Method and apparatus of node and user equipment in wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present disclosure provides a node and a user equipment in a wireless communication system and methods performed by the same. A method performed by a first node in a wireless communication system includes: transmitting a first message to a user equipment (UE) in case that L1 / L2 triggered mobility (LTM) cell switch is triggered and it is determined that key update needs to be performed, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; and transmitting a second message to a second node, wherein the second message includes at least one of third information related to a target cell of the UE, fourth information for indicating key update, and the first parameter.

Description

METHOD AND APPARATUS OF NODE AND USER EQUIPMENT IN WIRELESS COMMUNICATION SYSTEM

[0001] The present disclosure relates to a technical field of wireless communication, and more specifically, to a node and a user equipment in a wireless communication system and methods performed by the same.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “Sub 6GHz” bands such as 3.5GHz, but also in “Above 6GHz” bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz (THz) bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The present disclosure provides method and apparatus in a wireless communication system.

[0009] According to an aspect of an exemplary embodiment, there is provided method and apparatus in a wireless communication system.

[0010] Aspects of the present disclosure provide efficient communication methods in a wireless communication system.

[0011] The above and other aspects, features and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

[0012] FIG. 1 is an exemplary system architecture 100 of system architecture evolution (SAE);

[0013] FIG. 2 is an exemplary system architecture 200 according to various embodiments of the present disclosure;

[0014] FIG. 3 shows a schematic diagram of an example method according to embodiments of the present disclosure;

[0015] FIG. 4A shows a schematic diagram of an example method according to embodiments of the present disclosure;

[0016] FIG. 4B shows a schematic diagram of an example method according to embodiments of the present disclosure;

[0017] FIG. 5 shows a flowchart of a method 550 performed by a first node in a wireless communication system according to embodiments of the present disclosure;

[0018] FIG. 6 shows a flowchart of a method 600 performed by a second node in a wireless communication system according to embodiments of the present disclosure;

[0019] FIG. 7 shows a flowchart of a method 700 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure;

[0020] FIG. 8 shows a flowchart of a method 800 performed by a second node in a wireless communication system according to embodiments of the present disclosure;

[0021] FIG. 9A shows a flowchart of a method 900 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure;

[0022] FIG. 9B shows a flowchart of a method 910 performed by a target node in a wireless communication system according to embodiments of the present disclosure;

[0023] FIG. 10 shows a schematic diagram of a node 1000 in a wireless communication system according to embodiments of the present disclosure; and

[0024] FIG. 11 shows a schematic diagram of a user equipment 1100 in a wireless communication system according to embodiments of the present disclosure.

[0025] In order to meet an increasing demand for wireless data communication services since a deployment of 4G communication system, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called "beyond 4G network" or "post LTE system".

[0026] Wireless communication is one of the most successful innovations in modern history. Recently, a number of subscribers of wireless communication services has exceeded 5 billion, and it continues growing rapidly. With the increasing popularity of smart phones and other mobile data devices (such as tablet computers, notebook computers, netbooks, e-book readers and machine-type devices) in consumers and enterprises, a demand for wireless data services is growing rapidly. In order to meet rapid growth of mobile data services and support new applications and deployments, it is very important to improve efficiency and coverage of wireless interfaces.

[0027] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0028] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

[0029] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

[0030] The term "include" or "may include" refers to the existence of a corresponding disclosed function, operation or component which can be used in various embodiments of the present disclosure and does not limit one or more additional functions, operations, or components. The terms such as "include" and / or "have" may be construed to denote a certain characteristic, number, step, operation, constituent element, component or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, constituent elements, components or combinations thereof.

[0031] The term "or" used in various embodiments of the present disclosure includes any or all of combinations of listed words. For example, the expression "A or B" may include A, may include B, or may include both A and B.

[0032] Unless defined differently, all terms used herein, which include technical terminologies or scientific terminologies, have the same meaning as that understood by a person skilled in the art to which the present disclosure belongs. Such terms as those defined in a generally used dictionary are to be interpreted to have the meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present disclosure.

[0033] In the present disclosure, the names of all messages, information, methods, modules, etc. are only exemplary, and these messages, information, methods, modules, etc. may have any other names based on actual applications. In addition, herein, ordinal numbers such as "first" and "second" are only used to distinguish the referred objects (e.g., messages, information, etc.) or facilitate the description of the referred objects in certain cases. For example, in some cases, first information may also be second information or contain second information, and second information may also be first information or contain first information, which is not limited herein.

[0034] FIG.s discussed below and various embodiments for describing the principles of the present disclosure in this patent document are only for illustration and should not be interpreted as limiting the scope of the present disclosure in any way. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0035] FIG. 1 is an exemplary system architecture 100 of system architecture evolution (SAE). User equipment (UE) 101 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN) 102 is a radio access network, which includes a macro base station (eNodeB / NodeB) that provides UE with interfaces to access the radio network. A mobility management entity (MME) 103 is responsible for managing mobility context, session context and security information of the UE. A serving gateway (SGW) 104 mainly provides functions of user plane, and the MME 103 and the SGW 104 may be in the same physical entity. A packet data network gateway (PGW) 105 is responsible for functions of charging, lawful interception, etc., and may be in the same physical entity as the SGW 104. A policy and charging rules function entity (PCRF) 106 provides quality of service (QoS) policies and charging criteria. A general packet radio service support node (SGSN) 108 is a network node device that provides routing for data transmission in a universal mobile telecommunications system (UMTS). A home subscriber server (HSS)109 is a home subsystem of the UE, and is responsible for protecting user information including a current location of the user equipment, an address of a serving node, user security information, and packet data context of the user equipment, etc.

[0036] FIG. 2 is an exemplary system architecture 200 according to various embodiments of the present disclosure. Other embodiments of the system architecture 200 can be used without departing from the scope of the present disclosure.

[0037] User equipment (UE) 201 is a terminal device for receiving data. A next generation radio access network (NG-RAN) 202 is a radio access network, which includes a base station (a gNB or an eNB connected to 5G core network 5GC, and the eNB connected to the 5GC is also called ng-gNB) that provides UE with interfaces to access the radio network. An access control and mobility management function entity (AMF) 203 is responsible for managing mobility context and security information of the UE. A user plane function entity (UPF) 204 mainly provides functions of user plane. A session management function entity SMF 205 is responsible for session management. A data network (DN) 206 includes, for example, services of operators, access of Internet and service of third parties.

[0038] Exemplary embodiments of the present disclosure are further described below with reference to the accompanying drawings.

[0039] The text and drawings are provided as examples only to help understand the present disclosure. They should not be construed as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the disclosure herein, it is apparent to those skilled in the art that changes can be made to the illustrated embodiments and examples without departing from the scope of the present disclosure.

[0040] Detailed description of steps irrelevant to the present disclosure is omitted in the present disclosure. In the following embodiments, a 5G system is taken as an example, a CU is taken as an example of a central unit of the access network, and a DU is described as an example of a distributed unit. The methods may also be used for corresponding entities in other systems.

[0041] LTM (L1 / L2-triggered mobility, Layer 1 / Layer 2-triggered mobility) handover mode may also be called Layer 1 / Layer 2 handover (L1 / L2 handover), or LTM Cell Switch, or LTM cell handover, or L1 / L2 mobility. A base station or gNB-DU transmits an LTM Cell Switch Command to a UE through a MAC CE (MAC Control Eelement) of the MAC layer (L2, Layer 2) to indicate the UE to change a serving cell.

[0042] Key management (for example, key update) in an LTM handover mode would be enhanced, so as to realize an LTM handover between cells of different gNBs (also called inter-gNB), extend the application scope of the LTM handover mode, reduce the handover delay between cells of different gNBs and improve the handover performance.

[0043] Herein, inter-gNB may be called inter-CU (or inter-gNB-CU). Cell handover between different gNBs may also be called inter-gNB cell handover or inter-CU (or inter-gNB-CU) cell handover. Inter-gNB cell handover realized by an LTM handover mode may be called inter-gNB LTM or inter-CU LTM (or inter-gNB-CU LTM).

[0044] In a split structure of Central Unit (CU) / Distributed Unit (DU), the source cell and the target cell may be located in the same gNB (or the same gNB-CU), or may be located in different gNBs (or different gNB-CUs) in a handover; or the source cell and the target cell may be located in the same gNB-DU under the same gNB-CU, or may be located in different gNB-DUs under the same gNB-CU.

[0045] In the present disclosure, an LTM candidate cell may be referred to as a candidate cell. A target cell may be called a target candidate cell, or an LTM target candidate cell, or an LTM target cell.

[0046] In the present disclosure, gNB may also be used interchangeably with gNB-CU or gNB-DU. For example, a candidate gNB may also refer to a candidate gNB-CU or a candidate gNB-DU.

[0047] In a wireless communication system, data and / or signaling are encrypted using a security key (or may be referred to as key / Key for short). At the Access Stratum (AS), that is, on the air interface (Uu interface), the UE and the serving cell (serving base station) use the same AS security key to encrypt data and signaling. The key used on the air interface is called KgNB Key (or KgNB). Herein, the security key (or may be referred to as key / Key for short) on the Access Stratum would be updated. At the Non-Access Stratum (NAS), the UE and the core network use the same NAS Security Key for encryption, and the key used on NAS includes KAMF.

[0048] In the present disclosure, security key update (or key update) may refer to KgNB update, that is, to derive (or generate) a new key. The new key may be represented by KgNB*.

[0049] During a cell handover, if key update needs to be performed, after the UE accesses the target cell, a new key KgNB* will be used as the current key (current KgNB) to encrypt the user's service data and signaling between the UE and the current serving cell (that is, the target cell mentioned above or a target gNB thereof). On the other hand, the current key may be used to derive a next new key KgNB* for a next target cell.

[0050] During an LTM cell switch, optionally, there would be a key update. For example, if the source cell and the target cell are located in different gNBs (inter-CU LTM), there will be a key update. The LTM handover mechanism supports Subsequent LTM, that is, the network no longer needs to transmit signaling to provide candidate cell configuration information in the process of LTM cell switch between candidate cells.

[0051] During the LTM cell switch, if the key required by the target cell is different from the key for the source cell, the UE needs to derive a key for the target cell, and the target cell or target base station (gNB) and the UE need to use the same key. Methods for the UE and the base station or cell to derive a key for the target cell and methods for realizing the target cell (or the target base station) to use the same key with the UE (that is, methods for key update) are given by the following embodiments. Herein, it includes key update determination and key update.

[0052] During the LTM cell switch, there is layer 2 processing, and a method of indication of layer 2 processing is given in the present disclosure. The method is given by related embodiments.

[0053] I. Key update determination

[0054] When performing cell handover (or cell switch), determination of whether the key needs to be updated is performed first, and then key update is performed. In LTM, the determination of key update needs to be performed based on key update determination information.

[0055] (1) Key update determination information

[0056] The key update determination information is used to determine whether to perform key update during cell switch. Each candidate cell and serving cell will be configured with (or associated with, or corresponding to) key update determination information. When a target cell is determined, the key update determination information associated with the target cell (or called target candidate cell) serves as the first key update determination information, and the key update determination information associated with the current serving cell (including the source cell) serves as the second key update determination information.

[0057] When the UE is handed over to the target cell, the target cell serves as a new serving cell, and its associated key update determination information may serve as the second key update determination information. When a new target candidate cell is selected, the key update determination information associated with the new target candidate cell serves as the first key update determination information. When performing cell handover, at least one of the first key update determination information and the second key update determination information may be used to determine whether key update needs to be performed.

[0058] (2) Method for key update determination

[0059] A method for key update determination may be as follows:

[0060] - If the first key update determination information and the second key update determination information are the same, the key needs not to be updated; and

[0061] - If the first key update determination information and the second key update determination information are different, the key needs to be updated.

[0062] (3) Configuration method of key update determination information

[0063] The configuration method of key update determination information may include:

[0064] Configuration method 1: key update determination information is configured by the source gNB, that is, the key update determination information of candidate cells is uniformly configured by the source gNB for LTM handover (including subsequent LTM handover). Optionally, the key update determination information may be updated by a subsequent serving gNB (for example, the target gNB).

[0065] Configuration method 2: the source gNB provides an initial configuration of the key update determination information, and the candidate gNB performs a final configuration of the key update determination information. That is, the source gNB provides the initial configuration of the key update determination information of the requested LTM candidate cells to the candidate gNB, and if the candidate gNB requires to modify the key update determination information, the candidate gNB modifies and provides a final configuration of the key update determination information of the requested candidate cells to the source gNB.

[0066] Optionally, the key update determination information includes at least one of the following:

[0067] - gNB identifier (also called node identifier), for example, an identifier (ID) of the gNB to which the candidate cell or the source cell (serving cell) belongs.

[0068] - identifier used for key update determination, for example, an LTM security key indication identifier (for example, ltm-NoSecurityID), the naming of which is not limited in this application. Each candidate cell and source cell (serving cell) are configured with an identifier used for key update determination, and their values are set.

[0069] (4) Examples are given. Optionally, if the first key update determination information and the second key update determination information use the gNB ID, that is, gNB ID of the gNB to which the target cell belongs (called target gNB ID) and gNB ID of the gNB to which the source cell belongs (called source gNB ID), the method for determining whether the key needs to be updated may be as follows:

[0070] - If the two gNB ID are the same, that is, the target cell and the source cell belong to the same gNB, then the key needs not to be updated; and

[0071] - If the two gNB ID are different, that is, the target cell and the source cell belong to different gNBs, then the key needs to be updated.

[0072] If the first key update determination information and the second key update determination information use the identifier used for key update determination, that is, the identifier used for key update determination of the target cell and the identifier used for key update determination of the source cell, the method for determining whether the key needs to be updated may be:

[0073] - If the two identifiers used for key update determination are the same, that is, the identifiers used for key update determination of the target cell and the source cell are the same, the key needs not to be updated; and

[0074] - If the two identifiers used for key update determination are different, that is, the identifiers used for key update determination of the target cell and the source cell are different, the key needs to be updated.

[0075] II. Method for key update

[0076] The following embodiments provide methods for key update under an LTM handover mode. Herein, Embodiments 1 to 3 adopt Configuration method 1 of key update determination information; and Embodiments 4 to 5 adopt Configuration method 2 of key update determination information.

[0077] Embodiment 1 gives a method for key update under an LTM handover mode.

[0078] In Embodiment 1, during an LTM cell switch, the network indicates whether the UE needs to update the key and provides information of related parameters for key update. The UE determines whether key update needs to be performed according to the network indication, and performs key update according to the related parameters for key update. A specific method is as follows.

[0079] Step 300: the UE transmits a message to the source gNB-CU.

[0080] Optionally, the message contains a measurement result. Herein, measurement result may be used interchangeably with measurement report.

[0081] The source gNB-CU may select candidate cells for the LTM for the UE according to the measurement result and / or load condition of the cells.

[0082] Step 301, the source gNB-CU transmits a message to the candidate gNB-CUs (for example, candidates gNB1-CU and gNB2-CU, etc.).

[0083] Optionally, the source gNB-CU uses the message to request the candidate gNB-CUs for one or more candidate cells for LTM handover. The one or more candidate cells may belong to one or more candidate gNB-CUs. Optionally, the source gNB-CU may transmit one or more messages to the candidate gNB requesting different candidate cells.

[0084] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0085] The message may also include at least one of the following information:

[0086] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0087] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0088] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate identifier (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0089] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0090] -LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0091] -LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0092] -Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0093] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed. Optionally, if the key update determination information uses the gNB ID, the candidate gNB may also directly determine that the key update determination information is the candidate gNB ID and does not need to be provided by the source gNB.

[0094] Optionally, the source cell may also serve as an LTM candidate cell.

[0095] Step 302: the candidate gNB1-CU transmits a message to the candidate gNB1-DU.

