Base station and communication method

Abstract

A base station according to the present invention comprises: a control unit that determines execution of continuous mobility by lower layer triggered mobility (LTM) for a certain terminal; and a communication unit that transmits, to the certain terminal, a cell switching command which includes information pertaining to security. The control unit updates a security key on the basis of the information pertaining to security. The communication unit uses the security key to communicate with the certain terminal.

Description

Base station and communication method

[0001] The present invention relates to a base station and a communication method in a communication system.

[0002] 3GPP (registered trademark) (3rd Generation Partnership Project) is currently studying a wireless communication system called 5G or NR (New Radio) (hereinafter, the wireless communication system will be referred to as "5G" or "NR") in order to achieve a larger system capacity, a higher data transmission speed, and a 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 keeping latency in wireless sections to 1 ms or less.

[0003] In NR, a network architecture including 5GC (5G Core Network) corresponding 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) corresponding to E-UTRAN (Evolved Universal Terrestrial Radio Access Network), which is the RAN (Radio Access Network) in the network architecture of LTE, is being considered (for example, 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 functional extensions to support cases where LTM is performed while maintaining DC (Dual connectivity) (e.g., Non-Patent Document 2).

[0005] 3GPP TS 23.501 V18.4.0 (2023-12)3GPP TSG-RAN Meeting #101 RP-232618, Bengaluru, India, 11-15 September 20233GPP TS 33.501 V18.4.0 (2023-12)3GPP TS 38.473 V18.0.0 (2023-12)3GPP TS 38.413 V18.0.0 (2023-12)3GPP TS 38.331 V18.0.0 (2023-12)

[0006] Functional extensions to support subsequent mobility in lower layer triggered mobility (LTM) or conditional handover are being considered. For example, a secondary node (SN) change during dual connectivity (DC) has been supported in the past. However, when supporting subsequent mobility, problems related to security key updates are expected to occur.

[0007] The present invention has been made in view of the above points, and has as its object to update security keys during LTM (Lower layer Triggered Mobility).

[0008] According to the disclosed technology, a base station is provided which includes a control unit that decides to execute continuous mobility using LTM (Lower layer Triggered Mobility) for a certain terminal, and a communication unit that transmits a cell switching command including security-related information to the certain terminal, wherein the control unit updates a security key based on the security-related information, and the communication unit communicates with the certain terminal using the security key.

[0009] According to the disclosed technology, security keys can be updated during LTM (Lower layer Triggered Mobility).

[0010] FIG. 1 is a diagram for explaining an example of a communication system. FIG. 1 is a diagram for explaining an example of a communication system in a roaming environment. FIG. 2 is a diagram for explaining example (1) of key update in an embodiment of the present invention. FIG. 3 is a diagram for explaining example (2) of key update in an embodiment of the present invention. FIG. 4 is a diagram for explaining example (3) of key update in an embodiment of the present invention. FIG. 5 is a diagram for explaining example (5) of key update in an embodiment of the present invention. A diagram showing an example of the functional configuration of a base station 10 and a network node 30 in an embodiment of the present invention. A diagram showing an example of the functional configuration of a terminal 20 in an embodiment of the present invention. A diagram showing an example of the hardware configuration of a base station 10 and a terminal 20 in an embodiment of the present invention. A diagram showing an example of the configuration of a vehicle 2001 in an embodiment of the present invention.

[0011] 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.

[0012] In the operation of the wireless communication system according to the embodiment of the present invention, existing technology is used as appropriate. However, the existing technology is, for example, the existing LTE, but is not limited to the existing LTE. Furthermore, the term "LTE" used in this specification has a broad meaning including LTE-Advanced, and systems subsequent to LTE-Advanced (e.g., NR), or wireless LAN (Local Area Network), unless otherwise specified.

[0013] Furthermore, in the embodiments of the present invention, "configuring" radio parameters and the like may mean that predetermined values ​​are pre-configured, or that radio parameters notified from the network node 30 or the terminal 20 are set.

[0014] 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.

[0015] 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), 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.

[0016] 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 mutually connected via interfaces based on their respective services, Namf, Nsmf, Nnssf, Nnef, Nnrf, Nudm, Nausf, Npcf, and Naf.

[0017] The SMF is a network node 30 having 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 having a function of notifying other NFs (Network Functions) 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 (Network Slice Selection Assistance Information), determining an NSSAI to be set, 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 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.

[0018] 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.

[0019] 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.

[0020] 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 respective service-based interfaces, Namf, Nsmf, Nnssf, Nnef, Nnrf, Nudm, Nausf, Npcf, and Naf.

[0021] 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 a configured NSSAI, 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 FIG. 2 is a SEPP in the visited network, and the hSEPP is a SEPP in the home network.

[0022] 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.

[0023] 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. F1AP (F1 Application Protocol) may be used for signaling between the gNB-DU and the gNB-CU (see Non-Patent Document 4).

[0024] Functional extensions to support subsequent mobility in LTM (Lower layer Triggered Mobility), conditional handover, and the like are being considered. For example, conventionally, SN (Secondary Node) changes during DC (Dual connectivity) have been supported. On the other hand, when supporting continuous mobility, problems related to security key updates are expected to occur. Therefore, in this embodiment, an operation related to security key updates in LTM, in which the network instructs mobility using MAC-CE, is proposed.

[0025] Here, the K_gNB in ​​the MN must be refreshed, but due to forward security, there are specifications that do not allow security keys to be set in the UE in advance (see Non-Patent Document 3). It is not possible to calculate in advance the future K_gNB, NH (Next Hop parameter) and NCC (Next Hop Chaining Counter parameter) pair.

