Conditional early timing advance acquisition for conditional layer 1 / layer 2 triggered mobility

Abstract

Embodiments of the disclosure describe an apparatus that is configured to receive candidate cell configurations corresponding to one or more candidate cells for a C-LTM. Each candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition. The apparatus is also configured to monitor parameter(s) associated with each candidate cell to determine whether the at least one TA acquisition condition is met. The apparatus is further configured to transmit at least one of a L1 measurement report, an uplink MAC CE, and a UCI message corresponding to the at least one candidate cell. The apparatus is configured to transmit a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell. Furthermore, the apparatus is configured to receive the TA associated with the at least one candidate cell based on the transmitted RACH request message.

Description

CONDITIONAL EARLY TIMING ADVANCE ACQUISITION FOR CONDITIONALLAYER 1 / LAYER 2 TRIGGERED MOBILITYCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to India Provisional Application No. 202411084609, filed on November 5, 2024, and India Non-Provisional Application No. 202411084609, filed on March 28, 2025, the entire contents of which are incorporated herein by reference.FIELD

[0002] The present disclosure relates to conditional early Timing Advance (TA) acquisition for Conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM).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., base station or gNodeB (gNB) to another cell in a connected state while the user is on the move.

[0005] According to 3GPP Release 17, a transfer of cell change may be triggered by Layer 3 (L3) measurements and may be performed by Radio Resource Control (RRC) signaling. Further, the 3GPP Release-18 introduced Layerl / Layer 2 (L1 / L2) triggered mobility (LTM) for improvementsin handover latency and an interruption time compared to L3-based mobility. However, the LTM, as introduced in 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 handover between cells served by the same gNB. The LTM framework in Release 19, extended to support handover between cells served by different gNBs.SUMMARY

[0007] 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.

[0008] According to one embodiment of the present disclosure, an apparatus is disclosed. The apparatus is configured to receive one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM). The one or more candidate cell configurations are received from a gNodeB-Control Unit (gNB-CU) of a User Equipment’s (UE’s) serving cell. Each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition. The apparatus is configured to monitor one or more parameters associated with each of the one or more candidate cells based on the received one or more candidate cell configurations. The apparatus monitors the one or more parameters to determine whether the at least one TA acquisition condition is met. In response to determining that the at least one TA acquisition execution condition is met for at leastone candidate cell among the one or more candidate cells, the apparatus is configured to transmit at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control -ControlElement (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell. The apparatus transmits the at least one LI measurement report, the uplink MAC CE, and the UCI message to at least one gNB-Distributed Unit (gNB-DU) of the UE’s serving cell. Further, the at least one LI measurement report, the uplink MAC CE, and the UCI message is transmitted to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition. The apparatus is also configured to receive the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell. The PDCCH order is received in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message. The apparatus is configured to transmit a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell. The RACH request message is transmitted to the candidate gNB-DU of the at least one candidate cell. Further, the apparatus is configured to receive the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0009] According to another embodiment of the present disclosure, a method is disclosed. The method includes receiving one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM). The one or more candidate cell configurations are received by a User Equipment (UE) from a gNodeB-Control Unit (gNB-CU) of a UE’s serving cell. The method include monitoring, by the UE, one or more parameters associated with each of the one or more candidate cells to determine whether the atleast one TA acquisition condition is met. The one or more parameters are monitored based on the received one or more candidate cell configurations. In response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, the method includes transmitting at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control-Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell. The at least one of the LI measurement report, the uplink MAC CE, and the UCI is transmitted by the UE to at least one gNB-Distributed Unit (gNB-DU) of the UE’s serving cell. The at least one of the LI measurement report, the uplink MAC CE, and the UCI is transmitted to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition. The method includes receiving, by the UE, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell. The PDCCH order is received in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message. The method further includes transmitting a RACH request message with the received RACH preamble to acquire the TA associated with the at least one candidate cell. The RACH request message is transmitted from the UE to the candidate gNB-DU of the at least one candidate cell. Furthermore, the method includes receiving, by the UE, the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0010] According to another embodiment of the present disclosure, a non-transitory computer- readable medium storing instructions is disclosed. The instructions include one or more instructions that are executed by a User Equipment (UE) comprising one or more processors. The instructions cause the one or more processors to receive one or more candidate cell configurationscorresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM). The one or more candidate cell configurations are received from a gNodeB-Control Unit(gNB-CU) of a UE’s serving cell. Each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition. The instructions cause the one or more processors to monitor one or more parameters associated with each of the one or more candidate cells based on the received one or more candidate cell configurations. The one or more parameters are monitored to determine whether the at least one TA acquisition condition is met. In response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, the instructions cause the one or more processors to transmit at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control -Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell. The at least one LI measurement report, the uplink MAC CE, and the UCI message is transmitted to at least one gNB-Distributed Unit (gNB-DU) of the UE’s serving cell. Further, the at least one LI measurement report, the uplink MAC CE, and the UCI message is transmitted to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition. The instructions cause the one or more processors to receive the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell. The PDCCH order is received in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message. The instructions cause the one or more processors to transmit a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell. The RACH request message is transmitted to the candidate gNB-DU of the at leastone candidate cell. Further, the instructions cause the one or more processors to receive the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0011] 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

[0012] 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 gNB architecture, according to the state of the art;FIG. 2 illustrates a sequence flow diagram of an LTM procedure, in accordance with a conventional technique;FIGS. 3A-3B illustrate a sequence flow diagram of a C-LTM procedure, in accordance with one or more embodiments of the present disclosure;FIGS. 4A-4B illustrate a flowchart depicting a method for conditional early TA acquisition for the C-LTM, in accordance with an embodiment of the present disclosure; andFIG. 5 illustrates an embodiment of an example device, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0013] 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).

