Communication device, base station, and communication method

Abstract

A communication device (100) according to an embodiment comprises: a reception unit (112) that receives, from a base station (200), a radio resource control (RRC) message including LTM configuration information used to provide layer 1 / layer 2 triggered mobility (LTM) candidate information, and uses a media access control (MAC) control element (CE) to receive, from the base station, a cell change command that triggers a cell change; and a control unit (120) that executes an LTM cell change on the basis of the cell change command. The control unit determines whether or not to execute a security key update procedure when executing the LTM cell change, on the basis of an identifier included in the RRC message.

Description

Communication device, base station, and communication method CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims the benefit of priority from Patent Application No. 2023-168813, filed September 28, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a communication device, a base station, and a communication method.

[0003] In a mobile communication system conforming to the technical specifications of 3GPP (registered trademark; the same applies hereinafter) (Third Generation Partnership Project), a standardization project for mobile communication systems, the introduction of L1 (Layer 1) / L2 (Layer 2) triggered mobility (LTM) is planned. In LTM, a base station changes the serving cell of a communication device by transmitting a cell switch command to the communication device via a media access control (MAC) control element (CE) based on an L1 measurement report received from the communication device. Compared to a cell change based on a radio resource control (RRC) message, the communication device can dynamically perform a cell change and reduce mobility delay.

[0004] Currently, UE 100 performs a cell change (hereinafter, a first cell change) from a source cell to a target cell according to the setting information for LTM, and then performs a cell change (hereinafter, a second cell change) without RRC reconfiguration (i.e., without receiving an RRC reconfiguration message). The introduction of LTM (hereinafter, subsequent LTM) is being considered (see, for example, Non-Patent Document 1).

[0005] "R2-2211101" (Report of 3GPP TSG RAN WG2 meeting #119bis-e, Online)

[0006] A communication device according to a first aspect includes: a receiver that receives, from a base station, a Radio Resource Control (RRC) message including Layer 1 / Layer 2 Triggered Mobility (LTM) configuration information used to provide LTM candidate information; and a controller that performs an LTM cell change based on the cell change command, wherein the controller determines, based on an identifier included in the RRC message, whether to perform a security key update procedure when the LTM cell change is performed.

[0007] A base station according to a second aspect includes: a transmitter unit that transmits a Radio Resource Control (RRC) message to a communication device, the RRC message including LTM configuration information used to provide LTM candidate information, and transmits a cell change command to the communication device using a Medium Access Control (MAC) Control Element (CE) to trigger a cell change; and a controller that controls execution of an LTM cell change based on the cell change command, wherein the controller sets, based on an identifier included in the RRC message, whether to perform a security key update procedure when the LTM cell change is executed.

[0008] A communication method according to a third aspect is a communication method executed by a communication device, the communication method comprising: receiving, from a base station, a Radio Resource Control (RRC) message including Layer 1 / Layer 2 Triggered Mobility (LTM) configuration information used to provide LTM candidate information; receiving, from the base station, a cell change command for triggering a cell change using a Medium Access Control (MAC) Control Element (CE); and performing an LTM cell change based on the cell change command, wherein in the performing LTM cell change, it is determined, based on an identifier included in the RRC message, whether to perform a security key update procedure when performing the LTM cell change.

[0009] Objects, features, advantages, etc. of the present disclosure will become clearer from the following detailed description with reference to the accompanying drawings. FIG. 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram illustrating an example configuration of a protocol stack according to an embodiment. FIG. 3 is a diagram illustrating an overview of LTM. FIG. 4 is a diagram illustrating a configuration of a UE according to an embodiment. FIG. 5 is a diagram illustrating a configuration of a base station according to an embodiment. FIG. 6 is a sequence diagram (part 1) illustrating a first operation example according to an embodiment. FIG. 7 is a sequence diagram (part 2) illustrating the first operation example according to an embodiment. FIG. 8 is a diagram illustrating a hierarchical structure of an RRC reconfiguration message according to an embodiment. FIG. 9 is a flowchart (part 1) illustrating an example determination operation according to an embodiment. FIG. 10 is a flowchart (part 2) illustrating an example determination operation according to an embodiment. FIG. 11 is a diagram illustrating an example operation of a UE 100 according to an embodiment. FIG. 12 is a flowchart (part 3) illustrating an example determination operation according to an embodiment. FIG. 13 is a sequence diagram (part 1) illustrating a second operation example according to an embodiment. FIG. 14 is a sequence diagram (part 2) illustrating the second operation example according to an embodiment. Fig. 15 is a flowchart (part 1) for explaining an example of a distinction method according to an embodiment. Fig. 16 is a flowchart (part 2) for explaining an example of a distinction method according to an embodiment.

[0010] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0011] In addition to cases in which the base station that manages the source cell manages the target cell (i.e., cell change within the same base station), it is expected that cases in which a base station different from the base station that manages the source cell manages the target cell (i.e., cell change between different base stations) will also be introduced in the future as cases in which LTM (including subsequent LTM) is executed.

[0012] Here, when a cell change from a source cell to a target cell is executed by LTM, the UE 100 cannot distinguish whether the target base station that manages the target cell to which the change is made is the same as the base station that manages the source cell. For this reason, the UE 100 may always execute the security key update procedure even when the cell is changed within the same base station, or may not execute the security key update procedure when the cell is changed between different base stations, which may cause a concern that the security key update procedure may not be executed properly.

[0013] Therefore, one object of the present disclosure is to provide a communication device, a base station, and a communication method that enable the security key update procedure to be properly executed in LTM.

[0014] (System Configuration) First, the configuration of a mobile communication system 1 according to this embodiment will be described with reference to Fig. 1. The mobile communication system 1 is, for example, a system that complies with the 3GPP Technical Specification (TS). In the following, the mobile communication system 1 will be described using as an example a 5th Generation System (5G system) of the 3GPP standard, i.e., a mobile communication system based on NR (NR (New Radio) radio access).

[0015] The mobile communication system 1 includes a network 10 and a user equipment (UE) 100 that communicates with the network 10. The network 10 includes a next generation radio access network (NG-RAN) 20, which is a 5G radio access network, and a 5G core network (5GC) 30, which is a 5G core network.

[0016] The UE 100 is a communication device that communicates via the base station 200. The UE 100 may be a device used by a user. The UE 100 may be a mobile device such as a mobile phone terminal such as a smartphone, a tablet terminal, a laptop PC, a communication module, or a communication card. The UE 100 may be a vehicle (e.g., a car, a train, etc.) or a device provided therein (e.g., a Vehicle UE). The UE 100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein (e.g., an Aerial UE). The UE 100 may be a sensor or a device provided therein. Note that the UE 100 may be referred to by other names such as a terminal, a terminal device, a mobile station, a mobile terminal, a mobile device, a mobile unit, a subscriber station, a subscriber terminal, a subscriber device, a subscriber unit, a wireless station, a wireless terminal, a wireless device, a wireless unit, a remote station, a remote terminal, a remote device, or a remote unit. Furthermore, the UE 100 is an example of a terminal, and the terminal may include factory equipment or the like.

[0017] The 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, the base station 200 may be replaced with a cell. A cell constitutes the smallest unit of a communication area. One cell belongs to one frequency (carrier frequency). The term "cell" may refer to wireless communication resources or to a communication target of the UE 100. Each base station 200 can perform wireless communication with the UE 100 located in its own cell. The base station 200 communicates with the UE 100 using a RAN protocol stack. Details of the protocol stack will be described later. Furthermore, the base station 200 is connected to other base stations 200 (which may be referred to as neighbor base stations) via an Xn interface. The base station 200 communicates with the neighbor base stations via the Xn interface. In addition, the base station 200 provides NR user plane and control plane protocol termination for the UE 100 and is connected to the 5GC 30 via an NG interface. Such an NR base station 200 is sometimes referred to as a gNodeB (gNB).

[0018] The 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 specialized for U-plane processing. The AMF and the UPF are connected to the base station 200 via an NG interface.

[0019] (Configuration Example of Protocol Stack) Next, a configuration example of a protocol stack according to this embodiment will be described with reference to FIG.

[0020] The protocol of the wireless section between UE 100 and base station 200 includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) 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 the UE 100 and the PHY layer of the base station 200 via a physical channel.

[0022] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), random access procedures, etc. 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 transport format (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE 100.

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

[0024] The PDCP layer performs header compression / decompression and encryption / decryption.

[0025] A Service Data Adaptation Protocol (SDAP) layer may be provided as an upper layer above the PDCP layer. The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by an Access Stratum (AS).

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

[0027] The NAS layer, which is located above the RRC layer in the UE 100, performs session management and mobility management for the UE 100. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the core network device 300.

