Methods and apparatuses for lower layer mobility

Abstract

Techniques for an inter-secondary-node (SN) secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM) are provided For example, a method comprises: receiving, at a user equipment (UE) in a network from a network node (e.g., a master node (MN) of a master cell) of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for the inter-SN SCG LTM and security information for the one or more candidate secondary cells; and performing, at the UE, the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information.

Description

METHODS AND APPARATUSES FOR LOWER LAYER MOBILITYTECHNICAL FIELD

[0001] The present disclosure relates to a wireless communication system. Moreparticularly, the present disclosure relates to methods and apparatuses for lower layer mobilityin a wireless communication system. Even more specifically, the present disclosure relates tomethods and apparatuses for an inter-secondary-node (SN) secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM). BACKGROUND

[0002] Various embodiments relate to considerations in a (e.g., mobile / wireless)communication system or network, such as a fifth generation (5G) / New Radio (NR) system and a next-generation system beyond 5G. For example, various embodiments are applicable in a 3rd Generation Partnership Project (3GPP) standardized mobile / wireless communicationsystem or network of Release 19 onwards.

[0003] In 3GPP Rel-18, a new mobility mechanism was introduced, namely lower layer(L1 / L2) triggered mobility (LTM) as a cell switch procedure. LTM aims to reduce interruptiontime during handover. However, for 3GPP Rel-19, LTM requires enhancements, particularlywith respect to the preparation of inter-SN SCG LTM. LIST OF ACRONYMS AND ABBREVIATIONS

[0004] The following acronyms and abbreviations are used throughout the subjectdisclosure: CFRA Contention Free Random AccessCPC Conditional PSCell ChangeDL Down LinkLTM L1 / L2 Triggered MobilityMN Master NodeMCG Master Cell Group RACH Random Access procedureSCG Secondary Cell GroupS-CPAC Subsequent Conditional PSCell Addition or ChangeSSB Synchronization Signal BlockSN Secondary NodeTA Timing AdvanceTCI Transmission Configuration IndicatorUE User EquipmentUL UplinkSUMMARY

[0005] It is an object of the present disclosure to provide mechanisms to enable certainfeatures of lower layer mobility in a wireless communication system. In particular, there are provided methods and apparatuses for inter-SN SCG LTM.

[0006] According to some aspects, there is provided the subject matter of the independentclaims. Some additional aspects are defined in the dependent claims.

[0007] According to a first aspect of the present disclosure, a user equipment (UE) or anapparatus of such a UE for inter-SN SCG LTM is provided. The UE (e.g., a user device orterminal device) or the apparatus according to the first aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at leastone processor, cause the UE or apparatus at least to: receive, from a network node of a network,a reconfiguration message including a configuration of one or more candidate secondary cellsfor an inter-SN SCG LTM, and security information for the one or more candidate secondarycells; and perform the inter-SN SCG LTM to one of the one or more candidate secondary cellsbased on the configuration and the security information.

[0008] In some examples of the first aspect, the security information comprises anindication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

[0009] In some examples of the first aspect, the reconfiguration message comprises adedicated field for the indication.

[0010] In some examples of the first aspect, the instructions, when executed by the at leastone processor, further cause the UE or apparatus to: in response to determining, based on the indication, to perform the security update, perform the security update based on the security information.

[0011] In some examples of the first aspect, the security information comprises a securitykey counter configuration to enable the UE to derive a security key of a base station associated with the one of the one or more candidate secondary cells.

[0012] In some examples of the first aspect, the reconfiguration message comprises adedicated field for the security key counter configuration.

[0013] In some examples of the first aspect, the security key counter configurationcomprises one or more security key counters associated with the one or more candidate secondary cells.

[0014] In some examples of the first aspect, the instructions, when executed by the at leastone processor, further cause the UE or apparatus to: select, from the one or more security keycounters, a security key counter associated with the one of the one or more candidate secondarycells; and derive the security key of the basis station based on a master key and the selected security key counter.

[0015] In some examples of the first aspect, to perform the inter-SN SCG LTM theinstructions, when executed by the at least one processor, further cause the UE or apparatus to: use the derived security key to perform the inter-SN SCG LTM to the base station serving the one of the one or more candidate secondary cells.

[0016] In some examples of the first aspect, the security key is S-KgNB.

[0017] According to a second aspect of the present disclosure, a user equipment (UE) oran apparatus of such a UE for inter-SN SCG LTM is provided. The UE (e.g., a user device orterminal device) or the apparatus according to the second aspect comprises: means or modulesfor receiving, from a network node of a network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells (e.g., a receiver or receiving logic); and means or modules for performing the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information (e.g., aprocessor or processing logic).

[0018] In some examples of the second aspect, the UE or apparatus further comprisesmeans or modules for performing one or more of the examples according to the first aspect.

[0019] According to a third aspect of the present disclosure, a user equipment (UE) or anapparatus of such a UE for inter-SN SCG LTM is provided. The UE (e.g., a user device orterminal device) or the apparatus according to the third aspect comprises: circuitry to receive, from a network node of a network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells; and circuitry to perform the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information.

[0020] In some examples of the third aspect, the UE or apparatus further comprisescircuitry to perform one or more of the examples according to the first aspect.

[0021] According to a fourth aspect of the present disclosure, there is provided a methodfor inter-SN SCG LTM. The method may be performed by a user equipment (UE) of a wireless communication system. The method comprises: receiving, from a network node of the network,a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells; and performing the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information.

[0022] In some examples of the fourth aspect, the security information comprises anindication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

[0023] In some examples of the fourth aspect, the reconfiguration message comprises adedicated field for the indication.

[0024] In some examples of the fourth aspect, the method further comprises: in responseto determining, based on the indication, to perform the security update, performing the security update based on the security information.

[0025] In some examples of the fourth aspect, the security information comprises a securitykey counter configuration to enable the UE to derive a security key of a base station associated with the one of the one or more candidate secondary cells.

[0026] In some examples of the fourth aspect, the reconfiguration message comprises adedicated field for the security key counter configuration.

[0027] In some examples of the fourth aspect, the security key counter configurationcomprises one or more security key counters associated with the one or more candidate secondary cells.

[0028] In some examples of the fourth aspect, the method further comprises: selecting,from the one or more security key counters, a security key counter associated with the one ofthe one or more candidate secondary cells; and deriving the security key of the basis stationbased on a master key and the selected security key counter.

[0029] In some examples of the fourth aspect, performing the inter-SN SCG LTMcomprises: using the derived security key to perform the inter-SN SCG LTM to the base stationserving the one of the one or more candidate secondary cells.

[0030] In some examples of the fourth aspect, the security key is S-KgNB.

[0031] According to a fifth aspect of the present disclosure, a computer program productcomprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the fourth aspect as outlined above when said program is executed on a computer.

[0032] According to a sixth aspect of the present disclosure, a non-transitory computer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the fourth aspect as outline above.

[0033] According to a seventh aspect of the present disclosure, a network node (e.g., a basestation or network node) or an apparatus in such a network node for inter-SN SCG LTM isprovided. The network node (e.g., a base station or network device) or the apparatus according to the seventh aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: send, to a user equipment (UE) of a network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells.

[0034] In some examples of the seventh aspect, the security information comprises anindication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

[0035] In some examples of the seventh aspect, the reconfiguration message comprises adedicated field for the indication.

[0036] In some examples of the seventh aspect, the security information comprises asecurity key counter configuration to enable the UE to derive a security key of a base station associated with one of the one or more candidate secondary cells.

[0037] In some examples of the seventh aspect, the reconfiguration message comprises adedicated field for the security key counter configuration.

[0038] In some examples of the seventh aspect, the security key counter configurationcomprises one or more security key counters associated with the one or more candidatesecondary cells to enable the UE to select a security key counter associated with the one of theone of the one or more candidate secondary cells and derive the security key of the basis station.

[0039] In some examples of the seventh aspect, the security key is S-KgNB.

[0040] In some examples of the seventh aspect, the network node act as a master node(MN) of a master cell in the network.

[0041] In some examples of the seventh aspect, the instructions, when executed by the atleast one processor, further cause the network node or apparatus to: receive, from a secondarynode (SN) of a serving secondary cell in the network, a SN change required message including the one or more candidate secondary cells for the inter-SN SCG LTM; send, to a candidate SNof at least one of the one or more candidate secondary cells in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM; receive, from the candidate SN of the at least one candidate secondary cell, the configuration of the at least one candidate secondary cell. The configuration of the one or more candidate secondary cells for the inter-SN SCG LTM includes the configuration of the at least one candidate secondary cell.

[0042] In some examples of the seventh aspect, the SN change required message indicates,to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0043] In some examples of the seventh aspect, the SN change required message comprisesan information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0044] In some examples of the seventh aspect, the SN addition request message comprisesan information element to indicate, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0045] In some examples of the seventh aspect, the information element of the SN additionrequest message comprises one or more of: at least one security configuration for the inter-SNSCG LTM; and at least one identifier of another SN of the at least one candidate secondary celland at least one recommended candidate secondary cell.

[0046] In some examples of the seventh aspect, the at least one security configuration forthe inter-SN SCG LTM comprises one or more of: a security key of the SN of the servingsecondary cell or the candidate SN of the at least one candidate secondary cell, the security keybeing provided by the MN; and a security key counter to enable deriving a security key of abase station associated with the at least one candidate security cell.

[0047] In some examples of the seventh aspect, the SN addition request message indicates,to the candidate SN of the at least one candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0048] In some examples of the seventh aspect, the apparatus is comprised in a base stationof the network.

[0049] According to an eighth aspect of the present disclosure, a network node (e.g., a basestation or network node) or an apparatus in such a network node for inter-SN SCG LTM isprovided. The network node (e.g., a base station or network device) or the apparatus according to the eighth aspect comprises: means or modules for sending, to a user equipment (UE) of a network, a reconfiguration message including a configuration of one or more candidatesecondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells (e.g., a sender or sending logic).

[0050] In some examples of the eighth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the seventh aspect.

[0051] According to a nineth aspect of the present disclosure, a network node (e.g., a basestation or network node) or an apparatus in such a network node for an inter-SN SCG LTM isprovided. The network node (e.g., a base station or network device) or the apparatus according to the nineth aspect comprises: circuitry to send, to a user equipment (UE) of a network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells.

[0052] In some examples of the nineth aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the seventh aspect.

[0053] According to a tenth aspect of the present disclosure, there is provided a method foran inter-SN SCG LTM. The method may be performed by a network node (e.g., a base stationor network device) of a wireless communication system. The method comprises: sending, to a user equipment (UE) of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-SN SCG LTM, and security information for the one or more candidate secondary cells.

[0054] In some examples of the tenth aspect, the security information comprises anindication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

[0055] In some examples of the tenth aspect, the reconfiguration message comprises adedicated field for the indication.

[0056] In some examples of the tenth aspect, the security information comprises a securitykey counter configuration to enable the UE to derive a security key of a base station associated with one of the one or more candidate secondary cells.

[0057] In some examples of the tenth aspect, the reconfiguration message comprises adedicated field for the security key counter configuration.

[0058] In some examples of the tenth aspect, the security key counter configurationcomprises one or more security key counters associated with the one or more candidatesecondary cells to enable the UE to select a security key counter associated with the one of theone of the one or more candidate secondary cells and derive the security key of the basis station.

[0059] In some examples of the tenth aspect, the security key is S-KgNB.

[0060] In some examples of the tenth aspect, the network node act as a master node (MN)of a master cell in the network.

[0061] In some examples of the tenth aspect, the method further comprises: receiving, froma secondary node (SN) of a serving secondary cell in the network, a SN change required message including the one or more candidate secondary cells for the inter-SN SCG LTM; sending, to a candidate SN of at least one of the one or more candidate secondary cells in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM; receiving, from the candidate SN of the at least one candidate secondary cell, the configuration of the at least one candidate secondary cell. The configuration of the one or more candidate secondary cells for the inter-SN SCG LTM includes the configuration of the at least one candidate secondary cell.

[0062] In some examples of the tenth aspect, the SN change required message indicates, tothe MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0063] In some examples of the tenth aspect, the SN change required message comprisesan information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0064] In some examples of the tenth aspect, the SN addition request message comprisesan information element to indicate, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0065] In some examples of the tenth aspect, the information element of the SN additionrequest message comprises one or more of: at least one security configuration for the inter-SNSCG LTM; and at least one identifier of another SN of the at least one candidate secondary celland at least one recommended candidate secondary cell.

[0066] In some examples of the tenth aspect, the at least one security configuration for theinter-SN SCG LTM comprises one or more of: a security key of the SN of the serving secondarycell or the candidate SN of the at least one candidate secondary cell, the security key beingprovided by the MN; and a security key counter to enable deriving a security key of a basestation associated with the at least one candidate security cell.

[0067] In some examples of the tenth aspect, the SN addition request message indicates,to the candidate SN of the at least one candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0068] According to an eleventh aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the tenth aspect as outlined above when said program is executed on a computer.

[0069] According to a twelfth aspect of the present disclosure, a non-transitory computer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the tenth aspect as outline above.

[0070] According to a thirteenth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirteenth aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: receive, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM; send, to a candidate SN of the at least one candidate secondary cell in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM; receive, from the candidate SN of the at least one candidate secondary cell, a configuration of the at least one candidate secondary cell; and send, to a user equipment (UE), the configuration of the at least one candidate secondary cell to enable the UE to perform the inter-SN SCG LTM.

[0071] In some examples of the thirteenth aspect, the SN change required messageindicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0072] In some examples of the thirteenth aspect, the SN change required messagecomprises an information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0073] In some examples of the thirteenth aspect, the SN addition request messagecomprises an information element to indicate, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0074] In some examples of the thirteenth aspect, the information element of the SNaddition request message comprises one or more of: at least one security configuration for theinter-SN SCG LTM; and at least one identifier of another SN of the at least one candidate secondary cell and at least one recommended candidate secondary cell.

[0075] In some examples of the thirteenth aspect, the at least one security configurationfor the inter-SN SCG LTM comprises one or more of: a security key of the SN of the serving secondary cell or the candidate SN of the at least one candidate secondary cell, the security key being provided by the MN; and a counter to enable deriving a security key of a base station.

[0076] In some examples of the thirteenth aspect, the SN addition request messageindicates, to the candidate SN of the at least one candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0077] In some examples of the thirteenth aspect, the instructions, when executed by theat least one processor, further cause the network node or apparatus to: send, to the UE, security information associated with the at least one candidate secondary cell.

[0078] In some examples of the thirteenth aspect, the security information comprises oneor more of an indication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM and a counter to enable the UE to derive a security key of a base station for the inter-SN SCG LTM.

[0079] In some examples of the thirteenth aspect, the apparatus is comprised in a basestation of the network.

[0080] According to a fourteenth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to thefourteenth aspect comprises: means or modules for receiving, from a secondary node (SN) of aserving secondary cell in the network, a SN change required message including at least onecandidate secondary cell for an inter-SN SCG LTM (e.g., a receiver or receiving logic); meansor modules for sending, to a candidate SN of the at least one candidate secondary cell in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM (e.g., a sender or sending logic); means or modules for receiving, from the candidate SN of the at least one candidate secondary cell, a configuration of the at least one candidate secondary cell (e.g., the receiver or receiving logic); and means or modules for sending, to a user equipment (UE), the configuration of the at least one candidate secondary cell to enablethe UE to perform the inter-SN SCG LTM (e.g., the sender or sending logic).

[0081] In some examples of the fourteenth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the thirteenth aspect.

