Timing advance validity for conditional l1 / l2-triggered mobility (LTM)

Abstract

Embodiments include methods for a user equipment (UE) configured for conditional layer- 1 / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN). Such methods include receiving, from a RAN node via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. Such methods include, in response to receiving from the RAN node a timing advance (TA) value for the LTM candidate cell, initiating a time alignment timer and measuring a downlink (DL) reference signal (RS) of the LTM candidate cell, thereby obtaining a first measurement value. Such methods include subsequently measuring the DL RS of the LTM candidate cell, thereby obtaining a second measurement value, and determining whether the TA value is valid based on the first and second measurement values. Other embodiments include complementary methods for the RAN node.

Description

[0001] TIMING ADVANCE VALIDITY FOR CONDITIONAL L1 / L2-TRIGGERED MOBILITY (LTM)

[0002] TECHNICAL FIELD

[0003] The present disclosure relates generally to wireless networks and more specifically to

[0004] 5 techniques for improving conditional layer- l / layer-2 triggered mobility (LTM) of user equipment (UEs) across multiple cells in a radio access network (RAN), such as in relation to UEs acquiring and maintaining early uplink (UL) synchronization for LTM candidate cells.

[0005] BACKGROUND

[0006] The fifth generation (5G) of cellular systems has been standardized within the Third- Generation Partnership Project (3GPP). 5G was developed for maximum flexibility to support many different use cases including enhanced mobile broadband (eMBB), machine type communications (MTC), ultra-reliable low latency communications (URLLC), side-link device- to-device (D2D), and several other use cases. 5G was initially specified in 3GPP Release 15 (Rel-15) and continues to evolve through subsequent releases.

[0007] 15 Figure 1 illustrates a high-level view of an exemplary 5G network architecture, including 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

[0008] 20 Functions (AMFs) in the 5GC via respective NG-C interfaces and to one or more User Plane Functions (UPFs) in 5GC via respective NG-U interfaces. The 5GC can include various other network functions (NFs), such as Session Management Function (SMF).

[0009] In addition, the gNBs can be connected to each other via one or more Xn interfaces, such as Xn interface (140) between gNBs (100, 150). The radio technology for the NG-RAN is often referred to as “New Radio” (NR). With respect to the NR interface to UEs, each of the gNBs can support frequency division duplexing (FDD), time division duplexing (TDD), or a combination thereof. Each of the gNBs can serve a geographic coverage area including one or more cells and, in some cases, can also use various directional beams to provide coverage in the respective cells. In general, a downlink (DL) “beam” is a coverage area of a network-transmitted reference signal

[0010] 30 (RS) that may be measured or monitored by a UE.

[0011] 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 funchons. Each CU and DU can include various circuitry needed to perform their respective functions, including processing circuitry, communication interface circuitry (e.g., transceivers), and power supply circuitry. A gNB-CU connects to one or more gNB-DUs over respective Fl logical interfaces (e.g., 122 and 132 shown in Figure 1).

[0012] 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.

[0013] Even so, handover and other mobility procedures can have various problems related to robustness. For example, a HO command is normally sent when the radio conditions for the UE are already quite bad, such as at or near cell borders. As such, the HO command may need to be segmented (e.g., to allow for redundancy to protect against errors) and / or retransmitted one or more times before the UE receives it correctly. In such case, the HO command may not reach the UE before the degraded connection with the source node (e.g., the node hosting the UE’s current serving cell) is dropped. When the connection is severely degraded, the UE may not receive the HO command at all. Both scenarios result in HO failure to the target cell and possibly the UE declaring radio link failure (RLF) in the source cell.

[0014] To address various difficulties with handovers and other mobility procedures, 3GPP Rel- 16 introduced conditional handover (CHO) and SN-initiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 introduced various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood of successful reception. Execution of the mobility command is performed later based on an associated execution condition.

[0015] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconflguratlon message (in 5 G) or an RRCConnectionReconflguration message (in fourth-generation (4G) Long-Term Evolution (LTE)). When the UE detects execution condition(s) associated with one of the earlier- received reconfigurations, the UE executes the reconfiguration to perform the mobility procedure (e.g., HO, PSCell change / addition, etc ).

[0016] Even so, conditional (e g., CHO) and non-conditional (e.g., HO) mobility operations are triggered by layer 3 (L3) measurements and involve radio resource control (RRC) signaling to change primary cells and to release / add secondary cells as needed. Moreover, conventional inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI) resets, leading to increased latency, signaling overhead, and interruptions compared to intra-cell beam switching.

[0017] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 triggered mobility (LTM). In LTM, a UE is pre-configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.”

[0018] 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 serving cell.

[0019] The UE performs measurements on configured LTM candidate cells and reports these measurements to its serving RAN node, based on which the RAN node triggers execution of an LTM cell switch procedure by the UE to one of the configured LTM candidate cells. The RAN node may trigger LTM cell switch by sending the UE an LTM cell switch command.

[0020] Unlike conditional L3 mobility in which the UE initiates execution, LTM is initiated by a UE’s serving RAN node based on measurements reported by the UE. This introduces some delay in LTM cell switch. To capture advantages of both LTM and conditional L3 mobility, 3GPP Rel-19 will introduce conditional LTM (CLTM). Much like conditional L3 mobility, when a UE detects the execution condition(s) associated with an earlier-received LTM candidate cell configuration, the UE executes an LTM cell switch to the candidate cell.

[0021] SUMMARY

[0022] As mentioned above, in non-conditional LTM, the UE’s serving RAN node sends the UE a command for LTM cell switch to one of the UE’s configured LTM candidate cells. This command may include a TA value determined based on the UE’s earlier RACH transmission to the LTM candidate cell. Since there is no LTM cell switch command in CLTM, however, the serving RAN node is unable to provide a TA value for an LTM candidate cell at the time of LTM cell switch. One solution is to provide the TA value to the UE in an earlier message, although it is unclear how the UE determines whether this earlier-received TA value is still valid when the execution condition for LTM cell switch is fulfilled. An obj ect of embodiments of the present disclosure is to improve early UL synchronization and / or early TA acquisition for UEs in CLTM, such as by providing, enabling, and / or facilitating solutions to exemplary problems summarized above and described in more detail below.

[0023] Embodiments include methods (e.g., procedures) for a UE configured for CLTM in a radio access network (RAN, e.g., E-UTRAN, NG-RAN).

[0024] These exemplary methods include receiving, from a RAN node via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. These exemplary methods also include receiving from the RAN node a TA value for the LTM candidate cell and, in response to receiving the TA value, initiating a time alignment timer and measuring a downlink (DL) reference signal (RS) of the LTM candidate cell, thereby obtaining a first measurement value. These exemplary methods also include subsequently measuring the DL RS of the LTM candidate cell, thereby obtaining a second measurement value. These exemplary methods also include determining whether the TA value is valid based on the first and second measurement values.

[0025] In some embodiments, subsequently measuring the DL RS of the LTM candidate cell is responsive to determining that one or more of the following has occurred: the time alignment timer has expired, and the execution condition is fulfilled.. In some of these embodiments, these exemplary methods also include the following operations, after determining that the time alignment timer has expired and after determining that the TA value is valid based on the first and second measurement values:

[0026] • re-initiating the time alignment timer;

[0027] • upon expiration of the time alignment timer after re-initiation, measuring the DL RS of the LTM candidate cell, thereby obtaining a third measurement value; and

[0028] • determining whether the TA value is valid based on the first and third measurement values.

[0029] In some embodiments, determining whether the TA value is valid based on the first and second measurement values includes the following operations:

[0030] • determining a function of the first and second measurement values;

[0031] • determining that the TA value is valid when the function is less than a threshold; and

[0032] • determining that the TA value is invalid when the function is not less than the threshold.

[0033] Other embodiments include exemplary methods (e.g., procedures) for a RAN node configured to facilitate CLTM by UEs. In general, these exemplary methods may be complementary to the exemplary methods for a UE summarized above.

[0034] These exemplary methods include sending, to a UE via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. These exemplary methods also include obtaining a TA value for UE in the LTM candidate cell, sending the TA value to the UE, and receiving from the UE an indication of one or more of the following:

[0035] • an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell;

[0036] • an updated threshold is needed for the UE to determine validity of the TA value;

[0037] • the TA value is no longer valid;

[0038] • a cause for invalidity of the TA value;

[0039] • expiration of a UE time alignment timer for the TA value;

[0040] • validity of the TA value has been extended after expiration of the UE time alignment timer; and

[0041] • whether validity of the TA value may be extended after expiration of the UE time alignment timer.

[0042] In some embodiments, the indication is received after expiration of the UE time alignment timer. In some embodiments, these exemplary methods also include, in response to the indication, sending one or more of the following to the UE:

[0043] • an updated TA value for the LTM candidate cell;

[0044] • an order to transmit a further RA preamble to the LTM candidate cell;

[0045] • an updated threshold for determining validity of the TA value or the updated TA value;

[0046] • a further indication to extend validity of the TA value.

[0047] In some embodiments, obtaining the updated TA value for the UE in the LTM candidate cell based on one of the following:

[0048] • determining the updated TA value based on the further RA preamble received from the UE in the LTM candidate cell; or

[0049] • receiving the updated TA value from a second RAN node that provides the LTM candidate cell.

[0050] Other embodiments and variants of the exemplary methods summarized above are described herein. Other embodiments include UEs (e.g., wireless devices) and RAN nodes (e.g., base stations, eNBs, gNBs, ng-eNBs, etc.) configured to perform operations corresponding to any of the exemplary methods described herein. Other embodiments include non-transitory, computer- readable media storing program instructions that, when executed by processing circuitry, configure such UEs and RAN nodes to perform operations corresponding to any of the exemplary methods described herein.

[0051] These and other embodiments described herein may provide various advantages and / or benefits. For example, by enabling a UE to maintain an LTM candidate cell TA value received from its serving RAN node, embodiments may facilitate timely UE conditional LTM cell switch while reducing TA-related signaling with the serving RAN node. As another example, by using a time alignment timer and DL measurements as a basis for maintaining LTM candidate cell TA values, embodiments may enable UEs to easily determine TA validity in a timely and efficient manner. At a high level, embodiments may facilitate conditional LTM without connection interruption, excess signaling overhead, and excess UE energy consumption.