[0028] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0029] (Radio Frame Configuration) In a 5G system, downlink transmission and uplink transmission are configured within a radio frame having a duration of 10 ms. For example, a radio frame is represented by a system frame number (SFN) ranging from 0 to 1023. For example, a radio frame is configured with 10 subframes. For example, one subframe may be 1 ms. Furthermore, one subframe may be configured with one or more slots. For example, the number of symbols that make up one slot is 14 for a normal CP (Cyclic Prefix) and 12 for an extended CP. Furthermore, the number of slots that make up one subframe varies depending on the set subcarrier spacing. For example, for a normal CP, if the subcarrier spacing is set to 15 kHz, the number of slots per subframe is 1 (i.e., 14 symbols); if the subcarrier spacing is set to 30 kHz, the number of slots per subframe is 2 (i.e., 28 symbols); if the subcarrier spacing is set to 60 kHz, the number of slots per subframe is 4 (i.e., 56 symbols); and if the subcarrier spacing is set to 120 kHz, the number of slots per subframe is 8 (i.e., 128 symbols). Furthermore, if the subcarrier spacing is set to 60 kHz for an extended CP, the number of slots per subframe is 4 (i.e., 48 symbols). That is, the number of slots constituting one subframe is determined based on the subcarrier spacing set by the base station 200. Furthermore, the number of symbols constituting one subframe is determined based on the subcarrier spacing set by the base station 200. That is, the number of symbols constituting a 1 ms subframe is determined based on the subcarrier spacing set by the base station 200, and the length of each symbol (length in the time direction) changes.

[0030] (LTM) In a mobile communication system 1 conforming to the technical specifications of 3GPP, introduction of L1 (Layer 1) / L2 (Layer 2) triggered mobility (LTM) is planned. As shown in Fig. 3, in LTM, the following operations can be performed.

[0031] Step S10: LTM Preparation The UE 100 in the RRC connected state may perform the following operation as an operation for LTM preparation.

[0032] Step S11: The UE 100 transmits a measurement report message to the base station 200. The base station 200 determines to use the LTM and starts candidate cell preparation.

[0033] Step S12: The base station 200 transmits an RRC reconfiguration message including LTM candidate cell configuration of one or more candidate cells.

[0034] Step S13: The UE 100 stores the LTM candidate cell configuration. The UE 100 transmits an RRC reconfiguration complete (RRCReconfigurationComplete) message to the base station 200.

[0035] Step S20: Early synchronization The UE 100 may perform the following operation as the early synchronization operation.

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

[0037] Step S22: Before receiving the cell switch command, the UE 100 performs timing advance (TA) acquisition. The UE 100 may perform TA acquisition based on a PDCCH order (specifically, a PDCCH ordered RACH). The PDCCH order may be triggered only by the source cell.

[0038] Step S30: LTM execution The UE 100 may execute the following operation as the LTM execution operation.

[0039] Step S31: The UE 100 performs L1 measurement on the candidate cell configured by the LTM candidate cell configuration. The UL 100 transmits a lower-layer measurement report (hereinafter, L1 measurement report) based on the L1 measurement to the base station 200.

[0040] Step S32: The base station 200 determines to perform a cell change to the target cell. The base station 200 transmits a MAC CE that triggers the cell change by including a candidate configuration index of the target cell. The UE 100 switches the configuration of the target cell.

[0041] Step S33: If the cell change needs to include the execution of a random access (RA) procedure, the UE 100 executes the RA procedure toward the target cell.

[0042] Step S40: LTM Completion The UE 100 may perform the following operation as an operation for completing LTM.

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

[0044] It should be noted that UE 100 may execute steps S20 to S40 multiple times for subsequent LTM cell switching based on the configuration provided in step S12 without releasing the configuration.

[0045] As described above, in LTM, the base station 200 changes the serving cell of the UE 100 by transmitting a cell change command that triggers a cell change to the UE 100 by MAC CE based on the L1 measurement report received from the UE 100. Compared to a cell change based on an RRC message, the UE 100 can dynamically perform a cell change, and mobility delay can be reduced.

[0046] Currently, UE 100 performs a cell change (hereinafter, referred to as a first cell change) from a source cell to a target cell according to the setting information for LTM, and then performs a cell change (hereinafter, referred to as a second cell change) without RRC reconfiguration (i.e., without receiving an RRC reconfiguration message). The introduction of LTM (hereinafter, referred to as a subsequent LTM) is being considered.

[0047] In addition to cases in which the base station that manages the source cell manages the target cell (i.e., cell change within the same base station), it is expected that cases in which a base station different from the base station that manages the source cell manages the target cell (i.e., cell change between different base stations) will also be introduced in the future as cases in which LTM (including subsequent LTM) is executed.

[0048] Here, when a cell change from a source cell to a target cell is performed by LTM, the UE 100 cannot distinguish whether the target base station that manages the target cell to which the change is made is the same as the base station that manages the source cell. For this reason, the UE 100 may always perform a security key update procedure even when changing cells within the same base station, or may not perform a security key update procedure when changing cells between different base stations, which may result in the security key update procedure not being properly performed. Therefore, later, an operation for enabling the security key update procedure to be properly performed in LTM will be described.

[0049] Furthermore, since no specific operation is specified for cases where cell changes within the same base station and cell changes between different base stations coexist, there is a concern that LTM (and / or subsequent LTM) may not be properly executed. Therefore, operations for enabling LTM to be properly executed will be described below.

[0050] (Configuration of User Equipment) The configuration of the UE 100 according to the embodiment will be described with reference to Fig. 4. 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 radio signals to and from the base station 200. The communication unit 110 has at least one transmission unit 111 and at least one reception unit 112. The transmission unit 111 and the reception unit 112 may be configured to include multiple antennas and RF (Radio Frequency) circuits. The antenna converts a signal into radio waves and radiates the radio waves into space. The antenna also receives radio waves in space and converts the radio waves into a signal. The RF circuit performs analog processing of the signal transmitted and received via the antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0052] The control unit 120 performs various controls in 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 may be operations controlled by the control unit 120. The control unit 120 may include at least one processor capable of executing a program and a memory that stores the program. The processor may 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 the antenna and the RF circuit. The digital processing includes processing of a RAN protocol stack. 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 read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), and flash memory. All or a portion of the memory may be contained within the processor.

[0053] The control unit 120 may include a MAC processing unit that performs processing in the MAC layer and an upper layer processing unit that performs processing in a layer higher than the MAC layer. The MAC processing unit may be referred to as a MAC entity. The upper layer processing unit performs processing in a layer higher than the MAC layer. The upper 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 RRCP 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. Note that, for the upper layer processing unit, information from the MAC processing unit may be information from a lower layer.

[0054] Each of the MAC processing unit and the upper layer processing unit (PDCP processing unit and / or RRC processing unit) may be configured by one processor or multiple processors. The operations of the MAC processing unit and the upper layer processing unit may be operations of the control unit 120. Of the operations of each layer processing unit, the transmission and / or reception operations may be operations of the communication unit 110 (transmission unit 111 and / or reception unit 112).

[0055] In the UE 100 configured in this manner, the receiver 112 receives a cell change command from the base station via MAC CE, which triggers a cell change from a source cell to a target cell. The controller 120 executes the cell change based on the cell change command. The controller 120 determines, based on the determination information received from the base station 200, whether or not to execute a security key update procedure used for communication in the target cell when the cell change is executed. As a result, the UE 100 can appropriately execute the security key update procedure in the LTM by determining, based on the determination information, whether or not to execute the security key update procedure.

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

[0057] (Configuration of Base Station) The configuration of the base station 200 according to this embodiment will be described with reference to Fig. 5. The base station 200 includes a communication unit 210, a network communication unit 220, and a control unit 230.

[0058] The communication unit 210 receives, for example, a radio signal from the UE 100 and transmits the radio signal to the UE 100. The communication unit 210 has at least one transmission unit 211 and at least one reception unit 212. The transmission unit 211 and the reception unit 212 may be configured to include an RF circuit. The RF circuit performs analog processing of signals transmitted and received via an antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0059] The network communication unit 220 transmits and receives signals to and from the network. For example, the network communication unit 220 receives signals from adjacent base stations connected via an Xn interface, which is an interface between base stations, and transmits the signals to the adjacent base stations. The network communication unit 220 also receives signals from the core network device 300 connected via an NG interface, and transmits the signals to the core network device 300.

[0060] The control unit 230 performs various controls in the base station 200. The control unit 230 controls, for example, communication with the UE 100 via the communication unit 210. The control unit 230 also controls, for example, communication with a node (e.g., a neighboring base station, the core network device 300) via the network communication unit 220. The operations of the base station 200 described above and below may be controlled by the control unit 230. The control unit 230 may include at least one processor capable of executing a program and a memory that stores the program. The processor may execute the program to perform the operations of the control unit 230. The control unit 230 may include a digital signal processor that performs digital processing of signals transmitted and received via the antenna and the RF circuit. The digital processing includes processing of a RAN protocol stack. The memory stores programs executed by the processor, parameters related to the programs, and data related to the programs. All or a part of the memory may be included in the processor.

[0061] In base station 200 configured as described above, transmitter 211 transmits a cell change command to UE 100 by MAC CE. Transmitter 211 transmits, to UE 100, determination information used by UE 100 to determine whether or not to perform a security key update procedure used for communication in a target cell when a cell change is executed. As a result, UE 100 can appropriately execute the security key update procedure in LTM by determining whether or not to perform the security key update procedure based on the determination information.

[0062] 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 transmission unit 211 transmits the RRC message to the UE 100. The transmission unit 211 transmits a cell change command to the UE 100 by MAC CE, which triggers a cell change from the source cell of the base station 200 to a target cell. The control unit 230 generates an RRC message including determination information for determining whether or not a security key update process is required for each of the one or more LTM candidate cell configurations, so that the UE 100 stores each of the one or more LTM candidate cell configurations separately into a first LTM candidate cell configuration that does not require a security key update process used for communication in the target cell and a second LTM candidate cell configuration that requires a security key update process. This allows the UE 100 to appropriately distinguish between each of the one or more LTM candidate cell configurations. As a result, it is possible to appropriately perform a security key update procedure in LTM.

