Methods, apparatus and computer-readable media relating to l1 / l2 mobility wireless networks

Abstract

There is provided a method performed by a user equipment The method comprises: receiving (402) a Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiating (406) an LTM mobility procedure to the candidate cell using the LTM candidate cell configuration.

Description

METHODS, APPARATUS AND COMPUTER-READABLE MEDIA RELATING TO MOBILITY IN WIRELESS NETWORKSTECHNICAL FIELDEmbodiments of the present disclosure relate to wireless networks, and particularly to methods, apparatus and computer-readable media relating to mobility in wireless networks.BACKGROUNDLayer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM) in 3GPP Release 18 (Rel-18) and Release 19 (Rel-19)

[0001] In 3rd Generation Partnership Project (3GPP) Rel-18, a technical area entitled L1 / L2 based inter-cell mobility is included as part of a work item known as Further New Radio (NR) mobility enhancements. According to a Work Item Description (WID) entitled “Further NR mobility enhancements” (MediaTek Inc, Apple, 3GPP TSG RAN #102, Edinburgh, GB, December 11-15, 2023), the goal of L1 / L2 based inter-cell mobility (also known as L1 / L2 Triggered Mobility) is to enable a serving cell change, sometimes also known as an LTM cell switch or an LTM cell switch procedure, via L1 / L2 signalling, in order to reduce the latency, overhead and interruption time.

[0002] A basic principle with L1 / L2 triggered mobility is that a User Equipment (UE) is pre-configured, by the network, with an LTM configuration which includes information such as measurement configuration and a Radio Resource Control (RRC) configuration per LTM candidate cell, sometimes also known as an LTM candidate cell configuration. Such an LTM candidate cell configuration may be an RRCReconfiguration message or one or more Information Elements (IEs) / fields / parameters such as CellGroupConfig. The UE performs measurements on LTM candidate cells and beams in those cells, according to the measurement configuration included in the LTM configuration received by the network. The UE transmits LI measurement reports for LTM including LI- Reference Symbol / Signal Received Power (RSRP) measurements for up to four LTM candidate cells and up to four beams in each cell. When the network (e.g. a gNB or a gNB- Distributed Unit (DU)), receives the LI measurement report for LTM, it may use the content of this report to trigger an LTM cell switch towards one of the LTM candidate cells.

[0003] The network triggers the execution of an LTM cell switch procedure in the UE to one of these LTM candidate cells by transmitting an LTM cell switch command MediumAccess Control (MAC) Control Element (CE) to the UE. The LTM cell switch command includes information such as a reference to an LTM candidate cell configuration and an indication of a target beam in the LTM candidate cell. The UE then connects to the beam and switches to the LTM candidate cell configuration.

[0004] The overall procedures for LTM in Rel-18 are described in 3GPP Technical Specification (TS) 38.300 V18.0.0 (“NR and NG-RAN Overall Description; Stage 2”), subclause 9.2.3.5, and for the gNB- Central Unit (CU) / gNB-DU Architecture in 3GPP TS 38.401 V18.0.0 (“NG-RAN; Architecture description”), subclauses 8.2.1.4-8.2.1.6.

[0005] LTM in Rel-18 is limited to intra-gNB (including intra-CU intra-DU and intra-CU inter-DU) mobility. In 3GPP Rel-19, a work item on NR Mobility enhancements Phase 4 (see RP -240299, Revised Work Item: NR mobility enhancements Phase 4, Apple Inc, China Telecom, 3GPP TSG RAN #103, Maastricht, Netherlands, March 18-21, 2024) aims to enhance mobility features, including introducing support for inter-CU LTM according to the objective below:• Specify support for inter-CU Layer 2 Mobility (LTM) [RAN2, RAN3]• Prioritize the case when CU is acting as Master Node (MN) when Dual Connectivity (DC) is not configured• As secondary priority, support the case when NR-DC is configured and CU is acting as Secondary Node (SN) and Master Cell Group (MCG) is unchanged• As secondary priority, support the case when NR-DC is configured, CU is acting as MN and Secondary Cell (SCell) Group (SCG) is unchanged or SCG is released• Note: The case that LTM is configured in both MCG and SCG is excluded• Specify support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM• Coordination with SA3 needed with respect to security key handling• Note: Rel. 18 intra-CU LTM procedure is considered as baseline for adding inter-CU supportSUMMARY

[0006] There currently exist certain challenge(s).

[0007] In 3GPP Rel-18, LTM is limited to intra-CU mobility use cases (for both intra-DU and inter-DU). In other words, when the UE is in a serving cell of a serving CU, the UE canonly be configured with LTM candidate cell(s) also from that serving CU, which are either cells of the same serving DU, or a candidate DU, but not cells of a different CU. In 3GPP Rel- 19, the work item on NR Mobility enhancements Phase 4 (discussed above) is planned to introduce support for inter-CU LTM in the specifications. Thus, this expects to enable LTM for the mobility use cases requiring mobility between NR base stations, gNBs e.g. the UE may be configured with LTM candidate cells of a different serving CU. These gNBs (e.g. gNB- CU(s)) are connected to each other over the Xn interface, which is a direct interface that is needed to perform mobility within the radio access network (RAN).

[0008] In some mobility use cases requiring mobility between a first gNB and a second gNB, the first gNB does not have an Xn connection to the second gNB. For Layer 3 (L3) handover in such cases, the procedure needs to involve the Core Network (CN), such as the 5G Core Network (5GC). Moreover, for mobility use cases requiring mobility between a first gNB and a second gNB, even if there is an Xn connection between the first gNB and the second gNB, in a subset of those cases, such as when a change of security key involves the core network, e.g. at vertical key derivation or reconfiguration of Non Access Stratum (NAS) security, or when the mobility may require change of network slice, Public Land Mobile Network (PLMN) or core network node (such as change of Access and Mobility management Function (AMF)), the core network needs to be involved in the L3 handover procedure. Also, sometimes even for intra-CU or intra-gNB mobility use cases it may be required to change network slice, PLMN or core network node (such as change of AMF).

[0009] It is not clear how L1 / L2 triggered mobility would work between a first gNB and a second gNB which do not have an Xn connection. Moreover, it is not clear how LTM would work in cases when the core network needs to be involved, either for the inter-CU case or the intra-CU case. L3 handover supports the Next Generation (NG) -based handover cases. However, in LTM, the candidate cells are configured in advance and already at configuration the gNB needs to know whether a certain candidate cell has an Xn connection or not or whether there is a need to use the core network. Therefore, the solution for L3 handover over Next Generation (NG) cannot be used for LTM.

[0010] Specifically, it is not clear how the configuration of LTM and the execution of an LTM cell switch procedure should be performed in cases when an Xn connection is not available between a source gNB-CU and a candidate gNB-CU or when the configuration or execution of an intra-CU or inter-CU LTM cell switch procedure may need to involve the core network.

[0011] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges.

[0012] The disclosure presents methods for a UE to perform NG-based LTM, comprising receiving, from the network, a reconfiguration message including at least one NG-based LTM candidate cell configuration, receiving, from a first network node, an LTM cell switch command indicating an NG-based LTM candidate cell configuration controlled by a second network node, executing an NG-based LTM cell switch procedure while applying the indicated NG-based LTM candidate cell configuration including security key change, and transmitting, to the second network node, uplink data or signalling, using the applied NG-based LTM candidate cell configuration, to indicate successful completion of the LTM cell switch procedure.

[0013] The disclosure also presents methods for a first network node, such as a serving gNB, a serving gNB-CU or a serving CU, to handle NG-based LTM for a UE, comprising: transmitting, to the UE, a reconfiguration message including at least one NG-based LTM candidate cell configuration; and transmitting, to the UE, an LTM cell switch command indicating a NG-based LTM candidate cell configuration controlled by a second network node.

[0014] For example, the first network node may transmit, to the second network node, a request message to perform LTM configuration, and receive, from the second network node, a response message including at least one NG-based LTM candidate cell configuration. The request and response messages may be transmitted and received via a third network node.

[0015] Additionally or alternatively, the first network node may transmit, to the second network node, a message indicating execution of an LTM cell switch procedure for a UE, wherein the indication message is received via a third network node. The first network node may receive, from the second network node, an indication that the UE has successfully executed an LTM cell switch procedure wherein the indication message is received via a third network node.

[0016] The disclosure also presents methods for a second network node, such as a candidate gNB, a candidate gNB-CU or a candidate CU, to handle NG-based LTM for a UE, comprising: receiving, from a first network node, a request message to perform LTM configuration; and transmitting, to the first network node, a response message including at least one NG-based LTM candidate cell configuration, wherein the request and response messages are received and transmitted via a third network node.

[0017] For example, the second network node may receive, from a first network node, a message indicating execution of an LTM cell switch procedure for a UE. The indicationmessage may be received via a third network node. The second network node may further receive, from the UE, uplink data or signaling in a target cell controlled by a second network node. Additionally or alternatively, the second network node may transmit, to the first network node, an indication that the UE has successfully executed an LTM cell switch procedure, wherein the indication message is transmitted via a third network node.

[0018] The disclosure also presents methods for a third network node, such as a core network node (e.g., an AMF) to handle NG-based LTM for a UE, comprising: receiving, from a first network node, a request message to perform LTM configuration; transmitting, to a second network node, a request message to perform LTM configuration; receiving, from the second network node, a response message including at least one NG-based LTM candidate cell configuration; and transmitting, to the first network node, a response message including at least one NG-based LTM candidate cell configuration.

[0019] For example, the third network node may receive, from a first network node, a message indicating execution of an LTM cell switch procedure for a UE, and may transmit, to a second network node, a message indicating execution of an LTM cell switch procedure for a UE. The third network node may receive, from the second network node, an indication that the UE has successfully executed an LTM cell switch procedure. Additionally or alternatively, the third network node may transmit, to the first network node, an indication that the UE has successfully executed an LTM cell switch procedure.

[0020] In a first aspect of the disclosure, there is provided a method performed by a UE. The method comprises: receiving an LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiating an LTM mobility procedure to the candidate cell using the LTM candidate cell configuration.

[0021] In a second aspect of the disclosure, there is provided a method performed by a first network node. The method comprises: transmitting, to a UE, an LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

[0022] In a third aspect of the disclosure, there is provided a method performed by a second network node. The method comprises: receiving, from a third network node, a request message comprising a request for at least part of a LTM candidate cell configuration for a candidate cell served by the second network node, for a UE served by a first network node; andtransmitting, to the third network node, a response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

[0023] In a fourth aspect of the disclosure, there is provided a method performed by a third network node. The method comprises receiving, from a first network node, a first request message comprising a request for at least part of a LTM candidate cell configuration for a UE served by the first network node; and transmitting, to the first network node, a first response message comprising the at least part of the LTM candidate cell configuration for a candidate cell, wherein the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

[0024] In a fifth aspect of the disclosure, there is provided a UE. The UE comprises processing circuitry configured to cause the UE to: receive an LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiate an LTM mobility procedure to the candidate cell using the LTM candidate cell configuration

[0025] In a sixth aspect of the disclosure, there is provided a first network node. The first network node comprises processing circuitry configured to cause the first network node to: transmit, to a UE, an LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

[0026] In a seventh aspect of the disclosure, there is provided a second network node. The second network node comprises processing circuitry configured to cause the second network node to: receive, from a third network node, a request message comprising a request for at least part of an LTM, candidate cell configuration for a candidate cell served by the second network node, for a UE served by a first network node; and transmit, to the third network node, a response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobilityprocedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

[0027] In an eighth aspect of the disclosure, there is provided a third network node. The third network node comprises processing circuitry configured to cause the third network node to: receive, from a first network node, a first request message comprising a request for at least part of an LTM candidate cell configuration for a UE served by the first network node; and transmit, to the first network node, a first response message comprising the at least part of the LTM candidate cell configuration for a candidate cell, wherein the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

[0028] In a ninth aspect of the disclosure, there is provided a computer-readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method according to embodiments of any of the first to eight aspects.

[0029] Certain embodiments may provide one or more of the following technical advantage(s).

