Ta acquisition for inter-CU ltm

Abstract

Systems and methods are disclosed for Timing Advance (TA) acquisition for inter- Central Unit (CU) Layer 1 (L1) / Layer 2 (L2) Triggered Mobility (LTM). In one embodiment, a method performed by a User Equipment (UE) controlled by a first network node, for handling TA acquisition for at least one second cell controlled by a second network node, comprises transmitting a random access preamble on a second cell controlled by a second network node and receiving, from the first network node, a message including an indication of a TA value for the second cell controlled by the second network node, wherein the first network node is or comprises a first CU the second network node is or comprises a second CU, and the first CU and the second CU are different CUs.

Description

[0001] TA ACQUISITION FOR INTER-CU LTM

[0002] RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 680,356, filed August 7, 2024, the disclosure of which is hereby incorporated herein by reference in its entirety.

[0004] TECHNICAL FIELD

[0005] The present disclosure relates to a cellular communications network and, more specifically, to Timing Advance (TA) acquisition in a cellular communications network.

[0006] BACKGROUND

[0007] L1 / L2 Triggered Mobility (LTM) in 3GPP Rel-18 and Rel-19

[0008] In 3rdGeneration Partnership Project (3GPP) Release 18, a work item known as Further New Radio (NR) mobility enhancements is ongoing. This work item includes a technical area entitled Layer 1 (Ll) / Layer 2 (L2) based inter-cell mobility. According to the Work Item Description (WID) (see RP-233970, 3GPP work item description: Further NR mobility enhancements, MediaTek Inc, Apple, 3GPP TSG RAN #102, Edinburgh, GB, December 11-15, 2023), the goal of L1 / L2 based inter-cell mobility (also known as L1 / L2 Triggered Mobility (LTM)) is to enable a serving cell change, sometimes also known as an LTM cell switch or an LTM cell switch procedure, via L1 / L2 signaling, in order to reduce the latency, overhead, and interruption time.

[0009] The overall procedures for LTM in Release (Rel)-18 are described in 3GPP Technical Specification (TS) 38.300 vl8.1.0, subclause 9.2.3.5, and for the next generation Node B (gNB)- Central Unit (CU) / gNB-Distributed Unit (DU) Architecture in 3GPP TS 38.401 vl8.1.0, subclauses 8.2.1.4-8.2.1.6.

[0010] A basic principle with L1 / L2 triggered mobility is that the User Equipment (UE) is preconfigured, by the network, with an LTM configuration which includes information such as measurement configuration and a Radio Resource Control (RRC) configuration per LTM candidate cell, sometimes also known as a LTM candidate cell configuration. Such an LTM candidate cell configuration may be an RRCReconfiguration message or one or more Information Elements (IEs) / fields / parameters such as CellGroupConfig. The UE performs measurements on LTM candidate cells and beams in those cells, according to the measurement configuration included in the LTM configuration received by the network. The UE transmits LI measurement reports for LTM including LI -Reference Signal Received Power (RSRP) measurements for up to four LTM candidate cells and up to four beams in each cell. When the network (e.g., a gNB or a gNB-DU) receives the LI measurement report for LTM, it may use the content of this report to trigger an LTM cell switch towards one of the LTM candidate cells.

[0011] With the introduction of LTM, a functionality is added where the UE may perform early synchronization to cells different from the current serving cell as a way to reduce the interruption and latency during the actual mobility procedure (also known as an LTM cell switch procedure in case of using it for Ll / L2-Triggered Mobility). The procedure for early downlink (DL) sync, also known as early Transmission Configuration Indication (TCI) state activation, is triggered by the network by transmitting an early TCI state activation Medium Access Control (MAC) Control Element (CE) to the UE. The UE then activates the indicated TCI state(s) for the neighbor cell. When the UE has performed early DL sync for a cell prior to the mobility procedure, the delay caused by UE establishing DL sync towards that cell during the actual execution of the mobility procedure is avoided. One procedure for early uplink (UL) sync, also known as early Timing Advance (TA) acquisition, is triggered by the network transmitting a Physical Downlink Control Channel (PDCCH) order to the UE. The UE then transmits a random access preamble in the indicated neighbor cell, and the target node controlling the neighbor cell can calculate a TA which is then provided to the UE via the source node during the mobility procedure (such as LTM cell switch). As the UE has a valid TA for that cell, the use of random access towards that cell during the actual mobility procedure can be avoided.

[0012] The network triggers the execution of a LTM cell switch procedure in the UE to one of these LTM candidate cells by transmitting a LTM cell switch command MAC CE to the UE. The LTM cell switch command includes information such as a reference to an LTM candidate cell configuration and an indication of a target beam in the LTM candidate cell. The UE then connects to the beam and switches to the LTM candidate cell configuration.

[0013] LTM in Rel-18 is limited to intra-gNB (including intra-CU intra-DU and intra-CU inter- DU) mobility. In 3GPP Rel-19, a work item on NR Mobility enhancements Phase 4 (see RP- 240299, Revised Work Item: NR mobility enhancements Phase 4, Apple Inc, China Telecom, 3GPP TSG RAN #103, Maastricht, Netherlands, March 18-21, 2024) is ongoing, which aims to enhance mobility features, including introducing support for inter-CU LTM according to the objective below:

[0014] • Specify support for inter-CU Layerl / Layer 2 Mobility (LTM) [RAN2, RAN3] o Prioritize the case when CU is acting as MN when DC is not configured o As secondary priority, support the case when NR-DC is configured and CU is acting as SN and MCG is unchanged o As secondary priority, support the case when NR-DC is configured, CU is acting as MN and SCG is unchanged or SCG is released

[0015] ■ Note: The case that LTM is configured in both MCG and SCG is excluded o Specify support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM

[0016] ■ Coordination with SA3 needed with respect to security key handling o Note: Rel. 18 intra-CU LTM procedure is considered as baseline for adding inter-CU support

[0017] SUMMARY

[0018] Systems and methods are disclosed for Timing Advance (TA) acquisition for inter-Central Unit (CU) Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM). In one embodiment, a method performed by a User Equipment (UE) controlled by a first network node, for handling TA acquisition for at least one second cell controlled by a second network node, comprises transmitting a random access preamble on a second cell controlled by a second network node and receiving, from the first network node, a message including an indication of a TA value for the second cell controlled by the second network node, wherein the first network node is or comprises a first CU the second network node is or comprises a second CU, and the first CU and the second CU are different CUs. In this manner, the UE is enabled to perform a mobility procedure from the first cell to the second cell without using random access in cases when there is no direct connection between the first and second network nodes.

[0019] In one embodiment, the first network node is associated with a third network node, and the second network node is associated with the third network node. In one embodiment, the third network node is a core network node.

[0020] In one embodiment, the first network node is associated with a first core network node, and the second network node is associated with a second core network node.

[0021] In one embodiment, the UE is configured with dual connectivity. In one embodiment, the first network node is associated with a third network node which is a Master Node (MN), the first network node is a first SN, and the second network node is a second SN. In one embodiment, the first network node comprises a first CU of the first SN, and the second network node is a second CU of with the second SN. In one embodiment, the message including the indication of the TA value is a Medium Access Control (MAC) Control Element and / or a Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM) Cell Switch command including the TA value.

[0022] In one embodiment, the method further comprises receiving, from the first network node, a TA acquisition configuration, wherein the UE transmits the random access preamble in accordance with the TA acquisition configuration. In one embodiment, the TA acquisition configuration comprises any one or more of the following: a preamble index used for transmitting the random access preamble on the second cell controlled by the second network node, a Random Access Channel (RACH) configuration related to transmitting the random access preamble on the second cell controlled by the second network node, and a Random Access (RA) Radio Network Temporary Identity used by the UE for a random access procedure performed by the UE with respect to the second cell controlled by the second network node during which the UE transmits the random access preamble.

[0023] In one embodiment, the method further comprises performing a mobility procedure from a first cell controlled by the first network node to the second cell controlled by the second network node using the TA value indicated by the received indication. In one embodiment, the UE does not perform random access during the mobility procedure. In one embodiment, the method further comprises transmitting, to the second network node, a message confirming that the mobility procedure has been completed.

[0024] In one embodiment, the mobility procedure is triggered in response to a received indication from the first network node. In one embodiment, the received indication that triggers the mobility procedure is either a handover command or an LTM cell switch command. In one embodiment, the received indication that triggers the mobility procedure comprises the indication of the TA value. In one embodiment, the received indication that triggers the mobility procedure comprises an indication to the UE to not perform a random access as part of the mobility procedure.

[0025] In one embodiment, the mobility procedure is triggered in response to a condition being fulfilled.

[0026] In one embodiment, the mobility procedure is triggered in response to detecting a failure. In one embodiment, the failure is either a radio link failure or a mobility failure.

[0027] In one embodiment, the mobility procedure is any one of the following: an NG-based mobility procedure, an N2-based mobility procedure, a Layer 3 (L3) handover procedure, an LTM procedure, a conditional reconfiguration procedure, a conditional handover, a conditional Primary Secondary Cell Group (SCG) Cell (PSCell) addition, a conditional PSCell change, a beam management procedure, a Radio Resource Control (RRC) resume procedure, an RRC reestablishment procedure.

[0028] In one embodiment, the method further comprises receiving, from the first network node, an indication to trigger TA acquisition for the second cell, wherein transmitting the random access preamble on the second cell controlled by the second network node is responsive to receiving the indication to trigger TA acquisition for the second cell.

[0029] Corresponding embodiments of a UE are also disclosed. In one embodiment, a UE controlled by a first network node, for handling TA acquisition for at least one second cell controlled by a second network node, comprises a communication interface comprising a transmitter and a receiver, and processing circuitry associated with the communication interface. The processing circuitry is configured to cause the UE to transmit a random access preamble on a second cell controlled by a second network node and receive, from the first network node, a message including an indication of a TA value for the second cell controlled by the second network node, wherein the first network node is or comprises a first CU the second network node is or comprises a second CU, and the first CU and the second CU are different CUs.

[0030] Embodiments of a method performed by a first network node are also disclosed. In one embodiment, a method performed by a first network node, which controls a first cell, for handling TA acquisition for a second cell controlled by a second network node for a UE controlled by the first network node, comprises receiving, from the second network node or a third network node, a message including an indication of a TA value for the UE for a second cell controlled by the second network node and transmitting, to the UE, a message comprising the indication of the TA value for the UE for the second cell controlled by the second network node.

[0031] In one embodiment, the method further comprises receiving, from the second network node or the third network node, a message including a TA acquisition configuration and transmitting the TA acquisition configuration to the UE. In one embodiment, the method further comprises, prior to receiving the message including the TA acquisition configuration, transmitting, to the second network node or the third network node, a message including a request for the TA acquisition configuration.

[0032] In one embodiment, the method further comprises, prior to receiving the message including the indication of the TA value for the UE for the second cell controlled by the second network node, transmitting, to the UE, an indication to trigger TA acquisition for the second cell.

[0033] In one embodiment, the UE initiates a mobility procedure from the first cell controlled by the first network node to the second cell controlled by the second network node using the indicated TA value. In one embodiment, the method further comprises transmitting, to the UE, an indication to perform the mobility procedure to the second cell controlled by the second network node. In one embodiment, the transmitted indication to perform the mobility procedure to the second cell comprises the indication of the TA value for the second cell. In one embodiment, transmitted indication to perform the mobility procedure to the second cell comprises an indication to the UE to not perform a random access for the mobility procedure. In one embodiment, the mobility procedure is one of: an NG-based mobility procedure, an N2-based mobility procedure, a L3 handover procedure, an LTM procedure, a conditional reconfiguration procedure, a conditional handover, a conditional PSCell addition, a conditional PSCell change, a beam management procedure, an RRC resume procedure, an RRC re-establishment procedure.

[0034] In one embodiment, the methd further comprises transmitting, to the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0035] In one embodiment, the method further comprises receiving, from the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0036] In one embodiment, the second network node is different from the first network node or associated with a target CU different from a source CU associated with the first network node.

[0037] In one embodiment, the third network node is a core network node. In one embodiment, the core network node is not connected to the second network node.

[0038] In one embodiment, the third network node is a MN, and the UE is configured with dual connectivity.

[0039] In one embodiment, the first network node transmits the indication of the TA value when any one or more of the following conditions are fulfilled: a delay over a link between the first network node and the UE is below a threshold THR1; a delay over the link between a first CU of the first network node and a first DU of the first network node is below a threshold THR2; a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR3; a delay over a link between the first network node and the UE is below a threshold THR4; a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR5.

[0040] In one embodiment, the method further comprises transmitting, to the second network node or the third network node, a message to request the TA value for the second cell controlled by the second network node. In one embodiment, the method further comprises starting a timer when the first network node transmits the message to the second network node to request the TA value. In one embodiment, the method further comprises receiving, from the second network node or the third network node, a message comprising validity information associated with the TA value.

[0041] Corresponding embodiments of a first network node are also disclosed. In one embodiment, a first network node, which controls a first cell, for handling TA acquisition for a second cell controlled by a second network node for a UE controlled by the first network node, comprises processing circuitry configured to cause the first network node to receive, from the second network node or a third network node, a message including an indication of a TA value for the UE for a second cell controlled by the second network node and transmit, to the UE, a message comprising the indication of the TA value for the UE for the second cell controlled by the second network node.

[0042] Embodiments of a method performed by a second network node are also disclosed. In one embodiment, a method performed by a second network node for handling TA acquisition for a second cell controlled by the second network node for a UE controlled by a first network node, comprises receiving, from the UE, a random access preamble on the second cell controlled by the second network node and transmitting, to the first network node, a message including an indication of a TA value for the second cell controlled by the second network node.

[0043] Corresponding embodiments of a second network node are also disclosed. In one embodiment, a second network node for handling TA acquisition for a second cell controlled by the second network node for a UE controlled by a first network node, the second network node comprising processing circuitry configured to cause the second network node to receive, from the UE, a random access preamble on the second cell controlled by the second network node and transmit, to the first network node or a third network node, a message including an indication of a TA value for the second cell controlled by the second network node.

[0044] Embodiments of a method performed by a third network node are also disclosed. In one embodiment, a method performed by a third network node for handling TA acquisition for a second cell controlled by a second network node, for a UE controlled by a first network node, comprises transmitting, to the first network node, a message including an indication of a TA value for the UE for a second cell controlled by the second network node.

[0045] Corresponding embodiment of a third network node are also disclosed. In one embodiment, a third network node for handling TA acquisition for a second cell controlled by a second network node, for a UE controlled by a first network node, comprises processing circuitry configured to cause the third network node to transmit, to the first network node, a message including an indication of a TA value for the UE for a second cell controlled by the second network node.

[0046] BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0048] Figure 1 illustrates one example of a system in which embodiments of the present disclosure may be implemented.

