Method and apparatus for LTM and CLTM configurations

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The disclosure provides a method performed by a user equipment (UE) in a wireless communication system. The method comprises receiving, from a base station, a layer 1(L1) / layer2(L2) triggered mobility (LTM) configuration for at least one candidate cell associated with a conditional LTM (CLTM), upon fulfilment of LTM cell switch execution conditions for a candidate cell, in case that a value of field ltm-NoResetID in the LTM configuration for the candidate cell is not equal to a value of ltm-ServingCellNoResetID stored in the UE, performing at least one of a radio link control (RLC) re-establishment or a packet data convergence protocol (PDCP) recovery and replacing the value of field ltm-ServingCellNoResetID with the value of field ltm-NoResetID.

Description

METHOD AND APPARATUS FOR LTM AND CLTM CONFIGURATIONS

[0001] Embodiments disclosed herein relate to wireless communication networks, and more particularly to managing L1(layer1) / L2(layer2) Triggered Mobility (LTM) and Conditional LTM (CLTM) configurations in wireless communication networks.

[0002] Fifth generation (5G) mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “sub 6 gigahertz (GHz)” bands such as 3.5GHz, but also in “above 6GHz” bands referred to as millimeter wave (mmWave) including 28GHz and 39GHz. In addition, implementing sixth generation (6G) mobile communication technologies (referred to as Beyond 5G systems) in terahertz (THz) bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies is being considered.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced mobile broadband (eMBB), ultra reliable low latency communications (URLLC), and massive machine-type communications (mMTC), there has been ongoing standardization regarding beamforming and massive multi input multi output (MIMO) for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave. In addition, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of bandwidth part (BWP), new channel coding methods such as a low density parity check (LDPC) code for large amounts of data transmission and a polar code for highly reliable transmission of control information, layer two (L2) pre-processing, and network slicing for providing a dedicated network specialized to a specific service are also being used to support services and to satisfy performance requirements.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as vehicle-to-everything (V2X) technologies for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, new radio unlicensed (NR-U) technologies aimed at system operations conforming to various regulation-related requirements in unlicensed bands, new radio (NR) user equipment (UE) power saving technologies, non-terrestrial network (NTN) technologies, which are UE-satellite direct communication technologies for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning technologies.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as industrial Internet of things (IIoT) for supporting new services through interworking and convergence with other industries, integrated access and backhaul (IAB) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and dual active protocol stack (DAPS) handover, and two-step random access for simplifying random access procedures (for example, 2-step random access channel (RACH) for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining network functions virtualization (NFV) and software-defined networking (SDN) technologies, and mobile edge computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices will be connected to communication networks, and it is expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with extended Reality (XR) for efficiently supporting augmented reality (AR), virtual reality (VR), and mixed reality (MR). 5G performance improvement and complexity reduction may be accomplished by utilizing artificial intelligence (AI) and machine learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing new waveforms for providing coverage in THz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as full dimensional multiple input multiple output (FD-MIMO), array and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of THz band signals, high-dimensional space multiplexing technology using orbital angular momentum (OAM), reconfigurable intelligent surface (RIS) technology, full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] In wireless technologies such as 5G New Radio (NR), devices can move across different cells. Mobility is performed using a procedure called cell reselection in a Radio Resource Control (RRC)_IDLE mode. Till NR R17, mobility is performed using a procedure called handover in an RRC_CONNECTED mode. A network-controlled UE mobility applies to User Equipment (UEs) in the RRC_CONNECTED mode. The network-controlled UE mobility requires explicit RRC signaling to be triggered by a Radio Access network (RAN) in the NR. The handover in NR usually comprises of three steps: handover preparation, handover execution and handover completion. The gNB may configure the UE to report measurements, and based on the reported measurements or based on its own understanding of the network topology, the gNB may send an RRC reconfiguration message to handover the UE to a target cell from a source cell. The UE may access the target cell, and send the RRC reconfiguration complete message. In an alternative way introduced in 3GPP NR release 16, the gNB may configure the UE with the execution conditions for triggering handover. Once the execution conditions are satisfied, the UE may move to the target cell, and send the RRC reconfiguration complete message. In all the above methods, the UE may perform the handover by sending layer 3 (RRC) messages which causes considerable signaling overhead and latency issues. During handover, the UE may be configured to apply full configuration during a L3 handover, and if configured, the UE applies full configuration as described in section 5.3.5.11 of TS 38.331. The L3 handover may cause signaling overhead and delay in completing handover.

[0009] v18.5.0 of 3GPP specifications such as TS38.300, TS38.331, TS 38.321 can be considered as relevant background. 3GPP release 18 is considering Lower layers (L1 / L2 layers) Triggered Mobility (LTM) to solve the problem of latency or signaling overhead associated with the L3 mobility. As per 3GPP, the goal of LTM is to enable a serving cell change via L1 / L2 signaling, in order to reduce the latency, overhead, and interruption time. The network (gNB) may configure the UE with multiple candidate cells to allow fast application of configurations for candidate cells. The network may further send Media Access Control (MAC) Control Element (CE) (MAC CE) or L1 signaling to dynamically switch the UE from a source cell to one of the configured candidate cells. Further, the LTM can be triggered based on L1 measurements rather than L3 measurements.

[0010] 3GPP proposes to perform LTM, without reset of lower layers to avoid data loss and to reduce the additional delay of data recovery wherever it is possible. The gNB may provide an LTM candidate configuration, i.e., configure LTM candidate cells through one RRC reconfiguration message for a candidate target cell or through one CellGroupConfig for each candidate target cell or through any similar RRC structure or IE containing the similar fields (for example, a new IE LTM-CandidateConfig can be defined as ASN.1 sequence containing cellgroupconfig and some other information elements in the RRC reconfiguration). The gNB may further release or modify the candidate configurations. A UE may store the LTM configuration of other candidate cells even after moving to a candidate cell through LTM.

[0011] To avoid transmitting a large message over air interface, the gNB can provide the LTM candidate configuration as delta configuration instead of full configuration. The gNB can indicate the UE to use the source cell configuration as the reference for delta configuration or provide the reference configuration explicitly.

[0012] The gNB may provide the LTM candidate configuration, i.e., configure LTM candidate cells through one RRC reconfiguration message for a candidate target cell or through one CellGroupConfig for each candidate target cell or through any similar RRC structure or IE containing the similar fields (for example a new IE LTM-CandidateConfig can be defined as ASN.1 sequence containing CellGroupConfig and some other information elements in the RRC reconfiguration). The gNB can further release or modify the candidate configurations. A UE can store the LTM configuration of other candidate cells even after moving to a candidate cell through LTM. The gNB can also provide the UE with configuration for performing LTM measurements for different candidate frequencies and candidate cells, and reporting based on the performed LTM measurements.

[0013] The gNB provides a reference configuration, L1 measurement configuration and candidate cell configuration for LTM.

[0014] While Rel-18 of 3GPP supported LTM within the same gNB Centralized Unit (CU), Rel-19 is planning to introduce inter-CU LTM. For Secondary Node (SN) LTM, both intra-SN LTM and inter-SN LTM can be configured simultaneously. For inter-CU Secondary Cell Group (SCG) LTM configuration, the SN generates SCG part configuration, a Master Node (MN) includes it into its MN RRC configuration message. For inter-CU SCG LTM, the LTM cell switch command MAC CE is sent by the source SN. Upon execution of inter-SN SCG LTM, the UE sends an MN RRC reconfiguration complete message to the MN, which includes an SN RRC reconfiguration complete message.

[0015] The network implementation avoids the simultaneous execution for both Master Cell Group (MCG), and SCG LTM.

[0016] In release 19, the inter-CU MCG LTM with intra-SN PSCell change is supported.

[0017] With respect to dual connectivity, the following scenarios can coexist.

[0018] - Inter-MN LTM and intra-SN LTM

[0019] - Inter-SN LTM and intra-MN LTM

[0020] For a UE in dual connectivity, both the MN and SN can provide the LTM configuration including LTM candidate cells, LTM reference configuration. The MN and SN can also provide the LTM measurement configurations to the UE. The SN sends an inter-node RRC message CG-Config to the MN to inform about the configurations it has used, and to request about the configuration it can use. The MN sends an inter-node RRC message CG-ConfigInfo to the SN to inform about the configurations it is allowed to use, as well as other information. The reference configuration related to inter-SN LTM is included within the LTM-ConfigNRDC and send to the UE, wherein the CG-Config and CG-ConfigInfo also may include the reference configuration.

[0021] The network can also configure the UE with conditions for Conditional LTM (CLTM), and upon the fulfillment of those conditions, the UE executes conditional LTM cell switch. The conditions may be based on layer 1 measurements or layer 3 measurements.

[0022] In the prior arts, the below structure can be used for defining LTM and CLTM.

[0023] -- ASN1START-- TAG-LTM-CANDIDATE-STARTLTM-Candidate-r18 ::= SEQUENCE {ltm-CandidateId-r18 LTM-CandidateId-r18,ltm-CandidatePCI-r18 PhysCellId OPTIONAL, -- Need Mltm-SSB-Config-r18 LTM-SSB-Config-r18 OPTIONAL, -- Need Mltm-CandidateConfig-r18 OCTET STRING (CONTAINING RRCReconfiguration) OPTIONAL, -- Need Mltm-ConfigComplete-r18 ENUMERATED {true} OPTIONAL, -- Need Rltm-EarlyUL-SyncConfig-r18 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r18) OPTIONAL, -- Need Rltm-EarlyUL-SyncConfigSUL-r18 OCTET STRING (CONTAINING EarlyUL-SyncConfig-r18) OPTIONAL, -- Need Rltm-TCI-Info-r18 LTM-TCI-Info-r18 OPTIONAL, -- Need Mltm-NoResetID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Mltm-UE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need M...,[[ltm-NoSecurityChangeID-r19 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Mcltm-ExecutionConditions-r19 SetupRelease {CLTM-ExecutionConditions-r19} OPTIONAL -- Need M]]}LTM-SSB-Config-r18 ::= SEQUENCE {ssb-Frequency-r18 ARFCN-ValueNR,subcarrierSpacing-r18 SubcarrierSpacing,ssb-Periodicity-r18 ENUMERATED {ms5, ms10, ms20, ms40, ms80, ms160, spare2, spare1} OPTIONAL, -- Need Rssb-PositionsInBurst-r18 CHOICE {shortBitmap BIT STRING (SIZE (4)),mediumBitmap BIT STRING (SIZE (8)),longBitmap BIT STRING (SIZE (64))} OPTIONAL, -- Need Rss-PBCH-BlockPower-r18 INTEGER (-60..50) OPTIONAL, -- Need R...}CLTM-ExecutionConditions-r19 ::= SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF ExecutionConditions-r19ExecutionConditions-r19 ::= SEQUENCE {ltm-CandidateId-r19 LTM-CandidateId-r18,executionCondition-r19 CHOICE {l1-Conditions-r19 LTM-CSI-ReportConfigId-r18,l3-Conditions-r19 SEQUENCE (SIZE (1..2)) OF MeasId} OPTIONAL, -- Need R...}

[0024] ltm-CandidateConfig: This field includes an RRC reconfiguration message used to configure an LTM candidate configuration.

[0025] ltm-CandidatePCI: This field identifies the Physical Cell Identity (PCI) of the SpCell of the LTM candidate configuration contained in ltm-CandidateConfig.

[0026] ltm-EarlyUL-SyncConfig, and ltm-EarlyUL-SyncConfigSUL: A configuration used to perform the early UL synchronization procedure over an Uplink (UL) or Supplementary Uplink (SUL) carrier.

[0027] ltm-NoResetID: If the network configures this field for one LTM candidate configuration, then the network configures also for all LTM candidate configurations within ltm-CandidateToAddModList in LTM-Config and ensures that the UE has stored a value for ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID.

