Communication device, base station, and communication method

Abstract

A communication device (100) according to one embodiment is provided with: a reception unit (112) that receives, from a base station (200), a radio resource control (RRC) message including LTM configuration information for providing one or more pieces of Layer 1 / Layer 2 Triggered Mobility (LTM) candidate information, and that receives, from the base station, a Media Access Control (MAC) control unit (CE) including a cell change command for triggering an LTM cell change; and a control unit (120) that executes the LTM cell change on the basis of the cell change command. When the LTM cell change is executed, the control unit determines whether or not to execute a security key update procedure on the basis of information included in each of the one or more pieces of LTM candidate information.

Description

Cross-references of related applications

[0001] This application is based on and claims priority to patent application No. 2023-168900, filed on September 28, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to a communication device, a base station, and a communication method. Background Technology

[0003] In mobile communication systems conforming to the technical specifications of 3GPP (Third Generation Partnership Project), a standardization project for mobile communication systems, L1 / L2-Triggered Mobility (LTM) is planned to be introduced. In LTM, the base station, based on L1 measurement reports received from the communication equipment, sends a cell switch command to the communication equipment via the Media Access Control (MAC) CE, triggering a cell change, thereby changing the serving cell of the communication equipment. Compared to cell changes based on Radio Resource Control (RRC) messages, the communication equipment can dynamically perform cell changes, reducing mobility latency.

[0004] Currently, the introduction of the following LTM (hereinafter referred to as subsequence LTM) is being explored, namely, after UE 100 performs a cell change from the source cell to the target cell (hereinafter referred to as the first cell change) according to the configuration information used for LTM, it performs a cell change (hereinafter referred to as the second cell change) without RRC reconfiguration (i.e., without receiving RRC reconfiguration messages) (for example, see Non-Patent Literature 1). Existing technical documents Non-patent literature

[0005] Non-patent document 1: "R2-2211101" (Report from 3GPP TSG RAN WG2, meeting #119bis-e, online) Summary of the Invention

[0006] The communication equipment involved in the first aspect includes: a receiving unit that receives from a base station a Radio Resource Control (RRC) message including LTM configuration information for providing one or more Layer 1 / Layer 2 Mobility (LTM) candidate information, and a Media Access Control (MAC) control unit (CE) that includes a cell change command for triggering LTM cell change; and a control unit that executes the LTM cell change based on the cell change command. When executing the LTM cell change, the control unit determines whether to perform a security key update process based on information included in each of the more than one LTM candidate information.

[0007] The second aspect involves a base station comprising: a transmitting unit that sends a Radio Resource Control (RRC) message to a communication device, including LTM configuration information for providing one or more Layer 1 / Layer 2 triggered Mobility (LTM) candidate information, and sends a cell change command to the aforementioned communication device using a Media Access Control (MAC) control unit (CE) to trigger an LTM cell change; and a control unit that controls the execution of the aforementioned LTM cell change based on the aforementioned cell change command. When the aforementioned LTM cell change is executed, the control unit configures whether to perform a security key update process based on information included in each of the aforementioned one or more LTM candidate information.

[0008] The third aspect relates to a communication method executed by a communication device. This communication method includes: receiving from a base station a Radio Resource Control (RRC) message containing LTM configuration information for providing one or more Layer 1 / Layer 2 Triggered Mobility (LTM) candidate information; receiving from the base station a Media Access Control (MAC) Control Unit (CE), wherein the MACCE includes a cell change command that triggers an LTM cell change; and executing the LTM cell change based on the aforementioned cell change command. In the step of executing the LTM cell change, when executing the LTM cell change, a determination is made as to whether to execute a security key update process based on information included in each of the aforementioned one or more LTM candidate information. Attached Figure Description

[0009] The purpose, features, and advantages of this disclosure will become clearer from the following detailed description, taken in conjunction with the accompanying drawings. Figure 1 This is a diagram illustrating the configuration of a mobile communication system according to an embodiment. Figure 2 This is a diagram illustrating a configuration example of the protocol stack involved in the implementation. Figure 3 This is a diagram used to illustrate the overview of LTM. Figure 4 This is a diagram illustrating the configuration of the UE involved in the implementation method. Figure 5 This is a diagram illustrating the configuration of a base station according to an implementation method. Figure 6 This is a sequence diagram (one of) used to illustrate the first example of an action involved in the implementation method. Figure 7 This is a sequence diagram (second one) used to illustrate the first example of an action involved in the implementation method. Figure 8 This is a diagram illustrating the hierarchical structure of the RRC reconfiguration message involved in the implementation method. Figure 9 This is a flowchart (one of) used to illustrate an example of a determination action involved in the implementation method. Figure 10 This is a flowchart (second one) used to illustrate an example of a determination action involved in the implementation method. Figure 11 This is a diagram used to illustrate an example of the operation of the UE 100 according to the implementation method. Figure 12 This is a flowchart (third one) used to illustrate the determination action example involved in the implementation method. Figure 13 This is a sequence diagram (one of) used to illustrate a second example of an implementation method. Figure 14 This is a sequence diagram (second one) used to illustrate a second example of an action involved in the implementation method. Figure 15 This is a flowchart (one of) illustrating an example of a differentiation method involved in the implementation. Figure 16 This is a flowchart (second example) illustrating an example of a differentiation method involved in the implementation. Detailed Implementation

[0010] The mobile communication system according to the embodiments will be described with reference to the accompanying drawings. In the drawings, the same or similar parts are labeled with the same or similar reference numerals.

[0011] As LTM (including subsequence LTM) is performed, it is envisioned that, in addition to the case where the base station managing the source cell manages the target cell (i.e., cell change within the same base station), a case where the base station managing the target cell is different from the base station managing the source cell (i.e., cell change between different base stations) will also be introduced in the future.

[0012] In this case, when performing a cell change from the source cell to the target cell via LTM, UE 100 cannot distinguish whether the target base station of the destination cell is the same as the base station of the source cell. Therefore, there is a concern that, for example, since the security key update process is always performed even in cell changes within the same base station, or not performed in cell changes between different base stations, UE 100 may be unable to properly perform the security key update process.

[0013] Therefore, one of the objectives of this disclosure is to provide a communication device, base station, and communication method capable of appropriately performing a security key update process in an LTM.

[0014] (System Configuration) First, refer to Figure 1 The configuration of the mobile communication system 1 according to this embodiment will be described. The mobile communication system 1 is, for example, a system that conforms to the 3GPP Technical Specification (TS). Hereinafter, as the mobile communication system 1, a 5th Generation System (5G system) based on the 3GPP standard, that is, a mobile communication system based on NR (New Radio) radio access, will be described as an example.

[0015] The mobile communication system 1 includes a network 10 and user equipment (UE) 100 communicating with the network 10. The network 10 includes NG-RAN (Next Generation Radio Access Network) 20 as a 5G radio access network and 5GC (5G Core Network) 30 as a 5G core network.

[0016] UE 100 is a communication device that communicates via base station 200. UE 100 can be a device used by a user. UE 100 can be, for example, a mobile phone terminal such as a smartphone, a tablet computer terminal, a laptop PC (personal computer), a communication module, or a communication card, or other portable device. UE 100 can be a vehicle (e.g., a car, tram, etc.) or a device installed therein (e.g., Vehicle UE: Vehicle User Equipment). UE 100 can be a transport vehicle other than a vehicle (e.g., a ship, airplane, etc.) or a device installed therein (e.g., Aerial UE: Airborne User Equipment). UE 100 can be a sensor or a device installed therein. Furthermore, UE 100 can also be referred to as a terminal, terminal device, mobile station, mobile terminal, mobile device, mobile unit, subscriber station, subscriber terminal, subscriber device, subscriber unit, wireless station, wireless terminal, wireless device, wireless unit, remote station, remote terminal, remote device, or remote unit, or other names. Additionally, UE 100 is an example of a terminal, which may include factory equipment, etc.

[0017] NG-RAN 20 includes multiple base stations 200. Each base station 200 manages at least one cell. One or more base stations 200 may correspond to one or more cells. In this embodiment, base station 200 can be replaced by a cell. A cell constitutes the smallest unit of a communication area. A cell belongs to a frequency (carrier frequency). The term "cell" sometimes refers to a wireless communication resource and sometimes to a communication target of UE 100. Each base station 200 is capable of wireless communication with UE 100 located in its cell. Base station 200 communicates with UE 100 using the RAN's protocol stack. Details about the protocol stack are described later. In addition, base station 200 connects to other base stations 200 (also referred to as neighboring base stations) via the Xn interface. Base station 200 communicates with neighboring base stations via the Xn interface. In addition, base station 200 provides NR user plane and control plane protocol termination for UE 100, connected to 5GC30 via the NG interface. Such an NR base station 200 is sometimes referred to as a gNodeB (gNB).

[0018] 5GC 30 includes a core network device 300. The core network device 300 includes, for example, an AMF (Access and Mobility Management Function) and / or a UPF (User Plane Function). The AMF performs mobility management for the UE 100. The UPF provides functions dedicated to user plane (U-plane) processing. Both the AMF and UPF are connected to the base station 200 via an NG interface.

[0019] (Protocol stack configuration example) Next, refer to Figure 2 The following describes a configuration example of the protocol stack involved in this implementation.

[0020] The protocol for the radio segment between UE 100 and base station 200 includes the physical (PHY) layer, MAC (Medium Access Control) layer, RLC (Radio Link Control) layer, PDCP (Packet Data Convergence Protocol) layer, and RRC (Radio Resource Control) layer.

[0021] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE100 and the PHY layer of base station 200 via physical channels.

[0022] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of base station 200 via a transport channel. The MAC layer of base station 200 includes a scheduler. The scheduler determines the uplink and downlink transmission formats (transmission block size, modulation and coding scheme (MCS)) and allocates resources to UE 100.

[0023] The RLC layer utilizes the functions of the MAC layer and PHY layer to transmit data to the RLC layer on the receiving side. Data and control information are transmitted between the RLC layer of UE 100 and the RLC layer of base station 200 via a logical channel.

[0024] The PDCP layer performs header compression / expansion and encoding / decoding.

[0025] The SDAP (Service Data Adaptation Protocol) layer can be configured as a higher layer than the PDCP layer. The SDAP layer maps IP flows to radio bearers: IP flows are the unit for QoS (Quality of Service) control in the core network, while radio bearers are the unit for QoS control in the AS (Access Stratum).

[0026] The RRC layer responds to the establishment, re-establishment, and release of radio bearers to control logical channels, transport channels, and physical channels. RRC signaling for various configurations is transmitted between the RRC layer of UE 100 and the RRC layer of base station 200. When an RRC connection exists between the RRC layers of UE 100 and base station 200, UE 100 is in an RRC connected state. When there is no RRC connection between UE 100 and base station 200, UE 100 is in an RRC idle state. When the RRC connection between UE 100 and base station 200 is suspended, UE 100 is in an RRC inactive state.

[0027] Session management and mobility management for UE 100 are performed at the NAS layer, which is located higher than the RRC layer in UE 100. NAS signaling is transmitted between the NAS layer of UE 100 and the NAS layer of the core network device 300.

[0028] In addition to the wireless interface protocol, UE 100 also includes the application layer, etc.

[0029] (Wireless frame configuration) In 5G systems, downlink and uplink transmissions are configured within radio frames of 10ms duration. For example, radio frames are represented by System Frame Numbers (SFNs) from 0 to 1023. For example, a radio frame may consist of 10 subframes. For example, a subframe may be 1ms long. Furthermore, a subframe may include more than one time slot. For example, the number of symbols constituting a time slot is 14 in a standard CP (Cyclic Prefix) and 12 in an extended CP. Additionally, the number of time slots constituting a subframe varies depending on the configured subcarrier spacing. For example, for a standard CP, with a subcarrier spacing configured at 15kHz, the number of time slots per subframe is 1 (i.e., 14 symbols); with a subcarrier spacing configured at 30kHz, the number of time slots per subframe is 2 (i.e., 28 symbols); with a subcarrier spacing configured at 60kHz, the number of time slots per subframe is 4 (i.e., 56 symbols); and with a subcarrier spacing configured at 120kHz, the number of time slots per subframe is 8 (i.e., 128 symbols). Furthermore, for an extended CP, with a subcarrier spacing configured at 60kHz, the number of time slots per subframe is 4 (i.e., 48 symbols). That is, the number of time slots constituting one subframe is determined based on the subcarrier spacing configured by the base station 200. Additionally, the number of symbols constituting one subframe is determined based on the subcarrier spacing configured by the base station 200. That is, based on the subcarrier spacing configured by the base station 200, the number of symbols constituting a 1ms subframe is determined, and the length (length in the time direction) of each symbol varies.

