Downlink and uplink synchronization for layer-3 measurement based conditional-layer1 / layer2 triggered mobility

Abstract

Embodiments of the disclosure describe a method for Downlink (DL) and Uplink (UL) Synchronization for Layer-3 measurement based Conditional-Layer1 / Layer2 Triggered Mobility (C-LTM). The method includes configuring a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level. The method includes transmitting, by the gNB-CU, beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information of one or more LTM candidate cells to a serving gNB-DU. The method includes continuously monitoring one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU. The method includes determining whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization. The method includes initiating, by the gNB-CU, the DL synchronization in response to meeting the first predefined criteria.

Description

DOWNLINK AND UPLINK SYNCHRONIZATION FOR LAYER-3 MEASUREMENT BASED CONDITIONAL-LA YER1 / LAYER2 TRIGGERED MOBILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to Indian Provisional Application No. 202511009520, filed on February 5, 2025, and to Indian Non-Provisional Application No. 202511009520, filed on October 8, 2025, the entire contents of which are incorporated herein by reference.FIELD

[0002] The present disclosure relates to Downlink (DL) and Uplink (UL) Synchronization for Layer-3 measurement based Conditional-Layerl / Layer2 Triggered Mobility (C-LTM).BACKGROUND

[0003] The information disclosed in this background section is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

[0004] Layer 1 / Layer 2 Triggered Mobility (LTM), introduced in Release 18, presents significant advancements in reducing handover latency and minimizing interruption times when compared to traditional Layer 3-based mobility solutions. However, the initial implementation of the LTM in the Release 18 has certain limitations, such as the lack of support for an inter-Central Unit (CU)LTM. The objective of the Release 19 work item is to address and mitigate these constraints, thereby enhancing the overall mobility framework.

[0005] In the context of the LTM, a disaggregated or split architecture defined by the Third Generation Partnership Project (3GPP) delineates a decomposition of a gNodeB (gNB) into multiple logical entities. This architecture allows a single Distributed Unit (DU) to manage multiple cells, with a maximum capacity of 512 cells as specified in current standards. Within this disaggregated architecture, a gNB-Central Unit-Control Plane (gNB-CU-CP) is configured to host Packet Data Convergence Protocol (PDCP-c) and Radio Resource Control (RRC) layers, a gNB-Central Unit-User Plane (gNB-CU-CP) is configured to host Packet Data Convergence Protocol (PDCP-u) and Service Data Adaptation Protocol(SDAP) layers, while the glNB-DU accommodates the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers. The scheduling operations are executed at the gNB-DU, ensuring efficient resource allocation and management across a network.SUMMARY

[0006] This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the disclosure. This summary is neither intended to identify key or essential inventive concepts of the disclosure nor is it intended to determine the scope of the disclosure.

[0007] According to one embodiment of the present disclosure, a method is disclosed. The method includes configuring, by a gNodeB Centralized Unit (gNB-CU), a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level. The method furtherincludes transmiting, by the gNB-CU, beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information of one or more LTM candidate cells to a serving gNB-DU. The beam ID to TCI state mapping information is associated with one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU). The beam ID to TCI state information mapping enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells. This enables the UE to perform a C-LTM cell switch efficiently with reduced latency. The method further includes continuously monitoring, by the gNB-CU, one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU. The method further includes determining, by the gNB-CU, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization. The method further includes initiating, by the gNB-CU, the DL synchronization by transmitting information to the serving gNB-DU. The transmission information comprising at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE-reported periodic layer 3 measurements in response to meeting the first predefined criteria.

[0008] According to one embodiment of the present disclosure, a method is disclosed. The method includes determining, by a gNodeB Centralized Unit (gNB-CU), whether one or more beam-level L3 measurements of a Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization. The method further includes initiating, by the gNB-CU, the UL synchronizationfor a User Equipment (UE) by transmitting information of the candidate cell to the gNB-DU to trigger a Physical Downlink Control Channel (PDCCH) order for the UL synchronization to the UE, in response to meeting the second predefined criteria.

[0009] According to one embodiment of the present disclosure, a gNodeB Centralized Unit (gNB-CU) is disclosed. The gNB-CU configures a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level. The gNB-CU transmits beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information of one or more LTM candidate cells to a serving gNB-DU. The beam ID to TCI state mapping information is associated with the one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU). The beam ID to TCI state information mapping enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells. This enables the UE to perform a C-LTM cell switch efficiently with reduced latency. The gNB-CU continuously monitors one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU. The gNB-CU determines whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization. The gNB-CU initiates the DL synchronization by transmitting information to the serving gNB-DU. The transmission information comprising at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE-reported periodic layer 3 measurements in response to meeting the first predefined criteria.

[0010] According to one embodiment of the present disclosure, a gNodeB Centralized Unit (gNB-CU) is disclosed. The gNB-CU determines whether one or more beam-level L3 measurements of a Conditional -Lay erl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization. The gNB-CU initiates the UL synchronization for a User Equipment (UE) by transmitting information of the candidate cell to the gNB-DU to trigger a Physical Downlink Control Channel (PDCCH) order to the UE for the UL synchronization, in response to meeting the second predefined criteria.

[0011] According to one embodiment of the present disclosure, a non-transitory computer-readable medium stores instructions. The one or more instructions are executed by a gNodeB Centralized Unit (gNB-CU) that comprises one or more processors. The one or more processors configure a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level. The one or more processors transmit beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information of one or more LTM candidate cells to a serving gNB-DU. The beam ID to TCI state mapping information is associated with the one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU). The beam ID to TCI state information mapping enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells. This enables the UE to perform a C-LTM cell switch efficiently with reduced latency. The one or more processors continuously monitor one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU. The one or more processors determine whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cellmeets a first predefined criteria for a Downlink (DL) synchronization. The one or more processors initiate the DL synchronization by transmitting information to the serving gNB-DU. The transmission information comprising at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE-reported periodic layer 3 measurements in response to meeting the first predefined criteria.

[0012] To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will be rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting of its scope. The disclosure will be described and explained with additional specificity and detail in the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Features, aspects, and advantages of embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and wherein:FIG. 1 illustrates a disaggregated gNodeB (gNB)architecture, according to related art; FIG. 2 is a sequence flow diagram illustrating a signalling procedure for a Layerl / Layer 2 Triggered Mobility (LTM), according to related art;FIGS. 3-4 are sequence flow diagrams illustrating a signalling procedure for Downlink (DL) and Uplink (UL) Synchronization for Layer-3 measurement based ConditionaL Layerl / Layer2 Triggered Mobility (C-LTM), according to an embodiment as disclosed herein;FIG. 5 is a flow diagram illustrating a method for initiating the DL synchronization, according to an embodiment as disclosed herein;FIG. 6 is a flow diagram illustrating a method for transmitting a first Fl message to the serving gNB-DU to initiate the DL synchronization for the UE, according to an embodiment as disclosed herein;FIG. 7 is a flow diagram illustrating a method for initiating the UL synchronization, according to an embodiment as disclosed herein; andFIG. 8 illustrates a diagram of example components of an apparatus, according to an embodiment as disclosed herein.DETAILED DESCRIPTION

[0014] The following detailed description of example embodiments refers to the accompanying drawings. The present disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the present disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowchart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments, one or more operations may be omitted, one or more operations may be added, or one or more operations may be performed simultaneously (at least in part).