[0028] ltm-NoSeurityChangeID: If the network configures this field for one LTM candidate configuration, then the network configures also for all LTM candidate configurations within ltm-CandidateToAddModList in LTM-Config and ensures that the UE has stored a value for ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID.

[0029] ltm-UE-MeasuredTA-ID: If the network configures this field for one LTM candidate configuration, then the network configures also for all LTM candidate configurations within ltm-CandidateToAddModList in LTM-Config and ensures that the UE has stored a value for ltm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID. This field is absent if tag2 is present for this LTM candidate configuration.

[0030] LTM-Config:The IE LTM-Config is used to provide LTM configurations.LTM-Config information element-- ASN1START-- TAG-LTM-CONFIG-STARTLTM-Config-r18 ::= SEQUENCE {ltm-ReferenceConfiguration-r18 SetupRelease {ReferenceConfiguration-r18} OPTIONAL, -- Need Mltm-CandidateToReleaseList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-CandidateId-r18 OPTIONAL, -- Need Nltm-CandidateToAddModList-r18 SEQUENCE (SIZE (1..maxNrofLTM-Configs-r18)) OF LTM-Candidate-r18 OPTIONAL, -- Need Nltm-ServingCellNoResetID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Nltm-CSI-ResourceConfigToAddModList-r18 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ResourceConfigurations-r18)) OF LTM-CSI-ResourceConfig-r18OPTIONAL, -- Need Nltm-CSI-ResourceConfigToReleaseList-r18 SEQUENCE (SIZE (1..maxNrofLTM-CSI-ResourceConfigurations-r18)) OF LTM-CSI-ResourceConfigId-r18OPTIONAL, -- Need NattemptLTM-Switch-r18 ENUMERATED {true} OPTIONAL, -- Cond LTM-MCGltm-ServingCellUE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need N...,[[ltm-ServingCellNoSecurityChangeID-r19 INTEGER (1..maxNrofLTM-Configs-plus1-r18) OPTIONAL, -- Need Nltm-SK-Counters-r19 SetupRelease {SK-CounterList-r19} OPTIONAL, -- Need Mcltm-ServingCellExecutionConditions-r19 SetupRelease {CLTM-ExecutionConditions-r19} OPTIONAL -- Need M]]}SK-CounterList-r19 ::= SEQUENCE {sk-CounterList-r19 SEQUENCE (SIZE (1..maxSK-Counter-r18)) OF SK-Counter}LTM-ConfigSCG-r19 ::= SEQUENCE {ltm-ConfigurationSCG-r19 OCTET STRING (CONTAINING LTM-Config-r18) OPTIONAL, -- Need R}-- TAG-LTM-CONFIG-STOP-- ASN1STOP- LTM-ConfigNRDCThe IE LTM-ConfigNRDC is used to provide LTM configurations in NR-DC.LTM-ConfigNRDC information element-- ASN1START-- TAG-LTM-CONFIGNRDC-STARTLTM-ConfigNRDC-r19 ::= SEQUENCE {ltm-ConfigurationSCG-r19 SetupRelease {LTM-Config-r18} OPTIONAL -- Need Rltm-SK-CounterConfigToAddModList-r19 SEQUENCE (SIZE (1..maxSecurityCellSet-r18)) OF SK-CounterConfig-r18 OPTIONAL, -- Need Nltm-SK-CounterConfigToReleaseList-r19 SEQUENCE (SIZE (1..maxSecurityCellSet-r18)) OF SecurityCellSetId-r18 OPTIONAL, -- Need N...}-- TAG-LTM-CONFIGNRDC-STOP-- ASN1STOPltm-ConfigurationSCG: The network does not configure this field in an RRC reconfiguration message within an LTM-Config IE and ConditionalReconfiguration IE.CG-Config-v19xy-IEs ::= SEQUENCE {ltm-ReferenceConfiguration-r19 ReferenceConfiguration-r18 OPTIONAL,ltm-Config-r19 LTM-Config-r18 OPTIONAL,nonCriticalExtension SEQUENCE {} OPTIONAL}CG-ConfigInfo-v19xy-IEs ::= SEQUENCE {ltm-ReferenceConfiguration-r19 ReferenceConfiguration-r18 OPTIONAL,nonCriticalExtension SEQUENCE {} OPTIONAL}

[0031] As shown above ltm-ReferenceConfiguration is send from MN to SN or SN to MN or from CU to DU or DU to CU through CG-Config / CG-ConfigInfo.

[0032] In the existing methods, the details on performing the LTM cell switch, and the LTM based recovery for CLTM are not specified. Further, in the existing methods, MN / SN or CU / Distributed Unit (DU) sends the reference configuration every time while sending the CG-Config or CG-ConfigInfo.

[0033] Hence, there is a need in the art for solutions which will overcome the above-mentioned drawback(s), among others.

[0034] The principal object of embodiments herein is to disclose systems and methods for managing Lower layers (L1 / L2 layers) Triggered Mobility (LTM), and Conditional LTM (CLTM) configurations in wireless communication networks.

[0035] Another object of embodiments herein is to disclose systems and methods for performing LTM based recovery in wireless communication networks, when CLTM fails.

[0036] Another object of embodiments herein is to disclose systems and methods for providing internode signaling for LTM reference configuration in wireless communication networks.

[0037] Another object of embodiments herein is to disclose one or more network actions for configuring an inter-SN LTM, when an intra-SN LTM has already been configured, in wireless communication networks.

[0038] Accordingly, the embodiments herein provide a method performed by a user equipment (UE) in a wireless communication system. The method comprises receiving, from a base station, a layer 1(L1) / layer2(L2) triggered mobility (LTM) configuration for at least one candidate cell associated with a conditional LTM (CLTM); upon fulfilment of LTM cell switch execution conditions for a candidate cell, in case that a value of field ltm-NoResetID in the LTM configuration for the candidate cell is not equal to a value of ltm-ServingCellNoResetID stored in the UE, performing at least one of a radio link control (RLC) re-establishment or a packet data convergence protocol (PDCP) recovery; and replacing the value of field ltm-ServingCellNoResetID with the value of field ltm-NoResetID.

[0039] Accordingly, the embodiments herein provide a user equipment (UE) in a wireless communication system. The UE comprises a transceiver; and at least one processor coupled with the transceiver and configured to receive, from a base station, a layer 1(L1) / layer2(L2) triggered mobility (LTM) configuration for at least one candidate cell associated with a conditional LTM (CLTM); upon fulfilment of LTM cell switch execution conditions for a candidate cell, in case that a value of field ltm-NoResetID in the LTM configuration for the candidate cell is not equal to a value of ltm-ServingCellNoResetID stored in the UE, to perform at least one of a radio link control (RLC) re-establishment or a packet data convergence protocol (PDCP) recovery; and to replace the value of field ltm-ServingCellNoResetID with the value of field ltm-NoResetID.

[0040] Accordingly, the embodiments herein provide a method for handling Lower layer Triggered Mobility (LTM) configurations in a wireless communication network by a User Equipment (UE). The method comprises receiving an LTM configuration from a base station for at least one LTM candidate cell selected upon fulfilling one or more execution conditions for a Conditional LTM (CLTM) cell switch. The method comprises performing at least one of a Radio Link Control (RLC) reestablishment, and a Packet Data Convergence Protocol (PDCP) recovery, if a value of a first reset identification field in the LTM configuration of the LTM candidate cell is not equal to a value of a second reset identification field of a serving cell. Thereafter, the method comprises replacing the value of the second reset identification field of the serving cell with the value of the first reset identification field of the LTM candidate cell, on performing at least one of the RLC reestablishment, and the PDCP recovery.

[0041] Accordingly, the embodiments herein provide a UE which comprises a processor, and a memory module. The processor is coupled with the memory module. The processor is configured to receive an LTM configuration from a base station for at least one LTM candidate cell selected upon fulfilling one or more execution conditions for a CLTM cell switch. The processor is configured to perform at least one of an RLC reestablishment, and a PDCP recovery, if a value of a first reset identification field in the LTM configuration of the LTM candidate cell is not equal to a value of a second reset identification field of a serving cell. Further, the processor is configured to replace the value of the second reset identification field of the serving cell with the value of the first reset identification field of the LTM candidate cell, on performing at least one of the RLC reestablishment, and the PDCP recovery.

[0042] Accordingly, the embodiments herein provide a method for handling LTM configurations in dual connectivity by a sender node. The method comprises performing a mobility procedure, and initiating a Cell Group (CG) message to send to a receiver node on performing the mobility procedure. The method comprises verifying if there is a change in an LTM reference configuration, on initiating the CG message. The method comprises sending the CG message including the LTM reference configuration to the receiver node, if there is a change in the LTM reference configuration. Thereafter, the method comprises sending the CG message without including the LTM reference configuration to the receiver node, if there is no change in the LTM reference configuration. The receiver node applies the previously received LTM reference configuration.

[0043] Accordingly, the embodiments herein provide a sender node which comprises a processor, and a memory module. The processor is coupled with the memory module. The processor is configured to perform a mobility procedure, and initiate a CG message to send to a receiver node on performing the mobility procedure. The processor is configured to verify if there is a change in an LTM reference configuration, on initiating the CG message. The processor is configured to send the CG message including the LTM reference configuration to the receiver node, if there is a change in the LTM reference configuration. Further, the processor is configured to send the CG message without including the LTM reference configuration to the receiver node, if there is no change in the LTM reference configuration.

[0044] These and other aspects of the example embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating example embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the example embodiments herein without departing from the spirit thereof, and the example embodiments herein include all such modifications.

[0045] According to embodiments of the present disclosure, efficient handling of lower-layer (L1 / L2) triggered mobility, including Conditional LTM (CLTM) and LTM configurations, is enabled, thereby improving the reliability and robustness of mobility management in a wireless communication system.

[0046] In particular, even when execution of CLTM fails, communication continuity can be maintained through an LTM-based recovery procedure, which minimizes connection interruption and prevents degradation of quality of service (QoS).

[0047] Further, by determining whether to perform Radio Link Control (RLC) reestablishment and / or Packet Data Convergence Protocol (PDCP) recovery based on reset identification fields, and updating the corresponding state accordingly, inconsistencies between protocol layers can be avoided, and data integrity and transmission consistency can be ensured.

[0048] In addition, unnecessary reset procedures can be reduced, thereby improving resource efficiency, and enabling stable mobility support across various network environments.

[0049] Embodiments herein are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the following illustrator drawings. Embodiments herein are illustrated by way of examples in the accompanying drawings, and in which:

[0050] FIG. 1 depicts a block diagram of a system for handling LTM and CLTM configurations in a wireless communication network, according to embodiments as disclosed herein;

[0051] FIG. 2 depicts a block diagram of a processor of the UE, according to embodiments as disclosed herein;

[0052] FIG. 3 depicts a method for handling the LTM configurations by the UE in a wireless communication network, according to embodiments as disclosed herein;

[0053] FIG. 4 depicts an example method for handling the LTM configuration by the UE for performing UE based TA measurements, according to embodiments as disclosed herein;

[0054] FIG. 5 depicts another example method for handling the LTM configuration by the UE, according to embodiments as disclosed herein;

[0055] FIG. 6 depicts another example method for handling the LTM configuration by the UE, according to embodiments as disclosed herein;

[0056] FIG. 7 depicts a method for indicating support for LTM reference configuration by the UE, according to embodiments as disclosed herein;

[0057] FIG. 8 depicts a method for handling LTM configurations in dual connectivity by a sender node, according to embodiments as disclosed herein;

[0058] FIGS. 9A and 9B depict methods for handling the LTM reference configuration by a receiver node, according to embodiments as disclosed herein; and

[0059] FIG. 10 depicts a method for managing inter-SN LTM configuration, and intra-SN LTM configuration by the sender node, according to embodiments as disclosed herein.

