WO2025235178A1

WO2025235178A1 - Multi-trp ltm in inter-cu and intra-cu scenario

Info

Publication number: WO2025235178A1
Application number: PCT/US2025/025293
Authority: WO
Inventors: Subramanya CHANDRASHEKAR
Original assignee: Rakuten Symphony Inc; Rakuten Symphony Usa LLC
Current assignee: Rakuten Symphony Inc; Rakuten Symphony Usa LLC
Priority date: 2024-05-08
Filing date: 2025-04-18
Publication date: 2025-11-13
Anticipated expiration: 2026-11-08

Abstract

Embodiments disclosed herein provide a method and system for receiving, at a UE, from a serving CU, a configuration message indicative of a configuration for performing a timing acquisition procedure for TRPs associated with LTM candidate cells of at least one of primary and secondary TRPs of a target/candidate DU. Further, a PDCCH order, indicative of acquiring associated TA, is received at the UE from a serving DU. Furthermore, TRP identifiers of the LTM candidate cells are received at the UE, from the serving CU and/or the serving DU, along with the associated TA. The TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a RAR. Moreover, RACH-less LTM cell switch is performed, at the UE, with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

Description

MULTI-TRP LTM IN INTER-CU AND INTRA-CU SCENARIO

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority to Indian Provisional Patent Application No. 202441036407, filed on May 08, 2024, and Indian Non-Provisional Patent Application No. 202441036407, filed on February 28, 2025, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

[0002] The present disclosure relates to multi-Transmission and Reception Point (TRP) and Layerl/Layer 2 Triggered Mobility (LTM) in an Inter-Central Unit (CU) and Intra-CU scenario.

BACKGROUND

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

[0004] In 3rd Generation Partnership Project (3GPP), a disaggregated architecture of gNodeB (gNB) is defined as decomposing the gNB into multiple logical entities. The gNB is split into three logical nodes i.e., Central Unit Control plane (CU-CP), Central Unit User plane (CU-UP) and Distributed Unit (DU). A single DU may host multiple cells. For instance, the 3GPPP defines that a DU can host up to 512 cells. The CU (also referred as gNB-CU) hosts upper layers such as Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers, while the DU (also referred as gNB-DU) hosts lower layers such as Radio Link Control (RLC), Media Access Control (MAC), and Physical (PHY) layers. The scheduling operation takes place at the gNB-DU. Layerl/Layer 2 triggered mobility (LTM) was introduced in Rel-18 and offers improvements in handover latency and interruption time compared to Layer 3 based mobility. However, LTM as introduced in Rel-18 also has limited scope and in R19, the scope has been increased to include inter-gNB scenario and extended dual connectivity.

[0005] To support LTM involving change of serving cell in the disaggregated gNB architecture, there is a need for a mechanism in which handover preparation would be performed by the gNB- CU-CP, however, the execution would be performed autonomously by the gNB-DU without further interaction with the upper layers.

SUMMARY

[0006] The present disclosure relates to a method comprising the steps of receiving, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission- Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of primary and/or secondary TRPs of a target/candidate Distributed Unit (DU). Further, a PDCCH order, indicative of acquiring timing advance (TA) associated with at least one TRP, is received at the UE, from a serving DU. Furthermore, the method comprises receiving, at the UE, from the serving CU and/or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the primary and/or secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR). The method also involves performing, at the UE, Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

[0007] The present disclosure also relates to an apparatus configured to receive, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission- Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of primary and/or secondary TRPs of a target/candidate Distributed Unit (DU). Further, a PDCCH order, indicative of acquiring timing advance (TA) associated with the one or more TRPs, is received at the UE, from a serving DU. Furthermore, one or more TRP identifiers of the one or more LTM candidate cells of the primary and/or secondary TRP is received at the UE, from the serving CU and/or the serving DU, along with the associated TA. The associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR). The apparatus is also configured to perform, at the UE, Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA. [0008] The present disclosure also relates to an apparatus configured to receive, at a target/candidate Distributed Unit (DU), from a Centralized Unit (CU), a context setup request to set up a Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cell for a User Equipment (UE). The present disclosure also relates to an apparatus configured to prepare at least one LTM candidate cell with a primary and/or a secondary Transmission Reception Points (TRPs) belonging to the target/candidate DU. The primary and/or secondary Transmission Reception Points (TRPs) may be considered as two TRPs. For example, the configuration parameters pertaining to the primary and secondary TRPs are similar. Further, separate resources are allocated for primary and/or secondary TRPs including Random Access Channel (RACH) resources pertaining to the UE. Furthermore, a RACH request is received from the UE, to perform TA acquisition. The apparatus is also configured to transmit a Random Access Response (RAR) to the UE. The RAR includes one or more TRP identifiers of one or more LTM candidate cells and associated timing advance (TA).

[0009] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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:

[0011] FIG. 1 illustrates an existing disaggregated gNB architecture.

[0012] FIG. 2A and FIG. 2B illustrate two variants of LTM, i.e. intra-CU and inter-CU LTM in the disaggregated gNB architecture.

[0013] FIG. 3A-FIG. 3C illustrate multiple ways of communication related to multi-TRP, in accordance with some embodiments of the present disclosure.

[0014] FIG. 4 illustrates data structure of MAC PDU that carries Random Access Response (RAR).

[0015] FIG. 5A and FIG. 5B illustrate signaling diagram illustrating methods for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with some embodiments of the present disclosure. an aspect of the subject matter in accordance with one embodiment.

[0016] FIG. 6 illustrates a flowchart of a method for performing Timing Advance (TA) acquisition in a multi-TRP scenario, according to the embodiments as disclosed herein.

[0017] FIG. 7 illustrates a block diagram of the UE for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with an embodiment of the present disclosure. [0018] FIG. 8 illustrates a block diagram of the target/candidate gNB-DU 504 for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with an embodiment of the present disclosure.

[0019] FIG. 9 illustrates an embodiment of a device wherein the method for performing Timing Advance (TA) acquisition in a multi-TRP scenario, according to the embodiments as disclosed herein.