[0096] Optionally, the candidate gNB1-CU uses the message to request the candidate gNB1-DU for candidate cells for LTM handover and performs resource allocation.

[0097] Optionally, the message may be a UE CONTEXT SETUP REQUEST message, or other messages.

[0098] The message may also include at least one of the following information:

[0099] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0100] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0101] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate identifier (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0102] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0103] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0104] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0105] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0106] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0107] Step 303: the candidate gNB1-DU transmits a message to the candidate gNB1-CU.

[0108] Optionally, the candidate gNB1-DU uses the message to provide information of the requested candidate cells to the candidate gNB1-CU.

[0109] Optionally, the message may be a UE CONTEXT SETUP RESPONSE message, or other messages.

[0110] The message may also include at least one of the following information:

[0111] (1) Cell ID, indicating ID of the requested candidate cell, which may be the ID of the candidate cell requested in step 302. The cell ID may be a CGI (Cell Global ID) or other identifiers.

[0112] (2) LTM configuration information, indicating the configuration information of the cell indicated by the cell ID. It includes at least one of the following information:

[0113] -SSB configuration information, indicating time and frequency information of SSB (Synchronization Signal Block) of the cell indicated by the cell ID. The frequency information may be an ARFCN (absolute radio frequency channel number).

[0114] -Physical cell ID (PCI), indicating the physical cell ID of the cell indicated by the cell ID.

[0115] Step 304: the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the source gNB-CU.

[0116] Optionally, the candidate gNB1-CU (candidate gNB2-CU) uses the message to provide information of the requested candidate cells to the source gNB-CU. Corresponding to step 301, the candidate gNB1-CU may feed back one or more messages to the gNB-CU to provide information of the requested candidate cells.

[0117] Optionally, the message may be a HANDOVER REQUEST ACKNOWLEDGE message, or other messages.

[0118] The message may also include at least one of the following information:

[0119] (1) Cell ID, indicating an ID of a requested LTM candidate cell, which may be the ID of the candidate cell requested in step 301. The cell ID may be a CGI (Cell Global ID) or other identifiers.

[0120] (2) LTM configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with an LTM candidate cell.

[0121] (3) gNB ID, which indicates an ID of the gNB to which the cell indicated by the LTM cell ID belongs.

[0122] (4) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0123] (5) SSB configuration information, indicating time and frequency information of SSB of the cell indicated by the cell ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0124] (6) Physical cell ID (PCI), indicating the physical cell ID of the cell indicated by the cell ID.

[0125] (7) A container from a candidate target base station to a source base station, for example, a Target NG-RAN node To Source NG-RAN node Transparent Container, which contains a HandoverCommand message therein, and the message contains LTM candidate configuration information of the cell indicated by the cell ID provided by the candidate target base station (candidate gNB-CU), including Cell Group configuration information, Radio Bearer (RB) configuration information and so on.

[0126] If there is an LTM candidate cell in the source gNB-DU, steps 304a and 304b will be performed to complete the corresponding candidate cell configuration. Optionally, the source cell may also serve as an LTM candidate cell.

[0127] Step 304a: the source gNB-CU transmits a message to the source gNB-DU. The source gNB-CU uses the message to request the source gNB-DU for candidate cells for LTM handover and performs resource allocation.

[0128] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. For details of the content of the message, please refer to the message content in step 302, which will not be repeated here.

[0129] Step 304b: the source gNB-DU transmits a message to the source gNB-CU. The source gNB-DU uses the message to provide information of the requested candidate cells to the source gNB-CU.

[0130] Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0131] Step 305: the source gNB-CU determines related parameters for key update. If key update needs to be performed when performing LTM cell handover, that is, the target cell needs to use a new key, the source gNB-CU determines a parameter value associated with the new key (also called a parameter value corresponding to the new key or a related parameter of the new key). Optionally, the parameter value may be a value of an NCC parameter (also called a value of a corresponding NCC). The value of the NCC parameter may also be called an NCC value.

[0132] Herein, the method for determining an NCC value may be as follows:

[0133] - If there is an unused {NH, NCC} pair in the source gNB-CU, the NCC in the {NH, NCC} pair is used as the NCC associated with the new key. Herein, the NH (Next Hop) may also be called an NH parameter, and the NCC (Next Hop Chaining Counter) may also be called an NCC parameter.

[0134] - Otherwise, an NCC in an already used {NH, NCC} pair is used as the NCC associated with the new key.

[0135] Since there may be multiple candidate cells, steps 301-304 may need to be performed multiple times, so as to obtain related information of the candidate cells in the same candidate gNB or different candidate gNBs.

[0136] Step 306, the source gNB-CU transmits a message (which may be referred to as a third message herein) to the source gNB-DU.

[0137] The source gNB-CU provides the source gNB-DU with information of the candidate cells and the key update determination information configured for the source cell.

[0138] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0139] The message may also include at least one of the following information:

[0140] (1) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0141] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0142] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0143] - Key update determination information. The key update determination information associated with the LTM candidate cell (also referred to as fifth information associated with a candidate cell used for key update determination herein, which may include fifth information associated with a target cell used for key update determination). During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0144] (2) First key update related parameter information, which may also be referred to as a first parameter used for key update herein. During LTM handover, if key update needs to be performed, the first key update related parameter information is used for key update, that is, for deriving a new key. The first key update related parameter information is determined by the source gNB-CU in step 305. Optionally, the first key update related parameter may be an NCC value, that is, an NCC value associated with the derived new key. The NCC value is an NCC value determined by the source gNB-CU in step 305.

[0145] (3) Key update determination information. Key update determination information associated with the source cell (serving cell) (also referred to herein as sixth information associated with a source cell used for key update determination). During cell switch, the key update determination information may be used as the second key update determination information to determine whether the key update needs to be performed.

[0146] Step 307: the source gNB-DU transmits a message to the source gNB-CU.

[0147] Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0148] In steps 308 and 309, the source gNB-CU provides the newest information of all candidate cells to each candidate cell.

[0149] In steps 301-304, there may be some changes in the LTM candidate cells selected by the source gNB-CU. Optionally, requests for some candidate cells are rejected, or configuration parameters of candidate cells are increased, or configuration parameters of candidate cells are updated. Optionally, the source cell may also serve as an LTM candidate cell.

[0150] Step 308: the source gNB-CU transmits a message to the candidate gNB1-CU (candidate gNB2-CU). The message may be a HANDOVER REQUEST message, or other messages. The information that can be included in the message may be referred to step 301, which will not be repeated here.

[0151] Step 309: the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the source gNB-CU. The message may be a HANDOVER REQUEST ACKNOWLEDGE message, or other messages.

[0152] Step 310: the source gNB-CU transmits a downlink RRC message transfer (DL RRC MESSAGE TRANSFER) message or other messages to the source gNB-DU. The message may also include at least one of the following information:

[0153] (1) RRC Reconfiguration message, an RRC reconfiguration (RRCReconfiguration) message transmitted to the UE.

[0154] Step 311: the source gNB-DU transmits an RRCReconfiguration message to the UE. The source gNB-DU forwards the RRC reconfiguration message received in step 310 to the UE. The message may also include at least one of the following information:

[0155] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0156] - LTM candidate ID, indicating an LTM candidate configuration, which is corresponding to an LTM configuration ID and is associated with (or corresponding to) an LTM candidate cell.

[0157] - LTM candidate physical cell ID (LTM candidate PCI), indicating a physical cell ID of the candidate cell corresponding to (or associated with) the LTM candidate ID.

[0158] - SSB configuration information of LTM, indicating time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0159] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0160] Step 312, the UE transmits an RRC reconfiguration complete (RRCReconfigurationComplete) message to the source gNB-DU.

[0161] Step 313: the source gNB-DU transmits an uplink RRC message transfer (UL RRC MESSAGE TRANSFER) message to the source gNB-CU. The source gNB-DU forwards the RRC reconfiguration complete message received in step 312 to the source gNB-CU.

[0162] Step 314, an Early TA Acquisition process is performed. If a RACH-Less LTM handover process is supported, the network may trigger an Early TA Acquisition process.

[0163] Step 315: the UE transmits a Layer 1 (L1) measurement report to the source gNB-DU.

[0164] Step 316, LTM cell switch determination is performed. The source gNB-DU determines a target cell according to the measurement report received in step 315.

[0165] Step 317, key update determination is performed. The source gNB-DU determines whether the key needs to be updated for the target cell. The source gNB-DU determines the key update determination information associated with the target cell as the first key update determination information according to the candidate cell information received in step 306. Meanwhile, the source gNB-DU determines the key update determination information associated with the serving cell (source cell) received in step 306 as the second key update determination information. The source gNB-DU determines whether the key needs to be updated according to the first key update determination information and the second key update determination information. For the description of the method for determining whether the key needs to be updated, please refer to the description in "Method for key update determination".

[0166] Step 318: the source gNB-DU transmits a message to the UE, indicating the UE to perform cell switch. For example, the message may include first information indicating the UE to perform cell switch. Optionally, the message (which may be referred to as a first message herein) may be an LTM Cell Switch Command. The message is transmitted through MAC CE. The message or the first information may further include at least one of the following information:

[0167] (1) Target Configuration ID, which indicates the LTM configuration ID corresponding to the target cell. The source gNB-DU determines the Target Configuration ID corresponding to the target cell according to the candidate cell information obtained in step 306.

[0168] (2) Timing Advance Command, which indicates whether a TA value of the target cell is valid and / or indicates a TA (Timing Advance) value of the target cell.

[0169] (3) Transmission configuration indicator (TCI) related information, including TCI state ID and UL TCI state ID.

[0170] (4) Random Access Preamble index.

[0171] (5) Synchronization Signal / Physical Broadcast Channel (PBCH) index (SS / PBCH index).

[0172] (6) Physical Random Access Channel (PRACH) mask index (PRACH Mask index).

[0173] (7) Key update indication (herein, it may be called second information about the key update indication), indicating whether the key needs to be updated. The source gNB-DU determines whether the key needs to be updated after handing over to the target cell in step 317. There are two methods for the key update indication: Method 1, if the message contains the key update indication, the UE is indicated to update the key; and Method 2: a value for the key update indication is set, and if the value is 1 (or true), key update needs to be performed, and if the value is 0 (or false), key update needs not to be performed.

[0174] (8) Key update parameter indication, which indicates whether the first key update related parameter information exists. If the message may contain the key update parameter indication, it means that the message may contain the first key update related parameter information, and the UE will obtain the first key update related parameter information.

[0175] (9) First key update related parameter information (also referred to as a first parameter used for key update herein). During LTM handover, if key update needs to be performed, the first key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the first key update related parameter may be an NCC value, that is, an NCC value associated with deriving a new key. The first key update related parameter is obtained by the source gNB-DU in step 306.

[0176] The UE receives the message (LTM cell switch command), and if the message may contain a received key update indication or a key update indication with a value of 1 (or true), the UE will update the key and derive a new key KgNB* for the target cell. There are two methods for key derivation (that is, to derive KgNB*). A key derivation method may also be called an acquisition method of a new key or a derivation method of a new key.

[0177] Key derivation method 1, also called a horizontal derivation (acquisition) method: a new key KgNB* is derived (acquired) through the PCI (Physical Cell ID) of the target cell, the downlink ARFCN of the target cell and the current key KgNB (the key used by the current serving cell, or called the key of the current serving cell). In order to simplify the description of this process, it may also be said that a new key is derived using (through) the current key.

[0178] Key derivation method 2, also called a vertical derivation (acquisition) method: a new key KgNB* is derived (acquired) through the PCI of the target cell, the downlink ARFCN and NH parameter values of the target cell. Herein, there is a corresponding relationship between an NH and an NCC (or there is an association relationship between an NH and an NCC, that is, an NH and an NCC are associated with each other), that is, an NH can be determined through a corresponding NCC. For the UE, the network transmits an NCC value to the UE, and the UE determines a corresponding NH according to the NCC, thus deriving a new key. In order to simplify the description of this process, it may also be said that a new key is derived using (or through) NCC or {NH, NCC} pairs.

[0179] The UE determines a key derivation method according to the NCC value received through the message (LTM cell switch command). If the received NCC value is the same as the NCC value associated with the current key KgNB, a new key KgNB* is derived by key derivation method 1; otherwise, a new key KgNB* is derived by key derivation method 2.

[0180] Step 319: the source gNB-DU transmits a message (which may be called a second message herein) to the source gNB-CU, and indicates the source gNB-DU to transmit an LTM cell switch command to the UE.

[0181] Optionally, the message may be a DU-CU cell switch notification (DU-CU CELL SWITCH NOTIFICATION) message, or other messages. For example, the message may include information for the UE to perform cell switch.

[0182] The message may also include at least one of the following information:

[0183] (1) Target cell ID, which indicates the identification of the target cell of the UE. The cell ID may be a CGI, or other identifiers.

[0184] (2) TCI State ID.

[0185] (3) Key update indication related information. The key update indication related information includes at least one of the following information:

[0186] - A key update indication (also referred to herein as fourth information for indicating key update), indicating to perform key update.

[0187] - A key update parameter, indicating a parameter (e.g., a first parameter) used for key update. Optionally, the key update parameter may be an NCC value, that is, an NCC value associated with deriving a new key.

[0188] Herein, there are two methods of key update indication: Method 1, the key update indication related information is optional, and if the message contains the key update indication related information, key update is indicated. Method 2: a value for the key update indication is set, and if the value is 1 (or true), key update needs to be performed, and if the value is 0 (or false), key update needs not to be performed.

[0189] The above-mentioned target cell ID and / or TCI state ID, etc. may also be referred to as third information related to the target cell of the UE.

[0190] Step 320, key update is determined. The source gNB-CU determines whether the key needs to be updated, and if so, derives a new key.

[0191] (1) If the key update indication related information is not included in step 319, the source gNB-CU determines the first key update determination information according to the key update determination information associated with the target cell, and determines the second key update determination information according to the key update determination information associated with the serving cell (source cell). The source gNB-CU determines whether the key needs to be updated according to the first key update determination information and the second key update determination information. For the description of the method for determining whether the key needs to be updated, please refer to the description in "Method for key update determination", which is not repeated here.

[0192] If it is determined that key update needs to be performed, the source gNB-CU determines a key derivation method and derives a new key. The source gNB-CU compares the NCC determined in step 305with the NCC associated with the current key KgNB. If the two NCC values are the same, a new key KgNB* is derived by key derivation method 1; otherwise, a new key KgNB* is derived by key derivation method 2. For the method of key derivation, refer to the description of key derivation method 1 and key derivation method 2 in step 318. The source gNB-CU transmits the derived new key to the target gNB.

[0193] (2) If the key update indication related information is included in step 319, the source gNB-CU can know that key update will be performed in the LTM cell switch. If the key update parameter is included in step 319, the source gNB-CU can determine a key derivation method and derive a new key according to the key update parameter. Otherwise, the source gNB-CU determines a key derivation method and derives a new key according to the NCC determined in step 305. The determination of the key derivation method is the same as above (it may also be the description in (1) of step 320), and will not be repeated here.

[0194] Step 321: the source gNB-CU transmits a message (which may be called a fourth message herein) to the target gNB. If the target cell belongs to the candidate gNB1, the source gNB-CU transmits a message to the candidate gNB1 (or the candidate gNB1-CU), indicating to the target gNB that the source gNB transmits an LTM cell switch command to the UE to handover to the target gNB (candidate gNB1).

[0195] Optionally, the message may be a source CU-target CU cell switch notification (Source CU-target CU CELL SWITCH NOTIFICATION) message or other messages.

[0196] The message may also include at least one of the following information:

[0197] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0198] (2) Key information, indicating the key KgNBused by the target cell. The key is the new key KgNB* derived by the source cell.

