Facilitating user equipment early uplink synchronization after l1 / l2-triggered mobility

Abstract

Embodiments include methods for a user equipment (UE) configured for layer-1 / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN). Such methods include, while operating in a source cell, receiving an early uplink (UL) synchronization configuration for a 5 second LTM candidate cell and performing an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell. Such methods include subsequently receiving an indication to perform an early UL synchronization to the second LTM candidate cell. The indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell. Such methods include performing an early UL synchronization to the second 0 LTM candidate cell, based on the referenced parameters. Other embodiments include UEs configured to perform such methods.

Description

[0001] FACILITATING USER EQUIPMENT EARLY UPLINK SYNCHRONIZATION AFTER L1 / L2-TRIGGERED MOBILITY

[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), such as in relation to layer-1 (LI) or layer-2 (L2) triggered inter-cell mobility (LTM) operations followed by early uplink synchronization in another cell.

[0004] BACKGROUND

[0005] Currently the fifth generation (5G) of cellular systems is being standardized within the Third-Generation Partnership Project (3GPP). 5G is developed for maximum flexibility to support 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.

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

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

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

[0009] A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1). However, each gNB-DU can be connected to only one gNB-CU. The gNB-CU and its connected gNB-DU(s) are only visible to other gNBs and the 5GC as a gNB. In other words, the Fl interface is not visible beyond gNB-CU.

[0010] 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.

[0011] As specified in 3GPP document RP -223520, NR Rel-18 includes a Work Item on further NR mobility enhancements, including in the technical area of L1 / L2 based inter-cell mobility, also referred to as L1 / L2 triggered mobility (LTM). When the UE moves between the coverage areas of two cells, a serving cell change needs to be performed at some point. Conventionally, serving cell change was triggered by layer 3 (L3, e.g., RRC) measurements and involves RRC signaling to change primary cells (PCells) and to release / add secondary cells (SCells, e.g., when carrier aggregation is configured).

[0012] Currently, all inter-cell mobility involves complete LI and L2 resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, a goal of Rel-18 L1 / L2 mobility enhancements is to facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties.

[0013] In LTM, a UE is pre-configured by its serving RAN node with one radio resource control (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. Each LTM candidate cell configuration may include a configuration for early uplink (UL) synchronization (or “sync’) in the cell. Using the early UL sync configuration for an LTM candidate cell, the UE transmits on a random access channel (RACH) in the cell prior to receiving an LTM cell switch command for the cell, which may include a timing advance (TA) determined based on the UE’s earlier RACH transmission. In this manner, the UE can become UL synchronized with LTM candidate cells that are different from the UE’s current serving cell.

[0014] SUMMARY

[0015] According to 3GPP agreements, a UE may perform multiple LTM cell switch procedures without being reconfigured by the RAN. For example, after the UE has performed an LTM cell switch from a serving cell to a first target cell (e.g., a first LTM candidate cell), the UE may perform another LTM cell switch to a second target cell (e.g., a second LTM candidate cell) without receiving another RRCReconflguration message in the first target cell. This second LTM cell switch is often referred to as “subsequent LTM.”

[0016] When the UE is being served by the first target cell, the UE may need to perform early UL synchronization with the second LTM candidate cell before performing the LTM cell switch to that cell. However, there are various problems, issues, and / or difficulties that prevent the RAN node that provides the first target cell from causing the UE to perform early UL synchronization with the second LTM candidate cell.

[0017] An obj ect of embodiments of the present disclosure is to improve early UL synchronization of UEs for LTM, such as by providing, enabling, and / or facilitating solutions to overcome exemplary problems summarized above and described in more detail below.

[0018] Embodiments include methods (e.g., procedures) for a UE configured for LTM in a radio access network (RAN, e.g., E-UTRAN, NG-RAN).

[0019] These exemplary methods include receiving an early UL synchronization configurations for a second LTM candidate cell. These exemplary methods also include performing an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell. These exemplary methods also include subsequently receiving an indication to perform an early UL synchronization to the second LTM candidate cell. The indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell. These exemplary methods also include performing an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

[0020] In some embodiments, the indication is a physical downlink control channel (PDCCH) order. In some embodiments, the early UL synchronization configuration is received from a fourth RAN node via the source cell, which is provided by a first RAN node. Also, the first and second LTM candidate cells are provided by respective second and third RAN nodes, with the indication being received from the second RAN node via the target cell.

[0021] Various examples of information included in an early UL synchronization configuration are described herein below.

[0022] Other embodiments include exemplary methods (e.g., procedures) for a second RAN node configured to facilitate LTM by UEs. In general, these exemplary methods can be complementary to the exemplary methods for a UE summarized above.

[0023] These exemplary methods include receiving one of the following from a fourth RAN node:

[0024] • a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cells provided by a third RAN node, and a third LTM candidate cell provided by a first RAN node; or

[0025] • a request for one or more early UL synchronization configurations for the first LTM candidate.

[0026] These exemplary methods also include receiving from a UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell.

[0027] In some embodiments, the message received from the fourth RAN node is a UE context modification request. In other embodiments, the message received from the fourth RAN node is an LTM cell switch notification, which indicates initiation of the UE’s LTM cell switch to the first LTM candidate cell. In some embodiments, the message is received from the fourth RAN node before the UE’s LTM cell switch to the first LTM candidate cell.

[0028] In some embodiments, these exemplary methods also include sending to the UE an indication to perform an early UL synchronization to the second LTM candidate cell. The indication references one or more parameters in the early UL synchronization configuration for the second LTM candidate cell. In some of these embodiments, the indication is a PDCCH order. In some of these embodiments, the one or more parameters referenced by the indication include one or more of the following: a random access (RA) preamble, time / frequency RA resources, and one or more beams.

[0029] In some of these embodiments, these exemplary methods also include receiving from the third RAN node a timing advance (TA) value for the second LTM candidate cell, with the TA value being based on the early UL synchronization performed by the UE. Also, these exemplary methods include sending the TA value for the second LTM candidate cell to the UE. Other embodiments include exemplary methods (e.g., procedures) for a fourth RAN node configured to facilitate LTM by UEs. In general, these exemplary methods may be complementary to the exemplary methods for a UE and a second RAN node summarized above.

[0030] These exemplary methods include receiving from a first RAN node an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node. These exemplary methods also include sending one of the following to a second RAN node:

[0031] • a message that includes early UL synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cells provided by a third RAN node, and a third LTM candidate cell provided by the first RAN node; or

[0032] • a request for one or more early UL synchronization configurations for the first LTM candidate cell.

[0033] In some embodiments, these exemplary methods also include, before receiving the LTM cell switch notification, receiving the early UL synchronization configurations for the first, second, and third LTM candidate cells from the respective second, third, and first RAN nodes. In some of these embodiments, the message sent to the second RAN node is an LTM cell switch notification. In other of these embodiments, the message sent to the second RAN node is a UE context modification request.

[0034] In some of these embodiments, these exemplary methods also include sending to the UE an LTM configuration that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells. The message is sent to the second RAN node in response to sending the LTM configuration. In some variants of these embodiments, these exemplary methods also include, in response to sending the LTM configuration to the UE, sending to the third RAN node a further message that includes the early UL synchronization configurations.

[0035] In various embodiments summarized above, the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a CU)associated with the first, second, and third DUs.

[0036] Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g, base stations, eNBs, gNBs, ng-eNBs, 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.

[0037] These and other embodiments described herein may provide various advantages, benefits, and / or solutions to problems. For example, embodiments may enable a UE’s serving DU to initiate an early TA acquisition (also referred to as early UL synchronization) procedure by the UE, even when the UE has performed one or more LTM cell switch procedures since the UE’s last reconfiguration by the RAN (e.g., CU). As such, embodiments may remove the need for the RAN to reconfigure the UE after every LTM cell switch to facilitate early TA acquisition, thereby reducing signaling overhead while facilitating the advantages of early TA acquisition for LTM. At a high level, embodiments may improve LTM for UEs in RANs.

[0038] 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.

[0039] BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figures 1-2 show two high-level views of an exemplary 5G / NR network architecture.

[0041] Figure 3 shows an exemplary configuration of NR user plane (UP) and control plane (CP) protocol stacks.

[0042] Figure 4 shows a signaling diagram for an exemplary LTM cell switch procedure.

[0043] Figure 5 shows a signaling diagram for an early timing advance (TA) acquisition procedure by a UE.

[0044] Figures 6A-B show various aspects of intra-CU / inter-DU LTM of a UE.

[0045] Figures 7-11 show signaling diagrams for procedures involving sharing of early UL synchronization configurations among RAN nodes serving a plurality of LTM candidate cells, according to various embodiments of the present disclosure.

[0046] Figure 12 shows a flow diagram of an exemplary method for a UE (e.g., wireless device), according to various embodiments of the present disclosure.

[0047] Figure 13 shows a flow diagram of an exemplary method for a first RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0048] Figure 14 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.

[0049] Figure 15 shows a flow diagram of an exemplary method for a fourth RAN node (e.g., base station, eNB, gNB, CU, etc.), according to various embodiments of the present disclosure.

[0050] Figure 16 shows a communication system according to various embodiments of the present disclosure.

[0051] Figure 17 shows a UE according to various embodiments of the present disclosure.

[0052] Figure 18 shows a network node according to various embodiments of the present disclosure. Figure 19 shows a virtualization environment in which some embodiments of the present disclosure may be virtualized.

[0053] DETAILED DESCRIPTION

[0054] 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.

[0055] 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.

[0056] Furthermore, the following terms are used throughout the description given below:

[0057] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g, gNB in a 3GPP 5G / NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g. CU and DU), a high-power or macro base station, a low-power base station (c.g. micro, pi co, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0058] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), aPDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0059] • 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”.

[0060] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0061] • 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.