[0082] According to a fifteenth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the fifteenth aspect comprises: circuitry to receive, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM; circuitry to send, to a candidate SN of the at least one candidate secondary cell in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM; circuitry to receive, from the candidate SN of the at least one candidate secondary cell, a configuration of the at least one candidate secondary cell; and circuitry to send, to a user equipment (UE), the configuration of the at least one candidate secondary cell to enable the UE to perform the inter-SN SCG LTM.

[0083] In some examples of the fifteenth aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the thirteenth aspect.

[0084] According to a sixteenth aspect of the present disclosure, there is provided a methodfor inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a master node (MN) of a master cell in a network. The method comprises: receiving, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM; sending, to a candidate SN of the at least one candidate secondary cell in the network, a SN addition request message indicating, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM; receiving, from the candidate SN of the at least one candidate secondary cell, a configuration of the at least one candidate secondary cell; and sending, to a user equipment (UE), the configuration of the at least one candidate secondary cell to enable the UE to perform the inter-SN SCG LTM.

[0085] In some examples of the sixteenth aspect, the SN change required messageindicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0086] In some examples of the sixteenth aspect, the SN change required messagecomprises an information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0087] In some examples of the sixteenth aspect, the SN addition request messagecomprises an information element to indicate, to the candidate SN of the at least one candidate secondary cell, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0088] In some examples of the sixteenth aspect, the information element of the SNaddition request message comprises one or more of: at least one security configuration for the inter-SN SCG LTM; and at least one identifier of another SN of the at least one candidate secondary cell and at least one recommended candidate secondary cell.

[0089] In some examples of the sixteenth aspect, the at least one security configuration forthe inter-SN SCG LTM comprises one or more of: a security key of the SN of the serving secondary cell or the candidate SN of the at least one candidate secondary cell, the security key being provided by the MN; and a counter to enable deriving a security key of a base station.

[0090] In some examples of the sixteenth aspect, the SN addition request messageindicates, to the candidate SN of the at least one candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0091] In some examples of the sixteenth aspect, the method further comprises: sending,to the UE, security information associated with the at least one candidate secondary cell.

[0092] In some examples of the sixteenth aspect, the security information comprises oneor more of an indication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM and a counter to enable the UE to derive a security key of a base station for the inter-SN SCG LTM.

[0093] According to a seventeenth aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the sixteenth aspect as outlined above when said program is executed on a computer.

[0094] According to an eighteenth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the sixteenth aspect as outline above.

[0095] According to a nineteenth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in anetwork. The network node (e.g., a base station or network device) or the apparatus according to the nineteenth aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: in response to deciding to trigger to prepare for an inter-SN SCG LTM, send, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM. The SN change required message indicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0096] In some examples of the nineteenth aspect, the SN change required messagecomprises an information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0097] In some examples of the nineteenth aspect, the apparatus is comprised in a basestation of the network.

[0098] According to a twentieth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the twentieth aspect comprises: means or modules for, in response to deciding to trigger to prepare for an inter-SN SCG LTM, sending, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM (e.g., a sender or sending logic), The SN change required message indicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0099] In some examples of the twentieth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the nineteenth aspect.

[0100] According to a twenty-first aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the twenty-first aspect comprises: circuitry to, in response to deciding to trigger to prepare for an inter-SN SCG LTM, send, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCGLTM. The SN change required message indicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0101] In some examples of the twenty-first aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the nineteenth aspect.

[0102] According to a twenty-second aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as asecondary node (SN) of a serving secondary cell in a network. The method comprises: inresponse to deciding to trigger to prepare for an inter-SN SCG LTM, sending, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM. The SN change required message indicates, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0103] In some examples of the twenty-second aspect, the SN change required messagecomprises an information element to indicate, to the MN, that the SN change required message is to prepare for the inter-SN SCG LTM.

[0104] According to a twenty-third aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute stepsaccording to any one of the examples of the methods according to the twenty-second aspect asoutlined above when said program is executed on a computer.

[0105] According to a twenty-fourth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methodsaccording to the twenty-second aspect as outline above.

[0106] According to a twenty-fifth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a candidate secondary cell in anetwork. The network node (e.g., a base station or network device) or the apparatus accordingto the twenty-fifth aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: receive, from a master node (MN) of a master cell in the network, a SN addition request message indicating, to the candidate SN of the candidate secondary cell, that the SN addition request message is to prepare for an inter-SN SCG LTM; and send, to the MN, a configuration of the candidate secondary cell.

[0107] In some examples of the twenty-fifth aspect, the SN addition request messagecomprises an information element to indicate, to the SN, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0108] In some examples of the twenty-fifth aspect, the information element of the SNaddition request message comprises one or more of: at least one security configuration for the inter-SN SCG LTM; and at least one identifier of another SN of at least one other candidate secondary cell and at least one recommended candidate secondary cell.

[0109] In some examples of the twenty-fifth aspect, the at least one security configurationfor the inter-SN SCG LTM comprises one or more of: a security key of a SN of a serving secondary cell or the candidate SN of the candidate secondary cell, the security key being provided by the MN; and a counter to enable deriving a security key of a base station.

[0110] In some examples of the twenty-fifth aspect, the SN addition request messageindicates, to the candidate SN of the candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0111] In some examples of the twenty-fifth aspect, the apparatus is comprised in a basestation of the network.

[0112] According to a twenty-sixth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTMis provided. The network node act as a secondary node (SN) of a candidate secondary cell in anetwork. The network node (e.g., a base station or network device) or the apparatus accordingto the twenty-sixth aspect comprises: means or modules for receiving, from a master node (MN)of a master cell in the network, a SN addition request message indicating, to the candidate SN of the candidate secondary cell, that the SN addition request message is to prepare for an inter-SN SCG LTM (e.g., a receiver or receiving logic); and means or modules for sending, to theMN, a configuration of the candidate secondary cell (e.g., a sender or sending logic).

[0113] In some examples of the twenty-sixth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the twenty-fifth aspect.

[0114] According to a twenty-seventh aspect of the present disclosure, a network node(e.g., a base station or network node) or an apparatus in such a network node for inter-SN SCGLTM is provided. The network node act as a secondary node (SN) of a candidate secondary cellin a network. The network node (e.g., a base station or network device) or the apparatusaccording to the twenty-seventh aspect comprises: circuitry to receive, from a master node(MN) of a master cell in the network, a SN addition request message indicating, to the candidateSN of the candidate secondary cell, that the SN addition request message is to prepare for an inter-SN SCG LTM; and circuitry to send, to the MN, a configuration of the candidate secondary cell.

[0115] In some examples of the twenty-seventh aspect, the network node or apparatusfurther comprises circuitry to perform one or more of the examples according to the twenty- fifth aspect.

[0116] According to a twenty-eighth aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a secondary node (SN) of a candidate secondary cell in a network. The method comprises: receiving, from a master node (MN) of a master cell in the network, a SN addition request message indicating, to the candidate SN of the candidate secondary cell, that the SN addition request message is to prepare for an inter-SN SCG LTM; and sending, to the MN, a configuration of the candidate secondary cell.

[0117] In some examples of the twenty-eighth aspect, the SN addition request messagecomprises an information element to indicate, to the SN, that the SN addition request message is to prepare for the inter-SN SCG LTM.

[0118] In some examples of the twenty-eighth aspect, the information element of the SNaddition request message comprises one or more of: at least one security configuration for theinter-SN SCG LTM; and at least one identifier of another SN of at least one other candidatesecondary cell and at least one recommended candidate secondary cell.

[0119] In some examples of the twenty-eighth aspect, the at least one securityconfiguration for the inter-SN SCG LTM comprises one or more of: a security key of a SN of a serving secondary cell or the candidate SN of the candidate secondary cell, the security key being provided by the MN; and a counter to enable deriving a security key of a base station.

[0120] In some examples of the twenty-eighth aspect, the SN addition request messageindicates, to the SN of the candidate secondary cell, that a reference configuration for the inter- SN SCG LTM is requested.

[0121] According to a twenty-nineth aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the twenty-eighth aspect as outlined above when said program is executed on a computer.

[0122] According to a thirtieth aspect of the present disclosure, a non-transitory computer-readable medium containing computer-executable instructions which when run on one or moreprocessors perform the steps according to any one of the examples of the methods according tothe twenty-eighth aspect as outline above.

[0123] According to a thirty-first aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirty- first aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: receive, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG L1 / L2 Triggered Mobility (LTM); and send, to the SN of the serving secondary cell, a SN change refuse message to reject the SN change required message. The SN change refusemessage includes a cause indicating that the SN is to initiate preparing subsequent conditionalprimary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0124] In some examples of the thirty-first aspect, the cause indicates, to the SN, that aninter-master-node (MN) master cell group (MCG) LTM is configured.

[0125] In some examples of the thirty-first aspect, the instructions, when executed by theat least one processor, further cause the network node or apparatus to: determine whether the inter-MN MCG LTM is configured.

[0126] In some examples of the thirty-first aspect, the apparatus is comprised in a basestation of the network.

[0127] According to a thirty-second aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirty- second aspect comprises: means or modules for receiving, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM (i.e., a receiver or receiving logic); and means or modules for sending, to the SN of the serving secondary cell, a SN change refuse message to reject the SN change required message. The SN change refuse message includes acause indicating that the SN is to initiate preparing subsequent conditional primary secondarycell addition or change (S-CPAC) or conditional primary secondary cell change (CPC) (i.e., a sender or sending logic).

[0128] In some examples of the thirty-second aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the thirty-first aspect.

[0129] According to a thirty-third aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirty- third aspect comprises: circuitry to receive, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM; and circuitry to send, to the SN of the serving secondary cell, a SN change refuse message to reject the SN change required message. The SN change refusemessage includes a cause indicating that the SN is to initiate preparing subsequent conditionalprimary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0130] In some examples of the thirty-third aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the thirty-first aspect.

[0131] According to a thirty-fourth aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a master node (MN) of a master cell in a network. The method comprises: receiving, from a secondary node (SN) of a serving secondary cell in the network, a SN change required message including at least one candidate secondary cell for an inter-SN SCG LTM; and sending, to theSN of the serving secondary cell, a SN change refuse message to reject the SN change requiredmessage. The SN change refuse message includes a cause indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0132] In some examples of the thirty-fourth aspect, the cause indicates, to the SN, that aninter-master-node (MN) master cell group (MCG) LTM is configured.

[0133] In some examples of the thirty-fourth aspect, the method further comprises:determining, at the MN, whether the inter-MN MCG LTM is configured.

[0134] According to a thirty-fifth aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the thirty-fourth aspect as outlined above when said program is executed on a computer.

[0135] According to a thirty-sixth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the thirty-fourth aspect as outline above.

[0136] According to a thirty-seventh aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirty-seventh aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: in response to deciding to trigger to prepare for an inter-SN SCG LTM, send, to a master node (MN) of a master cell in the network, a SN change requiredmessage including at least one candidate secondary cell for the inter-SN SCG LTM; andreceive, from the MN, a SN change refuse message indicating that the MN rejects the SN change required message. The SN change refuse message includes a cause indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0137] In some examples of the thirty-seventh aspect, the cause indicates that an inter-master-node (MN) master cell group (MCG) LTM is configured at the MN.

[0138] In some examples of the thirty-seventh aspect, the apparatus is comprised in a basestation of the network.

[0139] According to a thirty-eighth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the thirty-eighth aspect comprises: means or modules for, in response to deciding to trigger to prepare for an inter-SN SCG LTM, sending, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM (e.g., a sender or sending logic); and means or modules for receiving, from the MN, a SN change refuse message indicating that the MN rejects the SN change required message (e.g., a receiver or receiving logic). The SN change refuse message includes a cause indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0140] In some examples of the thirty-eighth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to thethirty-seventh aspect.

[0141] According to a thirty-nineth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus accordingto the thirty-nineth aspect comprises: circuitry to, in response to deciding to trigger to preparefor an inter-SN SCG LTM, send, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM; and circuitry to receive, from the MN, a SN change refuse message indicating that the MN rejects the SN change required message, wherein the SN change refuse message includes a cause indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0142] In some examples of the thirty-nineth aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the thirty-seventh aspect.

[0143] According to a fortieth aspect of the present disclosure, there is provided a methodfor inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a secondary node (SN) of a serving secondary cell in a network. The method comprises: in response to deciding to trigger to prepare for an inter-SN SCG LTM, sending, to a master node (MN) of a master cell in the network, a SN change required message including at least one candidate secondary cell for the inter-SN SCG LTM; and receiving, from the MN, a SN change refuse message indicating that the MN rejects the SN change required message. The SN change refuse message includes a cause indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0144] In some examples of the fortieth aspect, the cause indicates that an inter-master-node (MN) master cell group (MCG) LTM is configured at the MN.

[0145] According to a forty-first aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute stepsaccording to any one of the examples of the methods according to the fortieth aspect as outlinedabove when said program is executed on a computer.

[0146] According to a forty-second aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methodsaccording to the fortieth aspect as outline above.

[0147] According to a forty-third aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the forty- third aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatusat least to: in response to determining that an inter-master-node (MN) master cell group (MCG)L1 / L2 Triggered Mobility (LTM) is configured, notify a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is configured; and receive, from the SN, a SN change required message including a request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0148] In some examples of the forty-third aspect, to notify the SN the instructions, whenexecuted by the at least one processor, cause the network node or apparatus to: send, to the SN, a message via a Xn interface, the message including a cause to notify that the inter-MN MCG LTM is configured.

[0149] In some examples of the forty-third aspect, the message is to prevent the SN frominitiating an inter-SN SCG LTM.

[0150] In some examples of the forty-third aspect, the apparatus is comprised in a basestation of the network.

[0151] According to a forty-fourth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the forty- fourth aspect comprises: means or modules for, in response to determining that an inter-master-node (MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) is configured, notifyinga secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is configured (e.g., a processor or notifying logic); and means or modules for receiving, from the SN, a SN change required message including a request for subsequent conditional primarysecondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC) (e.g., a receiver or receiving logic).

[0152] In some examples of the forty-fourth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the forty- third aspect.

[0153] According to a forty-fifth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the forty-fifth aspect comprises: circuitry to, in response to determining that an inter-master-node (MN)master cell group (MCG) L1 / L2 Triggered Mobility (LTM) is configured, notify a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is configured; and circuitry to receive, from the SN, a SN change required message including a request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0154] In some examples of the forty-fifth aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the forty-third aspect.

[0155] According to a forty-sixth aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a basestation or network device) of a wireless communication system. The network node act as amaster node (MN) of a master cell in a network. The method comprises: in response todetermining that an inter-master-node (MN) master cell group (MCG) L1 / L2 TriggeredMobility (LTM) is configured, notifying a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is configured; and receiving, from the SN, a SN change required message including a request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0156] In some examples of the forty-sixth aspect, notifying the SN comprises: sending, tothe SN, a message via a Xn interface, the message including a cause to notify that the inter-MN MCG LTM is configured.

[0157] In some examples of the forty-sixth aspect, the message is to prevent the SN frominitiating an inter-SN secondary cell group (SCG) LTM.

[0158] According to a forty-seventh aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute stepsaccording to any one of the examples of the methods according to the forty-sixth aspect as outlined above when said program is executed on a computer.

[0159] According to a forty-eighth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the forty-sixth aspect as outline above.

[0160] According to a forty-nineth aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the forty-nineth aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: receive, from a master node (MN) of a master cell in the networkSN, a notification that an inter-master-node (MN) master cell group (MCG) L1 / L2 TriggeredMobility (LTM) is configured at the MN; and send, to the MN, a SN change required message including a request for subsequent conditional primary secondary cell addition or change (S- CPAC) or conditional primary secondary cell change (CPC).

