Method and apparatus for handling layer1 and layer2 triggered mobility in wireless communication system

Abstract

Embodiments herein handles LTM. A target network node (203) receives first message from a source network node (201) for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203). Further, target network node (203) creates a second message for the LTM. The second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the target network node (203) transmits the second message to the source network node (201) as the acknowledgement for the first message.

Description

METHOD AND APPARATUS FOR HANDLING LAYER1 AND LAYER2 TRIGGERED MOBILITY IN WIRELESS COMMUNICATION SYSTEM

[0001] Embodiments disclosed herein relate to wireless communication system (or mobile communication system). More particularly, present disclosure relates to handling layer1 / layer2 triggered mobility or lower triggered mobility (LTM).

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “Sub 6GHz” bands such as 3.5GHz, but also in “Above 6GHz” bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz (THz) bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The principal object of the embodiments herein is to control layer 2 reset and early Timing Advance (TA) acquisition in Lower Triggered Mobility (LTM).

[0009] Another object of the invention is to reduce the delay during L3 mobility and in inter-gNB LTM.

[0010] Another object of the invention is to handle inter node communication for early synchronization and L2 reset.

[0011] Another objective of the invention is that the target network node includes an identifier or an information which identifies the LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset.

[0012] Another objective of the invention herein is that the source network node to provide ltm-NoResetID to the UE, if the value of ltm-NoResetID in the LTM candidate cell is the same as the value of ltm-ServingCellNoResetID in the serving cell of a cell group, then the UE shall not perform any L2 reset during an LTM cell switch procedure.

[0013] Another objective of the invention is to inform the target network node information about the list of LTM candidate cells that it has configured.

[0014] Another objective of the invention herein is to inform the configuration for the random access resource for early timing advance acquisition for the LTM candidate cell during LTM preparation.

[0015] Another objective of the invention herein is to share the information by the target network node to the source network node for configuring the UE for random access configuration for early TA may include random access occasions and random access resources and the total number of random access occasions.

[0016] According to an embodiment of the disclosure, a method performed by a first base station is provided. The method comprises: identifying a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station; and transmitting, to a second base station, a message including information on the TA for the LTM candidate cell, wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.

[0017] According to another embodiment of the disclosure, a method performed by a second base station is provided. The method comprises: receiving, from a first base station, a message including information on a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station; and identifying the TA for the LTM candidate cell, wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.

[0018] According to another embodiment of the disclosure, a first base station is provided. The first base station comprises: a transceiver; and a controller coupled with the transceiver and configured to: identify a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station, and transmit, to a second base station, a message including information on the TA for the LTM candidate cell, wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.

[0019] According to another embodiment of the disclosure, a second base station is provided. The second base station comprises: a transceiver; and a controller coupled with the transceiver and configured to: receive, from a first base station, a message including information on a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station, and identify the TA for the LTM candidate cell, wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.

[0020] In one aspect, the objectives are achieved by providing a method for handling Layer1 / Layer2 Triggered Mobility or Lower Triggered Mobility (LTM). The method includes receiving, by a target network node, a first message from a source network node for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node. Further, the method includes creating, by the target network node, a second message for the LTM. The second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the method includes transmitting, by the target network node, the second message to the source network node as the acknowledgement for the first message.

[0021] In an embodiment, the one or more LTM candidate cells that belongs to the same group does not require layer 2 reset.

[0022] In an embodiment, the first message is a Xn handover request message, and wherein the second message is a Xn handover request acknowledge message.

[0023] In an embodiment, the Random Access Channel (RACH) resources are allocated for each LTM candidate cell or for a group of LTM candidate cells.

[0024] In an embodiment, the first message comprises an LTM candidate cell index associated with each LTM candidate cell included in the list of the LTM candidate cells already configured and the identification information of the configured LTM candidate cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for each LTM candidate cell.

[0025] In an embodiment, configuration for the RACH resources for the early TA synchronization includes RACH-ConfigGeneric. The configuration is encoded using NR RRC ASN.1 format and send in the Xn message.

[0026] In an embodiment, the method includes determining, by the target network node, the early TA based on the random access from the UE. Further, the method includes sending, by the target network node, the early TA value to the source network node.

[0027] Accordingly, the embodiment herein is to provide a method for handling LTM. The method includes receiving, by a source network node, a second message from a target network node. The second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell. Further, the method includes creating, by the source network node, a Radio resource control (RRC) reconfiguration message based on the second message. Further, the method includes transmitting, by the source network node, the RRC reconfiguration message to the UE for performing the LTM operation.

[0028] In an embodiment, the method includes transmitting, by the source network node, RRC reconfiguration message to the UE for performing the LTM operation. Further, the method includes receiving, by the source network node, RRC reconfiguration complete message from the UE indicating the completion of the LTM operation. The LTM operation is performed by at least not performing layer 2 reset or by performing layer 2 reset. Further, the method includes transmitting, by the source network node, Physical Downlink Control Channel (PDCCH) order to the UE for performing TA synchronization. Further method includes receiving, by the source network node, an Xn message indicating success of the early TA synchronization. The Xn message comprises a timing advance value of the LTM candidate cell that is derived based on early TA acquisition. The method includes transmitting, by the source network node, received TA value to the UE in LTM cell switch command.

[0029] Accordingly, the embodiment herein is to provide a target network node for handling Lower Triggered Mobility (LTM). The target network node comprises a processor and a LTM controller coupled the processor. The LTM controller receives a first message from a source network node for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node. Further, the LTM controller creates a second message for the LTM. The second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the LTM controller transmits the second message to the source network node as the acknowledgement for the first message.

[0030] Accordingly, the embodiment herein is to provide a source network node for handling Lower Triggered Mobility (LTM). The source network node comprises a processor and a LTM controller coupled to the processor. The LTM controller receives a second message from a target network node. The second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the LTM controller creates a Radio resource control (RRC) reconfiguration message based on the second message. Further, the LTM controller transmits the RRC reconfiguration message to the UE for performing the LTM operation.

[0031] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications be made within the scope of the embodiments herein.

[0032] According to various embodiments of the disclosure, LTM related procedures can be efficiently enhanced.

[0033] These and other features, aspects, and advantages of the present embodiments are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0034] FIG. 1 is a schematic diagram that illustrates conventional next generation radio access network (NG-RAN) architecture, according to the prior art as disclosed herein;

[0035] FIG. 2 is a sequence diagram that illustrates a flow for Inter-node LTM preparation including early TA sync and L2 reset control, according to the embodiment as disclosed herein;

[0036] FIG. 3 is a sequence diagram that illustrates a flow for inter-node Xn handling of early TA sync, according to the embodiment as disclosed herein;

[0037] FIG. 4 is a block diagram that illustrates a target network node for handling LTM, according to the embodiment as disclosed herein;

[0038] FIG. 5 is a block diagram that illustrates a source network node for handling LTM, according to the embodiment as disclosed herein;

[0039] FIG. 6 is a flow diagram that illustrates a method for handling LTM by the target network node, according to the embodiment as disclosed herein;

[0040] FIG. 7 is a flow diagram that illustrates a method for handling LTM by the source network node, according to the embodiment as disclosed herein;

[0041] FIG. 8 is a block diagram showing a structure of a base station according to an embodiment of the disclosure; and

[0042] FIG. 9 is a block diagram showing a structure of a network entity (or, a network function) according to an embodiment of the disclosure.

