Evaluating an uplink timing advance (UL ta) for LTM candidate cells

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. Disclosed is a method by a user equipment (UE) for evaluating uplink timing advance (UL TA) measurement for one or more LTM (Lower Layer Triggered Mobility) candidate cells. The method comprise initiating a UL TA measurement during one of a multi-subscriber identity module (MUSIM) gap, a connected discontinuous reception (CDRX) cycle, a Layer 3 (L3) measurement gap, or a transmission (TX) when an uplink carrier aggregation (CA) capable device is configured; determining a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in a connected mode; receiving a cell switch command from a network apparatus based on the performance of a L1 measurement report for the one or more LTM candidate cells; initiating the cell switch command based on signal measurement for one or more conditional LTM candidate cells; and triggering a random access channel-less (RACH-less) LTM cell switch or handover based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells.

Description

EVALUATING AN UPLINK TIMING ADVANCE (UL TA) FOR LTM CANDIDATE CELLS

[0001] The proposed invention relate to image enhancement technique. More particularly, present disclosure relates to evaluating an Uplink Timing Advance (UL TA) for Lower Layer Triggered Mobility (LTM) candidate cells.

[0002] 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 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz 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.

[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 MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, 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 BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[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 V2X (Vehicle-to-everything) 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, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[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, IAB (Integrated Access and Backhaul) 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 DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step 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 that have been exponentially increasing will be connected to communication networks, and it is accordingly 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 AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction 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 not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also 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 (Artificial Intelligence) 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 the field of wireless communication, maintaining service continuity and uninterrupted data connections during connected mode mobility presents a significant challenge. User Equipment (UE) frequently needs to switch cells to maintain service continuity and ensure uninterrupted data connections. Prior to the 3rd Generation Partnership Project (3GPP) Release 18, UEs primarily relied on Legacy Handover or conditional handover mechanisms for cell switching. These methods often resulted in high handover interruption times, thereby affecting the quality of service.

[0009] To address the need for faster cell switching in the connected mode, 3GPP introduced a new specification in Release 18, known as Layer 1 / Layer 2 Triggered Mobility (LTM). In this specification, a Next Generation Node B (gNB) provides LTM candidate configurations through Radio Resource Control (RRC) signaling. The UE performs measurement evaluations for the LTM candidate cells and triggers a Layer 1 (L1) based measurement report for lower layer triggered mobility. Additionally, the gNB may provide the LTM candidate cell configuration along with an early Time Advancement (TA) configuration through the RRC signaling message. Subsequently, the UE is required to conduct the uplink (UL) TA measurement for the LTM candidate cells.

[0010] According to the 3GPP standards, two types of UL TA measurements are specified for effective mobility management. The first type is a Physical Downlink Control Channel (PDCCH) order-based UL TA measurement, where the gNB triggers the PDCCH order and calculates the TA value of the candidate cell. The second type is a UE-based UL TA measurement, where the UE measures the TA of the candidate cell and keeps it ready before receiving a cell switch command.

[0011] Further, the gNB triggers the cell switch through a Medium Access Control Element (MAC CE) for the LTM candidate cell. If the UE has measured the TA value for the target LTM candidate cell, it may apply the measured TA value and perform a Random Access Channel-less (RACH-less) LTM cell switch, thereby reducing the handover (HO) interruption time and latency. The LTM candidate cells may also be configured with the early UL TA configuration to facilitate the RACH-less LTM cell switch, enhancing robustness and minimizing interruption time during the handover.

[0012] However, when the network configures UE-based UL TA measurements for the LTM candidate cells in the RRC signaling, the UE must perform the UL TA measurements of the target candidate cells and store the measured TA value before receiving the LTM cell switch command for the target candidate cell. Additionally, the UE operates in the connected mode within a serving cell where data activity is continuous. During this period, the UE must identify a gap to conduct the UL TA measurements for the LTM candidate cell.

[0013] According to 3GPP specification TS 38300, the UE performs TA measurement for the candidate cells after being configured by the RRC. However, the exact time at which the UE performs the TA measurement is left to the UE's implementation. The maximum number of LTM candidate cells allowed is eight, with each TA measurement for the LTM candidate cell taking approximately 7 milliseconds.

[0014] Despite these advancements, there are still significant issues in the existing technology. There is a lack of a dedicated gap configured by the gNB for performing UE-based UL TA measurements. This may result in the UE failing to perform the TA measurements of the LTM candidates before switching cells, potentially leading to a RACH-based handover despite the network's UL TA configuration. Furthermore, there is a possibility of RACH failure during the LTM cell switch. Even in successful RACH-based handovers, there is an interruption time of approximately 7 milliseconds. This interruption during the LTM switch can cause service continuity failures and negatively impact the user experience.

[0015] Hence it is desirable to address the aforementioned problem and its disadvantages or at least provide a useful alternative.

[0016] The purpose of this application is to be able to solve at least one of the drawbacks of the prior art.

[0017] The principal object of the embodiments herein is to evaluate the uplink transmission power allocation for the LTM or Conditional LTM candidate cells in order to improve the handover and the cell switch performance.

[0018] Another object of the invention is to perform the UL TA synchronization for the LTM or Conditional LTM candidate cell configured with the early UL TA configuration during the data inactivity time in the UE based on various gaps configuration received from the network to ensure the RACH-less handover during the LTM cell switch.

[0019] Yet another object of the invention is to provide a method and the UE to request a Multi SIM (MUSIM) gap configuration from the network and use the configured MUSIM gaps to perform the UL TA synchronization for the LTM or Conditional LTM candidate cell configured with the early UL TA configuration.

[0020] Yet another objective of the invention is to provide a method and the UE to utilize a Connected Mode Discontinuous Reception (CDRX) sleep time or Layer 3 (L3) measurement gaps when the network configures the UE with the CDRX cycle or layer 2 (L2) measurement events. The present invention enables the UE to perform the UL TA synchronization for the LTM or Conditional LTM candidate cell configured with the early UL TA configuration leveraging periods of inactive downlink data during this time.

[0021] Yet another object of the invention is to provide a method and the UE to utilize an unused transceiver during periods of data inactivity. Additionally, the method allows the UE to synchronize with the UL TA for the LTM or Conditional LTM candidate cell that is configured with the early UL TA configuration in an Uplink Carrier Aggregation (UL CA) capable UE.

[0022] In an aspect, the objectives are achieved by providing a method for evaluating the UL TA measurement for one or more LTM or Conditional LTM candidate cells. Further, the method includes initiating by the UE the UL TA measurement during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or a transmission (TX) when the CA capable device is configured. Further, the method includes determining by the UE a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in the connected mode. Further, the method includes receiving by the UE the cell switch command from a network apparatus based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells. Further, the method includes initiating by the UE the cell switch command based on signal measurement for one or more conditional LTM candidate cells. Further, the method includes triggering by the UE the RACH-less LTM cell switch or handover based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate.

[0023] In another aspect, the objectives are achieved by the UE for evaluating the UL TA for the LTM or Conditional LTM candidate cells to enhance the handover and the cell switch performance. The UE further includes a memory, a processor, and an UL TA measurement controller coupled to the memory and the processor. The UL TA measurement controller initiates the UL TA measurement during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or the TX when the uplink CA capable device is configured. Further, the UL TA measurement controller determines the performance of the UL TA measurement for the one or more LTM candidate cells in the connected mode. The UL TA measurement controller further receives the cell switch command from the network apparatus based on the performance of the UL TA measurement for one or more LTM candidate cells. Further, The UL TA measurement controller initiates the cell switch command based on signal measurement for one or more conditional LTM candidate cell. The UL TA measurement controller further triggers the RACH-less LTM cell switch or the handover based on the performance of the UL TA measurement for one or more LTM candidate cells.

[0024] In yet another aspect, the objectives are achieved by the network apparatus for evaluating the UL TA for the LTM candidate cells to enhance the handover and the cell switch performance. Further, the network apparatus includes a memory, a processor, and a UL TA measurement controller. The UL TA measurement controller initiates the UL TA measurement during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or the TX when the uplink CA capable device is configured. Further, the UL TA measurement controller determines the performance of the UL TA measurement in the connected mode. Further, the UL TA measurement controller transmits the cell switch command from the network apparatus based on the performance of the UL TA measurement. Further, the UL TA measurement controller enables the RACH-less LTM cell switch or handover based on the performance of the UL TA measurement for the one or more LTM candidate cells.

[0025] The aspects of these embodiments will be better understood with the following description and accompanying drawings. The descriptions, while detailing preferred embodiments and specific details, are illustrative and not limiting. Various changes and modifications can be made within the scope of these embodiments without departing from the invention, which includes all such modifications.

[0026] The embodiments described herein significantly advance mobility performance by ensuring seamless, low-latency handover and cell switch procedures, particularly for Lower Layer Triggered Mobility (LTM).

[0027] This invention is 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 drawings in which:

[0028] Fig. 1 is a flowchart that illustrates the type of UL TA synchronization used in the LTM communication scenarios according to prior art.

[0029] Fig. 2 is a sequence diagram that illustrates a RACH-based LTM cell switch execution according to the prior art.

[0030] Fig. 3 is a sequence diagram that illustrates a RACH-less LTM cell switch execution according to the prior art.

[0031] Fig. 4 is a sequence diagram that illustrates the MUSIM (Multi SIM) GAP scenario according to the prior art.

[0032] Fig. 5A and Fig. 5B are graphical diagrams that illustrate scenarios of a long DRX cycle and a short DRX cycle according to the prior art.

[0033] Fig. 6 is a schematic diagram that illustrates the measurement gap configuration according to the prior art.

[0034] Fig. 7 is a sequence diagram that illustrates the scenario of an MSC according to the prior art.

[0035] Fig. 8 is a schematic representation that illustrates an LTM Cell Switching Process with the early UL TA configuration for the UE according to prior art.

[0036] Fig. 9 is a flowchart that illustrates a process for the LTM Cell Switching based on the configuration of the early UL TA for the candidate cell according to prior art.

[0037] Fig. 10A is a block diagram that illustrates the UE for evaluating the UL TA for the LTM candidate cells to enhance the handover and the cell switch performance according to the embodiment.

[0038] Fig. 10B is a block diagram that illustrates the network apparatus for evaluating the UL TA for the LTM candidate cells to enhance the handover and the cell switch performance according to the embodiment.

[0039] Fig. 11A is a flowchart of a method for evaluating the UL TA for LTM candidate cells to enhance the handover and the cell switch performance according to the embodiment.

[0040] Fig. 11B is a flowchart that illustrates a decision-making process for the LTM Cell Switching based on the configuration of the early UL TA for the candidate cell according to the embodiments as disclosed herein.

[0041] Fig. 12 is a sequence diagram that illustrates a process for the LTM cell UL TA synchronization for the LTM candidate cell configured with the early UL TA configuration during the data inactivity time according to the embodiment herein.

[0042] Fig. 13 is a schematic diagram that illustrates the UL TA measurement for the LTM candidate cell using various Gap configurations according to the embodiment herein.

[0043] Fig. 14 is a sequence diagram that illustrates the UL TA measurements during the MUSIM GAP according to the embodiments as disclosed herein.

[0044] Figs. 15A-15B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA measurements during the MUSIM GAP.

[0045] Fig. 16 is a sequence diagram that illustrates the UL TA measurements during the CDRX sleep time according to the embodiment herein.

[0046] Figs. 17A-17B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA measurements during the CDRX sleep time.

[0047] Fig. 18 is a sequence diagram that illustrates the UL TA measurements during the L3 Measurements Gap according to the embodiment herein.

[0048] Fig. 19A and Fig. 19B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA measurements during the L3 measurement gap.

[0049] Fig. 20 is a sequence diagram that illustrates the UL TA measurements using an additional transceiver in the UL CA (carrier aggregation) capable device according to the embodiment herein.

[0050] Figs. 21A-21B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA Measurements through an additional transceiver in the UL CA capable device.

[0051] Figs. 22A-22B are block diagrams that illustrate the LTM Latency comparison between the existing system and the proposed invention.

