Indicating timing advance (TA) values usable for subsequent l1 / l2-triggered mobility

Abstract

Embodiments include methods for a UE configured for LTM in a RAN. Such methods include performing early UL synchronizations with first / second LTM candidate cells provided by second / third RAN nodes respectively. Such methods include receiving a first command to perform 5 a first LTM cell switch from a source cell to the first LTM candidate cell and performing the first LTM cell switch based on a first TA value included with the first command and without a random access to the first LTM candidate cell during the first LTM cell switch. Such methods include receiving a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell and performing the second LTM cell switch based on a 0 second TA value included with the second command and without a random access to the second LTM candidate cell during the second LTM cell switch.

Description

[0001] INDICATING TIMING ADVANCE (TA) VALUES USABLE FOR SUBSEQUENT 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 intra-RAN sharing of timing advance (TA) values determined for a UE in order to facilitate subsequent layer-1 (LI) or layer-2 (L2) triggered intercell mobility (LTM) operations for the UE

[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.

[0009] NG RAN logical nodes (e.g., gNB 100) include a Central Unit (CU or gNB-CU, e.g., 110) and one or more Distributed Units (DU or gNB-DU, e.g., 120, 130). 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.

[0010] 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.

[0011] 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.

[0012] 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).

[0013] 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.

[0014] 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.

[0015] 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.

[0016] SUMMARY

[0017] 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.”

[0018] While in the original serving cell, the UE may have also performed an early UL synchronization with the second LTM candidate cell, based on which the RAN node serving the second LTM candidate cell obtains a TA value for the UE in that cell. When the UE performs the LTM cell switch, the UE’s TA value in the first target (LTM candidate) cell may be the same as or different than the UE’s TA value in the original serving cell. However, the RAN node serving the second LTM candidate cell is unaware of the UE’s TA value in the first target cell, which can cause various problems, issues, and / or difficulties for subsequent LTM.

[0019] 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.

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

[0021] These exemplary methods include, while operating in a source cell provided by a first RAN node, performing early uplink (UL) synchronizations with a first LTM candidate cell provided by a second RAN node and a second LTM candidate cell provided by a third RAN node. These exemplary methods also include receiving, from the first RAN node, a first command to perform a first LTM cell switch from the source cell to the first LTM candidate cell. The command includes or indicates a first TA value for use by the UE in the first LTM candidate cell. These exemplary methods also include performing the first LTM cell switch from the source cell to the first LTM candidate cell, based on the first TA value and without performing a random access (RA) to the first LTM candidate cell during the first LTM cell switch.

[0022] In some embodiments, these exemplary methods also includes the following operations:

[0023] • receiving, from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second TA value for use by the UE in the second LTM candidate cell; and

[0024] • performing the second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

[0025] In some embodiments, the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell.

[0026] Other embodiments include exemplary methods (e.g., procedures) for a first RAN node configured to facilitate LTM by UEs in a RAN. In general, these exemplary methods can be complementary to the exemplary methods for a UE summarized above.

[0027] These exemplary methods include sending, to a UE via a source cell provided by the first RAN node, an indication to perform respective early UL synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node. These exemplary methods also include subsequently receiving the following TA values:

[0028] • from the second RAN node, a first TA value for use by the UE in the first LTM candidate cell, and

[0029] • from the third RAN node, a second TA value for use by the UE in the second LTM candidate cell.

[0030] These exemplary methods also include sending to the UE a command to perform a first LTM cell switch from the source cell to the first LTM candidate cell. The command includes or indicates the first TA value. These exemplary methods also include sending, to the second RAN node, a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

[0031] In some embodiments, the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell. In some embodiments, the indication comprises one or more PDCCH orders. In some embodiments, the first message includes the second TA value in order to facilitate a second LTM cell switch by the UE from the first LTM candidate cell to the second LTM candidate cell, such as summarized above in relation to UE embodiments.

[0032] In some embodiments, the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell. In some embodiments, the first message is sent to the second RAN node via a fourth RAN node. In some of these embodiments, these exemplary methods also include the following operations:

[0033] • receiving, from the fourth RAN node, first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and

[0034] • sending the first and second early UL synchronization configurations to the UE via the source cell.

[0035] In some variants of these embodiments, the indication references one or more parameters in the respective first and second early UL synchronization configurations, and the respective early UL synchronizations are performed by the UE using parameters referenced by the indication.

[0036] Other embodiments include exemplary methods (e.g., procedures) for a second RAN node configured to facilitate LTM by UEs in a RAN. In general, these exemplary methods can be complementary to the exemplary methods for a UE and a first RAN node summarized above.

[0037] These exemplary methods include sending, to a fourth RAN node, an early UL synchronization configuration for a UE towards a first LTM candidate cell provided by the second RAN node. The UE is served by a source cell provided by a first RAN node. These exemplary methods also include receiving a RA preamble from the UE in the first LTM candidate cell, in accordance with the early UL synchronization configuration, and based on the RA preamble, determining a first TA value for the UE in the first LTM candidate cell. These exemplary methods also include sending the first TA value to the first RAN node via the fourth RAN node. These exemplary methods also include receiving respective TA values for the UE in one or more of the following: the source cell, the first LTM candidate cell, and a second LTM candidate cell provided by a third RAN node.

[0038] 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, the one or more TA values are received in response to sending the first TA value. In other embodiments, the one or more TA values are received in a request from the fourth RAN node to provide an LTM candidate cell configuration for the UE in the first LTM candidate cell. In such case, the early UL synchronization configuration for the UE in the first LTM candidate cell is sent to the fourth RAN node in response to the request. In some embodiments, the first message is received from the first RAN node via the fourth RAN node. In some embodiments, the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

[0039] Other embodiments include exemplary methods (e.g., procedures) for a fourth RAN node configured to facilitate LTM by UEs in a RAN. In general, these exemplary methods may be complementary to the exemplary methods for a UE, a first RAN node, and a second RAN node summarized above.

[0040] These exemplary methods include receiving the following for a UE served by a source cell provided by a first RAN node:

[0041] • from a second RAN node, a first TA value for the UE in a first LTM candidate cell provided by the second RAN node ; and

[0042] • from a third RAN node, a second TA value for the UE in a second LTM candidate cell provided by the third RAN node;

[0043] These exemplary methods also include sending the first TA value and the second TA value to the first RAN node. These exemplary methods also include sending to the second RAN node a first message that includes one or more of the following: the first TA value, and the second TA value.

[0044] In some embodiments, these exemplary methods also include the following operations:

[0045] • receiving, from the second and third RAN nodes, respective first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and

[0046] • sending the first and second early UL synchronization configurations to the UE via the first RAN node.

[0047] The first and second TA values are based on early UL synchronizations by the UE with the first and second LTM candidate cells, in accordance with the respective first and second early UL synchronization configurations.

[0048] In some embodiments, these exemplary methods also include receiving from the first RAN node a second message that includes or indicates one or more of the following TA values for the UE: the first TA value, the second TA value, and a TA value for the UE in the source cell. In some of these embodiments, the second message received from the first RAN node is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

[0049] In some variants of these embodiments, the first message is sent in response to receiving the second message. In some variants of these embodiments, the first message is also an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell. In some variants of these embodiments, the first message sent to the second RAN node also includes or indicates the TA value for the UE in the source cell (i.e., that was received in the second message).

[0050] In some of the embodiments summarized above, 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.

[0051] In some of the embodiments summarized above, for each of the first and second LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following:

[0052] • an identifier or index of a RA preamble;

[0053] • an identifier of the first RAN node;

[0054] • an SSB index;

[0055] • a RA configuration identifier

[0056] • an identifier of the UE; and

[0057] • an identifier of the associated LTM candidate cell.

[0058] Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g, base stations, eNBs, gNBs, ng-eNBs, CUs, DUs, etc.) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer-readable media storing program instructions that, when executed by processing circuitry, configure such UEs and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

[0059] These and other embodiments described herein may provide various advantages, benefits, and / or solutions to problems. For example, by sharing TA values previously determined for a UE’s LTM candidate cells, embodiments may enable a source RAN node for a subsequent LTM cell switch to be aware of the previous TA values determined for the UE’s other LTM candidate cells, which may enable the source RAN node to explicitly indicate what TA value for the UE to use for subsequent LTM to one of these LTM candidate cells. Furthermore, embodiments may remove the need for the RAN to reconfigure the UE after every LTM cell switch to facilitate early TA acquisition, and may enable subsequent LTM without UE random access to LTM candidate cells. As such, embodiments may reduce interruption time, handover delay, and risk of connection failure during subsequent LTM.

[0060] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 shows a high-level view of an exemplary 5G / NR network architecture.

[0062] Figure 2 shows exemplary NR user plane (UP) and control plane (CP) protocol stacks.

[0063] Figure 3 shows a logical architecture for an NG-RAN node.

[0064] Figure 4 shows a signaling diagram for an exemplary LTM cell switch procedure.

[0065] Figure 5 shows a signaling diagram for an early timing advance (TA) acquisition procedure by a UE.

[0066] Figures 6A-B show various aspects of intra-CU / inter-DU LTM of a UE.

[0067] Figure 7 shows a flow diagram of an exemplary method for a UE (e.g, wireless device), according to various embodiments of the present disclosure.

[0068] Figure 8 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.

