Handover failure processing method through physical layer and MAC layer indication in next generation mobile communication system

Abstract

The invention relates to operation of a terminal in a mobile communication system. An operation method of a terminal in a mobile communication system according to an embodiment of the present disclosure may comprise the steps of: receiving a radio resource control (RRC) message from a serving cell, the RRC message comprising an L1 / L2 triggered mobility (LTM) configuration; receiving, from the serving cell, a Media Access Control (MAC) Control Element (CE) indicating LTM handover; based on the LTM configuration, starting a timer and executing the LTM switching; and under the condition that the LTM is successfully switched, stopping the timer.

Description

Technical Field

[0001] The present disclosure relates to the operation of a terminal in a mobile communication system, and more particularly, to a method for defining handover failure and operations performed by a terminal when handover fails. Background Art

[0002] The 5G mobile communication technology defines wide frequency bands to achieve high transmission rates and new services, which can be deployed not only in the "sub-6 GHz" bands such as 3.5 GHz, but also in the millimeter wave bands of "above 6 GHz" including 28 GHz and 39 GHz. In addition, to achieve a transmission rate 50 times faster and an ultra-low latency as low as one-tenth of that of 5G mobile communication technology, the 6G mobile communication technology (referred to as the super 5G system) is considering deployment in the terahertz band (such as the 95 GHz to 3 THz band).

[0003] In the initial stage of the development of 5G mobile communication technology, to support services such as enhanced mobile broadband (eMBB), ultra-reliable low-latency communication (URLLC), and massive machine type communication (mMTC) and meet their performance requirements, continuous standardization work has been carried out on the following technologies: beamforming and massive MIMO technologies for reducing millimeter wave path loss and increasing propagation distance; parameter sets (such as supporting multiple subcarrier spacings) for efficiently utilizing millimeter wave resources and dynamic operation of time slot formats; initial access technologies supporting multi-beam transmission and broadband; the definition and operation of BWP (bandwidth part); new channel coding methods (such as LDPC (low-density parity-check) codes for high-capacity data transmission and polarization codes for highly reliable transmission of control information); L2 preprocessing; and network slicing technology for providing dedicated networks for specific services.

[0004] Currently, discussions on the improvement and performance enhancement of the initial 5G technology are being carried out for the services to be supported by 5G mobile communication technology, and the following technologies are involved in the physical layer standardization: vehicle-to-everything (V2X) technology, which aims to assist autonomous vehicles in making decisions based on the location and status information sent by vehicles and improve user convenience; license-free new radio (NR-U) technology, which aims to make the system operation comply with various regulatory requirements in license-free bands; NR UE energy-saving technology; non-terrestrial network (NTN) technology for UE-satellite direct communication to provide coverage in areas where communication with the terrestrial network is not possible; and positioning technology.

[0005] In addition, in the field of wireless interface architecture / protocols, standardization is continuously carried out for the following technologies: Industrial Internet of Things (IIoT) technologies that support new services through interoperability and integration with other industries; Integrated Access and Backhaul (IAB) technologies that provide nodes for network service area expansion by integrating support for wireless backhaul links and access links; Mobility enhancement technologies including conditional handover and Dual-Activation Protocol Stack (DAPS) handover; and Two-Step Random Access (2-step RACH in NR) for simplifying the random access procedure. Standardization is also carried out in the system architecture / service field for the following technologies: 5G baseline architectures (such as service-based architectures or service-based interfaces) for combining Network Function Virtualization (NFV) and Software-Defined Network (SDN) technologies, and Mobile Edge Computing (MEC) technologies for providing services based on UE location.

[0006] With the commercialization of 5G mobile communication systems, exponentially growing connected devices will access the communication network. Therefore, it is expected to enhance the functions and performance of 5G mobile communication systems and achieve integrated operation of connected devices. To this end, the following new research is planned: Extended Reality (XR) technologies for efficiently supporting Augmented Reality (AR), Virtual Reality (VR), Mixed Reality (MR), etc.; Utilizing Artificial Intelligence (AI) and Machine Learning (ML) to improve 5G performance and reduce complexity; AI service support; Metaverse service support; and Drone communication.

[0007] In addition, the development of 5G mobile communication systems will not only lay the foundation for the development of the following technologies: New waveforms for ensuring coverage in the terahertz band of 6G mobile communication technologies, Full-Dimensional MIMO (FD-MIMO), multi-antenna transmission technologies such as array antennas and massive antennas; Metamaterial lenses and antennas for improving terahertz signal coverage; High-dimensional spatial multiplexing technologies using Orbital Angular Momentum (OAM); Reconfigurable Intelligent Surfaces (RIS); but also lay the foundation for the development of the following technologies: Full-duplex technologies for improving 6G frequency efficiency and system network; AI-based communication technologies that utilize satellites and AI from the design stage to achieve system optimization and have built-in end-to-end AI support functions; and Next-generation distributed computing technologies that utilize ultra-high-performance communication and computing resources to implement complex services beyond the capabilities of UEs.

[0008] With the evolution of the above wireless communication systems, various services can be provided, so methods for effectively providing these services are needed. Summary of the Invention

[0009] Solution

[0010] A method for operating a terminal in a mobile communication system according to an embodiment of the present disclosure may include: receiving a radio resource control (RRC) message from a serving cell, the RRC message including an L1 / L2 triggered mobility (LTM) configuration; receiving a media access control (MAC) control element (CE) indicating an LTM handover from the serving cell; starting a timer and performing the LTM handover based on the LTM configuration; and stopping the timer when the LTM handover is successful.

[0011] Advantages of the Invention

[0012] Various embodiments of the present disclosure may provide an apparatus and a method capable of effectively providing services in a mobile communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The structure of a typical Long Term Evolution (LTE) system is shown; Figure 2 The radio protocol structure of a typical LTE system is shown; Figure 3 The structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown; Figure 4 The radio protocol structure of a next generation mobile communication system according to an embodiment of the present disclosure is shown; Figure 5 A block diagram showing the internal structure of a UE according to an embodiment of the present disclosure is shown; Figure 6 A block diagram showing the structure of a New Radio (NR) base station according to an embodiment of the present disclosure is shown; Figure 7 A flowchart showing the operations of a terminal, a central unit (CU), and a distributed unit (DU) for L1 / L2 triggered mobility (LTM) operations according to an embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0014] A method for operating a terminal in a mobile communication system according to an embodiment of the present disclosure may include: receiving a radio resource control (RRC) message from a serving cell, the RRC message including an L1 / L2 triggered mobility (LTM) configuration; receiving a media access control (MAC) control element (CE) indicating an LTM handover from the serving cell; starting a timer and performing the LTM handover based on the LTM configuration; and stopping the timer when the LTM handover is successful.