[0063] (First Operation Example) A first operation example will be described with reference to Figs. 6 to 8. Previous descriptions may be omitted. In the mobile communication system 1 of this operation example, the base station 200 includes a base station 201 and a base station 202. The base station 201 and the base station 202 manage different cells. The base station 202 may be, for example, a neighboring base station for the base station 201.

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

[0065] Note that, for UE 100, communication with base station 200 may be communication with a cell. Therefore, for UE 100, receiving information / messages, etc. from base station 200 may be receiving information / messages, etc. from a cell, and transmitting information / messages, etc. to base station 200 may be transmitting information / messages, etc. to a cell.

[0066] Step S101: The transmitter 111 of the UE 100 may transmit capability information to the base station 201. The base station 200 may receive the capability information from the UE 100.

[0067] The capability information may be information indicating whether or not the UE 100 supports cell change between different base stations by LTM (hereinafter, sometimes referred to as inter-base station LTM).

[0068] Furthermore, the capability information may be at least one of information indicating whether UE100 supports a cell change (hereinafter sometimes referred to as a second cell change) that is performed without receiving an RRC reconfiguration message after performing the first cell change described below, and information indicating whether UE100 supports subsequent LTM.

[0069] Here, the subsequent LTM may be any of the following operations: (i) an operation of performing a cell change (hereinafter sometimes referred to as a first cell change) in accordance with LTM configuration information received from the base station 200 (i.e., the source cell) and then performing a cell change without RRC reconfiguration; (ii) an operation of performing a cell change without receiving an RRC reconfiguration message in accordance with a first cell change; (iii) an operation of performing a cell change in accordance with the LTM configuration information in accordance with the first cell change without discarding the LTM configuration information (i.e., the LTM configuration information received from a previous source cell, not the current source cell); (iv) an operation of performing a cell change between L1 / L2 mobility candidates without RRC reconfiguration; (v) an operation of performing successive cell changes between L1 / L2 mobility candidates without RRC reconfiguration.

[0070] Note that the cell change in this operation example (i.e., the cell change due to the LTM) may be referred to as an LTM cell change. The LTM cell change may include a first cell change and a second cell change.

[0071] The first cell change may be a cell change according to LTM configuration information received directly from the source cell, and may also be referred to as a first LTM (or a first LTM cell change).

[0072] The second cell change may be a cell change according to LTM configuration information not directly received from the source cell. Therefore, the second cell change may be a cell change performed without RRC reconfiguration (without directly receiving an RRC reconfiguration message from the source cell). The second cell change may also be referred to as a subsequent LTM (or second LTM cell change).

[0073] Step S102: The transmitter 111 of the UE 100 transmits a measurement report (message) to the base station 201. The receiver 212 of the base station 201 receives the measurement report from the UE 100.

[0074] The control unit 230 of the base station 201 determines whether to use LTM. The control unit 230 may determine whether to use LTM based on, for example, a measurement report. If the control unit 230 determines to use LTM, it starts candidate cell preparation.

[0075] As a candidate cell preparation, the control unit 230 may select a candidate cell for the target cell in LTM based on the measurement report. The control unit 230 may select the candidate cell from among the cells managed by the base station 201, for example. The candidate cell may also be referred to as an LTM candidate cell.

[0076] Furthermore, the control unit 230 may generate setting information related to LTM (hereinafter, LTM setting information). The control unit 230 may include the generated LTM setting information (for example, LTM-Config) in an RRC reconfiguration message, for example (see E1 and E12 in FIG. 8). The control unit 230 may instruct the UE 100 to execute LTM (an operation related to LTM) by including the LTM setting information in the RRC reconfiguration message. The UE 100 may execute LTM (an operation related to LTM) when the LTM setting information is included in the RRC reconfiguration message.

[0077] The LTM configuration information (e.g., LTM-Config) may be information used to provide (one or more) LTM candidate cell configurations. The control unit 230 may include, in the LTM configuration information (e.g., LTM-Config), at least one of information on a list for releasing a candidate cell (hereinafter, sometimes referred to as an LTM candidate release list (e.g., ltm-CandidateToReleaseList)) and information on a list for adding or changing a candidate cell (hereinafter, sometimes referred to as an LTM addition / modification list (e.g., ltm-CandidateToAddModList)).

[0078] The LTM candidate release list may be a list of LTM candidate cell configurations to be removed. The LTM candidate release list may be configured by the identifiers of the candidate cells (e.g., ltm-CandidateId).

[0079] The LTM addition change list may be a list configured by LTM candidate information (e.g., LTM-Candidate). The LTM addition change list may be a list of LTM candidate cell settings to be added and / or changed. The LTM candidate information may include, for example, at least one of the following information. - 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 (Complete Configuration) or a differential configuration (Delta-Configuration) - Configuration information for setting information to be used for early synchronization (e.g., ltm-EarlyUL-SyncConfig) - Identifier indicating whether an L2 reset for the LTM candidate cell is not performed in the LTM cell change procedure (e.g., ltm-NoResetID) A list for adding / changing information used for early synchronization (e.g., ltm-Candidate-Tci-States-ToAddModList) An identifier for canceling (deleting) information used for early synchronization (e.g., ltm-Candidate-Tci-States-ToReleaseList)

[0080] The identifier of the candidate cell may be an identifier of the LTM candidate cell configuration. The LTM candidate cell configuration may 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 one LTM candidate cell. Thus, the LTM candidate cell configuration may include an RRC (re)configuration (RRC reconfiguration message) configured in the UE 100. The LTM candidate cell configuration may include cell group configuration information (e.g., CellGroupConfig) including serving cell configuration information (e.g., ServingCellConfig) and the like. The LTM configuration completion information may indicate whether the LTM candidate cell configuration in the LTM candidate cell configuration information is a complete configuration.

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

[0082] In this specification, when simply referred to as an RRC reconfiguration message, the RRC reconfiguration message may be an RRC reconfiguration message including LTM configuration information, or may 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 may be an RRC reconfiguration message transmitted from base station 200 (base station 201 in this operation example) (received by UE 100), or may be an RRC reconfiguration message included in the LTM candidate cell configuration corresponding to the target configuration identifier indicated by the MAC layer when LTM is executed. In addition, the control unit 120 may include a MAC processing unit that performs processing in the MAC layer and an upper layer processing unit that performs processing in layers higher than the MAC layer. The MAC processing unit may also be referred to as a MAC entity. The upper layer processing unit performs processing in layers higher than the MAC layer. The upper 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 RRCP 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. Note that, for the upper layer processing unit, information from the MAC processing unit may be information from a lower layer.

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

[0084] The control unit 230 may determine to use subsequent LTM when the capability information indicates that the UE 100 supports subsequent LTM (or second cell change). On the other hand, the control unit 230 may determine not to use subsequent LTM when the capability information indicates that the UE 100 does not support subsequent LTM (or second cell change). When the control unit 230 determines to use subsequent LTM, it may start candidate cell preparation. The control unit 230 may start candidate cell preparation in the same way as LTM.

[0085] The control unit 230 may determine, based on the capability information, whether or not the UE 100 supports the inter-base station LTM. When the capability information indicates that the UE 100 supports the inter-base station LTM, the control unit 230 may determine, based on the measurement report, whether or not to cause the UE 100 to perform an LTM cell change to a cell of another base station 200 (e.g., base station 201).

[0086] When the capability information indicates that UE 100 supports inter-base station LTM, control unit 230 may determine to cause UE 100 to perform an LTM cell change to a cell of another base station 200. On the other hand, when the capability information indicates that UE 100 does not support inter-base station LTM, control unit 230 may determine not to cause UE 100 to perform an LTM cell change to a cell of another base station 200. In this case, control unit 230 may omit the processing of step S103.

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

[0088] Step S103: The network communication unit 220 of the base station 201 transmits, for example, a handover request message requesting preparation of resources for handover to the base station 202. The network communication unit 220 of the base station 202 receives the handover request message from the base station 201. Note that the message may be a message other than the handover request message. The message may be a message used to request preparation for a cell change by LTM and / or subsequent LTM.

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

[0090] The control unit 230 of the base station 202 may determine whether to approve the LTM cell change based on, for example, the handover request message. If the control unit 230 approves the LTM cell change, the control unit 230 may execute the following process.

[0091] Step S104: The network communication unit 220 of the base station 202 transmits a Handover Request Acknowledge message to the base station 201 to inform the source base station (i.e., the base station 201) of the prepared resources at the target. The network communication unit 220 of the base station 201 receives the Handover Request Acknowledge message from the base station 202. The message may be a message used to notify approval of preparation for cell change by LTM and / or subsequent LTM.

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

[0093] If the control unit 230 does not approve the LTM cell change, it may, for example, send a handover preparation failure message to the base station 201 to inform the source base station (i.e., the base station 201) that the handover preparation has failed.

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

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

[0096] Step S106: The transmitter 111 of the UE 100 transmits an RRC reconfiguration completion message to the base station 201. The receiver 212 of the base station 201 receives the RRC reconfiguration completion message from the UE 100.

[0097] Step S107: As an early synchronization operation, downlink synchronization with each candidate cell may be performed. The control unit 120 of the UE 100 performs downlink synchronization based on, for example, an SSB transmitted from each candidate cell.