[0014] 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.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] The present disclosure relates to Work Item (WI) Rel 19 on Layer 1 / Layer 2 Triggered Mobility (LTM). The WI specifies support of conditional LTM (C-LTM) in Radio Access Network 1 (RAN 1 ), RAN 2, and RAN 3. The WI specifies UE-evaluated conditions for triggering LTM. The WI defines support for the C-LTM including subsequent LTM. The WI also prioritizes intra-CU LTM.

[0019] Layer 3 mobility has evolved over several releases. Further, Conditional Handover (CHO) and other conditional mobility procedures (Conditional PSCell Addition or Change (CP AC),Subsequent Conditional PSCell Addition or Change (SCPAC)) were developed to achieve high robustness by enabling the procedure to be executed without necessitating a signaling exchange with the source cell beforehand. LTM, as introduced in Rel-18, offers short interruption time, but not with the same level of robustness as the conditional L3 mobility procedures. However, it is required to have a system that can benefit from both the high robustness and short interruption.

[0020] Specifically, a C-LTM is a combination of techniques used for the conditional HO and the LTM. In the C-LTM, a source cell sends a conditional LTM configuration of a candidate cell via an RRCReconfiguration message to a User Equipment (UE), which includes the LTM candidate configurations, and the corresponding execution conditions. Each candidate cell provides a corresponding execution condition for the conditional LTM.

[0021] 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 C-LTM execution condition is met, the UE executes the C-LTM cell switch. For example, when the execution condition is met, the UE detaches from a 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, provided the TA of the candidate cell is invalid. The UE completes the RACH-less C-LTM HO procedure by sending an RRCReconfigurationComplete message to a target gNodeB-Distributed Unit (gNB-DU).

[0022] Moreover, the LTM procedure has been defined in TS 38.300. Specifically, the LTM is a procedure in which a gNB receives LI measurement report(s) from aUE, and the gNB may change a UE’s serving cell, based on the received LI measurement report(s), by a cell switch command signalled via a Medium Access Control-Control Element (MAC CE). The cell switch commandindicates an LTM candidate configuration that the gNB previously prepared and provided to the UE through Radio Resource Control (RRC) signalling. Thereafter, the UE switches to the target configuration according to the cell switch command. The LTM procedure can be used to reduce the mobility latency.

[0023] In LTM, it is possible to activate Transmission Configuration Indicator (TCI) states of one or multiple cells that are different from the current serving cell of the UE, when configured by a network. For instance, the TCI states of the LTM candidate cells can be activated in advance before any of those cells become the serving cell of the UE. This allows the UE to be Downlink (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 an LTM cell switch execution.

[0024] Moreover, when configured by the network, it is possible to initiate Uplink (UL) Timing Advance (TA) acquisition (called early TA) procedure of one or multiple cells that are different from the current serving cells. If the cell has the same Network Timing Advance (NTA) as the current serving cells or NTA=0, an early TA acquisition procedure is not required. The network may request the UE to perform early TA acquisition of a candidate cell before a cell switch. The early TA acquisition procedure is triggered by a Physical Downlink Control Channel (PDCCH) order as specified in clause 9.2.6 or realized through UE-based TA measurement as configured by the RRC. In the former case, the gNodeB (gNB)ZgNB-Distributed Unit (gNB-DU), to which the candidate cell belongs, calculates the TA value and sends the calculated TA value to the gNB / gNB- DU to which the serving cell belongs via the gNB-Centralized Unit (gNB-CU). The serving cell sends the TA value in the LTM cell switch command MAC CE when triggering the LTM cellswitch. In the latter case, i.e., the UE-based TA measurement, the UE performs TA measurement for the candidate cells after being configured by RRC but the exact time the UE performs TA measurement is up to UE implementation. The UE applies the measured TA value measured and performs a RACH-less LTM upon receiving the cell switch command if it does not include any valid TA value. The network may also send a TA value in the LTM cell switch command MAC CE without early TA acquisition.

[0025] Therefore, depending on the availability of a valid TA value, the UE performs either a RACH-less LTM or RACH-based LTM cell switch. If the valid TA value is provided in the cell switch command, the UE applies the TA value as 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 an available valid TA value. 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 a RACH-based LTM cell switch.

[0026] Furthermore, regardless of whether the UE is configured for UE-based TA measurement for a certain candidate cell, the UE may follow the PDCCH order, which includes performing a random access procedure towards one or more candidate cells. This also applies to the candidate cells for which the UE is capable of deriving TA values by itself. Additionally, regardless of whether the UE has already performed a random access procedure toward the candidate cells, the UE may follow the UE-based measurement configuration if configured by the network.

[0027] For the RACH-less LTM, the UE accesses the target cell using either a configured grant or a dynamic grant. The configured grant is provided in the LTM candidate configuration, and the UE selects the configured grant occasion associated with a beam indicated in the cell switchcommand. Upon initiation of the LTM cell switch to the target cell, the UE starts to monitor the PDCCH on the target cell for dynamic scheduling. Before RACH-less LTM procedure completion, the UE may not trigger random access procedures if the UE does not have a valid PUCCH resource for triggered Scheduling Requests (SRs).

[0028] Furthermore, in the LTM, security keys are maintained upon an LTM cell switch, and subsequent LTM is supported.

