LTM failure recovery method and device in wireless communication system

Abstract

In an operation of this wireless user device, the wireless user device can acquire LTM configuration information from a source cell on the basis of LTM. Then, the wireless user device can perform uplink / downlink pre-synchronization with one or more candidate cells. Afterward, the wireless user device can perform a first LTM attempt and, if the first LTM attempt fails, the wireless user device can perform a second LTM attempt.

Description

Method and device for LTM failure recovery in a wireless communication system

[0001] The present invention relates to a method and apparatus for recovering from an LTM (L1 / L2 layer triggered mobility) failure in a wireless communication system. Specifically, the invention relates to a method and apparatus for recovering when an LTM failure occurs after an LTM operation.

[0002]

[0003] The International Telecommunication Union (ITU) is developing the International Mobile Telecommunication (IMT) framework and standards, and recently, discussions for 5th generation (5G) communication are underway through a program called "IMT for 2020 and beyond."

[0004] In order to meet the requirements presented in "IMT for 2020 and beyond," discussions are underway to support various numerologies for time-frequency resource unit standards in 3GPP (3rd Generation Partnership Project) NR (New Radio) systems, taking into account various scenarios, service requirements, and potential system compatibility.

[0005] Mobility support measures may be necessary in wireless communication systems, and the following describes measures for this purpose.

[0006]

[0007] The present disclosure relates to a method and apparatus for recovering LTM failure in a wireless communication system.

[0008] The present disclosure relates to a method and apparatus for performing a second LTM attempt after a first LTM attempt in a wireless communication system.

[0009] The present disclosure relates to a method and apparatus for performing an LTM failure recovery procedure based on at least one of a random access channel (RACH) based LTM and a RACH-less based LTM in a wireless communication system.

[0010] The present disclosure relates to a method and apparatus for attempting LTM to a candidate cell within the same central unit (intra CU) as the source cell in a wireless communication system.

[0011] The present disclosure relates to a method and apparatus for attempting LTM to a candidate cell within an inter-CU different from the source cell in a wireless communication system.

[0012]

[0013] According to one embodiment of the present invention, in a wireless user device, a wireless transceiver, one or more processors, and a memory that stores instructions for a wireless device when executed by one or more processes, the operation of the wireless user device is: to obtain LTM configuration information based on LTM (L1 / L2 layer triggered mobility) from a source cell, the wireless user device to perform uplink / downlink pre-synchronization with one or more candidate cells, the wireless user device to perform a first LTM attempt, and if the first LTM attempt fails, to perform a second LTM attempt.

[0014] Additionally, according to one embodiment of the present invention, a method of operation of a wireless user device may include the steps of: obtaining LTM configuration information based on LTM (L1 / L2 layer triggered mobility) from a source cell; the wireless user device performing uplink / downlink pre-synchronization with one or more candidate cells; the wireless user device performing a first LTM attempt; and, if the first LTM attempt fails, performing a second LTM attempt.

[0015] In addition, the following points may apply in common.

[0016] According to one embodiment of the present invention, LTM configuration information may include information on one or more candidate cells and event condition information for performing LTM.

[0017] In addition, according to one embodiment of the present invention, a wireless user device may acquire a reference signal from one or more candidate cells and perform a measurement, and if an event condition is satisfied based on the measurement result, a first LTM attempt may be performed.

[0018] In addition, according to one embodiment of the present invention, when a wireless user device receives an LTM cell switch command MAC CE (medium access control element), it can perform a first LTM attempt based on the LTM cell switch command MAC CE.

[0019] In addition, according to one embodiment of the present invention, a wireless user device can obtain a timing advance command (TAC) for each of one or more candidate cells based on uplink / downlink pre-synchronization for one or more candidate cells.

[0020] In addition, according to one embodiment of the present invention, if the TA of a target cell performing a first LTM is valid based on the TAC for each of one or more candidate cells, the wireless user device may perform a first LTM attempt by transmitting an RRC reconstruction message to the target cell.

[0021] In addition, according to one embodiment of the present invention, if the TA of the target cell performing the first LTM based on the TAC for each of one or more candidate cells is invalid, the wireless user device may perform a first LTM attempt by performing a RACH (random access channel) procedure to the target cell.

[0022] Additionally, according to one embodiment of the present invention, the first LTM attempt may be determined to fail based on the timer expiration.

[0023] Additionally, according to one embodiment of the present invention, if the first LTM attempt fails, a second LTM attempt is configured on the wireless user device, and if the cell selected by the wireless user device based on the failure of the first LTM attempt is an LTM candidate cell, the second LTM attempt can be performed.

[0024] In addition, according to one embodiment of the present invention, if the TA of the LTM candidate cell selected by the wireless user device is valid, an RRC reconstruction message is transmitted to the LTM candidate cell to perform a second LTM attempt, and if the TA of the LTM candidate cell selected by the wireless user device is not valid, a RACH procedure is performed to the LTM candidate cell to perform a second LTM attempt.

[0025] In addition, according to one embodiment of the present invention, if the LTM candidate cell selected by the wireless user device is the same as the cell that performed the first LTM attempt, the wireless user device may perform a RACH procedure with the LTM candidate cell to perform a second LTM attempt.

[0026]

[0027] According to the present disclosure, a method for recovering from LTM failure in a wireless communication system can be provided.

[0028] According to the present disclosure, a method for performing a second LTM attempt after a first LTM attempt in a wireless communication system can be provided.

[0029] According to the present disclosure, a method for performing an LTM failure recovery procedure based on at least one of a RACH-based LTM and a RACH-less-based LTM in a wireless communication system can be provided.

[0030] According to the present disclosure, a method for attempting LTM with a candidate cell within the same CU (intra CU) as the source cell in a wireless communication system can be provided.

[0031] According to the present disclosure, a method for attempting LTM with a candidate cell within an inter-CU different from the source cell in a wireless communication system can be provided.

[0032]

[0033] FIG. 1 is a drawing for illustrating an NR frame structure to which the present disclosure can be applied.

[0034] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0035] FIG. 3 is a diagram showing cell-level mobility and beam-level mobility applicable to the present disclosure.

[0036] FIG. 4 is a diagram showing an LTM scenario applicable to the present disclosure.

[0037] FIG. 5 is a diagram showing signaling and setting information in the LTM preparation stage applicable to the present disclosure.

[0038] FIG. 6 is a diagram illustrating the signaling and setting procedure for an initial synchronization step applicable to the present disclosure.

[0039] FIG. 7 is a diagram illustrating a method by which a terminal applicable to the present disclosure performs uplink synchronization.

[0040] FIG. 8 is a diagram showing signaling for an LTM cell change execution procedure applicable to the present disclosure.

[0041] FIG. 9 is a drawing showing a cell change MAC CE applicable to the present disclosure.

[0042] FIG. 10 is a diagram showing the signaling of the LTM cell change completion step applicable to the present disclosure.

[0043] FIG. 11 is a diagram illustrating an inter-base station handover procedure applicable to the present disclosure.

[0044] FIG. 12 is a diagram illustrating a procedure for performing an intra-AMF / UPF conditional handover applicable to the present disclosure.

[0045] FIG. 13 is a diagram showing a cell switch command MAC CE applicable to the present disclosure.

[0046] FIG. 14 is a diagram showing a candidate cell TCI state activation / deactivation MAC CE applicable to the present disclosure.

[0047] FIG. 15 is a diagram illustrating an LTM failure handling method applicable to the present disclosure.

[0048] FIG. 16 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0049] FIG. 17 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0050] FIG. 18 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0051] FIG. 19 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0052] FIG. 20 is a diagram illustrating a RACH-less based LTM failure handling method in the event of an LTM failure applicable to the present disclosure.

[0053] FIG. 21 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0054] FIG. 22 is a flowchart illustrating a RACH-less based LTM retry method following a C-LTM failure applicable to the present disclosure.

[0055] FIG. 23 is a flowchart illustrating a RACH-less based LTM retry method following LTM failure applicable to the present disclosure.

[0056] FIG. 24 is a flowchart illustrating a RACH-less based LTM retry method following a C-LTM failure applicable to the present disclosure.

[0057] FIG. 25 is a flowchart illustrating a RACH-less based LTM retry method following LTM failure applicable to the present disclosure.

[0058] FIG. 26 is a diagram illustrating the operation method of a wireless user device to which the present disclosure applies.

[0059] FIG. 27 is a drawing showing a device configuration applicable to the present disclosure.

[0060]

[0061] Hereinafter, embodiments of the present disclosure are described in detail with reference to the attached drawings so that those skilled in the art can easily implement them. However, the present disclosure may be embodied in various different forms and is not limited to the embodiments described herein.

[0062] In describing the embodiments of the present disclosure, if it is determined that a detailed description of known configurations or functions may obscure the essence of the present disclosure, such detailed description is omitted. Furthermore, parts of the drawings unrelated to the description of the present disclosure have been omitted, and similar parts are denoted by similar reference numerals.

[0063] In the present disclosure, when a component is described as being "connected," "combined," or "joined" with another component, this may include not only a direct connection but also an indirect connection in which another component exists in between. Furthermore, when a component is described as "comprising" or "having" another component, this means that, unless specifically stated otherwise, it does not exclude the other component but may include an additional component.

[0064] In the present disclosure, terms such as first, second, etc. are used solely for the purpose of distinguishing one component from another and do not limit the order or importance of the components unless specifically stated otherwise. Accordingly, within the scope of the present disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and likewise, a second component in one embodiment may be referred to as a first component in another embodiment.

[0065] In this disclosure, distinct components are intended to clearly describe their respective features and do not imply that the components are separate. That is, multiple components may be integrated to form a single hardware or software unit, or a single component may be distributed to form multiple hardware or software units. Accordingly, such integrated or distributed embodiments are included within the scope of this disclosure, unless otherwise noted.

[0066] In the present disclosure, the components described in various embodiments do not necessarily mean essential components, and some may be optional components. Accordingly, embodiments consisting of a subset of the components described in one embodiment are also included within the scope of the present disclosure. Furthermore, embodiments including additional components in addition to the components described in various embodiments are also included within the scope of the present disclosure.

[0067] The present disclosure describes a wireless communication network, and operations performed in the wireless communication network may be performed in the process of controlling the network and transmitting or receiving signals by a system (e.g., a base station) governing the wireless communication network, or in the process of transmitting or receiving signals by a terminal connected to the wireless network.

[0068] It is self-evident that various operations performed for communication with a terminal in a network consisting of multiple network nodes, including a base station, can be performed by the base station or other network nodes other than the base station. The term 'Base Station (BS)' may be replaced by terms such as fixed station, Node B, eNodeB (eNB), ng-eNB, gNodeB (gNB), and Access Point (AP). Additionally, the term 'terminal' may be replaced by terms such as User Equipment (UE), Mobile Station (MS), Mobile Subscriber Station (MSS), Subscriber Station (SS), and non-AP Station (non-AP STA).

[0069] In the present disclosure, transmitting or receiving a channel includes the meaning of transmitting or receiving information or signals through said channel. For example, transmitting a control channel means transmitting control information or signals through the control channel. Similarly, transmitting a data channel means transmitting data information or signals through the data channel.

[0070] In the following description, the term NR (New Radio) system is used for the purpose of distinguishing the system to which various examples of the present disclosure are applied from existing systems, but the scope of the present disclosure is not limited by this term.

[0071] NR systems support various subcarrier spacing (SCS) while considering diverse scenarios, service requirements, and potential system compatibility. Furthermore, NR systems can support the transmission of physical signals / channels through multiple beams to overcome poor channel environments, such as high path loss, phase noise, and frequency offset occurring at high carrier frequencies. Through this, NR systems can support applications such as enhanced mobile broadband (eMBB), massive machine type communications (mMTC) / ultra machine type communications (uMTC), and ultra reliable and low latency communications (URLC).

[0072] Hereinafter, 5G mobile communication technology can be defined to include not only NR systems but also existing LTE-A (Long Term Evolution-Advanced) systems and LTE (Long Term Evolution) systems. 5G mobile communication may include not only newly defined NR systems but also technologies that operate considering backward compatibility with previous systems. Accordingly, the 5G mobile communication described below may include technologies that operate based on NR systems and technologies that operate based on previous systems (e.g., LTE-A, LTE), and is not limited to specific systems.

[0073] First, I would like to briefly explain the physical resource structure of the wireless communication system to which the present invention is applied.

[0074] FIG. 1 is a drawing for illustrating an NR frame structure to which the present disclosure can be applied.

[0075] In NR, the basic unit of the time domain is It could be, and N can be 4096. Meanwhile, the basic unit of the time domain in LTE is It could be, And, = can be 2048. The constant for the multiple relationship between the NR time base unit and the LTE time base unit is k= It can be defined as.

[0076] Referring to FIG. 1, the time structure of a frame for downlink / uplink (DL / UL) transmission is It can have. Here, one frame is It consists of 10 subframes corresponding to time. The number of consecutive OFDM symbols per subframe is = It may be possible. In addition, each frame may be divided into two half frames of the same size, half frame 1 may consist of subframes 0-4, and half frame 2 may consist of subframes 5-9.

[0077] represents the timing advance (TA) between the downlink (DL) and uplink (UL). Here, the transmission timing of the uplink transmission frame i is determined based on the downlink reception timing at the terminal and the following Equation 1.