[0015] A terminal in a mobile communication system according to an embodiment of the present disclosure may include a communication unit and a controller operably connected to the communication unit. Wherein, the controller is configured to: receive a radio resource control (RRC) message from a serving cell, the RRC message including an L1 / L2 triggered mobility (LTM) configuration; receive a media access control (MAC) control element (CE) indicating an LTM handover from the serving cell; start a timer and perform an LTM handover based on the LTM configuration; and stop the timer in the case where the LTM handover is successful.

[0016] Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0017] When describing the embodiments, descriptions related to well-known technologies in the relevant fields and those not directly related to the present disclosure will be omitted. Omitting unnecessary descriptions aims to avoid obscuring the gist of the present disclosure and to more clearly convey the core idea.

[0018] For the same reason, some elements in the drawings may be enlarged, omitted, or schematically drawn. In addition, the dimensions of the elements do not fully reflect the actual size. In each of the drawings, the same or corresponding elements are denoted by the same reference numerals.

[0019] Advantages, features, and implementation manners of the present disclosure will be apparent by referring to the embodiments described in detail below with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments and can be implemented in many different forms. The following embodiments are only used to fully disclose the present disclosure and to inform those skilled in the art of its scope. The present disclosure is only defined by the appended claims. Throughout the specification, the same or similar reference numerals denote the same or similar elements.

[0020] Herein, it should be understood that each block and combination of blocks in the flowchart illustrations can be implemented by computer program instructions. These instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing devices to generate a machine, so that when these instructions are executed by the computer processor or other programmable devices, devices for implementing the functions specified in the flowchart blocks can be created. The computer program instructions can also be stored in a computer-usable or readable memory, which can direct the computer or other programmable devices to operate in a specific manner, such that the instructions stored in the computer-usable or readable memory produce an article of manufacture including an instruction device for implementing the functions in the flowchart blocks. The computer program instructions can also be loaded onto a computer or other programmable devices to perform a series of operation steps on the computer or other programmable devices, thereby generating a computer-implemented process, such that the instructions executed on the computer or other programmable devices provide steps for implementing the functions in the flowchart blocks.

[0021] In addition, each block in the flowchart illustration may represent a code module, a code segment, or a portion of code, where the code includes one or more executable instructions for implementing a specified logical function. It should be noted that in some alternative implementations, the functions noted in the blocks may occur in a different order. For example, two consecutive blocks shown may actually be executed substantially in parallel, or sometimes in reverse order, depending on the functions involved.

[0022] As used in embodiments of the present disclosure, the term "unit" refers to a software element or a hardware element (such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC)), and a "unit" can perform a specific function. However, the meaning of "unit" is not limited to software or hardware. A "unit" can be configured to be stored in an addressable storage medium or executed by one or more processors. Thus, a "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, attributes, programs, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and parameters. The elements and functions provided by a "unit" can be combined into fewer elements or units, or divided into more elements or units. In addition, the elements and "units" can reproduce one or more CPUs in a device or a secure multimedia card. In addition, a "unit" in an embodiment may include one or more processors.

[0023] In the following description of the present disclosure, when a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present disclosure, that description will be omitted. The various embodiments of the present disclosure will be described below with reference to the accompanying drawings.

[0024] In the following description, for convenience of description, terms identifying access nodes, terms referring to network entities, terms referring to messages, terms referring to interfaces between network entities, terms referring to various identification information, etc. are used by way of example. Therefore, the present disclosure is not limited by the following terms, and other terms with equivalent technical meanings may also be used.

[0025] In the following description, a base station is an entity that allocates resources to terminals, and may be at least one of a gNode B, an eNode B, a Node B, a Base Station (BS), a radio access unit, a base station controller, and a node in a network. A terminal may include a User Equipment (UE), a Mobile Station (MS), a cellular phone, a smart phone, a computer, or a multimedia system capable of performing communication functions. Of course, the base station is not limited to the above examples. In the present disclosure, a "downlink (DL)" refers to a radio link through which a base station transmits signals to a terminal, and an "uplink (UL)" refers to a radio link through which a terminal transmits signals to a base station.

[0026] Wireless communication systems are evolving into broadband wireless communication systems to provide high-speed and high-quality packet data services using communication standards such as 3GPP's High-Speed Packet Access (HSPA), Long-Term Evolution (LTE or Evolved Universal Terrestrial Radio Access (E-UTRA)), LTE-Advanced (LTE-A), LTE-Pro, 3GPP2's High Rate Packet Data (HRPD), Ultra Mobile Broadband (UMB), IEEE 802.16e, etc., as well as typical voice-based services.

[0027] Since the 5G communication system, as a post-LTE communication system, must flexibly reflect various needs of users, service providers, etc., it must support services that meet various needs. Services considered in the 5G communication system include enhanced mobile broadband (eMBB) communication, massive machine type communication (mMTC), ultra-reliable low-latency communication (URLLC), etc.

[0028] According to some embodiments, eMBB aims to provide data rates higher than those supported by existing LTE, LTE-A, or LTE-Pro. For example, in a 5G communication system, eMBB must provide a peak data rate of 20 Gbps for the downlink and 10 Gbps for the uplink for a single base station. In addition, the 5G communication system must provide higher user-perceived data rates and maximum data rates to UEs. To meet these requirements, transceiver technologies including further enhanced multiple-input multiple-output (MIMO) transmission technologies may need to be improved. In addition, the data rates required for the 5G communication system can be obtained by using a frequency bandwidth of more than 20 MHz in the 3 to 6 GHz or above 6 GHz frequency bands, rather than transmitting signals using a maximum transmission bandwidth of 20 MHz in the 2 GHz band as in LTE.

[0029] In addition, mMTC is being considered to support application services such as the Internet of Things (IoT) in the 5G communication system. mMTC may have requirements such as supporting the connection of a large number of UEs within a cell, enhancing UE coverage, improving battery life, reducing UE costs, etc., to effectively provide IoT services. Since the IoT provides communication services while providing communication functions to various sensors and devices, it must support a large number of UEs within a cell (e.g., such as 1,000,000 UEs / km²). In addition, UEs supporting mMTC may require a wider coverage than other services provided by the 5G system because these UEs may be located in shadow areas such as building basements that are not covered by the cell due to the nature of the service. UEs supporting mMTC must be configured to be low-cost and may require an extremely long battery life of, for example, 10 to 15 years because it is not practical to frequently replace the UE battery.