[0030] (LTM) In a mobile communication system 1 conforming to 3GPP technical specifications, it is planned to introduce L1 (Layer 1) / L2 (Layer 2) triggered mobility (L1 / L2-Triggered Mobility: LTM). For example... Figure 3 As shown, the following actions can be performed in LTM.

[0031] Step S10: LTM preparation UE 100 in RRC connection state can perform the following actions as LTM preparation actions.

[0032] Step S11: UE 100 sends a Measurement Report message to base station 200. Base station 200 determines to use LTM and begins candidate cell preparation.

[0033] Step S12: Base station 200 sends an RRC reconfiguration message that includes the LTM candidate cell configuration of one or more candidate cells.

[0034] Step S13: UE 100 saves the LTM candidate cell configuration. UE 100 sends an RRC reconfiguration complete message to base station 200.

[0035] Step S20: Early synchronization UE 100 can perform the following actions as initial synchronization actions.

[0036] Step S21: Before receiving a cell handover command, UE 100 performs downlink (DL) synchronization with the candidate cell. UE 100 can perform DL synchronization based on a synchronization signal (SS) and a physical broadcast channel (PBCH) block (SSB).

[0037] Step S22: Before receiving a cell handover command, UE 100 performs a timed advance (TA) acquisition. UE 100 can perform TA acquisition based on a PDCCH command (specifically, a PDCCH ordered RACH). The PDCCH command can be triggered solely by the source cell.

[0038] Step S30: LTM execution UE 100 can perform the following actions as LTM actions.

[0039] Step S31: UE 100 performs L1 measurements in candidate cells configured by LTM candidate cell configuration. UE 100 sends a lower-layer measurement report (hereinafter referred to as L1 measurement report) based on L1 measurements to base station 200.

[0040] Step S32: Base station 200 determines to perform a cell change to the target cell. Base station 200 sends a MAC CE to trigger the cell change by including a candidate configuration index of the target cell. UE 100 switches the configuration of the target cell.

[0041] Step S33: When a random access (RA) procedure needs to be performed during a cell change, the UE 100 performs the RA procedure for the target cell.

[0042] Step S40: LTM completion UE 100 can perform the following actions as performed by LTM.

[0043] Step S41: UE 100 indicates that the cell change to the target cell was successfully completed.

[0044] Furthermore, UE 100 can execute steps S20 to S40 multiple times based on this configuration to perform subsequent LTM cell handover without releasing the configuration provided in step S12.

[0045] As described above, in LTM, base station 200 sends a cell change command to UE 100 via MAC CE based on the L1 measurement report received from UE 100, thereby changing the serving cell of UE 100. Compared with cell changes based on RRC messages, UE 100 can dynamically perform cell changes, which can reduce mobility latency.

[0046] Currently, the following LTM (hereinafter referred to as subsequence LTM) is being explored, namely, UE 100 performs a cell change from the source cell to the target cell (hereinafter referred to as the first cell change) according to the configuration information used for LTM, and then performs a cell change (hereinafter referred to as the second cell change) without RRC reconfiguration (i.e., without receiving RRC reconfiguration messages).

[0047] As LTM (including subsequence LTM) is performed, it is envisioned that, in addition to the case where the base station managing the source cell manages the target cell (i.e., cell change within the same base station), a case where the base station managing the target cell is different from the base station managing the source cell (i.e., cell change between different base stations) will also be introduced in the future.

[0048] Here, when performing a cell change from a source cell to a target cell via LTM, UE 100 cannot distinguish whether the target base station of the target cell managing the change destination is the same as the base station managing the source cell. Therefore, there is a concern that, for example, since a security key update process is always performed even in cell changes within the same base station, or not performed in cell changes between different base stations, UE 100 may be unable to properly perform the security key update process. Therefore, the actions for properly performing the security key update process in LTM will be explained later.

[0049] Furthermore, in cases where cell changes occur simultaneously within the same base station and between different base stations, the lack of specific prescribed actions raises concerns that LTM (and / or subsequence LTM) may not be properly executed. Therefore, actions for properly executing LTM will be explained later.

[0050] (User equipment configuration) Reference Figure 4 The configuration of the UE 100 according to the implementation method will be described. The UE 100 includes a communication unit 110 and a control unit 120.

[0051] The communication unit 110 performs wireless communication with the base station 200 by transmitting and receiving wireless signals. The communication unit 110 includes at least one transmitting unit 111 and at least one receiving unit 112. The transmitting unit 111 and the receiving unit 112 can be configured to include multiple antennas and RF (Radio Frequency) circuitry. The antennas convert signals into radio waves and radiate these waves into space. Additionally, the antennas receive radio waves in space and convert them back into signals. The RF circuitry performs analog processing on the signals transmitted and received via the antennas. The RF circuitry may include high-frequency filters, amplifiers, modulators, and low-pass filters, etc.

[0052] The control unit 120 performs various controls within the UE 100. The control unit 120 controls communication with the base station 200 via the communication unit 110. The operations of the UE 100 described above and below can be controlled by the control unit 120. The control unit 120 may include at least one processor capable of executing a program and a memory storing the program. The processor can execute the program to perform the operations of the control unit 120. The control unit 120 may include a digital signal processor that performs digital processing of signals transmitted and received via an antenna and RF circuitry. This digital processing includes processing of the RAN protocol stack. Furthermore, the memory stores the program executed by the processor, parameters related to the program, and data related to the program. The memory may include at least one of ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), RAM (Random Access Memory), and flash memory. All or part of the memory may be included within the processor.

[0053] The control unit 120 may include a MAC processing unit that performs processing at the MAC layer and a higher-level processing unit that performs processing at layers higher than the MAC layer. The MAC processing unit may be referred to as a MAC entity. The higher-level processing unit performs processing at layers higher than the MAC layer. The higher-level processing unit may include a PDCP processing unit that performs processing at the PDCP layer and an RRC processing unit that performs processing at the RRCCP layer. The PDCP processing unit may be referred to as a PDCP entity. The RRC processing unit may be referred to as an RRC entity. Furthermore, for the higher-level processing unit, information from the MAC processing unit may be information from lower layers.

[0054] Furthermore, each of the MAC processing unit and the higher-level processing units (PDCP processing unit and / or RRC processing unit) may include one processor or multiple processors. Moreover, the operation of the MAC processing unit and the higher-level processing units may be the operation of the control unit 120. The sending and / or receiving operations of each layer processing unit may be the operation of the communication unit 110 (transmitting unit 111 and / or receiving unit 112).

[0055] In the UE 100 configured in this way, the receiving unit 112 receives a cell change command from the base station via the MAC CE, which triggers a cell change from the source cell to the target cell. The control unit 120 executes the cell change based on the cell change command. Based on determination information received from the base station 200, the control unit 120 determines whether to execute a security key update process for communication in the target cell if a cell change is to be performed. Thus, by determining whether to execute the security key update process based on the determination information, the UE 100 can appropriately execute the security key update process in LTM.

[0056] Furthermore, in UE 100, receiving unit 112 receives an RRC message from a base station including LTM configuration information used to provide one or more LTM candidate cell configurations. When a cell change command triggering a cell change from the source cell to the target cell is received from base station 200 via MAC CE, control unit 120 performs a cell change based on the LTM candidate cell configuration of the candidate cell corresponding to the target cell in one or more LTM candidate cell configurations. Control unit 120 separately stores each LTM candidate cell configuration in one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require security key update processing for communication in the target cell and a second LTM candidate cell configuration that requires security key update processing. Therefore, UE 100 can, for example, distinguish whether security key update processing is required when applying the LTM candidate cell configuration based on the stored location. As a result, the security key update process can be appropriately performed in LTM.

[0057] (Base station configuration) Reference Figure 5 The configuration of the base station 200 according to the implementation method will be described. The base station 200 includes a communication unit 210, a network communication unit 220, and a control unit 230.

[0058] Communication unit 210, for example, receives wireless signals from UE 100 and transmits wireless signals to UE 100. Communication unit 210 includes at least one transmitting unit 211 and at least one receiving unit 212. Transmitting unit 211 and receiving unit 212 may be configured to include RF circuitry. The RF circuitry performs analog processing of signals transmitted and received via antenna. The RF circuitry may include high-frequency filters, amplifiers, modulators, and low-pass filters, etc.

[0059] The network communication unit 220 transmits and receives signals with the network. For example, the network communication unit 220 receives signals from neighboring base stations connected via an Xn interface, which serves as an inter-base station interface, and transmits signals to neighboring base stations. Additionally, the network communication unit 220 receives signals from, for example, a core network device 300 connected via an NG interface, and transmits signals to the core network device 300.

[0060] Control unit 230 performs various controls within base station 200. For example, control unit 230 controls communication with UE 100 via communication unit 210. Additionally, control unit 230 controls communication with nodes (e.g., neighboring base stations, core network device 300) via network communication unit 220. The operation of base station 200 described above and below can be controlled by control unit 230. Control unit 230 may include at least one processor capable of executing a program and a memory storing the program. The processor can execute the program to perform the operations of control unit 230. Control unit 230 may include a digital signal processor that performs digital processing of signals transmitted and received via antennas and RF circuitry. This digital processing includes processing of the RAN protocol stack. Furthermore, the memory stores the program executed by the processor, parameters related to the program, and data related to the program. All or part of the memory may be included within the processor.

[0061] In the base station 200 configured in this way, the transmitting unit 211 sends a cell change command to the UE 100 via the MAC CE. The transmitting unit 211 sends determination information to the UE 100, which is used by the UE 100 to determine whether to perform a security key update process for communication in the target cell when performing a cell change. Thus, by determining whether to perform the security key update process based on the determination information, the UE 100 can appropriately perform the security key update process in LTM.

[0062] Additionally, the control unit 230 of base station 200 generates an RRC message including LTM configuration information, which is used to provide one or more LTM candidate cell configurations. The sending unit 211 sends the RRC message to UE 100. The sending unit 211 sends a cell change command to UE 100 via MACCE, triggering a cell change from the source cell of base station 200 to the target cell. The control unit 230 generates an RRC message including determination information for determining whether security key update processing is needed for each LTM candidate cell configuration in one or more LTM candidate cell configurations, causing UE 100 to distinguish and save each LTM candidate cell configuration in one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require security key update processing for communication in the target cell and a second LTM candidate cell configuration that requires security key update processing. Therefore, UE 100 can appropriately distinguish each LTM candidate cell configuration in one or more LTM candidate cell configurations. As a result, the security key update process can be appropriately performed in LTM.

[0063] (Example of the first action) Reference Figures 6 to 8 The first example of operation will be described below. Sometimes, descriptions already given are omitted. In the mobile communication system 1 of this example of operation, base station 200 includes base station 201 and base station 202. Base station 201 and base station 202 manage different cells. Base station 202 may, for example, be a neighboring base station to base station 201.

[0064] UE 100 is in an RRC connection state with the cell (source cell) managed by base station 201. UE 100 then performs communication with base station 201 in the source cell until a cell change to the target cell is performed.

[0065] Furthermore, for UE 100, communication with base station 200 can be communication with the cell. Therefore, for UE 100, receiving information / messages from base station 200 can be receiving information / messages from the cell, and sending information / messages to base station 200 can be sending information / messages to the cell.

[0066] Step S101: The transmitting unit 111 of UE 100 can transmit capability information to base station 201. Base station 200 can receive capability information from UE 100.

[0067] Capability information can be information indicating whether UE 100 supports cell changes between different base stations via LTM (hereinafter, sometimes referred to as inter-base station LTM).