[0026] There are three methods for calculating K_gNB, as shown below in 1)-3) (existing specifications).

[0027] 1) Horizontal key derivation This may be possible when K_AMF is not updated. It may be calculable without additional parameters. If it can be updated between cell switches, an indication of the number of updates may be required.

[0028] 2) Vertical key derivation This may be possible when K_AMF is not updated. NH and K_gNB may be updated with an increment of NCC.

[0029] 3) K_AMF Update This may be performed when K_AMF is updated. A pair of {NH, NCC} may be sent to the gNB and UE. Only the first {NH, NCC} is configured in the gNB and UE from the AMF. Note that {NH, NCC} may or may not be reconfigured in the UE during vertical key derivation.

[0030] Based on the above calculation method of K_gNB, horizontal key derivation is possible in subsequent inter-CU LTM. Also, in subsequent inter-CU LTM, vertical key derivation is possible when NCC is incremented by 1, and is possible if incremented by 2 or more with notification. Note that K_AMF may be a parameter used for K_gNB derivation.

[0031] Here, the following operations 1) to 3) may be executed as operations related to updating the security key during successive inter-CU-LTM.

[0032] Operation 1) When receiving a cell switch command, the UE may know whether the horizontal key or the vertical key will be rekeyed before connecting to the target cell. Also, when receiving a cell switch command, the UE may know how much the NCC will be incremented if vertical key derivation is performed.

[0033] Operation 2) The CU may notify the DU of security-related information to be included in the Cell Switch Command (CSC) via the F1AP. Note that the DU does not have information about AS security, and conventionally, the CU sends security-related information to the UE by RRC signaling at the same time as issuing a handover command. On the other hand, in LTM, signaling to the UE is triggered by the DU, so the DU may be notified of security-related information.

[0034] Operation 3) As a joint operation of the RAN and the CN, the RAN may determine how long continuous inter gNB mobility can be performed without updating the K_AMF, and since the RAN determines how long continuous inter gNB mobility can be performed without updating the K_AMF, L3 signaling for changing the LTM setting may not be performed. Note that, since subsequent LTM may be interrupted when security updates are performed on the core network side, mobility settings may be optimized by knowing the timing of security updates on the core network side in advance.

[0035] Operation 1) will be described in detail below.

[0036] The cell switching command sent from the gNB to the UE may notify whether or not a key refresh is required and the method of key refresh.

[0037] Option 1: Table 1 shows an example of the cell switch command.

[0038]

[0039] The cell switching command may notify the NCC increment amount. If the flag K shown in Table 1 is set, key update is performed. If the NCC increment amount (Number of NCC increment) shown in Table 1 is 0, key update is performed by horizontal key derivation. If the NCC increment amount is other than 0, the NCC is incremented by the NCC increment amount, vertical keys are derived, and key update is performed.

[0040] Option 2: Table 2 shows an example of the cell switch command.

[0041]

[0042] The cell switching command may notify the number of horizontal key derivations or vertical key derivations. If the K flag shown in Table 2 is set, key refresh is performed. If the H / V flag shown in Table 2 is set, vertical key derivation is performed. If the H / V flag is not set, vertical key derivation is performed. Key refresh is performed the number of key refreshes (Number of key refreshes).

[0043] Option 3: Table 3 shows an example of the cell switch command.

[0044]

[0045] The cell switch command may notify the number of horizontal key derivations and the number of vertical key derivations. Vertical key refreshes are performed for the number of vertical key refreshes shown in Table 3, and then horizontal key refreshes are performed for the number of horizontal key refreshes. If both the number of vertical key refreshes and the number of horizontal key refreshes are 0, no key refresh is performed.

[0046] The gNB and UE may update the horizontal key and / or vertical key based on the information related to the horizontal key and / or vertical key included in the cell switching command and apply them to communication. In Table 2, the number of key refreshes is indicated by 3 bits, and in Table 3, the number of vertical key refreshes and the number of horizontal key refreshes are indicated by 4 bits. However, the bit length of each field is an example, and the bit length may be changed.

[0047] Operation 2) will be described in detail below.

[0048] The CU may notify the DU of security-related information to be included in the cell switch command via the F1AP. The following security-related information may be notified from the CU to the DU:

[0049] Whether and how to update the security key (horizontal or vertical) NCC increment amount Number of horizontal key derivations or number of horizontal key updates

[0050] Option 1: The DU may trigger the acquisition of security information from the CU. The CU may notify the DU of the following security or related information transmitted in the CSC. The DU triggers one of the Class 1 procedures 1)-3) below to acquire security-related information from the CU.

[0051] 1) UE Context Modification Required 2) Other existing procedures 3) New procedures

[0052] 3 is a diagram illustrating an example (1) of key updating according to an embodiment of the present invention. In step S100, the UE, DU, and CU perform LTM preparation. In step S101, the UE transmits an L1 measurement report to the DU. In step S102a or S102b, the DU may acquire security information from the CU. In step S103, the DU performs a cell switch decision. That is, the security information may be acquired either before or after the cell switch decision. In step S104, the DU transmits a cell switch command (CSC) including the security information to the UE.

[0053] Table 4 shows an example of information elements of the UE Context Modification Required message that the DU sends to the CU in step S102a or S102b to obtain security information.

[0054]

[0055] Table 5 shows an example of information elements of a UE Context Modification Confirm message that a CU that has received a UE context modification request sends to a DU to transmit security information.

[0056]

[0057] Table 6 shows an example of the information element Security Information included in the UE Context Change Confirmation.

