Indication of l2 reset assocated with conditional l1 / l2-triggered mobility (LTM) cell switch

Abstract

Embodiments include methods for a user equipment configured for conditional layer-1 / layer-2 triggered mobility (LTM) in a radio access network (RAN) Such methods include receiving, from a third RAN node via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each LTM candidate cell: LTM candidate cell configuration, group identifier, and execution condition for LTM cell switch. Such methods include, based on determining the execution condition is fulfilled for a first LTM candidate cell provided by a second RAN node, performing LTM cell switch to the first LTM candidate cell. Such methods include, based on group identifiers related to the first LTM candidate cell and the first serving cell, selectively performing an L2 reset in conjunction with the LTM cell switch and sending the first or second RAN node an indication of whether the L2 reset will be / was performed.

Description

[0001] INDICATION OF L2 RESET ASSOCATED WITH CONDITIONAL L1 / L2- TRIGGERED MOBILITY (LTM) CELL SWITCH

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks, and more specifically to techniques for improving mobility of user equipment (UEs) across multiple cells in a radio access network (RAN), specifically in relation to consistent handling of layer-2 (L2) reset after a UE’s cell switch to a candidate cell due to conditional layer- 1 (Ll) / L2 triggered mobility (LTM).

[0004] BACKGROUND

[0005] The fifth generation (5G) of cellular systems has been standardized within the Third- Generation Partnership Project (3GPP). 5G is developed for maximum flexibility to support many different use cases including 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. 5G was initially specified in 3GPP Release 15 (Rel-15) and continues to evolve through subsequent releases.

[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 (SMF).

[0007] 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 downlink (DL) “beam” is a coverage area of a network-transmitted reference signal (RS) that may be measured or monitored by a UE.

[0008] 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). 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 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. A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1).

[0009] 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.

[0010] Even so, handover and other mobility procedures can have various problems related to robustness. For example, a HO command is normally sent when the radio conditions for the UE are already quite bad, such as at or near cell borders. As such, the HO command may need to be segmented (e.g., to allow for redundancy to protect against errors) and / or retransmitted one or more times before it reaches the UE. In such case, the HO command may not reach the UE in time (or at all) before the degraded connection with the source node (e.g., the node hosting the UE’s current serving cell) is dropped. Failure of handover to a target cell may lead to the UE declaring radio link failure (RLF) in the source cell.

[0011] To address various difficulties with handovers and other mobility procedures, 3GPP Rel- 16 includes support for conditional handover (CHO) and SN-initiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 includes support for various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood that it is successfully transferred. The execution of the mobility command is done at later point in time based on an associated execution condition.

[0012] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconfiguration message (in NR) or an RRCConnectionReconfiguration message (in LTE). When the UE later detects the execution condition(s) associated with one of the earlier-received reconfigurations, the UE executes the associated reconfiguration to perform the mobility procedure (e.g., HO, PSCell change, PSCell addition, etc.).

[0013] Conditional (e.g., CHO) and non-conditional (e.g., HO) mobility operations are triggered by layer 3 (L3) measurements and involves radio resource control (RRC) signaling to change primary cells as well as to release / add secondary cells as needed. These conventional inter-cell mobility operations also involve complete layer 2 (L2) and layer 1 (LI) resets, leading to increased latency, signaling overhead, and interruption relative to intra-cell beam switching.

[0014] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). In LTM, a UE is pre -configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger the LTM cell switch procedure by sending the UE an LTM cell switch command.

[0015] There are some notable differences between Rel-18 LTM and L3 conditional mobility procedures. Lor example, unlike L3-triggered conditional mobility in which the UE initiates execution, LTM is initiated by a UE’s serving RAN node based on measurements reported by the UE. This introduces some amount of delay in an LTM cell switch.

[0016] To capture advantages of both LTM and L3 conditional mobility, 3 GPP Rel-19 will introduce the feature of conditional LTM (CLTM). Much like L3 conditional mobility, when a UE detects the execution condition(s) associated with an earlier-received LTM candidate cell configuration, the UE executes an LTM cell switch to the candidate cell.

[0017] SUMMARY

[0018] In Rel-18 LTM, a UE determines whether to perform a L2 reset during an LTM cell switch by comparing to group identifiers (IDs) assigned to the source and candidate (or target) cells for the LTM cell switch. While this determination is relatively straightforward for the UE, the corresponding determination by the DU serving the candidate cell (“candidate DU” or “C-DU”) requires additional information. In Rel-18 LTM, the C-DU is either informed in advance about the group IDs assigned to respective LTM candidate cells or is informed by the DU serving the source cell (“source DU” or “S-DU”) whether the UE’s LTM cell switch is done with or without L2 reset. As such, when the C-DU is notified by the S-DU that an LTM cell switch has been triggered for the UE, the C-DU is aware of whether the UE performs L2 reset and can take the corresponding action.

[0019] However, these techniques are not applicable for CLTM since the S-DU is not aware of the UE triggering the LTM cell switch based on the execution condition, and thus is unable to notify the C-DU. An object of embodiments of the present disclosure is to improve consistency of L2 resets between UEs and RAN nodes for CLTM, such as by providing, enabling, and / or facilitating solutions to overcome exemplary problems summarized above and described in more detail below.

[0020] Embodiments include methods (e.g., procedures) for a UE configured for CLTM in a RAN (e.g., E-UTRAN, NG-RAN).

[0021] These exemplary methods include receiving, from a third RAN node via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier (e.g., no reset ID) associated with the LTM candidate cell, and an execution condition for LTM cell switch to the LTM candidate cell. These exemplary methods also include, based on determining that an execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node, performing an LTM cell switch to the first LTM candidate cell.

[0022] These exemplary methods also include, based on the group identifier related to the first LTM candidate cell and a group identifier related to the first serving cell, selectively performing a layer-2 (L2) reset in conjunction with the LTM cell switch. These exemplary methods also include sending one of the following:

[0023] • to the first RAN node, an indication of whether the L2 reset will be performed in conjunction with the LTM cell switch; or

[0024] • to the second RAN node, an indication of whether the L2 reset was performed in conjunction with the LTM cell switch.

[0025] In some embodiments, selectively performing the L2 reset based on the group identifier related to the first LTM candidate cell and the group identifier related to the first serving cell includes the following operations:

[0026] • performing the L2 reset when the group identifier related to the first LTM candidate cell is different than the group identifier related to the first serving cell; and

[0027] • refraining from performing the L2 reset when the group identifier related to the first LTM candidate cell is the same as the group identifier related to the first serving cell.

[0028] Other embodiments include exemplary methods (e.g., procedures) for a second RAN node configured to facilitate CLTM by UEs. In general, these exemplary methods may be complementary to the exemplary methods for a UE summarized above.

[0029] These exemplary methods include sending, to a third RAN node, a configuration for a first LTM candidate cell provided by the second RAN node and an execution condition for LTM cell switch by a UE to the first LTM candidate cell. These exemplary methods also include receiving and storing the following information from the third RAN node:

[0030] • a first indication of the UE’s serving entity; and • respective group identifiers related to the following: the UE’s serving entity, the first LTM candidate cell, and one or more second LTM candidate cells for the UE.

[0031] These exemplary methods also include performing first operations or second operations. The first operations include the following:

[0032] • receiving from the third RAN node a second indication that the UE’s serving entity has changed; and

[0033] • updating the stored information based on the second indication;

[0034] Also, the second operations include the following:

[0035] • detecting an LTM cell switch by the UE to the first LTM candidate cell; and

[0036] • based on the stored information, selectively performing a layer-2 (L2) reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

[0037] In some embodiments, selectively performing the L2 reset based on the stored information includes the following operations:

[0038] • performing the L2 reset when the stored group identifier related to the first LTM candidate cell is different than the stored group identifier related to the first serving cell; and

[0039] • refraining from performing the L2 reset when the stored group identifier related to the first LTM candidate cell is same as the stored group identifier related to the first serving cell.

[0040] Other embodiments include exemplary methods (e.g., procedures) for a third RAN node configured to facilitate CLTM by UEs. In general, these exemplary methods may be complementary to the exemplary methods for a UE and a second RAN node, summarized above.

[0041] These exemplary methods include determines respective group identifiers related to the following: the UE’s serving entity, a first LTM candidate cell provided by a second RAN node, and one or more second LTM candidate cells for the UE. These exemplary methods also include receiving from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell. These exemplary methods also include, based on the group identifier related to the first LTM candidate cell and the group identifier related to the first serving cell, determining whether an L2 reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch. These exemplary methods also include sending to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

[0042] In some embodiments, determining whether L2 reset is needed for the UE includes the following operations:

[0043] • determining that the L2 reset is needed based on the group identifier related to the first LTM candidate cell being different than the group identifier related to the UE’s serving entity; and • determining that the L2 reset is not needed based on the group identifier related to the first LTM candidate cell being same as the group identifier related to the UE’s serving entity. In some of the embodiments summarized above, the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, and the third RAN node is a centralized unit (CU) associated with the first and second DUs. Other features and embodiments of the exemplary methods summarized above are described herein.

[0044] Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g, base stations, eNBs, gNBs, ng-eNBs, CUs, DUs, etc.) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program 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.

[0045] These and other embodiments described herein may provide various advantages and / or benefits. For example, by keeping a C-DU informed about whether an L2 reset is needed for an incoming UE that is performing CLTM, embodiments may avoid L2 misalignment between the UE and the RAN, as well as the further consequences of UE release, failure, and / or RRC reestablishment. At a high level, UE connectivity may be maintained after CLTM without interruption, excess signaling overhead, and excess UE energy consumption.

[0046] These and other objects, features, and advantages of embodiments of the present disclosure will become apparent upon reading the following Detailed Description in view of the Drawings briefly described below.

[0047] BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 shows a high-level view of an exemplary 5G / NR network architecture.

[0049] Figure 2 shows exemplary NR user plane (UP) and control plane (CP) protocol stacks.

[0050] Figure 3 shows a signaling diagram for an exemplary LTM cell switch procedure.

[0051] Figures 4-7 (each of which includes parts A and B) show signaling diagrams of various inter-DU / intra-CU conditional LTM procedures by a UE, according to various embodiments of the present disclosure..

[0052] Figure 8 shows a flow diagram of an exemplary method for a UE (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0053] Figure 9 shows a flow diagram of an exemplary method for a second RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0054] Figure 10 shows a flow diagram of an exemplary method for a third RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure. Figure 11 shows a communication system according to various embodiments of the present disclosure.

[0055] Figure 12 shows a UE according to various embodiments of the present disclosure.

[0056] Figure 13 shows a network node according to various embodiments of the present disclosure.

[0057] Figure 14 is a block diagram of a virtualization environment in which functions implemented by some embodiments of the present disclosure may be virtualized.

[0058] DETAILED DESCRIPTION

[0059] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided as examples to convey the scope of the subject matter to those skilled in the art.

[0060] 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.

[0061] Furthermore, the following terms are used throughout the description given below:

[0062] • 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 (e.g., micro, pico, 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. • 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), a PDN 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.

[0063] • 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”.

[0064] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0065] • 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.

[0066] • 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.

[0067] 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. 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.

[0068] 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.

[0069] 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 handles transfer over the NR radio interface, e.g., via modulation, coding, antenna mapping, and beam forming.

[0070] 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.

[0071] 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 ceil reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. An NR UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, NR RRC 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 UTE.

[0072] Fourth-generation (4G) Eong-Term Evolution (LTE) introduced dual connectivity (DC) whereby a UE can be 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). In particular, a UE is configured with a Master Cell Group (MCG) associated with the MN and a Secondary Cell Group (SCG) associated with the SN. Each cell group includes a primary cell (PCell) and may include one or more secondary cells (SCells). The PCell of the SCG is also referred to as primary SCG cell (PSCell). 5G / NR also supports various DC (or more generally, multi -connectivity) configurations for UEs.

