Mobility procedures and time alignment timer operation

Abstract

There is provided a method performed by a user equipment, UE The method comprises: receiving (202) a mobility configuration for a mobility procedure to a first candidate cell, the mobility configuration comprising a first time alignment timer, TAT, value for the first candidate cell and a candidate cell configuration for the first candidate cell, wherein the candidate cell configuration comprises a second TAT value for the first candidate cell. The method also comprises receiving (204) a timing advance, TA, value for the first candidate cell; starting (206) a first TAT for the first candidate cell according to the first TAT value, wherein the first TAT relates to the validity of the received TA value; and on performing the mobility procedure to the first candidate cell, starting (208) a second TAT for the first candidate cell based on the second TAT value while continuing to run the first TAT.

Description

[0001] Mobility procedures and time alignment timer operation

[0002] Technical Field

[0003] This disclosure relates to mobility procedures, and in particular to the validity of a timing advance value for a candidate cell.

[0004] Layer 1 (L1 ) / Layer 2 (L2) - Triggered Mobility (LTM) Release 18

[0005] LTM is a procedure in which a gNB (a base station in New Radio (NR)) receives L1 measurement report(s) from a User Equipment (UE) - which may also be called LTM lower layer measurements or LTM report - and on that basis the gNB changes UE’s serving cell by a cell switch command signalled via a Medium Access Control (MAC) Control Element (CE). The cell switch command indicates an LTM candidate cell configuration (also referred to as a LTM candidate configuration) that the gNB previously prepared and provided to the UE through Radio Resource Control (RRC) signalling. The UE then switches to the target cell / configuration according to the cell switch command. This is described in 3rdGeneration Partnership Project (3GPP) Technical Standard (TS) 38.300 v18.3.0 (2024-09) “3rdGeneration Partnership Project; Technical Specification Group Radio Access Network; NR; NR and NG-RAN Overall Description; Stage 2 (Release 18)”.

[0006] When configured by the network, it is possible to activate Transmission Configuration Indication (TCI) states of one or multiple cells that are different from the current serving cell. This is sometimes called pre-activation of a candidate TCI state, since this is pre-activating a TCI state of an LTM candidate cell before the UE receives the LTM cell switch command, i.e. before the LTM cell switch procedure. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell. This allows the UE to be downlink (DL) synchronised with those cells (or DL pre-sync), thereby facilitating a faster cell switch to one of those cells when cell switch is triggered. A cell switch command is conveyed in a MAC CE, which contains the necessary information to perform the LTM cell switch.

[0007] The overall procedure for LTM is shown in Fig. 1. With reference to the signalling in Fig. 1 , the procedure for LTM is as follows:

[0008] 1. The UE sends a MeasurementReport message to the gNB. The gNB decides to configure LTM and initiates LTM preparation.

[0009] 2. The gNB transmits an RRCReconfiguration message to the UE including the LTM candidate configurations. 3. The UE stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB.

[0010] 4a. The UE performs DL synchronisation with the candidate cell(s) before receiving the cell switch command. This is triggered upon reception by the UE of a “Candidate Cell TCI States Activation / Deactivation MAC CE” for LTM candidate cell(s) configured in CandidateTCI-State and CandidateTCI-UL-State. Upon reception in the UE’s MAC entity, the UE’s MAC entity receives a Candidate Cell TCI States Activation / Deactivation MAC CE on a Serving Cell, and the UE indicates to lower layers the information regarding the Candidate Cell TCI States Activation / Deactivation MAC CE.

[0011] 4b. The UE may also perform Uplink (UL) pre-synchronisation with the LTM candidate cell(s) if it receives the Physical Downlink Control Channel (PDCCH) order for early timing advance (TA) acquisition for those candidate cells.

[0012] 5. The UE performs L1 measurements on the configured candidate cell(s) and transmits L1 measurement reports to the gNB. L1 measurement should be performed as long as RRC reconfiguration (step 2) is applicable.

[0013] 6. The gNB decides to execute cell switch to a target cell and transmits a MAC CE triggering cell switch by including the candidate configuration index of the target cell. The UE switches to the target cell and applies the configuration indicated by candidate configuration index.

[0014] 7. The UE performs the random access procedure towards the target cell, if UE does not have a valid TA of the target cell. Otherwise, if the UE receives a valid TA value in LTM cell switch command using the early TA acquisition method in step 4b, the UE is not required to perform random access.

[0015] 8. The UE completes the LTM cell switch procedure by sending a RRCReconfigurationComplete message to the target cell. If the UE has performed a RA procedure in step 7, the UE considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For Random Access Channel (RACH)-less LTM, the UE considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data.

[0016] Conditional LTM - Release-19

[0017] Conditional handover (CHO) and the related conditional mobility procedures were introduced in NR for improving the mobility robustness by preparing the UE (and the CHO candidate cells) in advance before there are any radio link outages. The UE is provided with the RRC configuration of the candidate CHO cells, like LTM, and some CHO execution conditions. The CHO execution conditions being fulfilled leads the UE to directly perform the handover without sending any measurement report to the network, unlike LTM. However, there are other differences between the legacy CHO and LTM, for example, the CHO does not include the procedures of early UL and DL synchronisation in LTM Rel-18.

[0018] T o facilitate both the advantages of short handover interruption as well as better robustness, Rel-19 aims at introducing Conditional LTM (CLTM) as part of the mobility-related enhancements. The following Conditional LTM-related objectives have been agreed upon in a NR mobility enhancements phase 4 Work Item (Wl) (RP-241515, New WID: NR mobility enhancements Phase 4, 3GPP TSG RAN Meeting #104, Shanghai, China, June 17-20, 2024):

[0019] • Specify support of Conditional LTM [RAN2, RAN3, RAN1],

[0020] • Specify UE evaluated conditions for triggering LTM.

[0021] • Aim to support Conditional LTM including subsequent LTM.

[0022] In Conditional LTM, the UE is configured with the Conditional LTM execution conditions along with the LTM candidate cell configuration. The UE may perform early UL and DL synchronisation procedures before the cell switch and shall execute LTM cell switch upon the fulfilment of the provided execution conditions.

[0023] Latest agreements for CLTM - In RAN2#127-bis CLTM was discussed, and the following has been agreed:

[0024] The agreement in Point 8 above clarifies that the LIE receives a TA value before a CLTM cell switch command is triggered. How the TA value is delivered is still open (whether it is the source or target cell which deliver the TA and whether the TA value is delivered via a MAC CE or a Random Access Response (RAR)). Nevertheless, a further aspect is also how the LIE should handle the start, restart, and stop of the time alignment timer for the received TA as, in this case, is the LIE that should check the validity of the received TA value.

[0025] Summary

[0026] There currently exist certain challenge(s).

[0027] In legacy LTM, the LIE receives a TA value in the LTM cell switch command, triggering an LTM Cell Switch; and, when the TA value is received, the time alignment timer (TAT) is started. This timer is named timeAlignmentTimer 'm the 3GPP standards.

[0028] For CLTM, in the case of a RACH-less CLTM execution, the LIE triggers an LTM Cell Switch upon fulfilment of CLTM execution condition(s) (e.g. a beam of a candidate cell becomes an offset better than the serving beam of the PCell). That is, the LIE needs to receive a TA value before a CLTM cell switch will be triggered. This means that if the LIE starts the TAT at the time the CLTM cell switch procedure is executed, the TA value may no longer be valid, and this means that the LIE will perform either a RACH-based CLTM cell switch procedure or a RRC re-establishment procedure, which in both cases causes a long delay in the overall mobility procedure and connectivity interruption.

[0029] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges.

[0030] Embodiments of this disclosure proposed a method performed by a LIE that is configured with a configuration for a mobility procedure (e.g. CLTM and / or LTM, Information Element (IE) LTM-Config), where the configuration includes one or more TAT values. The method performed by the LIE comprises receiving a TA value before a LTM or CLTM cell switch procedure is initiated (e.g. before fulfilment of CLTM execution condition(s), before reception of an LTM Cell Switch Command), and in response starting the TAT for an LTM candidate cell (or Candidate TAT (CTAT)) with one of the received TAT values. When the LTM or CLTM cell switch procedure is initiated, the LIE applies another TAT value which is part of the CLTM or LTM candidate configuration but does not restart or stop the current TAT that is running. The mobility procedure may correspond to a CLTM procedure or an LTM procedure.

[0031] In some options of this disclosure, the UE receives a CTAT value for an LTM candidate cell to be applied when a TA value is received and the CTAT is to be started, which is before a LTM or CLTM cell switch procedure is executed. The UE receives another TAT value to be applied when (or after) a LTM or CLTM cell switch procedure is executed. In this example, the TAT value is received outside of the LTM or CLTM candidate cell configuration, whereas the TAT value to be applied when (or after) a LTM or CLTM cell switch procedure is executed is part of the LTM or CLTM candidate cell configuration.

[0032] In some options of this disclosure, the UE receives multiple TAT values to be applied when the TAT is started before a LTM cell switch procedure is executed and a CLTM cell switch procedure is executed (i.e. , one TAT value for LTM and one TAT value for CLTM). Also, the UE receives separate TAT values to be applied when (or after) a LTM or CLTM cell switch procedure is executed (i.e., one TAT value for LTM and one TAT value for CLTM).

[0033] Certain embodiments may provide one or more of the following technical advantage(s). As noted above, when using the conventional techniques, if the UE starts the TAT at the time the LTM cell switch procedure is executed (e.g. at CLTM execution), the TA value may no longer be valid and this means that the UE will perform either a RACH-based CLTM cell switch procedure or a RRC re-establishment procedure, which in both cases leads to a long delay in the overall mobility procedure and connectivity interruption. The techniques in this disclosure allow the UE to keep the TAT running for a received TA value before the LTM or CLTM cell switch procedure is triggered, and this guarantees that the TA value used at the time of the mobility execution is still valid.

