Inter-secondary node (SN) l1 / l2 triggered mobility (LTM) execution

Abstract

Embodiments include methods for a user equipment (UE) configured to perform an inter- secondary node (SN) layer-1 or layer-2 triggered inter-cell mobility (LTM) procedure in a radio access network (RAN). Such methods include receiving a medium access control (MAC) control element (CE) indicating that the UE should perform an inter-SN LTM procedure from a source secondary cell group (SCG) provided by a second RAN node to a target SCG provided by a third RAN node. The MAC CE is received from the second RAN node. Such methods include executing the inter-SN LTM procedure towards the target SCG and sending, to the third RAN node or to a first RAN node that provides the UE's master cell group (MCG), a first acknowledgement message indicating completion of the inter-SN LTM procedure. Other embodiments include complementary methods for the first, second, and third RAN nodes.

Description

[0001] INTER-SECONDARY NODE (SN) L1 / L2 TRIGGERED MOBILITY (LTM) EXECUTION

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks and more specifically to improving mobility of user equipment (UEs) across multiple cells in a wireless network, including execution of layer-1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) of a UE in dual connectivity (DC) between different secondary cells groups (SCGs) provided by different secondary nodes (SNs).

[0004] BACKGROUND

[0005] Currently the fifth generation (5G) of cellular systems is being standardized within the Third-Generation Partnership Project (3GPP). 5G is developed for maximum flexibility to support multiple and substantially different use cases. These include enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device-to-device (D2D), and several other use cases.

[0006] Figure 1 illustrates a high-level view of an exemplary 5G network architecture, consisting of a Next Generation Radio Access Network (NG-RAN, 199) and a 5G Core (5GC, 198). The NG-RAN can include one or more gNodeB’s (gNBs) connected to the 5GC via one or more NG interfaces, such as gNBs (100, 150) connected via respective interfaces (102, 152). More specifically, the gNBs can be connected to one or more Access and Mobility Management Functions (AMFs) in the 5GC via respective NG-C interfaces and to one or more User Plane Functions (UPFs) in 5GC via respective NG-U interfaces. The 5GC can include various other network functions (NFs), such as Session Management Function(s) (SMF).

[0007] Although not shown, in some deployments the 5GC can be replaced by an Evolved Packet Core (EPC), which conventionally has been used together with a fourth generation (4G) Long- Term Evolution (LTE) Evolved UMTS RAN (E-UTRAN). In such deployments, gNBs (e.g., 100, 150) can connect to one or more Mobility Management Entities (MMEs) in EPC 198 via respective Sl-C interfaces. Similarly, gNBs can connect to one or more Serving Gateways (SGWs) in EPC via respective NG-U interfaces.

[0008] In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a DL “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

[0009] NG RAN logical nodes (e.g., gNB 100) include a Central Unit (CU or gNB-CU, e.g., 110) and one or more Distributed Units (DU or gNB-DU, e.g., 120, 130), which are connected via respective Fl logical interfaces (e.g., 122 and 132). CUs are logical nodes that host higher-layer protocols and perform various gNB functions such controlling the operation of DUs. DUs are decentralized logical nodes that host lower layer protocols and can include, depending on the functional split option, various subsets of the gNB functions. Each DU can be connected to only a single CU. Each CU and DU can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., transceivers), and power supply circuitry.

[0010] LTE Rel-10 introduced support for channel bandwidths larger than 20 MHz, which continues into NR. To remain compatible with legacy UEs from earlier releases (e.g., Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the structure of a Rel-8 carrier. A Rel-10 UE can receive multiple CCs based on Carrier Aggregation (CA). The CCs can be considered “cells”, such that a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells). These are referred to collectively as a “cell group”. NR also supports CA starting in Rel-15.

[0011] LTE Rel-12 introduced dual connectivity (DC) whereby a UE is connected to two network nodes simultaneously, thereby improving connection robustness and / or capacity. In LTE DC, these two network nodes are referred to as “Master eNB” (MeNB) and “Secondary eNB” (SeNB), or more generally as master node (MN) and secondary node (SN). More specifically, a UE is configured with a Master Cell Group (MCG) provided by the MN and a Secondary Cell Group (SCG) provided by the SN. Each CG includes a primary cell (PCell) and optionally one or more secondary cells (SCells).

[0012] Several DC (or more generally, multi-connectivity) scenarios have been considered for NR. These include NR-DC that is similar to LTE DC except that both MN and SN (referred to as “gNBs”) use the NR interface to communicate with a UE. In addition, 5G includes various multi-RAT DC (MR-DC) scenarios in which a UE can be configured to utilize resources of two different nodes, one providing E-UTRA / LTE access and the other one providing NR access. One node acts as the MN (e.g., providing MCG) and the other as the SN (e.g., providing SCG), with the MN and SN being connected via a network interface and at least the MN being connected to a core network (e.g., EPC or 5GC).

[0013] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). In general, a RAN (e.g., NG-RAN) configures a UE to perform and report radio resource management (RRM) measurements to assist network-controlled mobility decisions, such as for handover from a serving cell to a neighbor cell. Seamless handovers ensure that the UE moves around in the coverage area of different cells without excessive interruption to data transmission. However, there will be scenarios when the network fails to handover the UE to the “correct” neighbor cell in time, which can cause the UE to declare radio link failure (RLF) or handover failure (HOF). This can occur before the UE sends a measurement report in a source cell, before the UE receives a handover command to a target cell, shortly after the UE executes a successful handover to the target cell, or upon a HOF to the target cell (e.g., upon expiry of timer T304, started when the UE starts synchronization with the target cell).

[0014] As specified in 3GPP document RP-213565, NR Rel-18 includes a Work Item on NR mobility enhancements, including in the technical area of L1 / L2 based inter-cell mobility, also referred to as L1 / L2 triggered mobility (LTM). When the UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, serving cell change is triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and PSCell (e.g., when dual connectivity is configured), as well as release / add SCells (e.g., when CA is configured).

[0015] Currently, all inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI, i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, a goal of Rel-18 L1 / L2 mobility enhancements is to facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties.

[0016] SUMMARY

[0017] According to 3GPP agreements, it is desirable to support LTM for a UE in NR-DC where MN and SN use the NR interface for the UE’s MCG and SCG, respectively. For example, it is desirable to support NR-DC LTM for changing the UE’s SCG (or PSCell) without involvement of the MN. In such case, the LTM configuration and execution of in the UE’s MCG is essentially independent from the LTM configuration and execution in the UE’s SCG, and vice versa. However, there can be various dependencies between the configuration of the new SCG and the configuration of the UE’s MCG, which can cause various problems, issues, and / or difficulties. Moreover, it is also unclear what operations a UE configured with an inter-SN LTM candidate cell configuration should take upon receiving an LTM cell switch command to the inter-SN LTM candidate cell, as well as what corresponding actions the RAN should take.

[0018] An object of embodiments of the present disclosure is to address these and related problems, issues, and / or difficulties, thereby facilitating UE LTM between cells in a RAN (e.g., NG-RAN). Some embodiments of the present disclosure include methods (e.g. , procedures) for a UE configured to perform an inter-SN LTM mobility procedure in a RAN.

[0019] These exemplary methods include receiving a lower layer signalling message (e.g., MAC CE) indicating that the UE should perform an inter-SN LTM procedure from a source SCG provided by a second RAN node to the target SCG provided by a third RAN node. The lower layer signalling message (e.g., MAC CE) is received from the second RAN node. These exemplary methods also include executing the inter-SN LTM procedure towards the target SCG and sending, to the third RAN or to a first RAN node that provides the UE’s MCG, a first acknowledgement message indicating completion of the inter-SN LTM procedure.

[0020] In some embodiments, the lower layer signaling message (e.g., MAC CE) includes one or more of the following information:

[0021] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0022] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0023] • an indication of a reference configuration to be used in the target SCG;

[0024] • an indication on whether the UE should perform random access in the target SCG;

[0025] • an indication of whether the UE should perform medium access control (MAC) reset in the target SCG;

[0026] • an indication of whether the UE should perform radio link control (RLC) re-establishment in the target SCG;

[0027] • an indication of whether the UE should perform packet data convergence protocol (PDCP) re-establishment or recovery in the target SCG;

[0028] • an indication of a timing advance (TA) value to be used in the target SCG;

[0029] • an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG;

[0030] • an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG;

[0031] • an identifier of a downlink (DL) BWP to be used in the target SCG;

[0032] • an indication of a state for a secondary cell (SCell) in the target SCG; and

[0033] • a grant of UL resources for the UE in the target SCG.

[0034] Also, executing the inter-SN LTM procedure towards the target SCN can include various operations, as described in more detail herein.

[0035] In some embodiments, these exemplary methods also include receiving, from the first RAN node or the second RAN node, an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by the third RAN node. One or more of the information in the lower layer signaling message (e.g., MAC CE) indicates or references corresponding parameters in the received one or more LTM configurations. In some of these embodiments, these exemplary methods can also include sending, to the first RAN node or the second RAN node, a layer- 1 measurement report related to one or more cells provided by the third RAN node, including at least one of the candidate cells that are part of the target SCG.

[0036] Other embodiments include methods (e.g., procedures) for a first RAN node configured to provide an MCG for a UE. In general, these exemplary methods are complementary to the exemplary methods for a UE summarized above and described in more detail herein.

[0037] These exemplary methods include determining to initiate an SN LTM procedure for the UE from an SCG provided by a second RAN node to a target SCG provided by a third RAN node. T These exemplary methods include, based on the determination to initiate, sending to the third RAN node a first request for an inter-SN LTM cell switch for the UE to the target SCG. These exemplary methods include receiving, from the third RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. These exemplary methods include receiving, from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

[0038] In some embodiments, determining to initiate the inter-SN LTM procedure for the UE includes receiving from the UE a layer- 1 measurement report related to one or more cells provided by the third RAN node. The determination to initiate is based on the layer- 1 measurement report. In some of these embodiments, these exemplary methods also include, based on the determination to initiate, sending to the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node, and receiving from the second RAN node a second response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. The first request is sent to the third RAN node based on the second response from the second RAN node.

[0039] In other embodiments, determining to initiate the inter-SN LTM procedure for the UE includes receiving from the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node. The determination to initiate is based on the second request. In some of these embodiments, the first request is sent to the third RAN node in response to receiving the second request from the second RAN node and these exemplary methods also include, based on the first response from the third RAN node, sending to the second RAN node a second response acknowledging the inter-SN LTM cell switch for the UE. In some embodiments, the first request sent to the third RAN node includes one or more of the following information:

[0040] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0041] • an indication of a reference configuration to be used in the target SCG;

[0042] • an indication of whether the UE should perform random access in the target SCG;

[0043] • an indication of whether the UE should perform MAC reset in the target SCG;

[0044] • an indication of whether the UE should perform RLC re-establishment in the target SCG;

[0045] • an indication of whether the UE should perform PDCP re-establishment or recovery in the target SCG;

[0046] • an indication of a TA value to be used in the target SCG;

[0047] • an indication of a beam or a TCI state to be used in the target SCG;

[0048] • an identifier of an UL BWP to be used in the target SCG;

[0049] • an identifier of a DL BWP to be used in the target SCG;

[0050] • an indication of a state for a SCell in the target SCG; and

[0051] • a grant of UL resources for the UE in the target SCG.

[0052] In some embodiments, these exemplary methods also include sending to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by the third RAN node.

[0053] Other embodiments include methods (e.g. , procedures) for a second RAN node configured to provide a source SCG for an inter-SN LTM mobility procedure by a UE. In general, these exemplary methods are complementary to the exemplary methods for a UE and a first RAN node, as summarized above and described in more detail herein.

[0054] These exemplary methods include the second RAN node performing first operations or second operations, in different embodiments. The first operations include the following:

[0055] • determining to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node;

[0056] • sending, to a first RAN node configured to provide an MCG for the UE, a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and

[0057] • receiving from the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE;

[0058] The second operations include the following: • receiving from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and

[0059] • sending to the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE.

[0060] These exemplary methods also include, after completion of the inter-SN LTM procedure by the UE, receiving from the first RAN node a third request to release or to deactivate the source SCG and / or other UE-associated resources in the second RAN node.

[0061] In some embodiments, determining to initiate the inter-SN LTM procedure for the UE includes receiving from the UE an layer- 1 measurement report related to one or more cells provided by the third RAN node. The determination to initiate is based on the layer- 1 measurement report.

[0062] In some embodiments, the first operations also include, based on the second response, sending to the UE a lower layer signalling message (e.g., MAC CE) indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node. For example, the lower layer signaling message (e.g., MAC CE) can have any of the content summarized above for UE embodiments.

[0063] In some variants of these embodiments, the first operations also include sending to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by a third RAN node. In some variants of these embodiments, the first operations also include, in response to sending the lower layer signaling message (e.g., MAC CE), sending to the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0064] Other embodiments include methods (e.g. , procedures) for a third RAN node configured to provide a target SCG for an inter-SN LTM mobility procedure by a UE. In general, these exemplary methods are complementary to the exemplary methods for a UE, a first RAN node, and a second RAN node, as summarized above and described in more detail herein.

[0065] These exemplary methods include receiving, from a first RAN node configured to provide an MCG for the UE, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node to the target SCG provided by the third RAN node. These exemplary methods include sending, to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. These exemplary methods include receiving, from the UE or the first RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE. In some embodiments, these exemplary methods also include receiving from the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0066] In some embodiments, the first request received from the first RAN node can have any of content summarized above for first RAN node embodiments. In some embodiments, the first response sent to the first RAN node includes one or more of the following information:

[0067] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0068] • an indication of a reference configuration to be used in the target SCG;

[0069] • an indication on whether the UE should perform random access in the target SCG;

[0070] • an indication on whether the UE should perform medium MAC reset in the target SCG;

[0071] • an indication on whether the UE should perform layer-2 reset in the target SCG;

[0072] • an indication of a TA value to be used in the target SCG;

[0073] • an indication of a beam or a transmission configuration indicator, TCI, state to be used in the target SCG;

[0074] • an identifier of an UL BWP to be used in the target SCG;

[0075] • an identifier of a DL BWP to be used in the target SCG;

[0076] • an indication of a state for an SCell, in the target SCG; and

[0077] • a grant of UL resources for the UE in the target SCG.

[0078] Other embodiments and variants of the various methods summarized above are described herein. Other embodiments include UEs and RAN nodes configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments also include non-transitory, computer-readable media storing computer-executable instructions that, when executed by processing circuitry, configure such UEs and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

[0079] These and other embodiments described herein can facilitate a UE to receive a configuration to be used for an inter-SN LTM cell switch. Also, embodiments can facilitate a fast setup of an SCG for the UE without necessarily releasing DC when an inter-SN LTM cell switch is performed. At a high level, embodiments can improve mobility in a RAN by making inter-SN LTM cell switch procedures faster and more reliable.

[0080] These and other objects, features, and advantages of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

[0081] BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 shows a high-level view of an exemplary 5G network architecture. Figure 2 shows an exemplary configuration of NR UP and CP protocol stacks.

[0083] Figure 3 shows a logical architecture for an NG-RAN node arranged in a split CU / DU architecture, such as illustrated in Figure 1.

[0084] Figure 4 shows a high-level illustration of DC in combination with CA.

