Signaling in successful RACH-less LTM completion

Abstract

Disclosed herein a User Equipment (UE) (201) is disclosed. The UE is configured to receive a Random-Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNB-DU (203). The UE is also configured to transmit, to a target gNB-DU (205), a first UL data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch. The UE is configured to transmit, to the target gNB-DU, a SR to receive dynamic grants to transmit a second UL data packet. The UE is configured to receive, from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request. The UE is configured to determine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

Description

SIGNALING IN SUCCESSFUL RACH-LESS LTM COMPLETIONCROSS-REFERENCE TO RELATED APPLICATION (S)

[0001] This application claims priority to Indian Provisional Application No. 202411016290, filed on March 07, 2024, and Indian non Provisional Application No. 202411016290, filed September 25, 2024; the entire contents of which are incorporated herein by reference.FIELD

[0002] The present disclosure relates to the signaling of successful Random Access Channel(RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) completion.BACKGROUND

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

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

[0005] According to the concluded 3 GPP Release 17, a transfer of cell change may be triggered by Layer 3 (L3) measurements and may be done by Radio Resource Control (RRC) signaling. Further, the concluded 3GPP Release-18 introduced Layerl / Layer 2 (L1 / L2) TriggeredMobility (LTM) for improvements in handover latency and an interruption time compared to L3 -based mobility.

[0006] Therefore, it is desired to address the above-mentioned disadvantages or other shortcomings in conventional solutions related to LTM cell switch procedures.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 present disclosure nor is it intended to determine the scope of the disclosure.

[0008] According to one embodiment of the present disclosure, a User Equipment (UE) is disclosed. The UE is configured to receive a Random Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU). The RACH-less LTM cell switch command is configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling. In response to the received RACH-less LTM cell switch command, the UE is configured to transmit a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to the target gNB-DU. The first UL data packet is transmitted to indicate a successful RACH-less LTM cell switch. After transmitting the first UL data packet, the UE is configured to transmit a Scheduling Request (SR) to the target gNB-DU. The SR is transmitted to receive dynamic grants to transmit a second UL data packet. The UE is configured to receive a second UL scheduling grant from the target gNB-DU, in response to the transmitted scheduling request from the target gNB-DU. In response to the received second UL scheduling grant, the UE isconfigured to determine that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

[0009] According to another embodiment of the present disclosure, a method is disclosed. The method includes receiving, by a User Equipment (UE), a Random Access Channel (RACH)- less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB- Distributed Unit (gNB-DU). The RACH-less LTM cell switch command is configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling. In response to receiving the RACH-less LTM cell switch command, the method includes transmitting a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch. The first UL data packet is transmitted by the UE to the target gNB-DU. After transmitting the first UL data packet, the method includes transmitting a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet. The SR is transmitted by the UE to the target gNB-DU. The method also includes receiving a second UL scheduling grant in response to the transmitted scheduling request. The second UL scheduling grant is received by the UE from the target gNB-DU. In response to the received second UL scheduling grant, the method includes determining, by the UE, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

[0010] According to another embodiment of the present disclosure, an apparatus is disclosed. The apparatus is configured to receive an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant. The apparatus is configured to receive the UL data packet from a User Equipment (UE). The apparatus is configured to assign, to the UE, a dynamic UL grant with a predefined grant value. The predefined grant value is assigned tothe dynamic UL grant to signal the reception of a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch.

[0011] According to another embodiment of the present disclosure, a method is disclosed. The method includes receiving an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant after a Random-Access Channel (RACH)-less Layerl / Layer 2 triggered Mobility (LTM) cell switch. The UL data packet is received by a target gNB-DU from the UE. The method also includes assigning a dynamic UL grant with a predefined grant value. The requested granted value is assigned to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate the successful RACH-less LTM cell switch. The dynamic UL grant is assigned by the target gNB-DU to the UE.

[0012] According to another embodiment of the present disclosure, a non-transitory computer- readable medium is disclosed. The non-transitory computer-readable medium stores instructions. The instructions comprise one or more instructions that are executed by a User Equipment (UE). The UE comprises one or more processors. The one or more instructions cause the one or more processors to receive a Random Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU). The RACH-less LTM cell switch command is configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling. In response to the received RACH-less LTM cell switch command, the one or more instructions cause the one or more processors to transmit, to the target gNB-DU, a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successfulRACH-less LTM cell switch. After transmitting the first UL data packet. The one or more instructions cause the one or more processors to transmit, to the target gNB-DU, a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet. The one or more instructions cause the one or more processors to receive, from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request. The one or more instructions cause the one or more processors to determine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

[0013] According to another embodiment of the present disclosure, a non-transitory computer- readable medium is disclosed. The non-transitory computer-readable medium stores instructions. The instructions comprise one or more instructions that are executed by a target gNodeB -Distributed Unit (gNB-DU) after a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch. The target gNB-DU comprises one or more processors. The one or more instructions cause the one or more processors to receive, from a User Equipment (UE), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant. The one or more instructions cause the one or more processors to assign, to the UE, a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate the successful RACH-less LTM cell switch.