[0161] In some examples of the forty-nineth aspect, to receive the notification theinstructions, when executed by the at least one processor, cause the network node apparatus to: receive, from the MN, a message via a Xn interface, the message including a cause to notify that the inter-MN MCG LTM is configured at the MN.

[0162] In some examples of the forty-nineth aspect, the message is to prevent the SN frominitiating an inter-SN secondary cell group (SCG) LTM.

[0163] In some examples of the forty-nineth aspect, the apparatus is comprised in a basestation of the network.

[0164] According to a fiftieth aspect of the present disclosure, a network node (e.g., a basestation or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the fiftieth aspect comprises: means or modules for receiving, from a master node (MN) ofa master cell in the network SN, a notification that an inter-master-node (MN) master cell group(MCG) L1 / L2 Triggered Mobility (LTM) is configured at the MN (e.g., a receiver or receiving logic); and means or modules for sending, to the MN, a SN change required message includinga request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC) (e.g., a sender or sending logic).

[0165] In some examples of the fiftieth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the forty- nineth aspect.

[0166] According to a fifty-first aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus accordingto the fifty-first aspect comprises: circuitry to receive, from a master node (MN) of a mastercell in the network SN, a notification that an inter-master-node (MN) master cell group (MCG)L1 / L2 Triggered Mobility (LTM) is configured at the MN; and circuitry to send, to the MN, a SN change required message including a request for subsequent conditional primary secondarycell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0167] In some examples of the fifty-first aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the forty-nineth aspect.

[0168] According to a fifty-second aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as asecondary node (SN) of a serving secondary cell in a network. The method comprises:receiving, from a master node (MN) of a master cell in the network SN, a notification that aninter-master-node (MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) isconfigured at the MN; and sending, to the MN, a SN change required message including a request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0169] In some examples of the fifty-second aspect, receiving the notification comprises:receiving, from the MN, a message via a Xn interface, the message including a cause to notify that the inter-MN MCG LTM is configured at the MN.

[0170] In some examples of the fifty-second aspect, the message is to prevent the SN frominitiating an inter-SN secondary cell group (SCG) LTM.

[0171] According to a fifty-third aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the fifty-second aspect as outlined above when said program is executed on a computer.

[0172] According to a fifty-fourth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the fifty-second aspect as outline above.

[0173] According to a fifty-fifth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the fifty- fifth aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatusat least to: in response to determining that an inter-master-node (MN) master cell group (MCG)L1 / L2 Triggered Mobility (LTM) is de-configured, notify a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is de-configured; and receive, from the SN, a notification indicating that an inter-SN SCG LTM is configured.

[0174] In some examples of the fifty-fifth aspect, to receive the notification theinstructions, when executed by the at least one processor, cause the network node or apparatus to: receive, from the SN, a message via a Xn interface, the message including a cause to notify that the inter-SN SCG LTM is configured.

[0175] In some examples of the fifty-fifth aspect, the apparatus is comprised in a basestation of the network.

[0176] According to a fifty-sixth aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the fifty- sixth aspect comprises: means or modules for, in response to determining that an inter-master-node (MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) is de-configured,notifying a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is de-configured (e.g., a processor or notifying logic); and means or modules for receiving, from the SN, a notification indicating that an inter-SN SCG LTM is configured (e.g., a receiver or receiving logic).

[0177] In some examples of the fifty-sixth aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the fifty- fifth aspect.

[0178] According to a fifty-seventh aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a master node (MN) of a master cell in a network. The network node (e.g., a base station or network device) or the apparatus according to the fifty- seventh aspect comprises: circuitry to, in response to determining that an inter-master-node(MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) is de-configured, notify asecondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is de-configured; and circuitry to receive, from the SN, a notification indicating that an inter- SN SCG LTM is configured.

[0179] In some examples of the fifty-seventh aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the fifty-fifth aspect.

[0180] According to a fifty-eighth aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a master node (MN) of a master cell in a network. The method comprises: in response todetermining that an inter-master-node (MN) master cell group (MCG) L1 / L2 TriggeredMobility (LTM) is de-configured, notifying a secondary node (SN) of a serving secondary cell in the network that the inter-MN MCG LTM is de-configured; and receiving, from the SN, a notification indicating that an inter-SN SCG LTM is configured.

[0181] In some examples of the fifty-eighth aspect, receiving comprises: receiving, fromthe SN, a message via a Xn interface, the message including a cause to notify that the inter-SN SCG LTM is configured.

[0182] According to a fifty-nineth aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the fifty-eighth aspect as outlined above when said program is executed on a computer.

[0183] According to a sixtieth aspect of the present disclosure, a non-transitory computer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the fifty-eighth aspect as outline above.

[0184] According to a sixty-first aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus accordingto the sixty-first aspect comprises at least one processor and at least one memory storing instructions. The instructions, when executed by the at least one processor, cause the network node or apparatus at least to: receive, from a master node (MN) of a master cell in the network,a notification that an inter-master-node (MN) master cell group (MCG) L1 / L2 TriggeredMobility (LTM) is de-configured at the MN; and send, to the MN, a notification indicating that an inter-SN SCG LTM is configured.

[0185] In some examples of the sixty-first aspect, to send the notification the instructions,when executed by the at least one processor, cause the network node or apparatus to: send, to the MN, a message via a Xn interface, the message including a cause to notify that the inter-SN SCG LTM is configured.

[0186] In some examples of the sixty-first aspect, the instructions, when executed by theat least one processor, cause the network node or apparatus to: in response to receiving the notification that the inter-MN MCG LTM is de-configured, configure the inter-SN SCG LTM at the SN.

[0187] In some examples of the sixty-first aspect, the apparatus is comprised in a basestation of the network.

[0188] According to a sixty-second aspect of the present disclosure, a network node (e.g.,a base station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus accordingto the sixty-second aspect comprises: means or modules for receiving, from a master node (MN)of a master cell in the network, a notification that an inter-master-node (MN) master cell group(MCG) L1 / L2 Triggered Mobility (LTM) is de-configured at the MN (e.g., a receiver or receiving logic); and means or modules for sending, to the MN, a notification indicating that an inter-SN SCG L1 / L2 Triggered Mobility (LTM) is configured (e.g., a sender or sending logic).

[0189] In some examples of the sixty-second aspect, the network node or apparatus furthercomprises means or modules for performing one or more of the examples according to the sixty- first aspect.

[0190] According to a sixty-third aspect of the present disclosure, a network node (e.g., abase station or network node) or an apparatus in such a network node for inter-SN SCG LTM is provided. The network node act as a secondary node (SN) of a serving secondary cell in a network. The network node (e.g., a base station or network device) or the apparatus accordingto the sixty-third aspect comprises: circuitry to receive, from a master node (MN) of a mastercell in the network, a notification that an inter-master-node (MN) master cell group (MCG)L1 / L2 Triggered Mobility (LTM) is de-configured at the MN; and circuitry to send, to the MN, a notification indicating that an inter-SN SCG LTM is configured.

[0191] In some examples of the sixty-third aspect, the network node or apparatus furthercomprises circuitry to perform one or more of the examples according to the sixty-first aspect.

[0192] According to a sixty-fourth aspect of the present disclosure, there is provided amethod for inter-SN SCG LTM. The method may be performed by a network node (e.g., a base station or network device) of a wireless communication system. The network node act as a secondary node (SN) of a serving secondary cell in a network. The method comprises: receiving, from a master node (MN) of a master cell in the network, a notification that an inter-master-node (MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) is de-configuredat the MN; and sending, to the MN, a notification indicating that an inter-SN SCG LTM isconfigured.

[0193] In some examples of the sixty-fourth aspect, sending the notification comprises:sending, to the MN, a message via a Xn interface, the message including a cause to notify that the inter-SN SCG LTM is configured at the SN.

[0194] In some examples of the sixty-fourth aspect, the method further comprises: inresponse to receiving the notification that the inter-MN MCG LTM is de-configured, configuring the inter-SN SCG LTM at the SN.

[0195] According to a sixty-fifth aspect of the present disclosure, a computer programproduct comprises program instructions stored on a computer readable medium to execute steps according to any one of the examples of the methods according to the sixty-fourth aspect as outlined above when said program is executed on a computer.

[0196] According to a sixty-sixth aspect of the present disclosure, a non-transitorycomputer-readable medium containing computer-executable instructions which when run on one or more processors perform the steps according to any one of the examples of the methods according to the sixty-fourth aspect as outline above.

[0197] The above-noted aspects and features may be implemented in systems, apparatuses,methods, articles and / or non-transitory computer-readable media depending on the desiredconfiguration. The present disclosure may be implemented in and / or used with a number ofdifferent types of devices, including but not limited to cellular phones, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.

[0198] This summary is intended to provide a brief overview of some of the aspects andfeatures according to the present disclosure. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope of thepresent disclosure in any way. Other features, aspects, and advantages of the present disclosurewill become apparent from the following detailed description, drawings, and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0199] A better understanding of the present disclosure can be obtained when the followingdetailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0200] FIGURE 1 is a schematic diagram of an example of a (mobile / wireless)communication system or network according to embodiments of the present disclosure;

[0201] FIGURE 2 is a block diagram of an example of an apparatus according toembodiments of the present disclosure;

[0202] FIGURE 3 is a signaling diagram of an example of a lower (L1 / L2) triggeredmobility (LTM) procedure;

[0203] FIGURE 4 is a signaling diagram of an example of a procedure for SN initiated SNchange in a dual connectivity scenario;

[0204] FIGURES 5 and 6 are flowcharts of methods or processes for inter-SN SCG LTMaccording to embodiments relating to first aspects of the present disclosure;

[0205] FIGURE 7 is a signaling diagram of an example of a method or process for inter-SN SCG LTM according to embodiments relating to first aspects of the present disclosure;

[0206] FIGURES 8 and 9 are flowcharts of methods or processes for inter-SN SCG LTMaccording to embodiments relating to second aspects of the present disclosure;

[0207] FIGURE 10 is a signaling diagram of an example of a method or process for inter-SN SCG LTM according to embodiments relating to second aspects of the present disclosure;

[0208] FIGURES 11 and 12 are flowcharts of methods or processes for inter-SN SCG LTMaccording to embodiments relating to third aspects of the present disclosure;

[0209] FIGURE 13 is a signaling diagram of an example of a method or process for inter-SN SCG LTM according to embodiments relating to third aspects of the present disclosure;

[0210] FIGURES 14 and 15 are flowcharts of methods or processes for inter-SN SCG LTMaccording to embodiments relating to fourth aspects of the present disclosure;

[0211] FIGURE 16 is a signaling diagram of an example of a method or process for inter-SN SCG LTM according to embodiments relating to fourth aspects of the present disclosure;

[0212] FIGURE 17 illustrates a schematic block diagram showing structures of an exampleof an apparatus to implement embodiments of the present disclosure.DETAILED DESCRIPTION

[0213] The examples and embodiments set forth below represent information to enablethose skilled in the art to practice the present disclosure. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the description and will recognize applications of these concepts not particularly addressed herein. These concepts and applications fall within the scope of the description.

[0214] In the following description, numerous specific details are set forth. However, it isunderstood that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of the description. Those of ordinary skill in the art, with the included description, will be able to implement appropriate functionality without undue experimentation.

[0215] References in the specification to "one embodiment," "an embodiment," "anexample embodiment," etc., indicate that the embodiment described may include a particularfeature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. When a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0216] It is to be noted that the detailed description, at times, refers to one or morespecifications being used as non-limiting and illustrative examples for certain architectures, network configurations and system deployments. More specifically, the detailed description refers to 3GPP standards, being used as non-limiting and illustrative examples. As such, thevarious embodiments provided herein can specifically employ terminology which is directlyrelated thereto. Such terminology is only used in the context of the non-limiting and illustrative examples and is not intended to limit the various embodiments in any way. Rather, any other system configuration or deployment may be utilized while complying with what is described herein and / or various embodiments are applicable to it.

[0217] For example, various embodiments are applicable in any (e.g., mobile / wireless)communication system, such as a 5G / NR system and a next-generation system beyond 5G. For example, various embodiments are applicable in a 3GPP-standardized mobile / wirelesscommunication system of Release 19 onwards.

[0218] Hereinafter, various embodiments are described using several variants and / oralternatives. It is generally to be noted that, according to certain implementations or constraints,all the described variants and / or alternatives may be provided alone or in any conceivablecombination (e.g., also including combinations of individual features of these various variants and / or alternatives).

[0219] The words "comprising" and "including" do not limit the embodiments to consistof only those features that have been mentioned, and embodiments may also contain, amongother things, e.g., features, structures, units, modules, or the like, that have not been specificallymentioned.

[0220] The wording "at least one of the following: ", "atleast one of ", or the like such as "one or more of", where thelist of two or more elements are joined by "and" or "or", mean at least any one of the elements,or at least any two or more of the elements, or at least all the elements.

[0221] According to various embodiments, any operations of sending or receiving maycomprise actual transmission or communication operations, i.e., transmitting or communicatingassociated messages or signals, but may additionally or alternatively comprise relatedprocessing operations, i.e., preparing / generating / issuing associated messages or signals beforesending and / or obtaining / handling / processing of associated messages or signals after receiving. For example, sending a message at / by an entity may comprise generating / issuing and / or transmitting / communicating thereof or a corresponding signal in / at / by the entity, and receiving a message at / by an entity may comprise obtaining / handling and / or processing thereof or acorresponding signal in / at / by the entity. A message may refer to and / or encompass any kind ofcorresponding information, signal, or the like.

[0222] In the drawings, it is to be noted that lines / arrows interconnecting individual blocksor entities are generally meant to illustrate an operational coupling there-between, which may be a physical and / or logical coupling, which on the one hand is implementation-independent(e.g., wired, or wireless) and on the other hand may also comprise an arbitrary number ofintermediary functional blocks or entities not shown. In flowcharts or sequence diagrams, theillustrated order of operations or actions is generally non-limiting and illustrative, and any otherorder of respective operations or actions is conceivable, if feasible.

[0223] Embodiments described may be implemented in a communication network, such asany of the following radio access technologies (RATs): World-wide Interoperability for Micro- wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGEradio access Network (GERAN), General Packet Radio Service (GRPS), Universal MobileTelecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE- Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0224] As used herein, the term “network device” or “network node” refers to a node in acommunication network via which user equipment may access the network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a non- terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0225] Moreover, in connection of split radio access network (RAN), the network devicemay refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a basestation. An interface between CU and DU may be referred to as an F1 interface in NR. In thesplit RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC),medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprisethe layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) layer and an internet protocol (IP) layer. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0226] The term “terminal device” refers to any end device that may be capable of wirelesscommunication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle- mounted wireless terminal devices, USB dongles, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain con- texts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0227] A term “resource”, as used herein, may refer to radio resources in time domain, infrequency domain, in space domain, and / or in code domain. Some examples of resources include e.g. a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” mayrefer to wirelessly transmitting and / or receiving via a wireless propagation channel on radioresources.

[0228] It is noted that 3GPP standard documents to which it is referred in the presentdisclosure are to be understood as incorporated herein by reference.

[0229] FIGURE 1 illustrates an example of a (mobile / wireless) communication system ornetwork according to embodiments of the present disclosure, i.e., an example of a (mobile / wireless) communication system or network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 providing one or more cells, such as cell 100, and a network node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. The cell may define a coverage area or a service area of the corresponding access node.