[0085] Figures 5-6 show high-level views of exemplary network architectures that support multi - RAT DC (MR-DC) using EPC and 5GC, respectively.

[0086] Figures 7-8 show UP radio protocol architectures from a network perspective for EN-DC with EPC and MR-DC with 5GC, respectively.

[0087] Figure 9 shows a high-level comparison of control plane (CP) architectures in LTE DC, EN-DC, and NR-DC.

[0088] Figure 10 (which includes Figures 10A-B) shows a signaling diagram for an exemplary inter-SN LTM cell switch procedure by a UE, according to some embodiments of the present disclosure.

[0089] Figures 11-12 show signaling diagrams for other exemplary inter-SN LTM cell switch procedures by a UE, according to other embodiments of the present disclosure.

[0090] Figure 13 shows an exemplary method (e.g, procedure) for a UE, according to various embodiments of the present disclosure.

[0091] Figure 14 (which includes Figures 14A-B) shows an exemplary method (e g, procedure) for a first RAN node, according to various embodiments of the present disclosure.

[0092] Figure 15 shows an exemplary method (e.g. , procedure) for a second RAN node, according to various embodiments of the present disclosure.

[0093] Figure 16 shows an exemplary method (e.g. , procedure) for a second RAN node, according to various embodiments of the present disclosure.

[0094] Figure 17 shows a communication system according to various embodiments of the present disclosure.

[0095] Figure 18 shows a UE according to various embodiments of the present disclosure.

[0096] Figure 19 shows a network node according to various embodiments of the present disclosure.

[0097] Figure 20 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

[0098] DETAILED DESCRIPTION

[0099] Embodiments briefly summarized above will now be described more fully with reference to the accompanying drawings. These descriptions are provided by way of example to explain the subject matter to those skilled in the art and should not be construed as limiting the scope of the subject matter to only the embodiments described herein. More specifically, examples are provided below that illustrate the operation of various embodiments according to the advantages discussed above.

[0100] In general, all terms used herein are to be interpreted according to their ordinary meaning to a person of ordinary skill in the relevant technical field, unless a different meaning is expressly defined and / or implied from the context of use. All references to a / an / the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise or clearly implied from the context of use. The operations of any methods and / or procedures disclosed herein do not have to be performed in the exact order disclosed, unless an operation is explicitly described as following or preceding another operation and / or where it is implicit that an operation must follow or precede another operation. Any feature of any embodiment disclosed herein can apply to any other disclosed embodiment, as appropriate. Likewise, any advantage of any embodiment described herein can apply to any other disclosed embodiment, as appropriate.

[0101] Furthermore, the following terms are used throughout the description given below:

[0102] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g, gNB in a 3GPP 5G / NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g. CU and DU), a high-power or macro base station, a low-power base station (c.g. micro, pi co, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0103] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), aPDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0104] • Wireless Device: As used herein, a “wireless device” (or “WD” for short) is any type of device that is capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other wireless devices. Communicating wirelessly can involve transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information through air. Unless otherwise noted, the term “wireless device” is used interchangeably herein with the term “user equipment” (or “UE” for short), with both of these terms having a different meaning than the term “network node”.

[0105] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0106] • Network Node: As used herein, a “network node” is any node that is either part of the radio access network (e.g, a radio access node or equivalent term) or of the core network (e.g., a core network node discussed above) of a cellular communications network. Functionally, a network node is equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a wireless device and / or with other network nodes or equipment in the cellular communications network, to enable and / or provide wireless access to the wireless device, and / or to perform other functions (e.g., administration) in the cellular communications network.

[0107] • Node: As used herein, the term “node” (without prefix) can be any type of node that can in or with a wireless network (including RAN and / or core network), including a radio access node (or equivalent term), core network node, or wireless device. However, the term “node” may be limited to a particular type (e.g., radio access node, IAB node) based on its specific characteristics in any given context.

[0108] The above definitions are not meant to be exclusive. In other words, various ones of the above terms may be explained and / or described elsewhere in the present disclosure using the same or similar terminology. Nevertheless, to the extent that such other explanations and / or descriptions conflict with the above definitions, the above definitions should control.

[0109] Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system and can be applied to any communication system that may benefit from them.

[0110] Figure 2 shows an exemplary configuration of NR user plane (UP) and control plane (CP) protocol stacks between a UE (210), a gNB (220), and an AMF (230). Physical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Convergence Protocol (PDCP) layers between UE and gNB are common to UP and CP. PDCP provides ciphering / deciphering, integrity protection, sequence numbering, reordering, and duplicate detection for both CP and UP, as well as header compression and retransmission for UP data.

[0111] On the UP side, Internet protocol (IP) packets arrive to PDCP as service data units (SDUs), and PDCP creates protocol data units (PDUs) to deliver to RLC. The Service Data Adaptation Protocol (SDAP) layer handles quality-of-service (QoS) including mapping between QoS flows and Data Radio Bearers (DRBs) and marking QoS flow identifiers (QFI) in UL and DL packets. RLC transfers PDCP PDUs to MAC through logical channels (LCH). RLC provides error detection / correction, concatenation, segmentation / reassembly, sequence numbering, reordering of data transferred to / from the upper layers. MAC provides mapping between LCHs and PHY transport channels, LCH prioritization, multiplexing into or demultiplexing from transport blocks (TBs), hybrid ARQ (HARQ) error correction, and dynamic scheduling (in gNB). PHY provides transport channel services to MAC and manages transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0112] On the CP side, the non-access stratum (NAS) layer between UE and AMF handles UE / gNB authentication, mobility management, and security control. RRC sits below NAS in the UE but terminates in the gNB rather than the AMF. RRC controls communications between UE and gNB at the radio interface as well as the mobility of a UE between cells in the NG-RAN. RRC also broadcasts system information (SI) and performs establishment, configuration, maintenance, and release of DRBs and Signaling Radio Bearers (SRBs) and used by UEs. Additionally, RRC controls addition, modification, and release of carrier aggregation (CA) and dual-connectivity (DC) configurations for UEs, and performs various security functions such as key management.

[0113] After a UE is powered ON it will be in the RRC__IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC_CONNECTED state (e.g., where data transfer can occur). The UE returns to RRC ..IDLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB.

[0114] An NR UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. The UE must perform a random-access (RA) procedure to move from RRC IDLE to RRC CONNECTED state, where the cell serving the UE is known and an RRC context is established for the UE in the serving gNB, such that the UE and gNB can communicate. As part of (or in conjunction with) the RA procedure, the UE also transmits an RRCSetupRequest message to the serving gNB. NR RRC also includes an RRC INACTIVE state in which a UE is known (e.g., via UE context) by the serving gNB. RRC_INACTIVE has some properties similar to a “suspended” condition used in LTE.

[0115] In addition to providing coverage via “cells,” as in LTE, NR networks also provide coverage via “beams.” In general, a DL “beam” is a coverage area of a network-transmitted RS that may be measured or monitored by a UE. In NR, for example, such RS can include any of the following, alone or in combination: SS / PBCH block (SSB), CSI-RS, tertiary reference signals (or any other sync signal), positioning RS (PRS), DMRS, phase-tracking reference signals (PTRS), etc. In general, SSB is available to all UEs regardless of RRC state, while other RS (e.g., CSI-RS, DM-RS, PTRS) are associated with specific UEs that have a network connection, i.e., in RRC CONNECTED state.

[0116] Figure 3 shows a logical architecture for an NG-RAN node (e.g., gNB or ng-eNB) arranged in the split CU / DU architecture, such as gNB 100 in Figure 1. This logical architecture separates the CU into CP and UP functionality, called CU-C (or CU-CP) and CU-U (or CU-UP) respectively. Furthermore, each of the NG, Xn, and Fl interfaces is split into a CP interface (e.g., NG-C) and a UP interface (e.g., NG-U). Moreover, the CU-U and CU-C can communicate via an El interface. Each DU may be connected to only one CU-C, and each CU-U may be connected to only one CU- C. However, a single DU may be connected to multiple CU-Us under the control of the same CU- C, or a single CU-U may be connected to multiple DUs under the control of the same CU-C. Note that the terms “Central Entity” and “Distributed Entity” in Figure 3 refer to physical network nodes.

[0117] Figure 4 shows a high-level illustration of a UE (440) arranged in DC and CA in a RAN (460). In this illustration, each of the UE’s MN (410) and the SN (420) can be an eNB or a gNB, in accordance with the various DC scenarios mentioned above. The MN provides the UE’s MCG (411) consisting of a PCell and three SCells arranged in CA, while the SN provides the UE’s SCG (421) consisting of a PSCell and three SCells arranged in CA. Figure 4 also shows a third RAN node (430), which provides a cell (431) that is proximate to the cells of the MCG and / or the cells of the SCG. For example, the UE may communicate with the third RAN node via the cell (431) in case of failure in the MCG (or PCell), failure in the SCG (or PSCell), or in mobility procedures in which the third RAN node is a target node for the UE. In some cases, the cell (431) may be part of a cell group (not shown) that the third RAN node can provide to UEs. The MN, the SN, and the third RAN node can be connected via appropriate interfaces, such as described in more detail below.

[0118] As briefly mentioned above, several DC (or more generally, multi-connectivity) scenarios have been considered for NR. 3GPP TR 38.804 (vl4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply either NR, LTE, or both. The following terminology is used to describe these exemplary DC scenarios or configurations:

[0119] • DC: LTE DC (i.e., both MN and SN employ LTE, as discussed above);

[0120] • EN-DC: LTE-NR DC where MN (eNB) employs LTE and SN (gNB) employs NR, and both are connected to EPC. • NGEN-DC: LTE-NR dual connectivity where a UE is connected to one ng-eNB that acts as a MN and one gNB that acts as a SN. The ng-eNB is connected to the 5GC and the gNB is connected to the ng-eNB via the Xn interface.

[0121] • NE-DC: LTE-NR dual connectivity where a UE is connected to one gNB that acts as a MN and one ng-eNB that acts as a SN. The gNB is connected to 5GC and the ng-eNB is connected to the gNB via the Xn interface.

[0122] • NR-DC (or NR-NR DC): both MN and SN employ NR.

[0123] • MR-DC (multi-RAT DC): a generalization of the Intra-E-UTRA Dual Connectivity (DC) described in TS 36.300, where a multiple Rx / Tx UE may be configured to utilize resources provided by two different nodes connected vianon-ideal backhaul, one providing E-UTRA access and the other one providing NR access. One node acts as the MN and the other as the SN. The MN and SN are connected via a network interface and at least the MN is connected to the core network. EN-DC, NE-DC, and NGEN-DC are different example cases of MR-DC.

[0124] Figure 5 shows a high-level view of an exemplary network architecture that supports EN- DC, including an E-UTRAN (599) and an EPC (598). As shown in the figure, the E-UTRAN can include en-gNBs (e.g, 510a,b) and eNBs (e.g, 520a, b) that are interconnected with each other via respective X2 (or X2-U) interfaces. The eNBs can be similar to those shown in Figure 1, while the ng-eNBs can be similar to the gNBs shown in Figure 3 except that they connect to EPC via an Sl-U interface rather than to 5GC via an X2 interface. The eNBs also connect to EPC via an SI interface, similar to the arrangement shown in Figure 1. More specifically, the en-gNBs and eNBs connect to MMEs (e.g, 530a, b) and S-GWs (e.g., 540a,b) in EPC.

[0125] Each of the en-gNBs and eNBs can serve a geographic coverage area including one or more cells (e.g., 511a-b and 521a-b). Depending on the cell in which it is located, a UE (e.g., 505) can communicate with the en-gNB or eNB serving that cell via the NR or LTE radio interface, respectively. In addition, a UE can be in EN-DC connectivity with a PCell (e.g., 521a) served by an eNB (e.g., 520a) and a PSCell (e.g., 511a) served by an en-gNB (e.g., 510a).

[0126] Figure 6 shows a high-level view of an exemplary network architecture that supports MR- DC and NR-DC configurations based on 5GC. More specifically, Figure 6 shows an NG-RAN (699) and a 5GC (698). The NG-RAN can include gNBs (e.g, 610a, b,c) and ng-eNBs (e.g, 620) that are interconnected with each other via respective Xn interfaces. The gNBs and ng-eNBs are also connected via the NG interfaces to the 5GC, more specifically to the access and mobility management functions (AMFs, e.g, 630a, b) via respective NG-C interfaces and to the user plane functions (UPFs, e.g, 640a, b) via respective NG-U interfaces. Moreover, the AMFs can communicate with one or more session management functions (SMFs, e.g., 650a, b) and network exposure functions (NEFs, e.g., 660a, b).

[0127] Each of the gNBs can be similar to those shown in Figure 5, while each of the ng-eNBs can be similar to the eNBs shown in Figure 1 except that they connect to 5GC via an NG interface rather than to EPC via an SI interface. Each of the gNBs and ng-eNBs can serve a geographic coverage area including one or more cells (e.g., 61 la-c and 621). The gNBs and ng-eNBs can also use various directional beams to provide coverage in the respective cells. Depending on the cell in which it is located, a UE (605, 606) can communicate with the gNB or ng-eNB serving that cell via the NR or LTE radio interface, respectively. In addition, a UE (e.g., 606) can be in MR-DC with a PCell (e.g., 621) served by an ng-eNB (e.g., 620) and a PSCell (e.g., 611b) served by a gNB (e.g., 610b), or vice versa. Likewise, a UE (e.g., 605) can be in NR-DC with a PCell (e.g., 611a) served by a first gNB (e.g., 610a) and a PSCell (e.g., 611c) served by a gNB (e.g., 610c).

[0128] Figures 7-8 show UP radio protocol architectures from a network perspective for MR-DC with EPC (e.g., EN-DC) and with 5GC (e.g., NGEN-DC, NE-DC, and NR-DC), respectively. In the EN-DC arrangement shown in Figure 9, an MCG bearer terminated in MN has PDCP layer of the RAT used by the MN, while all other bearers have NR PDCP layer. All bearers have lower layers associated with the RAT of the node(s) in which they are terminated. In the arrangement shown in Figure 10, all bearers have NR PDCP layers and lower layers associated with the RAT of the node(s) in which they are terminated. From a network perspective, each MCG, SCG, or and split bearer can be terminated either in MN or in SN. For example, the X2 or Xn interface between the nodes will carry traffic for SCG or split bearers terminated in MN PDCP layer to lower layers in SN. Likewise, X2 or Xn will carry traffic for MCG or split bearers terminated in SN PDCP layer to lower layers in MN. One difference between the architectures in Figures 9-10 is that the various bearers for MR-DC with 5GC are associated with QoS flows that are terminated in the SDAP layer above PDCP.

[0129] Figures 7-8 also have some DC-specific variations. In EN-DC with EPC, the network can configure either E-UTRA PDCP or NR PDCP for MN terminated MCG data radio bearers (DRBs) while NR PDCP is always used for all other DRBs. In MR-DC with 5GC, NR PDCP is always used for all DRB types. In NGEN-DC, E-UTRA RLC / MAC is used in the MN while NR RLC / MAC is used in the SN. In NE-DC, NR RLC / MAC is used in the MN while E-UTRA RLC / MAC is used in the SN. In NR-DC, NR RLC / MAC is used in both MN and SN.