[0030] Finally, as URLLC for mission-critical wireless communication services based on cellular networks, it can be used for remote control of robots or machines, industrial automation, drones, telemedicine, emergency alerts, etc. Therefore, URLLC must provide communication with ultra-low latency and ultra-high reliability. For example, services supporting URLLC must meet an air interface latency of less than 0.5 ms and may also require a packet error rate of no higher than 1 . Therefore, for services supporting URLLC, the 5G system must provide a shorter transmission time interval (TTI) than other services and may also need to allocate a large amount of resources in the frequency band to ensure the reliability of the communication link.

[0031] The above three services considered in the 5G communication system, namely eMBB, URLLC, and mMTC, can be multiplexed and transmitted in a single system. In this case, to meet the different requirements of each service, different transceiver technologies and transceiver parameters can be used between the services. However, the above mMTC, URLLC, and eMBB are only examples of different types of services, and the types of services applicable to this disclosure are not limited to the above.

[0032] In addition, based on the judgment of those skilled in the art, without significantly departing from the scope of this disclosure, this disclosure can be applied to other communication systems through appropriate modifications. It should be understood herein that each block and combination of blocks in the flowchart illustrations can be implemented by computer program instructions.

[0033] These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, or other programmable data processing devices, thereby generating a machine such that the instructions executed by the processor of the computer or other programmable device can create a device for implementing the functions specified in the flowchart block. The computer program instructions can also be stored in a computer-usable or readable memory, which can direct the computer or other programmable device to operate in a specific manner, such that the instructions stored in the computer-usable or readable memory produce an article of manufacture that includes an instruction device for implementing the functions in the flowchart block. The computer program instructions can also be loaded onto the computer or other programmable device to perform a series of operational steps on the computer or other programmable device, thereby generating a computer-implemented process such that the instructions executed on the computer or other programmable device provide steps for implementing the functions in the flowchart block.

[0034] In addition, each block in the flowchart illustration may represent a code module, a code segment, or a portion of code that contains one or more executable instructions for implementing a specified logical function. It should be noted that in some alternative implementations, the functions noted in the blocks may occur in a different order. For example, two consecutive blocks shown may actually be executed substantially in parallel, or sometimes in reverse order, depending on the functions involved. As used in embodiments of the present disclosure, the term "unit" refers to a software element or a hardware element (such as a Field Programmable Gate Array (FPGA) or an Application Specific Integrated Circuit (ASIC)), and a "unit" can perform a specific function. However, the meaning of "unit" is not limited to software or hardware. A "unit" can be constructed to be stored in an addressable storage medium or to execute on one or more processors. Thus, a "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, attributes, programs, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and parameters. The elements and functions provided by a "unit" can be combined into fewer elements or units, or divided into more elements or units. In addition, the elements and "units" can reproduce one or more CPUs in a device or a secure multimedia card. In addition, a "unit" in an embodiment can include one or more processors.

[0035] In the following description of the present disclosure, for convenience of description, terms and names defined in the 5GS and NR standards are used. These standards are standards specified by the 3GPP group among existing communication standards. However, the present disclosure is not limited by these terms and names, and the present disclosure can be equally applied to systems that comply with other standards. For example, the present disclosure can be applied to 3GPP 5GS / NR (the fifth generation mobile communication standard).

[0036] Figure 1 The structure of a typical LTE system is shown.

[0037] Refer to Figure 1 , as shown in the figure, the radio access network of the LTE system may include next-generation base stations (evolved Node B, hereinafter referred to as eNB, Node B, or base station) 1-05, 1-10, 1-15, and 1-20, a Mobility Management Entity (MME) 1-25, and a Serving Gateway (S-GW) 1-30. A User Equipment (hereinafter referred to as UE or terminal) 1-35 can access an external network through eNBs 1-05 to 1-20 and S-GW 1-30.

[0038] In Figure 1Among them, ENBs 1-05 to 1-20 can correspond to traditional Node Bs in the Universal Mobile Telecommunications System (UMTS). The ENBs can be connected to UEs 1-35 through wireless channels and perform more complex roles than traditional Node Bs. In the LTE system, all user traffic including real-time services over the Internet Protocol (such as VoIP) can be served through shared channels. Therefore, a device that collects status information such as the buffer status, available transmit power status, and channel status of UEs and performs scheduling accordingly is needed, and ENBs 1-05 to 1-20 can act as such a device. Generally, one eNB can control multiple cells. For example, to achieve a transmission rate of 100 Mbps, the LTE system can use Orthogonal Frequency Division Multiplexing (OFDM) in a bandwidth of, for example, 20 MHz as the radio access technology. In addition, the LTE system can adopt an Adaptive Modulation and Coding (AMC) scheme to determine the modulation scheme and channel coding rate according to the channel status of the UE. The S-GW 1-30 is a device that provides data bearers and can create or delete data bearers under the control of the MME 1-25. The MME is a device responsible for the mobility management function of the UE and various control functions, and it can be connected to multiple base stations.

[0039] Figure 2 Fig. shows the radio protocol structure of a typical LTE system.

[0040] Refer to Figure 2 , the radio protocol of the LTE system can include a Packet Data Convergence Protocol (PDCP) 2-05 or 2-40, a Radio Link Control (RLC) 2-10 or 2-35, and a Media Access Control (MAC) 2-15 or 2-30 on both the UE and ENB sides. The PDCP can be used to perform operations such as IP header compression / reconstruction. The main functions of the PDCP are summarized as follows. The PDCP is not limited to the functions shown in the following examples and can perform various functions.

[0041] - Header compression and decompression: only Robust Header Compression (ROHC)

[0042] - User data transmission

[0043] - In-sequence delivery (in-sequence delivery of upper-layer PDUs during the PDCP reconstruction process of RLC AM)

[0044] - Split bearers in dual connectivity (DC) (only support RLC AM): routing of PDCP PDUs for transmission and reordering of PDCP PDUs for reception

[0045] - Duplicate detection of lower-layer SDUs during the PDCP reconstruction process of RLC AM

[0046] - Retransmission of PDCP SDU during handover, and retransmission of PDCP PDU during PDCP data recovery process when splitting bearers in DC (for RLC AM)

[0047] - Encryption and decryption

[0048] - Timer-based SDU discard in the uplink

[0049] Radio Link Control (RLC) 2-10 or 2-35 can reconfigure the PDCP protocol data unit (PDU) to an appropriate size to perform Automatic Repeat reQuest (ARQ) operations. The main functions of RLC are summarized as follows. RLC is not limited to the functions in the following examples and can perform various functions.