[0098] Furthermore, as an operation of early synchronization, uplink synchronization with each candidate cell may be executed. The transmitter 211 of the base station 201 may, for example, transmit to the UE 100, a physical downlink control channel (PDCCH) order (i.e., downlink control information (DCI)) for starting an RA procedure for early synchronization in each candidate cell set for the UE 100 by the LTM candidate cell setting. The receiver 112 of the UE 100 may receive the PDCCH order from the base station 201. Note that the PDCCH order in early synchronization may be a PDCCH order (PDCCH ordered-RACH for TA Acquisition without RAR) used to acquire a TA value without an RA response. The control unit 120 of the UE 100 may start the RA procedure based on the PDCCH order.

[0099] In each candidate cell, the transmitter 111 of the UE 100 transmits an RA preamble (message 1) to the base station 201 on a physical random access channel (PRACH). In each candidate cell, the receiver 212 of the base station 201 receives the RA preamble from the UE 100. The controller 230 of the base station 201 calculates a timing advance (TA) value based on the RA preamble from the UE 100. The controller 230 may execute control to omit transmission of an RA response (i.e., message 2), which is a response to the RA preamble.

[0100] Note that the control unit 230 may include information instructing the UE 100 to execute RACH-less LTM in the RA response (i.e., message 2). The information may include information instructing the UE 100 to skip the RA procedure for LTM cell change. The information may be information instructing the UE 100 to execute RACH-less LTM when the UE 100 should apply the same TA as the source cell (base station 200 that manages the source cell).

[0101] Step S108: After performing L1 measurement in each candidate cell configured by the LTM configuration information, the transmitter 111 of UE 100 transmits an L1 measurement report to the base station 201. The receiver 212 of the base station 201 receives the L1 measurement report from UE 100. The L1 measurement report is a measurement report of a lower layer based on the L1 measurement. The L1 measurement report is transmitted in a layer lower than the RRC layer. Note that the measurement report in step S110 is transmitted in the RRC layer.

[0102] The control unit 230 of the base station 201 determines a target cell in LTM (i.e., an LTM target cell) based on the L1 measurement report. In addition, the control unit 230 may determine whether to cause the UE 100 to execute RACH-less LTM (RACH-less LTM) in which the UE 100 performs uplink transmission without executing an RA procedure between the UE 100 and the base station 201, or whether to cause the UE 100 to execute RACH-based LTM (RACH-base LTM) in which the RA procedure between the UE 100 and the base station 201, in the LTM execution.

[0103] The control unit 230 generates a MAC CE for transmitting the cell change command. This MAC CE may be referred to as an LTM cell change command MAC CE, for example. This MAC CE may also be referred to as a cell change command (i.e., may be a cell change command). Hereinafter, the LTM cell change command MAC CE may be referred to as a cell change command as appropriate. The cell change command may include, for example, at least one of the following information (i.e., fields): a target configuration identifier (Target Configuration ID) indicating the index of the candidate target configuration to apply to the LTM cell change; a timing advance command (Timing Advance Command) indicating whether the TA for the LTM target cell is valid; a transmission configuration indication (TCI state ID) state identifier indicating and activating the TCI state for the LTM target cell; an uplink TCI state identifier indicating and activating the uplink TCI state for the LTM target cell (UL TCI state ID); an identifier of the downlink bandwidth portion to be activated in the LTM target cell (DL BWP ID); an identifier of the uplink bandwidth portion to be activated in the LTM target cell (UL BWP ID). - Information related to contention-free random access (CFRA) resources

[0104] The target setting identifier may be an identifier of a candidate cell that will become a target cell, which is a cell after the change, among the identifiers of the candidate cells described above.

[0105] The Timing Advance Command (field) may indicate whether a TA (TA value) is valid for a 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 as the value of this field, this field may indicate that valid timing adjustment is not available for the primary timing advance group (PTAG) of the LTM target cell. In this case, the UE 100 needs to perform an RA procedure to the LTM target cell. That is, the UE 100 performs RACH-based LTM. On the other hand, when a value other than the predetermined value (e.g., FFF) is set as the value of this field, this field indicates an index value (i.e., TA value) used to control the amount of timing adjustment to be applied by the MAC entity of the UE 100. That is, the timing advance command (field) indicates that the RA procedure for the LTM cell change can be skipped. In this case, the UE 100 performs RACH-less LTM. Here, the predetermined value may be defined in advance by a specification or the like and may be a value known between the base station 201 and the UE 100.

[0106] The control unit 120 of the UE 100 may perform the RACH-less LTM when the same TA as that of the source cell (the base station that manages the source cell) should be applied (or will be applied). The control unit 120 may perform the RACH-less LTM when the timing advance command (field) is the same as the TA applied in the current source cell. Alternatively, the cell change command may include information (field) indicating (instructing) that the same TA as that of the source cell (the base station that manages the source cell) should be applied (or will be applied) separately from the timing advance command (field). The information (field) related to the CFRA resource may indicate the resource (e.g., radio resource, preamble index to use which RA preamble to use, etc.) to be used when the UE 100 performs CFRA.

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

[0108] The control unit 120 of the UE 100 switches the setting of the target cell based on the identifier of the candidate cell (i.e., the target setting identifier) ​​included in the cell change command (MAC CE). For example, the control unit 120 applies the LTM candidate cell setting associated with the identifier of the candidate cell that is the same as the target setting identifier included in the cell change command (MAC CE). For example, the MAC layer in the UE 100 may notify the RRC layer of information (and the target setting identifier) ​​notifying that the cell change command (MAC CE) has been received. Furthermore, when the RRC layer in the UE 100 is provided with information (and the target setting identifier) ​​notifying that the cell change command has been received from the MAC layer, the RRC layer may apply the candidate cell setting information associated with the identifier of the candidate cell that is the same as the target setting identifier. That is, the UE 100 (the RRC layer) may apply the LTM candidate cell setting based on receiving information indicating that the cell change procedure has been triggered by the MAC layer (information indicating that the cell change procedure has been triggered from the MAC layer). Here, the LTM candidate cell configuration may be an LTM candidate cell configuration corresponding to a target configuration identifier indicated from the MAC layer.

[0109] The control unit 120 determines whether to execute the RACH-based LTM or the RACH-less LTM based on the value 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 execute the RACH-based LTM. On the other hand, when a value other than the predetermined value (e.g., FFF) is set in the timing advance command, the control unit 120 determines to execute the RACH-less LTM. The control unit 120 may determine to execute the RACH-less LTM when the same TA as that of the current source cell is (should be) applied. The control unit 120 may determine whether the same TA as that of the current source cell is (should be) applied 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] When the control unit 120 of the UE 100 receives a cell change command by MAC CE from the base station 200, the control unit 120 executes a first cell change in accordance with the LTM setting information. In this operation example, the explanation will proceed assuming that the cell change is to a cell managed by the base station 201.

[0111] Step S110: The control unit 120 of the UE 100 executes a security key update determination. Specifically, the control unit 120 determines whether or not to execute a security key update procedure used for communication in the target cell when a cell change is executed, based on determination information (hereinafter, sometimes referred to as update determination information) received from the base station 201. Details of the security key update determination will be described later.

[0112] If the control unit 120 determines that the security key update procedure should be executed, the control unit 120 executes the security key update procedure. The control unit 120 executes the process of step S111. On the other hand, if the control unit 120 determines that the security key update procedure should not be executed, the control unit 120 omits (or skips) the security key update procedure.

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

[0114] The control unit 120 derives or updates the security key based on information for a security key update procedure (hereinafter, sometimes referred to as key update information). The key update information may include, for example, at least one 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 (Signaling Radio Bearer) requested for the UE 100 UP integrity protection and encryption instruction Counter information (e.g., "sk-Counter", "sk-counter-list")

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

[0116] The control unit 120 derives or updates a key used to protect communication between the UE 100 and a base station that manages the target cell (target base station) based on the security key.

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

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

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

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

[0121] The security key update procedure may be, for example, an AS (Access Stratum) security key update procedure.

[0122] Step S112: When the control unit 120 of the UE 100 determines to perform the RACH-based LTM, the control unit 120 performs a random access (RA) procedure.

[0123] Step S113: When the UE 100 executes the RACH-based LTM, the control unit 120 of the UE 100 may consider that the LTM execution procedure has been successfully executed (i.e., LTM completion has been executed) when the random access (RA procedure) has been successfully completed. The control unit 230 of the base station 201 may determine that the LTM execution procedure has been successfully executed (i.e., LTM completion has been executed) based on reception of a preamble in the RA procedure (contention-free RA (CFRA)) or reception of message 3 or message A in the RA procedure (contention-based RA (CBRA)).

[0124] On the other hand, when UE 100 executes RACH-less LTM, transmission unit 111 of UE 100 transmits uplink transmission (for example, initial uplink data) to base station 201. When control unit 120 of UE 100 determines that the network has successfully received the uplink transmission, it may consider that the LTM execution procedure has been successfully executed (i.e., LTM completion has been executed).

[0125] The receiver 112 of the base station 201 receives an uplink transmission from the UE 100. The controller 230 of the base station 201 may recognize that the UE 100 has changed the serving cell to the target cell based on the reception of the uplink transmission (e.g., initial uplink data) in the target cell. As a result, the controller 230 may determine that the LTM execution procedure has been successfully executed (i.e., LTM completion has been executed).

