Communication device and communication method

Abstract

A communication device (100) according to an embodiment is a communication device (100) that communicates with a primary cell group and a secondary cell group, the primary cell group being associated with a primary node (MN 200M), and the secondary cell group being associated with a secondary node (SN 200S). The communication device is provided with: a reception unit (121) that receives, from the master node, configuration information for configuring a plurality of conditional reconfigurations for configuring a plurality of candidate cells to the communication device; and a control unit (120) that performs condition reconfiguration for a cell in which an execution condition is satisfied among the plurality of candidate cells. The configuration information comprises information of a counter value, and the information of the counter value is used for deriving a security key of a secondary node associated with the cell. When the condition reconfiguration is executed, the control unit updates the counter value.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims the benefit of priority of patent application No. 2023-013372 filed on January 31, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a communication device and a communication method. Background Art

[0004] Dual Connectivity (DC) has been introduced in mobile communication systems that comply with the technical specifications of 3GPP (registered trademark, hereinafter referred to as the Third Generation Partnership Project), a standardization project for mobile communication systems. In DC, communication devices communicate with a master cell group (MCG) and a secondary cell group (SCG). The MCG is associated with a master node (also called a "primary base station"), and the SCG is associated with a secondary node (also called a "secondary base station").

[0005] In the 3GPP technical specification document, the primary node sends a security key (specifically, KSN) to the secondary node and sends a counter value (specifically, SN counter) used to derive the security key to the communication device. The communication device uses the counter value to derive the security key, and uses the derived security key to derive a key for protecting communications with the secondary node (see Non-Patent Document 1).

[0006] In recent years, for example, selective SCG activation has been discussed to enable continuous cell changes when a communication device moves at high speed. In selective SCG activation, while the communication device remains connected to the same primary cell (P cell), multiple conditional reconfigurations are configured on the communication device to configure multiple candidate target primary and secondary cells (candidate target PS cells). The communication device executes conditional reconfigurations for candidate target PS cells whose execution conditions are met among the multiple conditional reconfigurations to change the PS cell from the source PS cell to the candidate target PS cell. After the PS cell is changed, the communication device can also change the PS cell by using the maintained multiple conditional reconfigurations, thereby continuously changing the cell.

[0007] Prior art literature

[0008] Non-patent literature

[0009] Non-Patent Document 1: 3GPP TS 33.501 V17.8.0 “Security architecture and procedures for 5G System” Summary of the Invention

[0010] The communication device involved in the first aspect is a communication device (100) that communicates with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node (MN 200M) and the secondary cell group is associated with a secondary node (SN 200S). The communication device includes: a receiving unit (121) that receives configuration information from the primary node, the configuration information being used to configure multiple conditional reconfigurations for the communication device, the multiple conditional reconfigurations being used to configure multiple candidate cells; and a control unit (120) that performs conditional reconfiguration for cells among the multiple candidate cells for which execution conditions are satisfied. The configuration information includes information on a counter value, the counter value being used to derive a security key of a secondary node associated with the cell. When the conditional reconfiguration is performed, the control unit updates the counter value.

[0011] The second aspect relates to a communication method performed by a communication device (100), wherein the communication device (100) communicates with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node (MN 200M) and the secondary cell group is associated with a secondary node (SN 200S). The communication method comprises: receiving configuration information from the primary node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate cells; and performing conditional reconfiguration for a cell among the plurality of candidate cells for which an execution condition is satisfied. The configuration information comprises information on a counter value, the counter value being used to derive a security key of a target secondary node associated with the cell. The communication method comprises updating the counter value when the conditional reconfiguration is performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The objects, features, advantages and the like of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings.

[0013] Figure 1 It is a diagram showing the configuration of a mobile communication system involved in an embodiment.

[0014] Figure 2 This is a diagram showing a configuration example of a protocol stack in a mobile communication system according to an embodiment.

[0015] Figure 3This is a diagram showing an overview of dual connectivity (DC) according to an embodiment.

[0016] Figure 4 This is a sequence diagram for explaining an example of security in DC.

[0017] Figure 5 This is a diagram used to illustrate a hypothetical scenario.

[0018] Figure 6 It is a diagram showing the configuration of a user equipment (UE) involved in an embodiment.

[0019] Figure 7 It is a diagram showing the configuration of a base station involved in the embodiment.

[0020] Figure 8 This is a sequence diagram (part 1) of an operation example 1 according to the embodiment.

[0021] Figure 9 This is a sequence diagram (part 2) of the first example of operation according to the embodiment.

[0022] Figure 10 This is a sequence diagram (part 3) of the first example of operation according to the embodiment.

[0023] Figure 11 This is a diagram showing a configuration example of an RRC reconfiguration message according to an embodiment.

[0024] Figure 12 This is a sequence diagram of the second operation example according to the embodiment.

[0025] Figure 13 This is a sequence diagram of the third operation example according to the embodiment. DETAILED DESCRIPTION

[0026] The mobile communication system according to the embodiment will be described with reference to the accompanying drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0027] It is assumed that in order to enable continuous cell changes, the communication device uses multiple conditional reconfigurations without resetting after the PS cell change. Therefore, it is impossible to receive the latest counter value from the master node every time the PS cell is changed.

[0028] In this case, for example, each time the PS cell is changed to the same cell, the communication device must use the same counter value to derive the security key. As a result, the key used to protect communications between the communication device and the secondary node is the same as the key previously used, which may result in communications between the communication device and the secondary node not being properly protected.

[0029] Therefore, one of the objects is to provide a communication device and a communication method capable of appropriately protecting communication between the communication device and a secondary node.

[0030] (Configuration of mobile communication system)

[0031] Reference Figure 1 The configuration of a mobile communication system 1 according to the embodiment will be described. Mobile communication system 1 is, for example, a system compliant with the 3GPP Technical Specification (TS). Hereinafter, a 5th Generation System (5GS) based on the 3GPP standard, i.e., a mobile communication system based on NR (New Radio), will be described as an example of mobile communication system 1.

[0032] Mobile communication system 1 includes a network 10 and a user equipment (UE) 100 communicating with network 10. Network 10 includes NG-RAN (Next Generation Radio Access Network) 20, which is a 5G radio access network, and 5GC (5G Core Network) 30, which is a 5G core network.

[0033] UE 100 is an example of a communication device. UE 100 may be a device used by a user. UE 100 may be a user equipment specified in the technical specifications of 3GPP. UE 100 may be, for example, a mobile phone terminal such as a smartphone, a tablet terminal, a notebook PC (personal computer), a communication module, or a communication card, which are movable devices. UE 100 may be a vehicle (e.g., a car, a train, etc.) or a device installed therein (e.g., a vehicle UE). UE 100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device installed therein (e.g., an aerial UE). UE 100 may be a sensor or a device installed therein. UE 100 may also be referred to as 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, among other names. UE 100 is an example of a terminal, and a terminal may include factory equipment, etc.

[0034] NG-RAN 20 includes multiple base stations 200. Each base station 200 manages at least one cell. A cell constitutes the smallest unit of a communication area. For example, a cell belongs to one frequency (carrier frequency) and includes one component carrier. The term "cell" sometimes refers to a wireless communication resource and sometimes refers to a communication object of UE 100. Each base station 200 is capable of wireless communication with UE 100 located in this cell. The base station 200 communicates with UE 100 using the protocol stack of RAN. The base station 200 is connected to other base stations 200 (also referred to as neighboring base stations) via the Xn interface. The base station 200 communicates with neighboring base stations via the Xn interface. In addition, the base station 200 provides NR user plane and control plane protocol termination for UE 100, and is connected to 5GC 30 via the NG interface. Such an NR base station 200 is sometimes referred to as a gNodeB (gNB).

[0035] 5GC 30 includes a core network device 300. Core network device 300 includes, for example, an Access and Mobility Management Function (AMF) and / or a User Plane Function (UPF). The AMF manages the mobility of UE 100. The UPF provides functions dedicated to user plane processing. The AMF and UPF are connected to base station 200 via an NG interface.

[0036] Reference Figure 2 , a configuration example of a protocol stack in the mobile communication system 1 involved in the embodiment is described.

[0037] The protocol of the wireless segment between UE 100 and base station 200 includes a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an RRC (Radio Resource Control) layer.

[0038] 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.

[0039] A physical channel consists of multiple OFDM (Orthogonal Frequency Division Multiplexing) symbols in the time domain and multiple subcarriers in the frequency domain. A subframe includes multiple OFDM symbols in the time domain. A resource block is a resource allocation unit and includes multiple OFDM symbols and multiple subcarriers. A frame can be composed of 10ms and can include 10 subframes of 1ms each. Within a subframe, there can be a number of time slots corresponding to the subcarrier spacing.

[0040] Among physical channels, the Physical Downlink Control Channel (PDCCH) plays a central role in purposes such as downlink scheduling assignments, uplink scheduling grants, and transmit power control. For example, UE 100 uses the Cell-Radio Network Temporary Identifier (C-RNTI) and Modulation and Coding Scheme-C-RNTI (MCS-C-RNTI) or Configured Scheduling-RNTI (CS-RNTI) assigned to UE 100 by base station 200 to perform blind decoding of the PDCCH, and obtains the successfully decoded DCI as the DCI addressed to the UE. The DCI transmitted from base station 200 is supplemented with CRC parity bits scrambled using the C-RNTI and MCS-C-RNTI or CS-RNTI.