[0049] Figure 2 illustrates the overall message flow between the entities in a first example of the first set of embodiments for transfer of a Timing Advance (TA) value.

[0050] Figure 3 illustrates the overall message flow between the entities in a second example of the second set of embodiments for transfer a TA value.

[0051] Figures 4A and 4B (sometimes collectively referred to herein as Figure 4) illustrate a message sequence chart in accordance with one example embodiment of the present disclosure.

[0052] Figures 5 A and 5B (sometimes collectively referred to herein as Figure 5) illustrates a message sequence chart in accordance with another example embodiment of the present disclosure.

[0053] Figures 6A and 6B (sometimes collectively referred to herein as Figure 6) illustrate a message sequence chart in accordance with another example embodiment of the present disclosure.

[0054] Figure 7 shows an example of a communication system in accordance with some embodiments.

[0055] Figure 8 shows a User Equipment (UE) in accordance with some embodiments.

[0056] Figure 9 shows a network node in accordance with some embodiments.

[0057] Figure 10 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.

[0058] DETAILED DESCRIPTION

[0059] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure. Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0060] There currently exist certain challenge(s). In 3rdGeneration Partnership Project (3GPP) Release (Rel)-18, Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM) is limited to intra-Central Unit (CU) mobility use cases for both intra-Distributed Unit (DU) and inter-DU mobility. In other words, when a User Equipment (UE) is in a serving cell of a serving CU (or CU-Control Plane (CP)), the UE can only be configured with LTM candidate cell(s) also controlled by that serving CU, which are either cells of the same serving DU or a candidate DU, but not cells of a different CU. In 3GPP Rel-19, the work item on NR Mobility enhancements Phase 4 is planned to introduce support for inter-CU LTM in the specifications. Thus, this expects to enable LTM for the mobility use cases requiring mobility between New Radio (NR) base stations (i.e., between gNodeBs (gNBs)), e.g. the UE may be configured with LTM candidate cells of a different serving CU. These gNBs (e.g., gNB-CU(s)) are connected to each other over the Xn interface, which is a direct interface that is needed to perform mobility within the Radio Access Network (RAN).

[0061] Further, in some mobility use cases requiring mobility between a first gNB and a second gNB, the first gNB does not have Xn connection to the second gNB. For Layer 3 (L3) handover, in such cases, the L3 handover procedure needs to involve the core network, such as the 5G Core Network (5GC). Moreover, for the mobility use cases requiring mobility between a first gNB and a second gNB, even if there is an Xn connection between the first gNB and the second gNB, in a subset of those cases, such as when a change of security key needs to involve the core network, e.g. at vertical key derivation or reconfiguration of Non-Access Stratum (NAS) security, or when the mobility may require change of network slice, Public Land Mobile Network (PLMN), or core network node (such as change of Access and Mobility Management Function (AMF)), the core network needs to be involved in the L3 handover procedure. Also, sometimes even for intra-CU or intra-gNB mobility use cases, it may be required to change network slice, PLMN, or core network node (such as change of AMF).

[0062] It is not clear how L1 / L2 triggered mobility would work between a first gNB and a second gNB which do not have an Xn connection available between them. Moreover, it is not clear how LTM would work in cases when the core network needs to be involved, either for the inter-CU case or the intra-CU case. L3 handover supports the Next Generation (NG)-based handover cases. However, in LTM, the candidate cells are configured in advance and already at configuration the gNB needs to know whether a certain candidate cell has an Xn connection or not or whether there is a need to use the core network. Therefore, the solution for L3 handover over NG cannot be used for LTM.

[0063] Specifically, it is not clear how the procedure for early uplink (UL) sync will work during:

[0064] • inter-CU LTM from a first gNB to a second gNB which have an Xn connection available between them, and

[0065] • a mobility procedure (e.g., L3 handover or LTM) from a first gNB to a second gNB, which do not have an Xn connection available between them.

[0066] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. Embodiments of systems and methods for UE and network nodes to handle Timing Advance (TA) acquisition for a second cell, such as a neighboring cell, controlled by a second network node are disclosed. Embodiments of systems and methods for transferring an indication of a TA value from the second network node to a first network node are disclosed. The UE uses the indication of a TA value to avoid random access during a mobility procedure, e.g. LTM procedure or L3 handover, to the second cell. The indication of a TA value may have been determined by the second network node upon reception of a message, such as a random access preamble, transmitted from the UE to the second network node in the second cell.

[0067] Embodiments of systems and methods are also disclosed for a UE and network nodes for configuration of TA acquisition, wherein the first network node controlling the UE transmits, to a second network node controlling a second cell, a message to request TA acquisition configuration, and the second network node transmits, to the first network node, a message with a response including a TA acquisition configuration.

[0068] The first network node controls the UE and may be a source gNB, source CU, or source DU associated with a source CU. The second network node may be a target gNB different from the source gNB, a target CU, or a target DU associated with a target CU, where the source CU is different from the target CU.

[0069] In dependent embodiments, the transfer of TA value and configuration of TA acquisition may be performed via a third network node. In dependent embodiments, the third network node is at least one core network node. In dependent embodiments, the UE is configured for dual connectivity, such as NR Dual Connectivity (NR-DC), and the third network node is a Master Node (MN), the first network node may be a source Secondary Node (SN), and the second network node may be a target SN.

[0070] Certain embodiments may provide one or more of the following technical advantage(s). Embodiments of the present disclosure enable the UE to perform a mobility procedure from a first gNB to a second gNB without using random access in cases when there is no direct connection (e.g., Xn connection) between them. Embodiments of the present disclosure enable the second gNB to transfer an indication of a TA value to the first gNB via a core network, which facilitates the network to use a mobility procedure for the UE without using random access when there is no direct connection (e.g., Xn connection) between the first gNB and the second gNB. Embodiments of the present disclosure result in short interruption time during mobility in the above cases which in turn increases the service continuity for the applications and end users. The teachings of certain embodiments may improve latency and / or power consumption in the RAN.

[0071] The description herein refers to the term “NG-based mobility” for a UE, sometimes known as “N2-based mobility” for a UE. NG-based mobility is a process of a UE changing its cell from a source cell controlled by a first network node, such as a first gNB, to a target cell controlled by a second network node, such as a second gNB, for which the signaling from the first network node for preparation, execution, and / or completion of the cell change need to use a third network node, such as core network node (e.g. Access and Mobility management Function, AMF). At NG-based mobility, a layer 3 (L3) handover procedure, sometimes known as handover or basic handover (described in 3GPP TS 38.300 vl 8.1.0) may be used for preparation, execution, and / or completion and the signaling goes via a core network node, such as described in 3GPP TS 23.502 V18.5.0. In the context of the present disclosure, at NG-based mobility, an LTM for the preparation, execution, and / or completion and the signaling goes via a core network node. Alternatively, at NG-based mobility, a procedure such as a conditional reconfiguration procedure, such as Conditional Handover (CHO), conditional Primary Secondary Cell (PSCell) addition or Conditional PSCell change, CPA, CPC, CPAC. Or alternatively, a beam management procedure such as Inter-Cell Beam Management (ICBM), an RRC resume procedure, a RRC re-establishment procedure, a RRC connection establishment procedure, or a registration procedure.

[0072] The description herein refers to the term “L1 / L2 based inter-cell mobility” as used in the Rel-18 Work Item Description (see RP-233970) in 3GPP, though it interchangeably also uses the terms L1 / L2 mobility, Ll-mobility, LI based mobility, Ll / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility L1 / L2 Triggered Mobility, Lower-layer triggered Mobility or LTM. The overall procedure for LTM is described in 3GPP TS 38.300 vl8.1.0.The basic principle is that the UE receives a lower layer signaling (e.g. a Medium Access Control (MAC) Control Element (CE)) from the network indicating to the UE a change (or switch or activation) of its serving cell (e.g. change of Primary Cell (PCell), from a source to a target PCell), wherein a lower layer signaling is a message / signaling of a lower layer protocol, which may be referred as a L1 / L2 inter-cell mobility execution command or LTM cell switch command. The change of serving cell (e.g., change of PCell) may also lead to a change in Secondary Cell(s) (SCell(s)) for the same cell group, e.g. in case the command triggers the UE to change to another cell group configuration of the same type (e.g. another Master Cell Group (MCG) configuration). Before the UE receives the LTM cell switch command, the UE is configured by the network with one or more LTM candidate cells (e.g., reception of an RRC Reconfiguration message, with at least one LTM candidate cell configuration) A candidate cell configuration may include parameters in the Information Element (IE) CellGroupConfig per candidate cell and / or an embedded RRC Reconfiguration per candidate cell.

[0073] In the present disclosure, a Timing Advance (TA) value is acquired for the UE in a neighboring / target cell so that the UE can avoid transmission of a Physical Random Access Channel (PRACH) preamble (and reception of a corresponding Random Access Response (RAR) message) during the access to that target cell. The acquisition thus enables the UE to perform a Random Access Channel (RACH)-less access to the target cell during the handover procedure (where at least the PRACH preamble and the RAR can be skipped compared to the normal RACH procedure that is performed during a normal handover / Reconfiguration With Sync procedure).

[0074] A TA acquisition configuration may include information needed by the network nodes and / or the UE to perform a TA acquisition procedure, such as an indication of which method to use for TA acquisition, one or multiple RACH configuration(s), or one or multiple preamble index(s) used at UE transmission of random access (RA) preambles, or one or multiple RA-Radio Network Temporary Identity(s) (RNTI(s)). A TA acquisition configuration may be provided to the UE per neighbor cell, e.g. per LTM candidate cell.

[0075] Figure 1 illustrates one example of a system in which embodiments of the present disclosure may be implemented. As illustrated, the system includes a UE 101, a first network node

[0076] 102 and a second network node 103. The UE 101 is a wireless terminal, such as a cellular smartphone, sometimes connected to the first network node 102 over a wireless interface 104 and sometimes connected to the second network node 103, to which the UE 101 is connected over a wireless interface 105.

[0077] The first network node 102, sometimes referred to as first gNB, controls at least one first cell 107 (sometimes called serving cell or Special Cell (SpCell), PCell or PSCell, or, in the context of mobility, referred to as source cell). The second network node 103, sometimes referred to as second gNB, controls at least one second cell 108, which sometimes, e.g. in the context of mobility, is referred to as target cell, neighbor cell, candidate cell, target candidate cell, LTM candidate cell or inter-CU LTM candidate cell.

[0078] In the context of the present disclosure, the first network node 102 and the second network node 103 are different network nodes. The first network node 102 and the second network node

[0079] 103 may sometimes be interconnected over an interface 106, which may be an Xn or Xn-C type of interface. In some cases, the first network node and the second network node are not connected. In some cases, the first network node and the second network node may be connected to a third network node 115 over interfaces 116 and 117, respectively.

[0080] Sometimes, including in the context of mobility, such as L3 handover, CHO, or LTM, the first network node 102 may be referred to as either source network node, serving network node, source gNB, or serving gNB, and the second network node 103 may be referred to as either target network node, candidate network node, target gNB, or candidate gNB.

[0081] In case of a distributed CU / DU RAN architecture, also known as CU / DU split, each of the first network node 102 and / or the second network node 103 may be divided into a distributed unit (DU), sometimes known as gNB-DU or DU, and a central unit (CU), sometimes referred to as gNB-CU, CU, gNB-CU-Control Plane (CP), or gNB-CU-User Plane (UP). Thus, in such a case, the first network node 102 may be divided into a first CU 109, sometimes referred to as serving CU or source CU, and a first DU 110, and second network node 103 may be divided into a second CU 112, sometimes referred to as target CU or candidate CU, and a second DU 113.

[0082] Sometimes, references to the first network node 102 may refer to either the first CU 109 or the first DU 110. In other words, the following description may sometimes use the term “first network node 102” to refer to, e.g., a gNB and other times to refer to, e.g., the gNB-CU or gNB- DU. And sometimes, references to the second network node 103 may refer to either the second CU 112 or the second DU 113. In other words, the following description may sometimes use the term “second network node 103” to refer to, e.g., a gNB and other times to refer to, e.g., the gNB- CU or gNB-DU. In the context of the present disclosure, the first CU and the second CU are different CUs.

[0083] The first CU 109 and the first DU 110 are connected over an interface 111, which may be an Fl type of interface in case ofNG-RAN. Correspondingly, the second CU 112 and the second DU 113 are connected over an interface 114, which may be an Fl type of interface in case of NG- RAN.

[0084] In one example, the third network node 115 may be a core network node, for example a 5G Core (5GC) Network Node, such as an Access and Mobility management Function (AMF) or a User Plane Function (UPF) and / or a 6G CN node or function, and the interfaces 116 and 117 may in this case be NG-based interfaces or N2-based reference points, e.g. when the core network node is a 5GC Network Node, such as an AMF.

[0085] When the third network node 115 is a core network node, it may be realized as multiple core network nodes, such as a source core network node, e.g. source AMF, connected to the first network node 102, and a target core network node, such as a target AMF, connected to the second network node 103. These core network nodes are interconnected over an interface - this is not illustrated in Figure 1. In case of 5GC nodes, the interface between them may be an N14 reference point or an Namf type of service-based interface.

[0086] In another example, the UE 101 is configured with dual connectivity, such as NR-DC, with a Master Node (MN), sometimes also known as a master gNB, controlling master cell group (MCG) for the UE, and a Secondary Node (SN), sometimes known as a secondary gNB, controlling secondary cell group (SCG) for the UE. In this example, the first network node 102 and the second network node 103 are Secondary Nodes (SNs), also, each controlling a secondary cell group (SCG) for the UE. In the context of inter-SN mobility, the first network node 102 is known as the source SN and the second network node 103 is known as the target SN. And in this example, the third network node 115 may be a Master Node (MN), controlling a master cell group (MCG) for the UE.

[0087] In a first set of embodiments for a system and method for transfer of a TA value, an indication of a TA value from the second network node 103 is transferred directly to the first network node 102 over a connection, such as an Xn connection. In Figure 2, the overall message flow between the entities in a first example of the first set of embodiments for transfer a TA value is illustrated. The steps and messages in this example are as follows:

[0088] • Step 200: The UE 101 transmits a first message, such as a random access preamble, to the second cell 108, e.g. an LTM candidate cell, controlled by the second network node 103. a. The second network node 103 may be a gNB or a candidate DU (e.g., second DU 113) associated with a CU (e.g., second CU 112).