[0034] According to a first aspect, there is provided a method performed by a user equipment (UE). The method comprises: receiving a mobility configuration for a mobility procedure to a first candidate cell, the mobility configuration comprising a first time alignment timer (TAT) value for the first candidate cell and a candidate cell configuration for the first candidate cell. The candidate cell configuration comprises a second TAT value for the first candidate cell. The method further comprises receiving a timing advance (TA) value for the first candidate cell; starting a first TAT for the first candidate cell according to the first TAT value, wherein the first TAT relates to the validity of the received TA value; and, on performing the mobility procedure to the first candidate cell, starting a second TAT for the first candidate cell based on the second TAT value while continuing to run the first TAT.

[0035] According to a second aspect, there is provided a method performed by a radio access network (RAN) node. The method comprises one or both of: sending, to a UE, a mobility configuration for a mobility procedure to a first candidate cell, the mobility configuration comprising a first time alignment timer (TAT) value for the first candidate cell and candidate cell configuration for the first candidate cell (the candidate cell configuration comprising a second TAT value for the first candidate cell); and sending, to the UE, a timing advance (TA) value for the first candidate cell.

[0036] According to a third aspect, there is provided a computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method according to the first aspect, the second aspect, or any embodiments thereof.

[0037] According to a fourth aspect, there is provided a user equipment (UE) configured to perform the method according to the first aspect or any embodiments thereof.

[0038] According to a fifth aspect, there is provided a user equipment (UE) comprising a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative to perform the method according to the first aspect or any embodiments thereof.

[0039] According to a sixth aspect, there is provided a radio access network (RAN) node, configured to perform the method according to the second aspect or any embodiments thereof.

[0040] According to a seventh aspect, there is provided a radio access network (RAN) node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said RAN node is operative to perform the method according to the second aspect or any embodiments thereof.

[0041] According to an eighth aspect, there is provided a user equipment, UE, comprising: processing circuitry configured to cause the user equipment to perform any of the steps of the methods according to the first aspect; and power supply circuitry configured to supply power to the processing circuitry.

[0042] According to a ninth aspect, there is provided a radio access network, RAN, node, comprising: processing circuitry configured to cause the RAN node to perform any of the steps of the methods according to the second aspect; and power supply circuitry configured to supply power to the processing circuitry.

[0043] According to a tenth aspect, there is provided 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 the methods according to the first aspect; 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.

[0044] Brief Description of the Drawings

[0045] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings, in which:

[0046] Fig. 1 is a signalling diagram illustrating signalling flow for LTM;

[0047] Fig. 2 is a flow chart illustrating a method performed by a UE according to various embodiments;

[0048] Fig. 3 is a flow chart illustrating a method performed by a RAN node according to various embodiments;

[0049] Fig. 4 shows an example of a communication system in accordance with some embodiments;

[0050] Fig. 5 shows a UE in accordance with some embodiments;

[0051] Fig. 6 shows a RAN network node in accordance with some embodiments; and

[0052] Fig. 7 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.

[0053] Detailed Description

[0054] Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art.

[0055] This disclosure relates to a UE configured with a mobility procedure. The mobility procedure may correspond to a lower layer mobility, such as LTM an / or Conditional LTM.

[0056] This disclosure refers to the term “L1 / L2 based inter-cell mobility” as used in the Rel-18 Work Item Description RP-241515 “NR mobility enhancements Phase 4” referenced above, though it interchangeably also uses the terms L1 / L2 mobility, L1 -mobility, L1 based mobility, L1 / L2-centric inter-cell mobility, L1 / L2 inter-cell mobility L1 / L2 Triggered Mobility, Lower-layer triggered Mobility or LTM. The basic principle is that the UE receives a lower layer signalling (e.g. a MAC 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). Lower layer signalling is a message / signalling in 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 IE CellGroupConfig per candidate cell and / or an embedded RRC Reconfiguration per candidate cell.

[0057] In the techniques described herein, a Timing Advance (TA) value is acquired for the UE in a neighbouring / 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 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).

[0058] 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 Identifier(s) (RA-RNTI(s)). A TA acquisition configuration may be provided to the UE per neighbour cell, e.g. per LTM candidate cell.

[0059] This disclosure refers to a time alignment timer (TAT). The TAT is used by the UE to monitor how long the current timing advance (TA) value is considered to be valid, and thus effectively monitors how long the UE is considered to be uplink time aligned with the RAN node. Once the TAT expires, the TA value is no longer valid, and the UE is no longer considered to be uplink synchronised with the RAN node, and a new TA value is required. The TAT is named timeAlignmentTimer 'm the 3GPP standards.

[0060] Embodiments of this disclosure relate to Conditional LTM (CLTM), which can be viewed as a form of conditional reconfiguration. In CLTM, the UE is configured with at least one LTM candidate cell (referred to herein as a CLTM candidate cell), by receiving an LTM candidate cell configuration, as in legacy LTM (referred to herein as a Conditional LTM candidate cell configuration), and an associated execution condition (referred to herein as a CLTM execution condition). The evaluation of CLTM execution condition associated to a CLTM candidate cell is performed by the assessment of lower layer measurements, such as Layer 1 reference signal received power (L1-RSRP) and / or Synchronisation Signal-RSRP (SS-RSRP), derived from Synchronisation Signal Blocks (SSBs) and / or Channel State Information-Reference Signals (CSI- RSs) of either the source cell and / or an LTM candidate cell. Lower layer measurements, in this context, are measurements reported to support lower layer procedures like beam management, candidate cell TCI state activation / deactivation, early timing advance (TA) acquisition, and link adaptation, and they aren't filtered based on Layer 3 (L3) parameters, though there may or may not be some filtering of these measurements based on the other lower layer parameters. The reception of a CLTM execution condition may also involve receiving an indication of the condition and / or configuring it with parameters such as event identifier(s), offset(s), threshold(s), reference signal (RS) type, a trigger quantity such as RSRP, reference signal received quality (RSRQ) or signal-to-interference-plus-noise ratio (SINR), time-to-trigger (TTT), and so forth.

[0061] In the context of CLTM, the UE relies on evaluating one or two condition(s), referred to as CLTM execution condition(s), LTM execution condition(s), or triggering condition(s), or a combination thereof. When the condition(s) for a CLTM candidate cell is fulfilled, the UE performs a cell switch, which may be seen as a kind of LTM execution which is not triggered by the reception of an LTM cell switch command; this may also be considered as a kind of LTM cell switch, or LTM cell switch execution, or Conditional LTM cell switch, or Conditional LTM execution, or CLTM execution, or simply cell switch. According to the methods outlined in this disclosure, upon satisfaction of the execution condition(s), the UE initiates an LTM cell switch. The term LTM cell switch refers to the process of a UE changing its cell from a source cell to a target cell, using L1 / L2 triggered mobility (LTM). In the context of Conditional LTM execution, this disclosure refers to the serving cell before the LTM cell switch as source cell, old source cell, or previous source cell.

[0062] This disclosure also refers to the concept of an LTM candidate cell within the framework of Conditional LTM. The candidate cell may be referred to as a CLTM candidate cell, CLTM cell, candidate cell, candidate target cell, target cell, LTM candidate cell, LTM cell, or L1 / L2 inter-cell mobility candidate cell, depending on the context or terminology used in this disclosure. Essentially, it denotes a cell to which the UE is directed or switches to in the event of executing a conditional L1 / L2 inter-cell mobility procedure after meeting the associated execution condition(s) and may also be termed as new source cell or next source cell after the LTM cell switch. These cells may also be termed: candidate cells, mobility candidates, non-serving cells, additional cells, candidate target cell, target cell or deactivated cells. An LTM candidate cell might also pertain to a candidate cell in a 5thGeneration (5G) Radio Access Technology (RAT) like NR or a future 6thGeneration (6G) Radio Access Technology.

[0063] In embodiments of the method described herein, the UE receives an LTM candidate cell configuration for Conditional LTM, typically through a RRC Reconfiguration message, which is stored in the UE and applied upon fulfilment of the associated CLTM execution conditions. A LTM candidate cell configuration comprises the configuration which the UE needs to start to operate accordingly when it performs a Conditional LTM execution to that LTM candidate cell, e.g. on the fulfilment of CLTM execution conditions. A candidate cell configuration may include parameters in the information element (IE) CellGroupConfig per LTM candidate cell and / or an embedded RRC Reconfiguration per candidate cell. An LTM candidate cell configuration is associated with an identifier that is used in the signalling when referring to a certain LTM candidate cell configuration, such as when performing the early UL or DL synchronisation with that LTM cell. This identifier is sometimes known as the LTM candidate cell configuration identifier (ID) or LTM candidate configuration index (or similar).

[0064] In the context of this disclosure, the term “beam” may correspond to a spatial direction in which a Reference signal (RS), such as SSB-RS, Mobility Reference Signal (MRS), a CSI-RS, or a RS defined for a 6G radio interface, is transmitted (e.g., by a network node) or received (e.g. by the UE), or a spatial filter applied to a signal which is transmitted or received. Thus, transmitting signals in different beams corresponds to transmitting signals in different spatial directions. The beam measurement corresponds to a measurement on an RS transmitted in that beam, e.g., an SSB measurement and involves determining a measurement quantity value such as a Synchronisation Signal based Reference Signal Received Power (SS-RSRP) and / or Synchronisation Signal based Reference Signal Received Quality (SS-RSRQ) and / or Synchronisation Signal based Signal to Noise and Interference Ratio (SS-SINR). In this disclosure a beam can be identified by beam index and / or a Reference Signal (RS) index or identifier (ID), such as an SSB index, or a CSI-RS resource identifier (ID).