[0068] Additionally, the capability information may be at least one of the following: information indicating whether UE 100 supports cell changes performed without receiving RRC reconfiguration messages after performing the first cell change described later (hereinafter sometimes referred to as the second cell change), and information indicating whether UE 100 supports subsequence LTM.

[0069] Here, the subsequence LTM can be any of the following actions. (i) After performing a cell change (hereinafter sometimes referred to as the first cell change) in accordance with the LTM configuration information received from base station 200 (i.e., the source cell), the cell change action is performed without RRC reconfiguration. (ii) After performing the first cell change, perform the cell change action without receiving an RRC reconfiguration message. (iii) After performing the first cell change, without discarding the LTM configuration information (i.e., the LTM configuration information received from the previous source cell rather than the current source cell), perform the cell change action according to the LTM configuration information. (iv) Actions for cell changes between L1 / L2 mobility candidates without performing RRC reconfiguration • (v) Performing consecutive cell changes between L1 / L2 mobility candidates without performing RRC reconfiguration.

[0070] Furthermore, the cell change in this action example (i.e., the cell change via LTM) can be referred to as an LTM cell change. An LTM cell change can include a first cell change and a second cell change.

[0071] The first cell change can be a cell change based on LTM configuration information received directly from the source cell. The first cell change can be referred to as the first LTM (or the first LTM cell change).

[0072] The second cell change can be a cell change based on LTM configuration information not directly received from the source cell. Therefore, a second cell change can be a cell change performed without RRC reconfiguration (without directly receiving RRC reconfiguration messages from the source cell). The second cell change can be referred to as a subsequence LTM (or second LTM cell change).

[0073] Step S102: The transmitting unit 111 of UE 100 sends a measurement report (message) to the base station 201. The receiving unit 212 of base station 201 receives the measurement report from UE 100.

[0074] The control unit 230 of base station 201 determines whether to use LTM. The control unit 230 may determine whether to use LTM based, for example, a measurement report. If it is determined that LTM should be used, the control unit 230 begins candidate cell preparation.

[0075] The control unit 230 can select candidate cells for the target cell in LTM based on the measurement report, and prepare them as candidate cells. For example, the control unit 230 can select candidate cells from the cells managed by the base station 201. In addition, the candidate cells can be referred to as LTM candidate cells.

[0076] Additionally, the control unit 230 can generate configuration information related to LTM (hereinafter referred to as LTM configuration information). The control unit 230 can, for example, include the generated LTM configuration information (e.g., LTM-Config) in the RRC reconfiguration message (see reference). Figure 8 (E1 and E12). The control unit 230 can instruct the UE 100 to perform LTM (LTM-related actions) by including LTM configuration information in the RRC reconfiguration message. When LTM configuration information is included in the RRC reconfiguration message, the UE 100 can perform LTM (LTM-related actions).

[0077] LTM configuration information (e.g., LTM-Config) may be information used to provide configuration for (more than one) LTM candidate cells. The control unit 230 may include, for example, at least one of the following in the LTM configuration information (e.g., LTM-Config): a list for releasing candidate cells (hereinafter, sometimes referred to as the LTM candidate release list (e.g., ltm-CandidateToReleaseList)) or a list for adding or changing candidate cells (hereinafter, sometimes referred to as the LTM add / change list (e.g., ltm-CandidateToAddModList)).

[0078] The LTM candidate release list can be a list of LTM candidate cell configurations that are being removed. The LTM candidate release list can include the identifiers of the candidate cells (e.g., ltm-CandidateId).

[0079] The LTM addition change list can be a list that includes LTM candidate information (e.g., LTM-Candidate). The LTM addition change list can be a list of added and / or changed LTM candidate cell configurations. LTM candidate information may include, for example, at least any of the following. • Identifier of the candidate cell (e.g., ltm-CandidateId) • LTM candidate configuration information (e.g., ltm-CandidateConfig) • LTM configuration completion information (e.g., ltm-ConfigComplete) indicating whether the LTM candidate cell configuration is a complete configuration or a delta-configuration. • Configuration information used to configure information for initial synchronization (e.g., ltm-EarlyUL-SyncConfig) • Indicates whether an identifier (e.g., ltm-NoResetID) is not executed during the LTM cell change process for L2 candidate cells. • A list of information used for initial synchronization (e.g., ltm-Candidate-Tci-States-ToAddModList) • Identifiers used to eliminate (remove) information used for initial synchronization (e.g., ltm-Candidate-Tci-States-ToReleaseList)

[0080] The identifier of a candidate cell can be an identifier for an LTM candidate cell configuration. The LTM candidate cell configuration can be information indicating (or including) the LTM candidate cell configuration (which may be referred to as LTM candidate cell configuration information). The LTM candidate cell configuration may include an RRC reconfiguration message used to configure an LTM candidate cell. Therefore, the LTM candidate cell configuration may include an RRC (re)configuration (RRC reconfiguration message) configured for UE 100. The LTM candidate cell configuration may include cell group configuration information (e.g., CellGroupConfig), which includes serving cell configuration information (e.g., ServingCellConfig), etc. LTM configuration completion information may indicate whether the LTM candidate cell configuration within the LTM candidate cell configuration information is a complete configuration.

[0081] Furthermore, the LTM candidate cell configuration can be configured via LTM candidate information (e.g., LTM-Candidate) or indicated by LTM candidate information. The LTM candidate cell configuration can be referred to as LTM candidate cell configuration information. As described above, the LTM configuration information can include RRC reconfiguration information applied in the cell after a cell change. RRC reconfiguration information can be information indicating RRC reconfiguration or an RRC reconfiguration message.

[0082] Furthermore, in this specification, when simply referred to as an RRC reconfiguration message, the RRC reconfiguration message can be an RRC reconfiguration message including LTM configuration information, or it can be an RRC reconfiguration message included in the LTM candidate cell configuration. For example, when simply referred to as an RRC reconfiguration message, the RRC reconfiguration message can be an RRC reconfiguration message sent from base station 200 (base station 201 in this example) (received by UE 100), or it can be an RRC reconfiguration message included in the LTM candidate cell configuration corresponding to the target configuration identifier indicated from the MAC layer during LTM execution. Furthermore, the control unit 120 may include a MAC processing unit that performs processing in the MAC layer and a higher-layer processing unit that performs processing in layers higher than the MAC layer. The MAC processing unit may be referred to as a MAC entity. The higher-layer processing unit performs processing in layers higher than the MAC layer. The higher-layer processing unit may include a PDCP processing unit that performs processing in the PDCP layer and an RRC processing unit that performs processing in the RRC layer. The PDCP processing unit may be referred to as a PDCP entity. The RRC processing unit may be referred to as an RRC entity. Furthermore, for the higher-level processing unit, information from the MAC processing unit can be information from the lower level.

[0083] The control unit 230 of base station 201 can determine whether to use subsequence LTM. For example, the control unit 230 can determine whether to use subsequence LTM based on capability information from UE 100.

[0084] If the capability information indicates that UE 100 supports Subsequence LTM (or Second Cell Change), the control unit 230 can determine that Subsequence LTM will be used. Conversely, if the capability information indicates that UE 100 does not support Subsequence LTM (or Second Cell Change), the control unit 230 can determine that Subsequence LTM will not be used. When it is determined that Subsequence LTM will be used, the control unit 230 can begin candidate cell preparation. Similar to LTM, the control unit 230 can begin candidate cell preparation.

[0085] The control unit 230 can determine whether the UE 100 supports inter-base station LTM based on the capability information. If the capability information indicates that the UE 100 supports inter-base station LTM, the control unit 230 can determine whether to enable the UE 100 to perform LTM cell change to the cell of another base station 200 (e.g., base station 201) based on the measurement report.

[0086] If the capability information indicates that UE 100 supports inter-base station LTM, the control unit 230 can determine that UE 100 should perform an LTM cell change to the cell of another base station 200. Conversely, if the capability information indicates that UE 100 does not support inter-base station LTM, the control unit 230 can determine that UE 100 should not perform an LTM cell change to the cell of another base station 200. In this case, the control unit 230 can omit step S103.

[0087] When the UE 100 performs an LTM cell change to the cell of another base station 200 (e.g., base station 201) based on the measurement report, the control unit 230 may perform the following processing.

[0088] Step S103: For example, the network communication unit 220 of base station 201 sends a handover request message to base station 202, requesting resources to be prepared for handover. The network communication unit 220 of base station 202 receives the handover request message from base station 201. Alternatively, it could be a message other than a handover request message. This message could be a message requesting preparation for cell change via LTM and / or subsequence LTM.

[0089] The handover request message may include information requesting a cell change (LTM cell change) to the cell of base station 202 via LTM and / or sub-sequence LTM. The handover request message may include information for identifying candidate cells among the cells managed by base station 202.

[0090] The control unit 230 of base station 202 can, for example, determine whether to permit LTM cell change based on the handover request message. If LTM cell change is permitted, the control unit 230 can perform the following processing.

[0091] Step S104: The network communication unit 220 of base station 202 sends a Handover Request Acknowledge message to base station 201. This Handover Request Acknowledge message is used to notify the source base station (i.e., base station 201) of the resources prepared in the target location. The network communication unit 220 of base station 201 receives the Handover Request Acknowledge message from base station 202. This message may be used to notify the permission to prepare for cell change via LTM and / or subsequence LTM.

[0092] The handover request confirmation message may include information about the cells managed by base station 202, which is information that should be included in the LTM configuration information. For example, the control unit 230 of base station 202 may include at least part or all of the LTM candidate cell configuration (LTM candidate cell configuration information) related to the candidate cells of base station 202 in the message.

[0093] Furthermore, in cases where LTM cell changes are not permitted, for example, the control unit 230 may send a handover preparation failure message to the base station 201, which is used to notify the source base station (i.e., base station 201) of the handover preparation failure.

[0094] The control unit 230 of base station 201 may include the LTM candidate cell configuration (LTM candidate cell configuration information) related to the candidate cells of base station 202 in the LTM configuration information. Alternatively, the control unit 230 of base station 201 may generate not only its own LTM candidate cell configuration, but also the LTM candidate cell configuration of base station 202. The control unit 230 may include the generated LTM candidate cell configuration in the LTM configuration information. The control unit 230 generates an RRC message including the LTM configuration information.

[0095] Step S105: The transmitting unit 211 of base station 201 sends an RRC reconfiguration message including LTM configuration information to UE 100. The receiving unit 112 of UE 100 receives the RRC reconfiguration message from base station 201 as an RRC message. The control unit 120 of UE 100 stores the LTM configuration information.

[0096] Step S106: The transmitting unit 111 of UE 100 sends an RRC reconfiguration complete message to the base station 201. The receiving unit 212 of base station 201 receives the RRC reconfiguration complete message from UE 100.

[0097] Step S107: Downlink synchronization with each candidate cell can be performed as an initial synchronization action. The control unit 120 of UE 100 performs downlink synchronization, for example, based on the SSBs sent from each candidate cell.

[0098] Additionally, uplink synchronization with each candidate cell can be performed as an initial synchronization action. For example, the transmitting unit 211 of base station 201 can send a Physical Downlink Control Channel (PDCCH) command (i.e., Downlink Control Information (DCI)) to UE 100 from among the candidate cells configured for LTM candidate cells in the configuration of UE 100. This command is used to initiate the RA process for initial synchronization. The receiving unit 112 of UE 100 can receive the PDCCH command from base station 201. Furthermore, the PDCCH command in initial synchronization can be a PDCCH command for obtaining the TA value without a RAR response (PDCCH ordered-RACH for TA Acquisition without RAR). The control unit 120 of UE 100 can initiate the RA process based on the PDCCH command.

[0099] The transmitting unit 111 of UE 100 transmits the RA preamble (message 1) to base station 201 on the Physical Random Access Channel (PRACH) in each candidate cell. The receiving unit 212 of base station 201 receives the RA preamble from UE 100 in each candidate cell. The control unit 230 of base station 201 calculates the timing advance (TA) value based on the RA preamble from UE 100. The control unit 230 can perform control to omit the transmission of the RA response (i.e., message 2), which is a response to the RA preamble.