[0060] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0061] In describing the embodiments, descriptions related to technical contents well-known in the art and not associated directly with the disclosure will be omitted. Such an omission of unnecessary descriptions is intended to prevent obscuring of the embodiments disclosed herein, and more clearly transfer the embodiments disclosed herein.

[0062] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Further, the size of each element does not completely reflect the actual size. In the drawings, identical or corresponding elements are provided with identical reference numerals or different reference numerals.

[0063] The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or like reference numerals designate the same or like elements. Furthermore, in describing the disclosure, a detailed description of known functions or constitution incorporated herein will be omitted in the case that it is determined that the description may make the subject matter of the disclosure unnecessarily unclear. The terms which will be described below are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the operators, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

[0064] In the specific embodiments of the present disclosure described below, terms or components included in the disclosure may be expressed in singular or plural form depending on the specific embodiments presented. However, such singular or plural expressions are selected appropriately for convenience of description, and the present disclosure is not limited to a singular or plural number of components. A component expressed in the plural form may be implemented as a single component, and a component expressed in the singular form may be implemented as multiple components.

[0065] It is to be understood that the terminology used herein is for the purposes of describing particular embodiments only and is not intended to be limiting. The terms “comprising”, “having” and “including” are to be construed as open-ended terms unless otherwise noted.

[0066] Herein, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, may be performed based on computer program instructions. These computer program instructions may be loaded individually or collectively onto at least one processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which perform through any one of, or in any combination of, the at least one processor of the computer or other programmable data processing apparatus, create means for performing the functions specified in the flowchart block(s). These computer program instructions may also be stored in a non-transitory computer usable or computer-readable memory that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that perform the function specified in the flowchart block(s). The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable data processing apparatus to produce a computer executed process such that the instructions that perform on the computer or other programmable data processing apparatus provide steps for executing the functions specified in the flowchart block(s).

[0067] Further, each block may represent a module, segment, or portion of code, which includes one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks (or functions) shown in succession may in fact be performed substantially concurrently or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved.

[0068] As used in embodiments of the disclosure, a “module” may refer to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), which performs a predetermined function. However, the term including the word “module” does not always have a meaning limited to software or hardware. The “module” may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the “module” includes, for example, software elements, object-oriented software elements, components such as class elements and task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The components and functions provided by the “module” may be either combined into a smaller number of components and a “module,” or divided into additional components and a “module.” Moreover, the components and “modules” may be implemented to reproduce one or more central processing units (CPUs) within a device or a security multimedia card. Further, in the embodiments, the “module” may include one or more processors.

[0069] Any of the functions or operations described herein can be processed by one processor or a combination of processors. The one processor or the combination of processors is circuitry performing processing and includes circuitry like an Application Processor (AP, e.g. a CPU), a Communication Processor (CP, e.g., a modem), a Graphics Processing Unit (GPU), a Neural Processing Unit (NPU) (e.g., an Artificial Intelligence (AI) chip), a Wi-Fi chip, a Bluetooth® chip, a Global Positioning System (GPS) chip, a Near Field Communication (NFC) chip, connectivity chips, a sensor controller, a touch controller, a finger-print sensor controller, a display driver Integrated Circuit (IC), an audio CODEC chip, a Universal Serial Bus (USB) controller, a camera controller, an image processing IC, microprocessors, microcontrollers, digital signal processors, FPGA, ASIC, a Microprocessor Unit (MPU), a System on Chip (SoC), an IC, or the like. The one processor or the combination of processors executes instructions that can be stored in a memory, such as the operating system, in order to control the overall operation of the device. Also, the one processor or the combination of processors is also capable of executing other processes and programs resident in the memory, such as processes for the disclosure.

[0070] The drawings or flowcharts described below illustrate example methods that may be implemented according to the principles of the present disclosure, and various modifications may be made to the methods illustrated in the flowcharts of the present disclosure. For example, although illustrated as a series of steps, various steps in each drawing or flowchart may overlap, occur in parallel, occur in a different order, or be repeated. In other examples, any step may be omitted or replaced with another step.

[0071] The process of the flowchart may be performed by a device. One or more of the steps of the flowchart can be implemented by one or more processors / computer programs executing instructions to perform the noted functions.

[0072] The methods and apparatuses proposed in the embodiments of the present disclosure may be disclosed in connection with drawings disclosing flowcharts to illustrate example methods that may be implemented according to the principles of the present disclosure. Such flowcharts may contain different branches and / or sub-branches. It is understood that the principles of the present disclosure do not only contain the combination of all branches / sub-branches disclosed in the embodiment, but the present disclosure also contains at least one isolated branch / isolated sub-branch, in particular to a single branch / single sub-branch.

[0073] The methods and apparatuses proposed in the embodiments of the present disclosure are not limited to each embodiment individually, but may also be applied in combination of all or some of the embodiments proposed in the disclosure. Therefore, the embodiments of the present disclosure may be modified and applied without significantly departing from the scope of the present disclosure, as would be understood by those skilled in the art.

[0074] In this case, even if certain wordings are described differently across embodiments, they may be used interchangeably or in substitution or in combination if their underlying concepts are equivalent. For example, for the same or equivalent concept, even if one embodiment uses the expression "A" and another embodiment uses the expression "B", such expressions may be understood interchangeably, in substitution, or in combination.

[0075] Furthermore, throughout this disclosure, ordinal terms such as "first," "second," "third," etc., (and similar qualifiers) are used merely to distinguish between different instances, occurrences, configurations, messages, stages, elements or aspects of elements, operations, or information as described herein. Unless the context clearly dictates otherwise, the use of such ordinal terms does not itself require that the elements, operations, or information distinguished by these terms be structurally different, numerically distinct, or substantively dissimilar. For example, a "first signal" and a "second signal" may refer to instances of the same signal transmitted at different times or containing the same core information despite minor variations, or they may refer to signals with different content or characteristics, depending on the specific context. Similarly, a "first value" and a "second value" may represent the same magnitude but measured or applied in different circumstances, or they may represent different magnitudes. The interpretation should be guided by the specific technical context, function, and relationship described in the relevant portion of the specification and claims.

[0076] Furthermore, the terms “first ~”, “second ~”, etc., as described in the present disclosure with respect to various elements (e.g., information, objects, operation, sequences, or the like), should not limit those elements. These terms may only be intended to distinguish one element from another, and may not be intended to indicate a specific order. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element.

[0077] Furthermore, even if “first ~” and “second ~” are described in the present disclosure, it may be understood that element(s) referred to by “first ~” and “second ~” may be the same or different. For example, in case of element(s) being information, first information and second information may both be the same information, and, in some cases, are separate and different information.

[0078] In addition, the terms “if ~” and “in case that ~” as used in the disclosure or claims may be interpreted to include the meanings of “when (or upon) ~,” “in response to ~,” “based on ~,” or “according to ~,” and may be used interchangeably with these expressions. In addition, expressions other than those exemplified herein may also be used, as long as they have substantially the same meaning and do not impair the technical features of the present disclosure. If a method step (e.g., transmit a signal) is performed according to the disclosure of the application in connection with one of the above terms (such as “in case that ~” or the like), it may be interpreted to include the meanings (disclosure) of a prior determination that a feature has a specific state “~” (e.g., a bit length is above X), and then perform the method step in response to said determination.

[0079] The terms used in the following description to refer to access nodes, network entities, messages, interfaces between network entities, various types of identification information, and the like, are provided merely for the convenience of explanation by way of example. Therefore, the present disclosure is not limited to the terms described below, and other terms having equivalent technical meanings may also be used. Such terms may also be interchangeable with terms defined in any 3rd generation partnership project (3GPP) technical specifications (TS) or similar technical specifications, e.g., from ETSI, where appropriate.

[0080] The embodiments herein achieve systems and methods for managing Lower layers (L1 / L2 layers) Triggered Mobility (LTM), and conditional LTM (CLTM) in wireless communication networks. Referring now to the drawings, and more particularly to FIGS. 1 through 10, where similar reference characters denote corresponding features consistently throughout the figures, there are shown embodiments.

[0081] FIG. 1 depicts a block diagram of a system 100 for handling LTM and CLTM configurations in a wireless communication network. The system 100 comprises a User Equipment (UE) 102, a base station or network 104, a sender node 106, and a receiver node 108. The UE 102 is an electronic device capable of wireless communication and having various form factors, examples of the UE 102 may include a Mobile Station (MS), a cellular phone, a smartphone, a computer, a tablet, a wearable device, an Internet of Things (IoT) device, or any other device / system capable of performing wireless communication with the base station 104 and / or another UE or terminal through a wireless channel.

[0082] Hereinafter, the Base Station (BS) 104 is an entity that allocates resources to terminals, and may be at least one of a gNode B, an eNode B, a Node B, a 6G base station, a wireless access unit, a BS controller, or a node on a network.

[0083] Furthermore, the base station 104 of the present disclosure may include a split architecture comprising a Central Unit (CU), and a Distributed Unit (DU). In this structure, the CU is configured to process the higher layers of the control and user planes, while the DU is configured to process lower-layer radio resource functions. The embodiments of the present disclosure may be equally applicable to 5G base station architectures or 6G base station architectures in which such CU and DU functional splits are implemented.

[0084] Hereinafter, the expression that information is configured by the base station 104, as used in the present disclosure or claims, may, in context, be understood to mean that the terminal receives the corresponding information from the BS via a physical layer signaling or a higher layer signaling. Such an expression may be replaced with other terms having the same or substantially equivalent meaning.

[0085] In an embodiment herein, the sender node 106, and the receiver node 108 can be the base stations. The sender node 106 can include but not limited to a Master Node (MN), a Secondary Node (SN), the CU, and the DU. In an embodiment herein, the receiver node 108 can include but not limited to the MN, the SN, the CU, and the DU. The sender node 106, and the receiver node 108 can exchange data, and can be in communication with the UE 102.

[0086] Referring to FIG. 1, the UE 102 may include at least one transceiver (hereinafter, referred to as simply “transceiver”) 110, at least one processor (hereinafter, referred to as simply “processor”) 112, and at least one memory module (hereinafter, referred to as simply “memory”) 114. According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the transceiver 110, the processor 112, and the memory module 114 of the UE 102 may operate. However, components of the UE 102 are not limited to the example components illustrated in FIG. 1. In another embodiment, the UE 102 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in some embodiments, any combination of the transceiver 110, the processor 112, or the memory module 114 may be integrated in the form of one component.

[0087] The transceiver 110 may be a communication circuit or communication circuitry that enables the UE 102 to perform wireless communication with a node or an entity of the base station 104. For example, the transceiver 110 may enable the UE 102 to transmit or receive a signal to or from the base station 104 through cellular communication, or to transmit or receive a signal to or from another UE through cellular communication. For example, the transceiver 110 may support at least one of various cellular communication technologies including 3rd Generation (3G), 4th Generation (4G), Long Term Evolution (LTE), 5th Generation (5G) New Radio (NR), 6th Generation (6G), and various cellular wireless communication technologies supported by the transceiver 110 may include all subsequent generations of evolved wireless communications.

[0088] In an embodiment herein, the transceiver 110 may include various circuit structures used to transmit or receive signals to or from the base station 104 through a wireless channel. The signals may include control information and data. For example, the transceiver 110 may include a Radio Frequency (RF) transmitter for up-converting, and amplifying the frequency of a transmitted signal, and an RF receiver for low-noise-amplifying a received signal and down-converting the frequency thereof. The transceiver 110 may output a signal received through a wireless channel to the processor 112 and may transmit, through a wireless channel, a signal output from the processor 112.

