Reporting UE transmission timing error from target to source du during ltm

Abstract

Systems and methods related to reporting User Equipment (UE) transmission timing error from target to source Distributed Unit (DU) during Layer 1 (L1) / Layer 2 (L2) Triggering Mobility (LTM) are disclosed. In one embodiment, a method performed by a UE comprises receiving a first Timing Advance (TA) instruction from a DU in a cell either after a successful Random Access Channel (RACH)-less LTM cell switch to the cell or after an LTM recovery to the cell. The method further comprises generating a Self-Organizing Network (SON) report including a size of a first TA adjustment indicated by the first TA instruction and transmitting the SON report to a network node. In this manner, the network is enabled to optimize how it controls early uplink (UL) synchronization of LTM candidate cells.

Description

REPORTING UE TRANSMISSION TIMING ERROR FROM TARGET TO SOURCE DU DURING LTMRELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 702,443, filed October 2, 2024, the disclosure of which is hereby incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to a cellular communications system and, more specifically, Layer 1 (LI) / Layer 2 (L2) Triggered Mobility (LTM) in a cellular communications system.BACKGROUND1 General Background on 3 GPP Technology

[0003] In release 8 of the 3rdGeneration Partnership Project (3GPP) standard, the Evolved Packet System (EPS) was specified. EPS is based on the Long-Term Evolution (LTE) radio network and the Evolved Packet Core (EPC). It was originally intended to provide voice and mobile broadband (MBB) services but has continuously evolved to broaden its functionality. Since Release 13, Narrowband Internet of Things (NB-IoT) and LTE for Machine Type Communication (LTE-M) are part of the LTE specifications and provide connectivity to massive Machine Type Communications (mMTC) services.

[0004] In 3GPP release 15, the first release of the 5thGeneration (5G) System (5GS) was specified. This is a new generation radio access technology intended to serve use cases such as enhanced Mobile Broadband (eMBB), Ultra-Reliable and Low Latency Communication (URLLC) and mMTC services. 5G includes the New Radio (NR) access stratum interface and the 5G Core Network (5GC). The NR physical and higher layers reuse parts of the LTE specification, and additional components are introduced when motivated by the new use cases. One such component is the introduction of a sophisticated framework for beam forming and beam management to extend the support of the 3 GPP technologies to a frequency range going beyond 6 Gigahertz (GHz).

[0005] In the work on release 15 of the 3GPP standard, 3GPP also started the work to prepare NR for operation in a Non-Terrestrial Network (NTN). The work was performed within the Study Item “NR to support Non-Terrestrial Networks” and resulted in 3 GPP Technical Report (TR) 38.811 15.4.0. In 3GPP release 16, the work to prepare NR for operation in a Non-TerrestrialNetwork continued with the Study Item “Solutions for NR to support Non-Terrestrial Network” which resulted in 3GPP TR 38.821 16.2.0.

[0006] The Release 16 study item resulted in a Work Item being agreed for NR in Release 17, “Solutions for NR to support non-terrestrial networks (NTN)”, which is described in the Work Item Description RP-193234.2 L1 / L2 Triggered Mobility (LTM)

[0007] An overall description of Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM) is provided in section 9.2.3.5 of 3GPP Technical Specification (TS) 38.300 version 18.2.0. That section is copied and included below.######### Start of copy of section 9.2.3.5 of 3GPP TS 38.300 version 18.2.0 #########9.2.3.5.1 GeneralLTM is a procedure in which a gNB receives LI measurement report(s) from a UE, and on their basis the gNB may change UE serving cell by a cell switch command signalled via a MAC CE. The cell switch command indicates an LTM candidate configuration that the gNB previously prepared and provided to the UE through RRC signalling. Then the UE switches to the target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency as described in Annex G.When configured by the network, it is possible to activate TCI states of one or multiple cells that are different from the current serving cell. 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 DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when cell switch is triggered. All the activated TCI states except those received in the cell switch command are deactivated upon LTM cell switch execution.When configured by the network, it is possible to initiate UL TA acquisition (called early TA) procedure of one or multiple cells that are different from the current serving cells. If the cell has the same NTA as the current serving cells or NTA=0, early TA acquisition procedure is not required. The network may request the UE to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by PDCCH order as specified in clause 9.2.6 or realized through UE-based TA measurement as configured by RRC. In the former case, the gNB / gNB-DU to which the candidate cell belongs calculates the TA value and sends it to the gNB / gNB-DU to which the serving cell belongs via gNB-CU. The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering LTM cell switch. In the latter case, the UE performs TA measurement for the candidate cells after being configured by RRC but the exact time the UE performs TA measurement is up to UE implementation. The UE applies the TA value measured by itself and performs RACH-less LTM upon receiving the cell switch command, if it does not include any valid TA value. The network may also send a TA value in the LTM cell switch command MAC CE without early TA acquisition.Depending on the availability of a valid TA value, the UE performs either a RACH-less LTM or RACH-based LTM cell switch. If the valid TA value is provided in the cell switch command, the UE applies the TA value as instmcted by the network. In the case where UE-based TA measurement is configured, but no valid TA value is provided in the cell switch command, the UE applies the valid TA value by itself if available. The UE performs RACH-less LTM cell switch upon receiving the cell switch command whenever a valid TA value is available. If no valid TA value is available, the UE performs RACH-based LTM cell switch.Regardless of whether the UE is configured for UE-based TA measurement for a certain candidate cell, it will still follow the PDCCH order, which includes performing a random access procedure towards one or more candidate cells. This also applies to the candidate cells for which the UE is capable of deriving TA values by itself. Additionally, regardless of whether the UE has already performed a random access procedure towards the candidate cells, it will still follow the UE-based measurement configuration if configured by the network.For RACH-less LTM, the UE accesses the target cell using either a configured grant or a dynamic grant. The configured grant is provided in the LTM candidate configuration, and the UE selects the configured grant occasion associated with the beam indicated in the cell switch command. Upon initiation of LTM cell switch to the target cell, the UE starts to monitor PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the UE shall not trigger random access procedure if it does not have a valid PUCCH resource for triggered SRs.The following principles apply to LTM:- Security keys are maintained upon an LTM cell switch;- Subsequent LTM is supported.LTM supports both intra-gNB-DU and inter-gNB-DU mobility within the same gNB-CU. LTM supports both intrafrequency and inter-frequency mobility, including mobility to inter-frequency cell that is not a current serving cell. LTM is supported only for licensed spectmm. The following scenarios are supported:- PCell change in non-CA scenario and non-DC scenario;- PCell and SCell(s) change in CA scenario;- Dual connectivity scenario: including PCell and MCG SCell(s) change and intra-SN PSCell and SCG SCell(s) change without MN involvement. LTM for simultaneous PCell and PSCell change is not supported.While the UE has stored LTM candidate configurations the UE can also execute any L3 handover except for DAPS handover. In the RRC message which the UE applies for any L3 handover (except DAPS), LTM candidate configurations can be added / modified / released by the target cell.9.2.3.5.2 C-Plane HandlingCell switch command is conveyed in a MAC CE, which contains the necessary information to perform the LTM cell switch.The overall procedure for LTM is shown in Figure 9.2.3.5.2-1 below. Subsequent LTM is done by repeating the early synchronization, LTM cell switch execution, and LTM cell switch completion steps without releasing other LTM candidate configmations after each LTM cell switch completion. The general procedure over the air interface is applicable to SCG LTM. Further details of SCG LTM can be found in TS 37.340

[0021] ,[REPRODUCED HEREIN AS FIGURE 1]Figure 9.2.3.5.2-1. Signalling procedure for LTMThe procedure for LTM is as follows:1. The UE sends a MeasurementReport message to the gNB. The gNB decides to configure LTM and initiates LTM preparation.2. The gNB transmits mRRCReconfiguration 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.4a. The UE performs DL synchronization with the LTM candidate cell(s) before receiving the cell switch command. The UE may activate and deactivate TCI states of LTM candidate cell(s), as triggered by the gNB.4b. The UE may perform UL synchronization with LTM candidate cell(s) before receiving the cell switch command, by using UE-based TA measurement, if configured, and / or by transmitting a preamble towards the candidate cell, as triggered by the gNB. When UE-based TA measurement is configured, UE acquires the TA value(s) of the candidate cell(s) by measurement. UE performs early TA acquisition with the candidate cell(s) as requested by the network before receiving the cell switch command as specified in clause 9.2.6. This is done via CFRA triggered by a PDCCH order from the source cell, following which the UE sends preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due toCFRA towards the candidate cell(s), the UE does not receive random access response from the network for the purpose of TA value acquisition and the TA value of the candidate cell is indicated in the cell switch command. The UE does not maintain the TA timer for the candidate cell and relies on network implementation to guarantee the TA validity.5. The UE performs LI measurements on the configured LTM candidate cell(s) and transmits LI measurement reports to the gNB. LI measurement should be performed as long as RRC reconfiguration (step 2) is applicable.6. The gNB decides to execute cell switch to a target cell and transmits an LTM cell switch command MAC CE triggering cell switch by including a target configuration ID which indicates the index of the candidate configuration of the target cell, a beam indicated with a TCI state or beams indicated with DL and UL TCI states, and a timing advance command for the target cell, if available. The UE switches to the target cell and applies the candidate configuration indicated by the target configuration ID.7. The UE performs the random access procedure towards the target cell, if UE does not have valid TA of the target cell as specified in clause 5.18.35 of TS 38.321 [6] .8. The UE completes the LTM cell switch procedure by sending RRCReconfigurationComplete message to 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 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.The steps 4-8 can be performed multiple times for subsequent LTM cell switch executions using the LTM candidate configuration(s) provided in step 2.The procedure over the air interface described in Figure 9.2.3.5.2-1 is applicable to both intra-gNB-DU LTM and inter-gNB-DU LTM. The overall LTM procedures over Fl-C interface are captured in TS 38.401 [4].9.2.3.5.3 U-Plane HandlingAfter receiving an LTM cell switch command MAC CE, the UE performs MAC reset. Whether the UE performs RLC re-establishment and PDCP data recovery during cell switch is explicitly controlled by the network through RRC signalling.######### End of copy of section 9.2.3.5 of 3GPP TS 38.300 version 18.2.0 #########3 Self -Organizing Network

[0008] Self-Organizing Networks (SONs) is a collection of functions for automatic configuration, optimization, and healing of networks. The aim of the framework is to perform routine maintenance and optimization where necessary without additional configuration. To enable this functionality, multiple reports are defined and collected from the User Equipment (UE). Some relevant ones are introduced in the following, where the Successful Handover Report (SHR) and the Success Primary Secondary Cell Group (SCG) Cell (PSCell) Addition / Change Report (SPR) are of special interest in the context of the present disclosure).3.1 Successful PSCell Addition / Change Report (SPR)

[0009] A Successful PSCell Addition / Change Report (SPR) is generated by a UE performing a PSCell addition or change if the conditions set by the network are fulfilled. These conditions are configured to trigger the UE to generate an SPR in cases where a PSCell addition or change is successful but close to failing.3.2 Radio Link Failure (RLF) report

[0010] If a Radio Resource Control (RRC) connected UE (i.e., a UE in RRC CONNECTED state) declares radio link failure, it creates a Radio Link Failure (RLF) report, and the network can fetch the RLF report from the UE. In an RLF report, the UE includes necessary information and measurements for the network to analyze the radio condition and possibly physical location of the UE. The network thus can take appropriate action upon analyzing the RLF report. There are multiple scenarios where a UE may declare radio link failure - details can be found in 3GPP TS 38.300 and 3GPP TS 38.331 version 18.2.0.3.3 SCG Failure Information

[0011] A UE operating in dual connectivity mode may encounter problems in the Secondary Cell Group (SCG) and declare failure on the SCG connectivity leg. If the connection to the Master Cell Group (MCG) connectivity leg is active, the UE does not declare radio link failure; instead, the sends an SCGFailur eInformation RRC message to the Master Node (MN). Upon receiving the message, the MN can take necessary actions to solve the problems.3.4 Successful Handover Report (SHR)

[0012] A Successful Handover Report (SHR) is generated by a UE performing a Primary Cell (PCell) handover if the conditions set by the network are fulfilled. These conditions are configured to trigger the UE to generate an SHR in cases where a PCell handover is successful but close to failing.########### START OF EXTRACT FROM 3GPP TS 38.300 version 18.1.0 ###########15.5.2.7 Successful HOOne of the functions of Mobility Robustness Optimization is to detect a suboptimal successful handover event. The aim is to identify underlying conditions during successful ordinary handovers, successful DAPS handovers, or successful Conditional handovers.For analysis of successful handover, the UE may collect Successful Handover Report (SHR) based on configuration by network, if stored, and makes the SHR available to the network as specified in 3GPP TS 38.331

[0012] , The UE stores the SHR until it is fetched by the network or for 48 hours after the SHR is recorded.For SHR collected during intra-NR handover, if the target NR node fetches the SHR from the UE and the trigger of SHR is T310 / T312, it may forward the information to the source NR node, i.e. the node handling the cell reported as source cell in this SHR, by using the ACCESS ANDMOBILITY INDICATION message over Xn or by means of the Uplink RAN configuration transfer procedure and Downlink RAN configuration transfer procedure over NG.If the NG-RAN node that fetches the SHR from the UE is neither the source node nor the target node of the handover, it forwards the information to the node(s) which configured the SHR trigger causing the SHR to be generated, by using the ACCESS AND MOBILITY INDICATION message over Xn or by means of the Uplink RAN configuration transfer procedure and Downlink RAN configuration transfer procedure over NG.In case of failure shortly after successful Handover, the same mobility event may generate both a SHR and a RLF report. In this case, the node(s), which configured the SHR trigger causing the SHR, may take the duplication into account e.g. ignore the SHR.Upon retrieval of an SHR, the receiving node may analyze whether its mobility configuration needs adjustment.The SHR report can be used to detect one case of Intra-system Too Late Handover, namely when DAPS HO is configured but an RLF is detected in the source cell during a successful DAPS HO.############ END OF EXTRACT FROM 3GPP TS 38.300 version 18.1.0 ############

[0013] The triggering conditions for the generation of the SHR can be configured by the source cell (before the handover (HO) execution), or by the target cell (in the HO command):• Elapsed T304 above configured T304 threshold (condition configured by the target cell)• Elapsed T310 above configured T310 threshold (condition configured by the source cell)• Elapsed T312 above configured T312 threshold (condition configured by the source cell)• RLF in source cell during Dual Active Protocol Stacks (DAPS) HO (condition configured by the source cell)

[0014] In 3 GPP release 19, the SHR will be extended with new fields / Information Elements(IES) to be used when the reported mobility procedure is an LTM procedure. Read further about this in section 3.5 below.3.5 SON for LTM

[0015] Adding SON support for LTM is in the scope of the work with release 19 of the 3GPP standard. It is generally regarded to belong to the part of SON referred to as Mobility Robustness Optimization (MRO). At the time of writing, the work is far from completed but is progressing. So far, RAN3 and RAN2 have agreed on some information to be included in SON reports sent from the UE to the network, e.g. the RLF report and the SHR, wherein some of the information is chosen to be similar to what has been specified for those reports for handover and conditional handover. However, much work remains until a comprehensive feedback framework is in place to properly support optimization of the LTM configuration.