[0030] Embodiments of the disclosure enable the UE and network to handle configuration and execution of LTM for a UE in mobility use cases when there is no direct connection or interface between the serving base station and the candidate base station or when the core network needs to be involved, such as when slice or PLMN is changed. Thus, the proposed solutions enhance L1 / L2 triggered mobility to cover these mobility use cases and therefore reduce the interruption time in such cases, e.g., as compared to L3 mobility.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] For a better understanding of the embodiments of the present disclosure, and to show how it may be put into effect, reference will now be made, by way of example only, to the accompanying drawings, in which:

[0032] Fig. 1 shows a system according to embodiments of the disclosure;

[0033] Fig. 2 is a signalling flow according to embodiments of the disclosure;

[0034] Fig. 3 is a signalling flow according to further embodiments of the disclosure;

[0035] Fig. 4 is a flow chart illustrating a method performed by a user equipment in accordance with some embodiments;

[0036] Fig. 5 is a flow chart illustrating a method performed by a network node in accordance with some embodiments;

[0037] Fig. 6 is a flow chart illustrating a method performed by a network node in accordance with some embodiments;

[0038] Fig. 7 is a flow chart illustrating a method performed by a core network entity according to embodiments of the disclosure;

[0039] Fig. 8 is a flow chart illustrating a method performed by a user equipment in accordance with some embodiments;

[0040] Fig. 9 is a flow chart illustrating a method performed by a network node (e.g., a first network node, such as a source network node or a serving network node) in accordance with some embodiments;

[0041] Fig. 10 is a flow chart illustrating a method performed by a network node (e.g., a second network node, such as a candidate network node or a target network node) in accordance with some embodiments;

[0042] Fig. 11 is a flow chart illustrating a method performed by a network node (e.g., a third network node, such as a core network node, e.g., AMF / MME) in accordance with some embodiments;

[0043] Fig. 12 is a flow chart illustrating a method performed by a network node (e.g., a first network node, such as a source network node or a serving network node) in accordance with further embodiments;

[0044] Fig. 13 is a flow chart illustrating a method performed by a network node (e.g., a second network node, such as a candidate network node or a target network node) in accordance with further embodiments;

[0045] Fig. 14 is a flow chart illustrating a method performed by a network node (e.g., a third network node, such as a core network node, e.g., AMF / MME) in accordance with further embodiments;

[0046] Fig. 15 shows an example of a communication system in accordance with some embodiments;

[0047] Fig. 16 shows a UE in accordance with some embodiments;

[0048] Fig. 17 shows a network node in accordance with some embodiments;

[0049] Fig. 18 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized; and

[0050] Fig. 19 shows a network node in accordance with some embodiments.DETAILED DESCRIPTION

[0051] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0052] The text refers to the term “L1 / L2 based inter-cell mobility” as used in the Work Item Description entitled “Further NR mobility enhancements” (discussed above) and in 3GPP, though it interchangeably also uses the terms L1 / L2 mobility, Ll-mobility, LI based mobility, Ll / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility L1 / L2 Triggered Mobility, Lower- layer triggered Mobility or LTM. The basic principle is that the UE receives a lower layer signaling (e.g. a MAC CE) from the network indicating to the UE a change (or switch or activation) of its serving cell (e.g. change of Primary Cell (PCell), from a source to a target PCell), wherein a lower layer signaling is a message / signaling of a lower layer protocol, which may be referred as a L1 / L2 inter-cell mobility execution command or LTM cell switch command. The change of serving cell (e.g. change of PCell) may also lead to a change in Scell(s) for the same cell group e.g. in case the command triggers the UE to change to another cell group configuration of the same type (e.g. another MCG configuration). Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more LTM candidate cells (e.g. reception of an RRC Reconfiguration message, with at least one LTM candidate cell configuration) A candidate cell configuration may include parameters in the IE CellGroupConfig per candidate cell and / or an embedded RRC Reconfiguration per candidate cell.

[0053] The term “LTM cell switch procedure” refers to the process of a UE changing its cell from a source cell to a target cell (which may be called here a candidate cell or a neighbour cell), using LTM. In the context of LTM, an LTM cell switch procedure may sometimes also be known as dynamic switch, LTM switch, (LTM) cell switch, (LTM) serving cell change or (LTM) cell change. Even if the term change of cell is used, that may comprise a change of a whole cell group configuration, which includes a change in the Special Cell (SpCell) (e.g. change of PCell, or change of Primary Secondary Cell / SCG (PSCell) and a change in SCells of the cell group (e.g. addition, modification and / or release of one or more SCells). The LTM cell switch procedure may be triggered by the UE receiving an LTM cell switch command from the network. The source and target cells in a LTM cell switch procedure may be controlled by the same gNB, which sometimes is referred to as the intra-gNB case, or when the gNB uses a distributed CU / DU RAN architecture, the intra-CU inter-DU case or the intra-CU intra-DU case (depending on whether the cells are controlled by the same DU or different DUs). Whenthe source and target cells in an LTM cell switch procedure are controlled by different gNBs, this is sometimes referred to as the inter-gNB case, or inter-CU case, or sometimes known as an inter-CU LTM cell switch procedure.

[0054] The text refers to an “LTM configuration”. An LTM configuration is a configuration to be used for L1 / L2 triggered mobility or a configuration being related to L1 / L2 triggered mobility. An LTM configuration may include one or multiple of the following type of elements where each element contains a configuration of one aspect of LTM, for example as follows:• LTM candidate cell configuration(s),• lower layer information, such as physical layer configuration, MAC layer configuration or Radio Link Control (RLC) layer configuration, Cell Group configuration, serving cell configuration• higher layer information, such as RRC protocol parameters, such as timer values, Packet Data Convergence Protocol (PDCP) layer configuration, radio bearer configuration or measurement configuration• Configuration of measurements for LTM• Configuration for measurement reports for LTM• Channel State Information (CSI) resource configuration(s) for LTM• CSI report configuration for LTM• Configurations of early synchronization procedures, such as• Configurations for Downlink (DL) pre-sync for LTM, such as configurations for early Transmission Configuration Indication (TCI) state activation• Configurations for Uplink (UL) pre-sync for LTM, such as configurations for reception of Physical Downlink Control Channel (PDCCH) ordered triggered preamble transmission and reception of Timing Advance (TA)• Configurations for the execution of an LTM cell switch procedure for a given LTM candidate cell configuration (e.g., whether to perform random access procedure, whether to perform RLC reestablishment, or MAC reset, or PDCP recovery), a timer value, configured UL grants, dedicated Random Access (RA) preambles.• A configuration which the UE needs to start to operate accordingly when it performs an LTM cell switch procedure to an LTM candidate cell which is controlled by a different base station, e.g. gNB, from the current source base station e.g. serving gNB of the UE.• Information to perform security key refresh, e.g. the RRC IE MasterKeyUpdate or a RRC IE RadioBearerConfig that includes SecurityConfig with Security AlgorithmConfig.• Indication to perform a full configuration, e.g. the RRC field fullConfig.• Indication to perform L2 re-establishment, such as an indication to perform PDCP re-establishment for one or multiple bearers.

[0055] The text refers to an “NG-based LTM candidate cell” and an “NG-based LTM candidate cell configuration” (sometimes also referred to as a configuration of an NG-based LTM candidate cell). In the context of a UE being controlled by a first network node, such as a serving gNB, an NG-based LTM candidate cell is an LTM candidate cell which is controlled by a second network node, such as a candidate gNB, for which the signalling from the first network node, for the configuration of LTM or execution of an LTM cell switch procedure need to use a third network node, such as core network node (e.g. AMF). An NG-based LTM candidate cell configuration (configuration of an NG-based LTM candidate cell) may include the same information as an LTM candidate cell configuration, but it may also contain additional information needed for performing an LTM cell switch procedure to the NG-based LTM candidate cell, such as• Information for vertical or horizontal key derivation during handover or security key refresh as specified in 3GPP TS 33.501 (e.g. deriving or updating the KgNB key) such as a Next Hop (NH) parameter , a Next Hop Chaining Counter (NCC), or a NAS container (NASC) containing information such as a K_AMF_change_flag, downlink NAS COUNT, ngKSI, selected NAS security algorithms, and NAS MAC.• Information about network slices, such as Network Slice Selection Assistance Information (NSSAI), Single NSSAI (S-NSSAI) RRC information element or allowed NSSAI• Information about PLMNs, such as a PLMN Identifier (ID) or a list of PLMN IDs, an equivalent PLMN ID or a list of equivalent PLMN IDs• Information about registration area, tracking area (e.g. TA identity) or a RAN notification area (e.g. RAN notification area (RNA) identity)• Information about a core network node (e.g. AMF), such as an AMF -Identifier RRC information element, or about selection of core network node• Information about accepted and / or failed Protocol Data Unit (PDU) sessions• Information about accepted or failed radio bearers, Data Radio Bearers (DRBs), Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RABs) or Quality of Service (QoS) flows• QoS flow mapping information used for the mapping of QoS Flows to radio bearers or DRBs, such as the Service Data Adaptation Protocol- (SDAP) Config RRC information element• QoS profile information, such as QoS parameters, for example 5G QoS Identifier (5QI), Allocation and Retention Priority (ARP), Guaranteed Flow Bit Rate (GFBR), Maximum Flow Bit Rate (MFBR), Maximum Packet Loss Rate, Delay Critical Resource Type, Notification Control, Reflective QoS Attribute (RQA), Additional QoS Flow Information, Priority level, Packet Delay Budget, Packet Error Rate, Averaging window, Maximum Data Burst, Explicit Congestion Notification (ECN) information.• Dedicated system information, such as a dedicatedSIBl -Delivery, an dedicatedSystemlnformationDelivery or a System Information Block (SIB) 1 RRC information element• NAS information other than the information above, such as a NAS message / container or a list of NAS messages / containers• Information to be used for accessing an NG-based LTM candidate cell using a different target Radio Access Technology (RAT), such as an E-UTRA RRCConnectionReconfiguration message or one or multiple E-UTRA information elements• An indication of a reference configuration

[0056] Some of the NG-based LTM candidate cell configuration is processed by the first or second network node (e.g. serving gNB or candidate gNB), during LTM configuration, LTM cell switch procedure execution or during some other point in time, e.g. during synchronization towards the NG-based LTM candidate cell. Some parts of the NG-based LTM candidate cell configuration is transmitted to the UE and processed by the RRC layer, layer 2 or a NAS layerin the UE during LTM configuration, LTM cell switch procedure execution or during some other point in time, e.g. during synchronization towards the NG-based LTM candidate cell.

[0057] The term “security key refresh”, sometimes referred to as Access Stratum (AS) key refresh, refers to that the UE changes its security key, e.g. during a mobility procedure such as an LTM cell switch procedure. A security key refresh may comprise at least one of• The UE receives a Master Key Update parameter / IE (e.g. masterKeyUpdate) included in the LTM configuration, LTM candidate cell configuration or NG- based LTM candidate cell configuration (e.g. set by the Second network node or a candidate gNB or candidate gNB-CU).• When a NAS indication (e.g. NASC) is received (e.g. within the Master Key Update parameter / IE) the UE forwards the NAS indication to the upper layer (e.g. UE NAS layer) and the UE updates its NAS security context according to 3GPP TS 33.501 clause 6.9.2.3.4;• When a key set change indication (e.g. keySetChangelndicator) is received and / or is set to ‘true’ (e.g. within the Master Key Update parameter / IE) the UE derives or updates the KSNB key based on the KAMF key, as specified in TS 33.501;• The UE derives or updates the KSNB key (for the LTM candidate cell configuration or the NG-based LTM candidate cell configuration indicated in the LTM cell switch command) based on the current KSNB key or the NH, using the Next Hop Chaining Counter (NCC) parameter (e.g. nextHopChainingCount) value indicated in the received Master Key Update parameter / IE (e.g. MasterKeyUpdate), as specified in TS 33.501;• The UE derives the KRRCenc and Kupenc keys associated with a ciphering algorithm (e.g. cipheringAlgorithm indicated in the security AlgorithmConfig), as specified in TS 33.501;• The UE derives the KRRCint and Kupint keys associated with an integrity protection algorithm (e.g. integrityProtAlgorithm indicated in the security AlgorithmConfig), as specified in TS 33.501;• The UE receives a security algorithm configuration included in the LTM configuration, LTM candidate cell configuration or NG-based LTM candidate cell configuration, based on which the UE derives User plane (UP) keys and / orcontrol plane (CP) keys (e.g. for encryption and / or integrity protection) e.g. the KRRCenc and KuPenc keys, the KRRCint and Kupint keys.• The UE uses its current security algorithm configuration, based on which the UE derives User plane keys and / or control plane keys (e.g. for encryption and / or integrity protection) e.g. the KRRCenc and KuPenc keys, the KRRCint and Kupint keys.• The UE applies the provided ciphering algorithm and key during an PDCP entity re-establishment procedure;• The UE applies the provided integrity protection algorithm and key during an PDCP entity re-establishment procedure• The UE may derive the security key(s) when it receives the LTM configuration, LTM candidate cell configuration or NG-based LTM candidate cell configuration, but only used when the UE performs the LTM cell switch procedure. In that case, when the UE is configured with an LTM candidate cell or NG-based LTM candidate cell (e.g. a candidate to be a PCell) the UE derives one or more security key(s) associated to that LTM candidate cell or NG-based LTM candidate cell (e.g. UP integrity protection key, CP integrity protection key, UP encryption / ciphering key, CP encryption / ciphering key), but only starts to use one of the derived security key(s) when it performs the LTM cell switch procedure.

[0058] Figure 1 illustrates a system according to embodiments of the disclosure, and particularly a structure including entities involved in the disclosure. The UE 1001 is a wireless terminal, such as a cellular smartphone, sometimes connected to the first network node 1002 over a wireless interface 1004 and sometimes connected to a second network node 1003, to which the UE 1001 is connected over a wireless interface 1005.

[0059] The first network node 1002 controls a first cell 1007 (sometimes called serving cell or SpCell, PCell or PSCell, or, in the context of mobility, referred to as source cell). The second network node 1003 controls a second cell 1008, which sometimes, e.g. in the context of mobility, is referred to as target cell, neighbour cell, candidate cell, LTM candidate cell or inter-CU LTM candidate cell.

