Layer 1 / layer 2 triggered mobility between cells transmitting different reference signals

Abstract

An apparatus (700) is disclosed which receives, from a User Equipment (UE) (401), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB-Distributed Units (gNB-DUs) (303). The apparatus (700) identifies a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a LTM candidate cell, based on the received corresponding L3 measurement reports. The apparatus (700) determines that the identified cell to be configured as the LTM candidate cell, transmit a different RS than a UE's serving cell, of the UE (401). The apparatus (700) configures at least one of the UE's serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE's serving cell and the identified cell.

Description

LAYER 1 / LAYER 2 TRIGGERED MOBILITY BETWEEN CELLS TRANSMITTING DIFFERENT REFERENCE SIGNALSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to India Provisional Application No. 202411088481, filed on November 15, 2024, and India Non-Provisional Application No. 202411088481, filed on March 28, 2025, the entire contents of which are incorporated herein by reference.FIELD

[0002] The present disclosure relates to Layer 1 / Layer 2 Triggered Mobility (LTM) between cells transmitting different reference signals.BACKGROUND

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

[0004] Mobility or handover ensures seamless connectivity of an ongoing communication session of a User Equipment (UE) by transferring a session from one cell, i.e., a base station or a gNodeB (gNB) to another cell in a connected state while the user is on the move.

[0005] According to the concluded Third Generation Partnership Project (3GPP) Release 15, a transfer of cell change may be triggered by Layer 3 (L3) measurements and may be done by RadioResource Control (RRC) signaling. Further, the concluded 3GPP Release-18 introduced Layerl / Layer 2 (L1 / L2) triggered mobility (LTM) for improvements in handover latency and an interruption time compared to L3-based mobility. However, the LTM as introduced in the Release-18 is reduced in scope and also includes a number of limitations compared to the L3-based mobility.

[0006] Currently, the ongoing 3GPP Release- 19 work item (WI) aims to remove a number of these scope limitations. While Release-18 LTM may support mobility between cells served by the same gNB, the LTM framework in Release 19, extended to support handover between cells served by different gNBs.

[0007] In Rel-18, the LTM is limited to an intra-Centralized Unit (CU) mobility, and also, eventbased LI measurements are not supported. The data scheduling operations generally take place at a gNB-Distributed Unit (DU). However, in order to support L1 / L2 centric inter-cell change (i.e. change of serving cell) in a disaggregated gNB architecture, the Handover (HO) preparation phase i.e., providing a candidate / target cell configuration to the UE is performed by a gNB-CU-CP, that is autonomously executed by the gNB-DU without requiring further interaction with upper layers in the gNB-CU-CP.SUMMARY

[0008] 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.

[0009] According to one embodiment of the present disclosure, an apparatus is disclosed. The apparatus is configured to receive, from a User Equipment (UE), one or more Layer 3 (L3)measurement reports of one or more cells associated with one or more of a plurality of gNodeB-Distributed Units (gNB-DUs). The apparatus is configured to identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell. The cell to be configured as the LTM candidate cell is identified based on the received corresponding one or more L3 measurement reports. The apparatus is configured to determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than the UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE. The apparatus is configured to configure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

[0010] According to another embodiment of the present disclosure, a method is disclosed. The method includes receiving, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs). The method includes identifying a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell. The cell to be configured as the LTM candidate cell is identified based on the received corresponding one or more L3 measurement reports. The method includes determining that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE. The method includes configuring at least one of the UE’s servingcell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

[0011] According to another embodiment of the present disclosure, a non-transitory computer-readable medium is disclosed. The non-transitory computer-readable medium stores instructions. The instructions comprise one or more instructions that are executed at a gNodeB-Centralized Unit (gNB-CU). The gNB-CU comprises one or more processors. The one or more instructions cause the one or more processors to receive, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB-Distributed Units (gNB-DUs). The one or more processors identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell. The cell to be configured as the LTM candidate cell is identified based on the received corresponding one or more L3 measurement reports. The one or more processors determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE. The one or more processors configure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

[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. Thedisclosure 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 architecture of a gNodeB (gNB), according to the state of the art;FIG. 2 illustrates a configuration of Synchronization Signal Block (SSB)-Reference Signals (RSs) and Channel State Information (CSI)-RS, in accordance with a conventional technique;FIG. 3 illustrates a sequence flow diagram illustrating communication between a gNodeB-Centralized Unit (gNB-CU) and a gNB-Distributed Unit (gNB-DU), in accordance with one or more embodiments of the present disclosure;FIGS. 4A-4D illustrate a sequence flow diagram of inter-gNB-DU Layer 1 / Layer 2 Triggered Mobility (LTM) process, in accordance with an embodiment of the present disclosure;FIG. 5 illustrates a flowchart of an example method, in accordance with an embodiment of the present disclosure;FIG. 6 illustrates a flow chart of an example method to receive a served cell information, in accordance with an embodiment of the present disclosure; andFIG. 7 illustrates an embodiment of an example device, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0014] The following detailed description of example embodiments refers to the accompanying drawings. 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 the 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 one of the various embodiments. 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, 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 is not limiting of the 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, these 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 claimsand / or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of implementations includes each dependent claim in combination with every other claim 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” 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 the practice of the implementations.