[0078] [Mathematical Formula 1]

[0079]

[0080]

[0081] Here, can be a TA offset value resulting from duplex mode differences, etc. In FDD (Frequency Division Duplex), Although it has a value of 0, in TDD (Time Division Duplex), considering the margin for DL-UL switching time, It can be defined as a fixed value. For example, in TDD (Time Division Duplex) of FR1 (Frequency Range 1), which is a frequency below 6 GHz. is 39936 or 25600 It could be. 39936 is 20.327μs, and 25600 is 13.030 μs. Also, at FR2 (Frequency Range 2), which is a millimeter wave (mmWave) frequency is 13792 It could be. In this case, 13792 It is 7.020 μs.

[0082] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0083] Resource elements (REs) within a resource grid can be indexed according to each subcarrier spacing. Here, one resource grid can be created for each antenna port and for each subcarrier spacing. Uplink and downlink transmission and reception can be performed based on the corresponding resource grid.

[0084] In the frequency domain, a single Resource Block (RB) consists of 12 REs, and an index (nPRB) for one RB can be configured for each of the 12 REs. The index for an RB can be utilized within a specific frequency band or system bandwidth. The index for an RB can be defined as shown in Equation 2 below. Here, represents the number of subcarriers per RB, and k represents the subcarrier index.

[0085] [Mathematical Formula 2]

[0086]

[0087]

[0088] Various numerals can be configured to satisfy the various services and requirements of an NR system. For example, while an LTE / LTE-A system may support one subcarrier spacing (SCS), an NR system may support multiple SCSs.

[0089] A new numerology for an NR system that supports multiple SCSs can operate in frequency ranges or carriers such as 3 GHz or lower, 3 GHz-6 GHz, 6 GHz-52.6 GHz, or 52.6 GHz or higher to solve the problem that wide bandwidth could not be used in frequency ranges or carriers such as 700 MHz or 2 GHz.

[0090] Table 1 below shows examples of numerals supported by the NR system.

[0091] [Table 1]

[0092]

[0093]

[0094] Referring to Table 1 above, the numeral can be defined based on the subcarrier spacing (SCS), cyclic prefix (CP) length, and the number of OFDM symbols per slot used in the Orthogonal Frequency Division Multiplexing (OFDM) system. These values ​​can be provided to the terminal through the upper layer parameters DL-BWP-mu and DL-BWP-cp for the downlink, and through the upper layer parameters UL-BWP-mu and UL-BWP-cp for the uplink.

[0095] In Table 1 above, when the subcarrier spacing setting index (u) is 2, the subcarrier spacing (Δf) is 60 kHz, and normal CP and extended CP may be applied. For other numerals indexes, only normal CP may be applied.

[0096] A normal slot can be defined as the basic time unit used to transmit a single piece of data and control information in an NR system. The length of a normal slot can be set to the number of 14 OFDM symbols by default. In addition, unlike a slot, a subframe has an absolute time length of 1 ms in an NR system and can be used as a reference time for the length of other time intervals. Here, for the coexistence or backward compatibility of LTE systems and NR systems, time intervals similar to LTE subframes may be required in NR specifications.

[0097] For example, in LTE, data can be transmitted based on a unit of time called a Transmission Time Interval (TTI), and the TTI can be set in units of one or more subframes. Here, one subframe can be set to 1ms and can contain 14 OFDM symbols (or 12 OFDM symbols).

[0098] Additionally, non-slots may be defined in NR. A non-slot may refer to a slot having a number of symbols smaller than that of a normal slot by at least one symbol. For example, when providing low latency, such as in URLLC services, latency can be reduced through non-slots having a number of symbols smaller than that of a normal slot. Here, the number of OFDM symbols included in the non-slot may be determined by considering the frequency range. For example, in a frequency range of 6 GHz or higher, a non-slot with a length of 1 OFDM symbol may be considered. As an additional example, the number of OFDM symbols defining the non-slot may include at least 2 OFDM symbols. Here, the range of the number of OFDM symbols included in the non-slot may be set as the length of a mini-slot up to a predetermined length (e.g., normal slot length minus 1). However, as a specification for the non-slot, the number of OFDM symbols may be limited to a range of 2, 4, or 7 symbols, but is not limited thereto.

[0099] In addition, for example, in the unlicensed band below 6 GHz, subcarrier spacing corresponding to u 1 and 2 may be used, and in the unlicensed band above 6 GHz, subcarrier spacing corresponding to u 3 and 4 may be used. For example, when u is 4, it may be used for the Synchronization Signal Block (SSB).

[0100] [Table 2]

[0101]

[0102]

[0103] Table 2 shows the number of OFDM symbols per slot for normal CP by subcarrier spacing setting (u) ( ), number of slots per frame( ), number of slots per subframe( It represents ). Table 2 shows the values ​​described above based on a normal slot with 14 OFDM symbols.

[0104] [Table 3]

[0105]

[0106]

[0107] Table 3 shows the number of slots per frame and the number of slots per subframe based on a normal slot with 12 OFDM symbols per slot when extended CP is applied (i.e., when u is 2 and subcarrier spacing is 60 kHz).

[0108] As mentioned above, one subframe may correspond to 1ms on the time axis. Additionally, one slot may correspond to 14 symbols on the time axis. For example, one slot may correspond to 7 symbols on the time axis. Accordingly, the number of slots and symbols to be considered within 10ms corresponding to one radio frame may be set differently. Table 4 may show the number of slots and symbols according to each SCS. In Table 4, an SCS of 480kHz may not be considered, but is not limited to these examples.

[0109] [Table 4]

[0110]

[0111]

[0112] In a wireless communication system, a terminal can perform mobility-based operations. The terminal can change the serving cell (e.g., PCell / PSCell) based on mobility. For example, if the terminal detects a serving cell with better quality than the currently connected serving cell, it can change to the cell with better quality, thereby enabling efficient communication. Here, the terminal can perform measurements based on legacy mobility and report the measurement information to the network. Based on the terminal report, the network can determine whether a serving cell with better quality exists than the currently connected serving cell and perform a change to the serving cell with better quality.

[0113] For example, legacy mobility can be a Layer 3-based mobility operation based on L3 mobility. Specifically, the terminal performs measurements based on Layer 3-based signaling, transmits the measurement report to the network, and then changes the serving cell based on network instructions. That is, the terminal and the network can perform measurements based on RRC (radio resource signal) signaling to change the serving cell. When the terminal changes the serving cell based on L3 mobility, the terminal can connect to the new serving cell after resetting the RRC / PDCP (packet data convergence protocol) and resetting the MAC (medium access control) / PHY layer. In other words, while the terminal can reconfigure each layer when changing the serving cell based on mobility, performing this operation every time the terminal changes the serving cell can lead to problems such as prolonged latency and downtime, and increased overhead.

[0114] FIG. 3 is a diagram illustrating cell-level mobility and beam-level mobility applicable to the present disclosure. Referring to FIG. 3(a), the mobility of a terminal can be controlled at the cell level. Cell-level mobility can be configured and operated based on RRC signaling and may be a mobility control operation within a base station (e.g., intra gNB) or between base stations (e.g., inter gNB). That is, when a terminal changes the serving cell based on cell-level mobility, the terminal can perform a procedure to perform a handover to a new serving cell based on RRC signaling.

[0115] Referring to FIG. 3(b), the mobility of the terminal can be controlled at the beam level. Beam-level mobility may be an operation that controls the mobility of the terminal on a beam-by-beam basis. For example, the terminal may perform a beam-level mobility operation when controlling mobility to different cells within the same base station (e.g., intra gNB). As another example, the terminal may perform a beam-level mobility operation for inter-cell beam management (ICBM) as beam management between the same base stations. Here, beam-level mobility may be supported without RRC signaling, but is not limited thereto.

[0116] Considering the long latency and downtime and significant overhead mentioned above, LTM (L1 / L2 layer triggered mobility) operation may be considered. LTM may be a method of controlling mobility based on lower layers (L1 / L2) to support terminal mobility faster than the L3 mobility mentioned above. In LTM operation, when the base station receives the terminal's L1 measurement result, it can transmit an LTM cell switch command MAC CE (control element) (LTE cell switch command MAC CE) to the terminal instructing a cell change. That is, unlike L3 mobility, LTM is not performed based on RRC signaling but supports lower-layer-based mobility, thereby reducing latency and downtime and decreasing overhead. Specifically, the terminal transmits the L1 measurement result to the network, and the network can provide L2 signaling instructing LTM operation to the terminal, and LTM operation can be performed based on this.

[0117] FIG. 4 is a diagram illustrating an LTM scenario applicable to the present disclosure. Referring to FIG. 4(a), a terminal (410) can perform an LTM operation when moving to different distributed units (DU) within the same central unit (CU). That is, the terminal (410) can move to a different DU within the same CU by transmitting an L1 measurement report to a base station and receiving an LTM cell switch command MAC CE from the base station.

[0118] Referring to FIG. 4(b), the terminal (410) can perform an LTM operation when changing the serving cell within the same DU. The terminal (410) can change the serving cell within the same DU by transmitting an L1 measurement report to the base station and receiving an LTM cell switch command MAC CE from the base station. Additionally, referring to FIG. 4(c), the terminal (410) can perform an LTM operation when moving to a different CU. That is, the terminal (410) can move to a different CU by transmitting an L1 measurement report to the base station and receiving an LTM cell switch command MAC CE from the base station.

[0119] When performing an LTM operation, the network can determine a target cell among candidate LTM cells based on an L1 measurement report and transmit a MAC CE to the terminal (410) instructing it to change to the target cell.

[0120] For example, an intra-CU LTM procedure may be performed within the same CU. An intra-CU LTM procedure may be divided into LTM preparation, early sync, LTM cell switch execution, and LTM cell switch completion, but is not limited thereto.

[0121] FIG. 5 is a diagram showing signaling and setting information in the LTM preparation stage applicable to the present disclosure. Referring to FIG. 5, a terminal (510) can transmit a measurement report including signal strength information of a serving cell and an adjacent cell to a base station (520). For example, for convenience of explanation, the following description uses a gNB as the base station, but is not limited thereto and can be applied in the same way to a base station of another wireless system.

[0122] For example, the measurement report transmitted by the terminal (510) to the base station (520) during the LTM preparation phase may be an L3 measurement report. The base station (520) may determine one or more LTM candidate cells based on the measurement report and set one or more LTM candidate cell configuration information to the terminal (510) through an RRC message (e.g., RRC reconfiguration). The terminal (510) may receive an RRC message containing LTM candidate cell configuration information, set up an LTM candidate cell based thereon, and then transmit an RRC message (e.g., RRC reconfiguration complete) to the base station (520) to complete the LTM candidate cell configuration. Specifically, the LTM configuration may include the information in Table 5 below. However, the LTM configuration may include additional information and may not be limited to Table 5 below. In Table 5, the reference configuration may be RRC configuration information that applies commonly to all candidate cells, and the candidate to release list may include information on LTM candidate cells that need to be released based on the LTM candidate ID. Additionally, the candidate to addition & modification list may be a list of LTM candidate cells that need to be newly added or modified. That is, the LTM configuration information provided by the network to the terminal may include information on LTM candidate cells to be released and information on LTM candidate cells to be added or modified.

[0123] Additionally, the serving cell no reset ID may be an identifier with an integer value from 1 to 9 that indicates whether the terminal has a radio link control (RLC) layer information change and a PDCP data recovery trigger. The CSI resource config to addition & modification list may be CSI resource information that is newly added or modified, and the CSI resource config to release list may be CSI resource information that must be released.

[0124] Additionally, the attempt LTM switch may be a configuration that causes the terminal to perform an LTM cell switch to that cell when the terminal searches for a suitable cell and the cell selected by the terminal is an LTM candidate cell, and the corresponding parameter is configured in the candidate cell information. The serving cell UE measured TA ID may be an identifier used to determine whether the terminal performs a terminal-based TA (timing advance) measurement. That is, Table 5 may include information related to LTM settings, but is not limited thereto.

[0125] [Table 5]

[0126]

[0127]

[0128] Additionally, within the configuration for one or more LTM candidate cells, the information for a single LTM candidate cell may be as shown in Table 6. Specifically, the candidate ID is the identifier of the LTM candidate cell, the candidate PCI is the physical cell identifier of the candidate cell, and the synchronization signal block (SSB) configuration may include the SSB configuration information of the LTM candidate cell, and may include frequency information (ARFCN), subcarrier interval, period, burst position, and physical broadcast channel (PBCH) power information. Additionally, the candidate configuration may be RRC configuration information for the LTM candidate cell, and config complete may indicate whether the candidate configuration is the complete RRC information of the candidate cell. Additionally, the early UL sync config may be configuration information for performing early uplink synchronization. Initial uplink synchronization configuration information may include at least one of uplink frequency, RACH (random access channel) configuration, BWP (bandwidth part), number of RACH occasions, PRACH root sequence index, PRACH subcarrier interval, and timing advance offset information. Additionally, the SUL (supplemental uplink) initial uplink synchronization configuration (early UL sync config SUL) may include SUL configuration information for initial uplink synchronization.Additionally, the transmission configuration indicator (TCI) information may include TCI information, and the no reset ID may include a unique identifier of an LTM candidate cell that enables the terminal to determine whether to change RLC layer information and trigger PDCP data recovery. The terminal measured TA ID (UE measured TA ID) may be an identifier used to determine whether the terminal will perform terminal-based TA measurement, but is not limited thereto.