[0050] - Transmission of upper layer PDU

[0051] - Error correction by ARQ (only applicable to AM data transmission)

[0052] - Concatenation, segmentation and reassembly of RLC SDU (only applicable to UM and AM data transmission)

[0053] - Re-segmentation of RLC data PDU (only applicable to AM data transmission)

[0054] - Re-ordering of RLC data PDU (only applicable to UM and AM data transmission)

[0055] - Duplicate detection (only applicable to UM and AM data transmission)

[0056] - Protocol error detection (only applicable to AM data transmission)

[0057] - RLC SDU discard (only applicable to UM and AM data transmission)

[0058] - RLC reconstruction

[0059] Medium Access Control (MAC) 2-15 or 2-30 can be connected to multiple RLC layer devices configured in a single terminal, and multiplex RLC PDUs into MAC PDUs or demultiplex MAC PDUs into RLC PDUs. The main functions of MAC are summarized as follows. MAC is not limited to the functions in the following examples and can perform various functions.

[0060] - Mapping between logical channels and transport channels

[0061] - Multiplexing / demultiplexing between MAC SDUs belonging to one or different logical channels and transport blocks (TBs) transmitted to / from the physical layer on the transport channel

[0062] - Scheduling information reporting

[0063] - HARQ (Error correction by HARQ)

[0064] - Priority handling between logical channels of a single UE

[0065] - Priority handling between UEs by dynamic scheduling

[0066] - Multimedia Broadcast and Multicast Service (MBMS) service identification

[0067] - Transmission format selection

[0068] - Padding

[0069] The physical layer 2-20 or 2-25 can perform operations such as channel encoding and modulation on the upper layer data to obtain OFDM symbols and transmit them through the wireless channel, or perform demodulation on the OFDM symbols received through the wireless channel, perform channel decoding on them, and transmit them to the upper layer. The physical layer is not limited to the functions of these examples and can perform various functions.

[0070] Figure 3 The structure of a next-generation mobile communication system according to an embodiment of the present disclosure is shown.

[0071] Referring to Figure 3 , the radio access network of a next-generation mobile communication system (hereinafter referred to as NR or 5G) may include a new radio node B (hereinafter referred to as NR gNB or NR base station) 3-10 and a new radio core network (NR CN) 3-05. A new radio user equipment (NR UE or NR terminal) 3-15 can access an external network through the NR gNB 3-10 and the NR CN 3-05.

[0072] In Figure 3Among them, NR gNB 3-10 can correspond to the evolved Node B (eNB) in the traditional LTE system. The NR gNB can be connected to the NR UE 3-15 through a wireless channel and provide better services than the traditional Node B. In the next-generation mobile communication system, since all user traffic can be served through a shared channel, a device that can collect status information such as the buffer status, available transmit power status, and channel status of the UE and perform scheduling accordingly is required, and the NR NB 3-10 can act as this device. Generally, one NR gNB can control multiple cells. To achieve ultra-high-speed data transmission beyond the current LTE, the next-generation mobile communication system can adopt a bandwidth wider than the existing maximum bandwidth. In addition, the next-generation mobile communication system can adopt orthogonal frequency division multiplexing (OFDM) as the radio access technology and can additionally integrate beamforming technology. In addition, the next-generation mobile communication system can adopt an adaptive modulation and coding (hereinafter referred to as AMC) scheme to determine the modulation scheme and channel coding rate according to the channel status of the UE. The NR CN 3-05 can perform functions such as mobility support, bearer configuration, and QoS configuration. The NR CN is a device responsible for the mobility management function and various control functions of the UE and can be connected to multiple base stations. In addition, the next-generation mobile communication system can interoperate with the existing LTE system, and the NR CN 3-05 can be connected to the MME 3-25 through a network interface. The MME can be connected to the eNB 3-30, which is an existing base station.

[0073] Figure 4 Fig. shows the radio protocol structure of the next-generation mobile communication system according to an embodiment of the present disclosure.

[0074] Referring to Figure 4 , the radio protocol of the next-generation mobile communication system can include an NR service data adaptation protocol (SDAP) 4-01 or 4-45, an NR PDCP 4-05 or 4-40, an NR RLC 4-10 or 4-35, an NR MAC 4-15 or 4-30, and an NR PHY 4-20 or 4-25 on both the UE and NR base station sides.

[0075] The main functions of the NR SDAP 4-01 or 4-45 can include the following partial functions. The NR SDAP is not limited to the functions in the following examples and can perform various functions.

[0076] - User plane data transmission

[0077] - Mapping between QoS flows and data bearers for uplink and downlink (mapping between QoS flows and DRBs for DL and UL)

[0078] - Marking QoS flow IDs in DL packets and UL packets

[0079] - Reflection QoS Flow to DRB Mapping of UL SDAP PDU

[0080] Regarding the SDAP layer device, whether to use the header of the SDAP layer device or the function of the SDAP layer device can be configured for the UE through the RRC message according to the PDCP layer device, or according to the bearer, or according to the logical channel. If the SDAP header is configured, the non-access stratum (NAS) service quality (QoS) reflection configuration 1-bit indicator (NAS reflectiveQoS) and the access stratum (AS) QoS reflection configuration 1-bit indicator (AS reflective QoS) of the SDAP header can indicate to the UE that the UE can update or reconfigure the mapping information of the QoS flow and data bearer for the uplink and downlink. The SDAP header can include QoS flow ID information indicating QoS. The QoS information can be used as data processing priority, scheduling information, etc. to smoothly support the service.

[0081] The main functions of NR PDCP 4-05 or 4-40 can include the following partial functions. NR PDCP is not limited to the functions in the following examples and can perform various functions.

[0082] - Header Compression and Decompression: Only ROHC

[0083] - User Data Transmission

[0084] - In-order Delivery of Upper-layer PDUs

[0085] - Out-of-order Delivery of Upper-layer PDUs

[0086] - PDCP PDU Reordering upon Reception

[0087] - Duplicate Detection of Lower-layer SDUs

[0088] - Retransmission of PDCP SDUs

[0089] - Encryption and Decryption

[0090] - Timer-based SDU Discard in the Uplink

[0091] The reordering of the NR PDCP device can refer to the function of reordering the PDCP PDUs received from the lower layer in order based on the PDCP sequence number (SN). The reordering of the NR PDCP device can include the function of transmitting data to the upper layer in the rearranged order, the function of transmitting data directly without considering the order, the function of rearranging the order to record the lost PDCP PDUs, the function of reporting the status of the lost PDCP PDUs to the sender, and the function of requesting retransmission of the lost PDCP PDUs.