[0019] A disaggregated architecture is defined in Third Generation Partnership Project (3GPP) decomposing a gNodeB (gNB) into multiple logical entities. FIG. 1 illustrates the disaggregated architecture of a gNB 100, according to the state of the art. The multiple logical entities may include one or more first units 102 and one or more second units 104. The one or more first units 102 may be represented by at least one distributed unit (referred to as gNB-DU). The one or more second units 104 may be represented by a centralized unit (referred to as gNB-CU). The gNB-CU may be further split into a CU Control Plane (CP) part, also referred to as a gNB-CU-CP, and aCU User Plane (UP) part, also referred to as a gNB-CU-UP. Such a split enables the implementation of the CU-CP and CU-UP parts in different locations. For example, such a split of the gNB 100 into the plurality of logical entities enables flexibility, scalability, and efficiency in the deployment and operation of fifth generation (5G) networks. The disaggregated architecture of the gNB 100 may also include a Radio Unit (gNB-RU), not shown in FIG. 1.

[0020] The gNB-RU may be responsible for radio transmission and reception of signals. The gNB-RU may include physical Radio Frequency (RF) components such as antennas, power amplifiers, and anal og-to-digi tai converters. The gNB-RU may be located at a cell site or a radio tower, close to the antennas. Further, the gNB-DU may perform baseband processing functions such as physical layer processing, channel coding, and modulation / demodulation. For example, the gNB-DU may host a Radio Link Control (RLC), a Medium Access Control (MAC) layer, and a Physical (PHY) layer. The gNB-DU may also perform scheduling operations. Multiple gNB-RUs can be connected to a single gNB-DU, allowing for centralized processing of multiple radio units. Multiple gNB-DUs may be connected to a single gNB-CU. The gNB-CU may be responsible for higher-layer processing functions such as radio resource management, mobility management, and connection management. The gNB-CU may provide a centralized control point for multiple gNB-DUs, enabling network-wide coordination and optimization.

[0021] According to one configuration, the gNB-DU may host multiple cells (for example, a max of 512 as per current specifications). The gNB-CU-CP may host the Packet Data Convergence Protocol-control plane part (PDCP-c) and Radio Resource Control (RRC) layers. The scheduling operation takes place at the gNB-DU. The gNB-CU-CP may host one or more gNB-DUs and one or more gNB-CU-UPs. Also, the gNB-CU-UP may host the Packet Data Convergence Protocol-User Plane part (PDCP-U) and Service Data Adaptation Protocols (SDAP). More specifically, 3GPP Radio Access Network (RAN)3 cardinality for a 5G gNB defines that the gNB 100 may only include one gNB-CU-CP. There may be an “n” number of gNB-DUs controlled by a gNB-CU-CP. Further, there may be ‘m” number of gNB-CU-UP controlled by the gNB-CU-CP in the gNB 100. Also, one gNB-DU may be served by multiple gNB-CU-UPs. The various entities and / or network functions within the gNB 100 may communicate via one or more interfaces. The one or more interfaces include an Fl-C interface, an Fl-U interface, and an El interface. The Fl-C interface is a control plane interface between the gNB-CU and the gNB-DU within the gNB 100. The Fl-C interface is used for signaling and control messages related to radio resource management, mobility management, and configuration management. The Fl-C interface facilitates coordination between the gNB-CU and the gNB-DU for efficient network operation and service delivery. The Fl-U interface is a user plane interface between the gNB-CU and the gNB-DU in the gNB 100 architecture. The Fl-U is responsible for transporting user data packets between the gNB-CU and the gNB-DU. The Fl-U interface handles user plane data processing, including packet forwarding, Quality of Service (QoS) management, and encryption / decryption functions. The El interface in the gNB 100 connects the gNB-CU-UP entity with the gNB-CU-CP. Particularly, the gNB-CU-UP may communicate with the gNB-CU-CP over El-C interface. Further, gNB-CU-CP may communicate with gNB-DU over the Fl-C interface.

[0022] The present disclosure relates to Rel-19 of Work Item (WI) on mobility enhancements.

[0023] Particularly, the objective of the WI is to specify support for inter-CU Layerl / Layer 2 Triggered Mobility (LTM) [Radio Access Network (RAN)2, RAN3], and prioritize the case when CU is acting as Master Node (MN) when Dual Connectivity (DC) is not configured. As asecondary priority, support the case when New Radio-DC (NR-DC) is configured, the CU is acting as a Secondary Node (SN) and a Master Cell Group (MCG) is unchanged. As the secondary priority, support the case when the NR-DC is configured, the CU is acting as the MN, and a Secondary CG (SCG) is unchanged or the SCG is released. Specifically, this corresponds to a case that the LTM is configured in both the MCG and the SCG is excluded. Further, the WI also specifies support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM and ensure coordination with SA3 needed with respect to security key handling. Rel. 18 intra-CU LTM procedure is considered as baseline for adding inter-CU support.

[0024] Another objective of the WI is measurement related enhancements for the purpose of supporting LTM: [RAN2, RANI], Measurement related enhancements may be applicable to an intra-CU MCG / SCG LTM and an inter-CU MCG / SCG LTM. The WI also specifies necessary components to support event triggered LI measurement reporting [RAN2, RANI], RANI and RAN2 progress independently on the event triggered measurements objectives of their respective Multiple Input, Multiple Output (MIMO) and Mobility enhancement WIs. The WI also discloses to review progress at RAN# 105 to see if any modification of objectives is required to avoid / manage any overlap in the work and specify support for Channel State Information Reference Signal (CSLRS) measurements for LTM procedures and enable CSLRS based beam management, and / or other necessary physical layer operations on candidate cells before LTM [RANI],

[0025] Yet another objective of the WI is to specify support of conditional LTM [RAN2, RAN3, RANI], and specify UE evaluated conditions for triggering the LTM. The WI also aims to supportthe conditional LTM including subsequent LTM and prioritize an intra-CU LTM. The WI also ensures a checkpoint to review the objective at RAN#105. RAN WG works to not start before this checkpoint.