[0130] Figure 9 is a block diagram showing a high-level comparison of CP architectures in LTE DC, EN-DC, and NR-DC. One primary difference is that the SN has a separate NR RRC entity in EN-DC and NR-DC. This means that the SN can also control the UE, sometimes without the knowledge of the MN but often in coordination with the MN. In LTE-DC, the RRC decisions are always made by the MN (MN to UE). Even so, the LTE-DC SN still decides its own configuration because it is aware of its resources, capabilities etc. while the MN is not.

[0131] Another difference between LTE-DC and the others is the use of a split bearer for RRC. Split RRC messages are mainly used for creating diversity, and the sender can choose one of the links for scheduling the RRC messages, or it can duplicate the message over both links. In the DL, the path switching between the MCG or SCG legs (or duplication on both) is left to network implementation. On the other hand, for the UL, the network configures the UE to use the MCG, SCG, or both for RRC messages. The terms “leg”, “path” and “RLC bearer” are used interchangeably throughout this document.

[0132] When a UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Currently, a serving cell change is triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change PCell and / or PSCell (e.g., when dual connectivity is configured), as well as release / add SCells (e.g., when CA is configured).

[0133] A UE in RRC CONNECTED state can be configured to perform and report measurements of its serving cell(s) and neighbor cells to its serving RAN node. Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconflguration message with a reconflgurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by layer 3 (L3, i.e., RRC) and the messages exchanged are part of L3.

[0134] As specified in 3GPP document RP-213565, 3GPP Rel-18 includes a Work Item on NR mobility enhancements, including in the technical area of L1 / L2 based inter-cell mobility, also known as L1 / L2 triggered mobility (LTM). Conventionally, all inter-cell mobility operations are triggered by L3 RSRP measurements and involve complete layer 2 (L2) and layer 1 (LI, i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, a high-level goal of the Rel-18 L1 / L2 mobility enhancements is to facilitate serving cell change via L1 / L2 signaling to address these problems and / or difficulties. Some more specific goals include specifying the following:

[0135] • Configuration and maintenance for multiple candidate cells to allow fast application of configurations for candidate cells;

[0136] • Dynamic switch mechanism among candidate serving cells (including SpCell and SCell) for the potential applicable scenarios based on L1 / L2 signalling;

[0137] • LI enhancements for inter-cell beam management, including LI measurement and reporting, and beam indication;

[0138] • Timing Advance (TA) management; and • CU-DU interface signaling to support L1 / L2 mobility, if needed.

[0139] These Rel-18 L1 / L2 mobility enhancements also must consider the split CU / DU architecture shown in Figures 1 and 3-4, including for intra-DU and inter-DU / intra-CU cell changes. In the inter-DU / intra-CU scenario, the candidate cell for LTM is a cell served by a neighbor DU to the (serving or source) DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). Also, the Rel-18 L1 / L2 mobility enhancements should be applicable to standalone (i.e., no CA / DC), CA, and NR-DC with serving cell change within a cell group (e.g., MCG or SCG), as well as inter- / intra-frequency cell changes.

[0140] In LTM a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration”. This configuration may be an RRCReconflguration message or a portion thereof, such as one or more IEs / fields / parameters (e.g., CellGroupConflg IE). The UE performs measurements on these LTM candidate cells and transmits corresponding measurement reports to the RAN, which triggers the execution of a LTM cell switch procedure by the UE to one of the LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., MAC control element (CE)). Based on this commend, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this LTM candidate cell.

[0141] Since one of the goals of LTM is to reduce the interruption time for UE data transmissions, the UE needs to be ready to communicate with the target cell upon (or shortly after) receiving the L1 / L2 signaling for mobility execution from the source cell. For example, the UE must be able to transmit UL data or a scheduling request (SR) to the target cell and / or monitor a DL control channel (e.g., PDCCH) from the target cell. In other words, UE needs to know the cell that it is moving to so it can apply the corresponding configuration, including the correct timing alignment and / or transmission configuration indicator (TCI) state for the cell. Likewise, when the source DU transmits the L1 / L2 signaling for mobility execution, the target DU needs to be prepared for scheduling UL and DL transmissions for the UE in the target cell, and for receiving scheduling requests (SR) from the UE.

[0142] According to 3GPP agreements, it is desirable to support LTM for a UE in NR-DC where MN and SN use the NR interface for the UE’s MCG and SCG, respectively. For example, it is desirable to support NR-DC LTM for changing the UE’s SCG (or PSCell) without MN involvement. In such case, the LTM configuration and execution of in the UE’s MCG is essentially independent from the LTM configuration and execution in the UE’s SCG, and vice versa. However, there can be various dependencies between the configuration of the new SCG and the configuration of the UE’s MCG, which can cause various problems, issues, and / or difficulties. Moreover, it is also unclear what operations a UE configured with an inter-SN LTM candidate cell configuration should take upon receiving an LTM cell switch command to the inter- SN LTM candidate cell, as well as what corresponding actions the RAN should take.

[0143] Embodiments of the present disclosure address these and other problems, difficulties, and / or issues by providing flexible and efficient techniques for a UE to execute an inter-SN LTM cell switch procedure from a source SN to a target SN, upon receiving from the source SN an LTM cell switch command that includes an indication to apply an inter-SN LTM candidate cell configuration. In response to successful completion of the LTM cell switch, the UE transmits to the MN an acknowledgement message that includes an embedded acknowledgement message for the target SN.

[0144] In some embodiments, the inter-SN LTM candidate cell configuration includes both an SCG configuration and an MCG configuration, so that when the UE executes the LTM cell switch it generates a first RRCReconflgurationComplete message intended for the MN and a second RRCReconflgurationComplete message intended for the target SN.

[0145] As an alternative, the UE can receive the LTM cell switch command from the MN and transmit to the MN an acknowledgement message that includes an embedded acknowledgement message for the target SN.

[0146] Other embodiments include complementary methods for a first RAN node configured to provide an MCG for a UE (e.g., as an MN). The first RAN node can receive from a second RAN node (e.g., the UE’s source SN) a request to execute an inter-SN LTM cell switch procedure for the UE to a third RAN node (e.g., the UE’s target SN) and, after the requested procedure has been executed, transmit to the second and third RAN nodes an acknowledgement (or similar indication) that the intra-SN LTM cell switch procedure has been completed by UE.

[0147] Other embodiments include complementary methods for a second RAN node configured to provide an SCG for a UE (e.g., as a source SN). The second RAN node can receive from the UE a measurement report and, based on the measurement report, trigger (e.g., initiate) an inter- SN LTM cell switch procedure for the UE by sending an LTM cell switch command to the UE. The command includes an indication to apply an inter-SN LTM candidate cell configuration. In some embodiments, the inter-SN LTM candidate cell configuration includes both an SCG configuration and an MCG configuration, so that when the UE executes the LTM cell switch it generates a first RRCReconflgurationComplete message intended for the MN and a second RRCReconflgurationComplete message intended for the target SN.

[0148] Other embodiments include complementary methods for a third RAN node configured to provide an SCG for a UE (e.g., as a target SN). The third RAN node can receive from the first RAN node (e.g., UE’s MN) an indication of an inter-SN LTM cell switch procedure by the UE to an SCG provided by the third RAN node. The third RAN node can then transmit to the first RAN an acknowledgement (or similar indication) that the intra-SN LTM cell switch procedure has been completed by the UE

[0149] Embodiments can provide various benefits and / or advantages. For example, embodiments can facilitate a UE to receive a configuration to be used for an inter-SN LTM cell switch. Also, embodiments can facilitate a fast setup of an SCG for the UE without necessarily releasing DC when an inter-SN LTM cell switch is performed. At a high level, embodiments can improve mobility in a RAN by making inter-SN LTM cell switch procedures faster and more reliable.

[0150] In the present disclosure, the following terms may be used interchangeably: “L1 / L2 based inter-cell mobility”, “L1 / L2 mobility,” “LI -mobility,” “LI based mobility,” “Ll / L2-centric inter-cell mobility,” “L1 / L2 inter-cell mobility,” “inter-cell beam management,” “inter-DU L1 / L2 based inter-cell mobility”, and “L1 / L2 triggered mobility” (or LTM). These terms refer to a scenario in which a UE receives lower layer (i.e., below RRC, such as MAC or PHY) signaling from a network indicating for the UE to change of its serving cell (e.g., PCell) from a source cell to a target cell. The content of the lower layer signaling may be referred to as “LTM cell switch command”. Exemplary lower layer signaling includes LI DL control information (DCI) and L2 MAC control element (CE). Compared to conventional RRC signaling, lower layer signaling reduces processing time and interruption time during mobility and may also increase mobility robustness since the network can respond more quickly to changes in the UE’s channel conditions.

[0151] The change of serving cell (e.g., PCell) may also lead to a change in SCell(s) of 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). For example, an LTM cell switch may include a change in SpCell (e.g., PCell for MCG, PSCell for SCG) and a change (e.g., addition, modification and / or release) in SCells of the same cell group. This may happen when the command triggers the UE to change to another cell group configuration of the same type (e.g., another SCG configuration).

[0152] Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more “LTM candidate cell configurations” via an RRCReconflguration message. The terms “(LTM) candidate configuration”, “LTM configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0153] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconflguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”.

[0154] A UE may receive an LTM candidate cell configuration in complete form or as a delta (or difference) relative to a reference configuration (which may be signalled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0155] The lower layer signaling from the RAN may include an identifier (or index) associated with an LTM candidate cell configuration. The identifier may be sent together with an LTM cell switch command, indicating for the UE to perform an LTM cell switch to the associated LTM candidate cell.

[0156] The term “LTM configuration” refers to a data structure that is used for or related to UE LTM operations, and includes one or more of the following elements:

[0157] • One or more LTM candidate cell configurations, i.e., for respective LTM candidate cells;

[0158] • Measurement configuration for LTM, e.g., LI measurement and reporting configuration for LTM candidate cells;

[0159] • Configurations for DL pre-sync for LTM, e.g., for early TCI state activation;

[0160] • Configurations for UL pre-sync for LTM, e.g., for reception of PDCCH ordered preamble transmission and reception of TA;

[0161] • Configurations for execution of an LTM cell switch procedure according to a given LTM candidate cell configuration (e.g., whether to perform RA, RLC reestablishment, MAC reset, PDCP recovery, etc.).

[0162] The term “part of an LTM configuration” may refer to a subset of the elements in the above list, and / or a subset of items comprising any of the elements present (e.g., subset of configurations for DL pre-sync).

[0163] The phrase “LTM cell switch procedure” refers to the process of a UE switching (or changing) from a source cell to a target cell (i.e., an LTM candidate cell) using LTM. An LTM cell switch procedure may also be referred to as “L1 / L2 based inter-cell mobility execution”, “LTM execution”, “dynamic switch”, “LTM switch”, “(LTM) cell switch”, “(LTM) serving cell change”, or “(LTM) cell change”. Similarly, the phrase “switching to an LTM candidate cell configuration” means that the UE applies an LTM candidate cell configuration such that the associated LTM candidate cell becomes its new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, an LTM candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell.

[0164] Furthermore, an LTM cell switch procedure may involve a UE switching (or changing) from a source cell group to a target cell group using LTM. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and / or release of one or more SCells), and / or a swap between SpCell and SCell roles for two cells in the same cell group.

[0165] An “inter-SN LTM candidate cell configuration” (also referred to as “SCG LTM candidate cell configuration”) includes a configuration parameters the UE needs to operate in that LTM candidate cell when it performs inter-SN LTM cell switch procedure. For example, the UE may configure an SN / SCG according to a received inter-SN LTM candidate cell configuration and change a “state” of the SN / SCG to “activated” (or “deactivated”, as the case may be). An inter-SN LTM candidate cell configuration contains an SN / SCG configuration and optionally an MN / MCG configuration. In the optional case, during the inter-SN LTM cell switch procedure the UE may change both its SN / SCG configuration as well as its MN / MCG configuration. As a specific example, an inter-SN LTM candidate cell configuration may contain information used by the UE to perform security key change (e.g., secondary key or S-KgNB key refresh) during the execution of the inter-SN LTM cell switch procedure. An LTM cell switch command may indicate an inter-SN LTM candidate cell configuration.

[0166] Figure 10 (which includes Figures 10A-B) shows a signaling diagram for an exemplary inter-SN LTM cell switch procedure by a UE, according to some embodiments of the present disclosure. The signaling is between a UE (1010), a MN (1020) that provides an MCG for the UE, a source SN (1030) that provides a source SCG for the UE, and a target SN (1040) that provides a target SCG for the UE. In this procedure, the source SN decides to trigger LTM cell switch for the UE to a target SN and transmits lower layer signalling to the UE indicating the inter-SN LTM candidate target cell and possibly other information. Although operations shown in Figure 10 are given numerical labels, this is done to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0167] In operation 1, which can be considered a pre-requisite, the UE is in RRC_CONNECTED state with DC towards the MN that provides the UE’s MCG and the source SN that provides the UE’s SCG. In operation 2, the Source SN receives from the UE an LI measurement report message, such as a CSI report or similar measurement report. In operation 3, based on the message in operation 2, the source SN decides to trigger LTM cell switch for the UE’s SCG. In operation 4, the source SN transmits to the MN a request (or command) for an inter- SN LTM cell switch procedure for the UE’s SCG. The request may include the UE’s CSI report, an identity of a candidate target SN (i. e. , the target SN shown in the figure), a timing advance (TA) command containing a TA value to be used in a (candidate) target cell provided by the candidate target SN, and a TCI state to be used in the (candidate) target cell. For example, the request sent by the source SN can be an SN CHANGE REQUIRED message.

[0168] In operation 5, the MN transmits to the target SN a request (or command) for an inter- SN LTM cell switch procedure for the UE’s SCG. The request may include the UE’s CSI report, the identity of the target SN for the procedure, the TA command containing the TA value to be used in the (candidate) target cell provided by the (candidate) target SN, and the TCI state to be used in the (candidate) target cell. For example, the request sent by the MN can be an SN MODIFICATION REQUEST message.

[0169] In operation 6, the (candidate) target SN transmits a responsive message to the MN. For example, the responsive message can be an SN MODIFICATION REQUEST ACKNOWLEDGE message. In operation 7, the MN transmits a responsive message to the source SN. For example, the responsive message can be an SN CHANGE CONFIRM message.

[0170] In operation 8, the source SN transmits an LTM cell switch command to the UE to trigger the inter-SN LTM cell switch procedure for the UE. The LTM cell switch command may contain the identity of the target SN for the LTM cell switch, the TA command containing the TA value to be used in the target cell provided by the target SN, and the TCI state to be used in the target cell. In operations 9-10, the source SN sends to MN an indication of an LTM cell switch for the UE’s SCG and the MN forwards to this indication to the target SN. For example, this indication could be called SN LTM Cell Switch Indication or a similar name, and include the same information elements as the command sent in operation 8.

[0171] In operation 11, after completing the inter-SN LTM cell switch in accordance with the command in operation 8, the UE transmits to the MN an acknowledgement message, such as an RRCReconflgurationComplete message. In operation 12, the MN informs the target SN of the UE’s completion of the inter-SN LTM cell switch, e.g., by sending an SN RECONFIGURATION COMPLETE message. In operation 13, the target SN acknowledges to the MN the completion of the UE’s the inter-SN LTM cell switch. In operations 14-15, the MN sends an SN release request message to the source SN, based on which the source SN radio and CP resources associated with the UE’s context in the source SN and sends a responsive acknowledgement message to the MN.