[0089] • Step 202: The second network node 103 determines a Timing Advance (TA) value and includes an indication of the TA value in a second message transmitted to the first network node 102. a. The first network node 102 may be a gNB or a central unit (e.g., first CU 109). b. The second network node 103 may be a gNB or a central unit (e.g., second CU 112), which is different from the first CU 109. c. The message may be sent by UE associated signaling or by non-UE associated signaling. d. The message may include a single TA value and / or for one second cell and / or for a UE, or include multiple TA values and / or for multiple second cells and / or for multiple UEs. In other words, the message may include a single TA value, which may be indicated for one second cell 108, for the one UE 101, or for one second cell 108 for the one UE 101. Alternatively, the message may include multiple TA values, which may be for multiple second cells 108, for multiple UEs 101, for multiple second cells 108 for the one UE 101, or for multiple second cells 108 for multiple UEs 101.

[0090] • Step 204: The first network node 102 transmits the indication of the TA value to the UE 101 in a fourth message, such as a MAC CE, e.g. LTM cell switch command or an RRC message, e.g. a Handover Command / RRCReconfiguration message. a. In one example, the first network node 102 may be a gNB. b. In another example, the first network node 102 may be a DU (e.g., first DU 110) associated with a CU (e.g., first CU 109). In this example, the fourth message may be a MAC CE, e.g. LTM cell switch command. c. In yet another example, the first network node 102 may be a or a CU (e.g., first CU 109).

[0091] • Step 206: The UE 101 uses the indication of the TA value during a mobility procedure to the second cell 108 and avoid random access during the mobility procedure. In other words, the UE 101 uses the TA value associated to the LTM candidate cell of the second network node 103 and received from the first network node 102 to perform a RACH-less LTM execution, which further comprises the UE 101 transmitting a scheduling request (SR) on Physical Uplink Control Channel (PUCCH) and / or an UL information on Physical Uplink Shared Channel (PUSCH), without the need to send a PRACH preamble to the LTM candidate cell of the second network node at the moment of the RACH-less LTM execution.

[0092] In a second set of embodiments for systems and methods for transfer of a TA value, an indication of a TA value from the second network node 103 is transferred to the first network node 101 via the third network node 115. Figure 3 illustrates the overall message flow between the entities in a second example of the second set of embodiments for transfer a TA value.

[0093] In one subset of this second set of embodiments, the third network node 115 is at least one core network node, for example a 5GC Network Node, such as an AMF or a UPF and / or a 6G CN node or function. The first network node 102 may be source gNB or a source CU, associated with the core network node, or in case of multiple core network nodes, with a first core network node. Alternatively, the first network node 102 may be a source DU, associated with a source CU, which in turn is associated with the core network node or in case of multiple core network nodes, associated with a first core network node. The second network node 103 may be target gNB or a target CU associated with the core network node, or in case of multiple core network nodes, associated with a second core network node. Alternatively, the second network node 103 may be a target DU associated with a target CU, which in turn is associated with the core network node or in case of multiple core network nodes, associated with a second core network node.

[0094] An example of the message flow in this second subset of embodiments, as illustrated in Figure 3, is as follows.

[0095] • Step 300: The UE 101 transmits a first message, such as a random access preamble, to an LTM candidate cell (i.e., one of the second cells 108) of the second network node 103, e.g. a target gNB or a target DU associated with a target CU.

[0096] • Step 302: The second network node 103 determines a TA value and includes an indication of the TA value in a second message transmitted to the third network node 115, such as core network node, or, when the second network node 103 and the first network node 102 are associated with different core network nodes, a second core network node. a. In case the second network node 103 and the first network node 102 are associated with different core network nodes, the second core network node transfers the indication of a TA value in a fifth message from the second core network node to the first core network node.

[0097] • Step 304: The third network node 115, such as a core network node or a first core network node, transmits the indication of the TA value in a third message transmitted to the first network node 102.

[0098] • Step 306: The first network node 102 transmits the indication of a TA value to the UE 101 in a fourth message, such as a MAC CE, e.g. LTM cell switch command or an RRC message, e.g. a Handover Command / RRCReconfiguration message.

[0099] • Step 308: The UE 101 use the indication of a TA value during a mobility procedure to the second cell and avoid random access during the mobility procedure. In other words, the UE uses the TA value associated to the LTM candidate cell of the second network node and received from the first gNB to perform a RACH-less LTM execution; that further comprises the UE transmitting a scheduling request (SR) on PUCCH and / or an UL info on PUSCH, without the need to send a PRACH preamble to the LTM candidate cell of the second gNB at the moment of the RACH-less LTM execution.

[0100] In another subset of this second set of embodiments, the UE 101 is configured with dual connectivity, such as NR-DC, with a MN and a SN. In this example, the third network node 115 is a MN, sometimes also known as the master gNB, controlling an MCG for the UE 101. The first network node 102 is a source SN, also known as source secondary gNB, associated with the MN. The first network node 102 may alternatively be a source CU associated with the MN or a source DU associated with a source CU, which in turn is associated with the MN. The second network node 103 is a target SN, also known as target secondary gNB, or a target CU, or a target DU associated with a source CU, in the context for inter-SN mobility, such as inter-SN LTM.

[0101] Again referring to Figure 3, an example of the message flow in this subset is as follows.

[0102] • Step 300: The UE 101 transmits a first message, such as a random access preamble, to a LTM candidate cell (i.e., one of the second cells 108) of the second network node 103, e.g. a target SN, or a target DU associated with a target CU which is a different CU from the source CU.

[0103] • Step 302: The second network node 103 determines a TA value and includes an indication of the TA value in a second message transmitted to the third network node 115, e.g. the Master Node, MN. The message may be a new type of message, such as SCG TA INFORMATION NOTIFICATION. The message may include an identity of the LTM candidate cell, indication of TA value(s), a preamble index and the RA-RNTI.

[0104] • Step 304: The third network node 115 transmits the indication of the TA value in a third message transmitted to the first network node 102, e.g. a source SN or a source CU, which is a different CU from the target CU. The message may be a new type of message, such as SCG TA INFORMATION NOTIFICATION. The message may include an identity of the LTM candidate cell, indication of TA value(s), a preamble index and the RA-RNTI. In case of CU / DU split, the source CU may forward the indication of the TA value to the source DU.

[0105] • Step 306: The first network node 102, e.g. a source SN or a source DU associated with a source CU different from the target CU, transmits the indication of a TA value to the UE 101 in a fourth message, such as a MAC CE, e.g. LTM cell switch command or an RRC message, e.g. a Handover Command / RRCReconfiguration message.

[0106] • Step 308: The UE 101 uses the indication of a TA value during a mobility procedure to the second cell and avoid random access during the mobility procedure, such as an Inter-SN LTM cell switch procedure. In other words, the UE uses the TA value associated to the LTM candidate cell of the second network node and received from the first gNB to perform a RACH-less LTM execution; that further comprises the UE transmitting a scheduling request (SR) on PUCCH and / or an UL info on PUSCH, without the need to send a PRACH preamble to the LTM candidate cell of the second gNB at the moment of the RACH-less LTM execution.

[0107] In one set of embodiments which can be combined with the previous set of embodiments, the first network node 102 transmits, to the second network node 103 or the third network node 115, a request for indication of TA value(s) for one or multiple second cells 108. In one example the request is made for subsequent mobility, such as subsequent LTM, to a third cell towards which the UE 101 may perform a mobility procedure from the second cell. In one example, the first network node 102 receives, from the second network node 103 or the third network node 115, a response message including the TA value(s) for one or more of the requested cells.

[0108] In regard to configuration of TA acquisition, the TA acquisition configuration may include information needed by the network nodes and / or the UE to perform a TA acquisition procedure, such as a RACH configuration, or preamble index(es) used at transmission of random access (RA) preambles.

[0109] In one set embodiments for configuration of TA acquisition (referred to herein as Set 1), a connection between the first network node 102 and the second network node 103 is used for the configuration. The first network node 102 may be a first gNB or a first CU, and the second network node 103 may be a second gNB, such as a target gNB or a candidate gNB, or a second CU, such as target CU or a candidate CU. The first CU and second CU are different CUs. The configuration of TA acquisition may be performed as part of LTM configuration, such as during configuration of LTM candidate cells, or before the configuration of LTM candidate cells. Alternatively, the configuration of TA acquisition may be performed as a separate procedure, such as after the LTM configuration but before the LTM cell switch, which allows the TA acquisition configuration in a second network node to be allocated during a shorter period of time, which may enable a more efficient use of resources, such as preamble index(es) used at transmission of random access (RA) preambles. The configuration of TA acquisition may be initiated by either the first network node or the second network node.

[0110] In one example (Example 1A) of the Set 1 embodiments, the first network node 102 initiates configuration of TA acquisition during LTM candidate cell configuration by transmitting, to the second network node 103, a message including a request for a TA acquisition configuration as well as a request for an LTM candidate cell configuration for a second cell (target candidate cell). This message may be a HANDOVER REQUEST message or a new message. The second network node 103 prepares the TA acquisition configuration and the LTM candidate cell configuration and responds in a message, transmitted to the first network node 102, including the TA acquisition configuration and the LTM candidate cell configuration. This message may be a HANDOVER REQUEST ACKNOWLEDGE message or a new message.

[0111] In another example (Example IB) of the Set 1 embodiments, the first network node 102 initiates configuration of TA acquisition after the LTM configuration but before the LTM cell switch. In this example, the first network node 102 transmits, to the second network node 103, a message including a request for a of TA acquisition configuration. This message may be an existing message or a new message, such as LTM CONFIGURATION REQUEST. The message may include an indication of one or more cells, including the second cell. The second network node 103 prepares the TA acquisition configuration and responds in a message, transmitted to the first network node 102, including the TA acquisition configuration for one or more cells, including the second cell. This message may be an existing message or a new message, such as LTM CONFIGURATION RESPONSE.

[0112] In yet another example (Example 1C) of the Set 1 embodiments, the target network node (i.e., the second network node 103) initiates configuration of TA acquisition by transmitting, to the first network node 102, a message which includes a TA acquisition configuration, for one or cells, such as the second cell, controlled by the target network node. This message may be an existing message or a new message, such as a CONFIGURATION UPDATE message.

[0113] In another set (Set 2) of embodiments for configuration of TA acquisition, connections from a third network node 115 to the first network node 102 and the second network node 103 are used. This may be needed when the first network node 102 and the second network node 103 are not directly connected or when a third network node needs to be included in the configuration procedure for some reason.

[0114] In one subset (Subset 2A) of the Set 2 embodiments, the first network node 102 may be a first gNB or a first CU, and the second network node 103 may be a second gNB, such as a target gNB or a candidate gNB, or a second CU, such as target CU or a candidate CU. The first CU and second CU are different CUs. In this example, the third network node 115 may be a core network node, such as AMF, or even multiple core network nodes, such as when the first network node 102 and the second network node 103 are associated with different third network nodes, e.g. different AMFs.

[0115] In one example (Example 2A-1) of Subset 2A, the first gNB or a first CU initiates configuration of TA acquisition during LTM candidate cell configuration by transmitting, to the core network node (or first core network node in case of multiple core network nodes), a message including a request for a of TA acquisition configuration as well as a request for an LTM candidate cell configuration for a second cell (target candidate cell). This message may be a HANDOVER REQUIRED NGAP message, or a new type of message such as an UPLINK RAN CONFIGURATION TRANSFER NGAP message. The core network node, in case the second network node is associated with the same core network node, then transmits, to the second gNB or second CU, a message including a request for a of TA acquisition configuration as well as a request for an LTM candidate cell configuration for a second cell (target candidate cell). This message may be a HANDOVER REQUEST NGAP message or a new type of message such as a DOWNLINK RAN CONFIGURATION TRANSFER NGAP message. In case the second network node is associated with a second core network node other than the first core network node, the first core network node transmits, to the second core network node, a message that includes the request for a of TA acquisition configuration as well as a request for an LTM candidate cell configuration for a second cell (target candidate cell). This message may, for example, be a Namf_Communication_Create UEContext request message or a Namf_Communication_NlN2MessageTransfer message. The second core network node then transmits, to the second gNB or second CU, a message including a request for a TA acquisition configuration. This message may be a HANDOVER REQUEST NGAP message or a new type of message such as a DOWNLINK RAN CONFIGURATION TRANSFER NGAP message.

[0116] The second network node 103 prepares the TA acquisition configuration and the LTM candidate cell configuration. The second network node 103 responds in a message, transmitted, either to the core network node or to the second core network node in case the first network node 102 and the second network node 103 are associated with different core network nodes, including the TA acquisition configuration and the LTM candidate cell configuration. This message may be a HANDOVER REQUEST ACKNOWLEDGE message or a new message such as an UPLINK RAN CONFIGURATION TRANSFER NGAP message. In case the second network node 103 is connected to a different core network node than the first network node 102, the second core network node 103 transmits, to the first core network node, a message, such as a Namf_Communication_Create UE Context Response or

[0117] Namf_Communication_NlN2MessageTransfer, including the TA acquisition configuration and the LTM candidate cell configuration. The core network node, or the first core network node, transmits, to the first network node 102, e.g. first gNB or first CU, a message including the TA acquisition configuration and the LTM candidate cell configuration. This message may be a HANDOVER COMMAND NGAP message or a new type of message such as a DOWNLINK RAN CONFIGURATION TRANSFER NGAP message.

[0118] The first network node 102 then transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration and the LTM candidate cell configuration. The UE 101 then stores the configuration and responds, to the first network node 102, with a message, such as an RRCReconfigurationComplete message.

[0119] In another example (Example 2A-2) of this Subset 2A, the first gNB or a first CU initiates configuration of TA acquisition after the LTM configuration but before the LTM cell switch by transmitting to the core network node (or first core network node in case of multiple core network nodes), a message including a request for a of TA acquisition configuration. The remaining parts of the procedure are the same or similar as in the previous example, except that in this example the LTM candidate cell configuration is not performed.

[0120] The first network node 102 then transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE 101 then stores the configuration and responds, to the first network node 102, with a message, such as an RRCReconfigurationComplete message.

[0121] In yet another example (Example 2A-3) of Subset 2A, the target gNB or a second CU initiates configuration of TA acquisition by preparing the TA acquisition configuration and then transmitting, to the core network node (or second core network node in case of multiple core network nodes), a message which includes a TA acquisition configuration, for one or cells, such as the second cell, controlled by the target network node. This message may be an existing message, or a new type of message, such as an UPLINK RAN CONFIGURATION TRANSFER NGAP message. The core network node, in case the second network node 103 is associated with the same core network node, then transmits, to the first gNB or first CU, a message including the TA acquisition configuration. This message may be an existing message or a new type of message, such as a DOWNLINK RAN CONFIGURATION TRANSFER NGAP message.

[0122] In case the second network node 103 is associated with a second core network node other than the first core network node, the second core network node transmits, to the first core network node, a message, such as a Namf_Communication_Create UE Context Response or Namf_Communication_NlN2MessageTransfer, including the TA acquisition configuration. The core network node, or the first core network node, transmits, to the first network node 102, e.g. first gNB or first CU, a message including the TA acquisition configuration. This message may be a HANDOVER COMMAND NGAP message or a new type of message such as a DOWNLINK RAN CONFIGURATION TRANSFER NGAP message.