[0199] (3) First key update related parameter information, indicating parameter information used for deriving the key. Optionally, the first key update related parameter may be an NCC value, that is, the NCC value associated with deriving the key. The first key update related parameter is determined in step 305 and is transmitted to the target gNB together with the derived new key.

[0200] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0201] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0202] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0203] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0204] (5) Key update determination information, that is, the key update determination information associated with the target cell. When the UE accesses the target cell, the key update determination information is used as the second key update determination information to determine whether key update needs to be performed during cell switch. Optionally, if the key update determination information uses the gNB ID, the target gNB can also directly determine that the key update determination information is the target gNB ID, without providing it by the source gNB.

[0205] Optionally, there are two methods for the target cell to obtain the key update determination information of the candidate cell:

[0206] Method 1: obtain the key update determination information of the candidate cell in a candidate cell configuration stage and through step 301 or step 308.

[0207] Method 2: obtain the key update determination information of the candidate cell in a cell handover stage and through step 321.

[0208] In some embodiments, when the candidate cell is the target cell (the current serving cell), the key update determination information associated with the candidate cell is the key update determination information of the current serving cell, which will be used as the second key update determination information to determine whether key update needs to be performed for a subsequent handover. Therefore, in the message of step 301, 308 or 321:

[0209] - If no separate information for providing the key update determination information associated with the target cell is included (for example, information (5) is not included in step 321), the target gNB-CU may also obtain the key update determination information of the target cell (that is, the current serving cell) through the key update determination information of the candidate cells in the candidate cell information.

[0210] - If separate information for providing the key update determination information associated with the target cell is included (for example, information (5) is included in step 321), the target gNB-CU can directly use the separate information as the key update determination information of the target cell (that is, the current serving cell). The separate information is determined by the source gNB according to the key update determination information of the candidate cells in the candidate cell information.

[0211] In some embodiments, the candidate gNB1-CU determines the DU to which the target cell belongs according to the received target cell ID. If the target cell is located in the candidate gNB1-DU, the candidate gNB1-CU transmits a message to gNB1-DU, that is, step 322 is performed.

[0212] Step 322: the candidate gNB1-CU (target gNB-CU) transmits a message to the candidate gNB1-DU (target gNB-DU).

[0213] Optionally, the message may be a CU-DU cell switch notification (CU-DU CELL SWITCH NOTIFICATION) message, or other messages.

[0214] In some embodiments, the message may further include at least one of the following information:

[0215] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0216] (2) Candidate cell information, including information of one or more candidate cells. It provides information of all cells. The information of the candidate cells includes at least one of the following information:

[0217] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0218] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0219] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0220] (3) Key update determination information, that is, the key update determination information associated with the target cell. When the UE accesses the target cell, the key update determination information is used as the second key update determination information to determine whether key update needs to be performed during cell switch.

[0221] Step 323: the target gNB-DU (candidate gNB1-DU) detects a UE access process.

[0222] In some embodiments, when the UE receives the LTM cell switch command in step 318, it uses the configuration of the target cell and hands over to the target cell. If the UE does not have a valid TA value, random access procedure will be performed to the target cell. Otherwise, the UE performs a RACH-less LTM cell switch process. When the UE determines that the LTM cell switch has been successfully performed, that is, the UE accesses the target cell, step 324 is performed.

[0223] Step 324: the UE transmits a message to the target gNB-DU (candidate gNB1-DU).

[0224] Optionally, the message may be an RRC reconfiguration complete (RRCReconfigurationComplete) message, or other messages.

[0225] In some embodiments, the message may further include at least one of the following information:

[0226] (1) Key update related parameter information, which indicates parameter information for deriving the key used by the UE in the target cell. The key update related parameter may be an NCC value, indicating the NCC value associated with the key used by the UE, that is, the NCC value associated with the key used in the target cell.

[0227] Herein, the key update related parameter information is optional. If the LTM cell switch command received by the UE in step 318 contains a key update indication or a key update indication with a value of 1 (or true), the key update related parameter information will be included in the message (RRC reconfiguration message), otherwise it may not be included.

[0228] Step 325, the target gNB-DU (candidate gNB1-DU) transmits a message to the target gNB-CU (candidate gNB1-CU), and forwards the RRC reconfiguration complete message received in step 324 to the target gNB-CU.

[0229] Optionally, the message may be an uplink RRC message transfer (UL RRC MESSAGE TRANSFER) message, or other messages.

[0230] If the message may contain key update related parameter information, and if the key update related parameter is an NCC value, the target gNB-CU compares the NCC value with the NCC value obtained from the source gNB-CU in step 321:

[0231] - If they are not the same, an RRC connection release process will be triggered.

[0232] - If they are the same, it is considered that the UE accesses the target cell and transmits a message to AMF.

[0233] Step 326, the target gNB-CU (candidate gNB1-CU) transmits a message to AMF.

[0234] Optionally, the message may be a PATH SWITCH REQUEST message, or other messages.

[0235] The message may also include at least one of the following information:

[0236] (1) UE security capability, indicating the encryption algorithm supported by the UE.

[0237] Step 327: the AMF transmits a message to the target gNB-CU (candidate gNB1-CU).

[0238] Optionally, the message may be a PATH SWITCH REQUEST ACKNOWLEDGE message, or other messages.

[0239] When the AMF receives the PATH SWITCH REQUEST message in step 326, optionally, the AMF will add 1 to its locally saved NCC value to obtain a new NCC value, and calculate a new Next Hop (NH) value (the NH and the NCC are corresponding to each other), and transmit the recalculated {NH, NCC} pair to the target gNB.

[0240] The message may also include at least one of the following information:

[0241] (1) Security Context, which includes at least one of the following information:

[0242] - NCC parameter (Next Hop Chaining Counter).

[0243] - NH parameter (Next Hop, NH).

[0244] (2) New Security Context Indicator, which is used to indicate whether there is an initial key update.

[0245] Herein,

[0246] If the message contains a New Security Context Indicator which is of a value of "true", the target gNB-CU transmits a message to the UE, indicating the UE to perform initial key update, that is, steps 328a-328d are performed.

[0247] If the message does not contain a New Security Context Indicator, after receiving the message, the target gNB-CU saves the received new {NH, NCC} pair for a further handover (or called a subsequent handover) and deletes the currently stored unused {NH, NCC} pair. The new {NH, NCC} pair will be used for obtaining the key of user plane service and RRC signaling message and generating encryption parameters during a subsequent handover. In this case, it is not necessary to perform steps 328a-328d, but directly proceed to step 329a.

[0248] Step 328a: the target gNB-CU (candidate gNB1-CU) transmits a message to the target gNB-DU (candidate gNB1-DU) to indicate to perform key update.

[0249] Optionally, the message may be a downlink RRC message transfer (DL RRC MESSGE TRANSFER) message, or other messages.

[0250] The message may also include at least one of the following information:

[0251] (1) RRC Reconfiguration message, an RRC reconfiguration (RRCReconfiguration) message transmitted to the UE.

[0252] Step 328b: the target gNB-DU (candidate gNB1-DU) transmits a message to the UE and forwards the message received in step 328a to the UE.

[0253] Optionally, the message may be an RRCReconfiguration message, or other messages. The message may also include at least one of the following information:

[0254] (1) Key set change indicator (keySetChangeIndicator).

[0255] If the UE receives a message in which a key set change indicator is included and the key set change indicator is set to "true", the UE performs key update based on an AMF key (KAMF key), derives a new initial KgNB, and sets the NCC value to 0.

[0256] Step 328c: the UE transmits a message to the target gNB-DU, indicating that RRC reconfiguration is completed.

[0257] Optionally, the message may be an RRC reconfiguration complete (RRCReconfigurationComplete) message, or other messages.

[0258] Step 328d, the target gNB-DU transmits a message to the target gNB-CU, and forwards the message received in step 328c to gNB-CU.

[0259] Optionally, the message may be an uplink RRC message transfer (UL RRC MESSAGE TRANSFER) message, or other messages.

[0260] Step 329a: the target gNB-CU (candidate gNB1-CU) transmits a message to the target gNB-DU (candidate gNB1-DU). The target gNB-CU provides the target gNB-DU with related information of key update for a subsequent LTM cell handover.

[0261] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0262] The message may also include at least one of the following information:

[0263] (1) First key update related parameter information. When the target gNB-DU determines a next target cell for UE handover and needs to update the key, it indicates the UE to update the key, and transmits the first key update related parameter information to the UE. Optionally, the first key update related parameter may be an NCC value. The target gNB-CU transmits the NCC value received from the AMF to the target gNB-DU. When the target gNB-DU determines a next target cell for UE handover, if the key needs to be updated, the NCC value is transmitted to the UE. Optionally, the target gNB-DU may be transmitted to the UE through an LTM cell switch command, as in step 318.

[0264] Step 329b: the target gNB-DU (candidate gNB1-DU) transmits a feedback message to the target gNB-CU (candidate gNB1-CU).

[0265] Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages.

[0266] Embodiment 2 gives another method for key update under an LTM handover mode.

[0267] In Embodiment 2, in an LTM candidate cell configuration stage, the network side provides the key update determination information and key update related parameter information to the UE. When the UE receives an LTM cell switch command, it determines whether the key needs to be updated according to the key update determination information, and uses the key update related parameter to perform key update. The specific method is as follows.

[0268] Step 400: the UE transmits a message to the source gNB-CU.

[0269] Optionally, the message contains a measurement result.

[0270] The source gNB-CU may select candidate cells for the LTM for the UE according to the measurement result and / or load condition of the cells.

[0271] Step 400a: the source gNB-CU transmits a message to AMF, indicating that the UE uses an LTM mode to perform cell handover.

[0272] Optionally, the message may be a HANDOVER REQUIRED message, or other messages.

[0273] Step 400b, the AMF transmits a message (which may be called a fifth message herein) to the source gNB-CU. When performing LTM cell handover, if key update needs to be performed, the message provides related parameter information for the key update.

[0274] Optionally, the message may be a HANDOVER COMMAND message, or other messages.

[0275] The message may also include at least one of the following information:

[0276] (1) Second key update related parameter information, which may also be referred to as a second parameter used for key update herein. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC parameter values, that is, an NCC parameter value list (also called an NCC parameter list, or an NCC list or an NCC value list), or other parameters. The NCC parameter list sequentially contains one or more NCC parameter values.

[0277] (2) Third key update related parameter information, which may also be called a third parameter used for key update herein. When performing LTM handover, if key update needs to be performed, the third key update related parameter information is used for key update, that is, for deriving a new key. The third key update related parameter may be one or more {NH, NCC} pairs (that is, a {NH, NCC} pair list, which may also be called a {NH, NCC} parameter pair list), or other parameters. The {NH, NCC} parameter pair list sequentially contains one or more {NH, NCC} parameter pair values.

[0278] Herein, if the second key update related parameter is an NCC list and the third key update related parameter information is an {NH, NCC} pair list, then the order and values of NCCs in the NCC list are the same as the order and values in the {NH, NCC} pair list.

[0279] When the LTM handover is triggered, if the key needs to be updated, the UE may select the first unused NCC value from the NCC list in order (that is, according to the ranking order of NCC values in the NCC list), and determine the NH corresponding to the NCC, and then derive a new key. The gNB may select the first unused {NH, NCC} pair from the list of {NH, NCC} pairs, determine an NCC and the NH value corresponding to the NCC, and then derive a new key.

[0280] If the message contains the second key update related parameter information, the source gNB-CU directly includes the second key update related parameter information in the message (RRC reconfiguration message) and transmits it to the UE through steps 410 and 411. Otherwise, the source gNB-CU generates second key update related parameter information based on the received third key update related parameter information, and includes the second key update related parameter information in the message (RRC reconfiguration message) and transmits it to the UE through steps 410 and 411. Here, for the convenience of description, the related parameters used for key update transmitted to the UE may also be called a sixth parameter used for key update or a second parameter used for key update. In the embodiments of the present disclosure, in terms of the content, the sixth parameter or the second parameter may be or include the above-mentioned second key update related parameter received by the gNB-CU or the second key update related parameter information obtained from the third key update related parameter information, etc.

[0281] Step 401 is the same as step 301. For details, please refer to step 301, which will not be repeated here.

[0282] Step 402: the candidate gNB1-CU transmits a message to the candidate gNB1-DU.

[0283] Optionally, the candidate gNB1-CU uses the message to request the candidate gNB1-DU for candidate cells for LTM handover and performs resource allocation.

[0284] Optionally, the message may be a UE CONTEXT SETUP REQUEST message, or other messages.

[0285] The message may also include at least one of the following information:

[0286] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0287] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0288] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate identifier (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0289] (4) Candidate cell information, including information of one or more candidate cells. It provides information of candidate cells. The information of the candidate cells includes at least one of the following information:

[0290] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0291] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0292] Steps 403-404 are the same as steps 303-304. For details, please refer to steps 303-304, which will not be repeated here.

[0293] If there is an LTM candidate cell in the source gNB-DU, steps 404a and 404b will be performed to complete the corresponding candidate cell configuration. Optionally, the source cell may also serve as an LTM candidate cell.

[0294] Steps 404a-404b are the same as steps 304a-304b. For details, please refer to steps 304a-304b, which will not be repeated here.

[0295] Step 405a: the source gNB-CU transmits a message to AMF, indicating that the UE uses an LTM mode to perform cell handover.

[0296] Optionally, the message may be a HANDOVER REQUIRED message, or other messages.

[0297] Step 405b: AMF transmits a message to the source gNB-CU. When performing LTM cell handover, if key update needs to be performed, the message provides related parameter information for the key update. For details, please refer to the content in step 400b, which will not be repeated here.

[0298] Herein, steps 405a-405b have the same function as steps 400a-400b, that is, to obtain the related parameters provided by AMF for key update during cell handover. Steps 405a-405b and 400a-400b may be used as two methods to obtain the related parameters for the key update. The source gNB-CU may select to perform steps 405a-405b (that is, method 1) or steps 400a-400b (that is, method 2).

[0299] Step 406: the source gNB-CU transmits a message to the source gNB-DU.

[0300] Optionally, the source gNB-CU uses the message to provide the information of the candidate cells to the source gNB-DU.

[0301] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0302] Optionally, the message may also include at least one of the following information:

[0303] (1) Candidate cell information, including information of one or more candidate cells. It provides information of candidate cells. The information of the candidate cells includes at least one of the following information:

[0304] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0305] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0306] The source gNB-CU receives information of each candidate cell that accepts the request through step 404. The source gNB-CU configures key update determination information for the source cell. If the source cell is an LTM candidate cell, the key update determination information of the source cell will also be included in the information of the candidate cells as key update determination information of a candidate cell. The key update determination information of the source cell and the information of each candidate cell (including the key update determination information) are transmitted to the UE (through steps 410 and 411).

[0307] Step 407 is the same as step 307 which will not be repeated here.

[0308] In steps 408-409, the source gNB-CU transmits the newest information of all candidate cells to each candidate cell in step 408. In steps 401-404, there may be some changes in the LTM candidate cells selected by the source gNB-CU. Optionally, requests for some candidate cells are rejected, or configuration parameters of candidate cells are increased, or configuration parameters of candidate cells are updated. Optionally, the source cell may also serve as an LTM candidate cell.

[0309] Steps 408-409 are the same as steps 308-309, and will not be repeated here.

[0310] Step 410: the source gNB-CU transmits a downlink RRC message transfer (DL RRC MESSAGE TRANSFER) message or other messages to the source gNB-DU. The message may also include at least one of the following information:

[0311] (1) RRC Reconfiguration message, an RRC reconfiguration (RRCReconfiguration) message transmitted to the UE.