[0015] It will be apparent that systems and / or methods, described herein, may be implemented in different forms of hardware, software, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and / or methods should not limit their implementations. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It is understood that software and hardware may be designed to implement the systems and / or methods based on the description herein.

[0016] Even though particular combinations of features are recited in the claims and / or disclosed in the specification, the particular combinations are not intended to limit the disclosure of implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and / or disclosed in the specification. Even if a dependent claim directly depends on only one claim, the present disclosure may indicate that the dependent claim is dependent on other claims in the claim set.

[0017] No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” (in other words, nouns not mentioned in the plural) are intended to include one or more items, and may be used interchangeably with “one or more.” Also, as used herein, the terms “has,” “have,” “having,” “include,” “including,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Furthermore, expressions such as “at least one of [A] and [B],” “[A] and / or [B],” or “at least one of [A] or [B]” are to be understood as including only A, only B, or both A and B.

[0018] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

[0019] Throughout this disclosure, the term “serving gNB-DU” is the one that is actively providing a radio connection to a UE. The serving gNB-DU handles the UE’s data traffic and manages the lower layers of the radio protocol stack, including the Medium Access Control (MAC), Radio Link Control (RLC), and Physical (PHY) layers.

[0020] Throughout this disclosure, the term “source gNB-DU” is the serving gNB-DU at the beginning of a handover procedure. The source gNB-DU is the initial point of connection for the UE before the connection is transferred to a new target gNB-DU (e.g., candidate target gNB-DU).

[0021] FIG. 1 illustrates a disaggregated gNodeB (gNB) architecture 100, according to prior art.FIG. 1 illustrates one or more components and interfaces of the gNB in a 5G network. Central to this disaggregated gNB Architecture 100 is a gNB Central Unit (CU) and a gNB Distributed Unit (DU). The gNB-CU is divided into two parts: a gNB-CU Control Plane (CP), which manages signaling, user equipment registration, and mobility management, and a gNB-CU User Plane (UP), responsible for user data transmission to a User Plane Function (UPF). The gNB-DU handles realtime radio signal processing, including channel coding and resource management, allowing for reduced latency by being closer to a radio environment. The disaggregated gNB Architecture 100 may utilize one or more key interfaces, including an El interface that connects the gNB-DU to the gNB-CU, and Fl interfaces, with Fl -C managing control signaling and Fl -U facilitating user data transfer between the two units.

[0022] In order to support L1 / L2 triggered mobility (i.e., change of serving cell) in the disaggregated gNB architecture 100, a new mechanism is needed in which Handover (HO) preparation may take place at the gNB-CU-CP, but executed autonomously by the gNB-DU, without further interaction with the upper layers.

[0023] The primary objective of a Work Item (WI) is to define support for Conditional LTM (C-LTM) across Radio Access Network (RAN) 2, RAN3, and RANI. This involves establishing the conditions evaluated by a User Equipment (UE) that trigger the activation of the LTM. The focus is on facilitating the C-LTM, which includes subsequent LTM processes, while prioritizing intraCentral Unit (CU) LTM implementations. Additionally, a review checkpoint for this objective is scheduled at RAN 105, and activities within the RAN Working Group may not commence prior to this checkpoint.

[0024] In the context of the NR, mobility has evolved over several releases. Conditional Hand-Over (CHO) and other conditional mobility procedures (e.g., Conditional PSCell Change (CP AC), Subsequent Conditional PSCell Change (SCPAC), etc.) were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signalling exchange with a source cell beforehand. The LTM, as introduced in Release- 18, offers a short interruption time but not with the same level of robustness as the conditional L3 mobility procedures. In Release-19, enhancements should be specified so that the system may benefit from both high robustness and short interruptions.

[0025] The C-LTM is a combination of techniques used for the CHO and the LTM. In C-LTM, the source cell sends a C-LTM configuration of a candidate cell via a Radio Resource Control (RRC) reconfiguration message to the UE, which includes LTM candidate configurations andcorresponding execution conditions. Each candidate cell provides its own execution condition for the C-LTM. In the C-LTM, the UE is configured with one or more LTM candidate cells and specific execution conditions. Once the conditions are satisfied, the UE detaches from the source cell and applies the stored corresponding C-LTM candidate cell configuration for that selected candidate cell. The UE then performs a RACH-less C-LTM handover, provided the UE has acquired the candidate cell timing advance, to the candidate cell and finalizes the procedure by sending an RRC reconfiguration complete message to the target gNB-DU

[0026] According to 3GPP Technical Specification (TS) 38.300, the LTM is a procedure in which the gNB receives LI measurement report(s) from the UE, and on this basis, the gNB may change a UE serving cell by a cell switch command signalled via a Medium Access Control (MAC) Control Element (MAC CE). The cell switch command indicates an LTM candidate configuration that the gNB previously prepared and provided to the UE through RRC signalling. Then, the UE switches to a target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency. When configured by a network, there is a possibility to activate Transmission Configuration Indicator (TCI) states of one or multiple cells that are different from the current serving cell. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell. This allows the UE to be DL synchronized with those cells, thereby facilitating a faster cell switch to one of those cells when the cell switch is triggered. All the activated TCI states except those received in the cell switch command are deactivated upon LTM cell switch execution.

[0027] When configured by the network, there is a possibility to initiate a Uplink Timing Advance Acquisition (UL TA) acquisition (e.g., called an early TA) procedure of one or multiple cells thatare different from the current serving cells. If the cell has the same TA as the current serving cell or TA=0, an early TA acquisition procedure is not required. The network may request the UE to perform the early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by a Physical Downlink Control Channel (PDCCH) order as specified in clause 9.2.6 or realized through a UE -based TA measurement as configured by an RRC. In the former case, the gNB / gNB-DU, to which the candidate cell belongs, calculates the TA value and sends it to the gNB / gNB-DU to which the serving cell belongs via the gNB-CU. The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering the LTM cell switch. In the latter case, the UE performs the TA measurement for the candidate cells after being configured by the RRC, but the exact time the UE performs the TA measurement is up to the UE implementation. The UE applies the TA value measured by itself and performs RACH-less LTM upon receiving the cell switch command, if it does not include any valid TA value. The network may also send a TA value in the LTM cell switch command MAC CE without the early TA acquisition.

[0028] Depending on the availability of a valid TA value, the UE performs either the RACH-less LTM or a RACH-based LTM cell switch. If the valid TA value is provided in the cell switch command, the UE applies the TA value as instructed by the network. In the case where UE-based TA measurement is configured, but no valid TA value is provided in the cell switch command, the UE applies the valid TA value by itself, if available. The UE performs the RACH-less LTM cell switch upon receiving the cell switch command whenever a valid TA value is available. If no valid TA value is available, the UE performs the RACH-based LTM cell switch.