[0016] More specifically, regarding 3GPP discussion in RAN groups related to SON for LTM, some agreements and proposals are listed below.

[0017] RAN3 agreements reached at RAN3#124 are captured below:MRO for LTM:1. RAN3 to prioritize MCG LTM over SCG LTM.RAN3 takes RAN2#125-bis agreement on MRO for LTM scenarios as baseline for further study.For failures due to wrong selection of candidate LTM cell, CU is in charge of root cause analysis and performs optimization.For failures due to inappropriate cell switch triggering (e.g. wrong cell selection at cell switch, wrong cell switch timing, . . .) source DU performs optimization.

[0018] RAN3 agreements reached at RAN3#125 are captured below:• LTM: o Reuse the existing connection failure definition of too late handover, too early handover, handover to wrong cell for LTM failure case. Add a sentence for LTM handover. o FFS to enhance failure scenario. o Take the existing detection mechanism descriptions as baseline. o For failures due to inappropriate cell switch triggering, CU initiates analysis and may forwards the RLF report to the DU responsible for the failure. o CU needs to forward the RLF related information to DU using existing Access and Mobility Indication procedure. FFS for additional information needed.

[0019] Regarding RAN2 related discussion, some of the proposals related to SON for LTM as in R2 -2407333 (Huawei) are listed below:• Proposal 1: only the field description associated to the timeConnFailure IE needs to be updated accordingly. Otherwise, no specification impact for timeConnFailure and reconnectCellld is foreseen.• Proposal 2: introduce a new field in RLF report to indicate the LTM recovery cell.• Proposal 3 : RAN2 include the specific access type in the RLF report, i.e. whether it is RA- based or RA-less cell switch.• Proposal 4: RAN2 include in the RLF report whether the network provides the TA in the cell switch command.• Proposal 5: RAN2 include in the RLF report the time since the last reception of PDCCH order towards the target cell till reception of cell switch command.• Proposal 6: In case the UE is configured with LTM config, the RA-based access could be one triggering condition for the SHR report.• Proposal 7 : In case the UE is configured with LTM config, the HO interruption time could be one triggering condition for the SHR report.SUMMARY

[0020] Systems and methods related to reporting User Equipment (UE) transmission timing error from target to source Distributed Unit (DU) during Layer 1 (LI) / Layer 2 (L2) Triggering Mobility (LTM) are disclosed. In one embodiment, a method performed by a UE comprises receiving a first Timing Advance (TA) instruction from a DU in a cell either after a successful Random Access Channel (RACH)-less LTM cell switch to the cell or after an LTM recovery to the cell. The method further comprises generating a Self-Organizing Network (SON) report including a size of a first TA adjustment indicated by the first TA instruction and transmitting the SON report to a network node. In this manner, the network is enabled to optimize how it controls early uplink (UL) synchronization of LTM candidate cells, e.g. in particular in terms of timing, e.g. reducing the risk that a RACH-less LTM cell switch fails due to an incorrect TA.

[0021] In one embodiment, inclusion of the size of the first TA adjustment in the SON report is conditional.

[0022] In one embodiment, the cell is a target cell for a RACH-less LTM cell switch, the DU is a target DU associated to the target cell, the first TA instruction is received from the target DU in the target cell after the RACH-less LTM cell switch to the target cell, and the SON report is a Successful Handover Report (SHR). In one embodiment, the method further comprises, prior to generating the SHR, determining a time duration that elapsed between the RACH-less LTM cell switch and the UE’s reception of the first TA adjustment instruction and determining that a size of a first TA adjustment indicated by the first TA instruction is greater than a predefined or configured size threshold and the determined time duration is less than a predefined or configured time threshold. Generating the SHR and transmitting the SHR to the network node are in response to determining that the size of the first TA adjustment indicated by the first TA instruction is greater than the predefined or configured size threshold and the determined time duration is less than the predefined or configured time threshold. In another embodiment, the method further comprises, prior to generating the SHR, determining that a size of a first TA adjustment indicated by the first TA instruction indicates that a difference compared to a UE-based TA measurement is greater than a certain difference threshold, wherein generating the SHR and transmitting the SHR to the network node are in response to determining that the size of the first TA adjustment indicated bythe first TA instruction indicates that the difference compared to the UE-based TA measurement is greater than the certain difference threshold.

[0023] In one embodiment, the first TA instruction is received from the cell after LTM recovery to the cell, and the SON report is a Radio Link Failure (RLF) report. In one embodiment, the method further comprises, prior to receiving the first TA instruction from the DU in the cell after the LTM recovery, determining that a RACH-less LTM cell switch to a target LTM cell has failed and, in response thereto, performing the LTM recovery to the cell.

[0024] Corresponding embodiments of a UE are also disclosed. In one embodiment, a UE is adapted to receive a first TA instruction from a DU in a cell either after a successful RACH-less LTM cell switch to the cell or after an LTM recovery to the cell, generate a SON report including a size of a first TA adjustment indicated by the first TA instruction, and transmit the SON report to a network node.

[0025] In another embodiment, a UE comprises a communication interface comprising a transmitter and a receiver, and processing circuitry associated with the communication interface. The processing circuitry is configured to cause the UE to receive a first TA instruction from a DU in a cell either after a successful RACH-less LTM cell switch to the cell or after an LTM recovery to the cell, generate a SON report including a size of a first TA adjustment indicated by the first TA instruction, and transmit the SON report to a network node.

[0026] Embodiments of a method performed by target DU of a network node in cellular communications system for providing feedback information to a source DU regarding a timing error of a UE after a LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU. In one embodiment, the method comprises measuring a timing error of reception of one or more uplink transmissions received from the UE after a RACH-less LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU and sending feedback information about the timing error measured for the UE in the target cell to the source DU via one or more Central Units (CUs).

[0027] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

[0028] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for a first uplink transmission received from the UE in the target cell; a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period Tfollowing the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero.

[0029] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

[0030] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of a timing error(s) for the UE that is greater than a predefined or configured timing error threshold; a flag indicating a number of UE transmission timing errors or a number of UE transmission timing errors that are greater than a predefined or configured timing error threshold for a number of UEs; a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which UE transmission timing errors greater than a predefined or configured timing error threshold were detected; a list of UE identities and corresponding per-UE transmission timing error information; a number of UEs for which transmission timing errors were detected; a number of UEs for which transmission timing errors greater than a predefined or configured timing error threshold were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which transmission timing errors greater than a predefined or configured transmission timing error threshold were detected and a corresponding average transmission timing error.

[0031] In one embodiment, the source DU and the target DU share a common CU, and sending the feedback information about the timing error of the UE in the target cell comprises sending the feedback information to the common CU.

[0032] In one embodiment, the source DU is associated to a source CU and the target DU is associated to a target CU, and sending the feedback information about the timing error of the UE in the target cell comprises sending the feedback information to the target CU.

[0033] In one embodiment, the method further comprises determining that one or more conditions for sending the feedback information comprising the timing error of the UE in the target cell are satisfied, wherein sending the feedback information comprising the timing error of the UE in the target cell comprises sending the feedback information comprising the timing error of theUE in the target cell responsive to the one or more conditions being satisfied. In one embodiment, the one or more conditions comprise any one or more of the following: a reception timing error exceeded a threshold; the reception timing error exceeded a threshold and this was an Nthconsecutive RACH-less LTM cell switch between the source cell and the target cell where the reception timing error exceeded the threshold; the reception timing error exceeded a threshold and this was an N111RACH-less LTM cell switch between the source cell and the target cell where the reception timing error exceeded the threshold among an M latest RACH-less LTM cell switches between the same source cell and target cell; an average of the reception timing errors for an N latest RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; a sliding average of the reception timing errors for RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; an exponential average of the reception timing errors for RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; an age of a TA at a time the UE used the TA a first time in the target cell exceeds a threshold time T; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a time alignment timer configured for the UE; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a certain percentage of the time alignment timer configured for the UE; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a time alignment timer configured for the UE minus a certain value; the age of the TA at the time the UE used the TA the first time in the target cell exceeds the time alignment timer configured for the UE plus a certain value. In another embodiment, the one or more conditions comprise any one or more of the following: one transmission timing error is detected for the UE; at least N transmission timing errors are detected for the UE; at least N transmission timing errors are detected for at least one UE; at least N transmission timing errors are detected in a given time interval for at least one UE; one transmission timing error that is greater than a threshold transmission timing error is detected for the UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected for the UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected for at least one UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected in a given time interval for at least one UE.

[0034] Corresponding embodiments of a network node for providing feedback information to a source DU regarding a timing error of a UE after an LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU are also disclosed. In one embodiment, the network node comprises processing circuitry configured to cause the network node to measure a timing error of reception of one or more uplink transmissions received from the UE after aRACH-less LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU and send feedback information about the timing error measured for the UE in the target cell to the source DU via one or more CUs.

[0035] Embodiments of a method performed by a source DU of a network node in cellular communications system for receiving and using feedback information from a target DU regarding a timing error of a UE after a LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU are also disclosed. In one embodiment, the method comprises receiving from an associated CU feedback information about a timing error of reception of one or more uplink transmissions received from a UE at a target DU after a RACH-less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU and performing one or more actions based on the feedback information.

[0036] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

[0037] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for a first uplink transmission received from the UE in the target cell; a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of a timing error(s) for the UE that is greater than a predefined or configured timing error threshold; a flag indicating a number of UE transmission timing errors or a number of UE transmission timing errors that are greater than a predefined or configured timing error threshold for a number of UEs; a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which UE transmission timing errors greater than a predefined or configured timing error threshold were detected; a list of UE identities and corresponding per-UE transmission timing error information; a number of UEs for which transmission timing errors were detected; a number of UEs for which transmission timing errors greater than a predefined or configured timingerror threshold were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which transmission timing errors greater than a predefined or configured transmission timing error threshold were detected and a corresponding average transmission timing error.

[0038] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises an indication that a transmission timing error occurred.

[0039] In one embodiment, the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

[0040] In one embodiment, the one or more actions performed by the source DU based on the feedback information comprise one or more actions related to optimization of timing of early synchronizations for future potential LTM cell switches, refraining from using early uplink synchronization, refraining from using network-ordered early uplink synchronization, or refraining from using or relying on UE autonomous early uplink synchronization.

[0041] Corresponding embodiments of a network node for receiving and using feedback information from a target DU regarding a timing error of a UE after an LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU are also disclosed. In one embodiment, the network node comprises processing circuitry configured to cause the network node to receive from an associated CU feedback information about a timing error of reception of one or more uplink transmissions received from a UE at a target DU after a RACH- less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU and perform one or more actions based on the feedback information.

[0042] In another embodiment, a method performed by a CU of a network node in cellular communications system associated to target DU that operates a target cell for a LTM cell switch from a source cell operated by the source DU to the target cell operated by the target DU comprises sending, toward the source DU, information comprising a time alignment timer configured for the target cell for the LTM cell switch.

[0043] In one embodiment, the information comprising the time alignment timer is sent during a preparation phase of the LTM cell switch procedure.

[0044] In one embodiment, the method further comprises receiving feedback information about a timing error of reception of one or more uplink transmissions received from a UE at the target DU after a RACH-less LTM cell switch from the source cell operated by the source DU to the target cell operated by the target DU.

[0045] In one embodiment, the method further comprises transmitting feedback information about a timing error of reception of one or more uplink transmissions received from a UE at the target DU after a RACH-less LTM cell switch from the source cell operated by the source DU to the target cell operated by the target DU.

[0046] In another embodiment, a method performed by a target DU of a network node in cellular communications system for a LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU comprises sending, toward the source DU, an instruction for the source DU to initiate early uplink synchronization for a UE for which the LTM cell switch.BRIEF DESCRIPTION OF THE DRAWINGS

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

[0048] Figure 1 is a reproduction of Figure 9.2.3.5.2-1 of 3rdGeneration Partnership Project (3GPP) Technical Specification (TS) 38.300 V18.2.0.

[0049] Figures 2A and 2B illustrate exemplary procedures in which a target Distributed Unit (DU) of a Random Access Channel (RACH)-less Layer 1 (Ll) / Layer 2 (L2) Triggered Mobility (LTM) cell switch for a User Equipment (UE) provides feedback information regarding a timing error of reception of the UE’s transmission (i.e., the UE’s transmission timing error) to a source DU of the RACH-less LTM cell switch for the UE via a common Central Unit (CU) (Figure 2A) or via a target CU and a source CU (Figure 2B), in accordance with embodiments of the present disclosure.

[0050] Figure 3 is a flow chart that illustrates an example embodiment of the operation of UE to include an initial Time Alignment (TA) adjustment in a Successful Handover Report (SHR), in accordance with an embodiment of the present disclosure.

[0051] Figure 4 is a flow chart that illustrates an example embodiment of the operation of UE to include the initial TA adjustment in a Radio Link Failure (RLF) report, in accordance with an embodiment of the present disclosure.

[0052] Figure 5A illustrates an exemplary embodiment of the present disclosure that pertains to an intra-CU LTM cell switch.

[0053] Figure 5B illustrates an exemplary embodiment of the present disclosure that pertains to an inter-CU LTM cell switch.

[0054] Figure 6 is a flow chart that illustrates the operation of a UE where a size of a first TA adjustment in a target cell of an LTM cell switch is used as a trigger for SHR generation, in accordance embodiments of the present disclosure.

[0055] Figure 7 is a flow chart that illustrates the operation of a UE for SHR generation in case of autonomous UE-based TA measurement, in accordance with embodiments of the present disclosure.

[0056] Figure 8A illustrates another exemplary embodiment of the present disclosure that pertains to an intra-CU LTM cell switch.

[0057] Figure 8B illustrates another exemplary embodiment of the present disclosure that pertains to an inter-CU LTM cell switch.

[0058] Figure 9 shows an example of a communication system in accordance with some embodiments.

[0059] Figure 10 shows a UE in accordance with some embodiments.

[0060] Figure 11 shows a network node in accordance with some embodiments.

[0061] Figure 12 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.DETAILED DESCRIPTION

[0062] The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

[0063] 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.

[0064] There currently exist certain challenge(s). Early downlink (DL) and uplink (UL) synchronization in the Layer 1 (LI) / Layer 2 (L2) Triggered Mobility (LTM) candidate cell(s), in particular early UL synchronization (for which DL synchronization is a prerequisite), is important because it enables Random Access Channel (RACH)-less access in the LTM target cell once the LTM cell switch is executed. As such, receiving feedback on the performance of the early UL synchronization could be beneficial for the network for Self-Organizing Network (SON) purposes, e.g. enabling the network to tune / adapt / optimize its policies for how to control the early ULsynchronization. However, there is no similar feedback information in the existing SON framework which could be reused for SON for LTM, and 3 GPP has not yet worked out any such feedback information or feedback information mechanisms. This is a void that embodiments of the solution(s) described herein aim to fill.