[0020] It should be appreciated by those skilled in the art that any block diagram herein represents conceptual views of illustrative systems embodying the principles of the present subject matter. Similarly, it will be appreciated that any flow charts, flow diagrams, state transition diagrams, pseudo code, and the like represent various processes which may be substantially represented in computer readable medium and executed by a computer or processor, whether or not such computer or processor is explicitly shown.

DETAILED DESCRIPTION

[0021] The following detailed description of example embodiments refers to the accompanying drawings. The present disclosure provides illustrations and descriptions but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the present disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flow chart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part). [0022] It will be apparent that systems and/or methods described herein, may be implemented in different forms of hardware, software, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and/or methods should not limit their implementations. Thus, the operation and behavior of the systems and/or methods are described herein without reference to specific software code. It is understood that software and hardware may be designed to implement the systems and/or methods based on the description herein.

[0023] Even though particular combinations of features are recited in the claims and/or disclosed in the specification, the particular combinations are not intended to limit the disclosure of implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and/or disclosed in the specification. Even if a dependent claim directly depends on only one claim, the present disclosure may indicate that the dependent claim is dependent on other claims in the claim set.

[0024] No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles “a” and “an” (in other words, nouns not mentioned in the plural) are intended to include one or more items and may be used interchangeably with “one or more.” Also, as used herein, the terms “has,” “have,” “having,” “include,” “including,” or the like are intended to be open-ended terms. Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Furthermore, expressions such as “at least one of [A] and [B],” “[A] and/or [B],” or “at least one of [A] or [B]” are to be understood as including only A, only B, or both A and B.

[0025] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

[0026] FIG. 1 illustrates an existing disaggregated gNB architecture. In an existing (or conventional) disaggregated gNB architecture, a conventional gNB 100 may be decomposed into multiple logical entities, as defined in 3GPP. For example, the conventional gNB 100 may include a gNB-Control Unit-Control Plane (CU-CP) 101 (gNB-Control Unit-Control Plane (CU- CP) and a gNB-Control Unit-User Plane (CU-UP) 103 (gNB-Control Unit-User Plane (CU-UP). CU-CP and CU-UP is also referred hereinafter as gNB-Centralized Unit (CU) for the sake of brevity) and the gNB DU 102. Likewise, a single DU 102 may be responsible to host multiple cells (not shown). As an example, a single DU 102 may be responsible to host a maximum of 512 cells in current 3GPP specifications. The gNB-CU-CP 101 may host a Packet Data Convergence Protocol (PDCP-c) and a Radio Resource Control (RRC) layer, while the gNB-DU 102 hosts a Radio Link Control (RLC), a Medium Access Control (MAC), and a Physical (PHY) layer. The scheduling operation takes place at the gNB-DU 102. In order to support L1/L2 triggered mobility (LTM) cell switch, related to the changing of serving cell (not shown), in the disaggregated gNB architecture, a mechanism is implemented in which the handover preparation would be performed by the gNB-CU-CP 101, but the cell switch is executed autonomously by the gNB-DU 102 without any further interaction with the upper layers. For example, the mechanism involves performing the handover preparation by the gNB-CU-CP 101, but autonomously executing the handover by the gNB-DU 102 without further interaction with upper layers, such as PDCP and the RRC layer.

[0027] Conventionally, the disaggregated gNB architecture may also include a logical node, such as a gNB-CU-User Plane (gNB-CU-UP) 103 to host user plane part of the PDCP-u protocol of the gNB-CU 101 and/ or the Service Data Adaptation Protocol (SDAP) protocol. The gNB- CU-UP 103 terminates El interface connected with the gNB-CU-CP 101 and the Fl-U interface connected with the gNB-DU 102.

[0028] In Rel-18, LTM was limited to intra-CU scenario. In Rel-19, inter-gNB and NR-DC are included in the objectives of NR mobility enhancements, as indicated below:

• To specify support for inter-CU Layer 2 Mobility (LTM) [RAN2, RAN3]

• To prioritize the case when CU is acting as a Master Node (MN) when Dual Connectivity (DC) is not configured.

• As secondary priority, to support the case when NR-DC is configured and CU is acting as a Secondary Node (SN) and Master Cell Group (MCG) is unchanged.

• As secondary priority, to support the case when NR-DC is configured, CU is acting as the MN and Secondary Cell Group (SCG) is unchanged or SCG is released.

[0029] The objective excludes the case when LTM is configured in both MCG and SCG.

• Further, the objective includes specifying support for subsequent LTM mobility procedures aiming to avoid RRC configuration between cell switches as per Rel-18 LTM, and coordination with SA3 needed with respect to security key handling. The Rel-18 intra- CU LTM procedure is considered as the baseline for adding inter-CU support. [0030] Further, measurements related enhancements for the purpose of supporting LTM: [RAN2, RANI] include the following:

• Measurement related enhancements are applicable to Intra-CU MCG/SCG LTM and Inter- CU MCG/SCG LTM

• To specify necessary components to support event triggered LI measurement reporting [RAN2, RANI]

• To enable progress of RANI and RAN2 independently on the event triggered measurements objectives of their respective MIMO and Mobility enhancement objectives. Review progress at RAN# 105 to see if any modification of objectives is required to avoid/manage any overlap in the work.

• To specify support for CSLRS measurements for LTM procedures and enable CSLRS based beam management, and/or other necessary physical layer operations on candidate cells before LTM [RANI]

• To specify support of conditional LTM [RAN2, RAN3, RANI] o To prioritize intra-CU LTM o To have a checkpoint to review objective at RAN#105, and thereafter start RAN WG work.

• To specify RRM requirements related to the above objectives as necessary [RAN4], [0031] FIG. 2A and FIG. 2B illustrate two variants of LTM, i.e. intra-CU and inter-CU LTM in the disaggregated gNB architecture.