[0312] Step 411: the source gNB-DU transmits an RRCReconfiguration message (which may be called a seventh message herein) to the UE. The source gNB-DU forwards the RRC reconfiguration message received in step 410 to the UE. It contains configuration information of all LTM candidate cells. The message may also include at least one of the following information:

[0313] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0314] - LTM candidate ID, indicating an LTM candidate configuration, which is corresponding to an LTM configuration ID and is associated with (or corresponding to) an LTM candidate cell.

[0315] - LTM candidate physical cell ID (LTM candidate PCI), indicating a physical cell ID of the candidate cell corresponding to (or associated with) the LTM candidate ID.

[0316] - SSB configuration information of LTM, indicating time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0317] - Key update determination information, the key update determination information associated with the LTM candidate ID. During cell switch, the key update determination information is used to determine whether key update needs to be performed. Herein, the LTM candidate ID is associated with the LTM candidate cell.

[0318] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0319] (2) Second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, or other parameters. The NCC value list sequentially contains one or more NCC parameter values.

[0320] (3) Key update determination information, which is key update determination information associated with the source cell (serving cell). During cell switch, the key update determination information may be used as the second key update determination information to determine whether the key update needs to be performed.

[0321] The UE receives the message and stores the information in the message. The second key update related parameter information therein will be used to derive a new key during subsequent cell switch.

[0322] Steps 412-416 are the same as steps 312-316. For details, please refer to steps 312-316, which will not be repeated here.

[0323] Step 417: the source gNB-DU transmits a message to the UE, indicating the UE to perform cell switch. Optionally, the message may be an LTM Cell Switch Command. The message is transmitted through MAC CE. The message may also include at least one of the following information:

[0324] (1) Target Configuration ID, which indicates an LTM configuration ID corresponding to a target cell. The source gNB-DU determines the Target Configuration ID corresponding to the target cell according to the candidate cell information obtained in step 306.

[0325] (2) Timing Advance Command, which indicates whether a TA value of the target cell is valid and / or indicates a TA (Timing Advance) value of the target cell.

[0326] (3) TCI related information, including TCI state ID and UL TCI state ID.

[0327] (4) Random Access Preamble index.

[0328] (5) SS / PBCH index.

[0329] (6) PRACH Mask index.

[0330] The UE receives the message (LTM cell switch command) and determines whether the key update needs to be performed and to perform key update. The determination method is as follows: the UE determines a target cell according to the Target Configuration ID, so as to determine the key update determination information associated with the target cell and serve it as the first key update determination information. The key update determination information associated with the source cell (serving cell) is served as the second key update determination information. According to the first key update determination information and the second key update determination information, it is determined whether the key needs to be updated. For the description of the method for determining whether the key needs to be updated, please refer to the description in "Method for key update determination", which is not repeated here. Herein, the key update determination information associated with the target cell and the source cell is obtained by the UE in step 411.

[0331] If it is determined that key update needs to be performed, the UE determines a key derivation method and derives a new key. The UE derives a new key according to the second key update related parameter received in step 411. Optionally, if the second key update related parameter is an NCC list, the UE will select the first unused NCC from the NCC list in order to derive a new key. The derived new key will be used for the target cell.

[0332] Step 418: the source gNB-DU transmits a message to the source gNB-CU, indicating the source gNB-DU to transmit an LTM cell switch command to the UE.

[0333] Optionally, the message may be a DU-CU cell switch notification (DU-CU CELL SWITCH NOTIFICATION) message, or other messages.

[0334] The message may also include at least one of the following information:

[0335] (1) Target cell ID, which indicates the identification of the target cell of the UE. The cell ID may be a CGI, or other identifiers.

[0336] (2) TCI State ID.

[0337] Step 419: key update is determined. The source gNB-CU determines whether the key needs to be updated, and if so, derives a new key. The source gNB-CU determines the first key update determination information according to the key update determination information associated with the target cell, and determines the second key update determination information according to the key update determination information associated with the serving cell (source cell). The source gNB-CU determines whether the key needs to be updated according to the first key update determination information and the second key update determination information. For the description of the method for determining whether the key needs to be updated, please refer to the description in "Method for key update determination", which is not repeated here.

[0338] If it is determined that key update needs to be performed, the source gNB-CU determines a key derivation method and derives a new key. The source gNB-CU derives a new key according to a third key update related parameter obtained from AMF. Optionally, if the third key update related parameter is a {NH, NCC} pair list, the source gNB-CU will select the first unused {NH, NCC} pair (or the first unused NCC) from the {NH, NCC} pair list in order to derive a new key. The source gNB-CU transmits the derived new key and the NCC value associated with the new key to the target gNB.

[0339] Step 420, the source gNB-CU transmits a message (which may be referred to as a sixth message herein) to the target gNB. If the target cell belongs to the candidate gNB1, the source gNB-CU transmits a message to the candidate gNB1 (or the candidate gNB1-CU), indicating to the target gNB that the source gNB transmits an LTM cell switch command to the UE to handover to the target gNB (candidate gNB1).

[0340] Optionally, the message may be a source CU-target CU cell switch notification (Source CU-target CU CELL SWITCH NOTIFICATION) message or other messages.

[0341] The message may also include at least one of the following information:

[0342] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0343] (2) Key information, indicating the key KgNBused by the target cell. The key is the new key KgNB* derived by the source cell (source gNB) in step 419.

[0344] (3) First key update related parameter information, which indicates the parameter information used for deriving the key (also referred to as a fourth parameter used for key update or a fourth parameter associated with a new key herein). Optionally, the first key update related parameter may be an NCC value, that is, the NCC value associated with deriving the key. The first key update related parameter is the NCC value determined in step 419.

[0345] (4) Third key update related parameter information. When performing LTM handover, if key update needs to be performed, the third key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the third key update related parameter may be one or more {NH, NCC} pairs, or other parameters. (where the source gNB-CU deletes the used {NH, NCC} pairs from the list of {NH, NCC} pairs, or indicates which NCC values have been used, or indicates which {NH, NCC} pairs have been used). Herein, the {NH, NCC} pair list with the used {NH, NCC} pairs deleted may also be called a fifth parameter used for key update.

[0346] (5) Candidate cell information, including information of one or more candidate cells. It provides information of candidate cells. The information of the candidate cells includes at least one of the following information:

[0347] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0348] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0349] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0350] (6) Key update determination information, that is, the key update determination information associated with the target cell. When the UE accesses the target cell, the key update determination information is used as the second key update determination information to determine whether key update needs to be performed during cell switch. Optionally, if the key update determination information uses the gNB ID, the target gNB can also directly determine that the key update determination information is the target gNB ID, without providing it by the source gNB.

[0351] Herein, the third key update related parameter information is provided to the target gNB (target gNB-CU) for deriving a new key when the target cell (target gNB) performs a subsequent LTM handover. If the third key update related parameter information is a list of {NH, NCC} pairs, the target cell will sequentially select the first unused {NH, NCC} pair (or the first unused NCC) from the list of {NH, NCC} pairs for deriving a new key.

[0352] Optionally, there are two methods for the target cell to obtain the key update determination information of the candidate cell:

[0353] Method 1: obtain the key update determination information of the candidate cell in a candidate cell configuration stage and through step 401 or step 408.

[0354] Method 2: obtain the key update determination information of the candidate cell in a cell handover stage and through step 420.

[0355] When the candidate cell is the target cell (the current serving cell), the key update determination information associated with the candidate cell is the key update determination information of the current serving cell, which will be used as the second key update determination information to determine whether key update needs to be performed for a subsequent handover. Therefore, in the message of step 408 or 420:

[0356] - If no separate information for providing the key update determination information associated with the target cell is included (for example, information (6) is not included in step 420), the target gNB-CU may also obtain the key update determination information of the target cell (that is, the current serving cell) through the key update determination information of the candidate cells in the candidate cell information.

[0357] - If separate information for providing the key update determination information associated with the target cell is included (for example, information (6) is included in step 420), the target gNB-CU can directly use the separate information as the key update determination information of the target cell (that is, the current serving cell). The separate information is determined by the source gNB according to the key update determination information of the candidate cells in the candidate cell information.

[0358] The candidate gNB1-CU determines the DU to which the target cell belongs according to the received target cell ID. If the target cell is located in the candidate gNB1-DU, the candidate gNB1-CU transmits a message to gNB1-DU, that is, step 421 is performed.

[0359] Step 421: the candidate gNB1-CU (target gNB-CU) transmits a message to the candidate gNB1-DU (target gNB-DU).

[0360] Optionally, the message may be a CU-DU cell switch notification (CU-DU CELL SWITCH NOTIFICATION) message, or other messages.

[0361] The message may also include at least one of the following information:

[0362] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0363] (2) Candidate cell information, including information of one or more candidate cells. It provides information of candidate cells. The information of the candidate cells includes at least one of the following information:

[0364] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0365] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0366] Step 422: the target gNB-DU (candidate gNB1-DU) detects a UE access process.

[0367] When the UE receives an LTM cell switch command in step 417, it uses the configuration of the target cell and hands over to the target cell. If the UE does not have a valid TA value, random access procedure will be performed to the target cell. Otherwise, the UE performs a RACH-less LTM cell switch process. When the UE determines that the LTM cell switch has been successfully performed, that is, the UE accesses the target cell, step 423 is performed.

[0368] After the UE accesses the target cell, it retains the configuration information of the LTM candidate cells (the LTM candidate cell is associated with the LTM candidate ID) received in step 411, and uses the key update determination information associated with the target cell as the second key update determination information to determine whether the key needs to be updated during a subsequent cell handover.

[0369] Steps 423-424 are the same as steps 324-325. Please refer to steps 324-325 for details, and they will not be repeated here.

[0370] Step 425, the target gNB-CU (candidate gNB1-CU) transmits a message (also referred to as an eighth message herein) to the AMF.

[0371] Optionally, the message may be a PATH SWITCH REQUEST message, or other messages.

[0372] The message may also include at least one of the following information:

[0373] (1) LTM handover indication information, which indicates that the cell of the UE is adjusted by adopting an LTM handover mode.

[0374] (2) Candidate cell information list, including information of one or more candidate cells. The information of the candidate cells includes at least one of the following information:

[0375] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0376] (3) Key related information. The key related information includes at least one of the following information:

[0377] - Key information, the current key of the UE target cell (target gNB).

[0378] - NCC value, which is the NCC value associated with the current key of the UE target cell (target gNB) (also referred to as a fourth parameter used for deriving the current (new) key herein).

[0379] The key related information is transmitted to AMF, and the AMF can determine which parameters of the second key update related parameter information and / or the third key update related parameter information have been used. Optionally, if the second key update related parameter is an NCC list, the AMF can determine which NCC values have been used. Optionally, if the third key update related parameter information is a list of {NH, NCC} pairs, the AMF can determine which {NH, NCC} pairs have been used.

[0380] Step 426, the AMF transmits a message (also referred to as a ninth message herein) to the target gNB-CU (candidate gNB1-CU).

[0381] Optionally, the message may be a PATH SWITCH REQUEST ACKNOWLEDGE message, or other messages.

[0382] The message may also include at least one of the following information:

[0383] (1) Update indication of the second key update related parameter information, which indicates the second key update related parameter information.

[0384] (2) Second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters.

[0385] (3) Update indication of the third key update related parameter information, which indicates the third key update related parameter information.

[0386] (4) Third key update related parameter information. When performing LTM handover, if key update needs to be performed, the third key update related parameter information is used for key update, that is, for deriving a new key. The third key update related parameter may be one or more {NH, NCC} pairs (that is, a {NH, NCC} pair list, which may also be called a {NH, NCC} parameter pair list), or other parameters.

[0387] If the update indication of the second key update related parameter information exists, the second key update related parameter information provides new second key update related parameter information. The target gNB-CU transmits the new second key update related parameter information to the UE through steps 427a-427b.

[0388] If the update indication of the third key update related parameter information exists, the third key update related parameter information provides new third key update related parameter information. The target gNB-CU stores the new third key update related parameter information, and deletes the third key update related parameter information obtained from the source gNB-CU, and transmits the new second key update related parameter information to the UE through steps 427a-427b. The second key update related parameter information may be provided by AMF or generated by the target gNB based on the received third key update related parameter information.

[0389] (5) Security Context, which includes at least one of the following information:

[0390] - NCC parameter (Next Hop Chaining Counter).

[0391] - NH parameter (Next Hop NH).

[0392] (6) New Security Context Indicator, which is used to indicate whether there is an initial key update. If the message may contain the New Security Context Indicator and the value is "true".

[0393] Herein, the third key update related parameter information is provided to the target gNB (target gNB-CU) for deriving a new key when the target gNB performs a subsequent LTM handover. There are two methods to provide the third key update related parameter information to the target gNB:

[0394] - Method 1 for providing the third key update related parameter information: the third key update related parameter information is provided by the source gNB to the target gNB. That is, in the process of cell handover, the source gNB provides the third key update related parameter information to the target gNB through step 420. If the AMF updates the third key update related parameter, it transmits the new third key update related parameter information to the target gNB through step 426, and indicates that the third key update related parameter information is updated parameter information.

[0395] - Method 2 for providing the third key update related parameter information: the third key update related parameter information is provided by the AMF to the target gNB. That is, after the UE accesses the target cell, the AMF provides the third key update related parameter information to the target gNB in a path switch process (through step 426). If the AMF updates the third key update related parameter information, it transmits new third key update related parameter information to the target gNB and indicates that the third key update related parameter information is updated parameter information.

[0396] Herein, among the two methods, optionally, the third key update related parameter information provided to the target gNB may only contain a list of unused {NH, NCC} pairs, that is, the used {NH, NCC} pairs may be deleted.

[0397] Herein, if the message contains a New Security Context Indicator which is of a value of "true", after receiving the message, the target gNB-CU transmits a message to indicate the UE to perform initial key update, that is, to perform steps 427a and 427b.

[0398] If the message does not contain a New Security Context Indicator, after receiving the message, the target gNB-CU saves the received third key update related parameter information for a further handover (or called a subsequent handover). The third key update related parameter information will be used for obtaining the key of user plane service and RRC signaling message and generating encryption parameters during a subsequent handover.

[0399] If the message may contain the update indication of the second key update related parameter information and / or the update indication of the third key update related parameter information and / or the New Security Context Indicator with a value of "true", the target gNB will trigger an RRC reconfiguration process, that is, perform steps 427a and 427b to indicate the UE to update the second key update related parameter information and / or perform initial key update.

[0400] Step 427a: the target gNB-CU (candidate gNB1-CU) transmits a message to the target gNB-DU (candidate gNB1-DU).

[0401] Optionally, the message may be a downlink RRC message transfer (DL RRC MESSGE TRANSFER) message, or other messages.

[0402] The message may also include at least one of the following information:

[0403] (1) RRC Reconfiguration message, an RRC reconfiguration (RRCReconfiguration) message transmitted to the UE.

[0404] Step 427b: the target gNB-DU (candidate gNB1-DU) transmits a message to the UE and forwards the message received in step 427a to the UE.

[0405] Optionally, the message may be an RRCReconfiguration message, or other messages.

[0406] The message may also include at least one of the following information:

[0407] (1) Update indication of the second key update related parameter information, which indicates second key update related parameter information.

[0408] (2) Second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters. If the update indication of the second key update related parameter information exists, the second key update related parameter information provides a new second key update related parameter. The UE stores the new second key update related parameter, and deletes the existing stored second key update related parameter.

[0409] (3) Key set change indicator (keySetChangeIndicator). If the key set change indicator is set to "true", the UE performs key update based on an AMF key (KAMF key), derives a new initial KgNB, and sets the NCC value to 0.

[0410] Steps 427c-427d are the same as steps 328c-328d, and will not be repeated here.

[0411] Embodiment 3 gives another method for key update under an LTM handover mode.