[0092] The main functions of NR RLC 4-10 or 4-35 may include the following partial functions. NR RLC is not limited to the functions in the following examples and can perform various functions.

[0093] - Transmission of upper layer PDUs

[0094] - In-sequence delivery of upper layer PDUs

[0095] - Out-of-sequence delivery of upper layer PDUs

[0096] - Error correction via ARQ

[0097] - Concatenation, segmentation, and reassembly of RLC SDUs

[0098] - Re-segmentation of RLC data PDUs

[0099] - Reordering of RLC data PDUs

[0100] - Duplicate detection

[0101] - Protocol error detection

[0102] - RLC SDU discard

[0103] - RLC re-establishment

[0104] The in-sequence delivery of an NR RLC device may refer to the function of sequentially delivering the RLC SDUs received from the lower layer to the upper layer. If an original RLC SDU is split into multiple RLC SDUs and received, the in-sequence delivery function of the NR RLC device may include the function of reassembling the multiple RLC SDUs and delivering the reassembled RLC SDU.

[0105] The in-sequence delivery of an NR RLC device may include at least one of the following functions: if an original RLC SDU is segmented into multiple RLC SDUs and received, reassembling these RLC SDUs and delivering the reassembled RLC SDU; reordering the received RLC PDUs with reference to the RLC sequence number (SN) or the PDCP sequence number (SN); recording the RLC PDUs lost due to reordering; reporting the status of the lost RLC PDUs to the sender; and requesting retransmission of the lost RLC PDUs.

[0106] The in-sequence delivery of an NR RLC device may refer to the function of sequentially delivering only the RLC SDUs before the lost RLC PDU to the upper layer in the presence of lost RLC PDUs.

[0107] In-sequence delivery of the NR RLC device may include the following functions: Even if there are missing RLC SDUs, if a predetermined timer has expired, all RLC SDUs received before the timer started are sequentially transmitted to the upper layer.

[0108] In-sequence delivery of the NR RLC device may include the following functions: Even if there are missing RLC SDUs, if a predetermined timer has expired, all RLC SDUs received so far are sequentially transmitted to the upper layer.

[0109] The NR RLC device may process RLC PDUs in the order of reception, regardless of the sequence based on the sequence number (out-of-sequence delivery), and then transmit the processed RLC PDUs to the NR PDCP device.

[0110] If a segmentation is received, the NR RLC device may receive the segments stored in the buffer or to be received in the future, reconfigure these segments into a complete RLC PDU, process the RLC PDU, and then transmit the processed RLC PDU to the NR PDCP device.

[0111] The NR RLC layer may not include the concatenation function, but the concatenation function may be performed at the NR MAC layer or replaced by the multiplexing function of the NR MAC layer.

[0112] Out-of-sequence delivery of the NR RLC device 1035 or 1060 may refer to the function of directly transmitting the RLC SDUs received from the lower layer to the upper layer regardless of the order. Out-of-sequence delivery of the NR RLC device may include the following functions: If an original RLC SDU is segmented into multiple RLC SDUs and received, these RLC SDUs are reorganized and the reorganized RLC SDUs are transmitted. The out-of-sequence delivery function of the NR RLC device may include the function of storing the RLC sequence number (SN) or PDCP sequence number (SN) of the received RLC PDUs and arranging the order to record the missing RLC PDUs.

[0113] NR MAC 14-15 or 4-30 may be connected to multiple NR RLC layer devices configured in a UE, and the main functions of NR MAC may include the following partial functions. NR MAC is not limited to the functions in the following examples and may perform various functions.

[0114] - Mapping between logical channels and transport channels

[0115] - Multiplexing / demultiplexing of MAC SDUs

[0116] - Scheduling information reporting

[0117] - Error correction via HARQ

[0118] - Priority handling between logical channels of a single UE

[0119] - Priority handling between UEs through dynamic scheduling

[0120] - MBMS service identification

[0121] - Transmission format selection

[0122] - Padding

[0123] Operations executable by NR Physical (PHY) layer 4-20 or 4-25: Channel-encoding and modulating upper-layer data to obtain OFDM symbols and transmitting them through a wireless channel, or demodulating OFDM symbols received through a wireless channel, channel-decoding them, and transmitting them to the upper layer. The NR PHY layer is not limited to the functions of these examples and can execute various functions.

[0124] Figure 5 A block diagram showing the internal structure of a UE according to an embodiment of the present disclosure is shown.

[0125] Referring to Figure 5 , the UE may include a Radio Frequency (RF) processor 5-10, a baseband processor 5-20, a storage unit 5-30, and a controller 5-40.

[0126] The RF processor 5-10 may execute functions of transmitting and receiving signals through a wireless channel, such as frequency band conversion and amplification of signals. That is, the RF processor 5-10 may up-convert a baseband signal provided by the baseband processor 5-20 into an RF band signal, transmit the signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processor 5-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a Digital-to-Analog Converter (DAC), an Analog-to-Digital Converter (ADC), etc. Although Figure 5 only one antenna is shown, the UE may include multiple antennas. In addition, the RF processor 5-10 may include multiple RF chains. In addition, the RF processor 5-10 may execute beamforming. For beamforming, the RF processor 5-10 may adjust the phase and amplitude of each signal transmitted and received through multiple antennas or antenna elements. In addition, the RF processor 5-10 may execute Multiple-Input Multiple-Output (MIMO) and receive multiple layers when performing MIMO operations.

[0127] The baseband processor 5-20 can perform the conversion function between baseband signals and bitstreams according to the physical layer specifications of the system. For example, during data transmission, the baseband processor 5-20 can encode and modulate the transmitted bitstream to generate complex symbols. In addition, during data reception, the baseband processor 5-20 can demodulate and decode the baseband signals provided by the RF processor 5-10 to recover the received bitstream. For example, in an orthogonal frequency division multiplexing (OFDM) scheme, during data transmission, the baseband processor 5-20 can encode and modulate the transmitted bitstream to generate complex symbols, map the complex symbols to subcarriers, and configure OFDM symbols through inverse fast Fourier transform (IFFT) operations and cyclic prefix (CP) insertion. In addition, during data reception, the baseband processor 5-20 can divide the baseband signals provided by the RF processor 5-10 into OFDM symbols, recover the signals mapped to subcarriers through fast Fourier transform (FFT) operations, and recover the received bitstream through demodulation and decoding.