[0065] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. The purpose of the early UL synchronization feature is to ensure that the User Equipment (UE) transmits with the correct timing, i.e. using a correct timing advance, when accessing the LTM target cell. How close the UE’s transmission timing in the LTM target cell (in particular during the first transmission or the first few transmissions in the LTM target cell) is to the ideal transmission timing can thus be seen as a measure of how well the early UL synchronization mechanism worked or performed. In particular, if the UE’s transmission timing error (i.e. the amount by which the UE’s transmission timing deviated from the ideal transmission timing) is close to the limit where transmission timing error is so large that the network, e.g. the target Radio Access Network (RAN) node (e.g., gNodeB, gNB) Distributed Unit (DU), cannot receive the transmission (e.g. cannot properly detect and / or decode the transmission), this may be an indication that the early UL synchronization was close to failing and the source DU’s way of controlling the early UL synchronization mechanism may need to be adapted / tuned / optimized to reduce the risk of future LTM cell switch failures, e.g. between the same pair of cells, i.e. between the same LTM source and target cells.

[0066] The above discussion implies that it may be beneficial for the source DU of a RACH- less LTM cell switch for a UE to be informed of the UE’s transmission timing error (i.e. a measure of how good the UE’s Timing Advance (TA) was) when accessing the LTM target cell, in particular the timing error of the UE’s first transmission in the LTM target cell (or possibly one of the UE’s first few transmissions in the LTM target cell). To this end, embodiments of systems and methods are disclosed herein in which the target DU of an LTM cell switch may collect information about the concerned UE’s transmission timing error (i.e. how much its transmission timing deviated from the ideal transmission timing) and report this to the source DU (via a common RAN node (e.g., gNB) Central Unit (CU) in case of an intra-RAN node (e.g., intra-gNB) LTM cell switch or via the target DU’s CU and the source DU’s CU in case of an inter-RAN node (e.g., inter-gNB) LTM cell switch).

[0067] Certain embodiments may provide one or more of the following technical advantage(s). Embodiments of the present disclosure may enable the network to optimize how it controls early UL synchronization of LTM candidate cells, e.g. in particular in terms of timing, e.g. reducing the risk that a RACH-less LTM cell switch fails due to an incorrect TA.

[0068] Now, a more detailed description of embodiments of the present disclosure will be provided.

[0069] The following notes provide relevant information that is applicable to present disclosure. They include terminology explanations, generalizations, etc.The term “network” as used herein refers to a network node, which typically will be a gNB, but which may also be an evolved NodeB (eNB), or a base station or an access point in another type of network, or any other network node with the ability to directly or indirectly communicate with a UE. Refinements with finer granularity are also conceivable. For instance, a gNB may be an en-gNB, and if a split gNB architecture is applied (dividing the gNB into multiple separate entities or nodes), the term “node” may refer to a part of the gNB, such as a gNB-CU (often referred to as just CU), a gNB-DU (often referred to as just DU), a gNB-CU-Control Plane (CP) or a gNB-CU-User Plane (UP). Similarly, an eNB may be an ng-eNB, and if a split eNB architecture is applied (dividing the eNB into multiple separate entities or nodes), the term “network” (and the network node it implies) may refer to a part of the eNB, such as an eNB-CU, an eNB-DU, an eNB-CU-CP or an eNB-CU-UP. Furthermore, the term “network” (and the network node it implies) may also refer to an Integrated Access and Backhaul (lAB)-donor, lAB-donor-CU, lAB-donor-DU, lAB-donor-CU-CP, or an lAB-donor-CU-UP.The terms “LTM candidate cell” and “LTM target cell” are used herein. The term “LTM candidate cell” refers to a cell which has been prepared to be the potential target of an LTM cell switch, wherein the preparation consists of configuration data that has been provided to the UE and which the UE should apply if / when executing the LTM cell switch towards the concerned LTM candidate cell) as well as configuration data in the DU which serves and controls the LTM candidate cell. The term “LTM target cell” is used to refer to the LTM candidate cell for which execution of the LTM cell switch is triggered. Correspondingly, an “LTM candidate DU” refers to a DU that serves / controls one or more LTM candidate cell(s), and an “LTM target DU” refers to the DU that serves / controls the LTM target cell. In the context of this document, an LTM candidate cell may also simply be referred to as a “candidate cell” and an LTM target cell may be referred to as a “target cell”. Correspondingly, an LTM candidate DU may be referred to as a “candidate DU” and an LTM target DU may be referred to as a “target DU”. Furthermore, the source cell of an LTM cell switch (i.e., the cell in which the UE is connected when the LTM cell switch execution is triggered) may be referred to as the “LTM source cell” or, for simplicity, the“source cell”. Correspondingly, the DU controlling the LTM source cell may be referred to as the “LTM source DU” or, for simplicity, the “source DU”.That a UE generates a SON report (e.g., generates an SHR) and that UE logs a SON report (e.g., logs an SHR) are herein considered to be the same type of action.In the present disclosure, NR is used as the radio access technology of reference. However, this is only an example taken for simplicity and it should not be limiting. The methods described herein apply to any radio access technology which supports a mobility mechanism that uses RACH-less access in the target cell of the mobility procedure, in particular (but not only) when the mobility mechanism uses early UL synchronization in the cell that will become the target cell to support RACH-less access in the target cell.The terms information element (IE) and field are used herein more or less interchangeably. Also, the term parameter is sometimes used to denote the same concept.Param eters / IEs / fields used in ASN.1 code as well as in procedural text in the 3 GPP Radio Resource Control (RRC) specification for 5G / NR, i.e. 3GPP TS 38.331 (of which the most recent official version at the time of writing is version 18.3.0), are often named with a suffix indicating the number of the release of the 3 GPP standard the param eter / IE / field was introduced in (e.g. the suffix “-rl8” for a parameter / IE / field introduced in release 18 of the 3GPP standard). Parameters / IEs / fields following this naming convention are typically referred to both with and without the suffix, where the name including the suffix is used in the ASN. l code (and thus defines the formal name from the ASN. l compiler’s perspective), while the name without the suffix is used in running text, e.g. in field descriptions and procedural text. In this document, both name variants may occur for various parameters / IEs / fields.When writing message names of a communication protocol, two equivalent principles are used herein. The writing principle “<protocol name> <message name> message”, for example “XnAP HANDOVER REQUEST message”, and the writing principle “<message name> <protocol name> message”, for example “HANDOVER REQUEST XnAP message” are equivalent, both referring to a message (i.e., “<message name>”) of a communication protocol (i.e., “<protocol name>”), e.g., the HANDOVER REQEUST message of the communication protocol XnAP. The same writing format equivalence applies to other communication protocols, such as NGAP, RRC, and Medium Access Control (MAC).In the present disclosure, is the description frequently refers to a UE’ s transmission timing error. Note that this is equivalent to the reception timing error in the node receiving theUE’s transmission, i.e. the amount of time by which the reception timing deviated from the ideal reception timing, i.e. the time at which the UE’s transmission should have been received if the UE had used a perfect TA.In the present disclosure, a “flag” that may be conveyed via signaling typically refers to a binary indication, i.e. an indication that may have only two possible values, e.g. a singlebit indicator. A “flag” may also refer to an indicator that may have only one possible value, while absence of the indicator in a certain signaling message implicitly indicates the other value.In the present disclosure, “presence of a UE transmission timing error” (which, e.g., may be indicated / reported via signaling) means that a UE transmission timing error occurred.

[0070] The purpose of the early UL synchronization feature is to ensure that the UE transmits with the correct timing, i.e. using a correct timing advance, when accessing the LTM target cell. How close the UE’s transmission timing in the LTM target cell (in particular during the first transmission or the first few transmissions in the LTM target cell) is to the ideal transmission timing can thus be seen as a measure of how well the early UL synchronization mechanism worked or performed. In particular, if the UE’s transmission timing error (i.e. the amount by which the UE’s transmission timing deviated from the ideal transmission timing) is close to the limit where transmission timing error is so large that the network, e.g. the target DU, cannot receive the transmission (e.g. cannot properly detect and / or decode the transmission) may be an indication that the early UL synchronization was close to failing and the source DU’s way of controlling the early UL synchronization mechanism may need to be adapted / tuned / optimized to reduce the risk of future LTM cell switch failures, e.g. between the same pair of cells, i.e. between the same LTM source and target cells.

[0071] The above discussion implies that it may be beneficial for the source DU of a RACH- less LTM cell switch for a UE to be informed of the UE’s transmission timing error (i.e. a measure of how good the UE’s TA was) when accessing the LTM target cell, in particular the timing error of the UE’s first transmission in the LTM target cell (or possibly one of the UE’s first few transmissions in the LTM target cell).

[0072] For instance, if a DU repeatedly receives reports of UE transmission timing errors which are almost too large (and in the same direction, i.e. too early or too late arrival of the UE’s transmission at the target DU) in target cell(s) (e.g. a certain target cell) during LTM cell switch executions for which the DU is the source DU, it can deduce (or assume) that the reason for this is that the TA the UE used in the target cell, which was determined using early UL synchronization, may have been almost too old (and thus had become almost outdated) at the time of the LTM cellexecution. That the age of the UE’ s target cell TA (i.e. the time since the TA was determined based on early UL synchronization) was almost too old may in turn e.g. be because UEs often move fast (or faster than UEs typically move) in the part of the source cell in which the concerned target cell is a suitable target cell, e.g. in the area at or close to the border between the source cell and the target cell.

[0073] As a corrective / optimizing action, the DU (i.e. the source DU of these LTM cell switches) may ensure to keep the time between (the last) early UE synchronization in the concerned LTM candidate cell (i.e. the cell which the reported close to too large UE transmission timing errors were associated with) and the execution of the LTM cell switch towards that LTM candidate / target cell short (or shorter than the DU used to in conjunction with the LTM cell switch procedures the reports of almost too large UE transmission timing errors pertained to).

[0074] In accordance with embodiments of the present disclosure, the way to enable that the source DU is provided with feedback information regarding the UE’s transmission timing error in the target cell is that the target DU of the LTM cell switch procedure measures the timing error of the reception of the UE’s transmission (which is equivalent to the UE’s transmission timing error) and reports it to the source DU via the common CU (i.e. the CU which controls both the source DU and the target DU in an intra-gNB / intra-CU LTM cell switch), if the LTM cell switch is an intra-gNB LTM cell switch (see, e.g., Figure 2A), or via the two CUs of the two involved gNBs (i.e. the CU controlling the target DU and the CU controlling the source DU), if the LTM cell switch is an inter-gNB LTM cell switch (see, e.g., Figure 2B).

[0075] Example embodiments of a procedure in accordance with embodiments of the present disclosure are illustrated in Figure 2A and Figure 2B. Figure 2A illustrates an example in which a target DU of a RACH-less LTM cell switch for a UE provides feedback information regarding a timing error of reception of the UE’s transmission (which is equivalent to the UE’s transmission timing error) to a source DU of the RACH-less LTM cell switch for the UE via a common CU. Optional steps are represented by dashed lines. As illustrated, LTE preparation, early synchronization to candidate LTM cell(s), and RACH-less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU are performed, e.g., in the conventional manner (e.g., as discussed above in the Background with respect to Figure 1) (steps 200, 202, and 204). The UE transmits one or more UL transmissions on the target cell after the RACH-less LTM cell switch (step 206). The target DU measures a timing error of the reception of the UE’s UL transmission(s) (step 208). The target DU may also, in some embodiments, determine whether one or more conditions for reporting information about the measured timing error is(are) satisfied and, if so, proceeds to step 212 (otherwise the process may, for example,end) (step 210). Details regarding various examples and embodiments related to such conditions are described below and are equally applicable here to step 210. The target UE sends, to the source DU via the common CU, information about the measured timing error of the reception of the UE’s UL transmission(s) (steps 212 and 214). This information may be, for example, the measured timing error, an indication that there is a timing error (e.g., a timing error greater than a certain threshold), etc., as described below. Details regarding what information is sent from the target DU to the source DU and how this information is sent are described below and are equally appliable here to steps 212 and 214. The source DU may then perform one or more action(s) based on the received information about the timing error of the UE, as described in the various examples and embodiments described below (step 216).

[0076] Figure 2B illustrates another example that is similar to that of Figure 2A, but where the RACH-less LTM cell switch is an inter-CU LTM cell switch. Steps 200-210 and 216 are the same as described above with respect to Figure 2A. However, when sending the information about the timing error in step 212, the target DU first sends the information about the timing error to a target CU (step 212a), and the target CU sends the information about the timing error to the source CU (step 212b), which in turn sends the information about the timing error to the source DU (step 214).

[0077] The reception timing error that the target DU measures and reports (e.g., in steps 208 and 212) may for instance be one of: the reception timing error of the UE’ s first transmission in the LTM target cell, the reception timing error of one of the UE’s first few transmissions in the LTM target cell, e.g. one of the UE’s N first transmissions in the LTM target cell, where N may be: o specified in a standard, o configured in the DU, e.g. by the CU or by the Operations, Administration, and Maintenance (0AM) system or by the 0AM system via the CU, or o DU implementation specific, either hardcoded in the implementation or determined by an algorithm encoded in the implementation; the reception timing of one of the UE’ s transmissions during the first time period T following the UE’s access to the LTM target cell (which may include the UE’s first transmission in the LTM target cell), where T may be: o specified in a standard, o configured in the DU, e.g. by the CU or by the 0AM system or by the 0AM system via the CU, oro DU implementation specific, either hardcoded in the implementation or determined by an algorithm encoded in the implementation; the average reception timing of the UE’s first transmissions in the LTM target cell, e.g. the average reception timing of the UE’s N first transmissions in the LTM target cell, where N may be: o specified in a standard, o configured in the DU, e.g. by the CU or by the 0AM system or by the 0AM system via the CU, or o DU implementation specific, either hardcoded in the implementation or determined by an algorithm encoded in the implementation; the average reception timing of the UE’s first transmissions during the first time period T following the UE’s access to the LTM target cell (which may include the UE’s first transmission in the LTM target cell), where T may be: o specified in a standard, o configured in the DU, e.g. by the CU or by the 0AM system or by the 0AM system via the CU, or o DU implementation specific, either hardcoded in the implementation or determined by an algorithm encoded in the implementation.