[0412] The basic idea of Embodiment 3 and Embodiment 2 is the same, but a difference is that the AMF only provides the second key update related parameter information to the UE, and does not need to transmit the complete second key update related parameter information to gNB (including the source gNB and the target gNB), but only provides part of the parameter information to the gNB for deriving a new key for a subsequent handover. Therefore, Embodiment 3 will reuse the flowchart of Embodiment 2, that is, FIG. 4A. Only the differences between Embodiment 3 and Embodiment 2 will be described below. The differences between Embodiment 3 and Embodiment 2 mainly lie in step 400b or 405b and steps 425-426. The specific description is as follows:

[0413] The step 400a (or 405a) of Embodiment 3 is the same as the step 400a (or 405a) of Embodiment 2, and will not be repeated here.

[0414] In step 400b (or 405b) of Embodiment 3, the AMF transmits a message to the source gNB-CU. When performing LTM cell handover, if key update needs to be performed, the message provides related parameter information for the key update.

[0415] Optionally, the message may be a HANDOVER COMMAND message, or other messages.

[0416] The message may also include at least one of the following information:

[0417] (1) A key update related information container, which contains key update related information transmitted by the AMF to the UE. The source gNB receives the key update related information container and transmits it to the UE without parsing the container content. The key update related information may be second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters.

[0418] (2) Security Context, which provides parameters for deriving a key for the next handover:

[0419] - NCC parameter (Next Hop Chaining Counter).

[0420] - NH parameter (Next Hop NH).

[0421] Herein, the NCC value in the security context is the same as the first unused NCC value in the NCC list contained in the key update related information container. Herein, there is a corresponding relationship between NH parameters and NCC parameters in the security context.

[0422] When the key needs to be updated during a cell handover, the current serving cell (or the gNB-CU of the current serving cell (the source gNB or target gNB)) of the UE determines a key derivation method.

[0423] - If the message may contain the security context, gNB-CU will derive a new key according to key derivation method 2, and transmit the new key and the associated NCC value to the target gNB (through step 420).

[0424] - If the message does not contain the security context, gNB-CU will derive a new key according to key derivation method 1, and transmit the new key and the associated NCC value to the target gNB (through step 420).

[0425] In step 411 of Embodiment 3, the source gNB-DU transmits an RRCReconfiguration message to the UE. The source gNB-DU forwards the RRC reconfiguration message received in step 410 to the UE. The message may also include at least one of the following information:

[0426] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0427] - LTM candidate ID, indicating an LTM candidate configuration, which is corresponding to an LTM configuration ID and is associated with (or corresponding to) an LTM candidate cell.

[0428] - LTM candidate physical cell ID (LTM candidate PCI), indicating a physical cell ID of the candidate cell corresponding to (or associated with) the LTM candidate ID.

[0429] - SSB configuration information of LTM, indicating time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0430] - Key update determination information, that is, the key update determination information associated with the LTM candidate ID (associated with the LTM candidate cell). During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0431] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0432] (2) A key update related information container, which contains key update related information transmitted by the AMF to the UE. The key update related information may be second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters.

[0433] (3) Key update determination information, which is key update determination information associated with the source cell (serving cell). During cell switch, the key update determination information may be used as the second key update determination information to determine whether the key update needs to be performed.

[0434] The UE receives the message and stores the information in the message. Herein, the information in the key update related information container will be used to derive a new key in a subsequent cell switch.

[0435] In step 419 of Embodiment 3, key update is determined. The source gNB-CU determines whether the key needs to be updated, and if so, derives a new key. The source gNB-CU determines the first key update determination information according to the key update determination information associated with the target cell, and determines the second key update determination information according to the key update determination information associated with the serving cell (source cell). The source gNB-CU determines whether the key needs to be updated according to the first key update determination information and the second key update determination information. For the description of the method for determining whether the key needs to be updated, please refer to the description in "Method for key update determination", which is not repeated here.

[0436] If it is determined that key update needs to be performed, the source gNB-CU determines a key derivation method and derives a new key. The source gNB-CU determines the key derivation method according to the security context obtained from AMF in step 400b (or 405b) of Embodiment 3. See step 400b (or 405b) of Embodiment 3 for details.

[0437] In step 420 of Embodiment 3, the source gNB-CU transmits a message to the target gNB. If the target cell belongs to the candidate gNB1, the source gNB-CU transmits a message to the candidate gNB1 (or the candidate gNB1-CU), indicating to the target gNB that the source gNB transmits an LTM cell switch command to the UE to handover to the target gNB (candidate gNB1).

[0438] Optionally, the message may be a source CU-target CU cell switch notification (Source CU-target CU CELL SWITCH NOTIFICATION) message or other messages.

[0439] The message may also include at least one of the following information:

[0440] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0441] (2) Key information, indicating the key KgNBused by the target cell. The key is the new key KgNB* derived by the source cell (source gNB) in step 419.

[0442] (3) First key update related parameter information, indicating parameter information used for deriving the key. Optionally, the first key update related parameter may be an NCC value, that is, the NCC value associated with deriving the key. The first key update related parameter is the NCC value determined in step 419.

[0443] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0444] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0445] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0446] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0447] (5) Key update determination information, that is, the key update determination information associated with the target cell. When the UE accesses the target cell, the key update determination information is used as the second key update determination information to determine whether key update needs to be performed during cell switch. Optionally, if the key update determination information uses the gNB ID, the target gNB can also directly determine that the key update determination information is the target gNB ID, without providing it by the source gNB.

[0448] Step 425 of Embodiment 3 is the same as step 425 of Embodiment 2, and will not be repeated here. Herein, the AMF can determine the current key of the target cell and / or the NCC parameter for deriving the key (or the value of the NCC parameter associated with the current key) according to the obtained key related information.

[0449] In step 426 of Embodiment 3, the AMF transmits a message (also referred to as a ninth message herein) to the target gNB-CU (candidate gNB1-CU).

[0450] The AMF can determine which parameters of the second key update related parameter information and / or the third key update related parameter information have been used according to the key related information in step 425. Optionally, if the second key update related parameter is an NCC list and the third key update related parameter is a {NH, NCC} pair list, then the AMF can determine which NCC values have been used. The AMF sequentially selects the first unused NCC value and / or {NH, NCC} pair from the locally stored NCC list and / or {NH, NCC} pair list, determines the corresponding NH value according to the NCC, and transmits the NCC and NH as a recalculated {NH, NCC} pair to the target cell (target gNB) for a subsequent handover, and then derives a new key. The NCC value selected by the AMF is the same as the first unused NCC value in order in the NCC list stored on the UE side.

[0451] If the AMF updates the second key update related parameter information and / or the third key update related parameter information, it includes the generated new second key update related parameter information in a key update related information container and transmits the generated new second key update related parameter information to the target gNB, which forwards the generated new second key update related parameter information to the UE.

[0452] Optionally, the message may be a PATH SWITCH REQUEST ACKNOWLEDGE message, or other messages.

[0453] The message may also include at least one of the following information:

[0454] (1) Security Context, which provides related parameters for deriving the key:

[0455] - NCC parameter (Next Hop Chaining Counter).

[0456] - NH parameter (Next Hop NH).

[0457] (2) New Security Context Indicator.

[0458] (3) A key update related information container, containing key update related information transmitted to the UE. The source gNB receives the key update related information container and transmits it to the UE without parsing the container content. The key update related information may be second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters.

[0459] Herein, if the message may contain a New Security Context Indicator, then the security context is used to derive a new key, and the target gNB will perform step 427a, transmit an RRC reconfiguration message to the UE to indicate it to perform key update, and the updated key is used for the current target cell. If the message does not contain a New Security Context Indicator, the security context is used to derive a key for the next handover (the next target cell).

[0460] If the message may contain a key update related information container, that is, the AMF intends to transmit key update related information to the UE, the target gNB will perform step 427a, transmit an RRC reconfiguration message to the UE to indicate the UE to store new second key update related parameter information for key update in a subsequent cell switch.

[0461] Herein, if the message contains a key update related information container, the NCC value in the security context is the same as the first unused NCC value in order in the NCC list contained in the key update related information container. If the message does not contain a key update related information container, then the NCC value in the security context is the same as the first unused NCC value in order in the NCC list stored at the UE side. The NCC and NH in the security context are used to derive a new key when the target cell (target gNB) performs a subsequent handover.

[0462] Step 427a of Embodiment 3 is the same as step 427a of Embodiment 2.

[0463] In step 427b of Embodiment 3, the target gNB-DU (candidate gNB1-DU) transmits a message to the UE, and forwards the message received in step 427a to the UE.

[0464] Optionally, the message may be an RRCReconfiguration message, or other messages.

[0465] The message may also include at least one of the following information:

[0466] (1) A key update related information container, which contains key update related information transmitted by the AMF to the UE. The key update related information may be second key update related parameter information. When performing LTM handover, if key update needs to be performed, the second key update related parameter information is used for key update, that is, for deriving a new key. Optionally, the second key update related parameter may be one or more NCC values, that is, an NCC value list, which may also be called an NCC list, or other parameters.

[0467] (2) Key set change indicator (keySetChangeIndicator). If the key set change indicator is set to "true", the UE performs initial key update based on an AMF key (KAMFkey), derives a new initial KgNB, and sets the NCC value to 0.

[0468] If the message may contain a key update related information container, the UE stores information in the received key update related information container, and deletes the existing stored key update related information, for key update in a subsequent cell switch. If the key set change indicator is included and set to "true", the UE performs initial key update based on an AMF key (KAMFkey), derives a new initial KgNB, and sets the NCC value to 0.

[0469] Embodiment 4 gives another method for key update under an LTM handover mode.

[0470] The idea of the key updating method in Embodiment 4 is the same as that in Embodiment 1, but the difference is that the configuration of the key update determination information and the provision process of configuration information are different. Herein, Embodiment 4 adopts Configuration method 2 of key update determination information. Therefore, the flow of Embodiment 4 is the same as that of Embodiment 1. The description of Embodiment 4 will refer to the steps shown in the flow chart (FIG. 3) of Embodiment 1, only the steps different from those in Embodiment 1 will be described, and other steps please refer to the description in Embodiment 1.

[0471] When the candidate gNB receives a handover request transmitted by the source gNB, it determines the key update determination information configured for the requested LTM candidate cell, feeds back the determined key update determination information of the candidate cell to the source gNB and provides it to the candidate gNB-DU. This process involves the following steps.

[0472] Step 301: the source gNB-DU transmits a message to the candidate gNB-DU.

[0473] Optionally, the source gNB-CU uses the message to request one or more candidate cells from candidate gNB-CUs for LTM handover, and the candidate cells belong to one or more candidate gNB-CU. Optionally, the source gNB-CU may transmit one or more messages to the candidate gNBs to request different candidate cells.

[0474] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0475] The message may also include at least one of the following information:

[0476] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0477] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0478] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0479] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0480] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0481] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0482] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. The key update determination information is provided by the source gNB.

[0483] After the candidate gNB-CU determines the key update determination information of the requested candidate cell, it transmits the key update determination information of the requested candidate cell to the candidate gNB-DU (through step 302) and feeds it back to the source gNB through step 304.

[0484] Step 302: the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the candidate gNB1-DU (candidate gNB2-DU).

[0485] Optionally, the candidate gNB1-CU uses the message to request the candidate gNB1-DU for candidate cells for LTM handover and performs resource allocation.

[0486] Optionally, the message may be a UE CONTEXT SETUP REQUEST message, or other messages.

[0487] The message may also include at least one of the following information:

[0488] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0489] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0490] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0491] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0492] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0493] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0494] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed. The key update determination information is determined by the candidate gNB-CU.

[0495] Step 303: the candidate gNB1-DU (candidate gNB2-DU) transmits a feedback message to the candidate gNB1-CU (candidate gNB2-CU).

[0496] Optionally, the message may be a UE CONTEXT SETUP RESPONSE message, or other messages.

[0497] Step 304: the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the source gNB-CU.

[0498] Optionally, the candidate gNB1-CU (candidate gNB2-CU) uses the message to provide the information of the requested candidate cell to the source gNB-CU. Corresponding to step 301, the candidate gNB1-CU may feed back one or more messages to provide information of the requested candidate cells to the gNB-CU.

[0499] Optionally, the message may be a HANDOVER REQUEST ACKNOWLEDGE message, or other messages.

[0500] The message may also include at least one of the following information:

[0501] (1) Cell ID, indicating ID of the requested candidate cell, which may be the ID of the candidate cell requested in step 301. The cell ID may be a CGI (Cell Global ID) or other identifiers.

[0502] (2) LTM configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with an LTM candidate cell.

[0503] (3) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed. The key update determination information is determined by the candidate gNB-CU.

[0504] (4) SSB configuration information, indicating time and frequency information of SSB of the cell indicated by the cell ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0505] (5) Physical cell ID (PCI), indicating the physical cell ID of the cell indicated by the cell ID.

[0506] (6) A container from a candidate target base station to a source base station, for example, a Target NG-RAN node To Source NG-RAN node Transparent Container, which contains a HandoverCommand message therein, and the message contains LTM candidate configuration information of the cell indicated by the cell ID provided by the candidate target base station (candidate gNB-CU), including Cell Group configuration information, Radio Bearer (RB) configuration information and so on.

[0507] Step 306: the source gNB-CU transmits a message to the source gNB-DU.

[0508] The source gNB-CU transmits candidate cell information and key update determination information configured for the source cell to the source gNB-DU.

[0509] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0510] The message may also include at least one of the following information:

[0511] (1) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0512] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0513] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0514] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0515] (2) First key update related parameter information. During LTM handover, if key update needs to be performed, the first key update related parameter information is used for key update, that is, for deriving a new key. The first key update related parameter information is determined by the source gNB-CU in step 305. Optionally, the first key update related parameter may be an NCC value, that is, an NCC value associated with the derived new key. The NCC value is an NCC value determined by the source gNB-CU in step 305.

[0516] (3) Key update determination information, which is key update determination information associated with the source cell (serving cell). During cell switch, the key update determination information may be used as the second key update determination information to determine whether the key update needs to be performed.

[0517] Step 308: the source gNB transmits a message to the candidate gNB. The finally determined candidate cell information is provided to each candidate gNB (candidate cell). If the source cell is an LTM candidate cell, related information will be included in the candidate cell information.

[0518] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0519] The message may also include at least one of the following information:

[0520] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0521] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0522] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0523] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0524] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0525] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0526] - -Key update determination information, that is, the key update determination information associated with the LTM candidate cells.

[0527] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell.

[0528] Step 321: the source gNB-CU transmits a message to the target gNB. If the target cell belongs to the candidate gNB1, the source gNB-CU transmits a message to the candidate gNB1 (or the candidate gNB1-CU), indicating to the target gNB that the source gNB transmits an LTM cell switch command to the UE to handover to the target gNB (candidate gNB1).

[0529] Optionally, the message may be a source CU-target CU cell switch notification (Source CU-target CU CELL SWITCH NOTIFICATION) message or other messages.

[0530] The message may also include at least one of the following information:

[0531] (1) Target cell ID, which indicates the ID of the target cell for UE handover. The target cell ID may be a CGI or other identifiers.

[0532] (2) Key information, indicating the key KgNBused by the target cell. The key is the new key KgNB* derived by the source cell.

[0533] (3) First key update related parameter information, indicating parameter information used for deriving the key. Optionally, the first key update related parameter may be an NCC value, that is, the NCC value associated with deriving the key. The first key update related parameter is determined in step 305 and is transmitted to the target gNB together with the derived new key.

[0534] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0535] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0536] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0537] - Key update determination information. The key update determination information associated with the LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed.

[0538] (5) Key update determination information, that is, the key update determination information associated with the target cell. When the UE accesses the target cell, the key update determination information is used as the second key update determination information to determine whether key update needs to be performed during cell switch.