[0062] • 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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 RRCJODLE 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 RRCJODLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. 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 LTE. Figure 3 shows a logical architecture for an NG-RAN node (e.g., gNB or ng-eNB) arranged in the split CU / DU architecture, such as gNB 100 in Figure 1. This logical architecture separates the CU into CP and UP functionality, called CU-C (or CU-CP) and CU-U (or CU-UP) respectively. Furthermore, each of the NG, Xn, and Fl interfaces is split into a CP interface (e.g., NG-C) and a UP interface (e.g., NG-U). Moreover, the CU-U and CU-C can communicate via an El interface. Each DU may be connected to only one CU-C, and each CU-U may be connected to only one CU-C. However, a single DU may be connected to multiple CU-Us under the control of the same CU-C, or a single CU-U may be connected to multiple DUs under the control of the same CU-C. Note that the terms “Central Entity” and “Distributed Entity” in Figure 3 refer to physical network nodes.

[0069] 3GPP Rel-10 introduced support for channel bandwidths larger than 20 MHz in LTE networks. To remain compatible with UEs from earlier releases (e.g., LTE Rel-8), a wideband LTE Rel-10 carrier appears as multiple component carriers (CCs), each having the same structure as an LTE Rel-8 carrier. A Rel-10 UE can receive the multiple CCs based on Carrier Aggregation (CA). The CCs can also be considered “cells,” such that a UE in CA has one primary cell (PCell) and one or more secondary cells (SCells) that are referred to collectively as a “cell group.” LTE Rel-12 introduced dual connectivity (DC) whereby a UE is connected simultaneously to a master node (MN) that provides a master cell group (MCG) and a secondary node (SN) that provides a secondary cell group (SCG).

[0070] Each cell group includes one MAC entity, a set of logical channels with associated RLC entities, a primary cell (PCell or PSCell), and optionally one or more secondary cells (SCells). The term “Special Cell” (or “SpCell” for short) refers to the PCell of the MCG or the PSCell of the SCG depending on whether the UE’s MAC entity is associated with the MCG or the SCG. In non-DC operation (e.g., carrier aggregation), SpCell refers to the PCell. An SpCell is always activated and supports physical UL control channel (PUCCH) transmission and contention-based random access by UEs.

[0071] NR includes support for CA and DC in Rel-15 and thereafter. 3GPP TR 38.804 (vl4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply NR, LTE, or both.

[0072] 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 (e.g., when CA is configured). 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 RRCReconflguration message with a reconflgurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by layer 3 (L3, i.e., RRC) and the messages exchanged are part of L3.

[0073] 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.

[0074] 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).

[0075] 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).

[0076] 3GPP Rel-18 includes an NR mobility enhancement referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). Current L3-based inter-cell mobility procedures involve LI and L2 resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching. Thus, Rel-18 LTM is intended to facilitate serving cell changes via L1 / L2 signaling that reduce latency, signaling overhead, and interruptions. In LTM, a UE is pre-configured by its serving RAN with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration”. This configuration may be an RRCReconflguration message or a portion thereof, such as one or more lEs / fields / parameters (e.g., CellGroupConflg 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.

[0077] 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 (serving or 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).

[0078] Figure 4 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.

[0079] 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 RRCReconflguration 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 RRCReconflgurationComplete message to the gNB.

[0080] 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 SR from the UE. Accordingly, 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. 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.

[0081] 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.

[0082] 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.

[0083] 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 layer 3 (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.

[0084] 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.

[0085] 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 of 3GPP TS 38.321 (v!7.7.0). In operation 8, the UE completes the LTM cell switch procedure by sending RRCReconflgurationComplete 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.

[0086] To trigger LTM by a UE, the network sends the UE an LTM Cell Switch command an indication of an LTM candidate cell and an indication of a beam based on which the UE should access the indicated LTM candidate cell. In 5G / NR, the beam indication is given as a transmission configuration indicator (TCI) state identifier (ID) associated with the LTM candidate cell, which may be indicated by an LTM candidate configuration ID. In response, the UE performs the LTM cell switch, accesses the indicated cell / beam, and transmits a complete message.

[0087] Figure 5 shows a signaling diagram for an early TA acquisition procedure, which may be part of the LTM cell switch procedure shown in Figure 4. 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.

[0088] In operation 1, the gNB serving Cell A provides the TA acquisition configuration to the UE within the RRCReconflguration message. The TA acquisition configuration includes RRC configuration information required to send a random access preamble to Cell B so that the gNB serving Cell B can calculate a TA value to be used by the UE, e.g., in case the UE performs an LTM cell switch procedure to Cell B. The TA acquisition configuration may include information for one or multiple cells for which the UE should execute the TA acquisition procedure. In operation 2, the UE replies with the RRCReconflgurationComplete message.

[0089] In operation 3, the gNB serving Cell A sends the UE a PDCCH order message to initiate the UE’s TA acquisition procedure with Cell B. The PDCCH order includes additional information required to send a random access preamble to Cell B. In operation 4, the UE sends a random access preamble to Cell B in accordance with the configuration, so that the gNB serving Cell B belongs can calculate a TA value that may be used by the UE in Cell B, as mentioned above. Note that the gNB serving Cell A may indicate the retransmission of a random access preamble for TA acquisition in case no TA is obtained.

[0090] In operation 5, the gNB serving Cell A provides the TA value for Cell B, calculated by the gNB serving Cell B during the TA acquisition procedure, such as in an LTM cell switch command (e.g., MAC CE) that initiates the UE’s LTM cell switch procedure to Cell B. To summarize, an LTM candidate cell configuration may include a random access (or RACH) configuration based on which the UE performs early UL sync procedure, and the serving RAN node may send a PDCCH order that indicates certain parameters of the RACH configuration for an LTM candidate cell, which triggers the UE to initiates a random access procedure towards the LTM candidate cell according to the indicated parameters. For example, the UE selects an SSB of the LTM candidate cell indicated in the PDCCH order, selects a PRACH resource based on the selected SSB, and transmits a preamble using the selected PRACH resource. When the RAN node (e.g., candidate DU) serving the LTM candidate cell receives the random access preamble from the UE, it calculates a Timing Advance (TA) value for the UE in the LTM candidate cell and provides the TA value to the RAN node that provides the UE’s current serving cell (e.g., source DU). As mentioned above in relation to Figure 5, the serving RAN node may provide the TA value to the UE in an LTM cell switch command.

[0091] According to 3GPP agreements, a UE may perform multiple LTM cell switch procedures without the need of being reconfigured by the RAN. For example, after the UE has performed an LTM cell switch from a serving cell to a first target cell (e.g., a first LTM candidate cell), the UE may perform another LTM cell switch to a second target cell (e.g., a second LTM candidate cell previously configured) without receiving another RRCReconflguration message in the first target cell. This second LTM cell switch may be referred to as “subsequent LTM” or “subsequent LTM cell switch”.

[0092] If another TA acquisition procedure needs to be triggered upon subsequent LTM cell switches by the UE, the UE’s “new” serving DU (S-DU, e.g., of the first target cell) is unable to trigger the UE’s early UL sync to other configured LTM candidate cells. This is because the new S-DU is not aware of the RACH configurations for TA acquisition that were provided by other DUs that serve other LTM candidate cells for the UE. As such, the new S-DU is unable to send a PDCCH order indicating parameters of these RACH configurations, as required to initiate UE early UL synchronization.

[0093] This problem is further illustrated by Figures 6A-B, which shows various aspects of intra- CU / inter-DU LTM of a UE (610). A CU (650) is associated with three DUs: the UE’s initial S- DU (620, i.e., that provides the UE’s serving cell), candidate DU 1 (C-DU1, 630) that provides a first LTM candidate cell, and candidate DU 2 (C-DU2, 640) that provides a second LTM candidate cell.

[0094] In Figure 6A, the CU requests and receives early UL synchronization configurations from S-DU, C-DU1, and C-DU2, then provides all three early UL synchronization configurations to the S-DU. These early UL synchronization configurations are represented by rectangles filled with different patterns, as indicated in the legend. In Figure 6B, the S-DU sends the UE a PDCCH order to trigger the UE’s early UL synchronization with an LTM candidate cell served by C-DU2. The PDCCH order that indicates certain parameters of the RACH configuration for that LTM candidate cell, previously sent to the UE in Figure 6A. The UE transmits a random access preamble according to the PDCCH order, and C-DU2 determines an appropriate TA value for the UE and sends that TA value to the CU, which in turn provides it to the S-DU. Subsequently, the S-DU sends an LTM cell switch command to the UE for the LTM candidate cell served by C-DU2, and includes the received TA value. The S-DU sends a notification of the LTM cell switch to the CU, which forwards it to C- DU2. Subsequently, the UE transmits an RRCReconfigurationComplete message to C-DU2.

[0095] As shown in Figure 6B, after the UE’s LTM cell switch to the LTM candidate cell served by C-DU2 (new S-DU), only UE, CU, and previous S-DU are aware of the early UL synchronization configurations provided by S-DU, C-DU1, and C-DU2. Thus, the UE’s new S- DU - previously C-DU2 - is unaware of the early UL synchronization configurations provided by the UE’s previous S-DU (now “C-DU3”) and C-DU1, so is unable to send the UE a PDCCH order that references parameters in these configurations. On the UE side, before initiating early UL synchronization in an LTM candidate cell after the initial LTM cell switch, the UE would need to receive another RRCReconflguration message that includes an early UL synchronization configuration which is known at the C-DU of the LTM candidate cell.

[0096] Accordingly, embodiments of the present disclosure address these problems and / or issues by flexible and efficient techniques by which RAN nodes (e.g., CU, S-DU, C-DUs) can share relevant early UL synchronization configurations for a UE’s LTM candidate cells after the UE’s (initial) LTM cell switch procedure.