[0073] Seamless mobility is a key feature of 3GPP radio access technologies (RATs). 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 L3 (e.g., RSRP) measurements and involves RRC signaling to change PCell and PSCell (e.g., when dual connectivity is configured), as well as release / add SCells.

[0074] In general, a RAN (e.g., NG-RAN) configures a UE in RRC_CONNECTED state 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 target cell (e.g., PCell change). 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 RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by L3 and the RRC messages exchanged are part of L3.

[0075] These reconfigurations are prepared in advance by a target RAN node serving the target cell, upon a request from the UE’s serving RAN node. This request is transmitted over the Xn interface in case the serving and target RAN nodes are part of the NG-RAN. The reconfiguration in the handover command takes into account the UE’s existing RRC configuration in its current serving cell (also referred to as “source cell”), which are provided in the inter-node request. In some cases, the reconfiguration can be provided as a “delta” to the UE’s existing configuration in the source cell, which reduces the size of the handover command. The reconfiguration provided by the target RAN node contains all information the UE needs to access the target cell, e.g., random access configuration, a new cell radio network temporary identifier (C-RNTI) assigned to the UE in the target cell, and parameters enabling the UE to calculate security keys that it can use when communicating with the target cell (including sending a handover complete message).

[0076] In general, UE nobility in RRC CONNECTED state is network -based since the network has the most information about conditions such as cell loading (UEs and / or traffic), available node resources (e.g., processing), available frequencies, etc. 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 will declare radio link failure (RLF) or handover failure (HOF).

[0077] To address various difficulties with handovers and other mobility procedures, 3GPP Rel- 16 includes support for conditional handover (CHO) and SN-initiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 includes support for various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood that it is successfully transferred. The execution of the mobility command is done at later point in time based on an associated execution condition.

[0078] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconfiguration message (in NR) or an RRCConnectionReconfiguration message (in LTE). When the UE later detects the execution condition(s) associated with one of the earlier-received reconfigurations, the UE executes the associated reconfiguration to perform the mobility procedure (e.g., HO, PSCell change, PSCell addition, etc.).

[0079] Even so, conditional (e.g., CHO) and non -conditional (e.g., HO) are triggered by layer 3 (L3) measurements and involves radio resource control (RRC) signaling to change PCell and PSCell (e.g., when DC is configured), as well as release / add SCells as needed. Moreover, conventional 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.

[0080] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). In LTM, a UE is pre -configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger the LTM cell switch procedure by sending the UE an LTM cell switch command.

[0081] 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 RRCReconfiguration message or a portion thereof, such as one or more lEs / fields / parameters (e.g., CellGroupConfig IE). The UE performs measurements on configured 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 configured LTM candidate cells. This triggering is done by transmitting an LTM cell switch command to the UE in lower layer signaling (e.g., DCI or MAC CE). Based on this command, the UE connects to the associated LTM candidate cell and uses the previously received RRC configuration for this cell.

[0082] Regarding terminology, a candidate cell configured for a UE mobility procedure (e.g., LTM or L3) becomes a target cell when the UE performs the mobility procedure, either due to a command from the UE’s current serving RAN node or due to execution conditions being met at the UE. As such, in the context of conditions. As such, the terms “candidate,” “target,” and “candidate (target)” may be used interchangeably when referring to that cell or to the RAN node serving that cell. Likewise, the UE’s serving cell becomes when the UE performs the mobility procedure, and so the terms “source,” “serving,” and “serving (source)” may be used interchangeably when referring to that cell or to the RAN node serving that cell.

[0083] Eigure 3 shows a signaling diagram for an exemplary LTM cell switch procedure. Although the operations are shown with numerical labels, this is done to facilitate explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

[0084] In operation 1, the UE sends a MeasurementReport message to the gNB. Based on this message, the gNB decides to configure LTM for the UE and initiates preparation of one or more LTM candidate cells. In operation 2, the gNB sends an RRCReconfiguration message to the UE including LTM candidate cell configurations of one or more candidate cells. In operation 3, the UE stores the received LTM candidate cell configurations and transmits an RRCReconfigurationComplete message to the gNB.

[0085] Since a goal of LTM is to reduce interruption time for UE data transmissions, the UE needs to be ready to communicate with an LTM candidate 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 LTM candidate cell and / or monitor a DL control channel (e.g., PDCCH) from the LTM candidate 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 TCI state for the cell. Likewise, in the case of inter-DU LTM, 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 a SR from the UE.

[0086] The UE performs operations 4a-b before receiving any LTM cell switch command. In operation 4a, the UE performs early DL synchronization with the configured LTM candidate cells. Each LTM candidate cell configuration may include a configuration for early DL synchronization. In particular, this configuration for early DL synchronization may include a MAC CE that triggers early TCI state activation in the LTM candidate cell.

[0087] In operation 4b, when UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. Otherwise, in operation 4b, the UE performs early TA acquisition with the candidate cell(s) as requested by the network. This is done via contention-free random access (CFRA) triggered by a physical DL control channel (PDCCH) order from the source cell, following which the UE sends a RA preamble towards the indicated LTM candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the LTM candidate cell(s), the UE doesn’t receive RA response (with TA) from the LTM candidate cell; instead, TA for the LTM candidate cell is indicated in a subsequent LTM cell switch command. Similarly, the UE doesn’t maintain a TA timer for the LTM candidate cell but relies on the RAN to guarantee the TA validity.

[0088] In operation 5, the UE performs LI measurements on the configured LTM candidate cells and transmits LI measurement reports to the gNB. The UE performs such LI measurement as long as the LTM candidate cell configurations received in operation 2 remain applicable.

[0089] In operation 6, the gNB decides to trigger an LTM cell switch for the UE to one of the configured LTM candidate cells ( “target cell”) and transmits an LTM cell switch command, which is a MAC CE that includes an identifier (e.g., index) of the corresponding LTM candidate cell configurations provided to the UE in operation 2. The MAC CE may also include an identifier of a beam (e.g., a TCI State ID) by which the UE should access the target cell.

[0090] The gNB selects the identified beam based on the LI measurements reported by the UE. These are typically per-beam measurements, such as LI reference signal received power (RSRP) for synchronization signal / PBCH blocks (SSBs). These measurements may not be L3 filtered, so they may change relatively frequently as UE radio conditions change. As such, it may be challenging for the gNB to determine the optimal beam to indicate to the UE in the LTM cell switch command.

[0091] Upon receiving the LTM cell switch command, the UE monitors PDCCH on the indicated beam of the target cell. In other words, the UE considers the TCI state for the indicated beam / TCI state ID to be “activated” when performing the LTM cell switch. The UE also applies the configuration identified in the MAC CE.

[0092] In operation 7, if UE does not have valid TA of the target cell, the UE performs a RA procedure towards the target cell,. The UE performs CFRA if the LTM cell switch command contains the necessary information, as specified in clause 6.1.3.xy of 3GPP TS 38.321 (vl7.7.0). In operation 8, the UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to the gNB via the target cell. If the UE has performed a RA procedure in operation 7, the UE considers that LTM cell switch execution is successfully completed when the RA procedure is successfully completed. For RACH-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the gNB has successfully received its first UL data. The UE determines successful reception of its first UL data by receiving a PDCCH addressing the UE’s C-RNTI in the target cell, which schedules a new transmission following the first UL data. The PDCCH carries either a DL assignment or an UL grant addressing the same HARQ process as the first UL data.

[0093] The split CU / DU architecture shown in Figure 1 also supports LTM, 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 source DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell for LTM is a cell served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). Since the procedure shown in Figure 3 involves a single gNB, it can also be considered an intra-CU LTM cell switch.

[0094] In contrast, an inter-CU (or inter-gNB) LTM procedure involves a cell switch from a source cell served by a first CU / gNB to a candidate (target) cell served by a second CU / gNB. In addition to the operations described above in relation to Figure 3, UE actions performed during an inter-CU LTM cell switch procedure may also include other actions such as refresh of security keys. As such, an inter-CU LTM configuration may include the same information as an intra-CU LTM configuration as well as one or more of the following:

[0095] • Information needed to perform security key refresh, e.g. MasterKeyUpdate IE or a RadioBearerConfig IE that includes SecurityConfig with SecurityAlgorithmConfig

[0096] • Indication to perform L2 / PDCP re-establishment; and

[0097] • Indication to perform a full configuration, e.g., RRC field fullConfig. As mentioned above, one of the reasons LTM has lower latency than L3 mobility is avoidance of complete L1 / L2 resets. However, there may be some situations in which an L2 reset is required during LTM. In this context, “L2 reset” refers to full or partial MAC reset, RLC reestablishment, PDCP data recovery, PDCP re-establishment, or any combination thereof.

[0098] Consider the split CU / DU architecture in which lower layers (including L2) are implemented by the DU. If the UE is performing an intra-CU / inter-DU LTM cell switch, the C- DU serving the candidate (target) cell is different from the S-DU serving the UE’s source cell. In such case, the C-DU does not have corresponding L2 entities for the UE prior to the LTM cell switch, and thus cannot continue running these L2 entities after the LTM cell switch. In this case, the UE must perform an L2 reset in conjunction with the LTM cell switch. In contrast, an L2 reset is generally not required for intra-DU LTM cell switches.

[0099] In Rel-18 LTM, a UE determines whether to perform a L2 reset during an LTM cell switch by comparing to group identifiers (IDs) assigned to the source and candidate (or target) cells for the LTM cell switch. Lor example, two LTM candidate cells served by the same DU may be assigned to the same “no reset group” and given the “no reset ID” associated with that group, also referred to as a “group ID.”. As another example, two LTM candidate cells served by different DUs may be assigned to the same “no reset group” and given the same group ID, so long as the two DUs have common access to the same L2 entities. In the following, the term “group” will be used as an abbreviated reference to “no reset group” unless expressly stated otherwise. Likewise, the terms “group ID” or “ID” will be used as abbreviated references to “no reset ID” unless expressly stated otherwise

[0100] In particular, the UE RRC variable VarLTM-ServingCellNoResetID stores the group ID assigned to the UE’ s serving cell, based on which the UE determines whether an L2 reset is needed upon an LTM cell switch procedure. During LTM cell switch to a candidate (target) cell, the UE checks its stored VarLTM-ServingCellNoResetID against an Itm-NoResetID of the target cell, which is part of the LTM candidate cell configuration. If the two IDs match, the UE does not perform L2 reset in conjunction with the LTM cell switch. If the two IDs do not match, the UE performs L2 reset and updates its stored VarLTM-ServingCellNoResetID with Itm-NoResetID of the target cell.

[0101] While this ID-based determination is relatively straightforward for the UE, the corresponding determination by C-DU requires additional information. In Rel-18 LTM, it is assumed that the C-DU is always aware of when the source cell of an incoming UE is not from a source cell provided by that C-DU, i.e., an inter-DU LTM cell switch where the S-DU is different from the C-DU. Based on this information, the C-DU performs L2 reset for the incoming UE. On the other hand, during an intra-DU LTM cell switch in which the S-DU and the C-DU are identical, the S / C-DU does not perform L2 reset for the UE.

[0102] In Rel-18 LTM, the C-DU is made aware of this information in one of two ways. First, various DUs may be informed in advance (e.g. by CU) about group IDs assigned to respective LTM candidate cells, and thus can compare group IDs in a similar way as the UE. Second, the C- DU may be informed by the S-DU whether the UE’s LTM cell switch is done with or without L2 reset. In either case, when the C-DU is notified by the S-DU that an LTM cell switch has been triggered for the UE, the C-DU is aware of whether the UE performs L2 reset and can take the corresponding action.