[0069] Figure 9 shows a flow diagram of an exemplary method for a second RAN node (e.g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0070] Figure 10 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.

[0071] Figure 11 shows a communication system according to various embodiments of the present disclosure.

[0072] Figure 12 shows a UE according to various embodiments of the present disclosure.

[0073] Figure 13 shows a network node according to various embodiments of the present disclosure.

[0074] Figure 14 shows a virtualization environment in which some embodiments of the present disclosure may be virtualized.

[0075] DETAILED DESCRIPTION

[0076] 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.

[0077] 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.

[0078] Furthermore, the following terms are used throughout the description given below:

[0079] • Radio Access Node: As used herein, a “radio access node” (or equivalently “radio network node,” “radio access network node,” or “RAN node”) can be any node in a radio access network (RAN) that operates to wirelessly transmit and / or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g, gNB in a 3GPP 5G / NR network or an enhanced or eNB in a 3GPP LTE network), base station distributed components (e.g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, 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.

[0080] • 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.

[0081] • 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”.

[0082] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0083] • 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.

[0084] • 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] After a UE is powered ON it will be in the RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state e.g., where data transfer can occur). The UE returns to RRC ..IDLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor cells to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. 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.

[0091] 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.

[0092] 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).

[0093] 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.

[0094] 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.

[0095] 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).

[0096] 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.

[0097] 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.

[0098] 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).

[0099] 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).

[0100] 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.

[0101] 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.

[0102] 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). 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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. 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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 to which the TA acquisition procedure may be executed by the UE. In operation 2, the UE replies with the RRCReconflgurationComplete message.

[0113] In operation 3, the gNB serving Cell A sends a PDCCH order message to the UE in order 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.

[0114] 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.

[0115] 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).

[0116] Figures 6A-B illustrate 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. 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.

[0117] 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 (RA) 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.

[0118] 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.

[0119] As mentioned above in relation to Figures 5 and 6B, the serving RAN node may provide the TA value to the UE in an LTM cell switch command, which enables the UE to access the LTM candidate cell without performing random access (i.e., since it was done earlier). As one option, the serving RAN node may indicate to the UE that it should use the same TA value in the LTM candidate cell as currently being used in the serving cell, from which the LTM cell switch procedure is executed. 3GPP has agreed that, when indicating this same TA value, the serving RAN node should explicitly replicate the most recent TA value it sent to the UE.

[0120] 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”.

[0121] When the UE performs subsequent LTM without being reconfigured, however, there may be some problems, issues, and / or difficulties related to TA values. Consider the scenario in which the UE has a serving cell and first and second LTM candidate cells. While in the serving cell, the UE performed early UL synchronization to the first and second LTM candidate cells, based on which the RAN nodes serving those cells obtained TA values (e.g., TAI and TA2 respectively) for the UE. The UE also has a TA value in its serving cell (e.g., TAO).

[0122] Subsequently, the UE receives an LTM cell switch command to go to the first LTM candidate cell (as first target cell), with an indication to use the same TA value as in the source cell (i.e., TAO) when entering the first LTM candidate cell. While in the first target cell, the UE receives another LTM cell switch command to go to the second LTM candidate cell (as second target cell), with an indication to use the same TA value as in the source cell (i.e., first target cell) when entering the second LTM candidate cell. However, the RAN node serving the second LTM candidate (target) cell is not aware of what TA value was indicated to the UE in the command to switch to the first LTM candidate (target) cell.

[0123] As one option, the RAN node serving the second LTM candidate cell may cause the RAN node serving the first target cell to initiate a new early UL synchronization to the second LTM candidate cell, prior to the subsequent LTM. This is undesirable since it delays the LTM cell switch and risks causing a failure in the UE’s connection to the RAN. As another option, the RAN node serving the first target cell may indicate to the UE that subsequent LTM needs to be done with random access to the second LTM candidate cell, with undesirably increases connection interruption time and handover delay.

[0124] Another issue is that a UE may perform multiple subsequent LTM procedures sequentially, such that it is in coverage of each individual cell only briefly. In such case, the respective serving RAN nodes do not have enough time to initiate the UE’s early UL synchronization to other LTM candidate cells. Even so, there are scenarios in which a TA calculated in one cell can also be used in another cell, such as when the two cells are co-located or perfectly synchronized. In such a case, make sense for the serving cell to also forwarded all the TA value calculated / received to the “next” serving cell and / or other candidate cells.

[0125] While in the original serving cell, the UE may have also performed an early UL synchronization with the second LTM candidate cell, based on which the RAN node serving the second LTM candidate cell obtained a TA value for the UE in that cell. When the UE performs the LTM cell switch, the UE’s TA value in the first target (LTM candidate) cell may be the same as or different than the UE’s TA value in the original serving cell. However, the RAN node serving the second LTM candidate cell is unaware of the UE’s TA value in the first target cell, which can cause various problems, issues, and / or difficulties for subsequent LTM.

[0126] Accordingly, embodiments of the present disclosure address these problems and / or issues with flexible and efficient techniques by which RAN nodes (e.g., CU, S-DU, C-DUs) share relevant TA values for a UE’s LTM candidate cells determined by early UL synchronization, so that a source RAN node for a subsequent LTM cell switch procedure can explicitly indicate in the LTM cell switch command for the UE to use the same TA value as being used in the UE’s current serving cell (i.e., LTM source cell). In this context, “explicitly indicate” means that the source RAN node includes in the LTM cell switch command the TA value that the UE should use, which is the same TA value being used by the UE in the LTM source cell.

[0127] Embodiments of the present disclosure may provide various advantages and / or benefits. For example, by sharing TA values previously determined for a UE’s LTM candidate cells, embodiments enable a source RAN node for a subsequent LTM cell switch to be aware of the previous TA values determined for the UE’s other LTM candidate cells, which enables the source RAN node to explicitly indicate what TA value for the UE to use for subsequent LTM to one of these LTM candidate cells. Furthermore, embodiments may remove the need for the RAN to reconfigure the UE after every LTM cell switch to facilitate early TA acquisition, and may enable subsequent LTM without UE random access to LTM candidate cells. As such, embodiments may reduce interruption time, handover delay, and risk of connection failure during subsequent LTM.

[0128] Embodiments may be summarized as follows. 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 the TA value it included in the LTM cell switch command to the C-DU that serves the first LTM candidate cell. This TA value may be sent directly or via a common CU.

[0129] In other 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 not only the TA value it included in the LTM cell switch command, but also one or more other TA values for other UE LTM candidate cells, which were obtained based on the UE performing early UL synchronization while being served by the S-DU. The S-DU may send these TA values to the C- DU that serves the first LTM candidate cell and, optionally, to C-DUs serving other UE LTM candidate cells. These TA values may be sent directly or via a common CU.

[0130] In other embodiments, after triggering (via the UE’s S-DU) an early UL synchronization procedure by a UE towards an LTM candidate cell served by a C-DU, and receiving a TA value determined by the C-DU, the CU sends the TA value to C-DUs serving other LTM candidate cells for the UE. In a variant of these embodiments, the S-DU requests the CU to sends TA values for the LTM candidate cell - determined by C-DUs and sent to the CU - to C-DUs serving other LTM candidate cells for the UE.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] 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).

[0135] 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.

[0136] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConflg, SpCellConflg, or SCellConflg 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”.

[0137] A UE may receive an LTM candidate cell configuration in a 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.

[0138] 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.

[0139] 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):

[0140] • an LTM candidate configuration, i.e., for an LTM candidate cell;

[0141] • a measurement configuration, e.g., LI measurement and reporting configuration for the LTM candidate cell;

[0142] • a configuration for early DL synchronization, e.g., for early TCI state activation;

[0143] • a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

[0144] • 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.).

[0145] The term “part of an LTM configuration” may refer to a subset of the elements in the above list, and / or a subset of items comprising any of the elements present (e.g., subset of configurations for DL pre-sync). The phrase “LTM cell switch procedure” refers to the process of a UE switching (or changing) from a source cell to a target cell (i.e. , an LTM candidate cell) using LTM. An LTM cell switch procedure may also be referred to as “L1 / L2 based inter-cell mobility execution”, “LTM execution”, “dynamic switch”, “LTM switch”, “(LTM) cell switch”, “(LTM) serving cell change”, or “(LTM) cell change”. Similarly, the phrase “switching to an LTM candidate cell configuration” means that the UE applies an LTM candidate cell configuration such that the associated LTM candidate cell becomes its new special cell (SpCell, e.g., PCell for LTM in MCG or PSCell for LTM in SCG) or its new SCell. In other words, an LTM candidate cell can be a candidate for the UE’s PCell, PSCell, or SCell.

[0146] 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.

[0147] 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”.

[0148] Various features of the embodiments summarized above correspond to various operations illustrated in Figures 7-10, 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 summarized above. Furthermore, the exemplary methods shown in Figures 7-10 can be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 7- 10 show specific blocks in particular orders, the operations of the exemplary methods can be performed in different orders than shown and can be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0149] In particular, Figure 7 shows an exemplary method (e.g., procedure) for a UE configured for LTM in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by a UE (e.g, wireless device) such as described elsewhere herein.