[0041] In NR, UE 100 can use a bandwidth narrower than the system bandwidth (i.e., the bandwidth of the cell). The base station 200 configures a bandwidth part (BWP) including consecutive PRBs for UE 100. UE 100 sends and receives data and control signals in the active BWP. For example, up to four BWPs can be configured for UE 100. Each BWP can have a different subcarrier spacing, and the frequencies can overlap with each other. When multiple BWPs are configured for UE 100, the base station 200 can specify which BWP to activate through control in the downlink. As a result, the base station 200 can dynamically adjust the UE bandwidth according to the data traffic volume of UE 100, etc., which can reduce UE power consumption.

[0042] For example, base station 200 can configure up to three control resource sets (CORESETs) for each of up to four BWPs on a serving cell. A CORESET is a radio resource used for control information that UE 100 should receive. Up to 12 CORESETs can be configured on a serving cell for UE 100. Each CORESET includes an index from 0 to 11. For example, a CORESET includes six resource blocks (PRBs) and one, two, or three consecutive OFDM symbols in the time domain.

[0043] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), and random access procedures. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of base station 200 via transport channels. The MAC layer of base station 200 includes a scheduler. The scheduler determines the uplink and downlink transmission formats (transport block size, modulation and coding scheme (MCS)) and the resources allocated to UE 100.

[0044] The RLC layer uses the functions of the MAC layer and the PHY layer to transmit data to the RLC layer on the receiving side. 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.

[0045] The PDCP layer performs header compression / decompression and encoding / decoding.

[0046] The Service Data Adaptation Protocol (SDAP) layer can be configured as an upper layer of the PDCP layer. The SDAP layer maps IP flows to radio bearers. IP flows are the unit of QoS (Quality of Service) control in the core network, while radio bearers are the unit of QoS control in the access stratum (AS).

[0047] The RRC layer controls logical channels, transport channels, and physical channels in response to the establishment, reestablishment, and release of radio bearers. RRC signaling for various configurations 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 layer of the UE 100 and the RRC layer of the base station 200, the UE 100 is in the RRC connected state. When no RRC connection exists between the RRC layer of the UE 100 and the RRC layer of the base station 200, the UE 100 is in the RRC idle state. When the RRC connection between the RRC layer of the UE 100 and the RRC layer of the base station 200 is suspended, the UE 100 is in the RRC inactive state.

[0048] The NAS layer, located above the RRC layer, manages session and mobility for UE 100. NAS signaling is transmitted between the NAS layer of UE 100 and the NAS layer of core network device 300 (AMF). In addition to the radio interface protocol, UE 100 also includes an application layer, etc.

[0049] (DC Overview)

[0050] Reference Figure 3 , an overview of dual connectivity (DC) according to an embodiment of the present invention is described.

[0051] In DC, the UE 100 performs simultaneous communication with a master cell group (MCG) managed by a master node (MN) 200M and a secondary cell group (SCG) managed by a secondary node (SN) 200S. The MN 200M can be an NR base station (gNB) or an LTE base station (eNB). The MN 200M is also referred to as a master base station. In addition, in MR-DC (Multi-Radio Dual Connectivity), the master node is a radio access node that provides a control plane connection to the core network. The master node can be a master eNB (in EN-DC (E-UTRA-NR dual connectivity)), a master ng-eNB (in NGEN-DC (NG-RAN E-UTRA-NR dual connectivity)), or a master gNB (in NR-DC (NR-NR dual connectivity) and NE-DC (NR-E-UTRA dual connectivity)).

[0052] The SN 200S can be an NR base station (gNB) or an LTE base station (eNB). The SN 200S is also referred to as a secondary base station. Furthermore, in MR-DC, a secondary node is a radio access node that does not have a control plane connection to the core network and provides additional resources to the UE 100. The secondary node can be an en-gNB (in EN-DC), a secondary ng-eNB (in NE-DC), or a secondary gNB (in NR-DC and NGEN-DC).

[0053] For example, the MN 200M sends a predetermined message (eg, an SN Addition Request message) to the SN 200S, and the MN 200M sends an RRC Reconfiguration message to the UE 100, thereby starting DC.

[0054] UE 100 in the RRC connected state receives radio resources from the scheduler of each of MN 200M and SN 200S, which are connected to each other via a backhaul network communication section, and performs wireless communication using the radio resources of MN 200M and the radio resources of SN 200S. The network communication section between MN 200M and SN 200 may be an Xn interface or an X2 interface. MN 200M and SN 200 communicate with each other via this network communication section.

[0055] The MN 200M may have a control plane connection with the core network. The MN 200M provides primary radio resources for the UE 100. The MN 200M manages the MCG. The MCG is a group of serving cells associated with the MN 200M. The MCG includes a primary cell (PCell) and optionally one or more secondary cells (SCells).

[0056] The SN 200S may not have a control plane connection with the core network. The SN 200S provides additional radio resources to the UE 100. The SN 200S manages the SCG. The SCG is associated with the SN 200S. The SCG includes a primary and secondary cell (PS cell) and optionally one or more SCells. In addition, the PCell of the MCG and the PS cell of the SCG are also called special cells (SpCells).

[0057] (Security in DC)

[0058] cite Figure 4 , an example of security in DC is explained.

[0059] In step S11, UE 100 and MN 200M establish an RRC connection.

[0060] In step S12, the MN 200M sends an SN add request message or an SN change request message to the SN 200S. The message may include the security key (KSN) of the target secondary node (specifically, the SN 200S). The security key may also be referred to as a secondary key. In addition to the "KSN" label, the security key may also be labeled "KeNB," "KgNB," "S-KeNB," "S-KgNB," or "S-KeNB."

[0061] MN 200M can calculate a security key and distribute it to SN 200S. Based on the security key, SN 200S derives a key for protecting communication between UE 100 and SN 200S. SN 200S can derive the RRC key and UP key used between UE 100 and SN 200S as the key.

[0062] RRC keys are keys used for RRC signaling. They are keys derived from security keys by UE 100 and base station 200. RRC keys include a key (KRRCint) used only to protect RRC signaling with a specific integrity algorithm, and a key (KRRCenc) used only to protect RRC signaling with a specific encryption algorithm.

[0063] The UP key is a key used for uplink (UP) traffic. The UP key is derived from security keys by the UE 100 and the base station 200. The UP key can include a key (KRRCint) used only to protect UP traffic between the UE 100 and the base station 200 with a specific integrity algorithm, and a key (KRRCenc) used only to protect UP traffic with a specific encryption algorithm.

[0064] Furthermore, the MN 200M can send the UE security function and UP security policy received from the SMF (Session Management Function) to the SN 200S. In addition, the MN 200M can include information indicating the determination of enabling of UP integrity protection and encryption in the aforementioned message.

[0065] The SN 200S can allocate the necessary resources. In addition, the SN 200S can select the encryption algorithm and integrity algorithm with the highest priority from the configuration list that are also present in the UE security function. In addition, the SN 200S can activate the UP security policy.

[0066] In step S13, the SN 200S sends an SN Add Request Confirmation message or an SN Change Request message to the MN 200M. This message may indicate the availability of the requested resources and the identifier of the algorithm selected for the DRB (Data Radio Bearer) and / or SRB (Signaling Radio Bearer) requested for the UE 100.

[0067] In step S14, the MN 200M sends an RRC reconfiguration message to the UE 100 to indicate to the UE 100 the configuration of new DRBs and / or SRBs for the SN 200S.

[0068] The MN 200M may include an SN counter in the RRC reconfiguration message. The SN counter indicates a counter value used to derive a security key. The SN counter may be a parameter indicating that a new KSN is required.

[0069] In addition, the MN 200M may include these information in the RRC reconfiguration message in order to forward the UE configuration parameters including the algorithm identifier, UP integrity protection, and ciphering indication received from the SN 200S, for example.

[0070] After integrity verification, UE 100 accepts the RRC reconfiguration message. If the SN counter is included in the message, UE 100 derives (calculates) the security key for SN 200S based on the counter value indicated by the SN counter. Furthermore, UE 100 derives (calculates) the required RRC keys and UP keys based on the derived security key. UE 100 activates RRC and UP protection according to the received indication for each associated SRB and / or DRB.

[0071] In step S15, the UE 100 sends an RRC reconfiguration complete message to the MN 200M. At this point in time, the UE 100 activates the selected encryption / decryption and integrity protection keys with the SN 200S.

[0072] In step S16, the MN 200M sends an SN Reconfiguration Complete message to the SN 200S to notify the SN 200S of the configuration result. In response to receiving this message, the SN 200S can activate the selected encryption / decryption and integrity protection with the UE 100. If encryption / decryption and integrity protection are not activated at this stage, the SN 200S activates encryption / decryption and integrity protection in response to receiving a random access request from the UE 100.

[0073] In step S17, UE 100 and SN 200S perform a random access procedure. Thus, UE 100 communicates with the MCG managed by MN 200M and the SCG managed by SN 200S in DC. In this way, SN 200S can use security keys to derive RRC keys and UP keys to enable encryption and decryption for UE 100 and thus communicate with UE 100.