[0230] The network node 110 may provide a user equipment (UE) 120 (one or more UEs)with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node 110 to the UE 120 and uplink (UL)communication from the UE 120 to the network node 110. Examples of UL channels comprisephysical uplink control channel (PUCCH) for transmitting control information and physicaluplink shared channel (PUSCH) for transmitting data towards the network. Examples of DL channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0231] There may be a plurality of UEs 120, 122 in the system. Each of them may be servedby the same or by different network nodes 110, 112. UE 120, 122 may be configured with dual connectivity (DC), wherein the UE, e.g. UE 120, may be connected to multiple network nodes (e.g., both network node 110, 112). The UE 120, 122 may communicate with each other, in case device-to-device (D2D) communication interface is established between them via a so- called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or vehicle-to-vehicle (V2V), for example.

[0232] In the case of multiple network nodes in the communication network, the networknodes may be connected to each other via an interface. LTE specifications call such an interfaceas X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodesmay be called Xn interface.

[0233] The network nodes 110, 112 may be further connected via another interface to acore network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise e.g. a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signaling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the corenetwork as a 5G core (5GC). The 5G core may comprise e.g. an access and mobilitymanagement function (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signaling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0234] FIGURE 2 shows, by way of example, a block diagram of an apparatus 200according to embodiments of the present disclosure, i.e., an example of an apparatus to implement examples disclosed herein. The apparatus 200 comprises, for example, at least oneprocessor 210 and at least one memory 220 storing instructions 230 that, when executed by theat least one processor 210, cause the apparatus 200 at least to perform the method or methodsas disclosed herein, and any of the embodiments thereof. In an example, the at least one memory220 and the instructions 230 (e.g., a computer program code, software) are configured, with theat least one processor 210, to cause the apparatus 200 to perform the method or methods asdisclosed herein, and any of the embodiments thereof.

[0235] A processor 210 may comprise circuitry, or be constituted as circuitry or circuitries,the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein.

[0236] As used in this application, the term “circuitry” may refer to one or more or all ofthe following: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hard-ware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a user equipment, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that re-quires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for amobile device or a similar integrated circuit in server, a cellular network device, or othercomputing or network device.

[0237] The memory 220 may be implemented using any suitable data storage technology.The memory 220 may comprise a database for storing data. The memory 220 may be at leastin part external to apparatus 200 but accessible to apparatus 200.

[0238] The instructions 230 may be comprised in a computer readable medium or a non-transitory computer readable medium. A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storagepersistency (e.g. random-access memory, RAM, vs. read only memory, ROM).

[0239] For example, the apparatus 200 is a terminal device, such as the UE 120 / 122described with reference to FIGURE 1. As another example, the apparatus 200 is comprised insuch a terminal device, e.g., as a chipset configured to control the terminal device. Theapparatus 200 may be caused or configured to perform at least the method of FIGURE 5 and / orany one or more of the embodiments described.

[0240] As another example, the apparatus 200 is a network node such as the network node110 / 112 described with reference to FIGURE 1. In another embodiment, the apparatus 200 iscomprised in such a network node, e.g., as a chipset configured to control the network node.The apparatus 200 may be caused or configured to perform one more of the methods ofFIGURES 6, 8, 9, 11, 12, 14 and 15 and / or any one or more of the embodiments described.

[0241] The apparatus 200 may comprise one or more entities of any of protocol layers,such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In someembodiments, the entity is configured to perform one or more of the methods of FIGURES 6,8, 9, 11, 12, 14 and 15, and / or any one or more of the embodiments described.

[0242] The apparatus 200 comprises a radio interface 240. The radio interface 240 mayprovide the apparatus 200 with communication capabilities. The radio interface 240 may comprise a receiver configured to receive information in accordance with at least one cellularor non-cellular standard. The radio interface 240 may comprise a transmitter configured totransmit information in accordance with at least one cellular or non-cellular standard. The receiver may comprise more than one receiver. The transmitter may comprise more than onetransmitter. The radio interface 240 may comprise a transceiver configured to receive andtransmit information in accordance with at least one cellular or non-cellular standard. The transceiver may comprise more than one transceiver.

[0243] The apparatus 200 may comprise a user interface 250 comprising, for example, atleast one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 250 may be used to control the apparatus by the user. The user interface 250 may be externalto the apparatus 200. For example, the apparatus 200 may be connected to another device, suchas a computer, either via wireless or wired connection, and the apparatus 200 is controlled bythe user via the computer.

[0244] In an embodiment, at least some of the processes described herein may be carriedout by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may include software and / or hardware components of the apparatus 200. For example, the at least one processor 210, the memory 220, and the computer program code form means for carrying out the method or methods as disclosed herein, and any of the embodiments thereof.

[0245] As used herein the term “means” is to be construed in singular form, i.e. referringto a single element, or in plural form, i.e. referring to a combination of single elements.Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully over-lapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0246] Before referring to FIGURES 5 to 16 and describing the methods for inter-SN SCGLTM according to embodiments of the present disclosure, some background information andaspects related to the present disclosure will be provided.

[0247] In 3GPP Rel-18, a new mobility mechanism was introduced, namely lower layer(L1 / L2) triggered mobility (LTM), which aims to reduce interruption time during handover.

[0248] LTM is a cell switch procedure, where UE’s serving cell (PCell or PSCell) isswitched by the network by sending an LTM cell switch command. An LTM switch command may be delivered by MAC signaling using a MAC CE. Hence, not using RRC signaling (as in the case of L3 based handover). LTM cell switch decision is based on measurements (e.g., L1 measurements) that are performed and reported by the UE. Measurements and reporting arebased on LTM candidate cell configuration provided by the network for one or more LTMcandidate cells. An LTM candidate cell may be neighboring cells or a UE’s current serving cells (e.g., SCells).

[0249] In 3GPP Rel-18, LTM measurements on a neighboring candidate cell are performedusing SSBs transmitted by the candidate cell for which the SSB configuration is provided to the UE.

[0250] Before the cell switch, network may optionally activate one or more TCI state(s)for one or more candidate cells. Once a candidate cell TCI state is activated the UE may start tracking the time / frequency synchronization using the reference signals associated with the activated TCI state(s). The UE may also perform early UL synchronization before the cell switch if this is requested by the network.

[0251] The overall procedure for LTM is illustrated in the signaling diagram in FIGURE3, with reference to the network components schematically illustrated in FIGURE 1.

[0252] As described in 3GPP TS 38.300 V18.0.0, the procedure for LTM is as follows:

[0253] In step 1, the UE (e.g., the UE 120) sends a Measurement Report message to thebase station (e.g., the gNB 110), which provides access to the source cell (e.g., the cell 100). The gNB 110 decides to configure LTM and initiates LTM preparation.

[0254] In step 2, the gNB 110 transmits an RRC Reconfiguration message to the UE 120including the LTM candidate configurations.

[0255] In step 3, the UE 120 stores the LTM candidate configurations and transmits anRRC Reconfiguration Complete message to the gNB 110.

[0256] Steps 1 to 3 relate to a preparation phase (i.e., LTM preparation) of the LTMprocedure.

[0257] In step 4a, the UE 120 performs DL synchronization with the candidate cell(s) (e.g.,the candidate cell 102) before receiving the cell switch command.

[0258] In step 4b, when the UE-based TA measurement is configured, the UE 120 acquiresthe TA value(s) of the candidate cell(s) 102 by measurement. The UE 120 performs early TA acquisition with the candidate cell(s) 102 as requested by the network before receiving the cell switch command. This is done via CFRA triggered by a PDCCH order from the source cell100, following which the UE 120 sends preamble towards the indicated candidate cell(s) 102.In order to minimize the data interruption of the source cell 100 due to CFRA towards thecandidate cell(s) 102, the UE 120 does not receive a random-access response from the networkfor the purpose of TA value acquisition and the TA value of the candidate cell(s) 102 is insteadindicated in the cell switch command. The UE 120 does not maintain the TA timer for thecandidate cell(s) 102 and relies on network implementation to guarantee the TA validity.

[0259] Steps 4a and 4b relate to an early synchronization phase (i.e., Early sync) of theLTM procedure.

[0260] In step 5, the UE 120 performs L1 measurements on the configured candidate cell(s)102 and transmits L1 measurement reports to the source gNB 110. L1 measurement should be performed as long as the RRC reconfiguration (from step 2) is applicable.

[0261] In step 6, the gNB 110 decides to execute a cell switch from the source cell 100 tothe candidate or target cell (e.g., the cell 102) and transmits a MAC CE triggering cell switchby including the candidate configuration index of the target cell 102. The UE 120 then switches to the target cell 102 and applies the configuration indicated by candidate configuration index.

[0262] In step 7, the UE 120 performs the random-access procedure towards the target cell102, if the UE 120 does not have a valid TA of the target cell 102 as specified in 3GPP TS38.321 (e.g., clause 6.1.3.75).

[0263] Steps 6 to 7 relate to an execution phase (i.e., LTM execution) of the LTMprocedure.

[0264] In step 8, the UE 120 completes the LTM cell switch procedure by sending RRCReconfiguration Complete message to the base station (e.g., the gNB 112) providing access tothe target cell 102. If the UE 120 has performed a random-access procedure in step 7 then the UE 120 considers that LTM cell switch execution is successfully completed when the random- access procedure is successfully completed. For RACH-less LTM, the UE 120 considers that the LTM cell switch execution is successfully completed when the UE 120 determines that the network has successfully received its first UL data.

[0265] Step 8 relates to a completion phase (i.e., LTM completion) of the LTM procedure.

[0266] The steps 4 to 8 can be performed multiple times for subsequent LTM using theLTM candidate configuration(s) provided in step 2.

[0267] The procedure over the air interface described above is applicable to both intra-gNB-DU LTM and inter-gNB-DU LTM. The overall LTM procedures over F1-C interface are captured in 3GPP TS 38.401.

[0268] As seen above, in LTM, early TA acquisition, i.e., TA acquisition beforehandover / cell switch, can be performed in the following ways:

[0269] Firstly, the network can order the UE 120 to perform random access (RA) preambletransmission to a candidate cell 102. The candidate cell 102 uses the received RA preamble to estimate the TA and provides the TA estimate to the source cell 100. When the source cell 100 decides to trigger the cell switch, it provides the estimated TA value along with the cell switch command.

[0270] Secondly, during LTM preparation, the network can configure the UE 120 toperform UE-based TA measurements. UE-based TA measurements may be performed based on the TA of the serving cell 100 and the measured time difference between the candidate cell 102 and the serving cell 100. After being configured, the UE 120 is assumed to obtain a TA measurement before a cell switch command is issued by the gNB 110 providing access to the source cell 100.

[0271] Another purpose served by random access is that the target gNB 112 is notifiedabout the presence of the UE 120 and resources for the UE’s subsequent transmissions are provided to the UE 120. Hence, when RACH-less LTM cell switch is performed, a mechanism is required to support the initial transmission of the UE 120 to the target cell 102. A mechanism that supports this purpose is the provisioning of configured grants, which consist of sets of resources in the candidate / target cell that the UE 120 may use if / when it performs its initial transmission after handover / cell switch to the target cell 102. An alternative to this mechanism is to provide an access notification from the source cell 100 to the target cell 102, so that the target cell 102 can then provide a dynamic grant to the UE 120 for the target cell 102.

[0272] A similar RACH-less approach has also been proposed for baseline and conditionalhandover (BHO / CHO) as well to facilitate fast cell switch.

[0273] In a dual connectivity scenario, the secondary node (SN) change procedure may beinitiated either by master node (MN) or SN and is used to transfer a UE context from a sourceSN (S-SN) to a target SN (T-SN) and to change the secondary cell group (SCG) configurationin UE from one SN to another.

[0274] The dual connectivity scenario allows UE to simultaneously transmit and receivedata on multiple component carriers from two serving nodes or cell groups (e.g., a master node (MN) and a secondary node (SN)). The dual connectivity is allowed between two serving nodes operating in the same technology (both NR, both LTE, for example), or operating in different radio access technologies (RATs), such as MN operating in LTE while SN is operating in NR, or vice versa. For example, using an LTE MN and NR SN allows networks to employ both 4G and 5G to increase user throughput utilizing the wide 5G spectrum while providing the UE 120 / 122 with a wider coverage, thanks to the 4G spectrum.

[0275] The procedure for SN initiated SN change in the dual connectivity scenario isillustrated in the signaling diagram in FIGURE 4, with reference to the network componentsschematically illustrated in FIGURE 1. The procedure for SN initiated SN change is as follows:

[0276] In step 1, the source SN 420 initiates the SN change procedure by sending the SNChange Required message, which contains a candidate target node ID and may include the SCG configuration (to support delta configuration) and measurement results related to the target SN 430.

[0277] In steps 2 and 3, the MN 410 requests the target SN 430 to allocate resources forthe UE 120 by means of the SN Addition procedure, including the measurement results related to the target SN 430 received from the source SN 420. If data forwarding is needed, the target SN 430 provides data forwarding addresses to the MN 410. The target SN 430 includes the indication of the full or delta RRC configuration.

[0278] In steps 4 and 5, the MN 410 triggers the UE 120 to apply the new configuration.The MN 410 indicates the new configuration to the UE 120 in the MN RRC reconfiguration message including the SN RRC reconfiguration message generated by the target SN 430. The UE 120 applies the new configuration and sends the MN RRC reconfiguration complete message (step 5), including the SN RRC response message for the target SN 430, if needed.

[0279] In step 6, if the allocation of the target SN resources was successful, the MN 410confirms the change of the source SN 420.

[0280] In step 7, if the RRC connection reconfiguration procedure was successful, the MN410 informs the target SN 430 via SN Reconfiguration Complete message with the includedSN RRC response message for the target SN 430, if received from the UE 120. The UE 120synchronizes to the target SN 430.

[0281] In step 8, the UE 120 performs the random-access procedure towards the target cell102.

[0282] Steps 9 to 17 concern operations related to the transfer of the status and the UEcontext (for example).

[0283] In this respect, reference is also made to the SN initiated inter-SN subsequentConditional PSCell Addition or Change (CPAC) procedure described in 3GPP TS 37.340 (e.g.,clause 10.20) and the intra-SN SCG LTM without MN involvement procedure described in 3GPP TS 37.340 (e.g., clause 10.3.2).

[0284] An SCG LTM is defined as a PSCell cell switch procedure that the network triggersvia MAC CE.

[0285] For Rel-19, inter-SN SCG LTM with PCell (MCG) unchanged scenario with highpriority followed by inter-MN MCG LTM with PSCell (SCG) unchanged and PSCell (SCG) released may be prioritized. The present disclosure proposes enhancements to enable the preparation of inter-SN SCG LTM.

[0286] More specifically, in both MN initiated and SN initiated inter-SN SCG LTMpreparation scenarios, it is the MN that triggers the preparation of candidate SN, by requesting the candidate SN(s) to allocate resources for the UE by means of the SN Addition procedure. The MN may prepare one or multiple candidate target SNs.

[0287] In inter-SN SCG LTM, the candidate SN prepares the LTM candidateconfiguration, which includes SCG configuration and LTM CSI Resource configuration. The candidate SN may either prepare delta configuration if SCG reference configuration is included in the SN Addition Request or may prepare complete SCG configuration.

[0288] As part of S-CPAC functionality, an information element (IE) “S-CPAC Request”was introduced in the SN Addition Request message to indicate that the SN change is for S-CPAC. The “S-CPAC Request” IE includes “S-CPAC Security Configurations List” amongother set of information which is specific to S-CPAC and to differentiate S-CPAC.

[0289] In order to enable inter-SN SCG LTM, a dedicated and differentiating indication isneeded to indicate to the candidate target SNs that the preparation is for inter-SN SCG LTM. Without such an indication, the candidate target SN may not be able to know the request is forpreparation of resources for inter-SN SCG LTM, which additionally requires the preparation ofCSI Resource configuration for each prepared PSCell. In other words, without such anindication, the preparation of CSI Resource configuration for each prepared PSCell may not beperformed, leading to incorrect operation of the system.