[0032] In some embodiments, LTM for intra-CU and inter-CU may be depicted in two variants as shown in the FIG. 2 A and FIG. 2B. For example, FIG. 2A illustrates a first variant 200a in which the LTM candidate cells are configured in different gNBs. In another example, FIG. 2B illustrates a second variant 200b, in which the LTM candidate cells are configured in same gNB. [0033] FIG. 2A shows a serving gNB-CU 202a and a target/candidate gNB-CU 204a which are connected over an Xn interface. The serving gNB-CU 202a is associated with a serving gNB-DU 206a, where the serving gNB-CU 202a is connected with the serving gNB-DU 206a over an Fl interface. Further, the target/candidate gNB-CU 204a is associated with a target/candidate gNB- DU 208a, where the target/candidate gNB-CU 204a is connected with the target/candidate gNB- DU 208a over an Fl interface. Further, a User Equipment (UE) 210a is connected with the serving gNB-DU 206a. [0034] FIG. 2B shows a serving gNB-CU 202b. The serving gNB-CU 202b is associated with a serving gNB-DU 204b, where the serving gNB-CU 202b is connected with the serving gNB- DU 204b over an Fl interface. The serving gNB-CU 202b is associated with a target/candidate gNB-DU 206b, where the serving gNB-CU 202b is connected with the target/candidate gNB-DU 206b over an Fl interface. Further, a User Equipment (UE) 208b is connected with the serving gNB-DU 204b.

[0035] In Multiple Transmit/Receive Point (multi-TRP) operation, a gNB schedules the UE 210a from two TRPs which may belong to the same or different cells, providing better coverage, reliability and/or data rates for Physical Downlink Shared Channel (PDSCH), Physical Downlink Control Channel (PDCCH), Physical Uplink Shared Channel (PUSCH), and Physical Uplink Control Channel (PUCCH).

[0036] There are two different operation modes to schedule multi-TRP PDSCH transmissions. First operating mode is a single Downlink Control Information (DCI) and a second operating mode is a multi-DCI. In the single-DCI mode, the UE 210a is scheduled by the same DCI for both TRPs and in multi-DCI mode, the UE 210a is scheduled by independent DCIs from each TRP.

[0037] The UE 210a receives two PDCCH transmissions, one from each TRP, carrying the same DCI. For multi-TRP PUSCH repetition, according to indications in a single DCI or in a semistatic configured grant provided over RRC, the UE 210a performs PUSCH transmission of the same contents toward two TRPs with corresponding beam directions associated with different spatial relations. For multi-TRP PUCCH repetition, the UE 210a performs PUCCH transmission of the same contents toward two TRPs with corresponding beam directions associated with different spatial relations.

[0038] For inter-cell multi-TRP operation, for multi-DCI PDSCH transmission, one or more TCI states can be associated with SSB with a PCI different from the serving cell PCI. The activated TCI states can be associated with at most one PCI different from the serving cell PCI at a time.

[0039] FIG. 3A-FIG. 3C illustrate multiple ways of communication related to multi-TRP, in accordance with some embodiments of the present disclosure.

[0040] In some embodiments, there are different ways for this type of communication, that are summarized in the following illustrations. [0041] FIG. 3A illustrates a first way 300a of communication related to multi-TRP. FIG. 3A shows a serving gNB-DU 302a, a target/candidate gNB-DU 304a, and a UE 306a, which may be similar in structure and functioning with the corresponding features as described in FIG. 2A and FIG. 2B, and thus, the description of the same is omitted here for the sake of brevity. As shown in FIG. 3A, TRP1, associated with serving gNB-DU 302a, and TRP2, associated with target/candidate gNB-DU 304a, are transmitting two different PDSCH, such as PDSCH 308a and PDSCH 310a, respectively, but control signal (PDCCH/DCI) 312a for the two PDSCH 308a and 310a is transmitted by TRP1, only. In this case, if there is some problem in radio link with TRP1 and PDCCH reception fails, the communication via TRP2 as well is impacted.

[0042] FIG. 3B illustrates a second way 300b of communication related to multi-TRP. FIG. 3B shows a serving gNB-DU 302b, a target/candidate gNB-DU 304b, and a UE 306b, which may be similar in structure and functioning with the corresponding features as described in FIG. 2A and FIG. 2B, and thus, the description of the same is omitted here for the sake of brevity. As shown in FIG. 3B, TRP1 and TRP2 are transmitting two different PDSCH, such as PDSCH 308b and PDSCH 310b, respectively and each TRP is transmitting its own corresponding PDCCH/DCI, such as PDCCH 312b and PDCCH 314b, respectively. In this case, if there is any problem in radio link with one of the TRPs, the communication via other TRP can be intact.

[0043] FIG. 3C illustrates a third way 300c of communication related to multi-TRP. FIG. 3C shows a serving gNB-DU 302c, a target/candidate gNB-DU 304c, and a UE 306c, which may be similar in structure and functioning with the corresponding features as described in FIG. 2A and FIG. 2B, and thus, the description of the same is omitted here for the sake of brevity. As shown in FIG. 3C, TRP1 and TRP2 are used to jointly process the DL and UL signal.

[0044] The technical problem that the present disclosure addresses is based on the agreement that was made in RAN2 #125bis in the Rel-19 mobility enhancement objectives on early sync phase that include:

1. Early Downlink (DL) and Uplink (UL) sync is also supported for inter-CU LTM. Inform RAN3 of this. Early DL sync using Channel State Information Reference Signal (CSI- RS) should be considered, pending RANI approval.

2. PDCCH ordered early RACH is supported for inter-CU LTM.

3. For early Timing Advance (TA) acquisition. Rel-18 option is baseline. FFS for RAR based option. [0045] Specifically, the early TA acquisition refers to how the UE receives the TA from the LTM candidate cell to ensure a Random Access Channel (RACH)-less LTM cell switch. One of the main objectives of LTM is to ensure that the UE performs TA acquisition of an LTM candidate cell while the UE is still connected to the serving cell, so that the latency of RACH procedure during the actual serving cell change can be avoided. Further, this is executed by gNB- DU issuing a PDCCH order for the UE to perform UL sync (RACH) to a given candidate cell and acquire TA. UE performs RACH towards the indicated LTM candidate cell, but the TA is not sent to the UE directly in the Random Access Response. This is sent from the candidate DU to the gNB-CU and from gNB-CU to the serving DU. The serving DU sends the relevant TA to the UE in the LTM cell switch command, i.e. DL MAC CE.