[0100] Furthermore, the control unit 230 may include information in the RA response (i.e., message 2) instructing the execution of LTM without RACH. This information may include information instructing the UE 100 to skip the RA process for LTM cell change. This information may also indicate that LTM without RACH should be executed if the UE 100 wants to apply the same TA as the source cell (base station 200 managing the source cell).

[0101] Step S108: The transmitting unit 111 of UE 100 performs L1 measurements in each candidate cell configured by LTM configuration information, and then sends an L1 measurement report to base station 201. The receiving unit 212 of base station 201 receives the L1 measurement report from UE 100. The L1 measurement report is a measurement report based on the lower layer of L1 measurement. The L1 measurement report is sent at a layer below the RRC layer. In addition, the measurement report in step S110 is sent at the RRC layer.

[0102] The control unit 230 of base station 201 determines the target cell in LTM (i.e., LTM target cell) based on the L1 measurement report. Furthermore, during LTM execution, the control unit 230 can determine whether to have UE 100 perform RACH-less LTM or RACH-based LTM. RACH-less LTM is LTM where UE 100 performs uplink transmission without performing the RA procedure between UE 100 and base station 201, while RACH-based LTM is LTM where the RA procedure is performed between UE 100 and base station 201.

[0103] Control unit 230 generates a MAC CE for sending a cell change command. This MAC CE may, for example, be referred to as an LTM cell change command MAC CE. This MAC CE may also be referred to as a cell change command (i.e., it may be a cell change command). Hereinafter, the LTM cell change command MAC CE will sometimes be appropriately referred to as a cell change command. The cell change command may, for example, include at least any of the following information (i.e., fields). • Target Configuration ID, indicating the index of candidate target configurations applied to LTM cell changes. • A timing advance command indicating whether the TA used for the LTM target cell is valid. • An identifier (TCI state ID) indicating the TCI (Transmission Configuration Indication) status for the LTM target cell and indicating that the TCI state is active. • An identifier (UL TCI state ID) indicating the uplink TCI state used for the LTM target cell and indicating that the uplink TCI state is active. • Identifier of the downlink bandwidth portion activated in the LTM target cell (DL BWP ID) • Identifier (UL BWP ID) of the uplink bandwidth portion activated in the LTM target cell. Information associated with contention-free random access (CFRA) resources

[0104] The target configuration identifier can be the identifier of the candidate cell among the aforementioned candidate cell identifiers, which is the modified cell.

[0105] The timing advance command (field) can indicate whether the TA (TA value) is valid for the target cell (e.g., SpCell) corresponding to the target configuration (i.e., LTM candidate cell configuration) indicated by the target configuration identifier (field). When a predetermined value (e.g., FFF) is set to the value of this field, this field can indicate that timing adjustments valid for the Primary Timing Advance Group (PTAG) of the LTM target cell are unavailable. In this case, UE 100 needs to perform a RA procedure to the LTM target cell. That is, UE 100 performs RACH-based LTM. On the other hand, when a value other than the predetermined value (e.g., FFF) is set to the value of this field, this field indicates the index value (i.e., TA value) of the amount of timing adjustments to be applied by the MAC entity controlling UE 100. That is, the timing advance command (field) indicates that the RA procedure for LTM cell changes can be skipped. In this case, UE 100 performs LTM without RACH. Here, the predetermined value can be predefined by specifications, etc., and can be a value known between base station 201 and UE 100.

[0106] When applying (or applying) the same TA as the source cell (the base station managing the source cell), the control unit 120 of UE 100 can perform LTM without RACH. When the timing advance command (field) is the same as the TA applied in the current source cell, the control unit 120 can perform LTM without RACH. Alternatively, in addition to the timing advance command (field), the cell change command may also include information (fields) indicating that the same TA as the source cell (the base station managing the source cell) should be applied (or applied). Information (fields) associated with CFRA resources may indicate the resources used by UE 100 when performing CFRA (e.g., radio resources, which RA preamble to use, preamble index, etc.).

[0107] Step S109: The transmitting unit 211 of base station 201 sends a cell change command to UE 100 via MAC CE. The receiving unit 112 of UE 100 receives the cell change command from base station 201 via MAC CE.

[0108] The control unit 120 of UE 100 switches the configuration of the target cell based on the identifier of the candidate cell included in the cell change command (MAC CE) (i.e., the target configuration identifier). For example, the control unit 120 applies a candidate cell configuration that establishes a correspondence with the identifier of the candidate cell that is the same as the target configuration identifier included in the cell change command (MAC CE). For example, the MAC layer in UE 100 can notify the RRC layer of information (and the target configuration identifier) ​​that a cell change command (MAC CE) has been received. Additionally, if the MAC layer provides notification of the received cell change command (and the target configuration identifier), the RRC layer in UE 100 can apply candidate cell configuration information that establishes a correspondence with the identifier of the candidate cell that is the same as the target configuration identifier. That is, the RRC layer of UE 100 can apply the LTM candidate cell configuration based on receiving information indicating that a cell change process is triggered through the MAC layer. Here, the LTM candidate cell configuration can be the LTM candidate cell configuration corresponding to the target configuration identifier indicated from the MAC layer.

[0109] The control unit 120 determines whether to perform RACH-based LTM or RACH-free LTM based on the values ​​included in the timing advance command. When a predetermined value (e.g., FFF) is set in the timing advance command, the control unit 120 determines to perform RACH-based LTM. Conversely, when a value other than the predetermined value (e.g., FFF) is set in the timing advance command, the control unit 120 determines to perform RACH-free LTM. If the same TA as the current source cell needs to be applied, the control unit 120 can determine to perform RACH-free LTM. The control unit 120 can also determine whether to apply the same TA as the current source cell based on information received from the base station 201 (e.g., information included in the RA response and / or information included in the cell change command).

[0110] Upon receiving a cell change command from base station 200 via MAC CE, the control unit 120 of UE 100 performs a first cell change according to the LTM configuration information. In this example, we assume and explain the implementation of a cell change for a cell managed by base station 201.

[0111] Step S110: The control unit 120 of UE 100 performs a security key update determination. Specifically, the control unit 120 determines whether to perform a security key update process for communication in the target cell during a cell change based on determination information received from base station 201 (hereinafter, sometimes referred to as update determination information). Details of the security key update determination are described later.

[0112] If it is determined that a security key update process should be performed, the control unit 120 performs the security key update process. The control unit 120 performs the processing of step S111. On the other hand, if it is determined that a security key update process should not be performed, the control unit 120 omits (or skips) the security key update process.

[0113] Step S111: The control unit 120 performs a security key update process. The control unit 120 performs the security key update process, for example, based on information for the security key update process included in the RRC reconfiguration information (RRC reconfiguration message), which includes LTM candidate configuration information (e.g., ltm-CandidateConfig) of the candidate cell corresponding to the target cell.

[0114] The control unit 120 derives or updates the security key based on information used in the security key update process (hereinafter, sometimes referred to as key update information). The key update information may include, for example, at least any of the following information. Master key update information (e.g., "MasterKeyUpdate") Security Key • Identifier of the algorithm selected for the DRB (Data Radio Bearer) and / or SRB (Signalling Radio Bearer) requested for use in UE 100 • UP integrity protection and encryption instructions • Counter information (e.g., "sk-Counter", "sk-counter-list")

[0115] The security key can be referred to as "KeNB" or "KgNB". The counter information indicates the counter value used to derive the security key. The counter information can also be a parameter indicating that a new security key is required.

[0116] The control unit 120 uses a security key to export or update a key used for communication protection between the UE 100 and the base station (target base station) that manages the target cell.

[0117] The control unit 120 can derive or update the security key based on the counter value indicated by the counter information. Additionally, the control unit 120 can, for example, derive or update the required RRC key and UP key based on the derived security key.

[0118] In addition, the RRC key is a key used for RRC signaling. The RRC key is a key derived from the security key by UE 100 and base station 200. The RRC key may include a key (KRRCint) used only to protect RRC signaling with a specific integrity algorithm, and a key (KRRCenc) used only to protect RRC signaling with a specific encryption algorithm.

[0119] The UP key is a key used for uplink (UP) services. The UP key is derived from the security key by UE 100 and base station 200. The UP key may include a key (KRRCint) used only to protect UP services between UE 100 and base station 200 with a specific integrity algorithm, and a key (KRRCenc) used only to protect UP services with a specific encryption algorithm.

[0120] The control unit 120 of UE 100 can perform integrity verification based on key update information. Additionally, the control unit 120 can activate RRC and UP protection according to the key update information received for each associated SRB and / or DRB.

[0121] In addition, the security key update process can be, for example, the AS (Access Stratum) security key update process.

[0122] Step S112: If it is determined that RACH-based LTM is to be performed, the control unit 120 of UE 100 performs the random access (RA) procedure.

[0123] Step S113: When UE 100 performs RACH-based LTM, UE 100's control unit 120 can consider the LTM execution process as successfully executed (i.e., LTM execution completed) if the random access (RA) procedure is successfully completed. Base station 201's control unit 230 can determine that the LTM execution process has been successfully executed (i.e., LTM execution completed) based on the reception of the preamble in the RA procedure (contention-free RA (CFRA)) or the reception of message 3 or message A in the RA procedure (contention-based RA (CBRA)).

[0124] On the other hand, when UE 100 performs LTM without RACH, the transmitting unit 111 of UE 100 sends uplink transmission (e.g., first uplink data) to base station 201. If it is determined that the network can successfully receive the uplink transmission, the control unit 120 of UE 100 can consider the LTM execution process to have been successfully executed (i.e., LTM execution is complete).

[0125] The receiving unit 112 of base station 201 receives uplink transmissions from UE 100. The control unit 230 of base station 201 can identify that UE 100 has changed its serving cell to the target cell based on the reception of uplink transmissions (e.g., initial uplink data) in the target cell. Thus, the control unit 230 can determine that the LTM execution process has been executed normally (i.e., LTM execution is complete).

[0126] Subsequently, the control unit 120 of UE 100 determines whether the second cell change is permitted. The control unit 120 may determine whether the execution of the subsequence LTM is permitted (or whether the subsequence LTM can be executed).

[0127] If the second cell change is permitted, the control unit 120 can execute the processing in step S121. On the other hand, if the second cell change is not permitted, the control unit 120 can terminate the processing in this operation example. In this case, the control unit 120 can release the LTM configuration information received from the source cell before the cell change.

[0128] Furthermore, the control unit 120 can apply the RRC reconfiguration information (RRC reconfiguration message) included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell based on the execution of cell change, so as to perform communication with the target cell.

[0129] The control unit 120 of UE 100 can invalidate the LTM candidate cell configuration of the candidate cell corresponding to the target cell based on the execution of cell change to the target cell.

[0130] Steps S121 and S122: Steps S121 and S122 correspond to steps S107 and S108.

[0131] When the control unit 120 invalidates the LTM candidate cell configuration of the candidate cell corresponding to the target cell, the candidate cell that has established a correspondence with that LTM candidate cell configuration (i.e., the current serving cell) is not the target cell. Therefore, the control unit 120 does not send L1 measurement reports to the current serving cell. The control unit 120 can control the process so that L1 measurement reports for the cell that has established a correspondence with the invalidated LTM candidate cell configuration are not triggered.

[0132] Alternatively, the control unit 120 may omit sending an L1 measurement report to the source cell. The control unit 120 may control the process so that L1 measurement reports for cells associated with LTM candidate cell configurations including the source cell's identifier (e.g., cell ID) are not triggered.

[0133] Steps S121 to S127: Steps S121 to S127 correspond to steps S107 to S113.

[0134] In addition, similar to step S110, UE 100 can determine whether to perform the security key update process in the current serving cell (i.e., the cell after the second cell change).

[0135] In addition, the control unit 120 of UE 100 can reactivate invalidated LTM candidate cell configurations based on the execution of cell changes after the target cell is set as the source cell.

[0136] Furthermore, after the first cell change, UE 100 does not directly receive RRC reconfiguration messages from the current serving cell (i.e., the target cell before the cell change). Therefore, the cell change based on the cell change command in step S123 is the second cell change.