[0060] Each of first network node 1002 and the second network node 1003 may be a base station such as, when they e.g. are part of NG-RAN, e.g. a gNB. The first network node and the second network node may sometimes be interconnected over an interface 1006, which may be an Xn or Xn-C type of interface, for example when the first network node and secondnetwork node are of type gNB and part of an NG-RAN. In some cases, the first network node and the second network node are not interconnected.

[0061] In the context of mobility, such as L1 / L2 triggered mobility, the first network node 1002 may sometimes be referred to as either source network node, source gNB, serving network node or serving gNB, and the second network node 1003 may sometimes be referred to as either target network node, target gNB, candidate network node or candidate gNB.

[0062] In some cases, such as during intra-gNB or intra-CU mobility, the first network node and the second network node are the same network node.

[0063] In case of a distributed CU / DU RAN architecture, each of the first network node 1002 and / or the second network node 1003 may be divided into a distributed unit, sometimes known as gNB-DU or DU, and a CU, sometimes referred to as gNB-CU, gNB-CU-CP or gNB- CU-UP. Thus, in such a case the first network node 1002 may be divided into a first CU 1009, sometimes referred to as serving CU or source CU, and a first DU 1010, and second network node 1003 may be divided into a second CU 1012, sometimes referred to as target CU or candidate CU, and a second DU 1013. Sometimes the first CU is referred to as the first network node and the second CU is referred to as the second network node. In some cases, such as during intra-gNB or intra-CU mobility, the first CU 1009 and the second CU 1012 are the same node (same CU).

[0064] The first CU 1009 and the first DU 1010 are connected over an interface 1011, which may be an Fl type of interface in case of NG-RAN. Correspondingly, the second CU 1012 and the second DU 1013 are connected over an interface 1014, which may be an Fl type of interface in case of NG-RAN.

[0065] The first network node 1002 and the second network node 1003 may be connected to a third network node 1015 over interfaces 1016 and 1017, respectively. The third network node 1015 may be a core network node, such as an 5GC node, a User Plane Function (UPF) or an AMF. In the latter case, the interfaces 1016 and 1017 are both an NG type of interface or an N2 reference point. Sometimes the third network node are two different network nodes, one (e.g. a source AMF) connected with the first network node and one (e.g. a target AMF) connected with the second network node. These two different network nodes are interconnected over an interface, such as an N14 reference point or an Namf type of service-based interface.

[0066] Figure 15 below provides further detail regarding a system according to embodiments of the disclosure and its component parts.

[0067] As noted above, the disclosure presents methods for UE and network nodes to perform NG-based LTM. In the context of the present disclosure, NG-based LTM may include performing LTM procedures, such as configuration (sometimes referred to as preparation) of LTM for a UE, or execution of LTM (sometimes referred to as performing an LTM cell switch procedure), where the configuration or execution of LTM includes signalling over the NG interface towards a core network node or when the UE receives core network information (sometimes referred to as NAS information).

[0068] In one embodiment of the present disclosure, a first network node, such as a serving gNB or a serving CU, performs configuration of LTM for a UE using a third network node, such as a core network node, e.g. an AMF. In this embodiment the first network node transmits, to the UE a reconfiguration message including an LTM configuration containing at least one NG-based LTM candidate cell configuration. The first network node may obtain at least part of the LTM configuration towards the third network node, such as a core network node, such as an AMF, sometimes referred to as source AMF, over the NG interface. The AMF may provide at least part of the LTM configuration from a second network node, such as a candidate gNB or a candidate CU. Sometimes the AMF generates at least part of the LTM configuration by itself. In some cases, the configuration of LTM involves a second core network node, e.g. an AMF, sometimes referred to as target AMF. In these cases, the target AMF may use signalling towards the second network node and may also provide at least part of the part of the LTM configuration (such as security information).

[0069] In one embodiment of the present disclosure, the first network node triggers LTM cell switch for the UE towards an NG-based LTM candidate cell, which has been previously configured in the UE as part of the LTM configuration. The first network node transmits, to the UE, an LTM cell switch command indicating the NG-based LTM candidate cell configuration controlled by a second network node. The UE executes the LTM cell switch procedure, applies the indicated NG-based LTM candidate cell configuration including security key change and transmits, to the second network node, uplink data or signalling, using the applied NG-based LTM candidate cell configuration, to indicate successful completion of the LTM cell switch procedure. In this embodiment of the present disclosure, the first network node may indicate the execution of the LTM cell switch to the second network node via a third network node, such as a core network node (e.g. an AMF), over the NG interface. In some cases, the indication is first sent to a source AMF which passes the indication via the target AMF before it reaches the second network node.

[0070] In one embodiment of the present disclosure, the second network node may indicate the successful execution of LTM cell switch towards the first network node via a third network node, such as a core network node (e.g. AMF), over the NG interface. In some cases, the indication is first sent to a target AMF which passes the indication via the source AMF before it reaches the first network node.

[0071] Figure 2 illustrates a message sequence chart according to one embodiment of the disclosure. In this example, the UE is configured with at least one NG-based LTM candidate cell configuration in a candidate gNB. In this process, the core network may select a different target AMF to handle the configuration than the current source AMF controlling the UE.

[0072] Referring to Figure 2, the main steps in this example are as follows:

[0073] Step 201. The serving gNB receives, from the UE, an L3 measurement report including measurements of potential LTM candidate cells.

[0074] Step 202. The serving gNB decides to perform setup of LTM configuration and a configuration for at least one LTM candidate cell. In this example, the LTM candidate cell is controlled by a candidate gNB and the configuration need to use the NG interface via core network instead of Xn for instance in case there is no Xn interface between the serving and the candidate gNB.

[0075] Step 203. The serving gNB transmits a request message to the source AMF to request to generate an LTM configuration including at least one NG-based LTM candidate cell configuration. The request message may be an existing NG Application Protocol (NGAP) message, such as a HANDOVER REQUIRED message, or a new message, such as an LTM CONFIGURATION REQUIRED message or an RAN-CN TRANSPARENT TRANSFER message including an XnAP message. The message includes an identity of the target, such as a target cell ID (e.g. an globally unique cell identity such as NR- Cell Global Identity (CGI) or a node level cell identity for the NG-based LTM candidate cell), or an identity of the candidate gNB. The message may also include a Source to Target transparent container, including e.g. the current UE configuration and / or an LTM reference configuration, indication of UE radio access capabilities, indications of QoS flows or DRBs subject to data forwarding for each PDU session.

[0076] Step 204. The source AMF selects a target AMF, using an “AMF selection function”, as specified in 3GPP TS 23.501 section 6.3.5, for the NG-based LTM candidate cell. Factors to be considered in the selection may be for example be the serving PLMN based on the UEs current location or the location of the NG-based LTM candidate cell, the current or requested slice (indicated with NSSAI) or UE capabilities. The selected target AMF may bethe same or different AMF currently serving the UE (source AMF). If the selected target AMF is different from the source AMF, the source AMF transmits an Namf Communication CreateUEContext Request message to the target AMF to request setup of at least one NG-based LTM candidate cell configuration. The message includes security information to be used by the target AMF, for example a key AMF, uplink and downlink NAS COUNTS and a fresh {NH, NCC} pair.

[0077] Step 205. The target AMF (if the target AMF is different from the source AMF), or the source AMF (if they are the same), may create a NASC containing the K_AMF_change_flag, the received downlink NAS COUNT, ngKSI, selected NAS security algorithms, and NAS MAC. It determines the candidate gNB for the LTM candidate cell and sends a request message, to the candidate gNB to request an LTM configuration and setup of at least one NG-based LTM candidate cell configuration. The request message may be an existing NGAP message, such as a HANDOVER REQUEST message, or a new message, such as an LTM CONFIGURATION REQUEST message or a CN-RAN TRANSPARENT TRANSFER message including an XnAP message. The request message may include the created NASC, a security context to be used in the NG-based LTM candidate cell, such as a pair of a NH and a NCC parameters. The message also includes an identity of the target, such as a target cell ID (e.g. NR-CGI for the NG-based LTM candidate cell), or an identity of the candidate gNB. The message may also include a Source to Target transparent container, including e.g. the current UE configuration and / or an LTM reference configuration, indication of UE radio access capabilities, indications of QoS flows or DRBs subject to data forwarding for each PDU session.

[0078] Step 206. The candidate gNB creates an LTM configuration including a configuration for each of the indicated at least one NG-based LTM candidate cell in the received request. The NG-based LTM candidate cell configuration includes the received NASC. It also derives security key(s) based on the received security context.

[0079] Step 207. The candidate gNB responds to the target AMF with a message that includes the LTM configuration containing the at least one NG-based LTM candidate cell configuration. This message may be an existing NGAP message, such as a HANDOVER REQUEST ACKNOWLEDGE message, or a new message such as LTM CONFIGURATION RESPONSE or an RAN-CN TRANSPARENT TRANSFER message including an XnAP message.

[0080] Step 208. The target AMF responds to the source AMF with a Namf Communication CreateUEContext Response message that includes the LTM configuration containing the at least one NG-based LTM candidate cell configuration.

[0081] Step 209. The source AMF responds to the serving gNB in a message that includes an LTM configuration containing the at least one NG-based LTM candidate cell configuration, configuration containing the at least one NG-based LTM candidate cell configuration. This message may be an existing NGAP message, such as a HANDOVER COMMAND Imessage or a new message, such as an LTM CONFIGURATION RESPONSE or an CN-RAN TRANSPARENT TRANSFER message including an XnAP message.

[0082] Step 210. The serving gNB transmits the LTM configuration containing the at least one NG-based LTM candidate cell configuration in an RRCReconfiguration message.

[0083] Steps 211-212. The UE stores the received an LTM configuration containing the at least one NG-based LTM candidate cell configuration (including the NASC) and responds with an RRCReconfigurationComplete message to the serving gNB. In one example, the UE generates a complete configuration using an indicated reference configuration and a delta configuration. In another example, the NG-based LTM candidate cell configuration is a complete or a full configuration and the UE does not use a reference configuration.

[0084] Figure 3 illustrates a message sequence chart according to another embodiment of the disclosure. In this example, the UE executes an NG-based LTM cell switch procedure that involves relocation of AMF.

[0085] Referring to Figure 3, the main steps in this example are as follows.

[0086] Step 301. The UE is configured, by the source gNB, with an LTM configuration including at least one NG-based LTM candidate cell configuration. One of the at least NG- based LTM candidate cells are controlled by the target gNB. An example for configuration procedure is illustrated in Figure 2.

[0087] Step 302. The UE performs LI measurements on the configured LTM candidate cells, including the at least NG-based LTM candidate cells and transmits LI measurement reports to the source gNB.

[0088] Step 303. The source gNB decides to trigger an NG-based LTM cell switch for the UE.

[0089] Step 304. The source gNB transmits, to the UE, an LTM cell switch command, indicating an NG-based LTM candidate cell.

[0090] Step 305. The source gNB transmits, to the source AMF, a message that indicates the execution of an LTM cell switch. The message may be an existing message, such asHANDOVER REQUIRED or HANDOVER NOTIFY or UPLINK RAN STATUS TRANSFER, or a new message, such as RAN-CN CELL SWITCH NOTIFICATION or RAN- CN TRANSPARENT INFORMATION TRANSFER including an XnAP message. The message includes an indication of the target, such as a target cell identifier, e.g. NR-CGI, and / or an indication of the target gNB, such as a gNB ID. The message may also include a Source to Target transparent container, indication of target TCI state(s) and security information, such as security key(s) to be used in the target cell.

[0091] Steps 306-307. The source AMF transmits a message to the target AMF with the information about the LTM cell switch. In one example, this message is an Namf_Communication_NlN2MessageTransfer service operation that contains the information. The information about the LTM cell switch may be carried as a transparent container in this message, for example the message received by the source AMF from the source gNB in step 305. The target AMF acknowledges.

[0092] Step 308. The target AMF sends the information to indicate execution of a LTM cell switch to the target gNB. The message may be an existing message, such as HANDOVER COMMAND or HANDOVER SUCCESS or DOWNLINK RAN STATUS TRANSFER, or a new message, such as CN-RAN CELL SWITCH NOTIFICATION or CN-RAN TRANSPARENT INFORMATION TRANSFER including an XnAP message. The message includes an indication of the target, such as a target cell identifier, e.g. NR-CGI, and / or an indication of the target gNB, such as a gNB ID. The message may also include a Source to Target transparent container, indication of target TCI state(s) and security information, such as security key(s) to be used in the target cell.

[0093] Step 309. Upon reception of the LTM cell switch command, the UE executes the NG-based LTM cell switch, including applying the indicated NG-based LTM candidate cell configuration and performing security key refresh (sometimes referred to a security key change). As part of this, the RRC layer in the UE may pass the NASC, if included in the applied NG-based LTM candidate cell configuration, to the NAS layer in the UE. If the NAS container is included the UE updates its NAS security context according to 3GPP TS 33.501 clause 6.9.2.3.4.