[0046] FIG. 4 illustrates data structure of Medium Access Control Protocol Data Units (MAC PDU) that carries Random Access Response (RAR).

[0047] The agreement 3, made in RAN2#125bis, indicates that in Rel-19, the baseline is Rel- 18 solution and the solution of sending TA via the Random Access Response (RAR) to the UE directly is For Further study (FFS). For example, FIG. 4 shows indices and respective backoff parameter value, as per an example implementation. Further, FIG. 4 shows RAR grant field and associated number of bits.

[0048] FIG. 5A and FIG. 5B illustrate signaling diagram illustrating methods for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with some embodiments of the present disclosure. an aspect of the subject matter in accordance with one embodiment.

[0049] FIG. 5A and FIG. 5B show an interaction between a UE 500, a serving gNB-DU 502, a target/candidate gNB-DU 504, a serving gNB-CU 506, and a target/candidate gNB-CU 508. FIG. 5B is in continuation with FIG. 5A.

[0050] The sequence diagram may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, units, and functions, which perform specific functions or implement specific abstract data types.

[0051] The order in which the steps of the sequence diagram are described are not intended to be construed as a limitation, and any number of the described blocks of the sequence diagram can be combined in any order to implement the method illustrated in the sequence diagram. Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject matter described herein. Furthermore, the method illustrated in the sequence diagram can be implemented in any suitable hardware, software, firmware, or combination thereof.

[0052] One or more steps have been described below with the help of a target/candidate cell for ease of description, while it may be appreciated that the one or more steps may also be performed with one or more target/candidate cells.

[0053] Referring to FIG. 5 A, at S501, UE 500 is configured with LTM in one or more target/candidate cells at source gNB. In the context of this use-case, the terms “source” and “serving” are used interchangeably.

[0054] At step S502, the UE 500 transmits an RRC Measurement Report L3 to the serving gNB- CU 506.

[0055] At step S503, the serving gNB-CU 506 checks if any new Inter-gNB CU LTM candidate cell needs to be prepared.

[0056] At step S504, the serving gNB-CU 506 sends a Handover request to the target/candidate gNB-CU 508 over an Xn interface, to initiate an inter-CU candidate cell preparation. The Handover request may include LTM candidate cell ID and mTRP configuration that the candidate gNB-DU has to prepare.

[0057] At step S505, the target/candidate gNB-CU 508 sends the UE Context Setup Request to the target/candidate gNB-DU 504 over an Fl interface. The Context Setup Request may include LTM candidate cell ID and mTRP configuration.

[0058] At step S506, the target/candidate gNB-DU 504 may prepare Inter-gNB CU LTM candidate cell.

[0059] At step S507, the target/candidate gNB-DU 504 sends a UE Context Setup Response to the target/candidate gNB-CU 508. The UE Context Setup Response may include cell group configuration.

[0060] At step S508, the target/candidate gNB-CU 508 sends a Handover request Acknowledgement, including cell group configuration for mTRP, to the serving gNB-CU 506.

[0061] At step S509, the serving gNB-CU 506 sends an RRC Reconfiguration, including LTM target cell configuration for mTRP, to the UE 500.

[0062] At step S510, the UE 500 sends an LI Measurement Report to the serving gNB-DU 502. [0063] At step S511, the serving gNB-DU 502 decides to send a PDCCH order to UE 500 to acquire TA for both TRPs.

[0064] At step S512, the serving gNB-DU 502 sends a PDCCH Order, including required Cell ID and TRP ID, to the UE 500.

[0065] At step S513, upon completion of S512, the UE 500 sends a RACH Request to the target/candidate gNB-DU 504.

[0066] Referring to FIG. 5B, in continuation with the steps of FIG. 5A, at S514, the target/candidate gNB-DU 504 indicates TA and corresponding TRP ID in RAR. Further, the target/candidate gNB-DU 504 sends TA/TRP info to the serving gNB-DU 502.

[0067] At step S515, the target/candidate gNB-DU 504 sends Random Access Response, including associated TRP and TA, to the UE 500.

[0068] At step S516, the target/candidate gNB-DU 504 sends UE Context modification required command, including associated TRP and the corresponding TA, to the target/candidate gNB-CU 508.

[0069] At step S517, the target/candidate gNB-CU 508 sends UE Context modification Acknowledgement to the target/candidate gNB-DU 504.

[0070] At step S518, the target/candidate gNB-CU 508 sends a Handover request modification message to the serving gNB-CU 506 including associated TRP and the corresponding TA.

[0071] At step S519, the serving gNB-CU 506 sends Handover request modification Acknowledgement to the target/candidate gNB-CU 508.

[0072] At step S520, the serving gNB-CU 506 sends UE context modification request, including associated TRP and TA, to the serving gNB-DU 502. This includes the TRPs and the corresponding TA

[0073] At step S521, the serving gNB-DU 502 sends a UE context modification response to the serving gNB-CU 506.

[0074] At step S522, the UE 500 sends an LI Measurement Report to the serving gNB-DU 502.

[0075] At step S523, the serving gNB-DU 502 sends TA only if TA acquisition was not successful over RAR. This is indicated by target gNB-DU to the serving gNB-DU.

[0076] At step S524, the serving gNB-DU 502 sends a MAC CE: Serving cell change command, including required Cell ID, beam ID, TCI states, to the UE 500. [0077] At step S525, the UE 500 initiates to perform LTM cell switch and uses TA received to perform RACH-less LTM.

[0078] At step S526, the UE 500 sends RACH-less LTM (UL data packet) to the serving gNB- CU 506.

[0079] At step S527, the serving gNB-CU 506 performs a successful LTM cell switch.

[0080] At step S528, upon performing S527, the serving gNB-CU 506 sends a Cell change notification to the target/candidate gNB-CU 508.