[0014] 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 is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting its scope.The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.BRIEF DESCRIPTION OF DRAWINGS

[0015] Features, aspects, and advantages of certain exemplary 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 art;FIGS. 2A-2B illustrate a sequence of operations between a UE and a gNB-CU via a gNB-DUl and a gNB-DU2, in accordance with an embodiment of the present disclosure;FIGS. 3A-3B illustrate a sequence of operations between the UE and the gNB-CU via the gNB- DUl and the gNB-DU2, in accordance with another embodiment of the present disclosure;FIG. 4 illustrates a flow chart of an example method implemented by the UE, in accordance with an embodiment of the present disclosure;FIG. 5 illustrates a flow chart of an example method implemented by a target gNB -DU, in accordance with an embodiment of the present disclosure; andFIG. 6 illustrates an embodiment of an example device, in accordance with an embodiment of the present disclosure.DETAILED DESCRIPTION

[0016] 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 beincorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowchart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part).

[0017] 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.

[0018] 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.

[0019] 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 maybe 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.

[0020] In Rel-18, the following agreement was made in the context of indicating a successful Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch. From TS 38.321 :For a Radio Access Channel (RACH) -less LTM, Radio Access Network 2 (RAN2) assumes that a User Equipment (UE) determines a successful reception of its first Uplink (UL) data based on receiving a Physical Downlink Control Channel (PDCCH) addressing the UE ’s Cell Radio Network Temporary Identifier (C-RNTI) in a target cell scheduling a new transmission after the first UL data, (FFS if specified contents should be transmitted with this transmission, e.g. as LTE Medium Access Control-Control Element (LTEMAC CE)).

[0021] After executing the RACH-less LTM cell switch, a source gNodeB -Distributed Unit (gNB-DU) sends the RACH preamble, selected Temporary Cell Identity (TCI) state info and beam information, delivered to the UE, in the LTM cell switch command (for example, a MAC CE) to a target gNB-DU. Based on this, the target gNB-DU may decide to perform prescheduling and schedule a new transmission to the UE and provide UL scheduling grants, i.e. dynamic grants. The UE may have already initiated sending of UL data (real or padded bits or RRC message) using configured grants (i.e., the UL scheduling grants) allocated by the target gNB-DU during LTM candidate cell preparation, to indicate a successful RACH-less LTM cell switch at slot #N. The target gNB-DU may or may not receive the UL data. If the target gNB- DU receives the UL data successfully, then the UL data will be received at slot#N+2.

[0022] As described previously, in a scenario where the UE and the gNB do not have data to transmit in the UL and DL for a particular time duration, the UE is not aware whether the first UL data was successfully received at the gNB (i.e., the target gNB-DU) (which was sent to signal a successful RACH-less LTM cell switch completion), as there is no Hybrid Automatic Repeat Request (HARQ) confirmation from the gNB in the DL and it was sent using CG before the DG was allocated. Hence, it is important to notify the UE about the success / failure of the delivery of the UL data packet.

[0023] FIG. 1 illustrates a disaggregated architecture of a gNB 100, in accordance with a conventional technique. The disaggregated architecture is defined in 3GPP decomposing the gNB 100 into multiple logical entities. The multiple logical entities may include one or more first units 102 may be represented by at least one distributed unit (gNB-DU) and the one or more second units 104 may be represented by a centralized unit (gNB-CU). The gNB-CU may be further split into a CU Control Plane (CP) part, also referred to as gNB-CU-CP, and a CU User Plane (UP) part, also referred to as 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.

[0024] 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.Particularly, 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. The gNB-CU may be responsible for higher-layer processing functions such as radio resource management, mobility management, and connection management. The gNB-CU may provide a centralized control point for multiple gNB-DUs, enabling network-wide coordination and optimization.

[0025] According to one configuration, a 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 (SDAP). 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-UP. 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, Fl-U, and El interfaces 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 F 1 -U is responsible for transporting userdata 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 / decry ption functions. The El interface in the gNB 100 connects the entity with the gNB-CU and / or the gNB 100 to core network elements, such as the 5G Core (5GC) network functions.

[0026] In Rel-18, the LTM is limited to 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 serving cell) in the disaggregated gNB architecture 100, the HO preparation phase i.e., providing the candidate / target cell configuration to the UE is performed by gNB-CU-CP, that is autonomously executed by the gNB-DU without requiring further interaction with the upper layers in gNB-CU-CP.