[0129] [Table 6]

[0130]

[0131]

[0132] FIG. 6 is a diagram illustrating a signaling and setup procedure for an initial synchronization step applicable to the present disclosure. Referring to FIG. 6, when a terminal (610) receives setup information for an LTM candidate cell, it can perform downlink and uplink synchronization for the candidate cell in advance before performing LTM. That is, the terminal (610) can perform early synchronization after LTM preparation. By performing synchronization in advance through early synchronization, the terminal (610) can reduce the delay time that occurs when moving to the candidate cell.

[0133] Specifically, the terminal (610) can perform downlink synchronization based on SSB information included in LTM candidate cell information (LTM candidate). Additionally, the terminal (610) can receive a PDCCH (physical downlink control channel) instructing the LTM candidate cell to perform RACH from the serving cell, and can perform uplink synchronization through RACH based thereon.

[0134] Specifically, FIG. 7 is a diagram illustrating a method by which a terminal applicable to the present disclosure performs uplink synchronization. Referring to FIG. 7, the terminal (710) can determine whether the TA ID (ltm-UE-MeasuredTA-ID) of the LTM candidate cell is the same as the TA ID (ltm-ServingCellUE-MeasuredTA-ID) of the current serving cell. If the TA ID of the LTM candidate cell and the TA ID of the current serving cell are the same, the terminal (710) can perform TA measurement and may not perform initial uplink synchronization. On the other hand, if the TA ID of the candidate cell is different from the TA ID of the current serving cell, the terminal (710) can receive a PDCCH from the serving cell instructing the base station (720) to perform RACH to the LTM candidate cell and can transmit a RACH preamble to the LTM candidate cell. However, the terminal (710) may not receive a random access response (RAR) after transmitting a RACH preamble, unlike the existing RACH procedure. Therefore, the terminal (710) may not perform monitoring for receiving a RAR from an LTM candidate cell, and thus may not interfere with the scheduling of the serving cell. For example, in the existing RACH procedure, TA information may be included in the RAR, and the terminal (710) may obtain TA information through the RAR. Since the terminal (710) does not receive a RAR from an LTM candidate cell, the TA information may be included in a cell switch command MAC CE that instructs LTM execution later, and this will be described later.

[0135] FIG. 8 is a diagram illustrating signaling for an LTM cell change execution procedure applicable to the present disclosure. Referring to FIG. 8, a terminal (810) may receive a plurality of LTM candidate cells (830, 840) based on the above description. For example, the terminal (810) may receive a reference signal (RS) from one or more of the received LTM candidate cells (830, 840) and measure the signal strength thereof. Afterward, the terminal (810) may report an L1 measurement result (L1 measurement report) to a source cell (820). The network may determine whether to switch LTM cells based on the L1 measurement result obtained from the terminal (810) and may transmit a MAC CE to the terminal (810) instructing a cell change to a specific LTM candidate cell among the received LTM candidate cells (830, 840). That is, the terminal (810) may receive a cell switch command MAC CE. When the terminal (810) receives a cell switch command MAC CE (or cell switch command MAC CE), the terminal (810) may determine whether it has a valid TA for the cell. If the terminal (810) has a valid TA for the cell, the terminal (810) may not perform a RACH procedure based on a dynamic grant / configured grant (DG / CG). That is, the terminal (810) may perform a RACH-less operation. On the other hand, if the terminal (810) does not have a valid TA for the cell, the terminal (810) may perform a RACH procedure for the cell.

[0136] For example, FIG. 9 illustrates a cell switch command MAC CE applicable to the present disclosure. However, FIG. 9 is merely one example and is not limited thereto. Referring to FIG. 9, the cell switch command MAC CE may include a Target Config ID. The Target Config ID may be a target LTM candidate ID. That is, it may be cell identifier information that the terminal needs to change. Additionally, the cell switch command MAC CE may include a Timing Advance Command (TA). The TA command may indicate a valid TA value as a value from 0 to FFE. For example, if the TA command is a first value (e.g., FFF), the TA command field may indicate that there is no valid TA value for the target cell. Additionally, the cell switch command MAC CE may include a C field, and the C field may be a field indicating whether to perform contention-free random access. Additionally, it may include a Random Access Preamble index within the cell switch command MAC CE, and the Random Access Preamble index may indicate a CFRA preamble resource. Additionally, the SS / PBCH index within the cell switch command MAC CE may indicate an SSB for determining a RACH occasion. Additionally, the PRACH Mask index within the cell switch command MAC CE may indicate available RACH occasion locations.

[0137] FIG. 10 is a diagram illustrating the signaling of an LTM cell change completion step applicable to the present disclosure. Referring to FIG. 10, a terminal (1010) may perform a RACH-less procedure or a RACH procedure based on whether it possesses a valid TA of a target LTM candidate cell in an LTM cell change execution procedure, as described above.

[0138] Here, when the terminal (1010) attempts to change to a target LTM candidate cell through a RACH procedure, the terminal (1010) can complete the LTM cell change by sending an RRC Reconfiguration complete message to the network within the RACH procedure. On the other hand, when the terminal (1010) attempts to change to a target LTM candidate cell based on a RACH-less procedure, the terminal (1010) can complete the LTM cell change by sending an RRC Reconfiguration complete message to the network through the DG / CG.

[0139] FIG. 11 is a diagram illustrating an inter-base station handover procedure applicable to the present disclosure.

[0140] For example, cell-level mobility can be triggered based on explicit RRC signaling. Referring to FIG. 11, a source base station (e.g., source gNB, 1120) can initiate a handover by transmitting a handover request message to a target base station (target gNB, 1130) via an Xn interface. The target base station (1130) can perform admission control and provide a new RRC configuration to the source base station (1120) via a handover request acknowledge message. The source base station (1120) can transmit the new RRC configuration information received from the target base station (1130) in an RRC reconfiguration message to the terminal (1110). The RRC reconfiguration message may include a cell identifier (e.g., Cell ID) and information necessary to connect to the target cell. As described above, the terminal (1110) can connect to the target cell by obtaining the information necessary to connect to the target cell without checking system information. For example, the RRC reconfiguration message may include information necessary for at least one of contention-based random access and contention-free random access operations. Additionally, the RRC reconfiguration message may include beam-specific information, but is not limited to such embodiments. Based on the RRC reconfiguration message, the terminal (1110) can change the RRC connection to the target base station (1130) and transmit an RRC reconfiguration complete message to the target base station (1130).

[0141] For example, in the case of a DAPS (dual active protocol stack) handover, the terminal (1110) can continue receiving downlink data from the source base station (1120) until the source cell connection is released. Additionally, the terminal (1110) can continue transmitting uplink data to the source base station (1120) until the random connection procedure to the target base station (1130) is completed.

[0142] Here, only the source PCell (primary cell) and the target PCell can use DAPS handover. For example, CA (carrier aggregation), DC (dual connectivity), SUL (supplementary uplink), Multi-TRP (transmission reception point), EHC, CHO (conditional handover), UDC, NR sidelink setup, and V2X sidelink setup may not be set by the target base station until the terminal's connection is disconnected by the source base station (1120) before the handover command is transmitted to the terminal (1110), and until the DAPS handover is completed. Here, handover methods triggered by RRC signaling other than DAPS handover may require the terminal to reset the MAC (medium access control) and RLC (radio link control). For example, when the terminal receives a handover command, the terminal may create a MAC entity for the target and establish an RLC entity. The establishment of RLC entities may be an operation that configures a DTCH (dedicated traffic channel) logical channel associated with each DRB (data radio bearer) associated with DAPS. Additionally, PDCP (packet data convergence protocol) entities may be reconfigured with security and ROHC (robust header compression) functions for each source and target in relation to each DRB associated with DAPS, and the reconfigured PDCP entities may be associated with RLC entities configured on the source and target, respectively, but are not limited to such operations.

[0143] For example, RRC handover with PDCP entity reset and RRC handover without PDCP entity reset may be supported. Here, for DRBs using RLC AM (acknowledge mode), which is a mode that uses a response to data transmission, the PDCP layer may be re-established with a security key change. Alternatively, for DRBs using RLC AM mode, the PDCP layer may initiate a data recovery procedure without a security key change.

[0144] Also, as an example, the PDCP layer for DRBs using RLC UM (unacknowledged mode), a mode that does not use acknowledgments for data transmission, can be re-established with a security key change. Alternatively, the PDCP layer for DRBs using RLC UM mode can be maintained without a security key change. The PDCP layer for SRBs (signaling radio bearers) can be maintained by discarding stored PDCP PDUs (protocol data units) and SDUs (service data units) without a key change, or it can be re-established with a key change.

[0145] In addition, as an example, if the target base station uses the same DRB configuration as the source base station, sequence delivery or duplication avoidance can be guaranteed in the case of data forwarding during the handover process.

[0146] In addition, as an example, a timer-based handover failure procedure may be supported. An RRC connection re-establishment procedure, excluding CHO, DAPS, and LTM cell change scenarios, may be used to recover the connection from a handover failure.

[0147] For example, if the DAPS handover fails, the terminal can return to the source cell configuration and resume the connection with the source cell. If the source cell link is not released, the terminal can report the DAPS handover failure without performing the RRC connection re-establishment procedure.

[0148] As another example, in the case where the CHO fails—specifically when the initial attempt to execute the CHO fails or the handover fails—the terminal can perform cell selection. Here, if the cell selected by the terminal is a candidate cell for the CHO and the network is configured to have the terminal attempt the CHO after a handover / CHO failure, the terminal can execute the CHO. Conversely, if the network is not configured to have the terminal attempt the CHO after a handover / CHO failure, the terminal can perform the RRC connection re-establishment procedure.

[0149] As another example, in the case of an LTM failure where an attempt to execute an LTM fails or a handover fails, the terminal can perform cell selection. Here, if the cell selected by the terminal is an LTM candidate cell and the network is configured to have the terminal attempt an LTM after a handover / LTM execution failure, the terminal can execute the LTM. On the other hand, if the network is not configured to have the terminal attempt an LTM after a handover / LTM execution failure, the terminal can perform the RRC connection re-establishment procedure.

[0150] Beam level mobility can be triggered without explicit RRC signaling. Beam level mobility can be applied within a single cell or between cells. When beam level mobility is applied between cells, it may be inter-cell beam management (ICBM). For ICBM, the terminal may transmit and receive dedicated channels / signals via a transmission reception point (TRP) associated with a PCI other than the serving cell's physical cell ID (PCI). Conversely, non-dedicated channels / signals may be received only via a TRP associated with the serving cell's PCI. The base station may provide the terminal with measurement settings via RRC signaling, including SSB / CSI (synchronization signal block / channel state information) resources, resource sets, and settings for reporting and trigger requirements for channel / interference measurement reporting. In ICBM, measurement settings may include SSB resources associated with the serving cell's PCI and other PCIs. Beam level mobility can be handled by control signaling of the physical and MAC layers, and the RRC layer may not need to know which beam is currently in use. Additionally, SSB-based beam level mobility can operate based on the SSB associated with the initial DL BWP (bandwidth part). Here, CSI-RS-based beam level mobility operation can be performed in other DL BWPs.

[0151] Conditional handover (CHO) is an operation in which a handover is performed only when specific conditions are met. For example, in conventional handover procedures, the decision to perform a handover was essentially determined by the terminal and the network. In other words, signaling between the network and the terminal may have been required for the handover to occur. However, in areas outside the cell or dead zones where signal strength changes rapidly, signaling exchange between the terminal and the network may be difficult, potentially leading to a handover failure.

[0152] Considering the above points, the terminal may perform a conditional handover (CHO) operation to perform a handover when specific conditions are satisfied. That is, if one or more handover execution conditions are satisfied, the terminal may perform a handover operation based on the CHO. Specifically, the terminal may receive a CHO configuration and, based thereon, begin evaluating the execution conditions of the CHO. For example, the terminal may stop evaluating execution conditions when a previous handover or conditional handover is performed.

[0153] The CHO configuration may include configurations of conditional handover candidate cells generated by candidate base stations (e.g., candidate gNB(s)) and execution conditions generated by the source base station (e.g., Source gNB). The execution conditions of the CHO may consist of one or more trigger conditions (e.g., CHO event A3 / A5). For example, when evaluating the conditional handover conditions of a single candidate cell, only one Reference Signal (RS) type is supported, and up to two different trigger elements (e.g., RSRP, RSRQ, SINR) may be set simultaneously, but are not limited thereto. As another example, the terminal may perform a handover procedure if it receives a handover command before a specific conditional handover execution condition is satisfied. Here, while the conditional handover is in progress, the terminal may not perform monitoring of the source cell.

[0154] FIG. 12 is a diagram illustrating a procedure for performing an intra-AMF / UPF conditional handover applicable to the present disclosure. Referring to FIG. 12, in an intra-NR RAN conditional handover, message exchange between base stations can be performed without signaling of the core network (e.g., 5GC) during the conditional handover preparation and execution phases. During the conditional handover, resource release at the source base station (e.g., Source gNB) can be triggered by the target base station (e.g., Target gNB).