[0052] The embodiments and their features are detailed with reference to the non-limiting illustrations in the accompanying drawings and description. Well-known components and techniques are omitted to avoid unnecessary detail. The described embodiments are not mutually exclusive and can be combined to form new embodiments. The term "or" is non-exclusive unless stated otherwise. The examples provided are to aid understanding and enable skilled practitioners to apply the embodiments, and should not be seen as limiting their scope.

[0053] As is traditional in the field, embodiments may be described and illustrated in terms of blocks which carry out a described function or functions. These blocks, which may be referred to herein as units or modules or the like, are physically implemented by analog or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by firmware. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the disclosure.

[0054] The accompanying drawings aid in understanding the technical features, but the embodiments are not limited to these drawings. The disclosure includes any alterations, equivalents, and substitutes beyond those depicted. Terms like "first" and "second" are used for distinction and do not limit the elements.

[0055] Fig. 1 is a flowchart illustrating the types of UL TA synchronization used in LTM communication scenarios according to the prior art. The figure highlights two primary approaches for cell switching in LTM (101): the RACH-less LTM cell switch (102) and the RACH-based LTM cell switch (103). In the RACH-less LTM cell switch (102), two methods are included to perform early UL TA measurements on the LTM (101) candidate cell. One method is the PDCCH Order-Based Measurement (105), and the other is the UE-Based Measurement method (104).

[0056] The RACH-based LTM cell switch is required if the UE (201) does not have a valid TA or if the TA is not configured by the network in the MAC CE (LTM Cell switch command). In such cases, the UE (201) must perform the RACH-based LTM cell switch (106).

[0057] In the UE-Based Measurement method (104), the UE (201) performs UL TA measurements for a target cell using the early UL configuration received from the gNB through RRC signaling. The UE (201) may then apply the measured TA value upon receiving the cell switch command for the target cell.

[0058] In the PDCCH Order-Based Measurement (105), the UE (201) initiates the preamble to the gNB based on the specified preamble index upon receiving the PDCCH order from a target network apparatus (203). The target network apparatus (203) calculates the TA value based on the preamble transmission from the UE (201) and shares it with a source network apparatus (202). Upon triggering the cell switch command, the source network apparatus (202) may include the TA value in the MAC CE command (108).

[0059] When the UE (201) is configured with the UL TA for the LTM candidate cell, it must perform the UE-based UL TA measurement in the connected mode before the LTM cell switch is triggered. The UE (201) applies the measured TA value during the LTM cell switch to enable the RACH-less LTM cell switch.

[0060] However, the network does not provide a dedicated gap for UL TA measurements for the LTM candidate cells. It is left to the UE (201) implementation to determine the optimal timing for performing the UL TA measurements before the LTM cell switch command is provided.

[0061] Fig. 2 is the sequence diagram that illustrates the RACH-based LTM cell switch execution according to the prior art. This includes communication between the UE (201), the source network apparatus (202), and the target network apparatus (203).

[0062] At step S1, the initial process starts with the source network apparatus (202). The source network apparatus (202) sends the RRC Reconfiguration message indicating the LTM candidate cell. At step S2, the UE (201) sends the RRC Reconfiguration Complete message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell. At step S3, the UE (201) performs L1-based measurements for the LTM candidate cell and sends the L1-based LTM measurement report to the source network apparatus (202). At step S4, based on the L1-based LTM measurement report, the source network apparatus (202) communicates with the target network apparatus (203) to prepare for the LTM cell switch. The source network apparatus (202) triggers the LTM cell switch by managing with the target network apparatus (203). At step S5, the source network apparatus (202) sends the LTM Cell Switch Command using the MAC CE without the TA configuration and instructs the UE (201) to initiate the RACH-based cell switch procedure. At step S6, the UE (201) performs the RACH procedure with the target network apparatus (203). The UE (201) sends the RACH preamble to the target network apparatus (203) in a message 1 (MSG 1). At step S7, the target network apparatus (203) responds with a message 2 (MSG 2), which includes a Random-Access Response (RAR) that includes the TA value. At step S8, the UE (201) confirms the LTM Cell Switch completion to the target network apparatus (203) once the RACH procedure is successfully completed.

[0063] Fig. 3 is the sequence diagram that illustrates the RACH-less LTM cell switch (102) execution, according to the prior art. At step S1, initial process starts with the source network apparatus (202), the source network apparatus (202) sends the RRC Reconfiguration message, which includes the LTM candidate cell with the early TA configuration details. At step S2, the UE (201) sends the 'RRC Reconfiguration Complete' message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell. At step S3, the early TA Preparation is initiated. The target network apparatus (203) triggers the PDCCH order to the UE (201), and the UE (201) sends the preamble based on the preamble index provided.

[0064] At steps S4 and S5, the target network apparatus (203) provides the early TA to the source network apparatus (202). The source network apparatus (202) initiates the early TA acquisition by providing the preamble related parameters for synchronization during the RACH procedure. This enables the UE (201) to identify the correct configuration for accessing the target cell. At step S6, the UE (201) based ULTA measurement is initiated. The UE (201) sends the RACH Preamble (MSG 1) to the target network apparatus (203) as part of the RACH procedure. At step S7, the target network apparatus (203) provides the TA value directly through the MSG 2 (RAR Response with TA Value). This process confirms the synchronization between the UE (201) and the target network apparatus (203). The UE (201) stores the value and applies the TA configuration during the LTM cell switch. At step S9, the UE (201) evaluates the LTM candidate cell and prepares and sends the measurement report to the source network apparatus (202).

[0065] At step S10, the source network apparatus (202) triggers the LTM Cell Switch process based on the UE's measurement report and other mobility conditions. At step S11, the source network apparatus (202) provides the LTM Cell Switch Command through the MAC CE to the UE (201). The LTM Cell Switch Command includes a necessary configuration to complete the LTM cell switch. At steps S12 and S13, the UE (201) completes the RACH-less based LTM cell switch with the target network apparatus (203) and acknowledges the completion of the LTM cell switch process.

[0066] In the existing system, during the connected mode mobility, the UE (201) has to switch cells frequently to maintain service continuity and the uninterrupted data connections. Until 3GPP Release 18, the UE (201) performed either a legacy handover or a conditional handover to execute the cell switch, which resulted in high HO interruption times. To enable faster cell switching in the connected mode compared to traditional handovers, the LTM is introduced by the 3GPP standards in the Release 18 specification. The LTM Candidate cell configuration IE in the 3GPP 38.331 Release V18.0.0 is shown below:

[0067] -- ASN1START

[0068] -- TAG-LTM-CANDIDATE-START

[0069] LTM-Candidate-r18 ::= SEQUENCE {

[0070] ltm-CandidateId-r18 LTM-CandidateId-r18,

[0071] ltm-CandidatePCI-r18 PhysCellId,

[0072] ltm-EarlyUL-SyncConfig-r18 SetupRelease { EarlyUL-SyncConfig-r18 }

[0073] ltm-EarlyUL-SyncConfigSUL-r18 SetupRelease { EarlyUL-SyncConfig-r18

[0074] ... ...

[0075] ltm-UE-MeasuredTA-ID-r18 INTEGER (1..maxNrofLTM-Configs-r18-plus-1) ...

[0076] }

[0077] TO

[0078] -- ASN1START

[0079] -- TAG-EARLYUL-SYNCCONFIG-START

[0080] EarlyUL-SyncConfig-r18 ::= SEQUENCE {

[0081] frequencyInfoUL-r18 FrequencyInfoUL,

[0082] rach-ConfigGeneric-r18 RACH-ConfigGeneric,

[0083] bwp-GenericParameters-r18 BWP,

[0084] ssb-PerRACH-Occasion-r18 ENUMERATED {oneEighth, oneFourth, oneHalf, one, two, four, eight, sixteen

[0085] prach-RootSequenceIndex-r18 CHOICE {

[0086] l839 INTEGER (0..837),

[0087] l139 INTEGER (0..137)

[0088] } ltm-PRACH-SubcarrierSpacing-r18 SubcarrierSpacing

[0089] n-TimingAdvanceOffset-r18 ENUMERATED { n0, n25600, n39936, spare1

[0090] The table below provides a description for each information field that is disclosed in the LTM Candidate cell configuration IE.

[0091] Information FieldDescriptionrach-ConfigGenericRACH parameters for performing a random access procedure on a candidate cell.n-TimingAdvanceOffsetThe N_TA-Offset to be applied for all uplink transmissions on a candidate cell.ssb-PerRACH-OccasionThis field indicated the number of SSBs for RACH occasion.frequencyInfoULThis field provides basic parameters of an uplink carrier for PRACH transmission on a candidate cell.ltm-EarlyUL-SyncConfig, ltm-EarlyUL-SyncConfigSULA configuration used to perform the early UL synchronization procedure over an UL or SUL carrier.

[0092] Fig. 4 is a sequence diagram illustrating the MUSIM GAP scenario. In the MUSIM device, the UE stays in an RRC_CONNECTED state in one network (NW1) (401) while remaining idle on another NW2 (402). The UE needs to switch its RRC_CONNECTED state from the NW1 (401) to the NW2 (402) for activities such as paging, reading SIB information, performing measurements, or answering incoming calls, effectively switching between two SIMs.

[0093] In the MUSIM device, the UE remains in the RRC_CONNECTED state on the NW1 (401) while temporarily switching to the NW2 (402). This ensures that connectivity is maintained in the NW1 (401), as indicated by the scheduling gap preference provided to the NW1 (401). The UE operates in the RRC_CONNECTED mode on SIM 1. The NW1 (401) configures four MUSIM Gap configurations one periodic and three aperiodic with priority. The UE utilizes these MUSIM gaps to perform activities related to the other SIM(s).

[0094] The MUSIM GAP scenario includes the NW1 (401), the NW2 (402). Initially, the UE operates in the RRC_CONNECTED mode on SIM 1. At step S1, the gNB sends a UE Capability Enquiry to the NW1 (401). In response, at step S2, the NW1 (401) sends a UE Capability Information indicating musimLeaveConnected-r17 support to the gNB. At step S3, the gNB sends the RRC Configuration musim-GAP Assistance Configuration to the NW1 (401), which then sends the RRC Reconfiguration with the MUSIM GAP configuration assistance to the UE.

[0095] Steps S4 and S5 involve completing the RRC reconfiguration process and establishing data communication between the NW1 (401) and the gNB. At step S6, the NW1 (401) sends the UE Assistant Information, including the MUSIM GAP preference list, to the gNB. Subsequently, at step S7, the gNB sends the RRC Reconfiguration MUSIM GAP Configuration v17 to the UE. Furthermore, at step S8, the NW1 (401) sends the RRC Reconfiguration to the UE. At this stage, the UE switches to network the NW2 (402), listens for paging, or reads SIB in gaps configured by the network apparatus without losing the CONNECTED MODE.

[0096] The RRC Reconfiguration Information Element (IE) for the MUSIM is provided below:

[0097] -- ASN1START

[0098] -- TAG-MUSIM-GAPCONFIG-START

[0099] MUSIM-GapConfig-r17 ::= SEQUENCE {

[0100] musim-GapToReleaseList-r17 SEQUENCE (SIZE (1..3)) OF MUSIM-GapId-r17

[0101] musim-GapToAddModList-r17 SEQUENCE (SIZE (1..3)) OF MUSIM-Gap-r17

[0102] musim-AperiodicGap-r17 MUSIM-GapInfo-r17 ..., [[

[0103] musim-GapKeep-r18 ENUMERATED {true} ]]

[0104] }

[0105] MUSIM-Gap-r17 ::= SEQUENCE {

[0106] musim-GapId-r17 MUSIM-GapId-r17,

[0107] musim-GapInfo-r17 MUSIM-GapInfo-r17

[0108] }

[0109] Figs. 5A-5B are graphical diagrams that illustrate the scenarios of the long DRX cycle and the short DRX cycle according to the prior art. The CDRX is introduced to enhance the UE (201) battery power consumption. Based on the CDRX configurations, the UE (201) periodically wakes up for a specific duration to monitor the Physical Downlink Control Channel (PDCCH) for uplink or downlink data before returning to a sleep state.

