WO2025230552A1

WO2025230552A1 - Inter-gnb layer 2 triggered mobility in a communication environment

Info

Publication number: WO2025230552A1
Application number: PCT/US2024/034506
Authority: WO
Inventors: Subramanya CHANDRASHEKAR; Vihang KAMBLE
Original assignee: Rakuten Symphony Inc; Rakuten Mobile USA LLC
Current assignee: Rakuten Symphony Inc; Rakuten Mobile USA LLC
Priority date: 2024-04-30
Filing date: 2024-06-18
Publication date: 2025-11-06
Anticipated expiration: 2026-10-30

Abstract

Disclosed herein is an apparatus configured to receive, at a target centralized unit control plane (gNB-CU-CP), a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP. Further, the apparatus is configured to prepare one or more target centralized unit user planes (gNB-CU-UPs) for the LTM to a target cell and prepare one or more target distributed units (gNB-DUs) after preparing the one or more target gNB-CU-UPs. Further, the apparatus is configured to detect, at a target gNB-DU, a successful LTM cell switch to the target cell, transmit, after detecting the successful LTM cell switch, an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs, and trigger, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

Description

TITLE: INTER-GNB LAYER 2 TRIGGERED MOBILITY IN A COMMUNICATION ENVIRONMENT

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Indian Patent Application No. 202411034381, filed on April 30, 2024; the entire contents of which are incorporated herein by reference.

FIELD

[0002] The present disclosure relates to inter-gNB Layer 2 Triggered Mobility (LTM) in a communication environment.

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] The emergence of Fifth Generation (5G) communication technology, i.e., 5G cellular systems, has reshaped the telecommunication landscape. Currently, 5G cellular systems are being standardized within the Third-Generation Partnership Project (3 GPP).

[0005] Wireless communications at User Equipment (UEs) are generally provided by means of a communication network distributed over different regions referred to as cells. The cells may be served by corresponding base stations. In 5G cellular networks, a Next Generation Radio Access Network (NG-RAN) may be connected to a 5G Core (5GC) network. The NG-RAN may include one or more gNodeBs (gNBs) that may act as base stations and facilitate communication between the UEs and the 5GC. Each of the gNBs may serve a specific region including one or more cells. The gNBs may form a part of the NG-RAN and facilitate communication between the UEs and a 5GC network. [0006] In 5G cellular systems, rhe gNBs may include multiple logical entities. The logical entities may include a Centralized Unit (CU), one or more Distributed Units (DU), and one or more Radio Unit (RUs). The CU may further be logically split into control plane portion (CU- CP) and one or more user plane portions (CU-UP).

[0007] Further, mobility refers to a process of transferring an ongoing communication session of a UE from one cell to another cell. When the UE moves between coverage areas of two cells, a cell switch (change in a serving cell) needs to be performed. Mobility is required for seamless connectivity and continuity of service for a user associated with the UE, thereby ensuring uninterrupted communication, and maintaining quality of service for the UE, particularly when the UE is moving to different locations.

[0008] Currently, Release 18 has introduced Layer 1 (LI) and Layer 2 (L2) based Mobility (LTM) to enable serving cell change via L1/L2 signaling. The LI and L2 based mobility facilitates maintaining established configuration of the upper layers while minimizing changes of re-configuration of the lower layers. However, LI and L2 based mobility is currently limited to intra-CU and intra gNB mobility (mobility between the cells of the same or different gNB-DUs of the same gNB, however, served by the same CU-UP).

[0009] There is a need for a technique that enables inter-gNB LTM or inter-CU LTM, i.e. mobility from one gNB (e.g., a serving CU-CP) to a different gNB (e.g., a target CU-CP). In inter-gNB LTM, it is important to consider security key changes associated with the respective CU-UPs, in contrast to intra-CU mobility in which the impact of security key changes was not considered. Thus, in inter-gNB LTM, security key changes as well as the associated handover changes in the target gNB are to be considered. Further, in the scenario of CU-UPs being associated with different data bearers, data forwarding from one CU-UP to another CU-UP for the bearers also needs to be considered. Moreover, optimal timing for triggering downlink data transmission at the target gNB, after inter-gNB LTM needs to be considered.

[0010] However, as described above, conventional techniques do not provide methods for inter- gNB LTM. Thus, it is desired to address at least the above-mentioned shortcomings. SUMMARY

[0011] 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 invention nor is it intended to determine the scope of the disclosure.

[0012] Disclosed herein is an apparatus configured to receive, at a target centralized unit control plane (gNB-CU-CP) associated with the apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP. Further, the apparatus is configured to prepare, based on the received request, one or more target centralized unit user planes (gNB-CU-UPs) associated with the apparatus for the LTM to a target cell. Further, the apparatus is configured to prepare one or more target distributed unit (gNB- DUs) associated with the apparatus after preparing the one or more target gNB-CU-UPs. Further, the apparatus is configured to detect, at a target gNB-DU among the one or more target gNB- DUs, a successful LTM cell switch to the target cell. Furthermore, the apparatus is configured to transmit, after detecting the successful LTM cell switch, an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs. Moreover, the apparatus is configured to trigger, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

[0013] Disclosed herein is an apparatus configured to determine, at a serving centralized unit control plane (gNB-CU-CP) associated with the apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required. Further, the apparatus is configured to transmit, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE. Further, the apparatus is configured to receive from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations. Further, the apparatus is configured to transmit, to a serving distributed unit (gNB-DU) associated with the apparatus, cell identification and centralized unit user plane (gNB- CU-UP) mapping information associated with the apparatus. Furthermore, the apparatus is configured to determine, during an LTM cell switch decision at the serving DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB- CU-UP associated with the target cell. Moreover, the apparatus is configured to transmit, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB-CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

[0014] Disclosed herein is a method that comprises receiving, at a target centralized unit control plane (gNB-CU-CP) associated with an apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP. Further, the method comprises preparing, based on the received request, one or more target centralized unit user planes (gNB-CU-UPs) associated with the apparatus for the LTM to a target cell. Further, the method comprises preparing one or more target distributed units (gNB-DUs) associated with the apparatus after preparing the one or more target gNB-CU-UPs. Further, the method comprises detecting, at a target gNB-DU among the one or more target gNB-DUs, a successful LTM cell switch to the target cell. Further, the method comprises, after detecting the successful LTM cell switch, transmitting an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs. Further, the method comprises triggering, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

[0015] Disclosed herein is a method that comprises determining, at a serving centralized unit control plane (gNB-CU-CP) associated with an apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required. Further, the method comprises transmitting, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE. Further, the method comprises receiving from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations. Further, the method comprises transmitting, to a serving distributed unit (gNB- DU) associated with the apparatus, cell identification and centralized unit user plane (gNB-CU- UP) mapping information associated with the apparatus. Further, the method comprises determining, during an LTM cell switch decision at the serving gNB-DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB- CU-UP associated with the target cell. Further, the method comprises transmitting, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB-CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

[0016] The disclosed apparatus and method enable inter-gNB LTM for a UE by taking into consideration security key changes required and the association of different data bearers of the UE with the gNB-CU-UPs. Moreover, the disclosed apparatus and method enable optimized data forwarding and initiation of downlink data transmission in the inter-gNB LTM.

[0017] 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

[0018] 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 an example block diagram of a communication environment depicting a configuration of a plurality of Next Generation Radio Access Network (NG-RAN) nodes and a User Equipment (UE), in accordance with an embodiment of the present disclosure;

FIG. 2 illustrates a block diagram depicting the disaggregated architecture of a first NG-RAN node and a second NG-RAN node, in accordance with an embodiment of the present disclosure;

FIGS. 3A-3C illustrate signalling diagrams for an inter-gNB LTM scenario, in accordance with an embodiment of the present disclosure;

FIG. 4A illustrates a process flow depicting a method for inter-gNB LTM of the UE, in accordance with an embodiment of the present disclosure; FIG. 4B illustrates a process flow depicting another method for inter-gNB LTM of the UE, in accordance with an embodiment of the present disclosure; and

FIG. 5 illustrates an embodiment of a device, in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

[0019] The following detailed description of example embodiments refers to the accompanying drawings. The present disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the present disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowchart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part).