[0078] In some embodiments, the target DU does not transfer the UE’s transmission timing error per se, but rather indicates (in the information sent in step 212) to the source DU that a transmission timing error occurred, e.g. that it was greater than a configured or standardized threshold. To this end, in some embodiments, the target DU of the LTM cell switch procedure reports to the source DU via the common CU (i.e., the CU which controls both the source DU and the target DU in an intra-gNB / intra-CU LTM cell switch), if the LTM cell switch is an intra-gNB LTM cell switch (see, e.g., Figure 2A), or via the two CUs of the two involved gNBs (i.e., the CU controlling the target DU and the CU controlling the source DU), if the LTM cell switch is an inter-gNB LTM cell switch (see, e.g., Figure 2B), indication(s) concerning the presence of timing error(s), or sub-optimally large timing error(s) (e.g., exceeding a configured or standardized threshold) for one or a list of UEs. Non-limiting examples of such indications can be: a flag indicating the presence of UE transmission timing error(s) for one UE (e.g., in a UE- associated signaling message);a flag indicating the presence of too large UE transmission timing error(s) for one UE (e.g., in a UE-associated signaling message) wherein the aspect of a timing error being too large can be based on the definition detailed elsewhere in the context of embodiments of the present disclosure; a flag indicating the presence of a sub-optimally large UE transmission timing error(s) (e.g., in a UE-associated signaling message); a flag indicating a number of UE transmission timing errors or a number of too large transmission timing errors or a number of sub-optimally large UE transmission timing error (e.g. exceeding a configured or standardized threshold) for a number of UEs (e.g., in a non- UE-associated signaling message comprising aggregated information concerning the number of UE transmission timing errors or the number of too large UE transmission timing errors or the number of sub-optimally large UE transmission timing errors detected by the target DU for a number of UEs, wherein the number of UEs (as one option) also may be indicated or (as another option) may not be indicated; a list of UE identities indicating UEs for which UE transmission timing errors were detected (e.g., in a non-UE-associated signaling message, comprising a list of UE identities, indicating the UEs for which transmission timing error(s) was(were) detected); a list of UE identities indicating UEs for which too large UE transmission timing errors were detected (e.g., in a non-UE-associated signaling message, comprising a list of UE identities, indicating the UEs for which too large transmission timing error(s) was(were) detected); a list of UE identities indicating UEs for which sub-optimally large UE transmission timing errors (e.g., UE transmission timing errors exceeding a configured or standardized threshold) were detected (e.g., in a non-UE-associated signaling message, comprising a list of UE identities, indicating the UEs for which too large transmission timing error(s) was(were) detected); a list of UE identities and corresponding per-UE transmission timing error information (e.g., in a non-UE-associated signaling message, comprising a list of UE identities and associated UE transmission timing error information); a number of UEs for which transmission timing errors were detected (e.g., in a non-UE- associated signaling message, comprising an aggregated value indicating the number of UEs - such as the number of UEs in a certain time interval - for which transmission timing errors were detected by the target DU);a number of UEs for which too large transmission timing errors were detected (e.g., in a non-UE-associated signaling message, comprising an aggregated value indicating the number of UEs - such as the number of UEs in a certain time interval - for which too large transmission timing errors were detected by the target DU); a number of UEs for which sub-optimally large transmission timing errors were detected (e.g., in a non-UE-associated signaling message, comprising an aggregated value indicating the number of UEs - such as the number of UEs in a certain time interval - for which sub-optimally large transmission timing errors were detected by the target DU); a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which too large transmission timing errors were detected and a corresponding average transmission timing error. a number of UEs for which sub-optimally large transmission timing errors (e.g., UE transmission timing errors exceeding a configured or standardized threshold) were detected and a corresponding average transmission timing error.

[0079] With this piece of information (i.e. any kind of UE transmission timing error information described above), the source DU can (e.g., in step 216) determine e.g., not to let a TA acquired through early uplink synchronization get too old before triggering the LTM cell switch for future UEs configured with LTM in the same cell or in the same part of the cell, or when other circumstances are similar to what they were for the LTM cell switches for which UE transmission timing error information has been reported. To achieve this, the source DU may delay the early UL synchronization longer than it would otherwise have done, or the source DU may trigger repeated early UL synchronizations with shorter intervals (i.e., more frequent early UL synchronizations) than it typically does or would have done if the reported UE transmission error feedback information had not been received. In general, the source DU may use (e.g., in step 216) the feedback information it receives about the UEs’ transmission timing errors in the target cell / DU to optimize the timing(s) of the early UL synchronizations for future potential LTM cell switches. A further corrective or optimizing action the source DU may decide to perform is to refrain from using early UL synchronization or refrain from using network-ordered early UL synchronization (using PDCCH order and UE transmission of a random access preamble in the LTM candidate cell) or refrain from using or relying on UE autonomous early UL synchronization. The source DU may do any of the above, e.g. for one or more of: future LTM cell switches;future potential LTM cell switches (where “potential” refers to the fact that at the time of early UL synchronization, it is not certain that the LTM cell switch will actually be executed); future LTM cell switches in similar situations, i.e. with similar circumstances, e.g.: when the LTM cell switch or potential LTM cell switch is configured to be performed from the same source cell to the same LTM candidate cell (or target cell) as was the case in the LTM cell switches which the reported UE transmission timing information pertained to, when the LTM cell switch or potential LTM cell switch is configured to be performed from the same source cell to the same SSB beam or CSLRS beam or group of beams or to the same TCI state in the same LTM candidate cell (or target cell) as was the case in the LTM cell switches which the reported UE transmission timing information pertained to; when the LTM cell switch or potential LTM cell switch is expected to be performed from the same part of the source cell, or from the same beam (e.g. SSB beam or CSI-RS beam) or group of beams in the source cell, or from the same TCI state in the source cell, to the same LTM candidate cell (or target cell) as was the case in the LTM cell switches which the reported UE transmission timing information pertained to, when the LTM cell switch or potential LTM cell switch is expected to be performed from the same part of the source cell, or from the same beam (e.g. SSB beam or CSI-RS beam) in the source cell, or from the same TCI state in the source cell, to the same SSB beam or CSI-RS beam or to the same TCI state in the same LTM candidate cell (or target cell) as was the case in the LTM cell switches which the reported UE transmission timing information pertained to;

[0080] The source DU may do any of the above for: a certain UE; any UE; all UEs;UEs of a certain type or certain types;UEs of a certain category or certain categories;UEs running certain applications, e.g. URLLC applications;UEs with certain capabilities or UEs lacking certain capabilities;UEs in similar situations, e.g. with similar circumstances, as the UEs for which transmission timing error information was previously reported (see above).

[0081] It is a possible option to specify one or two new F1AP message(s) for conveying the reported feedback information (i.e. the measured reception timing error) from the target DU to the CU and from the CU to the source DU, as well as a new XnAP message for conveying the feedback information between the CUs in case of an inter-gNB LTM cell switch, but a more preferable option may be to reuse existing messages and extend them with new IES for the transmission / reception timing error feedback information. To this end, a new IE could be specified in the ACCESS SUCCESS F1AP message, or possibly in the DU-CU ACCESS MOBILITY INDICATION Fl AP message, for conveying the transmission / reception timing error information from the target DU to the CU. And for conveying the transmission / reception timing error information from the CU to the source DU, a new IE could be specified in the UE CONTEXT RELEASE COMMAND F1AP message or in the ACCESS AND MOBILITY INDICATION F1AP message.

[0082] Reporting the UE’s transmission timing error (or equivalently the reception timing error in the target DU) from the target DU to the source DU is one way of conveying the desired feedback information that enables the source DU to assess how well the early UL synchronization performed. However, other, similar but slightly different, information could be reported (e.g., in steps 212 and 214) instead to provide the same insight for the source DU. Alternatives to reporting the UE’s transmission timing error (or equivalently the reception timing error in the target DU) from the target DU to the source DU include e.g.:Reporting from the target DU to the source DU the margin to a too large UE transmission timing error, i.e. the difference between the UE’s transmission timing error and a too large transmission timing error, where a too large transmission timing error is a transmission timing error that is so large that it prevents the target DU from successfully receiving the transmission, e.g. a transmission timing error that exceeds the length of the cyclic prefix (CP) used on the PUSCH.Reporting the size of the first network-controlled TA adjustment (e.g., the size of the TA adjustment indicated in the first Timing Advance Command MAC CE) the target DU sends to the UE in the target cell.

[0083] The various variants of the reporting from the target DU to the source DU described above, may, as a possible option or variation of the solution, be conditional (see, e.g., step 210), i.e. the target DU could be configured, mandated by a standard, or hardcoded by implementationto send the report with the feedback information only if one or more certain condition(s) is(are) fulfilled. Such a condition (of which more than one may be combined) could, e.g., be that: the reception timing error exceeded a threshold (wherein the threshold may be configured, specified in a standard, or hardcoded by implementation); the reception timing error exceeded a threshold (wherein the threshold may be configured, specified in a standard, or hardcoded by implementation) and this was the N111consecutive RACH-less LTM cell switch between the same source cell and target cell where the reception timing error exceeded the threshold (where N may be configured, specified in a standard, or hardcoded by implementation); the reception timing error exceeded a threshold (wherein the threshold may be configured, specified in a standard, or hardcoded by implementation) and this was the NthRACH-less LTM cell switch between the same source cell and target cell where the reception timing error exceeded the threshold among the M latest RACH-less LTM cell switches between the same source cell and target cell (where N may be configured, specified in a standard, or hardcoded by implementation, and M may be configured, specified in a standard, or hardcoded by implementation); the average of the reception timing errors for the N latest RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold, which may be configured, specified in a standard, or hardcoded by implementation (and wherein N may be configured, specified in a standard, or hardcoded by implementation); the sliding average of the reception timing errors for RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold (which may be configured, specified in a standard, or hardcoded by implementation); the exponential average of the reception timing errors for RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold (wherein the threshold may be configured, specified in a standard, or hardcoded by implementation, and the parameter deciding how fast the impact of older samples (i.e. reception timing errors) decline may be configured, specified in a standard or hardcoded by implementation); the age of the TA at the time the UE used it the first time in the target cell exceeds a threshold time T, where T may be configured, specified in a standard , or hardcoded by implementation (if the TA the UE used in the target cell was established using network- controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell SwitchCommand MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA); the age of the TA at the time the UE used it the first time in the target cell exceeds the time alignment timer configured for the UE (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA); the age of the TA at the time the UE used it the first time in the target cell exceeds X% of the time alignment timer configured for the UE (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA), where X may be configured, specified in a standard, or hardcoded by implementation; the age of the TA at the time the UE used it the first time in the target cell exceeds the time alignment timer (TAT) configured for the UE minus t (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA), i.e. TAage > TAT - 1 (where TAage is the age of the TA, TAT is the time alignment timer value configured for the UE, and t is a non-negative value smaller than or equal to TAT, i.e. 0 < t <TAT), where t may be configured, specified in a standard, or hardcoded by implementation; the age of the TA at the time the UE used it the first time in the target cell exceeds the time alignment timer (TAT) configured for the UE plus t (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA), i.e. TAage > TAT + 1 (where TAage is the age of the TA, TAT is the time alignment timer value configured for the UE, and t is a non-negative value, i.e. t > 0, where t may be configured, specified in a standard, or hardcoded by implementation;the age of the TA at the time the UE used it the first time in the target cell exceeds the time alignment timer (TAT) configured for the UE plus t (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA), i.e. TAage > TAT + 1 (where TAage is the age of the TA, TAT is the time alignment timer value configured for the UE, and t is a value fulfilling -TAT < t <TAT), where t may be configured, specified in a standard, or hardcoded by implementation.

[0084] As additional variants, the reporting from the target DU to the source DU, may, as a possible option or variation of the solution, be conditional, i.e. the target DU could be configured, mandated by a standard, or hardcoded by implementation to send the report with the feedback information only if one or more of the following (additional) condition(s) (possibly in combination) is(are) fulfilled: one transmission timing error is detected for a certain UE; at least N transmission timing errors are detected for a certain UE; at least N transmission timing errors are detected for at least one UE; at least N transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE; one too large transmission timing error is detected for a certain UE; at least N too large transmission timing errors are detected for a certain UE; at least N too large transmission timing errors are detected for at least one UE; at least N too large transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE; one suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing error is detected for a certain UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected for a certain UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected for at least one UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE;

[0085] In the possible conditions listed above which in some way involves the age of the time alignment timer, the target DU may count the age of the time alignment timer from the time when the target DU determined the time alignment timer or from the time when the target DU provided the determined time alignment timer (along with other UE context information) to the CU which the CU (or the source CU in case of an inter-CU LTM cell switch) sent to the UE as preparation for a potential LTM cell switch, i.e. the target DU determines the age of the time alignment timer as the time that has elapsed since the target DU provided the target cell time alignment timer (for the concerned UE, i.e. the UE that performed the LTM cell switch) to the CU. The target DU may send this information to the CU, e.g. in one of the F1AP messages UE CONTEXT MODIFICATION RESPONSE, UE CONTEXT MODIFICATION REQUIRED, UE CONTEXT SETUP RESPONSE, or DU-CU TA INFORMATION TRANSFER.

[0086] Some additional alternative or complementing embodiments will now be described.

[0087] Including the initial TA adjustment in SON reports:

[0088] In embodiments that are alternative or complementing to the embodiments described above, the UE may include in an SHR (pertaining to a RACH-less LTM cell switch) the size of the TA adjustment indicated in the first TA adjustment instruction received from the target DU in the target cell after the LTM cell switch (i.e. the size of the TA adjustment indicated in the first Timing Advance Command MAC CE the UE received in the target cell after the LTM cell switch).

[0089] Figure 3 is a flow chart that illustrates an example embodiment of the operation of UE to include the initial TA adjustment in a SHR. As illustrated, the UE performs a RACH-less LTM cell switch to a target cell (step 300). The UE receives a first TA adjustment instruction from the target DU in the target cell after the RACH-less LTM cell switch (step 302). The UE generates a SHR including a size of the first TA adjustment (step 304). As discussed below, including of the size of the first TA adjustment in the SHR may, in some embodiments, be conditional. The UE transmits the SHR to a network node (e.g., the target DU) (step 306).

[0090] Optionally, the inclusion of this information (i.e., the size of the first TA adjustment) in the SHR (e.g., in step 304) may be conditioned by the time that elapsed between the LTM cell switch and the reception of the first TA adjustment instruction in the target cell. For instance, the UE may be configured, or requested by its serving CU, or by the serving DU, or may be mandated by a standard, or may be hardcoded by implementation to include in the SHR (when an SHR pertaining to a RACH-less LTM is triggered) the size of the TA adjustment indicated in the first TA adjustment instruction received from the target DU in the target cell if the elapsed time between the LTM cell switch and the reception of the first TA adjustment instruction from the target DU in the target cell is shorter than a threshold time T, where T may be configured (e.g. by the CUserving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the SHR an indication of the time that elapsed between the LTM cell switch and the reception of the first TA adjustment instruction from the target DU in the target cell.

[0091] As another option, inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the target cell of a RACH-less LTM cell switch in the SHR (pertaining to the LTM cell switch) (e.g., generated in step 304) may be conditioned by the time that elapsed between the last preamble transmission in the target cell the UE performed triggered by a Physical Downlink Control Channel (PDCCH) order in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction in the target cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include in the SHR (when an SHR pertaining to a RACH-less LTM is triggered) the size of the TA adjustment indicated in the first TA adjustment instruction received from the target DU in the target cell if the elapsed time between the last preamble transmission in the target cell the UE performed triggered by a PDCCH order in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction from the target DU in the target cell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the SHR an indication of the time that elapsed between the last preamble transmission in the target cell the UE performed triggered by a PDCCH order in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction from the target DU in the target cell.