[0058]

[0059] As shown in Table 6, the security information may include information indicating whether to perform a security key update, information indicating whether to perform a horizontal key update, information indicating whether to perform a vertical key update, the NCC increment amount, information indicating the number of horizontal key updates, and information indicating the number of horizontal key derivations.

[0060] Note that maxnoofNCCIncrement and / or maxnoofKeyRefreshes may be determined depending on the number of bits that can be transmitted by the CSC. Note that the settings related to security key updates, their amounts, and numbers may be indicated in the following formats 1) or 2) in addition to the above examples.

[0061] 1) Whether to perform a security key update (no, yes), the number of NCC increments, and the number of horizontal key updates. 2) Whether to not perform a security key update, perform a horizontal key update, or perform a vertical key update (no, horizontal, vertical), and the number of key updates.

[0062] Option 2: The CU may notify the source DU for which LTM is set if there is an update to the security information. The CU may notify the DU of the following security information or related information transmitted by the CSC. When preparing LTM or when there is a change in the security information, the CU triggers one of the following procedures 1)-3) to transmit the security-related information to the DU.

[0063] 1) UE Context Modification Required 2) Other existing procedures 3) New procedures

[0064] FIG. 4 is a diagram illustrating an example (2) of key updating according to an embodiment of the present invention. In step S200, the UE, DU, and CU perform LTM preparation. In step S201, the UE transmits an L1 measurement report to the DU. In step S202a, S202b, or S202c, the DU may acquire security information from the CU. In step S203, the DU performs a cell switch decision. For example, security information acquisition may be performed whenever inter-CU-LTM preparation is performed, or may be performed whenever an update to the security information occurs. In step S204, the DU transmits a cell switch command (CSC) including security information to the UE.

[0065] Table 5 shows an example of information elements of a UE Context Modification Request message that the CU sends to the DU in step S202a, step S202b, or step S202b to transmit security information.

[0066] Table 6 shows an example of the information element Security Information included in the UE Context Modify Request.

[0067] As shown in Table 6, the security information may include information indicating whether to perform a security key update, information indicating whether to perform a horizontal key update, information indicating whether to perform a vertical key update, the NCC increment amount, information indicating the number of horizontal key updates, and information indicating the number of horizontal key derivations.

[0068] Note that maxnoofNCCIncrement and / or maxnoofKeyRefreshes may be determined depending on the number of bits that can be transmitted by the CSC. Note that the settings related to security key updates, their amounts, and numbers may be indicated in the following formats 1) or 2) in addition to the above examples.

[0069] 1) Whether to perform a security key update (no, yes), the number of NCC increments, and the number of horizontal key updates. 2) Whether to not perform a security key update, perform a horizontal key update, or perform a vertical key update (no, horizontal, vertical), and the number of key updates.

[0070] Operation 3) will be described in detail below.

[0071] As a joint operation of the RAN and the CN, the AMF or OAM may provide information regarding the K_AMF update interval to the gNB. The AMF or OAM may also notify the gNB of the following as information regarding the validity period and / or key update of the K_AMF (security policy).

[0072] The next scheduled time for the K_AMF to be updated (absolute or relative time) The remaining number of times that vertical key derivation can be performed without updating the K_AMF The remaining number of times that horizontal key derivation can be performed without updating the K_AMF The remaining number of times that horizontal key derivation can be performed without performing vertical key derivation The current NAS DL and / or UL COUNT

[0073] Option 1: The AMF may include information about the validity period and / or key update of the K_AMF in the K_gNB update instruction sent to the gNB during K_AMF update (NAS-SMC (Security Mode Command)). Alternatively, the AMF may initiate an update instruction to the gNB independently of the K_gNB update. This information may be included in an existing or new class 2 NGAP procedure (see Non-Patent Document 5).

[0074] 5 is a diagram illustrating an example (3) of key update in an embodiment of the present invention. In step S301, the UE, gNB, and AMF perform NAS-SMC for security key update. In step S302, the AMF sends a UE Context Modification Request including a security policy to the gNB.

[0075] Table 7 shows an example of the IEs included in the UE context modification request.

[0076]

[0077] As shown in Table 7, the UE context modification request may include the following information:

[0078] Security Key (see Non-Patent Document 5) UL CP Security Information (see Non-Patent Document 5) DL CP Security Information (see Non-Patent Document 5) Validity period of K_AMF Remaining number of times that vertical key update can be performed without updating K_AMF Remaining number of times that horizontal key update can be performed without updating K_AMF or remaining number of times that horizontal key derivation can be performed without performing vertical key derivation

[0079] In Table 7, maxSecKeyLifetime may be defined as the maximum time for which a security key is to continue to be used. maxnoofVerticalKeyRef may be defined as the maximum number of remaining vertical key derivations that can be performed before the next K_AMF update. maxnoofHorizontalKeyRef may be defined as the maximum number of remaining horizontal key derivations that can be performed before the next K_AMF update or vertical key derivation.

[0080] Option 2: When the gNB triggers subsequent mobility, etc., it may request the AMF to obtain information regarding the validity period and / or key update of the K_AMF as needed.

[0081] 6 is a diagram illustrating an example (4) of key update in an embodiment of the present invention. In step S401, the gNB decides to perform mobility (mobility decision). In step S402, the gNB sends a UE Context Resume Request including a security policy request to the AMF. In step S403, the AMF sends a UE Context Resume Response including the security policy to the gNB. In step S404, the gNB sends an RRCReconfiguration (see non-patent document 6) to the UE, taking into account the security policy or security-related circumstances.

[0082] Table 8 shows an example of the IEs included in the UE context resume request.

[0083]

[0084] As shown in Table 8, the UE context resume request includes an IE indicating the security policy requirement.

[0085] Table 7 shows an example of an IE included in the UE context resume response.

