Method and device for supporting LTM operation in wireless communication system

Abstract

An operation of a wireless device may comprise: acquiring, from a network, an L1 / L2 layer triggered mobility (LTM) configuration including information on LTM candidate cells; acquiring a reference signal from each of the LTM candidate cells and performing a measurement report; acquiring, on the basis of the measurement report, a cell switch command medium access control control element (MAC CE) indicating cell switching to a first cell among the LTM candidate cells; and performing serving cell switching to the first cell by recognizing an intra central unit (CU) LTM operation and an inter CU LTM operation.

Description

Method and device for supporting LTM operation in a wireless communication system

[0001] The present invention relates to a method and device for supporting LTM (L1 / L2 layer triggered mobility) operation in a wireless communication system. Specifically, the present invention relates to a method for supporting intra-CU (central unit) LTM and inter-CU LTM operation.

[0002]

[0003] The International Telecommunication Union (ITU) is developing the International Mobile Telecommunication (IMT) framework and standards, and is currently discussing fifth-generation (5G) communications through a program called "IMT for 2020 and beyond."

[0004] To meet the requirements presented in "IMT for 2020 and beyond," the 3rd Generation Partnership Project (3GPP) NR (New Radio) system is being discussed to support various numerologies based on time-frequency resource units, taking into account various scenarios, service requirements, and potential system compatibility.

[0005] In wireless communication systems, mobility support measures may be required, and measures for this purpose are described below.

[0006]

[0007] The present invention can provide a method and device for supporting LTM operation in a wireless communication system.

[0008] The present invention can provide a method and device for supporting LTM operation in an environment where one or more CUs and one or more DUs (distributed units) coexist in a wireless communication system.

[0009] The present invention can provide a method and device for indicating whether to change a CU based on intra CU LTM and inter CU LTM operations in a wireless communication system.

[0010] The present invention can provide a method and device for applying a CU identifier based on intra CU LTM and inter CU LTM operations in a wireless communication system.

[0011] The present invention can provide a method and device for utilizing a medium access control element (MAC CE) including LTM-related information in a wireless communication system.

[0012]

[0013] In one embodiment, a wireless device may include a memory that stores instructions for the wireless device when executed by a wireless transceiver, one or more processors, and one or more processes. Wherein, an operation of the wireless device may include: obtaining an LTM configuration including information on an LTM (L1 / L2 layer triggered mobility) candidate cell from a network, obtaining a reference signal from each of the LTM candidate cells to perform a measurement report, obtaining a cell switch command MAC CE (medium access control control element) that instructs cell switching to a first cell among the LTM candidate cells based on the measurement report, and recognizing an intra-CU (central unit) LTM operation and an inter-CU LTM operation to perform serving cell switching to the first cell.

[0014] In addition, according to one embodiment, each piece of information about an LTM candidate cell included in an LTM configuration includes CU identifier information of each LTM candidate cell, and the terminal stores a CU identifier variable for a serving cell based on the LTM configuration, and after recognizing a CU identifier of a first cell, if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are the same, performs an intra CU LTM operation, and if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are different, performs an inter CU LTM operation.

[0015] Additionally, according to one embodiment, the LTM configuration includes CU identifier information for a serving cell of the terminal, and the terminal stores a CU identifier variable for the serving cell based on the CU identifier information for the serving cell, receives a cell switch command MAC CE including a CU identifier of a first cell to recognize the CU identifier of the first cell, and performs an intra-CU LTM operation when the CU identifier of the first cell and the stored CU identifier variable are the same, and performs an inter-CU LTM operation when the CU identifier of the first cell and the stored CU identifier variable are different.

[0016] Additionally, according to one embodiment, the cell switch command MAC CE may include a first indicator, such that if the first indicator is a first value, intra CU LTM operation may be performed, and if the first indicator is a second value, inter CU LTM operation may be performed.

[0017] Additionally, according to one embodiment, when an intra CU LTM operation is performed, the terminal may perform a MAC reset operation after changing the serving cell to the first cell, and when an inter CU LTM operation is performed, the terminal may perform a MAC reset, security key update, and PDCP (packet data convergence protocol) re-establishment operations after changing the serving cell to the first cell.

[0018] Additionally, according to one embodiment, the terminal may perform a RACH (random access channel)-less procedure if TA (timing advance) is valid after changing the serving cell to the first cell, and may perform a RACH procedure if TA is invalid.

[0019]

[0020] According to the present disclosure, there is an effect of providing a method for supporting LTM operation in a wireless communication system.

[0021] According to the present disclosure, there is provided a method for supporting LTM operation in an environment where one or more CUs and one or more DUs (distributed units) coexist in a wireless communication system.

[0022] According to the present disclosure, there is an effect of providing a method for indicating whether to change a CU based on intra CU LTM and inter CU LTM operations in a wireless communication system.

[0023] According to the present disclosure, there is provided an effect of providing a method for applying a CU identifier based on intra CU LTM and inter CU LTM operations in a wireless communication system.

[0024] According to the present disclosure, there is an effect of providing a method for utilizing MAC CE including LTM-related information in a wireless communication system.

[0025]

[0026] FIG. 1 is a drawing for explaining an NR frame structure to which the present disclosure can be applied.

[0027] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0028] FIG. 3 is a diagram showing cell level mobility and beam level mobility applicable to the present disclosure.

[0029] Figure 4 is a diagram illustrating an LTM scenario applicable to the present disclosure.

[0030] FIG. 5 is a diagram showing signaling and setup information in the LTM preparation stage applicable to the present disclosure.

[0031] FIG. 6 is a diagram illustrating signaling and setup procedures for an initial synchronization step applicable to the present disclosure.

[0032] FIG. 7 is a diagram illustrating a method for a terminal applicable to the present disclosure to perform uplink synchronization.

[0033] FIG. 8 is a diagram illustrating signaling for an LTM cell change execution procedure applicable to the present disclosure.

[0034] FIG. 9 is a diagram showing a cell change MAC CE applicable to the present disclosure.

[0035] FIG. 10 is a diagram illustrating signaling of an LTM cell change completion step applicable to the present disclosure.

[0036] FIG. 11 is a diagram illustrating an inter-CU LTM operation scenario applicable to the present disclosure.

[0037] FIG. 12 is a diagram illustrating a scenario in which LTM is performed in a complex manner based on intra CUs and inter CUs applicable to the present disclosure.

[0038] FIG. 13 is a diagram illustrating a method for signaling LTM settings from a network to a terminal to distinguish one or more gNB-CUs applicable to the present disclosure.

[0039] FIG. 14 is a diagram illustrating an operation of comparing CU IDs in an LTM cell switch operation applicable to the present disclosure.

[0040] FIG. 15 is a diagram illustrating a method for performing an LTM operation in an environment in which multiple gNB CUs are present, applicable to the present disclosure.

[0041] FIG. 16 is a diagram illustrating a method for performing an inter CU LTM operation applicable to the present disclosure.

[0042] FIG. 17 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0043] FIG. 18 is a diagram illustrating an operation of comparing CU IDs in an LTM cell switch operation applicable to the present disclosure.

[0044] FIG. 19 is a diagram showing a cell switch command MAC CE applicable to the present disclosure.

[0045] FIG. 20 is a diagram illustrating a method for performing an LTM operation in an environment in which multiple gNB CUs are present, applicable to the present disclosure.

[0046] FIG. 21 is a diagram illustrating a method for performing an inter CU LTM operation applicable to the present disclosure.

[0047] FIG. 22 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0048] FIG. 23 is a diagram illustrating a method of indicating intra CU and inter CU through MAC CE in an LTM cell switch operation applicable to the present disclosure.

[0049] FIG. 24 is a diagram showing a cell switch command MAC CE applicable to the present disclosure.

[0050] FIG. 25 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0051] Figure 26 is a flowchart for LTM operations applicable to the present disclosure.

[0052] Figure 27 is a drawing showing a device configuration applicable to the present disclosure.

[0053]

[0054] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0055] In describing embodiments of the present disclosure, detailed descriptions of known configurations or functions will be omitted if they are deemed to obscure the gist of the present disclosure. Furthermore, portions of the drawings that are irrelevant to the description of the present disclosure have been omitted, and similar portions are designated with similar reference numerals.

[0056] In the present disclosure, when a component is said to be "connected," "coupled," or "connected" to 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 said to "include" or "have" another component, unless otherwise specifically stated, this does not exclude the other component, but rather implies that the other component may be included.

[0057] In this disclosure, terms such as first, second, etc. are used solely to distinguish one component from another, and do not limit the order or importance of components unless specifically stated otherwise. Accordingly, within the scope of this disclosure, a first component in one embodiment may be referred to as a second component in another embodiment, and similarly, a second component in one embodiment may be referred to as a first component in another embodiment.

[0058] In this disclosure, distinct components are used to clearly illustrate their respective characteristics, and do not necessarily imply that the components are separated. That is, multiple components may be integrated into a single hardware or software unit, or a single component may be distributed into multiple hardware or software units. Therefore, even if not specifically mentioned, such integrated or distributed embodiments are also included within the scope of this disclosure.

[0059] In the present disclosure, the components described in various embodiments are not necessarily essential components, and some may be optional components. Therefore, embodiments comprising a subset of the components described in one embodiment are also within the scope of the present disclosure. Furthermore, embodiments including other components in addition to the components described in various embodiments are also within the scope of the present disclosure.