[0092] As yet another option, if the UE uses an autonomously determined TA during a RACH- less LTM cell switch, inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the target cell of a RACH-less LTM cell switch in the SHR (pertaining to the LTM cell switch) (e.g., generated in step 304) may be conditioned by the time that elapsed between the last autonomous target cell TA determination the UE performed in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction in the target cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include in the SHR (when an SHR pertaining to a RACH-less LTM is triggered) the size of the TA adjustment indicated in the first TA adjustment instruction received from the target DU in the target cell if the elapsed time between the last autonomous target cell TA determination the UE performed in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction in the targetcell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the SHR an indication of the time that elapsed between the last autonomous target cell TA determination the UE performed in the source cell prior to the LTM cell switch and the reception of the first TA adjustment instruction in the target cell.

[0093] In other embodiments that are alternative or complementing to the embodiments described above, the UE may include in an RLF report triggered by an LTM cell switch failure the size of the TA adjustment indicated in the first TA adjustment instruction (e.g. the first Timing Advance Command MAC CE or the first Timing Advance Command in a RAR) received from the network after a RACH-less LTM recovery in the cell that was the target cell of the failed LTM cell switch. In case of a RACH-less LTM recovery in another cell than the source and target cells of the failed LTM cell switch, the UE may include the size of the TA adjustment indicated in the first TA adjustment instruction received in the LTM recovery cell after the LTM recovery.

[0094] Figure 4 is a flow chart that illustrates an example embodiment of the operation of UE to include the initial TA adjustment in a RLF report. As illustrated, the UE determines that a RACH-less LTM cell switch to a target cell has failed (step 400) and performs an LTM recovery either to the target cell of the LTM cell switch or some cell other than the source and target cells of the LTM cell switch (step 402). The UE receives a first TA adjustment instruction from the DU in the cell after the LTM recovery (step 404). The UE generates a RLF report including a size of the first TA adjustment (step 406). As discussed below, including of the size of the first TA adjustment in the RLF report may, in some embodiments, be conditional. The UE transmits the RLF report to a network node (e.g., the DU operating the cell in which the UE performed the LTM recovery) (step 408).

[0095] Optionally, inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the LTM recovery in the RLF report (triggered by an LTM cell switch failure prior to the LTM recovery) (e.g., in step 406) may be conditioned by the time that elapsed between the failed LTM cell switch (either the trigger of the LTM cell switch or the determination of that the LTM cell switch has failed, i.e. expiration of timer T304) and the reception of the first TA adjustment instruction in the LTM recovery cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include the size of the TA adjustment indicated in the first TA adjustment instruction received in the LTM recovery cell if the time that elapsed between the failed LTM cell switch (either the trigger of the LTM cell switch or the determination of that the LTM cell switch has failed, i.e. expiration of timer T304) and the reception of the first TA adjustmentinstruction in the LTM recovery cell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the RLF report an indication of the time that elapsed between the failed LTM cell switch (either the trigger of the LTM cell switch or the determination of that the LTM cell switch has failed, i.e. expiration of timer T304) and the reception of the first TA adjustment instruction in the LTM recovery cell. Optionally, the above is restricted to cases where the failed LTM cell switch was a RACH-less LTM cell switch.

[0096] As another option, inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the LTM recovery in an RLF report (triggered by an LTM cell switch failure prior to the LTM recovery) (e.g., in step 406) may be conditioned by the time that elapsed between the LTM recovery and the reception of the first TA adjustment instruction in the LTM recovery cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include the size of the TA adjustment indicated in the first TA adjustment instruction received in the LTM recovery cell if the time that elapsed between the LTM recovery and the reception of the first TA adjustment instruction in the LTM recovery cell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the RLF report an indication of the time that elapsed between the LTM recovery and the reception of the first TA adjustment instruction in the LTM recovery cell. Optionally, the above is restricted to cases where the failed LTM cell switch was a RACH-less LTM cell switch.

[0097] As yet another option (applicable only to failed RACH-less LTM cell switches where the TA determination during early UL synchronization was determined by the network based on a PDCCH ordered RA preamble transmission by the UE in the target cell), inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the LTM recovery in the RLF report (triggered by a RACH-less LTM cell switch failure prior to the LTM recovery) (e.g., in step 406) may be conditioned by the time that elapsed between the last preamble transmission in the LTM recovery cell the UE performed triggered by a PDCCH order in the source cell prior to the failed LTM cell switch and the reception of the first TA adjustment instruction in the LTM recovery cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include the size of the TA adjustment indicated in the first TA adjustment instruction received in the LTM recovery cell if the elapsed time between the last preamble transmission in the LTM recovery cell the UE performed triggered by a PDCCH order in the source cell prior to the failed LTM cell switch andthe reception of the first TA adjustment instruction in the LTM recovery cell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the RLF report an indication of the time that elapsed between the last preamble transmission in the LTM recovery cell the UE performed triggered by a PDCCH order in the source cell prior to the failed LTM cell switch and the reception of the first TA adjustment instruction in the LTM recovery cell.

[0098] As yet another option (applicable only to failed RACH-less LTM cell switches where the TA determination during early UL synchronization was determined autonomously by the UE through measurements), inclusion of the size of the TA adjustment indicated in the first TA adjustment instruction the UE receives in the LTM recovery in the RLF report (triggered by a RACH-less LTM cell switch failure prior to the LTM recovery) (e.g., in step 406) may be conditioned by the time that elapsed between the last autonomous target cell TA determination the UE performed (while still in the source cell) prior to the failed RACH-less LTM cell switch and the reception of the first TA adjustment instruction in the LTM recovery cell. For instance, the UE may be configured, or requested by its serving CU, or may be mandated by a standard, or may be hardcoded by implementation to include the size of the TA adjustment indicated in the first TA adjustment instruction received in the LTM recovery cell if the elapsed time between the last autonomous target cell TA determination the UE performed (while still in the source cell) prior to the failed RACH-less LTM cell switch and the reception of the first TA adjustment instruction in the LTM recovery cell is shorter than a threshold time T, where T may be configured (e.g. by the CU serving the UE in the source cell), or specified in a standard, or may be hardcoded by implementation. Additionally, the UE may include in the RLF report an indication of the time that elapsed between the last autonomous target cell TA determination the UE performed (while still in the source cell) prior to the failed RACH-less LTM cell switch and the reception of the first TA adjustment instruction in the LTM recovery cell.

[0099] In all or any of the above embodiments and options where the UE includes in a SON report the size of a TA adjustment (where the TA adjustment is denoted as ATA) in a TA adjustment instruction received from the network (e.g. in a target cell of an LTM cell switch or in an LTM recovery cell), the TA adjustment size may be indicated as: an absolute value, i.e. the reported TA adjustment size = |ATA|, or, equivalently, the ATA, if TA > 0 reported TA adjustment size = or —ATA, if TA < 0 the actual value, i.e. the reported TA adjustment size = ATA.

[0100] Sending the configured time alignment timer from the target DU to the source DU :

[0101] In the context of the present disclosure, an additional option that could be considered is to let the CU indicate to the source DU (during the preparation phase) the Time Alignment Timer configured for the target cell as an explicit Fl AP IE, e.g. as a new IE in the Early Sync Candidate Cell Information Item IES IE in the UE CONTEXT MODIFICATION REQUEST Fl AP message (or possibly in the UE CONTEXT MODIFICATION REQUIRED F1AP message or the UE CONTEXT SETUP RESPONSE F1AP message. In an inter-CU LTM case (which is in the scope of release 19 of the 3 GPP standard), the target CU could include the time alignment timer (configured in the target cell RRCReconfiguration) as an explicit IE in the HANDOVER REQUEST ACKNOWLEDGE message to the source CU, which would forward it to the source DU. The target time alignment timer configured to be used by the UE in the LTM candidate / target cell would provide a hint to the source DU of how old it may let the UE's TA become before executing the LTM cell switch.

[0102] Examples embodiments are shown in Figures 5A and 5B. In particular, Figure 5A illustrates an example pertaining to an intra-CU LTM cell switch. As shown, a common CU (for the target DU and source DU of the LTM cell switch) sends, to the source DU, a time alignment timer configured for the target cell (e.g., as an explicit F1AP IE as described above). Figure 5B illustrates an example pertaining to an inter-CU LTM cell switch. As shown, the target CU sends, to the source CU, a time alignment timer configured for the target cell (e.g., as an explicit IE in the HANDOVER REQUEST ACKNOWLEDGE message) (step 500a), and the source CU sends the time alignment timer configured for the target cell to the source DU (step 500b), as described above. The details above regarding the various aspects of the embodiments related to sending the configured time alignment timer from the target DU to the source DU are equally applicable to the corresponding steps of Figures 5 A and 5B.

[0103] Using the size of the first TA adjustment in the target cell as a trigger for SHR generation:

[0104] An initial UL transmission timing error in the target cell that is close to being so large that the target DU would fail to receive it can be seen as a case of a close to failing LTM cell switch. As such, this could be of interest to use as a trigger for SHR generation (i.e., if the UL transmission timing error is close to being too large, e.g. close to the size of the cyclic prefix (CP)). A problem is, however, that the UE does not know the timing error of its UL transmissions. Instead, the size of the TA adjustment in the first received TA adjustment instruction (e.g., Timing Advance Command MAC CE) received from the target DU in the target cell could be used as indirect information about the UE’s UL transmission(s) in the target cell. However, to be a reasonablyaccurate indirect measure of the timing error of the UE’s initial transmission in the target cell (which is the most relevant UL transmission timing error for the evaluation of the performance of the early UL synchronization), not too long time could have elapsed between the LTM cell switch (with the UE’s initial UE transmission in the target cell) and the UE’s reception of the first TA adjustment instruction (e.g. Timing Advance Command MAC CE) in the target cell. Hence, together with the configuration of how large the size of the TA adjustment in the first received TA adjustment instruction in the target cell must be to trigger SHR generation (e.g. denoted as the threshold size), there could be a configured threshold duration which the elapsed time between the LTM cell switch (with the UE’s initial UL transmission in the target cell) and the UE’s reception of the first TA adjustment instruction must not exceed in order for SHR generation to be triggered by a large TA adjustment.

[0105] The threshold size could be configured, e.g., in the form of any of the following: A number of time units, where the time unit may be, e.g., the basic time unit in NR (i.e., Tc= 0.509 nanoseconds), the basic time unit in LTE (i.e., Ts= 32.552 nanoseconds), microseconds or nanoseconds.A percentage, or fraction, of the CP used for PUSCH transmissions in the target cell, or more specifically, a percentage, or fraction, of the CP used for the UE’s initial UL transmission in the target cell.

[0106] The threshold duration could be configured, e.g., in the form of a number of time units, e.g. milliseconds.

[0107] The threshold duration may, in some embodiments, be optional to configure in this SHR trigger configuration.

[0108] The threshold size and the threshold duration may be configured in the source cell (e.g. using RRC signaling, e.g. in the system information from the CU, or using MAC signaling from the DU), but it would also be possible that they are configured by the LTM candidate / target DU (or target CU in case of an inter-CU LTM cell switch preparation) and conveyed to the UE in the LTM candidate / target cell RRC configuration signaled to the UE in the source cell as preparation for a potential LTM cell switch. It would also be possible that the source CU or DU configures one of the threshold parameters while the target DU or CU configures the other threshold parameter.

[0109] In this regard, Figure 6 is a flow chart that illustrates the operation of a UE where the size of the first TA adjustment in the target cell of the LTM cell switch as a trigger for SHR generation, in accordance with the embodiments above. As illustrated, the UE performs a RACH- less LTM cell switch to a target cell (step 600). The UE receives a first TA adjustment instructionfrom the target DU in the target cell after the RACH-less LTM cell switch (step 602). The UE determines a time duration that elapsed between the LTM cell switch (with the UE’s initial UL transmission in the target cell) and the UE’s reception of the first TA adjustment instruction, as described above (step 604). The UE determines whether a size of the first TA adjustment is greater than a certain size threshold and the determined time duration is less than a certain time threshold, as described above (step 606). If the size of the first TA adjustment instruction is greater than the certain size threshold and the determined time duration is less than the certain time duration, the UE generates a SHR, which optionally includes the size of the first TA adjustment (step 608). Including of the size of the first TA adjustment in the SHR may, in some embodiments, be conditional. The UE transmits the SHR to a network node (e.g., the target DU) (step 610). The details above regarding the various aspects of the embodiments related to using the size of the first TA adjustment in the target cell of the LTM cell switch as a trigger for SHR generation are equally applicable to the corresponding steps of Figure 6.

[0110] SHR generation in case of UE-based TA measurement:[OHl] The UE may be configured by the network, or instructed by the standard, to generate an SHR in case of UE-based TA measurement (i.e. UE autonomous early UL synchronization), if the size of first TA adjustment instruction received from the target cell indicates a difference compared to the UE-based TA measurement that is larger than a certain threshold. In one option, the SHR generation is triggered only if, in addition to the criterion based on the size of first TA adjustment, also another time-related criterion is fulfilled, e.g., if not too long time has elapsed between the LTM cell switch (with the UE’s initial UL transmission in the target cell) and the UE’s reception of the first TA adjustment instruction (e.g. Timing Advance Command MAC CE) in the target cell.

[0112] In one option, the UE is instructed to generate an SHR if the time elapsed between the time when the UE-based TA measurement became available and the reception of the LTM cell switch command from the source DU is larger than a configured or standardized threshold. In this case, the source DU can deduce the age of the TA measurement as measured by the UE and if a sub-optimally large timing error is detected by the target DU (and reported to the source DU), the source DU can decide e.g. to not allow UE-based TA measurements, or make use of networkbased early UL synchronization instead.

[0113] In some embodiments, the UE may include information about in SON report(s), e.g. in an SHR, an SPR or an RLF report, also if the SON report is triggered by something else than described above, e.g. irrespective of how the SON report is triggered.

[0114] In this regard, Figure 7 is a flow chart that illustrates the operation of a UE for SHR generation in case of autonomous UE-based TA measurement, in accordance with the embodiments above. As illustrated, the UE performs a RACH-less LTM cell switch to a target cell (step 700). The UE receives a first TA adjustment instruction from the target DU in the target cell after the RACH-less LTM cell switch (step 702). The UE determines whether a size of the first TA adjustment indicates a difference compared to the UE-based TA measurement being greater than a certain difference threshold (step 704). If so, the UE generates a SHR, which optionally includes the size of the first TA adjustment (step 706). Including of the size of the first TA adjustment in the SHR may, in some embodiments, be conditional. The UE transmits the SHR to a network node (e.g., the target DU) (step 708). The details above regarding the various aspects of the embodiments related to SHR generation in case of autonomous UE-based TA measurement are equally applicable to the corresponding steps of Figure 7.

[0115] The CU or target DU instructs the source DU to initiate early UL synchronization:

[0116] In some embodiments, an LTM candidate DU (i.e., a potential target DU) may, instruct the source DU when to initiate early UL synchronization for a UE for which the LTM candidate DU has been prepared for a potential coming LTM cell switch. The LTM candidate DU may do this via a common CU (in an intra-gNB LTM case) or via its own CU and the source DU’s CU (in an inter-gNB LTM case). The LTM candidate DU may base these instructions, e.g. the timing of these instructions, on previous experience of UE transmission timing errors from UEs performing LTM cell switch, e.g. LTM cell switches from the same source cell (and optionally to the same target cell and / or beam or TCI state).