[0097] Embodiments of the present disclosure may provide various advantages and / or benefits. For example, embodiments enable aUE’s serving DU to initiate an early TA acquisition procedure by the UE, even when the UE has performed one or more LTM cell switch procedures since the UE’s last reconfiguration by the RAN (e.g., CU). As such, embodiments may remove the need for the RAN to reconfigure the UE after every LTM cell switch to facilitate early TA acquisition, thereby reducing signaling overhead while facilitating the advantages of early TA acquisition for LTM.

[0098] After LTM cell switch to an LTM candidate cell, a UE does not need to receive another early UL synchronization configuration for another LTM candidate cell, but can directly receive a PDCCH order referencing a previously received early UL synchronization configuration for the other LTM candidate cell. This reduces the UE’s signaling with the RAN and facilitates faster early UL synchronization for subsequent LTM. In some embodiments, after triggering an LTM cell switch procedure by a UE to a first LTM candidate cell (e.g., based on an LTM cell switch command), the UE’s S-DU sends one or more previously received early UL synchronization configurations for other LTM candidate cells to the C-DU that serves the first LTM candidate cell. These configurations may be sent directly or via a common CU. These embodiments may be referred to as “S -DU-triggered”, possibly with some CU involvement for forwarding the early UL synchronization configurations.

[0099] In other embodiments, after receiving a message from the UE’s S-DU that an LTM cell switch procedure to a first LTM candidate cell has been triggered by the S-DU, the CU sends one or more previously received early UL synchronization configurations for other LTM candidate cells to the C-DU that serves the first LTM candidate cell. For example, the CU may retrieve the configurations that were previously stored by the CU during LTM configuration of the UE. These embodiments may be referred to as “CU-triggered”.

[0100] Additional benefits and / or advantages of the S -DU-triggered and CU-triggered embodiments may include that the UE’s new S-DU after the LTM cell switch becomes aware of early UL synchronization configurations only when necessary, and informs other C-DUs of early UL synchronization configurations only when necessary. For example, a DU may serve an LTM candidate cell for which no LTM cell switch is triggered due to UE movement patterns, in which case the DU does not receive unnecessary early UL synchronization configurations for the UE. An additional benefit and / or advantage is that the CU may have the possibility to update early UL synchronization configurations, such as removing ones for DU(s) that are no longer available (e.g., due to failure).

[0101] In other embodiments, after collecting early UL synchronization configurations for LTM candidate cells from the S-DU or the C-DU that serves these respective cells, the CU sends the collected early UL synchronization configurations not only to the UE’s S-DU (as done conventionally) but also to any C-DU that provided an early UL synchronization configuration. For example, each C-DU receives early UL synchronization configurations provided by the UE’s S-DU and other C-DUs. An additional benefit of these embodiments is that C-DUs are prepared for a UE’s subsequent LTM before it occurs, since they receive early UL synchronization configurations when LTM is initially configured for the UE.

[0102] In other embodiments, when a CU requests a DU to provide an early UL synchronization configuration for a UE to an LTM candidate cell served by the DU, the CU includes in the request a list of DUs for which the recipient DU should provide early UL synchronization configurations for the LTM candidate cell. The recipient DU responds with the requested early UL synchronization configurations, which the CU sends to the respective DUs in the list. In other embodiments, after a C-DU receives a message from a UE indicating that the UE’s LTM cell switch procedure to an LTM candidate cell provided by the C-DU is complete (e.g., RRCReconflgurationComplete'), the C-DU (new S-DU) may request the CU to provide the latest early UL synchronization (or RACH) configurations for other DUs associated with the CU. The CU collects the requested early UL synchronization (or RACH) configurations and sends them to the requesting C-DU (new S-DU).

[0103] An additional benefit of these embodiments is that a UE’ s new S-DU after LTM cell switch may request updated early UL synchronization configurations when existing configurations are or may be out-of-date. For example, the new S-DU may use a validity timer whose expiration indicates one or more early UL synchronization configurations are out-of-date.

[0104] In some embodiments, a UE receives early UL synchronization configurations for respective first and second LTM candidate cells while operating in a source cell provided by an S-DU. The first and second LTM candidate cells are provided by first and second C-DUs. After performing an LTM cell switch to the first LTM candidate cell provided by the first C-DU (which becomes the new S-DU), the UE receives a PDCCH order from the new S-DU that references the second early UL synchronization configuration received in the source cell, and initiates an early UL synchronization procedure towards the second LTM candidate cell. This early UL synchronization procedure is performed without the UE being reconfigured (e.g., by an RRCReconflguration message) after the LTM cell switch procedure.

[0105] In the present disclosure, the following terms may be used interchangeably: “L1 / L2 based inter-cell mobility”, “L1 / L2 mobility,” “LI -mobility,” “LI based mobility,” “Ll / L2-centric inter-cell mobility,” “L1 / L2 inter-cell mobility,” “inter-cell beam management,” “inter-DU L1 / L2 based inter-cell mobility”, and “L1 / L2 triggered mobility” (or LTM). These terms refer to a scenario in which a UE receives lower layer (i.e., below RRC, such as MAC or PHY) signaling from a network indicating for the UE to change of its serving cell (e.g., PCell) from a source cell to a target cell.

[0106] The content of the lower layer signaling may be referred to as “LTM cell switch command”. Exemplary lower layer signaling includes LI DL control information (DCI) and L2 MAC control element (CE). Compared to conventional RRC signaling, lower layer signaling reduces processing time and interruption time during mobility and may also increase mobility robustness since the network can respond more quickly to changes in the UE’s channel conditions.

[0107] 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.

[0108] 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). For example, an LTM cell switch may include a change in SpCell (e.g., PCell for MCG, PSCell for SCG) and a change (e.g., addition, modification and / or release) in SCells of the same cell group. This may happen when the command triggers the UE to change to another cell group configuration of the same type (e.g., another SCG configuration).

[0109] Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more “LTM candidate cell configurations” via an RRCReconflguration message. The terms “(LTM) candidate configuration”, “(LTM) candidate target cell configuration”, and “(LTM) target candidate (cell) configuration” may be used interchangeably with LTM candidate cell configuration.

[0110] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConfig, SpCellConfig, or SCellConfig and / or an embedded RRCReconflguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”.

[0111] 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. 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.

[0112] 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):

[0113] • an LTM candidate configuration, i.e., for an LTM candidate cell;

[0114] • a measurement configuration, e.g., LI measurement and reporting configuration for the LTM candidate cell;

[0115] • a configuration for early DL synchronization, e.g., for early TCI state activation;

[0116] • a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

[0117] • 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.).

[0118] 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).

[0119] 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.

[0120] 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.

[0121] The phrase “early TA acquisition” describes a procedure executed by a UE and a RAN node to determine a timing advance (TA) value for the UE in an LTM candidate cell prior to the RAN triggering (and the UE performing) an LTM cell switch to the LTM candidate cell. This phrase is used synonymously herein with “TA acquisition”, “early UL synchronization”, “early UL sync”, “early synchronization”, and “early sync”.

[0122] Figures 7-10 show signaling diagrams for procedures involving sharing of early UL synchronization configurations among RAN nodes serving a plurality of LTM candidate cells, according to various embodiments of the present disclosure. The procedures involve a UE (710) and a CU (750). The CU is associated with three DUs: the UE’s initial S-DU (720, that provides the UE’s serving cell), candidate DU 1 (C-DU1, 730) that provides a first LTM candidate cell, and candidate DU 1 (C-DU1, 740) that provides a second LTM candidate cell.

[0123] In Figures 7-10, early UL synchronization configurations associated with different DUs are represented by rectangles filled with different patterns, as indicated in the respective legends. Some operations in Figures 7-10 correspond to operations in Figures 5-6, with the above descriptions of these operations applying equally to Figures 7-10.

[0124] Figure 7 shows a procedure in which the UE’s previous S-DU (720) sends the early UL synchronization configurations for the UE’s configured LTM candidate cells to C-DU2 (740), which has become the UE’s new S-DU after the previous S-DU triggered an LTM cell switch by the UE to an LTM candidate cell served by C-DU2. In this example, the previous S-DU sends the early UL synchronization configurations to the CU in an LTM cell switch notification message, which the CU forwards to the new S-DU. After the UE performs an initial LTM cell switch such that C-DU2 is now the UE’s new S-DU, the new S-DU sends a PDCCH order to the UE, indicating for the UE to perform an early UL synchronization to an LTM candidate cell served by C-DU1. Since the new S-DU previously received the early UL synchronization configuration for this cell while it was C-DU2, the new S-DU’s PDCCH order can reference this early UL synchronization configuration (which the UE also previously received). Accordingly, the UE can transmit a random access preamble in LTM candidate cell according to the PDCCH order. The embodiments shown in Figure 7 may be referred to as “S-DU-triggered”.

[0125] Figure 8 shows a procedure in which the CU, after receiving an LTM cell switch notification message from the UE’s S-DU indicating that an LTM cell switch procedure to an LTM candidate cell served by C-DU2 has been triggered by the S-DU, sends previously received early UL synchronization configurations for the UE to C-DU2 (i.e., new S-DU) in an LTM cell switch notification message. For example, the CU may retrieve the configurations that it previously stored during LTM configuration of the UE. These embodiments may be referred to as “CU-triggered”. Although not shown, the procedure in Figure 8 may include a PDCCH order and subsequent early UL synchronization as shown in Figure 7.

[0126] Figure 9 shows a procedure in which the CU, after collecting early UL synchronization configurations for LTM candidate cells from the S-DU or the C-DU that serves these respective cells, sends the collected early UL synchronization configurations not only to the UE’s S-DU (as done conventionally) but also to any C-DU that provided an early UL synchronization configuration. As illustrated in Figure 9, this may be done prior to triggering any LTM cell switch by the UE, i.e., before the UE’s S-DU changes. For example, each C-DU receives early UL synchronization configurations provided by the UE’s S-DU and other C-DUs. A new message may be defined for sending these early UL synchronization configurations to the C-DUs. After receiving these configurations, each DU is prepared to trigger UE early UL synchronization for subsequent LTM.