[0110] Fig. 5A discloses the graphical diagram that illustrates the long DRX cycle. In the long DRX cycle (500a, 500b), a DRX-on duration timer (504) wakes the UE (201) and allows it to monitor the PDCCH. If no uplink or downlink data is received during the DRX-on duration timer (504), the UE (201) enters into the sleep mode until the next on-duration occasion. If the UE (201) detects any PDCCH scheduling or PDCCH data (502), the UE (201) starts or restarts the DRX-inactivity timer (503a) and waits for the data.

[0111] Fig. 5B discloses the graphical diagram that illustrates the short DRX cycle. The long DRX cycle (500a, 500b) disclosed in Fig. 5A is inefficient for periodic data transmissions. To address this limitation, the network introduces the short DRX cycle (505a, 505b), characterized by a shorter duration compared to the long DRX cycle (500a, 500b). In scenarios where both the long and short DRX cycles are configured, the UE (201) transitions to the short DRX cycle (505a, 505b) upon detecting the PDCCH data during the DRX-on duration timer (504) of the long DRX cycle (500a, 500b). If no PDCCH data (502) is detected, the UE (201) continues to operate under the long DRX cycle (500a, 500b) configuration.

[0112] The RRC configuration IE for the DRX configuration is as given below:

[0113] -- ASN1START

[0114] -- TAG-DRX-CONFIG-START

[0115] DRX-Config ::= SEQUENCE {

[0116] drx-onDurationTimer CHOICE {

[0117] subMilliSeconds INTEGER (1..31),

[0118] milliSeconds ENUMERATED {

[0119] ms1, ms2, ms3, ms4, ms5, ms6, ms8, ms10, ms20, ms30, ms40, ms50, ms60,

[0120] ms80, ms100, ms200, ms300, ms400, ms500, ms600, ms800, ms1000, ms1200,

[0121] ms1600, spare8, spare7, spare6, spare5, spare4, spare3, spare2, spare1 }

[0122] },

[0123] drx-InactivityTimer ENUMERATED {

[0124] ms0, ms1, ms2, ms3, ms4, ms5, ms6, ms8, ms10, ms20, ms30, ms40, ms50, ms60, ms80,

[0125] ms100, ms200, ms300, ms500, ms750, ms1280, ms1920, ms2560, spare9, spare8,

[0126] spare7, spare6, spare5, spare4, spare3, spare2, spare1},

[0127] Fig. 6 is a schematic diagram illustrating the measurement gap configuration according to the prior art. This measurement gap configuration enables the UE (201) to perform measurements for target frequencies without disrupting ongoing serving cell activities, such as uplink or downlink transmission. The measurement gaps are predefined intervals during which the UE (201) pauses its regular operations to measure inter-frequencies, intra-frequencies, or inter-RAT frequencies. In New Radio (NR), the gap durations may vary between 15 ms to 6 ms, with repetition periodicities of 20 ms, 40 ms, 80 ms, and 160 ms, as shown for subframes #4, #5, #6, and #7 in the provided schematic.

[0128] In NR, the measurement gaps are characterized by specific parameters such as the gap offset, a Measurement Gap Repetition Period (MGRP), and a gap length. For example, with a gap offset of 24 subframes, an MGRP of 40 ms, and a gap length of 4 ms, the UE (201) is scheduled to perform measurements during predefined intervals (602), such as subframes #4, #5, #6, and #7. This configuration supports inter-frequency, intra-frequency, and inter-RAT frequency measurements, ensuring connectivity while maintaining measurement efficiency. As illustrated in Fig. 6, the measurement gaps span across multiple System Frame Numbers (SFN), with the example representing the measurement gap occurring across frames with SFN values of 22, 23, 24, and 25 (601a-601e).

[0129] The RRC configuration IE for the measurement gap is as given below:

[0130] -- ASN1START

[0131] -- TAG-MEASGAPCONFIG-START

[0132] MeasGapConfig ::= SEQUENCE {

[0133] gapFR2 SetupRelease { GapConfig } ...,

[0134] [[

[0135] gapFR1 SetupRelease { GapConfig }

[0136] gapUE SetupRelease { GapConfig } ]],

[0137] GapConfig ::= SEQUENCE {

[0138] gapOffset INTEGER (0..159),

[0139] mgl ENUMERATED {ms1dot5, ms3, ms3dot5, ms4, ms5dot5, ms6},

[0140] mgrp ENUMERATED {ms20, ms40, ms80, ms160},

[0141] mgta ENUMERATED {ms0, ms0dot25, ms0dot5},

[0142] According to the 3GPP specification TS 38300, the UE (201) performs TA measurement for the candidate cells after being configured by the RRC. The exact time the UE (201) performs the TA measurement is determined by the UE (201) implementation. The maximum number of LTM candidate cells can be 8, and the TA measurement for each LTM or Conditional LTM candidate cell can take up to a maximum of approximately 7ms.

[0143] Due to the absence of a dedicated gap configured by the network apparatus (208) for performing the UE-based UL TA measurement, the UE (201) may fail to perform the TA measurements of the LTM or Conditional LTM candidate cells before the LTM cell switch. This failure can lead to the necessity of performing a RACH-based Handover, despite the network-configured UL TA configuration. There is a possibility of RACH failure during the LTM cell switch, and even in successful cases, the interruption time during the RACH-based Handover is approximately 7ms. This interruption causes service continuity failure and negatively impacts the user experience.

[0144] Fig. 7 is a sequence diagram that illustrates the scenario of the MSC according to the prior art. At step S1, the source network apparatus (202) sends the RRC Reconfiguration message to the UE (201). This RRC Reconfiguration is related to the LTM candidate cell with the early TA configuration and the measurement gap.

[0145] In step S2, the UE (201) responds to the source network apparatus (202) with the "RRC Reconfiguration Complete" message, indicating that the UE (201) has accepted and applied the reconfiguration. Further, the UE (201) initiates the evaluation of the LTM candidate cell. The UE (201) does not use the measurement gap configuration for the LTM ULTA measurement. Instead, the UE (201) utilizes other mechanisms, such as the RACH-based LTM cell switch (106), to collect necessary data upon the LTM cell switch.

[0146] At step S3, the UE (201) performs the L1-based measurements for the LTM candidate cell and sends the L1-based LTM measurement report to the source network apparatus (202). Based on this L1-based LTM measurement report, the source network apparatus (202) communicates with the target network apparatus (203) at step S4 to prepare for the LTM cell switch. The source network apparatus (202) triggers the LTM cell switch by coordinating with the target network apparatus (203).

[0147] In step S5, the source network apparatus (202) sends the LTM cell switch command using the MAC CE to the UE (201) to initiate the RACH-based UL synchronization for the cell switch. The UE (201) performs the RACH-based uplink synchronization with the target network apparatus (203) at step S6, ensuring timing alignment and uplink synchronization in the new cell.

[0148] Furthermore, at step S7, the UE (201) completes the cell switch and confirms it to the target network apparatus (203). This completes the cell switch process and confirms the continuity of service.

[0149] Fig. 8 is a schematic representation illustrating the LTM cell switching process with the early UL TA configuration for the UE (201). At steps S1 and S2, the source network apparatus (202) sends the RRC reconfiguration details to the UE (201) for the LTM candidate target cell. The UE (201) is configured with the LTM candidate cells and the early UL TA by the source network apparatus (202). Due to continuous data transfer in the current LTM cell, the UE (201) does not perform the UL TA measurement for the LTM candidate cell before receiving the LTM cell switch command.

[0150] At step S3, the source network apparatus (202) sends the LTM cell switch command to the UE (201) for the target LTM candidate cell. Upon receiving the LTM cell switch command from the source network apparatus (202) for the LTM candidate cell with the UE-based UL TA configuration, the UE (201) initiates RACH-based LTM cell switching.

[0151] At steps S4 and S5, the UE (201) performs the UL synchronization by transmitting the MSG1 to the target network apparatus (203). The UE (201) then waits for the MSG2, with the maximum RAR window duration being 64 ms. There is an increased chance of RAR failure, which leads to the LTM cell switch failure. In the case of a successful RACH procedure, the time taken is approximately 7 ms.

[0152] This process highlights that the UL TA configuration provided by the network is not effectively utilized for performing the RACH-less handover. As a result, this affects the interruption delay and impacts service continuity.

[0153] Fig. 9 is a flow chart illustrating the process for LTM cell switching based on the configuration of the early TA for the candidate cell according to the prior art. At step 901, the method includes configuring the UE (201) with the LTM candidate cell configuration by the network apparatus (208). At step 902, the method includes checking whether the early TA configuration is received for the LTM candidate cell by the network apparatus (208). If the early TA configuration is received, the process proceeds to step 903 (the LTM candidate with early TA configuration). If the early TA configuration is not received, the flow proceeds to step 904 (the LTM candidate without the early TA configuration), where the RACH-based LTM cell switch is performed.

[0154] At steps 903 and 904, the method includes checking if the UE-based TA measurements are configured for the LTM candidate with the early TA configuration. If the UE-based TA measurement is not configured, the flow proceeds to step 907. If the UE-based TA measurement is configured, the flow proceeds to step 909. At steps 907 and 908, the method includes sending the PDCCH order to the UE (201) for the LTM candidate cell by the network apparatus (208) and performing the RACH-less LTM cell switch (102) by the UE (201). At step 909, the method defaults to performing the RACH-based LTM cell switch by the UE (201).

[0155] At steps 910 and 911, the method includes checking whether the gap for the early TA measurement is provided by the network apparatus (208). If no gap is configured, the UE (201) defaults to performing the RACH-based LTM cell switch. The 3GPP does not provide either the exact time to perform the TA measurements or the gaps to perform the UL TA measurements for the LTM candidate cells. This leads to the condition where the UE (201) may miss performing the UL TA measurements, resulting in a RACH-based LTM cell switch (106) even for LTM candidate cells with the early UL TA configuration. Consequently, the UE (201) does not utilize the UL TA configuration and performs the RACH-based handover, increasing the interruption time during the LTM handover.

[0156] In the existing system, the maximum number of LTM candidate cells can be 8, and the TA measurement for each LTM candidate cell can take up to a maximum of ~7ms. Furthermore, the existing system does not configure a dedicated gap by the network apparatus (208) to perform the UE-based UL TA measurement. The UE (201) may fail to perform the TA measurements of the LTM candidate before the LTM cell switch, leading to a RACH-based handover even though the network configured the UL TA configuration. There is a possibility of RACH failure during the LTM cell switch, and the interruption time in the success case of the RACH-based handover is ~7ms, causing interruption during the LTM cell switch. This results in service continuity failure and affects the user experience.

[0157] The proposed invention utilizes a method to perform UL TA synchronization for the LTM candidate cell configured with the early UL TA configuration during data inactivity time in the UE (201) based on various gap configurations available in the UE (201) received from the network. This allows a RACH-less LTM cell switch.

[0158] The Fig. 10 is the block diagram that illustrated the UE for evaluating the UL TA for the LTM candidate cells to enhance the handover and the cell switch performance, according to the embodiment.

[0159] Examples of the UE (201) include, but are not limited to, Consumer Electronics (such as Mobile Phones and Smartphones), Tablets, Wearable Devices, Computing Devices (such as Laptops, Notebooks, Desktops, Workstations, etc.), IoT Devices, Automotive Systems (such as connected cars, Autonomous Vehicles, Vehicle-to-Everything (V2X) communication devices, etc.), Enterprise Devices such as robotics, Specialized Equipment (such as Medical Devices, Public Safety Devices, etc.), and Media Devices (such as Gaming Consoles, Streaming Devices, etc.).

[0160] Examples of the wireless communication network system include, but are not limited to, Cellular Networks (such as 2G, 3G, 4G, 5G, Beyond 5G (B5G) / 6G, or advanced cellular networks), Local Area Networks (LANs) (such as Wi-Fi, Li-Fi, etc.), Personal Area Networks (PANs) (such as Bluetooth, Zigbee, Z-Wave, etc.), Wide Area Networks (WANs) (such as Satellite Communication Networks, Long Range Wide Area Network, Narrowband IoT, Low-bandwidth communication for IoT, etc.), Metropolitan Area Networks (MANs), Machine-to-Machine (M2M), Ad Hoc and Mesh Networks, and Emerging and Advanced Networks.

