Terminal device, base station device, and control method for efficiently updating security keys

Abstract

A terminal device following a cellular communication standard of 3GPP receives, from a first base station device in connection, first setup information of LTM of each of a plurality of base station devices including a candidate of a handover destination of a second base station device and a third base station device, and second setup information for updating a security key respectively associated with the first setup information, associates the first setup information with the second setup information for each of the plurality of base station devices, performs a handover to the second base station device, updates the security key using the second setup information associated with the first setup information of the second base station device in response to the handover to the second base station device, and, after the performance of the handover, updates the second setup information associated with the first setup information of the third base station device while maintaining the held first setup information of the third base station device.

Description

Technical Field

[0001] This invention relates to a technology for updating security keys in cellular communication systems. Background Technology

[0002] In cellular communication standards such as 5G, which follow the 3GPP (3rd Generation Partnership Project, registered trademark) framework, Layer 1 / Layer 2 Triggered Mobility (LTM) mechanisms are introduced to shorten handover time. Previously, LTM was used for handover within a shared gNB-Central Unit (CU), not for handover across gNB-CUs. Therefore, in previous LTMs, it was not necessary to update parameters related to security keys used for encryption and integrity protection. Summary of the Invention

[0003] The problem that the invention aims to solve Going forward, we anticipate the application of LTM across gNB-CUs. In this case, it will be necessary to update the security key-related parameters as described above.

[0004] means for solving problems This invention provides an efficient technique for updating security key-related parameters during LTM-based handover.

[0005] One aspect of the terminal device according to the present invention is a terminal device conforming to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein the terminal device comprises: a receiving unit that receives, from a first base station device in a connection, first setting information for Layer 1 / Layer 2 Triggered Mobility (LTM) regarding each of a plurality of candidate base station devices including a second base station device and a third base station device as handover destinations, and second setting information associated with the first setting information for updating a security key; a holding unit that holds the first setting information and the second setting information in association for each of the plurality of base station devices; an execution unit that executes a handover to the second base station device; and an updating unit that, in response to the handover to the second base station device, updates the security key using the second setting information associated with the first setting information of the second base station device, and, after the execution of the handover, updates the second setting information associated with the first setting information while maintaining the held first setting information regarding the third base station device.

[0006] According to one aspect of the present invention, a base station apparatus is a base station apparatus conforming to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein the base station apparatus comprises: a providing unit, which, as a candidate handover destination, provides a first layer 1 / layer 2 triggered mobility (LTM) setting information and a second setting information associated with the first setting information for updating a security key to a first other base station apparatus to which the terminal apparatus is connected; a connecting unit, which connects to the terminal apparatus via handover of the terminal apparatus; a generating unit, which generates a security key used in communication with the terminal apparatus using the second setting information; an obtaining unit, which, after the handover is performed, obtains the first setting information and the second setting information from the base station apparatus regarding the second other base station apparatus as a candidate handover destination of the terminal apparatus; and a sending unit, which, while the terminal apparatus is holding the first setting information regarding the second other base station apparatus, sends a message to the terminal apparatus containing the second setting information regarding the second other base station apparatus but not the first setting information.

[0007] Invention Effects According to the present invention, parameters related to the security key during LTM-based handover can be updated efficiently.

[0008] Other features and advantages of the invention will become apparent from the following description with reference to the accompanying drawings. Furthermore, in the drawings, the same reference numerals are used to denote the same or identical configurations. Attached Figure Description

[0009] The accompanying drawings, which are included in and form a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0010] Figure 1 This is a diagram illustrating an example of the structure of a wireless communication system.

[0011] Figure 2 This is a diagram illustrating an example of the processing associated with updating previous security keys.

[0012] Figure 3 This is a diagram illustrating an example of the processing associated with updating previous security keys.

[0013] Figure 4 This is a diagram illustrating an example of the processing associated with updating the security key in this embodiment.

[0014] Figure 5 This is a diagram illustrating an example of the processing associated with updating the security key in this embodiment.

[0015] Figure 6This is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device.

[0016] Figure 7 This is a diagram illustrating an example of the functional configuration of a terminal device.

[0017] Figure 8 This is a diagram illustrating an example of the functional configuration of a base station device. Detailed Implementation

[0018] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Furthermore, the following embodiments are not intended to limit the invention to which the technical solution pertains. Additionally, not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more features from the plurality of features described in the embodiments may be arbitrarily combined. Furthermore, identical or identical components are labeled with the same reference numerals, and repeated descriptions are omitted.

[0019] Figure 1 This describes an example of the configuration of a wireless communication system according to this embodiment. This wireless communication system is a cellular communication system conforming to the 3GPP (3rd Generation Partnership Project, registered trademark) cellular communication standard, configured to include base station devices (e.g., base station device 101, base station device 102) and terminal devices (e.g., terminal device 111). Furthermore, it is assumed that terminal device 111 is currently connected to base station device 101, and then moves towards base station device 102 to perform a handover to base station device 102. Furthermore, in Figure 1 For ease of explanation, only two base station devices and one terminal device are shown in the diagram, but of course, there can be multiple such devices.

[0020] In such a wireless communication system, when terminal device 111 is handed over, the processing flow related to the security key may differ depending on whether base station devices 101 and 102 are associated with a shared Access and Mobility Management Function (AMF) (or whether an Xn interface has been established). Regarding the difference in this step, using... Figure 2 as well as Figure 3 Examples will be used to illustrate this. Furthermore, in Figure 2 as well as Figure 3 In this document, parts particularly relevant to this embodiment will be described in detail, while other matters will only be described in general terms.