[0150] The exemplary method includes the operations of block 730, where while operating in a source cell provided by a first RAN node, the UE performs respective early uplink (UL) synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node. The exemplary method also includes the operations of block 740, where the UE receives, from the first RAN node, a first command to perform a first LTM cell switch from the source cell to the first LTM candidate cell. The command includes or indicates a timing advance (TA) value for use by the UE in the first LTM candidate cell. The exemplary method also includes the operations of block 750, where the UE performs the first LTM cell switch from the source cell to the first LTM candidate cell, based on the first TA value and without performing a random access (RA) to the first LTM candidate cell during the LTM cell switch.

[0151] In some embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0152] • (760) receiving, from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second TA value for use by the UE in the second LTM candidate cell; and

[0153] • (770) performing the second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

[0154] 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. The arrangement shown in Figures 6A-B is an example of these embodiments.

[0155] In some embodiments, the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell.

[0156] In some embodiments, the exemplary method also includes the operations of block 720, where the UE receives, via the source cell, an indication to perform early UL synchronizations with the first and second LTM candidate cells. The respective early UL synchronizations are performed in accordance with the indication. In some of these embodiments, the indication comprises one or more physical downlink control channel (PDCCH) orders.

[0157] In some of these embodiments, the exemplary method also includes the operations of block 710, where the UE receives, from a fourth RAN node via the source cell, first and second early UL synchronization configurations for the respective first and second LTM candidate cells. The respective early UL synchronizations are performed based on the first and second early UL synchronization configurations.

[0158] In some variants of these embodiments, the indication references one or more parameters in the first and second early UL synchronization configurations, and the respective early UL synchronizations are performed using the one or more parameters referenced by the indication. In some further variants, performing the early UL synchronization with the first LTM candidate in block 730 includes the operations of sub-block 731, where the UE transmits a RA preamble using RA resources of the first LTM candidate cell. The RA preamble and / or the RA resources are referenced by the indication. For example, the RA resources referenced by the indication may include one or more of the following: time / frequency resources, and one or more beams.

[0159] 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:

[0160] • an identifier or index of a random access (RA) preamble;

[0161] • an identifier of the first RAN node;

[0162] • a synchronization signal / PBCH (SSB) index;

[0163] • a RA configuration identifier

[0164] • an identifier of the UE; and

[0165] • an identifier of the associated LTM candidate cell.

[0166] In addition, Figure 8 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.

[0167] The exemplary method includes the operations of block 830, where the first RAN node sends, to a UE via a source cell provided by the first RAN node, an indication to perform respective early UL synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node. The exemplary method also includes the operations of block 835, where the first RAN node subsequently receives the following timing advance (TA) values:

[0168] • from the second RAN node, a first TA value for use by the UE in the first LTM candidate cell, and

[0169] • from the third RAN node, a second TA value for use by the UE in the second LTM candidate cell.

[0170] The exemplary method also includes the operations of block 850, where the first RAN node sends to the UE a command to perform a first LTM cell switch from the source cell to the first LTM candidate cell. The command includes or indicates the first TA value. The exemplary method also includes the operations of block 860, where the first RAN node sends one of the following:

[0171] • to the fourth RAN node, a request to send the second and third RAN nodes TA values determined based on the early UL synchronizations; or • to the second RAN node, a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

[0172] In some embodiments, the exemplary method also includes the operations of block 840, where the first RAN node determines a TA value for the UE in the source cell.

[0173] In some embodiments, the first TA value is received from the second RAN node via a fourth RAN node. lin some embodiments, the first message is sent to the second RAN node via the fourth RAN node. In some embodiments, the second TA value is received from the third RAN node via the fourth RAN node. 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. The arrangement shown in Figures 6A-B is an example of these embodiments.

[0174] In some embodiments, the first message includes the second TA value in order to facilitate a second LTM cell switch by the UE from the first LTM candidate cell to the second LTM candidate cell, such as described above in relation to UE embodiments.

[0175] In some embodiments, the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell. In some embodiments, the indication (e.g., in block 830) comprises one or more PDCCH orders.

[0176] In some of these embodiments, the request is sent to the fourth RAN node in block 860 before sending the command in block 850, and the request includes one or more of the following: a TA value for use by the UE in the source cell (e.g., as determined in block 840), the first TA value, and the second TA value.

[0177] In other of these embodiments, the first message is sent to the second RAN node in block 860 in response to sending the command in block 850. In other of these embodiments, the first message is sent to the second RAN node in block 860 in response to receiving the first and second TA values in block 835.

[0178] In some embodiments, the first message may also be sent to the third RAN node in block 860. In some of these embodiments, the first message sent to the third RAN node may include one or more of the following: a TA value for use by the UE in the source cell (e.g., as determined in block 840), the first TA value, and the second TA value. In some of these embodiments, the first message is sent to the third RAN node via the fourth RAN node.

[0179] In other embodiments, the request sent to the fourth RAN node in block 860 is responsive to sending the indication in block 830.

[0180] In some embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers: • (810) receiving, from the fourth RAN node, first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and

[0181] • (820) sending the first and second early UL synchronization configurations to the UE via the source cell.

[0182] In some of these embodiments, the indication references one or more parameters in the respective first and second early UL synchronization configurations, and the respective early UL synchronizations are performed by the UE using parameters referenced by the indication. In some variants 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.

[0183] 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:

[0184] • an identifier or index of a RA preamble;

[0185] • an identifier of the first RAN node;

[0186] • an SSB index;

[0187] • a RA configuration identifier

[0188] • an identifier of the UE; and

[0189] • an identifier of the associated LTM candidate cell.

[0190] Some further examples for the embodiments illustrated in Figure 8 are given below. In one example, the first RAN node only sends in block 860 the TA value included in the LTM cell switch command in block 850. In another example, the first RAN node sends one or more TA values that are not included in the LTM cell switch command. These are TA values received from the other LTM candidate cells, which are not the LTM candidate cell included in the LTM cell switch command. In another example, the first RAN node sends the TA value included in the LTM cell switch command and the other one or more TA values from other LTM candidate cells.

[0191] In one example, the first RAN node only sends the TA value(s) to the second RAN node indicated in the LTM cell switch command. In another example, the first RAN node sends the TA value(s) to a different RAN node(s) than indicated in the LTM cell switch command (i.e., not the second RAN node).

[0192] In one example, after receiving a TA value from an LTM candidate cell, the first RAN node sends to the same LTM candidate cell all the TA values received from all other LTM candidate cells. In another example, after receiving a TA value from an LTM candidate cell, the first RAN node sends to the same LTM candidate cell all the TA values received from all other LTM candidate cells which has sent already a TA value or for which a TA value is expected.

[0193] In one example, the first RAN node sends the one or more TA values to other RAN node(s) that it commanded or requested to initiate early TA acquisition procedure(s) for the UE in LTM candidate cell(s). In another example, the first RAN node sends the one or more TA values to RAN nodes other than RAN node(s) that it commanded or requested to initiate early TA acquisition procedure(s) for the UE.

[0194] In one example, the first RAN node sends the one or more TA values when receiving a request to configure an LTM candidate cell configuration. As a more specific example, the first RAN node receives from the fourth RAN node (e.g., CU) a request to configure an LTM candidate cell and if the first RAN node has TA values stored from other LTM candidate cells, it provides these TA value together with the LTM candidate cell configuration.

[0195] In one example, the first RAN node sends the one or more TA values to the fourth RAN node (e.g., CU), which transparently forward these TA values to the one or more other RAN nodes (e.g. DUs) indicated by the indicated by the first RAN node. In another example, the fourth RAN node reads the received TA values and autonomously determines to which RAN nodes the TA values should be sent.

[0196] In addition, Figure 9 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.

[0197] The exemplary method includes the operations of block 920, where the second RAN node receives, from a UE served by a source cell provided by a first RAN node, a RA preamble in a first LTM candidate cell provided by the second RAN node. The exemplary method also includes the operations of blocks 930-940, where based on the RA preamble, the second RAN node determines a first TA value for use by the UE in the first LTM candidate cell and sends the first TA value to the first RAN node via the fourth RAN node. The exemplary method also includes the operations of block 950, where the second RAN node receives from the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and second TA value for use by the UE in a second LTM candidate cell provided by a third RAN node.

[0198] In some embodiments, the exemplary method includes the operations of block 910, where the second RAN node sends, to the fourth RAN node, an early UL synchronization configuration for a UE towards a first LTM candidate cell provided by the second RAN node. The RA preamble is received (e.g., in block 920) in accordance with the early UL synchronization configuration. In some of these embodiments, the early UL synchronization configuration for the UE in the first LTM candidate cell includes one or more of the following:

[0199] • an identifier or index of a random access (RA) preamble;

[0200] • an identifier of the first RAN node; • a synchronization signal / PBCH (SSB) index;

[0201] • a RA configuration identifier

[0202] • an identifier of the UE; and

[0203] • an identifier of the first LTM candidate cell.

[0204] 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. The arrangement shown in Figures 6A-B is an example of these embodiments.

[0205] In some embodiments, the first message is received in response to sending the first TA value. In other embodiments, the first message is a request from the fourth RAN node to provide an LTM candidate cell configuration for the UE in the first LTM candidate cell. In such case, the early UL synchronization configuration for the UE in the first LTM candidate cell is sent to the fourth RAN node in response to the request.

[0206] In some embodiments, the exemplary method also includes the operations of block 960, where after sending the first TA value in block 940 and without receiving a further RA preamble from the UE in the first LTM candidate cell, the second RAN node receives from the UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell.