[0074] (Imagine a scenario)

[0075] cite Figure 5 , explaining the hypothetical scenario. In recent years, for example, selective SCG activation has been discussed to enable continuous cell changes when UE 100 moves at high speed. In selective SCG activation, while UE 100 maintains the same PC cell, multiple conditional reconfigurations are configured for UE 100 to configure multiple candidate target primary and secondary cells (candidate target PS cells). UE 100 executes conditional reconfigurations for candidate target PS cells whose execution conditions are satisfied among the multiple conditional reconfigurations to change the PS cell from the source PS cell to the candidate target PS cell. After the PS cell change, UE 100 can also change the PS cell by using the maintained multiple conditional reconfigurations, thereby continuously changing the cell.

[0076] Here, it is assumed that in order to enable continuous cell changes, UE 100 uses multiple condition reconfigurations without resetting even after PS cell change. Therefore, it is impossible to receive the latest counter value (specifically, SN counter) from MN 200M every time PS cell change is made.

[0077] In this case, for example, each time the PS cell is changed to the same cell, the UE 100 must use the same counter value to derive the security key. As a result, the key used to protect the communication between the UE 100 and the SN 200S is the same as the key used previously, which may cause the communication between the UE 100 and the SN 200S to be inadequately protected.

[0078] For example, Figure 5 As shown, MN 200M manages MCG (PCell), SN 200S1 manages cells C11 and C12, SN 200S2 manages cells C21 and C22, and SN 200S3 manages cells C31 and C32.

[0079] UE 100 communicates with cell C11, which is the MCG of MN 200M and the SCG of SN 200S1, via DC. It is assumed that UE 100 is configured with conditional reconfigurations for each of cells C11, C12, C21, C22, C31, and C32 as multiple conditional reconfigurations.

[0080] In the use of Figure 5 As shown in the path A, UE 100 uses the pre-configured multiple condition reconfiguration to change the PS cell from cell C11 to cell C21, and then changes the PS cell from cell C21 to cell C11. In this case, the PS cell can be changed without receiving the MN 200M. Figure 4 14. Therefore, when the PS cell is changed from cell C21 to cell C11, UE 100 uses the counter value used before the PS cell was changed to cell C21 to derive the security key. As a result, even when multiple PS cell changes are performed, UE 100 uses the same security key to implement communication protection when cell C11 is set as the PS cell.

[0081] In addition, since the SN 200S1 associated with the cell C11 and the cell C12 is the same, when using Figure 5 As shown in path B, UE 100 uses multiple pre-configured conditional reconfigurations to change the PS cell from cell C11 to cell C21, and then changes the PS cell from cell C21 to cell C12. Currently, the counter value is the same in the configurations of cells C11 and C12. Therefore, similar to path A, even when multiple PS cell changes are performed, UE 100 uses the same security key to implement communication protection when cells C11 and C12 are set as PS cells.

[0082] Although security keys have traditionally been changed each time a PS cell is changed for security reasons, selective SCG activation uses the same security keys for communication protection when the PS cell is changed to a specific cell, raising concerns that communications between UE 100 and SN 200S may not be properly protected. An embodiment described later will describe operations for properly protecting communications between UE 100 and SN 200S.

[0083] (Configuration of user equipment)

[0084] Reference Figure 6, the configuration of the UE 100 according to the embodiment will be described. The UE 100 includes a communication unit 110 and a control unit 120.

[0085] The communication unit 110 wirelessly communicates with the base station 200 by sending and receiving wireless signals. The communication unit 110 includes at least one transmitting unit 111 and at least one receiving unit 112. The transmitting unit 111 and the receiving unit 112 can be configured to include multiple antennas and RF circuits. The antennas convert signals into radio waves and radiate these waves into space. Furthermore, the antennas receive radio waves in space and convert them into signals. The RF circuits perform analog processing on the signals transmitted and received by the antennas. The RF circuits may include high-frequency filters, amplifiers, modulators, and low-pass filters.

[0086] The control unit 120 performs various controls within the UE 100. The control unit 120 controls communication with the base station 200 via the communication unit 110. The operations of the UE 100 described above and below may be controlled by the control unit 120. The control unit 120 may include at least one processor capable of executing programs and a memory storing the programs. The processor can execute the programs 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 RF circuit. This digital processing includes processing of the RAN protocol stack. Furthermore, the memory stores programs executed by the processor, parameters related to the programs, and data related to the programs. The memory may include at least one of ROM (Read Only Memory), EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), RAM (Random Access Memory), and flash memory. All or a portion of the memory may be included within the processor.

[0087] The UE 100 configured in this way communicates with the MCG and SCG, the MCG being associated with the MN 200M and the SCG being associated with the SN 200S. The receiving unit 112 receives configuration information from the MN 200M, the configuration information being used to configure a plurality of conditional reconfigurations to the UE 100, the plurality of conditional reconfigurations being used to configure a plurality of candidate target primary and secondary (PS) cells. The control unit 120 performs conditional reconfiguration on a cell among the plurality of candidate target PS cells for which the execution conditions are satisfied. The configuration information includes information on a counter value, which is used to derive the security key of the target SN 200S associated with the cell. When the conditional reconfiguration is performed, the control unit 120 updates the counter value. Thus, even when the PS cell is changed to a specific cell, different security keys are used to implement communication protection, thereby enabling appropriate protection of the communication between the UE 100 and the SN 200S.

[0088] Furthermore, the receiving unit 112 receives configuration information from the MN 200M for configuring multiple conditional reconfigurations for the UE 100. These conditional reconfigurations are used to configure multiple candidate target primary and secondary (PS) cells. The control unit 120 updates a counter value used to derive security keys for target SNs 200S associated with cells whose execution conditions are satisfied from among the multiple candidate target PS cells. The transmitting unit 111 transmits confirmation information to the network 10, confirming the security keys derived based on the updated counter value. This allows the network 10 to identify the security keys derived based on the counter value updated by the UE 100 and appropriately protect communications between the UE 100 and the SNs 200S.

[0089] (Base station configuration)

[0090] Reference Figure 7 The configuration of the base station 200 according to the embodiment will be described. The base station 200 includes a communication unit 210, a network communication unit 220, and a control unit 230.

[0091] Communication unit 210, for example, receives wireless signals from UE 100 and transmits wireless signals to UE 100. Communication unit 210 includes at least one transmitting unit 211 and at least one receiving unit 212. Transmitting unit 211 and receiving unit 212 may be configured to include RF circuits. RF circuits perform analog processing of signals transmitted and received via an antenna. RF circuits may include high-frequency filters, amplifiers, modulators, and low-pass filters.

[0092] Network communication unit 220 transmits and receives signals to and from the network. For example, network communication unit 220 receives signals from and transmits signals to adjacent base stations connected via an Xn interface, which is an interface between base stations. Furthermore, network communication unit 220 receives signals from and transmits signals to core network device 300 connected via an NG interface, for example.

[0093] The control unit 230 performs various controls in the base station 200. For example, the control unit 230 controls communication with the UE 100 via the communication unit 210. In addition, the control unit 230 controls communication with nodes (for example, adjacent base stations, core network devices 300) via the network communication unit 220. The actions of the base station 200 described above and below may be actions controlled by the control unit 230. The control unit 230 may include at least one processor capable of executing programs and a memory storing programs. The processor may execute the program to perform the actions of the control unit 230. The control unit 230 may include a digital signal processor that performs digital processing of signals sent and received via the antenna and RF circuit. The digital processing includes processing of the protocol stack of the RAN. In addition, the memory stores the program executed by the processor, parameters related to the program, and data related to the program. All or part of the memory may be included in the processor.

[0094] The base station 200 configured in this manner operates as a MN 200M in a network 10, which includes the MN 200M associated with the MCG configured for the UE 100 and the SN 200S associated with the SCG configured for the UE 100. In the base station 200, a transmitting unit 211 transmits configuration information to the UE 100, the configuration information being used to configure a plurality of conditional reconfigurations for configuring a plurality of candidate target primary and secondary (PS) cells. A receiving unit 212 receives, from the UE 100, the updated counter value, determination information for deriving a security key for a target secondary node associated with a cell whose execution condition is satisfied from among the plurality of candidate target PS cells, the determination information being used to determine the security key to be derived based on the updated counter value.

[0095] In addition, the base station 200 operates as an SN 200S in the network 10, which includes an MN 200M associated with the MCG configured for the UE 100, and an SN 200S associated with the SCG configured for the UE 100. In the base station 200, the receiving unit 212 receives, via the master node that transmits configuration information to the UE 100, determination information from the UE 100 whose counter value has been updated, the configuration information being used to configure a plurality of conditional reconfigurations for configuring a plurality of candidate target primary and secondary (PS) cells for the communication device, the counter value being used to derive a security key of a target secondary node associated with a cell whose execution condition is satisfied from among the plurality of candidate target PS cells, and the determination information being used to determine the security key derived based on the updated counter value.

[0096] Thereby, the SN 200S that has received the confirmation information from the MN 200M or the MN 200M can grasp the security key derived based on the counter value updated by the UE 100, and thus can appropriately protect the communication between the UE 100 and the SN 200S.