[0155] As a specific example, when the terminal (1210) establishes a connection or updates the TA (timing advance) for the last time, the access management function (AMF, 1250) may provide mobility control information to the source base station (1220). For example, information regarding roaming and access restrictions may be included in the terminal information (UE context) within the source base station (1220). Next, the source base station (1220) may set a measurement configuration for the terminal (1210) so that the terminal (1210) performs measurement procedures and reports. Here, the source base station (1220) may decide to perform a conditional handover based on the measurement report according to the measurement configuration if certain conditions are satisfied. The source base station (1220) may request a conditional handover to one or more candidate cells included in one or more base stations. For example, the source base station (1220) may transmit a handover request message to each of the cells. After that, the target base station (1230) can perform an admission control operation. For example, when slice information is transmitted to the target base station (1230), the target base station (1230) may recognize the slice and perform admission control. Here, if there are PDU sessions associated with slices that the target base station (1230) does not support, the target base station (1230) may reject the PDU sessions. After that, the target base station (1230) can transmit a handover request response to the source base station (1220). Candidate target base stations (1240) can also transmit a handover request response to the source base station (1220).For example, each candidate base station (1240) may transmit a conditional handover request acknowledge message to the source base station (1220), including conditional handover candidate cell configuration information. Then, the source base station (1220) may transmit an RRC reconfiguration message to the terminal (1210), including conditional handover execution conditions and configuration information of the conditional handover candidate cells. The terminal (1210) may transmit an RRC reconfiguration complete message to the source base station (1220). Here, if early data forwarding is applied, the source base station (1220) may transmit an early status transfer message. The early status transfer message may be for DAPS (dual active protocol stack) operation, but is not limited thereto.

[0156] After receiving conditional handover setting information, the terminal (1210) maintains a connection with the source base station (1220) and can evaluate conditional handover execution conditions for conditional handover candidate cells. If the execution condition is satisfied for at least one conditional handover cell, the terminal (1210) can disconnect from the source base station (1220) and apply the stored setting information to the selected candidate cell. Afterward, the terminal (1210) can perform synchronization with the candidate cell and complete the RRC handover procedure by sending an RRC configuration complete message to the target base station (1230). After completing the RRC handover procedure, the terminal (1210) can release the stored conditional handover setting information.

[0157] Here, the target base station (1230) may send a handover success message to the source base station (1220) to indicate whether the terminal (1210) has successfully connected to the target cell. In response to this, the source base station (1220) may send an SN status transfer message to the target base station (1230). If the source base station (1220) cancels the conditional handover of the terminal (1210), it may send a handover cancel message to other candidate target base stations (1240) or other signaling connection entities.

[0158] The target base station (1230) can send a path switch request message to the AMF (1250). The path switch request message may be a message that triggers the AMF (1250) to change the DL data path of the core network to the target base station (1230). Additionally, it may allow the establishment of an interface (e.g., NG-C) toward the target base station (1230).

[0159] The core network (e.g., 5GC) changes the DL data path to the target base station (1230), and the user plane function (UPF, 1260) can release U-plane / TNL resources toward the source base station (1220) after transmitting one or more "end marker" packets per PDU session / tunnel to the existing path toward the source base station (1220). The AMF (1250) can indicate that the path change is complete by sending a path switch request acknowledge message to the target base station (1230). The target base station (1230) can notify the completion of the handover by sending a UE context release message to the source base station (1220) based on the path switch request acknowledge received from the AMF (1250). Afterward, the source base station (1220) can release the radio and control plane (C-Plane) resources associated with the terminal.

[0160] Next, we can consider methods for performing beam management. That is, beam management can be performed in wireless communication systems. In particular, beam management technology may be essential in the FR2 (frequency range 2) (24250 MHz - 52600 MHz) band. On the other hand, beam management may not be used in the FR1 (frequency range 1) (410 MHz - 7125 MHz) band, which uses a band similar to existing wireless communication systems (e.g., LTE), but is not limited thereto.

[0161] For example, spatial domain control can be performed based on digital domain precoding technology for effective communication between a base station and a terminal. The base station can select and use a preferred precoding matrix from the UL / DL codebook, which can be applied to the transmission of beams with a specific directionality. For example, in 5G FR2, since the path loss experienced by the signal can be significant, it may be required to use a narrower beam. Here, analog domain beam control using phase shifting may be used, but is not limited thereto.

[0162] As another example, DL beam management in a wireless communication system can utilize a transmission configuration indication (TCI) framework. Here, the beam of a specific channel / signal (e.g., PDSCH, PDCCH, CSI-RS) that a terminal must receive can be indicated by the TCI. The TCI can consist of a source reference signal (RS) and a quasi-colocation (QCL) type to be applied. For example, a base station can transmit downlink control information (DCI) regarding physical downlink shared channel (PDSCH) scheduling to a terminal, and the DCI may include the TCI used to receive the PDSCH. Upon receiving the DCI, the terminal can subsequently set analog beamforming coefficients based on the TCI indicated for PDSCH reception. In the above case, since the TCI is indicated solely for PDSCH reception, it can be used as an individual TCI framework. That is, an independent TCI can be indicated for each channel / signal reception (e.g., PDSCH, PDCCH, CSI-RS).

[0163] This individual per-channel beam indication framework can be applied in the same way to the uplink. For example, a base station can transmit a DCI for PUSCH (physical uplink shared channel) scheduling to a terminal. The DCI may include a sounding reference signal resource indicator (SRI) used for PUSCH transmission. Upon receiving the DCI, the terminal can set analog beamforming coefficients based on the SRI indicated for subsequent PUSCH transmission. In other words, the terminal can obtain independent beam indications for each channel / signal (e.g., PUSCH, PUCCH), just as it does for DL.

[0164] As another example, independent beam indication can be performed for each channel, allowing the base station to perform flexible configuration. However, control signaling to indicate the appropriate beam for each channel may increase, which can act as overhead for the base station. For example, in FR2 operation, the base station may use one or more beams to communicate with the terminal. Here, even if the base station sets mostly identical or similar beams, it is necessary to provide independent configuration for each channel, and consequently, overhead may increase. Considering the above points, a common beam indication operation for multiple channels can be applied in multi-input multi-output (MIMO) for UL / DL transmission and reception. Common beam indication (i.e., TCI state) can be performed through one of the integrated common TCI state pools configured by the upper layer. When a common TCI state is indicated, that indication is not used for a single specific channel but can be used for multiple channels / signals simultaneously. For example, the Common TCI state can be applied commonly to CSI-RS, CORESET, and PDSCH, and can also be applied to uplink channels such as PUSCH, PUCCH (physical uplink control channel), and SRS (sounding reference signal), but is not limited to such embodiments.

[0165] As another example, a base station can establish a joint TCI state pool through RRC signaling. Here, a common TCI state can be applied to multiple DL / UL channels. If the base station establishes a DL TCI state pool and a UL TCI state pool respectively, the common TCI state may be applied only to DL channels or only to UL channels.

[0166] For example, in a wireless communication system, both a joint TCI state pool and a separate TCI state pool may be supported. Here, the joint TCI state pool method can efficiently manage beams applicable to both DL and UL. On the other hand, the separate TCI state pool can simplify terminal operation by associating power control parameters used only in the uplink. That is, the terminal may perform power control procedures for TCI states associated only with the UL TCI state pool, but may not be limited to this.

[0167] Based on the above, the following describes the operation to support LTM (L1 / L2 layer triggered mobility) in an intra-CU situation. For example, in wireless communication systems (e.g., Rel-19 Mobility enhancements), LTM operation is defined considering inter-CU situations, and event-based L1 measurement result reporting may be applied to reduce signaling overhead associated with existing periodic / non-periodic L1 measurement result reporting. For example, Table 7 below may be an LTM operation in an inter-CU situation applied in wireless communication systems, but is not limited thereto.

[0168] [Table 7]

[0169]

[0170]

[0171] The following describes the operation in which the terminal checks the conditions for triggering LTM, and if the conditions are satisfied, the terminal performs LTM on an LTM candidate cell.

[0172] For example, regarding LTM operations, the network may instruct the terminal to perform LTM by transmitting an LTM cell switch command MAC CE (medium access control control element). Here, in the case of conditional LTM, the terminal may perform the LTM operation according to certain conditions without receiving the LTM cell switch command MAC CE. That is, the terminal may need to perform the LTM operation without utilizing the information within the MAC CE, and an action may be required for this purpose.

[0173] FIG. 13 is a diagram illustrating a cell switch command MAC CE applicable to the present disclosure. Referring to FIG. 13, a terminal that receives an LTM cell switch command MAC CE can perform a random access procedure initialization. Specifically, if a random access resource is explicitly provided within the LTM cell switch command MAC CE, the terminal can perform a random access procedure by setting a 4-step RACH (random access channel) based on the explicitly provided random access resource. When the terminal performs a random access procedure, if a "ra-PreambleIndex" is explicitly provided in the "Random Access Preamble index" within the LTM cell switch command MAC CE, the terminal can set the preamble index to the transmitted preamble index (ra-PreambleIndex) within the LTM cell switch command MAC CE and select a synchronized signal block (SSB) transmitted together. Additionally, the terminal can perform preamble transmission by determining a possible PRACH occasion among the PRACH occasions allowed in the selected SSB according to the "PRACH Mask index" restriction indicated within the LTM cell switch command MAC CE.

[0174] Additionally, if the "Timing Advance Command" within the LTM cell switch command MAC CE is not set to FFF (fractional frequency factor), the terminal may apply the indicated "Timing Advance Command" to the PTAG (Primary timing advance group) and (re)start the time alignment timer. That is, the terminal may perform uplink time alignment using the timing advance value indicated in the LTM cell switch command MAC CE, unless the timing advance value indicated in the LTM cell switch command MAC CE is measured by the terminal.

[0175] As another example, if the "Timing Advance Command" within the LTM cell switch command MAC CE is set to FFF and the terminal successfully measures the timing advance, the terminal can apply the measured timing advance to the PTAG and (re)start the time alignment timer.

[0176] Additionally, the terminal may set the configured grant (CG) of the uplink for the LTM cell switch to CG type 1, but may not be limited thereto. If the SSB associated with the transmission configuration indicator (TCI) indicated by the "TCI state ID" field in the LTM cell switch command MAC CE is the same as the SSB associated with the configured uplink grant, the terminal may select the SSB associated with the TCI state indicated by the LTM cell switch command MAC CE and transmit the SSB index to the lower layer. That is, the terminal may determine that the configured uplink grant is valid. On the other hand, if the SSB associated with the TCI indicated by the "TCI state ID" field in the LTM cell switch command MAC CE is not the same as the SSB associated with the configured uplink grant, the terminal may determine that the configured uplink grant is invalid.

[0177] Additionally, when the terminal receives an LTM cell switch command, the terminal's MAC layer may indicate to the lower layer that an LTM cell switch procedure is to occur along with a target configuration ID. Here, the terminal may receive a request from the upper layer for a MAC reset. If the TAC (timing advance command) value within the LTM cell switch command is not FFF, or if the TAC value is FFF but the terminal successfully measures the timing advance to the indicated LTM target cell, the terminal may be deemed to apply the timing advance and perform a RACH-less LTM cell switch operation. That is, if the TAC value is indicated within the LTM cell switch command, or if the terminal successfully measures the TA (timing advance) of the target cell even if the TAC value is not indicated, the terminal may perform a cell switching operation without performing a random access procedure.

[0178] For example, the terminal may use an SSB associated with the TCI state indicated by the "TCI state ID" field within the LTM cell switch command for the configured grant selection of the first uplink transmission of the LTM candidate cell. Here, the LTM candidate cell may be an LTM candidate cell for the RACH-less LTM cell switch described above. The terminal may indicate the TCI state information within the LTM cell switch command to the lower layer, and LTM cell switching may be performed as described above.

[0179] For example, regarding TCI and SSB, LTM TCI information (LTM TCI Info) may be included for each LTM candidate within the LTM configuration, and the parameters for this may be as shown in Table 8 below.

[0180] [Table 8]

[0181]

[0182]

[0183] For example, the TCI state ID indicated within the LTM cell switch command MAC CE may mean an identifier distinguishing one or more candidate TCI states within "ltm-DL-OrJointTCI-StateTO-AddModList", and the candidate TCI states may include the information in Table 9 below.

[0184] [Table 9]

[0185]

[0186]

[0187] Quasi-Colocation (QCL) can refer to cases where channels have similar characteristics. For example, regarding a single antenna port with a hypothetical antenna presumed to be experiencing the same channel, two different antenna ports may have similar channel characteristics in certain situations, even if they are not perfectly identical; in such cases, the two different antenna ports may be in a QCL relationship.

[0188] In wireless communication systems (e.g., NR), four QCL types (A, B, C, D) can be defined based on channel characteristics (e.g., Doppler shift, Doppler spread, average delay, delay spread, spatial Rx parameter). However, they are not limited to these. If a terminal recognizes that two antenna ports in a QCL relationship have similar channel characteristics, it can recognize the channel of the other antenna port through the channel information of one antenna port. In the QCL types, Types A, B, and C are used for channel estimation, while Type D can be used for beam management in beamforming. For example, when a terminal receives a downlink data channel or a control channel through a specific antenna port, the terminal can utilize the channel characteristics of the SSB or CSI-RS (channel state information reference signal) ports in a QCL relationship. Here, the QCL relationship between reference signals can be indicated through the transmission configuration index (TCI) described above.

[0189] FIG. 14 is a diagram showing a candidate cell TCI state activation / deactivation MAC CE applicable to the present disclosure.

[0190] Referring to FIG. 14, the candidate cell ID may be an identifier of an LTM candidate cell to which the corresponding MAC CE can be applied, and may correspond to "ltm-CandidateId". Additionally, in FIG. 14, the Pi field may indicate whether a TCI codepoint indicates multiple TCI states or a single TCI state. For example, if the Pi field value is 1, the i-th TCI codepoint may include both a DL TCI state and an UL TCI state. On the other hand, if the Pi field value is 0, the i-th TCI codepoint may include only a DL / joint TCI state or an UL TCI state. In FIG. 14, the D / U field may indicate whether a TCI state ID within the same octet indicates a DL / joint TCI state or a UL TCI state. When the D / U field value is 1, the TCI state ID may indicate a DL / joint TCI state, and when the D / U field value is 0, the TCI state ID may indicate a UL TCI state.

