the MN. The SCG failure information may include the used sk counter value and / or a new failure cause value, for example, "sk counter value is invalid."

[0050] If the network detects a possibility of tampering with the security key based on a report from the UE, the network may stop the LTM or switch to Layer 3 handover.The base station may detect a possibility of tampering with the security key based on information exchanged with other base stations and a report from the UE.

[0051] According to the above-described embodiment, in the LTM, when an LTM fails due to a mismatch in the NCC value in the cell switch command MAC-CE, an RLF (Radio Link Failure) report is recorded and reported to the network, thereby automating or enhancing the operation of the LTM.

[0052] That is, it is possible to improve security in LTM (Lower layer Triggered Mobility).

[0053] (Device configuration) Next, a description will be given of examples of functional configurations of the base station 10, network node 30, and terminal 20 that perform the processes and operations described above. The base station 10, network node 30, and terminal 20 include functions for performing the above-described embodiments. However, the base station 10, network node 30, and terminal 20 may each include only a part of the functions of the embodiments.

[0054] <Base Station 10 and Network Node 30> FIG. 8 is a diagram showing an example of the functional configuration of the base station 10 and the network node 30. As shown in FIG. 8, the base station 10 has a transmitting unit 110, a receiving unit 120, a setting unit 130, and a control unit 140. The functional configuration shown in FIG. 8 is merely an example. As long as the operations according to the embodiment of the present invention can be performed, the names of the functional divisions and functional units may be any. Note that the network node 30 may have the same functional configuration as the base station 10. Furthermore, a network node 30 having multiple different functions in the system architecture may be composed of multiple network nodes 30 separated by function.

[0055] The transmitter 110 includes a function of generating a signal to be transmitted to the terminal 20 or another network node 30, and transmitting the signal by wire or wirelessly. The receiver 120 includes a function of receiving various signals transmitted from the terminal 20 or another network node 30, and acquiring, for example, information of a higher layer from the received signal. A communication unit including the transmitter 110 and the receiver 120 may be configured.

[0056] The transmitter 110 includes a function of generating a signal to be transmitted to the terminal 20 and transmitting the signal wirelessly. The transmitter 110 also transmits setting information, instructions, notifications, etc. related to a low-power wake-up signal to the terminal 20. The transmitter 110 also transmits notifications related to switching of monitoring operations to the terminal. The receiver 120 includes a function of receiving various signals transmitted from the terminal 20 and acquiring, for example, information of higher layers from the received signals. The transmitter 110 also has a function of transmitting PSS, SSS, PBCH, DL / UL control signals, etc. to the terminal 20. The receiver 120 also receives inter-network node messages from other network nodes.

[0057] The setting unit 130 stores preset setting information and various setting information to be transmitted to the terminal 20. The content of the setting information is, for example, information related to the operations described in the embodiments.

[0058] The control unit 140 controls settings, instructions, and notifications related to the operations described in the embodiments. The function unit related to signal transmission in the control unit 140 may be included in the transmitting unit 110, and the function unit related to signal reception in the control unit 140 may be included in the receiving unit 120.

[0059] <Terminal 20> Fig. 9 is a diagram showing an example of the functional configuration of terminal 20 in the embodiment of the present invention. As shown in Fig. 9, terminal 20 has transmitting unit 210, receiving unit 220, setting unit 230, and control unit 240. The functional configuration shown in Fig. 9 is merely an example. As long as the operations related to the embodiment of the present invention can be performed, the names of the functional divisions and functional units may be any. Transmitting unit 210 and receiving unit 220 may be collectively referred to as a communication unit.

[0060] The transmitter 210 creates a transmission signal from transmission data and transmits the transmission signal wirelessly. The transmitter 210 also transmits capability information related to the low-power wake-up signal to the base station 10. The receiver 220 receives various signals wirelessly and acquires higher layer signals from the received physical layer signals. The receiver 220 also has a function of receiving PSS, SSS, PBCH, DL / UL / SL control signals, etc. transmitted from the base station 10. The receiver 220 also receives paging notification information and configuration information, instructions, and notifications related to the low-power wake-up signal from the base station 10. For example, the receiver 220 receives a low-power wake-up signal from the base station 10. The setting unit 230 stores various configuration information received by the receiver 220 from the base station 10. The setting unit 230 also stores pre-configured configuration information. The content of the configuration information is, for example, information related to the operations described in the embodiments.