[0094] Steps 310-311. The UE submits an RRCReconfigurationComplete message for transmission in the target cell using the applied NG-based LTM candidate cell configuration including the new security key and security context. The UE transmits the first UL data or signalling in the target cell using the applied NG-based LTM candidate cell configuration. This first UL data or signalling may be a random access procedure, a scheduling request, a MACbuffer status report (BSR), the RRCReconfigurationComplete message or uplink user data in RLC PDU(s). When the UE receives an indication from the target gNB that the first UL data or signalling has been received, it considers the NG-based LTM cell switch procedure as completed.

[0095] Step 312. When the target gNB has detected the first UL data or signalling from the UE in the target cell using the applied NG-based LTM candidate cell configuration, it transmits a message to the target AMF, to indicate the arrival of the UE after the LTM cell switch. This message may be an existing NGAP message such as a HANDOVER NOTIFY, or a new message, such as LTM CELL SWITCH INDICATION or RAN-CN TRANSPARENT INFORMATION TRANSFER including an XnAP message. The message may include an indication of the target cell (such as an NR CGI). The message may in one example include a request to configure an NG-based LTM candidate cell in the source gNB.

[0096] Steps 313-315. The target AMF transmits a message, for example a Namf_Communication_N2InfoNotify service operation, to the source AMF to indicate the UE arrival in the target cell. The message may include an indication of the target cell, such as NR CGI. Upon reception, the source AMF starts a timer to supervise the release of the UE resources including the source gNB UE context. The source AMF acknowledges. In one example, the indication sent to the source AMF include a request to configure an NG-based LTM candidate cell in the source gNB.

[0097] Steps 316-317. Upon expiry of the timer, the source AMF in this example requests a release of the UE context in the source gNB, by transmitting a UE context release command message, and the source gNB acknowledges. In one example, the source gNB is configured with an NG-based LTM candidate cell and the source AMF indicates this in the transmitted message to the source gNB, for example, by including a request to configure an NG-based LTM candidate cell in the transmitted message.

[0098] Step 318. Triggered by the NG-based LTM cell switch procedure, the UE may perform a registration procedure, such as when entering a new Tracking Area, selecting a new network slice or selecting a new PLMN.

[0099] Steps 319-320. The target gNB may configure the UE with a new LTM configuration, for example modification of NG-based LTM candidate cell configurations including new security information for subsequent LTM cell switches.

[0100] Figure 4 depicts a method in accordance with particular embodiments. The method of Figure 4 may be performed by a UE or wireless device (e.g. the UE 1512 or UE 1600 as described later with reference to Figures 15 and 16 respectively). The method may involvesignalling with a first network node, a second network node and one or more third network nodes. The first network node and / or the second network node may be radio access network nodes, such as base stations, eNBs, gNBs, etc. The first network node may be a serving node for the UE. In the context of UE mobility, the first network node may also be called the source network node or gNB, etc. The second network node may be a serving node for the candidate cell. In the context of a UE mobility procedure, the second network node may be called a target network node. The one or more third network nodes may include at least one core network node. For example, the core network node may manage mobility for a radio access network, such as an AMF or a Mobility Management Entity (MME). The methods set out below with respect to Figures 5, 6 and 7 describe complementary methods in the first network node, the second network node and a third network node respectively, and the skilled reader is directed to read these flowcharts in combination as part of the overall disclosure. Figures 8 to 14 are also relevant.

[0101] The method begins at step 402, in which the UE receives a LTM candidate cell configuration for a candidate cell. The LTM candidate cell configuration comprises an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes (e.g., core network nodes, such as AMF / MME). See, for example, step 210 in Figure 2 above.

[0102] The indication that the mobility procedure involves communication with one or more third network nodes may be implicit or explicit. For example, an explicit indication may comprise a field or other parameter in the configuration that is set to indicate that the mobility procedure involves communicate with one or more third network nodes. An implicit indication may comprise a particular type of message that is associated with such mobility procedures (e.g, a dedicated IE or other information container), the presence of one or more fields that are associated with such mobility procedures (see below), etc.

[0103] The indication that the mobility procedure involves communication with one or more third network nodes is alternatively expressed herein as “NG-based”, e.g., the mobility procedure involves communication over an interface between the RAN and the core network (called NG interface in 5G). Such an LTM candidate cell configuration may comprise the same information as conventional LTM candidate cell configurations, plus additional information such as one or more of information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area,tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radio-access technology (e.g., different to a RAT used to communicate with the first network node).

[0104] The LTM candidate cell configuration may be received from the first network node in a reconfiguration message (e.g., RRCReconfiguration). Such a message may comprise a single LTM candidate cell configuration, or multiple LTM candidate cell configurations (e.g., for different candidate cells). In one embodiment, the reconfiguration message is received within a handover command.

[0105] In step 404, the UE detects a triggering event. In one embodiment, the triggering event comprises the user equipment receiving a cell switch message or command from the first network node. See step 304 in Figure 3, for example. The cell switch message may comprise an indication of the LTM candidate cell configuration. Alternatively, the triggering event may comprise the fulfillment of some execution condition (e.g., based on radio measurements of signals transmitted by the first network node and / or the second network node) or the detection of an event.

[0106] In step 406, responsive to the triggering event, the UE initiates a LTM mobility procedure to the candidate cell using the LTM candidate cell configuration. Initiating the LTM mobility procedure may comprise determining a new security key for use in communicating with the second network node. The user equipment may further transmit uplink data or signalling to the second network node to indicate that the LTM mobility procedure to the second network node is complete; see step 311 in Figure 3 above, for example. For example, the UE may perform one or more of a random-access procedure with the candidate cell; transmitting a scheduling request to the candidate cell; transmitting a buffer status report to the candidate cell; transmitting an RRCReconfigurationComplete message to the candidate cell; and transmitting uplink user data to the candidate cell.

[0107] Step 406 may additionally or alternative comprise one or more of entering a new tracking area or RAN notification area; selecting a new network slice; selecting a new PLMN; selecting a different RAT for accessing the second network node.

[0108] Figure 5 depicts a method in accordance with particular embodiments. The method of Figure 5 may be performed by a first network node (e.g. the network node 1510 or network node 1700 as described later with reference to Figures 15 and 17 respectively). The method may involve signalling with a user equipment, a second network node and one or more third network nodes. The first network node and / or the second network node may be radio access network nodes, such as base stations, eNBs, gNBs, etc. The first network node may be a serving node for the UE. In the context of UE mobility, the first network node may also be called the source network node or gNB, etc. The second network node may be a serving node for the candidate cell. In the context of a UE mobility procedure, the second network node may be called a target network node. The one or more third network nodes may include at least one core network node. For example, the core network node may manage mobility for a radio access network, such as an AMF or a MME. The methods set out herein with respect to Figures 4, 6 and 7 describe complementary methods in the user equipment, the second network node and a third network node respectively, and the skilled reader is directed to read these flowcharts in combination as part of the overall disclosure. Figures 8 to 14 are also relevant.

[0109] The method begins at step 502, in which the first network node transmits, to the third network node, a request message comprising a request for at least part of a LTM candidate cell configuration for a candidate cell. See, for example, step 203 in Figure 2. The request message may comprise an indication of a configuration used by the user equipment for communication with the first network node. The indication of the configuration used by the user equipment for communication with the first network node may comprise one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

[0110] In step 504, the first network node receives, from the third network node, a response message comprising the at least part of the LTM candidate cell configuration. See, for example, step 209 in Figure 2. The response message may additionally comprise an identity of the second network node, for example.[OHl] In some embodiments, responsive to receiving the response message from the third network node, the first network node may establish a direct interface (e.g., Xn interface) with the second network node.

[0112] In step 506, the first network node transmits, to a user equipment, the LTM candidate cell configuration for a candidate cell. The LTM candidate cell configurationcomprises an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes (e.g., core network nodes, such as AMF / MME). See, for example, step 210 in Figure 2 above.

[0113] The indication that the mobility procedure involves communication with one or more third network nodes may be implicit or explicit. For example, an explicit indication may comprise a field or other parameter in the configuration that is set to indicate that the mobility procedure involves communicate with one or more third network nodes. An implicit indication may comprise a particular type of message that is associated with such mobility procedures (e.g, a dedicated IE or other information container), the presence of one or more fields that are associated with such mobility procedures (see below), etc.

[0114] The indication that the mobility procedure involves communication with one or more third network nodes is alternatively expressed herein as “NG-based”, e.g., the mobility procedure involves communication over an interface between the RAN and the core network (called NG interface in 5G). Such an LTM candidate cell configuration may comprise the same information as conventional LTM candidate cell configurations, plus additional information such as one or more of: information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radio-access technology (e.g., different to a RAT used to communicate with the first network node).

[0115] The LTM candidate cell configuration may be transmitted to the UE in a reconfiguration message (e.g., RRCReconfiguration). Such a message may comprise a single LTM candidate cell configuration, or multiple LTM candidate cell configurations (e.g., for different candidate cells). In one embodiment, the reconfiguration message is transmitted within a handover command.

[0116] In step 508, the first network node transmits a cell switch message to the user equipment. See step 304 in Figure 3, for example. The cell switch message may comprise an indication of the LTM candidate cell configuration. The cell switch message may be transmitted, for example, on the basis of information contained within LI measurement reports from the UE, of measurements performed by the UE on transmissions by the first and / or second network nodes.

[0117] In step 510, the first network node transmits a notification message to the second network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node. See step 305 in Figure 3, for example. The notification message may be transmitted to the second network node via the third network node (and potentially more than one third network node, e.g., source AMF and target AMF).

[0118] Figure 6 depicts a method in accordance with particular embodiments. The method of Figure 6 may be performed by a second network node (e.g. the network node 1510 or network node 1700 as described later with reference to Figures 15 and 17 respectively). The method may involve signalling with a user equipment, a first network node and one or more third network nodes. The first network node and / or the second network node may be radio access network nodes, such as base stations, eNBs, gNBs, etc. The first network node may be a serving node for the UE. In the context of UE mobility, the first network node may also be called the source network node or gNB, etc. The second network node may be a serving node for the candidate cell. In the context of a UE mobility procedure, the second network node may be called a target network node. The one or more third network nodes may include at least one core network node. For example, the core network node may manage mobility for a radio access network, such as an AMF or a MME. The methods set out below with respect to Figures 4, 5 and 7 describe complementary methods in the user equipment, the first network node and a third network node respectively, and the skilled reader is directed to read these flowcharts in combination as part of the overall disclosure. Figures 8 to 14 are also relevant.

[0119] The method begins at step 602, in which the second network node receives, from a third network node, a request message comprising a request for at least part of a LTM candidate cell configuration for a candidate cell served by the second network node, for a user equipment served by a first network node. See, for example, steps 204 and 205 in Figure 2. The request message may comprise an indication of a configuration used by the user equipment for communication with the first network node. The indication of the configuration used by the user equipment for communication with the first network node may comprise one of more of a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; anindication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE. The request message may originate from a first network node, and be forwarded to the second network node via the third network node. The request message may comprise or correspond to a request for set-up of the LTM candidate cell configuration.

[0120] In step 604, the second network node generates at least part of the LTM candidate cell configuration. See step 206 in Figure 2, for example. The LTM candidate cell configuration may be generated using the indication of the configuration used by the UE in the request message received in step 602.

[0121] The LTM candidate cell configuration comprises an indication that a mobility procedure from a first network node to the second network node serving the candidate cell involves communication with one or more third network nodes (e.g., core network nodes, such as AMF / MME).

[0122] The indication that the mobility procedure involves communication with one or more third network nodes may be implicit or explicit. For example, an explicit indication may comprise a field or other parameter in the configuration that is set to indicate that the mobility procedure involves communicate with one or more third network nodes. An implicit indication may comprise a particular type of message that is associated with such mobility procedures (e.g, a dedicated IE or other information container), the presence of one or more fields that are associated with such mobility procedures (see below), etc.

[0123] The indication that the mobility procedure involves communication with one or more third network nodes is alternatively expressed herein as “NG-based”, e.g., the mobility procedure involves communication over an interface between the RAN and the core network (called NG interface in 5G). Such an LTM candidate cell configuration may comprise the same information as conventional LTM candidate cell configurations, plus additional information such as one or more of: information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment;information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radio-access technology (e.g., different to a RAT used to communicate with the first network node).

[0124] In step 606, the second network node transmits, to the third network node, a response message comprising the at least part of the LTM candidate cell configuration. See step 207 in Figure 2, for example. The at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes. The response message may additionally comprise an identity of the second network node, for example.

[0125] In some embodiments, responsive to receiving the response message from the third network node, the first network node may establish a direct interface (e.g., Xn interface) with the second network node.

[0126] In step 608, the second network node receives, from the first network node via one or more third network nodes, a notification message that the UE has switched cells to the candidate cell. That is, the method of Figure 6 may further comprise the second network node receiving a notification message from the first network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node. The notification message may be received from the first network node via one or more third network nodes. See step 308 in Figure 3, for example.