[0027] Further, as per current techniques in 5G, a UE does not receive any Hybrid Automatic Repeat Request (HARQ) confirmation in downlink (DL) from the network for any uplink (UL) data sent by the UE. This data reception acknowledgment may be indicated using a New Data Indicator (ND I) field. If the UE has more UL data in its buffers and sends a scheduling request to the gNB, then there is further dynamic UL grants allocation. The UE sends a data packet in the UL to the gNB to indicate a successful RACH-less LTM cell switch. If there is no UL data, the UE creates a UL data packet using padded bits and sends it to signal completion. Even the RRC Reconfiguration Acknowledge message sent by the UE to indicate successful application of the target configuration can be considered as UL data.

[0028] In case there is UL data in the UE’s buffers, the UE will send a scheduling request and receive more UL dynamic grants. This way, the UE can be sure of the LTM completion when it receives the grants from the target gNB-DU. However, in case the UE does not have data tosend in UL, the UE is not aware whether the UL data sent to signal completion of LTM was successfully received at gNB as there is no HARQ confirmation from the gNB in DL. Hence, if the UE is not notified about the gNB receiving the UL data packet successfully, related timers may expire, and the UE may declare Radio Link Failure (RLF).

[0029] FIGS. 2A-2B illustrate a sequence of operations among a UE 201, a gNB-DUl 203, a gNB-DU2 205, and a gNB-Control Unit (gNB-CU) 207, in accordance with an embodiment of the present disclosure. The UE 201 is configured with the LTM with one or more candidate / target cells. In the illustrated embodiment, the gNB-DUl 203 may correspond to a source gNB-DU and the gNB-DU2 205 may correspond to a target gNB-DU.

[0030] Referring to FIG. 2A, at operation 202, the UE 201 transmits an L3 measurement report to the gNB-CU 207. In response to the received L3 measurement report, at operation 204, the gNB-CU 207 determines whether to add an inter gNB-DU candidate cell. Upon determining to add the inter gNB-DU candidate cell, the gNB-CU 207 transmits a UE context setup request to the gNB-DU2 205 (i.e., a candidate / target DU), at the operation 206. The UE context setup request corresponds to a request to perform LTM target cell preparation. At operation 208, the gNB-DU2 205 transmits a UE context setup response to the gNB-CU 207. The context setup response may include LTM candidate / target cell configuration (i.e., cellGroupConfig). The LTM candidate cell configuration may include information and / or parameters associated with the candidate / target cells that are prepared by the gNB. The LTM candidate cell configuration may enable the UE to perform a cell switch to one of these candidate / target cells effectively and efficiently.

[0031] At operation 210, the gNB-CU 207 transmits a Radio Resource Control (RRC) reconfiguration message to the UE 201. The RRC reconfiguration message includes the LTMcandidate cell configuration as received by the gNB-CU 207 from the gNB-DU2. At operation 212, the UE 201 stores the LTM candidate cell configuration based on the received RRC reconfiguration message. Further, at operation 214, the UE 201 transmits an LI measurement report to the gNB-DUl 203 (i.e., the source DU) for the LTM-configured cells. At operation 216, the gNB-DUl 203 decides to send a PDCCH order to the UE to acquire Timing Advance (TA) of the inter-gNB-DU candidate cell(s). At operation 218, the gBN-DU 1 sends the PDCCH order with a cell ID. The cell ID may correspond to a cell ID of the LTM candidate cell with which the TA acquisition is to be performed. At operation 220, the UE 201 transmits a RACH (preamble) to the candidate / target gNB-DU2 205.

[0032] At operation 222, the candidate / target gNB-DU2 205 transmits a UE context modification required message to the gNB-CU 207. The UE context modification required message may include the UE’s TA and the cell ID. At operation 224, the gNB-CU 207 transmits the UE context modification Acknowledgement (Ack) to the gNB-DU2 205. At operation 226, the gNB-CU 207 decides to forward the received TA to the serving gNB-DU (i.e., the gNB- DUl 203). Therefore, at operation 228, the gNB-CU 207 transmits the UE context modification request. The UE context modification request includes the TA and the corresponding cell ID to the serving gNB-DUl 203. At operation 230, the gNB-DUl 203 transmits UE Context modification response to the gNB-CU 207. Further, at operation 232, the serving gNB-DUl 203 transmits the MAC CE including cell ID, RACH preamble, Beam ID, and TA to the UE 201.

[0033] At operation 234, the UE 201 performs the RACH-less LTM cell switch to the target gNB-DU 205 cell. Further, the UE 201 may prepare for transmission of UL data packets. If there is no UL data, a UL data packet with padded bits is created. Alternatively, an RRCReconfiguration Acknowledge message sent by the UE can also be considered for the first UL data packet.

[0034] Referring to FIG. 2B, at operation 236, the gNB-DUl 203 sends the selected RACH preamble, selected TCI state, a beam ID, and the cell ID to the target gNB-DU (i.e., gNB-DU2 205).