[0061] As described in the embodiments, the control unit 240 controls settings, instructions, and notifications related to the operations described in the embodiments. A functional unit related to signal transmission in the control unit 240 may be included in the transmitting unit 210, and a functional unit related to signal reception in the control unit 240 may be included in the receiving unit 220.

[0062] (Hardware configuration) The block diagrams (FIGS. 8 and 9) used to explain the above embodiments show functional blocks. These functional blocks (components) are realized by hardware, software, or a combination of these. Furthermore, the method for realizing each functional block is not particularly limited. That is, each functional block may be realized by using one device that is physically or logically coupled, or may be realized by using two or more physically or logically separated devices that are connected directly or indirectly (for example, by wire, wirelessly, etc.) and these multiple devices. The functional block may be realized by combining the one device or the multiple devices with software.

[0063] For example, a base station, a terminal, a network node, etc. according to an embodiment of the present disclosure may function as a computer that performs processing of the wireless communication method of the present disclosure. Fig. 10 is a diagram illustrating an example of the hardware configuration of a base station and a terminal according to an embodiment of the present disclosure. The above-described base station 10 and terminal 20 may be physically configured as a computer device including a processor 1001, a memory 1002, a storage 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, etc.

[0064] In the present disclosure, the term "apparatus" may be interchangeable with any two terms selected from a set of terms such as circuit, device, unit, module, chip, means, etc. The hardware configurations of the base station 10 and the terminal 20 may be configured to include one or more of the devices shown in the drawings, or may be configured to exclude some of the devices.

[0065] Each function in the base station 10 and the terminal 20 is realized by loading predetermined software (programs) onto hardware such as the processor 1001, memory 1002, etc., so that the processor 1001 performs calculations, controls communication by the communication device 1004, and controls the reading, writing, or both reading and writing of data in the memory 1002 and storage 1003.

[0066] The processor 1001, for example, runs an operating system to control the entire computer. The processor 1001 may be configured as a central processing unit (CPU) including an interface with peripheral devices, a control device, an arithmetic unit, a register, etc. For example, a baseband signal processing unit, a call processing unit, etc. may be realized by the processor 1001. Although only one processor 1001 is shown in the figure, there may be multiple processors.

[0067] The processor 1001 also reads programs (program codes), software modules, data, etc. from the storage 1003, the communication device 1004, or both the storage 1003 and the communication device 1004 into the memory 1002, and executes various processes in accordance with the programs. The programs used are those that cause a computer to execute at least some of the operations described in the above-described embodiments. For example, the control unit 401 of the terminal 20 may be implemented by a control program stored in the memory 1002 and running on the processor 1001, and similar implementations may be made for other functional blocks. While the above-described various processes have been described as being executed by a single processor 1001, they may also be executed simultaneously or sequentially by two or more processors 1001. The processor 1001 may be implemented by one or more chips. The programs may be transmitted from a network via a telecommunications line, or may be provided to the computer via the communication device 1004, for example.

[0068] The present disclosure also provides a computer program product including a computer program, which may implement the steps of the methods described in the above embodiments when the computer program is executed by a computer (e.g., the processor 1001).

[0069] The memory 1002 is a computer-readable recording medium and may be configured, for example, as a read-only memory (ROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a random access memory (RAM), or a combination of at least two of these. The memory 1002 may also be called a register, a cache, a main memory (primary storage device), or the like. The memory 1002 can store executable programs (program codes), software modules, and the like for implementing a wireless communication method according to an embodiment of the present disclosure.

[0070] Storage 1003 is a computer-readable recording medium, and may be, for example, an optical disk such as a CD-ROM (Compact Disc ROM), a hard disk drive, a flexible disk, a magneto-optical disk (e.g., a compact disk, a digital versatile disk, a Blu-ray disc), a smart card, a flash memory (e.g., a card, a stick, a key drive), a floppy disk, a magnetic strip, or a combination of at least two of these. Storage 1003 may also be referred to as an auxiliary storage device. The above-mentioned storage medium may be, for example, memory 1002, storage 1003, or a database, server, or other appropriate medium including both memory 1002 and storage 1003.