[0086] As shown in Table 7, the UE context resume response may include the following information:

[0087] Security Key (see Non-Patent Document 5) UL CP Security Information (see Non-Patent Document 5) DL CP Security Information (see Non-Patent Document 5) Validity period of K_AMF Remaining number of times that vertical key update can be performed without updating K_AMF Remaining number of times that horizontal key update can be performed without updating K_AMF or remaining number of times that horizontal key derivation can be performed without performing vertical key derivation

[0088] In Table 7, maxSecKeyLifetime may be defined as the maximum time for which a security key is to continue to be used. maxnoofVerticalKeyRef may be defined as the maximum number of remaining vertical key derivations that can be performed before the next K_AMF update. maxnoofHorizontalKeyRef may be defined as the maximum number of remaining horizontal key derivations that can be performed before the next K_AMF update or vertical key derivation.

[0089] Option 3: The OAM may provide the gNB with information regarding the validity period and / or key update of the K_AMF.

[0090] 7 is a diagram illustrating an example (5) of key updating in an embodiment of the present invention. In step S501, the OAM transmits a UE Context Resume Response including a security policy to the gNB. In step S502, the gNB decides to perform mobility (mobility decision). In step S503, the gNB transmits an RRCReconfiguration (see Non-Patent Document 6) to the UE, taking into account the security policy or security-related circumstances.

[0091] In addition, the control by the message or signaling used in operation 3) may be realized by an external interface (e.g., O1, E2 or A1 of an O-RAN (Open Radio Access Network)), and the information transmitted by the message or signaling may be reported by the external interface.

[0092] According to the above-described embodiment, in subsequent inter-CU-LTM, security keys can be updated without the need for L3 signaling, thereby reducing the signaling overhead related to mobility while maintaining security.

[0093] That is, security keys can be updated during LTM (Lower layer Triggered Mobility).

[0094] (Device Configuration) Next, a description will be given of an example of the functional configuration 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.

[0095] <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.

[0096] 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.

[0097] The setting unit 130 stores in a storage device preset setting information and various setting information to be transmitted to the terminal 20, and reads out from the storage device as needed. The content of the setting information is, for example, information related to LTM.

[0098] The control unit 140 performs processing related to LTM as described in the embodiment. The control unit 140 also performs processing related to communication with the terminal 20. 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.

[0099] <Terminal 20> Fig. 9 is a diagram showing an example of the functional configuration of the terminal 20. As shown in Fig. 9, the terminal 20 has a transmitting unit 210, a receiving unit 220, a setting unit 230, and a 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. In addition, the communication device that becomes the resource holder 20 may have the same functional configuration as the terminal 20.

[0100] The transmitter 210 creates a transmission signal from transmission data and transmits the transmission signal wirelessly. 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 NR-PSS, NR-SSS, NR-PBCH, DL / UL control signals, reference signals, and the like transmitted from the network node 30. A communication unit including the transmitter 210 and the receiver 220 may be configured.

[0101] The setting unit 230 stores various setting information received from the network node 30 by the receiving unit 220 in a storage device and reads it from the storage device as needed. The setting unit 230 also stores setting information that is set in advance. The content of the setting information is, for example, information related to LTM.

[0102] The control unit 240 performs processing related to LTM as described in the embodiment. The function unit related to signal transmission in the control unit 240 may be included in the transmitting unit 210, and the function unit related to signal reception in the control unit 240 may be included in the receiving unit 220.

[0103] (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 any combination of at least one of hardware and software. Furthermore, the method for realizing each functional block is not particularly limited. That is, each functional block may be realized using a single device that is physically or logically coupled, or may be realized using two or more physically or logically separated devices that are directly or indirectly connected (for example, using wires, wirelessly, etc.) and these multiple devices. The functional block may be realized by combining software with the single device or the multiple devices.

[0104] Functions include, but are not limited to, judgment, determination, assessment, calculation, computation, processing, derivation, investigation, search, confirmation, reception, transmission, output, access, resolution, selection, selection, establishment, comparison, assumption, expectation, consideration, broadcasting, notifying, communicating, forwarding, configuring, reconfiguring, allocating, mapping, and assignment. For example, a functional block (component) that performs transmission is called a transmitting unit or transmitter. As mentioned above, there are no particular limitations on how these functions are implemented.

[0105] For example, the network node 30, the terminal 20, 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 the base station 10 and the terminal 20 according to an embodiment of the present disclosure. The network node 30 may have the same hardware configuration as the base station 10. The above-described base station 10 and the terminal 20 may be physically configured as a computer device including a processor 1001, a storage device 1002, an auxiliary storage device 1003, a communication device 1004, an input device 1005, an output device 1006, a bus 1007, etc.

[0106] In the following description, the term "apparatus" can be interpreted as a circuit, a device, a unit, etc. The hardware configuration of the base station 10 and the terminal 20 may be configured to include one or more of the apparatuses shown in the drawings, or may be configured to exclude some of the apparatuses.

[0107] Each function in the base station 10 and the terminal 20 is realized by loading specified software (programs) onto hardware such as the processor 1001, the memory device 1002, etc., so that the processor 1001 performs calculations, controls communication by the communication device 1004, and controls at least one of reading and writing data in the memory device 1002 and the auxiliary memory device 1003.

[0108] The processor 1001 controls the entire computer by running, for example, an operating system. 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, the above-mentioned control unit 140, control unit 240, etc. may be realized by the processor 1001.