[0103] However, CLTM introduces some difficulties related to a C-DU determining whether L2 reset is needed for an incoming UE. For example, the UE’s S-DU is not aware of the UE triggering LTM cell switch to a candidate (target) cell based on the execution condition, so the S-DU is unable to notify the C-DU (e.g., via a CELL SWITCH NOTIFICATION message). Thus, the C- DU is initially unaware of an incoming UE’s source cell and S-DU, and thus is unable to determine based on group ID information whether an L2 reset is needed for the incoming UE. This lack of information can result in L2 misalignment with the incoming UE, which in turn may cause the serving CU to release the UE or the UE to experience a failure and trigger RRC re-establishment. Both outcomes result in relatively long connectivity interruptions to the UE, increased signaling overhead, and increased UE energy consumption

[0104] Accordingly, embodiments of the present disclosure address these problems and / or issues by various techniques that informing a C-DU that provides a candidate (target) for a UE’s CLTM procedure, whether the UE has performed an L2 reset in conjunction with an LTM cell switch to the candidate (target) cell. Based such information, the C-DU can perform (or refrain from performing) corresponding L2 reset operations.

[0105] Embodiments of the present disclosure can provide various advantages and / or benefits. For example, by keeping a C-DU informed about whether an L2 reset is needed for an incoming UE that is performing CLTM, embodiments may avoid L2 misalignment between UE and RAN and the further consequences of UE release, failure, and / or RRC re-establishment. As such, UE connectivity may be maintained after CLTM without interruption, excess signaling overhead, and excess UE energy consumption.

[0106] 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,” “L1 / 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.

[0107] 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 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.

[0108] The term “LTM candidate cell” refers to a cell for which the UE is configured for LTM, specifically a cell the UE can move to in a LTM cell switch procedure in response to receiving an LTM cell switch command. An LTM candidate cell may also be referred to herein as “candidate cell”, “(LTM) candidate, “mobility candidate”, “non-serving cell”, “additional cell”, “(LTM) target candidate cell”, “(LTM) target candidate”, and comparable terms. A UE may perform and report measurements (e.g., CSI measurements) on an LTM candidate cell, based on which the UE’s serving RAN node may make an informed decision about which beam (or TCI state) and / or cell to switch the UE. An LTM candidate cell may be a candidate to be a target PCell or PSCell, or an SCell of a cell group (e.g., MCG SCell). In the case of LTM fast recovery, when a failure is detected and the UE selects an LTM candidate cell, the UE performs an LTM cell switch towards the selected LTM candidate cell (e.g., by applying the associated LTM candidate cell configuration) rather than performing RRC re-establishment.

[0109] 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 an LTM cell switch command triggers the UE to change to another cell group configuration of the same type (e.g., another MCG configuration). Lor 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).

[0110] 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 RRCReconfiguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0111] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconfiguration 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”.

[0112] 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 signaled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0113] 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.

[0114] The term “LTM configuration” refers to a data structure that is used for or related to UE LTM operations, and may include one or more of the following elements (non-exclusive):

[0115] • an LTM candidate cell configuration, such as one or more of the following for an LTM candidate cell: o lower layer information, such as Ll / PHY configuration, L2 / MAC / RLC configuration, cell group configuration, serving cell configuration, etc.; and o higher layer information, such as L3 / RRC parameter and / or timer values, PDCP configuration, radio bearer configuration, L3 / RRC measurement configuration, etc.;

[0116] • a measurement configuration, e.g., measurements for LTM, measurement reports for LTM, CSI resource configuration for LTM, CSI report configuration for LTM, etc.;

[0117] • a configuration for early DL synchronization, e.g., for early TCI state activation;

[0118] • a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

[0119] • a configuration 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.).;

[0120] • additional information needed for an intra-CU / gNB LTM cell switch procedure.

[0121] 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). 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. furthermore, an LTM cell switch 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. More generally, embodiments are not limited to cells but are applicable to any UE switch from a first (or source) set of radio resources to a second (or target) set of radio resources.

[0122] Embodiments will now be described in more detail. In some embodiments that may be referred to as “UE centric,” during a CLTM procedure, the UE indicates to the C-DU whether the UE performs L2 reset in conjunction with LTM cell switch to the candidate (target) cell served by the C-DU. Based on such information, the C-DU can perform (or refrain from performing) corresponding L2 reset operations. For example, the UE selectively performs L2 reset based on a comparison of the group (or “no reset”) IDs assigned to the source and candidate (target) cells, and informs the C-DU of whether the L2 reset is performed and / or the result of the group ID comparison.

[0123] In some of these embodiments, the indication by the UE to the C-DU can be or include one or more of the following:

[0124] • An explicit indication whether L2 reset has been performed;

[0125] • An identifier associated with the S-DU, e.g., serving cell index, cell index, cell global identity (CGI), gNB identifier, S-DU identifier, etc.

[0126] • the UE’s stored Itm-ServingCellNoResetID or other such group ID associated with the source cell of the LTM procedure;

[0127] • an identifier of an LTM candidate cell configuration used for the source cell, i.e., in case the source cell was also an LTM candidate cell;

[0128] • an identifier of the LTM candidate cell that is the target cell for the LTM cell switch. In other of these embodiments, the indication by the UE to the C-DU can be sent during a RA procedure to the candidate (target) cell, e.g., using a specific RA configuration. For example, the UE may indicate whether L2 reset has been performed by using a specific RA preamble, a specific RA preamble format, and / or one or more specific time / frequency (T / F) RA resources. The specific RA configuration (e.g., RA preamble) to be used for this indication may be configured by the CU, the S-DU, or the C-DU (e.g., via broadcast), or may be pre-determined by specification.

[0129] In other of these embodiments, the indication by the UE to the C-DU can be (or be included in) a LI message sent to the C-DU prior to sending an indication that the LTM cell switch has been completed. For example, the LI message may be any existing or newly-defined uplink control information (UCI) message. As another example, the LI message may a scheduling request (SR), either an existing format extended to include new information or a new format specifically defined for this purpose.

[0130] In other of these embodiments, the indication by the UE to the C-DU can be (or be included in) a MAC protocol data unit (PDU) or control element (CE) sent to the C-DU prior to sending an indication that the LTM cell switch has been completed. For example, a buffer status report (BSR) MAC CE may be used, either an existing format extended to include new information or a new format specifically defined for this purpose.

[0131] In other of these embodiments, the indication by the UE to the C-DU can be (or be included in) an RRC message. For example, the RRC message may be an RRCReconfigurationComplete message sent by the UE to indicate that the LTM cell switch has been successfully completed.

[0132] Alternately, the RRC message may be a different message (e.g., UEAssistancelnformatiori) sent by the UE prior to a message indicating that the LTM cell switch has been successfully completed. Other existing or newly-defined RRC messages may also be used.

[0133] In various embodiments, the explicit indication of whether L2 reset has been performed can be one or more of the following:

[0134] • an enumerated field where “true” indicates that L2 reset has been performed and “false” indicates that L2 reset has not been performed (or vice versa).

[0135] • an enumerated field whose presence indicates that L2 reset has been performed and whose absence indicate that L2 reset has not been performed (or vice versa).

[0136] • a 1 -bit field where “1” indicates that L2 reset has been performed and “0” indicates that L2 reset has not been performed (or vice versa).

[0137] • a Boolean field where “true” indicates that L2 reset has been performed and “false” indicates that L2 reset has not been performed (or vice versa). Although various embodiments discussed above are based on the UE sending the indication the C-DU, it is also possible that the UE sends the indication about L2 reset to the S- DU, which may in turn send it to the CU and / or to the C-DU.

[0138] In other embodiments that may be referred to as “DU centric,” a C-DU that has configured one or more CLTM candidate cells for a UE receives information about its own “no reset” group assignments and those for other C-DUs that have provided CLTM candidate cells for the UE. Alternately, the group assignments may be associated with cell groups provided by the respective C-DUs. The C-DU also receives updates about which DU is the UE’s current S-DU. When the UE performs CLTM execution to a candidate cell provided by the C-DU (e.g. when the C-DU receives a scheduling request and / or random access preamble from the UE), the C-DU is aware of the S-DU for the incoming UE and the S-DU’s group assignment. Based the S-DU’s and its own group assignments, the C-DU can determine the whether the UE will perform L2 reset due to group change and, consequently, whether the C-DU needs to perform corresponding L2 reset operations.

[0139] In some embodiments, the C-DU is informed about the UE’s current S-DU when the UE accesses that DU. In other embodiments, the C-DU is informed about the UE’s current S-DU when the C-DU is requested by the CU to configure one or more candidate cells for (C)LTM. In other words, the C-DU is informed about the UE’s S-DU when requested by the CU to prepare LTM candidate cell configurations for the UE.

[0140] For example, a UE in a serving (source) cell provided by the S-DU is configured with conditional LTM candidate cells provided by C-DU(l), C-DU(2), C-DU(3), and C-DU(4). In this example, C-DU(4) is identical to the S-DU. C-DU(l) and C-DU(2) are assigned the same “no reset” ID corresponding to group A, while C-DU(3) and C-DU(4) are assigned the same “no reset” ID corresponding to group B. All C-DUs are aware of their own and other C-DUs’ group assignments. For example, the group information may be obtained once and remain the same as long as context is stored at the C-DUs.

[0141] C-DU(l), C-DU(2), and C-DU(3) are informed that the UE is currently connected to the S-DU / C-DU(4), such as when UE accessed the S-DU and / or when (C)LTM was being configured for the UE. When the UE performs CLTM execution to a candidate cell provided by C-DU(l), C- DU(I) in group A is aware that the UE is incoming from the S-DU in group B and, consequently, the UE will perform L2 reset due to group change. C-DU(l) performs corresponding L2 reset for the UE. Additionally, C-DU(2), C-DU(3), and C-DU(4) are informed that the UE is currently connected to S-DUZC-DU(l), which facilitates subsequent CLTM procedures by the UE. In other words, C-DUs that have provided LTM candidate configurations for the UE need to be informed (e.g., by CU) every time the UE changes S-DU, so that each C-DU can determine whether it needs to perform corresponding L2 reset operations if the UE performs an LTM cell switch to a candidate cell provided by that C-DU.

[0142] As a more specific example, C-DU(l) detects the incoming UE and transmits an Access Success message to the CU (e.g. over F1AP). In response to that message, the CU transmits the indication of the UE’s S-DU change to the other C-DU(s), i.e., C-DU(2), C-DU(3), and C-DU(4). Since the L2 reset group information is available in these C-DUs, they are able to determine whether L2 reset is required or not if / when the UE executes subsequent CLTM to a candidate cell provided by one of them, since they know where the UE is coming from C-DU(l).

[0143] Continuing this example, the UE executes subsequent CLTM to a candidate cell provided by C-DU(2) from the source cell provided by C-DU(l), including accessing the candidate cell by sending a SR over PUCCH, uplink control information (UCI) over a pre -configured grant, and / or a RA preamble using RA resources. C-DU(2) detects the incoming UE and transmits an Access Success message to the CU (e.g. over F1AP). In response to that message, the CU transmits the indication of the UE’s S-DU change to the other C-DU(s), i.e., C-DU(l), C-DU(3), and C-DU(4). Since C-DU(2) is aware that the UE is incoming from C-DU(l) assigned to the same group, C- DU(2) determines that the UE does not perform L2 reset and that corresponding L2 reset operations are not required.