[0123] The first network node 102 then transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE then stores the configuration and responds, to the first network node, with a message, such as an RRCReconfigurationComplete message.

[0124] In another subset (Subset 2B) of the Set 2 embodiments, the UE 101 is configured with dual connectivity, such as NR-DC, with a MN and a SN. In this example, the third network node 115 is a MN, sometimes also known as the master gNB, controlling an MCG for the UE 101. The first network node 102 is a source SN, also known as source secondary gNB, associated with the MN. The first network node 102 may alternatively be a source CU associated with the MN or a source DU associated with a source CU, which in turn is associated with the MN. The second network node 103 is a target SN, also known as target secondary gNB, or a target CU, or a target DU associated with a source CU in the context for inter-SN mobility, such as inter-SN LTM.

[0125] In one example (Example 2B-1) of Subset 2B, the first network node 102, e.g. source SN or a source CU, initiates configuration of TA acquisition during LTM candidate cell configuration by transmitting, to the third network node 115, e.g. the MN, a message including a request for a of TA acquisition configuration. This message may be an SN MODIFICATION REQUIRED XnAP message or a new type of message. The third network node 115 will then transmit a message, to the second network node 103, e.g. target SN, or target CU, including a request for a TA acquisition configuration. This message may be an SN ADDITION REQUEST XnAP message or a new type of message. The second network node 103 prepares the TA acquisition configuration and responds in a message, transmitted to the third network node 115, e.g. MN, including the TA acquisition configuration. This message may be an SN ADDITION REQUEST ACKNOWLEDGE XnAP message or a new type of message.

[0126] In one example, after receiving the response from the second network node 103, the third network node 115 transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE 101 then stores the configuration and responds, to the third network node 115, with a message, such as an RRCReconfigurationComplete message. The third network node then responds to the first network node with a message to confirm the configuration of TA acquisition information, such as an SN MODIFICATION CONFIRM XnAP message or a new type of message.

[0127] In another example, after receiving the response from the second network node 103, the third network node 115 responds to the first network node 102 with a message to confirm the configuration of TA acquisition information, such as an SN MODIFICATION CONFIRM XnAP message or a new type of message. The first network node 102 then transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE 101 then stores the configuration and responds, to the first network node 102, with a message, such as an RRCReconfigurationComplete message. This example may be used when an SRB3 is configured.

[0128] In another example (Example 2B-2) of Subset 2B, the first network node 102, e.g. source SN or a source CU, initiates configuration of TA acquisition after the LTM configuration but before the LTM cell switch. This example is same or similar to the previous example but it does not include LTM candidate cell configuration and different messages may be used, including new messages, such as LTM CONFIGURATION REQUEST and LTM CONFIGURATION RESPONSE. In yet another example (Example 2B-3) of Subset 2B, the second network node 103, e.g. target SN or a target CU, initiates configuration of TA acquisition by preparing the TA acquisition configuration and then transmitting, to the third network node, e.g. the MN, a message that includes the TA acquisition configuration. This message may be an existing message or a new message, such as a CONFIGURATION UPDATE message. In one example, after receiving the message from the second network node 103, the third network node 115 transmits, to the UE 101, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. In another example, after receiving the message from the second network node 103, the third network node 115 transmits a message, to the first network node 102, that includes the TA acquisition configuration. This message may be an existing message or a new message, such as a CONFIGURATION UPDATE message.

[0129] Some example embodiments of the present disclosure are as follows:

[0130] Embodiment Al. A method performed by a User Equipment, UE, controlled by a first network node to handle Timing Advance (TA) acquisition for at least one second cell, controlled by a second network node, the method comprising

[0131] • transmitting, to the second network node, a first message, such as a random access preamble,

[0132] • receiving, from the first network node, a message including an indication of a TA value for a second cell controlled by the second network node.

[0133] Embodiment Ala. The method of embodiment Al, wherein the first network node is associated with a first CU.

[0134] Embodiment Alaa. The method of embodiment Al or Ala, wherein the second network node is associated with a second CU.

[0135] Embodiment Alb. The method of embodiment Al, wherein the first network node is associated with a first CU, the second network node is associated with a second CU, and the first CU and second CU are different CUs.

[0136] Embodiment Ale. The method of embodiment Al, wherein the first network node is associated with a third network node.

[0137] Embodiment Alee. The method of embodiment Al, wherein the second network node is associated with a third network node.

[0138] Embodiment Aid. The method of embodiment Ale or Alee, wherein the third network node is a core network node. Embodiment Ale. The method of embodiment Al, wherein the first network node is associated with a first core network node and the second network node is associated with a second core network node.

[0139] Embodiment Alf. The method of embodiment Al, wherein the UE is configured with dual connectivity, such as NR-DC.

[0140] Embodiment Alg. The method of embodiment Alf, wherein the first network node is associated with a third network node, the first network node is a first Secondary Node, SN, the second network node is a second SN, and the third network node is a Master Node, MN.

[0141] Embodiment Alh. The method of embodiment Alg, wherein the first network node is associated with a first CU, the second network node is associated with a second CU, the first CU is associated with the first SN, and the second CU is associated with the second SN.

[0142] Embodiment Ali. The method of embodiment Al, wherein the message including the indication of the TA value is a MAC Control Element and / or an LTM Cell Switch command including the TA value.

[0143] Embodiment Alj. The method of embodiment Al, further comprising receiving, from the first network node, a TA acquisition configuration.

[0144] Embodiment A2. The method of embodiment Al, wherein the UE performs a mobility procedure from the first network node to the second network node to the second cell.

[0145] Embodiment A3. The method of embodiment A2, wherein the UE uses the indication of the TA value during the mobility procedure.

[0146] Embodiment A4. The method of embodiment A2 or A3, wherein the UE does not perform random access during the mobility procedure.

[0147] Embodiment A5. The method of embodiment Al, further comprising receiving, from the first network node, an indication to trigger TA acquisition for the second cell.

[0148] Embodiment A6. The method of any of embodiment A2 to A4, further comprising transmitting, to the second network node, a message confirming that the mobility procedure has been completed.

[0149] Embodiment A7. The method of any of embodiments A2 to A4 or A6, wherein the mobility procedure is triggered in response to a received indication, such as a handover command or an LTM cell switch command, from the first network node.

[0150] Embodiment A8. The method of any of embodiments A2 to A4 or A6, wherein the mobility procedure is triggered in response to a condition being fulfilled. Embodiment A9. The method of any of embodiments A2 to A4 or A6, wherein the mobility procedure is triggered in response to detecting a failure, such as radio link failure or mobility failure.

[0151] Embodiment A10. The method of embodiment A7, wherein the received indication includes the indication of a TA value.

[0152] Embodiment Al 1. The method of embodiment A7 or Al 0, wherein received indication includes an indication to the UE to not perform a random access (e.g., not perform a random access as part of the mobility procedure).

[0153] Embodiment Al 2. The method of any of embodiments A2 to A4 or A6 to Al l, wherein the mobility procedure is one of:

[0154] • An NG-based mobility procedure

[0155] • An N2-based mobility procedure

[0156] • A L3 handover procedure

[0157] • A L1 / L2 triggered mobility procedure

[0158] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0159] • A beam management procedure

[0160] • An RRC resume procedure

[0161] • An RRC re-establishment procedure

[0162] Embodiment Al 3. The method of embodiment Alj, wherein the TA acquisition configuration includes a preamble index used at transmission of random access (RA) preambles.

[0163] Embodiment Bl. A method performed by a first network node, such as a source gNB, a source CU or a source DU associated with a source CU, for handling Timing Advance (TA) acquisition for at least one second cell, controlled by a second network node, for a UE controlled by the first network node, the method comprising,

[0164] • receiving, from a second network node or a third network node, a message including an indication of one or more TA values (e.g., one or more TA values for one or more second cells controlled by the second network node); [NOTE: The receiving at the first network node can be achieved from a second network node, e.g., directly via an associated interface or via one or more third network nodes.]

[0165] • transmitting, to the UE, a message including the indication of the one or more TA values. Embodiment B2. The method of embodiment Bl, further comprising receiving, from the second network node or the third network node, a message including a TA acquisition configuration. Embodiment B3. The method of embodiment B2, further comprising transmitting, to the second network node or the third network node, a message including a request for TA acquisition configuration.

[0166] Embodiment B4. The method of any of embodiments Bl to B3, further comprising transmitting, to the UE, an indication to trigger TA acquisition for the second cell.

[0167] Embodiment B5. The method of any of embodiments Bl to B4, wherein the UE initiates a mobility procedure from the first network node to the second network node to the second cell (e.g., using the indicated TA value).

[0168] Embodiment B6. The method of embodiment B5, further comprising transmitting, to the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0169] Embodiment B7. The method of embodiment B5, further comprising receiving, from the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0170] Embodiment B8. The method of any of embodiments Bl to B7, wherein the second network node is different from the first network node or associated with a target CU different from the source CU associated with the first network node.

[0171] Embodiment B9. The method of any of embodiments Bl to B8, wherein the third network node is a core network node.

[0172] Embodiment BIO. The method of embodiment B9, wherein the core network node is not connected to the second network node.

[0173] Embodiment Bl l. The method of any of embodiments Bl to BIO, wherein the third network node is a Master Node, MN, and the UE is configured with dual connectivity.

[0174] Embodiment Bl 2. The method of embodiment B5, further comprising transmitting, to the UE, an indication, such as a handover command or an LTM cell switch command, to perform the mobility procedure to the second cell.

[0175] Embodiment Bl 3. The method of embodiment Bl 2, wherein the transmitted indication includes the indication of the TA value.

[0176] Embodiment B 14. The method of embodiment B12 or B13, wherein transmitted indication includes an indication to the UE to not perform a random access.

[0177] Embodiment B15. The method of embodiment B5, wherein the mobility procedure is one of:

[0178] An NG-based mobility procedure

[0179] An N2-based mobility procedure • A L3 handover procedure

[0180] • A L1 / L2 triggered mobility procedure

[0181] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0182] • A beam management procedure

[0183] • An RRC resume procedure

[0184] • An RRC re-establishment procedure

[0185] Embodiment B16. The method of embodiment B13, wherein the first network node sends the indication of the TA value when one or more of the following conditions are fulfilled:

[0186] • a delay over a link between the first network node and the UE is below a threshold THR1 ;

[0187] • a delay over the link between a first CU of the first network node and a first DU of the first network node is below a threshold THR2;

[0188] • a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR3;

[0189] • a delay over a link between the first network node and the UE is below a threshold THR4;

[0190] • a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR5.

[0191] Embodiment Bl 7. The method embodiment Bl, wherein, if the first network node determines that no TA value should be delivered to the UE within an indication, the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0192] Embodiment B18. The method embodiment Bl, wherein the first network node receives from the second network node or a third network node an indication that a RACH-based mobility procedure should be triggered at the UE.

[0193] Embodiment Bl 9. The method of embodiment Bl 6, wherein instead of delay the first network node may consider any one or more of the following metrics:

[0194] • Load over a link

[0195] • Number of messages over a certain time period

[0196] • Whether is possible to ping a certain node

[0197] • Indication from other node

[0198] • Number of past failures

[0199] • Number of failures over a certain time period Embodiment B20. The method of embodiment Bl, further comprising transmitting, to the second network node or the third network node, a message to request the one or more TA value(s) for the at least one second cell(s), either for the initial LTM, or subsequent LTM.

[0200] Embodiment B21. The method of embodiment B20, further comprising receiving, from the second network node or the third network node, a response message including the TA value(s) for the at least one second cell(s).

[0201] Embodiment B22. The method of embodiment B21, further comprising starting a timer when the first network node sends the message to the second network node to request the TA value(s).

[0202] • Embodiment B22a: The method of embodiment B21, wherein, when the timer expires but the first network node does not receive any TA value(s), the first network node considers the procedure as a failure and may re-send a request to the second network node.

[0203] Embodiment B23. The method of embodiment Bl, further comprising receiving, from the second network node or the third network node, a message including validity information, such as one or more validity timer(s), associated with the TA value(s).

[0204] Embodiment Cl. A method performed by a second network node, such as a target gNB, a target CU or a target DU associated with a target CU, for handling Timing Advance (TA) acquisition for a second cell or multiple candidate cells controlled by the second network node, for a UE controlled by a first network node, the method comprising:

[0205] • receiving, from the UE, a first message, such as a random access preamble;

[0206] • transmitting, to the first network node or a third network node, a second message including an indication of one or more TA value(s) for one or more second cells (e.g., one or more candidate cells) controlled by the second network node. o NOTE: The transmitting to the first network node can be achieved via a direct interface or via one or more third network nodes.

[0207] Embodiment C2. The method of embodiment Cl, further comprising transmitting, to the first network node or the third network node, a message including a TA acquisition configuration.

[0208] Embodiment C3. The method of embodiment C2, further comprising receiving, from the first network node or the third network node, a message including a request for TA acquisition configuration.

[0209] Embodiment C4. The method of embodiment Cl, wherein the UE initiates a mobility procedure from the first network node to the second network node to one of the one or more second cells (e.g., using the indicated TA value for that second cell). Embodiment C5. The method of embodiment C4, further comprising receiving, from the first network node or the third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0210] Embodiment C6. The method of embodiment C4, further comprising transmitting, to the second network node or the third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0211] Embodiment C7. The method of embodiment C4, further comprising receiving, from the UE, a message confirming that the mobility procedure has been completed or is canceled.

[0212] Embodiment C8. The method of any of embodiments Cl to C7, wherein the first network node is different from the second network node or associated with a source CU different from the target CU associated with the second network node.

[0213] Embodiment C9. The method of any of embodiments Cl to C8, wherein the third network node is a core network node.

[0214] Embodiment CIO. The method of embodiment C9, wherein the core network node is not connected to the first network node.

[0215] Embodiment Cl l. The method of any of embodiments Cl to CIO, wherein the third network node is a Master Node, MN, and the UE is configured with dual connectivity.

[0216] Embodiment Cl 2. The method of embodiment C4, wherein the UE does not perform random access during the mobility procedure.

[0217] Embodiment C13. The method of embodiment C4, wherein the mobility procedure is one of:

[0218] • An NG-based mobility procedure

[0219] • An N2-based mobility procedure

[0220] • A L3 handover procedure

[0221] • A L1 / L2 triggered mobility procedure

[0222] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0223] • A beam management procedure

[0224] • An RRC resume procedure

[0225] • An RRC re-establishment procedure

[0226] Embodiment Cl 4. The method of embodiment Cl, wherein the second network node transmits the second message (including the TA value(s)) to the first network node or third network node when one or more of the following conditions are fulfilled: • a delay over a link between the second network node and the third network node associated with the second network node is below a threshold THR6;

[0227] • a delay over a link between the second CU and the second DU is below a threshold THR7;

[0228] • a delay over a link between the second network node and third network node associated with the second network node is below a threshold THR8.