[0127] Figure 10 shows a procedure in which a C-DU, after receiving a message from a UE indicating that the UE’s LTM cell switch procedure to an LTM candidate cell provided by the C- DU is complete (e.g., RRCReconflgurationComplete), the C-DU (new S-DU) requests the CU to provide the latest early UL synchronization configurations for other DUs associated with the CU. In this procedure, the CU requests and receives updated early UL synchronization configurations from C-DU1 and C-DU2, and sends them to the new S-DU that requested them. After receiving these configurations, the new S-DU is prepared to trigger UE early UL synchronization for subsequent LTM.

[0128] Figure 11 shows a signaling diagram for a procedure involving sharing of early UL synchronization configurations among RAN nodes serving a plurality of LTM candidate cells, according to other embodiments of the present disclosure. The procedures involve a CU-CP (1110) and three associated DUs: DU1 (1120), DU2 (1130), and DU3 (1140). As in Figures 7- 10, different early UL synchronization configurations are represented by rectangles filled with different patterns, as indicated in the legend.

[0129] In Figure 11, the CU-CP requests DU3 to provide an early UL synchronization configuration for a UE to an LTM candidate cell “C” served by the DU. For example, the request may be a UE context setup request or a UE context modification request. In this request, the CU includes an identifier (e.g., cell global identity, CGI) of LTM candidate cell “C” and a list of DUs (e.g., respective identifiers) for which DU3 should provide early UL synchronization configurations for the LTM candidate cell. The recipient DU responds with the requested early UL synchronization configurations, each associated with an identifier of the intended recipient DU. For example, the response may be a UE context setup response or a UE context modification response, according to the type of request message.

[0130] The CU sends the received early UL synchronization configurations to the respective DUs in the list. For example, the CU may send each of these early UL synchronization configurations in a UE context setup request or a UE context modification request, along with the LTM candidate cell identifier. Various features of the embodiments described above correspond to various operations illustrated in Figures 12-15, which show exemplary methods (e.g., procedures) for a UE, a first RAN node, a second RAN node, and a fourth 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 12-15 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 12- 15 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.

[0131] In particular, Figure 12 shows an exemplary method (e.g., procedure) for a UE configured for LTM in a radio access network (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.

[0132] The exemplary method includes the operations of block 1210, where the UE an early uplink (UL) synchronization configurations for a second LTM candidate cell. The exemplary method also includes the operations of block 1230, where the UE performs an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell. The exemplary method also includes the operations of block 1240, where the UE subsequently receives an indication to perform an early UL synchronization to the second LTM candidate cell. The indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell. The exemplary method also includes the operations of block 1250, where the UE performs an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

[0133] In some embodiments, the indication is a physical downlink control channel (PDCCH) order. In some embodiments, the early UL synchronization configuration for the second LTM candidate cell is received (e.g., in block 1210) from a fourth RAN node via the source cell, which is provided by a first RAN node. The first and second LTM candidate cells are provided by respective second and third RAN nodes, and the indication is received (e.g., in block 1240) from the second RAN node via the target cell.

[0134] In some of these embodiments, the first RAN node is a first DU, the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a CU associated with the first, second, and third DUs.

[0135] In some of these embodiments, performing the LTM cell switch from the source cell to the first LTM candidate cell as target cell in block 1230 includes the operations of sub-block 1231, where the UE transmits, to the fourth RAN node via the target cell, a reconfiguration complete message indicating that the LTM cell switch has been completed.

[0136] In some of these embodiments, performing the early UL synchronization to the second LTM candidate cell based on the referenced parameters in block 1230 includes the operations of block 1231, where the UE transmits a random access (RA) preamble using RA resources of the second LTM candidate cell. The RA preamble and / or the RA resources are referenced by the indication. In some variants of these embodiments, the RA resources referenced by the indication include one or more of the following: time / frequency resources, and one or more beams.

[0137] In some variants of these embodiments, the exemplary method also includes the operations of block 1260, where after performing the early UL synchronization to the second LTM candidate cell in block 1250, the UE receives from the second RAN node a timing advance (TA) value determined by the third RAN node based on the transmitted RA preamble. In some further variants, the TA value is received in a command for an LTM cell switch from the target cell to the second LTM candidate cell.

[0138] In some embodiments, the early UL synchronization configuration for the second LTM candidate cell is received (e.g., in block 1210) with an early UL synchronization configuration for the first LTM candidate cell In such embodiments, the exemplary method also includes the operations of block 1220, where prior to the LTM cell switch, the UE performs an early UL synchronization to the first LTM candidate cell based on the received early UL synchronization configuration for the first LTM candidate cell.

[0139] In some embodiments, the early UL synchronization configuration for the second LTM candidate cell includes one or more of the following:

[0140] • an identifier or index of a random access (RA) preamble;

[0141] • an identifier of the first RAN node;

[0142] • a synchronization signal / PBCH (SSB) index;

[0143] • a RA configuration identifier

[0144] • an identifier of the UE; and

[0145] • an identifier of the second LTM candidate cell.

[0146] In addition, Figure 13 shows an exemplary method (e.g., procedure) for a first RAN node configured to facilitate 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.

[0147] The exemplary method includes the operations of block 1330, where the first RAN node receives, from a fourth RAN node, an LTM configuration for a UE served by a source cell provided by the first RAN node. The LTM configuration includes early UL synchronization configurations for first and second LTM candidate cells provided by respective second and third RAN nodes. The exemplary method also includes the operations of block 1340, where the first RAN node sends the received LTM configuration to the UE via the source cell. The exemplary method also includes the operations of block 1360, where the first RAN node initiates an LTM cell switch for the UE from the source cell to the first LTM candidate cell, as a target cell.

[0148] In some embodiments, the exemplary method also includes the operations of block 1210, where the first RAN node sends to the fourth RAN node an early UL synchronization configuration for the source cell. The received LTM configuration includes the early UL synchronization configuration for the source cell, as a third LTM candidate cell for the UE.

[0149] In some embodiments, the exemplary method also includes the operations of block 1370, where after initiating the LTM cell switch, the first RAN node sends to the fourth RAN node an LTM cell switch notification that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells. Figure 7 shows an example of these embodiments.

[0150] In other embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0151] • (1320) receiving, from the UE, a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the source cell; and

[0152] • (1325) sending to the fourth RAN node a request for updated early UL synchronization configurations for the UE.

[0153] The LTM configuration is received from the fourth RAN node in response to the request. Figure 10 shows an example of these embodiments.

[0154] In other embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0155] • (1380) receiving from the fourth RAN node a request to provide early UL synchronization configurations for use by one or more other RAN nodes, wherein the request identifies the following: the source cell as a third LTM candidate cell, and the one or more RAN nodes for which the requested early UL synchronization configurations should be provided;

[0156] • (1385) for each of the identified RAN nodes, determining a corresponding early UL synchronization configuration for the third LTM candidate cell; and

[0157] • (1390) sending to the fourth RAN node a response that includes the early UL synchronization configurations determined for the respective identified RAN nodes.

[0158] Figure 11 shows an example of these embodiments.

[0159] In some embodiments, the exemplary method also includes the operations of block 1345, where after sending the received LTM configuration but before initiating the LTM cell switch, the first RAN node sends to the UE an indication to perform an early UL synchronization to the first LTM candidate cell. The indication references one or more parameters in the early UL synchronization configuration for the first LTM candidate cell. In some of these embodiments, the indication is a physical downlink control channel (PDCCH) order. In some of these embodiments, the one or more parameters referenced by the indication include one or more of the following: a random access (RA) preamble, time / frequency RA resources, and one or more beams.

[0160] In some of these embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0161] • (1350) receiving from the second RAN node a TA value for the first LTM candidate cell, based on the early UL synchronization performed by the UE; and

[0162] • (1355) sending the TA value for the first LTM candidate cell to the UE.

[0163] In some variants of these embodiments, the TA value is sent to the UE in an LTM cell switch command that initiates the LTM cell switch for the UE.

[0164] In some embodiments, the first RAN node is a first DU, the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a CU associated with the first, second, and third DUs. In some embodiments, for each of the first and second LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following:

[0165] • an identifier or index of a RA preamble;

[0166] • an identifier of the first RAN node;

[0167] • an SSB index;

[0168] • a RA configuration identifier

[0169] • an identifier of the UE; and

[0170] • an identifier of the LTM candidate cell.

[0171] In addition, Figure 14 shows an exemplary method (e.g., procedure) for a second RAN node configured to facilitate LTM by 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.

[0172] The exemplary method includes the operations of block 1410, where the second RAN node receives one of the following from a fourth RAN node:

[0173] • a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cells provided by a third RAN node, and a third LTM candidate cell provided by a first RAN node; or

[0174] • a request for one or more early UL synchronization configurations for the first LTM candidate. The exemplary method also includes the operations of block 1450, where the second RAN node receives from a UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell.

[0175] In some embodiments, the message received from the fourth RAN node is an LTM cell switch notification, which indicates initiation of the UE’s LTM cell switch to the first LTM candidate cell. Figures 7-8 show examples of these embodiments. In other embodiments, the message received from the fourth RAN node is a UE context modification request.

[0176] In some embodiments, the message is received from the fourth RAN node before the UE’s LTM cell switch to the first LTM candidate cell. Figure 9 shows an example of these embodiments. In some of these embodiments, the exemplary method also includes the operations of block 1460, where the second RAN node sends to the UE an indication to perform an early UL synchronization to the second LTM candidate cell. The indication references one or more parameters in the early UL synchronization configuration for the second LTM candidate cell.