[0109] The processor 1001 also reads programs (program codes), software modules, data, etc. from at least one of the auxiliary storage device 1003 and the communication device 1004 into the storage device 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 140 of the base station 10 shown in FIG. 8 may be implemented by a control program stored in the storage device 1002 and running on the processor 1001. For example, the control unit 240 of the terminal 20 shown in FIG. 9 may be implemented by a control program stored in the storage device 1002 and running on the processor 1001. While the above-described various processes have been described as being executed by one 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 also be transmitted from a network via a telecommunications line.

[0110] The storage device 1002 is a computer-readable recording medium and may be configured, for example, by at least one of a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a random access memory (RAM), etc. The storage device 1002 may also be called a register, a cache, a main memory, etc. The storage device 1002 can store executable programs (program codes), software modules, etc. for implementing a communication method according to an embodiment of the present disclosure.

[0111] The secondary storage device 1003 is a computer-readable recording medium, and may be, for example, at least one of 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 (registered trademark) disk), a smart card, a flash memory (e.g., a card, a stick, a key drive), a floppy (registered trademark) disk, a magnetic strip, etc. The above-mentioned storage medium may be, for example, a database, a server, or other appropriate medium including at least one of the storage device 1002 and the secondary storage device 1003.

[0112] The communication device 1004 is hardware (transmission / reception device) for communicating between computers via at least one of a wired network and a wireless network, 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, etc. to realize at least one of frequency division duplex (FDD) and time division duplex (TDD). For example, a transmission / reception antenna, an amplifier unit, a transmission / reception unit, a transmission path interface, etc. may be realized by the communication device 1004. The transmission / reception unit may be implemented as a transmission unit and a reception unit that are physically or logically separated.

[0113] The input device 1005 is an input device (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, etc.) that receives input from the outside. The output device 1006 is an output device (e.g., a display, a speaker, an LED lamp, etc.) that outputs to the outside. Note that the input device 1005 and the output device 1006 may be integrated into one device (e.g., a touch panel).

[0114] Furthermore, each device such as the processor 1001 and the storage device 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.

[0115] Furthermore, the base station 10 and the 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), or a field programmable gate array (FPGA), and some or all of the functional blocks may be realized by the hardware. For example, the processor 1001 may be implemented using at least one of these pieces of hardware.

[0116] Fig. 11 shows an example configuration of a vehicle 2001. As shown in Fig. 11, the vehicle 2001 includes a drive unit 2002, a steering unit 2003, an accelerator pedal 2004, a brake pedal 2005, a shift lever 2006, front wheels 2007, rear wheels 2008, an axle 2009, an electronic control unit 2010, various sensors 2021 to 2029, an information service unit 2012, and a communication module 2013. Each aspect / embodiment described in the present disclosure may be applied to a communication device mounted on the vehicle 2001, and may be applied to the communication module 2013, for example.

[0117] The drive unit 2002 is configured, for example, by an engine, a motor, or a hybrid of an engine and a motor. The steering unit 2003 includes at least a steering wheel (also called a handle) and is configured to steer at least one of the front wheels and the rear wheels based on the operation of the steering wheel operated by the user.

[0118] The electronic control unit 2010 is composed of a microprocessor 2031, a memory (ROM, RAM) 2032, and a communication port (IO port) 2033. Signals are input to the electronic control unit 2010 from various sensors 2021 to 2029 provided in the vehicle 2001. The electronic control unit 2010 may also be called an ECU (Electronic Control Unit).

[0119] The signals from the various sensors 2021 to 2029 include a current signal from a current sensor 2021 that senses the current of the motor, a rotation speed signal of the front and rear wheels obtained by a rotation speed sensor 2022, an air pressure signal of the front and rear wheels obtained by an air pressure sensor 2023, a vehicle speed signal obtained by a vehicle speed sensor 2024, an acceleration signal obtained by an acceleration sensor 2025, an accelerator pedal depression amount signal obtained by an accelerator pedal sensor 2029, a brake pedal depression amount signal obtained by a brake pedal sensor 2026, a shift lever operation signal obtained by a shift lever sensor 2027, and a detection signal for detecting obstacles, vehicles, pedestrians, etc. obtained by an object detection sensor 2028.

[0120] The information service unit 2012 is composed of various devices, such as a car navigation system, an audio system, speakers, a television, and a radio, for providing (outputting) various types of information, such as driving information, traffic information, and entertainment information, and one or more ECUs for controlling these devices. The information service unit 2012 uses information acquired from external devices via the communication module 2013 or the like to provide various types of multimedia information and multimedia services to the occupants of the vehicle 2001. The information service unit 2012 may include input devices (e.g., a keyboard, a mouse, a microphone, a switch, a button, a sensor, a touch panel, etc.) that accept input from the outside, and may also include output devices (e.g., a display, a speaker, an LED lamp, a touch panel, etc.) that output information to the outside.

[0121] The driving assistance system unit 2030 is composed of various devices that provide functions for preventing accidents and reducing the driving burden on the driver, such as millimeter-wave radar, LiDAR (Light Detection and Ranging), cameras, positioning locators (e.g., GNSS, etc.), map information (e.g., high-definition (HD) maps, autonomous vehicle (AV) maps, etc.), gyro systems (e.g., IMU (Inertial Measurement Unit), INS (Inertial Navigation System), etc.), AI (Artificial Intelligence) chips, and AI processors, as well as one or more ECUs that control these devices. In addition, the driving assistance system unit 2030 transmits and receives various information via the communication module 2013 to realize the driving assistance function or the autonomous driving function.