[0035] At operation 238, the source gNB-DUl 203 transmits a UE Context Modification Required message, including the RACH preamble, the cell ID, and the beam ID, to the gNB- CU 207. At operation 240, the gNB-CU 207 transmits a UE context modification acknowledge message to the gNB-DUl 203.

[0036] At operation 242, the gNB-CU 207 determines to forward the received RACH preamble, the cell ID, and the beam ID to the target gNB-DU2 205. At operation 244, the gNB-CU 207 transmits a UE context modification request including the RACH preamble, the cell ID, and the beam ID to the gNB-DU 205. At operation 246, the gNB-DU2 205 transmits a UE context modification response to the gNB-CU 207, in response to the received UE context modification request.

[0037] At operation 248, the target gNB-DU2 205 may decide to perform pre-scheduling for the UE and allocate dynamic grant(s) on the PDCCH after receiving the information in operation 242 from the source gNB-DUl 203. At operation 250, the UE 201 monitors the PDCCH using a Cell Radio-Network Temporary Identifier (C-RNTI) to receive the dynamic grants (i.e., the UL dynamic grants). At operation 252, the UE 201 transmits a first UL data packet to the gNB-DU2 205 to indicate that the UE has successfully completed the RACH-less LTM cell switch to the designated target cell. However, the UE may have used Configured Grant for the purpose of sending first UL data and hence need not have waited for operation248 before initiating 252. Please note that there is no dependency between operations 248 and 252 and hence 252 may have been initiated earlier to 248 or in parallel at the network and UE respectively.

[0038] At operation 254, the gNB-DU2 205 receives the first UL data packet and is notified of a successful LTM cell switch. However, at operation 256, the UE 201 is not aware whether the UL data delivery is successful or unsuccessful, as no HARQ is transmitted by the gNB-DU2 205, and additionally, there is no other form of confirmation. Moreover, the dynamic grant allocation in this use-case is based on pre-scheduling and not upon the reception of the first UL data packet. Hence, the UE 201 sends another Scheduling Request (SR) (i.e., 2ndSR) to receive further UL dynamic grants, at operation 258.

[0039] At operation 260, the gNB-DU2 205 allocates the dynamic grant on the PDCCH corresponding to the new SR (2nd data packet). At operation 262, the UE 201 monitors the PDCCH using the C-RNTI to receive the newly allocated UL dynamic grants. For example, at operation 264, the UE 201 receives the UL grant(s) corresponding to the transmitted new SR and determines that the first UL data was delivered successfully, because the 2ndscheduling request was served. Thus, at operation 266, the UE 201 transmits the second padded user data packet to gNB-DU2 205. Further, the UE 201 transmits a RRC reconfiguration acknowledgement to the gNB-CU 207, at operation 268.

[0040] Thus, in the UE-based operations as described in FIGS. 2A-2B, the UE initiates the SR to send a second UL data packet / second dummy UL data packet to the gNB. If the new UL grant corresponding to the SR (for the same HARQ process) is received, then the UE can implicitly determine that the RACH-less success indication (i.e., the first UL data packet) is also delivered successfully to the gNB. If not, the UE can detect an LTM cell switch failure,upon the expiry of a timer. The timer may be referred to as an LTM failure timer that may define a time period for which a UE may wait before declaring the LTM cell switch failure. Meanwhile, if the LTM failure timer has not expired, the UE 201 may send another SR to request a UL grant for the same data.

[0041] FIGS. 3A-3B illustrate a sequence of operations among the UE 201, the gNB-DUl 203, the gNB-DU2205, and the gNB-CU 207, in accordance with another embodiment of the present disclosure. The operations 302-352 are similar to the operations 202-252, as explained in reference to the FIGS. 2A-2B. Accordingly, a detailed description of the operations 302-352 has been omitted for the sake of brevity.

[0042] For example, at operation 302, the UE 201 transmits the L3 measurement report to the gNB-CU 207. At operation 304, the gNB-CU 207 determines whether to add inter gNB-DU candidate cell(s). At operation 306, the gNB-CU 207 transmits the UE context setup request to the gNB-DU2 205 (i.e., a candidate / target DU) requesting LTM target cell preparation. At operation 308, the gNB-DU2 205 transmits the UE context setup response with LTM candidate / target cell configuration (cellGroupConfig) to the gNB-CU 207. At operation 310, the gNB-CU 207 transmits the RRC reconfiguration message to the UE 201. At operation 312, the UE 201 stores the LTM candidate cell based on the received RRC reconfiguration message. Further, at operation 314, the UE 201 transmits the LI measurement report to the gNB-DUl 203 (source DU) for the LTM-configured cells. At operation 316, the serving gNB-DUl 203 decides to send the PDCCH order to the UE to acquire the TA of the inter-gNB-DU candidate cell. At operation 318, the gBN-DUl sends a PDCCH order with cell ID. At operation 320, the UE 201 transmits RACH (preamble) to the candidate / target gNB-DU2 205.