[0177] In some variants of these embodiments, the indication is a PDCCH order. In some variants of these embodiments, the one or more parameters referenced by the indication include one or more of the following: a RA preamble, time / frequency RA resources, and one or more beams. In some variants of these embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0178] • (1470) receiving from the third RAN node a TA value for the second LTM candidate cell, the TA value being based on the early UL synchronization performed by the UE; and

[0179] • (1480) sending the TA value for the second LTM candidate cell to the UE. For example, the TA value is sent to the UE in an LTM cell switch command.

[0180] In other embodiments, the request is received from the fourth RAN node before initiation of the UE’s LTM cell switch to the first LTM candidate cell, and the exemplary method also includes the operations of block 1420, where the second RAN node sends to the fourth RAN node a response that includes the requested one or more early UL synchronization configurations for the first LTM candidate cell. In some of these embodiments, the request is for a single early UL synchronization configurations for the first LTM candidate cell. Figure 10 is an example of these embodiments.

[0181] In other of these embodiments, the request identifies the first LTM candidate cell and one or more RAN nodes for which the requested early UL synchronization configurations should be provided. Also, the exemplary method also includes the following operations

[0182] • (1430) for each of the identified RAN nodes, determining a corresponding early UL synchronization configuration for the first LTM candidate cell; and

[0183] • (1440) sending to the fourth RAN node a response that includes the early UL synchronization configurations determined for the respective identified RAN nodes. Figure 11 is an example of these embodiments.

[0184] In some embodiments, the first RAN node is a first DU, the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a CU associated with the first, second, and third DUs. In some embodiments, for each of the first, second, and third LTM candidate cells, the early UL synchronization configuration for the LTM candidate cell includes one or more of the following:

[0185] • an identifier or index of a RA preamble;

[0186] • an identifier of the first RAN node;

[0187] • an SSB index;

[0188] • a RA configuration identifier

[0189] • an identifier of the UE; and

[0190] • an identifier of the LTM candidate cell.

[0191] In addition, Figure 15 shows an exemplary method (e.g., procedure) for a fourth RAN node configured to facilitate 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.

[0192] The exemplary method includes the operations of block 1540, where the fourth RAN node receives from a first RAN node an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node. The exemplary method includes the operations of block 1570, where the fourth RAN node sends one of the following to a second RAN node:

[0193] • a message that includes early UL synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cells provided by a third RAN node, and a third LTM candidate cell provided by the first RAN node; or

[0194] • a request for one or more early UL synchronization configurations for the first LTM candidate cell.

[0195] In some embodiments, the early UL synchronization configurations for the first, second, and third LTM candidate cells are included in or with the received LTM cell switch notification, and the message sent to the second RAN node is an LTM cell switch notification that includes the early UL synchronization configurations. Figure 7 shows an example of these embodiments.

[0196] In other embodiments, the exemplary method also includes the operations of block 1510, where before receiving the LTM cell switch notification in block 1540, the fourth RAN node receives the early UL synchronization configurations for the first, second, and third LTM candidate cells from the respective second, third, and first RAN nodes. In some of these embodiments, the exemplary method also includes the operations of block 1520, where the fourth RAN node stores the received early UL synchronization configurations. The message sent to the second RAN node in block 1560 is an LTM cell switch notification that includes the stored early UL synchronization configurations (i.e. , retrieved from their storage locations). Figure 8 shows an example of these embodiments. In other of these embodiments, the message sent to the second RAN node is a UE context modification request.

[0197] In other of these embodiments, the exemplary method also includes the operations of block 1525, where the fourth RAN node sends to the UE an LTM configuration that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells. The message is sent to the second RAN node in block 1560 in response to sending the LTM configuration. Figure 9 shows an example of these embodiments. In some variants of these embodiments, the exemplary method also includes the operations of block 1530, where in response to sending the LTM configuration, the fourth RAN node sends to the third RAN node a further message that includes the early UL synchronization configurations.

[0198] In other embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0199] • (1550) after completion of the LTM cell switch, receiving from the second RAN node a request for updated early UL synchronization configurations for the UE;

[0200] • (1555) sending to the first and third RAN nodes respective requests for updated early UL synchronization configurations for the respective third and second LTM candidate cells;

[0201] • (1560) receiving updated early UL synchronization configurations from the first and third RAN node in accordance with the respective requests;

[0202] The message sent to the second RAN node in block 1570 includes the updated early UL synchronization configurations for the second and third LTM candidate cells. Figure 10 shows an example of these embodiments.

[0203] In other embodiments, the request sent to the second RAN node identifies the following: the first LTM candidate cell, and one or more RAN nodes for which the requested early UL synchronization configurations should be provided. Also, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0204] • (1580) receiving from the second RAN node a response that includes respective early UL synchronization configurations associated with the first LTM candidate cell and the respective identified RAN nodes; and

[0205] • (1590) sending, to each of the identified RAN nodes, the received early UL synchronization configuration associated with the first LTM candidate cell and the identified RAN node. Figure 11 shows an example of these embodiments.

[0206] In some embodiments, the first RAN node is a first DU, the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a CU associated with the first, second, and third DUs. In some embodiments, for each of the first, second, and third LTM candidate cells, the early UL synchronization configuration for the LTM candidate cell includes one or more of the following:

[0207] • an identifier or index of a RA preamble;

[0208] • an identifier of the first RAN node;

[0209] • an SSB index;

[0210] • a RA configuration identifier

[0211] • an identifier of the UE; and

[0212] • an identifier of the LTM candidate cell.

[0213] 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.

[0214] Figure 16 shows an example of a communication system 1600 in accordance with some embodiments. In this example, communication system 1600 includes a telecommunication network 1602 that includes an access network 1604 (e.g., RAN) and a core network 1606, which includes one or more core network nodes 1608. Access network 1604 includes one or more access network nodes, such as network nodes 1610a-b (one or more of which may be generally referred to as network nodes 1610), 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 1602 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1602 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 1602, including one or more network nodes 1610 and / or core network nodes 1608.

[0215] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (O-DU), an open central unit (O-CU), including an O-CU control plane (O-CU- CP) or an O-CU user plane (O-CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e. g. , r App), or any combination thereof (the adj ective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the 0-RAN Alliance or comparable technologies. Network nodes 1610 facilitate direct or indirect connection of UEs, such as by connecting UEs 1612a-d (one or more of which may be generally referred to as UEs 1612) to core network 1606 over one or more wireless connections.

[0216] 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 1600 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 1600 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0217] UEs 1612 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1610 and other communication devices. Similarly, network nodes 1610 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1612 and / or with other network nodes or equipment in telecommunication network 1602 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1602.

[0218] In the depicted example, core network 1606 connects network nodes 1610 to one or more hosts, such as host 1616. 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 1606 includes one or more core network nodes (e.g., 1608) 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 1608. Example core network nodes include functions 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).

[0219] Host 1616 may be under the ownership or control of a service provider other than an operator or provider of access network 1604 and / or telecommunication network 1602, and may be operated by the service provider or on behalf of the service provider. Host 1616 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.

[0220] As a whole, communication system 1600 of Figure 16 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.

[0221] In some examples, telecommunication network 1602 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1602 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1602. For example, telecommunication network 1602 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs. In some examples, UEs 1612 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 1604 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1604. 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).

[0222] In the example, hub 1614 communicates with access network 1604 to facilitate indirect communication between one or more UEs (e.g., 1612c and / or 1612d) and network nodes (e.g., 1610b). In some examples, hub 1614 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1614 may be a broadband router enabling access to core network 1606 for the UEs. As another example, hub 1614 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 1610, or by executable code, script, process, or other instructions in hub 1614. As another example, hub 1614 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 1614 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1614 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1614 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1614 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0223] Hub 1614 may have a constant / persistent or intermittent connection to network node 1610b. Hub 1614 may also allow for a different communication scheme and / or schedule between hub 1614 and UEs (e.g., 1612c and / or 1612d), and between hub 1614 and core network 1606. In other examples, hub 1614 is connected to core network 1606 and / or one or more UEs via a wired connection. Moreover, hub 1614 may be configured to connect to an M2M service provider over access network 1604 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1610 while still connected via hub 1614 via a wired or wireless connection. In some embodiments, hub 1614 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1610b. In other embodiments, hub 1614 may be a non-dedicated hub - that is, a device capable of routing communications between the UEs and network node 1610b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0224] In some embodiments, UE 1612 may be configured to perform various operations described above, such as the exemplary method shown in Figure 12. In some embodiments, one or more network nodes 1610 may be configured to perform various operations described above, such as the exemplary methods shown in Figures 13-15.

[0225] Figure 17 shows a UE 1700 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.

[0226] 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).

[0227] UE 1700 includes processing circuitry 1702 that is operatively coupled via a bus 1704 to an input / output interface 1706, a power source 1708, a memory 1710, a communication interface 1712, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 17. 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.

[0228] Processing circuitry 1702 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 1710. Processing circuitry 1702 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 1702 may include multiple central processing units (CPUs).

[0229] In the example, input / output interface 1706 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 1700. 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.

[0230] In some embodiments, power source 1708 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 1708 may further include power circuitry for delivering power from power source 1708 itself, and / or an external power source, to the various parts of UE 1700 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1708. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1708 to make the power suitable for the respective components of UE 1700 to which power is supplied.

[0231] Memory 1710 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 1710 includes one or more application programs 1714, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1716. Memory 1710 may store, for use by UE 1700, any of a variety of various operating systems or combinations of operating systems.

[0232] Memory 1710 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 1710 may allow UE 1700 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 1710, which may be or comprise a device-readable storage medium.

[0233] Processing circuitry 1702 may be configured to communicate with an access network or other network using communication interface 1712. Communication interface 1712 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1722. Communication interface 1712 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 1718 and / or a receiver 1720 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1718 and receiver 1720 may be coupled to one or more antennas (e.g., antenna 1722) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0234] In the illustrated embodiment, communication functions of communication interface 1712 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 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. Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1712, 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).