[0071] The communication device 1004 is hardware (transmitting / receiving device) for communicating between computers via a wired network, a wireless network, or both wired and wireless networks, and is also referred to as, for example, a network device, a network controller, a network card, or a communication module. The communication device 1004 may be configured to include a high-frequency switch, a duplexer, a filter, a frequency synthesizer, or a combination of at least two of these. For example, a transmitting / receiving antenna, an amplifier unit, a transmitting / receiving unit, or a transmission path interface may be realized by the communication device 1004. The transmitting / receiving unit may be implemented as a transmitting unit and a receiving unit that are physically or logically separated.

[0072] The input device 1005 is an input device that accepts input from the outside (for example, a keyboard, a mouse, a microphone, a switch, a button, a sensor, or a combination of at least two of these). The output device 1006 is an output device that outputs to the outside (for example, a display, a speaker, an LED lamp, or a combination of at least two of these). The input device 1005 and the output device 1006 may be integrated into one device (for example, a touch panel).

[0073] Furthermore, each device, such as the processor 1001 and the memory 1002, is connected by a bus 1007 for communicating information. The bus 1007 may be configured using a single bus, or may be configured using different buses between each device.

[0074] Furthermore, base station 10 and terminal 20 may be configured to include hardware such as a microprocessor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), a graphics processing unit (GPU), a neural processing unit (NPU), or a combination of at least two of these, and some or all of the functional blocks may be realized by the hardware. For example, processor 1001 may be implemented using at least one of these pieces of hardware.

[0075] <Configuration of this embodiment> (Section 1) a control unit that detects a handover failure while executing LTM (Lower layer Triggered Mobility); a transmitting unit configured to transmit a message reporting a handover failure to a base station, the message including information indicating that the failure is related to security. (Section 2) 2. The terminal of claim 1, wherein the transmitter transmits a message to the base station including information indicating whether a handover failure report is available. (Section 3) 2. The terminal according to claim 1, wherein the transmission unit includes a used NCC (Next hop chaining counter) value in a message reporting the handover failure and transmits the message to the base station. (Section 4) 2. The terminal according to claim 1, wherein the transmitting unit includes the used sk counter value in a message reporting the handover failure and transmits the message to the base station. (Section 5) The terminal described in claim 1, wherein the transmitting unit includes information indicating that the used NCC (Next hop chaining counter) value or the used sk counter value is invalid in a message reporting the handover failure and transmits the message to the base station. (Section 6) A procedure for detecting handover failures during LTM (Lower layer Triggered Mobility) execution; and a procedure of transmitting a message reporting a handover failure to the base station, the message including information indicating that the failure is related to security.

[0076] Any of the above configurations can improve security in LTM (Lower layer Triggered Mobility). Also, according to paragraphs 2 to 5, in LTM, when an LTM failure occurs due to a mismatch in the NCC value in the cell switch command MAC-CE, an RLF (Radio Link Failure) report is recorded and reported to the network, thereby automating or strengthening the operation of LTM.

[0077] (Supplementary explanation of the embodiment) Although the embodiments of the present invention have been described above, the disclosed invention is not limited to such embodiments, and those skilled in the art will understand various modifications, alterations, alternatives, and substitutions. While specific numerical examples have been used to facilitate understanding of the invention, unless otherwise specified, these numerical values ​​are merely examples, and any appropriate values ​​may be used. The division of items in the above description is not essential to the present invention; two or more items may be combined as needed, and items described in one item may apply to items described in another item (unless inconsistent). The boundaries between functional units or processing units in the functional block diagram do not necessarily correspond to the boundaries between physical components. The operations of multiple functional units may be performed by a single physical component, or the operations of a single functional unit may be performed by multiple physical components. The order of the processing steps described in the embodiments may be reversed as long as there is no contradiction. For convenience of processing description, the base station 10 and terminal 20 have been described using functional block diagrams. However, such devices may be implemented using hardware, software, or a combination thereof. The software operated by the processor of the base station 10 in accordance with an embodiment of the present invention and the software operated by the processor of the terminal 20 in accordance with an embodiment of the present invention may each be stored in random access memory (RAM), flash memory, read-only memory (ROM), EPROM, EEPROM, registers, hard disk (HDD), removable disk, CD-ROM, database, server or any other suitable storage medium.