[0065] In this disclosure, a beam or RS may be linked to a TCI state, for example, by configuring the RS (e.g. SSB) as the Quasi Co-Located (QCL) source of a TCI state configuration. An activated TCI state of an LTM candidate cell could also be termed as a pre-activated TCI state. This is because the UE receives the TCI state activation MAC CE command for one or more beam(s) (e.g. SSBs) within the LTM candidate cell before the CLTM execution. This is done to activate the LTM candidate cell before the UE receives the command to perform an LTM Cell Switch, or before fulfilment of the CLTM execution condition(s) in the case of Conditional LTM.

[0066] This disclosure uses the term “early DL synchronisation” or DL pre-sync to describe the action performed by the UE of pre-activating a TCI state (or activation of a candidate TCI state) of at least one LTM candidate cell configuration before performing an LTM cell switch to that LTM cell. In this case, the TCI state on a given LTM candidate cell is “activated in advance”, or “preactivated”. Therefore, the terms “early DL synchronisation”, or “DL pre-synchronisation”, or “early TCI state activation”, or “TCI state pre-activation” can be exchanged in the methods without any loss of meaning. This disclosure may also use the terms “start downlink synchronisation” and “TCI state activation” interchangeably and “stop downlink synchronisation” and “TCI state deactivation” interchangeably.

[0067] In the method outlined for both LTM and CLTM, the LTM candidate cells may have similar “UL sync, characteristics", i.e. the LTM candidate cells belong to the same “UL sync. Group", and may be identified by some group identity (e.g. UL sync group ID). Such LTM candidate cells may have an identical TA value applied to the UE for the group of LTM candidate cells for the same Time alignment timer in case the UE executes cell switch to any of those candidate target cells. This operation may also be modelled as a Timing Advance Group (TAG) which is defined as a group of serving cells per UE that is configured by RRC and that, for the cells with an UL configured, using the same timing reference cell and the same TA value. It should be noted that in this case “similar UL sync. Characteristics” means that the conditions for time alignment between two or more cells are similar from the UE perspective. This may happen, e.g., when two cells are very close to each other with a relatively small coverage or when two cells are overlapping each other’s coverage area (even if deployed on different frequencies).

[0068] According to the techniques in this disclosure, the UE keeps / retains / stores at least one TAT for at least one serving cell, and at least one TAT for an LTM candidate cell; then, upon LTM Cell Switch to the at least one LTM candidate cell for which the TAT is running, the UE does not stop that TAT, but that TAT becomes a TAT for a serving cell (since that LTM candidate cell becomes a new serving cell).

[0069] In one set of embodiments, a UE configured with a mobility configuration (e.g. an IE LTM- Config) for a mobility procedure (e.g. a lower layer mobility, such as LTM and / or Conditional LTM) receives, within the mobility configuration, a first TAT value to be applied (expiry value). The first TAT value is for an LTM candidate cell. This first TAT value is provided outside the LTM and / or CLTM candidate cell configuration (i.e. it is not within the candidate configuration to be applied upon LTM Cell Switch, not within the OCTET STRING). The first TAT value is applied by the UE before a LTM and / or a CLTM cell switch procedure is executed. This first TAT value can be received by the UE according to one or more of the following options:

[0070] • In a RRC message which includes a configuration for a mobility procedure and one or more LTM and / or CLTM candidate cell configurations.

[0071] • In a MAC CE which is used to deliver to the UE a TA value which is referring to LTM and / or CLTM, received by the UE before the CLTM or LTM execution. o In one option this is NOT an LTM Cell Switch Command MAC CE, i.e. this is a different MAC CE than the LTM Cell Switch Command MAC CE.

[0072] • In a MAC CE which is used to indicate to the UE to activate / deactivate one or more TCI states on an LTM and / or CLTM candidate cell configuration.

[0073] In some related embodiments, in the LTM and / or CLTM candidate cell configurations, the UE also receives a second TAT value which the UE needs to apply at the time an LTM cell switch or a CLTM execution (e.g. CLTM cell switch procedure) is initiated. In this case, the second TAT value is received by the UE within the LTM and / or CLTM candidate cell configuration (i.e. within the OCTET STRING with the RRCReconfiguration applied and / or used by the UE only during the CLTM execution / LTM Cell Switch).

[0074] In some embodiments, the first and second TAT values received by the UE can be specific to LTM or CLTM. Alternatively, the first and second TAT values can be general, meaning that the same value can be used for both LTM and CLTM. In some options, the first TAT value and second TAT value have exactly the same value. In further options, only the first TAT value is provided to the UE, and this means that the first TAT value is used by the UE before and during (after) the LTM and / or CLTM cell switch procedure is initiated.

[0075] In some embodiments, the UE, upon the reception of a TA value which is received before any LTM and / or CLTM cell switch procedure is triggered, the UE stores the TA value, but does not apply it. The UE starts the TAT according to the first received TAT value. The start of the TAT according to the first TAT value can be according to one or more of the following conditions:

[0076] • A reception of a TA value.

[0077] • The sending of a RACH preamble to a candidate cell (e.g. LTM and / or CLTM candidate cell).

[0078] • Activation of a TCI state of a candidate cell (e.g. LTM and / or CLTM candidate cell).

[0079] • Fulfilment of conditional criteria for initiating a TA acquisition procedure.

[0080] • Fulfilment of conditional criteria for activating one or more TCI state(s) of candidate cell (e.g. LTM and / or CLTM candidate cell).

[0081] In another set of embodiments, the UE, upon receiving a signalling from the network to initiate an LTM cell switch procedure, or upon determining that a CLTM cell switch procedure needs to be initiated (e.g. because conditional execution conditions have been fulfilled), applies the second TAT value, but does not restart or stop the TAT (which was started according to the first TAT value) if there is a TAT running for the indicated LTM and / or CLTM candidate cell configuration to which the cell switch procedure needs to be performed.

[0082] In some embodiments, if the UE has no TAT running according to the first TAT received for the LTM and / or CLTM candidate cell configuration to which the cell switch needs to be performed, the UE applies the second TAT value and starts the TAT for the LTM and / or CLTM candidate cell configuration, e.g. upon performing random access to the candidate cell and receiving a TA value in a Random Access Response (RAR).

[0083] In other embodiments, if the UE has a TAT running according to the first TAT received for the LTM and / or CLTM candidate cell configuration to which the cell switch needs to be performed, the UE decides whether to not restart or stop the running TAT according to the received value of the second TAT. In an example, if the value of the second TAT value is greater than the first TAT value, the running TAT is not restarted or stopped. In another example, if the value of the second TAT value is smaller than the first TAT value, the running TAT is restarted according to the value of the received second TAT. In yet another example, if the value of the second TAT value is smaller than the first TAT value, the running TAT is stopped and the UE applies the value of the received second TAT, but the UE decides to perform an LTM and / or CLTM cell switch procedure by performing a random access procedure.

[0084] In some embodiments, if the UE has a TAT running according to the first TAT received for the LTM and / or CLTM candidate cell configuration, the TAT can be stopped or restarted according to one or more of the following conditions:

[0085] • A reception of a new TA value.

[0086] • The sending of a RACH preamble to a candidate cell (e.g., LTM and / or CLTM candidate cell).

[0087] • Activating a new TCI state for a candidate cell (e.g., LTM and / or CLTM candidate cell) or a serving cell.

[0088] • Fulfilment of conditional criteria for initiating a TA acquisition procedure, and acquiring a new TA value.

[0089] • Fulfilment of conditional criteria for activating one or more TCI state(s) of candidate cell (e.g., LTM and / or CLTM candidate cell).

[0090] • When the UE receives an LTM Cell Switch command (and the timer is running).

[0091] • When the UE triggers a Conditional LTM execution, upon fulfilment of one or more CLTM execution condition(s) (and the timer is running).

[0092] • When the receives a handover command (e.g. RRC Reconfiguration including reconfiguration with sync).

[0093] • When the UE receives an RRC message which release the LTM or CLTM candidate configuration for which the timer was started.

[0094] • When the UE receives an RRC message which reconfigure the UL and DL early synchronisation of the LTM or CLTM candidate configuration for which the timer was started.

[0095] • When the measurement quantity, e.g. RSRP, RSRQ, SINR, for the SSB reference signal (RS) included in the PDCCH order for TA acquisition of the LTM candidate cell or the measurement quantity for the best beam in the LTM candidate cell goes below a certain pre-defined threshold.

[0096] • When the UE determines that the difference between the first measured value (i.e., RSRP, RSRQ, SINR) and the second measured value (i.e., RSRP, RSRQ, SINR) is greater than the maximum allowed difference between the two measurements. The first measured value is obtained at the time of TA acquisition and the second measured value is obtained later at any other time instant, either for the SSB RS included in the PDCCH order for TA acquisition of the LTM candidate cell or for the best beam in the LTM candidate cell.

[0097] In some embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value for the first LTM candidate cell. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) including a second TA value (which may be different than the first TA value). In response to the LTM Cell Switch command the UE releases the stored TA value (i.e. releases the first TA value) and applies the second TA value. The handling of the TAT(s) may be performed according to one or more of the previous embodiments, e.g. keep the TAT running without stopping it, for the LTM candidate cell which becomes the new serving cell.