[0052] 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.

[0053] BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 shows an exemplary 5G / NR network architecture.

[0055] Figure 2 shows exemplary 5G / NR user plane (UP) and control plane (CP) protocol stacks.

[0056] Figure 3 shows an exemplary procedure for configured grant small data transmission (CG- SDT) by a UE.

[0057] Figure 4 shows a signaling diagram for an exemplary LTM cell switch procedure.

[0058] Figure 5 shows a timing diagram that illustrates some embodiments of the present disclosure.

[0059] Figure 6 (which includes Figures 6A-B) shows a flow diagram of an exemplary method for a UE (e g., base station, eNB, gNB, DU, etc.), according to various embodiments of the present disclosure.

[0060] Figure 7 shows a flow diagram of an exemplary method for a RAN node (e.g., base station, eNB, gNB, DU, etc. , according to various embodiments of the present disclosure.

[0061] Figure 8 shows a communication system according to various embodiments of the present disclosure.

[0062] Figure 9 shows a UE according to various embodiments of the present disclosure.

[0063] Figure 10 shows a network node according to various embodiments of the present disclosure.

[0064] Figure 11 is a block diagram of a virtualization environment in which various embodiments of the present disclosure may be virtualized.

[0065] DETAILED DESCRIPTION

[0066] 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.

[0067] 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.

[0068] Furthermore, the following terms are used throughout the description given below:

[0069] • 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 an LTE network), base station distributed components (e g., CU and DU), a high-power or macro base station, a low-power base station (e.g., micro, pico, femto, or home base station, or the like), an integrated access backhaul (IAB) node, a transmission point (TP), a transmission reception point (TRP), a remote radio unit (RRU or RRH), and a relay node.

[0070] • Core Network Node: As used herein, a “core network node” is any type of node in a core network. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a serving gateway (SGW), a PDN Gateway (P-GW), a Policy and Charging Rules Function (PCRF), an access and mobility management function (AMF), a session management function (SMF), a user plane function (UPF), a Charging Function (CHF), a Policy Control Function (PCF), an Authentication Server Function (AUSF), a location management function (LMF), or the like.

[0071] • 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”.

[0072] • Radio Node: As used herein, a “radio node” can be either a “radio access node” (or equivalent term) or a “wireless device.”

[0073] • 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.

[0074] • 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] After a UE is powered ON it will be in RRC IDLE state until an RRC connection is established with the network, at which time the UE will transition to RRC CONNECTED state (e.g., where data transfer can occur). The UE returns to RRCJODLE after the connection with the network is released. In RRC IDLE state, the UE’s radio is active on a discontinuous reception (DRX) schedule configured by upper layers. During DRX active periods (also referred to as “DRX On durations”), an RRC_IDLE UE receives SI broadcast in the cell where the UE is camping, performs measurements of neighbor ceils to support cell reselection, and monitors a paging channel on PDCCH for pages from 5GC via gNB. A UE in RRC IDLE state is not known to the gNB serving the cell where the UE is camping. However, 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.

[0081] 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 earner 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 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.”

[0082] LTE Rel-12 introduced DC whereby a UE can be connected to two network nodes simultaneously, thereby improving connection robustness and / or capacity. 5G / NR also supports various DC (or more generally, multi-connectivity) configurations for UEs. 3GPP TR 38.804 (v!4.0.0) describes various exemplary DC scenarios or configurations in which the MN and SN can apply NR, LTE, or both. In particular, a UE is configured with a Master Cell Group (MCG) provided by a master node (MN) and a Secondary Cell Group (SCG) provided by a secondary node (SN). Each cell group includes one MAC entity, a set of logical channels with associated RLC entities, a primary cell (i.e., PCell for MCG, PSCell for SCG), and optionally one or more SCells.

[0083] While in RRC_CONNECTED state, the UE maintains a timing advance (TA) value for its UL transmissions to the serving gNB. The TA value indicates how much earlier in time the UE should initiate its UL transmissions to compensate for the propagation delay between the UE and the gNB antenna / receiver. The UEs in a cell apply individualized TAs to ensure that their respective UL transmissions arrive to the gNB receiver in the appropriate (e.g., scheduled) time window.

[0084] The UE obtains an initial TA value when it performs random access (RA) to a cell. In particular, the UE transmits a RA preamble (also called “msgl”) in the cell, based on which the gNB determines the TA value and provides it to the UE in a RA response (also called “msg2”). While in RRC CONNECTED state in the cell, the UE maintains and updates TA based on continuous monitoring of the alignment of the DL signal from the gNB with the expected arrival window. Also, if the gNB notices the UE’s UL transmissions falling out of synchronization, it can send the UE a PDCCH order that causes the UE to send another RA preamble, based on which the gNB can determine and provide a new TA value.

[0085] In general, the UE has no TA value while in RRC IDLE and RRC_ INACTIVE states since it does not perform UL transmissions in these states. There is one exception for RRC_INACTIVE state, specifically when the UE has been assigned a configured grant (CG) for small data transmission (SDT) when moving from RRC CONNECTED state to RRC_INACTIVE state. This CG enables the UE to immediately transmit any UL data that has arrived at its buffer while in RRC INACTIVE state. This transmission requires TA alignment and since the UE does not continuously adjust TA while in RRC_INACTIVE, another technique for TA alignment was introduced for CG-SDT in 3GPP Rel-17 and Rel-18.

[0086] In particular, Figure 3 shows an exemplary procedure for CG-SDT by a UE. Initially, the UE is in RRC_CONNECTED state with a gNB and has maintained TA in its serving cell. The gNB determines to send the UE to RRC_INACTIVE and sends an RRCRelease message that includes a CG for SDT, i.e., an sdt-Config information element (IE). The CG may include a plurality of periodic grants of UL resources, which the UE uses as needed for arrival of UL data. Upon entering RRC INACTIVE state, the UE stops TA maintenance and measures DL reference signal received power (RSRP), which it stores for later use. When UL data arrives prior to one of periodic grants, the UE again measures DL RSRP and compares against the stored DL RSRP. If the difference is less than a threshold, the UE assumes that the most recent TA value is still valid and uses it for transmitting the UL data in the granted resources.

[0087] The UE’s various serving cells (e.g., PCell, PSCell, SCells) may be divided into one or more timing alignment groups (TAGs). The UE also uses various timers during TA maintenance. According to 3GPP TS 38.321 (v) section 5.2, the gNB configures (i.e., via RRC) the following in the UE for maintenance of UL time alignment:

[0088] • timeAlignmentTimer (per TAG), which controls how long the UE MAC entity considers the serving cells of a TAG to be UL time aligned;

[0089] • inactivePosSRS-TimeAlignmentTimer, which controls how long the UE MAC entity considers the Positioning SRS transmission in RRC INACTIVE (3GPP TS 38.321 section 5.26) to be UL time aligned;

[0090] • cg-SDT -TimeAlignmentTimer, which controls how long the UE MAC entity considers the UL transmission for CG-SDT to be uplink time aligned; and

[0091] • inactivePosSRS-ValidityAreaTAT which controls how long the UE MAC entity considers Positioning SRS transmission in RRC INACTIVE (3GPP TS 38.321 section 5.26) to be UL time aligned when SRS positioning validity area is configured.

[0092] 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).

[0093] In general, a RAN (e.g., NG-RAN) configures a UE in RRC_CONNECTED state to perform and report radio resource management (RRM) measurements to assist network- controlled mobility decisions, such as for handover from a serving cell to a target cell (e.g., PCell change). Upon the reported measurements meeting a certain condition or threshold, the serving RAN node may send a handover command to the UE, indicating a target cell for the handover. In NR, the handover command is an RRCReconfiguration message with a reconfigurationWithSync field. The procedure to perform a handover is sometimes also referred to as “L3 mobility”, as it is controlled by L3 and the RRC messages exchanged are part of L3.

[0094] 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 is based on 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.

[0095] 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).

[0096] 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).

[0097] To address various difficulties with handovers and other mobility procedures, 3GPP Rel- 16 includes support for conditional handover (CHO) and SN-mitiated intra-SN conditional PSCell change (CPC) procedures while Rel-17 includes support for various other conditional mobility procedures. A main principle of conditional mobility is separation of transmission and execution of a mobility (e.g., handover) command. This allows the mobility command to be sent earlier to UE when the radio conditions are still good, thus increasing the likelihood that it is successfully transferred. The execution of the mobility command is done at later point in time based on an associated execution condition.

[0098] Conditional mobility procedures are based on a conditional reconfiguration framework in which the network provides a UE with one or more reconfigurations, each with associated execution condition(s). Each reconfiguration can be provided in an RRCReconfiguration message (in NR) or an RRCConnectionReconflguration message (in LTE). When the UE later detects the execution condition(s) associated with one of the earlier-received reconfigurations, the UE executes the associated reconfiguration to perform the mobility procedure (e.g., HO, PSCell change, PSCell addition, etc.).

[0099] Even so, conditional (e g., CHO) and non-conditional (e.g., HO) are triggered by layer 3 (L3) measurements and involves radio resource control (RRC) signaling to change PCell and PSCell (e.g., when DC is configured), as well as release / add SCells as needed. Moreover, conventional inter-cell mobility involves complete layer 2 (L2) and layer 1 (LI, i.e., PHY) resets, leading to longer latency, increased signaling overhead, and longer interruptions than for intra-cell beam switching.

[0100] 3GPP Rel-18 includes new mobility procedures that facilitate serving cell changes via L1 / L2 signaling to address these problems and / or difficulties. These new procedures are often referred to as L1 / L2 based inter-cell mobility or L1 / L2 triggered mobility (LTM). In LTM, a UE is pre-configured by its serving RAN node with one RRC configuration per LTM candidate cell, sometimes referred to as an “LTM candidate cell configuration.” The UE performs measurements on configured LTM candidate cells and transmits corresponding measurement reports to the RAN node, based on which the RAN node triggers execution of a LTM cell switch procedure by the UE to one of the configured LTM candidate cells The RAN node may trigger the LTM cell switch procedure by sending the UE an LTM cell switch command.