[0117] In further embodiments, this instruction to the source DU may be initiated by the common CU (in an intra-gNB LTM case) or by LTM candidate DU’s CU (e.g., in case of an inter- gNB LTM). As one option, the common CU or the LTM candidate DU’s CU may base this on information from the LTM candidate DU, e.g. the kind of experience information described above for the embodiments where the LTM candidate DU originates the instruction.

[0118] In yet further embodiments, an LTM candidate DU may, preferably during the preparation of the LTM cell switch (e.g. when configuration information, e.g. the RRCReconfiguration the UE should apply in a target cell, is transferred), send to the source DU (via the common CU (in case of an intra-gNB LTM) or via its own CU and the source DU’s CU (in case of an inter-gNB LTM) information, or an instruction (or recommendation), of how old the source DU can allow a TA to get after early UL synchronization until the LTM cell switch execution is triggered. If this age is exceeded before the source DU has triggered the LTM cell switch execution (i.e., before the source DU sends the LTM Cell Switch Command MAC CE tothe UE), the source DU should (at least preferably) initiate another early UL synchronization before triggering the LTM cell switch execution. As an alternative, the source DU may choose to let the UE perform a RACH-based LTM cell switch if the TA obtained through early UL synchronization has become older than the (recommended or stipulated) age limit indicated by the LTM candidate DU. The LTM candidate DU may determine the TA age limit, e.g. based on previous experience of UE transmission timing errors from UEs performing LTM cell switch, e.g. LTM cell switches from the same source cell (and optionally to the same target cell and / or beam or TCI state).

[0119] In even further embodiments, the information about the age limit of a TA obtained through early UL synchronization that is sent to the source DU may be initiated by the common CU (in an intra-gNB LTM case) or by LTM candidate DU’s CU (e.g., in case of an inter-gNB LTM). As one option, the common CU or the LTM candidate DU’s CU may base this on information from the LTM candidate DU, e.g. the kind of experience information described above for the embodiments where the LTM candidate DU originates the TA age limit information.

[0120] Examples embodiments are shown in Figures 8A and 8B. In particular, Figure 8A illustrates an example pertaining to an intra-CU LTM cell switch. As shown, the target DU for the LTM cell switch sends, to the common CU, an instruction for the source DU to initiate early UL synchronization for a UE, as described above (step 800). The common CU forwards the instruction to the source DU (step 802). Figure 8B illustrates an example pertaining to an inter- CU LTM cell switch. As shown, the target DU for the LTM cell switch sends, to the target CU, an instruction for the source DU to initiate early UL synchronization for a UE, as described above (step 800a). The target CU forwards the instruction to the source CU (step 800b), which in turn forwards the instruction to the source DU (step 802). The details above regarding the various aspects of the embodiments related to sending such an instruction to the source DU are equally applicable to the corresponding steps of Figures 8A and 8B.

[0121] Figure 9 shows an example of a communication system 900 in accordance with some embodiments.

[0122] In the example, the communication system 900 includes a telecommunication network 902 that includes an access network 904, such as a Radio Access Network (RAN), and a core network 906, which includes one or more core network nodes 908. The access network 904 includes one or more access network nodes, such as network nodes 910A and 910B (one or more of which may be generally referred to as network nodes 910), or any other similar Third Generation Partnership Project (3GPP) access nodes or non-3GPP Access Points (APs). Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to animplementation 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 902 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 902 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 902, including one or more network nodes 910 and / or core network nodes 908.

[0123] Examples of an ORAN network node include an Open Radio Unit (O-RU), an Open Distributed Unit (O-DU), an Open Central Unit (O-CU), including an O-CU Control Plane (O- CU-CP) or an O-CU User Plane (O-CU-UP), a RAN intelligent controller (near-real time or non- real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective “open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an Al, Fl, Wl, El, E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an O-2 interface defined by the O-RAN Alliance or comparable technologies. The network nodes 910 facilitate direct or indirect connection of User Equipment (UE), such as by connecting UEs 912A, 912B, 912C, and 912D (one or more of which may be generally referred to as UEs 912) to the core network 906 over one or more wireless connections.

[0124] 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 900 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 900 may includeand / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0125] The UEs 912 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 910 and other communication devices. Similarly, the network nodes 910 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 912 and / or with other network nodes or equipment in the telecommunication network 902 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 902.

[0126] In the depicted example, the core network 906 connects the network nodes 910 to one or more hosts, such as host 916. 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 906 includes one more core network nodes (e.g., core network node 908) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof are generally applicable to the corresponding components of the core network node 908. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier De-Concealing Function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0127] The host 916 may be under the ownership or control of a service provider other than an operator or provider of the access network 904 and / or the telecommunication network 902, and may be operated by the service provider or on behalf of the service provider. The host 916 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.

[0128] As a whole, the communication system 900 of Figure 9 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system 900 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); UniversalMobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable Second, Third, Fourth, or Fifth Generation (2G, 3G, 4G, or 5G) standards, or any applicable future generation standard (e.g., Sixth Generation (6G)); Wireless Local Area Network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any Low Power Wide Area Network (LPWAN) standards such as LoRa and Sigfox.

[0129] In some examples, the telecommunication network 902 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunication network 902 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 902. For example, the telecommunication network 902 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing enhanced Mobile Broadband (eMBB) services to other UEs, and / or massive Machine Type Communication (mMTC) / massive Internet of Things (loT) services to yet further UEs.

[0130] In some examples, the UEs 912 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 904 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 904. Additionally, a UE may be configured for operating in single- or multi -Radio Access Technology (RAT) or multi -standard mode. For example, a UE may operate with any one or combination of WiFi, New Radio (NR), and LTE, i.e. being configured for Multi -Radio Dual Connectivity (MR-DC), such as Evolved UMTS Terrestrial RAN (E-UTRAN) NR - Dual Connectivity (EN-DC).

[0131] In the example, a hub 914 communicates with the access network 904 to facilitate indirect communication between one or more UEs (e.g., UE 912C and / or 912D) and network nodes (e.g., network node 910B). In some examples, the hub 914 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 914 may be a broadband router enabling access to the core network 906 for the UEs. As another example, the hub 914 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 910, or by executable code, script, process, or other instructions in the hub 914. As another example, the hub 914 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 anotherexample, the hub 914 may be a content source. For example, for a UE that is a Virtual Reality (VR) headset, display, loudspeaker or other media delivery device, the hub 914 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 914 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 914 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0132] The hub 914 may have a constant / persistent or intermittent connection to the network node 910B. The hub 914 may also allow for a different communication scheme and / or schedule between the hub 914 and UEs (e.g., UE 912C and / or 912D), and between the hub 914 and the core network 906. In other examples, the hub 914 is connected to the core network 906 and / or one or more UEs via a wired connection. Moreover, the hub 914 may be configured to connect to a Machine-to-Machine (M2M) service provider over the access network 904 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 910 while still connected via the hub 914 via a wired or wireless connection. In some embodiments, the hub 914 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 910B. In other embodiments, the hub 914 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and the network node 910B, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0133] Figure 10 shows a UE 1000 in accordance with some embodiments. As used herein, a UE refers to a device capable, configured, arranged, and / or operable to communicate wirelessly with network nodes and / or other UEs. Examples of a UE include, but are not limited to, a smart phone, mobile phone, cell phone, Voice over Internet Protocol (VoIP) phone, wireless local loop phone, desktop computer, Personal Digital Assistant (PDA), wireless camera, gaming console or device, music storage device, playback appliance, wearable terminal device, wireless endpoint, mobile station, tablet, laptop, Laptop Embedded Equipment (LEE), Laptop Mounted Equipment (LME), smart device, wireless Customer Premise Equipment (CPE), vehicle, vehicle-mounted or vehicle embedded / integrated wireless device, etc. Other examples include any UE identified by the 3 GPP, including a Narrowband Internet of Things (NB-IoT) UE, a Machine Type Communication (MTC) UE, and / or an enhanced MTC (eMTC) UE.

[0134] A UE may support Device-to-Device (D2D) communication, for example by implementing a 3 GPP standard for sidelink communication, Dedicated Short-Range Communication (DSRC), Vehi cl e-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).

[0135] The UE 1000 includes processing circuitry 1002 that is operatively coupled via a bus 1004 to an input / output interface 1006, a power source 1008, memory 1010, a communication interface 1012, and / or any other component, or any combination thereof. Certain UEs may utilize all or a subset of the components shown in Figure 10. 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.

[0136] The processing circuitry 1002 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 1010. The processing circuitry 1002 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 1002 may include multiple Central Processing Units (CPUs).

[0137] In the example, the input / output interface 1006 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 1000. 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. Anoutput 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.

[0138] In some embodiments, the power source 1008 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 1008 may further include power circuitry for delivering power from the power source 1008 itself, and / or an external power source, to the various parts of the UE 1000 via input circuitry or an interface such as an electrical power cable. Delivering power may be, for example, for charging of the power source 1008. Power circuitry may perform any formatting, converting, or other modification to the power from the power source 1008 to make the power suitable for the respective components of the UE 1000 to which power is supplied.

[0139] The memory 1010 may be or be configured to include memory such as Random Access Memory (RAM), Read Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), magnetic disks, optical disks, hard disks, removable cartridges, flash drives, and so forth. In one example, the memory 1010 includes one or more application programs 1014, such as an operating system, web browser application, a widget, gadget engine, or other application, and corresponding data 1016. The memory 1010 may store, for use by the UE 1000, any of a variety of various operating systems or combinations of operating systems.

[0140] The memory 1010 may be configured to include a number of physical drive units, such as Redundant Array of Independent Disks (RAID), flash memory, USB flash drive, external hard disk drive, thumb drive, pen drive, key drive, High Density Digital Versatile Disc (HD-DVD) optical disc drive, internal hard disk drive, Blu-Ray optical disc drive, Holographic Digital Data Storage (HDDS) optical disc drive, external mini Dual In-line Memory Module (DIMM), Synchronous Dynamic RAM (SDRAM), external micro-DIMM SDRAM, smartcard memory such as a tamper resistant module in the form of a Universal Integrated Circuit Card (UICC) including one or more Subscriber Identity Modules (SIMs), such as a Universal SIM (USIM) and / or Internet Protocol Multimedia Services Identity Module (ISIM), other memory, or any combination thereof. The UICC may for example be an embedded UICC (eUICC), integrated UICC (iUICC) or a removable UICC commonly known as a ‘SIM card.’ The memory 1010 may allow the UE 1000 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 1010, which may be or comprise a device-readable storage medium.

[0141] The processing circuitry 1002 may be configured to communicate with an access network or other network using the communication interface 1012. The communication interface 1012 may comprise one or more communication subsystems and may include or be communicatively coupled to an antenna 1022. The communication interface 1012 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 1018 and / or a receiver 1020 appropriate to provide network communications (e.g., optical, electrical, frequency allocations, and so forth). Moreover, the transmitter 1018 and receiver 1020 may be coupled to one or more antennas (e.g., the antenna 1022) and may share circuit components, software, or firmware, or alternatively be implemented separately.

[0142] In the illustrated embodiment, communication functions of the communication interface 1012 may include cellular communication, WiFi communication, LPWAN communication, data communication, voice communication, multimedia communication, short- range communications such as Bluetooth, NFC, location-based communication such as the use of the Global Positioning System (GPS) to determine a location, another like communication function, or any combination thereof. Communications may be implemented according to one or more communication protocols and / or standards, such as IEEE 802.11, Code Division Multiplexing Access (CDMA), Wideband CDMA (WCDMA), GSM, LTE, NR, UMTS, WiMax, Ethernet, Transmission Control Protocol / Intemet Protocol (TCP / IP), Synchronous Optical Networking (SONET), Asynchronous Transfer Mode (ATM), Quick User Datagram Protocol Internet Connection (QUIC), Hypertext Transfer Protocol (HTTP), and so forth.

[0143] Regardless of the type of sensor, a UE may provide an output of data captured by its sensors, through its communication interface 1012, 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).

[0144] 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 surfacesor 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.

[0145] A UE, when in the form of an loT device, may be a device for use in one or more application domains, these domains comprising, but not limited to, city wearable technology, extended industrial application, and healthcare. Non-limiting examples of such an loT device are a device which is or which is embedded in: a connected refrigerator or freezer, a television, a connected lighting device, an electricity meter, a robot vacuum cleaner, a voice controlled smart speaker, a home security camera, a motion detector, a thermostat, a smoke detector, a door / window sensor, a flood / moisture sensor, an electrical door lock, a connected doorbell, an air conditioning system like a heat pump, an autonomous vehicle, a surveillance system, a weather monitoring device, a vehicle parking monitoring device, an electric vehicle charging station, a smart watch, a fitness tracker, a head-mounted display for Augmented Reality (AR) or VR, a wearable for tactile augmentation or sensory enhancement, a water sprinkler, an animal- or item-tracking device, a sensor for monitoring a plant or animal, an industrial robot, an Unmanned Aerial Vehicle (UAV), and any kind of medical device, like a heart rate monitor or a remote controlled surgical robot. A UE in the form of an loT device comprises circuitry and / or software in dependence of the intended application of the loT device in addition to other components as described in relation to the UE 1000 shown in Figure 10.

[0146] 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 3 GPP NB-IoT standard. In other scenarios, a UE may represent a vehicle, such as a car, a bus, a truck, a ship, an airplane, or other equipment that is capable of monitoring and / or reporting on its operational status or other functions associated with its operation.

[0147] 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.

[0148] Figure 11 shows a network node 1100 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged, and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment in a telecommunication network. Examples of network nodes include, but are not limited to, APs (e.g., radio APs), Base Stations (BSs) (e.g., radio BSs, Node Bs, evolved Node Bs (eNBs), NR Node Bs (gNBs)), and O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0149] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized digital units, distributed units (e.g., in an O-RAN access node), and / or Remote Radio Units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such RRUs may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a Distributed Antenna System (DAS).

[0150] Other examples of network nodes include multiple Transmission Point (multi-TRP) 5G access nodes, Multi -Standard Radio (MSR) equipment such as MSR BSs, network controllers such as Radio Network Controllers (RNCs) or BS Controllers (BSCs), Base Transceiver Stations (BTSs), transmission points, transmission nodes, Multi-Cell / Multicast Coordination Entities (MCEs), Operation and Maintenance (O&M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0151] The network node 1100 includes processing circuitry 1102, memory 1104, a communication interface 1106, and a power source 1108. The network node 1100 may be composed of multiple physically separate components (e.g., a NodeB component and an RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1100 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair may in some instances be considered a single separate network node. In some embodiments, the network node 1100 may be configured to support multiple RATs. In such embodiments, some components may be duplicated (e.g., separate memory 1104 for different RATs) and some components may be reused (e.g., a same antenna 1110 may be shared by different RATs). The network node 1100 may also includemultiple sets of the various illustrated components for different wireless technologies integrated into network node 1100, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, Long Range Wide Area Network (LoRaWAN), Radio Frequency Identification (RFID), or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within the network node 1100.