[0029] In the context of handover execution, the cell switch command is conveyed in the MAC CE, which contains the necessary information to perform the LTM cell switch. The overall procedure for the LTM is shown in FIG. 2. Subsequently, the LTM is performed by repeating the early synchronization, LTM cell switch execution, and LTM cell switch completion steps without releasing other LTM candidate configurations after each LTM cell switch completion.

[0030] FIG. 2 is a sequence flow diagram illustrating a signalling procedure 200 for the LTM, according to prior art. The sequence flow diagram includes several operations outlined as follows.

[0031] At operation-201, the UE 200a sends a measurement report message to the gNB 200b, wherein the UE 200a is in an RRC connected mode. The gNB 200b decides to configure the LTM and initiates LTM preparation. At operation-202, the gNB 200b transmits an RRC reconfiguration message to the UE 200a, including the LTM candidate configurations of the one or more LTM candidate cells. The assumption here is that the LTM candidate cell preparation happens between the gNB-CU and one or more gNB-DU. At operation-203, the UE 200a stores the LTM candidate configurations and transmits an RRC reconfiguration complete message to the gNB 200b.

[0032] At operation-204a, the UE 200a performs the DL synchronization with the LTM candidate cell(s) before receiving the cell switch command. The UE 200a may activate the TCI states of the LTM candidate cell(s), as triggered by the gNB 200b. At operation-204b, the UE 200a may perform the UL synchronization with the LTM candidate cell(s) before receiving the cell switch command, by using the UE-based TA measurement, if configured, and / or by transmitting a RACH preamble towards the candidate cell, as triggered by the gNB 200b. When the UE-based TA measurement is configured, the UE 200a acquires the TA value(s) of the candidate cell(s) by measurement. The UE 200a performs the early TA acquisition with the candidate cell(s) asrequested by the network before receiving the cell switch command as specified in clause 9.2.6. This is performed via a Contention-Free Random Access (CFRA) triggered by a PDCCH order from the source cell, following which the UE 200a sends a RACH preamble towards the indicated candidate cell. In order to minimize the data interruption of the source cell due to CFRA towards the candidate cell(s), the UE 200a does not receive a random access response from the network for the purpose of TA value acquisition, and the TA value of the candidate cell is sent to the source gNB-DU via the gNB-CU and is indicated in the cell switch command to the UE 200a. The UE 200a does not maintain a Timing Advance (TA) timer for the candidate cell and relies on network implementation to guarantee the TA validity.

[0033] At operation-205, the UE 200a performs LI measurements on the configured LTM candidate cell(s) and transmits LI measurement reports to the gNB 200b. LI measurement should be performed as long as RRC reconfiguration (operation 202) is applicable. At operation-206, the gNB 200b decides to execute a cell switch to a target cell. The gNB 200b transmits an LTM cell switch command MAC CE triggering cell switch by including a target configuration ID which indicates an index of the candidate configuration of the target cell, a beam indicated with a TCI state or beams indicated with DL and UL TCI states, and a timing advance command for the target cell, if available. The UE 200a switches to the target cell and applies the candidate configuration indicated by the target configuration ID.

[0034] At operation-207, the UE 200a performs the random access procedure towards the target cell, if the UE 200a does not have a valid TA of the target cell as specified in clause 5.18.35 of TS 38.321 [6], At operation-208, the UE 200a completes the LTM cell switch procedure by sending the RRC reconfiguration complete message to the target cell. If the UE 200a has performed theRA procedure in operation 207, the UE 200a considers that LTM cell switch execution is successfully completed when the random access procedure is successfully completed. For the RACH-less LTM, the UE 200a considers that the LTM cell switch execution is successfully completed when the UE 200a determines that the network has successfully received its first UL data.

[0035] The operations 204-208 may be performed multiple times for subsequent LTM cell switch executions using the LTM candidate configuration(s) provided in operation 202.

[0036] In addition, the procedure over the air interface described in FIG. 2 applies to both intra-gNB-DU LTM and inter-gNB-DU LTM. The overall LTM procedures over the Fl -C interface are captured in TS 38.401 [4], Due to the above-mentioned various functionalities or operations, the LTM may offer several advantages. For instance, the LTM enhances network efficiency by allowing quicker handovers between cells, reducing latency, and improving user experience during calls or data sessions. The LTM optimizes resource allocation, enabling better management of bandwidth and reducing congestion. Additionally, the LTM supports seamless connectivity for users on the move, ensuring consistent service quality. By operating at lower layers, the LTM minimizes the overhead associated with higher-layer protocols, leading to faster response times and improved overall system performance.

[0037] In the context of the C-LTM, the following agreements were established in RAN2#127bis: the supporting RACH-less Conditional intra-CU LTM and early Timing Advance (TA) acquisition ordered by PDCCH for conditional LTM.

[0038] The following agreements were established in RAN2 128: the triggering condition for conditional LTM can be based on Layer 3 (L3) measurements, with conditions CondEventA3 andCondEventA5 serving as the baseline for executing conditional LTM. The network can also configure various measurement reports, such as LI periodic, semi-persistent, aperiodic, and event-triggered reports, or L3 measurement reports for conditional LTM to trigger early RACH ordered by PDCCH. For C-LTM, the Candidate Cell TCI States activation / deactivation MAC Control Element (CE) is reused for quickly activating or deactivating TCI states of a candidate configuration. Condition evaluation occurs at the MAC level for LI -based conditional LTM and at the RRC level for L3 -based conditional LTM.

[0039] For RACH-less C-LTM, both UL and DL synchronization must be performed, regardless of whether the method is LI -based or L3 -based.

[0040] In LI -based C-LTM:a. The UL synchronization relies on the UE’s LI measurement reports. When the criteria for acquiring a candidate cell’s TA are met, the serving gNB-DU sends a PDCCH order to the UE, including the cell ID.b. For the DL synchronization, based on the received measurements, TCI states of one or more cells different from the current serving cell can be activated. The UE receives a DL MAC CE to synchronize with these cells, allowing for a quicker switch when needed. All activated TCI states, except those indicated in the cell switch command, are deactivated during the LTM cell switch. When using LI measurements, the Cell Radio Identifier (CRI) or SSB ID maps to the target cell’s TCI state, and this information is communicated to the UE by the source DU using the MAC CE for DL synchronization.