[0060] The present disclosure describes a wireless communication network, and operations performed in the wireless communication network may be performed in a process of controlling the network and transmitting or receiving a signal in a system (e.g., a base station) that manages the wireless communication network, or in a process of transmitting or receiving a signal in a terminal connected to the wireless network.

[0061] It is self-evident that various operations performed for communication with terminals 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. 'Base station (BS)' can be replaced by terms such as fixed station, Node B, eNodeB (eNB), ng-eNB, gNodeB (gNB), and access point (AP). In addition, 'terminal' can be replaced by terms such as UE (User Equipment), MS (Mobile Station), MSS (Mobile Subscriber Station), SS (Subscriber Station), and non-AP station (non-AP STA).

[0062] In the present disclosure, transmitting or receiving a channel means transmitting or receiving information or a signal through the channel. For example, transmitting a control channel means transmitting control information or a signal through the control channel. Similarly, transmitting a data channel means transmitting data information or a signal through the data channel.

[0063] 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; however, the scope of the present disclosure is not limited by this term.

[0064] NR systems support a variety of subcarrier spacings (SCS) to accommodate diverse scenarios, service requirements, and potential system compatibility. Furthermore, NR systems can support the transmission of physical signals / channels across multiple beams to overcome challenging channel conditions, such as high path loss, phase noise, and frequency offsets that occur at high carrier frequencies. This enables NR systems to 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 (URLLC).

[0065] Hereinafter, 5G mobile communication technology can be defined to include not only the NR system, but also the existing LTE-A (Long Term Evolution-Advanced) system and LTE (Long Term Evolution) system. 5G mobile communication may include technology that operates in consideration of backward compatibility with previous systems as well as the newly defined NR system. Therefore, the 5G mobile communication below may include technology that operates based on the NR system and technology that operates based on previous systems (e.g., LTE-A, LTE), and is not limited to a specific system.

[0066] First, we would like to briefly explain the physical resource structure of the NR system to which the present invention is applied.

[0067] FIG. 1 is a drawing for explaining an NR frame structure to which the present disclosure can be applied.

[0068] In NR, the basic unit of time domain is It can be, , and N can be 4096. Meanwhile, in LTE, the basic unit of the time domain is It can be, And, =2048. The constant for the multiplication relationship between the NR time base unit and the LTE time base unit is k= can be defined as

[0069] Referring to Figure 1, the time structure of a frame for downlink / uplink (DL / UL) transmission is can have. Here, one frame is It consists of 10 subframes corresponding to time. The number of consecutive OFDM symbols in each subframe is = It can be. In addition, each frame is divided into two half frames of the same size, half frame 1 can be composed of sub frames 0-4, and half frame 2 can be composed of sub frames 5-9.

[0070] 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, based on the following mathematical expression 1.

[0071] [Mathematical Formula 1]

[0072]

[0073] Here, It may be a TA offset value that occurs due to differences in duplex mode, etc. In FDD (Frequency Division Duplex), has a value of 0, but in TDD (Time Division Duplex), it takes into account 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 13.030μs. Also, at FR2 (Frequency Range 2), which is a millimeter wave (mmWave) frequency, is 13792 It could be. At this time, 13792 is 7.020 μs.

[0074] FIG. 2 is a diagram showing an NR resource structure to which the present disclosure can be applied.

[0075] 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 each subcarrier spacing. Uplink and downlink transmission and reception can be performed based on the corresponding resource grid.

[0076] In the frequency domain, one Resource Block (RB) consists of 12 REs, and each of the 12 REs can be configured with an index (nPRB) for one RB. 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 in the following mathematical expression 2. Here, represents the number of subcarriers per RB, and k represents the subcarrier index.

[0077] [Equation 2]

[0078]

[0079]

[0080] Different numerologies can be configured to meet the diverse services and requirements of NR systems. For example, while LTE / LTE-A systems can support a single subcarrier spacing (SCS), NR systems can support multiple SCSs.

[0081] A new numerology for NR systems supporting multiple SCSs can operate in frequency ranges or carriers such as below 3GHz, 3GHz-6GHz, 6GHZ-52.6GHz or above 52.6GHz to address the issue of not being able to use wide bandwidth in frequency ranges or carriers such as 700MHz or 2GHz.

[0082] Table 1 below shows examples of numerologies supported by the NR system.

[0083] [Table 1]

[0084]

[0085] Referring to Table 1 above, the numeral can be defined based on the subcarrier spacing (SCS), cyclic prefix (CP) length, and number of OFDM symbols per slot used in the Orthogonal Frequency Division Multiplexing (OFDM) system. The above 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.

[0086] 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 can be applied. For other numerology indices, only normal CP can be applied.

[0087] 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 OFDM symbols, which is 14 by default. Furthermore, unlike slots, a subframe has an absolute time length equivalent to 1 ms in an NR system and can be used as a reference time for the length of other time intervals. Here, for coexistence or backward compatibility between LTE and NR systems, a time interval similar to an LTE subframe may be required in the NR standard.

[0088] For example, in LTE, data can be transmitted based on a unit of time called a Transmission Time Interval (TTI), which can be set to one or more subframes. Here, one subframe can be set to 1ms and can contain 14 OFDM symbols (or 12 OFDM symbols).

[0089] In addition, a non-slot can be defined in NR. A non-slot can mean a slot having a number that is at least one symbol smaller than a normal slot. For example, in the case of providing low latency such as URLLC service, latency can be reduced through a non-slot having a number of symbols smaller than a normal slot. Here, the number of OFDM symbols included in a non-slot can be determined by considering the frequency range. For example, a non-slot with a length of 1 OFDM symbol can be considered in a frequency range of 6 GHz or higher. As an additional example, the number of OFDM symbols defining a non-slot can include at least 2 OFDM symbols. Here, the range of the number of OFDM symbols included in a non-slot can be set as the length of a mini-slot up to a predetermined length (e.g., the normal slot length - 1). However, as a specification of a non-slot, the number of OFDM symbols may be limited to 2, 4, or 7 symbols, but is not limited thereto.

[0090] Additionally, for example, in unlicensed bands below 6 GHz, subcarrier spacing where u equals 1 and 2 may be used, and in unlicensed bands above 6 GHz, subcarrier spacing where u equals 3 and 4 may be used. For example, when u equals 4, it may be used for SSB (Synchronization Signal Block).

[0091] [Table 2]

[0092]

[0093] 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 ( ) is shown. Table 2 shows the above-described values ​​based on a normal slot having 14 OFDM symbols.

[0094] [Table 3]

[0095]

[0096] Table 3 shows the number of slots per frame and the number of slots per subframe based on normal slots with 12 OFDM symbols per slot when extended CP is applied (i.e., when u is 2 and the subcarrier spacing is 60 kHz).

[0097] 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 that can 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, the 480kHz SCS may not be considered, but is not limited to these examples.

[0098] [Table 4]

[0099]

[0100]

[0101] In a wireless communication system, a terminal can perform mobility-based operations. The terminal can change its serving cell (e.g., PCell / PSCell) based on its mobility. For example, if the terminal detects a serving cell with better quality than the current serving cell, it can switch to the higher-quality cell, thereby enabling efficient communication. Here, the terminal can perform measurements based on its 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 current serving cell and switch to the higher-quality serving cell.

[0102] For example, legacy mobility may be a Layer 3-based mobility operation based on L3 mobility. Specifically, the terminal may perform measurements based on Layer 3-based signaling, transmit a measurement report to the network, and then change the serving cell based on network instructions. That is, the terminal and the network may 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 may reset the RRC / PDCP (packet data convergence protocol) and the MAC (medium access control) / PHY layer before connecting to the new serving cell. In other words, when the terminal changes the serving cell based on mobility, the terminal may perform new configurations for each layer. However, performing this operation every time the terminal changes the serving cell may result in problems such as increased delay and downtime, and increased overhead.

[0103] 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 on a cell-by-cell basis. Cell-level mobility can be configured and operated based on RRC signaling, and can 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 a serving cell based on cell-level mobility, the terminal can perform a procedure for performing a handover to a new serving cell based on RRC signaling.

[0104] Referring to Fig. 3(b), the mobility of a terminal can be controlled at the beam level. Beam-level mobility may be an operation that controls the mobility of a terminal on a beam-by-beam basis. For example, a terminal may perform beam-level mobility operations when controlling mobility to different cells within the same base station (e.g., intra gNB). As another example, a terminal may perform beam-level mobility operations 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 may not be limited thereto.

[0105] Considering the long delay and downtime and large overhead described 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 described above. In the LTM operation, when the base station receives the L1 measurement result of the terminal, it may transmit an LTM cell switch command MAC control element (CE) (LTE cell switch command MAC CE) to the terminal, which instructs cell change. In other words, LTM is not performed based on RRC signaling, unlike L3 mobility, and can support lower layer-based mobility, thereby reducing delay and downtime and lowering overhead. Specifically, the terminal may transmit the L1 measurement result to the network, and the network may provide L2 signaling instructing the LTM operation to the terminal, based on which the LTM operation may be performed.