[0539] As in Embodiment 1, there are two methods for the target cell to obtain the key update determination information of the candidate cell:

[0540] Method 1: obtain the key update determination information of the candidate cell in a candidate cell configuration stage and through step 301 or step 308.

[0541] Method 2: obtain the key update determination information of the candidate cell in a cell handover stage and through step 321.

[0542] The method for determining the key update determination information of the target cell is described in step 321 of Embodiment 1, and will not be repeated here.

[0543] Other steps and description are the same as those in Embodiment 1. Please refer to the detailed description of other steps in Embodiment 1, which will not be repeated here.

[0544] Embodiment 5 gives another method for key update under an LTM handover mode.

[0545] The idea of the key updating method in Embodiment 5 is the same as that in Embodiment 2, but the difference is that the configuration method of key update determination information and the provision process of configuration information are different. Herein, Embodiment 5 adopts Configuration method 2 of key update determination information. Therefore, the flow of Embodiment 5 is the same as that of Embodiment 2. The description of Embodiment 5 will refer to the steps shown in the flow chart of Embodiment 2 (FIG. 4A), and only the steps different from those in Embodiment 2 will be described, and other steps please refer to the description in Embodiment 2.

[0546] Step 401: the source gNB-DU transmits a message to the candidate gNB-DU.

[0547] Optionally, the source gNB-CU uses the message to request one or more candidate cells from candidate gNB-CUs for LTM handover, and the candidate cells belong to one or more candidate gNB-CU. Optionally, the source gNB-CU may transmit one or more messages to the candidate gNBs to request different candidate cells.

[0548] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0549] The message may also include at least one of the following information:

[0550] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0551] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0552] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0553] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0554] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0555] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0556] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. The key update determination information is provided by the source gNB.

[0557] Step 404: the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the source gNB-CU.

[0558] Optionally, the candidate gNB1-CU (candidate gNB2-CU) uses the message to provide the information of the requested candidate cells to the source gNB-CU. Corresponding to step 401, the candidate gNB1-CU may feed back one or more messages to provide information of the requested candidate cells to the gNB-CU.

[0559] Optionally, the message may be a HANDOVER REQUEST ACKNOWLEDGE message, or other messages.

[0560] The message may also include at least one of the following information:

[0561] (1) Cell ID, indicating ID of the requested candidate cell, which may be the ID of the candidate cell requested in step 301. The cell ID may be a CGI (Cell Global ID) or other identifiers.

[0562] (2) LTM configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with an LTM candidate cell.

[0563] (3) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell. During cell switch, the key update determination information is used to determine whether key update needs to be performed. The key update determination information is determined by the candidate gNB-CU.

[0564] (4) SSB configuration information, indicating time and frequency information of SSB of the cell indicated by the cell ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0565] (5) Physical cell ID (PCI), indicating the physical cell ID of the cell indicated by the cell ID.

[0566] (6) A container from a candidate target base station to a source base station, for example, a Target NG-RAN node To Source NG-RAN node Transparent Container, which contains a HandoverCommand message therein, and the message contains LTM candidate configuration information of the cell indicated by the cell ID provided by the candidate target base station (candidate gNB-CU), including Cell Group configuration information, Radio Bearer (RB) configuration information and so on.

[0567] In some embodiments, the source gNB-CU receives information of each candidate cell that accepts the request through step 404, which includes the key update determination information of each candidate cell. The source gNB-CU configures key update determination information for the source cell. If the source cell is an LTM candidate cell, related information will be included in the candidate cell information. Herein, the key update determination information of the source cell will be used as the key update determination information of the candidate cell.

[0568] In some embodiments, the source gNB-CU transmits all candidate cell information (including the key update determination information) to each candidate cell (through step 408), and transmits the key update determination information of the source cell and the information of each candidate cell (including the key update determination information) to the UE (through steps 410 and 411). Herein, steps 410 and 411 refer to steps 410 and 411 in Embodiment 2, and are not repeated here.

[0569] Step 408: the source gNB transmits a message to the candidate gNB, to provide the finally determined candidate cell information to the candidate gNB (candidate cell).

[0570] For each candidate cell, the source gNB transmits a message to the candidate gNB, which may contain the information of the candidate cell and other candidate cells.

[0571] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0572] The message may also include at least one of the following information:

[0573] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0574] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0575] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0576] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0577] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0578] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0579] - Key update determination information, that is, the key update determination information associated with the LTM candidate cells.

[0580] (5) Key update determination information, that is, the key update determination information associated with the requested LTM candidate cell.

[0581] Other steps are the same as those in Embodiment 2. Please refer to the detailed description in Embodiment 2 and do not repeat them here.

[0582] Embodiment 6 gives another method for key update under an LTM handover mode.

[0583] The idea of the key updating method in Embodiment 6 is the same as that in Embodiment 3, but the difference is that the configuration method of key update determination information and the provision process of configuration information are different. Herein, Embodiment 6 adopts Configuration method 2 of key update determination information. Therefore, the flow of Embodiment 6 is the same as that of Embodiment 3. The description of Embodiment 6 will refer to the steps shown in the flow chart (FIG. 4a) of Embodiment 3, and only the steps different from those in Embodiment 3 will be described, and other steps will be described with reference to Embodiment 3.

[0584] Embodiment 6 is different from Embodiment 3 in steps 401, 404 and 408. Steps 401, 404 and 408 of Embodiment 6 are the same as those of Embodiment 5. The detailed description can be found in Embodiment 5, which will not be repeated here.

[0585] III. Method for realizing Layer 2 (L2) reset indication

[0586] When performing LTM cell switch, there are two cases for L2 processing:

[0587] Case 1: UE and base station perform MAC reset, RLC re-establishment and PDCP re-establishment or PDCP data recovery.

[0588] Case 2: UE and base station perform MAC reset, and not perform RLC re-establishment and PDCP data recovery.

[0589] Case 1 may be called to perform (or execute) an L2 reset process, and Case 2 may be called not to perform (or not to execute) an L2 reset process.

[0590] Whether the UE performs L2 reset during an LTM cell switch will be decided based on L2 reset indication information. The L2 reset indication information is related to a cell, and optionally, the L2 reset indication information of a candidate cell (or related to a candidate cell) is the L2 reset identification of the candidate cell (which may be identified by LTM-NoResetID), and the L2 reset indication information of a source cell (serving cell) (or related to a source cell) is the L2 reset identification of the source cell (which may be identified by LTM-ServingCellNoResetID). When a candidate cell serves as a target cell, the L2 reset indication information of the candidate cell is used as the L2 reset indication information of the new source cell (serving cell).

[0591] Method for determining whether to perform an L2 reset process:

[0592] If the L2 reset identification of a selected target cell is the same as the L2 reset identification of the source cell, an L2 reset process needs not to be performed. Otherwise, an L2 reset process needs to be performed.

[0593] The L2 reset indication information is transmitted to the UE by the base station (or network).

[0594] Embodiments 7-8 respectively provide methods for realizing L2 reset indication under an LTM handover mode.

[0595] Embodiment 7 gives a method for realizing L2 reset indication under an LTM handover mode.

[0596] In Embodiment 7, each candidate gNB provides L2 reset indication information related to the candidate cells, which is uniformly configured by the source gNB.

[0597] The flow of Embodiment 7 is shown in FIG. 4B. Steps 500-512 are the same as steps 300-312 in Embodiment 1, that is, configuring LTM candidate cells for the UE. In the description of the steps, only the information and description related to the configuration of L2 reset indication information will be described, and other information and descriptions refer to Embodiment 1, and will not be repeated here.

[0598] Step 500 is the same as step 300. For details, please refer to step 300 of Embodiment 1, which will not be repeated here.

[0599] Step 501 is the same as step 301, which will not be repeated here.

[0600] The candidate gNB configures L2 reset indication information of the candidate cells, and provides the L2 reset indication information of the candidate cells to the candidate gNB-DU and the source gNB.

[0601] Step 502: the candidate gNB1-CU transmits a message to the candidate gNB1-DU.

[0602] Optionally, the candidate gNB1-CU uses the message to request the candidate gNB1-DU for candidate cells for LTM handover and performs resource allocation.

[0603] Optionally, the message may be a UE CONTEXT SETUP REQUEST message, or other messages.

[0604] In some embodiments, the message may further include at least one of the following information:

[0605] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0606] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0607] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0608] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0609] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0610] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0611] (5) L2 reset indication information of the candidate cell, that is, L2 reset indication information related to the requested LTM candidate cell. That is, the L2 reset identification of the requested candidate cell.

[0612] Step 503 is the same as step 303, which will not be repeated here.

[0613] Step 504, the candidate gNB1-CU (candidate gNB2-CU) transmits a message to the source gNB-CU.

[0614] Optionally, the candidate gNB1-CU (candidate gNB2-CU) uses the message to provide the information of the requested candidate cell to the source gNB-CU.

[0615] Optionally, the message may be a HANDOVER REQUEST ACKNOWLEDGE message, or other messages.

[0616] In some embodiments, the message may further include at least one of the following information:

[0617] (1) Cell ID, indicating an ID of a requested LTM candidate cell, which may be the ID of the candidate cell requested in step 301. The cell ID may be a CGI (Cell Global ID) or other identifiers.

[0618] (2) LTM configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with an LTM candidate cell.

[0619] (3) gNB ID, which indicates an ID of the gNB to which the cell indicated by the LTM cell ID belongs.

[0620] (4) SSB configuration information, indicating time and frequency information of SSB of the cell indicated by the cell ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0621] (5) Physical cell ID (PCI), indicating the physical cell ID of the cell indicated by the cell ID.

[0622] (6) A container from a candidate target base station to a source base station, for example, a Target NG-RAN node To Source NG-RAN node Transparent Container, which contains a HandoverCommand message therein, and the message contains LTM candidate configuration information of the cell indicated by the cell ID provided by the candidate target base station (candidate gNB-CU), including Cell Group configuration information, Radio Bearer (RB) configuration information and so on.

[0623] (7) L2 reset indication information of the candidate cell, that is, L2 reset indication information related to the requested LTM candidate cell. That is, the L2 reset identification of the requested candidate cell.

[0624] In some embodiments, if there is an LTM candidate cell in the source gNB-DU, steps 505a and 505b will be performed to complete the corresponding candidate cell configuration. Optionally, the source cell may also serve as an LTM candidate cell.

[0625] Step 505a: the source gNB-CU transmits a message to the source gNB-DU. The source gNB-CU uses the message to request candidate cells from the source gNB-DU for LTM handover, and provides the configured L2 reset indication information of the candidate cells.

[0626] Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages. Refer to step 502 for the content of the message, which will not be repeated here.

[0627] Step 505b: the source gNB-DU transmits a message to the source gNB-CU. The source gNB-DU uses the message to provide information of the requested candidate cells to the source gNB-CU.

[0628] Optionally, the message may be a UE CONTEXT MODIFICATION RESPONSE message, or other messages. The specific content of the message is shown in step 503, which will not be repeated here.

[0629] In some embodiments, the source gNB-CU uniformly configures the received L2 reset indication information of all candidate cells. It is ensured that L2 reset indication information of candidate cells in the same candidate gNB can be distinguished, and L2 reset indication information of different candidate gNBs can be distinguished. For example, there are two candidate cells Cell1 and Cell2 in candidate gNB1, and the L2 reset identifications configured by candidate gNB1 for Cell1 and Cell2 are 1 and 2, respectively. There are three candidate cells Cell3, Cell4 and Cell5 in the candidate gNB2, and the L2 reset identifications configured by the candidate gNB2 for Cell3, Cell4 and Cell5 are 1, 2 and 1, respectively. Then the source gNB configures the L2 reset identifications of the five candidate cells Cell1, Cell2, Cell3, Cell4 and Cell5 as 1, 2, 3, 4 and 3 respectively.

[0630] In some embodiments, the source gNB-CU will also configure the L2 reset indication information of the source cell for the source cell (serving cell). The L2 reset identification of the source cell and the L2 reset identification of the candidate cell are also uniformly determined by the source gNB-CU.

[0631] In some embodiments, the source gNB-CU transmits the uniformly configured L2 reset indication information of the source cell and all candidate cells to the source gNB-DU and the UE, and / or transmits L2 reset indication information of all candidate cells to other candidate gNBs.

[0632] Therefore, the source gNB-DU and the UE can determine which inter-cell handover requires L2 reset and which inter-cell handover does not require L2 reset according to the L2 reset identifications of the source cell and the five candidate cells.

[0633] Step 506: the source gNB-CU transmits a message to the source gNB-DU. Optionally, the message may be a UE CONTEXT MODIFICATION REQUEST message, or other messages.

[0634] In some embodiments, the message may further include at least one of the following information:

[0635] (1) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0636] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0637] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is related to an LTM candidate cell.

[0638] - L2 reset indication information of the candidate cell, that is, L2 reset indication information related to the requested LTM candidate cell. That is, the L2 reset identification of the requested candidate cell.

[0639] (2) L2 reset indication information of the source cell, that is, the L2 reset indication information related to the source cell. That is, the L2 reset identification of the source cell.

[0640] Step 507 is the same as step 307, which will not be repeated here.

[0641] In steps 508-509, the source gNB-CU provides the newest information of all candidate cells to each candidate cell. Steps 508-509 are optional. If step 508 is performed, the source gNB-CU transmits a message to the candidate gNB1-CU (candidate gNB2-CU). The message may be a HANDOVER REQUEST message, or other messages. The information contained in the message is the same as in step 506, which will not be repeated here.

[0642] Step 510: the source gNB-CU transmits a downlink RRC message transfer (DL RRC MESSAGE TRANSFER) message or other messages to the source gNB-DU. The message may also include at least one of the following information:

[0643] (1) RRC Reconfiguration message, an RRC reconfiguration (RRCReconfiguration) message transmitted to the UE.

[0644] Step 511: the source gNB-DU transmits an RRCReconfiguration message to the UE. The source gNB-DU forwards the RRC reconfiguration message received in step 510 to the UE.

[0645] In some embodiments, the message may further include at least one of the following information:

[0646] (1) LTM candidate configuration related information of one or more LTM candidate cells. The LTM candidate configuration related information includes at least one of the following information:

[0647] - LTM candidate ID, indicating an LTM candidate configuration, which is corresponding to an LTM configuration ID and is associated with (or corresponding to) an LTM candidate cell.

[0648] - LTM candidate physical cell ID (LTM candidate PCI), indicating a physical cell ID of the candidate cell corresponding to (or associated with) the LTM candidate ID.

[0649] - SSB configuration information of LTM, indicating time and frequency information of SSB of the candidate cell corresponding to (or associated with) the LTM candidate ID. The frequency information includes the ARFCN of SSB, that is, the ARFCN of the candidate cell.

[0650] - LTM candidate configuration information, including Cell Group configuration information, Radio Bearer (RB) configuration information, etc.

[0651] - L2 reset indication information of the candidate cell, that is, L2 reset indication information related to the requested LTM candidate cell. That is, the L2 reset identification of the requested candidate cell.

[0652] (2) L2 reset indication information of the source cell, that is, the L2 reset indication information related to the source cell. That is, the L2 reset identification of the source cell.

[0653] Steps 512-516 and 312-316 have the same functions, and the detailed description is given in steps 312-316 of Embodiment 1, which will not be repeated here.

[0654] Step 518 is the same as step 318. For details, please refer to step 318 of Embodiment 1, which will not be repeated here.

[0655] When the UE receives an LTM cell switch command, it will determine whether to perform an L2 reset process based on the "Method for determining whether to perform an L2 reset process".

[0656] Embodiment 8 gives another method for realizing L2 reset indication under an LTM handover mode.

[0657] In Embodiment 8, a value range of L2 reset indication information related to each candidate cell is provided by the source gNB, and the final value thereof is determined by the candidate gNB.