[0020] 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.

[0021] 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.

[0022] 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. The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from the practice of the implementations.

[0023] Now embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

[0024] FIG. 1 illustrates an example block diagram of a communication environment 100 depicting a configuration of a plurality of Next Generation Radio Access Network (NG-RAN) nodes and a User Equipment (UE), according to one or more embodiments disclosed herein. The plurality of NG-RAN nodes may include a first NG-RAN node 110 and a second NG-RAN node 120 different from the first NG-RAN node 110. The first NG-RAN node 110 and the second NG- RAN node 120 may be configured to communicate with the UE 130, as depicted in FIG. 1. The configurations as disclosed in FIG. 1 may be understood as parts of the configuration of the NG- RAN nodes 110, 120 and the UE 130. Hereinafter, it is understood that terms including “unit” or “module” at the end may refer to the unit for processing at least one function or operation and may be implemented in hardware, software, or a combination of hardware and software.

[0025] In an embodiment, the communication environment may be a 5^th Generation (5G) New Radio (NR) communication environment. The first NG-RAN node 110 may alternatively be referred to as a first gNodeB (gNB) or a serving gNB. The second NG-RAN node 120 may alternatively be referred to as a second gNB or a candidate/target gNB. [0026] In an embodiment, the UE 130 may be a mobile telephone, a smartphone, a tablet, a personal computer, a Personal Digital Assistant (PDA), a data terminal, etc.

[0027] It is appreciated that although the first and second NG-RAN nodes 110, 120 are depicted in FIG. 1, the communication environment 100 may include additional NG-RAN nodes as well, and the details explained in the present disclosure for the first and second NG-RAN nodes 110, 120 are equally applicable for additional NG-RAN nodes as well. Further, the communication environment 100 may include additional UEs (not shown) and details in the present disclosure explained with reference to the UE 130 are equally applicable for the additional UEs as well.

[0028] Referring to FIG. 1, the first NG-RAN node 110 may include an apparatus 111 comprising one or more processor(s) 112 (also, referred to as the processor 112), a storage unit (e.g., memory 114), and a communication unit 116 (e.g., communicator or communication interface). The first NG-RAN node 110 may perform functions for transmitting and receiving signals. The memory 114 may include executable instructions that, when executed by the processor, cause the apparatus 111 to perform the steps as described with reference to FIGS. 3 and 4A-4B.

[0029] As an example, the processor 112 may be a single processing unit or a number of units, all of which could include multiple computing units. The processor 112 may be implemented as one or more microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and/or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor 112 is configured to fetch and execute computer-readable instructions and data stored in the memory. The processor 112 may include one or a plurality of processors. At this time, one or a plurality of processors 112 may be a general-purpose processor, such as a Central Processing Unit (CPU), an Application Processor (AP), or the like, and an Al-dedicated processor such as a Neural Processing Unit (NPU). The processor 112 may control the processing of input data in accordance with a predefined operating rule or Artificial Intelligence (Al) model stored in the non-volatile memory and the volatile memory, i.e., the memory 114. The predefined operating rule or artificial intelligence model is provided through training or learning. [0030] The memory 114 may include any non-transitory computer-readable medium known in the art including, for example, volatile memory, such as Static Random-Access Memory (SRAM) and Dynamic Random-Access Memory (DRAM), and/or non-volatile memory, such as Read- Only Memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes.

[0031] In some embodiments, the apparatus 111 may be implemented as dedicated hardware units. In some embodiments, the apparatus 111 may be implemented in the form of virtualized software units in hardware or cloud environments.

[0032] The second NG-RAN node 120 may also include an apparatus 121 comprising one or more processor(s) 122 (also, referred to as the processor 122), a storage unit (e.g., memory 124), and a communication unit 126 (e.g., communicator or communication interface). The functionalities and features of the processor 122, communication unit 126, and memory 124 of the second NG-RAN node 120 may be similar to those of the processor 112, communication unit 116, and memory 114, respectively of the first NG-RAN node 110. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the present disclosure.

[0033] Further, the UE 130 may also include one or more processor(s) 132 (also, referred to as processor 132), a storage unit (e.g., memory 134), and a communication unit 136 (e.g., communicator or communication interface). The functionalities and features of the processor 132, communication unit 136, and memory 134 may be similar to those of the processor 112, communication unit 116, and memory 114, respectively of the first NG-RAN node 110. Therefore, a detailed explanation of the same is omitted herein for the sake of brevity of the present disclosure.

[0034] In an embodiment, each of the first NG-RAN node 110 and the second NG-RAN node 120 may have a disaggregated architecture. Further, each of the first NG-RAN node 110 and the second NG-RAN node 120 may be configured to provide layer 3 mobility or layer 1/layer 2 triggered mobility (LTM) when the UE 130 coupled to the first NG-RAN node 110 undergoes reallocation to the second NG-RAN node 120. The UE 130 may be coupled to the first NG-RAN node 110, referred to as serving gNB, and undergoes handover to the second NG-RAN node 120, referred to as target gNB. [0035] FIG. 2 illustrates a block diagram depicting the disaggregated architecture of the first NG-RAN node 110 and the second NG-RAN node 120, in accordance with an embodiment of the present disclosure. The first NG-RAN node 110 (the serving gNB) may include a serving Centralized Unit (gNB-CU) 212. The serving gNB-CU 212 may be logically split into a serving CU Control Plane (gNB-CU-CP) 214 and one or more serving CU User Planes (gNB-CU-UPs) 216. The one or more serving gNB-CU-UPs 216 may alternatively be referred to as ‘the serving gNB-CU-UP 216’. The serving gNB-CU-CP 214 may be communicatively coupled with the one or more serving gNB-CU-UPs 216 over an El communication interface.

[0036] The serving gNB-CU 212 may be communicatively coupled to one or more Distributed Units (gNB-DUs) 218, where one of the gNB-DUs may be a serving gNB-DU. In particular, the serving gNB-CU-CP 214 may be coupled to the one or more gNB-DUs 218 via a Fl-C communication interface while the one or more serving gNB-CU-UPs 216 may be coupled to the one or more gNB-DUs 218 via a Fl-U communication interface. The gNB-DU that serves the UE amongst the one or more gNB-DUs 218 may alternatively be referred to as ‘the serving gNB- DU 218’. Further, the one or more gNB-DUs may be communicatively coupled to one or more serving Radio Units (gNB-RUs) via a fronthaul network. The one or more gNB-RUs may be communicatively coupled to multiple UEs, such as, the UE 130.

[0037] The components of the first NG-RAN node 110 may be connected to a core network using a backhaul link. The serving gNB-CU 212 may be configured for the execution of Radio Resource Control (RRC) protocols and Packet Data Convergence Protocol (PDCP) protocols of a radio stack. The serving gNB-DU 218 may be configured for execution of Radio Link Control (RLC), Medium Access Control (MAC) and upper parts of Physical (PHY) layer protocols of the radio stack. The serving gNB-DU 218 may additionally include Fl Application Protocol (Fl-AP) sublayer, General Packet Radio Service (GPRS) Tunnelling Protocol (GTPU) sublayer, a Stream Control Transmission Protocol (SCTP) sublayer, a User Datagram Protocol (UDP) sublayer, and an Internet Protocol (IP) sublayer. In an embodiment, the serving gNB-CU-CP 214 may also include the Fl-AP, SCTP, and IP sublayers along with PDCP-control (PDCP-C) sublayer. In an embodiment, the serving gNB-CU-UP 216 may include service data adaptation protocol (SDAP) sublayer, PDCP -user (PDCP-U) sublayer, GTPU sublayer, UDP sublayer, and IP sublayer. The serving gNB-RUs may be configured for execution of lower parts of PHY layer protocols as well as provide antenna capabilities for communication with UEs.