[0191] Additionally, in FIG. 14, the TCI state ID may indicate a TCI state distinguished by a TCI state ID (TCI-StateId) within "ltm-DL-OrJointTCIStateToAddModList" or a TCI-uplink-state ID (TCI-UL-StateId) within "ltm-UL-TCI-StatesToAddModList". For example, if the D / U field is 1, it indicates a TCI state ID of 7 bits in length, and if the D / U field is 0, the remaining 6 bits excluding the first bit may indicate a TCI-uplink-state ID (TCI-UL-StateId).

[0192] For example, Table 10 below may be a TCI state indicated by a candidate TCI state enable / disable MAC CE. However, Table 10 is merely one example for convenience of explanation and is not limited thereto.

[0193] [Table 10]

[0194]

[0195]

[0196] Next, handover failure behavior can be considered. For example, a wireless communication system may support timer-based handover failure behavior. An RRC connection reset procedure may be used when a handover fails in at least one of the DAPS handover, CHO, and LTM cell switch scenarios. For example, if a DAPS handover fails, the terminal may return to the source cell configuration and resume the source cell connection. Here, if the source link is not released, the terminal may report a DAPS handover failure without RRC connection re-establishment.

[0197] As another example, if the initial attempt to execute a CHO or the HO fails, the terminal can perform cell selection. Here, if the cell selected by the terminal is a CHO candidate cell and the network has set the terminal to attempt a CHO after the handover / CHO failure, the terminal can execute the CHO; otherwise, the RRC re-establishment procedure can be performed.

[0198] As another example, if LTM execution is performed by the LTM cell switch MAC CE but fails, or if the HO fails, the terminal can perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network has set up an LTM attempt after the handover / LTM execution failure, the terminal can attempt a RACH (random access channel) based LTM execution. In other cases, the terminal can perform the RRC re-establishment procedure.

[0199] For example, operations supporting LTM (L1 / L2 layer triggered mobility) can be performed in an intra-CU situation within a wireless communication system. For example, event-based L1 measurement result reporting and conditional LTM can be executed in an intra-CU situation, thereby reducing signaling overhead associated with conventional periodic / non-periodic L1 measurement result reporting. Here, a RACH-less based LTM retry can be performed as a method to recover when the terminal fails an LTM or conditional LTM attempt, and a method for this is described below.

[0200] As described above, if a failure occurs in at least one of (C)HO, DAPS, and LTM, the terminal may attempt at least one of re-establishing RRC through cell reselection and reconnecting with the source cell as a recovery procedure. Alternatively, the terminal may perform at least one of RACH-based CHO and LTM to another candidate cell based on network settings.

[0201] FIG. 15 is a diagram illustrating an LTM failure handling method applicable to the present disclosure. Referring to FIG. 15, a terminal (1510) may receive a MAC CE from a source cell (1520) instructing the execution of LTM to candidate cell 1 (1530). That is, the terminal (1510) may receive an LTM cell switch command MAC CE from the source cell (1520). Here, the MAC CE may include parameters for connecting to candidate cell 1 (1530) (e.g., target candidate cell ID, TAC, RACH related information, TCI-state ID, etc.). When the terminal (1510) receives the LTM cell switch MAC CE (i.e., is instructed to change the LTM cell), the terminal (1510) may activate a timer (T304) to detect an LTM failure. Here, the terminal (1510) may attempt to connect to a target candidate cell (candidate cell 1, 1530) directed to RACH-less (or RACH-based). For example, if the terminal (1510) performs an LTM cell change based on RACH-less, the terminal (1510) may send an RRC reconfiguration complete message to the target candidate cell using a configured grant resource or a dynamic grant resource transmitted by the target candidate cell. For another example, if the terminal (1510) performs an LTM cell change based on RACH, the terminal (1510) may perform a RACH procedure to the target candidate cell using a RACH resource directed in the LTM cell switch command MAC CE, and send an RRC reconfiguration complete message to the target candidate cell using an allocated uplink resource.For example, the terminal (1510) may stop the timer when the RACH procedure for the SpCell is successful, which may mean LTM success. For another example, the terminal (1510) may stop the timer when it receives a signal from the lower layer that the RACH-less procedure is completed, which may mean LTM success. For a specific example, when the terminal (1510) completes a RACH-less based LTM cell change, the terminal (1510) may receive a PDCCH (DL assignment or UL grant) from the target candidate cell instructing a new scheduling scrambled with a C-RNTI (cell-radio network temporary identifier). In the above case, the terminal (1510) may determine that the RACH-less procedure is completed by determining that the first uplink transmission has been successfully performed, which may mean LTM success.

[0202] On the other hand, if the timer expires without the aforementioned operation, the terminal (1510) may determine that the LTM has failed. If an LTM failure occurs, the terminal (1510) may perform cell reselection. Here, an attempt to LTM to another candidate cell is activated based on network settings, and if the cell selected in the cell reselection is one of the LTM candidate cells, the terminal (1510) may attempt a RACH-based LTM to that cell. For example, when the terminal (1510) attempts LTM to another LTM candidate cell, the terminal (1510) may obtain the TAC (timing advance code) of the target cell through the RACH procedure. Therefore, since the terminal (1510) cannot support a RACH-less-based connection to another candidate cell after an LTM failure occurs, a RACH-based LTM may be attempted, but it may not be limited to this.

[0203] For example, in LTM, an early synchronization procedure may be performed to reduce service downtime. Early synchronization may be a task that performs DL / UL synchronization with candidate cells in advance before mobility operations occur at the terminal. DL synchronization can be performed by the terminal detecting the synchronization signal blocks (SSBs) of the candidate cells. Additionally, uplink synchronization can be performed by the terminal sending a preamble to the candidate cells and the candidate cells sending timing advance command (TAC) information to the source cell.

[0204] The terminal needs to receive TAC information of candidate cells from the network to support conditional LTM. That is, the terminal may have received TAC information for one or more candidate cells from the network prior to the occurrence of conditional LTM, but is not limited to this. For example, a source cell may receive TAC information from one or more candidate cells and transmit it to the terminal via MAC CE or RRC messages.

[0205] Based on the above, if the terminal possesses TAC information for one or more candidate cells, the terminal can perform an LTM attempt once more based on a RACH-less procedure even if an LTM failure occurs, and a method for this is described below. Through the above, the terminal can respond to mobility failure actions in a faster manner than a RACH-based LTM cell change even if an LTM failure occurs. Therefore, the terminal can have less service downtime than a RACH-based retry method when an LTM failure occurs.

[0206] FIG. 16 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure. Referring to FIG. 16, a terminal (1610) may perform a first LTM attempt with a source cell (1620) and a candidate cell within the intra-CU. Afterward, the terminal (1610) may also perform a second LTM attempt with a source cell (1620) and a candidate cell within the intra-CU.

[0207] For example, in the LTM preparation stage, the source cell (1620) may set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal via an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 16, the candidate cells within the LTM configuration may include candidate cell 1 (1630) and candidate cell 2 (1640) as other candidate cells within the CU that includes the source cell (1620). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (1650) as other candidate cells within the CU that does not include the source cell.

[0208] Next, pre-synchronization may be performed. The terminal (1610) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal sends a preamble to one or more candidate cell(s) but may not receive a random access response (RAR).

[0209] Next, the terminal (1610) can perform an LTM operation and complete the LTM operation. The terminal (1610) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (1610) can determine the candidate cell that satisfies the set event conditions as the target cell and perform LTM. The terminal (1610) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (1610) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (1610) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (1610) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (1610) performs the RACH-less procedure, the terminal (1610) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0210] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when the C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the RACH-based (or RACH-less-based) procedure is started.

[0211] Here, when the timer expires (i.e., when the RACH procedure fails or the terminal (1610) does not receive a PDCCH instructing a new scheduling from the target cell in the RACH-less procedure), the terminal (1610) can perform a cell selection procedure. The terminal (1610) can attempt LTM once more by network settings. Specifically, if a parameter (attemptLTM-Switch) that allows the terminal (1610) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (1610) can attempt LTM connection to that cell.

[0212] Referring to FIG. 16, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (1610) determines that the condition set for candidate cell 1 (1630) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (1610) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (1610) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 1 (1630) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (1610) can perform a cell re-selection procedure. Here, if the cell selected by the terminal (1610) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 16, the network may instruct the terminal to perform an LTM attempt one more time, and the terminal (1610) may have selected candidate cell 2 (1640) during the cell selection process. Accordingly, the terminal (1610) may attempt a second RACH (or RACH-less) based LTM with candidate cell 2 (1640).

[0213] Here, there was previously a method of performing an LTM attempt with a selected cell based on RACH, and additionally, to reduce latency, a method of performing an LTM attempt with a selected cell based on RACH-less could be considered. For example, the terminal (1610) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. Here, the determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0214] For example, a RACH-less based LTM second attempt can be performed when the terminal (1610) determines that there is TAC information for candidate cell 2 (1640) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (1610) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (1610) determines that there is no TAC information for candidate cell 2 (1640) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (1610) can send an RRC reconfiguration completion message through the RACH procedure.

[0215] As another example, in the step where the terminal (1610) performs and completes the LTM operation, if there is TAC information for candidate cell 2 (1640) within the received candidate cell's TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0216] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0217] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0218] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0219] FIG. 17 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure.

[0220] Referring to FIG. 17, the terminal (1710) can perform a first LTM attempt with a source cell (1720) and a candidate cell within the intra-CU. After that, the terminal (1710) can also perform a second LTM attempt with a source cell (1720) and a candidate cell within the inter-CU.

[0221] For example, in the LTM preparation stage, the source cell (1720) can set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal via an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 17, the candidate cells within the LTM configuration may include candidate cell 1 (1730) and candidate cell 2 (1740) as other candidate cells within the CU that includes the source cell (1720). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (1750) as another candidate cell within the CU that does not include the source cell.

[0222] Next, pre-synchronization may be performed. The terminal (1710) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal may transmit a preamble to one or more candidate cell(s) but may not receive a RAR. Here, one or more candidate cell(s) may derive a timing advance command (TAC) based on the preamble received from the terminal (1710) and transmit it to the source cell (1720).

[0223] Next, the terminal (1710) can perform an LTM operation and complete the LTM operation. The terminal (1710) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (1710) can determine the candidate cell that satisfies the set event conditions as the target cell and perform LTM. The terminal (1710) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (1710) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (1710) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (1710) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (1710) performs the RACH-less procedure, the terminal (1710) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0224] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when the C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the RACH-based (or RACH-less-based) procedure is started.

[0225] Here, when the timer expires (i.e., when the RACH procedure fails or the terminal (1710) does not receive a PDCCH instructing a new scheduling from the target cell in the RACH-less procedure), the terminal (1710) can perform a cell selection procedure. The terminal (1710) can attempt LTM once more by network settings. Specifically, if a parameter (attemptLTM-Switch) that allows the terminal (1710) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (1710) can attempt LTM connection to that cell.

[0226] Referring to FIG. 17, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (1710) determines that the condition set for candidate cell 1 (1730) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (1710) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (1710) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 1 (1730) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (1710) can perform a cell re-selection procedure. If the cell selected by the terminal (1710) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 17, the network instructs the terminal to perform an LTM attempt one more time, and the terminal (1710) may have selected candidate cell 2 (1750) during the cell selection process. Accordingly, the terminal (1710) may attempt a second LTM based on RACH (or RACH-less) with candidate cell 3 (1750).

[0227] Here, there was previously a method of attempting LTM with a selected cell based on RACH, and additionally, to reduce the latency, a method of attempting LTM with a selected cell based on RACH-less could be considered. That is, the terminal (1710) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. Here, the determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0228] For example, a RACH-less based LTM second attempt can be performed when the terminal (1710) determines that there is TAC information for candidate cell 3 (1750) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (1710) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (1710) determines that there is no TAC information for candidate cell 3 (1750) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (1710) can send an RRC reconfiguration completion message through the RACH procedure.

[0229] As another example, in the step where the terminal (1710) performs and completes the LTM operation, if there is TAC information for candidate cell 3 (1750) within the received candidate cell TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0230] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0231] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0232] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0233] FIG. 18 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure. Referring to FIG. 18, a terminal (1810) may perform a first LTM attempt with a candidate cell within the inter-CU with the source cell (1820). Afterward, the terminal (1810) may also perform a second LTM attempt with a candidate cell within the intra-CU with the source cell (1820).

[0234] For example, in the LTM preparation stage, the source cell (1820) may set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal via an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 18, the candidate cells within the LTM configuration may include candidate cell 1 (1830) and candidate cell 2 (1840) as other candidate cells within the CU that includes the source cell (1820). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (1850) as another candidate cell within the CU that does not include the source cell.

[0235] Next, pre-synchronization may be performed. The terminal (1810) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal may send a preamble to one or more candidate cell(s) but may not receive a RAR.

[0236] Next, the terminal (1810) can perform an LTM operation and complete the LTM operation. The terminal (1810) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (1810) can determine the candidate cell that satisfies the set event conditions as the target cell and perform LTM. The terminal (1810) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (1810) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (1810) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (1810) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (1810) performs the RACH-less procedure, the terminal (1810) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0237] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when the C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the RACH-based (or RACH-less-based) procedure is started.