[0229] Embodiment C15. The method of embodiment Cl or C4, wherein, if the second network node determines that no TA value should be delivered to the first network node or the third network node, the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0230] Embodiment Cl 6. The method of Cl or C4 wherein the second network node indicates to the first network node or the third network node that a RACH-based mobility procedure should be triggered.

[0231] Embodiment Cl 7. The method of embodiment C4, wherein instead of delay the second network node may consider any one or more of the following metrics:

[0232] • Load over a link

[0233] • Number of messages over a certain time period

[0234] • Whether is possible to ping a certain node

[0235] • Indication from other node "

[0236] • Number of past failures

[0237] • Number of failures over a certain time period

[0238] Embodiment Cl 8. The method of embodiment Cl, further comprising receiving, from the first network node or the third network node, a message to request TA acquisition for the UE.

[0239] Embodiment Cl 9. The method of embodiment Cl 4, wherein transmitting the second message comprises transmitting, to the first network node or the third network node, a response message including the one or more TA values for the one or more second cells.

[0240] Embodiment C20. The method of embodiment Cl, wherein the second network node transmits, to the second network node or the third network node, a message, including validity information, such as validity timer(s) associated with the TA value(s).

[0241] Embodiment DI. A method performed by a third network node for handling Timing Advance (TA) acquisition for at least one second cell controlled by a second node, for a UE, controlled by a first network node, the method comprising: transmitting, to the first network node, a third message including an indication of one or more TA value(s).

[0242] Embodiment D2. The method of embodiment DI, wherein the third network node is one of

[0243] A core network node, such as an AMF, associated with the first network node • A core network node, such as an AMF, associated with the second network node

[0244] • A Master Node, MN, when the UE is configured for dual connectivity

[0245] Embodiment D3. The method of embodiment DI, further comprising receiving, from the second network node, a second message including an indication of the one or more TA value(s).

[0246] Embodiment D4. The method of embodiment DI, wherein the one or more TA values are for one or more second cells controlled by the second network node.

[0247] Embodiment D5. The method of embodiment DI, wherein the second network node is a core network node.

[0248] Embodiment D6. The method in embodiment DI, further comprising receiving, from the second network node, a message comprising an indication indicating that a mobility procedure for the UE is successfully completed or is canceled.

[0249] Embodiment D7. The method of embodiment DI , wherein the third network node transmits the third message to the first network node when one or more of the following conditions are fulfilled:

[0250] • a delay over a link between the first network node and the third network node is below a threshold THR9;

[0251] • a delay over a link between the third network node and the second network node is below a threshold THR10;

[0252] • a delay over a link between the first network node and the third network node is below a threshold THRU.

[0253] Embodiment D8. The method of embodiment DI or D7, wherein the third network node determines that no TA value should be delivered to the first network node and the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0254] Embodiment D9. The method of embodiment D8, wherein the third network node indicates to the first network node that a RACH-based mobility procedure should be triggered.

[0255] Embodiment DIO. The method of embodiment D8, wherein the third network node receives from the second CN node an indication that a RACH-based mobility procedure should be triggered.

[0256] Embodiment Dl l. The method in embodiment D7, wherein instead of delay the third network node may consider any one or more of the following metrics:

[0257] • Load over a link

[0258] Number of messages over a certain time period Whether is possible to ping a certain node Indication from other node " • Number of past failures

[0259] • Number of failures over a certain time period

[0260] Embodiment DI 2. The method of embodiments D3 and D4 wherein the third network node receives, from the second network node, a message, including validity information, such as validity timer(s) corresponding to the TA value(s).

[0261] Figures 4A and 4B (sometimes collectively referred to herein as Figure 4) illustrate a message sequence chart in accordance with one example embodiment of the present disclosure. In this example, a configuration of TA acquisition is performed as part of LTM configuration, where the first network node (source DU, source CU) and the second network node (target DU, target CU) has an Xn connection and a Timing Advance is acquired for a second cell controlled by the target DU and target CU, in order to perform a RACH-less LTM cell switch.

[0262] Referring to Figure 4, the steps in this example are as follows.

[0263] Step 400: The source CU transmits a request message to the target CU to request configuration of TA acquisition for a target candidate cell. This message may be a HANDOVER REQUEST message or a new message.

[0264] Steps 402-404: The target CU prepares the TA acquisition configuration and the LTM candidate cell configuration and as part of this, requests at least part of this information from the target DU.

[0265] Step 406: The target CU responds in a message, transmitted to the source CU, including the TA acquisition configuration and the LTM candidate cell configuration. This message may be a HANDOVER REQUEST ACKNOWLEDGE message or a new message.

[0266] Steps 408-416: The source CU then transmits, to the UE, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE then stores the configuration and responds, to the source CU, with a message, such as an RRCReconfigurationComplete message.

[0267] Step 418: The source DU triggers the TA acquisition by transmitting a lower layer signaling, such as a PDCCH order, to the UE. This signaling may include indication of TA acquisition configuration, such as preamble index(es) for a least one second cell, e.g. an LTM candidate cell.

[0268] Step 420: The UE transmits a random access preamble, to the second cell, to the target DU.

[0269] Step 422-424: The target DU calculates a Timing Advance (TA) value based on the received transmission from the UE and transmits the TA value to the target CU in a DU-CU TA INFO NOTIFICATION message. Step 426: The target CU includes an indication of the TA value in a message (in the context of this description also known as the second message) transmitted to the source CU. The message may be a new message, such as TA INFORMATION NOTIFICATION.

[0270] Step 428: The source CU forwards the TA value to the source DU in a CU-DU TA INFO NOTIFICATION message.

[0271] Step 430: The source DU triggers an LTM cell switch for the UE, e.g. based on received LI measurement reports from the UE and transmits an LTM cell switch command. The command includes the TA value and indication of the LTM candidate cell (second cell).

[0272] Steps 432-434: The UE executes an LTM cell switch to the second cell, avoiding performing random access and sends an RRCReconfigurationComplete message to the target DU which forwards the message to the target CU.

[0273] Figures 5 A and 5B (sometimes collectively referred to herein as Figure 5) illustrates a message sequence chart in accordance with another example embodiment of the present disclosure. In this example, a configuration of TA acquisition is performed as part of inter-CU LTM configuration, where the first network node (source gNB) and the second network node (target gNB) does not have an Xn connection and they are associated with different core network nodes (source AMF and target AMF, respectively).

[0274] A Timing Advance is then acquired for a second cell (in the example also referred to as target candidate cell) controlled by the target gNB, in order to perform a RACH-less LTM cell switch between the gNBs.

[0275] Referring to Figure 5, the steps in this example are as follows.

[0276] Step 500: The source gNB transmits a request message to the source AMF to request configuration of TA acquisition for a target candidate cell. The request message may be an existing NGAP message, such as a HANDOVER REQUIRED message, or a new message, such as an UPLINK RAN CONFIGURATION TRANSFER message. In this example, the message also includes a request to generate an LTM candidate cell configuration and it also includes an identity of the target candidate cell.

[0277] Step 502: The source AMF signal to a target AMF for the LTM candidate cell as the target AMF is in this example different than the source AMF. The source AMF transmits a Namf_Communication_CreateUEContext Request message to the target AMF to request to request configuration of TA acquisition. In this example, the message also includes a request to generate an LTM candidate cell configuration and it also includes an identity of the target candidate cell. Step 504: The target AMF sends a request message, to the target gNB to request to request configuration of TA acquisition. In this example, the message also includes a request to generate an LTM candidate cell configuration and it also includes an identity of the target candidate cell.

[0278] Step 506: The target gNB prepares the TA acquisition configuration and an LTM candidate cell configuration. The target gNB responds to the target AMF with a message that includes the TA acquisition configuration and an LTM candidate cell configuration for the target candidate cell. This message may be an existing NGAP message, such as a HANDOVER REQUEST ACKNOWLEDGE message, or a new message.

[0279] Step 508: The target AMF responds to the source AMF with a

[0280] Namf_Communication_CreateUEContext Response message that includes the TA acquisition configuration and an LTM candidate cell configuration for the target candidate cell.

[0281] Step 510: The source AMF responds to the source gNB in a message that includes the TA acquisition configuration and an LTM candidate cell configuration for the target candidate cell. This message may be an existing NGAP message, such as a HANDOVER COMMAND message or a new message.

[0282] Step 512: The source gNB transmits, to the UE, the TA acquisition configuration and an LTM candidate cell configuration for the target candidate cell in an RRCReconfiguration message.

[0283] Steps 514-516: The UE stores the received TA acquisition configuration and an LTM candidate cell configuration for the target candidate cell and responds with an RRCReconfigurationComplete message to the source gNB.

[0284] Step 518: The source gNB transmits to the UE an indication, in lower layer signalling, such as a PDCCH order, to trigger TA acquisition for the target cell that is in the target gNB. The indication may include an indication of a TA acquisition configuration, such as a preamble index and an identifier of the LTM candidate cell for the target cell.

[0285] Step 520: The UE sends a random access preamble to the target gNB in the target cell, using the indicated TA acquisition configuration.

[0286] Step 522: The target gNB determines a Timing Advance, TA, value based on the received transmission from the UE.

[0287] Step 524: The target gNB signals the TA value in a message transmitted to the target core network node. This message may be an existing NGAP message, such as an Uplink RAN Status Transfer message, message, or a new message such as UL TA INFO NOTIFICATION.

[0288] Step 526-528: The target AMF sends this information to the source AMF via the Namf_Communication_NlN2MessageTransfer service operation and the source AMF acknowledges. Step 530: The source AMF signals the TA value in a message transmitted to the source gNB. This message may be an existing NGAP message, such as a Downlink RAN Status Transfer message, message, or a new message such as DL TA INFO NOTIFICATION.

[0289] Steps 532-534: The UE performs LI measurements on the configured LTM candidate cells, including the at least NG-based LTM candidate cells and transmits LI measurement reports to the source gNB. The source gNB decides to trigger an LTM cell switch for the UE and transmits an LTM cell switch command to the UE, including the TA value and indication of the LTM candidate cell.

[0290] Steps 536-538: The UE performs LTM switch to the second cell controlled by the target gNB avoiding to perform random access and sends an RRCReconfigurationComplete message to the target gNB.

[0291] Figures 6A and 6B (sometimes collectively referred to herein as Figure 6) illustrate a message sequence chart in accordance with another example embodiment of the present disclosure. In this example, the UE is configured with NR-DC, and a configuration of TA acquisition is performed as part of LTM configuration. Then the UE executes an inter-CU LTM procedure for the SCG, also known as an inter-SN LTM procedure. In this example, the source SN corresponds to the first network node, the target SN corresponds to the second network node and the Master Node, MN, corresponds to the third network node.

[0292] In this example, a Timing Advance is acquired for a second cell controlled by the target SN, in order to perform a RACH-less LTM cell switch towards the second cell controlled by the target SN.

[0293] Referring to Figure 6, the main steps in this example are as follows.

[0294] Step 600: The source SN initiates the configuration of LTM and TA acquisition by transmitting an SN MODIFICATION REQUIRED XnAP message (or a new type of message) to the MN.

[0295] Step 602: The MN transmits a SN ADDITION REQUEST XnAP message (or a new type of message) to the target SN to request configuration of TA acquisition and an LTM candidate cell.

[0296] Step 604: The target SN prepares the TA acquisition configuration, it responds in a message, transmitted, to the MN, including the TA acquisition configuration. This message may be an SN ADDITION REQUEST ACKNOWLEDGE XnAP message or a new type of message.

[0297] Steps 606-610: In this example, after receiving the response from the target SN, the MN transmits, to the UE, a message, such as an RRCReconfiguration message, including the TA acquisition configuration. The UE then stores the configuration and responds, to the MN, with a message, such as an RRCReconfigurationComplete message.

[0298] Step 612: The MN then responds to the source SN with a message to confirm the configuration of TA acquisition information, such as an SN MODIFICATION CONFIRM XnAP message or a new type of message.

[0299] Step 614: The source SN transmits to the UE an indication, in lower layer signalling, such as a PDCCH order, to trigger TA acquisition for the target cell (second cell) that is in the target SN. The indication may include an indication of a TA acquisition configuration, such as a preamble index and an identifier of the LTM candidate cell for the target cell.

[0300] Step 616: The UE sends a random access preamble to the target SN in the target cell, using the indicated TA acquisition configuration.

[0301] Step 618: The target SN determines a Timing Advance, TA, value based on the received transmission from the UE.

[0302] Steps 620-622: The target SN transmits the indication of the TA value in a message to the MN, which forwards the information to the source SN in a message. These messages may be a new type of message, such as SCG TA INFORMATION NOTIFICATION.

[0303] Step 624: The source SN decides to trigger an LTM cell switch for the UE and transmits an LTM cell switch command to the UE, including the TA value and indication of the LTM candidate cell, i.e. the target cell.

[0304] Steps 626-632: The UE performs LTM switch to the second cell controlled by the target SN, avoiding to perform random access in the target cell, and sends an RRCReconfigurationComplete message to the MN. The MN indicates to the target SN the execution of SCG mobility for the UE and modifies (or deletes) the UE context in the source SN.

[0305] Some other embodiments of the present disclosure are as follows. In one embodiment, the first network node sends to the UE, as part of an LTM configuration for a candidate cell, an indication instructing the UE to use RACH based LTM towards that LTM candidate cell, due to an expected high (or extra) delay in TA acquisition for the LTM candidate cell. Examples of reasons for the expected high (or extra) delay can be any one, or a combination of: Xn connection is not setup or not enabled (or is temporarily not available) between the first network node serving the source cell and the second network node serving the LTM candidate cell; the source cells and the LTM candidate cells are served by different gNB-CUs; a security key change is needed; the Fl delay between the gNB-CU and the gNB-DU controlling the source cell in the first network node is higher than a threshold; the Fl delay between the gNB-CU and the gNB-DU controlling the candidate LTM cell in the second network node is higher than a threshold; the first network node and the second network node are connected to different AMFs.

[0306] In this case, the UE receiving the indication is instructed to perform normal RACH procedure (instead of RACH-less) during the LTM execution.

[0307] Figure 7 shows an example of a communication system 700 in accordance with some embodiments.

[0308] In the example, the communication system 700 includes a telecommunication network 702 that includes an access network 704, such as a Radio Access Network (RAN), and a core network 706, which includes one or more core network nodes 708. The access network 704 includes one or more access network nodes, such as network nodes 710A and 710B (one or more of which may be generally referred to as network nodes 710), or any other similar Third Generation Partnership Project (3GPP) access nodes or non-3GPP Access Points (APs). 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, the telecommunication network 702 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 702 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 the telecommunication network 702, including one or more network nodes 710 and / or core network nodes 708.