[0029] The Rel 18 LTM supports both an intra-gNB-DU and an inter-gNB-DU mobility within the same gNB-CU. Also, the LTM supports both an intra-frequency and an inter-frequency mobility, including mobility to an inter-frequency cell that is not a current serving cell. However, the LTM is supported only for licensed spectrum. For example, the following scenarios are supported in the LTM:• Primary Cell (PCell) change in a non-Carrier Aggregation (CA) scenario and a nonDual Connectivity (DC) scenario;• PCell and Secondary Cell (SCell(s)) change in the CA scenario;• DC scenario including PCell and Master Cell Ground (MCG) SCell(s) change and an intra-SN Primary and Secondary cells (PSCell) and Secondary Cell Ground (SCG) SCell(s) change without MN involvement. However, the LTM for simultaneous PCell and PSCell change is not supported.

[0030] While the UE has stored LTM candidate configurations, the UE can also execute any L3 handover except for the Dual Active Protocol Stack (DAPS) handover. In the RRC message that the UE uses to request any Layer 3 handover (excluding DAPS), the target cell has the ability to add, modify, or release LTM candidate configurations.

[0031] In general, a cell switch command is conveyed in a MAC CE, which contains the required information to perform the LTM cell switch.

[0032] Moreover, a disaggregated architecture is defined in 3GPP decomposing the 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 that may be represented by at least one distributed unit (referred to as gNB-DU) and 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 a CU 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 5G networks. The disaggregated architecture of the gNB 100 may also include a Radio Unit (gNB-RU), not shown in FIG. 1.

[0033] The gNB-RU may be responsible for the radio transmission and reception of signals. The gNB-RU may include physical Radio Frequency (RF) components such as antennas, power amplifiers, and analog-to-digital 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 responsiblefor 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.

[0034] 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 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 (SDAPs). More specifically, 3GPP RAN3 cardinality for the 5G gNB 100 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 including 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.

[0035] In Rel-18, the LTM is limited to an intra-CU mobility. The data scheduling operations generally take place at the gNB-DU. However, in order to support L1 / L2 centric inter-cell change (i.e. change of the serving cell) in the disaggregated gNB architecture, the HO preparation phase i.e., providing the candidate / target cell configuration to the UE is performed by the gNB-CU-CP, that is autonomously executed by the gNB-DU without requiring further interaction with the upper layers in gNB-CU-CP.

[0036] However, there is a need for Handover (HO) preparation that takes place at the gNB-CU- CP, but is executed autonomously by the gNB-DU, without further interaction with the upper layers.

[0037] FIG. 2 illustrates a sequence flow diagram of an LTM procedure 200, in accordance with the Rel 18 framework. The sequence flow diagram includes a sequence of operations between a UE 201 and a gNB 203. The gNB 203 may have a similar architecture as explained in reference to the gNB 100 (shown in FIG. 1). The UE 201 may be in an RRC connected state with the gNB 203.

[0038] At operation 202, the UE 201 transmits a measurement report message to the gNB 203. At operation 204, the gNB 203 decides to configure the LTM and initiates LTM preparation i.e., preparation of LTM candidate configurations, based on the received measurement report message.

[0039] At operation 206, the gNB 203 transmits an RRCReconfiguration message to the UE 201. The RRCReconfiguration message includes the LTM candidate configurations.

[0040] At operation 208, the UE 201 stores the LTM candidate configurations and transmits an RRCReconfigurationComplete message to the gNB 203. Therefore, the operations 202-208 may correspond to LTM preparation.

[0041] At operation 210, the UE 201 performs DL synchronization with the LTM candidate cell(s) before receiving a cell switch command from the gNB 203. The UE 201 may activate and deactivate TCI states of the LTM candidate cell(s), as triggered by the gNB 203.

[0042] At operation 212, the UE 201 may perform UL synchronization with the LTM candidate cell(s) before receiving the cell switch command. The UE 201 may perform the UL synchronization by using UE-based TA measurement, if configured, and / or by transmitting a preamble towards the candidate cell, as triggered by the gNB 203. When the UE-based TA measurement is configured, the UE 201 acquires the TA value(s) of the candidate cell(s) by measurement. The UE 201 may perform early TA acquisition with the LTM candidate cell(s) as requested by the network before receiving the cell switch command as specified in clause 9.2.6. The UE 201 may perform the early TA acquisition via Contention Free Random Access (CFRA) procedure triggered by a PDCCH order from the source cell, following which the UE 201 sends a preamble towards the indicated candidate cell. In order to minimize data interruption of the source cell due to the CFRA towards the LTM candidate cell(s), the UE 201 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 indicated in the cell switch command. Moreover, the UE 201 may not maintain a TA timer for the LTM candidate cell and relies on network implementation to guarantee the TA validity. Specifically, the operations 210 and 212 correspond to early synchronization with the LTM candidate cell(s).

[0043] At operation 214, the UE 201 performs LI measurements on the configured LTM candidate cell(s) and transmits LI measurement reports to the gNB 203. The UE 201 may perform the LI measurements as long as the RRC reconfiguration (received at operation 206) is applicable.

[0044] At operation 216, the gNB 203 may determine to execute a cell switch to a target cell. At operation 218, the gNB 203 transmits an LTM cell switch command MAC CE triggering cell switch. The LTM cell switch command may include 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. At operation 220, the UE 201 switches to the target cell and applies the candidate configuration indicated by the target configuration ID.