[0235] 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.

[0236] 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 1700 shown in Figure 17.

[0237] 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.

[0238] 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.

[0239] In some embodiments, UE 1700 may be configured to perform various operations described above, such as the exemplary method shown in Figure 12.

[0240] Figure 18 shows a network node 1800 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).

[0241] 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).

[0242] 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).

[0243] Network node 1800 includes processing circuitry 1802, memory 1804, communication interface 1806, and power source 1808. Network node 1800 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 1800 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 1800 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1804 for different RATs) and some components may be reused (e.g., a same antenna 1810 may be shared by different RATs). Network node 1800 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1800, 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 1800.

[0244] Processing circuitry 1802 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 1800 components, such as memory 1804, to provide network node 1800 functionality.

[0245] In some embodiments, processing circuitry 1802 includes a system on a chip (SOC). In some embodiments, processing circuitry 1802 includes radio frequency (RF) transceiver circuitry 1812 and / or baseband processing circuitry 1814. In some embodiments, RF transceiver circuitry 1812 and / or baseband processing circuitry 1814 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 1812 and / or baseband processing circuitry 1814 may be on the same chip or set of chips, boards, or units.

[0246] Memory 1804 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 1802. Memory 1804 may store any suitable instructions, data, or information, including a computer program, software, an application including logic, rules, code, tables, and / or other instructions (collected denoted computer program 1804a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1802 and utilized by network node 1800. Memory 1804 may be used to store any calculations made by processing circuitry 1802 and / or any data received via communication interface 1806. In some embodiments, processing circuitry 1802 and memory 1804 is integrated.

[0247] Communication interface 1806 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 1806 comprises port(s) / terminal(s) 1816 to send and receive data, for example to and from a network over a wired connection. Communication interface 1806 also includes radio frontend circuitry 1818 that may be coupled to, or in certain embodiments a part of, antenna 1810. Radio front-end circuitry 1818 comprises filters 1820 and amplifiers 1822. Radio front-end circuitry 1818 may be connected to an antenna 1810 and processing circuitry 1802. The radio front-end circuitry may be configured to condition signals communicated between antenna 1810 and processing circuitry 1802. Radio front-end circuitry 1818 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1818 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1820 and / or amplifiers 1822. The radio signal may then be transmitted via antenna 1810. Similarly, when receiving data, antenna 1810 may collect radio signals which are then converted into digital data by radio front-end circuitry 1818. The digital data may be passed to processing circuitry 1802. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0248] In certain alternative embodiments, network node 1800 does not include separate radio front-end circuitry 1818, instead, processing circuitry 1802 includes radio front-end circuitry and is connected to antenna 1810. Similarly, in some embodiments, all or some of RF transceiver circuitry 1812 is part of communication interface 1806. In still other embodiments, communication interface 1806 includes one or more ports or terminals 1816, radio front-end circuitry 1818, and RF transceiver circuitry 1812, as part of a radio unit (not shown), and communication interface 1806 communicates with baseband processing circuitry 1814, which is part of a digital unit (not shown).

[0249] Antenna 1810 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1810 may be coupled to radio front-end circuitry 1818 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1810 is separate from network node 1800 and connectable to network node 1800 through an interface or port. Antenna 1810, communication interface 1806, and / or processing circuitry 1802 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 1810, communication interface 1806, and / or processing circuitry 1802 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.

[0250] Power source 1808 provides power to the various components of network node 1800 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1808 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1800 with power for performing the functionality described herein. For example, network node 1800 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 1808. As a further example, power source 1808 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.

[0251] Embodiments of network node 1800 may include additional components beyond those shown in Figure 18 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 1800 may include user interface equipment to allow input of information into network node 1800 and to allow output of information from network node 1800. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1800.

[0252] In some embodiments, one or more network nodes 1800 may be configured to perform various operations described above, such as the exemplary methods shown in Figures 13-15.

[0253] Figure 19 is a block diagram illustrating a virtualization environment 1900 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 1900 hosted by one or more 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 1900 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an 0-2 interface.

[0254] Applications 1902 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1900 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein. In some embodiments, one or more virtual nodes 1902 may be configured to perform various operations described above, such as the exemplary methods shown in Figures 13-15.

[0255] Hardware 1904 includes processing circuitry, memory that stores software and / or instructions (collected denoted computer program 1904a, 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 1906 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1908a-b (one or more of which may be generally referred to as VMs 1908), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1906 may present a virtual operating platform that appears like networking hardware to the VMs 1908.

[0256] VMs 1908 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1906. Different embodiments of the instance of a virtual appliance 1902 may be implemented on one or more of VMs 1908, 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.

[0257] In the context of NFV, each VM 1908 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 1908, and that part of hardware 1904 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 1908 on top of the hardware 1904 and corresponds to the application 1902.

[0258] Hardware 1904 may be implemented in a standalone network node with generic or specific components. Hardware 1904 may implement some functions via virtualization. Alternatively, hardware 1904 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 1910, which, among others, oversees lifecycle management of applications 1902. In some embodiments, hardware 1904 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 1912 which may alternatively be used for communication between hardware nodes and radio units.

[0259] 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.

[0260] 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.

[0261] 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.

[0262] 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 known to a skilled person.

[0263] 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.

[0264] 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 while such terms can be used synonymously herein, there can be instances when such terms are not intended to be used synonymously.

[0265] Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0266] Al. A method for a user equipment (UE) configured for layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: receiving, from a fourth RAN node via a source cell provided by a first RAN node, early uplink (UL) synchronization configurations for first and second LTM candidate cells provided by respective second and third RAN nodes; performing an LTM cell switch from the source cell to the first LTM candidate cell, as a target cell; receiving, from the second RAN node via the target cell, an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell; and performing an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

[0267] A2. The method of embodiment Al, wherein the indication is a physical downlink control channel (PDCCH) order.

[0268] A3. The method of any of embodiments A1-A2, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a centralized unit (CU) associated with the first, second, and third DUs.

[0269] A4. The method of any of embodiments Al -A3, wherein performing the early UL synchronization to the second LTM candidate cell based on the referenced parameters comprises transmitting a random access (RA) preamble using RA resources of the second LTM candidate cell, wherein the RA preamble and / or the RA resources are referenced by the indication.

[0270] A5. The method of embodiment A4, further comprising, after performing the early UL synchronization, receiving from the second RAN node a timing advance (TA) value determined by the third RAN node based on the transmitted RA preamble.

[0271] A6. The method of embodiment A5, wherein the TA value is received in a command for an LTM cell switch from the target cell to the second LTM candidate cell.

[0272] A7. The method of any of embodiments A4-A6, wherein the RA resources referenced by the indication include one or more of the following: time / frequency resources, and one or more beams.

[0273] A8. The method of any of embodiments A1-A7, wherein performing the LTM cell switch from the source cell to the first LTM candidate cell as target cell comprises transmitting, to the RAN node via the target cell, a reconfiguration complete message indicating that the LTM cell switch has been completed.

[0274] A9. The method of any of embodiments A1-A8, further comprising, prior to the LTM cell switch, performing an early UL synchronization to the first LTM candidate cell based on the received early UL synchronization configuration for the first LTM candidate cell.

[0275] A10. The method of any of embodiments A1-A9, wherein for each of the first and second LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following: an identifier or index of a random access (RA) preamble; an identifier of the first RAN node; a synchronization signal / PBCH (SSB) index; a RA configuration identifier an identifier of the UE; and an identifier of the associated LTM candidate cell.

[0276] BL A method for a first radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: receiving, from a fourth RAN node, an LTM configuration for a UE served by a source cell provided by the first RAN node, wherein the LTM configuration includes early uplink (UL) synchronization configurations for first and second LTM candidate cells provided by respective second and third RAN nodes; sending the received LTM configuration to the UE via the source cell; and initiating an LTM cell switch for the UE from the source cell to the first LTM candidate cell, as a target cell.

[0277] B2. The method of embodiment Bl, further comprising sending to the fourth RAN node an early UL synchronization configuration for the source cell, wherein the received LTM configuration includes the early UL synchronization configuration for the source cell, as a third LTM candidate cell for the UE.

[0278] B3. The method of any of embodiments B1-B2, further comprising, after initiating the LTM cell switch, sending to the fourth RAN node an LTM cell switch notification that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells. B4. The method of any of embodiments B1-B2, further comprising receiving, from the UE, a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the source cell; and sending to the fourth RAN node a request for updated early UL synchronization configurations for the UE, wherein the LTM configuration is received from the fourth RAN node in response to the request.

[0279] B5. The method of any of embodiments B1-B2, further comprising: receiving from the fourth RAN node a request to provide early UL synchronization configurations for use by one or more other RAN nodes, wherein the request identifies the following: the source cell as a third LTM candidate cell, and the one or more RAN nodes for which the requested early UL synchronization configurations should be provided; for each of the identified RAN nodes, determining a corresponding early UL synchronization configuration for the third LTM candidate cell; and sending to the fourth RAN node a response that includes the early UL synchronization configurations determined for the respective identified RAN nodes.

[0280] B6. The method of any of embodiments B1-B5, further comprising, after sending the received LTM configuration but before initiating the LTM cell switch, sending to the UE an indication to perform an early UL synchronization to the first LTM candidate cell, wherein the indication references one or more parameters in the early UL synchronization configuration for the first LTM candidate cell.

[0281] B7. The method of embodiment B6, wherein the indication is a physical downlink control channel (PDCCH) order.

[0282] B8. The method of any of embodiments B6-B7, wherein the one or more parameters referenced by the indication include one or more of the following: a random access (RA) preamble, time / frequency RA resources, and one or more beams.