[0043] At operation 322, the candidate / target gNB-DU2 205 transmits the UE context modification required message to the gNB-CU 207. The UE context modification required message may include the UE’s TA and the cell ID. At operation 324, the gNB-CU 207 transmits the UE context modification acknowledgment to the gNB-DU2205. At operation 326, the gNB- CU 207 decides to forward the received TA to the serving gNB-DU. Therefore, at operation 328, the gNB-CU 207 transmits the UE context modification request including the received TA and the corresponding cell ID to the serving gNB-DUl 203. At operation 330, the gNB-DUl 203 transmits UE Context modification response to the gNB-CU 207. Further, at operation 332, the gNB-DUl 203 transmits the MAC CE including the cell ID, the RACH preamble, the beam ID, and the TA to the UE 201. At operation 334, the UE 201 performs the RACH-less LTM cell switch to the target gNB-DU cell.

[0044] Referring to FIG. 3B, at operation 336, the gNB-DUl 203 sends the selected RACH preamble, the beam ID, and the cell ID to the target gNB-DU (i.e., gNB-DU2205). At operation 338, the gNB-DUl 203 transmits the UE context modification required message to the gNB- CU 207. At operation 340, the gNB-CU 207 transmits the UE context modification acknowledge message to the gNB-DU2 205. At operation 342, the gNB-CU 207 determines to forward the received RACH preamble, the cell ID, and the beam ID to the gNB-DU2 205. At operation 344, the gNB-CU 207 transmits the UE context modification request including the RACH preamble, the cell ID, and the beam ID to the gNB-DU 205. At operation 346, the gNB- DU2 205 transmits the UE context modification response to the gNB-CU 207. At operation 348, the gNB-DU2 205 decides to perform pre-scheduling and allocates the dynamic grant(s) on the PDCCH. At operation 350, the UE 201 monitors the PDCCH using the C-RNTI to receive the dynamic grants. At operation 352, the UE 201 transmits the first user data packet tothe gNB-DU2 205, using the CG that was allocated at the time of candidate cell preparation. Please note that there is no dependency between operations 350 and 352 and hence 352 may have been initiated earlier to 350 or in parallel at the network and UE respectively.

[0045] Further, at operation 354, the gNB-DU2 205 receives the data packet transmitted by the UE 201. The gNB-DU2 205 also detects the successful LTM switch. However, the UE 201 is still not aware if the UL data delivery was successful or not. At operation 356, the gNB-DU2 205 proactively allocates dynamic grants on PDCCH (even without SR). In one embodiment, the gNB-DU2 may allocate the dynamic grant with a predefined grant value. The predefined grant value may be preconfigured and known to the UE 201 and the gNB-DU2. In one nonlimiting embodiment, the predefined grant value may be preconfigured by a network operator and stored at the UE 201 and the gNB-DU2. At operation 358, the UE 201 monitors the PDCCH using the C-RNTI to receive the UL dynamic grants. The UE 201 monitoring the PDCCH for grants is possible if the UE is aware that the gNB-DU will proactively allocate grants (at the reception of a padded UL data packet) without an SR. Thus, the UE 201 may be preconfigured with the information of said proactive allocations. Thus, at operation 360, when the UE 201 receives a new UL grant, the UE 201 determines that the first UL data is delivered successfully. Further, at operation 362, the UE 201 transmits the RRC reconfiguration acknowledgment to the gNB-CU 207.

[0046] Thus, in the network-based operations as described in FIGS. 3A-3B, if the gNB-DU receives the first UL data packet from the UE (indication of a successful RACH-less LTM cell switch), the gNB-DU proactively assigns the UL grant (minimum) without being requested by the UE and schedules a PDCCH addressing the UE’s C-RNTI in the target cell to ensure that the UE is aware of the successful UL data delivery to the gNB.

[0047] FIG. 4 illustrates a flow chart of an example method 400, in accordance with another embodiment of the present disclosure. The method 400 may be performed by the UE 201.

[0048] At step 402, the UE 201 receives a RACH-less LTM cell switch command from a gNB- DU (for example, the gNB-DUl 203). In one embodiment, the RACH-less LTM cell switch command may be configured to trigger the UE to perform a cell switch to a target gNB (for example, the gNB-DU2 205) cell through L1 / L2 signaling.

[0049] At step 404, the UE 201 may transmit a first UL data packet to the target gNB-DU. The first UL data packet is transmitted via one of a configured UL scheduling grants and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch. In one embodiment, the configured UL scheduling grant and / or the dynamic UL scheduling grant may be assigned to the UE during the LTM candidate cell preparation and post LTM cell switch respectively. The first UL data packet may include one of one or more real data bits or one or more padded data bits or a UL signaling RRC message.