[0098] In a set of embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value for the first LTM candidate cell. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) including a second TA value (which may be different than the first TA value). In response to the LTM Cell Switch command the UE applies the stored TA value and releases / ignores the second TA value received in the LTM Cell Switch (CS) command. The handling of the TAT(s) may be performed according to one or more of the previous embodiments, e.g. keep the TAT running without stopping it, for the LTM candidate cell which becomes the new serving cell.

[0099] In some embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value for the first LTM candidate cell. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) including a second TA value. In response to the LTM Cell Switch command the UE applies the stored TA value and releases / ignores the second TA value received in the LTM CS command, except when the second TA value indicates that the UE is to perform a Random Access procedure (e.g. second TA value equals ‘FFF’). In that case, the UE needs to perform the actions according to the second TA value (i.e. perform an LTM Cell Switch using a Random Access procedure), and release the stored TA value for the LTM candidate cell. In that case, the TAT for the LTM candidate cell is considered expired, and a TAT is started upon LTM Cell Switch for the LTM candidate cell which becomes the new serving cell.

[0100] In other embodiments, the UE is configured with Conditional LTM and two or more LTM candidate cells which share the similar “UL synchronisation characteristics”, i.e. the TA value acquired for one of the LTM candidate cells in the “UL sync. Group" is applicable to the other LTM candidate cells in the same UL sync, group. The UE receives a first TA value for one of the LTM candidate cells before Conditional LTM execution, i.e., before the fulfilment of CLTM execution conditions. Then, the UE receives an LTM Cell Switch Command corresponding to one of those LTM candidate cells in the UL sync, group, including an indication of the LTM candidate cell (e.g. Target Candidate ID corresponding to the LTM candidate cell) including a second TA value (which may be different to the first TA value). In response to the LTM Cell Switch command, the UE either releases the stored TA value (i.e. releases the first TA value) and applies the second TA value for the candidate target cell, or the UE applies the stored TA value and releases / ignores the second TA value received in the LTM CS command. In addition, the UE also releases the first TA value with respect to the other LTM candidate cells in the given UL sync, group, i.e., the UE does not retain the first TA value for the other LTM candidate cells in the UL sync, group upon receiving the second TA value for the target LTM candidate cell. The handling of the TAT(s) may be performed according to one or more of the previous embodiments e.g. keep the TAT running without stopping it, for the LTM candidate cell which becomes the new serving cell.

[0101] In other embodiments, the UE is configured with Conditional LTM and two or more LTM candidate cells which share the similar “UL synchronization characteristics”, i.e., the TA value acquired for one of the LTM candidate cells in the “UL sync. Group" is applicable to the other LTM candidate cells in the same UL sync, group. The UE receives a first TA value for one of the LTM candidate cells before Conditional LTM execution, i.e., before the fulfilment of CLTM execution conditions. Then, the UE receives an LTM Cell Switch Command corresponding to one of those LTM candidate cells in the UL sync, group, including an indication of the LTM candidate cell (e.g. Target Candidate ID corresponding to the LTM candidate cell) including a second TA value (which may be different to the first TA value). In response to the LTM Cell Switch command, the UE either releases the stored TA value (i.e. releases the first TA value) and applies the second TA value for the candidate target cell, or the UE applies the stored TA value and releases / ignores the second TA value received in the LTM CS command. In addition, the UE retains the first TA value with respect to the other LTM candidate cells in the given UL sync, group, i.e., the UE does not release the first TA value for the other LTM candidate cells in the UL sync, group upon receiving the second TA value for the target LTM candidate cell. The handling of the TAT(s) may be performed according to one or more of the previous embodiments, e.g. keep the TAT running without stopping it, for the LTM candidate cell which becomes the new serving cell.

[0102] It should be noted that, according to the techniques in this disclosure, the UE keeps at least one TAT for at least one serving cell, and at least a Candidate TAT (CTAT) for an LTM candidate cell; then, upon LTM Cell Switch to the at least one LTM candidate cell for which the CTAT is running, the UE stops the CTAT for the LTM candidate cell, but starts a TAT for that LTM candidate cell which is becoming the new serving cell. Then, the UE sets the value (expiry) of the TAT for that LTM candidate cell as one of the following: (i) the expiry value is the value configured in the RRC container for the LTM candidate cell (within the OCTET STRING) ‘minus’ the elapsed time of the CTAT for that LTM candidate cell; or (ii) the expiry value is the value configured in the RRC container for the LTM candidate cell (within the OCTET STRING), but the TAT is started not with ‘0’ (zero) but with the elapsed time of the CTAT for that LTM candidate cell.

[0103] In some embodiments, a UE configured with a mobility procedure (e.g. LTM and / or CLTM and / or a unified LTM procedure) receives a Time Alignment Timer (TAT) value associated to an LTM candidate cell (or multiple LTM candidate cell(s), e.g. in a same group), for a TAT associated to an LTM candidate cell, also denoted a Candidate TAT (CTAT). This may also be called a TAT for a candidate cell, to distinguish from that TAT(s) the UE runs for other types of cells, e.g. serving cell(s) and / or cell(s) configured for multi-Transmission-Reception Point (TRP) schemes.

[0104] This CTAT is a timer (a type of TAT) for determining whether the UE is UL sync with an LTM candidate cell. This CTAT is a timer in addition to the TAT(s) defined for the serving cell(s) the UE is connected to, which need to be running to determine how the UE performs UL transmissions to serving cell(s), e.g. Scheduling Requests via Physical Uplink Control Channel (PUCCH) or via Random Access. In other words, the UE may have at least a TAT(s) for at least one serving cell (e.g. the source cell before the LTM Cell Switch) and at least a CTAT for the LTM candidate cell.

[0105] In one option, a CTAT may be associated to a group of LTM candidate cells. The UE may be configured with multiple CTAT(s).

[0106] The UE starts the CTAT when the UE receives a TA value for the LTM candidate cell, (e.g. in a MAC CE) received prior to the CLTM execution (e.g. before the CLTM execution condition(s) is fulfilled for the LTM candidate cell), or prior to the LTM Cell Switch command. While the CTAT for the LTM candidate cell is running, the UE considers the TA value as valid for the LTM candidate cell (i.e. UE in UL sync with the LTM candidate cell). When the CTAT expires, the UE considers the TA value as not valid (i.e. UE in UL sync with the LTM candidate cell), which may be used for determining whether the UE performs RACH-less CLTM or LTM execution (in case the TAT is running), or RACH-based CLTM or LTM execution (in case TAT has expired).

[0107] Different options are set out below for the handling of the CTAT when the LTM Cell Switch is triggered, and the handling of the TAT for the new serving cell, after the LTM Cell Switch and / or CLTM execution.

[0108] In some embodiments, when the CTAT for the LTM candidate cell (e.g. cell A) is running and CLTM is executed for that LTM candidate cell (and the UE selects that LTM candidate cell for CLTM execution e.g. UE going to cell A), the UE stops the CTAT and starts a TAT for that LTM candidate cell (cell A) which is to become the new serving cell, e.g. the new PCell the UE is moving to. Then, the UE sets the value (i.e. the expiry value) for the TAT of the cell A to be the TAT value configured in the LTM candidate cell configuration which is only applied during CLTM execution (RRCReconfiguration container, e.g. within the OCTET STRING). Since the UE has received the TA value before the CLTM execution, such a value is probably longer than it should be, so it is expected that the network would trigger an adjustment before the TA becomes invalid.

[0109] In other embodiments, when the CTAT for the LTM candidate cell (e.g. cell A) is running and CLTM is executed for that LTM candidate cell (and the UE selects that LTM candidate cell for CLTM execution, e.g. UE going to cell A), the UE stops the CTAT and starts a TAT for that LTM candidate cell (cell A) which is to become the new serving cell, e.g. the new PCell the UE is moving to. Then, the UE sets the value (expiry value) for the TAT of the cell A to be the TAT value configured in the LTM candidate cell configuration that is applied during CLTM execution (RRCReconfiguration container, e.g. within the OCTET STRING) “minus” the duration of time elapsed since the UE has received the TA value for that LTM candidate cell that becomes the new serving cell. Such amount of time elapsed since the UE has received the TA value for that LTM candidate cell that becomes the new serving cell is equivalent to the current value of the CTAT timer. In other words, the UE sets the value for the TAT of the cell A to be the TAT value configured in the LTM candidate cell configuration which is applied during CLTM execution (RRCReconfiguration container, e.g. within the OCTET STRING) “minus” the current value of the CTAT (before that is stopped).

[0110] In other embodiments, when the CTAT for the LTM candidate cell (e.g. cell A) is running and CLTM is executed for that LTM candidate cell (and the UE selects that LTM candidate cell for CLTM execution, e.g. UE going to cell A), the UE keeps the CTAT running even after the LTM Cell Switch, and does not start the TAT for that LTM candidate cell (cell A), at least temporarily. Then, when the UE receives a new TA value in cell A, after the CLTM execution, the UE starts the TAT with the value in the RRCReconfiguration which was in the OCTET STRING. In other words, in this option the UE keeps running the CTAT temporarily after it expires at least once and / or after a new random access is triggered in cell A. By keeping the CTAT running for the LTM candidate cell (Cell A) after the LTM CS to cell A, without the need to change its expiry value, there is no need to convert timer values upon LTM CS. However, at some point later the UE needs to start the actual TAT meant to be running for a serving cell.