[0658] The flow of Embodiment 8 is the same as that of Embodiment 7, and the description of Embodiment 8 will refer to the steps shown in the flow chart of Embodiment 7 (FIG. 4B).

[0659] Step 500 is the same as step 500 in Embodiment 7, which will not be repeated here.

[0660] Step 501: the source gNB-DU transmits a message to the candidate gNB-DU.

[0661] Optionally, the source gNB-CU uses the message to request one or more candidate cells from candidate gNB-CUs for LTM handover, and the candidate cells belong to one or more candidate gNB-CU. Optionally, the source gNB-CU may transmit one or more messages to the candidate gNBs to request different candidate cells.

[0662] Optionally, the message may be a HANDOVER REQUEST message, or other messages.

[0663] In some embodiments, the message may further include at least one of the following information:

[0664] (1) Cell ID, that is, ID of a requested LTM candidate cell. The cell ID may be a CGI (Cell Global ID) or other identifiers. The cell may be a target candidate cell for LTM handover.

[0665] (2) LTM Indicator, which indicates that the requested candidate cell is used for an LTM handover.

[0666] (3) LTM configuration ID, which indicates an associated (or corresponding) LTM configuration ID of the requested candidate cell. The LTM configuration ID corresponds to an LTM candidate ID (LTM Candidate ID), and the LTM candidate ID indicates an LTM candidate configuration.

[0667] (4) Candidate cell information, including information of one or more candidate cells, in which information of all candidate cells is provided. The candidate cell information includes at least one of the following information:

[0668] - LTM Cell ID, which indicates the ID of an LTM candidate cell. The LTM Cell ID may be a CGI (Cell Global ID) or other identifiers.

[0669] - LTM Configuration ID, corresponding to an LTM Candidate ID, which indicates an LTM candidate configuration and is associated with (or corresponding to) an LTM candidate cell.

[0670] (5) Value range of L2 reset indication information, which indicates a value range of L2 reset indication information related to the candidate cell(s), that is, a value range of the L2 reset identification of the candidate cells. According to the value range, the candidate gNB configures the value of the L2 reset indication information related to the requested candidate cell (that is, the value of the L2 reset identification of the requested candidate cell), and transmits the configured value to the candidate gNB-DU through step 502 and fed back to the source gNB-CU through step 504.

[0671] Steps 502-505b are the same as steps 502-505b in Embodiment 7, and are not repeated here.

[0672] In some embodiments, the source gNB-CU will receive L2 reset indication information of all the candidate cells. The L2 reset indication information of the candidate cells is determined by the candidate gNBs based on the value range of the L2 reset indication information provided by the source gNB. The source gNB-CU will also configure the L2 reset indication information of the source cell for the source cell (serving cell). The source gNB-CU transmits L2 reset indication information of the source cell and all candidate cells to the source gNB-DU and the UE, and / or transmits L2 reset indication information of all candidate cells to other candidate gNBs.

[0673] Steps 506-517 are the same as steps 506-517 in Embodiment 7, and are not repeated here.

[0674] It should be understood that, depending on the application scenarios, the various example aspects, methods, steps, processes, etc. described above in connection with the attached drawings can be combined and implemented in any way, including implementing in an order different from that shown in the drawings or deleting one or more steps in the drawings, etc., and there is no limitation here.

[0675] Next, FIG. 5 shows a flowchart of a method 510 performed by a first node in a wireless communication system according to embodiments of the present disclosure.

[0676] As shown in FIG. 5, a method 550 performed by a first node in a wireless communication system according to embodiments of the present disclosure may include: in step S501, transmitting a first message to a user equipment (UE) in case that L1 / L2 triggered mobility (LTM) cell switch is triggered and it is determined that key update needs to be performed, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; and in step S502, transmitting a second message to a second node, wherein the second message includes at least one of third information related to a target cell of the UE, fourth information for indicating key update, and the first parameter.

[0677] According to embodiments of the present disclosure, the method further includes: receiving a third message from the second node, wherein the third message includes fifth information associated with a candidate cell used for key update determination, sixth information associated with a source cell used for key update determination, and the first parameter; and determining whether key update needs to be performed based on fifth information associated with the target cell and the sixth information.

[0678] According to embodiments of the present disclosure, the fifth information is configured by the second node or a candidate node to which the candidate cell belongs; wherein the fifth information includes at least one of: an identification of the candidate node to which the candidate cell belongs, and a first identification associated with the candidate cell used for key update determination.

[0679] According to embodiments of the present disclosure, the sixth information is configured by the second node, wherein the sixth information includes at least one of: an identification of a source node to which the source cell belongs, and a second identification associated with the source cell used for key update determination.

[0680] According to embodiments of the present disclosure, the first parameter includes a Next Hop Chaining Counter (NCC) parameter, which is used to derive a new key for the target cell.

[0681] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0682] FIG. 6 shows a flowchart of a method 600 performed by a second node in a wireless communication system according to embodiments of the present disclosure.

[0683] As shown in FIG. 6, a method 600 performed by a second node in a wireless communication system according to embodiments of the present disclosure may include: in step S601, determining a first parameter used for key update; in step S602, determining whether key update needs to be performed; in step S603, deriving a new key for a target cell based on the first parameter used for key update in case that it is determined that key update needs to be performed; and in step S604, transmitting a fourth message to the target node, wherein the fourth message includes the new key and the first parameter used for key update.

[0684] According to embodiments of the present disclosure, the method further includes: receiving a second message from a first node, wherein the second message includes at least one of third information related to a target cell of a user equipment (UE), fourth information for indicating key update and the first parameter, wherein the determining whether key update needs to be performed includes determining whether key update needs to be performed based on the fourth information for indicating key update.

[0685] According to embodiments of the present disclosure, the method further includes: transmitting a third message to the first node, wherein the third message includes fifth information associated with a candidate cell used for key update determination, sixth information associated with a source cell used for key update determination, and the first parameter, wherein the fourth information for indicating key update is determined by the first node based on fifth information associated with a target cell and the sixth information.

[0686] According to embodiments of the present disclosure, the fifth information is configured by the second node or a candidate node to which the candidate cell belongs; wherein the fifth information includes at least one of: an identification of the candidate node to which the candidate cell belongs, and a first identification associated with the candidate cell used for key update determination.

[0687] According to embodiments of the present disclosure, the sixth information is configured by the second node, wherein the sixth information includes at least one of: an identification of a source node to which the source cell belongs, and a second identification associated with the source cell used for key update determination.

[0688] According to embodiments of the present disclosure, the first parameter includes a Next Hop Chaining Counter (NCC) parameter, which is used to derive a new key for the target cell.

[0689] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: determining whether key update needs to be performed based on fifth information associated with a target cell used for key update determination and sixth information associated with a source cell used for key update determination; wherein, the determining whether key update needs to be performed further includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0690] FIG. 7 shows a flowchart of a method 700 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure.

[0691] As shown in FIG. 7, a method 700 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure may include: in step S701, receiving a first message from a first node, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; in step S702, deriving a new key for a target cell based on the second information about the key update indication and the first parameter; and in step S703, transmitting the first parameter to a target node.

[0692] FIG. 8 shows a flowchart of a method 800 performed by a second node in a wireless communication system according to embodiments of the present disclosure.

[0693] As shown in FIG. 8, a method 800 performed by a second node in a wireless communication system according to embodiments of the present disclosure may include: in step S801, receiving a fifth message from a third node, wherein the fifth message includes a second parameter and / or a third parameter; and in step S802, transmitting the second parameter to a first node, wherein the second parameter is forwarded by the first node to a user equipment (UE) through a seventh message, and the second parameter is used by the UE to derive a new key for a target cell when it is determined that key update needs to be performed; wherein the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters for deriving a new key; and wherein the third parameter includes a list of Next Hop (NH) parameter and NCC parameter pairs or an NH parameter and NCC parameter pair for deriving a new key, and the third parameter is used by the second node to derive a new key for the target cell when it is determined that key update needs to be performed.

[0694] According to embodiments of the present disclosure, the method further includes: determining whether key update needs to be performed based on fifth information associated with a target cell used for key update determination and sixth information associated with a source cell used for key update determination.

[0695] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0696] According to embodiments of the present disclosure, the method further includes: in case that it is determined that key update needs to be performed, determining a fourth parameter used for key update based on the third parameter used for key update, and deriving a new key for the target cell based on the fourth parameter; and transmitting a sixth message to a target node, wherein the sixth message includes at least one of the new key, a fifth parameter used for key update and the fourth parameter associated with the new key, wherein the fourth parameter includes an NCC parameter from which the new key is derived, and wherein the fifth parameter includes a list of parameter pairs after the third parameter excludes an NH parameter and NCC parameter pair corresponding to the fourth parameter.

[0697] According to embodiments of the present disclosure, the deriving a new key for the target cell includes: in case that the third parameter includes a list of NH parameter and NCC parameter pairs for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the first unused NH parameter and NCC parameter pair selected from the list, which is served as the fourth parameter; and in case that the third parameter includes an NH parameter and NCC parameter pair for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the NH parameter and NCC parameter pair, which is served as the fourth parameter.

[0698] FIG. 9A shows a flowchart of a method 900 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure.

[0699] As shown in FIG. 9A, a method 900 performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure may include: in step S901, receiving a seventh message from a first node, wherein the seventh message includes a second parameter used for key update, fifth information associated with a candidate cell used for key update determination, and sixth information associated with a source cell used for key update determination; in step S902, determining whether key update needs to be performed based on fifth information associated with a target cell and the sixth information; in step S903, determining a fourth parameter used for key update; and in step S904, transmitting the fourth parameter to the target node. In some embodiments, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0700] According to embodiments of the present disclosure, the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters used for key update, and the fourth parameter includes a Next Hop Chaining Counter (NCC) parameter.

[0701] According to embodiments of the present disclosure, the method further includes: in case that it is determined that key update needs to be performed, deriving a new key for the target cell based on the first unused NCC parameter in the list of NCC parameters, which is served as the fourth parameter.

[0702] FIG. 9B shows a flowchart of a method 910 performed by a target node in a wireless communication system according to embodiments of the present disclosure.

[0703] As shown in FIG. 9B, a method 910 performed by a target node in a wireless communication system according to embodiments of the present disclosure may include: in step S911, transmitting an eighth message to a third node, wherein the eighth message includes a fourth parameter used for deriving a current key; in step S912, receiving a ninth message from the third node, wherein the ninth message includes a Next Hop Chaining Counter (NCC) parameter used for key update and a corresponding Next Hop (NH) parameter; and in step S913, deriving a new key for a new target cell by using the NCC parameter; wherein, the NCC parameter is the first unused NCC parameter selected by the third node from a second parameter.

[0704] According to embodiments of the present disclosure, the method further includes: receiving a ninth message from the third node, wherein the ninth message includes a Next Hop Chaining Counter (NCC) parameter used for key update and a corresponding Next Hop (NH) parameter; and deriving a new key for a new target cell by using the NCC parameter; wherein, the NCC parameter is the first unused NCC parameter selected by the third node from a second parameter.

[0705] In the embodiments of the present disclosure, the first node may be a source gNB-DU, the second node may be a source gNB-CU, and the third node may be a core network node, such as an AMF.

[0706] It should be understood that the methods 550, 600, 700, 800, 900, 910, etc. according to the embodiments of the present disclosure may also include one or more of the methods or steps described above in connection with any examples or drawings, which are not repeated here.

[0707] Next, FIG. 10 shows a schematic diagram of a node 1000 in a wireless communication system according to embodiments of the present disclosure.

[0708] As shown in FIG. 10, a node 1000 (which may be, for example, a first node (e.g., a source gNB-DU), a second node (e.g., gNB-CU), a third node (e.g., AMF), a target node or any other network node as described above) according to embodiments of the present disclosure may include a transceiver 1010 and a processor 1020. The transceiver 1010 may be configured to transmit and receive signals. The processor 1020 may be coupled to the transceiver 1010 and may be configured to (e.g., control the transceiver 1010 to) perform any method performed by a node in a wireless communication system according to embodiments of the present disclosure.

[0709] As shown in FIG. 10, a node 1000 (which may be, for example, a first node (e.g., a source gNB-DU), a second node (e.g., gNB-CU), a third node (e.g., AMF), a target node or any other network node as described above) according to embodiments of the present disclosure may include a transceiver 1010 and a processor 1020. a node 1000 (which may be, for example, a first node (e.g., a source gNB-DU), a second node (e.g., gNB-CU), a third node (e.g., AMF), a target node or any other network node as described above) according to embodiments of the present disclosure may further include a memory. However, the components of the node are not limited thereto. For example, the node may include more or fewer components than those described above. In addition, the processor 1020, the transceiver 1010, and the memory may be implemented as a single chip. Also, the processor 1020 may include at least one processor.

[0710] The transceiver 1010 collectively refers to a base station receiver and a base station transmitter, and may transmit / receive a signal to / from a terminal or a network entity. The signal transmitted or received to or from the terminal or a network entity may include control information and data. The transceiver 1010 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 1010 and components of the transceiver 1010 are not limited to the RF transmitter and the RF receiver.

[0711] Also, the transceiver 1010 may receive and output, to the processor 1020, a signal through a wireless channel, and transmit a signal output from the processor 1020 through the wireless channel.

[0712] The memory may store a program and data required for operations of the node (e.g., base station) (which may be, for example, a first node (e.g., a source gNB-DU), a second node (e.g., gNB-CU), a third node (e.g., AMF), a target node or any other network node as described above). Also, the memory may store control information or data included in a signal obtained by the node (e.g., base station). The memory may be a storage medium, such as read-only memory (ROM), random access memory (RAM), a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0713] The processor 1020 may control a series of processes such that the node (e.g., base station) (which may be, for example, a first node (e.g., a source gNB-DU), a second node (e.g., gNB-CU), a third node (e.g., AMF), a target node or any other network node as described above) operates as described above. For example, the transceiver 1010 may receive a data signal including a control signal transmitted by the terminal, and the processor 1020 may determine a result of receiving the control signal and the data signal transmitted by the terminal.

[0714] FIG. 11 shows a schematic diagram of a user equipment (UE) 1100 in a wireless communication system according to embodiments of the present disclosure.

[0715] As shown in FIG. 11, a user equipment 1100 according to embodiments of the present disclosure may include a transceiver 1110 and a processor 1120. The transceiver 1110 may be configured to transmit and receive signals. The processor 1120 may be coupled to the transceiver 1110 and may be configured to (e.g., control the transceiver 1110 to) perform any method performed by the user equipment according to embodiments of the present disclosure. Herein, a processor may also be called a controller. Herein, nodes may also be called node devices.

[0716] As shown in FIG. 11, a user equipment 1100 according to embodiments of the present disclosure may include a transceiver 1110 and a processor 1120. a user equipment 1100 according to embodiments of the present disclosure may further include a memory. The transceiver 1110, the memory, and the processor 1120 of the user equipment (UE) may operate according to a communication method of the user equipment (UE) described above. However, the components of the user equipment (UE) are not limited thereto. For example, the user equipment (UE) may include more or fewer components than those described above. In addition, the processor 1120, the transceiver 1110, and the memory may be implemented as a single chip. Also, the processor 1120 may include at least one processor.

[0717] The transceiver 1110 collectively refers to a user equipment (UE) receiver and a user equipment (UE) transmitter, and may transmit / receive a signal to / from a base station or a network entity. The signal transmitted or received to or from the base station or a network entity may include control information and data. The transceiver 1110 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 1110 and components of the transceiver 1110 are not limited to the RF transmitter and the RF receiver.

[0718] Also, the transceiver 1110 may receive and output, to the processor 1120, a signal through a wireless channel, and transmit a signal output from the processor 1120 through the wireless channel.