[0126] Thereafter, the control unit 120 of the UE 100 determines whether the second cell change is permitted. The control unit 120 may determine whether the execution of the subsequent LTM is permitted (or whether the subsequent LTM is (executable)).

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

[0128] In addition, based on the execution of the cell change, the control unit 120 may perform communication with the target cell by applying the RRC reconfiguration information (RRC reconfiguration message) included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell.

[0129] The control unit 120 of the UE 100 may disable the LTM candidate cell setting of the candidate cell corresponding to the target cell based on the execution of the 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 disables the LTM candidate cell configuration of a candidate cell corresponding to the target cell, the candidate cell associated with the LTM candidate cell configuration (i.e., the current serving cell) is not included in the target cell. Therefore, the control unit 120 does not include the current serving cell in the target L1 measurement report. The control unit 120 may perform control so that the L1 measurement report for the cell associated with the disabled LTM candidate cell configuration is not triggered.

[0132] Furthermore, the control unit 120 may, for example, omit transmitting an L1 measurement report for the source cell to the source cell. The control unit 120 may also perform control so that an L1 measurement report for a cell associated with an LTM candidate cell configuration including an identifier (e.g., a cell ID) of the source cell is not triggered.

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

[0134] In addition, UE100 may determine whether to perform a security key update procedure in the current serving cell (i.e., the cell after performing the second cell change), similarly to step S110.

[0135] Furthermore, the control unit 120 of the UE 100 may enable the disabled LTM candidate cell setting based on the execution of a cell change after the target cell is set as the source cell.

[0136] Note that the UE 100 has not directly received an RRC reconfiguration message from the current serving cell (i.e., the target cell before the cell change) after the first cell change. Therefore, the cell change based on the cell change command in step S123 is a second cell change.

[0137] As described above, the transmitter 211 of the base station 200 transmits a cell change command to the UE 100 by using a MAC CE. The transmitter 211 transmits to the UE 100 update determination information used by the UE 100 to determine whether or not to perform an update procedure for a security key used for communication in a target cell when a cell change is performed. Furthermore, the receiver 112 of the UE 100 receives, from the base station by using a MAC CE, a cell change command that triggers a cell change from a source cell to a target cell. The controller 120 performs a cell change based on the cell change command. The controller 120 determines, based on the update determination information received from the base station 200, whether or not to perform an update procedure for a security key used for communication in a target cell when a cell change is performed. As a result, the UE 100 can appropriately perform the security key update procedure in the LTM by determining whether or not to perform the security key update procedure based on the update determination information.

[0138] Furthermore, the control unit 120 may omit transmitting the L1 measurement report for the source cell to the source cell, thereby preventing the UE 100 from performing unnecessary L1 measurement reporting.

[0139] Furthermore, the control unit 120 of the UE 100 may disable the LTM candidate cell setting 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 may enable the disabled LTM candidate cell setting based on the execution of a cell change after the target cell is set as the source cell. As a result, since the LTM candidate cell setting is disabled for the current serving cell of the UE 100, L1 measurement reporting can be omitted. As a result, it is possible to prevent the UE 100 from performing unnecessary L1 measurement reporting. On the other hand, after the UE 100 performs a cell change from the serving cell (source cell), the LTM candidate cell setting for the cell is enabled, so the UE 100 becomes a target for L1 measurement reporting. Therefore, the UE 100 can perform an LTM cell change for the same cell.

[0140] (Determination Operation Related to Security Key Update Procedure) Next, an example of the determination operation of the UE 100 will be described with reference to Fig. 8 to Fig. 12. The control unit 120 of the UE 100 determines whether or not to execute a security key update procedure used for communication in the target cell when a cell change is performed, by at least one of the following methods.

[0141] In the first method, the control unit 120 makes the determination based on update determination information included in the MAC CE (see FIG. 9).

[0142] Step S211: The control unit 120 determines whether or not the MAC CE includes update determination information. The MAC CE here is a MAC CE (LTM cell change command MAC CE) used to transmit a cell change command.

[0143] If the MAC CE includes update determination information, the control unit 120 may execute the process of step S212. If the MAC CE does not include update determination information, the control unit 120 may execute the process of step S214.

[0144] The update determination information may indicate, for example, whether to execute a security key update procedure. The update determination information may indicate whether the security key needs to be changed. In this case, the control unit 120 may execute the process of step S212.

[0145] Alternatively, the update determination information may indicate that the security key update procedure is to be executed when the update determination information is included in the LTM cell change command MAC CE. Alternatively, the update determination information may indicate that the security key update procedure is not to be executed when the update determination information is not included in the LTM cell change command MAC CE. In this case, the control unit 120 may omit the process of step S212.

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

[0147] Step S213: The control unit 120 determines to execute a security key update procedure. In this case, the control unit 120 may execute the security key update procedure based on information for the security key update procedure (key update information) included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell.

[0148] Step S214: The control unit 120 determines not to execute the security key update procedure. In this case, the control unit 120 may omit the security key update procedure. The control unit 120 may omit the security key update procedure regardless of whether or not key update information is included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell. Therefore, the control unit 120 may omit the security key update procedure even if key update information is included in the LTM candidate cell configuration of the candidate cell corresponding to the target cell.

[0149] This determination may be performed by the MAC processing unit of the control unit 120. The MAC processing unit may determine whether or not the LTM cell change command MAC CE includes update determination information.

[0150] When the MAC processing unit executes the process of step S213, the MAC processing unit may notify a higher layer (than the MAC layer) of the identifier of the target cell (for example, a target setting identifier) ​​included in the LTM cell change command MAC CE and the contents of the update determination information. The MAC processing unit may notify the higher layer of the target setting identifier and the update determination information. The MAC processing unit may notify the higher layer of an indication indicating the execution of a security key update procedure, instead of (the contents of) the update determination information.

[0151] In this case, the RRC processing unit may be notified of the target setting identifier and (contents of) the update determination information from a layer lower than the RRC layer. The RRC processing unit may execute a security key update procedure based on the notification.

[0152] On the other hand, when the MAC processing unit executes the process of step S214, it is not necessary to notify the upper layer of the target setting identifier but notify the upper layer of the update determination information (contents thereof).

[0153] In this case, the RRC processing unit may be notified of the target setting identifier from a layer lower than the RRC layer, but may not be notified of (the content of) the update determination information. Based on the notification, the RRC processing unit may omit the security key update procedure. If the (content of) the update determination information or the indication is not notified, the RRC processing unit may omit the security key update procedure.

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

[0155] As described above, the update determination information may be included in the MAC CE including the cell change command. This allows the network 10 to instruct the UE 100 whether to execute the security key update procedure when instructing the UE 100 to execute the cell change. The network 10 can flexibly control the execution of the security key update procedure.

[0156] Furthermore, the control unit 120 of the UE 100 may determine whether to execute the security key update procedure based on whether the MAC CE including the cell change command includes determination information. As a result, under a predetermined condition (for example, a condition in which the UE 100 is not caused to execute the security key update procedure), it is not necessary to include the determination information, and therefore the amount of information to be included in the MAC CE can be reduced.

[0157] Furthermore, the control unit 120 of the UE 100 may include a MAC processing unit that performs processing in the MAC layer. When the MAC CE including the cell change command includes a target cell identifier and determination information, the MAC processing unit may notify a layer higher than the MAC layer of the target cell identifier and the contents of the determination information. This allows the higher layer (e.g., RRC layer) that performs a security key update procedure to make a determination based on the target cell identifier and the contents of the determination information in the higher layer. Furthermore, even if it becomes necessary to use the determination information in the higher layer (e.g., RRC layer), the determination information can be used.

[0158] Furthermore, the receiving unit 112 of the UE 100 may receive an RRC message including the LTM setting information from the base station 200. When the control unit 120 determines not to execute the security key update procedure based on the update determination information, the control unit 120 may omit the security key update procedure even if information for the update procedure is included in the LTM candidate cell setting of the candidate cell corresponding to the target cell. This enables the network 10 to flexibly control the execution of the security key update procedure.

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

[0160] The determination identifier may be an identifier for identifying the manager of the cell. The determination identifier may, for example, indicate the base station 200 to which the (candidate) cell belongs. The determination identifier may, for example, indicate the central unit (CU) of the base station 200 to which the (candidate) cell belongs. The determination identifier may, for example, be called a cell set ID (cell-set-ID).

[0161] The determination identifier may be the same value for cells of the same base station 200, for example. The determination identifier may be different values ​​for cells of different base stations 200. Furthermore, the determination identifier may be the same value for cells of base stations 200 with the same central unit (CU), for example. The determination identifier may be the same value for cells of base stations 200 with the same CU, for example. The determination identifier may be different values ​​for cells of base stations 200 with different CUs.

[0162] The determination identifier may be included in the RRC reconfiguration message in step S105, for example. For example, as shown in Fig. 8, the RRC reconfiguration message received by the UE 100 from the serving cell (source cell) includes RRC reconfiguration information (e.g., RRCReconfiguration) (see field E1 in Fig. 8). The RRC reconfiguration information includes LTM setting information (e.g., LTM-Config) applied in the serving cell (source cell) (see field E12 in Fig. 8). The LTM setting information corresponds to the LTM setting information described in step S102.

[0163] The LTM setting information includes an LTM addition modification list (e.g., ltm-CandidateToAddModList) (see field E22 in FIG. 8). The LTM addition modification list is 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 fields E31 and E32 in FIG. 8).