[0045] At operation 222, the UE 201 performs the RACH procedure towards the target cell, if the UE 201 does not have a valid TA of the target cell as specified in clause 5.18.35 of TS 38.321 [6].

[0046] The operations 214 to 222 may correspond to LTM cell switch execution.

[0047] At operation 224, the UE 201 completes the LTM cell switch procedure by sending the RRCReconfigurationComplete message to the target cell. If the UE 201 has performed a Random Access (RA) procedure at operation 222, the UE 201 considers that LTM cell switch execution is successfully completed when the RACH procedure is successfully completed. For the RACH-less LTM, the UE 201 considers that LTM cell switch execution is successfully completed when the UE determines that the network has successfully received its first UL data.

[0048] Subsequent 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. For example, the operations 210-224 may be performed multiple times for the subsequent LTM cell switch executions using the LTM candidate configuration(s) provided in step 206. The general procedure over the air interface applies to SCG LTM. Further details of SCG LTM may be found in TS 37.340

[0021] ,

[0049] Further, RAN2#127bis made the following agreement:• RACH-less Conditional intra-CU LTM is supported.• PDCCH ordered early TA acquisition is supported for the C-LTM.

[0050] Therefore, even during the C-LTM, there is a need for the UE 201 to acquire TA of the LEE in the C-LTM candidate cell by performing UL-Sync(RACH) procedure with the candidate cell based on the PDCCH order from the serving gNB-DU. The TA is required at the LEE 201 to perform RACH-less C-LTM cell switch to the target cell.

[0051] However, the early TA acquisition based on the PDCCH order from the gNB-DU is inefficient as it would require the LEE 201 to report periodic or event-based LI measurements to the gNB-DU and then the gNB-DU will have to determine the candidate cell for early sync. Some conventional solutions enable LEL / DL sync during the C-LTM. However, such solutions are valid when a RACH preamble used for the TA acquisition can be identified at the candidate gNB-DU i.e., RACH preambles are segregated and identifiable for the TA acquisition and normal RACH (including RACH for LTM cell switch) purposes.

[0052] Currently, a RACH procedure can be executed for different purposes. For example, a normal RACH procedure is executed during any HO (including LTM cell switch) or reconfiguration with sync or any other legacy reason. Several actions may be undertaken at the gNB-DU upon execution of such a RACH procedure, based on when the RACH procedure is performed (for example, an RRC state, an ongoing HO, reconfiguration with sync, etc.). A RACH procedure may also be executed to perform the early TA acquisition during the LTM. In this case, the gNB-DU measures the TA of the UE 201 in the candidate cell and transmits the TA to the serving gNB-DU via the gNB-CU. Because this functionality at the candidate gNB-DU is differentfrom that of the normal RACH, there needs to be a way to distinguish the RACH procedure used for TA acquisition from the normal RACH.

[0053] The current technique for distinguishing the RACH procedures requires that each gNB-DU allocate a dedicated pool of RACH preambles to each of its neighboring gNB-DUs. This dedicated pool of RACH preambles is shared by all UEs of one gNB-DU. The serving gNB-DU allocates a RACH preamble from the dedicated pool of RACH preambles (corresponding to the candidate the gNB-DU) while issuing the PDCCH order to the UE 201 to acquire a candidate cell TA. Thereafter, the serving gNB-DU sends an available RACH preamble from the dedicated pool of RACH preambles in the PDCCH order sent to the UE 201 for acquiring TA. The candidate gNB-DU will identify the source gNB-DU, and the purpose of the RACH procedure based on the RACH preamble used by the UE 201 during the RACH procedure.

[0054] Advanced solutions to acquire TA based on execution condition from the candidate cell are limited in scope due to the existing solutions to distinguish the RACH procedures at the candidate gNB-DU. The UE 201 acquiring candidate cell TA based on execution condi tion(s) also implies that a RACH preamble cannot be allocated to the UE 201 from the pool of RACH preambles to perform RACH procedure, as the solutions propose to perform TA acquisition based on an execution condition, without the PDCCH order from the serving gNB-DU.

[0055] The present disclosure provides a method to retain the benefit of suppress / reduce periodic LI measurement reports from the UE 201 and also perform early TA acquisition based on execution condition.

[0056] FIGS. 3A-3B illustrate a sequence flow diagram of a C-LTM procedure 300, in accordance with one or more embodiments of the present disclosure. The sequence flow diagram includes asequence of operations between the UE 201 and the gNB 203. The gNB 203 may include a gNB- CU and one or more gNB-DUs, as explained with reference to FIG. 1. The UE 201 may be in an RRC connected state with the gNB 203 and an associated cell may be referred to as the UE’s serving cell. The operations of FIGS. 3A-3B which are similar to the operations as explained in reference FIG. 2 have been provided with similar reference numerals, and a detailed explanation of such steps has been omitted for the sake of brevity.

[0057] At operation 302, the UE 201 transmits an L3 measurement report message to the gNB 203. The L3 measurement report message may include one or more radio measurement corresponding the gNB 203 and / or one or more neighboring gNBs. In one embodiment, the L3 measurement report may include information such as, but not limited to, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Signal to Interference and Noise Ratio (SINR), and any relevant parameters. At operation 304, the gNB 203 determines to configure the C-LTM and initiates preparation of C-LTM candidate configurations, based on the received L3 measurement report message.