[0089] In an embodiment herein, the UE 102 may include a plurality of transceivers. For example, in the case of supporting Evolved-Universal Terrestrial Radio Access-New Radio (E-UTRA-NR) Dual Connectivity (EN-DC), the UE 102 may include a first transceiver supporting the 4G LTE wireless communication and a second transceiver supporting the 5G NR wireless communication. According to another embodiment, in the case of supporting NR-Dual Connectivity (NR-DC), the UE 102 may include a plurality of transceivers supporting the 5G NR wireless communication. According to still another embodiment, in the case of supporting near field wireless communication, the UE 102 may separately include a transceiver supporting at least one standard in the group of wireless communication protocol standards as defined in the protocol standards for Bluetooth, Wireless Local Area Network (WLAN) network (including institute of electrical and electronics engineers (IEEE) 802.11-2016 standard or its amendments, e.g., 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be, without being limited thereto).

[0090] The processor 112 may control general operations of the UE 102 according to embodiments of the disclosure. The processor 112 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processing operations. The processor 112 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory module 114, individually, collectively or in any combination thereof. Further, the processor 112 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme.

[0091] The processor 112 may be electrically, operatively, and / or communicatively coupled to the transceiver 110 to control the transceiver 110.

[0092] The processor 112 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. For example, the processor 112 may include a Communication Processor (CP) configured to control communication operations and an Application Processor (AP) configured to control execution of an upper layer (for example, an application layer). In a specific embodiment, at least a part of the processor 112 may be included in one chip and the other part of the processor 112 may be included in another chip. Otherwise, at least one processor may be included in another component, for example, the transceiver 110 or the memory module 114.

[0093] The processor 112 may perform or control or cause an operation of the UE 102 for executing at least one or a combination of methods according to embodiments of the disclosure. To this end, the processor 112 may execute a computer program, codes, or instructions stored in the memory module 114, so as to control other components of the UE 102 to enable execution of various operations.

[0094] In an embodiment herein, the processor 112 further comprises a configuration managing module 202, as depicted in FIG. 2.

[0095] In an embodiment herein, the configuration managing module 202 can receive an LTM configuration from a base station for at least one LTM candidate cell where the LTM candidate cell is selected upon fulfilling one or more execution conditions for a Conditional LTM (CLTM) cell switch. The LTM candidate cell can be managed by the base station 104. In an embodiment herein, the CLTM execution condition is L3 condition (condition based on L3 measurements). In an embodiment herein, the CLTM execution condition is L1 condition (condition based on L1 measurements). The configuration managing module 202 can perform at least one of a Radio Link Control (RLC) reestablishment, and a Packet Data Convergence Protocol (PDCP) recovery, if a value of a first reset identification field in the LTM configuration of the LTM candidate cell is not equal to a value of a second reset identification field of a serving cell. In an embodiment herein, the first reset identification field of the LTM candidate cell is an ltm-NoResetID field. The ltm-NoResetID field indicates that at least one of the RLC reestablishment, and the PDCP recovery need not be performed during an LTM cell switch when the ltm-NoResetID field is equal to a NoResetID field of the serving cell. In an embodiment herein, the second reset identification field of the serving cell is an ltm-ServingCellNoResetID field. The ltm-ServingCellNoResetID field indicates that at least one of the RLC reestablishment, and the PDCP recovery need not be performed during the LTM cell switch when a NoResetID field of the LTM candidate cell is equal to the ltm-ServingCellNoResetID field. In an embodiment herein, the configuration managing module 202 can replace the value of the second reset identification field of the serving cell with the value of the first reset identification field of the LTM candidate cell, on performing at least one of the RLC reestablishment, and the PDCP recovery.

[0096] In an embodiment herein, the configuration managing module 202 can verify if one or more UE based Timing Advance (TA) measurements is configured in at least one neighbour LTM candidate cell, based on the LTM configuration of the LTM candidate cell that has fulfilled one or more execution conditions for the CLTM cell switch. The configuration managing module 202 can compare the LTM configuration of the LTM candidate cell with the LTM configuration of the neighbour LTM candidate cell, if the UE based TA measurements are configured in the neighbour LTM candidate cell. The configuration managing module 202 can perform the UE based TA measurements on the neighbour cell, if the LTM configuration of the LTM candidate cell is equal to the LTM configuration of the neighbour LTM candidate cell.

[0097] In an embodiment herein, the configuration managing module 202 can verify if the LTM configuration of the LTM candidate cell that has fulfilled one or more execution conditions for the CLTM cell switch includes a flag indicating that it is a complete configuration. The configuration managing module 202 can combine a reference configuration of a UE configuration with the LTM configuration of the LTM candidate cell, if the LTM configuration of the LTM candidate cell does not include the flag indicating that it is a complete configuration. The configuration managing module 202 can release one or more radio bearers, and one or more logical channels of the UE configuration, if the LTM configuration of the LTM candidate cell does not include the flag indicating that it is a complete configuration.

[0098] Above embodiments allow the execution of Conditional LTM for the UE 102 through wherein the new cell’s configuration can be applied seamlessly even in case of a subsequent LTM execution through a conditional LTM.

[0099] In an embodiment herein, the configuration managing module 202 can verify if the UE 102 is configured for an LTM based recovery by the network or base station 104. The configuration managing module 202 can detect at least one of a radio link failure, and a reconfiguration with sync failure of a Master Cell Group (MCG) for an LTM cell switch procedure triggered upon at least one of the fulfilment of one or more execution conditions for the CLTM cell switch, and reception of an LTM cell switch command, if the UE 102 is configured for the LTM based recovery. The configuration managing module 202 can detect if the LTM candidate cell selected upon fulfilling one or more execution conditions for the CLTM cell switch is associated with the MCG, on detecting at least one of the radio link failure, and the reconfiguration with sync failure of the MCG. The configuration managing module 202 can verify if a value of a first security identification (ltm-NoSecurityChangeID) field indicated by the selected LTM candidate cell is equal to a value of a second security identification (ltm-ServingCellNoSecurityChangeID) field of a source cell. The configuration managing module 202 can perform the CLTM cell switch procedure for the selected LTM candidate cell, if the selected LTM candidate cell is associated with the MCG, and the value of the ltm-NoSecurityChangeID field is equal to the value of the ltm-ServingCellNoSecurityChangeID field. These embodiments allow the recovery of the UE through conditional LTM configuration when a secured operation after recovery is possible. If the UE 102 attempts recovery without applying these embodiments, then the UE 102 may not have a new security configuration (such as NCC value in NR) and the UE 102 may face a number of security attacks in the recovered cell.

[0100] In an embodiment herein, the sender node 106 can perform a mobility procedure. The sender node 106 can initiate a Cell Group (CG) message to send to the receiver node 108, on performing the mobility procedure. The CG message is at least one of a CG-Config message, and a CG-ConfigInfo message. The sender node 106 can verify if there is a change in an LTM reference configuration, on initiating the CG message. In an embodiment herein, the sender node 106 can send the CG message including the LTM reference configuration to the receiver node 108, if there is a change in the LTM reference configuration. In an embodiment herein, the sender node 106 can send the CG message without including the LTM reference configuration to the receiver node 108, if there is no change in the LTM reference configuration. In this case, the receiver node 108 applies the previously received LTM reference configuration. This reduces the signaling overhead for exchanging LTM reference configuration between MN and SN or CU and DU in dual connectivity. As the LTM reference configuration may include thousands of bytes, unless the embodiments are applied, it can lead to congestion between the network nodes.

[0101] In an embodiment herein, the sender node 106 can initiate configuration for an inter-SN LTM, if the sender node 106 is SN. The sender node 106 may release an intra-SN LTM candidate cell configuration, on initiating the configuration for the inter-SN LTM. The sender node 106 may send the intra-SN LTM candidate cell configuration to the MN, and the MN may configure the intra-SN LTM candidate cell configuration using an LTM configuration NRDC (ltm-ConfigNRDC) field or similar fields. This ensures that UE 102 can be configured with both Intra-SN LTM cell switch and Inter-SN LTM cell switch and they can be stored for subsequent mobility. If the Intra-SN configuration is not released, it will be too complex for the UE 102 to handle Inter-SN LTM.

[0102] In an embodiment herein, the memory module 114 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory module 114 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or Read-Only Memory (ROM), semipermanent memory, such as Random Access Memory (RAM), cache memory, or a combination thereof.

[0103] The memory module 114 may be electrically, operatively, and / or communicatively coupled to the processor 112 and may be accessed by the processor 112.

[0104] The memory module 114 may store a computer program, codes, or instructions executable by the processor 112. According to an embodiment, a computer program, codes, or instructions executable by the processor 112 may be either stored in a single memory device or separated and stored in a distributed manner in two or more memory devices. By executing the instructions stored in the memory module 114, the processor 112 may perform various functions according to an embodiment of the disclosure.

[0105] In an embodiment herein, operations of the UE 102 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory module 114 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0106] FIG. 3 depicts a method 300 for handling the LTM configurations by the UE 102 in a wireless communication network. The method 300 comprises receiving an LTM configuration from a base station for at least one LTM candidate cell which is selected upon fulfilling one or more execution conditions for a CLTM cell switch, as depicted in step 302. The method 300 comprises verifying if a value of an ltm-NoResetID field in the LTM configuration of the LTM candidate cell is equal to a value of an ltm-ServingCellNoResetID field of a serving cell, as depicted in step 304. The method 300 comprises performing at least one of an RLC reestablishment, and a PDCP recovery, if the value of the ltm-NoResetID field is not equal to the value of the ltm-ServingCellNoResetID field, as depicted in step 306. Thereafter, the method 300 comprises replacing the value of the ltm-ServingCellNoResetID field with the value of the ltm-NoResetID field, as depicted in step 308, on performing at least one of the RLC reestablishment, and the PDCP recovery.

[0107] The various actions in method 300 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 3 may be omitted.

[0108] FIG. 4 depicts an example method 400 for handling the LTM configuration by the UE 102 for performing the UE based TA measurements. The method 400 comprises receiving the LTM configuration from a base station for at least one LTM candidate cell which is selected upon fulfilling one or more execution conditions for a CLTM cell switch, as depicted in step 402. The method 400 comprises verifying if one or more UE based TA measurements is configured in at least one neighbour LTM candidate cell, as depicted in step 404, based on the LTM configuration of the LTM candidate cell that has fulfilled the one or more execution conditions for the CLTM cell switch. The method 400 comprises comparing the LTM configuration of the LTM candidate cell with the LTM configuration of the neighbour LTM candidate cell, as depicted in step 406, if the UE based TA measurements are configured in the neighbour LTM candidate cell. Thereafter, the method 400 comprises performing the UE based TA measurements on the neighbour cell, as depicted in step 408, if the LTM configuration of the LTM candidate cell is equal to the LTM configuration of the neighbour LTM candidate cell. The UE based TA measurements may be performed as long as the UE 102 remains in the cell to which it has switched.

[0109] The various actions in method 400 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 4 may be omitted.

[0110] FIG. 5 depicts another example method 500 for handling the LTM configuration by the UE 102. The method 500 comprises receiving the LTM configuration from a base station for at least one LTM candidate cell which is selected upon fulfilling one or more execution conditions for a CLTM cell switch, as depicted in step 502. The method 500 comprises verifying if the LTM configuration of the LTM candidate cell includes a flag indicating that it is a complete configuration, as depicted in step 504. The method 500 comprises combining a reference configuration of the UE configuration with the LTM configuration of the LTM candidate cell, as depicted in step 506, if the LTM configuration of the LTM candidate cell does not include the flag indicating that it is a complete configuration. Thereafter, the method 500 comprises releasing one or more radio bearers, and one or more logical channels of the UE configuration, as depicted in step 508, if the LTM configuration of the LTM candidate cell does not include the flag indicating that it is a complete configuration.