[0172] Figure 11 shows a signaling diagram for another exemplary inter-SN LTM cell switch procedure by a UE, according to other embodiments of the present disclosure. The signaling is between a UE (1010), a MN (1020) that provides an MCG for the UE, a source SN (1030) that provides a source SCG for the UE, and a target SN (1040) that provides a target SCG for the UE. In this procedure, the MN triggers an LTM cell switch for the UE to a target SN. The source SN provides a new SCG configuration and the MN transmits lower layer signalling to the UE which results in that the UE operates with the target SN after the LTM cell switch. Although operations shown in Figure 11 are given numerical labels, this is done to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0173] In operation 1, which can be considered a pre-requisite, the UE is in RRC_CONNECTED state with DC towards the MN that provides the UE’s MCG and the source SN that provides the UE’s SCG. In operation 2, the Source SN receives from the UE an LI measurement report message, such as a CSI report or similar measurement report. In operation 3, the MN receives from the UE an LI measurement report message, such as a CSI report or similar measurement report.

[0174] In operations 4-5, the MN decides to trigger an inter-SN LTM cell switch procedure for the UE’s SCG and transmits to the target SN a request (or command) for an inter-SN LTM cell switch procedure for the UE’s SCG. In operation 6, the source SN sends the MN a responsive message (e.g., acknowledgement) that may include the UE’s CSI report from operation 2 and an identity of a candidate target SN for the procedure, i.e., the target SN shown.

[0175] In operation 7, the MN transmits to the target SN a request (or command) for an inter- SN LTM cell switch procedure for the UE’s SCG. The request may include the contents of the message received in operation 6. For example, the request sent by the MN can be an SN MODIFICATION REQUEST message. In operation 8, the (candidate) target SN transmits a responsive message to the MN. The responsive message may include the identity of the (candidate) target SN. For example, the responsive message can be an SN MODIFICATION REQUEST ACKNOWLEDGE message.

[0176] In operation 9, the MN selects an inter-SN LTM candidate cell configuration for the UE based on its own measurements and the indicated target candidate SN. The MN transmits to the UE lower layer signalling (e.g., MAC CE, DCI) to trigger the LTM cell switch procedure. This lower layer signalling may be referred to as an LTM cell switch command, and contains an indication of an inter-SN LTM candidate cell configuration and optionally other information such as a TA command containing a TA value to be used in the target cell provided by the target SN, a TCI state to be used in the target cell, etc.

[0177] In operation 10, the UE executes the LTM cell switch procedure according to the command from the MN, and applies the indicated inter-SN LTM candidate cell configuration resulting in a change of SN from the source SN to the target SN. If the UE has established DL synchronization with the target SN and has received (in the command or before the command) a TCI state indication for target cell provided by the SN, it may use that information in the target cell. I the UE has a valid TA for the target cell (from the command or before the command), it may use that information in the target cell. In some embodiments, the LTM cell switch command may indicate that the UE should continue to use a TCI state and / or a TA already used by the UE for the target cell and / or the target SN.

[0178] In operation 11, after completing the inter-SN LTM cell switch in accordance with the command, the UE transmits to the MN an acknowledgement message, such as an RRCReconfigurationComplete message. The acknowledge message may contain an embedded RRCReconfigurationComplete message intended for the target SN. Alternatively, the UE may transmit an acknowledgement message (e.g., RRCReconfigurationComplete') directly to the target SN rather than embedding it in the acknowledgement message to the MN.

[0179] In operation 12, the MN informs the target SN of the UE’s completion of the inter-SN LTM cell switch, e g., by sending an SN RECONFIGURATION COMPLETE message. If received from the UE, the MN may also forward the embedded RRCReconfigurationComplete message to the target SN. In operations 13-14, the MN sends an SN release request message to the source SN, based on which the source SN radio and CP resources associated with the UE’s context in the source SN.

[0180] In operation 13, the target SN acknowledges to the MN the completion of the UE’s the inter-SN LTM cell switch. In operations 14-15, the MN sends an SN release request message to the source SN, based on which the source SN radio and CP resources associated with the UE’s context in the source SN and sends a responsive acknowledgement message to the MN.

[0181] Figure 12 shows a signaling diagram for another exemplary inter-SN LTM cell switch procedure by a UE, according to some embodiments of the present disclosure. The signaling is between a UE (1010), a MN (1020) that provides an MCG for the UE, a source SN (1030) that provides a source SCG for the UE, and a target SN (1040) that provides a target SCG for the UE. In this procedure, the source SN initiates an LTM cell switch for the UE to a target SN. The MN transmits lower layer signalling to the UE indicating the inter-SN LTM candidate target cell and possibly other information. Although operations shown in Figure 12 are given numerical labels, this is done to facilitate explanation rather than to require or imply any specific operational order, unless expressly stated otherwise.

[0182] In operation 1, which can be considered a pre-requisite, the UE is in RRC_CONNECTED state with DC towards the MN that provides the UE’s MCG and the source SN that provides the UE’s SCG. In operation 2, the Source SN receives from the UE an LI measurement report message, such as a CSI report or similar measurement report. In operations 3-4, the source SN decides to trigger an inter-SN LTM cell switch procedure for the UE’s SCG and transmits to the MN a request (or command) for an inter-SN LTM cell switch procedure for the UE’s SCG. The request may include the UE’s CSI report, an identity of a candidate target SN (i.e., the target SN shown in the figure), a TA command containing a TA value to be used in a (candidate) target cell provided by the (candidate) target SN, and a TCI state to be used in the (candidate) target cell. For example, the request sent by the source SN can be an SN CHANGE REQUIRED message.

[0183] In operation 5, the MN transmits to the target SN a request (or command) for an inter- SN LTM cell switch procedure for the UE’s SCG. The request may include the UE’s CSI report, the identity of the target SN for the procedure, the TA command containing the TA value to be used in the (candidate) target cell provided by the (candidate) target SN, and the TCI state to be used in the (candidate) target cell. For example, the request sent by the MN can be an SN MODIFICATION REQUEST message.

[0184] In operation 6, the (candidate) target SN transmits a responsive message to the MN. The responsive message may include the identity of the (candidate) target SN, the TA command containing the TA value to be used in the (candidate) target cell provided by the (candidate) target SN, and the TCI state to be used in the (candidate) target cell. For example, the responsive message can be an SN MODIFICATION REQUEST ACKNOWLEDGE message.

[0185] In operation 7, the MN selects an inter-SN LTM candidate cell configuration for the UE based on the indicated target candidate SN. The MN transmits to the UE lower layer signalling (e.g., MAC CE, DCI) to trigger the LTM cell switch procedure. This lower layer signalling may be referred to as an LTM cell switch command, and contains an indication of an inter-SN LTM candidate cell configuration and optionally other information such as the TA command containing a TA value to be used in the target cell provided by the target SN, the TCI state to be used in the target cell, etc. In operation 8, the MN transmits an acknowledgement message to the source SN, such as an SN CHANGE CONFIRM message.

[0186] In operation 9, the UE executes the LTM cell switch procedure according to the command from the MN, and applies the indicated inter-SN LTM candidate cell configuration resulting in a change of SN from the source SN to the target SN. In operation 10, after completing the inter-SN LTM cell switch in accordance with the command, the UE transmits to the MN an acknowledgement message, such as an RRCReconfigurationComplete message. The acknowledge message may contain an embedded RRCReconfigurationComplete message intended for the target SN. Alternatively, the UE may transmit an acknowledgement message (e.g., RRCReconfigurationComplete') directly to the target SN rather than embedding it in the acknowledgement message to the MN. In operation 11, the MN informs the target SN of the UE’s completion of the inter-SN LTM cell switch, e.g., by sending an SN RECONFIGURATION COMPLETE message. If received from the UE, the MN may also forward the embedded RRCReconfigurationComplete message to the target SN. In operations 12-13, the MN sends an SN release request message to the source SN, based on which the source SN radio and CP resources associated with the UE’s context in the source SN.

[0187] In general, the messages exchanged among the MN, source SN, and target SN in the RAN can be via any appropriate inter-node interface (e.g., Xn) and based on any appropriate protocol (e.g., XnAP). Moreover, in such protocol, any of the messages may be existing protocol messages (augmented with new information as needed) or newly-defined messages specific to embodiments of the present disclosure.

[0188] Some of the techniques and / or procedures described herein can be embodied in 3GPP specifications. The following is some example text that can be added to 3GPP TS 38.423 (XnAP protocol specification) v!7.4.0, in accordance with embodiments of the present disclosure. Ellipses indicate less relevant text omitted for brevity.

[0189] *** Begin 3GPP 38.423 text ***

[0190] 8.3.x SN LTM Cell Switch Indication

[0191] 8.3.x.1 General

[0192] This procedure is used to indicate execution of an inter-SN L1 / L2 triggered mobility. The procedure uses UE-associated signalling.

[0193] 8.3.X.2 Successful Operation - M-NG-RAN node initiated

[0194] The M-NG-RAN node initiates the procedure by sending the SN LTM CELL SWITCH INDICATION message to the Target S-NG-RAN node.

[0195] 8.3.x.3 Successful Operation - S-NG-RAN node initiated

[0196] The Source S-NG-RAN node initiates the procedure by sending the SN LTM CELL SWITCH INDICATION message to the M-NG-RAN node.

[0197] 9.1 2.x SN LTM CELL SWITCH INDICATION

[0198] This message is sent to indicate execution of L1 / L2 triggered mobility.

[0199] Direction: S-NG-RAN node M-NG-RAN node and M-NG-RAN node S-NG-RAN node.

[0200] *** End 3GPP 38.423 text ***

[0201] The embodiments described above can be further illustrated with reference to Figures 13- 16, which depict exemplary methods (e.g. , procedures) for a UE, a first RAN node, a second RAN node, and a third RAN node, respectively. Put differently, various features of the operations described below correspond to various embodiments described above. Even so, the description of Figures 13-16 may refer to other embodiments not explicitly described above.

[0202] The exemplary methods shown in Figures 13-16 can be used cooperatively to provide benefits, advantages, and / or solutions to problems described herein. Although Figures 13-16 illustrate the exemplary methods by specific blocks in particular orders, the operations corresponding to the blocks can be performed in different orders than shown and can be combined and / or divided into blocks and / or operations having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0203] In the descriptions of Figures 13-16, the adjectives “first,” “second,” and “third” are generally not used in an ordinal sense. Rather, they are used in a nominal sense for consistent labelling of terms used in the descriptions of Figures 13-16 and in the claims. For example, a “second request” denotes a different “request” than a “first request” but does not require the existence of a “first request” that precedes the “second request.”

[0204] In more detail, Figure 13 illustrates an exemplary method (e.g., procedure) for a UE configured to perform an inter-SN LTM mobility procedure in a RAN, according to various embodiments of the present disclosure. The exemplary method shown in Figure 13 can be performed by a UE (e.g., wireless device) such as described elsewhere herein.

[0205] The exemplary method includes the operations of block 1320, where the UE receives a lower layer signalling message (e.g., MAC CE) indicating that the UE should perform an inter- SN LTM procedure from a source secondary cell group (SCG) provided by a second RAN node to the target SCG provided by a third RAN node. The lower layer signalling message (e.g., MAC CE) is received from the second RAN node. The exemplary method also includes the operations of blocks 1330-1340, where the UE executes the inter-SN LTM procedure towards the target SCG and sends, to the third RAN or to a first RAN node that provides the UE’s master cell group (MCG), a first acknowledgement message indicating completion of the inter-SN LTM procedure.

[0206] In some embodiments, the first acknowledgement message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure. In some of these embodiments, the first acknowledgement message is sent to the first RAN node and the second acknowledgement message is intended for the third RAN node. Figures 10-12 show examples of these embodiments. In other of these embodiments, the first acknowledgement message is sent to the third RAN node and the second acknowledgement message is intended for the first RAN node.

[0207] In some of these embodiments, the first and second acknowledgement messages are, or include, respective RRCReconflgurationComplete messages.

[0208] In other embodiments, the first acknowledgement message is sent to the first RAN node and the exemplary method also includes the operations of block 1350, where the UE sends to the third RAN node a second acknowledgement message indicating completion of the inter-SN LTM procedure.

[0209] In some embodiments, executing the inter-SN LTM procedure towards the target SCG in block 1330 includes one or more of the following operations, labelled with corresponding sub-block numbers:

[0210] • (1331) performing refresh of one or more security keys used for communication with the UE’s SCG;

[0211] • (1332) deriving or updating one or more security keys used for communication with the UE’s SCG;

[0212] • (1333) performing radio link control (RLC) re-establishment for one or more SCG RLC bearers;

[0213] • (1334) performing packet data convergence protocol (PDCP) re-establishment for one or more of the UE’s SN-terminated radio bearers;

[0214] • (1335) performing a medium access control (MAC) reset for the UE’s SCG; and

[0215] • (1336) performing a random access procedure in a cell of the target SCG;

[0216] In some embodiments, the lower layer signaling message (e.g., MAC CE) in block 1320 includes one or more of the following information:

[0217] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0218] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0219] • an indication of a reference configuration to be used in the target SCG;

[0220] • an indication on whether the UE should perform random access in the target SCG; • an indication of whether the UE should perform medium access control (MAC) reset in the target SCG;

[0221] • an indication of whether the UE should perform radio link control (RLC) re-establishment in the target SCG;

[0222] • an indication of whether the UE should perform packet data convergence protocol (PDCP) re-establishment or recovery in the target SCG;

[0223] • an indication of a timing advance (TA) value to be used in the target SCG;

[0224] • an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG;

[0225] • an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG;

[0226] • an identifier of a downlink (DL) BWP to be used in the target SCG;

[0227] • an indication of a state for a secondary cell (SCell) in the target SCG; and

[0228] • a grant of UL resources for the UE in the target SCG.

[0229] In some of these embodiments, the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG. In some of these embodiments, the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE. In some of these embodiments, one or more of the information in the lower layer signaling message indicates or references corresponding parameters in the received one or more LTM configurations.

[0230] In some embodiments, the exemplary method also includes the operations of block 1310, where the UE receives, from the first RAN node or the second RAN node, an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by the third RAN node. One or more of the information in the lower layer signaling message (e.g., MAC CE) indicates or references corresponding parameters in the received one or more LTM configurations. In some of these embodiments, the exemplary method also includes the operations of block 1315, where the UE sends, to the first RAN node or the second RAN node, an LI measurement report related to one or more cells provided by the third RAN node, including at least one of the candidate cells that are part of the target SCG.

[0231] In addition, Figure 14 (which includes Figures 14A-B) illustrates an exemplary method (e.g., procedure) for a first RAN node configured to provide an MCG for a UE, according to various embodiments of the present disclosure. The exemplary method shown in Figure 14 can be performed by a RAN node (e.g., base station, gNB, etc.) or unit(s) thereof (e.g., CU and / or DU) such as described elsewhere herein.