[0043] It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawing. Further, those of ordinary skill in the art will appreciate that elements in the drawing are illustrated for simplicity and may not have been necessarily drawn to scale. For example, the dimension of some of the elements in the drawing may be exaggerated relative to other elements to help to improve the understanding of aspects of the invention. Furthermore, the elements may have been represented in the drawing by conventional symbols, and the drawings may show only those specific details that are pertinent to the understanding the embodiments of the invention so as not to obscure the drawing with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

[0044] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0045] For the purposes of interpreting this specification, the definitions (as defined herein) will apply and whenever appropriate the terms used in singular will also include the plural and vice versa. It is to be understood that the terminology used herein is for the purposes of describing particular embodiments only and is not intended to be limiting. The terms “comprising”, “having” and “including” are to be construed as open-ended terms unless otherwise noted.

[0046] The words / phrases "exemplary", “example”, “illustration”, “in an instance”, “and the like”, “and so on”, “etc.”, “etcetera”, “e.g.,”, “i.e.,” are merely used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein using the words / phrases "exemplary", “example”, “illustration”, “in an instance”, “and the like”, “and so on”, “etc.”, “etcetera”, “e.g.,”, “i.e.,” is not necessarily to be construed as preferred or advantageous over other embodiments.

[0047] Embodiments herein may be described and illustrated in terms of blocks which carry out a described function or functions. These blocks, which may be referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and may optionally be driven by a firmware. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block may be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments may be physically separated into two or more interacting and discrete blocks without departing from the scope of the disclosure. Likewise, the blocks of the embodiments may be physically combined into more complex blocks without departing from the scope of the disclosure.

[0048] It should be noted that elements in the drawings are illustrated for the purposes of this description and ease of understanding and may not have necessarily been drawn to scale. For example, the flowcharts / sequence diagrams illustrate the method in terms of the steps required for understanding of aspects of the embodiments as disclosed herein. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. Furthermore, in terms of the system, one or more components / modules which comprise the system may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the present embodiments so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0049] The accompanying drawings are used to help easily understand various technical features and it should be understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the present disclosure should be construed to extend to any modifications, equivalents, and substitutes in addition to those which are particularly set out in the accompanying drawings and the corresponding description. Usage of words such as first, second, third etc., to describe components / elements / steps is for the purposes of this description and should not be construed as sequential ordering / placement / occurrence unless specified otherwise.

[0050] The various embodiments discussed below for describing the principles of the disclosure in the patent document are for illustration only and should not be interpreted as limiting the scope of the disclosure in any way. Those skilled in the art will understand that the principles of the disclosure can be implemented in any suitably arranged wireless communication system. For example, although the following detailed description of the embodiments of the disclosure will be directed to LTE and / or 5G communication systems, those skilled in the art will understand that the main points of the disclosure can also be applied to other communication systems with similar technical backgrounds and channel formats with slight modifications without departing from the scope of the disclosure. The technical schemes of the embodiments of the present application can be applied to various communication systems, and for example, the communication systems may include global systems for mobile communications (GSM), code division multiple access (CDMA) systems, wideband code division multiple access (WCDMA) systems, general packet radio service (GPRS) systems, long term evolution (LTE) systems, LTE frequency division duplex (FDD) systems, LTE time division duplex (TDD) systems, universal mobile telecommunications system (UMTS), worldwide interoperability for microwave access (WiMAX) communication systems, 5th generation (5G) systems or new radio (NR) systems, etc. In addition, the technical schemes of the embodiments of the present application can be applied to future-oriented communication technologies. In addition, the technical schemes of the embodiments of the present application can be applied to future-oriented communication technologies.

[0051] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. It should be noted that the same reference numerals in different drawings will be used to refer to the same elements already described.

[0052] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term “or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples are not be construed as limiting the scope of the embodiments herein.

[0053] As is traditional in the field, embodiments are described and illustrated in terms of blocks that carry out a described function or functions. These blocks, which referred to herein as managers, units, modules, hardware components or the like, are physically implemented by analog and / or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits and the like, and optionally be driven by firmware and software. The circuits, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments be physically separated into two or more interacting and discrete blocks without departing from the scope of the proposed method. Likewise, the blocks of the embodiments be physically combined into more complex blocks without departing from the scope of the proposed method.

[0054] The accompanying drawings are used to help easily understand various technical features and it is understood that the embodiments presented herein are not limited by the accompanying drawings. As such, the proposed method is construed to extend to any alterations, equivalents and substitutes in addition to those which are particularly set out in the accompanying drawings. Although the terms first, second, etc. used herein to describe various elements, these elements are not be limited by these terms. These terms are generally used to distinguish one element from another.

[0055] Generally, in the NG-RAN architecture, the NG-RAN consists of a set of g-NodeB (gNB)s connected to a 5thGeneration Core (5GC) through a NG interface. The gNBs can be interconnected through the Xn interface. During mobility, source gNB and target gNB exchange messages over Xn interface. Xn messages or the Information elements in the messages may have criticality specified. If some messages are not understood or supported by the recipient or if some of the information elements in the messages are not understood or supported by the recipient, “criticality” specifies how the recipient handles the message. Criticality “reject” means the recipient will reject the message if the message or IE is not understood by the recipient. Criticality “ignore” means the recipient will ignore the message or the IE, if the message or IE is not understood by the recipient. Criticality “notify” means the recipient will notify the sender, if the message or IE is not understood by the recipient. The gNB may consist of a gNB-CU (gNB-Control Unit or gNB-Central Unit) and one or more gNB-DU(s) (gNB-Distributed Unit). A gNB-CU and a gNB-DU is connected via F1 interface.

[0056] LTM configuration is provided to the UE by a source gNB. The LTM configuration includes information to identify whether the UE needs to perform the L2 reset. L2 reset, in the scope of this invention includes one or more of re-establishing the applicable RLC (Radio Link Control) entities, performing PDCP (Packet Data Convergence Protocol) data recovery for the applicable radio bearers, after applying the LTM configuration and other similar actions. Some UEs may perform MAC (Medium Access Control) reset even if they are configured for not performing L2 reset. If intra-CU LTM is also supported along with inter-CU LTM, while executing LTM between the candidate cells within the same DU of target gNB, there is no need for L2 reset. However, conveying the information needs to the UE by the source gNB needs to be addressed.