[0050] At step 406, the UE 201 transmits a Scheduling Request (SR) to the target gNB-DU (gNB-DU2 205). The SR is transmitted to request for scheduling grants to transmit a second UL data packet. The SR is transmitted after transmitting the first UL data packet. In one embodiment, the second UL data packet includes one or more real or padded data bits.

[0051] At step 408, the UE 201 receives a second UL scheduling grant in response to the transmitted scheduling request. In one embodiment, the second UL scheduling grant may correspond to the dynamic UL scheduling grant with the predefined grant value.

[0052] In response to the received second UL scheduling grant, at step 410, the UE 201 determines that the indication (i.e., the first UL data packet) of the successful RACH-less LTM cell switch to the target gNB-DU (the gNB-DU2 205) is successfully delivered.

[0053] In one embodiment, after transmitting the SR, the UE 201 may initiate an LTM failure timer. Further, in response to an expiry of the LTM failure timer and non-receipt of the second UL scheduling grant, the UE 201 may determine that the successful RACH-less LTM cell switch indication delivery to the target gNB-DU through the L2 signaling is unsuccessful.

[0054] FIG. 5 illustrates a flow chart of an example method 500, in accordance with another embodiment of the present disclosure. The method 500 may be performed by the target gNB- DU (the gNB-DU2 205).

[0055] At step 502, the gNB-DU2 205 receives the UL data packet via one of the configured UL scheduling grant or the dynamic UL scheduling grant from the UE 201. The UL data packet is received after a RACH-less Layerl / Layer 2 triggered Mobility (LTM) cell switch.

[0056] At step 504, the gNB-DU2 205 assigning, by the target gNB to the UE, a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch. In one embodiment, the dynamic UL grant corresponds to a Physical Downlink Control Channel (PDCCH) addressing the UE’s Cell-Radio Network Temporary Identifier (C-RNTI).

[0057] FIG. 6 illustrates an embodiment of a device / apparatus 600. As shown in FIG. 8, the device 600 includes a processor 610, a memory 620, a storage component 630, an input component 640, an output component 650, a communication interface 660, and a bus 670. The device 600 may be associated with the UE 201, the gNB-DUl 203, the gNB-DU2 205, and the gNB-CU 207. In one embodiment, the device 600 may correspond to the UE 201. In one embodiment, the device 600 may correspond to an apparatus implemented at the target gNB- DU (i.e., the gNB-DU2205). The one or more components of the device 600 may be configuredto implement one or more operations / functionalities of the present disclosure as discussed above.

[0058] The processor 610, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 610 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 610 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.

[0059] The memory 620 includes a non-transitory computer readable medium. The memory 620 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 610. The memory 620 comprises machine-readable instructions which are executable by the processor 610. These machine-readable instructions when executed by the processor 610 cause the processor 610 to perform one or more method steps of an embodiment described above.

[0060] The storage component 630 stores information and / or software related to the operation and use of the device 600. For example, the storage component 630 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.

[0061] The input component 640 is configured to receive information, such as user input. For example, the input component 640 may include, but not be limited to, a touch screen display, akeyboard, a keypad, a mouse, a button, a switch, and / or a microphone. Additionally, or alternatively, the input component 640 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0062] The output component 650 is configured to provide output information from the device 600. For example, the output component 650 may be, but not limited to, a display, a speaker, an instruction device to an external device, and / or one or more light-emitting diodes (LEDs).

[0063] The communication interface 660 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 660 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 600 and other devices. In other words, the standard of the communication interface 660 is not limited.

[0064] The bus 670 acts as an interconnect between the processor 610, the memory 620, the storage component 630, the input component 640, the output component 650, and the communication interface 660 of the device 600. The bus 670 may include a wired interconnection or a wireless interconnection.

[0065] The number and arrangement of components shown in FIG. 6 are provided as an example. In practice, device 600 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 8. Additionally, or alternatively, a set of components (e.g., one or more components) of the device 600 may perform one or more functions described as being performed by another set of components of the device 600. Further, one or more method steps described in any of theembodiments may be performed utilizing a plurality of devices 600 in communication with one another.