[0122] The communication module 2013 can communicate with the microprocessor 2031 and components of the vehicle 2001 via the communication port. For example, the communication module 2013 transmits and receives data via the communication port 2033 to and from the drive unit 2002, steering unit 2003, accelerator pedal 2004, brake pedal 2005, shift lever 2006, front wheels 2007, rear wheels 2008, axle 2009, microprocessor 2031 and memory (ROM, RAM) 2032 in the electronic control unit 2010, and sensors 2021 to 29, which are provided in the vehicle 2001.

[0123] The communication module 2013 is a communication device that can be controlled by the microprocessor 2031 of the electronic control unit 2010 and can communicate with an external device. For example, it transmits and receives various information to and from the external device via wireless communication. The communication module 2013 may be located either inside or outside the electronic control unit 2010. The external device may be, for example, a base station, a mobile station, or the like.

[0124] The communication module 2013 may transmit at least one of signals from the above-mentioned various sensors 2021-2028 input to the electronic control unit 2010, information obtained based on the signals, and information based on input from the outside (user) obtained via the information service unit 2012 to an external device via wireless communication. The electronic control unit 2010, the various sensors 2021-2028, the information service unit 2012, etc. may be referred to as input units that accept input. For example, the PUSCH transmitted by the communication module 2013 may include information based on the above-mentioned input.

[0125] The communication module 2013 receives various information (traffic information, traffic signal information, vehicle-to-vehicle information, etc.) transmitted from external devices and displays it on an information service unit 2012 provided in the vehicle 2001. The information service unit 2012 may be called an output unit that outputs information (for example, outputs information to a device such as a display or speaker based on the PDSCH (or data / information decoded from the PDSCH) received by the communication module 2013). The communication module 2013 also stores the various information received from external devices in a memory 2032 that can be used by the microprocessor 2031. Based on the information stored in the memory 2032, the microprocessor 2031 may control the drive unit 2002, steering unit 2003, accelerator pedal 2004, brake pedal 2005, shift lever 2006, front wheels 2007, rear wheels 2008, axles 2009, sensors 2021 to 2029, etc. provided in the vehicle 2001.

[0126] (Summary of embodiment) As described above, according to an embodiment of the present invention, a base station is provided which includes a control unit that determines to execute continuous mobility by LTM (Lower layer Triggered Mobility) for a certain terminal, and a communication unit that transmits a cell switching command including security-related information to the certain terminal, wherein the control unit updates a security key based on the security-related information, and the communication unit communicates with the certain terminal using the security key.

[0127] With the above configuration, in subsequent inter-CU-LTM, security keys can be updated without requiring L3 signaling, thereby reducing the signaling overhead related to mobility while maintaining security. In other words, security keys can be updated during LTM (Lower layer Triggered Mobility).

[0128] The control unit may update vertical keys or horizontal keys based on the security information. With this configuration, security keys can be updated without requiring L3 signaling in subsequent inter-CU-LTM, thereby reducing signaling overhead related to mobility while maintaining security.

[0129] The control unit may update the vertical key or the horizontal key based on at least one of an increment amount of a Next Hop Chaining Counter parameter (NCC), the number of updates of the vertical key, and the number of updates of the horizontal key, which are included in the security-related information. With this configuration, in subsequent inter-CU-LTM, security keys can be updated without requiring L3 signaling, thereby reducing signaling overhead related to mobility while maintaining security.

[0130] The control unit may update the security information when preparing for LTM. With this configuration, in subsequent inter-CU-LTM, security keys can be updated without requiring L3 signaling, thereby reducing signaling overhead related to mobility while maintaining security.

[0131] The communication unit may receive information indicating a validity period of a parameter for deriving the security key from an Access and Mobility Management Function (AMF). With this configuration, in subsequent inter-CU-LTM, security keys can be updated without requiring L3 signaling, thereby reducing signaling overhead related to mobility while maintaining security.

[0132] As described above, according to an embodiment of the present invention, a communication method is provided in which a base station executes the following procedures: determining to execute continuous mobility by LTM (Lower layer Triggered Mobility) for a certain terminal; transmitting a cell switching command including security-related information to the certain terminal; updating a security key based on the security-related information; and communicating with the certain terminal using the security key.

[0133] With the above configuration, in subsequent inter-CU-LTM, security keys can be updated without requiring L3 signaling, thereby reducing the signaling overhead related to mobility while maintaining security. In other words, security keys can be updated during LTM (Lower layer Triggered Mobility).

[0134] (Supplementary Notes on the Embodiments) 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; matters described in two or more items may be used in combination as needed, and matters described in one item may apply to matters described in another item (as long as there is no contradiction). Boundaries between functional units or processing units in functional block diagrams do not necessarily correspond to 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 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, but such devices may be realized by 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, register, hard disk (HDD), removable disk, CD-ROM, database, server, or any other suitable storage medium.

[0135] Furthermore, 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), 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), System Information Block (SIB)), other signals, or a combination thereof. Furthermore, the RRC signaling may be referred to as an RRC message, and may be, for example, an RRC Connection Setup message, an RRC Connection Reconfiguration message, or the like.