[0081] At step S529, the UE 500 sends an RRC reconfiguration Acknowledgement to the target/candidate gNB-CU 508.

[0082] FIG. 6 illustrates a flowchart of a method for performing Timing Advance (TA) acquisition in a multi-TRP scenario, according to the embodiments as disclosed herein.

[0083] As illustrated in FIG. 6, the method 600 may comprise one or more steps. The method 600 may be described in the general context of computer executable instructions. Generally, computer executable instructions can include routines, programs, objects, components, data structures, procedures, modules, and functions, which perform particular functions or implement particular abstract data types.

[0084] The order in which the method 600 is described is not intended to be construed as a limitation, and any number of the described method blocks can be combined in any order to implement the method. Additionally, individual blocks may be deleted from the methods without departing from the scope of the subject matter described herein. Furthermore, the method can be implemented in any suitable hardware, software, firmware, or combination thereof.

[0085] At step 602, a configuration message is received at a User Equipment (UE), from a serving Centralized Unit (CU). The configuration message is indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of primary and/or secondary TRPs of a target/candidate Distributed Unit (DU).

[0086] At step 604, a PDCCH order is received at the UE, from a serving DU. The PDCCH order is indicative of acquiring timing advance (TA) associated with the one or more TRPs.

[0087] At step 606, one or more TRP identifiers of the one or more LTM candidate cells of the primary and/or secondary TRPs, along with the associated TA, are received at the UE, from the serving CU and/or the serving DU. The associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR).

[0088] At step 608, a Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch is performed at the UE, with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

[0089] In some embodiments, the RAR, including the TA of the primary and/or secondary TRPs, is received at the UE, from the one or more LTM candidate cells of the primary and/or secondary TRPs of the target/candidate DU. For example, the RAR is received in response to transmitting a RACH request to perform TA acquisition, based on receiving the PDCCH order from the serving DU. In some example embodiments, the serving DU is configured to indicate to the UE in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the TAs and the corresponding TRP IDs from the serving DU.

[0090] In an embodiment, the UE is configured to receive a flag from the serving DU in the Random Access Response. In an example, the flag is indicative of TRP ID corresponding to the TA.

[0091] In an embodiment, the serving CU is configured to indicate the one or more LTM candidate cells of the primary and/or secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

[0092] In an embodiment, the LTM candidate cells of the primary and/or secondary TRPs include one of intra-CU or inter-CU candidate cells.

[0093] FIG. 7 illustrates a block diagram of the UE 500 for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with an embodiment of the present disclosure.

[0094] FIG. 7 is explained in conjunction with the UE 500 of FIG. 5A and FIG. 5B. With reference to FIG. 7, there is shown a block representation of the UE 500.

[0095] In an embodiment, the UE 500 comprises a Central Processing Units 700 (also referred as “CPUs” or “one or more processors 700”), a memory 702, and Input/ Output (EO) interface 704.

[0096] In an embodiment, the memory 702 may include data 706 and one or more units 708. The one or more units 708 may be configured to perform the steps of the present disclosure using the data 706, to implement TA acquisition in a multi-TRP scenario. In an embodiment, each of the one or more units 708 may be a hardware unit which may be configured external to the memory 702 and coupled with the processor 700. As used herein, the term units 708 refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a Field-Programmable Gate Arrays (FPGA), Programmable System-on-Chip (PSoC), a combinational logic circuit, and/or other suitable components that provide described functionality. The one or more units 708, when configured with the described functionality defined in the present disclosure, will result in a novel hardware.

[0097] In one implementation, the data 706 may include, for example, input data 710. In one implementation, the units 708 may include, for example, an input unit 712, a receiving unit 714, and a function performing units 716. It will be appreciated that such units 708 may be represented as a single unit or a combination of different units.

[0098] In an embodiment, the input unit 712 may be configured to receive input data 710 including a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of primary and/or secondary TRPs of a target/candidate Distributed Unit (DU). In another embodiments, the input data 710 also includes a PDCCH order indicative of acquiring TA associated with the one or more TRPs. In some embodiments, the input data 710 also includes one or more TRP identifiers of the one or more LTM candidate cells of the primary and/or secondary TRPs, along with the associated TA.

[0099] In an embodiment, the receiving unit 714 may receive, at a UE 500, from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of primary and/or secondary TRPs of a target/candidate Distributed Unit (DU). Further, the receiving unit 714 may receive, at the UE, from a serving DU, a PDCCH order indicative of acquiring timing advance (TA) associated with the one or more TRPs.

[0100] Further, the receiving unit 714 may receive, at the UE 500, from the serving CU and/ or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the primary and/or secondary TRPs, along with the associated TA. The associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR). Furthermore, the function performing unit 716 may perform, at the UE, Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

[0101] In some embodiments, the RAR, including the TA of the primary and/or secondary TRPs, is received at the UE 500, from the one or more LTM candidate cells of the primary and/or secondary TRPs of the target/candidate DU. For example, the RAR is received in response to transmitting a RACH request to perform TA acquisition, based on receiving the PDCCH order from the serving DU. In some example embodiments, the serving DU is configured to indicate to the UE 500 in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the TAs and the corresponding TRP IDs from the serving DU. [0102] In an embodiment, the UE is configured to receive a flag from the serving DU in the Random Access Response. In an example, the flag is indicative of TRP ID corresponding to the TA.

[0103] In an embodiment, the serving CU is configured to indicate the one or more LTM candidate cells of the primary and/or secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

[0104] In an embodiment, the LTM candidate cells of the primary and/or secondary TRPs include one of intra-CU or inter-CU candidate cells.

[0105] A person skilled in the art will appreciate that the processor 700 may be configured to perform the steps of the present disclosure using the data 706 instead of the one or more units 708, to implement TA acquisition in a multi-TRP scenario.

[0106] A person skilled in the art will appreciate that any techniques other than the above- mentioned technique may be used to perform the steps performed by the one or more units 708, which are configured to implement TA acquisition in a multi-TRP scenario.