[0161] The UE (201) includes a processor (204), memory (206), an I / O interface (205), and a UL TA measurement controller (207). The processor (204) communicates with the memory (206), the I / O interface (205), and the UL TA measurement controller (207). It executes instructions stored in the memory (206) to perform various processes. The processor (204) can include one or a plurality of processors and can be a general-purpose processor such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an artificial intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0162] The memory (206) of the UE (201) includes storage locations addressable through the processor (204). It is not limited to volatile memory and / or non-volatile memory and can include one or more computer-readable storage media. Non-volatile storage elements can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In some examples, the memory (206) may be considered a non-transitory storage medium, indicating that it is not embodied in a carrier wave or a propagated signal. However, the term non-transitory should not be interpreted to mean that the memory (206) is non-movable. The memory (206) can store larger amounts of information than the memory. For example, a non-transitory storage medium may store data that can change over time (e.g., in Random Access Memory (RAM) or cache).

[0163] The memory (206) includes messages such as request messages, response messages, RRC reconfiguration messages, and cell switch commands used for configuring UL TA measurement, initiating RACH procedures, and performing LTM evaluation. It also includes information related to devices such as MUSIM capable devices, carrier aggregation (CA)-enabled devices, and the UE (201) performing UL TA measurement.

[0164] The I / O interface (205) transmits information between the memory (206), the UE (201), and external peripheral devices. These peripheral devices are the input-output devices associated with the UE (201).

[0165] The UL TA measurement controller (207) is coupled to the memory (206) and the processor (204), allowing for efficient data transfer and communication between the components. This ensures that the UL TA measurement controller (207) can access and process the UL TA measurement data in real-time. The UL TA measurement controller (207) is an innovative integrated circuit implemented within the UE (201). In an embodiment, the structure of this integrated circuit includes a multi-core architecture that enables UL TA measurements for the LTM candidate cells. Each core is optimized for specific tasks such as UL TA measurement analysis, LTM candidate cell evaluation, and adaptive handover decision-making.

[0166] The innovative integrated circuit for the UL TA measurement is made of a combination of analog and digital components designed to optimize power consumption and network responsiveness. The analog components include a low-noise amplifier and a high-precision analog-to-digital converter to ensure accurate signal processing. The digital components consist of a microcontroller unit (MCU) and a digital signal processor (DSP) that work in tandem to control UL TA evaluation and cell switch triggers.

[0167] Further, the UL TA measurement controller (207) initiates the UL TA measurement during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or the TX when the uplink CA-capable device is configured. The UL TA measurement controller (207) determines the performance of the UL TA measurement for one or more LTM or Conditional LTM candidate cells in the connected mode. The UL TA measurement controller (207) receives the cell switch command from the network apparatus based on the performance of the L1measurement for one or more LTM candidate cells. The UL TA measurement controller (207) in the network apparatus (208) triggers the RACH-less LTM cell switch (102) or handover based on the performance of the UL TA measurement for one or more LTM candidate cells upon receiving the cell switch command.

[0168] The UL TA measurement controller (207) initiates the UL TA measurement during the MUSIM gap. Further, the UL TA measurement controller (207) generates the request message by adding the UE (201) assistance information with the MUSIM gap preference list. The UL TA measurement controller (207) transmits the request message to the network apparatus for the MUSIM gap configuration. The MUSIM gap configuration includes periodic and aperiodic gaps. UE receives the response message from the network apparatus which includes the MUSIM gap. The UL TA measurement controller (207) in the UE (201) perform the UL TA measurements by initiating the RACH procedure for one or more LTM candidate cells during the MUSIM gap configuration.

[0169] The UL TA measurement controller (207) determines whether the RACH procedure is successful within the configured MUSIM gap provided in the MUSIM gap configuration. Further, the UL TA measurement controller (207) stores the UL TA value associated with one or more LTM candidate cells when the RACH procedure is successful within the configured MUSIM gap. The UL TA measurement controller (207) attempts the RACH procedure in the following MUSIM gap when the RACH procedure is successful and applies the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0170] The UL TA measurement controller (207) initiates the UL TA measurement during the CDRX cycle. Further, the UL TA measurement controller (207) configures the early UL TA configuration for the LTM or Conditional LTM candidate cells. The UL TA measurement controller (207) receives the CDRX message from the network apparatus. The CDRX message includes CDRX cycles. The UL TA measurement controller (207) determines whether the UL TA measurement can be performed during the CDRX sleep time based on the CDRX cycles. The UL TA measurement controller (207) performs the UL TA measurement by initiating the RACH procedure with one or more LTM or Conditional LTM candidate cells based on the CDRX sleep time.

[0171] The UL TA measurement controller (207) initiates the UL TA measurement during the L3 measurement gap. Further, the UL TA measurement controller (207) configures the early UL TA configuration for the LTM candidate cells. The UL TA measurement controller (207) transmits the request message to the network apparatus for the LTM evaluation for the one or more candidate LTM or Conditional LTM cells. The request message includes the UE (201) assistance information and may receive the RRC reconfiguration message from the network apparatus. The RRC reconfiguration message includes the measurement configuration information to conduct the L3 measurement. The measurement configuration information includes the L3 measurement gap. The UL TA measurement controller (207) configures to perform the UL TA measurement by initiating the RACH procedure for one or more LTM or Conditional LTM candidate cells during the L3 measurement gap.

[0172] The UL TA measurement controller (207) determines whether the RACH procedure is successful within the configured L3 measurement gap. Further, the UL TA measurement controller (207) stores the UL TA value associated with one or more LTM or Conditional LTM candidate cells when the RACH procedure is successful within the L3 measurement gap. The UL TA measurement controller (207) attempts the RACH procedure in the following measurement gap when the RACH procedure is unsuccessful within the L3 measurement gap and applies the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0173] The UL TA measurement controller (207) initiates the UL TA measurement during the TX when the UL CA-capable device is configured with the early UL TA configuration for the LTM candidate cells. Further, the UL TA measurement controller (207) determines the unused TX in the UL CA-capable device during the LTM evaluation. The UL TA measurement controller (207) performs the UL TA measurement by initiating the RACH procedure for one or more LTM or Conditional LTM candidate cells using the unused TX.

[0174] The UL TA measurement controller (207) determines whether the RACH procedure is successful using the unused TX. The UL TA measurement controller (207) stores the UL TA value associated with one or more LTM candidate cells when the RACH procedure is successful within the configured measurement gap. Further, the UL TA measurement controller (207) attempts the RACH procedure in the following measurement gap when the RACH procedure is unsuccessful using the unused TX and applies the stored UL TA value for one or more LTM or Conditional LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0175] The UL TA measurement controller (207) initiates the UL TA measurement during the MUSIM gap. Further, the UL TA measurement controller (207) in the UE (201) generates the request message by adding the UE (201) assistance information with the MUSIM gap preference list. The UL TA measurement controller (207) in the UE (201) transmits the request message to the network apparatus for the MUSIM gap configuration. The MUSIM gap configuration includes periodic and aperiodic gaps. The UL TA measurement controller (207) in the UE (201) receives the response message from the network apparatus. The response message includes the MUSIM gap. The UL TA measurement controller (207) in the UE (201) performs the UL TA measurement by initiating the RACH procedure for one or more LTM candidate cells during the MUSIM gap configuration.

[0176] The UL TA measurement controller (207) in the UE (201) determines whether the RACH procedure is successful within at least one configured MUSIM gap provided in the MUSIM gap configuration. Further, the UL TA measurement controller (207) in the UE (201) stores the UL TA value associated with one or more LTM candidate cells when the RACH procedure is successful within the configured MUSIM gap. The UL TA measurement controller (207) in the UE (201) attempts the RACH procedure in the following MUSIM gap when the RACH procedure is unsuccessful and applies the stored UL TA value for one or more LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0177] In scenarios where the UL TA measurement controller (207) encounters repeated failures in the RACH procedure, adaptive measures are taken to enhance the robustness of the UL TA measurement process. The controller (207) may dynamically adjust the parameters of the RACH procedure, such as the timing advance and power levels, to optimize the chances of successful communication with the LTM candidate cells. Additionally, the UL TA measurement controller (207) can leverage historical data and machine learning algorithms to predict the optimal conditions for RACH success, thereby minimizing the number of attempts required.

[0178] Furthermore, the UL TA measurement controller (207) is designed to operate efficiently under varying network conditions and device capabilities. When dealing with high mobility scenarios, the controller (207) can prioritize the timing of UL TA measurements to coincide with periods of relative stability in the UE's (201) movement. This ensures that the measurements are more accurate and reflective of the actual network conditions. In low mobility or stationary scenarios, the controller (207) can afford to be more aggressive in its measurement scheduling, taking advantage of the reduced variability in signal conditions.

[0179] Furthermore the integration of the UL TA measurement controller (207) with other network management systems allows for a holistic approach to network optimization. By sharing UL TA measurement data with network planning and optimization tools, the overall network performance can be continuously improved. This collaborative approach ensures that the UL TA measurements not only serve immediate handover and cell switch decisions but also contribute to long-term enhancements in network coverage, capacity, and user experience.

[0180] The UL TA measurement controller (207) in the UE (201) is configured for the UL TA measurement during the CDRX cycle. The UL TA measurement controller (207) in the UE (201) configures the early UL TA configuration for the LTM candidate cells. The UL TA measurement controller (207) in the UE (201) receives the CDRX message from the network apparatus. The CDRX message includes the CDRX cycles. The UL TA measurement controller (207) in the UE (201) determines whether the UL TA measurement can be performed during the CDRX sleep time based on the CDRX cycles. The UL TA measurement controller (207) in the UE (201) performs the UL TA measurement by initiating the RACH procedure with the one or more LTM candidate cells based on the CDRX sleep time.

[0181] The UL TA measurement controller (207) in the UE (201) initiates the UL TA measurement during the L3 measurement gap. The UL TA measurement controller (207) in the UE (201) is configured for the early UL TA configuration for the LTM candidate cells. The UL TA measurement controller (207) in the UE (201) transmits the request message to the network apparatus for the LTM evaluation of one or more candidate LTM cells. The request message includes the UE (201) assistance information. The UL TA measurement controller (207) in the UE (201) receives the RRC reconfiguration message from the network apparatus. The RRC reconfiguration message includes measurement configuration information to conduct the L3 measurement. The measurement configuration information includes the L3 measurement gap. The UL TA measurement controller (207) in the UE (201) performs the UL TA measurement by initiating the RACH procedure for one or more LTM candidate cells during the L3 measurement gap.

[0182] The UL TA measurement controller (207) in the UE (201) determines whether the RACH procedure is successful within the configured L3 measurement gap. The UL TA measurement controller (207) in the UE (201) stores the UL TA value associated with one or more LTM candidate cells when the RACH procedure is successful within the L3 measurement gap. The UL TA measurement controller (207) in the UE (201) attempts the RACH procedures in the following measurement gap when the RACH procedure is unsuccessful within the L3 measurement gap and applies the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0183] The UL TA measurement controller (207) in the UE (201) initiates the UL TA measurement during the TX. The UL TA measurement controller (207) in the UE (201) is configured for the early UL TA configuration for the LTM candidate cells. The UL TA measurement controller (207) in the UE (201) determines the unused TX in the UL CA-capable device during the LTM evaluation. The UL TA measurement controller (207) in the UE (201) performs the UL TA measurement by initiating the RACH procedure for one or more LTM candidate cells using the unused TX.

[0184] The UL TA measurement controller (207) in the UE (201) determines whether the RACH procedure is successful using the unused TX. The UL TA measurement controller (207) in the UE (201) stores the UL TA value associated with one or more LTM candidate cells when the RACH procedure is successful within the configured measurement gap. The UL TA measurement controller (207) in the UE (201) attempts the RACH procedures in the following measurement gap when the RACH procedure is unsuccessful using the unused TX and applies the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM cell switch (102) or handover.