[0097] (Operation Example of Mobile Communication System)

[0098] Hereinafter, an example of the operation of the mobile communication system will be described. In addition, descriptions of the same contents as those already described may be omitted.

[0099] (Action Example 1)

[0100] Reference Figures 4 to 11 , the operation example 1 of the mobile communication system 1 involved in the embodiment is described. Figure 5 as well as Figure 8 As shown in FIG, it is assumed that DC is configured through UE 100, MN 200M and SN 200S1. Figure 8 In the initial stage, UE 100 communicates with the MCG (P cell) of MN 200M and the SCG of SN 200S1. Cell C11 of SN 200S1 is a PS cell. In the following, the communication between UE 100 and MCG (P cell) is appropriately described as the communication between UE 100 and MN 200M. Similarly, the communication between UE 100 and each SCG (PS cell) is appropriately described as the communication between UE 100 and each SN 200S. Figure 8 Regarding SN 200S3, it is omitted.

[0101] In this example, UE 100 is as follows: Figure 5 The following describes the case where the moving path B is taken as an example.

[0102] like Figure 8As shown, in step S101, the control unit 230 of the MN 200M requests the candidate target SN to allocate resources to the UE through the SN addition process, thereby starting a conditional SN change. Specifically, the network (NW) communication unit 220 of the MN 200M sends an SN addition request message to each candidate target SN. In this action example, the candidate target SNs are SN 200S1, SN 200S2, and SN 200S3. The NW communication units 220 of SN 200S1 to SN 200S3 receive the SN addition request message. In addition, the request can indicate that it is a request for CPAC (Conditional PSCell Addition / Change).

[0103] The NW communication unit 220 of the MN 200M can provide candidate cells recommended by the MN 200M based on the latest measurement results, so that the candidate target SN selects and configures an SCG cell. The NW communication unit 220 of the MN 200M can provide an upper limit on the number of PS cells that the candidate target SN can prepare.

[0104] The control unit 230 of each candidate target SN specifies a list of PS cells from the cell list indicated in the measurement result. In addition, the control unit 230 of each candidate target SN specifies SCells of other SCGs.

[0105] In addition, the MN 200M and each SN 200S may also perform the same operation as step S12.

[0106] In step S102, the NW communication unit 220 of each candidate target SN transmits an SN addition request confirmation message to the MN 200M. The NW communication unit 220 of the MN 200M receives the SN addition request confirmation message from each candidate target SN.

[0107] The control unit 230 of each candidate target SN may include an RRC reconfiguration message in the SN add request confirm message, the RRC reconfiguration message including the new SCG radio resource configuration. In addition, the MN 200M and each SN 200S may also perform the same actions as step S13.

[0108] In step S103, the transmitting unit 211 of the MN 200M transmits an RRC reconfiguration message to the UE 100. The receiving unit 112 of the UE 100 receives the RRC reconfiguration message from the MN 200M.

[0109] The RRC reconfiguration message includes configuration information for configuring multiple conditional reconfigurations to the UE 100. The multiple conditional reconfigurations are conditional reconfigurations for configuring multiple candidate target PS cells. The configuration information may be CPC configuration information. Figure 11 As shown, the configuration information may be, for example, "RRCReconfiguration-IEs" or "conditionalReconfiguration". The configuration information includes one or more conditional reconfiguration information (e.g., condRRCReconfig). Each conditional reconfiguration information (condRRCReconfig) includes an RRC reconfiguration (RRCReconfiguration) message that is applied when an execution condition is met. The configuration information may be a list of RRC reconfiguration messages associated with an execution condition.

[0110] The RRC reconfiguration message included in the conditional reconfiguration information includes configuration information for configuring the candidate target PS cell. The RRC reconfiguration message does not include a predetermined field (e.g., a "conditionalReconfiguration" field or a "daps-Config" field). The RRC reconfiguration message includes information about a counter value used to derive a security key for the target SN.

[0111] The information of the counter value may include an SN counter indicating the counter value. The SN counter may be referred to as a "sk-Counter." The SN counter may be a counter used in the initial configuration and refresh of the security key of the target SN.

[0112] The counter value information may include an initial counter value and an offset value. The initial counter value and the offset value are used to update the counter value. The receiving unit 112 of the UE 100 receives the initial counter value and the offset value from the MN 200M as the counter value information.

[0113] like Figure 11 As shown in E11 of FIGURE 1, the initial counter value (sk-Counter_ini) and the offset value (OffSN) may be included in the conditional reconfiguration information (condRRCReconfig). In this case, the offset value may be a value specifically configured in each of the plurality of conditional reconfiguration information. Alternatively, as shown in FIGURE 1 Figure 11 As shown in E12 of FIG, the initial counter value (sk-Counter_ini) may be included in the conditional reconfiguration information. Figure 11As shown in E13 of FIG, the offset value (OffSN) may be included in RRCReconfiguration separately from conditionalReconfiguration. In this case, the offset value may be a value commonly configured in a plurality of conditional reconfiguration messages.

[0114] In addition, the counter value information may include a list associating each of multiple counter values ​​with the number of PS cell changes. This list may be associated with the configuration of the execution condition (e.g., Trigger Event Cfg). The PS cell change count NKSN may be a value common to all candidate target PS cells. Therefore, the number of PS cell changes can be counted regardless of the PS cell to which the change is made.

[0115] The information on the counter value may include, for each of a plurality of candidate target SNs, a list associating each of a plurality of counter values ​​with the number of changes to the PS cell. The number of changes NKSN may be a value specifically configured for each candidate target SN. As information on the counter value, for example, within the RRC reconfiguration information, a list of a plurality of counter values ​​for each candidate target SN may be configured in parallel. In addition, as information on the counter value, for example, within each of a plurality of conditional reconfiguration information (condRRCReconfig), a list of a plurality of counter values ​​for the target SN that manages the PS cell corresponding to the conditional reconfiguration information may be included.

[0116] The counter value information may include a list associating each of the multiple counter values ​​with the number of PS cell changes for each of the multiple candidate target PS cells. The PS cell change number NKSN may be a value specifically configured for each candidate target PS cell.

[0117] The configuration information may include information configuring execution conditions that need to be satisfied in order to trigger execution of the conditional reconfiguration ("condExecutionCond", "condExecutionCondSCG", etc.).

[0118] The control unit 120 of the UE 100 applies the RRC reconfiguration complete message and saves the configuration information. In addition, the UE 100 and the MN 200M may also perform the same operation as step S14.

[0119] In step S104, the transmitting unit 111 of the UE 100 transmits an RRC reconfiguration complete message to the MN 200M. The receiving unit 212 of the MN 200M receives the RRC reconfiguration complete message from the UE 100. Furthermore, the UE 100 and the MN 200M can perform the same operations as in step S15. Thereafter, the MN 200M and each SN 200S can perform the same operations as in step S16.

[0120] In step S105 , the control unit 120 of the UE 100 measures the radio signals from each cell.

[0121] In step S106, the control unit 120 of the UE 100 evaluates the execution condition based on the measurement result. Specifically, the control unit 120 determines whether the execution condition (event) of the candidate target PS cell is met based on the measurement result. When the execution condition is met, the control unit 120 of the UE 100 regards the target candidate cell corresponding to the satisfied execution condition as a triggered cell. When there are multiple triggered cells, the control unit 120 selects one of the multiple triggered cells to perform conditional reconfiguration. When there is only one triggered cell, the control unit 120 regards the cell as the cell selected for performing conditional reconfiguration. The control unit 120 starts to perform conditional reconfiguration for the selected cell and performs the following actions. In this action example, the control unit 120 selects cell C21 and starts to perform conditional reconfiguration.

[0122] In step S107, the control unit 120 of the UE 100 applies the conditional reconfiguration information of the selected cell. Thus, the control unit 120 of the UE 100 applies the RRC reconfiguration included in the conditional reconfiguration information of the selected cell.

[0123] In step S108, the control unit 120 of the UE 100 updates the counter value. When conditional reconfiguration is executed, the control unit 120 updates the counter value. In this operation example, the control unit 120 of the UE 100 updates the counter value before starting the random access (RA) procedure by executing conditional reconfiguration.

[0124] The control unit 120 may update the counter value in response to the application of the conditional reconfiguration information for the selected cell. The control unit 120 may update the counter value in response to the application of the RRC reconfiguration (RRCReconfiguration) included in the conditional reconfiguration information for the selected cell. The control unit 120 may update the counter value based on the number of changes NKSN of PS cells from the source PS cell to the target PS cell using the configuration information. The number of changes NKSN may be replaced by the number of applications of the RRC reconfiguration. The control unit 120 can use any of the following methods to update the counter value.

[0125] In the first method, the control unit 120 can update the counter value by calculating the counter value. For example, the control unit 120 can determine (calculate) the counter value using the following formula. The control unit 120 can regard the determined counter value (sk-Counter_Mob) as the updated counter value.

[0126] sk-Counter_Mob=sk-Counter_ini+OffKSN×NKSN

[0127] The initial counter value (sk-Counter_ini) may be a value commonly configured for all candidate target PS cells. Alternatively, the initial counter value may be a value specifically configured for each candidate target PS cell. The initial counter value may be a value specifically configured for each candidate target SN.