[0238] Here, when the timer expires (i.e., when the RACH procedure fails or the terminal (1810) does not receive a PDCCH instructing a new scheduling from the target cell in the RACH-less procedure), the terminal (1810) can perform a cell selection procedure. The terminal (1810) can attempt LTM once more by network settings. Specifically, if a parameter (attemptLTM-Switch) that allows the terminal (1810) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (1810) can attempt LTM connection to that cell.

[0239] Referring to FIG. 18, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (1810) determines that the condition set for candidate cell 3 (1850) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (1810) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (1810) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 3 (1850) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (1810) can perform a cell re-selection procedure. If the cell selected by the terminal (1810) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 18, the network may instruct the terminal to perform an LTM attempt one more time, and the terminal (1810) may have selected candidate cell 2 (1840) during the cell selection process. Accordingly, the terminal (1810) may attempt a second LTM based on RACH (or RACH-less) with candidate cell 2 (1840).

[0240] Here, there was previously a method of attempting LTM with a selected cell based on RACH, and additionally, to reduce the delay time, a method of attempting LTM with a selected cell based on RACH-less could be considered. That is, the terminal (1810) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. Here, the determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0241] For example, a RACH-less based LTM second attempt can be performed when the terminal (1810) determines that there is TAC information for candidate cell 2 (1840) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (1810) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (1810) determines that there is no TAC information for candidate cell 2 (1840) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (1810) can send an RRC reconfiguration completion message through the RACH procedure.

[0242] As another example, in the step where the terminal (1810) performs and completes the LTM operation, if there is TAC information for candidate cell 2 (1840) within the received candidate cell's TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0243] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0244] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0245] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0246] FIG. 19 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure. Referring to FIG. 19, a terminal (1910) may perform a first LTM attempt with a source cell (1920) and a candidate cell within an inter-CU. Afterward, the terminal (1910) may also perform a second LTM attempt with a source cell (1920) and a candidate cell within an inter-CU.

[0247] For example, in the LTM preparation stage, the source cell (1920) may set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal via an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 19, the candidate cells within the LTM configuration may include candidate cell 1 (1930) and candidate cell 2 (1940) as other candidate cells within the CU that includes the source cell (1920). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (1950) and candidate cell 4 (1960) as other candidate cells within the CU that does not include the source cell.

[0248] Next, pre-synchronization may be performed. The terminal (1910) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal transmits a preamble to one or more candidate cell(s) but may not receive a RAR.

[0249] Next, the terminal (1910) can perform an LTM operation and complete the LTM operation. The terminal (1910) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (1910) can determine the candidate cell that satisfies the set event conditions as the target cell and perform LTM. The terminal (1910) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (1910) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (1910) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (1910) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (1910) performs the RACH-less procedure, the terminal (1910) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0250] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when the C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the RACH-based (or RACH-less-based) procedure is started.

[0251] Here, when the timer expires (i.e., when the RACH procedure fails or the RACH-less procedure does not receive a PDCCH instructing a new scheduling from the target cell), the terminal (1910) can perform a cell selection procedure. The terminal (1910) can attempt LTM once more by network configuration. Specifically, if a parameter (attemptLTM-Switch) that allows the terminal (1910) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (1910) can attempt LTM connection to that cell.

[0252] Referring to FIG. 19, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (1910) determines that the condition set for candidate cell 1 (1930) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (1910) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (1910) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 3 (1950) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (1910) can perform a cell re-selection procedure. If the cell selected by the terminal (1910) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 19, the network may instruct the terminal to perform an LTM attempt one more time, and the terminal (1910) may have selected candidate cell 4 (1960) during the cell selection process. Accordingly, the terminal (1910) may attempt a second RACH (or RACH-less) based LTM with candidate cell 4 (1960).

[0253] Here, there was previously a method of attempting LTM with a selected cell based on RACH, and additionally, to reduce the delay time, a method of attempting LTM with a selected cell based on RACH-less could be considered. That is, the terminal (1910) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. Here, the determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0254] For example, a RACH-less based LTM second attempt can be performed when the terminal (1910) determines that there is TAC information for candidate cell 4 (1960) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (1910) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (1910) determines that there is no TAC information for candidate cell 4 (1960) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (1910) can send an RRC reconfiguration completion message through the RACH procedure.

[0255] As another example, in the step where the terminal (1910) performs and completes the LTM operation, if there is TAC information for candidate cell 4 (1960) within the received candidate cell TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0256] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0257] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0258] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0259] As another example, regarding C-LTM failure, the first LTM attempt can be performed on a candidate cell located within the source cell and inter-CU, and the second LTM attempt can be performed on a candidate cell located within a different CU from the source cell and the candidate cell used in the first LTM attempt.

[0260] Specifically, consider a case where the first LTM attempt is performed on a candidate cell in CU 'A', and it is determined that the first LTM failed due to the expiration of the timer (e.g., T304). In the above case, the terminal is configured to perform the LTM attempt one more time, and a candidate cell in CU 'B' can be selected during the cell selection process. The terminal can perform a second LTM attempt on that cell. Here, as described above, the terminal can perform the LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. The determination of whether the TA is valid can be made based on the TAC information of the candidate cell received by the terminal, as described above.

[0261] FIG. 20 is a diagram illustrating a RACH-less based LTM failure handling method in the event of an LTM failure applicable to the present disclosure.

[0262] Referring to FIG. 20, the terminal (2010) can perform a first LTM attempt with a candidate cell within the inter-CU with the source cell (2020). After that, the terminal (2010) can also perform a second LTM attempt with a candidate cell within the inter-CU with the source cell (2020).

[0263] For example, in the LTM preparation stage, the source cell (2020) may set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal through an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 20, the candidate cells within the LTM configuration may include candidate cell 1 (2030) and candidate cell 2 (2040) as other candidate cells within the CU that includes the source cell (2020). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (2050) and candidate cell 4 (2060) as other candidate cells within the CU that does not include the source cell.

[0264] Next, pre-synchronization may be performed. The terminal (2010) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal may send a preamble to one or more candidate cell(s) but may not receive a RAR.

[0265] Next, the terminal (2010) can perform an LTM operation and complete the LTM operation. The terminal (2010) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (2010) can determine the candidate cell that satisfies the set event conditions as the target cell and perform LTM. The terminal (2010) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (2010) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (2010) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (2010) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (2010) performs the RACH-less procedure, the terminal (2010) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0266] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the LTM cell switch command MAC CE is indicated. As yet another example, the timer to determine whether the LTM operation is successful may be operated from the time when a RACH-based (or RACH-less-based) procedure is started.

[0267] Here, when the timer expires (i.e., when the RACH procedure fails or the terminal (2010) does not receive a PDCCH instructing a new scheduling from the target cell in the RACH-less procedure), the terminal (2010) can perform a cell selection procedure. The terminal (2010) can attempt LTM once more by network settings. Specifically, if a parameter (attemptLTM-Switch) that allows the terminal (2010) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (2010) can attempt LTM connection to that cell.

[0268] Referring to FIG. 20, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (2010) determines that the condition set for candidate cell 1 (2030) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (2010) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (2010) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 3 (2050) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (2010) can perform a cell re-selection procedure. If the cell selected by the terminal (2010) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 20, the network instructs the terminal to perform an LTM attempt one more time, and the terminal (2010) may have selected candidate cell 4 (2040) during the cell selection process. Accordingly, the terminal (2010) can attempt a second LTM based on RACH (or RACH-less) with candidate cell 4 (2040).

[0269] Here, there was previously a method of attempting LTM with a selected cell based on RACH, and additionally, to reduce latency, a method of attempting LTM with a selected cell based on RACH-less could be considered. That is, the terminal (2010) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. The determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0270] For example, a RACH-less based LTM second attempt can be performed when the terminal (2010) determines that there is TAC information for candidate cell 4 (2060) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (2010) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (2010) determines that there is no TAC information for candidate cell 4 (2060) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (2010) can send an RRC reconfiguration completion message through the RACH procedure.

[0271] As another example, in the step where the terminal (2010) performs and completes the LTM operation, if there is TAC information for candidate cell 4 (2060) within the received candidate cell TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0272] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0273] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0274] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0275] FIG. 21 is a diagram illustrating a conditional LTM failure recovery procedure applicable to the present disclosure. Referring to FIG. 21, a terminal (2110) may perform a first LTM attempt with a source cell (2120) and a candidate cell within the intra-CU. Afterward, the terminal (2110) may also perform a second LTM attempt with a source cell (2120) and a candidate cell within the intra-CU.

[0276] For example, in the LTM preparation stage, the source cell (2120) may set the LTM configuration for the terminal based on an L3 measurement report. The LTM configuration may include RRC configuration information for one or more candidate cell(s). The LTM configuration may be set for the terminal through an RRC reconfiguration message. For example, within the RRC reconfiguration message, LTM execution event conditions for one or more candidate cell(s) may be set. Referring to FIG. 21, the candidate cells within the LTM configuration may include candidate cell 1 (2130) and candidate cell 2 (2140) as other candidate cells within the CU that includes the source cell (2120). Additionally, the candidate cells within the LTM configuration may include candidate cell 3 (2150) and candidate cell 4 (2160) as other candidate cells within the CU that does not include the source cell.

[0277] Next, pre-synchronization may be performed. The terminal (2110) may perform downlink and uplink pre-synchronization with one or more candidate cell(s). When performing uplink pre-synchronization, the terminal may send a preamble to one or more candidate cell(s) but may not receive a RAR.

[0278] Next, the terminal (2110) can perform an LTM operation and complete the LTM operation. The terminal (2110) can check the L1 measurement results of the reference signals (e.g., reference signal, SSB, CSI-RS) of one or more candidate cells and check whether the set event conditions are satisfied. The terminal (2110) can determine the candidate cell satisfying the set event conditions as the target cell and perform LTM. The terminal (2110) can perform a RACH-based or RACH-less LTM operation based on whether the TA of the target cell is valid and can transmit an RRC reconstruction message. As a specific example, if the terminal (2110) determines that the TA for the target cell is valid, it can transmit an RRC reconstruction completion message through the configured uplink grant resources or dynamic grant resources obtained from the target cell. As another example, if the terminal (2110) determines that the TA for the target cell is invalid, it can perform a RACH procedure to the target cell through the indicated RACH resources. Here, when performing the RACH procedure, the terminal (2110) may consider the LTM procedure to be completed when it determines that the RACH procedure is completed. On the other hand, when the terminal (2110) performs the RACH-less procedure, the terminal (2110) may consider the LTM procedure to be completed when it receives a PDCCH instructing a new scheduling from the target cell.

[0279] In addition, a timer (e.g., T304, LTM failure timer) may be operated to determine whether the LTM operation is successful. The timer to determine whether the LTM operation is successful may be operated from the time when C-LTM is determined. As another example, the timer to determine whether the LTM operation is successful may be operated from the time when the LTM cell switch command MAC CE is indicated. As yet another example, the timer to determine whether the LTM operation is successful may be operated from the time when a RACH-based (or RACH-less-based) procedure is started.

[0280] Here, when the timer expires (i.e., when the RACH procedure fails or when the terminal (2110) does not receive a PDCCH instructing a new scheduling from the target cell in the RACH-less procedure), the terminal (2110) can perform a cell selection procedure. The terminal (2110) can attempt LTM once more by network settings. Specifically, more specifically, if a parameter (attemptLTM-Switch) that allows the terminal (2110) to perform LTM once more is enabled, and the cell selected in the cell selection procedure described above is an LTM candidate cell, the terminal (2110) can attempt LTM connection to that cell.

[0281] Referring to FIG. 21, the terminal can check whether the L1 measurement result condition of the candidate cell(s) is satisfied according to the conditional LTM setting. In the event evaluation phase, the terminal (2110) determines that the condition set for candidate cell 1 (2130) is satisfied and can attempt a RACH (or RACH-less) based LTM. That is, the terminal (2110) can perform a first LTM attempt. Here, if a RACH-less based LTM is performed, the terminal (2110) can determine that the LTM has failed if it does not receive a PDCCH instructing new scheduling from candidate cell 1 (2130) within a timer (e.g., T304). Here, if the network is configured to allow the LTM attempt to be performed one more time (i.e., attemptLTM-Switch = 'true'), the terminal (2110) can perform a cell re-selection procedure. If the cell selected by the terminal (2110) is an LTM candidate cell, the terminal can perform the LTM attempt one more time. In FIG. 21, the network may instruct the terminal to perform an LTM attempt one more time, and the terminal (2110) may have selected candidate cell 2 (2140) during the cell selection process. Accordingly, the terminal (2110) may attempt a second LTM based on RACH (or RACH-less) with candidate cell 2 (2140).

[0282] Here, there was previously a method of attempting LTM with a selected cell based on RACH, and additionally, to reduce latency, a method of attempting LTM with a selected cell based on RACH-less could be considered. That is, the terminal (2110) can perform an LTM attempt based on RACH or RACH-less depending on whether the TA of the selected cell is valid. Here, the determination of whether the TA is valid can be made based on the TAC information of the candidate cell received at the stage where the terminal performs and completes the LTM operation.

[0283] For example, a RACH-less based LTM second attempt can be performed when the terminal (2110) determines that there is TAC information for candidate cell 2 (2140) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, and that the TA is valid. That is, the terminal (2110) can send an RRC reconfiguration completion message to the cell using the configured grant resource. On the other hand, a RACH-based LTM second attempt can be performed when the terminal (2110) determines that there is no TAC information for candidate cell 2 (2140) within the TAC information of the candidate cell received at the stage of performing and completing the LTM operation, or that the TA is invalid. That is, the terminal (2110) can send an RRC reconfiguration completion message through the RACH procedure.