[0026] Further, the Conditional LTM (C-LTM) is a combination of techniques used for conditional Handover (HO) and the LTM. In C-LTM, a source cell sends a conditional LTM configuration of a candidate cell via RRCReconfiguration message to a User Equipment (UE), which includes LTM candidate configurations, and corresponding execution conditions. Each candidate cell provides corresponding execution condition for the conditional LTM. Once provided with the execution condition, UEs in other cells check if the UEs are suitable to be served by the cell which provides the execution condition. Herein, a condition is related to measuring a reference signal and evaluating the measurement in an absolute manner or relative to another measurement carried out by the same UE.

[0027] Accordingly, in the C-LTM, the UE is configured with one or more LTM candidate cell(s) and C-LTM execution condition(s), and when the execution condition is met, the UE executes the C-LTM cell switch. For example, when the execution condition is met, the UE detaches from the source cell, and applies the stored corresponding C-LTM candidate cell configuration for a selected candidate cell, and optionally performs a Random Access Channel (RACH)-less C-LTM HO to that candidate cell. The UE completes the RACH-less C-LTM HO procedure by sending a RRCReconfigurationComplete message to a target gNodeB-Distributed Unit (gNB-DU).

[0028] Further, an LI event based measurement is useful for both the LTM and the C-LTM.

[0029] FIG. 2 illustrates a configuration of Synchronization Signal Block (SSB)- RSs and CSL RSs, in accordance with a conventional technique.

[0030] RAN2 may support the SSB and CSI-RS for LI measurement resource configuration in LTM configuration. However, RAN2 requires the same type of RS between a current beam (of a serving cell) and a new beam (of the candidate cells). There are possibilities where the UE could be configured with different types of the RSs between the current beam (of the serving cell) and candidate beams (of the candidate cells) because an indicated Transmission Configuration Indication (TCI) state is dynamically changed.

[0031] RAN2 #127bis made the below mentioned agreement regarding the configuration of the RS at the source and candidate cells:a. Option 1: Network (NW) configures both types of RSs (SSB and CSI-RS) for the new beam(s), the UE could select the same type of beam when the UE evaluates the LI event measurement.b. Option 2: Only one type of RS is configured for the new beam as an NW restriction, and the UE performs the LI measurement when a type of the RS of the current beam is the same as the new beam for the event LI measurement.c. Option 3: The NW provides an offset which can be applied to one type of RS to evaluate the different types of RSs. For example, if the current beam is SSB and the measured beam for the candidate cell is CSI-RS, the UE applies the configured offset to the measured CSI-RS value and then compares it with the current beam quality i.e. SSB measurement.d. Option 4: Rely on network configuration, i.e., the same RS type is configured. e. Option 5: Which type of RS to be used in measurement may be configured by the NW. Then, the UE only considers the configured RS type in the measurement.f. Option 6: The RS for the current beam of a serving cell is the same as or associated with Quasi Co Location (QCL) RS provided in the indicated TCI state, i.e. using the same type of RS as the candidate beam.

[0032] The same RS type should be used for both serving and neighboring cells for event LTM3 and event LTM5.

[0033] Now, in Rel-18 LTM, the existing solution is based on Option 4, i.e. the UE relies on network configuration to configure the same type of RS. This option has some limitations as a serving gNB-DU cannot be aware of the RS transmitted by a candidate / target LTM cell.

[0034] Additionally, Option 1 is expensive and hence it is not feasible to configure all UEs with both reference signals all the time. Option 2 is an inflexible option and causes mobility limitations.

[0035] Option 3 is not agreed in 3GPP. Option 5 is configuring over RRC in advance, which is majorly the same as the Option 2, but the inflexibility is pushed to the UE side.

[0036] Option 6 indicates which RS to be measured at the candidate cell, by providing a pointer to the current beam of the serving cell.

[0037] Further, referring to FIG.2, cells represented by 201, are considered to belong to one DU or one gNB. The cells 201 are configured to transmit the SSB reference signals. Further, the cells, represented by 203, are considered to belong to another DU or another gNB. The cells 203 are configured to transmit the CSI reference signals. In an embodiment, the two sets of cells may operate at different frequencies. For the UE in one of the cells transmitting the SSB RSs, it could become inevitable to perform an inter-frequency HO and move to CSLRS based cells. Furthermore, the current options mentioned above (Options 1-6) in RAN2 fail to address this issue.

[0038] Thus, RAN2 provides a way forward to addressing the above-mentioned issue where the LTM is configured between two cells transmitting different RSs in the present disclosure. In Release 18 LTM, RAN2 agreed that a candidate cell preparation is performed by a gNB-Centralized Unit (CU) based on Layer 3 (L3) measurements, while an LTM cell switch execution is performed by a gNB -Distributed Unit (DU) based on periodic Layer 1 (LI) measurements. The present disclosure, as disclosed, relates to an apparatus 700 (as shown in FIG. 7) and a method (as shown in FIG. 5) for performing mobility between cells by a user equipment (UE), where the cells support different RS. The different RSs indicate that the RS transmitted by a candidate / target cell is different from the source cell. The UE requests the transmission of both reference signals for a predefined duration, by the candidate cell to overcome the problems as mentioned above.