[0719] The memory may store a program and data required for operations of the user equipment (UE). Also, the memory may store control information or data included in a signal obtained by the user equipment (UE). The memory may be a storage medium, such as read-only memory (ROM), random access memory (RAM), a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0720] The processor 1120 may control a series of processes such that the user equipment (UE) operates as described above. For example, the transceiver 1110 may receive a data signal including a control signal transmitted by the base station or the network entity, and the processor 1120 may determine a result of receiving the control signal and the data signal transmitted by the base station or the network entity.

[0721] Embodiments of the present disclosure provide a method performed by a first node in a wireless communication system, which includes: transmitting a first message to a user equipment (UE) in case that L1 / L2 triggered mobility (LTM) cell switch is triggered and it is determined that key update needs to be performed, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; and transmitting a second message to a second node, wherein the second message includes at least one of third information related to a target cell of the UE, fourth information for indicating key update, and the first parameter.

[0722] According to embodiments of the present disclosure, the method further includes: receiving a third message from the second node, wherein the third message includes fifth information associated with a candidate cell used for key update determination, sixth information associated with a source cell used for key update determination, and the first parameter; and determining whether key update needs to be performed based on fifth information associated with the target cell and the sixth information.

[0723] According to embodiments of the present disclosure, the fifth information is configured by the second node or a candidate node to which the candidate cell belongs; wherein the fifth information includes at least one of: an identification of the candidate node to which the candidate cell belongs, and a first identification associated with the candidate cell used for key update determination.

[0724] According to embodiments of the present disclosure, the sixth information is configured by the second node, wherein the sixth information includes at least one of: an identification of a source node to which the source cell belongs, and a second identification associated with the source cell used for key update determination.

[0725] According to embodiments of the present disclosure, the first parameter includes a Next Hop Chaining Counter (NCC) parameter, which is used to derive a new key for the target cell.

[0726] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0727] Embodiments of the present disclosure provide a method performed by a second node in a wireless communication system, including: determining a first parameter used for key update; determining whether key update needs to be performed; deriving a new key for a target cell based on the first parameter used for key update in case that it is determined that key update needs to be performed; and transmitting a fourth message to the target node, wherein the fourth message includes the new key and the first parameter used for key update.

[0728] According to embodiments of the present disclosure, the method further includes: receiving a second message from a first node, wherein the second message includes at least one of third information related to a target cell of a user equipment (UE), fourth information for indicating key update and the first parameter, wherein the determining whether key update needs to be performed includes determining whether key update needs to be performed based on the fourth information for indicating key update.

[0729] According to embodiments of the present disclosure, the method further includes: transmitting a third message to the first node, wherein the third message includes fifth information associated with a candidate cell used for key update determination, sixth information associated with a source cell used for key update determination, and the first parameter, wherein the fourth information for indicating key update is determined by the first node based on fifth information associated with a target cell and the sixth information.

[0730] According to embodiments of the present disclosure, the fifth information is configured by the second node or a candidate node to which the candidate cell belongs; wherein the fifth information includes at least one of: an identification of the candidate node to which the candidate cell belongs, and a first identification associated with the candidate cell used for key update determination.

[0731] According to embodiments of the present disclosure, the sixth information is configured by the second node, wherein the sixth information includes at least one of: an identification of a source node to which the source cell belongs, and a second identification associated with the source cell used for key update determination.

[0732] According to embodiments of the present disclosure, the first parameter includes a Next Hop Chaining Counter (NCC) parameter, which is used to derive a new key for the target cell.

[0733] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: determining whether key update needs to be performed based on fifth information associated with a target cell used for key update determination and sixth information associated with a source cell used for key update determination; wherein, the determining whether key update needs to be performed further includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0734] Embodiments of the present disclosure provide a method performed by a user equipment (UE) in a wireless communication system, including: receiving a first message from a first node, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; deriving a new key for a target cell based on the second information about the key update indication and the first parameter; and transmitting the first parameter to a target node.

[0735] Embodiments of the present disclosure provide a method performed by a second node in a wireless communication system, including: receiving a fifth message from a third node, wherein the fifth message includes a second parameter and / or a third parameter; and transmitting the second parameter to a first node, wherein the second parameter is forwarded by the first node to a user equipment (UE) through a seventh message, and the second parameter is used by the UE to derive a new key for a target cell when it is determined that key update needs to be performed; wherein the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters for deriving a new key; and wherein the third parameter includes a list of Next Hop (NH) parameter and NCC parameter pairs or an NH parameter and NCC parameter pair for deriving a new key, and the third parameter is used by the second node to derive a new key for the target cell when it is determined that key update needs to be performed.

[0736] According to embodiments of the present disclosure, the method further includes: determining whether key update needs to be performed based on fifth information associated with a target cell used for key update determination and sixth information associated with a source cell used for key update determination.

[0737] According to embodiments of the present disclosure, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0738] According to embodiments of the present disclosure, the method further includes: in case that it is determined that key update needs to be performed, determining a fourth parameter used for key update based on the third parameter used for key update, and deriving a new key for the target cell based on the fourth parameter; and transmitting a sixth message to a target node, wherein the sixth message includes at least one of the new key, a fifth parameter used for key update and the fourth parameter associated with the new key, wherein the fourth parameter includes an NCC parameter from which the new key is derived, and wherein the fifth parameter includes a list of parameter pairs after the third parameter excludes an NH parameter and NCC parameter pair corresponding to the fourth parameter.

[0739] According to embodiments of the present disclosure, the deriving a new key for the target cell includes: in case that the third parameter includes a list of NH parameter and NCC parameter pairs for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the first unused NH parameter and NCC parameter pair selected from the list, which is served as the fourth parameter; and in case that the third parameter includes an NH parameter and NCC parameter pair for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the NH parameter and NCC parameter pair, which is served as the fourth parameter.

[0740] Embodiments of the present disclosure provide a method performed by a user equipment (UE) in a wireless communication system, including: receiving a seventh message from a first node, wherein the seventh message includes a second parameter used for key update, fifth information associated with a candidate cell used for key update determination, and sixth information associated with a source cell used for key update determination; determining whether key update needs to be performed based on fifth information associated with a target cell and the sixth information; determining a fourth parameter used for key update; and transmitting the fourth parameter to the target node; wherein, the determining whether key update needs to be performed includes: when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / or when the fifth information and the sixth information are the same, determining that the key update needs not to be performed.

[0741] According to embodiments of the present disclosure, the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters used for key update, and the fourth parameter includes a Next Hop Chaining Counter (NCC) parameter.

[0742] According to embodiments of the present disclosure, the method further includes: in case that it is determined that key update needs to be performed, deriving a new key for the target cell based on the first unused NCC parameter in the list of NCC parameters, which is served as the fourth parameter.

[0743] Embodiments of the present disclosure provide a method performed by a target node in a wireless communication system, including: transmitting an eighth message to a third node, wherein the eighth message includes a fourth parameter used for deriving a current key; receiving a ninth message from the third node, wherein the ninth message includes a Next Hop Chaining Counter (NCC) parameter used for key update and a corresponding Next Hop (NH) parameter; and deriving a new key for a new target cell by using the NCC parameter; wherein, the NCC parameter is the first unused NCC parameter selected by the third node from a second parameter.

[0744] According to embodiments of the present disclosure, the method further includes: receiving a sixth message from a second node, wherein the sixth message includes at least one of a new key, a fifth parameter used for key update and a fourth parameter for deriving the new key, wherein the new key is used as a current key for the target cell.

[0745] Embodiments of the present disclosure provide a user equipment (UE) in a wireless communication system, including: a transceiver configured to transmit and receive signals; and a controller coupled to the transceiver and configured to perform the method performed by a user equipment (UE) in a wireless communication system according to embodiments of the present disclosure.

[0746] Embodiments of the present disclosure provide a node device in a wireless communication system, including: a transceiver configured to transmit and receive signals; and a controller coupled to the transceiver and configured to perform the method performed by a node in a wireless communication system (e.g., a first node and / or a second node and / or a target node, etc.) according to embodiments of the present disclosure.

[0747] Embodiments of the present disclosure provide a computer-readable medium having stored thereon computer-readable instructions that, when executed by a processor, can be used to implement any method according to embodiments of the present disclosure.

[0748] Embodiments of the present disclosure provide a configuration for LTM handover, which realizes inter-gNB cell handover by adopting an LTM handover mode, thereby extending the application scope of the LTM handover mode, reducing the handover delay between cells of different gNBs, and improving the handover performance.

[0749] Various embodiments of the present disclosure may be implemented as computer-readable codes embodied on a computer-readable recording medium from a specific perspective. A computer-readable recording medium is any data storage device that can store data readable by a computer system. Examples of computer-readable recording media may include read-only memory (ROM), random access memory (RAM), compact disk read-only memory (CD-ROM), magnetic tape, floppy disk, optical data storage device, carrier wave (e.g., data transmission via the Internet), etc. Computer-readable recording media can be distributed by computer systems connected via a network, and thus computer-readable codes can be stored and executed in a distributed manner. Furthermore, functional programs, codes and code segments for implementing various embodiments of the present disclosure can be easily explained by those skilled in the art to which the embodiments of the present disclosure are applied.

[0750] It will be understood that the embodiments of the present disclosure may be implemented in the form of hardware, software, or a combination of hardware and software. The software may be stored as program instructions or computer-readable codes executable on a processor on a non-transitory computer-readable medium. Examples of non-transitory computer-readable recording media include magnetic storage media (such as ROM, floppy disk, hard disk, etc.) and optical recording media (such as CD-ROM, digital video disk (DVD), etc.). Non-transitory computer-readable recording media may also be distributed on computer systems coupled to a network, so that computer-readable codes are stored and executed in a distributed manner. The medium can be read by a computer, stored in a memory, and executed by a processor. Various embodiments may be implemented by a computer or a portable terminal including a controller and a memory, and the memory may be an example of a non-transitory computer-readable recording medium suitable for storing program (s) with instructions for implementing embodiments of the present disclosure. The present disclosure may be realized by a program with code for concretely implementing the apparatus and method described in the claims, which is stored in a machine (or computer)-readable storage medium. The program may be electronically carried on any medium, such as a communication signal transmitted via a wired or wireless connection, and the present disclosure suitably includes its equivalents.

[0751] What has been described above is only the specific implementation of the present disclosure, but the scope of protection of the present disclosure is not limited thereto. Anyone who is familiar with this technical field may make various changes or substitutions within the technical scope disclosed in the present disclosure, and these changes or substitutions should be covered within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be based on the scope of protection of the claims.

Claims

1.A method performed by a first node in a wireless communication system, comprising:transmitting a first message to a user equipment (UE) in case that L1 / L2 triggered mobility (LTM) cell switch is triggered and it is determined that key update needs to be performed, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; andtransmitting a second message to a second node, wherein the second message includes at least one of third information related to a target cell of the UE, fourth information for indicating key update, and the first parameter.2.The method of claim 1, further comprising:receiving a third message from the second node, wherein the third message includes fifth information associated with a candidate cell used for key update determination, sixth information associated with a source cell used for key update determination, and the first parameter; anddetermining whether key update needs to be performed based on fifth information associated with the target cell and the sixth information.3.The method of claim 2, wherein,the fifth information is configured by the second node or a candidate node to which the candidate cell belongs;wherein the fifth information includes at least one of:an identification of the candidate node to which the candidate cell belongs, and a first identification associated with the candidate cell used for key update determination.4.The method of claim 2, wherein,the sixth information is configured by the second node,wherein the sixth information includes at least one of:an identification of a source node to which the source cell belongs, and a second identification associated with the source cell used for key update determination.5.The method of claim 1, wherein,the first parameter includes a Next Hop Chaining Counter (NCC) parameter, which is used to derive a new key for the target cell.6.The method of claim 2, wherein the determining whether key update needs to be performed comprises:when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / orwhen the fifth information and the sixth information are the same, determining that the key update needs not to be performed.7.A method performed by a second node in a wireless communication system, comprising:determining a first parameter used for key update;determining whether key update needs to be performed;deriving a new key for a target cell based on the first parameter used for key update in case that it is determined that key update needs to be performed; andtransmitting a fourth message to the target node, wherein the fourth message includes the new key and the first parameter used for key update.8.The method of claim 7, further comprising:receiving a fifth message from a third node, wherein the fifth message includes a second parameter and / or a third parameter; andtransmitting the second parameter to a first node, wherein the second parameter is forwarded by the first node to a user equipment (UE) through a seventh message, and the second parameter is used by the UE to derive a new key for a target cell when it is determined that key update needs to be performed;wherein the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters for deriving a new key; andwherein the third parameter includes a list of Next Hop (NH) parameter and NCC parameter pairs or an NH parameter and NCC parameter pair for deriving a new key, and the third parameter is used by the second node to derive a new key for the target cell when it is determined that key update needs to be performed.9.The method of claim 8, further comprising:determining whether key update needs to be performed based on fifth information associated with a target cell used for key update determination and sixth information associated with a source cell used for key update determination,wherein the determining whether key update needs to be performed comprises:when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / orwhen the fifth information and the sixth information are the same, determining that the key update needs not to be performed.10.The method of claims 8, further comprising:in case that it is determined that key update needs to be performed, determining a fourth parameter used for key update based on the third parameter used for key update, and deriving a new key for the target cell based on the fourth parameter; andtransmitting a sixth message to a target node, wherein the sixth message includes at least one of the new key, a fifth parameter used for key update and the fourth parameter associated with the new key,wherein the fourth parameter includes an NCC parameter from which the new key is derived,wherein the fifth parameter includes a list of parameter pairs after the third parameter excludes an NH parameter and NCC parameter pair corresponding to the fourth parameter,wherein the deriving a new key for the target cell comprises:in case that the third parameter includes a list of NH parameter and NCC parameter pairs for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the first unused NH parameter and NCC parameter pair selected from the list, which is served as the fourth parameter; andin case that the third parameter includes an NH parameter and NCC parameter pair for deriving a new key, deriving a new key for the target cell based on an NCC parameter in the NH parameter and NCC parameter pair, which is served as the fourth parameter.11.A method performed by a user equipment (UE) in a wireless communication system, comprising:receiving a first message from a first node, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update;deriving a new key for a target cell based on the second information about the key update indication and the first parameter; andtransmitting the first parameter to a target node.12.The method of claim 11, further comprising:receiving a seventh message from a first node, wherein the seventh message includes a second parameter used for key update, fifth information associated with a candidate cell used for key update determination, and sixth information associated with a source cell used for key update determination;determining whether key update needs to be performed based on fifth information associated with a target cell and the sixth information;determining a fourth parameter used for key update; andtransmitting the fourth parameter to the target node;wherein, the determining whether key update needs to be performed comprises:when the fifth information and the sixth information are different, determining that the key update needs to be performed; and / orwhen the fifth information and the sixth information are the same, determining that the key update needs not to be performed.13.The method of claim 12, wherein the second parameter includes a list of Next Hop Chaining Counter (NCC) parameters used for key update, and the fourth parameter includes a Next Hop Chaining Counter (NCC) parameter14.The method of claim 13, further comprising:in case that it is determined that key update needs to be performed, deriving a new key for the target cell based on the first unused NCC parameter in the list of NCC parameters, which is served as the fourth parameter.15.A node device in a wireless communication system, comprising:a transceiver configured to transmit and receive signals; anda controller coupled to the transceiver and configured to:transmit a first message to a user equipment (UE) in case that L1 / L2 triggered mobility (LTM) cell switch is triggered and it is determined that key update needs to be performed, wherein the first message includes at least one of second information about a key update indication and a first parameter used for key update; andtransmit a second message to a second node, wherein the second message includes at least one of third information related to a target cell of the UE, fourth information for indicating key update, and the first parameter.

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