[0152] The processing circuitry 1102 may comprise a combination of one or more of a microprocessor, controller, microcontroller, CPU, DSP, ASIC, FPGA, or any other suitable computing device, resource, or combination of hardware, software, and / or encoded logic operable to provide, either alone or in conjunction with other network node 1100 components, such as the memory 1104, to provide network node 1100 functionality.

[0153] In some embodiments, the processing circuitry 1102 includes a System on a Chip (SOC). In some embodiments, the processing circuitry 1102 includes one or more of Radio Frequency (RF) transceiver circuitry 1112 and baseband processing circuitry 1114. In some embodiments, the RF transceiver circuitry 1112 and the baseband processing circuitry 1114 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of the RF transceiver circuitry 1112 and the baseband processing circuitry 1114 may be on the same chip or set of chips, boards, or units.

[0154] The memory 1104 may comprise any form of volatile or non-volatile computer- readable memory including, without limitation, persistent storage, solid state memory, remotely mounted memory, magnetic media, optical media, RAM, ROM, mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD), or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device- readable, and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1102. The memory 1104 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 1102 and utilized by the network node 1100. The memory 1104 may be used to store any calculations made by the processing circuitry 1102 and / or any data received via the communication interface 1106. In some embodiments, the processing circuitry 1102 and the memory 1104 are integrated.

[0155] The communication interface 1106 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 1106 comprises port(s) / terminal(s) 1116 to send and receive data, for example to and from a network over a wired connection. The communication interface 1106 alsoincludes radio front-end circuitry 1118 that may be coupled to, or in certain embodiments a part of, the antenna 1110. The radio front-end circuitry 1118 comprises filters 1120 and amplifiers 1122. The radio front-end circuitry 1118 may be connected to the antenna 1110 and the processing circuitry 1102. The radio front-end circuitry 1118 may be configured to condition signals communicated between the antenna 1110 and the processing circuitry 1102. The radio front-end circuitry 1118 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 1118 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combination of the filters 1120 and / or the amplifiers 1122. The radio signal may then be transmitted via the antenna 1110. Similarly, when receiving data, the antenna 1110 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1118. The digital data may be passed to the processing circuitry 1102. In other embodiments, the communication interface 1106 may comprise different components and / or different combinations of components.

[0156] In certain alternative embodiments, the network node 1100 does not include separate radio front-end circuitry 1118; instead, the processing circuitry 1102 includes radio front-end circuitry and is connected to the antenna 1110. Similarly, in some embodiments, all or some of the RF transceiver circuitry 1112 is part of the communication interface 1106. In still other embodiments, the communication interface 1106 includes the one or more ports or terminals 1116, the radio front-end circuitry 1118, and the RF transceiver circuitry 1112 as part of a radio unit (not shown), and the communication interface 1106 communicates with the baseband processing circuitry 1114, which is part of a digital unit (not shown).

[0157] The antenna 1110 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 1110 may be coupled to the radio front-end circuitry 1118 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 1110 is separate from the network node 1100 and connectable to the network node 1100 through an interface or port.

[0158] The antenna 1110, the communication interface 1106, and / or the processing circuitry 1102 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node 1100. Any information, data, and / or signals may be received from a UE, another network node, and / or any other network equipment. Similarly, the antenna 1110, the communication interface 1106, and / or the processing circuitry 1102 may be configured to perform any transmitting operations described herein as being performed by the network node 1100. Any information, data, and / or signals may be transmitted to a UE, another network node, and / or any other network equipment.

[0159] The power source 1108 provides power to the various components of the network node 1100 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1108 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1100 with power for performing the functionality described herein. For example, the network node 1100 may be connectable to an external power source (e.g., the power grid or an electricity outlet) via input circuitry or an interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1108. As a further example, the power source 1108 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.

[0160] Embodiments of the network node 1100 may include additional components beyond those shown in Figure 11 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 1100 may include user interface equipment to allow input of information into the network node 1100 and to allow output of information from the network node 1100. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1100. In some embodiments providing a core network node, such as core network node 108 of FIG. 9, some components, such as the radio front-end circuitry 1118 and the RF transceiver circuitry 1112 may be omitted.

[0161] Figure 12 is a block diagram illustrating a virtualization environment 1200 in which functions implemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices, and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more Virtual Machines (VMs) implemented in one or more virtualization environments 1200 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, a UE, a core network node, or a host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1200 includes components defined by the O-RAN Alliance, such as an O-Cloudenvironment orchestrated by a Service Management and Orchestration Framework via an 0-2 interface. Virtualization may facilitate distributed implementations of a network node, a UE, a core network node, or a host.

[0162] Applications 1202 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment 1200 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0163] Hardware 1204 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, an input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1206 (also referred to as hypervisors or Virtual Machine Monitors (VMMs)), provide VMs 1208A and 1208B (one or more of which may be generally referred to as VMs 1208), and / or perform any of the functions, features, and / or benefits described in relation with some embodiments described herein. The virtualization layer 1206 may present a virtual operating platform that appears like networking hardware to the VMs 1208.

[0164] The VMs 1208 comprise virtual processing, virtual memory, virtual networking, or interface and virtual storage, and may be run by a corresponding virtualization layer 1206. Different embodiments of the instance of a virtual appliance 1202 may be implemented on one or more of VMs 1208, 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.

[0165] In the context of NFV, a VM 1208 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 1208, and that part of the hardware 1204 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 1208 on top of the hardware 1204 and corresponds to the application 1202.

[0166] The hardware 1204 may be implemented in a standalone network node with generic or specific components. The hardware 1204 may implement some functions via virtualization. Alternatively, the hardware 1204 may be part of a larger cluster of hardware (e.g., such as in a datacenter or CPE) where many hardware nodes work together and are managed via management and orchestration 1210, which, among others, oversees lifecycle management of the applications 1202. In some embodiments, the hardware 1204 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1212 which may alternatively be used for communication between hardware nodes and radio units.

[0167] 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.

[0168] 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 particularembodiments, 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.

[0169] Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

[0170] Some exemplary embodiments of the present disclosure are as follows:Group A Embodiments

[0171] Embodiment 1 : A method performed by User Equipment, UE, the method comprising any one or more of the following: performing (300) a Random Access Channel, RACE!, -less Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch to a target LTM cell; receiving (302) a first Timing Advance, TA, instruction from a target Distributed Unit, DU, in the target cell after the RACH-less LTM cell switch; generating (304) a Successful Handover Report, SHR, including a size of a first TA adjustment indicated by the first TA instruction; and transmitting (306) the SHR to a network node.

[0172] Embodiment 2: The method of embodiment 1, wherein inclusion of the size of the first TA adjustment in the SHR is conditional.

[0173] Embodiment 3: A method performed by User Equipment, UE, the method comprising any one or more of the following: determining (400) that a Random Access Channel, RACH,-less Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch to a target LTM cell has failed; performing (402) LTM recovery to a cell; receiving (404) a first Timing Advance, TA, instruction from a Distributed Unit, DU, in the cell after the LTM recovery; generating (406) a Radio Link Failure, RLF, report including a size of a first TA adjustment indicated by the first TA instruction; and transmitting (408) the RLF report to a network node.

[0174] Embodiment 4: The method of embodiment 3, wherein inclusion of the size of the first TA adjustment in the RLF report is conditional.

[0175] Embodiment 5: A method performed by User Equipment, UE, the method comprising any one or more of the following: performing (600) a Random Access Channel, RACH,-less Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch to a target LTM cell; receiving (602) a first Timing Advance, TA, instruction from a target Distributed Unit, DU, in the target cell after the RACH-less LTM cell switch; determining (604) a time duration that elapsed between the LTMcell switch and the UE’s reception of the first TA adjustment instruction; determining (606) that a size of a first TA adjustment indicated by the first TA instruction is greater than a predefined or configured size threshold and the determined time duration is less than a predefined or configured time threshold; in response to the determining (606), generating (608) a Successful Handover Report, SHR, including the size of a first TA adjustment indicated by the first TA instruction; and transmitting (610) the SHR to a network node.

[0176] Embodiment 6: A method performed by User Equipment, UE, the method comprising any one or more of the following: performing (700) a Random Access Channel, RACH,-less Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch to a target LTM cell; receiving (702) a first Timing Advance, TA, instruction from a target Distributed Unit, DU, in the target cell after the RACH-less LTM cell switch; determining (704) that a size of a first TA adjustment indicated by the first TA instruction indicates that a difference compared to a UE-based TA measurement is greater than a certain difference threshold; in response to the determining (704), generating (706) a Successful Handover Report, SHR, including the size of a first TA adjustment indicated by the first TA instruction; and transmitting (708) the SHR to a network node.Group B Embodiments

[0177] Embodiment 7: A method performed by target Distributed Unit, DU, of a network node in cellular communications system for providing feedback information to a source DU regarding a timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to a target cell operated by the target DU, the method comprising: measuring (208) a timing error of reception of one or more uplink transmissions received from the UE after a Random Access Channel, RACH,-less LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU; and sending (212) feedback information about the timing error measured for the UE in the target cell, to the source DU via one or more Central Units, CUs.

[0178] Embodiment 8: The method of embodiment 7, wherein the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

[0179] Embodiment 9: The method of embodiment 7, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for first uplink transmission received from the UE in the target cell,a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1 ; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero.

[0180] Embodiment 10: The method of embodiment 7, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that a transmission timing error occurred.

[0181] Embodiment 11 : The method of embodiment 7, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

[0182] Embodiment 12: The method of embodiment 7, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of too large UE transmission timing error(s) (e.g., timing error(s) that are greater than a predefined or configured timing error threshold) for the; a flag indicating the presence of a sub-optimally large UE transmission timing error(s); a flag indicating a number of UE transmission timing errors or a number of too large transmission timing errors or a number of sub-optimally large UE transmission timing errors (e.g., exceeding a configured or standardized threshold) for a number of UEs; a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which too large UE transmission timing errors were detected; a list of UE identities indicating UEs for which sub-optimally large UE transmission timing errors were detected; a list of UE identities and corresponding per-UE transmission timing error information;a number of UEs for which transmission timing errors were detected; a number of UEs for which too large transmission timing errors were detected; a number of UEs for which sub-optimally large transmission timing errors were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which too large transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which sub-optimally large transmission timing errors were detected and a corresponding average transmission timing error.

[0183] Embodiment 13: The method of any of embodiments 7 to 12, wherein the source DU and the target DU share a common CU, and sending (212) the feedback information about the timing error of the UE in the target cell comprises sending (212) the feedback information to the common CU.

[0184] Embodiment 14: The method of any of embodiments 7 to 12, wherein the source DU is associated to a source CU and the target DU is associated to a target CU, and sending (212) the feedback information about the timing error of the UE in the target cell comprises sending (212a) the feedback information to the target CU.

[0185] Embodiment 15: The method of any of embodiments 7 to 14, wherein sending (212) the feedback information comprising the timing error of the UE in the target cell is conditional.

[0186] Embodiment 16: The method of any of embodiments 7 to 14, further comprising: determining that one or more conditions for sending (212) the feedback information comprising the timing error of the UE in the target cell are satisfied; wherein sending (212) the feedback information comprising the timing error of the UE in the target cell comprises sending (212) the feedback information comprising the timing error of the UE in the target cell responsive to the one or more conditions being satisfied.

[0187] Embodiment 17: The method of embodiment 16, wherein the one or more conditions comprise any one or more of the following: the reception timing error exceeded a threshold; the reception timing error exceeded a threshold and this was an Nthconsecutive RACH- less LTM cell switch between the same source cell and target cell where the reception timing error exceeded the threshold (e.g., where N may be configured, specified in a standard, or hardcoded by implementation); the reception timing error exceeded a threshold (e.g., wherein the threshold may be configured, specified in a standard, or hardcoded by implementation) and this was an NthRACH-less LTM cell switch between the same source cell and target cell where the reception timing error exceeded the threshold among an M latest RACH-less LTM cell switches between the same source cell and target cell (where N may be configured, specified in a standard, or hardcoded by implementation, and M may be configured, specified in a standard, or hardcoded by implementation); an average of the reception timing errors for an N latest RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold, which may be configured, specified in a standard, or hardcoded by implementation (and wherein N may be configured, specified in a standard, or hardcoded by implementation); a sliding average of the reception timing errors for RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold (which may be configured, specified in a standard, or hardcoded by implementation); an exponential average of the reception timing errors for RACH-less LTM cell switches between the same source cell and target cell exceeds a threshold (wherein the threshold may be configured, specified in a standard, or hardcoded by implementation, and the parameter deciding how fast the impact of older samples (i.e. reception timing errors) decline may be configured, specified in a standard or hardcoded by implementation); an age of a TA at a time the UE used it the first time in the target cell exceeds a threshold time T, where T may be configured, specified in a standard, or hardcoded by implementation; an age of a TA at a time the UE used it the first time in the target cell exceeds a time alignment timer configured for the UE; the age of the TA at the time the UE used it the first time in the target cell exceeds X% of the time alignment timer configured for the UE (if the TA the UE used in the target cell was established using network-controlled early UL synchronization, i.e. using a PDCCH ordered preamble transmission in the target cell and sending the determined TA to the UE in the LTM Cell Switch Command MAC CE, which is a prerequisite for the target DU to be able to determine the age of the TA), where X may be configured, specified in a standard, or hardcoded by implementation; an age of a TA at a time the UE used it the first time in the target cell exceeds a time alignment timer (TAT) configured for the UE minus t (where t may be configured, specified in a standard, or hardcoded by implementation);an age of a TA at a time the UE used it the first time in the target cell exceeds a time alignment timer (TAT) configured for the UE plus t (where t may be configured, specified in a standard, or hardcoded by implementation).

[0188] Embodiment 18: The method of embodiment 16, wherein the one or more conditions comprise any one or more of the following: one transmission timing error is detected for the UE; at least N transmission timing errors are detected for the UE; at least N transmission timing errors are detected for at least one UE; at least N transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE; one too large transmission timing error is detected for the UE; at least N too large transmission timing errors are detected for the UE; at least N too large transmission timing errors are detected for at least one UE; at least N too large transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE; one suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing error is detected for the UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected for the UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected for at least one UE; at least N suboptimally large (e.g., exceeding a configured or standardized threshold) transmission timing errors are detected in a given time interval (or specified reporting period) for at least one UE.

[0189] Embodiment 19: A method performed by source Distributed Unit, DU, of a network node in cellular communications system for receiving and using feedback information from a target DU regarding a timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to a target cell operated by the target DU, the method comprising: receiving (214), from an associated CU, feedback information about a timing error of reception of one or more uplink transmissions received from the UE at a target DU after a Random Access Channel, RACH,-less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU; and performing (216) one or more actions based on the feedback information.

[0190] Embodiment 20: The method of embodiment 19, wherein the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

[0191] Embodiment 21 : The method of embodiment 19, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for first uplink transmission received from the UE in the target cell, a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1 ; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero.