[0137] As described above, the transmitting unit 211 of base station 200 sends a cell change command to UE 100 via MAC CE. The transmitting unit 211 sends update determination information to UE 100, which is used by UE 100 to determine whether to perform a security key update process for communication in the target cell when performing a cell change. Additionally, the receiving unit 112 of UE 100 receives the cell change command from the base station via MAC CE, which triggers a cell change from the source cell to the target cell. The control unit 120 performs the cell change based on the cell change command. The control unit 120 determines whether to perform a security key update process for communication in the target cell when performing a cell change based on the update determination information received from base station 200. Thus, by determining whether to perform a security key update process based on the update determination information, UE 100 can appropriately perform the security key update process in LTM.

[0138] Furthermore, the control unit 120 can omit sending the L1 measurement report for the source cell to the source cell. This avoids the UE 100 executing unused L1 measurement reports.

[0139] Furthermore, the control unit 120 of UE 100 can invalidate the LTM candidate cell configuration of the candidate cell corresponding to the target cell based on the execution of a cell change to the target cell. The control unit 120 can also validate the invalidated LTM candidate cell configuration based on the execution of a cell change after the target cell has been set as the source cell. Therefore, since the LTM candidate cell configuration is invalidated for the current serving cell of UE 100, L1 measurement reports can be omitted. As a result, UE 100 can avoid executing unused L1 measurement reports. On the other hand, after UE 100 performs a cell change from the serving cell (source cell), since the LTM candidate cell configuration for that cell is validated, it becomes the object of L1 measurement reports. Therefore, UE 100 can perform LTM cell changes for the same cell.

[0140] (Decision actions related to the security key update process) Next, refer to Figures 8 to 12 Here is an example of the decision action of UE 100. The control unit 120 of UE 100 determines whether to perform a security key update process for communication in the target cell when performing a cell change by at least one of the following methods.

[0141] In the first method, the control unit 120 determines the update determination information included in the MAC CE (see reference). Figure 9 ).

[0142] Step S211: Control unit 120 determines whether the MAC CE includes update determination information. Here, the MAC CE is the MAC CE used to send cell change commands (LTM cell change command MAC CE).

[0143] If the MAC CE includes update determination information, the control unit 120 can perform the processing in step S212. If the MAC CE does not include update determination information, the control unit 120 can perform the processing in step S214.

[0144] Updating the decision information can, for example, indicate whether to perform a security key update process. The updated decision information can indicate whether a change to the security key is required. In this case, the control unit 120 can execute the processing in step S212.

[0145] Alternatively, if the update determination information is included in the LTM cell change command MAC CE, the update determination information can instruct the execution of the security key update process. If it is not included in the LTM cell change command MAC CE, the update determination information can instruct that the security key update process not be executed. In this case, the control unit 120 can omit the processing of step S212.

[0146] Step S212: The control unit 120 determines whether the update determination information indicates the execution of the security key update process. If the update determination information indicates the execution of the security key update process (or indicates that the security key needs to be changed), the control unit 120 executes step S213. On the other hand, if the update determination information indicates that the security key update process is not executed (or indicates that the security key does not need to be changed), the control unit 120 executes step S214.

[0147] Step S213: The control unit 120 determines that a security key update process should be performed. In this case, the control unit 120 can perform the security key update process based on information (key update information) included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell for the security key update process.

[0148] Step S214: The control unit 120 determines that it will not perform the security key update process. In this case, the control unit 120 can omit the security key update process. Regardless of whether the key update information is included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell, the control unit 120 can omit the security key update process. Therefore, even if the key update information is included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell, the control unit 120 can omit the security key update process.

[0149] Furthermore, this determination can be performed by the MAC processing unit of the control unit 120. The MAC processing unit can determine whether the LTM cell change command MAC CE includes update determination information.

[0150] When performing step S213, the MAC processing unit may notify higher layers (above the MAC layer) of the target cell identifier (e.g., target configuration identifier) ​​and the content of the update decision information included in the LTM cell change command MAC CE. The MAC processing unit may also notify higher layers of the target configuration identifier and the update decision information. Instead of the update decision information (its content), the MAC processing unit may notify higher layers of an instruction to execute the security key update process.

[0151] In this case, the RRC processing unit can be notified of the target configuration identifier and update decision information (content) from a lower layer (below the RRC layer). The RRC processing unit can then perform the security key update process based on this notification.

[0152] On the other hand, when performing step S214, the MAC processing unit may notify the higher layer of the target configuration identifier, but may not notify the higher layer of the update decision information.

[0153] In this case, the RRC processing unit can be notified of the target configuration identifier from a lower layer (below the RRC layer) without being notified to update the decision information (content). Based on this notification, the RRC processing unit can omit the security key update process. If the decision information (content) or indication is not notified, the RRC processing unit can omit the security key update process.

[0154] Alternatively, this determination may be performed by the RRC processing unit of control unit 120. When the LTM cell change command MAC CE includes the target cell identifier and update determination information, the MAC processing unit may notify the higher layer of the target cell identifier and the content of the update determination information. When the LTM cell change command MAC CE includes update determination information, the MAC processing unit does not notify the higher layer of the content of the update determination information. If the content of the update determination information or the indication is not notified, the RRC processing unit may treat the LTM cell change command MAC CE as not including update determination information and perform the determination according to this determination process.

[0155] As described above, the update decision information can be included in the MAC CE containing the cell change command. Therefore, network 10 can instruct UE 100 whether to perform a security key update procedure when a cell change is indicated. Network 10 can flexibly control the execution of the security key update procedure.

[0156] Furthermore, the control unit 120 of UE 100 can determine whether to perform the security key update process based on whether decision information is included in the MAC CE including the cell change command. Therefore, under predetermined conditions (e.g., conditions under which UE 100 does not perform the security key update process), decision information may not be included, thus reducing the amount of information included in the MAC CE.

[0157] Additionally, the control unit 120 of UE 100 may include a MAC processing unit that performs processing at the MAC layer. When the MAC CE including the cell change command includes the identifier of the target cell and determination information, the MAC processing unit can notify the layer above the MAC layer of the content of the target cell's identifier and determination information. Thus, at a higher layer, determination can be performed based on the identifier of the target cell and the content of the determination information at a higher layer (e.g., the RRC layer) where the security key update process is performed. Furthermore, the determination information can be used even when a need arises at a higher layer (e.g., the RRC layer).

[0158] Furthermore, the receiving unit 112 of UE 100 can receive RRC messages including LTM configuration information from base station 200. If, based on update determination information, it is determined that the security key update process will not be executed, even if the LTM candidate cell configuration of the candidate cell corresponding to the target cell includes information for the update process, the control unit 120 can omit the security key update process. Therefore, network 10 can flexibly control the execution of the security key update process.

[0159] In the second method, the control unit 120 makes a determination based on the determination identifier (see reference). Figure 10 ).

[0160] The decision identifier can be an identifier used to identify the management source of the cell. For example, the decision identifier can be an identifier indicating the base station 200 to which the (candidate) cell belongs. For example, the decision identifier can be an identifier indicating the central cell (CU) of the base station 200 to which the (candidate) cell belongs. The decision identifier can be referred to as the cell-set-ID.

[0161] For example, for cells with the same base station 200, the determination identifier can have the same value. For cells with different base stations 200, the determination identifier can have different values. Additionally, for example, for cells with the same central unit (CU) from base stations 200, the determination identifier can have the same value. For example, for cells with the same CU from base stations 200, the determination identifier can have the same value. For cells with different CUs from base stations 200, the determination identifier can have different values.

[0162] The determination identifier may, for example, be included in the RRC reconfiguration message in step S105. For example, such as... Figure 8 As shown, for UE 100, the RRC reconfiguration message received from the serving cell (source cell) includes RRC reconfiguration information (e.g., RRCReconfiguration) (see reference). Figure 8 The E1 field). RRC reconfiguration information includes the LTM configuration information (e.g., LTM-Config) applied in the serving cell (source cell) (see [reference]). Figure 8 (Field E12). This LTM configuration information is equivalent to the LTM configuration information described in step S102.

[0163] LTM configuration information includes the LTM add change list (e.g., ltm-CandidateToAddModList) (see reference). Figure 8The field E22). The LTM addition change list includes a list of multiple LTM candidate information (e.g., first LTM candidate information (e.g., LTM-Candidate#1), second LTM candidate information (e.g., LTM-Candidate#2), ...) (see [reference]). Figure 8 Fields E31 and E32).

[0164] First LTM candidate information (refer to) Figure 8 Field E31 in the document includes the identifier of the first candidate cell (e.g., ltm-CandidateId#1) and the first LTM candidate configuration (e.g., ltm-candidateconfig). The first LTM candidate configuration (see...) Figure 8 Field E312 includes RRC reconfiguration information (e.g., RRCReconfiguration) (see reference). Figure 8 The field E41). RRC reconfiguration information can be an RRC reconfiguration message. Similarly, the second LTM candidate information E32 includes the identifier of the second candidate cell (e.g., ltm-CandidateId#2) and the second LTM candidate configuration. Second LTM candidate configuration (refer to...) Figure 8 Each of the fields in E322 includes RRC reconfiguration information (e.g., RRCReconfiguration) (see [reference]). Figure 8 (Field E42).

[0165] The decision identifier may include the decision identifier of the source cell (hereinafter, sometimes referred to as the source decision identifier) ​​and the decision identifier of the candidate cell (hereinafter, sometimes referred to as the candidate decision identifier).

[0166] For example, the source determination identifier may include a field that is different from the LTM configuration information (field E12) (e.g., Figure 8 The source determination identifier can be a field in the LTM configuration information (field E12) that is different from the field in the LTM change list (e.g., field E11). Figure 8 In field E21).

[0167] Candidate decision identifiers can be included in various LTM candidate cell configurations within one or more LTM candidate cell configurations. Additionally, candidate decision identifiers can be included, for example, in fields within an LTM candidate cell configuration (e.g., field E31) that are different from fields within the LTM candidate configuration information (e.g., field E312) (e.g., field E311). Furthermore, candidate decision identifiers can be included, for example, in fields within an RRC reconfiguration applied when a cell change is performed (e.g., field E41) (e.g., field E51).

[0168] Step S221: The control unit 120 determines whether the determination identifier of the source cell (hereinafter, sometimes referred to as the source determination identifier) ​​and the determination identifier of the candidate cell corresponding to the target cell (hereinafter, sometimes referred to as the target determination identifier) ​​are the same. If the source determination identifier and the target determination identifier are the same, the control unit 120 performs the processing of step S223. On the other hand, if the source determination identifier and the target determination identifier are different, the control unit 120 performs the processing of step S222.

[0169] Furthermore, if the target determination identifier is included in both the first field (e.g., field E31) and the second field (e.g., field E51) in the LTM candidate cell configuration, the control unit 120 may refer to either of the following target determination identifiers. That is, the control unit 120 may determine whether the referenced target determination identifier is the same as the source determination identifier.

[0170] The control unit 120 may refer to the target determination identifier in the first field. Furthermore, when performing the receiving process of the RRC reconfiguration message, the control unit 120 may refer to the determination identifier (e.g., cell set ID) included in the location where LTM configuration information is stored (e.g., variable (UE-LTM-Candidate-r18)).

[0171] Additionally, the control unit 120 may refer to the target determination identifier in the second field. In this case, the control unit 120 may use the referenced target determination identifier to perform the RRC reconfiguration process (reception process) applied during cell change.

[0172] Furthermore, the first field is a field within the LTM candidate cell configuration (e.g., field E31), and is a field different from the fields within the LTM candidate configuration information (e.g., field E312) (e.g., field E311). The second field is a field within the RRC reconfiguration applied when performing a cell change (e.g., field E41) (e.g., field E51).

[0173] As described above, by specifying a reference destination with a target determination identifier, the control unit 120 can perform processing appropriately even when the target determination identifier contains both LTM candidate cell configurations included in the first field and the second field, and LTM candidate cell configurations included only in one of the first field and the second field.

[0174] Step S222: Step S222 is the same as step S213.

[0175] Step S223: Step S223 is the same as step S214.

[0176] Furthermore, after performing a cell change, the control unit 120 can store the determination identifier of the candidate cell corresponding to the target cell as the determination identifier of the source cell. Therefore, even when the UE 100 performs a cell change through subsequence LTM, appropriate determination can be made.