[0232] The exemplary method includes the operations of block 1420, where the first RAN node determines to initiate an SN LTM procedure for the UE from an SCG provided by a second RAN node to a target SCG provided by a third RAN node. The exemplary method also includes the operations of block 1440, where based on the determination to initiate, the first RAN node sends to the third RAN node a first request for an inter-SN LTM cell switch for the UE to the target SCG. The exemplary method also includes the operations of block 1450, where the first RAN node receives, from the third RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. The exemplary method also includes the operations of block 1470, where the first RAN node receives, from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

[0233] For example, the first request sent in block 1440 can be an SN MODIFICATION REQUEST message and the first response received in block 1450 can be an SN MODIFICATION REQUEST ACKNOWLEDGE message.

[0234] In some embodiments, the acknowledgement message is a first acknowledgement message received from the UE. The first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure, and the exemplary method also includes the operations of block 1475, where the first RAN node sends the second acknowledgement message to the third RAN node. Figures 10-12 show examples of these embodiments. In other embodiments, the acknowledgement message is a second acknowledgement message generated by the UE and received from the third RAN node.

[0235] In some of these different embodiments, the first and second acknowledgement messages are, or include, respective RRCReconflgurationComplete messages. For example, the second acknowledgement message sent or received by the first RAN node can be an SN RECONFIGURATION COMPLETE message including an RRCReconflgurationComplete message generated by UE.

[0236] In some embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0237] • (1480) in response to the first acknowledgement message, sending to the second RAN node a third request to release or to deactivate the source SCG and / or other UE- associated resources in the second RAN node; and

[0238] • (1490) receiving from the second RAN node a third response acknowledging the third request. Figure 10B operations 14-15, Figure 11 operations 13-14, and Figure 12 operations 12-13 show examples of these embodiments. For example, the third request can be an SN release request message and third response can be an SN release request acknowledgement message.

[0239] In some embodiments, the exemplary method also includes the operations of block 1460, where the first RAN node sends to the UE a lower layer signalling message (e.g., MAC CE) indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node. In such case, the first acknowledgement message is received from the UE (e.g., in block 1470).

[0240] In some of these embodiments, the lower layer signaling message (e.g., in block 1460) includes one or more of the following information:

[0241] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0242] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0243] • an indication of a reference configuration to be used in the target SCG;

[0244] • an indication of whether the UE should perform random access in the target SCG;

[0245] • an indication of whether the UE should perform MAC reset in the target SCG;

[0246] • an indication of whether the UE should perform RLC re-establishment in the target SCG;

[0247] • an indication of whether the UE should perform PDCP re-establishment or recovery in the target SCG;

[0248] • an indication of a TA value to be used in the target SCG;

[0249] • an indication of a beam or a TCI state to be used in the target SCG;

[0250] • an identifier of an UL BWP to be used in the target SCG;

[0251] • an identifier of a DL BWP to be used in the target SCG;

[0252] • an indication of a state for a SCell in the target SCG; and

[0253] • a grant of UL resources for the UE in the target SCG.

[0254] In some variants of these embodiments, the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG. In some variants of these embodiments, the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE. In some of these embodiments, one or more of the information in the lower layer signaling message (e.g., MAC CE) indicates or references corresponding parameters in the received one or more LTM configurations. In some embodiments, the exemplary method also includes the operations of block 1410, where the first RAN node sends to the message that includes one of the target SCG provided by the third RAN node. For example, in embodiments where the lower layer signaling message (e.g., MAC CE) is sent to the UE in block 1460, one or more of the information in the lower layer signaling message (e.g., MAC CE) may indicate or reference corresponding parameters in the one or more LTM configurations.

[0255] In some embodiments, the first request sent to the third RAN node (e.g., in block 1440) includes one or more of the following information:

[0256] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0257] • an indication of a reference configuration to be used in the target SCG;

[0258] • an indication of whether the UE should perform random access in the target SCG;

[0259] • an indication of whether the UE should perform MAC reset in the target SCG;

[0260] • an indication of whether the UE should perform RLC re-establishment in the target SCG;

[0261] • an indication of whether the UE should perform PDCP re-establishment or recovery in the target SCG;

[0262] • an indication of a TA value to be used in the target SCG;

[0263] • an indication of a beam or a TCI state to be used in the target SCG;

[0264] • an identifier of an UL BWP to be used in the target SCG;

[0265] • an identifier of a DL BWP to be used in the target SCG;

[0266] • an indication of a state for a SCell in the target SCG; and

[0267] • a grant of UL resources for the UE in the target SCG.

[0268] In some embodiments, determining to initiate the inter-SN LTM procedure for the UE in block 1420 includes the operations of sub-block 1421, where the first RAN node receives from the UE an LI measurement report related to one or more cells provided by the third RAN node. The determination to initiate is based on the LI measurement report. Figure 11 shows an example of these embodiments.

[0269] In some of these embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0270] • (1425) based on the determination to initiate, sending to the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and

[0271] • (1430) receiving, from the second RAN node, a second response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. In such case, the first request is sent to the third RAN node based on the second response from the second RAN node.

[0272] In other embodiments, determining to initiate the inter-SN LTM procedure for the UE in block 1420 includes the operations of block 1422, where the first RAN node receives from the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node. The determination to initiate is based on the request. Figures 10 and 12 show examples of these embodiments.

[0273] In some of these embodiments, the first request is sent to the third RAN node in response to receiving the second request from the second RAN node, and the exemplary method also includes the operations of block 1455, where based on the first response from the third RAN node, the first RAN node sends to the second RAN node a second response acknowledging the inter-SN LTM cell switch for the UE. Figure 10 operation 7 is an example of these embodiments.

[0274] In some of these embodiments, the exemplary method also includes the operations of block 1435, where the first RAN node receives from the second RAN node an indication that the inter- SN LTM cell switch has been initiated for the UE. Figure 10 operation 9 is an example of these embodiments. For example, the indication in block 1435 can be an SN LTM CELL SWITCH INDICATION message, such as defined above. In some variants of these embodiments, the first RAN node can forward to the third RAN node the indication received from the second RAN node, e g., in another SN LTM CELL SWITCH INDICATION message.

[0275] In some embodiments, the first request sent to the third RAN node (e.g., in block 1440) includes one or more of the following:

[0276] • measurements by the UE on one or more cells provided by the third RAN node;

[0277] • an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE;

[0278] • identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE;

[0279] • an indication of one or more suggested beams or TCI states for the UE in the target SCG;

[0280] • a configuration for the UE’s MCG provided by the first RAN node;

[0281] • a configuration for the UE’s SCG provided by the second RAN node; and

[0282] • an indication of a suggested TA value for the UE in the target SCG.

[0283] In addition, Figure 15 illustrates an exemplary method (e.g., procedure) for a second RAN node configured to provide a source SCG for an inter-SN LTM mobility procedure by a UE, according to various embodiments of the present disclosure. The exemplary method shown in Figure 15 can be performed by a RAN node (e.g., base station, gNB, etc.) or unit(s) thereof (e.g., CU and / or DU) such as described elsewhere herein.

[0284] The exemplary method includes the UE performing first operations or second operations, in different embodiments. The first operations include the following, labelled with corresponding block numbers:

[0285] • (1520) determining to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node;

[0286] • (1530) sending to the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and

[0287] • (1540) receiving from the first RAN node a second response acknowledging the inter- SN LTM cell switch for the UE;

[0288] The second operations include the following, labelled with corresponding block numbers:

[0289] • (1560) receiving from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and

[0290] • (1570) sending to the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE.

[0291] Figures 10 and 12 show examples of the first operations while Figure 11 shows an example of the second operations. The exemplary method also includes the operations of block 1580, where after completion of the inter-SN LTM procedure by the UE, the second RAN node receives from the first RAN node a third request to release or to deactivate the source SCG and / or other UE- associated resources in the second RAN node.

[0292] In some embodiments, determining to initiate the inter-SN LTM procedure for the UE in block 1520 includes the operations of sub-block 1521, where the second RAN node receives from the UE an LI measurement report related to one or more cells provided by the third RAN node. The determination to initiate is based on the LI measurement report.

[0293] In some embodiments, the second request sent to the first RAN node (e.g., in block 1530) or received from the first RAN node (e.g., in block 1560) includes one or more of the following:

[0294] • measurements by the UE of the one or more candidate cells provided by the third RAN node;

[0295] • an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE;

[0296] • identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE; • a UE measurement configuration for the one or more candidate cells;

[0297] • an indication of one or more suggested beams or TCI states for the UE in a target SCG that includes the one or more candidate cells provided by the third RAN node;

[0298] • a configuration for the UE’s SCG provided by the second RAN node; and

[0299] • an indication of a suggested TA value for the UE in the target SCG.

[0300] In some embodiments, the first operations also include the operations of block 1550, where based on the second response (e.g., in block 1540), the second RAN node sends to the UE a lower layer signalling message (e.g., MAC CE) indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node.

[0301] In some of these embodiments, the lower layer signaling message (e.g., MAC CE) in block 1550 includes one or more of the following information:

[0302] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0303] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0304] • an indication of a reference configuration to be used in the target SCG;

[0305] • an indication on whether the UE should perform random access in the target SCG;

[0306] • an indication of whether the UE should perform MAC reset in the target SCG;

[0307] • an indication of whether the UE should perform RLC re-establishment in the target SCG;

[0308] • an indication of whether the UE should perform PDCP re-establishment or recovery in the target SCG;

[0309] • an indication of a TA value to be used in the target SCG;

[0310] • an indication of a beam or a TCI state to be used in the target SCG;

[0311] • an identifier of an UL BWP to be used in the target SCG;

[0312] • an identifier of a DL BWP to be used in the target SCG;

[0313] • an indication of a state for a SCell in the target SCG; and

[0314] • a grant of UL resources for the UE in the target SCG.

[0315] In some variants of these embodiments, the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG. In some variants of these embodiments, the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE. In some variants of these embodiments, the first operations also include the operations of block 1510, where the second RAN node sends to the UE a reconfiguration message (e.g., an RRCReconflguration message) that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by a third RAN node. In such case, one or more of the information in the lower layer signaling message (e.g., MAC CE) in block 1550 indicates or references corresponding parameters in the one or more LTM configurations.

[0316] In some variants of these embodiments, the second request sent to the first RAN node includes one or more of the information in the lower layer signaling message (e.g., MAC CE) sent to the UE. In some variants of these embodiments, the first operations also include, in response to sending the lower layer signaling message (e.g., MAC CE), sending to the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0317] In some embodiments, the exemplary method also includes the operations of block 1590, where the second RAN node sends to the first RAN node a third response acknowledging the third request. For example, the third request can be an SN release request message and third response can be an SN release request acknowledgement message.

[0318] In addition, Figure 16 illustrates an exemplary method e.g., procedure) for a third RAN node configured to provide a target SCG for an inter-SN LTM mobility procedure by a UE, according to various embodiments of the present disclosure. The exemplary method shown in Figure 16 can be performed by a RAN node (e.g., base station, gNB, etc.) or unit(s) thereof (e.g., CU and / or DU) such as described elsewhere herein.

[0319] The exemplary method includes the operations of block 1610, where the third RAN node receives, from a first RAN node configured to provide an MCG for the UE, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node to the target SCG provided by the third RAN node. The exemplary method also includes the operations of block 1620, where the third RAN node sends, to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG. The exemplary method also includes the operations of block 1620, where the third RAN node can receive, from the UE or the first RAN node, an acknowledgement message indicating completion of the inter- SN LTM procedure for the UE.

[0320] In some embodiments, the acknowledgement message is a first acknowledgement message received from the UE. Also, the first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure. In addition, the exemplary method also includes the operations of block 1640, where the third RAN node sends the second acknowledgement message to the first RAN node. In other embodiments, the acknowledgement message is a second acknowledgement message generated by the UE and received from the first RAN node. Figures 10-12 show examples of these embodiments.

[0321] In various embodiments, the first and second acknowledgement messages are, or include, XQS^QcX QRRCReconflgurationComplete messages. For example, the second acknowledgement message sent or received by the third RAN node can be an SN RECONFIGURATION COMPLETE message including an RRCReconfigurationComplete message generated by UE.

[0322] In some embodiments, the first request received from the first RAN node in block 1610 includes one or more of the following information:

[0323] • measurements by the UE on one or more cells provided by the third RAN node;

[0324] • an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE;

[0325] • identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE;

[0326] • an indication of one or more suggested beams or TCI states for the UE in the target SCG;

[0327] • a configuration for the UE’s MCG provided by the first RAN node;

[0328] • a configuration for the UE’s SCG provided by the second RAN node; and

[0329] • an indication of a suggested TA value for the UE in the target SCG.

[0330] In some embodiments, the first response sent to the first RAN node in block 1620 includes one or more of the following information:

[0331] • an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure;

[0332] • an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG;

[0333] • an indication of a reference configuration to be used in the target SCG;

[0334] • an indication on whether the UE should perform random access in the target SCG;

[0335] • an indication of whether the UE should perform MAC reset in the target SCG;

[0336] • an indication of whether the UE should perform RLC re-establishment in the target SCG;

[0337] • an indication of whether the UE should perform PDCP re-establishment or recovery in the target SCG;

[0338] • an indication of a TA value to be used in the target SCG;

[0339] • an indication of a beam or a TCI state to be used in the target SCG;

[0340] • an identifier of an UL BWP to be used in the target SCG;

[0341] • an identifier of a DL BWP to be used in the target SCG;

[0342] • an indication of a state for an SCell in the target SCG; and • a grant of UL resources for the UE in the target SCG.

[0343] In some of these embodiments, the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG. In some of these embodiments, the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE.

[0344] In some of these embodiments, the exemplary method also includes the operations of block 1625, where the third RAN node receives from the first RAN node an indication that the inter- SN LTM cell switch has been initiated for the UE. Figure 10 operation 10 is an example of these embodiments. For example, the indication in block 1625 can be an SN LTM CELL SWITCH INDICATION message, such as defined above.

[0345] Although various embodiments are described above in terms of methods, techniques, and / or procedures, the person of ordinary skill will readily comprehend that such methods, techniques, and / or procedures can be embodied by various combinations of hardware and software in various systems, communication devices, computing devices, control devices, apparatuses, non-transitory computer-readable media, computer program products, etc.

[0346] Figure 17 shows an example of a communication system 1700 in accordance with some embodiments. In this example, communication system 1700 includes a telecommunication network 1702 that includes an access network 1704 (e.g., RAN) and a core network 1706, which includes one or more core network nodes 1708. Access network 1704 includes one or more access network nodes, such as network nodes 1710a-b (one or more of which may be generally referred to as network nodes 1710), or any other similar 3GPP access nodes or non-3GPP access points.

[0347] 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. Rather, network nodes may include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1702 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1702 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 telecommunication network 1702, including one or more network nodes 1710 and / or core network nodes 1708.

[0348] 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. , r App), or any combination thereof (the adj ective “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 0-2 interface defined by the 0-RAN Alliance or comparable technologies. Network nodes 1710 facilitate direct or indirect connection of UEs, such as by connecting UEs 1712a-d (one or more of which may be generally referred to as UEs 1712) to core network 1706 over one or more wireless connections.