[0283] B9. The method of any of embodiments B6-B8, further comprising receiving from the second RAN node a timing advance (TA) value for the first LTM candidate cell, based on the early UL synchronization performed by the UE, and sending the TA value for the first LTM candidate cell to the UE.

[0284] BIO. The method of embodiment B9, wherein the TA value is sent to the UE in an LTM cell switch command that initiates the LTM cell switch for the UE.

[0285] Bl 1. The method of any of embodiments Bl -BIO, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a centralized unit (CU) associated with the first, second, and third DUs.

[0286] Bl 2. The method of any of embodiments Bl-Bl 1, wherein for each of the first and second LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following: an identifier or index of a random access (RA) preamble; an identifier of the first RAN node; a synchronization signal / PBCH (SSB) index; a RA configuration identifier an identifier of the UE; and an identifier of the associated LTM candidate cell.

[0287] CL A method for a second radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: receiving one of the following from a fourth RAN node: a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cells provided by a third RAN node, and a third LTM candidate cell provided by a first RAN node; or a request for one or more early UL synchronization configurations for the first LTM candidate cell; and receiving, from a UE, a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell. C2. The method of embodiment Cl, wherein the message received from the fourth RAN node is an LTM cell switch notification, which indicates initiation of the UE’s LTM cell switch to the first LTM candidate cell.

[0288] C3. The method of embodiment Cl, wherein the message is received from the fourth RAN node before the UE’s LTM cell switch to the first LTM candidate cell.

[0289] C4. The method of any of embodiments C2-C3, further comprising sending to the UE an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the early UL synchronization configuration for the second LTM candidate cell.

[0290] C5. The method of embodiment C4, wherein the indication is a physical downlink control channel (PDCCH) order.

[0291] C6. The method of any of embodiments C4-C5, wherein the one or more parameters referenced by the indication include one or more of the following: a random access (RA) preamble, time / frequency RA resources, and one or more beams.

[0292] C7. The method of any of embodiments C4-C6, further comprising: receiving from the third RAN node a timing advance (TA) value for the second LTM candidate cell, the TA value being based on the early UL synchronization performed by the UE; and sending the TA value for the second LTM candidate cell to the UE.

[0293] C7a. The method of embodiment C7, wherein the TA value is sent to the UE in an LTM cell switch command.

[0294] C8. The method of embodiment Cl, wherein the request is received from the fourth RAN node before initiation of the UE’s LTM cell switch to the first LTM candidate cell, and the method further comprises sending to the fourth RAN node a response that includes the requested one or more early UL synchronization configurations for the first LTM candidate cell.

[0295] C9. The method of embodiment C8, wherein the request is for a single early UL synchronization configurations for the first LTM candidate cell. CIO. The method of embodiment C8, wherein: the request identifies the following: the first LTM candidate cell, and one or more RAN nodes for which the requested early UL synchronization configurations should be provided; and the method further comprises: for each of the identified RAN nodes, determining a corresponding early UL synchronization configuration for the first LTM candidate cell; and sending to the fourth RAN node a response that includes the early UL synchronization configurations determined for the respective identified RAN nodes.

[0296] Cl 1. The method of any of embodiments Cl -CIO, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a centralized unit (CU) associated with the first, second, and third DUs.

[0297] Cl 2. The method of any of embodiments Cl-Cl 1, wherein for each of the first, second, and third LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following: an identifier or index of a random access (RA) preamble; an identifier of the first RAN node; a synchronization signal / PBCH (SSB) index; a RA configuration identifier an identifier of the UE; and an identifier of the associated LTM candidate cell.

[0298] DI. A method for a fourth radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the method comprising: receiving from a first RAN node an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node; and sending one of the following to the second RAN node: a message that includes early uplink (UL) synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cells provided by a third RAN node, or a third LTM candidate cell provided by the first RAN node; or a request for one or more early UL synchronization configurations for the first LTM candidate cell.

[0299] D2. The method of embodiment DI, wherein the early UL synchronization configurations for the first, second, and third LTM candidate cells are included in or with the received LTM cell switch notification, and the message sent to the second RAN node is an LTM cell switch notification that includes the early UL synchronization configurations.

[0300] D3. The method of embodiment DI, further comprising, before receiving the LTM cell switch notification, receiving the early UL synchronization configurations for the first, second, and third LTM candidate cells from the respective second, third, and first RAN nodes.

[0301] D4. The method of embodiment D3, further comprising storing the received early UL synchronization configurations, wherein the message sent to the second RAN node is an LTM cell switch notification that includes the stored early UL synchronization configurations.

[0302] D5. The method of embodiment D3, further comprising sending to the UE an LTM configuration that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells, wherein the message is sent to the second RAN node in response to sending the LTM configuration.

[0303] D6. The method of embodiment D5, further comprising, in response to sending the LTM configuration, sending to the third RAN node a further message that includes the early UL synchronization configurations.

[0304] D7. The method of embodiment DI, further comprising: after completion of the LTM cell switch, receiving from the second RAN node a request for updated early UL synchronization configurations for the UE; sending to the first and third RAN nodes respective requests for updated early UL synchronization configurations for the respective third and second LTM candidate cells; receiving updated early UL synchronization configurations from the first and third RAN node in accordance with the respective requests; wherein the message sent to the second RAN node includes the updated early UL synchronization configurations for the second and third LTM candidate cells.

[0305] D8. The method of embodiment DI, wherein: the request sent to the second RAN node identifies the following: the first LTM candidate cell, and one or more RAN nodes for which the requested early UL synchronization configurations should be provided; and the method further comprises: receiving from the second RAN node a response that includes respective early UL synchronization configurations associated with the first LTM candidate cell and the respective identified RAN nodes; and sending, to each of the identified RAN nodes, the received early UL synchronization configuration associated with the first LTM candidate cell and the identified RAN node.

[0306] D9. The method of any of embodiments D1-D8, wherein the first RAN node is a first distributed unit (DU), the second RAN node is a second DU, the third RAN node is a third DU, and the fourth RAN node is a centralized unit (CU) associated with the first, second, and third DUs.

[0307] DIO. The method of any of embodiments D1-D9, wherein for each of the first, second, and third LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following: an identifier or index of a random access (RA) preamble; an identifier of the first RAN node; a synchronization signal / PBCH (SSB) index; a RA configuration identifier an identifier of the UE; and an identifier of the associated LTM candidate cell.

[0308] EL A user equipment (UE) configured for layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate 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-A10.

[0309] E2. A user equipment (UE) configured for layer- 1 (L2) / layer-2 (L2) 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-A10.

[0310] E3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured for layer-1 (L2) / layer-2 (L2) 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-A10.

[0311] E4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for layer- 1 (L2) / layer-2 (L2) 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-A10.

[0312] FL A first radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the first 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 Bl -Bl 2.

[0313] F2. A first radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the first RAN node being further configured to perform operations corresponding to the methods of any of embodiments B1-B12. F3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the first RAN node to perform operations corresponding to the methods of any of embodiments Bl -Bl 2.

[0314] F4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a first radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the first RAN node to perform operations corresponding to the methods of any of embodiments Bl -Bl 2.

[0315] Gl. A second radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) 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 Cl -Cl 2.

[0316] G2. A second radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) 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 C1-C12.

[0317] G3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) 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 Cl -Cl 2.

[0318] G4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a second radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) 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 C1-C12.

[0319] Hl. A fourth radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the fourth 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 DI -DIO.

[0320] H2. A fourth radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), the fourth RAN node being further configured to perform operations corresponding to the methods of any of embodiments D1-D10.

[0321] H3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a fourth radio access network (RAN) node configured to facilitate layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the fourth RAN node to perform operations corresponding to the methods of any of embodiments DI -DIO.

[0322] H4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of a fourth radio access network (RAN) node configured to facilitate layer- 1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) by user equipment (UEs), configure the fourth RAN node to perform operations corresponding to the methods of any of embodiments DI -DIO.

Claims

CLAIMS1. A method for a user equipment, UE, configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: while operating in a source cell, receiving (1210) an early uplink, UL, synchronization configuration for a second LTM candidate cell; performing (1230) an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell; subsequently receiving (1240) an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell; and performing (1250) an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

2. The method of claim 1, wherein the indication is a physical downlink control channel, PDCCH, order.

3. The method of any of claims 1-2, wherein: the early UL synchronization configuration is received from a fourth RAN node via the source cell, which is provided by a first RAN node; the first and second LTM candidate cells are provided by respective second and third RAN nodes; and the indication is received from the second RAN node via the target cell.

4. The method of claim 3, wherein performing (1230) the LTM cell switch to the first LTM candidate cell as target cell comprises transmitting (1231), to the fourth RAN node via the target cell, a reconfiguration complete message indicating that the LTM cell switch has been completed.

5. The method of any of claims 3-4, wherein the first RAN node is a first distributed unit, DU; the second RAN node is a second DU; the third RAN node is a third DU; and the fourth RAN node is a centralized unit, CU, associated with the first, second, and third DUs.

6. The method of any of claims 3-5, wherein performing (1250) the early UL synchronization to the second LTM candidate cell based on the referenced parameters comprises transmitting (1251) a random access, RA, preamble using RA resources of the second LTM candidate cell, wherein the RA preamble and / or the RA resources are referenced by the indication.

7. The method of claim 6, wherein the RA resources referenced by the indication include one or more of the following: time / frequency resources, and one or more beams.

8. The method of any of claims 6-7, further comprising, after performing (1250) the early UL synchronization to the second LTM candidate cell, receiving (1260) from the second RAN node a timing advance, TA, value determined by the third RAN node based on the transmitted RA preamble.

9. The method of claim 8, wherein the TA value is received in a command for an LTM cell switch from the target cell to the second LTM candidate cell.