[0207] In some of these embodiments, timing alignment of the reconfiguration complete message in the first LTM candidate cell is based on a TA value used by the UE for timing alignment in the source cell. In some variants of these embodiments, the received TA values include the TA value used by the UE for timing alignment in the source cell.

[0208] In some of these embodiments, the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

[0209] In some of these embodiments, the received TA values include a second TA value for the second LTM candidate cell, based on an early UL synchronization by the UE with the second LTM candidate cell. In such case, the exemplary method also includes the operations of block 980, where the second RAN node sends to the UE a command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell. The command includes the received second TA value. In some variants of these embodiments, the exemplary method also includes the operations of block 970, where based on the received second TA value, the second RAN node refrains from initiating an early UL synchronization of the UE with the second LTM candidate cell, prior to sending the command in block 980.

[0210] In some embodiments, the one or more TA values are received from one of the following: the first RAN node, or the fourth RAN node.

[0211] Some further examples of the embodiments illustrated in Figure 9 are given below. In one example, when providing an LTM candidate cell configuration, the second RAN node also includes one or more TA values related to the first (source) RAN node and one or more other RAN nodes (e.g. third RAN node) serving other LTM candidate cells. In another example, the second RAN node receives from the first RAN node or the third RAN node one or more TA values within a notification (or indication) that an LTM cell switch procedure has been triggered for the UE. In another example, the second RAN node receives from the first RAN node or the third RAN node one or more TA values after having sent a TA value to the first RAN node or the third RAN node, due to an early TA acquisition procedure triggered at the UE.

[0212] In one example, the second RAN node receives for each TA value an identifier of an associated RAN node, such that each TA value is linked to a specific RAN node.

[0213] In one example, communication between the first and second RAN nodes may be via a direct interface between them (e.g., between DUs). In one example, communication between the first and second RAN nodes may be via the fourth RAN node (e.g., CU), such as via a F1AP interface. In either case, the communication may involve existing or newly-defined messages.

[0214] In addition, Figure 10 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.

[0215] The exemplary method includes the operations of block 1030, where the fourth RAN node receives the following for a UE served by a source cell provided by a first RAN node:

[0216] • from a second RAN node, a first TA value for use by the UE in a first LTM candidate cell provided by the second RAN node ; and

[0217] • from a third RAN node, a second TA value for use by the UE in a second LTM candidate cell provided by the third RAN node;

[0218] The exemplary method includes the operations of block 1040, where the fourth RAN node sends the first TA value and the second TA value to the first RAN node. The exemplary method also includes the operations of block 1080, where the fourth RAN node sends to the second RAN node a first message that includes one or more of the following: the first TA value, and the second TA value.

[0219] 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. The arrangement shown in Figures 6A-B is an example of these embodiments. In some embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0220] • (1010) receiving, from the second and third RAN nodes, respective first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and

[0221] • (1020) sending the first and second early UL synchronization configurations to the UE via the first RAN node.

[0222] The first and second TA values are based on early UL synchronizations by the UE with the first and second LTM candidate cells, in accordance with the respective first and second early UL synchronization configurations.

[0223] In some of these embodiments, for each of the first and second LTM candidate cells, the associated early UL synchronization configuration includes one or more of the following:

[0224] • an identifier or index of a RA preamble;

[0225] • an identifier of the first RAN node;

[0226] • an SSB index;

[0227] • a RA configuration identifier

[0228] • an identifier of the UE; and

[0229] • an identifier of the associated LTM candidate cell.

[0230] In some of these embodiments, the first message may be sent according to one of the following: responsive to receiving the second TA value, responsive to sending the second TA value to the first RAN node, or based on receiving the first early UL synchronization configuration.

[0231] In some of these embodiments, the first message may also be sent to the third RAN node. In such case, the first message may be sent to the third RAN node according to one of the following: responsive to receiving the first TA value, responsive to sending the first TA, or based on receiving the second early UL synchronization configuration.

[0232] In some embodiments, the exemplary method also includes the operations of block 1060, where the fourth RAN node receives one of the following from the first RAN node:

[0233] • a request to send one or more TA values for the UE to at least one of the second and third RAN nodes; or

[0234] • a second message that includes or indicates one or more of the following TA values for the UE: the first TA value, the second TA value, and a TA value for the UE in the source cell.

[0235] In some of these embodiments, the exemplary method also includes the operations of blocks 1050 and 1070, where the fourth RAN node stores the received first and second TA values and, based on the request, retrieves the stored first and second TA values. Each of the retrieved first and second TA values is included in the first message sent to the second RAN node and, optionally, to the third RAN node.

[0236] In some of these embodiments, the request from the first RAN node indicates which of the second and third RAN nodes should receive each of the one or more TA values, and the first message is sent to the second RAN node and / or the third RAN node in accordance with the indication.

[0237] In other of these embodiments, the second message received from the first RAN node is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell. In some variants of these embodiments, the first message is sent in response to receiving the second message. In some variants of these embodiments, the first message is also an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell. In some variants of these embodiments, the first message sent to the second RAN node also includes or indicates the TA value for the UE in the source cell (i.e., that was received in the second message).

[0238] Some further examples of the embodiments illustrated in Figure 10 are given below.

[0239] In one example, when the fourth RAN node receives an indication from the first RAN node that an LTM cell switch procedure has been triggered at the UE together with one or more TA values, the fourth RAN node share all the received TA values received from the first RAN node with other RAN nodes (e.g., other DUs). In another example, the fourth RAN node sends the TA value(s) to the RAN node serving the LTM candidate cell towards which an LTM cell switch has been triggered at the UE. In another example, the fourth RAN node sends the TA value(s) to all other RAN nodes that have provided (to the fourth RAN node) an LTM candidate cell configuration to be sent to the UE. In another example, the fourth RAN node sends the TA value(s) to all other RAN nodes that have provided (to the fourth RAN node) a TA value due to an early TA acquisition procedure at the UE. In another example, the fourth RAN node sends the TA value(s) to all other RAN nodes that have provided (to the fourth RAN node) a configuration for initiating an early DL synchronization procedure at the UE.

[0240] In one example, the fourth RAN node sends the one or more TA values after receiving an indication from a first RAN node that an early TA acquisition procedure has been triggered at the UE. As a more specific example, when the fourth RAN node receives the TA value from the target network node towards which the first RAN node has triggered the early TA acquisition procedure, the fourth RAN node will automatically send the received TA value to one or more other RAN nodes. In one example, the recipient RAN node(s) for the TA values is / are indicated explicitly by the first RAN node, after the first RAN node triggers an early TA acquisition procedure at the UE. In another example, the recipient RAN node(s) for the TA values is / are any other RAN node than a RAN node to which the first RAN node triggered an early TA acquisition procedure.

[0241] In one example, the fourth RAN node first sends a request to the first, second, and third RAN node to provide LTM candidate cell configurations and then receives the requested LTM candidate cell configuration together with one or more TA values. Subsequently, the fourth RAN node sends all received TA values to each RAN node that provided an LTM candidate cell configuration.

[0242] In another example, when requesting LTM candidate cell configurations, the fourth RAN node can indicate that one or more TA values should be also sent, if available. After receiving these TA values, the fourth RAN node sends them to the other RAN nodes.

[0243] In one example, the communication between the fourth RAN node (e.g., CU) and the first, second, and third RAN nodes (e.g., DUs) is via a F1AP interface. Existing and / or newly defined F1AP messages can be used for this communication.

[0244] 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.

[0245] Figure 11 shows an example of a communication system 1100 in accordance with some embodiments. In this example, communication system 1100 includes a telecommunication network 1102 that includes an access network 1104 (e.g., RAN) and a core network 1106, which includes one or more core network nodes 1108. Access network 1104 includes one or more access network nodes, such as network nodes 11 lOa-b (one or more of which may be generally referred to as network nodes 1110), or any other similar 3GPP access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, telecommunication network 1102 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 1102 that supports an ORAN specification (e.g., published by the O-RAN Alliance or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in telecommunication network 1102, including one or more network nodes 1110 and / or core network nodes 1108.

[0246] 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 O-RAN Alliance or comparable technologies. Network nodes 1110 facilitate direct or indirect connection of UEs, such as by connecting UEs 1112a-d (one or more of which may be generally referred to as UEs 1112) to core network 1106 over one or more wireless connections.

[0247] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, communication system 1100 may include any number of wired or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. Communication system 1100 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0248] UEs 1112 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 1110 and other communication devices. Similarly, network nodes 1110 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 1112 and / or with other network nodes or equipment in telecommunication network 1102 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 1102. In the depicted example, core network 1106 connects network nodes 1110 to one or more hosts, such as host 1116. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be directly coupled to hosts. Core network 1106 includes one or more core network nodes (e.g., 1108) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of core network node 1108. Example core network nodes include functions of 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).

[0249] Host 1116 may be under the ownership or control of a service provider other than an operator or provider of access network 1104 and / or telecommunication network 1102, and may be operated by the service provider or on behalf of the service provider. Host 1116 may host a variety of applications to provide one or more service. Examples of such applications include live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0250] As a whole, communication system 1100 of Figure 11 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0251] In some examples, telecommunication network 1102 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 1102 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 1102. For example, telecommunication network 1102 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs.