[0128] The offset value (OffKSN) may be a value based on the number of candidate target SNs configured by the configuration information. The offset value may be a value that is increased according to the number of candidate target SNs. The offset value may be, for example, a value greater than the number of candidate target SNs configured by the configuration information. The control unit 230 of the base station 200 may configure the number of candidate target SNs as the offset value. The control unit 120 of the UE 100 may configure the number of candidate target SNs as the offset value. In addition, the control unit 120 may determine the number of candidate target SNs based on the number of conditional reconfiguration information. The control unit 120 may determine the number of candidate target SNs based on the number of candidate target SNs included in the conditional reconfiguration information.

[0129] (a) When the number of changes NKSN is a value common to all candidate target PS cells:

[0130] When the RRC reconfiguration message is directly received from the MN 200M as in step S104, the control unit 120 may configure the number of changes NKSN to 0. When the execution condition is satisfied and it is determined that the RRC reconfiguration included in the conditional reconfiguration message has been received, the control unit 120 may increase the number of changes NKSN by 1. Thus, the control unit 120 counts the number of PS cell changes using the configuration information as the number of changes NKSN. The control unit 120 may count the number of PS cell changes NKSN each time the PS cell is changed, regardless of the PS cell to which the change is made.

[0131] (b) When the number of changes NKSN is a value specifically configured for each candidate target SN:

[0132] When the RRC reconfiguration message is received directly from the MN 200M, the control unit 120 may reset the number of change counts NKSN previously configured for the UE 100 for all candidate target SNs. The control unit 120 may configure the newly configured number of change counts NKSN for all candidate target SNs based on the directly received RRC reconfiguration message, setting each number of change counts NKSN to 0. When it is determined that the RRC reconfiguration included in the conditional reconfiguration information has been received due to the execution condition being satisfied, and it is determined that the target SN is different from the source SN (inter-SN CPC), the control unit 120 may increase the number of change counts NKSN associated with the target SN by 1. Therefore, the control unit 120 counts the number of change counts NKSN specifically for each candidate target secondary node.

[0133] (c) When the number of changes NKSN is a value configured specifically for each candidate target PS cell:

[0134] When the RRC reconfiguration message is received directly from the MN 200M, the control unit 120 may reset the number of change counts NKSN previously configured for the UE 100 for all candidate target PS cells. Based on the directly received RRC reconfiguration message, the control unit 120 may configure newly configured number of change counts NKSN for all candidate target PS cells, setting each number of change counts NKSN to 0. When it is determined that the RRC reconfiguration included in the conditional reconfiguration information has been received due to the execution condition being satisfied, the control unit 120 may increment the number of change counts NKSN associated with the target PS cell by 1. Thus, the control unit 120 counts the number of change counts NKSN specifically for each candidate target PS cell.

[0135] In the second method, the control unit 120 updates the counter value based on a list that associates each of the multiple counter values ​​with a change count NKSN. The control unit 120 may set the counter value corresponding to the change count NKSN to the updated counter value. In this case, the control unit 120 may count the PS cell change count NKSN each time a PS cell change occurs, regardless of the PS cell to which the change is made.

[0136] In the third method, the control unit 120 updates the counter value based on a list that associates each of multiple counter values ​​for the corresponding candidate target SN with a change count NKSN. In this case, the control unit 120 configures the change count NKSN for each candidate target SN. The control unit 120 can count the change count NKSN specifically for each candidate target SN and set the counter value corresponding to the change count NKSN associated with the target SN among the multiple counter values ​​as the updated counter value. In this case, the control unit 120 can count the change count NKSN specifically for each candidate target secondary node.

[0137] In the fourth method, the control unit 120 updates the counter value based on a list that associates each of multiple counter values ​​for the corresponding candidate target PS cell with a change count NKSN. In this case, the control unit 120 configures the change count NKSN for each candidate target PS cell. The control unit 120 can count the change count NKSN specifically for each candidate target PS cell and set the counter value among the multiple counter values ​​corresponding to the change count NKSN associated with the target PS cell as the updated counter value. In this case, the control unit 120 can count the change count NKSN specifically for each candidate target PS cell.

[0138] If the target SN is associated with both the source and target PS cells, the control unit 120 may skip updating the counter value. That is, if a PS cell change (intra-SN CPC) is performed within the same SN 200S, the control unit 230 may skip updating the counter value.

[0139] The control unit 120 can determine whether the target SN is associated with both the source PS cell and the target PS cell (is an intra-SN CPC) based on the configuration information currently configured for the UE 100 (e.g., information included in SpCellConfig) and the information included in the conditional reconfiguration information of the selected cell (e.g., MeasObject and / or RRCRReconfiguration). The configuration information currently configured for the UE 100 is compared with the information included in the conditional reconfiguration information of the selected cell. If the information related to the source PS cell and the target PS cell is the same, the control unit 120 can determine that the target SN is associated with both the source PS cell and the target PS cell. Otherwise, the control unit 120 can determine that the target SN is not associated with both the source PS cell and the target PS cell.

[0140] In addition, the control unit 120 of the UE 100 can derive (update) the security key based on the updated counter value. The control unit 120 can derive the RRC key and the UP key using the derived security key.

[0141] In step S109 , the transmitting unit 111 of the UE 100 transmits an RRC reconfiguration complete message to the MN 200M. The receiving unit 212 of the MN 200M receives the RRC reconfiguration complete message from the UE 100 .

[0142] The control unit 120 of the UE 100 may include determination information for determining the security key derived based on the updated counter value in the RRC reconfiguration complete message.

[0143] The control unit 120 may include the confirmation information in a message (e.g., an SN RRC Reconfiguration Complete message described later) sent to the target SN via the MN 200M. The control unit 120 may include this message in the RRC Reconfiguration Complete message. Thus, the transmission unit 111 can transmit the confirmation information to the network 10 via a message sent to the target SN via the MN 200M.

[0144] The control unit 120 may include confirmation information in the message setting the MN 200M as the terminating end. The confirmation information may be included in a field other than the message sent by the MN 200M to the target SN, included in the RRC Reconfiguration Complete message. Thus, the transmitting unit 111 can send the confirmation information to the network 10 via the message setting the MN 200M as the terminating end.

[0145] The determination information may include the updated security key. The determination information may include the updated counter value. The determination information may include calculation information used to calculate the updated counter value. The calculation information may include, for example, the number of PS cell changes NKSN used to calculate the updated counter value.

[0146] When the determination information is included in a field other than the SN RRC Reconfiguration Complete message within the RRC Reconfiguration Complete message, the control unit 230 of the MN 200M can acquire the determination information. On the other hand, when the determination information is included in the SN RRC Reconfiguration Complete message within the RRC Reconfiguration Complete message, the control unit 230 of the MN 200M does not acquire the determination information.

[0147] like Figure 9As shown, in step S110, the NW communication unit 220 of the MN 200M may send an SN release request message to the SN 200S1. The NW communication unit 220 of the SN 200S1 may receive the SN release request message from the MN 200M. Thus, the MN 200M notifies the SN 200S1, which is the source SN, to stop providing user data.

[0148] In step S111, the NW communication section 220 of the SN 200S1 may transmit an SN release request confirmation message to the MN 200M. The NW communication section 220 of the MN 200M may receive the SN release request message from the SN 200S1.

[0149] In step S112, the NW communication unit 220 of the MN 200M transmits an SN reconfiguration complete message to the SN 200S2. The NW communication unit 220 of the SN 200S2 receives the SN reconfiguration complete message from the MN 200M. Thus, the MN 200M notifies the SN 200S2 of the PS cell selected by the UE 100.

[0150] The control unit 230 of the MN 200M may include an SN RRC Reconfiguration Complete message, the SN RRC Reconfiguration Complete message including the confirmation information, in the SN Reconfiguration Complete message. Consequently, the NW communication unit 220 of the MN 200M transmits the SN RRC Reconfiguration Complete message including the confirmation information to the SN 200S2. Alternatively, the control unit 230 of the MN 200M may include the confirmation information along with the SN RRC Reconfiguration Complete message in the SN Reconfiguration Complete message. Consequently, if the confirmation information includes a security key, the NW communication unit 220 of the MN 200M transmits the security key to the SN 200S2. The control unit 230 of the MN 200M may include information for calculating the security key in the SN Reconfiguration Complete message.

[0151] In step S113, the control unit 230 of the SN 200S2 determines the security key. In this operation example, the control unit 230 determines the security key based on the determination information.

[0152] In a case where the determination information includes a security key, the control unit 230 may determine the security key included in the determination information as a security key for protecting communication with the UE 100 .

[0153] The control unit 230 may derive a security key based on the information for calculating the security key and the determination information. The control unit 230 may determine the derived security key as a security key for protecting communications with the UE 100 .

[0154] The control unit 230 can derive the RRC key and UP key used between the UE 100 and the SN 200S2 based on the determined security key. In addition, the MN 200M and the SN 200S2 can also perform the same operation as step S16.

[0155] In step S114, UE 100 and SN 200 S2 perform a random access procedure. Thereafter, UE 100 communicates with MCG and cell C21 in DC.