[0185] Fig. 10B is a block diagram that illustrates the network apparatus for evaluating the UL TA for LTM candidate cells to enhance handover and cell switch performance according to the embodiment. The network apparatus (208) includes various hardware and software components that facilitate communication between user equipment and network infrastructure. Examples of the network apparatus (208) can include, but are not limited to, Base Stations (such as macro cells, small cells, femtocells, picocells) for wireless communication, Antennas and RF Units (e.g., MIMO beamforming) to enhance signal coverage and data throughput, Core Network Equipment (e.g., MMEs, S-GWs, P-GWs in 4G, AMFs, UPFs in 5G) for data routing, mobility, and session control, Network Function Virtualization (NFV) and Software-Defined Networking (SDN) for dynamic resource allocation and scalability, Edge Computing Nodes (e.g., MEC servers) for low-latency processing, Backhaul and Transport Equipment (e.g., fiber-optic links, microwave relays, Ethernet switches) to connect base stations to the core network, Network Management Systems (NMS) and Operation Support Systems (OSS) for network configuration, fault management, and optimization, Radio Network Controllers (RNCs) in 3G, Distributed Units (DUs) and Centralized Units (CUs) in 5G, Network Slicing Components for virtualized resource allocation, Security elements (e.g., Firewalls, IDS, AAA Servers) for secure communication.

[0186] The network apparatus (208) includes the processor (209), the memory (211), an I / O interface (210), and the UL TA measurement controller (212). The network apparatus (208) communicates with the UE (201) for self-optimization during the handover. For example, the network apparatus (208) can include, but is not limited to, a base station, access point, central server, or similar equipment. Further, the processor (209) of the network apparatus (208) communicates with the memory (211), the I / O interface (210), and the UL TA measurement controller (212). The processor (209) executes instructions stored in the memory (211) to perform various processes. The processor (209) can include one or a plurality of processors, can be a general-purpose processor such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial Intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0187] Further, the memory (211) of the network apparatus (208) includes storage locations to be addressable through the processor (209). The memory (211) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (211) can include one or more computer-readable storage media. The memory (211) can include non-volatile storage elements. For example, non-volatile storage elements can include magnetic hard disks, optical disks, floppy disks, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. The memory (211) includes messages such as request messages, response messages, RRC reconfiguration messages, and cell switch commands used for configuring UL TA measurement, initiating RACH procedures, and performing LTM evaluation. The memory (211) includes information related to devices such as MUSIM capable devices, carrier aggregation (CA)-enabled devices, and the network apparatus (208) performing UL TA measurement.

[0188] The I / O interface (210) transmits the information between the memory (211) and external peripheral devices. The peripheral devices are the input-output devices associated with the network apparatus (208).

[0189] The UL TA measurement controller (212) is coupled to the memory (211) and the processor (210). This coupling allows for efficient data transfer and communication between the components, ensuring that the UL TA measurement controller (212) can access and process the UL TA data in real-time. The UL TA measurement controller (212) is an innovative integrated circuit that is implemented in the network apparatus (208). In an embodiment, the structure of such an innovative integrated circuit includes a multi-core architecture that enables evaluation of UL TA measurements for LTM candidate cells in a communication system. Each core is optimized for specific tasks such as signal processing, UL TA measurement analysis, LTM candidate cell evaluation, and determining cell switch performance. The innovative integrated circuit for the UL TA measurement processing is made of a combination of analog and digital components designed to optimize power consumption and network performance. The analog components include a low-noise amplifier and a high-precision analog-to-digital converter to ensure accurate signal processing. The digital components consist of a microcontroller unit (MCU) and a digital signal processor (DSP) that work in tandem to dynamically adjust the UL TA measurement.

[0190] The network apparatus (208) for evaluating the UL TA for LTM candidate cells to enhance handover and cell switch performance. Further, the network apparatus (208) includes the memory (211), the processor (209), and the UL TA measurement controller (212). The UL TA measurement controller (212) initiates the UL TA measurement during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or the TX when the uplink CA capable device is configured. Further, the UL TA measurement controller (212) determines the performance of the UL TA measurement for the one or more LTM candidate cells in the connected mode. Further, the UL TA measurement controller (212) transmits the cell switch command from the network apparatus (208) based on the performance of the UL TA measurement for the one or more LTM candidate cells. Further, the UL TA measurement controller (212) enables the RACH-less LTM cell switch (102) or handover based on the performance of the UL TA measurement for the one or more LTM candidate cells upon receiving the cell switch command.

[0191] Fig. 11A is the flowchart of the method for evaluating the UL TA for the LTM candidate cells to enhance the handover and the cell switch performance according to the embodiment. At step 111, the method includes initiating the UL TA measurement by the UE (201) during one of the MUSIM gap, the CDRX cycle, the L3 measurement gap, or the TX when the UL CA capable device is configured. At step 112, the method includes determining the performance of the UL TA measurement for the one or more LTM candidate cells in the connected mode by the UE (201). At step 113, the method includes receiving the cell switch command from the network apparatus (208) by the UE (201) based on the performance of the UL TA measurement for the one or more LTM candidate cells. At step 114, the method includes initiating the cell switch command based on the signal measurement reports from the UE (201) for one or more conditional LTM candidate cells and triggering the RACH-less LTM cell switch (102) or the handover by the UE (201) based on the performance of the UL TA measurement for the one or more LTM candidate cells upon receiving the cell switch command.

[0192] Fig. 11B is the flowchart that illustrates the process for the LTM cell switching based on the configuration of the early TA for the candidate cell according to the embodiments as disclosed herein. At step 115, the method includes configuring the UE (201) with the LTM candidate cell configuration by the network apparatus (208). At step 116, the method includes checking whether the early TA configuration is received for the LTM candidate cell by the network apparatus (208). If the early TA configuration is received, then it proceeds with step 117 (the LTM candidate with the early TA configuration). If the LTM candidate with early TA configuration is not received, the flow proceeds to step 118 (the LTM candidate without the early TA configuration) where the RACH-based LTM cell switch is performed. At step 119, the method includes checking if the UE-based TA measurements are configured for the LTM candidate with the early TA configuration. If the UE-based TA measurement is not configured, then the flow proceeds to step 121. If the UE-based TA measurement is configured, then the flow proceeds to step 123.

[0193] At steps 121 and 122, the method includes sending the PDCCH order to the UE (201) for the LTM candidate cell by the network apparatus (208) and performing the RACH-less LTM cell switch (102) by the UE (201). At step 123, the method includes configuring the UE-based TA measurement. At step 124, the method includes checking whether the UE (201) is configured with the CDRX, the MUSIM, the gap, or the measurement gap by the network apparatus (208) (also referred as network apparatus). If not configured, the flow proceeds with step 125. If configured, the flow passes to step 126. At step 125, the method includes performing the RACH-based LTM cell switch (106) by the network apparatus (208). At steps 126 and 127, the method includes performing the UL TA measurement for the LTM candidate cells in the gap by the UE (201) and performing the RACH-less LTM cell switch.

[0194] Fig.12 is the sequence diagram that illustrates the process for the LTM cell UL TA synchronization for the LTM or Conditional LTM candidate cell configured with the early UL TA configuration during the data inactivity time, according to the embodiment herein.

[0195] The proposed solution performs the UL TA synchronization for the LTM or Conditional LTM candidate cell configured with the early UL TA configuration during the data inactivity time in the UE (201). This synchronization is based on network configurations such as MUSIM gaps, CDRX sleep time, L3 measurement gaps configuration, or unused transceiver in the UL CA capable UE (201) to ensure a RACH-less handover during the LTM cell switch.

[0196] The MUSIM Gap configuration, as the first solution, may be requested by the UE (201) through the UE (201) assistance information. The network then provides the MUSIM Gap Configuration, which includes periodic and aperiodic gaps. During MUSIM gaps, the network cannot schedule DL data activity.

[0197] During the CDRX cycle, when data is not received in On-Duration time, the UE (201) may move to sleep time, during which DL data may not be received from the network. As a second alternative solution, the UE (201) may utilize the sleep time to perform the UL TA measurement of the LTM candidate cells and store the UL TA values before the LTM cell switch.

[0198] Since the LTM candidate cells are configured for LTM cell switching, the likelihood of handover being triggered through L3 measurements decreases. To address this, as a second alternative solution, the UE (201) may utilize the unused measurement gaps originally configured for L3 measurements by the network to perform the UL TA measurements for the LTM candidate cells. This ensures efficient use of resources while preparing for the LTM cell switching.

[0199] Additionally, some UEs support multiple transceivers, enabling simultaneous UL data activity through two transceivers (UL CA support). However, in scenarios where only one transceiver is configured for data activity and the other transceiver remains idle, the idle transceiver can be leveraged. As a third alternative solution, the UE (201) may use the unused transceiver to perform the UL TA measurements for the LTM candidate cells in devices capable of UL CA.

[0200] The LTM candidate cells are configured with the UL configuration. At step S1, the LTM candidate cells are configured with the UL configuration. The UE (201) performs the UL TA synchronization for the LTM candidate cell configured with the early UL TA configuration during the data inactivity time in the UE (201) based on network configurations such as MUSIM gaps, CDRX sleep time, L3 measurement gaps configuration, or unused transceiver in the UL CA capable UE to ensure a RACH-less handover during the LTM cell switch.

[0201] At step S2, the UE (201) sends MSG1 to the target network apparatus (203) and requests the MUSIM Gap configuration through the UE (201) Assistance Information. In response, at step S3, the network apparatus (208) provides the MUSIM Gap Configuration (MSG 2), which includes both periodic and aperiodic gaps. The UE (201) performs the UL TA measurement of the LTM candidate cells during the MUSIM Gap configuration and stores the UL TA value before the LTM cell switch. MSG 2 includes the RAR response with the TA information.

[0202] During the measurement gap, at step S4, the UE (201) utilizes the unused measurement gaps of the L3 measurement configured by the network to perform the UL TA measurement of the LTM candidate cells. In the measurement gap scenario, the UE (201) sends MSG1 to the target network apparatus (203) for early synchronization for the LTM candidate cell. The target network apparatus (203) sends MSG2 with the RAR Response with the TA value at step S5.

[0203] In the CDRX scenario, at step S6, the UE (201) utilizes the sleep time to perform the UL TA measurement of the LTM candidate cells and store the UL TA value before the LTM cell switch. The UE (201) sends MSG1 to the target network apparatus (203) for the TA measurement calculation during the DRX sleep cycle. The target network apparatus (203) sends MSG2 with the RAR Response with the TA value at step S7.

[0204] At step S8, the UE (201) utilizes the unused transceiver in the ULCC to perform the UL TA measurement of the LTM candidate cells in the UL CA capable device. In the ULCC scenario, the UE (201) sends MSG1 to the target network apparatus (203) for the TA measurement. The target network apparatus (203) responds with MSG2 including the RAR Response containing the TA value at step S9. The UE (201) transmits MSG1 to the target network apparatus (202) to initiate TA measurement, and the target network apparatus (202) responds with MSG2, including the Random Access Response (RAR) containing the TA value, at step S9.

[0205] The UE (201) sends the L1 based LTM measurement report to the source network apparatus (202) at step S10. The source network apparatus (202) triggers the LTM Cell switch process based on the UE's measurement report and other mobility conditions at step S11. The source network apparatus (202) provides the LTM cell switch command through the MAC CE to the UE (201) at step S12. The LTM Cell Switch Command includes the necessary configuration to complete the LTM cell switch. Furthermore, at step S13, the UE (201) completes the RACH-less based LTM cell switch with the target network apparatus (203) and acknowledges the completion of the LTM cell switch process.

[0206] The procedure for the UE (201) Based UL TA measurements using the proposed invention is as given below:

[0207] “If UE configured with LTM Candidate cell with early UL config

[0208] ▶ If NTA of serving cell same as candidate cell or NTA =0

[0209] Early TA measurement is not required.

[0210] ▶ If gNB trigger PDCCH order for LTM candidate cell

[0211] ▶ UE will initiate preamble transmission based on PDCCH trigger and source network apparatus retrieves TA value of LTM candidate

[0212] ▶ If UE has to perform UE based UL TA measurements

[0213] ▶ UE will measure UL TA value of LTM candidate cell before LTM cell switch

[0214] ▶ UE will measure UL TA on data inactivity gaps based on proposed solution

[0215] ▶ if UE has TA value upon receiving the LTM Cell switch command

[0216] ▶ Perform RACH Less LTM cell switch.