[0290] From another perspective, the security configuration for inter-SN SCG LTMrequires a structure and dedicated IE in SN Addition procedure on Xn interface. The LTMconfiguration container over RRC is to be enhanced to include a dedicated identifier to carrycandidate SN specific security configuration.

[0291] Furthermore, if an MCG LTM is configured at MN, and SN initiated inter-SN SCGLTM trigger is received by the MN (via SN CHANGE REQUIRED) from source SN, then the handling of this situation (i.e., inter-MN MCG LTM configured at the MN and SN initiated inter-SN SCG LTM) is to be specified.

[0292] Also, it is necessary to allow the serving SN to configure inter-SN SCG LTM wheninter-MN MCG LTM is de-configured at the MN. Therefore, it is required to notify the MNabout the configuration of inter-SN SCG LTM at the serving SN to prevent the MN fromconfiguring inter-MN SCG LTM when inter-SN SCG LTM is configured at the serving SN.

[0293] Now, methods for inter-SN SCG LTM according to embodiments of the presentdisclosure will be described.

[0294] First aspects of the present disclosure that are directed to provide a structure anddedicated IE for the security configuration for inter-SN SCG LTM in the SN Addition procedure and a dedicated and differentiating indication to indicate to the candidate target SNs that the preparation is for inter-SN SCG LTM will be described hereinbelow with reference to methods for inter-SN SCG LTM shown in FIGURES 5 to 7. These first aspects also enhance the LTM configuration container over RRC to include a dedicated identifier to carry candidateSN specific security configuration. The indication enables the candidate target SN to know thatthe request is for preparation of resources for inter-SN SCG LTM, which additionally requires the preparation of CSI Resource configuration for each prepared PSCell.

[0295] FIGURE 5 illustrates a flowchart of a method 500 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 5 illustrates at least someof the first aspects of the present disclosure.

[0296] The method 500 or process may be performed in a wireless communication system.For example, the method 500 or process may be performed in a 5G system as described abovewith reference to FIGURE 1. More specifically, the method 500 is performed by a userequipment (UE) of the wireless communication system such as user device or terminal device,or by an apparatus for use in UE. For example, the UE may be represented by any one of theUEs 120 and 122 of the wireless network as described above with reference to FIGURE 1.

[0297] The method 500 illustrated in FIGURE 5 may form part of the preparation andexecution phase for the inter-SN SCG LTM during which the UE 120 / 122 is prepared for theSN change and during which the UE 120 / 122 performs the SN change.

[0298] It is to be noted that examples of the method 500 are not limited to the sequence ofoperations illustrated in FIGURE 5. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0299] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node.More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0300] The method 500 starts at operation 510. In operation 510, the UE 120 / 122 receivesa reconfiguration message from the network node (e.g., the MN such as gNB 110 of cell 100).The reconfiguration message includes a configuration of one or more candidate secondary cellsfor inter-SN SCG LTM and security information for the one or more candidate secondary cells.

[0301] In operation 540, the UE 120 / 122 performs (i.e., executes) the inter-SN SCG LTMto one of the one or more candidate secondary cells based on the configuration and the securityinformation, both received in operation 510. In other words, the UE 120 / 122 performs a changefrom the serving SN (e.g., gNB 112 of cell 102) of a (serving) secondary cell (i.e., cell 102) to a target SN of the candidate (target) secondary cell.

[0302] In some examples, the reconfiguration message may comprise a RRCReconfiguration message including an LTM configuration (e.g., LTM config), which is alsoreferred to herein as LTM configuration container. The LTM configuration container may comprise a SCG reference configuration (e.g., SCG_Reference_Config) and a deltaconfiguration (e.g., Delta Config). In some examples, the LTM configuration container mayfurther comprise a dedicated field (e.g., SecurityGroupIdInfo or Security_Group_Id_Info)carrying security configuration associated with the LTM candidate configuration prepared bythe network node. In other words, the dedicated field is to carry the security information for theone or more candidate secondary cells.

[0303] In some examples, the security information may comprise an indication to informthe UE 120 / 122 whether or not to perform a security update when applying the configurationupon performing, in operation 540, the inter-SN SCG LTM. In the reconfiguration message,the dedicated field (e.g., SecurityGroupIdInfo) for the indication may be provided.

[0304] In some examples, the UE 120 / 122 may determine, based on the indication, whetheror not to perform the security update. In case where the indication indicates the UE 120 / 122 toperform the security update, the UE 120 / 122 determines to perform the security update, and theUE 120 / 122 may perform, in operation 520 (optional), the security update based on the securityinformation received in operation 510.

[0305] In some examples, the security information may further comprise a security keycounter configuration to enable the UE 120 / 122 to derive a security key of a base stationassociated with the one of the one or more candidate secondary cells. The security key may beS-KgNB that may be updated as a part of the security update. In the reconfiguration message, adedicated field (e.g., sk-counterConfiguration) for the security key counter configuration maybe provided. It is to be noted that the dedicated field in the RRC Reconfiguration message is tocarry security config when the inter-SN SCG LTM is configured / enabled. That is, the dedicated field is optional and not present when the inter-SN SCG LTM is not configured. In some examples, the security key counter configuration may comprise one or more security keycounters associated with the one or more candidate secondary cells. The one or more securitykey counters may form a list of security key counters from which the UE 120 / 122 may selectthe security key counter used to derive the security key (e.g., S-KgNB) for inter-SN SCG LTM.

[0306] In some examples, in operation 530 (optional), the UE 120 / 122 may select asecurity key counter associated with the one of the one or more candidate secondary cells fromthe one or more security key counters included in the security key counter configuration, andderive the security key of the basis station (e.g., the S-KgNB) based on a master key and the selected security key counter.

[0307] The security key of the basis station derived in operation 530 may, in someexamples, be used by the UE 120 / 122 in operation 540 to perform the inter-SN SCG LTM. That is, the derived security key is used by the UE 120 / 122 to perform the inter-SN SCG LTM to the base station serving the one of the one or more candidate secondary cells.

[0308] FIGURE 6 illustrates a flowchart of a method 600 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 6 illustrates at least someof the first aspects of the present disclosure.

[0309] The method 600 or process may be performed in a wireless communication system.For example, the method 600 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 600 is performed by a network node of the wireless communication system such as a base station or a master node, or by an apparatus for use in a network node. For example, the network node may be represented by anyone of the base stations 110 and 112 of the wireless network as described above with referenceto FIGURE 1.

[0310] The method 600 illustrated in FIGURE 6 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0311] It is to be noted that examples of the method 600 are not limited to the sequence ofoperations illustrated in FIGURE 6. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0312] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and 102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 to simultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0313] In operation 640, the network node sends, a reconfiguration message to the UE120 / 122. The reconfiguration including a configuration of one or more candidate secondarycells for the inter-SN SCG LTM and security information for the one or more candidatesecondary cells. As described above, the configuration and the security information may beused by the UE 120 / 122 to perform the inter-SN SCG LTM and, optionally, the security updatein connection with the inter-SN SCG LTM.

[0314] In some examples, the reconfiguration message may comprise a RRCReconfiguration message including an LTM configuration (e.g., LTM config). The LTM configuration may comprise a SCG reference configuration (e.g., SCG_Reference_Config) and a delta configuration (e.g., Delta Config). In some examples, the LTM configuration mayfurther comprise a dedicated field (e.g., SecurityGroupIdInfo or Security_Group_Id_Info)carrying security configuration associated with the LTM candidate configuration prepared bythe network node. In other words, the dedicated field is to carry the security information for theone or more candidate secondary cells.

[0315] In some examples, the security information may comprise an indication to informthe UE 120 / 122 whether or not to perform a security update when applying the configurationupon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.In the reconfiguration message, the dedicated field (e.g., SecurityGroupIdInfo) for the indication may be provided.

[0316] In some examples, the security information may further comprise a security keycounter configuration to enable the UE 120 / 122 to derive a security key of a base station associated with the one of the one or more candidate secondary cells. The security key may be S-KgNB. In the reconfiguration message, a dedicated field (e.g., sk-counterConfiguration) for the security key counter configuration may be provided. In some examples, the security key counter configuration may comprise one or more security key counters associated with the oneor more candidate secondary cells. The one or more security key counters may form a list ofsecurity key counters from which the UE 120 / 122 may select the security key counter used to derive the security key (e.g., S-KgNB) for inter-SN SCG LTM.

[0317] In some examples of the method 600, the network node may act as the master node(MN) of the master cell serving the UE 120 / 122.

[0318] To prepare the inter-SN SCG LTM, in operation 610 (optional), the network nodemay receive a SN change required message (e.g., SN CHANGE REQUIRED) from a secondarynode (SN) of a serving secondary cell, i.e., a secondary cell also serving the UE 120 / 122 (e.g.,gNB 112 serving cell 102). The SN change required message includes the one or morecandidate secondary cells for the inter-SN SCG LTM.

[0319] In operation 620, the network node may send a SN addition request message (e.g.,SN ADDITION REQUEST) to a SN of at least one of the one or more candidate secondary cells.The SN of the at least one of the one or more candidate secondary cells may also be referred toas a candidate SN as the candidate secondary cell (e.g., the PSCell) may belong to a sameserving SN. The SN addition request message indicates that the SN addition request messageis to prepare for the inter-SN SCG LTM to the candidate SN of the at least one candidatesecondary cell.

[0320] In operation 630, the network node may receive the configuration of the at least onecandidate secondary cell from the candidate SN of the at least one candidate secondary cell.The configuration of the one or more candidate secondary cells for the inter-SN SCG LTM send to the UE 120 / 122 in operation 640 may include the configuration of the at least onecandidate secondary cell received in operation 630.

[0321] In some examples, the SN change required message may indicate that the SNchange required message is to prepare for the inter-SN SCG LTM. For example, the SN changerequired message may comprise an information element (e.g., Inter-SN SCG LTM REQUESTInfo) to indicate that the SN change required message is to prepare for the inter-SN SCG LTM.

[0322] In some examples, the SN addition request message may comprise an informationelement to indicate that the SN addition request message is to prepare for the inter-SN SCGLTM (e.g., Inter-SN SCG LTM REQUEST Info) to the candidate SN of the at least one candidatesecondary cell. The information element of the SN addition request message may comprise oneor more security configurations for the inter-SN SCG LTM and / or one or more identifiers ofother SNs of the at least one candidate secondary cell and at least one recommended candidatesecondary cell. The one or more security configurations may comprise one or more securitykeys of the SNs of the serving secondary cell or the SN(s) of the at least one candidate secondarycell, the security key being provided by the MN, and one or more security key counters toenable deriving one or more security keys of base stations associated with the at least onecandidate security cell. The SN addition request message indicates, to the candidate SN of theat least one candidate secondary cell, that a reference configuration for the inter-SN SCG LTM is requested.

[0323] FIGURE 7 illustrates a signaling diagram of an example of a method or process forinter-SN SCG LTM according to embodiments of the present disclosure. FIGURE 7 illustratesat least some of the first aspects of the present disclosure.

[0324] More specifically, the signaling diagram illustrates a SN initiated inter-SN SCGLTM with SRB3 not configured procedure. Although the signaling diagram is directed to theSN initiated inter-SN SCG LTM with SRB3 not configured procedure, it is to be understood that the present disclosure and embodiments / examples disclosed herein are not limited to the SN initiated inter-SN SCG LTM with SRB3 not configured procedure.

[0325] Aspects of the signaling diagram are described above with reference to FIGURES5 and 6. The SN initiated inter-SN SCG LTM with SRB3 not configured procedure illustratedin FIGURE 7 is as follows:

[0326] In step 1, the UE 120 / 122 is configured with dual connectivity without SRB3 andSCG LTM assumed.

[0327] In step 2, optionally SCG LTM (e.g., as part of SN Addition procedure) isconfigured.

[0328] In step 4, the UE 120 / 122 reports L3 measurements of cells (e.g., from other gNBs).

[0329] In step 5, the source SN 720 (e.g., the gNB 112) decides to trigger inter-SN SCGLTM preparation of candidate SNs.

[0330] In step 6, the source SN 720 triggers SN CHANGE REQUIRED message with aninformation element (e.g., Inter-SN SCG LTM Request Information IE as described above) toenable the MN 710 (e.g., gNB 110) to know the request is for the preparation of inter-SN SCGLTM. The source SN 720 may include a list of reported cells in the SN CHANGE REQUIREDmessage.

[0331] In step 7, the MN 710 initiates SN ADDITION REQUEST message with aninformation element (e.g., Inter-SN SCG LTM Request Information IE) to enable the candidateSN 740 to know the request is for the preparation of inter-SN SCG LTM. This enables thecandidate SN 740 to prepare the LTM candidate configuration, which includes the SCG configuration and the LTM CSI Resource configuration.

[0332] In step 8, the candidate SN 740 includes the LTM CSI resource configuration forthe prepared PSCell in the SN to MN transparent container along with the SCG configuration (which may be delta configuration or full configuration).

[0333] In step 9 and 10, the MN 710 initiates SN MODIFICATION procedure to signalthe LTM candidate configuration including the CSI resource configuration to the source SN 720. This step may be needed because the LTM candidate configuration of all the preparedcandidate SNs 740 shall be constructed in a SN RRC Reconfiguration message which may beforwarded to the MN 710 via SN MODIFICATION REQUIRED message if split SRB1 isconfigured or directly sent to the UE 120 / 122 if SRB3 is configured. Moreover, the source SN720 uses the CSI resource configuration to generate a single CSI resource configuration to be used for SCG LTM.

[0334] Step 11 and 12 may be needed to signal the LTM candidate configuration includingthe CSI resource configuration to all the candidate SNs 740 to support inter-SN subsequent PSCell change.

[0335] In step 14, the RRC Reconfiguration message includes the LTM candidateconfiguration container with the dedicated field (e.g., SecurityGroupIdInfo) as described aboveto carry security configuration associated with the prepared LTM candidate configuration. Insome examples, the dedicated field (e.g., SecurityGroupIdInfo) may be similar to the fieldaccording to the S-CPAC functionality (e.g., SecurityCellSetId).

[0336] Steps 4 to 17 relate to a preparation phase 4 of the SN initiated inter-SN SCG LTMwith SRB3 not configured procedure.

[0337] In an execution phase 18, particularly including steps 19 to 39 shown in FIGURE7, the LTM is executed and completed. The execution phase 18 and its steps correspond to theexecution and completion phases and their steps shown in FIGURES 3 and 4 (for example).

[0338] The (dedicated) fields as described above may be included in, or update, themessages structures of Xn and RRC messages.

[0339] For example, the SN ADDITION REQUEST message described in 3GPP TS38.423 (e.g., clause 9.1.2.1) may be updated such that the semantics description of the IE / Group Name “S-NG-RAN node Security Key” indicate that this IE is ignored if the S-CPAC RequestInformation IE or Inter-SN SCG LTM Request Information IE is present in the ConditionalPSCell Addition Information Request IE. Furthermore, the following optional IE / Group Names“Inter-SN SCG LTM Request Information IE” indicating that SN addition is for inter-SN SCGLTM preparation and “Inter-SN SCG LTM Reference Configuration Request” indicating that the reference configuration for inter-SN SCG LTM is requested may be added.