[0041] For instance, consider a scenario where a user is traveling on a high-speed train while streaming videos on a smartphone. As the train moves through different regions, maintaining seamless connectivity becomes essential to ensure uninterrupted video playback. Initially, the smartphone connects to the nearest cell (e g., gNB-DU) using the DL and UL synchronization, providing a stable connection for streaming. However, as the train approaches a new area with better network coverage from a different cell, the network must facilitate a quick transition to this new cell without disrupting the user’s experience. To achieve this, the network utilizes RACH-less C-LTM, allowing for a faster switch between cells. Early TA acquisition enables the connection to the new cell to be established before the current connection is lost. The smartphone continuously sends LI measurement (e g., Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Signal-to-Interference-plus-Noise Ratio (SINR), etc.) reports to the network, indicating signal strength and quality. Once the network determines that the signal from the new cell meets the necessary criteria for a successful transition, it sends a PDCCH order to the smartphone, including the new LTM candidate cell ID. During the synchronization process, the UL synchronization is initiated based on the LI measurement reports, allowing the smartphone to communicate with the candidate cell. Simultaneously, the DL synchronization activates TCI states for the candidate cell, ensuring that the smartphone can receive reference signals from this cell. The DL MAC CE is sent to synchronize the smartphone with the candidate cell. As the train approaches the candidate cell, the smartphone switches to this cell seamlessly, maintaining the video stream without buffering or loss of connectivity.

[0042] Despite the above-mentioned advantages, several challenges / problems / limitations are encountered in the existing Ll-based C-LTM, which are mentioned below.

[0043] The LI measurement(s) cannot always be guaranteed due to the inability of some devices to perform the LI measurement.

[0044] For instance, consider a scenario where some User Equipment (UE), particularly simpler or low-cost loT devices, may lack the hardware or software capabilities required for frequent or continuous LI measurements. Additionally, continuous LI measurements demand considerable resources, making them unsuitable for UEs with strict energy-saving requirements, such as NB-loT, which may prefer higher-layer conditions that consume less power. Furthermore, in certain modes, such as IDLE or power-saving, devices may not have access to real-time LI measurement data.

[0045] To address the above-mentioned challenges / problems / limitations, a disclosed method provides a unique strategy for the DL and the UL synchronization for the Layer-3 measurementbased C-LTM, as described in conjunction with FIG.3 to FIG. 8. Not all devices can consistently perform or report LI measurements for triggering conditions. This situation compels the network to design to incorporate L3-based measurements as an alternative. For instance, consider a scenario associated with a handover trigger. The handover trigger may require monitoring when the RSRP falls below a certain threshold (e.g., an LI condition). If the UE cannot reliably measure the RSRP at the LI due to limitations, the trigger could instead depend on an L3 event like “Event A3”, which occurs when a neighboring cell becomes better than the serving cell. As a result, the network utilizes the L3-based C-LTM to ensure continued connectivity. This approach allows the network to manage the transition effectively, even when LI reports are unavailable.

[0046] The L3-based C-LTM offers several advantages that enhance network performance and device compatibility. First, the L3-based C-LTM allows networks to support a wider range ofdevices, including low-cost loT equipment that may not have advanced LI measurement capabilities. This ensures seamless operation across diverse hardware. Additionally, using higher-layer conditions helps reduce power consumption, which is especially important for energysensitive devices like Narrowband Internet of Things (NB-IoT).

[0047] The L3 -based C-LTM may be used when devices are in power-saving modes, maintaining functionality even without real-time LI measurements. This simplifies network management by providing a consistent measurement framework and allows for more flexible triggering mechanisms, such as “Event A3”. Additionally, the L3-based measurements may lower operational costs by reducing the need for high-end hardware in user devices, making it more economical to deploy networks with varied device capabilities. Moreover, the L3-based C-LTM may enhance interoperability, ensuring that triggers work effectively across different network types and standards, which is vital for a cohesive user experience.

[0048] Referring now to the drawings, and more particularly to FIGS. 3 to 8, where similar reference characters denote corresponding features consistently throughout the figures, their preferred embodiments are shown.

[0049] FIGS. 3-4 are sequence flow diagrams illustrating a signalling procedure (hereinafter referred to as “method 300”) for the DL and UL synchronization for the Layer-3 measurementbased C-LTM, according to an embodiment as disclosed herein. The method 300 may execute multiple operations to maintain / manage TA during the C-LTM, which are given below. The signaling procedure involves multiple entities, specifically a UE 300a, a source gNB-DU 300b, a candidate gNB-DU 300c, and a gNB-CU 300d.

[0050] In the signaling procedure, at an initial stage, user data travels from the UE 300a to the source gNB-DU 300b and is then forwarded by the source gNB-DU 300b to the gNB-CU 300d (e.g., gNB-CU-UP) for processing and onward transmission to the core network.

[0051] At operation-301, the procedure initiates with the execution of one or more operations pertaining to Layer 3 (L3) measurement control and reporting procedure. The operation-301 is critical for assessing the quality of the radio environment. At operation-302, the gNB-CU 300d evaluates and makes a decision regarding the addition of an LTM candidate cell, based on the L3 measurement report received from the UE 300a. At operation-303, the gNB-CU 300d issues a UE context setup request to the candidate gNB-DU 300c to prepare the LTM candidate cell configuration. This request is essential for establishing the context necessary for the UE’s LTM cell switch operation in the candidate gNB-DU 300c. At operation-304, the candidate gNB-DU 300c responds to the gNB-CU 300d with a UE context setup response. This UE context setup response returns the LTM candidate cell configuration and confirms the successful establishment of the UE context in the candidate gNB-DU 300c.

[0052] At operation-305, following the context setup, the gNB-CU 300d sends a UE context modification request to the source gNB-DU 300b. This UE context modification request is aimed at modifying the existing UE context to notify the prepared LTM candidate cell configuration and consolidate the source configuration, e.g.: CSI report configuration. At operation-306, the source gNB-DU 300b processes the modification request and sends back a UE context modification response to the gNB-CU 300d, indicating the success or failure of the modification. This message includes the final consolidated CSI report configuration to be sent to the candidate gNB-DU 300c.

[0053] At operation-307, the gNB-CU 300d then transmits a UE context modification request to the candidate gNB-DU 300c. This is necessary to synchronize the CSI-RS-related configuration, as consolidated by the source gNB-DU 300b. At operation-308, the candidate gNB-DU 300c replies with an UE context modification response to the gNB-CU 300d, confirming the acceptance of the modifications made to the UE context. At operation-309, the gNB-CU 300d proceeds to send a downlink RRC message transfer, specifically an RRC Reconfiguration message, to the source gNB-DU 300b. This message is pivotal for sending the prepared LTM candidate cell configuration to the UE 300a. At operation-310, the source gNB-DU 300b forwards the RRC reconfiguration message to the UE 300a, ensuring that the LTM candidate cell configuration provided by the candidate gNB-DU 300c is delivered to the UE 300a.

[0054] At operation-311, the UE 300a acknowledges the successful reconfiguration by transmitting an RRC reconfiguration complete message back to the source gNB-DU 300b. At operation-312, the source gNB-DU 300b sends an uplink RRC message transfer to the gNB-CU 300d that contains the RRC message from the UE 300a, completing the signaling procedure and ensuring that all entities are synchronized with the LTM candidate cell configuration.

[0055] At operation-313, the UE 300a sends a periodic or event based L3 measurement report to the gNB-CU 300d. At operation-314, the gNB-CU 300d determines that the UL and DL synchronization has to be initiated by the UE 300a for the candidate cell. At operation-315, the gNB-CU 300d sends an F 1 message, which includes a C-LTM candidate Cell ID or a configuration index to which the UL synchronization is to be performed This message may also include the L3 measurements transmitted by the UE 300a. From the DL synchronization perspective, a beam ID of the LTM candidate cell for which the TCI state activation is required at the UE 300a is included.