[0217] ▶ Else

[0218] ▶ Perform RACH Based LTM cell switch.

[0219] UE Based UL TA measurements using the proposed solution:

[0220] If UE support MUSIM feature, then UE will requested MUSIM gap

[0221] If Network configured musim gap (periodic or Aperiodic gaps) as response for UE MUSIN gap request.

[0222] ▶ Use the gap configuration to do UL TA measurement for LTM candidate cell.

[0223] If UE Configured with CDRX configuration

[0224] ▶ Use drx inactivity time(sleep time)period to do UL TA measurement for LTM candidate

[0225] If UE Configured with measurement gap for neighbour cell measurement

[0226] ▶ Use measurement gap configured for neighbour cell evaluation to do UL TA measurements for LTM candidate.

[0227] If UE supports UL carrier aggregation and configured with multiple UL CC

[0228] ▶ Use unused UL CC (Transceiver) to do UL TA measurement for LTM candidate."

[0229] Fig. 13 is the schematic diagram that illustrates the UL TA measurement for the LTM or Conditional LTM candidate cell using various gap configurations. FIG13 discloses in what manner the UE (201) utilizes various gap configurations such as the MUSIM gaps, the L3 measurement gaps, the CDRX sleep time, and the ULCC (unused transceiver) gaps to perform the UL TA measurements of the LTM candidate cell. At step S1, the source network apparatus (202) sends the RRC reconfiguration details to the UE (201) for the LTM candidate target cell, and then the UE (201) is configured with the UL TA settings for the LTM candidate cells. At step S2, the UE (201) monitors for the data inactivity periods based on the network's configurations such as MUSIM gaps, CDRX sleep time, L3 measurement gaps, or unused transceivers in UL CA-capable UEs. During these periods, the UE (201) may perform the UL TA measurements for the LTM candidate cells. This ensures that the UE (201) is synchronized with the LTM candidate cells before the handover. Once the UE (201) identifies the LTM candidate cells using the gap configurations, it performs the early UL TA synchronization by sending the preamble to the target network apparatus (203). The target network apparatus (203) responds with the RAR information and completes synchronization. After completion of synchronization, the source network apparatus (202) issues the cell switch command to the UE (201). The cell switch command includes the DL and the UL data for finalizing the handover.

[0230] At steps S3 and S4, the UE (201) completes the UL TA measurement for the LTM candidate cells before the LTM cell switch is triggered. The measurements are stored for use during the handover. By performing the measurements and synchronizations during the inactivity gaps, the UE (201) enables the RACH-less LTM cell switch. This results in a better success rate for the cell switches and reduces the overall handover interruption time, achieving a switch time of approximately ~2ms.

[0231] Fig. 13 is the schematic diagram that illustrates the UL TA measurement for the LTM candidate cell using various gap configurations. Fig. 13 discloses in what manner the UE (201) utilizes various gap configurations such as the MUSIM gaps, the L3 measurement gaps, the CDRX sleep time, and the ULCC (unused transceiver) gaps to perform the UL TA measurements of the LTM candidate cell. At step S1, the source network apparatus (202) sends the RRC reconfiguration details to the UE (201) for the LTM candidate target cell and then the UE (201) is configured with the UL TA settings for the LTM candidate cells.

[0232] At step S2, the UE (201) monitors for the data inactivity periods based on the network's configurations such as MUSIM gaps, CDRX sleep time, L3 measurement gaps, or unused transceivers in UL CA-capable UEs. During these periods, the UE (201) may perform the UL TA measurements for the LTM candidate cells. This ensures that the UE (201) is synchronized with the LTM candidate cells before the handover. Once the UE (201) identifies the LTM candidate cells using the gap configurations, it performs the early UL TA synchronization by sending the preamble to the target network apparatus (203). The target network apparatus (203) responds with the RAR information and completes synchronization. After completion of synchronization, the source network apparatus (202) issues the cell switch command to the UE (201). The cell switch command includes the DL and the UL data for finalizing the handover.

[0233] At steps S3 and S4, the UE (201) completes the UL TA measurement for the LTM candidate cells before the LTM cell switch is triggered. The measurements are stored for use during the handover. By performing the measurements and synchronizations during the inactivity gaps, the UE (201) enables the RACH-less LTM cell switch. This results in a better success rate for the cell switches and reduces the overall handover interruption time, achieving a switch time of approximately ~2ms.

[0234] Fig. 14 is the sequence diagram that illustrates the UL TA measurements during MUSIM GAP according to the embodiment herein. At step S1, the process starts with the source network apparatus (202). The source network apparatus (202) sends the RRC Reconfiguration message, which includes the LTM candidate cell with the early TA configuration details. At step S2, the UE (201) sends the RRC Reconfiguration Complete message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell. At step S3, the UE (201) requests the network apparatus (208) to provide the MUSIM Gap configuration by sending the UE Assistance information with the MUSIM-Gap Preference List to use the gaps for performing the UL TA synchronization. At step S4, the source network apparatus (202) configures the MUSIM-GapConfig (periodic and aperiodic gap) through the RRC signaling message. At step S5, the UE (201) acknowledges the reconfiguration by sending the RRC Reconfiguration Complete message back to the source network apparatus (202) and confirms that the UE (201) has applied the gap configuration. Further, the UE (201) utilizes the MUSIM gap to perform the UE (201) based UL TA measurement for the LTM Candidate cell by performing the RACH to the candidate target cell. During the configured MUSIM gaps (periods of data inactivity), the UE (201) initiates the synchronization process with the target network apparatus (203).

[0235] At step S6, during the configured MUSIM gaps (periods of data inactivity), the UE (201) sends the MSG 1 (a synchronization signal) to the target network apparatus (203) to initiate the UL TA synchronization. At step S7, if the RACH is successful, the target network apparatus (203) responds with the MSG 2 that includes the RAR message along with the calculated TA values. This confirms that the UE (201) is synchronized with the target cell. Additionally, if the RACH is successful in one gap, the UE (201) stores the TA value associated with the candidate cell. If RACH is unsuccessful, the RACH may be attempted in the following gap until the successful synchronization is achieved. At step S8, the UE (201) sends the L1 based LTM measurement report to the source network apparatus (202). At step S9, the source network apparatus (202) triggers the LTM cell switch process based on the UE's (201) measurement report. At step S10, the source network apparatus (202) provides the LTM cell switch command through the MAC CE to the UE (201). Upon receiving the LTM cell switch command for a pre-measured candidate cell, the UE (201) applies the stored UL TA value and performs the RACH-less LTM cell switch (102) to the target network apparatus (203). At step S11, the UE (201) completes the RACH-less LTM cell switch (102) with the target network apparatus (203) and sends an acknowledgment to confirm the successful completion of the LTM cell switch process.

[0236] In an embodiment, the RACH-less approach in the proposed invention eliminates the delay associated with the RACH procedures and provides the data flows with minimal interruption (typically ~2ms). Further, the proposed invention may reduce the HO latency, the data interruption time, and increase the success rate of the LTM cell switch.

[0237] Figs. 15A and 15B are block diagrams illustrating the comparison between the existing system and the proposed invention in relation to the UL TA measurements during the MUSIM GAP.

[0238] Fig. 15A illustrates the UL TA measurements during the MUSIM GAP according to prior art. At step S1, the UE (201) with the LTM Candidate (with early TA configuration) is connected to an F1 / cell (1501). The UE (201) operates SIM 1 (1502a) and SIM 2 (1502b). In this scenario, SIM 1 remains idle. At step S2, SIM 1 (1502a) utilizes the MUSIM gap (1503) for paging and monitoring activities, while SIM 2 (1502b) remains idle during the MUSIM gap (1503) to avoid interference. At steps S3 and S4, the F1 / cell (1501) measurement criteria are evaluated, and the L1 measurement (L1 physical measurements) triggers the signal to the network apparatus (208) to initiate the handover. At step S5, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE layer. At steps S6 and S7, UL synchronization is established between the UE (201) and the target network apparatus (203). Further, the LTM cell switch occurs, and the UE (201) moves to the target network apparatus (203). This process delays the uplink synchronization with the target network apparatus (203), requiring the RACH-based LTM cell switch, which introduces further latency and synchronization inaccuracies. Additionally, in the existing system, the UE (201) does not utilize the MUSIM gap (1503) for the UL TA measurement for the LTM candidate cell. Therefore, the UE (201) performs the RACH-based LTM cell switch (106).

[0239] Fig. 15B illustrates the UL TA measurements during the MUSIM GAP (1503) according to the proposed invention. At step S1, the UE (201) with the LTM Candidate (with early TA configuration) is connected to the F1 / cell (1501). The UE (201) operates SIM 1 (1502a) and SIM 2 (1502b). In this scenario, SIM 1 (1502a) remains idle. At step S2, SIM 2 (1502b) utilizes the MUSIM gap (1503) to perform early TA measurement for the F1 / cell (1501) to ensure proper timing and synchronization for the LTM candidate evaluation. At step S3, the F1 / cell (1501) undergoes L1 (Layer 1) measurement evaluation to determine if the target cell meets the required performance thresholds. At step S4, based on the measurement evaluation, the L1 measurement report is triggered and sent to the network apparatus (208). At steps S5 and S6, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE. Further, the UE (201) switches to the target network apparatus (203) and completes the handover with minimal interruption (~2ms).

[0240] In the UL TA measurements during the MUSIM GAP (1503), the UE (201) leverages the MUSIM gap (1503) for the UL TA measurement without requiring the RACH, allowing the RACH-less LTM cell switch. In the proposed invention, SIM 2 (1502b) uses the MUSIM gap (1503) for the early TA measurement, reducing dependency on the RACH. Further, the handover interruption time is reduced to approximately ~2ms, and the process introduces the efficient RACH-less LTM cell switch (102), optimizing the handover mechanism.

[0241] In an embodiment, the proposed invention utilizes the MUSIM gap (1503) for the UL TA measurement, thereby eliminating the dependency on the RACH and enabling the RACH-less LTM cell switch. This reduces handover interruption time to approximately ~2ms compared to longer delays in the existing system. The proposed invention ensures a faster, more efficient, and accurate handover mechanism.

[0242] Fig. 16 is the sequence diagram that illustrates the UL TA measurements during the CDRX sleep time according to the embodiment herein. At steps S1 and S2, the process starts with the source network apparatus (202). The source network apparatus (202) sends the RRC Reconfiguration (CDRX sleep) message. In response, the UE (201) sends the RRC Reconfiguration Complete message back to the source network apparatus (202). During the CDRX time at step S3, the UE (201) may not monitor the PDCCH during the sleep time of the cycle. This is because there is no uplink or downlink transmission between the UE (201) and the target network apparatus (203) as per the established standards. At steps S4 and S5, the source network apparatus (202) sends the RRC Reconfiguration message, which includes the LTM candidate cell with the early TA configuration details. The UE (201) sends the RRC Reconfiguration Complete message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell.

[0243] Further, the UE (201) utilizes the CDRX sleep time to perform the UE-based UL TA measurement for the LTM candidate cell by performing the RACH to the candidate target cell. During the configured CDRX sleep time, the UE (201) initiates the synchronization process with the target network apparatus (203). At step S6, during the CDRX sleep time, the UE (201) sends the MSG 1 (a synchronization signal) to the target network apparatus (203) to initiate the UL TA synchronization.

[0244] If the RACH is successful at step S7, the target network apparatus (203) responds with the MSG 2 that includes the RAR message along with the calculated TA values. This confirms the UE (201) is synchronized with the target cell. Additionally, if the RACH is successful in one gap, the UE (201) stores the TA value associated with the candidate cell. If the RACH is unsuccessful, the RACH may be attempted in the following gap until successful synchronization is achieved. At step S8, the UE (201) sends the L1-based LTM measurement report to the source network apparatus (202). The source network apparatus (202) triggers the LTM cell switch process based on the UE's (201) measurement report at step S9. At step S10, the source network apparatus (202) provides the LTM cell switch command through the MAC CE to the UE (201). Upon receiving the LTM cell switch command for the pre-measured candidate cell, the UE (201) applies the stored UL TA value and performs the RACH-less LTM cell switch (102) to the target network apparatus (203).