[0111] The various actions in method 500 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 5 may be omitted.

[0112] FIG. 6 depicts another example method 600 for handling the LTM configuration by the UE 102. The method 600 comprises verifying if the UE 102 is configured for an LTM based recovery by the network or base station 104, as depicted in step 602. The method 600 comprises detecting at least one of a radio link failure, and a reconfiguration with sync failure of an MCG for an LTM cell switch procedure, as depicted in step 604, triggered upon at least one of the fulfilment of one or more execution conditions for the CLTM cell switch, and reception of an LTM cell switch command, if the UE 102 is configured for the LTM based recovery. The method 600 comprises detecting if the LTM candidate cell selected upon fulfilling one or more execution conditions for the CLTM cell switch is associated with the MCG, as depicted in step 606, on detecting at least one of the radio link failure, and the reconfiguration with sync failure of the MCG. The method 600 comprises verifying if a value of a ltm-NoSecurityChangeID field indicated by the selected LTM candidate cell is equal to a value of a ltm-ServingCellNoSecurityChangeID field of a source cell, as depicted in step 608. Thereafter, the method 600 comprises performing the CLTM cell switch procedure for the selected LTM candidate cell, if the selected LTM candidate cell is associated with the MCG, and the value of the ltm-NoSecurityChangeID field is equal to the value of the ltm-ServingCellNoSecurityChangeID field, as depicted in step 610.

[0113] The various actions in method 600 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 6 may be omitted.

[0114] In an embodiment herein, the UE 102 informs the network or base station 104 whether it supports reference configuration in an MN Radio Resource Control (RRC) message. This information may be provided during a UECapabilityInformation transfer procedure (such as in a UECapabilityInformation message in NR).

[0115] FIG. 7 depicts a method 700 for indicating support for LTM reference configuration by the UE 102. The method 700 comprises receiving a UE capability enquiry from the network or base station 104, as depicted in step 702. Thereafter, the method 700 comprises sending the UE capability information including the support of LTM reference configuration in an MN RRC message (not embedded SN RRC message or SN RRC message in SRB3) to the network, as depicted in step 704, on receiving the UE capability enquiry.

[0116] The various actions in method 700 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 7 may be omitted.

[0117] In an embodiment herein, the UE 102 informs the network or base station 104 whether it supports reference configuration in ltm-ConfigNRDC (or equivalent fields in other Radio Access Technology (RAT)). This information may be provided during a UECapabilityInformation transfer procedure (such as in UECapabilityInformation message in NR).

[0118] In an embodiment herein, the UE 102 informs the network or base station 104 whether it supports more than one reference configuration (such as one in ltm-Config and one in ltm-ConfigNRDC). This information may be provided during a UECapabilityInformation transfer procedure (such as in UECapabilityInformation message in NR).

[0119] The network or base station 104 configures the reference configuration according to the received capability.

[0120] For example, upon fulfilment of CLTM cell switch conditions, the UE 102 performs one or more of the following steps:

[0121] 1. If the value of field ltm-NoSecurityChangeID (or equivalent field which informs that security keys are not to be changed when the field equals to the field such as NoSecurityChangeID of the serving cell or equivalent field during LTM cell switch to the candidate) indicated by the LTM candidate cell which has fulfilled CLTM evaluation condition is not equal to the value of ltm-ServingCellNoSecurityChangeID (or equivalent field which informs that security keys of candidate cells are not to be changed during LTM cell switch to the candidate when the NoSecurityChangeID or equivalent field of the candidate cell is equal to this field), then the UE 102 derives new ciphering and integrity keys and applies them for all Secondary Cell Group (SCG) bearers which are configured with ciphering and integrity. The UE 102 also performs PDCP reestablishment and RLC reestablishment, and also stores / replaces the stored value of ltm-ServingCellNoSecurityChangeID with the value of ltm-NoSecurityChangeID in the LTM-Candidate which has fulfilled CLTM evaluation condition or the cell selected as candidate for LTM cell switch when multiple LTM candidates have fulfilled CLTM evaluation conditions.

[0122] 2. If the LTM candidate cell which has fulfilled CLTM evaluation condition or the cell selected as candidate for LTM cell switch when more than one cell has fulfilled CLTM evaluation condition does not contain the field ltm-NoResetID (or equivalent field which informs that RLC reestablishment and PDCP recovery are not to be performed when the field equals to the field such as NoResetID of the serving cell or equivalent field during LTM cell switch), and if the UE 102 does not have any value stored of ltm-ServingCellNoResetID (or equivalent field which informs that RLC reestablishment and PDCP recovery are not to be performed during LTM cell switch when the NoResetID or equivalent field of the candidate cell is equal to this field), or if the value of field ltm-NoResetID is not equal to the value of ltm-ServingCellNoResetID, then the UE 102 performs PDCP recovery and RLC reestablishment and stores / replaces the stored value of ltm-ServingCellNoResetID with the value of ltm-NoResetID in the LTM-Candidate which has fulfilled CLTM evaluation condition.

[0123] 3. The UE 102 checks if it is configured for the UE based TA measurements in the neighbour LTM candidate cells based on an information in the LTM candidate cell which has fulfilled CLTM evaluation. If the information in the LTM candidate cell which has fulfilled CLTM evaluation is equal to the information for a neighbour LTM candidate cell, then the UE 102 may perform UE based TA measurements on the neighbour cell. Otherwise, the UE 102 may not perform UE based TA measurements on the neighbour cell.

[0124] 4. The UE 102 checks if there is a flag indicating whether the LTM candidate cell which has fulfilled CLTM evaluation has complete configuration or the reference configuration based on a flag in that candidate. If the flag is not configured, then the UE 102 combines the reference configuration and the candidate configuration, and applies the LTM configuration.

[0125] 5. The UE 102 releases the radio bearers and logical channels which are not part of the LTM candidate cell’s configuration which has fulfilled CLTM evaluation or the LTM reference configuration (in case the LTM candidate configuration does not include ltm-ConfigComplete).

[0126] In an embodiment herein, if the UE 102 is configured by the network or base station 104 for LTM based recovery (such as using attemptLTM-Switch in NR), and the UE 102 detected reconfiguration with sync failure of the MCG for an LTM cell switch procedure triggered upon the fulfilment of CLTM execution condition, and the UE 102 has selected a cell which is one of the LTM candidate cells associated with the MCG, then the UE 102 performs LTM cell switch procedure for the selected cell. The methods help to reduce the delay in recovery after a CLTM switch failure. In an embodiment herein, the UE 102 may discard the timing advance received from the selected cell, and stop the corresponding TA timer in the Media Access Control (MAC) while it attempts for LTM based recovery after CLTM switch failure. In an embodiment herein, the UE 102 may perform random access during the LTM based recovery when the CLTM based LTM cell switch has failed.

[0127] In an embodiment herein, according to TS 38.331,

[0128] 1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the indication by lower layers or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the fulfilment of CLTM execution condition as specified in clause 5.3.5.18.6; and

[0129] 1> ifattemptLTM-Switchis configured; and

[0130] 1> if the selected cell is one of the LTM candidate cells in theLTM-Candidate IEwithinltm-Configassociated with the MCG:

[0131] 2> perform the LTM cell switch procedure for the selected LTM candidate cell according to the actions specified in 5.3.5.18.6;

[0132] In an embodiment herein, if the UE 102 is configured by the network or base station 104 for LTM based recovery (such as using attemptLTM-Switch), and the UE 102 detected reconfiguration with sync failure of the MCG for an LTM cell switch procedure triggered upon the fulfilment of CLTM execution condition, and the UE 102 has selected a cell which is one of the LTM candidate cells associated with the MCG, and if the value of field ltm-NoSecurityChangeID indicated by the selected cell is equal to the configured value of ltm-ServingCellNoSecurityChangeID of the source cell from which UE 102 tried to perform LTM cell switch (i.e., the source cell / PCell in which UE 102 has satisfied the CLTM execution condition), then the UE 102 performs LTM cell switch procedure for the selected cell.

[0133] In an embodiment herein, if the UE 102 is configured by the network or base station 104 for LTM based recovery (such as using attemptLTM-Switch), and the UE 102 detected radio link failure or reconfiguration with sync failure of the MCG for an LTM cell switch procedure triggered by the reception of LTM cell switch command, and the UE 102 has selected a cell which is one of the LTM candidate cells associated with the MCG, and if the value of field ltm-NoSecurityChangeID indicated by the selected cell is equal to the configured value of ltm-ServingCellNoSecurityChangeID of the source cell from which the UE 102 tried to perform LTM cell switch (i.e., the source cell / PCell in which UE 102 has satisfied the CLTM execution condition), then the UE 102 performs LTM cell switch procedure for the selected cell.

[0134] In an embodiment herein, the UE 102 considers the LTM candidate cell in ltm-Config and ltm-ConfigNRDC for LTM based recovery.

[0135] In an embodiment herein, according to TS 38.331,

[0136] 1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the indication by lower layers or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the fulfilment of CLTM execution condition as specified in clause 5.3.5.18.6; and

[0137] 1> if attemptLTM-Switch is configured; and

[0138] 1> if the selected cell is one of the LTM candidate cells in the LTM-Candidate IE within ltm-Config or ltm-ConfigNRDC associated with the MCG:

[0139] 2> if the value of field ltm-NoSecurityChangeID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition is equal to the value of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID:

[0140] 3> perform the LTM cell switch procedure for the selected LTM candidate cell according to the actions specified in 5.3.5.18.6;

[0141] In an embodiment herein, the UE 102 considers LTM candidate cells in ltm-Config only for LTM based recovery. LTM candidate cells in ltm-ConfigNRDC are not considered for LTM based recovery.

[0142] In an embodiment herein, according to TS 38.331,

[0143] 1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the indication by lower layers or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the fulfilment of CLTM execution condition as specified in clause 5.3.5.18.6; and

[0144] 1> ifattemptLTM-Switchis configured; and

[0145] 1> if the selected cell is one of the LTM candidate cells in theLTM-CandidateIE withinltm-Configassociated with the MCG:

[0146] 2>if the value of fieldltm-NoSecurityChangeIDcontained within theLTM-CandidateIE inltm-Configwhich has fulfilled CLTM execution condition is equal to the value ofltm-ServingCellNoSecurityChangeIDwithinVarLTM-ServingCellNoSecurityChangeID:

[0147] 3> perform the LTM cell switch procedure for the selected LTM candidate cell according to the actions specified in 5.3.5.18.6;

[0148] 5.3.5.18.6 LTM cell switch execution

[0149] Upon the indication by lower layers that an LTM cell switch procedure is triggered, or upon performing LTM cell switch following cell selection performed while timer T311 was running, as specified in 5.3.7.3, or upon the fulfilment of CLTM cell switch conditions, the UE shall:

[0150] 1> if this procedure is triggered due to fulfilment of CLTM cell switch conditions:

[0151] 2> if more than one LTM candidate configuration has triggered this procedure:

[0152] 3> select one of the LTM candidate configurations as the selected cell for the LTM cell switch execution;

[0153] 1> stop the LTM conditions evaluation (based on L1 and / or L3 measurements), if any, for all the LTM candidate configurations associated with the cell group for which the LTM cell switch procedure is triggered;

[0154] 1> if LTM conditions evaluation was done based on L1 measurements:

[0155] 2> inform lower layers to stop the LTM cell switch conditions evaluation or all LTM candidate configurations;

[0156] 1> if the LTM-Candidate IE for the selected LTM candidate configuration includes the field cltm-ExecutionConditions:

[0157] 2> if the field l3-Conditions is included within cltm-ExecutionConditions:

[0158] 3> perform the LTM cell switch conditions evaluation based on L3 measurements as specified in 5.3.5.18.x according to the received cltm-ExecutionConditions;

[0159] 2> else if the field l1-Conditions is included within cltm-ExecutionConditions:

[0160] 3> inform lower layers to initiate the LTM cell switch conditions evaluation based on L1 measurements according to the received field cltm-ExecutionConditions.