[0164] The first LTM candidate information (see field E31 in FIG. 8 ) includes an identifier of a first candidate cell (e.g., ltm-CandidateId#1) and a first LTM candidate configuration (e.g., ltm-candidateconfig). The first LTM candidate configuration (see field E312 in FIG. 8 ) includes RRC reconfiguration information (e.g., RRCReconfiguration) (see field E41 in FIG. 8 ). The RRC reconfiguration information may be an RRC reconfiguration message. Similarly, the second LTM candidate information E32 includes an identifier of a second candidate cell (e.g., ltm-CandidateId#2) and a second LTM candidate configuration. Each of the second LTM candidate configurations (see field E322 in FIG. 8) includes RRC reconfiguration information (e.g., RRCReconfiguration) (see field E42 in FIG. 8).

[0165] The determination identifier may include a determination identifier of a source cell (hereinafter, may be referred to as a source determination identifier) ​​and a determination identifier of a candidate cell (hereinafter, may be referred to as a candidate determination identifier).

[0166] The source determination identifier may be included, for example, in a field (e.g., field E11 in FIG. 8) separate from the LTM setting information (field E12). Also, the source determination identifier may be included in a field (e.g., field E21 in FIG. 8) separate from the LTM addition / change list, which is a field in the LTM setting information (field E12).

[0167] The candidate determination identifier may be included in each of one or more LTM candidate cell configurations. Furthermore, the candidate determination identifier may be included in, for example, a field (e.g., field E311) in 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). Furthermore, the candidate determination identifier may be included in, for example, a field (e.g., field E51) in an RRC reconfiguration (e.g., field E41) that is applied when a cell change is performed.

[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 executes the process of step S223. On the other hand, if the source determination identifier and the target determination identifier are different, the control unit 120 executes the process of step S222.

[0169] Note that, for example, when the target determination identifier is included in both a first field (e.g., field E311) and a second field (e.g., field E51) in the LTM candidate cell setting (e.g., field E31), the control unit 120 may refer to any 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. When performing a reception process of an RRC reconfiguration message (RRCReconfiguration), the control unit 120 may refer to a determination identifier (for example, a cell set ID) included in a location where the contents of the LTM setting information are stored (for example, a variable (UE-LTM-Candidate-r18)).

[0171] Furthermore, 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 referred target determination identifier to perform the RRC reconfiguration process (reception process) that is applied when the cell change is performed.

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

[0173] As described above, by specifying the reference destination of the target determination identifier, the control unit 120 can appropriately process even when there is a mixture of LTM candidate cell settings in which the target determination identifier is included in both the first field and the second field and LTM candidate cell settings in which the target determination identifier is included in only one of the first field and the second field.

[0174] Step S222: Step S222 is similar to step S213.

[0175] Step S223: Step S223 is similar to step S214.

[0176] In addition, after performing the cell change, the control unit 120 may store the determination identifier of the candidate cell corresponding to the target cell as the determination identifier of the source cell. Thereby, even when the UE 100 performs the cell change by the subsequent LTM, it is possible to make an appropriate determination.

[0177] As shown in Fig. 11 , the control unit 120 may execute a security key update procedure if the target determination identifier (e.g., cell-set-id) is not the same as the source determination identifier (e.g., VarCellSetID) (see X1 in Fig. 11 ). The control unit 120 may execute a security key update procedure (AS security key update procedure and / or security key update procedure) if the RRC reconfiguration message includes key update information (e.g., masterKeyUpdate and / or sk-Counter) (see X2 in Fig. 11 ).

[0178] As described above, the control unit 120 may determine not to execute the security key update procedure when 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 may determine to execute the security key update procedure when the determination identifier of the source cell and the determination identifier of the candidate cell corresponding to the target cell are different. As a result, the UE 100 can omit the execution of the security key update procedure when the source cell and the target cell are managed by the same management source. As a result, the execution of an unnecessary security key update procedure can be omitted, and the processing of the UE 100 can be reduced. On the other hand, the UE 100 can execute the security key update procedure when the source cell and the target cell are managed by different management sources. The UE 100 can appropriately execute the security key update procedure in the LTM.

[0179] In the third method, the control unit 120 makes the determination based on the key update information (see FIG. 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 may execute the process of step S233. If the LTM candidate cell configuration includes key update information and update determination information (associated with the target cell) has been received, the control unit 120 may execute the process of step S232. If the LTM candidate cell configuration includes key update information and update determination information (associated with the target cell) has not been received, the control unit 120 may execute the process of step S233. If the LTM candidate cell configuration does not include key update information, the control unit 120 may execute the process of step S234.

[0181] Note that the control unit 230 of the base station 200 may include key update information in the LTM candidate cell configuration of a candidate cell that requires a security key update procedure, and may not include key update information in the LTM candidate cell configuration of a candidate cell that does not require a security key update procedure.

[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 may include key update information in all of the LTM candidate cell settings of the candidate cell.

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

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

[0185] Step S233: Step S233 is similar to step S213.

[0186] Step S234: Step S234 is similar to step S214.

[0187] (Second Operation Example) A second operation example will be described with reference to Fig. 13 to Fig. 16. The previous description may be omitted. In this operation example, a case will be described in which the UE 100 distinguishes and stores the LTM candidate cell configuration.

[0188] Steps S301 to S305: Steps S301 to S305 are similar to steps S101 to S105.

[0189] For example, as described in step S231 above, the control unit 120 of the base station 201 may include key update information in the LTM candidate cell configuration of a candidate cell that requires a security key update procedure. The LTM candidate cell configuration of a candidate cell that does not require a security key update procedure may not include key update information. 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 201 may include key update information in all of the LTM candidate cell configurations of the candidate cell.

[0190] Furthermore, the control unit 230 of the base station 201 may include the key update information for all LTM candidate cell configurations. In this case, the control unit 230 may indicate to the UE 100 whether or not it is necessary to perform a security key update procedure, based on the determination information.

[0191] Step S306: The control unit 120 of the UE 100 distinguishes and stores the LTM candidate cell configurations. The control unit 120 may distinguish and store each of the one or more LTM candidate cell configurations as a first LTM candidate cell configuration that does not require execution of a security key update procedure used for communication in the target cell, and a second LTM candidate cell configuration that requires execution of a security key update procedure. The control unit 120 may distinguish and store the LTM candidate cell configurations in response to reception of an RRC reconfiguration message.

[0192] The control unit 120 may distinguish the LTM candidate cell configurations based on determination information for determining whether or not it is necessary to perform a security key update procedure for each of the one or more LTM candidate cell configurations. Details of the method by which the control unit 120 distinguishes the LTM candidate cell configurations will be described later.

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

[0194] Steps S307 to S310: Steps S307 to S310 are similar to steps S106 to S109.

[0195] Step S311: The control unit 120 may determine to omit the execution of the security key update procedure when performing a cell change based on the first LTM candidate cell configuration, whereas the control unit 120 may determine to perform the security key update procedure when performing a cell change based on the second LTM candidate cell configuration.

[0196] Steps S312 to S323: Steps S312 to S323 are the same as steps S110 to S123. In this operation example, the description will proceed assuming that the MAC CE includes the identifier of the candidate cell managed by the base station 202.

[0197] Step S324: Step S324 is similar to step S311.

[0198] The control unit 120 determines to perform a cell change based on the second LTM candidate cell configuration because the MAC CE includes an identifier of a candidate cell managed by the base station 202. Therefore, the control unit 120 may determine to perform a security key update procedure.

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

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

[0201] Alternatively, the control unit 120 may release all of the first LTM candidate cell configurations that do not include key updating information from among the first LTM candidate cell configurations. The control unit 120 may newly classify the first LTM candidate cell configurations that include key updating information from among the first LTM candidate cell configurations as second LTM candidate cell configurations.

[0202] Step S329: When all of the first LTM candidate cell settings have been released, the control unit 120 may notify the network 10 that all of the first LTM candidate cell settings have been released. In this operation example, the transmission unit 111 may transmit release information indicating that all of the first LTM candidate cell settings have been released to the base station 202 in the target cell.

[0203] The release information may include, for example, identification information for identifying the base station 201 that directly provided the LTM candidate cell configuration to the UE 100. The identification information may be, for example, a determination identifier of the source cell before the execution of the cell change. Furthermore, the release information may include information for identifying the first LTM candidate cell configuration released by the UE 100.

[0204] The transmitter 111 of the UE 100 may transmit, for example, an RRC reconfiguration complete message including the release information to the base station 202. The RRC reconfiguration complete message may be transmitted based on a reception process of the RRC reconfiguration message included in the LTM candidate cell configuration.

[0205] The control unit 230 of the base station 202 may execute the following process based on the reception of the release information. Even if the control unit 230 does not receive the release information, for example, when an RRC connection is established with the UE 100 that has executed a cell change to the cell of the base station 202 based on the LTM candidate cell configuration transmitted to the base station 201, the control unit 230 may execute the following process for the base station 201 that has directly provided the LTM candidate cell configuration to the UE 100.