[0106] 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 (DUs) within the same central unit (CU). That is, the terminal (410) can transmit an L1 measurement report to the base station and receive an LTM cell switch command MAC CE from the base station to move to a different DU within the same CU.

[0107] 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. In addition, referring to Fig. 4(c), the terminal (410) can perform an LTM operation when moving to another CU. That is, the terminal (410) can transmit an L1 measurement report to the base station and receive an LTM cell switch command MAC CE from the base station to move to another CU.

[0108] 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 instructing the terminal (410) to change to the target cell.

[0109]

[0110] For example, an intra-CU LTM procedure may be performed within the same CU. The intra-CU LTM procedure may be divided into, but is not limited to, LTM preparation, early sync, LTM cell switch execution, and LTM cell switch completion.

[0111] Figure 5 is a diagram illustrating signaling and configuration information during the LTM preparation phase applicable to the present disclosure. Referring to Figure 5, a terminal (510) can transmit a measurement report containing signal strength information of serving cells and forward cells to a base station (520). For convenience of explanation, the following description uses a gNB as the base station, but is not limited thereto and can be applied equally to base stations of other wireless systems.

[0112] For example, the measurement report that the terminal (510) transmits to the base station (520) in 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 may configure 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 the RRC message including the LTM candidate cell configuration information, configure the LTM candidate cell based on the RRC message, 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 information of Table 5 below. However, the LTM configuration may further include other information and may not be limited to Table 5 below. In Table 5, the reference configuration may be RRC configuration information commonly applied to all candidate cells, and the candidate to release list may include information on LTM candidate cells to be released based on the LTM candidate ID. In addition, the candidate to addition & modification list may be a list of LTM candidate cells to be newly added or modified. In other words, the LTM configuration information that the network provides to the terminal may include information on LTM candidate cells to be released and information on LTM candidate cells to be added / changed.

[0113] Additionally, the serving cell no reset ID may be an identifier indicating whether the terminal triggers RLC (radio link control) layer information change and PDCP data recovery, with a value of integer 1 to 9. The CSI resource config to addition & modification list may be newly added or modified CSI resource information, and the CSI resource config to release list may be CSI resource information that must be released.

[0114] In addition, the attempt LTM switch may be configured to cause the UE to perform an LTM cell switch to a cell selected by the UE when searching for a suitable cell, if the cell selected by the UE 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 UE performs UE-based TA (timing advance) measurement. That is, Table 5 may include information related to LTM configuration, but may not be limited thereto.

[0115] [Table 5]

[0116]

[0117]

[0118] In addition, within the configuration for one or more LTM candidate cells, information about one LTM candidate cell may be as shown in Table 6. Specifically, the candidate ID is an identifier of the LTM candidate cell, the candidate physical cell ID (candidate PCI) is a physical cell identifier of the candidate cell, and the SSB (synchronization signal block) configuration (SSB config) may include SSB configuration information of the LTM candidate cell, and may include frequency information (ARFCN), subcarrier spacing, period, position within a burst, and physical broadcast channel (PBCH) power information. In addition, the candidate configuration (candidate config) may be RRC configuration information for the LTM candidate cell, and configuration complete (config complete) may indicate whether the candidate configuration is complete RRC information of the candidate cell. In addition, the early UL sync config may be configuration information for performing early uplink synchronization. The initial uplink synchronization configuration information may include at least one of an uplink frequency, a random access channel (RACH) configuration, a bandwidth part (BWP), the number of RACH occasions, a PRACH root sequence index, a PRACH subcarrier spacing, and timing advance offset information. In addition, a supplemental uplink (SUL) 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 non-reset ID (No reset ID) may include a unique identifier of an LTM candidate cell that allows the UE to determine whether RLC layer information changes and PDCP data recovery triggers. The UE measured TA ID may be, but is not limited to, an identifier used to determine whether the UE performs UE-based TA measurements.

[0119] [Table 6]

[0120]

[0121]

[0122] FIG. 6 is a diagram illustrating signaling and configuration procedures for an initial synchronization step applicable to the present disclosure. Referring to FIG. 6 , upon receiving configuration information for an LTM candidate cell, the terminal (610) 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.

[0123] Specifically, the terminal (610) can perform downlink synchronization based on SSB information included in LTM candidate cell information (LTM candidate). In addition, the terminal (610) can receive a physical downlink control channel (PDCCH) that instructs RACH performance from a serving cell to an LTM candidate cell, and perform uplink synchronization through the RACH based on this.

[0124] Specifically, FIG. 7 is a diagram illustrating a method for a terminal applicable to the present disclosure to perform uplink synchronization. Referring to FIG. 7, a terminal (710) can determine whether a TA ID (ltm-UE-MeasuredTA-ID) of an LTM candidate cell is identical to a TA ID (ltm-ServingCellUE-MeasuredTA-ID) of a current serving cell. If the TA ID of the LTM candidate cell is identical to the TA ID of the current serving cell, 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, which instructs the base station (720) to perform RACH to the LTM candidate cell, and can transmit a RACH preamble to the LTM candidate cell. However, unlike the existing RACH procedure, the terminal (710) may not receive a random access response (RAR) after transmitting the RACH preamble. Accordingly, the terminal (710) may not monitor for RAR reception from the 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 the TA information through the RAR. Since the terminal (710) does not receive an RAR from the LTM candidate cell, the TA information may be included in a cell switch command MAC CE (cell switch command MAC CE) that instructs LTM execution later, which will be described later.

[0125] 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 be configured with multiple LTM candidate cells (830, 840) based on the above-described method. For example, the terminal (810) may receive a reference signal (RS) from one or more configured LTM candidate cells (830, 840) and measure the signal strength thereof. Thereafter, the terminal (810) may report an L1 measurement result (L1 measurement report) to a source cell (820). The network may determine whether to perform LTM cell switching based on the L1 measurement result obtained from the terminal (810), and may transmit a MAC CE indicating a cell change to a specific LTM candidate cell among the configured LTM candidate cells (830, 840) to the terminal (810). That is, the terminal (810) can receive a cell switch command MAC CE. When the terminal (810) receives the cell switch command MAC CE (or cell switch command MAC CE), the terminal (810) can determine whether it has a valid TA for the corresponding cell. If the terminal (810) has a valid TA for the corresponding cell, the terminal (810) may not perform a RACH procedure based on a dynamic grant / configured grant (DG / CG). That is, the terminal (810) can perform a RACH-less operation. On the other hand, if the terminal (810) does not have a valid TA for the corresponding cell, the terminal (810) can perform a RACH procedure for the corresponding cell.

[0126] As an example, FIG. 9 is a diagram illustrating a cell switch command MAC CE applicable to the present disclosure. However, FIG. 9 is only an example and may not be limited thereto. Referring to FIG. 9, the cell switch command MAC CE may include a target configuration ID. The target configuration ID may be a target LTM candidate ID. In other words, it may be cell identifier information that the terminal needs to change. In addition, the cell switch command MAC CE may include a TA command (Timing Advance Command). The TA command may indicate a valid TA value from 0 to FFE. For example, when 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. In addition, the cell switch command MAC CE may include a C field, and the C field may be a field indicating whether contention-free random access is to be performed. In addition, the cell switch command MAC CE may include a random access preamble index, and the random access preamble index may indicate a CFRA preamble resource. In addition, the SSB index (SS / PBCH index) in the cell switch command MAC CE may indicate an SSB for determining a RACH occasion. In addition, the PRACH Mask index in the cell switch command MAC CE may indicate an available RACH occasion location, and the TCI state ID in the cell switch command MAC CE may indicate and activate a TCI state for an LTM target cell.For example, the TCI state ID may be an identifier for indicating one TCI state within Ltm-DL-OrJointTCI-StateToAddModList, and if the unifiedTCI-StateType within the Target Config ID is joint, the TCI state ID field may be a joint TCI state, otherwise it may be a downlink TCI state. Additionally, the UL TCI state ID may indicate and activate an uplink TCI state for the LTM target cell. The most significant bit of the UL TCI state ID is considered as a reserved bit, and the remaining 6 bits may be the TCI-UL-StateId of ltm-UL-TCIStatesToAddModList.

[0127] FIG. 10 is a diagram illustrating 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 or not it possesses a valid TA of a target LTM candidate cell in an LTM cell change execution procedure, as described above.

[0128] 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 transmitting 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 transmitting an RRC Reconfiguration complete message to the network through the DG / CG.

[0129]

[0130] In a wireless communication system, an operation supporting LTM may be performed. For example, an operation supporting LTM may be performed in an intra-CU situation. That is, a terminal may support switching to a different serving cell within the same CU based on the LTM operation. As another example, an operation supporting LTM may be performed in an inter-CU situation. That is, a terminal may support switching to a serving cell within a CU different from the CU of the serving cell based on the LTM operation.

[0131] In addition, the L1 measurement result report that the terminal reports to the base station for the above-described LTM operation may be performed based on at least one of periodic reporting, aperiodic reporting, and event-based reporting. That is, the L1 measurement result report may also be triggered by a specific event, and the network may transmit a cell switch command MAC CE to the terminal to change the serving cell to a specific LTM candidate cell among the LTM candidate cells based on the L1 measurement result report obtained from the terminal.