[0058] At operation 306, the gNB 203 transmits an RRCReconfiguration message to the UE 201. The RRCReconfiguration message includes the C-LTM candidate configurations, C-LTM LI execution condition(s), and TA acquisition execution condition(s). In one embodiment, the gNB- CU associated with the gNB 203, i.e., the gNB of the UE’s serving cell, may transmit the C-LTM candidate cell configurations. Specifically, the UE 201 may be configured with a new execution condition associated with the TA acquisition referred to as the TA acquisition execution condition. The TA acquisition execution condition is different from the LI execution condition associated with a C-LTM cell switch execution. In alternative embodiments, an offset may be added to the“LI execution condition associated with C-LTM cell switch execution” to render the “execution condition associated with TA acquisition”. In one or more embodiments, each C-LTM candidate cell configuration may be provided with two different execution conditions, one associated with the TA acquisition and another associated with the C-LTM cell switch execution.

[0059] At operation 308, the UE 201 stores the LTM candidate configurations, C-LTM LI execution condition(s), and the TA acquisition execution condition(s). Thereafter, the UE 201 transmits an RRCReconfigurationComplete message to the gNB 203. Therefore, the operations 302-308 may correspond to the LTM preparation.

[0060] Thereafter, at operation 309, the UE 201 monitors the received C-LTM LI execution condition(s) and TA acquisition execution condition(s).

[0061] In an embodiment, upon satisfying the execution condition associated with the TA acquisition, the UE 201 may send at least one of an LI measurement report (as shown in operation 309-1), an Uplink Media Access Control-Control Element (UL MAC CE), and an Uplink Control Information (UCI) message to the gNB-DU associated with the gNB 203. The UE 201 transmits / sends the at least one of the LI measurement report, the UL MAC CE, and the UCI to request the PDCCH order for early TA acquisition to the indicated candidate cell. The UE 201 may indicate the intended candidate cell for the TA acquisition and the request to send PDCCH order to the gNB-DU associated with the gNB 203. The gNB-DU associated with the gNB 203 sends the PDCCH order, including the RACH preamble corresponding to a candidate / target gNB- DU of the candidate cell, to ask the UE 201 to acquire the C-LTM candidate cell TA.

[0062] Based on the request from the UE 201, the gNB-DU associated with the gNB 203 sends the PDCCH order which includes the RACH preamble from the pool RACH preambles and the candidate cell ID to perform the TA acquisition, as shown by step 309-2.

[0063] At operation 310, the UE 201 performs DL synchronization with the LTM candidate cell(s). The UE 201 may activate and / or deactivate one or more TCI states of the LTM candidate cell(s), as triggered by the gNB 203.

[0064] At operation 312, the UE 201 may perform UL synchronization with the LTM candidate cell(s), i.e., the TA acquisition procedure. The early TA acquisition procedure is triggered by the UE 201 towards the C-LTM candidate cell, whenever the PDCCH order is received. The UE 201 performs the RACH procedure with the corresponding C-LTM candidate cell / gNB-DU and the C- LTM candidate cell returns the TA. The C-LTM candidate cell TA can be returned to the UE 201 directly in the Random -Access Response (RAR) message. Alternatively, the Rel 18 mechanism of using the gNB-CU to deliver the TA to the serving gNB-DU is also feasible.

[0065] After acquiring the TA, at operation 313, the UE 201 keeps evaluating the C-LTM cell switch execution condition. Whenever the C-LTM cell switch execution condition is met, the UE 201 performs a RACH-less HO to the designated C-LTM candidate cell.

[0066] In one embodiment, at operation 314, the UE 201 performs LI measurements on the configured C-LTM candidate cell(s) and transmits LI measurement reports to the gNB 203. At operation 316, the UE 201 may determine to execute a cell switch to a target cell, when the LI execution condition is satisfied. At operation 318, the UE 201 detach from the source and apply target cell configuration. The target cell configuration may corresponds to one of the one or more configured C-LTM candidate cell configurations received at step 306. At operation 320, the UE201 performs the RACH procedure towards the target cell, if the UE 201 does not have a valid TA of the target cell as specified in clause 5.18.35 of TS 38.321 [6], At operation 322, the UE 201 completes the LTM cell switch procedure by sending a RRCReconfigurationComplete message to the target cell.

[0067] The present disclosure provides fast UL synchronization, i.e., early TA acquisition. The present disclosure also enables the C-LTM procedure with less signaling and measurement overhead on the UE 201 and the network (for example, the gNB 203).

[0068] FIGS. 4A-4B illustrate a flowchart depicting a method for conditional early TA acquisition for the C-LTM, in accordance with an embodiment of the present disclosure. The method 400 may be performed by the UE 201.

[0069] At step 402, the UE 201 transmits one or more measurement reports corresponding to the one or more candidate cells and / or the UE’s serving cell. In one embodiment, the one or more candidate cells may correspond to one or more neighboring cells associated with the UE 201. The one or more measurement reports may indicate recording conditions associated with the one or more neighboring cells and / or the UE’s serving cell.

[0070] At step 404, the UE 201 receives one or more candidate cell configurations corresponding to one or more candidate cells for the C-LTM, from the gNB-CU of the UE’s serving cell. Each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition and a cell switch execution condition. The one or more candidate cell configuration comprises predefined parameters and / or information that enable the UE 201 to efficiently switch to a target cell when certain conditions are met. In one or more embodiments, the one or more candidate cell configuration comprises information such as, but not limited to, cellidentify information (for example, a Physical Cell Identity (PCI), a New radio Cell GlobalIdentifier (NCGI), measurement configuration, mobility-related configuration information, and / or other related parameters. The TA acquisition execution condition may indicate one or more conditions and / or trigger events which enables the UE 201 to perform early TA acquisition.