[0127] Figure 7 depicts a method in accordance with particular embodiments. The method of Figure 7 may be performed by a third network node (e.g. the core network node 1508 or network node 1900 as described later with reference to Figures 15 and 19 respectively). The method may involve signalling with a user equipment, a first network node and a second network node. The first network node and / or the second network node may be radio access network nodes, such as base stations, eNBs, gNBs, etc. The first network node may be a serving node for the UE. In the context of UE mobility, the first network node may also be called the source network node or gNB, etc. The second network node may be a serving node for the candidate cell. In the context of a UE mobility procedure, the second network node may be called a target network node. The one or more third network nodes may include at least one core network node. For example, the core network node may manage mobility for a radio access network, such as an AMF or a MME. The methods set out herein with respect to Figures 4, 5 and 6 describe complementary methods in the user equipment, the first networknode and the second network node respectively, and the skilled reader is directed to read these flowcharts in combination as part of the overall disclosure. Figures 8 to 14 are also relevant.

[0128] The method begins at step 702, in which the third network node receives, from a first network node, a first request message comprising a request for at least part of an LTM candidate cell configuration for a user equipment served by the first network node. See, for example, step 203 in Figure 2. The first request message may comprise an indication of a configuration used by the user equipment for communication with the first network node. The indication of the configuration used by the user equipment for communication with the first network node may comprise one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE. The request message may comprise or correspond to a request for set-up of the LTM candidate cell configuration.

[0129] In step 704, the third network node transmits a second request message (e.g., comprising substantially similar data to that which was received in step 702) to a second network node. See, for example, steps 204 and 205 in Figure 2. Thus, the second request message may comprise an indication of a configuration used by the user equipment for communication with the first network node. The indication of the configuration used by the user equipment for communication with the first network node may comprise one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

[0130] In step 706, the third network node receives, from the second network node, a second response message. The second response message comprises the at least part of the LTM candidate cell configuration. The at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

[0131] The LTM candidate cell configuration comprises an indication that a mobility procedure from a first network node to the second network node serving the candidate cell involves communication with one or more third network nodes (e.g., core network nodes, such as AMF / MME).

[0132] The indication that the mobility procedure involves communication with one or more third network nodes may be implicit or explicit. For example, an explicit indication maycomprise a field or other parameter in the configuration that is set to indicate that the mobility procedure involves communicate with one or more third network nodes. An implicit indication may comprise a particular type of message that is associated with such mobility procedures (e.g, a dedicated IE or other information container), the presence of one or more fields that are associated with such mobility procedures (see below), etc.

[0133] The indication that the mobility procedure involves communication with one or more third network nodes is alternatively expressed herein as “NG-based”, e.g., the mobility procedure involves communication over an interface between the RAN and the core network (called NG interface in 5G). Such an LTM candidate cell configuration may comprise the same information as conventional LTM candidate cell configurations, plus additional information such as one or more of information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radio-access technology (e.g., different to a RAT used to communicate with the first network node). The second response message may additionally comprise an identity of the second network node.

[0134] In step 708, the third network node transmits, to the first network node, a first response message comprising the at least part of the LTM candidate cell configuration for a candidate cell. The LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes. The first response message may additionally comprise an identity of the second network node.

[0135] In step 710, the third network node receives a first notification message from the first network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node. See step 305 in Figure 3, for example. The third network node may further transmit, to the second network node, a second notificationmessage comprising an indication that the user equipment has switched to the candidate cell. See step 306 in Figure 3, for example. The second notification message may be sent to the second network node via one or more further third network nodes (e.g., Target AMF).

[0136] Figure 8 illustrates a flow chart with the main steps performed by the UE in one example of the disclosure. Referring to Figure 8, the main steps performed by the UE in this example are as follows.

[0137] Step 801. The UE receives, from the network, reconfiguration message (such as RRCReconfiguration) including an LTM configuration containing at least one an NG-based LTM candidate cell configuration.

[0138] Step 802. The UE receives, from a first network node, an LTM cell switch command indicating an NG-based LTM candidate cell configuration controlled by a second network node.

[0139] Step 803. The UE executes an NG-based LTM cell switch procedure while applying the indicated NG-based LTM candidate cell configuration including security key change.

[0140] Step 804. The UE transmits, to the second network node, uplink data or signalling, in a target cell using the applied NG-based LTM candidate cell configuration, to indicate successful completion of the LTM cell switch procedure.

[0141] Figure 9 illustrates a flow chart with the main steps performed by the first network node in one example of the disclosure for configuration of NG-based LTM. Referring to Figure 9, the main steps performed by the serving network node in this example are as follows.

[0142] Step 901. The first network node decides to perform setup of an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0143] Step 902. The first network node transmits, to a third network node, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0144] Step 903. The first network node receives, from the third network node, a response message including an LTM configuration containing at least one configuration of an NG-based LTM candidate cell.

[0145] Step 904. The first network node transmits, to the UE, a configuration message including an LTM configuration containing at least one NG-based LTM candidate cell configuration.

[0146] Figure 10 illustrates a flow chart with the main steps performed by the second network node in one example of the disclosure for configuration of NG-based LTM. Referringto Figure 10, the main steps performed by the second network node in this example are as follows.

[0147] Step 1001. The second network node receives, from a third network node, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0148] Step 1002. The second network node generates an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0149] Step 1003. The second network node transmits, to the third network node, a response message including an LTM configuration containing at least one configuration of an NG-based LTM candidate cell.

[0150] Figure 11 illustrates a flow chart with the main steps performed by the third network node in one example of the disclosure for configuration of NG-based LTM. Referring to Figure 11, the main steps performed by the third network node in this example are as follows.

[0151] Step 1101. The third network node receives, from a first network node, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0152] Step 1102. The third network node transmits, to a second network node, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration.

[0153] Step 1103. The third network node receives, from the second network node, a response message including an LTM configuration containing at least one configuration of an NG-based LTM candidate cell.

[0154] Step 1104. The third network node transmits, to the first network node, a response message including an LTM configuration containing at least one configuration of an NG-based LTM candidate cell.

[0155] Figure 12 illustrates a flow chart with the main steps performed by the first network node in one example of the disclosure for execution of NG-based LTM.

[0156] Referring to Figure 12, the main steps performed by the first network node in this example are as follows.

[0157] Step 1201. The first network node, transmits, to the UE, an LTM cell switch command indicating a NG-based LTM candidate cell configuration controlled by a second network node.

[0158] Step 1202. The first network node transmits, to the second network node, a message indicating execution of an LTM cell switch procedure for a UE, wherein the indication message is transmitted via a third network node.

[0159] Step 1203. The first network node receives, from the second network node, an indication that the UE has successfully executed an LTM cell switch procedure wherein the indication message is received via a third network node.

[0160] Figure 13 illustrates a flow chart with the main steps performed by the second network node in one example of the disclosure for execution of NG-based LTM. Referring to Figure 13, the main steps performed by the second network node in this example are as follows.

[0161] Step 1301. The second network node receives, from a first network node, a message indicating execution of an LTM cell switch procedure for a UE, wherein the indication message is received via a third network node.

[0162] Step 1302. The second network node receives, from the UE, uplink data or signaling, in a target cell controlled by the second network node, indicating successful completion of the LTM cell switch procedure.

[0163] Step 1303. The second network node transmits, to the first network node, an indication that the UE has successfully executed an LTM cell switch procedure, wherein the indication message is transmitted via a third network node.

[0164] Figure 14 illustrates a flow chart with the main steps performed by the third network node in one example of the disclosure for execution of NG-based LTM.

[0165] Referring to Figure 14, the main steps performed by the third network node in this example are as follows.

[0166] Step 1401. The third network node receives, from a second network node, a message indicating execution of an LTM cell switch procedure for a UE.

[0167] Step 1402. The third network node transmits, to the second network node, a message indicating execution of an LTM cell switch procedure for a UE.

[0168] Step 1403. The third network node receives, from the second network node, an indication that the UE has successfully executed an LTM cell switch procedure.

[0169] Step 1404. The third network node transmits, to the first network node, an indication that the UE has successfully executed an LTM cell switch procedure.

[0170] Figure 15 shows an example of a communication system 1500 in accordance with some embodiments.

[0171] In the example, the communication system 1500 includes a telecommunication network 1502 that includes an access network 1504, such as a radio access network (RAN),and a core network 1506, which includes one or more core network nodes 1508. The access network 1504 includes one or more access network nodes, such as network nodes 1510a and 1510b (one or more of which may be generally referred to as network nodes 1510), or any other similar 3rd Generation Partnership Project (3GPP) access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, the telecommunication network 1502 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 1502 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in the telecommunication network 1502, including one or more network nodes 1510 and / or core network nodes 1508.

[0172] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O- CU-CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. The network nodes 1510 facilitate direct or indirect connection of user equipment (UE), such as by connecting UEs 1512a, 1512b, 1512c, and 1512d (one or more of which may be generally referred to as UEs 1512) to the core network 1506 over one or more wireless connections.

[0173] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires,cables, or other material conductors. Moreover, in different embodiments, the communication system 1500 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. The communication system 1500 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0174] The UEs 1512 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with the network nodes 1510 and other communication devices. Similarly, the network nodes 1510 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 1512 and / or with other network nodes or equipment in the telecommunication network 1502 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in the telecommunication network 1502.

[0175] In the depicted example, the core network 1506 connects the network nodes 1510 to one or more host computing systems, such as host 1516. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. The core network 1506 includes one more core network nodes (e.g., core network node 1508) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 1508. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0176] The host 1516 may be under the ownership or control of a service provider other than an operator or provider of the access network 1504 and / or the telecommunication network 1502. The host 1516 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controllingor otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0177] As a whole, the communication system 1500 of Figure 15 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0178] In some examples, the telecommunication network 1502 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 1502 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 1502. For example, the telecommunications network 1502 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0179] In some examples, the UEs 1512 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 1504 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 1504. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN- DC).

[0180] In the example, the hub 1514 communicates with the access network 1504 to facilitate indirect communication between one or more UEs (e.g., UE 1512c and / or 1512d) and network nodes (e.g., network node 1510b). In some examples, the hub 1514 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 1514 may be a broadband routerenabling access to the core network 1506 for the UEs. As another example, the hub 1514 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1510, or by executable code, script, process, or other instructions in the hub 1514. As another example, the hub 1514 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 1514 may be a content source. For example, for a UE that is a VR device, display, loudspeaker, or other media delivery device, the hub 1514 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 1514 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 1514 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0181] The hub 1514 may have a constant / persistent or intermittent connection to the network node 1510b. The hub 1514 may also allow for a different communication scheme and / or schedule between the hub 1514 and UEs (e.g., UE 1512c and / or 1512d), and between the hub 1514 and the core network 1506. In other examples, the hub 1514 is connected to the core network 1506 and / or one or more UEs via a wired connection. Moreover, the hub 1514 may be configured to connect to an M2M service provider over the access network 1504 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 1510 while still connected via the hub 1514 via a wired or wireless connection. In some embodiments, the hub 1514 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to the network node 1510b. In other embodiments, the hub 1514 may be a non-dedicated hub -that is, a device which is capable of operating to route communications between the UEs and network node 1510b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0182] Figure 16 shows a UE 1600 in accordance with some embodiments. The UE 1600 presents additional details of some embodiments of the UE 1512 of Figure 1. As used herein, a UE refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage / playback device, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME),an Augmented Reality (AR) or Virtual Reality (VR) device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3 GPP), including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0183] A UE may support device-to-device (D2D) communication, for example by implementing a 3 GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), orvehicle- to-everything (V2X). In other examples, a UE may not necessarily have a user in the sense of a human user who owns and / or operates the relevant device. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but which may not, or which may not initially, be associated with a specific human user (e.g., a smart sprinkler controller). Alternatively, a UE may represent a device that is not intended for sale to, or operation by, an end user but which may be associated with or operated for the benefit of a user (e.g., a smart power meter).

[0184] The UE 1600 includes processing circuitry 1602 that is operatively coupled via a bus 1604 to an input / output interface 1606, a power source 1608, a memory 1610, a communication interface 1612, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 16. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc.

[0185] The processing circuitry 1602 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in the memory 1610. The processing circuitry 1602 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, the processing circuitry 1602 may include multiple central processing units (CPUs). The processing circuitry 1602 may be configured to cause the UE 1602 to perform the methods as described with reference to any of Figures 4 and 4, and / or the signalling and actions of the UE in Figure 2 or 3.

[0186] In the example, the input / output interface 1606 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into the UE 1600. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0187] In some embodiments, the power source 1608 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. The power source 1608 may further include power circuitry for delivering power from the power source 1608 itself, and / or an external power source, to the various parts of the UE 1600 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1608. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1608 to make the power suitable for the respective components of the UE 1600 to which power is supplied.

[0188] The memory 1610 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 1610 includes one or more application programs 1614, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1616. The memory 1610 may store, for use by the UE 1600, any of a variety of various operating systems or combinations of operating systems.

[0189] The memory 1610 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, externalhard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD- DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ The memory 1610 may allow the UE 1600 to access instructions, application programs and the like, stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in the memory 1610, which may be or comprise a device-readable storage medium.