[0136] Each aspect / embodiment described in the present disclosure may be implemented using any of the following standards: LTE (Long Term Evolution), LTE-Advanced (LTE-A), SUPER 3G, IMT-Advanced, 4G (4th generation mobile communication system), 5G (5th generation mobile communication system), 6th generation mobile communication system (6G), xth generation mobile communication system (xG) (xG (x is, for example, an integer or a decimal number)), FRA (Future Radio Access), NR (new Radio), New radio access (NX), Future generation radio access (FX), W-CDMA (registered trademark), GSM (registered trademark), CDMA2000, UMB (Ultra Mobile Broadband), IEEE 802.11 (Wi-Fi (registered trademark)), IEEE 802.16 (WiMAX (registered trademark)), IEEE 802.17 (WiMAX (registered trademark)), IEEE 802.19 (WiMAX (registered trademark)), IEEE 802.20 (WiMAX (registered trademark)), IEEE 802.21 (Wi-Fi (registered trademark)), IEEE 802.22 (WiMAX (registered trademark)), IEEE 802.23 (WiMAX (registered trademark)), IEEE 802.24 (WiMAX (registered trademark)), IEEE 802.25 (WiMAX (registered trademark)), IEEE 802.26 (WiMAX (registered trademark)), IEEE 802.27 (WiMAX (registered trademark)), IEEE 802.28 (WiMAX (registered trademark)), IEEE 802.29 (WiMAX (registered trademark)), IEEE 802.30 (WiMAX (registered trademark)), IEEE 802.31 (Wi-Fi (registered trademark)), IEEE 802.32 (WiMAX (registered trademark)), IEEE 802.33 (WiMAX (registered trademark)), IEEE 802.34 ( The present invention may be applied to at least one of systems using 802.20, UWB (Ultra-Wide Band), Bluetooth (registered trademark), or other suitable systems, and next-generation systems that are extended, modified, created, or defined based on these systems. The present invention may also be applied to a combination of multiple systems (e.g., a combination of LTE and / or LTE-A with 5G).

[0137] The order of the procedures, sequences, flowcharts, etc. of each aspect / embodiment described herein may be rearranged 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.

[0138] In this specification, a specific operation described as being performed by the base station 10 may be performed by its upper node in some cases. In a network consisting of one or more network nodes having the base station 10, it is clear that various operations performed for communication with the terminal 20 may be performed by at least one of the base station 10 and another network node other than the base station 10 (such as, but not limited to, an MME or an S-GW). Although the above example illustrates a case where there is one other network node other than the base station 10, the other network node may be a combination of multiple other network nodes (such as an MME and an S-GW).

[0139] The information, signals, etc. described in the present disclosure may be output from a higher layer (or a lower layer) to a lower layer (or a higher layer), or may be input / output via multiple network nodes.

[0140] Input and output information may be stored in a specific location (for example, memory) or may be managed using a management table. Input and output information may be overwritten, updated, or added to. Output information may be deleted. Input information may be sent to another device.

[0141] In the present disclosure, the determination may be made by a value represented by one bit (0 or 1), by a Boolean value (true or false), or by a comparison of numerical values ​​(e.g., comparison with a predetermined value).

[0142] Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executable files, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0143] Software, instructions, information, etc. may also be transmitted or received over a transmission medium. For example, if software is transmitted from a website, server, or other remote source using wired technologies (such as coaxial cable, fiber optic cable, twisted pair, Digital Subscriber Line (DSL)), and / or wireless technologies (such as infrared, microwave), then these wired and / or wireless technologies are included within the definition of transmission media.

[0144] The information, signals, etc. described in this disclosure may be represented using any of a variety of different technologies. For example, data, instructions, commands, information, signals, bits, symbols, chips, etc. that may be referred to throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or magnetic particles, optical fields or photons, or any combination thereof.

[0145] Note that terms described in this disclosure and terms necessary for understanding this disclosure may be replaced with terms having the same or similar meanings. For example, at least one of a channel and a symbol may be a signal (signaling). Furthermore, a signal may be a message. Furthermore, a component carrier (CC) may be called a carrier frequency, a cell, a frequency carrier, etc.

[0146] As used in this disclosure, the terms "system" and "network" are used interchangeably.

[0147] Furthermore, the information, parameters, etc. described in the present disclosure may be expressed using absolute values, may be expressed using relative values ​​from a predetermined value, or may be expressed using other corresponding information. For example, a radio resource may be indicated by an index.

[0148] The names used for the above-described parameters are not intended to be limiting in any way. Furthermore, the mathematical expressions using these parameters may differ from those explicitly disclosed in this disclosure. The various channels (e.g., PUCCH, PDCCH, etc.) and information elements may be identified by any suitable names, and therefore the various names assigned to these various channels and information elements are not intended to be limiting in any way.

[0149] In the present disclosure, terms such as "base station (BS)," "radio base station," "base station device," "fixed station," "NodeB," "eNodeB (eNB)," "gNodeB (gNB)," "access point," "transmission point," "reception point," "transmission / reception point," "cell," "sector," "cell group," "carrier," and "component carrier" may be used interchangeably. A base station may also be referred to by terms such as a macrocell, a small cell, a femtocell, and a picocell.

[0150] A base station can accommodate one or more (e.g., three) cells. When a base station accommodates multiple cells, the overall coverage area of ​​the base station can be partitioned into multiple smaller areas, and each smaller area can also be provided with communication services by a base station subsystem (e.g., a small indoor base station (RRH: Remote Radio Head)). The terms "cell" or "sector" refer to part or all of the coverage area of ​​a base station and / or base station subsystem that provides communication services within that coverage.

[0151] In the present disclosure, the base station transmitting information to a terminal may be interpreted as the base station instructing the terminal to control or operate based on the information.

[0152] In this disclosure, the terms "Mobile Station (MS)," "user terminal," "User Equipment (UE)," "terminal," and the like may be used interchangeably.

[0153] A mobile station may also be referred to by those skilled in the art 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, or some other suitable terminology.