[0038] Further, the second NG-RAN node 120 (target gNB) may include a candidate/target gNB-CU 222. The candidate/target gNB-CU 222 may be logically split into a target gNB-CU- CP 224 and one or more candidate/target gNB-CU-UPs 226. Further, the second NG-RAN node 120 may include one or more candidate/target gNB-DUs 228 and one or more candidate/target RUs (not shown). The one or more candidate/target gNB-CU-UPs 226 may alternatively be referred to as ‘the candidate/target gNB-CU-UP 226’. The one or more candidate/target gNB- DUs 228 may alternatively be referred to as ‘the candidate/target gNB-DU 228’. The functionality described above for the serving gNB-CU-CP 214, the one or more serving gNB- CU-UPs 216 and the one or more serving DUs are also applicable for the candidate/target gNB- CU-CP 224, the one or more candidate/target gNB-CU-UPs 226 and the one or more candidate/target DUs.

[0039] Accordingly, as depicted in FIG. 2, the serving gNB-CU-CP 214, the one or more serving gNB-CU-UPs 216, and the one or more serving gNB-DUs 218 are associated with the serving gNB, i.e., the first NG-RAN node 110. Further, the candidate/target gNB-CU-CP 224, the one or more candidate/target gNB-CU-UPs 226, and the one or more candidate/target gNB- DUs 228 are associated with the candidate/target gNB, i.e., the second NG-RAN node 120.

[0040] Referring collectively to FIGS. 1-2, functionalities to enable inter-gNB LTM or inter- CU LTM, i.e. mobility from one gNB (e.g., a serving CU-CP) to a different gNB (e.g., a target CU-CP) is described. Security key changes associated with the respective CU-UPs are considered in contrast to intra-CU mobility in which the impact of security key changes was not considered. Further, in the scenario of CU-UPs being associated with different data bearers, data forwarding from one CU-UP to another CU-UP for the bearers is also considered. Moreover, optimal timing for triggering downlink data transmission at the target gNB, after inter-gNB LTM is also considered.

[0041] the first NG-RAN node 110 (serving gNB) may be configured to provide LTM for inter-gNB handover case. When the UE 130 moves from the coverage area of a serving cell to a candidate/target cell, then a serving cell change needs to be performed. In an embodiment, the serving cell is associated with a serving gNB (for instance, the first NG-RAN node 110) and the target cell is associated with a target gNB (for instance, the second NG-RAN node 120). As the serving cell and target cell are associated with different gNBs, the handover is an inter-gNB handover. The inter-gNB handover may alternatively be referred to as an inter-CU handover (handover from CU associated with the serving gNB to CU associated with the target gNB). That is, the inter-gNB handover may occur when the UE 130 coupled with the first NG-RAN node 110 (serving gNB) undergoes handover from the serving gNB-CU-CP 214 to the target gNB-CU- CP 224 of the second NG-RAN node 120 (target gNB) for one or more services. In an embodiment, the LTM may be performed to a target cell selected from one or more candidate cells for the LTM cell switch. It is appreciated that the details of the inter-gNB LTM procedure may be explained with reference to a target cell associated with the second NG-RAN node 120 (target gNB). The target cell may be considered as a target candidate cell, i.e., a cell from among the one or more candidate cells that has been chosen for an LTM cell switch execution.

[0042] In the present disclosure, prior to selection of the target cell may be referred to as a target/candidate cell. In this regard, prior to selection of the target cell, the associated NG-RAN node may be referred to as candidate/target NG-RAN node. Similarly, the gNB entities may be referred to as candidate/target gNB-CU, candidate/target gNB-CU-CP, candidate/target gNB- CU-UP, and candidate/target gNB-DU. Once the selection of target cell is complete, the same entities may be referred to as target NG-RAN node, target gNB-CU, target gNB-CU-CP, target gNB-CU-UP, and target gNB-DU. It is appreciated that the terms ‘target’ and ‘candidate/target’ may be used interchangeably in the present disclosure. In an embodiment, the serving gNB-CU- CP 214 may determine the particular cell among the candidate cells that has to be selected as the target cell. It is appreciated that the inter-gNB LTM procedure may be applicable for other candidate cells as well.

[0043] Initially, the UE 130 may be in communication with the first NG-RAN node 110 (serving gNB). The UE 130 is configured with LTM with one or more candidate cells associated with one or more candidate DUs. The one or more candidate DUs may be associated with candidate NG-RAN nodes which may include the second NG-RAN node 120 (the target gNB).

[0044] The serving gNB-CU-CP 214 may be configured to receive a Radio Resource Control (RRC) measurement report from the UE 130. In an embodiment, the RRC measurement report may include L3 measurements. When the RRC measurement report is received at the serving gNB-CU-CP 214, the serving gNB-CU-CP 214 may be configured to determine that an inter gNB LTM candidate/target cell preparation for the UE 130 is required. For instance, the serving gNB- CU-CP 214 may determine that a service handover is required for one or more services of the UE 130. The one or more services refer to services where the UE 130 is to be served by a different gNB-DU other than the serving gNB-DU 218, in this case, the target gNB-DU 228. In an embodiment, the LTM target cell may be one of the multiple candidate cells. In the current embodiment, the LTM target cell may be a target cell associated with the second NG-RAN node 120 (for instance, associated with the one or more target gNB-DUs) 228.

[0045] Thus, the serving gNB-CU-CP 214 determines that the inter-gNB LTM candidate/target cell preparation for the UE 130 is required based on the received RRC measurement report, indicating that the UE 130 will undergo handover for one or more services.

[0046] Upon determining that the inter-gNB target cell preparation is required, the serving gNB-CU-CP 214 may be configured to transmit a request to the target gNB-CU-CP 224 of the second NG-RAN node 120. The request may be indicative of the LTM candidate/target cell preparation for the UE 130. In an embodiment, the request may be a handover request. In an embodiment, the serving gNB-CU-CP 214 may transmit the request over an Xn interface.

[0047] The candidate/target gNB-CU-CP 224 may be configured to receive the request indicative of the LTM target cell preparation. The target gNB-CU-CP 224 may be configured to prepare the one or more candidate/target gNB-CU-UPs 226 and the one or more candidate/target DU cells for the LTM. Prior to the LTM candidate/target cell preparation at the one or more candidate/target gNB-DUs 228, an El procedure between the candidate/target gNB-CU-CP 224 and the one or more candidate/target gNB-CU-UPs 226 may be performed. That is, the candidate/target gNB-CU-CP 224 may be configured to prepare the one or more candidate/target gNB-CU-UPs 226 before preparing the candidate/target cell at the one or more candidate/target gNB-DUs 228. The El procedure may be performed to fetch one or more security keys associated with the one or more candidate/target gNB-CU-UPs 226.

[0048] Upon receiving the request indicative of the LTM candidate/target cell preparation at the candidate/target gNB-CU-CP 224, the one or more candidate/target gNB-CU-UPs 226 may be prepared for the LTM to the target cell. The candidate/target gNB-CU-CP 224 may be configured to indicate, via an Information Element (IE), LTM preparation phase to the one or more candidate/target gNB-CU-UPs 226. In an embodiment, the candidate/target gNB-CU-CP 224 may be configured to transmit a bearer context setup request to the one or more candidate/target gNB-CU-UPs 226 including the IE indicating the LTM preparation phase. The bearer context setup request may indicate the LTM candidate/target cell preparation to the one or more candidate/target gNB-CU-UPs 226. In an embodiment, the bearer context setup request may additionally indicate relocation of CU-UPs (i.e., relocation from one or more serving gNB-CU- UPs 216 to one or more target gNB-CU-UPs 226). In an embodiment, the bearer context setup request may be transmitted over an El interface.

[0049] The one or more candidate/target gNB-CU-UPs 226 may receive the bearer context setup request and generate the one or more security keys. Further, the one or more candidate/target gNB-CU-UPs 226 may be configured to transmit a bearer context setup response to the target gNB-CU-CP 224. The bearer context setup response may be indicative of the one or more security keys associated with the one or more candidate/target gNB-CU-UPs 226. In an embodiment, the bearer context setup response may be transmitted over the El interface.