[0066] Examples of the techniques and apparatus described herein include, but are not limited to, the following enumerated embodiments:[1] A User Equipment (UE) configured to: receive a RACH-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB-Distributed Unit (gNB-DU), the RACH-less LTM cell switch command being configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling; transmit, to the target gNB-DU, a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch; after transmitting the first UL data packet, transmit, to the target gNB-DU, a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receive, from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request; and determine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.[2] The UE as described in [1], wherein after transmission of the SR, the apparatus is further configured to: initiate an LTM failure timer; andin response to the target gNB-DU and non -receipt of the second UL scheduling grant, determine that the successful RACH-less LTM cell switch indication delivery to the target gNB-DU is unsuccessful.[3] The UE as described in any of [l]-[2], wherein the first UL data packet includes one of one or more real data bits or one or more padded data bits or a UL signaling RRC message.[4] The UE in any of [l]-[3], wherein the second UL data packet includes one or more real or padded data bits.[5] The UE in any of

[0001] -[4], wherein the source gNB-DU and the target gNB-DU correspond to different gNBs.[6] A method comprising: receiving, by a User Equipment (UE), a RACH-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU), the RACH- less LTM cell switch command being configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling; transmitting, by the UE to the target gNB-DU, a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch; after transmitting the first UL data packet, transmitting, by the UE to the target gNB- DU, a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receiving, by the UE from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request; anddetermining, by the UE, in response to the received second UL scheduling grant, that the indication of a successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.[7] The method as described in [6], wherein after transmission of the SR, the method further comprises: initiating, by the UE, an LTM failure timer; in response to an expiry of the LTM failure timer and non-receipt of the second UL scheduling grant, determining, by the UE, that the successful RACH-less LTM cell switch indication delivery to the target gNB-DU through L2 signaling is unsuccessful.[8] The method as described in any of [6]-[7], wherein the first UL data packet includes one of one or more real data bits or one or more padded data bits or a UL signaling RRC message.[9] The method as described in any of [6]-[8], wherein the second UL data packet includes one or more real or padded data bits.

[0010] The method as described in any of [6]-[9], wherein the source gNB-DU and the target gNB-DU correspond to different gNBs.

[0011] An apparatus configured to: receive, from a User Equipment (UE), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant; and assign, to the UE, a dynamic UL grant with a predefined grant value to signal the reception of a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch.

[0012] The apparatus as described in

[0011] , wherein the dynamic UL grant corresponds to a Physical Downlink Control Channel (PDCCH) addressing the UE’s Cell-Radio Network Temporary Identifier (C-RNTI).

[0013] The apparatus as described in any of

[0011] -

[0012] , wherein the apparatus is a target gNodeB (gNB-DU) after the RACH-less LTM cell switch.

[0014] A method comprising: receiving, by a target gNodeB-DU (gNB-DU), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant from a User Equipment (UE) after a Random-Access Channel (RACH)-less Layerl / Layer 2 triggered Mobility (LTM) cell switch; and assigning, by the target gNB-DU to the UE, a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch.

[0015] The method as described in

[0014] , wherein the dynamic UL grant corresponds to a Physical Downlink Control Channel (PDCCH) addressing the UE’s Cell-Radio Network Temporary Identifier (C-RNTI).

[0016] A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a User Equipment (UE), the UE comprising one or more processors, cause the one or more processors to: receive a Random-Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU), the RACH-less LTM cell switch command being configured to trigger the UE to perform a cell switch to a target gNB-DU through L2 signaling; transmit, to the target gNB-DU, a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch; after transmitting the first UL data packet, transmit, to the target gNB-DU, a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receive, from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request; and determine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

[0017] A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a target gNodeB -Distributed Unit (gNB-DU) after a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch, the target gNB-DU comprising one or more processors, cause the one or more processors to: receive, from a User Equipment (UE), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant; and assign, to the UE, a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate the successful RACH-less LTM cell switch.

[0067] The present disclosure thus allows indication of a successful LTM cell switch to the gNB, and the awareness is also sent to the UE. Further, RLF / RRC re-establishment is avoided.

[0068] 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. The UE and the gNB may include respective processors, communication units, and storage units (e.g., memory). The communication units may perform functions for transmitting and receiving signals. The storage units may include executable instructions that, when executed by the corresponding processors, cause the corresponding UE and gNB to perform the functions as described above with reference to Figures 2A-5.

[0069] 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.

[0070] 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.

[0071] 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 inthe specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0072] 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.

[0073] 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. A User Equipment (UE) (201) configured to : receive a Random-Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU) (203), the RACH-less LTM cell switch command being configured to trigger the UE (201) to perform a cell switch to a target gNB-DU (205) through L2 signaling; in response to the received RACH-less LTM cell switch command, transmit, to the target gNB-DU (205), a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch; after transmitting the first UL data packet, transmit, to the target gNB-DU (205), a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receive, from the target gNB-DU (205), a second UL scheduling grant in response to the transmitted scheduling request; and determine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU (205) is successfully delivered.

2. The UE (201) as claimed in claim 1, wherein after transmission of the SR, the UE 201 is further configured to: initiate an LTM failure timer; andin response to the target gNB-DU (205) and non-receipt of the second UL scheduling grant, determine that the successful RACH-less LTM cell switch indication delivery to the target gNB-DU (205) is unsuccessful.