[0132] As an example, the following describes a method for a terminal to recognize a CU that includes a serving cell after performing inter-CU LTM, when LTM is supported in an inter-CU and when LTM operations are mixed in an inter-CU / intra-CU configuration. However, the terminal operation may not be limited to the above-described situation and may be extended to other situations.

[0133] FIG. 11 is a diagram illustrating an inter-CU LTM operation scenario applicable to the present disclosure.

[0134] The terminal (1110) can perform an LTM operation with different DUs within a CU. In addition, the terminal (1110) can change the serving cell by performing an LTM operation with another CU through inter-CU LTM. For example, the terminal (1110) can perform an LTM operation based on network settings to move to an adjacent cell, and can move to a cell of a node included in a CU other than the master node (MN) or secondary node (SN) that includes the serving cell.

[0135] For example, FIG. 11 may be a case where a terminal (1110) performs data / control signaling from an MN and an SN to two nodes based on dual connectivity (DU). However, this is a configuration for convenience of explanation and may not be limited thereto. In FIG. 11, a source MN may refer to a node that includes cells (PCell, SCell) within a master cell group (MCG), and an SN may refer to a node that includes cells (PSCell, SCell) within a secondary cell group (SCG). Here, the PCell and PSCell may refer to special cells (SpCells) within each node that perform SCell configuration, RRC configuration, and other functions for the terminal (1110). In FIG. 11, a serving cell of the terminal (1110) may be changed from a cell within the source MN to a cell of the target MN based on an LTM operation.

[0136] FIG. 12 is a diagram illustrating a scenario in which LTM is performed in a complex manner based on intra-CUs and inter-CUs applicable to the present disclosure. In an actual network environment, one or more gNB-CUs and one or more gNB-DUs may be configured in a complex manner as shown in FIG. 12. For example, one or more gNB-DUs may be connected to and operated by a gNB-CU, and a terminal (1210) may detect multiple cells in an area where the terminal is located, and the gNB-DUs included in each cell may be the same or different. In the case where the gNB-DUs are different, the gNB-DUs may be connected to the same gNB-CU or different gNB-CUs. In other words, in an actual network environment, a situation in which one or more gNB-CUs and one or more gNB-DUs are configured in a complex manner may be considered, but may not be limited thereto. For example, in FIG. 12, there is an environment in which gNB-CU 1 (1221), gNB-CU 2 (1222), and gNB-CU 3 (1223) coexist, and each of the gNB-CUs (1221, 1222, 1223) can be connected to one or more gNB-DUs. In addition, each gNB-DU can include one or more cells. However, this is a configuration for convenience of explanation and may not be limited thereto.

[0137] For example, the network may obtain signal strength results of one or more neighboring cells from the terminal (1210) considering the LTM operation. The terminal (1210) may transmit L1 measurement results for the serving cell and LTM candidate cells to the network through one or more neighboring cells, as described above.

[0138] As a specific example, in FIG. 12, the terminal (1210) may be connected to a cell within gNB-DU 1-1 (1231) included in gNB-CU 1 (1221). That is, the serving cell of the terminal may be included in gNB-DU 1-1 (1231) included in gNB-CU 1 (1221). Here, the LTM candidate cells based on the LTM operation may include candidate cell 1 in gNB-DU 1-1 (1231) included in gNB-CU 1 (1221), candidate cell 2 in gNB-DU 1-2 (1232) included in gNB-CU 1 (1221), candidate cell 3 in gNB-DU 2-1 (1233) included in gNB-CU 2 (1222), and candidate cell 4 and candidate cell 5 in gNB-DU 3-1 (1234) included in gNB-CU 3 (1223), but this is for convenience of explanation and may not be limited thereto. Since the terminal (1210) must be able to move to an adjacent cell at any time, a single LTM configuration may be configured with a mixture of intra-CU-LTM and inter-CU LTM. That is, the network may provide the terminal with an LTM configuration configured with a mixture of intra-CU-LTM and inter-CU LTM. For example, Table 7 below may be an LTM configuration provided by the network to the terminal, but this is only one example and may not be limited thereto. In Table 7, the LTM configuration may include a configuration for an LTM candidate cell in consideration of an environment in which one or more CUs and one or more DUs coexist.

[0139] [Table 7]

[0140]

[0141]

[0142] Since the network can provide LTM configurations that take into account the mobility of the terminal, the LTM configurations can consider one or more CUs and one or more DUs, as described above. However, the terminal needs to perform intra-CU LTM and inter-CU LTM operations differently.

[0143] Specifically, intra-CU LTM may be an operation that supports mobility of a terminal to another cell within the same gNB-CU, and inter-CU LTM may be an operation that supports mobility to a gNB-CU different from the current serving gNB-CU. For example, if the gNB-CU serving the terminal changes, the RRC / PDCP layer within the gNB-CU may change, and thus, the security key and bearer may be modified.

[0144] Here, the network may not consider the unique identifier of the gNB-CU in the RAN, and considering the above, the RAN may need to use an identifier to identify when the serving gNB-CU changes. If the network verifies the network unique identifier due to a gNB-CU change and performs the change procedure, additional signaling may be required, resulting in overhead.

[0145] Considering the above, the following describes an identifier for distinguishing one or more gNB-CUs distributed on a network, and an operation based on the identifier. That is, a terminal can support intra-CU LTM and inter-CU LTM operations based on the identifier for distinguishing gNB-CUs. In addition, the identifier for a gNB-CU can support subsequent LTM. That is, a terminal can perform an operation for changing the identifier of the current gNB-CU after an LTM operation, and this is described in relation to this.

[0146] For example, an identifier distinguishing a gNB-CU (hereinafter, gNB-CU identifier) ​​may be applied considering intra-CU LTM and inter-CU LTM operations. The UE may perform an operation of comparing the current gNB-CU identifier with the gNB-CU identifier of the target LTM candidate cell. In addition, the UE may change the gNB-CU identifier after completing the LTM operation to support a subsequent LTM. For example, the gNB-CU identifiers of each of the serving cell and the candidate cell may be indicated to distinguish between intra-CU LTM and inter-CU LTM operations, which will be described later. For another example, the MAC CE may indicate the identifier of the gNB-CU or indicate intra-CU LTM / inter-CU LTM itself to distinguish between intra-CU LTM and inter-CU LTM operations, which will be described later.

[0147] FIG. 13 is a diagram illustrating a method for signaling LTM settings from a network to a terminal to distinguish one or more gNB-CUs applicable to the present disclosure.

[0148] Referring to FIG. 13, a terminal (1310) may be in an RRC connection state with a source gNB-CU (1320), and may consider candidate gNB-CU 1 (candidate gNB-CU 1, 1330) and gNB-CU 2 (candidate gNB-CU 2, 1340) as gNB-CUs that include LTM candidate cells. That is, candidate gNB-CU 1 (candidate gNB-CU 1, 1330) and gNB-CU 2 (candidate gNB-CU 2, 1340) may be candidate gNB-CUs determined by the source gNB-CU (1320) based on an L3 measurement report from the terminal. However, this is merely a configuration for convenience of explanation and may not be limited thereto.

[0149] Specifically, the terminal (1310) can report L3 measurement results to the source gNB-CU (1320) based on measurement and measurement reporting settings configured in the network (i.e., the source gNB-CU). (S1301) Then, the source gNB-CU (1320) can select a candidate LTM cell based on the L3 measurement report obtained from the terminal (1310), transmit an LTM request to the candidate gNB-CU including the cell, and receive an LTM response from the candidate gNB-CU. (S1302) Then, the source gNB-CU (1320) can transmit an RRC message (e.g., RRC reconfiguration) to the terminal (1310), and the RRC message can include LTM configuration information based on the LTM response received by the source gNB-CU (1320). That is, the terminal (1310) can obtain LTM configuration information from the source gNB-CU (1320). Here, the LTM configuration may include information on one or more LTM candidate cells, and the LTM candidate cells may be included in candidate gNB-CU 1 (1330) or candidate gNB-CU 2 (1340). Thereafter, the UE may transmit an RRC message (e.g., RRC reconfiguration complete) message to the source gNB-CU (1320). (S1304) Here, the LTM candidate cells determined by the source gNB-CU (1320) may be cells included in the source gNB-CU (1320), gNB-CU 1 (1330), or gNB-CU 2 (1340), and the LTM configuration may be determined based on this as shown in Table 8. Specifically, in Table 8, the LTM configuration may include CU ID information as a CU identifier for each LTM candidate cell, through which the gNB-CU including the corresponding LTM candidate cell may be recognized. Here, the CU ID identifier can be expressed as an integer, based on which the gNB-CU can be distinguished in the network.In Table 8 below, the CU ID is expressed as an integer, but this is only an example and is not limited thereto. That is, the CU identifier may also be expressed in other forms. In addition, when the network instructs the terminal to configure the LTM, the LTM configuration may indicate the source CU ID so that the terminal can recognize the current CU ID, and the terminal may store the source CU ID as a variable (e.g., VarSourceCU-ID). That is, the terminal can recognize the source CU and candidate CUs to which the terminal is currently connected based on the CU identifier.