[0144] To summarize the above-described embodiments, a C-DU that provides one or more LTM candidate cell configurations for a UE performs the following operations:

[0145] • obtaining information about the UE’s current S-DU and / or serving cell, based on which the C-DU is prepared to determine whether corresponding L2 reset operations are needed in case the UE access one of the C-DU’s LTM candidate cells;

[0146] • upon detecting that the UE accesses one of the C-DU’s LTM candidate cells, determining whether the UE performed L2 reset and whether corresponding L2 reset operations are needed; and

[0147] • sending an indication to the CU that the C-DU is now the UE’s S-DU, which facilitates subsequent (C)LTM for the UE.

[0148] Figures 4-6 show signaling diagrams of various inter-DU / intra-CU conditional LTM procedures by a UE (460), according to various embodiments of the present disclosure. In particular, Figures 4-6 are based on the same arrangement discussed in the examples above, namely a UE in a serving (source) cell provided by an S-DU is configured with conditional LTM candidate cells provided by C-DU(l), C-DU(2), C-DU(3), and C-DU(4), labelled respectively as 410-440. All ofthese DUs are associated with the same CU (450). Moreover, C-DU(4) is identical to the UE’s initial S-DU. C-DU(l) and C-DU(2) are assigned the same “no reset” ID corresponding to group A, while C-DU(3) and C-DU(4) are assigned the same “no reset” ID corresponding to group B.

[0149] Each of Figures 4-6 is shown in two parts, A and B. Although some operations shown in Figures 4-6 are given numerical labels, this is done to facilitate explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

[0150] Figure 4 will now be described in more detail. In operation 1, the UE is configured (e.g., by CU via its S-DU) with (C)LTM candidate cells provided by C-DU(3), C-DU(2), C-DU(l), and is S-DU / C-DU(4). In operation 2, each of the C-DUs that provided a candidate cell for the UE is informed (e.g., CU) about the following:

[0151] • (2a) That the UE is currently in a serving (source) cell provided by S-DU / C-DU(4);

[0152] • (2b) That C-DU(l) and C-DU(2) (including the LTM candidate cells provided by these DUs) are assigned to no L2 reset group A; and

[0153] • (2c) that C-DU(3) and C-DU(4) (including the LTM candidate cells provided by these DUs) are assigned to no L2 reset group B.

[0154] In accordance with embodiments discussed above, LTM cell switches between cells provided by DUs assigned the same no reset group do not require L2 reset, while LTM cell switches between cells provided by DUs assigned different no reset groups (or IDs) require L2 reset. One option for operations 2b-2c is for the CU to provide group IDs associated with C-DUs, so that LTM cell switch between LTM candidate cells provided by C-DUs associated with the same group ID do not require L2 reset. Another option for operations 2b-2c is for the CU to provide group IDs associated with LTM candidate cells, so that LTM cell switch between LTM candidate cells associated with the same group ID do not require L2 reset.

[0155] The information that the UE is currently in a serving (source) cell provided by S-DU / C- DU(4) may include an identifier of the serving cell and / or an identifier of S-DU / C-DU(4), and may be provided in operation 2a in various ways. In some embodiments, the CU can send this information to each DU in a message (e.g., UE Context Modification Required, UE Context Setup Request) that requests the DU to configure one or more CLTM candidate cells for the UE.

[0156] In some variants, this request message from the CU to each DU can also include the no reset group assignments for the DU and other C-DUs that have configured CLTM candidate cells for the UE (or information that allows the DU to derive these assignments). In other words, the operations 2a-c in Figure 4 can be combined into a single message to each C-DU.

[0157] In other variants, this request message from the CU to each DU does not include the no reset group assignments, such as when the CU has not determined which of the DUs will accept their requests to configure CLTM candidate cells. Instead, after the set of C-DUs and CLTM candidate cells for the UE is determined, the CU sends each C-DU a second message (e.g., UE Context Modification Required, UE Context Setup Request) that includes the no reset group assignments for the respective C-DUs (or information that allows each C-DU to derive these assignments)

[0158] In operation 3, the UE detects fulfillment of an LTM execution condition associated with an LTM candidate cell provided by C-DU(l). In operation 4, the UE accesses this LTM candidate cell, e.g., by transmitting a SR via PUCCH and / or a PRACH preamble via RA resources.

[0159] In operation 5, C-DU(l) detects UE access to its LTM candidate cell and is aware (based on operation 2) that the UE is incoming from a source cell provided by S-DU / C-DU(4). Based on the no reset group information also received in operation 2, C-DU(l) is also aware that it is assigned to a different no reset group than S-DU / C-DU(4), such that the UE will perform an L2 reset based on this difference. Based on this determination, C-DU(l) knows that the UE’s S-DU is of a different L2 reset group (group B) compared to C-DU(l) (group A), so it determines that the UE performed (or will perform) L2 reset and thus performs corresponding L2 reset operations for the UE in the candidate (target) cell.

[0160] In operation 6, C-DU(l) sends the CU an Access Success message to indicate that the UE executed CLTM. For example, the message includes a cause value associated with CLTM execution and / or an identity of the candidate (target) cell for the UE’s successful LTM cell switch. In operation 7, the UE sends C-DU(l) an RRCReconfigurationComplete message to the C-DU(l), signifying successful execution of the LTM cell switch. In operation 8, C-DU(l) sends the CU a UL RRC MESSAGE TRANSFER message that includes the RRCReconfigurationComplete message from the UE.

[0161] In response to the Access Success message from C-DU(l) (operation 6) or the RRCReconfigurationComplete from the UE via C-DU(l) (operation 8), the CU indicates to C- DU(2), C-DU(3), and C-DU(4) that the UE is currently served by C-DU(l) (now S-DU), which facilitates subsequent CLTM procedures by the UE. For example in operations 9a-9c, the CU sends respective indications to C-DU(4), C-DU(3), and C-DU(2), based on which these DUs update their context information for the UE.

[0162] Subsequently, while being served by C-DU(l), the UE detects fulfillment of an LTM execution condition associated with an LTM candidate cell provided by C-DU(2). Subsequent operations are similar to operations 4-9 described above, except in relation to C-DU(2) rather than C-DU(l). For example, the CU sends to C-DU(4), C-DU(3), and C-DU(l) respective indications that the UE is currently served by C-DU(2) (now S-DU), which facilitates subsequent CLTM procedures by the UE.

[0163] Figure 5 shows a variant of the embodiments illustrated by Figure 4. The operations shown in Figure 5 are substantially identical to the operations shown in Figure 4, except that instead of indicating the UE’s current S-DU in operations 9a-c (and later operations), the CU indicates the no reset group (e.g., group ID) to which the UE’s current serving DU is assigned. When combined with group assignments in operation 2b-c, this information enables each C-DU to know whether E2 reset is needed for an incoming UE.

[0164] Figure 6 shows another variant the embodiments illustrated by Figure 4. The operations shown in Figure 6 are substantially identical to the operations shown in Figure 4, except that instead of indicating the UE’s current S-DU in operations 9a-c (and later operations), the CU only sends an indication when a UE’s current S-DU is assigned to a different no reset group than the UE’s previous S-DU. In Figure 6 operations 9a-c, the CU sends indications to C-DU(4), C-DU(3), and C-DU(2) that the UE has switched from an S-DU assigned to group A to an S-DU assigned to group B. After the UE’s subsequent LTM cell switch between S-DUs assigned to group B, however, the CU does not send any indications to the C-DUs. As such, this variant may reduce CU-DU signaling compared to other variants shown in Figures 4-5.

[0165] In other embodiments that may be referred to as “CU centric,”, a CU is associated with multiple DUs, one of which is a UE’s current S-DU and one or more of which are C-DUs that have configured one or more CLTM candidate cells for the UE. The CU may provide these configurations to the UE, according to known techniques. The CU is aware of the respective “no reset” group assignments for the S-DU and C-DUs and, in some embodiments, may have performed the group assignments. Each time the UE performs a cell switch based on CLTM, the C-DU that provides the target cell informs the CU of the change. Based on the CU’s knowledge of the group IDs of the UE’s previous S-DU and the C-DU / new S-DU, the CU determines whether the UE will perform L2 reset and informs the C-DU of result of the group ID comparison and / or whether corresponding L2 reset operations are needed for the UE.

[0166] In some of these embodiments, when the CU determines that the UE’s previous S-DU and the C-DU / new S-DU are in the same L2 no reset group, the CU may also send the C-DU information that facilitates CLTM execution without L2 reset, such as L2 context information (e.g. variables, state information, counters, etc.) from the S-DU.

[0167] Consider the example mentioned above, in which a UE in a serving (source) cell provided by the S-DU is configured with conditional LTM candidate cells provided by C-DU(l), C-DU(2), C-DU(3), and C-DU(4). In this example, C-DU(4) is identical to the S-DU. C-DU(l) and C-DU(2) are both assigned the same “no reset” ID corresponding to group A, while C-DU(3) and C-DU(4) are both assigned the same “no reset” ID corresponding to group B. The CU is aware of these group assignments.

[0168] The CU is also aware that the UE is initially connected to a serving cell provided by S- DU / C-DU(4), based on communication with that DU. When the UE performs CLTM execution to a candidate cell provided by C-DU(l), C-DU(l) sends an indication of this change to the CU, such as in an access success message. Based on its knowledge that C-DU(l) is in group A and that the S-DU is in group B, the CU determines that the UE will perform L2 reset due to group change, and sends an indication of this status to C-DU(l), which can act accordingly as described above. In addition, the CU may perform certain E2 reset operations (e.g., PDCP re-establishment) for L2- type protocol layers that are hosted by the CU rather than the DUs.

[0169] In these CU-centric embodiments, since the CU provides this information only to C-DU(l) that provides the candidate (target) cell for the ETM cell switch, other C-DUs do not need to be kept informed about updates to the UE’s serving cell / C-DU as in other embodiments described above. Rather, the C-DU that becomes the UE’s new S-DU needs to inform the CU of the change, based on which the CU can determine whether the UE performs L2 reset and indicate to that C- DU whether corresponding L2 reset operations are required. This may reduce CU-DU signaling required for CLTM procedures.

[0170] Figure 7 shows a signaling diagram of an inter-DU / intra-CU conditional LTM procedure by a UE, according to some embodiments of the present disclosure. In particular, Figure 7 is based on the same arrangement discussed in the examples above, namely a UE in a serving (source) cell provided by an S-DU is configured with conditional LTM candidate cells provided by C-DU(l), C-DU(2), C-DU(3), and C-DU(4). Moreover, C-DU(4) is identical to the UE’s initial S-DU. C- DU(1) and C-DU(2) are assigned the same “no reset” ID corresponding to group A, while C- DU(3) and C-DU(4) are assigned the same “no reset” ID corresponding to group B. The respective entities are assigned the same reference numbers as the corresponding entities in Figures 4-6.

[0171] Figure 7 is shown in two parts, A and B. Although some operations shown in Figure 7 are given numerical labels, this is done to facilitate explanation rather than to require or imply any particular operational order, unless expressly stated otherwise.

[0172] In operation 1, the UE is configured (e.g., by CU via its S-DU) with (C)LTM candidate cells provided by C-DU(3), C-DU(2), C-DU(l), and is S-DU / C-DU(4). In operation 2, the CU determines the following:

[0173] • (2a) That the UE is currently in a serving (source) cell provided by S-DU / C-DU(4);

[0174] • (2b) That C-DU(l) and C-DU(2) (including the LTM candidate cells provided by these DUs) are assigned to no L2 reset group A; and

[0175] • (2c) that C-DU(3) and C-DU(4) (including the LTM candidate cells provided by these DUs) are assigned to no L2 reset group B.