[0161] 1> if the LTM cell switch is triggered on the MCG; or

[0162] 1> if the LTM cell switch is triggered on the SCG and the UE has an ltm-ConfigNRDC:

[0163] 2> release / clear all current dedicated and common radio configurations which have neither been received via Signaling Radio Bearer 1 (SRB1) within mrdc-SecondaryCellGroup, nor via SRB3 except for the following:

[0164] - the radio bearer configuration (configured via RadioBearerConfig)

[0165] - the logicalChannelIdentity and logicalChannelIdentityExt of RLC bearers configured in RLC-BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];

[0166] - the bh-LogicalChannelIdentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];

[0167] - the UE variables VarLTM-ServingCellNoResetID, VarLTM-ServingCellUE-MeasuredTA-ID, and VarLTM-ServingCellNoSecurityChange;

[0168] - the ltm-Config and ltm-ConfigNRDC (if configured);

[0169] - the MCG C-RNTI;

[0170] - the AS security configurations associated with the master key;

[0171] - the logged measurement configuration;

[0172] - the successHO-Config;

[0173] 3> if the LTM cell switch is triggered on the SCG and the LTM candidate configuration to be applied is configured via ltm-ConfigNRDC:

[0174] - the ServingCellConfigCommon of the PCell;

[0175] 1> if the LTM cell switch is triggered on the SCG:

[0176] 2> release / clear all current dedicated and common radio configurations which have been received either via SRB1 within mrdc-SecondaryCellGroup, or via SRB3 except for the following:

[0177] - the radio bearer configuration (configured via RadioBearerConfig IE)

[0178] - the logicalChannelIdentity and logicalChannelIdentityExt of RLC bearers configured in RLC-BearerConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];

[0179] - the bh-LogicalChannelIdentity of BH RLC channels configured in BH-RLC-ChannelConfig and the associated RLC entities, their state variables, buffers, and timers, except for triggering the associated RLC entities to reset the variable RETX_COUNT its initial value, as specified in TS 38.322 [4];

[0180] - the UE variables VarLTM-ServingCellNoResetID and VarLTM-ServingCellUE-MeasuredTA-ID;

[0181] - the ltm-Config;

[0182] - the AS security configurations associated with the secondary key;

[0183] 1> for each SRB / DRB in the current UE configuration:

[0184] 2> if the LTM cell switch is triggered on the MCG and the SRB / DRB using the master key; or

[0185] 2> if the LTM cell switch is triggered on the SCG and the SRB / DRB using the secondary key:

[0186] 3> keep the associated PDCP and SDAP entities, their state variables, buffers and timers;

[0187] 3> release all fields related to the SRB / DRB configuration except for srb-Identity and drb-Identity;

[0188] 3> apply the default SRB configuration defined in 9.2.1 for the corresponding SRB;

[0189] NOTE 00: For all radio bearers and RLC bearers included in the LTM candidate configuration to be applied at an LTM cell switch execution (i.e., as derived from the LTM reference configuration and the LTM candidate configuration), even if those radio bearers and RLC bearers were configured before the LTM cell switch execution, the network includes fields as specified for the initial setup of radio bearers and RLC bearers and sets the values previously stored by the UE for the fields that cannot be modified according to presence conditions or field descriptions.

[0190] 1> apply the default L1 parameter values as specified in corresponding physical layer specifications except for the parameters for which values are provided in SIB1;

[0191] 1> use the default values specified in 9.2.3 for timers T310, T311 and constants N310, N311 associated with the cell group(s) for which the RRCReconfiguration message is applied due to the triggered LTM cell switch procedure, where T310, N310, and N311 are for both MCG and SCG, and T311 is only for the MCG;

[0192] 1> apply the default MAC Cell Group configuration as specified in 9.2.2 for the cell group(s) for which the RRCReconfiguration message is applied due to the triggered LTM cell switch procedure;

[0193] 1> for each srb-Identity in the current UE configuration:

[0194] 2> apply the default SRB configuration defined in 9.2.1 for the corresponding SRB;

[0195] 1> if the field ltm-NoSecurityChangeID is configured for the LTM-Candidate IE and if the UE does not have any value stored of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID; or

[0196] 1> if the value of field ltm-NoSecurityChangeID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition is not equal to the value of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID:

[0197] 2> if the LTM cell switch is triggered on the SCG:

[0198] 3> consider the first sk-Counter value in the ltm-SK-Counters within the VarLTM-ServingCellNoSecurityChangeID as the selected sk-Counter value, and perform security key update procedure as specified in 5.3.5.7;

[0199] 3> remove the selected sk-Counter value from the ltm-SK-Counters within the VarLTM-ServingCellNoSecurityChangeID;

[0200] 2> at the end of the procedure, after applying the RRCReconfiguration message in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC for each drb-Identity value that is part of the current UE configuration:

[0201] 3> if the PDCP entity of this DRB is not configured with cipheringDisabled:

[0202] 4>configure the PDCP entity with the ciphering algorithm and KUPenc key associated with the master key (KeNB / KgNB) or secondary key (S-KgNB / S-KeNB), as indicated in keyToUse, i.e. the ciphering configuration shall be applied to all subsequent PDCP PDUs received and sent by the UE;

[0203] 3> if the PDCP entity of this DRB is configured with integrityProtection:

[0204] 4> configure the PDCP entity with the integrity protection algorithms according to securityConfig and apply the KUPint key associated with the master key (KeNB / KgNB) or the secondary key (S-KgNB) as indicated in keyToUse;

[0205] 3> if drb-ContinueROHC is included in pdcp-Config:

[0206] 4> indicate to lower layer that drb-ContinueROHC is configured;

[0207] 3> if drb-ContinueEHC-DL is included in pdcp-Config:

[0208] 4> indicate to lower layer that drb-ContinueEHC-DL is configured;

[0209] 3> if drb-ContinueEHC-UL is included in pdcp-Config:

[0210] 4> indicate to lower layer that drb-ContinueEHC-UL is configured;

[0211] 3> if drb-ContinueUDC is included in pdcp-Config:

[0212] 4> indicate to lower layer that drb-ContinueUDC is configured;

[0213] 3> re-establish the PDCP entity of this DRB as specified in TS 38.323 [5], clause 5.1.2;

[0214] 3> re-establish the corresponding RLC entity as specified in TS 38.322 [4];

[0215] 2> at the end of the procedure, after applying the LTM configuration in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC for each srb-Identity value that is part of the current UE configuration:

[0216] 3> if the UE has selected a new sk-Counter value due to this LTM cell switch procedure:

[0217] 4> configure the PDCP entity to apply the integrity protection algorithm and KRRCint key associated with the master key (KeNB / KgNB) or the secondary key (S-KgNB), as indicated in keyToUse, i.e. the integrity protection configuration shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

[0218] 4> configure the PDCP entity to apply the ciphering algorithm and KRRCenc key associated with the master key (KeNB / KgNB) or the secondary key (S-KgNB) as indicated in keyToUse, i.e. the ciphering configuration shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

[0219] 4> re-establish the PDCP entity of this SRB as specified in TS 38.323 [5];

[0220] 3> else:

[0221] 4> trigger the PDCP entity to perform SDU discard as specified in TS 38.323 [5];

[0222] 3> re-establish the corresponding RLC entity as specified in TS 38.322 [4];

[0223] 2> if the value of field ltm-NoSecurityChangeID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition is not equal to the value of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID:

[0224] 3> replace the value of ltm-ServingCellNoSecurityChangeID in VarLTM-ServingCellNoSecurityChangeID with the value of ltm-NoSecurityChangeID in the LTM-Candidate in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition;

[0225] 1> else if the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition does not contain the field ltm-NoResetID and if the UE does not have any value stored of ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID; or

[0226] 1> if the value of field ltm-NoResetID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition is not equal to the value of ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID:

[0227] 2> for each logicalChannelIdentity and logicalChannelIdentityExt that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:

[0228] 3> if servedRadioBearer is set to drb-Identity:

[0229] 4> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying the LTM configuration in ltm-CandidateConfig within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0230] 2> for each bh-LogicalChannelIdentity that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:

[0231] 3> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying the LTM configuration in ltm-CandidateConfig within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0232] 2> if the LTM cell switch is triggered on the MCG:

[0233] 3> update the master security key by performing the AS security key update procedure as specified in 5.3.5.7;

[0234] 2> else if the LTM cell switch is triggered on the SCG:

[0235] 3> consider the first sk-Counter value in the ltm-SK-Counters within the VarLTM-ServingCellNoSecurityChange associated to the the field ltm-NoSecurityChangeID as the selected sk-Counter value, and update the secondary key by performing security key update procedure as specified in 5.3.5.7;

[0236] 3> remove the selected sk-Counter value from the ltm-SK-Counters within the VarLTM-ServingCellNoSecurityChange;

[0237] 2> at the end of the procedure, for each drb-Identity value that is part of the current UE configuration:

[0238] 3> if the LTM cell switch is triggered on the MCG; or

[0239] 3> if the LTM cell switch is triggered on the SCG and this DRB is using the secondary key; or

[0240] 3> if the LTM cell switch is triggered on the SCG and the keyToUse for this DRB is changed:

[0241] 4> if the PDCP entity of this DRB is not configured with cipheringDisabled:

[0242] 5> configure the PDCP entity with the ciphering algorithm and KUPenc key associated with the master key (KgNB) or secondary key (S-KgNB), as indicated in keyToUse, i.e. the ciphering configuration shall be applied to all subsequent PDCP PDUs received and sent by the UE;

[0243] 4> if the PDCP entity of this DRB is configured with integrityProtection:

[0244] 5> configure the PDCP entity with the integrity protection algorithms according to securityConfig and apply the KUPint key associated with the master key (KgNB) or the secondary key (S-KgNB) as indicated in keyToUse;

[0245] 4> if drb-ContinueROHC is included in pdcp-Config:

[0246] 5> indicate to lower layer that drb-ContinueROHC is configured;

[0247] 4> if drb-ContinueEHC-DL is included in pdcp-Config:

[0248] 5> indicate to lower layer that drb-ContinueEHC-DL is configured;

[0249] 4> if drb-ContinueEHC-UL is included in pdcp-Config:

[0250] 5> indicate to lower layer that drb-ContinueEHC-UL is configured;

[0251] 4> if drb-ContinueUDC is included in pdcp-Config:

[0252] 5> indicate to lower layer that drb-ContinueUDC is configured;

[0253] 4> re-establish the PDCP entity of this DRB as specified in TS 38.323 [5], clause 5.1.2;

[0254] 3> else if LTM cell switch is triggered on the SCG and this DRB is using the master key:

[0255] 4> if the RLC entity of an RLC bearer associated with this DRB is re-established or released during LTM cell switch execution:

[0256] 5> if this DRB is an AM DRB:

[0257] 6>after the end of this procedure, trigger the PDCP entity of this DRB to perform data recovery as specified in TS 38.323 [5], after applying the LTM configuration in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0258] 2> at the end of the procedure, for each srb-Identity value that is part of the current UE configuration:

[0259] 3> if the LTM cell switch is triggered on the MCG; or

[0260] 3> if the LTM cell switch is triggered on the SCG and the SRB is using the secondary key:

[0261] 4> configure the PDCP entity to apply the integrity protection algorithm and KRRCint key associated with the master key (KgNB) or the secondary key (S-KgNB), as indicated in keyToUse, i.e. the integrity protection configuration shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