[0156] Furthermore, the control unit 230 of the UE 100 may update the counter value at a timing other than step S108. For example, the control unit 230 may update the counter value after the RA procedure for cell C21 is initiated by executing conditional reconfiguration and before an RRC message is sent to cell C21 during the RA procedure. The RRC message in this case is, for example, Message 3.

[0157] like Figure 10 As shown, steps S115 to S119 are steps S105 to S109. In this operation example, the control unit 120 of the UE 100 selects the cell C12 as the PS cell.

[0158] In step S120, similarly to step S110, the NW communication unit 220 of the MN 200M transmits an SN release request message to the SN 200S 2. In step S121, similarly to step S111, the NW communication unit 220 of the SN 200S 2 transmits an SN release request confirmation message to the MN 200M.

[0159] In step S122, similar to step S112, the NW communication unit 220 of the MN 200M sends an SN reconfiguration complete message to the SN 200S1. In step S123, similar to step S113, the control unit 230 of the SN 200S1 determines the security key. In step S124, similar to step S114, the UE 100 and the SN 200S1 perform the RA procedure. Thereafter, the UE 100 communicates with the MCG and cell C12 in DC.

[0160] As described above, in this example operation, the receiving unit 112 of the UE 100 receives configuration information from the MN 200M for configuring multiple conditional reconfigurations for the UE 100. These conditional reconfigurations are used to configure multiple candidate target PS cells. The control unit 120 performs conditional reconfiguration on cells among the candidate target PS cells for which the execution conditions are met. The configuration information includes information about a counter value, which is used to derive the security key of the target SN associated with the cell for which the conditional reconfiguration is performed. When the conditional reconfiguration is performed, the control unit 120 updates the counter value. This allows communication protection to be achieved using different security keys even when the PS cell is changed to a specific cell, thereby appropriately protecting communications between the UE 100 and the SN 200S. Furthermore, when conditional reconfiguration is performed, that is, before the PS cell is changed, the control unit 120 updates the counter value. Therefore, since the UE 100 updates the counter value before the security key is used for communication protection, communications between the UE 100 and the SN 200S can be appropriately protected.

[0161] In addition, the control unit 120 may update the counter value before starting the RA process for the cell by performing conditional reconfiguration. As a result, the UE 100 can perform the RA process and subsequent communications while appropriately protecting the communication between the UE 100 and the SN 200S without updating the counter value during the RA process.

[0162] Furthermore, after the RA procedure for a cell is initiated by executing conditional reconfiguration, and before an RRC message is sent to the cell during the RA procedure, the control unit 120 updates the counter value. This allows the counter value to be updated before communication protection begins using a key derived from a security key, enabling the RA procedure and subsequent communications to be performed while appropriately protecting communications between the UE 100 and the SN 200S.

[0163] Furthermore, the control unit 120 may update the counter value based on the number of PS cell changes NKSN from the source PS cell to the target PS cell using the configuration information. Since the number of PS cell changes NKSN changes each time the PS cell is changed, it is possible to avoid using the same counter value to derive security keys.

[0164] Furthermore, the control unit 120 may count the number of times the PS cell is changed using the configuration information as the number of changes. This allows the UE 100 to avoid storing the number of changes specifically for each PS cell, for example, and thus reduce the processing load.

[0165] Furthermore, the control unit 120 can specifically count the number of changes for each candidate target SN 200S. This allows the UE 100 to avoid storing the number of changes specifically for each PS cell, for example, thereby reducing the processing load. Furthermore, when changing PS cells within an SN 200S, the counter value is not changed, thereby suppressing unnecessary increases in the counter value (and the associated overhead).

[0166] Furthermore, the control unit 120 may count the number of changes specifically for each candidate target PS cell. This prevents the same security key from being derived even if other items used to calculate the counter value are the same, since the number of changes NKSN changes each time the PS cell is changed.

[0167] Furthermore, the receiving unit 112 can receive, from the MN 200M, an initial counter value and an offset value for updating the counter value as counter value information. Thus, by appropriately changing the initial counter value and the offset value, the counter value can be changed without significantly modifying the existing system that includes an SN counter (sk-Counter) for each SN 200S and complies with 3GPP technical specifications. As a result, even when the PS cell is changed to a specific cell, communication protection is achieved using a different security key, thereby appropriately protecting communications between the UE 100 and the SN 200S.

[0168] In addition, the initial counter value may be a value specifically configured for each candidate target PS cell. Thus, the MN 200M can flexibly control the counter value.

[0169] In addition, the initial counter value may be a value commonly configured for all candidate target PS cells. Therefore, regardless of the number of candidate target PS cells, UE 100 does not need to maintain multiple initial counter values ​​or select a corresponding initial counter value from among multiple initial counter values, which can reduce processing load.

[0170] In addition, the offset value can be a value based on the number of candidate target SNs 200S configured by the configuration information. Therefore, even if the number of candidate target SNs 200S increases, the counter value calculated based on the offset value will not be repeated, thereby avoiding the use of the same counter value to derive the security key.

[0171] In addition, the counter value information may include a list associating each of the plurality of counter values ​​with a change count. The control unit 120 may set the counter value corresponding to the change count NKSN to the updated counter value. This eliminates the need for the UE 100 to use a formula to calculate the counter value, thereby reducing the processing load.

[0172] Furthermore, the counter value information may include a list associating each of the multiple counter values ​​with a number of changes for each of the multiple candidate target PS cells. The control unit 120 may specifically count the number of changes for each candidate target PS cell. The control unit 120 may set the counter value corresponding to the number of changes among the multiple counter values ​​for the corresponding candidate target PS cell as the updated counter value. This eliminates the need for UE 100 to use a formula to calculate the counter value, reducing processing load.

[0173] Furthermore, if the target SN 200S is associated with both the source PS cell and the target PS cell, the control unit 120 can skip updating the counter value. Since security keys are assigned to each target SN 200S, even when the PS cell is changed within the same target SN 200S, communication between the UE 100 and the SN 200S can be properly protected even if security key derivation is omitted. This allows for proper communication protection while reducing the processing load on the UE 100.

[0174] Furthermore, in this example operation, the receiving unit 112 of the UE 100 receives configuration information from the MN 200M, which is used to configure multiple conditional reconfigurations for the UE 100. These conditional reconfigurations are used to configure multiple candidate target primary and secondary (PS) cells. The control unit 120 updates a counter value used to derive the security key of the target SN associated with the cell whose execution conditions are satisfied from among the multiple candidate target PS cells. The transmitting unit 111 transmits confirmation information to the network 10, which confirms the security key derived based on the updated counter value. This allows the network 10 to understand the security key derived based on the counter value updated by the UE 100 and appropriately protect communications between the UE 100 and the SN 200S.

[0175] Furthermore, the transmitter 111 of the UE 100 can transmit identification information including the security key to the network 10. This allows the network 10 to understand the security key derived by the UE 100. This allows the processing of calculating the security key to be omitted, thereby reducing the processing load.

[0176] Furthermore, the transmitting unit 111 may transmit identification information including the updated counter value to the network 10. The network 10 can grasp the security key derived by the UE 100 based on the updated counter value.

[0177] Furthermore, the transmitter 111 may transmit determination information including calculation information for calculating the updated counter value to the network 10. This allows the network 10 to grasp the security key derived by the UE 100 based on the calculation information.

[0178] In addition, the transmitting unit 111 may transmit the determination information to the network 10 via a message, and the message is transmitted to the target SN 200S via the MN 200M. In this way, the UE 100 can transmit directly to the target SN 200S. The target SN 200S can determine the security key using the determination information.

[0179] Furthermore, the transmission unit 111 can transmit the identification information to the network 10 using a message that sets the MN 200M as the terminating end. This allows the UE 100 to transmit a message to the MN 200M, and the MN 200M to grasp the identification information.

[0180] Furthermore, in this example operation, in base station 200 operating as MN 200M, transmitting unit 211 transmits configuration information for configuring multiple conditional reconfigurations for the communication device to UE 100. The multiple conditional reconfigurations are used to configure multiple candidate target primary and secondary (PS) cells. Receiving unit 212 receives, from UE 100, an updated counter value, determination information for deriving, from the multiple candidate target PS cells, a security key for a target secondary node associated with a cell for which an execution condition is satisfied. The determination information is used to determine the security key derived based on the updated counter value. Furthermore, in the base station 200 operating as the SN 200S, the receiving unit 212 receives confirmation information from the UE 100, whose counter value has been updated, via the MN 200M that transmits configuration information to the UE 100. The configuration information is used to configure multiple conditional reconfigurations for the communication device, the multiple conditional reconfigurations being used to configure multiple candidate target primary and secondary (PS) cells, the counter value being used to derive security keys for target SNs associated with cells whose execution conditions are satisfied from among the multiple candidate target PS cells, and the confirmation information being used to determine the security keys derived based on the updated counter value. The SN 200S that receives the confirmation information from the MN 200M or the MN 200M is able to grasp the security keys derived based on the counter value updated by the UE 100, and thus can appropriately protect communications between the UE 100 and the SN 200S.

[0181] In addition, the receiving unit 212 may receive a message that is sent to the target secondary node via the primary node and includes the identification information. The NW communication unit 220 may send the message to the target SN 200S. Thus, the target SN 200S can determine the security key through the identification information.