[0154] At least one of the base station and the mobile station may be referred to as a transmitting device, a receiving device, a communication device, etc. At least one of the base station and the mobile station may be a device mounted on a mobile object, the mobile object itself, etc. The mobile object refers to a movable object, and may move at any speed. Naturally, this also includes cases where the mobile object is stationary. Examples of the mobile object include, but are not limited to, vehicles, transport vehicles, automobiles, motorcycles, bicycles, connected cars, excavators, bulldozers, wheel loaders, dump trucks, forklifts, trains, buses, handcars, rickshaws, ships and other watercraft, airplanes, rockets, satellites, drones (registered trademark), multicopters, quadcopters, balloons, and objects mounted thereon. The mobile object may also be a mobile object that moves autonomously based on an operational command. It may be a vehicle (e.g., a car, an airplane, etc.), an unmanned mobile object (e.g., a drone, an autonomous vehicle, etc.), or a robot (manned or unmanned). At least one of the base station and the mobile station may be a device that does not necessarily move during communication operations. For example, at least one of the base station and the mobile station may be an IoT (Internet of Things) device such as a sensor.

[0155] Furthermore, a base station in the present disclosure may be read as a user 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 user terminal is replaced with communication between multiple terminals 20 (which may be called, for example, Device-to-Device (D2D) or Vehicle-to-Everything (V2X)). In this case, the terminal 20 may be configured to have the functions of the base station 10 described above. Furthermore, terms such as "uplink" and "downlink" may be read as terms corresponding to terminal-to-terminal communication (for example, "side"). For example, terms such as an uplink channel and a downlink channel may be read as a side channel.

[0156] Similarly, the user terminal in the present disclosure may be read as a base station, in which case the base station may be configured to have the functions of the user terminal described above.

[0157] As used in this disclosure, the terms "determining" and "determining" may encompass a wide variety of actions. "Determining" and "determining" may include, for example, judging, calculating, computing, processing, deriving, investigating, looking up, searching, inquiring (e.g., searching in a table, database, or other data structure), ascertaining, and the like. "Determining" and "determining" may also include receiving (e.g., receiving information), transmitting (e.g., sending information), input, output, accessing (e.g., accessing data in memory), and the like. Furthermore, "judgment" and "decision" can include regarding resolving, selecting, choosing, establishing, comparing, etc. as having been "judged" or "decided." In other words, "judgment" and "decision" can include regarding some action as having been "judged" or "decided." Furthermore, "judgment (decision)" can be interpreted as "assuming," "expecting," "considering," etc.

[0158] The terms "connected," "coupled," or any variation thereof, refer to any direct or indirect connection or coupling between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" to each other. The coupling or connection between elements may be physical, logical, or a combination thereof. For example, "connected" may be read as "access." As used in this disclosure, two elements may be considered to be "connected" or "coupled" to each other using one or more wires, cables, and / or printed electrical connections, as well as electromagnetic energy having wavelengths in the radio frequency range, microwave range, and optical (both visible and invisible) range, as some non-limiting and non-exhaustive examples.

[0159] The reference signal may be abbreviated as RS (Reference Signal) or may be called a pilot depending on the applicable standard.

[0160] As used in this disclosure, the phrase "based on" does not mean "based only on," unless expressly stated otherwise. In other words, the phrase "based on" means both "based only on" and "based at least on."

[0161] 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.

[0162] The "means" in the configuration of each of the above devices may be replaced with "part," "circuit," "device," etc.

[0163] When the terms "include," "including," and variations thereof are used in this disclosure, these terms are intended to be inclusive, similar to the term "comprising." Furthermore, when the term "or" is used in this disclosure, it is not intended to be an exclusive or.

[0164] 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.

[0165] In the present disclosure, the term "A and B are different" may mean "A and B are different from each other." The term may also mean "A and B are each different from C." Terms such as "separate" and "coupled" may also be interpreted in the same way as "different."

[0166] The aspects / embodiments described in this disclosure may be used alone, in combination, or switched depending on the implementation. Notification of predetermined information (e.g., notification that "X is true") is not limited to explicit notification, but may be implicit (e.g., not notifying the predetermined information).

[0167] Although the present disclosure has been described in detail above, it is clear to those skilled in the art that the present disclosure is not limited to the embodiments described herein. The present disclosure can be implemented in modified and altered forms without departing from the spirit and scope of the present disclosure as defined by the claims. Therefore, the description of the present disclosure is intended to be illustrative and does not have any limiting meaning on the present disclosure.

[0168] REFERENCE SIGNS LIST 10 Base station 110 Transmitter 120 Receiver 130 Setting unit 140 Controller 20 Terminal 210 Transmitter 220 Receiver 230 Setting unit 240 Controller 30 Network node 1001 Processor 1002 Storage device 1003 Auxiliary storage device 1004 Communication device 1005 Input device 1006 Output device

Claims

1. A base station comprising: a control unit that determines to execute continuous mobility using LTM (Lower layer Triggered Mobility) for a certain terminal; and a communication unit that transmits a cell switching command including security-related information to the certain terminal, wherein the control unit updates a security key based on the security-related information; and the communication unit communicates with the certain terminal using the security key.

2. The base station according to claim 1, wherein the control unit updates vertical keys or horizontal keys based on the security-related information.

3. The base station according to claim 1, wherein the control unit updates the vertical key or the horizontal key based on at least one of the NCC (Next Hop Chaining Counter parameter) increment amount, the number of vertical key updates, and the number of horizontal key updates included in the security-related information.

4. The base station according to claim 1, wherein the control unit updates the security-related information when preparing for LTM.

5. The base station according to claim 1, wherein the communication unit receives information indicating a validity period of a parameter for deriving the security key from an AMF (Access and Mobility Management Function).

6. A communication method in which a base station executes the following steps: determining to perform continuous mobility using LTM (Lower layer Triggered Mobility) for a certain terminal; sending a cell switching command including security-related information to the certain terminal; updating a security key based on the security-related information; and communicating with the certain terminal using the security key.

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