[0262] 4> configure the PDCP entity to apply the ciphering algorithm and KRRCenc key associated with the master key (KgNB) or the secondary key (S-KgNB) as indicated in keyToUse, i.e. the ciphering configuration shall be applied to all subsequent messages received and sent by the UE, including the message used to indicate the successful completion of the procedure;

[0263] 4> re-establish the PDCP entity of this SRB as specified in TS 38.323 [5];

[0264] 2> if the value of field ltm-NoSecurityChangeID contained in the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC indicated by lower layers or for the selected cell in accordance with 5.3.7.3 is not equal to the value of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChange:

[0265] 3> replace the value of ltm-ServingCellNoSecurityChangeID in VarLTM-ServingCellNoSecurityChange with the value of ltm-NoSecurityChangeID in the LTM-Candidate in ltm-Config or ltm-ConfigNRDC indicated by lower layers or for the selected cell in accordance with 5.3.7.3;

[0266] 1> else if the field ltm-NoSecurityChangeID is not configured for the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC indicated by lower layers and if the UE does not have any value stored of ltm-ServingCellNoSecurityChangeID within VarLTM-ServingCellNoSecurityChangeID; or

[0267] 1> if the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC indicated by lower layers or for the selected cell in accordance with 5.3.5.18.8 or 5.3.7.3 does not contain the field ltm-NoResetID and if the UE does not have any value stored of ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID; or

[0268] 1> if the value of field ltm-NoResetID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC indicated by lower layers or for the selected cell in accordance with 5.3.5.18.8 for CLTM or 5.3.7.3 is not equal to the value of ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID:

[0269] 2> for each logicalChannelIdentity and logicalChannelIdentityExt that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:

[0270] 3> if servedRadioBearer is set to drb-Identity:

[0271] 4> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying the LTM configuration in ltm-CandidateConfig within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0272] 2> for each bh-LogicalChannelIdentity that is part of the current UE configuration for the cell group for which the LTM cell switch procedure is triggered:

[0273] 3> after the end of this procedure, re-establish the corresponding RLC entity as specified in TS 38.322 [4], after applying tcellhe LTM configuration in ltm-CandidateConfig within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0274] 2> for each drb-Identity value that is part of the current UE configuration:

[0275] 3> if this DRB is an AM DRB:

[0276] 4> after the end of this procedure, trigger the PDCP entity of this DRB to perform data recovery as specified in TS 38.323 [5], after applying the LTM configuration in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC;

[0277] 2> if the value of field ltm-NoResetID contained within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition is not equal to the value of ltm-ServingCellNoResetID within VarLTM-ServingCellNoResetID:

[0278] 3> replace the value of ltm-ServingCellNoResetID in VarLTM-ServingCellNoResetID with the value of ltm-NoResetID in the LTM-Candidate in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition;

[0279] 1> if the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition contains the field ltm-UE-MeasuredTA-ID:

[0280] 2> if the value of ltm-UE-MeasuredTA-ID is not equal to the value of ltm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID:

[0281] 3> replace the value of ltm-ServingCellUE-MeasuredTA-ID in VarLTM-ServingCellUE-MeasuredTA-ID with the value received within ltm-UE-MeasuredTA-ID;

[0282] 3> for each LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC:

[0283] 4> if the value of ltm-UE-MeasuredTA-ID within LTM-Candidate IE is equal to the value of ltm-ServingCellUE-MeasuredTA-ID within VarLTM-ServingCellUE-MeasuredTA-ID:

[0284] 5> inform lower layers that the UE is configured with UE-based TA measurements for the LTM-Candidate;

[0285] 4> else:

[0286] 5> inform lower layers that the UE is not configured with UE-based TA measurements for the LTM-Candidate;

[0287]

[0005] NOTE 0: The UE is not expected to perform UE-based TA measurements for an SpCell.

[0288] 1> else if the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC which has fulfilled CLTM execution condition does not contain the field ltm-UE-MeasuredTA-ID:

[0289] 2> inform lower layers that the UE is not configured with UE-based TA measurements for the LTM-Candidate.

[0290] 1> if ltm-ConfigComplete is not included within the LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC indicated by lower layers or for the selected cell which has fulfilled CLTM execution condition:

[0291] 2> consider ltm-ReferenceConfiguration in ltm-Config or ltm-ConfigNRDC, associated with the cell group for which the LTM cell switch procedure is triggered, to be the current UE configuration for the fields and configurations to be released by the actions above in this procedure;

[0292] 2> if measConfig is included within ltm-ReferenceConfiguration in ltm-Config or ltm-ConfigNRDC;

[0293] 3> perform the measurement configuration procedure as specified in clause 5.5.2 by considering the measConfig within ltm-ReferenceConfiguration in ltm-Config or ltm-ConfigNRDC as the received measConfig:

[0294] NOTE 1: When the UE 102 considers the reference configuration to be the current UE configuration, the UE 102 should store fields and configurations that are part of the reference configuration but should not execute any actions or procedures triggered by the reception of an RRC reconfiguration message which are described in clause 5.3.5.3, unless specified otherwise in this clause.

[0295] 1> if the LTM cell switch is triggered by an indication from lower layers:

[0296] 2> apply the RRCReconfiguration message in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config or ltm-ConfigNRDC identified by the LTM candidate configuration identity received from lower layers according to clause 5.3.5.3;

[0297] 1> else (LTM cell switch triggered upon cell selection performed while timer T311 was running):

[0298] 2> apply the RRCReconfiguration message in ltm-CandidateConfig within LTM-Candidate IE in ltm-Config related to the LTM candidate configuration identity for the selected cell (i.e., in accordance with 5.3.7.3) according to clause 5.3.5.3;

[0299] 1> if the LTM cell switch is triggered on the MCG:

[0300] 2> release the radio bearer(s) using the master key and the MCG logical channel(s) that were part of the UE configuration before of this LTM cell switch procedure but not part of the LTM candidate configuration either which has fulfilled CLTM execution condition, or the LTM reference configuration (in case the LTM candidate configuration does not include ltm-ConfigComplete).

[0301] 1> else, if the LTM cell switch is triggered on the SCG:

[0302] 2> release the radio bearer(s) using the secondary key and the SCG logical channel(s) that were part of the UE configuration before this LTM cell switch procedure but not part of the LTM candidate configuration either indicated by lower layers or for the selected cell in accordance with 5.3.5.18.8 or 5.3.7.3, or the LTM reference configuration (in case the LTM candidate configuration does not include ltm-ConfigComplete);

[0303] 1> if ltm-ExecutionCondition is configured within the LTM-Candidate IE for the selected LTM candidate configuration:

[0304] 2> if the field l3-Conditions is included within ltm-ExecutionCondition:

[0305] 3> perform the LTM cell switch conditions evaluation based on L3 measurements as specified in 5.3.5.18.8 according to the received ltm-ExecutionCondition once this procedure is completed;

[0306] 2> else if the field l1-Conditions is included within ltm-ExecutionCondition:

[0307] 3> request lower layers to initiate the LTM cell switch conditions evaluation based on L1 measurements according to the received field ltm-ExecutionCondition once this procedure is completed.

[0308] NOTE 2: When ltm-ConfigComplete is not included for an LTM candidate configuration, before an LTM cell switch is triggered a UE implementation may generate and store an RRC reconfiguration message by applying the received LTM candidate configuration on top of the LTM reference configuration, and the stored RRC reconfiguration message is applied when the LTM cell switch is triggered. It is up to the UE 102 to ensure that the RRC reconfiguration applied at the time of LTM cell switch is in accordance with the latest LTM reference configuration and LTM candidate configuration.

[0309] 5.3.7.3 Actions following cell selection while T311 is running:

[0310] 1> if the cell selection is triggered by detecting radio link failure of the MCG or re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the indication by lower layers or fulfilment of LTM cell switch execution conditions as specified in clause 5.3.5.18.6; and

[0311] 1> if the selected cell is one of the LTM candidate cells in theLTM-CandidateIE withinltm-Configassociated with the MCG; and

[0312] 1> if at least one of the following conditions is fulfilled:

[0313] 2> the selected cell does not have the fieldltm-NoSecurityChangeIDconfigured and the UE does not have any value stored ofltm-ServingCellNoSecurityChangeIDwithinVarLTM-ServingCellNoSecurityChange; or

[0314] 2> the cell selection is triggered by detecting radio link failure of the MCG and the selected cell has altm-NoSecurityChangeIDconfigured with a value which is equal to the value ofltm-ServingCellNoSecurityChangeIDwithinVarLTM-ServingCellNoSecurityChange; or

[0315] 2> the cell selection is triggered by detecting re-configuration with sync failure of the MCG for an LTM cell switch procedure triggered upon the indication by lower layers as specified in clause 5.3.5.18.8 or 5.3.5.18.6 and the selected cell has altm-NoSecurityChangeIDconfigured with a value which is equal to the value ofltm-NoSecurityChangeIDconfigured within the LTM candidate configuration for which the re-configuration with sync failure is detected:

[0316] 3> if the UE supports RLF-Report for MCG LTM cell switch, set theltm-RecoveryCellIdin theVarRLF-Reportto the global cell identity, if available, otherwise to the physical cell identity and carrier frequency of the selected cell;

[0317] 3> perform the LTM cell switch procedure for the selected LTM candidate cell according to the actions specified in 5.3.5.18.6;

[0318] 5.3.5.18.1 LTM configuration:

[0319] The network configures the UE 102 with one or more LTM candidate configurations within the LTM-Config IE.

[0320] An ltm-Config included within an RRC reconfiguration message received via SRB1 is for LTM on the MCG. It may include an SCG configuration and / or ltm-ServingCellNoSecurityChangeID.

[0321] An ltm-Config included within an RRC reconfiguration message either received via SRB3, or embedded in an RRC reconfiguration message received via SRB1 is for LTM on the SCG. It does not include any MCG configuration and does not include ltm-ServingCellNoSecurityChangeID.

[0322] An ltm-ConfigNRDC included within an RRCReconfiguration message received via SRB1 is for LTM on the SCG. It includes the MCG configuration and may include ltm-ServingCellNoSecurityChangeID.

[0323] In NR-DC, the UE 102 may be configured for ltm-Config for MCG LTM and ltm-Config for SCG LTM. If the network wants to configure ltm-ConfigNRDC, it needs to release ltm-Config for SCG LTM, as the simultaneous configuration of ltm-Config for MCG LTM, ltm-Config for SCG LTM and ltm-ConfigNRDC for SCG LTM are not supported. Inter-SN LTM is configured using ltm-ConfigNRDC, while Intra-SN LTM can be configured with ltm-Config.

[0324] In an embodiment herein, in dual connectivity the MN can inform the LTM reference configuration in a CG-ConfigInfo to the SN. If the MN sends a new CG-ConfigInfo to the SN, then the MN verifies if there is a change in LTM reference configuration. If there is a change in LTM reference configuration, then the MN includes the LTM reference configuration in the CG-ConfigInfo. If there is no change in the LTM reference configuration, then the MN sends the CG-ConfigInfo without including the LTM reference configuration and the SN applies the previously received LTM reference configuration.

[0325] FIG. 8 depicts a method 800 for handling LTM configurations in dual connectivity by a sender node 106. The method 800 handles the LTM reference configuration by the sender node 106 (which can be MN or SN or CU or DU). The method 800 comprises performing a mobility procedure, as depicted in step 802. The method 800 comprises initiating a CG message to send to a receiver node 108, as depicted in step 804, on performing the mobility procedure. The method 800 comprises verifying if there is a change in an LTM reference configuration, as depicted in step 806, on initiating the CG message. Thereafter, the method 800 comprises sending the CG message including the LTM reference configuration to the receiver node 108, as depicted in step 808, if there is a change in the LTM reference configuration. Else, the method 800 comprises sending the CG message without including the LTM reference configuration to the receiver node 108, as depicted in step 810, if there is no change in the LTM reference configuration. Here, the receiver node 108 applies the previously received LTM reference configuration.