[0021] Figure 2This example illustrates a process flow where the base station device (base station device 101) representing the source of the handover (and the base station device (base station device 102) representing the destination of the handover) are associated with a shared AMF, and an Xn interface is established between these base station devices. In this process, for example, when the conditions for initiating handover are met in terminal device 111, a measurement report is notified from terminal device 111 to base station device 101 (S201). If, based on this measurement report, it is determined that terminal device 111 should hand over to base station device 102, then base station device 101 uses the pre-handover parameters K used in base station device 101, which is the current connection destination of terminal device 111. NG-RAN The handover K, which should be used in the communication between base station device 102 and terminal device 111, is derived from parameters such as next hop chain count (NCC). NG-RAN (S202). Then, base station device 101 sends a handover request message to base station device 102 (S203). At this time, the derived K is included in the handover request message. NG-RAN The terminal device 111 uses the NCC value when deriving this value. Furthermore, similar to a normal handover, the terminal device 111 performs processing such as notifying the terminal device 111 of connection setup information for the handover destination base station device 102. Then, the terminal device 111 executes a random access procedure with the base station device 102 to establish a connection. At this time, the base station device 102 sets the key set change indicator to "No" and sends an RRC reconfiguration message containing the NCC value to the terminal device 111 (S204). RRC is an abbreviation for Radio Resource Control. Thus, the terminal device 111 can use the NCC value and the generated K key (K) of the security key currently maintained within the device for communication with the base station device 101. NG-RAN The parameters, such as K, are used to derive the security key generated for communication with base station device 102. NG-RAN In response, terminal device 111 sends an RRC reconfiguration complete message to base station device 102 (S205). Then, base station device 102 sends an NGAP path handover request message to the AMF associated with it (S206). In response to this message, the AMF sends an NGAP path handover request permission message to base station device 102 (S207). This message includes the next hop (NH) and NCC as options for enabling base station device 102 to export the post-handover K when terminal device 111 performs a handover from base station device 102 to another base station device. NG-RAN The base station device 102 stores the received NH and NCC (S208). Thus, when base station devices 101 and 102 are associated with a shared AMF, terminal device 111 can use the NCC value obtained from base station device 102 and the currently maintained K... NG-RAN K is used to generate the security key used in communication with base station device 102. NG-RAN Update.

[0022] Figure 3 This example illustrates a processing flow where the source base station device (base station device 101) and the destination base station device (base station device 102) are associated with different AMFs. In this process, with... Figure 2 Similarly, a measurement report is sent from terminal device 111 to base station device 101 (S301), based on which handover processing begins. Base station device 101 sends an NGAP handover request message to the AMF associated with its device, forwarding the handover request to other AMFs associated with the base station device 102 at the handover destination (S302). Then, the AMF at the handover destination sends an NGAP handover request message to the base station device 102 at the handover destination (S303). Furthermore, this message includes the NAS container, NH, and NCC as data for newly generated K. NG-RAN The information. Furthermore, NAS is an abbreviation for Non-Access Stratum. Base station device 102 stores the received NH and NCC (S304), and generates K based on the received information. NG-RAN (S305). That is, in Figure 3 In the processing, a new K is generated. NG-RAN K used before the handover NG-RAN It is not used for generating a new key. Then, base station device 102 sends an NGAP handover request permission to the AMF (S306), and correspondingly, the AMF from the handover source sends an NGAP handover command to base station device 101 (S307). At this time, K can be derived. NG-RAN The information is notified to the terminal device 111 via an RRC reconfiguration message through the base station device 101 (S308). After that, the terminal device 111 completes the connection by performing a random access procedure with the base station device 102 (S309).

[0023] Furthermore, the same K is generated in terminal device 111 and its connected destination base station device. NG-RAN Using KNG-RAN Generate a confidential key K for user data. UPsec .

[0024] In this embodiment, the terminal device 111 is configured as a base station device that changes its connection destination using Layer 1 / Layer 2 Triggered Mobility (LTM) to shorten the handover period. LTM can also be interpreted as an abbreviation for Lower Layer Triggered Mobility. Conventionally, LTM is only used for handovers between base station devices connected to a shared gNB-Center Unit (CU). Therefore, in conventional LTM-based handovers, the configuration information (parameters) associated with the security key is not updated. In contrast, in handovers across gNB-CUs, the configuration information associated with the security key needs to be updated. In this embodiment, a step is provided to efficiently update the configuration information (parameters) used to generate the security key in LTM-based handovers across gNB-CUs.

[0025] Figure 4 This diagram illustrates an example of the handover steps across the gNB-CU involved in this embodiment. Figure 4 The example shown illustrates a base station device with two candidate handover destinations. It is assumed that these candidate base station devices for handover destinations are associated with an AMF different from the base station device connecting to the destination. Therefore, in Figure 4 The example omits AMF, but it is assumed that each base station device performs... Figure 2 , Figure 3 That involves processing communication with the AMF.

[0026] In this process, the base station device at the transfer source (connected to the terminal device) sends a transfer request message to multiple candidate base station devices at the transfer destination based on, for example, the measurement results of the terminal device (S401). Then, the candidate base station devices at the transfer destination respond to this message by returning a transfer request ACK message (S402, S403). Furthermore, the transfer request ACK message includes LTM configuration information, which includes a master key update as information for updating the security key. Alternatively, as an example, the LTM configuration may not include the master key update, and these updates may be notified and managed separately. It is assumed that the LTM configuration and the master key update are associated with each other. Here, the master key update includes (set to "yes") a key set change indicator, NAS container, and NCC, for example, in the case of changing the associated AMF. Alternatively, in the case of not changing the associated AMF, the master key update includes (set to "no") a key set change indicator and NCC. The base station device at the transfer source forwards the LTM configuration containing the master key update to the terminal device (S404). Then, upon receiving this information, the terminal device sends a response message to the (connected) base station device at the transfer source (S405). Furthermore, the forwarding of the LTM configuration in S404 can be performed, for example, using an RRC reconfiguration message, and the response to this message can be performed using an RRC reconfiguration completion message.