[0078] The aspects / embodiments described in the present disclosure may be categorized as Long Term Evolution (LTE), LTE-Advanced (LTE-A), International Mobile Telecommunications-Advanced (IMT-Advanced), 4th generation mobile communication system (4G), 5th generation mobile communication system (5G), 5G-Advanced (5G-A), 6th generation mobile communication system (6G), xth generation mobile communication system (x is, for example, an integer or a decimal number)), Future Radio Access (FRA), New Radio (NR), New radio access (NX), Future generation radio access (FX), Open Radio Access Network (O-RAN), Wideband Code Division Multiple Access (W-CDMA) (registered trademark), Global System for Mobile communications (GSM) (registered trademark), CDMA2000, Ultra Mobile Broadband (UMB), Institute of Electrical and Electronics Engineers (IEEE) Engineers) 802.11, IEEE802.11x (where x is any character string such as b, a, g, n, ac, ax, be, or bn, and when x=n it is called Wi-Fi4, when x=ac it is called Wi-Fi5, when x=ax it is called Wi-Fi6 or Wi-Fi6E, when x=be it is Wi-Fi7, and when x=bn it is called Wi-Fi8, etc. Wi-Fi is a registered trademark.), IEEE802.16 (WiMAX (registered trademark), IEEE802.20, UWB (Ultra-Wide Band), Bluetooth (registered trademark), network virtualization technology (e.g., NFV (Network Function Virtualization), SFC (Service Function Chaining), SDN (Software Defined Networking)), or LPWA (Low Power Wide Area). Furthermore, each aspect / embodiment described in the present disclosure may be applied to a system based on a combination of at least two of these technologies. Furthermore, "based on" naturally refers not only to a system that uses the technology, but also to a system that uses an extension or modification of the technology.

[0079] In the present disclosure, any two terms selected from a set of terms such as "base station (BS)", "radio base station", "fixed station (fixed station)", "NodeB", "eNodeB (eNB)", "gNodeB (gNB)", "access point (AP)", "transmission point (TP)", "reception point (RP)", "transmission / reception point (TRP)", "radio unit (RU)", "remote unit (RU)", "control unit (CU)", "distributed unit (DU)", "remote radio head (RRH)", "node", "gateway", "terrestrial base station", "stratospheric base station", "unmanned aerial vehicle", "high altitude platform station (HAPS)", "airborne platform", "panel", "cell", "radio access network (RAN)", and "network" may be used interchangeably.

[0080] Each cell accommodated by a base station may be referred to by terms such as a macro cell, a small cell, a femto cell, a pico cell, a serving cell, or a super cell. In the present disclosure, any two terms selected from a set of terms such as "cell," "sector," "cell group," "carrier," "component carrier," "cluster," "bandwidth part (BWP)," and "carrier bandwidth" may be used interchangeably.

[0081] In the present disclosure, any two terms selected from the set of terms such as "Mobile Station (MS)", "user terminal", "User Equipment (UE)", "Device", "Module" and "Terminal" may be used interchangeably.

[0082] A terminal may be referred to as a subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, router (e.g., home router, mobile router, etc.), TCU (Telematics Control Unit), or some other suitable terminology.

[0083] The base station and the terminal may each be composed of one or more devices. The devices constituting at least a portion of the base station and the terminal may be called a transmitting device, a receiving device, a communication device, etc. Note that the devices constituting at least a portion of the base station and the terminal may be, for example, an object itself, such as a vehicle, a transport vehicle, an automobile, a motorcycle, a bicycle, a connected car, an excavator, a bulldozer, a wheel loader, a dump truck, a forklift, a train, a bus, a handcar, a rickshaw, a ship and other watercraft, an airplane, a rocket, an unmanned aerial vehicle, a stratospheric base station (e.g., a High Altitude Platform Station (HAPS)), an artificial satellite (e.g., a Low Earth Orbit (LEO) satellite, a Medium Earth Orbit (MEO) satellite, a Geostationary Earth Orbit (GEO) satellite), a drone (registered trademark), a multicopter, a quadcopter, a balloon, or an Internet of Things (IoT) device (e.g., a smart meter, a sensor), or may include, but are not limited to, an object or device mounted on the object. Furthermore, the object may be a moving object (hereinafter referred to as a "moving object"; this does not exclude the case where the moving object is in a stationary state where it is not moving), or may be a fixedly positioned object (hereinafter referred to as a "non-moving object").

[0084] Furthermore, a base station in the present disclosure may be read as a terminal. For example, the aspects / embodiments of the present disclosure may be applied to a configuration in which communication between a base station and a terminal is replaced with communication between multiple terminals (which may be called, for example, D2D (Device-to-Device) or V2X (Vehicle-to-Everything)) or communication of a non-terrestrial network (NTN). In this case, the terminal 20 may be configured to have at least some of the functions of the base station 10 described above. Furthermore, terms such as "uplink" and "downlink" may be read as terms corresponding to communication between terminals (for example, "sidelink") or terms corresponding to NTN (for example, feeder link or service link). For example, an uplink channel or a downlink channel may be read as a sidelink channel.