[0349] 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, communication system 1700 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. Communication system 1700 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0350] UEs 1712 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1710 and other communication devices. Similarly, network nodes 1710 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1712 and / or with other network nodes or equipment in telecommunication network 1702 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1702.

[0351] In the depicted example, core network 1706 connects network nodes 1710 to one or more hosts, such as host 1716. 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. Core network 1706 includes one or more core network nodes (e.g., 1708) 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 core network node 1708. 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).

[0352] Host 1716 may be under the ownership or control of a service provider other than an operator or provider of access network 1704 and / or telecommunication network 1702, and may be operated by the service provider or on behalf of the service provider. Host 1716 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 controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0353] As a whole, communication system 1700 of Figure 17 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.

[0354] In some examples, telecommunication network 1702 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1702 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1702. For example, telecommunication network 1702 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.

[0355] In some examples, UEs 1712 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 1704 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1704. 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).

[0356] In the example, hub 1714 communicates with access network 1704 to facilitate indirect communication between one or more UEs (e.g., 1712c and / or 1712d) and network nodes (e.g., network node 1710b). In some examples, hub 1714 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1714 may be a broadband router enabling access to core network 1706 for the UEs. As another example, hub 1714 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 1710, or by executable code, script, process, or other instructions in hub 1714. As another example, hub 1714 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, hub 1714 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1714 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1714 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1714 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0357] Hub 1714 may have a constant / persistent or intermittent connection to network node 1710b. Hub 1714 may also allow for a different communication scheme and / or schedule between hub 1714 and UEs (e.g., 1712c and / or 1712d), and between hub 1714 and core network 1706. In other examples, hub 1714 is connected to core network 1706 and / or one or more UEs via a wired connection. Moreover, hub 1714 may be configured to connect to an M2M service provider over access network 1704 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1710 while still connected via hub 1714 via a wired or wireless connection. In some embodiments, hub 1714 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1710b. In other embodiments, hub 1714 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1710b, but which is additionally capable of operating as a communication start and / or end point for certain data channels. Figure 18 shows a UE 1800 in accordance with some embodiments. 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 device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0358] A UE may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), or vehicle-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).

[0359] UE 1800 includes processing circuitry 1802 that is operatively coupled via bus 1804 to input / output interface 1806, power source 1808, memory 1810, communication interface 1812, and optionally one or more other components not explicitly shown. Certain UEs may utilize all or a subset of the components shown in Figure 18. 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.

[0360] Processing circuitry 1802 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 memory 1810. Processing circuitry 1802 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, processing circuitry 1802 may include multiple central processing units (CPUs).

[0361] In the example, input / output interface 1806 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 UE 1800. 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.

[0362] In some embodiments, power source 1808 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. Power source 1808 may further include power circuitry for delivering power from power source 1808 itself, and / or an external power source, to the various parts of UE 1800 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 1808. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1808 to make the power suitable for the respective components of UE 1800 to which power is supplied.

[0363] Memory 1810 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, memory 1810 includes one or more application programs 1814, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1816. Memory 1810 may store, for use by UE 1800, any of a variety of various operating systems or combinations of operating systems.

[0364] Memory 1810 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard 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.’ Memory 1810 may allow UE 1800 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 memory 1810, which may be or comprise a device-readable storage medium.

[0365] Processing circuitry 1802 may be configured to communicate with an access network or other network using communication interface 1812. Communication interface 1812 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1822. Communication interface 1812 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 transmitter 1818 and / or receiver 1820 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1818 and / or receiver 1820 may be coupled to one or more antennas (e.g., 1822) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0366] In the illustrated embodiment, communication functions of communication interface 1812 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 / intemet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0367] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1812, 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., an alert is sent when moisture is detected), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient). 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.

[0368] 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 head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), 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 UE 1800 shown in Figure 18.

[0369] 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 of such 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 3GPP 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.

[0370] 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.

[0371] Figure 19 shows a network node 1900 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and O-RAN nodes or components of an O-RAN node (e g., O-RU, O-DU, O-CU).

[0372] 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 O-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).

[0373] 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), base transceiver 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).

[0374] Network node 1900 includes processing circuitry 1902, memory 1904, communication interface 1906, and power source 1908. Network node 1900 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 network node 1900 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, network node 1900 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1904 for different RATs) and some components may be reused (e.g., a same antenna 1910 may be shared by different RATs). Network node 1900 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1900, 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 1900.

[0375] 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 memory 1904, to provide network node 1900 functionality.

[0376] In some embodiments, processing circuitry 1902 includes a system on a chip (SOC). In some embodiments, processing circuitry 1902 includes radio frequency (RF) transceiver circuitry 1912 and / or baseband processing circuitry 1914. In some embodiments, RF transceiver circuitry 1912 and / or baseband processing circuitry 1914 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 1912 and / or baseband processing circuitry 1914 may be on the same chip or set of chips, boards, or units.

[0377] 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 computer-executable memory devices that store information, data, and / or instructions that may be used by processing circuitry 1902. 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 (collected denoted computer program 1904a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1902 and utilized by network node 1900. Memory 1904 may be used to store any calculations made by processing circuitry 1902 and / or any data received via communication interface 1906. In some embodiments, processing circuitry 1902 and memory 1904 is integrated.

[0378] Communication interface 1906 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, communication interface 1906 comprises port(s) / terminal(s) 1916 to send and receive data, for example to and from a network over a wired connection. Communication interface 1906 also includes radio frontend circuitry 1918 that may be coupled to, or in certain embodiments a part of, antenna 1910. Radio front-end circuitry 1918 comprises filters 1920 and amplifiers 1922. Radio front-end circuitry 1918 may be connected to an antenna 1910 and processing circuitry 1902. The radio front-end circuitry may be configured to condition signals communicated between antenna 1910 and processing circuitry 1902. Radio front-end circuitry 1918 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1918 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1920 and / or amplifiers 1922. The radio signal may then be transmitted via antenna 1910. Similarly, when receiving data, antenna 1910 may collect radio signals which are then converted into digital data by radio front-end circuitry 1918. The digital data may be passed to processing circuitry 1902. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0379] In certain alternative embodiments, network node 1900 does not include separate radio front-end circuitry 1918, instead, processing circuitry 1902 includes radio front-end circuitry and is connected to antenna 1910. Similarly, in some embodiments, all or some of RF transceiver circuitry 1912 is part of communication interface 1906. In still other embodiments, communication interface 1906 includes one or more ports or terminals 1916, radio front-end circuitry 1918, and RF transceiver circuitry 1912, as part of a radio unit (not shown), and communication interface 1906 communicates with baseband processing circuitry 1914, which is part of a digital unit (not shown).

[0380] Antenna 1910 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1910 may be coupled to radio front-end circuitry 1918 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1910 is separate from network node 1900 and connectable to network node 1900 through an interface or port.

[0381] Antenna 1910, communication interface 1906, and / or processing circuitry 1902 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, antenna 1910, communication interface 1906, and / or processing circuitry 1902 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. 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). Power source 1908 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1900 with power for performing the functionality described herein. For example, 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 power source 1908. As a further example, power source 1908 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.

[0382] Embodiments of 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, network node 1900 may include user interface equipment to allow input of information into network node 1900 and to allow output of information from network node 1900. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1900.

[0383] Figure 20 is a block diagram illustrating a virtualization environment 2000 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 2000 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 2000 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.

[0384] Applications 2002 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 2000 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein. Hardware 2004 includes processing circuitry, memory that stores software and / or instructions (collected denoted computer program 2004a, which may be in the form of a computer program product) 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 layers 2006 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 2008a-b (one or more of which may be generally referred to as VMs 2008), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 2006 may present a virtual operating platform that appears like networking hardware to VMs 2008.

[0385] VMs 2008 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 2006. Different embodiments of the instance of a virtual appliance 2002 may be implemented on one or more of VMs 2008, 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.

[0386] In the context of NFV, each VM 2008 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each VM 2008, and that part of hardware 2004 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 2008 on top of hardware 2004 and corresponds to application 2002.

[0387] Hardware 2004 may be implemented in a standalone network node with generic or specific components. Hardware 2004 may implement some functions via virtualization. Alternatively, hardware 2004 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 function 2010, which, among others, oversees lifecycle management of applications 2002. In some embodiments, hardware 2004 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 2012 which may alternatively be used for communication between hardware nodes and radio units.

[0388] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the spirit and scope of the disclosure. Various embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

[0389] The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein.

[0390] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0391] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0392] Furthermore, functions described herein as being performed by a wireless device or a network node may be distributed over a plurality of wireless devices and / or network nodes. In other words, it is contemplated that the functions of a network node and a wireless device described herein are not limited to performance by a single physical device and, in fact, can be distributed among several physical devices.

[0393] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0394] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood, that although these terms (and / or other terms that can be synonymous to one another) can be used synonymously herein, there can be instances when such words can be intended to not be used synonymously.

[0395] The techniques and apparatus described herein include, but are not limited to, the following enumerated examples:

[0396] Al. A method for a user equipment (UE) configured to perform an inter-secondary node (SN) layer- 1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure in a radio access network (RAN), the method comprising: receiving an RRCReconflguration message that includes one or more Ll / L2-triggered mobility (LTM) configurations associated with respective one or more candidate cells, wherein: the RRCReconflguration message is received from a first RAN node that provides the UE’s master cell group (MCG) or from a second RAN node that provides the UE’s secondary cell group (SCG); the one or more candidate cells are part of a target SCG provided by a third RAN node; receiving, from the first RAN node or the second RAN node, a lower layer signalling message indicating that the UE should perform an inter-SN LTM procedure from the SCG provided by the second RAN node to the target SCG provided by the third RAN node; executing the inter-SN LTM procedure towards the target SCG; and sending, to the first RAN node or the third RAN, a first acknowledgement message indicating completion of the inter-SN LTM procedure.

[0397] A2. The method of embodiment Al, wherein the first acknowledgement message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure.

[0398] A2a. The method of embodiment A2, wherein one or the following applies: the first acknowledgement message is sent to the first RAN node and the second acknowledgement message is intended for the third RAN node; or the first acknowledgement message is sent to the third RAN node and the second acknowledgement message is intended for the first RAN node.

[0399] A2b. The method of any of embodiments A2-A2a, wherein the first and second acknowledgement messages are, or include, respective RRCReconflgurationComplete messages.

[0400] A3. The method of embodiment Al, wherein the first acknowledgement message is sent to the first RAN node, and the method further comprises sending to the third RAN node a second acknowledgement message indicating completion of the inter-SN LTM procedure.

[0401] A4. The method of any of embodiments Al -A3, wherein executing the inter-SN LTM procedure towards the target SCG includes one or more of the following: performing refresh of one or more security keys used for communication with the UE’s SCG; deriving or updating one or more security keys used for communication with the UE’s SCG; performing radio link control (RLC) re-establishment for one or more SCG RLC bearers; performing packet data convergence protocol (PDCP) re-establishment for one or more of the UE’s SN-terminated radio bearers; performing a medium access control (MAC) reset for the UE’s SCG; and performing a random access procedure in a cell of the target SCG.

[0402] A5. The method of any of embodiments A1-A4, wherein the lower layer signaling message includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform medium access control (MAC) reset in the target SCG; an indication of whether the UE should perform radio link control (RLC) reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol (PDCP) re-establishment or recovery in the target SCG; an indication of a timing advance (TA) value to be used in the target SCG; an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG; an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG; an identifier of a downlink (DL) BWP to be used in the target SCG; an indication of a state for a secondary cell (SCell) in the target SCG; and a grant of UL resources for the UE in the target SCG.

[0403] A5a. The method of embodiment A5, wherein the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG.

[0404] A5b. The method of any of embodiments A5-A5a, wherein the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE. A5c. The method of any of embodiments A5-A5b wherein one or more of the information in the lower layer signaling message indicates or references corresponding parameters in the received one or more LTM configurations.

[0405] A6. The method of any of embodiments Al-A5c, wherein one or more of the following applies: the lower layer signaling message is at a protocol layer below a radio resource control (RRC) protocol layer; and the lower layer signaling message is one of the following: MAC Control Element (MAC CE), or physical layer (PHY) Downlink Control Information (DCI).

[0406] Bl. A method for a first radio access network (RAN) node configured to provide a master cell group (MCG) for a user equipment (UE), the method comprising: determining to initiate an inter-secondary node (SN) layer- 1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure for the UE from a source secondary cell group (SCG) provided by a second RAN node to a target SCG provided by a third RAN node; based on the determination to initiate, sending to the third RAN node a first request for an inter-SN LTM cell switch for the UE to the target SCG; receiving, from the third RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receiving, from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

[0407] B2. The method of embodiment Bl, wherein: the acknowledgement message is a first acknowledgement message received from the UE; the first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure; and the method further comprises sending the second acknowledgement message to the third RAN node.

[0408] B2a. The method of embodiment Bl, wherein the acknowledgement message is a second acknowledgement message generated by the UE and received from the third RAN node. B3. The method of any of embodiments B2-B2a, wherein the first and second acknowledgement messages are, or include, respective RRCReconflgurationComplete messages.

[0409] B4. The method of any of embodiments B1-B3, further comprising: in response to the first acknowledgement message, sending to the second RAN node a third request to release or to deactivate the source SCG and / or other UE- associated resources in the second RAN node; and receiving from the second RAN node a third response acknowledging the third request.

[0410] B5. The method of any of embodiments B1-B4, further comprising sending to the UE a lower layer signalling message indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node, wherein the first acknowledgement message is received from the UE.

[0411] B5a. The method of embodiment B5, wherein the lower layer signaling message includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform medium access control (MAC) reset in the target SCG; an indication of whether the UE should perform radio link control (RLC) reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol (PDCP) re-establishment or recovery in the target SCG; an indication of a timing advance (TA) value to be used in the target SCG; an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG; an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG; an identifier of a downlink (DL) BWP to be used in the target SCG; an indication of a state for a secondary cell (SCell) in the target SCG; and a grant of UL resources for the UE in the target SCG.

[0412] B5b. The method of embodiment B5a, wherein the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG

[0413] B5c. The method of any of embodiments B5a-B5b, wherein the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE.

[0414] B5d. The method of any of embodiments B5a-B5c, wherein: the method further comprises sending to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by a third RAN node; and one or more of the information in the lower layer signaling message indicates or references corresponding parameters in the one or more LTM configurations.

[0415] B5e. The method of any of embodiments B5-B5e, wherein one or more of the following applies: the lower layer signaling message is at a protocol layer below a radio resource control (RRC) protocol layer; and the lower layer signaling message is one of the following: MAC Control Element (MAC CE), or physical layer (PHY) Downlink Control Information (DCI).

[0416] B5f. The method of any of embodiments B5-B5e, wherein the first request sent to the third RAN node includes one or more of the information in the lower layer signaling message sent to the UE.

[0417] B6. The method of any of embodiments B1-B4, wherein determining to initiate the inter- SN LTM procedure for the UE comprises receiving from the UE an LI measurement report related to one or more cells provided by the third RAN node, wherein the determination to initiate is based on the LI measurement report. B6a. The method of embodiment B6, further comprising: based on the determination to initiate, sending to the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and receiving, from the second RAN node, a second response acknowledging the inter-SN LTM cell switch for the UE to the target SCG, wherein the first request is sent to the third RAN node based on the second response from the second RAN node.