[0176] The UE may determine this information based on information obtained from the C-DUs during configuration of CLTM candidate cells for the UE. In accordance with embodiments discussed above, LTM cell switches between cells provided by DUs assigned to the same no reset group (or ID) do not require L2 reset, while LTM cell switches between cells provided by DUs assigned to different no reset groups (or IDs) require L2 reset. One option is for the CU to assign group IDs to the respective C-DUs, so that LTM cell switch between LTM candidate cells provided by C-DUs associated with the same group ID do not require L2 reset. Another option is for the CU to assign group IDs to LTM candidate cells, so that LTM cell switch between LTM candidate cells associated with the same group ID do not require L2 reset.

[0177] The determination that the UE is currently in a serving (source) cell provided by S-DU / C- DU(4) may be based on an identifier of the serving cell and / or an identifier of S-DU / C-DU(4), and may be made in various ways. For example, the CU may receive a message (e.g. Access Success) from the S-DU when the UE has accessed a cell provided by the S-DU in an LTM, CLTM, or L3 mobility procedure.

[0178] In operation 3, the UE detects fulfillment of an LTM execution condition associated with an LTM candidate cell provided by C-DU(l). In operation 4, the UE accesses this LTM candidate cell, e.g., by transmitting a SR via PUCCH and / or a PRACH preamble via RA resources. In operation 5, C-DU(l) sends the CU an Access Success message to indicate that the UE executed CLTM. For example, the message includes a cause value associated with CLTM execution and / or an identity of the candidate (target) cell for the UE’s successful LTM cell switch.

[0179] In operation 6, the CU is aware that that the UE now served by a cell provided by C-DU(l) (now the UE’s S-DU) was previously served by a cell provided by C-DU(4). Based on the no reset group information determined in operation 2, the CU is also aware that C-DU(l) is assigned to a different no reset group than C-DU(4), such that the UE will perform an L2 reset based on this difference. Based on this determination, the CU sends to C-DU(l) an indication to perform corresponding L2 reset operations (e.g., MAC reset, RLC re-establishment) for the UE in its serving cell. In addition, the CU may perform certain L2 reset operations (e.g., PDCP reestablishment) for L2-type protocol layers that are hosted by the CU rather than the C-DU(l).

[0180] In operation 8, the UE sends C-DU(l) an RRCReconfigurationComplete message to the C-DU(l), signifying successful execution of the LTM cell switch. In operation 9, C-DU(l) sends the CU a UL RRC MESSAGE TRANSFER message that includes the RRCReconfigurationComplete message from the UE.

[0181] Subsequently in operation 10, while being served by C-DU(l), the UE detects fulfillment of an LTM execution condition associated with an LTM candidate cell provided by C-DU(2). In operation 11, the UE accesses this LTM candidate cell, e.g., by transmitting a SR via PUCCH and / or a PRACH preamble via RA resources. In operation 12, C-DU(2) sends the CU an Access Success message to indicate that the UE executed CLTM. For example, the message includes a cause value associated with CLTM execution and / or an identity of the candidate (target) cell for the UE’s successful LTM cell switch.

[0182] In operation 13, the CU is aware that that the UE now served by a cell provided by C- DU(2) (now the UE’s S-DU) was previously served by a cell provided by C-DU(l). Based on the no reset group information determined in operation 2, the CU is also aware that C-DU(l) is assigned to the same no reset group as C-DU(2), such that the UE will not perform an L2 reset in relation to this LTM cell switch. As such, the CU determines that no corresponding L2 reset operations (e.g., MAC reset, RLC re-establishment, PDCP re-establishment) are needed for the UE in its serving cell.

[0183] Various features of the embodiments described above correspond to various operations illustrated in Figures 8-10, which show exemplary methods (e.g., procedures) for a UE, a second RAN node, and a third RAN node, respectively. In other words, various features of the operations described below correspond to various embodiments described above. Furthermore, the exemplary methods shown in Figures 8-10 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 8-10 show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0184] In particular, Figure 8 shows an exemplary method (e.g., procedure) for a UE configured for conditional LTM in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by a UE (e.g., wireless device) such as described elsewhere herein.

[0185] The exemplary method includes the operations of block 810, where the UE receives, from a third RAN node via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier (e.g., no reset ID) related to the LTM candidate cell, and an execution condition for LTM cell switch to the LTM candidate cell. The exemplary method also includes the operations of blocks 830-840, where based on determining that an execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node, the UE performs an LTM cell switch to the first LTM candidate cell.

[0186] The exemplary method also includes the operations of block 850, where based on the group identifier related to the first LTM candidate cell and a group identifier (e.g., no reset ID) related to the first serving cell, the UE selectively performs a layer-2 (L2) reset in conjunction with the LTM cell switch. The exemplary method also includes the operations of block 860, where the UE sends one of the following:

[0187] • to the first RAN node, an indication of whether the L2 reset will be performed in conjunction with the LTM cell switch; or

[0188] • to the second RAN node, an indication of whether the L2 reset was performed in conjunction with the LTM cell switch.

[0189] In some embodiments, the group identifier related to the first LTM candidate cell is associated with one of the following: the first LTM candidate cell, or the second RAN node that provides the first LTM candidate cell. Likewise, the group identifier related to the first serving cell is associated with one of the following: the first serving cell, or the first RAN node that provides the first serving cell.

[0190] In some embodiments, selectively performing the L2 reset based on the group identifier related to the first LTM candidate cell and the group identifier related to the first serving cell in block 850 includes the following operations, labelled with corresponding sub-block numbers:

[0191] • (851) performing the L2 reset when the group identifier related to the first LTM candidate cell is different than the group identifier related to the first serving cell; and

[0192] • (852) refraining from performing the L2 reset when the group identifier related to the first LTM candidate cell is the same as the group identifier related to the first serving cell.

[0193] In some embodiments, the group identifier related to the first serving cell is stored in a UE variable before the LTM cell switch and the exemplary method also includes the operations of block 880, where after performing the LTM cell switch, the UE updates the UE variable to store the group identifier related to the first LTM candidate cell.

[0194] In some embodiments, the indication sent in block 860 includes one or more of the following:

[0195] • an explicit indication of whether the L2 reset was or will be performed;

[0196] • an identifier of the first RAN node;

[0197] • an identifier of the first serving cell;

[0198] • an identifier of an LTM candidate cell configuration for the first serving cell;

[0199] • the group identifier related to the first serving cell; and

[0200] • an indication of whether the group identifier related to the first LTM candidate cell is the same as the group identifier related to the first serving cell

[0201] In some embodiments, the exemplary method also includes the operations of block 820, where the UE performs measurements of the first serving cell and each of the LTM candidate cells, thereby obtaining measurement values. The execution condition is fulfilled by a measurement value obtained for the first LTM candidate cell. In some embodiments, the exemplary method also includes the operations of block 870, where the UE sends to the second RAN node a message indicating that the LTM cell switch to the first LTM candidate cell has been completed. In some of these embodiments, the message is an RRCReconfigurationComplete message intended for the third RAN node and includes the indication of whether the L2 reset was performed. In other of these embodiments, the indication is sent to the second RAN node before sending the message, as or in one of the following:

[0202] • a random access (RA) message based on a RA configuration associated with L2 reset indications,

[0203] • a layer- 1 (LI) message or control information;

[0204] • a L2 protocol data unit (PDU) or control element (CE); or

[0205] • a radio resource control (RRC) message intended for the third RAN node.

[0206] In other embodiments, the indication of whether the L2 reset will be performed is sent to the first RAN node before performing the LTM cell switch.

[0207] In some embodiments, the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, and the third RAN node is a centralized unit (CU) associated with the first and second DUs.

[0208] In addition, figure 9 shows an exemplary method (e.g., procedure) for a second RAN node configured to facilitate conditional LTM for UEs, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng -eNB, DU, etc.) such as described elsewhere herein.

[0209] The exemplary method includes the operations of block 910, where the second RAN node sends, to a third RAN node, a configuration for a first LTM candidate cell provided by the second RAN node and an execution condition for LTM cell switch by a UE to the first LTM candidate cell. The exemplary method includes the operations of block 920, where the second RAN node receives and stores the following information from the third RAN node:

[0210] • a first indication of the UE’s serving entity; and

[0211] • respective group identifiers related to the following: the UE’s serving entity, the first LTM candidate cell, and one or more second LTM candidate cells for the UE.

[0212] Subsequently the second RAN node performs either first operations or second operations. The first operations include the following, labelled with corresponding block numbers:

[0213] • (930) receiving from the third RAN node a second indication that the UE’s serving entity has changed; and

[0214] • (940) updating the stored information based on the second indication.

[0215] Also, the second operations include the following, labelled with corresponding block numbers:

[0216] • (950) detecting an LTM cell switch by the UE to the first LTM candidate cell; and • (960) based on the stored information, selectively performing a layer-2 (L2) reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

[0217] In some embodiments, the first indication is of one of the following: a first serving cell provided by a first RAN node, or the first RAN node. In some embodiments, the respective group identifiers are associated with the first serving cell (i.e., the UE’s serving entity), the first LTM candidate cell, and the one or more second LTM candidate cells. In other embodiments, the respective group identifiers are associated with the first RAN node (i.e., the UE’s serving entity) that provides the first serving cell, the second RAN node that provides the first LTM candidate cell, and one or more RAN nodes that provide the one or more second LTM candidate cells.

[0218] In some embodiments, selectively performing the L2 reset based on the stored information in block 960 includes the following operations, labelled with corresponding sub-block numbers:

[0219] • (961) performing the L2 reset when the stored group identifier related to the first LTM candidate cell is different than the stored group identifier related to the first serving cell; and

[0220] • (962) refraining from performing the L2 reset when the stored group identifier related to the first LTM candidate cell is same as the stored group identifier related to the first serving cell.

[0221] In some embodiments, the second operations also include the following, labelled with corresponding block numbers:

[0222] • (970) sending to the third RAN node a third indication that the UE has performed LTM cell switch to the first LTM candidate cell; and

[0223] • (980) updating the stored information to indicate one of the following: that the first LTM candidate cell is the UE’s current serving cell, or that the second RAN node is the UE’s current serving node.

[0224] In some embodiments, the second indication that the UE’s serving entity has changed is one of the following:

[0225] • a cell identifier of the second LTM candidate cell that is now the UE’s serving cell;

[0226] • a group identifier associated with the second LTM candidate cell that is now the UE’s serving cell;

[0227] • a node identifier of a RAN node that provides the second LTM candidate cell; or

[0228] • a group identifier associated with the RAN node that provides the second LTM candidate cell.

[0229] In some of these embodiments, the second indication is received only when the group identifier related to the second LTM candidate cell is different than the group identifier related to the first serving cell. In some embodiments, the first indication is received from the first RAN node in a request for configurations for one or more LTM candidate cells for the UE. In such case, the configuration for the first LTM candidate cell and the execution condition are sent to the third RAN node in response to the request. In some of these embodiments, the respective group identifiers are also received from the first RAN node in or with the request. In other of these embodiments, the respective group identifiers are received from the third RAN node in response to sending the configuration for the first LTM candidate cell and the execution condition (e.g., in block 910).

[0230] In some embodiments, the first RAN node is a first DU, the second RAN node is a second DU, and the third RAN node is a CU associated with the first and second DUs.

[0231] In addition, figure 10 shows an exemplary method (e.g., procedure) for a third RAN node configured to facilitate conditional LTM for UEs, according to various embodiments of the present disclosure. The exemplary method can be performed by a RAN node (e.g., base station, eNB, gNB, ng -eNB, CU, etc.) such as described elsewhere herein.