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

[0103] 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 specific operational order, unless expressly stated otherwise.

[0104] In operation 1 , the UE (410) sends aMeasurementReport message to the gNB (420). 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 RRCReconfigurationComplete message to the gNB.

[0105] 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.

[0106] The UE performs operations 4a-b before receiving any LTM cell switch command. In operation 4a, the UE performs early DL synchronization with the configured LTM candidate cells. Each LTM candidate cell configuration may include a configuration for early DL synchronization, which may also be referred to as an “LTM candidate TCI state configuration” or more simply as a “TCI state configuration.” For example, the TCI state configuration may include an RRC CandidateTCI-State IE and / or an RRC CandidateTCI-UL-State IE. Once configured in this manner, early TCI state activation in an LTM candidate cell may be triggered by a MAC CE from the serving RAN node.

[0107] 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, a TA value for the LTM candidate cell is indicated in a subsequent LTM cell switch command (e.g. , operation 6 below). Similarly, the UE doesn’t maintain a TA timer for the LTM candidate cell but relies on the RAN to guarantee the TA validity.

[0108] 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.

[0109] 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, as well as a TA value for the UE to use when transmitting to the target cell. The gNB selects the identified beam based on the LI measurements reported by the UE.

[0110] 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.

[0111] In operation 7, if UE did not receive a TA value for the target cell, the UE performs a RA procedure towards the target cell. The UE performs CFRA if the LTM cell switch command contains the necessary information, as specified in clause 6.1.3.xy of 3GPP TS 38.321 (vl7.7.0). In operation 8, the UE completes the LTM cell switch procedure by transmitting an RRCReconflgurationComplete message to the gNB via the target cell, using the TA value obtained in operation 6 or 7. If the UE performed a RA procedure in operation 7, the UE considers LTM cell switch execution successfully completed when the RA procedure is successfully completed. For RACH-less LTM, the UE considers LTM cell switch execution 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 and scheduling anew 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.

[0112] The split CU / DU architecture shown in Figure 1 also supports LTM, including for intra- DU and inter-DU / intra-CU cell changes. In the inter-DU / intra-CU scenario, the candidate cell for LTM is a cell served by a neighbor DU to the source DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). In the intra-DU scenario, the candidate cell for LTM is a cell served by the same DU that currently provides the UE’s PCell (or PSCell, for SCG change in DC). Since the procedure shown in Figure 8 involves a single gNB, it can also be considered an intra-CU LTM cell switch.

[0113] In contrast, an inter-CU (or inter-gNB) LTM procedure involves a cell switch from a source cell served by a first CU / gNB to a candidate (target) cell served by a second CU / gNB. In addition to the operations described above in relation to Figure 5, UE actions performed during an inter-CU LTM cell switch procedure may also include other actions such as refresh of security keys. As such, an inter-CU LTM configuration may include the same information as an intra-CU LTM configuration as well as one or more of the following: • Information needed to perform security key refresh, e.g., MasterKeyUpdate IE or a RadioBearerConflg IE that includes SecurityConfig with SecurityAlgorithmConfig,'

[0114] • Indication to perform L2 / PDCP re-establishment; and

[0115] • Indication to perform a full configuration, e.g., RRC field fullConflg.

[0116] As discussed above, in Rel-18 (non-conditional) LTM, the UE’s serving RAN node sends the UE a command for LTM cell switch to one of the UE’s configured LTM candidate cells, and the command may include a TA value determined based on the UE’s earlier RA transmission towards the LTM candidate cell. In case of intra-DU / intra-gNB LTM, the RAN node serving the LTM candidate cell may determine the TA value for the UE and provide it to the UE’s current serving RAN node.

[0117] Since there is no LTM cell switch command in Rel-19 CLTM, however, the serving RAN node is unable to provide a TA value for an LTM candidate cell at the time of the LTM cell switch. One solution is to provide the TA value to the UE in an earlier message, although it is unclear how the UE should determine whether this earlier-received TA value is still valid when the execution condition for LTM cell switch is fulfilled.

[0118] Although the CG-SDT procedure shown in Figure 3 suggests a possible solution based on comparing DL RSRP values, it has some drawbacks that make it unsuitable for CLTM. For example, if the UE waits until the LTM execution condition is fulfilled to compare DL RSRP values, it is very likely that the UE is unable to acquire a new TA value from its serving RAN node since the execution condition typically involves deteriorating conditions in the source cell.

[0119] Accordingly, embodiments of the present disclosure address these and related problems and / or issues by various techniques by which a UE can validate a previously-obtained TA value for an LTM candidate cell by comparing DL RSRP values obtained at two different times: 1) a first DL RSRP value obtained upon receiving the TA value, which also causes the UE to initiate a time alignment timer; and 2) a second DL RSRP value obtained upon expiration of the time alignment timer. Note that the second DL RSRP value may be the most recently measured (or “cunent”) DL RSRP value for that LTM candidate cell, even if it was measured prior to timer expiration.

[0120] While the time alignment timer is running (i.e., prior to expiration), the UE considers as valid the TA value obtained in conjunction with timer initiation. When the timer expires, the UE determines validity of the TA value based on the DL RSRP comparison. If the UE determines that the TA value is valid, the UE may use it when performing an LTM cell switch to the LTM candidate cell, thus avoiding the need for RA (“RACH-less”). If the UE determines that the TA value is invalid, the UE must perform RA to the LTM candidate cell as part of the LTM cell switch (“RACH-based”) or obtain an updated TA value for the LTM candidate cell prior to LTM cell switch.

[0121] In some embodiments, the comparison of the first and second DL RSRP values may also be based on a threshold, which may be configured for the UE by its serving RAN node. For example, when a difference between the first and second DL RSRP values is less than the threshold, the UE determines that the TA value is valid. Otherwise, when a difference between the first and second DL RSRP values is greater than or equal to the threshold, the UE determines that the TA value is invalid. Note that the threshold may also be adapted such that validity is based on the difference being less than or equal to the threshold.

[0122] In some embodiments, upon determining that the TA value is valid based on the DL RSRP comparison, the UE may re-initiate the time alignment timer. The UE maintains the first DL RSRP value obtained upon reception of the TA value. When the re-initiated timer expires, the UE may determine the validity of the TA value based on a (new) second DL RSRP value obtained in conjunction with this timer expiration.

[0123] Embodiments of the present disclosure may provide various advantages and / or benefits. For example, by enabling a UE to maintain an LTM candidate cell TA value received from its serving RAN node, embodiments may facilitate timely UE conditional LTM cell switch while reducing TA-related signaling with the serving RAN node. As another example, by using a time alignment timer and DL RSRP as a basis for maintaining LTM candidate cell TA values, embodiments may enable UEs to easily determine TA validity in a timely and efficient manner. At a high level, embodiments may facilitate conditional LTM without connection interruption, excess signaling overhead, and excess UE energy consumption.

[0124] In the present disclosure, the following terms may be used interchangeably: “L1 / L2 based inter-cell mobility”, “L1 / L2 mobility,” “Ll-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.

[0125] 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. 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.

[0126] 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).

[0127] 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.

[0128] An LTM candidate cell configuration may be included in an RRC IE such as CellGroupConflg, SpCellConflg, or SCellConfig and / or an embedded RRCReconflguration message for an LTM candidate cell. An LTM candidate cell configuration includes configuration parameters the UE needs to operate in that LTM candidate cell when it performs an LTM cell switch procedure, e.g., upon reception of the LTM cell switch command. As some more specific examples, an LTM candidate cell configuration can include a PCell configuration and one or more SCell configurations of an MCG, or a PSCell configuration and one or more SCell configurations of an SCG. The exact content and / or structure of the IE and / or embedded message for an LTM candidate cell configuration may be called “RRC model for the candidate configuration” or more simply “RRC model”. A UE may receive an LTM candidate cell configuration in complete form or as a delta (or difference) relative to a reference configuration (which may be signaled separately). In the latter case, the actual LTM candidate configuration is a combination of the delta configuration and the reference configuration.

[0129] 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.

[0130] 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):

[0131] • an LTM candidate cell configuration, such as one or more of the following for an LTM candidate cell: o lower layer information, such as Ll / PHY configuration, L2 / MAC / RLC configuration, cell group configuration, serving cell configuration, etc.; and o higher layer information, such as L3 / RRC parameter and / or timer values, PDCP configuration, radio bearer configuration, L3 / RRC measurement configuration, etc.;

[0132] • a measurement configuration, e.g., measurements for LTM, measurement reports for LTM, CSI resource configuration for LTM, CSI report configuration for LTM, etc.;

[0133] • a configuration for early DL synchronization, e.g., for early TCI state activation;

[0134] • a configuration for early UL synchronization, e.g., for transmission of PDCCH ordered preamble transmission and reception of timing advance (TA);

[0135] • 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.).;

[0136] • additional information needed for an intra-CU / gNB LTM cell switch procedure.

[0137] 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).

[0138] 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.

[0139] Furthermore, an LTM cell switch may involve a UE switching (or changing) from a source cell group to a target cell group using LTM. For example, this may involve a change in the SpCell for a cell group (e.g., PCell for MCG, PSCell for SCG), a change in SCells of the cell group (e.g., addition, modification, and / or release of one or more SCells), and / or a swap between SpCell and SCell roles for two cells in the same cell group. More generally, embodiments are not limited to cells but are applicable to any UE switch from a first (or source) set of radio resources to a second (or target) set of radio resources.