[0039] The apparatus 700 and the method 500 disclose that each distributed unit (referred to here as gNB-DU) exchanges default RS with at least one of centralized unit (referred to here as gNB-CU) and neighboring gNB-DUs. Each gNB-DU exchanges the default RS that is used by all the cells covered by the gNB-DU. Further, to initiate the exchanges, the apparatus 700 and the method 500 disclose that the gNB-DU includes a default RS information for its cells in an Fl Setup Request (e.g.: in a served cell information) to the gNB-CU. Further, the gNB-CU may optionally include the default RS information of all the neighboring gNB-DU cells of a given gNB-DU in an Fl Setup response message. The apparatus 700 and the method 500 disclose the possibility of modification of the default RS using the “Fl: gNB-DU Configuration Update” message and redelivered from the gNB-CU to neighboring gNB-DUs using a “Fl: gNB-CU Configuration Update” message.

[0040] Further, the apparatus 700 and the method 500 detect, at the gNB-CU, that a neighboring cell of a UE’s serving cell does not transmit the same RS as the source cell. The apparatus 700 and the method 500 detects, based on information provided by the gNB-DU and an L3 measurement report (to the gNB-CU) sent by the UE. Further, the apparatus 700 and the method 500 detect that there is a requirement to configure the reported cell as a Conditional-LTM (C-LTM) or LTM candidate cell. Thus, in one embodiment, the apparatus 700 and the method 500 disclose that the serving gNB-CU requests the candidate gNB-DU to transmit both a Synchronization Signal Block (SSB)-RS and a CSI-RS for a predefined period of time or until a re-notification is transmitted. Further, in another embodiment, the apparatus 700 and the method 500 disclose that the gNB-CU requests the serving gNB-DU to transmit both the SSB-RS and the CSI-RS for the predefined duration or until a notification event. This configuration is selected when there are capability issues at a candidate / target gNB-DU.

[0041] Whenever such an LTM candidate cell is prepared (with both RSs), the gNB-CU indicates this to the serving gNB-DU over an Fl interface, when the LTM report configuration (config) is prepared. When the candidate / target gNB-DU transmits both RSs, the serving gNB-CU prepares the cell as the LTM candidate cell and also configures the UE to measure and report both the RSs simultaneously and at least the common RS, in the LI measurements. A Transmission Configuration Indicator (TCI) state activation for the given candidate cell is also performed corresponding to both the RSs. In LI measurement reports, the UE includes reports of both the CSI-RS and the SSB-RS for the corresponding candidate cell, as the UE is configured to report both the RSs. Additionally, the UE is configured to report the common RS between a current beam of a UE’s serving cell and a new beam of a candidate cell.

[0042] The serving gNB-DU therefore may compare the common RS between the current beam of the UE’s serving cell and the new beam of the candidate cell and perform mobility actions based on the comparison. Further, any dynamic changes to the RS configuration are indicated to the UE using Media Access Control - Control Element (MAC CE) in the downlink. Further, the details of operations as performed in the present disclosure are explained in the subsequent paragraphs with respect to FIGS. 3 to 6.

[0043] FIG.3 illustrates a sequence flow diagram illustrating communication between a gNodeB-Centralized Unit (gNB-CU) 301 and a plurality of gNB -Distributed Units (gNB-DUs) (herein referred to as a gNB-DU 303), in accordance with one or more embodiments of the present disclosure.

[0044] In an embodiment, the gNB-CU 301 receives the served cell information from each of the plurality of gNB-DUs 303. The served cell information includes the default Reference Signal (RS) information per cell, associated with a plurality of cells. The plurality of cells is associated with the corresponding gNB-DU. The served cell information includes a DU identifier (DU ID), a cell identifier (ID), and the default RS information of the corresponding cell. Each gNB-DU 303 exchanges with the gNB-CU 301 (and optionally all its neighbor gNB-DUs), the default RS that is used by all the cells / the plurality of cells covered by the gNB-DU 303. Additionally, the gNB-CU 301 receives an update from each gNB-DU 303 whenever the default RS information of the corresponding cell is modified.

[0045] Further, to receive the served cell information, a plurality of operations is explained in detail in the subsequent paragraphs.

[0046] At operation 305, the gNB-CU 301 receives at least one of an Fl setup request message and a gNB-DU Configuration Update message. The at least one of the Fl setup request message and the gNB-DU Configuration Update message indicates the served cell information associated with the plurality of cells associated with the corresponding gNB-DU. Further, the at least one of the Fl setup request message and the gNB-DU Configuration Update message indicates the default RS information for the cells associated to the gNB-CU 301. The gNB-CU 301 receives the at least one of the Fl setup request message and the gNB-DU Configuration Update message from each of the plurality of gNB-DUs 303.

[0047] At operation 307, the gNB-CU 301 transmits at least one of an Fl setup response message and a gNB-DU Configuration Update response message. The at least one of the Fl setup response message and the gNB-DU Configuration Update response message includes the served cell information associated with the plurality of cells associated with all neighbouring gNB-DUs of the corresponding gNB-DU. The gNB-CU 301 transmits at least one of the Fl setup response message and the gNB-DU Configuration Update response message to each of the plurality of gNB-DUs 303. The gNB-CU 301 may optionally include the default RS information of all the neighbour gNB-DU cells of a given gNB-DU in the Fl Setup response message.