[0027] Subsequently, based on the Layer 1 (physical layer) measurement results (L1 measurement) measured in the terminal device, the base station device to which the terminal device is connected determines to perform a handover, and sends a cell handover command indicating the handover to the terminal device from the base station device (S406, S407). The terminal device performs random access procedures, etc., with the base station device indicated by the handover destination in the command (S408, S409), and establishes a connection with the base station device using the LTM configuration regarding that base station device. Additionally, at this time, the terminal device uses the master key update information included in the LTM configuration to update the K... NG-RAN Update. For example, if the terminal device receives an update that includes (set to "Yes") a key set change indicator, NAS container, or NCC master key update, it will not update the key set change indicator based on the currently used key. NG-RAN And based on the received information, a new K is generated. NG-RAN Additionally, if the terminal device receives a key set change indicator (set to "No") and an NCC master key update, it will use the currently used K... NG-RAN K used after being transferred from NCC NG-RAN .

[0028] Here, the method for updating the setting information associated with the security key after the handover is explained. First, in the case where, after connecting to the base station device at the handover destination, and associating with the candidate base station device from that base station device at the handover destination with a shared AMF, that is, the base station device at the handover destination (the base station device that becomes a base station device in communication after the handover) generates K. NG-RAN The following example illustrates the handling of a specific situation. If an RRC reconfiguration completion message is received from the terminal device, the base station device at the transfer destination sends a transfer success message (S410) to the base station device at the transfer source indicating successful transfer. At this time, the transfer success message includes the K data maintained by the base station device at the transfer destination. NG-RAN And NCC (i.e., the K generated based on the master key update contained in the LTM configuration of this device). NG-RAN And NCC). The base station equipment of the transfer source is transferred to other candidate base station equipment (in Figure 4 In the example, the backup base station device #2) notifies the base station device that the terminal device's connection destination has been changed (in... Figure 4 In the example, the connection destination changes to candidate base station device #1. At this time, the base station device of the handover source requests to send the K included in the handover success message to other candidate base station devices. NG-RAN The system also receives information from the NCC and forwards an LTM configuration containing the updated master key to the base station device at the transfer destination (S411). In response to the request, the candidate base station device updates the master key and sends an LTM configuration containing the master key update information to the base station device at the transfer destination (S412).

[0029] Next, for the case where, after connecting to the base station device at the handover destination, it is associated with different AMFs along with the candidate base station device from that base station device at the handover destination, i.e., the candidate base station device after handover (the base station device that continues to be a candidate base station device after handover), K is generated. NG-RAN The following example illustrates the handling of a specific situation. If an RRC reconfiguration completion message is received from the terminal device, the base station device at the transfer destination sends a transfer success message (S410) to the base station device at the transfer source indicating successful transfer. In this case, the transfer success message may not include the K data maintained by the base station device at the transfer destination. NG-RAN And the NCC. The base station device of the transfer source, through the first AMF associated with the base station device of the transfer source, and the second AMF associated with the base station device that was not selected as the transfer destination but also becomes a candidate base station device after the transfer, notifies the candidate base station device of the change in the connection destination of the terminal device (in Figure 4 In this example, the connection destination is changed to candidate base station device #1. At this time, the second AMF associated with the candidate base station device notifies the candidate base station device of the NAS container, NH, and NCC as used for the newly generated K. NG-RAN The information. Afterwards, the candidate base station device uses the NAS container, NH, and NCC to update the master key, via the second AMF associated with this device and the base station device at the transfer destination (in... Figure 4 In the example, the third AMF associated with the candidate base station device #1 sends an LTM configuration containing the master key update information to the base station device at the handover destination.

[0030] Furthermore, the candidate base station device determines, for example, whether it is connected to a shared AMF (whether an Xn interface has been established) with the base station device at the handover destination, and decides the content of the master key update. For example, if the candidate base station device is associated with a shared AMF with the base station device at the handover destination, it can generate a master key update that includes a key set change indicator set to "No" and the notified NCC. Alternatively, if the candidate base station device is associated with a different AMF with the base station device at the handover destination, it can obtain the NAS container, NH, and NCC by querying the AMF associated with it, and generate a master key update that includes a key set change indicator set to "Yes," the NAS container, and the NCC. Then, the candidate base station device sends the generated master key update to the base station device at the handover destination.

[0031] If update information for the master key update is received from the candidate base station device, it is then handed over to the destination base station device (in Figure 4 In the example, the candidate base station device #1) sends the received master key update information to the terminal device in a form associated with the LTM configuration of the candidate base station device (S413). If the master key update is received, the terminal device will send the candidate base station device (in...) to the terminal device. Figure 4 In the example, the LTM configuration of the candidate base station device #2) is updated with the received information containing the master key update. Then, after the master key update is completed, the terminal device sends a response message (S414) to the base station device at the handover destination. In one example, an RRC reconfiguration message is used when the information is sent in S413, and the terminal device can send an RRC reconfiguration completion response message as S414 to the base station device at the handover destination. However, this is just an example, and other messages can also be used.

[0032] In this processing example, the terminal device receives parameters associated with the security key (master key update) as part of the LTM configuration. Then, in the event of an LTM-based handover, the terminal device can reuse the LTM configuration of a candidate base station device that was not selected as its handover destination. However, since the settings associated with the security key in the LTM configuration should be updated, this settings can be obtained via the base station device at the handover destination. Therefore, for candidate base station devices that should still be processed as handover destinations after the handover, the terminal device can efficiently update the settings associated with the security key while maintaining most of the LTM configuration.