[0050] Further, the one or more security keys may be transmitted to the one or more candidate/target gNB-DUs 228. In particular, after preparing the one or more target gNB-CU- UPs 226, the one or more candidate/target DUs may be prepared in order to prepare the LTM candidate/target cells. That is, the one or more target gNB-DUs cells may be prepared after preparing the one or more target gNB-CU-UPs 226. The one or more security keys generated by the one or more candidate/target gNB-CU-UPs 226 may be used by the one or more candidate/target gNB-DUs 228 during the LTM candidate/target cell preparation. In an embodiment, the candidate/target gNB-CU-CP 224 may be configured to transmit the one or more security keys to the one or more candidate/target gNB-DUs 228. In an embodiment, the one or more security keys may be transmitted in a UE context setup request. In an embodiment, the UE context setup request may additionally include Tunnel Endpoint Identifiers (TEIDs) of the one or more target gNB-CU-UPs 226. In an embodiment, the UE context setup request may be transmitted over an Fl interface. [0051] In an embodiment, the UE 130 may be associated with multiple data bearers. In an embodiment, the one or more candidate/target CU-UPs and the one or more candidate/target gNB-DUs 228 are prepared corresponding to each data bearer associated with the UE 130. The target gNB-CU-CP 224 may be configured to identify the CU-UPs associated with each of the data bearers of the UE 130. In an embodiment, each of the data bearers may be associated with a common CU-UP. In an embodiment, each of the data bearers may be associated with a distinct CU-UP. In an embodiment, the one or more target gNB-CU-UPs 226 corresponding to all the data bearers of the UE are prepared prior to preparing the one or more candidate/target DUs. As the El procedure is performed prior to the candidate/target cell preparation at the one or more candidate/target gNB-DUs 228, the security keys associated with the one or more target gNB- CU-UPs 226 can be provided to the one or more candidate/target gNB-DUs 228. Moreover, resource reservation at the one or more candidate/target gNB-CU-UPs 226 may be delayed and data transmission may be suspended by indicating that the preparation is for an LTM candidate/target cell.

[0052] The target gNB-CU-CP 224 may be configured to receive a response from the one or more candidate/target DUs over the Fl interface. Upon receiving the response from the one or more candidate/target DUs, the candidate/target gNB-CU-CP 224 may be configured to transmit a bearer context modification procedure to update the downlink TEID provided by the candidate/target gNB-DU to the corresponding candidate/target gNB-CU-UP. Further, the candidate/target gNB-CU-CP 224 may be configured to transmit a response to the LTM target cell preparation request (handover request) received from the serving gNB-CU-CP 214. In an embodiment, the response sent to the serving gNB-CU-CP 214 may include one or more LTM candidate/target cell configurations. In an embodiment, the response may be a handover response transmitted over the Xn interface.

[0053] Further, the serving gNB-CU-CP 214 may be configured to transmit the LTM candidate/target cell identification and gNB-CU-UP mapping information to the serving gNB- DU 218. The serving gNB-DU 218 may thus be informed of the LTM candidate/target cell and the one or more candidate/target gNB-CU-UPs 226. In an embodiment, the LTM candidate/target cell identification and gNB-CU-UP mapping information may be transmitted in a UE context modification request over the Fl interface. The serving gNB-DU 218 may be configured to store the received LTM candidate/target cell identification and gNB-CU-UP mapping information. The received LTM candidate/target cell identification and gNB-CU-UP mapping information may be stored, for instance, in the memory 114.

[0054] The serving gNB-DU 218 may be configured to generate a configuration parameter for the target cell(s). The configuration parameter may be, for instance, CellGroupConfig. The serving gNB-DU 218 may be configured to transmit the CellGroupConfig in a UE context modification response to the serving gNB-CU-CP 214. Further, the serving gNB-CU-CP 214 may be configured to indicate the LTM target cell configuration to the UE 130. In an embodiment, the LTM target cell configuration may indicate to the UE 130 that the LTM candidate/target cell is served by the one or more target gNB-CU-UPs 226 and whether a Packet Data Convergence Protocol (PDCP) entity has to be reset. In an embodiment, the serving gNB-CU-CP 214 may be configured to transmit an RRC reconfiguration message to the UE 130 indicating the LTM target cell configuration.

[0055] Further, the serving gNB-DU 218 may be configured to determine a requirement of data forwarding during the LTM cell switch decision, based on the gNB-CU-UP serving the target gNB-DU. The decision to perform the LTM cell switch for the UE 130 may further be based on Radio Resource Management (RRM) criteria. In an embodiment, the serving gNB-DU 218 may be configured to determine whether radio conditions associated with the target cell are greater than a pre-defined threshold. In an embodiment, the serving gNB-DU 218 may be notified by the serving gNB-CU-CP 214 regarding the TEIDs associated with the candidate/target CU-UPs of the UE 130. For instance, the UE 130 may have multiple services served by different candidate/target CU-UPs, and the serving gNB-DU 218 is informed of the corresponding CU-UP TEIDs. In an embodiment, the information regarding the corresponding TEIDs may be provided to the serving gNB-DU 218 at the time of a first LTM candidate cell preparation.

[0056] In an embodiment, the serving gNB-DU 218 may be configured to receive an LI measurement report from the UE 130. The LI measurement report may indicate radio conditions of the LTM candidate/target cells measured by the UE 130 to the serving gNB-DU 218. Based on the LI measurement report, the serving gNB-DU 218 may be configured to determine whether data forwarding is required. The data forwarding is required when the serving gNB-DU 218 and the target gNB-DU 228 are served by different gNB-CU-UPs. In the present scenario, as the serving gNB-DU 218 is served by the serving gNB-CU-UP 216 and the target gNB-DU 228 is served by the one or more target gNB-CU-UPs 226, data forwarding would be required from the one or more serving gNB-CU-UPs 216 to the one or more target gNB-CU-UPs 226.

[0057] The serving gNB-DU 218 may be configured to transmit a message to the serving gNB- CU-UP 216, the message indicating that data forwarding to the one or more target gNB-CU-UPs 226 is to be initiated. The message may additionally include identifiers (IDs) associated with the one or more target gNB-CU-UPs 226, thus notifying the serving gNB-CU-UP 216 regarding the one or more target gNB-CU-UPs 226.

[0058] In an embodiment, the message may be a user-plane based control Packet Data Unit (PDU) indicating the serving gNB-CU-UP 216 to initiate data forwarding to the target gNB-CU- UP 226. The control PDU may include control plane information in a user plane data packet. Upon receiving the control PDU, the serving gNB-CU-UP 216 may be configured to transmit forwarded data to the target gNB-CU-UP 226. In an embodiment, forwarded data refers to transmission of unsent data PDUs at the source to the target gNB-CU-UP 226. In an embodiment, forwarded data refers to the transmission of unsent and unacknowledged data PDUs at the source to the target gNB-CU-UP 226.

[0059] In an embodiment, the serving gNB-CU-UP 216 may be indicated to initiate data forwarding using Fl and El signaling. In such an embodiment, the serving gNB-DU 218 may be configured to transmit a first message, to initiate data forwarding, over the Fl interface to the serving gNB-CU-CP 214. Further, the serving gNB-CU-CP 214 may be configured to transmit a second message to the serving gNB-CU-UP 216 over the El interface to initiate data forwarding. Upon receiving the second message, the serving gNB-CU-UP 216 may be configured to transmit forwarded data to the one or more target gNB-CU-UPs 226.

[0060] The one or more target gNB-CU-UPs 226 may be configured to receive the forwarded data from the serving gNB-CU-UP 216 currently serving the UE 130.