[0284] As another example, in the step where the terminal (2110) performs and completes the LTM operation, if there is TAC information for candidate cell 2 (2140) within the received candidate cell's TAC information and it is determined that the TA is valid, but the second LTM is attempted with the same cell as the target cell in the first LTM attempt, then an RRC reconstruction completion message can be transmitted through the RACH procedure.

[0285] As described above, the conditional LTM setting is based on the assumption that it is configured during the LTM preparation phase; however, this is not limited thereto, and it is also possible for the network to configure the conditional LTM based on the terminal's L1 measurement results during the phase where the LTM operation is performed and completed, and it is not limited to a specific form.

[0286] In the above-described case, the TAC information of the candidate cell can be transmitted to the source cell through the F1 interface between the CU and the DU (or the Xn interface between the CU and the CU). For example, if the LTM candidate cell in the second LTM attempt is the same cell as in the first LTM attempt, the terminal can perform a RACH-based LTM attempt because the first LTM attempt failed, regardless of whether the TA is valid, as described above.

[0287] In addition, if LTM execution occurs and fails due to the LTM cell switch command MAC CE or the satisfaction of a conditional LTM condition, or if the HO fails, the terminal may perform cell reselection. Here, if the cell selected by the terminal is an LTM candidate cell and the network sets up an LTM attempt after the failure of handover / LTM execution, and if it is determined that the TA of the selected cell is valid, the terminal may perform RACH-less based LTM, and except for the cases described above, may perform an RRC re-establishment procedure.

[0288] FIG. 22 is a flowchart illustrating a RACH-less based LTM retry method following a C-LTM failure applicable to the present disclosure. A recovery procedure following a C-LTM (conditional LTM) failure may be performed. Specifically, a second RACH-less based LTM may be attempted based on the C-LTM. Referring to FIG. 22, the terminal may receive an LTM configuration and a conditional LTM configuration from the network (S2201). Subsequently, the terminal may receive a TAC for one or more candidate cells (S2202). The terminal may send a preamble to one or more candidate cells via a PDCCH obtained from the source cell for uplink pre-synchronization. One or more candidate cells that have received the preamble may derive a TAC based on the received preamble and transmit it to the source cell. The source cell may transmit the TAC received from one or more candidate cells to the terminal via a MAC CE or RRC message. Subsequently, if the LTM condition for a candidate cell is satisfied (S2203), the terminal can perform L1 measurements on one or more candidate cells from the pre-synchronization step and check whether the measurement result satisfies one or more set conditions. The terminal can attempt the first LTM on the cell that satisfies the condition (S2204). Based on the LTM condition for a candidate cell, if the condition for a specific candidate cell is satisfied, the terminal can determine that cell as the target cell and attempt the first LTM procedure. Here, depending on whether the TA for the cell is valid, a RACH-based or RACH-less-based first LTM may be attempted. Subsequently, the LTM failure timer may expire (S2205). Specifically, the terminal can start a timer to determine whether the first LTM attempt failed from the time the C-LTM is determined.As another example, the terminal may start a timer from the time it starts a RACH-based or RACH-less-based procedure. If the terminal fails to successfully complete the RACH procedure or fails to receive a PDCCH instructing new scheduling after transmitting an RRC reconfiguration completion message transmitted through a configured grant resource, the timer may expire. When the timer expires, a procedure to recover from an LTM failure may be initiated. In the procedure to recover from an LTM failure, the terminal may perform cell selection. (S2206) When the LTM failure timer expires, the terminal determines that the first LTM attempt failed and may perform a cell selection procedure to recover from the LTM failure.

[0289] Here, the terminal can check whether a second LTM attempt is active, and whether a second LTM attempt is active can be set by the network (S2207). This is as described above. Here, the terminal can check whether the selected cell is an LTM candidate cell (S2208). If the cell selected by the terminal is an LTM candidate cell, the terminal can check whether the TA of the selected cell is valid (S2209). That is, the terminal can determine in the cell selection step whether the selected cell is an LTM candidate cell and whether the TA (timing alignment) is valid. The TA may be indicated by the network in the TAC (timing advance code) reception step for one or more candidate cells. The terminal can determine whether the TA for the cell is valid based on the TAT (timing advance timer) or the terminal implementation. After that, the terminal may attempt a second LTM based on RACH-less based on whether the TA is valid (S2210). If the second LTM attempt is activated and the cell selected in the cell selection step is an LTM candidate cell and the TA is valid, the terminal may perform a second LTM attempt based on RACH-less. Here, the RACH-less basis may be a method of sending an RRC reconfiguration completion message to the selected cell using a configured grant resource, as described above.

[0290] FIG. 23 is a flowchart illustrating a RACH-less based LTM retry method following LTM failure applicable to the present disclosure.

[0291] A recovery procedure following an LTM failure may be performed. Specifically, a second LTM based on RACH-less may be attempted based on the LTM failure. Referring to FIG. 23, the terminal may receive an LTM configuration and a conditional LTM configuration from the network (S2301). Subsequently, the terminal may receive a TAC for one or more candidate cells (S2302). The terminal may send a preamble to one or more candidate cells via a PDCCH obtained from the source cell for uplink pre-synchronization. One or more candidate cells that have received the preamble may derive a TAC based on the received preamble and transmit it to the source cell. The source cell may transmit the TAC received from one or more candidate cells to the terminal via a MAC CE or RRC message. After that, the terminal can receive an LTM cell switch command MAC CE (S2303). That is, the terminal can receive an LTM cell switch command MAC CE that instructs a cell change to a specific LTM candidate cell. The terminal can attempt a first LTM to the candidate cell indicated in the MAC CE (S2304). That is, the terminal can attempt a cell change to the candidate cell indicated within the LTM cell switch command MAC CE, and can attempt a first LTM based on RACH or RACH-less depending on whether the TA for the cell is valid.

[0292] After that, the LTM failure timer may expire (S2305). Specifically, the terminal may start a timer to determine whether the first LTM attempt failed from the time it receives the LTM cell switch command MAC CE. As another example, the terminal may start the timer from the time it starts a RACH-based or RACH-less-based procedure. The timer may expire if the terminal fails to successfully complete the RACH procedure or fails to receive a PDCCH instructing new scheduling after transmitting an RRC reconfiguration completion message transmitted through the configured grant resource. When the timer expires, a procedure to recover from the LTM failure may be started. In the procedure to recover from the LTM failure, the terminal may perform cell selection (S2306). When the LTM failure timer expires, the terminal determines that the first LTM attempt failed and may perform a cell selection procedure to recover from the LTM failure.

[0293] Here, the terminal can check whether a second LTM attempt is active, and whether a second LTM attempt is active can be set by the network (S2307). This is as described above. Here, the terminal can check whether the selected cell is an LTM candidate cell (S2308). If the cell selected by the terminal is an LTM candidate cell, the terminal can check whether the TA of the selected cell is valid (S2309). That is, the terminal can determine in the cell selection step whether the selected cell is an LTM candidate cell and whether the TA (timing alignment) is valid. The TA may be indicated by the network in the TAC (timing advance code) reception step for one or more candidate cells. The terminal can determine whether the TA for the cell is valid based on the TAT (timing advance timer) or the terminal implementation. After that, the terminal may attempt a second LTM based on RACH-less based on whether the TA is valid (S2310). If the second LTM attempt is activated and the cell selected in the cell selection step is an LTM candidate cell and the TA is valid, the terminal may perform a second LTM attempt based on RACH-less. Here, the RACH-less basis may be a method of sending an RRC reconfiguration completion message to the selected cell using a configured grant resource, as described above.

[0294] FIG. 24 is a flowchart illustrating a RACH-less based LTM retry method following a C-LTM failure applicable to the present disclosure. A recovery procedure following a C-LTM (conditional LTM) failure may be performed. Specifically, a second RACH-less based LTM may be attempted based on the C-LTM. Referring to FIG. 24, a terminal may receive an LTM configuration and a conditional LTM configuration from a network (S2401). Subsequently, the terminal may receive a TAC for one or more candidate cells (S2402). The terminal may send a preamble to one or more candidate cells via a PDCCH obtained from a source cell for uplink pre-synchronization. One or more candidate cells that have received the preamble may derive a TAC based on the received preamble and transmit it to the source cell. The source cell may transmit the TAC received from one or more candidate cells to the terminal via a MAC CE or RRC message. Subsequently, if the LTM condition for a candidate cell is satisfied (S2403), the terminal can perform L1 measurements on one or more candidate cells from the pre-synchronization step and check whether the measurement result satisfies one or more set conditions. The terminal can attempt the first LTM on the cell that satisfies the condition (S2404). Based on the LTM condition for a candidate cell, if the condition for a specific candidate cell is satisfied, the terminal can determine that cell as the target cell and attempt the first LTM procedure. Here, depending on whether the TA for the cell is valid, a RACH-based or RACH-less-based first LTM may be attempted. Subsequently, the LTM failure timer may expire (S2405). Specifically, the terminal can start a timer to determine whether the first LTM attempt failed from the time the C-LTM is determined.As another example, the terminal may start a timer from the point at which it initiates a RACH-based or RACH-less-based procedure. The timer may expire if the terminal fails to successfully complete the RACH procedure or fails to receive a PDCCH instructing new scheduling after transmitting an RRC reconfiguration completion message sent via a configured grant resource. When the timer expires, a procedure to recover from an LTM failure may be initiated. In the procedure to recover from an LTM failure, the terminal may perform cell selection (S2406). When the LTM failure timer expires, the terminal determines that the first LTM attempt has failed and may perform a cell selection procedure to recover from the LTM failure. Here, if the cell selected by the terminal in the cell selection procedure is the same cell as the cell used for the first LTM attempt (2407), the terminal may perform a second RACH-based LTM attempt (S2412).

[0295] The terminal can check whether the second LTM attempt is active, and whether the second LTM attempt is active can be set by the network (S2408). Here, if the second LTM attempt is not active by the network, the terminal can perform the RRC re-establishment procedure to the selected cell (S2413).

[0296] If a second LTM attempt is active, the terminal can check whether the selected cell is an LTM candidate cell (S2409). Here, if the cell selected by the terminal is not an LTM candidate cell, the terminal can perform an RRC re-establishment procedure with the selected cell (S2413). On the other hand, if the cell selected by the terminal is an LTM candidate cell, the terminal can check whether the TA of the selected cell is valid (S2410). That is, the terminal can determine whether the selected cell is an LTM candidate cell and whether the TA (timing alignment) is valid during the cell selection step. The TA may be indicated by the network during the TAC (timing advance code) reception step for one or more candidate cells. The terminal can determine whether the TA for the cell is valid based on the TAT (timing advance timer) or the terminal implementation. Subsequently, the terminal may attempt a second LTM based on RACH-less based on whether the TA is valid (S2411). If the second LTM attempt is activated, the cell selected in the cell selection step is an LTM candidate cell, and the TA is valid, the terminal may perform a second LTM based on RACH-less based. Here, RACH-less based may be a method of sending an RRC reconfiguration completion message to the selected cell using the configured grant resource. On the other hand, if the TA is invalid, the terminal may attempt a second LTM based on RACH (S2412).

[0297] FIG. 25 is a flowchart illustrating a RACH-less based LTM retry method following an LTM failure applicable to the present disclosure. A recovery procedure following an LTM failure may be performed. Specifically, a second RACH-less based LTM may be attempted based on the LTM. Referring to FIG. 24, the terminal may receive an LTM configuration and a conditional LTM configuration from the network (S2501). Subsequently, the terminal may receive a TAC for one or more candidate cells (S2502). The terminal may send a preamble to one or more candidate cells via a PDCCH obtained from the source cell for uplink pre-synchronization. One or more candidate cells that have received the preamble may derive a TAC based on the received preamble and transmit it to the source cell. The source cell may transmit the TAC received from one or more candidate cells to the terminal via a MAC CE or RRC message. After that, the terminal can receive an LTM cell switch command MAC CE (S2503). That is, the terminal can receive an LTM cell switch command MAC CE that instructs a cell change to a specific LTM candidate cell. The terminal can attempt a first LTM to the candidate cell indicated in the MAC CE (S2504). That is, the terminal can attempt a cell change to the candidate cell indicated within the LTM cell switch command MAC CE, and can attempt a first LTM based on RACH or RACH-less depending on whether the TA for the cell is valid.

[0298] After that, the LTM failure timer may expire (S2505). Specifically, the terminal may start a timer to determine whether the first LTM attempt failed from the time it receives the LTM cell switch command MAC CE. As another example, the terminal may start the timer from the time it starts a RACH-based or RACH-less-based procedure. The timer may expire if the terminal fails to successfully complete the RACH procedure or fails to receive a PDCCH instructing new scheduling after transmitting an RRC reconfiguration completion message transmitted through the configured grant resource. When the timer expires, a procedure to recover from the LTM failure may be started. In the procedure to recover from the LTM failure, the terminal may perform cell selection (S2506). When the LTM failure timer expires, the terminal determines that the first LTM attempt failed and may perform a cell selection procedure to recover from the LTM failure. Here, if the cell selected by the terminal in the cell selection procedure is the same cell as the cell that attempted the first LTM (2507), the terminal may perform a second LTM attempt based on RACH (S2512).