[0033] In addition, Figure 4 The example shown illustrates a scenario where only one candidate base station device is transferred, but it can be assumed that multiple such candidate base station devices exist. In this case, when the base station device at the transfer destination notifies the configuration information associated with the security key (master key update), information indicating which candidate base station device this configuration information relates to is also notified. For example, for each LTM configuration set in the terminal device, if an identification information (LTM configuration id) is assigned, the configuration information associated with the security key can be notified in association with that identification information. In one example, if only the master key updates of some candidate base station devices are updated, the LTM configuration id associated with that candidate base station device and the master key update of that candidate base station device are notified to the terminal device in association. Furthermore, the identification information of the base station device can also be notified in association with the configuration information associated with the security key. That is, any identification information can be used as long as the configuration information associated with the security key of the updated object can be determined. Alternatively, when notifying configuration information related to all candidate base station devices, the configuration information can be arranged and notified in a predetermined order, such as ascending or descending order of the LTM configuration ID. In this case, since it is possible to determine which candidate base station device (LTM configuration ID) the configuration information relates to based on the order in which the configuration information is notified, it is not necessary to notify the identification information in an explicitly indicated manner.

[0034] Furthermore, while the above description addresses the processing related to the primary cell group (MCG), the same processing can be applied to the secondary cell group (SCG). That is, the base station device providing the candidate cell for the secondary cell can also include information about the SK-counter parameter related to the security key used for the SCG in the LTM configuration and notify the terminal device. Then, after a change in the connection destination cell based on a cell handover command, the updated information related to the SK-counter in the LTM configuration can be notified to the terminal device from the base station device providing the changed connection destination cell. Additionally, the LTM configuration can also include both the master key update for the MCG and the SK-counter for the SCG. In this case, after the LTM-based handover is performed, the terminal device and the base station device communicate using dual connectivity using both the primary and secondary cells, but the master key update is used in the generation of the security key for the primary cell, and the SK-counter is used in the generation of the security key for the secondary cell. Additionally, if there is an unselected LTM configuration after the handover is executed, and this LTM configuration includes both the master key update for MCG and the SK-counter for SCG, the terminal device will be notified of the update information for both the master key update and the SK-counter after the handover.

[0035] In addition, Figure 4 The example shown illustrates a scenario where a base station device from the handover source sends a message to a candidate base station device that was not selected as the handover destination, requesting the forwarding of LTM configuration to the base station device at the handover destination. However, this is just an example; for instance, the base station device at the handover destination could also request the transmission of LTM configuration to a candidate base station device. An example of the processing flow in that case will be provided. Figure 5 It indicates. In Figure 5 In the example, for with Figure 4 The same treatment applies, using the same reference numerals for the accompanying drawings while omitting the descriptions.

[0036] In this process, if a handover success message is received from the base station device at the handover destination, the base station device from the handover source forwards the LTM configuration of the candidate base station device that was not selected as the handover destination and received in S403 to the base station device at the handover destination (S501). Furthermore, the forwarding of this LTM configuration can be performed via a handover success ACK message as a response to the handover success message. However, this is just one example; the forwarding of the LTM configuration can also be performed based on other messages. Then, the base station device at the handover destination requests configuration information for updating the security key from the candidate base station device that was not selected as the handover destination and corresponds to the received LTM configuration (S502). The base station device at the handover destination can, for example, request a master key update using a handover request message. Furthermore, this message can include the K key used by the base station device at the handover destination. NG-RAN The base station device is maintaining NCC information. Additionally, the message may include information indicating that the terminal device (from the transfer source base station device) has been notified of the LTM configuration, which includes updated configuration information corresponding to the security key to be acquired. Regarding the LTM configuration previously notified to the transfer source base station device, the candidate base station device identifies a need for an update to the security key configuration information and updates it, sending the updated configuration information to the transfer destination base station device (S503). At this time, it is not necessary to send information contained in the LTM configuration other than the master key update to the transfer destination base station device. The candidate base station device can, for example, use a transfer request ACK message to send the updated configuration information to the transfer destination base station device. If the master key update is acquired, the transfer destination base station device forwards the information to the terminal device (S413).

[0037] Thus, in Figure 5 In the process of handling, it can also be with Figure 4 Similarly, the terminal device is notified of updated configuration information related to the security key. Furthermore, in the above embodiment, when the base station device at the transfer destination and the candidate base station device after transfer are associated with a shared AMF, i.e., the base station device at the transfer destination (the base station device that becomes a base station device in communication after transfer) generates K. NG-RAN The handling of this situation has been explained, but the replacement base station device after the handover (the base station device that continues to be a replacement base station device after the handover) can also generate K. NG-RAN That is, the base station device at the transfer destination and the candidate base station device after the transfer can also be associated with different AMFs. In this case, the base station device at the transfer destination sends data to the candidate base station device (in [location missing]) via the first AMF associated with the base station device and the second AMF associated with the candidate base station device that continues to be the transfer destination. Figure 5 In the example, the backup base station device #2) notifies the base station device that the terminal device's connection destination has been changed (in... Figure 5 In the example, the connection destination is changed to candidate base station device #1. At this time, the second AMF notifies the candidate base station device of the NAS container, NH, and NCC as the basis for generating a new K. NG-RAN Information. Afterwards, the backup base station device (in...) Figure 5 In the example, candidate base station device #2) uses the NAS container, NH, and NCC to update the master key, and transmits it to the base station device at the transfer destination via the second AMF and the first AMF (in Figure 5In the example, the candidate base station device #1) sends the master key update information or an LTM configuration containing the master key update information. Then, if the master key update is obtained, the base station device at the destination forwards the information to the terminal device (S413).