[0245] Furthermore, at step S11, the UE (201) completes the RACH-less LTM cell switch (102) with the target network apparatus (203) and sends the acknowledgment to confirm the successful completion of the LTM cell switch process.

[0246] The present invention is illustrated through Fig. 17A and Fig. 17B, which are block diagrams comparing the existing system with the proposed invention in relation to the UL TA measurements during the CDRX sleep time.

[0247] Fig. 17A illustrates the UL TA measurements during the CDRX sleep time according to the prior art. At step S1, the UE (201) is connected to the F1 or Cell 1 (1501), which supports early timing adjustments to prepare for handover, and the UE (201) is in a low-power mode called CDRX (1702). At step S2, while in the low-power mode, the UE (201) "sleeps" when no data is being transmitted; however, the UE (201) periodically wakes up to check for signals.

[0248] At steps S3 and S4, while in the CDRX (1702), the UE (201) evaluates the F1 / cell (1501) measurement criteria, and the L1 measurement triggers the signal to the network apparatus (208) to initiate the handover. At step S5, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE layer. At steps S6 and S7, UL synchronization is established between the UE (201) and the target network apparatus (203). Here, the UE (201) sends the request (MSG 1) and waits for the response from the network (RAR), which takes about ~7ms. Further, the LTM cell switch occurs, and the UE (201) moves to the target network apparatus (203).

[0249] In the existing system, the UE (201) does not utilize the CDRX (1702) (data inactivity time) for early UL TA measurement. Therefore, the UE (201) performs the RACH-based LTM cell switch (106).

[0250] Fig. 17B illustrates the UL TA measurements during the CDRX sleep times according to the proposed invention. At step S1, the UE (201) is connected to the F1 or Cell 1 (1501) that supports early timing adjustments to prepare for the handover, and the UE (201) is in the low-power mode called CDRX (1702). At step S2, while in the CDRX sleep mode, the UE (201) performs early UL TA measurements for the LTM candidate (F1 / cell1). At steps S3 and S4, the UE (201), still in CDRX (1702), evaluates the F1 / cell (1501) measurement criteria. The L1 measurement triggers the signal to the network apparatus (208) to initiate the handover. At step S5, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE layer. Subsequently, at step S6, the UE (201) switches to the target network apparatus (203) and completes the handover with minimal interruption (~2 ms).

[0251] In one embodiment, the proposed invention utilizes the CDRX sleep time (1702) for the UL TA measurement, thereby eliminating the dependency on the RACH and enabling the RACH-less LTM cell switch (102). This reduces handover interruption time to approximately ~2 ms compared to longer delays (approximately ~7 ms) in the existing system. The proposed invention reduces HO latency, minimizes data interruption time, and increases the success rate of the LTM cell switch.

[0252] Fig. 18 is the sequence diagram that illustrates the UL TA measurements during the L3 measurements gap according to an embodiment herein. The process starts at steps S1 and S2 with the source network apparatus (202). The source network apparatus (202) sends the 'RRC Reconfiguration' (CDRX sleep) message, and the UE (201) sends the 'RRC Reconfiguration Complete' message back to the source network apparatus (202). During the allocated measurement gaps at step S3, the UE (201) performs the L3 signal measurements to evaluate the quality and strength of the signal from a neighboring cell or inter-RAT frequency. Later, the UE (201) sends the measurement report to the target network apparatus (203). However, existing handover procedures require more time for measurement evaluation and cell switching than the LTM. At steps S4 and S5, the source network apparatus (202) sends the 'RRC Reconfiguration' message, which includes the LTM candidate cell with the early TA configuration details. The UE (201) sends the 'RRC Reconfiguration Complete' message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell). The UE (201) may further monitor the L3 measurement gaps and re-use the transmitter antenna to perform the RACH to the LTM candidate cell in the available measurement gaps. During the L3 configured measurement, the UE (201) initiates the synchronization process with the target network apparatus (203). At step S6, during the configured L3 measurement gap, the UE (201) sends the MSG 1 to the target network apparatus (203) to initiate the UL TA synchronization. If the RACH is successful at step S7, the target network apparatus (203) responds with the MSG 2 that includes the RAR message along with the calculated TA values. This confirms that the UE (201) is synchronized with the target cell. Additionally, if the RACH is successful in one gap, the UE (201) stores the TA value associated with the candidate cell. If the RACH is unsuccessful, the RACH may be attempted in the following gap until successful synchronization is achieved.

[0253] At step S8, the UE (201) sends the L1 based LTM measurement report to the source network apparatus (202). The source network apparatus (202) triggers the LTM cell switch process based on the UE's measurement report at step S9. The source network apparatus (202) provides the LTM Cell switch command through the MAC CE to the UE (201) at step S10. Upon receiving the LTM cell switch command for the pre-measured candidate cell, the UE (201) applies the stored UL TA value and performs the RACH-less LTM cell switch (102) to the target network apparatus (203). Furthermore, at step S11, the UE (201) completes the RACH-less LTM cell switch (102) with the target network apparatus (203) and sends the acknowledgment to confirm the successful completion of the LTM cell switch process. The objective of the proposed L3 measurement gap is to decrease HO latency and data interruption time while improving the success rate of the LTM cell switching.

[0254] Figs. 19A and 19B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA measurements during the L3 measurement gap. Fig. 19A illustrates the UL TA measurements during the L3 measurement gap according to the prior art. At step S1, the UE (201) is connected to the F2 or cell 2 (1901) with the L3 measurement while simultaneously being disconnected from the F1 cell (1501). At step S2, the F2 or cell 2 (1901) utilizes the measurement gap (1902) for the candidate cell measurement. At steps S3 and S4, the F2 or cell 2 (1901) measurement criteria are evaluated, and the measurement report triggers the signal to the network apparatus (208) to initiate the handover. At step S5, the network apparatus (208) sends the handover command to the UE (201). At steps S6 and S7, the UL synchronization is established between the UE (201) and the target network apparatus (203), further completing the handover to the target network apparatus (203). This process delays the uplink synchronization with the target network apparatus (203), requiring the RACH-based LTM cell switch, which introduces further latency and synchronization inaccuracies. Additionally, in the existing system, the UE (201) does not utilize the measurement gap for the early UL TA measurement for the LTM candidate cell. As a result, the UE (201) performs the RACH-based LTM cell switch (106), and the HO interruption time takes approximately ~7ms for a successful RACH-based handover.

[0255] Figure 19B illustrates the UL TA measurements during the L3 measurement gap according to the proposed invention. At step S1, the UE (201) is connected to the F1 or cell 1 (1501) with early TA configuration while simultaneously being disconnected from the F2 or cell 2 (1901). At step S2, the F1 or cell 1 (1501) utilizes the measurement gap (1902) to perform the early TA measurement for the candidate cell to ensure proper timing and synchronization for the LTM candidate evaluation. At step S3, the F1 or cell 1 (1501) undergoes L1 (Layer 1) measurement evaluation to determine if the target cell meets the required performance thresholds. At step S4, based on the measurement evaluation, the L1 measurement report is triggered and sent to the network apparatus (208). At step S5, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE. At step S6, the UE (201) switches to the target network apparatus (203) and completes the handover with minimal interruption (~2ms).

[0256] In an embodiment, the proposed invention utilizes the measurement gap (1902) for the UL TA measurement, thereby eliminating the dependency on the RACH and enabling the RACH-less LTM cell switch (102). This reduces handover interruption time to approximately ~2ms compared to longer delays (approximately ~7ms) in the existing system. The proposed invention reduces the HO latency and data interruption time and increases the success rate of the LTM cell switch.

[0257] Fig. 20 is the sequence diagram that illustrates the UL TA measurements using the additional transceiver in the UL CA capable device, according to embodiment herein. At steps S1 and S2, the process begins with a source network apparatus - Primary Component Carrier (PCC) (202b) sending an RRC Reconfiguration (ULCA config SCC) message. In response, the user equipment (UE) (201) sends an RRC Reconfiguration Complete message back to the source network apparatus (202).

[0258] During the data transfer process at step S3, some UE (201) devices with hardware support for UL CA can utilize multiple transceivers to enhance UL throughput. The network apparatus (208) may configure multiple Component Carriers (CC) to the UE (201), thereby improving throughput performance. However, the UE (201) does not always utilize all UL CCs for data transfer, and one of the CCs may remain idle for a period of time.

[0259] At steps S4 and S5, the source network apparatus (202) sends an RRC Reconfiguration message, which includes the LTM candidate cell with early UL configuration details. The UE (201) sends an RRC Reconfiguration Complete message back to the source network apparatus (202) and initiates the evaluation of the LTM candidate cell. During the LTM evaluation process, the UE (201) may check for an unused transceiver in the UL CA capable device to utilize it for UL TA measurement of the LTM candidate cells.

[0260] At step S6, during the UL CC used for early TA measurement, the UE (201) sends MSG 1 (a synchronization signal) to the target network apparatus (203) to initiate UL TA synchronization. The UE (201) may reuse the Tx antenna to perform the RACH to the LTM candidate target cell. If the RACH is successful at step S7, the target network apparatus (203) responds with MSG 2, which includes the RAR message along with the calculated TA values. This confirms that the UE (201) is synchronized with the target cell. Additionally, if the RACH is successful in one gap, the UE (201) stores the TA value associated with the candidate cell.

[0261] At step S8, the UE (201) sends the L1 based LTM measurement report to the source network apparatus (202). At step S9, the source network apparatus (202) triggers the LTM cell switch process based on the UE's measurement report. At step S10, the source network apparatus (202) provides the LTM cell switch command through the MAC CE to the UE (201). Upon receiving the LTM cell switch command for the pre-measured candidate cell, the UE (201) applies the stored UL TA value and performs the RACH-less LTM cell switch (102) to the target network apparatus (203).

[0262] Further, at step S11, the UE (201) completes the RACH-less LTM cell switch (102) with the target network apparatus (203) and sends an acknowledgment to confirm the successful completion of the LTM cell switch process.

[0263] The proposed invention enables the UE (201) to utilize the unused transceiver, where data is inactive, to perform UL TA synchronization for the LTM candidate cell configured with early UL TA configuration in the UL CA capable device. This solution assists in maintaining service continuity with reduced handover latency or data interruption time.

[0264] Figs. 21A and 21B are block diagrams that illustrate the comparison between the existing system and the proposed invention in relation to the UL TA measurements through the additional transceiver in the UL CA capable UE. Fig. 21A illustrates the UL TA measurements through the additional transceiver in the UL CA capable device according to the prior art.

[0265] At step S1, the UE (201) is equipped with UL CA capability and has multiple UL CC. The multiple UL CC includes ULCC1 (1201a) and UL CC2 (1201b). Further, F1 or Cell 1 (1501) is identified as the LTM candidate with the early TA configuration. At step S2, the UE (201) transmits data to both UL CC1 and UL CC2. During the data transmission, the UE (201) performs the required measurements for uplink synchronization. At steps S3 and S4, the F1 or Cell 1 (1501) measurement criteria are evaluated, and the measurement report triggers the signal to the network apparatus (208) to initiate the handover. At step S5, the network apparatus (208) sends the handover command to the UE (201). At steps S6 and S7, UL synchronization is established between the UE (201) and the target network apparatus (203). Further, the handover completion to the target network apparatus (203) occurs. This process delays the uplink synchronization with the target network apparatus (203), requiring the RACH-based LTM cell switch, which introduces further latency and synchronization inaccuracies.

[0266] In the existing system, the UE (201) does not utilize ULCC1 (1201a) and UL CC2 (1201b) for data transmission. As a result, the UE (201) performs the RACH-based LTM cell switch (106). The HO interruption time takes approximately ~7ms for a successful RACH-based handover.