[0048] This may be modified using the “Fl: gNB-DU Configuration Update” message and redelivered from gNB-CU 301 to neighboring gNB-DUs using the “Fl: gNB-CU Configuration Update” message.

[0049] In an embodiment, the above-mentioned operations as discussed are performed by the apparatus 700 deployed at the gNB-CU 301. The apparatus 700 is deployed at one of the gNB-CU301, a gNB, or a base station. In one embodiment, the apparatus 700 is deployed at the gNB-CU 301. In another embodiment, the apparatus 700 is deployed at the one of the gNB, or base station.

[0050] FIGS. 4A-4D illustrate a sequence flow diagram of an inter-gNB-DU Layer 1 / Layer 2 Triggered Mobility (LTM) process 400, in accordance with an embodiment of the present disclosure.

[0051] Initially, after the connection setup has been completed, at step 409, user data may be exchanged between a UE 401 and a source gNB-DU 403. Similarly, at step 411, the user data may be exchanged between the source gNB-DU 403, a candidate gNB-DU 405, and a gNB-CU 407. In one embodiment, the gNB-CU 407 corresponds to the gNB-CU 301.

[0052] At operation 413, one or more L3 measurement reports may be exchanged between the UE 401 and the gNB-CU 407.

[0053] At operation 415, the gNB-CU 407 may determine an LTM configuration decision based on the L3 measurement reports.

[0054] At operation 417, the gNB-CU 407 may transmit a UE context setup request to the candidate gNB-DU 405 to prepare and LTM / CLTM candidate cell.

[0055] At operation 419, the candidate gNB-DU 405 may transmit a UE context setup response to the gNB-CU 407, which comprises of the cellGroupConfig for the candidate cell, in response to receiving the UE context setup request.

[0056] At operation 421, the gNB-CU 407 may transmit a UE context modification request to the source gNB-DU 403 which comprises of the candidate cell configuration.

[0057] At operation 423, the source gNB-DU 403 may transmit a UE context modification response to the gNB-CU 407, in response to receiving the UE context modification request.

[0058] At operation 425, the gNB-CU 407 may transmit a UE context modification request to the candidate gNB-DU 405 which comprises of the candidate cell configuration meant for the UE 401.

[0059] At operation 427, the candidate gNB-DU 405 may transmit a UE context modification response to the gNB-CU 407, in response to receiving the UE context modification request.

[0060] At operation 429, the gNB-CU 407 may transmit Downlink Radio Resource Control (DL RRC) message transfer including RRC Reconfiguration to the source gNB-DU 403. This includes the candidate cell configuration.

[0061] At operation 433, the source gNB-DU 403 may transmit the RRC Reconfiguration to the UE 401, in response of receiving the DL RRC message transfer.

[0062] At operation 435, the UE 401 may transmit the RRC Reconfiguration complete to the source gNB-DU 403, in response to receiving the RRC Reconfiguration.

[0063] At operation 437, the source gNB-DU 403 may transmit an uplink (UL) RRC message transfer including RRC reconfiguration complete to the gNB-CU 407, in response of receiving the RRC Reconfiguration complete.

[0064] At operation 441, the source gNB-DU 403 may transmit early Timing Advance (TA) acquisition command to the UE 401, based on a received LI measurements.

[0065] At operation 443, the candidate gNB-DU 405 may transmit a DU-CU TA information transfer to the gNB-CU 407.

[0066] At operation 445, the gNB-CU 407 may transmit a CU-DU TA information transfer to the source gNB-DU 403.

[0067] At operation 447, the UE 401 may transmit the LI measurement report to the source gNB- DU 403.

[0068] At operation 449, the source gNB-DU 403 may perform the LTM cell switch decision.

[0069] At operation 451, the source gNB-DU 403 may transmit a cell switch command to the UE 401, after performing the LTM cell switch decision.

[0070] At operation 453, the source gNB-DU 403 may transmit a DU-CU cell switch notification including one or more of a target cell ID and a TCI state, to the gNB-CU 407.

[0071] At operation 457, the gNB-CU 407 may transmit a CU-DU cell switch notification including one or more of the target cell ID and the TCI state ID to the candidate gNB-DU 405.

[0072] Thereafter, at operation 461, the source gNB-DU 403 may transmit a downlink data delivery status to the gNB-CU 407.

[0073] At operation 463, the UE 401, the source gNB-DU 403, and the candidate gNB-DU 405 may perform such that the gNB-DU may detect the UE access.

[0074] At operation 465, the candidate gNB-DU 405 may transmit an access success including a target Cell ID message to the gNB-CU 407.

[0075] At operation 469, the UE 401 may transmit RRC Reconfiguration complete to the candidate gNB-DU 405.

[0076] At operation 471, the candidate gNB-DU 405 may transmit the UL RRC message transfer (including the RRC Reconfiguration complete) to the gNB-CU 407.

[0077] At operation 475, the gNB-CU 407 may transmit a UE context release command (prepared cells to be released) to the source gNB-DU 403.

[0078] At operation 479, the source gNB-DU 403 may transmit a UE context release completed to the gNB-CU 407.

[0079] Further, lastly, a user data 481 may be present between the UE 401 and the candidate gNB- DU 405 and a user data 483 may be present between the candidate gNB-DU 405 and the gNB-CU 407.

[0080] Herein, a list of Information Elements (IES) that are added to specific messages as a result of the present disclosure is provided below:

[0081] In an embodiment, the UE Context Setup Request may include a new optional IE indicating “Activate dual RS” or “Activate CSI-RS”. With the addition of the optional IE, an optional time duration may also be included.