[0038] Furthermore, in the above embodiments, an example was described where the LTM configuration includes setting information for updating the security key (master key update), but this is not the only possibility. For example, the setting information may not be included in the LTM configuration, but may be included in the cell handover command of S407. For example, in the case where the base station device of the handover source and the base station device of the handover destination are associated with a shared AMF, such as... Figure 2 As shown in S204, it is possible to notify the terminal device of NCC information without notifying the terminal device of the NAS container. In this case, the base station device of the handover source can be configured to send without including the configuration information in the LTM configuration, and send with the configuration information (NCC) included in the cell handover command. In this case, the key set change indicator can also be omitted. In addition, when the handover is performed according to the cell handover command, the LTM configuration ID or information that can determine the LTM configuration ID is included in the cell handover command. The terminal device uses the LTM configuration ID or information that can determine the LTM configuration ID to determine the base station device of the handover destination. In order to communicate with the base station device of the handover destination, the terminal device updates K using the NCC included in the cell handover command. NG-RAN Furthermore, the cell handover command can include the NCC value itself, or it can include other information that can identify the NCC. For example, identification information can be pre-assigned for each of multiple NCCs through LTM configuration, and this identification information can also be included in the cell handover command. Accordingly, based on the signaling of the RRC layer, in the LTM configuration notified in an environment where encryption is performed, the identification information used to determine the NCC is sent. In a cell handover command without encryption, only the identification information is sent, thereby preventing the eavesdropper from determining the NCC even if the cell handover command is intercepted.

[0039] Alternatively, for some candidate base station devices, as described above, the LTM configuration may include setting information for security key updates, while for other candidate base station devices, the LTM configuration may not include such setting information, but this setting information may be notified according to the cell handover command. Furthermore, even if the LTM configuration includes setting information for security key updates, at least a portion of this setting information may be sent according to the cell handover command. In this case, the setting information included in the LTM configuration can be updated and used using the setting information specified according to the cell handover command. In one example, suppose the first base station device as the handover source and the second base station device as the handover destination are associated with different AMFs, and the second base station device and a candidate third base station device not selected as the handover destination are associated with a shared AMF. In this case, before the handover from the first base station device to the second base station device, as described above, the master key update is notified to the terminal device in association with the LTM configurations of the second and third base station devices. In this case, the master key update includes a key set change indicator set to "yes", a NAS container, and an NSS. Subsequently, if a handover occurs from the first base station device to the second base station device, the master key of the third base station device will be updated to the old information and needs to be updated. On the other hand, in the case of a handover from the second base station device to the third base station device, the security key update does not require information such as the NAS container; the NCC information is sufficient. Therefore, after the handover from the first base station device to the second base station device, the notification regarding the master key update of the third base station device can be omitted, and the notification can be based on the NCC information determined by the subsequent cell handover command. Accordingly, the terminal device continues to retain the old information about the third base station device, but can determine the NCC based on the cell handover command, and can use the NCC to update the security key without using the old information.

[0040] Furthermore, when the LTM configuration only includes SCG setting information, when adding a secondary cell corresponding to that LTM configuration, it is not necessary to update the security key related to the MCG; only the security key of the secondary cell needs to be generated / updated. The updating of the setting information (SK-counter) related to the security key of the secondary cell in this case can also be performed through a different process than described above.

[0041] For example, a base station device can send a list of configuration information (SK-counter) associated with the security key of the SCG (using an RRC reconfiguration message) to the terminal device in the connection for each of the base station devices that provide candidate cells to become MCGs. For example, for Figure 4 or Figure 5Each of the candidate base station devices #1 and #2 in the network is configured with a separate list of SK-counters, and the terminal device sends this list to the terminal device. Additionally, the terminal device also maintains this list of SK-counters for the base station devices in the network providing the MCG cell. For example, the terminal device can maintain SK-counters A1, A2, ..., A16 for the base station devices in the network, and SK-counters B1, B2, ..., B16 for candidate base station device #1. That is, a separate list of SK-counters is defined for each candidate base station device capable of providing the MCG cell. Then, if a cell handover command indicating an additional secondary cell is received in communication with the base station devices in the network, the terminal device uses SK-counter A1 at the beginning of the list to generate a security key for that secondary cell. Subsequently, if a cell handover command indicating a different secondary cell is received in communication with the base station devices in the network, the terminal device uses SK-counter A2 to update the security key for the changed secondary cell. At this time, the terminal device removes the currently used SK-counter A1 from the list. In this way, when the SCG is changed without changing the MCG, the terminal device can sequentially update the security key for the SCG using the SK-counters included in the pre-notified list. That is, a list of SK-counters can be provided for each MCG, for multiple SCGs that can be set together with that MCG for shared use. Therefore, as long as the MCG remains unchanged, the terminal device can repeatedly update the security key for the SCG using the SK-counters included in the list according to each SCG change. Therefore, it is also possible to update the security key for each SCG change without performing the aforementioned steps. Figure 4 , Figure 5 The example shown is an inquiry to the base station device (which provides the SCG candidate).

[0042] Subsequently, assuming the terminal device receives a cell handover command indicating a change in the MCG (handover), handing over the cell to candidate base station device #1. Then, upon receiving an additional cell handover command indicating the SCG, the terminal device generates a security key for that SCG using the SK-counter B1 at the beginning of the list associated with candidate base station device #1. The terminal device then removes the previously used SK-counter A2 from the list. In this way, by setting the list of SK-counters separately for each MCG, the security key for the secondary cell can be efficiently generated after the handover.

[0043] Furthermore, the base station connected to the terminal device can instruct the terminal device to delete part or all of the list of configured SK-counters. This instruction can be sent from the base station to the terminal device, for example, using an RRC reconfiguration message. Furthermore, the deletion of the list can be performed by an explicit instruction from the base station, or without an instruction from the base station if predetermined conditions are met. For example, the list associated with the MCG of the handover source maintained in the terminal device can be deleted based on a cell handover command, previous handovers, or a change in the MCG. Furthermore, if the MCG of the handover source is processed as a candidate for handover destination after handover, it is assumed that the LTM configuration for that MCG and the SCG corresponding to that MCG will not be deleted. In this case, the list may not be deleted. Alternatively, the list set as a candidate for an MCG not selected as a handover destination by the terminal device can be deleted based on a change in the MCG. In this case, it can be decided whether to delete the list based on whether the LTM configuration is maintained. For example, the list of candidate settings for MCGs excluded from the candidates for the handover destination could be deleted along with the LTM configuration, while the list of candidate settings for other MCGs could remain intact. Alternatively, the decision to delete the list could be based on the base station device at the handover destination. In this case, the configuration information used for this decision could be communicated to the terminal device in advance. Alternatively, the base station device could notify the terminal device of information specifying the criteria for deleting the list, and the terminal device could delete the list based on those criteria.