[0182] Furthermore, the confirmation information may include a security key. The receiving unit 212 may receive the confirmation information via a message with the MN 200M as the terminating end. The NW communication unit 220 may transmit the security key to the target secondary node. This allows the control unit 230 to grasp the security key derived by the UE 100. This allows the calculation of the security key to be omitted, reducing the processing load.

[0183] (Action Example 2)

[0184] Reference Figure 12 Next, a second operation example of the mobile communication system 1 according to the embodiment will be described. In this operation example, the SN 200S2 requests a security key or information for calculating a security key from the MN 200M. Descriptions of parts identical to those in the first operation example will be omitted.

[0185] Steps S140 to S142 are the same as steps S110 to S112. In this action example, the control unit 120 of the UE 100 may include the determination information in the message (eg, SN RRC Reconfiguration Complete message) sent to the target SN via the MN 200M.

[0186] In the case that the SN reconfiguration complete message (the confirmation information included therein) does not include the security key, the control unit 230 of the SN 200S2 may perform the following actions.

[0187] In step S143, the NW communication unit 220 of the SN 200S2 transmits a request message for requesting a security key or information for calculating a security key to the MN 200M. The NW communication unit 220 of the MN 200M receives the request message from the SN 200S2.

[0188] The request message may include the determination information. Thus, the NW communication unit 220 of the MN 200M receives the determination information from the SN 200S2. In addition, the request message may be an existing message or a new message.

[0189] In step S144, the NW communication section 220 of the MN 200M transmits a response message to the request message to the SN 200S 2. The NW communication section 220 of the SN 200S 2 receives the response message from the MN 200M.

[0190] Similar to step S113, the control unit 230 of the MN 200M may derive the security key based on the determination information. The control unit 230 may include the derived security key in the response message. Alternatively, the control unit 230 may determine, based on the determination information, calculation information for calculating (deriving) the security key from the determination information. The control unit 230 may include the calculation information in the response message.

[0191] In step S145, similarly to step S113, the control unit 230 of the SN 200S2 determines the security key. The control unit 230 determines the security key based on the security key or calculation information included in the response message.

[0192] The control unit 230 may determine the security key included in the response message as the security key for protecting communication with the UE 100. Alternatively, the control unit 230 may derive the security key based on the calculation information and determination information included in the response message. The control unit 230 may determine the derived security key as the security key for protecting communication with the UE 100.

[0193] Step S146 is the same as step S114.

[0194] As described above, the NW communication unit 220 of the MN 200M can receive the identification information from the SN 200S 2. The NW communication unit 220 can send the security key or information for calculating the security key to the SN 200S 2.

[0195] (Action Example 3)

[0196] Reference Figure 13 Next, a third operation example of the mobile communication system 1 according to the embodiment will be described. In this operation example, the MN 200M determines a security key. Descriptions of parts identical to those of the above operation examples will be omitted.

[0197] Steps S160 to S162 are the same as steps S110 to S112. In this example, the control unit 120 of the UE 100 may include the determination information in a message (e.g., a field other than the SN RRC Reconfiguration Complete message in the RRC Reconfiguration Complete message) with the MN 200M as the terminating end. The determination information may include the updated counter value or calculation information used to calculate the updated counter value.

[0198] In step S163, similarly to step S113, the control unit 230 of the MN 200M determines the security key based on the determination information. The control unit 230 may calculate the updated counter value based on the calculation information. The control unit 230 derives the security key based on the updated counter value.

[0199] In step S164, the NW communication unit 220 of the MN 200M transmits the security key to the SN 200S2. The NW communication unit 220 of the MN 200M can transmit the security key to the SN 200S2 via an existing message or a new message. The NW communication unit 220 of the SN 200S2 receives the security key from the MN 200M. The security key is the security key included in the confirmation information or the security key derived by the control unit 230.

[0200] Step S165 is the same as step S114.

[0201] As described above, the determination information may include the updated counter value or calculation information used to calculate the updated counter value. The control unit 230 may derive a security key based on the updated counter value. The NW communication unit 220 may transmit the security key derived by the control unit 230 to the SN 200S2. This allows the MN 200M to derive the security key, similar to conventional operations, while preventing the SN 200S2 from deriving the security key. This reduces the impact on the SN 200S2.

[0202] [Other embodiments]

[0203] In the above embodiment, the processing of steps S110 and S111 (and similar steps) can be omitted. For example, when selective SCG activation is being performed, the control unit 230 of the MN 200M can suspend (skip) the transmission of the SN Release Request message. When the transmission of the SN Release Request message to the UE 100 is configured in association with the configuration of selective SCG activation (e.g., multiple conditional reconfigurations), the control unit 230 of the MN 200M can suspend (skip) the transmission of the message. In addition, the control unit 230 of the MN 200M can suspend (skip) the transmission of the SN Release Request message based on, for example, confirmation information received from the UE 100.

[0204] In the third example of action in the above embodiment, the process of step S163 may be performed before the process of step S162. In this case, the control unit 230 of the MN 200M may include the determined security key in the SN Reconfiguration Complete message. In step S162, the NW communication unit 220 of the MN 200M may send the security key to the SN 200S2 via the SN Reconfiguration Complete message. In this case, the process of step S164 may be omitted.

[0205] In the above embodiment, the case where the RA procedure is successful is used as an example. If the RA procedure fails, the transmitting unit 111 of the UE 100 may transmit failure information to the MN 200M indicating the failure of the RA procedure. Upon receipt of the failure information, the transmitting unit 211 of the MN 200M may transmit configuration information for configuring a counter value to the UE 100. For example, similar to step S103, the MN 200M may transmit configuration information to the UE 100, which is used to configure multiple conditional reconfigurations for the UE 100. The control unit 120 of the UE 100 may discard the configuration information stored for selective SCG activation and perform selective SCG activation based on the configuration information.

[0206] The action sequence (and action flow) in the above-mentioned embodiment does not have to be executed in chronological order along the order recorded in the flowchart or sequence diagram. For example, the steps in the action can be executed in an order different from the order recorded as a flowchart or sequence diagram, or can be executed in parallel. In addition, a part of the steps in the action can be deleted, and further steps can be added in the process. In addition, the action sequence (and action flow) in the above-mentioned embodiment can be implemented separately, or two or more action sequences (and action flows) can be combined to implement. For example, a part of the steps of an action flow can be added to other action flows, or a part of the steps of an action flow can be replaced with a part of the steps of other action flows.

[0207] In the above embodiment, as the mobile communication system 1, an NR-based mobile communication system is described as an example. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a TS system that complies with LTE (Long Term Evolution) or any other generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be, for example, an eNB that provides an E-UTRA user plane and control plane protocol termination for the UE 100 in LTE. The mobile communication system 1 may also be a TS system that complies with a standard other than the 3GPP standard. The base station 200 may be an IAB (Integrated Access and Backhaul) host or an IAB node.

[0208] A program that causes a computer to execute each process performed by UE 100 or base station 200 may also be provided. The program may be recorded in a computer-readable medium. Using a computer-readable medium, the program can be installed in the computer. Here, the computer-readable medium on which the program is recorded may also be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, but may be a recording medium such as a CD-ROM (Compact Disk Read Only Memory) or a DVD-ROM (Digital Versatile Disc Read Only Memory). In addition, the circuits that execute each process performed by UE 100 or base station 200 may be integrated, and at least a portion of UE 100 or base station 200 may be configured as a semiconductor integrated circuit (chip set, SoC (System On Chip)).

[0209] In the above embodiments, “transmit” may refer to performing processing of at least one layer within the protocol stack for transmission, or may refer to physically sending a signal wirelessly or by wire. Alternatively, “transmit” may refer to a combination of performing processing of at least one layer and physically sending a signal wirelessly or by wire. Similarly, “receive” may refer to performing processing of at least one layer within the protocol stack for reception, or may refer to physically receiving a signal wirelessly or by wire. Alternatively, “receive” may refer to a combination of performing processing of at least one layer and physically receiving a signal wirelessly or by wire. Similarly, “obtain / acquire” may refer to obtaining information from stored information, or may refer to obtaining information from information received from other nodes, or may refer to obtaining the information by generating information. Similarly, unless otherwise expressly stated, the phrases “based on” and “depending on / in response to” do not mean “based only on” or “based only in response to”. The phrase “based on” refers to both “based only on” and “based at least in part on”. Similarly, the record of "in response to" refers to both "only in response to" and "at least in part in response to". Similarly, "include" and "comprise" do not mean to include only the listed items, but may include only the listed items, or may include other items in addition to the listed items. Similarly, in the present disclosure, "or" does not refer to logical exclusive OR, but to logical OR. Furthermore, any reference to elements using the "first", "second" and other titles used in the present disclosure does not limit the quantity or order of these elements as a whole. These titles can be used in the present disclosure as a convenient method to distinguish between two or more elements. Therefore, the reference to the first element and the second element does not mean that only two elements can be adopted therein, or that the first element must precede the second element in some form. In the present disclosure, for example, when articles such as a, an and the in English are added by translation, these articles can include multiple unless the context clearly indicates that multiple are not included.