[0085] The present disclosure is also applicable to cases where at least some of the devices constituting the base station and the terminal operate outside the earth (for example, in the atmosphere or outer space).

[0086] In addition, the term "terminal" in the present disclosure may be read as "base station." In this case, the base station 10 may be configured to have the functions of the terminal 20 described above.

[0087] The notification of information is not limited to the aspects / embodiments described in the present disclosure, and may be performed using other methods. For example, the notification of information may be performed by physical layer signaling (e.g., Downlink Control Information (DCI) and Uplink Control Information (UCI)), higher layer signaling (e.g., Radio Resource Control (RRC) signaling, Medium Access Control (MAC) signaling, broadcast information (Master Information Block (MIB) and System Information Block (SIB))), other signals, or a combination of at least two of these. Note that the physical layer signaling may be referred to as Layer 1 (L1) control information. The MAC signaling may be referred to as a MAC Control Element (CE) or a MAC Protocol Data Unit (PDU), for example. Furthermore, the RRC signaling may be referred to as an RRC message or an information element (IE) in the RRC message. The RRC message may be, for example, a message used for controlling an RRC connection (for example, setup, reconfiguration, establishment, reestablishment, release, or resume), mobility, a measurement report, or notification of a terminal's capabilities, or may be an information element within the message. Furthermore, notification of information may be explicit or implicit. Note that explicit notification of certain information means notification of the certain information itself, and implicit notification of certain information may mean notification of information other than the certain information, or may mean that the certain information is considered to have been notified when a certain condition is satisfied.Furthermore, notification of information may include not only notification between the same layers of different devices (e.g., between a lower layer or an upper layer of the base station 10 and the terminal 20) but also notification between different layers in the same or different devices (e.g., between a lower layer and an upper layer in the base station 10 or the terminal 20). Furthermore, notification of information from one device to another device may be performed via one or more devices. Regarding any information (e.g., a variable, a constant, a parameter, a setting) described in the present disclosure, even if not specifically stated in the above embodiments, information indicating / specifying (or related to) the any information (value) may be notified from any first device (e.g., a terminal / base station) to any second device (e.g., a base station / terminal).

[0088] The order of the procedures, sequences, flowcharts, etc. of each aspect / embodiment described in this disclosure may be changed unless it is consistent. For example, the methods described in this disclosure present elements of various steps using an example order, and are not limited to the particular order presented.

[0089] In the present disclosure, a specific operation described as being performed by a base station may be performed by its upper node or by some of its upper nodes (e.g., CU, RU, or DU, etc.) in some cases. It is clear that various operations performed for communication with a terminal in a RAN or core network may be performed by at least some of the base station and other network nodes other than the base station. The other network node may be one node or a combination of multiple nodes. The network node is, for example, a node provided in various core networks such as EPC (Evolved Packet Core) and 5GC (5G Core Network), and provides one or more network functions (NF: Network Functions), but is not limited to this.

[0090] Furthermore, in the present disclosure, the operation of "a terminal receives information from a base station" accompanies the operation of "the base station transmits the information to the terminal," "the base station generates the information," or both. Similarly, the operation of "a terminal transmits information to a base station" accompanies the operation of "the base station receives the information from the terminal." Furthermore, the operation of "a terminal is configured to ..." or "configure UE to ..." may include the operation of "a base station transmits configuration information regarding the configuration of the terminal" and the operation of "a terminal configures a predetermined operation based on the configuration information."

[0091] Each aspect / embodiment described in the present disclosure may be used alone, in combination, or switched depending on the implementation.

[0092] The present disclosure has been described above, but it is for illustrative purposes only, and the present invention is not limited to the aspects / embodiments described in the present disclosure. The present disclosure can be implemented in modified and altered forms without departing from the spirit of the invention. The present disclosure and its modifications and alterations are included in the scope of the present invention and its equivalents.

[0093] As used in this disclosure, any reference to an element using a designation such as "first," "second," etc. does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements. Thus, a reference to a first and a second element does not imply that only two elements may be employed or that the first element must in some way precede the second element.