[0140] Figure 5 shows a timing diagram that illustrates some embodiments of the present disclosure. As a pre-condition, the UE may have received from its serving RAN node a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. Initially, at tO, a UE receives from the serving RAN node a first TA value for the LTM candidate cell configured for the UE. In response, the UE initiates a time alignment timer for the LTM candidate cell and measures DL RSRP for the LTM candidate cell, thereby obtaining a first measurement value X. The TA value is assumed to be valid until tl, when the time alignment timer expires. Upon expiration, the UE again measures DL RSRP for the LTM candidate cell, thereby obtaining a second measurement value Yl. The UE determines that the first TA value remains valid at tl if (X-Yl) is less than a threshold, which may have been previously configured for the UE (e.g., via RRC). Otherwise, if (X-Yl) is not less than the threshold, the UE determines that the first TA value is invalid at tl .

[0141] As shown in Figure 5, the UE may measure DL RSRP for the LTM candidate cell to obtain measurement values Yn at subsequent times tn, n=2, 3, 4, etc., so long as an execution condition associated with the LTM candidate cell remains unfulfilled. Similar to the operations at tl, the UE determines that the first TA value remains valid at tn if (X-Yn) is less than a threshold, which may have been previously configured for the UE (e.g., via RRC). Otherwise, if (X-Yn) is not less than the threshold, the UE determines that the first TA value is invalid at tn.

[0142] In some embodiments, the UE stops monitoring TA validity in this manner when the UE executes CLTM and / or when the serving RAN node sends the UE an RRCRelease message that transitions the UE to RRC_INACTIVE state (e.g., message including suspendConflg IE) or to RRC_IDLE state (e.g., message without suspendConflg IE). When an execution condition is fulfilled between tn and t(n+l), the UE performs an LTM cell switch to the LTM candidate cell in accordance with the TA value validity. In other words, if the TA value is determined to be value at tn, the UE performs LTM cell switch based on transmitting in the target cell using the valid first TA value without performing RA. In other embodiments, the UE determines the validity of the previously-received TA value responsive to an execution condition for the LTM candidate cell being fulfilled. In other words, the UE is not concerned with validity of the TA value for the LTM candidate cell until it is needed for an LTM cell switch. When the execution condition for the LTM candidate cell is fulfilled (e.g., at time tz), the UE first determines whether the time alignment timer has expired. If not expired, the UE considers the TA value to be valid. If expired, the UE measures DL RSRP for the LTM candidate cell to obtain a new measurement value Yz. Similar to the operations described above, the UE determines that the TA value remains valid at tz if (X-Yz) is less than a threshold, which may have been previously configured for the UE (e.g., via RRC). Otherwise, if (X-Yz) is not less than the threshold, the UE determines that the TA value is invalid at tz. If the TA value is determined to be valid, the UE may use it to perform LTM cell switch without RA to the LTM candidate cell.

[0143] Although the above-described embodiments utilize RSRP-based measurements and thresholds for determining TA validity, other embodiments may utilize reference signal received quality (RSRQ) or signal-to-interference-and-noise ratio (SINR) measurements and thresholds for determining TA validity. The measured DL RS may include synchronization signal / PBCH block (SSB) and / or channel state information (CSI) RS.

[0144] Although the above-described embodiments utilize differences between DL RSRP measurements, other functions of the two DL RSRP measurements may also be compared to the threshold for TA validity determination. One example function is absolute value of the difference between DL RSRP measurements.

[0145] In various embodiments, the TA value may be received from the serving RAN node in a MAC CE, an RRC message, or downlink control information (DCI). In some embodiments, the UE receives the TA value along with one or more of the following information (e.g., in the same message):

[0146] • an initial (or terminal) value for the time alignment timer, which counts down (or up) to expiration;

[0147] • a first indication of whether the UE is allowed to extend the validity of the TA value after expiration of the timer;

[0148] • a second indication of whether the UE is allowed to request another TA value after expiration of the timer; and

[0149] • the threshold to which the DL RS measurement difference is compared (or an indication thereof); and

[0150] • a condition for determining validity of the TA value. In some of these embodiments, either the first indication or the second indication may be a second threshold for speed or velocity. Upon expiration of the timer, the UE determines its speed or velocity and compares it to the second threshold. If the UE’s speed or velocity is above the second threshold, the UE is not allowed to extend the validity of the TA value (first indication) or is allowed to request another TA value (second indication). If the UE’s speed or velocity is at or below the second threshold, the UE is allowed to extend the validity of the TA value (first indication) or is not allowed to request another TA value (second indication).

[0151] In some of these embodiments, either the first indication or the second indication may be a third threshold for signal quality. Upon expiration of the timer, the UE measures signal quality (e.g., DL RSRP) in the LTM candidate cell and compares it to the third threshold. If the UE’s measured signal quality is above the third threshold, the UE is allowed to extend the validity of the TA value (first indication) or is allowed to request another TA value (second indication). If the UE’s measured signal quality is at or below the third threshold, the UE is not allowed to extend the validity of the TA value (first indication) or is not allowed to request another TA value (second indication).

[0152] In some of these embodiments, either the first indication or the second indication may be a mobility state indicator, which may indicate one or more of a discrete set of mobility states (e.g., stationary, low mobility, medium mobility, high mobility, etc.). Upon expiration of the timer, the UE determines its mobility state and compares it to the mobility state indicator. If the UE’s mobility state matches or corresponds to the mobility state indicator, the UE is allowed to extend the validity of the TA value (first indication) or is allowed to request another TA value (second indication). If the UE’s mobility state does not match or correspond to the mobility state indicator, the UE is not allowed to extend the validity of the TA value (first indication) or is not allowed to request another TA value (second indication).

[0153] Note that each of the condition, the second threshold, the third threshold, and the mobility state indication described above may be used in addition to or instead of the threshold for the DL RS measurement difference, for determining whether the previously-received TA value remains valid after expiration of the time alignment timer. When the previously-received TA value remains valid after expiration of the time alignment timer, this can be thought of as extending the validity of the TA value.

[0154] In some of these embodiments, the indication of an initial (or terminal) value for the time alignment timer may be in one of the following forms:

[0155] • an index of an entry in an enumerated list of timer values (e.g., 10ms, 100ms, 200ms, Isec, 2sec, etc ), which may have been previously configured in the UE (e.g., via RRC);

[0156] • an integer that identifies a number of time units (e.g., Nxlms, NxlOms, etc.); and • a reference to a previously-configured timer value.

[0157] In some of these embodiments, the indication of the threshold may be in one of the following forms:

[0158] • an index of an entry in an enumerated list of threshold values (e.g., 1 dB, 2 dB, 4 dB, 6 dB, 10 dB, etc.), which may have been previously configured in the UE (e g., via RRC);

[0159] • an integer that identifies a number of threshold units (e.g., NxldB, Nx2dB, etc.); and

[0160] • a reference to a previously-configured threshold value.

[0161] In case the UE is only configured with a TA value (and optionally an initial / terminal value for the time alignment timer), the UE is not allowed to extend the validity of the TA value after expiration of the timer. In other words, the previously-received TA value becomes invalid upon timer expiration. However, if the UE is also configured with a second indication that it is allowed to request another TA value after expiration of the timer, the UE may request a new TA in accordance with the second indication.

[0162] In some embodiments, upon expiration of the time alignment timer associated with the previously-received TA value, the UE transmits an indication of one or more of the following to the serving RAN node:

[0163] • an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell;

[0164] • an updated threshold is needed for the UE to determine validity of previously-received TA value for the LTM candidate cell;

[0165] • the previously-received TA value is no longer valid;

[0166] • a cause for invalidity of the previously-received TA value (e.g., timer expiration, DL measurements do not meet configured threshold, etc.);

[0167] • expiration of the time alignment timer for the previously-received TA value;

[0168] • the validity of the previously-received TA value has been extended after expiration of the time alignment timer; and

[0169] • whether the validity of the previously-received TA value may be extended after expiration of the time alignment timer.

[0170] In some of these embodiments, the UE may include the previously-received TA value that has been determined to be invalid. In some of these embodiments, the UE may include an early UL synchronization configuration being used for t

[0171] In various embodiments, the above-described indication can be transmitted in uplink control information (UCI), a MAC CE, or an RRC message. In some embodiments, in response to transmitting the above-described indication to the serving RAN node, the UE receives one or more of the following from the serving RAN node:

[0172] • an updated TA value for the LTM candidate cell;

[0173] • an order (e g., PDCCH order) to transmit a further RA preamble to the LTM candidate cell

[0174] • an updated threshold for determining validity of the previously -received TA value or the updated TA value; and

[0175] • a further indication to extend validity of the previously-received TA value.

[0176] In some embodiments, if the UE determines that the previously-received TA value is / remains valid after expiration of the time alignment timer, the UE re-initiates the time alignment timer. Upon the next expiration of the timer, the UE determines whether the previously-received TA value is / remains valid based on another measurement of the DL RS of the LTM candidate cell. For example, this other measurement may correspond to Y2, Y3, Y4, etc. described above in relation to Figure 5, with the validity determination made in a similar manner. This process may be repeated as needed.

[0177] In some embodiments, when the UE determines that the previously-received TA value for the LTM candidate cell is no longer valid, the UE transmits a further (i.e., another) RA preamble towards the LTM candidate cell. In response, the serving RAN node can provide an updated TA value for the UE. The further RA preamble can be transmitted according to the same configuration used to transmit the RA preamble on which the previously-received TA value was based.

[0178] Other embodiments include methods for a RAN node configured to facilitate conditional LTM for UEs that it serves. The RAN node sends to a UE (e.g., via a source cell provided by the RAN node) a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. The RAN node obtains a TA value for a UE in an LTM candidate cell and sends the TA value to the UE. Subsequently, the RAN node receives from the UE an indication of one or more of the following:

[0179] • an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell;

[0180] • an updated threshold is needed for the UE to determine validity of the previously -received TA value for the LTM candidate cell;

[0181] • the previously-received TA value is no longer valid;

[0182] • a cause for invalidity of the previously-received TA value (e.g., timer expiration, DL measurements do not meet configured threshold, etc.);

[0183] • expiration of a time alignment timer for the previously-received TA value;

[0184] • the validity of the previously-received TA value has been extended after expiration of the time alignment timer; and • whether the validity of the previously-received TA value may be extended after expiration of the time alignment timer.