[0150] [Table 8]

[0151]

[0152]

[0153] FIG. 14 is a diagram illustrating an operation of comparing CU IDs in an LTM cell switch operation applicable to the present disclosure. Referring to FIG. 14, signaling for distinguishing between intra-CU LTM and inter-CU LTM operations may be provided to a terminal. Specifically, a terminal (1410) may measure signal strength based on a reference signal for an LTM candidate cell in an LTM configuration to perform L1 measurement and reporting. (S1401) The terminal may periodically report L1 measurement reports for LTM candidate cells to a source cell. As a specific example, in Table 8 described above, the LTM candidate cells configured based on the LTM configuration may be candidate cells A to F (1430, 1440, 1450, 1460, 1470, 1480), respectively, and the terminal may perform L1 measurement for each of the LTM candidate cells. However, this is only for convenience of explanation and may not be limited to the number of candidate cells.

[0154] Thereafter, the source cell (1420) may determine LTM cell switching based on the L1 measurement report, and may transmit a MAC CE to the terminal (1410) based on this to instruct LTM-based cell switching. (S1402) Here, the cell switch command MAC CE may include a target configuration ID (target Config ID) and may instruct any one target LTM candidate cell among up to 8 LTM candidate cells. Here, the terminal may compare the CU ID for the target configuration ID with the CU ID of the current source cell. (S1403) For example, if the target configuration ID within the MAC CE is 3 based on Table 8, LTM candidate cell 2 may be instructed, and the terminal (1410) may compare the CU ID (CU ID = 1) of the LTM candidate cell 2 with the CU ID (CU ID = 0) of the source cell. That is, the terminal (1410) can check whether the stored source CU ID and the CU ID of the target setting ID are the same based on the stored source CU ID variable (e.g. VarSourceCU-ID). If the CU IDs are the same, the terminal (1410) can perform an intra CU LTM operation and perform a MAC reset based on this. However, since it is the same CU ID, the security key and RRC / PDCP re-establishment may not be performed. On the other hand, the terminal (1410) can perform an inter CU LTM operation if the CU IDs are different, and can perform a security key and RRC / PDCP re-establishment together with a MAC reset based on this.

[0155] After that, the terminal (1410) can perform a RACH procedure if the TA of the LTM candidate cell is invalid, and can perform a RACH-less procedure if the TA is valid, and is not limited to a specific form. (S1404)

[0156]

[0157] As another example, a terminal can maintain LTM settings after performing LTM. That is, the terminal can maintain LTM settings based on subsequent LTMs. The terminal can support subsequent LTMs based on the same CU in intra-CU LTM. That is, the terminal can maintain LTM settings after performing LTM.

[0158] Here, the terminal can support subsequent LTM by considering the terminal's mobility even in inter-CU LTM. To this end, it is necessary to recognize the changed CU. For example, the terminal can update the stored source CU identifier variable (e.g., VarSourceCU-ID) based on the changed CU to a new CU identifier, thereby enabling subsequent LTM support.

[0159] FIG. 15 is a diagram illustrating a method for performing an LTM operation in an environment where multiple gNB CUs are present, applicable to the present disclosure, and FIG. 16 is a diagram illustrating a method for performing an inter-CU LTM operation in the environment of FIG. 15. Referring to FIG. 15, a gNB CU may have one or more gNB DUs, and a gNB DU may have multiple cells. For example, FIG. 15 only illustrates the current serving cell of the terminal and the LMT candidate cells, but the present disclosure may not be limited thereto. In FIG. 15, a terminal (1510) may be connected to one cell within gNB-DU 1 (1531) of gNB CU 1 (1521), and candidate cell 1 within the LTM configuration may be included in gNB CU 1 (1521) and gNB DU 1 (1531), and candidate cell 2 and candidate cell 3 may be cells included in gNB DU 2 (1532) of gNB CU 2 (1522).

[0160] Here, referring to FIG. 16, the terminal (1610) may receive LTM settings from the source cell (1621) of gNB-CU 1 / gNB-DU 1 (1620) and then be instructed by the network to perform LTM to LTM candidate cell 2 (1631). LTM candidate cell 2 (1631) may be a cell within gNB-CU 2 / gNB-DU 2 (1630). Accordingly, the terminal may perform a serving cell change based on the inter CU LTM operation. However, this is for convenience of explanation and may not be limited thereto. Here, when the terminal (1610) performs inter CU LTM, it may perform a source CU ID update operation stored as a source CU identifier variable (e.g., VarSourceCU-ID) to support subsequent LTM.

[0161] Specifically, the terminal (1610) can perform L1 measurement and reporting on LTM candidate cells based on LTM settings. (S1601) The terminal can receive reference signals from LTM candidate cells, measure signal strength based on the reference signals, and report measurement information on each LTM candidate cell to the source cell (1621).

[0162] After that, the terminal (1610) can receive a cell switch command MAC CE from the source cell (1621). (S1602) The source cell (1621) can determine LTM cell switching based on the acquired L1 measurement report and transmit the cell switch command MAC CE to the terminal (1610) to instruct LTM cell switching. Here, the cell switch command MAC CE can include a target configuration ID and can indicate a target LTM candidate cell identifier of one of up to eight configured LTM candidate cells. For example, in FIG. 16, the terminal (1610) can obtain a cell switch command MAC CE that instructs LTM to LTM candidate cell 2 (1631). The terminal (1610) can compare the gNB CU ID of the target configuration ID with the gNB-CU ID of the source cell based on the cell switch command MAC CE. (S1603) That is, the terminal can compare the stored source CU identifier variable (e.g. VarSourceCU-ID) currently controlled by the serving cell with the CU ID of the target setting ID.

[0163] The terminal (1610) can check whether the stored source CU ID and the CU ID of the target setting ID are the same based on the CU ID variable (e.g. VarSourceCU-ID) of the stored source cell. If the CU IDs are the same, the terminal (1610) can perform an intra CU LTM operation and perform a MAC reset based on this. However, since the CU IDs are the same, the security key and RRC / PDCP re-establishment may not be performed. On the other hand, the terminal (1610) can perform an inter CU LTM operation if the CU IDs are different, and based on this, the terminal can perform a security key and RRC / PDCP re-establishment together with a MAC reset. In addition, the terminal (1610) can update the CU ID variable (e.g. VarSourceCU-ID) based on the gNB-CU ID of the target configuration ID. (S1604) That is, if the stored CU ID variable (e.g. VarSourceCU-ID) and the target LTM candidate CU ID are different, the terminal (1610) can perform an inter-CU LTM operation and update the CU ID variable, thereby supporting subsequent LTM operations. For example, in FIG. 16, the terminal (1610) can update the CU ID variable to the CU ID of candidate cell 2, and thereafter maintain the LTM configuration without RRC configuration.

[0164] After that, the terminal (1610) can perform a RACH procedure if the TA of the LTM candidate cell is invalid, and can perform a RACH-less procedure if the TA is valid, and is not limited to a specific form. (S1605)

[0165] FIG. 17 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0166] Referring to FIG. 17, a terminal may obtain information on one or more LTM candidate cells and information on a source gNB-CU identifier. (S1710) The terminal may obtain an LTM configuration including information on one or more LTM candidate cells and information on a source gNB-CU identifier from a network via an RRC message. The network may determine one or more LTM candidate cells based on L3 measurement results previously reported by the terminal, as described above. In addition, the LTM configuration may include an identifier for each of the LTM candidate cells and an identifier of a gNB CU corresponding to each of the LTM candidate cells. The terminal may store a CU ID including a current serving cell in a source gNB CU identifier variable (e.g., VarSourceCU-ID) based on the LTM configuration. After that, the terminal can obtain reference signals from LTM candidate cells, measure signal strength, and perform L1 measurement and reporting. (S1720) After that, the terminal can receive a cell switch command MAC CE for performing cell switching to an LTM candidate cell based on the L1 measurement report from the network. (S1730) For example, the terminal can check whether the cell switch command MAC CE is received, and if not, can continuously perform L1 measurement and reporting. On the other hand, if the terminal receives the cell switch command MAC CE, the terminal can move to the target LTM candidate cell, and can compare the CU identifier of the target LTM candidate cell with the CU identifier of the source cell.(S1740) For example, the cell switch command MAC CE may include at least one piece of information from among a target configuration ID, a TA command (Timing Advance Command), a TCI state ID, an uplink TCI state ID, a random access preamble index, an SSB index (SS / PBCH index), and a PRACH mask index, as illustrated in FIG. 9.

[0167] After that, the terminal can compare the CU identifier of the target LTM candidate cell with the CU identifier of the source cell to determine whether it is an inter CU LTM (S1750). Here, if the CU identifier of the target LTM candidate cell and the CU identifier of the source cell are different, it may be an inter CU LTM, and the terminal can update the CU identifier variable of the source cell (S1760). After that, the terminal can complete the LTM procedure by performing a RACH or RACH-less procedure depending on whether TA is valid (S1770). On the other hand, if the CU identifier of the target LTM candidate cell and the CU identifier of the source cell are the same, it may be an intra CU LTM, and the LTM procedure can be completed by performing a RACH or RACH-less procedure depending on whether TA is valid.

[0168]

[0169] As another example, when supporting intra-CU LTM and inter-CU LTM operations based on an identifier for distinguishing gNB-CUs, the UE may receive LTM configurations as shown in Table 9 below from the network. Here, the CU ID identifier may be expressed as an integer, and the gNB-CU may be distinguished in the network based on this. In Table 9 below, the CU ID is expressed as an integer, but this is only one example and is not limited thereto. That is, the CU identifier may also be expressed in other forms. When the network provides the LTM configuration to the UE, the network may indicate the source CU ID within the LTM configuration to indicate the current CU ID to the UE, and the UE may store a source CU identifier variable (e.g., VarSourceCU-ID) based on the LTM configuration.