[0094] The radio resource may be defined by a combination of resource units in one or more domains, such as the time domain, the frequency domain, the spatial domain, the code domain, and the power domain.

[0095] For example, resources in the time domain may be defined by one or more time units. The one or more time units may include, but are not limited to, a radio frame, a subframe, a slot, a symbol, a transmission time interval (TTI), or a combination of at least two of these. The time unit may be a fixed-length time unit independent of numerology, a variable-length time unit dependent on numerology, or both. Examples of fixed-length time units include, but are not limited to, a subframe consisting of one or more slots and a radio frame including multiple subframes. Examples of variable-length time units include, but are not limited to, a symbol and a slot including a fixed number of symbols. A certain time unit may be divided into shorter time units. Examples of shorter time units include, but are not limited to, a minislot consisting of fewer symbols than the number of symbols constituting a slot. The above-described time units may include, for example, time units used as units for scheduling, link adaptation, etc. Furthermore, any time unit in the present disclosure may be read as another time unit.

[0096] Numerology is a parameter that defines the physical layer structure, and may be a parameter based on at least one of subcarrier spacing (SCS), symbol length, cyclic prefix length, and sampling time, for example.

[0097] Resources in the frequency domain may be defined, for example, by one or more frequency units. The one or more frequency units may include, for example, subcarriers, resource blocks (RBs), bandwidth parts (BWPs), carrier bandwidths, or a combination of at least two of these, but the terminology of the frequency units is not limited to these. The number of subcarriers included in a frequency unit may be a fixed number regardless of numerology, or may be a variable number that changes depending on numerology. For example, an RB is composed of a predetermined number of consecutive subcarriers in the frequency domain, and the number of subcarriers included in the RB may be the same regardless of numerology, for example, 12, but is not limited to this. A BWP may be composed of, for example, one or more consecutive RBs within a certain carrier bandwidth, but is not limited to this. One or more BWPs may be configured within one carrier for terminal 20, and at least one of the BWPs may be activated. Any frequency unit in the present disclosure may be interchangeable with another frequency unit.

[0098] Furthermore, resources in both the time domain and the frequency domain may be defined by one or more time / frequency units each consisting of a time unit and a frequency unit, such as, but not limited to, a resource element (RE) consisting of one symbol and one subcarrier, a resource element group (REG) consisting of a predetermined number of REs, or a control resource set (CORESET) consisting of a predetermined number of symbols and a predetermined number of RBs.

[0099] Furthermore, resources in the spatial domain may be defined, for example, by one or more spatial units, including, but not limited to, a beam, a layer of MIMO (Multi-Input Multi-Output), an antenna port, or a combination of at least two of these.

[0100] Furthermore, the resources in the code domain may be defined by one or more code units, such as, but not limited to, a cyclic shift (CS), an orthogonal cover code (OCC), or a combination thereof.

[0101] In this disclosure, where articles are added by translation, such as a, an, and the in English, the disclosure may include that the nouns following these articles are in the plural form.

[0102] The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc. [Explanation of symbols]

[0103] 10 base station 110 Transmitter 120 Receiver 130 Setting section 140 Control Unit 20 terminals 210 Transmitter 220 Receiving unit 230 Setting Section 240 Control Unit 30 network nodes 1001 processor 1002 Storage device 1003 Auxiliary storage device 1004 Communication equipment 1005 Input Device 1006 Output Device

Claims

1. a control unit that detects a handover failure while executing LTM (Lower layer Triggered Mobility); a transmitting unit configured to transmit a message reporting a handover failure to a base station, the message including information indicating that the failure is related to security.

2. The terminal of claim 1 , wherein the transmitter transmits a message to the base station including information indicating whether a handover failure report is available.

3. The terminal according to claim 1 , wherein the transmission unit transmits a used NCC (Next hop chaining counter) value to the base station in a message reporting the handover failure.

4. 2. The terminal according to claim 1, wherein the transmitter includes the used sk counter value in a message reporting the handover failure and transmits the message to the base station.

5. The terminal according to claim 1, wherein the transmitting unit includes information indicating that the used NCC (Next hop chaining counter) value or the used sk counter value is invalid in a message reporting the handover failure and transmits the message to the base station.

6. A procedure for detecting handover failure during execution of LTM (Lower layer Triggered Mobility); and a procedure of transmitting a message reporting a handover failure to the base station, the message including information indicating that the failure is related to security.

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