[0082] In an embodiment, the UE Context Modification Request may include information such as “Dual RS activated” or “CSI-RS activated” + Cell ID + DU ID of the LTM candidate cell.

[0083] Further, the RRC Reconfiguration message may configure the UE 401 to measure and report both the RSs from the associated LTM candidate cell. There is no new IE added here, and it is a configuration.

[0084] Any other dynamic modifications in RS transmission may be signaled to the UE 401 using the MAC CE.

[0085] Additionally, during the inter-CU LTM, the same changes that are mentioned above over the Fl interface may have to be carried out over an Xn interface between Next Generation Radio Access Network (NG-RAN) nodes. It is proposed to send the default RS of the gNB-DU to all its neighboring DUs for a futuristic use-case where in sixth-generation (6G), if a DU-DU interface is envisaged, communication can happen directly over the DUs. In such cases, the request to activate both RS can be sent directly to the neighboring DU. Alternatively, in the case of the DU-DU interface, the default RS information exchange could happen directly between the DUs withoutthe involvement of the gNB-CU. In case of a proposal where the gNB-CU notifies the candidate gNB-DU to stop transmitting dual RS is adopted, then new IES are added to an existing Fl message, or a new message is introduced to perform this functionality.

[0086] The operations as disclosed in the present disclosure ensure C-LTM mobility between cells transmitting different RSs. This is a SEP and has impacts to Fl / MAC / RRC specifications.

[0087] FIG. 5 illustrates a flow chart of an example method 500, in accordance with an embodiment of the present disclosure. The method 500 may be performed by the apparatus 700.

[0088] At step 502, the apparatus 700 may receive the served cell information from each of the plurality of gNB-DUs 303. The served cell information includes the default Reference Signal (RS) information per cell, associated with the plurality of cells associated with the corresponding gNB-DU. Further, the served cell information includes the DU identifier (DU ID), the cell identifier (ID), and the default RS information of the corresponding cell. Furthermore, the detailed operation performed by the apparatus 700 to receive the served cell information is explained later in subsequent paragraphs in conjunction with Figure 6.

[0089] At step 504, the apparatus 700 may receive the one or more Layer 3 (L3) measurement reports of one or more cells. The one or more cells may be associated with one or more of the plurality of gNB- DUs 303. The apparatus 700 may receive the one or more L3 measurement reports from the UE 401 as shown at operation 413 in FIG. 4 A.

[0090] At step 506, the apparatus 700 identifies a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs 303. The apparatus 700 identifies the cell to be configured as the LTM candidate cell, based on the received corresponding one or more L3 measurement reports as shown at operation 415 in FIG. 4 A.

[0091] At step 508, the apparatus 700 determines that the identified cell to be configured as the LTM candidate cell of the UE 401, transmits a different RS than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs 303. The apparatus 700 determines, based on the default RS information of the UE’s serving cell and the identified cell 700.

[0092] At step 510, the apparatus 700 configures at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell. The apparatus 700 configures at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs to provide at least one common RS between the UE’s serving cell and the identified cell. The apparatus 700 configures the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell for a predefined time interval or until the notification event.

[0093] At step 514, further, the apparatus 700 configured the UE 401 to measure at least a common RS among the plurality of different RSs. The apparatus 700 configured the UE 401 to measure at least the common RS, in response to configuring the at least one of the UE’s serving cell of the UE 401 and the identified cell to transmit the plurality of different RSs. The plurality of different RSs includes Channel State Information (CSI)-RS, and Synchronization signal Block (SSB)-RS. In another embodiment, the apparatus 700 configured the UE 401 to measure the plurality of different RSs for the identified cell and the UE’s serving cell. This enables the apparatus 700 to effectively compare the UE’s serving cell and identified cell based on the one or more Layer 3 (L3) measurement reports of the one or more cells received for at least the common RS and / or each of the plurality of different RSs. This configuration also enables the UE 401 to measure the one ormore Layer 3 (L3) measurement reports of the one or more cells received for at least the common RS and / or each of the plurality of different RSs.

[0094] FIG. 6 illustrates a flow chart of an example method 600 to receive the served cell information, in accordance with an embodiment of the present disclosure. The method 600 may be performed by the apparatus 700.

[0095] At step 602, the apparatus 700 receives the at least one of the Fl setup request message and the gNB-DU Configuration Update message. The apparatus 700 receives the at least one of the Fl setup request message and the gNB-DU Configuration Update message from each of the plurality of gNB-DUs 303. The at least one of the Fl setup request message and the gNB-DU Configuration Update message indicate the served cell information associated with the plurality of cells associated with the corresponding gNB-DU.

[0096] At step 604, the apparatus 700 transmits the at least one of the Fl setup response message and the gNB-DU Configuration Update response message . The apparatus 700 transmits the at least one of the Fl setup response message and the gNB-DU Configuration Update response message to each of the plurality of gNB-DUs 303. The at least one of the Fl setup response message and the gNB-DU Configuration Update response message includes the served cell information associated with the plurality of cells associated with all neighboring gNB-DUs of the corresponding gNB-DU.

[0097] FIG. 7 illustrates an embodiment of the device / apparatus 700, in accordance with an embodiment of the present disclosure. The device / apparatus 700 may be deployed at one of the gNB-CU 301, thegNB, or the base station. As shown in FIG. 7, the device 700 includes a processor 710, a memory 720, a storage component 730, an input component 740, an output component 750,a communication interface 760, and a bus 770. The one or more components of the device 700 may be configured to implement one or more operations / functionalities of the present disclosure as discussed above.