[0170] Here, Table 9 may only include the source CU ID, which is the current CU ID, within the LTM setting, unlike Table 8, and the CU ID that includes each LTM candidate cell may not be indicated.

[0171] [Table 9]

[0172]

[0173]

[0174] FIG. 18 is a diagram illustrating an operation of comparing CU IDs in an LTM cell switch operation applicable to the present disclosure. Referring to FIG. 18, signaling for distinguishing between intra-CU LTM and inter-CU LTM operations may be provided to a terminal. Specifically, a terminal (1810) may measure signal strength based on a reference signal for an LTM candidate cell in an LTM configuration to perform L1 measurement and reporting. (S1801) The terminal may periodically report L1 measurement reports for LTM candidate cells to a source cell. As a specific example, in Table 9 described above, the LTM candidate cells configured based on the LTM configuration may be candidate cells A to F (1830, 1840, 1850, 1860, 1870, 1880), respectively, and the terminal may perform L1 measurement for each of the LTM candidate cells. However, this is only for convenience of explanation and may not be limited to the number of candidate cells.

[0175] Thereafter, the source cell (1820) can decide LTM cell switching based on the L1 measurement report, and can transmit MAC CE to the terminal (1810) based on this to instruct LTM cell switching. (S1802) Here, the cell switch command MAC CE can include a target Config ID and can indicate any one target LTM candidate cell among up to 8 LTM candidate cells. In addition, the cell switch command MAC CE can indicate a CU ID together with an identifier of the target LTM candidate cell, and the terminal can compare the CU ID in the cell switch command MAC CE with the CU ID of the current source cell that it is storing. (S1803) The terminal (1810) can perform an intra CU LTM operation based on whether the stored source CU ID and the CU ID in the cell switch command MAC CE are the same based on the stored source CU ID variable (e.g. VarSourceCU-ID), and if the CU IDs are the same, can perform a MAC reset based on this. However, since the CU ID is the same, the security key and RRC / PDCP re-establishment may not be performed. On the other hand, if the CU ID is different, the terminal (1810) can perform an inter-CU LTM operation, and based on this, perform the security key and RRC / PDCP re-establishment along with a MAC reset. After that, the terminal (1810) can perform the RACH procedure if the TA of the LTM candidate cell is invalid, and can perform the RACH-less procedure if the TA is valid, and is not limited to a specific form. (S1804)

[0176] FIG. 19 is a diagram illustrating a cell switch command MAC CE applicable to the present disclosure. As in FIG. 18, the terminal may receive the cell switch command MAC CE including the CU ID, recognize the CU ID of the LTM candidate cell, and compare it with the stored CU ID to perform an intra-CU LTM or inter-CU LTM operation, as described above. Specifically, when the terminal first receives the LTM configuration from the network, the terminal may store the controlled source CU identifier of the serving cell as a CU identifier variable (e.g., VarSourceCU-ID). The terminal may perform an intra-CU LTM or inter-CU LTM operation based on the CU ID included in the cell switch command MAC CE and compare it with the stored CU ID. As an example, the CU ID in the cell switch command MAC CE in FIG. 19 may be configured with 3 bits, but the present invention may not be limited thereto. As another example, the CU ID in the cell switch command MAC CE may be indicated with 2 bits or 1 bit. As another example, the number of CU ID bits may be set larger, and based on this, it may also indicate whether or not to perform a security key update, but this may not be limited thereto.

[0177] As another example, the terminal can maintain the LTM configuration after performing LTM. That is, the terminal can maintain the LTM configuration based on the subsequent LTM. The terminal can support the subsequent LTM based on the same CU in the intra-CU LTM. That is, the terminal can maintain the LTM configuration after performing the LTM. Here, the terminal can support the subsequent LTM by considering the mobility of the terminal even in the inter-CU LTM. To this end, the terminal needs to recognize the changed CU. For example, the terminal can update the source CU identifier variable based on the changed CU and change it to a new CU identifier, thereby enabling subsequent LTM support.

[0178] FIG. 20 is a diagram illustrating a method for performing an LTM operation in an environment where multiple gNB CUs are present, applicable to the present disclosure, and FIG. 21 is a diagram illustrating a method for performing an inter-CU LTM operation in the environment of FIG. 20. Referring to FIG. 20, a gNB CU may have multiple gNB DUs, and a gNB DU may have multiple cells. For example, FIG. 20 only illustrates the current serving cell of the terminal and the LMT candidate cell, but the present disclosure may not be limited thereto. In FIG. 20, the terminal (2010) may be connected to one cell within gNB-DU 1 (2031) of gNB CU 1 (2021), and candidate cell 1 within the LTM configuration may be included in gNB CU 1 (2021) and gNB DU 1 (2031), and candidate cell 2 and candidate cell 3 may be cells included in gNB DU 2 (2032) of gNB CU 2 (2022).

[0179] Here, referring to FIG. 21, the terminal (2110) may receive LTM settings from the source cell (1621) of gNB-CU 1 / gNB-DU 1 (1620) and then be instructed by the network to perform LTM on LTM candidate cell 2 (2131). Here, LTM candidate cell 2 (2131) may be a cell within gNB-CU 2 / gNB-DU 2 (2130). That is, the terminal may perform an inter-CU LTM operation. However, this is for convenience of explanation and may not be limited thereto. Here, when the terminal (2110) performs an inter-CU LTM, it may perform an operation to update a source CU ID stored as a variable to support subsequent LTM.

[0180] Specifically, the terminal (2110) can perform L1 measurement and reporting on LTM candidate cells based on the LTM setting. (S2101) That is, the terminal can receive reference signals from LTM candidate cells, measure signal strength based on the reference signals, and report the measured signal strength to the source cell (2121).

[0181] After that, the terminal (2110) can receive a cell switch command MAC CE from the source cell (2121). (S2102) The source cell (2121) can determine LTM cell switching based on the acquired L1 measurement report, and transmit the cell switch command MAC CE to the terminal (2110) to instruct LTM cell switching. Here, the cell switch command MAC CE may include a target configuration ID and may indicate an identifier of one target LTM candidate cell among up to eight configured LTM candidate cells. In addition, the cell switch command MAC CE may include an identifier of gNB CU 2 including LTM candidate cell 2. For example, in FIG. 21, the terminal (2110) can obtain a cell switch command MAC CE that instructs cell switching based on LTM to LTM candidate cell 2 (2131), and compare the CU ID in the cell switch command MAC CE with the gNB-CU ID of the source cell. (S2103) That is, the terminal can compare the stored source gNB-CU identifier variable (e.g. VarSourceCU-ID) currently controlled by the serving cell with the CU ID in the MAC CE.

[0182] The terminal (2110) can check whether the stored source CU ID and the CU ID in the MAC CE are the same based on the CU ID variable (e.g. VarSourceCU-ID) of the stored source cell. If the CU IDs are the same, the terminal (2110) can perform an intra CU LTM operation and perform a MAC reset based on this. However, since the CU IDs are the same, the security key and RRC / PDCP re-establishment may not be performed. On the other hand, the terminal (2110) can perform an inter CU LTM operation if the CU IDs are different, and based on this, the terminal can perform a security key and RRC / PDCP re-establishment together with a MAC reset. In addition, the terminal (2110) can update the CU ID variable (e.g. VarSourceCU-ID) based on the CU ID in the MAC CE. (S2104) That is, if the stored CU ID variable (e.g. VarSourceCU-ID) and the CU ID in the MAC CE are different, the terminal (2110) can perform an inter-CU LTM operation and update the CU ID variable. For example, in FIG. 21, the terminal (2110) can update the CU ID variable to a value of 2, which is the CU ID of candidate cell 2, and thereafter maintain the LTM configuration without an RRC configuration.

[0183] After that, the terminal (2110) can perform a RACH procedure if the TA of the LTM candidate cell is invalid, and can perform a RACH-less procedure if the TA is valid, and is not limited to a specific form. (S2105)

[0184] FIG. 22 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0185] Referring to FIG. 22, a terminal may obtain information on one or more LTM candidate cells and information on a source gNB-CU identifier. (S2210) The terminal may obtain an LTM configuration including information on one or more LTM candidate cells and information on a source gNB-CU identifier from a network via an RRC message. The network may determine one or more LTM candidate cells based on L3 measurement results previously reported by the terminal, as described above. In addition, the LTM configuration may include an identifier and a source CU ID for each of the LTM candidate cells, which may be different from FIG. 17. The terminal may store a CU ID including a current serving cell in a source gNB CU identifier variable (e.g., VarSourceCU-ID) based on the LTM configuration. After that, the terminal can obtain reference signals from LTM candidate cells, measure signal strength, and perform L1 measurement and reporting. (S2220) After that, the terminal can receive a cell switch command MAC CE for performing cell switching to an LTM candidate cell based on the L1 measurement report from the network. (S2230) For example, the terminal can check whether the cell switch command MAC CE is received, and if not, can continuously perform L1 measurement and reporting. On the other hand, if the terminal receives the cell switch command MAC CE, the terminal can move to the target LTM candidate cell. Here, the cell switch command MAC CE can include the CU ID of the target LTM candidate cell, and the terminal can compare the CU identifier of the target LTM candidate cell with the CU identifier of the source cell based on the cell switch command MAC CE.(S2240) For example, the cell switch command MAC CE may include at least one piece of information from among a CU ID, a target configuration ID, a TA command (Timing Advance Command), a TCI state ID, an uplink TCI state ID, a random access preamble index, an SSB index (SS / PBCH index), and a PRACH mask index, which may be as shown in FIG. 19.