[0177] In addition, such as Figure 11 As shown, in cases where the target determination identifier (e.g., cell-set-id) and the source determination identifier (e.g., VarCellSetID) are not the same (see reference). Figure 11 In the case of an RRC reconfiguration message including key update information (e.g., masterKeyUpdate and / or sk-Counter), the control unit 120 can perform a security key update procedure (AS security key update procedure and / or security key update procedure) (see [reference]). Figure 11 (X2).

[0178] As described above, if the determination identifier of the source cell and the determination identifier of the candidate cell corresponding to the target cell are the same, the control unit 120 can determine that the security key update process will not be performed. If the determination identifier of the source cell and the determination identifier of the candidate cell corresponding to the target cell are different, the control unit 120 can determine that the security key update process will be performed. Therefore, when the source cell and the target cell are the same management source, the UE 100 can omit the execution of the security key update process. This eliminates unnecessary execution of the security key update process and reduces the processing of the UE 100. On the other hand, when the source cell and the target cell are different management sources, the UE 100 can perform the security key update process. The UE 100 can appropriately perform the security key update process in LTM.

[0179] In the third method, the control unit 120 determines based on the key update information (see reference). Figure 12 ).

[0180] Step S231: The control unit 120 determines whether the LTM candidate cell configuration of the candidate cell corresponding to the target cell includes key update information. For example, if the LTM candidate cell configuration includes key update information, the control unit 120 can perform the process of step S233. If the LTM candidate cell configuration includes key update information and update determination information (associated with the target cell) is received, the control unit 120 can perform the process of step S232. If the LTM candidate cell configuration includes key update information and update determination information (associated with the target cell) is not received, the control unit 120 can perform the process of step S233. If the LTM candidate cell configuration does not include key update information, the control unit 120 can perform the process of step S234.

[0181] Furthermore, the control unit 230 of the base station 200 can include key update information in the LTM candidate cell configuration of candidate cells that require a security key update process, and can exclude key update information in the LTM candidate cell configuration of candidate cells that do not require a security key update process.

[0182] For example, when a cell managed by another base station 200 is set as a candidate cell, the control unit 230 of the base station 200 can configure all LTM candidate cells of that candidate cell to include key update information.

[0183] Furthermore, for example, when a cell managed by another base station 200 is set as a candidate cell, even if it is an LTM candidate cell configuration of that candidate cell, the control unit 230 may not include key update information. In this case, the control unit 230 can send update determination information to the UE 100, so that if the UE 100 changes its cell to that candidate cell, it can determine that a change in the security key is required.

[0184] Step S232: Step S232 is the same as step S212. If the update determination information indicates that the security key update process should be performed (or indicates that the security key needs to be changed), the control unit 120 performs the processing of step S233. On the other hand, if the update determination information indicates that the security key update process should not be performed (or indicates that the security key does not need to be changed), the control unit 120 performs the processing of step S234.

[0185] Step S233: Step S233 is the same as step S213.

[0186] Step S234: Step S234 is the same as step S214.

[0187] (Example of the second action) Reference Figures 13 to 16 The second action example will be explained. Sometimes, descriptions that have already appeared are omitted. In this action example, the case where UE 100 selectively saves the LTM candidate cell configuration will be explained.

[0188] Steps S301 to S305: Steps S301 to S305 are the same as steps S101 to S105.

[0189] For example, as explained in step S231 above, the control unit 120 of base station 201 can include key update information in the LTM candidate cell configuration of candidate cells that require a security key update process. It can also exclude key update information from the LTM candidate cell configuration of candidate cells that do not require a security key update process. For example, when a cell managed by another base station 200 is set as a candidate cell, the control unit 230 of base station 201 can include key update information in the LTM candidate cell configuration of that candidate cell.

[0190] Furthermore, the control unit 230 of base station 201 can configure key update information for all LTM candidate cells. In this case, the control unit 230 can instruct UE 100 whether a security key update process needs to be performed based on the determination information.

[0191] Step S306: The control unit 120 of UE 100 distinguishes and saves LTM candidate cell configurations. The control unit 120 can distinguish and save each LTM candidate cell configuration from one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require performing a security key update process for communication in the target cell, and a second LTM candidate cell configuration that requires performing a security key update process. The control unit 120 can distinguish and save LTM candidate cell configurations in response to receiving an RRC reconfiguration message.

[0192] The control unit 120 can distinguish LTM candidate cell configurations based on determination information. This determination information is used to determine whether a security key update process needs to be performed for each LTM candidate cell configuration in one or more LTM candidate cell configurations. The method by which the control unit 120 distinguishes these configurations will be described in detail later.

[0193] For example, the control unit 120 can save the configuration of the first LTM candidate cell in a first storage area. The control unit 120 can save the configuration of the first LTM candidate cell as a first variable (e.g., VarLTMCandidateNoSec). On the other hand, the control unit 120 can save the configuration of the second LTM candidate cell in a second storage area. The control unit 120 can save the configuration of the second LTM candidate cell as a second variable (e.g., VarLTMCandidateWithSec).

[0194] Steps S307 to S310: Steps S307 to S310 are the same as steps S106 to S109.

[0195] Step S311: When performing a cell change based on the first LTM candidate cell configuration, the control unit 120 may determine that the security key update process should be omitted. On the other hand, when performing a cell change based on the second LTM candidate cell configuration, the control unit 120 may determine that the security key update process should be performed.

[0196] Steps S312 to S323: Steps S312 to S323 are the same as steps S110 to S123. In this example, it is assumed that the MAC CE includes and describes the identifiers of the candidate cells managed by base station 202.

[0197] Step S324: Step S324 is the same as step S311.

[0198] Since the MAC CE includes the identifier of the candidate cell managed by base station 202, control unit 120 determines that cell change should be performed based on the second LTM candidate cell configuration. Therefore, control unit 120 can determine that a security key update process should be performed.

[0199] Steps S326 and S327: Same as steps S126 and S127. In this example, UE 100 performs a cell change to the cell managed by base station 202 based on the second LTM candidate cell configuration.

[0200] Step S328: When performing a cell change in accordance with the second LTM candidate cell configuration, the control unit 120 may release all first LTM candidate cell configurations (stored in the first storage area).

[0201] Alternatively, the control unit 120 can release all first LTM candidate cell configurations that do not include key update information from the first LTM candidate cell configuration. The control unit 120 can then reclassify the first LTM candidate cell configurations that include key update information into second LTM candidate cell configurations.

[0202] Step S329: When all first LTM candidate cell configurations are released, the control unit 120 may notify the network 10 to release all first LTM candidate cell configurations. In this example, the sending unit 111 may send release information to the base station 202 from the target cell, the release information indicating the release of all first LTM candidate cell configurations.

[0203] The release information may include, for example, identification information used to identify the base station 201 that directly provides the LTM candidate cell configuration to the UE 100. The identification information may, for example, be a determination identifier of the source cell before the cell change was performed. Additionally, the release information may include information determining the first LTM candidate cell configuration released by the UE 100.

[0204] The transmitting unit 111 of UE 100 may, for example, send an RRC reconfiguration completion message including release information to base station 202. The RRC reconfiguration completion message may be a message sent based on the reception processing of RRC reconfiguration messages included in the LTM candidate cell configuration.

[0205] The control unit 230 of base station 202 can perform the following processing based on the receipt of release information. Even if release information is not received, for example, when an RRC connection is established with UE 100 that performs cell change to cell of base station 202 based on LTM candidate cell configuration sent to base station 201, the control unit 230 can also perform the following processing for base station 201 that directly provides the LTM candidate cell configuration to UE 100.

[0206] Step S330: The network communication unit 220 of base station 202 sends release information to base station 201. The network communication unit 220 of base station 201 receives release information from base station 202.

[0207] The release information can be release information received from UE 100, or information indicating the content of the release information received from UE 100. This release information may include information determining the first LTM candidate cell configuration released by UE 100.

[0208] Step S331: The control unit 230 of base station 201 can release the configuration of the first LTM candidate cell based on the received release information.

[0209] As described above, the receiving unit 112 of UE 100 receives an RRC message from the base station including LTM configuration information, which is used to provide one or more LTM candidate cell configurations. When a cell change command triggering a cell change from the source cell to the target cell is received from the base station 200 via the MAC CE, the control unit 120 performs a cell change based on the LTM candidate cell configuration of the candidate cell corresponding to the target cell in one or more LTM candidate cell configurations. The control unit 120 separately stores each LTM candidate cell configuration in one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require the security key update process for communication in the target cell and a second LTM candidate cell configuration that requires the security key update process. Therefore, UE 100 can, for example, distinguish whether a security key update process needs to be performed when applying the LTM candidate cell configuration based on the stored location. As a result, the security key update process can be appropriately performed in LTM.

[0210] Additionally, the RRC message may include decision information used to determine whether a security key update process needs to be performed for each LTM candidate cell configuration in one or more LTM candidate cell configurations. The control unit 120 can differentiate one or more LTM candidate cell configurations into a first LTM candidate cell configuration and a second LTM candidate cell configuration based on the decision information. Furthermore, the control unit 230 of the base station 200 generates an RRC message including LTM configuration information used to provide one or more LTM candidate cell configurations. The sending unit 211 sends the RRC message to the UE 100. The sending unit 211 sends a cell change command to the UE 100 via the MAC CE, triggering a cell change from the source cell to the target cell of the base station 200. The control unit 230 generates an RRC message including determination information for determining whether security key update processing is needed for each LTM candidate cell configuration in one or more LTM candidate cell configurations. This causes the UE 100 to separately store each LTM candidate cell configuration in one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require security key update processing for communication in the target cell and a second LTM candidate cell configuration that requires security key update processing. Therefore, the UE 100 can distinguish between the first LTM candidate cell configuration and the second LTM candidate cell configuration by receiving an RRC message containing one or more LTM candidate cell configurations.

[0211] Additionally, the control unit 120 can store the first LTM candidate cell configuration in a first storage area. The control unit 120 can also store the second LTM candidate cell configuration in a second storage area. When performing a cell change according to the second LTM candidate cell configuration, the control unit 120 can release all first LTM candidate cell configurations stored in the first storage area. Here, the candidate cells associated with the first LTM candidate cell configurations are cells managed by the same base station 200. On the other hand, since the candidate cells associated with the second LTM candidate cell configurations require a security key update process, they are likely cells managed by different base stations 200. Therefore, when the UE 100 performs a cell change according to the first LTM candidate cell configuration after performing a cell change according to the second LTM candidate cell configuration, it may need to perform a security key update process. Since the UE 100 classifies the first LTM candidate cell configurations as those that do not require a security key update process, by releasing all first LTM candidate cell configurations stored in the first storage area, it is possible to prevent the security key update process from being omitted even though it is required.

[0212] Furthermore, when all first LTM candidate cell configurations are released, the control unit 120 can notify the network 10 of the release of all first LTM candidate cell configurations. Thus, the network 10 can know that the UE 100 has released the first LTM candidate cell configurations. As a result, it is possible to avoid the network 10 issuing instructions to perform cell changes according to the first LTM candidate cell configurations.

[0213] (Distinguishing methods) Next, refer to Figure 15 as well as Figure 16 An example of the differentiation method for UE 100 will be described below. The control unit 120 of UE 100 can differentiate LTM candidate cell configurations based on determination information used to determine whether a security key update process needs to be performed for each LTM candidate cell configuration in one or more LTM candidate cell configurations. The control unit 120 can differentiate one or more LTM candidate cell configurations into a first LTM candidate cell configuration and a second LTM candidate cell configuration based on the determination information. The control unit 120 of UE 100 can differentiate LTM candidate cell configurations using at least one of the following methods.

[0214] Furthermore, this determination information can be updated determination information. As described above, the RRC message (e.g., the RRC reconfiguration message in step S305) can include determination information.

[0215] In the first method, the control unit 120 distinguishes based on the determination identifier as update determination information (see reference). Figure 15 ).