[0057] As LTM configuration is provided to the UE by the source gNB, for inter-CU LTM, when the candidate cells are on the target gNB, source gNB needs to get the configuration for early synchronization of random access parameters. When the UE performs early sync, it is known that candidate DU informs the TA value to its CU and the CU provides it to source DU which again sends it to the UE. But for Inter-CU LTM, the CU of candidate DU and the CU of source DU can be different. Thus, there is no way by which the source gNB can configure this value to the UE.

[0058] Thus, it is desired to address the above-mentioned disadvantages or other shortcomings or at least provide a useful alternative.

[0059] Accordingly, the embodiments disclose a method for handling Lower Triggered Mobility (LTM). The method includes receiving, by a target network node, a first message from a source network node for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node. Further, the method includes creating, by the target network node, a second message for the LTM. The second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the method includes transmitting, by the target network node, the second message to the source network node as the acknowledgement for the first message.

[0060] Accordingly, the embodiments disclose a method for handling LTM. The method includes receiving, by a source network node, a second message from a target network node. The second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell. Further, the method includes creating, by the source network node, a Radio resource control (RRC) reconfiguration message based on the second message. Further, the method includes transmitting, by the source network node, the RRC reconfiguration message to the UE for performing the LTM operation.

[0061] Accordingly, the embodiments disclose a target network node for handling Lower Triggered Mobility (LTM). The target network node comprises a processor and a LTM controller coupled the processor. The LTM controller receives a first message from a source network node for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node. Further, the LTM controller creates a second message for the LTM. The second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the LTM controller transmits the second message to the source network node as the acknowledgement for the first message.

[0062] Accordingly, the embodiments disclose a source network node for handling Lower Triggered Mobility (LTM). The source network node comprises a processor and a LTM controller coupled to the processor. The LTM controller receives a second message from a target network node. The second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. Further, the LTM controller creates a Radio resource control (RRC) reconfiguration message based on the second message. Further, the LTM controller transmits the RRC reconfiguration message to the UE for performing the LTM operation.

[0063] FIG. 1 is a schematic diagram that illustrates conventional NG-RAN architecture, according to the prior art as disclosed herein.

[0064] NG-RAN architecture, the NG-RAN (103) consists of a set of g-NodeB (gNB)s connected to a 5thGeneration Core (5GC) (101) through a NG interface. The gNBs (105, 107) can be interconnected through the Xn interface. During mobility, source gNB (105) and target gNB (107) exchanges messages over Xn interface. Xn messages or the Information elements in the messages may have criticality specified. If some messages are not understood or supported by the recipient or if some of the information elements in the messages are not understood or supported by the recipient, “criticality” specifies how the recipient handles the message. Criticality “reject” means the recipient will reject the message if the message or IE is not understood by the recipient. Criticality “ignore” means the recipient will ignore the message or the IE, if the message or IE is not understood by the recipient. Criticality “notify” means the recipient will notify the sender, if the message or IE is not understood by the recipient. The gNB (107) can consist of a gNB-CU (gNB-Control Unit or gNB-Central Unit) (109) and one or more gNB-DU(s) (gNB-Distributed Unit) (111). A gNB-CU (109) and a gNB-DU (111) is connected via F1 interface

[0065] In wireless technologies like 5G NR, devices can move across different cells. Mobility is performed using a procedure called cell reselection in the RRC_IDLE mode. Till the NR R17, mobility is performed using a procedure called handover in the RRC_CONNECTED mode. Network controlled mobility applies to the User Equipment's (UE)s in the RRC_CONNECTED. It requires explicit RRC signalling to be triggered by the gNB in the NR. Handover in NR usually consists of three steps: handover preparation, handover execution and handover completion. The gNB may configure the UE to report measurements and based on the reported measurements or based on its own understanding of the network topology, gNB will send RRC Reconfiguration message to handover the UE to another cell called target cell from the source cell. UE accesses the target cell and sends RRC Reconfiguration complete message. In an alternative way introduced in 3gpp NR release 16, gNB may configure the UE with the execution conditions for triggering handover and once the execution conditions are satisfied, the UE may move to target cell and sends the RRC Reconfiguration complete. 3gpp also introduced a new handover called DAPS handover in release 16. In all these methods, UE performs handover by sending layer 3 (RRC) messages which causes considerable signalling overhead and latency issues. We can refer to the handover, and conditional handover (CHO) as layer 3 mobility. In case of dual connectivity, UE may perform PSCellChange or Conditional PSCellChange. In the context of dual connectivity, we can refer PSCellChange or Conditional PSCellChange also as layer 3 mobility. i.e. Handover, Conditional Handover, PSCellChange, Conditional PSCellChange etc. refers to L3 mobility. Also, PSCellChange or Conditional PSCellChange is referred as SCG layer 3 mobility and the handover and CHO as MCG layer 3 mobility in the context of dual connectivity.

[0066] Further, the UE can receive RRC configuration for updating some of the security parameters. The 3gpp release 18 is considering Lower Layers (L1 / L2 layers) Triggered Mobility, also known as LTM to solve the problem related to latency, signalling overhead etc. associated with layer 3 mobility. As per 3gpp, the goal of LTM is to enable a serving cell change via L1 / L2 signalling, in order to reduce the latency, overhead and interruption time. Network (gNB) may configure the UE with multiple candidate cells to allow fast application of configurations for candidate cells. Network may further send MAC control element (CE) or L1 signalling to dynamically switch the UE from a source cell to one of the configured candidate cells. Further, LTM can be triggered based on L1 measurements rather than L3 measurements.

[0067] The 3gpp proposes to perform the LTM, without reset of lower layers like MAC to avoid data loss and to reduce the additional delay of data recovery wherever it is possible. The gNB provides configuration to the UE to inform it whether there is a lower layer reset needed or not upon performing cell switch. The gNB may provide a LTMCandidateConfiguration, i.e. configure the LTM candidate cells through one RRCReconfiguration message for a candidate target cell. The gNB may further release or modify the candidate configurations. A UE may store the LTM configuration of other candidate cells even after moving to a candidate cell through LTM. gNB also may provide the UE with configuration for performing LTM measurements for different candidate frequencies and candidate cells and reporting based on the performed LTM measurements. 3gpp supports subsequent LTM, ie after one LTM candidate cell becomes a source cell due to LTM, UE may store LTM candidate configuration and continue to report LTM measurements (L1 measurements for LTM) and the new serving cell may send LTM cell switch command to the UE and UE performs LTM. Such an LTM is called subsequent LTM.