[0186] After that, the terminal can compare the CU identifier of the target LTM candidate cell included in the cell switch command MAC CE with the CU identifier of the source cell to determine whether it is an inter CU LTM. (S2250) Here, if the CU identifier of the target LTM candidate cell and the CU identifier of the source cell are different, it may be an inter CU LTM, and the terminal can update the CU identifier variable of the source cell. (S2260) After that, the terminal can complete the LTM procedure by performing a RACH or RACH-less procedure depending on whether TA is valid. (S2270) On the other hand, if the CU identifier of the target LTM candidate cell and the CU identifier of the source cell are the same, it may be an intra CU LTM, and the LTM procedure can be completed by performing a RACH or RACH-less procedure depending on whether TA is valid.

[0187]

[0188] As another example, when supporting intra-CU LTM and inter-CU LTM operations based on an identifier for distinguishing gNB-CUs, the terminal may obtain an LTM configuration as shown in Table 10 below. As an example, the LTM configuration in Table 10 may not include a CU ID, unlike Tables 8 and 9.

[0189] [Table 10]

[0190]

[0191]

[0192] FIG. 23 is a diagram illustrating a method for indicating intra CU and inter CU through MAC CE in an LTM cell switch operation applicable to the present disclosure. Referring to FIG. 23, intra CU LTM and inter CU LTM can be indicated through MAC CE. Specifically, the terminal (2310) can measure signal strength based on a reference signal for an LTM candidate cell in an LTM configuration and perform L1 measurement and reporting. (S2301) The terminal can periodically report L1 measurement reports for LTM candidate cells to the source cell. As a specific example, the LTM candidate cells configured based on the LTM configuration in Table 10 described above can be candidate cells A to F (2330, 2340, 2350, 2360, 2370, 2380), respectively, and the terminal can perform L1 measurement for each of the LTM candidate cells. However, this is only for convenience of explanation and may not be limited to the number of candidate cells.

[0193] Thereafter, the source cell (2320) may determine LTM cell switching based on the L1 measurement report, and may transmit a cell switch command MAC CE to the terminal (2310) based on the determination, thereby instructing LTM cell switching. (S2302) Here, the cell switch command MAC CE may include a target Config ID and may indicate any one target LTM candidate cell among up to eight LTM candidate cells. In addition, the cell switch command MAC CE may include an indicator for distinguishing between intra-CU LTM and inter-CU LTM. For example, the indicator for distinguishing between intra-CU LTM and inter-CU LTM may be a 1-bit value, but may not be limited thereto. The terminal may distinguish between intra-CU LTM and inter-CU LTM and confirm it through the above-described indicator in the cell switch command MAC CE. (S2303) The terminal (2310) may perform a MAC reset when intra-CU LTM is indicated. However, since the CU ID is the same as the intra CU LTM, security key and RRC / PDCP re-establishment may not be performed.

[0194] On the other hand, if inter-CU LTM is indicated, the terminal (2310) can perform a MAC reset and security key and RRC / PDCP re-establishment. Thereafter, the terminal (2310) can perform a RACH procedure if the TA of the LTM candidate cell is invalid, or a RACH-less procedure if the TA is valid, without being limited to a specific format. (S2304)

[0195] FIG. 24 is a diagram illustrating a cell switch command MAC CE applicable to the present disclosure. The terminal may receive the cell switch command MAC CE including an indicator for distinguishing between intra-CU LTM and inter-CU LTM as in FIG. 23, and may recognize whether the CU ID of the LTM candidate cell is different from the CU ID of the current serving cell. That is, the terminal may be instructed to perform intra-CU LTM or inter-CU LTM operation and may perform an operation based on the instruction. For example, in FIG. 24, the cell switch command MAC CE may include a 1-bit I field as an indicator for distinguishing between intra-CU LTM and inter-CU LTM, but may not be limited thereto. For example, when the I field in the cell switch command MAC CE is a first value (e.g., 0), the terminal may perform intra-CU LTM with the target configured ID cell. On the other hand, when the I field in the cell switch command MAC CE is a second value (e.g., 1), the terminal may perform inter-CU LTM with the target configured ID cell. Here, the indicator for distinguishing between intra-CU LTM and inter-CU LTM can be located at the very beginning as 1 bit within the cell switch command MAC CE, but is not limited thereto and can exist at other locations. As a specific example, one of the reserved bits in the R field in FIG. 24 can be an I field, and several consecutive bits of the R field can be I fields. In addition, when the indicator for distinguishing between intra-CU LTM and inter-CU LTM is 0, it indicates intra-CU LTM, and when the indicator for distinguishing between intra-CU LTM and inter-CU LTM is 1, it indicates inter-CU LTM, but is not limited thereto. For example, when the indicator for distinguishing between intra-CU LTM and inter-CU LTM is 0, it can indicate inter-CU LTM, and when the indicator for distinguishing between intra-CU LTM and inter-CU LTM is 1, it can indicate intra-CU LTM.

[0196] As another example, the terminal can recognize the intra-CU LTM and inter-CU LTM operations based on whether the indicator field (e.g., I field) for distinguishing between intra-CU LTM and inter-CU LTM in the cell switch command MAC CE is toggled. Specifically, the terminal can set the initial value to 1 after receiving the first LTM configuration. Here, the terminal can perform the intra-CU LTM operation if the indicator field for distinguishing between intra-CU LTM and inter-CU LTM in the cell switch command MAC CE indicates 1. On the other hand, the terminal can perform the inter-CU LTM operation if the indicator field for distinguishing between intra-CU LTM and inter-CU LTM in the cell switch command MAC CE is toggled to 0. In other words, the terminal can distinguish between the intra-CU LTM and inter-CU LTM operations depending on whether the indicator field for distinguishing between intra-CU LTM and inter-CU LTM is toggled.

[0197] FIG. 25 is a flowchart illustrating a method for distinguishing intra-CU and inter-CU LTM operations applicable to the present disclosure.

[0198] Referring to FIG. 25, the terminal can obtain information on one or more LTM candidate cells and information on a source gNB-CU identifier. (S2510) The terminal can obtain an LTM configuration including information on one or more LTM candidate cells from the network via an RRC message. The network can determine one or more LTM candidate cells based on the L3 measurement results previously reported by the terminal, as described above. In addition, the LTM configuration may include only identifiers for each of the LTM candidate cells, which may be different from FIG. 17 and FIG. 22. Thereafter, the terminal can obtain reference signals from the LTM candidate cells, measure signal strength, and perform L1 measurement and reporting. (S2520) Thereafter, the terminal can receive a cell switch command MAC CE for performing cell switching to an LTM candidate cell based on the L1 measurement report from the network. (S2530) For example, the terminal can check whether the cell switch command MAC CE has been received, and if not, can continuously perform L1 measurement and reporting. On the other hand, when the terminal receives the cell switch command MAC CE, the terminal can move to the target LTM candidate cell. Here, the cell switch command MAC CE may include an indicator for distinguishing between intra-CU LTM and inter-CU LTM, and the terminal can recognize intra-CU LTM and inter-CU LTM based on the indicator value.(S2540) For example, the cell switch command MAC CE may include at least one piece of information from among an indicator for distinguishing between intra CU LTM and inter CU LTM, a target configuration ID, a TA command (Timing Advance Command), a TCI state ID, an uplink TCI state ID, a random access preamble index, an SSB index (SS / PBCH index), and a PRACH mask index, as shown in FIG. 24.

[0199] Thereafter, the terminal can identify the intra CU LTM and the inter CU LTM based on the indicator for distinguishing between the intra CU LTM and the inter CU LTM included in the cell switch command MAC CE. Here, if the intra CU LTM is indicated, the terminal can perform the intra CU LTM operation, and if the inter CU LTM is indicated, the terminal can perform the inter CU LTM operation. Thereafter, the terminal can complete the LTM procedure by performing a RACH or RACH-less procedure depending on whether the TA is valid or not (S2550). On the other hand, if the CU identifier of the target LTM candidate cell and the CU identifier of the source cell are the same, it may be an intra CU LTM, and the LTM procedure can be completed by performing a RACH or RACH-less procedure depending on whether the TA is valid or not.

[0200] Fig. 26 is a flowchart illustrating an LTM operation applicable to the present disclosure. Referring to Fig. 26, a terminal may obtain an LTM configuration including information on LTM candidate cells from a network (S2610), and may perform a measurement report by obtaining a reference signal from each LTM candidate cell (S2620). Thereafter, the terminal may obtain a cell switch command MAC CE from the network, which instructs cell switching to a first cell among the LTM candidate cells based on the measurement report (S2630), and may perform serving cell switching to the first cell by recognizing an intra-CU LTM operation and an inter-CU LTM operation based on the cell switch command MAC CE (S2640).