[0190] The processing circuitry 1602 may be configured to communicate with an access network or other network using the communication interface 1612. The communication interface 1612 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1622. The communication interface 1612 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1618 and / or a receiver 1620 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1618 and receiver 1620 may be coupled to one or more antennas (e.g., antenna 1622) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0191] In the illustrated embodiment, communication functions of the communication interface 1612 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking(SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0192] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1612, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0193] As another example, a UE comprises an actuator, a motor, or a switch, related to a communication interface configured to receive wireless input from a network node via a wireless connection. In response to the received wireless input the states of the actuator, the motor, or the switch may change. For example, the UE may comprise a motor that adjusts the control surfaces or rotors of a drone in flight according to the received input or to a robotic arm performing a medical procedure according to the received input.

[0194] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to the UE 1600 shown in Figure 16.

[0195] As yet another specific example, in an loT scenario, a UE may represent a machine or other device that performs monitoring and / or measurements, and transmits the results ofsuch monitoring and / or measurements to another UE and / or a network node. The UE may in this case be an M2M device, which may in a 3GPP context be referred to as an MTC device. As one particular example, the UE may implement the 3 GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0196] In practice, any number of UEs may be used together with respect to a single use case. For example, a first UE might be or be integrated in a drone and provide the drone’s speed information (obtained through a speed sensor) to a second UE that is a remote controller operating the drone. When the user makes changes from the remote controller, the first UE may adjust the throttle on the drone (e.g. by controlling an actuator) to increase or decrease the drone’s speed. The first and / or the second UE can also include more than one of the functionalities described above. For example, a UE might comprise the sensor and the actuator, and handle communication of data for both the speed sensor and the actuators.

[0197] Figure 17 shows a network node 1700 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR. NodeBs (gNBs)), 0-RAN nodes or components of an 0-RAN node (e.g, 0-RU, 0-DU, O-CU).

[0198] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g, in an 0-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0199] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), basetransceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0200] The network node 1700 includes a processing circuitry 1702, a memory 1704, a communication interface 1706, and a power source 1708. The network node 1700 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1700 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 1700 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1704 for different RATs) and some components may be reused (e.g., a same antenna 1710 may be shared by different RATs). The network node 1700 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1700, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1700.

[0201] The processing circuitry 1702 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1700 components, such as the memory 1704, to provide network node 1700 functionality. For example, the processing circuitry 1702 may be configured to cause the network node, when configured as a first network node, such as a source network node or a serving network node, to perform the methods as described with reference to any of Figures 5, 8 and 5, and / or any of the signalling or actions of the Serving gNB in Figure 2 or the Source gNB in Figure 3. The processing circuitry 1702 may be configured to cause the network node, when configured as a second network node, such as a candidate network node or a target network node, to perform themethods as described with reference to any of Figures 6, 9 and 6, and / or any of the signalling or actions of the Candidate gNB in Figure 2 or the Target gNB in Figure 3.

[0202] In some embodiments, the processing circuitry 1702 includes a system on a chip (SOC). In some embodiments, the processing circuitry 1702 includes one or more of radio frequency (RF) transceiver circuitry 1712 and baseband processing circuitry 1714. In some embodiments, the radio frequency (RF) transceiver circuitry 1712 and the baseband processing circuitry 1714 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1712 and baseband processing circuitry 1714 may be on the same chip or set of chips, boards, or units.

[0203] The memory 1704 may comprise any form of volatile or non-volatile computer- readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computerexecutable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1702. The memory 1704 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 1702 and utilized by the network node 1700. The memory 1704 may be used to store any calculations made by the processing circuitry 1702 and / or any data received via the communication interface 1706. In some embodiments, the processing circuitry 1702 and memory 1704 is integrated.

[0204] The communication interface 1706 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 1706 comprises port(s) / terminal(s) 1716 to send and receive data, for example to and from a network over a wired connection. The communication interface 1706 also includes radio front-end circuitry 1718 that may be coupled to, or in certain embodiments a part of, the antenna 1710. Radio front-end circuitry 1718 comprises filters 1720 and amplifiers 1722. The radio front-end circuitry 1718 may be connected to an antenna 1710 and processing circuitry 1702. The radio front-end circuitry may be configured to condition signals communicated between antenna 1710 and processing circuitry 1702. The radio front-end circuitry 1718 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 1718 may convert the digital data into aradio signal having the appropriate channel and bandwidth parameters using a combination of filters 1720 and / or amplifiers 1722. The radio signal may then be transmitted via the antenna 1710. Similarly, when receiving data, the antenna 1710 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1718. The digital data may be passed to the processing circuitry 1702. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0205] In certain alternative embodiments, the network node 1700 does not include separate radio front-end circuitry 1718, instead, the processing circuitry 1702 includes radio front-end circuitry and is connected to the antenna 1710. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1712 is part of the communication interface 1706. In still other embodiments, the communication interface 1706 includes one or more ports or terminals 1716, the radio front-end circuitry 1718, and the RF transceiver circuitry 1712, as part of a radio unit (not shown), and the communication interface 1706 communicates with the baseband processing circuitry 1714, which is part of a digital unit (not shown).

[0206] The antenna 1710 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 1710 may be coupled to the radio frontend circuitry 1718 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 1710 is separate from the network node 1700 and connectable to the network node 1700 through an interface or port.

[0207] The antenna 1710, communication interface 1706, and / or the processing circuitry 1702 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, the antenna 1710, the communication interface 1706, and / or the processing circuitry 1702 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0208] The power source 1708 provides power to the various components of network node 1700 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1708 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1700 with power for performing the functionality described herein. For example, the network node 1700 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power sourcesupplies power to power circuitry of the power source 1708. As a further example, the power source 1708 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0209] Embodiments of the network node 1700 may include additional components beyond those shown in Figure 17 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the network node 1700 may include user interface equipment to allow input of information into the network node 1700 and to allow output of information from the network node 1700. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1700. In some embodiments providing a core network node, such as core network node 108 of FIG. 15, some components, such as the radio front-end circuitry 1718 and the RF transceiver circuitry 1712 may be omitted.

[0210] Figure 19 shows a network node 1900 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment, in a telecommunication network. The network node 1900 may be operable as a core network node, a core network function or, more generally, a core network entity, such as the core network node 1508 described above with respect to Figure 15). Examples of network nodes in this context include core network entities such as one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), Policy Control Function (PCF) and / or a User Plane Function (UPF).

[0211] The network node 1900 includes processing circuitry 1902, a memory 1904, a communication interface 1906, and a power source 1908, and / or any other component, or any combination thereof. The network node 1900 may be composed of multiple physically separate components, which may each have their own respective components. In certain scenarios in which the network node 1900 comprises multiple separate components, one or more of the separate components may be shared among several network nodes.

[0212] The processing circuitry 1902 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor,application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1900 components, such as the memory 1904, network node 1900 functionality. For example, the processing circuitry 1902 may be configured to cause the network node to perform the methods as described with reference to any of Figures 7, 10 and 7, and / or the signalling or actions of any of the Serving AMF or the Candidate AMF in Figure 2 or the Source AMF or the Target AMF in Figure 3.

[0213] The memory 1904 may comprise any form of volatile or non-volatile computer- readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computerexecutable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1902. The memory 1904 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 1902 and utilized by the network node 1900. The memory 1904 may be used to store any calculations made by the processing circuitry 1902 and / or any data received via the communication interface 1906. In some embodiments, the processing circuitry 1902 and memory 1904 is integrated.

[0214] The communication interface 1906 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE.

[0215] The power source 1908 provides power to the various components of network node 1900 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1908 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1900 with power for performing the functionality described herein. For example, the network node 1900 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1908. As a further example, the power source 1908 may comprise a source of power in the form of a battery or battery pack which isconnected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0216] Embodiments of the network node 1900 may include additional components beyond those shown in Figure 19 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the network node 1900 may include user interface equipment to allow input of information into the network node 1900 and to allow output of information from the network node 1900. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1900.

[0217] Figure 18 is a block diagram illustrating a virtualization environment 1800 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1800 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1800 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface. Virtualization may facilitate distributed implementations of a network node, UE, core network node, or host.

[0218] Applications 1802 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0219] Hardware 1804 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers1806 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1808a and 1808b (one or more of which may be generally referred to as VMs 1808), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. The virtualization layer 1806 may present a virtual operating platform that appears like networking hardware to the VMs 1808.

[0220] The VMs 1808 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1806. Different embodiments of the instance of a virtual appliance 1802 may be implemented on one or more of VMs 1808, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts referred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0221] In the context of NFV, a VM 1808 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1808, and that part of hardware 1804 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs 1808 on top of the hardware 1804 and corresponds to the application 1802.

[0222] Hardware 1804 may be implemented in a standalone network node with generic or specific components. Hardware 1804 may implement some functions via virtualization. Alternatively, hardware 1804 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1810, which, among others, oversees lifecycle management of applications 1802. In some embodiments, hardware 1804 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1812 which may alternatively be used for communication between hardware nodes and radio units.

[0223] Although the computing devices described herein (e.g., UEs, network nodes) may include the illustrated combination of hardware components, other embodiments may comprisecomputing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[0224] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer- readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer- readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