[0128] The baseband processor 5-20 and the RF processor 5-10 can transmit and receive signals as described above. Therefore, the baseband processor 5-20 and the RF processor 5-10 can be referred to as a transmitter, a receiver, a transceiver, or a communication unit. In addition, at least one of the baseband processor 5-20 and the RF processor 5-10 can include multiple communication modules to support multiple different radio access technologies. In addition, at least one of the baseband processor 5-20 and the RF processor 5-10 can include different communication modules to process signals in different frequency bands. For example, different radio access technologies can include wireless LAN (such as IEEE 802.11), cellular networks (such as LTE), etc. In addition, different frequency bands can include super high frequency (SHF) (such as 2 NRHz) bands and millimeter wave (mmWave) (such as 60 GHz) bands. The UE can use the baseband processor 5-20 and the RF processor 5-10 to send / receive signals to / from the base station. These signals can include control information and data.

[0129] The storage unit 5-30 stores data such as basic programs, application programs, and configuration information required for the operation of the UE. In particular, the storage unit 5-30 can store information about a second access node configured to perform wireless communication by using a second radio access technology. In addition, the storage unit 5-30 can provide the stored data according to the request of the controller 240.

[0130] The controller 5-40 controls the overall operation of the UE. For example, the controller 5-40 may transmit / receive signals through the baseband processor 5-20 and the RF processor 5-10. In addition, the controller 5-40 may record data in and read data from the storage unit 5-30. To this end, the controller 5-40 may include at least one processor. For example, the controller 5-40 may include a communication processor (CP) configured to perform communication control and an application processor (AP) configured to control an upper layer such as an application program.

[0131] Figure 6 A structural block diagram of a New Radio (NR) base station according to an embodiment of the present disclosure is shown.

[0132] Referring to Figure 6 , the base station may include an RF processor 6-10, a baseband processor 6-20, a backhaul communication unit 6-30, a storage unit 6-40, and a controller 6-50.

[0133] The RF processor 6-10 may perform functions of transmitting and receiving signals through a wireless channel, such as frequency band conversion and amplification of signals. That is, the RF processor 6-10 may up-convert a baseband signal provided by the baseband processor 6-20 into an RF band signal, transmit the signal through an antenna, and may down-convert an RF band signal received through the antenna into a baseband signal. For example, the RF processor 6-10 may include a transmit filter, a receive filter, an amplifier, a mixer, an oscillator, a DAC, and an ADC. Although Figure 6 only one antenna is shown, the base station may include multiple antennas. In addition, the RF processor 6-10 may include multiple RF chains. In addition, the RF processor 6-10 may perform beamforming. To perform beamforming, the RF processor 6-10 may adjust the phase and amplitude of each signal transmitted and received through multiple antennas or antenna elements. The RF processor may transmit one or more layers to perform a downlink MIMO operation.

[0134] The baseband processor 6-20 can perform the conversion function between baseband signals and bitstreams according to the physical layer specifications of the first radio access technology. For example, during data transmission, the baseband processor 6-20 can encode and modulate the transmitted bitstream to generate complex symbols. In addition, during data reception, the baseband processing unit 6-20 can demodulate and decode the baseband signals provided by the RF processing unit 6-10 to recover the received bitstream. For example, in the OFDM scheme, during data transmission, the baseband processor 6-20 can encode and modulate the transmitted bitstream to generate complex symbols, map the complex symbols to subcarriers, and configure OFDM symbols through IFFT operations and CP insertion. In addition, during data reception, the baseband processor 6-20 can divide the baseband signals provided by the RF processor 6-10 into OFDM symbol units, recover the signals mapped to subcarriers through FFT operations, and then recover the received bitstream through demodulation and decoding. The baseband processor 6-20 and the RF processor 6-10 can send and receive signals as described above. Therefore, the baseband processor 6-20 and the RF processor 6-10 can be referred to as a transmitter, a receiver, a transceiver, a communication unit, or a wireless communication unit. The base station can use the baseband processor 6-20 and the RF processor 6-10 to send / receive signals to / from the UE. These signals can include control information and data.

[0135] The backhaul communication unit 6-30 can provide an interface for communicating with other nodes in the network. That is, the backhaul communication unit 6-30 can convert the bitstream transmitted from the master base station to other nodes (such as an auxiliary base station, a core network) into a physical signal, and convert the physical signal received from other nodes into a bitstream.

[0136] The storage unit 6-40 stores data such as basic programs, application programs, and configuration information required for the operation of the base station. In particular, the storage unit 6-40 can store information about the bearers allocated to the connected UEs, measurement results reported by the connected UEs, etc. In addition, the storage unit 6-40 can store reference information for determining whether to provide multi-connection to the UE or suspend multi-connection. In addition, the storage unit 6-40 can provide the stored data according to the request of the controller 6-50.

[0137] The controller 6-50 controls the overall operation of the base station. For example, the controller 6-50 can send / receive signals through the baseband processor 6-20 and the RF processor 6-10, or through the backhaul communication unit 6-30. In addition, the controller 6-50 can record data in the storage unit 6-40 and read data from it. For this purpose, the controller 6-50 can include at least one processor.

[0138] In the case of a handover indicated by the physical layer or the MAC layer, it is necessary to define a handover failure. In the embodiments of the present disclosure, a timer is introduced, and the conditions for starting the timer / conditions for stopping the timer are configured. When the timer expires, the handover is considered a failure and a processing operation is performed.

[0139] According to the embodiments of the present disclosure, a handover failure can be recognized by the network, and the UE can transition back to an operable state again.

[0140] Figure 7 The operation flowcharts of a UE, a central unit (CU), and a distributed unit (DU) for L1 / L2-triggered mobility (LTM) operations according to the embodiments of the present disclosure are shown.

[0141] Refer to Figure 7, the CU can transmit to the UE, via the serving cell, information on the beam to be measured in the beams of adjacent cells (especially adjacent cells operating under the same CU's DU), especially for adjacent cells. This information can be transmitted together with time information or the conditions for transmitting measurement results. The beam information can be provided as TCI state information. In addition, this information can be included in the DCI or DL MAC CE for transmission. The UE receiving this information can measure the configured beams of the corresponding adjacent cells. The UE can report the measurement results when a given condition is triggered and / or at a specific period. The CU receiving the corresponding report can request the L1 / L2-triggered mobility (LTM) configuration for a specific cell operating under the DU it controls and request its configuration information from the DU. The DU can transmit the LTM configuration information related to the corresponding target cell back to the CU. The CU can assign a specific ID to the configuration information in units of RRCReconfiguration, CellGroupconfiguration, or cell configuration and transmit this specific ID to the UE associated with the configuration information. The CU can transmit this information in a list form. In this case, the message used can be the RRCReconfiguration message. The UE receiving this list can store the LTM configuration information containing this list in a variable for LTM. Thereafter, when receiving a signal / message from the network indicating the execution of LTM towards a specific LTM target cell, the UE can apply the LTM configuration associated with this target cell and indicate HO and / or application completion to the target cell. When the network (such as a base station) transmits a signal indicating the execution of LTM, the network can first transmit, via MAC CE, a list of IDs of available target cells for the UE to perform specific operations and can use DCI to actually indicate the execution of LTM towards a specific target cell. In this case, the UE can, for example, first perform DL synchronization or perform RA on the target cells pre-notified by the network via MAC CE. The indication of LTM execution via DCI can include a single specific LTM ID, and the UE can perform a handover to the cell corresponding to this ID. In another embodiment, the specific ID can be indicated only via MAC CE without using DCI, thereby indicating the execution of LTM. What can indicate the successful execution of a handover can be a UL RRC message, or it can be a UL MAC CE or UCI.