[0267] Fig. 21B illustrates the UL TA measurements through the additional transceiver in the UL CA capable device according to the proposed invention. At step S1, the UE (201) is equipped with UL CA capability and has multiple UL CC. The multiple UL CC includes ULCC1 (1201a) and UL CC2 (1201b). Further, F1 or Cell 1 (1501) is identified as the LTM candidate with the early TA configuration. At steps S2 and S3, the UE (201) uses ULCC1 (1201a) for data transmission and ULCC2 (1201b) for the LTM ULTA measurements evolution for F1 or Cell 1 (1501). At steps S4 and S5, the F1 or Cell 1 (1501) measurement criteria are evaluated, and the measurement report triggers the signal to the network apparatus (208) to initiate the handover.

[0268] At steps S6 and S7, the network apparatus (208) sends the handover command to the UE (201) through the MAC CE. Further, the LTM cell switch completes to the target network apparatus (203) and achieves the handover with minimal service interruption of approximately ~2ms. This efficient handover is achieved through the RACH-less LTM cell switch (102) process, where the UE (201) continues to use ULCC1 (1201a) for data transmission while ULCC2 (1201b) handles the evolution of the LTM ULCA measurements. The UE (201) performs these ULCA measurements for the LTM candidate before executing the cell switch, enabling a smooth transition without the need for the RACH procedure.

[0269] Fig.22A illustrates the LTM Latency cell switch process according to the prior art. At step S1, the process begins with the LTM candidate configuration is initiation, where the network configures the candidate cell. This step includes the RRC signaling, taking time denoted as 'TRRC' (1301). Further, the 'TRRC' (1301) refers to the time taken for the RRC signaling to configure the candidate cell.

[0270] At step S2, once the LTM candidate is configured, the process moves to a Transmission configuration indicator (TCI) state is activation, requiring a Transmission configuration indicator Mode (TCMD) (1302) time for processing the DL Synchronization for the candidate cell. At step S3, the UE (201) reconfiguration is processed. During the UE (201) reconfiguration phase, the UE (201) processes the received RRC reconfiguration messages, including two components such as 'TLTM-RRC-Processing' (1303) and a 'TLTM-Processing' (1304).The 'TLTM-RRC-Processing' (1304) Time for RRC-level processing and the TLTM-Processing (1304) time for additional internal UE (201) reconfiguration to prepare for the switch.

[0271] At step S4, the UE (201) then initiates tracking the target cells time and frequency parameters which includes a 'TFIRST-RS' (1305) time and a 'TRS-proc ' (1306) time. The TFIRST-RS (1305) time for detecting the first Reference Signal (RS). The 'TRS-proc' (1306) time needed for processing these signals to achieve synchronization. At step S5, the UE (201) performs the uplink synchronization with the target network apparatus (203). The 'TLTM-UL' (1307) time for initiating the uplink communication using the preamble and a TRAR (1308) time for receiving and processing the RAR. At step S6, the process achieves with the transmission of data using the indicated beam on the new cell, with a 'Tfirst-data' (1309) representing the time required to transmit the first data packet under the updated TCI state.

[0272] Fig.22B illustrates the LTM Latency cell switch process according to proposed invention. At step S1, the process begins with the LTM candidate configuration is initiation, where the network configures the candidate cell. This step includes the RRC signaling, taking time denoted as TRRC (1301). Further, the 'TRRC' (1301) refers to the time taken for the RRC signaling to configure the candidate cell. At step S2, once the LTM candidate is configured, the process moves to the TCI state is activation, requiring the TCMD (1302) time for processing and DL Synchronization for the candidate cell. The proposed solution performs the UL TA measurements in the advance and eliminates the need for the RACH-based uplink synchronization. At step S3, the UE (201) then initiates the UL synchronization with the RAR and the preamble. At step S4, the UE directly applies a new configuration parameter for the target cell, skipping the RACH process. This process significantly reduces the handover delays and eliminates potential RACH failure At step S5, the UE (201) starts data transmission and reception on the new cell with minimal interruption. The interruption time is reduced to approximately ~2ms, which is about 1 / 3rd of the RACH-based process.

[0273] The proposed invention significantly reduces the handover interruption time, improves reliability, and enhances the service continuity compared to the existing RACH-based handover process. The proposed RACH-less handover enhances the overall user experience by eliminating the RACH process, ensuring negligible delays during the handover and providing an almost interruption-free experience. This is particularly advantageous for an Ultra-Reliable Low-Latency Communication (URLLC) use cases, where connectivity is important for maintaining the reliability and responsiveness of applications. Additionally, the proposed invention reduces the probability of handover failures by avoiding potential issues associated with the RACH process, thus improving service continuity.

[0274] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a user equipment (UE) for evaluating uplink timing advance (UL TA) measurement for one or more LTM (Lower Layer Triggered Mobility) candidate cells, the method comprising:initiating a UL TA measurement during one of a multi-subscriber identity module (MUSIM) gap, a connected discontinuous reception (CDRX) cycle, a Layer 3 (L3) measurement gap, or a transmission (TX) when an uplink carrier aggregation (CA) capable device is configured;determining a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in a connected mode;receiving a cell switch command from a network apparatus based on the performance of a L1 measurement report for the one or more LTM candidate cells;initiating the cell switch command based on signal measurement for one or more conditional LTM candidate cells; andtriggering a random access channel-less (RACH-less) LTM cell switch or handover based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells.2.The method of claim 1, wherein initiating the UL TA measurement during the MUSIM gap comprises:generating a request message by adding UE assistance information with a MUSIM gap preference list;transmitting a request message to the network apparatus for a MUSIM gap configuration, wherein the MUSIM gap configuration includes periodic and aperiodic gaps;receiving a response message from the network apparatus, wherein the response message comprises the MUSIM gap; andperforming the UL TA measurement by initiating a random-access channel (RACH) procedure for the one or more LTM or Conditional LTM candidate cells during the MUSIM gap configuration.3.The method of claim 2, further comprising:determining whether the RACH procedure is successful within at least one configured MUSIM gap provided in the MUSIM gap configuration; andperforming one of:storing a UL TA value associated with the one or more LTM candidate cells when the RACH procedure is successful within at least one configured MUSIM gap, andattempting a RACH procedure in a subsequent MUSIM gap when the RACH procedure is unsuccessful, and applying the stored UL TA value for the one or more LTM or Conditional LTM candidate cells to perform the RACH-less LTM cell switch or handover.4.The method of claim 1, wherein initiating the UL TA measurement during the CDRX cycle comprises:configuring an early UL TA configuration for the LTM candidate cells;receiving a CDRX message from the network apparatus, wherein the CDRX message comprises CDRX cycles;determining whether the UL TA measurement can be performed during a CDRX sleep time based on the CDRX cycles; andperforming the UL TA measurement by initiating a RACH procedure with the one or more LTM or Conditional LTM candidate cells based on the CDRX sleep time.5.The method of claim 1, wherein initiating the UL TA measurement during the L3 measurement gap comprises:configuring the early UL TA configuration for the LTM candidate cells;transmitting a request message to the network apparatus for a LTM evaluation for the one or more candidate LTM or Conditional LTM cells, wherein the request message comprises the UE assistance information;receiving a RRC reconfiguration message from the network apparatus, wherein the RRC reconfiguration message comprises measurement configuration information to conduct L3 measurement, wherein the measurement configuration information comprising the L3 measurement gap; andperforming the UL TA measurement by initiating a RACH procedure for the one or more LTM candidate cells during the L3 measurement gap.6.The method of claim 5, further comprising:determining whether the RACH procedure is successful within the configured L3 measurement gap; andperforming one of:storing a UL TA value associated with the one or more LTM or Conditional LTM candidate cells when the RACH procedure is successful within the L3 measurement gap, andattempting a RACH procedure in a subsequent measurement gap when the RACH procedure is unsuccessful within the L3 measurement gap, and applying the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM or Conditional LTM cell switch or handover.7.The method of claim 1, wherein initiating the UL TA measurement during the TX when the UL CA-capable device is configured comprises:configuring an early UL TA configuration for the LTM candidate cells;determining an unused TX in the UL CA-capable device during LTM evaluation; andperforming the UL TA measurement by initiating a RACH procedure for the one or more LTM candidate cells using the unused TX.8.The method of claim 7, comprises:determining whether the RACH procedure is successful using the unused TX; andperforming one of:storing a UL TA value associated with the one or more LTM or Conditional LTM candidate cells when the RACH procedure is successful within a configured measurement gap, andattempting a RACH procedures in a subsequent measurement gap when the RACH procedure is unsuccessful using the unused TX, and applying the stored UL TA value for the one or more LTM candidate cells to perform the RACH-less LTM cell switch or handover.9.A method performed by a network apparatus for evaluating uplink timing advance (UL TA) measurement for one or more LTM (Lower Layer Triggered Mobility) candidate cells, the method comprising:initiating an UL TA measurement during one of a multi-subscriber identity module (MUSIM) gap, a connected discontinuous reception (CDRX) cycle, a Layer 3 (L3) measurement gap, or a transmission (TX) when an uplink carrier aggregation (CA) capable device is configured;determining a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in a connected mode;transmitting a cell switch command based on the performance of the L1 measurement report or the one or more LTM or Conditional LTM candidate cells; andenabling a random access channel-less (RACH-less) LTM cell switch or handover based on a UL TA measurement for the one or more LTM or Conditional LTM candidate cells.10.A UE for evaluating an Uplink Timing Advance (UL TA) for LTM candidate cells to enhance handover and cell switch performance, comprising:a memory;a processor; andan UL TA measurement controller coupled to the memory and the processor, and configured to:initiates a UL TA measurement during one of a multi-subscriber identity module (MUSIM) gap, a connected discontinuous reception (CDRX) cycle, a Layer 3 (L3) measurement gap, or a transmission (TX) when an uplink carrier aggregation (CA) capable device is configured,determines a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in a connected mode,receives a cell switch command from a network apparatus based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells,initiate the cell switch command based on signal measurement for one or more conditional LTM candidate cells, andtriggers a random access channel-less (RACH-less) LTM cell switch or handover based on the performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells.11.The UE of claim 10,wherein the UL TA measurement controller is further configured to:generate a request message by adding UE assistance information with a MUSIM gap preference list,transmit a request message to the network apparatus for a MUSIM gap configuration, wherein the MUSIM gap configuration includes periodic and aperiodic gaps,receive a response message from the network apparatus, wherein the response message comprises the MUSIM gap, andperform the UL TA measurement by initiating a random-access channel (RACH) procedure for the one or more LTM or Conditional LTM candidate cells during the MUSIM gap configuration.12.The UE of claim 10,wherein the UL TA measurement controller is further configured to:configure an early UL TA configuration for the LTM candidate cells,receive a CDRX message from the network apparatus, wherein the CDRX message comprises CDRX cycles;determine whether the UL TA measurement can be performed during a CDRX sleep time based on the CDRX cycles, andperform the UL TA measurement by initiating a RACH procedure with the one or more LTM or Conditional LTM candidate cells based on the CDRX sleep time.13.The UE of claim 10,wherein the UL TA measurement controller is further configured to:configure the early UL TA configuration for the LTM candidate cells,transmit a request message to the network apparatus for a LTM evaluation for the one or more candidate LTM or Conditional LTM cells, wherein the request message comprises the UE assistance information,receive a RRC reconfiguration message from the network apparatus, wherein the RRC reconfiguration message comprises measurement configuration information to conduct L3 measurement, wherein the measurement configuration information comprising the L3 measurement gap, andperform the UL TA measurement by initiating a RACH procedure for the one or more LTM candidate cells during the L3 measurement gap.14.A network apparatus for evaluating an Uplink Timing Advance (UL TA) for LTM candidate cells to enhance handover and cell switch performance, comprising:a memory ;a processor; andan UL TA measurement controller coupled to the memory and the processor, and configured to:initiates UL TA measurement during one of a multi-subscriber identity module (MUSIM) gap, a connected discontinuous reception (CDRX) cycle, a Layer 3 (L3) measurement gap, or a transmission (TX) when an uplink carrier aggregation (CA) capable device is configured,determines a performance of the UL TA measurement for the one or more LTM or Conditional LTM candidate cells in a connected mode,transmits a cell switch command from a network apparatus based on the performance of theL1 measurement report or the one or more LTM or Conditional LTM candidate cells, andenables a random access channel-less (RACH-less) LTM cell switch or handover based on a UL TA measurement for the one or more LTM or Conditional LTM candidate cells.

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