[0340] Accordingly, the SN ADDITION REQUEST message that is to be sent by the M-NG-RAN node (i.e., the MN 710) to the S-NG-RAN node (i.e., the SN 720) to request thepreparation of resources for dual connectivity operation for a specific UE (e.g., UE 120 / 122)may comprise: IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality MessageM 9.2.3.1 YES rejectType M-NG-M NG-RANAllocated atYES rejectRAN node node UE the M-NG- UE XnAP XnAP ID RAN node ID 9.2.3.16 UE SecurityM 9.2.3.49 YES rejectCapabilities S-NG-RANM 9.2.3.51 This IE is YES rejectnode ignored if the Security S-CPAC Key Request Information IEor Inter-SNIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality SCG LTM Request Information IE is present inthe Conditional PSCell Addition Information Request IE.S-NG-RANM UEThe UEYES rejectnode UE Aggregate Aggregate Aggregate Maximum Maximum Bit Maximum Bit Rate Rate is split Bit Rate 9.2.3.17 into M-NG- RAN node UE Aggregate Maximum Bit Rate and S- NG-RAN node UE Aggregate Maximum Bit Rate which are enforced by M-NG-RAN node and S- NG-RAN node respectively. SelectedO PLMNThe selectedYES ignorePLMN Identity PLMN of the 9.2.2.4 SCG in the S-IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality NG-RAN node. MobilityO 9.2.3.53 YES ignoreRestriction List Index toO 9.2.3.23 YES rejectRAT / Frequ ency Selection Priority PDU1 YES rejectSession Resources To Be Added List >PDU 1.. NOTE: If – Session <maxn neither the Resources oofPD PDU Session To Be USessio Resource Added ns> Setup Info – Item SN terminated IE nor the PDU Session Resource Setup Info – MN terminated IE is present in a PDU Session Resources ToIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality Be Added Item IE, abnormal conditions as specified in clause 8.3.1.4 apply. >>PDUM 9.2.3.18 –Session ID>>S-NSSAI M 9.2.3.21 –>>S-NG-O PDU– RAN node Session PDU Aggregate Session Maximum Aggregate Bit Rate Maximum 9.2.3.69 Bit Rate >>PDUO 9.2.1.5 –Session Resource Setup Info – SN terminated >>PDUO 9.2.1.7 –Session Resource Setup Info – MN terminated M-NG-M OCTETIncludes theYES rejectRAN node STRING CG-ConfigInfo to S-NG- message asIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality RAN node defined in Container subclause 11.2.2 of TS 38.331

[0010] S-NG-RANO NG-RANAllocated atYES rejectnode UE node UE the S-NG- XnAP ID XnAP ID RAN node 9.2.3.16 ExpectedO 9.2.3.81 YES ignoreUE Behaviour RequestedO ENUMERAIndicates thatYES rejectSplit SRBs TED (srb1, resources for srb2, Split SRBs are srb1&2, ...) requested.PCell ID O Global NG- YES rejectRAN Cell Identity 9.2.2.27 DesiredO 9.2.3.77 YES ignoreActivity Notification Level Available C- DRB List Indicates theYES rejectDRB IDs ifSNtermi 9.2.1.29 list of DRB nated IDs that the S- NG-RAN node may use for SN-terminated bearers.IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality S-NG-RANO Bit RateThe S-NG-YES rejectnode 9.2.3.4 RAN node Maximum Maximum Integrity Integrity Protected Protected Data Data RateRate Uplink isUplink a portion of the UE’s Maximum Integrity Protected Data Rate in the Uplink, which is enforced by the S-NG- RAN node for the UE’s SN terminated PDU sessions. If the S-NG- RAN node Maximum Integrity Protected Data Rate Downlink IE is not present, this IE applies to both UL and DL. S-NG-RANO Bit RateThe S-NG-YES rejectnode 9.2.3.4 RAN node Maximum MaximumIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality Integrity Integrity Protected Protected Data Data Rate Rate Downlink Downlink is a portion of the UE’s Maximum Integrity Protected Data Rate in the Downlink, which is enforced by the S-NG- RAN node for the UE’s SN terminated PDU sessions. LocationO ENUMERAIndicates thatYES ignoreInformation TED the user’s at S-NODE (pscell, ...) Location reporting Information at S-NODE is to be provided. MR-DCO 9.2.2.33 Information YES ignoreResource used to Coordinatio coordinate n resource Information utilisation between M- NG-RAN node and S-NG- RAN node.IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality MaskedO 9.2.3.32 YES ignoreIMEISV NE-DCO 9.2.2.38 YES ignoreTDM Pattern SNO ENUMERAThis IEYES rejectAddition TED (SN indicates the Trigger change, trigger for S- Indication inter-MN NG-RAN node HO, intra- Addition MN HO, ...) Preparation procedure TraceO 9.2.3.55 YES ignoreActivation RequestedO ENUMERAIndicates thatYES ignoreFast MCG TED (true, the resources recovery via ...) for fast MCG SRB3 recovery via SRB3 are requested. UE RadioO 9.2.3.138 YES rejectCapability ID Source NG-O Global NG-The NG-RANYES ignoreRAN Node RAN Node Node ID of the ID ID source NG- 9.2.2.3 RAN node, or the source SN in e.g. NR-DC to NR-DCIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality (conditional) handover. ManagemenO MDT YES ignoret Based PLMN List MDT 9.2.3.133 PLMN List UE HistoryO 9.2.3.64 YES ignoreInformation UE HistoryO 9.2.3.110 YES ignoreInformation from the UE PSCellO ENUMERA YES ignoreChange TED History (reporting full history, ...) IAB NodeO ENUMERA YES rejectIndication TED (true, ...) No PDUO ENUMERAThis IE appliesYES ignoreSession TED (true, only if the UE Indication ...) is an IAB-MT. CHOO YES rejectInformatio n SN Addition >Source M-M Global NG-– NG-RAN RAN Node node ID ID 9.2.2.3IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality >Source M-M NG-RANAllocated at – NG-RAN node UE the source M- node UE XnAP ID NG-RAN node XnAP ID 9.2.3.16 >EstimatedO INTEGER– Arrival (1..100) Probability SCGO 9.2.3.154 YES ignoreActivation Request ConditionaO YES rejectl PSCell Addition Informatio n Request >MaximumM INTEGERIndicates the – Number of (1..8, ...) maximum PSCells To number of Prepare PSCells that the target SN may prepare. >EstimatedO INTEGERIndicates the – Arrival (1..100) arrival Probability probability for the UE towards the candidate target SN. >S-CPACO 9.2.3.192 Indicates that YES rejectRequest SN addition is InformationIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality for S-CPAC preparation. >S-CPACO ENUMERAIndicates thatYES ignoreReference TED the reference Configurati (request, configuration on Request …) for S-CPAC is requested. >Inter-SNO 9.2.3.xxx Indicates that YES rejectSCG LTM SN addition is Request for Inter-SN Information SCG LTM IE preparation. >Inter-SNO ENUMERAIndicates thatYES ignoreSCG LTM TED the reference Reference (request, configuration Configurati …) for Inter-SN on Request SCG LTM is requested. S-NG-RANO UE SliceThis IEYES rejectnode UE Maximum indicates the S- Slice Bit Rate NG-RAN node Maximum List portion of the Bit Rate 9.2.3.167 UE Slice Aggregate Maximum Bit Rate as specified in TS 23.501 [7] F1-O ENUMERAThis IE appliesYES rejectterminating TED (true, only if the UE ...) is an IAB-MT.IE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality IAB-donor Indicator SelectedO NIDThis IE,YES ignoreNID 9.2.2.65 together with the Selected PLMN IE,indicates the SNPN proposed for the SCG to the S-NG-RAN node. QMCO 9.2.3.197 This IE YES ignoreCoordinatio contains n Request information for managing configuration and reporting of one or more QoE and / or RAN visible QoE measurements at the S-NG- RAN node subject to addition. Source SNO QMCThis IEYES ignoreto Target Configurati contains S- SN QMC on NG-RAN Information Information node-related 9.2.3.156 QMCIE / GroupPresence Range IE type andSemanticsCriticality AssignedName reference description Criticality Configuration Information to be forwarded to the target S- NG-RAN node. Source M-O Global NG-The NG-RANYES ignoreNG-RAN RAN Node Node ID of the node ID ID source M-NG- 9.2.2.3 RAN node in e.g. NR-DC to NR-DC handover. IABO ENUMERAIndicates theYES ignoreAuthorizati TED IAB node´s on Status (authorized, authorization not status. authorized, …)

[0341] For example, the IE “Inter-SN SCG LTM Request Information” indicating that SNaddition is for inter-SN SCG LTM preparation may have the following structure: Inter-SN SCG LTM Request Information IE / GroupPresence Range IE TypeSemantics Description Name and Reference Inter-SNM 9.2.3.xxx Indicates the securitySCG LTM configurations for Inter-SN SCG Security LTM, which will replace the previous configuration if any.Configurati ons List Inter-SN 0.. SCG LTM <maxnoofTar Multiple getSNsMinus Target S- One> NG-RAN Node List >Target S-M Global NG-Other candidate SN under NG-RAN RAN Node preparation for inter-SN SCG node ID ID LTM. 9.2.2.3 >RecommeM OCTETIncludes either the nded STRINGcandidateCellInfoListMN in caseCandidate of MN-initiated inter-SN SCG PSCells LTM or in case of SN-initiated inter-SN SCG LTM, contained in the CG-ConfigInfo messageas defined in 3GPP TS 38.331.

[0342] For example, the IE “Inter-SN SCG LTM Security Configurations List” may havethe following structure: Inter-SN SCG LTM Security Configurations List IE / GroupPresence Range IE TypeSemantics Description Name and Reference Inter-SN 1 SCG LTM Security Configurati ons List>Inter-SN 1.. SCG LTM <maxnoofSec Security urityConfigur Configurati ations> ons Item >>S-NG-M BITThe S-KSN which is provided by RAN node STRINGthe M-NG-RAN node (e.g.,Security (SIZE(256)) 3GPP TS 33.501). Key >>SK-M INTEGERcounter (0..65535)

[0343] For example, the IE “LTM-Candidate” concerning an LTM candidate configurationto add or modify among the RRC information elements specified in 3GPP TS 38.331 may include the dedicated fields “SecurityGroupIdInfo” and “sk-CounterConfiguration” as described above: LTM-Candidate-- ASN1START-- TAG-LTM-CANDIDATE-STARTLTM-Candidate-r19 ::= SEQUENCE { ltm-CandidateId-r19 LTM-CandidateId-r19, ltm-CandidatePCI-r19 PhysCellIdOPTIONAL, -- Need Mltm-SSB-Config-r19 LTM-SSB-Config-r19OPTIONAL, -- Need Mltm-CandidateConfig-r19 OCTET STRING (CONTAININGRRCReconfiguration) OPTIONAL, -- Need Mltm-ConfigComplete-r19 ENUMERATED {true} OPTIONAL, -- Need R ltm-EarlyUL-SyncConfig-r19 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r19) OPTIONAL, -- Need Rltm-EarlyUL-SyncConfigSUL-r19 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r19) OPTIONAL, -- Need Rltm-TCI-Info-r19 LTM-TCI-Info-r19OPTIONAL, -- Need Mltm-NoResetID-r19 INTEGER (1..maxNrofLTM-Configs-plus1-r19)OPTIONAL, -- Need Nltm-UE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r19)OPTIONAL, -- Need NSecurityGroupIdInfo-r19 SecurityGroupIdInfo-r19OPTIONAL, -- Cond inter-SNSCGLTMsk-CounterConfiguration-r19 SK-CounterConfiguration-r19OPTIONAL -- Cond inter-SNSCGLTM...}

[0344] As described above, the dedicated field “SecurityGroupIdInfo” is used to determinewhether the UE should perform the security update when the LTM candidate configuration isapplied at the UE upon inter-SN SCG LTM execution and the dedicated field “sk-CounterConfiguration” includes a list of sk-Counter from which the UE should select the sk-counter used to derive S-KgNB for inter-SN SCG LTM:LTM-Candidate field descriptions ltm-CandidateConfig This field includes an RRC Reconfiguration message used to configure an LTM candidateconfiguration. ltm-CandidateId This field indicates an LTM candidate configuration. ltm-CandidatePCI This field identifies the PCI of the SpCell of the configuration contained in ltm- CandidateConfig. ltm-ConfigComplete This field indicates whether the LTM candidate configuration within ltm-CandidateConfig isa complete configuration. ltm-EarlyUL-SyncConfig, ltm-EarlyUL-SyncConfigSUL A configuration used to perform the early UL synchronization procedure over an UL or SUL carrier. SecurityGroupIdInfo This field is used to determine whether UE should perform security update when ltm candidate config is applied at the UE upon inter SN SCG LTM execution. sk-counterConfiguration Includes a list of sk-Counter from which the UE should select the sk-counter used to deriveS-KgNB for inter-SN SCG LTM.

[0345] That is, the methods of FIGURES 5 to 7 concern the preparation of candidate SNsfor inter-SN SCG LTM initiated either by the MN or the SN. In both cases it is the MN that triggers the preparation of candidate SN, by requesting the candidate SN(s) to allocate resources for the UE by means of the SN Addition procedure.

[0346] In the SN ADDITION REQUEST message, an indication “Inter-SN SCG LTMRequest Information IE” is provided to consider that the procedure is triggered for inter-SNSCG LTM. For the SN initiated inter-SN SCG LTM scenario, in the SN CHANGE REQUIREDmessage (going from source SN to source MN), an indication “Inter-SN SCG LTM RequestInformation IE” is provided to enable the MN to consider the procedure is triggered for inter-SN SCG LTM preparation. The indication “Inter-SN SCG LTM Request Information IE” shallenable the candidate SN to prepare LTM CSI resource configuration in addition to the SCG configuration for the prepared PSCells.

[0347] Furthermore, in the SN ADDITION REQUEST message, “Inter-SN SCG LTM”functionality support is introduced and a dedicated field to enable the MN to request the candidate SN for the preparation of SCG reference configuration explicitly also when “Inter- SN SCG LTM” preparation is requested is provided. The SN ADDITION REQUEST message is to describe the handling of IE “S-NG-RAN node Security Key” to include the inter-SN SCGLTM scenario (i.e., the handling that the IE must be ignored also when “Inter-SN SCG LTMRequest Information IE” is present).

[0348] The information element “ltm-CandidateConfig” may include a dedicated field“SecurityGroupIdInfo” to carry security configuration associated with the prepared LTMcandidate configuration.

[0349] The methods of FIGURES 5 to 7 enable the candidate SN to identify anddifferentiate the preparation for inter-SN SCG LTM such that the candidate SN is enabled toprepare CSI resource configuration for the prepared PSCells. Furthermore, the methods of FIGURES 5 to 7 allow to provide security configuration associated with the prepared candidateLTM configuration to be used in the inter-SN SCG LTM.

[0350] Further (second) aspects of the present disclosure that are directed to a handlingprocedure if an MCG LTM is configured at MN, and SN initiated inter-SN SG LTM trigger isreceived by the MN (via SN CHANGE REQUIRED) from source SN will be describedhereinbelow with reference to methods for inter-SN SCG LTM shown in FIGURES 8 to 10.

[0351] FIGURE 8 illustrates a flowchart of a method 800 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 8 illustrates at least some of the second aspects of the present disclosure.

[0352] The method 800 or process may be performed in a wireless communication system.For example, the method 800 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 800 is performed by a networknode (e.g., a network node acting as a master node (MN) of a master cell such as gNB 110serving cell 100 as described above with reference to FIGURE 1) of the wirelesscommunication system such as a base station or a master node, or by an apparatus for use in a network node.