[0185] In case the RAN node provides the LTM candidate cell, the RAN node may determine the TA value based on an RA preamble received from the UE in the LTM candidate cell, according to known techniques. In case the LTM candidate cell is provided by a second RAN node, the RAN node may receive the TA value from the second RAN node, which determines it based on the RA preamble in a similar manner.

[0186] In various embodiments, the TA value may be sent to the UE in a MAC CE, an RRC message, or downlink control information (DCI). In some embodiments, the RAN node sends the TA value along with one or more of the following information (e.g., in the same message):

[0187] • an initial (or terminal) value for the time alignment timer;

[0188] • a first indication of whether the UE is allowed to extend the validity of the TA value after expiration of the timer;

[0189] • a second indication of whether the UE is allowed to request another TA value after expiration of the timer; and

[0190] • a threshold to which the UE should compare a DL RS measurement difference (or an indication thereof); and

[0191] • a condition for determining validity of the TA value.

[0192] In various embodiments, the above-listed information can have any of the same content, structure, characteristics, properties, form, etc. as the corresponding information described above in relation to UE embodiments.

[0193] In various embodiments, the above-described indication can be received from the UE in UCI, a MAC CE, or an RRC message. In some embodiments, in response to receiving the abovedescribed indication from the UE, the RAN node transmits one or more of the following to the UE:

[0194] • an updated TA value for the LTM candidate cell;

[0195] • an order (e.g., PDCCH order) to transmit a further RA preamble to the LTM candidate cell;

[0196] • an updated threshold for determining validity of the previously -received TA value or the updated TA value; and

[0197] • a further indication to extend validity of the previously-received TA value.

[0198] In embodiments where the RAN node provides the LTM candidate cell, the RAN node may determine the updated TA value based on the further RA preamble received from the UE in the LTM candidate cell, according to known techniques. In embodiments where a second RAN node provides the LTM candidate cell, the RAN node may receive the updated TA value from the second RAN node, which determines it based on the further RA preamble in a similar manner. In some of these embodiments, the RAN node can receive from the second RAN node an indication that the previously-received TA value for the LTM candidate cell is no longer valid. In such case, the RAN node may send the UE an order to transmit a further RA preamble to the LTM candidate cell.

[0199] Various features of the embodiments described above correspond to various operations illustrated in Figures 6-7, which show exemplaiy methods (e g., procedures) for a UE and a RAN node, respectively. In other words, various features of the operations described below correspond to various embodiments described above. Furthermore, the exemplary methods shown in Figures 6-7 may be used cooperatively to provide various benefits, advantages, and / or solutions to problems described herein. Although Figures 6-7 show specific blocks in particular orders, the operations of the exemplary methods may be performed in different orders than shown and may be combined and / or divided into blocks having different functionality than shown. Optional blocks or operations are indicated by dashed lines.

[0200] In particular, Figure 6 (which includes Figures 6A-B) shows an exemplary method (e.g., procedure) for a UE configured for conditional LTM in a RAN, according to various embodiments of the present disclosure. The exemplary method can be performed by any appropriate UE (e.g., wireless device) such as described elsewhere herein.

[0201] The exemplary method includes the operations of block 610, where the UE receives, from a RAN node via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. The exemplary method also includes the operations of blocks 625-630, where in response to receiving from the RAN node a TA value for the LTM candidate cell, the UE initiates a time alignment timer and measures a DL RS of the LTM candidate cell, thereby obtaining a first measurement value (e.g., X in Figure 5). The exemplary method also includes the operations of block 640, where the UE subsequently measures the DL RS of the LTM candidate cell, thereby obtaining a second measurement value (e.g., Y1 in Figure 5). The exemplary method also includes the operations of block 650, where the UE determines whether the TA value (i.e., received in block 625) is valid based on the first and second measurement values.

[0202] In some embodiments, subsequently measuring the DL RS of the LTM candidate cell in block 640 is responsive to the operations of block 635, where the UE determines that one or more of the following has occurred: the time alignment timer has expired, and the execution condition is fulfilled. In some of these embodiments, the exemplary method also includes the following operations (labelled with corresponding block numbers) after determining that the time alignment timer has expired (e.g., in block 635) and after determining that the TA value is valid based on the first and second measurement values (e g., in block 650):

[0203] • (655) re-initiating the time alignment timer;

[0204] • (660) upon expiration of the time alignment timer after re-initiation, measuring the DL RS of the LTM candidate cell, thereby obtaining a third measurement value; and

[0205] • (665) determining whether the TA value is valid based on the first and third measurement values.

[0206] In some embodiments, the exemplary method also includes the operations of block 620, where the UE transmits a random access (RA) preamble to the LTM candidate cell. The TA value is received in block 625 in response to transmitting the RA preamble. In some embodiments, determining whether the TA value is valid based on the first and second measurement values in block 650 includes the following operations, labelled with corresponding sub-block numbers:

[0207] • (651) determining a function of the first and second measurement values;

[0208] • (652) determining that the TA value is valid when the function is less than a threshold; and

[0209] • (653) determining that the TA value is invalid when the function is not less than the threshold.

[0210] In some of these embodiments, the function is first measurement value minus second measurement value (i.e., difference). In other of these embodiments, the function is absolute value of a difference between the first and second measurement values. In some of these embodiments, the threshold, the first measurement value, and the second measurement value are based on one of the following: reference signal received power (RSRP), reference signal received quality (RSRQ), or signal-to-interference-and-noise ratio (SINR).

[0211] In some embodiments, the exemplary method also includes the operations of block 615, where the UE receives one or more of the following configuration information from the RAN node:

[0212] • an initial or terminal value for the time alignment timer (e.g., used to initiate in block 630);

[0213] • a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the time alignment timer;

[0214] • a second indication of whether the UE is allowed to request another TA value after expiration of the time alignment timer; and

[0215] • a threshold usable for determining whether the TA value is valid; and

[0216] • a condition usable for determining whether the TA value is valid.

[0217] In some embodiments, the exemplary method also includes the operations of block 670, where based on determining that the execution condition is fulfilled (e.g., in block 635), the UE selectively performs an LTM cell switch to the LTM candidate cell based on whether the TA value is determined to be valid. In some of these embodiments, selectively performing the LTM cell switch to the LTM candidate cell in block 670 includes the following operations, labelled with corresponding sub-block numbers:

[0218] • (671) when the TA value is determined to be invalid, performing a RA to the LTM candidate cell, thereby obtaining an updated TA value; and

[0219] • (672) when the TA value is determined to be valid, transmitting a message to the LTM candidate cell based on the TA value and without performing the RA to the LTM candidate cell.

[0220] In some embodiments, the exemplary method also includes the operations of block 680, where the UE transmits an indication of one or more of the following to the RAN node:

[0221] • an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell;

[0222] • an updated threshold is needed for the UE to determine validity of the TA value;

[0223] • the TA value is no longer valid;

[0224] • a cause for invalidity of the TA value;

[0225] • expiration of the time alignment timer for the TA value;

[0226] • validity of the TA value has been extended after expiration of the time alignment timer; and

[0227] • whether validity of the TA value may be extended after expiration of the time alignment timer.

[0228] In some of these embodiments, transmitting the indication is responsive to one of the following: determining whether the TA value is valid (e.g., in block 650), or determining that the time alignment timer has expired (e.g., in block 635). In some of these embodiments, the exemplary method also includes the operations of block 685, where in response to the indication, the UE receives one or more of the following from the RAN node:

[0229] • an updated TA value for the LTM candidate cell;

[0230] • an order to transmit a further RA preamble to the LTM candidate cell;

[0231] • an updated threshold for determining validity of the TA value or the updated TA value;

[0232] • a further indication to extend validity of the TA value.

[0233] In some embodiments, the exemplary method also includes the following operations, labelled with corresponding block numbers:

[0234] • (690) based on determining that the TA value is invalid (e.g., in block 650), transmitting a further RA preamble to the LTM candidate cell; and • (695) in response to the further RA preamble, receiving from the RAN node an updated TA value for the LTM candidate cell.

[0235] In addition, Figure 7 shows an exemplary method (e.g., procedure) for a RAN node configured to facilitate conditional LTM for UEs, according to various embodiments of the present disclosure. The exemplary method can be performed by any appropriate RAN node (e.g., base station, eNB, gNB, ng-eNB, DU, etc.) such as described elsewhere herein.

[0236] The exemplary method includes the operations of block 710, where the RAN node sends, to a UE via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell. The exemplary method also includes the operations of blocks 730-740, where the RAN node obtains a TA value for UE in the LTM candidate cell and sends the TA value to the UE. The exemplary method also includes the operations of block 750, where the RAN node receives from the UE an indication of one or more of the following:

[0237] • an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell;

[0238] • an updated threshold is needed for the UE to determine validity of the TA value;

[0239] • the TA value is no longer valid;

[0240] • a cause for invalidity of the TA value;

[0241] • expiration of a UE time alignment timer for the TA value;

[0242] • validity of the T A value has been extended after expiration of the UE time alignment timer; and

[0243] • whether validity of the TA value may be extended after expiration of the UE time alignment timer.

[0244] In some embodiments, the indication is received after expiration of the UE time alignment timer. In some embodiments, the exemplary method also includes the operations of block 720, where the RAN node sends one or more of the following configuration information to the UE:

[0245] • an initial or terminal value for the UE time alignment timer;

[0246] • a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the UE time alignment timer;

[0247] • a second indication of whether the UE is allowed to request another TA value after expiration of the UE time alignment timer; and

[0248] • a threshold usable for determining whether the TA value is valid; and

[0249] • a condition usable for determining whether the TA value is valid.

[0250] In some of these embodiments, the threshold is based on RSRP, RSRQ, or SINR. In some embodiments, the LTM candidate cell is provided by the RAN node and obtaining the TA value in block 730 includes the operations of sub-block 731, where the RAN node determines the TA value based on a RA preamble received from the UE in the LTM candidate cell. In other embodiments, the LTM candidate cell is provided by a second RAN node and obtaining the TA value in block 730 includes the operations of sub-block 732, where the RAN node receives the TA value from the second RAN node.