[0418] B7. The method of any of embodiments B1-B4, wherein determining to initiate the inter- SN LTM procedure for the UE comprises receiving from the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node, wherein the determination to initiate is based on the request.

[0419] B7a. The method of embodiment B7, wherein: the first request is sent to the third RAN node in response to receiving the second request from the second RAN node; and the method further comprises, based on the first response from the third RAN node, sending to the second RAN node a second response acknowledging the inter-SN LTM cell switch for the UE.

[0420] B7b. The method of any of embodiments B8-B7a, further comprising receiving from the second RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0421] B8. The method of any of embodiments Bl-B7b, wherein the first request sent to the third RAN node includes one or more of the following: measurements by the UE on one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE; identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator (TCI) states for the UE in the target SCG; a configuration for the UE’s MCG provided by the first RAN node; a configuration for the UE’s SCG provided by the second RAN node; and an indication of a suggested timing advance (TA) value for the UE in the target SCG.

[0422] Cl. A method for a second radio access network (RAN) node configured to provide a source secondary cell group (SCG) for an inter-secondary node (SN) layer-1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), the method comprising: performing first operations or second operations, wherein the first operations include: determining to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node; sending to the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and receiving from the first RAN node a second response acknowledging the inter- SN LTM cell switch for the UE; wherein the second operations include: receiving from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and sending to the first RAN node a second response acknowledging an inter-SN LTM cell switch for the UE; the method further comprises, after completion of the inter-SN LTM procedure by the UE, receiving from the first RAN node a third request to release or to deactivate the source SCG and / or other UE-associated resources in the second RAN node.

[0423] C2. The method of embodiment Cl, wherein determining to initiate the inter-SN LTM procedure for the UE comprises receiving from the UE an LI measurement report related to one or more cells provided by the third RAN node, wherein the determination to initiate is based on the LI measurement report.

[0424] C3. The method of any of embodiments C1-C2, wherein the second request sent to, or received from, the first RAN node includes one or more of the following: measurements received from the UE of one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE; identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator (TCI) states for the UE in the target SCG; and an indication of a suggested timing advance (TA) value for the UE in the target SCG.

[0425] C4. The method of any of embodiments C1-C3, wherein the first operations also include, based on the second response, sending to the UE a lower layer signalling message indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node.

[0426] C4a. The method of embodiment C4, wherein the lower layer signaling message includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of inter-SN LTM cell switch or of LTM cell switch for the UE’s SCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform medium access control (MAC) reset in the target SCG; an indication of whether the UE should perform radio link control (RLC) reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol (PDCP) re-establishment or recovery in the target SCG; an indication of a timing advance (TA) value to be used in the target SCG; an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG; an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG; an identifier of a downlink (DL) BWP to be used in the target SCG; an indication of a state for a secondary cell (SCell) in the target SCG; and a grant of UL resources for the UE in the target SCG. C4b. The method of embodiment C4a, wherein the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG

[0427] C4c. The method of any of embodiments C4a-C4b, wherein the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE.

[0428] C4d. The method of any of embodiments C4a-C4c, wherein: the first operations also include sending to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by a third RAN node; and one or more of the information in the lower layer signaling message indicates or references corresponding parameters in the one or more LTM configurations.

[0429] C4e. The method of any of embodiments C4-C4e, wherein one or more of the following applies: the lower layer signaling message is at a protocol layer below a radio resource control (RRC) protocol layer; and the lower layer signaling message is one of the following: MAC Control Element (MAC CE), or physical layer (PHY) Downlink Control Information (DCI).

[0430] C4f. The method of any of embodiments C4-C4e, wherein the second request sent to the first RAN node includes one or more of the information in the lower layer signaling message sent to the UE.

[0431] C5. The method of any of embodiments C4-C4f, wherein the first operations also include, in response to sending the lower layer signaling message, sending to the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0432] C6. The method of any of claims C1-C5, further comprising sending to the first RAN node a third response acknowledging the third request. DI. A method for a third radio access network (RAN) node configured to provide a target secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), the method comprising: receiving, from a first RAN node configured to provide a master cell group (MCG) for the UE, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node to the target SCG provided by the third RAN node; sending, to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receiving, from the UE or the first RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

[0433] D2. The method of embodiment DI, wherein: the acknowledgement message is a first acknowledgement message received from the UE; the first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure; and the method further comprises sending the second acknowledgement message to the first RAN node.

[0434] D2a. The method of embodiment DI, wherein the acknowledgement message is a second acknowledgement message generated by the UE and received from the first RAN node.

[0435] D2b. The method of any of embodiments D2-D2a, wherein the first and second acknowledgement messages are, or include, respective RRCReconflgurationComplete messages.

[0436] D3. The method of any of embodiments Dl-D2b, wherein the first request received from the first RAN node includes one or more of the following: measurements by the UE on one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE; identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter- SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator (TCI) states for the UE in the target SCG; a configuration for the UE’s MCG provided by the first RAN node; a configuration for the UE’s SCG provided by the second RAN node; and an indication of a suggested timing advance (TA) value for the UE in the target SCG.

[0437] D4. The method of any of embodiments D1-D3, wherein the first response sent to the first RAN node includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication on whether the UE should perform medium access control (MAC) reset in the target SCG; an indication on whether the UE should perform L2 reset in the target SCG; an indication of a timing advance (TA) value to be used in the target SCG; an indication of a beam or a transmission configuration indicator (TCI) state to be used in the target SCG; an identifier of an uplink (UL) bandwidth part (BWP) to be used in the target SCG; an identifier of a downlink (DL) BWP to be used in the target SCG; an indication of a state for a secondary cell (SCell) in the target SCG; and a grant of UL resources for the UE in the target SCG.

[0438] D4a. The method of embodiment D4, wherein the indication of the TA value is one of the following: an explicit TA value, an indication to use a TA value for the source SCG also in the target SCG, or an indication to use a previously obtained TA value associated with the target SCG.

[0439] D4b. The method of any of embodiments D4-D4a, wherein the indication of the beam or TCI state is one of the following: an explicit beam or TCI state for the target SCG, or an indication to use a beam or TCI state for the target SCG that was previously activated by the UE. D5. The method of any of embodiments Dl-D4b, further comprising receiving from the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

[0440] El. A user equipment (UE) configured to perform an inter-secondary node (SN) layer-1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with the RAN via a master cell group (MCG) and at least one secondary cell group (SCG); and processing circuitry operably coupled to the communication interface circuitry, wherein the processing circuitry and communication interface circuitry are further configured to perform operations corresponding to any of the methods of embodiments A1-A7.

[0441] E2. A user equipment (UE) configured to perform an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure in a radio access network (RAN), the UE being further configured to perform operations corresponding to any of the methods of embodiments A1-A7.

[0442] E3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A7.

[0443] E4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured to perform an intersecondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure in a radio access network (RAN), configure the UE to perform operations corresponding to any of the methods of embodiments A1-A7.

[0444] FL A first radio access network (RAN) node configured to provide a master cell group (MCG) for a user equipment (UE), the first RAN node comprising: communication interface circuitry configured to communicate with the UE via the MCG and with second and third RAN nodes configured to provide source and target secondary cell groups (SCGs) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by the UE; and processing circuitry operably coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments BIBS.

[0445] F2. A first radio access network (RAN) node configured to provide a master cell group (MCG) for a user equipment (UE), the first RAN node being further configured to perform operations corresponding to any of the methods of embodiments B1-B8.

[0446] F3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to provide a master cell group (MCG) for a user equipment (UE), configure the first RAN node to perform operations corresponding to any of the methods of embodiments B1-B8.

[0447] F4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to provide a master cell group (MCG) for a user equipment (UE), configure the first RAN node to perform operations corresponding to any of the methods of embodiments B1-B8.

[0448] Gl. A second radio access network (RAN) node configured to provide a source secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered intercell mobility (LTM) procedure by a user equipment (UE), the second RAN node comprising: communication interface circuitry configured to communicate with the UE via the SCG and with a first RAN node configured to provide a master cell group (MCG) for the UE; and processing circuitry operably coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments Cl- C6.

[0449] G2. A second radio access network (RAN) node configured to provide a source secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter- cell mobility (LTM) procedure by a user equipment (UE), the second RAN node being further configured to perform operations corresponding to any of the methods of embodiments C1-C6.

[0450] G3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to provide a source secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), configure the second RAN node to perform operations corresponding to any of the methods of embodiments C1-C6.

[0451] G4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to provide a source secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), configure the second RAN node to perform operations corresponding to any of the methods of embodiments C1-C6.

[0452] HL A third radio access network (RAN) node configured to provide a target secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), the third RAN node comprising: communication interface circuitry configured to communicate with the UE via the target SCG and with a first RAN node configured to provide a master cell group (MCG) for the UE; and processing circuitry operably coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to any of the methods of embodiments Dl- D5.

[0453] H2. A third radio access network (RAN) node configured to provide a target secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), the third RAN node being further configured to perform operations corresponding to any of the methods of embodiments D1-D5.

[0454] H3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a third radio access network (RAN) node configured to provide a target secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), configure the third RAN node to perform operations corresponding to any of the methods of embodiments D1-D5.

[0455] H4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a third radio access network (RAN) node configured to provide a target secondary cell group (SCG) for an inter-secondary node (SN) layer- 1 (L2) or layer-2 (L2) triggered inter-cell mobility (LTM) procedure by a user equipment (UE), configure the third RAN node to perform operations corresponding to any of the methods of embodiments D1-D5.

Claims

CLAIMS1. A method for a user equipment, UE, configured to perform an inter-secondary node, SN, layer- 1 or layer-2 triggered inter-cell mobility, LTM, procedure in a radio access network, RAN, the method comprising: receiving (1320) a medium access control, MAC, control element, CE, indicating that the UE should perform an inter-SN LTM procedure from a source secondary cell group, SCG, provided by a second RAN node to a target SCG provided by a third RAN node, wherein the MAC CE is received from the second RAN node; executing (1330) the inter-SN LTM procedure towards the target SCG; and sending (1340), to the third RAN node or to a first RAN node that provides the UE’s master cell group, MCG, a first acknowledgement message indicating completion of the inter-SN LTM procedure.

2. The method of claim 1, wherein the first acknowledgement message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure.

3. The method of claim 2, wherein one or the following applies: the first acknowledgement message is sent to the first RAN node and the second acknowledgement message is intended for the third RAN node; or the first acknowledgement message is sent to the third RAN node and the second acknowledgement message is intended for the first RAN node.

4. The method of any of claims 2-3, wherein the first and second acknowledgement messages are, or include, respective RRCReconfigurationComplete messages.

5. The method of claim 1, wherein the first acknowledgement message is sent to the first RAN node, and the method further comprises sending (1350) to the third RAN node a second acknowledgement message indicating completion of the inter-SN LTM procedure.

6. The method of any of claims 1-5, wherein executing (1330) the inter-SN LTM procedure towards the target SCG includes one or more of the following: performing (1331) refresh of one or more security keys used for SCG communication;deriving or updating (1332) one or more security keys used for SCG communication; performing (1333) radio link control, RLC, re-establishment for one or more SCG RLC bearers; performing (1334) packet data convergence protocol, PDCP, re-establishment for one or more of the UE’s SN-terminated radio bearers; performing (1335) an SCG MAC reset; and performing (1336) a random access procedure in a cell of the target SCG.

7. The method of any of claims 1-6, wherein the MAC CE includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of an inter-SN LTM cell switch or of an LTM cell switch for the UE’s SCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform MAC reset in the target SCG; an indication of whether the UE should perform radio link control, RLC, reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol, PDCP, re-establishment or recovery in the target SCG; an indication of a timing advance, TA, value to be used in the target SCG; an indication of a beam or a transmission configuration indicator, TCI, state to be used in the target SCG; an identifier of an uplink, UL, bandwidth part, BWP, to be used in the target SCG; an identifier of a downlink, DL, BWP to be used in the target SCG; an indication of a state for a secondary cell, SCell, in the target SCG; and a grant of UL resources for the UE in the target SCG.

8. The method of claim 7, wherein: the method further comprises receiving (1310), from the first RAN node or the second RAN node, an RRC Reconfiguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by the third RAN node; andone or more of the information in the MAC CE indicates or references corresponding parameters in the received one or more LTM configurations.

9. The method of claim 8, further comprising sending (1315), to the first RAN node or the second RAN node, a layer- 1 measurement report related to one or more cells provided by the third RAN node, including at least one of the candidate cells that are part of the target SCG.

10. A method for a first radio access network, RAN, node configured to provide a master cell group, MCG, for a user equipment, UE, the method comprising: determining (1420) to initiate an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure for the UE from a source secondary cell group, SCG, provided by a second RAN node to a target SCG provided by a third RAN node; based on the determination to initiate, sending (1440) to the third RAN node a first request for an inter-SN LTM cell switch for the UE to the target SCG; receiving (1450), from the third RAN node, a first response acknowledging the inter- SN LTM cell switch for the UE to the target SCG; and receiving (1470), from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

11. The method of claim 10, wherein: the acknowledgement message is a first acknowledgement message received from the UE; the first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure; and the method further comprises sending (1475) the second acknowledgement message to the third RAN node.

12. The method of claim 10, wherein the acknowledgement message is a second acknowledgement message generated by the UE and received from the third RAN node.

13. The method of any of claims 11-12, wherein the first and second acknowledgement messages are, or include, respective RRCReconfigurationComplete messages.

14. The method of any of claims 10-13, further comprising: in response to the first acknowledgement message, sending (1480) to the second RAN node a third request to release or to deactivate the source SCG and / or other UE- associated resources in the second RAN node; and receiving (1490) from the second RAN node a third response acknowledging the third request.

15. The method of any of claims 10-14, further comprising sending (1410) to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by the third RAN node.

16. The method of any of claims 10-15, wherein the first request sent to the third RAN node includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of an inter-SN LTM cell switch or of an LTM cell switch for the UE’sSCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform MAC reset in the target SCG; an indication of whether the UE should perform radio link control, RLC, reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol, PDCP, re-establishment or recovery in the target SCG; an indication of a timing advance, TA, value to be used in the target SCG; an indication of a beam or a transmission configuration indicator, TCI, state to be used in the target SCG; an identifier of an uplink, UL, bandwidth part, BWP, to be used in the target SCG; an identifier of a downlink, DL, BWP to be used in the target SCG; an indication of a state for a secondary cell, SCell, in the target SCG; and a grant of UL resources for the UE in the target SCG.

17. The method of any of claims 10-16, wherein determining (1420) to initiate the inter-SN LTM procedure for the UE comprises receiving (1421) from the UE a layer-1 measurementreport related to one or more cells provided by the third RAN node, wherein the determination to initiate is based on the layer- 1 measurement report.

18. The method of claim 17, further comprising: based on the determination to initiate, sending (1425) to the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and receiving (1430), from the second RAN node, a second response acknowledging the inter-SN LTM cell switch for the UE to the target SCG, wherein the first request is sent to the third RAN node based on the second response from the second RAN node.

19. The method of any of claims 10-16, wherein determining (1420) to initiate the inter-SN LTM procedure for the UE comprises receiving (1422) from the second RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node, wherein the determination to initiate is based on the request.