[0061] In an embodiment, the LTM cell switch may be a Random Access Channel (RACH)- less LTM. In such an embodiment, timing advance of the target cell may be procured prior to the cell switch. In another embodiment, the LTM cell switch may be a RACH-based LTM. In such an embodiment, the RACH procedure is to be performed at the time of the cell switch. [0062] Further, a target gNB-DU 228 among the one or more candidate/target gNB-DUs may be configured to detect a successful LTM cell switch to the target cell, based on reception of uplink data from UE. Once the LTM cell switch determination is successful, the target gNB-DU 228 may be configured to transmit an LTM cell switch notification message to the one or more target gNB-CU-UPs 226 associated with different data bearers of the UE 130. The LTM cell switch notification message indicates a successful LTM cell switch. In an embodiment, the LTM cell switch notification message may additionally indicate that downlink data transmission may be triggered.

[0063] In an embodiment, the target gNB-DU 228 sending the LTM cell switch notification message ensures that the downlink data transmission is initiated after a successful LTM cell switch. In an embodiment, the target gNB-DU 228 may be configured to send a cell change notification to the target gNB-CU-CP 224 over the Fl interface.

[0064] The one or more candidate/target gNB-CU-UPs 226 may be configured to initiate downlink data transmission to the UE 130 based on the received LTM cell switch notification message. In an embodiment, the LTM cell switch notification message from the target gNB-DU 228 to the one or more target gNB-CU-UPs 226 may be a user plane-based control PDU. In case of the UE having multiple bearers associated with different target gNB-CU-UPs 226, each of the different target gNB-CU-UPs 226 may receive a different control PDU from the target gNB-DU 228. In another embodiment, the LTM cell switch notification message from the target gNB-DU 228 to the one or more target gNB-CU-UPs 226 may be a control plane signaling message, i.e., a combination of Fl and El signaling. For instance, the target gNB-DU 228 may send an Fl message to the target gNB-CU-CP 224 and further, the target gNB-CU-CP 224 may send an El message to the one or more target gNB-CU-UPs 226.

[0065] The inter-gNB LTM may thus be completed. The inter-gNB LTM may be performed considering the security key changes required at the second NG-RAN node 120 (target gNB) due to the change in the one or more target gNB-CU-UPs 226. Further, the association of different data bearers of the UE with the one or more target gNB-CU-UPs 226 is also considered during the inter-gNB LTM procedure. LTM can thus be performed even when there are multiple gNB- CU-UPs for one or more or all services of the UE. Moreover, optimized data forwarding to the one or more target gNB-CU-UPs is facilitated. In addition, optimized downlink data transmission to the UE is also facilitated.

[0066] Reference is now made to FIGS. 3A-3C depicting signalling diagrams 300A-300C for an inter-gNB LTM scenario, in accordance with an embodiment of the present disclosure. The signalling diagrams 300A-300C depict the exchange of signals and messages between the first NG-RAN node 110 (serving gNB) and the second NG-RAN node 120 (target gNB), in particular, among the gNB-CU-CP 214, 224, the one or more gNB-CU-UPs, and the one or more gNB-DUs associated with the first NG-RAN node 110 (serving gNB) and the second NG-RAN node 120 (target gNB).

[0067] Initially, as seen in FIG. 3 A, at step 302, the UE 130 may be configured with lower layer mobility with one or more candidate/target cells associated with one or more candidate DUs.

[0068] At step 304, the UE 130 may transmit a RRC measurement report to the serving gNB- CU-CP 214. At step 306, based on the received RRC measurement report, the serving gNB-CU- CP 214 may determine that an inter gNB LTM target cell preparation for the UE 130 is required.

[0069] At step 308, the serving gNB-CU-CP 214 may transmit a handover request to the target gNB-CU-CP 224 over the Xn interface. The handover request may indicate LTM target cell preparation for the UE 130.

[0070] At step 310, the target gNB-CU-CP 224 may transmit a bearer context setup request to the one or more target gNB-CU-UPs 226 over the El interface. The bearer context setup request may indicate the LTM target cell preparation and relocation of CU-UPs. In an embodiment, the target gNB-CU-UPs 226 may implicitly determine that data transmission is not expected immediately, and resource reservation can be delayed. In another embodiment, the target gNB- CU-UPs 226 may be informed by the target gNB-CU-CP 224 that data transmission is not expected immediately, and resource reservation can be delayed.

[0071] At step 312, the one or more target gNB-CU-UPs 226 may transmit a bearer context setup response to the target gNB-CU-CP 224 over the El interface. The bearer context setup response may indicate one or more security keys associated with the one or more target gNB- CU-UPs 226. At step 314, the target gNB-CU-CP 224 may transmit the one or more security keys to the one or more target gNB-DUs 228 in a UE context setup request over the Fl interface. The UE context setup request may include uplink TEIDs of the one or more target gNB-CU-UPs 226.

[0072] At step 316, the one or more target gNB-DUs 228 may transmit a UE context setup response to the target gNB-CU-CP 224 including CellGroupConfig, i.e., control plane IE indicating configuration parameters for the associated LTM candidate cell. The candidate/target gNB-DU may also include the downlink TEIDs of the data bearers of the UE. The target gNB- CU-CP may notify the corresponding target gNB-CU-UPs regarding the downlink TEIDs. In an embodiment, data tunnels may be established at the time of data forwarding in the scenario where delayed resource reservation is performed.

[0073] At step 318, the target gNB-CU-CP 224 may transmit a handover response over the Xn interface to the serving gNB-CU-CP 214, the handover response including one or more LTM candidate/target cell configurations.

[0074] Further, as seen in FIG. 3B, at step 320, the serving gNB-CU-CP 214 may transmit a UE context modification request over the Fl interface to the serving gNB-DU 218. The UE context modification request may indicate the cell identification and gNB-CU-UP mapping information to the serving gNB-DU 218.

[0075] At step 322, the serving gNB-DU 218 may store the received LTM candidate cell identification and gNB-CU-UP mapping information and generate CellGroupConfig for all the target cells. At step 324, the serving gNB-DU 218 may transmit a UE context modification response to the serving gNB-CU-CP 214 indicating the CellGroupConfig.

[0076] At step 326, the serving gNB-CU-CP 214 may transmit a RRC reconfiguration message to the UE 130 indicating the LTM target cell configuration. At step 328, the UE 130 sends a LI measurement report to the serving gNB-DU 218 for all the configured LTM candidate cells.

[0077] At step 330, based on the received LI measurement report, the serving gNB-DU 218 may determine whether radio conditions associated with the target cell are greater than a predefined threshold. Further, the serving gNB-DU 218 may determine a requirement of data forwarding during the LTM cell switch decision. As described previously, the data forwarding is required when the serving gNB-DU 218 and the target gNB-DU 228 are served by different gNB- CU-UPs, such as in the current scenario of inter-gNB LTM. [0078] Further, as seen in FIG. 3C, at step 332, the serving gNB-DU 218 may transmit a control PDU to the serving gNB-CU-UP 216 indicating that data forwarding to the one or more target gNB-CU-UPs 226 is to be initiated, and further, indicating the one or more target gNB-CU-UP IDs. As described previously, in an alternate embodiment, a combination of Fl and El signaling may be used to indicate initiation of data forwarding.

[0079] At step 334, the serving gNB-CU-UP 216 may transmit the forwarded data to the one or more target gNB-CU-UPs 226. As described above, forwarded data refers to the transmission of unsent data PDUs at source to the one or more target gNB-CU-UPs 226.

[0080] At step 336, the serving gNB-DU 218 may send a Medium Access Control (MAC) Control Element (CE) command to the UE 130 indicating LTM serving cell switch. At step 338, a user data packet may be transmitted to the target gNB-DU or optionally, a RACH procedure may be performed, based on which a successful LTM cell switch may be determined. At step 340, a target gNB-DU 228 among the one or more candidate/target gNB-DUs may detect a successful LTM cell switch to the target cell.

[0081] At step 342, the target gNB-DU 228 may transmit an LTM cell switch notification message as a control-PDU to the one or more target gNB-CU-UPs 226. The control-PDU may indicate a successful LTM cell switch at the target gNB-DU and a trigger to initiate downlink data transmission. As described previously, in an alternate embodiment, a combination of Fl and El signaling may be used to indicate initiation of data transmission.

[0082] At step 344, downlink data transmission to the UE 130 is initiated.