[0353] The method 800 illustrated in FIGURE 8 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0354] It is to be noted that examples of the method 800 are not limited to the sequence ofoperations illustrated in FIGURE 8. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0355] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0356] The method 800 starts at operation 810. In operation 810, the network node receivesa SN change required message (e.g., SN CHANGE REQUIRED) from a secondary node (SN)of a serving secondary cell (e.g., gNB 112 serving cell 102). The SN change required messageincludes at least one candidate secondary cell for the inter-SN SCG LTM. The SN changerequired message may, in some examples, include the Inter-SN SCG LTM Request Info asdescribed above.

[0357] In operation 820, the network node sends a SN change refuse message (e.g., SNCHANGE REFUSE) to reject the SN change required message to the SN of the servingsecondary cell. The SN change refuse message includes a cause (e.g., a cause value) indicating that the SN is to initiate preparing subsequent conditional primary secondary cell addition orchange (S-CPAC) or conditional primary secondary cell change (CPC). The cause may indicatethat an inter-master-node (MN) master cell group (MCG) L1 / L2 Triggered Mobility (LTM) isconfigured (e.g., INTER-CU MCG LTM configured or INTER-MN MCG LTM configured).The network node may determine that the inter-MN MCG LTM is configured, in response to which the SN change refuse message is sent.

[0358] In response to receiving the SN change refuse message, the SN of the servingsecondary cell may initiate the S-CPAC or CPC.

[0359] FIGURE 9 illustrates a flowchart of a method 900 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 9 illustrates at least some of the second aspects of the present disclosure.

[0360] The method 900 or process may be performed in a wireless communication system.For example, the method 900 or process may be performed in a 5G system as described abovewith reference to FIGURE 1. More specifically, the method 900 is performed by a networknode (e.g., a network node acting as a secondary node (SN) of a serving secondary cell such asgNB 112 serving cell 102 as described above with reference to FIGURE 1) of the wirelesscommunication system such as a base station or a secondary node, or by an apparatus for usein a network node.

[0361] The method 900 illustrated in FIGURE 9 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0362] It is to be noted that examples of the method 900 are not limited to the sequence ofoperations illustrated in FIGURE 9. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0363] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0364] In operation 920, the network node sends a SN change required message (e.g., SNCHANGE REQUIRED) to a master node (MN) of a master cell (e.g., gNB 110 of cell 100).The SN change required message includes at least one candidate secondary cell for the inter-SN SCG LTM. The network node may send the SN changed required message in response todeciding, in operation 910, to trigger to prepare for the inter-SN SCG LTM. The SN changerequired message may, in some examples, include the Inter-SN SCG LTM Request Info asdescribed above.

[0365] In operation 930, the network node receives a SN change refuse message (e.g., SNCHANGE REFUSE) from the MN. The SN change refuse indicates that the MN rejects the SN change required message. The SN change refuse message includes a cause (e.g., a cause value) indicating that the SN is to initiate preparing subsequent conditional primary secondary celladdition or change (S-CPAC) or conditional primary secondary cell change (CPC). The causemay indicate that an inter-master-node (MN) master cell group (MCG) L1 / l2 TriggeredMobility (LTM) is configured at the MN (e.g., INTER-CU MCG LTM configured or INTER-MN MCG LTM configured) to the SN.

[0366] In response to receiving the SN change refuse message in operation 930, the SN ofthe serving secondary cell may initiate S-CPAC or CPC in operation 940 (optional).

[0367] FIGURE 10 illustrates a signaling diagram of an example of a method or processfor inter-SN SCG LTM according to embodiments of the present disclosure. FIGURE 10 illustrates at least some of the second aspects of the present disclosure.

[0368] Aspects of the signaling diagram are described above with reference to FIGURES8 and 9. The procedure illustrated in FIGURE 10 is as follows:

[0369] In step 1, the UE 120 / 122 is configured with dual connectivity without SRB3 andSCG LTM assumed.

[0370] In step 2, optionally SCG LTM (e.g., as part of SN Addition procedure) isconfigured.

[0371] In steps 4 and 5, the UE 120 / 122 reports L1 / L3 measurements of cells.

[0372] In step 6, based on the L3 measurements received in step 5, the inter-MN MCGLTM is configured at the MN 1010.

[0373] In steps 7 and 8, based on UE measurements, the source SN 1020 initiates the inter-SN SCG LTM. In particular, the source SN 1020 may prepare candidate target SN(s) for the inter-SN SCG LTM and send SN CHANGE REQUIRED message to the MN 1010. The SNCHANGE REQUIRED message may include the Inter-SN SCG LTM Request Info as describedabove.

[0374] In step 9, the MN 1010 rejects the SN CHANGE REQUIRED message by initiatingthe SN CHANGE REFUSE message with a cause “Inter-CU MCG LTM configured” (or “Inter-MN MCG LTM configured”). The decision to reject the SN CHANGE REQUIRED messagemay be based on the configuration of the inter-MN MCG LTM at MN in step 6.

[0375] In step 10, the source SN 1020 initiates the preparation of S-CPAC (for example).

[0376] Steps 4 to 17 of FIGURE 10 relate to a preparation phase 3 of the procedure. In anexecution phase 18, particularly including steps 19 to 32 shown in FIGURE 10, the S-CPAC procedure (for example) is executed and completed. The execution phase 18 and its steps correspond to the execution and completion phases and their steps shown in FIGURES 3 and 4 (for example).

[0377] For example, the SN CHANGE REFUSE message specified in 3GPP TS 38.423may further allow including the cause value “Inter-CU MCG LTM configured” (or “Inter-MNMCG LTM configured”) as described above: SN CHANGE REFUSESNodeChangeRefuse ::= SEQUENCE {protocolIEs ProtocolIE-Container {{ SNodeChangeRefuse-IEs}},... }SNodeChangeRefuse-IEs XNAP-PROTOCOL-IES ::= { {ID id-M-NG-RANnodeUEXnAPID CRITICALITY ignore TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}|{ID id-S-NG-RANnodeUEXnAPID CRITICALITY ignore TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}|{ ID id-Cause CRITICALITY ignore TYPE CausePRESENCE mandatory}| {ID id-CriticalityDiagnostics CRITICALITY ignore TYPECriticalityDiagnostics PRESENCE optional }, ... }

[0378] The cause specified in 3GPP TS 38.423 may further include the cause value “Inter-CU MCG LTM configured” (or “Inter-SN MCG LTM configured”):Cause Cause ::= CHOICE { radioNetwork CauseRadioNetworkLayer,transport CauseTransportLayer, protocol CauseProtocol,misc CauseMisc,choice-extension ProtocolIE-Single-Container { {Cause-ExtIEs} }} Cause-ExtIEs XNAP-PROTOCOL-IES ::= { ... }}

[0379] The methods of FIGURES 8 to 10 allow to prevent inter-SN SCG LTM preparationif the inter-MN MCG LTM is configured at MN.

[0380] Further (third) aspects of the present disclosure that are, similar to the secondaspects, also directed to a handling procedure if an MCG LTM is configured at MN will bedescribed hereinbelow with reference to methods for inter-SN SCG LTM shown in FIGURES11 to 13.

[0381] FIGURE 11 illustrates a flowchart of a method 1100 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 11 illustrates at least someof the third aspects of the present disclosure.

[0382] The method 1100 or process may be performed in a wireless communicationsystem. For example, the method 1100 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 1100 is performedby a network node (e.g., a network node acting as a master node (MN) of a master cell such asgNB 110 serving cell 100) of the wireless communication system such as a base station or amaster node, or by an apparatus for use in a network node.

[0383] The method 1100 illustrated in FIGURE 11 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0384] It is to be noted that examples of the method 1100 are not limited to the sequenceof operations illustrated in FIGURE 11. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0385] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0386] In operation 1120, the network node notifies a secondary node (SN) of a servingsecondary cell in the network that an inter-master-node (MN) master cell group (MCG) L1 / L2Triggered Mobility (LTM) is configured (e.g., at the MN). The notification may be sent by thenetwork node in response to determining, in operation 1110, that the inter-MN MCG LTM isconfigured at the MN.

[0387] In operation 1130, the network node receives a SN change required message (e.g.,SN CHANGE REQUIRED) from the SN. The SN change required message includes a request for subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cell change (CPC).

[0388] In some examples, the network node may notify the SN of the serving secondarycell by sending a message (e.g., MNToSNIndication) to the SN. The message may be sent viathe Xn interface. In some examples, the message may include a cause (e.g., a cause value) tonotify that the inter-MN MCG LTM is configured at the MN. The cause may comprise “Inter-CU MCG LTM configured” (or “Inter-MN MCG LTM configured”) as described above.

[0389] FIGURE 12 illustrates a flowchart of a method 1200 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 12 illustrates the secondaspects of the present disclosure.

[0390] The method 1200 or process may be performed in a wireless communicationsystem. For example, the method 1200 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 1200 is performed by a network node (e.g., a network node acting as a secondary node (SN) of a serving secondarycell such as gNB 112 serving cell 102) of the wireless communication system such as a basestation or a secondary node, or by an apparatus for use in a network node.

[0391] The method 1200 illustrated in FIGURE 12 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0392] It is to be noted that examples of the method 1200 are not limited to the sequenceof operations illustrated in FIGURE 12. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0393] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0394] The method 1200 starts at operation 1210. In operation 1210, the network nodereceives a notification that an inter-master-node (MN) master cell group (MCG) L1 / L2Triggered Mobility (LTM) is configured at a master node (MN) of the master cell, from the MN. In some examples, the notification enables the network node to prevent initiating the inter- SN SCG LTM preparation. Instead, the network node may initiate the subsequent conditional primary secondary cell addition or change (S-CPAC) or conditional primary secondary cellchange (CPC) preparation.

[0395] In operation 1220, the network node sends a SN change required message (e.g., SNCHANGE REQUIRED) to the MN. The SN change required message includes a request for S- CPAC or CPC.

[0396] In some examples, the network node may receive a message (e.g.,MNToSNIndication) from the MN. The message may be sent via the Xn interface. In someexamples, the message may include a cause (e.g., a cause value) to indicate that the inter-MNMCG LTM is configured at the MN. The cause may comprise “Inter-CU MCG LTMconfigured” (or “Inter-MN MCG LTM configured”) as described above.

[0397] FIGURE 13 illustrates a signaling diagram of an example of a method or processfor inter-SN SCG LTM according to embodiments of the present disclosure. FIGURE 13illustrates at least some of the third aspects of the present disclosure.

[0398] Aspects of the signaling diagram are described above with reference to FIGURES11 and 12. The procedure illustrated in FIGURE 12 is as follows:

[0399] In step 1, the UE 120 / 122 is configured with dual connectivity without SRB3 andSCG LTM assumed.

[0400] In step 2, optionally SCG LTM (e.g., as part of SN Addition procedure) isconfigured.

[0401] In step 4, the UE 120 / 122 reports L3 measurements of cells.

[0402] In step 5, based on the L3 measurements received in step 4, the inter-MN MCGLTM is configured at the MN 1310. In particular, the MN 1310 configures the inter-MN MCGLTM.

[0403] In step 6, the MN 1310 notifies the source SN 1320 via a Xn message (e.g.,MNToSNIndication) about inter-MN MCG LTM being configured at MN.

[0404] In step 8, the source SN 1320 decides to initiate SN CHANGE REQUIRED toconfigure inter-SN preparation. The source SN 1320 however prevents the initiation of inter- SN SCG LTM but may allow the S-CPAC or CPC preparation.

[0405] In step 9, the source SN 1320 initiates S-CPAC preparation (for example).

[0406] Steps 4 to 16 of FIGURE 16 relate to a preparation phase 3 of the procedure. In anexecution phase 17, particularly including steps 18 to 31 shown in FIGURE 13, the S-CPAC procedure is executed and completed. The execution phase 17 and its steps correspond to the execution and completion phases and their steps shown in FIGURES 3 and 4.

[0407] For example, the Xn message (e.g., MNToSNIndication) may have the followingstructure: MNToSNIndication MNToSNIndication ::= SEQUENCE { protocolIEs ProtocolIE-Container {{MNToSNIndication-IEs}},... } MNToSNIndication-IEs XNAP-PROTOCOL-IES ::= { {ID id-M-NG-RANnodeUEXnAPID CRITICALITY reject TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}|{ ID id-S-NG-RANnodeUEXnAPID CRITICALITY reject TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}| {ID id-Cause CRITICALITY ignore TYPE CausePRESENCE mandatory}|, ... }

[0408] The cause specified in 3GPP TS 38.423 may further include the cause value “Inter-CU MCG LTM configured” (or “Inter-MN MCG LTM configured”):Cause Cause ::= CHOICE { radioNetwork CauseRadioNetworkLayer,transport CauseTransportLayer,protocol CauseProtocol,misc CauseMisc,choice-extension ProtocolIE-Single-Container { {Cause-ExtIEs} }} Cause-ExtIEs XNAP-PROTOCOL-IES ::= { ...}CauseRadioNetworkLayer ::= ENUMERATED {lTM-triggered, no-Backhaul-Resource, mIAB-node-not-authorized, iAB-not-authorized, Inter-CU MCG LTM configured}

[0409] The methods of FIGURES 11 to 13 allow to prevent inter-SN SCG LTMpreparation if the inter-MN MCG LTM is configured at MN.

[0410] Further (fourth) aspects of the present disclosure that are directed to a handlingprocedure if an MCG LTM is de-configured at MN will be described hereinbelow withreference to methods for inter-SN SCG LTM shown in FIGURES 14 to 16. More specifically,the fourth aspects allow the serving SN to configure inter-SN SCG LTM when inter-MN MCGLTM is de-configured and to notify the MN about the configuration of inter-SN SCG LTM toprevent MN configuring inter-MN SCG LTM when inter-SN SCG LTM is configured.

[0411] FIGURE 14 illustrates a flowchart of a method 1400 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 14 illustrates at least some of the fourth aspects of the present disclosure.

[0412] The method 1400 or process may be performed in a wireless communicationsystem. For example, the method 1400 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 1400 is performedby a network node (e.g., a network node acting as a master node (MN) of a master cell such asgNB 110 serving cell 100) of the wireless communication system such as a base station or amaster node, or by an apparatus for use in a network node.

[0413] The method 1400 illustrated in FIGURE 14 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0414] It is to be noted that examples of the method 1400 are not limited to the sequenceof operations illustrated in FIGURE 14. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0415] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node. More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0416] In operation 1420, the network node notifies a secondary node (SN) of a servingsecondary cell that an inter-master-node (MN) master cell group (MCG) L1 / L2 TriggeredMobility (LTM) is de-configured (e.g., at the MN). The notification (e.g., MNToSNIndicationas described above) may be sent by the network node in response to determining in operation1410 that the inter-MN MCG LTM is de-configured at the MN. The notification may include acause (e.g., cause value) to notify that the inter-MN MCG LTM is de-configured at the MN.The cause may comprise “Inter-MN MCG LTM de-configured”.

[0417] In operation 1430, the network node is notified by the SN that an inter-SNsecondary cell group (SCG) L1 / L2 Triggered Mobility (LTM) is configured at the SN.

[0418] In some examples, the network node may be notified by the SN by receiving, fromthe SN, a message (e.g., SNToMNIndication). The message may be sent via the Xn interface.In some examples, the message may include a cause (e.g., a cause value) to notify that the inter-SN SCG LTM is configured at the SN. The cause may comprise “Inter-SN SCG LTMconfigured”.

[0419] In some examples, the message (e.g., SNToMNIndication) may also allow to notifya cause (e.g., a cause value) indicating that the inter-SN SCG LTM is de-configured at the SN.The cause may comprise “Inter-SN SCG LTM de-configured” and may be notified in case theSN determines that the inter-SN SCG LTM is de-configured.