[0071] At step 406, the UE 201 monitor the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition execution condition is met. The UE 201 may monitor the one or more parameters based on the received one or more candidate cell configurations. In one embodiment, the one or more parameters may include, but are not limited to, RSRP, RSRQ, and SINR. In one embodiment, the TA acquisition execution condition may define a threshold value corresponding to each of the one or more monitored parameters. The UE 201 may compare a measured value corresponding to the one or more parameters with the corresponding threshold value to determine whether the at least one TA acquisition execution is met.

[0072] At step 408, the UE 201 transmits the at least one of the LI measurement report, the uplink MAC CE, and the UCI message to at least one gNB- DU of the UE’s serving cell. The UE 201 transmits the at least one of the LI measurement report, the uplink MAC CE, and the UCI message in response to determining that the at least one TA acquisition execution condition is met. Further, the UE 201 transmits the at least one of the LI measurement report, the uplink MAC CE, and the UCI message to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition.

[0073] At step 410, the UE 201 receives the PDCCH order in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message. The PDCCH ordermay include a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell. In one embodiment, the PDCCH order may convey critical scheduling and control information. The PDCCH order may trigger the UE 201 to perform a RACH procedure to receive TA value and perform UL synchronization.

[0074] Thereafter, at step 412, the UE 201 transmits a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell. The UE 201 transmits the RACH request message to the candidate gNB-DU of the at least one candidate cell. The RACH request message with the received RACH preamble indicates to the candidate gNB- DU that the RACH request message corresponds to TA acquisition. Thus, the UE 201 is not required to store the RACH preamble corresponding to each of the gNB-DU associated with the one or more candidate cell. The UE 201 may receive the required RACH preamble and perform the TA acquisition. The RACH preamble is received only for a target cell for which TA acquisition execution condition is met which reduces signaling overhead on the UE 201 and the network, thereby enables the UE 201 to perform the C-LTM procedure effectively and efficiently.

[0075] At step 414, the UE 201 receives the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0076] At step 416, the UE 201 monitors the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one cell switch execution condition is met for the at least one candidate cell among the one or more candidate cells. The UE 201 monitors the one or more parameters based on the received one or more candidate cell configurations.

[0077] At step 418, the UE 201 performs a RACH-less handover to the at least one candidate cell based on the received TA in response to determining that the at least one cell switch execution condition is met for the at least one candidate cell. In one embodiment, the cell switch execution condition may define a threshold value corresponding to each of the one or more monitored parameters to perform the cell switch with the corresponding candidate cell. The UE 201 may compare a measured value corresponding to the one or more parameters with the corresponding threshold value to determine whether the at least one cell switch execution is met. In one embodiment, the UE 201 receives a Random Access Response (RAR) message in response to the transmitted RACH request message from the gNB-DU associated with the at least one candidate cell. The RAR message may include the TA for the at least one candidate cell. In another embodiment, the UE 201 may receive the TA associated with the at least one candidate cell via the gNB-DU of the UE’s serving cell through the gNB-CU of the UE’s serving cell.

[0078] In one embodiment, the UE 201 may also receive one or more activated Transmission Configuration Indicator (TCI) states from the gNB-DU of the UE’s serving cell. The UE 201 may receive the one or more activated TCI states based on the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message. Furthermore, the UE 201 may perform Downlink (DL) synchronization with the at least one candidate cell based on the received one or more activated TCI states.

[0079] Thus, the early TA acquisition enables the UE 201 to perform C-LTM with a target / candidate cell effectively and effectively.

[0080] While the above-discussed steps in FIGS. 4A-4B are shown and described in a particular sequence, the steps may occur in variations to the sequence in accordance with variousembodiments. Further, a detailed description related to the various steps of FIGS. 4A-4B is already covered in the description related to FIGS. 3A-3B and is omitted herein for the sake of brevity.

[0081] FIG. 5 illustrates an embodiment of a device / apparatus 500. The device / apparatus 500 may correspond to the UE 201 and / or the gNB 203. As shown in FIG. 5, the device 500 includes a processor 510, a memory 520, a storage component 530, an input component 540, an output component 550, a communication interface 560, and a bus 570. The one or more components of the device 500 may be configured to implement one or more operations / functionalities of the present disclosure as discussed above.

[0082] The processor 510, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 510 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 510 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.

[0083] The memory 520 includes a non-transitory computer readable medium. The memory 520 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 510. The memory 520 comprises machine-readable instructions which are executable by the processor 510. These machine-readable instructions when executed by the processor 510 cause the processor 510 to perform one or more method steps of an embodiment described above.

[0084] The storage component 530 stores information and / or software related to the operation and use of the device 500. For example, the storage component 530 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.

[0085] The input component 540 is configured to receive information, such as user input. For example, the input component 540 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 540 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0086] The output component 550 is configured to provide output information from the device 500. For example, the output component 550 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).

[0087] The communication interface 560 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 560 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 500 and other devices. In other words, the standard of the communication interface 560 is not limited.

[0088] The bus 570 acts as an interconnect between the processor 510, the memory 520, the storage component 530, the input component 540, the output component 550, and thecommunication interface 560 of the device 500. The bus 570 may include a wired interconnection or a wireless interconnection.

[0089] The number and arrangement of components shown in FIG. 5 are provided as an example. In practice, device 500 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 5. Additionally, or alternatively, a set of components (e.g., one or more components) of the device 500 may perform one or more functions described as being performed by another set of components of the device 500. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of devices 500 in communication with one another.