[0107] FIG. 8 illustrates a block diagram of the target/candidate gNB-DU 504 for performing Timing Advance (TA) acquisition in a multi-TRP scenario, in accordance with an embodiment of the present disclosure.

[0108] FIG. 8 is explained in conjunction with the target/candidate gNB-DU 504 of FIG. 5A and FIG. 5B. With reference to FIG. 8, there is shown a block representation of the target/candidate gNB-DU 504. [0109] In an embodiment, the target/candidate gNB-DU 504 comprises a Central Processing Units 800 (also referred as “CPUs” or “one or more processors 800”), a memory 802, and Input/ Output (I/O) interface 804.

[0110] In an embodiment, the memory 802 may include data 806 and one or more units 808. The one or more units 808 may be configured to perform the steps of the present disclosure using the data 806, to implement TA acquisition in a multi-TRP scenario. In an embodiment, each of the one or more units 808 may be a hardware unit which may be configured external to the memory 802 and coupled with the processor 800. As used herein, the term one or more units 808 refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a Field- Programmable Gate Arrays (FPGA), Programmable System-on-Chip (PSoC), a combinational logic circuit, and/or other suitable components that provide described functionality. The one or more units 708, when configured with the described functionality defined in the present disclosure, will result in a novel hardware.

[0U1] In one implementation, the data 806 may include, for example, input data 810. In one implementation, the one or more units 808 may include, for example, an input unit 812, a receiving unit 814, an allocation unit 816, and a transmission unit 818. It will be appreciated that such one or more units 808 may be represented as a single unit or a combination of different units.

[0112] In an embodiment, the input unit 812 may be configured to receive input data 810 including one or more TRP identifiers of one or more LTM candidate cells and associated timing advance (TA).

[0113] In an embodiment, the receiving unit 814 may receive, at the target/candidate gNB-DU 504, from a Centralized Unit (CU), a UE context setup request to prepare a Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cell for a User Equipment (UE). Further, at least one LTM candidate cell may be prepared with a primary and a secondary TRPs belonging to the target/candidate DU. Furthermore, the allocation unit 816 may allocate separate resources for primary and/or secondary TRPs including Random Access Channel (RACH) resources pertaining to the UE. The receiving unit 814 may receive, from the UE, a RACH request to perform TA acquisition. Further, the transmission unit 818 may transmit, to the UE, a Random Access Response (RAR). The RAR includes one or more TRP identifiers of one or more LTM candidate cells and associated timing advance (TA). [0114] In an embodiment, the processor 800 may indicate to the source DU whether or not the one or more TRP identifiers and associated TA is delivered to the UE in a RAR message.

[0115] In an embodiment, the receiving unit 814 may receive, from the UE based on the one or more TRP identifiers and associated TA, a request to perform a network function. Further, based on the request, the network function may be performed.

[0116] In an embodiment, the network function is a Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch function.

[0117] A person skilled in the art will appreciate that the processor 800 may be configured to perform the steps of the present disclosure using the data 806 instead of the one or more units 808, to implement TA acquisition in a multi-TRP scenario.

[0118] A person skilled in the art will appreciate that any techniques other than the above- mentioned technique may be used to perform the steps performed by the one or more units 808, which are configured to implement TA acquisition in a multi-TRP scenario.

[0119] FIG. 9 illustrates an embodiment of a device 900 wherein the method for performing for performing dynamic resource optimization in a distributed unit node of a wireless communication network may be implemented, according to the embodiments as disclosed herein. It will be appreciated that the device 900 is associated with the UE 500. As shown in FIG. 9, the device 900 comprises a processor 910, a memory 920, a storage component 930, an input component 940, an output component 950, a communication interface 960, and a bus 970.

[0120] The processor 910, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 910 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 910 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.

[0121] Memory 920 includes a non-transitory computer readable medium. Memory 920 includes a random-access memory (RAM), a read only memory (ROM), and/or another type of dynamic or static storage device (e.g., a flash memory, a magnetic memory, and/or an optical memory) that stores information and/or instructions for use by processor 910. The memory 920 comprises machine-readable instructions which are executable by the processor 910. These machine-readable instructions when executed by the processor 910 cause the processor 910 to perform one or more method steps of an embodiment described above.

[0122] Storage component 930 stores information and/or software related to the operation and use of the device 900. For example, storage component 930 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.

[0123] Input component 940 is configured to receive information, such as user input. For example, the input component 940 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 940 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and/or an actuator).

[0124] Output component 950 is configured to provide output information from the device 900. For example, the output component 950 may be, but not limited to, a display, a speaker, instructions to an external device, and/or one or more light-emitting diodes (LEDs).

[0125] Communication interface 960 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 960 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 900 and other devices. In other words, the standard of the communication interface 960 is not limited.

[0126] The bus 970 acts as an interconnect between the processor 910, the memory 920, the storage component 930, the input component 940, the output component 950, and the communication interface 960 of the device 900. The bus 970 may include a wired interconnection or a wireless interconnection.

[0127] The number and arrangement of components shown in FIG. 9 are provided as an example. In practice, device 900 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 9. Additionally, or alternatively, a set of components (e.g., one or more components) of device 900 may perform one or more functions described as being performed by another set of components of device 900. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of devices 900 in communication with one another. [0128] In an embodiment [1], a method comprising: receiving, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of at least one of primary and secondary TRPs of a target/candidate Distributed Unit (DU); receiving, at the UE, from a serving DU, a PDCCH order indicative of acquiring timing advance (TA) associated with the one or more TRPs; receiving, at the UE, from the serving CU and/or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the at least one of primary and secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR); and performing, at the UE, Random- Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

[0129] In an embodiment [2], in the method, described in the embodiment [1], further comprises: receiving, at the UE, from the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU, the RAR including the TA of the at least one of primary and secondary TRPs, in response to transmitting a RACH request to perform TA acquisition, based on receiving the PDCCH order from the serving DU, wherein the serving DU is configured to indicate to the UE in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the TAs and the corresponding TRP IDs from the serving DU.