20. The method of claim 19, wherein: the first request is sent to the third RAN node in response to receiving the second request from the second RAN node; and the method further comprises, based on the first response from the third RAN node, sending (1455) to the second RAN node a second response acknowledging the inter-SN LTM cell switch for the UE.

21. The method of any of claims 19-20, further comprising receiving (1435) from the second RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

22. The method of any of claims 10-21, wherein the first request sent to the third RAN node includes one or more of the following: measurements by the UE on one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE;identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter- SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator, TCI, states for the UE in the target SCG; a configuration for the MCG; a configuration for the source SCG; and an indication of a suggested timing advance, TA, value for the UE in the target SCG.

23. A method for a second radio access network, RAN, node configured to provide a source secondary cell group, SCG, for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE, the method comprising: performing first operations or second operations, wherein the first operations include: determining (1520) to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node; sending (1530), to a first RAN node configured to provide a master cell group, MCG, for the UE, a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and receiving (1540) from the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE; wherein the second operations include: receiving (1560) from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and sending (1570) to the first RAN node a second response acknowledging an inter-SN LTM cell switch for the UE; the method further comprises, after completion of the inter-SN LTM procedure by the UE, receiving (1580) from the first RAN node a third request to release or to deactivate at least one of the following: the source SCG, and other UE- associated resources in the second RAN node.

24. The method of claim 23, wherein determining (1520) to initiate the inter-SN LTM procedure for the UE comprises receiving (1521) from the UE a layer-1 measurement reportrelated to one or more cells provided by the third RAN node, wherein the determination to initiate is based on the layer- 1 measurement report.

25. The method of any of claims 23-24, wherein the second request sent to, or received from, the first RAN node includes one or more of the following: measurements received from the UE of one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE; identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator, TCI, states for the UE in the target SCG; and an indication of a suggested timing advance, TA, value for the UE in the target SCG.

26. The method of any of claims 23-25, wherein the first operations also include, based on the second response, sending to the UE a medium access control, MAC, control element, CE, indicating that the UE should perform an inter-SN LTM procedure from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node.

27. The method of claim 26, wherein the MAC CE includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of an inter-SN LTM cell switch or of an LTM cell switch for the UE’s SCG; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication of whether the UE should perform MAC reset in the target SCG; an indication of whether the UE should perform radio link control, RLC, reestablishment in the target SCG; an indication of whether the UE should perform packet data convergence protocol, PDCP, re-establishment or recovery in the target SCG; an indication of a timing advance, TA, value to be used in the target SCG;an indication of a beam or a transmission configuration indicator, TCI, state to be used in the target SCG; an identifier of an uplink, UL, bandwidth part, BWP, to be used in the target SCG; an identifier of a downlink, DL, BWP to be used in the target SCG; an indication of a state for a secondary cell, SCell, in the target SCG; and a grant of UL resources for the UE in the target SCG.

28. The method of claim 27, wherein: the first operations also include sending (1510) to the UE an RRCReconflguration message that includes one or more LTM configurations associated with respective one or more candidate cells that are part of the target SCG provided by a third RAN node; and one or more of the information in the MAC CE indicates or references corresponding parameters in the one or more LTM configurations.

29. The method of any of claims 27-28, wherein the second request sent to the first RAN node includes one or more of the information in the MAC CE sent to the UE.

30. The method of any of claims 27-29, wherein the first operations also include, in response to sending (1550) the MAC CE, sending (1555) to the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

31. A method for a third radio access network, RAN, node configured to provide a target secondary cell group, SCG, for an inter-secondary node, SN, layer-1 or layer-2 triggered intercell mobility, LTM, procedure by a user equipment, UE, the method comprising: receiving (1610), from a first RAN node configured to provide a master cell group, MCG, for the UE, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node to the target SCG provided by the third RAN node; sending (1620), to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receiving (1630), from the UE or the first RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

32. The method of claim 31, wherein:the acknowledgement message is a first acknowledgement message received from the UE; the first acknowledge message includes an embedded or encapsulated second acknowledgement message indicating completion of the inter-SN LTM procedure; and the method further comprises sending (1640) the second acknowledgement message to the first RAN node.

33. The method of claim 31, wherein the acknowledgement message is a second acknowledgement message generated by the UE and received from the first RAN node.

34. The method of any of claims 32-33, wherein the first and second acknowledgement messages are, or include, respective RRCReconfigurationComplete messages.

35. The method of any of claims 31-34, wherein the first request received from the first RAN node includes one or more of the following information: measurements by the UE on one or more cells provided by the third RAN node; an identity of the third RAN node as a candidate target SN for the inter-SN LTM cell switch by the UE; identities of one or more cells provided by the third RAN node as candidate cells for a target SCG for the inter-SN LTM cell switch by the UE; an indication of one or more suggested beams or transmission configuration indicator, TCI, states for the UE in the target SCG; a configuration for the MCG; a configuration for the source SCG; and an indication of a suggested timing advance, TA, value for the UE in the target SCG.

36. The method of any of claims 31-35, wherein the first response sent to the first RAN node includes one or more of the following information: an indication of an inter-SN candidate cell configuration, to be used for the inter-SN LTM procedure; an indication of a reference configuration to be used in the target SCG; an indication on whether the UE should perform random access in the target SCG; an indication on whether the UE should perform medium access control, MAC, reset in the target SCG;an indication on whether the UE should perform layer-2 reset in the target SCG; an indication of a timing advance, TA, value to be used in the target SCG; an indication of a beam or a transmission configuration indicator, TCI, state to be used in the target SCG; an identifier of an uplink, UL, bandwidth part, BWP, to be used in the target SCG; an identifier of a downlink, DL, BWP to be used in the target SCG; an indication of a state for a secondary cell, SCell, in the target SCG; and a grant of UL resources for the UE in the target SCG.

37. The method of any of claims 31-36, further comprising receiving (1625) from the first RAN node an indication that the inter-SN LTM cell switch has been initiated for the UE.

38. User equipment, UE (210, 440, 1010, 1712, 1800, 2206) configured to perform an intersecondary node, SN, layer- 1 or layer-2 triggered inter-cell mobility, LTM, procedure in a radio access network, RAN (460, 1604), the UE comprising: communication interface circuitry (1812) configured to communicate with the RAN via a master cell group, MCG (411), and at least one secondary cell group, SCG (421); and processing circuitry (1802) operably coupled to the communication interface circuitry, wherein the processing circuitry and communication interface circuitry are configured to: receive a medium access control, MAC, control element, CE, indicating that the UE should perform an inter-SN LTM procedure from a source secondary cell group, SCG, provided by a second RAN node (220, 420, 1030, 1710, 1900, 2002) to a target SCG provided by a third RAN node (220, 420, 1040, 1710, 1900, 2002), wherein the MAC CE is received from the second RAN node; execute the inter-SN LTM procedure towards the target SCG; and send, to the third RAN node or to a first RAN node (220, 410, 1020, 1710, 1900, 2002) that provides the UE’s master cell group, MCG, a first acknowledgement message indicating completion of the inter-SN LTM procedure.

39. The UE of claim 38, wherein the processing circuitry and communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 2-9.

40. User equipment, UE (210, 440, 1010, 1712, 1800) configured to perform an intersecondary node, SN, layer- 1 or layer-2 triggered inter-cell mobility, LTM, procedure in a radio access network, RAN (460, 1604), the UE being further configured to: receive a medium access control, MAC, control element, CE, indicating that the UE should perform an inter-SN LTM procedure from a source secondary cell group, SCG, provided by a second RAN node (220, 420, 1030, 1710, 1900, 2002) to a target SCG provided by a third RAN node (220, 420, 1040, 1710, 1900, 2002), wherein the MAC CE is received from the second RAN node; execute the inter-SN LTM procedure towards the target SCG; and send, to the third RAN node or to a first RAN node (220, 410, 1020, 1710, 1900, 2002) that provides the UE’s master cell group, MCG, a first acknowledgement message indicating completion of the inter-SN LTM procedure.

41. The UE of claim 40, being further configured to perform operations corresponding to any of the methods of claims 2-9.

42. Non-transitory, computer-readable medium (1810) storing computer-executable instructions that, when executed by processing circuitry (1802) of equipment, UE (210, 440, 1010, 1712, 1800) configured to perform an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure in a radio access network, RAN (460, 1604), configure the UE to perform operations corresponding to any of the methods of claims 1-9.

43. Computer program product (1814) comprising computer-executable instructions that, when executed by processing circuitry (1802) of equipment, UE (210, 440, 1010, 1712, 1800) configured to perform an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure in a radio access network, RAN (460, 1604), configure the UE to perform operations corresponding to any of the methods of claims 1-9.

44. First radio access network, RAN, node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for a user equipment, UE (210, 440, 1010, 1712, 1800), the first RAN node comprising:communication interface circuitry (1906, 2004) configured to communicate with the UE via the MCG and with second and third RAN nodes (220, 420, 1030, 1040, 1710, 1900, 2002) configured to provide source and target secondary cell groups, SCGs (421) for inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedures by the UE; and processing circuitry (1902, 2004) operably coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: determine to initiate an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure for the UE from a source secondary cell group, SCG, provided by the second RAN node to a target SCG provided by the third RAN node; based on the determination to initiate, send to the third RAN node a first request for an inter- SN LTM cell switch for the UE to the target SCG; receive, from the third RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receive, from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

45. The first RAN node of claim 44, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 11-22.

46. First radio access network, RAN, node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for a user equipment, UE (210, 440, 1010, 1712, 1800), the first RAN node being further configured to: determine to initiate an inter-secondary node, SN, layer- 1 or layer-2 triggered inter-cell mobility, LTM, procedure for the UE from a source secondary cell group, SCG, provided by a second RAN node (220, 420, 1030, 1710, 1900, 2002) to a target SCG provided by a third RAN node (220, 420, 1040, 1710, 1900, 2002); based on the determination to initiate, send to the third RAN node a first request for an inter-SN LTM cell switch for the UE to the target SCG; receive, from the third RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; andreceive, from the UE or the third RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

47. The first RAN node of claim 46, being further configured to perform operations corresponding to any of the methods of claims 11-22.

48. Non-transitory, computer-readable medium (1904, 2004) storing computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a first radio access network, RAN, node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for a user equipment, UE (210, 440, 1010, 1712, 1800), configure the first RAN node to perform operations corresponding to any of the methods of claims 10-22.

49. Computer program product (1904a, 2004a) comprising computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a first radio access network, RAN, node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for a user equipment, UE (210, 440, 1010, 1712, 1800), configure the first RAN node to perform operations corresponding to any of the methods of claims 10-22.

50. Second radio access network, RAN, node (220, 420, 1030, 1710, 1900, 2002) configured to provide a source secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), the second RAN node comprising: communication interface circuitry (1906, 2004) configured to communicate with the UE via the SCG and with a first RAN node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for the UE; and processing circuitry (1902, 2004) operably coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: perform first operations or second operations, wherein the first operations include: determine to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node (220, 420, 1040, 1710, 1900, 2002); send, to the first RAN node, a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the secondRAN node to the target SCG provided by the third RAN node; and receive from the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE; wherein the second operations include: receive from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and send to the first RAN node a second response acknowledging an inter- SN LTM cell switch for the UE; wherein the processing circuitry and the communication interface circuitry are further configured to, after completion of the inter-SN LTM procedure by the UE, receive from the first RAN node a third request to release or to deactivate at least one of the following: the source SCG, and other UE-associated resources in the second RAN node.

51. The second RAN node of claim 50, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 24-30.

52. Second radio access network, RAN, node (220, 420, 1030, 1710, 1900, 2002) configured to provide a source secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), the second RAN node being further configured to: perform first operations or second operations, wherein the first operations include: determine to initiate an inter-SN LTM procedure for the UE from the source SCG to a target SCG provided by a third RAN node (220, 420, 1040, 1710, 1900, 2002); send, to a first RAN node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG, for the UE, a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; andreceive from the first RAN node a second response acknowledging the inter-SN LTM cell switch for the UE; wherein the second operations include: receive from the first RAN node a second request for an inter-SN LTM cell switch for the UE from the source SCG provided by the second RAN node to the target SCG provided by the third RAN node; and send to the first RAN node a second response acknowledging an inter-SN LTM cell switch for the UE; the second RAN node being further configured to, after completion of the inter-SN LTM procedure by the UE, receive from the first RAN node a third request to release or to deactivate at least one of the following: the source SCG, and other UE-associated resources in the second RAN node.

53. The second RAN node of claim 52, being further configured to perform operations corresponding to any of the methods of claims 24-30.

54. Non-transitory, computer-readable medium (1904, 2004) storing computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a second radio access network, RAN, node (220, 420, 1030, 1710, 1900, 2002) configured to provide a source secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), configure the second RAN node to perform operations corresponding to any of the methods of claims 23-30.

55. Computer program product (1904a, 2004a) comprising computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a second radio access network, RAN, node (220, 420, 1030, 1710, 1900, 2002) configured to provide a source secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), configure the second RAN node to perform operations corresponding to any of the methods of claims 23-30.

56. Third radio access network, RAN, node (220, 420, 1040, 1710, 1900, 2002) configured to provide a target secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), the third RAN node comprising:communication interface circuitry (1906, 2004) configured to communicate with the UE via the target SCG and with a first RAN node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG (411) for the UE; and processing circuitry (1902, 2004) operably coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from the first RAN node, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node (220, 420, 1030, 1710, 1900, 2002) to the target SCG provided by the third RAN node; send, to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receive, from the UE or the first RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

57. The third RAN node of claim 56, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to any of the methods of claims 32-36.

58. Third radio access network, RAN, node (220, 420, 1040, 1710, 1900, 2002) configured to provide a target secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), the third RAN node being further configured to: receive, from a first RAN node (220, 410, 1020, 1710, 1900, 2002) configured to provide a master cell group, MCG, for the UE, a first request for an inter-SN LTM cell switch for the UE from a source SCG provided by a second RAN node (220, 420, 1030, 1710, 1900, 2002) to the target SCG provided by the third RAN node; send, to the first RAN node, a first response acknowledging the inter-SN LTM cell switch for the UE to the target SCG; and receive, from the UE or the first RAN node, an acknowledgement message indicating completion of the inter-SN LTM procedure for the UE.

59. The third RAN node of claim 58, being further configured to perform operations corresponding to any of the methods of claims 32-36.

60. Non-transitory, computer-readable medium (1904, 2004) storing computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a third radio access network, RAN, node (220, 420, 1040, 1710, 1900, 2002) configured to provide a target secondary cell group, SCG (421) for an inter-secondary node, SN, layer-1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), configure the third RAN node to perform operations corresponding to any of the methods of claims 31-36.

61. Computer program product (1904a, 2004a) comprising computer-executable instructions that, when executed by processing circuitry (1902, 2004) of a third radio access network, RAN, node (220, 420, 1040, 1710, 1900, 2002) configured to provide a target secondary cell group, SCG (421) for an inter-secondary node, SN, layer- 1 or layer-2 triggered inter-cell mobility, LTM, procedure by a user equipment, UE (210, 440, 1010, 1712, 1800), configure the third RAN node to perform operations corresponding to any of the methods of claims 31-36.

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