[0090] 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 gNodeB-Control Unit (gNB-CU) of a User Equipment’s (UE’s) serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitor, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmit, to at least one gNB-Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control -Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition; receive, in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmit, to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell; and receive the TA associated with the at least one candidate cell based on the transmitted RACH request message.[2] The apparatus as described in [1], wherein each of the one or more candidate cell configurations comprises at least one cell switch execution condition apart from the at least one TA acquisition execution condition, and the apparatus is configured to: monitor, based on the received one or more candidate cell configurations, the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one cell switch execution condition is met for the at least one candidate cell among the one or more candidate cells; and in response to determining that the at least one cell switch execution condition is met for the at least one candidate cell, perform a RACH-less handover to the at least one candidate cell based on the received TA.[3] The apparatus as described in any one of [1] to [2], wherein to receive the TA associated with the at least one candidate cell based on the transmitted RACH request message, the apparatus is configured to: receive, from the gNB-DU associated with the at least one candidate cell, a Random Access Response (RAR) message including the TA.[4] The apparatus as described in any one of [1] to [3], wherein the apparatus is configured to receive the TA associated with the at least one candidate cell via the gNB-DU of the UE’s serving cell through the gNB-CU of the UE’s serving cell.[5] The apparatus as described in any one of [1] to [4], wherein prior to receiving the one or more candidate cell configurations corresponding to the one or more candidate cells, the apparatus is configured to: transmit, to the gNB-CU, one or more measurement reports corresponding to the one or more candidate cells.[6] The apparatus as described in any one of [1] to [5], further configured to: receive, from the gNB-DU of the UE’s serving cell, one or more activated Transmission Configuration Indicator (TCI) states based on the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message.[7] The apparatus as described in any one of [1] to [6], wherein the RACH request message with the received RACH preamble indicates to the candidate gNB-DU that the RACH request message corresponds to TA acquisition.[8] The apparatus as described in any one of [1] to [7], wherein the one or more parameters comprises one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and Signal to Interference and Noise Ratio (SINR).[9] The apparatus as described in any one of [1] to [8], wherein the apparatus corresponds to a User Equipment (UE).

[0010] A method comprising: receiving, by a User Equipment (UE) from a gNodeB-Control Unit (gNB-CU) of a UE’s serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitoring, by the UE, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmitting, by the UE, to at least one gNB -Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control-Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition;receiving, by the UE, in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmitting, from the UE to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire the TA associated with the at least one candidate cell; and receiving, by the UE, the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0011] The method as described in

[0010] , wherein each of the one or more candidate cell configurations comprises at least one cell switch execution condition apart from the at least one TA acquisition execution condition, and the method comprises: monitoring, by the UE, based on the received one or more candidate cell configurations, the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one cell switch execution condition is met for the at least one candidate cell among the one or more candidate cells; and in response to determining that the at least one cell switch execution condition is met for the at least one candidate cell, performing, by the UE, a RACH-less handover to the at least one candidate cell based on the received TA.

[0012] The method as described in any one of

[0010] to

[0011] , wherein receiving the TA associated with the at least one candidate cell based on the transmitted RACH request message comprises: receiving, by the UE from the gNB-DU associated with the at least one candidate cell, a Random Access Response (RAR) message including the TA.

[0013] The method as described in any one of

[0010] to

[0012] , wherein receiving the TA associated with the at least one candidate cell comprises: receiving, by the UE, the TA associated with the at least one candidate cell via the gNB-DU of the UE’s serving cell through the gNB-CU of the UE’s serving cell.

[0014] The method as described in any one of

[0010] to

[0013] , wherein prior to receiving the one or more candidate cell configurations corresponding to the one or more candidate cells, the method comprises: transmitting, from the UE to the gNB-CU, one or more measurement reports corresponding to the one or more candidate cells.

[0015] The method as described in any one of

[0010] to

[0014] , further comprises: receiving, by the UE from the gNB-DU of the UE’s serving cell, one or more activated Transmission Configuration Indicator (TCI) states based on the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message.

[0016] The method as described in any one of

[0010] to

[0015] , wherein the RACH request message with the received RACH preamble indicates to the candidate gNB-DU that the RACH request message corresponds to TA acquisition.

[0017] The method as described in any one of

[0010] to

[0016] , wherein the one or more parameters comprises one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), and Signal to Interference and Noise Ratio (SINR).

[0018] A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a User Equipment (UE) comprising one or more processors, cause the one or more processors to:receive, from a gNodeB-Control Unit (gNB-CU) of a UE’s serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitor, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmit, to at least one gNB- Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control-Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition; receive, in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmit, to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire the TA associated with the at least one candidate cell; and receive the TA associated with the at least one candidate cell based on the transmitted RACH request message.

[0091] The present disclosure enables faster UL synchronization, i.e., early TA acquisition. The present disclosure reduces signaling and measurement overhead on the UE and the network that is required to perform RACH-less C-LTM cell switching.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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 thespecification 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.

[0096] 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.

[0097] 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 Claim:

1. An apparatus configured to: receive, from a gNodeB-Control Unit (gNB-CU) of a User Equipment’s (UE’s) serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more - candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitor, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmit, to at least one gNB- Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control -Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition; receive, in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmit, to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire TA associated with the at least one candidate cell; andreceive the TA associated with the at least one candidate cell based on the transmittedRACH request message.