[0111] In other embodiments, when the CTAT for the LTM candidate cell (e.g. cell A) is running and CLTM is executed for that LTM candidate cell (and the UE selects that LTM candidate cell for CLTM execution, e.g. UE going to cell A), the UE stops the CTAT and starts a TAT for that LTM candidate cell (cell A) with the current (latest) value (i.e. the elapsed value) of the CTAT for the same cell, i.e. cell A. For example, when the CTAT for cell A has a 2 seconds value (i.e. UE received TA value two seconds before the LTM Cell Switch), the UE starts the TAT already with 2 seconds, instead of 0 seconds. Then, in one option, the UE sets the expiry value for the TAT of the cell A to be the TAT value configured in the LTM candidate cell configuration which is applied during CLTM execution (RRCReconfiguration container, e.g. within the OCTET STRING). In other words, the UE sets the expiry value for the TAT of the cell A to be the TAT value configured in the LTM candidate cell configuration which is applied during CLTM execution (RRCReconfiguration container, e.g. within the OCTET STRING), but the TAT starts with the latest value of the CTAT for the same cell, so that the expiry of the timer coincides with the time in which TA is considered invalid.

[0112] In some embodiments, when the CTAT for the LTM candidate cell (e.g. cell A) is running and CLTM is executed for that LTM candidate cell (and the UE selects that LTM candidate cell for CLTM execution, e.g. UE going to cell B), the UE stops the CTAT and starts a TAT after receiving a new TAT value from the Cell B which is to become the new serving cell, e.g. the new PCell the UE is moving to. Then, the UE sets the value (i.e. the expiry value) for the TAT with the value received from the cell B to be the TAT value after the LTM candidate cell switch is completed. The new TAT timer may be sent to the UE using a new message after the LTM cell switch is complete. The new message can be a MAC CE or a RRC message or a Downlink Control Information (DCI) indication.

[0113] In some options, the UE starts the TAT for the LTM candidate cell (cell A) which is to become the new serving cell before stopping the TAT for the former serving cell. In other words, the UE first considers the TAT expired (e.g. during MAC reset), and when the UE determines that it has received the TA value earlier for the LTM Candidate cell to become the new serving cell, and that the CTAT is running, the UE performs the actions above. TAT terminology for both Serving and LTM candidate cells

[0114] In some embodiments, a UE configured with a mobility procedure (e.g. LTM and / or CLTM and / or a unified LTM procedure) receives a Time Alignment Timer (TAT) value associated to an LTM candidate cell (or multiple LTM candidate cell(s) e.g. in a same group), for a TAT associated to an LTM candidate cell. This may also be called a TAT for a candidate cell, to distinguish from that TAT(s) the UE runs for other types of cells, e.g. serving cell(s) and / or cell(s) configured for multi-TRP schemes.

[0115] In other words, the UE may have at least a TAT(s) for at least one serving cell (e.g. the source cell before the LTM Cell Switch) and at least a TAT for the LTM candidate cell.

[0116] The difference is that a TAT for a serving cell is started when the UE is already configured with that serving cell or when the UE connects to that serving cell, e.g. handover, and / or a random access procedure to the serving cell. However, the TAT for an LTM candidate cell may be started earlier, upon reception of a TA value while the UE is connected to another serving cell, i.e. even before that LTM candidate cell becomes an actual serving cell in an LTM Cell Switch.

[0117] In related embodiments, the UE has at least one TAT running for at least one serving cell, and the UE has at least one TAT running for at least LTM Candidate cell. Then, when LTM Cell Switch is triggered (e.g. on reception of an LTM Cell Switch Command, or upon fulfilment of a CLTM execution condition) the UE performs one or more of the following actions:

[0118] UE considers the TAT for the serving cell(s) as expired, e.g. as part of the MAC reset procedure, triggered by the LTM Cell Switch and / or the CLTM execution.

[0119] UE keeps running the TAT for the LTM Candidate Cell that becomes the new serving cell, o In some options, the expiry value remains the same, as previously configured; o In another option, the expiry value is a value configured in the LTM candidate configuration applied only upon CLTM execution. o In another option, the expiry value is a value configured in the LTM candidate configuration applied only upon CLTM execution “minus” the current TAT value for the LTM candidate cell (i.e. the elapsed value since it has started).

[0120] In some embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value for the first LTM candidate cell. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) and including a second TA value (which may be different than the first TA value). In response to the LTM Cell Switch command, the UE releases the stored TA value (i.e. releases the first TA value) and applies the second TA value. The handling of the CTAT and the TAT may be performed according to one or more of the previous embodiments.

[0121] For example, the UE stops the CTAT of the first LTM candidate cell upon reception of the LTM Cell Switch Command for the first LTM candidate cell and starts TAT for the first LTM candidate cell which is becoming the new serving cell. Here, the TAT is started with the elapsed time of the CTAT of the LTM candidate cell (and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell).

[0122] For example, the UE considering the CTAT of the first LTM candidate cell expired upon reception of the LTM Cell Switch Command for the first LTM candidate cell and starting TAT for the first LTM candidate cell which is becoming the new serving cell. o In some options the TAT is started with the elapsed time of the CTAT of the LTM candidate cell (and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell). o In some options the TAT is started with zero and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell. It should be noted that in this case the adjustment is taken care of by the network implementation.

[0123] In some embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value for the first LTM candidate cell. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) including a second TA value (which may be different to the first TA value). In response to the LTM Cell Switch command, the UE applies the stored TA value and releases / ignores the second TA value received in the LTM CS command.

[0124] The handling of the CTAT and the TAT may be performed according to one or more of the previous embodiments.

[0125] For example, the UE stops the CTAT of the first LTM candidate cell upon reception of the LTM Cell Switch Command for the first LTM candidate cell and starts TAT for the first LTM candidate cell which is becoming the new serving cell. Here, the TAT is started with the elapsed time of the CTAT of the LTM candidate cell (and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell).

[0126] For example, the UE considering the CTAT of the first LTM candidate cell expired upon reception of the LTM Cell Switch Command for the first LTM candidate cell and starting TAT for the first LTM candidate cell which is becoming the new serving cell. o In some options the TAT is started with the elapsed time of the CTAT of the LTM candidate cell (and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell). o In some options the TAT is started with zero and the value of the expiry time is the value configured in the OCTET STRING RRC container for the LTM candidate cell. It should be noted that in this case the adjustment is taken care of by the network implementation.

[0127] In some embodiments, the UE is configured with a first LTM candidate cell for CLTM and receives (e.g. before CLTM execution, before fulfilment of CLTM execution conditions) a first TA value for the first LTM candidate cell. Upon reception, the UE stores the first TA value. Then, the UE receives an LTM Cell Switch Command including an indication of the first LTM candidate cell (e.g. Target Candidate ID corresponding to the first LTM candidate cell) including a second TA value. In response to the LTM Cell Switch command, the UE applies the stored TA value and releases / ignores the second TA value received in the LTM CS command, except when the second TA value indicates that the UE is to perform a Random Access procedure (e.g. if the second TA value is equal to ‘FFF’). In that case, the UE needs to perform the actions according to the second TA value (i.e. perform an LTM Cell Switch using a Random Access procedure), and release the stored TA value for the LTM candidate cell. In that case, the TAT for the LTM candidate cell is considered to be expired and a TAT is started upon LTM Cell Switch for the LTM candidate cell which becomes the new serving cell.

[0128] Fig. 2 is a flow chart illustrating a method performed by a UE according to various embodiments. The method may be performed by a UE, e.g. the UE 412 as described later with reference to Fig. 4). The UE may perform the method in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0129] The method begins at step 202 with the UE receiving a mobility configuration for a mobility procedure to a first candidate cell. The mobility configuration comprises a first TAT value for the first candidate cell and a candidate cell configuration for the first candidate cell. The candidate cell configuration comprises a second TAT value for the first candidate cell.

[0130] The mobility configuration can be an LTM configuration for an LTM mobility procedure to a first LTM candidate cell. Alternatively, the mobility configuration can be a CLTM configuration for a CLTM mobility procedure to a first CLTM candidate cell. The CLTM configuration can comprise a CLTM execution condition, and the CLTM mobility procedure can be performed following fulfilment of the CLTM execution condition.

[0131] In step 204, the UE receives a TA value for the first candidate cell. The UE may store the received TA value.

[0132] In step 206, the UE starts a first TAT for the first candidate cell according to the first TAT value. The first TAT relates to the validity of the received TA value.

[0133] In step 208, on performing the mobility procedure to the first candidate cell, the UE starts a second TAT for the first candidate cell based on the second TAT value while continuing to run the first TAT. Continuing to run the first TAT can comprise not restarting or stopping the first TAT on performing the mobility procedure. 18. In step 208 the second TAT can be started with a TAT value that is one of: (i) the value obtained by subtracting a remaining time value of the first TAT from the second TAT value; (ii) the second TAT value (where the second TAT is started at the remaining time value of the first TAT); and (iii) a value received by the UE from the first candidate cell after performing the mobility procedure.

[0134] In embodiments where the mobility configuration is an LTM configuration for an LTM mobility procedure to a first LTM candidate cell, the LTM mobility procedure can be performed following receipt of a lower layer mobility command or an LTM Cell Switch Command. The lower layer mobility command or LTM Cell Switch Command may comprise a second TA value for the first candidate cell, and, on performing the mobility procedure to the first candidate cell, the method can further comprise applying the second TA value for the first candidate cell. Alternatively, the lower layer mobility command or LTM Cell Switch Command can comprise a second TA value for the first candidate cell, and, on performing the mobility procedure to the first candidate cell, the second TA value for the first candidate cell can be ignored or discarded.

[0135] In step 204, the UE receives a TA value for the first candidate cell.