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

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

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

[0209] As described above, the receiver 112 of the UE 100 receives from the base station an RRC message including LTM configuration information used to provide one or more LTM candidate cell configurations. When the controller 120 receives a cell change command from the base station 200 via the MAC CE, which triggers a cell change from a source cell to a target cell, the controller 120 executes a cell change based on the LTM candidate cell configuration of a candidate cell corresponding to the target cell among the one or more LTM candidate cell configurations. The controller 120 stores each of the one or more LTM candidate cell configurations, distinguishing between a first LTM candidate cell configuration that does not require execution of a security key update procedure used for communication in the target cell and a second LTM candidate cell configuration that requires execution of a security key update procedure. This allows the UE 100 to distinguish, for example, whether or not execution of a security key update procedure is required when applying the LTM candidate cell configuration based on the stored location. As a result, the security key update procedure can be appropriately executed in LTM.

[0210] The RRC message may also include determination information for determining whether or not a security key update procedure needs to be performed for each of the one or more LTM candidate cell configurations. The control unit 120 may distinguish the 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 230 of the base station 200 also generates an RRC message including LTM configuration information used to provide the one or more LTM candidate cell configurations. The transmission unit 211 transmits the RRC message to the UE 100. The transmission unit 211 transmits a cell change command to the UE 100 by a MAC CE, which triggers a cell change from the source cell of the base station 200 to a target cell. The control unit 230 generates an RRC message including determination information for determining whether or not a security key update process is required for each of the one or more LTM candidate cell settings so that the UE 100 stores each of the one or more LTM candidate cell settings separately as a first LTM candidate cell setting that does not require a security key update process used for communication in the target cell and a second LTM candidate cell setting that requires a security key update process. As a result, the UE 100 can distinguish between the first LTM candidate cell setting and the second LTM candidate cell setting by receiving an RRC message including the one or more LTM candidate cell settings.

[0211] Furthermore, the control unit 120 may store the first LTM candidate cell configuration in a first storage area. The control unit 120 may store the second LTM candidate cell configuration in a second storage area. When a cell change is performed according to the second LTM candidate cell configuration, the control unit 120 may release all of the first LTM candidate cell configurations stored in the first storage area. Here, the candidate cells associated with the first LTM candidate cell configuration are cells managed by the same base station 200. On the other hand, the candidate cell associated with the second LTM candidate cell configuration is likely to be a cell managed by a different base station 200 because a security key update procedure needs to be performed. 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 be necessary to perform a security key update procedure. Since UE100 distinguishes the first LTM candidate cell setting as one for which the security key update procedure does not need to be executed, by releasing all of the first LTM candidate cell settings stored in the first storage area, it is possible to prevent the security key update procedure from being omitted even though the security key update procedure needs to be executed.

[0212] Furthermore, when all of the first LTM candidate cell settings have been released, the control unit 120 may notify the network 10 that all of the first LTM candidate cell settings have been released. This allows the network 10 to understand that the UE 100 has released the first LTM candidate cell settings. As a result, the network 10 can avoid instructing the UE 100 to perform a cell change in accordance with the first LTM candidate cell settings.

[0213] (Distinguishing Method) Next, an example of a distinguishing method of UE 100 will be described with reference to Fig. 15 and Fig. 16 . The control unit 120 of UE 100 can distinguish the LTM candidate cell configurations based on determination information for determining whether or not it is necessary to perform a security key update procedure for each of one or more LTM candidate cell configurations. The control unit 120 may distinguish the 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 may distinguish the LTM candidate cell configurations by at least one of the following methods.

[0214] As described above, the RRC message (for example, the RRC reconfiguration message in step S305) may include the determination information.

[0215] In the first method, the control unit 120 distinguishes between the update determination information based on a determination identifier (see FIG. 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. The control unit 120, for example, selects a candidate determination identifier associated with one of one or more LTM candidate cell configurations. If the source determination identifier and the selected candidate determination identifier are the same, the control unit 120 executes the process of step S412. On the other hand, if the source determination identifier and the selected candidate determination identifier are different, the control unit 120 executes 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 as 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 as a second LTM candidate cell configuration.

[0219] The control unit 120 executes the processes of steps S411 to S413 for all of the one or more LTM candidate cell settings. As a result, the one or more LTM candidate cell settings are classified into a first LTM candidate cell setting and a second LTM candidate cell setting.

[0220] As described above, the RRC message may include, as the determination information, a determination identifier for identifying the manager of the cell. The control unit 120 may distinguish an LTM candidate cell setting of a candidate cell having the same determination identifier as the determination identifier of the source cell as a first LTM candidate cell setting. The control unit 120 may distinguish an LTM candidate cell setting of a candidate cell having a determination identifier different from the determination identifier of the source cell as a second LTM candidate cell setting. This allows the control unit 120 to identify the manager of the cell, thereby making it possible to avoid not executing the security key update procedure when the source cell and the target cell are managed by different managers.

[0221] In the second method, the control unit 120 distinguishes between the update determination information based on the key update information (see FIG. 16).

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

[0223] The control unit 120 may execute the process of step S422 for an LTM candidate cell configuration that does not include information for the update procedure among the one or more LTM candidate cell configurations. The control unit 120 may execute the process of step S423 for an LTM candidate cell configuration that includes information for the update procedure among the one or more LTM candidate cell configurations.

[0224] Furthermore, the control unit 120 may determine whether each of the one or more LTM candidate cell configurations includes key updating information based on information indicating whether each of the one or more LTM candidate cell configurations includes key updating information (hereinafter, referred to as predetermined information). Note that the predetermined information may indicate whether each of the LTM candidate cell configurations includes key updating information.

[0225] When the predetermined information indicates that the LTM candidate cell configuration does not include key updating information, the control unit 120 may execute the process of step S422 for the LTM candidate cell configuration. On the other hand, when the predetermined information indicates that the LTM candidate cell configuration includes key updating information, the control unit 120 may execute the process of step S423 for the LTM candidate cell configuration.

[0226] The predetermined information may be included in, for example, a field (e.g., field E11 in FIG. 8) separate from the LTM configuration information (field E12). Also, the predetermined information may be included in a field (e.g., field E21 in FIG. 8) separate from the field in the LTM addition / change list, which is a field in the LTM configuration information (field E12). In this case, the predetermined information may indicate whether all LTM candidate cell configurations include key update information.

[0227] The predetermined information may be included in each of one or more LTM candidate cell configurations. Furthermore, the predetermined information may be included in, for example, a field (e.g., field E311) in 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). Furthermore, the predetermined information may be included in, for example, a field (e.g., field E51) in an RRC reconfiguration (e.g., field E41) that is applied when a cell change is performed. In this case, the predetermined information may indicate whether the LTM candidate cell configuration in which the predetermined information is included includes key update information.

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

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

[0230] As described above, the control unit 120 of the UE 100 may distinguish an LTM candidate cell configuration that does not include key update information from among one or more LTM candidate cell configurations as a first LTM candidate cell configuration. The control unit 120 may distinguish an LTM candidate cell configuration that includes key update information from among one or more LTM candidate cell configurations as a second LTM candidate cell configuration. As a result, the security key update procedure can be appropriately performed in the LTM by omitting the execution of the security key update procedure for (only) an LTM candidate cell configuration in which the security key update procedure cannot be performed, while performing the security key update procedure for an LTM candidate cell configuration in which the security key update procedure can be performed.

[0231] Furthermore, the LTM configuration information may include information (i.e., predetermined information) indicating whether each of the one or more LTM candidate cell configurations includes information for an update procedure. The control unit 120 may distinguish the 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 of the one or more LTM candidate cell configurations includes information for an update procedure. This allows the control unit 120 to determine whether each of the one or more LTM candidate cell configurations includes information for an update procedure based on the predetermined information, without having to check whether each LTM candidate cell configuration includes key update information.

[0232] (Other Embodiments) In the above-described embodiment, the control unit 120 of the UE 100 may, for example, prioritize the first method over the second method for the distinction method of the second operation example. Therefore, the control unit 120 may, for example, distinguish an LTM candidate cell configuration including key update information as the first LTM candidate cell configuration. Alternatively, the control unit 120 may prioritize the second method over the first method. Therefore, the control unit 120 may distinguish an LTM candidate cell configuration as the first LTM candidate cell configuration even if the source determination identifier and the selected candidate determination identifier are different.

[0233] In the above-described embodiments, "release" may be replaced with, for example, any of discard, ignore, clear, deactivate, and the like.

[0234] In the above-described embodiment, an NR-based mobile communication system has been described as an example of the mobile communication system 1. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system compliant with the TS of either LTE (Long Term Evolution) or another generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol termination toward the UE 100 in LTE. The mobile communication system 1 may be a system compliant with the TS of a standard other than the 3GPP standard. The base station 200 may be an IAB (Integrated Access and Backhaul) donor or an IAB node.

[0235] In the above-described embodiment, an NR-based mobile communication system has been described as an example of the mobile communication system 1. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system conforming to the TS of either LTE or another generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol termination for the UE 100 in LTE. The mobile communication system 1 may be a system conforming to the TS of a standard other than the 3GPP standard.

[0236] The steps in the operations of the above-described embodiments do not necessarily have to be executed in chronological order according to the order depicted in the flow diagrams or sequence diagrams. For example, the steps in the operations may be executed in an order different from that depicted in the flow diagrams or sequence diagrams, or may be executed in parallel. Some of the steps in the operations may be deleted, or additional steps may be added to the process. Furthermore, the above-described operational flows are not limited to being executed independently, but may be executed by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0237] A program may be provided that causes a computer to execute each process performed by the UE 100 or the base station 200. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM (Compact Disk Read Only Memory) or a DVD-ROM (Digital Versatile Disc Read Only Memory). Furthermore, circuits that execute each process performed by the UE 100 or the base station 200 may be integrated, and at least a part of the UE 100 or the base station 200 may be configured as a semiconductor integrated circuit (chip set, SoC (System On Chip)).