[0056] At operation-316 and 317, the source gNB-DU 300b transmits the PDCCH order to perform early TA acquisition to the UE 300a, and the UE 300a executes a RACH procedure with the candidate gNB-DU 300c to acquire candidate cell TA. At operation-318, the candidate gNB-DU 300c transmits DU-CU TA information to the gNB-CU 300d. At operation-319, the gNB-CU 300d transmits CU-DU TA information to the source gNB-DU 300b. In other words, the serving gNB-DU 300b receives the UE’s TA of the candidate cell from the gNB-CU 300d (after the UE 300a has performed the RACH procedure). At operation-320, the serving gNB-DU 300b sends the TA and the TCI state activation information in a single MAC CE.

[0057] Herein, in one embodiment, the TA (also known as Timing Advance (TA) value) is associated with the LTM candidate gNB-DU cell from the candidate gNB-DU 300c.

[0058] At operation-321, the UE 300a makes a decision to trigger the C-LTM cell switch when an execution condition is satisfied. At operation-322, the UE 300a executes the RACH-less C-LTM procedure with the identified candidate gNB-DU 300c. At operation-323, the source gNB-DU 300b transmits a DU-CU cell switch notification to the gNB-CU 300d, which includes a target cell identifier (ID) and a Transmission Configuration Indicator (TCI) state ID. At operation-324, in response, the gNB-CU 300d forwards a CU-DU cell switch notification to the candidate gNB-DU 300c, also containing the target cell ID and TCI state ID. It has to be noted here that operations 323 and 324 are feasible only if the UE 300a reports the selected CLTM target cell ID and selected TCI state to the source gNB-DU 300b before executing the CLTM cell switch. At operation-325, concurrently, the source gNB-DU 300b provides a downlink data delivery status update to the gNB-CU 300d.

[0059] At operation-326, the candidate / target gNB-DU 300c detects the UE 300a access / acknowledges the access attempt from the UE 300a. At operation-327, the candidate gNB- DU 300c confirms successful access to the gNB-CU 300d. At operation-328, the UE 300a completes the RRC reconfiguration process by sending an RRC reconfiguration complete message to the candidate gNB-DU 300c. At operation-329, the candidate gNB-DU 300c transmits an uplink RRC message transfer, specifically the RRC reconfiguration complete notification, to the gNB-CU 300d

[0060] At operation-330, the gNB-CU 300d issues a UE context release command to the source gNB-DU 300b to terminate the existing context i.e., to release the LTM configuration. At operation-331, the source gNB-DU 300b acknowledges the release of the UE context by sending a UE context release complete message back to the gNB-CU 300d. As a result, at the final stage, user data travels from the UE 300a to the candidate gNB-DU 300c and is then forwarded by the candidate gNB-DU 300c to the gNB-CU 300d (e g., gNB-CU-UP) for processing and onward transmission to the core network.

[0061] FIG. 5 is a flow diagram illustrating a method 500 for initiating the DL synchronization, according to an embodiment as disclosed herein. The method 500 may execute multiple operations for initiating the DL synchronization, which are given below.

[0062] At operation-501, the method 500 includes configuring, by the gNB-CU 300d, the UE 300a to perform one or more periodic L3 measurements at a beam level. In some example embodiments, the UE 300a is configured with the C-LTM, the gNB-CU 300d is operatively connected to the serving gNB-DLT(e.g., source gNB-DU 300b) and at least one candidate gNB-DU 300c, and the UE 300a is operatively connected to the serving gNB-DU 300b, as illustrated in FIGS. 4-5. Theat least one candidate gNB-DU 300c comprises at least one candidate cell configured for a C-LTM handover for the UE 300a.

[0063] At operation-502, the method 500 includes transmitting, by the gNB-CU 300d, beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information of one or more LTM candidate cells to the serving gNB-DU 300b. The beam ID to TCI state mapping information is associated with the one or more C-LTM candidate cells of the at least one candidate gNB-DU 300c.

[0064] In some example embodiments, the beam ID to TCI state mapping information enables the serving gNB-DU 300b to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE 300a to perform a C-LTM cell switch.

[0065] In some example embodiments, the beam ID to TCI state mapping information may include, for example, but is not limited to, Channel State Information Reference Signal (CSLRS) resource identifiers or Synchronization Signal Block (SSB) identifiers corresponding to the at least one candidate gNB-DU 300c.

[0066] At operation-503, the method 500 includes continuously monitoring, by the gNB-CU 300d, one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU 300c. At operation-504, the method 500 includes determining, by the gNB-CU 300d, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for the DL synchronization.

[0067] In response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria, at operation-505, the method 500 includes initiating, by the gNB-CU 300d, the DL synchronization by transmitting information to the serving gNB-DU 300b, comprises at least one of the beam Id corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE reported periodic layer3 measurements, as described in conjunction with FIG. 6.Further, a detailed description related to the various operations of FIG. 5 is covered in the description related to FIGS. 3-4 and is omitted herein for the sake of brevity.

[0068] FIG. 6 is a flow diagram illustrating a method 600 for transmitting a first Fl message to the serving gNB-DU 300b to initiate the DL synchronization for the UE 300a, according to an embodiment as disclosed herein. The method 600 may execute multiple operations for initiating the DL synchronization, which are given below.

[0069] At operation-601, the method 600 includes determining, by the gNB-CU 300d, an Identity (ID) of the C-LTM candidate cell and corresponding beam information that is required for TCI state activation based on the one or more beam-level L3 measurements.

[0070] At operation-602, the method 600 includes transmitting, by the gNB-CU 300d, a first Fl message to the serving gNB-DU 300b.

[0071] In some example embodiments, the first Fl message indicates the serving gNB-DU 300b to transmit a downlink MAC Control Element (MAC-CE) message to initiate the DL synchronization for the UE 300a.

[0072] In some example embodiments, the downlink MAC-CE message may include, for example, but is not limited to, a candidate Cell ID, a Timing Advance (TA) value, the beam ID, and the one or more optimal TCI states.

[0073] In some example embodiments, the first Fl message may include, for example, but is not limited to, the determined cell ID of the C-LTM candidate cell, the corresponding beam information, and the one or more UE-reported periodic L3 measurements.

[0074] In some example embodiments, the method 600 further includes triggering, by the gNB-DU, DL synchronization towards the UE 300a by indicating the TCI state to be activated for the candidate C-LTM cell using the downlink MAC CE command.

[0075] FIG. 7 is a flow diagram illustrating a method 700 for initiating the UL synchronization, according to an embodiment as disclosed herein. The method 700 may execute multiple operations for initiating the UL synchronization, which are given below.