10. The method of any of claims 1-9, wherein: the early UL synchronization configuration for the second LTM candidate cell is received with an early UL synchronization configuration for the first LTM candidate cell; and the method further comprises, prior to the LTM cell switch, performing (1220) an early UL synchronization to the first LTM candidate cell based on the received early UL synchronization configuration for the first LTM candidate cell.

11. The method of any of claims 1-10, wherein the early UL synchronization configuration for the second LTM candidate cell includes one or more of the following: an identifier or index of a random access, RA, preamble; an identifier of the first RAN node; a synchronization signal / PBCH, SSB, index; a RA configuration identifier; an identifier of the UE; and an identifier of the second LTM candidate cell.

12. A method for a second radio access network, RAN, node configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: receiving (1410) from a fourth RAN node a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cell provided by a third RAN node, and a third LTM candidate cell provided by a first RAN node; and receiving (1450) from a UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell.

13. The method of claim 12, wherein the message received from the fourth RAN node is a UE context modification request.

14. The method of claim 12, wherein the message received from the fourth RAN node is an LTM cell switch notification, which indicates initiation of the UE’s LTM cell switch to the first LTM candidate cell.

15. The method of claim 12-13, wherein the message is received from the fourth RAN node before the UE’s LTM cell switch to the first LTM candidate cell.

16. The method of any of claims 14-15, further comprising sending (1460) to the UE an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the early UL synchronization configuration for the second LTM candidate cell.

17. The method of claim 16, wherein the indication is a physical downlink control channel, PDCCH, order.

18. The method of any of claims 16-17, wherein the one or more parameters referenced by the indication include one or more of the following: a random access, RA, preamble; time / frequency RA resources; and one or more beams.

19. The method of any of claims 16-18, further comprising:receiving (1470) from the third RAN node a timing advance, TA, value for the second LTM candidate cell, the TA value being based on the early UL synchronization performed by the UE; and sending (1480) the TA value for the second LTM candidate cell to the UE.

20. The method of claim 19, wherein the TA value is sent to the UE in an LTM cell switch command.

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; the third RAN node is a third DU; and the fourth RAN node is a centralized unit, CU, associated with the first, second, and third DUs.

22. The method of any of claims 12-21, wherein for each of the first, second, and third LTM candidate cells, the early UL synchronization configuration for the LTM candidate cell includes one or more of the following: an identifier or index of a random access, RA, preamble; an identifier of the first RAN node; a synchronization signal / PBCH, SSB, index; a RA configuration identifier an identifier of the UE; and an identifier of the LTM candidate cell.

23. A method for a fourth radio access network, RAN, node configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: receiving (1540) from a first RAN node an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node; and sending (1570) to the second RAN node a message that includes early uplink, UL, synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cell provided by a third RAN node, and a third LTM candidate cell provided by the first RAN node.

24. The method of claim 23, further comprising, before receiving (1540) the LTM cell switch notification, receiving (1510) the early UL synchronization configurations for the first, second, and third LTM candidate cells from the respective second, third, and first RAN nodes.

25. The method of claim 24, wherein the message sent to the second RAN node is one of the following: an LTM cell switch notification, or a UE context modification request.

26. The method of claim 24, further comprising sending (1525) to the UE an LTM configuration that includes the early UL synchronization configurations for the first, second, and third LTM candidate cells, wherein the message is sent to the second RAN node in response to sending (1525) the LTM configuration.

27. The method of claim 26, further comprising, in response to sending (1525) the LTM configuration to the UE, sending (1530) to the third RAN node a further message that includes the early UL synchronization configurations.

28. The method of any of claims 23-27, wherein the first RAN node is a first distributed unit, DU; the second RAN node is a second DU; the third RAN node is a third DU; and the fourth RAN node is a centralized unit, CU, associated with the first, second, and third DUs.

29. The method of any of claims 23-28, wherein for each of the first, second, and third LTM candidate cells, the early UL synchronization configuration for the LTM candidate cell includes one or more of the following: an identifier or index of a random access, RA, preamble; an identifier of the first RAN node; a synchronization signal / PBCH, SSB, index; a RA configuration identifier an identifier of the UE; and an identifier of the LTM candidate cell.

30. User equipment, UE (210, 710, 1612, 1700) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1604), the UE comprising: communication interface circuitry (1712) configured to communicate with RAN nodes (100, 150, 220, 720, 730, 740, 750, 1610, 1800, 1902); andprocessing circuitry (1702) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: while operating in a source cell, receive an early uplink, UL, synchronization configuration for a second LTM candidate cell; perform an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell; subsequently receive an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell; and perform an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

31. The UE of claim 30, 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.

32. User equipment, UE (210, 710, 1612, 1700) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1604), the UE being further configured to: while operating in a source cell, receive an early uplink, UL, synchronization configuration for a second LTM candidate cell; perform an LTM cell switch from the source cell to a first LTM candidate cell, as a target cell; subsequently receive an indication to perform an early UL synchronization to the second LTM candidate cell, wherein the indication references one or more parameters in the received early UL synchronization configuration for the second LTM candidate cell; and perform an early UL synchronization to the second LTM candidate cell, based on the referenced parameters.

33. The UE of claim 32, being further configured to perform operations corresponding to the methods of any of claims 2-11.

34. Non-transitory, computer-readable medium (1710) storing computer-executable instructions that, when executed by processing circuitry (1702) of user equipment, UE (210, 710, 1612, 1700) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1604), configure the UE to perform operations corresponding to the methods of any of claims 1-11.

35. A computer program product (1714) comprising computer-executable instructions that, when executed by processing circuitry (1702) of user equipment, UE (210, 710, 1612, 1700) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1604), configure the UE to perform operations corresponding to the methods of any of claims 1-11.

36. Second radio access network, RAN, node (100, 150, 220, 730, 1130, 1610, 1800, 1902) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), the second RAN node comprising: communication interface circuitry (1806, 1904) configured to communicate with UEs and with a fourth RAN node (100, 150, 220, 750, 1110, 1610, 1800, 1902); and processing circuitry (1802, 1904) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive from the fourth RAN node a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cell provided by a third RAN node (100, 150, 220, 740, 1140, 1610, 1800, 1902), and a third LTM candidate cell provided by a first RAN node (100, 150, 220, 720, 1120, 1610, 1800, 1902); and receive from a UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell.

37. The second RAN node of claim 36, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 13-22.

38. Second radio access network, RAN, node (100, 150, 220, 730, 1130, 1610, 1800, 1902) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), the second RAN node being further configured to: receive from a fourth RAN node (100, 150, 220, 750, 1110, 1610, 1800, 1902) a message that includes early UL synchronization configurations for the following: a first LTM candidate cell provided by the second RAN node, a second LTM candidate cell provided by a third RAN node (100, 150, 220, 740, 1140, 1610, 1800, 1902), and a third LTM candidate cell provided by a first RAN node (100, 150, 220, 720, 1120, 1610, 1800, 1902); and receive from a UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell, as a target cell.

39. The second RAN node of claim 38, being further configured to perform operations corresponding to the methods of any of claims 13-22.

40. Non-transitory, computer-readable medium (1804, 1904) storing computer-executable instructions that, when executed by processing circuitry (1802, 1904) of a second radio access network, RAN, node (100, 150, 220, 730, 1130, 1610, 1800, 1902) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), configure the second RAN node to perform operations corresponding to the methods of any of claims 12-22.

41. Computer program product (1804a, 1904a) comprising computer-executable instructions that, when executed by processing circuitry (1802, 1904) of a second radio access network, RAN, node (100, 150, 220, 730, 1130, 1610, 1800, 1902) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), configure the second RAN node to perform operations corresponding to the methods of any of claims 12- 22.

42. Fourth radio access network, RAN, node (100, 150, 220, 750, 1110, 1610, 1800, 1902) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), the fourth RAN node comprising: communication interface circuitry (1806, 1904) configured to communicate with UEs and with other RAN nodes; andprocessing circuitry (1802, 1904) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive from a first RAN node (100, 150, 220, 720, 1120, 1610, 1800, 1902) an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node (100, 150, 220, 730, 1130, 1610, 1800, 1902); and send to the second RAN node a message that includes early uplink, UL, synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cell provided by a third RAN node (100, 150, 220, 740, 1140, 1610, 1800, 1902), and a third LTM candidate cell provided by the first RAN node.

43. The fourth RAN node of claim 42, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 24-29.

44. Fourth radio access network, RAN, node (100, 150, 220, 750, 1110, 1610, 1800, 1902) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), the fourth RAN node being further configured to: receive from a first RAN node (100, 150, 220, 720, 1120, 1610, 1800, 1902) an LTM cell switch notification, which indicates initiation of a UE’s LTM cell switch to a first LTM candidate cell provided by a second RAN node (100, 150, 220, 730, 1130, 1610, 1800, 1902); and send to the second RAN node a message that includes early uplink, UL, synchronization configurations for at least two of the following: the first LTM candidate cell, a second LTM candidate cell provided by a third RAN node (100, 150, 220, 740, 1140, 1610, 1800, 1902), and a third LTM candidate cell provided by the first RAN node.

45. The fourth RAN node of claim 44, being further configured to perform operations corresponding to the methods of any of claims 24-29.

46. Non-transitory, computer-readable medium (1804, 1904) storing computer-executable instructions that, when executed by processing circuitry (1802, 1904) of a fourth radio access network, RAN, node (100, 150, 220, 750, 1110, 1610, 1800, 1902) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), configure the fourth RAN node to perform operations corresponding to the methods of any of claims 23-29.

47. Computer program product (1804a, 1904a) comprising computer-executable instructions that, when executed by processing circuitry (1802, 1904) of a fourth radio access network, RAN, node (100, 150, 220, 750, 1110, 1610, 1800, 1902) configured to facilitate 1 ay er- 1 / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 710, 1612, 1700), configure the fourth RAN node to perform operations corresponding to the methods of any of claims 23- 29.

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