3. The UE (201) as claimed in claim 1, wherein the first UL data packet includes one of one or more real data bits or one or more padded data bits or a UL signaling RRC message.

4. The UE (201) as claimed in claim 1, wherein the second UL data packet includes one or more real or padded data bits.

5. The UE (201) as claimed in claim 1, wherein the source gNB-DU and the target gNB- DU 203 correspond to different gNBs.

6. A method (400) comprising: receiving (402), by a User Equipment (UE) (201), a Random- Access Channel (RACH)- less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB- Distributed Unit (gNB-DU) (203), the RACH-less LTM cell switch command being configured to trigger the UE (201) to perform a cell switch to a target gNB-DU (205) through L2 signaling; in response to receiving the RACH-less LTM cell switch command, transmitting (404), by the UE (201) to the target gNB-DU (205), a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch;after transmitting the first UL data packet, transmitting (406), by the UE (201) to the target gNB-DU (205), a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receiving (408), by the UE (201) from the target gNB-DU (205), a second UL scheduling grant in response to the transmitted scheduling request; and determining (410), by the UE (201), in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU (205) is successfully delivered.

7. The method (400) as claimed in claim 6, wherein after transmission of the SR, the method (400) further comprises: initiating, by the UE (201), an LTM failure timer; in response to an expiry of the LTM failure timer and non-receipt of the second UL scheduling grant, determining, by the UE (201), that the successful RACH-less LTM cell switch indication delivery to the target gNB-DU (205) through the L2 signaling is unsuccessful.

8. The method (400) as claimed in claim 6, wherein the first UL data packet includes one of one or more real data bits or one or more padded data bits or a UL signaling RRC message.

9. The method (400) as claimed in claim 6, wherein the second UL data packet includes one or more real or padded data bits.

10. The method (400) as claimed in claim 6, wherein the source gNB-DU (203) and the target gNB-DU (205) correspond to different gNBs.

11. An apparatus (600) configured to: receive, from a User Equipment (UE) (201), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant; and assign, to the UE (201), a dynamic UL grant with a predefined grant value to signal the reception of a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch.

12. The apparatus (600) as claimed in claim 11, wherein the dynamic UL grant corresponds to a Physical Downlink Control Channel (PDCCH) addressing the UE’s Cell-Radio Network Temporary Identifier (C-RNTI).

13. The apparatus (600) as claimed in claims 11, wherein the apparatus (600) is a target gNodeB -Distributed Unit (gNB-DU) (205) after the RACH-less LTM cell switch.

14. A method (500) comprising: receiving (502), by a target gNodeB -Distributed Unit (gNB-DU) (205), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant from a User Equipment (UE) (201) after a Random -Access Channel (RACH)-less Layerl / Layer 2 triggered Mobility (LTM) cell switch; andassigning (504), by the target gNB-DU (205), a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate a successful RACH-less LTM cell switch.

15. The method (500) as claimed in claim 14, wherein the dynamic UL grant corresponds to a Physical Downlink Control Channel (PDCCH) addressing the UE’s Cell-Radio Network Temporary Identifier (C-RNTI).

16. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a User Equipment (UE), the UE (201) comprising one or more processors, cause the one or more processors to: receive a Random-Access Channel (RACH)-less Layer 1 / Layer 2 Triggered Mobility (LTM) cell switch command from a source gNodeB -Distributed Unit (gNB-DU), the RACH- less LTM cell switch command being configured to trigger the UE (201) to perform a cell switch to a target gNB-DU through L2 signaling; in response to the received RACH-less LTM cell switch command, transmit, to the target gNB-DU, a first Uplink (UL) data packet via one of a configured UL scheduling grant and a dynamic UL scheduling grant to indicate a successful RACH-less LTM cell switch; after transmitting the first UL data packet, transmit, to the target gNB-DU, a Scheduling Request (SR) to receive dynamic grants to transmit a second UL data packet; receive, from the target gNB-DU, a second UL scheduling grant in response to the transmitted scheduling request; anddetermine, in response to the received second UL scheduling grant, that the indication of the successful RACH-less LTM cell switch to the target gNB-DU is successfully delivered.

17. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a target gNodeB -Distributed Unit (gNB-DU) (205) after a Random-Access Channel (RACH)-less Layerl / Layer 2 Triggered Mobility (LTM) cell switch, the target gNB-DU (205) comprising one or more processors, cause the one or more processors to: receive, from a User Equipment (UE) (201), an Uplink (UL) data packet via one of a configured UL scheduling grant or a dynamic UL scheduling grant; and assign, to the UE (201), a dynamic UL grant with a predefined grant value to signal the reception of a successful RACH-less LTM cell switch indication or a successful reception of the UL data packet meant to indicate the successful RACH-less LTM cell switch.

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