[0252] In some examples, UEs 1112 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to access network 1104 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 1104. Additionally, a UE may be configured for operating in single- or multi-RAT or multi-standard mode. For example, a UE may operate with any one or combination of Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0253] In the example, hub 1114 communicates with access network 1104 to facilitate indirect communication between one or more UEs (e.g., 1112c and / or 1112d) and network nodes (e.g., 1110b). In some examples, hub 1114 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 1114 may be a broadband router enabling access to core network 1106 for the UEs. As another example, hub 1114 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1110, or by executable code, script, process, or other instructions in hub 1114. As another example, hub 1114 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, hub 1114 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 1114 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 1114 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 1114 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0254] Hub 1114 may have a constant / persistent or intermittent connection to network node 1110b. Hub 1114 may also allow for a different communication scheme and / or schedule between hub 1114 and UEs (e.g., 1112c and / or 1112d), and between hub 1114 and core network 1106. In other examples, hub 1114 is connected to core network 1106 and / or one or more UEs via a wired connection. Moreover, hub 1114 may be configured to connect to an M2M service provider over access network 1104 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 1110 while still connected via hub 1114 via a wired or wireless connection. In some embodiments, hub 1114 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to network node 1110b. In other embodiments, hub 1114 may be a non-dedicated hub - that is, a device capable of routing communications between the UEs and network node 1110b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0255] In some embodiments, UE 1112 may be configured to perform various operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 7. In some embodiments, one or more network nodes 1110 may be configured to perform various operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 8-10.

[0256] Figure 12 shows a UE 1200 in accordance with some embodiments. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), smart device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by 3GPP, including a narrow band internet of things (NB-IoT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0257] 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).

[0258] UE 1200 includes processing circuitry 1202 that is operatively coupled via a bus 1204 to an input / output interface 1206, a power source 1208, a memory 1210, a communication interface 1212, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 12. The level of integration between the components may vary from one UE to another UE. Further, certain UEs may contain multiple instances of a component, such as multiple processors, memories, transceivers, transmitters, receivers, etc. Processing circuitry 1202 is configured to process instructions and data and may be configured to implement any sequential state machine operative to execute instructions stored as machine-readable computer programs in memory 1210. Processing circuitry 1202 may be implemented as one or more hardware-implemented state machines (e.g., in discrete logic, field- programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), etc.); programmable logic together with appropriate firmware; one or more stored computer programs, general-purpose processors, such as a microprocessor or digital signal processor (DSP), together with appropriate software; or any combination of the above. For example, processing circuitry 1202 may include multiple central processing units (CPUs).

[0259] In the example, input / output interface 1206 may be configured to provide an interface or interfaces to an input device, output device, or one or more input and / or output devices. Examples of an output device include a speaker, a sound card, a video card, a display, a monitor, a printer, an actuator, an emitter, a smartcard, another output device, or any combination thereof. An input device may allow a user to capture information into UE 1200. Examples of an input device include a touch-sensitive or presence-sensitive display, a camera (e.g., a digital camera, a digital video camera, a web camera, etc.), a microphone, a sensor, a mouse, a trackball, a directional pad, a trackpad, a scroll wheel, a smartcard, and the like. The presence-sensitive display may include a capacitive or resistive touch sensor to sense input from a user. A sensor may be, for instance, an accelerometer, a gyroscope, a tilt sensor, a force sensor, a magnetometer, an optical sensor, a proximity sensor, a biometric sensor, etc., or any combination thereof. An output device may use the same type of interface port as an input device. For example, a Universal Serial Bus (USB) port may be used to provide an input device and an output device.

[0260] In some embodiments, power source 1208 is structured as a battery or battery pack. Other types of power sources, such as an external power source (e.g., an electricity outlet), photovoltaic device, or power cell, may be used. Power source 1208 may further include power circuitry for delivering power from power source 1208 itself, and / or an external power source, to the various parts of UE 1200 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging power source 1208. Power circuitry may perform any formatting, converting, or other modification to the power from power source 1208 to make the power suitable for the respective components of UE 1200 to which power is supplied.

[0261] Memory 1210 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, memory 1210 includes one or more application programs 1214, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1216. Memory 1210 may store, for use by UE 1200, any of a variety of various operating systems or combinations of operating systems.

[0262] Memory 1210 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a USIM and / or ISIM, other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card.’ Memory 1210 may allow UE 1200 to access instructions, application programs and the like, stored on transitory or non- transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system may be tangibly embodied as or in memory 1210, which may be or comprise a device-readable storage medium.

[0263] Processing circuitry 1202 may be configured to communicate with an access network or other network using communication interface 1212. Communication interface 1212 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1222. Communication interface 1212 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 1218 and / or a receiver 1220 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmitter 1218 and receiver 1220 may be coupled to one or more antennas (e.g., antenna 1222) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0264] In the illustrated embodiment, communication functions of communication interface 1212 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented 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.

[0265] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1212, via a wireless connection to a network node. Data captured by sensors of a UE can be communicated through a wireless connection to a network node via another UE. The output may be periodic (e.g., once every 15 minutes if it reports the sensed temperature), random (e.g., to even out the load from reporting from several sensors), in response to a triggering event (e.g., when moisture is detected an alert is sent), in response to a request (e.g., a user initiated request), or a continuous stream (e.g., a live video feed of a patient).

[0266] 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.

[0267] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or Virtual Reality (VR), a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to UE 1200 shown in Figure 12.

[0268] 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.

[0269] 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.

[0270] In some embodiments, UE 1200 may be configured to perform various operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 7.

[0271] Figure 13 shows a network node 1300 in accordance with some embodiments. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (e.g., radio base stations, Node Bs, eNBs, gNBs), and O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0272] 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).

[0273] 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).

[0274] Network node 1300 includes processing circuitry 1302, memory 1304, communication interface 1306, and power source 1308. Network node 1300 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which network node 1300 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, network node 1300 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1304 for different RATs) and some components may be reused (e.g., a same antenna 1310 may be shared by different RATs). Network node 1300 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1300, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1300.

[0275] Processing circuitry 1302 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1300 components, such as memory 1304, to provide network node 1300 functionality.

[0276] In some embodiments, processing circuitry 1302 includes a system on a chip (SOC). In some embodiments, processing circuitry 1302 includes one or more of radio frequency (RF) transceiver circuitry 1312 and baseband processing circuitry 1314. In some embodiments, RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1312 and baseband processing circuitry 1314 may be on the same chip or set of chips, boards, or units.

[0277] Memory 1304 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by processing circuitry 1302. Memory 1304 may store any suitable instructions, data, or information, including a computer program, software, an application including logic, rules, code, tables, and / or other instructions (collectively denoted computer program 1304a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1302 and utilized by network node 1300. Memory 1304 may be used to store any calculations made by processing circuitry 1302 and / or any data received via communication interface 1306. In some embodiments, processing circuitry 1302 and memory 1304 is integrated.

[0278] Communication interface 1306 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, communication interface 1306 comprises port(s) / terminal(s) 1316 to send and receive data, for example to and from a network over a wired connection. Communication interface 1306 also includes radio frontend circuitry 1318 that may be coupled to, or in certain embodiments a part of, antenna 1310. Radio front-end circuitry 1318 comprises filters 1320 and amplifiers 1322. Radio front-end circuitry 1318 may be connected to an antenna 1310 and processing circuitry 1302. The radio front-end circuitry may be configured to condition signals communicated between antenna 1310 and processing circuitry 1302. Radio front-end circuitry 1318 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1318 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1320 and / or amplifiers 1322. The radio signal may then be transmitted via antenna 1310. Similarly, when receiving data, antenna 1310 may collect radio signals which are then converted into digital data by radio front-end circuitry 1318. The digital data may be passed to processing circuitry 1302. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0279] In certain alternative embodiments, network node 1300 does not include separate radio front-end circuitry 1318, instead, processing circuitry 1302 includes radio front-end circuitry and is connected to antenna 1310. Similarly, in some embodiments, all or some of RF transceiver circuitry 1312 is part of communication interface 1306. In still other embodiments, communication interface 1306 includes one or more ports or terminals 1316, radio front-end circuitry 1318, and RF transceiver circuitry 1312, as part of a radio unit (not shown), and communication interface 1306 communicates with baseband processing circuitry 1314, which is part of a digital unit (not shown). Antenna 1310 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1310 may be coupled to radio front-end circuitry 1318 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1310 is separate from network node 1300 and connectable to network node 1300 through an interface or port.

[0280] Antenna 1310, communication interface 1306, and / or processing circuitry 1302 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, antenna 1310, communication interface 1306, and / or processing circuitry 1302 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0281] Power source 1308 provides power to the various components of network node 1300 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1308 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1300 with power for performing the functionality described herein. For example, network node 1300 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of power source 1308. As a further example, power source 1308 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0282] Embodiments of network node 1300 may include additional components beyond those shown in Figure 13 for providing certain aspects of the network node’s functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, network node 1300 may include user interface equipment to allow input of information into network node 1300 and to allow output of information from network node 1300. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1300.

[0283] In some embodiments, one or more network nodes 1300 may be configured to perform various operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 8-10.

[0284] Figure 14 is a block diagram illustrating a virtualization environment 1400 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 1400 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 1400 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.

[0285] Applications 1402 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1400 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 1402 may be configured to perform various operations attributed to a RAN node in various embodiments described above, including the exemplary methods shown in Figures 8-10.