[0309] 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 adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. The network nodes 710 facilitate direct or indirect connection of User Equipment (UE), such as by connecting UEs 712A, 712B, 712C, and 712D (one or more of which may be generally referred to as UEs 712) to the core network 706 over one or more wireless connections.

[0310] 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, the communication system 700 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. The communication system 700 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0311] The UEs 712 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with the network nodes 710 and other communication devices. Similarly, the network nodes 710 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 712 and / or with other network nodes or equipment in the telecommunication network 702 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in the telecommunication network 702.

[0312] In the depicted example, the core network 706 connects the network nodes 710 to one or more hosts, such as host 716. 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. The core network 706 includes one more core network nodes (e.g., core network node 708) 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 the core network node 708. 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). The host 716 may be under the ownership or control of a service provider other than an operator or provider of the access network 704 and / or the telecommunication network 702, and may be operated by the service provider or on behalf of the service provider. The host 716 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.

[0313] As a whole, the communication system 700 of Figure 7 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system 700 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 Second, Third, Fourth, or Fifth Generation (2G, 3G, 4G, or 5G) standards, or any applicable future generation standard (e.g., Sixth Generation (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.

[0314] In some examples, the telecommunication network 702 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunication network 702 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 702. For example, the telecommunication network 702 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 Internet of Things (loT) services to yet further UEs.

[0315] In some examples, the UEs 712 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 704 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 704. Additionally, a UE may be configured for operating in single- or multi-Radio Access Technology (RAT) or multi-standard mode. For example, a UE may operate with any one or combination of WiFi, New Radio (NR), and LTE, i.e. being configured for Multi-Radio Dual Connectivity (MR-DC), such as Evolved UMTS Terrestrial RAN (E-UTRAN) NR - Dual Connectivity (EN-DC).

[0316] In the example, a hub 714 communicates with the access network 704 to facilitate indirect communication between one or more UEs (e.g., UE 712C and / or 712D) and network nodes (e.g., network node 71 OB). In some examples, the hub 714 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 714 may be a broadband router enabling access to the core network 706 for the UEs. As another example, the hub 714 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 710, or by executable code, script, process, or other instructions in the hub 714. As another example, the hub 714 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, the hub 714 may be a content source. For example, for a UE that is a Virtual Reality (VR) headset, display, loudspeaker or other media delivery device, the hub 714 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 714 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 714 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0317] The hub 714 may have a constant / persistent or intermittent connection to the network node 710B. The hub 714 may also allow for a different communication scheme and / or schedule between the hub 714 and UEs (e.g., UE 712C and / or 712D), and between the hub 714 and the core network 706. In other examples, the hub 714 is connected to the core network 706 and / or one or more UEs via a wired connection. Moreover, the hub 714 may be configured to connect to a Machine-to-Machine (M2M) service provider over the access network 704 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 710 while still connected via the hub 714 via a wired or wireless connection. In some embodiments, the hub 714 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to the network node 710B. In other embodiments, the hub 714 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and the network node 710B, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0318] Figure 8 shows a UE 800 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged, and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, Voice over Internet Protocol (VoIP) phone, wireless local loop phone, desktop computer, Personal Digital Assistant (PDA), wireless camera, 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 the 3GPP, including aNarrowband Internet of Things (NB-IoT) UE, a Machine Type Communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0319] 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).

[0320] The UE 800 includes processing circuitry 802 that is operatively coupled via a bus 804 to an input / output interface 806, a power source 808, memory 810, a communication interface 812, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 8. 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.

[0321] The processing circuitry 802 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 the memory 810. The processing circuitry 802 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, the processing circuitry 802 may include multiple Central Processing Units (CPUs). In the example, the input / output interface 806 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 the UE 800. 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.

[0322] In some embodiments, the power source 808 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. The power source 808 may further include power circuitry for delivering power from the power source 808 itself, and / or an external power source, to the various parts of the UE 800 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 808. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 808 to make the power suitable for the respective components of the UE 800 to which power is supplied.

[0323] The memory 810 may be or be configured to include memory such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 810 includes one or more application programs 814, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 816. The memory 810 may store, for use by the UE 800, any of a variety of various operating systems or combinations of operating systems.

[0324] The memory 810 may be configured to include a number of physical drive units, such as Redundant Array of Independent Disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, High Density Digital Versatile Disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, Holographic Digital Data Storage (HDDS) optical disc drive, external mini Dual In-line Memory Module (DIMM), Synchronous Dynamic RAM (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a tamper resistant module in the form of a Universal Integrated Circuit Card (UICC) including one or more Subscriber Identity Modules (SIMs), such as a Universal SIM (USIM) and / or Internet Protocol Multimedia Services Identity Module (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 a ‘SIM card.’ The memory 810 may allow the UE 800 to access instructions, application programs, and the like stored on transitory or non-transitory memory media, to off-load data, or to upload data. An article of manufacture, such as one utilizing a communication system, may be tangibly embodied as or in the memory 810, which may be or comprise a device-readable storage medium.

[0325] The processing circuitry 802 may be configured to communicate with an access network or other network using the communication interface 812. The communication interface 812 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 822. The communication interface 812 may include one or more transceivers used to communicate, such as by communicating with one or more remote transceivers of another device capable of wireless communication (e.g., another UE or a network node in an access network). Each transceiver may include a transmitter 818 and / or a receiver 820 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 818 and receiver 820 may be coupled to one or more antennas (e.g., the antenna 822) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0326] In the illustrated embodiment, communication functions of the communication interface 812 may include cellular communication, WiFi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, NFC, location-based communication such as the use of the Global Positioning System (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband CDMA (WCDMA), GSM, LTE, NR, UMTS, WiMax, Ethernet, Transmission Control Protocol / Intemet Protocol (TCP / IP), Synchronous Optical Networking (SONET), Asynchronous Transfer Mode (ATM), Quick User Datagram Protocol Internet Connection (QUIC), Hypertext Transfer Protocol (HTTP), and so forth.

[0327] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 812, 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).

[0328] 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.

[0329] A UE, when in the form of an 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 television, 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 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 the UE 800 shown in Figure 8.

[0330] 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, an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0331] 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.

[0332] Figure 9 shows a network node 900 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment in a telecommunication network. Examples of network nodes include, but are not limited to, APs (e.g., radio APs), Base Stations (BSs) (e.g., radio BSs, Node Bs, evolved Node Bs (eNBs), NR Node Bs (gNBs)), and O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0333] 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 RRUs 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).

[0334] Other examples of network nodes include multiple Transmission Point (multi-TRP) 5G access nodes, Multi-Standard Radio (MSR) equipment such as MSR BSs, network controllers such as Radio Network Controllers (RNCs) or BS 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).

[0335] The network node 900 includes processing circuitry 902, memory 904, a communication interface 906, and a power source 908. The network node 900 may be composed of multiple physically separate components (e.g., a NodeB component and an RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 900 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, the network node 900 may be configured to support multiple RATs. In such embodiments, some components may be duplicated (e.g., separate memory 904 for different RATs) and some components may be reused (e.g., a same antenna 910 may be shared by different RATs). The network node 900 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 900, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, Long Range Wide Area Network (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 the network node 900.

[0336] The processing circuitry 902 may comprise a combination of one or more of a microprocessor, controller, microcontroller, CPU, DSP, ASIC, FPGA, 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 900 components, such as the memory 904, to provide network node 900 functionality.

[0337] In some embodiments, the processing circuitry 902 includes a System on a Chip (SOC). In some embodiments, the processing circuitry 902 includes one or more of Radio Frequency (RF) transceiver circuitry 912 and baseband processing circuitry 914. In some embodiments, the RF transceiver circuitry 912 and the baseband processing circuitry 914 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 the RF transceiver circuitry 912 and the baseband processing circuitry 914 may be on the same chip or set of chips, boards, or units.

[0338] The memory 904 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, RAM, 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 the processing circuitry 902. The memory 904 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 capable of being executed by the processing circuitry 902 and utilized by the network node 900. The memory 904 may be used to store any calculations made by the processing circuitry 902 and / or any data received via the communication interface 906. In some embodiments, the processing circuitry 902 and the memory 904 are integrated.

[0339] The communication interface 906 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 906 comprises port(s) / terminal(s) 916 to send and receive data, for example to and from a network over a wired connection. The communication interface 906 also includes radio front-end circuitry 918 that may be coupled to, or in certain embodiments a part of, the antenna 910. The radio front-end circuitry 918 comprises filters 920 and amplifiers 922. The radio front-end circuitry 918 may be connected to the antenna 910 and the processing circuitry 902. The radio front-end circuitry 918 may be configured to condition signals communicated between the antenna 910 and the processing circuitry 902. The radio front-end circuitry 918 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 918 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 920 and / or the amplifiers 922. The radio signal may then be transmitted via the antenna 910. Similarly, when receiving data, the antenna 910 may collect radio signals which are then converted into digital data by the radio front-end circuitry 918. The digital data may be passed to the processing circuitry 902. In other embodiments, the communication interface 906 may comprise different components and / or different combinations of components.

[0340] In certain alternative embodiments, the network node 900 does not include separate radio front-end circuitry 918; instead, the processing circuitry 902 includes radio front-end circuitry and is connected to the antenna 910. Similarly, in some embodiments, all or some of the RF transceiver circuitry 912 is part of the communication interface 906. In still other embodiments, the communication interface 906 includes the one or more ports or terminals 916, the radio front-end circuitry 918, and the RF transceiver circuitry 912 as part of a radio unit (not shown), and the communication interface 906 communicates with the baseband processing circuitry 914, which is part of a digital unit (not shown).

[0341] The antenna 910 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 910 may be coupled to the radio front-end circuitry 918 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 910 is separate from the network node 900 and connectable to the network node 900 through an interface or port.

[0342] The antenna 910, the communication interface 906, and / or the processing circuitry 902 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node 900. Any information, data, and / or signals may be received from a UE, another network node, and / or any other network equipment. Similarly, the antenna 910, the communication interface 906, and / or the processing circuitry 902 may be configured to perform any transmitting operations described herein as being performed by the network node 900. Any information, data, and / or signals may be transmitted to a UE, another network node, and / or any other network equipment.

[0343] The power source 908 provides power to the various components of the network node 900 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 908 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 900 with power for performing the functionality described herein. For example, the network node 900 may be connectable to an external power source (e.g., the power grid or an electricity outlet) via input circuitry or an interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 908. As a further example, the power source 908 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0344] Embodiments of the network node 900 may include additional components beyond those shown in Figure 9 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, the network node 900 may include user interface equipment to allow input of information into the network node 900 and to allow output of information from the network node 900. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 900. In some embodiments providing a core network node, such as core network node 108 of FIG. 7, some components, such as the radio frontend circuitry 918 and the RF transceiver circuitry 912 may be omitted.

[0345] Figure 10 is a block diagram illustrating a virtualization environment 1000 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 virtualization environments 1000 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, a UE, a core network node, or a 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 1000 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. Virtualization may facilitate distributed implementations of a network node, a UE, a core network node, or a host.

[0346] Applications 1002 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1000 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0347] Hardware 1004 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, an input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1006 (also referred to as hypervisors or Virtual Machine Monitors (VMMs)), provide VMs 1008A and 1008B (one or more of which may be generally referred to as VMs 1008), and / or perform any of the functions, features, and / or benefits described in relation with some embodiments described herein. The virtualization layer 1006 may present a virtual operating platform that appears like networking hardware to the VMs 1008.

[0348] The VMs 1008 comprise virtual processing, virtual memory, virtual networking, or interface and virtual storage, and may be run by a corresponding virtualization layer 1006. Different embodiments of the instance of a virtual appliance 1002 may be implemented on one or more of VMs 1008, 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. In the context of NFV, a VM 1008 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1008, and that part of the hardware 1004 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 1008 on top of the hardware 1004 and corresponds to the application 1002.

[0349] The hardware 1004 may be implemented in a standalone network node with generic or specific components. The hardware 1004 may implement some functions via virtualization. Alternatively, the hardware 1004 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 1010, which, among others, oversees lifecycle management of the applications 1002. In some embodiments, the hardware 1004 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 1012 which may alternatively be used for communication between hardware nodes and radio units.

[0350] Although the computing devices described herein (e.g., UEs, network nodes) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or software needed to perform the tasks, features, functions, and methods disclosed herein. Determining, calculating, obtaining, or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components that make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non- computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[0351] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non-transitory computer-readable storage medium or not, the processing circuitry can be configured to perform the described functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

[0352] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

[0353] Some exemplary embodiments of the present disclosure are as follows:

[0354] Group A Embodiments

[0355] Embodiment 1: A method performed by a User Equipment, UE, controlled by a first network node, for handling Timing Advance, TA, acquisition for at least one second cell controlled by a second network node, the method comprising: transmitting (200; 300; 420; 520; 616), to the second network node, a first message (e.g., a random access preamble); and receiving (204; 306; 430; 534; 624), from the first network node, a message including an indication of a TA value for a second cell controlled by the second network node.

[0356] Embodiment 2: The method of embodiment 1, wherein the first network node is associated with a first Central Unit, CU.

[0357] Embodiment 3 : The method of embodiment 1 or 2, wherein the second network node is associated with a second CU.

[0358] Embodiment 4: The method of embodiment 1, wherein the first network node is associated with a first CU, the second network node is associated with a second CU, and the first CU and second CU are different CUs. Embodiment 5: The method of embodiment 1, wherein the first network node is associated with a third network node.

[0359] Embodiment 6: The method of embodiment 1, wherein the second network node is associated with a third network node.

[0360] Embodiment 7: The method of embodiment 5 or 6, wherein the third network node is a core network node.

[0361] Embodiment 8: The method of embodiment 1, wherein the first network node is associated with a first core network node and the second network node is associated with a second core network node.

[0362] Embodiment 9: The method of embodiment 1, wherein the UE is configured with dual connectivity (e.g., NR-DC).

[0363] Embodiment 10: The method of embodiment 9, wherein the first network node is associated with a third network node, the first network node is a first Secondary Node, SN, the second network node is a second SN, and the third network node is a Master Node, MN.

[0364] Embodiment 11: The method of embodiment 10, wherein the first network node is associated with a first CU, the second network node is associated with a second CU, the first CU is associated with the first SN, and the second CU is associated with the second SN.

[0365] Embodiment 12: The method of embodiment 1, wherein the message including the indication of the TA value is a MAC Control Element and / or an LTM Cell Switch command including the TA value.

[0366] Embodiment 13: The method of embodiment 1, further comprising receiving (410; 512; 606), from the first network node, a TA acquisition configuration.

[0367] Embodiment 14: The method of embodiment 13, wherein the TA acquisition configuration includes a preamble index used at transmission of random access (RA) preambles.