[0225] The following groups of numbered statements set out embodiments of the disclosure.Group A Embodiments1. A method performed by a user equipment, the method comprising:receiving a LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiating a LTM mobility procedure to the candidate cell using the LTM candidate cell configuration.2. The method of embodiment 1, wherein the indication that the mobility procedure involves communicate with one or more third network nodes is implicit or explicit.3. The method of embodiment 1 or 2, wherein the LTM candidate cell configuration comprises one or more of information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radio-access technology (e.g., different to a RAT used to communicate with the first network node).4. The method of any preceding embodiment, wherein the triggering event comprises the user equipment receiving a cell switch message from the first network node.5. The method of embodiment 4, wherein the cell switch message comprises an indication of the LTM candidate cell configuration.6. The method of any preceding embodiment, wherein initiating the LTM mobility procedure to the candidate cell comprises determining a new security key for use in communicating with the second network node.7. The method of any preceding embodiment, further comprising transmitting uplink data or signalling to the second network node to indicate that the LTM mobility procedure to the second network node is complete.8. The method of embodiment 7, wherein transmitting uplink data or signalling comprises one or more of: a random-access procedure; transmitting a scheduling request; transmitting a buffer status report; transmitting an RRCReconfigurationComplete message; and transmitting uplink user data.9. The method of any preceding embodiment, wherein the LTM candidate cell configuration is received in a reconfiguration message (e.g., RRCReconfiguration).10. The method of embodiment 9, wherein the reconfiguration message comprises a plurality of LTM candidate cell configurations for a plurality of candidate cells.11. The method of embodiment 9, wherein the reconfiguration message is received within a handover command.12. The method of any preceding embodiment, wherein initiating the LTM mobility procedure comprises one or more of: entering a new tracking area or RAN notification area; selecting a new network slice; selecting a new PLMN; selecting a different RAT for accessing the second network node.13. The method of any preceding embodiment, wherein the first network node and / or the second network node are radio access network nodes.14. The method of any preceding embodiment, wherein the one or more third network nodes include at least one core network node.15. The method of embodiment 14, wherein the core network node manages mobility for a radio access network.16. The method of embodiment 15, wherein the core network node comprises an Access and Mobility Management Function (AMF) or a Mobility Management Entity (MME).Group B Embodiments17. A method performed by a first network node, the method comprising: transmitting, to a user equipment, a LTM candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.18. The method of embodiment 17, further comprising obtaining at least part of the LTM candidate cell configuration from a third network node.19. The method of embodiment 18, wherein obtaining the at least part of the LTM candidate cell configuration from the third network node comprises transmitting, to the third network node, a request message comprising a request for at least part of the LTM candidate cell configuration and receiving, from the third network node, a response message comprising the at least part of the LTM candidate cell configuration.20. The method of embodiment 19, wherein the request message comprises an indication of a configuration used by the user equipment for communication with the first network node.21. The method of embodiment 20, wherein the indication of the configuration used by the user equipment for communication with the first network node comprises one of more of a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.22. The method of any one of embodiments 19 to 21, wherein the response message comprises an identity of the second network node.23. The method of any one of embodiments 18 to 22, further comprising establishing a direct interface (e.g., Xn interface) with the second network node.24. The method of any one of embodiments 17 to 23, wherein the LTM candidate cell configuration comprises one or more of information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; informationrelating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radioaccess technology (e.g., different to a RAT used to communicate with the first network node).25. The method of any one of embodiments 17 to 24, further comprising transmitting a cell switch message to the user equipment.26. The method of embodiment 25, wherein cell switch message comprises an indication of the LTM candidate cell configuration.27. The method of any one of embodiments 17 to 26, further comprising transmitting a notification message to the second network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node.28. The method of embodiment 27, wherein the notification message is transmitted to the second network node via the third network node.29. The method of any one of embodiments 17 to 28, wherein the first network node and / or the second network node are radio access network nodes.30. The method of any one of embodiments 17 to 29, wherein the one or more third network nodes include at least one core network node.31. The method of embodiment 30, wherein the core network node manages mobility for a radio access network.32. The method of embodiment 31, wherein the core network node comprises an Access and Mobility Management Function (AMF) or a Mobility Management Entity (MME).33. A method performed by a second network node, the method comprising: receiving, from a third network node, a request message comprising a request for at least part of a LTM candidate cell configuration for a candidate cell served by the second network node, for a user equipment served by a first network node; and transmitting, to the third network node, a response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.34. The method of embodiment 33, wherein the request message comprises an indication of a configuration used by the user equipment for communication with the first network node.35. The method of embodiment 34, wherein the indication of the configuration used by the user equipment for communication with the first network node comprises one of more of a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.36. The method of any one of embodiments 33 to 35, wherein the response message comprises an identity of the second network node.37. The method of any one of embodiments 33 to 36, further comprising establishing a direct interface (e.g., Xn interface) with the first network node.38. The method of any one of embodiments 33 to 37, wherein the LTM candidate cell configuration comprises one or more of information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more acceptedand / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radioaccess technology (e.g., different to a RAT used to communicate with the first network node).39. The method of any one of embodiments 33 to 38, further comprising generating the at least part of the LTM candidate cell configuration.40. The method of any one of embodiments 33 to 39, further comprising receiving a notification message from the first network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node.41. The method of embodiment 40, wherein the notification message is received from the first network node via the third network node.42. The method of any one of embodiments 33 to 41, wherein the first network node and / or the second network node are radio access network nodes.43. The method of any one of embodiments 33 to 42, wherein the one or more third network nodes include at least one core network node.44. The method of embodiment 43, wherein the core network node manages mobility for a radio access network.45. The method of embodiment 44, wherein the core network node comprises an Access and Mobility Management Function (AMF) or a Mobility Management Entity (MME).Group C Embodiments46. A method performed by a third network node, the method comprising: receiving, from a first network node, a first request message comprising a request for at least part of a LTM candidate cell configuration for a user equipment served by the first network node; and transmitting, to the first network node, a first response message comprising the atleast part of the LTM candidate cell configuration for a candidate cell, wherein the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.47. The method of embodiment 46, wherein the first request message comprises an indication of a configuration used by the user equipment for communication with the first network node.48. The method of embodiment 47, wherein the indication of the configuration used by the user equipment for communication with the first network node comprises one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.49. The method of any one of embodiments 46 to 48, wherein the first response message comprises an identity of the second network node.50. The method of any one of embodiments 46 to 48, further comprising: transmitting, to the second network node, a second request message comprising a request for at least part of the LTM candidate cell configuration for the candidate cell served by the second network node; and receiving, from the second network node, a second response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.51. The method of embodiment 50, wherein the second request message comprises an indication of a configuration used by the user equipment for communication with the first network node.52. The method of embodiment 51, wherein the indication of the configuration used by the user equipment for communication with the first network node comprises one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; anindication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.53. The method of any one of embodiments 50 to 52, wherein the second response message comprises an identity of the second network node.54. The method of any one of embodiments 46 to 53, wherein the LTM candidate cell configuration comprises one or more of: information enabling the user equipment to derive a security key for communication with the second network node (e.g., Master Key Update); information relating to network slices in which the candidate cell is configured; information relating to one or more PLMNs within which the candidate cell is configured; an indication of a registration area, tracking area or RAN notification area in which the candidate cell is located; information about one or more core network nodes (e.g., AMFs) serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed PDU sessions for the user equipment; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the user equipment; information related to one or more QoS profiles for the user equipment; system information for the candidate cell; non-access stratum information for the user equipment; and information enabling the user equipment to access the candidate cell using a different radioaccess technology (e.g., different to a RAT used to communicate with the first network node).55. The method of any one of embodiments 46 to 54, further comprising receiving a first notification message from the first network node, comprising an indication that the user equipment has switched to the candidate cell served by the second network node, and transmitting, to the second network node, a second notification message comprising an indication that the user equipment has switched to the candidate cell.56. The method of embodiment 55, wherein the second notification message is sent to the second network node via one or more further third network nodes.57. The method of any one of embodiments 46 to 56, wherein the first network node and / or the second network node are radio access network nodes.58. The method of any one of embodiments 46 to 57, wherein the one or more third networknodes include at least one core network node.59. The method of embodiment 58, wherein the core network node manages mobility for a radio access network.60. The method of embodiment 59, wherein the core network node comprises an Access and Mobility Management Function (AMF) or a Mobility Management Entity (MME).Group D Embodiments61. A user equipment, compri sing : processing circuitry configured to cause the user equipment to perform any of the steps of any of the Group A embodiments above or the Group V embodiments below; and power supply circuitry configured to supply power to the processing circuitry.62. A network node, the network node comprising: processing circuitry configured to cause the network node to perform any of the steps of any of the Group B embodiments above or the Group W or X embodiments below; power supply circuitry configured to supply power to the processing circuitry.63. A user equipment (UE), the UE comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to cause the user equipment to perform any of the steps of any of the Group A embodiments above or the Group V embodiments below; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to theUE.64. A core network node, the network node comprising: processing circuitry configured to cause the core network node to perform any of the steps of any of the Group C embodiments above or the Group Y embodiments below; power supply circuitry configured to supply power to the processing circuitry.

[0226] The following groups of statements set out further embodiments of the disclosure.UE methodsVI. Method for a User Equipment, UE, to perform NG-based LTM, comprising receiving, from a network node, a reconfiguration message (e.g. RRCReconfiguration) including an LTM configuration containing at least one NG-based LTM candidate cell configuration, receiving, from a first network node, an LTM cell switch command indicating an NG-based LTM candidate cell configuration controlled by a second network node, executing an NG-based LTM cell switch procedure while applying the indicated NG-based LTM candidate cell configuration including security key change, and transmitting, to the second network node, uplink data or signalling, using the applied NG-based LTM candidate cell configuration, to indicate successful completion of the LTM cell switch procedure.V2. The method in VI wherein the UE receives a NAS container.• The method, wherein the UE updates its NAS security context.• The method, wherein the NAS container is included in the applied indicated NG-based LTM candidate cell configuration.V3. The method in VI wherein the UE performs one of• entering a new Tracking Area (TA) or RAN notification area (RNA)• selecting a new network slice• selecting a new PLMN• selecting a target RAT typeV4. The method in VI or V3, wherein the UE performs a registration procedure.V5. The method in VI, wherein the at least one NG-based LTM candidate cell configuration contains at least one of• Information for vertical or horizontal key derivation during handover or security key refresh, such as a Master Key Update parameter including a NAS Container (NASC).• Information about network slices• Information about PLMNs• Information about registration area, tracking area (e.g. TA identity) or a RAN notification area (e.g. RNA identity)• Information about a core network node• Information about accepted and / or failed PDU sessions• Information about accepted or failed radio bearers, DRBs, E-RABs or QoS flows• QoS flow mapping information• QoS profile information• Dedicated system information• Non-Access Stratum (NAS) information• Information to be used for accessing an NG-based LTM candidate cell using a different target radio access technology (RAT)V6. The method in VI wherein the uplink data or signaling is one of a random access procedure, a scheduling request, a MAC buffer status report (BSR), an RRCReconfigurationComplete message or uplink user data in RLC PDU(s).V7. The method in VI, wherein the reconfiguration message (e.g. RRCReconfiguration) including an LTM configuration containing at least one NG-based LTM candidate cell configuration is received by the UE within an RRC message which is used to command handover or LTM switches from NR to NR or to another RAT type.V8. The method in VI, wherein the UE determines that the LTM cell switch command indicates an NG-based LTM candidate cell according to explicit or implicit indication within the LTM configuration.Methods (first network node)W 1. Method for a first network node, such as a serving gNB or a serving CU, to handle NG- based LTM for a UE, comprising,• transmitting, to the UE, a reconfiguration message including an LTM configuration containing at least one NG-based LTM candidate cell configuration• transmitting, to the UE, an LTM cell switch command indicating a NG-based LTM candidate cell configuration controlled by a second network nodeWla. The method in Wl, wherein the reconfiguration message including an LTM configuration containing at least one NG-based LTM candidate cell configuration is deliveredto the UE within a RRC messages used to command handover or LTM cell switch from NR to NR (via NG) or to another RAT type.Configuration methods (first network node)W2. The method in W1 wherein the first network node transmits, to a third network node, such as an Access and Mobility management Function (AMF), a request message over NG interface to generate an LTM configuration including at least one NG-based LTM candidate cell configuration.• In one alternative the request message includes a list of one or more NG-based LTM candidate cells.• In another alternative the request message includes only one NG-based LTM candidate cell, and one or more messages are sent per cell basis.• In one example the request message can be Handover Required, or a new message, e.g., LTM Configuration Required or RAN-CN TRANSPARENT TRANSFER.W3. The method in W2 wherein the request to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes the current reference configuration for intra-CU LTM candidate configuration that is used by the UE.W3a. The method in W2 wherein the request to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes the current RRC configuration used by the UE.W3b. The method in W2 wherein the request to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes a list of supported UE capabilities. W3c. The method in W2 wherein the request to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes a list of current LTM candidate cell configurations configured at the UE.W4. The method in W2 wherein the first network node receives, from a third network node, a response message over NG including an LTM configuration containing at least one NG-based LTM candidate cell configuration.• In one alternative the response message includes one or more NG-based LTM candidate cell configurations.• In another alternative one or more response message are received, each one including only one NG-based LTM candidate cell.• In one example the response message can be Handover Command, or a new message, e.g., LTM Configuration Confirm.W4a. The method in W2, wherein the response message may also include an identification (e.g., global identifier) of a second network node.W4b. The method in W2 and / or W4b, wherein the first network node, upon the reception of an identifier of a second network node in the response message by the third network node, triggers an Xn setup procedure with the second network node.W5. The method in W1 wherein the reconfiguration message indicates setup, modification or release of an NG-based LTM candidate cell configuration.W6. The method in Wl, wherein the at least one NG-based LTM candidate cell configuration contains at least one of• Information for vertical or horizontal key derivation during handover or security key refresh, such as a Master Key Update parameter including a NAS Container (NASC).• Information about network slices• Information about PLMNs• Information about registration area, tracking area (e.g. TA identity) or a RAN notification area (e.g. RNA identity)• Information about a core network node• Information about accepted and / or failed PDU sessions• Information about accepted or failed radio bearers, DRBs, E-RABs or QoS flows• QoS flow mapping information• QoS profile information• Dedicated system information• Non-Access Stratum (NAS) information• Information to be used for accessing an NG-based LTM candidate cell using a different target radio access technology (RAT)• An indication of a reference configurationW7. The method in Wl wherein the first network node receives, from the UE, a response message confirming the UE has received the LTM configuration.Execution methods (first network node)W8. The method in Wl wherein the first network node transmits, to the second network node, a message indicating execution of an LTM cell switch procedure for a UE.W9. The method in W8 wherein the indication message is transmitted via a third network node over NG.W10. The method in W8 wherein the message indicating execution of an LTM cell switch procedure for a UE includes at least one of• an indication of the target cell (e.g. NR CGI)• an indication of the target gNB, such as a gNB ID• an indication of the target gNB-DU, such as a gNB-DU ID• a Source to Target transparent container• target TCI state(s)• security information, such as security key(s) to be used in the target cell• a RAT typeW1 1. The method in W1 wherein the first network node receives, from the second network node, a message indicating that the UE has successfully executed an LTM cell switch procedure W12. The method in W11 wherein the indication message is received via a third network node over NG.W13. The method in Wi l wherein the message indicating the UE has successfully executed an LTM cell switch procedure contains one of:• an indication of the target cell (such as an NR CGI)• a request to configure an NG-based LTM candidate cell in the source gNB• a request to release the UE contextMethods (second network node)XL Method for a second network node, such as a candidate gNB or a candidate CU, to handle NG-based LTM for a UE, comprising,• receiving, from a third network node over NG, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration• transmitting, to a third network node, a response message over NG including an LTM configuration containing at least one NG-based LTM candidate cell configuration.Configuration methods (second network node)X2. The method in XI wherein the request to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes at least one of:• a list of one or NG-based LTM candidate cell.• only one NG-based LTM candidate cell.• the current reference configuration for intra-CU LTM candidate configuration that is used by the UE.• the list of current LTM candidate cells configured at the UE• the current RRC configuration used at the UE• the list of supported UE capabilitiesX3. The method in XI, wherein the request message is a Handover Request, or a new message, e.g., LTM Configuration Request.X4. The method in XI, wherein the response message includes at least one of• one or more NG-based LTM candidate cell configurations.• only one NG-based LTM candidate cell configuration.X4a. The method in XI, wherein after transmitting the response message the second network node receives a request to establish an Xn interface with the first network node.X5. The method in XI, wherein the second network node transmits multiple response messages.X6. The method in XI, wherein the response message is a Handover Request Acknowledge, or a new message, e.g., LTM Configuration ResponseX7. The method in XI, wherein the at least one NG-based LTM candidate cell configuration contains at least one of:• Information for vertical or horizontal key derivation during handover or security key refresh, such as a Master Key Update parameter including a NAS Container (NASC).• Information about network slices• Information about PLMNs• Information about registration area, tracking area (e.g. TA identity) or a RAN notification area (e.g. RNA identity)• Information about a core network node• Information about accepted and / or failed PDU sessions• Information about accepted or failed radio bearers, DRBs, E-RABs or QoS flows• QoS flow mapping information• QoS profile information• Dedicated system information• Non-Access Stratum (NAS) information• Information to be used for accessing an NG-based LTM candidate cell using a different target radio access technology (RAT)Execution methods (second network node)X8. The method in XI wherein the second network node receives, from a first network node, a message indicating execution of an LTM cell switch procedure for a UEX9. The method in X8 wherein the indication message is received via a third network node over NG.XI 0. The method in X8 wherein the message indicating execution of an LTM cell switch procedure for a UE contains at least one of:• an indication of the target cell (e.g. NR CGI)• an indication of the target gNB, such as a gNB ID• an indication of the target gNB-DU, such as a gNB-DU ID• a Source to Target transparent container• target TCI state(s)• security information, such as security key(s) to be used in the target cell• a RAT typeXI 1. The method in XI wherein the second network node receives, from the UE, uplink data or signaling in a target cell controlled by a second network node.X12. The method in XI 1 wherein the uplink data or signaling is one of a random access procedure, a scheduling request, a MAC buffer status report (BSR), an RRCReconfigurationComplete message or uplink user data in RLC PDU(s).XI 3. The method in XI wherein the second network node transmits, to the first network node, a message indicating that the UE has successfully executed an LTM cell switch procedure.X14. The method in X13 wherein the indication message is transmitted via the third network node over NG.XI 5. The method in XI 3 wherein the message indicating the UE has successfully executed an LTM cell switch procedure contains one of:• an indication of the target cell (such as an NR CGI)• a request to configure an NG-based LTM candidate cell in the source gNB• a request to release the UE contextMethods (third network node)Y 1. Method for a third network node, such as an Access and Mobility management Function, AMF, to handle NG-based LTM for a UE, comprising,• receiving, from a first network node over NG, a request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration• transmitting, to a first network node, a response message over NG including an LTM configuration containing at least one NG-based LTM candidate cell configuration.Configuration methods (third network node)Y2. The method in Y1 wherein the third network node transmits, to a second network node, a request message over NG to generate an LTM configuration including at least one NG-based LTM candidate cell configuration and receives, from the second network node, a response message over NG including an LTM configuration containing at least one NG-based LTM candidate cell configuration.Y3. The methods in Y1 or Y2 wherein the request message to generate an LTM configuration including an NG-based LTM candidate cell configuration also includes the current reference configuration for intra-CU LTM candidate configuration that is used by the UE.Y4. The method in Yl, wherein the at least one NG-based LTM candidate cell configuration contains at least one of:• Information for vertical or horizontal key derivation during handover or security key refresh, such as a Master Key Update parameter including a NAS Container (NASC).• Information about network slices• Information about PLMNs• Information about registration area, tracking area (e.g. TA identity) or a RAN notification area (e.g. RNA identity)• Information about a core network node• Information about accepted and / or failed PDU sessions• Information about accepted or failed radio bearers, DRBs, E-RABs or QoS flows• QoS flow mapping information• QoS profile information• Dedicated system information• Non-Access Stratum (NAS) information• Information to be used for accessing an NG-based LTM candidate cell using a different target radio access technology (RAT)Y5. The method in Yl, wherein the request message to generate an LTM configuration including an NG-based LTM candidate cell configuration is a Handover Required message, or a new message, e.g., LTM Configuration Required or RAN-CN TRANSPARENT TRANSFER.Y6. The method in Yl, wherein the response message including an LTM configuration containing at least one NG-based LTM candidate cell configuration is a Handover Command message, or a new message, e.g., LTM Configuration Confirm or CN-RAN TRANSPARENT TRANSFER.Y6. The method in Y2, wherein the request message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration is a Handover Request message, or a new message, e.g., LTM Configuration Request or CN-RAN TRANSPARENT TRANSFER.Y7. The method in Y2, wherein the response message to generate an LTM configuration including at least one NG-based LTM candidate cell configuration is a Handover Request Acknowledge message, or a new message, e.g., LTM Configuration Response or RAN-CN TRANSPARENT TRANSFERExecution methods (third network node)Y8. The method in Yl wherein the third network node receives, from a first network node, a message over NG indicating execution of an LTM cell switch procedure for a UE, and transmits, to a second network node, a message indicating execution of an LTM cell switch procedure for a UE.Y9. The method in Yl wherein the third network node receives, from the second network node, an indication over NG that the UE has successfully executed an LTM cell switch procedure. Y10. The method in Yl wherein the third network node transmits, to the first network node, an indication over NG that the UE has successfully executed an LTM cell switch procedure.Yl 1. The method in Yl wherein the messages indicating execution of an LTM cell switch procedure for a UE contains at least one of:• an indication of the target cell (e.g. NR CGI)• an indication of the target gNB, such as a gNB ID• an indication of the target gNB-DU, such as a gNB-DU ID• a Source to Target transparent container• target TCI state(s)• security information, such as security key(s) to be used in the target cell• a RAT type Y12. The method in Y9 or Y10 wherein the message indicating that the UE has successfully executed an LTM cell switch procedure contains at least one of:• an indication of the target cell (such as an NR CGI)• a request to configure an NG-based LTM candidate cell in the source gNB• a request to release the UE context • the list of current LTM candidate cells configured at the UE• the current RRC configuration used at the UE• the list of supported UE capabilities