[0083] At step 346, the target gNB-DU 228 may send a LTM serving cell change notification to the target gNB-CU-CP 224 over the Fl interface. At step 348, the target gNB-CU-CP 224 sends a RRC reconfiguration acknowledgement to the UE 130.

[0084] It is appreciated that a detailed description related to the various steps of FIG. 3 is already covered in the description related to FIG. 2 and is omitted herein for the sake of brevity.

[0085] FIG. 4 A illustrates a process flow depicting a method 410 for inter-gNB LTM of the UE 130, in accordance with an embodiment of the present disclosure. In one embodiment, the steps of the method 410 may be performed by the apparatus 111 associated with the first NG- RAN node 110 (serving gNB), as discussed above with reference to FIGS. 2-3.

[0086] At step 411, a determination is made at the serving gNB-CU-CP 214 that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required.

[0087] At step 412, a request indicative of the LTM target cell preparation for the UE 130 is transmitted to the target gNB-CU-CP 224 associated with the target cell.

[0088] At step 413 , a response to the transmitted request including one or more LTM target cell configurations is received from the target gNB-CU-CP 224.

[0089] At step 414, cell identification and centralized unit user plane (gNB-CU-UP) mapping information is transmitted to the serving gNB-DU 218.

[0090] At step 415, a determination is made during an LTM cell switch decision at the serving gNB-DU 218 whether data forwarding is required from the serving gNB-CU-UP 216 associated with the apparatus to the target gNB-CU-UP 226 associated with the target cell.

[0091] At step 416, a message to initiate data forwarding to the target gNB-CU-UP 226 is transmitted to the serving gNB-CU-UP 216. The data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP 226.

[0092] While the above-discussed steps in FIG. 4A are shown and described in a particular sequence, the steps may occur in variations to the sequence in accordance with various embodiments. Further, a detailed description related to the various steps of FIG. 4A is already covered in the description related to FIGS. 2-3 and is omitted herein for the sake of brevity.

[0093] FIG. 4B illustrates a process flow depicting a method 420 for inter-gNB LTM of the UE 130, in accordance with an embodiment of the present disclosure. In one embodiment, the steps of the method 420 may be performed by the apparatus 121 associated with the second NG-RAN node 120 (target gNB), as discussed above with reference to FIGS. 2-3.

[0094] At step 421 , a request indicative of the LTM target cell preparation for a user equipment (UE) is received at the target gNB-CU-CP 224 from the serving gNB-CU-CP 214. [0095] At step 422, one or more target gNB-CU-UPs 226 are prepared for the LTM to the target cell.

[0096] At step 423, one or more target gNB-DUs 228 are prepared for the LTM to the target cell after preparing the one or more target gNB-CU-UPs 226.

[0097] At step 424, a successful LTM cell switch to the target cell is detected at a target gNB- DU 228 among the one or more target gNB-DUs.

[0098] At step 425, an LTM cell switch notification message is transmitted from the target gNB-DU 228 to the one or more target gNB-CU-UPs 226 after detecting the successful LTM cell switch.

[0099] At step 426, downlink data transmission to the UE 130 is triggered at the one or more target gNB-CU-UPs 226 based on the received LTM cell switch notification message.

[0100] While the above-discussed steps in FIG. 4B are shown and described in a particular sequence, the steps may occur in variations to the sequence in accordance with various embodiments. Further, a detailed description related to the various steps of FIG. 4B is already covered in the description related to FIGS. 2-3 and is omitted herein for the sake of brevity.

[0101] The present disclosure provides apparatus and methods for inter-gNB LTM. As described above, the inter-gNB LTM may be performed considering the security key changes required at the second NG-RAN node (target gNB) and the association of different data bearers of the UE with the one or more target gNB-CU-UPs. In addition, the present disclosure facilitates optimized data forwarding at the right time and initiation of downlink data transmission in the inter-gNB LTM scenario.

[0102] Further, the present disclosure also describes non-transitory computer program products (i.e., physically embodies computer program products) or non-transitory computer-readable mediums encoded with executable instructions that store instructions. The executable instructions, when executed by one or more processors, such as the processors 112 and 122, causes the one or more processors to perform a method for inter-gNB LTM as described in the present disclosure, as elaborated in preceding paragraphs. Examples of computer-readable mediums include non-volatile, hard-coded type mediums such as read-only memories (ROMs) or erasable, electrically programmable read-only memories (EEPROMs), and user-recordable type mediums such as floppy disks, hard disk drives and compact disk read-only memories (CD- ROMs) or digital versatile disks (DVDs).

[0103] FIG. 5 illustrates an embodiment of a device 500 associated with each of the first NG- RAN node 110 and second NG-RAN node 120. As shown in FIG. 5, the device 500 includes a processor 510 (for instance, analogous to processors 112, 122), a memory 520 (for instance, analogous to memories 114, 124), a storage component 530, an input component 540, an output component 550, a communication interface 560 (for instance, analogous to the communication unit 124), and a bus 570.

[0104] The processor 510, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 510 may be embodied as a multi-core processor, a single core processor, or a combination of one or more multi-core processors and/or one or more single core processors, a distributed processing system, or the like. The processor 510 may be a Central Processing Unit (CPU)a graphics processing unit (GPU), an accelerated processing unit (APU), an application-specific integrated circuit (ASIC), or another type of processing component.

[0105] Memory 520 includes a non-transitory computer readable medium. Memory 520 includes a random-access memory (RAM), a read only memory (ROM), and/or another type of dynamic or static storage device (e.g., a flash memory, a magnetic memory, and/or an optical memory) that stores information and/or instructions for use by processor 510. The memory 520 comprises machine-readable instructions which are executable by the processor 510. These machine-readable instructions when executed by the processor 510 cause the processor 510 to perform one or more method steps of an embodiment described above.

[0106] Storage component 530 stores information and/or software related to the operation and use of the device 500. For example, storage component 530 may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, and/or a solid-state disk), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, a magnetic tape, and/or another type of non-transitory computer-readable medium, along with a corresponding drive. [0107] Input component 540 is configured to receive information, such as user input. For example, the input component 540 may include, but not be limited to, a touch screen display, a keyboard, a keypad, a mouse, a button, a switch, and/or a microphone. Additionally, or alternatively, the input component 540 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and/or an actuator).

[0108] Output component 550 is configured to provide output information from the device 500. For example, the output component 550 may be, but not limited to, a display, a speaker, instructions to an external device, and/or one or more light-emitting diodes (LEDs).

[0109] Communication interface 560 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 560 can be a wired connection, a wireless connection, or a combination of wired and wireless connections, and can be a direct connection or an indirect connection via a communication network that exists between the device 500 and other devices. In other words, the standard of the communication interface 560 is not limited.

[0110] The bus 570 acts as an interconnect between the processor 510, the memory 520, the storage component 530, the input component 540, the output component 550, and the communication interface 560 of the device 500. The bus 570 may include a wired interconnection or a wireless interconnection.

[0111] The number and arrangement of components shown in FIG. 5 are provided as an example. In practice, device 500 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 5. Additionally, or alternatively, a set of components (e.g., one or more components) of device 500 may perform one or more functions described as being performed by another set of components of device 500. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of devices 500 in communication with one another.

[ 1 ] . An apparatus configured to: receive, at a target centralized unit control plane (gNB-CU-CP) associated with the apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP; prepare, based on the received request, one or more target centralized unit user planes (gNB-CU- UPs) associated with the apparatus for the LTM to a target cell; after preparing the one or more target gNB-CU-UPs, prepare one or more target distributed unit (gNB-DUs) associated with the apparatus; detect, at a target gNB-DU among the one or more target gNB-DUs, a successful LTM cell switch to the target cell; after detecting the successful LTM cell switch, transmit an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs; and trigger, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

[2], The apparatus described in [1], wherein: the serving gNB-CU-CP is associated with a first Next Generation Radio Access Network (NG- RAN) node, and the target gNB-CU-CP, the one or more target gNB-CU-UPs, and the one or more target gNB- DUs are associated with a second NG-RAN node different from the first NG-RAN node.