[0136] Certain embodiments can further comprise applying the TA value for uplink transmissions by the UE to the first candidate cell on performing the mobility procedure to the first candidate cell.

[0137] The first TAT may be started according to step 206 before the mobility procedure is performed.

[0138] The TA value for the first candidate cell may be received in step 204 before the mobility procedure is performed.

[0139] In some embodiments, the first TAT is started in step 206 in response to receiving the TA value.

[0140] In some embodiments, prior to the mobility procedure the UE is served by a source cell, and the UE has a source TAT running for a TA value for the source cell. In this case, on performing the mobility procedure to the first candidate cell, the UE can stop the source TAT for the TA value for the source cell. Stopping the source TAT can comprise resetting a MAC entity.

[0141] In some embodiments, the candidate cell configuration for the first candidate cell and the first TAT value are for a first type of mobility procedure. The mobility configuration can further comprise a third TAT value and a candidate cell configuration for a second candidate cell. The candidate cell configuration for the second candidate cell can be for a second type of mobility procedure, and one of the first and second types of mobility procedure is LTM, and the other one of the first and second types of mobility procedure is CLTM.

[0142] In some embodiments, in the event that the first TAT expires before the UE performs the mobility procedure to the first candidate cell, the UE can perform a RACH-based mobility procedure.

[0143] Fig. 3 depicts a method performed by a RAN node in accordance with particular embodiments. The RAN node may be the RAN network node 410 as described later with reference to Fig. 4. The RAN node may perform the method in response to executing suitably formulated computer readable code. The computer readable code may be embodied or stored on a computer readable medium, such as a memory chip, optical disc, or other storage medium. The computer readable medium may be part of a computer program product.

[0144] The method begins at step 302 with the RAN node sending a mobility configuration for a mobility procedure to a first candidate cell to a UE. The mobility configuration comprises a first TAT value for the first candidate cell and candidate cell configuration for the first candidate cell. The candidate cell configuration comprises a second TAT value for the first candidate cell.

[0145] The mobility configuration may be an LTM configuration for an LTM mobility procedure to a first LTM candidate cell. The LTM mobility procedure may be performed following the sending of a lower layer mobility command or an LTM Cell Switch Command to the UE. The lower layer mobility command or LTM Cell Switch Command may comprise a second TA value for the first candidate cell. Alternatively, the mobility configuration can be a CLTM configuration for a CLTM mobility procedure to a first CLTM candidate cell. The CLTM configuration may comprise a CLTM execution condition, and the CLTM mobility procedure may be performed following fulfilment of the CLTM execution condition.

[0146] In step 304, the RAN node sends a TA value for the first candidate cell to the UE.

[0147] The RAN node may further send an indication to the UE that the UE is to perform the mobility procedure to the first candidate cell.

[0148] The following ordered statements set out various exemplary embodiments of the techniques described herein.

[0149] A1. A method at a UE configured with a mobility procedure, comprising: receiving a mobility configuration which include at least one LTM candidate cell configuration and / or at least one CLTM candidate cell configuration, and one or more TAT values to be applied receiving a TA value for the mobility procedure (LTM and / or CLTM) for an LTM candidate cell starting a TAT for the LTM candidate cell related to the received TA value for the LTM candidate cell triggering an LTM cell switch procedure to the LTM candidate cell applying the TA value related to the LTM candidate cell and / or CLTM candidate cell without restarting or stopping the TAT which is already running for the applied LTM and / or CLTM candidate cell configuration.

[0150] A2a. A method of A1 , wherein triggering the LTM cell switch procedure comprises i) receiving a lower layer mobility command including an indication of the LTM candidate cell; or, ii) determining the fulfilment of a CLTM execution condition for the LTM Candidate cell.

[0151] A2b. A method of A1 , further comprising upon receiving the TA value, storing the TA value and applying the TA value in response to the triggering of the LTM cell switch procedure.

[0152] A2c. A method of A1 , wherein upon triggering the LTM cell switch procedure to the LTM candidate cell, resetting a MAC entity and as part of that, stopping TAT(s) for one or more serving cell(s), except the TAT for the LTM candidate cell which is becoming the new serving cell.

[0153] A2. A method in A1 , wherein the UE receives a first TAT value to be applied when the TAT value is started before a LTM or CLTM cell switch procedure is executed and a second TAT value to be applied when (or after) a LTM or CLTM cell switch procedure is executed.

[0154] A3. A method in A1 , wherein the UE receives separate TAT value to be applied when the TAT value is started before a LTM cell switch procedure is executed and when a CLTM cell switch procedure is executed (i.e. , one TAT value for LTM and one TAT value for CLTM).

[0155] A4. A method in A1 , A2b and all, further comprising upon triggering the LTM cell Switch procedure, receiving the lower layer mobility command including an indication of the LTM candidate cell and includes a second TA value, wherein in response to the LTM cell Switch command the UE releases the stored TA value and applies the second TA value. A4’. A method in A1 , A2b and all, further comprising upon triggering the LTM cell Switch procedure, receiving the lower layer mobility command including an indication of the LTM candidate cell and includes a second TA value, wherein in response to the LTM cell Switch command the UE ignores the second TA value and applies the stored TA value.

[0156] NOTE: according to this modelling, the UE keeps at least one TAT for at least one serving cell, and at least one TAT for an LTM candidate cell; then, upon LTM Cell Switch to the at least one LTM candidate cell for which the TAT is running, the UE does not stop that TAT, but that TAT becomes a TAT for a serving cell (since that LTM candidate cell becomes a new serving cell).

[0157] A1*. (this is an alternative to Embodiment A1) A method at a UE configured with a mobility procedure, comprising: receiving a Timing Advance (TA) value for an LTM candidate cell; starting a first candidate TAT (CTAT) associated to the LTM candidate cell in response to receiving the TA value for the LTM candidate cell, wherein the first CTAT is set to a first value (expiry value) received in an LTM configuration associated to the LTM candidate cell; triggering the execution of an LTM cell switch procedure to the LTM candidate cell; applying the TA value for the LTM candidate cell and starting a second TAT for the LTM candidate cell, wherein the LTM candidate cell becomes a new serving cell in the LTM Cell switch procedure;

[0158] A) setting the second TAT timer with a value (expiry value) configured in an RRC Reconfiguration contained in the LTM candidate cell configuration “minus” the current (i.e., the remaining timer value) value of the CTAT of the LTM candidate cell,

[0159] B) or setting the second TAT timer with a value (expiry value) configured in an RRC Reconfiguration contained in the LTM candidate cell configuration, while considering the starting time of the second TAT timer as the current value (i.e., the remaining timer value) of the CTAT of the LTM candidate cell.

[0160] C) or setting the second TAT timer with a value (expiry value) that is received from the candidate LTM cell after the cell switch command using a separate message.

[0161] NOTE: For example, suppose the UE receives the TA value at time to and starts the first TAT, where the timer value is T2; then the UE executes the LTM cell switch procedure at time tO+T 1 , while the first TAT is running (current value = T1); then the UE starts the second TAT and sets the value (expiry value) to the value configured in the RRC container for the LTM candidate cell (within the OCTET STRING) as T2-T1 ; or, the UE starts the second TAT with T2, and simply sets the value (expiry value) to the value configured in the RRC container. Or in alternative examples, the network (NW) may send the value of the second TTT (which may be T2-T 1 , which was maintained or counted at the NW) and UE sets the second TTT value based on the received value from the NW.

[0162] A2*. A method of A1*, further comprising the UE stopping or considering expired the first TAT timer for the LTM candidate cell which became the new serving cell.

[0163] A3*. A method of A1*, further comprising receiving the TA value for the LTM candidate cell before the LTM Cell Switch procedure and applying the TA value for the LTM candidate cell during the LTM Cell Switch procedure, wherein the TA value is not received in an LTM Cell Switch command.

[0164] A4*. A method of A1*, wherein the first TAT corresponds to a Candidate TAT.

[0165] A5*. A method of A1* and A2*, wherein the UE stopping or considering expired the first TAT timer for the LTM candidate cell which became the new serving cell as part of a MAC reset procedure.

[0166] A6. A method in A1 , A2b and all, further comprising upon triggering the LTM cell Switch procedure, receiving the lower layer mobility command including an indication of the LTM candidate cell and includes a second TA value, wherein in response to the LTM cell Switch command the UE releases the stored TA value and applies the second TA value.

[0167] A6’. A method in A1 , A2b and all, further comprising upon triggering the LTM cell Switch procedure, receiving the lower layer mobility command including an indication of the LTM candidate cell and includes a second TA value, wherein in response to the LTM cell Switch command the UE ignores the second TA value and applies the stored TA value.

[0168] NOTE: according to this modelling, the UE keeps at least one TAT for at least one serving cell, and at least a Candidate TAT (CTAT) for an LTM candidate cell; then, upon LTM Cell Switch to the at least one LTM candidate cell for which the CTAT is running, the UE stops the CTAT for the LTM candidate cell, but starts a TAT for that LTM candidate cell which is becoming the new serving cell. Then, the UE sets the value (expiry) of the TAT for that LTM candidate cell as one of the following: i) the expiry value is the value configured in the RRC container for the LTM candidate cell (within the OCTET STRING) ‘minus’ the elapsed time of the CTAT for that LTM candidate cell; or ii) the expiry value is the value configured in the RRC container for the LTM candidate cell (within the OCTET STRING), but the TAT is started not with ‘0’ (zero) but with the elapsed time of the CTAT for that LTM candidate cell.

[0169] B1. A method at a network node which configured a UE with a mobility procedure, comprising:

[0170] Transmitting a signalling to the UE which includes a TA value to be applied for a LTM and / or CLTM candidate cell configuration.