[0232] The exemplary method includes the operations of block 1030, where the third RAN node determines respective group identifiers (e.g., no reset IDs) related to the following: the UE’s serving entity, a first LTM candidate cell provided by a second RAN node, and one or more second LTM candidate cells for the UE. The exemplary method also includes the operations of block 1040, where the third RAN node receives from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell. The exemplary method also includes the operations of block 1050, where based on the group identifier related to the first LTM candidate cell and the group identifier related to the first serving cell, the third RAN node determines whether a layer-2 (L2) reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch. The exemplary method also includes the operations of block 1060, where the third RAN node sends to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

[0233] In some embodiments, the respective group identifiers are associated with a first serving cell (i.e., the UE’s serving entity), the first LTM candidate cell, and the one or more second LTM candidate cells. In other embodiments, the respective group identifiers are associated with a first RAN node (i.e., the UE’s serving entity) that provides the first serving cell, the second RAN node that provides the first LTM candidate cell, and one or more RAN nodes that provide the one or more second LTM candidate cells. In some of these embodiments, the first RAN node is a first DU, the second RAN node is a second DU, and the third RAN node is a CU associated with the first and second DUs.

[0234] In some embodiments, determining whether L2 reset is needed for the UE in block 1050 includes the following operations, labelled with corresponding sub-block numbers: • (1051) determining that the L2 reset is needed based on the group identifier related to the first LTM candidate cell being different than the group identifier related to the UE’s serving entity; and

[0235] • (1052) determining that the L2 reset is not needed based on the group identifier related to the first LTM candidate cell being same as the group identifier related to the UE’s serving entity.

[0236] In some embodiments, the exemplary method also includes the operations of block 1020, where the third RAN node sends, to the UE via the first serving cell, a conditional LTM configuration that includes the following: a configuration for the first LTM candidate cell, an execution condition for LTM cell switch by the UE to the first LTM candidate cell, respective configurations for the one or more second LTM candidate cells, and respective execution conditions for LTM cell switch by the UE to the one or more second LTM candidate cells.

[0237] In some embodiments, the exemplary method also includes the operations of block 1010, where the UE receives, from the first RAN node, a further indication that the UE has performed LTM cell switch to a third LTM candidate cell provided by the first RAN node, such that the third LTM candidate cell has become a serving entity for the UE. As such, the third RAN node may determine the group identifier related to the third LTM candidate cell (i.e., as the UE’s serving entity) in block 1030.

[0238] 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. figure 11 shows an example of a communication system 1100 in accordance with some embodiments. In this example, communication system 1100 includes a telecommunication network 1102 that includes an access network 1104 (e.g., RAN) and a core network 1106, which includes one or more core network nodes 1108. Access network 1104 includes one or more access network nodes, such as network nodes 11 lOa-b (one or more of which may be generally referred to as network nodes 1110), or any other similar 3GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1102 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1102 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 1102, including one or more network nodes 1110 and / or core network nodes 1108.

[0239] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 1110 facilitate direct or indirect connection of UEs, such as by connecting UEs 1112a-d (one or more of which may be generally referred to as UEs 1112) to core network 1106 over one or more wireless connections.

[0240] 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 1100 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 1100 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0241] UEs 1112 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1110 and other communication devices. Similarly, network nodes 1110 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1112 and / or with other network nodes or equipment in telecommunication network 1102 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1102.

[0242] In the depicted example, core network 1106 connects network nodes 1110 to one or more hosts, such as host 1116. 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 1106 includes one or more core network nodes (e.g., 1108) 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 1108. 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).

[0243] Host 1116 may be under the ownership or control of a service provider other than an operator or provider of access network 1104 and / or telecommunication network 1102, and may be operated by the service provider or on behalf of the service provider. Host 1116 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.

[0244] As a whole, communication system 1100 of Figure 11 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. In some examples, telecommunication network 1102 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1102 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1102. For example, telecommunication network 1102 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)ZMassive loT services to yet further UEs.

[0245] In some examples, UEs 1112 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 1104 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1104. 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).

[0246] In the example, hub 1114 communicates with access network 1104 to facilitate indirect communication between one or more UEs (e.g., 1112c and / or 1112d) and network nodes (e.g., 1110b). In some examples, hub 1114 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1114 may be a broadband router enabling access to core network 1106 for the UEs. As another example, hub 1114 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 1110, or by executable code, script, process, or other instructions in hub 1114. As another example, hub 1114 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 1114 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1114 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1114 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1114 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0247] Hub 1114 may have a constant / persistent or intermittent connection to network node 1110b. Hub 1114 may also allow for a different communication scheme and / or schedule between hub 1114 and UEs (e.g., 1112c and / or 1112d), and between hub 1114 and core network 1106. In other examples, hub 1114 is connected to core network 1106 and / or one or more UEs via a wired connection. Moreover, hub 1114 may be configured to connect to an M2M service provider over access network 1104 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1110 while still connected via hub 1114 via a wired or wireless connection. In some embodiments, hub 1114 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1110b. In other embodiments, hub 1114 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1110b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0248] In some embodiments, any of network nodes 1110 may be configured to perform operations attributed to a RAN node in various embodiments described above, including Figures 4-7 and 9-10. In some embodiments, any of UEs 1112 may be configured to perform operations attributed to a UE in various embodiments described above, including Figures 4-8.

[0249] Figure 12 shows a UE 1200 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.

[0250] 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).

[0251] UE 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input / output interface 1206, a power source 1208, a memory 1210, a communication interface 1212, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 12. 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.

[0252] Processing circuitry 1202 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 1210. Processing circuitry 1202 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 1202 may include multiple central processing units (CPUs).

[0253] In the example, input / output interface 1206 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 1200. 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.

[0254] In some embodiments, power source 1208 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 1208 may further include power circuitry for delivering power from power source 1208 itself, and / or an external power source, to the various parts of UE 1200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1208. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1208 to make the power suitable for the respective components of UE 1200 to which power is supplied.

[0255] Memory 1210 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 1210 includes one or more application programs 1214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1216. Memory 1210 may store, for use by UE 1200, any of a variety of various operating systems or combinations of operating systems.

[0256] Memory 1210 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 1210 may allow UE 1200 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 1210, which may be or comprise a device-readable storage medium.

[0257] Processing circuitry 1202 may be configured to communicate with an access network or other network using communication interface 1212. Communication interface 1212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1222. Communication interface 1212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1218 and / or a receiver 1220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1218 and receiver 1220 may be coupled to one or more antennas (e.g., antenna 1222) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0258] In the illustrated embodiment, communication functions of communication interface 1212 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.

[0259] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0260] 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.

[0261] 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 1200 shown in Figure 12. 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.

[0262] 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.

[0263] In some embodiments, UE 1200 may be configured to perform operations attributed to a UE in various embodiments described above, including Figures 4-8.

[0264] Figure 13 shows a network node 1300 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (APs) (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).

[0265] 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).

[0266] 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).

[0267] Network node 1300 includes processing circuitry 1302, memory 1304, communication interface 1306, and power source 1308. Network node 1300 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 1300 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 1300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1304 for different RATs) and some components may be reused (e.g., a same antenna 1310 may be shared by different RATs). Network node 1300 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1300, 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 1300.

[0268] Processing circuitry 1302 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 1300 components, such as memory 1304, to provide network node 1300 functionality.

[0269] In some embodiments, processing circuitry 1302 includes a system on a chip (SOC). In some embodiments, processing circuitry 1302 includes one or more of radio frequency (RF) transceiver circuitry 1312 and baseband processing circuitry 1314. In some embodiments, RF transceiver circuitry 1312 and baseband processing circuitry 1314 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 1312 and baseband processing circuitry 1314 may be on the same chip or set of chips, boards, or units.

[0270] Memory 1304 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 1302. Memory 1304 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 1304a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1302 and utilized by network node 1300. Memory 1304 may be used to store any calculations made by processing circuitry 1302 and / or any data received via communication interface 1306. In some embodiments, processing circuitry 1302 and memory 1304 is integrated.

[0271] Communication interface 1306 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 1306 comprises port(s) / terminal(s) 1316 to send and receive data, for example to and from a network over a wired connection. Communication interface 1306 also includes radio frontend circuitry 1318 that may be coupled to, or in certain embodiments a part of, antenna 1310. Radio front-end circuitry 1318 comprises filters 1320 and amplifiers 1322. Radio front-end circuitry 1318 may be connected to an antenna 1310 and processing circuitry 1302. The radio front-end circuitry may be configured to condition signals communicated between antenna 1310 and processing circuitry 1302. Radio front-end circuitry 1318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1320 and / or amplifiers 1322. The radio signal may then be transmitted via antenna 1310. Similarly, when receiving data, antenna 1310 may collect radio signals which are then converted into digital data by radio front-end circuitry 1318. The digital data may be passed to processing circuitry 1302. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0272] In certain alternative embodiments, network node 1300 does not include separate radio front-end circuitry 1318, instead, processing circuitry 1302 includes radio front-end circuitry and is connected to antenna 1310. Similarly, in some embodiments, all or some of RF transceiver circuitry 1312 is part of communication interface 1306. In still other embodiments, communication interface 1306 includes one or more ports or terminals 1316, radio front-end circuitry 1318, and RF transceiver circuitry 1312, as part of a radio unit (not shown), and communication interface 1306 communicates with baseband processing circuitry 1314, which is part of a digital unit (not shown).

[0273] Antenna 1310 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1310 may be coupled to radio front-end circuitry 1318 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1310 is separate from network node 1300 and connectable to network node 1300 through an interface or port.

[0274] Antenna 1310, communication interface 1306, and / or processing circuitry 1302 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 1310, communication interface 1306, and / or processing circuitry 1302 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.

[0275] Power source 1308 provides power to the various components of network node 1300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1308 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1300 with power for performing the functionality described herein. For example, network node 1300 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 1308. As a further example, power source 1308 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.

[0276] Embodiments of network node 1300 may include additional components beyond those shown in Figure 13 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 1300 may include user interface equipment to allow input of information into network node 1300 and to allow output of information from network node 1300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1300.

[0277] In some embodiments, network node 1300 may be configured to perform operations attributed to a RAN node in various embodiments described above, including Figures 4-7 and 9- 10. Figure 15 is a block diagram illustrating a virtualization environment 1500 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 1500 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 1500 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.

[0278] Applications 1502 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1500 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein. For example, one or more virtual nodes 1502 may be configured to perform operations attributed to a RAN node in various embodiments described above, including Figures 4-7 and 9-10.

[0279] Hardware 1504 includes processing circuitry, memory that stores software and / or instructions (collected denoted computer program 1504a, 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 1506 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1508a-b (one or more of which may be generally referred to as VMs 1508), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1506 may present a virtual operating platform that appears like networking hardware to the VMs 1508.

[0280] VMs 1508 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1506. Different embodiments of the instance of a virtual appliance 1502 may be implemented on one or more of VMs 1508, 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.

[0281] In the context of NFV, each VM 1508 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 1508, and that part of hardware 1504 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 1508 on top of the hardware 1504 and corresponds to the application 1502.

[0282] Hardware 1504 may be implemented in a standalone network node with generic or specific components. Hardware 1504 may implement some functions via virtualization. Alternatively, hardware 1504 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 1510, which, among others, oversees lifecycle management of applications 1502. In some embodiments, hardware 1504 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 1512 which may alternatively be used for communication between hardware nodes and radio units.

[0283] 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.

[0284] 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. 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.

[0285] 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.

[0286] 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.

[0287] 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 such terms may be used synonymously herein, there may be instances when such terms are not intended to be used synonymously. Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0288] Al . A method for a user equipment (UE) configured for conditional layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: receiving, from a third RAN node via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier associated with the first LTM candidate cell, and an execution condition for LTM cell switch to the first LTM candidate cell; based on determining that an execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node, performing an LTM cell switch to the first LTM candidate cell; based on the group identifier associated with the first LTM candidate cell and a group identifier associated with the first serving cell, selectively performing a layer-2 (L2) reset in conjunction with the LTM cell switch; and sending, to the second RAN node or to the first RAN node, an indication of whether the L2 reset was or will be performed in conjunction with the LTM cell switch.