[0286] Hardware 1404 includes processing circuitry, memory that stores software and / or instructions (collectively denoted computer program 1404a, 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 1406 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1408a and 1408b (one or more of which may be generally referred to as VMs 1408), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1406 may present a virtual operating platform that appears like networking hardware to the VMs 1408.

[0287] VMs 1408 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1406. Different embodiments of the instance of a virtual appliance 1402 may be implemented on one or more of VMs 1408, 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.

[0288] In the context of NFV, each VM 1408 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 1408, and that part of hardware 1404 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 1408 on top of the hardware 1404 and corresponds to the application 1402.

[0289] Hardware 1404 may be implemented in a standalone network node with generic or specific components. Hardware 1404 may implement some functions via virtualization. Alternatively, hardware 1404 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 1410, which, among others, oversees lifecycle management of applications 1402. In some embodiments, hardware 1404 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 1412 which may alternatively be used for communication between hardware nodes and radio units.

[0290] 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.

[0291] The term unit, as used herein, can have conventional meaning in the field of electronics, electrical devices and / or electronic devices and can include, for example, electrical and / or electronic circuitry, devices, modules, processors, memories, logic solid state and / or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and / or displaying functions, and so on, as such as those that are described herein. Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processor (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according to one or more embodiments of the present disclosure.

[0292] 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.

[0293] 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.

[0294] 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”). Although such terms may be used synonymously herein, there may also be instances where such terms are not intended to be used synonymously. Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0295] 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: while operating in a source cell provided by a first RAN node, performing early uplink (UL) synchronizations with a first LTM candidate cell provided by a second RAN node and a second LTM candidate cell provided by a third RAN node; receiving, from the first RAN node, a command to perform an LTM cell switch from the source cell to the first LTM candidate cell, wherein the command includes or indicates a timing advance (TA) value for the UE in the source cell; performing the LTM cell switch from the source cell to the first LTM candidate cell, based on the TA value and without performing a random access (RA) to the first LTM candidate cell during the LTM cell switch.

[0296] A2. The method of embodiment Al, wherein the TA value included with the command is the same as a first TA value determined based on the early UL synchronization with the first LTM candidate cell.

[0297] A3. The method of any of embodiments A1-A2, further comprising: receiving, from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second timing advance (TA) value determined based on the UE’s early UL synchronization with the second LTM candidate cell; and performing the second LTM cell switch from the source cell to the first LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

[0298] A4. The method of any of embodiments Al -A3, further comprising receiving, via the source cell, an indication to perform the early UL synchronizations with the first and second LTM candidate cells, wherein the early UL synchronizations are performed in accordance with the indication.

[0299] A5. The method of embodiment A4, wherein the indication comprises one or more physical downlink control channel (PDCCH) orders.

[0300] A6. The method of any of embodiments A4-A5, further comprising receiving, from a fourth RAN node via the source cell, first and second early UL synchronization configurations for the respective first and second LTM candidate cells, wherein the early UL synchronizations are performed based on the respective first and second early UL synchronization configurations.

[0301] A7. The method of embodiment A6, wherein the indication references one or more parameters in the respective first and second early UL synchronization configurations, and the first and second early UL synchronization are performed using parameters reference by the indication.

[0302] A8. The method of embodiment A7, wherein performing the early UL synchronization with the first LTM candidate comprises transmitting a random access (RA) preamble using RA resources of the first LTM candidate cell, wherein the RA preamble and / or the RA resources are referenced by the indication.

[0303] A9. The method of embodiment A8, wherein the RA resources referenced by the indication include one or more of the following: time / frequency resources, and one or more beams.

[0304] A10. The method of any of embodiments A6-A9, 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.

[0305] All. The method of any of embodiments Al -Al 0, 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. 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: sending, to a UE via a source cell provided by the first RAN node, an indication to perform early uplink (UL) synchronizations with a first LTM candidate cell provided by a second RAN node and a second LTM candidate cell provided by a third RAN node; determining a timing advance (TA) value for the UE in the source cell; sending to the UE a command to perform an LTM cell switch from the source cell to the first LTM candidate cell, wherein the command includes or indicates the TA value determined for the UE in the source cell; and sending one of the following: to the fourth RAN node, a request to send the second and third RAN nodes TA values determined based on the early UL synchronizations; or a message to at least one of the second and third RAN nodes, the message including one or more TA values for the UE.

[0306] Bia. The method of embodiment Bl, wherein the TA value included with the command is the same as a first TA value determined based on the UE’s early UL synchronization with the first LTM candidate cell.

[0307] B2. The method of any of embodiments Bl -Bl a, wherein the indication comprises one or more physical downlink control channel (PDCCH) orders.

[0308] B3. The method of any of embodiments B1-B2, further comprising receiving, from the second and third RAN nodes via a fourth RAN node, respective first and second TA values for the UE in the respective first and second LTM candidate cells, wherein the first and second TA values are based on the respective early UL synchronizations.

[0309] B3a. The method of embodiment B3, wherein the request is sent to the fourth RAN node before sending the command, and the request includes one or more of the following: the determined TA value, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell

[0310] B4. The method of embodiment B3, wherein the message sent to at least one of the second and third RAN nodes is responsive to one of the following: receiving the first and second TA values, or sending the command.

[0311] B5. The method of any of embodiments B3-B4, wherein one or more of the following TA values are included in the message sent to the second RAN node: the TA value included with or indicated by the command, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell.

[0312] B6. The method of embodiment B5, wherein the message is sent to the second RAN node via the fourth RAN node.

[0313] B7. The method of any of embodiments B3-B6, wherein the one or more of the following TA values are included in the message sent to the third RAN node: the TA value included with or indicated by the command, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell.

[0314] B8. The method of embodiment B7, wherein the message is sent to the third RAN node via the fourth RAN node.

[0315] B9. The method of any of embodiments B1-B3, wherein the request sent to the fourth RAN node is responsive to sending the indication.

[0316] BIO. The method of any of embodiments B1-B9, further comprising: receiving, from the fourth RAN node, first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and sending the first and second early UL synchronization configurations to the UE via the source cell.

[0317] Bl 1. The method of embodiment BIO, wherein the indication references one or more parameters in the respective first and second early UL synchronization configurations, and the first and second early UL synchronization are performed by the UE using parameters referenced by the indication.

[0318] Bl 2. The method of embodiment Bl 1, 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.

[0319] Bl 3. The method of any of embodiments Bl -Bl 2, 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.

[0320] B14. The method of any of embodiments B1-B13, 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.

[0321] 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: sending, to a fourth RAN node, an early uplink (UL) synchronization configuration for a UE towards a first LTM candidate cell provided by the second RAN node, wherein the UE is served by a source cell provided by a first RAN node; receiving a random access (RA) preamble from the UE in the first LTM candidate cell, in accordance with the early UL synchronization configuration; based on the RA preamble, determining a first timing advance (TA) value for the UE in the first LTM candidate cell; sending the first TA value to the first RAN node via the fourth RAN node; and receiving respective TA values for the UE in one or more of the following: the source cell, the first LTM candidate cell, and a second LTM candidate cell provided by a third RAN node.

[0322] C2. The method of embodiment Cl, wherein the one or more TA values are received in response to sending the first TA value. C3. The method of embodiment Cl, wherein: the one or more TA values are received in a request from the fourth RAN node to provide an LTM candidate cell configuration for the UE in the first LTM candidate cell; and the early UL synchronization configuration for the UE in the first LTM candidate cell is sent to the fourth RAN node in response to the request.

[0323] C4. The method of embodiment C3, wherein the early UL synchronization configuration for the UE in the first 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 first LTM candidate cell.

[0324] C5. The method of any of embodiments C1-C4, wherein the received TA values include the first TA value sent to the first RAN node via the fourth RAN node.

[0325] C6. The method of embodiment Cl, further comprising, after sending the first TA value and without receiving a further RA preamble from the UE in the first LTM candidate cell, receiving from the UE a reconfiguration complete message indicating that the UE has completed an LTM cell switch to the first LTM candidate cell.

[0326] C7. The method of embodiment C6, wherein timing alignment of the reconfiguration complete message in the first LTM candidate cell is based on a TA value used by the UE for timing alignment in the source cell.

[0327] C8. The method embodiment C7, wherein the received TA values include the TA value used by the UE for timing alignment in the source cell.

[0328] C9. The method of any of embodiments C6-C8, wherein the one or more TA values are received in or with a notification that the LTM cell switch to the first LTM candidate cell has been initiated. CIO. The method of any of embodiments C6-C9, wherein: the received TA values include a second TA value for the second LTM candidate cell, based on an early UL synchronization by the UE with the second LTM candidate cell; and the method further comprises sending to the UE a command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the command includes the received second TA value.

[0329] Cl 1. The method of embodiment CIO, further comprising, based on the received second TA value, refraining from initiating an early UL synchronization of the UE with the second LTM candidate cell, prior to sending the command.

[0330] Cl 2. The method of any of embodiments Cl-Cl 1, wherein the one or more TA values are received from one of the following: the first RAN node, or the fourth RAN node.

[0331] Cl 3. The method of any of embodiments Cl -Cl 2, 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.