2. The apparatus as claimed in claim 1, wherein each of the one or more candidate cell configurations comprises at least one cell switch execution condition apart from the at least one TA acquisition execution condition, and the apparatus is configured to: monitor, based on the received one or more candidate cell configurations, the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one cell switch execution condition is met for the at least one candidate cell among the one or more candidate cells; and in response to determining that the at least one cell switch execution condition is met for the at least one candidate cell, perform a RACH-less handover to the at least one candidate cell based on the received TA.

3. The apparatus as claimed in claim 1, wherein to receive the TA associated with the at least one candidate cell based on the transmitted RACH request message, the apparatus is configured to: receive, from the gNB-DU associated with the at least one candidate cell, a Random Access Response (RAR) message including the TA.

4. The apparatus as claimed in claim 1, wherein the apparatus is configured to receive the TA associated with the at least one candidate cell via the gNB-DU of the UE’s serving cell through the gNB-CU of the UE’s serving cell.

5. The apparatus as claimed in claim 1, wherein prior to receiving the one or more candidate cell configurations corresponding to the one or more candidate cells, the apparatus is configured to: transmit, to the gNB-CU, one or more measurement reports corresponding to the one or more candidate cells.

6. The apparatus as claimed in claim 1, further configured to: receive, from the gNB-DU of the UE’s serving cell, one or more activated Transmission Configuration Indicator (TCI) states based on the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message.

7. The apparatus as claimed in claim 1, wherein the RACH request message with the received RACH preamble indicates to the candidate gNB-DU that the RACH request message corresponds to TA acquisition.

8. The apparatus as claimed in claim 1, wherein the one or more parameters comprises one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), andSignal to Interference and Noise Ratio (SINR).

9. The apparatus as claimed in claim 1, wherein the apparatus corresponds to a UserEquipment (UE).

10. A method compri sing : receiving, by a User Equipment (UE) from a gNodeB-Control Unit (gNB-CU) of a UE’s serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitoring, by the UE, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmitting, by the UE, to at least one gNB -Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control-Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition; receiving, by the UE, in response to the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random AccessChannel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmitting, from the UE to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire the TA associated with the at least one candidate cell; and receiving, by the UE, the TA associated with the at least one candidate cell based on the transmitted RACH request message.

11. The method as claimed in claim 10, wherein each of the one or more candidate cell configurations comprises at least one cell switch execution condition apart from the at least one TA acquisition execution condition, and the method comprises: monitoring, by the UE, based on the received one or more candidate cell configurations, the one or more parameters associated with each of the one or more candidate cells to determine whether the at least one cell switch execution condition is met for the at least one candidate cell among the one or more candidate cells; and in response to determining that the at least one cell switch execution condition is met for the at least one candidate cell, performing, by the UE, a RACH-less handover to the at least one candidate cell based on the received TA.

12. The method as claimed in claim 10, wherein receiving the TA associated with the at least one candidate cell based on the transmitted RACH request message comprises:receiving, by the UE from the gNB-DU associated with the at least one candidate cell, a Random Access Response (RAR) message including the TA.

13. The method as claimed in claim 10, wherein receiving the TA associated with the at least one candidate cell comprises: receiving, by the UE, the TA associated with the at least one candidate cell via the gNB- DU of the UE’s serving cell through the gNB-CU of the UE’s serving cell.

14. The method as claimed in claim 10, wherein prior to receiving the one or more candidate cell configurations corresponding to the one or more candidate cells, the method comprises: transmitting, from the UE to the gNB-CU, one or more measurement reports corresponding to the one or more candidate cells.

15. The method as claimed in claim 10, further comprises: receiving, by the UE from the gNB-DU of the UE’s serving cell, one or more activated Transmission Configuration Indicator (TCI) states based on the transmitted at least one of the LI measurement report, the uplink MAC CE, and the UCI message.

16. The method as claimed in claim 10, wherein the RACH request message with the received RACH preamble indicates to the candidate gNB-DU that the RACH request message corresponds to TA acquisition.

17. The method as claimed in claim 10, wherein the one or more parameters comprises one of Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), andSignal to Interference and Noise Ratio (SINR).

18. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a User Equipment (UE) comprising one or more processors, cause the one or more processors to: receive, from a gNodeB-Control Unit (gNB-CU) of a UE’s serving cell, one or more candidate cell configurations corresponding to one or more candidate cells for a conditional Layer 1 / Layer 2 Triggered Mobility (C-LTM), wherein each of the one or more candidate cell configurations comprises at least one Timing Advance (TA) acquisition execution condition; monitor, based on the received one or more candidate cell configurations, one or more parameters associated with each of the one or more candidate cells to determine whether the at least one TA acquisition condition is met; in response to determining that the at least one TA acquisition execution condition is met for at least one candidate cell among the one or more candidate cells, transmit, to at least one gNB- Distributed Unit (gNB-DU) of the UE’s serving cell, at least one of a Layer 1 (LI) measurement report, an uplink Medium Access Control-Control Element (MAC CE), and an Uplink Control Information (UCI) message corresponding to the at least one candidate cell to request a Physical Downlink Control Channel (PDCCH) order from the gNB-DU for performing early TA acquisition;receive, in response to the transmitted at least one of the I measurement report, the uplink MAC CE, and the UCI message, the PDCCH order including a Random Access Channel (RACH) preamble corresponding to a candidate gNB-DU of the at least one candidate cell; transmit, to the candidate gNB-DU of the at least one candidate cell, a RACH request message with the received RACH preamble to acquire the TA associated with the at least one candidate cell; and receive the TA associated with the at least one candidate cell based on the transmittedRACH request message.

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