[0201] For example, each piece of information about an LTM candidate cell included in an LTM configuration includes CU identifier information of each LTM candidate cell, and the terminal can store a CU identifier variable for the serving cell based on the CU identifier information of each LTM candidate cell included in the LTM configuration. Thereafter, the terminal recognizes the CU identifier of the first cell based on the cell switch command MAC CE, and if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are the same, performs an intra-CU LTM operation, and if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are different, performs an inter-CU LTM operation, which may be as shown in FIGS. 11 to 17.

[0202] As another example, the LTM configuration includes CU identifier information for the serving cell of the terminal, and the terminal can store a CU identifier variable for the serving cell based on the CU identifier information for the serving cell. Thereafter, the terminal receives a cell switch command MAC CE including the CU identifier of the first cell to recognize the CU identifier of the first cell, and if the CU identifier of the first cell and the stored CU identifier variable are the same, performs an intra-CU LTM operation, and if the CU identifier of the first cell and the stored CU identifier variable are different, performs an inter-CU LTM operation, which may be as shown in FIGS. 18 to 22.

[0203] As another example, the cell switch command MAC CE received by the terminal may include a first indicator. Here, if the first indicator is a first value, an intra-CU LTM operation may be performed, and if the first indicator is a second value, an inter-CU LTM operation may be performed, as illustrated in FIGS. 23 to 25 .

[0204] In addition, as an example, when an intra-CU LTM operation is performed, the terminal may perform a MAC reset operation after changing the serving cell to the first cell. On the other hand, when an inter-CU LTM operation is performed, the terminal may perform a MAC reset, security key update, and PDCP re-establishment operations after changing the serving cell to the first cell. In addition, as an example, after changing the serving cell to the first cell, the terminal may perform a RACH-less procedure if the TA is valid, and perform a RACH procedure if the TA is invalid.

[0205] Figure 27 is a drawing showing a device configuration to which the present disclosure can be applied.

[0206] Referring to FIG. 27, a first device (2700) and a second device (2750) can communicate with each other. In this case, as an 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 another example, the first device (2700) and the second device (2750) may be satellite IAB nodes. In other words, 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.

[0207] 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 a higher layer processing unit (2727) and a physical layer processing unit (2740). The higher layer processing unit (2727) may process operations of a medium access control (MAC) layer, a radio resource control (RRC) layer, or higher layers. The physical layer processing unit (2740) may process operations of a 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 unit (2712) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO (Multiple Input Multiple Output) transmission and reception. In addition, beamforming may be supported. The memory (2716) may store information processed by the processor (2720), software related to the operation of the first device (2700), an operating system, applications, 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.

[0208] 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) may perform baseband-related signal processing and may include a higher layer processing unit (2780) and a physical layer processing unit (2790). The higher layer processing unit (2780) may process operations of a MAC layer, an RRC layer, or higher layers. The physical layer processing unit (2790) may process operations of a 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 unit (2762) may include one or more physical antennas, and when it includes multiple antennas, it may support MIMO transmission and reception. In addition, 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), an operating system, applications, etc., and may include components such as a buffer. 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. In addition, the second device (2750) according to the present invention may be the vehicle itself. In addition, 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, and 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 sidelink for services such as Internet access, service execution, navigation, real-time information, autonomous driving, and safety and risk diagnosis. Furthermore, any type of communication device capable of sidelink operation, such as an AR / VR device or sensor that performs relay operations, may be included.

[0209] Here, the vehicles / terminals to which the present invention is applied may include autonomous vehicles / driving terminals, semi-autonomous vehicles / driving terminals, non-autonomous vehicles / driving terminals, etc. Meanwhile, although the second device (2750) according to an 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 merely an example, and should not be construed as limiting the application of the present invention to the described example. In addition, the second device (2750) according to an example of the present invention may also include various types of communication devices capable of performing cooperation to support interactive services utilizing sidelink. In other words, the second device (2750) may not only directly support interactive services utilizing sidelink, but may also be utilized as a cooperation device to support interactive services utilizing sidelink.

[0210] Here, as an example, the terminal device (second device, 2750) can obtain an LTM configuration including information on LTM candidate cells from the network, and can obtain a reference signal from each LTM candidate cell to perform a measurement report. Thereafter, the terminal device (2750) can obtain a cell switch command MAC CE from the network that instructs cell switching to a first cell among the LTM candidate cells based on the measurement report, and can perform serving cell switching to the first cell by recognizing an intra-CU LTM operation and an inter-CU LTM operation based on the cell switch command MAC CE. As an example, each piece of information on LTM candidate cells included in the LTM configuration includes CU identifier information of each LTM candidate cell, and the terminal device (2750) can store a CU identifier variable for the serving cell based on the CU identifier information of each LTM candidate cell included in the LTM configuration. Thereafter, the terminal device (2750) recognizes the CU identifier of the first cell based on the cell switch command MAC CE, and if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are the same, performs an intra CU LTM operation, and if the CU identifier of the first cell and the CU identifier variable for the stored serving cell are different, performs an inter CU LTM operation.

[0211] As another example, the LTM configuration includes CU identifier information for a serving cell of the terminal device (2750), and the terminal device (2750) can store a CU identifier variable for the serving cell based on the CU identifier information for the serving cell. Thereafter, the terminal device (2750) receives a cell switch command MAC CE including the CU identifier of the first cell to recognize the CU identifier of the first cell, and if the CU identifier of the first cell and the stored CU identifier variable are the same, perform an intra CU LTM operation, and if the CU identifier of the first cell and the stored CU identifier variable are different, perform an inter CU LTM operation. As another example, the cell switch command MAC CE received by the terminal device (2750) can include a first indicator. Here, if the first indicator is a first value, the intra CU LTM operation can be performed, and if the first indicator is a second value, the inter CU LTM operation can be performed. In addition, as an example, when an intra CU LTM operation is performed, the terminal device (2750) may perform a MAC reset operation after changing the serving cell to the first cell. On the other hand, when an inter CU LTM operation is performed, the terminal device (2750) may perform a MAC reset, security key update, and PDCP re-establishment operations after changing the serving cell to the first cell. In addition, as an example, after changing the serving cell to the first cell, the terminal may perform a RACH-less procedure if the TA is valid, and may perform a RACH procedure if the TA is invalid.

[0212] Additionally, various embodiments of the present disclosure may be implemented by hardware, firmware, software, or a combination thereof. In the case of hardware implementation, the embodiments may be implemented by one or more Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), general processors, controllers, microcontrollers, microprocessors, etc.

[0213] The scope of the present disclosure includes software or machine-executable instructions (e.g., operating systems, applications, firmware, programs, etc.) that cause operations according to the methods of various embodiments to be executed on a device or a computer, and a non-transitory computer-readable medium having such software or instructions stored thereon and executable on the device or computer.

[0214] The various embodiments of the present disclosure are not intended to list all possible combinations but rather to illustrate 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.

[0215]

[0216]

[0217]

[0218] The above may also apply to other systems.

Claims

1. In wireless devices, 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 device is: Obtain an LTM configuration containing information about LTM (L1 / L2 layer triggered mobility) candidate cells from the network, Obtain a reference signal from each of the above LTM candidate cells and perform a measurement report, Based on the above measurement report, a cell switch command MAC CE (medium access control control element) is obtained to instruct cell switching to the first cell among the LTM candidate cells, A wireless device that performs serving cell switching to the first cell by recognizing intra-CU (central unit) LTM operation and inter-CU LTM operation.

2. In paragraph 1, Each piece of information about the LTM candidate cell included in the above LTM setting includes CU identifier information for each LTM candidate cell, The terminal stores a CU identifier variable for a serving cell based on the LTM setting, and after recognizing a CU identifier of a first cell, if the CU identifier of the first cell and the stored CU identifier variable for the serving cell are the same, performs the intra CU LTM operation. A wireless device that performs the inter CU LTM operation when the CU identifier of the first cell and the CU identifier variable for the stored serving cell are different.

3. In paragraph 1, The above LTM setting includes CU identifier information for the serving cell of the terminal, The terminal stores a CU identifier variable for the serving cell based on CU identifier information for the serving cell, Recognize the CU identifier of the first cell by receiving the cell switch command MAC CE including the CU identifier of the first cell, If the CU identifier of the first cell and the stored CU identifier variable are the same, the intra CU LTM operation is performed, A wireless device that performs the inter CU LTM operation when the CU identifier of the first cell and the stored CU identifier variable are different.

4. In paragraph 1, The above cell switch command MAC CE includes the first branch, If the first indicator is the first value, the intra CU LTM operation is performed, A wireless device that performs the inter CU LTM operation when the first indicator is the second value.

5. In paragraph 1, When the above intra CU LTM operation is performed, the terminal changes the serving cell to the first cell and then performs a MAC reset operation, A wireless device, wherein when the above inter CU LTM operation is performed, the terminal changes the serving cell to the first cell and then performs the MAC reset, security key update, and PDCP (packet data convergence protocol) re-establishment operations.

6. In paragraph 1, A wireless device, wherein the terminal performs a RACH (random access channel)-less procedure if TA (timing advance) is valid after changing the serving cell to the first cell, and performs a RACH procedure if TA is invalid.

Images