[3], The apparatus described in [1], wherein the LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs includes at least one of a control plane signaling message or a user-plane based control packet data unit (PDU) indicating completion of a successful LTM cell switch and initiation of downlink data transmission to the UE.

[4] . The apparatus described in [ 1 ], wherein to prepare the one or more target gNB-CU-UPs and the one or more target gNB-DUs, the apparatus is configured to prepare, using the target gNB-CU-CP, the one or more target CU-UPs and the one or more target gNB-DUs corresponding to each data bearer associated with the UE. [5] . The apparatus described in [ 1 ], wherein to prepare the one or more target gNB-CU-UPs, the apparatus is configured to: transmit a bearer context setup request to the one or more target gNB-CU-UPs, the bearer context setup request indicating the one or more target gNB-CU-UPs of the LTM target cell preparation; and receive a bearer context setup response indicative of one or more security keys associated with the one or more target gNB-CU-UPs, respectively.

[6], The apparatus described in [5], wherein to prepare the one or more target gNB-DUs, the apparatus is configured to transmit the corresponding security keys and Tunnel Endpoint Identifiers (TEIDs) of the one or more target gNB-CU-UPs to the one or more target gNB-DUs.

[7], The apparatus described in [1], further configured to receive, at the one or more target gNB-CU-UPs, forwarded data from a serving gNB-CU-UP currently serving the UE;

[8], The apparatus described in [4], wherein each of the bearer context setup request and the bearer context setup response is transmitted over an El interface, and wherein the request indicative of LTM target cell preparation is received over an Xn interface.

[9], An apparatus configured to: determine, at a serving centralized unit control plane (gNB-CU-CP) associated with the apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required; transmit, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE; receive from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations; transmit, to a serving distributed unit (gNB-DU) associated with the apparatus, cell identification and centralized unit user plane (gNB-CU-UP) mapping information associated with the apparatus; determine, during an LTM cell switch decision at the serving DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB-CU-UP associated with the target cell; and transmit, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB- CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

[10], The apparatus described in [9], wherein: the serving gNB-CU-CP, the serving gNB-DU, and the serving gNB-CU-UP are associated with a first Next Generation Radio Access Network (NG-RAN) node, and the target gNB-CU-CP and the target gNB-CU-UP are associated with a second NG-RAN node different from the first NG-RAN node.

[11], The apparatus described in [9], wherein to transmit the message to initiate data forwarding, the apparatus is configured to: transmit, to the serving CU-UP, a user-plane based control PDU to initiate data forwarding to the target CU-UP; and transmit, to the target CU-UP, forwarded data.

[12], The apparatus described in [9], wherein to transmit the message to initiate data forwarding, the apparatus is configured to: transmit, to the serving gNB-CU-CP, a first message over F 1 interface to initiate data forwarding; transmit, to the serving gNB-CU-UP from the serving gNB-CU-CP, a second message over El interface initiate data forwarding to the target gNB-CU-UP; and transmit forwarded data to the target gNB-CU-UP.

[13], The apparatus described in [9], wherein to determine the requirement of data forwarding, the apparatus is configured to: receive, at the serving gNB-DU, LI measurement report from the UE; determine, based on the LI measurement report, whether data forwarding is required, wherein data forwarding is required when the serving gNB-DU and a target gNB-DU are served by different gNB-CU-UPs.

[14], The apparatus described in [9], wherein to determine that the inter-gNB LTM target cell preparation for the UE is required, the apparatus is configured to: receive, at the serving gNB-CU-CP, a radio resource control (RRC) measurement report from the UE; and determine, based on the received RRC measurement report, that the inter-gNB LTM target cell preparation for the UE is required.

[15], The apparatus described in [9], wherein the cell identification and gNB-CU-UP mapping information is transmitted in a UE context modification request over an Fl interface.

[16], The apparatus described in [9], wherein the request indicative of LTM target cell preparation for the UE is transmitted over an Xn interface.

[17], A method compri sing : receiving, at a target centralized unit control plane (gNB-CU-CP) associated with an apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP; preparing, based on the received request, one or more target centralized unit user planes (gNB- CU-UPs) associated with the apparatus for the LTM to a target cell; preparing one or more target distributed units (gNB-DUs) associated with the apparatus after preparing the one or more target gNB-CU-UPs; detecting, at a target gNB-DU among the one or more target gNB-DUs, a successful LTM cell switch to the target cell; after detecting the successful LTM cell switch, transmitting an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs; and trigger, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

[18], The method described in [17], wherein: the serving gNB-CU-CP is associated with a first Next Generation Radio Access Network (NG- RAN) node, and the target gNB-CU-CP, the one or more target gNB-CU-UPs, and the one or more target gNB- DUs are associated with a second NG-RAN node different from the first NG-RAN node.

[19], The method described in [17], wherein the LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs includes at least one of a control plane signaling message or a user-plane based control packet data unit (PDU) indicating completion of a successful LTM cell switch and initiation of downlink data transmission to the UE.

[20], The method described in [17], wherein preparing the one or more target gNB-CU-UPs and the one or more target gNB-DUs comprises preparing, using the target gNB-CU-CP, the one or more target CU-UPs and the one or more target gNB-DUs corresponding to each data bearer associated with the UE.

[21], The method described in [17], wherein preparing the one or more target gNB-CU-UPs comprises: transmitting a bearer context setup request to the one or more target gNB-CU-UPs, the bearer context setup request indicating the one or more target gNB-CU-UPs of the LTM target cell preparation; and receiving a bearer context setup response indicative of one or more security keys associated with the one or more target gNB-CU-UPs, respectively.

[22], The method described in [21], wherein preparing the one or more target gNB-DUs comprises transmitting the corresponding security keys and Tunnel Endpoint Identifiers (TEIDs) of the one or more target gNB-CU-UPs to the one or more target gNB-DUs.

[23], The method described in [17], further comprising receiving, at the one or more target gNB-CU-UPs, forwarded data from a serving gNB-CU-UP currently serving the UE; [24] . The method described in [20], wherein each of the bearer context setup request and the bearer context setup response is transmitted over an El interface, and wherein the request indicative of LTM target cell preparation is received over an Xn interface.

[25], A method comprising: determining, at a serving centralized unit control plane (gNB-CU-CP) associated with an apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required; transmitting, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE; receive from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations; transmitting, to a serving distributed unit (gNB-DU) associated with the apparatus, cell identification and centralized unit user plane (gNB-CU-UP) mapping information associated with the apparatus; determining, during an LTM cell switch decision at the serving gNB-DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB- CU-UP associated with the target cell; and transmitting, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB- CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

[26], The method described in [25], wherein: the serving gNB-CU-CP, the serving gNB-DU, and the serving gNB-CU-UP are associated with a first Next Generation Radio Access Network (NG-RAN) node, and the target gNB-CU-CP and the target gNB-CU-UP are associated with a second NG-RAN node different from the first NG-RAN node. [27]. The method described in [25], wherein transmitting the message to initiate data forwarding, comprises: transmitting, to the serving CU-UP, a user-plane based control PDU to initiate data forwarding to the target CU-UP; and transmitting, to the target CU-UP, forwarded data.

[28], The method described in [25], wherein transmitting the message to initiate data forwarding, comprises: transmitting, to the serving gNB-CU-CP, a first message over Fl interface to initiate data forwarding; transmitting, to the serving gNB-CU-UP from the serving gNB-CU-CP, a second message over El interface initiate data forwarding to the target gNB-CU-UP; and transmitting forwarded data to the target gNB-CU-UP.

[29], The method described in [25], wherein determining the requirement of data forwarding, comprises: receiving, at the serving gNB-DU, LI measurement report from the UE; determining, based on the LI measurement report, whether data forwarding is required, wherein data forwarding is required when the serving gNB-DU and a target gNB-DU are served by different gNB-CU-UPs.