[0332] 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 the following for a UE served by a source cell provided by a first RAN node: from a second RAN node, a first timing advance (TA) value for the UE in a first LTM candidate cell provided by the second RAN node ; and from a third RAN node, a second TA value for the UE in a second LTM candidate cell provided by the third RAN node; sending the received first and second TA values to the first RAN node; and sending at least one message including one or more TA values for the UE, each message being sent to the second RAN node or the third RAN node.

[0333] D2. The method of embodiment DI, further comprising: receiving, from the second and third RAN nodes, respective first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and sending the first and second early UL synchronization configurations to the UE via the first RAN node, wherein the first and second TA values are based on early UL synchronizations by the UE with the first and second LTM candidate cells, in accordance with the respective first and second early UL synchronization configurations.

[0334] D2a. The method of embodiment D2, wherein the at least one message includes a first message sent to the second RAN node, wherein the first message includes the second TA value and is sent according to one of the following: responsive to receiving the second TA value, responsive to sending the second TA value to the first RAN node, or based on receiving the first early UL synchronization configuration.

[0335] D2b. The method of any of embodiments D2-D2a, wherein the at least one message includes a second message sent to the third RAN node, wherein the second message includes the first TA value and is sent according to one of the following: responsive to receiving the first TA value, responsive to sending the first TA, or based on receiving the second early UL synchronization configuration.

[0336] D2c. The method of any of embodiments D2-D2b, further comprising receiving from the first RAN node a TA value for the UE in the source cell, wherein each of the at least one message also includes the TA value for the UE in the source cell.

[0337] D3. The method of any of embodiments D1-D2, further comprising receiving one of the following from the first RAN node: a request to send one or more TA values for the UE to at least one of the second and third RAN nodes; or a message including one or more TA values for the UE that should be sent to at least one of the second and third RAN nodes.

[0338] D4. The method of embodiment D3, further comprising storing the received first and second TA values and, based on the request, retrieving the stored first and second TA values, wherein each of the retrieved first and second TA values is included in at least one of the messages sent to the second and third RAN nodes. D5. The method of any of embodiments D3-D4, wherein the request from the first RAN node indicates which of the second and third RAN nodes should receive each of the one or more TA values, and the message is sent to at least one of the second and third RAN nodes in accordance with the indication.

[0339] D6. The method of embodiment D3, wherein the message received from the first RAN node is an LTM cell switch notification that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell, and the messages sent to the second and third RAN nodes are respective LTM cell switch notification messages.

[0340] D7. The method of embodiment D3, wherein one or more of the following TA values are included in the message received from the first RAN node: a TA value for the UE in the source cell, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell.

[0341] D8. The method of embodiment D7, wherein one or more of the following TA values in the message from the first RAN node are included in the message sent to the second RAN node: the TA value for the UE in the source cell, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell.

[0342] D9. The method of any of any of embodiments D7-D8, wherein one or more of the following TA values in the message from the first RAN node are included in the message sent to the third RAN node: the TA value for the UE in the source cell, the first TA value for the UE in the first LTM candidate cell, and the second TA value for the UE in the second LTM candidate cell.

[0343] DIO. The method of any of embodiments D7-D9, wherein the message received from the first RAN node includes an indication of which of the second and third RAN nodes should receive each of the included one or more TA values, and the message is sent to at least one of the second and third RAN nodes in accordance with the indication.

[0344] Dll. The method of any of embodiments D 1 -D 10, 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. D12. The method of any of embodiments Dl-Dl 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.

[0345] 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 Al-All.

[0346] 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 Al -All.

[0347] 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 Al-Al l.

[0348] 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 Al -Al 1.

[0349] 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 4.

[0350] 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-B14.

[0351] 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 4.

[0352] 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 4.

[0353] 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 C1-C13. 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-C13.

[0354] 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 3.

[0355] 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-C13.

[0356] 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 -DI 2.

[0357] 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-D12.

[0358] 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 D1-D12.

[0359] 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 -DI 2.

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 provided by a first RAN node, performing (730) respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node; receiving (740), from the first RAN node, a first command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the first command includes or indicates a first timing advance, TA, value for use by the UE in the first LTM candidate cell; performing (750) the first LTM cell switch from the source cell to the first LTM candidate cell, based on the first TA value and without performing a random access, RA, to the first LTM candidate cell during the first LTM cell switch; receiving (760), from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second TA value for use by the UE in the second LTM candidate cell; and performing (770) the second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

2. The method of claim 1, wherein the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell.

3. The method of any of claims 1-2, further comprising receiving (720), via the source cell, an indication to perform early UL synchronizations with the first and second LTM candidate cells, wherein the respective early UL synchronizations are performed in accordance with the indication.

4. The method of claim 3, wherein the indication comprises one or more physical downlink control channel, PDCCH, orders.

5. The method of any of claims 3-4, further comprising receiving (710), from a fourth RAN node via the source cell, first and second early UL synchronization configurations for the respective first and second LTM candidate cells, wherein the respective early UL synchronizations are performed based on the first and second early UL synchronization configurations.

6. The method of claim 5, wherein the indication references one or more parameters in the first and second early UL synchronization configurations, and the respective early UL synchronization are performed using the one or more parameters referenced by the indication.

7. The method of claim 6, wherein performing (730) early UL synchronization with the first LTM candidate comprises transmitting (731) a RA preamble using RA resources of the first LTM candidate cell, wherein the RA preamble and / or the RA resources are referenced by the indication.

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

9. The method of any of claims 5-8, 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.

10. The method of any of claims 1-9, 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 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.

11. A method for a first radio access network, RAN, node configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising:sending (830), to a UE via a source cell provided by the first RAN node, an indication to perform respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node; subsequently receiving (835) the following timing advance, TA, values: from the second RAN node, a first TA value for use by the UE in the first LTM candidate cell, and from the third RAN node, a second TA value for use by the UE in the second LTM candidate cell; sending (850) to the UE a command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the command includes or indicates the first TA value; and sending (860) to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

12. The method of claim 11, wherein the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell.

13. The method of claim 11-12, wherein the indication comprises one or more physical downlink control channel, PDCCH, orders.

14. The method of any of claims 11-13, wherein one or more of the following applies: the first message is sent to the second RAN node in response to sending (850) the command; and the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

15. The method of any of claims 11-14, wherein the first message includes the second TA value in order to facilitate a second LTM cell switch by the UE from the first LTM candidate cell to the second LTM candidate cell.

16. The method of any of claims 11-15, wherein the first message is sent to the second RAN node via a fourth RAN node.

17. The method of claim 16, 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.

18. The method of any of claims 17-17, further comprising: receiving (810), from the fourth RAN node, first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and sending (820) the first and second early UL synchronization configurations to the UE via the source cell.

19. The method of claim 18, wherein the indication references one or more parameters in the respective first and second early UL synchronization configurations, and the respective early UL synchronizations are performed by the UE using parameters referenced by the indication.

20. The method of claim 19, 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.

21. The method of any of claims 11 -20, 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.

22. 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 (920), from a UE served by a source cell provided by a first RAN node, a random access, RA, preamble in a first LTM candidate cell provided by the second RAN node; based on the RA preamble, determining (930) a first timing advance, TA, value for use by the UE in the first LTM candidate cell;sending (940) the first TA value to the first RAN node via a fourth RAN node; and receiving (950) from the first RAN node a first message that includes or indicates one or more of the following: the first TA value, and second TA value for use by the UE in a second LTM candidate cell provided by a third RAN node.

23. The method of claim 22, further comprising sending (910), to the fourth RAN node, an early uplink, UL, synchronization configuration for a UE towards the first LTM candidate, wherein the RA preamble is received in accordance with the early UL synchronization configuration.

24. The method of claim 23, wherein the early UL synchronization configuration for the UE in the first LTM candidate cell includes one or more of the following: an identifier or index of a 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 first LTM candidate cell.

25. The method of any of claims 22-24, wherein one or more of the following applies: the first message is received from the first RAN node via the fourth RAN node; and the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

26. The method of claim 25, further comprising, after sending (940) the first TA value and without receiving a further RA preamble from the UE in the first LTM candidate cell during the LTM cell switch, receiving (960) from the UE a reconfiguration complete message indicating that the UE has completed the LTM cell switch to the first LTM candidate cell.

27. The method of claim 26, wherein one or more of the following applies: timing alignment of the reconfiguration complete message in the first LTM candidate cell is based on the first TA value; and the first message also includes the TA value used by the UE for timing alignment in the source cell.

28. The method of any of claims 22-27, wherein the first TA value is based on the UE’s early UL synchronization with the first LTM candidate cell and the second TA value is based on the UE’s early UL synchronization with the second LTM candidate cell.

29. The method of any of claims 22-28, further comprising sending (980) to the UE a command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the command includes the received second TA value.

30. The method of claim 29, further comprising, based on the received second TA value, refraining from initiating (970) an early UL synchronization of the UE with the second LTM candidate cell, prior to sending the command.

31. The method of any of claims 22-30, 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.

32. 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 (1030) the following for a UE served by a source cell provided by a first RAN node: from a second RAN node, a first timing advance, TA, value for use by the UE in a first LTM candidate cell provided by the second RAN node; and from a third RAN node, a second TA value for use by the UE in a second LTM candidate cell provided by the third RAN node; sending (1040) the first TA value and the second TA value to the first RAN node; and sending (1080) to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

33. The method of claim 32, further comprising: receiving, from the second and third RAN nodes, respective first and second early UL synchronization configurations for the respective first and second LTM candidate cells; and sending the first and second early UL synchronization configurations to the UE via the first RAN node,wherein the first and second TA values are based on early UL synchronizations by the UE with the first and second LTM candidate cells, in accordance with the respective first and second early UL synchronization configurations.