[0171] Transmitting a signalling to the UE to indicate that a LTM cell switch procedure needs to be initiated toward a LTM candidate cell configuration.

[0172] Fig. 4 shows an example of a communication system 400 in accordance with some embodiments.

[0173] In the example, the communication system 400 includes a telecommunication network 402 that includes an access network 404, such as a radio access network (RAN), and a core network 406, which includes one or more core network nodes 408. The access network 404 includes one or more access network nodes, such as access network nodes 410a and 410b (one or more of which are also referred to as RAN network nodes or RAN nodes 410 herein), or any other similar 3rdGeneration Partnership Project (3GPP) access nodes or non-3GPP access points (AP). 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 402 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 402 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 402, including one or more network nodes 410 and / or core network nodes 408.

[0174] 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 (RIC) (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an A1 , F1 , W1 , E1 , 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 (SMO) Framework via an 0-2 interface defined by the O-RAN Alliance or comparable technologies.

[0175] The network nodes 410 facilitate direct or indirect connection of wireless devices (also referred to interchangeably herein as user equipment (UE)), such as by connecting UEs 412a, 412b, 412c, and 412d (one or more of which may be generally referred to as UEs 412) to the core network 406 over one or more wireless connections. The access network nodes 410 may be, for example, access points (APs) (e.g. radio access points), base stations (BSs) (e.g. radio base stations, Node Bs, evolved Node Bs (eNBs) and New Radio (NR) NodeBs (gNBs)).

[0176] 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 400 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 400 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0177] The wireless devices / UEs 412 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 410 and other communication devices. Similarly, the access network nodes 410 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 412 and / or with other network nodes or equipment in the telecommunication network 402 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 402.

[0178] In the depicted example, the core network 406 connects the access network nodes 410 to one or more host computing systems, such as host 416. 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 406 includes one more core network nodes (e.g. core network node 408) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the wireless devices / UEs, access network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 408. 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 (ALISF), 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).

[0179] The host 416 may be under the ownership or control of a service provider other than an operator or provider of the access network 404 and / or the telecommunication network 402. The host 416 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.

[0180] As a whole, the communication system 400 of Figure 4 enables connectivity between the wireless devices / UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2ndGeneration (2G), 3rdGeneration (3G), 4thGeneration (4G), 5thGeneration (5G) standards, or any applicable future generation standard (e.g. 6thGeneration (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.

[0181] In some examples, the telecommunication network 402 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 402 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 402. For example, the telecommunications network 402 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC) / Massive loT services to yet further UEs. In some examples, the UEs 412 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 404 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 404. 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 Wi-Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UTRA (UMTS Terrestrial Radio Access) Network) New Radio - Dual Connectivity (EN- DC).

[0182] In the example, the hub 414 communicates with the access network 404 to facilitate indirect communication between one or more UEs (e.g., UE 412c and / or 412d) and network nodes (e.g., network node 410b). In some examples, the hub 414 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 414 may be a broadband router enabling access to the core network 406 for the UEs. As another example, the hub 414 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 410, or by executable code, script, process, or other instructions in the hub 414. As another example, the hub 414 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 414 may be a content source. For example, for a UE that is a VR device, display, loudspeaker, or other media delivery device, the hub 414 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 414 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 414 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy Internet of Things (loT) devices.

[0183] The hub 414 may have a constant / persistent or intermittent connection to the network node 410b. The hub 414 may also allow for a different communication scheme and / or schedule between the hub 414 and UEs (e.g., UE 412c and / or 412d), and between the hub 414 and the core network 406. In other examples, the hub 414 is connected to the core network 406 and / or one or more UEs via a wired connection. Moreover, the hub 414 may be configured to connect to a machine-to-machine (M2M) service provider over the access network 404 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 410 while still connected via the hub 414 via a wired or wireless connection. In some embodiments, the hub 414 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 410b. In other embodiments, the hub 414 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 410b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0184] Fig. 5 shows a wireless device or UE 500 in accordance with some embodiments. The UE 500 presents additional details of some embodiments of the UE 412 of Fig. 4. As used herein, a wireless device / UE refers to a device capable, configured, arranged and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a wireless device / UE include, but are not limited to, a smart phone, mobile phone, cell phone, voice over IP (VoIP) phone, wireless local loop phone, desktop computer, personal digital assistant (PDA), wireless cameras, gaming console or device, music storage / playback device, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, laptop-embedded equipment (LEE), laptopmounted equipment (LME), an Augmented Reality (AR) or Virtual Reality (VR) device, wireless customer-premise equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3rd Generation Partnership Project (3GPP), including a narrow band internet of things (NB-loT) UE, a machine type communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0185] A wireless device / 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).

[0186] The UE 500 includes processing circuitry 502 that is operatively coupled via a bus 504 to an input / output interface 506, a power source 508, a memory 510, a communication interface 512, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Fig. 5. 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. The processing circuitry 502 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 510. The processing circuitry 502 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 502 may include multiple central processing units (CPUs). The processing circuitry 502 may be configured to cause the UE 502 to perform the methods as described herein.

[0187] In the example, the input / output interface 506 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 500. 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.

[0188] In some embodiments, the power source 508 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 508 may further include power circuitry for delivering power from the power source 508 itself, and / or an external power source, to the various parts of the UE 500 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 508. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 508 to make the power suitable for the respective components of the UE 500 to which power is supplied.

[0189] The memory 510 may be or be configured to include memory such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 510 includes one or more application programs 514, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 516. The memory 510 may store, for use by the UE 500, any of a variety of various operating systems or combinations of operating systems.

[0190] The memory 510 may be configured to include a number of physical drive units, such as redundant array of independent disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, high-density digital versatile disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, holographic digital data storage (HDDS) optical disc drive, external mini-dual in-line memory module (DIMM), synchronous dynamic random access memory (SDRAM), external micro-DIMM SDRAM, smartcard memory such as tamper resistant module in the form of a universal integrated circuit card (UICC) including one or more subscriber identity modules (SIMs), such as a Universal SIM (USIM) and / or Integrated SIM (ISIM), other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUlCC), integrated UICC (iUICC) or a removable UICC commonly known as ‘SIM card’. The memory 510 may allow the UE 500 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 510, which may be or comprise a device-readable storage medium.

[0191] The processing circuitry 502 may be configured to communicate with an access network or other network using the communication interface 512. The communication interface 512 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 522. The communication interface 512 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 518 and / or a receiver 520 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 518 and receiver 520 may be coupled to one or more antennas (e.g., antenna 522) and may share circuit components, software or firmware, or alternatively be implemented separately.

[0192] In the illustrated embodiment, communication functions of the communication interface 512 may include cellular communication, Wi-Fi communication, LPWAN communication, data communication, voice communication, multimedia communication, short-range communications such as Bluetooth, near-field communication, location-based communication such as the use of the global positioning system (GPS) or other Global Navigation Satellite System (GNSS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented in according to one or more communication protocols and / or standards, such as IEEE 802.11 , Code Division Multiplexing Access (CDMA), Wideband Code Division Multiple Access (WCDMA), GSM, LTE, New Radio (NR), UMTS, WiMax, Ethernet, transmission control protocol / internet protocol (TCP / IP), synchronous optical networking (SONET), Asynchronous Transfer Mode (ATM), QUIC, Hypertext Transfer Protocol (HTTP), and so forth.

[0193] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 512, 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).

[0194] 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.

[0195] A UE, when in the form of an Internet of Things (loT) device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a TV, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a 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 500 shown in Figure 5.

[0196] 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-loT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship and an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0197] 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.

[0198] Fig. 6 shows a network node, access network node or RAN node 600 in accordance with some embodiments.

[0199] As used herein, access network node or RAN network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other RAN network nodes or equipment, or core network nodes, in a telecommunication network. Examples of access network nodes include, but are not limited to, access points (APs) (e.g. radio access points), base stations (BSs) (e.g. radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), Open-RAN (O-RAN) nodes or components of an O-RAN node (e.g., O- RU, O-DU, O-CU).

[0200] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0201] Other examples of network nodes include multiple transmission point (multi-TRP) 5G access nodes, multi-standard radio (MSR) equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g. Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0202] The RAN network node 600 includes a processing circuitry 602, a memory 604, a communication interface 606, and a power source 608. The RAN network node 600 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the RAN network node 600 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 RAN network node 600 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 604 for different RATs) and some components may be reused (e.g., a same antenna 610 may be shared by different RATs). The RAN network node 600 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 600, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within RAN network node 600.

[0203] The processing circuitry 602 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application-specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 600 components, such as the memory 604, to provide RAN network node 600 functionality. For example, the processing circuitry 602 may be configured to cause the RAN network node to perform the methods as described herein. In some embodiments, the processing circuitry 602 includes a system on a chip (SOC). In some embodiments, the processing circuitry 602 includes one or more of radio frequency (RF) transceiver circuitry 612 and baseband processing circuitry 614. In some embodiments, the radio frequency (RF) transceiver circuitry 612 and the baseband processing circuitry 614 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 612 and baseband processing circuitry 614 may be on the same chip or set of chips, boards, or units.

[0204] The memory 604 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 602. The memory 604 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 602 and utilized by the RAN node 600. The memory 604 may be used to store any calculations made by the processing circuitry 602 and / or any data received via the communication interface 606. In some embodiments, the processing circuitry 602 and memory 604 is integrated.