[0130] In an embodiment [3], in the method, described in the embodiment [2], wherein the UE is configured to receive, from the serving DU, a flag in the Random Access Response, wherein the flag is indicative of TRP ID corresponding to the TA.

[0131] In an embodiment [4], in the method, described in the embodiment [1], wherein the serving CU is configured to indicate the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

[0132] In an embodiment [5], in the method, described in the embodiment [1], wherein the LTM candidate cells of the at least one of primary and secondary TRPs include one of intra-CU or inter-CU candidate cells. [0133] In an embodiment [6], an apparatus is configured to: receive, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of at least one of primary and secondary TRPs of a target/candidate Distributed Unit (DU); receive, at the UE, from a serving DU, a PDCCH order indicative of acquiring timing advance (TA) associated with the one or more TRPs; receive, at the UE, from the serving CU and/ or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the at least one of primary and secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR); and perform, at the UE, Random-Access Channel (RACH)- less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

[0134] In an embodiment [7], in the apparatus, described in the embodiment [6], further comprises: receive, at the UE, from the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU, the RAR including the TA of the at least one of primary and secondary TRPs, in response to transmitting a RACH request to perform TA acquisition, based on receiving the PDCCH order from the serving DU, wherein the serving DU is configured to indicate to the UE in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the Tas and corresponding TRP IDs from the serving DU.

[0135] In an embodiment [8], in the apparatus, described in the embodiment [7], wherein the UE is configured to receive, from the serving DU, a flag in the Random Access Response, wherein the flag is indicative of TRP ID corresponding to the TA.

[0136] In an embodiment [9], in the apparatus, described in the embodiment [6], wherein the serving CU is configured to indicate the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

[0137] In an embodiment [10], in the apparatus, described in the embodiment [6], wherein the LTM candidate cells of the at least one of primary and secondary TRPs include one of intra-CU or inter-CU candidate cells. [0138] In an embodiment [11], an apparatus is configured to: receive, at a target/candidate Distributed Unit (DU), from a Centralized Unit (CU), a context setup request to setup an Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cell for a User Equipment (UE); prepare at least one LTM candidate cell with a primary and a secondary Transmission Reception Points (TRPs) belonging to the target/candidate DU; allocate separate resources for at least one of primary and secondary TRPs including Random Access Channel (RACH) resources pertaining to the UE; receive, from the UE, a RACH request to perform TA acquisition; and transmit, to the UE, a Random Access Response (RAR), wherein the RAR includes one or more TRP identifiers of one or more LTM candidate cells and associated timing advance (TA).

[0139] In an embodiment [12], the apparatus, described in the embodiment [11], is further configured to: indicate to the source DU whether or not the one or more TRP identifiers and associated TA is delivered to the UE in a RAR message.

[0140] In an embodiment [13], in the apparatus, described in the embodiment [11], is further configured to: receive, from the UE based on the one or more TRP identifiers and associated TA, a request to perform a network function; and perform, based on the request, the network function. [0141] In an embodiment [14], in the apparatus, described in the embodiment [11], wherein the network function is a Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch function.

[0142] In an embodiment [15], a non-transitory computer-readable medium having program instructions stored thereon, executed by an apparatus for wireless communication, is disclosed. The program instructions may comprise: receiving, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of at least one of primary and secondary TRPs of a target/candidate Distributed Unit (DU); receiving, at the UE, from a serving DU, a PDCCH order indicative of acquiring timing advance (TA) associated with the one or more TRPs; receiving, at the UE, from the serving CU and/or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the at least one of primary and secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR); and performing, at the UE, Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA. [0143] Timing Advance acquisition in inter-CU LTM:

[0144] Agreements on early sync phase:

• RAR-based TA acquisition is not supported for inter-CU LTM for non-conditional LTM. FFS on conditional LTM.

[0145] Timing Advance acquisition is a key step in LTM. This enables the UE to perform RACH-less LTM to the identified target cell. This is true with inter-CU LTM candidate cells as well. In RAN2 #126, the above agreement was made where the below described Rell8 solution was agreed as the baseline.

• UE performs RACH to the candidate gNB-DU based on a PDCCH order from the serving gNB- DU to acquire TA.

• The candidate gNB-DU sends the UE’s TA to the serving gNB-DU via the gNB-CU.

• The serving gNB-DU delivers the TA to the UE in the DL MAC CE used for sending the LTM cell switch command.

[0146] As per the present subject matter, the RAR based option which is about delivering the UE’s candidate cell TA in the Random-Access Response directly to the UE instead of delivering over the backhaul. This provides an optimization over the baseline solution as the backhaul latency (avg. 6-8ms over two Fl interfaces in R18) in delivering the TA is avoided. In case of inter-CU LTM, this backhaul latency to deliver the candidate cell TA to the serving gNB-DU will have an additional increase because of the Xn interface between the two gNBs. Therefore, as per the present subject matter, it is beneficial to deliver the TA directly to the UE, especially in the inter-CU LTM scenario.

[0147] Observation 1: During LTM, it is advantageous to deliver the LTM candidate cell TA directly to the UE.

[0148] Moreover, as mentioned in the highlighted agreement, providing TA in the RAR is probably inevitable in case of conditional LTM, as the gNB-DU will not issue an LTM serving cell switch command to the UE. In a scenario, where RAR based TA acquisition is supported for C-LTM, as per the present subject matter, it is too limiting and inflexible to not allow use of RAR for TA delivery for non-conditional LTM.

[0149] Therefore, the present subject matter proposes that the agreement from RAN2#126 is reconsidered and both options i.e., RAR based option and the Rel 18 baseline option are supported, and the usage can be decided based on implementation. The serving gNB-DU may also be informed whether the TA has been delivered to the UE in the RAR message.

[0150] Proposal 1: Delivery of LTM candidate cell TA using the RAR based solution directly to the UE is supported, in addition to the Rel 18 baseline solution for nonconditional LTM also.