[0098] The processor 710, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 710 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and / or one or more single core processors, a distributed processing system, or the like. The processor 710 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.

[0099] The memory 720 includes a non-transitory computer readable medium. The memory 720 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 the processor 710. The memory 720 comprises machine-readable instructions which are executable by the processor 710. These machine-readable instructions when executed by the processor 710 cause the processor 710 to perform one or more method steps of an embodiment described above.

[0100] The storage component 730 stores information and / or software related to the operation and use of the device 700. For example, the storage component 730 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.

[0101] The input component 740 is configured to receive information, such as user input. For example, the input component 740 may include, but not be limited to, a touch screen display, a keyboard, a keypad, a mouse, a button, a switch, and / or a microphone. Additionally, or alternatively, the input component 740 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0102] The output component 750 is configured to provide output information from the device 400. For example, the output component 750 may be, but not be limited to, a display, a speaker, an instruction device to an external device, and / or one or more light-emitting diodes (LEDs).

[0103] The communication interface 760 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 760 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 device 700 and other devices. In other words, the standard of the communication interface 760 is not limited.

[0104] The bus 770 acts as an interconnect between the processor 710, the memory 720, the storage component 730, the input component 740, the output component 750, and the communication interface 760 of the device 700. The bus 770 may include a wired interconnection or a wireless interconnection.

[0105] The number and arrangement of components shown in FIG. 7 are provided as an example. In practice, device 700 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 7. Additionally, or alternatively, a set of components (e.g., one or more components) of the device 700 may performone or more functions described as being performed by another set of components of the device 700. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of devices 700 in communication with one another.

[0106] Examples of the techniques and apparatus described herein include, but are not limited to, the following enumerated embodiments:[1] An apparatus configured to:receive, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfigure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.[2] The apparatus as described in [1], wherein prior to receiving the one or more L3 measurement reports, the apparatus is configured to:receive from each of the plurality of gNB- DUs, a served cell information including a default RS information per cell, associated with the plurality of cells associated with the corresponding gNB-DU.[3] The apparatus as described in any one of [1] to [2], wherein to receive the served cell information, the apparatus is configured to:receive, from each of the plurality of gNB-DUs, at least one of an Fl setup request message, and a gNB-DU Configuration Update message indicating the served cell information associated with the plurality of cells associated with the corresponding gNB-DU; andtransmit, to each of the plurality of gNB-DUs, at least one of an F 1 setup response message, and a gNB-DU Configuration Update response message comprising the served cell information associated with the plurality of cells associated with all neighboring gNB-DUs of the corresponding gNB-DU.[4] The apparatus as described in any one of [1] to [3], wherein to determine that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell, the apparatus is configured to:determine that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell among the plurality of cells associated with the plurality of gNB-DUs, of the UE, based on a default RS information of the UE’s serving cell and the identified cell.[5] The apparatus as described in any one of [1] to [4], wherein to configure the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell, the apparatus is configured to perform one of:configure the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell for a predefined time interval; or configure, the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell until a notification event.[6] The apparatus as described in any one of [1] to [5], wherein in response to configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs, the apparatus is configured to:configure the UE to measure at least a common RS among the plurality of different RSs.[7] The apparatus as described in any one of [1] to [6], wherein the plurality of different RSs comprises Channel State Information (CSI)-RS and Synchronization signal Block (SSB)-RS.[8] The apparatus as described in any one of [1] to [7], wherein the apparatus is deployed at one of a gNodeB-Centralized Unit (gNB-CU), a gNB, or a base station.[9] The apparatus as described in any one of [1] to [8], wherein the served cell information comprises a DU identifier (DU ID), a cell identifier (ID), and the default RS information of the corresponding cell.

[0010] A method comprising:receiving from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identifying a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determining that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfiguring at least one of the UE’ s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

[0011] The method as described in

[0010] , wherein prior to receiving the one or more L3 measurement reports, the method comprises:receiving from each of a plurality of gNB- DUs, a served cell information including a default RS information per cell, associated with the plurality of cells associated with the corresponding gNB-DU.

[0012] The method as described in any one of

[0010] to

[0011] , wherein for receiving the served cell information, the method comprises:receiving, from each of the plurality of gNB-DUs, at least one of an Fl setup request message and a gNB-DU Configuration Update message indicating the served cell information associated with the plurality of cells associated with the corresponding gNB-DU; and transmitting, to each of the plurality of gNB-DUs, at least one of an Fl setup response message and a gNB-DU Configuration Update response message comprising the served cell information associated with the plurality of cells associated with all neighboring gNB-DUs of the corresponding gNB-DU.

[0013] The method as described in any one of

[0010] to

[0012] , wherein for determining that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell, the method comprises:determining that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’ s serving cell among the plurality of cells associated with the plurality of gNB-DUs, of the UE, based on the default RS information of the UE’s serving cell and the identified cell.

[0014] The method as described in any one of

[0010] to

[0013] , wherein for configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell, the method comprises:configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell for a predefined time interval; or configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell until a notification event.

[0015] The method as described in any one of

[0010] to

[0014] , wherein in response to configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs, the method comprises:configuring the UE to measure at least a common RS among the plurality of different RSs.

[0016] The method as described in any one of

[0010] to

[0015] , wherein the plurality of different RSs comprises Channel State Information (CSI)-RS and Synchronization signal Block (SSB)-RS.