34. The method of claim 33, 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.

35. The method of any of claims 32-34, further comprising receiving from the first RAN node a second message that includes or indicates one or more of the following TA values for the UE: the first TA value, the second TA value, and a TA value for the UE in the source cell.

36. The method of claim 35, wherein the second message received from the first RAN node is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

37. The method of any of claims 35-36, wherein one or more of the following applies: the first message is sent in response to receiving the second message; and the first message is an LTM cell switch notification message that indicates the first RAN node has initiated an LTM cell switch for the UE to the first LTM candidate cell.

38. The method of any of claims 35-37, wherein the first message sent to the second RAN node also includes or indicates the TA value for the UE in the source cell.

39. The method of any of claims 32-38, 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.

40. User equipment, UE (210, 610, 1112, 1200) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), the UE comprising:communication interface circuitry (1212) configured to communicate with RAN nodes (110, 120, 130, 220, 620, 630, 640, 650, 1110, 1300, 1402); and processing circuitry (1202) 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 provided by a first RAN node (perform respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node; receive, from the first RAN node, a first command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the first command includes or indicates a first timing advance, TA, value for use by the UE in the first LTM candidate cell; perform the first LTM cell switch from the source cell to the first LTM candidate cell, based on the first TA value and without performing a random access, RA, to the first LTM candidate cell during the first LTM cell switch; receive, from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second TA value for use by the UE in the second LTM candidate cell; and perform the second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

41. The UE of claim 40, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-10.

42. User equipment, UE (210, 610, 1112, 1200) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), the UE being further configured to: while operating in a source cell provided by a first RAN node (120, 130, 220, 620, 1110, 1300, 1402), perform respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node (120, 130, 220, 630, 1110,1300, 1402) and with a second LTM candidate cell provided by a third RAN node (120, 130, 220, 640, 1110, 1300, 1402); receive, from the first RAN node, a first command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the first command includes or indicates a first timing advance, TA, value for use by the UE in the first LTM candidate cell; perform the first LTM cell switch from the source cell to the first LTM candidate cell, based on the first TA value and without performing a random access, RA, to the first LTM candidate cell during the first LTM cell switch; receive, from the second RAN node, a second command to perform a second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, wherein the second command includes or indicates a second TA value for use by the UE in the second LTM candidate cell; and perform the second LTM cell switch from the first LTM candidate cell to the second LTM candidate cell, based on the second TA value and without performing a RA to the second LTM candidate cell during the second LTM cell switch.

43. The UE of claim 42, being further configured to perform operations corresponding to the methods of any of claims 2-10.

44. Non-transitory, computer-readable medium (1210) storing computer-executable instructions that, when executed by processing circuitry (1202) of user equipment, UE (210, 610, 1112, 1200) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-10.

45. A computer program product (1214) comprising computer-executable instructions that, when executed by processing circuitry (1202) of user equipment, UE (210, 610, 1112, 1200) configured for layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 1104), configure the UE to perform operations corresponding to the methods of any of claims 1-10.

46. First radio access network, RAN, node (120, 130, 220, 620, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the first RAN node comprising:communication interface circuitry (1306, 1404) configured to communicate with UEs and with other RAN nodes (110, 220, 630, 640, 650, 1110, 1300, 1402); and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: send, to a UE via a source cell provided by the first RAN node, an indication to perform respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node and with a second LTM candidate cell provided by a third RAN node; subsequently receive the following timing advance, TA, values: from the second RAN node, a first TA value for use by the UE in the first LTM candidate cell, and from the third RAN node, a second TA value for use by the UE in the second LTM candidate cell; send to the UE a command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the command includes or indicates the first TA value; and send to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

47. The first RAN node of claim 46, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 12-21.

48. First radio access network, RAN, node (120, 130, 220, 620, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the first RAN node being further configured to: send, to a UE via a source cell provided by the first RAN node, an indication to perform respective early uplink, UL, synchronizations with a first LTM candidate cell provided by a second RAN node (120, 130, 220, 630, 1110, 1300, 1402) and with a second LTM candidate cell provided by a third RAN node (120, 130, 220, 640, 1110, 1300, 1402); subsequently receive the following timing advance, TA, values: from the second RAN node, a first TA value for use by the UE in the first LTM candidate cell, andfrom the third RAN node, a second TA value for use by the UE in the second LTM candidate cell; send to the UE a command to perform a first LTM cell switch from the source cell to the first LTM candidate cell, wherein the command includes or indicates the first TA value; and send to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

49. The first RAN node of claim 48, being further configured to perform operations corresponding to the methods of any of claims 12-21.

50. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a first radio access network, RAN, node (120, 130, 220, 620, 1110, 1300, 1402) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), configure the first RAN node to perform operations corresponding to the methods of any of claims 11-21.

51. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a first radio access network, RAN, node (120, 130, 220, 620, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), configure the first RAN node to perform operations corresponding to the methods of any of claims 11-21.

52. Second radio access network, RAN, node (120, 130, 220, 630, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the second RAN node comprising: communication interface circuitry (1306, 1404) configured to communicate with UEs and with other RAN nodes (110, 220, 620, 640, 650, 1110, 1300, 1402); and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from a UE served by a source cell provided by a first RAN node (120, 130, 220, 620, 1110, 1300, 1402), a random access, RA, preamble in a first LTM candidate cell provided by the second RAN node;based on the RA preamble, determine a first timing advance, TA, value for use by the UE in the first LTM candidate cell; send the first TA value to the first RAN node via a fourth RAN node (110, 220, 650, 1110, 1300, 1402); and receiving from the first RAN node a first message that includes or indicates one or more of the following: the first TA value, and second TA value for use by the UE in a second LTM candidate cell provided by a third RAN node (120, 130, 220, 640, 1110, 1300, 1402).

53. The second RAN node of claim 52, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 23-31.

54. Second radio access network, RAN, node (120, 130, 220, 630, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the second RAN node being further configured to: receive, from a UE served by a source cell provided by a first RAN node (120, 130, 220, 620, 1110, 1300, 1402), a random access, RA, preamble in a first LTM candidate cell provided by the second RAN node; based on the RA preamble, determine a first timing advance, TA, value for use by the UE in the first LTM candidate cell; send the first TA value to the first RAN node via a fourth RAN node (110, 220, 650, 1110, 1300, 1402); and receiving from the first RAN node a first message that includes or indicates one or more of the following: the first TA value, and second TA value for use by the UE in a second LTM candidate cell provided by a third RAN node (120, 130, 220, 640, 1110, 1300, 1402).

55. The second RAN node of claim 54, being further configured to perform operations corresponding to the methods of any of claims 23-31.

56. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a second radio access network, RAN, node (120, 130, 220, 630, 1110, 1300, 1402) configured to facilitate layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200),configure the second RAN node to perform operations corresponding to the methods of any of claims 22-31.

57. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a second radio access network, RAN, node (120, 130, 220, 630, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), configure the second RAN node to perform operations corresponding to the methods of any of claims 22- 31.

58. Fourth radio access network, RAN, node (110, 220, 650, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the fourth RAN node comprising: communication interface circuitry (1306, 1404) configured to communicate with UEs and with other RAN nodes (120, 130, 220, 620, 630, 640, 1110, 1300, 1402); and processing circuitry (1302, 1404) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive the following for a UE served by a source cell provided by a first RAN node: from a second RAN node, a first timing advance, TA, value for use by the UE in a first LTM candidate cell provided by the second RAN node; and from a third RAN node, a second TA value for use by the UE in a second LTM candidate cell provided by the third RAN node; send the first TA value and the second TA value to the first RAN node; and send to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

59. The fourth RAN node of claim 58, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 33-39.

60. Fourth radio access network, RAN, node (110, 220, 650, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), the fourth RAN node being further configured to: receive the following for a UE served by a source cell provided by a first RAN node (120, 130, 220, 620, 1110, 1300, 1402): from a second RAN node (120, 130, 220, 630, 1110, 1300, 1402), a first timing advance, TA, value for use by the UE in a first LTM candidate cell provided by the second RAN node; and from a third RAN node (120, 130, 220, 640, 1110, 1300, 1402), a second TA value for use by the UE in a second LTM candidate cell provided by the third RAN node; send the first TA value and the second TA value to the first RAN node; and send to the second RAN node a first message that includes or indicates one or more of the following: the first TA value, and the second TA value.

61. The fourth RAN node of claim 60, being further configured to perform operations corresponding to the methods of any of claims 33-39.

62. Non-transitory, computer-readable medium (1304, 1404) storing computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a fourth radio access network, RAN, node (110, 220, 650, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), configure the fourth RAN node to perform operations corresponding to the methods of any of claims 32- 39.

63. Computer program product (1304a, 1404a) comprising computer-executable instructions that, when executed by processing circuitry (1302, 1404) of a fourth radio access network, RAN, node (110, 220, 650, 1110, 1300, 1402) configured to facilitate layer-l / layer-2 triggered intercell mobility, LTM, by user equipment, UEs (210, 610, 1112, 1200), configure the fourth RAN node to perform operations corresponding to the methods of any of claims 32-39.

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