[0238] In the above-described embodiments, "transmit" may mean performing processing at least one layer in a protocol stack used for transmission, or may mean physically transmitting a signal wirelessly or via a wired connection. Alternatively, "transmit" may mean a combination of performing processing at least one layer and physically transmitting a signal wirelessly or via a wired connection. Similarly, "receive" may mean performing processing at least one layer in a protocol stack used for reception, or may mean physically receiving a signal wirelessly or via a wired connection. Alternatively, "receive" may mean a combination of processing at least one layer and physically receiving a signal wirelessly or via a wired connection. Similarly, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. Similarly, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." Similarly, "include" and "comprise" do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Similarly, in this disclosure, "or" does not mean an exclusive or, but rather a logical or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements.Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0239] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0240] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0241] (Supplementary Note 1) A communication device comprising: a receiver that receives a cell change command that triggers a cell change from a source cell to a target cell from a base station by a medium access control (MAC) control element (CE); and a controller that executes the cell change based on the cell change command, wherein the controller determines, based on determination information received from the base station, whether to execute a security key update procedure used for communication in the target cell when the cell change is executed.

[0242] (Supplementary Note 2) The communication device according to Supplementary Note 1, wherein the determination information is included in the MAC CE including the cell change command.

[0243] (Supplementary Note 3) The communication device according to Supplementary Note 1 or 2, wherein the control unit determines whether to execute the security key update procedure based on whether the determination information is included in the MAC CE including the cell change command.

[0244] (Supplementary Note 4) The communication device according to any one of Supplementary Notes 1 to 3, wherein the control unit includes a MAC processing unit that executes processing in a MAC layer, and when the MAC CE including the cell change command includes an identifier of the target cell and the determination information, the MAC processing unit notifies a layer higher than the MAC layer of the identifier of the target cell and content of the determination information.

[0245] (Supplementary Note 5) The communication device according to any one of Supplementary Notes 1 to 4, wherein the receiving unit receives a Radio Resource Control (RRC) message from the base station, the RRC message including, as the determination information, a determination identifier for identifying a cell manager; and the control unit determines not to perform the security key update procedure if the determination identifier of the source cell and the determination identifier of a candidate cell corresponding to the target cell are the same; and determines to perform the security key update procedure if the determination identifier of the source cell and the determination identifier of the candidate cell corresponding to the target cell are different.

[0246] (Supplementary Note 6) The communication device according to Supplementary Note 5, wherein after executing the cell change, the control unit stores a determination identifier of the candidate cell corresponding to the target cell as a determination identifier of the source cell.

[0247] (Supplementary Note 7) The communication device according to any one of Supplementary Notes 1 to 6, wherein the receiving unit receives from the base station a radio resource control (RRC) message including one or more Layer 1 / Layer 2 triggered mobility (LTM) configuration information used to provide one or more LTM candidate cell configurations, and the control unit, when determining not to perform the security key update procedure based on the determination information, omits the security key update procedure even if the LTM candidate cell configuration of a candidate cell corresponding to the target cell includes information for the update procedure.

[0248] (Supplementary Note 8) The communication device according to any one of Supplementary Notes 1 to 7, wherein the control unit omits transmitting a Layer 1 (L1) measurement report for the source cell to the source cell.

[0249] (Supplementary Note 9) The communication device according to any one of Supplementary Notes 1 to 8, wherein the control unit disables the LTM candidate cell setting of a candidate cell corresponding to the target cell based on the execution of the cell change to the target cell, and enables the disabled LTM candidate cell setting based on the execution of the cell change after the target cell is set as the source cell.

[0250] (Supplementary Note 10) A base station comprising: a transmitter that transmits a cell change command that triggers a cell change from a source cell to a target cell to a communication device by a medium access control (MAC) control element (CE), and the transmitter transmits to the communication device determination information that is used by the communication device to determine whether or not to perform an update procedure for a security key used for communication in the target cell when the cell change is executed.

[0251] (Supplementary Note 11) A communication method executed by a communication device, comprising: receiving a cell change command from a base station by a medium access control (MAC) control element (CE), the cell change command triggering a cell change from a source cell to a target cell; executing the cell change based on the cell change command; and determining, based on determination information received from the base station, whether to execute a security key update procedure used for communication in the target cell when executing the cell change.

[0252] (Supplementary Note 12) A communication device (100) comprising: a receiver (112) that receives, from a base station (200), a Radio Resource Control (RRC) message including Layer 1 / Layer 2 Triggered Mobility (LTM) configuration information used to provide LTM candidate information, and receives from the base station a cell change command that triggers a cell change using a Medium Access Control (MAC) control element (CE); and a controller (120) that performs an LTM cell change based on the cell change command, wherein the controller determines, based on an identifier included in the RRC message, whether to perform a security key update procedure when performing the LTM cell change.

[0253] (Supplementary Note 13) The communication device according to Supplementary Note 12, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

[0254] (Supplementary Note 14) The communication device according to Supplementary Note 13, wherein the control unit stores the identifier value of the candidate cell as the identifier value of the serving cell when the identifier value of the serving cell is not the same as the identifier value of the candidate cell.

[0255] (Supplementary Note 15) A base station (200) comprising: a transmitter (211) that transmits a Radio Resource Control (RRC) message including Layer 1 / Layer 2 Triggered Mobility (LTM) setting information used to provide LTM candidate information to a communication device (100), and transmits a cell change command that triggers a cell change to the communication device using a Medium Access Control (MAC) control element (CE); and a controller (230) that controls execution of an LTM cell change based on the cell change command, wherein the controller sets whether to perform a security key update procedure when the LTM cell change is executed based on an identifier included in the RRC message.

[0256] (Supplementary Note 16) The base station according to Supplementary Note 15, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

[0257] (Supplementary Note 17) The base station according to Supplementary Note 16, wherein if the serving cell identifier value is not the same as the candidate cell identifier value, the candidate cell identifier value is stored as the serving cell identifier value.

[0258] (Supplementary Note 18) A communication method for a communication device (100), comprising: a step of receiving, from a base station (200), a radio resource control (RRC) message including Layer 1 / Layer 2 triggered mobility (LTM) configuration information used to provide LTM candidate information; a step of receiving, from the base station (200), a cell change command for triggering a cell change using a medium access control (MAC) control element (CE); and a step of performing an LTM cell change based on the cell change command, wherein in the step of performing the LTM cell change, the communication method determines, based on an identifier included in the RRC message, whether to perform a security key update procedure when performing the LTM cell change.

[0259] (Supplementary Note 19) The communication method according to Supplementary Note 18, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

[0260] (Supplementary Note 20) The communication method according to Supplementary Note 19, wherein, in the step of performing the LTM cell change, if the identifier value of the serving cell is not the same as the identifier value of the candidate cell, the identifier value of the candidate cell is stored as the identifier value of the serving cell.

Claims

1. A communications device (100), comprising: a receiver (112) that receives a radio resource control (RRC) message including Layer 1 / Layer 2 triggered mobility (LTM) setting information used to provide LTM candidate information from a base station (200), and receives a cell change command that triggers a cell change from the base station using a medium access control (MAC) control element (CE); and a controller (120) that performs an LTM cell change based on the cell change command, wherein the controller determines whether or not to perform a security key update procedure when performing the LTM cell change based on an identifier included in the RRC message.

2. The communication device according to claim 1, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

3. The communication device according to claim 2, wherein the control unit stores the identifier value of the candidate cell as the identifier value of the serving cell when the identifier value of the serving cell is not the same as the identifier value of the candidate cell.

4. A base station (200), comprising: a transmitter (211) that transmits a radio resource control (RRC) message including Layer 1 / Layer 2 triggered mobility (LTM) setting information used to provide LTM candidate information to a communication device (100), and transmits a cell change command to trigger a cell change to the communication device using a medium access control (MAC) control element (CE); and a control unit (230) that controls execution of an LTM cell change based on the cell change command, wherein the control unit sets, based on an identifier included in the RRC message, whether or not to execute a security key update procedure when the LTM cell change is executed.

5. The base station according to claim 4, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

6. The base station according to claim 5, wherein if the serving cell identifier value is not the same as the candidate cell identifier value, the candidate cell identifier value is stored as the serving cell identifier value.

7. A communication method of a communication device (100), comprising: a step of receiving, from a base station (200), a radio resource control (RRC) message including Layer 1 / Layer 2 triggered mobility (LTM) setting information used for providing LTM candidate information; a step of receiving, from the base station using a medium access control (MAC) control element (CE), a cell change command for triggering a cell change; and a step of performing an LTM cell change based on the cell change command, wherein, in the step of performing the LTM cell change, the communication method determines whether or not to perform a security key update procedure when performing the LTM cell change based on an identifier included in the RRC message.

8. The communication method according to claim 7, wherein the identifiers include a serving cell identifier and a candidate cell identifier.

9. The communication method according to claim 8, further comprising: storing the identifier value of the candidate cell as the identifier value of the serving cell if the identifier value of the serving cell is not the same as the identifier value of the candidate cell in the step of performing the LTM cell change.

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