[0368] Embodiment 15: The method of any of embodiments 1 to 14, wherein the UE performs a mobility procedure from the first network node to the second network node to the second cell.

[0369] Embodiment 16: The method of embodiment 15, wherein the UE uses the indication of the TA value during the mobility procedure.

[0370] Embodiment 17: The method of embodiment 15 or 16, wherein the UE does not perform random access during the mobility procedure.

[0371] Embodiment 18: The method of embodiment 1, further comprising receiving (418; 518; 614), from the first network node, an indication to trigger TA acquisition for the second cell. Embodiment 19: The method of any of embodiments 15 to 17, further comprising transmitting (432; 538; 626), to the second network node, a message confirming that the mobility procedure has been completed.

[0372] Embodiment 20: The method of any of embodiments 15 to 17 or 19, wherein the mobility procedure is triggered in response to a received indication, such as a handover command or an LTM cell switch command, from the first network node.

[0373] Embodiment 21 : The method of any of embodiments 15 to 17 or 19, wherein the mobility procedure is triggered in response to a condition being fulfilled.

[0374] Embodiment 22: The method of any of embodiments 15 to 17 or 19, wherein the mobility procedure is triggered in response to detecting a failure, such as radio link failure or mobility failure.

[0375] Embodiment 23 : The method of embodiment 20, wherein the received indication includes the indication of a TA value.

[0376] Embodiment 24: The method of embodiment 20 or 23, wherein received indication includes an indication to the UE to not perform a random access (e.g., not perform a random access as part of the mobility procedure).

[0377] Embodiment 25: The method of any of embodiments 15 to 17 or 19 to 24, wherein the mobility procedure is one of:

[0378] • An NG-based mobility procedure

[0379] • An N2-based mobility procedure

[0380] • A L3 handover procedure

[0381] • A L1 / L2 triggered mobility procedure

[0382] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0383] • A beam management procedure

[0384] • An RRC resume procedure

[0385] • An RRC re-establishment procedure

[0386] Group B Embodiments

[0387] Embodiment 26: A method performed by a first network node (e.g., a source gNB, a source CU or a source DU associated with a source CU) for handling Timing Advance, TA, acquisition for at least one second cell controlled by a second network node, for a UE controlled by the first network node, the method comprising: receiving (202; 304; 426 or 428; 530; 622), from a second network node or a third network node, a message including an indication of one or more TA values (e.g., one or more TA values for one or more second cells controlled by the second network node); and transmitting (204; 306; 430; 532; 624), to the UE, a message including the indication of the one or more TA values.

[0388] Embodiment 27: The method of embodiment 26, further comprising receiving (406 or 408; 510; 604), from the second network node or the third network node, a message including a TA acquisition configuration.

[0389] Embodiment 28: The method of embodiment 27, further comprising transmitting (400; 500; 600), to the second network node or the third network node, a message including a request for TA acquisition configuration.

[0390] Embodiment 29: The method of any of embodiments 26 to 28, further comprising transmitting (410; 518; 614), to the UE, an indication to trigger TA acquisition for the second cell.

[0391] Embodiment 30: The method of any of embodiments 26 to 29, wherein the UE initiates a mobility procedure from the first network node to the second network node to the second cell (e.g., using the indicated TA value).

[0392] Embodiment 31: The method of embodiment 30, further comprising transmitting, to the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0393] Embodiment 32: The method of embodiment 30, further comprising receiving, from the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0394] Embodiment 33: The method of any of embodiments 26 to 32, wherein the second network node is different from the first network node or associated with a target CU different from the source CU associated with the first network node.

[0395] Embodiment 34: The method of any of embodiments 26 to 33, wherein the third network node is a core network node.

[0396] Embodiment 35: The method of embodiment 34, wherein the core network node is not connected to the second network node.

[0397] Embodiment 36: The method of any of embodiments 26 to 35, wherein the third network node is a Master Node, MN, and the UE is configured with dual connectivity.

[0398] Embodiment 37: The method of embodiment 30, further comprising transmitting, to the UE, an indication, such as a handover command or an LTM cell switch command, to perform the mobility procedure to the second cell.

[0399] Embodiment 38: The method of embodiment 37, wherein the transmitted indication includes the indication of the TA value. Embodiment 39: The method of embodiment 37 or 38, wherein transmitted indication includes an indication to the UE to not perform a random access.

[0400] Embodiment 40: The method of embodiment 30, wherein the mobility procedure is one of:

[0401] • An NG-based mobility procedure

[0402] • An N2-based mobility procedure

[0403] • A L3 handover procedure

[0404] • A L1 / L2 triggered mobility procedure

[0405] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0406] • A beam management procedure

[0407] • An RRC resume procedure

[0408] • An RRC re-establishment procedure

[0409] Embodiment 41 : The method of embodiment 38, wherein the first network node sends the indication of the TA value when one or more of the following conditions are fulfilled:

[0410] • a delay over a link between the first network node and the UE is below a threshold THR1 ;

[0411] • a delay over the link between a first CU of the first network node and a first DU of the first network node is below a threshold THR2;

[0412] • a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR3;

[0413] • a delay over a link between the first network node and the UE is below a threshold THR4;

[0414] • a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR5.

[0415] Embodiment 42: The method of embodiment 26, wherein, if the first network node determines that no TA value should be delivered to the UE within an indication, the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0416] Embodiment 43: The method of embodiment 26, wherein the first network node receives from the second network node or a third network node an indication that a RACH-based mobility procedure should be triggered at the UE.

[0417] Embodiment 44: The method of embodiment 41, wherein instead of delay the first network node may consider any one or more of the following metrics:

[0418] • Load over a link

[0419] Number of messages over a certain time period

[0420] Whether is possible to ping a certain node • Indication from other node

[0421] • Number of past failures

[0422] • Number of failures over a certain time period

[0423] Embodiment 45: The method of embodiment 26, further comprising transmitting, to the second network node or the third network node, a message to request the one or more TA value(s) for the at least one second cell(s), either for the initial LTM, or subsequent LTM.

[0424] Embodiment 46: The method of embodiment 45, further comprising receiving, from the second network node or the third network node, a response message including the TA value(s) for the at least one second cell(s).

[0425] Embodiment 47 : The method of embodiment 46, further comprising starting a timer when the first network node sends the message to the second network node to request the TA value(s).

[0426] Embodiment 48: The method of embodiment 47, wherein, when the timer expires but the first network node does not receive any TA value(s), the first network node considers the procedure as a failure and may re-send a request to the second network node.

[0427] Embodiment 49: The method of embodiment 26, further comprising receiving, from the second network node or the third network node, a message including validity information, such as one or more validity timer(s), associated with the TA value(s).

[0428] Embodiment 50: A method performed by a second network node (e.g., a target gNB, a target CU or a target DU associated with a target CU) for handling Timing Advance (TA) acquisition for a second cell or multiple candidate cells controlled by the second network node, for a UE controlled by a first network node, the method comprising: receiving (200), from the UE, a first message (e.g., a random access preamble); and transmitting (202; 302), to the first network node or a third network node, a second message including an indication of one or more TA values for one or more second cells (e.g., one or more candidate cells) controlled by the second network node.

[0429] Embodiment 51 : The method of embodiment 50, further comprising transmitting, to the first network node or the third network node, a message including a TA acquisition configuration.

[0430] Embodiment 52: The method of embodiment 51, further comprising receiving, from the first network node or the third network node, a message including a request for TA acquisition configuration.

[0431] Embodiment 53: The method of embodiment 50, wherein the UE initiates a mobility procedure from the first network node to the second network node to one of the one or more second cells (e.g., using the indicated TA value for that second cell). Embodiment 54: The method of embodiment 53, further comprising receiving, from the first network node or the third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0432] Embodiment 55: The method of embodiment 53, further comprising transmitting, to the second network node or the third network node, an indication of a mobility procedure initiated by the UE to the second cell.

[0433] Embodiment 56: The method of embodiment 53, further comprising receiving, from the UE, a message confirming that the mobility procedure has been completed or is canceled.

[0434] Embodiment 57: The method of any of embodiments 50 to 56, wherein the first network node is different from the second network node or associated with a source CU different from the target CU associated with the second network node.

[0435] Embodiment 58: The method of any of embodiments 50 to 57, wherein the third network node is a core network node.

[0436] Embodiment 59: The method of embodiment 58, wherein the core network node is not connected to the first network node.

[0437] Embodiment 60: The method of any of embodiments 50 to 59, wherein the third network node is a Master Node, MN, and the UE is configured with dual connectivity.

[0438] Embodiment 61 : The method of embodiment 53, wherein the UE does not perform random access during the mobility procedure.

[0439] Embodiment 62: The method of embodiment 53, wherein the mobility procedure is one of:

[0440] • An NG-based mobility procedure

[0441] • An N2-based mobility procedure

[0442] • A L3 handover procedure

[0443] • A L1 / L2 triggered mobility procedure

[0444] • A conditional reconfiguration procedure, such as conditional handover, conditional PSCell addition or Conditional PSCell change

[0445] • A beam management procedure

[0446] • An RRC resume procedure

[0447] • An RRC re-establishment procedure

[0448] Embodiment 63: The method of embodiment 50, wherein the second network node transmits the second message (including the TA value(s)) to the first network node or third network node when one or more of the following conditions are fulfilled:

[0449] • a delay over a link between the second network node and the third network node associated with the second network node is below a threshold THR6; • a delay over a link between the second CU and the second DU is below a threshold THR7;

[0450] • a delay over a link between the second network node and third network node associated with the second network node is below a threshold THR8.

[0451] Embodiment 64: The method of embodiment 50 or 53, wherein, if the second network node determines that no TA value should be delivered to the first network node or the third network node, the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0452] Embodiment 65: The method of embodiment 50 or 53 wherein the second network node indicates to the first network node or the third network node that a RACH-based mobility procedure should be triggered.

[0453] Embodiment 66: The method of embodiment 53, wherein instead of delay the second network node may consider any one or more of the following metrics:

[0454] • Load over a link

[0455] • Number of messages over a certain time period

[0456] • Whether is possible to ping a certain node

[0457] • Indication from other node "

[0458] • Number of past failures

[0459] • Number of failures over a certain time period

[0460] Embodiment 67: The method of embodiment 50, further comprising receiving, from the first network node or the third network node, a message to request TA acquisition for the UE.

[0461] Embodiment 68: The method of embodiment 63, wherein transmitting the second message comprises transmitting, to the first network node or the third network node, a response message including the one or more TA values for the one or more second cells.

[0462] Embodiment 69: The method of embodiment 50, wherein the second network node transmits, to the second network node or the third network node, a message, including validity information, such as validity timer(s) associated with the TA value(s).

[0463] Embodiment 70: A method performed by a third network node for handling Timing Advance (TA) acquisition for at least one second cell controlled by a second node, for a UE controlled by a first network node, the method comprising: transmitting (304), to the first network node, a third message including an indication of one or more TA values.

[0464] Embodiment 71: The method of embodiment 70, wherein the third network node is one of

[0465] • A core network node, such as an AMF, associated with the first network node

[0466] • A core network node, such as an AMF, associated with the second network node

[0467] • A Master Node, MN, when the UE is configured for dual connectivity Embodiment 72: The method of embodiment 70, further comprising receiving (302), from the second network node, a second message including an indication of the one or more TA values.

[0468] Embodiment 73: The method of embodiment 70, wherein the one or more TA values are for one or more second cells controlled by the second network node.

[0469] Embodiment 74: The method of embodiment 70, wherein the second network node is a core network node.

[0470] Embodiment 75: The method in embodiment 70, further comprising receiving, from the second network node, a message comprising an indication indicating that a mobility procedure for the UE is successfully completed or is canceled.

[0471] Embodiment 76: The method of embodiment 70, wherein the third network node transmits the third message to the first network node when one or more of the following conditions are fulfilled:

[0472] • a delay over a link between the first network node and the third network node is below a threshold THR9;

[0473] • a delay over a link between the third network node and the second network node is below a threshold THR10;

[0474] • a delay over a link between the first network node and the third network node is below a threshold THRU.

[0475] Embodiment 77: The method of embodiment 70 or 76, wherein the third network node determines that no TA value should be delivered to the first network node and the first network node indicates to the UE to execute a RACH-based mobility procedure.

[0476] Embodiment 78: The method of embodiment 77, wherein the third network node indicates to the first network node that a RACH-based mobility procedure should be triggered.

[0477] Embodiment 79: The method of embodiment 77, wherein the third network node receives from the second CN node an indication that a RACH-based mobility procedure should be triggered.

[0478] Embodiment 80: The method of embodiment 77, wherein instead of delay the third network node may consider any one or more of the following metrics:

[0479] • Load over a link

[0480] • Number of messages over a certain time period

[0481] • Whether is possible to ping a certain node

[0482] • Indication from other node "

[0483] • Number of past failures

[0484] • Number of failures over a certain time period Embodiment 81: The method of embodiment 73, wherein the third network node receives, from the second network node, a message, including validity information, such as validity timer(s) corresponding to the TA value(s).

[0485] Group C Embodiments

[0486] Embodiment 82: A user equipment, comprising: processing circuitry configured to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0487] Embodiment 83: A network node, the network node comprising: processing circuitry configured to perform any of the steps of any of the Group B embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0488] Embodiment 84: A user equipment (UE) comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

Claims

1. CLAIMS1. A method performed by a User Equipment, UE, (101) controlled by a first network node (102), for handling Timing Advance, TA, acquisition for at least one second cell (108) controlled by a second network node (103), the method comprising transmitting (200; 300; 420; 520; 616) a random access preamble on a second cell (108) controlled by a second network node (103); and receiving (204; 306; 430; 534; 624), from the first network node (102), a message including an indication of a TA value for the second cell (108) controlled by the second network node (103); wherein the first network node (102) is or comprises a first Central Unit, CU, (109), the second network node (103) is or comprises a second CU (112), and the first CU (109) and the second CU (112) are different CUs.

2. The method of claim 1, wherein the first network node (102) is associated with a third network node (115), and the second network node (103) is associated with the third network node (115).

3. The method of claim 2, wherein the third network node (115) is a core network node.

4. The method of claim 1, wherein the first network node (102) is associated with a first core network node, and the second network node (103) is associated with a second core network node.

5. The method of claim 1, wherein the UE (101) is configured with dual connectivity.

6. The method of claim 5, wherein: the first network node (102) is associated with a third network node (115) which is a Master Node, MN; the first network node (102) is a first Secondary Node, SN; and the second network node (103) is a second SN.

7. The method of claim 6, wherein the first network node (102) comprises a first Central Unit, CU, of the first SN, and the second network node (103) is a second CU of with the second SN.

8. The method of any of claims 1 to 7, wherein the message including the indication of theTA value is a Medium Access Control, MAC, Control Element and / or an Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, Cell Switch command including the TA value.