[0151] Delivering the LTM candidate cell TA using the RAR can also be useful in a multi-TRP scenario where TAs for two TRPs are required to be delivered to the UE. The TRP ID or the Cell ID may be used to identify and associate the TA.

[0152] Observation 2: Delivery of candidate cell TA using the Random-Access Response (RAR) can be performed for a UE in multi-TRP configuration also.

[0153] In a non-limiting embodiment of the present disclosure, one or more non-transitory computer-readable media may be utilized for implementing the embodiments consistent with the present disclosure. A computer-readable medium refers to any type of physical memory (such as memory 920) on which information or data readable by a processor may be stored. Thus, a computer-readable media may store one or more instructions for execution by the at least one processor 910, including instructions for causing the at least one processor 910 to perform steps or stages consistent with the embodiments described herein. The term “computer-readable media” should be understood to include tangible items and exclude carrier waves and transient signals. By way of example, and not limitation, such computer-readable media can comprise Random Access Memory (RAM), Read-Only Memory (ROM), volatile memory, non-volatile memory, hard drives, Compact Disc (CD) ROMs, Digital Video Disc (DVDs), flash drives, disks, and any other known physical storage media.

[0154] Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable media having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material.

[0155] The various illustrative logical blocks, units, and operations described in connection with the present disclosure may be implemented or performed with a general-purpose processor, discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general-purpose processor may include a microprocessor, but in the alternative, the processor may include any commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a plurality of microprocessors, or any other such configuration.

[0156] 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 or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

We Claim:

1. A method comprising: receiving, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure with one or more Transmission-Reception Points (TRPs) associated with one or more layer 1/ layer 2 triggered mobility (LTM) candidate cells of at least one of primary and secondary TRPs of a target/candidate Distributed Unit (DU); receiving, at the UE, from a serving DU, a PDCCEI order indicative of acquiring Timing Advance (TA) associated with the one or more TRPs; receiving, at the UE, from the serving CU and/or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the at least one of primary and secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a random access response (RAR); and performing, at the UE, random-access channel (RACH)-less layer 1/ layer 2 triggered mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

2. The method as claimed in claim 1, further comprises: receiving, at the UE, from the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU, the RAR including the TA of the at least one of primary and secondary TRPs, in response to transmitting a RACH request to perform TA acquisition, based on receiving the PDCCH order from the serving DU, wherein the serving DU is configured to indicate to the UE in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the TAs and the corresponding TRP IDs from the serving DU.

3. The method as claimed in claim 2, wherein the UE is configured to receive, from the serving DU, a flag in the Random Access Response, wherein the flag is indicative of TRP ID corresponding to the TA.

4. The method as claimed in claim 1, wherein the serving CU is configured to indicate the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

5. The method as claimed in claim 1, wherein the LTM candidate cells of the at least one of primary and secondary TRPs include one of intra-CU or inter-CU candidate cells.

6. An apparatus configured to: receive, at a User Equipment (UE), from a serving Centralized Unit (CU), a configuration message indicative of a configuration for performing a timing acquisition procedure for one or more Transmission-Reception Points (TRPs) associated with one or more Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cells of at least one of primary and secondary TRPs of a target/candidate Distributed Unit (DU); receive, at the UE, from a serving DU, a PDCCH order indicative of acquiring timing advance (TA) associated with the one or more TRPs; receive, at the UE, from the serving CU and/ or the serving DU, one or more TRP identifiers of the one or more LTM candidate cells of the at least one of primary and secondary TRPs, along with the associated TA, wherein the associated TA is received from a network, upon configuration or if TA acquisition is detected as unsuccessful over a Random Access Response (RAR); and perform, at the UE, Random-Access Channel (RACH)-less Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch with the target/candidate DU based on the received one or more TRP identifiers and the associated TA.

7. The apparatus as claimed in claim 6, wherein the apparatus is further configured to: receive, at the UE, from the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU, the RAR including the TA of the at least one of primary and secondary TRPs, in response to transmitting a RACE! request to perform TA acquisition, based on receiving the PDCCH order from the serving DU, wherein the serving DU is configured to indicate to the UE in the PDCCH order, whether to wait for the TA in the RAR from the target/candidate DU or to wait for the Tas and corresponding TRP IDs from the serving DU.

8. The apparatus as claimed in claim 7, wherein the UE is configured to receive, from the serving DU, a flag in the Random Access Response, wherein the flag is indicative of TRP ID corresponding to the TA.

9. The apparatus as claimed in claim 6, wherein the serving CU is configured to indicate the one or more LTM candidate cells of the at least one of primary and secondary TRPs of the target/candidate DU to share the one or more TRP identifiers and the associated TA with at least one of directly with the UE over a RAR, or with the UE through the serving DU.

10. The apparatus as claimed in claim 6, wherein the LTM candidate cells of the at least one of primary and secondary TRPs include one of intra-CU or inter-CU candidate cells.

11. An apparatus configured to: receive, at a target/candidate Distributed Unit (DU), from a Centralized Unit (CU), a context setup request to set up a Layer 1/ Layer 2 Triggered Mobility (LTM) candidate cell for a User Equipment (UE); prepare at least one LTM candidate cell with a primary and a secondary Transmission Reception Points (TRPs) belonging to the target/candidate DU; allocate separate resources for at least one of primary and secondary TRPs including Random Access Channel (RACH) resources pertaining to the UE; receive, from the UE, a RACH request to perform TA acquisition; and transmit, to the UE, a Random Access Response (RAR), wherein the RAR includes one or more TRP identifiers of one or more LTM candidate cells and associated timing advance (TA).

12. The apparatus as claimed in claim 11, wherein the apparatus is further configured to: indicate to the source DU whether or not the one or more TRP identifiers and associated TA is delivered to the UE in a RAR message.

13. The apparatus as claimed in claim 11, wherein the apparatus is further configured to: receive, from the UE based on the one or more TRP identifiers and associated TA, a request to perform a network function; and perform, based on the request, the network function.

14. The apparatus as claimed in claim 13, wherein the network function is a Layer 1/ Layer 2 Triggered Mobility (LTM) cell switch function.