[0044] Furthermore, in the above example, the processing of the LTM configuration when the terminal device receives the LTM configuration from a connected base station device and then performs a handover is described. This processing also applies to LTM configurations maintained before the handover. That is, the terminal device receives setting information for updating the LTM configuration and security key from a base station device previously connected to the currently connected base station device. Then, the terminal device can maintain the LTM configuration for a candidate base station device that was not selected as the handover destination while updating the portion of the setting information for updating the security key through a handover to the currently connected base station device. Afterward, the terminal device can perform the above processing if a further handover is performed. That is, the terminal device can maintain the LTM configuration received from a base station device that is not currently connected while updating only the setting information for updating the security key contained therein or associated with that information.

[0045] Figure 6This section illustrates an example of the hardware configuration of a base station device and a terminal device according to this embodiment. In one example, the base station device and the terminal device are configured with a processor 601, a ROM 602, a RAM 603, a storage device 604, and a communication circuit 605. The processor 601 is a computer configured with one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application-Specific Integrated Circuit), and reads and executes programs stored in the ROM 602 and the storage device 604, thereby performing overall control processing of the device and the aforementioned processing. The ROM 602 is a read-only memory that stores programs, various parameters, and other information related to the processing performed by the base station device and the terminal device. The RAM 603 functions as the working space when the processor 601 executes programs, and also serves as a random access memory for storing temporary information. The storage device 604 is configured with, for example, a removable external storage device. The communication circuit 605 is configured with, for example, 5G or subsequent standard wireless communication circuits. Furthermore, in Figure 6 The diagram illustrates a communication circuit 605, but the base station device and the terminal device can have multiple communication circuits. For example, the base station device and the terminal device can have wireless communication circuits for each type of 5G and subsequent standards, and a shared antenna for these circuits. Furthermore, the base station device and the terminal device can also have individual antennas suitable for each standard. Additionally, the base station device can also have wired communication circuits used for communication with other base station devices and nodes in the core network. Furthermore, the terminal device can also have communication circuits conforming to wireless communication standards other than cellular communication standards such as Wireless Local Area Network (LAN) and Bluetooth (registered trademark). Moreover, the base station device and the terminal device can have separate communication circuits 605 for each of the multiple usable frequency bands, or they can have a shared communication circuit 605 for at least a portion of these frequency bands.

[0046] Figure 7 This illustrates an example of the functional configuration of a terminal device. The terminal device, for example, includes a setting information receiving unit 701, an LTM setting and holding unit 702, a key information management unit 703, a key generation unit 704, and a communication unit 705. Furthermore, in... Figure 7 This diagram only shows functions particularly relevant to this embodiment; other functions that the terminal device may have are omitted from the illustrations. For example, the terminal device naturally possesses other functions typically found in terminal devices conforming to 5G, subsequent standards, etc. Furthermore, Figure 7 This is a general representation of the functional blocks; each functional block can be implemented as a single unit or in more detail. Additionally, Figure 7Each function can be implemented, for example, by the processor 601 executing programs stored in ROM 602 and storage device 604, or by the processor inside communication circuit 605 executing predetermined software. Furthermore, since the details of the processing performed by each functional unit are as described above, only a general overview of the terminal device's functions will be given here.

[0047] The configuration information receiving unit 701 receives various configuration information from the connected base station devices. For example, the configuration information receiving unit 701 receives pre-configuration information for LTM (Local Time Management) regarding candidate base station devices as the handover destination. Furthermore, the pre-configuration information, such as configuration information for establishing an RRC layer connection with the candidate base station device, is configuration information notified to the terminal device even when no actual handover has occurred. The pre-configuration information corresponds to the LTM configuration described above. Additionally, the configuration information receiving unit 701 receives configuration information for generating / updating security keys (e.g., master key update, SK-counter). The LTM configuration holding unit 702 holds the pre-configuration information for LTM received by the configuration information receiving unit 701. Furthermore, the LTM configuration holding unit 702 is configured, for example, to continue holding pre-configuration information (LTM configuration) regarding candidate base station devices not selected as handover destinations after the handover is executed. Furthermore, the LTM configuration holding unit 702 can, for example, delete the currently held pre-configuration information based on instructions from the base station device of the handover source and the base station device of the handover destination. Alternatively, the LTM setting and retention unit 702 may, for example, set a validity period for preset information and delete the preset information if the validity period is met. In this case, the validity period can be notified from the base station device in the connection when the preset information is received.

[0048] The key information management unit 703 maintains and manages setting information such as security keys or parameters used to generate the security keys for each of the connected base station devices and the candidate base station devices at the handover destination. For example, the key information management unit 703 manages the setting information of the security keys received from the connected base station devices along with the LTM configuration, ensuring that this setting information is up-to-date. For instance, if the key information management unit 703 receives setting information (master key update) from the base station device at the handover destination regarding at least a portion of the setting information of a candidate base station device that was not selected as the handover destination, it replaces the currently maintained setting information with the received setting information. Additionally, the key information management unit 703 can also obtain the setting information used to generate the security keys based on cell handover commands. Therefore, the key information management unit 703 is able to maintain the security key setting information in an up-to-date state. Furthermore, the key information management unit 703 can maintain a list of SK-counters for each MCG that can be used as a secondary cell when using that MCG. When the SCG connected to the destination is changed or added, the SK-counter values ​​are sequentially retrieved from this list to generate a security key for that SCG. Additionally, if an SCG is changed or deleted, the key information management unit 703 can remove the generated SK-counter values ​​for the security keys of unused SCGs from the list.