[0420] FIGURE 15 illustrates a flowchart of a method 1500 or process for inter-SN SCGLTM according to embodiments of the present disclosure. FIGURE 15 illustrates at least someof the fourth aspects of the present disclosure.

[0421] The method 1500 or process may be performed in a wireless communicationsystem. For example, the method 1500 or process may be performed in a 5G system as described above with reference to FIGURE 1. More specifically, the method 1500 is performed by a network node (e.g., a network node acting as a secondary node (SN) of a serving secondarycell such as gNB 112 serving cell 102) of the wireless communication system such as a basestation or a secondary node, or by an apparatus for use in a network node.

[0422] The method 1500 illustrated in FIGURE 15 may form part of the preparation phasefor the inter-SN SCG LTM during which the UE 120 / 122 is prepared for the SN change.

[0423] It is to be noted that examples of the method 1500 are not limited to the sequenceof operations illustrated in FIGURE 15. Unless explicitly stated differently, the operations may also be performed in any other sequence, even in parallel.

[0424] The UE 120 / 122 is connected to, and served by, the network. The UE 120 / 122 islocated in an area (i.e., a cell 100) served by a base station (e.g., gNB 110) or a network node.More specifically, in some examples, the UE 120 / 122 is dual connected to both cells 100 and102 and is served by both base stations (i.e., gNB 110 and 112) allowing the UE 120 / 122 tosimultaneously transmit and receive data on multiple component carriers from two serving (network) nodes or cell groups (e.g., a master node (MN) serving a master cell and a secondarynode (SN) serving a secondary cell).

[0425] The method 1500 starts at operation 1510. In operation 1510, the network nodereceives a notification that an inter-master-node (MN) master cell group (MCG) L1 / L2Triggered Mobility (LTM) is de-configured at a master node (MN) of a master cell, from theMN. For example, the notification (e.g., MNToSNIndication as described above) may includea cause (e.g., a cause value) to notify that the inter-MN MCG LTM is de-configured at the MN.The cause may comprise “Inter-MN MCG LTM de-configured”. In some examples, thenotification enables the network node to configure the inter-SN SCG LTM.

[0426] In operation 1520, the network node notifies the MN that the inter-SN SCG LTMis configured (e.g., at the SN). The notification may be sent in response to determining that theinter-SN SCG LTM is configured at the SN.

[0427] In some examples, the network node may notify the MN by sending a message (e.g.,SNToMNIndication) to the MN. The message may be sent via the Xn interface. In someexamples, the message may include a cause (e.g., a cause value) to notify that the inter-SN SCGLTM is configured at the SN. The cause may comprise “Inter-SN SCG LTM configured”.

[0428] In some examples, the message (e.g., SNToMNIndication) may also allow to notifya cause (e.g., a cause value) indicating that the inter-SN SCG LTM is de-configured at the SN.The cause may comprise “Inter-SN SCG LTM de-configured” and may be notified in responseto determining that the inter-SN SCG LTM is de-configured at the SN.

[0429] FIGURE 16 illustrates a signaling diagram of an example of a method or processfor inter-SN SCG LTM according to embodiments of the present disclosure. FIGURE 16 illustrates at least some of the fourth aspects of the present disclosure.

[0430] Aspects of the signaling diagram are described above with reference to FIGURES14 and 15. The procedure illustrated in FIGURE 16 is as follows:

[0431] In step 1, the UE 120 / 122 is configured with dual connectivity without SRB3 andSCG LTM assumed.

[0432] In step 2, optionally SCG LTM (e.g., as part of SN Addition procedure) isconfigured.

[0433] In step 4, the UE 120 / 122 reports L3 measurements of cells.

[0434] In step 5, based on the L3 measurements received in step 4, the inter-MN MCGLTM is configured at the MN 1610. In particular, the MN 1610 configures the inter-MN MCGLTM.

[0435] In step 6, the MN 1610 indicates to the serving SN 1620 that the inter-MN MCGLTM is configured via a Xn message (e.g., MNToSNIndication) with a cause (e.g., “Inter-MNMCG LTM configured”). The Xn message prevents the serving SN 1620 to configure the inter-SN SCG LTM, thereby preventing simultaneous LTM execution in MCG and SCG.

[0436] In step 7, the UE 120 / 122 reports L3 measurements of cells.

[0437] In step 8, due to step 6, the serving SN 1620 prevents to configure the inter-SNSCG LTM while the inter-MN MCG LTM is configured at the MN 1610. The serving SN 1620may instead configure S-CPAC or CPC.

[0438] In step 9, the inter-MN MCG LTM may be de-configured at the MN 1610.

[0439] In step 10, the MN 1610 notifies the serving SN 1620 via a Xn message (e.g.,MNToSNIndication) with a cause value “Inter-MN MCG LTM de-configured”. The messagewith the cause value enables the serving SN 1620 to configure the inter-SN SCG LTM (i.e.,step 11).

[0440] In step 12, the serving SN 1620 decides to configure the inter-SN SCG LTM.

[0441] In step 13, the serving SN 1620 notifies the MN 1610 via a Xn message (e.g.,SNToMNIndication) with a cause value “Inter-SN SCG LTM configured”. The message withthe cause value prevents the MN 1610 to configure the inter-MN MCG LTM.

[0442] Steps 4 to 13 of FIGURE 16 relate to a preparation phase 3 of the procedure.

[0443] For example, the Xn message (e.g., MNToSNIndication) may have the structuredescribed above.

[0444] The cause specified in 3GPP TS 38.423 may further include the cause value “Inter-CU MCG LTM de-configured” (or “Inter-MN MCG LTM de-configured”): Cause Cause ::= CHOICE { radioNetwork CauseRadioNetworkLayer,transport CauseTransportLayer,protocol CauseProtocol,misc CauseMisc,choice-extension ProtocolIE-Single-Container { {Cause-ExtIEs} }} Cause-ExtIEs XNAP-PROTOCOL-IES ::= { ... } CauseRadioNetworkLayer ::= ENUMERATED { cell-not-available, handover-desirable-for-radio-reasons, handover-target-not-allowed,}

[0445] For example, the Xn message (e.g., SNToMNIndication) may have the followingstructure: SNToMNIndicationSNToMNIndication ::= SEQUENCE {protocolIEs ProtocolIE-Container {{SNToMNIndication-IEs}},... } SNToMNIndication-IEs XNAP-PROTOCOL-IES ::= { {ID id-M-NG-RANnodeUEXnAPID CRITICALITY reject TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}|{ ID id-S-NG-RANnodeUEXnAPID CRITICALITY reject TYPE NG-RANnodeUEXnAPID PRESENCE mandatory}|{ ID id-Cause CRITICALITY ignore TYPE Cause PRESENCE mandatory}|, ... }

[0446] The cause specified in 3GPP TS 38.423 may further include the cause value “Inter-CU SCG LTM configured” (or “Inter-SN SCG LTM configured”) and optionally also the causevalue “Inter-CU SCG LTM de-configured” (or “Inter-SN SCG LTM de-configured”):CauseCause ::= CHOICE {radioNetwork CauseRadioNetworkLayer,transport CauseTransportLayer,protocol CauseProtocol,misc CauseMisc,choice-extension ProtocolIE-Single-Container { {Cause-ExtIEs} } } Cause-ExtIEs XNAP-PROTOCOL-IES ::= { ... } CauseRadioNetworkLayer ::= ENUMERATED { cell-not-available, handover-desirable-for-radio-reasons, handover-target-not-allowed,invalid-AMF-Set-ID, no-radio-resources-available-in-target-cell, partial-handover, reduce-load-in-serving-cell, resource-optimisation-handover, time-critical-handover, tXnRELOCoverall-expiry, tXnRELOCprep-expiry, unknown-GUAMI-ID, unknown-local-NG-RAN-node-UE-XnAP-ID, inconsistent-remote-NG-RAN-node-UE-XnAP-ID, encryption-and-or-integrity-protection-algorithms-not-supported, not-used-causes-value-1, multiple-PDU-session-ID-instances, unknown-PDU-session-ID,unknown-QoS-Flow-ID, multiple-QoS-Flow-ID-instances, switch-off-ongoing, not-supported-5QI-value, tXnDCoverall-expiry,tXnDCprep-expiry, action-desirable-for-radio-reasons, reduce-load, resource-optimisation,}

[0447] The methods of FIGURES 14 to 16 allow the serving SN to configure the inter-SNSCG LTM when the inter-MN MCG LTM is de-configured at the MN and to notify the MNabout the configuration of the inter-SN SCG LTM at the serving SN, thereby preventing theMN to configure the inter-MN SCG LTM when the inter-SN SCG LTM is configured at theserving SN.

[0448] An apparatus according to an example of the present disclosure may represent orrealize / embody a (e.g., part of a) a user equipment (UE) as an example of a terminal device, wireless device, or entity. Such apparatus may be illustrated or realized as is shown in FIGURE 2.

[0449] Such apparatus may also be illustrated or realized as is shown in FIGURE 17 (i.e.,the apparatus 1700 shown in FIGURE 17 in a configuration). The apparatus 1700 may comprise(at least) one or more unit / means / circuitry, denoted by receiving section 1720, which represent any implementation for (or configured to) receiving a reconfiguration message including a configuration of one or more candidate secondary cells for inter-SN SCG LTM and security information for the one or more candidate secondary cells, and (at least) one or more unit / means / circuitry, denoted by processing section 1730, which represent any implementation for (or configured to) performing the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information. Additionally, the apparatus 1700 may comprise (at least) one or more unit / means / circuitry, denoted by transmitting section 1710, which represent any implementation for (or configured to) transmitting L1 / L3 measurements and / or messages to network nodes of the network.

[0450] An apparatus according to an example of the present disclosure may represent orrealize / embody a (e.g., part of a) a network entity (such as any kind of base station or the like)as an example of a network device or entity. Such apparatus may be illustrated or realized as isshown in FIGURE 2.

[0451] Such apparatus may also be illustrated or realized as is shown in FIGURE 17 (i.e.,the apparatus 1700 shown in FIGURE 17 in another configuration). The apparatus 1700 maycomprise (at least) one or more unit / means / circuitry, denoted by transmitting section 1710,which represent any implementation for (or configured to) sending a reconfiguration messageincluding a configuration of one or more candidate secondary cells for inter-SN SCG LTM and security information associated with for the one or more candidate secondary cells. Additionally, the apparatus 1700 may comprise (at least) one or more unit / means / circuitry, denoted by receiving section 1720, which represent any implementation for (or configured to) receiving messages from the UE (for example), and (at least) one or more unit / means / circuitry, denoted by processing section 1730, which represent any implementation for (or configured to) performing operations for serving the UE (for example).

[0452] For further details regarding the operability / functionality of the apparatuses (orunits / means thereof) according to some examples of the present disclosure, reference is made to the above description in connection with any one of FIGURES 1 to 16, respectively.

[0453] The apparatuses according to some examples of the present disclosure maycomprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as oneentity, different modules and memory may be implemented in one or more physical or logical entities.

[0454] The apparatuses may comprise or be coupled to other units or modules etc., such asradio parts or radio heads, used in or for transmission and / or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0455] It is noted that whilst embodiments have been described in relation to LTE and 5GNR, similar principles can be applied in relation to other networks and communication systemswhere enforcing fast connection re-establishment is required. Therefore, although certainembodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein.

[0456] It is also noted herein that while the above describes examples, there are severalvariations and modifications which may be made to the disclosed solution without departing from the scope of the present disclosure.

[0457] In general, the various examples may be implemented in hardware or specialpurpose circuits, software, logic, or any combination thereof. Some aspects of the presentdisclosure may be implemented in hardware, while other aspects may be implemented infirmware or software which may be executed by a controller, microprocessor, or othercomputing device, although the present disclosure is not limited thereto. While various aspectsof the present disclosure may be illustrated and described as block diagrams, flow charts, orusing some other pictorial representation, it is well understood that these blocks, apparatus,systems, techniques, or methods described herein may be implemented in, as non-limitingexamples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0458] Embodiments of the present disclosure may be implemented by computer softwareexecutable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, alsocalled program product, including software routines, applets and / or macros, may be stored inany apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry outembodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0459] Further in this regard it should be noted that any blocks of the logic flow as in thefigures may represent program steps, or interconnected logic circuits, blocks and functions, ora combination of program steps and logic circuits, blocks, and functions. The software may bestored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

[0460] The memory may be of any type suitable to the local technical environment andmay be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems,fixed memory, and removable memory. The data processors may be of any type suitable to thelocal technical environment, and may comprise one or more of general-purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), FPGA, gate level circuits and processors based on multi- core processor architecture, as non-limiting examples.

[0461] Embodiments of the present disclosure may be practiced in various componentssuch as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0462] The foregoing description has provided by way of non-limiting examples a full andinformative description of examples of the present disclosure. However, various modificationsand adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this inventionwill still fall within the scope of the present disclosure as defined in the appended claims.Indeed, there is an additional example comprising a combination of one or more examples with any of the other examples previously discussed.

Claims

CLAIMS 1. An apparatus of a user equipment (UE) in a network, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive, from a network node of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter- secondary-node (SN) secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM), and security information for the one or more candidate secondary cells; and perform the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information.

2. The apparatus of claim 1, wherein the security information comprises an indication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

3. The apparatus of claim 2, wherein the reconfiguration message comprises a dedicated field for the indication.

4. The apparatus of claim 2 or 3, wherein the instructions, when executed by the at least one processor, further cause the apparatus to: in response to determining, based on the indication, to perform the security update, perform the security update based on the security information.

5. The apparatus of any of claims 1 to 4, wherein the security information comprises a security key counter configuration to enable the UE to derive a security key of a base station associated with the one of the one or more candidate secondary cells.

6. The apparatus of claim 5, wherein the reconfiguration message comprises a dedicated field for the security key counter configuration.

7. The apparatus of claim 5 or 6, wherein the security key counter configuration comprises oneor more security key counters associated with the one or more candidate secondary cells.

8. The apparatus of claim 7, wherein the instructions, when executed by the at least one processor, further cause the apparatus to: select, from the one or more security key counters, a security key counter associatedwith the one of the one or more candidate secondary cells; and derive the security key of the basis station based on a master key and the selected security key counter.

9. The apparatus of claim 8, wherein to perform the inter-SN SCG LTM the instructions, when executed by the at least one processor, further cause the apparatus to: use the derived security key to perform the inter-SN SCG LTM to the base station serving the one of the one or more candidate secondary cells.

10. The apparatus of any one of claims 5 to 9, wherein the security key is S-KgNB.

11. A method, comprising: receiving, at a user equipment (UE) in a network from a network node of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-secondary-node (SN) secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM), and security information for the one or more candidate secondary cells; and performing, at the UE, the inter-SN SCG LTM to one of the one or more candidate secondary cells based on the configuration and the security information.

12. An apparatus of a network node in a network, comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: send, to a user equipment (UE) of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-secondary-node (SN)secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM), and security information for theone or more candidate secondary cells.

13. The apparatus of claim 12, wherein the security information comprises an indication to inform the UE whether to perform a security update when applying the configuration upon performing the inter-SN SCG LTM to one of the one or more candidate secondary cells.

14. The apparatus of claim 13, wherein the reconfiguration message comprises a dedicated field for the indication.

15. The apparatus of claim 13 or 14, wherein the apparatus is comprised in a base station of the network.

16. A method, comprising, at a network node in a network: sending, to a user equipment (UE) of the network, a reconfiguration message including a configuration of one or more candidate secondary cells for an inter-secondary-node (SN) secondary cell group (SCG) L1 / L2 Triggered Mobility (LTM), and security information for the one or more candidate secondary cells.

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