[0192] Embodiment 22: The method of embodiment 19, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that a transmission timing error occurred.

[0193] Embodiment 23: The method of embodiment 19, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

[0194] Embodiment 24: The method of embodiment 19, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of too large UE transmission timing error(s) (e.g., timing error(s) that are greater than a predefined or configured timing error threshold) for the; a flag indicating the presence of a sub-optimally large UE transmission timing error(s); a flag indicating a number of UE transmission timing errors or a number of too large transmission timing errors or a number of sub-optimally large UE transmission timing errors (e.g., exceeding a configured or standardized threshold) for a number of UEs;a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which too large UE transmission timing errors were detected; a list of UE identities indicating UEs for which sub-optimally large UE transmission timing errors were detected; a list of UE identities and corresponding per-UE transmission timing error information; a number of UEs for which transmission timing errors were detected; a number of UEs for which too large transmission timing errors were detected; a number of UEs for which sub-optimally large transmission timing errors were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which too large transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which sub-optimally large transmission timing errors were detected and a corresponding average transmission timing error.

[0195] Embodiment 25: A method performed by a Central Unit, CU, of a network node in cellular communications system associated to target DU that operates a target cell for a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to the target cell operated by the target DU, the method comprising: sending (500, 500a), toward the source DU, information comprising a time alignment timer configured for the target cell for the LTM cell switch (e.g., during a preparation phase of the LTM cell switch procedure).

[0196] Embodiment 26: A method performed by a target Distributed Unit, DU, of a network node in cellular communications system for a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by a source DU to a target cell operated by the target DU, the method comprising: sending (800; 800a), toward the source DU, an instruction for the source DU to initiate early uplink synchronization for a UE for which the LTM cell switch.Group C Embodiments

[0197] Embodiment 27: A user equipment comprising: processing circuitry configured to perform any of the steps of any of the Group A embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0198] Embodiment 28: A network node comprising: processing circuitry configured to perform any of the steps of any of the Group B embodiments; and power supply circuitry configured to supply power to the processing circuitry.

[0199] Embodiment 29: A user equipment (UE) comprising: an antenna configured to send and receive wireless signals; radio front-end circuitry connected to the antenna and to processing circuitry, and configured to condition signals communicated between the antenna and the processing circuitry; the processing circuitry being configured to perform any of the steps of any of the Group A embodiments; an input interface connected to the processing circuitry and configured to allow input of information into the UE to be processed by the processing circuitry; an output interface connected to the processing circuitry and configured to output information from the UE that has been processed by the processing circuitry; and a battery connected to the processing circuitry and configured to supply power to the UE.

Claims

CLAIMS1. A method performed by a User Equipment, UE, for reporting UE transmission timing error in association with Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, the method comprising: receiving (302; 404; 602; 702) a first Timing Advance, TA, instruction from a Distributed Unit, DU, in a cell either after a successful Random Access Channel, RACH,-less LTM, cell switch to the cell or after an LTM recovery to the cell; generating (304; 406; 608; 706) a Self-Organizing Network, SON, report including a size of a first TA adjustment indicated by the first TA instruction; and transmitting (306; 408; 610; 708) the SON report to a network node.

2. The method of claim 1, wherein inclusion of the size of the first TA adjustment in the SON report is conditional.

3. The method of claim 1 or 2, wherein the cell is a target cell for a RACH-less LTM cell switch, the DU is a target DU associated to the target cell, the first TA instruction is received from the target DU in the target cell after the RACH-less LTM cell switch to the target cell, and the SON report is a Successful Handover Report, SHR.

4. The method of claim 3, further comprising, prior to generating (608) the SHR: determining (604) a time duration that elapsed between the RACH-less LTM cell switch and the UE’s reception of the first TA adjustment instruction; and determining (606) that a size of a first TA adjustment indicated by the first TA instruction is greater than a predefined or configured size threshold and the determined time duration is less than a predefined or configured time threshold; wherein generating (608) the SHR and transmitting (610) the SHR to the network node are in response to determining (606) that the size of the first TA adjustment indicated by the first TA instruction is greater than the predefined or configured size threshold and the determined time duration is less than the predefined or configured time threshold.

5. The method of claim 3, further comprising, prior to generating (706) the SHR: determining (704) that a size of a first TA adjustment indicated by the first TA instruction indicates that a difference compared to a UE-based TA measurement is greater than a certain difference threshold; wherein generating (706) the SHR and transmitting (708) the SHR to the network node arein response to determining (704) that the size of the first TA adjustment indicated by the first TA instruction indicates that the difference compared to the UE-based TA measurement is greater than the certain difference threshold.

6. The method of claim 1 or 2, wherein the first TA instruction is received from the cell after LTM recovery to the cell, and the SON report is a Radio Link Failure, RLF, report.

7. The method of claim 6, further comprising, prior to receiving (404) the first TA instruction from the DU in the cell after the LTM recovery: determining (400) that a RACH-less LTM cell switch to a target LTM cell has failed; and in response thereto, performing (402) the LTM recovery to the cell.

8. A User Equipment, UE, for reporting UE transmission timing error in association with Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, the UE (1000) adapted to: receive (302; 404; 602; 702) a first Timing Advance, TA, instruction from a Distributed Unit, DU, in a cell either after a successful Random Access Channel, RACH,-less LTM cell switch to the cell or after an LTM recovery to the cell; generate (304; 406; 608; 706) a Self-Organizing Network, SON, report including a size of a first TA adjustment indicated by the first TA instruction; and transmit (306; 408; 610; 708) the SON report to a network node.

9. The UE of claim 8, further adapted to perform the method of any of claims 2 to 7.

10. A User Equipment, UE, (1000), for reporting UE transmission timing error in association with Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, the UE (1000) comprising: a communication interface (1012) comprising a transmitter (1018) and a receiver (1020); and processing circuitry (1002) associated with the communication interface (1012), the processing circuitry (1012) configured to cause the UE (1000) to: receive (302; 404; 602; 702) a first Timing Advance, TA, instruction from a Distributed Unit, DU, in a cell either after a successful Random Access Channel, RACH,- less LTM cell switch to the cell or after an LTM recovery to the cell; generate (304; 406; 608; 706) a Self-Organizing Network, SON, report including a size of a first TA adjustment indicated by the first TA instruction; andtransmit (306; 408; 610; 708) the SON report to a network node.

11. The UE (1000) of claim 10, wherein the processing circuitry (1002) is further configured to cause the UE (1000) to perform the method of any of claims 2 to 7.

12. A method performed by target Distributed Unit, DU, of a network node in cellular communications system for providing feedback information to a source DU regarding a timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to a target cell operated by the target DU, the method comprising: measuring (208) a timing error of reception of one or more uplink transmissions received from the UE after a Random Access Channel, RACH,-less LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU; sending (212) feedback information about the timing error measured for the UE in the target cell to the source DU via one or more Central Units, CUs.

13. The method of claim 12, wherein the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

14. The method of claim 12, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for a first uplink transmission received from the UE in the target cell, a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1 ; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero.

15. The method of claim 12, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

16. The method of claim 12, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of a timing error(s) for the UE that is greater than a predefined or configured timing error threshold; a flag indicating a number of UE transmission timing errors or a number of UE transmission timing errors that are greater than a predefined or configured timing error threshold for a number of UEs; a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which UE transmission timing errors greater than a predefined or configured timing error threshold were detected; a list of UE identities and corresponding per-UE transmission timing error information; a number of UEs for which transmission timing errors were detected; a number of UEs for which transmission timing errors greater than a predefined or configured timing error threshold were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which transmission timing errors greater than a predefined or configured transmission timing error threshold were detected and a corresponding average transmission timing error.

17. The method of any of claims 12 to 16, wherein the source DU and the target DU share a common CU, and sending (212) the feedback information about the timing error of the UE in the target cell comprises sending (212) the feedback information to the common CU.

18. The method of any of claims 12 to 16, wherein the source DU is associated to a source CU and the target DU is associated to a target CU, and sending (212) the feedback information about the timing error of the UE in the target cell comprises sending (212a) the feedback information tothe target CU.

19. The method of any of claims 12 to 18, further comprising: determining that one or more conditions for sending (212) the feedback information comprising the timing error of the UE in the target cell are satisfied; wherein sending (212) the feedback information comprising the timing error of the UE in the target cell comprises sending (212) the feedback information comprising the timing error of the UE in the target cell responsive to the one or more conditions being satisfied.

20. The method of claim 19, wherein the one or more conditions comprise any one or more of the following: a reception timing error exceeded a threshold; the reception timing error exceeded a threshold and this was an Nthconsecutive RACH- less LTM cell switch between the source cell and the target cell where the reception timing error exceeded the threshold; the reception timing error exceeded a threshold and this was an NthRACH-less LTM cell switch between the source cell and the target cell where the reception timing error exceeded the threshold among an M latest RACH-less LTM cell switches between the same source cell and target cell; an average of the reception timing errors for an N latest RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; a sliding average of the reception timing errors for RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; an exponential average of the reception timing errors for RACH-less LTM cell switches between the source cell and the target cell exceeds a threshold; an age of a TA at a time the UE used the TA a first time in the target cell exceeds a threshold time T; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a time alignment timer configured for the UE; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a certain percentage of the time alignment timer configured for the UE; the age of the TA at the time the UE used the TA the first time in the target cell exceeds a time alignment timer configured for the UE minus a certain value;the age of the TA at the time the UE used the TA the first time in the target cell exceeds the time alignment timer configured for the UE plus a certain value.

21. The method of claim 19, wherein the one or more conditions comprise any one or more of the following: one transmission timing error is detected for the UE; at least N transmission timing errors are detected for the UE; at least N transmission timing errors are detected for at least one UE; at least N transmission timing errors are detected in a given time interval for at least one UE; one transmission timing error that is greater than a threshold transmission timing error is detected for the UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected for the UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected for at least one UE; at least N transmission timing errors that are greater than a threshold transmission timing error are detected in a given time interval for at least one UE.

22. A network node for providing feedback information to a source DU regarding a timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to a target cell operated by the target DU, the network node comprising processing circuitry configured to cause the network node to: measure (208) a timing error of reception of one or more uplink transmissions received from the UE after a Random Access Channel, RACH,-less LTM cell switch from a source cell operated by a source DU to a target cell operated by the target DU; send (212) feedback information about the timing error measured for the UE in the target cell to the source DU via one or more Central Units, CUs.

23. The network node of claim 22, wherein the processing circuitry is further configured to cause the network node to perform the method of any of embodiments 13 to 21.

24. A method performed by a source Distributed Unit, DU, of a network node in cellular communications system for receiving and using feedback information from a target DU regardinga timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to a target cell operated by the target DU, the method comprising: receiving (214) from an associated Central Unit, CU, feedback information about a timing error of reception of one or more uplink transmissions received from a UE at a target DU after a Random Access Channel, RACH,-less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU; and performing (216) one or more actions based on the feedback information.

25. The method of claim 24, wherein the feedback information about the timing error measured for the UE in the target cell comprises a reception timing error value.

26. The method of claim 24, wherein the feedback information about the timing error measured for the UE in the target cell comprises any of the following: a reception timing error measured for a first uplink transmission received from the UE in the target cell, a reception timing error of one of a first N uplink transmissions received from the UE in the target cell, wherein N is a predefined or configured integer value that is greater than or equal to 1 ; a reception timing error of one of one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; an average reception timing error of a first M uplink transmissions received from the UE in the target cell, wherein M is an integer value greater than 1; an average reception timing error of a first one or more uplink transmissions received from the UE in the target cell during a first time period T following the UE’s access to the target cell, wherein T is a predefined or configured amount of time that is greater than zero; a flag indicating a presence of a UE transmission timing error(s) for the UE; a flag indicating a presence of a timing error(s) for the UE that is greater than a predefined or configured timing error threshold; a flag indicating a number of UE transmission timing errors or a number of UE transmission timing errors that are greater than a predefined or configured timing error threshold for a number of UEs;a list of UE identities indicating UEs for which UE transmission timing errors were detected; a list of UE identities indicating UEs for which UE transmission timing errors greater than a predefined or configured timing error threshold were detected; a list of UE identities and corresponding per-UE transmission timing error information; a number of UEs for which transmission timing errors were detected; a number of UEs for which transmission timing errors greater than a predefined or configured timing error threshold were detected; a number of UEs for which transmission timing errors were detected and a corresponding average transmission timing error; a number of UEs for which transmission timing errors greater than a predefined or configured transmission timing error threshold were detected and a corresponding average transmission timing error.

27. The method of claim 24, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that a transmission timing error occurred.

28. The method of claim 24, wherein the feedback information about the timing error measured for the UE in the target cell comprises an indication that the measured timing error for the UE on the target cell is greater than a predefined or configured timing error threshold.

29. The method of claim 24, wherein the one or more actions performed by the source DU based on the feedback information comprise one or more actions related to optimization of timing of early synchronizations for future potential LTM cell switches, refraining from using early uplink synchronization, refraining from using network-ordered early uplink synchronization, or refraining from using or relying on UE autonomous early uplink synchronization.

30. A network node for receiving and using feedback information from a target Distributed Unit, DU, regarding a timing error of a User Equipment, UE, after a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by a source Distributed Unit, DU, to a target cell operated by the target DU, the network node comprising processing circuitry configured to cause the network node to: receive (214) from an associated Central Unit, CU, feedback information about a timing error of reception of one or more uplink transmissions received from a UE at a target DU after aRandom Access Channel, RACH,-less LTM cell switch from a source cell operated by the source DU to a target cell operated by the target DU; and perform (216) one or more actions based on the feedback information.

31. The network node of claim 30, wherein the processing circuitry is further configured to cause the network node to perform the method of any of claims 25 to 29.

32. A method performed by a Central Unit, CU, of a network node in cellular communications system associated to target DU that operates a target cell for a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by the source DU to the target cell operated by the target DU, the method comprising: sending (500, 500a), toward the source DU, information comprising a time alignment timer configured for the target cell for the LTM cell switch.

33. The method of claim 32, wherein the information comprising the time alignment timer is sent during a preparation phase of the LTM cell switch procedure.

34. The method of claim 32 further comprising receiving feedback information about a timing error of reception of one or more uplink transmissions received from a UE at the target DU after a Random Access Channel, RACH,-less LTM cell switch from the source cell operated by the source DU to the target cell operated by the target DU.

35. The method of claim 32 further comprising transmitting feedback information about a timing error of reception of one or more uplink transmissions received from a UE at the target DU after a Random Access Channel, RACE!, -less LTM cell switch from the source cell operated by the source DU to the target cell operated by the target DU.

36. A method performed by a target Distributed Unit, DU, of a network node in cellular communications system for a Layer 1, LI, / Layer 2, L2, Triggered Mobility, LTM, cell switch from a source cell operated by a source DU to a target cell operated by the target DU, the method comprising: sending (800; 800a), toward the source DU, an instruction for the source DU to initiate early uplink synchronization for a UE for which the LTM cell switch.

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