[0076] At operation-701, the method 700 includes determining, by the gNB-CU 300d, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for the UL synchronization. At operation-702, the method 700 includes initiating, by the gNB-CU 300d, the UL synchronization for the UE 300a in response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria. Further, a detailed description related to the various operations of FIG. 7 is covered in the description related to FIGS. 3-4 and is omitted herein for the sake of brevity.

[0077] In some example embodiments, for initiating the UL synchronization, the method 700 includes transmitting, by the gNB-CU 300d, a second Fl message to the serving gNB-DU 300bto initiate a Physical Downlink Control Channel (PDCCH) order and trigger a Timing Advance (TA) acquisition process, the serving gNB-DU 300b sends the PDCCH order to the UE 300a for initiating the UL synchronization towards a candidate cell, based on the second Fl message.

[0078] In some example embodiments, the second Fl message may include, for example, but is not limited to, the cell ID, the candidate cell configuration index, and the one or more UE-reported periodic L3 measurements.

[0079] For instance, consider a scenario associated with an urban environment where a user is using their smartphone (e.g., the UE 300a) to stream a live concert video. The user is moving through a city park, transitioning from one area to another, which requires seamless connectivity to maintain high-quality video streaming. In this scenario, the gNB-CU 300d plays a crucial role in managing the connection of the UE 300a.

[0080] As the user moves, the gNB-CU 300d configures the UE 300a to perform periodic L3 measurements at the beam level. This means that the UE 300a is constantly checking the quality of the signal from various cells in the vicinity, including the one it is currently connected to and other potential candidate towers nearby. The gNB-CU 300d is connected to the serving gNB-DU 300b, which is responsible for maintaining the user’s connection, as well as the at least one candidate gNB-DU 300c that may offer a better signal.

[0081] While the user enjoys the concert, the gNB-CU 300d sends mapping information that links the beam IDs to TCI state mapping information. This information allows the gNB-DU 300b to quickly identify which candidate cells might provide a stronger signal for the UE 300a. As the UE 300a conducts its periodic L3 measurements, the gNB-CU 300d continuously monitors these readings to evaluate the performance of the candidate cells. As the user moves closer to a differentcell, the L3 measurements indicate that one of the candidate cells meets the predefined criteria (e.g., first predefined criteria and second predefined criteria ) for the DL synchronization and the UL synchronization, via utilizing the first Fl message and the second Fl message, suggesting it can deliver a stronger, more reliable connection.

[0082] In response, the gNB-CU 300d initiates the DL / UL synchronization process by transmitting the relevant beam ID and the L3 measurement data to the serving gNB-DU 300b.This allows the UE 300a to switch seamlessly to the new candidate cell without interrupting the live stream, ensuring that the user continues to enjoy the concert with minimal buffering or quality loss, and enhances user experience in dynamic environments, as one of the advantages of the disclosed method.

[0083] FIG. 8 illustrates a diagram of example components of an apparatus, according to an embodiment as disclosed herein.

[0084] FIG. 8 illustrates a diagram of example components of an apparatus 800, according to an embodiment as disclosed herein. As shown in FIG. 8, the apparatus 800 comprises a processor 810, a memory 820, a storage component 830, an input component 840, an output component 850, a communication interface 860, and a bus 870.

[0085] In some example embodiments, the apparatus 800 may relate to at least one of the UE 300a, the source gNB-DU, and / or service gNB-DU 300b, the candidate gNB-DU 300c, and the gNB-CU 300d

[0086] In some example embodiments, the processor 810, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 810 may be embodied as a multi-core processor, a single core processor, or a combination of oneor more multi-core processors and / or one or more single core processors, a distributed processing system, or the like. The processor 810 may be a Central Processing Unit (CPU), a Graphics Processing Unit (GPU), an Accelerated Processing Unit (APU), an Application-Specific Integrated Circuit (ASIC), or another type of processing component.

[0087] In some example embodiments, the memory 820 includes a non-transitory computer readable medium. Memory 820 includes a Random-Access Memory (RAM), a Read Only Memory (ROM), and / or another type of dynamic or static storage device (e.g., a flash memory, a magnetic memory, and / or an optical memory) that stores information and / or instructions for use by processor 810. The memory 820 comprises machine-readable instructions which are executable by the processor 810. These machine-readable instructions, when executed by the processor 810 cause the processor 810 to perform one or more method steps of an embodiment described above.

[0088] In some example embodiments, the storage component 830 stores information and / or software related to the operation and use of the apparatus 800. For example, the storage component 830 may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, and / or a solid-state disk), a Compact Disc (CD), a Digital Versatile Disc (DVD), a floppy disk, a cartridge, a magnetic tape, and / or another type of non-transitory computer-readable medium, along with a corresponding drive.

[0089] In some example embodiments, the input component 840 is configured to receive information, such as user input. For example, the input component 840 may include, but not be limited to, a touchscreen display, a keyboard, a keypad, a mouse, a button, a switch, and / or a microphone. Additionally, or alternatively, the input component 840 may include a sensor forsensing information (e.g., a Global Positioning System (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0090] In some example embodiments, the output component 850 is configured to provide output information from the apparatus 800. For example, the output component 850 may be, but is not limited to, a display, a speaker, instructions to an external device, and / or one or more Light-Emitting Diodes (LEDs).

[0091] In some example embodiments, the communication interface 860 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 860 can be a wired connection, a wireless connection, or a combination of wired and wireless connections, and can be a direct connection or an indirect connection via a communication network that exists between the apparatus 800 and other devices. In other words, the standard of the communication interface 860 is not limited.

[0092] In some example embodiments, the bus 870 acts as an interconnect between the processor 810, the memory 820, the storage component 830, the input component 840, the output component 850, and the communication interface 860 of the apparatus 800. The bus 870 may include a wired interconnection or a wireless interconnection.

[0093] In some example embodiments, the number and arrangement of components shown in FIG.8 are provided as an example. In practice, the apparatus 800 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 8. Additionally, or alternatively, a set of components (e.g., one or more components) of the apparatus 800 may perform one or more functions described as being performed by another set of components of the apparatus 800. Further, one or more method steps / operations described in anyof the embodiments may be performed utilizing the apparatus 800 in communication with one another.