[0251] In some embodiments, the exemplary method also includes the operations of block 720, where in response to the indication (e.g., in block 750), the RAN node sends one or more of the following to the UE:

[0252] • an updated TA value for the UE in the LTM candidate cell;

[0253] • an order to transmit a further RA preamble to the LTM candidate cell;

[0254] • an updated threshold for determining validity of the TA value or the updated TA value;

[0255] • a further indication to extend validity of the TA value.

[0256] In some of these embodiments, the exemplary method also includes the operations of block 760, where the RAN node obtains the updated TA value based on one of the following operations, labelled with corresponding sub-block numbers:

[0257] • (761) determining the updated TA value based on the further RA preamble received from the UE in the LTM candidate cell; or

[0258] • (762) receiving the TA value from a second RAN node that provides the LTM candidate cell.

[0259] 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.

[0260] Figure 8 shows an example of a communication system 800 in accordance with some embodiments. In this example, communication system 800 includes a telecommunication network 802 that includes an access network 804 (e.g., RAN) and a core network 806, which includes one or more core network nodes 808. Access network 804 includes one or more access network nodes, such as network nodes 810a-b (one or more of which may be generally referred to as network nodes 810), 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 802 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in telecommunication network 802 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in telecommunication network 802, including one or more network nodes 810 and / or core network nodes 808.

[0261] 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 anon-real time control application (e g., rApp), 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 O-2 interface defined by the O-RAN Alliance or comparable technologies. Network nodes 810 facilitate direct or indirect connection of UEs, such as by connecting UEs 812a-d (one or more of which may be generally referred to as UEs 812) to core network 806 over one or more wireless connections.

[0262] 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 800 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 800 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0263] UEs 812 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with network nodes 810 and other communication devices. Similarly, network nodes 810 are arranged, capable, configured, and / or operable to communicate directly or indirectly with UEs 812 and / or with other network nodes or equipment in telecommunication network 802 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in telecommunication network 802.

[0264] In the depicted example, core network 806 connects network nodes 810 to one or more hosts, such as host 816. 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 806 includes one or more core network nodes (e.g., 808) 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 808. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-concealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0265] Host 816 may be under the ownership or control of a service provider other than an operator or provider of access network 804 and / or telecommunication network 802, and may be operated by the service provider or on behalf of the service provider. Host 816 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.

[0266] As a whole, communication system 800 of Figure 8 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox. In some examples, telecommunication network 802 is a cellular network that implements 3GPP standardized features. Accordingly, telecommunication network 802 may support network slicing to provide different logical networks to different devices that are connected to telecommunication network 802. For example, telecommunication network 802 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.

[0267] In some examples, UEs 812 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 804 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from access network 804. 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).

[0268] In the example, hub 814 communicates with access network 804 to facilitate indirect communication between one or more UEs (e.g., 812c and / or 812d) and network nodes (e.g., network node 810b). In some examples, hub 814 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, hub 814 may be a broadband router enabling access to core network 806 for the UEs. As another example, hub 814 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 810, or by executable code, script, process, or other instructions in hub 814. As another example, hub 814 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 814 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, hub 814 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which hub 814 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, hub 814 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0269] Hub 814 may have a constant / persistent or intermittent connection to network node 810b. Hub 814 may also allow for a different communication scheme and / or schedule between hub 814 and UEs (e.g., 812c and / or 812d), and between hub 814 and core network 806. In other examples, hub 814 is connected to core network 806 and / or one or more UEs via a wired connection. Moreover, hub 814 may be configured to connect to an M2M service provider over access network 804 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with network nodes 810 while still connected via hub 814 via a wired or wireless connection. In some embodiments, hub 814 may be a dedicatedhub - that is, ahub whose primary function is to route communications to / fromthe UEs from / to network node 810b. In other embodiments, hub 814 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 810b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0270] In some embodiments, any of UEs 812 may be configured to perform operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 6. In some embodiments, any of network nodes 810 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary method shown in Figure 7.

[0271] Figure 9 shows a UE 900 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.

[0272] 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).

[0273] UE 900 includes processing circuitry 902 that is operatively coupled via a bus 904 to an input / output interface 906, a power source 908, a memory 910, a communication interface 912, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 9. 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.

[0274] Processing circuitry 902 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 910. Processing circuitry 902 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 902 may include multiple central processing units (CPUs).

[0275] In the example, input / output interface 906 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 900. 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.

[0276] In some embodiments, power source 908 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 908 may further include power circuitry for delivering power from power source 908 itself, and / or an external power source, to the various parts of UE 900 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of power source 908. Power circuitry may perform any formatting, converting, or other modification to the power from power source 908 to make the power suitable for the respective components of UE 900 to which power is supplied.

[0277] Memory 910 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 910 includes one or more application programs 914, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 916. Memory 910 may store, for use by UE 900, any of a variety of various operating systems or combinations of operating systems.

[0278] Memory 910 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 versable 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 910 may allow UE 900 to access instrucbons, 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 910, which may be or comprise a device-readable storage medium.

[0279] Processing circuitry 902 may be configured to communicate with an access network or other network using communication interface 912. Communication interface 912 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 922. Communication interface 912 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 transmiter 918 and / or a receiver 920 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, transmiter 918 and receiver 920 may be coupled to one or more antennas (e.g., antenna 922) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0280] In the illustrated embodiment, communication functions of communication interface 912 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / intemet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0281] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 912, 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).

[0282] 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.

[0283] 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 900 shown in Figure 9. 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.

[0284] 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.

[0285] In some embodiments, UE 900 may be configured to perform operations attributed to a UE in various embodiments described above, including the exemplary method shown in Figure 6.

[0286] Figure 10 shows a network node 1000 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).

[0287] 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).

[0288] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSRBSs, 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).

[0289] Network node 1000 includes processing circuitry 1002, memory 1004, communication interface 1006, and power source 1008. Network node 1000 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 1000 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 1000 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1004 for different RATs) and some components may be reused (e.g., a same antenna 1010 may be shared by different RATs). Network node 1000 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1000, 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 1000.

[0290] Processing circuitry 1002 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 1000 components, such as memory 1004, to provide network node 1000 functionality.

[0291] In some embodiments, processing circuitry 1002 includes a system on a chip (SOC). In some embodiments, processing circuitry 1002 includes one or more of radio frequency (RF) transceiver circuitry 1012 and baseband processing circuitry 1014. In some embodiments, RF transceiver circuitry 1012 and baseband processing circuitry 1014 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 1012 and baseband processing circuitry 1014 may be on the same chip or set of chips, boards, or units.

[0292] Memory 1004 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 1002. Memory 1004 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions (collected denoted computer program 1004a, which may be in the form of a computer program product) capable of being executed by processing circuitry 1002 and utilized by network node 1000 Memory 1004 may be used to store any calculations made by processing circuitry 1002 and / or any data received via communication interface 1006. In some embodiments, processing circuitry 1002 and memory 1004 is integrated.

[0293] Communication interface 1006 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 1006 comprises port(s) / terminal(s) 1016 to send and receive data, for example to and from a network over a wired connection. Communication interface 1006 also includes radio frontend circuitry 1018 that may be coupled to, or in certain embodiments a part of, antenna 1010. Radio front-end circuitry 1018 comprises filters 1020 and amplifiers 1022. Radio front-end circuitry 1018 may be connected to an antenna 1010 and processing circuitry 1002. The radio front-end circuitry may be configured to condition signals communicated between antenna 1010 and processing circuitry 1002. Radio front-end circuitry 1018 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. Radio front-end circuitry 1018 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 1020 and / or amplifiers 1022. The radio signal may then be transmitted via antenna 1010. Similarly, when receiving data, antenna 1010 may collect radio signals which are then converted into digital data by radio front-end circuitry 1018. The digital data may be passed to processing circuitry 1002. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0294] In certain alternative embodiments, network node 1000 does not include separate radio front-end circuitry 1018, instead, processing circuitry 1002 includes radio front-end circuitry and is connected to antenna 1010. Similarly, in some embodiments, all or some of RF transceiver circuitry 1012 is part of communication interface 1006. In still other embodiments, communication interface 1006 includes one or more ports or terminals 1016, radio front-end circuitry 1018, and RF transceiver circuitry 1012, as part of a radio unit (not shown), and communication interface 1006 communicates with baseband processing circuitry 1014, which is part of a digital unit (not shown).

[0295] Antenna 1010 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. Antenna 1010 may be coupled to radio front-end circuitry 1018 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, antenna 1010 is separate from network node 1000 and connectable to network node 1000 through an interface or port.

[0296] Antenna 1010, communication interface 1006, and / or processing circuitry 1002 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 1010, communication interface 1006, and / or processing circuitry 1002 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.

[0297] Power source 1008 provides power to the various components of network node 1000 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). Power source 1008 may further comprise, or be coupled to, power management circuitry to supply the components of network node 1000 with power for performing the functionality described herein. For example, network node 1000 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 1008. As a further example, power source 1008 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 batteiy may provide backup power should the external power source fail.

[0298] Embodiments of network node 1000 may include additional components beyond those shown in Figure 10 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 1000 may include user interface equipment to allow input of information into network node 1000 and to allow output of information from network node 1000. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for network node 1000.

[0299] In some embodiments, network node 1000 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary method shown in Figure 7. Figure 11 is a block diagram illustrating a virtualization environment 1100 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 1100 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host Further, in embodiments in which the virtual node does not require radio connectivity (e g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1100 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an O-2 interface.

[0300] Applications 1102 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1100 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 1102 may be configured to perform operations attributed to a RAN node in various embodiments described above, including the exemplary method shown in Figure 7.

[0301] Hardware 1104 includes processing circuitry, memory that stores software and / or instructions (collected denoted computer program 1104a, which may be in the form of a computer program product) executable by hardware processing circuitiy, 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 1106 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1108a-b (one or more of which may be generally referred to as VMs 1108), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. Virtualization layer 1106 may present a virtual operating platform that appears like networking hardware to the VMs 1108.