[0068] The proposed solution provides a method for handling the LTM particularly during inter-gNB handover. In the proposed solution node the target network node (hereinafter “target network node” is interchangeably used as “target gNB”) includes an identifier or an information, which identifies the LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset in Handover Request Acknowledge message to source network node (hereinafter “source network node” is interchangeably used as “source gNB) and the source gNB generates a list of cells for which UE can move without L2 reset using this information. Also, in the proposed solution the target gNB informs the configuration for the random access resource for early timing advance acquisition for the LTM candidate cell during LTM preparation to source gNB in an Xn message such as Xn Handover Request Acknowledge message. Also, in the proposed solution the target gNB informs the timing advance of the LTM candidate cell it has derived through early Timing Acquisition to the source gNB in a Xn message. Target gNB sends a new Xn message for informing the source gNB the timing advance of the LTM candidate cell it has derived through the early Timing Acquisition. Hence, the proposed solution ensures efficient utilization of resources, saves time and ensures a quick handover process. Also, the proposed solution reduces the loss of data during the data transmission and ensures a quick data transmission. Also, the proposed solution avoids overhead on air interface.

[0069] FIG. 2 is a sequence diagram that illustrates a flow for Inter-node LTM preparation including early TA sync and L2 reset control, according to the embodiment as disclosed herein.

[0070] At step S1, the source network node (201) sends the first message (hereinafter the “first message” is interchangeably used as “Xn Handover Request message”) such as Xn Handover Request for LTM preparation to the target network node (203). The first message includes a first information about one or more LTM candidate cells to be configured by the target network node (203).

[0071] Further at step S2, the target network node (203) prepares for LTM reserve RACH resource for early TA sync. Also, the target network node (203) creates a second message for the LTM.

[0072] Further, at step S3, the target network node (203) sends the second message such as Xn Handover Request ACK including random access resources for early synchronization of timing advance and targetltm-NoResetID to the source gNB (201). The second message includes at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message.

[0073] Further, at step S4, the source network node (201) maps the received targetltm-NoResetID to the ltm-NoResetId by allocating different values for cells from different target gNBs (203) and keeping same values for cells from same target gNBs with the same targetltm-NoResetID. Step S4 is an optional step. If the source gNB doesn't perform this step, it will forward the same value received from target gNB to the UE.

[0074] Further at step S5, the source gNB (201) create RRCReconfiguration message using the ltm-NoResetId, resources for early the TA Sync and other resources.

[0075] Further, at step S6, the Source gNB (201) sends the RRCReconfiguration message including LTM-Config to the UE (205).

[0076] FIG. 3 is a sequence diagram that illustrates a flow for inter-node Xn handling of early TA sync, according to the embodiment as disclosed herein.

[0077] At step S1, the source gNB CU (209) sends RRCReconfiguration message including LTM-Config to the UE (205).

[0078] Further, at step S2, the UE (205) responds with RRCReconfigurationComplete message indicating the completion of LTM.

[0079] Further, at step S3, the source gNB-DU (207) sends a PDCCH order for early TA sync to the UE (205).

[0080] Further, at step S4, in response to receiving the PDCCH order, UE (205) sends a Random Access for early TA sync to the target gNB-DU (213).

[0081] Further, at step S5, the target gNB-DU (213) sends a FLAP message indicating early TA sync to the Target gNB-CU (211).

[0082] Further, at step S6 the target gNB-CU (211) sends the Xn Access message including the timing advance, beam information etc. to the source gNB CU (209).

[0083] In an embodiment herein, a LTM Candidate Cell Configuration is a configuration associated with an LTM candidate cell. An LTM candidate cell configuration can be a complete LTM candidate cell configuration or a delta (difference) configuration with respect to an LTM reference configuration.

[0084] In an embodiment herein, a LTM Reference Configuration is a configuration provided by the network to the UE (205) that is common to all the configured LTM candidate cells or a group of configured LTM candidate cells. It is used by the UE (205) to generate a complete LTM candidate cell configuration (i.e., by applying an LTM candidate cell configuration on top of an LTM reference configuration).

[0085] In an embodiment herein, a complete LTM Candidate Cell Configuration is a configuration that contains all the necessary fields needed to perform an LTM cell switch procedure. This configuration can be an LTM candidate cell configuration itself or be generated by applying an LTM candidate cell configuration on top of an LTM reference configuration.

[0086] In an embodiment herein, a LTM candidate cell configurations are defined as following table 1:

[0087]

[0088] Below Table. 2 and Table. 3 define the various fields of the LTM-candidate configurations.

[0089]

[0090]

[0091] In an embodiment, for the LTM-CandidateId. The IE LTM-CandidateId is used to identify an LTM candidate cell configuration as following table 4.

[0092]

[0093] The below Table. 5 defines the fields of the LTM-candidatetoAddmodlist configurations.

[0094]

[0095] Accordingly, the embodiment herein, the UE (205) performs early Timing Advance (TA) acquisition upon receiving a PDCCH order from the network to perform early TA acquisition. EarlyULSyncConfig contains the required configuration for the same.

[0096] In an embodiment, for the Candidate-Tci-States, where the IE Candidate-Tci-States defines a group of one or more TCI states for the early DL synchronization procedure as following table 6.

[0097]

[0098] In an embodiment, is for the LTM-CSI-ReportConfig, where the IE LTM-CSI-ReportConfig is used to configure report on the cell in which the LTM-CSI-ReportConfig is included, as following table 7.

[0099]

[0100] In an embodiment, is for the LTM-CSI-ResourceConfigId, where the IE LTM-CSI-ReportConfigId is used to identify an LTM-CSI-ReportConfig as following table 8.

[0101]

[0102] In an embodiment, is for the LTM-CSI-ResourceConfig, where the IE LTM-CSI-ResourceConfig defines a group of one or more CSI resources for an LTM candidate cell configuration as following table 9.

[0103]

[0104] In an embodiment, is for the LTM-CSI-ResourceConfigId

[0105] The IE LTM-CSI-ResourceConfigId is used to identify an LTM-CSI-ResourceConfig as following table 10.

[0106]

[0107] To fasten the execution of LTM cell switch. In the existing 3gpp technologies such as NR, Inter-gNB handovers are always L3 handovers. 3gpp specifications such as TS 38.401 describes L3 mobility for Intra gNB and Inter-gNB. There is no Inter-gNB LTM in the existing 3gpp system.

[0108] In the known prior arts source RAN node such as source gNB (201) requests LTM for a UE (205) to target RAN node such as target gNB (203). i.e. source RAN node informs target RAN node that LTM is required for a UE (205) using existing Xn handover request (or any other Xn message which may be also a new Xn message). The target RAN node performs LTM related actions such as LTM preparation, reserving necessary resources for LTM and may include an IE (for e.g. LTM Information Acknowledge IE) acknowledging that LTM preparation is successfully done in the Xn message such as HANDOVER REQUEST ACKNOWLEDGE message.