[0205] The communication interface 606 is used in wired or wireless communication of signalling and / or data between network nodes, the access network, the core network, and / or UE. As illustrated, the communication interface 606 comprises port(s) / terminal(s) 616 to send and receive data, for example to and from a network over a wired connection. The communication interface 606 also includes radio front-end circuitry 618 that may be coupled to, or in certain embodiments a part of, the antenna 610. Radio front-end circuitry 618 comprises filters 620 and amplifiers 622. The radio front-end circuitry 618 may be connected to an antenna 610 and processing circuitry 602. The radio front-end circuitry may be configured to condition signals communicated between antenna 610 and processing circuitry 602. The radio front-end circuitry 618 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 618 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of filters 620 and / or amplifiers 622. The radio signal may then be transmitted via the antenna 610. Similarly, when receiving data, the antenna 610 may collect radio signals which are then converted into digital data by the radio frontend circuitry 618. The digital data may be passed to the processing circuitry 602. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0206] In certain alternative embodiments, the RAN node 600 does not include separate radio front-end circuitry 618, instead, the processing circuitry 602 includes radio front-end circuitry and is connected to the antenna 610. Similarly, in some embodiments, all or some of the RF transceiver circuitry 612 is part of the communication interface 606. In still other embodiments, the communication interface 606 includes one or more ports or terminals 616, the radio front-end circuitry 618, and the RF transceiver circuitry 612, as part of a radio unit (not shown), and the communication interface 606 communicates with the baseband processing circuitry 614, which is part of a digital unit (not shown).

[0207] The antenna 610 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 610 may be coupled to the radio front-end circuitry 618 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 610 is separate from the network node 600 and connectable to the network node 600 through an interface or port.

[0208] The antenna 610, communication interface 606, and / or the processing circuitry 602 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, the antenna 610, the communication interface 606, and / or the processing circuitry 602 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipment.

[0209] The power source 608 provides power to the various components of network node 600 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 608 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 600 with power for performing the functionality described herein. For example, the network node 600 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 608. As a further example, the power source 608 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. Embodiments of the network node 600 may include additional components beyond those shown in Fig. 6 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 600 may include user interface equipment to allow input of information into the network node 600 and to allow output of information from the network node 600. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 600. In some embodiments providing a core network node, such as core network node 108 of Fig. 4, some components, such as the radio front-end circuitry 618 and the RF transceiver circuitry 612 may be omitted.

[0210] Fig. 7 is a block diagram illustrating a virtualization environment 700 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 700 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, access network node, RAN node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g. a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 700 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 an access network node, network node, RAN node, UE, core network node, or host.

[0211] Applications 702 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0212] Hardware 704 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, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 706 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 708a and 708b (one or more of which may be generally referred to as VMs 708), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. The virtualization layer 706 may present a virtual operating platform that appears like networking hardware to the VMs 708.

[0213] The VMs 708 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 706. Different embodiments of the instance of a virtual appliance 702 may be implemented on one or more of VMs 708, 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.

[0214] In the context of NFV, a VM 708 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 708, and that part of hardware 704 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 708 on top of the hardware 704 and corresponds to the application 702.

[0215] Hardware 704 may be implemented in a standalone network node with generic or specific components. Hardware 704 may implement some functions via virtualization. Alternatively, hardware 704 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 710, which, among others, oversees lifecycle management of applications 702. In some embodiments, hardware 704 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 signalling can be provided with the use of a control system 712 which may alternatively be used for communication between hardware nodes and radio units.

[0216] 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.

[0217] 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.

[0218] The foregoing merely illustrates the principles of the disclosure. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous systems, arrangements, and procedures that, although not explicitly shown or described herein, embody the principles of the disclosure and can be thus within the scope of the disclosure. Various exemplary embodiments can be used together with one another, as well as interchangeably therewith, as should be understood by those having ordinary skill in the art.

Claims

Claims1 . A method performed by a user equipment, UE, the method comprising: receiving (202) a mobility configuration for a mobility procedure to a first candidate cell, the mobility configuration comprising a first time alignment timer, TAT, value for the first candidate cell and a candidate cell configuration for the first candidate cell, wherein the candidate cell configuration comprises a second TAT value for the first candidate cell; receiving (204) a timing advance, TA, value for the first candidate cell; starting (206) a first TAT for the first candidate cell according to the first TAT value, wherein the first TAT relates to the validity of the received TA value; and on performing the mobility procedure to the first candidate cell, starting (208) a second TAT for the first candidate cell based on the second TAT value while continuing to run the first TAT.

2. The method of claim 1 , wherein continuing to run the first TAT comprises not restarting or stopping the first TAT on performing the mobility procedure.

3. The method of claim 1 or 2, wherein the method further comprises, on performing the mobility procedure to the first candidate cell, applying the TA value for uplink transmissions by the UE to the first candidate cell.

4. The method of any of claims 1-3, wherein the mobility configuration is a Layer 1 / Layer 2 Triggered Mobility, LTM, configuration for a LTM mobility procedure to a first LTM candidate cell.

5. The method of claim 4, wherein the LTM mobility procedure is performed following receipt of a lower layer mobility command or a LTM Cell Switch Command.

6. The method of claim 5, wherein the lower layer mobility command or LTM Cell Switch Command comprises a second TA value for the first candidate cell, and wherein, on performing the mobility procedure to the first candidate cell, applying the second TA value for the first candidate cell.

7. The method of claim 5, wherein the lower layer mobility command or LTM Cell Switch Command comprises a second TA value for the first candidate cell, and wherein, on performing the mobility procedure to the first candidate cell, the second TA value for the first candidate cell is ignored or discarded.

8. The method of any of claims 1-3, wherein the mobility configuration is a Conditional Layer 1 / Layer 2 Triggered Mobility, CLTM, configuration for a CLTM mobility procedure to a first CLTM candidate cell.

9. The method of claim 8, wherein the CLTM configuration comprises a CLTM execution condition, and wherein the CLTM mobility procedure is performed following fulfilment of the CLTM execution condition.

10. The method of any of claims 1-9, wherein the first TAT is started before the mobility procedure is performed.

11. The method of any of claims 1-10, wherein the TA value for the first candidate cell is received before the mobility procedure is performed.

12. The method of any of claims 1-11 , wherein the first TAT is started in response to receiving the TA value.

13. The method of any of claims 1-12, wherein the method further comprises storing the received TA value.

14. The method of any of claims 1-13, wherein, prior to the mobility procedure, the UE is served by a source cell and the UE has a source TAT running for a TA value for the source cell, and wherein the method further comprises: on performing the mobility procedure to the first candidate cell, stopping the source TAT for the TA value for the source cell.

15. The method of claim 14, wherein stopping the source TAT comprises resetting a Medium Access Control, MAC, entity.

16. The method of any of claims 1-15, wherein the candidate cell configuration for the first candidate cell and the first TAT value are for a first type of mobility procedure, and wherein the mobility configuration further comprises a third TAT value and a candidate cell configuration for a second candidate cell, wherein the candidate cell configuration for the second candidate cell is for a second type of mobility procedure, and wherein one of the first and second types of mobilityprocedure is Layer 1 / Layer 2 Triggered Mobility, LTM, and the other one of the first and second types of mobility procedure is Conditional LTM, CLTM.

17. The method of any of claims 1-16, wherein in the event that the first TAT expires before performing the mobility procedure to the first candidate cell, performing a Random Access Channel-, RACH-, based mobility procedure.

18. The method of any of claims 1-17, wherein the second TAT is started with a TAT value that is one of:(i) the value obtained by subtracting a remaining time value of the first TAT from the second TAT value;(ii) the second TAT value, wherein the second TAT is started at the remaining time value of the first TAT ; and(iii) a value received by the UE from the first candidate cell after performing the mobility procedure.

19. A method performed by a radio access network, RAN, node, the method comprising one or both of: sending (302), to a User Equipment, UE, a mobility configuration for a mobility procedure to a first candidate cell, the mobility configuration comprising a first time alignment timer, TAT, value for the first candidate cell and candidate cell configuration for the first candidate cell, wherein the candidate cell configuration comprises a second TAT value for the first candidate cell; and sending (304), to the UE, a timing advance, TA, value for the first candidate cell.

20. The method of claim 19, wherein the method further comprises: sending, to the UE, an indication that the UE is to perform the mobility procedure to the first candidate cell.

21. The method of claim 19 or 20, wherein the mobility configuration is a Layer 1 / Layer 2 Triggered Mobility, LTM, configuration for a LTM mobility procedure to a first LTM candidate cell.

22. The method of claim 21 , wherein the LTM mobility procedure is to be performed following the sending of a lower layer mobility command or a LTM Cell Switch Command to the UE.

23. The method of claim 22, wherein the lower layer mobility command or LTM Cell Switch Command comprises a second TA value for the first candidate cell.

24. The method of claim 19 or 20, wherein the mobility configuration is a Conditional Layer 1 / Layer 2 Triggered Mobility, CLTM, configuration for a CLTM mobility procedure to a first CLTM candidate cell.

25. The method of claim 24, wherein the CLTM configuration comprises a CLTM execution condition, and the CLTM mobility procedure is to be performed following fulfilment of the CLTM execution condition.

26. A computer program product comprising a computer readable medium having computer readable code embodied therein, the computer readable code being configured such that, on execution by a suitable computer or processor, the computer or processor is caused to perform the method of any of claims 1-25.

27. A user equipment, UE, configured to perform the method of any of claims 1-18.

28. A user equipment, UE, comprising a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative to perform the method of any of claims 1-18.

29. A radio access network, RAN, node, configured to perform the method of any of claims 19- 25.

30. A radio access network, RAN, node comprising a processor and a memory, said memory containing instructions executable by said processor whereby said RAN node is operative to perform the method of any of claims 19-25.

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