[0049] The key generation unit 704 generates a security key using the setting information (master key update, SK-counter) maintained and managed by the key information management unit 703. The communication unit 705 uses the security key generated by the key generation unit 704 to communicate with the base station device connected to the destination.

[0050] Figure 8 This illustrates an example of the functional configuration of a base station device. For example, a base station device includes a setting information acquisition unit 801, a setting information provision unit 802, a setting information notification unit 803, a key generation unit 804, and a communication unit 805. Furthermore, in... Figure 8 This diagram only shows functions particularly relevant to this embodiment; other functions that the base station device can have are omitted from the illustrations. For example, the base station device naturally possesses other functions generally found in base station devices conforming to 5G, subsequent standards, etc. Furthermore, Figure 8 This is a general representation of the functional blocks; each functional block can be implemented as a single unit or further refined. Additionally, Figure 8 Each function can be implemented, for example, by the processor 601 executing programs stored in ROM 602 and storage device 604, or by the processor inside communication circuit 605 executing predetermined software. Furthermore, since the details of the processing performed by each functional unit are as described above, only a general overview of the base station device's functions will be given here.

[0051] The configuration information acquisition unit 801 acquires configuration information from other base station devices. For example, during a connection with a terminal device, the configuration information acquisition unit 801 acquires LTM configuration for LTM transfer to other base station devices, and configuration information (master key update, SK-counter) for generating or updating security keys during communication with other base station devices. Furthermore, the configuration information acquisition unit 801 can acquire configuration information for LTM configuration and security key generation or updating by sending a request message (e.g., a transfer request) to a candidate base station device that will become a transfer destination from this device. Additionally, for example, when a terminal device connects to another base station device through a transfer from this device, the configuration information acquisition unit 801 acquires configuration information regarding the LTM configuration and security key generation or updating of the candidate base station device that will become a transfer destination from this device. Here, the configuration information associated with the LTM configuration and security key can be acquired from the candidate base station device at the transfer destination based on a forwarding request for configuration information associated with the LTM configuration and security key from the base station device at the transfer source to the candidate base station device at the transfer destination. Alternatively, the LTM configuration can be received from the base station device that is the transfer source, and the configuration information associated with the security key can be received from the candidate base station device that becomes the transfer destination. The configuration information providing unit 802 provides configuration information associated with the LTM configuration and the security key to other base station devices. That is, the information provided by the configuration information providing unit 802 of the first base station device is obtained by the configuration information obtaining unit 801 of the second base station device.

[0052] The configuration information notification unit 803 notifies the terminal device in the connection of the acquired configuration information. For example, the configuration information notification unit 803 notifies both parties of the configuration information associated with the LTM configuration and the security key for a base station device that does not maintain the LTM configuration in the terminal device. On the other hand, the configuration information notification unit 803 can not notify the LTM configuration but only the configuration information associated with the security key for a base station device that maintains the LTM configuration in the terminal device. For example, the configuration information notification unit 803 can receive an RRC reconfiguration completion message from the terminal device during the handover process, and after establishing the connection, send the configuration information associated with the security key (and the LTM configuration) through the RRC reconfiguration message. Alternatively, the configuration information notification unit 803 can also include the configuration information (NCC) associated with the security key of the base station device at the handover destination in the cell handover command. In this case, the configuration information notification unit 803 holds the configuration information acquired by the configuration information acquisition unit 801 in advance until the handover time, and notifies the terminal device of the configuration information during the handover.

[0053] The key generation unit 804, for example, generates a security key using setting information (such as master key update) that is previously stored for generating a security key for communication with the terminal device, when the connection to the terminal device is transferred. Furthermore, the key generation unit 804 updates this setting information based on requests from other base station devices (e.g., the first or second other base station device in the case of a transfer from a first other base station device to a second other base station device) or the AMF, and maintains the updated setting information. In addition, the updated setting information can be provided to other base station devices through the setting information providing unit 802, and notified to the terminal device from the other base station devices. The communication unit 805 establishes a connection with the terminal device and communicates using the security key generated by the key generation unit 804.

[0054] As described above, in this embodiment, security keys can be efficiently shared and updated between terminal devices and networks (base station devices) performing LTM-based handover. Therefore, it can contribute to Goal 9 of the UN-led Sustainable Development Goals (SDGs): “Building resilient infrastructure, advancing sustainable industrialization and expanding innovation.”

[0055] The invention is not limited to the above-described embodiments and can be modified and altered in various ways within the scope of the invention's intent.

[0056] This application claims priority based on Japanese Patent Application No. 2024-056621, filed on March 29, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device that conforms to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein, The terminal device has: The receiving unit receives from the first base station device in the connection first configuration information regarding each of a plurality of candidate base station devices including the second base station device and the third base station device as the handover destination, the first configuration information being the first configuration information and the second configuration information being associated with the first configuration information for updating the security key. The holding unit, for each of the plurality of base station devices, holds the first setting information in association with the second setting information; The execution unit performs the handover to the second base station device; as well as The update unit, in response to the handover to the second base station device, updates the security key using the second setting information associated with the first setting information of the second base station device, and after the handover is executed, updates the second setting information associated with the first setting information while maintaining the first setting information held about the third base station device.

2. The terminal device according to claim 1, wherein, After the handover to the second base station device, the receiving unit receives the updated second setting information for the third base station device from the second base station device. The updating unit updates the second setting information by replacing the second setting information held by the third base station device with the received second setting information.

3. The terminal device according to claim 2, wherein, The receiving unit receives identification information capable of identifying the second setting information regarding at least a portion of the plurality of third base station devices, namely the fourth base station device, and updated second setting information regarding the fourth base station device. The updating unit replaces the second setting information identified by the identification information with the received second setting information.

4. The terminal device according to claim 3, wherein, The first setting information is the LTM configuration, and the identification information is the LTM configuration ID.