[0109] Accordingly, the embodiment herein is for methods for controlling layer 2 reset and early timing advance acquisition in LTM. The target gNB (203) informs the configuration for the random access resource for early timing advance acquisition for the LTM candidate cell during LTM preparation. The information is included in an Xn message such as a Xn Handover Request Acknowledge message. The configuration for the random access resource for early timing advance acquisition is encoded in NR RRC ASN.1 format. The information shared by the target gNB (203) is provided in a container in the Xn message send by target gNB (203). Further, the information shared by the target gNB (203) is encoded in NR RRC ASN.1 format and included in an Xn message such as Xn Handover Request Acknowledge. Further, the information shared by target gNB (203) to source gNB (201) for configuring the UE (205) for the random access configuration for early TA includes random access occasions and random access resources and the total number of random access occasions. It may also include the RACH-ConfigGeneric (such as defined in NR TS 38.331) for the cell.

[0110] In an embodiment, a target gNB (203) includes an identifier or an information which identifies the LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset. This information / identifier (for e.g. referred to as targetltm-NoResetID) may be included in Xn message such as Xn Handover Request Acknowledge message. In an embodiment criticality of targetltm-NoResetID is ignore.

[0111] The Source gNB (201), receiving this information from target gNB (203) generates a list of cells for which UE (205) can move without L2 reset using this information. For e.g. if the source gNB (201) prepares two LTM candidate cells in a neighbor gNB and the above identifier (targetltm-NoResetID) is the same, source gNB (201) includes both the LTM candidate cells in the same list itself. For e.g. let us consider that a targetgNB gNB 1 has provided ltm-NoResetID values as 1 for two candidate cells C1 and C2 and the targetgNB gNB 2 has provided ltm-NoResetID values as 1 for two candidate cells C3 and C4. Source gNB (201) generates two lists (such as LTM-CandidateResetNoL2-Lists-r18) one with identifiers for C1 and C2 and other with identifiers for C3 and C4. (ie. one LTM-CandidateResetNoL2-List-r18 contains C1 and C2) and the other LTM-CandidateResetNoL2-List-r18 contains C3 and C4.

[0112] In an alternate embodiment, target gNB (203) doesn't include the targetltm-NoResetID in the Xn Handover Request ACK message. Source gNB (201) includes each of the LTM candidate cell from a different target gNB in a separate LTM-CandidateResetNoL2-List.

[0113] In an embodiment, source gNB (201) provides ltm-NoResetID to the UE (205). If the value of ltm-NoResetID in the LTM candidate cell is the same as the value of ltm-ServingCellNoResetID in the serving cell of a cell group, then the UE (205) shall not perform any L2 reset (such as RLC reestablishment or PDCP recovery) during an LTM cell switch procedure. Source gNB (201) may map the targetltm-NoResetID to the ltm-NoResetID to ensure that there is no duplication of ltm-NoResetID when multiple target gNBs (205) send the same targetltm-NoResetID for one or more candidate cells. Source gNB (201) may also ensure that the ltm-NoResetID provided for the LTM candidate cells of any target gNB (203) is different from the ltm-NoResetID provided by itself. For e.g. let us consider that a targetgNB gNB 1 has provided ltm-NoResetID values as 1 for two candidate cells C1 and C2 and the targetgNB gNB 2 has provided ltm-NoResetID values as 1 for a LTM candidate cell C3. Source gNB may ensure that ltm-NoResetID send to the UE for C1, C2 are the same and also that the ltm-NoResetID for C1 / C2 is different from the ltm-NoResetID of C3. For e.g. source gNB may include ltm-NoResetID as 1 for C1 / C2 and ltm-NoResetID as 2 for C3.

[0114] In an alternate embodiment, the target gNB doesn't include the targetltm-NoResetID in the Xn Handover Request ACK message. Source gNB allocates a ltm-NoResetID value which is different from any of the candidate cells configured by the source gNB or any of the target gNBs and include the same in the ltm-candidateconfig. Upon executing LTM to a target cell in a different gNB, the UE performs L2 reset.

[0115] In an alternate embodiment, the target gNB (203) doesn't include the targetltm-NoResetID in the Xn Handover Request ACK message. Source gNB (201) allocates a ltm-NoResetID value which is different from any of the candidate cells configured by the source gNB (201) or any of the target gNBs (203) and include the same in the ltm-candidateconfig. Upon executing LTM to a target cell in a different gNB, the UE performs L2 reset.

[0116] In an embodiment, the source RAN node informs target RAN node information about the list of LTM candidate cells that it has configured. In an embodiment, this information includes one or more of the candidate cell index, the physical cell identifier and NR ARFCN. In an embodiment, this may be communicated using Xn Handover Request message. In an embodiment, this may be included in an Xn IE such as LTM Information Request IE. In an embodiment, this may be communicated using an InterNode-RRC message such as Handover Preparation Information. In an embodiment, the list of LTM candidate cells may include only the list of LTM candidate cells to which the subsequent LTM may be performed.

[0117] In an embodiment, the assigned criticality of targetltm-NoResetID is ignore. (Definition of criticality is as per / as referenced in the TS 38.423).

[0118] Further, for the Configuration of Early TA in Inter-gNB. In an embodiment, target gNB (203) informs the source gNB (201) configuration for the random access resources for early timing advance acquisition for the LTM candidate cell during LTM preparation. This information may be included in Xn message such as Xn Handover Request Acknowledge message. This may be encoded in RRC ASN.1 format. For e.g. this may be provided in a container in the Xn message send by target gNB (203). This will help in implementing RRC and Xn encoding separately, there by avoiding duplicate implementation for the transfer of information to source Gnb and UE.

[0119] Alternately, this information may be encoded in Xn ASN.1 format and included in an Xn message such as Xn Handover Request Acknowledge.

[0120] In an embodiment, the assigned criticality of early TA IE (or equivalent IE) is ignored. Alternatively, the assigned criticality of early TA IE (or equivalent IE) may be rejected.

[0121] In an embodiment, the information shared by target gNB (203) to source gNB (201) for configuring the UE (205) for random access configuration for early TA may include random access occasions and random access resources and the total number of random access occasions. It may also include the RACH-ConfigGeneric for the cell also.

[0122] In an embodiment, the target gNB (203) informs the source gNB (201) the contention based random access configuration in the Xn message such as Xn Handover Request Acknowledge message. This may include random access occasions and random access resources and the total number of random access occasions encoded in NR RRC ASN.1 format.

[0123] Further, for the Early TA acquisition, the Source gNB (201) informs the UE (205) to perform random access for early TA acquisition on the target LTM candidate cell. This may be done by DU of source gNB (201). UE (205) performs the random access for early TA acquisition on the target LTM candidate cell.

[0124] In an embodiment target gNB (203) informs the timing advance of the LTM candidate cell it has derived through early Timing Acquisition to the source gNB (201). This may be provide in a Xn message by target gNB CU (211). Target gNB CU (211) may receive this information from target gNB DU (213). In an embodiment, this may be provided in Xn messages such as SN STATUS TRANSFER.