[0094] Examples of the techniques and apparatus described herein include, but are not limited to, the following enumerated embodiments:[1] A method comprising:configuring, by a gNodeB Centralized Unit (gNB-CU), a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmitting, by the gNB-CU, beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB -Distributed Unit (gNB -DU), to a serving gNB -DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitoring, by the gNB-CU, one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB- DU;determining, by the gNB-CU, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiating, by the gNB-CU, the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE-reported periodic layer 3 measurements.[2] The method as described in [1], wherein initiating the DL synchronization for the UE comprises:determining, by the gNB-CU, an Identity (ID) of the C-LTM candidate cell and corresponding beam information that is required for TCI state activation based on the one or more beam-level L3 measurements; andtransmitting, by the gNB-CU, a first Fl message to the serving gNB-DU, wherein the first Fl message indicates the serving gNB-DU to transmit a downlink MAC Control Element (MAC-CE) message to initiate the DL synchronization for the UE.[3] The method as described in any of [1] to [2], wherein the gNB-DU triggers the DL synchronization towards the UE by indicating the TCI state to be activated for the candidate C-LTM cell using the downlink MAC CE command[4] The method as described in any of [1] to [3], wherein the first Fl message comprises at least one of the determined cell ID of the C-LTM candidate cell, the corresponding beam information, and the one or more UE-reported periodic L3 measurements.[5] The method as described in any of [1] to [4],wherein the downlink MAC-CE message comprises at least one of a candidate Cell ID, a Timing Advance (TA) value, the beam ID, and the one or more optimal TCI states.[6] The method as described in any of [1] to [5], wherein the beam ID to TCI state mapping information comprises at least one of Channel State Information Reference Signal (CSI- RS) resource identifiers or Synchronization Signal Block (SSB) identifiers corresponding to the at least one candidate gNB-DU.[7] The method as described in any of [1] to [6], comprising:determining, by the gNB-CU, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiating, by the gNB-CU, the UL synchronization for the UE.[8] The method as described in any of [1] to [7], wherein initiating the UL synchronization comprises:transmitting, by the gNB-CU, a second Fl message to the serving gNB-DU to initiate a Physical Downlink Control Channel (PDCCH) order and trigger a Timing Advance (TA) acquisition process,wherein the serving gNB-DU sends the PDCCH order to the UE for initiating the UL synchronization towards a candidate cell, based on the second Fl message.[9] The method as described in any of [1] to [8], wherein the second Fl message comprises at least one of a cell Identity (ID) and a candidate cell configuration index, and the one or more UE -reported periodic L3 measurements.

[0010] The method as described in any of [1] to [9],wherein the UE is configured with the C-LTM, the gNB-CU is operatively connected to the gNB-DU and at least one candidate gNB-DU, and the UE is operatively connected to the serving gNB-DU; andwherein the at least one candidate gNB-DU comprises at least one candidate cell configured for a C-LTM handover for the UE.[Hl A method comprising::determining, by a gNodeB Centralized Unit (gNB-CU), whether one or more beamlevel L3 measurements of a Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiating, by the gNB-CU, the UL synchronization for a User Equipment (UE) by transmitting information of the candidate cell to the gNB-DU to trigger a Physical Downlink Control Channel (PDCCH) order for the UL synchronization to the UE.

[0012] A gNodeB Centralized Unit (gNB-CU) configured to:configure a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmit beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layerl / Layer2 Triggered Mobility (C- LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU), to a serving gNB-DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitor one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU;determine whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiate the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCT state of the LTM candidate cell that needs to be activated, and / or the one or more UE- reported periodic layer 3 measurements.

[0013] The gNB-CU as described in

[0012] , wherein to initiate the DL synchronization for the UE, the gNB-CU is configured to:determine an Identity (ID) of the C-LTM candidate cell and corresponding beam information that is required for TCI state activation based on the one or more beam-level L3 measurements; andtransmit a first Fl message to the serving gNB-DU, wherein the first Fl message indicates the serving gNB-DU to transmit a downlink MAC Control Element (MAC-CE) message to initiate the DL synchronization for the UE.

[0014] The gNB-CU as described in any of

[0012] to

[0013] ,wherein the gNB-DU triggers the DL synchronization towards the UE by indicating the TCI state to be activated for the candidate C-LTM cell using the downlink MAC CE command;wherein the first Fl message comprises at least one of the determined cell ID of the C-LTM candidate cell and the corresponding beam information, and the one or more UE- reported periodic L3 measurements; andwherein the downlink MAC-CE message comprises at least one of a candidate Cell ID, a Timing Advance (TA) value, the beam ID, and the one or more optimal TCI states.

[0015] The gNB-CU as described in any of

[0012] to

[0014] ,wherein the beam ID to TCI state mapping information comprises at least one of Channel State Information Reference Signal (CSI-RS) resource identifiers or Synchronization Signal Block (SSB) identifiers corresponding to the at least one candidate gNB-DU;wherein the UE is configured with the C-LTM, the gNB-CU is operatively connected to the gNB-DU and at least one candidate gNB-DU, and the UE is operatively connected to the serving gNB-DU; andwherein the at least one candidate gNB-DU comprises at least one candidate cell configured for a C-LTM handover for the UE.

[0016] The gNB-CU as described in any of

[0012] to

[0015] , wherein the gNB-CU is configured to:determine whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determine that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiate the UL synchronization for the UE.

[0017] The gNB-CU as described in any of

[0012] to

[0016] , wherein to initiate the UL synchronization, the gNB-CU is configured to:transmitting, by the gNB-CU, a second Fl message to the serving gNB-DU to initiate a Physical Downlink Control Channel (PDCCH) order and trigger a Timing Advance (TA) acquisition process,wherein the serving gNB-DU sends the PDCCH order to the UE for initiating the UL synchronization towards a candidate cell, based on the second Fl message.

[0018] The gNB-CU as described in any of

[0012] to

[0017] , wherein the second Fl message comprises at least one of a cell Identity (ID) and a candidate cell configuration index, and the one or more UE-reported periodic L3 measurements.

[0019] A gNodeB Centralized Unit (gNB-CU) configured to:determine whether one or more beam-level L3 measurements of a Conditional- Layerl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; and in response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiate the UL synchronization for a User Equipment (UE).

[0020] A non-transitory computer-readable medium storing instructions, the instructions comprising:one or more instructions that, when executed by an apparatus, the apparatus comprising one or more processors, cause the one or more processors to:configure a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmit beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB -Distributed Unit (gNB-DU), to a serving gNB-DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitor one or more beam-level L3 measurements of a C- LTM candidate cell associated with the at least one candidate gNB-DU;determine whether the one or more beam-level L3 measurements of the C- LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiate the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated, and / or the one or more UE-reported periodic layer 3 measurements.

[0095] The various actions, acts, blocks, steps, or the like in the flow / sequence diagrams may be performed in the order presented, in a different order, or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like may be omitted, added, modified, skipped, or the like without departing from the scope of the disclosure.

[0096] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements can be at least one of a hardware device or a combination of hardware devices and software modules.

[0097] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, variousworking modifications may be made to the method in order to implement the inventive concept as taught herein.

[0098] The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.

[0099] Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0100] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

[0101] 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 thegeneric 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 at least one embodiment, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

CLAIMSWe claim:

1. A method comprising:configuring, by a gNodeB Centralized Unit (gNB-CU), a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmitting, by the gNB-CU, beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU), to a serving gNB-DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitoring, by the gNB-CU, one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB- DU;determining, by the gNB-CU, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiating, by the gNB-CU, the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated and / or the one or more UE-reported periodic layer 3 measurements.

2. The method as claimed in claim 1, wherein initiating the DL synchronization for the UE comprises:determining, by the gNB-CU, an Identity (ID) of the C-LTM candidate cell and corresponding beam information that is required for TCI state activation based on the one or more beam-level L3 measurements; andtransmitting, by the gNB-CU, a first Fl message to the serving gNB-DU, wherein the first Fl message indicates the serving gNB-DU to transmit a downlink MAC Control Element (MAC-CE) message to initiate the DL synchronization for the UE.