[0216] Step S411: The control unit 120 determines whether the determination identifier of the source cell (hereinafter referred to as the source determination identifier) ​​and the determination identifier of the candidate cell corresponding to the target cell (hereinafter referred to as the candidate determination identifier) ​​are the same. For example, the control unit 120 selects a candidate determination identifier associated with one of more than one LTM candidate cell configurations. If the source determination identifier is the same as the selected candidate determination identifier, the control unit 120 performs the process of step S412. On the other hand, if the source determination identifier is different from the selected candidate determination identifier, the control unit 120 performs the process of step S413.

[0217] Step S412: The control unit 120 classifies the LTM candidate cell configuration associated with the selected candidate determination identifier into a first LTM candidate cell configuration.

[0218] Step S413: The control unit 120 classifies the LTM candidate cell configuration associated with the selected candidate determination identifier into a second LTM candidate cell configuration.

[0219] The control unit 120 performs steps S411 to S413 for all LTM candidate cell configurations. As a result, the LTM candidate cell configurations are distinguished into a first LTM candidate cell configuration and a second LTM candidate cell configuration.

[0220] As described above, the RRC message can include a determination identifier used to identify the management source of the cell as determination information. The control unit 120 can classify the LTM candidate cell configuration of candidate cells with the same determination identifier as the source cell as a first LTM candidate cell configuration. The control unit 120 can also classify the LTM candidate cell configuration of candidate cells with a different determination identifier than the source cell as a second LTM candidate cell configuration. Therefore, since the control unit 120 can identify the management source of the cell, it can avoid failing to perform the security key update process when the management sources of the source cell and the target cell are different.

[0221] In the second method, the control unit 120 uses update determination information to distinguish based on the key update information (see reference). Figure 16 ).

[0222] Step S421: The control unit 120 determines whether the LTM candidate cell configuration includes information for the security key update process (hereinafter referred to as key update information). For example, the control unit 120 determines whether each LTM candidate cell configuration in more than one LTM candidate cell configuration includes key update information.

[0223] The control unit 120 can perform the processing of step S422 for one or more LTM candidate cell configurations that do not include information for the update process. The control unit 120 can also perform the processing of step S423 for one or more LTM candidate cell configurations that include information for the update process.

[0224] Furthermore, the control unit 120 can determine whether each LTM candidate cell configuration includes key update information based on information indicating whether each LTM candidate cell configuration in one or more LTM candidate cell configurations includes key update information (hereinafter referred to as predetermined information). In addition, the predetermined information may be information indicating whether key update information exists in each LTM candidate cell configuration.

[0225] If the predetermined information indicates that the LTM candidate cell configuration does not include key update information, the control unit 120 can perform the processing of step S422 for that LTM candidate cell configuration. On the other hand, if the predetermined information indicates that the LTM candidate cell configuration includes key update information, the control unit 120 can perform the processing of step S423 for that LTM candidate cell configuration.

[0226] Pre-defined information may include, for example, fields that differ from those in the LTM configuration information (field E12) (e.g., Figure 8 In field E11). Additionally, pre-defined information may include fields within the LTM configuration information (field E12) that are different from the fields in the LTM change list (e.g., Figure 8 In field E21), the pre-defined information can indicate whether all LTM candidate cell configurations include key update information.

[0227] The pre-defined information can be included in each of the more than one LTM candidate cell configurations. Additionally, the pre-defined information can be included, for example, in a field within the LTM candidate cell configuration (e.g., field E31) that is different from a field in the LTM candidate configuration information (e.g., field E312) (e.g., field E311). Furthermore, the pre-defined information can be included, for example, in a field within an RRC reconfiguration applied when a cell change is performed (e.g., field E41) (e.g., field E51). In this case, the pre-defined information can indicate whether the LTM candidate cell configuration including the pre-defined information includes key update information.

[0228] Step S422: The control unit 120 classifies the LTM candidate cell configuration into a first LTM candidate cell configuration. That is, the control unit 120 classifies the LTM candidate cell configuration that does not include key update information into a first LTM candidate cell configuration.

[0229] Step S423: The control unit 120 classifies the LTM candidate cell configuration into a second LTM candidate cell configuration. That is, the control unit 120 classifies the LTM candidate cell configuration including key update information into a second LTM candidate cell configuration.

[0230] As described above, the control unit 120 of UE 100 can classify LTM candidate cell configurations that do not include key update information from among one or more LTM candidate cell configurations as first LTM candidate cell configurations. The control unit 120 can also classify LTM candidate cell configurations that include key update information from among one or more LTM candidate cell configurations as second LTM candidate cell configurations. Therefore, by omitting the execution of the security key update process only for LTM candidate cell configurations where the security key update process cannot be performed, and simultaneously executing the security key update process for LTM candidate cell configurations where the security key update process can be performed, the security key update process can be appropriately executed in LTM.

[0231] Furthermore, the LTM configuration information may include information indicating whether each LTM candidate cell configuration in one or more LTM candidate cell configurations includes information for the update process (i.e., predetermined information). The control unit 120 can classify one or more LTM candidate cell configurations into a first LTM candidate cell configuration and a second LTM candidate cell configuration based on the information indicating whether each LTM candidate cell configuration in one or more LTM candidate cell configurations includes information for the update process. Therefore, for each LTM candidate cell configuration, even without confirming whether key update information exists, the control unit 120 can determine whether each LTM candidate cell configuration in one or more LTM candidate cell configurations includes information for the update process based on the predetermined information.

[0232] (Other implementation methods) In the above embodiments, the control unit 120 of UE 100, for example, can prioritize the first method over the second method in the differentiation method for the second action example. Therefore, for example, even if an LTM candidate cell configuration includes key update information, the control unit 120 can differentiate it as a first LTM candidate cell configuration. Alternatively, the control unit 120 can prioritize the second method over the first method. Therefore, even if the source determination identifier is different from the selected candidate determination identifier, the control unit 120 can differentiate it as a first LTM candidate cell configuration.

[0233] In the above embodiments, "release" can be replaced by any of the following: discard, ignore, clear, deactivate, etc.

[0234] In the above embodiments, mobile communication system 1 is described as an example of an NR-based mobile communication system. However, mobile communication system 1 is not limited to this example. Mobile communication system 1 can be a TS system conforming to any other generation of systems (e.g., 6th generation) compliant with LTE (Long Term Evolution) or 3GPP standards. Base station 200 can be, for example, an eNB providing E-UTRA user plane and control plane protocol termination for UE 100 in LTE. Mobile communication system 1 can also be a TS system conforming to standards other than 3GPP standards. Base station 200 can be an IAB (Integrated Access and Backhaul) host or IAB node.

[0235] In the above embodiments, mobile communication system 1 has been described as an example of an NR-based mobile communication system. However, mobile communication system 1 is not limited to this example. Mobile communication system 1 can be a TS system of any other generation system (e.g., 6th generation) conforming to LTE or 3GPP standards. Base station 200 can be, for example, an eNB providing E-UTRA user plane and control plane protocol termination for UE 100 in LTE. Mobile communication system 1 can also be a TS system conforming to standards other than 3GPP standards.

[0236] The steps in the operations described in the above embodiments do not necessarily have to be executed in chronological order as shown in the flowchart or sequence diagram. For example, the steps in the operations may be executed in an order different from that shown in the flowchart or sequence diagram, or they may be executed in parallel. In addition, a part of a step in the operation may be deleted, or further steps may be added to the process. Furthermore, the above-described operation flows are not limited to being implemented independently, and two or more operation flows may be combined for implementation. For example, a part of a step in one operation flow may be added to another operation flow, or a part of a step in one operation flow may be replaced by a part of a step in another operation flow.

[0237] Programs may also be provided to enable a computer to perform the various processes performed by the UE 100 or the base station 200. The programs may be recorded on a computer-readable medium. Using a computer-readable medium, programs can be installed on the computer. Here, the computer-readable medium on which the programs are recorded may also be a non-transient recording medium. There are no particular limitations on the non-transient recording medium, but it may be, for example, a CD-ROM (Compact Disk Read Only Memory) or DVD-ROM (Digital Versatile Disc Read Only Memory). Alternatively, the circuitry for performing the various processes performed by the UE 100 or the base station 200 may be integrated, and at least a portion of the UE 100 or the base station 200 may be configured as a semiconductor integrated circuit (chipset, SoC (System on Chip)).

[0238] In the above embodiments, "transmit" can refer to performing processing at least one layer within a protocol stack for transmission, or it can refer to physically transmitting a signal wirelessly or via a wired connection. Alternatively, "transmit" can also refer to a combination of performing the aforementioned processing at least one layer and physically transmitting a signal wirelessly or via a wired connection. Similarly, "receive" can refer to performing processing at least one layer within a protocol stack for reception, or it can refer to physically receiving a signal wirelessly or via a wired connection. Alternatively, "receive" can refer to a combination of performing the aforementioned processing at least one layer and physically receiving a signal wirelessly or via a wired connection. Similarly, "obtain / acquire" can refer to obtaining information from stored information, obtaining information from information received from other nodes, or obtaining information by generating information. Similarly, unless otherwise explicitly stated, the descriptions "based on" and "depending on / in response to" do not mean "only based on" or "only in response to". The description "based on" means "only based on" and "at least partially based on". Similarly, the phrase "responding to" refers to both "responding only to" and "responding at least partially to". Likewise, "include" and "comprise" do not mean only including the listed items, but rather that they may include only the listed items or other items in addition to the listed items. Likewise, in this disclosure, "or" does not refer to logical XOR, but rather to logical OR. Furthermore, any reference to elements using terms such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of these elements. These terms may be used in this disclosure as a convenient way to distinguish between two or more elements. Therefore, reference to a first element and a second element does not mean that only two elements can be used therein, or that the first element must precede the second element in some form. In this disclosure, for example, where articles such as "a," "an," and "the" are added through translation, these articles may include multiple articles unless the context explicitly indicates that multiple articles are not included.

[0239] It is understood that although this disclosure has been described with reference to embodiments, this disclosure is not limited to those embodiments or constructions. This disclosure also includes various modifications and equivalent variations. In addition, various combinations, methods, and further combinations and methods that include only one element, more or fewer elements therein also fall within the scope and spirit of this disclosure.

[0240] (Postscript) Features related to the above embodiments are noted.

[0241] (Postscript 1)

[0242] A communication device, comprising:

[0243] The receiving unit receives from the base station a Radio Resource Control (RRC) message including LTM configuration information for providing one or more Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configurations; and

[0244] When the control unit receives a cell change command from the aforementioned base station via the Media Access Control (MAC) control unit (CE) that triggers a cell change from the source cell to the target cell, it executes the aforementioned cell change based on the LTM candidate cell configuration of the candidate cell corresponding to the aforementioned target cell in one or more LTM candidate cell configurations.

[0245] The aforementioned control unit separately stores each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require the execution of the security key update process for communication in the aforementioned target cell and a second LTM candidate cell configuration that requires the execution of the aforementioned security key update process.

[0246] (Postscript 2)

[0247] According to the communication device described in Appendix 1, the aforementioned RRC message includes determination information, which is used to determine whether the aforementioned security key update process needs to be performed for each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations.

[0248] Based on the aforementioned determination information, the control unit distinguishes the aforementioned one or more LTM candidate cell configurations into the aforementioned first LTM candidate cell configuration and the aforementioned second LTM candidate cell configuration.

[0249] (Note 3)

[0250] According to the communication equipment described in Appendix 2, the aforementioned RRC message includes a determination identifier for identifying the management source of the cell as the aforementioned determination information.

[0251] The aforementioned control unit distinguishes the LTM candidate cell configurations of candidate cells with the same determination identifier as the aforementioned source cell as the aforementioned first LTM candidate cell configuration.

[0252] The aforementioned control unit distinguishes the LTM candidate cell configurations of candidate cells with determination identifiers different from those of the aforementioned source cell as the aforementioned second LTM candidate cell configurations.

[0253] (Note 4)

[0254] According to the communication equipment described in Appendix 2 or 3

[0255] The aforementioned control unit distinguishes the LTM candidate cell configurations that do not include information used in the aforementioned update process from the aforementioned one or more LTM candidate cell configurations as the aforementioned first LTM candidate cell configuration.

[0256] The aforementioned control unit distinguishes the LTM candidate cell configuration, which includes information used for the aforementioned update process, from the aforementioned one or more LTM candidate cell configurations into the aforementioned second LTM candidate cell configuration.