[0125] In an embodiment, target gNB (203) sends a new Xn message for informing the source gNB (201) the timing advance of the LTM candidate cell it has derived through the early Timing Acquisition. In the proposed invention the message such as Xn Access Success message. Xn Access Success message can include Source NG-RAN node UE XnAP ID, Target NG-RAN node UE XnAP ID and the Timing Advance value. It can also include the information about the beam to be used in the target cell after the cell switch, such as SSB Index and the identifier of the bandwidth part to be used.

[0126] In an embodiment assigned criticality for the Source NG-RAN node UE XnAP ID, Target NG-RAN node UE XnAP ID are reject. In an embodiment the assigned criticality for the timing advance value, SSB index and the BWP identifier are ignore. Alternately, the assigned criticality of the timing advance value, SSB index and the BWP identifier may be reject.

[0127] In an example embodiment, the above embodiments may be represented as below in TS 38.423. The XN ACCESS SUCCESS (or any similar message on Xn) message is sent. The message is sent by the target NG-RAN node to the source NG-RAN node to indicate that the Access for Early TA is successful. The Direction is from the NG-RAN node2 to the NG-RAN node1. Example is represented in following table 11.

[0128]

[0129] In an embodiment for the HANDOVER REQUEST ACKNOWLEDGE message. The message is sent by the target NG-RAN node to inform the source NG-RAN node about the prepared resources at the target. The Direction is from the target NG-RAN node to the source NG-RAN node. Example is represented in following table 12.

[0130]

[0131]

[0132] In an alternate embodiment, the source gNB (201) configure the random access resources for early Timing Advance in the LTM candidate configuration only if the candidate cells belong to itself (i.e. gNB ensures that the random access resources for early TA is provided only for Intra-gNB LTM).

[0133] In an embodiment, the target gNB CU (211) receives the timing advance, beam identifier (SSB index), BWP identifier from the target gNB DU (213), through a F1AP message such as F1AP Access indication. It is possible that the target gNB CU (211) and Source gNB CU (209) are the same (i.e. the embodiments are applicable for Intra-gNB LTM also) In an embodiment the criticality of the timing advance, beam identifier (SSB index), BWP identifier in the F1AP Access Indication message is ignore. Alternately, the criticality of the timing advance, beam identifier (SSB index) and BWP identifier in the F1AP Access Indication message is reject.

[0134] FIG. 4 is a block diagram that illustrates a target network node for handling LTM, according to the embodiment as disclosed herein.

[0135] The Target network node (203) includes a processor (217), a memory (221), an I / O interface (219) and a LTM controller (223). The target network node (203) can be an gNodeB, a network device, a base station and the like. Further, the processor (217) of the target network node (203) communicates with the memory (221), the I / O interface (219) and the LTM controller (223). The processor (217) is configured to execute instructions stored in the memory (221) and to perform various processes. The processor (217) can include one or a plurality of processors, can be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0136] Further, the memory (221) of the target network node (203) includes storage locations to be addressable through the processor (217). The memory (221) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (221) can include one or more computer-readable storage media. The memory (221) can include non-volatile storage elements. For example, non-volatile storage elements can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. The memory (221) can store the media streams such as audios stream, video streams, haptic feedbacks and the like. Also, the memory (221) of the target network node (203) can store several information received the at least one source network node (201). For example, the memory can store several information such as first message (Xn handover request message) that includes the first information about one or more LTM candidate cells to be configured by the target network node.

[0137] The I / O interface (219) transmits the information between the memory (221) and external peripheral devices. The peripheral devices are the input-output devices associated with the target network node (203). The I / O interface (219) receives several information from the at least one source network node (201). The several information received from the network apparatus can include but not limited to first message (Xn handover request message) that includes the first information about one or more LTM candidate cells to be configured by the target network node.

[0138] The LTM controller (223) communicates with the I / O interface (219) and memory (221) for handling LTM. The LTM controller (223) is an innovative hardware that is realized through the physical implementation of both analog and digital circuits, including logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive and active electronic components, as well as optical components. The LTM controller (223) of the target network node (203) receives a first message from the source network node (201) for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203). Further, the LTM controller (223) creates the second message for the LTM. The second message includes at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message. The creation of the second message indicates that the UE can perform the handover to the candidate LTM cell without L2 layer reset. Hence, the indication results in efficient resource utilization, resulting in quick handover and faster transmission of the data. Further, the LTM controller (223) transmits the second message to the source network node as the acknowledgement for the first message.

[0139] FIG. 5 is a block diagram that illustrates a source network node for handling LTM, according to the embodiment as disclosed herein.

[0140] The source network node (201) includes a processor (225), a memory (229), an I / O interface (227) and a LTM controller (231). The source network node (203) can be an gNodeB, a network device, a base station and the like. Further, the processor (225) of the source network node (201) communicates with the memory (229), the I / O interface (227) and the LTM controller (231). The processor (225) is configured to execute instructions stored in the memory (229) and to perform various processes. The processor (225) can include one or a plurality of processors, can be a general-purpose processor, such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0141] Further, the memory (229) of the source network node (201) includes storage locations to be addressable through the processor (225). The memory (229) is not limited to a volatile memory and / or a non-volatile memory. Further, the memory (229) can include one or more computer-readable storage media. The memory (229) can include non-volatile storage elements. For example, non-volatile storage elements can include magnetic hard discs, optical discs, floppy discs, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. The memory (229) can store the media streams such as audios stream, video streams, haptic feedbacks and the like. Also, the memory (229) of the source network node (201) can store several information received the at least one target network node (203). For example, the memory can store several information such as second message (Xn handover request acknowledgement message) that includes identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell.

[0142] The I / O interface (227) transmits the information between the memory (229) and external peripheral devices. The peripheral devices are the input-output devices associated with the source network node (201). The I / O interface (227) receives several information from the at least one target network node (203). The several information received from the target network node (203) can include but not limited to identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell.

[0143] The LTM controller (231) communicates with the I / O interface (227) and memory (229) for handling LTM. The LTM controller (231) is an innovative hardware that is realized through the physical implementation of both analog and digital circuits, including logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive and active electronic components, as well as optical components. The LTM controller (231) of the source network node (201) transmits the first message to the target network node (203) for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node. Further, the LTM controller (231) receives the second message from a target network node (203). The second message includes at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell. Further, the LTM controller (231) creates the Radio resource control (RRC) reconfiguration message based on the second message. Further, the LTM controller (231) transmits the RRC reconfiguration message to the UE (205) for performing the LTM operation.

[0144] FIG. 6 is a flow diagram that illustrates a method for handling LTM by the target network node, according to the embodiment as disclosed herein.

[0145] At block 601, the method includes receiving the first message from a source network node (201) for initiating a LTM preparation. The first message includes the first information about one or more LTM candidate cells to be configured by the target network node.

[0146] At block 603, the method includes creating the second message for the LTM. The second message includes at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message.