[30], The method described in [25], wherein determining that the inter-gNB LTM target cell preparation for the UE is required, comprises: receiving, at the serving gNB-CU-CP, a radio resource control (RRC) measurement report from the UE; and determining, based on the received RRC measurement report, that the inter-gNB LTM target cell preparation for the UE is required.

[31], The method described in [25], wherein the cell identification and gNB-CU-UP mapping information is transmitted in a UE context modification request over an Fl interface. [32], The method described in [25], wherein the request indicative of LTM target cell preparation for the UE is transmitted over an Xn interface.

[0112] 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.

[0113] It is understood that terms including “unit” or “module” at the end may refer to the unit for processing at least one function or operation and may be implemented in hardware, software, or a combination of hardware and software.

[0114] 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.

[0115] 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.

[0116] Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0117] 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.

[0118] 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 adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of at least one embodiment, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

We Claim:

1. An apparatus configured to: receive, at a target centralized unit control plane (gNB-CU-CP) associated with the apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP; prepare, based on the received request, one or more target centralized unit user planes (gNB- CU-UPs) associated with the apparatus for the LTM to a target cell; after preparing the one or more target gNB-CU-UPs, prepare one or more target distributed units (gNB-DUs) associated with the apparatus; detect, at a target gNB-DU among the one or more target gNB-DUs, a successful LTM cell switch to the target cell; after detecting the successful LTM cell switch, transmit an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs; and trigger, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

2. The apparatus as claimed in claim 1, wherein: the serving gNB-CU-CP is associated with a first Next Generation Radio Access Network (NG- RAN) node, and the target gNB-CU-CP, the one or more target gNB-CU-UPs, and the one or more target gNB- DUs are associated with a second NG-RAN node different from the first NG-RAN node.

3. The apparatus as claimed in claim 1, wherein the LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs includes at least one of a control plane signaling message or a user-plane based control packet data unit (PDU) indicating completion of a successful LTM cell switch and initiation of downlink data transmission to the UE.

4. The apparatus as claimed in claim 1, wherein to prepare the one or more target gNB- CU-UPs and the one or more target gNB-DUs, the apparatus is configured to prepare, using the target gNB-CU-CP, the one or more target CU-UPs and the one or more target gNB-DUs corresponding to each data bearer associated with the UE.

5. The apparatus as claimed in claim 4, wherein to prepare the one or more target gNB- CU-UPs, the apparatus is configured to: transmit a bearer context setup request to the one or more target gNB-CU-UPs, the bearer context setup request indicating the one or more target gNB-CU-UPs of the LTM target cell preparation; and receive a bearer context setup response indicative of one or more security keys associated with the one or more target gNB-CU-UPs, respectively.

6. The apparatus as claimed in claim 5, wherein to prepare the one or more target gNB- DUs, the apparatus is configured to transmit the corresponding security keys and Tunnel Endpoint Identifiers (TEIDs) of the one or more target gNB-CU-UPs to the one or more target gNB-DUs.

7. The apparatus as claimed in claim 1, further configured to receive, at the one or more target gNB-CU-UPs, forwarded data from a serving gNB-CU-UP currently serving the UE.

8. The apparatus as claimed in claim 4, wherein each of the bearer context setup request and the bearer context setup response is transmitted over an El interface, and wherein the request indicative of LTM target cell preparation is received over an Xn interface.

9. An apparatus configured to: determine, at a serving centralized unit control plane (gNB-CU-CP) associated with the apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required; transmit, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE; receive from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations; transmit, to a serving distributed unit (gNB-DU) associated with the apparatus, cell identification and centralized unit user plane (gNB-CU-UP) mapping information associated with the apparatus; determine, during an LTM cell switch decision at the serving DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB-CU-UP associated with the target cell; and transmit, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB- CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

10. The apparatus as claimed in claim 9, wherein: the serving gNB-CU-CP, the serving gNB-DU, and the serving gNB-CU-UP are associated with a first Next Generation Radio Access Network (NG-RAN) node, and the target gNB-CU-CP and the target gNB-CU-UP are associated with a second NG-RAN node different from the first NG-RAN node.

11. The apparatus as claimed in claim 9, wherein to transmit the message to initiate data forwarding, the apparatus is configured to: transmit, to the serving CU-UP, a user-plane based control PDU to initiate data forwarding to the target CU-UP; and transmit, to the target CU-UP, forwarded data.

12. The apparatus as claimed in claim 9, wherein to transmit the message to initiate data forwarding, the apparatus is configured to: transmit, to the serving gNB-CU-CP, a first message over an Fl interface to initiate data forwarding; transmit, to the serving gNB-CU-UP from the serving gNB-CU-CP, a second message over an El interface to initiate data forwarding to the target gNB-CU-UP; and transmit forwarded data to the target gNB-CU-UP.

13. The apparatus as claimed in claim 9, wherein to determine the requirement of data forwarding, the apparatus is configured to: receive, at the serving gNB-DU, an LI measurement report from the UE; determine, based on the LI measurement report, whether data forwarding is required, wherein data forwarding is required when the serving gNB-DU and a target gNB-DU are served by different gNB-CU-UPs.

14. The apparatus as claimed in claim 9, wherein to determine that the inter-gNB LTM target cell preparation for the UE is required, the apparatus is configured to: receive, at the serving gNB-CU-CP, a radio resource control (RRC) measurement report from the UE; and determine, based on the received RRC measurement report, that the inter-gNB LTM target cell preparation for the UE is required.

15. The apparatus as claimed in claim 9, wherein the cell identification and gNB-CU-UP mapping information is transmitted in a UE context modification request over an Fl interface.

16. The apparatus as claimed in claim 9, wherein the request indicative of LTM target cell preparation for the UE is transmitted over an Xn interface.

17. A method comprising: receiving, at a target centralized unit control plane (gNB-CU-CP) associated with an apparatus, a request indicative of a Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) from a serving gNB-CU-CP; preparing, based on the received request, one or more target centralized unit user planes (gNB- CU-UPs) associated with the apparatus for the LTM to a target cell; preparing one or more target distributed units (gNB-DUs) associated with the apparatus after preparing the one or more target gNB-CU-UPs; detecting, at a target gNB-DU among the one or more target gNB-DUs, a successful LTM cell switch to the target cell; after detecting the successful LTM cell switch, transmitting an LTM cell switch notification message from the target gNB-DU to the one or more target gNB-CU-UPs; and triggering, at the one or more target gNB-CU-UPs based on the received LTM cell switch notification message, downlink data transmission to the UE.

18. The method as claimed in claim 17, wherein: the serving gNB-CU-CP is associated with a first Next Generation Radio Access Network (NG- RAN) node, and the target gNB-CU-CP, the one or more target gNB-CU-UPs, and the one or more target gNB- DUs are associated with a second NG-RAN node different from the first NG-RAN node.

19. A method comprising: determining, at a serving centralized unit control plane (gNB-CU-CP) associated with an apparatus, that an inter gNB Layer 2 Mobility (LTM) target cell preparation for a user equipment (UE) is required; transmitting, to a target gNB-CU-CP associated with a target cell, a request indicative of the LTM target cell preparation for the UE; receiving from the target gNB-CU-CP, a response to the transmitted request including one or more LTM target cell configurations; transmitting, to a serving distributed unit (gNB-DU) associated with the apparatus, cell identification and centralized unit user plane (gNB-CU-UP) mapping information associated with the apparatus; determining, during an LTM cell switch decision at the serving gNB-DU, whether data forwarding is required from a serving gNB-CU-UP associated with the apparatus to a target gNB-CU-UP associated with the target cell; and transmitting, to the serving gNB-CU-UP, a message to initiate data forwarding to the target gNB-CU-UP, wherein the data forwarding includes transmission of unsent data packet data units (PDUs) at source to the target gNB-CU-UP.

20. The method as claimed in claim 19, wherein: the serving gNB-CU-CP, the serving gNB-DU, and the serving gNB-CU-UP are associated with a first Next Generation Radio Access Network (NG-RAN) node, and the target gNB-CU-CP and the target gNB-CU-UP are associated with a second NG-RAN node different from the first NG-RAN node.