[0257] (Note 5)

[0258] According to any one of Appendices 2 to 4, the aforementioned LTM configuration information includes information indicating whether each of the aforementioned LTM candidate cell configurations in the more than one LTM candidate cell configurations includes information for the aforementioned update process.

[0259] The aforementioned control unit distinguishes the aforementioned one or more LTM candidate cell configurations into the aforementioned first LTM candidate cell configuration and the aforementioned second LTM candidate cell configuration based on information indicating whether each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations includes information for the aforementioned update process.

[0260] (Note 6)

[0261] The communication device according to any one of Appendices 1 to 5,

[0262] The aforementioned control unit stores the configuration of the first LTM candidate cell in the first storage area.

[0263] The aforementioned control unit stores the configuration of the second LTM candidate cell in the second storage area.

[0264] When the aforementioned cell change is performed in accordance with the aforementioned second LTM candidate cell configuration, the aforementioned control unit releases all of the aforementioned first LTM candidate cell configurations stored in the aforementioned first storage area.

[0265] (Note 7)

[0266] According to the communication device described in Appendix 6, when all the first LTM candidate cell configurations are released, the aforementioned control unit notifies the network that all the aforementioned first LTM candidate cell configurations have been released.

[0267] (Postscript 8)

[0268] A type of base station,

[0269] The control unit generates a Radio Resource Control (RRC) message that includes LTM configuration information for providing one or more Layer 1 / Layer 2 Triggered Mobility (LTM) candidate cell configurations; and

[0270] The sending unit sends the aforementioned RRC message to the communication equipment.

[0271] The aforementioned transmitting unit sends a cell change command to the aforementioned communication equipment via the Media Access Control (MAC) control unit (CE). The aforementioned cell change command triggers a change from the source cell of the aforementioned base station to the target cell.

[0272] The aforementioned control unit generates the aforementioned RRC message, which includes determination information for determining whether the aforementioned security key update process needs to be performed for each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations. This causes the aforementioned communication device to separately save each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not need to perform the security key update process for communication in the aforementioned target cell and a second LTM candidate cell configuration that needs to perform the aforementioned security key update process.

[0273] (Note 9)

[0274] A communication method, executed by a communication device, comprising:

[0275] The steps of receiving a radio resource control (RRC) message from a base station, which includes LTM configuration information for providing one or more Layer 1 / Layer 2 triggered mobility (LTM) candidate cell configurations;

[0276] Upon receiving a cell change command triggering a cell change from the source cell to the target cell from the aforementioned base station via the Media Access Control (MAC) Control Unit (CE), the aforementioned cell change steps are executed based on the LTM candidate cell configuration of the candidate cell corresponding to the aforementioned target cell in one or more LTM candidate cell configurations; and

[0277] The aforementioned control unit distinguishes between storing each LTM candidate cell configuration in the aforementioned one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require performing the security key update process for communication in the aforementioned target cell and a second LTM candidate cell configuration that requires performing the aforementioned security key update process.

[0278] (Postscript 10)

[0279] A communication device (100) includes:

[0280] The receiving unit (112) receives from the base station (200) a Radio Resource Control (RRC) message including LTM configuration information for providing one or more Layer 1 / Layer 2 Trigger Mobility (LTM) candidate information, and receives from the base station a Media Access Control (MAC) Control Unit (CE), wherein the MAC CE includes a cell change command that triggers LTM cell change; and

[0281] The control unit (120) executes the aforementioned LTM cell change based on the aforementioned cell change command.

[0282] When performing the aforementioned LTM cell change, the control unit determines whether to perform the security key update process based on the information in each LTM candidate information included in the aforementioned one or more LTM candidate information.

[0283] (Postscript 11)

[0284] According to the communication equipment described in Appendix 10, the aforementioned cell change command includes a target configuration identifier.

[0285] When performing the LTM cell change based on the LTM candidate information corresponding to the aforementioned target configuration identifier, the control unit determines whether to perform the security key update process based on the aforementioned information included in the LTM candidate information corresponding to the aforementioned target configuration identifier.

[0286] (Postscript 12)

[0287] According to the communication device described in Appendix 10 or 11, the aforementioned one or more LTM candidate information includes LTM candidate information for LTM cell changes performed in response to the aforementioned security key update process and / or LTM candidate information for LTM cell changes not performed in response to the aforementioned security key update process.

[0288] (Postscript 13)

[0289] According to the communication device described in Appendix 12, the aforementioned control unit stores LTM candidate information for LTM cell changes performed in response to the aforementioned security key update process in a first storage area, and stores LTM candidate information for LTM cell changes not performed in response to the aforementioned security key update process in a second storage area.

[0290] (Postscript 14)

[0291] A base station (200) includes:

[0292] The transmitting unit (211) sends a Radio Resource Control (RRC) message to the communication device (100) including LTM configuration information for providing one or more Layer 1 / Layer 2 Trigger Mobility (LTM) candidate information, and uses the Media Access Control (MAC) control unit (CE) to send a cell change command that triggers LTM cell change to the aforementioned communication device; and

[0293] The control unit (230) controls the execution of the aforementioned LTM cell change based on the aforementioned cell change command.

[0294] When the aforementioned LTM cell change is executed, the aforementioned control unit configures whether to execute the security key update process based on the information in each LTM candidate information included in the aforementioned one or more LTM candidate information.

[0295] (Postscript 15)

[0296] According to the base station described in Appendix 14, the aforementioned cell change command includes a target configuration identifier.

[0297] When the aforementioned LTM cell change based on the aforementioned LTM candidate information corresponding to the aforementioned target configuration identifier is executed, the aforementioned control unit configures whether to execute the aforementioned security key update process based on the aforementioned information included in the aforementioned LTM candidate information corresponding to the aforementioned target configuration identifier.

[0298] (Postscript 16)

[0299] According to the base station described in Appendix 14 or 15, the aforementioned one or more LTM candidate information includes LTM candidate information for the aforementioned LTM cell change in which the aforementioned security key update process is performed and / or LTM candidate information for LTM cell change in which the aforementioned security key update process is not performed.

[0300] (Postscript 17)

[0301] According to the base station described in Appendix 16, the LTM candidate information for the aforementioned LTM cell change performed in response to the aforementioned security key update process is stored in the aforementioned communication device in a first storage area, and the LTM candidate information for the LTM cell change not performed in response to the aforementioned security key update process is stored in the aforementioned communication device in a second storage area.

[0302] (Postscript 18)

[0303] A communication method, which is a communication method of a communication device (100), includes:

[0304] The steps of receiving a radio resource control (RRC) message from a base station (200) including LTM configuration information for providing one or more Layer 1 / Layer 2 triggered mobility (LTM) candidate information;

[0305] The steps of receiving a Media Access Control (MAC) Control Unit (CE) from the aforementioned base station, including a cell change command that triggers LTM cell change; and

[0306] Based on the aforementioned cell change command, the aforementioned LTM cell change steps are executed.

[0307] In the aforementioned LTM cell change step, when performing the aforementioned LTM cell change, it is determined whether to perform the security key update process based on the information in each LTM candidate information included in the aforementioned one or more LTM candidate information.

[0308] (Postscript 19)

[0309] According to the communication method described in Appendix 18, the aforementioned cell change command includes a target configuration identifier.

[0310] In the step of performing the aforementioned LTM cell change, when performing the aforementioned LTM cell change based on the aforementioned LTM candidate information corresponding to the aforementioned target configuration identifier, it is determined whether to perform the aforementioned security key update process based on the aforementioned information included in the aforementioned LTM candidate information corresponding to the aforementioned target configuration identifier.

[0311] (Postscript 20)

[0312] According to the communication method described in Appendix 18 or 19, the aforementioned one or more LTM candidate information includes LTM candidate information for LTM cell changes performed in response to the aforementioned security key update process and / or LTM candidate information for LTM cell changes not performed in response to the aforementioned security key update process.

[0313] (Postscript 21)

[0314] According to the communication method described in Appendix 20, in the step of performing the aforementioned LTM cell change, the LTM candidate information of the aforementioned LTM cell change performed in response to the aforementioned security key update process is stored in a first storage area, and the LTM candidate information of the LTM cell change not performed in response to the aforementioned security key update process is stored in a second storage area.

Claims

1. A communication device (100), comprising: The receiving unit (112) receives from the base station (200) a radio resource control (RRC) message including LTM configuration information for providing one or more Layer 1 / Layer 2 triggered mobility (LTM) candidate information, and receives from the base station a media access control (MAC) control unit (CE), the MAC CE including a cell change command that triggers LTM cell change; as well as The control unit (120) executes the LTM cell change based on the cell change command. When performing the LTM cell change, the control unit determines whether to perform the security key update process based on the information in each LTM candidate information included in the more than one LTM candidate information.

2. The communication device according to claim 1, wherein the cell change command includes a target configuration identifier. When the control unit performs an LTM cell change based on the LTM candidate information corresponding to the target configuration identifier, it determines whether to perform the security key update process based on the information included in the LTM candidate information corresponding to the target configuration identifier.

3. The communication device according to claim 1 or 2, wherein the one or more LTM candidate information includes LTM candidate information for LTM cell changes performed in response to the security key update process and / or LTM candidate information for LTM cell changes not performed in response to the security key update process.

4. The communication device according to claim 3, wherein the control unit stores LTM candidate information for LTM cell changes performed in response to the security key update process in a first storage area, and stores LTM candidate information for LTM cell changes not performed in response to the security key update process in a second storage area.

5. A base station (200), comprising: The transmitting unit (211) sends a radio resource control (RRC) message to the communication device (100) including LTM configuration information for providing one or more Layer 1 / Layer 2 trigger mobility (LTM) candidate information, and uses the media access control (MAC) control unit (CE) to send a cell change command that triggers LTM cell change to the communication device; as well as The control unit (230) controls the execution of the LTM cell change based on the cell change command. When the LTM cell change is executed, the control unit configures whether to execute the security key update process based on the information in each LTM candidate information included in the more than one LTM candidate information.

6. The base station according to claim 5, wherein the cell change command includes a target configuration identifier. When an LTM cell change is performed based on the LTM candidate information corresponding to the target configuration identifier, the control unit configures whether to perform the security key update process based on the information included in the LTM candidate information corresponding to the target configuration identifier.

7. The base station according to claim 5 or 6, wherein the more than one LTM candidate information includes LTM candidate information for LTM cell changes in which the security key update process is performed and / or LTM candidate information for LTM cell changes in which the security key update process is not performed.

8. The base station according to claim 7, wherein the LTM candidate information of the LTM cell change performed in response to the security key update process is stored in a first storage area in the communication device, and the LTM candidate information of the LTM cell change not performed in response to the security key update process is stored in a second storage area in the communication device.

9. A communication method, which is a communication method of a communication device (100), comprising: The steps of receiving a radio resource control (RRC) message from a base station (200) including LTM configuration information for providing one or more Layer 1 / Layer 2 triggered mobility (LTM) candidate information; The step of receiving a media access control (MAC) control unit (CE) from the base station, including a cell change command that triggers LTM cell change; as well as The steps for performing the LTM cell change based on the cell change command are as follows. In the step of performing the LTM cell change, when performing the LTM cell change, it is determined whether to perform the security key update process based on the information in each LTM candidate information included in the more than one LTM candidate information.

10. The communication method according to claim 9, wherein the cell change command includes a target configuration identifier. In the step of performing the LTM cell change, when performing the LTM cell change based on the LTM candidate information corresponding to the target configuration identifier, it is determined whether to perform the security key update process based on the information included in the LTM candidate information corresponding to the target configuration identifier.

11. The communication method according to claim 9 or 10, wherein the more than one LTM candidate information includes LTM candidate information for LTM cell changes performed in response to the security key update process and / or LTM candidate information for LTM cell changes not performed in response to the security key update process.

12. The communication method according to claim 11, wherein in the step of performing the LTM cell change, LTM candidate information for the LTM cell change performed in response to the security key update process is stored in a first storage area, and LTM candidate information for the LTM cell change not performed in response to the security key update process is stored in a second storage area.

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