[0302] VMs 1108 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1106. Different embodiments of the instance of a virtual appliance 1102 may be implemented on one or more of VMs 1108, 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.

[0303] In the context of NFV, each VM 1108 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 1108, and that part of hardware 1104 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 1108 on top of the hardware 1104 and corresponds to the application 1102.

[0304] Hardware 1104 may be implemented in a standalone network node with generic or specific components. Hardware 1104 may implement some functions via virtualization. Alternatively, hardware 1104 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 1110, which, among others, oversees lifecycle management of applications 1102. In some embodiments, hardware 1104 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 1112 which may alternatively be used for communication between hardware nodes and radio units.

[0305] 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.

[0306] 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 memoiy, 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.

[0307] As described herein, device and / or apparatus can be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of a device or apparatus, instead of being hardware implemented, be implemented as a software module such as a computer program or a computer program product comprising executable software code portions for execution or being run on a processor. Furthermore, functionality of a device or apparatus can be implemented by any combination of hardware and software. A device or apparatus can also be regarded as an assembly of multiple devices and / or apparatuses, whether functionally in cooperation with or independently of each other. Moreover, devices and apparatuses can be implemented in a distributed fashion throughout a system, so long as the functionality of the device or apparatus is preserved. Such and similar principles are considered as known to a skilled person.

[0308] 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.

[0309] In addition, certain terms used in the present disclosure, including the specification and drawings, can be used synonymously in certain instances (e.g., “data” and “information”). It should be understood that although such terms may be used synonymously herein, there may be instances when such terms are not intended to be used synonymously. Embodiments of the techniques and apparatus described herein also include, but are not limited to, the following enumerated examples:

[0310] Al. A method for a user equipment (UE) configured for conditional layer-1 (L2) / layer-2 (L2) triggered inter-cell mobility (LTM) in a radio access network (RAN), the method comprising: receiving, from a first RAN node via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; receiving from the first RAN node a timing advance (TA) value for the LTM candidate cell; in response to receiving the TA value, initiating a time alignment timer and measuring a downlink (DL) reference signal (RS) of the LTM candidate cell, thereby obtaining a first measurement value; subsequently measuring the DL RS of the LTM candidate cell, thereby obtaining a second measurement value; and determining whether the TA value is valid based on the first and second measurement values.

[0311] Ala. The method of embodiment Al, wherein subsequently measuring the DL RS of the LTM candidate cell is responsive to one or more of the following: expiration of the time alignment timer, and determining that the execution condition is fulfilled.

[0312] Alb. The method of embodiment Ala, further comprising after expiration of the time alignment timer and determining that the TA value is valid based on the first and second measurement values: re-initiating the time alignment timer; upon expiration of the time alignment timer after re-initiation, measuring the DL RS of the LTM candidate cell, thereby obtaining a third measurement value; and determining whether the TA value is valid based on the first and third measurement values.

[0313] A2. The method of any of embodiments Al-Alb, further comprising transmitting a random access (RA) preamble to the LTM candidate cell, wherein the TA value is received in response to transmitting the RA preamble.

[0314] A3. The method of any of embodiments A1-A2, wherein determining whether the TA value is valid based on the first and second measurement values comprises: determining a function of the first and second measurement values; determining that the TA value is valid when the function is less than a threshold; and determining that the TA value is invalid when the function is not less than the threshold.

[0315] A3a. The method of embodiment A3, wherein the function is one of the following: first measurement value minus second measurement value, or absolute value of a difference between the first and second measurement values.

[0316] A3b. The method of any of embodiments A3-A3a, wherein the threshold, the first measurement value, and the second measurement value are based on one of the following: reference signal received power (RSRP), reference signal received quality (RSRQ), and signal- to-interference-and-noise ratio (SINR).

[0317] A4. The method of any of embodiments Al-A3b, further comprising receiving one or more of the following configuration information from the first RAN node: an initial or terminal value for the time alignment timer; a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the time alignment timer; a second indication of whether the UE is allowed to request another TA value after expiration of the time alignment timer; and a threshold usable for determining whether the TA value is valid; and a condition usable for determining whether the TA value is valid.

[0318] A5. The method of any of embodiments A1-A4, further comprising, based on determining that the execution condition is fulfilled, selectively performing an LTM cell switch to the LTM candidate cell based on whether the TA value is determined to be valid.

[0319] A5a. The method of embodiment A4, wherein selectively performing the LTM cell switch to the LTM candidate cell comprises: when the TA value is determined to be invalid, performing a random access (RA) to the LTM candidate cell, thereby obtaining an updated TA value; and when the TA value is determined to be valid, transmitting a message to the LTM candidate cell based on the TA value and without performing a RA to the LTM candidate cell.

[0320] A6. The method of any of embodiments A1-A4, further comprising transmitting an indication of one or more of the following to the first RAN node: an updated TA value is needed for maintaining early UL synchronization with the LTM candidate cell; an updated threshold is needed for determining validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of the time alignment timer for the TA value; validity of the TA value has been extended after expiration of the time alignment timer; and whether validity of the TA value may be extended after expiration of the time alignment timer.

[0321] A6a. The method of embodiment A6, wherein transmitting the indication is responsive to one of the following: determining whether the TA value is valid, or expiration of the time alignment timer.

[0322] A6b. The method of any of embodiments A6-A6a, further comprising, in response to the indication, receiving one or more of the following from the first RAN node: an updated TA value for the LTM candidate cell; an order to transmit a further random access (RA) preamble to the LTM candidate cell; an updated threshold for determining validity of the TA value or the updated TA value; a further indication to extend validity of the TA value.

[0323] A7. The method of any of embodiments Al-A6b, further comprising: based on determining that the TA value is invalid, transmitting a further random access (RA) preamble to the LTM candidate cell; and in response to the further RA preamble, receiving from the first RAN node an updated TA value for the LTM candidate cell.

[0324] BL A method for a first radio access network (RAN) node configured to facilitate conditional lay er- 1 / layer-2 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, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; obtaining a timing advance (TA) value for UE in the LTM candidate cell; sending the TA value to the UE; and subsequently receiving from the UE an indication of one or more of the following: an updated TA value is needed for maintaining early UL synchronization with the LTM candidate cell; an updated threshold is needed for determining validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of a UE time alignment timer for the TA value; validity of the TA value has been extended after expiration of the UE time alignment timer; and whether validity of the TA value may be extended after expiration of the UE time alignment timer.

[0325] Bia. The method of embodiment Bl, wherein the indication is received after expiration of the UE time alignment timer.

[0326] B2. The method of any of embodiments Bl -Bl a, further sending one or more of the following configuration information to the UE: an initial or terminal value for the UE time alignment timer; a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the UE time alignment timer; a second indication of whether the UE is allowed to request another TA value after expiration of the UE time alignment timer; and a threshold usable for determining whether the TA value is valid; and a condition usable for determining whether the TA value is valid.

[0327] B2a. The method of embodiment B2, wherein the threshold is based on one of the following: reference signal received power (RSRP), reference signal received quality (RSRQ), and signal- to-interference-and-noise ratio (SINR). B3. The method of any of embodiments Bl-B2a, wherein the LTM candidate cell is provided by the first RAN node and obtaining the TA value comprises determining the TA value based on a random access (RA) preamble received from the UE in the LTM candidate cell.

[0328] B4. The method of any of embodiments Bl-B2a, wherein the LTM candidate cell is provided by a second RAN node and obtaining the TA value comprises receiving the TA value from the second RAN node.

[0329] B5. The method of any of embodiments B1-B4, further comprising, in response to the indication, sending one or more of the following to the UE: an updated TA value for the LTM candidate cell; an order to transmit a further random access (RA) preamble to the LTM candidate cell; an updated threshold for determining validity of the TA value or the updated TA value; a further indication to extend validity of the TA value.

[0330] B5a. The method of embodiment B5, further comprising obtaining the updated TA value based on one of the following: determining the updated TA value based on the further RA preamble received from the UE in the LTM candidate cell; or receiving the TA value from a second RAN node that provides the LTM candidate cell.

[0331] CL A user equipment (UE) configured for conditional layer-l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE comprising: communication interface circuitry configured to communicate with RAN nodes; and processing circuitry operatively coupled to the communication interface circuitry, whereby the processing circuitry and the communication interface circuitry are configured to perform operations corresponding to the methods of any of embodiments A1-A7.

[0332] C2. A user equipment (UE) configured for conditional layer-l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), the UE being further configured to perform operations corresponding to the methods of any of embodiments A1-A7. C3. A non-transitory, computer-readable medium storing computer-executable instructions that, when executed by processing circuitry of a user equipment (UE) configured for conditional layer-l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A7.

[0333] C4. A computer program product comprising computer-executable instructions that, when executed by processing circuitry of user equipment (UE) configured for conditional layer- l / layer-2 triggered inter-cell mobility (LTM) in a radio access network (RAN), configure the UE to perform operations corresponding to the methods of any of embodiments A1-A7.

[0334] DI. A first radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 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 B1-B5A.

[0335] D2. A first radio access network (RAN) node configured to facilitate conditional layer- l / layer-2 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-B5A.

[0336] D3. 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 conditional layer-l / layer-2 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 B1-B5A.

[0337] D4. 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 conditional layer-l / layer-2 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 B1-B5A.

Claims

CLAIMS1. A method for a user equipment, UE, configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN, the method comprising: receiving (610), from a RAN node via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; in response to receiving (625) from the RAN node a timing advance, TA, value for the LTM candidate cell, initiating (630) a time alignment timer and measuring a downlink, DL, reference signal, RS, of the LTM candidate cell, thereby obtaining a first measurement value; subsequently measuring (640) the DL RS of the LTM candidate cell, thereby obtaining a second measurement value; and determining (650) whether the TA value is valid based on the first and second measurement values.

2. The method of claim 1, wherein subsequently measuring the DL RS of the LTM candidate cell is responsive to determining (635) that one or more of the following has occurred: the time alignment timer has expired, and the execution condition is fulfilled.