[0289] A2. The method of embodiment Al, wherein selectively performing the L2 reset based on the group identifier associated with the first LTM candidate cell and the group identifier associated with the first serving cell comprises: performing the L2 reset when the group identifier associated with the first LTM candidate cell is different than the group identifier associated with the first serving cell; and refraining from performing the L2 reset when the group identifier associated with the first LTM candidate cell is the same as the group identifier associated with the first serving cell.

[0290] A3. The method of any of embodiments A1-A2, wherein the group identifier associated with source cell is stored in a UE variable and the method further comprises, after performing the LTM cell switch, storing the group identifier associated with the first LTM candidate cell in the UE variable as the group identifier associated with the first serving cell. A4. The method of any of embodiments Al -A3, wherein the indication includes one or more of the following: an explicit indication of whether the L2 reset was or will be performed; an identifier of the first RAN node; an identifier of the first serving cell; an identifier of an LTM candidate cell configuration for the first serving cell; the group identifier associated with the first serving cell; and an indication of whether the group identifier associated with the first LTM candidate cell is the same as the group identifier associated with the first serving cell

[0291] A5. The method of any of claims A1-A4, further comprising performing measurements of the first serving cell and each of the LTM candidate cells thereby obtaining measurement values, wherein the execution condition is fulfilled by a measurement value obtained for the first LTM candidate cell.

[0292] A6. The method of any of embodiments A1-A5, further comprising sending to the second RAN node a message indicating that the LTM cell switch to the first LTM candidate cell has been completed.

[0293] A6a. The method of embodiment A6, wherein the message is an RRCReconfigurationComplete message intended for the third RAN node and the indication is included in the message.

[0294] A6b. The method of embodiment A6, wherein the indication is sent to the second RAN node before sending the message, as or in one of the following: a random access (RA) message based on a RA configuration associated with L2 reset indications, a layer- 1 (LI) message or control information; a L2 protocol data unit (PDU) or control element (CE); or a radio resource control (RRC) message intended for the third RAN node.

[0295] A7. The method of any of embodiments A1-A5, wherein the indication is sent to the first RAN node before performing the LTM cell switch.

[0296] A8. The method of any of embodiments A1-A7, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, and the third RAN node is a centralized unit (CU) associated with the first and second DUs.

[0297] Bl . A method for a second radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility (UTM) by user equipment (UEs), the method comprising: sending, to a third RAN node, a configuration for a first UTM candidate cell provided by the second RAN node and an execution condition for UTM cell switch by a UE to the first LTM candidate cell; receiving and storing the following information from the third RAN node: a first indication of one of the following: a first serving cell that is the UE’s current serving cell, or a first RAN node that is the UE’s current serving node; and respective group identifiers associated with the following: the first serving cell, the first LTM candidate cell, and one or more second LTM candidate cells provided by one or more other RAN nodes; or the first RAN node, the second RAN node, and the one or more other RAN nodes; subsequently performing either first operations or second operations, wherein the first operations include: receiving from the third RAN node a second indication of one of the following: the UE’s current serving cell is now one of the second LTM candidate cells is, or the UE’s current serving node is now one of the other RAN nodes; updating the stored information based on the second indication; wherein the second operations include: detecting an LTM cell switch by the UE to the first LTM candidate cell; and based on the stored information, selectively performing a layer-2 (L2) reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

[0298] B2. The method of embodiment Bl, wherein selectively performing the L2 reset based on the stored information comprises: performing the L2 reset when the stored group identifier associated with the first LTM candidate cell or with the second RAN node is different than the stored group identifier associated with the first serving cell or with the first RAN node; and refraining from performing the L2 reset when the stored group identifier associated with the first LTM candidate cell or with the second RAN node is the same as the stored group identifier associated with the first serving cell or with the first RAN node.

[0299] B3. The method of any of embodiments B 1 -B2, wherein the second operations also include: sending to the third RAN node a third indication that the UE has performed LTM cell switch to the first LTM candidate cell; and updating the stored information to indicate one of the following: that the first LTM candidate cell is the UE’s current serving cell, or that the second RAN node is the UE’s current serving node.

[0300] B4. The method of any of embodiments B1-B3, wherein the second indication of the change is one of the following: a cell identifier of the second LTM candidate cell that is now the UE’s current serving cell; the group identifier associated with the second LTM candidate cell that is now the UE’s current serving cell; a node identifier of the other RAN node that is now the UE’s current serving node; or the group identifier associated with the other RAN node that is now the UE’s current serving node.

[0301] B4a. The method of embodiment B4, wherein the second indication is received only when the group identifier associated with the other RAN node or with the second LTM candidate cell is different than the group identifier associated with the first RAN node or with the first serving cell.

[0302] B5. The method of any of embodiments B 1 -B4a, wherein the first indication is received from the first RAN node in a request for configurations for one or more LTM candidate cells for the UE, wherein the configuration for the first LTM candidate cell and the execution condition are sent in response to the request. B5a. The method of embodiment B5, wherein the respective group identifiers are also received from the first RAN node in the request.

[0303] B5b. The method of embodiment B5, the respective group identifiers are received from the first RAN node in response to sending the configuration for the first LTM candidate cell and the execution condition.

[0304] B6. The method of any of embodiments Bl-B5b, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, and the third RAN node is a centralized unit (CU) associated with the first and second DUs.

[0305] Cl . A method for a third radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility (UTM) by user equipment (UEs), the method comprising: determining respective group identifiers associated with the following: a first serving cell for a UE, a first LTM candidate cell for the UE, and one or more second LTM candidate cells for the UE; or a first RAN node that provides the first serving cell, a second RAN node that provides the first LTM candidate, and other RAN nodes that provide the one or more second LTM candidate cells; receiving from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell; and based on the group identifier associated with the first LTM candidate cell and the group identifier associated with the first serving cell, determining whether a layer-2 (L2) reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch; and sending to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

[0306] C2. The method of embodiment Cl, wherein determining whether L2 reset is needed for the UE comprises: determining that the L2 reset is needed based on the group identifier associated with the first LTM candidate cell or the second RAN node being different than the group identifier associated with the first serving cell or the first RAN node; and determining that the L2 reset is not needed based on the group identifier associated with the first LTM candidate cell or the second RAN node being the same as the group identifier associated with the first serving cell or the first RAN node.

[0307] C3. The method of any of embodiments C1-C2, further comprising sending, to the UE via the first serving cell, a conditional LTM configuration that includes the following: a configuration for the first LTM candidate cell and an execution condition for LTM cell switch by the UE to the first LTM candidate cell, and respective configurations for the one or more second LTM candidate cells and respective execution conditions for LTM cell switch by the UE to the one or more second LTM candidate cells.

[0308] C4. The method of any of embodiments C1-C3, further comprising receiving, from the first RAN node, a further indication that the UE has performed LTM cell switch to a third LTM candidate cell provided by the first RAN node, such that the third LTM candidate cell becomes the first serving cell for the UE.

[0309] C5. The method of any of embodiments C1-C4, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, and the third RAN node is a centralized unit (CU) associated with the first and second DUs.

[0310] DI. A user equipment (UE) configured for conditional layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments A1-A8.

[0311] D2. A user equipment (UE) configured for conditional layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments A1-A8.

[0312] D3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured for conditional layer-l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A8.

[0313] D4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for conditional layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A8.

[0314] El . A second radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the second RAN node comprising: communication interface circuitry configured to communicate with UEs and with other RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments B1-B6.

[0315] E2. A second radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the second RAN node being further configured to perform operations corresponding to the methods of any of embodiments B1-B6.

[0316] E3. 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 facilitate conditional layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the second RAN node to perform operations corresponding to the methods of any of embodiments B1-B6.

[0317] E4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the second RAN node to perform operations corresponding to the methods of any of embodiments B1-B6. Fl. A third radio access network (RAN) node configured to facilitate conditional layer- 1 / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the third RAN node comprising: communication interface circuitry configured to communicate with UEs and with other RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments C1-C5.

[0318] F2. A third radio access network (RAN) node configured to facilitate conditional layer- 1 / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), the third RAN node being further configured to perform operations corresponding to the methods of any of embodiments C1-C5.

[0319] F3. 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 facilitate conditional layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the third RAN node to perform operations corresponding to the methods of any of embodiments C1-C5.

[0320] F4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a third radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility (LTM) by user equipment (UEs), configure the third RAN node to perform operations corresponding to the methods of any of embodiments C1-C5.

Claims

CLAIMS1 . A method for a user equipment, UE, configured for conditional layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: receiving (810), from a third RAN node via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier related to the LTM candidate cell, and an execution condition for LTM cell switch to the LTM candidate cell; based on determining (830) that the execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node, performing (840) an LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and a group identifier related to the first serving cell, selectively performing (850) a layer-2, L2, reset in conjunction with the LTM cell switch; and sending (860) one of the following: to the first RAN node, an indication of whether the L2 reset will be performed in conjunction with the LTM cell switch; or to the second RAN node, an indication of whether the L2 reset was performed in conjunction with the LTM cell switch.

2. The method of claim 1, wherein: the group identifier related to the first LTM candidate cell is associated with one of the following: the first LTM candidate cell, or the second RAN node that provides the first LTM candidate cell; and the group identifier related to the first serving cell is associated with one of the following: the first serving cell, or the first RAN node that provides the first serving cell.

3. The method of claim 1, wherein selectively performing (850) the L2 reset based on the group identifier related to the first LTM candidate cell and the group identifier related to the first serving cell comprises:performing (851) the L2 reset when the group identifier related to the first LTM candidate cell is different than the group identifier related to the first serving cell; and refraining from performing (852) the L2 reset when the group identifier related to the first LTM candidate cell is the same as the group identifier related to the first serving cell.

4. The method of any of claims 1-3, wherein the group identifier related to the first serving cell is stored in a UE variable before the LTM cell switch and the method further comprises, after performing (840) the LTM cell switch, updating (880) the UE variable to store the group identifier related to the first LTM candidate cell.

5. The method of any of claims 1-4, wherein the indication sent to the first RAN node or the second RAN node includes one or more of the following: an explicit indication of whether the L2 reset was or will be performed; an identifier of the first RAN node; an identifier of the first serving cell; an identifier of an LTM candidate cell configuration for the first serving cell; the group identifier related to the first serving cell; and an indication of whether the group identifier related to the first LTM candidate cell is the same as the group identifier related to the first serving cell6. The method of any of claims 1-5, further comprising performing (820) measurements of the first serving cell and each of the LTM candidate cells thereby obtaining measurement values, wherein the execution condition is fulfilled by a measurement value obtained for the first LTM candidate cell.

7. The method of any of claims 1-6, further comprising, after performing (840) the LTM cell switch to the first LTM candidate cell, sending (870) to the second RAN node a message indicating that the LTM cell switch to the first LTM candidate cell has been completed.

8. The method of claim 7, wherein the message is an RRCReconfigurationComplete message intended for the third RAN node and includes the indication of whether the L2 reset was performed.

9. The method of claim 7, wherein the indication of whether the L2 reset was performed is sent to the second RAN node before sending the message, as or in one of the following: a random access, RA, message based on a RA configuration associated with L2 reset indications, a layer-1, LI, message or control information; a L2 protocol data unit, PDU, or control element, CE; or a radio resource control, RRC, message intended for the third RAN node.