[0017] The method as described in any one of

[0010] to

[0016] , wherein the served cell information comprises a DU identifier (DU ID), a cell identifier (ID), and the default RS information of the corresponding cell.

[0018] A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed at a gNodeB-Centralized Unit (gNB-CU), the gNB-CU comprising one or more processors, cause the one or more processors to:receive, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfigure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

[0107] The present disclosure thus allows C-LTM mobility between the plurality of cells transmitting the different reference signals. This is a SEP and has impacts to Fl / MAC / RRC specifications. This is planned to be proposed in 3GPP as a new proposal to Rel 19 WI on Mobilityenhancements. 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.

[0108] 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, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

[0109] 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.

[0110] 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.[oni] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and anycomponent(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.

[0112] 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 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

WE CLAIM1. An apparatus configured to:receive, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfigure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

2. The apparatus as claimed in claim 1, wherein prior to receiving the one or more L3 measurement reports, the apparatus is configured to:receive from each of the plurality of gNB-DUs, a served cell information including a default RS information per cell, associated with the plurality of cells associated with the corresponding gNB-DU.

3. The apparatus as claimed in claim 2, wherein to receive the served cell information, the apparatus is configured to:receive, from each of the plurality of gNB-DUs, at least one of an Fl setup request message, and a gNB-DU Configuration Update message indicating the served cell information associated with the plurality of cells associated with the corresponding gNB-DU; andtransmit, to each of the plurality of gNB-DUs, at least one of an Fl setup response message, and a gNB-DU Configuration Update response message comprising the served cell information associated with the plurality of cells associated with all neighboring gNB-DUs of the corresponding gNB-DU.

4. The apparatus as claimed in claim 1, wherein to determine that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell, the apparatus is configured to;determine that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell among the plurality of cells associated with the plurality of gNB-DUs, of the UE, based on a default RS information of the UE’s serving cell and the identified cell.

5. The apparatus as claimed in claim 1, wherein to configure the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell, the apparatus is configured to perform one ofconfigure the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell for a predefined time interval; or configure, the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell until a notification event.

6. The apparatus as claimed in claim 1, wherein in response to configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs, the apparatus is configured to:configure the UE to measure at least a common RS among the plurality of different RSs.

7. The apparatus as claimed in claim 1, wherein the plurality of different RSs comprises Channel State Information (CSI)-RS, and Synchronization signal Block (SSB)-RS.

8. The apparatus as claimed in claim 1, wherein the apparatus is deployed at one of a gNodeB-Centralized Unit (gNB-CU), a gNB, or a base station.

9. The apparatus as claimed in claim 2, wherein the served cell information comprises a DU identifier (DU ID), a cell identifier (ID), and the default RS information of the corresponding cell.

10. A method comprising:receiving from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identifying a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determining that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfiguring at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

11. The method as claimed in claim 10, wherein prior to receiving the one or more L3 measurement reports, the method comprises:receiving from each of a plurality of gNB- DUs, a served cell information including a default RS information per cell, associated with the plurality of cells associated with the corresponding gNB-DU.

12. The method as claimed in claim 11, wherein for receiving the served cell information, the method comprises:receiving, from each of the plurality of gNB-DUs, at least one of an Fl setup request message and a gNB-DU Configuration Update message indicating the served cell information associated with the plurality of cells associated with the corresponding gNB-DU; and transmitting, to each of the plurality of gNB-DUs, at least one of an Fl setup response message and a gNB-DU Configuration Update response message comprising the served cell information associated with the plurality of cells associated with all neighboring gNB-DUs of the corresponding gNB-DU.

13. The method as claimed in claim 10, wherein for determining that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’s serving cell, the method comprises:determining that the identified cell to be configured as the LTM candidate cell, transmits the different RS than the UE’ s serving cell among the plurality of cells associated with the plurality of gNB-DUs, of the UE, based on the default RS information of the UE’s serving cell and the identified cell.

14. The method as claimed in claim 10, wherein for configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell, the method comprises:configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell for a predefined time interval; or configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs in the corresponding cell until a notification event.

15. The method as claimed in claim 10, wherein in response to configuring the at least one of the UE’s serving cell and the identified cell to transmit the plurality of different RSs, the method comprises:configuring the UE to measure at least a common RS among the plurality of different RSs.

16. The method as claimed in claim 10, wherein the plurality of different RSs comprises Channel State Information (CSI)-RS and Synchronization signal Block (SSB)-RS.

17. The method as claimed in claim 10, wherein the served cell information comprises a DU identifier (DU ID), a cell identifier (ID), and the default RS information of the corresponding cell.

18. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed at a gNodeB-Centralized Unit (gNB-CU), the gNB-CU comprising one or more processors, cause the one or more processors to:receive, from a User Equipment (UE), one or more Layer 3 (L3) measurement reports of one or more cells associated with one or more of a plurality of gNodeB- Distributed Units (gNB-DUs);identify a cell among the one or more cells associated with the one or more of the plurality of gNB-DUs, to be configured as a Layerl / Layer 2 Triggered Mobility (LTM) candidate cell, based on the received corresponding one or more L3 measurement reports;determine that the identified cell to be configured as the LTM candidate cell, transmits a different Reference Signal (RS) than a UE’s serving cell among a plurality of cells associated with the plurality of gNB-DUs, of the UE; andconfigure at least one of the UE’s serving cell and the identified cell to transmit a plurality of different RSs in the corresponding cell, to provide at least one common RS between the UE’s serving cell and the identified cell.

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