[0147] At block 605, the method includes transmitting the second message to the source network node (201) as the acknowledgement for the first message.

[0148] FIG. 7 is a flow diagram that illustrates a method for handling LTM by the source network node, according to the embodiment as disclosed herein.

[0149] At block 701, the method includes transmitting the first message to a target network node (203) for initiating a LTM preparation. The first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203).

[0150] At block 703, the method includes receiving the second message from a target network node (203). The second message includes at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell.

[0151] At block 705, the method includes creating the Radio resource control (RRC) reconfiguration message based on the second message.

[0152] At block 707, the method includes transmitting the RRC reconfiguration message to the UE (205) for performing the LTM operation.

[0153] The methods for early TA are applicable for any mobility where the UE performs early uplink synchronisation, i.e. it is not necessarily only for LTM.

[0154] The methods for controlling L2 reset are applicable for any mobility where the UE can perform mobility without L2 reset based on some configurations, i.e. it is not necessarily only for LTM.

[0155] The various actions, acts, blocks, steps, or the like in the method is performed in the order presented, in a different order or simultaneously. Further, in some embodiments, some of the actions, acts, blocks, steps, or the like are omitted, added, modified, skipped, or the like without departing from the scope of the proposed method.

[0156] FIG. 8 illustrates a block diagram of a terminal (or a user equipment (UE)), according to embodiments of the present disclosure.

[0157] As shown in FIG. 8, a terminal according to an embodiment may include a transceiver 810, a memory 820, and a processor (or a controller) 830. The transceiver 810, the memory 820, and the processor (or controller) 830 of the terminal may operate according to a communication method of the terminal described above. However, the components of the terminal are not limited thereto. For example, the terminal may include more or fewer components than those described in Fig. 8. In addition, the processor (or controller) 830, the transceiver 810, and the memory 820 may be implemented as a single chip. Also, the processor (or controller) 830 may include at least one processor.

[0158] The transceiver 810 collectively refers to a terminal station receiver and a terminal transmitter, and may transmit / receive a signal to / from a base station or another terminal. The signal transmitted or received to or from the terminal may include control information and data. The transceiver 810 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 810 and components of the transceiver 810 are not limited to the RF transmitter and the RF receiver.

[0159] Also, the transceiver 810 may receive and output, to the processor (or controller) 830, a signal through a wireless channel, and transmit a signal output from the processor (or controller) 830 through the wireless channel.

[0160] The memory 820 may store a program and data required for operations of the terminal. Also, the memory 820 may store control information or data included in a signal obtained by the terminal. The memory 820 may be a storage medium, such as read-only memory (ROM), random access memory (RAM), a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0161] The processor (or controller) 830 may control a series of processes such that the terminal operates as described above. For example, the processor (or controller) 830 may receive a data signal and / or a control signal, and the processor (or controller) 830 may determine a result of receiving the signal transmitted by the base station and / or the other terminal.

[0162] FIG. 9 illustrates a block diagram of a base station, according to embodiments of the present disclosure.

[0163] As shown in FIG. 9, the base station of the present disclosure may include a transceiver 910, a memory 920, and a processor (or, a controller) 930. The transceiver 910, the memory 920, and the processor (or controller) 930 of the base station may operate according to a communication method of the base station described above. However, the components of the base station are not limited thereto. For example, the base station may include more or fewer components than those described in Fig. 9. In addition, the processor (or controller) 930, the transceiver 910, and the memory 920 may be implemented as a single chip. Also, the processor (or controller) 930 may include at least one processor.

[0164] The transceiver 910 collectively refers to a base station receiver and a base station transmitter, and may transmit / receive a signal to / from a terminal, another base station, and / or a core network function(s) (or entity(s)). The signal transmitted or received to or from the base station may include control information and data. The transceiver 910 may include a RF transmitter for up-converting and amplifying a frequency of a transmitted signal, and a RF receiver for amplifying low-noise and down-converting a frequency of a received signal. However, this is only an example of the transceiver 910 and components of the transceiver 910 are not limited to the RF transmitter and the RF receiver.

[0165] Also, the transceiver 910 may receive and output, to the processor (or controller) 930, a signal through a wireless channel, and transmit a signal output from the processor (or controller) 930 through the wireless channel.

[0166] The memory 920 may store a program and data required for operations of the base station. Also, the memory 920 may store control information or data included in a signal obtained by the base station. The memory 920 may be a storage medium, such as ROM, RAM, a hard disk, a CD-ROM, and a DVD, or a combination of storage media.

[0167] The processor (or controller) 930 may control a series of processes such that the base station operates as described above. For example, the processor (or controller) 930 may receive a data signal and / or a control signal, and the processor (or controller) 930 may determine a result of receiving the signal transmitted by the terminal and / or the core network function.

[0168] The above description is only an exemplary implementation of the present invention, and is not intended to limit the scope of protection of the present invention, which is determined by the appended claims.

[0169] According to an embodiment of the disclosure, method for handling Lower Triggered Mobility (LTM) comprising: receiving, by a target network node (203), a first message from a source network node (201) for initiating a LTM preparation, wherein the first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203); creating, by the target network node (203), a second message for the LTM, wherein the second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message; and transmitting, by the target network node (203), the second message to the source network node (201) as the acknowledgement for the first message.

[0170] According to an embodiment of the disclosure, wherein the one or more LTM candidate cells that belongs to the same group does not require layer 2 reset.

[0171] According to an embodiment of the disclosure, wherein the first message is a Xn handover request message, and wherein the second message is a Xn handover request acknowledge message.

[0172] According to an embodiment of the disclosure, wherein the Random Access Channel (RACH) resources are allocated for each LTM candidate cell or for a group of LTM candidate cells.

[0173] According to an embodiment of the disclosure, , wherein the first message comprises an LTM candidate cell index associated with each LTM candidate cell included in the list of the LTM candidate cells already configured and the identification information of the configured LTM candidate cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for each LTM candidate cell.

[0174] According to an embodiment of the disclosure, wherein configuration for the RACH resources for the early TA synchronization includes RACH-ConfigGeneric, wherein the configuration is encoded using NR RRC ASN.1 format and send in the Xn message.

[0175] According to an embodiment of the disclosure, the method comprising: determining, by the target network node (203), the early TA based on the random access from the UE (205); and sending, by the target network node (203), the early TA value to the source network node (201).

[0176] According to an embodiment of the disclosure, method for handling LTM, comprising: transmitting, by a source network node (201), a first message to a target network node (203) for initiating a LTM preparation, wherein the first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203); receiving, by a source network node (201), a second message from a target network node (203), wherein the second message comprises at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell; creating, by the source network node (201), a Radio resource control (RRC) reconfiguration message based on the second message; and transmitting, by the source network node (201), the RRC reconfiguration message to the UE (205) for performing the LTM operation.