Claims

CLAIMS1. A method performed by a user equipment, UE, the method comprising: receiving (402) a Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiating (406) an LTM mobility procedure to the candidate cell using the LTM candidate cell configuration.

2. The method of claim 1, wherein the indication that the mobility procedure involves communicating with one or more third network nodes is implicit or explicit.

3. The method of claim 1 or 2, wherein the LTM candidate cell configuration comprises one or more of information enabling the UE to derive a security key for communication with the second network node; information relating to network slices in which the candidate cell is configured; information relating to one or more Public Land Mobile Networks, PLMNs, within which the candidate cell is configured; an indication of a registration area, tracking area or Radio Access Network, RAN, notification area in which the candidate cell is located; information about one or more core network nodes serving the candidate cell and / or a cell served by the first network node; information relating to one or more accepted and / or failed Protocol Data Unit, PDU, sessions for the UE; information about quality-of-service flow mapping; information relating to one or more accepted and / or failed radio bearers for the UE; information related to one or more Quality of Service, QoS, profiles for the UE; system information for the candidate cell; non-access stratum information for the UE; and information enabling the UE to access the candidate cell using a different radio-access technology.

4. The method of any preceding claim, wherein the triggering event comprises the UE receiving a cell switch message from the first network node.

5. The method of claim 4, wherein the cell switch message comprises an indication of the LTM candidate cell configuration.

6. The method of any preceding claim, wherein initiating the LTM mobility procedure to the candidate cell comprises determining a new security key for use in communicating with the second network node.

7. The method of any preceding claim, further comprising transmitting uplink data or signalling to the second network node to indicate that the LTM mobility procedure to the second network node is complete.

8. The method of claim 7, wherein transmitting uplink data or signalling comprises one or more of: a random-access procedure; transmitting a scheduling request; transmitting a buffer status report; transmitting an RRCReconfigurationComplete message; and transmitting uplink user data.

9. The method of any preceding claim, wherein the LTM candidate cell configuration is received in a reconfiguration message, and wherein the reconfiguration message comprises a plurality of LTM candidate cell configurations for a plurality of candidate cells or the reconfiguration message is received within a handover command.

10. A method performed by a first network node, the method comprising: transmitting (506), to a user equipment, UE, a Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

11. The method of claim 10, further comprising obtaining at least part of the LTM candidate cell configuration from a third network node.

12. The method of claim 11, wherein obtaining the at least part of the LTM candidate cell configuration from the third network node comprises transmitting (502), to the third network node, a request message comprising a request for at least part of the LTM candidate cell configuration and receiving (504), from the third network node, a response message comprising the at least part of the LTM candidate cell configuration.

13. The method of claim 12, wherein the request message comprises an indication of a configuration used by the user equipment UE for communication with the first network node.

14. The method of claim 13, wherein the indication of the configuration used by the UE for communication with the first network node comprises one of more of: a reference configuration for intra- Central Unit, CU, LTM candidate configuration; a Radio Resource Control, RRC, configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

15. The method of any one of claims 12 to 14, wherein the response message comprises an identity of the second network node.

16. The method of any one of claims 11 to 15, further comprising establishing a direct interface with the second network node.

17. The method of any one of claims 10 to 16, further comprising transmitting (508) a cell switch message to the UE, wherein the cell switch message optionally comprises an indication of the LTM candidate cell configuration.

18. A method performed by a second network node, the method comprising: receiving (602), from a third network node, a request message comprising a request for at least part of a Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell served by the second network node, for a user equipment, UE, served by a first network node; and transmitting (606), to the third network node, a response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

19. The method of claim 18, wherein the request message comprises an indication of a configuration used by the UE for communication with the first network node.

20. The method of claim 19, wherein the indication of the configuration used by the UE forcommunication with the first network node comprises one of more of a reference configuration for intra- Central Unit, CU, LTM candidate configuration; a Radio Resource Control, RRC, configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

21. The method of any one of claims 18 to 20, wherein the response message comprises an identity of the second network node.

22. The method of any one of claims 18 to 21, further comprising establishing a direct interface with the first network node.

23. The method of any one of claims 18 to 22, further comprising generating (604) the at least part of the LTM candidate cell configuration.

24. A method performed by a third network node, the method comprising: receiving (702), from a first network node, a first request message comprising a request for at least part of a Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a user equipment, UE, served by the first network node; and transmitting (708), to the first network node, a first response message comprising the at least part of the LTM candidate cell configuration for a candidate cell, wherein the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

25. The method of claim 24, wherein the first request message comprises an indication of a configuration used by the UE for communication with the first network node.

26. The method of claim 25, wherein the indication of the configuration used by the UE for communication with the first network node comprises one of more of a reference configuration for intra- Central Unit, CU, LTM candidate configuration; a Radio Resource Control, RRC, configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

27. The method of any one of claims 24 to 26, wherein the first response message comprises an identity of the second network node.

28. The method of any one of claims 24 to 26, further comprising: transmitting (704), to the second network node, a second request message comprising a request for at least part of the LTM candidate cell configuration for the candidate cell served by the second network node; and receiving (706), from the second network node, a second response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

29. The method of claim 28, wherein the second request message comprises an indication of a configuration used by the UE for communication with the first network node.

30. The method of claim 29, wherein the indication of the configuration used by the UE for communication with the first network node comprises one of more of: a reference configuration for intra-CU LTM candidate configuration; a RRC configuration; an indication of one or more UE capabilities; and an indication of one or more LTM candidate cell configurations configured at the UE.

31. The method of any one of claims 28 to 30, wherein the second response message comprises an identity of the second network node.

32. A user equipment, UE, comprising processing circuitry configured to cause the UE to: receive a Layer 1, LI / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes; and responsive to a triggering event, initiate an LTM mobility procedure to the candidate cell using the LTM candidate cell configuration.

33. The UE of claim 32, wherein the processing circuitry is further configured to cause the UE to perform the method of any of claims 2-9.

34. A first network node comprising processing circuitry configured to cause the first network node to: transmit, to a user equipment, UE, a Layer 1, LI / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell, the LTM candidate cell configuration comprising an indication that a mobility procedure from a first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

35. The first network node of claim 34, wherein the processing circuitry is further configured to cause the first network node to perform the method of any of claims 11-17.

36. A second network node comprising processing circuitry configured to cause the second network node to: receive, from a third network node, a request message comprising a request for at least part of a Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a candidate cell served by the second network node, for a user equipment, UE, served by a first network node; and transmit, to the third network node, a response message comprising the at least part of the LTM candidate cell configuration, wherein the at least part of the LTM candidate cell configuration comprises an indication that a mobility procedure from the first network node to the second network node serving the candidate cell involves communication with one or more third network nodes.

37. The second network node of claim 36 wherein the processing circuitry is further configured to cause the second network node to perform the method of any of claims 19-23.

38. A third network node comprising processing circuitry configured to cause the third network node to: receive, from a first network node, a first request message comprising a request for at least part of an Layer 1, Ll / Layer 2, L2, Triggered Mobility, LTM, candidate cell configuration for a user equipment, UE, served by the first network node; and transmit, to the first network node, a first response message comprising the at least part of the LTM candidate cell configuration for a candidate cell, wherein the LTMcandidate cell configuration comprises an indication that a mobility procedure from the first network node to a second network node serving the candidate cell involves communication with one or more third network nodes.

39. The third network node of claim 38, wherein the processing circuitry is further configured to cause the third network node to perform the method of any of claims 25-31.

40. A computer-readable medium comprising instructions that, when executed on at least one processor, cause the at least one processor to perform the method according to any of claims I to 31.

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