[0299] The terminal can check whether the second LTM attempt is active, and whether the second LTM attempt is active can be set by the network (S2508). Here, if the second LTM attempt is not active by the network, the terminal can perform the RRC re-establishment procedure to the selected cell (S2513).

[0300] If a second LTM attempt is active, the terminal can check whether the selected cell is an LTM candidate cell (S2509). Here, if the cell selected by the terminal is not an LTM candidate cell, the terminal can perform an RRC re-establishment procedure with the selected cell (S2513). On the other hand, if the cell selected by the terminal is an LTM candidate cell, the terminal can check whether the TA of the selected cell is valid (S2510). That is, the terminal can determine whether the selected cell is an LTM candidate cell and whether the TA (timing alignment) is valid during the cell selection step. The TA may be indicated by the network during the TAC (timing advance code) reception step for one or more candidate cells. The terminal can determine whether the TA for the cell is valid based on the TAT (timing advance timer) or the terminal implementation. Subsequently, the terminal may attempt a second LTM based on RACH-less based on whether the TA is valid (S2511). If the second LTM attempt is activated, the cell selected in the cell selection step is an LTM candidate cell, and the TA is valid, the terminal may perform a second LTM based on RACH-less based. Here, the RACH-less based method may be a method of sending an RRC reconfiguration completion message to the selected cell using the configured grant resource. On the other hand, if the TA is invalid, the terminal may attempt a second LTM based on RACH (S2512).

[0301] FIG. 26 is a flowchart illustrating the operation method of a wireless user device to which the present disclosure applies.

[0302] Referring to FIG. 26, a wireless user device can obtain LTM configuration information based on LTM (L1 / L2 layer triggered mobility) from a source cell (S2610). Then, the wireless user device can perform uplink / downlink pre-synchronization with one or more candidate cells (S2620). Then, the wireless user device can perform a first LTM attempt (S2630), and if the first LTM attempt fails, the wireless user device can perform a second LTM attempt (S2640). Here, the LTM configuration information may include information about one or more candidate cells and event condition information for performing LTM. For example, the wireless user device can obtain a reference signal from one or more candidate cells and perform a measurement, and if the event condition is satisfied based on the measurement result, it can perform a first LTM attempt.

[0303] As another example, when a wireless user device receives an LTM cell switch command MAC CE (medium access control element), it can perform a first LTM attempt based on the LTM cell switch command MAC CE.

[0304] Additionally, the wireless user device may obtain a timing advance command (TAC) for each of one or more candidate cells based on uplink / downlink pre-synchronization for one or more candidate cells. If the TA of the target cell performing the first LTM is valid based on the TAC for each of one or more candidate cells, the wireless user device may perform a first LTM attempt by transmitting an RRC reconstruction message to the target cell. Additionally, if the TA of the target cell performing the first LTM is invalid based on the TAC for each of one or more candidate cells, the wireless user device may perform a first LTM attempt by performing a random access channel (RACH) procedure to the target cell. Here, the first LTM attempt may be determined to fail based on the timer expiration. Additionally, if the first LTM attempt fails, a second LTM attempt is configured on the wireless user device, and if the cell selected by the wireless user device based on the failure of the first LTM attempt is an LTM candidate cell, the second LTM attempt may be performed. Here, if the TA of the LTM candidate cell selected by the wireless user device is valid, the wireless user device can perform a second LTM attempt by transmitting an RRC reconstruction message to the LTM candidate cell, and if the TA of the LTM candidate cell selected by the wireless user device is invalid, the wireless user device can perform a second LTM attempt by performing a RACH procedure to the LTM candidate cell. Additionally, if the LTM candidate cell selected by the wireless user device is the same as the cell that performed the first LTM attempt, the wireless user device can perform a second LTM attempt by performing a RACH procedure with the LTM candidate cell.

[0305] FIG. 27 is a drawing showing a device configuration to which the present disclosure can be applied.

[0306] Referring to FIG. 27, the first device (2700) and the second device (2750) can communicate with each other. In this case, for example, the first device (2700) may be a base station device and the second device (2750) may be a terminal device. In another example, both the first device (2700) and the second device (2750) may be terminal devices. In yet another example, the first device (2700) and the second device (2750) may be satellite IAB nodes. That is, the first device (2700) and the second device (2750) may be devices that communicate with each other based on NR-based communication and are not limited to a specific form.

[0307] The first device (2700) may include a processor (2720), an antenna unit (2712), a transceiver (2714), and a memory (2716). The processor (2720) performs baseband-related signal processing and may include an upper layer processing unit (2727) and a physical layer processing unit (2740). The upper layer processing unit (2727) may process operations of the MAC (Medium Access Control) layer, the RRC (Radio Resource Control) layer, or higher upper layers. The physical layer processing unit (2740) may process operations of the physical (PHY) layer (e.g., uplink reception signal processing, downlink transmission signal processing). In addition to performing baseband-related signal processing, the processor (2720) may also control the overall operation of the first device (2700). The antenna section (2712) may include one or more physical antennas, and if it includes multiple antennas, it may support MIMO (Multiple Input Multiple Output) transmission and reception. Additionally, it may support beamforming. The memory (2716) may store information processed by the processor (2720), software related to the operation of the first device (2700), operating system, application, etc., and may include components such as a buffer. The processor (2720) of the first device (2700) may be configured to implement the operation of the first device in the embodiments described in the present invention.

[0308] The second device (2750) may include a processor (2770), an antenna unit (2762), a transceiver (2764), and a memory (2766). For example, in the present invention, the second device (2750) may communicate with the first device (2700). The processor (2770) performs baseband-related signal processing and may include an upper layer processing unit (2780) and a physical layer processing unit (2790). The upper layer processing unit (2780) may process operations of the MAC layer, RRC layer, or higher upper layers. The physical layer processing unit (2790) may process operations of the PHY layer (e.g., downlink reception signal processing, uplink transmission signal processing, sidelink signal processing). In addition to performing baseband-related signal processing, the processor (2770) may also control the overall operation of the second device (2750). The antenna section (2762) may include one or more physical antennas, and if it includes multiple antennas, it may support MIMO transmission and reception. Additionally, it may support beamforming. The memory (2766) may store information processed by the processor (2770), software related to the operation of the second device (2750), operating systems, applications, etc., and may include components such as buffers. The second device (2750) according to an example of the present invention may be associated with a vehicle. For example, the second device (2750) may be integrated into the vehicle, located in the vehicle, or located on the vehicle. Additionally, the second device (2750) according to the present invention may be the vehicle itself. Furthermore, the second device (2750) according to the present invention may be at least one of a wearable terminal, an AV / VR, an IoT terminal, a robot terminal, or a public safety terminal.The terminal device (2750) to which the present invention is applicable may include any type of communication device that supports interactive services utilizing sidelinks for services such as internet access, service execution, navigation, real-time information, autonomous driving, safety and risk diagnosis. Additionally, it may include any type of communication device that acts as an AR / VR device capable of sidelink operation or a sensor to perform relay operations.

[0309] Here, the vehicle / terminal to which the present invention is applied may include an autonomous vehicle / terminal, a semi-autonomous vehicle / terminal, a non-autonomous vehicle / terminal, etc. Meanwhile, although the second device (2750) according to one example of the present invention is described as being associated with a vehicle, one or more of the UEs may not be associated with a vehicle. This is an example, and the application of the present invention should not be interpreted as being limited to the example described. In addition, the second device (2750) according to one example of the present invention may include various types of communication devices capable of performing cooperation to support interactive services utilizing sidelinks. That is, the second device (2750) may be utilized not only when it directly supports interactive services utilizing sidelinks, but also as a cooperation device to support interactive services utilizing sidelinks.

[0310] Here, for example, a terminal device (second device, 2750) can obtain LTM configuration information based on LTM (L1 / L2 layer triggered mobility) from a source cell. Then, the terminal device (2750) can perform uplink / downlink pre-synchronization with one or more candidate cells. Then, the terminal device (2750) can perform a first LTM attempt, and if the first LTM attempt fails, the terminal device (2750) can perform a second LTM attempt. Here, the LTM configuration information may include information about one or more candidate cells and event condition information for performing LTM. For example, the terminal device (2750) can obtain a reference signal from one or more candidate cells and perform a measurement, and if the event condition is satisfied based on the measurement result, it can perform a first LTM attempt.

[0311] As another example, when the terminal device (2750) receives an LTM cell switch command MAC CE (medium access control element), it can perform a first LTM attempt based on the LTM cell switch command MAC CE.

[0312] Additionally, the terminal device (2750) may obtain a timing advance command (TAC) for each of one or more candidate cells based on uplink / downlink pre-synchronization for one or more candidate cells. If the TA of the target cell performing the first LTM is valid based on the TAC for each of one or more candidate cells, the terminal device (2750) may perform the first LTM attempt by transmitting an RRC reconstruction message to the target cell. Additionally, if the TA of the target cell performing the first LTM is invalid based on the TAC for each of one or more candidate cells, the terminal device (2750) may perform the first LTM attempt by performing a random access channel (RACH) procedure to the target cell. Here, the first LTM attempt may be determined to fail based on the timer expiration. Additionally, if the first LTM attempt fails, a second LTM attempt is configured in the terminal device (2750), and if the cell selected by the terminal device (2750) based on the failure of the first LTM attempt is an LTM candidate cell, the second LTM attempt may be performed. Here, if the TA of the LTM candidate cell selected by the terminal device (2750) is valid, an RRC reconstruction message is transmitted to the LTM candidate cell to perform a second LTM attempt, and if the TA of the LTM candidate cell selected by the terminal device (2750) is not valid, a RACH procedure is performed to the LTM candidate cell to perform a second LTM attempt. Additionally, if the LTM candidate cell selected by the terminal device (2750) is the same as the cell that performed the first LTM attempt, the terminal device (2750) can perform a RACH procedure with the LTM candidate cell to perform a second LTM attempt.

[0313] In addition, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of implementation by hardware, it may be implemented by one or more ASICs (Application Specific Integrated Circuits), DSPs (Digital Signal Processors), DSPDs (Digital Signal Processing Devices), PLDs (Programmable Logic Devices), FPGAs (Field Programmable Gate Arrays), general processors, controllers, microcontrollers, microprocessors, etc.

[0314] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating system, application, firmware, program, etc.) that enable an operation according to a method of various embodiments to be executed on a device or computer, and a non-transitory computer-readable medium on which such software or instructions, etc. are stored and executable on a device or computer.

[0315] The various embodiments of the present disclosure are not intended to list all possible combinations but to describe representative aspects of the present disclosure, and the matters described in the various embodiments may be applied independently or in combination of two or more.

[0316]

[0317] The above-mentioned matters may also be applied to other systems.

Claims

1. In a wireless user device, Wireless transceiver; One or more processors; and A memory that stores instructions for the wireless device when executed by one or more of the above processes, The operation of the above wireless user device is: LTM configuration information is obtained from the source cell based on LTM (L1 / L2 layer triggered mobility), and The wireless user device performs uplink / downlink pre-synchronization with the one or more candidate cells, and The above wireless user device performs a first LTM attempt, and A wireless user device that performs a second LTM attempt if the first LTM attempt fails.

2. In Paragraph 1, A wireless user device wherein the above LTM configuration information includes information on one or more candidate cells and event condition information for performing LTM.

3. In Paragraph 2, A wireless user device that acquires a reference signal from one or more candidate cells and performs a measurement, and performs the first LTM attempt if an event condition is satisfied based on the measurement result.

4. In Paragraph 2, A wireless user device that, upon receiving an LTM cell switch command MAC CE (medium access control element), performs the first LTM attempt based on the LTM cell switch command MAC CE.

5. In Paragraph 1, A wireless user device that acquires a timing advance command (TAC) for each of the one or more candidate cells based on uplink / downlink pre-synchronization for the one or more candidate cells.

6. In Paragraph 5, A wireless user device that performs the first LTM attempt by transmitting the RRC reconstruction message to the target cell if the TA of the target cell performing the first LTM is valid based on the TAC for each of the one or more candidate cells.

7. In Paragraph 5, A wireless user device that performs the first LTM attempt by performing a RACH (random access channel) procedure to the target cell if the TA of the target cell performing the first LTM is invalid based on the TAC for each of the one or more candidate cells.

8. In Paragraph 1, A wireless user device in which the above-mentioned first LTM attempt is determined to fail based on timer expiration.

9. In Paragraph 1, A wireless user device that, if the first LTM attempt fails, configures a second LTM attempt on the wireless user device, and performs the second LTM attempt if the cell selected by the wireless user device based on the failure of the first LTM attempt is an LTM candidate cell.

10. In Paragraph 9, If the TA of the LTM candidate cell selected by the wireless user device is valid, the second LTM attempt is performed by transmitting an RRC reconstruction message to the LTM candidate cell, and A wireless user device that performs a RACH procedure to the LTM candidate cell to perform the second LTM attempt if the TA of the LTM candidate cell selected by the wireless user device is invalid.

11. In Paragraph 9, A wireless user device that, when the LTM candidate cell selected by the wireless user device is the same as the cell that performed the first LTM attempt, performs the RACH procedure with the LTM candidate cell to perform the second LTM attempt.

12. In a method of operating a wireless user device, A step of obtaining LTM configuration information based on LTM (L1 / L2 layer triggered mobility) from a source cell; The step of the wireless user device performing uplink / downlink pre-synchronization with the one or more candidate cells; The step of the wireless user device performing a first LTM attempt; and A method of operation comprising the step of performing a second LTM attempt if the first LTM attempt fails.

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