[0177] According to an embodiment of the disclosure, the method comprises: transmitting, by the source network node (201), RRC reconfiguration message to the UE (205) for performing the LTM operation; receiving, by the source network node (201), RRC reconfiguration complete message from the UE (205) indicating the completion of the LTM operation, wherein the LTM operation is performed by at least not performing layer 2 reset or by performing layer 2 reset; transmitting, by the source network node (201), Physical Downlink Control Channel (PDCCH) order to the UE (205) for performing TA synchronization; and receiving, by the source network node (201), an Xn message indicating success of the early TA synchronization, wherein the Xn message comprises a timing advance value of the LTM candidate cell that is derived based on early TA acquisition; and transmitting, by the source network node (201), received TA value to the UE (205) in LTM cell switch command.

[0178] According to an embodiment of the disclosure, a target network node (203) for handling Lower Triggered Mobility (LTM) comprises: a processor (217); and a LTM controller (223) coupled to the processor (217), wherein the LTM controller (217) is configured to: receive a first message from a source network node (201) for initiating a LTM preparation, wherein the first message comprises first information about one or more LTM candidate cells to be configured by the target network node (203); create a second message for the LTM, wherein the second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message; and transmit the second message to the source network node (201) as the acknowledgement for the first message.

[0179] According to an embodiment of the disclosure, wherein the one or more LTM candidate cells that belongs to same group does not require layer 2 reset.

[0180] According to an embodiment of the disclosure, wherein the first message is a Xn handover request message, and wherein the second message is a Xn handover request acknowledge message.

[0181] According to an embodiment of the disclosure, wherein the Random Access Channel (RACH) resources are allocated for each LTM candidate cell or for a group of LTM candidate cells.

[0182] According to an embodiment of the disclosure, wherein the first message comprises an LTM candidate cell index associated with each LTM candidate cell included in the list of the LTM candidate cells already configured and the identification information of the configured LTM candidate cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for each LTM candidate cell.

[0183] According to an embodiment of the disclosure, wherein configuration for the RACH resources for the early TA synchronization includes RACH-ConfigGeneric where in the configuration is encoded using NR RRC ASN.1 format and send in the Xn message.

[0184] According to an embodiment of the disclosure, wherein the LTM controller is configured to: determine the early TA based on the random access from the UE (205); and send the early TA value to the source network node (201).

[0185] According to an embodiment of the disclosure, a source network node (201) for handling Lower Triggered Mobility (LTM) comprises: a processor (225); and a LTM controller (231) coupled to the processor (225), wherein the LTM controller (225) is configured to: receive a second message from a target network node (203), wherein the second message comprises of at least one of an identification information that identifies each LTM candidate cell as part of a group of cells in which the UE (205) can move without performing L2 reset and a configuration for Random Access Channel (RACH) resources for the early TA synchronization for the LTM candidate cell based on the first message; create a Radio resource control (RRC) reconfiguration message based on the second message; and transmit the RRC reconfiguration message to the UE (205) for performing the LTM operation.

[0186] According to an embodiment of the disclosure, wherein the LTM controller is configured to: transmit RRC reconfiguration message to the UE (205) for performing the LTM operation; receive RRC reconfiguration complete message from the UE (205) indicating the completion of the LTM operation, wherein the LTM operation is performed by at least not performing layer 2 reset or by performing layer 2 reset; transmit Physical Downlink Control Channel (PDCCH) order to the UE (205) for performing TA synchronization; and receive an Xn message indicating success of the early TA synchronization, wherein the Xn message comprises a timing advance value of the LTM candidate cell that is derived based on early TA acquisition; and transmit received TA value to the UE (205) in LTM cell switch command.

[0187] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0188] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0189] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0190] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0191] 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 embodiments and examples, those skilled in the art will recognize that the embodiments and examples disclosed herein can be practiced with modification within the scope of the embodiments as described herein.

[0192] 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 are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a first base station in a wireless communication system, the method comprising:identifying a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station; andtransmitting, to a second base station, a message including information on the TA for the LTM candidate cell,wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.2.The method of claim 1, wherein the TA for the LTM candidate cell is obtained based on an early TA acquisition for the LTM candidate cell and is delivered from a distributed unit (DU) of the first base station to a central unit (CU) of the first base station.3.The method of claim 1, wherein the message is an Xn message, andwherein the Xn message includes at least one of the information on the TA, a bandwidth part (BWP) identifier for a cell switch associated with the LTM, or a synchronization signal block (SSB) index for the cell switch associated with the LTM.4.The method of claim 1, wherein the LTM is an inter-CU LTM between the first base station and the second base station.5.A method performed by a second base station in a wireless communication system, the method comprising:receiving, from a first base station, a message including information on a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station; andidentifying the TA for the LTM candidate cell,wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.6.The method of claim 5, wherein the TA for the LTM candidate cell is obtained based on an early TA acquisition for the LTM candidate cell, andwherein the LTM is an inter-CU LTM between the first base station and the second base station.7.The method of claim 5, wherein the message is an Xn message, andwherein the Xn message includes at least one of the information on the TA, a bandwidth part (BWP) identifier for a cell switch associated with the LTM, or a synchronization signal block (SSB) index for the cell switch associated with the LTM.8.A first base station in a wireless communication system, the first base station comprising:a transceiver; anda controller coupled with the transceiver and configured to:identify a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station, andtransmit, to a second base station, a message including information on the TA for the LTM candidate cell,wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.9.The first base station of claim 8, wherein the TA for the LTM candidate cell is obtained based on an early TA acquisition for the LTM candidate cell and is delivered from a distributed unit (DU) of the first base station to a central unit (CU) of the first base station.10.The first base station of claim 8, wherein the message is an Xn message, andwherein the Xn message includes at least one of the information on the TA, a bandwidth part (BWP) identifier for a cell switch associated with the LTM, or a synchronization signal block (SSB) index for the cell switch associated with the LTM.11.The first base station of claim 8, wherein the LTM is an inter-CU LTM between the first base station and the second base station.12.A second base station in a wireless communication system, the second base station comprising:a transceiver; anda controller coupled with the transceiver and configured to:receive, from a first base station, a message including information on a timing advance (TA) for a layer 1 / layer 2 triggered mobility (LTM) candidate cell of the first base station, andidentify the TA for the LTM candidate cell,wherein the first base station is a candidate base station for an LTM, and the second base station is a source base station for the LTM.13.The second base station of claim 12, wherein the TA for the LTM candidate cell is obtained based on an early TA acquisition for the LTM candidate cell.14.The second base station of claim 12, wherein the message is an Xn message, andwherein the Xn message includes at least one of the information on the TA, a bandwidth part (BWP) identifier for a cell switch associated with the LTM, or a synchronization signal block (SSB) index for the cell switch associated with the LTM.15.The second base station of claim 12, wherein the LTM is an inter-CU LTM between the first base station and the second base station.

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