3. The method as claimed in claim 2, wherein the gNB-DU triggers the DL synchronization towards the UE by indicating the TCI state to be activated for the candidate C-LTM cell using the downlink MAC CE command.

4. The method as claimed in claim 2, wherein the first Fl message comprises at least one of the determined cell ID of the C-LTM candidate cell, the corresponding beam information, and the one or more UE-reported periodic L3 measurements.

5. The method as claimed in claim 2,wherein the downlink MAC-CE message comprises at least one of a candidate Cell ID, a Timing Advance (TA) value, the beam ID, and the one or more optimal TCI states.

6. The method as claimed in claim 1, wherein the beam ID to TCI state mapping information comprises at least one of Channel State Information Reference Signal (CSI-RS) resource identifiers or Synchronization Signal Block (SSB) identifiers corresponding to the at least one candidate gNB-DU.

7. The method as claimed in claim 1, further comprising:determining, by the gNB-CU, whether the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiating, by the gNB-CU, the UL synchronization for the UE.

8. The method as claimed in claim 7, wherein initiating the UL synchronization comprises:transmitting, by the gNB-CU, a second Fl message to the serving gNB-DU to initiate a Physical Downlink Control Channel (PDCCH) order and trigger a Timing Advance (TA) acquisition process,wherein the serving gNB-DU sends the PDCCH order to the UE for initiating the UL synchronization towards a candidate cell, based on the second Fl message.

9. The method as claimed in claim 7, wherein the second Fl message comprises at least one of a cell Identity (ID) and a candidate cell configuration index, and the one or more UE- reported periodic L3 measurements.

10. The method as claimed in claim 1,wherein the UE is configured with the C-LTM, the gNB-CU is operatively connected to the gNB-DU and at least one candidate gNB-DU, and the UE is operatively connected to the serving gNB-DU, andwherein the at least one candidate gNB-DU comprises at least one candidate cell configured for a C-LTM handover for the UE.

11. A method comprising:determining, by a gNodeB Centralized Unit (gNB-CU), whether one or more beamlevel L3 measurements of a Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefinedcriteria, initiating, by the gNB-CU, the UL synchronization for a User Equipment (UE) by transmitting information of the candidate cell to the gNB-DU to trigger a Physical Downlink Control Channel (PDCCH) order for the UL synchronization to the UE.

12. A gNodeB Centralized Unit (gNB-CU) configured to:configure a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmit beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layer l / Layer2 Triggered Mobility (C- LTM) candidate cells of at least one candidate gNB-Distributed Unit (gNB-DU), to a serving gNB-DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitor one or more beam-level L3 measurements of a C-LTM candidate cell associated with the at least one candidate gNB-DU;determine whether the one or more beam -level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiate the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated, and / or the one or more UE- reported periodic layer 3 measurements.

13. The gNB-CU as claimed in claim 12, wherein to initiate the DL synchronization for the UE, the gNB-CU is configured to:determine an Identity (ID) of the C-LTM candidate cell and corresponding beam information that is required for TCI state activation based on the one or more beam-level L3 measurements; andtransmit a first Fl message to the serving gNB-DU, wherein the first Fl message indicates the serving gNB-DU to transmit a downlink MAC Control Element (MAC-CE) message to initiate the DL synchronization for the UE.

14. The gNB-CU as claimed in claim 13,wherein the gNB-DU triggers the DL synchronization towards the UE by indicating the TCI state to be activated for the candidate C-LTM cell using the downlink MAC CE command,wherein the first F 1 message comprises at least one of the determined cell ID of the C-LTM candidate cell and the corresponding beam information, and the one or more UE- reported periodic L3 measurements, andwherein the downlink MAC-CE message comprises at least one of a candidate Cell ID, a Timing Advance (TA) value, the beam ID, and the one or more optimal TCI states.

15. The gNB-CU as claimed in claim 12,wherein the beam ID to TCI state mapping information comprises at least one of Channel State Information Reference Signal (CSI-RS) resource identifiers or Synchronization Signal Block (SSB) identifiers corresponding to the at least one candidate gNB-DU,wherein the UE is configured with the C-LTM, the gNB-CU is operatively connected to the gNB-DU and at least one candidate gNB-DU, and the UE is operatively connected to the serving gNB-DU, andwherein the at least one candidate gNB-DU comprises at least one candidate cell configured for a C-LTM handover for the UE.

16. The gNB-CU as claimed in claim 12, further configured to:determine whether the one or more beam -level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiate the UL synchronization for the UE.

17. The gNB-CU as claimed in claim 16, wherein to initiate the UL synchronization, the gNB- CU is configured to:transmit, by the gNB-CU, a second Fl message to the serving gNB-DU to initiate a Physical Downlink Control Channel (PDCCH) order and trigger a Timing Advance (TA) acquisition process,wherein the serving gNB-DU sends the PDCCH order to the UE for initiating the UL synchronization towards a candidate cell, based on the second Fl message.

18. The gNB-CU as claimed in claim 17, wherein the second Fl message comprises at least one of a cell Identity (ID) and a candidate cell configuration index, and the one or more UE-reported periodic L3 measurements.

19. A gNodeB Centralized Unit (gNB-CU) configured to:determine whether one or more beam-level L3 measurements of a Conditional- Layerl / Layer2 Triggered Mobility (C-LTM) candidate cell indicate that the C-LTM candidate cell meets a second predefined criteria for an Uplink (UL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the second predefined criteria, initiate the UL synchronization for a User Equipment (UE).

20. A non-transitory computer-readable medium storing instructions, the instructions comprising:one or more instructions that, when executed by an apparatus, the apparatus comprising one or more processors, cause the one or more processors to:configure a User Equipment (UE) to perform one or more periodic Layer 3 (L3) measurements at a beam level;transmit beam Identity (ID) to Transmission Configuration Indicator (TCI) state mapping information, of one or more Conditional-Layerl / Layer2 Triggered Mobility (C-LTM) candidate cells of at least one candidate gNB -Distributed Unit (gNB-DU), to a serving gNB-DU,wherein the beam ID to TCI state mapping information enables the serving gNB-DU to identify and activate one or more optimal TCI states for a C-LTM candidate cell among the one or more C-LTM candidate cells, for the UE to perform a C-LTM cell switch;continuously monitor one or more beam-level L3 measurements of a C- LTM candidate cell associated with the at least one candidate gNB-DU;determine whether the one or more beam-level L3 measurements of the C- LTM candidate cell indicate that the C-LTM candidate cell meets a first predefined criteria for a Downlink (DL) synchronization; andin response to determining that the one or more beam-level L3 measurements of the C-LTM candidate cell indicate that the C-LTM candidate cell meets the first predefined criteria,initiate the DL synchronization by transmitting information to the serving gNB-DU, comprises at least one of the beam ID corresponding to the TCI state of the LTM candidate cell that needs to be activated, and / or the one or more UE-reported periodic layer 3 measurements.

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