[0142] After successfully executing the LTM HO, the UE can maintain the pre-configured LTM configuration without erasing it.

[0143] In an embodiment, if the target cell configuration of LTM corresponds to RRCReconfiguation, that is, when the UE receives the LTM configuration of the UE from the network (such as a base station), the configuration applied to each target cell during HO is an RRCReconfiguration message, and when the LTM execution indication is received, the UE applies the RRCReconfiguration message corresponding to the indicated LTM ID. The timer usage indicator and the timer value may be included in the RRCReconfiguration message corresponding to the LTM ID and transmitted to the UE.

[0144] If the LMT configuration is included in the RRCReconfiguration message, the timer value and / or the timer usage indicator may be included and transmitted by the target CU in reconfigWithSync of spcellconfig included in the RRCReconfiguration message, and the RRCReconfiguration message may be included in the LTM configuration container of the external RRCReconfig for transmission.

[0145] Timer operation: - Timer start: When LTM is triggered (that is, when RRCReconfig including reconfigWithSync is applied in the LTM configuration triggered (indicated) by the serving cell) or when the MAC CE or DCI for triggering LTM is received - Timer stop: When the RACH procedure for the LTM target cell is successful, or when the RRCReconfigurationComplete message is successfully transmitted to the LTM target cell (skipping RACH is indicated in the RRCReconfig message) In an embodiment, if the target cell configuration of LTM corresponds to CellGroupConfig, that is, when the UE receives the LTM configuration of the UE from the network (such as a base station), the configuration to be applied to each target cell during LTM HO is a CellGroupConfig or an RRCReconfiguration message (CellGroupConfig and the common configuration are transmitted together as the transmission configuration), and when the LTM execution indication is received, the UE applies the CellGroupConfig / RRCReconfiguration message corresponding to the indicated LTM ID.

[0146] - Configuration: In the case of CellGroupConfig, the target CU (the same CU as the source in the LTM case) includes and transmits the timer value / timer usage indicator in reconfigWithSync of specellConfig in the LTM configuration field of the external RRCReconfig, and / or introduces and transmits a separate timer in the LTM configuration (similarly applicable to the MAC specification).

[0147] - Operation: - Start: When LTM is triggered (when applying CellGroupConfig in the LTM configuration triggered (indicated) by the serving cell) or when receiving a MAC CE or DCI for triggering LTM (similarly applicable to the MAC specification or R1 specification), start the operation.

[0148] - Stop: When the RACH with the LTM target cell is successful, or when successfully transmitting the LTM completion indication to the LTM target cell via an RRC UL message / UL MAC CE / UCI (similarly applicable when indicating to skip the RACH)

[0149] If the indicator indicating the RACH omission may be included in the reconfigWithSync field of specellConfig in CellGroupConfig or the position in spcellconfig. In this case, the timing advance information and UL grant configuration information used by the target cell can be included and transmitted to the UE. When including this indicator, the UE may need to apply the indicated target cell configuration when performing LTM, and then transmit an RRC / MACCE / UCI containing the completion indication to the target cell. In this case, without a separate random access procedure, the UE can apply the given timing advance (TA) and use the given UL grant configuration information to transmit a completion message / signal to the target cell. The UL grant configuration information is the frequency information and time information of the UL resource, and the time information can be configured by the period value of the repeated UL grant, the indicator in units of a specific SFN or subframe / slot, and the offset value indicating the available position at a specific time from this indicator.

[0150] In addition, in the case of performing RACH based on the configuration information to be used at handover, the configuration information may include indicators indicating the execution of CFRA and CBRA and the available random access configuration information. The random access configuration information may include the RA preamble ID or preamble indication information, or the time or frequency information of the RA occasion. When the UE receives such an indication, it can perform RA to the target cell when performing LTM. In this case, the completion message transmitted at the completion of LTM can be transmitted using the TA value and UL grant information obtained during the RA process.

[0151] In an embodiment, the candidate target cell configuration may correspond to a value of the cell configuration.

[0152] - Configuration: In the case of cell configuration, the target CU (the same CU in the case of LTM) includes and transmits a timer value / timer usage indicator in reconfigWithSync of spcellConfig in the LTM configuration field of the external RRCReconfig, or introduces and transmits a separate timer in the LTM configuration

[0153] - Operation

[0154] - Start: When LTM is triggered (when cellconfig (or spcellConfig) is applied in the LTM configuration triggered (indicated) by the serving cell) or when a MAC CE or DCI for triggering LTM is received (similarly applicable to the MAC specification or R1 specification)

[0155] - Stop: When the RACH with the LTM target cell is successful or when an LTM completion indication is successfully transmitted to the LTM target cell via an RRC UL message / UL MAC CE / UCI (when it is indicated to skip the RACH)

[0156] If an indicator indicating RACH omission may be included in the reconfigWithSync field of specellConfig in CellGroupConfig or in the position in spcellconfig. In this case, the timing advance information and UL grant configuration information to be used by the target cell may be included and transmitted to the UE. When this indicator is included, the UE may need to apply the indicated target cell configuration when performing LTM and then transmit an RRC / MACCE / UCI containing the completion indication to the target cell. In this case, without a separate random access procedure, the UE may apply the given timing advance (TA) and use the given UL grant configuration information to transmit a completion message / signal to the target cell. The UL grant configuration information is the frequency information and time information of the UL resource, and the time information may be configured by the period value of the repeated UL grant, the indicator in units of a specific SFN or subframe / slot, and the offset value indicating the available position at a specific time from this indicator.

[0157] In addition, in the case of performing RACH based on the configuration information to be used at handover, the configuration information may include indicators indicating the execution of CFRA and CBRA and the available random access configuration information. The random access configuration information may include RA preamble ID or preamble indication information, or time or frequency information of the RA occasion. When the UE receives such an indication, it may perform RA to the target cell when performing LTM. In this case, the completion message transmitted when LTM is completed may be transmitted using the TA value and UL grant information obtained during the RA procedure.