3. The method of claim 2, further comprising after determining (635) that the time alignment timer has expired and after determining (650) that the TA value is valid based on the first and second measurement values: re-initiating (655) the time alignment timer; upon expiration of the time alignment timer after re-initiation, measuring (660) the DL RS of the LTM candidate cell, thereby obtaining a third measurement value; and determining (665) whether the TA value is valid based on the first and third measurement values.

4. The method of any of claims 1-3, further comprising transmitting (620) a random access, RA, preamble to the LTM candidate cell, wherein the TA value is received in response to transmitting the RA preamble.

5. The method of any of claims 1-4, wherein determining (650) whether the TA value is valid based on the first and second measurement values compnses:determining (651) a function of the first and second measurement values; determining (652) that the TA value is valid when the function is less than a threshold; and determining (653) that the TA value is invalid when the function is not less than the threshold.

6. The method of claim 5, wherein the function is one of the following: first measurement value minus second measurement value, or absolute value of a difference between the first and second measurement values.

7. The method of any of claims 5-6, wherein the threshold, the first measurement value, and the second measurement value are based on one of the following: reference signal received power, RSRP; reference signal received quality; RSRQ; or signal-to-interference-and-noise ratio, SINR.

8. The method of any of claims 1-7, further comprising receiving (615) one or more of the following configuration information from the RAN node: an initial or terminal value for the time alignment timer; a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the time alignment timer; a second indication of whether the UE is allowed to request another TA value after expiration of the time alignment timer; and a threshold usable for determining whether the TA value is valid; and a condition usable for determining whether the TA value is valid.

9. The method of any of claims 1-8, further comprising, based on determining (635) that the execution condition is fulfilled, selectively performing (670) an LTM cell switch to the LTM candidate cell based on whether the TA value is determined to be valid.

10. The method of claim 9, wherein selectively performing (670) the LTM cell switch to the LTM candidate cell comprises: when the TA value is determined to be invalid, performing (671) a random access, RA, to the LTM candidate cell, thereby obtaining an updated TA value; andwhen the TA value is determined to be valid, transmitting (672) a message to the LTM candidate cell based on the TA value and without performing the RA to the LTM candidate cell.

11. The method of any of claims 1-8, further comprising transmitting (680) an indication of one or more of the following to the RAN node: an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell; an updated threshold is needed for the UE to determine validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of the time alignment timer for the TA value; validity of the TA value has been extended after expiration of the time alignment timer; and whether validity of the TA value may be extended after expiration of the time alignment timer.

12. The method of claim 11, wherein transmitting (680) the indication is responsive to one of the following: determining (650) whether the TA value is valid, determining (635) that the time alignment timer has expired.

13. The method of any of claims 11-12, further comprising, in response to the indication, receiving (685) one or more of the following from the RAN node: an updated TA value for the LTM candidate cell; an order to transmit a further random access preamble to the LTM candidate cell; an updated threshold for determining validity of the TA value or the updated TA value; a further indication to extend validity of the TA value.

14. The method of any of claims 1-13, further comprising: based on determining (650) that the TA value is invalid, transmitting (690) a further random access, RA, preamble to the LTM candidate cell; and in response to the further RA preamble, receiving (695) from the RAN node an updated TA value for the LTM candidate cell.

15. A method for a radio access network, RAN, node configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs, the method comprising: sending (710), to a UE via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; obtaining (730) a timing advance, TA, value for UE in the LTM candidate cell; sending (740) the TA value to the UE; and subsequently receiving (750) from the UE an indication of one or more of the following: an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell; an updated threshold is needed for the UE to determine validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of a UE time alignment timer for the TA value; validity of the TA value has been extended after expiration of the UE time alignment timer; and whether validity of the TA value may be extended after expiration of the UE time alignment timer.

16. The method of claim 15, wherein the indication is received after expiration of the UE time alignment timer.

17. The method of any of claims 15-16, further sending (720) one or more of the following configuration information to the UE: an initial or terminal value for the UE time alignment timer; a first indication of whether the UE is allowed to extend validity of the TA value after expiration of the UE time alignment timer; a second indication of whether the UE is allowed to request another TA value after expiration of the UE time alignment timer; and a threshold usable for determining whether the TA value is valid; and a condition usable for determining whether the TA value is valid.

18. The method of claim 17, wherein the threshold is based on one of the following: reference signal received power, RSRP; reference signal received quality, RSRQ; or signal-to- interference-and-noise ratio, SINR.

19. The method of any of claims 15-18, wherein the LTM candidate cell is provided by the RAN node and obtaining (730) the TA value comprises determining (731) the TA value based on a random access, RA, preamble received from the UE in the LTM candidate cell.

20. The method of any of claims 15-18, wherein the LTM candidate cell is provided by a second RAN node and obtaining (730) the TA value comprises receiving (732) the TA value from the second RAN node.

21. The method of any of claims 15-20, further comprising, in response to the indication, sending (770) one or more of the following to the UE: an updated TA value for the UE in the LTM candidate cell; an order to transmit a further random access, RA, preamble to the LTM candidate cell; an updated threshold for determining validity of the TA value or the updated TA value; a further indication to extend validity of the TA value.

22. The method of claim 21, further comprising obtaining (760) the updated TA value for the UE in the LTM candidate cell based on one of the following: determining (761) the updated TA value based on the further RA preamble received from the UE in the LTM candidate cell; or receiving (762) the updated TA value from a second RAN node that provides the LTM candidate cell.

23. User equipment, UE (210, 410, 812, 900) configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 804), the UE comprising: communication interface circuitry (912) configured to communicate with RAN nodes; and processing circuitry (902) operatively coupled to the communication interface circuitry, wherein the processing circuitry and the communication interface circuitry are configured to: receive, from a RAN node (100, 150, 220, 420, 810, 1000, 1102) via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell;in response to reception of a timing advance, TA, value for the LTM candidate cell from the RAN node, initiate a time alignment timer and measure a downlink, DL, reference signal, RS, of the LTM candidate cell, thereby obtaining a first measurement value; subsequently measure the DL RS of the LTM candidate cell, thereby obtaining a second measurement value; and determine whether the TA value is valid based on the first and second measurement values.

24. The UE of claim 23, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 2-14.

25. User equipment, UE (210, 410, 812, 900) configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 804), the UE being further configured to: receive, from a RAN node (100, 150, 220, 420, 810, 1000, 1102) via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; in response to reception of a timing advance, TA, value for the LTM candidate cell from the RAN node, initiate a time alignment timer and measure a downlink, DL, reference signal, RS, of the LTM candidate cell, thereby obtaining a first measurement value; subsequently measure the DL RS of the LTM candidate cell, thereby obtaining a second measurement value; and determine whether the TA value is valid based on the first and second measurement values.

26. The UE of claim 25, being further configured to perform operations corresponding to the methods of any of claims 2-14.

27. Non-transitory, computer-readable medium (910) storing computer-executable instructions that, when executed by processing circuitry (902) of user equipment, UE (210, 410, 812, 900) configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in aradio access network, RAN (199, 804), configure the UE to perform operations corresponding to the methods of any of claims 1-14.

28. Computer program product (914) comprising computer-executable instructions that, when executed by processing circuitry (902) of user equipment, UE (210, 410, 812, 900) configured for conditional layer-l / layer-2 triggered inter-cell mobility, LTM, in a radio access network, RAN (199, 804), configure the UE to perform operations corresponding to the methods of any of claims 1-14.

29. Radio access network, RAN, node (100, 150, 220, 420, 810, 1000, 1102) configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 410, 812, 900), the RAN node comprising: communication interface circuitry (1006, 1104) configured to communicate with UEs and with other RAN nodes; and processing circuitry (1002, 1104) 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, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; obtain a timing advance, TA, value for UE in the LTM candidate cell; send the TA value to the UE; and subsequently receive from the UE an indication of one or more of the following: an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell; an updated threshold is needed for the UE to determine validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of a UE time alignment timer for the TA value; validity of the TA value has been extended after expiration of the UE time alignment timer; and whether validity of the TA value may be extended after expiration of the UE time alignment timer.

30. The RAN node of claim 29, wherein the processing circuitry and the communication interface circuitry are further configured to perform operations corresponding to the methods of any of claims 16-22.

31. Radio access network, RAN, node (100, 150, 220, 420, 810, 1000, 1102) configured to facilitate conditional layer-l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 410, 812, 900), the RAN node being further configured to: send, to a UE via a source cell, a configuration for an LTM candidate cell and an execution condition for LTM cell switch by a UE to the LTM candidate cell; obtain a timing advance, TA, value for UE in the LTM candidate cell; send the TA value to the UE; and subsequently receive from the UE an indication of one or more of the following: an updated TA value is needed for the UE to maintain early UL synchronization with the LTM candidate cell; an updated threshold is needed for the UE to determine validity of the TA value; the TA value is no longer valid; a cause for invalidity of the TA value; expiration of a UE time alignment timer for the TA value; validity of the TA value has been extended after expiration of the UE time alignment timer; and whether validity of the TA value may be extended after expiration of the UE time alignment timer.

32. The RAN node of claim 31, being further configured to perform operations corresponding to the methods of any of claims 16-22.

33. Non-transitory, computer-readable medium (1004, 1104) storing computer-executable instructions that, when executed by processing circuitry (1002, 1104) of a radio access network, RAN, node (100, 150, 220, 420, 810, 1000, 1102) configured to facilitate conditional layer- l / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 410, 812, 900), configure the RAN node to perform operations corresponding to the methods of any of claims 15-22.

34. Computer program product (1004a, 1104a) comprising computer-executable instructions that, when executed by processing circuitry (1002, 1104) of a radio access network, RAN, node(100, 150, 220, 420, 810, 1000, 1102) configured to facilitate conditional lay er- 1 / layer-2 triggered inter-cell mobility, LTM, by user equipment, UEs (210, 410, 812, 900), configure the RAN node to perform operations corresponding to the methods of any of claims 15-22.

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