10. The method of any of claims 1-6, wherein the indication of whether the L2 reset will be performed is sent to the first RAN node before performing (840) the LTM cell switch to the first LTM candidate cell.

11. The method of any of claims 1-10, wherein the first RAN node is a first distributed unit, DU, the second RAN node is a second DU, and the third RAN node is a centralized unit, CU, associated with the first and second DUs.

12. A method for a second radio access network, RAN, node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, ETM, by user equipment, UEs, the method comprising: sending (910), to a third RAN node, a configuration for a first LTM candidate cell provided by the second RAN node and an execution condition for LTM cell switch by a UE to the first LTM candidate cell; receiving and storing (920) the following information from the third RAN node: a first indication of the UE’s serving entity; and respective group identifiers related to the following: the UE’s serving entity, the first LTM candidate cell, and one or more second LTM candidate cells for the UE; subsequently performing either first operations or second operations, wherein the first operations include: receiving (930) from the third RAN node a second indication that the UE’s serving entity has changed; updating (940) the stored information based on the second indication; wherein the second operations include: detecting (950) an LTM cell switch by the UE to the first LTM candidate cell; andbased on the stored information, selectively performing (960) a layer-2, L2, reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

13. The method of claim 12, wherein: the first indication is of one of the following: a first serving cell provided by a first RAN node, or the first RAN node; and the respective group identifiers are associated with one of the following: the first serving cell, the first LTM candidate cell, and the one or more second LTM candidate cells; or the first RAN node, the second RAN node, and one or more RAN nodes that provide the one or more second LTM candidate cells.

14. The method of any of claims 12-13, wherein selectively performing (960) the L2 reset based on the stored information comprises: performing (961) the L2 reset when the stored group identifier related to the first LTM candidate cell is different than the stored group identifier related to the UE’s serving entity; and refraining from performing (962) the L2 reset when the stored group identifier related to the first LTM candidate cell is the same as the stored group identifier related to the UE’s serving entity.

15. The method of any of claims 12-14, wherein the second operations also include: sending (970) to the third RAN node a third indication that the UE has performed LTM cell switch to the first LTM candidate cell; and updating (980) the stored information to indicate one of the following: that the first LTM candidate cell is the UE’s serving cell, or that the second RAN node is the UE’s serving node.

16. The method of any of claims 12-15, wherein the second indication that the UE’s serving entity has changed is one of the following: a cell identifier of the second LTM candidate cell that is now the UE’s serving cell; a group identifier associated with the second LTM candidate cell that is now the UE’s serving cell; a node identifier of a RAN node that provides the second LTM candidate cell; ora group identifier associated with the RAN node that provides the second LTM candidate cell.

17. The method of claim 16, wherein the second indication is received only when the group identifier related to the second LTM candidate cell is different than the group identifier related to the UE’s serving entity.

18. The method of any of claims 12-17, wherein: the first indication is received from the first RAN node in a request for configurations for one or more LTM candidate cells for the UE; and the configuration for the first LTM candidate cell and the execution condition are sent to the third RAN node in response to the request.

19. The method of claim 18, wherein the respective group identifiers are also received from the first RAN node in or with the request.

20. The method of claim 18, the respective group identifiers are received from the third RAN node in response to sending the configuration for the first LTM candidate cell and the execution condition.

21. The method of any of claims 12-20, wherein the first RAN node is a first distributed unit, DU, the second RAN node is a second DU, and the third RAN node is a centralized unit, CU, associated with the first and second DUs.

22. A method for a third radio access network, RAN, node configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: determining (1030) respective group identifiers related to the following: the UE’s serving entity, a first LTM candidate cell provided by a second RAN node, and one or more second LTM candidate cells for the UE; receiving (1040) from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and the group identifier related to the UE’s serving entity, determining (1050) whether a layer-2, L2, reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch; and sending (1060) to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

23. The method of claim 22, wherein the respective group identifiers are associated with one of the following: a first serving cell, the first LTM candidate cell, and the one or more second LTM candidate cells; or a first RAN node that provides the first serving cell, the second RAN node that provides the first LTM candidate cell, and one or more RAN nodes that provide the one or more second LTM candidate cells.

24. The method of claim 23, wherein the first RAN node is a first distributed unit, DU, the second RAN node is a second DU, and the third RAN node is a centralized unit, CU, associated with the first and second DUs.

25. The method of any of claims 22-24, wherein determining (1050) whether L2 reset is needed for the UE comprises: determining (1051) that the L2 reset is needed based on the group identifier related to the first LTM candidate cell being different than the group identifier related to the UE’s serving entity; and determining (1052) that the L2 reset is not needed based on the group identifier related to the first LTM candidate cell being same as the group identifier related to the UE’s serving entity.

26. The method of any of claims 22-25, further comprising sending (1020), to the UE via the first serving cell, a conditional LTM configuration that includes the following: a configuration for the first LTM candidate cell, an execution condition for LTM cell switch by the UE to the first LTM candidate cell, respective configurations for the one or more second LTM candidate cells, and respective execution conditions for LTM cell switch by the UE to the one or more second LTM candidate cells.

27. The method of any of claims 22-26, further comprising receiving (1010), from the first RAN node, a further indication that the UE has performed LTM cell switch to a third LTM candidate cell provided by the first RAN node, such that the third LTM candidate cell has become a serving entity for the UE.

28. User equipment, UE (210, 310, 460, 1112, 1200) configured for conditional layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), the UE comprising: communication interface circuitry (1212) configured to communicate with RAN nodes; and processing circuitry (1202) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from a third RAN node (100, 150, 220, 320, 450, 1110, 1300, 1402) via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier related to the LTM candidate cell, and an execution condition for LTM cell switch to the LTM candidate cell; based on a determination that the execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node (100, 150, 220, 320, 410, 1110, 1300, 1402), perform an LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and a group identifier related to the first serving cell, selectively perform a layer-2, L2, reset in conjunction with the LTM cell switch; and send one of the following: to the first RAN node, an indication of whether the L2 reset will be performed in conjunction with the LTM cell switch; or to the second RAN node, an indication of whether the L2 reset was performed in conjunction with the LTM cell switch.

29. The UE of claim 28, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-11.

30. User equipment, UE (210, 310, 460, 1112, 1200) configured for conditional layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), the UE being further configured to: receive, from a third RAN node (100, 150, 220, 320, 450, 1110, 1300, 1402) via a first serving cell provided by a first RAN node, a conditional LTM configuration that includes the following for each of one or more LTM candidate cells: an LTM candidate cell configuration, a group identifier related to the LTM candidate cell, and an execution condition for LTM cell switch to the LTM candidate cell; based on a determination that the execution condition is fulfilled for a first one of the LTM candidate cells provided by a second RAN node (100, 150, 220, 320, 410, 1110, 1300, 1402), perform an LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and a group identifier related to the first serving cell, selectively perform a layer-2, L2, reset in conjunction with the LTM cell switch; and send one of the following: to the first RAN node, an indication of whether the L2 reset will be performed in conjunction with the LTM cell switch; or to the second RAN node, an indication of whether the L2 reset was performed in conjunction with the LTM cell switch.

31. The UE of claim 30, being further configured to perform operations corresponding to the methods of any of claims 2-11.

32. Non-transitory, computer-readable medium (1210) storing computer-executable instructions that, when executed by processing circuitry (1202) of user equipment, UE (210, 310, 460, 1112, 1200) configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-11.

33. Computer program product comprising computer-executable instructions that, when executed by processing circuitry (1202) of user equipment, UE (210, 310, 460, 1112, 1200) configured for conditional layer- l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-11.

34. Second radio access network, RAN, node (100, 150, 220, 320, 410, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), the second RAN node comprising: communication interface circuitry (1306, 1404) configured to communicate with UEs and with other RAN nodes; and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: send, to a third RAN node (100, 150, 220, 320, 450, 1110, 1300, 1402), a configuration for a first LTM candidate cell provided by the second RAN node and an execution condition for LTM cell switch by a UE to the first LTM candidate cell; receive and store the following information from the third RAN node: a first indication of the UE’s serving entity; and respective group identifiers related to the following: the UE’s serving entity, the first LTM candidate cell, and one or more second LTM candidate cells for the UE; subsequently perform either first operations or second operations, wherein the first operations include: receive from the third RAN node a second indication that the UE’s serving entity has changed; update the stored information based on the second indication; wherein the second operations include: detect an LTM cell switch by the UE to the first LTM candidate cell; and based on the stored information, selectively perform a layer-2, L2, reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

35. The second RAN node of claim 34, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 13-21 .

36. Second radio access network, RAN, node (100, 150, 220, 320, 410, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), the second RAN node being further configured to: send, to a third RAN node (100, 150, 220, 320, 450, 1110, 1300, 1402), a configuration for a first LTM candidate cell provided by the second RAN node and an execution condition for LTM cell switch by a UE to the first LTM candidate cell; receive and store the following information from the third RAN node: a first indication of the UE’s serving entity; and respective group identifiers related to the following: the UE’s serving entity, the first LTM candidate cell, and one or more second LTM candidate cells for the UE; subsequently perform either first operations or second operations, wherein the first operations include: receive from the third RAN node a second indication that the UE’s serving entity has changed; update the stored information based on the second indication; wherein the second operations include: detect an LTM cell switch by the UE to the first LTM candidate cell; and based on the stored information, selectively perform a layer-2, L2, reset for the UE in the first LTM candidate cell in conjunction with the LTM cell switch.

37. The second RAN node of claim 36, being further configured to perform operations corresponding to the methods of any of claims 13-21 .

38. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a second radio access network, RAN, node (100, 150, 220, 320, 410, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), configure the second RAN node to perform operations corresponding to the methods of any of claims 12-21 .

39. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a second radio access network, RAN, node (100, 150, 220, 320, 410, 1110, 1300, 1402) configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460,1112, 1200), configure the second RAN node to perform operations corresponding to the methods of any of claims 12-21 .

40. Third radio access network, RAN, node (100, 150, 220, 320, 450, 1110, 1300, 1402) configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), the third RAN node comprising: communication interface circuitry (1306, 1404) configured to communicate with UEs and with other RAN nodes; and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: determine respective group identifiers related to the following: the UE’s serving entity, a first LTM candidate cell provided by a second RAN node (100, 150, 220, 320, 410, 1110, 1300, 1402), and one or more second LTM candidate cells for the UE; receive from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and the group identifier related to the UE’s serving entity, determine whether a layer-2, L2, reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch; and send to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

41. The third RAN node of claim 40, wherein the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of claims 23-27.

42. Third radio access network, RAN, node (100, 150, 220, 320, 450, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), the third RAN node being further configured to: determine respective group identifiers related to the following: the UE’s serving entity, a first LTM candidate cell provided by a second RAN node (100, 150, 220, 320, 410, 1110, 1300, 1402), and one or more second LTM candidate cells for the UE; receive from the second RAN node an indication that the UE has performed LTM cell switch to the first LTM candidate cell; based on the group identifier related to the first LTM candidate cell and the group identifier related to the UE’s serving entity, determine whether a layer-2, L2, reset is needed for the UE in the first LTM candidate cell, in conjunction with the LTM cell switch; and send to the second RAN node a second indication of whether the L2 reset is needed for the UE in the first LTM candidate cell.

43. The third RAN node of claim 42, being further configured to perform operations corresponding to the methods of any of claims 23-27.

44. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a third radio access network, RAN, node (100, 150, 220, 320, 450, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), configure the third RAN node to perform operations corresponding to the methods of any of claims 22-27.

45. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a third radio access network, RAN, node (100, 150, 220, 320, 450, 1110, 1300, 1402) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 310, 460, 1112, 1200), configure the third RAN node to perform operations corresponding to the methods of any of claims 22-27.

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