[0210] It will be understood that although the present disclosure is described in terms of embodiments, the present disclosure is not limited to such embodiments or configurations. The present disclosure also includes various variations and equivalents. In addition, various combinations and methods, and further combinations and methods including only one element, more elements, or fewer elements, also fall within the scope and spirit of the present disclosure.

[0211] (Note)

[0212] Features related to the above-mentioned embodiment are supplementarily noted.

[0213] (Note 1)

[0214] A communication device is a communication device for communicating with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node, and the secondary cell group is associated with a secondary node, and the communication device includes:

[0215] a receiving unit, receiving configuration information from the master node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate target primary and secondary (PS) cells; and

[0216] The control unit performs conditional reconfiguration on a cell among the plurality of candidate target PS cells for which the execution condition is satisfied,

[0217] The configuration information includes information about a counter value, and the information about the counter value is used to derive a security key of a target secondary node associated with the cell.

[0218] When the conditional reconfiguration is performed, the control unit updates the counter value.

[0219] (Note 2)

[0220] According to the communication device of Supplementary Note 1, the control unit updates the counter value before starting a random access procedure to the cell by executing the conditional reconfiguration.

[0221] (Note 3)

[0222] According to the communication device of Supplementary Note 1, the control unit updates the counter value after starting a random access procedure to the cell by executing the conditional reconfiguration and before sending a radio access control (RRC) message to the cell during the random access procedure.

[0223] (Note 4)

[0224] According to the communication device according to any one of Supplementary Notes 1 to 3, the control unit updates the counter value based on the number of changes of the PS cell from the source PS cell to the target PS cell using the configuration information.

[0225] (Note 5)

[0226] According to the communication device described in Supplementary Note 4, the control unit counts the number of times the PS cell is changed using the configuration information as the number of changes.

[0227] (Note 6)

[0228] According to the communication device described in Supplementary Note 4, the control unit specifically counts the number of changes for each candidate target slave node.

[0229] (Note 7)

[0230] According to the communication device described in Supplementary Note 4, the control unit specifically counts the number of changes for each of the candidate target PS cells.

[0231] (Note 8)

[0232] According to the communication device according to any one of Supplementary Notes 1 to 7, the receiving unit receives, as the information of the counter value, an initial counter value and an offset value for updating the counter value from the master node.

[0233] (Note 9)

[0234] According to the communication device described in Supplementary Note 8, the aforementioned initial counter value is a value specifically configured for each aforementioned candidate target PS cell.

[0235] (Note 10)

[0236] According to the communication device described in Supplementary Note 8, the aforementioned initial counter value is a value configured in common for all the aforementioned candidate target PS cells.

[0237] (Note 11)

[0238] According to the communication device described in any one of Supplementary Notes 8 to 10, the offset value is a value based on the number of candidate target secondary nodes configured by the configuration information.

[0239] (Note 12)

[0240] The communication device according to any one of supplementary notes 4 to 11, wherein the information on the counter value includes a list associating each of a plurality of counter values ​​with the number of changes.

[0241] The control unit sets a counter value corresponding to the number of changes as an updated counter value.

[0242] (Note 13)

[0243] The communication device according to any one of supplementary notes 4 to 11, wherein the information of the counter value comprises a list associating each of the plurality of counter values ​​with the number of changes for each of the plurality of candidate target PS cells;

[0244] The control unit specifically counts the number of changes for each candidate target PS cell.

[0245] The control unit sets a counter value corresponding to the number of changes among the plurality of counter values ​​for the corresponding candidate target PS cell as an updated counter value.

[0246] (Note 14)

[0247] According to the communication device of any one of Supplementary Notes 1 to 13, when the target secondary node is associated with the source PS cell and the target PS cell, the control unit skips updating the counter value.

[0248] (Note 15)

[0249] A communication method is performed by a communication device, wherein the communication device communicates with a primary cell group and a secondary cell group, the primary cell group is associated with a primary node, and the secondary cell group is associated with a secondary node, the communication method comprising:

[0250] receiving configuration information from the master node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate target primary and secondary (PS) cells; and

[0251] For the cells among the aforementioned multiple candidate target PS cells for which the execution conditions are met, the step of performing conditional reconfiguration is performed.

[0252] The configuration information includes information about a counter value, and the information about the counter value is used to derive a security key of a target secondary node associated with the cell.

[0253] The aforementioned communication method includes the step of updating the aforementioned counter value when the aforementioned conditional reconfiguration is performed.

[0254] (Note 16)

[0255] A communication device (100) is provided for communicating with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node (MN 200M), and the secondary cell group is associated with a secondary node (SN 200S). The communication device comprises:

[0256] A receiving unit (121) receives configuration information from the master node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate cells; and

[0257] The control unit (120) performs conditional reconfiguration on a cell among the plurality of candidate cells for which the execution condition is satisfied,

[0258] The configuration information includes information about a counter value, and the information about the counter value is used to derive a security key of a secondary node associated with the cell.

[0259] When the conditional reconfiguration is performed, the control unit updates the counter value.

[0260] (Note 17)

[0261] According to the communication device of Supplementary Note 16, the control unit updates the counter value before starting a random access procedure to the cell by executing the conditional reconfiguration.

[0262] (Note 18)

[0263] According to the communication device described in Supplement 16 or 17, the control unit updates the counter value after starting the random access procedure to the cell by executing the conditional reconfiguration and before sending a radio access control (RRC) message to the cell during the random access procedure.

[0264] (Note 19)

[0265] According to any one of Supplementary Notes 16 to 18, the information on the counter value includes a list of a plurality of counter values.

[0266] (Note 20)

[0267] According to the communication device according to any one of Supplementary Notes 16 to 19, when the secondary node is associated with a source PS cell and a target PS cell, the control unit skips updating of the counter value.

[0268] (Note 21)

[0269] A communication method is performed by a communication device (100), wherein the communication device (100) communicates with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node (MN 200M) and the secondary cell group is associated with a secondary node (SN 200S), and the communication method comprises:

[0270] receiving configuration information from the master node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate cells; and

[0271] For cells among the aforementioned multiple candidate cells for which the execution condition is satisfied, a step of performing conditional reconfiguration is performed.

[0272] The configuration information includes information about a counter value, and the information about the counter value is used to derive a security key of a target secondary node associated with the cell.

[0273] The aforementioned communication method includes the step of updating the aforementioned counter value when the aforementioned conditional reconfiguration is performed.

[0274] (Note 22)

[0275] According to the communication method described in Supplementary Note 21, in the updating step, the counter value is updated before starting a random access procedure to the cell by performing the conditional reconfiguration.

[0276] (Note 23)

[0277] According to the communication method described in Note 21 or 22, in the aforementioned updating step, the aforementioned counter value is updated after the random access process to the aforementioned cell is started by performing the aforementioned conditional reconfiguration and before a radio access control (RRC) message is sent to the aforementioned cell during the aforementioned random access process.

Claims

1. A communication device, comprising: a communication device (100) for communicating with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a master node (MN 200M), and the secondary cell group is associated with a secondary node (SN 200S), the communication device comprising: A receiving unit (121) receives configuration information from the master node, the configuration information being used to configure a plurality of conditional reconfigurations for the communication device, the plurality of conditional reconfigurations being used to configure a plurality of candidate cells; and A control unit (120) performs conditional reconfiguration on a cell among the plurality of candidate cells for which an execution condition is satisfied, The configuration information includes information about a counter value, where the information about the counter value is used to derive a security key of a secondary node associated with the cell. When the conditional reconfiguration is performed, the control section updates the counter value.

2. The communication device according to claim 1, The control unit updates the counter value before starting a random access procedure for the cell by performing the conditional reconfiguration.

3. The communication device according to claim 1, The control unit updates the counter value after starting a random access procedure for the cell by executing the conditional reconfiguration and before transmitting a radio access control (RRC) message to the cell in the random access procedure.

4. The communication device according to any one of claims 1 to 3, The counter value information includes a list of multiple counter values.

5. The communication device according to any one of claims 1 to 3, The control unit skips updating of the counter value when the secondary node is associated with a source PS cell and a target PS cell.

6. A communication method, performed by a communication device (100), wherein the communication device (100) communicates with a primary cell group and a secondary cell group, wherein the primary cell group is associated with a primary node (MN 200M) and the secondary cell group is associated with a secondary node (SN 200S), the communication method comprising: a step of receiving configuration information from the master node, wherein the configuration information is used to configure a plurality of conditional reconfigurations for the communication device, wherein the plurality of conditional reconfigurations are used to configure a plurality of candidate cells; as well as For cells among the multiple candidate cells for which the execution condition is satisfied, a step of performing conditional reconfiguration is performed, The configuration information includes information about a counter value, where the information about the counter value is used to derive a security key of a target secondary node associated with the cell. The communication method includes the step of updating the counter value when the conditional reconfiguration is performed.

7. The communication method according to claim 6, In the updating step, the counter value is updated before starting a random access procedure to the cell by performing the conditional reconfiguration.

8. The communication method according to claim 6, In the updating step, the counter value is updated after a random access procedure to the cell is started by performing the conditional reconfiguration and before a radio access control (RRC) message is sent to the cell in the random access procedure.

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