5. The terminal device according to claim 2, wherein, A predetermined order is assigned to the plurality of the third base station devices. The receiving unit receives updated information consisting of multiple sets of second setting information arranged in the predetermined order for all of the multiple third base station devices. The updating unit determines, according to the predetermined order, which of the plurality of third base station devices each of the received plurality of second setting information corresponds to, and replaces the second setting information held for each of the plurality of third base station devices with the received second setting information based on the determination result.

6. The terminal device according to claim 2, wherein, After the RRC reconfiguration completion message is sent during the handover based on the execution unit, the receiving unit receives the updated second setting information from the second base station device via the RRC reconfiguration message.

7. The terminal device according to claim 1, wherein, The second setting information is master key update. The master key update includes a key set change indicator set to "yes", the next-hop chain count (NCC and non-access stratum (NAS) container), or The master key update includes a key set change indicator and NCC that are set to no.

8. The terminal device according to claim 1, wherein, The second setting information includes the SK-counter.

9. The terminal device according to claim 1, wherein, The execution unit performs the handover upon receiving a cell handover command instructing the handover to the second base station device. When the cell handover command contains the second setting information related to the second base station device, and there is second setting information held by the second base station device, the update unit uses the second setting information contained in the cell handover command to update the security key.

10. The terminal device according to claim 1, wherein, The receiving unit also receives the first setting information for each of the plurality of fifth base station devices, and a list of the second setting information shared by the plurality of fifth base station devices, which provide candidate cells to become secondary cells when a cell provided by a base station device in the connection is the primary cell. When the secondary cell is changed without changing the primary cell, the update unit removes the second setting information used before the change of the secondary cell from the list, and uses one of the second setting information contained in the list to update the security key for communication in the changed secondary cell.

11. The terminal device according to claim 10, wherein, The receiving unit also receives a list of first setting information for each of the plurality of fifth base station devices, in the case where each of the plurality of base station devices provides a cell that becomes the primary cell, and a list of second setting information shared by the plurality of fifth base station devices. The list of the second setting information for the second base station device and the list of the second setting information for the third base station device are defined separately.

12. The terminal device according to claim 11, wherein, The holding unit maintains a list of the second setting information regarding the connection of the base station device and the case where each of the plurality of base station devices provides a cell that becomes the primary cell.

13. The terminal device according to claim 12, wherein, The holding unit deletes the list of the second setting information based on an instruction from the base station device in the connection.

14. The terminal device according to claim 12, wherein, When the terminal device is handed over to the second base station device, the holding unit deletes the list of the second setting information regarding the case where a cell provided by a candidate base station device that becomes a primary cell after the handover is no longer the handover destination.

15. A base station apparatus that conforms to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein, The base station device has: The providing unit, as a candidate for the handover destination, provides the first other base station device to which the terminal device is connecting with first configuration information for Layer 1 / Layer 2 triggered mobility (LTM) and second configuration information associated with the first configuration information for updating the security key. The connection unit is connected to the terminal device through the handover of the terminal device; The generation unit uses the second setting information to generate a security key used in communication with the terminal device; The acquisition unit, after the handover is executed, acquires the first setting information and the second setting information of the second alternative base station device as a candidate handover destination of the terminal device from the base station device; as well as The sending unit, while the terminal device is maintaining the first setting information about the second other base station device, sends a message to the terminal device that does not contain the first setting information but contains the second setting information about the second other base station device.

16. The base station apparatus according to claim 15, wherein, After receiving the RRC reconfiguration complete message from the terminal device during the handover, the sending unit sends an RRC reconfiguration message containing the second setting information about the second other base station device to the terminal device.

17. The base station apparatus according to claim 15, wherein, The sending unit sends a cell handover command to the terminal device instructing it to hand over to the second other base station device, which includes the second setting information about the second other base station device.

18. The base station apparatus according to claim 15, wherein, The providing unit also provides updated second setting information to the third other base station device after the terminal device has been transferred from the first other base station device to the third other base station device. In the event that the terminal device is transferred from the third other base station device to the base station device, the generation unit uses the updated second setting information provided to the third other base station device to generate the security key.

19. The base station apparatus according to claim 15, wherein, The acquisition unit, in response to a request from the base station device of the handover source, acquires the first setting information and the second setting information sent by the second other base station device regarding the second other base station device.

20. The base station apparatus according to claim 15, wherein, The acquisition unit obtains the first setting information and the second setting information of the second other base station device by receiving a message containing the first setting information about the second other base station device from the base station device of the transfer source, and sending a message requesting the second setting information to the second other base station device based on the message.

21. A control method, executed by a terminal device conforming to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein, The control method includes the following steps: The first base station device in the connection receives first configuration information for each of a plurality of candidate base station devices, including the second base station device and the third base station device, regarding the Layer 1 / Layer 2 triggered mobility (LTM) of each of the plurality of base station devices as the handover destination, and second configuration information associated with the first configuration information for updating the security key. For each of the plurality of base station devices, the first setting information is maintained in association with the second setting information; Perform the handover to the second base station device; as well as In response to the handover to the second base station device, the security key is updated using the second setting information associated with the first setting information of the second base station device, and after the handover is executed, the second setting information associated with the first setting information is updated while maintaining the first setting information held about the third base station device.

22. A control method, executed by a base station device conforming to the 3rd Generation Partnership Project (3GPP) cellular communication standard, wherein, The control method includes the following steps: As a candidate for handover destination, the terminal device is provided with first configuration information for Layer 1 / Layer 2 triggered mobility (LTM) and second configuration information associated with the first configuration information for updating the security key. Connected to the terminal device through the handover of the terminal device; The second setting information is used to generate a security key for communication with the terminal device. After the handover is executed, the first setting information and the second setting information of the second alternative base station device as a candidate handover destination of the terminal device are obtained from the base station device; as well as While the terminal device is maintaining the first setting information about the second other base station device, a message containing the second setting information about the second other base station device but not the first setting information is sent to the terminal device.

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