9. The method of any of claims 1 to 8, further comprising receiving (410; 512; 606), from the first network node, a TA acquisition configuration, wherein the UE (101) transmits the random access preamble in accordance with the TA acquisition configuration.

10. The method of claim 9, wherein the TA acquisition configuration comprises any one or more of the following: a preamble index used for transmitting the random access preamble on the second cell (108) controlled by the second network node (103), a Random Access Channel, RACH, configuration related to transmitting the random access preamble on the second cell (108) controlled by the second network node (103), and a Random Access, RA, Radio Network Temporary Identity used by the UE (101) for a random access procedure performed by the UE (101) with respect to the second cell (108) controlled by the second network node (103) during which the UE (101) transmits the random access preamble.

11. The method of any of claims 1 to 10, further comprising performing (206; 308) a mobility procedure from a first cell (107) controlled by the first network node (102) to the second cell (108) controlled by the second network node (103) using the TA value indicated by the received indication.

12. The method of claim 11, wherein the UE (101) does not perform random access during the mobility procedure.

13. The method of any of claims 11 to 12, further comprising transmitting (432; 538; 626), to the second network node, a message confirming that the mobility procedure has been completed.

14. The method of any of claims 11 to 13, wherein the mobility procedure is triggered in response to a received indication from the first network node (102).

15. The method of claim 14, wherein the received indication that triggers the mobility procedure is either a handover command or a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch command.

16. The method of claim 14 or 15, wherein the received indication that triggers the mobility procedure comprises the indication of the TA value.

17. The method of any of claims 14 to 16, wherein the received indication that triggers the mobility procedure comprises an indication to the UE to not perform a random access as part of the mobility procedure.

18. The method of any of claims 11 to 13, wherein the mobility procedure is triggered in response to a condition being fulfilled.

19. The method of any of claims 11 to 13, wherein the mobility procedure is triggered in response to detecting a failure.

20. The method of claim 19, wherein the failure is either a radio link failure or a mobility failure.

21. The method of any of claims 11 to 20, wherein the mobility procedure is any one of the following:• an NG-based mobility procedure,• an N2-based mobility procedure,• a Layer 3, L3, handover procedure,• an LTM procedure,• a conditional reconfiguration procedure,• a conditional handover,• a conditional Primary Secondary Cell Group, SCG, Cell, PSCell, addition,• a conditional PSCell change,• a beam management procedure,• a Radio Resource Control, RRC, resume procedure,• an RRC re-establishment procedure.

22. The method of any of claims 1 to 21, further comprising receiving (418; 518; 614), from the first network node, an indication to trigger TA acquisition for the second cell, wherein transmitting (200; 300; 420; 520; 616) the random access preamble on the second cell (108) controlled by the second network node (103) is responsive to receiving (418; 518; 614) theindication to trigger TA acquisition for the second cell (108).

23. A User Equipment, UE, (101; 800) controlled by a first network node (102), for handling Timing Advance, TA, acquisition for at least one second cell (108) controlled by a second network node (103), the UE (101; 800) comprising a communication interface (812) comprising a transmitter (818) and a receiver (820); and processing circuitry (802) associated with the communication interface (812), the processing circuitry (802) configured to cause the UE (101; 800) to: transmit (200; 300; 420; 520; 616) a random access preamble on a second cell (108) controlled by a second network node (103); and receive (204; 306; 430; 534; 624), from the first network node (102), a message including an indication of a TA value for the second cell (108) controlled by the second network node (103); wherein the first network node (102) is or comprises a first Central Unit, CU, (109), the second network node (103) is or comprises a second CU (112), and the first CU (109) and the second CU (112) are different CUs.

24. The UE (101; 800) of claim 23, wherein the processing circuitry (802) is further configured to cause the UE (101; 800) to perform the method of any of claims 2 to 22.

25. A User Equipment, UE, (101) controlled by a first network node (102), for handling Timing Advance, TA, acquisition for at least one second cell (108) controlled by a second network node (103), the UE (101) adapted to perform the method of any of claims 1 to 22.

26. A method performed by a first network node (102), which controls a first cell (107), for handling Timing Advance, TA, acquisition for a second cell (108) controlled by a second network node (103) for a User Equipment, UE, (101) controlled by the first network node (102), the method comprising, receiving (202; 304; 426 or 428; 530; 622), from the second network node (103) or a third network node (115), a message including an indication of a TA value for the UE (101) for a second cell (108) controlled by the second network node (103); and transmitting (204; 306; 430; 532; 624), to the UE (101), a message comprising the indication of the TA value for the UE (101) for the second cell (108) controlled by the secondnetwork node (103).

27. The method of claim 26, further comprising: receiving (406 or 408; 510; 604), from the second network node (103) or the third network node (115), a message including a TA acquisition configuration; and transmitting (408 or 410; 510 or 512; 606) the TA acquisition configuration to the UE (101).

28. The method of claim 27, further comprising, prior to receiving (406 or 408; 510; 604) the message including the TA acquisition configuration, transmitting (400; 500; 600), to the second network node (103) or the third network node (115), a message including a request for the TA acquisition configuration.

29. The method of any of claims 26 to 28, further comprising, prior to receiving (202; 304; 426 or 428; 530; 622) the message including the indication of the TA value for the UE (101) for the second cell (108) controlled by the second network node (103), transmitting (410; 518; 614), to the UE (101), an indication to trigger TA acquisition for the second cell (108).

30. The method of any of claims 26 to 29, wherein the UE (101) initiates a mobility procedure from the first cell (107) controlled by the first network node (102) to the second cell (108) controlled by the second network node (103) using the indicated TA value.

31. The method of claim 30, further comprising transmitting, to the UE (101), an indication to perform the mobility procedure to the second cell (108) controlled by the second network node (103).

32. The method of claim 31, wherein the transmitted indication to perform the mobility procedure to the second cell (108) comprises the indication of the TA value for the second cell (108).

33. The method of claim 31 or 32, wherein transmitted indication to perform the mobility procedure to the second cell (108) comprises an indication to the UE (101) to not perform a random access for the mobility procedure.

34. The method of any of claims 30 to 33, wherein the mobility procedure is one of:• an NG-based mobility procedure,• an N2-based mobility procedure,• a Layer 3, L3, handover procedure,• a L1 / L2 Triggered Mobility, LTM, procedure,• a conditional reconfiguration procedure,• a conditional handover,• a conditional Primary Secondary Cell Group, SCG, Cell, PSCell, addition,• a conditional PSCell change,• a beam management procedure,• a Radio Resource Control, RRC, resume procedure,• an RRC re-establishment procedure.

35. The method of claim 30, further comprising transmitting (630), to the second network node (103) or a third network node (115), an indication of a mobility procedure initiated by the UE to the second cell.

36. The method of claim 30, further comprising receiving, from the second network node or a third network node, an indication of a mobility procedure initiated by the UE to the second cell.

37. The method of any of claims 26 to 36, wherein the second network node (103) is different from the first network node (102) or associated with a target CU (112) different from a source CU (109) associated with the first network node (102).

38. The method of any of claims 26 to 37, wherein the third network node (115) is a core network node.

39. The method of claim 38, wherein the core network node is not connected to the second network node (103).

40. The method of any of claims 26 to 39, wherein the third network node (115) is a Master Node, MN, and the UE (101) is configured with dual connectivity.

41. The method of any of claims 26 to 40, wherein the first network node transmits theindication of the TA value when any one or more of the following conditions are fulfilled:• a delay over a link between the first network node and the UE is below a threshold THR1 ;• a delay over the link between a first CU of the first network node and a first DU of the first network node is below a threshold THR2;• a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR3;• a delay over a link between the first network node and the UE is below a threshold THR4;• a delay over a link between the first network node and the third network node associated with the first network node is below a threshold THR5.

42. The method of any of claims 26 to 41, further comprising transmitting, to the second network node or the third network node, a message to request the TA value for the second cell controlled by the second network node (103).

43. The method of claim 42, further comprising starting a timer when the first network node transmits the message to the second network node to request the TA value.

44. The method of any of claims 26 to 43, further comprising receiving, from the second network node or the third network node, a message comprising validity information associated with the TA value.

45. A first network node (102), which controls a first cell (107), for handling Timing Advance, TA, acquisition for a second cell (108) controlled by a second network node (103) for a User Equipment, UE, (101) controlled by the first network node (102), the first network node (102) comprising processing circuitry (902) configured to cause the first network node (102) to: receive (202; 304; 426 or 428; 530; 622), from the second network node (103) or a third network node (115), a message including an indication of a TA value for the UE (101) for a second cell (108) controlled by the second network node (103); and transmit (204; 306; 430; 532; 624), to the UE (101), a message comprising the indication of the TA value for the UE (101) for the second cell (108) controlled by the second network node (103).

46. The first network node of claim 45, wherein the processing circuitry (902) is further configured to cause the first network node to perform the method of any of claim 27 to 44.

47. A first network node (102), which controls a first cell (107), for handling Timing Advance, TA, acquisition for a second cell (108) controlled by a second network node (103) for a User Equipment, UE, (101) controlled by the first network node (102), the first network node (102) adapted to perform the method of any of claims 26 to 44.

48. A method performed by a second network node (103) for handling Timing Advance, TA, acquisition for a second cell controlled by the second network node (108) for a User Equipment, UE, (101) controlled by a first network node (102), the method comprising: receiving (200), from the UE (101), a random access preamble on the second cell (108) controlled by the second network node (103); and transmitting (202; 302), to the first network node (1020 or a third network node (115), a message including an indication of a TA value for the second cell (108) controlled by the second network node (103).

49. The method of claim 48, further comprising transmitting (405; 506; 604), to the first network node (102) or the third network node (115), a message including a TA acquisition configuration.

50. The method of claim 49, further comprising receiving (400; 504), from the first network node (102) or the third network node (115), a message including a request for TA acquisition configuration.

51. The method of claim 48, wherein the UE (101) initiates a mobility procedure from a first cell (107) controlled by the first network node (102) to the second cell (108) controlled by the second network node (103) using the indicated TA value for the second cell (108).

52. The method of claim 51, further comprising receiving, from the first network node or the third network node, an indication of the mobility procedure initiated by the UE to the second cell.

53. The method of claim 51, further comprising transmitting, to the second network node or the third network node, an indication of the mobility procedure initiated by the UE to the second cell.

54. The method of claim 51 , further comprising receiving, from the UE, a message confirming that the mobility procedure has been completed or is canceled.

55. The method of claim 51, wherein the UE does not perform random access during the mobility procedure.

56. The method of claim 51, wherein the mobility procedure is one of:• an NG-based mobility procedure,• an N2-based mobility procedure,• a L3 handover procedure,• a L1 / L2 triggered mobility procedure,• a conditional reconfiguration procedure,• a conditional handover,• a conditional PSCell addition,• a conditional PSCell change,• a beam management procedure,• an RRC resume procedure,• an RRC re-establishment procedure.

57. The method of any of claims 48 to 56, wherein the first network node is different from the second network node or associated with a source CU different from a target CU associated with the second network node.

58. The method of any of claims 48 to 57, wherein the third network node is a core network node.

59. The method of claim 58, wherein the core network node is not connected to the first network node.

60. The method of any of claims 48 to 59, wherein the third network node is a Master Node, MN, and the UE is configured with dual connectivity.

61. The method of claim 48, wherein the second network node transmits the message including the indication of the TA value to the first network node or the third network node when one ormore of the following conditions are fulfilled:• a delay over a link between the second network node and the third network node associated with the second network node is below a threshold THR6;• a delay over a link between the second CU and the second DU is below a threshold THR7;• a delay over a link between the second network node and third network node associated with the second network node is below a threshold THR8.

62. The method of claim 48, further comprising receiving, from the first network node or the third network node, a message to request TA acquisition for the UE.

63. The method of claim 62, wherein transmitting the second message comprises transmitting, to the first network node or the third network node, a response message including the one or more TA values for the one or more second cells.

64. The method of claim 48, wherein the second network node transmits, to the first network node or the third network node, a message, including validity information associated with the indicated TA value.

65. A second network node (103) for handling Timing Advance, TA, acquisition for a second cell controlled by the second network node (108) for a User Equipment, UE, (101) controlled by a first network node (102), the second network node (103) comprising processing circuitry (902) configured to cause the second network node (103) to receive (200), from the UE (101), a random access preamble on the second cell (108) controlled by the second network node (103); and transmit (202; 302), to the first network node (1020 or a third network node (115), a message including an indication of a TA value for the second cell (108) controlled by the second network node (103).

66. The second network node (103) of claim 65, wherein the processing circuitry (902) is further configured to cause the second network node (103) to perform the method of any of claims 49 to 64.

67. A second network node (103) for handling Timing Advance, TA, acquisition for a second cell controlled by the second network node (108) for a User Equipment, UE, (101) controlled bya first network node (102), the second network node (103) adapted to perform the method of any of claims 48 to 64.

68. A method performed by a third network node (115) for handling Timing Advance, TA, acquisition for a second cell (108) controlled by a second network node (103), for a User Equipment, UE, (101) controlled by a first network node (102), the method comprising: transmitting (304), to the first network node (102), a message including an indication of a TA value for the UE (101) for a second cell (108) controlled by the second network node (103).

69. The method of claim 68, wherein the third network node is one of• a core network node associated with the first network node• a core network node associated with the second network node• a Master Node, MN, where the UE is configured for dual connectivity70. The method of claim 68, further comprising receiving, from the second network node, a second message including the indication of the TA value.

71. The method of claim 68, wherein the second network node is a core network node.

72. The method in claim 68, further comprising receiving, from the second network node, a message comprising an indication indicating that a mobility procedure for the UE is successfully completed or is canceled.

73. The method of claim 68, wherein the third network node transmits the message comprising the indication of the TA value to the first network node when one or more of the following conditions are fulfilled:• a delay over a link between the first network node and the third network node is below a threshold THR9;• a delay over a link between the third network node and the second network node is below a threshold THR10;• a delay over a link between the first network node and the third network node is below a threshold THRU.

74. A third network node (115) for handling Timing Advance, TA, acquisition for a secondcell (108) controlled by a second network node (103), for a User Equipment, UE, (101) controlled by a first network node (102), the third network node (115) comprising processing circuitry (902) configured to cause the third network node (115) to: transmit (304), to the first network node (102), a message including an indication of a TA value for the UE (101) for a second cell (108) controlled by the second network node (103).

75. The third network node (115) of claim 74, wherein the processing circuitry (902) is further configured to cause the third network node (115) to perform the method of any of claims 69 to 73.

76. A third network node (115) for handling Timing Advance, TA, acquisition for a second cell (108) controlled by a second network node (103), for a User Equipment, UE, (101) controlled by a first network node (102), the third network node (115) adapted to perform the method of any of claims 68 to 73.

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