[0326] The various actions in method 800 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 8 may be omitted.

[0327] FIGS. 9A and 9B depict methods 900, 910 for handling the LTM reference configuration by the receiver node 108 (which can be MN (when the sender node 106 is SN) or SN (when the sender node 106 is MN) or CU (when the sender node 106 is DU) or DU (when the sender node 106 is CU)).

[0328] As depicted in FIG. 9A, in step 902, the receiver node 108 receives the CG-Config / CG-ConfigInfo including LTM reference configuration from the sender node 106. The receiver node 108 stores the received LTM reference configuration from the CG-Config / CG-ConfigInfo, and applies the received LTM reference configuration, as depicted in step 904.

[0329] As depicted in FIG. 9B, in step 906, the receiver node 108 receives the CG-Config / CG-ConfigInfo without the LTM reference configuration from the sender node 106. The receiver node 108 applies the previously received LTM reference configuration, as depicted in step 908.

[0330] The various actions in method 900, 910 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 9 may be omitted

[0331] In an embodiment herein, the CU of the sender node 106 or the receiver node 108 informs the LTM reference configuration in CG-ConfigInfo / CG-Config to the DU of the sender node 106 or the receiver node 108. If the CU sends a new CG-ConfigInfo / CG-Config to the DU, then the CU verifies if there is a change in the LTM reference configuration. If there is a change in the LTM reference configuration, the CU includes the LTM reference configuration in the CG-ConfigInfo / CG-Config. If there is no change in the LTM reference configuration, then the CU else sends the CG-ConfigInfo / CG-Config without including the LTM reference configuration, and the DU applies the previously received LTM reference configuration.

[0332] In an embodiment herein, the DU informs the LTM reference configuration in CG-ConfigInfo to the CU. If the DU sends a new LTM reference configuration to the CU, the DU verifies if there is a change in the LTM reference configuration. If there is a change in LTM reference configuration, the DU includes the LTM reference configuration in the CG-ConfigInfo. If there is no change in the LTM reference configuration, the DU sends the CG-ConfigInfo without including the LTM reference configuration, and the CU uses the previously received LTM reference configuration.

[0333] CG-Config / CG-ConfigInfo are exemplary names and can also mean any Information Element (IE) in a different RAT such as 6G or 7G for providing the information between MN and SN over any interface.

[0334] In an embodiment herein, according to TS 38.331,

[0335] For fields in CG-Config and CG-ConfigInfo listed below, absence of the field means that the receiver node 108 maintains the values informed via the previous message. Note that every time there is a change in the configuration covered by a listed field, the MN or SN shall include the field, and it shall provide the full configuration provided by that field unless stated otherwise. Otherwise, if there is no change, the field can be omitted:

[0336] - configRestrictInfo;

[0337] - gapPurpose;

[0338] - measGapConfig (for which delta signaling applies);

[0339] - measGapConfigFR2 (for which delta signaling applies);

[0340] - measResultCellListSFTD;

[0341] - measResultSFTD-EUTRA;

[0342] - sftdFrequencyList-EUTRA;

[0343] - sftdFrequencyList-NR;

[0344] - ue-CapabilityInfo;

[0345] - servFrequenciesMN-NR;

[0346] - musim-GapConfigInfo-r18;

[0347] - musim-CapRestrictionInfo-r18;

[0348] - ltm-ReferenceConfigurationSCG-r19;

[0349] - ltm-UE-MeasuredTA-ID-r19;

[0350] -- ltm-ReferenceConfiguration-r19;

[0351] - ltm-ReferenceConfigurationMCG-r19.

[0352] For other fields in CG-Config and CG-ConfigInfo, the sender node 106 shall always signal the appropriate value even if same as indicated in the previous inter-node message, unless explicitly stated otherwise.

[0353] The embodiments help to reduce the signalling overhead during the LTM reference configuration transfer. The receiver node 108 may send the internode message such as CG-Config or CG-ConfigInfo for a number of purposes such as Discontinuous Reception (DRX) configuration, measurement gap configuration, and so on.

[0354] Configuration of intra-SN LTM with Inter-SN LTM:

[0355] In an embodiment herein, an SN which has configured intra-SN LTM candidate cells over SRB3, or through an SN RRC reconfiguration message embedded in an MN RRC reconfiguration message over SRB1 releases the configured intra-SN LTM candidate cell configuration, when / if it decides to configure the inter-SN LTM. The SN may also send the intra-SN LTM candidates which were configured over SRB3 or through an SN RRC reconfiguration message embedded in MN RRC reconfiguration message over SRB1, to MN and MN may configure them using ltm-ConfigNRDC in an MN RRC reconfiguration message. In an embodiment herein, the SN doesn’t configure the SN LTM using ltm-Config associated with SCG when ltm-ConfigNRDC is configured. This ensures that the UE 102, and the network 104 can apply the inter-SN LTM configuration in a simplified way, by avoiding the complexities of maintaining multiple versions of configurations, in multiple formats.

[0356] FIG. 10 depicts a method 1000 for managing inter-SN LTM configuration, and intra-SN LTM configuration by the sender node 106. The method 1000 comprises initiating configuration for an inter-SN LTM, as depicted in step 1002, if the sender node 106 is the SN. The method 1000 comprises releasing an intra-SN LTM candidate cell configuration, as depicted in step 1004, on initiating the configuration for the inter-SN LTM. Thereafter, the method 1000 comprises sending the intra-SN LTM candidate cell configuration to the MN, as depicted in step 1006, and the MN configures the intra-SN LTM candidate cell configuration using an LTM configuration NRDC (ltm-ConfigNRDC) field.

[0357] The various actions in method 1000 may be performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some actions listed in FIG. 10 may be omitted.

[0358] Meanwhile, although specific embodiments of the present disclosure have been described in detail, various modifications may be made without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be defined by the claims and equivalents thereof.

Claims

A method performed by a user equipment (UE) in a wireless communication system, the method comprising:receiving, from a base station, a layer 1(L1) / layer2(L2) triggered mobility (LTM) configuration for at least one candidate cell associated with a conditional LTM (CLTM);upon fulfilment of LTM cell switch execution conditions for a candidate cell, in case that a value of field ltm-NoResetID in the LTM configuration for the candidate cell is not equal to a value of ltm-ServingCellNoResetID stored in the UE, performing at least one of a radio link control (RLC) re-establishment or a packet data convergence protocol (PDCP) recovery; andreplacing the value of field ltm-ServingCellNoResetID with the value of field ltm-NoResetID.The method of claim 1,wherein, in case that the value of field ltm-NoResetID in the LTM configuration for the candidate cell is equal to the value of field ltm-ServingCellNoResetID stored in the UE, the RLC re-establishment and the PDCP recovery are not performed.The method of claim 1, further comprising:in case that a value of ltm-UE-MeasuredTA-ID for the candidate cell is not equal to a value of ltm-ServingCellUE-MeasuredTA-ID stored in the UE, replacing the value of ltm-ServingCellUE-MeasuredTA-ID with the value of ltm-UE-MeasuredTA-ID for the candidate cell; andfor each LTM candidate configuration in the LTM configuration, performing UE-based TA measurement associated with the LTM candidate configuration, in case that the value of ltm-UE-MeasuredTA-ID in the LTM candidate configuration is equal to the value of ltm-ServingCellUE-MeasuredTA-ID.The method of claim 1, further comprising:considering an LTM reference configuration in the LTM configuration to be a current UE configuration and configurations to be released, in case that information indicating a complete configuration is not included in a LTM candidate configuration for the candidate cell in the LTM configuration.The method of claim 1, further comprising:releasing radio bearers and logical channels that are not part of the LTM candidate configuration for the candidate cell or the LTM reference configuration.The method of claim 1, further comprising:performing a cell selection based on a radio link failure or a re-configuration with sync failure associated with the CLTM; andin case that a cell selected based on the cell selection is one of the at least one candidate cell and the cell has a ltm-NoSecurityChangeID configured with a value which is equal to a value of ltm-NoSecurityChangeID configured within the LTM candidate configuration of a cell for which the UE performed the CLTM, performing an LTM cell switch procedure for the cell selected based on the cell selection.The method of claim 1,for dual connectivity (DC),wherein, in case that an ltm-Config for a secondary cell group (SCG) LTM is configured, an ltm-ConfigNRDC for the SCG LTM is not configured for the UE, andwherein, in case that the ltm-ConfigNRDC for the SCG LTM is configured, the ltm-Config for SCG LTM is not configured for the UE.The method of claim 1,wherein, in case that a configuration field is not included in the LTM configuration, the UE maintains a previously stored value associated with the configuration field,wherein, in case that the configuration field is included in the LTM configuration, the UE changes a value associated with the configuration field indicated by the configuration field, andwherein the configuration field includes an LTM reference configuration.A user equipment (UE) in a wireless communication system, the UE comprising:a transceiver; andat least one processor coupled with the transceiver and configured to:receive, from a base station, a layer 1(L1) / layer2(L2) triggered mobility (LTM) configuration for at least one candidate cell associated with a conditional LTM (CLTM);upon fulfilment of LTM cell switch execution conditions for a candidate cell, in case that a value of field ltm-NoResetID in the LTM configuration for the candidate cell is not equal to a value of ltm-ServingCellNoResetID stored in the UE, perform at least one of a radio link control (RLC) re-establishment or a packet data convergence protocol (PDCP) recovery; andreplace the value of field ltm-ServingCellNoResetID with the value of field ltm-NoResetID.The UE of claim 9, wherein the at least one processor is further configured to:in case that a value of ltm-UE-MeasuredTA-ID for the candidate cell is not equal to a value of ltm-ServingCellUE-MeasuredTA-ID stored in the UE, replace the value of ltm-ServingCellUE-MeasuredTA-ID with the value of ltm-UE-MeasuredTA-ID for the candidate cell; andfor each LTM candidate configuration in the LTM configuration, perform UE-based TA measurement associated with the LTM candidate configuration, in case that the value of ltm-UE-MeasuredTA-ID in the LTM candidate configuration is equal to the value of ltm-ServingCellUE-MeasuredTA-ID.The UE of claim 9,wherein the at least one processor is further configured to consider an LTM reference configuration in the LTM configuration to be a current UE configuration and configurations to be released, in case that information indicating a complete configuration is not included in a LTM candidate configuration for the candidate cell in the LTM configuration.The UE of claim 9,wherein the at least one processor is further configured to release radio bearers and logical channels that are not part of the LTM candidate configuration for the candidate cell or the LTM reference configuration.The UE of claim 9,wherein the at least one processor is further configured to perform a cell selection based on a radio link failure or a re-configuration with sync failure associated with the CLTM; andin case that a cell selected based on the cell selection is one of the at least one candidate cell and the cell has a ltm-NoSecurityChangeID configured with a value which is equal to a value of ltm-NoSecurityChangeID configured within the LTM candidate configuration of a cell for which the UE performed the CLTM, performing an LTM cell switch procedure for the cell selected based on the cell selection.The UE of claim 9, for dual connectivity (DC),wherein, in case that an ltm-Config for a secondary cell group (SCG) LTM is configured, an ltm-ConfigNRDC for the SCG LTM is not configured for the UE, andwherein, in case that the ltm-ConfigNRDC for the SCG LTM is configured, the ltm-Config for SCG LTM is not configured for the UE.The UE of claim 9,wherein, in case that a configuration field is not included in the LTM configuration, the UE maintains a previously stored value associated with the configuration field,wherein, in case that the configuration field is included in the LTM configuration, the UE changes a value associated with the configuration field indicated by the configuration field, andwherein the configuration field includes an LTM reference configuration.

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