[0158] In an embodiment, in the case not corresponding to the above embodiments, that is, different from the existing method of transmitting values for each target cell, a separate timer for LTM operation may be introduced.

[0159] The purpose of LTM is to minimize RRC intervention to reduce the interruption time. Therefore, the CU may indicate the use of a common timer and configure a single value. This single value may be included in the LTM container for transmission. In addition, the same value may be used for all candidate cells.

[0160] - Configuration: Regardless of whether the configuration of the candidate target cell is RRCReconfiguration, Cell Group Config, or Cell Configuration (or spcell Config), the single timer usage indicator and / or timer value may be separately indicated in the LTM container.

[0161] - Operation: The start and stop operation conditions of the timer may be configured to be consistent with the start and stop conditions defined in the above embodiments.

[0162] In an embodiment, failure may be defined as follows.

[0163] - If the timer related to the failure expires, it may be regarded as a failure.

[0164] In an embodiment, as a processing operation at the time of failure, the UE may perform at least one of the following operations.

[0165] - The UE may maintain the LTM configuration information before LTM execution.

[0166] - The UE may use the configuration information before LTM execution to select the source cell before LTM execution and access that source cell.

[0167] - The UE may perform a normal cell selection operation in the RRC reconstruction operation to select a cell and access it, rather than accessing the source cell.

[0168] ■ If the selected cell is a candidate cell associated with the conditional handover or LTM configuration stored in the UE, the UE may access the cell by applying the conditional handover or LTM configuration.

[0169] - After accessing the above cell, the UE may indicate to the base station that the LTM execution has failed. This indication may be transmitted to the accessed cell via UL MAC CE or DCI.

[0170] ■ In this case, the failed LTM configuration ID or the failed cell ID during LTM execution, and / or an indicator indicating that the LTM execution has failed may be transmitted via an RRC message.

[0171] - If the timer configuration and start / stop operations are executed at the MAC / PHY layer, the MAC / PHY layer may transmit a timer expiration or LTM failure indicator to the RRC layer when the timer expires.

[0172] - The network may indicate to execute these operations, i.e., the operations of reporting the failure of LTM execution.

[0173] The method disclosed in the claims and / or the method of the embodiments described in the present disclosure may be implemented by hardware, software, or a combination of hardware and software.

[0174] When implemented by software, a computer-readable storage medium for storing one or more programs (software modules) may be provided. One or more programs stored in the computer-readable storage medium may be configured to be executed by one or more processors in an electronic device. At least one program includes instructions for causing the electronic device to execute the methods of the various embodiments of the present disclosure as defined in the claims and / or as disclosed herein.

[0175] These programs (software modules or software) may be stored in a non-volatile memory including random access memory and flash memory, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), magnetic disk storage devices, compact disc read-only memory (CD-ROM), digital versatile disc (DVD), or other types of optical storage devices, or magnetic tapes. Alternatively, some or all of their combinations may constitute the memory for storing the programs. In addition, the electronic device may include multiple such memories.

[0176] In addition, the programs may be stored in a connectable storage device accessible to the electronic device via a communication network such as the Internet, intranet, local area network (LAN), wide area network (WLAN), storage area network (SAN), or a combination thereof. The storage device may access the electronic device through an external port. In addition, a separate storage device on the communication network may access a portable electronic device.

[0177] In the drawings depicting the methods of the present disclosure, the order of description does not necessarily correspond to the order of execution of the steps. The order relationship between the steps may be changed or the steps may be executed in parallel.

[0178] Alternatively, in the drawings depicting the methods of the present disclosure, some elements may be omitted, and only some elements are included without departing from the essential spirit and scope of the present disclosure.

[0179] In addition, in the methods of the present disclosure, without departing from its essential spirit and scope, part or all of the content of each embodiment may be combined and implemented.

[0180] The embodiments of the present disclosure described and illustrated in the specification and drawings are only specific examples presented for the convenience of explaining the technical content of the present disclosure and helping understanding, and are not intended to limit the scope of the present disclosure. That is, it is obvious to those skilled in the art that other variations can be realized based on the technical idea of the present disclosure. In addition, the above embodiments can be used in combination as needed.

Claims

1. A method for operating a terminal in a mobile communication system, the method comprising: Receiving a radio resource control (RRC) message from a serving cell, the RRC message including an L1 / L2 triggered mobility (LTM) configuration; Receiving a media access control (MAC) control element (CE) indicating an LTM handover from the serving cell; Based on the LTM configuration, starting a timer and performing the LTM handover; And Stopping the timer when the LTM handover is successful.

2. The method according to claim 1, wherein The LTM handover is determined to be successful when a random access channel (RACH) procedure with a target cell is successful.

3. The method according to claim 1 further comprises: When the timer expires, determining that the LTM handover has failed.

4. The method according to claim 3 further comprises: Performing an RRC reestablishment procedure for cell selection.

5. The method according to claim 4 further comprises: When the LTM configuration includes information related to the cell selected during the RRC reestablishment procedure, accessing the selected cell based on the LTM configuration.

6. The method according to claim 1, wherein The timer is a timer related to the RRC layer.

7. The method according to claim 1, wherein The RRC message includes a timer usage indicator and a timer value.

8. A terminal in a mobile communication system, the terminal comprising: A communication unit; And A controller operably connected to the communication unit, Wherein the controller is configured to: Receive a radio resource control (RRC) message from a serving cell, the RRC message including an L1 / L2 triggered mobility (LTM) configuration; Receive a media access control (MAC) control element (CE) indicating an LTM handover from the serving cell; Based on the LTM configuration, start a timer and perform the LTM handover; And Stop the timer when the LTM handover is successful.

9. The terminal according to claim 8, wherein, The controller is configured to: determine that the LTM handover is successful when a random access channel (RACH) procedure with a target cell is successful.

10. The terminal according to claim 8, wherein, The controller is configured to: determine that the LTM handover has failed when the timer expires.

11. The terminal according to claim 10, wherein, The controller is configured to perform an RRC reestablishment procedure for cell selection.

12. The terminal according to claim 11, wherein, The controller is configured to: when the LTM configuration includes information related to the cell selected during the RRC reestablishment procedure, access the selected cell based on the LTM configuration.

13. The terminal according to claim 8, wherein, The timer is a timer related to the RRC layer.

14. The terminal according to claim 8, wherein, The RRC message includes a timer usage indicator and a timer value.

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